Investigations of leachability characteristics of metal contaminants from plating and galvanising solid wastes by TCLP

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1 ndian Journal of Chemical Technology- Vol. 4, November 1997, pp nvestigations of leachability characteristics of metal contaminants from plating and galvanising solid wastes by TCLP B Singh", M Mudgal, Alka Mishra, Divya Dawar & B Chakradhar Regional Research Laboratory, Council of Scientific & ndustrial Research, Bhopal , ndia Received March 1997; accepted 13 October 1997 n the present investigation, Toxicity Characteristics Leaching Procedure (TCLP) has been employed to investigate the leachability characteristics of metal contaminants from plating and galvanising wastes. Atomic absorption spectroscopy (AAS) analysis of extracts of Cr-plating waste indicates that leachability of Cr, Fe, Pb and Mn in secondary extract is high as compared to primary extract. Occurrence of notably high concentration of Zn and Fe in primary extract of galvanising waste suggests their immediate leachability in s6il. Toxicity due to Pb and Mn of plating and galvanising waste is expected to be quite high in immediate and long-term duration because of their significant leachability in primary and secondary extract. With an increase of temperature from 30 to 60 C, the leachability of Cr from plating waste and Zn from galvanising waste increases significantly while a slight increase of leachability of Fe, Pb and Mn is noticed in both wastes. Estimation of leachability of metal based hazardous waste is quite necessary to predict the extent of toxicity of metal contaminants in the soil immediately and in long-term duration. Analytical methods based on colorimetry or atomic absorption spectroscopy quantify the total concentration of metals in hazardous waste but it does not give any idea about the role of heavy metals in increasing the leachability in the soil. n leachate procedures, little research work has been carried out to identify and estimate the leachability of metals in soil. An approach commonly used for studying the mobility of metals in soil is to use selective sequential extraction procedure 1.2 in which the extract of increasing strength estimates the distribution of metals among the other exchangeable constituents. Recently developed leaching procedures 3-5 are used to examine the leachability characteristics of a particular solid waste in soil which determine the element mass fraction available for leaching in a wide range of ph. However, above procedures do not provide any idea about immediate or long-term leachability of metal contaminates in soil. For correspondence Zero Head Extractor (ZHE) has been designed to determine extraction potential (EP) toxicity of a particular metal or organic contaminants in immediate or long-term duration. EP toxicity is a major characteristics by which a hazardous waste can be identified. This characteristic is a measure of the likelihood that the waste will leach out toxic contaminants. The procedure used to estimate the extent of toxicity characteristics of particular contaminants of hazardous waste by this set-up is commonly known as Toxicity Characteristics Leaching Procedure (TCLPt 7 TCLP determines the mobility of organic and inorganic analytes of liquid, solid or multiphasic wastes in the form of primary and secondary extracts. Primary extract is a measure of immediate leachability of toxic contaminants while secondary extract determines the long-term mobility of-contaminants. n the present.investigation, TCLP has been employed to estimate the toxicity effects of some of the toxic metals, viz., chromium, zinc, iron, lead and manganese in the temperature range of 30 to 60 C of plating and galvanising ETP.waste sludges. Besides, estimation of toxicity effects of a particular metal, understanding the leachability

2 SNGH et al.: LEACHABLTY CHARACTERSTCS OF METAL CONTAMNANTS 2 characteristics of plating and ga1vanising waste were also the main objectives of present work. Experimental Procedure The plating and galvanising hazardous waste samples were collected from the sludge generated after neutralisation of inlets from respective effluent treatment plant. The solid wastes were dried at 150 C for four hours to remove moisture. Samples were then digested as per standard method8 and particular metal was analysed by AAS..n TCLP operation, first step is the preparation of the extraction fluid in which sample is dissolved for extraction of primary and secondary extract. Extraction fluid was prepared by taking 64.3 ml of.on sodium hydroxide and 5.7 ml acetic acid (density, 1.05) in 500 rnl volumetric flask. The remaining volume was maintained by adding deionised water and ph of solution became Then 25 g of dried solid waste was taken in Zero Head Extractor (ZHE ) barrel (capacity, nearly 500 m1) and extraction fluid was added in the ratio of 1:20 as reported elsewhere 6.7. The details of various parts of Zero Head Extractor ( ZHE ) is given in Fig. 1. The nitrogen gas was used for maintaining the requisite pressure in the ZHE assembly. A glass fibre filter of 0.8 J.l.m pore size is used for extraction which was placed in between the support screens of ZHE barrel as shown in Fig. 1. The ZHE was connected with all the fittings and then the pressure was increased to 50 psi the increment. being 10 psi at every two minutes. The primary leachate was collected in the syringe, fitted at the top of the ZHE for every 10 psi increase and 50 ml of total leachate was collected as a primary extract. The pressure vessel was then connected with the ZHE and the capacity was made up to its original volume by adding the extraction fluid. The ZHE was fitted and kept in the rotatory agitator for 18 h. After completion of agitation all the fittings were connected again and using the same procedure, as adopted for pnmary leachate the same extent, secondary leachate was collected. To study the temperature effect on leachability, extraction fluid was heated on heating mentle in a round bottom flask and temperature was maintained at 30, 40, 50, and 60 C within an accuracy of ±2 C. The extraction fluid was then transferred into the ZHE barrel and leachates were extracted as per above procedure. After extraction, leachates were acidified and analysed using AAS for different metals fractions present in the waste extracts. Results and Discussion Estimation of extraction potential (EP) toxicity-elemental concentration of major constituents like Cr, Fe, Pb and Mn of plating and Zn, Fe, Pb, Mn of galvanising wastes are given in Table 1. Analysis results indicate that plating waste contains low concentration of Fe, Pb and Mn in comparison to their concentration present in galvanising waste. A low concentration of Cr is found in plating waste but a marginally high concentration of Zn is measured in galvanising waste (Table ). The percentage of EP toxicity of above metals in primary and secondary extracts of plating and galvanising wastes are compared in Figs 2 and 3, respectively. Percentage EP toxicity for particular metal has been estimated from its total concentration present in the specific waste. t is interesting to note that % EP toxicity of Cr in plating waste is nearly two times more in secondary extract than primary extract. The increase of EP toxicity of Fe, Pb and Mn in Fig. -Various parts of Zero -Headspace Extractor (ZHE) Table -Concentration of major metal contaminants present in the plating and galvanising wastes (mglg) Solid waste system Cr- plating waste Galvanising waste Metal Q)ntaminants Cr Fe Pb Mn Zn S.S S S

