| 摘要: | 砷具有急毒性、慢毒性及致癌性，而製革、玻璃器皿製造、無線高頻通訊的高科技產品所需砷化鎵晶片製程等排放含砷工業廢水，可能危及承受水體，其處理與控制遂成為環境保護的重要課題。為降低對人體的危害，世界衛生組織 (World Health Organization，WHO)於1993年建議飲水中砷濃度低於10μg/L，而為保護承受水體，我國放流水標準中規定砷之排放限值為0.5mg/L。
本研究利用電磁場輔助奈米級元素鐵連續分批式反應槽處理水中砷離子，探討不同溶液pH控制(起始pH＝5.4空氣曝氣及全程控制pH＝5.4)、曝氣種類(二氧化碳及空氣)及砷離子起始濃度(250及500 mg/L)條件下，奈米級元素鐵還原去除水中砷離子之能力，反應過程中一並分析或測定溶液中pH、ORP、DO及Fe2+濃度等參數之變動趨勢。
本研究發現於二氧化碳曝氣、奈米級元素鐵添加量3.33 g/L條件下，奈米級元素鐵可於第一批次反應60分鐘內將水中砷離子濃度分別由250 mg/L及500mg/L之起始濃度降低至115及290 mg/L，而其他批次奈米級元素鐵去除砷離子之能力則隨批次增加而降低，反應後水中殘留砷離子之濃度分別介於115~230 mg/L及290~ 470 mg/L。
而在空氣曝氣並控制起始溶液pH 為5.4、奈米級元素鐵添加量為3.33 g/L條件下，經五批次反應後水中砷離子之殘留濃度可分別由250mg/L及500 mg/L降低至94~175 mg/L及211~342 mg/L。
另外，在空氣曝氣並持續控制溶液pH為5.4、奈米級元素鐵添加量為3.33 g/L條件下，於起始砷離子濃度500 mg/L時奈米級元素鐵可連續三批次完全去除中砷離子，而在起始砷離子濃度250 mg/L條件下，可連續五批次完全去除水中砷離子。
而在反應後回收固相產物發現，以XRD測定其表面晶相時，發現表面具有As2O、As2O3、As2O5、As0及Fe0等晶相物存在，顯示奈米級元素鐵去除水中砷離子之可能機制包括吸附、沉澱及還原作用等。
The arsenic is a material with acute chronic toxicity and carcinogenicity, industrial leather making glassware manufacture, manufacturing of high-techwireless high frequency communication product, discharge wastewater with arsenic compound, arsenic might cause pollution problem on natural water and soil. Therefore, for a environment concern. World Health Organization (WHO) suggested that the arsenic concentration in drinking water should be less than 10 μg/L. USEPA will execute the guideline in 2006. In addition Taiwan EPA had reduced the maximum arsenic concentration in drinking water from 50 μg/L m to 10 μg/L. Meanwhile the limitation of arsenic concentration in the industrial effluent is 0.5 mg/L.
This study investigates the removal of arsenate from aqueous solution by nano zero valent iron (NZVI) in a batch reactor with the electric-magnetic field assisted. The effects of different solution pH control condition ( pH=5.4 controlled initially and the pH=5.4 controlled continuously ), the kinds of aeration gases (carbon dioxide and air) and the initially arsenic concentration density (250 and 500mg/L) on the removal of arsenic were examined solution pH, ORP, DO and Fe2+, were also monitored determined throughout the reduction experiments.
Based on the results of experiment ,it was found that the residual arsenic concentration decreased from 250 and 500 mg/L to 115 and 290 mg/L in batch respectively with a reaction 60 min, and CO2 aeration and 3.33 g/L NZVI addition. The removal of arsenic reclined with the increase of batch number, with a removal efficiency rages of 115-230 mg/L and 290-470 mg/L respectively.
When the solution, was controlled initially at 5.4 with air aeration and 3.33 g/L NZVI addition, the concentration of arsenic decrease from the initial concentrations of 250 mg/L and 500 mg/L to 94-175 mg/L and 211-342 mg/L, respectively.
Furthermore, when solution was controlled at pH 5.4 and aerated with air coupled with 3.33g/L NZVI addition. The removal of arsenic were 100% for the initial arsenic concentration of 250 mg/Lin all 5 batch operation. For the initial arsenic concentration of 500 mg/L, arsenic was removal completely in the first three batches.
Based on the XRD patterns of the solid products left in the reactor, if was found .that there was As2O、As2O3、As2O5、As0and Fe0 existing on the surface of reduals, of was proposed that the possible mechanism of arsenic removal by NZVI included adsorption、precipitation and reduction. |
