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Adsorption of heavy metals at low concentrations using granular coals 1976

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"ADSORPTION OF HEAVY METALS AT LOW CONCENTRATIONS USING GRANULAR COALS" by U.^Tin Tun B.Sc. (Eng.), U n i v e r s i t y of Manitoba, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of C i v i l Engineering We accept t h i s t h e s i s as conforming to the req u i r e d standard The U n i v e r s i t y of B r i t i s h Columbia May, 1976 0 U. Tin Tun, 1976 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f ^Qt,WH>'cM CAQ<̂ >Q1 ^ Qvv/(l ^ • A ^ M J U L V * WS^, The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 D a t e 3//V)rW/ 1976 ABSTRACT The adsorption of low concentrations of heavy metals, such as z i n c , copper, le a d and mercury, by various B r i t i s h Columbia coals was i n v e s t i g a t e d . Five B r i t i s h Columbia coals were used as adsorbents f o r the four heavy metals described above. Batch t e s t s were run on a l l f i v e c o a l s , namely, Hat Creek O x i d i s e d , Hat Creek Unoxidised, Cominco O x i d i s e d , Cominao Ash Waste and Cominco Production Coal. The optimum contact time f o r batch t e s t s was found to be 60 mins. Batch t e s t s provided a quick comparison of the adsorptive c a p a c i t i e s of the f i v e c o a l s . Based on the batch t e s t s data, the best performing c o a l from each of the Hat Creek and Cominco groups, namely, Hat Creek Oxidised and Cominco Ash Waste were chosen f o r f u r t h e r i n v e s t i g a - tory work using column t e s t s . For the column t e s t s , the i n f l u e n t concentrations were 2 mg/£ and l e s s f o r z i n c , copper and lea d . Column work w i t h mercury was c a r r i e d out wi t h i n f l u e n t concentrations of 5 yg/& and l e s s . Column t e s t s showed the f o l l o w i n g : - a) Varying the c r o s s - s e c t i o n a l area of the c o a l column from .001 f t 2 to .002 f t 2 has no s i g n i f i c a n t i n f l u e n c e on the adsorptive c a p a c i t y . Both columns have diameters more than 10 times that of the average c o a l p a r t i c l e . b) The most c r u c i a l f a c t o r a f f e c t i n g adsorptive c a p a c i t y i s the pH of the i n f l u e n t . There i s a d e f i n i t e decrease i n c a p a c i t y w i t h decreasing pH. c) The capacity decreases w i t h i n c r e a s i n g flow r a t e , but the r e l a t i o n s h i p i s not l i n e a r . The decrease i n c a p a c i t y due to a flow r a t e increase from 1 to 3 Igpm/ft 2 i s much greater than the i i i i i decrease i n capacity due to an increase from 3 to 5 I g p m / f t . d) Comparing the adsorptive a f f i n i t i e s of z i n c , copper and l e a d , i t i s seen that l e a d d i s p l a y e d the greatest a f f i n i t y w i t h copper second and z i n c t h i r d . At 10% breakthrough c o n c e n t r a t i o n , the c a p a c i t i e s d i s p l a y e d by Cominco Ash Waste c o a l f o r l e a d , copper and z i n c were i n the r a t i o of 12:6:1. The i n f l u e n t pH and i n i t i a l c oncentrations i n v o l v e d were 4.0 and 2 mg/£ r e s p e c t i v e l y , and the flow r a t e was 1 Igpm/ft 2. e) Using i n f l u e n t s c o n t a i n i n g a mixture of z i n c , copper and l e a d r e s u l t s i n s m a l l e r i n d i v i d u a l c a p a c i t i e s f o r Zn, Cu and Pb than would be achieved w i t h s i n g l e s o l u t e i n f l u e n t s . But the t o t a l o v e r a l l c a p a c i t y of the c o a l f o r heavy metals i s greater w i t h mixed i n f l u e n t s than w i t h any s i n g l e s o l u t e i n f l u e n t . f) Tests w i t h mercury i n f l u e n t s show that d e t e r i o r a t i o n of the c o n c e n t r a t i o n of the mercury s o l u t i o n occurs at concentration of 5 yg/I and l e s s . ? g) Of the two coals chosen f o r column t e s t work, Hat Creek Oxidised i s the s u p e r i o r c o a l w i t h regard to the adsorptive c a p a c i t y of heavy metals. Tests run at an i n f l u e n t pH of 4.0 and i n f l u e n t concentrations of 2 mg/£ of each metal, showed the r a t i o of c a p a c i t i e s of Hat Creek O x i d i s e d : Darco a c t i v a t e d carbon: Cominco Ash Waste f o r Zn to be 12.1 : 1.2 : 1.0, f o r Cu to be 11.9 : 1.7 : 1.0 and f o r Pb to be 3.8 : 0.7 : 1.0. An attempt was made to c o r r e l a t e the column e f f l u e n t pH w i t h the e f f l u e n t metal c o n c e n t r a t i o n . I t was found that t h i s c o r r e l a t i o n i s more pronounced at lower i n f l u e n t pH values. i v During the course of the column work, a growth of fungus was observed at the top of the c o a l columns. I t i s p o s s i b l e that adsorptive c a p a c i t i e s were a f f e c t e d by t h i s fungus. TABLE OF CONTENTS ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ACKNOWLEDGEMENTS CHAPTERPTER 1 INTRODUCTION 1 2 GENERAL NOTES ON ADSORBENTS AND ADSORBATES USED IN THIS STUDY 4 2.1 Types of Coal 4 2.2 Coal P r e p a r a t i o n 5 2.3 Percent Recovery of 28/48 S i z e F r a c t i o n from Raw Commercial Coal 5 2.4 Optimizing the Coal P r e p a r a t i o n Procedure f o r Increased Percent Recovery of 28/48 S i z e F r a c t i o n 5 2.5 Sy n t h e t i c Wastewaters 6 3 BATCH TESTS 8 3.1 I n t r o d u c t i o n 8 3.2 Batch T e s t i n g Procedure 9 3.3 Determination of Optimum Contact Time 10 3.4 E f f e c t s o o f pH on Adsorptive Capacity of Coal 14 3.5 E f f e c t s of I n i t i a l Concentration Change and Coal Weight Change on Percent Removal 16 3.6 Adsorption Isotherms f o r Copper 19 3.7 Adsorption Isotherms f o r Lead 24 3.8 Adsorption Isotherms f o r Zi n c 26 v PAGE i i v v i i v i i i x VI CHAPTER 3.9 Adsorption Isotherms f o r Mercury 3.10 Batch Tests - Summary and Conclusions COLUMN TESTS 4.1 I n t r o d u c t i o n 4.2 Column Testing Apparatus 4.3 Column T e s t i n g Procedure 4.4 Breakthrough Curve C a l c u l a t i o n s 4.5 Breakthrough Curves f o r Zinc a) E f f e c t of Varying the C r o s s - S e c t i o n a l Area of the Coal Bed b) E f f e c t of Varying the I n f l u e n t pH c) E f f e c t of Varying the Flow Rate d) E f f e c t of Varying the I n f l u e n t Concentration 4.6 Breakthrough Curves f o r Copper 4.7 Breakthrough Curves f o r Lead 4.8 Breakthrough Curves f o r I n f l u e n t s Containing a Mixture of Z i n c , Copper and Lead 4.9 C o r r e l a t i o n of E f f l u e n t pH w i t h E f f l u e n t Concentration 4.10 Breakthrough Curves f o r Mercury 4.11 Column Tests - Summary and Conclusions RECOMMENDATIONS BIBLIOGRAPHY PAGE 33 33 37 37 39 41 43 43 45 47 51 54 61 65 69 77 83 86 92 94 LIST OF TABLES PAGE TABLE 2.1 S y n t h e t i c Wastewaters 7 3.1 E f f e c t s of pH on the Adsorptive Capacity of Coal 15 3.2 E f f e c t of Changing Coal Weight & I n i t i a l Concentration i n the Same P r o p o r t i o n on the Percent Removal 18 3.3 Comparison of H.C. OX and CO:ASH 35 3.4 Comparison of the C a p a c i t i e s of Two Coals f o r Each of the Four Heavy Metals 36 4.1 Contact Times f o r a 10-inch Column at Given Flow Rates 38 4.2 E f f e c t of Changing C r o s s - S e c t i o n a l Area of the Coal Bed 45 4.3 E f f e c t of Varying the I n f l u e n t pH 48 4.4 E f f e c t of Varying the Flow Rate 52 4.5 E f f e c t of Varying the I n f l u e n t pH 58 4.6 Comparison of Adsorptive C a p a c i t i e s of Columns Run w i t h Z i n c I n f l u e n t s of 0.5 mg/£ and 2.0 mg/I 59 4.7 E f f e c t of Varying pH w i t h Copper I n f l u e n t s 63 4.8 Comparison of Adsorptive C a p a c i t i e s f o r Copper and Zinc 65 4.9 C a p a c i t i e s f o r Lead 68 4.10(a) Adsorption C a p a c i t i e s Using Mixed I n f l u e n t s 74 4.10(b) A Comparison Between H.C. OX, CO:ASH and DARCO A c t i v a t e d Carbon w i t h Regard to 'their C a p a c i t i e s f o r the Three Metals from Mixed I n f l u e n t s at a pH of 4.0 75 4.10(c) Percent Decrease i n Capacity on Changing the I n f l u e n t to One Containing a Mixture of Solutes 75 v i x LIST OF FIGURES FIGURE PAGE 3.1(a) Contact Time - E q u i l i b r i u m Concentration f o r Copper 11 3.1(b) Contact Time - E q u i l i b r i u m Concentration f o r Copper 12 3.1(c) Contact Time - E q u i l i b r i u m Concentration f o r Copper 13 3.2 E f f e c t s on Percent Removal When Changing One Parameter While Keeping the Other F i x e d 17 3.3(a) Copper Adsorption Isotherms 20 3.3(b) Copper Adsorption Isotherms 21 3.3(c) Copper Adsorption Isotherms 22 3.3(d) Copper Adsorption Isotherms 23 3.4 Lead Adsorption Isotherms 25 3.5(a) Zinc Adsorption Isotherms 27 3.5(b) Zi n c Adsorption Isotherms 28 3.5(c) Z i n c Adsorption Isotherms 29 3.6(a) Mercury Ads o r p t i o n Isotherms 30 3.6(b) Mercury Adsorption Isotherms 31 3.6(c) Mercury Adsorption Isotherms 32 4.1(a) Constant H y d r a u l i c Head Apparatus 40 4.1(b) Double Tank Feed M o d i f i c a t i o n 40 4.2 A T y p i c a l Breakthrough Curve 44 4.3 E f f e c t of Changing C r o s s - S e c t i o n a l Area of the Coal Bed 46 4.4 E f f e c t of Varying the I n f l u e n t pH 49 4.5 E f f e c t of Varying Flow Rate f o r CO:ASH 55 4.6 E f f e c t of Varying Flow Rate f o r H.C. OX 56 v i i i i x FIGURE PAGE 4.7 E f f e c t of Varying the I n f l u e n t pH 57 4.8 E f f e c t of Varying the pH on Coal Capacity f o r Copper 62 4.9(a) E f f e c t of Varying the pH w i t h Lead I n f l u e n t s 66 4.9(b) Fungus Growing at the Top of Coal Column 67 4.10(a) Breakthrough Curves f o r H.C.OX w i t h Mixed I n f l u e n t s 71 4.10(b) Breakthrough Curves f o r C0:ASH w i t h Mixed I n f l u e n t s 72 4.10(c) Breakthrough Curves f o r DARCO A c t i v a t e d Carbon w i t h Mixed I n f l u e n t s 73 4.11 Breakthrough Curves f o r Mercury 84 ACKNOWLEDGEMENTS The author wishes to express h i s g r a t i t u d e to Dr. W.K. Oldham f o r h i s help and enduring patience. Thanks are a l s o extended to Dr. R.D. Cameron, Dr. D.S. Mavinic and Mrs. E. McDonald f o r t h e i r k i n d a s s i s t a n c e on various aspects of the research. G r a t i t u d e i s also owed to Mr. P. Siewert of M i n e r a l Engineering Department f o r h i s help on the pr e p a r a t i o n of the coals and to Mr. A.S. D h i l l o n of Geochemistry Department f o r h i s help on mercury d e t e c t i o n . The author a l s o wishes to express h i s g r a t i t u d e to the P o l l u t i o n C o n t r o l Branch, Water Resources S e r v i c e , Department of Lands, F o r e s t s , and Water Resources of the Province of B r i t i s h Columbia f o r p r o v i d i n g the necessary funds f o r t h i s research. x Chapter 1 INTRODUCTION A l o t of research has been done and an adequate amount of data compiled on the adsorption of organic p o l l u t a n t s by a c t i v a t e d carbon. Advanced waste treatment p l a n t s such as the one at Lake Tahoe, C a l i f o r n i a , f o r example, employ granular a c t i v a t e d carbon to remove various types of organic c o n s t i t u e n t s i n the wastewaters w i t h a good degree of success. Weber and M o r r i s i n t h e i r work w i t h a c t i v a t e d carbons and organic s o l u t e s reported high adsorption c a p a c i t i e s f o r organics such as nitrochlorobenzene and high molecular weight s u l f o n a t e d alkylbenzenes. (12) The Rand Corporation conducted a study w i t h a 10,000 gal/day p i l o t p l a n t w i t h 18/120 mesh c o a l as a consumable precoat f i l t e r f o r t r e a t i n g raw sewage and secondary e f f l u e n t . They reported a 90% decrease i n suspended s o l i d s and about 50% decrease i n phosphates and C.O.D. when raw sewage or secondary e f f l u e n t was t r e a t e d w i t h the c o a l f i l t e r . R e l a t i v e l y speaking, there has not been much work done on c o a l as (3) an adsorbent of i n o r g a n i c s such as the heavy metals. Hendren reported good adsorption c a p a c i t i e s f o r l e a d , copper and z i n c using granular c o a l s . The coals used were from B r i t i s h Columbia, namely, Hat Creek and Crowsnest c o a l s . Of s e v e r a l s i z e f r a c t i o n s t e s t e d , 28/48 mesh f r a c t i o n was found to d i s p l a y good adsorption c a p a c i t i e s as w e l l as s a t i s f a c t o r y h y d r a u l i c flow p r o p e r t i e s . The major p o r t i o n of h i s work was done at i n f l u e n t waste con- c e n t r a t i o n s of 10-100 mg/£. Sigworth and S m i t h ^ l i s t e d the adsorption p o t e n t i a l s of various i n o r g a n i c compounds by a c t i v a t e d carbon. They a t t r i b u t e d mercury and l e a d w i t h high adsorption a f f i n i t i e s . According to t h e i r l i s t , copper and z i n c were c l a s s i f i e d as having only a s l i g h t p o t e n t i a l f o r adsorption by a c t i v a t e d carbon. B r i t i s h Columbia has vast c o a l reserves. The present production of 1 2 c o a l i n B r i t i s h Columbia i s about 7 m i l l i o n tons per year. I t , t h e r e f o r e , seems both l o g i c a l and wise that the p o s s i b l e p o t e n t i a l f o r using B.C. coals as adsorbents f o r heavy metals, p r i o r to i t s use as a f u e l , should be w e l l i n v e s t i g a t e d . Another good reason f o r doing such an i n v e s t i g a t i o n would be an economic one. Although c e r t a i n types of a c t i v a t e d carbon may d i s p l a y f a i r a dsorption c a p a c i t i e s f o r heavy metals, a c t i v a t e d carbon i s r e l a t i v e l y expen- s i v e at about $500/ton. The present p r i c e of c o a l i s $15-$22 per ton. I t may w e l l turn out that the cost of using a c o a l system to remove heavy metals i s cheapter than using an a c t i v a t e d carbon system. When making an economic comparison of the two systems, one must take i n t o account the percent recovery of usable c o a l s i z e f r a c t i o n s from the raw commercial c o a l as w e l l as the i n d i v i d u a l adsorptive c a p a c i t i e s on a u n i t weight b a s i s . The percent recovery of u s e f u l c o a l s i z e f r a c t i o n s t h a t can serve as adsorbents i n column operations w i l l c r u c i a l l y determine the economics of such a c o a l system. The n o t i o n that c o a l adsorption may f a r e poorly at very low concen- t r a t i o n s of i n f l u e n t heavy metal has been i n the minds of many. To i n v e s t i g a t e t h i s aspect of c o a l use, the i n f l u e n t heavy metal concentrations used i n t h i s research are a l l very low. For z i n c , copper and l e a d , the i n f l u e n t concentra- t i o n s are i n the range of 0.5 mg/£ to 2.0 mg/£. In the case of mercury, the i n f l u e n t c o n c e n t r a t i o n used f o r the column t e s t s was 5 ug/Jl. These concentrations are i n the range of permissable l e v e l s o u t l i n e d by the P o l l u t i o n C o n t r o l Branch f o r the above heavy metals i n i n d u s t r i a l e f f l u e n t s . In t h i s r esearch, f i v e d i f f e r e n t B r i t i s h Columbia coals were st u d i e d under batch c o n d i t i o n s . The e f f e c t s of contact time, of pH, and of varying 3 i n i t i a l concentrations were i n v e s t i g a t e d . The batch t e s t s provided a quick comparison of the performance of the f i v e c o a l s . One type of c o a l from each of the Hat Creek group and the Cominco group was chosen f o r f u r t h e r i n v e s t i - gations under column operating c o n d i t i o n s . The column t e s t s used a c o a l bed w i t h a c r o s s - s e c t i o n a l area of .001 f t 2 and a c o a l depth of 10 inches. During the column s t u d i e s , the e f f e c t s of v a r y i n g c r o s s - s e c t i o n a l area, i n f l u e n t pH, flow r a t e and i n f l u e n t concentration were al s o i n v e s t i g a t e d . Although the l a b o r a t o r y s c a l e column t e s t s cannot supply data that are immediately u s e f u l f o r f u l l s c a l e design, they nonetheless give worthwhile i n f o r m a t i o n on r e l a t i v e adsorption c a p a c i - t i e s under flow-through column op e r a t i o n c o n d i t i o n s . The column data can then be used to compare with other documented removal methods. Chapter 2 GENERAL NOTES ON ADSORBENTS AND ADSORBATES USED IN THIS STUDY 2.1 Types of Coal The adsorbents used i n t h i s research are a l l coals n a t i v e to B r i t i s h Columbia. Five coals were used i n the Batch Tests and two of these f i v e were chosen f o r Column Tests. The f i v e coals are:- 1. Hat Creek Oxidised i s the c o a l picked up from the surface of the c o a l seams at Hat Creek. 