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Removal of heavy metals using granular coal Riaz, Muhammad 1974

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REMOVAL OF HEAVY METALS USING GRANULAR COAL by MUHAMMAD RIAZ B.Sc., Lyallpur University, Pakistan, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of Civil Engineering We accept this thesis as conforming to the required standard: THE UNIVERSITY OF BRITISH COLUMBIA August, 1974 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t  o f the r e q u i r e m e n t s  f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I agree t h a t t he 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  and s t u d y . I f u r t h e r  agree 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 pu rposes may be g r a n t e d by the Head o f my Depar tment 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 no 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 . Depar tment o f Civi l Engineering The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8 , Canada Date August 1 9 , 1974 ABSTRACT In view of very high toxicity potential of some heavy metals to aquatic life, there is a need for critical evaluation of known methods and development of new methods for purifying water and waste-water containing heavy metals. In this study, batch tests were performed to evaluate the relative efficiencies of six British Columbia coals in removing heavy metals (copper, lead, mercury and zinc) from water. On the basis of batch test data obtained, the best two coals, Kaiser Coal-Stock Pile Refuse and Kaiser Coal-Special Plant Feed, were tested on a continuous flow laboratory scale. The emphasis was placed on metal concentrations of 2 mg/1 and less for copper, lead and zinc and 5 vg/1 for mercury. The effects of adsorbate concentration, flow rate through the column (contact time), and pH of the solution on the adsorptive capacity of coal were investigated. A solution containing 0.5 mg/1 of each of copper, lead and zinc was tested to investigate the ability of the coal to remove metals from a mixture of many metals. The adsorptive capacity of the best two coals was also compared with some commercially available adsorbents. On the basis of capacity and rate of adsorption, Kaiser Coal-Stock Pile Refuse was found to be the best of the six coals tested. For the specific testing conditions in this investigation, the better metal-removing efficiency of coal as compared with activated carbon and nitrohumic acid indicate that the coal may be a feasible alternate to purify effluents containing heavy metals TABLE OF CONTENTS Page LIST OF TABLES v LIST OF FIGURES vi ACKNOWLEDGEMENT ix CHAPTER 1 INTRODUCTION 1 CHAPTER 2 RESEARCH RATIONALE 6 2.1 Heavy Metals - a Problem 6 2.1.1 Heavy Metals Sources 6 2.1.2 Heavy Metals Toxicity 9 2.2 Removal of Heavy Metals 12 2.2.1 Biological Treatment 12 2.2.2 Chemical Treatment 15 2.2.3 Carbon Adsorption 15 2.2.4 Granular Coal 18 2.3 Choice of Research Process 19 CHAPTER 3 MATERIAL AND PROCEDURE 21 3.1 Types of Coal 21 3.2 Coal Preparation 21 3.3 Synthetic Wastewater 23 3.4 Measurement of Concentration 24 3.5 Batch Testing Procedure 24 3.5.1 Contact Time 26 3.5.2 Amount of Coal 26 3.5.3 Adsorption Isotherms 34 3.6 Column Testing Procedure 36 3.6.1 Column Setup 36 3.6.2 Experimental Procedure 39 Page CHAPTER 4 RESULTS AND DISCUSSIONS 40 4.1 Batch Tests 40 4.1.1 Capacity of Coals 40 4.1.2 Ranking of the Coals 49 4.1.3 Effect of pH 53 4.1.4 Comparison of Coal with Other Adsorbents 53 4.2 Column Tests 65 4.2.1 Removal of Metals 67 4.2.2 Effect of Adsorbate Concentration on Column Efficiency 74 4.2.3 Effect of Flow Rate (Contact Time) on Column Efficiency 77 4.2.4 Effect of Solution pH on Column Efficiency 80 4.2.5 Removal of Mixed Metals 82 CHAPTER 5 CONCLUSIONS 92 REFERENCES 97 APPENDIX I COLUMN BREAKTHROUGH CURVES 99 APPENDIX II SAMPLE CALCULATIONS 108 LIST OF TABLES OBJECTIVES FOR EFFLUENT DISCHARGES -MINING, MINE-MILLING, SMELTING AND ASSOCIATED INDUSTRIES HEAVY METALS LOADS BY SELECTED COMMUNITIES SOLUBILITY PRODUCTS OF CATIONIC HEAVY METAL OXIDES OR HYDROXIDES LIME COAGULATION AND RECARBONATION ANALYSIS AND RANKS OF KAISER COAL SAMPLES SYNTHETIC WASTEWATER USED FOR EACH METAL STANDARDIZED INSTRUMENT PARAMETERS FOR DIFFERENT METALS LIST OF FIGURES Figure Page 3.1 EFFECT OF CONTACT TIME ON ADSORPTION 27 3.2 EFFECT OF CONTACT TIME ON ADSORPTION 28 3.3 EFFECT OF COAL DOSAGE ON ADSORPTION OF COPPER 29 3.4 EFFECT OF COAL DOSAGE ON ADSORPTION OF COPPER 30 3.5 EFFECT OF COAL DOSAGE ON ADSORPTION OF ZINC 31 3.6 EFFECT OF COAL DOSAGE ON ADSORPTION OF LEAD 32 3.7 EFFECT OF COAL DOSAGE ON ADSORPTION OF MERCURY 33 3.8 SCHEMATIC DIAGRAM OF COLUMN SETUP 38 4.1 ADSORPTION ISOTHERMS FOR COPPER 41 4.2 ADSORPTION ISOTHERMS FOR COPPER 42 4.3 ADSORPTION ISOTHERMS FOR LEAD 44 4.4 ADSORPTION ISOTHERMS FOR LEAD 45 4.5 ADSORPTION ISOTHERMS FOR ZINC 47 4.6 ADSORPTION ISOTHERMS FOR ZINC 48 4.7 ADSORPTION ISOTHERMS FOR MERCURY 50 4.8 ADSORPTION ISOTHERMS FOR MERCURY 51 4.9 EFFECT OF pH ON ADSORPTION OF COPPER 54 4.10 EFFECT OF pH ON ADSORPTION OF LEAD 55 4.11 EFFECT OF pH ON ADSORPTION OF ZINC 56 4.12 EFFECT OF pH ON ADSORPTION OF MERCURY 57 Figure 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 44.24 4.25 4.26 4.27 4.28 4.29 Page ADSORPTION ISOTHERMS FOR COPPER 60 ADSORPTION ISOTHERMS FOR LEAD 61 ADSORPTION ISOTHERMS FOR MERCURY 62 ADSORPTION ISOTHERMS FOR ZINC 63 BREAKTHROUGH CURVES FOR ZINC 66 ADSORPTION CAPACITY OF COAL FOR COPPER 68 ADSORPTION CAPACITY OF COAL FOR LEAD 70 ADSORPTION CAPACITY OF COAL FOR ZINC 71 ADSORPTION CAPACITY OF COAL FOR MERCURY 73 EFFECT OF ADSORBATE CONCENTRATION ON CAPACITY OF COAL 75 EFFECT OF FLOW RATE ON COLUMN BREAK-THROUGH CURVES FOR ADSORPTION OF COPPER WITH STOCK PILE REFUSE COAL 78 EFFECT OF FLOW RATE ON ADSORPTION CAPACITY OF COAL 79 EFFECT OF pH ON ADSORPTION OF ZINC IN A COLUMN OF GRANULAR COAL 81 BREAKTHROUGH CURVES FOR COPPER, LEAD AND ZINC MIXTURE WITH STOCK PILE REFUSE COAL 83 BREAKTHROUGH CURVES FOR COPPER, LEAD AND ZINC MIXTURE WITH SPECIAL PLANT FEED SAMPLE 84 COMPARISON OF COAL CAPACITY FOR REMOVING METALS FROM SOLUTION OF INDIVIDUAL METALS AND THEIR MIXTURE FOR STOCK PILE REFUSE COAL 85 BREAKTHROUGH CURVES FOR ZINC AND COPPER FROM THEIR PURE SOLUTIONS AND FROM THE MIXTURE OF METALS WITH STOCK PILE REFUSE COAL 86 TOTAL ADSORPTION CAPACITY OF COAL (mg of metal/g) WITH SOLUTIONS CON-TAINING MIXTURE OF METALS AND INDIVIDUAL METALS FOR STOCK PILE REFUSE COAL TOTAL ADSORPTION CAPACITY OF COAL (y mole of metal/g) WITH SOLUTIONS CONTAINING MIXTURE OF METALS AND INDIVIDUAL METALS FOR STOCK PILE REFUSE COAL BREAKTHROUGH CURVE FOR COPPER, LEAD AND ZINC MIXTURE WITH DARCO ACTIVATED CARBON ACKNOWLEDGEMENT I am deeply grateful to my supervisor, Dr. W.K. Oldham, for his guidance during the preparation and completion of this study. His criticism and suggestions were of the utmost importance and are sincerely appreciated. This manuscript could not have been completed without the assistance of a number of individuals. Miss Gloria Reed cheerfully spent many hours in typing the manuscript. To all those, who gave of their time so willingly, I express deep gratitude. This investigation was supported by the Pollution Control Branch of the Department of Lands, Forests and Water Resources of the Province of British Columbia. Chapter I INTRODUCTION Considerable interest is currently being shown regarding metals concentration in both receiving waters and wastewater effluents. The publicity on mercury contamination of fish and the subsequent health hazards has focused attention on the pollution potentials of other heavy metals. The following metals have been identified as having very high or high pollution potential (1, 5). 1. Very high pollution potential Silver Lead Gold Antimony Cadmium Tin Chromium Selenium Copper Zinc Mercury Nickel 2. High pollution potential Barium Molybdenum Bismuth Titanium Iron Uranium Manganese There is growing concern about the preservation of the environment in British Columbia. Increasing population, industrial growth, and public pressure are forcing the Province to enact stricter pollution control standards for industrial and municipal effluent discharges. The suggested maximum metal concentration for effluent discharges from mining, mine milling, smelting and associated industries to any body of marine or fresh water is shown in Table I. These strict standards have uncovered the need for critical evaluation of heavy metals removal efficiencies of existing, and development of new, advanced water and wastewater treatment processes. For many years, crushed anthracite coal-has been used as a filtering medium for water supplies. Only during the past decade, however, has the use of coal as an adsorbent for purifying wastewater been examined. Most of the research has been directed towards the removal of organics from domestic sewage. These research programs were initiated with the idea that low fuel value coals could be used for purifying wastewater and still be useful as an energy source. A U.S. Department of Interior report (20) recommends the use of coal for post, or "tertiary" treatment of secondary sewage plant effluent. The ability of certain British Columbia coals to remove dis-solved constituents from water has been the subject of much discussion and many claims. Both batch and laboratory scale column tests on the capa-bility of coal for removing heavy metals from water have been reported (8,12) and seem encouraging. However, most of the experiments had been performed at relatively high metal concentrations and were limited to only two coals found in British Columbia. Therefore, nothing can be said about the effectiveness of coal to remove heavy metals at trace levels. There is, therefore, a need for more investigation with emphasis on low metal concentration. In this study, the emphasis has been placed on concentrations of 2 mg/1 and less for metals such as copper, lead and TABLE I OBJECTIVES FOR EFFLUENT DISCHARGES - MINING, MINE-MILLING, SMELTING AND ASSOCIATED INDUSTRIES Specific elements and Material contained in the effluent, at Marine water compounds*** the point of discharge, which passes discharge an approved 0.45 micron pore-sized mg/1 filter. (Except where total values are required) Aluminum (Al) Dissolved in the effluent 0.50 1.00 10.0 0.50 1.00 10.0 Ammonia as N it II ii n 0.50+ 1.00 10.0 0.50+ 1.00 10.0 Antimony (Sb) ii II ii n 0.05 0.25 1.00 0.05 0.25 1.00 Arsenic (As) ii ii ii ii 0.05 0.25 1.00 0.05 0.25 1.00 Cadmium (Cd)tt ii II ii ii 0.005 0.01 0.02 0.005 0.01 0.02 Chromium (Cr) Dissolved in the effluent 0.05 0.30 0.50 0.05 0.30 0.50 Cobalt (Co) II II M II 0.10 0.50 1.00 0.10 0.50 1.00 Copper (Cu) II II ii II 0.05 0.30 1.00 0.05 0.30 1.00 Cyanide (CN) Total Cyanide : in the effluent 0.10 0.50 2.00 0.10 0.50 2.00 Fluoride (F) Dissolved in the effluent 2.50 5.00 15.0 2.50 5.00 15.0 Iron (Fe) ii II ii ii 0.30 1.00 5.00 0.30 1.00 5.00 Lead (Pb) ii II ii ii 0.05 0.10 0.50 0.05 0.10 0.50 Manganese (Mn) ii II II II 0.05 0.50 1.50 0.05 0.50 1.50 Magnesium (Mg) ii II II ii 150 300 500 Mercury (Hg) Total in the effluent O.OOlt 0.003 0.01 0.001+ 0.003 0.01 Molybdenum (Mo) Dissolved in the effluent 0.50t 1.00 10.0 0.50+ 1.00 10.0 Nickel (Ni) ii ii II ii 0.30 0.50 1.00 0.30 0.50 1.00 Fresh water discharge mg/1 u> Nitrates/Nitrites (as N) " " 10.0 25 50 10.0 25 50 Phosphate (as P) Total In the effluent 2.00 5.00 10.0 2.00 5.00 10.0 Selenium (Se) Dissolved in the effluent 0.05 0.10 1.00 0.05 0.10 1.00 Silver (Ag) " " 0.10 0.50 1.00 0.10 0.50 1.00 Sulphate (S04> " " " " 50t 250 1000 Uranyl (U02) " " " " 2.00 5.00 10.0 2.00 5.00 10.0 Zinc (Zn) ^ " 0.50 5.00 10.0 0.50 5.00 10.0 Note 1 - Acceptable concentrations for characteristics not appearing in this list are to be determined as required. Note 2 - When all liquids are totally recycled, the applicability of the above objectives will be assessed. *** Initially, semi-quarterly sampling on effluents and at control and test stations in receiving waters; quarterly sampling on effluent discharged to closed systems. t Tentative, subject to review. ++ Subject to review where applied to smelters. -p-zinc and 5 yg/1 for mercury. The specific objectives of the investiga-tion were: 1) to perform batch tests, for quantitative evaluation of the relative efficiencies of six different B.C. coals in removing heavy metals from water; 2) to evaluate the heavy metals removal capacity of the best two coals on a continuous flow laboratory scale; 3) to evaluate the effect of pH on the adsorption capacity of coal for different metals; 4) to evaluate the effect of adsorbate concentration on the adsorption capacity of coal under dynamic flow conditions; 5) to evaluate the effect of flow rate (contact time) in the granular coal column on the removal of metals; 6) to evaluate the removal of metals from a solution containing mixture of metals under dynamic flow conditions; 7) to compare the metal -removing capacity of coal with some of the other potential adsorbents. Chapter 2 RESEARCH RATIONALE 2.1 Heavy Metals - a Problem The heavy metals are of concern because of their high potential toxicity to various biological organisms at extremely low concentrations. While many of these metals are associated with particular industrial effluents, there is quite a high background concentration of some of these in variety of other waters and wastewaters. 