冻融及耦合酸化作用下土壤中重金属的浸出性及其机制解析

Leachability of potentially toxic elements from soils:New insights into coupled effects of acidification and freeze-thaw

冻融与不同pH溶液的耦合作用下土壤中重金属浸出行为尚缺乏研究。本研究采用TCLP测试评估了冻融及耦合酸化处理前后土壤中重金属的浸出毒性,并采用孔隙(颗粒)与裂隙图像识别与分析系统(PCAS)和地球化学模拟软件(PHREEQC)分别探究土壤矿物颗粒的微观结构和矿物学演化特征。结果表明,经过30次冻融循环后,As、Cd、Cu、Mn、Pb和Zn的最大浸出浓度分别为0.22 mg/L、0.61 mg/L、2.46 mg/L、3.08 mg/L、29.36 mg/L和8.07 mg/L。在冻融和酸化的耦合作用下,土壤颗粒的孔隙度增加了4.79%。孔隙和裂缝的演化所引起的颗粒结构破坏证实了这一结果。在冻融作用下,土壤颗粒的各向异性增加,而在冻融与酸化的耦合作用下,土壤颗粒的各向异性降低。SEM-EDS、PCAS量化和PHREEQC模拟的结果表明,重金属的释放机制不仅与矿物颗粒的微观结构演化特征有关,还受质子腐蚀以及矿物的溶解和沉淀的影响。这些结果将为季节性冻土地区污染场地土壤修复评价提供重要参考。

Little was known about the leaching behavior of potentially toxic elements(PTEs)from soils under the interaction between freeze-thaw(F-T)cycle and the solutions of varying pH values.In this study,PTEs leachability from soils before and after F-T tests was evaluated using toxicity characteristics leaching procedure(TCLP)test.The microstructure and mineralogical evolution of soil mineral particles were conducted using pores(particles)and cracks analysis system(PCAS)and PHREEQC.The results indicated that during 30 F-T cycles,the maximum leaching concentrations of PTEs were 0.22 mg/L for As,0.61 mg/L for Cd,2.46 mg/L for Cu,3.08 mg/L for Mn,29.36 mg/L for Pb and 8.07 mg/L for Zn,respectively.Under the coupled effects of F-T cycle and acidification,the porosity of soil particles increased by 4.79%,as confirmed by the microstructure damage caused by the evolution of pores and cracks.The anisotropy of soil particles increased under F-T effects,whereas that decreased under the coupled effects of F-T cycle and acidification.The results from SEM-EDS,PCAS quantification and PHREEQC modeling indicated that the release mechanism of PTEs was not only associated with the microstructure change in mineral particles,but also affected by protonation,as well as the dissolution and precipitation of minerals.Overall,these results would provide an important reference for soil remediation assessments in seasonal frozen areas.