缺氧沉积物中重金属形态连续萃取方法的稳定性研究

Study on Stability of Sequential Extraction Method for Heavy Metal Speciations in Anoxic Sediments

考察了海水养殖区域缺氧沉积物中重金属形态连续萃取法萃取过程中溶液pH值、温度变化和胶体形成对形态分离结果的影响。结果表明,连续萃取法Step1萃取酸溶态时,萃取液pH值的轻微升高使Pb和Zn的萃取结果明显降低;Step2萃取还原态时,萃取液pH值明显升高对重金属的萃取结果影响很小;Step3萃取有机质结合态时,萃取液pH值的降低对重金属萃取结果影响较小(除Pb外)。由于连续萃取法中各步萃取反应的热力学过程不同,Step1和Step2萃取后溶液温度轻微升高而在Step3中溶液温度稍微降低,溶液温度变化(<2.5℃)对重金属形态的影响很小。在Step1、Step2和Step4萃取过程中胶体的形成和存在,对萃取液Cd、Zn和Cu有明显的吸附影响;而在Step3萃取中萃取剂的分散作用有效控制了溶液中胶体的形成。因此采用连续萃取方法评价沉积物中的重金属形态时,控制萃取液pH值和胶体形成有利于提高萃取结果的稳定性和准确性。

Effects of the variations of pH value,temperature and colloidal particles in extractant solutions on heavy metals speciations were investigated by the sequential extraction procedure（SEP） used in anoxic sediments at mariculture zone.The results showed that a slight increasement of pH values of extractant solutions lead to the decrease of concentrations of Cd and Zn in Step1 of SEP for acid soluble speciations,However,the obvious variations of pH values of extractant solutions had no significant influence on heavy metals speciations in Step2 for reducible fraction and Step3 for organic matter bound fraction（except Pb）,respectively.The temperature of extractant solutions were slightly increased in Step1 and Step2 and decreased in Step3 due to the different reaction thermodynamics in extraction steps of SEP,and the variations of temperature（2.5 ℃） had little effects on the concentrations of heavy metals speciations.Due to adsorption,the formation of colloid in Step1,Step2 and Step4 resulted in the decrease of Cd,Zn and Cu concentrations,respectively.However,the formation of colloid was controlled by extractant in Step3.Therefore,controlling pH and colloid in extractant solutions were available to improve the stability and accuracy of extraction results when SEP was applied to evaluate heavy metals speciations in anoxic sediments.