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Aspects of the inorganic amorphous system of humo ferric podzols of the Lower Main Land [sic] of British… Visentin, Girolamo 1973

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c' ASPECTS OF THE INORGANIC AMORPHOUS SYSTEM OF HUMO FERRIC PODZOLS OF THE LOWER MAIN LAND OF BRITISH COLUMBIA by Girolamo V i s e n t i n B . S . A . , U n i v e r s i t y of Padua - I t a l y , 1 9 6 6 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of S o i l Science We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1 9 7 3 i i In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or duplication of this thesis for financial gain shall not be allowed without my written permission. Department of Soil Science The University of British Columbia Vancouver 8, Canada. * • • 111 ABSTRACT A study was made toj ( i ) investigate the nature and the st r u c t u r a l organization of the inorganic amorphous system i n podzol s o i l s of B r i t i s h Columbia, ( i i ) evaluate the relationships between t h i s natural system and a r t i f i c i a l amorphous iron-aluminosilicate systems. Results of t h i s study ,are described i n a series of three papers, each des-cr i b i n g phases of t h i s study. The successive selective d i s s o l u t i o n analysis, combined with infrared spectroscopy technique proved to be suitable f o r q u a l i t a t i v e as well as quantitative determin-ation of the inorganic amorphous system of the s o i l s studied. A s t r u c t u r a l model f o r a r t i f i c a l amorphous iron-aluminosilicate systems i s discussed and although not considered to be perfect, presents a useful picture of iron-aluminosilicate structures as i t offers an explanation for some of the experimental findings recorded. Strong correlations have been found through chemical and physical analyses between the amorphous inorganic system of the s o i l s studied and a r t i f i c i a l l y -prepared iron-aluminosilicate systems, and close s t r u c t u r a l organization between the two systems i s inf e r r e d . i v ACKNOWLEDGEMENTS The author wishes to express h i s sincere appreciation to Dr, L.M. Lavkulich, Department of S o i l Science, for his i n t e r e s t , d i r e c t i o n , and assistance throughout the project and i n the preparation of t h i s thesis. Appreciation i s also expressed to Mr. B, von Spindler, Miss S. McMeekin, and Mr. W. Cheang f o r a s s i s -tance..with laboratory work during various stages of the study, and to Miss Beth Loughran for assistance with the draughting of figures for t h i s t h e s i s . The author would l i k e to extend deep appreciation to his wife, Maria Luisa, f o r her assistance, encouragement, and many s a c r i f i c e s during the course of thi s study. V TABLE OF CONTENTS Page INTRODUCTION I - AN EVALUATION OF THE AMORPHOUS INORGANIC SYSTEM OF SELECTED BRITISH COLUMBIA PODZOL SOILS Introduction 2 The importance of the inorganic amorphous system i n s o i l s 4 The pedogenesis of the inorganic ' amorphous system 7 Methods of removal of the inorganic amorphous system 8 Material and Methods 17 The s o i l s used 17 Chemical characterization 21 Aluminum and iron determination 26 Preparation of the s o i l samples f o r extraction - 26 Results and Conclusion on the Extraction Procedures 32 Mineralogical Studies 37 Successive Extraction Experiment and Infrared Spectroscopy f o r Characterization of the Amorphous Inorganic System i n S o i l Clays 38 Results and Discussion on Successive Extraction Experiment 48 Infrared Spectroscopy Studies 59 Conclusion 67 Literature Cited 69 v i II - STRUCTURE AND PROPERTIES OF AMORPHOUS 'IRON- P a g S ALUMINOSILICATE SYSTEMS Introduction 73 Materials and Methods 80 Results and Discussion 82 Stru c t u r a l Model 97 Conclusion 101 Literature Cited 103 III - THE AMORPHOUS INORGANIC SYSTEM OF SOIL COMPARED TO AN ARTIFICIAL AMORPHOUS IRON-ALUMINOSILICATE SYSTEM Introduction 105 Materials and Methods 106 Results and Discussion 110 Conclusion 126 Literature Cited 1 2 8 v i i LIST OF TABLES Table Page - 1. Extraction a b i l i t y of sodium pyrophos-phate, ammonium oxalate, and sodium d i t h i o n i t e 15 2.1 Abbotsford Series, A mini humo-ferric podzol 17 2.2 Marble H i l l . A mini humo-ferric podzol 18 2.3 Ryder Series, A mini humo-ferric podzol 19 2.4 Summer ser i e s . A gleyed orthic humo-f e r r i c podzol 20 3.1 Abbotsford - Selected Properties 22 3.2 Marble H i l l - Selected Properties 23 3.3 Ryder - Selected Properties 24 3.4 Summer - Selected Properties 25 4.1 Comparison of S i data (from the s o i l as a whole) given by extraction withs oxalate, pyrophosphate, and d i t h i o n i t e 29 4.2 Comparison of Fe data (from the S o i l as a whole) given by extraction with: oxalate, pyrophosphate, and d i t h i o n i t e 30 4.3 Comparison of A l data (from the s o i l as a whole) given by extraction with: oxalate, pyrophosphate, and d i t h i o n i t e 31 5. Differences between oxalate- and pyro-phosphate-extracted Fe and between d i t h i o n i t e - and oxalate- extracted Fe 35 6. Main minerals present i n Ryder, Summer Abbotsford, and Marble H i l l as deter-mined by X-ray d i f f r a c t i o n 38 7. Ryder - Successive extractions on <Z/K clay 49 8. Summer - Successive extractions on <2p clay 50 v i i i Table Page 9 . Ryder - Amorphous material extracted from < 2/4 clay by successive extrac-tions: 5% Na2CCU + Na pyrophosphate + acid ammonium oxalate. Included are: % lo s s , % clay content, molar r a t i o of amorphous oxides, sum of amorphous oxides, surface area, % amorphous oxides i n s o i l 52 10. Summer - Amorphous material extracted from < 2 p clay by successive extrac-tions: Na2CCU + acid NHj, oxalate + d i t h i o n i t e . JThe table also includes: molar r a t i o of amorphous oxides, % sum of amorphous oxides, fo clay content, % amorphous oxides i n s o i l , % l o s s , surface area 53 1 1 . Surface area (m /g) of Bf3 Ryder horizon clay and the surface of the same a f t e r : sodium carbonate, acid ammonium oxalate, and d i t h i o n i t e treatments. °2 II - 1. Chemical composition, elemental and oxide r a t i o s , s p e c i f i c surface area, C eE„C., X-ray d i f f r a c t i o n 8 6 2 . Dry f i x a t i o n of potassium by iron-alumino-s i l i c a gels " 8 8 3 . AS -2 successive treatments data and r a t i o s 90 4. Comparison between data obtained a f t e r successive (a+b+c) extraction and data afte r acid digestion procedure on AS -2 sample 91 III - 1. Percent amorphous AlpO^o Fe ?CU, S i 0 ~ . i n Clay-R3, AC-R3 and i n •'AS-2* as extracted by successive s e l e c t i v e d i s s o l u t i o n s and d i t h i o n i t e only; amorphous oxides molar r a t i o 1 1 2 2 . Total percent of amorphous material i n Clay-R3, AC-R3» and AS-2 as extracted by successive selective dissolutions and di t h i o n i t e only; percent loss a f t e r treatments, surface area of the untreated samples and a f t e r treatments 114 i x Table Page 3. T o t a l elemental analysis of AC-R3» AS-l, AS-2 and AS-3 118 4„ To t a l percent of A l , Fe, S i oxides r e c a l -culated from Table 3 on air-d r y basis. 118 5. Atomic ratios Al/Al+Si, oxides molar r a t i o s , percent oxides i n AC-R3* AS-1, AS-2 and AS-3 calculated from the data of t o t a l elemental analysis and the data of successive extractions 119 X LIST OF FIGURES Figure Page - 1. Comparison of aluminum ex t rac t ion methods. Oxalate versus c i t r a t e - b i e a r b o n a t e -d i t h i o n i t e 33 2, Comparison of i r o n e x t r a c t i o n methods. Oxalate versus c i t r a t e - b i c a r b o n a t e -d i t h i o n i t e 34 3o Amorphous extracted i r o n (by di f ference between oxalate and pyrophosphate extracted i r o n ) , and c lay content i n Ryder 36 4 . Amorphous extracted i r o n (by d i f f e r e n c e between oxalate and pyrophosphate extracted i r o n ) , and c lay content i n Summer 36 5 . A schematic representat ion of successive extract ions of inorganic amorphous system and corresponding analyses 43 6 0 D i s t r i b u t i o n along the Ryder p r o f i l e of A l , Fe and S i oxides extracted by successive treatments j < 2/u c l a y content 55 7. D i s t r i b u t i o n along the Summer p r o f i l e of A l , Fe and S i oxides extracted by succes-s ive treatments; < 2^ c lay content 55 8.1 Ryder - D i s t r i b u t i o n along the p r o f i l e of t o t a l amorphous oxides extracted by successive treatments? % <2j* c lay 56 8.2 Summer - D i s t r i b u t i o n along the p r o f i l e of t o t a l amorphous oxides extracted by successive treatments; fo<2j* c lay 56 9a» Comparison between i n f r a r e d spectra of untreated Clay-R3 and the Clay-R3 a f t e r (a+b) e x t r a c t i o n 63 b . D i f f e r e n t i a l i n f r a r e d spectra between untreated Clay-R3 ( i n sample-beam) and the Clay-R3 a f t e r (a+b) e x t r a c t i o n ( i n reference-beam). 63 Figure x i Page 10a„ Comparison between infrared spectra of untreated Clay-R3 and the Clay-R3 af t e r (a+b+c) extraction 64 b. D i f f e r e n t i a l infrared spectra between untreated Clay-R3 ( i n sample-beam) and the Clay-R3 a f t e r (a+b+c) extraction ( i n reference-beam) 64 11a. Comparison between infrared spectra of the untreated Clay-R3 and the Clay-R3 a f t e r (a+b+c+d) extraction 65 b. D i f f e r e n t i a l infrared spectra of the untreated Clay-R3 ( i n sample-beam) and the Clay-R3 a f t e r (a+b+c+d) extraction ( i n reference-beam) . 6 5 12. D i f f e r e n t i a l infrared spectra of Clay-R3 after (a+b) extraction ( i n sample-beam) and Clay-R3 after (a+b+c+d) extraction ( i n reference-beam) 66 13. D i f f e r e n t i a l infrared spectra of Clay-R3 af t e r (a+b+c) extraction ( i n sample-beam) and Clay-R3 after (a+b+c+d) extraction ( i n reference-beam) 66 14. Comparison between infrared spectra of untreated Clay-R3 and Clay-R3 afte r four successive extractions 66 II - 1. Schematic s t r u c t u r a l relationships in silicoaluminas 78 2. Cation exchange capacity and surface area of synthetic iron-aluminosilicate hydrogels as determined at pH 7.0 i n function of % AlgOyAlgO-j + S i 0 2 85 3. Schematic representation and s t r u c t u r a l formulas of iron-aluminosilicate core-phase and polyhydroxy-iron and -aluminum phases with varying A l / A l + S i atomic r a t i o 100 4. Comparison of infrared spectra of i r o n -aluminosilicate standards AS-1, AS-2, and AS-3 93 x i i Figure Page 5. Infrared spectra of iron-aluminosilicate standards AS -1 , AS-2 and AS-3 a f t e r dehydration (at 300 C) 94 III - 1. Comparison "between infrared spectra of AC-R3 (amorphous concentrate of Ryder Bf3 horizon) and AS-2 (amorphous iron-aluminosilicate standard) 121 2.1 AC-R3 infrared spectra a f t e r successive extractions 122 2.2 AC-R3 infrared spectra a f t e r successive extractions and heating at 300 C 123 3.1 AS-2 infrared spectra a f t e r successive extractions 124 3.2 AS-2 infrared spectra a f t e r successive extractions and heating at 300 C 125 1. INTRODUCTION The importance of the s o i l inorganic amorphous system f o r the characterization of chemical and the physical properties of s o i l has been established by much research even though the amount of amorphous material present may be only.a few percent. . This system i s described as a complex polymeric system composed of d i f f e r e n t i n t e r a c t i n g phases; an attempt has been made i n t h i s study to d i s t i n g u i s h among these various phases because t h e i r r e l a t i v e d i s t r i b u t i o n within the s o i l p r o f i l e i s f e l t to have an important bearing on the physico-chemical properties of the s o i l , on the i n t e r p r e t -ation,of s o i l genesis, and on the studies connected with the i n t e n s i t y and condition of weathering. The other objective of t h i s thesis was to i n v e s t i -gate the nature of the component phases of the natural inorganic amorphous system and the s t r u c t u r a l organization of the system i t s e l f . For t h i s purpose, the nature of the phases and the structure of a r t i f i c i a l amorphous i r o n -aluminosilicate systems have been studied on the basis that they could have t h e i r counterpart i n the natural environment. In seeking relationships between natural and a r t i f i c i a l systems, successive s e l e c t i v e d i s s o l u t i o n analysis combined with infrared spectroscopy has been shown to be suitable for the purpose of t h i s study. 2. AN EVALUATION OP THE AMORPHOUS INORGANIC SYSTEM OF SELECTED BRITISH COLUMBIA PODZOL SOILS INTRODUCTION The f i n e s t p a r t i c l e s contained i n the clay f r a c t i o n of most s o i l s are amorphous to X-ray and often contribute s i g n i f i c a n t l y to the bulk of s o i l s . Their high r e a c t i v i t y has invited investigations into t h e i r quantitative determination and t h e i r composition. Any attempt at defining t h i s amorphous system other than by an operational means would be naive because the system lacks functional homogeneity and,, consequently, lacks unique reactions whereby i t may be unambiguously, d i s t i n -guished. It i s i n fact a complex system i n which very often d i f f e r e n t i n t e r a c t i n g phases occur contemporaneously, i n d i f f e r e n t proportions, depending upon the type of parent material undergoing weathering and the evolutive dynamics of the s o i l . Another concept seems to be inherent to t h i s polyphase system* i t appears, i n f a c t 0 to be quite r e a l i s t i c to assume there exists a continuum from t o t a l l y disordered to poorly ordered phases i n t h i s systemj i n the disordered phases atoms or molecules of a s o l i d deviate from those of corresponding c r y s t a l l i n e s o l i d s due to defects such as vacancies, i n t e r s t i t i a l atoms and grain boundaries (Fieldes,;,., 1966). A high proportion of defects results i n a highly disordered state which l n extreme cases could approach complete random-ness . If a precise deflnation of the amorphous polyphase system i s possible, the system could, be defined i n terms of physical and chemical properties of the s o i l material, which are conveyed to the s o i l by the inorganic amorphous system. Amorphous materials are known to be common i n pod-z o l i c or spodic horizons of Podzol s o i l s . The adopted c r i t e -r i a f o r spodic horizons by the U.S.D.A. S o i l Survey Staff are high C.E.C. (150 meq/100 g clay), high 15-bar water retention a pH of more than 9.k i n NaF, more than \% of organic matter, and the presence of a low-temperature endotherm i n D.T.A. (S o i l Survey Staff et a l . , I 9 6 7 ) . Even with the term "allophane" there i s disagree-ment among authors who have t r i e d to define i t ; some of them (Fieldes, 1966; Fleldes and Fulkert, 1966) recognize allophane, i n general, as having many q u a l i t a t i v e s i m i l a r i -t i e s i n chemical behaviour that depend upon t h e i r nature as random-structured hydrous aluminosilicates and that d i f f e r -ences among allophanes are, i n general, due to composition. On the other hand, Lai and Swindale (I969) have more recently defined allophanes hydrated aluminosilicate mine-r a l s , amorphous to X-ray and without ordered c r y s t a l l i n e structure, implying with the term '•mineral" a more d e f i n i t e composition and a more c h a r a c t e r i s t i c arrangement of atoms. 4 . THE IMPORTANCE OF THE INORGANIC AMORPHOUS SYSTEM IN SOILS. S o i l clay mineralogists and pedologists, while supporting the view that the clay f r a c t i o n may contain an appreciable amount of amorphous inorganic material, s t i l l have some reservations as to i t s importance i n determining and governing the chemical and physical properties of associated c r y s t a l l i n e clay minerals. From the studies of many authors (Fieldes, et a l . , 1951; M i t c h e l l and Farmer, I960} De Mumbrum, I960} Sumner, 1963? Greenland and Oades, 1969; Deshpande et a l , , 1968$ Yuan, 1 9 6 8 j Briner and Jackson, 1969; Raman and Mortland, 1969i P a r f i t t , 1972) i t appears that numerous correlations exist between p a r t i c u l a r macromorphological features of the s o i l p r o f i l e and the nature and amount, of the inorganic amorphous system, as well as the in t e r r e l a t i o n s h i p s between th i s system and the physico-chemical properties of c r y s t a l -l i n e clay. In f a c t , evidence i s available to show that properties such as anion absorption, swelling, and surface area, are modified by the presence of amorphous i r o n oxides even though few thorough investigations have been undertaken. Sumner (1963) has demonstrated that i r o n oxides behave amphoterically i n s o i l and contribute s i g n i f i c a n t l y to the buffer capacity of t r o p i c a l s o i l s r i c h i n iron oxides. 5. Deshpane et a l , (1968) examining the role of iron oxides i n r e l a t i o n to aggregate s t a b i l i t y , paying p a r t i c u l a r attention to the r e l a t i v e importance of Fe and A l , reported s i g n i f i c a n t evidence of the part played by "free** aluminum oxides i n enhancing the s t a b i l i t y of micro- and macro-aggregates. The degree of structure and consistence of some s o i l s has been related to the bonding action of free sesqui-oxides on. the surface of the primary p a r t i c l e s . These authors postulate i n t e r a c t i o n of the p o s i t i v e charges of A l oxides, with the negatively-charged clay p a r t i c l e s . They also, concluded that most of the iron was present i n small, d i s c r e t e , negatively-charged p a r t i c l e s which had r e l a t i v e l y l i t t l e e f f e c t on the physical and physico-chemical properties of the s o i l . Greenland and Oades (19&9) i n t h e i r work on changes i n physical properties associated with the removal of free iron oxides from d i f f e r e n t s o i l s arrived at d i f f e r e n t conc-lusions than those of Deshpane et a l , (1968) , Aluminum oxides and hydroxides, and a small part.of the free i r o n could be present i n an active form as coating on clay p a r t i c l e s , and these active oxides are believed to be responsible f o r most, of the p o s i t i v e charges developed by the s o i l . The reduction, of exchange negative charges accessible to hydrogen ions, creates an important immunity to acid weathering, pro-vides pH functional C.E.C., latent or t i t r a t a b l e a c i d i t y , and sites, with strong a f f i n i t i e s f o r phosphorus, boron, 6. molybdenum, and other metals important i n plant n u t r i t i o n . Freshly formed i r o n hydroxides are knownto be active i n the sense that they have high i s o e l e c t r i c points and are therefore predominantly p o s i t i v e l y charged up to about pH 8 . 