United States Environmental Protection Agency Industrial Environmental Research Laboratory Research Triangle Park NC 27711 EPA-600/2-79-204 November 1979 Research and Development Coagulation and Precipitation of Selected Metal Ions from Aqueous Solutions ------- RESEARCH REPORTING SERIES Research reports of the Office of Research and Development, U.S. Environmental Protection Agency, have been grouped into nine series. These nine broad cate- gories were established to facilitate further development and application of en- vironmental technology. Elimination of traditional grouping was consciously planned to foster technology transfer and a maximum interface in related fields. The nine series are: 1. Environmental Health Effects Research 2. Environmental Protection Technology 3. Ecological Research 4. Environmental Monitoring 5. Socioeconomic Environmental Studies 6. Scientific and Technical Assessment Reports (STAR) 7. Interagency Energy-Environment Research and Development 8. "Special" Reports 9. Miscellaneous Reports This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT RESEARCH AND DEVELOPMENT series. Reports in this series result from the effort funded under the 17-agency Federal Energy/Environment Research and Development Program. These studies relate to EPA's mission to protect the public health and welfare from adverse effects of pollutants associated with energy sys- tems. The goal of the Program is to assure the rapid development of domestic energy supplies in an environmentally-compatible manner by providing the nec- essary environmental data and control technology. Investigations include analy- ses of the transport of energy-related pollutants and their health and ecological effects; assessments of, and development of, control technologies for energy systems; and integrated assessments of a wide range of energy-related environ- mental issues. EPA REVIEW NOTICE This report has been reviewed by the participating Federal Agencies, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Government, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. This document is available to the public through the National Technical Informa- tion Service, Springfield, Virginia 22161. ------- EPA-600/2-79-204 November 1979 Coagulation and Precipitation of Selected Metal Ions from Aqueous Solutions by C.W. Westbrook and P.M. Grohse Research Triangle Institute P.O. Box 12194 Research Triangle Park, North Carolina 27709 Contract No. 68-02-2612 Task No. 103 Program Element No. IBB610 EPA Project Officer: John S. Ruppersberger Industrial Environmental Research Laboratory Office of Environmental Engineering and Technology Research Triangle Park, NC 27711 Prepared for U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Research and Development Washington, DC 20460 ------- ABSTRACT Laboratory jar tests were conducted to develop data on the removal from aqueous solution of 12 metal ions of environmental concern. The project, which was of very limited scope, provides initial screening data only. Thus, coagulants were evaluated at only two dose levels (1.1 and 1.5 stoichiometric), no combinations of metals or coagulants were evaluated, and no attempt was made to optimize precipitation conditions. The metal ions tested were: Al+3, Be+2, Bi+3, Cr"1"3, Mo+3, Sb+3, V+3, +2 +3 +4 +3 +5 Zn , Ti , Se , As , As . Treatment chemicals used were: lime (Ca(OH)2), sodium sulfide (Na2S), alum (A1K(S04)2), and ferrous sulfate (FeS04). Chromium, aluminum, and titanium concentrations were reduced to below 0.5 mg/2. at pH 8 by lime addition. Alum was effective for titanium removal (probably due to pH effects) and marginally effective for vanadium and arsenic (+5). Beryllium, bismuth, zinc, and titanium were reduced to below 1 mg/a by sodium sulfide