| 摘要: | 含鉻廢水傳統的處理方法為化學沈澱 (chemical precipitation)、離子交換等，新的處理技術之一例如元素金屬還原法 (Zero Valent metal reduction)，提供取代傳統處理方法之另一選擇。
本研究探討元素鐵還原水中六價鉻離子之可行性。研究過程將分別探討不同溶液之起始pH值 (3、4及5)、元素鐵添加量 (Cr6+：Fe0)、元素鐵粒徑大小 (10、50、150mm)、起始六價鉻離子濃度 (9及20 mg/L)及元素鐵經酸洗前處理操作等因子對水中六價鉻離子去除之影響。反應過程除測定水中殘餘之六價鉻離子濃度外，亦一併分析反應過程溶液中之pH、ORP (Oxidation Reduction Potential)、DO (Dissolved Oxygen)、亞鐵離子濃度等參數，作為探討六價鉻與元素鐵細部反應作用機制之依據。
本研究結果發現，元素鐵還原水中六價鉻離子過程，溶液之起始Cr6+濃度為9 mg/L、10mm之元素鐵、Cr6+：Fe0為1：120，於控制不同起始pH為3、4及5條件，經12小時反應後，起始pH為3時，元素鐵對水中Cr6+之去除率達100%，而在pH為4及5條件下，溶液之Cr6+濃度不變，元素鐵無法去除水中六價鉻；改變Cr6+：Fe0比分別為1：40、1：80及1：120，經反應12小時後，發現Cr6+：Fe0為1：80及1：120條件下，元素鐵對水中Cr6+之去除率皆達100%，而Cr6+：Fe0為1：40，Cr6+去除率僅為23%；水中起始Cr6+濃度分別為9及20 mg/L，元素鐵對水中Cr6+之去除率分別為100及28%，顯示增加Cr6+起始濃度不利於提昇Cr6+之去除率；於添加10mm經酸洗前處理之元素鐵並控制Cr6+：Fe0為1：120、Cr6+起始濃度為9及20 mg/L，發現於反應時間30分鐘後可將水中六價鉻濃度降至為0 mg/L。綜合上述，水中起始pH為3、重量比 (Cr6+：Fe0)為1：120、10mm元素鐵及將元素鐵經酸洗前處理，為本研究去除水中六價鉻離子最佳處理條件。而元素鐵還原水中六價鉻離子之過程所回收固相樣品經X-Ray Diffratometer分析，發現表面可能具有FeCr2O4鉻化合物存在。
Traditional ways, such as “chemical precipitation”, ion exchange” and so on, are used for the treatment of chromium (VI) containment wastewater. However, new treatment technologies, such as Zero Valent Iron (ZVI) reduction, is developed in order to replace the traditional methods.
This study focuses on the feasibility of reducing the aqueous chromium (VI) ions by using ZVI. Experiments were designed to investigate the effects of different ZVI dosage, Cr6+/Fe0 ratio, particle size of ZVI (10, 50, 150mm), acid pretreatment of ZVI, initial solution pH (3, 4, 5), initial Cr6+ concentration (9, 20mg/L) on the removal of Cr6+. In the reduction reaction, not only the concentration of aqueous Cr6+ remained in the solution, but also the solution pH, ORP, DO, Fe2+ ions, total iron, total Cr were also monitored and analyzed.
There are several finding regarding the reduction process of Cr6+ using ZVI iron. First of all, when the parameters were set at 9mg/L of Cr6+, 10mm of ZVI particle size, Cr6+/ZVI ratio weight ration 1:120, solution pH was designed as the variable. The solution pHs were controlled in pH 3, pH 4, and pH 5, respectively. Result show that under pH 3, Cr6+ was removed completely in a 12 hours reaction time. Furthermore, when the ratio of Cr6+/ZVI changed from 1:120 to 1:80 to 1:40, removal of Cr6+ was still unchanged for Cr6+/ZVI ration 1:80. As for the weight ratio of 1:40, the removal efficiency dropped significantly to be 23%. Regarding the effect of initial Cr6+ concentration on the Cr6+ removal, it was found the removal efficiency reduced from 100% of initial concentration 9mg/L to 28% of initial concentration 20mg/L in a 12 hours of reaction period. In addition, acid pretreatment of ZVI promoted the Cr6+ removal rate. The reaction time for total removal of Cr6+ reduced from 12 hours to 30 minutes. Base on the experimental data, the best condition for the removal of Cr6+ concluded as following: pH 3, the weight ratio of (Cr6+：Fe0) 1：120 and using 10mm of acid pretreated ZVI. The species of chromium on the surface of ZVI was verified as FeCr2O4 by X-Ray Diffratometer. |