2.1.1 Heavy Metals Sources In a U.S. Environmental Protection Agency survey (15), the concentrations of zinc, copper, lead, nickel, mercury and chromium were determined in samples collected from street surfaces in many cities. The results of the survey are shown in Table II. The fact that the weighted average of the total heavy metals is as high as 1.6 pounds per curb mile is rather alarming. Considering that the subject of individual heavy metal's effects on the environment is only slightly understood at best, and considering further that so little conclusive work has been done regarding the synergistic effects of combinations of metals, there is every reason for concern over the high quantities reported. Another thing to note is that, from the standpoint of concentration alone, zinc and lead have the heaviest loading and the trends are born out in all the cities tested. Such trends were also found by Hendren and Oldham (11) in a storm sewer discharge study of Okanagan Valley cities in British Columbia. The study findings were as follows: TABLE II HEAVY METALS LOADS BY SELECTED COMMUNITIES (lb/curb mile) (15) TOTAL CITY CHROMIUM COPPER ZINC NICKEL MERCURY LEAD CADMIUM HEAVY M San Jose I 0.20 0.50 1.4 0.13 0.30 1.9 0.0033 4.5 San Jose II 0.14 0.02 0.28 0.085 0.085 0.90 (0.0031) 1.5 Phoenix I - - - - - - - -Phoenix II 0.029 0.058 0.36 0.038 0.022 0.12 (0.0031) 0.63 Milwaukee 0.047 0.59 2.1 0.032 (0.082)a 1.5 0.0032 4.5 Baltimore 0.45 0.33 1.3 0.077 (0.082)a 0.47 0.0026 2.8 Seattle 0.081 0.075 0.37 0.028 0.034 0.50 (0.0031) 1.09 Atlanta 0.011 0.066 0.11 0.021 0.023 0.077 (0.0031) 0.31 Tulsa 0.0033 0.032 0.062 0.011 0.019 0.030 (0.0031) 0.16 Bucyrus - - - - - - - -Weighted Average 0.11 0.20 0.65 0.05 0.073 0.57 1.6 Notes: a) Estimated values b) Estimates based on other observations. 1) Concentrations of total unfiltered heavy metals (As, Cd, Cu, Hg, Ni, Pb, Zn) ranged from 0.02 to 17.5 ppm. 2) Concentration of dissolved heavy metals ranged from 0.01 to 14.2 ppm. 3) Metals of highest concentrations were lead and zinc followed by copper. Zinc concentration in Vernon storm water was as high as 14 ppm. 4) Arsenic, cadmium, nickel and mercury were present in very small amounts. Together they comprised less than 5 percent of the total heavy metal concentration. Since the discovery of mercury levels as high as 7 rag/1 (9) in fish taken from Lake St. Clair during early 1970, various agencies throughout Canada and the United States have moved quickly to identify and halt all known sources of direct mercury pollution into the aquatic ecosystem. As a result during the three months of the summer of 1970, all industrial plants reduced their discharge by 85 percent, from 285 to 40 pounds per day (6). However, because of the inherent nature of the mercury to accumulate, even with a total ban on mercury, water would still receive 50% (6) as much mercury as before the ban by way of normal leaching from natural formations where it had accumulated. The following figures show the natural concentration of mercury in aquatic systems (6). Natural mercury - streams, rivers and lakes 0.03 ppb oceans 0.03-5 ppb In diet From natural background and environmental contamination 0.02-0.05 ppm Natural mercury - fish Max. 0.2 ppm Drinking water USPHS recommendation 0.005 ppm Mercury concentrations of 0.05 to,0.48 yg/1 have been reported (9) for rain water. A limited study of five municipalities in Central Illinois (10) revealed mercury concentrations in sewage ranging from 0.1 to 7.9 yg/1. The geometric mean of the total mercury concentration ranged from 1.3 to 1.8 yg/1. In all but one municipality, the industrial waste connec-tions to sewer systems were not significant. This suggests a back-ground concentration of mercury in public sewer systems solely devoid of industrial waste influence. A review of the literature indicates that lead, zinc and copper represent the greatest heavy metal loading in surface waters. The concentration of mercury is relatively low, but its inherent accumulative nature and multiplying effect in the food chain can have adverse effect on marine as well as human life. Therefore, these four metals: lead, copper, zinc and mercury, are considered to be of utmost concern in the aquatic environment. However, the lack of definitive information concern ing the individual toxic effects of other metals (particularly their synergistic effects with each other or other compounds) precludes an assumption that because other metals represent an insignificant amount of total heavy metal, they have no serious impact on receiving waters. 2.1.2 Heavy Metals Toxicity Concern over the toxicity of metals has developed because: 1) these elements are widely distributed throughout the environment 2) they are not degraded and hence persist in nature for extended periods of time; 3) generally, they are toxic to living organisms at fairly low concentrations; 4) they tend to be either biologically magnified or cumulative in plants and animals; and 5) certain metals can be converted to more toxic forms in the environment. The toxicity of the four heavy metals (Cu, Pb, Hg and Zn) of concern in this study is summarized in the following paragraphs. a) Copper In human and other higher organisms, copper is not particularly toxic. It does not exhibit biological magnification, as do many other heavy metals. USPHS drinking water standards limit copper to 1.0 mg/1. Recommended limits (15) for other uses are 0.1 mg/1 for irrigation water, 0.05 mg/1 for salt water organ-isms, and only 0.02 mg/1 for fresh water organisms. These values recognize the fact that copper is toxic to lower biological forms. Indeed, copper compounds are typically used in low concentrations to control aquatic weeds and algae.(15). b) Lead The effects of lead on biological.forms are quite varied. In vertebrate animals, lead is a cumulative poison which typically concentrates in bone. The tendency for accumulation is reflected in a long biological half-life in man of 1460 days (5). In humans, lead may cause brain damage, convulsion, behavioural disorders, and ultimately death (5). It is estimated (15) that humans consume about 0.3 mg daily in their diets. USPHS drinking water standards limit lead to 0.05 mg/1. At somewhat higher concentrations.it has been reported (15) to be moderately toxic to fish and other aquatic organisms. c) Mercury During the past 25 years, there have been two docu-mented occurrences of human mercury poisoning from eating con-taminated fish. Both incidents were in Japan, the first one being in Minamata in the early 1950*s and the second one in Niigata in 1965 (17). With respect to the toxicity of inorganic mercury in the form of mercuric ion, the reported studies (9) indicate that for short term exposures, the mercury concentrations in the range of 1 mg/1 are fatal to fish. For long term exposures of 10 days or more, mercury levels as low as 10 to 20 yg/1 have been found to be fatal to fish. While mercury concentrations greater than 10 -20 yg/1 can be toxic to aquatic organisms, sublethal levels are also absorbed and biologically magnified. It has been reported (9) that fresh water phytoplankton, macrophytes, and fish, potentially can have a magnification factor of 1000. USPHS drinking water standards limit mercury to 5 yg/1. d) Zinc Most common zinc compounds are not particularly toxic in low to moderate concentrations, nor are they particularly soluble in water. It is estimated (15) that people consume on the order of 10 to 20 mg of zinc daily in their diets. From the standpoint of water supplies, 5 mg/1 is the USPHS drinking water limit. Aquatic organisms are more sensitive than humans to zinc. Concentrations as low as 0.1 to 1.0 mg/1 have been found lethal to fish and other aquatic animals (15). Lethal threshold concentrations of copper, zinc and lead in Rainbow Trout in fresh water are reported (21) to be higher for higher values of hardness. Copper is reported (15) to have a synergistic effect with zinc toxicity. 2.2 Removal of Heavy Metals Some laboratory and pilot scale studies have been performed to evaluate the efficiencies of a wide range of waste-treatment processes to remove heavy metals (1, 2, 3, 4, 7, 8, 12, 13, 14). 2.2.1 Biological Treatment The removal of heavy metals during primary and secondary treatment can proceed by two mechanisms. 1) precipitation of metal hydroxides, which are removed with the sludges; 2) sorption of soluble trace metals by the sludges. The precipitation of metal hydroxides is governed by the concentration of the metal ion in solution and the pH. Generally, as the pH increases, the solubility of the metal hydroxide decreases. This relationship is expressed by the equation for the solubility product of a compound. [ M ^ ] [OH-]2 = K g p. = solubility product As the concentration of the hydroxyl ion increases with increasing pH, I j the concentration of M x must decrease for the solubility product to remain constant. The solubility products of several cationic heavy metal oxides and hydroxides are listed in Table III. Jenkins et al. (13) have reported the precipitation of copper, chromium, nickel and zinc by sewage. They found that within the concentration range of 0.5 - 100 mg/1 Cu, the percentage precipi-tated increased with the concentration of copper and decreased with decreasing pH. At 100 mg/1 Cu and with a contact period of 2 hours, 75 percent of the copper was precipitated, whereas with 10 mg/1 Cu 40 percent was precipitated. At pH 3, the maximum precipitated was only about 20 percent compared to 85 percent at pH 7 - 8. Soluble nickel salts were also precipitated by sewage, with removals ranging between 50 and 60 percent. A reduction in pH produced little"effect upon the precipitation of nickel. Soluble salts of zinc were precipi-tated by neutral sewage (pH = 7-8) to the extent of 60 percent at 100 mg/1 Zn, but increased to 80 percent at 10 mg/1 Zn. The efficiency of precipitation was reduced to 50 - 60 percent at pH 5 and less than 20 percent at pH 3. The precipitation of chromium (Cr+^) was dependent on the period of contact to a much greater extent than the other metals. At low concentration, 50 - 70 percent was precipitated at the 0.5 mg/1 chromium level in sewage for periods up to 24 hours, but instantaneous precipitation effected less than 20 percent removal. It appears that the removal of chromate in sewage depends upon the reduction of hexavalent chromium to the trivalent form and subsequent precipitation of trivalent chromium. Barth et al. (3) conducted pilot scale studies on the effect of heavy metals on biological treatment process and reported a material balance of the metals through an activated sludge process. They found TABLE III SOLUBILITY PRODUCTS OF CATIONIC HEAVY METAL OXIDES OR HYDROXIDES^1' Compound Ag20 Au(OH) Ba C03 A Ba SO. 4 Cd(OH)^ Cr(OH)^ Cu(OH)2 Fe (OH)^ Fe(OH)3 HgO Ni(OH)2 Pb20(OH)2 SnO Zn(OH) Solubility Product ,-8 2 x 10 -45 8.5 x 10 1.6 x 10"9 ,-10 1 x 10 2 x 10 1 x 10 3 x 10 -14 -30 -19 -15 1.8 x 10 .