Removal of nickel from aqueous solutions by clay-based beds

The use of spray-dried natural clays for the removal of nickel ions in aqueous solution is discussed in this paper. Two different clays were tested and their mineralogical composition and physical characteristics related to efficiency of nickel removal. In particular, relevant parameters including flow rate and overall removal efficiency were evaluated for 4.8 cm depth filters. The removal efficiency of the tested clays was generally similar or greater than that of granular activated carbon (GAC). The mineralogical composition of the clays, particularly the presence of montmorilonite, might explain this behaviour. Higher cation exchange capacity and development of surface negative charge on clay particles in contact with water also contribute to this promising performance, despite the lower available specific surface area of the spray-dried grains in comparison with granular activated carbon. The calcination of pressed pellets made of contaminated filter grains gives consolidated ceramic bodies that can be used in the fabrication of common products like wall or floor tiles, where nickel ions remain firmly attached and inertized.