Utilization of phosphorylated starch as a selective depressant for serpentine in the flotation of nickel sulfide ore

Serpentine is the primary gangue for the flotation enrichment of pentlandite. In this study, phosphorylated starch (PS) was synthesized via the esterification reaction of sodium phosphate with starch and employed as the depressant in separating pentlandite and serpentine through flotation. Micro-flotation results indicated that PS exhibited superior selective depressing effects on serpentine compared to causticized starch (CS). Electrostatic repulsion between pentlandite and serpentine interrupted their hetero-coagulation, as demonstrated by zeta potential measurements and DLVO calculations. Adsorption experiments demonstrated that PS selectively adsorbed onto the serpentine surface rather than on the pentlandite surface. The analysis result of X-ray photoelectron spectroscopy (XPS) and density functional theory calculations (DFT) suggested that PS strongly adsorbed onto the serpentine (magnesium active sites) surface (001) through chelation, forming phosphooxygen-magnesium (P-O-Mg) bonds, instead of adsorbing on pentlandite. In conclusion, in the flotation process of sulfide ores from serpentine, PS may be regarded as an effective and selective depressant.