Mineral transformation in treating low-grade bauxite using the calcification–carbonization process and preparing cement clinker with the obtained residue

Abstract

Abstract During the Bayer process for alumina production, the molecular formula of the bauxite residue is approximately equivalent to Na2O·Al2O3·1.7SiO2·nH2O. This means that 1\u202fkg of SiO2 in bauxite will produce 1\u202fkg of Al2O3 and 0.608\u202fkg of Na2O in bauxite residue. Thus, the extraction efficiency of alumina is low when processing low-grade bauxite. In addition, it is difficult to utilize bauxite tailings with solid alkali in the structure. In this study, low-grade bauxite was treated using a calcification–carbonization process. A new type of residue (C-C residue) with a different structure from that of traditional bauxite residue was obtained. A cement clinker was prepared with C-C residue as the main ingredient at a dosage of 50%. The experimental results show the alumina extraction efficiency reached 75.82% when processing low-grade bauxite of A/S 3.06 using the calcification–carbonization process. This is higher than the 61.44% of the Bayer process. The main phases of C-C residue [CaCO3, amorphous Ca(4−2x)SixO4, and undecomposed Ca3Al2(SiO4)(OH)4] convert into Ca2SiO4, Ca3SiO5, and Ca2FexAl(2−x)O5 after calcination. The calcification–carbonization process combined with cement production helped low-grade bauxite achieve highly efficient and clean alumina production, which is conducive to the sustainable development of alumina industry.