Simultaneous competitive adsorption of heavy metals by some Egyptian soils S.El-Demerdashe, M. E. Abdel–Rahman.

Abstract EN

Teavy metal cations can be introduced into agricultural soils by application of sewage sludge, composts and industrial wastes which is commonly and increasingly used in Egypt.

Therefore, heavy metal adsorption reactions, in a competitive system, are important to determine heavy metal availability to plants and their mobility throughout the soil.

This study was conducted to evaluate the selectivity sequence and estimates the competitive adsorption of several heavy metals in seven soil samples having different chemical and mineralogical characteristics.

The competition affected the behavior of heavy metal cations in such a way that the soils adsorbed less Zn, Cd and Ni and more Pb and Cu with increasing their total concentrations.

On the other hand, the occupancy of the adsorption complex by the heavy metals was proportional to the relative concentration applied.

As the applied concentration increased Pb and Cu adsorption increased, while Zn, Cd and Ni adsorption decreased.

The maximum adsorption capacity (b) for the heavy metal cations was calculated. The soils of Wadi El–Tumeilat and Wadi El-Arish showed the highest maximum adsorption values, in the order of 77.52 and 71.94 mmol l-1, respectively, whereas the soils of El-Bahariya Oasis (El-Heiz) and El-Hammam showed the lowest values, in the orders of 14.08 and 24.10 mmol l-1, respectively.

On the basis of the proportion of increase or decrease in heavy metals adsorption, the selectivity sequence was evaluated.

The most common sequence was Pb > Cu > Cd > Ni > Zn.

Lead, Cu and Cd were the heavy metal cations most strongly adsorbed by all soils, whereas Ni and Zn were the least adsorbed.