2. Hat Creek Unoxidised i s obtained from a mixture of core samples of the Hat Creek c o a l d e p o s i t s . The core samples were from depths of 50' - 1,000' below the surface of the ground. 3. Cominco Oxidised i s the c o a l that had been exposed to o x i d a t i o n processes and consequently had l o s t i t s coking p r o p e r t i e s . 4. Cominco Ash Waste i s the c o a l w i t h a high percentage of i n e r t ashes and non v o l a t i l e matter. I t i s the waste product i n a c o a l c l e a n i n g process. 5. Cominco Production i s the c o a l that i s produced f o r marketing. The l a s t three coals described above, namely, the Cominco coals were a l l s u p p l i e d d i r e c t l y by Consolidated Mining and Smelting Company, L t d . from T r a i l , B r i t i s h Columbia. They were r e c e i v e d i n a crushed form and were sealed i n p l a s t i c bags. The abbreviations used h e r e i n f o r the f i v e coals are as f o l l o w s ; - H.C. OX - Hat Creek Oxidised H.C. UN - Hat Creek Unoxidised CO: OX Cominco Oxidised CO:ASH Cominco Ash Waste C0:PR0D Cominco Production 4 5 2.2. Coal P r e p a r a t i o n The c o a l was washed w i t h tap water to get r i d of d i r t p a r t i c l e s . A f t e r being d r i e d i n an oven, i t was put through a T r a y l o r Gyratory Crusher w i t h h" opening (-3% mesh), and then put through a Massco Cone Crusher w i t h an .0083" opening (-65 mesh). I t was subsequently dry-sieved using a mechanical shaker and 28/48 mesh screens. Wet s i e v i n g of the 28/48 c o a l p a r t i c l e s was then done to remove the f i n e s stuck to the 28/48 p a r t i c l e s . Further removal of f i n e s was accomplished by backwashing the c o a l i n a p l e x i - glass column. When almost a l l the f i n e s were removed, the c o a l was d r i e d at 103° C. f o r about 40 hours. I t was then t r a n s f e r r e d i n t o a b o t t l e , f l u s h e d w i t h n i t r o g e n gas and kept sealed u n t i l use. A f t e r each sample e x t r a c t i o n , the b o t t l e was r e f l u s h e d w i t h n i t r o g e n and resea l e d . 2.3 Percent Recovery of 28/48 S i z e F r a c t i o n from Raw Commercial Coal (3) Based on Hendren's f i n d i n g s on the opt i m a l p a r t i c l e s s i z e f r a c - t i o n w i t h respect to adsorptive c a p a c i t y as w e l l as h y d r a u l i c flow, the 28/48 Ty l e r mesh s i z e f r a c t i o n was chosen f o r t h i s e n t i r e research. F o l l o w i n g the c o a l crushing procedure o u t l i n e d p r e v i o u s l y , about 13% of the i n i t i a l raw c o a l weight was recovered i n the 28/48 s i z e range i n the case of H.C. OX. The percent recovery f i g u r e i n the 28/48 s i z e range f o r CO:ASH was about 14%. 2.4 Optimizing the Coal P r e p a r a t i o n Procedure f o r Increased Percent Recovery of 28/48 Si z e F r a c t i o n A poi n t to note i s that a 65 mesh was used i n the f i n a l crusher. This means most of the c o a l was crushed to a s i z e . f i n e r than the 28/48 s i z e range, and most of the c o a l t h e r e f o r e went r i g h t through the 48 screen. 6 Thus, the crushing procedure w i l l prove c r u c i a l when the o v e r a l l economics of the system are considered. There i s no reason not to expect the percent recovery i n the 28/48 s i z e f r a c t i o n to be increased tremendously from the f i g u r e s s t a t e d above f o r the two coals i f the f o l l o w i n g steps are taken:- 1. Use the proper type of crusher or a s e r i e s of crushers that w i l l minimize the f r a c t i o n of c o a l smaller than 48 mesh s i z e . 2. Use an optimal c l o s e d - c i r c u i t system that allows recrushing of c o a l p a r t i c l e s bigger than 28 mesh s i z e . 3. Use the type of screen that w i l l minimize f u r t h e r p a r t i c l e break-up. 4. Use a method of removal of the remaining slime and f i n e s that w i l l not enhance f u r t h e r f r a c t u r e of the c o a l p a r t i c l e s . U n f o r t u n a t e l y , there w i l l always be a c e r t a i n percentage l o s t as slime and f i n e s which are removed by wet s i e v i n g and backwashing processes. Slime i s made up of f i n e s s m a l l e r than .08 mm or 200 mesh s i z e . Slime r e s i s t s w e t ting a c t i o n of the water and f l o a t s to the top. 2.5 Sy n t h e t i c Wastewaters The waste s o l u t i o n s were prepared s y n t h e t i c a l l y i n the l a b o r a t o r y . The m a t e r i a l s used to make up a 1000 mg/£ stock s o l u t i o n of the heavy metal are l i s t e d i n TABLE 2.1. 7 TABLE 2.1 SYNTHETIC WASTEWATERS HEAVY METAL MATERIALS USED TO MAKE 1000 mg/Jl STOCK SOLUTION SOLUTE SOLVENT Cu Copper Oxide D i l u t e N i t r i c A c i d Zn Zi n c Oxide I I I I I I Pb Lead Metal I I I I I I Hg Mercuric C h l o r i d e D i s t i l l e d Water The m a t e r i a l s used are the same as the ones used i n Atomic Absorption stock s o l u t i o n s . The prepared 1000 mg/i stock s o l u t i o n was then used to make up d i l u t i o n s of a d e s i r e d concentration. When the prepared waste s o l u t i o n was found to be too a c i d i c , the pH was adjusted as r e q u i r e d by a d d i t i o n of NaOH. P r e l i m i n a r y t e s t s showed that NaOH does not i n t e r f e r e w i t h the adsorption process. Chapter 3 BATCH TESTS 3.1 I n t r o d u c t i o n Emphasis was l a i d on i n i t i a l concentrations of 2 mg/£ and l e s s . Throughout the batch t e s t s , a l l f i v e c oals were t e s t e d w i t h 2 mg/& i n i t i a l c oncentrations of copper, lead and z i n c , w i t h the best two coals being f u r t h e r subjected to t e s t s w i t h i n i t i a l concentrations of 1 mg/£ and 0.5 mg/£, as w e l l as w i t h some higher concentrations. Copper t e s t s were the exception where a l l f i v e coals were subjected to t e s t s w i t h higher concentrations. Mercury t e s t s were done i n very low concentrations of 15 - 50 'Hg/£ f o r most of the batch t e s t s . An optimum p r a c t i c a l contact time was i n v e s t i g a t e d f o r two reasons: to save time, and to minimize p a r t i c l e break-up of the c o a l which i s favoured w i t h long periods of shaking. I t was suspected that the pH would play an important r o l e i n the adsorption process. The e f f e c t s of pH on the adsorptive c a p a c i t y of c o a l were i n v e s t i g a t e d w i t h z i n c , copper and lead s o l u t i o n s . From the batch t e s t s data, a p l o t of capacity (mg adsorbed/ g of coal) versus e q u i l i b r i u m c o n c e n t r a t i o n (mg/£) can be drawn. Such data d i s p l a y i s c a l l e d an "ADSORPTION ISOTHERM", which i s simply a f u n c t i o n a l expression f o r the v a r i a t i o n of adsorption w i t h c o n c e n t r a t i o n of adsorbate i n bulk s o l u t i o n at constant temperature. Commonly, the amount of adsorbed m a t e r i a l per u n i t weight of adsorbent increases w i t h i n c r e a s i n g c o n c e n t r a t i o n , but not i n d i r e c t p r o p o r t i o n . The major p o r t i o n of the batch t e s t s i n v o l v e d determing the adsor p t i o n isotherms f o r the four heavy metals under study, ( i . e . , Zn, Cu, Pb and Hg) under various c o n d i t i o n s of pH, i n i t i a l c o n c e n t r a t i o n , type of 8 9 adsorbent and other parameters. 3.2 Batch Testing Procedure A) For Copper, Lead and Zinc 1. The r e q u i r e d amount of c o a l was placed i n a 250 ml Erlenmeyer f l a s k . 2. One hundred m i l l i l i t r e s of the s y n t h e t i c wastewater of known conce n t r a t i o n was added to the f l a s k . 3. The f l a s k was c l o s e d w i t h a rubber stopper and shaken w i t h a w r i s t - a c t i o n shaker f o r the r e q u i r e d contact time. Shaking i n t e n s i t y was such that the wastewater was w e l l a g i t a t e d but not severe enough to move the c o a l around and break the p a r t i c l e s . 4. The c o a l was f i l t e r e d o f f and the c l e a r f i l t r a t e was analysed by Atomic Adsorption Spectroscopy f o r the e q u i l i b r i u m c o n c e n t r a t i o n of metal i o n s . The a n a l y s i s f o r copper, l e a d and z i n c was i n accordance w i t h "Water A n a l y s i s by Atomic Adsorption - V a r i a n Techtron". B) For Mercury The procedure i s the same as f o r copper, z i n c and lea d described p r e v i o u s l y up to the point when the shaking i s completed. The solvent t e s t i n g i s accomplished as f o l l o w s : - a) Instead of f i l t e r i n g , 50 m£ of wastewater i s simply decanted i n t o a t e s t tube. Decanting i s done i n s t e a d of f i l t r a t i o n to avoid any mercury being adsorbed by the f i l t e r paper. b) The decanted s o l u t i o n i s placed i n a c o o l e r f o r about 1 hour. 10 c) 0.5 ml of concentrated ^SO^ * s then added to the sample to allow overnight storage of the sample without v o l a t i l i z a t i o n of mercury. d) Before t e s t i n g on the atomic absorption spectrophotometer, 0. 5 ml of 6 percent potassium permanganate i s added. The t e s t tube i s then shaken and allowed to s i t f o r about 20 minutes. e) Three m i l l i l i t r e s of sample i s t r a n s f e r r e d to a t e s t i n g f l a s k and d i l u t e d up to 100 ml. f) 0.5 m i l of 10 percent hydroxylamine h y d r o c h l o r i d e i s added. g) Two m i l l i l i t r e s of 10 percent SnCJ^ 1 S added j u s t before a n a l y s i s by the c o l d vapour technique according to "Water A n a l y s i s by Atomic Absorption - Varian Techtron". The above procedure gives r i s e to a d e t e c t i o n l i m i t of .05 yg/£ of mercury. Confidence decreases w i t h l e v e l s below .05. vg/l due to background i n t e r f e r e n c e . 3.3 Determination of Optimum Contact Time Batch t e s t s were done on H.C. OX and H.C. UN to determine the e q u i l i b r i u m c o n c e n t r a t i o n at various contact times. The pH of the s o l u t i o n was. 2.0 and the r e s u l t s are shown i n Figure 3.1(a). The same k i n d of t e s t s were done w i t h the Cominco coals at a pHof5.2. The data obtained f o r t h i s s e r i e s of t e s t s are shown i n Figure 3.1(b). From the r e s u l t s , the f o l l o w i n g conclusions can be made:- 1. Contact time of 60 mins. w i l l achieve n e a r l y a l l of the u l t i m a t e removal ( i . e . , 93 percent and greater of the u l t i m a t e removal). 2. A c i d or n e u t r a l c o nditions do not i n f l u e n c e the optimum contact 11 FIG. 3.1 (a) CONTACT TIME - EQUILIBRIUM CONCENTRATION FOR COPPER 12 FIG. 3.1 (b) CONTACT T IME - EQUILIBRIUM CONCENTRATION FOR COPPER Contact Time - minutes 13 FIG. 3.1 (c) CONTACT TIME - EQUILIBRIUM CONCENTRATION FOR COPPER Contact time - minutes 14 time. The e q u i l i b r i u m contact time curve l e v e l s out by the end of 60 mins. The Cominco coals were next batch t e s t e d w i t h copper at an i n i t i a l c o n c entration of 10 mg/1 i n s t e a d of 50 mg/Jl. The weight of c o a l was a l s o p r o p o r t i o n a t e l y decreased f i v e times from 20 gm to 4 gm (Figure 3.1(c)). The r e s u l t s i n d i c a t e that an optimum contact time of 60 minutes s t i l l holds at d i f f e r e n t concentrations and c o a l weights. This f a c t i s f u r t h e r supported by r e s u l t s i n Figure 3.2, where an optimum contact time of 1 hour i s s t i l l v a l i d at d i f f e r e n t combinations of c o a l weight and i n i t i a l c o n centration. Extending the contact time to 3 or 4 hours c o n t r i b u t e s very l i t t l e to f u r t h e r removal and may even enhance p a r t i c l e break-up and consequent s i z e reduction of the 28/48 c o a l . 3.4 E f f e c t s of pH on Adsorptive Capacity of Coal Several batch t e s t s were performed to i n v e s t i g a t e the e f f e c t of pH on the adsorption process. Since H.C. OX had so f a r d i s p l a y e d a greater a d s o r p t i v e c a p a c i t y than the other c o a l s , i t was used f o r t h i s set of batch t e s t s . The concen- t r a t i o n of waste was i n i t i a l l y 2 mg/il, the weight of c o a l was 1 gm and the contact time was 1 hour. Tests were performed at pH values of 1.5, 2.5, 4.0 and 5.8 f o r s o l u t i o n s c o n t a i n i n g each of copper, lea d and z i n c . The r e s u l t s are shown i n t a b u l a r form i n Table 3.1. There i s a d e f i n i t e r e l a t i o n s h i p between pH and adsorptive c a p a c i t y . At pH of 1.5 the cap a c i t y was n i l f o r a l l three metals at these low concentrations. With the increase of pH there i s a corresponding r i s e i n c a p a c i t y , i n the case of l e a d , the c o a l had adsorbed the metal to w e l l below the d e t e c t i o n l i m i t at a pH of 5.5. 15 TABLE 3.1 EFFECTS OF pH ON THE ADSORPTIVE CAPACITY OF COAL I n i t i a l c oncentration = 2.0 mg/I Coal = H.C. OX Coal Weight = 1 gm Metal pH E q u i l i b r i u m c oncentration a f t e r 1 hour (mg/A) mg Adsorbed / gm c o a l Cu 1.5 2.00 0.000 2.5 1.20 0.080 4.0 0.30 0.170 5.6 0.25 0.175 Zn 1.5 . 2.00 0.000 2.5 1.62 0.038 4.0 0.43 0.157 6.2 0.30 0.170 Pb 1.5 2.00 0.000 2.5 0.80 0.120 4.0 0.00 0.200 5.5 0.00 0.200 16 Fol l o w i n g the trend of the r e s u l t s , the c a p a c i t y should even be greater at a pH of 7 but, s i n c e the emphasis was on a c i d i c wastes, no t e s t s were done at higher pH values. I t can be seen that the r a t e of change i n adsorptive c a p a c i t y per u n i t change i n pH i s d i f f e r e n t f o r each metal. 3.5 E f f e c t s of I n i t i a l Concentration Change & Coal Weight Change on Percent Removal Table 3.2 shows the e f f e c t of changing c o a l weight and i n i t i a l c o n c e n t r a t i o n i n the same p r o p o r t i o n on the percent removal achieved. With 20 gm of c o a l and 50 mg/Ji^Cu, 91 percent removal i s achieved. By reducing both parameters to h a l f (10 gm of c o a l and 25 mg/£ Cu) 87 percent removal i s achieved and when the parameters are d i v i d e d by 5 to 4 gm of c o a l and 10 mg/£ Cu, 92 percent removal i s seen. Taking the noise and other inherent e r r o r s i n t o c o n s i d e r a t i o n , i t can be concluded that when c o a l weight and i n i t i a l c o n c entration are both changed i n the same p r o p o r t i o n , the percent removal stays about the same. The percent removals were c a l c u l a t e d from values at contact time of 60 minutes. Figure 3.2 shows the r e s u l t s of v a r y i n g one parameter by f i v e times while keeping the other parameter f i x e d . The f o l l o w i n g p o i n t s summarize the data:- 1. S t a r t i n g o f f w i t h 1 gm of Cominco Ash c o a l and 50 mg/Jl Cu r e s u l t e d i n 19 percent removal at 1 hour contact time; 2. In c r e a s i n g the amount of c o a l 5 times and using the same 50 mg/£ Cu s o l u t i o n r e s u l t e d i n 47 percent removal at 1 hour; 3. With a copper c o n c e n t r a t i o n of 10 mg/£ and the same c o a l weight, 73 percent removal was obtained i n 1 hour - an increase i n percent removal over that of case (1) by 54 percent. This i s about double FIG. 3.2 1 7 E F F E C T S ON PERCENT REMOVAL WHEN CHANGING \ ONE P A R A M E T E R WHILE KEEPING THE OTHER \ FIXED Igm COAL 19 % Removal 5 9™ COAL 4 7 % Removal pH = 5.2 CoaI = Cominco Ash Waste Element = Cu gm COAL 73%^Removal 30 45 6CK 120 Contact time - minutes 180 210 18 TABLE 3.2 EFFECT OF CHANGING COAL WEIGHT & INITIAL CONCENTRATION IN THE SAME PROPORTION ON THE PERCENT REMOVAL Coal = Cominco Ash Waste pH = 5.2 Coal Weight (gm) I n i t i a l Concentration Gag/A Cu) E q u i l i b r i u m Concentration @ 1 hr (mg/Jl Cu) Percent Removal of Cu 20 50 4.5 91 10 25 3.3 87 4 10 0.8 92 the increase achieved by i n c r e a s i n g the c o a l weight 5 times. This increase i n percent removal when the waste c o n c e n t r a t i o n i s lowered promises a good p o l i s h i n g job by c o a l treatment at low concentrations. A p o s s i b l e e x p l a n a t i o n f o r t h i s increase i n percent removal on d i l u t i o n could be the very s l i g h t i n c r e a s e i n pH on d i l u t i o n . At 50 mg/£ the pH was 5.2 and at 10 mg/£ the pH was approximately 5.3. Another p o s s i b l e e x p l a n a t i o n could be the change i n the c o n t r o l l i n g or l i m i t i n g phase of the r e a c t i o n . At high s o l u t e c o n c e n t r a t i o n s , the a v a i l a b l e exchange s i t e s might be l i m i t i n g ; w h i l e at lower s o l u t e c o n c e n t r a t i o n s , the boundary l a y e r c o n c e n t r a t i o n gradient might be l i m i t i n g . 