Kinetic Investigation of Initial Oxidative Dissolution of Pyrite in Alkaline Media (pH 9–12) and Influence of Ca and Mg: A Fundamental Study for Pyrite Depression in Froth Flotation

Froth flotation is a common mineral processing technique that is used to remove low economic gangue minerals, such as pyrite, from ore. The main hydrophilization mechanism on the pyrite surface is explained by the formation of hydrophilic iron (Fe) hydroxide and its complexation with calcium (Ca) and magnesium (Mg) ions; however, few quantitative results are available to determine the best physico-chemical condition to depress pyrite floatability. Fe-hydroxide formation, i.e., oxidative dissolution on a pyrite surface, is a kinetically control reaction; thus, this study investigated the short-term pyrite oxidation rate (~ 360 min) and the influence of the copresence of Ca and Mg under alkaline pH conditions (9, 10.5, and 12) as a fundamental study to establish optimal flotation and/or pre-treatment conditions for pyrite depression. The oxidative dissolution rates of pyrite increased after 120–150 min of reaction compared with the first reaction time: the rate constant (log k) increased from − 10.08 to − 9.5 in the absence of Ca and Mg. X-ray photoelectron spectroscopy analysis results showed that the formation of Fe_1−xS₂ became the dominant reaction in the first reaction stage; thereafter, S–S bond cleavage in the second reaction stage resulted in the acceleration of pyrite decomposition. Smaller rate constants resulted for the Ca and Mg solutions because of the formation of Ca and Mg hydroxides under alkaline conditions. However, this decrease in oxidation rate could influence the pyrite surface hydrophilization less, and hydrophilization has become the main reason for pyrite depression enhancement. Graphical Abstract: [Figure not available: see fulltext.]