Linking chromium (Cr) speciation with its stability in soils is vital because insoluble Cr(VI) and chemical adsorbed Cr(VI) could hinder the remediation efficiency and release Cr(VI) for a prolonged period of time. In this study, we investigated key Cr species to probe the mechanisms controlling the release of insoluble Cr(VI) at Cr-contaminated sites using synchrotron-based X-ray absorption near-edge structure (XANES) for the first time. Chromite, stichtite and Cr-silicate were predominant forms of Cr(III). Insoluble Cr(VI) was hosted by layered double hydroxides (LDHs) such as brownmilerite and hydrotalcite. Anion competition tests documented a substitution of absorbed Cr(VI) by SO₄^2- and NO₃^-. Acid extraction released 6.7-25.7% more Cr(VI) than anion extraction, possibly attributing to the erosion of LDH and CaCrO₄ in calcite rather than Cr-bearing minerals. Brown and red soils released maximally 62% and 44% of total Cr(VI) by 10 mol/(kg soil) and 2 mol/(kg soil) of H⁺, respectively. SO₄^2-, H₂O and H⁺ contributed to more release of total Cr(VI) in brown soils (22%, 33% and 7%) than red soils (25%, 17% and 2%). More crystalline Cr structures were found after chemical stabilization, indicating a higher Cr stability in chemically stabilized soils. Cr and Mn exhibited an overlapped distribution pattern in both contaminated and chemically stabilized soils, hinting at the re-oxidation of Cr(III). Insoluble Cr(VI) could be released by acidic rainfalls and soil organic matters, posing potential threats to Cr long-term stability in field-scale remediation.

将铬 (Cr) 形态与其在土壤中的稳定性联系起来至关重要，因为不溶性 Cr(VI) 和化学吸附的 Cr(VI) 可能会阻碍修复效率并长时间释放 Cr(VI)。在这项研究中，我们首次使用基于同步加速器的 X 射线吸收近边结构 (XANES) 研究了关键的 Cr 物种，以探索控制 Cr 污染部位不溶性 Cr(VI) 释放的机制。铬铁矿、辉石和硅酸铬是 Cr(III) 的主要形式。不溶性 Cr(VI) 以层状双氢氧化物 (LDHs) 为主体，如褐煤和水滑石。阴离子竞争试验记录了吸收的 Cr(VI) 被 SO ₄ ^2-和 NO ₃ ^-替代. 酸萃取比阴离子萃取多释放 6.7-25.7% 的 Cr(VI)，这可能是由于 LDH 和 CaCrO ₄在方解石而非含铬矿物中的侵蚀。 通过 10 mol/(kg 土壤) 和 2  mol/(kg 土壤) 的 H ⁺ ，棕色和红色土壤分别最大释放总 Cr(VI) 的 62% 和 44% 。SO ₄ ^2- , H ₂ O 和 H ⁺与红壤（25%、17% 和 2%）相比，棕壤（22%、33% 和 7%）中总 Cr(VI) 的释放量更大。化学稳定后发现了更多的结晶铬结构，表明化学稳定土壤中铬的稳定性更高。Cr 和 Mn 在污染土壤和化学稳定土壤中表现出重叠分布模式，暗示 Cr(III) 的再氧化。酸性降雨和土壤有机质可释放不溶性 Cr(VI)，对田间修复中 Cr 的长期稳定性构成潜在威胁。