treatment. Ferrous sulfate was not effective in removing antimony, selenium, or arsenic (+5). Additional treatment with a flocculent-coagulant, i.e., organic polymer, may be required for the consistent removal of the fine suspension formed by some of the metal ion-coagulant systems tested. in ------- CONTENTS Abstract i'11 Tables v Acknowledgement V1* 1.0 Introduction 1 2.0 Summary and Conclusions 2 3.0 Background Information 6 4.0 Test Data. 8 4.1 Reagents and Solutions 8 4.2 Coagulant Dosage Calculations 9 4.3 Test Procedures 10 4.4 Atomic Absorption Analysis 10 4.5 Test Results 11 iv ------- TABLES Number Page 1. Summary of Results 4 2. Test Results ; 12 ------- ACKNOWLEDGEMENT This report has been submitted by Research Triangle Institute in partial fulfillment of the requirements of EPA Contract No. 68-02-2612, Task 103. The authors are grateful to Mr. John Ruppersberger for his advice and assis- tance. RTI also wishes to express its appreciation to Mr. Jack Robertson of Catalytic, Inc. and to J. M. Cohen of EPA - Cincinnati for their comments and suggestions on the work. vi ------- 1.0 INTRODUCTION The requirements of the 1977 Amendments to the Clean Water Act emphasize the control of "Toxic" or "Priority Pollutants." In addition to the 13 metals designated as toxic and which are to be.controlled by Best Available Technology Economically Achievable regulations that industry must meet by July 1, 1984, there are other metals and non- metals of environmental and health concern. Although a number of highly effective methods continue to become available for removal of heavy metals from wastewater, chemical precipi- tation is currently the most commonly used and practical technique and is possibly the best approach for coping with the metals removal problem up to and including 1984. The purpose of this project was to develop specific data for incor- poration into a wastewater treatability model. As such, the scope of work was specific and limited. Each metal ion was to be treated with a specific chemical at two dose levels (1.1 and 1.5 stoichiometric) with the final pH in the range 6-9. RTI also evaluated some other pH's and chemicals where these specified conditions proved to be inappropriate. All experiments were simple jar tests using analytical grade re- agents and distilled water as the medium. We recognize that the variable chemical environment found in actual wastewater can affect the removal of metal ions present. However, to provide a consistent data base for use in the model, this variability was reduced substantially by using distilled water. Section 2 of this report summarizes the data obtained and conclusions that can be drawn. Section 3 presents some background information that was obtained on the metal ions and coagulation methods tested. The test proce- dures and test results are presented "in Section 4. ------- 2.0 SUMMARY AND CONCLUSIONS Table 1 summarizes the test data obtained. The first two columns give the metal ion and coagulant(s) tested. Columns three and four give the stoichiometric ratio (see Section 3) for the coagulants and the final pH, respectively. The fifth column gives the concentration of metal ion remain- ing (typically 100 mg/n initially) in the solution after filtration by a Whatman No. 40 filter (medium porosity) which may be similar to that expect- ed from clarification and sand filtration. The last column gives the metal ion concentration obtained after washing the precipitate, suspending it (shaken by hand at infrequent intervals) in water for 24 hours, and filtering through a 0.8 p millipore filter. This information is useful for situations where physical-chemical sludges generated must be washed before disposal and as an estimate of the Teachability of the sludge. The data show that