Selective extraction of sodium from red mud by dry digestion

Abstract

The strong alkalinity of red mud prevents its application as soil aggregates, adsorbing materials, fillers, and building materials. Direct acid leaching is an effective method for dealkalization of red mud. However, the formation of silica gel in the process causes significant processing difficulties. Herein, a dry digestion method was introduced to red mud for the selective recovery of Na with suppressed formation of silica gel. The optimum conditions of dry digestion and leaching were obtained as follows: temperature of 50 °C, H2SO4 concentration of 1 mol/L, curing time of 30 min, and leaching solid–liquid ratio of 1:3. Almost 85% Na was leached, where Si dissolution was suppressed to 0.7% and no silica gel was formed. X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS) results revealed that the large particles of quartz with circular crystals and gypsum with bar-shaped crystals were generated during dry digestion. The particle size of red mud after leaching increased and formed a reunion phenomenon, which improved the filtration performance. Compared with the traditional process, the proposed dealkalization process is conducive to subsequent utilization.