Leaching Kinetics and Mechanism of Laterite with NH4Cl-HCl Solution

Extraction of Rare-Earth Elements from Silicate-Based Ore through Hydrometallurgical Route

The European Union and several countries/regions classified the rare-earth elements (REEs), such as lanthanum, cerium, neodymium, and scandium, as critical due to the risk of supply interruption. For this reason, the growing demand for REEs has resulted in forgotten reserves receiving economic interest. So, the search for new sources and the development of chemical process is important, such as silicate-based ore. Since there is almost no literature on the extraction of REEs from this source, a new approach was developed in the present study. Direct leaching and acid baking were studied using sulfuric acid. The effect of the acid concentration, temperature, solid-liquid ratio, oxidizing/reducing medium, and acid dosage were studied. Results showed that the extraction of REEs achieved up to 80% at 90 °C in oxidizing medium, and scandium and iron achieved 13.5% and 65.0%, respectively. For the acid baking experiments, the results were better than direct leaching for REEs at over 85%. The scandium leaching rate was lower than direct leaching. On the other hand, the extraction of iron was lower in acid baking than direct leaching. The iron and scandium extraction rates were higher in lower temperatures (<200 °C) and acid dosages, achieving 50% and 6.3%, respectively. Future studies should explore thermal treatment before acid leaching.

The leaching behavior of copper and iron recovery from reduction roasting pyrite cinder

Pyrite cinder (PyC) is an iron-enriched solid waste material, which is an important iron resource for steel industry. However, the separation or extraction of iron minerals and heavy metals from PyC was ineffective, because of the fine disseminated granularity and the intergrowth between iron minerals and toxic heavy metals during high temperature roasting. In this paper, a novel method to extract copper and iron from the PyC by reduction roasting-leaching-magnetic separation was proposed. The effect of various parameters on the copper leaching behavior were studied, and the corresponding kinetics model was established. Under the optimized leaching conditions, the maximum copper leaching recovery of 82.18% was reached. A high-quality iron concentrate with Fe content of 65.58% and copper content of 0.17% was obtained subsequently from the leaching residuals through magnetic separation. It showed that the leaching process was controlled by mixed diffusion and chemical reaction, with a corresponding activation energy of 27.97 kJ/mol. The free copper oxide, combined copper oxide and secondary copper sulfide were extracted completely in H₂SO₄ solution. However, chalcopyrite as a form of primary copper sulfide dissolved partly. The leaching mechanism was confirmed by chemical phase and XPS analysis.