pH adjustment (lime addition) is effective for the removal only of Al , Cr , and Ti . Alum is effective for the removal of +3 Ti , probably due to pH effects, and marginally effective in the control of V+3 and As+5.' Removal of Be+2, Bi+3, Zn+2, Ti+3 was effected by Na2S addi- tions. Ferrous sulfate was not effective for the removal of Sb , Se , or As . Mo , Sb , Se , As , and As were not effectively removed by the coagulants used for these ions (Mo and As were tested only with Na2S; all coagulants were used with the remaining three) under the conditions used. Aluminum hydroxide becomes more soluble as the pH is raised above 8. Therefore, optimum control will be obtained between pH 5 and pH 7. Several of the test solutions, most notably AT, Cr, and Zn, appeared to be somewhat turbid after filtration. Some of these were reanalyzed after standing for one day. The original Zn solution had been discarded before we observed that some of the solutions cleared on prolonged standing. Duplicate experi- ments were performed and the solution allowed to stand"3 hours before being filtered. In all cases a substantially lower metal concentration was obtained. ------- This indicates that some of the precipitate formed is very finely divided. To adequately remove the metals from solution, particularly when lime or H&2^ is used, may require the use of an additional coagulant, i.e., organic polymer. It will also be observed that a number of cases occurred where the metal concentration was higher from the resuspended precipitate filtrate than in the original test solution filtrate. The effect is apparently not due to suspended solids since the original filtrate passed through a medium porosity filter, Whatman 40, whereas the resuspended particulate .filtrate passed through a fine filter, 0.8 v millipore. When the precipitate was washed, ions present in the original test solution were removed. Thus, one might conclude that these ions reduce the solubility of the precipitate and/or effect the desorption of the metal from the precipitate. This implies that some precau- tions should be taken in the washing and/or disposal of these sludges. ------- TABLE 1. SUMMARY OF RESULTS Metal Al+3 4-7 Be d , Q Bi J Cr+3 Mo+3 J.O Sb+3 y+3 Coagulant Ca(OH)2 Alum Ca(OH)2 Na9S c. Na2S Ca(OH)2 Na0S c. Alum Ca(OH)2 Na2S FeS04 Na2S Ca(OH)2 Alum Stoichiometric Ratio - - - _ 1.1 1.5 - 1.1 1.1 1.5 1.1 1.5 - _ - - 1.1 1.1 1.5 - 1.1 1.1 1.1 1.5 - - 1.1 Final pH 7.0 8.0 9.0 10.0 7.3 6.9 8.0 8.0 8.9 9.2 8.0 8.0 7.0 8.0 9.0 10.0 7.5 7.2 8.3 8.0 6.6 8.0 8.5 8.5 8.0 10.0 7.0 Metal Filtrate Solubility from mg/A Solids, mg/& 5 (0.4)* 0.4 * 31 (20) 48 > 50 16 MOO 0.3 < 0.03 < 0.03 < 0.5 2.5 10 0.6 if 12 (0.4) 0.12 No reaction 22 12 ^ 50 13 10 > 50 > 50 32 27 20 < 0.1 1.1 6.4 16 21 0.2 0.05 < 0.03 < 0.1 < 0.05 < 0.05 occurred 8.4 13 . 1.7 1.6 Value obtained after one day aging. (Continued) 4 ------- TflRI F 1 Metal Zn+2 T1+3 SeH As+5 As*3 Coagulant Na2S Alum Na2S Ca(OH)2 Na2S Ca(OH)2 Alum FeS04 Na2S Ca(OH)2 Alum FeS04 Na2S Stoichiometric Ratio 1.1 1.5 1.1 1.5 1.1 1.5 1.1 1.1 1.1 1.1 1.5 1.1 1.5 - 1.1 1.1 1.1 1.5 - 1.1 1.1 1.1 1.5 Final PH 8.5 7.0 8.0 8.0 8.6 7.3 7.0 8.8 8.6 8.0 8.0 8.0 8.0 8.5 10.0 7.2 8.0 5.5 9.6 8.0 7.0 8.0 5.0 5.5 Filtrate mg/2. 