Olive husk: An alternative sorbent for removing heavy metals from aqueous streams

Sorption properties of olive husk were investigated under equilibrium (batch tests) and dynamic (column tests) conditions in order to assess the possibility of using such a waste material for removing heavy metals from aqueous streams. Husk samples were contacted, at 25°C, with aqueous solutions of nitric salts of Pb, Cd, Cu, and Zn. Sorption isotherms obtained from equilibrium data were fitted and interpreted by the Freundlich model. Metals-saturated husk samples resulting from column tests were air-dried and incinerated to simulate combustion in order to assess the fate of sorbed metals. The results demonstrated that, under both equilibrium and dynamic conditions, metal sorption capacity of the husk was in the sequence Pb>Cd>Cu>Zn. For all the metals, calculated Freundlich constants decreased by increasing initial metal concentration or decreasing solution pH. In dynamic tests, a significant reduction of sorption capacity was recorded (except for copper) when a metal was fed simultaneously to the others: Pb (77%); Cd (93%); Zn (68%). Combustion tests carried out on metals-saturated husk samples showed that the average losses of lead and cadmium, as volatile species, were always three to four times greater than the losses of copper and zinc, in both single-metal- and multimetal-saturated samples.