Improved dewaterability of iron oxide dispersions: the role of polymeric flocculant type, pH and shear

Abstract

Substantial amounts of recyclable water are trapped in mineral waste tailings dams annually due to less than effective dewatering processes. To address this, a study has been conducted of the flocculation performance of four high molecular weight (>5 × 106 Da) polyacrylamides, non-ionic homopolymer (PAM N), anionic carboxylate substituted copolymer (PAM A), anionic sulfonate substituted copolymer (PAM S), and cationic trimethyl amino ethyl substituted copolymer (PAM C), on the dewaterability of iron oxide suspensions as a function of pH. Significant polymer structure-mediated and pH-dependent trends were observed. Upon flocculation with up to 500 g polymer/t solid, settling rates in the range of 3-100 m/h were observed, along with sediment solid loading in the range 35-40 wt%. Settling rates varied depending on polymeric flocculant type, and were higher for anionic and cationic polymers than for non-ionic polymers. Settling was most efficient at and below the iso-electric point (iep, pH 8.5). Polymer structure type did not have any noticeable impact on the extent of pulp consolidation. Moderate shear significantly improved the consolidation (55 wt% solid) of pre-sedimented pulps. For the selection of a flocculant, a polymer that displayed an opposite charge to that of the particles appeared to provide improved flocculation and dewatering performance.