EVALUATION OF AN HCL PROCESS FOR LEACHING OF LOW-GRADE HIGHLY SILICEOUS BAUXITE ORE

摘要

This paper presents the results of the experimental work done to find out the extraction percentage of alumina content in ore samples of bauxite from four mines of Khushab (the Sultan Mehdi, Chamil More, Nadi and Niaz mines), after they were subjected to leaching with hydrochloric acid (HCl). The alumina (Al_2O_3) content of the raw ore samples was 39.51%, 38.23%, 45.01% and 37.17%, whereas silica content was 40.64%, 42.26%, 36.50% and 44.41%, respectively. The petrographic study showed that there are fine-grained dissemination of geothite. A minor amount of quartz was also present in the ore. X-ray diffraction (XRD) studies and photo-micrographs of thin sections showed that all four samples were mainly mono-hydrate boehmite (Al_2O_3*H_2O), with kaolinite and quartz as main impurities. Results showed that the ore samples from the Niaz mine had lowest leaching recovery of alumina, due to the lowest alumina content in the ore, despite their better response to leaching. On the other hand, Nadi mine samples containing the lowest silica and highest alumina content showed lower recoveries of Al_2O_3. It was observed that with the exception of Nadi, all the samples from highly siliceous low grade Khushab bauxite ore were quite reasonably amenable to HCl leaching, making the acid process suitable to leaching most of this ore at atmospheric pressure. An overall average of 72.06% alumina extraction and 42.27% recovery is possible from the samples of ore from the Sultan Mehdi, Chamil More and Niaz mines, excluding the Nadi mine, which was considered unsuitable for leaching.