Development of hydrometallurgical purification process for Nigerian gypsum ore in hydrochloric acid. Part II: Recovery of pure gypsum from leached liquor

As the world grapples with the challenges of resource scarcity and sustainability, the need to develop indigenous raw materials has gained paramount importance. To achieve self-sufficiency and reduce dependence on foreign sources, harnessing hydrometallurgical processes to extract valuable elements from ores presents a promising solution. Raw gypsum from Postikum, Nigeria, was leached in hydrochloric acid to obtain a pure calcium sulphate dihydrate. The dissolution kinetics have been reported elsewhere. This present study focused on optimizing the recovery of pure gypsum by varying acid concentration, temperature, and solid-liquid ratio. Additionally, the recyclability of regenerated hydrochloric acid was tested. The characterization of the raw gypsum ore (RWG), leached residue (LR), and recovered pure gypsum (RCG) was done using SEM-EDS, XRF, and XRD, respectively. The recovered gypsum was characterised by a brilliant white colour in contrast to the initial brown colour of the ore. XRF results show that RWG contains 50.48% SO3 while RCG contains 57.72 %. XRD results revealed that RWG contains gypsum, magnesite, mordenite, witherite, and calcite, LR contains mordenite, witherite and quartz while RCG consists of gypsum crystal phase only with no impurities. Remarkably, 85% RCG was successfully recovered at the fourth recycle stage of HCl lixiviant. These findings demonstrate that hydrometallurgical treatment of gypsum ore with hydrochloric acid can produce very pure gypsum.