The heavy metals contents (Pb, Cu, Fe, Cr, Cd, Zn, Mn and Ni) in Municipal dumpsite compost were determined by the sequential extraction method. Chemical parameters such as pH, conductivity, and organic carbon contents of the samples were also determined. Analysis of the extracts was carried out by atomic absorption spectrophotometer machine (Buck Scientific VPG 210). Results of these analyses showed that Pb, Ni, Cr, Mn and Fe were largely associated with residual fraction (53.06%, 56.26%, 58.15%, 59.14% and 64.10% respectively). Cu, Cd and Zn were largely associated with non-residual fractions (71.42%, 54.44%, and 54.15% respectively). Calculated mobility and bioavailability factors of Cd, Zn and Cu were also high (54.
Stability constants of complexes of four divalent metal ions viz. Cu2+, Pb2+,Mg2+ and Cd2+ with humic acids (HA) were determined by potentiometric titration of humic acids with the corresponding salt of the divalent metals in aqueous media under non-acid-condition. The log K (logarithm of the stability constant) ranged from 1.0942 to 2.7471 for metal-humic acid complexes were determined using point-wise computational method. The order of stability constants were obtained as follows: Cu >Pb> Cd > Mg for metal -HA complexes respectively, indicating a higher degree of complexation with Cu metal ion.
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