0 and have very large surface areas. Fieldes et a l . ( 1 9 5 1 ) during a survey of the islands of Lower Cooks Group have observed that the oxides of A l , Fe, and T i appeared to be the only possible sources of the high C.E . c . , and since c r y s t a l l i n e forms of these oxides have low capacities they f e l t that the amorphous oxides could be responsible. i Phosphate retention studies on natural s o i l s as , well as on synthetic i r o n and aluminum oxides and hydroxides (Gastuche e t . a l . , 1 9 6 3 ; Cloos et a l . , 1 9 6 8 ) , have shown that, i n general, the inorganic amorphous system exhibits a high p o t e n t i a l of phosphate absorption and a low degree of a v a i l a b i l i t y , whereas the reverse was observed f o r c r y s t a l r l i n e material. , , S p e c i f i c exchange effects shown by s o i l s , including p r e f e r e n t i a l retention and f i x a t i o n of cations such as K, NH^». Rb, and Cs, have been almost exclusively ascribed to c r y s t a l l i n e p h y l l o s i l i c a t e s i n the clay f r a c t i o n . Van Reeuwijk and De V i l l i e r s ( 1 9 6 7 ) » using synthetic aluminosilicate gels to provide a model f o r at least some natural allophane and the clay mineral formation reactions i n which these gels are involved, investigated the cation 7. exchange specificity with particular reference to potassium. They f e l t i t was premature to accept their positive results • of K-fixation by so i l s , although i t i s possible they may have some relevance to that kind of fixation which occurs in certain soils in the moist state. THE PEDOGENESIS OF THE INORGANIC AMORPHOUS SYSTEM. The different phases of the system are believed to be transient products of the weathering of primary minerals, and of random-structured aluminosilicates. The next, step, in the process which is most l i k e l y to occur is an hydrolitic polymerization of aquo-ions present in solu-tion or a, relatively rapid precipitation at low temperatures and pressures giving rise to disordered hydroxy polymers„ The particular polyphase formations are believed to occur only^where specific weathering conditions are consistently establish,ed, such as a uniformly distributed r a i n f a l l , of 1200.mm or more annually, , The fundamental mechanism of decomposition in the pedological neoformations is that of hydrolysis which brings about a depolymerization of the orderly arranged iron.and aluminosilicate frameworks, with release i n the medium of the constituents in the form of S i (OH)^ monomer acids, insoluble Al (0H)y and hydrated iron oxides, a l l lackingorderly arrangement. 8. Subsequent leaching of bases and accesses to G 0 2 would lower the pH and lead to co p r e c i p i t a t i o n of a f e r s i a l l i t i c amorphous phase along with p r e c i p i t a t i o n of hydrous aluminum and hydrous iron amorphous polymeric phases e The nature of these neogenic polyphases i s such that i t allows them to associate i n d i f f e r e n t ways with the components of the c o l l o i d a l f r a c t i o n of the s o i l j hydroxy-Al and Fe (III) polymers can be associated with negatively charged c r y s t a l l i n e p h y l l o s i l i c a t e s , or intimately associated with each other. A l and Fe can also be complexed with organic matter or substitutedisomorphously i f o r S i i n SiOg-Alg G^-FegO^ coprecipitates. METHODS OF REMOVAL OF THE INORGANIC AMORPHOUS SYSTEM.;" 1 The early researchers were pr i m a r i l y concerned with the removal of the inorganic amorphous system and i n p a r t i c u l a r of the iro n oxides, i n order to improve the resolution of the c r y s t a l l i n e minerals by X-ray d i f f r a c t i o n . When they found changes i n the clay a f t e r the extraction they began to r e a l i z e that these amorphous materials might be important i n the characterization and development of s o i l s . There i s now evidence that s o i l forming processes,! as well as parent materials, are important i n the kinds and s t a b i l i t y of the amorphous materials occurring in, s o i l . As mentioned i n the introduction, the clay f r a c -t i o n of s o i l contains the f i n e s t and therefore the most 9* surface-reactive p a r t i c l e s and as can be appreciated many of the properties of s o i l are determined by the nature of these fract i o n s even when the amount present may be merely a few percent. Although i t i s inevitable the chemical pre-treatment w i l l r e s u l t i n some alteration' of these properties, these need not necessarily be disadvantageous and a car e f u l and controlled degradation of the clay f r a c t i o n should pro-vide valuable information concerning i t s composition and properties. Studies based upon the r e l a t i v e s t a b i l i t y of a component or a group of components i n clays to s p e c i f i c chemical reagents provide a useful approach to the i d e n t i -f i c a t i o n and estimation of the constituents of such complex systems. The more recent e f f o r t s of researchers have been towards the rapid and e f f i c i e n t removal of sesquioxides and the d i f f e r e n t i a t i o n and characterization of the amorphous sesquioxides as d i f f e r e n t i a t e d from c r y s t a l l i n e sesquioxides, Tamm (1932) was among the f i r s t to propose a method of removing sesquioxides from s o i l as a means of dis t i n g u i s h -ing between podzols and brown earths, Muir (1961), using Tamm's acid NH^ oxalate procedure f e l t that the method's primary use was to determine the rate of s o i l development and to di s t i n g u i s h between types of s o i l s , rather than as a method to clean up clays f o r mineralogical analysis. 1 0 . Other researchers were more concerned with the removal of the sesquioxides B e s p e c i a l l y i r o n oxides 6 Deb (1950) , i n studying the importance of i r o n oxides i n podzolization, l a t e r i z a t i o n and phosphate f i x a t i o n , compared Tamm's procedure with a procedure u t i l i z i n g Na-di t h i o n i t e as a reducing agent, with a sodium acetate-t a r t r a t e buffer» Deb concluded that the sesquioxides extracted by Tamm's procedure, increased the C.E.C. by uncovering additional exchange s i t e s on the clay, while his procedure lowered the C.E.C. and removed amorphous as well as c r y s t a l l i n e sesquioxides which possess some cation exchange c a p a b i l i t y or destroyed some of the clay. Mehra and Jackson ( i960) tested several methods of extraction against one proposed by them which was a sodium c i t r a t e system buffered with sodium bicarbonate and containing sodium d i t h i o n i t e . The sodium c i t r a t e acts as a chelating agent helping to remove some aluminum coat-ings and s i l i c a cements. The Na-bicarbonate kept the pH within a narrow range where there would be les s problems with p r e c i p i t a t i o n , as was the case with Deb's sunlight-oxalate procedure. Gorbunov et a l . (1961) , i n comparing a l l the methods discussed above, as well as others e found that none of the methods removed a l l the sesquioxides i n one treatment. They found that Tamm's or Mehra and Jackson's methods appeared more s p e c i f i c f o r amorphous sesquioxides. 11. while Deb's procedure was most s p e c i f i c f o r hydrated i r o n oxides. C o f f i n (1961) defined "free" i r o n to include iron oxides and other forms of i r o n found i n s o i l s but not as part of the c r y s t a l l i n e l a t t i c e of other minerals present. The purpose of his studies was to evaluate the e f f i c i e n c y of some of the more widely used hydrosulphite methods, and to determine the role of such factors as pH, temperature, and reagent concentration i n the removal of free iron from s o i l s . He proposed just one extraction •.. c a r r i e d out at 50°C and at pH 4 . 7 5 with a 5% solution of sodium hydrosulphite i n a 0 „ 2 M c i t r a t e buffer. C o f f i n reported an average standard deviation of + 0„034?S ir o n for duplicate values. Franzmeier et a l , (1963) have considered the use of sodium pyrophosphate as a chelating agent i n t h e i r studies of spodic horizons and compared t h e i r r e s u l t s with Mehra and Jackson's method. Pyrophosphate was selected f o r i t s a b i l i t y to extract organic matter and aluminum as well as iron. They found that the maximum ext r a c t i o n - e f f i c i e n c y occurred at pH 7 .3 with less d i s s o l u t i o n of s i l i c a t e minerals. Their r e s u l t s showed that multiple extractions with pyrophosphate-dithionite and c i t r a t e - d i t h i o n i t e removed s i m i l a r amounts of iron and that one extraction of pyrophosphate-dithionite removed about 75% as much iron as multiple extractions of c i t r a t e - d i t h i o n i t e . 12. More aluminum was extracted by pyrophosphate-dithionite than c i t r a t e - d i t h i o n i t e regardless of the number of t r e a t -ments. McKeague and Day (1966) tested Mehra and Jackson's c i t r a t e - d i t h i o n i t e procedure i n comparison with acid NH^-oxalate using a wide range of iron-enriched horizons of Canadian s o i l s , as well as prepared amorphous and c r y s t a l l i n e iron and aluminum oxides» They also tested the e f f e c t s of pH, time of extraction, etc., i n attempting to propose an e f f i c i e n t extraction method u t i l i z i n g oxalate. An extrac-t i o n at pH 3 . 0 with a four hour shaking time and carried out i n darkness gave the best r e s u l t s , with very l i t t l e s i l i c a d i s s o l u t i o n . They reported that both procedures extracted more ir o n and aluminum from f r e s h l y prepared amor-phous aluminum material than from s i l i c a t e minerals. Also, oxalate-extractable aluminum exceeded c i t r a t e - d i t h i o n i t e aluminum i n most cases and that some iron and aluminum dissolved by the oxalate occur as metal-organic complexes. These authors claimed that the oxalate values give an estimate of the amorphous materials formed by weathering processing regardless of the s o i l parent material, pH, organic matter content or amount of t o t a l iron oxides. They concluded that t h e i r procedure was e s p e c i a l l y useful as an i n d i c a t o r of development of podzol B horizons i n s o i l s derived from parent material high i n i r o n content, as well as being a better extractor of 13. aluminum than c i t r a t e - d i t h i o n i t e . The oxalate-extractable Fe and Al served i n d i f f e r e n t i a t i n g certain classes of s o i l that are defined i n the Canadian System of C l a s s i f i c a t i o n (C.S.S.C. 1970). They also found that a l l podzol B horizons had d i s t i n c t accumulation of oxalate-extractable aluminum and that the oxalate-iron and aluminum values were associated with horizons having a high pH dependent C.E.C. and high phos-phorus f i x i n g capacity. McKeague, i n a l a t e r report (1967) t i n an evaluation of 0.1M pyrophosphate and pyrophosphate-dithionite i n comparison with oxalate as extractants of the accumulation products i n podzols and some other s o i l s , concluded that the Franzmeier.'s procedure was not s p e c i f i c enough i n extracting iron and i s l e s s suitable for estimating the accumulation products in podzol-like B horizons than acid NH^-oxalate and 0.1M pyrophosphate. Although the d i s t i n c t i o n between amor-phous and more or l e s s . c r y s t a l l i n e forms of extractable-Fe i n s o i l s i s useful, a further d i f f e r e n t i a t i o n of the . amorphous f r a c t i o n i s necessary. Some s o i l s developed i n volcanic ash and some prominently mottled cambic horizons contain high amounts of inorganic Fe and they cannot be distinguished by t h e i r content of oxalate-extractable Fe from spodic horizons i n which Fe i s usually associated with organic matter. McKeague et a l , (1970) have proposed a d i f f e r e n t i a t i o n of forms of extractable 14. iron and aluminum i n s o i l s by a further characterization of the form of Fe and A l extracted from known substances t>y pyrophosphate i n r e l a t i o n to oxalate and d i t h i o n i t e . They concluded that t h e i r data provided evidence that an approximate d i f f e r e n t i a t i o n can be made among organic-complexed Fe, amorphous inorganic Fe, and more or less c r y s t a l l i n e Fe by selective extractions of s o i l s with pyro-phosphate, oxalate and d i t h i o n i t e . Data for synthetic Fe- and A l - f u l v i c acid complexes, Fe- and Al-hydrous oxides, and f o r spodic horizons i n r e l a t i o n to other s o i l s indicate that pyrophosphate i s reasonably s p e c i f i c f o r Fe organic complexes and'somewhat les s s p e c i f i c f o r A l -organic complexes. The difference between oxalate and pyrophosphate extractable Fe gives a measure of amorphous inorganic Fe and d i t h i o n i t e minus oxalate-extractable Fe provides an estimate of more or less c r y s t a l l i n e Fe oxides„ These extractants are believed to be l e s s useful i n d i s t i n g u i s h -ing forms of A l i n s o i l s . A summary of the extracting a b i l i t y of the d i f f e r e n t reagents f o r Fe and A l i s presented i n the following table. 15. TABLE 1. Extraction a b i l i t y of sodium pyrophosphate, ammonium oxalate and sodium d i t h i o n i t e f o r iron and aluminum i n s o i l s * INORGANIC IRON AND ALUMINUM COMPOUNDS ORGANIC COMPLEXES S i l i c a t e s Well crys-t a l l i z e d oxides Amorphous hydroxides Acid Acid soluble insoluble fulvate humate (pH 3.8) Na-dithionite (pH3.0) Acid NH^-oxalate (pH 10.0) Na-pyrophosphate good extraction poor extraction * Modified from Bascomb, I968. 16. The purpose of t h i s study was to compare the various extraction procedures on selected s o i l s from the Lower Fraser Valley and to elucidate the ef f e c t s of the extractants on s o i l clays by means of X-ray d i f f r a c t i o n and infrared spectroscopy. 17. MATERIALS AND METHODS Four podzol soils representative of four s o i l series of British Columbia were considered in this studyt Abbotsford, Marble H i l l , Ryder and Summer series. Brief descriptions of these s o i l profiles are given in Tables 2 . 1 , 2 , 2 , 2 . 3 , and 2 . 4 . TABLE 2 . 1 ABBOTSFORD SERIES: A MINI HUMO-FERRIC PODZOL HORIZON DEPTH DESCRIPTION cm  Ap 0-15 Raw to part i a l l y decomposed, mainly deciduous materials,; abrupt boundary. Bf^hcc 15 -25 Dark reddish brown (5YR 3 / 4 M ) j gravelly sandy loam; weak, fine, subangular blockyj very friable when moist5 numerous hard concretions; clear to gradual boundary. Bf-cc 25 -50 Brown reddish (5YR 4/4M); loamy sand; weak, fine, subangular blocky; friable when moist, numerous concretions; gradual boundary, Bf^cc 50-68 Reddish brown (5YR 4/4M ) ; loamy sand; J weak, fine, subangular blocky; friable when moist, scattered fine concretions5 clear boundary. BI1C 6 8 - ? 5 Dark yellowish-brown (10YR 4/4M): gravelly loamy sand; firm in place, breaking to single grain when disturbed? loose when moist; diffuse boundary. IIC 75 + Grayish-brown (10YR 5/3M): the same as above for the rest. The parent material of this podzol, collected in the Abbotsford area (along Hamm street, one mile from the intersection of Hamm and Huntingdon Roads) at 67 meters elevation (A.S.L.) on a gentle slope, is shallow aeolian deposits over glacial outwash. The drainage is classified as well to rapid? no ground water was present in the cont-r o l section with good moisture relationships. The root distribution is good. 18. TABLE 2 .2 MARBLE HILLs A MINI HUMO-FERRIG PODZOL HORIZON DEPTH DESCRIPTION (cm) ; , L-H 0 -15 Raw to well decomposed mixture of deciduous and coniferous materials; abrupt boundary. Bf 1 1 5 - 6 5 Dark yellowish-brown (10 YR k/kM) t s i l t loam; weak, medium, subangular blocky, scattered so f t to hard concre-tions; f r i a b l e when moist and abundant roots; gradual boundary. B f 2 65-80 Yellowish-brown (10 YR 5 A M ); s i l t loam; weak, medium, subangular blocky, scat-tered soft to hard concretions; f r i a b l e when moist, abundant roots; clear boundary. B II C 80-90- Brown to yellowish-brown (10 YR 5/3.5M); gravelly sandy loam; weak, medium, sub-angular blocky breaking to single grain; very f r i a b l e when moist, common roots 5 gradual boundary. IIC 9 0 - 1 0 5 Grayish-brown (10 YR 5/3M) to variegated; gravelly sand; single-grained; loose when moist, occasional roots; gradual boundary. The Marble H i l l podzol samples were collected i n the Abbotsford-Clearbrook area at an elevation of 50 meters (A.S.L.) with 2-5% gentle slopes, on Clearbrook road at the C.D.A. small f r u i t - t r e e Experimental Farm. The parent mater-i a l i s a s i l t y aeolian deposit over gravelly and sandy g l a c i a l outwash deposits. The drainage i s c l a s s i f i e d as well. No ground water was present i n the control section and the moisture status was good. The surface textures are either loam or s i l t y loam, which remain constant towards the lower horizons i n the p r o f i l e where a coarse underlay i s encountered. 19. TABLE 2.3 RYDER SERIES s A MINI HUMO-FERRIC PODZOL HORIZON DEPTH DESCRIPTION . (cm)  Ap 0-10 Very dark grayish-brown (10 YR 3/2M); s i l t loam? weak, f i n e , subangular b l o c k y , b r e a k i n g to weak, f i n e g r a n u l a r s t r u c -t u r e ; f r i a b l e when moist, abundant r o o t s 5 abrupt boundary. Bf- 10-30 Dark reddish-brown (5 YR 3AM); s i l t loam; weak, f i n e , subangular b l o c k y ; f r i a b l e when moist, abundant r o o t s ; g r a d u a l boundary. B f ? 30-60 Reddish-brown to dark-brown (5 YR 4/4 -7.5 YR 4/4M); s i l t loam; weak, f i n e , subangular b l o c k y ; f r i a b l e when moist; abundant t o common r o o t s ; g r a d u a l boundary. B f o 6 0 - 9 0 Dark brown (7.5 YR 4/4M)1 s i l t loam; weak, f i n e , subangular b l o c k y ; f r i a b l e when moist, common r o o t s ; g r a d u a l boundary, BIIC 90-105 Dark yellowish-brown (10 YR 4/4M); g r a v e l l y sandy loam; massive; f r i a b l e when moist; g r a d u a l boundary. C 105-140 O l i v e brown (2.5 YR 4/4M); g r a v e l l y . loamy sand; massive; f r i a b l e when moist; gr a d u a l boundary. The Ryder p o d z o l was c o l l e c t e d i n the Abbots-f o r d area, on a ge n t l e slope (10-12%), about 80 meters e l e v a t i o n (A.S.L.) a l o n g McCallum road ( h a l f mile from the i n t e r s e c t i o n o f McCallum and McConnell r o a d ) . The pa r e n t m a t e r i a l i s a s i l t y a e o l i a n m a t e r i a l over g l a c i a l t i l l . The drainage i s c l a s s i f i e d as w e l l w i t h no ground water p r e s e n t ; good moisture c o n d i t i o n s and r o o t p e n e t r a t i o n . 20. TABLE 2.4 SUMMER SERIES: A GLEYED ORTHIC HUMO-FERRIC PODZOL HORIZON DEPTH DESCRIPTION (cm) L-F-H 0-15 Moderately to well decomposed forest l i t t e r containing pieces of charcoal; abundant roots. Ae 15-22 Gray 9 (10 YR 6/2M); medium to fine sand; very weak, fine subangular blocky, break-ing to single grains; very f r i a b l e to loose when moist; clear boundary. Bf 22-50 Dark-reddish brown (5 YR 2.5/2.5M); mottles are many, prominent, yellowish-red to dark-red (5 YR 4-/6 - 2.5 YR 3/6) moist; sandy loam; mainly massive, but some strong, medium blocky structure i n l o c a l i z e d pockets; f r i a b l e to firm when moist, occasional roots; diffuse boundary. Bfcg 50-90 Grayish-brown (10 YR 5/2M); mottles common, d i s t i n c t , dark reddish brown (5 YR 3/4 moist); medium sand; massive; f r i a b l e to firm when moist, scattered, dark reddish brown concretions up to one inch i n diameter. BC 90-110 W W 11*11* NS A t | XA J . W V Vf f • \JL talJL JTL X C U U 1 D J 1 U J (5 YR 3/4 moist); medium sand; mi very f r i a b l e when moist; di f f u s e boundary. Cg 110-120 Grayish brown (10 YR 5/2M); mottles; common, d i s t i n c t , reddish-brown (5 YR 5/3)5 sand and s i l t y clay; massive; firm when moist; d i f f u s e boun-dary. HCg 120-135 Grayish brown (10 YR 5/2M); common, d i s t i n c t , reddish brown mottles (5 YR 5/3)i s i l t y clay; massive; p l a s t i c and s t i c k y when moist; diffuse boundary. 21. The Summer was collected in the U.B.C. campus along Chancellor Boulevard at an elevation of about 18 meters (A.S.L.) and slope not over 2% . The parent material i s sandy, raised l i t t o r a l and beach deposits over marine and glacial-marine deposits. The int e r n a l drainage Is impeded by the impermeable glacio-marine underlay and cemented o r s t e i n horizons. The result i s a perched water table. Rooting depth i s r e s t r i c t e d by the cemenfced subsoil. The p r o f i l e consists of well developed e l u v i a l and cemented i l l u v i a l horizons with mottles i n the lower part. CHEMICAL CHARACTERIZATION Chemical characterization of these four s o i l s was done on the s o i l as a whole by routine laboratory procedures and the res u l t s are reported i n Tables; 3 « 1 . 