19 3.6 Adsorption Isotherms f o r Copper 1. Figure 3.3(a) shows adsorption isotherms f o r copper w i t h a l l f i v e types of c o a l s . The i n i t i a l concentrations of copper i s 2 mg/Z and the c o a l weight i s changed from 1.0 to 10.0 gm to give the data p o i n t s on the isotherm. A l l f i v e coals brought the c o n c e n t r a t i o n down to 0.3 mg/£ and l e s s . The best performance i s d i s p l a y e d by C0:0X and CO:ASH where the e q u i l i b r i u m c o n c e n t r a t i o n i s brought down to 0.05 mg/Z. For a quick comparison w i t h a c t i - vated carbon, some Darco A c t i v a t e d Carbon (Grade 12 x 20) was a l s o t e s t e d . The r e s u l t i n g adsorption isotherm f o r a c t i v a t e d carbon shows the copper concentra- t i o n being brought down to undetectable l e v e l s . Taking instrument noise i n t o account, i t could be i n t e r p r e t e d that there i s p r a c t i c a l l y no d i f f e r e n c e between the batch removal e f f i c i e n c y of a c t i v a t e d carbon and C0:ASH or C0:0XIDISED at low i n i t i a l concentrations of copper. 2. Figure 3.3(b) shows isotherm data f o r C0:ASH and H.C.OX coals w i t h i n i t i a l concentrations of 1.0 mg/£. and 0.5 mg/£ of copper. The c o a l weight was v a r i e d from 0.5 gm to 3.0 gm to give the p o i n t s on the isotherm. The data shows that CO:ASH reduces the concentration to .01 mg/Z when t r e a t i n g a s o l u t i o n of 1.0 mg/Z, and to undetectable l e v e l s when t r e a t i n g a s o l u t i o n c o n t a i n i n g 0.5 mg/Z. I t i s f u r t h e r evident th/at CO:ASH provides higher removal e f f i c i e n c i e s at these low s o l u t e concentrations than does H.C. OX. 3. Figure 3.3(c) shows copper isotherms f o r a l l f i v e c o a l s , using c o a l weights of 0.5 gm and i n i t i a l s o l u t e c o n c e n t r a t i o n ranging from 2 mg/Z to 300 mg/Z of copper. At higher c o n c e n t r a t i o n s , both of the Hat Creek coals have a greater c a p a c i t y than any of the Cominco c o a l s . The H.C. OX reaches a c a p a c i t y of 6.0 mg Cu/gm c o a l at an e q u i l i b r i u m c o n c e n t r a t i o n of about 170 mg/Z Cu. CO:ASH and C0:0X seem to behave i d e n t i c a l l y w i t h regard to copper i n both high 20 FIG. 3.3 (a) COPPER ADSORPTION ISOTHERMS pH = 5.3 In it ia l concentration = 2mg/ l i t re X X H.C . Oxidized A A H.C . Unoxidized • — • Co; Production o—o Co: Ash • — • Co = Oxidized • — • Act vated Carbon I—I—I I I I I I I I 0.05 0.1 0.2 0.4 0.6 0.8 Equilibrium concentrat ion - mg / litre Cu INITIAL CONCENTRATION 0 I 1 1 1 1 1 I I I I I I I i i 0 O.OI 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Equilibrium concentration mg/litre Cu FIG. 3.3(c) COPPER ADSORPTION ISOTHERMS. 22 pH = 5.0 — 5.4 Coal weight = 0.5g Equilibrium concentration mg/litre Cu  24 and low e q u i l i b r i u m concentrations. 4. Figure 3.3(d) shows adsorption isotherms f o r H.C. OX and CO:ASH while the CO:ASHhas. a greater capacity at copper concentrations of 2 mg/£ and l e s s . (Note the i n t e r s e c t i o n of two isotherms at about 0.5 mg/ii, e q u i l i b r i u m c o n c e n t r a t i o n ) . Considering the copper isotherm r e s u l t s and a few other p r a c t i c a l f a c t o r s , C0:ASH and H.C. OX were chosen f o r t e s t s w i t h i n i t i a l concentrations of 1.0 mg/Jo and 0.5 mg/£ w h i l e v a r y i n g the c o a l weight and a l s o f o r t e s t s w i t h a f i x e d c o a l weight of 1 gm w h i l e v a r y i n g the i n i t i a l concentrations from 2 mg/Z - 50 mg/£. This procedure i s a p p l i e d i n z i n c and l e a d t e s t s a l s o . 3.7 Adsorption Isotherms f o r Lead 1. A l l f i v e coals were t e s t e d using a s o l u t e concentration of 2 mg/Ji of l e a d , w h i l e the c o a l weight was v a r i e d from 1.0 to 4.0 gm. The pH was 5.2. A l l f i v e coals reduced the s o l u t e c o n c e n t r a t i o n to undetectable l e v e l s i n a l l the t e s t s performed. This "super" performance may be e x p l a i n a b l e by e i t h e r a very high a f f i n i t y of the coals f o r l e a d , or the r e l a t i v e l y high d e t e c t i o n l i m i t f o r l e a d . The d e t e c t i o n l i m i t s f o r the elements of concern are shown below. coals using c o a l weights of 1.0 gm and i n i t i a l copper concentrations ranging from 2 mg/I to 50 mg/£. H.C. OX performs b e t t e r at higher concentrations Element Detection L i m i t by Atomic Absorption Hg .05 yg/£ f o r a 3 mil sample ( c o l d vapour technique) Zn 0.01 mg/£ (flame technique) Cu 0.04 mg/£ (flame technique) Pb 0.10 mg/£ (flame technique)  26 2. Figure 3.4 shows the adsorption isotherms of a l l f i v e coals using an adsorbent weight of 1.0 gm and i n i t i a l lead concentrations ranging from 2mg/£ tb.50mg/£. Hat Creek coals perform b e t t e r than Cominco coals at higher concentrations. H.C. OX performed the best and achieved a capacity of 5 mg adsorbed/gm of c o a l at an e q u i l i b r i u m concentration of 1.2 mg/i. 3.8 Adsorption Isotherms f o r Zinc 1. Figure 3.5(a) shows the adsorption isotherms f o r a l l f i v e coals using an i n i t i a l c oncentration of 2 mg/i Zn w i t h adsorbent weights being v a r i e d from 0.5 gm to 4.0 gm. The Hat Creek coals were found to be b e t t e r performers i n t h i s concentration range,, w i t h the H.C. OX reducing the z i n c concentration to 0.12 mg/£ (using 4 gm of c o a l ) . The Hat Creek coals have isotherms w i t h p r a c t i c a l l y no s c a t t e r whatsoever. This could mean that the Hat Creek coals have adsorption p r o p e r t i e s more homogeneously d i s t r i b u t e d throughout the c o a l mass than the Cominco c o a l s . 2. Figure 3.5(b) shows the isotherms f o r H.C. OX and C0:ASH coals w i t h i n i t i a l s o l u t e concentrations of 1.0 mg/£ Zn and 0.5 mg/£ Zn. The c o a l weight was v a r i e d from 0.5 gm to 3.0 gm. The H.C. OX shows a g r e a t e r capa- c i t y than C0:ASH at a l l e q u i l i b r i u m concentrations t e s t e d . With an i n i t i a l c o ncentration of 0.5 mg/£, the H.C. OX reduced the concentration to 0.02 mg/£. With an i n i t i a l z i n c concentration of 0.5 mg/ft, the isotherms f o r the two coals came c l o s e r to each other, i n d i c a t i n g a smaller d i f f e r e n c e i n c a p a c i t y w i t h i n t h i s range of e q u i l i b r i u m concentrations. 3. Isotherms f o r H.C. OX and C0:ASH w i t h i n i t i a l z i n c concentra- t i o n s ranging from 2\mg/£ to 50 mg/£ are shown i n Figure 3.5(c). The c o a l weight was f i x e d at 1.0 gm. H.C. OX performs b e t t e r , showing a capacity of 2.13 mg adsorbed/gm c o a l at an e q u i l i b r i u m s o l u t e c o n c e n t r a t i o n of 28.7 mg/£. ,1 1 1 I I I I I I I I I I I 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 E q u i l i b r i u m c o n c e n t r a t i o n m g / l i t r e Zn FIG. 3.5(b) Z I N C ADSORPTION ISOTHERMS 28 pH = 6.0 Initial concentration = I mg/litre Zn and 0.5mg/litre Zn 0 0.03 0.05 0.10 0.15 0.20 0.25 0.30 Equilibrium concentration mg/litre Zn  30. 3.9 Adsorption Isotherms f o r Mercury 1. I n Figure 3.6(a) r e s u l t s are shown from a s e r i e s of t e s t s using i n i t i a l s o l u t e concentrations of 50 yg/£ Hg, w i t h c o a l weights v a r y i n g from 1 gm to 4 gm. The isotherms show that the Hat Creek coals have higher adsorptive c a p a c i t i e s than do the Cominco c o a l s . The two Cominco coals have very s i m i l a r isotherms, i n d i c a t i n g very s i m i l a r adsorptive p r o p e r t i e s . 2. Figure 3.6(b) shows i s o t h e r m ' r e s u l t s f o r H.C. OX and C0:ASH with i n i t i a l mercury concentrations of 15 yg/ft and 30 yg/£. The c o a l weight was v a r i e d from 0.5 gm to 3.0 gm. H.C. OX d i s p l a y s a greater c a p a c i t y than CO:ASH at a l l e q u i l i b r i u m concentrations t e s t e d . With an i n i t i a l concentra- t i o n of 15 yg/£, H.C. OX produced an e f f l u e n t c o n t a i n i n g 3 yg/£, i n d i c a t i n g good percent removal even at t h i s low i n i t i a l c o n c e n t r a t i o n . 3. The isotherms f o r H.C. OX and CO:ASH w i t h i n i t i a l concentra- t i o n s ranging from 100 yg/£ to 2000 yg/£ ( i . e . , from .1 mg/£ to 2.0 mg/£) are shown i n Figure 3.6(c). The c o a l weight used was 1.0 gm. The slope of the H.C. OX isotherm i s very much steeper than that of the CO:ASH isotherm i n d i - c a t i n g a s i g n i f i c a n t c apacity advantage using H.C. OX. I t reached a c a p a c i t y of 0.18 mg adsorbed/gm c o a l at an e q u i l i b r i u m mercury concentration of 0.21 mg/£. 3.10 Batch Tests - Summary and Conclusions 1. The optimum contact time f o r batch t e s t s to achieve a high percentage of u l t i m a t e e q u i l i b r i u m concentration w i t h i n a short p r a c t i c a l p e r i o d of time was found to be 1 hour. 2. The adsorptive capacity of c o a l f o r copper, l e a d and z i n c was found to increase as the pH was r a i s e d from 1.5 to 6.2. The r a t e of change i n a dsorptive capacity per u n i t change i n pH i s d i f f e r e n t f o r each metal. F I G . 3.6(a) MERCURY ADSORPTION ISOTHERMS pH = 5.8 Initial concentration = 50ug/l (0.050mg/litre) Equilibrium concentration mg/litre Hg FIG. 3.6 (b) MERCURY ADSORPTION ISOTHERMS pH = 5.8 Initial concentration = 15 ug/l and 30 ug/l of Hg 0 I I I I I I 0 0.005 0.010 0.015 0.020 Equilibrium concentration mg/litre Hg pH = 5.4 — 5.8 Coal weight = 1 g Initial concentrations = IOOug/1 — 2,OOOug/l m 3J 34 3. When c o a l weight and i n i t i a l metal concentration are both changed i n the same p r o p o r t i o n , the percent removal stays about the same. 4. D i l u t i n g the waste r e s u l t e d i n a s i g n i f i c a n t l y greater i n crease i n percent removal than would be obtained when the c o a l weight i s increased i n s t e a d by the same p r o p o r t i o n . 5. (a) Of the two Hat Creek coals, H.C. OX was the b e t t e r per- former w i t h copper, z i n c and mercury as the adsorbate. In the case of l e a d , H.C. OX has a greater capacity w i t h i n the 2 mgl I - 50 mg/H e q u i l i b r i u m con- c e n t r a t i o n range. No d i f f e r e n t i a t i o n could be made when the e q u i l i b r i u m con- c e n t r a t i o n was below 2 mg/H Pb. Among the Cominco c o a l s , C0:0X and CO:ASH dis p l a y e d the same isotherm w i t h 2 mg/i Cu i n i t i a l c o n centration. In almost a l l of the remaining experiments w i t h l e a d , z i n c and mercury, CO:OX appeared to be only m a r g i n a l l y b e t t e r than CO:ASH. On the b a s i s of these r e s u l t s , H.C. OX and CO:ASH were chosen as the best of each c o a l type f o r the column t e s t phase of the p r o j e c t . CO:ASH was chosen because i t performed almost as w e l l as C0:0X, and i t has a b e t t e r production p o t e n t i a l because of i t s greater a v a i l a b i l i t y . (b) Table 3.3 shows the comparison of H.C. OX and CO:ASH wi t h regard to t h e i r adsorptive c a p a c i t i e s . Table 3.3 i n d i c a t e s adsorptive s u p e r i o r i t y : of H.C. OX w i t h l e a d , z i n c and mercury. In the case of copper, H.C. OX has a greater adsorptive capacity i n the higher i n i t i a l c o n centration range (2.0 mg/Jl - 50 mg/1), w h i l e i n the lower i n i t i a l c oncentration range of 2.0 mg/i and l e s s the s i t u a t i o n i s reversed and CO:ASH proved to be the sup e r i o r one. (c) Table 3.4 shows a comparison of performance of a p a r t i - c u l a r c o a l w i t h each of the four heavy metals. Within the e q u i l i b r i u m concen- 35 t r a t i o n range of .03 mg/Z to 30.0 mg/£, l e a d has the greatest a f f i n i t y f o r adsorption by both c o a l s . Copper proved to have the second highest a f f i n i t y , z i n c t h i r d and mercury l a s t w i t h regard to adsorption by both c o a l s . TABLE 3.3 COMPARISON OF H.C. OX AND CO:ASH Note: The c o a l w i t h a b e t t e r adsorption performance i s p r i n t e d i n the re l e v a n t s l o t . Element I n i t i a l Concentrations of Wastewater 0.5 mg/£ 1.0 mg/£ 2.0 mg/£ 2.0 mg/£ - 50 mg/£ Cu CO:ASH CO:ASH CO:ASH H.C. OX Pb UNDIFFERENTIABLE -* -»- H.C. OX Zn H.C. OX H.C. OX H.C. OX H.C. OX 15 ug/£ 30 yg/£ 50 yg/£ 100 yg/£ - (.1 mg/£ - • 2000 yg/£ 2.0 mg/£) Hg H.C. OX H.C. OX H.C. OX H.C. OX 36 TABLE 3.4 Comparison of the C a p a c i t i e s of Two Coals For Each of the Four Heavy Metals E q u i l i b r i u m Capacity (mg adsorbed/gm coal) Coal Concentration (mg/Jl) Pb Cu Hg Zn .05 BDL* ,.015 .035 .080 .10 >.10 .10 .07 .25 .50 3.20 .50 .35 .37 H.C. OX l.O 4.80 .90 .55 5.0 >5.0 2.50 .98 10.0 >5.0 3.00 1.27 30.0 >5.0 4.80 2.17 .03 BDL* .18 .003 .03 .10 > .20 .20 .008 .032 .50 1.50 .43 .035 .08 CO:ASH 1.0 1.68 .50 .065 .155 5.0 1.98 .95 .20 10.0 2.30 1.28 .25 30.0 3.10 1.38 .45 NOTE: 1. * BDL means the e q u i l i b r i u m concentration i s below d e t e c t i o n l i m i t and consequently the capacity cannot be determined. 