Sustainable application of sodium removal from red mud: Cleaner production of silicon-potassium compound fertilizer

Abstract

The treatment of red mud, solid waste produced from alumina preparation, is an urgent topic for reducing environmental pollution and recycling valuable elements to comprehensively utilize secondary resources. In this study, a novel method for producing silicon-potassium compound fertilizer by KOH hydrothermal leaching in red mud is proposed to remove sodium and simultaneously obtain a high-quality mineral fertilizer containing silicon and potassium. The results reveal that potassium aluminum silicate with high crystallinity can be formed from KAlO2 solution reacting with K2SiO3 at a temperature above 80 °C. With a 360 g/L K2O hydrothermal leaching temperature of 240 °C, the Na2O content of the red mud transformation residue can be reduced to 0.5%, the full K2O content reaches 12.35%, and the effective K2O and SiO2 contents can reach 12.20% and 18.59%, respectively. When the molar ratio of Na2O to K2O is lower than 0.0625 in the sodium-potassium mixed solution, the red mud transformation residue indices obtained from hydrothermal treatment are close to the abovementioned values. All meet the market requirements of inorganic compound fertilizers and have great potential in agricultural applications, which provides a good solution for the large-scale harmless and sustainable reuse of red mud.