Optimization of a Rare Earth and Aluminum Leaching Process from Weathered Crust Elution-Deposited Rare Earth Ore with Surfactant CTAB

Abstract

Ammonium sulfate is typically employed as a leaching agent in the in situ leaching of weathered crust elution-deposited rare earth ore. However, it is associated with challenges such as low efficiency in mass transfer for rare earth (RE) leaching, high usage of the leaching agent, and prolonged leaching duration. To address the issues mentioned above, the surfactant cetyltrimethyl ammonium bromide (CTAB) was compounded with 2% ammonium sulfate to form a leaching agent in this paper. The effects of CTAB concentration, temperature, pH, and leaching agent flow rate on the rare earth (RE) and aluminum (Al) leaching mass transfer process from RE ore were investigated using chromatographic plate theory. The results revealed that CTAB addition improved the RE mass transfer process while moderately inhibiting the Al mass transfer efficiency. Increasing the temperature and pH of the leaching solution led to higher theoretical plate numbers for RE and Al leaching, lowered theoretical plate height (HETP), and enhanced leaching mass transfer efficiency. However, under high temperature and alkaline conditions, the mass transfer efficiency begins to decrease, indicating that high temperature and alkaline conditions are not conducive to the synergistic enhancement of RE and Al leaching by CTAB. Considering that clay minerals have good pH buffering properties, adjusting the pH of the leaching solution during rare earth ore leaching operations was deemed unnecessary. The optimal mass transfer conditions for leaching RE and Al were identified as 2% ammonium sulfate concentration, 0.00103 mol/L CTAB concentration, pH range of 5.2–5.5 for the leaching solution, 0.6 mL/min leaching solution flow rate, and room temperature. The rare earth leaching mass transfer effect could be enhanced during summer operations.