Abstract:

In situ immobilization, as a simple and efficient chemical remediation method for soil heavy metals, is widely recognized as an important strategy for ensuring safe production of cadmium (Cd)-contaminated farmlands. To identify efficient and economical immobilizers for Cd-contaminated soils, mine tailings and limestone were mixed at different ratios and calcined under various high-temperature conditions. These processes yielded two types of immobilizers: Calcium Silicate Powder (CSP) and Calcium Silicate Sphere (CSS). The optimal preparation conditions were determined, and the characteristics of the silicon released were investigated using citric acid leaching. Through anaerobic-aerobic soil incubation experiments, the impacts of the immobilizer types and their application rates on Cd availability in soil were evaluated. The results showed that CSP contained 20.3% available silicon, with a silica activation percentage of 60.8%, which was significantly higher than that of the individual tailings or limestone powders. Compared to CSP, CSS had a lower initial dissolution percentage of 2.6%, indicating stronger slow-release properties. Both immobilizers significantly increased soil pH and reduced ferrous ion concentrations in pore water, thereby effectively lowering Cd availability in the soil. At an application rate of 0.8% of the soil mass, CSP and CSS reduced the water-soluble Cd content in the soil by 90.2% and 61.4%, respectively, and Cd extracted by calcium chloride decreased by 42.4% and 24.3%, respectively, compared to the control without an immobilizer. Moreover, exchangeable Cd in the soil was significantly reduced by 15.6% with 0.8% CSP application and was converted to the residual fraction. In summary, both calcium silicate-based immobilizers significantly increased the soil pH and available silicon content. While CSS demonstrates a stronger slow-release capacity, CSP exhibits exceptional efficacy in reducing the availability of Cd in soil owing to its extensive specific surface area and robust adsorption capability. These findings highlight the potential of CSP and CSS to remediate Cd-contaminated soil.

Key words: calcium silicate-based material, cadmium, slow-release property, soil passivation, paddy soil, remediation

摘要：

原位钝化技术作为一种简洁高效的土壤重金属化学修复手段，被广泛认为是实现镉污染农田安全生产的重要技术途径。为寻求高效经济的镉污染土壤钝化材料，以不同比例尾矿与石灰石进行混合，通过高温煅烧制备出粉末状（Calcium Silicate Powder，CSP）和球形（Calcium Silicate Sphere，CSS）硅钙基钝化材料。采用柠檬酸浸提缓释法研究两种硅钙基材料有效硅的释放特性，并通过土壤厌氧-好氧培养试验，评估不同形状硅钙基材料及其投加量对土壤中镉有效性的影响。结果表明，制备的CSP有效硅含量达20.3%，二氧化硅的活化率显著提高至60.8%，显著高于单一尾矿粉或石灰石粉。两种材料相比，CSS的初期溶出率为2.6%，表现出良好的缓释特性。两种硅钙基材料的施用显著提高了土壤pH值，降低了孔隙水中亚铁离子浓度，进而有效减少了土壤中镉的有效性。当两种材料的投加量为0.8%时，与对照组（不添加钝化材料）相比，CSP和CSS使土壤水溶态镉含量分别降低90.2%和61.4%，CaCl₂提取态镉分别降低42.4%和24.3%，且土壤中可交换态镉显著转化为残渣态镉，其中添加0.8%CSP的效果最佳，可交换态镉降低了15.6%。综上，两种硅钙基材料均能显著提高土壤pH及有效硅含量，CSS相比CSP具有更显著的缓释特性，而CSP因比表面积大、吸附能力强，在降低土壤镉有效性方面效果更为优异，在镉污染土壤修复中具有重要应用潜力。

关键词: 硅钙基材料, 镉, 缓释特性, 土壤钝化, 水稻土, 修复