钝化剂对土壤性质及镉生物有效性的影响研究

为研究土壤重金属钝化稳定化技术中钝化剂施加对土壤物理化学性质及镉生物有效性的影响,通过培养试验结合定期密集采样监测方法,研究羟基磷灰石(HAP)、小麦生物炭(WB)、巯基改性坡缕石(MPG)施加对镉污染碱性土壤pH值、EC值、团聚体组成和DTPA-Cd变化规律的影响,并分析不同因子间的相关关系。结果表明:HAP显著提高土壤pH值0.16～0.30个单位(P0.01),降低土壤EC值;WB则降低土壤pH值0.09～0.32个单位,显著提高土壤有机质、增加土壤EC值(P0.05);MPG处理对土壤pH值和EC值无显著影响。与对照组(不施加钝化剂)相比,3种钝化剂施加后短时间内(5 d)土壤中2mm和2～20mm团聚体比例增加,随着钝化稳定时间的延长,土壤中20mm团聚体占比逐渐增大;对比3种钝化剂对Cd2+的钝化效果,MPG钝化效果最佳,40d后DTPA-Cd含量较对照组降低3.01 mg·kg-1。相关性分析表明,HAP和WB通过改变土壤pH值影响土壤DTPA-Cd含量,XRD表明HAP通过磷酸镉沉淀降低土壤DTPA-Cd含量,HAP和MPG处理组土壤Cd2+的稳定化导致各粒径团聚体比例的变化。研究表明,MPG可显著降低镉的生物有效性且对土壤理化性质无显著影响,可作为碱性土壤原位钝化技术中钝化剂的优先选择。

Influence of passivation on soil properties and bioavailability of cadmium in soils

Three soil passivators hydroxyapatite(HAP), wheat biochar(WB), and mercapto-modified palygorskite(MPG) were selected for this study. Their effects on soil pH, EC, microaggregates, and Cd availability in the soil were investigated using the dynamic monitoring method. Meanwhile, the passivation mechanisms were explored using X-ray diffraction analysis(XRD) during the processes of in situ immobilization remediation of Cd-contaminated soil. Our results showed that, compared with the control group, the proportion of <2 mm and 2~20 mm aggregates increased on the 5th day of passivation, whereas the proportion of >20 mm aggregates gradually increased with the prolongation of passivation time. In addition to the MPG treatment, the application of passivators all had significant effects on soil pH and EC. When comparing the passivation effects of the three passivators, MPG exhibited the best repair effect. At 40th day, the DTPA-Cd content of the MPG treatment group was 3.01 mg·kg^-1 lower compared to that of the control group. Correlation analysis showed that HAP and WB groups affected DTPA-Cd content by changing soil pH, and that the stabilization of soil Cd ions in the HAP and MPG treatment groups caused a change in the proportion of each particle size aggregate. The Cd immobilization by HAP resulted from precipitation, with the presence of Cd₃(PO₄) ₂ confirmed using XRD. Considering the effects of available soil Cd concentrations and physicochemical properties, MPG can be used as a preferred passivator for the in situ passivation of alkaline soil.