3.2, 3 « 3 . and 3•4. The organic matter was determined according to the pro-cedure outlined by A l l i s o n ( 1 9 6 5 ) ; t o t a l Nitrogen was deter-mined following the procedure suggested by Bremner ( 1 9 6 5 ) ; C.E.C. was determined by NH^OAc saturation and semi-micro Kjeldahl procedure (Chapman, 19 6 5 ) ; and the pH was determined with the procedure outlined by Peech ( I 9 6 5 ) . The chemical di s s o l u t i o n procedures which were used are: (a) 5% sodium carbonate, b a s i c a l l y as outlined by F o l l e t ( I 9 6 5 K (b) sodium pyrophosphate as proposed by Bascomb ( 1 9 6 8 ) , (c) acid ammonium oxalate as proposed by Tamm (1932) and r e v i -ewed by McKeague and Day ( I 9 6 6 ) , (d) c i t r a t e - b i c a r b i n a t e - d i t h i -onite as suggested by Mehra and Jackson ( i 9 6 0 ) . 22. TABLE 3.1 ABBOTSFORD - SELECTED PROPERTIES PH pH (O.OlM O.M. N Sample Horizon (H90) Ca C l 9 ) % (t o t a l ) C/N : z % A l Ap 5.96 4.97 3.27 0.09 21.00 A2 Bfjhcc 5.89 5.00 3.53 0.11 18.54 A3 B f 2 c c 6 , 0 7 5 , 4 7 °*^ 8 0 , 0 2 14.00 A4 B f 3 c c 5.95 5.46 0.97 0.03 18.66 A5 BIIC 5.92 5.43 0.37 0.02 10.50 A6 IIC 5.72 5.57 0.08 0.01 5.00 Exchangeable Cations (me/100 g of s o i l ) C.E.C. — — r — (me/lOOg B.S. Sample Horizon Ca K Mg Na of s o i l ) % Al Ap 3.38 0.31 0.28 0,07 14.47 27,92 A2 Bfjhcc 3.55 0,42 0.16 0.08 14.23 29.59 A3 BfgCC 1.25 0.23 0.12 0,08 12.77 13.16 A4 Bf^cc 1.03 0.23 0,09 0,08 14.37 9.95 A5 BIIC 0.65 0,15 0,09 0,09 10.19 9,62 A6 IIC 0,28 0.03 0,03 0.08 9.28 4„53 23. TABLE 3.2 MARBLE HILL - SELECTED PROPERTIES Sample Horizon pH (H 20) pH (0.01M CaCl 2) P.M. N ( t o t a l ) % C/N Ml, L-H 5.32 4.70 15.04 0.50 17.40 M2 B f l 5.33 4,78 2.63 0.10 15.20 M3 Bf 2 5.33 4.88 2.65 0.10 15.20 M4* BIIC 5.35 4.95 0.96 0,04 14.00 M5 IIC 5.1? 4.95 0.32 0.02 9.00 Exchangeable Cations n „ n (i/loo g of s o i l ) Ui/lboe B.S. imple Horizon Ca K Mg Na of s o i l ) Ml L-H 14.00 0.&2 1.26 0.22 37.90 42.48 M2 B f t 2.00 0.34 0.09 0,08 20.23 12.31 M3 Bf 2 1.16 0,20 0.12 0,09 19.64 8.01 M4 BIIC 0,6:6 0.09 0.11 0.24 8.25 13.41 M5 IIC 0.46 0.03 0.03 0.09 5.07 12.20 TABLE 3 . 3 RYDER - SELECTED PROPERTIES pH N pH (O.Ol M. O.M. (total) Sample Horizon (H 20) Ca C l 2 ) % $ C/N Rl Ap 5.82 5. 10 15.38 0.31 28.71 R2 B f l 5. 95 5 . 15 2 .77 0,10 16.00 R3 Bf2 5. 95 5.26 I . 8 9 0.08 13.62 R4 Bf3 5. 95 5.26 1.06 0.04 15 .25 R5 BIIC 5 . 90 5. 30 0 .59 0 .03 11.33 R6 C 5.94 5. 35 0.49 0.03 9 . 3 3 Exchangeable Cations (me/100 g of s o i l ) C ,E ,C e (me/100 g B.S. imple Horizon Ca Mg K Na of s o i l ) % t Rl Ap 17.50 2.00 1.10 0 .14 51.20 39.88 R2 B f l 1 .98 0 .38 0.41 0 ,06 29,10 9 . 7 6 R3 Bf2 1.40 0 . 35 0 .23 0.08 25.70 8,24 R4 Bf3 1.13 0 .33 0 .25 0.10 19 .35 9 . 5 3 R5 BIIC 0 .43 0.08 0.14 0.06 12.61 5.92 R6 C 0 .33 0.10 0 .15 0 .07 10.53 6 . 5 0 25. TABLE 3.4 SUMMER - SELECTED PROPERTIES imple Horizon PH (H 20) PH (0,01 M. Ca C l 2 ) O.M. % N ( t o t a l ) % C/N SI L-F-H 3.60 3.10 49.00 l o O l 28,04 S2 Ae 4.35 3.94 1.20 0.05 13.80 S 3 5.62 5.25 .1.33 0.05 15.40 S4 Bfcg 5.90 5.56 0.49 0.02 14.00 S5 BC 6.20 5.80 0.19 0.01 11.00 S6 Cg 6.55 5.94 0.16 0.01 ' 9.00 S? H C g 6.30 5.85 0.13 0.01 7.00 Exchangeable Cations CE.C. (me/100 g of s o i l ) (me/100 g B.S. Sample Horizon Ca K Mg Na of s o i l ) fo SI L-F-H 10.50 0.36 0.81 0.60 137.50 8.92 S2 Ae 0,45 0.03 0.04 0.11 12,50 5.04 S3 Bfh ; 1.30 0.05 0.24 0.17 13.75 12.80 S4 Bfcg 0.78 0.03 0.18 0.14 8.75 12,91 S5 BC 0.80 0.05 0.15 0,14 15.00 7.60 S 6 Cg 4.08 0.17 1,08 0,34 11.25 50.40 S7 I l C g 8.00 0,16 0.95 0.26 15.00 62.47 2 6 . ALUMINUM AND IRON DETERMINATION Atomic absorption spectroscopy (A.A.) was used f o r aluminum determination because of i t s r a p i d i t y and p r e c i s i o n . Pawluk ( 1 9 6 ? ) has demonstrated the accuracy of the method by comparison w i t h an accepted g r a v i m e t r i c method. The g r e a t e s t s e n s i t i v i t y from experimental work i s 0 . 5 ppm percent a b s o r p t i o n , from 0 t o kO ppm aluminum. I n order to have good r e s u l t s f o r A l a n a l y s i s u s i n g c i t r a t e - d i t h i o n i t e and pyrophosphate e x t r a c t e d samples i t i s necessary t o t r e a t the standards e x a c t l y the same as the unknown samples. The s a l t content must a l s o be kept low i n order to prevent f o u l i n g of the burner head. Atomic absorption spectophotometry was a l s o used f o r i r o n determination. Pawluk (1967) u s i n g a P e r k i n -Elmer 303t determined a s e n s i t i v i t y to i r o n of 0 , 3 ppm F e i percent of absorption and could detect as l i t t l e as 0.05ppm Fe, He compared the r e s u l t s obtained by A.A. w i t h those obtained by the accepted c o l o r i m e t r i c procedure u t i l i z i n g O-phenanthroline, The r e s u l t s obtained by the two procedures were i n c l o s e agreement, and he found t h a t the r e p r o d u c i b i l i t y of r e s u l t s were b e t t e r w i t h atomic . absorption than with c o l o r i m e t r i c . method. PREPARATION OF THE SOIL SAMPLE FOR EXTRACTION To prepare the s o i l samples f o r the s e l e c t i v e 27. d i s s o l u t i o n procedure, organic matter was destroyed by sodium h y p o c h l o r i t e (NaOCl) at pH 9 . 5 (Anderson 1963) . The method has been t e s t e d by L a v k u l i c h and Wiens (1970)$ t h e i r r e s u l t s suggested a b e t t e r d e s t r u c t i o n of organic matter than w i t h hydrogen peroxide and l e s s d e s t r u c t i o n of mineral f r a c t i o n . No sample g r i n d i n g was done f o r any of the e x t r a c t i o n procedure i n order t o avoid l o s s of f i n e c l a y with a consequent lowering of the r e s u l t a n t v a l u e s . A f t e r s i e v i n g (100 mesh sie v e ) and mixing a l a r g e sample, a " r e p r e s e n t a t i v e " subsample was withdrawn and served as sample source f o r the l a b o r a t o r y a n a l y s i s of i r o n , aluminum, and s i l i c o n . The major source of e r r o r i s i n o b t a i n i n g a sample t h a t represents an average of the ho r i z o n as i t . occurs in,the f i e l d . The organic matter removal procedure was as follows« 20 g of s o i l , prepared as described above, were put i n t o a 250 ml c e n t r i f u g e p l a s t i c b o t t l e j 4-0 ml of NaOCl s o l u t i o n (minimum 6% a v a i l a b l e c h l o r i n e ) , which was adjusted to pH 9 . 5 immediately p r i o r to use, was added. A f t e r mixing thoroughly, the b o t t l e s were put i n a b o i l i n g wa^erbath f o r 15 minutes (with a second s t i r r i n g d u r i n g the b o i l i n g p e r i o d ) . C e n t r i f u g a t i o n f o r 10 minutes at 2200 rpm was c a r r i e d out fo l l o w e d by decantation of the suspension and the decantate was saved f o r s e l e c t i v e 28. elemental analysis (Mn. Fe, A l , S i ) . The above treatment was repeated f i v e times, each time the supernatant l i q u i d was co l l e c t e d a f t e r centrifugation. Elemental analysis on the NaOCl-decantate re-vealed the presence of traces of Fe, Al and S i only i n the sample with the highest percent (over 10%) organic matter. For the selective extractions of iron, aluminum and s i l i c o n , accepted lab procedures were followed as out' l i n e d by Bascomb ( 1 9 6 8 ) , for O.lM sodium pyrophosphate extraction;? by McKeague and Day (1966) f o r acid ammonium oxalate extraction, and by Mehra and Jackson ( i 9 6 0 ) f o r , c i t r a t e - d i t h i o n i t e extraction. The calculated r e s u l t s are reported i n Tables 4.1, 4.2, and 4.3 i n which a comparison of the data from the three d i f f e r e n t extractions for each element ( S i , Fe, Al) are given i n percent. 29. TABLE 4.1 COMPARISON OF SI DATA (from whole s o i l ) e x t r a c t e d bys OXALATE PYROPHOSPHATE DITHIONITE S i S i S i SOIL HORIZON — — % RYDER R l Ap 0.11 0,09 0.07 R2 B f l 0.70 0.10 0.23 R3 B f 2 1.25 0.09 0.25 R 4 Bfj 0.85 Oe09 0,28 R5 BIIC 0.20 0,15 0,20 R6 C 0.10 0.11 0.15 MARBLE HILL Ml L-H - • - -M2 Bf± 0,62 0,12 0,43 M3 B f 2 1*37 0012 0,40 M4 BIIC 0,98 0.10 0,23 M5 IIC 0.20 0.11 0,18 SUMMER SI L-F-H - -S2 Ae 0.10 0.07 0,35 S3 Bf>. 1,20 0.09 0,25 S4 Bfcg 0,80 0.10 0.25 S5 BC 0,40 0.08 0,20 s6 Cg - 0,14 0,15 S7 HCg - 0,12 0.23 ABBOTSFORD A l Ap - -A2 Bf-jhcc 0.50 0,10 0.25 A 3 B f 2 c c 1.30 0,07 0.23 A4 Bf^cc 0*90 0,06 0,23 A5 BIIC 1,00 0.07 0,20 A6 IIC o.4o 0.07 0.10 TABLE 4.2 COMPARISON OF FE DATA (from whole s o i l ) e x t r a c t e d by* 30. OXALATE PYROPHOSPHATE DITHIONITE Fe Fe Fe SOIL HORIZON — % RYDER RI Ap . 1.40 0.08 1.84 R2 B f l 1.54 0.13 1.93 R3 B f 2 1.50 0.07 ,1.76 R4 Bf^ 1.40 0,04 1.63 R5 BIIC 0.99 0.03 1.03 R6 C 0.99 0,02 0.75 MARBLE HILL Ml L-H - - -M2 B f l 1,62 0,25 2.16 M3 B f 2 1.40 0.16 1.96 M4 BIIC 1.0? 0.05 1.28 M5 IIC 1.06 0.03 0.84 SUMMER SI L-F-H - - -S2 Ae 0,08 0.05 0.18 S3 Bfh' 0.61 0.09 0.94 s4 Bfcg 0.95 0.06 1.29 S5 BC 0.43 0.04 0.65 s6 Cg 0,26 0.02 0.56 S7 I l C g 0,51 0.02 0,85 ABBOTSFORD A l Ap - - -A2 B ^ h c c 0.88 0.15 1.57 A3 B f 2 c c 0,80 0,03 1,65 A4 Bf^cc 0.98 0.03 1.76 A5 BIIC 0.56 0.01 1.28 A6 IIC 0^22 0.01 0,66 31. TABLE 4 . 3 COMPARISON OP AL DATA (from whole s o i l ) extracted byj OXALATE PYROPHOSPHATE DITHIONITE A l A l A l SOIL HORIZON 0 RYDER Rl Ap 1.05 0 .55 0 . 4 5 R 2 B f l 1.90 0 .55 0 . 9 5 R3 B f 2 1.90 0 , 4 1 0 . 8 2 R4 Bf^ 1.50 0.32 0 ,68 R5 BIIC 1.45 0 .33 0 . 5 3 R6 C 1.45 0.29 0 .43 MARBLE HILL Ml L-H - - -M 2 B f l 2.20 0.80 1 .25 M3 B f 2 2.10 0.62 1 .10 M 4 BIIC 1.60 0 . 4 0 0.68 M5 IIC 1.20 0.30 0 . 4 0 SUMMER SI L-F-H - *m -S 2 Ae 0.30 0 , 1 9 0 . 1 8 S3 Bfh 2 .15 0,47 0 .88 S 4 Bfcg 1.20 0 , 2 8 0 .55 S5 BC 0 . 8 0 0 , 2 1 0 . 3 5 s6 eg 0.20 0 . 0 8 0 . 1 3 S7 HCg 0,20 0,06 0 .13 ABBOTSFORD A l .- Ap • - - -A 2 Bf 1hcc 1.50 0 .51 0 .90 A3 • BfgCC 2.00 0 .31 0 .78 A4 B f ^ C C 1 . 8 1 0.32 0 , 8 0 A 5 BIIC 1,65 0 . 2 5 0 . 4 8 A6 IIC 0.90 0.17 0 . 2 5 32. RESULTS AND CONCLUSIONS OF THE EXTRACTION PROCEDURES The a b i l i t y of the oxalate procedure to remove more aluminum than the citrate-bicarbonate-dithionite procedure is readily evident and Figure 1 shows this rela-tionship. On the other hand, the citrate-bicarbonate-dithionite procedure extracts slightly higher quantities, of iron than the oxalate procedure? of course, the citrate-bicarbonate-dithionite method extracts amorphous as well,as crystalline forms of iron; while the oxalate method reportedly extracts only the amorphous iron compounds. This explains the differences in the values. Only two oxalate iron values exceeded the citrate-bicarbonate-dithionite values. The different extraction a b i l i t y of these two procedures i s illustrated in Figure 2, As reported previously, the difference between oxalate and pyrophosphate - extractable Fe gives a measure of amorphous inorganic Fe? while the difference between dithionite and oxalate - extractable Fe provides an estimate of more or less crystalline Fe - oxidese(McKeague et a l 1971). In Table 5B an account of these differences is given for the four s o i l s . Figures 3 and k illustrate the distribution of the amorphous extractable Al and Fe as i t results from Table 5» for the Ryder and Summer soils only. The distribution of clay is also provided along with the amorphous Fe distribution? the two distributions down the profile appear to be quite closely related. 33. 0 0.4 0.8 1.2 1.6 PERCENT CITRATE-BICARB.-DITHIONITE EXTRAC. ALUMINUM FIGURE 1. COMPARISON OF ALUMINUM EXTRACTION METHODS: OXALATE VS CITRATE-BICARBONATE-DITHIONITE, 34 1 1 r O PERCENT OXALATE EXTRACTABLE IRON FIGURE 2, COMPARISON OF IRON EXTRACTION METHODS: OXALATE VS •DITHIONITE. 3 5 -TABLE 5" D i f f e r e n c e s Between Oxalate- and Pyrophosphate- E x t r a c t e d Fe and D i t h i o n i t e - and Oxalate- E x t r a c t e d Fe OXAL - PYROPH DITH - OXAL (amorphous i r o n ) (+ c r y s t . i r o n ) SAMPLE HORIZON % Fe " fo Fe • RYDER RI Ap R2 B f l i 9 4 i 0 . 3 8 R3 B f 2 1A3 0 9 2 6 R4 Bfj 1 .36 0 . 2 3 R5 BIIC 0 . 9 6 0.04 R6 C 0 . 9 7 -MARBLE HILL Ml L-H - -M2 B f t 1 .37 0 . 5 4 M3 B f 2 1.24 0 . 5 6 M4 BIIC 1 . 0 2 0 . 2 1 M5 IIC 1 . 0 3 -SUMMER SI L-F-H - -S2 Ae 0 . 0 3 0 . 1 0 S 3 Bf;> 0 . 5 2 0.33 S4 B f c g 0 . 8 9 0 . 3 4 S5 BC 0 . 3 9 0.22 S6 Cg 0.24 0 , 3 0 S7 H C g 0.48 0 . 3 4 ABBOTSFORD A l Ap - -A2 B f 1 h c c 0 . 7 3 0 . 6 9 A3 B f 2 c c 0.77 0 . 8 5 A4 B f ^ C C 0 . 9 5 0 . 7 8 A5 BUG 0.55 0 . 7 2 A6 IIC 0 . 2 1 0.44 FIGURE 3, AMORPHOUS EXTRACTED IRON "(BY DIFFERENCE BETWEEN OXALATE AND PYROPHOSPHATE EXTRACTED IRON), AND CLAY CONTENT IN RYDER. % E l e m e n t a l Fe 1 % <2 p. C L A Y FIGURE 4, AMORPHOUS EXTRACTED IRON (BY DIFFERENCE BETWEEN OXALATE AND PYROPHOSPHATE EXTRACTED I RON), AND CLAY CONTENT IN SUMMER. 3?» . MINERALOGIGAL STUDIES X-ray d i f f r a c t i o n analysis of the< 2^ clay f r a c t i o n from the d i f f e r e n t horizon of the four s o i l s were obtained on a P h i l l i p s X-ray difractometer 9 using Cu K<< ra d i a t i o n . The samples were s i m i l a r i n showing only weak and d i f f u s e r e f l e c t i o n s i n the clay mineral range. I t appears 9 i n f a c t , that an amorphous coating on the crys-t a l l i n e p h y l l o s i l i c a t e minerals prevents the l a t t e r to become oriented on t h e i r basal planes so as to mask or scatter the d i f f r a c t i o n peaks. Occurrence of the amorphous phase as discrete p a r t i c l e s or as an external coating could not only prevent the layers from assuming p a r a l l e l orien-t a t i o n , but also absorb some of the d i f f r a c t i o n from well-c r y s t a l l i z e d clay, i Treatment with oxalate improved dramatically the resolution of the peaks, so that i t was possible to i d e n t i f y the main minerals present which are presented i n Table 6 , 38 . TABLE 6 Dominant minerals p r e s e n t i n Ryder, Summer, Abbo t s f o r d , and Marble H i l l as determined by X-ray d i f f r a c t i o n . SOIL SERIES PROFILE MAIN MINERALS Ryder RI Verm., C h i . , 111., Amph., Q., F. R2, R3 C h i . , Verm., 111., Q., F. R4-, R5, R6 C h i . , Verm,, Q., F. Marble H i l l Ml Verm., C h i . , 111., Q., F. M2 Mt., C h i . , 111., Q., F. M3. M4-, M5 Verm., C h i . , 111., Q., F. Abbotsford A l , A2, A3* A4-, A5. A6 Verm., C h i . , I l l , , Q., F. Summer S2 Verm., C h i . , Amph., Q., F. ( p l a g i o c l a s e ) S3. S4-, S5, S 6 , S7 Verm., C h i . , 111., Amph., Q., F. ( p l a g i o c l a s e ) # Notes Verm. ( V e r m i c u l i t e ) s C h i . ( C h l o r i t e ) s Mt. (M o n t m o r i l l o n i t e ) 5 111, ( I l l i t e ) s Amph. (Amphiboles): Q. (Quartz)s F. ( F e l d s p a r ) . 3 9 . In the Marble H i l l s o i l , m o ntmorillonite ;. (smectite) i n the B f 1 i s not present as an independent mineral but seems to occur i n t e r s t r a t i f i e d w i t h c h l o r i t e and mica ( i l l i t e ) . M o n t m o r i l l o n i t e i s i d e n t i f i e d by g l y c e r o l s o l v a t i o n with which i t e x h i b i t s : an expansion o of i t s b a s a l spacing (15 A at room r e l a t i v e humidity 40 - 50$ R.H.) to about 18 X: upon hea t i n g to 550°C, the mineral c o l l a p s e s enhancing the 10 A peak. An i n t e g -r a l s e r i e s of peaks a s s o c i a t e d w i t h the l a r g e s t b a s a l 0 spacing of 14 A which does not expand by g l y c e r o l sorp-t i o n and does not s h i f t upon heating at 550°C, assures the presence of c h l o r i t e . Smectite can o r i g i n a t e i n a number of ways. One i s by i n h e r i t a n c e , f o r example the A l b e r t a Podzol described by Pawluk ( i 9 6 0 ) . A second i s by s y n t h e s i s from the amorphous a l u m i n o s i l i c a t e s and/or the s o l u b l e c o n s t i t u e n t elements (Jackson, 1965) . The t h i r d p o s s i b l e o r i g i n of smectite i s as d i r e c t a l t e r a t i o n product of mica (Jackson, 1965) ; Potassium may be p a r t i a l l y removed from each l a y e r g i v i n g mica-smectit;e i n t e r s t r a t i f i c a t i o n i n the a-b d i r e c t i o n s or i t may be s e l e c t i v e l y removed i n t e r n a l l y from c e r t a i n l a y e r s (the " p r e f e r e n t i a l weathering plane" of Jackson et a l . , 1952) g i v i n g i n t e r s t r a t i f i c a t i o n i n the c - a x i s d i r e c t i o n . S e v e r a l examples of these types of i n t e r s t r a t i f i c a t i o n have been considered by Sudo et a l ( i 9 6 0 ) . 40. I n t e r s t r a t i f i c a t i o n s of v e r m i c u l i t e - i l l i t e -c h l o r i t e (present i n d i f f e r e n t p r o p o r t i o n s ) are claimed f o r the other horizons of the Marble H i l l s o i l and f o r a l l horizons of Ryder, Summer, and Abbotsford s o i l s . The determination of t h i s type of i n t e r s t r a t i -f i c a t i o n was based on a combination of the c h a r a c t e r i s t i c s of each component-layer. 0 a 10 A c l a y mica ( l l l i t e ) has a 10 A ba s a l spac-ing and i t s i n t e g r a l s e r i e s of higher order r e f l e c t i o n s do not s h i f t upon e i t h e r s o l v a t i o n w i t h g l y c e r o l or heating at 550°C. V e r m i c u l i t e maintains i t s 14 A peak upon s o l v a t i o n w i t h g l y c e r o l and under high r e l a t i v e humidity, which d i s t i n g u i s h e s i t from smectite, which, as seen above, expands i t s b a s a l spacing to about 18 A, At 550°G, v e r m i c u l i t e s h i f t s to 10 A peak and t h a t d i s -t i n g u i s h e s i t from c h l o r i t e which does not s h i f t upon heating at 55° ° C C h l o r i t e presence i s assessed, as mentioned p r e v i o u s l y , by an i n t e g r a l s e r i e s of peaks (7.01 A, 4.7 A, 3.5A) associated with the ba s a l spacing of 14 A which does not expand by g l y c e r o l s o r p t i o n and does not s h i f t upon hea t i n g at 550°C. Because the same peaks are assigned to k a o l i n i t e which has the same behaviour upon s a t u r a t i o n w i t h Mg and K and heat i n g to 300°C and 55°°C, an examination by an i n f r a r e d a bsorption technique was needed to d e f i n i t e l y assess the presence of c h l o r i t e . 41. For Ryder and Summer s o i l s the c h l o r i t e appears to he an F e - r i c h type of c h l o r i t e as i n d i c a t e d by the f a c t t h a t the f i r s t and the t h i r d b a s a l r e f l e c t i o n s are weak and the second and f o u r t h order b a s a l r e f l e c t i o n s are stron g ( C a r r o l l , 1 9 7 0 ) , I n t e r s t r a t i f i e d mixtures of the three components, m i c a - v e r m i c u l i t e - c h l o r i t e were the predominant and the most s i g n i f i c a n t m a t e r i a l s present. SUCCESSIVE EXTRACTIONS AND INFRARED SPECTROSCOPY FOR THE CHARACTERIZATION OF THE INORGANIC AMORPHOUS SYSTEM IN SOIL CLAYS, S e l e c t i v e d i s s o l u t i o n a n a l y s i s i n v o l v i n g treatment wi t h a l k a l i s has been used to obta i n some estimates of the amorphous c o n s t i t u e n t s i n s o i l c l a y s . These procedures f o r amorphous m a t e r i a l s e x p l o i t the f a c t that the r e a c t i o n r a t e v a r i e s widely according to s p e c i f i c surface area, extent of s t r u c t u r a l order, and chemical bond s t r e n g t h , and i s a c c o r d i n g l y higher or much higher f o r amorphous than f o r most c r y s t a l l i n e m a t e r i a l s . Hashimoto and Jackson ( i 9 6 0 ) p r e s c r i b e d a treatment of c l a y w i t h NaOH and they concluded t h a t s u b s t a n t i a l amounts of allophane, f r e e s i l i c a and alumina were brought i n t o s o l u t i o n by a treatment w i t h an excess of 0,5 N NaOH at the b o i l i n g p o i n t f o r a r e s t r i c -ted time ( 2 , 5 minutes). Only s m a l l amounts of c r y s t a l l i n e c l a y minerals were d i s s o l v e d d u r i n g the same d i g e s t i o n p e r i o d . 