汞與戴奧辛污染土壤熱脫附處理研究

Effects of Thermal Desorption on Removal Effectiveness of Mercury and Dioxin Contaminants

李欣怡(Shing-Yi Li)

指導教授 ： 席行正

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00333

摘要

本研究主要藉由中石化(CPDC)之熱脫附實驗室，以模廠級旋轉窯進行土壤熱脫附實驗。首先以實驗室管柱試驗初步定義土壤受熱影響程度與可能操作之脫附條件(i.e., 較適脫附操作溫度)，之後將該條件配合不同之脫附溫度與延時獲取放大數據後，應用於旋轉窯反應器，以獲得於不同脫附條件下土壤質地變化與土壤中汞與戴奧辛殘量變化情形。實驗測試包含四個土樣(以A、B、D、E代碼表示)於350、450、500、550、700及800℃脫附處理之物化特性、汞與 PCDD/Fs 殘量變化情形、汞型態分佈及戴奧辛物種分佈。結果顯示加熱後土壤pH皆由原本的中性或弱鹼轉變為強鹼性，土壤中有機質含量隨加熱溫度升高而減少。所有土樣中之汞(6.7–480 mg kg-1)經500℃持溫0.5小時模廠熱脫附條件下，濃度均可降低至管制標準以下(20 mg kg-1)，PCDD/Fs 毒性當量亦可低於管制標準(1000 ng I-TEQ kg-1)。PCDD/Fs經低溫熱脫附試驗下(350℃、450℃)，高氯PCDD/Fs脫氯分解形成低氯PCDD/Fs。原始土壤中 PCDD/Fs 組成顯示，OCDD及OCDF為主要化合物，熱脫附前與熱脫附後土壤中所含 PCDD/Fs 則多以 PCDD為主。汞之型態分佈顯示，熱脫附前與熱脫附後之型態分佈均以殘餘態為主，顯示該場址之汞不論處理前後其生物可利用性均偏低。建議未來可測試較低脫附溫度以節省能耗。考慮後續土壤再利用，亦可考量於明火條件下適度降低熱脫附處理溫度。本研究促進瞭解污染物經熱處理後之再分配行為，期許所得結果能做為未來實廠建構與熱脫附參數選擇之依據。

關鍵字

汞 ； 戴奧辛 ； 熱脫附 ； 序列萃取

並列摘要

This study examines the effectiveness of thermal desorption of CPDC’s contaminated soils using a bench-scale column reactor and a pilot-scale rotary reactor. The test parameters include desorption temperature, duration, and carrier gas flow rate. bench-scale column reactor is used to preliminarily understand the thermal parameters of soils. Four soil samples (A, B, D, E) contained various amounts of Hg and PCDD/Fs were then tested for their desorption properties at 350, 450, 500, 550, 700 and 800℃. The resulting physical and chemical properties and distribution of mercury fractionations and dioxin profiles were then accessed. The experimental results showed that the soil pH changed from neutral or weak basic into a strongly basic. Soil organic matter content decreased with elevating the desorption temperature. At all of the test temperatures, Hg concentration can be reduced to < 20 mg kg-1, the soil standard by Taiwan EPA, from the concentrations between 6.7–480 mg kg-1. The TEQ of PCDD/Fs at 500℃ for 0.5 hr after treatment reduced to < 1000 ng I-TEQ kg-1. High chlorine PCDD/Fs dechlorination decomposition to low chlorine PCDD / Fs at law temperatures (350, 450). OCDD and OCDF were the major dioxin homologues in the soils, before and after thermal desorption. Mercury fractionation examinations showed that mercury was mainly in residual form before and after thermal desorption. These results suggested that the bioavailability of mercury in the contaminated site was relatively low. Considering reutilization of thermally treated soil, a lower desorption temperature can be tested on the targeting soils to save energy under the direct-heating desorption operations. This study provided a better comprehension in the repartitioning of these contaminants in soil. Results presented here may provide useful suggestions for the scale-up thermal treatment processes in the future.

並列關鍵字

mercury ； PCDD/Fs ； thermal desorption ； sequential extraction procedure

參考文獻

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