海湾河口表层沉积物中重金属形态连续萃取方法的优化研究

Optimization of Sequential Extraction Method for Heavy Metal Fractions in Surface Sediments of Bay and Estuary

采用单一萃取程序对建立的重金属形态连续萃取方法的萃取条件进行优化。分别以Ca和Mg、Fe、有机质(OM)和酸可挥发性硫(AVS)作为萃取剂释放酸溶态、还原态、有机质结合态和硫化物结合态等重金属目标形态的表征参量,考察萃取剂对相应目标形态的萃取能力和选择性。分别根据表征参量和重金属在萃取溶液中的含量变化确定最优萃取时间和萃取样液比。结果表明,优化萃取条件后,萃取剂对目标形态重金属均有很强的释放能力。酸溶态萃取剂对其它非残留态影响很小;还原态萃取剂除对酸溶态有少量提取外,对其它形态影响较小;有机质结合态萃取剂对硫化物结合态有少量萃取,对其它形态影响较小。硫化物结合态在酸溶态、还原态和有机质结合态之后萃取,避免了对这三种形态的影响。优化后的连续萃取方法对重金属形态有较好的选择性,可对海湾和河口表层沉积物中重金属的目标形态进行较为合理地分离和评价。

To separate and evaluate heavy metal fractions properly, the proposed sequential extraction method was optimized by single extraction procedure. Ca and Mg, Fe, organic matter and acid volatile sulfide were selected as the indicator parameters of acid soluble fraction（ F1 ）, reducible fraction（ F2）, organic matter bound fraction （ F3 ） and sulfide bound fraction （ F4 ）, respectively, and the extraction capability and selectivity of extractant for the target fraction were investigated. The optimum extraction time and ratio of sample weight to extractant volume were chosen according to the extraction results of indicator parameters and heavy metals in leachates. The results showed that under the optimized conditions, the selected extractants could primely release the target fraction of heavy metals. The extractant for F1 fraction almost unaffected other non-residual fractions ; and the extractant for F2 fraction would not extract other fractions except for a small quantity of F1 fraction ; and the extractant for F3 fraction was unable to release other fractions except for a small amount of F4 fraction. F4 fraction extraction was extracted after extractions of F1, F2 and F3 fractions, which could be avoided to release these fractions. The proposed sequential extraction method showed better selectivity for heavy metals fractions, and could be applied in the separation and evaluation of target fractions of heavy metals in sediments of bay and estuary.