4-2. F o l l e t et a l . (1965) s t u d i e d a procedure which in v o l v e s p r o t r a c t e d contact with Doth c o l d and hot weak a l k a l i n e s o l u t i o n ( 5 % NagCO^), i n order t o detect the a l k a l i - s o l u b l e m a t e r i a l i n a podzol and a non-calcareous humic gley s o i l i n which c r y s t a l l i n e l a y e r s i l i c a t e s predominate. They found t h a t , as f a r as the c r y s t a l l i n e minerals are concerned, successive treatments with c o l d and hot d i l u t e NagCO^ s o l u t i o n d i d not r e s u l t i n apprec-i a b l e d i s s o l u t i o n . They used repeated e x t r a c t i o n s t o reduce the s i l i c a and alumina removed to a small and v i r t u a l l y constant l e v e l of about 0.2 - 0.5% of the sample weight. The a s s o c i a t i o n of amorphous s i l i c a t e s w i t h " f r e e " i r o n oxides has a l s o been i n f e r r e d from d i s s o l u t i o n of s i l i c o n and aluminum i n a d d i t i o n to i r o n during removal of e x t r a c t a b l e i r o n oxides from s o i l c l a y s (Me.hra and Jackson, I960? F o l l e t et a l . , 1 9 6 5 ) . Assuming t h a t the in o r g a n i c amorphous m a t e r i a l i n the c l a y f r a c t i o n of the s o i l s s t u d i e d i s a complex polyphase system, i t was f e l t t h a t an appropriate approach to remove i t s e l e c t i v e l y from the system i n order t o charac-t e r i z e and ob t a i n a b e t t e r understanding of the composition and the s t r u c t u r e of the system i t s e l f was necessary. <• In t h i s study, an attempt was made to combine chemical s e l e c t i v e d i s s o l u t i o n procedures w i t h p h y s i c a l techniques on two of the s o i l s e r i e s used before 1 Ryder and Summer, as shown s c h e m a t i c a l l y i n Figure 5. FIGURE 5 A schematic r e p r e s e n t a t i o n of successive e x t r a c t i o n s of inorga n i c amorphous system and corresponding analyses. < 2)i clay successive sample treatment Fraction remaining Analysis applied no treatment X-ray; IR; Surface area 5% Na 2 C0 3 (a) H II M (a) + Na-pyrophosphate (b) C n I I II c (a+b)+ Ac. NH4-oxalate (c) 4 (a + b + c) + citrate-dithionite (d) II II II 44. The most u s e f u l technique i n t h i s p a r t i c u l a r experiment was f e l t to be i n f r a r e d spectroscopy because, u n l i k e X-ray d i f f r a c t i o n , the c o n t r i b u t i o n s of the s o l u b l e and i n s o l u b l e components t o any absorption band are addi -t i v e , and the double-beam spectrophotometer enables the d i f f e r e n c e s between the two samples to be recorded simply. The s p e c t r a alone provide much inf o r m a t i o n regarding the mineralogy and composition of a r a t h e r wide range of m a t e r i a l s , from amorphous to w e l l c r y s t a l l i z e d s i l i c a t e s , aluminum and i r o n oxides and hydroxides. The c l a y s of the two s o i l s e r i e s used i n t h i s experiment were obtained by s u p e r - c e n t r i f u g i n g the 100-mesh sieved s o i l s p r e v i o u s l y t r e a t e d w i t h NaOCl (at pH 9 .5 ) to remove the organic matter. The < 2^ c l a y s were then f r e e z e - d r i e d . The adopted procedure i n d e t a i l i s as fol l o w s s 1 . Weigh four f r a c t i o n s (a, b, c, d) (200 mg each) of each sample i n t o a 50 ml c e n t r i f u g e p l a s t i c tube, whose t a r e has been taken on an air-dry b a s i s , 2 , Add 16 ml of % NagCO^ s o l u t i o n heating at 90°0 f o r f i f t e e n minutes i n a waterbath. ( A single treatment was f e l t to be s u f f i c i e n t and adopted for t h i s studyo and only for f i f t e e n minutes becauseo checking the rate of d i s s o l u t i o n , i t (continued) was found that i t decreased very r a p i d l y and the i n f r a r e d s p e c t r a - d i f f e r e n t i a l s p e c t r a i n t h i s case - showed no s i g n i f i c a n t changes except i n t o t a l percent t r a n s m i s s i o n between those t r e a t e d f o r f i v e minutes i n the s i n g l e and f o r t h i r t y minutes i n the double treatments). Mix the samples i n t e r m i t t e n t l y \during the h e a t i n g p e r i o d . C e n t r i f u g e at 2500 rpm f o r ten minutes. The supernatant s o l u t i o n should be p e r f e c t l y c l e a r . Determine S i and A l (no Fe i s brought i n t o s o l u t i o n ) on the e x t r a c t s by atomic a b s o r p t i o n spectrophotometry. A l l the t r e a t e d samples a f t e r the d i s s o l u t i o n e x t r a c t i o n were washed three times w i t h 10 ml of IM NaCH^COO/NaCl ( l / l ) mixture adjusted to pH 5 . 0 with a c e t i c a c i d (the acetate alone r e s u l t e d i n d i s p e r s i o n of the sample). This washing was repeated a f t e r each s e l e c t i v e d i s s o l u t i o n t r e a t -ment that followed i n order t o avoid secondary e f f e c t s of the treatment i t s e l f on the measurements due to changes i n the st a t u s of exchangeable cations„ The excess of the washing mixture was then removed by successive washing with 10 ml of water/raethanol ( l / l ) , 10 ml of methanol/acetone ( l / l ) , and 10 ml of acetone. 6. From one (a) of the four r e p l i c a t e s , take a s u i t a b l e p o r t i o n of undried sample f o r X-ray d i f f r a c t i o n . The remainder of t h i s r e p l i c a (a) i s saved f o r i n f r a r e d and surface area determin-a t i o n . 7. The remainder of r e p l i c a (a) and the three r e p l i -cates l e f t (b, c, d) are f r e e z e - d r i e d , put i n the p l a s t i c tubes and weighed ( i n order to know the weight l o s s due to the treatment and the amount of sample used f o r the next treatment). 8. Treat the (b, c, d) r e p l i c a t e s w i t h 20 ml 0.1 M Na-pyrophosphate (Na^PgO^) adjusted to pH 10,0 with HCl and shake f o r about s i x t e e n hours at 25°C i n a controlled-temperature chamber. 9. Centrifuge at 8200 rpm f o r ten minutes and then wash as per number 5. 10. From the (b) r e p l i c a t e , take, as i n number 6, a s u i t a b l e p o r t i o n of sample f o r X-ray and f r e e z e -dry the remainder of (b) and the two l e f t ( c , d) r e p l i c a t e s - put the l a t t e r i n the p l a s t i c tubes and we i g h . 11. On the e x t r a c t s determine S i , Fe and A l , a f t e r proper d i l u t i o n , by atomic absorption spectroscopy. 12. The two remaining r e p l i c a t e s ( c , d) are now t r e a t e d w i t h 10 ml of a c i d NH^- oxalate (at pH 3*0) and shaken i n darkness f o r four hours. 47 • 13• Centrifuge at 2500 rpm f o r ten minutes, taking care that the supernatant solution i s p e r f e c t l y clear. 14. Determine S i , Fe, and A l on the extracts by atomic absorption spectrophotometry. 1 5 . Wash as per number 5 and repeat the procedure described i n number 6 . 16. The remaining freeze-dried r e p l i c a t e (d) i s put into a p l a s t i c tube, weighed and then treated with 16 ml of 0 , 3 M Na-citrate, 2 ml of 1 M NaHCO^ and about 400 mg of d i t h i o n i t e (Na2S20^) powder. 17. Carry out the extraction i n a waterbath at 80°C for f i f t e e n minutes s t i r r i n g continuously for the f i r s t minute and then intermittently f o r the rest of the period. Repeat the same treatment two more times. Centrifuge at 1600 - 2200 rpm„ 18. Wash again as per number 5 and repeat the procedure of number 6$ freeze-dry the sample. 19. On the extracts, determine S i , Fe and A l , aft e r proper d i l u t i o n , by atomic absorption spectrophoto-metry. Weigh:the sample f o r loss determination. These experiments were designed to determine the nature of the material dissolved by the treatments applied, and i t was th e r e f o r e e s s e n t i a l t h a t no dispersed c l a y be l o s t during the t r a n s f e r r i n g , washing and decanting procedures. Care was taken to ensure t h a t the c l a y remained f l o c c u l a t e d throughout the treatments and washings• The r e s u l t s of these successive e x t r a c t i o n s are reported i n Tables 9 and 10 i n % of each element. For the Summer s e r i e s , i n Table 10, the data of the Na-pyrophos-phate e x t r a c t i o n are not reported because no appreciable amounts of the three elements could be detected i n the s o l u t i o n . RESULTS AND DISCUSSION ON SUCCESSIVE EXTRACTION EXPERIMENT A few general observations about Tables 7 and 8,on the percent elemental data e x t r a c t e d a f t e r each treatment i n both c l a y s f o l l o w s . A higher amount f o r a l l elements and a f t e r a l l treatments i s g e n e r a l l y observed f o r Summer i n comparison to Ryder. On both c l a y s no detectable Fe was ext r a c t e d by 5% Na 2C0y For a l l three elements, the highest amount e x t r a c -ted i s observed a f t e r a c i d NH^-oxalate treatment. Follow-ing d i t h i o n i t e treatment, the e x t r a c t i o n of A l and S i i s much lower than a f t e r o x a l a t e , while the e x t r a c t i o n of Fe.; i s s t i l l q u i t e high. , I t i s i n t e r e s t i n g to compare the Fe, A l and S i data a f t e r oxalate "successive" e x t r a c t i o n s reported i n Tables 7 and 8 w i t h those reported i n Tables 4.1, 4.2, and 49. TABLE 7 RYDER SUCCESSIVE EXTRACTIONS ON < 2yu CLAY 5% Na- T o t a l D i t h -Na2CO^ Pyroph. o x a l . Amorph. ionit< Sample Horizon (a) (D) (c) (a+b+c) Aluminum (fo by wt) Rl Ap 0.165 0.30 2.75 3.215 0,39 R2 B f l 0.184 0,37 4,62 5.174 0.63 R3 B f 2 0.14? 0.36 4.10 4.637 0.81 R4 Bf^ 0.164 0.32 3.75 4.234 0.69 R5 BIIC 0.164 0,39 5.01 5.564 0.80 R6 C 0.193 0.33 4.34 4.863 0.42 S i l i c o n (f> by wt) Rl Ap 0.009 0.055 0.55 0.614 0,30 R2 B f l 0.013 0.055 1.50 1.568 0.30 R3 B f 2 0,013 0.047 1.76 1.820 0.33 R4 B f ^ 0.011 0.046 1.51 1.567 0,29 R5 BIIC 0.011 0.047 2.38 2.438 0,34 R6 C 0.009 0.054 2,14 2,203 0.34 Iron ( [fo by wt) Rl Ap - O.09 5.25 5.34 2.99 R2 B f l - 0.04 5.19 5.23 4.36 R3 B f 2 - 0.04 5.14 5.18 5.27 R4 Bf-j - 0.03 4.53 4.56 4.15 R5 BIIC - 0.03 3.05 3.06 3.88 R6 C - 0,02 2.08 2,10 1.61 TABLE 8 50 SUMMER SUCCESSIVE EXTRACTIONS ON < 2yu CLAY % NH^- Total Dith-Na2C0^ oxalate Amorph, ionit< Sample Horizon (a) (b) (a + b) (d) Aluminum (fo by wt) S2 Ae 0.69 0.80 1.49 0.09 S3 Bfv; 3,48 , 9,87 13.35 0.52 S4 Bfcg 3.24 9.24 12.48 0.52 S5 BC 3,06 7.89 10.95 0.78 S6 eg 0.46 1.12 1.58 0.17 S7 HCg 0.31 1.04 1.17 0.13 S i l i c o n (fo by wt) S2 Ae - 0.46 0.46 0.14 S3 Bfh • - 5,80 5.80 0.37 S4 Bfcg - 4.80 4,80 0.32 S5 BC - 4.76 4.76 0.60 s6 Cg - 0.86 0,86 0.30 S 7 HCg - 0.86 0.86 0.29 Iron (f, by wt) S2 Ae - 0,61 0,61 0.69 S3 Bfh - 2.72 2.72 1.76 S4 Bfcg - 6.29 6.29 3.09 S5 Be - 7.41 7.41 5.58 S6 . Cg - 1.53 1.53 0.80 S7 HCg - 2.32 2,32 0,85 51 > 4.3 a f t e r oxalate "separate" e x t r a c t i o n s . The d i f f e r e n c e s are q u i t e s t r i k i n g , and the f a c t t h a t the amounts e x t r a c t e d by oxalate a f t e r the samples were p r e v i o u s l y t r e a t e d with 5% NagCOy are so much higher than those a f t e r a simple oxalate treatment, can be explained by assuming that the a l k a l i treatment provides an increase i n the d i s p e r s i o n of c l a y . In p a r t i c u l a r , i t appears t h a t most of the " f r e e " i r o n oxides i n the two c l a y s i s i n a c c e s s i b l e to oxalate u n t i l the a l k a l i - s o l u b l e a l u m i n o s i l i c a t e s have been removed. The f a c t that no Fe i s brought i n t o s o l u t i o n by NagCO^ does not n e c e s s a r i l y imply t h a t the s i l i c a and alumina are f r e e and uncombined with i r o n oxides i n the o r i g i n a l c l a y . The s i l i c a and alumina not removed by a l k a l i treatment w i l l be d i s s o l v e d , along with i r o n , by a c i d NH^-oxalate; consequently, i t i s considered that t h i s l a t t e r f r a c t i o n i s much more c l o s e l y a s s o c i a t e d w i t h the i r o n oxides. , A few observations on the data of Tables 9 and 10 seem worthwhile to make. The molar r a t i o s of AlgO^ and Fe 20^ i n respect to S i 0 2 both decrease with depth i n the Ryder, while the molar r a t i o of Fe 20^ i n the Summer increases w i t h depth from S3 (Bfh) down. The t o t a l percent amorphous m a t e r i a l c a l c u l a t e d a f t e r Na2C0-j and oxalate e x t r a c t i o n on 12 c l a y (AlgO^ + F e2 ^ 3 + S ^ 2 ^ f°ll° w q u i t e c l o s e l y , i n both c l a y s , the percent l o s s e s c a l c u l a t e d a f t e r the same e x t r a c t i o n s , TABLE 9 RYDER Amorphous m a t e r i a l e x t r a c t e d from ^2yu c l a y s by successive e x t r a c t i o n s ? % NagCO^ + Na-pyrophosphate + Acid NH^-oxalate. I n the t a b l e are a l s o i n c l u d e d : % l o s s ; % c l a y content; molar r a t i o of amorphous oxides; fo sum of amorphous oxides; surface area j fo amorphous oxides i n the s o i l o Sample R l R2 R3 R4 R5 R6 % A I 2 O 3 60O8 9.78 8,76 8.00 10 .52 9.19 fo FegO^ 7.64 7.48 7.40 6.52 4.40 3.00 % SiO^ 1.31 3o36 3.90 3 . 3 5 5.22 4.71 % (AlgO^ + FegO^ + S i 0 2 ) 15.03 20.62 20.06 17 .87 20,14 16.90 S i 0 2 / AlgO^ / F e 2 0 3 1 A . 6 1 /2.9 1 /2.2 1 /2 . 4 1 / 2 1 A . 9 - molar r a t i o / 5 . 8 /2.Z A . 9 /1.9 /0 . 8 /0.6 %<2/«clay 11.53 8.63 9.00 8 . 8 3 7 .30 5.12 f> Amorph, i n s o i l 1 .73 1 .78 1.81 1 ,58 1.47 0 .86 fo l o s s 12.72 23.07 22.40 18 ,97 23.17 17 .25 Surface area (m /g) 123.02 170 .87 176.97 124.71 109.22 87.04 Note: The percent of A l g O y FegO^, and S i 0 2 are c a l c u l a t e d from the " t o t a l amorphous" ( a + b + c ) given i n Table 7. TABLE 10 SUMMER Amorphous m a t e r i a l e x t r a c t e d from <2j\ c l a y by successive e x t r a c t i o n s ! 5% Na 2C0^ + Acid NH^-oxalate + d i t h i o n i t e . The t a b l e a l s o includes» molar r a t i o of amorphous oxides? i sum of amorphous oxides? % < 2 ^ c l a y ? % amorphous oxides i n s o i l ? % l o s s ; surface area. Sample S2 S3 S4 S5 S6 S7 % AlgO-j 2.82 25.23 23.59 20.69 2.99 2,21 fo F e 2 0 ^ 0.87 3.89 8.99 10.60 2.19 3.32 % S i 0 2 0.98 12.41 10.27 10.18 1,84 1.84 % (A1 20^ + F e 2 0 ^ + S i 0 2 ) 4.67 41.53 42.85 41,47 7.02 7.37 S i 0 2 / A 1 2 0 ^ / Fe 20-^ - molar r a t i o 1 /2.9 /0.9 1 /2.00 /0.3 1 /2.3 /0.9 1 /2.0 A . o 1 A . 6 A . 2 1 A . 2 A . 8 % < 2^A c l a y 2.80 6.50 11.80 2.4 8,1 7.9 io amorph. i n s o i l 0.13 2.69 5.05 1.00 0,57 0,58 % l o s s 5.02 42.14 43.20 42.07 8,00 8.08 Surface area (m /g) 64.96 172.45 206.35 158.37 99.12 103,89 Note: The % AlgO^, FegO^ and S i 0 2 are c a l c u l a t e d from " t o t a l amorphous" (a + b) given i n Table 8, and while i t seems q u i t e uniformly d i s t r i b u t e d down the p r o f i l e i n Ryder, i t i s low ( 4 , 6 7 % ) i n the e l u v i a t e d h o r i z o n (Ae), q u i t e high and uniform i n B f h , Bfcg and B.C., and low again i n Cg and IIGg horizons of the Summer c l a y . In t h i s c l a y , the t o t a l amorphous content i n the i l l u v i a t e d horizons i s much higher than i n the correspondent i l l u v i a t i o n horizons of Ryder c l a y (at l e a s t two time s ) . Looking at Figure 8.1 and 8 . 2 i n which the t o t a l amorphous content f o r the two c l a y s i s represented, along w i t h percent of * 2^ c l a y d i s t r i b u t i o n down the pro-f i l e s , i t can be observed, that the t o t a l amorphous m a t e r i a l d i s t r i b u t i o n s f o l l o w c l o s e l y the percent of <2^ c l a y d i s t r i b u t i o n s except f o r the B.C. sample of the Summer c l a y , i n which, even though the percent of <2yu c l a y i s very low ( 2 . 4 % ) , the amorphous accumulation i s very high ( 4 1 , 4 7 % ) , when one observes again i n Tables 9 and 10, the d i s t r i b u t i o n of percent amorphous as c a l c u -l a t e d f o r the s o i l as a whole, i t can be that i t f i r s t increases to a maximum i n Bf3 f o r Ryder and i n Bf c g f o r Summer, then i t decreases u n i f o r m l y towards the lower horizons. . Figure 6 and 7 represent the d i s t r i b u t i o n s of % AlgO^, Fe 20^ and S i 0 2 , as ex t r a c t e d by successive treatments of 5% Na 2C0^ and a c i d NH^-oxalate, from ^ 2 j l * c l a y s , and the d i s t r i b u t i o n of the < 2yu c l a y i t s e l f . 55 '2 EXTRACTED BY SUCCESSIVE TREATMENTS (% AS PRESENTED IN TABLE 9); AND< 2/1 CLAY CONTENT. % A l 20 3 ~ Fe 20 3 - Si02 ' % <2g CLAY FIGURE 7, SUMMER - DISTRIBUTION ALONG THE PROFILE OF Al 2O3 - F*^ - Si0 2 EXTRACTED BY SUCCESSIVE TREATMENTS (% AS PRESENTED IN TABLE 10); AND < 2fJL CLAY. 5 6 . Total Amorphous- % (SiC>2 + A l 2 0 3 + F e 2 0 3 ) i % <2/j. CLAY FIGURE 8.1. RYDER - DISTRIBUTION ALONG THE PROFILE OF TOTAL AMORPHOUS (% Si0 2 + I A l 2 0 3 + I F e ^ ) (AS PRESENTED IN TABLE 9) EXTRACTED,. BY.. SUCCESSIVE. TREATMENTS;. AND .%.< 2 CLAY, Total Amorphous - % (Si02 + A I 2O3 + Fe 203) ' % <2^ CLAY F I G U R E 8.2.' SUMMER - DISTRIBUTION ALONG THE PROFILE OF TOTAL AMORPHOUS (% Si0 2 + A) 20 3 + % Si0 2) (AS PRESENTED IN TABLE 10) EXTRACTED BY SUCCESSIVE TREATMENTS; AND I < 2 LL CLAY. $ 7 . I t can be observed thats ( i ) The d i s t r i b u t i o n s of the amorphous components c l o s e l y f o l l o w that of the c l a y , except as pointed out p r e v i o u s l y f o r t o t a l amorphous m a t e r i a l i n the B.C. Summer h o r i z o n . ( i i ) The A1 20^ content i s g e n e r a l l y higher i n both c l a y s i n respect to S i 0 2 and Fe 20^ contents. Low i n Ap and Ae hor i z o n s , increases d r a s t i -c a l l y i n the i l l u v i a l horizons i n which i t maintains i t s e l f reasonably constant, and then i t l e v e l s o f f at lower depths, ( i i i ) The Fe 20^ d i s t r i b u t i o n f o l l o w s the same p a t t e r n as the< 2^ c l a y d i s t r i b u t i o n and the content i s uniformly high through a l l the horizons from Ap to Bf3 decreasing d r a s t i c a l l y i n BIIC and C horizons i n the Ryder c l a y . In the Summer c l a y , the Fe 20^ content f o l l o w s the same p a t t e r n described f o r A1 20^ content. ( i v ) The S i 0 2 content i n Ryder i s q u i t e low i n Ap ho r i z o n , i t goes up reaching a maximum i n the B f 2 , decreases i n Bf3 and increases again i n the two lower horizons, In the Summer i t i s a l s o very low i n Ae, increases to a maximum i n Bfh horizon and decreases c o n s t a n t l y with depth. The d i s t r i b u t i o n of the above three amorphous components seems to be c o n s i s t e n t , p a r t i c u l a r l y i n the Summer c l a y , w i t h a model of weathering i n a podzol s o i l p r o f i l e of a material having the composition of the G horizon clay. The high content of amorphous components i n Bfh, Bfcg, and BC horizons of Summer clay seems to he due not only to the process of i l l u v i a t i o n from the upper horizons, but also to accumulation due to the impeded drainage i n the subsoil. 