The Influence of Specific Ions and Oxyhydroxo Species in Plant Water on the Bubble-Particle Attachment of Pyrrhotite

Previous studies have considered the effect of using recycled process water in froth flotation and whether certain ions are responsible for what is observed in the final concentrate in terms of mineral grades and recoveries. The attachment of mineral particles to air bubbles is a fundamental subprocess of flotation, without which separation of valuable minerals from nonvaluables cannot occur; it is, therefore, of interest to assess the effect of specific ionic species on bubble-particle attachment. The effects of oxyhydroxo species on bubble-particle interactions were studied with three synthetic plant water (SPWs) of increasing ionic strengths at pH 11 as it is known to through solution speciation that at this pH, oxyhydroxo species may be present in significant concentrations. The presence of these oxyhydroxo species such as magnesium and calcium hydroxides in alkaline pulps were confirmed by many researchers and proven to affect bubble and particle surface charges. Furthermore, to ascertain whether there were certain ions within the plant water that impacted the bubble-particle attachment more significantly than others, tests were carried out with carefully selected single salt solutions. The SPWs at pH 11 resulted in very poor pyrrhotite attachment probabilities and recoveries as compared to the attachment probabilities and recoveries that were obtained with these waters at pH 6.5. Increasing the ionic strength of SPWs resulted in a decrease in pyrrhotite attachment probabilities more evidently at pH 11. Thus, it can be concluded that the presence of CaOH⁺, (MgOH)₂, and MgOH⁺ species hinders the flotation of pyrrhotite particles. Studies on selected single salts showed that Na⁺ resulted in better pyrrhotite attachment probability and recovery compared to Ca²⁺. Furthermore, upon studying the anion effect, SO₄ ^2- performed better than NO₃ ^- when paired with Ca²⁺, thus indicating a negative effect on flotation response when Ca²⁺ and NO₃ ^- ions are used together. These results can be attributed to the action of species such as Ca²⁺, CaNO₃ ⁺, and CaSO₄(aq.) on the zeta potential and their consequential effect on the electrical double layer. The outcomes of this work should be of significant importance for an effective management of ions in recycled process water in the froth flotation process.