Remediation of Cadmium in Alkaline Soil Using Thiol-Modified Attapulgite Combined with Manganese Sulfate

Remediation of heavy metal contamination in alkaline soils has long been overlooked, with the core challenge lying in the need to balance treatment efficiency against the risk of exacerbating soil alkalinity. Mineral-based materials are regarded as highly promising remediation agents due to their excellent soil compatibility, low cost, and minimal disturbance to soil physicochemical properties. However, current research predominantly focuses on the adsorption characteristics of heavy metals in aqueous systems or the application of single materials in soil, which often fails to achieve the desired remediation outcomes. Therefore, this study aims to develop a synergistic remediation strategy integrating soil immobilization and crop antagonism tailored for alkaline Cd-contaminated soils. Thiol-modified attapulgite (TA) and manganese sulfate (MnSO 4 ) were selected as the remediation materials. A series of soil incubation experiments and pot trials involving pak choi and wheat were conducted to systematically investigate the effects of individual and combined applications of TA and MnSO 4 on soil Cd leaching, speciation distribution, crop Cd uptake, and soil pH. The results demonstrated that TA significantly reduced Cd leaching in soil pore water through adsorption and facilitated the transformation of bioavailable Cd to stable fractions. In contrast, MnSO 4 exerted dual effects by not only underwent hydrolysis to form manganese oxides capable of adsorbing heavy metals but also compete with Cd during the crop uptake of soil nutrients. Notably, the combined application of TA and MnSO 4 achieved a synergy between soil Cd passivation and the inhibition of crop Cd uptake, ensuring that Cd content in the edible parts (both in pak choi and wheat) complies with national quality standards without causing significant changes in soil pH. These findings provide a valuable reference for the safe utilization of large-scale alkaline Cd-contaminated farmland and hold significant practical and strategic value for promoting green and sustainable agricultural development. Further studies should focus on optimizing the mixing ratio and application timing of TA and MnSO 4 , along with evaluating their long-term field performance, to offer more comprehensive theoretical and data support for the industrial implementation of this technology.