59 INFRARED SPECTROSCOPY STUDIES Great care has to be taken i n p r e p a r i n g samples f o r i n f r a r e d spectroscopic a n a l y s i s , e s p e c i a l l y when com-parisons are made f o r d i f f e r e n c e s or s i m i l a r i t i e s between two samples. In t h i s study, not only a q u a l i t a t i v e compari-son but a l s o a q u a n t i t a t i v e comparison was attempted. As mentioned p r e v i o u s l y , i n the d e t a i l procedure of these successive e x t r a c t i o n s , the samples were f r e e z e -d r i e d a f t e r each successive e x t r a c t i o n , and l e f t f o r seventy-two hours i n a d e s s i c a t o r with MgtNO^Jg-^HgO (about 55% R.H.) f o r e q u i l i b r a t i o n , KBr p e l l e t s were pre-pared weighing, to the f o u r t h decimal p l a c e , a 1 mg sub-sample d i r e c t l y i n t o a sm a l l mortar to which 99 rag of KBr (co n c e n t r a t i o n of sample/KBr = 1/100) was added so as to avoid l o o s i n g the sample i n t r a n s f e r r i n g i t from a weighing boat to a sm a l l mortar i n which the sample i s very g e n t l y ground (no hard g r i n d i n g was necessary because the vacuum freeze dryer gave s o f t minutely-powdered samples). C a r e f u l mixing and g r i n d i n g enabled the p r e p a r a t i o n of transparent p e l l e t s , w i t h f a i r l y even d i s t r i b u t i o n of the sample w i t h i n the KBr when i t underwent a t e n ton-pressure i n vacuum procedure. The p e l l e t s were run f o r i n f r a r e d s p e c t r a immediately a f t e r p r e p a r a t i o n . The KBr p e l l e t s were prepared under the same c o n d i t i o n s by the same operator at a l l times so that the sp e c t r a obtained are considered to be reasonably comparable. The assurance t h a t the KBr p e l l e t s are i n the same c o n d i t i o n i s q u i t e important i n the so c a l l e d " d i f f e r e n t i a l i n f r a r e d spectroscopy",, The d i f f e r e n t .spectra were, i n f a c t , obtained by p l a c i n g the KBr p e l l e t s prepared from the c l a y s before and a f t e r the treatment i n the "sample beam" and i n the "reference beam" of the spectrophotometer, r e s p e c t i v e l y ? while the ordin a r y s p e c t r a were obtained by u s i n g a pure KBr p e l l e t as reference. Any imbalance among the KBr p e l l e t s due to causes other than s e l e c t i v e d i s s o l u t i o n gives r i s e to absorption e f f e c t s i n the d i f f e r e n c e spectra,, In the present study, the observed v a r i a t i o n s between r e p l i c a t e s of p e l l e t s i n the major S i - 0 s t r e t c h i n g , OH s t r e t c h i n g , and 0H(H 20) bending a b s o r p t i o n bands d i d not exceed 2 - 3% of the absorbance. I t i s b e l i e v e d t h a t the s p e c t r a presented below (which r e f e r s to R3 sample of Ryder c l a y ) are s i g n i f i c a n t as f a r as the d i f f e r e n t d i s s o l u t i o n a b i l i t y of the d i f f e r e n t reagents used i s concerned. They are a l s o q u i t e comparable as to the trend t h a t can be seen i n the data of successive e x t r a c t i o n s presented i n Table 7 , The S i - 0 bands are the strongest bands i n the s i l i c a t e s t r u c t u r e and can be r e a d i l y recognized i n the i n f r a r e d s p e c t r a of such minerals by a very s t r o n g band i n the r e g i o n 900 - 1100 cm ( s t r e t c h i n g ) as w e l l as l e s s intense bands i n the 400 - 800 cm"1 r e g i o n (bending). The OH group r e t a i n s s u f f i c i e n t i n d i v i d u a l i t y i n the i n f r a r e d s p e c t r a of complex l a y e r s i l i c a t e s t r u c -tures to he c o n s i s t e n t l y recognized. The absorption bands i n the 3000 - 3800 cm r e g i o n are due to the s t r e t c h i n g v i b r a t i o n s of protons against oxygen. The presence of t r i v a l e n t ions i n octahedral s i t e s produces bending modes of the type H-0-A1 or H-0-Fe^ + i n the 800 -1 to 920 cm r e g i o n . The OH-stretching and OH-bending frequencies are markedly a f f e c t e d by the i o n t o which they are coordinated and t h e i r environment. The absence of any d i s t i n c t OH-stretching frequencies i n the 3600 - 3700 cm" r e g i o n and the presence of the broad OH-stretching and OH bending bands are i n t e r p r e t e d to mean tha t the samples c o n t a i n amorphous m a t e r i a l s . These regions are important i n a ssessing the impact of the presence of amorphous m a t e r i a l s . In f a c t , the amount of water absorbed on the surfaces of s o i l mineral phases present i n the samples i s r e l a t e d to the surface area and t h i s r e l a t i o n can be r e a d i l y seen by comparison of the s p e c t r a i n Figure 14 w i t h the surface area data i n Table 11 f o r the B f 3 Ryder ho r i z o n . (Table 11 - page 62.) .62. TABLE 11 Surface area (m /g) of Bf3 Ryder h o r i z o n c l a y and the surface area of the same a f t e r : (a) 5% NaCO^ (b) A c i d NH^-oxalate (c) D i t h i o n i t e . Sample Surface Area (m /gr) R3 - Untreated c l a y 1 7 7 . 0 R3 - a 1 4 1 . 9 R3 - b 5 1 . 6 R3 - c 4-5.2 In Figure 9a, 10a, and 11a, the s p e c t r a of untreated c l a y (Ryder Bf3) and those of the same c l a y a f t e r the three d i s s o l u t i o n treatments are drawn f o r comparison. The s p e c t r a show tha t the samples were a f f e c t e d d i f f e r e n t l y by the d i f f e r e n t treatments, i f one observes the absorption bands i n the 3000 - 3700 cm"1 and 1635 cm"1 ( s t r u c t u r a l HgO) r e g i o n s i t h i s suggested the presence of some high surface area amorphous i n o r g a n i c m a t e r i a l s . The band around 1000 cm ( S i - 0 s t r e t c h i n g ) i s not a f f e c t e d as much. An o v e r a l l p i c t u r e of how the s i n g l e e x t r a c t i o n treatment a f f e c t e d the c l a y sample i s presented i n Table 1 4 . In Figure 9b, 10b, and l i b are presented the d i f f e r -ent s p e c t r a between the untreated c l a y and the c l a y a f t e r ( a + b ) , ( a + b + c ) and a f t e r (a + b + e + d) e x t r a c t i o n r e s p e c t i v e l y . The spe c t r a have been obtained by p l a c i n g the untreated c l a y i n the sample-beam and the t r e a t e d ones i n Figure 9a . 4000 3000 2000 1600 1200 800 400 WAVENUMBER CM"1 Figure 9o. Comparison between infrared spectra of untreated Clay-R3 and Clay-R3 after (a + b) extraction [•}. Figure 9b. Differential infrared spectra between untreated Clay-R3 (in sample-beam) and Clay-R3 after (a + b) extraction (in ref erence-beam). Figure 10a 4000 3000 2000 1600 1200 800 400 WAVENUMBER CM"1 Figure 10a. Comparison between infrared spectra of untreated Clay-R3 and Clay-R3 after ( a t b + c ) extraction (e). Figure 10b. Differential infrared spectra between untreated Clay-R3 (in sample-beam) and Clay-R3 after (a + b + c) extraction (in reference-beam). F igure l la . F igure ! ia. Comparison between infrared spectra of the untreated C lay -R3 and C l a y - R o after ( a + b + c + d) extraction Figure l ib . D i f ferent ia l infrared spectra of the untreated Clay-R3 (in sample-beam) and Clay-R3 after (a + b + c + d ) extract ion (in refe rence - beam ). 4000 3000 2000 1600 1200 800 400 WAVENUMBER CM-1 Figure 12. Differential infrared spectra of. C lay -R3 after (a + b) extraction (in sample-beam) and C lay -R3 after ( a + b + c ) extraction (in reference-beam). Figure 13. Differential infrared spectra of Clay-R3 after (a+b + c) extraction (in sample-beam) and Clay-R3 after ( a + b + c + d) extraction (in reference-beam). ON ON 3000 2000 1600 1200 800 400 WAVENUMBER CM~' Comparison beteen infrared spectra of untreated C l a y r R 3 and C l a y - R 3 successive extractions: (a) 5 % Na2CC>3 and Na - Pyrophosphate, (b) Ac. NH 4 - oxa la te , (c) Dithionite. 675. the reference-beam, so th a t Figure 9b represents the spectrum of the a l u m i n o s i l i c a t e amorphous phase extracted by 5% Na2C0^; i n Figure 10a i s the combined spectrum of the a l u m i n o s i l i c a t e amorphous carbonate-soluble phase p l u s the iron-aluminum polyhydroxy amorphous phase brought i n t o s o l u t i o n by a c i d NH/j,-oxalate, which completes the c l e a n i n g a c t i o n of the c r y s t a l l i n e minerals. The spectrum of the l a t t e r phase alone i s represented i n Figure 1 2 , obtained by p l a c i n g the sample a f t e r carbonate treatment i n the sample-beam and the sample a f t e r oxalate treatment i n the reference-beam. F i n a l l y , i n Figure 13» i s presented the spectrum of t h a t p o r t i o n of the c r y s t a l l i n e m a t e r i a l which has been attacked and brought i n t o s o l u t i o n by c i t r a t e - d i t h i o n i t e treatment. I t i s assumed, t h a t a l l the amorphous m a t e r i a l s have already been removed a f t e r a c i d NH^-oxalate successive e x t r a c t i o n . F o l l o w i n g t h i s treatment, the c h a r a c t e r i s t i c broad band of the OH-stretching mode due to amorphous m a t e r i a l i s s u b s t i t u t e d by the c h a r a c t e r i s t i c bands of,the c r y s t a l l i n e minerals present i n the sample. CONCLUSION I t appears t h a t successive s e l e c t i v e d i s s o l u t i o n a n a l y s i s , combined with the i n f r a r e d spectrophotometry technique, has-proved to be a s u i t a b l e procedure f o r unlock^ i n g the door to q u a l i t a t i v e as w e l l as q u a n t i t a t i v e determin-a t i o n of the inorganic amorphous system of s o i l . 68. The primary purpose of the f i r s t procedure adopted in t h i s study was to evaluate the extraction a b i l i t y of d i f f e r e n t extractants as to t h e i r usefulness i n characterizing the Bf horizons of Podzol s o i l s . From the results found the a b i l i t y of the oxalate procedure to remove more aluminum than the c i t r a t e - d i t h i o n i t e procedure i s readi l y evident. On the other hand, the c i t r a t e -d i t h i o n i t e procedure extracts higher quantities of iron than the oxalate method. This writer agrees with McKeague that the c i t r a t e -d i t h i o n i t e procedure i s less s p e c i f i c than the oxalate proce-dure because the former removes c r y s t a l l i n e iron compounds from the s o i l , e s p e c i a l l y from s o i l s high i n clay. The oxalate i r o n values showed no appreciable increase of iron with increa-sing clay content. This indicates that the oxalate method d i f f e r e n t i a t e s more s p e c i f i c a l l y between amorphous and cry-s t a l l i n e forms of i r o n . Thus the oxalate extractable iron ( and aluminum ) values can separate s o i l s l n c l a s s i f i c a t i o n systems better than the c i t r a t e - d i t h i o n i t e extractable iron ( and aluminum ) values. The successive d i s s o l u t i o n analysis allows the separation of at least two c l e a r l y d i f f e r e n t phases of the amorphous material present i n the clay: the f i r s t phase, which i s dissolved by 5% sodium carbonate, i s represented by an amorphous aluminosilicate and possibly free amorphous alumina and s i l i c a ; the material separated out by the succe-ssive oxalate treatment represents a phase much more s p e c i f i c 68a than that one obtained with no previuos a l k a l i treatment. In t h i s second phase s i l i c a ani alumina are most l i k e l y to be clo s e l y associated with each other and with the amorphous iron oxides. The Infrared spectroscopy and the surface area determination a f t e r each successive treatment allowed cha-r a c t e r i z a t i o n of each phase from a physical point of view. On the basis of t h i s study i t seems premature to suggest that the successive extraction procedure can be used with any usefulness i n devising c r i t e r i a f o r c l a s s i f i c a t i o n purposes. Much more confidence could be put on the r e s u l t s obtained by successive d i s s o l u t i o n analysis i f there would be less uncertainty i n regard to the s p e c i f i c i t y of chemical di s s o l u t i o n procedures, and the significance, i n terms of s t r u c t u r a l order or disorder, of the fract i o n s which they dissolve. 69/. LITERATURE CITED 1, A l l i s o n , LoE, 1965. Organic carbon. In A,C. Black et a l , (ed,) Methods of s o i l a n a l y s i s , P a r t 2. I W - 1378, 2, Anderson, J,U, 1963. An improved pretreatment f o r m i n e r a l o g i c a l a n a l y s i s of samples c o n t a i n i n g organic matter. Clays and Clay M i n e r a l s . 10s 380 - 388. 3, Bascomb, c,L, 1968, D i s t r i b u t i o n of pyrophosphate-e x t r a c t a b l e i r o n and organic carbon i n s o i l s of var i o u s groups, J , S o i l S c i . 19s 251 - 267, 4, Bremner, J.M, 1965o T o t a l n i t r o g e n . I n C A . Black et a l . (ed.) Methods of s o i l a n a l y s i s , P a r t 2, Chemical and m i c r o b i o l o g i c a l p r o p e r t i e s . Agronomy 9s 1149 - 1178. ' 5, B r i n e r , G.P,, and M,L. Jackson, 1969. A l l o p h a n i c m a t e r i a l i n A u s t r a l i a n s o i l s d e r i v e d from P l e i s t o c e n e b a s a l t . Aust. J . S o i l Res, 7s 163 - 169. 6, C a r r o l l , D, 1970, Clay m i n e r a l s : a guide t o t h e i r X-ray i d e n t i f i c a t i o n . The G e o l o g i c a l S c i , Amer. S p e c i a l paper 126, 7, Chapman, H.D, 1965. C a t i o n Exchange Capacity. In C A , Black et a l , (ed,) Methods of s o i l a n a l y s i s , P a r t 2. 891 - ^0*4. 8, Cloos, P., A, H e r b i l l o n , J , E c h e v e r r i a , 1968, A l l o p h a n e - l i k e s y n t h e t i c s i l i c o a l u m i n a s phosphate ads o r p t i o n and a v a i l a b i l i t y . Trans, 9th I n t e r , Cong, S o i l S c i , lis 733 - 743. 9, C o f f i n , D.E, 1961, A method f o r determination of fr e e i r o n i n s o i l s and c l a y s . Can* J . S o i l S c i , 43s 7 - 1 7 . 10, Deb, B.C 1950. The e s t i m a t i o n of f r e e i r o n oxides i n c l a y s and t h e i r removal, J , S o i l S c i , 1: 212 - 220, 11, DeMumbrum, L,E,, and G, Chesters. 1967, I s o l a t i o n and c h a r a c t e r i z a t i o n of some s o i l allophanes. S o i l S c i , Soc, Amer, Proc. 28? 355 - 359. 70. 12, Deshpande, T.L., D.J. Greenland, and J.P. Quirk, 1968. Changes i n s o i l p r o p e r t i e s a s s o c i a t e d with-foe removal of i r o n and aluminum oxides„ J . S o i l S c i . 19* 1 - 108, 13, D e , V i l l i e r s , J.M. 1969. Pedosesquioxides - Composi-t i o n and c o l l o i d a l i n t e r a c t i o n s i n s o i l genesis during the Quaternary. J , S o i l S c i , 107» 454 - 461. 14, P i e l d e s , M, 1966, The nature of allophane i n s o i l s . P a r t 1, S i g n i f i c a n c e of s t r u c t u r a l randomness i n pedogenesis. NZ. J l . S c i 9% 599 - 607, 15, F i e l d e s , M, and R.J. Funkert. 1966. The nature of allophane i n s o i l s . P a r t 2. D i f f e r e n c e s i n composi-t i o n . N,Z. J l . S o i l S c i , 9» 608 - 622. 16, F o l l e t t , A.C., W.J. McHardy, B.D, M i t c h e l l , and B.F.L, Smith 1964, Chemical d i s s o l u t i o n techniques i n the study of s o i l c l a y s . P a r t 1-2, Clay M i n e r a l s 6s 23 - 43. 17, Franzmeier, D.P., B.F, Hajek, and C.H. Simonson, 1963. Use of amorphous m a t e r i a l t o i d e n t i f y spodic h o r i z o n s . S o i l S c i , Soc. Amer. Proc. 29s 737 - 743. 18, Gastuche» M.C,, F» T o u s s a i n t 9 J , J , F r i p i a t , R, To u i l l a u x o and M, Van Meerssche, 1963. Clay Minerals 5§ 227 ~ 233. 19, Gorbunov 9 N.I., G.S, Dzyaevich, and B.M. Tunik, 1961. Methods of determining n o n - s i l i c a t e amorphous and c r y s t a l l i n e sesquioxides i n s o i l s and c l a y s . S o v i e t S o i l S c i . l i s 1252 - 1259. 20, Greenland, D.J., and J.M, Oades, 1969. Iro n hydrpxides and c l a y s u r f a c e s . 9th I n t e r . Cong. S o i l S c i . 2s 657 - 667. 21, Hashimoto, I . , and M.L. Jackson, I960. Rapid d i s s o l u -t i o n of allophane and k a o l i n i t e - h a l l o y s i t e a f t e r . dehydration. Clay and Clay m i n e r a l s . Proc. 7th Conf. 102 - 113. 22, Jackson, M.L, 1958. S o i l chemical a n a l y s i s . P r e n t i c e H a l l Inc. Englewood C l i f f s , N.J. 468 p. 23, L a i , S,, and L.D. Swindale, 1969. Chemical p r o p e r t i e s of allophane from Hawaiian and Japanese s o i l s . S o i l S c i . Soc. Amer. Proc. 33: 804 - 808. 24, L a v k u l i c h , L,M., and J.H. Wiens. 1970. Comparison of organic matter d e s t r u c t i o n by hydrogen peroxide and sodium h y p o c h l o r i t e and i t s e f f e c t s on s e l e c t e d mineral c o n s t i t u e n t s . S o i l S c i . Soc. Amer. Proc. 34s 755 - 758. 71. 25, McKeague,, J,A,, and J.H, Day* 1966, D i t h i o n i t e and oxalate e x t r a c t a b l e Fe and A l as a i d s i n d i f f e r e n -t i a t i n g ' v a r i o u s c l a s s e s of s o i l s , Can.J, S o i l S c i , 46 s 13-22. 26, McKeague J.A, 1967. An e v a l u a t i o n of 001 M pyro-phosphate and phrophosphate-dithionite i n comparison w i t h oxalate as e x t r a c t a n t s of the accumulation products i n podzols and some other s o i l s . Can. J , S o i l S c i , 47s 95 - 99. 27, McKeague, J.A., J,E, Brydon, and N,M„ M i l e s , 1971. D i f f e r e n t i a t i o n of. forms of e x t r a c t a b l e i r o n and aluminum i n s o i l s . S o i l S c i . Soc, Amer. Proc, 35* 3 3 - 3 7 . 28, Mehra, O.P., and M.L, Jackson, I960, I r o n oxide removal from s o i l s and c l a y s by a c i t r a t e - d i t h i o n i t e system buffered w i t h sodium bicarbonate. 7th N a t l , Confo on Clays and Clay M i n e r a l s , pp, 31.7 - 327, 29, M i t c h e l l , B.D., V.C, Farmer, and W.J, McHardy. I960, Amorphous i n o r g a n i c m a t e r i a l s i n s o i l s . Adv. Agron. 16s 327 - 383. 30, Muir, A, 1961, The podzol and p o d z o l i c s o i l s , Adv, i n Agron. 13? 1 - 56, 31, P a r f i t t , R.L, 1972. Amorphous m a t e r i a l i n some Papua New Guinea s o i l s . S o i l S c i . Soc, Amer, Proc. 36s 683 - 691. 32, Pawluk, S, 1967. S o i l a n a l y s i s by atomic a b s o r p t i o n spectrophotometry. Atomic Absorption Newsletter. V o l , 6, No, 3. PP. 53 - 56. 33, Peech, M. 1965. Hydrogen-ion a c t i v i t y . I n A.C. Black et a l . (ed.) Methods of s o i l a n a l y s i s , P a r t 2 9T4~ 926. 34, Raman, K.V,, and M.M. Mortland, 1969/1970. Amorphous m a t e r i a l i n a spodosol: some m i n e r a l o g i c a l and chemical p r o p e r t i e s . Geoderma, 3s 37 - 44, 35* S o i l Survey S t a f f , S o i l Conservation S e r v i c e and U.S. Department of A g r i c u l t u r e . 1967. S o i l C l a s s i -f i c a t i o n . A comprehensive System. 7th Approximation U.S. Government P r i n t i n g O f f i c e , Washington, D.C, 36. Sumner, E.M. 1963. E f f e c t of i r o n oxides on p o s i t i v e and negative charges i n c l a y s and s o i l s . C l a y M i n e r a l s . 5: 218 - 238. 72. 37. Tamm, O.C., 1932. Uber die Oxalatmethode i n der Chemischen Bodeanalyse, Meddel, S t a t . Skogsfor-sokanst. Sweden. H 2?: 1 - 20. 38. Van Reeuwijk, L.P., and J.M. De V i l l i e r s . 1968. Potassium f i x a t i o n of amorphous a l u m i n o s i l i c a g e l s . S o i l S c i . Soc. Amer. Proc. 32: 238 - 240. 39. Wada, K,, and DiJ. s1970. S e l e c t i v e d i s s o l u t i o n and d i f f e r e n t i a l i n f r a r e d spectroscopy f o r c h a r a c t e r i z -a t i o n of amorphous c o n s t i t u e n t s i n s o i l c l a y s . C l a y Minerals 8: 241 - 253. 40. Yuan, T.L. 1968. Composition of the amorphous mater i a l i n the c l a y f r a c t i o n of some e n t i s o l s , i n c e p t i -s o l s , and spodosols, J , S e r i e s Paper No. 2981, F l o r i d a A g r i c u l t u r a l Experimental S t a t i o n s , G a i n e s v i l l e , F l o r i d a , 32601. 73. STRUCTURE AND PROPERTIES OF AMORPHOUS IRON-ALUMINOSILICATE SYSTEMS INTRODUCTION In s o i l genesis, the r o l e of amorphous alumino-s i l i c a t e s have been repeatedly r e f e r r e d t o as being important i n d i f f e r e n t i a t i o n of d i f f e r e n t c l a s s e s of s o i l s . Few studies," however, have been conducted on the s t r u c t u r e and p r o p e r t i e s of amorphous i r o n - a l u m i n o s i l i c a t e systems.. Because of the problems of contamination of amorphous systems w i t h c r y s t a l l i n e m a t e r i a l and v a r i o u s kinds of organic matter," many i n v e s t i g a t o r s have turned t h e i r a t t e n t i o n to s y n t h e t i c a l u m i n o s i l i c a g e l systems. This approach i s based on the assumption t h a t p r o p e r l y prepared a r t i f i c i a l g els can be compared wi t h i n o r g a n i c amorphous systems i n the n a t u r a l weathering environment f o r chemical and p h y s i c a l c h a r a c t e r i s t i c s and consequently, f o r s t r u c t u r a l composition. The approach used i n t h i s study was t o prepare s y n t h e t i c i r o n - a l u m i n o s i l i c a t e g e l systems and t o study t h e i r chemical and p h y s i c a l p r o p e r t i e s and attempt to define the s t r u c t u r a l arrangement of these g e l systems. To date, no s t u d i e s have been reported i n the l i t e r a t u r e on complex c o p r e c i p i t a t e s of the iron-alumino-s i l i c a t e g e l system which are b e l i e v e d to be reasonably s i m i l a r to t h e i r r e a l counterparts i n nature. 