Studies on divalent ion uptake of transition metal cations by calcite through crystallization and cation exchange process

The uptake of transition metal cations of Fe, Cu, Zn, Cd and Pb with calcium carbonate in the form of calcite was investigated. The uptake reaction was found to be in the following order: Pb2+ > Cu2+ Zn2+ > Cd2+ approximate to Fe2+; and the amount of uptake (meq/g) cations has been found to increase with the increase of the metal ion concentration and reaction time. The uptake of these ions was mainly considered to be due to the crystallization that happens through decomposition reaction mechanism as in case of Pb2+, Cu2+ and Zn2+ and cation exchange of surface Ca2+-ions present in lattice structure of carbonate solid with metal cations, as in the case of Fe2+ and Cd2+. The different affinities of calcite toward these cations can be used for waste ions fixations or decontamination. (C) 2003 Kluwer Academic Publishers.