Leaching mechanism of ion-adsorption rare earth by mono valence cation electrolytes and the corresponding environmental impact

lon-adsorption rare earth (IARE) is a very important resource which is adsorbed on clay mineral surface and can be leached by appropriate electrolyte solutions. A comprehensive understanding of the leaching mechanism is crucial for achieving high extraction efficiency with low cost and less environmental impact. In this paper, a series of inorganic electrolytes with different concentrations were employed to leach the IARE, and the relationship between leaching efficiency (LE) of IARE and zeta potential of the leached clay mineral particles (CMPs) was investigated. A linear relationship between the LE of IARE and zeta potential of CMPs is observed for every electrolyte. However, the slope (S) of the linear relationship greatly depends on the type of the cations and follows a sequence of S(NH4+) > S(K+)> S(Na+). In addition, in the case of ammonium or potassium ions, the slope is almost the same for both SO42- and Cl-. But for sodium ions, a significant difference of slope is observed with the order of S(SO42-) > S(Cl-). These facts suggest that the cations play a dominating role in affecting the leaching of IARE, while the anions also contribute to the LE of IARE. Based on the electric double layer model and hydration theory, a leaching mechanism is proposed to illustrate the dependence of zeta potential on the LE of IARE and the residual ion concentration in rinsing solutions which is considered to be the main factor influencing the environment of mine district. This work may provides a promising route for enhancing the LE and estimating the environmental impact of remaining electrolytes in mine tailing. (C) 2018 Elsevier Ltd. All rights reserved.