-38 6 x 10 3 x 10 - 2 6 2 x 10 - 6 -15 1.6 x 10 ,-61 1 x 10 3 x 10 -17 * Barium compounds that will form preferentially to the hydroxides in most waters. the average efficiencies of the process for removing the metals were 44, 75, 28 and 89 percent for hexavalent chromium, copper, nickel and zinc respectively. Each metal was studied in 5 concentration increments over the range of 1 to 20 mg/1. A survey of four municipal wastewater treatment plants was conducted by Barth et al. (4) and the distribution +6 of chromium (Cr ), copper, nickel and zinc through these plants indicated a satisfactory correlation with the pilot plant results. 2.2.2 Chemical Treatment Chemical treatment with lime results in a reduction of heavy metal concentrations, since many of the metals form insoluble metal hydroxides at high pH. It might be possible to reduce some of the metal concentrations below that predicted by the solubility products, because of adsorption of the metal ions by the chemical floe. Table IV shows the percentage removal of a number of different metals by lime coagulation treatment. For those metals where actual plant or good laboratory data were not available, the concentration reduction was estimated from solubility data. 2.2.3 Carbon Adsorption Activated carbon may be contacted with wastewater directly or following some pretreatment, depending on the characteristics of waste-water. Lindstedt and O'Connor (14) have reported that activated carbon caused a reduction of over 96% for cadmium, hexavalent chromium and silver. The cause of this is not known, but it appears possible that some of the organics in the wastewater stream serve as a co-adsorbate, TABLE IV LIME COAGULATION AND RECARBONATION (1) Concentration Concentration Before Treatment After Treatment Final Percent mg/1.. mg/1 pH Removal Metal Antimony Arsenic1 Barium1 Bismuth Cadmium Chromium (+6) Chromium (+3) Copper Gold Iron Lead Manganese Trace 0.0137 0.056 7,400 15,700 7 7 302 13 17 2.0 2.3 2.0 21.0 Mercury -1.3 (sol) 0.0002 (sol) 0.00075 0.050 2.7 0.79 1 0.05 Trace <.001 (sol) 2.4 0.1 1.23 <.0001 (sol)2 <0.1 l.l3 0.05 Oxide soluble 11 11 11 11 11 >11 >11 8.7 8.7 8 9.5 9.1 11 9.1 10.8 10.5 11 10.8 10.5 9.5 -90 <10 =50 94.5 11 99.9+ 99.9+ 86 93 99+ 90+ 82 99+ 40 90+ 96 45 95 <10 Table IV - Cont'd . . . . Metal Concentration Before Treatment mg/1 Concentration After Treatment mg/1 Final . pH Percent Removal Molybdenum Trace 8.2 =10 Nickel 160 0.08 8.7 99.9+ 5 0.5 8 90 5 0.5 9.5 90 100 1.5 10.0 99 Selenium 0.0123 0.0103 >11 16.2 Silver 0.0546 0.0164 >11 97 Telurium1'4 (<0.001?) 11 (?90+) Titanium1'4 (<0.001?) 11 (?90+) Uranium^ ? ? Zinc .007 (sol) 11 90+ NOTES: 1. The potential removal of these metals was estimated from solubility data. 2. Barium and lead reductions and solubilities are based upon the carbonate. 3. These data were from experiments using iron and manganese in the organic form. 4. Titanium and Telurium solubility and stability data made the potential reduction estimates unsure. 5. Uranium forms complexes with carbonate ion. Quantitative data were unavailable to allow determination of this effect. 6. Temperature; Ambient 20 - 25°C. linking the metal ions and the carbon. Hexavalent chromium adsorption on activated carbon has been studied on laboratory and pilot plant scale (7). At pH 2 - 3, removal was deemed effective. However no chromium reduction during carbon contact was realized for pH greater than three. Maximum adsorption was achieved in 10 minutes. On pilot plant level, adsorption and removal of hexavalent chromium was found to be greater than 99 percent in most of the runs. Argo and Culp (2) had evaluated the heavy metal removal efficiency of a pilot scale treatment system of lime coagulation and settling, mixed media filtration, and activated carbon adsorption. They found that the system was very effective in reducing the concentration of cadmium, hexavalent chromium, zinc and copper from a secondary waste treatment plant effluent, the average removal efficiency being 72, 78, 89 and 92 percent for copper, zinc, cadmium and hexavalent chromium respectively. 2.2.4 Granular Coal Recently, the possible use of granular coal for removing heavy metals from water and wastewater has been under investigation. Coulthard and Fadl (8) reported that Hat Creek coal* had a removal capacity of 21 mg Hat Creek coal is a lignite variety with low calorific value. of lead per gram of coal. Hendren (12) reported on the capability of ifk B.C. coals from Hat Creek and Crows Nest areas for removing lead, zinc and copper from water. He observed that by passing a solution containing as low as 0.7 mg/1 of copper through a granular coal column, the effluent concentration was not detectable (<0.05 mg/1) on an atomic absorption spectrophotometer. 2.3 Choice of Research Process Almost all the treatment processes reviewed in the previous section are still in the investigative stages at either laboratory or pilot plant scale. Each one has severe limitations of its own. Bio-logical treatment seems to be effective in reducing the concentration of heavy metals, but not sufficiently to meet many of the new discharge regulations that are being promulgated in North America. Furthermore, the process itself could be upset by higher doses of heavy metals, and the removal efficiency is not consistent. In chemical treatment, the precipitated floe has poor settling characteristics and has to be removed by filtration. The effluent has objectionably high pH and needs recarbonation before being discharged. All these factors make the process relatively expensive. Activated carbon columns have often been used as a component of a tertiary treatment process for removing organics from secondary treatment plant effluents. The columns are found to be very effective in reducing the heavy metal concentrations to trace levels. The exact mechanism of removal is not known as yet. It could be complexation of ** Crows Nest coal is a medium volatile bituminous type. metals with organics, followed by adsorption of the organics "onto the carbon. If that is the case, the carbon may not remove metals from waters having no organics in it. Granular coal appears to be very effective in reducing the concentrations of heavy metals in water to trace levels. Because of large, relatively cheap coal reserves in British Columbia, the possibility exists that coal can be used in removing metals from water and may even prove to be a substitute for expensive adsorbents like activated carbon. Therefore, it was considered advisable to study the relative efficiencies of a number of British Columbia coals in removing heavy metals from water and to select the best two coals for compari-son with other potential adsorbents. Chapter 3 MATERIAL AND PROCEDURE 3.1 Types of Coal Six different coal samples, four from Kaiser Resources Limited and two from Northern Coal Mines Limited were used in this investigation. a) Kaiser Coal: The four coal samples were as follows: * 1) oxidized stock pile sample (K.C. OSP ) 2) Special waste lagoon sample (K.C. SWL) 3) Special plant feed sample (K.C. SPF) 4) Stock pile refuse sample (K.C. SPR) The results of analysis of four coal samples and their ranks are shown in Table V. The specific gravity of two coals used for column tests was 113.4 and 93.4 lb/cu. ft. for Kaiser coal stock pile refuse and special plant feed sample, respectively. b) Northern Coal: The two coal samples were as follows: 1) Oxidized sample (N.C. oxidized) 2) Unoxidized sample (N.C. unoxidized) Aft This coal is of "High volatile B Bituminous" rank. 3.2 Coal Preparation The coal samples were ground to relatively consistent grain * The abbreviations used in tables and figures for different coals. ** Trenholme, L.S., Northern Coal Mines Limited, 1177 W. Eastings, Vancouver, B.C.. TABLE V ANALYSIS* AND RANKS OF KAISER COAL SAMPLES Coal type Volatile Matter % Ash Content % Fixed Carbon % Moisture % Coal Rank K.C. OSP 20.7 12.9 60.9 5.5 N High volatile K.C. SWL 14.5 68.5 16.7 0.3 A bituminous > K.C. SPF " 19.3 19.4 57.6 3.7 K.C. SPR 16.9 48.4 34.0 0.7 > Mickelson,1 G., Kaiser Resources Limited, P.O. Box 2000, Sparwood, B.C. sizes (28/48 mesh). During this process, the coal was first cleaned of any foreign particles and was dried at room temperature. The air dried coal was then crushed to the small grain sizes by passing it first through a Taylor Gyratory Crusher and then through a Massco Cone Crusher. The crushed coal was dry sieved using a mechanical shaker and 28/48 mesh screens. The coal particles retained over 48 mesh sieve were washed with tap water to remove the fines stuck to them. Further removal of fines were accom-plished by back-washing the coal in a plexi-glass column. The coal was then dried at 103°C and stored at room temperature in sealed bottles. 3.3 Synthetic Wastewater It was considered appropriate to use synthetic rather than actual wastewater for three reasons. 1) Actual wastewater varies in strength and composition, making experimental results difficult to interpret. 2) Measurements are made simpler and more accurate when..using synthetic wastewater. 3) lit was desired to avoid the possibility of organic complexa-tion of the heavy metals. Table VI indicates the synthetic wastewaters used for different metals. TABLE VI SYNTHETIC WASTEWATER USED FOR EACH METAL Metal Copper CUS04.5H20 + distilled water Lead Pb(N03)2 + distilled water Zinc Zn S0..7Ho0 + distilled water 4 2 Mercury Atomic Absorption standard mercury reference solution, 1000 ppm (stock solution), A stock solution of 1000 mg/1 concentration was prepared for each metal and diluted to desired concentration with distilled water. 3.4 Measurement of Concentration The atomic absorption spectrophotometer (Jarrell Ash MV-500 Model) was used for the measurement of metals concentration. The flame atomic absorption technique (burning of sample in a flame to enable individual atoms to float freely) was used for three metals: copper, lead and zinc. The same technique was used for mercury analysis at concentrations of 5 mg/1 and higher. However, for lower mercury con-centrations, the flameless or cold vapour method was employed. The samples containing copper, lead or zinc were kept in glass tubes at room temperature. The samples having mercury concentra-tions of 5 mg/1 and higher were acidified by adding enough HNO^ to lower the pH to below 2 and were analyzed, as were those of copper, lead or zinc, within 24 hours. For lower concentrations of mercury, the Jarrell Ash (19) procedure of determination of mercury by flameless atomic absorption was employed. This procedure enabled mercury detection to a level of 0.5 yg/1 in a 100 ml sample. The standardized instrument settings and detection limits for each metal were as shown in Table VII. 3.5 Batch Testing Procedure Batch tests were performed to study the relative efficiencies of six different coals in removing heavy metals from synthetic waste-TABLE VII STANDARDIZED INSTRUMENT PARAMETERS FOR DIFFERENT METALS Metal Lamp Fuel Support Flame Wave Working Detection Limit Current Stoichiometry Length nm Range Absorption Scale Concentration Scale (Expanded) Copper 3 mA ii acetylene II Air II oxidizing II 324.7 218.2 <20 mg/1 10-100 mg/1 .0:1 mg/.l 0.03 mg/1 Lead 6 mA ii II II II II II II 217.0 283.3 <20 mg/1 10-100 mg/1 0.2 mg/1 0.1 mg/1 Zinc 5 mA II II II II ii II II 213.9 307.6 <20 mg/1 10-100 mg/1 0.01 mg/1 — Mercury 3 mA ii II ii 253.7 5-100 mg/1 - -ii Flameless met Dr cold vap lod •ur 253.7 <5 mg/1 0.5 yg/1 in a 100 milli-liter sam-ple water. The measured quantities of granulated coal were mixed with measured amounts of wastewater containing various concentrations of copper, lead, zinc or mercury and the mixture was agitated gently with a Burrell Wrist Action Shaker for a definite period at room temperature. 