序列萃取方法劃分土壤鎵與銦物種的適用性之探討

Abstract

隨著高科技產業的發展，其製程中常使用的新興元素如鎵和銦之環境風險逐漸增加，並可能對生物與人類造成危害。土壤受金屬污染對於生態與人類之影響，主要取決於金屬污染物在各個化學相態中的分布情形，一般透過序列萃取方法來劃分化學相態，藉此評估其有效性與移動性。同一種序列萃取方法並非適用於劃分所有金屬元素的化學相態，因此目前已發展出許多不同方法，其中以Tessier法與BCR法的使用最為廣泛。然而，目前尚未有針對鎵和銦序列萃取方法之適用性的討論，因此，本實驗之研究目的是探討序列萃取Tessier法與BCR法劃分土壤中鎵和銦物種之適用性。本實驗利用已知鎵、銦濃度的伊萊石、方解石、水鈉錳礦、水鐵礦、針鐵礦及腐植酸進行單一試劑萃取，確認試劑溶解能力與專一性，並以此預測序列萃取結果。接著進行序列萃取實驗，計算預測值與實際值之相關性與一致性以評估其適用性。最後使用外添加鎵與銦的三種土壤進行序列萃取實驗，並與XAS物種鑑定結果進行比對，驗證萃取方法之適用性。實驗結果顯示Tessier與BCR序列萃取方法中的單一試劑對方解石、伊萊石、腐植酸劃分結果雖不具有專一性，但仍可對其萃取作用進行評估。Tessier法對針鐵礦的劃分效果較佳，BCR法則無法萃取出其中的目標元素。水鈉錳礦及水鐵礦在兩種方法中皆具有良好的劃分效果。含鎵與含銦材料的序列萃取結果顯示，Tessier法皆較BCR法更適用於所有含鎵礦物與腐植酸；含銦礦物與腐植酸除方解石以外皆適用Tessier法，而BCR法也適用於伊萊石、水鈉錳礦和水鐵礦中。若以土壤中的組成比例考量，Tessier法對含銦礦物與腐植酸仍較BCR法更為適用。外添加鎵和銦土壤的序列萃取結果顯示Tessier法與BCR法皆適用於評估土壤中鎵和銦的有效性及其物種分布。

Gallium(Ga) and indium(In) are widely used in high-tech industries, which resulted in their release into the environment and the increased risks of exposure to public health. The impact of soil metal pollution on ecological and public healths depends on the abundance and distribution of metal pollutants in various chemical phases. Given that, sequential extraction methods have been developed to determine metal fractionation to provide information about the availability and mobility of metal pollutants in soil. However, a sequential extraction method is often not applicable to all metal pollutants. Therefore, different methods have been developed and evaluated, and Tessier and BCR method are the most widely used ones so far. For Ga and In, it is unknown whether the sequential extraction methods are suitable for the fractionation of Ga and In in soil. Therefore, the purpose of this study is to assess the applicability of the Tessier and BCR sequential extraction method to the fractionation of Ga and In in soil. Illite, calcite, birnessite, ferrihydrite, goethite and humic acid with known Ga and In concentrations were prepared and extracted with each reagent to confirm the specificity of the reagent in extracting Ga and In, After single extraction, sequential extraction methods were conducted for those materials to determine the correlation and consistency between the predicted value and the actual value. Finally, three soils spiked with Ga or In were used for sequential extraction experiments to evaluate the analytical performance of the extraction method through the comparison with the corresponding XAS speciation results. The experimental results show that the fractionation results of calcite, illite, and humic acid with a single reagent in the two sequential extraction methods are not as expected; Tessier method has a better extraction effect on goethite, and BCR method cannot extract the target elements in goethite. Birnessite and ferrihydrite have good extraction effects in the two methods. The sequential extraction results of Ga-bearing or In-bearing materials show that Tessier method is more suitable for all Ga-bearing minerals and humic acid than BCR method. Tessier method is suitable for In-bearing minerals and humic acid except for calcite, and BCR method is also suitable for illite, birnessite and ferrihydrite. For the soil, the Tessier method is more suitable for In-bearing minerals and humic acid than BCR method. The sequential extraction results of Ga- or In-spiked soil show that both Tessier method and BCR method are suitable for evaluating the availability of Ga and In in soil.