Interaction mechanisms of H3PO4, H2SO4, and corn starch depressants with phosphate ore surface

This work explores comparative depressive mechanisms of corn starch, sulfuric acid (H 2 SO 4 ), and phosphoric acid (H 3 PO 4 ) on natural phosphate ore. The objective of the present paper study was to investigate the interaction mechanisms induced by these agents using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Three essentially different mechanisms were found. Corn starch operates through a non-reactive surface adsorption, evidenced by the absence of new phases, leading to the preservation of francolite matrix. Conversely, at high concentration, H 2 SO 4 induces a highly aggressive, non-selective chemical dissolution evidenced by the loss of francolite peaks and massive precipitation of gypsum (CaSO 4 ⋅2 H 2 O) on the surface, resulting in significant material loss. The most nuanced mechanism is observed with H 3 PO 4 , which promotes a selective surface precipitation reaction. High concentrations of H 3 PO 4 lead to the formation of brushite (CaHPO 4 ⋅2 H 2 O), confirmed by new crystalline peaks. This layer blocks the collector adsorption site and therefore chemically depresses the particles without a high level of dissolution that would occur with H 2 SO 4 . These results are essential for the further development of flotation operations to achieve maximum selectivity and process economy in phosphates upgrading.