3.5.1 Contact Time Preliminary batch tests were conducted for exposure periods of between 15 minutes and 12 hours to determine optimum contact time. Figures 3.1 and 3.2 show the adsorption of copper from water as a function of contact time. A rapid approach towards equilibrium was evident. Generally the reductions obtained at one hour were only a few percent less than those obtained at longer exposure, and consequently a one hour contact period was adopted for all further testing. 3.5.2 Amount of Coal The minimum amount of coal necessary for effective removal of heavy metals from a known volume of solution, was determined. The batch tests were performed for different metals by varying the amount of coal used while keeping the wastewater concentration constant. The volume of wastewater used was arbitrarily chosen as 100 milliliters (ml). The results of these tests are shown in Figures 3.3 to 3.7. The figures show that one gram of coal was enough to reach the lowest residual concentration with a solution containing 2 mg/1 of copper or zinc. Also, with a solution of one mg/1 of copper, one gram of coal was found sufficient to achieve equilibrium concentration lower than that obtained with 2 mg/1 of copper. The residual concentration dropped A A -  K .C .SWL A A - K.C.SPR + — + - K.C.SPF Figure 3.1. EFFECT OF CONTACT TIME ON ADSORPTION A A - K . C . S W L A A - K.C.SPR + + - K .C .SPF Figure 3.2. EFFECT OF CONTACT TIME ON ADSORPTION. 2.0i <D CT> e c o c a> a c o c_> e 3 3 cr UJ • 8 1.6 1.4 .2 .0 0.8 0.6 0 . 4 0. 2 0 0 A A - K.C.SWL A & - K .C.SPR + — + - K.C.spf • — • - K.C.OSP O — O - N.C.Unoxid ized • — • - N.C.Oxid ized In i t ia l Concen t ra t ion = 2 mg/ l i t re Contact T ime = 6 0 m i n u t e s pH = 5 .6 0 .5 1.0 1.5 Coa I D o s a g e - g r a m s 2 . 0 I .0 A - K.C. SWL A & - K.C. SPR + - K .C.SPF - K .C.OSP — O - N.C.Unoxidized N.C.Ox id ized In i t ia l Concentrat ion = I m g / l i t r e Contact T ime = 6 0 minutes 0 . 5 1.0 1 . 5 Coal D o s a g e - g r a m s 2.0 2.Or A A - K .C. SWL —A - K.C. SPR — + - K.C. SPF — • - K.C. OSP - N . C . Unoxidized - N. C. Oxidized In i t ia l Concent ra t ion = 2 m g / l i t r e Contact Time = 6 0 minu tes 0 . 5 1.0 1.5 Coal D o s a g e - g r a m s 2 .0 A A - K .C . SWL 33. & & - K .C . SPR + + " K.C. SPF • • - K.C. OSP O — O - N.C. Unox id ized E — Q - N. C. Oxidized In i t ia l Concentrat ion = lOOmg/ l i t re Contact T ime = 6 0 minutes pH = 5 .0 0 . 5 1.0 1.5 Coa l D o s a ge - g r a m s 2 . 0 still further to below the detectable limit of 0.03 mg/1 while using a solution of 0.5 mg/1 copper. With, such low residual copper concentra-tion for all coal doses, the data points could not be shown on a graph; Similar results were found with zinc as the adsorbate. Using solutions containing 2 mg/1 and 1 mg/1 of lead, the equilibrium concentrations were less than the detectable limit of 0.1 mg/1. As only comparative data were desired, the solution containing 20 mg/1 of lead was used. For the same.reasoning, a mercury concentra-tion of 100 mg/1 was selected for determining relative adsorption iso-therms for the various coals. In addition, the loss of mercury due to volatilization was relatively insignificant at this higher concentration. A coal dosage of greater than one gram did not decrease the equilibrium concentration at low adsorbate concentrations. This indicates that for a coal dosage of one gram or greater, and the range of concentra-tions to be tested ( 2 mg/1 and less), the removal is only dependent on adsorbate concentration. Even at higher adsorbate concentrations, the decrease in the equilibrium concentration was relatively small. For example, using a solution containing 20 mg/1 of lead, special waste lagoon coal resulted in equilibrium concentrations of 5.7, 3.6, 2.4 and 0.8 mg/1 for coal weight of 0.5, 1, 1.5 and 2 grams respectively. Therefore, one gram of coal per 100 ml. of adsorbate solution was adopted for all further testing. 3.5.3 Adsorption Isotherms An adsorption isotherm is a constant temperature plot of the capacity of an adsorbent to remove a particular material -from solution versus the equilibrium concentration of the same material in contact with the adsorbent. Isotherms provide useful information in that they: 1) provide a comparison of the capacities of different coals to remove a common impurity; 2) provide a comparison of the capacity of one coal to remove different impurities; 3) provide general information that may help clarify the process involved in removal of impurities. For the preparation of adsorption isotherms, a series of batch tests were performed under the following conditions: Volume of waste water = 100 ml; Amount of coal used = 1 gram; pH of the wastewater = 5 — 5.8 (depending on adsorbate concentration); Temperature = room temperature (23°C); and Contact time = 60 minutes The tests were conducted over a wide range of initial adsorbate concentra-tions varying from 0.5 mg/1 to 100 mg/1 for copper, lead and zinc and 5 yg/1 to 100 mg/1 for mercury. This was considered appropriate because the maximum capacity of coal to remove metals could be determined at higher adsorbate concentrations, whereas the tests at lower concentrations would give the information about minimum obtainable residual concentrations under specified test conditions. The information required to plot the isotherm was obtained as follows. 1) One gram of coal of a given grain size (28/48 mesh) was added to different Erlenmeyer flasks. 2) Different concentrations of synthetic wastewater were added to flasks in the amount of 100 ml. 3) The flasks were closed with rubber stoppers and agitated gently with a Burrell Wrist Action Shaker for 60 minutes. The action of the shaker was set such that the wastewater was well agitated but the coal was not sufficiently agitated to cause excessive coal particle abrasion. 4) The coal was filtered off and the clear filtrate was analyzed by an atomic absorption spectrophotometer for the residual concentration of impurity in each flask. 5) The weight of impurity adsorbed per gram of coal was calculated. 3.6 Column Testing Procedure On the basis of the batch test results, the two best coals, Kaiser Coal-Stock Pile Refuse and Kaiser Coal-Special Plant Feed, were tested on a continuous flow laboratory scale column. 3.6.1 Column Setup It was decided that the column apparatus should meet the follow-ing requirements. 1) It should be of such a size that a large number of test runs could be made conveniently within a reasonable length of time. 2) It should be of such minimum',.dimensions-thatanormal full-scale design parameters (flow rate and column depth) could be simulated to some reasonable extent. 3) It should have design features which assure the continuous supply of influent at a constant head for a long enough period so that break-through curves could be obtained at low influent con cen t r at i on. A diagram of the column set up is shown in Figure 3.8. A 2 series of 50 ml burrets, each having a cross-sectional area of 0.956 cm were used as columns. Glass beads and glass wool were placed at the bottom of column to act as a filter and to prevent the plugging of the outlet valve with coal. An acid-washed plastic car-boy of about 8.5 liters capacity was used as a reservoir. The top of the reservoir was connected by plastic tubing with the top of a separatory funnel of one liter capa-city, thus prohibiting the entrance of air into the reservoir and separatory funnel except through their outlets, which were submerged in an Erlenmeyer flask to about one centimeter depth. The wastewater was syphoned from the flask to the column at a rate adjusted by the valve at the column outlet. As the water level in the flask dropped sufficiently to expose the outlets to the atmosphere, an air bubble rushed into the funnel. Thus, the change in equilibrium forces caused enough water to flow to bring the water level in the flask to its original level. The separatory funnel was used because its short and straight outlet, as compared to that of reservoir, provided an easy and quick passage to the air bubble. Moreover, it also increased the capacity of the reservoir by one liter. R e s e r v o i r Si phon Separa to ry funneI Er lenmeyer f l ask Coa I c o l u m n Cont ro l v a l v e Out f l ow Figure 3.8 SCHEMATIC DIAGRAM OF COLUMN SET UP. 3.6.2 Experimental Procedure A weighed amount of known grain size (28/48 mesh) coal was placed in each column to a depth of 10 inches. Because of different specific gravities, the weights of the two coals required to fill each column to the same depth were different. While 20 grams were required to fill the column with Kaiser Coal-Special Plant Seed sample, it took 25 grams of Kaiser Coal-Stock Pile Refuse sample to fill the other column to the same depth. To avoid any discrepancies in the characteristics of influent wastewater, two columns (each with one coal sample) were simultaneously connected to the same reservoir. The flow rate through the column was adjusted to approximately 2 1 gpm/ft , with the help of a valve at the column outlet. Thus, provid-ing a contact time of 5.2 minutes on empty column basis and 2.3 minutes on the basis of actual pore space in the column. A few columns were also 2 run at a flow rate of approximately 5 gpm/ft to study the effect of contact time on coal capacity. Effluent samples were collected in acid-washed plastic tubes. A few samples were also taken at the end of supply line to check the influent concentration. The time span required to reach column break-through varied, depending upon the type of coal, nature of impurity, concentration of impurity in the influent, flow rate through the column, and pH of the influent. A breakthrough curve (volume passed through the column vs. effluent concentration) was plotted for each run. Chapter 4 RESULTS AND DISCUSSIONS 4.1 Batch Tests Only comparative data were sought in the batch test phase of the investigation. By maintaining carefully controlled conditions during this phase of the testing, the relative capacities of different coals could hopefully be determined, and the obviously less efficient ones deleted from further testing. 4.1.1 Capacity of Coals a) Copper: The isotherms plotted from the copper removal batch tests are shown in Figures 4.1 and 4.2. The curves show the follow-ing: 1) the capacity of the coal increases with increasing equili-brium concentration of copper in solution up to approxi-mately 50 mg/1. At concentration greater than 50 mg/1 the coal capacity does not change significantly; 2) the maximum capacity attained was 1.2 mg copper per gram of coal. This value was achieved using an initial copper concen-tration of 100 mg/1; 3) the coal has the ability to produce a residual concentra-tion of less than the detectable limit of 0.03 mg/1 when using an initial solution containing 0,5 mg/1 of copper; 4) for the particular grain size of coal and adsorbate concen^ trations used, the six coals could tentatively be ranked as follows (in decreasing order of removal efficiency): A A - K .C .SWL & A - K.C. SPR + + - K.C. S PF • — • - K.C.OSP - N . C . Unoxidized 10 20 30 40 50 60 70 Equi l ib r ium Concent ra t ion - m g / l i t r e 100 • 0.20 K.C. SPR 4- - K.C. SPF • - K.C. OS P O - N.C. Unoxidized • - N - c . Oxid ized 0.1 0.2 0.3 Equi l ibr ium Concen t ra t ion - m g / l i t r e a) Kaiser Coal - Stock Pile Refuse Sample b) Kaiser Coal - Special Plant Feed sample c) Kaiser Coal - Special Waste Lagoon sample d) Kaiser Coal - Oxidized Stock Pile sample e) Northern Coal Mines - Unoxidized sample f) Northern Coal Mines - Oxidized sample b) Lead: Figures 4.3 and 4.4 show the isotherms obtained from the batch tests when using lead as the adsorbate. Examination of the curves show: 1) the capacity of the coal for lead removal increases with increasing metal concentration up to 50 mg/1. At concen-trations greater than 50 mg/1 the coal capacity does not change significantly. An exception is Kaiser Coal—Special Waste Lagoon sample, the capacity of which increases signi-ficantly up to 100 mg/1 of initial lead concentration. 