1.2 > 50 0.07 0.6 < 0.5 < 0.5 < 0.1 < 0.5 < 0.5 0.2 0.3 < 0.1 > 50 > 50 MOO MOO MOO MOO MOO 39 6.0 MOO 25 18 Metal Solubility from Solids, mg/£ 0.7 1.1 5 5 0.2 0.8 0.4 < 0.1 0# # Probably indicates no Se in the precipitate. ------- 3.0 BACKGROUND INFORMATION A number of literature sources, listed at the end of this section, were consulted to determine appropriate precipitation conditions and other re- quired information. The data accumulated is not a complete review of the literature available on the subject. ,+3 Al Be3 A1(OH)3 is amphoteric (soluble at both low and high pH). The solu- bility product is about 2 x 10"33 (5 x 10"8 mg/fc Al) at pH 7. Aluminum sulfide cannot be prepared in aqueous solution. Bi+3 Cr+3 Sb+3 is amphoteric. The sulfide reportedly decomposes in aqueous solution. The sulfate is very water soluble. The hydroxide is not amphoteric. The water solubility is about 0.0014 gm/A (1.1 mg/A Bi). The sulfide can be formed in aqueous solution and has a solubility of about 0.00018 gm/A (0-14 mg/A). The "hydroxide" is thought to be merely a hydrated form of the oxide. The compound is amphoteric dissolving in excess strong base. The approximate solubility is 0.00064 mg/A. The sulfide cannot be made in aqueous solution. The sulfate is very water soluble. The hydroxide solubility is about 2 gms/A (1300 mg/A Mo+3). The sulfide is slightly soluble in water. The oxide is amphoteric. The sulfide can be formed in acid solu- tion (up to about pH 6) and has a solubility of about 0.0018 gm/A (1.3 mg/A Sb). The sulfide is soluble in neutral to alkaline 6 ------- Zn*2 Se+4 solutions and in solutions containing excess alkali sulfide (^S)- The oxide is basic (soluble in acid solution) and slightly soluble in water. Although the sulfide is insoluble in water, it is soluble in alkali sulfides. The hydroxide is amphoteric and when formed in aqueous solution forms a gelatinous precipitate. The solubility product is about 2 x 10"14 indicating the hydroxide is slightly soluble in water. The sulfide is white and has a solubility product of about 1 x 10"23. ZnS(a) has a water solubility of 0.0069 gm/A (4.6 rag/A In) while ZnS(P) has a solubility of 0.00065 gm/£ (0.44 rag/A Zn). The sulfide is soluble at pH less than 6. The oxide is very water soluble. The sulfide is insoluble in water but dissolves in excess sulfide reagent. As+3, As+5 The arsenic oxides are quite soluble in water. Arsenic(V) sulfide has a water solubility of 0.0014 gm/ji (0.6 mg/£ As) and arsenic (III) sulfide's water solubility is 0.0005 gm/ji (0.3 mg/ji As). Both sulfides are soluble at pH's above 6 and also are soluble in excess alkali metal sulfide (Na2S). Sources Handbook of Chemistry and Physics, 45th Edition, The Chemical Rubber Co., 1964. Fundamentals of Analytical Chemistry, Skoog and West, Holt, Rinehart and Winston, Inc., 1963. Inorganic Reactions and Structure, E. S. Gould, Holt, Rinehart and Winston, Inc., 1962. Calculations of Analytical Chemistry, Hamilton and Simpson, McGraw- Hill Book Co., Inc., 1960. General Chemistry, Miller and Babor, Wm. C. Brown Co., 1965. ------- 4.0 TEST DATA 4.1 REAGENTS AND SOLUTIONS All reagents used were analytical grade. All test solutions, except molybdenum and bismuth, were prepared containing 100 mg/£ of the metal ion. Lime (Ca(OH)2) and ferrous sulfate (FeSO^-7 H20) were added as dry powders. Alum (AlK(SO^,)2i12 H20) was weighed out before each test and dissolved in 30 ml of water before addition. A stock solution, prepared before each series of tests, of sodium sulfide (Na,,S'9 H20) containing 10 gms/£ was added to the test solutions using pipets. The test solutions were prepared as follows: +3 Aluminum - Al 0.1000 gm of aluminum wire was dissolved in dilute (3N) HC1 and diluted to 1 liter. Beryllium - Be*2. 2.0758 gms of Be(N03)2-3 H20 (F.W. 187.07) was dissolved in water and diluted to 1 liter. Bismuth - Bi . 0.0853 gm bismuth metal was dissolved in dilute (3N) HNO, o and diluted to 1 liter. Bi concentration was 85.3 mg/£. Chromium - Cr*3. 0.7695 gm Cr(N03)3'9 H20 (F.W. 400.15) dissolved in water and diluted to 1 liter. J.O Molybdenum -Mo . 0.2 gm MoCU suspended in water for 24 hours, filtered and analyzed by A.A. Mo concentration was 5.0 mg/£. Antimony - Sb*3. 0.1874 gm SbCl3 (F.W. 228.11) dissolved in dilute HC1 and diluted to 1 liter. Vanadium - V+3. 