74. M i l l i k e n et a l , (1950) suggested that amorphous aluminosilicates are composed of s i l i c a and alumina p a r t i c l e s , interbonded by the condensation of hydroxyl groups at t h e i r interfaces. The s i l i c a tetrahedral structure w i l l induce the l o c a l formation of fourfold coordinated aluminum giving r i s e to-an aluminate-like structure. Above a c r i t i c a l alumina content (15 - 30%) they found that the amount of aluminate decreases s t e a d i l y with decreasing percentage of s i l i c a . The excess of alumina i n the silico-alumina mix-ture c r y s t a l l i z e s into bohemite and h y d r a r g i l l i t e with six -f o l d coordination. Synthetic aluminosilicates characterized by large s p e c i f i c surface area and high surface a c i d i t y , are commonly used as cracking catalysts. In the numerous contributions dealing with the structure of amorphous aluminosilicates, emphasis i s l a i d on the type of aluminum bonding; and i n order to explain the a c i d i t y and c a t a l y t i c a c t i v i t y of such compounds, i t has been suggested that the catalyst i s not merely a mixture of s i l i c o n and aluminum, but a r e a l chemical combination of both elements. This assumes that a p o s i t i v e hydrogen ion i s associated with a tetrahedral aluminum, and that the c a t a l y t i c a c t i v i t y i s due to t h i s a c i d i c hydrogen. The active constituent has been proposed and written as (HA1 S i O ^ ) ^ (Henin et a l , 1963) . 75. Tamele (1950) had p r e v i o u s l y considered the ex p l a n a t i o n f o r the formation of a c i d s i t e s i n alumino-s i l i c a t e s as the condensation of the surface hydroxyl groups of the incompletely polymerized s i l i c a hydrogel w i t h hydroxyl groups of the h y d r o l i z e d aluminum i o n s . Danforth (I960) i n o p p o s i t i o n t o M i l l i k e n et a l . (1950), suggested that aluminum i s present i n a l u m i n o s i l i -cates i n three formss (a) f r e e alumina (b) aluminum bound to s i l i c a ^ and (c) aluminum hydroxide n e u t r a l i z i n g a c i d exchange s i t e s . He considered that an aluminum tetrahedron s h a r i n g corners w i t h s i l i c a t e t r a h e d r a a c t s as Bronsted a c i d . Alumina l i n k e d by two or three bonds t o s i l i c a , would form a Lewis a c i d on dehydration. De Kimpe et a l , (1961) s t u d i e d the i n f l u e n c e of simultaneous a d d i t i o n s of aluminum and s i l i c o n i n the common pH range of aluminum hydroxide p r e c i p i t a t i o n w i t h the hope t h a t the r e c r y s t a l l i z a t i o n of the hydroxide might be retarded and the formation of a l a y e r s i l i c a t e s t r u c t u r e might be f a c i l i t a t e d . X-ray s t u d i e s of such g e l s gave no i n d i c a t i o n of c r y s t a l l i z e d aluminum hydroxide. The l a c k of X-ray r e f l e c t i o n s has been explained by p o s t u l a t i n g t h a t s i l i c a c o n t r o l s the development of the system, imposing mainly i t s three-dimensional framework. Though the y i e l d of c r y s t a l l i n e phase was very poor i n the experiments c a r r i e d out by these authors i n the presence of aluminum0" a d e t a i l e d study of the g e l phase di d show a tendency towards o r g a n i z a t i o n . 76, K a o l i n i t e appeared at low pH, where the s i x f o l d coordinated s t r u c t u r e of aluminum was s t a b i l i z e d . At high pH v a l u e s , a m i c a - l i k e c l a y mineral appeared„ as the f o u r f o l d coordinated aluminum increased i n the g e l s t r u c t u r e . De Kimpe et a l (I96I) concluded t h a t i t seems reasonable t o a t t r i b u t e the low y i e l d of the c r y s t a l l i n e phase t o ; ( i ) the i n s o l u b i l i t y of s i l i c a at the pH values under study which induced the p o l y m e r i z a t i o n of an alumina-s i l i c a g e l , and ( i i ) the aluminum i o n e a s i l y interchanges by isomorphous s u b s t i t u t i o n w i t h s i l i c o n . The hexaco-ordinated form being s t a b l e only at low pH. Leonard e t - a l . ( 1 9 6 4 ) , according to t h e i r s t u d i e s on amorphous a l u m i n o s i l i c a t e s by X-ray f l u o r e s c e n t spectro-scopy and i n f r a r e d spectroscopy, reported t h a t , as f a r as aluminum atoms are concerned, three d i f f e r e n t oxygen enviro n -ments can be d i s t i n g u i s h e d , corresponding r e s p e c t i v e l y t o * ( i ) alumina octahedra, ( i i ) alumina t e t r a h e d r a s h a r i n g corners, or ( i i i ) alumina t e t r a h e d r a s h a r i n g edges. The d i s t r i b u t i o n of these three d i f f e r e n t types depends upon the aluminum content and the pretreatment temperature„ The spectroscopy of X-ray fluorescence l i n e s provides the p o s s i b i l i t y of a d i r e c t c h a r a c t e r i z a t i o n , of the c o o r d i n a t i o n numbers of aluminum and s i l i c o n i n v a r i o u s amorphous a l u m i n o s i l i c a t e s at d i f f e r e n t h y d r a t i o n l e v e l s . 77. With X-ray f l u o r e s c e n c e , i n e f f e c t , one measures the emission wavelength of A l Ko( (or S i Ko( ), u s i n g a r e f l e c t i o n from an EDTA c r y s t a l i n the r e g i o n of 29 = 142.5°; Small hut s i g n i f i c a n t s h i f t s i n the angular p o s i t i o n of the A l K<* (or S i K°( ) l i n e are obtained f o r d i f f e r e n t coordina-t i o n s t a t e s ; The r e s u l t s are c a l i b r a t e d by reference to Al— PO^ and A l ^ - S i 2 0^ (OH)^ ( K a o l i n i t e ) . A c a l i b r a -t i o n l i n e i s drawn between the 2 © -values obtained with AI 1* PO^ and k a o l i n i t e 9 from which an estimate i s obtained, of the pro p o r t i o n s of A l ions i n the two c o o r d i n a t i o n s t a t e s i n a mixture. Although high accuracy cannot be claimed f o r these estimates of A l ~ and A l ~ , n e v e r t h e l e s s , when the r e s u l t s f o r the g e l s are examined g r a p h i c a l l y , a c l e a r trend i s seen towards s i x f o l d c o o r d i n a t i o n as the AlgO^/AlgO^ + S i 0 2 r a t i o increases beyond,: a c e r t a i n l i m i t , , or as pH c o n d i t i o n s become more a c i d i c . D i s c u s s i n g t h e i r r e s u l t s , Leonard et a l , , (1964) observed t h a t the samples poor i n aluminum and d r i e d at 100°C c o n t a i n A l e s s e n t i a l l y i n t e t r a h e d r a l form, at the opposite extreme, the pure alumina sample composed of a mixture of bohemite and b a y e r i t e , contained s i x f o l d coordinated atoms only. I n the intermediate range, the samples are composed of mixtures of the two forms, the JjT A l contents decreasing l i n e a r l y w i t h i n c r e a s i n g A l contents. According t o these authors, the s t a b i l i t y of the t e t r a h e d r a l form i s secured by four s i l i c a t e t r a h e d r a surrounding an aluminum tetrahedron (Figure I A ) , when the . 7 8 . 0 1 - 0 - Si -1 0 -1 0 0 H* i o 1 Si - 0 0 — i Si 1 1 0 1 i 0 1 1 0 i - 0 - Si — 0 -— 0 I 0 Increasing amounts of AI and hydration. i I 0 0 1 i O - S i - 0 — Si 1 H ' i 0 0 - Si - 0 -H I H v X'/ \ • X ' / \ Al . ; Al Al . Al / • / ' \ / i X ' \ / 0. I 0 - S i - 0 I 0 0 I Si i 0 i 0 H 0 0 I 0 H Si - 0 -l 0 i Stable Dehydration c 0 i 0 1 0 - 0 - Si -| 1O - S i -| 0 - Si - 0 -• 0 1 0 l 0 1 Al / ' / 0 1 x • \ Al • V / 0 0 1 Al 0 Al " \ / 0 0 1 - O - S i -| O - S i - 0 - Si - 0 -0 i 1 0 1 0 1 FI G U R E 1. SCHEMATIC STRUCTURAL RELATIONSHIPS IN SILICOALUMINAS (FROM LEONARD et at. 79 . aluminum content i s high enough to preclude such an arrange-ment, s i x f o l d c o o r d i n a t i o n numbers become dominants the content of c o n s t i t u t i o n a l water increases a c c o r d i n g l y (Figure I B ) . In t h i s chapter, an attempt w i l l be given to give evidence f o r the phase c o n s t i t u t i o n and s t r u c t u r e composi-t i o n of s e l e c t e d i r o n a l u m i n o s i l i c a t e g e l systems. In a subsequent chapter, a comparison w i l l be drawn between these a r t i f i c i a l systems and n a t u r a l amorphous concentrates obtained by an a c i d d i s p e r s i o n procedure from a s o i l . 80. MATERIALS AND METHODS (a) Samples preparation Three samples with d i f f e r e n t molar SiOg/AlgOy' Fe 20^ r a t i o s were prepared i n p l a s t i c beakers by adding dropwise and with vigorous continuous s t i r r i n g a mixed solution of 0.6 M f e r r i c chloride (Fe Cl^'oHgO) and aluminum chloride (Al C l ^ "6H20) to a s o l u t i o n of 0.6 M sodium metasilicate (Na 2 SiO^ 9H 20): the cold coprecipi-t a t i o n was carried out at pH 7,0. The Si/Al/Fe r a t i o and concentration were adjusted so that at least 5 g of gel was obtained from each beaker. The compositions r e a l i z e d are given i n Table 1, . ' The slow addition of S i , A l and Fe ions at the pH studied was believed to be favorable f o r the f i x a t i o n of SiO^ tetrahedra at the time of the formation of the i r o n and aluminum hydroxide framework. The samples were allowed to stand overnight, the pH was readjusted the next morning, the samples were cenrtrir-fuge-washed repeatedly and freeze dried. On these samples, physical and chemical determinations were conducted, (b) Investigation Methods Among the physical determinations conducted were X-ray d i f f r a c t i o n (Cu KX r a d i a t i o n ) , infrared spectroscopy {1% concentration i n KBr p e l l e t s and Beckman Ir-20 spectro-photometer), s p e c i f i c surface area determination by ethylene g l y c o l monoethyl ether sorption procedure. 8 1 . The samples were also chemically analyzed by acid d i g e s t i o n and the elements determined by atomic absorption spectrophotometry (S i determined by d i f f e r e n c e ) . Successive extract ions by 5% NagCO^, ac id NH^-oxalate and c i ta te -bicarbonate d i t h i o n i t e were attempted. Potassium f i x a t i o n was determined according to the procedure out l ined below and the ca t ion exchange capacity ( C . E . C . ) was determined by sa tura t ing the sample with Na-acetate s o l u t i o n , washing with ethanol , r e p l a c i n g sodium with ammonium and determining the displaced sodium with atomic absorption spectrophotometry. K - F i x a t i o n Procedure I s o l a t i o n of amorphous i r o n - a l u m i n o s i l i c a t e s from s o i l s appears to be impossible because of t h e i r general i n s t a b i l i t y i n reagents such as a l k a l i s and acids commonly employed during ex t rac t ion of the c o l l o i d a l system. Thus, i t was considered opportune to place r e l i a n c e on a synthetic system to provide at l eas t a model f o r the natural inorganic amorphous system. The samples used f o r t h i s experiment were the same as out l ined p r e v i o u s l y (AS-1, A S-2, A S - 3 ) ; and the method that fol lows i s modified from Van Reeuwijk and De V i l l i e r s ( 1 9 6 8 ) . Subsamples of 100 g of f r e e z e - d r i e d gels were e q u i l i -brated with 50 ml of IN KCl s o l u t i o n at pH 7.0 (adjusted with small amounts of HCl or KCH with no appreciable e f f e c t s 8 2 . on the n o r m a l i t y of K C l ) , The adjustment of pH was repeated a f t e r the suspension were l e f t s t a n d i n g o v e r n i g h t . The samples were c e n t r i f u g e d and washed seven times with 15 ml of IN s o l u t i o n s of NH^ C l , Na C l , Ca C l 2 and MgCl 2, respec-t i v e l y , a l l at pH 7 , 0 i n order to remove e x t r a c t a b l e potassium. The excess e l e c t r o l y t e was removed by washing once with w a t e r i e t h a n o l ( I t l ) and once w i t h watersacetone (1:1) mixtures. The samples were t r a n s f e r r e d to t a r e d c r u c i b l e s , d r i e d at 105°C o v e r n i g h t and weighted. They were d i g e s t e d i n HF/HC10^ (20/1) on a sandbath and the r e s i d u e s were taken up i n IN HC1. The r e s u l t i n g s o l u t i o n s , appro-p r i a t e l y d i l u t e d , were analyzed by atomic a b s o r p t i o n s p e c t -r o p h o t o m e t r y f o r potassium, which had been d r y - f i x e d by the h y d r o g e l s . RESULTS AND DISCUSSION F o r s t r u c t u r e c h a r a c t e r i z a t i o n , i t would have been. u s e f u l t o measure the c o o r d i n a t i o n s t a t e of the three elements: S i , A l , Fe, on the a r t i f i c i a l c o p r e c i p i t a t e s by X-ray f l u o r e s c e n c e s p e c t r o s c o p y . However, not b e i n g able to do so, s t r u c t u r e i n f e r e n c e s w i l l be drawn from s i m i l a r s t u d i e s p r e v i o u s l y proposed by other authors (De Kimpe e t a l . (1961)? Leonard e t a l , (1964)? F r i p i a t et a l . (1965); Leonard e t a l . (1966)? , Cloos e t a l , (1968 and 1969) . The experimental r e s u l t s are summarized i n Tables 1, 2 , 3 and 4, - 83 o Samples A S - l , AS-2, AS-3 are c h a r a c t e r i z e d , r e s p e c t i v e l y by a low, medium-high, and high aluminum content, while the i r o n content i s c o n s t a n t l y a medium val u e , as can be seen from the atomic r a t i o s and % elemental r a t i o s . The s p e c i f i c surface area p r o g r e s s i v e l y decreased with the i n c r e a s i n g A l / A l + S i atomic r a t i o and the same behaviour can be noted f o r C.E.c, These trends were expected i f one considers the f a c t t h a t going from an A l / A l + S i atomic r a t i o of 0,30 t o 0,79 p r o g r e s s i v e l y mpre ordered s t r u c t u r e s are b u i l d i n g up i n the polymeric phases present. At higher A l / A l 4 S i v a l u e s , (0,85) Gloos et a l . (1969) has shown the presence of a c r y s t a l l i n e phase com-posed of a mixture of pseudobohemite and b a y e r i t e . The progressive o r d e r i n g of the polyphase system i s considered r e s p o n s i b l e f o r the abrupt decrease of both surface area (m /g) and C.E.C, as one goes from the low value to high values of the A l / A l + S i atomic r a t i o , (see Figure 2). The C.E.C. of the i n t e r n a l core of these i r p n -a l u m i n o s i l i c a polyphase systems, which are considered t o be p l a y i n g the r o l e of anions, might be balanced, at l e a s t to some extent, by hydroxy-iron-aluminum ions or po l y n u c l e a r cations of i n c r e a s i n g complexity, thus decreasing the. net charge per Al or Fe atom as the atomic r a t i o s decrease. 84, The G.E.C. - composition rel a t i o n s h i p f o r synthetic alumino-s i l i c a hydrogels has been found (De V i l l i e r s , 1970) to peak at the point of 22% AlgO^ / AlgO^ + S i 0 2 composition (molar r a t i o S i 0 2/Al 2 0 ^ of 6.0). This point, according to De V i l l i e r s , corresponds with one-in-four su b s t i t u t i o n of Al f o r S i i n a tetrahedral framework, which therefore appears tp be the maximum. At molar r a t i o s below 6 .0 , a decrease i n C.E.G. with increasing AlgO^ content suggests that alumina i n excess of 22% was not accommodated i n the s i l i c a t e structure and was present probably i n a s i x f o l d coordinated state as a second phase, (see Figure 2). MOLAR S i 0 2 / AI2O3 . rat io o cr E >-O < a. < o LU O 2 < o X LU O I-< 3 0 0 200 J 100 H 0 6 4.8 0 . 5 0.3 n N / \ \ / \ N \ \ 20 COMPOSITION .1 40 4 0 0 r -300 200 100 60 80 100 (% A I 2 0 3 . / A I 2 0 3 + s i 0 2 ) FIGURE 2, CATION EXCHANGE CAPACITY AND SURFACE AREA OF SYNTHETIC IRON-ALUMINOSILICATE HYDROGELS AS DETERMINED AT PH 7 , 0 IN FUNCTION OF 1 A^OTJ/A^O^+SI O2 . THE POINTS AT 221 AND 0% FOR C . E . C , ARE BORROWED FROM J . M . DE V l L L I E R S / 1 9 7 0 , A . C. E, C, B, SURFACE AREA 86. TABLE 1. Chemical compos i t i o n , elemental and oxide ratio: s p e c i f i c surface area, C.E.C.> X-•Ray D i f f r a c t i o n Data. Sample AS-1 AS-2 AS-3 Ignition loss % 28.64 35.05 33.81 S i 0 2 <fo 35,05 16.97 13.83 A1 ?0 3 % 12.53 33.32 43.24 23.78 14.16 9.12 Total 100.00 100.00 .100.00 Al/A l + S i atomic r a t i o 0.30 0.70 0.79 Fe/Fe + S i atomic r a t i o 0.33 0.39 0.32 S i 0 2 : A1?0^: Fe 20^ molar r a t i o 1:0.36:0.68 1:1,96:0.86 1:3.12:0.66 % AlgO^/AlpO^ + SiO ? % Fe 20-j/Fe ?0^ + SiO ? 26.33 40.42 66.40 ' 46.35 75.77 39.74 So (m2/gr.) 392.36 294.34 219.5^ C.E.C. (meq./lOO gr. ) 287.17 52.89. 20.14 X-Ray D i f f r a c t i o n amorphous amorphous amorphous 87. As mentioned p r e v i o u s l y by van Reeuwijk and De V i l l i e r s , the a b i l i t y t o r e p l a c e K by the counter ions NH^, Na, Ca and Mg, i s a f u n c t i o n of t h e i r i o n i c p o t e n t i a l (charge/radius = 0.70 f o r NH^, 1.0 f o r Na, 2.0 f o r Ca, and 3.0 f o r Mg) and of t h e i r s o l v a t e d s i z e . From Table 2, i t appears that the dry f i x a t i o n of K by the g e l s decreases w i t h i n c r e a s i n g % r a t i o s of AlgO^/ A1 20^ + S i 0 2 and i t can be^ seen a l s o that K - f i x a t i o n i s c o v a r i a n t w i t h C.E.C, which decreases i n a s i m i l a r f a s h i o n . This seems to be i n accordance w i t h the d i l u t i o n of the polymeric core and b l o c k i n g of i t s negative charge by the i n c r e a s i n g amounts of the c o a t i n g Fe and A l hydroxide phases. SUCCESSIVE EXTRACTIONS For d e t a i l s of the successive e x t r a c t i o n s , see Chapter 3 i n which a comparison i s made between the a r t i f i -c i a l standards and the n a t u r a l amorphous concentrates from two s o i l s . The a r t i f i c i a l sample t r e a t e d here was AS-2, and the treatments which i t was submitted to were i n succession: (a) 5% NagCO-j (h) a c i d NH^-oxalate and (c) c i t r a t e -b i c a r b o n a t e - d i t h i o n i t e . The % S i 0 2 , % kl^Oy % F e ^ (on oven-dried - 105°C - b a s i s ) and % l o s s a f t e r the t r e a t -ments have been c a l c u l a t e d and presented i n Table 3 together w i t h s p e c i f i c surface area (So) v a l u e s , v a r i o u s elemental and oxide r a t i o s and X-ray d i f f r a c t i o n data. TABLE 2 DRY FIXATION OF K BY IRON-ALUMINOSILICA GELS Sample GEL COMPOSITION ^~Al^o^7Xr 2o 3 + s i o 2 AS-1 AS-2 AS-3 26.33 66.4-0 75.77 pH of KOI satur a t i o n 7.0 7.0 7.0 K FIXED AGAINST EXCHANGE BYs NH 4 Na Ca Mg meq./lOO gr. 42 6 0 63 110 155 287.17 21 28 39 52.89 8 14- 22 20,14 C.E.C. 89. A few p o i n t s t o note i n Table 3 ares (a) 97.16$ of the t o t a l sample has been removed by d i t h i o n i t e treatment, l e a v i n g only 2.84 % of undissolved m a t e r i a l , (b). the high agreement between the t o t a l % from successive e x t r a c t i o n s and the % l o s s a f t e r the treatments, and, (c) the'dramatic drop of the surface area a f t e r (a + b) treatments, A comparison of these data (Table.3) w i t h data obtained f o r sample AS-2 from the a c i d d i g e s t i o n procedure (but the data i s c a l c u l a t e d to take i n t o account the l o s s on i g n i t i o n of adsorbed and s t r u c t u r a l water) i s presented i n Table 4, As can be:seen from Table 4, the % AlgO^, Fe 20^, S i 0 2 and the v a r i o u s r a t i o s c a l c u l a t e d a f t e r the successive 5% Na 2C0^ + ac i d NR^,-oxalate + d i t h i o n i t e e x t r a c t i o n s , are c l o s e l y r e l a t e d to the corresponding percentages and r a t i o s c a l c u l a t e d a f t e r a c i d d i g e s t i o n . 90. TABLE 3 AS-2 SUCCESSIVE TREATMENTS DATA AND RATIOS. Sample and Treatments **AS-2 *AS-2(a) *AS-2 (a+b) *AS-2(a+b+c) f AlgO^ % Fe 20^ f> S i 0 2 T o t a l % S i 0 2 , A120^, Fe 20^ E x t r a c t i o n Loss a f t e r e x t r a c t i o n s S i 0 2 / A l 2 0 3 / F e 2 0 3 molar r a t i o A l / A l + S i atomic r a t i o Fe/Fe + S i atomic r a t i o % AI 2O 3/AI 2O^ + S i 0 2 % Fe 20^/Fe 20^ + S i 0 2 Surface area - So -(m 2/gr) X-Ray d i f f r a c t i o n 9.43 0.70 294.34 44.06 40.30 18.38 15.94 75.50 74.60 1/2.5/1.1 0.74 0.46 71.75 53.55 31. 