Enhanced recovery of water due to ammonia nitrogen contamination caused by mining processes

During in situ mining processes, high concentrations of ammonium sulfate solution are directly injected into the mountain to replace the rare earth. However, the residual ammonia nitrogen (AN) in the vadose zone from this injected solution is a serious pollutant of groundwater and soil. Unfortunately, in situ leaching methods using clean water are not effective at removing the AN. In this work, we developed a novel leaching method and examined its efficiency, as well as studied the mechanisms behind the adsorption and desorption of AN. It was found that the majority of the ammonium adsorbed in the soil was in soluble and exchangeable forms. The saturated adsorption capacity under mining conditions was 810 mg kg⁻¹, where only 36 % of the adsorbed AN was able to be leached out by water. However, the amount of AN leached out increased to 85 % when a KCl solution was used as the leaching agent at an optimized concentration of 2.8 mM. Furthermore, this improved leaching agent worked well at a wide range of solution pHs. Therefore, this method is an efficient means by which to remediate AN contamination after mining processes of RE ores.