0.1471 gm V203 (F.W. 149.884) dissolved in dilute HN03 and diluted to 1 liter. Zinc - Zn*2. 0.1000 gm zinc metal dissolved in HC1 and diluted to 1 liter. Titanium - Ti+3. 0.3220 gm TiCl3 (F.W. 154.26) dissolved in dilute HC1 and diluted to 1 liter. Selenium - Se . 0.1633 gm H2Se03 (F.W. 128.97) dissolved in water and diluted to 1 liter. ------- Arsenic - As . 100 ml of arsenic A.A. standard (1000 mg/£) diluted to 1 liter. Arsenic - As*3. 0.1320 gm As203 (F.W. 197.84) dissolved in dilute HC1 and diluted to 1 liter. 4.2 COAGULANT DOSAGE CALCULATIONS Below are representative calculations of the coagulant dosage required for each coagulant used (except lime which was used for pH adjustment only). Alum. Calculations were based on the assumption that the metal sulfate is formed simply to provide a consistent technique for alum addition. The assumption is not necessarily valid since metal ion removal probably takes +2 place by adsorption on the aluminum hydroxide floe that forms. 2 Be + A1K(S04)2 ->• 2 BeS04. 500 ml of a 100 mg/i Be"1"2 solution contains 50 mg Be"1" . 50 mg * 9.012 gms/raole Be"1"2 = 5.548 millimoles/500 ml. Since the stoichio- +2 metric requirement is 0.5 millimole alum per millimole Be , 5.548/2 = 2.774 millimoles alum required for stoichiometric addition. Therefore, for a 1.1 stoichiometric addition, 1.1 x 2.774 = 3.051 millimoles are required. Since alum has a formular weight of 474.39, one millimole is 0.4744 gm. 3.051 millimoles alum is 1.4476 gms. The complete calculation is: ((50 mg * 9.012 mg/millimole) * 2) x 1.1 x 0.4744 gm/millimole = 1.4476 gms. Na^S. Calculations are based on the assumption the metal sulfide is formed. Bi 3 + 1.5 Na2S-9 H20 ->• 1/2 Bi2S3. 500 ml of an 85.3 mg/J. Bi3 solution con- tains 0.2058 millimole. Since 1.5 millimoles of the sulfide are required per millimole of Bi and one millimole of Na,,S'9 H20 is 0.24018 gm, the sulfide dosage required for 1.1 stoichiometry is (1.1)(1.5)(0.2058)(0.24018) = 0.0816 gm. The sulfide stock solution (10 gms/100 ml) contains 0.1 gm/ml. Thus 0.816 ml is required for the test. Ferrous Sulfate. The calculations assume the sulfate is formed (to provide a consistent basis for addition) although metal ion removal may actually occur by adsorption on the ferrous (-ic) hydroxide floe formed. Sb + 1.5 FeS04-7 H20 -> 1/2 Sb2(S04)3. 500 ml of a 100 mg/£ Sb+3 solution contains 0.4107 millimole. Since 1.5 millimoles of FeS04 7 H20 weighing 0.2781 gm per ------- millimole are required per millimole of Sb+3, (1.1)(1.5) x (0.4107)(0.2781) = 0.1885 gm FeS04'7 H20 are required for a 1.1 stoichiometric dosage. 4.3 TEST PROCEDURES One liter of the metal ion solution was prepared as previously described. The solution was equally divided and placed in two 1 liter flasks. A magnet- ic stirrer and a pH measuring electrode were also placed in the flask. The initial pH was measured and adjusted as necessary using appropriate strength NaOH or HC1. The selected coagulant was then added and the solution rapidly agitated for about one minute. The pH was measured and adjusted as required. Stirring was then reduced to that required to keep the precipitate in suspen- sion and maintained for 14 minutes. The suspension was then filtered through Whatman No. 40 filter paper. The filtrate was retained for atomic adsorption analysis. The solids collected were thoroughly washed with distilled water and resuspended (shaken by hand at infrequent intervals) in about TOO ml of distilled water. After 24 hours, this suspension was filtered through a 0.8 y millipore filter and the filtrate retained for A.A. analysis. Table 2 shows that the initial pH's were generally quite low compared to typical wastewater values. Operating in this manner, precipitates of A1(OH)3 and Fe(OH)2 did not form immediately when alum and ferrous sulfate were added. Since these compounds were soluble, they were completely mixed into the solution before the pH was raised to develop the floe. This technique could not be used with Na,,S because the H2S which would be formed would escape from the solution. Only the sulfide solution (and lime, of course) had any measurable effect on the initial pH. Addition of HC1 was required to control the pH rise caused by the addition of this strong caustic solution. 