Simultaneously stabilizing of arsenic (As) and cadmium (Cd) in co-contaminated soil presents substantial challenges due to their contrasting chemical properties. Schwertmannite (Sch) is recognized as a potent adsorbent for As pollution, with alkali modification showing promising results in the simultaneous immobilization of both As and Cd. This study systematically investigated the long-term stabilization efficacy of alkali-modified Sch in Cd–As co-contaminated farmland soil over a 200-day flooding-drying period. The results revealed that As showed significant mobility in flooded conditions, whereas Cd exhibited increased soil availability under drying phases. The addition of Sch did not affect the trends in soil pH and Eh fluctuations; nonetheless, it led to an augmentation in the levels of amorphous iron oxides and SO concentration in soil pore water. At a dosage of 0.5% Sch, there was a notable decrease in the mobility and soil availability of As and Cd under both flooding (34.5% and 53.6% at Day 50) and drying conditions (27.0% and 29.4% at Day 130), primarily promoting the transformation of labile metal(loid) fraction into amorphous iron oxide-bound forms. Throughout the flooding-drying treatment period, Sch maintained stable mineral morphology and mineralogical phase, highlighting its long-term stabilization effect. The findings of this study emphasize the promising application of Sch-based soil remediation agents in mitigating the challenges arising from As–Cd co-contamination. Further research is warranted to explore their application in real farmland settings and their impact on the uptake of toxic metal(loid)s by plants.

中文翻译：

---

长期淹干条件下施威特曼石高效共稳定农田土壤砷、镉

由于砷 (As) 和镉 (Cd) 的化学性质截然不同，同时稳定共污染土壤中的砷 (As) 和镉 (Cd) 面临着巨大的挑战。施韦特曼石 (Sch) 被认为是砷污染的有效吸附剂，碱改性在同时固定砷和镉方面显示出有希望的结果。本研究系统地研究了碱改性Sch在200天淹干期Cd-As共同污染农田土壤中的长期稳定效果。结果表明，砷在洪水条件下表现出显着的流动性，而镉在干燥阶段表现出增加的土壤有效性。 Sch的添加不影响土壤pH和Eh的波动趋势；然而，它导致土壤孔隙水中无定形氧化铁和二氧化硫浓度的增加。当 Sch 剂量为 0.5% 时，在洪水（第 50 天为 34.5% 和 53.6%）和干燥条件（第 130 天为 27.0% 和 29.4%）下，As 和 Cd 的移动性和土壤有效性均显着下降。主要促进不稳定金属（类）部分转化为无定形氧化铁结合形式。在整个淹干处理过程中，Sch保持了稳定的矿物形态和矿物相，凸显了其长期稳定效果。本研究的结果强调了基于 Sch 的土壤修复剂在缓解 As-Cd 共同污染带来的挑战方面的应用前景。需要进一步的研究来探索它们在真实农田环境中的应用及其对植物吸收有毒金属（类）的影响。