Leaching of rare earths and aluminum in weathered crust elution-deposited rare earth ore using magnesium sulfate: Effect of aluminum content in leaching agent solution

Aluminum is the main impurity of the weathered crust elution-deposited rare earth ore (WCED-REO). Efficient leaching of rare earths and low leaching of aluminum are of great importance for the leaching of the WCED-REO. The effects of pH, MgSO₄ concentration and Al³⁺ concentration of the leaching agent solution on the column leaching behaviors of WCED-REO using magnesium sulfate were investigated. Experimental data show that controlling the MgSO₄ concentration to 0.15 mol/L, pH of the leaching agent solution to 2, the leaching amount of aluminum from the rare earth ore gradually decreases with the increase of Al³⁺ concentration in the leaching agent solution, indicating that Al³⁺ in the leaching agent solution may act as leaching agent to participate in the ion exchange of RE³⁺, but the leaching amounts of rare earths change insignificantly as the Al³⁺ concentration is increased. Increasing the MgSO₄ concentration is beneficial to the leaching of aluminum, and when the Al³⁺ concentration is 0.04 mol/L (Al accumulation), the amount of Al³⁺ leached from the rare earth ore increased gradually with increasing the MgSO₄ concentration. The pH of the leaching agent solution has a significant influence on the leaching of aluminum in the rare earth ore, and the leaching amount of aluminum from the rare earth ore increases gradually with decreasing the pH. When the Al³⁺ concentration is 0.04 mol/L (Al accumulation) and the pH of the leaching agent solution is above 2.0, the aluminum in the leaching agent solution can be back-adsorbed onto the rare earth ore, and the amount of the back-adsorbed Al³⁺ increases with increasing the pH of the leaching agent solution. The injection rate of the leaching agent solution has slight effect on the leaching behavior of rare earths and aluminum. In summary, leaching of Al³⁺ and consumption of MgSO₄ can be reduced by regulating the accumulation of aluminum, MgSO₄ concentration and pH.