Adsorption and desorption of heavy metals in soil varying in organic carbon
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Date
2009
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Publisher
CCSHAU
Abstract
A laboratory experiment was conducted to study the adsorption and desorption
of heavy metals in soils varying in levels of organic carbon. Four metals Cr, Ni, Cd
and Pb were chosen which are most effective in critical concentrations for plant
growth. Soil samples were collected from different plots from on going long term
field experiment on, “Effect of FYM and fertilizer nitrogen application in pearl millet
– wheat cropping sequence” at soil Research Farm, CCS HAU, Hisar since 1967,
receiving different levels of FYM. Collected soil samples from all the plots were
analyzed for their organic carbon content. From these 10 samples with graded levels
of organic carbon were chosen for the present study. The levels of organic carbon of
these samples were: 0.3%, 0.45%, 0.93%, 1.23%, 1.5%, 1.65%, 1.8% 1.92%, 2.19%
and 2.28%.Equilibration time was determined by taking soil sample having about 2%
organic carbon level and treating it with 50 μg/cm3 concentrations of heavy metals (Cr, Ni,
Cd and Pb) in 0.005MCaCl2 electrolyte solution and shaking it up to 24 hours. A constant
adsorption was achieved after 4 hours of shaking time for all metals. Hence 4 hours shaking
time was adopted for further adsorption studies Adsorption percentage and distribution
coefficient increased with increase in organic carbon levels in soil. Adsorption percentage
and distribution coefficient were maximum for Pb followed by Cd, Ni, and Cr. A linear
relation between metal adsorbed and levels of organic carbon in soil (R2 value for all 4
metals ranged from 0.8170 to 0.9876) was found for all the metals up to the concentrations
taken in this study. Adsorption percentage and distribution coefficient of all metals
decreased with increase in metal concentration at all organic carbon levels. Freundlich
constants K and n increased with increase in organic carbon contents of soils. Langmuir
constants; adsorption maxima (B) and bonding energy (D) also increased with increase in
levels of organic carbon in soil. The highest value of B was observed for Ni followed by Pb,
Cd and Cr. The highest value of D among metals was observed for Cr followed by Cd, Pb
and Ni. The adsorption data were fitted very well to the Freundlich equations than to
Langmuir equation and gave highly significant R2 values ranging from 0.9759 to 0.9990 for
Freundlich equation. The desorption of adsorbed metals by 0.005M CaCl2 electrolyte
solution was low at lowest concentration of metals but increased with increasing
concentration of metals in soils. Desorption (per cent of adsorbed) decreased with increase
in organic carbon levels in soil at all concentrations. The order of desorption (%), (of
adsorbed) was Pb < Cr < Ni < Cd. Desorption of all metals as least in the soil with highest
organic carbon level.
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Keywords
Bacteria, Azotobacter, Sowing, Planting, Insecticides, Biological development, Pesticides, Biofertilizers, Wheats, Wood