2) the maximum capacity of coal to remove lead was found to be 3.7 mg per gram of coal at an initial lead concentration of 100 mg/1; 3) a residual concentration of less than the detectable limit of 0.1 mg/1 was achieved when the initial lead concentration was 2 mg/1 and less; 4) for the particular coal grain size and adsorbate concentra-tions used, the coals can be ranked as follows: a) Kaiser Coal - Special Waste Lagoon sample b) Kaiser Coal - Stock Pile Refuse sample 5.0 i o o 4 .0 o H— o cn N 3 .0 •a a> £3 t— o </) TJ O 2. 0 CP E i 1 . 0 o o CL O O 10 20 30 40 50 60 70 8< Equ i l i b r ium Concen t ra t ion - mg / l i t r e 100 c) Kaiser Coal - Special Plant Feed sample d) Northern Coal Mines - Unoxidized sample e) Kaiser Coal - Oxidized Stock Pile sample f) Northern Coal Mines - Oxidized sample. c) Zinc: Isotherms obtained from batch test data using zinc as the adsorbate are shown in Figures 4.5 and 4.6. The isotherms indicate the following: 1) the capacity of coal to remove zinc increases up to an initial concentration of 50 mg/1. At higher concentrations the increase in capacity to remove zinc is relatively very small; 2) the maximum capacity of the best coal was found to be 1.5 mg zinc per gram of coal. This was achieved at an adsorbate concentration of 100 mg/1; 3) even at very low initial zinc concentrations, the coals are capable of about 90% metal removal (e.g. at 0.5 mg/1 initial concentration, the residual concentration achieved was about 0.05 mg/1); 4) for the particular coal grain size and adsorbate concentra-tions used, the coals tested can be ranked as follows: a) Kaiser Coal - Special Waste Lagoon sample b) Kaiser Coal - Stock Pile Refuse sample c) Kaiser Coal - Special Plant Feed sample d) Kaiser Coal - Oxidized Stock Pile sample - K . C . S W L A - K.C. SPR 2.Or + - K.C. SPF - K .C .OSP o o o o o> .6 1.2-TD 03 £3 i— O " 0.8 "O o CP E ?  0 4 o o Q. O o O O - N.C. Unoxidized Q • - N .C .Ox id i zed 0 30 40 50 60 70 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 100 e) Northern Coal Mines - Unoxidized sample f) Northern Coal Mines - Oxidized sample d) Mercury: The isotherms of mercury removal by different coals are shown in Figures 4.7 and 4.8. These isotherms indicate the following: 1) the capacity of the coal to remove mercury increases up to an initial concentration of about 40 mg/1. At higher concentrations, the relative increase in the capacity is very small; 2) the maximum capacity of coal to remove mercury was found to be 1.5 mg per gram of coal at an initial mercury concen-tration of 100 mg/1; 3) a residual concentration of as low as 1 yg/1 was achieved when the initial mercury concentration was 5 yg/1; 4) for the particular coal grain size and adsorbate concentra-tions used, the six coal samples can be ranked as follows: a) Kaiser Coal - Special Plant Feed sample b) Kaiser Coal - Oxidized Stock Pile sample c) Northern Coal Mines - Oxidized sample d) Northern Coal Mines - Unoxidized sample e) Kaiser Coal - Stock Pile Refuse sample f) Kaiser Coal - Special Waste Lagoon sample 4.1.2 Ranking of the Coals The results of the batch tests show that for three metals (copper, lead and zinc), the six coals showed a distinct division into two 1.8 1.6 1.4 o o o o cn "O a) i— o </> "O o .2 1.0 a> ' 0.8 >> a o a. o O 0.6 0 . 4 0.2 51. > - K.C. SWL — ^ - K .C.SPR — + - K . C . S P F • — - K .C .OSP O — O - N. C. Unoxidized • - N.C. Ox id ized 0 5 10 Equ i l i b r ium C o n c e n t r a t i o n ^ g / l i t re groups. Three of the Kaiser coals (Special Waste Lagoon, Stock Pile Refuse and Special Plant Feed samples) provided the highest removals for these metals. The ratings on the basis of mercury uptake were considerably different, with the Special Plant Feed sample ranking first, and the Stock Pile Refuse and Special Waste Lagoon sample ranked fifth and sixth respectively. Though Stock Pile Refuse and Special Waste Lagoon samples performed relatively poorly at lower concentrations, the maximum removal capacity (at 100 mg/1 initial mercury concentration) of these coals approached those of Northern Coal Mines oxidized and unoxidized coals. (See Figures 4.7 and 4.8). On the basis of their overall performance the six coal samples can be rated as follows: (1) Kaiser Coal - Special Waste Lagoon sample (2) Kaiser Coal - Stock Pile Refuse sample (3) Kaiser Coal - Special Plant Feed sample (4) Kaiser Coal - Oxidized Stock Pile sample (5) Northern Coal Mines - Unoxidized sample (6) Northern Coal Mines - Oxidized sample Although the special waste lagoon sample ranked first, it was considered appropriate to choose stock pile refuse and special plant feed samples for column tests for the following reasons: 1) the capacity of the special waste lagoon sample for all four metals was very close to that of the stock pile refuse sample; 2) the supply of special waste lagoon material was considered inadequate for developing a commercial scale.process for treatment of waste waters containing heavy metals; 3) in removing mercury from water, the special plant feed sample performed distinctly better than other samples. 4.1.3 Effect of pH Adsorption isotherms were obtained to show the effect of solution pH on the capacity of the coal to remove heavy metals. The tests were only performed for the top ranking coals. The curves in Figures 4.9 to 4.12 show that pH had a significant effect on the capa-city of the coals. By lowering the pH of the solution from 5 to 3, the capacity of the coal was decreased by 14 to 45% for copper, lead and mercury. However, with solutions containing zinc sulphate, the same decrease in pH level decreased the capacity of coals when using adsor-bate concentration of up to 20 mg/1 while at higher concentrations, the results were inconsistent, with the capacity of the coal being seemingly increased substantially for some tests (See Figure 4.11). A further decrease in pH to 1.5 reduced the coal capacity to remove heavy metals to almost zero. Since the main objective of the study was to investigate the heavy metals removal affected by coal, pH values (7 and above) at which removal by precipitation and filtration was possible, were not tested. 4.1.4 Comparison of Coal with Other Adsorbents The metal removing capacities of the two selected coals (K.C. SPR and K.C. SPF) were compared with some commercially available adsor-bents . The following materials were used: a) Nitrohumic acid (NHA)* - This specially prepared resin for heavy * Supplied by Hokutan Chemical Industry Co. Ltd., Tokyo, Japan. , 5 r A A - K.C. SWL A A - K.C. SPR 0 10 20 pH = 5 - 5 . 7 3 0 4 0 5 0 6 0 70 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 80 9 0 100 Figure 4.10 EFFECT OF pH ON ADSORPTION OF LEAD. Equi l ib r ium C o n c e n t r a t i o n - m g / l i t r e metals removal is made from slightly carbonized coal that has been nitrified. This highly polymerized organic acid compound is reported to possess the characteristics of both an ion ex-change and a chelating agent. At relatively high metallic ion concentrations, the ion exchange reaction is dominating (eq. I) while at lower concentrations, the chelating action is dominant (eq. II). R-COOH + igMe^ — R - C 0 0 l g M e + + H + I +Me"H" — R C T ^ M e + 2H+ II Url «= U The equilibrium in the above reactions is easily moved to the left by strong acid. Thus, adding strong acid, such as hydro-chloric acid, the resin should be easily regenerated. The nitrdhumic acid is generally an alkali soluble powder. There-fore, for its application to remove metals from solution, it should be made insoluble in alkali without losing power of adsorption. The resin has the following physical characteristics: 1) shape of particles - spherical or oval; 2) diameter of particles - 1.0-1.1 mm; 3) density of particles - 0.59-0.61 Kg/1 (in dry conditions); 2 4) average hardness of particles - 51-60 Kg/cm (in dry condition) - 17-20 Kg/cm^ (in humid condition) (calculated by the pressure it takes to destroy them) b) Kaolinite clay* - Kaolinite particles are plate-like in nature, being built up of flat crystalline units. Chemically, these units are aluminum silicate - and are held together rather * Clay sample taken from soil mechanics laboratories of the Department of Civil Engineering ,at the University of British Columbia, Canada. rigidly by oxygen and hydroxyl linkages. Because of the tightness with which their structural units are held together, the effective surface area of kaolinite is restricted to its outer faces. Kaolinite crystals usually are hexagonal with clean cut edges. The particle diameters generally range from 0.1 to 5 microns with the majority falling within 0.2 to 2 microns, c) Montmorillonite Clay* - The flake-like crystals of montmorillo-nite are also composed of crystalline units. Each unit is made up of two silica sheets with an alumina sheet tenaciously bound in between by mutually shared oxygen atoms. These units are loosely held together by hydroxyl linkage, thus providing enormous internal surface area. Normally, montmorillonite erystals range in diameter from 0.01 to 1 micron. They are thus much smaller than the average kaolinite micelle. Batch tests identical to those performed for coal, were conduct-ed to prepare adsorption isotherms for copper, lead, mercury and zinc. These isotherms are shown in Figures 4.13 to 4.16 and indicate the following: 1) both kaolinite and montmorillonite clays hkve higher removal capacity for copper than the coals. However, the difference is not significant, particularly at low equilibrium concentra-tions. Nitrohumic acid performed significantly less efficiently than coal in removing copper from water at the concentrations tested. However, this may not be true for higher initial * Clay sample, taken from soil mechanics laboratories of the Department of Civil Engineering at The University of British Columbia, Canada. 0.20 - 0.15 c a> JO o </) •o o o> "O a> JQ o "O O o> E 0.10 A - & - K.C. SPR * - * - K.C. SPF • - M o n t m o r i l l o n i t e Clay o - o - Kaol in Clay • - • - N i t r o h u m i c A c i d o o o 0.05 u f 0.0 -L 0.0 0.05 0.1 0.15 0.2 0.25 E q u i l i b r i u m concen t ra t i on - m g / l i t r e 0.3 0.35 4 . 0 3 . 0 A - A - K.C. SPR * - * - K . C . S P F • - Mon tmor i l l on i te Clay O - O - Kao l in Clay • - N i t rohumic Ac id c a> JD 3 2.0 tn •o o o cn •o Q) jQ o U) TD a 6.0 4 .0 E o o o 3 .0 o 2 . 0 • .0 0.0 l .o 2.0 3.0 4 .0 5.0 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 7.7 I. 6 1.4 «_ I. 2 c a> XI o 10 TJ O 1.0 CJ> N "O a) X} - 0.8 to T3 O CJ> ^ >. 0. 6 o o a o o 0.4 0.2 A - A - K .C .SPR * - K.C. SPF • M o n t m o r i l l o n i t e Clay O - O - K a o l i n C lay • - • - N i t r o h u m i c A c i d 0 . 