以微胞加強超過濾系統截留濃縮六價鉻: 陰離子及螯合劑的影響

Effects of co-existing anions and chelating agent on the retention characteristics of chromate by MEUF

虞中維(Jhong-Wei Yu)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2014年)

摘要

微胞加強超過濾程序 (Micellar enhanced ultrafiltration, MEUF) 為一可以有效地截留並濃縮溶液中離子型汙染物(六價鉻)及有機物的方法。然而，廢水中同時存在的其他陰離子 (NO3-, SO42-) 會與六價鉻酸鹽產生競爭效應的現象而影響到其截留效果；此外廢水中存在的螯合劑 (EDTA) 與此程序中採用的界面活性劑微胞 (Micelle) 也會產生交互作用而影響到離子型汙染物的截留效率。上述三種陰離子 (Cr(VI), NO3-, SO42-) 及 EDTA 分別以不同的莫爾濃度比例組成薄膜進流液，再添加陽離子型界面活性劑，十六烷基三甲基溴化銨 (CTAB) 使之形成微胞並以 UF 薄膜在固定的操作條件下將其截留濃縮，並於濾液端分析其水質及薄膜的相對通量。
進流液中只含有一種陰離子時，其截留效率為 Cr(VI) 99.7%> SO42- 84.1% > NO3- 81.0%，而當進流液中同時含有上述三種陰離子時，其截留率也同樣呈現此一趨勢，顯示離子與微胞的交互作用，不只需要考慮其荷電性質，離子本身的物理化學性質也為一重要因素。另外，硫酸根對於六價鉻截留效率的影響也大於硝酸根，顯示離子之電價於此程序中為一重要的性質。而當 EDTA 的濃度從 1mM 上升至 2mM 時，六價鉻的截留效率則從 99.7% 下降至 98.7%，其他陰離子也呈現不同的下降趨勢，但 EDTA 對於 CTAB 的截留效率卻有些微提升的現象。當進流液溫度上升至 40℃ 時，相對通量從 0.68 上升至 0.94，而陰離子之截留率則皆下降 5% 左右，離子汙染物因溫度上升而增加其熱的擾動，對於其吸附於界面活性劑微胞有不利的影響；溫度對於界面活性劑微胞的穩定性也為一關鍵因素。

關鍵字

六價鉻 ； 十六烷基三甲基溴化銨 ； MEUF ； 微胞 ； 硫酸鹽 ； 硝酸鹽 ； EDTA

並列摘要

Micellar enhanced ultrafiltration (MEUF) is an effective process for anion removal such as chromium was commonly applied. But the efficiency was affected by the presence of anion and chelating agent in the matrix since anion would compete with chromium and chelating agent would interact with surfactant aggregates used in the MEUF process. Therefore, co-existence of anions (nitrate and sulfate) and chelating agent (EDTA) were evaluated in a single and multi-component aqueous solution for chromate removal by MEUF with cationic surfactant (CTAB) in this study, since nitrate, sulfate and EDTA were commonly used in electroplating industry together with chromium. Under constant transmembrane pressure drop (40 psi), temperature (25oC) andsurfactant/chromium (S/M) molar ratio of 3 (S/M=3mM/1mM) for various co-existed anions and chelating agent concentration, the removal efficiencies of chromate, co-existed anions, surfactant and chelating agent, and relative permeate flux were measured.
First of all, in the single-component anion (only one anion was used) solutions, the order of removal efficiency was: chromate 99.7%>sulfate 84.1%> nitrate 81.0%. These results indicate that chromate anion preferentially binds on the CTAB micelles but less binding power for sulfate and nitrate. On the other hand, in the multi-component anions (chromium together with co-existing anions) solution, the removal efficiency of chromate decreased (99.7% to 97.5%) with the increasing of sulfate and nitrate. In addition, in presence of EDTA in the aqueous solution decreased the removal of anions slightly because net charge on micelle surface may be neutralized by the negative charge group of EDTA. The organic compounds were solubilized at the core of micelle and/or penetrate into the palisade layer of micelle by hydrophobic effects. The retention of surfactant was enhanced by the addition of electrolytes into solution, because the counterion dissolved from electrolyte screened the repulsive electrostatic force between the head groups of cationic surfactant molecule.

並列關鍵字

co-existing anions ； chromate ； micellar enhanced ultrafiltration ； EDTA

參考文獻

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