Application of a fungal cellulase as a green depressant of hematite in the reverse anionic flotation of a high-phosphorus iron ore

Abstract

In this study, a fungal cellulase enzyme was applied to improve the selective separation of apatite from hematite during the reverse anionic flotation of a high-phosphorus iron ore. Bench-scale flotation tests were conducted on pure hematite and apatite minerals, their artificial mixture, and a high-phosphorus iron ore sample, using oleic acid as a collector. Flotation tests on single minerals showed that cellulase was a good depressant of hematite, but had no depressing effect on apatite at pH 10. The phosphorus content in the concentrate product of the flotation of artificially mixed pure minerals was reduced from 1.96% to 0.03%, with iron grade and recovery of 64.15% and 94.74%, respectively, using 4x10−5 mol/L oleate and 0.02% cellulase at pH 10. By applying the optimum separation conditions to the flotation of a natural high-phosphorus iron ore, the phosphorus content in the concentrate was reduced from 0.84% to 0.19% at an iron recovery of 67.85%. The mechanism of the cellulase depressing effect was investigated through Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. The results showed that cellulase enzyme was adsorbed on the surfaces of both minerals; however, the depressing effect was significant in case of hematite but not apatite. This might be attributed to the coverage of apatite surface with a close-packed layer of oleate molecules, which made the surface of apatite hydrophobic enough to counter the polarity induced upon cellulase adsorption.