Effect of potassium chloride on leaching process of residual ammonium from weathered crust elution-deposited rare earth ore tailings

Ammonium sulfate has been widely applied as a leaching agent to leach rare earth from weathered crust elution deposited rare earth ore because of its higher selectivity. However, large amount of ammonium remained on the ore body after the completion of rare earth leaching, and it was necessary to leach it from the ore body from the environmental point of view. In this work, potassium chloride was used as a leaching agent and effects of potassium chloride concentration, leaching agent pH, liquid/solid ratio and flow rate on the leaching process of ammonium were investigated in detail. It was found that potassium chloride could effectively leach the residual ammonium from rare earth tailings, and the leaching efficiency and leaching rate of residual ammonium were significantly higher than that with deionized water. Leaching agent pH almost had no effects on the leaching process of residual ammonium in the range of 2-6, and a greater impact on it at pH 8. The flow rate could effectively enhance the leaching efficiency. The optimum conditions of leaching residual ammonium were 0.06 mol/L of potassium chloride, pH 5.5-6.5 of leaching agent, 2:1 of liquid/solid ratio and 0.6 mL/min of flow rate. At these conditions, the leaching efficiency of residual ammonium was 95.78%, and the concentration of ammonium in the leachate at the final stage was 0.89 mg/L, which could meet the requirements for environment. The leaching process of ammonium in rare earth ore tailings was controlled by the inner particle diffusing according to the kinetic analysis. The reaction order was 0.117. These results suggest a promising route for the environmental remediation of weathered crust elution-deposited rare earth ore after in-situ leaching.