Optimization of leaching and desilication stages in alumina extraction from Zarand coal washing plant wastes

Extraction of alumina from the wastes of Zarand coal washing plant is one of the suitable methods for reduction of environmental of pollutions. Extraction of alumina from these wastes consists of several processes, sintering the ashes produced from combustion of the wastes with limestone, leaching of alumina from the sinter and elimination of silica from leachate are the most important stages of the process. In this investigation, the important parameters of the processed such as temperature, contact time, solid to liquid and liquid to liquid ratios and type of the solvents used are studied. The results of the experiments showed that in leaching stage about 75% alumina and 3% silica were extracted and in desilication stage approximately all the silica wase eliminated.The XRD pattern of sinter, red mud and desilication precipitate showed that the aluminum losses in leaching stage mainly was in 3CaO.Al2O3 and Na2O.Al2O3.3SiO2.2H2O phases and in desilication stage mainly was in CaO.Al2O3.4SiO2.6H2O.