Understanding the role of water quality in separation of rare earth minerals from iron oxide minerals in a flotation circuit

Abstract

In many mineral processing plants, using saline water has become necessary to improve water efficiency. However, the dissolved ions in the water such as Ca2+ and Mg2+ may have a significant negative impact on the flotation of RE (rare earth) minerals due to the chemical reaction with flotation reagents used in RE flotation. Although some researchers investigated flotation performance of pure rare earth minerals, there is no study investigating the role of water quality in the separation of rare earth minerals from iron oxide minerals in a flotation circuit. This study focused on investigating the effect of divalent cations like Ca2+ and Mg2+ on the flotation of RE minerals using a fatty acid collector and Na2SiO3 depressant. The results showed that the presence of Ca2+ and Mg2+ decreased the selectivity and recovery of RE minerals due to the formation of insoluble calcium and magnesium carboxylate, leading to the reduced residual collector concentration. Furthermore, the divalent cations acted as a bridge between the oxygen atoms of the adsorbed SiO32− and carboxylate ions, resulting in increased adsorption of fatty acid collector ions and higher recovery of FeO. Rheological measurements also revealed that the presence of Ca2+ and Mg2+ significantly increased the flotation pulp viscosity, which could be attributed to the reduced repulsive forces between particles due to the compression of electrical double layer. This study provides valuable insights into the mechanisms underlying the effects of Ca2+ and Mg2+ on RE mineral flotation.