微胞輔助超過濾法去除水中微量之金屬離子

徐勇演

指導教授 ： 莊瑞鑫

元智大學/工程學院/化學工程與材料科學學系/碩士(2002年)

摘要

摘 要
微胞輔助超過濾法(MEUF)分離技術的基本原理是選擇適當的界面活性劑，加入廢水中與污染物形成微胞，再經超過濾薄膜，於特定操作壓力下將污染物去除，得到高品質的透過液。本文即以MEUF法分離水中銫、鍶、鈷、錳、鋅、銅、鉻等七種金屬離子，於水溶液中加入十二烷基磺酸鈉(Sodium dodecyl sulfate ; SDS)，SDS於溶液中形成微胞後，微胞表面具有負電性，金屬離子被吸附於表面，再以UF膜濾除微胞及吸附在微胞表面的金屬離子，則可獲得極高的濾除效率。
實驗中採用PA-TFC(Polyamide thin-film composite)及PES (Polyethersulfone)二種不同材質薄膜，在有/無界面活性劑下，觀察薄膜對金屬離子分離情形。實驗分三部分進行：(1)以導電度法測量界面活性劑之CMC值；(2)批次式分離實驗中，以單/雙/多成分金屬離子與SDS形成微胞，求得最佳S/M(界面活性劑莫耳/金屬莫耳)比值，並調整溶液pH值及加入單價電解質(NaCl)，觀察薄膜對金屬離子排拒率關係；(3)連續掃流式分離實驗中，在不同操作壓力及掃流速度下，觀察薄膜對多成分金屬離子之透過通量及排拒率關係。
結果顯示以導電度法測得SDS溶液之CMC值為8.1 mM左右。批次式分離實驗中，以PA-TFC膜(MWCO = 1000)於304 kPa壓力下，進料溶液未加入SDS時，薄膜對金屬離子之排拒率只有10~20%左右；當進料溶液中加入SDS至大於CMC值後，薄膜對多價金屬離子之排拒率均可達99%以上。當進料溶液中加入NaCl時，會使排拒率降低。在最佳S/M比值條件下，改變操作壓力或調整pH值，薄膜對金屬離子之排拒率變化不顯著，均可達98%以上。另外，以四種不同規格之螺旋纏繞式膜，進行連續掃流式分離實驗，在最佳S/M比值條件下，顯示增加操作壓力及掃流速度均會增加薄膜之透過量，且薄膜對金屬離子之排拒率均可達99%以上。

關鍵字

微胞 ； 超過濾法 ； 界面活性劑

並列摘要

Abstract
Micellar-enhanced ultrafiltration (MEUF) is a promising separation technique for removal of multivalent metal ions from aqueous solutions. In this technique, an appropriate surfactant is added to a polluted water stream to form highly charged micelles onto which the metal ions are adsorbed or bound. Then the solution is processed by an ultrafiltration membrane with pore sizes small enough to block the passage of the micelles and adsorbed ions.
Studies on the removal of metal ions including Cs+, Sr2+, Zn2+, Mn2+, Co2+, Cu2+, Cr3+ from aqueous solutions were performed by the MEUF method. Under the conditions of adding or without adding the model anionic surfactant, sodium dodecyl sulfate (SDS), PA-TFC (polyamide-thin film composite) and PES(polyethersulfone) membranes of different pore sizes were used to evaluate the separation efficiencies of metal ions from aqueous solutions. Experiments made involve the following items: (1) determination of the critical micelle concentration (CMC) of surfactants by the electric conductivity method; (2) determination of the optimum mole ratios of SDS to metal ions (S/M) in the single, binary and multi-component systems and investigation of the factors affecting the membrane rejections for metal ions by adjusting pH and adding NaCl electrolyte to the solutions; (3) investigation of the variation of membrane rejections and permeate fluxes under different transmembrane pressures and cross flow velocities in the multi-component system.
Results show that the CMC of SDS solution is at about 8.1 mM. At the transmembrane pressure of 304 kPa and without adding SDS, membrane rejections of metal ions range from 10 to 20 percent for TFC membrane with molecule weight cut-off (MWCO) of 1000. While adding SDS to solutions at a concentration well above the CMC, membrane rejections higher than 99 percent for multivalent metal ions can be attained. While adding NaCl electrolyte to the solutions, the membrane rejections significantly decrease. Once keeping solutions at the optimum S/M ratios, changing pressure or pH doesn’t obviously affect the membrane rejections. In addition, continuous separation experiments were conducted with four kinds of spiral-wounded membranes. It reveals that the permeate fluxes across membrane increase with transmembrane pressures and cross flow velocities. Under proper operational conditions, rejections above 99% for multivalent metal ions can be attained and the permeate quality meets the regulated discharge standards.

並列關鍵字

HASH(0xb73b3fc)

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