2. Several blanks are shown i n the Hg column due to the f a c t that Hg was not te s t e d at these higher c o n c e n t r a t i o n s . Chapter 4 COLUMN TESTS 37 4.1 I n t r o d u c t i o n Based on the r e s u l t s of the batch t e s t s , H.C. OX'from the Hat Creek group and CO:ASH from the Cominco group of coals were chosen f o r f u r t h e r i n v e s t i g a t o r y work w i t h continuous flow, fixed-bed columns. On the b a s i s of the data from the batch t e s t s and from a few pre- l i m i n a r y column t e s t s at various values of the i n f l u e n t pH, the maximum adsorptive capacity of a p a r t i c u l a r column was suspected to occur at an i n f l u e n t pH near n e u t r a l i t y (6 to 7?5). I n i t i a l r e s u l t s i n d i c a t e d that at such a n e u t r a l pH, and under the l a b o r a t o r y c o n d i t i o n s used i n t h i s r e s e a r c h , i t would take more than ten or eleven days f o r any s i g h of metal breakthrough to occur. To overcome t h i s i m p r a c t i c a l i t y w i t h regard to the time f a c t o r , the pH was reduced to 4.0, which gave r i s e to a breakthrough w i t h i n a reasonable p e r i o d of time;-- Then an e x t r a p o l a t i o n f a c t o r , d erived from previous column t e s t data.was employed to give an estimate of the adsorptive capacity at an i n f l u e n t pH of 6.0 «W.5. J. The i n f l u e n t metal concentrations were at 2 mg/£ and l e s s f o r z i n c , copper and l e a d , and l e s s than 5 yg/£ f o r mercury. These f i g u r e s are i n the neighbourhood of permissable l e v e l s , set up by the P o l l u t i o n C o n t r o l Board of B r i t i s h Columbia, f o r discharge of these metals i n t o v a r i o u s types of r e c e i v i n g waters. The flow rates t e s t e d were between one and f i v e Igpm/ft 2. These flow rates are r e p r e s e n t a t i v e of the ones used i n r a p i d sand f i l t r a t i o n and a c t i v a t e d carbon adsorption systems. The c o a l depth was maintained at ten inches f o r the f o l l o w i n g reasons: 1) to ensure that the depth i s greater than the c r i t i c a l bed depth to prevent p e n e t r a t i o n of conc e n t r a t i o n i n excess of breakthrough c o n c e n t r a t i o n at zero time; 38 2) to s a t i s f y p r a c t i c a l c o n s i d e r a t i o n s that the breakthrough does not take too long a p e r i o d of time. E x c e s s i v e l y deep beds of c o a l w i l l r e s u l t i n long periods of time f o r breakthroughs to occur. The depth of the c o a l bed i s an important c r i t e r i o n whenever comparative work i s done, s i n c e the contact time i s p r i m a r i l y dependent on the bed depth f o r a given flow r a t e . Table 4.1 shows the corresponding contact times f o r the flow r a t e s l i s t e d , based on an empty column and a c o a l - f i l l e d column of 10 inches. TABLE 4.1 CONTACT TIMES FOR A 10-INCH COLUMN AT GIVEN FLOW RATES FLOW RATE CONTACT TIME (Min) Igpm/ft 2 inches/min Empty Column C o a l - f i l l e d Column 1 1.92 5.21 2.86 5 9.60 1.04 0.58 For the c a l c u l a t i o n of the a c t u a l contact time f o r a c o a l - f i l l e d column, the p o r o s i t y of the c o a l column i s necessary. From the l i t e r a t u r e on bed p o r o s i t y , packing, e t c . (11, pp.537), a graph, r e l a t i n g s p h e r i c i t y , type of packing and p o r o s i t y , was used to estimate the p o r o s i t y . With an assumed s p h e r i c i t y of the p a r t i c l e s of 0.6 and a normal type of packing, the r e s u l t a n t p o r o s i t y was estimated at 0.55. 39 Example C a l c u l a t i o n f o r A c t u a l C o n t a c t Time 1 I g p m / f t 2 = 1.92 i n / m i n Based on an empty column of 10 i n c h e s c o n t a c t time = 10 i n X 1 1.92 i n / m i n = 5.21 min U s i n g the p o r o s i t y f a c t o r o f 0.55, the a c t u a l c o n t a c t time of c o a l - f i l l e d column of 10 i n c h e s = 5.21 min X 0.55 = 2.86 min The major p o r t i o n o f the column work ( i . e . , i n v e s t i g a t i n g the e f f e c t s of pH, flow r a t e , e t c . ) was done w i t h z i n c as the a d s o r b a t e . Z i n c was chosen because i t i s more s e n s i t i v e on the 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 e r than copper or l e a d . The g e n e r a l o b j e c t i v e of the column t e s t s was to o b t a i n some f i g u r e s f o r the c a p a c i t i e s of the two c o a l s t e s t e d f o r z i n c , copper and l e a d a t i n f l u e n t pH v a l u e s of 4.0 and 5.7. T e s t s f o r mercury were run w i t h i n f l u e n t s i n the 5 yg/£ range, w i t h an e f f l u e n t pH of 7.5. 4.2 Column T e s t i n g Apparatus From p r e l i m i n a r y column t e s t s , i t was apparent t h a t b r e a k t h r o u g h would, g e n e r a l l y , not o c c u r b e f o r e 24 hours had e l a p s e d . T h i s n e c e s s i t a t e d a h o l d i n g tank o f adequate s i z e f o r the i n f l u e n t i n o r d e r t h a t the tank c o u l d be f i l l e d once i n every 24 hours o r so f o r p r a c t i c a l c o n v e n i e n c e . F i g u r e 4.1(a) and F i g u r e 4.1(b) a r e s c h e m a t i c diagrams of the apparatus used. As t h e l i q u i d p a sses through the c o a l column and out through the b u r e t t e , the l i q u i d l e v e l 40 To B T o C FIG. 4.1 (b) DOUBLE TANK FEED MODIFICATION G l a s s wool Glass beads FIG. 4.1 (a) CONSTANT HYDRAULIC HEAD APPARATUS A INFLUENT HOLDING TANK B SEPARATORY F U N N E L C E R L E N M E Y E R F L A S K D B U R E T T E 41 i n C w i l l f a l l . J u s t as the l e v e l f a l l s below that of the opening of the tubing connected to B, a i r w i l l enter through the hole i n the stopper of C, as shown, and up through the tubing i n t o B. This w i l l reduce the p a r t i a l vacuum i n A and B and more l i q u i d w i l l f a l l i n t o C u n t i l the p a r t i a l vacuum i n A and B above the l i q u i d l e v e l s i s i n e q u i l i b r i u m w i t h the h y d r a u l i c heads supported i n A and B. Thus, we have a constant head of AH as shown i n Figure 4.1(a) to d r i v e the l i q u i d through the c o a l column. For the flow r a t e to remain constant a f t e r being s e t , i t i s e s s e n t i a l that the h y d r a u l i c d r i v i n g head remains constant. The element B (separatory funnel) can be simply replaced by a s t r a i g h t tubing. Using a separatory funnel provides the system w i t h a d d i t i o n a l i n f l u e n t storage volume. Figure 4.1(b) shows the modified set-up that was used when running t e s t s at 5 Igpm/ft 2 where a l a r g e r i n f l u e n t storage volume was necessary. Here, there are two tanks, i n s t e a d of one, connected to the r e s t of the apparatus according to the same p r i n c i p l e s . 4.3 Column T e s t i n g Procedure A) Copper, Lead and Z i n c The l a b o r a t o r y procedure c o n s i s t s of the f o l l o w i n g steps:- 1) The i n f l u e n t s o l u t i o n of a d e s i r e d metal c o n c e n t r a t i o n i s prepared and i t s pH adjusted to the d e s i r e d value. 2) Enough c o a l to f i l l 10 inches of the b u r e t t e i s weighed out i n a beaker. 3) D i s t i l l e d water i s added so that the c o a l i n the beaker i s completely submerged. The contents are then subjected to a slow b o i l ' f o r . about - f i v e minutes i n order to expel..; a l l the entrapped a i r and to 42 thoroughly wet the c o a l . 4) The wetted c o a l i s then t r a n s f e r r e d i n t o the b u r e t t e , which i s packed at the bottom w i t h g l a s s wool and glass beads. During t h i s t r a n s f e r , the c o a l i n the b u r e t t e i s c a r e f u l l y kept submerged to prevent any re-entrapment of a i r . 5) The i n f l u e n t s o l u t i o n i s introduced i n t o the c o a l column, and the b u r e t t e v a l v e i s adjusted to achieve the d e s i r e d flow r a t e . 6) The e f f l u e n t i s sampled at d e s i r e d i n t e r v a l s . 7) The pH of the e f f l u e n t samples i s measured. 8) The metal co n c e n t r a t i o n of the e f f l u e n t samples i s measured w i t h an Atomic Absorption Spectrophotometer as i n the Batch T e s t i n g Procedure. For most of the t e s t s , the system was kept running u n t i l the e f f l u e n t concentration exceeded a l e v e l of twenty to t h i r t y percent of the i n f l u e n t concentration. B) Mercury The procedure i s the same as f o r z i n c , copper and l e a d , but the e f f l u e n t samples are subjected to a pretreatment described below, before being t e s t e d on the Atomic Absorption Spectrophotometer. This pretreatment c o n s i s t s of the f o l l o w i n g steps :- 1) 100 ml of the e f f l u e n t i s c o l l e c t e d and cooled i n a r e f r i g e r a t o r f o r about 1 hour. Care must be taken that the container of the c o l l e c t e d e f f l u e n t has a p e r f e c t s e a l i n g cap that w i l l prevent any v o l a t i l i z a t i o n of the mercury. 2) 1 mJl of concentrated s u l f u r i c a c i d i s added to the cooled sample. This i s done to f i x the mercury i n the s o l u t i o n b e t t e r and thus to enable overnight storage. 43 3) About 20 minutes before t e s t i n g on the Atomic Absorption Spectrophotometer, 1 m£ of 6 percent potassium permanganate i s added. The container i s then shaken and allowed to s i t . 4) The t o t a l contents of the co n t a i n e r , 100 ml of e f f l u e n t and 2 ml of reagents,are t r a n s f e r r e d to a t e s t i n g f l a s k . 5) Then 0.5 ml of 10 percent NH^OH.HCl i s added. 6) F i n a l l y 2.0 ml of 10 percent S n C ^ i s added j u s t before a n a l y s i s on the Atomic Absorption Spectrophotometer by the c o l d vapour technique. The above procedure enabled accurate d e t e c t i o n down to a l i m i t of 0.05 pg/A. 4.4 Breakthrough Curve C a l c u l a t i o n s A t y p i c a l breakthrough curve i s shown i n Figure 4.2. An a r b i t r a r y breakthrough concentration of 0.5 mg/l was chosen. A h o r i z o n t a l l i n e i s drawn through t h i s 0.5 mg/'l mark to i n t e r s e c t the curve and a v e r t i c a l l i n e i s then drawn through t h i s i n t e r s e c t i o n . A f t e r having determined the m i l l i g r a m s of z i n c adsorbed and the m i l l i g r a m s of z i n c passed through, ( r e f e r to F i g u r e 4.2) the f o l l o w i n g two c a l c u l a t i o n s can be done. 1) mg of Zn adsorbed = mg of Zn adsorbed per gm of c o a l , gm of c o a l i n column 2) mg of Zn passed out through e f f l u e n t l i t r e s of tr e a t e d e f f l u e n t at breakthrough c o n c e n t r a t i o n = Average e f f l u e n t c o n c e n t r a t i o n i n mg/l 4.5 Breakthrough Curves f o r Z i n c The batch t e s t s showed that the adsorption isotherms f o r z i n c had the l e a s t s c a t t e r of the heavy metals t e s t e d . Due to t h i s f a c t and the f a c t that FIG.4.2 A TYPICAL BREAKTHROUGH CURVE 44 THIS AREA BELOW THE CURVE REPRESENTS THE WEIGHT OF ZINC IN MILLIGRAMS PASSED OUT THROUGH THE EFFLUENT 45 z i n c i s more s e n s i t i v e on the Atomic Absorption Spectrophotometer than le a d or copper, z i n c was chosen as the main impurity f o r column t e s t s to i n v e s t i g a t e the e f f e c t s of a b s o r p t i v e c a p a c i t y caused by:- a) V a r i a t i o n s i n c r o s s - s e c t i o n a l area of the c o a l bed. b) " i n i n f l u e n t pH. c) " i n flow r a t e . d) " i n i n f l u e n t metal co n c e n t r a t i o n . a) E f f e c t of Varying the C r o s s - S e c t i o n a l Area of the Coal Bed A f t e r a few t r i a l column t e s t s w i t h burettes of various diameters a v a i l a b l e i n the l a b o r a t o r y , the choice of the c r o s s - s e c t i o n a l area to be used was narrowed down between that of the 50 ml b u r e t t e (.001 f t 2 ) and that of the 100 ml b u r e t t e (.002 f t 2 ) . Using the smaller area of .001 f t 2 would mean a p r a c t i c a l convenience of having to use l e s s c o a l per column and l e s s t o t a l l i q u i d to reach breakthrough. On the other hand, care must be taken not to go below the c r i t i c a l diameter and encourage w a l l e f f e c t s , which w i l l reduce the adsorptive c a p a c i t y of the c o a l column. Figure 4.3 shows the breakthrough curves f o r the column t e s t s performed using bed areas of .001 f t 2 and .002 f t 2 . From TABLE 4.2, i t i s apparent that there i s only a s l i g h t decrease i n a dsorptive c a p a c i t y when the c r o s s - s e c t i o n a l area was changed from 0.002 f t 2 to 0.001 f t 2 . Therefore, i t was decided to use the 50 ml b u r e t t e w i t h a 0.001 f t 2 f o r the r e s t of the study. I t was suspected though, that w a l l e f f e c t s would be experienced i f a s m a l l e r diameter b u r e t t e than the 50 ml b u r e t t e were used. m Influent =2.0 mg/1 Zn Influent pH = 5.7 Flow rate = I l gpm/ft . 2 Bed depth = 10 inches Coa l = C O ' A S H BED C R O S S - S E C T I O N A L A R E A * * . 0 0 2 f t . 2 o - o . 0 0 1 f t . 2 COAL WEIGHT 3 8 gm 2 0 gm 12 14 16 18 2 0 V O L U M E OF LIQUID TREATED (L ITRES) 3 0 m O O "n o x > z: -z. o o ^3 O CO CO CO _' m a > m > o m o g CD m o ON 47 TABLE 4.2 EFFECT OF CHANGING CROSS-SECTIONAL AREA OF THE COAL BED C r o s s - s e c t i o n a l Area of Capacity (mg/gm) Average E f f l u e n t Coal Bed at Concentration (mg/ ) at ( f t ) 10% 25% 50% - 10% 25% : so% 0.001 0.378 0.503 0.624 .046 .133 .310 0.002 0.438 0.540 0.692 .042 .113 .308 Note- 10%, .25%, 50% r e f e r s to the breakthrough co n c e n t r a t i o n of 10% of the i n f l u e n t , 25% of the i n f l u e n t and 50% of the i n f l u e n t . This n o t a t i o n w i l l be used henceforth i n the TABLES. b) E f f e c t of Varying the I n f l u e n t pH Many other researchers have found that the pH of the i n f l u e n t plays a c r i t i c a l r o l e i n determining the adsorptive c a p a c i t y . The pH of a s o l u t i o n from which adsorption occurs may, f o r one or more of a number of reasons, i n f l u e n c e the extent of adsorption. Because hydrogen and hydroxide ions are adsorbed q u i t e s t r o n g l y , the adsorption of other ions i s i n f l u e n c e d by the pH (9) of the s o l u t i o n . Weber found t h a t , i n ge n e r a l , adsorption of t y p i c a l organic p o l l u t a n t s from water i s increased w i t h decreasing pH. In many cases, t h i s may r e s u l t from n e u t r a l i s a t i o n of negative charges at the surface of the carbon w i t h i n c r e a s i n g hydrogen-ion c o n c e n t r a t i o n , thereby reducing hindrance of d i f f u s i o n and making a v a i l a b l e more of the a c t i v e surface of the carbon. Figure 4.4 shows the breakthrough curves obtained at i n f l u e n t pH values of 3.0, 4.0 and 5.7 f o r both H.C. OX and C0:ASH c o a l s . There i s a d e f i n i t e decrease i n adsorptive c a p a c i t y w i t h decreasing pH i n both cases. TABLE 4.3 summarises the r e s u l t s of Figure 4.4 i n a t a b u l a r form. H.C. OX at a breakthrough of 10 percent shows a ca p a c i t y decrease of 84 percent when the TABLE 4.3 E F F E C T O N I l N G w A D S Q ^ R P t i O N J 3 F , " V A R ^ ' g i - T H E I N F L U E N T p H Breakthrough Cone, as Percent of I n f l u e n t Cone. I n f l u e n t pH Cape (mg/ HSCf.'OXK i c i t y 'gm) CO:ASH Average Cone, (n H.C.OX E f f l u e n t CO:ASH Throug ( l i t r H.C.OX hput* es) CO:ASH 10% = .2mg/£ 3 0.138 .013 .030 .252 ,0.85 0.10 4 1.582 .074 .017 .070 10.33 0.72 5.7 9.716 .370 .010 .027 63.47 3.72 25% = .5mg/£ 3 0.204 .014 .107 .194 1.41 0.13 4 1.805 .105 .059 .110 12.00 1.15 5.7 10.481 .491 .037 .126 69.33 5.22 50%%==1.0mg/£ 3 0.260 .018 .323 .344 1.95 0.22 4 •1.96.1 ,'146 .129 .345 13.33 1.68 5.7 10.943 .627 .082 .310 74.00 7.40 *THROUGHPUT s i g n i f i e s the t o t a l volume of l i q u i d that has passed through the column at any p a r t i c u l a r time. Influent = 2mg/1 Zn Flow rate= I l g p m / f t 2 Bed depth = 10 inches Coal w e i g h t = H . C 0 X = l 3gm CO^ASH =20gm 12 13 v 5 8 5 9 6 0 62 V O L U M E O F LIQUID T R E A T E D (L ITRES) 6 6 6 8 7 0 72 7 4 50 pH was depressed from 5.7 to 4.0. On f u r t h e r depressing the pH to 3.0, the decrease i n cap a c i t y was 99 percent. S i m i l a r l y , at breakthrough concentrations of 25 percent and 50 percent of i n f l u e n t c o n c e n t r a t i o n , the decrease i n capacity was 83 percent and 82 percent, r e s p e c t i v e l y , when the pH was depressed from 5.7 to 4.0. On f u r t h e r depression of pH to 3.0, the decrease i n c a p a c i t y was 98 percent and 98 percent, r e s p e c t i v e l y . Thus, f o r H.C. OX under the t e s t c o n d i t i o n s s t a t e d i n Figure 4.4, the average capacity decrease, over the range of 10 percent to 50 percent breakthrough c o n c e n t r a t i o n s , i s 83 percent when the pH was depressed from 5.7 to 4.0, and 98 percent when f u r t h e r depressed to a pH of 3.0. S i m i l a r l y , f o r CO:ASH at 10 percent, 25 percent and 50 percent breakthrough co n c e n t r a t i o n s , the decrease i n ca p a c i t y on depression of pH from 5.7 to 4.0 i s 80 percent, 79 percent and 77 percent, r e s p e c t i v e l y . On f u r t h e r depression of pH to 3.0, the cap a c i t y decrease i s 96 percent, 97 percent and 97 percent, r e s p e c t i v e l y . Thus, f o r CO:ASH under the same t e s t c o n d i t i o n s the average capacity decrease i s 79 percent when the pH i s lowered from 5.7 to 4.0, and 97 percent when the pH i s f u r t h e r depressed to 3.0. The percent decreases i n adsorption w i t h decreasing pH f o r both : types of coals are approximately the same. This decrease i n adsorption w i t h (9) decreasing pH i s contrary to what Weber found. The reason f o r t h i s d i s c r e - pancy may be due to the f a c t that he was working w i t h organic p o l l u t a n t s and a c t i v a t e d carbon w h i l e i n t h i s study the combination i s heavy metals and granular c o a l . Since the hydrogen i o n can also be adsorbed, i t i s suspected that the hydrogen i o n i s i n competition w i t h the heavy metal i o n f o r the a c t i v e s i t e s on the c o a l s u r f a c e . As the pH i s depressed, the hydrogen i o n concentration increases and more a c t i v e s i t e s are made u n a v a i l a b l e to the heavy metal. Thus, the drop i n cap a c i t y on lowering the pH may be p a r t l y due to t h i s competition by the hydrogen i o n . Another reason f o r t h i s drop i n cap a c i t y may be due to 51 a change i n the complex fo r m u l a t i o n of the heavy metal w i t h decreasing pH. The lower pH favors the awuo complex which may not be as r e a d i l y adsorbed. (3) Hendrey found the same decrease i n adsorption w i t h decreasing pH i n h i s work on heavy metals w i t h granular c o a l . Since the pH f a c t o r i s so c r u c i a l to the favourable outcome of the adsorption system using granular c o a l , more research should be done i n t h i s area to f i n d out the exact r e l a t i o n - ships between pH and adsorption. An important point to make note of i s that some k i n d of pre-treatment may be necessary when t r e a t i n g a c i d i c wastes w i t h t h i s type of system, i n order that the pH of the wastes may be increased to ensure reasonable adsorption c a p a c i t i e s . c) E f f e c t of Varying the Flow Rate The e f f e c t of flow r a t e on the a d s o r p t i v e c a p a c i t y was i n v e s t i g a t e d by v a r y i n g the flow r a t e between 1-5 Igpm/ft 2, a range r e p r e s e n t a t i v e of flow rates employed i n modern r a p i d sand f i l t r a t i o n and a c t i v a t e d carbon ads o r p t i o n systems. Due to the l a b o r a t o r y equipment a v a i l a b l e and other p r a c t i c a l con- s i d e r a t i o n s , the exact flow rates used were 1.01 Igpm/ft 2, 3.04 Igpm/ft 2 and 5.06 Igpm/ft 2. Whenever flow r a t e s of 1 Igpm/ft 2, 3 Igpm/ft 2 and 5 Igpm/ft 2 are mentioned i n t h i s t h e s i s , the exact values are the ones mentioned above. I f the adsorption c a p a c i t i e s of two columns, s i m i l a r i n a l l respects but the flow r a t e , are f o r a l l p r a c t i c a l purposes the same, then the l o g i c a l i n d u s t r i a l b e n e f i t would be to use the higher flow r a t e and save the cost of b u i l d i n g columns w i t h l a r g e r diameters when t r e a t i n g higher volumes of waste- water. However, the p o s s i b i l i t y of saving operating cost by b u i l d i n g a l a r g e r column must al s o be borne i n mind. Figure 4.5 and Figure 4.6 show the breakthrough curves at d i f f e r e n t flow rates obtained f o r C0:ASH and H.C. OX, r e s p e c t i v e l y . TABLE 4.4 i s a TABLE 4 . 4 EFFECT ON ZINC.vADSQRPTION- OF '.VARYENGtfTHEI'iFLOW RATE Breakthrough Cone, as Percent of Influent Cone. Flow Rate (Igpm/ft2) Cap (mg H.C.OX acity /gm) CO:ASH Average Cone. ( •H.H.C.Y0X, Effluent mg/A) ;oeo;:-ASH H. Throuj ( l i t : : .HY.C.OXO ghput res) AGO:ASH 10% 1 9.716 .386 .008 .039 62.8 3.85 3 5.402 .231 .032 .065 35.4 2.33 5 5.571 .161 .019 .106 36.3 1.66 •25% 25% 1 10.481 .503 .040 .124 68.9 5.30 3 7.080 .358 .123 .190 48.7 3.85 5 6.696 .288 .087 .194 45.3 3.12 50% 1 — .627 — .289 — 7.33 3 9.697 .536 .363 .429 76.0 6.76 5 8.258 .491 .266 .493 61.2 6.45 53 a t a b u l a r summary of the above two f i g u r e s . I t shows the c a p a c i t y , average e f f l u e n t c o n c e n t r a t i o n and the corresponding throughput at 10 percent, 25 percent and 50 percent breakthrough concentrations. At a breakthrough concentration of 10 percent, H.C. OX undergoes a 44 percent decrease i n cap a c i t y when flow r a t e was changed from 1 to 3 Igpm/ft 2 and a 43 percent decrease when the flow r a t e was r a i s e d to 5 Igpm/ft 2. '--At the breakthrough concentration of 25 percent, i t s u f f e r s a 32 percent c a p a c i t y decrease at 3 Igpm/ft 2 and a 36 percent c a p a c i t y decrease at 5 Igpm/ft 2. The data f o r 50 percent breakthrough c o n c e n t r a t i o n was not obtainable f o r 1 Igpm/ft 2 due to time c o n s i d e r a t i o n s . For CO:ASH, at 10 percent breakthrough c o n c e n t r a t i o n , the c a p a c i t y decrease was 40 percent when flow r a t e was changed from 1 to 3 Igpm/ft 2, and 58 percent when flow r a t e was changed to 5 Igpm/ft 2. At 25 percent breakthrough c o n c e n t r a t i o n , the capacity decrease was 29 percent at 3 Igpm/ft 2 and 43 percent at 5 Igpm/ft 2. At 50 percent breakthrough c o n c e n t r a t i o n , i t was only 15 percent at 3 Igpm/ft 2 and 22 percent at 5 Igpm/ft 2. Both coals d i s p l a y e d a s i g n i f i c a n t drop i n cap a c i t y when the flow r a t e was changed from 1 to 3 Igpm/ft 2. However, when the flow r a t e was f u r t h e r r a i s e d to 5 Igpm/ft 2, the a d d i t i o n a l percent decrease i n c a p a c i t y was much sm a l l e r . In the case of CO:ASH, at a l l three breakthrough c o n c e n t r a t i o n s , the a d d i t i o n a l percent decrease i n c a p a c i t y when flow r a t e was f u r t h e r r a i s e d to 5 Igpm/ft 2 was approximately h a l f the percent decrease i n c a p a c i t y when flow r a t e was changed from 1 to 3 Igpm/ft 2 ( i . e . , at 25 percent breakthrough co n c e n t r a t i o n s , the decrease was 29 percent at 3 Igpm/ft 2 and 43 percent at 5 Igpm/ft , an a d d i t i o n a l decrease of 14 percent, which i s approximately h a l f of 29 percent.) As f o r H.C. OX, t h i s a d d i t i o n a l percent decrease i n 54 c a p a c i t y when flow r a t e was f u r t h e r r a i s e d to 5 Igpm/ft 2 was small compared to the percent decrease when flow r a t e was changed from 1 to 3 Igpm/ft 2. L i t e r a t u r e on a c t i v a t e d carbon adsorption s t a t e s that the throughput corresponding to a p a r t i c u l a r breakthrough co n c e n t r a t i o n i s decreased w i t h increased flow r a t e . Figure 4.5 and Figure 4.6 agree w i t h t h i s general statement. An i n t e r e s t i n g point to note, however, i s that the curves converge at higher breakthrough c o n c e n t r a t i o n s , i n d i c a t i n g that the percent d i f f e r e n c e i n c a pacity between d i f f e r e n t flow rates decreases as the p e r m i s s i b l e break- through concentration i s increased. Thus, the choice between b u i l d i n g t h i c k e r columns or stepping up the flow r a t e , as discussed e a r l i e r , would r e s t h e a v i l y on the p o l l u t i o n c o n t r o l r e g u l a t i o n s on allowed waste l e v e l s i n the e f f l u e n t . I f the allowed l e v e l i s very low, the breakthrough co n c e n t r a t i o n w i l l have to be correspondingly low and the use of high flow rates may be i m p r a c t i c a l . On the other hand, i f a higher breakthrough co n c e n t r a t i o n i s p e r m i s s i b l e , then a higher flow r a t e may be contemplated. Of course, these d e c i s i o n s could be made only a f t e r a c a r e f u l examination of the breakthrough curves and a thorough a n a l y s i s of c a p i t a l and operating costs. d) E f f e c t of Varying the I n f l u e n t Concentration Figure 4.7 shows the breakthrough curves f o r t e s t s run w i t h an i n f l u e n t c o n c e n t r a t i o n of 0.5 mg/£. By changing the i n f l u e n t c o n c e n t r a t i o n from 2 mg/I (as used i n previous t e s t s ) to 0.5 mg/£, an attempt was made to f i n d out whether the capacity at a p a r t i c u l a r breakthrough c o n c e n t r a t i o n would increase or decrease, given a l l other parameters to be the same. The main o b j e c t i v e here i s to compare the c a p a c i t i e s at a common breakthrough concentra- t i o n , namely 0.2 mg/Jl, f o r t e s t s run at a pH of 5.7 but w i t h d i f f e r e n t i n f l u e n t FIG. 4 . 5 EFFECT OF VARYING FLOW RATE FOR CO=ASH 55 o o | Igpm/ft.2 • • 3 Igpm/ft2 * * 5 Igpm/ft.2 Influent = 2 mg/l Zn. pH =5.7 Bed depth = 10 inches Coal weight = 20gm 2:0 •— 1.5 •• cn E, 1.3 •- Z o l l - - rr i. i z 1.0- Ul .9 • o z o o h- .7 ••• z LU _ l .5 • EF  .4 •• .2 •• 0 / / / / 0 I 2 3 4 5 6 7 8 9 10 II VOLUME OF LIQUID TREATED (LITRES) -o I Igpm/ft.2 -• 3 Igpm/ft.2 -* 5 Igpm/ft.2 Influent = 2 mg/l Zn pH = 5.7 Bed depth = 10 inches Coal weight' = 13 gm m -n m o -< FT ^ 9 m o p b x 40 50 60 VOLUME OF LIQUID TREATED (LITRES) ON -.5 pH = 4.0 T 4 CO'ASH Zl H.C. OX •+ pH=4.0 -* pH=5.7 pH=4.0 cn e < rr U J o z o o U J 3 U_ LL. LLI + 3 / Influent =0.5mg/l Zn. Flow rote= I Igpm/ft Bed depth = 10 inches Coal weight = 20gm (C0:ASH) = l3gm(H.C.0X) pH=5.7 pH=4.0 0 12 14 16 18 VOLUME OF LIQUID TREATED(LITRES) . m -n Z 3 P F ° m . —I > 3D -a -< I 2 58 concentrations. The.pertinent data on Fi g u r e 4.7 i s shown i n TABLE 4.5. TABLE 4.5 EFFECT OF VARYING THE INFLUENT pH Breakthrough Concentration as percent of i n f l u e n t cone. I n f l u e n t pH Capac (mg/g H.C.OX, : i t y ;m) . CO:ASH Average Concen (mg H.C.OXX E f f l u e n t t r a t i o n / A ) CO:ASH Throu ( l i H.C.OX ghput t r e s ) CO: ASH 10% --?.05')mg/Jrj'/~- 4 5.7 .708 ** .026 .332 .003 ** .019 .009 18.40 ** 1.05 13.43 25% = .125mg/A 4 5.7 .751 ** .037 .426 .009 ** .050 .028 19.75 ** 1.60 17.83 = .2 mg/A 4 5.7 .786 ** .057 .486 .021 ** .096 .051 21.33 ** 2.83 21.66 50% = .25 mg/A 4 5.7 1.025 ** .078 .533 .090 ** .142 .074 32.16 ** 4.22 24.71 Footnote:- A column was not run f o r H.C. OX at a pH of 5.7 due to time c o n s i d e r a t i o n s . The capacity f o r H.C. OX at a pH of 5.7, flow r a t e of 1 Igpm/ft 2, i n f l u e n t c o n c e n t r a t i o n of 0.5 mg/A Zn and at a breakthrough c o n c e n t r a t i o n of 0.2 mg/A was a r r i v e d at by using a f a c t o r as described below. Data from TABLE 4.3 and TABLE 4.5 were combined to form TABLE 4.6, which shp which shows a comparison of c a p a c i t i e s at a breakthrough con c e n t r a t i o n of 0.2 mg/A f o r t e s t s run w i t h z i n c i n f l u e n t s of 0.5 mg/A and 2.0 mg/A, and at a flow r a t e of 1 Igpm/ft 2. From TABLE 4.6, w i t h i n f l u e n t c o n c e n t r a t i o n of 2 mg/A, 370 CO:ASH di s p l a y e d a ca p a c i t y increase by a f a c t o r of 'Q-J^ ~ -*,u ^ u e t o t* i e P** increase from 4 to 5.7. But at an i n f l u e n t c o n c e n t r a t i o n of 0.5 mg/A and under 486 the same change i n pH, i t shows an increase by a f a c t o r of ' = 8.53. 59 TABLE 4.6 COMPARISON OF ADSORPTIVE CAPACITIES OF COLUMNS RUN WITH ZINC INFLUENTS OF 0.5 mg/£ AND 2.0 mg/l, Breakthrough Concentration (mg/i Zn) I n f l u e n t Cone, (mg/l Zn) I n f l u e n t pH Capa (mg H.C.OX c i t y /gm) CO:ASH 0.2 0.5 4 5.7 .786 8.23* .057 .486 2.0 4 5.7 1.582 9.716 . .074 .370 *by c a l c u l a t i o n , not t e s t - see pg. 60 Therefore, the r a t i o : i n c r e a s e f a c t o r w i t h 0.5 mg/l, i n f l u e n t _ 8.53 increase f a c t o r w i t h 2.0 mg/l i n f l u e n t 5 For H.C. OX, w i t h an i n f l u e n t c o n c e n t r a t i o n of 2 mg/1 and under the same change of pH, the ca p a c i t y increase i s by a f a c t o r y p f ^* = 6.14. Using 1.582 the r a t i o described above, H.C. OX w i t h an i n f l u e n t c oncentration of 0.5 mg/l should experience an increase i n c a p a c i t y by a f a c t o r of c6.14 X 1.706 = 10.5 ( i . e . assuming that the same r a t i o of f a c t o r s i s v a l i d f o r H.C. OX a l s o ) . Therefore, the ca p a c i t y of H.C. OX at 0.2 mg/A e f f l u e n t c o n c e n t r a t i o n , w i t h an i n f l u e n t pH of 5.7 and an i n f l u e n t c oncentration of 0.5 mg/A, should be about .786 X 10.5 = 8.23 mg/gm. Looking at TABLE 4.6, at the common breakthrough c o n c e n t r a t i o n of 0.2 mg/£, CO:ASH w i t h an i n f l u e n t pH of 4.0 :shows a decrease i n c a p a c i t y from .074 to 0057 (23 percent decrease) when i n f l u e n t c o n c e n t r a t i o n was changed from 2.0 mg/£ to 0.5 mg/£. But at a pH of 5.7, CO:ASH, under the same changes, experiences an in c r e a s e i n capacity from .370 to .486 (31 percent i n c r e a s e ) . 60 S i m i l a r l y , f o r H.C. OX, at 0.2 mg/A breakthrough concentration and at a pH of 4.0, there i s a decrease i n cap a c i t y from 1.582 to 0.786 (50 percent decrease) and at a pH of 5.7,the decrease i s from 9.716 to 8.230 (15 percent decrease) when i n f l u e n t c oncentration was changed from 2.0 mg/£ to 0.5 mg/A. This l a s t f i g u r e of 8.230 f o r the cap a c i t y of H.C. OX at a pH of 5.7 i s only an estimate a r r i v e d at by using derived f a c t o r s as described p r e v i o u s l y . Only a long-term column t e s t w i l l provide a more exact e v a l u a t i o n of the c o a l capacity under the i n d i c a t e d operating c o n d i t i o n s . The pH of the i n f l u e n t seems to be an important f a c t o r i n determining the change i n cap a c i t y that occurs when the i n f l u e n t c o n c e n t r a t i o n i s changed. For both c o a l s , there i s a decrease i n cap a c i t y when i n f l u e n t c oncentration i s lowered from 2.0 mg/£ to 0.5 mg/£ at a pH of 4.0. But at a pH of 5.7 and under the same i n f l u e n t c o n c e n t r a t i o n changes, CO:ASH experiences an increase w h i l e H.C. OX s t i l l shows a decrease i n c a p a c i t y . Under a set of c o n d i t i o n s where the cap a c i t y increases on lowering the i n f l u e n t c o n c e n t r a t i o n , an important p r a c t i c a l a p p l i c a t i o n i s obvious. For example, two v o l u m e t r i c a l l y equal waste streams o f , say, z i n c and copper of 2 mg/il each could be combined to r e s u l t i n 1 mg/£ each of Zn and Cu before being passed through a c o a l column. This would r e s u l t i n b e t t e r adsorption c a p a c i t i e s than i f the waste streams were passed through separate columns i n d i v i d u a l l y . From the data above, i t i s c l e a r that c l o s e a t t e n t i o n must be pa i d to the i n f l u e n t pH before any attempts are made i n c e r t a i n cases to b e t t e r the adsorption capacity by lowering the i n f l u e n t c o n c e n t r a t i o n . I n v e s t i g a t i n g the ca p a c i t y s e n s i t i v i t y to pH change at d i f f e r e n t i n f l u e n t c o n c e n t r a t i o n s , i t i s seen from TABLE 4.6 that at the common 0.2 mg/£ breakthrough, C0:ASH shows an 80 percent decrease w i t h an i n f l u e n t c o n c e n t r a t i o n 61 of 2 mg/£ and an 88 percent decrease w i t h an i n f l u e n t c o n c e n t r a t i o n of 0.5 mg/£ when the pH i s changed from 5.7 to 4.0 i n both cases. H.C. OX shows a decrease of 84 percent w i t h i n f l u e n t of 2 mg/£, w h i l e at an i n f l u e n t of 0.5 mg/£ the decrease was 91 percent under the same change i n pH. The percent decrease i n capacity due to lowering of pH i s greater i n the case of 0.5 mg/£ i n f l u e n t c o n c e n t r a t i o n , i n d i c a t i n g a g r e a t e r s e n s i t i v i t y of c a p a c i t y response to pH change at lower i n f l u e n t concentrations. 