Biobeneficiation of bauxite ore through bacterial desilication

Abstract

ABSTRACT Bauxite is an important mineral ore that is widely used in aluminum industry for metallurgical and refractory purposes. However bauxite contains silica as an impurity which degrades its quality. Silica forms complex with the caustic used during the processing of ore thereby forming precipitates. This leads to unnecessary wastage of caustic that contributes to the higher processing costs. Moreover, the use of excess caustic to neutralize the reactive silica during the process increases the alkalinity of the waste product so called red mud which imposes severe disposal problem. Therefore, the removal of silica from bauxite ore by a feasible and environmental friendly method is of paramount importance. The current study focuses on the beneficiation of low quality bauxite ores, through the process of bioleaching of silica. Bacterial desilication was carried out using indigenous bacterial cultures isolated from the ore. Bacterial colonies were successfully isolated and potential silica leaching strains was screened. Various process parameters such as pH, temperature, aeration time, inoculum size, age of the inoculum and bauxite percentage were studied through Taguchi method for process optimization. Optimum conditions for bioleaching of silica were obtained as pH 7.5, temperature 25ºC, initial aeration time of 30 minutes, bauxite percentage of 5% using 48 hours old 5% inoculums were established by Taguchi method,. Furthermore, optimum process conditions were used for bioleaching of silica under for different lengths of time i.e. 5, 15, 20, 25 days. Biological leaching results showed a maximum of 41% silica was recovered at the end of 25 days. Further, biochemical characterization of the potential bacterial culture proved it to be of Bacillus sp.