Specific Ion Effects on the Behaviour of Mixtures of Sodium Iso-Butyl Xanthate and Sodium Di-Ethyl Dithiophosphate during the Flotation of a Cu-Ni-PGM Ore: Effects of Na⁺ and Ca²⁺

Inorganic electrolytes present in the process water used during froth flotation may have both beneficial and detrimental effects. These effects are said to be ion specific as some ions may result in enhanced froth stability, increased mineral recoveries and decreased concentrate grades while others may bring the opposite effects. Onsite process water quality variations have intensified the need to understand the relationship between inorganic electrolytes and flotation reagents on flotation performance. The use of mixtures of thiol collectors in sulfide flotation is a common practice across the globe, however very little investigations have considered these in process waters of varying compositions. This study considers the effect of common cations, Na⁺ and Ca²⁺ in process water on the behaviour of mixtures of thiol collectors. Single salt solutions of NaCl and CaCl₂ at an ionic strength of 0.0213 mol.dm^-3 were used to investigate the behaviour of mixtures of two thiol collectors. These were carefully selected so as to understand how mixtures of thiol collectors behave in the presence of a monovalent cation versus a polyvalent cation. Bench-scale froth flotation tests were conducted using a Cu-Ni-PGM ore from the Merensky reef. The results have shown that the divalent cation, Ca²⁺, resulted in higher %Cu and Ni recoveries at all collector mixtures compared to the monovalent cation, Na⁺. The concentrate grades were however slightly compromised as slightly more gangue reported to the concentrate in the presence of Ca²⁺. This behaviour is attributed to the effect of polyvalent cations on bubble coalescence and froth stability.