476 Breakthrough Curves f o r Copper The adsorption c a p a c i t i e s f o r copper were i n v e s t i g a t e d f o r both coals using an i n f l u e n t of 2 mg/£ Cu and a flow r a t e of 1 Igpm/ft 2 at i n f l u e n t pH values of 4.0 and 5.7. There are only three breakthrough curves shown i n Figure 4.8, although four columns were t e s t e d . The curve f o r H.C. OX at a pH of 5.7 i s absent i n Figure 4.8 s i n c e i t s e f f l u e n t c o n c e n t r a t i o n was s t i l l undetectable a f t e r 5 days of throughput ( i . e . 33.4 l i t r e s ) . Therefore, r a t h e r than spend more time w a i t i n g f o r the breakthrough, a d e c i s i o n was made to stop the column and estimate the adsorption capacity of H.C. OX at a pH of 5.7 by the use of a f a c t o r , as i n d i c a t e d i n s e c t i o n 4.4(d). A t a b u l a r summary of Figure 4.8 w i t h respect to c a p a c i t y and the corresponding throughput and average e f f l u e n t concentration i s shown i n Table 4.7. The main o b j e c t i v e s f o r running t h i s s e r i e s of columns were: 1) To determine the adsorption c a p a c i t y f o r copper at a pH of 5.7 and under the t e s t c o n d i t i o n s described i n Figure 4.8. 2) To determine the change i n c a p a c i t y f o r copper at d i f f e r e n t pH values. FIG. 4.8 f CM o cvi oo in ^ ro oo — O ^ ^ ^ , <a- ro OJ _ -+ T T I — I — I — I — H 1 — I — | — I — I — h (I/DUJ ) N 0 I 1 V U 1 N 3 0 N C O l N 3 n ~ l d d 3 63 The adsorption c a p a c i t i e s f o r H.C. OX at a pH of 5.7 are shown i n i t a l i c s i n Table 4.7 si n c e these f i g u r e s were not a r r i v e d at ex p e r i m e n t a l l y , TABLE 4.7 EFFECT OF VARYING pH WITH. COPPER INFLUENTS Breakthrough Concentration as Percent of I n f l u e n t Cone. I n f l u e n t pH Capa (mg/ H.C.OX H.C.OX c i t y gm) 'CO: ASH CO:ASH Aver a E f f l u e Cone.( H.C.OX ge nt mg/Z) CO:ASH Throu ( l i H.C.OX ghput t r e s ) CO: ASH 10% = 0.2 mg/£ 4 5.7 3.986 12.396 0.467 1.182 .008 .016 .032 25.95 4.72 12.00 25% = 0.5 mg/iH 4 5.7 4.281 13.442 0.545 1.370 .038 .072 .081 28.25 5.62 14.30 50% =1.0 mg/£ 4 5.7 4.634 15.524 • 0.634 1.601 .116 .206 .220 31.80 7.11 17.90 but estimated by the procedure described below. For C0:ASH w i t h a z i n c i n f l u e n t of 2 mg/a (Table 4.3), at the 10 percent breakthrough c o n c e n t r a t i o n , the capacity i n c r e a s e f a c t o r due to the pH change from 4.0 to 5.7 i s . 370 = 5.00. Using a copper i n f l u e n t of 2 mg/£ under the same c o n d i t i o n s , .074 1 182 the increase f a c t o r i s — ~ = 2.53 (Table 4.7). Therefore, the r a t i o of 0.467 increase f a c t o r w i t h Cu i n f l u e n t 2.53 c n , = = . 5ub- i n c r e a s e f a c t o r w i t h Zn i n f l u e n t 5.00 Now f o r H.C. OX w i t h a z i n c i n f l u e n t of 2 mg/i, the cap a c i t y increase f a c t o r under the same c o n d i t i o n s , i s ^* = 6.14. Therefore, f o r H.C. OX, w i t h a 1.582 copper i n f l u e n t of 2 mg/£ and under the same pH changes, the capacity increase f a c t o r should be 66.14 X .506 = 3.11. M u l t i p l y i n g the cap a c i t y of H.C. OX at 64 a pH of 4.0 (Table 4.7) by t h i s f a c t o r provides a c a l c u l a t e d c a p a c i t y of H.C. OX at the higher pH of 12.396 mg/gm. S i m i l a r l y , at breakthrough concentrations of 25 percent and 50 percent, the increase f a c t o r s w i t h copper i n f l u e n t s f o r H.C. OX are 3.14 and 3.35, r e s p e c t i v e l y . M u l t i p l y i n g these f a c t o r s by the corresponding c a p a c i t i e s of H.C. OX at a pH of 4.0 r e s u l t s i n the estimated c a p a c i t i e s at a pH of 5.7 as shown i n TABLE 4.7 i n i t a l i c s . Data i n TABLE 4.7 i n d i c a t e s a decrease i n adsorption capacity w i t h decreasing pH f o r both types of c o a l as i n the case w i t h z i n c adsorbate. From TABLE 4.7 again, f o r C0:ASH at breakthrough concentrations of 10 percent, 25 percent and 50 percent, the percent decrease i n c a p a c i t y due to the pH change from 5.7 to 4.0 i s 61 percent, 60 percent and 60 percent, r e s p e c t i v e l y . Thus, over the range of breakthrough concentrations s t a t e d above, the average percent decrease i n capacity f o r CO:ASH due to a change of pH from 5.7 to 4.0 i s 60 percent. In the case of H.C. OX, due to the same change i n pH, the percent decrease i n capacity at 10 percent, 25 percent and 50 percent break- through concentrations i s 68 percent, 68 percent and 70 percent, r e s p e c t i v e l y . This gives an average percent decrease of 69 percent f o r H.C. OX under the same c o n d i t i o n s . The average percent decrease due to the depression of pH i s about the same f o r both c o a l s , as was the case w i t h z i n c adsorbate. Comparing the percent decrease i n c a p a c i t y of copper and z i n c due to the lowering of pH from 5.7 to 4.0, i t i s seen from TABLE 4.3 and TABLE 4.7 that both coals d i s p l a y a lower percent decrease w i t h copper i n f l u e n t s . From TABLE 4.3 and TABLE 4.7, the r a t i o s of c a p a c i t i e s f o r copper v s . . c a p a c i t i e s f o r z i n c are shown i n TABLE 4.8. I t i s c l e a r from TABLE 4.8 that the d i f f e r e n c e i n terms of percentage between a d s o r p t i v e c a p a c i t i e s f o r copper and z i n c i s greater at the lower pH of 4.0 f o r both types of c o a l . 65 TABLE 4.8 COMPARISON OF ADSORPTIVE CAPACITIES FOR COPPER AND ZINC Range of Capacity f o r Copper Breakthrough I n f l u e n t Capacity f o r Zinc Concentrations pH H.C. OX CO:ASH 4 •.22;4-v"V!255 4.3 ^6.3 10% - 50% 5.7 1.3 ^1.4 2.6 - V 3.2 This d i f f e r e n c e i s more pronounced i n the case of C0:ASH. 4.7 Breakthrough Curves f o r Lead Three columns were t e s t e d w i t h lead as the adsorbate, two of them using CO:ASH w i t h i n f l u e n t pH values of 5.7 and 4.0, and the t h i r d one w i t h H.C. OX at a pH of 4.0. The other parameters were as s t a t e d i n F i g . 4.9(a) , H.C.OOX at a pH of 5.7 was not t e s t e d because there was good reason to b e l i e v e that i t would take an e x c e s s i v e l y long p e r i o d of time f o r i t s breakthrough to occur. Thus, an estimate f o r the c a p a c i t y of H.C. OX at a pH of 5.7 was the goal i n s t e a d . This estimate would be based on the three columnstested and on previous data from z i n c and copper t e s t s . The main o b j e c t i v e s here were similar-to<r. those f o r copper t e s t s ; •that.is; to determine the c a p a c i t y at a pH of 5.7 and under the t e s t c o n d i t i o n s s t a t e d i n Figure 4.9(a) and also to i n v e s t i g a t e the percent decrease i n capa- c i t y f o r l e a d on lowering the pH). Figure 4.9(a) shows only one breakthrough curve, that of CO:ASH at a pH of 4.0. The other two columns were stopped without^ having reached t h e i r breakpoints due to excessive flow problems caused by the appearance of a fungus. As the fungus accumulated at the top of the c o a l column, the pressure drop E F F L U E N T CONCENTRATION U N D E T E C T A B L E A F T E R CO = A S H at p H = 5 . 7 - 4 0 Litres H.C. OX at p H = 4 . 0 - 6 0 Litres Influent = 2 mg/ l Pb Flow rate = I Igpm/ft. 2 Bed depth = 10 inches Coal we ight - H.C. OX = I 3 gm C 0 : A S H = 2 0 g m pH=4 . 0 ( C O : A S H ) 2 4 6 8 10 12 14 16 18 2 0 V O L U M E O F LIQUID T R E A T E D ( L ITRES) 6 7 FIG. 4.9(b) FUNGUS GROWING AT THE TOP OF COAL COLUMN 68 across the c o a l bed Increased. When the flow r a t e could no longer be maintained at 1 Igpm/ft 2 even on f u l l y opening the bu r e t t e v a l v e , a vacuum was a p p l i e d at the e f f l u e n t end of the b u r e t t e . This enabled the maintenance of the flow r a t e a 1 Igpm/ft 2 f o r about another 8 l i t r e s of throughput. The flow r a t e then dropped again due to f u r t h e r accumulation of the fungus. At t h i s p o i n t the runs were discontinued. In the case of CO:ASH at a pH of 5.7, the throughput on d i s c o n t i n - u a t i o n was 40 l i t r e s w h i l e f o r H.C. OX at a pH of 4.0, i t was 60 l i t r e s . As shown on F i g . 4 (. 19(b), the white f l u f f y fungus was about 1/8 inch t h i c k on top of the c o a l column when the runs were stopped. I t a l s o permeated i n t o the voids between the c o a l p a r t i c l e s to about 1/4 i n c h from the top of the c o a l column. Figure 4.9(b) al s o shows pockets of gas created along the length of the c o a l , column due to the vacuum a p p l i e d at the e x i t end. TABLE 4.9 i s a t a b u l a r r e p r e s e n t a t i o n of Figure 4.9(a). No attempt i s made to estimate the blanks shown i n TABLE 4.9 because there are too many unknowns i n v o l v e d . However, a minimum estimate can be made f o r H.C. OX at a TABLE 4.9 CAPACITIES FOR LEAD Breakthrough Concentration As Percent of I n f l u e n t Cone. I n f l u e n t pH Capac] (mg/j H.C.OX -ty ;m) CO:ASH Averaj E f f l u e Cone, (ii H.C.OX 5e :nt ig/A) CO: ASH Throu ( l i t H.C.OX ghput res) CO:ASH 10% = 0.2 mg/ 4 5.7 — 0.903 — .017 — 9.11 25% = 0.5 mg/ 4 5.7 — 1.101 — .088 — 11.42 50% = 1.0 mg/ 4 5.7 1.329 — .252 — 15.14 69 pH of 4.0 from the data on MIXED INFLUENTS. (TABLE 4.10(a)). Since the capacity f o r a p a r t i c u l a r metal using an i n f l u e n t c o n t a i n i n g that metal only as adsorbate i s greater than the cap a c i t y f o r the same metal when the i n f l u e n t contains t h a t metal p l u s a ^mixture of other metals (See s e c t i o n 4.7), the capa c i t y f o r lead of H.C. OX at a pH of 4.0 w i t h mixed i n f l u e n t s i s a minimum estimate f o r the same cap a c i t y when the i n f l u e n t c o n s i s t s only of lead . At 10 percent breakthrough, t h i s minimum estimate of the ca p a c i t y f o r lead of H.C. OX at a pH of 4.0 i s 2.536 mg/gm as shown i n TABLE 4.10(a). Data from TABLES 4.3, 4.7 and 4.9 show th a t f o r COrASH, at a pH of 4.0 and at 10% breakthrough c o n c e n t r a t i o n , the r a t i o of c a p a c i t i e s f o r z i n c : copper : lead i s equal to 1 : 6 : 12. 4.8 Breakthrough Curves f o r I n f l u e n t s Containing a Mixture of Z i n c , Copper and Lead I n waste streams such as m u n i c i p a l sewage, there u s u a l l y i s a mixture of d i s s o l v e d heavy metals i n s t e a d of j u s t one s i n g l e adsorbate. These va r i o u s heavy metals i n s o l u t i o n may mutually enhance ad s o r p t i o n , may act r e l a t i v e l y (9) independently or may mutually depress adsorption. Some researchers have fround w i t h a c t i v a t e d carbon and mixed s o l u t i o n s that each s o l u t e competes i n some way w i t h the adsor p t i o n of the other. I t was found that the presence of the other s o l u t e s i n the mixture adversely a f f e c t s the adsorption of a p a r t i c u l a r s o l u t e , l e a d i n g to a more r a p i d breakthrough of t h i s s o l u t e when using a mixed s o l u t i o n than when using a pure s o l u t i o n c o n t a i n i n g only that p a r t i c u l a r s o l u t e . A column each f o r H.C. OX, CO:ASH and DARCO A c t i v a t e d Carbon GRADE 12X20 was run at 1 Igpm/ft 2 and at a pH of 4.0. The i n f l u e n t used c o n s i s t e d of 2 mg/£ each of z i n c , copper and lead . The pH was chosen as 4.0 in s t e a d of 5.7, because at 5.7 the breakthrough times would be e x c e s s i v e l y l o n g , e s p e c i a l l y f o r H.C. OX. The b a s i c o b j e c t i v e s f o r running the above mentioned three columns 70 were the f o l l o w i n g : - 1) To compare the three types of adsorbents w i t h regard to t h e i r a d sorptive c a p a c i t i e s f o r z i n c , copper and lead from water c o n t a i n i n g a mixture of these metals at a pH of 4.0. 2) To determine the change i n c a p a c i t i e s f o r z i n c , copper and lead at a pH of 4.0 that occurs when a mixed i n f l u e n t i s used r a t h e r than a pure s o l u t i o n c o n t a i n i n g only one adsorbate. As i n the lead t e s t s , the white fungus appeared i n a l l three columns. For CO:ASH and DARCO Ac t i v a t e d Carbon, the fungus appeared only a f t e r t o t a l breakthroughs f o r a l l three metals had occurred. But i n the case of H.C. OX, the fungus appeared before the lead and copper breakthrough curves could begin to r i s e s h a r p l y . I t may be due to the fungus, that f o r H.C. OX,' the e f f l u e n t concentration f o r lea d began to drop and that f o r copper f a i l e d to r i s e sharply a f t e r the appearance of the fungus at a throughput of about 18 l i t r e s . This can be observed q u i t e c l e a r l y i n Figure 4.10(a). The appearance of the fungus i n the columns c o n t a i n i n g C0:ASH and DARCO A c t i v a t e d Carbon a l s o took place at a throughput of about 18 l i t r e s , but t o t a l breakthroughs f o r a l l three metals i n these two columns had occurred long before throughput reached 18 l i t r e s . The curves f o r CO:ASH and DARCO Acti v a t e d Carbon are shown i n Figure 4.10(b) and Figure 4.10(c), r e s p e c t i v e l y . A summary of the important data from Figures 4.10(a), 4.10(b) and 4.10(c) i s presented i n TABLE 4.10(a). A performance comparison between H.C. OX, CO:ASH and DARCO A c t i v a t e d Carbon w i t h regard to t h e i r c a p a c i t i e s f o r the three metals from mixed i n f l u e n t s , at a pH of 4.0, may be made from the data i n TABLE 4.10(a). For the sake of c l a r i t y and b r e v i t y , t h i s comparison, as shown i n TABLE 4.10(b), i s done only f o r the 10 percent breakthrough . concentration, .('ing/ )0. 2img/&)«le!t i S a e l e a r „ th:atiH,<2(. c0X £is the.best -per- former of the three. H.C. OX i s about 12 times better., than C0:ASH cn E rr LU O z o c_> UJ 3 Lu UJ 0- X — -O CU - * PB - A ZN Ph = 4.0 Influent = 2mg/l each of Cu., Pb. and Zn Flow rate = I Igpm/ft.2 Bed depth = 10 inches Coal weight = 13 gm 10 12 14 16 18 VOLUME OF LIQUID TREATED ( LITRES) 20 22 24 26 27 CD JJ m > JO o c CD X o c JO < m co ~n o JJ o 6 X CD 6 ^ Q X m o c m V O L U M E O F LIQUID T R E A T E D ( L I T R E S ) E < or o z: o o 111 3 U - U J Q O CU. x— * PB. * !• ZN. Ph=4.0 Influent = 2mg/l each of Zn., Pb. and Cu. Flow rate = I Igpm/ft.2 Bed depth = 10 inches Coal weight = 9.5gm. 6 7 8 10 12 14 16 VOLUME OF LIQUID TREATED (LITRES) t- 18 -+- 20 22 CO m > —\ X JO o c CD o c < m c o 3 O 5 5 m o o > CD o X m o c m o CO TABLE 4.10(a) ADSORPTION CAPACITIES USING MIXED INFLUENTS Metal Tested = Zn, I n f l u e n t pH = 4.0 Breakthrough Cone, as Percent of I n f l u e n t Cone. H.C.OX Capacity c''(mgf/gm)' C0:ASH Ave ; Coi Act.C rage EfAve c. (mg/Gor H.C.OX srage E f f l i i c . (mg/l) CO:ASH lent Act.C 1 H.C.OX 'hroughput ( l i t r e s ) CO:ASH Act.C : 10% 0.871 0.072 0.088 .00188 .033 .062 5.70 0.77 0.41 • 25% 1.036 0.106 0.133 .086 .116 .168 7.00 1.09 0.60 50% 1.190 0.122 0.165 .196 .266 .326 8.50 1.42 0.85 !