Ionic strength of flotation medium and consequential effects

Abstract

Environmental factors and water scarcity have led to the recirculation of greater quantities of water in mineral processing plants. Recycling water or using alternate water sources, e.g. seawater, for flotation can result in an increase in ionic concentrations and lower water quality. Water recirculation and lower water quality can increase ionic strength which can cause corrosion, scale formation, changes in water recovery to the froth phase, precipitation of species on the mineral surfaces causing accidental activation or passivation, agglomeration of particles (double layer compression), loss in selectivity in flotation-lower grade and recovery, froth persistence, and impact bubble-particle interaction. However, in certain cases the effect of ionic strength is not the main factor affecting flotation; reagent type and dosage can have a more significant impact. The ionic species, temperature and their interactions can affect flotation significantly. Certain ionic species like sulfate, sodium, calcium, base metals, chlorine and thiosulphates have threshold concentrations. If these concentration are exceeded, flotation would be negatively effected. The solution chemistry of dissolved species and ionic strength in water is discussed in terms of effects on decay length (double layer compression) on particles, froth properties, threshold concentrations, water film destabilisation, water recovery to froth phase, bubble properties, surface chemistry (precipitates formation and adhesion on particles) and metallurgy. The effects of ionic strength, temperature, species in solution and their interactions on mineral flotation, and sources of variation in water quality are also presented in this article. This review will serve as fundamental knowledge for further study on the effects of water quality. Research gaps and challenges are also discussed.