82 53.74 22.32 19.91 97.16 96.00 1/2.6/1.1 0.76 0.44 72.96 52/85 amorphous ** not t r e a t e d sample * (a) = Sfo Sodium Carbonate E x t r a c t i o n (a+b) = Sfo Sodium Carbonate + Ac. ,NH^  Oxalate . E x t r a c t i o n (a+b+c) = % Sodium Carbonate + A c i d NH^ Oxalate + D i t h i o n i t e E x t r a c t i o n 9 1 . TABLE 4 Comparison between data obtained aft e r successive (a+b+c) extraction and data a f t e r acid digestion procedure on AS-2 sample. Sample and Treatments AS-2 (a+b+c) AS-2 (Acid Dig.) Ignition loss fo 35.05 35.05 % AlgO^ 36.40 33.32 % Fe 20^ 16.19 14.16 fo S i 0 2 18.15 16.97 S i 0 2 / A l 2 0 ^ / F e 2 0 ^ molar r a t i o 1/2.01/0.88 1/1.96/0.86 A l / Al + S i atomic r a t i o 0.70 0.70 Fe / Fe + S i atomic r a t i o 0.40 0 .39 % A1 20 3 / A1 20 3 + S i 0 2 65.52 66.40 % F e 2 0 3 / FegO^ + S i 0 2 47.15 46.35 92o INFRARED SPECTROSCOPY STUDIES The most int e r e s t i n g features to be considered on the I.R. spectra concern the bands i n the 1300 - 500 cm"1 wavelength domain, and in; p a r t i c u l a r , the S i - 0 stretching band. As i t can be seen from the spectra presented i n Figure 4, t h i s band i s well developed for a l l the three samples and comes out at 1025 cm" i n AS-1 (AlgO^ / AlgO^ + S^°2 = 26.33$) and i s much more d i s t i n c t and pro-nounced than i n samples AS-2 and AS-3 where i t comes out _1 at 95° cm This behaviour can be explained taking i n proper account the schematic structures proposed i n Figure 1. Looking, i n fact, at Figure IB, we can see that Fe or,: Al octahedra are included i n a s i l i c o n tetrahedra network} th i s i n c l u s i o n may be assumed to decrease the S i - 0 stretch-ing frequency because the organization of the s i l i c o n network i s perturbated with consequent weakening of the cohesion between tetrahedra; and that appears to have, happened for AS-2 and AS-3 which are most l i k e l y to be i n the s i t u a t i o n presented i n Figure IB 1 i n opposition to AS-1, which i s most l i k e l y to be i n the s i t u a t i o n presented i n Figure IA. Upon dehydration (or dehydroxilation) going from sample AS-1, low i n alumina content, to AS-2 and AS-3» high i n alumina content, no r e a l change can be noted i n AS-1; -1 (Figure 5) the frequency of S i - 0 band i s s t i l l at 1025 cm , AS-1 Figure 5. Comparison of infrared spectra of iron-aluminosilicate artif icial standards AS- I , A S - 2 , and AS-3 after dehydration (at 300°C). 95. but an increase i n the frequency of Si-0 band f o r AS-2 and AS-3 from 950 cm"1 at 100°C, to 1025 cm"1 at 300°C can be observed. The explanation f o r t h i s k i n d of behaviour can be found r e f e r r i n g once again to the schematic s t r u c t u r e s proposed i n Figure 1, I t i s obvious t h a t t e t r a h e d r a pf the type shown i n Figure IA do not change upon dehydration,, but the octahedra of Figure IB w i l l p r o g r e s s i v e l y transform i n t o t e t r a h e d r a s i m i l a r to Figure 1C. In AS-1 (low A l content), the type A i s the only one present and consequently the t e t r a h e d r a network i s almost not a f f e c t e d by dehydration, that i s why no changes i n Si-0 band frequency occur. .But f o r AS-2 and AS-3 samples (high i n A l content) the dehydra-t i o n b r i n g s about a C type of s t r u c t u r e which can be under-stood i n terms of i n c r e a s i n g the s i l i c o n t e t r a h e d r a o r g a n i -z a t i o n with the consequent i n c r e a s i n g i n the Si-0 s t r e t c h i n g frequency observed f o r these two samples. A behaviour s i m i l a r to tha t one j u s t described can be observed on the s p e c t r a of AS-2 taken a f t e r successive e x t r a c t i o n s (Figure 6), One can note a progr e s s i v e increase i n the frequency of Si-0 s t r e t c h i n g band from 1025 cm to 1060 and f i n a l l y to 1110 cm" as we go from the sample t r e a t e d with 5% Na2C0^ to those t r e a t e d w i t h a c i d NH^-oxalate and d i t h i o n i t e . With these successive treatments, there i s i n f a c t , p rogressive removal (as explained l a t e r i n t h i s chapter) of polyhydroxy Fe and A l phases which are a c t u a l l y p e r t u b a t i n g the s i l i c o n t e t r a h e d r a network, consequently improving the s i l i c o n t e t r a h e d r a o r g a n i z a t i o n which b r i n g s untreated 4 0 0 0 3 0 0 0 Figure 3.1 2 0 0 0 1600 WAVENUMBER CM*' ssive extractions: (a) 5 % N a 2 C 0 3 . Infrared spectra of A S - 2 untreated and after succe (b) Ac. N H 4 - o x a l a t e , (c) Dithionite. 9 7 . about a b e t t e r r e s o l u t i o n of the band and an increase, i n the S i - 0 s t r e t c h i n g frequency as shown i n the s p e c t r a of As-2 a f t e r 5% NagCO^ + a c i d NH^-oxalate extraction, o r , even b e t t e r , a f t e r % NagCO^ + a c i d NH^-oxalate + d i t h i o n i t e e x t r a c t i o n . On these s p e c t r a , other bands are i n t e r e s t i n g t o note i the band at 1280 cm"*3" appearing i n AS-2 (a) and AS-2 (a + b) s p e c t r a and not present i n AS-2 ( a + b + c ) spectrum. The highest frequency can be assigned to A1-0-H bending and the two lower frequencies to A l - 0 s t r e t c h i n g mode and t h a t would e x p l a i n why they do not show up i n AS-2 ( a + b + c ) and why they disappear even from the AS-2 (a) and AS-2 (a + b) s p e c t r a upon dehydration. STRUCTURAL MODEL (a) Formation of an i r o n - a l u m i n o s i l i c a t e phase. The co n d i t i o n s under which the experiment was conducted have simultaneously favoured the depolymerization of s i l i c a , whose concen t r a t i o n was q u i t e c l o s e to i t s s o l u -b i l i t y product and the depolymerization of the aluminum and i r o n hydroxides. Each c a t i o n (as F e ^ + and Al^ 4") i n s o l u t i o n i s coordinated w i t h s i x molecules of water and c o n t r i b u t e s h a l f a p o s i t i v e charge t o each? the p r e c i p i t a t i o n of the c a t i o n would correspond t o the s u b s t i t u t i o n of an OH f o r a H o0. 98. The structure of the hydroxide obtained w i l l then depend upon the ease with v/hich the HgO remaining can be eliminated aft e r the OH f i x a t i o n . The removal of t h i s hydrated water seems to occur rather e a s i l y i n the case of divalent ions whose diameter i s large and the charge to volume r a t i o low, consequently, the a t t r a c t i o n for the water molecules of divalent ions i s less strong than for t r i v a l e n t ions such as Fe and A l . On t h i s basis, the existence of basic ions, l i k e R (H 20)^ (OH) 2 (where R indicates A l ^ + or Fe^ +) i n agreement with chemic.o-physical conditions (pH 7.0 and weak d i l u t i o n ) can be postulated. To the extent that these ions e x i s t , they w i l l lend themselves to the formation of a phase having the following possible formula i n the presence of s i l i c a : 2 S i (OH)^ + R (H 20)^ (0H)J > H H H 0 0 0 1 I H I HO — Si — 0 — R — 0 — Si — OH I I I 0 0 0 H H H In t h i s phase, A l and Fe appear to be f o u r f o l d coordinated i n p a r t i a l l y s u b s t i t u t i n g for tetrahedral s i l i c o n . 99. F r i p i a t and coworkers (1965)» u s i n g a system pre-pared from aluminum isopropoxide and e t h y l s i l i c a t e have a r r i v e d at the same b a s i c model and they found that i n the 0 - 0.40 percent A l / A l + S i atomic r a t i o range, only h a l f of the A l present i s f o u r f o l d coordinated: the remainder of the A l i s s i x f o l d coordinated and th e r e f o r e not p a r t of the a l u m i n o s i l i c a t e phase. In the composition range 0.40 -1.0 A l / A l + S i , they observed an increase of the number of s u b s t i t u t i o n s of A l f o r S i i n the a l u m i n o s i l i c a t e phase, as w e l l as an increase of s i x f o l d coordinated aluminum i n the phase c o a t i n g the a l u m i n o s i l i c a t e core. Above 0.80 A l / A l + S i atomic r a t i o , they have observed a demixing of c r y s t a l l i n e alumina but have recorded the presence of, pseudobohemite i n a d d i t i o n to b a y e r i t e . The a l u m i n o s i l i c a t e phase i s thus composed of elementary p a r t i c l e s c a r r y i n g negative charges which a r i s e from f o u r f o l d coordinated aluminum i n the t e t r a h e d r a l s i l i c a framework. (°) Formation of A l and Fe Hydroxides complexes. 3+ 3+ As mentioned e a r l i e r , each A l or Fe^ i o n i n s o l u t i o n i s coordinated w i t h s i x HgO molecules which c o n t r i -butes h a l f a p o s i t i v e charge to each. When a hydroxyl i o n 3+ 3+ i s attached t o an A l v or Fe-' i o n , h a l f of i t s negative charge w i l l be used to n e u t r a l i z e h a l f a p o s i t i v e charge c o n t r i b u t e d by the A l ^ + or Fe-^+ i o n , l e a v i n g another h a l f negative charge on the 0H~ u n s a t i s f i e d and a v a i l a b l e to b a l -3+ 3+ ance h a l f a p o s i t i v e charge from another A l ^ or Fe-' i o n . amorphous n H 2 0 21 R+05(OH) • m H 2 0 2.5 e-amorphous 40 0. 40 1 _ Al /Al + Si 0 .80 FIGURE 3 , S C H E M A T I C R E P R E S E N T A T I O N AND S T R U C T U R A L FORMULAS OF I R O N - A L U M I N O S I L I C A T E C O R E - P H A S E AND P O L Y H Y D R O X Y - 1 RON A N D A L U M I N U M P H A S E S WITH V A R Y I N G A l / A l + S i A T O M I C R A T I O S . I - AMORPHOUS I R O N - A L U M I N O S I L I C A T E CORE ( A l A N D Fe T E T R A H E D R A L L Y C O - O R D I N A T E D ) . I I - AMORPHOUS P O L Y H Y D R O X Y - I R O N A N D A L U M I N U M C O A T I N G P H A S E ( A l AND Fe O C T A H E D R A L L Y C O - p R D I N A T E D ) . R = A l 3 + OR F e 3 + * TH E MODELS C O R R E S P O N D TO THE S P E C I F I E D F I G U R E S I N A B S C I S S A . ** M O D I F I E D AND S I M P L I F I E D FROM CLOOS ai. ( 1 9 6 9 ) . ' 101, The OH i s thus shared equally "by the two A l ^ or ¥& ions and functions as a bridge between them. This i s considered to be the fundamental p r i n c i p l e underlying polymerization of hydroxy-aluminum or ir o n ions i n solution. Secondly,, i t i s believed that the hydroxy-aluminum or iron ions tend to polymerize i n a six-membered r i n g unit or multiples of such units. This s t r u c t u r a l arrangement unit was e a r l i e r proposed f o r A l with a composi-t i o n A l ^ (OH) also a phase, as mentioned before, R (H 20)^(0H) 2 + can be l o g i c a l l y proposed f o r the hydroxy-Al or Fe ions structure i n solution. The charges i n the core phase ( i . e . , the iron-aluminosilicate anions) are balanced, at lea s t p a r t l y , by mono and polynuclear hydroxy-aluminum or iron cations of increasing complexity and decreasing net charge per R atom as the R/R + S i atomic r a t i o increases (R = A l ^ + or F e ^ + ) . CONCLUSION The s t r u c t u r a l model discussed, although not considered to be perfect, presents a useful picture of iron-alumino-s i l i c a t e structures as i t offers an explanation f o r some of the experimental observations recorded. Referring, f o r example, to Table 3« "the fact that % NagCO^ treatment removed 9.43$ AlgO^ and only a small f r a c t i o n of S i 0 2 (0.70$) can be explained assuming that the s i x f o l d coordinated aluminum on the core surface i s removed f i r s t by the treatment, 102. leaving almost intact the i n t e r n a l structure. Also, the fact that v i r t u a l l y no Fe i s removed by the 5% NagCO^ treatment can be possibly explained by assum-ing that most of the iron (as most of the aluminum) i s tetrahedrally substituted i n the core structure of the main amorphous phase or i t may be present as polyhydroxy iron i n octahedral coordination coating the core but much more strongly attached than the aluminum. Thus, iron cannot be removed by the r e l a t i v e l y mild 5% Na^COo treatment. 103 o LITERATURE CITED 1. Cloos, P., A. Herb i l l o n , J . Echeverria. 1968. Allophane-like synthetic silicoaluminas. Trans, 9 t h Inter, Congr. S o i l S c i . II 733 - 743. 2. Cloos, P., A.J. Leonard, J.P. Moreau, A, Herbillon, J . J . F r i p i a t . 1969. Structural organization i n amorphous silicoaluminas. Clay and Clay Minerals, 17: 279 - 289. 3. Danforth, J.D. i 9 6 0 . Structures and chemical charact-e r i s t i c s of cracking c a t a l i s t s . Actes II Congr, Int. Catalyse, Paris 1: 1271 - 1277. 4. De Kimpe, C , M.C. Gastuche, and G.W. Brindley. 1961. Ionic coordination i n a l u m i n o s i l i c i c gels i n r e l a t i o n to clay mineral formation, Amer, Mineral, 46: 1370 - 1381, 5. De V i l l i e r s , J.M, 1970, Quantitative determination of allophane i n s o i l . S o i l S c i , 112: 2 - 12. 6. F r i p i a t , J . J . , A. Leonard, J.B, Uytterhoeven. 1965. Structure and properties of amorphous silicoaluminas, II Lewis and Brb'nsted acid s i t e s . J, Phys, Chem. 69s 3274 - 3279. 7. Henin, S,, and S. C a i l l e r e . 1963. Sinthese des mineraux a basse temperature: E s s a i de mise au point. R. colloque Int, C.N.R.S. Paris, No 105: 107 - 115. 8. Leonard, A., S. Suzuky, J . J . F r i p i a t , and C, De Kimpe. 1964, Structure and properties of amorphous silicoaluminas, I, Structure and properties from X-ray fluorescence spectroscopy and infrared spectros-copy. J. Phys. Chem, 68: 2608 - 2617. 9. Leonard, A,, F. Van Cauwelaert, J . J , F r i p i a t . 1967. Structure and properties of amorphous silicoaluminas. I I I . Hydrated aluminas and t r a n s i t i o n aluminas. J. Phys. Chem. 71s 695 - 708. 10. M i l l i k e n , T.,.G.A. M i l l i s , and A.G. Oblat. 1950. The chemical c h a r a c t e r i s t i c s and structure of cracking c a t a l i s t s . Discussion Faraday Soc. 8s 280 - 289, 104. 11. Tamele, M.W., 1950. Chemistry of the surface and the a c t i v i t y of the aluminosilica cracking c a t a l i s t s . Discussion Faraday Soc. 8s 270 - 279. 12. Van Reeuwiijk, L.P., and J.M. De V i l l i e r s . 1968. Potassium f i x a t i o n by amorphous aluminosilica gels. S o i l S c i . Soc. Amer. Proc. 32s 238 - 240. I05o 'THE INORGANIC AMORPHOUS SYSTEM OF SOIL COMPARED TO AN ARTIFICIAL AMORPHOUS IRON-ALUMINOSILICATE SYSTEM INTRODUCTION In the f i r s t chapter, the amorphous inorganic material of s o i l has been described as a polyphase complex system lacking homogeneity and unity of reactions. Any attempt at subdividing single phases of t h i s sytem i s frustrated by i t s complexity; the im p o s s i b i l i t y of s e l e c t i v e l y separating a phase without a l t e r i n g the chemical and physical nature and i d e n t i t y i n i t s own complex context. So the r i s k of creating chemical a r t i f a c t s i s quite high and therefore the r e s u l t s obtained i n the e f f o r t of separating these phases appear to be misleading. Despite t h i s , the chemical and physical studies of s o i l has allowed us to gain a deep insight into the chemical nature and the physical behaviour of amorphous inorganic materials. It i s clear that the more we learn about the structure and composition of these polyphase systems, the more we w i l l be able to explore t h e i r o r i g i n , t h e i r nature, and t h e i r importance i n s o i l systems. Faced with evident d i f f i c u l t i e s i n di r e c t studies of inorganic amorphous system i n s o i l , and casting around for an alternative approach, many researchers have proposed to investigate the complexity of t h i s system through much more 106. simple a r t i f i c i a l models, the composition of which can be controlled and the s t r u c t u r a l organization more e a s i l y under-stood. To these, the natural system i t s e l f can be related by s i m i l a r responses to the same chemical and physical analyses. In t h i s study, the a r t i f i c i a l model discussed i n chapter two, f o r which a phase co n s t i t u t i o n and a s t r u c t u r a l organization have been proposed, w i l l be compared with a natural amorphous concentrate derived by acid dispersion from a < 2/* clay. In t h i s manner, studies on correlations between a r t i f i c i a l and natural systems could allow us to i n f e r some conclusions regarding the nature and the structure of, the inorganic amorphous system i n the s o i l studied. This implies that the model proposed has to be prepared: ad hoc for the s p e c i f i c amorphous system with which we are dealing, because of the uniqueness of these systems i n each d i f f e r e n t s o i l . In other words, we are aware that so f a r no universal model can be proposed on the basis of the correlations observed i n our s p e c i f i c case. MATERIALS AND METHODS Choice of clay material (^2^) f o r study was based on the c r i t e r i o n of a high proportion of amorphous inorganic material and a low inherent organic matter content. From previous study, the clay f r a c t i o n of the B f 3 horizon of the Ryder s o i l appeared to s u i t the objectives. 107. I t was f e l t d e s i r e a b l e to concentrate the amorphous ino r g a n i c m a t e r i a l i n such a manner as to exclude the hulk of the c r y s t a l l i n e l a y e r s i l i c a t e s . ' Thus, a more r e l i a b l e c h a r a c t e r i z a t i o n of the amorphous system would be p o s s i b l e . The method s e l e c t e d f o r c o n c e n t r a t i o n was an a c i d d i s p e r s i o n procedure. However 8 only a small amount (about 15$) of the t o t a l c l a y f r a c t i o n was s u s c e p t i b l e to such d i s p e r s i o n , while the main body of the c l a y f r a c t i o n remained i n the f l o c c u l a t e d s t a t e . The amorphous m a t e r i a l f r a c t i o n a t e d by t h i s means assumed a p o s i t i v e charge i n the H-saturated c o n d i t i o n . The amount of c r y s t a l l i n e c l a y detected i n the dispersed m a t e r i a l may be i n t e r l a y e r e d w i t h the amorphous i r o n -a l u m i n o s i l i c a t e polymeric phases or may be p h y s i c a l l y bonded to t h i s p o s i t i v e l y - c h a r g e d f r a c t i o n which has been i s o l a t e d by the procedure o u t l i n e d below. ACID DISPERSION PROCEDURE The d i s p e r s i o n was performed on the < 2j* c l a y of Bf3 h o r i z o n of the Ryder s o i l s once i t was separated by s u p e r c e n t r i f u g a t i o n from the s o i l which was p r e v i o u s l y l e f t i n water overnight to f a c i l i t a t e soaking and easy d i s p e r s i o n i n l a t e r procedures, and then p r e t r e a t e d w i t h NaOCl at pH 9 . 5 (four treatments i n b o i l i n g waterbath f o r 15 minutes) to destroy the organic matter ( L a v k u l i c h and Wiens, 1 9 7 0 ) . 108. To the c l a y , soaked i n water and b r i e f l y ( ten minutes) t r e a t e d i n an u l t r a s o n i c d i s p e r s i o n u n i t ( B r o n w i l l -B i o s o n i k I I I 5 at i n t e n s i t y 9 0 ) , was added, 0 . 1 N HC1 i n s u f f i c i e n t amount to b r i n g the pH down to 3 , 0 . The f i n e s t c l a y f r a c t i o n became dispersed (while the main body remained f l o c c u l a t e d ) , and was separated by c e n t r i f u g a t i o n at 2500 rpm f o r ten minutes. To completely remove the excess HCl, repeated washings w i t h d i s t i l l e d water were necessary u n t i l d i s p e r s i o n was accomplished (almost no f i n e p a r t i c u l e s should remain a f t e r c e n t r i f u g a t i o n i n the supernatant l i q u i d ) . Each of the seven washings necessary, were performed as followss to 250 ml b o t t l e s , w i t h two to three grams of c l a y , d i s t i l l e d water was added to f i l l about three-quarters of the b o t t l e , t h i s was shaken f o r ten minutes and then c e n t r i f u g e d .at 2500 rpm f o r ten minutes. To b r i n g down t h i s amorphous concentrated c l a y from the separated f r a c t i o n , c e n t r i f u g a t i o n , i n a Lourdes supercentrifuge at 12,000 rpm f o r twenty minutes was necessary. A small amount of water was added to the c e n t r i -fuged amorphous concentrate (enough to make a s l u r r y ) and i t was b r i e f l y ( f i v e minutes) t r e a t e d again i n the u l t r a s o n i c u n i t p r i o r t o f r e e z e - d r y i n g , A s o f t , minutely-powdered m a t e r i a l was obtained. The a c i d d i s p e r s i o n technique has been used by a number of authors to o b t a i n d i s p e r s i o n of v o l c a n i c s o i l s (Davis, 1933f B i r r e l and F i e l d e s , 1952) but has r a r e l y been used f o r other s o i l s . 