壓力輔助有機酸萃取污染土壤重金屬

Pressure-assisted organic acid extraction of heavy metal from contaminated soil

林稚展(Jhih-Jhan Lin)

指導教授 ： 陳庭堅

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2011年)

https://doi.org/10.6346/NPUST.2011.00145

摘要

台灣人口稠密、土地資源利用有限，加上工業廢水與廢棄物不當排放，使得台灣土地受重金屬污染事件頻傳。壓力循環促進萃取(Pressure cycles-assisted extraction, PCAE)技術可提升試劑對重金屬之萃取效果，因此本研究利用有機酸試劑輔以PCAE萃取技術去除土壤中之重金屬，探討在不同參數下對現地污染土及人工配製污染土之萃取效果，而實驗過程中將以傳統振盪方法及EDTA試劑作為比較。
實驗結果顯示，使用PCAE萃取重金屬效率普遍大於傳統振盪方法。使用乙酸無法使現地污染土中鎘濃度降至管制值以下，故以甲酸及檸檬酸作為主要有機酸試劑種類。隨著加壓-減壓循環次數增加，現地污染土重金屬萃取鎘效率有上升趨勢(p < 0.05)，而循環次數達40次時，其萃取效率普遍優於傳統振盪方法。重金屬萃取效率亦會隨著萃取壓力提升而增加，然而卻無統計顯著差異。在150 psi時、循環次數40次條件下，0.1 M檸檬酸可將現地污染土之鎘濃度降至法規管制值以下。PCAE循環一次所需的時間增加其萃取效率也會隨著增加，但是變化量不大。使用濃度0.1 M甲酸或檸檬酸可以使鎘、銅、鎳、鋅降至食用作物管制值以下，但萃取效率皆大於相同濃度下傳統振盪方法。固液比1:20(25 g/500 ml)可使供試土壤與萃取試劑充分混合進而提升萃取效率，為較佳萃取參數。而有機酸在土壤中可被雨水淋洗出來，並易於生物分解，因此也可以改善對土壤造成的酸化現象。
雖然在實驗中EDTA重金屬萃取效率普遍優於有機酸試劑，但是以PACE輔助有機酸萃取土壤重金屬，可以將大多數重金屬濃度降至法規管制值以下，因此以有機酸試劑取代螯合劑甚至無機酸試劑是可行的。

關鍵字

土壤 ； 重金屬 ； 有機酸 ； 整治復育 ； 壓力循環促進萃取

並列摘要

Taiwan is densely populated with limited resources. Improper discharges of industrial wastes and wastewaters have resulted in contamination of soil with heavy metals. In this study, the method of pressure cycles-assisted extraction (PCAE) has been used with chelating agents including citric acid to remove heavy metals from soil under different conditions; the results have been compared favorably with conventional extraction techniques.
The results showed that the heavy metal extraction efficiencies with PCAE was generally better than with conventional extraction techniques. The increasing extraction efficiency with increasing pressure and that cadmium removal meeting regulatory standard was achieved with 0.1 M citric acid using 40 cycles at compressing pressure of 150 psi. The use of acetic acid did not meet the regulatory standard; therefore, formic acid and citric acid were experimented. Increasing the time for completing a pressure cycle resulted in removal improvement, and the cycling time of one min per cycle was selected based on effectiveness and cost consideration. When 0.1 M formic acid or citric acid was used, the removal of cadmium, copper, nickel, and zinc from soil was more effective than conventional technique and it met soil standard for food crops. The solid to liquid ratio of 1:20 (i.e. 25 g/500 ml) was effective for extraction. The acidification of soil by organic acids is limited as they can be removed by leaching and biodegraded.
Though EDTA is most effective among the tested chelating agents, it can be effectively substituted by other organic acids such as citric acid while meeting regulatory standards for most metals when pressure assisted extraction is employed. The use of mild organic acids and even inorganic acids appears feasible with PCAE.

並列關鍵字

soil ； heavy-metal ； organic acid ； soil remediation ； Pressure cycles

參考文獻

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