化學萃取整治時效快速、可針對重金屬在土壤中以不同形態存在而使用不同的萃取試劑,移除土壤中的目標污染物。本論文以兩種螯合劑(EDTA、檸檬酸)及三種還原劑(連二亞硫酸鈉、鹽酸羥胺和焦亞硫酸鈉)作為四種受重金屬汙染土壤(A、B、C、D)之萃取試劑,探討萃取試驗最佳化條件、試劑組合及以BCR序列萃取法了解重金屬在土壤中之型態,另外,以1.0 N HCl進行傳統酸洗法萃取四種土壤中重金屬,並與上述螯合劑及還原劑比較優劣。實驗結果顯示,HCl、檸檬酸及EDTA對鎘、鉻、銅、鎳、鉛、鋅之移除效率較佳;焦亞硫酸鈉及鹽酸羥胺可移除部分土樣中的鎘、銅、鎳、鉛、鋅;連二亞硫酸鈉移除重金屬效果最差,僅可移除部分土樣之鎘與鋅。序列萃取顯示,原供試汙染土壤中鎘之型態分布主要以一弱鍵結、高度移動性之酸可溶及可交換態為主(約佔45 %);鉻、鎳、鉛主要以殘餘態為主;銅和鋅則以可還原態及殘餘態為主,預期以還原劑能破壞可還原態之重金屬來提升移除效率。 以還原劑及螯合劑萃取供試汙染土壤後之序列萃取顯示,大部分移除的重金屬型態主要為殘餘態,而焦亞硫酸鈉、連二亞硫酸鈉及鹽酸羥胺僅還原部分土樣中的氧化物而釋出重金屬,又以焦亞硫酸鈉還原氧化物後溶解之重金屬比例最多(約10 %)。混合試劑皆可大幅移除土樣中的6種重金屬,還原劑與檸檬酸及EDTA分別混和後發現,以EDTA混合還原劑的效果最佳,進一步比較EDTA與三種還原劑混合以移除重金屬之效果則以25℃、pH 6之0.1 M EDTA及1.0 M焦亞硫酸鈉之效果最好,可用來代替傳統HCl萃取以減少廢酸液的處理成本及廢液量。 關鍵詞 : 土壤重金屬、化學萃取、序列萃取、螯合劑、還原劑
Chemical extraction is a time effective technique for remediation of heavy metal contaminated soil. However, heavy metals exist as different forms in the soils, which are needed to design an assembly of extraction reagents remove them from the soils. In this study, two kinds of chelators (EDTA and citric acid) and three kinds of reducing agent (sodium dithionite, hydroxylamine hydrochloride, and sodium metabisulfite) were applied as the extracting mixture to remove six heavy metals from 4 contaminated soils. Investigation on the optimal extraction conditions of the test at combination reagent and BCR sequential extraction to understand the fraction of heavy metals in the soil. In addition, the traditional 1.0 N HCl acid washing extracted four heavy metals in soil and comparison with the pros and cons of these chelating agents and reducing agents. Experimental results show that, HCl, citric acid, and EDTA to remove cadmium, chromium, copper, nickel, lead, zinc are better efficiency; sodium metabisulfite and hydroxylamine hydrochloride may remove cadmium, copper, nickel, lead, zinc in some soil; dithionite to remove heavy metals is worst, only be partially removed cadmium and zinc in soil samples . Sequential extraction showed that the forms cadmium in contaminated soil is mainly distributed in a weak bond, acid soluble and exchangeable fraction is mobility of highly dominated (about 45%); chromium, nickel, lead mainly to the residual fraction; copper and zinc places reducible fraction and residual fraction, is expected to be restored to reducing heavy metals can damage the state to improve the removal efficiency. Sequential extraction with reducing agents and chelating agents after extraction of contaminated soil test shows that most of the major forms of heavy metal removal of residual fraction, and sodium metabisulfite, sodium dithionite and hydroxylamine hydrochloride only partially reduction oxides and soil samples release of heavy metals, most (about 10%) the proportion of heavy metals and metabisulfite dissolved after the reduction of oxides. Mixed reagent can be significantly removed six soil samples of heavy metals, reducing agents and citric acid and EDTA were mixed after the discovery, to the best effect of reducing agent EDTA mix, reducing further comparison of three mixed with EDTA to remove heavy metals effect places 25 ℃, pH 6 of 0.1 M EDTA with 1.0 M sodium metabisulfite and the effect is best used to replace the HCl extraction to reduce waste disposal costs and the amount of waste acid. Keywords: soil heavy metal, chemical extraction, sequential extraction procedure.
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