Extraction of aluminium from mudstone using a two-step acid leaching method

Laboratory studies were conducted to produce a 44.29 g/L aluminum sulfate solution by leaching mudstone (coal mine waste), with an 83% recovery rate. This was achieved through two steps: firstly, roasting and leaching the roasted material, and secondly, roasting the residue mixed with sodium carbonate, followed by leaching the roasted material. The favorable operating conditions included a 1:1 mixing ratio, 1-h roasting time at 800 °C, leaching temperature of 100 °C, agitation speed of 200 rpm, a solid-to-liquid ratio of 1:4, 60% sulfuric acid concentration, and 3 h of agitation time. This study is significant because it yielded a novel high recovery percentage and produced aluminum sulfate solution, which can be crystallized to alum and purified to water.