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Speciation of heavy metals in electroplating industry sludge and wastewater residue using inductively coupled plasma.

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The occurrence of heavy metals in industrial wastewater is of interest because they are often present at significant levels and if discharged into surface waters can have severe effects on the environment and public health. The determination of total heavy metal content does not provide useful information about the risks of bioavailability, the capacity for remobilisation and the behavior of the metals in the environment (Luoma, 1989; Di Toro, et al., 1990; Sims and Sklin, 1991, Hsu and Lo, 2001). Metal speciation, in this context, is taken to mean the fractionation of the total metal content into exchangeable (bound to exchangeable sites of clay minerals), acid extractable (bound to carbonates and hydroxides), reducible (bound to Fe/Mn oxides), oxidisable (bound to organic matter/ sulfides) and residual (bound to clay minerals) forms. The chemical forms of the metal control its bioavailability or mobility (Norvell, 1984). The exchangeable and acid extractable fractions are mobile fractions that are easily bioavailable. Metals in oxic sediments are mainly distributed in different operationally defined geochemical phases, such as carbonates, total organic carbon (TOC), and Fe – Mn oxides, which have diverse binding abilities with various metals and have contrasting influences on the metal bioavailability (Tessier and Camp bell, 1987; Bryan and Langston, 1992; Coquery and Wekboum, 1999). For anoxic sediments, the acid-volatile sulfide (AVS, or the sulfides removed from sediment by cold acid extraction) is considered as an important factor in affecting the bioavailability of most divalent metals having a high affinity with sulfide (Di Toro, et al., 1990; Ankley, et al., 1996; USEPA, 2001). It is necessary to know the physical and chemical properties of any solid waste before their disposal, and particularly their elemental contents, both in terms of total concentrations and the amount that is potentially biologically effective. However, the determination of specific chemical species or binding forms is difficult and often virtually impossible. For this reason, sequential extraction procedures are commonly applied because they provide information about the fractionation of metals in the different lattices of the solid sample, which is a good compromise method that gives information on the environmental contamination risk. (Campos, et al., 1998, Scancar, et al., 2000, Pueyo,et al., 2001). Method developed by Tessier, et al., (1979) is the one widely used for this purpose. Kazi, et al., (2005) evaluates the mobility of toxic metals in untreated industrial wastewater sludge. The results from the partitioning study indicate that more easily mobilized forms (acid exchangeable) of Cd were dominant. The oxidizable fraction was dominant for all four toxic metals (Cr, Pb, Ni, Cd). It was observed that levels of leachable toxic metals from industrial wastewater sludge were low compared to the amount of metal extracted in the exchangeable fraction of the BCR protocol. Karbassi and Shankar, (2005) reported that in the coastal sediment cores Cu, Zn and Fe are associated with organic matter and detrital particles, whereas Ni and Co are predominantly associated with the insoluble fraction. While abundance of calcareous shells in some zones has lead to the dilution of most of the metals, it appears that Pb and Mn are associated with this phase. Later, Karbassi, et al. (2006) reported that higher elemental concentrations have been observed in estuarine zone when compared with riverine sediments (except for Al, Fe, Pb and Mn). Saeedi, et al., (2004) reported the potential of reverine suspended particulate matter and bottom sediments in adsorbing dissolved metals like Cd, Mn. Ni, Cu, Zn. The presence of metals in sea sediments and increase in their concentration may be indicative of human influence on aquatic environment like agricultural, industrial activities. The sequential extraction scheme as per the Standard, Measurements and Testing Programme of the European Commission was studied by Alonso, et al., (2005) for the sludge samples from anaerobic wastewater stabilization ponds. Elements namely Al, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Ti and Zn were determined in the sludge extracts by ICPAES. In relation to current international legislation forthe use of sludge for agricultural purposes, none of the metal concentrations exceeded maximum permitted levels. Overall, heavy metals were mainly associated with the two less-available fractions (34 % oxidizable metal and 55 % residual metal). Only Mn and Zn showed the highest share of the available (exchangeable and reducible) fractions (25 – 48 %). In this present paper, wastewater residue and sludge samples collected from two plating industries located in Chennai, India was examined for distribution of heavy metals like Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sn, and Zn, using ICP - AES and chemical fractions of these heavy metals by sequential extraction to assess their potential environmental impacts.



Related Work

Wastewater residue, electroplating sludge, sequential extraction, metal speciation

Sponsors

  • A & N Technologies
  • Indair
  • Mc Clelland Engineers Pvt. Ltd
  • Dowac Systems & Projects India Pvt. Ltd.
  • VALVCO INTERNATIONAL
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