- - i Metal Tested = Cu, I n f l u e n t pH = 4.0 10% 2.393 0.201 0.337 .019 .037 .048 15.60 2.05 1.58 25% 2.773 0.280 0.443 .079 .137 .142 18.63 2.95 2.31 50% 0.347 0.603 — .303 .330 — 4.08 3.44 Metal Tested = Pb, I n f l u e n t pH = 4.0 • 10% 2.536 0.675 0.489 .015 .041 .054 16.48 6.84 2.33 25% — 0.931 0.659 — .134 .136 — 9.95 3.33 50% — 1.183 0.844 — .313 .323 — 13.94 4.77 TABLE 4.10(b) A COMPARISON BETWEEN H.C. OX, CO:ASH AND DARCO ACTIVATED CARBON WITH REGARD TO THEIR CAPACITIES FOR THE THREE METALS FROM MIXED INFLUENTS AT A pH OF 4.0 M Metal Tested Breakthrough Cone, as Percent of I n f l u e n t Cone. CO:ASH DARCO Act. Carbon H.C. OX Zn 10% 0.072 0.088 0.871 Capacity (mg/gm) 1.0 1.2 12.1 R e R e i a t i v i a C a p a c i t y * Cu 10% 0.201 0.337 2.393 Capacity (mg/gm) 1.0 1.7 11.9 R e l a t i v e Capacity* Pb 10% 0.675 0.489 2.536 Capacity (mg/gm) 1.0* 0.7 3.8 R e l a t i v e Capacity* * " R e l a t i v e Capacity" s i g n i f i e s the r a t i o of c a p a c i t i e s w i t h the capacity of C0:ASH as the base. PERCENT DECREASE IN CAPACITY ON CHANGING THE INFLUENT TO ONE CONTAINING A MIXTURE OF SOLUTES Metal Capaci Heavy Metal :y (BiGap.g£ S i n g l e Solute H.C. 0 i t y (mg/gm) Mixture of Solutes X % Decrease Capacil S i n g l e Solute CO:ASH :y (mg/gm) Mixture of Solutes % Decrease Zn 1.582 0.871 45 0.074 0.072 3 Cu 3.986 2.393 40 0.467 0.201 57 Pb 2.536 — 0.903 0.675 25 I n f l u e n t pH = 4.0 Breakthrough co n c e n t r a t i o n = 10 percent of i n f l u e n t concentration 76 f o r z i n c and copper and about 4 times b e t t e r than CO:ASH f o r l e a d . DARCO a c t i v a t e d charcoal has the same range of adso r p t i v e c a p a c i t y as CO:ASH. I t i s s l i g h t l y b e t t e r than CO:ASH i n the case of z i n c and copper, and s l i g h t l y worse than CO:ASH i n the case of lead. I t i s somewhat s u r p r i s i n g that an a c t i v a t e d carbon w i t h a tremendous advantage i n surface area showed a poor performance i n comparison w i t h H.C. OX. But, on the other hand, the raw m a t e r i a l used to prepare the carbon, the method and temperature of a c t i v a t i o n and the type of gas used f o r a c t i v a t i o n may a l l a f f e c t the s e l e c t i v i t y of the f i n a l product. With the rel e v a n t data from TABLES 4.3, 4.7, 4.9 and 4.10(a), a comparison was made between the c a p a c i t i e s experienced w i t h s i n g l e s o l u t e i n f l u e n t s and w i t h i n f l u e n t s c o n t a i n i n g a mixture of s o l u t e s . ThenpH i n both cases was 4.0. The percent decrease i n c a p a c i t y , due to t h i s change i n the nature of the i n f l u e n t , i s c a l c u l a t e d f o r z i n c , copper and l e a d at a 10 percent breakthrough c o n c e n t r a t i o n ( i . e . , 0.2 mg/A), as shown i n TABLE 4.10(c). H.C. OX seems to experience about the same percent decrease i n capa c i t y f o r both z i n c and copper on changing the i n f l u e n t to one of mixed s o l u t e s . U n f o r t u n a t e l y , the f i g u r e f o r l e a d under s i n g l e s o l u t e i n f l u e n t i s un a v a i l a b l e due to the fungus problem as described i n s e c t i o n 4.6. Thus, nothing can be concluded f o r lead i n t h i s respect. The percent decrease i n ca p a c i t y d i s p l a y e d by CO:ASH under t h i s change of i n f l u e n t i s greatest f o r copper (57%). In the case of l e a d , the percent decrease i s 25 percent, w h i l e f o r zincethe decrease was only 3 percent. Therefore, i t can be concluded that the cap a c i t y f o r a heavy metal decreases when there are other heavy metals present i n the i n f l u e n t . This i s probably due to the occupation of some a c t i v e s i t e s by these other heavy 77 metals. Under t h i s environment of competition f o r a c t i v e s i t e s , the c a p a c i t y f o r a p a r t i c u l a r heavy metal i s l e s s than that obtained under a competition- f r e e environment of a s i n g l e s o l u t e i n f l u e n t . I t may als o be noted that the t o t a l c a p a c i t y f o r z i n c , copper and lead from a mixed i n f l u e n t d i s p l a y e d by the H.C. OX column i s equal to 5.800 mg/gm which i s much more than the cap a c i t y f o r any i n d i v i d u a l heavy metal from a s i n g l e s o l u t e i n f l u e n t . CO:ASH a l s o e x h i b i t e d t h i s c h a r a c t e r i s t i c w i t h a t o t a l c a pacity f o r z i n c , copper and lead of 0.948 mg/gm from a mixed i n f l u e n t . With a s i n g l e s o l u t e , a p a r t i c u l a r type of a c t i v e s i t e only i s occupied. This p a r t i c u l a r type may form j u s t a sm a l l f r a c t i o n of the t o t a l s i t e s . But w i t h a mixture of s o l u t e s , more than one type of a c t i v e s i t e i s used up. Thus, a greater f r a c t i o n of the t o t a l s i t e s i s u t i l i s e d . 4.9 C o r r e l a t i o n of E f f l u e n t pH wi t h E f f l u e n t Concentration In the e a r l y part of the column t e s t s , the pH of the e f f l u e n t was measured at the beginning and j u s t before the end of the run. (Just f o r the sake of i n f o r m a t i o n , t h i s was done w i t h the f i r s t few columns.) I t was noted that the pH of the e f f l u e n t was about 6.0 i n the beginning and very c l o s e to the pH of the i n f l u e n t j u s t before the end of the t e s t . A n o t i o n was nurtured that the pH of the, e f f l u e n t could somehow serve as an i n d i c a t o r of the e f f l u e n t concentration of the metal. The hydrogen i o n i s adsorbable. Therefore, when the e f f l u e n t pH decreases from about 6.0 to the pH of the i n f l u e n t near the end of the t e s t , a conc l u s i o n may be drawn that breakthrough w i t h regard to the hydrogen i o n has occurred. I f t h i s breakthrough of the hydrogen i o n c o i n c i d e s w i t h that o:f the metal, then a c l e a r - c u t cor- r e l a t i o n can be drawn between e f f l u e n t pH and the e f f l u e n t concentration of the metal. I f the two breakthroughs do not c o i n c i d e , the pH of the e f f l u e n t 78 corresponding to the breakthrough of the metal may be noted. Then t h i s pH of the e f f l u e n t noted can serve as an i n d i c a t o r of the metal breakthrough i n f u t u r e i d e n t i c a l columns, provided: 1) This value of the pH has been proven to remain constant whenever breakthrough of the metal occurs. 2) The e f f l u e n t pH s t e a d i l y approaches that of the i n f l u e n t as the experiment proceeds, without s u f f e r i n g any random decreases and increases. I f some ki n d of c o r r e l a t i o n between e f f l u e n t pH and e f f l u e n t metal concentration can be brought to l i g h t , the author can t h i n k of two d i r e c t b e n e f i t s such as: 1) In the course of research work, an inexpensive and compact pH meter may be used to i n d i c a t e the beginning of the metal breakthrough. Once the breakthrough i s about to set i n , then the e f f l u e n t c oncentration may be tes t e d on the more expensive and cumbersome Atomic Absorption Spectrophotometer to get the data f o r the breakthrough curve. This procedure would e l i m i n a t e the time and t r o u b l e of using the Atomic Absorption Spectrophotometer before the beginning of the metal breakthrough. 2) In the p r a c t i c a l a p p l i c a t i o n of c o a l adsorption columns, the pH meter may be used r o u t i n e l y to i n d i c a t e the s a t u r a t i o n s t a t e of the column, once the c o r r e l a t i o n between the e f f l u e n t pH and the e f f l u e n t metal c o n c e n t r a t i o n has been worked out under a c t u a l p l a n t c o n d i t i o n s . TABLE 4.11 COMPARISON OF EFFLUENT pH AND EFFLUENT CONCENTRATION Test Parameters TEST NUMBERS (1) (2) (3) (4) (5) (6) (7) (8) Coal Type CO:ASH H.C.OX H.C.OX CO:ASH H.C.OX CO:ASH H.C.OX CO:ASH Flow Rate (Igpm/ft2) 1 1 1 1 1 1 1 1 Influent pH 3.0 3.0 4.0 4.0 4.0 4̂ 0 4.0 4.0 Influent Cone. 2mg/AZn 2mg/£Zn 2mg/£Cu 4mg/£Cu 2mg/£ Pb 2mg/£ Pb 0. 5mgA, Zn 0.5mg/£Zn oAo 5 B8 5?2 : Q'M 7?0 6?4 A B A BB A B A B 6.100 5.8 0.00 5.2 0.00 7.0 0.00 6.4 0.00 6.2 0.00 6.2 0.00 6.0 0.00 6.1 1.27 3.4 0.00 5.7 0.00 6.0 0.00 6.9 0.00 6.7 0.00 4.3 0.00 6.1 0.11 5.9 1.27 3.3 0.00 5.4 0.00 5.9 0.00 6.3 0.00 6.6 0.40 4.2 0.00 5.8 0.17 5.4 1.32 3.2 0.05 5.7 0.00 4.3 0.00 6.9 0.00 6.1 0.70 4.2 0.00 6.3 0.21 4.5 1.35 3.3 0.18 5.4 0.00 4.2 0.00 5.6 0.00 4.0 0.80 4.2 0.00 6.1 0.31 4.2 1.37 3.2 1.21 3.3 0.30 4.1 1.10 4.2 0.00 4.0 1.30 4.1 0.12 5.6 - 0.32 4.5 1.51 3.2 1.22 3.2 0.40 4.1 1.35 4.2 1.50 4.1 0.20 4.8 0.33 4.2 1.64 3.1 0.60 4.0 1.80 4.1 0.22 4.3 0.37 4.1 1.23 4.0 0.23 4.2 0.43 4.0 NOTE:- A = Effluent concentration in mg/£ B = Effluent pH vo TABLE 4.11 (Continued) Test Parameters TEST NUMBERS J (9) (10) (11) (12) Coal Type H.C. OX CO:ASH H.C. OX CO:ASH Flow Rate (Igpm/ft 2) 1 1 1 1 I n f l u e n t pH 4.0 4.0 5.7 5.7 I n f l u e n t Cone. 2mg JSmg /'I ~ eacnn of Zn, Cu & Pb ?b-5:P2mg/£ each of Zn, Cu & Pb 2mg/£ Zn 2mg/£ Cu A(Zn) A(Cu) A(Pb) BB A(Zn) A((Cu) A(Pb) B A B A B 0.00 0.00 0.00 §.1 0.04 0.00 0.00 6.3 0.00 7.0 0.00 6.6 0.00 0.00 0.00 5.8 1.70 0.20 0.00 5.6 0.00 6.0 0.00 6.0 0.18 0.00 0.00 5.9 2.00 1.50 0.20 4.2 0.00 7.6 0.00 6.8 0.42 0.00 0.00 5.6 2.00 1.70 0.30 4.1 0.00 5.9 0.05 6.2 2.00 0.05 0.00 5.0 2.00 2.00 0.75 4.1 0.00 7.5 0.40 5.8 2.00 0.10 0.00 4.6 2.00 2.00 1.45 4.0 0.00 7.0 0.70 6.9 2.00 0.15 0.10 4.3 2.00 2.00 1.60 4.0 0.27 5.7 1.10 6.7 2.00 0.65 0.15 4.1 1.20 7.0 1.25 5.7 TABLE 4.11 (Continued) Test TEST NUMBERS Parameters (13) (14) (15) (16) (17) Coal Type H.C . OX. C00,: ASH H.C. OX CO:ASH CO:ASH Flow Rate (Igpm/ft 2) 3 3 5 5 1 I n f l u e n t pH 5 .7 5. 7 5. 7 5.7 5.7 I n f l u e n t Cone. ' 22-mg/JGZn 2mg/l Zn 2mg/£Zn 2mg/£ Zn 0.5mg/£Zn A B A B A B A B A B 0.00 6.1 0.00 6.6 0.00 7.1 00000 66,33 0,0000 66'; 9 0.04 7.0 0.15 6.8 0.00 7.2 0.17 6.1 0.00 7.0 0.14 5.9 0.30 6.7 0.17 6.6 0.46 7.2 0.00 7.2 0.53 7.0 0.47 6.6 0.55 5.8 0.67 7.1 0.00 6.3 0.77 5.7 0.65 6.4 0.73 5.7 0.89 7.3 0.01 6.3 0.85 5.7 0.81 6.5 •1.00 6.1 1.21 6.5 0.05 6.7 1.06 7.0 1.04 6.1 1.29 6.0 1.33 7.2 0.07 6.7 1.11 7.2 1.39 6.3 1.37 5.7 1.44 6.0 0.10 6.2 1.67 6.2 0.21 7.2 82 TABLE 4.11 i s a comparison of the e f f l u e n t pH with the metal.con- centration i n the e f f l u e n t . Tests #1 and #2 show that the e f f l u e n t pH drops s t e a d i l y as the e f f l u e n t concentration increases. Thus, a c o r r e l a t i o n i s possible under the test parameters described i n Tests #1 and #2. The drop i n pH from about 5.0 to 3.4 occurred r a p i d l y over a small change i n e f f l u e n t concentration while the change i n pH from 3.4 to 3.0 occurs more slowly. This i s due to the fact that for every unit change of pH, the molar concentration of hydrogen ion undergoes a change by a factor of 10. Thus, when the pH drops -3 4 -5 -4 from 5.0 to 3.4, the change i n molar concentration i s 10 - 10 = 3.8 X 10 ; -3 -3.4 -4 while i t takes a change i n molar concentration of 10 - 10 " = 6.0 X 10 to bring about a drop i n pH from 3.4 to 3.0. The pH of the e f f l u e n t seems to fluctuate i n value when i t i s above 5.0 and only follows a d e f i n i t e downward trend below a pH of 4.0 with increasing breakthrough of the metal. This i s e a s i l y understood when one understands that i t only takes 10 - 10 = —6 4" 8.0 X 10 moles/H of H ion to cause a s h i f t i n pH of 5.7 to 5.0, while i t -3 9 - 4 0 -6 takes 10 ' - 10 ' = 26.0 X 10 molesM for the needle to s h i f t from 4.0 to 3.9. Thus, the f l u c t u a t i o n of the e f f l u e n t pH between 5.0 and 5.7 may be i n part due to the dynamic nature of the equilibrium adsorption process where the hydrogen ions are i n a state of give and take with i n f i n i t e s i m a l s h i f t s i n the net gain or net loss during the unsaturated stage of the column. These s h i f t s i n the net gain or net loss show up i n the pH range of 5.0 to 5.7 because the changes i n H + ion concentration necessary to produce a change i n pH i n this range are extremely small. Tests #3 to #10 have an i n f l u e n t pH of 4.0. Of these t e s t s , pH cor- r e l a t i o n i s possible for Tests #3, 4, 6, 7 and 8. Test #5 shows no promist of such a c o r r e l a t i o n . The i n f l u e n t consists of a z i n c , copper and lead mixture i n Tests #9 & 10. For Test #9, c o r r e l a t i o n i s possible for the copper breakthrough and 83 discouraging f o r z i n c and lead breakthroughs. In the case of Test #10, the c o r r e l a t i o n i s f a i r f o r copper and le a d f r a c t i o n s and not p o s s i b l e f o r the z i n c , s i n c e the breakthrough f o r z i n c occurred at an e f f l u e n t pH above 5.6, and as p r e v i o u s l y mentioned, the pH of the e f f l u e n t randomly f l u c t u a t e s i n the range of 5.0 to 5.7. The pH of the i n f l u e n t was 5.7 f o r Tests #11 to #17. C o r r e l a t i o n i s d e f i n i t e l y not p o s s i b l e f o r a l l these t e s t s s i n c e the e f f l u e n t pH f l u c t u a t e s randomly between 7.6 and 5.7 w i t h i n c r e a s i n g e f f l u e n t metal co n c e n t r a t i o n . The e f f l u e n t pH i s not l i k e l y to go below 5.7 s i n c e the i n f l u e n t pH happens to be 5.7. • Therefore, t e s t s w i t h an i n f l u e n t pH of 5.7 have no hope of such a c o r r e l a t i o n . A c o n c l u s i o n may be drawn that when the i n f l u e n t pH i s as low as 3.0, a c o r r e l a t i o n between the e f f l u e n t pH and the e f f l u e n t metal c o n c e n t r a t i o n i s most l i k e l y to occur. When the i n f l u e n t pH i s above 5.0, the chances of such a c o r r e l a t i o n are p r a c t i c a l l y n i l . But, when the i n f l u e n t pH i s about 4.0, the p o s s i b i l i t y of such a c o r r e l a t i o n w i l l depend on the t e s t parameters, i . e . , the p a r t i c u l a r combination of c o a l type and type of heavy metal i n the i n f l u e n t . 4.10 Breakthrough Curves f o r Mercury Figure 4.11 shows p l o t s of e f f l u e n t c o n c e n t r a t i o n of mercury versus volume of l i q u i d t r e a t e d . The i n f l u e n t c o n c e n t r a t i o n of mercury i s shown as a s e r i e s of exponential curves j o i n e d by v e r t i c a l l i n e s . The i n f l u e n t c o n c e n t r a t i o n i s at 5 yg/£ when a new batch of i n f l u e n t i s made and put i n t o the system. But the next day, about 6 hours before r e f i l l i n g the system w i t h 5 yg/A Hg, the i n - f l u e n t i n the system was t e s t e d and found to be 2.1 yg/& Hg. This i n d i c a t e s t h a t the mercury had v o l a t i l i s e d overnight from 5 ug/£ to 2.1 yg/£. For l a c k of more AVERAGE INFLUENT = 3.lOug/1 Hg INFLUENT — pH =7.5 COAL WEIGHT •I 1 1 1- 1 1 1 1—H 1 1 1 1 • ' 1 : • 0 I 2 3 4 5 6 7 8 9 10 15 20 25 30 VOLUME OF LIQUID TREATED (Litres) 85 data, t h i s d e t e r i o r a t i o n of the i n f l u e n t c o n c e n t r a t i o n i s assumed to be exponential and, t h e r e f o r e , represented by exponential decay curves. When a new batch of 5 yg/& i n f l u e n t enters the system, the i n f l u e n t c o n c e n t r a t i o n shoots back up to 5 yg/£ and t h i s moment i s represented by the v e r t i c a l l i n e s j o i n i n g the exponential curves. Sigworth and S m i t h ^ ^ mentioned a s i m i l a r f l u c t u a t i o n of the i n f l u e n t c o ncentration i n adsorption systems of a c t i v a t e d carbon and methyl mercury c h l o r i d e i n f l u e n t s . For purposes of c a p a c i t y c a l c u l a t i o n s i f breakthroughs had been reached, 3.45 yg/£ would have been chosen as the average i n f l u e n t c o n c e n t r a t i o n f o r = t h e n t i m e F v a r i a t i o n l o f i n f l u e n t mercury assumed i n Figure 4.11. A column each f o r H.C. OX and CO:ASH was run at a pH of 7.5. The main o b j e c t i v e f o r running these two columns was to f i n d out the c a p a c i t i e s of the two coals f o r mercury i n the i n f l u e n t range of 5 yg/A and at near n e u t r a l pH of 7.5. The breakthroughs f o r both columns f a i l e d to occur even a f t e r a throughput of 30 l i t r e s . I t was decided to stop the runs r a t h e r than w a i t i n d e f i n i t e l y f o r the breakthroughs that showed no signs of approaching. Sigworth and S m i t h ^ reported a column t e s t i n v o l v i n g granular a c t i v a t e d carbon and methyl mercuric c h l o r i d e i n f l u e n t of 25 yg/£ which f a i l e d to show a breakthrough even a f t e r a throughput time of 3 months. According to the two authors, mercury was ca t e g o r i s e d as a metal of good adsorption p o t e n t i a l . Lead was a l s o c l a s s e d as good but a l i t t l e below mercury. Copper was cla s s e d as a metal of s l i g h t a d sorption p o t e n t i a l and z i n c was a l s o i n the s l i g h t category but below copper. Since F i g u r e 4.11 shows two h o r i z o n t a l l i n e s f o r the e f f l u e n t con- c e n t r a t i o n s of the two columns without any hi n g of breakthroughs, the c a p a c i t i e s at p a r t i c u l a r breakthrough concentrations cannot be c a l c u l a t e d . I t can be noted, however, that the percent removal of mercury i s 75; percent i n the case of CO:ASH 86 and 90 percent i n the case of H.C. OX. The percent removals were based on the average i n f l u e n t c o ncentration of 3.1,. .ug/&. The e f f l u e n t from the H.C. OX column has an average of 0.3 ug/£ and t h i s c o n c e n t r a t i o n i n the e f f l u e n t stayed almost constant w i t h i n c r e a s i n g throughput. The e f f l u e n t from the C0:ASH column e x h i b i t e d the same s o r t of behavior w i t h an average e f f l u e n t concentration of 0.8 pg/£. I t i s suspected that the reason f o r the e f f l u e n t c o n c e n t r a t i o n never being at 0.0 yg/& even at the beginning of the run may be due to the extremely low d r i v i n g f o r c e of 3.45 ug/£ i n f l u e n t c o n c e n t r a t i o n . This may make i t very hard f o r the adsorbent to t o t a l l y adsorb the mercury "even when the adsorbent i s h i g h l y unsaturated at the beginning of the t e s t . 