Competitive sorption and desorption of trace elements by Tunisian Aridisols Calcorthids.

The sorption and retention processes play an important role in determining the bioavaibility and fate of trace elements in soils. Sorption and desorption of Pb(2+), Zn(2+), Ni(2+), Cu(2+), and Co(2+) in three Tunisian Aridisols Calcorthids (AR1, AR2, and AR3) were studied using batch experiments. Sorption and retention capacities were determined by means of K r parameter and they were related to soil properties. The results showed that in all studied soils, K r values for Pb(2+) and Cu(2+) were higher than those of Zn(2+), Ni(2+), and Co(2+) indicating that soils have higher affinity for the first ones. The high sorption and retention capacity of the three studied soils is ascribed to their alkaline pH and their high carbonates contents favoring the precipitation of these elements. Moreover, bivariate correlation analysis showed that sorption and retention of the studied cations was also strongly correlated with clay fraction and Fe oxides contents. All soils show high sorption irreversibility of Pb(2+), Zn(2+), Ni(2+), Cu(2+), and Co(2+). The soils with highest sorption capacity show also the highest irreversibility.