A study of polyacrylate and hydroxamate co-dosing flocculation of stabilised bauxite residue material

A novel and reliable method for stabilising bauxite residue material is demonstrated, allowing greater control and understanding for bauxite residue flocculation studies. Using the stabilised bauxite residue and a flocculation method utilising the focussed beam reflectance measurement (FBRM) probe, the ageing of Bayer process emulsion flocculants was examined and found that there is little change in flocculant activity from either stock solution or dilute test solution as a function of time (up to 80 h). In addition, the polyacrylate/hydroxamate co-dosing flocculation of bauxite residue, a system commonly applied in Bayer process alumina refineries, was examined. The supernatant turbidity achieved from flocculation was found to decrease with increasing hindered settling rate, despite variation in solids loading, and the relationship followed a decaying power function. At a fixed flocculant dosage, it was found that the optimum solids concentration required for maximum thickener throughput, and that required for minimal liquor overflow solids, varies significantly, and this is discussed in terms of the flocculant chemistry.