以中空纖維薄膜接觸器同時萃取金屬陰陽離子之效率與質傳分析

Efficiency and Mass Transfer Analysis on Simultaneous Extraction of metallic Cations and Anions from Water in Hollow-Fiber Membrane

林素霞(Su-Hsia Lin)

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/博士(2002年)

摘要

無資料

關鍵字

中空纖維薄膜萃取 ； 溶劑萃取 ； 重金屬萃取

並列摘要

Abstract
Wastewater discharged from the manufacturing process of printed circuit boards for electroless copper plating , metal finishing industries, and washing effluents of remediation of metal-contaminated soils often contain heavy metals and chelating agents such as EDTA (ethylenediaminetetra-acetic acid). The streams containing strong chelating agents may make conventional treatment methods less efficient, particularly for chemcial precipitation and biodegration. When chelating agent is in excess to metal ions, the solution will contain metallic cations and anions. In this thesis, a non-dispersive solvent extraction process using hollow fiber contactors was proposed to treat the resulting solutions.
In this paper, the mass transfer of simultaneous extraction and stripping of Cu2+ and CuL2- (H4L = EDTA) from aqueous solution with a kerosene mixture of LIX64N and Aliquat 336 in hollow fiber devices was studied. To achieve this goal, the extraction equilibria of CuL2-/HCl-Aliquat 336/kerosene and Cu2+/HCl-LIX64N/kerosene systems were first examined. The kinetics of CuL2- extraction with Aliquat 336 in kerosene was then investigated. Furthermore, mass transfer of single systems, CuL2--Aliquat 336-HCl and Cu2+-LIX64N-HCl, in hollow fiber modules was studied.
The distribution of CuL2- between Aliquat 336/kerosene and HCl solution as well as Cu2+ between LIX64N/kerosene and HCl solution were measured by batch extraction experiments. The non-ideal phenomena were considered on the aqueous and organic phases. It was shown that the equilibrium constants could be expressed as
The initial extraction and stripping rates of CuL2- with Aliquat 336 in kerosene were separately measured using a direct mixing cell. The extraction rate was affected by the concentrations of CuL2- and Aliquat 336 under the conditions studied ([CuL2-] = 0.8~8 mol/m3, [Aliquat 336] = 10~50 mol/m3, [Cl-]s = 100~1000 mol/m3). However, the stripping rate was a function of the concentration of complex in the organic phase only. At 25 oC, the rate equations could be written by
extraction rate: , kf = (5.3±0.3)x 10-6 m9/4/(mol3/4 s)
stripping rate: , kb = (2.6 ±0.15)x 10-71/s
On the basis of kinetic results and nature of the extractant, the reaction between the tertimer of Aliquat 336 ( ) formed in the interface and CuL2- was rate limiting. A plausible mechanism was proposed and the derived rate equation was consistent with experimental results.
Simultaneous extraction and stripping were studied in microporous poly(propylene) hollow fibers. At steady state, mass transfer rate in the single system of Cu2+-LIX64N (HR)-HCl, for example, could be expressed as
where KE and KB are the overall mass coefficients based on the concentration differences indicated above in extraction and stripping modules, respectively. They were given by
In the mixed system, the time-dependent quantity (a) and extraction efficiency (b) were introduced by considering the effect of preferential extraction of Cu2+ on the extraction Cu(II) and mutual interaction of the two extractants in the organic phase. The modified mass transfer model agreed with the experimental data.
In the extraction module, the terms in the right-hand side of 1/KE equation are the resistances of feed layer diffusion, chemical reaction, membrane diffusion, and organic layer diffusion. In the stripping module, the terms in the right-hand side of 1/KB equation are the resistances of stripping layer diffusion, chemical reaction, membrane diffusion, and organic layer diffusion. Based on the equilibrium and kinetic data, and the individual mass transfer coefficients, the fractional resistance of each step to the overall process can be calculated.
For CuL2--Aliquat 336-HCl single system, the resistance of organic layer diffusion and interfacial reaction was ignored in the extraction module. The controlling steps were both aqueous layer and membrane diffusion; the former was dominant at low CuL2- concentration, low Cl- concentration, and high Aliquat 336 concentration. In the stripping module, the contribution of interfacial reaction and organic layer diffusion could be ignored. This process was dominantly governed by membrane diffusion, and aqueous layer diffusion was important only at low stripping acidity, high complex and Aliquat 336 concentrations.
For Cu2+-LIX64N-HCl single system, the resistances of organic layer and membrane diffusion could be ignored in the extraction module. The limiting steps were both aqueous layer diffusion and interfacial reaction; and the former was predominant at low Cu2+ concentration, high aqueous pH, and high LIX64N concentration. In the stripping module, the contribution of interfacial reaction and organic layer diffusion was ignored. This process was dominantly governed by membrane diffusion. The difference of controlling steps of the above two single systems was likely due to the fact that the reaction between CuL2- and Aliquat 336 was faster than between Cu2+ and LIX64N.
For the mixed system, the resistance of organic layer diffusion was ignored in the extraction module under the ranges studied. This process was mainly governed by aqueous layer diffusion at t = 0. However, the resistance of aqueous layer diffusion gradually decreased and of interfacial reaction increased with extraction time, and the main resistance shifted back to aqueous layer diffusion at t > 40 min. In the stripping module, however, the resistances of aqueous layer diffusion and chemical reaction were small. It was governed by membrane diffusion from t = 0 and the resistance of organic layer diffusion gradually increased to equal amount with of membrane diffusion at 30 min.

並列關鍵字

Hollow-Fiber Membrane Extraction ； Extractant Extraction ； heavy metal recovery

參考文獻

Ahmed T.; Semmens M. J., Use of sealed end hollow fibers for bubbleless membrane aeration: experimental studies. J. Membr. Sci., 69, 1-10 (1992a).

Ahmed T.; Semmens M. J., The use of independently sealed microporous hollow fiber membranes for oxygenation of water: model development. J. Membr. Sci., 69, 11-20 (1992b).

Ahmed T.; Semmens M. J., Use of transverse flow hollow fibers for bubbleless membrane aeration. Water Res., 30, 440-446 (1996).

Alexander P. R.; Callahan R. W., Liquid-liquid extraction and stripping of gold with microporous hollow fibers. J. Membr. Sci., 35, 57-71 (1987).

Alonso A. I.; Urtiaga A. M.; Irabien A.; Ortiz I., Extraction of Cr(VI) with Aliquat 336 in hollow fiber contactors: Mass transfer analysis and modeling. J. Membr. Sci., 49, 901 (1994).