An integrated approach to sustainable mine wastewater treatment: Magnesium recovery with anion exchange membranes

With recent emphasis on sustainable and efficient mineral valorization, novel approaches to treating mineral wastewater in natural settings bring both environmental and economic value. This paper presents the results of an applied research to develop an integrated approach to sustainable wastewater treatment that includes an ion exchange process to recover copper and cobalt from mine wastewater, followed by the membrane recovery of magnesium. Th e paper investigat es magnesium hydroxide crystallization process employing an anion exchange membrane (AEM) cell. This process involves the penetration of OH - ions from the alkaline solution through the AEM to the feed solution in exchange for Cl - ions and precipitation of Mg(OH) 2 as solid particles. The wastewater was sampled from different mine waste sources from the copper mine tailings dam in South Australia, all containing significant amounts of critical metals, including magnesium, copper, and cobalt. The results have demonstrated the potential for sustainable magnesium hydroxide recovery methods. The findings suggest that the most influential process parameters for magnesium hydroxide recovery and purity are magnesium concentration in the feed solution and sodium hydroxide to magnesium ratio in the alkaline solution and feed solution, respectively. It was also established that the overall recovery of cobalt, copper and magnesium in a combination of ion exchange and AEM processes was achieved at a level near 100%. The purity of magnesium hydroxide precipitate was achieved in the range of 90% to 96.6% and depends mainly on the presence of impurities in brine. • An integration of membrane technology for magnesium hydroxide recovery from mine wastewater solutions with preparatory ion exchange recovery of copper and cobalt has been investigated • Two types of anion exchange membranes have been compared from the point of view of crystallization efficiency • The key process parameters are magnesium concentration in the brine solution and sodium hydroxide to magnesium ratio in the alkaline solution and brine respectively • Higher purity of magnesium products requires thorough removal of other metals prior AEM crystallization