3 300 NDAN J. CHEM. TECHNOL., NOVEMBER 1997 = ; J) '"..... PLATNG WASTE.. "! > t: 01.5 )( o :. :::::... ::::. :::::: -:-;.:....' 1::::1 '. ', fh: , F. Cr pb Mft METAL eontamwn Fig. 2-Percentage EP toxicity of Fe, Cr, Ph and Mn in primary (1li)and secondary (m) extracts of Cr- plating waste 6' GAL\\NSNG WASTE Fe Pb Mn METAL CONTAMNANTS Fig. 4-Comparative EP toxicity of Fe, Pb and Mn in primary extract of plating (1m and galvanising (S) wastes 6 o 0 -- _L....- L. 111 "# 4P? ;fjhfjj ll : Fig.3-Percentage EP toxicity of Fe, Ph, Mn and Zn in primary (CD) and secondary (m) extracts of gavanising waste secondary extract was low as compared to increase of EP toxicity of Cr ( Fig. 2 ). Leachability characteristics of above metals predict toxicity of Cr, Fe, Pb and Mn of plating waste may increase substantially' high in long term duration because of their high concentration in secondary extract. n galvanising waste, a slight increase of % EP toxicity of Zn and Fe is found in secondary extract than primary extract (Fig. 3). Though, a little more EP toxicity values are estimated for Pb and Mn of galvanising waste in secondary extract than primary extract (Fig. 3). Occurrence of quite high % EP toxicity of Zn and Fe in primary and secondary extracts of galvanising waste suggests that their toxicity may increase marginally in o JO 40 SO 60 TE MPERATURE,oC Fig. 5-Variations ofep toxicity with temperature for Cr (0) and Zn () of Cr-plating and galvanising wastes, respectively immediate and long-term duration. Fig. 4 determines a comparative % EP toxicity of Fe, Pb and Mn in primary extract of plating and galvanising waste. From the available trend one may easily find the high toxic nature of plating waste because of the occurrence of nearly two and half times o.f more % EP toxicity of Pb and Mn than that in galvanising waste. Effect of temperature on EP toxicity-- The effect of temperature on the EP toxicity of above metals in primary extract has been determined by conducting test in the temperature range of C for both wastes. The trend of increase of % "'111., 1/ '.1', " 111 'TrY"! '

4 SNGH et at.: LEACHABLTY CHARACTERSTCS OF METAL CONTAMNANTS 301 EP toxicity characteristics with temperature for Cr in plating waste and Zn in galvanising waste are given in Fig. 5. A linear increase of % EP toxicity values with temperature for Cr and Zn in their respective waste system attributes their apparent increase of leachability with rise of tempature. The trend of variations of % EP toxicity of Fe, Pb and Mn in primary extract with temperature for plating and galvanising waste are plotted in Figs 6 and 7, respectively. A slight increase of EP toxicity of above metals with increase of temperature as shown in Figs. 6 and 7 indicates that temperature increase slowly increases the leachability of Fe, Pb and Mn of plating and galvanising wastes. When industrial solid waste comes in contact with soil, its start absorption of water. When waste is saturated with water, water moves through the waste via gravity and is contaminated with waste constituents through partitioning process9 The concentration of contaminants depends upon the leachable. constituents in the waste, the ease of mass transfer and ratio of column depth. Other factors include contaminants solubility, surface area, contact time and pho n addition, the contaminated water passes through physico chemical reactions like oxidation, reduction, absorption, precipitation and desorption in soil Therefore, during infiltration of contaminated water some contaminants are trapped by adsorption with soil constituents. The more strong pollutants are adsorbed by soil constituents, the less likely are leached down to soil profile or to be available for uptake of plant. Similarly if solubility of contaminants in soil solution will be more, their leachability potential may likely be more if adsorption reaction in soil does not predominate.. TCLP is principally based on solubilization and filtration process keeping other parameters like solution ph and filtration pressure (exerted by soil) constant in soil condition. On the basis of the above mechanism of contaminants infiltration into soil, it is inferred that metals like Cr, Fe, Pb and Mn present in plating waste are strongly bounded by other constituents of waste. Thus, they are not able to release easily in primary extract. This may be the reason for the occurrence of low toxicity level of above metals in primary extract of plating waste. Their high toxicity values in secondary extract is mainly due to the increase of their solubility in solution. Presence of high concentration of Cr, Fe, Pb and Mn in secondary extract of plating waste indicates that leachability of these metals may increase more with passage of time which is an indication of long-term leaching effect. The extractable Cr may oxidise to Cr (V) oxidation state with passage of J. PLATNG WASTE ti GALVANSNG WASTE 2.5 f- * M M A. >- 000 J(J( t( K t: e;1 0.' 0 ifi Fig TEMPERATURE,oC 7-Variations o.er for Fe (*) Pb (0) and of Percentage Mn (d) in galvanising EP toxicity wastes with temperature

