来源：Science Direct
Prolonged MgSO4 in-situ leaching (ISL) of ion-adsorption rare earth element deposits may alter rare earth elements (REEs) vertical distribution, fractionation, and speciation, but field evidence is lacking. Here, current authors conducted a nine-month continuous MgSO4 ISL in an operational deposit (Fujian, China) and compared depth-resolved (0–13 m) soil properties, REEs contents, and sequential extraction fractions before and after leaching. Results show that MgSO4 injection induced ore-zone acidification (at 3–4 m), particle-size restructuring, and downward organic matter transport. The highest leaching rates of REEs reached 60.5% for light REEs (LREEs) (at 4 m), and 82.9% for heavy REEs (HREEs) (at 11 m), with HREEs showing stronger and more uniform loss due to efficient sulfate complexation. Fractionation indices increased ((La/Yb)n, (La/Sm)n, (Gd/Yb)n), along with more positive Ce/Ce* and less negative Eu/Eu* (where “*” denotes the chondrite-normalized anomaly), indicating preferential LREEs retention and redox-driven Ce/Eu anomalies. Strikingly, the exchangeable REEs fraction (F1) rose from 25.2% to 41.3%. At the same time, carbonate-bound, Fesingle bondMn oxide-bound, and residual fractions declined, implying net transformation of REEs into more labile forms. Correlation analyses confirm that sulfate complexation and cation exchange override natural pH control as dominant mobilization mechanisms. Thus, nine-month MgSO4 ISL not only extracts target REEs but also profoundly enriches the exchangeable REE pool, posing a potential environmental risk after mine closure.