Comparative analysis on the effects of soil and Dicranopteris pedata taking MgSO4 and (NH4)2SO4 as leaching agents

Abstract

In-situ leaching of ion-adsorbed rare earth ores (IAREO) is generally considered to have adverse impacts on the mine environment. However, studies on the effects of MgSO₄ and (NH₄)₂SO₄ as leaching agents on the surface environment of IAREO are scarce. In this study, MgSO₄ and (NH₄)₂SO₄ were selected as leaching agents for extracting rare earth elements (REE) in two IAREO mines, respectively. The collected samples from the mining area before leaching, and 1, 3, and 6 months after leaching four times to investigate the environmental impact during the process. The soil pH value decreased significantly, by 6.90 %, after 6 months of leaching with (NH₄)₂SO₄. Additionally, total nitrogen (TN) and NH₄⁺-N contents decreased under MgSO₄ leaching at the mine, while NH₄⁺-N decreased and NO₃^--N increased at the mine under the leaching of (NH₄)₂SO₄. Consequently, the increase in NO₃^--N significantly influenced REE enrichment in the aboveground organs of Dicranopteris pedata (D. pedata). After leaching for 3 months, the leaves REE content, bioconcentration factor (BF), and translocation factor (TF) of D. pedata reached the maximum. Meanwhile, the exchangeable and residual REE that can affect REE enrichment in D. pedata have increased, while the Fe/Mn oxide-bound REE which accounted for the major portion of REE decreased. The results of the study confirmed that the MgSO₄ leaching agent is more environmentally friendly compared to (NH₄)₂SO₄ in nitrogen contamination and that D. pedata has the potential to phytoremediate nitrogen and REE pollution in IAREO tailing areas.