4.4 ATOMIC ABSORPTION ANALYSIS All analyses were completed on a Perkins-Elmer Model 603 atomic absorp- tion instrument which has background correction. Air/acetylene or N20/acety- lene flames were used as appropriate. A model 2100 Heated Graphite Furnace accessory was used for Ti, Mo as well as those metals having a concentration below 0.5 mg/£,. Electrodeless discharge lamps were used for As, Se, Sb, and Bi. Hollow Cathode lamps were used for other metals. Concentrations of the 10 ------- metals in the test solutions were determined by comparison with known concen- trations of the metals. In addition, the method of standard additions (adding a known amount of the test metal to the solution) was used to check the ana- lytical results. 4.5 TEST RESULTS Table 2 gives the test results and a comment on the precipitate formed. Unless otherwise indicated, the initial concentration of metal ion was 100 mg/a. 11 ------- TABLE 2. TEST RESULTS Metal Sb« Sb*3 Be+2 Be*2 T1+3 T1+3 C/3 Cr+3 Al+3 Al+3 B1+3 Bi+3 Set4 Se+4 _i_O V"1"3 As+5 As*5 Coagulant Type Dose Alum Alum Alum Alum Alum Alum Lime Lime Lime Lime Na2S Na?S c~ Na2S Na2S Na2S Na9S £ 1.5 1.1 1.1 1.5 1.1 1.5 M - _ _ 1.1 1.5 1.1 1.5 1.1 1.5 1.1 1.5 pH at pH after Test Start Addition 1.5 1.5 3.3 3.3 2.4 2.4 3.2 3.2 1.5 1.5 6.1 5.8 6.2 5.7 6.1 6.2 5.6 7.4 1.6 1.1 3.3 3.6 2.5 2.6 10.0 8.0 8.0 10.0 8.9 9.2 8.0 8.5 7.6 8.0 6.4 9.6 Final PH 8.3 7.2 7.3 6.9 8.6 7.3 10.0 8.0 8.0 10.0 8.9 9.2 8.0 8.5 8.5 8.5 5.5 9.6 Filtrate Cone . , mg/Ji 12 22 > 50 16 < 0.5 < 0.5 0.12 0.06 0.4 48 < 0.03* < 0.03* > 50 > 50 > 50 > 50 'vlOO 'vlOO Washed Filter Cone . , 13 8.4 16 21 < 0.05 < 0.05 1.1 6.4 0.05 < 0.03 0 0 1.7 1.6 - _ Comment Fine white needles formed on addition. Solids form at pH 4.5. Light blue solids form on addition. Turbid at pH 5.7 fine dispersed solids. Turbid at pH 6. Dark brown solids slow settling fines. Cloudy yellow sus- pension, probably sulfur. Dark green-brown soln. no solids evident. Colorless, clear _ _ ^ . * solution. Initial concentration 85 mg/£. (Continued) ------- TABLE 2. (Continued) Metal +3 T1 J Zn+2 Zn2 Se+4 Se+4 v+3 _ Sb 4-9 Be+2 +R As , v+j • o Cr+3 Cr ** A1+3 „ Al d Coagulant Type Dose Na2S 1.1 Na2S 1.5 Na2S 1.1 Na2S 1.5 Lime Alum 1.1 Lime Lime Lime Lime Lime Lime Lime Lime Lime pH at Test Start 7.1 7.2 6.3 6.2 3.3 3.3 1.1 1.0 4.1 1.2 8.0 3.5 3.5 1.5 1.5 pH after Addition 9.7 9.9 6.8 7.0 9.8 3.3 7.9 8.0 8.0 8.0 10.0 9.0 7.0 7.0 9.0 Final pH 8.8 8.6 8.5 7.0 9.8 7.2 7.9 8.0 8.0 8.0 10.0 9.0 7.0 7.0 9.0 Washed Filtrate Filter Cone . , Cone . , mg/ & mg/ a < 0.5 < 0.5 1.2 0.7 > 50 1.1 MOO MOO 32 ^50 MOO 39 27 H 12 (0.4)ff 10 < 0.1 5 (0.4)# < 0.1 # 31 (20)ff Comment White solids, turbid suspension. White solids, turbid suspension. Clear Alum precipitate Brown solution, discrete particles. Slow settling white solids. Light blue gelat- inous precipitate. Milky colored suspension. No precipitate formed . Filtered solution turbid but clears on prolonged stand- ing. Milky, clears on standing. # Concentration determined after one day settling. (Continued) ------- TABLE 2. (Continued) Coagulant Metal Ti Ti+3 V +5 As b Zn"1"2 +2 Zn L Mo+3 Bi+3 Bi J Be+3 _ Sb J _ Ti . *% Ti+3 Se+4 Type Lime Alum Alum Alum Na9S L. Na2S Na2S Na?S Na9S C Na9S L. Na9S c. Na9S FeSO, Dose 1 1 1 1 1 1 1 1 1 1 1 1 1 — .1 .1 .1 .1 .5 .1 .1 .5 .1 .1 .1 .5 .1 pH at pH after Test Start Addition 2.5 2.5 1.0 1.0 6.6 5.6 5.4 5.0 4.6 3.8 4.8 5.8 5.2 3.1 8 7 7 7 9 10 8 10 10 6 Held at Held at Held at 3 .2 .0 .0 .0 .8 .3 .8 .5 .4 .8 7 8 8 .1 Final pH 8. 