Sorption of heavy metals on clay minerals and oxides: a review

Sorption of heavy metals plays a vital role in controlling environmental pollution. Here, we reviewed the sorption of heavy metals such as Ni, Co, Cu, Zn, V, Pb, Hg, In, As, Cd, Cr, Ga, Cs, Mn, V, Eu, Mo, Th, TI and Cr on metal oxides and clay minerals. The mechanism of association between these ions and the host minerals, and the factors controlling their sorption are discussed in detail. Both chemical and empirical methods of describing sorption mechanism are discussed. The sorption processes depend on the pH, metal concentration, ionic strength, temperature, time, adsorbent dosage, type of ion, surface area, type of adsorbent modification and nature of adsorbent. The review confirmed that both metal oxides and clay have capability of sequestering heavy metals, however, combination of both metal oxides and modified clay have enhanced capability of removing heavy metals from aqueous solution. These inorganic adsorbents have the regeneration and recycling potentials and can be used to remediate and sequester economic metals for commercial purposes, however, this needs future investigation.