Abstract
The present work investigated the permeation of indium ions through a polymer inclusion membrane (PIM), prepared with cellulose triacetate (CTA) as the base polymer, tris(2-butoxyethyl) phosphate (TBEP) as the plasticizer and di-(2-ethylhexyl)phosphoric acid (D2EHPA) as the extractant. With 5 M HCl aqueous solution as the strip solution, we observed an initial indium permeability of 2.4 × 10−4 m/min. However, the permeability decreases with time, dropping to about 3.4 × 10−5 m/min after 200 min of operation. Evidence was obtained showing that hydrolysis of CTA occurred, causing a dramatic decrease in the feed pH (protons transported from strip to feed solutions) and a loss of extractant and plasticizer from the membrane, and then leading to the loss of indium permeability. To alleviate the problem of hydrolysis, we proposed an operation scheme called polymer inclusion membranes with strip dispersion: dispersing the strip solution in extractant-containing oil and then bringing the dispersion to contact with the polymer membrane. Since the strong acid was dispersed in oil, the membrane did not directly contact the strong acid at all times, and membrane hydrolysis was thus alleviated and the loss of indium permeability was effectively prevented. With the proposed scheme, a stable indium permeability of 2.5 × 10−4 m/min was obtained during the whole time period of the permeation experiment.
Highlights
Recovery and reuse of metal ions from industrial waste-streams can be of great help for environmental pollution control and for cost reduction
The results show that Supported liquid membrane (SLM) had higher ion permeability while polymer inclusion membrane (PIM) had higher stability in cyclic and multi-hour operations
Polymer Inclusion Membranes with Strip Dispersion (PIMSD), solution solution in in the the feed feed cell cell was was the the same same as as that that for for in the conventional PIM, but placed in the strip cell was a liquid prepared by dispersing HCl aqueous solution (5 M) in a mixture of di-(2-ethylhexyl)phosphoric acid (D2EHPA), Isopar‐L and 1‐dodecanol
Summary
Recovery and reuse of metal ions from industrial waste-streams can be of great help for environmental pollution control and for cost reduction. Because of the water repellence of the hydrophobic membrane, the aqueous feed and strip solutions cannot penetrate into the membrane pores, and stable oil–water interfaces can form to allow for ion extraction and stripping Though it is a promising scheme for practical. The extractant-containing plasticized polymer membrane is placed in between the feed and strip solutions With such a scheme, because the strip solution is usually highly acidic [14] or basic, the long-term operation would not be stable if the polymer membrane is not stable in highly acidic environment, such as being subject to hydrolysis.
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