The influential role of pulp chemistry, flocculant structure type and shear rate on dewaterability of kaolinite and smectite clay dispersions under couette Taylor flow conditions

Abstract

Improving the dewatering behaviour of mineral waste tailings is an important issue central to sustainable hydrometallurgical processing of minerals worldwide. Chemical additive-mediated, flocculation processes are generally employed to amply sedimentation behaviour of colloidally stable mineral dispersions. In this paper, studies carried out to investigate mineral particle surface chemistry/structure, polymeric flocculant structure type, shear rate and their links with improved dewaterability of colloidal kaolinite and smectite dispersions at pH 7.5 are presented. The results show that, following orthokinetic flocculation under laminar couette Taylor flow conditions with high molecular weight, non-ionic polyacrylamide homopolymer (PAM N), anionic polyacrylamide copolymers: carboxylate substituted (PAM A) and sulphonate substituted (PAM S), and non-conventional non-ionic polyethylene oxide (PEO), distinct clay mineral specific, polymer type and shear dependent dewatering behaviour was displayed. Sedimentation rates were markedly higher for kaolinite pulps, however and the extents of pulp consolidation were substantially similar for both kaolinite and smectite pulps under common flocculation conditions. The pulps flocculated with PAM S polymer showed greatest dewatering behaviour, followed by PEO and then PAM A and PAM N. For each flocculated pulp, an optimum shear rate which led to maximum settling rate exists and some cases led to greater consolidation for PEO based pulps. The findings which are compared with those obtained by a 2-blade impeller sheared orthokinetic flocculation exemplify how judicious choice of polymeric flocculant and shear rate may be effectively used to significantly enhance the dewaterability of colloidally stable clay mineral dispersions.