7. 7. 7. 8. 8. 7. 8. 8. 8. 6. 8. 8. 8. 2 0 0 0 0 0 5 0 0 0 6 0 0 0 Washed Filtrate Filter Cone., Cone., mg/fc < 0. < 0. 2. 6. 0. 0. 5f < 0. 2. 0. 13 0. 0. ^100 mg/K, 1 < 0.1 1 0.2 0 0 07 5 6 5 5 5 3 0.2 2 0.8 3 0.4 Comment White solids. Immediate solids formation. Brown solids, easily settled. Milky solution. Fluffy blue-white solids. No reaction Reddish-brown solids easily settled. Cloudy, poor settling. Orange, poor settling. Turbid, white solids. Iron hydroxide Initial concentration 5 (Continued) precipitate. ------- Coagulant Metal Sb As As As +3 +5 +3 +•? Type FeS04 FeSO. *t c. Na9S Dose 1.1 1.1 1.1 1.5 PH Test 5 5 4 3 at Start .0 .1 .5 .5 Held pH after Addition 5 8 10 at .0 .0 6 Final pH 8.0 8.0 5.0 5.5 Filtrate Cone . , mg/fc 10 MOO 25 18 Washed Filter Cone . , mg/& Comment Cloudy, yellow solution, settling. poor ------- TECHNICAL REPORT DATA (Please read Instructions on the reverse before completing} 1. REPORT NO. EPA-600/2-79-204 3. RECIPIENTS ACCESSION NO. 4. TITLE AND SUBTITLE Coagulation and Precipitation of Selected Metal Ions from Aqueous Solutions S. REPORT DATE November 1979 6. PERFORMING ORGANIZATION CODE 7. AUTHOH(S) C.W. Westbrook and P.M. Grohse 8. PERFORMING ORGANIZATION REPORT NO. 9. PERFORMING ORGANIZATION NAME AND ADDRESS Research Triangle Institute P.O. Box 12194 Research Triangle Park, North Carolina 10. PROGRAM ELEMENT NO. 1BB610 11. CONTRACT/GRANT NO. 68-02-2612, Task 103 12. SPONSORING AGENCY NAME AND ADDRESS EPA, Office of Research and Development Industrial Environmental Research Laboratory Research Triangle Park, NC 27711 15. SUPPLEMENTARY NOTES 62, 919/541-2733. 13. TYPE OF REPORT AND PERIOD COVERED Task Final; 6-10/79 14. SPONSORING AGENCY CODE EPA/600/13 •••^••^•••^^••^•••••^^•^•^••••••i project officer is John S. Ruppersberger, Mail Drop 16. ABSTRACT The report gives results of laboratory jar tests to develop data on the re- moval from aqueous solution of 12 metal ions of environmental concern. The project, of very limited scope, provides initial screening data only: coagulants were evaluated at only two dose levels (1.1 and 1. 5 stoichiometric), no combinations of metals or coagulants were evaluated, and no attempt was made to optimize precipitation condi- tions. The 12 metal ions were: Al(+3), Be(+2), Bi(+3), Cr(+3), Mo(+3), Sb(+3), V(+3), Zn(+2), Ti(+3), Se(+4), As (+3), and As(+5). Treatment chemicals used were lime, sodium sulfide, alum, and ferrous suliate. Cr(+3), Al(+3), and Ti(+3) concen- trations were reduced to below 0. 5 mg/1 at pH 8 by lime addition. Alum was effective for Ti(+3) removal (probably due to pH effects) and marginally effective for V(+3) and As(+ 5). Be(+ 2), Bi(+ 3), Zn(+ 2), and Ti(+ 3) were reduced to below 1 mg/1 by sodium sulfide treatment. Ferrous sulfate was not effective in removing Sb(+3), Se(+4), or As(+5). Additional treatment with a flocculent-coagulant (e.g. , organic polymer) may be required for the consistent removal of the fine suspension formed by some of the metal ion-coagulent systems tested. 17. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.lDENTIFIERS/OPEN ENDED TERMS c. COS AT i Field/Group Pollution Metals Ions Solutions Precipitation Coagulants Calcium Hydroxides Alums Iron Sulfate Flocculents Pollution Control Stationary Sources Metal Ions Aqueous Solutions Sodium Sulfide 13B 07B 11F,07B 07D,20H 06O,11G 13. DISTRIBUTION STATEMENT Release to Public 19. SECURITY CLASS (ThisReport) Unclassified 21. NO. OF PAGES 20. SECURITY CLASS (Thispage) Unclassified 22. PRICE EPA form 2220-1 (9-73) ------- |