The Changes of Soil Properties of Ion-adsorption Type Rare Earth Ore with Non-ammonium Leaching Agents

Non-ammonium leaching is an important way for the green development of ion-adsorption rare earth ores. However, the effects of different non-ammonium leaching agents on soil ecological environment remain unclear. This study employs raw ore as a control, indoor column leaching experiments were conducted to compare the effects of three non-ammonium leaching agents (magnesium sulfate, calcium chloride, and calcium chloride-aluminum sulfate) and ammonium sulfate on the physicochemical properties, microbial quantity, and enzyme activities of leached tailings, and to explore the primary limiting factors for vegetation restoration in tailings under different leaching agents. Results show that non-ammonium leaching agents reduce the loss of soil potassium and supplement abundant calcium or magnesium compared with ammonium sulfate. Microorganisms respond differently to non-ammonium and ammonium salt leaching agents, with lower soil basal respiration and culturable bacterial counts observed in the non-ammonium treated groups, while the magnesium sulfate treatment exhibits the highest phosphatase and catalase activities. Moreover, leaching with calcium chloride and calcium chloride-aluminum sulfate significantly reduce microbial biomass carbon content. No heavy metal pollution is found in any tailing soil, and the comprehensive soil quality ranking from high to low is: Ammonium sulfate>magnesium sulfate>calcium chloride>calcium chloride-aluminum sulfate. Besides the inherent nutrient deficiency, which lacks organic matter, nitrogen, available phosphorus, and available potassium in the original ore soil, the imbalanced calcium-magnesium ratio caused by non-ammonium leaching and the residual aluminum after calcium chloride-aluminum sulfate leaching are identified as limiting factors for vegetation restoration of tailing soil.