4.11 Column Tests - Summary and Conclusions Conclusions drawn from the i n v e s t i g a t i o n s c a r r i e d out i n the Column Tests are as f o l l o w s : 1) No s i g n i f i c a n t change i n c a p a c i t y occurs by v a r y i n g the c r o s s - s e c t i o n a l area of the c o a l bed w i t h i n the range of 0.001 ft 2 - 0 . 0 0 2 f t 2 . The 28/48 s i z e f r a c t i o n has an average diameter of 0.7 mm. The c o a l bed c r o s s - s e c t i o n a l area of 0.001 f t 2 has a diameter of 10.9 mm, which i s 16 times bigger than 0.7 mm. S i m i l a r l y , c r o s s - s e c t i o n a l area of 0.002 f t 2 corresponds to a diameter of 15.4 mm, which i s 22 times greater than the average p a r t i c l e diameter. For p a r t i c l e s shaped as those of 28/48 c o a l , the w a l l e f f e c t would most probably set i n i f the column diameter were l e s s than about 10 times the average p a r t i c l e diameter. Therefore, the use of columns s m a l l e r than those s e l e c t e d f o r t h i s work would run the r i s k of p r o v i d i n g u n r e a l i s t i c r e s u l t s . 2) A d e f i n i t e decrease i n adsorptive c a p a c i t y i s evident w i t h decreasing i n f l u e n t pH. The percent decrease i n cap a c i t y f o r a 87 given decrease i n pH i s approximately the same f o r both H.C. OX and CO:ASH w i t h z i n c i n f l u e n t s . Since the pH of the i n f l u e n t i s a c r i t i c a l f a c t o r i n determining the adso r p t i v e c a p a c i t y , s p e c i a l emphasis should be l a i d on the i n v e s t i g a t i o n of more d e t a i l e d r e l a t i o n s h i p s between pH and ca p a c i t y i n f u t u r e research of t h i s type. Of a l l the t e s t parameters w i t h the exception of c o a l type, the i n f l u e n t pH i s the most c r u c i a l as f a r as adso r p t i v e c a p a c i t y i s concerned. A decrease i n pH means a decrease i n c a p a c i t y . Therefore, f o r a c i d i c wastes, such as c e r t a i n i n d u s t r i a l wastes, some form of pre-treatment to r a i s e the pH before passing the wastes through the c o a l column may be an important c o n s i d e r a t i o n . 3) As the flow r a t e was increased from 1 Igpm/ft 2 to 5 Igpm/ft 2, a corresponding decrease i n adsorptive capacity was n o t i c e d . This decrease was h i g h l y s i g n i f i c a n t when the flow r a t e was increased from 1 to 3 Igpm/ft 2. On f u r t h e r i n c r e a s i n g the r a t e by another 2 Igpm/ft 2 to 5 Igpm/ft 2, the corresponding decrease i n c a p a c i t y was much sm a l l e r than the previous one. This suggests the r e l a t i v e ease of changing the r a t e from 3-5 Igpm/ft 2, should occasion demand i t , without s u f f e r i n g s i g n i f i c a n t decreases i n ca p a c i t y . -The percent decreases i n c a p a c i t y , due to i n c r e a s i n g flow r a t e , become lessmail'ef.ess at higher breakthrough concentrations. Thus, the choice of whether to use a higher flow r a t e or b u i l d a t h i c k e r column i s al s o i n f l u e n c e d by the p e r m i s s i b l e breakthrough c o n c e n t r a t i o n which would be set by the l o c a l r e g u l a t o r y agency. 4) Whether the c a p a c i t y would decrease or increase upon lowering 88 the i n f l u e n t c o n c e n t r a t i o n was found to depend on the i n f l u e n t pH and on the type of c o a l . At a pH of 4.0, the general trend i s a decrease i n c a p a c i t y on lowering the i n f l u e n t c o n c e n t r a t i o n . At a pH of. 5.7, the type of c o a l used determines the d i r e c t i o n of change of capacity w i t h decreasing i n f l u e n t c o n c e n t r a t i o n . This i n d i c a t e s the p o s s i b i l i t y of combining waste streams to lower the i n f l u e n t concen- t r a t i o n of the waste components w i t h the aim of r a i s i n g the a d s o r p t i v e c a p a c i t i e s . Of course, t h i s s o r t of d i l u t i o n before treatment would p e r t a i n only to cases where the adsorbent - pH combination favours an increase i n c a p a c i t y on lowering the i n f l u e n t c o n c e n t r a t i o n . The percent decrease i n c a p a c i t y due to a decrease i n pH i s more pronounced at lower i n f l u e n t concentrations. Consequently, more a t t e n t i o n w i l l have to be p a i d to pH c o n d i t i o n s of waste streams of lower i n f l u e n t c o ncentrations. 5) The c a p a c i t y increases as the i n f l u e n t pH increases from 3.0 to 5.7. The highest c a p a c i t i e s a r r i v e d at i n t h i s research were those corresponding to a pH of 5.7. TABLE 4.12 l i s t s the c a p a c i t i e s f o r z i n c , copper and l e a d to 10 percent breakthrough c o n c e n t r a t i o n , where i n f l u e n t pH and c o n c e n t r a t i o n i s 5.7 and 2 mg/£, r e s p e c t i v e l y , and the flow r a t e i s 1 Igpm/ft 2. " '.iaiUnder; the same :conditions, but w i t h an i n f l u e n t pH of 4.0, the r a t i o of c a p a c i t i e s f o r z i n c : copper : l e a d i s equal to 1 : 6 : 12 f o r CO:ASH c o a l . The high capacity f o r l e a d may be p a r t l y due to the f a c t that lead has a high atomic weight. This order of magnitude of a d s o r p t i v e c a p a c i t i e s f o r the three metals i s i n agreement w i t h the r e s u l t s of the Batch Tests. 89 TABLE 4.12 CAPACITIES AT A pH OF 5.7 AND AT A BREAKTHROUGH CONCENTRATION OF 10 PERCENT OF INFLUENT CONCENTRATION CAPA Zn mg/gm CITIES mg/g Cu mg/gm m Pb mg/gm CO:ASH 0.370 1.182 — H.C. OX 9.716 12.396 — Note: 1) Capacity; x>f H.C. OX f o r copper i s shown i n i t a l i c s s i n c e t h i s f i g u r e i s only an estimate and not a r r i v e d at experimentally (S e c t i o n 4.5) 2) The c a p a c i t i e s f o r lead are undetermined s i n c e the runs were stopped before the occurrence of break- throughs (S e c t i o n 4.7) 6) From column t e s t s at a pH of 4.0 wi t h i n f l u e n t s c o n t a i n i n g 2 mg/£ each of z i n c , copper and l e a d , the adsorptive c a p a c i t i e s of DARCO A c t i v a t e d Carbon are i n the same range as those of CO:ASH. The c a p a c i t i e s of H.C. OX are much higher than those of the a c t i v a t e d carbon or C0:ASH. With regard to z i n c and copper, H.C.OX i s 12 times higher i n c a p a c i t y than C0:ASH. In the case of l e a d , H.C. OX d i s - played a cap a c i t y 4 times that of CO:ASH. There i s a mutual i n h i b i t i o n of adsorption when there i s more than one heavy metal i n the i n f l u e n t . Although the adso r p t i v e c a p a c i t y decreases f o r each i n d i v i d u a l metal when the i n f l u e n t i s a mixture rathernthan a s i n g l e s o l u t e s o l u t i o n , the t o t a l c a p a c i t y f o r heavy metals achieved w i t h mixed i n f l u e n t s i s higher than any of the i n d i v i d u a l c a p a c i t i e s encountered w i t h s i n g l e s o l u t e i n f l u e n t s . This suggests the p o s s i b i l i t y of combining waste streams, c o n t a i n i n g 90 different heavy metals, before passing them through the adsorption column. Such a procedure would result in a higher total capacity of the coal than would be achieved i f the individual streams were passed through separate columns. 7) An attempt was made to correlate the effluent pH with the metal concentration in the effluent. It was found that the effluent pH is generally around 6.0 at the beginning of each column test, and decreases with column age unt i l the effluent pH reaches that of the influent when column exhaustion has occurred. The chances of a correlation between effluent pH and effluent metal concentration increase with decreasing pH of the influent. In other words, the correlation is more evident when the influent pH i s farther away from 6.0. At an influent pH of 5.7, there was no correlation. At an influent pH of 4.0, the occurrence of a correlation depended on the combination of coal type and type of heavy metal in the influent. And at an influent pH of 3.0, the correlation was pronounced. For columns where this correlation exists, a saving in time and expenses may be realised by using a pH meter instead of other sophisticated equipment that i s more expensive and cumbersome. 8) The tests with mercury proved to be somewhat d i f f i c u l t . The influent concentration of mercury deteriorated with time. Thus, for column capacity calculation purposes, the original influent concen- tration of 5 yg/Jt could not be used as a base, but rather, an average influent concentration over the period of the test had to be deter- mined. Capacities could not be calculated since the runs were stopped before breakthroughs occurred. It might have taken intolerably long periods of time for breakthroughs to have occurred. The presence of 91 mercury i n the e f f l u e n t was detectable even at the very beginning of each column t e s t . The e f f l u e n t c o n c e n t r a t i o n was 0.3 ug/£ and 0 . 8 u g / £ f o r H.C. OX and CO:ASH, r e s p e c t i v e l y , r i g h t from the beginning to the end of the t e s t s . This gives a percent removal, based on the average i n f l u e n t c o n c e n t r a t i o n of 77 percent f o r C0:ASH and 91 percent f o r H.C. OX. For f u t u r e research w i t h mercury, a more s t a b l e form or complex of mercury should be used i n s t e a d of H g C^j which was used i n t h i s research. Using a more s t a b l e complex of mercury, p r e f e r a b l y a type of complex found i n sewage, would e l i m i n a t e the problem of the d e t e r i o r a t i n g c o n c e n t r a t i o n of mercury when running column t e s t s w i t h i n f l u e n t s of extremely low mercury concentrations. 92 Chapter 5 RECOMMENDATIONS Based on t h i s research and other works done on the adsorption of heavy metals by granular c o a l s , f u r t h e r research i s i n d i c a t e d : - 1) Since H.C. OX i s f a r s u p e r i o r than the other types of c o a l t e s t e d , f i r s t p r i o r i t y should be given to t h i s c o a l f o r use as an adsorbent i n an advanced waste treatment process. 2) Attempts should be made to grow some c u l t u r e s of the fungus, mentioned i n t h i s t h e s i s , so that fungal spores could be obtained f o r an exact i d e n t i f i c a t i o n of the fungus. Research should a l s o be done on the i n v e s t i g a t i o n of the heavy metal removal mechanism of the fungus. Is the heavy metal being converted i n t o some form of a s a l t c r y s t a l and entrapped i n the mycelium, or i s i t simply being adsorbed by the mycelium, are questions of high i n t e r e s t . 3) More d e t a i l e d a n a l y s i s on the c o r r e l a t i o n between e f f l u e n t pH and metal c o n c e n t r a t i o n i n the e f f l u e n t should be done w i t h columns where the i n f l u e n t pH i s l e s s than 4.0. There i s no c o r r e l a t i o n when the i n f l u e n t pH i s above 4.0. (Refer to S e c t i o n 4.9) 4) For f u t u r e research w i t h mercury i n f l u e n t s , a more s t a b l e complex of mercury should be used. This i s to overcome the problem of d e t e r i o r a t i n g i n f l u e n t c o n c e n t r a t i o n experienced i n t h i s research, where HgC^ was used as an i n f l u e n t . 5) Removal of heavy metals i n s o l u t i o n using granular coals should be f u r t h e r i n v e s t i g a t e d w i t h organics present i n the waste s o l u t i o n . The goal of t h i s i n v e s t i g a t i o n should be to determine the removal e f f i c i e n c i e s at low heavy metal concentrations from a r e a l m unicipal sewage. 93 6 ) The p o s s i b l e use o f g r a n u l a r c o a l as a f u e l s o u r c e , a f t e r h a v i n g used i t as an a d s o r b e n t , s h o u l d be i n v e s t i g a t e d . Should t h i s p o s s i b i l i t y p r o ve t o be f e a s i b l e , t h e n t h i s advanced waste treatment system u s i n g g r a n u l a r c o a l s may b e - e c o n o m i c a l l y s u p e r i o r t o o t h e r treatment systems. Having a power p l a n t c l o s e by the treatment f a c i l i t y would h e l p the economic p i c t u r e tremendously. Should H.C. OX be chosen as the adsorbent m a t e r i a l , i t s h o u l d f i r s t be shown t h a t H.C. OX p o s s e s s e s the r e q u i r e d p r o p e r t i e s needed f o r use as a s a t i s f a c t o r y f u e l c o a l . 7) The f i n a l s t e p taken s h o u l d be to i n v e s t i g a t e where the adsorbed heavy metals would end up when the c o a l i s burned as a f u e l . I f they s t a y down w i t h the ash, then a l a n d f i l l w i t h the n e c e s s a r y p r e c a u t i o n s t o p r e v e n t l e a c h i n g would be t h e i r f i n a l d e s t i n a t i o n . I f they f l y up the s t a c k , then s p e c i a l a i r p o l l u t i o n c o n t r o l measures may have t o be under t a k e n . BIBLIOGRAPHY Culp, R.L. and Culp, G.L., 1971. "Advanced Wastewater Treatment". E c k e n f e l d e r , J r . , W.W. , 1966. "Industrial Water Pollution Control". McGraw-Hill S e r i e s i n S a n i t a r y Science. Hendren, M.K., 1974. "Coal Treatment of Wastewaters". Thesis f o r Master of A p p l i e d Science, C i v i l E ngineering, U n i v e r s i t y of B r i t i s h Columbia. Leonard, J.W. and M i t c h e l l , D.R., 1968. "COAL Preparation". Seeley W. Mudd S e r i e s . M e t c a l f & Eddy Inc., 1972. "Wastewater Engineering". McGraw-Hill S e r i e s i n Water Resources and Environmental Engineering. Netzer, A. and Norman, J.D., 1972. "Removal of Trace Metals from Wastewater by Activated Carbon". MfcMaster U n i v e r s i t y , Wastewater Research Group - Report 72-305-1. Shannon, E. and S i l v e s t o n , P., "Studies on the Use of Coal for Waste Treatment"3 Water - 1968, Chemical Eng. Progress Symposium S e r i e s , pp. 198-206. Sigworth, E.A. and Smith, S.B., 1972. Adsorption of Inorganic Compounds by Activated Carbon.- J o u r n a l AWWA, 64-386. Vermeulen, T., 1958. Separation by Adsorption Methods. Advanced Chemical Engineering 2:147. Weber, W.J., 1972. "Physicochemical Processes for Water Quality Control" - W i l e y - I n t e r s c i e n c e . Weber, W.J. and M o r r i s , J . C , 1964. Equilibria and Capacities for Adsorption on Carbon. Amer. Soc. C i v i l Engs., S a n i t a r y D i v . , 90 (SA3):79. Wenzel, L.A. et a l . , 1959. "Principles of Unit Operations". John Wiley & Sons, Inc. "Development of a Coal Based Sewage Treatment Process"3 O f f i c e of Coal Research, U.S. Dept. of the I n t e r i o r , U.S. Government P r i n t i n g O f f i c e , Washington, D.C. (1972).

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