Study on the interactions of two models of enzymes as eco-friendly depressants in flotation separation of apatite from hematite

Two models of hydrolytic enzymes, namely alpha-amylase and lipase, were investigated as eco-friendly depressants of hematite to separate apatite from hematite by reverse flotation, utilizing oleate as a collector. The effect of both enzymes on the flotation behaviors of apatite and hematite minerals was studied through a series of micro -flotation tests. The interactions between oleate and the enzymes with the surfaces of both minerals were studied through zeta potential, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. Micro-flotation tests of single minerals revealed that the recovery of hematite decreased remarkably upon adding alpha-amylase or lipase, especially at alkaline pH (8.0-11.2), while that of apatite was not affected. For mixed minerals, selective flotation of apatite from hematite was successfully achieved, and alpha-amylase showed better selectivity than lipase. Zeta potential and FTIR studies revealed that oleate adsorbed more intensively onto apatite than hematite at pH 10.0, which might have influenced the subsequent adsorption of the enzymes and their depressing effect. XPS analyses further indicated that alpha-amylase could adsorb more strongly and selectively onto hematite than apatite by means of chemical interactions with the active Fe sites on the hematite surface, which depressed the flotation of hematite.