結合熱脫附及化學萃取法整治同時受多種重金屬污染之土壤

Remediation of multiple-heavy metals contaminated soils by thermal desorption and chemical extraction

黃宥端(Yu-Tuan Huang)

指導教授 ： 許正一

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2009年)

https://doi.org/10.6346/NPUST.2009.00273

摘要

在眾多土壤污染整治策略中，很難有單一種技術能同時有效移除汞及其他重金屬，因此結合多種技術所形成之整治鏈是處理多種重金屬污染土壤的趨勢。本論文使用三個不同來源之汞(180-1320 mg/kg)污染土壤，其中有一土壤亦含有高濃度之鉻、銅、鎳、鉛及鋅，因此將以化學萃取及熱脫附技術，移除汞等多種重金屬。在化學萃取中，利用HCl、CaCl2及EDTA在三種不同濃度(0.05 M、0.1 M及0.2 M)下萃取重金屬，而以去除率最佳的0.2 M EDTA做為化學萃取條件，之後再行熱脫附處理。熱脫附處理前，以熱重分析方法，做為設定土壤熱脫附參數之依據。另一整治順序則在熱脫附，再以0.2 M EDTA進行化學萃取。另外，各種處理前、後的土壤，分析其物理、化學及礦物特性變化，希望能針對供試土壤建議一整治鏈模式。
實驗結果顯示，化學萃取對鎘、銅、鉛及鋅之去除率為81.9、62.9、75.2及100 %，但對汞之去除率低於38.0 %，因此有必要再進行熱脫附以提高汞的去除率。各土壤最佳熱脫附條件下，土壤殘餘汞濃度皆低於台灣土壤污染管制標準(20 mg/kg)，熱脫附後土壤有機碳含量減少0.06-0.11 %，粒徑分佈與游離鐵、錳含量則無明顯變化。當熱脫附溫度達550 ℃時，高嶺石即產生脫水現象而損失，土壤顆粒表面變粗糙並有許多片狀堆疊之膠結物質，土壤膠結可能是造成熱脫附後化學萃取萃取率降低的主因。序列萃取結果顯示，熱脫附後土壤中銅、鎳及鉛從鐵/錳氧化物轉移至與碳酸鹽或有機質結合。修正後汞之序列萃取方法回收率為86.6 %-109 %，土樣A中汞主要型態為殘餘態(96.1 %)，而土壤B及C中主要型態為可交換態(82.3 %及82.5 %)。
先進行熱脫附再進行化學萃取使鎘、鉻、銅、鉛及鋅的去除率降低，但化學萃取先後順序對熱脫附移除土壤中汞無明顯影響，因此建議此類同時受含汞等多種重金屬污染之土壤應先以化學萃取整治後再進行熱脫附。

關鍵字

土壤 ； 重金屬 ； 熱脫附 ； 化學萃取 ； 熱重分析 ； 序列萃取

並列摘要

Many strategies of remediation have been applied for contaminated soil, but it is hard to get a technology which could fully remove mercury and other heavy metals simultaneously. To treat multiple heavy metals contaminated soils, treatment chain becomes a tendency to combine diverse treatment technologies.
Three test soils are mercury (180-1320 mg/kg) contaminated soils from various sites, and one of them is also contaminated by concentrated Cr, Cu, Ni, Pb, and Zn. The objective of thesis is using chemical extraction associated with thermal desorption technologies to remove mercury and other heavy metals in contaminated soils. Using HCl, CaCl2 and EDTA with three concentration (0.05 M, 0.1 M, and 0.2 M) and assessing removal of heavy metals, then set the suitable extract reagent and concentration of chemical extraction according to the removal.
Before thermal desorption, thermal desorption was performed to optimize the operation parameters including the rate of increaseing temperature, and retention time by the results of thermogravimetric analysis. One treatment chain of the experiment is chemical extraction with 0.2 M EDTA comes after thermal desorption, another one is using chemical extraction firstly and combine with thermal desorption. The soil before and after thermal desorption was analyzed for physical and chemical properties and mineral composition for the suggestion in screening a suitable treatment chain.
The experimental results indicated that removal rate of Cd, Cu, Pb and Zn by chemical extraction was 81.9, 62.9, 75.2, and 100 %, respectively, but less than 38.0 % for mercury. Therefore, further thermal desorption was necessary for mercury removal. Thermal desorption with the optimal parameters effectively reduced the Hg concentration in the soils and met the soil control standard (20 mg/kg). After thermal desorption, organic carbon reduced by 0.06-0.11%, but no obvious change occurred in particle size distribution and Fed and Mnd levels. While heating temperature up to 550 ℃, kaolinite became dehydrated and was further destructed. The soil particle surface became rough and cohered with small sheets. Coaguation of soil particles might cause the reduction of chemical extraction after thermal desorption. With respect to the results of sequential extraction procedure, Cu, Ni, and Pb was desorbed from Fe/Mn oxides and was consequently bonded to organic matters. The recovery of adjusted sequential extraction procedure for mercury ranged between 86.6 % and 109 %. Majority of mercury in soil A was associated with residual fraction (96.1 %), and were associated with exchangeable fraction in soil B and C (82.3 % and 82.5 %).
Treatment chain with thermal desorption firstly decreased removal of Cd, Cr, Cu, Pb, and Zn by 0.2 M EDTA, but treatment chain with chemical extraction first or later did not obviously affected the removal of mercury. We suggest that treatment chain with chemical extraction first and thermal desorption later is suitable for remediation of multiple heavy metals contaminated soils.

並列關鍵字

soil ； heavy metal ； thermal desorption ； chemical extraction ； thermogravimetric analysis ； sequential extraction procedure

參考文獻

李春樹，2003，銅鋅鉛在污染土壤中之化學型態及其萃取性研究，博士論文，國立成功大學，環境工程學研究所，台南。

鄭光喆，2007，重金屬污染土壤之不同單一與連續性抽出方法評估，碩士論文，國立中興大學，土壤環境科學系，台中。

Abumaizar, R. J., and Smith, E. H., 1999, "Heavy metal contaminants removal by soil washing," J. Hazar. Mater., B70: 71-86.

Arunachalam, J., Emons, H., Krasnodebska, B., and Mohl, C., 1995, "Sequential extraction studies on homogenized forest soil samples," Sci.Total Environ., 181: 147-159.

Biester, H., and Scholz, C., 1997, "Determination of mercury binding forms in contaminated soils: Mercury pyrolysis versus sequential extractions," Environ. Sci. Technol., 31: 233-239.