應用奈米薄膜程序處理鋁蝕刻廢液中鉬酸及磷酸之截留機制研究

Rejection Mechanism of Molybdate and Phosphate from Etching Wastewater by Nanofiltration Processes

吳嘉瑜(Chia-Yu Wu)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境規劃與管理研究所/碩士(2014年)

https://doi.org/10.6841/NTUT.2014.00371

摘要

本研究利用奈米薄膜 (NF) 對於不同價數離子之選擇性及分離機制，應用於光電面板廠製程排放水中純化、濃縮含鉬與磷酸之蝕刻廢液。本實驗選用兩款奈米薄膜分別為 TS80 (TriSep) 及 DL (GE Osmonics) 進行薄膜特性比較，以連續式循環實驗及單程濃縮試驗，藉由調整進流水 pH 值、操作壓力及系統體積濃縮比 (VCR%)，探討不同水質及操作條件下研究污染物之截留效率，並利用均相溶液擴散模式計算溶液通過奈米薄膜的質傳係數，比較溶質及溶劑通過薄膜之變化趨勢。根據模擬水質實驗結果，設定適當操作參數應用於實場原水處理，依所得之截留效率及出流水水質判斷實廠應用的可行性。
實驗比較兩款市售性能材質相仿之奈米薄膜，TS80 在不同酸鹼度條件下對於鉬酸及磷酸之截留效力皆較 DL 佳，濾液通量及溶質透過能力雖較 DL 低，但在中性及鹼性範圍內，其通量與 DL 相仿；以有機物截留試驗測得 TS 80 之薄膜孔徑 0.752nm 略小於 DL 之 0.809 nm；在薄膜特性方面，以針對陰離子之離子截留效力的選擇上，TS80 具有較負的膜面電位、較小的薄膜孔徑以及較高的親水性，判斷此膜型為較符合本研究目的之薄膜，並選用做為後續截留實驗之奈米薄膜系統操作。
由實驗結果可得，操作壓力在 40 – 120psi 範圍內，奈米薄膜對於研究污染物之截留效率隨壓力升高皆有降低之趨勢，前後截留效率相差約 10%，濾液通量則以線性增加；隨進流液酸鹼值 pH 由 2 提高至 10，溶液中存在研究物種價數變化皆由單價轉變為二價陰離子，兩者呈現之截留率變化趨勢相仿，在酸性條件下之去除效率皆低於鹼性，此結果表現出奈米薄膜對於單價及多價數離子之攔阻效力具明顯差異，並顯示 Donnan 效應在奈米薄膜截留離子之影響顯著。測試奈米薄膜對於不同酸鹼度之進流水質隨體積濃縮截留效率之變化，結果顯示研究污染物之截留率並未因 VCR% 增加而升高，濾液通量亦無明顯下降之趨勢，由於本階段實驗採低壓低進流濃度操作，薄膜對離子的截留效力受體積濃縮造成濃度極化現象影響較小，主要之攔阻機制仍以膜與離子間之靜電效應影響較為顯著。
以模擬實廠水質之實驗結果決定適當之操作條件，進行奈米薄膜應用於實廠原水試驗，測試在不同酸鹼條件下，奈米薄膜對於鉬酸及磷酸皆有良好的截留效率，在高 pH 條件下，Mo(VI) 及 PO4–P 之截留率皆可達 95% 以上。以進流液 pH 值及 VCR% 作為操作變數，針對實廠原水與模擬水質截留效率進行結果比較，結果顯示在測試酸鹼度的範圍內，模擬水質測得濾液通量約為實廠原水的 1.5 倍，然而奈米薄膜對於研究污染物測得截留效率則以實廠原水較佳，且截留率可達 90% 之 pH 範圍較廣 (pH ~ 4 – 10)；隨進流體積濃縮比增加，濾液通量及溶質之透過能力皆有微幅下降之趨勢，研究污染物之截留率增加，結果顯示以奈米薄膜處理實廠原水濃度極化發生較為明顯。

關鍵字

奈米薄膜 ； 蝕刻液 ； 鉬酸 ； 磷酸 ； 均相溶液擴散模式 ； Donnan 效應 ； 電荷排斥

並列摘要

In this study, the advantages of the selectivity and separation mechanism of nanofiltration are utilized to separate and concentrate molybdenum and phosphate with different charges in the etchant solution discharge from the panel plant. Two types of commercial flat–sheet nanofiltration membranes (NF), TS80 (TriSep) and DL (GE Osmonics), were performed in this study and compared with the characteristics and retention efficiency. The experiment investigates the influence of the rejection efficiency by solution pH and operated conditions such as pressure and VCR%. The transfer coefficients were calculated by linear-solution-diffusion model to compare the trend in different filtrate conditions.
The clean NF membranes were characterized by physical-chemical properties, and two types of commercial NF with similar filtration characteristics and negative charge were compared. The results show that, TS80 membrane has a higher retention efficiency under testing pH condition, although the permeate flux was lower than the DL, it had been getting identical in the neutral and the alkaline. The filtration process was conducted with different molecular weight of organics, and Spiegler – Kedem and SHP model were utilized to calculate the membrane pore size. The result showed that TS80 (0.752nm) is slightly smaller than DL (0.809nm). To compare the efficacy of anion removal, TS80 has more negative surface potential, smaller pore size and higher hydrophilicity, and TS80 was used in the nanofiltration system to investigate the operation condition effect.
The experiment results show that the retention rate for the study pollutant decreased slightly about 10% while the operating pressure increased from 40psi to 120psi, and the permeate flux increased linearly. When pH in the tank increased from 2 to 10, species in solution changed into the multivalent ions. The retention trends of molybdate and phosphate were similar. The removal efficiency under basic condition was much higher than that under the acidic condition, and the significant difference between monovalent and divalent ions rejection proved that Donnan effect has a profound impact. The result of volume concentration test show that the targets rejection had no clear change with VCR% increased neither had flux. The concentration polarization caused by concentrating the feed solution did not affect significantly because the low pressure and feed concentration were set. The main mechanism influenced the targets rejection was electrostatic repulsion between charge ions and negative membrane.
The appropriate operating conditions were determined by the simulated solution testing results, and applied to the full scale plant raw wastewater. The experimental results achieved both great retention efficiency of molybdate and phosphate by using nanofiltration system under different pH condition, especially in alkaline condition. The targets rejection was set more than 95%. The pH and VCR% in the tank as the operating variables were used to compare the experimental results of simulated and plant raw water. The comparison shows the permeate flux of simulate solution was 1.5 times more than the plant; however, the testing rejection of two targets in raw water were both better than simulated solution, and could achieve 90% retention efficiency in wide pH range (pH 4 ~ 10); as the volume concentrate ratio increased, the permeate flux and solute permeability of raw water both declined slightly, otherwise the rejection of study targets increased due to the concentration polarization.

並列關鍵字

nanofiltration ； etchant ； molybdate ； phosphate ； Donnan effect ； charge repulsion ； Linear-solution-diffusion-model

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