0 5 10 E q u i l i b r i u m c o n c e n t r a t i o n p g / l i t r e 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 adsorbate concentrations since the nitrohumic acid provided significantly greater removal capacity than coal at higher initial lead concentration while it performed inefficiently as compared with coal at lower initial lead concentrations (see Figure 4.14); 2) montmorillonite, the nitrohumic acid and kaolinite provided higher removal capacity for lead than coal and ranked in descending order in the sequence listed above. The materials were significantly different in their efficiencies, with removal capacities being up to about 40, 4 and 1.4 times higher than coal for montmorillonite, nitrohumic acid, and kaolinite respectively; 3) the coal has higher capacity for mercury adsorption than other materials at low equilibrium concentrations. At higher concentrations the clays have higher capacities as compared to stock pile refuse coal but lower than the special plant feed coal; 4) for zinc, both clays performed significantly better than coal and were capable of reducing zinc concentration to 0.01 mg/1 which is five times lower than that achieved by coal. The capacity of the nitrohumic acid for zinc removal is almost comparable to that of coal. The results of these tests clearly indicate that for the range of concentrations tested, the nitrohumic acid has lower efficiency in removing two of the four tested metals (Cu and Hg) from water as compared with coal. Moreover, this material imparts a definite brown coloration to the water, thus rendering it more undesirable from an esthetic point of view. The clays rank higher than coal for all tested metals except mercury. Of the two clays, the montmorillonite always ranked first, which was expected because of its large surface area as compared to kaolinite. The capacity of coal for various metals has been shown (8, 12) to increase with decrease in grain size. Therefore, it might be possible to have coal capacity equal to or even higher than the capacity of the clays by using comparable particle sizes. However, this has a clear disadvantage of causing excessive head losses through coal columns. Thus, there has to be a lower grain size limit, feasible for use in flow-through columns. It is quite obvious that clays are well below the particle size that would allow them to be used in columns like granular coal. 4.2 Column Tests Since granular columns are used as dynamic systems, not only are the equilibrium adsorption properties of the coal important, but also the rate of adsorption. Reference to Figure 4.17 will indicate the effect of this adsorption rate. The figure shows breakthrough curves obtained by passing water containing zinc through two packed columns of granular coal. The breakthrough curve for the Kaiser Coal-Stock Pile Refuse is comparatively steeper than that for the Kaiser Coal-Special Plant Feed. The difference in slope is due to a higher rate of adsorption for the stock pile refuse than for the special plant feed coal. Generally, greater rates of adsorption are desired for maximum efficiency of the coal. In actual use, operation of a column is discontinued when the effluent Vo lume passed through - l i ters CJl ON Figure 4.17 BREAKTHROUGH CURVES FOR Z INC. concentration reaches an unacceptable value. The coal with the steeper breakthrough curve will, therefore, have the longer service life even though the relative capacities of the coals at complete exhaustion (effluent concentration equals influent concentration) may be the same or even reversed. 4.2.1 Removal of Metals To estimate the capacity of coal to remove heavy metals under dynamic flow conditions, the breakthrough curves for each metal were analyzed to determine the capacity for several arbitrarily chosen effluent concentrations. The detection limit of each metal was the lowest effluent concentration for which the coal capacity was determined. The breakthrough curves and sample calculations are shown in Appendices I and II. a) Copper The copper removing capacity of coal, as calculated from the breakthrough curves, is plotted against the ratio of effluent con-centration to influent concentration, C/Cq, in Figure 4.18. The curves show the following: 1) the capacity of the coal increases with increas-ing effluent concentration (higher C/Cq value), the increase being relatively smaller at higher effluent concentration; 2) for the same allowable effluent concentration, each coal has a higher removal capacity at an influent concentration of 0.5 mg/1 than at 2 mg/1; 3) the two coals gave different relative results at the two influent copper concentrations. At 2 mg/1 of influent copper, - 0 . 7 o o o o o> T3 a> JO I— o 10 "O o £ 0 .5 o o CL o o c/c, the two coals performed about evenly, while at 0.5 mg/1, the special plant feed coal performed better than stock pile refuse coal; 4) for influent concentration of 2 mg/1, the special plant feed coal has a higher total adsorption capacity than stock pile refuse coal. However, it did not perform as well as stock pile refuse coal at lower effluent concentrations. This in-dicates that the stock pile refuse coal has a higher adsorp-tion rate (i.e. the breakthrough curve is steeper). b) Lead The capacity of the coal to remove lead from synthetic waste-water at different effluent concentrations is shown in Figure 4.19. The data indicates the following: 1) the capacity of coal for lead adsorption increases with increas-ing effluent concentration. However, the change in capacity is relatively small at higher effluent concentrations; 2) for the same effluent concentration, both coals possess a higher adsorption capacity at the lower influent concentration of lead; 3) for both levels of influent concentration, stock pile refuse coal has significantly higher adsorption capacity than special plant feed coal. c) Zinc Figure 4.20 shows the capacity of each coal to remove zinc from synthetic wastewater. The data indicates the following: 2 .2 2 . 0 h K.C. SPR I .8 o o o 1.6 CP "O a> JQ i _ o <n •o | 4 o 1 • ^  o> E o 1.2 o Q. O o 1.0 0.8 0.6 0 0. 2 m g / l lmg/1 ( In f luent  concentrat ion) I n f l uen t  pH = 5 .7 - 5 .8 2 Flow rate = I Gpm / f t Column depth = 10 inches 0.2 0.3 c / a 0 . 4 0 .5 I m g / I 2 m g / l 0.6 0 . 7 0 . 6 o o ^ 0 . 5 o C7> \ T3 a> -Q 8 0 . 4 -a 0 a» E 1 >. •t: 0 . 3 o o a. o O 0 .2 0. I -0 0. I - 0 . 5 m g / l i ter A — 0 . 5 m g / l i t e r ( In f l uen t  c o n c e n t r a t i o n ) •2mg/liter A - K.C. SPR - K .C. SPF In f l uen t  pH = 5 . 7 - 5 . 8 2 Flow rate = I g p m / f t . Co lumn depth = lOin. 0 . 2 0 . 3 0 .4 0 .5 C/C, 1) the capacity of the coal increases with increasing effluent concentration. At higher effluent concentrations the change in capacity is relatively small. An exception is special plant feed coal which shows a continuing linear increase in capacity for influent concentration of 2 mg/1. This suggests a very low adsorption rate for special plant feed coal; 2) ,for influent concentrations of 2 mg/1, stock pile refuse coal gave distinctly better results than special plant feed coal; 3) for influent concentration.of 0.5 mg/1, stock pile refuse coal has lower total adsorption capacity than special plant feed coal; However, at low values of C/CQ, it has a higher capacity which indicates that it possesses a higher adsorption rate (i.e. a steep breakthrough curve). d) Mercury The adsorption capacity of coal for mercury from a solution containing 4.76 yg/1 of mercury is shown in Figure 4.21. Examination of this figure shows the following: 1) the adsorption capacity of the coal for mercury increases with increasing effluent concentration, with the change being rela-tively smaller at higher effluent concentration; 2) under the specified test conditions, the special plant feed coal has higher total adsorption capacity for mercury than stock pile refuse coal. But its lesser performance at lower values of C/Cq indicates that it possesses a slower adsorption rate than the stock pile refuse coal. 1.8 1.6 _ 1.4 o o o .2 o> N XJ © JO S " 0 "O o CP >,0.8 o o Q. O ° 0.6 0 . 4 0 .2 0.0 0. I n f l u e n t  pH = 5 . 6 Flow ra te = l g p m / f t 2 Co lumn depth = 10 in. Inf luent  concent ra t ion 4.76yug/ l K . C . S P F 0.2 1 0 .3 C / C K.C. S P R 0 . 4 0 . 5 Figure 4.21 ADSORPTION CAPACITY OF COAL FOR M E R C U R Y . In general, the stock pile refuse coal has a higher adsorp-tive capacity for different metals, particularly at low values of C/CQ, which suggests that it possesses a higher adsorption rate. Therefore, on the basis of adsorption rate and capacity, at least, stock pile refuse coal is rated better than the special plant feed coal. However, nothing is known about the ability of coals to withstand handling and slurry transfer, which is of paramount importance in water and wastewater treatment. Excessive attrition losses may create fines to an extent that causes intolerable head losses in adsorption columns. Unfortunately, at present, it appears that plant scale experience is the only reliable means of predicting the desirability of a granular coal with respect to mechanical attrition losses. 4.2.2 Effect of Adsorbate Concentration on Column Efficiency The effect of adsorbate concentration on the metal-removing capacity of the coal is shown in Figure 4.22. The capacities were cal-culated for the column effluent concentration of 0.1 mg/1 of lead and 0.05 mg/1 for both copper and zinc. These concentrations were selected for the following reasons: 1) they represented the breakpoint concentrations on the break-through curves of each metal; 2) they were very close or equal to the detectable level of these metals. For both copper and lead, the two coals have higher adsorption capacities at the lower adsorbate concentration. However, in the case of zinc, stock pile refuse coal has greater capacity at the higher adsorbate concentration. 2 . 0 i -1.5 1.0 o o o CP \ "O <D S3 o (/) T3 O cn e I >. .t: 0 . 5 o o CL O O 0 .92 1.60 0 .78 0 .52 0.60 0 .30 1.04 0 .69 0.59 0.47 0 .46 0.12 _L Influent  concentration 2 0 .5 2 0.5 Coal type K.C. SPR K.C. SPF M e t a l C o p p e r Break th rough  conc. 0 . 0 5 m g / l Figure 4 . 2 2 EFFECT OF ADSORBATE CONCENTRATION ON CAPACITY 2 1 2 1 K.C. SPR K.C. SPF L e a d 0.1 m g / I 2 0.5 2 0 .5 K.C. SPR K.C. SPF Z i n c 0.05 mg /1 Ui The capacity of special plant feed coal is much, higher at the lower influent concentrations tested, the difference amounting to some 50, 160 and 280 percent for lead, copper and zinc respectively. For stock pile refuse coal, the capacities at the lower influent concen-trations are only 15 and 20 percent greater than at higher influent concentration for copper and lead respectively. The much wider differ-ence in adsorptive capacity of special plant feed coal can be explained by its documented lower adsorption rate as compared to stock pile refuse coal. One of the important parameters to be considered is the nature of the process which controls the rate at which the dissolved substances are removed from dilute aqueous solution by solid adsorbents. There are essentially three consecutive steps in the adsorption of materials from solution by porous adsorbants such as granular coal (18): 1) transfer of adsorbate molecules through the surface film or boundary layer to the adsorbent; 2) diffusion of the adsorbate within the pores of the adsorbent; 3) uptake of the adsorbate molecules by the active surface' including formation of the bonds between the adsorbate and the adsorbent. Step 3 is considered to be very rapid, since equilibrium on non-porous adsorbents can be accomplished in a matter of minutes. Steps 1 and 2 are generally, held to be rate limiting. For a process in which the overall rate is controlled by film diffusion, the variation of rate should be directly proportional to the concentration of solute, thus leading to an increase in the capacity of the adsorbent at higher adsorbate concentrations. If diffusion of solute within the pores and capillaries of the adsorbent limits the rate, the variation of rate with concentra-tion is not expected to be linear. Therefore, the capacity of the adsorbent at higher influent concentration may even decrease at low column effluent concentrations. The higher coal capacities for low adsorbate concentrations, observed in this investigation, suggest that for the range of concentra-tions tested, the gross rate of uptake may be controlled by the trans-port of the adsorbate within the porous coal particles rather than the transport of the adsorbate through the surface film or boundary layer to the adsorbent. 