Development of a recycling-based chromium wastewater treatment system using nanoscale zero-valent iron (nZVI)

[[abstract]]電鍍廢水通常含有多數的重金屬如鉻、鎳、銅、鋅等，若未經處理直接排放到環境中則會造成危害。常用之重金屬廢液處理方法有化學混凝、電混凝、離子交換、電解、蒸發及吸附等。近年來，一些新穎的方法如奈米碳管、奈米光觸媒及奈米級零價鐵等，亦已被應用於重金屬之吸附或還原處理上。奈米級零價鐵具比表面積高、反應性高及還原性強等特性，對水中重金屬具有相當良好之處理成效。 本研究利用實驗室自行合成之奈米級零價鐵(nanoscale zero-valent iron , nZVI)，先利用批次實驗來進行處理含鉻系廢液中之鉻金屬，藉由奈米級零價鐵大量的比表面積及強還原性對目標污染物進行吸附與還原作用，除了可將目標污染物從廢液中移除外，亦改變其氧化態，使其毒性大大降低。後續利用瓶杯試驗(Jar test)來模擬實廠的應用並將處理後所產生之鐵鉻污泥進行回收再利用。 本研究於批次實驗當中所使用之鉻系廢水總鉻含量約為1300 mg/L，其中六價鉻含量為880 mg/L。實驗以批次方式進行，在頂空分別為氮氣及空氣情況下，探討空氣中的氧及奈米級零價鐵的劑量對含鉻廢水的去除效率，經過實驗結果顯示，在頂空氮氣及頂空空氣間似乎並無太大差異。接著再利用瓶杯試驗來處理電鍍廠中之鉻系廢水，其中總鉻含量約540 mg/L，其中六價鉻含量為400 mg/L。利用添加不同劑量之奈米級零價鐵分別在於不同攪拌速度下進行實驗，實驗結果顯示，奈米級零價鐵在添加10 g/L及15 g/L下，在4小時反應時間之內，均能將電鍍廢液中之鉻金屬去除。在不同轉速下當中，以250 rpm最能將鉻金屬給去除。最後再將沉澱於反應器底下的鐵鉻污泥收集，利用1 N鹽酸100 mL進行反應60分鐘的酸洗濃縮實驗，實驗結果顯示添加15g及20g的鐵鉻污泥有較高的鉻鐵離子濃縮液，但依照添加的比例來計算以添加10g的鐵鉻污泥效果較佳。[[abstract]]Electroplating wastewater containing heavy metals is usually a majority of the genus such as chromium, nickel, copper, zinc, etc., if not handled directly discharged into the environment will cause harm. Heavy metals commonly used method of waste handling chemical coagulation, electro coagulation, ion exchange, electrolysis, evaporation and adsorption, etc. In recent years, some new methods, such as nanotubes, nano photocatalyst and nanoscale zero-valent iron, etc., have also been used for the adsorption of heavy metals on the reduction or handling. Nanoscale zero-valent iron with a high specific surface area, high reactivity and reducing other characteristics of heavy metals in water has a fairly good deal of success. In this study, laboratory-synthesized nanoscale zero-valent iron (nZVI). First experiment to use batch processing of liquid waste containing chromium, by nanoscale zero valent iron large amount of surface area and strong reduction of the target pollutant adsorption and reduction of conduct, in addition to the target contaminants can be removed from the waste, but also to change its oxidation state, so toxicity greatly reduced. Follow-use Jar test to simulate real iron-chromium sludge treatment plant applications and conduct arising from recycling. Chromium used in this study, which the department of wastewater in batch experiments total chromium content of about 1300 mg/L, which hexavalent chromium content of 880 mg/L. Experiments carried out in batches, in the headspace with nitrogen and air were the case, investigate the oxygen in the air and a dose of nanoscale zero-valent iron removal efficiency for wastewater containing chromium, after the experimental results show , between the headspace with nitrogen and air headspace seems not much difference. And then use Jar test to handle chromium electroplating wastewater plants, of which the total chromium content of about 540 mg/L, which hexavalent chromium content of 400 mg/L. The use of different doses of nanoscale zero-valent iron experiments were carried out under different is that the stirring speed, experimental results show that nanoscale zero-valent iron in adding 10 g/L and 15 g/L down within 4 hours of reaction time, can be in the chrome plating waste removal. At different speeds among, 250 rpm is the most capable to remove chromium. Finally then precipitated iron-chromium sludge collected at the bottom of the reactor, using 1 N hydrochloric acid 100mL the reaction was concentrated in experiment 60 minutes, experimental results show that adding 15g and 20g of iron-chromium sludge has high chromium ions concentrate. However, according to the proportion of the added calculated to add 10g of iron-chromium sludge was better.[[note]]碩