Leaching Characteristics of Disordered Birnessite and Goethite Doped with Ni, Co and Cu in Sorption Mode

Leaching behaviour of well characterized disordered birnessite (δ-MnO2) and goethite (α-FeOOH) samples, doped with Ni, Co and Cu in sorption mode, has been studied. In sulfuric acid leaching, the elements doped in goethite phase are easily leached as compared to the disordered birnessite phase. The different leaching characteristics of the doped elements from the two host phases are explained in terms of sorption mechanisms involved during synthesis, namely, ‘surface complexation’ for goethite and ‘ion exchange with subsequent structural incorporation’ for disordered birnessite. The rapid dissolution of δ-MnO2 in sulfurous acid facilitates the dissolution of doped elements. It has been observed that there exists a negative correlation between leachability in sulfuric acid and crystal field stabilization energy (CFSE) of the doped elements. The implication of results is presented in the context of mechanism of incorporation of Ni, Co and Cu in deep-sea manganese nodules and leaching characteristics of nodules.