5 302 NDAN 1. CHEM. TECHNOL., NOVEMBER 1997 time. Cr state is easily soluble, toxic and mobile in nature \2. t is reportedl3 that concentration of Cr as low as 0.5 ppm in solution and 5 ppm in soil can be toxic to plants and animals. n comparison to % EP toxicity of Cr and Fe of plating waste, high toxicity values were obtained for Zn and Fe in primary and secondary extracts of galvanising waste. t may be attributed that Zn and Fe of galvanising waste are relatively more soluble in nature. Their toxicity in long-term effect may increase further because of estimation of their high concentration in secondary extract. t is interesting to determine the toxicity characteristics of Pb and Mn in plating and galvanising waste because both wastes showed a marginally higher EP toxicity of these metals in primary and secondary extracts. The main reason for the occurrence of higher toxicity of Pb and Mn is mainly due to their high solubility in extract. t may also be suggested that Pb and Mn are relatively loosely bounded with other constituents of waste and solubilizes easily in the extract. The increase of EP toxicity of Cr and Zn of plating and galvanising waste with rise of temperature is attributed due to increase of solubility of these metals from their original composition. Perhaps temperature increase is not very effecivein increasing the solubility of Fe, Pb and Mn of both wastes since there is no any significant increase of leachability of the above metals was found even at 60 C. From the extraction and estimation of above metals of plating and galvanising wastes., one may assess that waste composition is mainly responsible for increasing or decreasing of leachability of particular metal in the soil. n plating waste, leachability of Cr, Fe, Pb and Mn seems to be increased with passage of time. ron present in plating waste is slightly leachable immediately. When iron present with Zn in galvanising waste, their leachability increases substantially alongwith Zn. Moreover, a further study by conducting leaching test of above heavy metals in actual soil condition may verify the validity of present test procedure. Conclusions 1 A substantial increase of EP toxicity of Cr, Fe, Pb and Mn in secondary extract of plating waste indicates their long term leachability effect. 2 Occurrence of quite high EP toxicity of Zn and Fe of galvanising waste in primary and secondary extracts predict their immediate and long-term leachability in the soil. 3 Presence of significantly high EP toxicity of Pb and Mn in both wastes suggests their higher leachable characteristics. 4 ncrease of temperature generally increases the EP toxicity of Cr and Zn of plating and galvanising waste, respectively. Acknowledgement Authors are grateful to Prof T C Rao, Director, RRL, Bhopal, for his constant encouragement and providing all the facilities to carryout the work. References 1 Tessier A, Cambell P G & Bisson M, Anal Chem, 51 (1979) Shuma L M, Soil Sci, 150 (1985) Eighmy T T, Eusden J D, Krazanowski J E, Domingo D A, Stampfli D, Martin, J R & Erickson P W, Environ Sci Tech, 29 (1995) Berti W R, Cunningham S D, in Trace Substances Environmental and Health, edited by C R Cothern, (Science Reviews, Northwood U.K.), 1994,43. 5 Miller W P, Martin D C, Zelazny LW, Soil Sci Am J, 50 (1986) Berti W and Cunningham S D, Environ Sci Technol, 31 (1997) CFR, Part 261, Fed Regist, No 126 pp Vogel A, Text book of Quantitative norganic Analysis, (Longman London), Michael L, LaG vega D, Buckinghon L, Evans C, Hazardous aste Management, (Mc Graw-Hill, New York), 1993, Management of Hazardous Waste Leachate, (Report Prepared for US EP A by Touhill, Shuckrow and Associates, Pittsburg,P A) Sept Alloway B J & Ayres D C, Chemical Principle of Environmental Pol/ution, (Chapman Hall, London), 1994, Mertz W, Phys Rev, 49 (1963) Turner M A, Fast R H, Soil Sci Sac Am Pros, 35 (1971) 755. t