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    Title: Integration of PEUF and chemical reduction for copper removal and recovery : effect of pH and polyelectrolytes
    Other Titles: 以聚電解質加強超過濾結合化學還原法去除及回收重金屬銅:pH和不同聚電解質的影響
    Authors: 周依宣;Chou, Yi-Hsuan
    Contributors: 淡江大學水資源及環境工程學系博士班
    李奇旺;Li, Chi-Wang
    Keywords: 化學還原法;;聚乙烯亞胺;連二亞硫酸鈉;聚電解質;chemical reduction;Copper;Dithionite;PEUF;PEI;PSS;PAA;polyelectrolyte
    Date: 2017
    Issue Date: 2018-08-03 15:05:46 (UTC+8)
    Abstract: 本研究以聚電解質加強超過濾(PEUF)結合化學還原法去除及回收重金屬(銅),探討pH和不同聚電解質的影響。在以化學還原法處理聚電解質加強超過濾(PEUF)濃縮液(PEI及銅)的結果中發現,當固定銅:還原劑(Na2S2O4):PEI的莫耳比,並逐漸提升銅的初始濃度時,銅的去除率會隨著初始濃度降低而下降。另一組實驗則為固定銅的初始濃度,改變PEI:Cu(II)的莫耳比,測試銅去除率之變化。結果顯示當PEI的濃度提高,則銅的去除率會隨之下降。透過TEM和更換濾膜(超濾膜)的實驗,證實去除率的降低是因奈米顆粒穿透0.45 μm的濾膜所造成。
    研究中也分別探討以化學還原法處理三種不同的聚電解質(PSS, PAA, PEI)的PEUF濃縮液之銅去除率差異。結果中發現,若是以化學還原法處理PSS的含銅濃縮液,則無論操作在任一pH條件下,去除率均可達到約95%,且聚電解質不會附著在還原的銅顆粒上。在PAA系統中,銅的去除率在鹼性條件下有些微下降,不過除了pH10有降到85%以外,其它pH仍有95%以上的去除率。PEI是三種聚電解質中表現最差的,除了pH3、4有達到85%以外,其它pH的銅去除率都只有在40%以下。而三種不同聚電解質中的含銅濃縮液經化學還原法處理後所還原出的銅顆粒,大部均以氧化亞銅(Cu2O)及金屬銅(Cu)兩種形式存在。且經熱重分析儀(TGA)分析後,除了PEI系統中所產生的銅顆粒有聚電解質附著,PSS和PAA的還原銅顆粒都沒有聚電解質附著在上面。
    綜合上述結果,以化學還原法回收PEUF濃縮液中的銅,在PSS的系統中,無論操作在任何pH條件下(pH3-10),銅去除率均可高達99-100%。不過由於PSS為帶負電的聚電解質,僅能靠靜電吸附吸引帶正電的污染物。若是水中存在的是帶負電的污染物(如:CuEDTA2-),則PSS無法在PEUF系統中將其去除,也因此PEI仍是較為合適的選擇。此外實驗結果中也顯示,當水中有EDTA的存在時,以化學還原法去除PEI系統中的銅時,其去除率也較沒有EDTA時更高。
    另外為了解以化學還原法回收PEUF濃縮液中的銅和聚電解質時,是否會對聚電解質的結構或鍵結能力造成破壞或是影響,實驗中也以螢光滴定法和吸附穿透法測試PEI在多次重覆使用後,對銅離子鍵結力的影響。實驗結果中發現,還原劑(Na2S2O4)確實會造成溶液中離子強度提升,而降低了PEI對銅的鍵結能力,不過透過連續式系統的操作,還原劑(Na2S2O4)會隨著出流水流出,使系統中的離子強度不致累積提升。
    總結,以聚電解質加強超過濾(PEUF)結合化學還原法去除及回收重金屬(銅)的實驗中發現,PEI是較合適的聚電解質選項。雖然在瓶杯試驗中,因為奈米顆粒的形成,使得銅的去除率偏低。但透過連續式的系統中,不但顆粒有機會在系統中成長使粒徑增加,進而提升銅的去除率;連二亞硫酸鈉所造成的離子強度影響,也可以透過連續式的系統,將水中的離子強度保持在一定的濃度。
    Chemical reduction was firstly employed to treat synthetic wastewaters of various compositions prepared to simulate the retentate stream of polyelectrolyte enhanced ultrafiltration (PEUF). With fixed Cu:polyethylenimine (PEI) monomer:dithionite molar ratio, increasing copper concentration increases copper removal efficiency. Under fixed Cu:dithionite molar ratio and fixed Cu concentration, increasing PEI monomer:copper molar ratio decreases copper removal efficiency. The formation of nano-sized copper particles, which readily pass through 0.45 μm filter used for sample pretreatment before residual copper analysis, might be the reason behind the decreasing copper removal efficiency observed. Particle size analysis shows that the size of copper particles, which are formed through reduction reaction, increases with decreasing pH value and increasing reaction time. As ultrafiltration is capable of removing these nano-sized particles, integration of chemical reduction and PEUF is proposed to simultaneously achieve regeneration of polyelectrolyte and recovery of copper in one process. Results show that the proposed process could achieve almost complete copper removal without being affected by reaction pH.
    Three polyelectrolytes (PSS, PAA, and PEI) containing various functional groups and having various molecular weight were also studied to explore their effects on the copper removal in PEUF and on the copper recovery by chemical reduction under various pH conditions. With PSS as the polyelectrolyte, copper was removed reasonably well (75%) by PEUF even under acidic pH value of 3. With PAA which contains carboxylic group, a weak acidic functional group relative to sulfonic group in PSS, copper removal was a bit low (~60%) under pH of 3.0 but increased substantially at pH of 4.0. On the other hand, a branched PEI having amine group interacted with Cu ions through coordination bonding; the highest Cu removal of 94% was obtained at pH of 3 and Cu to PEI monomer molar ratio of 1:5. The copper removal efficiency decreased slightly with increasing pH. The decreasing removal efficiency of Cu at alkaline pH values is due to the high permeation of PEI through membrane compared to both PSS and PAA.
    For copper recovery by chemical reduction, the complete copper recovery was realized and was almost independent of pH for solution containing PSS. The copper recovery efficiencies were more than 95% for PAA solution with pH values ranging from 3 to 9 at reaction time of one hour. For PEI, the recovery efficiencies ranged from 20~96% and were pH dependent. Aggregated and settled readily copper particles were produced by chemical reduction in PSS solution. XRD analysis identified cuprous oxide in all of the samples collected. Dependent of pH and polyelectrolytes, additional peaks matching those of elemental copper were identified. TGA analysis showed that solids produced from PSS and PAA systems contained no polyelectrolytes while solid collected from PEI system contained 32% of polyelectrolyte.
    The destruction of polyelectrolyte after chemical reduction was investigated by both fluorescence quenching titration and adsorption breakthrough method. The maximum binding capacity of PEI decreases dramatically for several times of reused causing by increasing of ionic strength, which can be flushed out through the membrane with continuous system.
    Appears in Collections:[Graduate Institute & Department of Water Resources and Environmental Engineering] Thesis

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