Highly selective recovery of rare earth elements from mine wastewater by modifying kaolin with phosphoric acid

Recovery of rare earth elements (REEs) from mine wastewater is essential for maintaining rare earth reserves and sustainable application of REEs. In the present study, we prepared a phosphoric acid modified kaolin (P-K) adsorbent by a simple mechanochemical process for the selective recovery of REEs from rare earth wastewater. The impacts of phosphoric acid dosage, milling duration, initial pH, temperature, initial ion concentration, and adsorbent dosage on the selective adsorption of REEs were investigated. The findings demonstrate that the adsorption of REEs by P-K follows pseudo-second-order kinetic model and the Langmuir isotherm model, and is dominated by chemical adsorption, with a maximum adsorption capacity of 19.82 mg/g at 50 celcius. Additionally, in an original mine wastewater, the recovery rate of REEs can reach more than 90%, whereas the adsorption rates of calcium, magnesium and, ammonia nitrogen (whose concentration is 18 times that of REEs) are nearly zero, indicating that P-K has extremely high selectivity for REEs. Furthermore, the feedstock solution containing 40 mg/L of REEs may be concentrated to 3510 mg/L following enrichment treatment, and 99.9% of the REEs are eluted using a low concentration of hydrochloric acid. The findings illustrate that P-K has a wide range of po-tential applications in the treatment of rare earth industrial effluents.