Behavior and mechanism of sodium sulfite depression of almandine from rutile in flotation system

Sodium sulfite has been utilized in the mineral industry principally as a depressant for a variety of sulfide ores. In this study, it was tested as a depressant in flotation of oxidized ore from its silicate mineral gangue. Selective flotation of rutile from almandine was investigated using sodium sulfite as a regulator and an octadecyl amine polyoxyethylene ether (AC1815) mixed with Styryl phosphonic acid (SPA) as a composite collector. The investigation was conducted through a series of micro-flotation tests of single and artificially mixed minerals. In addition to that, the measurements of contact angle, zeta potential, and X-ray photoelectron spectroscopy (XPS) were also conducted to unravel the adsorption mechanism of the depressant onto the surfaces of the two minerals. The experimental results clearly demonstrated that sodium sulfite acting in the form of SO32− at pH range 6–8 was more selective adsorbed on almandine surface compared to that of rutile, leading to a high selectivity for the flotation of rutile. The XPS results revealed a strong interaction between the active ferrous sites of almandine and SO32− of the sodium sulfite through reduction forming a hydrophilic metal sulphate layer and metal ox-hydroxides surfaces, which in turn reduced adsorption sites for collector and led to a decrease of surface hydrophobicity thereby strongly depressing the flotation of almandine. [Display omitted] •Sodium sulfite exhibits selective depression towards silicate almandine.•Electrostatic and chemical interaction between the depressant and almandine•Sodium sulfite reduce the Fe3+ sites on almandine surface.