The effect of clay type and dispersion conditions on electroosmotic consolidation behaviour of model kaolinite and Na-exchanged smectite pulps

Abstract

Effective dewatering and disposal of mineral waste tailings continue to be important issues for the minerals industry globally. Conventional hydrometallurgical processes involving low grade ores produce voluminous amounts of dilute dispersions, fine particles and equivalently large volumes of intractable waste tailings of low solid density. For tailings rich in clay minerals, conventional flocculant-mediated gravity sedimentation (thickening) used for dewatering achieves fast settling rates but poor sediment consolidation, even after several years of dam impoundment. Hence cost-effective methods that achieve compact pulp consolidation and enhanced process water recycling are warranted.In the present work, batch electroosmotic (EO) consolidation behaviour of single and binary mixtures of model kaolinite and two types of Na-exchanged smectite pulps was investigated. Specifically the influence of clay type, ionic strength, pulp interfacial chemistry (particle zeta potential) and swelling behaviour on efficacy of EO was assessed. EO consolidation of pre-sedimented pulps at pH 7.5 was effective for kaolinite and a low-Na exchanged smectite whose interfacial chemistry was altered and swelling behaviour suppressed via Ca(II) ions addition. EO consolidation achieved 10–15wt.% solid increases, resulting in ‘spadeable’ pulps at acceptable power consumption rates. No such significant improvement was achieved for the high-Na exchanged smectite, contrary to expectation.