OCCURRENCE AND CHARACTERIZATION OF Zn AND Mn IN BAUXITE

摘要

Zinc is one of the secondary elemental constituents occurring in Caribbean bauxite and the associated non-bauxitic material. It is generally believed that Zn in bauxite could either occur in gahnite or sphalerite, or substitute for Fe in goethite. Manganese represents an appreciable impurity in Caribbean bauxites and is identified on diffractograms as lithiophorite (Li,Al)MnO_2(OH)_2. As Zn has been observed to increase with the MnO content, the objective of this work was to better understand the mineralogical nature of Zn and Mn compounds. Data representative of 340 bauxite samples of different origins was assembled. It was found that Zn in bauxite could not possibly substitute for Fe in goethite or hematite. Strong evidence was obtained that Zn occurs in the same compound as Mn. The application of the Rietveld-XRD method to the quantification and characterization of a new mineral called zincophorite Al(Zn_xMn_(1-x))O_2(OH)_2 is discussed. Caustic solubility of ZnO in bauxite is also assessed.