Selective aggregation of fine quartz by polyaluminum chloride to mitigate its entrainment during fine and ultrafine mineral flotation

Abstract

• Polyaluminum chloride (PAC) could lower quartz entrainment in galena flotation. • Adding xanthate before PAC suppressed the depressive effect of PAC on galena. • PAC selectively aggregated fine quartz particles in the galena-quartz mixture. • The rate of PAC adsorption onto quartz surfaces was higher than on galena. • PAC adsorbed on quartz through both charge neutralization and Al bridging. Fine and ultrafine hydrophilic particles are typically left in a dispersed state in a flotation pulp when novel fine mineral flotation technologies are developed. These dispersed fine and ultrafine gangue particles can enter flotation concentrate by mechanical entrainment, lowering concentrate grade. The problem is becoming increasingly more pervasive as the required liberation size of value minerals in ores decreases. In this work, polyaluminum chloride (PAC) was investigated to study its effect on the reduction of quartz entrainment in the batch flotation of synthetic mixtures of quartz and galena. Apart from the evaluation of quartz entrainment, micro-flotation of galena, batch flotation of artificial mixtures of galena and quartz, the aggregation/dispersion behaviors of quartz and galena and their mixtures in the presence of PAC were studied by sedimentation, turbidity, focused beam reflectance measurement (FRBM) coupled with optical microscope observations and scanning electron microscope (SEM), and zeta potential measurements. The results indicated that the addition of PAC reduced quartz entrainment without adversely affecting galena flotation, so that the flotation separation efficiency was increased from 74% (without PAC) to 77% (when PAC was added prior to xanthate) and 80% (when xanthate was added prior to PAC) at PAC concentrations below 150 mg/L. PAC was found to aggregate the fine quartz but not galena. It was observed that PAC preferentially adsorbed on quartz in the quartz-galena mixtures, so that it lowered the entrainment of quartz and improved separation efficiency.