Effects of ammonium sulfate on the release and morphological transformation of heavy metals from soil in ionic rare earth mining areas

Due to the combined pollution of ammonia nitrogen and heavy metals in the soil caused by leaching in the ionic rare earth mining areas, the mechanism of the effect of ammonium sulfate residue on the migration, transformation and morphology of heavy metals in the soil was studied. Soil column leaching and indoor soil culture experiments were carried out to investigate the changes in the morphology and mobility of NH₄⁺-N, Zn, Cu, and Cr after different concentrations of leaching agents were input into the soil. The experimental results showed that the leaching agents mainly existed in the form of NH₄⁺-N in the contaminated soil, and the proportion of NO₃^--N was low. Compared with the control group, after leaching with ammonium sulfate leaching solution, the pH value and cation exchange capacity (CEC) of the soil were reduced, and the activity of heavy metal ions was enhanced during the cultivation period. The contents of weakly acidic Cr, Cu, and Zn increased by 8.29%, 5.21% and 4.53%, respectively. The results showed that ammonium sulfate enhanced soil acidification, promoted heavy metals migration, and transformed the heavy metals form from the bioavailable state to the available one.