EFFECT OF CAUSTIC AND CARBONATE ON THE FLOCCULATION OF HEMATITE IN SYNTHETIC BAYER LIQUORS

Polyacrylate flocculation of haematite in synthetic Bayer liquors has been studied to determine the effect of increasing caustic strength an d carbonate concentration. The drop in flocculation efficiency observe d with increasing caustic concentration (0.09 to 6.23 M) was shown not to be due to changes in the flocculant adsorption density or the floc culant molecular size in solution. The reduction in the settling rate could be only partially explained by the physical effect of the higher solution viscosity. Consequently, it is postulated that the increased viscosity also causes a shift in the balance between the rate of floc culant adsorption and the interparticle collision rate, which reduces the proportion of flocculant molecules forming bridges between particl es. The drop in flocculation efficiency with increasing carbonate (0.0 3 to 0.63 M) in the synthetic Bayer liquor was attributed to the slow rate at which flocculant can displace carbonate adsorbed on the haemat ite surface. (C) 1998 Elsevier Science B.V. All rights reserved.