4.2.3 Effect of Flow Rate (Contact Time) on Column Efficiency In a flow through adsorption process, the contact time is one of the most important design factors. Figure 4.23 shows that the column effluent concentration (relative to total throughput volume) rises faster at higher flow rate (lower contact time). This indicates that a higher capacity of the coal to adsorb metals could be achieved by providing greater contact time. Although the capacity of the coal is much less at higher flow rate, it is still capable of reducing the effluent concen-tration to trace levels (see Figures 4.23 and 4.24) for sometime after it is first put into operation. This suggests that the coal columns will continue to function satisfactorily even at reduced contact time, but the operating costs will be substantially greater. Therefore, the optimum contact time will be that which results in the minimum total capital and operating costs over the life of the plant. Contact time less than the V o l u m e p a s s e d t h r o u g h - l i ters Figure 4.23 EFFECT OF FLOW RATE ON COLUMN BREAKTHROUGH CURVES FOR ADSORPTION OF COPPER WITH STOCK P ILE REFUSE COAL . c/c0 Figure 4 .24 EFFECT OF FLOW RATE ON ADSORPTION CAPACITY OF COAL. optimum reduces the capital costs hut produces excessive operating costs. Contact time greater than the optimum reduces operating costs but involves excessive capital costs. 4.2.4 Effect of Solution. pH. on Column Efficiency The pH of a solution may for one or more of a number of reasons influence the extent of adsorption. Illustration of a rather marked effect of pH on adsorption in a column of granular coal is given ' in Figure 4.25. Two solutions, each containing 2 mg/1 of zinc, but having different values of pH (3 and 5.7 respectively) were passed through separate columns. At the lower pH, the capacity of the column was found to be much lower than at the higher pH value (see Figure 4.25). Similar results were also noticed with solutions of other metals. The decrease in capacity might be due to: 1) the neutralization of negative charges at the surface of the coal with increasing hydrogen ion concentration, thereby reducing the forces attracting positively charged metal ions; 2) preferential adsorption of hydrogen ions by coal with increasing hydrogen ion concentration, thereby causing a hindrance to the adsorption of other metal ions by reducing the active surface area of the coal. The detrimental effect of pH on the adsorption of metals noticed in this study, does not necessarily hold true for other metals or adsor-+6 bents. Cheremisinoff et al. (7) reported that adsorption of chromium (Cr ) on activated carbon was effective at pH 2-3,.with no chromium reduction for 2 . 0 ^ } p H = 5.7 We i g h t of coa I : & - A - K.C.SPR = 2 5 g - K .C.SPF = 2 0 g F low rate = I gpm / f t 2 C o l u m n dep th = 10 in . 6 8 10 12 V o l u m e passed through - l i te rs 14 16 Figure 4 .25 EFFECT OF pH ON ADSORPTION OF ZINC IN A COLUMN 00 M pH greater than 3. This could be due to the different nature of activated carbon as compared to coal, because the charges at the surface of the carbon depend on the composition of the raw materials and the techniques of activation. 4.2.5 Removal Of Mixed Metals In the application of coal for the purification of water and wastewater, most installations will be expected to simultaneously remove a number of dissolved metals. To provide an indication of adsorption preference, a solution containing 0.5 mg/1 of each of copper, lead and zinc was passed through the column packed with granular coal. Figures 4.26 and 4.27 illustrate the breakthrough curves for adsorption of each metal from their mixture. It is readily apparent that coal has distinctly different adsorptive affinities for lead, copper and zinc, in that des-cending order. This result is in accordance with the adsorptive capacity of coal for each metal determined on an individual basis. Figure 4.28 shows a comparison of the capacity of one coal to remove copper and zinc from individual solution and from a combined solution of copper, zinc and lead. The lead comparison is not shown, as an individual solution containing 0.5 mg/1 was not tested. It is obvious that the presence of other metals in the solution detracts from the re-moval capacity for the single metal. Similar inhibition was noted in the removal of lead but a numerical comparison can not be given for the reason stated above. As shown in Figure 4.29, the decrease in capacity is caused by a much more rapid breakthrough of these metals while the shape of the breakthrough curves remain unchanged. Thus, the coal retains its capability of reducing the effluent concentration of different metals V o l u m e passed through - liters 03 OJ Figure 4 .26 BREAKTHROUGH CURVES FOR COPPER, LEAD AND ZINK MIXTURE WITH STOCK PILE REFUSE COAL. Figure 4 .27 BREAKTHROUGH CURVES FOR COPPER,LEAD AND ZINC MIXTURE WITH SPECIAL PLANT FEED SAMPLE. Oo •P-0 . 7 0 . 6 0.5 0 . 4 o o o H— o CP \ "O (U O (/) T3 f 0.3 o -*— a> E M— o CP E 0 . 2 o o CL O u 0.1 - A — Zn A - A - M i x e d Meta ls so lu t i on 0 . 5 m g / l of each Zn,Cu and Pb A - A - Indiv idual metal s o l u t i o n 0 . 5 m g / I .A -Cu •A—Zn 0 0.1 0.2 0.3 0 . 4 0 .5 C / C for  i d i c a t e d m e t a l o Figure 4 .28 COMPARISON OF COAL CAPACITY FOR REMOVING METALS FROM SOLUTION OF INDIVIDUAL METALS AND THEIR MIXTURE FOR STOCK PI LE REFUSE COAL . A - A - M i x e d me ta l s s o l u t i o n - 0 . 5 m g / l of each Cu, Pb and Zn - I nd i v i d u a l metal so lu t i on - 0 . 5 m g / 1 10 15 2 0 25 3 0 35 4 0 4 5 V o l u m e p a s s e d t h r o u g h - l i t e r s 5 0 Figure 4 . 2 9 BREAKTHROUGH CURVES FOR ZINC AND COPPER FROM THEIR PURE SOLUTIONS AND FROM THE MIXTURE OF METALS WITH STOCK PILE REFUSE COAL. in the mixture to a level comparable with that of effluent from solutions of single metals. The total adsorptive capacity (combined removal of all the three metals in the mixture) of one coal at several C/C values of o each of copper and zinc in the mixture is compared with the capacity of coal to remove copper and zinc from individual metal solutions (see Figures 4.30 and 4.31). It is apparent that the presence of other metals in the solution causes a depression in the total capacity of the coal, reducing it to about 85 and 60 percent (on the Basis of mg of metal/g of coal) of the adsorptive capacity with individual metal solutions of copper and zinc respectively. For example, for C/C value of 0.1 (copper concen-o tration of 0.05 mg/1 in the column effluent), the stock pile refuse coal has a total adsorptive capacity of 0.52 mg/g of coal for mixed metals solution as compared with a capacity of 0.64 mg/g of coal for pure copper solution. This could be due to reduction in the number of open sites by adsorption of one metal, causing a reduction in the "concentration" of adsorbent available as a driving force to produce adsorption of the other metals, thus producing a mutually depressing effect on the total adsorption capa-city. On the basis of mole weight of metal removed per gram of coal, the difference is further magnified because of the higher atomic weight of lead (mole weight = weight in grams/atomic weight i.e. for same weight in grams of each metal, lead will have lower mole weight as compared with copper and zinc) being removed along with copper and zinc from a solution mixture of three metals. 0.8 r 0 . 7 g 0.6 o o cn N TJ © -e 0 .5 o (/) TJ O O <U E 0.4 CP E o 0 . 3 o Q. O O O O 0.2 0. 0 A - A -Mixed me ta l so lu t i on - 0 . 5 m g / I of e a c h Cu, Pb, Zn I n d i v i d u a l me ta l s o l u t i o n - 0 . 5 m g / 0.1 0.2 0 .3 0 .4 0 .5 C / C 0 f o r  i n d i c a t e d m e t a l Figure 4 . 3 0 TOTAL ADSORPTION CAPACITY OF COAL(mg of metal/g) WITH SOLUTIONS CONTAINING MIXTURE OF METALS AND INDIVIDUAL METALS FOR STOCK PILE R E F U S E COAL. C / C Q for  indicated metal Figure 4.31 TOTAL ADSORPTION CAPACITY OF COAL {fx mole of  metal/g) WITH SOLUTIONS CONTAINING MIXTURE OF METALS AND INDIVIDUAL METALS FOR STOCK PILE REFUSE COAL . For comparison purposes, the solution containing the mixture of metals was passed through an identical column packed with activated carbon*. The results of the column tests are shown in Figure 4.32. A comparison of Figure 4.32 with those of 4.26 and 4.27 makes it clear that activated carbon is substantially less effective than both special plant feed and stock pile refuse coal. The low metal removing efficiency of activated carbon may, in part, be due to its coarse grain size in comparison with coal. The poor results obtained in these tests do not necessarily reflect the results that would be obtained when dealing with a waste-water containing organics as well as soluble metals. In the latter case, good removal might very well be expected, due to complexation of the metals and the organics, with the organic ligand being adsorbed onto the activated carbon. However, it is to be anticipated that activated carbon would probably not be effective in removing heavy metals from solutions in a wastewater that contains no substantial amount of dis-solved organics. Similar tests were planned for kaolinite, montmorillonite clays and nitrohumic acid. However, due to the almost impermeable nature of clays and presence of large quantities of fines in the nitrohumic acid and its characteristic of being easily abraded,.it was not possible to pass the water through the columns packed with these materials at the desired rate with the available facilities. The performance of these materials on batch tests did not justify the extra time and expense involved in finding a method of successfully testing them on a flow-through basis. * DARCO - activated carbon; Grade (12x20), Atlas Chemical Industries, Inc. Chemical Division, Wilmington, Delaware 19899, U.S.A. Weight of carbon = lOg I n f l u e n t  pH F low rate = l g p m / f t ! Column depth = 10 inches 3 4 5 6 7 V o l u m e p a s s e d th rough - l i t e rs 8 10 II vO Figure 4 .32 BREAKTHROUGH CURVE FOR COPPER, LEAD AND ZINC MIXTURE WITH DARCO ACTIVATED CARBON. Chapter 5 CONCLUSIONS The conclusions of the study are as follows: 1) all six coals tested have the ability to remove high percent-ages of copper, lead and zinc from distilled water solutions containing as little as 0.5 mg/1 of these metals; 2) the best two coals: Kaiser Coal-Stock Pile Refuse and Kaiser Coal-Special Plant Feed, have the ability to reduce the metal concentration by 90 - 99 percent from an influent containing as little as 0.5 mg/1 of copper, lead or zinc. On a continuous-flow laboratory scale, effluent concentrations lower than the detectable level on an atomic absorption spectrophotometer were obtained; 3) all six coals tested have the ability to remove mercury from solution containing as little as 5 yg/1 of the metal. Even at this low concentration, the best coals were capable of about 80 percent metal removal. Under dynamic flow conditions the column effluent concentration of less than 1 yg/1 was obtained; 4) for copper, lead and zinc, stock pile refuse coal has a higher capacity and rate of adsorption than special plant feed coal. * The highest unit capacity recorded was 1.92 mg while using a Adsorptive capacity per gram of coal; calculated for that length of run that produces a final effluent concentration of 0.05 mg/1 for copper and zinc, 