序列萃取方法中萃取試劑選擇性之探討

Abstract

序列萃取方法依其操作型定義將存在於土壤或底泥中的重金屬區分為不同型態，並針對各型態之重金屬進行定量。然而，常見之序列萃取方法可能因所使用的萃取劑選擇性不佳，導致重金屬之分布型態被錯估。本研究之目的為探討Tessier萃取方法與BCR萃取方法對於鉛、銅、鋅、鎳化合物之選擇性，以及前述化合物與人造底泥混合後所得樣品之選擇性。 本研究依照Tessier萃取方法及BCR萃取方法，針對已知純金屬化合物進行批次萃取實驗，結果顯示Tessier萃取方法對可交換態和與鐵錳氧化物結合態或能提供較可信之萃取結果，然而對與碳酸鹽結合態和與硫化物結合態之萃取結果則可能有較大偏差，其原因在於當重金屬含量較高時(50% w/w)，所使用之萃取劑選擇性可能較差。而針對BCR萃取方法之實驗，顯示此方法對可氧化態或能提供較可信之結果，但對酸可溶態及可還原態之結果則可能有較大偏差。對於加入人造底泥之實驗，結果和純金屬化合物實驗有些許不同．Tessier萃取方法對可交換態和與硫化物結合態能提供較佳結果，而BCR方法則對可氧化態能提供較佳之結果。

Sequential extraction method could be used to group heavy metals in soil or sediment into different fractions to evaluate their bioavailability. However, conventional sequential extraction methods could give false assessment of heavy metal fractionation if the selectivity of extracting reagent is poor. The objectives of this research are to investigate: 1. the selectivity of Tessier extraction method and BCR extraction method for pure lead, copper, zinc and nickel compounds, and 2. the selectivity of Tessier extraction method and BCR extraction method for mixture of heavy metal compounds in the presence of synthetic sediments. Results from batch extraction experiments using pure metal compounds indicated Tessier method may provide better fractionation for exchangeable and Fe/Mn oxide fraction. However, results of carbonates and sulfide fraction may show deviations if heavy metal contents are high (more than 50% w/w), which could result from the poor selectivity of reagents. BCR method may provide better fractionation for oxidizable fraction, but not for acid soluble and reducible fraction. For second part of experiments, Tessier method may provide better fractionations for exchangeable and sulfide fraction. BCR method may provide better fractionations only for the oxidizable fraction.