Deep Insight on the Occurrence Feature of Iron Minerals in a Cyanide Leaching Residue and Its Effective Recovery with Magnetic Separation

Abstract

The occurrence features of ultrafine iron minerals in a cyanide leaching residue produced from a superlarge gold mining company in Yunnan Province were determined with chemical composition analysis, iron phase analysis, and mineral liberation analysis (MLA). The results show that the residue contains 26.74% iron, mainly occurring in the form of magnetite (26.33%) and limonite (69.41%), in which 67.40% magnetite and 73.00% limonite particles are fully liberated with particle sizes ranging from 9.6 µm to 75.0 µm. The rest are adjacent and wrapped intergrowths. Low-intensity magnetic separation and pulsating high-gradient magnetic separation were, respectively, proposed to recover magnetite and limonite from the residue, and under the optimized conditions, a high-grade magnetite concentrate assaying 64.05% Fe with 85.59% magnetite recovery and a qualified limonite concentrate assaying 50.94% Fe with 54.33% limonite recovery were, respectively, produced. The iron recovery for −30 µm fraction in the magnetite and limonite concentrates reached as high as 51.46%. It was found that the iron recovery for −30µm ultrafine fraction is lower than those of coarser fractions, as a result of the relatively enhanced hydrodynamic drag acting onto the particles, compared with the magnetic force. Entrainment occurs between the ultrafine iron minerals and gangues, thereby reducing the iron grade for the ultrafine fraction. This research outcome would provide a valuable reference for the economic and effective utilization of iron resources from such residues.