To flocculant effect on the kinetics of dewatering and washing processes of red muds from low silicon bauxites in alumina production

The purpose of the paper is to study the effect of flocculants on the kinetics of thickening and washing processes of red muds obtained from low silicon bauxites in the production of alumina. To study the kinetics of red mud slurry thickening the method of controlling the pulp level during the settling process is used. The method of decants with decreasing concentrations is applied in the study of decanting countercurrent washing. The flocculant solutions are prepared according to a certain method, which allows to obtain working solutions of flocculants that have the maximum effect on red mud slurry clarification (high clarification rate, low content of dispersed particles in the drain). The effect of flocculants on the thickening and washing kinetics of red muds obtained from low silicon bauxites is studied. It has been determined that flocculants influence the formation of thickening zones. It is noticed that, the isoelectric state is equally observed for both pulps treated and non-treated with reagents at a certain concentration of alkaline aluminate or alkaline solution corresponding to the maximum clarification rate (maximum productivity of the thickener and thickener-washer). The use of flocculants at the stage of thickening ensures the subsequent increase in the performance of washers in washing stages. The maximum performance is demonstrated by the washer where the concentration of the dissolved valuable substance corresponds or is close to the concentration of the isoelectric state. In this case, the thickener-washer provides a clarified solution with a minimum content of dispersed particles. It has been found out that the use of flocculants influences the formation and the length of the main thickening zones. Under statistical conditions of flocculated pulp deposition, a decrease in the clarified zone depth is observed whereas the transition zone is significantly developed. A similar effect of flocculants has been noted for all stages of countercurrent decantating washing of red mud in the conditions when the concentration of the dissolved valuable substance (aluminate solution) decreases from the first to the last stage of washing.

alumina production, bauxites, red mud, flocculation, washing, decantation, aluminate solutions