The Behavior of Gangue During the Flotation of a Sulfidic PGM-Bearing Ore in Response to Various Monovalent and Divalent Ions in Process Water

Abstract

Mineral concentrators are becoming increasingly aware of the importance of the quality of the water that they feed into their milling and flotation circuits. It is speculated that different inorganic constituents of process water may yield different flotation results owing to the electrolyte-reagent-mineral interactions occurring in the pulp phase. These interactions are said to be specific to ion type, reagent type, and mineral or ore type. It therefore stands to reason that there is a need to develop an understanding of the specific ion effects on both the pulp phase and the froth phase phenomena, such that the chemistry and the quality of process water can be monitored and controlled in a manner that does not negatively affect the flotation performance. Previous research has shown that inorganic electrolytes may impact the hydrophobicity and the floatability of mineral particles and could in turn affect froth stability, entrainment, and thus mineral grades and recoveries. In this study, the floatability of a Cu-Ni-PGM-bearing Merensky ore is tested on a bench-scale flotation system in various single salt solutions, viz., CaCl₂, CaSO₄, Ca(NO₃)₂, MgCl₂, Mg(NO₃)₂, MgSO₄, NaCl, NaNO₃, and Na₂SO₄, in order to examine specific ion effects on gangue recovery. Coagulation and zeta potential tests are conducted in order to establish the nature of the impact that specific ions have on the behavior of gangue in flotation. The findings of this work have shown that single salt solutions containing ${\text{NO}}_3^{-}$ ions resulted in a strong depression of gangue compared to those solutions containing Cl^- and SO₄ ^2- ions. It was also shown that the divalent Ca²⁺ and Mg²⁺ showed a stronger depression of gangue compared to the monovalent Na⁺. Ca²⁺, in comparison to Na⁺, resulted in an increase in the coagulation of the ore as well as an increase in the zeta potential of talc. Overall, the findings of this paper suggest that the presence of Ca²⁺ and Mg²⁺ in process water would most likely create conditions that promote gangue depression.

Keywords: flotation; gangue; inorganic electrolytes; ions; sulfides; talc; water.