過硫酸鹽是整治油品污染土壤之現地化學氧化法 (In situ chemical oxidation, ISCO) 常用的氧化劑,可透過活化產生氧化還原電位 (Redox potential, Eh) 較高的自由基以降解有機污染物。蛇紋岩土壤具高背景值濃度的鉻、鎳與鈷,其中六價鉻在環境中較三價鉻易移動且是已知的致癌物。許多研究指出使用ISCO後土壤pH或Eh值會改變,可能使土壤重金屬的溶出及價態變化,但使用過硫酸鹽整治蛇紋岩土壤或重金屬污染土壤時,其重金屬釋出動態機制至今尚未明瞭,因此本研究目的為添加不同活化處理的過硫酸鹽與土壤反應,以瞭解重金屬釋出情形。蛇紋岩土壤來自臺灣東部,重金屬污染土壤則採自彰化縣。批次實驗於土壤分別添加只有過硫酸根之未活化、兩種Fe2+濃度活化及鹼活化過硫酸根等四種處理反應並取樣測定。結果顯示過硫酸鹽濃度會隨時間消耗而減少並釋出H+,使溶液pH值下降,影響土壤膠體的表面電荷及吸附性,增加重金屬溶出,而重金屬的溶出量亦取決重金屬鍵結型態。在本研究條件下,過硫酸根殘留量較實際高,所以重金屬釋出量可能較高,污染土壤溶液可有鉻55.9 mg/L、鎳59.5 mg/L、銅112 mg/L及鋅168 mg/L的釋出量,蛇紋岩土壤溶液,以鹼活化的處理可釋出最高濃度為5.9 mg Cr (VI)/L,因為高pH值下鉻主要以六價存在。於此研究條件及結果下,並僅以氧化能力與移動性較高的六價鉻為考量,可知105 mM Fe2+活化過硫酸鹽之處理有較佳氧化能力,雖然會使土壤釋出較高濃度的重金屬,但因為Fe2+濃度較高,會與目標污染物競爭自由基且也會還原六價鉻,導致生成六價鉻的濃度較低,雖然過硫酸根的殘留量較現地應用時高出許多,會較推薦105 mM Fe2+活化過硫酸鹽處理於整治應用上。
Persulfate is a common oxidant used for in situ chemical oxidation (ISCO), and it is usually activated by amendments such as Fe2+, EDTA-Fe2+ or alkaline to generate free radical which had higher redox potential to degrade the target pollutants. Serpentines soils contain high natural background concentrations of Cr, Ni and Co. However, Cr (VI) is carcinogenic and more mobile than Cr (III). Soil pH and Eh change after using ISCO and thus affect the mobility of heavy metals in soils. Three serpentine soils were collected from eastern Taiwan and anthropogenic polluted soils were sampled from Changhua county in western Taiwan. To explore heavy metals released from serpentine soils and polluted soils with different persulfate treatments, soils were spiked persulfate activated by two concentrations of Fe2+ and alkaline. The results showed that the concentration of remained persulfate decreased with time and generated H+ caused pH decreased, and thus increased heavy metals released. In this syudy, the polluted soils released 55.9 mg Cr/L, 59.5 mg Ni/L, 112 mg Cu/L, and 168 mg Zn/L were higher than serpentine soils because of the high level exchangeable fraction . Additionally, released Cr (VI) was higher from serpentine soils than polluted soils, and the alkaline activated treatment had highest content (5.9 mg Cr (VI)/L ) because of high pH value. Under the condition of this study, heavy metals may release more than in real condition because of higher concentration of persulfate remained. However, concerning about redox potential and Cr (VI) release, 105 mM Fe2+ activated treatment is better than other treatments because it had higher redox potential and Fe2+ may compete free radical and reduce Cr (VI).