Process optimization for integrated mineralization of carbon dioxide and metal recovery of red mud

Indirect carbonation of red mud (RM), the alkaline waste of Jajarm alumina production plant, was carried out via a novel ex-situ multistep route. The process includes three consecutive stages of acid leaching of RM for extraction of minerals including aluminum (Al), magnesium (Mg), iron (Fe), calcium (Ca), and etc, pH swing process for achieving a high purity calcium source, and finally carbonation process. The influence of time, temperature, acid types, and acid concentration on the extraction performance were studied to assess the optimum process conditions. The optimized parameters in aspects of acid molarity, type, temperature and extraction time was achieved by by 2 M hydrochloric acid (HCl) at 40 degrees C within 30 min, respectively. About 85 % of calcium was extracted from RM at 80 degrees C within 2 h by HCl with the concentration of 1 M. The pH swing process was employed to ensure high purity Ca-containing solution by increasing the pH from 2.3 (leached solution) to 9.5. The carbonation of Ca-enriched leachate with sodium carbonate (Na2CO3), produced from the scrubbing of CO2 by sodium hydroxide (NaOH), was carried out and calcium carbonate (CaCO3) with considerable purity of 98 % was obtained. The carbonation efficiency was estimated at 32.71 %. Furthermore, the benefit of ex-situ mineral carbon sequestration on the site that both RM and CO2 are simultaneously attainable can improve the cost-efficiency of the process.