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Year: 2016, Issue: June

Sequential chemical leaching behaviour of metals at selected stations in the Chilika lake.


Sunil K. Pattanaik, K. S. Bhatt and A. K. Panigrahi


Sequential chemical leaching, Metals, Chilika lake.
Sequential chemical leaching behaviour of metals was studied in select 10 stations out of 15 stations of Chilika lake selected for study. The sequence of leaching of heavy metals by 1M MgCl i.e. exchangeable phase, follow 2 the order Co>Pb>Zn>Cr>Cu>Ni>Mn>Fe with respect to their absolute concentration. The sequence of leaching of heavy metals by 1M MgCl i.e. exchangeable phase is Co (1.48-12.1%, average 6.96%) Pb (1.0-9.9%; average 3.96%) 2 >Zn (1.40-4.04, average 3.06%) Cr (0.7-3.87%; average 2.3%) >Cu (0.7-5.3%; average 2.1%) > Ni (0.2-2.2%; average 1.3%) > Mn (0.4-1.2%; average 0.6%) > Fe (0.02-0.17% average 0.09% of the total metal content). Other metals such as Cr, Cu, Co and Ni are also available in higher percentages at station 11 in the exchangeable phase perhaps originated from the pollution sources, which is nearer to Balugaon ghatt entering as adsorbed ions. It may be stated that the concentration of heavy metals and consequently their distribution in this fraction may be considered to be very low and geochemically insignificant organic matter have a scavenging effect and may provide a sink for heavy metals. The sequence of leaching of heavy metals by NaOAc (pH=5.0) i.e. carbonate phase in the lake sediments was Pb (6.4- 23.4%; average 14.3%) > Mn (8.3-21.9%; average 12.6%) > Cr (2.7-13.7%; average 9.87%) > Co(2.9-13.3%, Avg. 7.84%) > Ni (0.5-12.1%; average 6.4%) > Cu (3.2-10.9%; average 6.6%) > Zn (2.0-9.2%, averqage 6.7%) Fe > (0.4- 1.4%; average 0.7%), Pb (average 14.3%), Mn (average 12.6%), Cr (average 9.8 %) and Ni (average 6.4%) represent an appreciable portion of the total metal content, which are most likely the results from similarity in their ionic radii to that of Ca, which allows them to substitute Ca in Carbonate phase. The reducible phase seems to be little geochemical significance as the elements bound to this fraction. The metals in Fe-Mn oxide phase, which has been proved to be sensitive to anthropogenic inputs, retained 4.6-26.6% of Co, 11.4-22.6 of Ni, followed by Pb (10.4-34.2%), Cr (10.9-21.4), Mn (10.9-19.6), Cu (5.8-22.0), Zn (8.1-18.1) and Fe (5.7-9.9). The metals like Ni, Pb, Mn, Cr and Cu are almost equally contributed to this phase. The organic bound fraction in this present study are normally Pb>Zn>Cu>Ni>Cr (except Fe and Mn).

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