催化劑對底泥重金屬生物溶出之影響

Abstract

生物溶出法 (Bioleaching) 因對環境較具親和力，且處理成本低且操作容易，因此漸受重視。然而並未被實際應用於商業或實場上之操作，主要是因為微生物之生長速率不如化學反應速率快速，若欲達一定處理效率則需較長之反應時間。若欲提高重金屬之生物溶出速率，則需改善重金屬溶出時之電化學機制，以加速重金屬之溶出。目前已發現可添加陽離子作為生物溶出反應之催化劑，其能於固體晶格結構間與硫化物可中之金屬離子進行置換，且能提高氧化還原電位而加速其間的電流反應，進而促進重金屬之溶出速率。 本研究中，主要於反應起點添加硝酸銀與鐵離子，並且於反應至底泥pH值達3時添加鐵離子，，探討添加金屬離子對生物溶出底泥重金屬之影響，瞭解使用催化劑於生物溶出法去除底泥中重金屬可能造成的影響。結果顯示於反應起點添加銀離子能加速酸化速率、硫酸根產生與重金屬溶出效率的影響，以添加濃度為 15 mg/L之生物溶出程序的結果為最佳，添加濃度超過30 mg/L則發生抑制現象，底泥中銅、鋅與鉻皆有極高之溶出效率，其次為鎳與錳，而鉛之效率最差。以溶出反應動力模式模擬溶出情形，獲得重金屬之溶出速率常數，其中以銅、鋅、鎳與鉻的促進效果最為顯著。結果顯示銀離子的影響主要為提高溶出反應速率常數而加速重金屬的溶出。同時亦發現添加銀離子不影響生物溶出程序中所使用的兩種硫氧化菌之生長。 於生物溶出程序反應起點添加鐵離子的結果，則顯示鐵離子對於酸化速率、硫酸根產生與重金屬溶出效率之影響，發現鐵離子的添加無法促進生物溶出程序中重金屬之溶出，但鐵離子添加濃度為 0.55 g/L時，銅與鋅的溶出效率仍為最佳。因此比較兩種金屬離子對於生物溶出程序之影響，可知發現對底泥的酸化速率、硫酸根的產生與重金屬的溶出效率與速率皆以添加銀離子之結果較佳。於反應至底泥pH值達3時添加氯化鐵，生物溶出程序的結果中則發現鐵離子能加速酸化速率、硫酸根產生與重金屬溶出效率的影響皆以添加濃度為 1 g/L之生物溶出程序的結果為最佳。並且主要的影響是重金屬鍵結相態中的鐵錳氧化相。並顯示於反應至底泥pH值達3時添加添加銀離子，不影響生物溶出程序中所使用的兩種硫氧化菌之生長。

Because of the affinity to the environment, low costs of treatment and ease of operation, bioleaching is increasingly paid attention. The reason why it is not commercially applied is that it needs more reaction time than that of chemical reaction. It is necessary to improve electrochemical mechanism for accelerating the leaching of heavy metal. Presently, it is known that adding cation as catalyst of reaction to bioleaching can exchange the metal ion of sulfide in lattice structure and raise ORP for accelerating the electrochemical reaction, consequently promoting rate of heavy metalin the bioleaching process. In this study, the effects of catalyst on bioleaching of heavy metal from contaminated sediment were investigated. Adding ferric and silver ions at the beginning of the bioleaching process, and adding ferric ion when sediment pH reached 3, could accelerate the rates of acidification, sulfate production and metal solubilization. The optimal concentration of silver added in the bioleaching was 15 mg/L. When adding 30 mg/L of silver ion to the bioleaching, inhibition of acidification, sulfate production and metal solubilization were found. The rate and efficiency of metal solubilization from contaminated sediment is in the decreasing order: Cu > Zn > Mn> Ni> Cr > Pb. It was concluded that the kinetics of metal solubilization was catalyzed by addition of silver ion in the bioleaching process. Adding ferric ions at the beginning of reaction was not able to promote the rate of metal solubilization in bioleaching Therefore, it was found that adding silver ion can obtain the better rates of acidification, sulfate production and metal solubilization. In the experiments of adding ferric ion when sediment pH reached 3, the optimal concentration of 1g/L was obtained. It also revealed that adding ferric ions when sediment pH reached 3 would not influence the growth of thionbacillus bacteria during the bioleaching process.