Cr(VI) Extraction Using Aliquat 336 in a Hollow Fiber Module Made of Chitosan

Abstract

Chitosan hollow fiber modules have been prepared and tested for solvent extraction of Cr(VI) from dilute solutions using Aliquat 336 as the carrier. Chitosan membranes serve as a reactive barrier between aqueous and organic phases: both passive and active transport through the membranes are suspected to occur, depending on the experimental conditions and the characteristics of the membrane. The pH of the solution is a key parameter for the efficient extraction of Cr(VI): pH should be maintained below pH 4.5. Extraction kinetics and equilibrium are also controlled by the solvent used to dilute the carrier: kerosene is better than cumene and xylene. The reacetylation of chitosan, resulting from the reaction of acetic anhydride with the biopolymer (after water exchange with methanol as the solvent), is expected to increase its resistance to chemical degradation in very acidic solutions but decreases its extraction efficiency.

Sorption equilibrium of Cr(VI) ions by strong base anion exchangers with pyridine structures

“…Literature data report that the tertiary amine extractants Alamine 336 and Aliquat 336 are effective reagents for the removal of Cr(VI). [3][4][5] The major drawback of solvent extraction is the loss of extractant/solvent in large-scale industrial applications. Solvent-impregnated resins have been used as a new alternative method in various applications for the treatment of metal effluent containing heavy metals.…”

A novel method for obtaining a high‐concentration chitosan solution and preparing a high‐strength chitosan hollow‐fiber membrane with an excellent adsorption capacity

“…The dilute CS solution was collected in a glass beaker and subsequently placed in a water bath with the temperature maintained at 60 C. The solution in the beaker was slowly stirred, and the solvent (i.e., acetic acid and water) in the solution was gradually evaporated off to give a more and more concentrated CS solution. When the concentration of the CS solution was about to reach the level needed to spin the hollow-fiber membrane, as determined from the weight of the content in the beaker, heating was stopped, and the solution was allowed to slowly cool to room temperature (23)(24) C). The beaker was then covered with Parafilm, and the content was degassed in a centrifuge (9000 rpm) for 5 min to remove any air bubbles trapped in the solution.…”

“…For normal CS with a molecular weight of 100,000-300,000 g/mol, homogeneous solutions with CS concentrations at a maximum of 3-5 wt % have been successfully obtained. 22,23,26 To further increase the CS concentration, it has been found that CS could not be adequately dissolved, even after a dozen days, because of the extremely high viscosity, which prevented the polymer chains from being fully opened. However, evidence has indicated that CS hollow-fiber membranes prepared from solutions of CS concentrations up to 3-5 wt % had tensile strengths less than 0.1 MPa and were not strong enough even for selfsupport in their wet state.…”

“…There have been three representative reports in the literature about the preparation of CS hollow-fiber membranes. [22][23][24] The authors of the first two studies 22,23 prepared CS dope solutions with about 3-5 wt % concentrations, and the spun hollowfiber membranes did not seem to have good self-supporting capability in wet state. The third study reported 24 CS dope solutions with concentrations up to 7 wt % by using ''Low-viscosity'' CS, and the strength of the spun hollow-fiber membranes was increased by increasing the crystallinity of CS in the spinning process.…”

Diffusion of biological molecules through hollow chitosan fibers

“…This property is also the key to a number of physical modifications: the protonation of amino groups causes the polymer to dissolve, and this a necessary step in the conditionings of new forms such as gel beads, [1][2][3][4] films (plane membranes), [5][6][7][8][9] fibers, 10,11 and hollow fibers. [12][13][14][15][16] The contribution of diffusion mechanisms to the control of applications involving chitosan-based materials can be explained by the poor porosity of the raw material. [17][18][19][20] For this reason, a major challenge in recent decades has been the conditioning of chitosan in the form of gels to alleviate the impact of porosity limitations.…”