109 o De Mumbrum and Chesters (1964) have obtained a concentrate of amorphous m a t e r i a l by t h i s d i s p e r s i o n technique from s e v e r a l s o i l s , but no q u a n t i t a t i v e i n f o r m a t i o n on the amount of c l a y obtained was given. Raman and Mortland (1969), w i t h the pur-pose of o b t a i n i n g i n f o r m a t i o n on the amounts of amorphous ino r g a n i c c o l l o i d s i n spodosols, employed two d i f f e r e n t d i s -p e r s i o n techniques: the normal a l k a l i d i s p e r s i o n (Ua^CQj s o l u t i o n at pH 9.5) and a pH 3.7 a c i d d i s p e r s i o n procedure. When c l a y from both the a c i d and a l k a l i d i s p e r s i o n procedures was subjected to a 0.5 N NaOH d i s s o l u t i o n (Hashimoto and Jackson, i960), they found that the one obtained a f t e r a l k a l i d i s p e r s i o n contained higher r e s i d u a l c r y s t a l l i n e m a t e r i a l than the a c i d - d i s p e r s e d c l a y . They t h e r e f o r e used t h i s procedure to study i n d e t a i l the p r o p e r t i e s of the amorphous separates which were found to c o n t a i n between 54 to 64$ amorphous m a t e r i a l . The comparison and a l l c o r r e l a t i o n s i n t h i s e x p e r i -ment are drawn between the Bf^ amorphous concentrate (which w i l l be c a l l e d AC-R3 i n a l l r e f e r r a l s ) and the ad hoc-prepared a r t i f i c i a l i r o n - a l u m i n o s i l i c a t e standard, denominated AS -2. , the p r e p a r a t i o n and the c h a r a c t e r i s t i c s of which have been already described i n chapter two. In seeking f o r c o r r e l a t i o n s between the n a t u r a l amorphous system and the a r t i f i c i a l one, the f o l l o w i n g chemical and p h y s i c a l analyses were performed: 110. ( i ) successive s e l e c t i v e d i s s o l u t i o n a n a l y s i s i n order to determine the t o t a l % of amorphous AlgO^, FegO^, S i 0 2 present i n the samples and then c a l c u l a t i o n of atomic and molar r a t i o s of these oxides t o see t h e i r r e l a t i v e d i s t r i b u t i o n i n the sample„ The d e t a i l e d method followed f o r the successive s e l e c t i v e e x t r a c -t i o n s has already been o u t l i n e d i n chapter one, t o which the reader has to r e f e r . The successive e x t r a c -t i o n s were performed i n t h i s order: (a) 5% Na 2C0^ (b) a c i d NH^ oxalate and (c) c i t r a t e - d i t h i o n i t e . Percent l o s s and s p e c i f i c surface area were c a l c u l a t e d a f t e r the second (a+b) and the t h i r d (a+b+c) t r e a t -ment , ( i i ) t o t a l elemental a n a l y s i s by a c i d d i g e s t i o n was c a r r i e d out to have a comparison w i t h the r e s u l t s of successive s e l e c t i v e d i s s o l u t i o n analyses. ( i i i ) X-ray d i f f r a c t i o n and i n f r a r e d spectroscopy on the untreated samples and a f t e r each s i n g l e successive e x t r a c t i o n were conducted, RESULTS AND DISCUSSION The r e s u l t s of successive s e l e c t i v e d i s s o l u t i o n a n a l y s i s on the amorphous concentrate AC-R3 and a r t i f i c i a l standard AS-2, along w i t h the r e s u l t s of the same successive d i s s o l u t i o n s on C l a y - R 3 which i s the < 2^ c l a y of R3 s o i l sample not subjected tp a c i d d i s p e r s i o n , are reported i n Table 1, 111. A few inte r e s t i n g observations can be derived from these data: The % of S i 0 2 , AlgO^ and FegO^ af t e r 5% NagCO^ + acid NH^-oxalate extraction (indicated as 'a+b' i n the Table) are markedly higher i n AC-R3 than in Clay-R3» which indicates a higher presence of amorphous material i n the concentrate i n respect to the non-acid-dispersed clay. The same trend i s observed for the percent obtained aft e r 5% NagCO-j '+ acid NH^-oxalate + d i t h i o n i t e extraction (indicated as 'a+b+c* i n the Table). Comparison of the data of AC-R3 with those of AS-2 after (a+b) extraction, shows a s l i g h t l y higher percent of SiOg and AlgO^ and s l i g h t l y lower percent FegO-j for AS-2 with respect to AC-R3» and the same can be said f o r the data after (a+b+c) extraction. These close relationships among the amorphous species present i n the natural and a r t i f i c i a l system can be seen more e a s i l y when expressed as the S i 0 2 / AlgO^ / FegO^ molar r a t i o s ; i n pa r t i c u l a r , one can observe a high c o r r e l a t i o n between AC-R3 (a+b) (molar r a t i o 1/2.85/1.?6) and AS-2 (a+b) (molar r a t i o 1/2.54/L15). 112. TABLE 1 Percent amorphous A1 20 3 * F e 2 ( - S i 0 2 i n Clay-R3, AC-R3 and i n AS-2 as extracted by successive selective d i s s o l u t i o n and d i t h i o n i t e only and S i 0 2 / A l 2 0 3 / F e 2 0 j molar r a t i o fo fo fo S i 0 2 / Sample Si0 2 A1 20 3 F e2° 3 Al 20^/Fe 20^ Clay-R3 (a+b) 3.89 8.77 7.41 1/2.25/1.90 Clay-R3 (a+b+c) 4.60 10.30 14.94 1/2.24/3.22 AC-R3 (a+b) 11.17 31.88 19.62 1/2.85/1.76 AC-R3 (a+b+c) 12.61 33.12 29.37 1/2.62/2.32 AC-R3 (Dith. only) 1.93 10.21 15.73 1/5.29/8.15 AS-2 (a+b) 15.94 40.30 18.38 1/2.54/1.15 AS-2 (a+b+c) 21.91 49.74 22.32 1/2,27/1,02 AS-2 (Dith. only) 2.57"" 20,98 13.94 1/8.16/5.42 untreated clay R3 amorphous concentrate R3 a r t i f i c i a l iron-aluminosilicate No, 2 -sodium carbonate + acid NH^-oxalate extraction sodium carbonate + acid NHu-oxalate + d i t h i o n i t e extract separate extraction with d i t h i o n i t e alone Clay-R3 AC-R3 AS-2 (a+b) (a+b+c) (Dith. only) 113. Incidentally, the AC-R3 (a+b) molar r a t i o i s also very close to that of Clay~R3 (a+b) (molar r a t i o 1/2,25/1.90). A marginal observation should not be missed on Table 1 regarding the $ Si0 2» AlgO^, FegO^ af t e r a d i t h i o n i t e separ-ate extraction (indicated as *Dith. only' i n the Table) f o r AC-R3 (Dith. only) and AS-2 (Dith. only) as compared to the same $ af t e r (a+b+c) extraction for the same two samples. I t appears quite clear that the amount of material removed by a d i t h i o n i t e treatment alone i s much less than the amount removed by the three successive selective extractions. In Table 2, there are again some indications of good correlations between AC-R3 and AS-2 f o r t o t a l percent of (AlgO^ + FegO^ + S i 0 2 ) and the surface area a f t e r (a+b) and (a+b+c) extractions. Comparing the t o t a l percent (AlgO^ + Fe^O^ + SiOg) of Clay-R3 (a+b), AC-R3 (a+b), AS-2 (a+b) which are 20.10%, 62.67$ and 74,60$, respectively, one can note how much higher the proportion of amorphous material i s present i n AC-R3 compared to Clay-R3l the same trend can be noted f o r the same samples a f t e r (a+b+c) extraction. Both the extractions (a+b) and (a+b+c) i n AS-2 are higher, i n amounts than i n AC-R3 but t h i s i s c l e a r l y understood when one considers the fact that AS-2 i s t o t a l l y amorphous, while i n AC-R3» there i s s t i l l a f r a c t i o n of c r y s t a l l i n e minerals. 114 0 TABLE 2 Total % of the amorphous material (AlgO^ + F e 2 ° 3 + s ^ ° 2 ^ ^ n Clay-R3» AC-R3t and AS-2 as extracted by successive selective d i s s o l u t i o n and d i t h i o n i t e only (see Table l ) s % losses a f t e r treatments; surface area of the untreated samples and af t e r treatments. Sample Total % (A1 2 0^ Fe 2 0 ^ + S i 0 2 ) + % losses Surface Area (m2 / g) * Clay-R3 -_ - 176.97 Clay-R3 (a+b) 20.10 2 3 . 9 9 51.57 Clay-R3 (a+b+c) 29.80 35.56 4 5 . 2 3 * AC-R3 - - 280.53 • AC-R3 (a+b) 62.67 6 5 . 7 0 46.50 AC-R3 (a+b+c) 73.03 81.38 33.57 AC-R3 (Dith. only) 27.90 3 3 . 3 0 -* AS-2 - - 294,34 AS-2 (a+b) 74.60 7 5 . 5 0 . 4 4 . 0 6 AS-2 (a+b+c) 93.97 97.16 31.82 AS-2 (Dith. only) 37.50 3 7 . 9 5 -* indicates: untreated sample For Clay-R3, AC-R3, AS-2, (a+b), (a+b+c) - see Table 1. ' 115. The percent weight losses are i n good agreement with the t o t a l percent extracted? one can note, a closer r e l a t i o n s h i p i n AS-2 than i n AC-R3 or i n Clay-R3 and t h i s i s probably due to the fact that other elements present i n the l a s t two samples were not determined. The best c o r r e l a t i o n found f o r these amorphous natural and a r t i f i c i a l systems appears to be i n the surface area. As one looks at the figures given f o r untreated samples of Clay-R3, AC-R3. and AS-2, as compared to those of the same sample afte r (a+b), f o r example, the amorphous mat-e r i a l present i n these samples i s the responsible element for the large surface area values. In f a c t , as t h i s i s removed (see surface area aft e r 'a+b' extraction) the surface area drops dramatically. It has also to be pointed out, that the larger the proportion of amorphous material i n the sample, the larger i s the surface area value. Incidentally, one can note that between the values of the surface area a f t e r (a+b) and (a+b+c) extractions, the difference i s very small; as small as the differences i n the t o t a l percent of amorphous material extracted by the two mentioned extractions. The value of t o t a l percent of amorphous material given f o r AC-R3 af t e r (a+b+c) extraction: (73.03$) canbe r e l i a b l y assumed to represent much more c l o s e l y the exact t o t a l amorphous percent than that one given a f t e r (a+b) extraction. 116. To help explain t h i s , X-ray d i f f r a c t i o n spectra were examined: ( i ) the AS-2 sample gives no d i f f r a c t i o n peaks following any of the extractions ( i i ) the AC-R3* the amorphous concentrate, which, as can be noted i n Table 2, has s t i l l a f r a c t i o n of c r y s t a l l i n e material present gave X-ray d i f f r a c t i o n spectra c h a r a c t e r i s t i c of the amorphous material u n t i l i t was treated with d i t h i o n i t e i n addition to % NagCD^ and acid NH^-oxalate. Therefore, t h i s f a c t suggests that not a l l the amorphous material was removed af t e r oxalate extraction and that only following the d i t h i o n i t e extraction can i t be concluded b y i X-ray, that a l l the amorphous material has been removed; and that i s why i t i s believed that the t o t a l percent value af t e r (a+b+c) extraction can better represent the t o t a l amorphous present i n the'AC-R3 sample. This conclusion appears to be also sustained by the findings on infrared spectroscopy which w i l l be commented on l a t e r i n t h i s chapter. Table 3 gives the t o t a l elemental analysis data f o r AC-R3, AS-1, AS-2, AS-3. The percent of AlgO-jt FegO^, and S i 0 2 are recalculated and expressed on an air-d r y basis, as reported i n Table 4. This was done to: make a comparison between the percent of these oxides a f t e r t o t a l elemental analysis and a f t e r (a+b+c) successive extraction f o r the two samples AC-R3 and AS-2. In t h i s regard, one can note, from Table 4 that: ( i ) the percent A l 9 O q and S i O ? are much 11?, lower i n AC-R3 a f t e r (a+b+c) e x t r a c t i o n than a f t e r t o t a l elemental a n a l y s i s . While the same (a+b+c) e x t r a c t i o n appears to remove a l l the i r o n (29.37% against 29.42% as r e s u l t s from t o t a l elemental a n a l y s i s ) , ( i i ) f o r AS-2, which i s completely amorphous, the f i g u r e s f o r the two analyses are almost the same except f o r % S i 0 2 which i s lower a f t e r (a+b+c) e x t r a c t i o n than a f t e r t o t a l elemental a n a l y s i s and t h a t p a r t i a l l y accounts f o r the undissolved residue remaining a f t e r (a+b+c) e x t r a c t i o n , as i t i s reported i n Table 2 (100 - 93.97 = 6,03% r e s i d u e ) . Make a comparison between AS-2 percent oxides values and those of AS-1 and AS-3» which can give an idea of the r e l a t i v e p r o p o r t i o n of the three oxides i n the a r t i f i c i a l standards prepared. Table 5 has two s e c t i o n s : the upper s e c t i o n r e p o r t s the atomic r a t i o s A l / A l + S i , the molar r a t i o s SiOg/AlgO^/FegO^, the % AlgO^/AlgO^ + S i 0 2 , and % ?e2Qj/Fe20j + S i 0 2 as c a l c u l a t e d a f t e r t o t a l elemental a n a l y s i s f o r AC-R3» AS-1, AS-2 and AS-35 while the lower s e c t i o n r e p o r t s the same r a t i o s and percent f o r the same samples i n a d d i t i o n to the Glay-R3 sample as c a l c u l a t e d a f t e r both (a+b) and (a+b+c) e x t r a c t i o n s . Some of the most i n t e r e s t i n g r e l a t i o n s h i p s i n c l u d e : r a t i o s and the percentage values presented i n Table 5 f o r AC-R3 a f t e r (a+b) and a f t e r (a+b+c) e x t r a c t i o n are i n very c l o s e agreement w i t h the correspondent data of AS-2. These f i n d i n g s are considered important to derive some conclusions on the composition and s t r u c t u r a l o r g a n i z a t i o n of t h i s n a t u r a l amorphous system. This w i l l be attempted by i n c o r p o r a t i n g the f i n d i n g s on the i n f r a r e d s t u d i e s . 118. TABLE 3 T o t a l Elemental A n a l y s i s of AC-R3, and AS-1, AS-2, AS-3 % Oxides AC-R3 AS-1 AS-2 AS-3 F E 2 ° 3 21.05 23,78 14.66 9.12 ft T n 1\ J- \: ^  35.29 12.53 o o o o JJ«.J •-43.24 Mn 0 2 0-.30 - -1.20 - -K 20 0.80 - - -Na 20 4.31 4.16 1.27 1.15 H ?0 21.67 24.48 33.78- 32.66 s i o 2 15.38 35.05 16.97 13.83 TABLE 4 T o t a l % of AlgO^, ? E 2 ° 3 a n d S i 0 2 r e c a l c u l a t e d ' from Table 3 on an a i r - d r y b a s i s i n order to compare with the data rep o r t e d i n Table 1 and obtained a f t e r s uccessive s e l e c t i v e d i s s o l u t i o n a n a l y s i s (a+b+c). fo -Oxides AC-R3 AS-1 AS-2 AS-3 (a+b+c) AC-R3 (a+b+c) AS-2 A l 2 ° 3 45.05 16.58 50.31 64.27 33.12 49.74 Fe ?0^ 29.42 31.^9 22.34 13.54 29.37 22.32 s i o 2 18.92 47.77 26.08 21.04 12.61 21.91 119. TABLE 5 Samples AC-R3 AS-1 AS-2 AS -3 Atomic r a t i o : Alg/Al+Si: molar r a t i o : SiOg/AlgO^ + F e 2 0 3 : % A l 2 p 3 / A l 2 0 3 + S i 0 2 of AC-R3» AS - 1 , AS - 2 , AS-3 c a l c u l a t e d from the data of t o t a l elemental a n a l y s i s ; and the same from cl a y samples R3 (a+b); clay - R 3 (a+b+c), AC-R3 (a+b), AC-R3 (a+b+c), AS-2 (a+b), AS -2 (a+b+c), f o l l o w i n g successive ex t r a c t i o n s . . A l / A l + S i (atomic r a t i o ) 0 . 7 3 0 . 3 0 0 . 7 0 0 . 7 9 S i 0 2 / A l 2 0 ^ / F e 2 0 ^ 1 / 2 . 2 9 / 1 . 3 8 1 / 0 . 3 6 / 0 . 6 8 1 / 1 . 9 6 / 0 . 8 6 1 / 3 . 1 2 / 0 . 6 6 AlgO^/ A 1 9 0 ^ + S i 0 2 6 8 . 2 9 2 6 . 3 3 66.40 75.77 F e 2 0 3 / F e 2 0 ^ + S i 0 2 57.77 40.4-2 46.35 39.74 •Clay-R3 (a+b) Clay - R 3 (a+b+c) AC-R3 . (a+b) AC-R3 (a+b+c) AS-2 (a+b) AS-2 (a+b+c) 0 . ? 4 0 . 7 1 0 . 7 7 0 . 7 4 -0 . 7 9 0 . 7 2 1 / 2 . 2 5 / 1 . 9 0 1 / 2 . 2 4 / 3 . 2 2 1 / 2 . 8 5 / 1 . 7 6 1 / 2 . 6 2 / 2 . 3 2 1 / 2 . 5 4 / 1 . 1 5 1 / 2 . 2 7 / 1 . 0 2 6 9 . 2 8 6 9 . 2 6 74 .06 72 ,42 7 1 . 6 6 6 9 . 4 2 6 5 . 5 7 7 6 . 4 5 6 3 . 7 2 6 9 . 9 6 5 3 . 5 5 50 .46 f 120, INFRARED SPECTROSCOPY STUDIES Looking at Figure 1, one can note a high compara-b i l i t y between the s p e c t r a of the n a t u r a l and the a r t i f i c i a l amorphous system. This close r e l a t i o n s h i p was pointed out d u r i n g the d i s c u s s i o n of chemical analyses and surface area determinations. The same c o m p a r a b i l i t y can a l s o be observed f o r the s p e c t r a of the two systems recorded a f t e r successive e x t r a c t i o n s and presented i n Figures 2,1 and 3.1» although a much more marked r e d u c t i o n of the Si-0 s t r e t c h i n g band around 1000 cm i s n o t i c e d f o r the AS-2 sample, which i s t o t a l l y amorphous, wi t h respect to AC-R3D which contains 30 - k0% of c r y s t a l l i n e m a t e r i a l . I t i s i n t e r e s t i n g to note on both s e r i e s of s p e c t r a , i n Figures 2,1 and 3°1» a p r o g r e s s i v e i n c r e a s i n g of the frequency of the Si-0 s t r e t c h i n g bands once again, t h i s increase i s more marked f o r the AS-2 sample, as one should expect, than f o r the AC-R3 sample, A f u r t h e r i n c r e a s i n g of the Si-0 s t r e t c h i n g ,band i s evidenced by the i n f r a r e d s p e c t r a of the two samples a f t e r dehydration at 30°°C» as Figures 2.2 and 3,2 c l e a r l y show. This behaviour i s i n t e r p r e t e d as an i n d i c a t i o n of the e f f e c t of the removing of the d i f f e r e n t amorphous phases from the systems the l e s s d i s ordered s t a t u s of the remaining s i l i c a framework gives a Si-0 s t r e t c h i n g band at higher frequency than t h a t of the same s i l i c a framework d i f f e r e n t l y i n t e r r e l a t e d with disordered phases. AS-2 _ r , , , : . , 1 , • 1 1 1 • 1 4000 3000 2000 1600 1200 800 400 WAVENUMBER CM-1 Figure I. Comparison between infrared spectra of AS-2 and AC-R3. untreated Figure 2.2. Infrared spectra of AC-R3 untreated (dehydrated at 300°C) and after successive extractions and heating at 300°C: (a) 5 % NagCC^. (b)Ac. NH^-oxalate , (c) Dithionite. untreated Figure 3.1 Infrared spectra of A S - 2 untreated and after successive extractions: (a) 5 % NagCC^. (b)Ac. NH4-oxalate, (c) Dithionite. untreated Infrared spectra of A S - 2 untreated (dehydrated at 300°C) and after successive extractions and heating at 300°C : (a) 5 % N a 2 C 0 3 , (b) Ac. NH 4 -oxalate , (c) Dithionite. 1 2 6 . CONCLUSION There i s l i t t l e doubt about the high degree of s i m i l a r i t y e x i s t i n g between the natural amorphous system separated from a Bf3 horizon clay of the Ryder s o i l series and the a r t i f i c i a l l y prepared amorphous iron-aluminosilicate. This s i m i l a r i t y has been demonstrated consistently by chemical and physical analyses. Some doubt may be expressed i n the close s i m i l a r i t y between the natural amorphous materials and the a r t i f i c i a l l y prepared sample as to s t r u c t u r a l arrangement of the constituent elements. Undoubtedly, the natural amor-phous material i s more complex than the simple a r t i f i c i a l model composition and arrangement, yet s t r i k i n g s i m i l a r i t i e s e x i s t . On the basis of evidence presented, i t can be postulated that the inorganic amorphous system i n the s o i l s studied i s a polyphase system with either an aluminosilicate or iron-aluminosilicate core. This core phase i s composed of elementary discrete p a r t i c l e s apparently carrying a negative charge, which originates from fo u r f o l d coordinated Fe or A l i n the tetrahedral s i l i c a framework. Surrounding t h i s core, complex inter a c t i n g polyhydroxy Fe and A l phases interact mainly by virtue of t h e i r p o s i t i v e charge. 127 o It appears that the combination of successive selective extractions with infrared spectroscopy i s a very useful approach to gain a better understanding of the nature of these phases. The approach of reconstructing a natural system through the s i m p l i f i c a t i o n of a r t i f i c i a l models appears to be useful as a method to disclose the structure of amorphous inorganic materials i n s o i l s . 128, LITERATURE CITED 1, B i r r e l l , K.S, and M. Fieldes. 1952, Allophane i n volcanic ash s o i l s . J, S o i l S c i , 3 s 156 - 166, 2 , - Davis, E.B., 1933. Studies i n the dispersion and deflocculation of c e r t a i n s o i l s . New Zealand J, S c i . Technol, 14: 228 - 232. 3 , De Mumbrum, L,E,, and G. Chesters, 1964. I s o l a t i o n and characterization of some s o i l allophanes. S o i l S c i . Soc. Am. Proc. 2 8 : 355 - 399 . 4, Hashimoto I, and M.L. Jackson, i 9 6 0 . Rapid d i s s o l -ution of allophane and k a o l i n i t e - h a l l o y s i t e a f t e r dehydration. Clays Clay Minerals, Proc. 7th Natl. Conf. Clays Clay Minerals. 1958: 102 - 113, 5 , Raman, K.V., and M.M. Mortland. 1969. Amorphous material i n a spodosol: some mineralogical and chemical properties. Geoderma. 3 : 37 - 44, 

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