The process of adsorption-desorption of zinc and copper in highly weathered soils may affect their mobility and toxicity. In this study, we evaluated the effect of sewage sludge application on the adsorption-desorption behavior of Zn and Cu in highly weathered soils. Laboratory batch experiments were carried out to investigate the adsorption and desorption of Zn and Cu in an Oxisol and Ultisol amended with three rates of sewage sludge (T1=0% (control), T2=5% and T3 =10% sludge). The findings showed that sewage sludge application had significantly affected the processes of adsorption-desorption of the tested soils. This is shown by the systematic change of the distribution coefficients (Kd). Comparison between Kd values for both soils indicated the following selectivity of metals: Cu > Zn. It is clear that Zn adsorption was lower than that of the Cu. Generally, metals adsorption-desorption was higher in the Ultisol compared to that of the Oxisol which was due to Ultisol having higher CEC and OM content in comparison to those of the Oxisol. The adsorption isotherms of Zn and Cu of both soils were well fitted to linear Freundlich and Langmuir equations (with minimum R2 = 0.96 and maximum R2 = 0.99, respectively). The adsorption-desorption of metals was strongly correlated (p<0.05) with sewage sludge rates, CEC and OM.

Ramadan Mohamed Aishah, Jusop Shamshuddin, Che Ishak Fauziah, Abdu Arifin and Qurban Ali Panhwar