Study on the effect of structural sodium dissolution on the physical properties of red mud treated by sulfuric acid

Abstract

Red mud is a strong alkaline solid waste produced by the alumina industry. Although it has found frequent use in building applications, its sodium content causes unwanted effects like “Frost”, demanding the removal of Na+ from red mud. Effective removal of Na+ can result in improving the performance of red mud as a material and increase its applicability. However, the removal of Na+ remains a key problem that needs to be addressed. In this paper, a comprehensive and systematic study has been carried out on the commonly used method of sulfuric acid dealkalization and its influence on the physical properties of red mud has been investigated. The variation of mineral phase content species in red mud and the mechanism of Na+ removal during acid leaching has been studied by regulating the sulfuric acid concentration. The red mud residues have been characterized using a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer Emmett Teller (BET) based on nitrogen adsorption–desorption. The results show that the Na+ leaching yield gradually increases with the increase in sulfuric acid concentration. Further, the Na-H, Na-O, Si-O, and Ca-O bonds in the main Na+ assigned mineral phase cancrinite are broken in a certain order based on the differences of bond energies at different acid concentrations. The results of this study can help to successfully address the issue of treatment of Na+ in bauxite slag and lessen the environmental contamination brought on by the subsequent discharge of waste liquid. Additionally, after treatment, the discharged waste liquid might be converted into usable products. The findings of this work have crucial implications for future-focused research in addition to offering a plausible pathway for ion alterations throughout the red mud dealkalization process.