Study of organopolymer-coated iron beads in catalyzing chlorophenols (CPs) degradation

[[abstract]]氯酚常用做早期農藥製作原料，如製作處理不當時，往往造成土壤及地下水污染。在眾多可用整治技術中，化學氧化如Fenton法，可有效去除含氯數低之氯酚，但缺點是所需使用藥劑量高且催化用鐵離子無法重複使用。本研究室所擁之專利技術顯示，使用EDTA-Fe可更有效率執行氯酚之氧化降解，且幾丁聚醣(chitosan)可作為EDTA-Fe附著單體，使反應中催化物質可重複使用。惟實驗中發現，此顆粒擔體在長時間處理液相氯酚污染時易崩塌，極需改良，以利處理受氯酚污染水體。 本研究擬改用鐵珠作為單體被覆有機聚合物如幾丁聚醣及EDTA等，做為反應催化顆粒並探討液相氯酚去除效率，目的包括：(1)決定鐵珠覆膜之最適方法，(2)測試覆膜鐵珠在催化氧化上之特性，及(3)研究覆膜鐵珠降解CPs之最適條件。本研究所用催化氧化技術是以H2O2為氧化劑，主要實驗設計部分是將鐵珠先經由表面前處理(砂磨、酸洗)後，測試鐵珠與有機聚合物如EDTA及幾丁聚醣等結合性，並探討其對液相氯酚之降解效果。 由因次實驗和氯酚降解數據顯示在pH~5、攪拌速度125 rpm及浸泡時間24小時為最適EDTA被覆於鐵珠的操作條件，鐵珠單位面積被覆量約1 62 mg-EDTA/cm2。當使用幾丁聚醣減少鐵溶出量時，鐵珠經EDTA被覆並以250℃烘乾再被覆幾丁聚醣所做成之鐵珠，又稱為E+C鐵珠，在10 mL的0 12%雙氧水溶液中浸泡24小時，其鐵溶出量最低-少於0 0102 mg。而且使用0 12%過氧化氫和十顆E+C鐵珠處理20 mL液相氯酚(1 000 mg/L)，經2小時後，對3-MCP、3 4-DCP及3 5-DCP降解效果分別為89 4、86 3和88 6%。在重複使用鐵珠的實驗中，E+C鐵珠經過連續5次重複使用後，催化氧化效果仍維持有86%以上的氯酚平均降解效率，而pH值維持穩定在3 3左右。後續應用到連續反應槽中，以0 25%過氧化氫配合568顆E+C鐵珠(有效總表面積=285 51 cm2)來處理液相氯酚，經過五天後，對氯酚降解效率保持在95%以上，pH值在反應66小時內，仍保持在3以上; 如鐵珠未經處理，則其反應後液相pH會快速降到2以下。[[abstract]]Chlorophenols (CPs) was used as raw chemicals for manufacturing various pesticides Poor practices during their manufacturing processes resulted in soil and groundwater contamination Chemical oxidation could remove lowerly chlorinated phenols in liquid effectively yet the reuse of catalyst needs further consideration and so does the high dosage of peroxide One of our patents demonstrates that chitosan could work as an absorbent to bind EDTA-Fe and degrade chlorophenols with less addition of peroxide One disadvantage was the chitosan particles were easy to collapse and deserve further investigation In this study iron beads were used as supporting media and were coated with chiosan and EDTA to serve as catalytic particles and peroxide as an oxidant for treating liquid chlorophenols The objectives include: (1) to determine the most feasible mean in making EDTA-coated iron beads (2) to examine the characteristics of EDTA-coated iron beads in chlorophenol oxidation and (3) to investigate the optimal degradation conditions using the EDTA-coated iron beads Main experimental procedure included polishing the iron bead surface by sand paper and acid rinse followed by organopolymer(s) coating and the obtained particles were tested their catalytic efficiency in terms of chlorophenol degradation The obtained data revealed that at pH ~5 mixing intensity of 125 rpm and EDTA submerging time of 24 hours the optimal EDTA-coating conditions resulted with specific EDTA coating amount per unit iron surface area of 1 62 mg-EDTA/ cm2 Oven dried the EDTA-coated particles at 250 ℃ followed by coating a chitosan layer resulted in minimal iron leaching out (less than 0 0102 mg when submerged 10 iron beads in 10 mL of 0 12% peroxide liquid for 24 hours) and such particles were called as E+C iron beads Using 10 E+C iron beads along with initial peroxide concentration of 0 12% to treat 20 mL of 1 000 mg-CPs/L for 2 hours the degradation rates of 3-MCP 3 4-DCP and 3 5-DCP were 89 4 86 3 and 88 6% respectively When consecutive use of the E+C iron beads for 5 times the over all averaged CPs degradation maintained at 86% and pH remained stable at 3 3 In continuous runs 568 iron beads (i e total effective surface area= 285 51 cm2) with 0 25% of peroxide present catalyzed 95% plus of CPs degradation for 66 hours (total treated volume of 2 6 L) at pH above 3 If iron beads had not coated the pH dropped abruptly to less than