以奈米級零價鐵處理實廠含鉻電鍍廢水之研究

電鍍工業是一項結合傳統與高科技技術之產業，然而在電鍍製程中，往往產生龐大的電鍍廢液，對環境造成危害。本研究利用實驗室自行合成之奈米級零價鐵(nanoscale zero-valent iron, nZVI)，處理電鍍廢液中之鉻金屬，並將處理後所產生之鐵鉻污泥回收再製奈米級零價鐵與分離出濃縮之三價鉻離子溶液。本研究所使用之電鍍廠廢水總鉻含量約1,400 mg/L，其中六價鉻含量約為1,000 mg/L。實驗以批次方式進行，在密閉系統與半開放式系統中，探討不同劑量之奈米級零價鐵添加對含鉻廢水之處理效率，並比較在不同溫度控制下奈米級零價鐵對廢水中鉻的移除效率。密閉系統實驗結果顯示，奈米級零價鐵添加劑量0.1、0.5、1、2及5 g/L下，在24小時反應時間內，溶液中總鉻去除效率分別為7.9、30、57.1、100及100%。其中，添加奈米級零價鐵劑量5 g/L之組別於反應時間5分鐘內，溶液中總鉻去除效率已達到100%。總鉻移除過程中，可於液相中偵測到三價鉻之生成，並隨實驗時間增長被去除。XPS分析結果證實，奈米級零價鐵表面可發現三價鉻之存在。實驗結果顯示，奈米級零價鐵可迅速將六價鉻還原成三價鉻並吸附於其表面上，其對廢水中總鉻之去除能力約為0.7~0.8 g Cr/g nZVI。此外，奈米級零價鐵對廢水中之NO3-、NO2-、PO43-及SO42-亦具有良好之處理成效。不同溫度下之實驗結果顯示，環境溫度的提高有助於加速奈米級零價鐵移除總鉻的反應速率。奈米級零價鐵對水中鉻之吸附，符合擬二階反應動力式及Freundlich等溫方程式。實驗結果亦顯示，在半開放系統中，氧氣的置換確實會影響奈米級零價鐵去除總鉻之效率。奈米級零價鐵與電鍍廢液反應後所產生之鐵鉻污泥，可藉由濃鹽酸酸洗將吸附於奈米級零價鐵表面上之三價鉻離子回收濃縮，而剩餘之失效鐵顆粒，可再製成奈米級零價鐵供後續處理使用。實驗結果顯示，再製之奈米級零價鐵對總鉻之去除能力與直接合成者相當。本研究成果顯示，利用奈米級零價鐵除可迅速有效處理含鉻電鍍廢液，再製之奈米級零價鐵亦具有重複使用於處理程序中之潛力。

關鍵字

奈米級零價鐵；電鍍廢水；鉻；吸附；還原；奈米級零價鐵再製

並列摘要

In this study, nanoscale zero-valent iron (nZVI) was applied to treat chromium-containing wastewater collected from an electroplating plant. Batch experiments were conducted to evaluate the efficiency of chromium removal under closed and semi-closed conditions. The wastewater used in this study contained approximately 1,400 mg/L of total chromium (total Cr), including 1,000 mg/L of hexavalent chromium (Cr6+). Results of the closed system experiments show that the removal efficiencies of total Cr by 0.1, 0.5, 1, 2 and 5 g/L of nZVI were 7.8, 30.3, 57.1, 100, and 100%, respectively, during 24 hours of reaction. The removal efficiency of total Cr reached 100% rapidly with the addition of 5 g/L nZVI during a 5-minute reaction. Trivalent chromium (Cr3+) was detected in the aqueous phase during the removal of Cr6+. X-ray photoelectron spectroscopy (XPS) analysis confirmed that Cr3+ was present on the surface of nZVI. This indicates that nZVI can reduce Cr6+ effectively, and then adsorbs Cr3+ onto its surface. The total Cr removal capacity of nZVI was approximately 0.7-0.8 g total Cr/g nZVI. In addition, nZVI was capable of removing anions including NO3-、NO2-、PO43- and SO42-. Results also show that the removal rate of total Cr by nZVI increased with increased temperature. The adsorption of Cr by nZVI fits the pseudo-second-order kinetic model and the Freundlich isotherm. The results of the semi-closed system experiments show that the removal efficiency of total Cr was decreased due to oxygen penetration. The adsorbed Cr3+ can be recovered from the produced iron-chromium sludge by hydrochloric acid pickling, and then the residual spent iron particles can be collected to reproduce nZVI for further applications. Experimental results reveal that the removal efficiency of total Cr by the reproduced nZVI was similar to that of directly synthesized nZVI. The results of this study show that the application of nZVI can treat chromium-containing wastewater rapidly and effectively. In addition, the reproduced nZVI also has the potential to be reused in the treatment process.

並列關鍵字

Nanoscale zero-valent iron (ZVI) ； electroplating wastewater ； chromium ； adsorption ； reduction ； nZVI reproduction

參考文獻

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以奈米級零價鐵處理實廠含鉻電鍍廢水之研究

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