各種化學氧化法處理柴油污染蛇紋岩土壤鉻及鎳之溶出

Abstract

現地化學氧化法是用來處理油品污染的方法之一，但有許多研究指出可能造成土壤中之金屬溶出。本實驗使用台灣東部萬榮鄉（WR）與台東市（ST）富含鉻、鎳之蛇紋岩土壤，製備成柴油污染土壤，並利用過錳酸鉀、過錳酸鉀加酸及過硫酸鈉等氧化劑處理，探討是否會造成鉻及鎳之溶出污染。將土壤以氧化劑處理後，測定溶液相之鉻及鎳溶出量，並將土壤以1 N KCl抽出兩次後，分別測定土壤中殘餘之柴油量、0.01 M KH2PO4可抽出之有效性Cr(VI)含量以及利用鹼性消化法測定土壤中之總Cr(VI)含量。結果顯示柴油之移除效果為過錳酸鉀加酸（超過70 %）>過錳酸鉀（約50 %）>過硫酸鈉（小於30 %）。以過錳酸鉀處理下，兩種土壤於反應14天期間土壤溶液中皆未測得鎳，過錳酸鉀加酸處理則在溶液中測得高濃度鎳，於ST與WR土壤溶液中分別為13.8及0.34 mg L-1，而過硫酸鈉處理有最高量之鎳溶出，ST與WR土壤溶液中分別為34.0及2.05 mg L-1。在鉻溶出量部分，除WR土壤之過錳酸鉀處理無測得外，其餘處理下兩種土壤之鉻溶出量皆超過地下水管制標準，超過量由20倍至210倍不等。在氧化期間土壤中測得之總六價鉻含量依序為過錳酸鉀加酸（ST與WR分別為184與22.4 mg kg-1）> 過錳酸鉀（ST與WR分別為26.1與3.50 mg kg-1） > 過硫酸鈉 （ST與WR分別為5.38與6.72 mg kg-1）。而土壤中之有效性Cr(VI)除過錳酸鉀加酸處理外其餘皆很低。 結果顯示以過錳酸鉀、過錳酸鉀加酸及過硫酸鈉處理本研究中之兩種柴油污染蛇紋岩土壤，除ST及WR土壤以過錳酸鉀處理外，皆會造成鉻及鎳之溶出，並產生高毒性及高移動性之Cr(VI)，因此採用這些化學氧化法須審慎考量當地土壤之性質，以免造成鉻及鎳之溶出污染。

In situ chemical oxidation is commonly used as a remediation method of contamination of petroleum hydrocarbons, but there have been reported in many literatures that chemical oxidation methods may cause dissolution of metals in soil. In this research, two serpentine soils in the east of Taiwan, ST and WR, which were rich in chromium (Cr) and nickel (Ni) were artificial diesel contaminated (10000 mg kg-1). Then the soils were remediated with potassium permanganate (KMnO4), acidified potassium permanganate (KMnO4+H+), and sodium persulfate (Na2S2O8) to investigated whether the dissolution of Cr and Ni occurred. After treating with oxidants, the concentrations of Cr and Ni in soil solutions were determined, and the remained soils were extracted with 1 N KCl twice. Next, the remained diesel concentration in soils were extracted by ultrasonic extraction and determined by GC/FID. Subsequently, available Cr(VI) and total Cr(VI) of the remained soils were analyzed by 0.01 M KH2PO4 extraction and alkaline digestion respectively. The results showed the efficiency of removal of diesel were in the order of KMnO4+H+ (> 70 %) > KMnO4 (~ 50 %) > Na2S2O8 (< 30 %). Except that Ni was not detected in the soil solution treated with KMnO4 during 14-day reaction, nickel concentration was respectively found to be 13.8 and 0.34 mg L-1 in ST and WR soil solution with KMnO4+H+ treatment. Na2S2O8 treatment resulted the highest Ni dissolution and the values were 34.0 and 2.05 mg L-1 in ST and WR soil solution respectively. As for the Cr dissolution, the Cr concentration in soil solutions of ST treated with the three oxidants and WR treated with KMnO4+H+ and Na2S2O8 were 20~210 times exceeding the groundwater pollution control standards (0.05 mg L-1). Total Cr(VI) concentration of the remained soils after oxidants treatment were in the order: KMnO4+H+ (184 and 22.4 mg kg-1 in ST and WR soil respectively ) > KMnO4 (26.1 and 3.50 mg kg-1 in ST and WR soil respectively) > Na2S2O8 (5.38 and 6.72 mg kg-1 in ST and WR soil respectively ). Available Cr(VI) in soils were low except the soils treated with KMnO4+H+ (54.4 and 10.0 mg kg-1 in ST and WR soil respectively). The results indicated that application of KMnO4, KMnO4+H+, and Na2S2O8 in remediation of diesel-contaminated serpentine soils in this research would cause Cr and Ni dissolution and produce Cr(VI) possessing higher toxicity and movement in soil. Therefore, to avoid dissolution of Cr and Ni, the soil properties should be carefully concerned when using these chemical oxidation methods to remediate the diesel contaminated soil.