Effect of sludge on sorption of cadmium in calcareous soils

The amount of Cd sorbed (x/m) by untreated and treated soils increased while, per cent of added Cd sorbed (XAd) and distribution coefficient (Kd) decreased with increasing Cd concentration in solution indicating that affinity of soils for Cd decreased with increasing Cd concentration in solution indicating that affinity of soils for Cd decreased with fractional surface coverage or increase in concentration of Cd in solution phase. Cd sorption by untreated and treated soils was satisfactorily described by Freundlich (R2 = 0.994 to 0.998) and two-surface Langmuir equations (R2 = 0.987 to 999). The value of Freundlich constant (Kf) and total sorption capacity (b1 + b2) calculated from the two-surface Langmuir equation increased due to enrichment of soil with sludge @ 25 and 50 g kg-1. Total sorption capacity and Freundlich Kf were positively and significantly correlated with organic carbon and CEC of the soils indicating that application of sludge to the soils had a dominating role in enhancing the Cd sorption due to increase in organic surfaces/adsorption sites to the soils and formation of stable complexes with organic matters.