- 學位論文
流動式電極電容去離子(FCDI)系統處理含鉻(VI)廢水
Flow-Electrode Capacitive Deionization (FCDI) System to Treat Chromium (VI)-Containing Wastewater
摘要
廢水之鉻污染經工業排放或不當處理，將嚴重影響人類健康與環境生態，鉻在自然水體中價態分為三價鉻 Cr(III)與六價鉻 Cr(VI)，而六價鉻Cr(VI)毒性較三價鉻Cr(III)強，如何有效處理廢污水中的鉻值得關注。 本研究提出新穎的流動電極電容去離子系統(Flow-Electrode Capacitive Deionization, FCDI)應用於處理廢水之鉻污染。研究中測試四種流動式電極材料，發現最適合應用於 FCDI 系統去除鉻之流動式電極材料為 Fe3O4/AC (1:1)複合材料；Fe3O4/AC (1:1)複合材料是由 140-160 nm 圓形奈米 Fe3O4顆粒佈滿活性碳材料，Fe3O4/AC (1:1)保有立方尖晶石(spinel)結晶結構之(311)晶格面；BET 比表面積為173.48 m2 /g，中孔佔總孔體積的比例(Vmeso/Vtot)為99%，比電容值為15.07 F/g (當掃描速率為1 mV/s)。 研究中先以5 wt% AC為 FCDI 流動式電極材料，以 SCC 操作模式，測試FCDI系統的最佳參數，處理1000 mg/L K2Cr2O7 時，FCDI 系統擁有最優異的 Cr 平均鹽類去除效率(Average Salt Removal Rate, ASRR)為1.04×10-4 mmol/min/cm2，充電效率(34.32%)與能源消耗(1.61 kWh/mol)表現也很優良，表示 FCDI 系統可處理高濃度 K2Cr2O7 溶液，能擁有良好的去除水中鉻的效能；使用1.6 V 處理1000 mg/L K2Cr2O7 於pH 值為 4時， FCDI系統擁有最優異的 Cr 平均鹽類去除效率(ASRR: 1.21×10-4 mmol/min/cm2)，與優良的充電效率(37.89%)與能源消耗(1.95 kWh/mol)。 以5 wt% Fe3O4/AC (1:1)複合材料為 FCDI 流動式電極材料，並以 SCC 操作模式與1.6 V 操作時，FCDI 系統擁有優異的 Cr 平均鹽類去除速率(ASRR)為 0.92×10-4 mmol/min/cm2，相較於活性碳流動式電極材料擁有較高的充電效率 (64.84%)與較低的能源消耗(1.02 kWh/mole)，顯示本研究水熱合成之 Fe3O4/AC (1:1)複合材料為深具潛力的去除水中鉻之流動式電極材料。 以回收再用5 wt% Fe3O4/AC (1:1)複合材料為 FCDI 流動式電極材料，也可以看到效果跟原本的複合材料相比，Cr 平均鹽類去除速率(ASRR)從0.92×10-4 mmol/min/cm2可略增為1.04×10-4 mmol/min/cm2；但充電效率則有顯著下降，由64.84%降低至38.24%，能耗也從1.02 增加至1.89 kWh/mole，代表Fe3O4/AC (1:1)複合材料可被清洗再次回收使用，但仍需更多次使用或更長期的回收再用之後續研究。 當溶液中存在相同莫耳濃度(6.8 mM)之陰離子與鉻酸根離子時，SO42– 的存在相較於 Cl- 或 NO3- 造成更顯著的競爭效應，當SO42– 共存於溶液時，Cr 之 2 hr ASRR 顯著下降27%，由原本的 0.92×10-4 mmol/min/cm2，降為0.68×10-4 mmol/min/cm2。
並列摘要
Chromium pollution in wastewater, resulting from industrial discharges or improper treatment, severely affects human health and environmental ecology. In natural water bodies, chromium exists in two valence states: trivalent chromium Cr(III) and hexavalent chromium Cr(VI). Hexavalent chromium Cr(VI) is more toxic than trivalent chromium Cr(III). Effective treatment of chromium in wastewater is thus a critical concern. This study proposed an innovative Flow-Electrode Capacitive Deionization (FCDI) system for treating chromium-containing wastewater. Four types of flow-electrode materials were tested and the Fe3O4/AC (1:1) composite material was found to be the most suitable for removing chromium in the FCDI system. The Fe3O4/AC (1:1) composite consisted of 140-160 nm spherical nano Fe3O4 particles distributed on activated carbon, maintaining a spinel crystal structure with a (311) lattice plane. It had a BET surface area of 173.48 m²/g, with 99% mesopores of the total pore volume, and a specific capacitance of 15.07 F/g (at a scan rate of 1 mV/s). 5 wt% AC was firstly employed as the FCDI flow-electrode material, operating in SCC mode, to determine the optimal parameters for chromium removal. When treating 1000 mg/L K2Cr2O7, the FCDI system achieved an average salt removal rate (ASRR) of 1.04×10-4 mmol/min/cm², with a charging efficiency of 34.32% and an energy consumption of 1.61 kWh/mol, indicating its effectiveness in handling high concentrations of K2Cr2O7. Using 1.6 V to treat 1000 mg/L K2Cr2O7 at pH 4, the system showed the best performance with an ASRR of 1.21×10-4 mmol/min/cm², a charging efficiency of 37.89%, and an energy consumption of 1.95 kWh/mol. With 5 wt% Fe3O4/AC (1:1) composite material as the FCDI flow-electrode material, operating in SCC mode and at 1.6 V, the FCDI system achieved an ASRR of 0.92×10-4 mmol/min/cm², a high charging efficiency of 64.84%, and a low energy consumption of 1.02 kWh/mol, highlighting the potential of hydrothermally synthesized Fe3O4/AC (1:1) composite material for chromium removal from wastewater. Reusing 5 wt% Fe3O4/AC (1:1) composite material for FCDI also demonstrated effective chromium removal, with a slightly increased ASRR from 0.92×10-4 to 1.04×10-4 mmol/min/cm². However, the charging efficiency significantly decreased from 64.84% to 38.24%, and energy consumption increased from 1.02 to 1.89 kWh/mol, indicating that Fe3O4/AC (1:1) composite material can be cleaned and reused, but further research is needed to assess its long-term reuse feasibility. In the presence of anions at the same molar concentration (6.8 mM) with chromate ions, SO4²⁻ had a more pronounced negative impact on the removal of negatively charged chromate ions compared to Cl⁻ or NO3⁻. When SO4²⁻ coexisted in the chromate solution, ASRR significantly dropped 27% from 0.92 × 10-4 mmol/min/cm2 to 0.68 × 10-4 mmol/min/cm2.