0.1 mg/1 for lead and 1.5 yg/1 for mercury. solution containing 1 mg/1 of lead. The minimum unit capa-city attained was 0.12 mg for special plant feed coal with a solution containing 2 mg/1 of zinc; 5) for an influent concentration of 4.76 yg/1 of mercury, special plant feed coal had a unit capacity of 1.3 yg as compared with 1.05 yg for stock pile refuse coal; 6) for the range of concentrations used, the coal had a higher unit capacity for low influent metal concentration (see Figure 4.22). The difference was very significant in the case of special plant feed coal, with the unit capacity being 280 percent higher for an influent containing 0.5 mg/1 than for an influent contain-ing 2 mg/1 zinc. For stock pile refuse coal the unit capacity for lower influent concentrations tested was only 15.4 and 20 percent greater than that of higher concentrations for copper and lead respectively; 7) the order of the removal capacities of various metals tested was the same for both batch and continuous flow column tests, with the lead, copper, zinc and mercury ranking in a descending order as listed; 8) increasing flow rate through the columns has the effect of de-creasing the unit capacity of coal. A five-fold increase in flow rate decreased the unit capacity of stock pile refuse coal for copper ions to 54% of the initial capacity; 9) by lowering the influent pH from 5.7 to 3, the capacity of the coal was decreased to a negligible level for all metals tested; for a solution containing 0.5 mg/1 of each, of lead, copper and zinc, the coal had distinctly different adsorptive affini-ties, in descending order as listed; the presence of other metals in solution not only caused a depression in the adsorptive capacity of coal for individual metals in the mixture, but also decreased the total adsorptive capacity of the coal to about 85 and 60 percent (on the basis of mg of metal/gio of coal) of the capacity with individual metal solutions of copper and zinc respectively; under dynamic flow conditions, activated carbon is inefficient as compared with coal in removing metals from water containing no organics in it. The low metal removing efficiency of activated carbon may, in part, be due to its coarse grain size in com-parison with coal. The poor performance of activated carbon in these tests, however, may not be representative of its effective-ness in removing metals when dealing with a wastewater contain-ing organics as well as soluble metals. In the presence of organics, high metal removing efficiency may well be expected due to complexation of metals and organics, with the organic ligand being adsorbed on to the activated carbon; on the basis of batch tests results, the coal had generally higher removal capacity than nitrohumic acid for the lower initial concentrations of the metals tested. However for the only metal (lead) tested at higher initial concentrations, the nitrohumic acid had removal capacity up to 4 times that of coal. Therefore, it is to be anticipated that the nitrohumic acid may perform more efficiently at higher initial concentrations; 14) batch tests comparison indicated a higher metals removing capacity of kaolinite and montmorillonite clays than the best two coals. This cah'-be explained, in part, by very fine grain size (large surface area) of the clays as compared with coal. The difference was very significant in the case of lead, with the removal capacity of montmorillonite being up to 50 times as much as that of the coals. In general, the residual concentration achieved with clays, for the same initial con-centration of the metals tested, were lower than the coals. For example, with an initial concentration of 0.5 mg/1 of zinc, the residual concentration was five times less than that achieved by the best coal (i.e. 0.01 mg/1 for clays as compared with 0.05 mg/1 for coal). However, because of their very fine grain size, the clays cannot be used in columns like granular coal. On the basis of capacity and rate of adsorption, the Kaiser Coal-Stock Pile Refuse sample is the best of all the six coals used in this investigation. For the range of concentrations tested, the coal has the ability to reduce the column effluent concentrations to a level lower than the suggested allowable concentrations (22) for industrial effluent discharges into fresh or marine waters in British Columbia. At such a low effluent concentration, the adsorptive capacity of the coal is relatively low. Therefore, a relatively large amount of coal is needed to treat a given volume of wastewater. However, the adsorptive capacity of the coal can be increased by providing a greater contact time. This can be achieved by using one large column or more than one column in series. No column tests were performed with influent metal concen-trations higher than 2 mg/1. On the basis of batch tests data, however, it is to be anticipated that coal will have higher adsorptive capacity while dealing with wastewater containing higher metal concentrations. But, to achieve the effluent concentrations comparable to those for the influent concentrations tested (2 mg/1 and less), substantially greater column contact time may be required. The higher metal concentrations of such magnitude are usually associated with metal finishing industries (Electroplating plants, etc.) which generally have small volumes of wastewater. Under such conditions, relatively long column contact time can be provided to achieve low effluent concentrations and higher adsorp-tive capacity of coal. This suggests that the coal may be a feasible alternate for purifying effluents containing heavy metals from metal finishing industries. As regard with the use of coal to remove trace . metals from domestic wastewater (sewage), it is anticipated that the metals removing capacity of coal may be decreased, due to interference caused by organics present in the wastewater. However, higher metals removing capacity may very well be expected, due to complexation of the metals and the organics, with the organic ligand being adsorbed onto coal. REFERENCES 1. Argo, D.G. and G.L. Culp, Heavy Metals Removal In Wastewater Treat-ment Processes: Part I. Water and Sewage Works 119(8):62-65, August, 1972. 2. Argo, D.G. and G.L. Culp, Heavy Metals Removal in Wastewater Treat-ment Processes: Part II - pilot plant operation. Water and Sewage Works 119(9):128-132, September, 1972. 3. Barth, E.F., M.B. Ettinger, B.U. Salotto and J.N. McDermott, Summary Report on the Effects of Heavy Metals on Biological Treatment Processes. Journal WPCF 37:86-96, January, 1965. 4. Barth, E.F., J.N. English, B.V. Salotto, B.N. Jackson and M.B. Ettinger, Field Survey of Four Municipal Wastewater Treatment Plants Receiving Metallic Wastes. Journal WPCF 37:1101-1117, August, 1965. 5. Buhler, D.R., Environmental Contamination by Toxic Metals. Heavy Metals in the Environment. Water Resources Research Institute, Oregon State University, SEMN WR016.73:l-36, January, 1973. 6. Cheremisinoff, P.N. and Y.H. Habib, Cadmium, Chromium, Lead and Mercury: a plenary account for water pollution - Part I. Water and Sewage Works 119(7):73-85, July, 1972. 7. Cheremisinoff, P.N. and Y.H. Habib', Cadmium, Chromium, Lead aiid Mercury: a plenary account for water pollution - Part II removal techniques. Water and Sewage Works 119(8):46-51, August, 1972. 8. Coulthard, T.L. and Mrs. Samia Fadl, The Adsorption of Water Pollutants by a Coal Sorption Process. Paper No. 73-506 presented at Can. Soc. Agr. Eng. Annual Meeting at Victoria, B.C., August, 1973. 9. D'ltri, F.M., Mercury in the Aquatic Ecosystem, p. 1-73 in G.E. Glass (ed.) Bioassay Techniques and Environmental Chemistry. Ann Arbor Science Publisher, Inc. P.O. Box 1425, Ann Arbor, Michigan, 1973. 10. Evans, R.L., T.S. William and S. Lin, Mercury in Public Sewer Systems. Water and Sewage Works 120(2):74-76, February, 1973. 11. Hendren, M.K. and W.K. Oldham, Storm Sewer Discharge Study, Okanagan Basin Study Task 133, September, 1973. 12. Hendren, M.K., Heavy Metals Removal by Using Coal. Unpublished M.A.Sc. Thesis, University of British Columbia, Vancouver, British Columbia, 1974. 13. Jenkins, S.H., D.G. Keight and A. Ewins, The Solubility of Metal Hydroxides in Water, Sewage and Sewage Sludge - II, The Precipitation of Metals by Sewage. Int. Jour. Air Water Poll. 8:679-693, 1964. 14. Linstedt, K.D., C.P. Hauck and J.T. O'Connor, Trace Element Removal in Advanced Wastewater Treatment Processes. Jour. WPCF 43: 1507-1513, July, 1971. 15. Sartor, J.D. and G.B. Boyl, Water Pollution Aspects of Street Surface Contaminants. Environmental Protection Technology Series EPA -R2-72-081, November, 1972. 16. Sawyer, C.N. and P.L. McCarty, Chemistry for Sanitary Engineers. Second Edition, McGraw-Hill Book Company, 1967. 17. Turney, W.G., Mercury Pollution: Michigan's Action Program. Jour. WPCF 43:1427-1438, July, 1971. 18. Weber, W.J. Jr., Physiochemical Processes for Water Quality Control. Chapter 5: 199-259. Wiley-Interscience, a division of John Wiley & Sons Inc., New York. 19. , Determination of mercury by Flameless Atomic Absorption. Jarrell Ash - Atomic Absorption Analytical Method. No. Hg-1, August, 1970. 20. , Development of a Coal Based Sewage Treatment Process. Research and Development Report No. 55. Office of Coal Research, U.S. Department of Interior, Washington, D.C. , 1971. 21. , Guidelines for Water Quality Objectives and Standards. Technical Bulletin No. 67. Department of the Environment, Ottawa, 1972. 22. , Pollution Control Objectives for Mining, Mine Milling and Smelting Industries of British Columbia. Department of Lands, Forest and Water Resources, Water Resources Service, Victoria, B.C., December, 1973. APPENDIX I COLUMN BREAKTHROUGH CURVES 0.5i- In f luen t  concen t ra t i on a> 0 . 4 \ CP E i o 0 .3 c a> £ 0.2 o o c a> ^ 0.1 UJ Weigh t of c o a l : K.C. SPR = 27g K.C. SPF = 2 0 g I n f l u e n t  pH = 5 . 7 F low ra te = I g p m / f t . C o l u m n dep th = 10 in. I I * — 0 10 15 2 0 25 30 35 V o l u m e passed through - l i ters 4 0 45 50 o o V o l u m e p a s s e d t h r o u g h - l i t e r s Figure 2 BREAKTHROUGH CURVES FOR COPPER WITH SPECIAL PLANT FEED COAL. V o l u m e passed through - l i ters Figure 3 BREAKTHROUGH CURVES FOR COPPER WITH STOCK PILE REFUSE COAL. Weigh t of coa I : A - & - K.C. SPR - K . C . S P F I n f l u e n t  pH F l o w r a t e Co lumn d e p t h 2 5 g 2 0 g 5 . 8 Igpm / f  t f 10 in. 15 20 25 3 0 35 V o l u m e passed through - l i t e rs H O 2 . 0 .5 -1.0 -0 . 5 0 0 Wei g ht of coa I : - K . C . SPR * - * - K . C . S P F Flow ra te C o l u m n d e p t h 10 15 2 0 2 5 Vo lume passed through - l i te rs = 25 g = 20 g 2 = l gpm/ f t . = lO in . -pH = 5.7 3 0 35 4 0 5.0 r 4 . 0 3 . 0 2 2.0 | I .0 Weigh t of c o a I : A - A - K.C. SPR = 2 5 g * - * - K.C. SPF = 2 0 g I n f l u e n t  pH = 5 . 6 Flow rate = l g p m / f t 2 Co lumn depth = 10 in. 0 _L 0 3 4 5 6 V o l u m e p a s s e d t h r o u g h - l i ters 8 10 H O Uv 0.5 <D .t: 0 . 4 0 .3 0.2 ® 0. I 0 0 W e i g h t of coa I : K.C.SPR = 27g * - * - K . C . SPF = 2 0 g I n f l u e n t  pH = 5 . 8 2 F low ra te = I g p m / f t . C o l u m n depth - 10 in. 8 12 16 20 2 4 V o l u m e passed through - l i t e r s 28 32 36 o ON 2 . 0 i -^ } p H = 5.-6 8 10 V o l u m e p a s s e d through - l i ters o APPENDIX E SAMPLE CALCULATIONS 0.5 Inf luent  concentrat ion 5 10 15 20 25 Vo lume p a s s e d through - l i te rs BREAKTHROUGH CURVE FOR ZINC WITH STOCKPILE REFUSE COAL . For effluent concentration of X mg/1 mg of metal removed/gram of coal Area ACDF - Area CDE weight of coal For X = 0.05 mg/1 Area ACDF = 0.5 x 23.8 • 11.90 mg Area CDE =0.17 mg. Coal weight = 25 grams mg of metal removed/gram of coal = 11.30 - 0.17 25 11.73 25 = 0.47 similarly, the coal capacity for other effluent concentrations can be determined. 

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