Preparation and characterization of PDMS-D2EHPA extraction gel membrane for metal ions extraction and stability enhancement

A novel extraction gel membrane (EGM) was prepared via gelation technique by forming polydimethylsiloxane-di (2-ethylhexyl) phosphoric acid (PDMS-D2EHPA) extraction gel layer on the outer surface of PVDF ultrafiltration hollow fibers. This special design aims to achieve both efficient mass transfer within the thin extraction gel layer and improvement in operating stability by preventing the extractant (D2EHPA) loss from EGM. The physical and chemical properties of the prepared EGM were studied via a series of characterization techniques, and the fixed-site jumping carrier mechanism for EGM was confirmed. The influences of the EGM preparation parameters on its performance in nickel separation were investigated systematically. The optimal extraction efficiency and stability of EGM were achieved by the EGM prepared from the ratio of 10:8.0:0.2 for PDMS / TEOS / DBTL, 24 wt% PDMS concentration, 40 min-coating and a low level (15-25%) of relative humidity. Using EGM prepared from these conditions, long-term operating stability was tested and the flux results were compared to that of the conventional supported liquid membrane (SLM) process. It was shown that the flux attenuation of the EGM was only 34.11% within 120 h, while that of the conventional SLM was 100% within 45 h. Simultaneously, the initial flux of EGM was as high as 2436.30 mg m−2 h−1 which was 7.1 times of that of the conventional SLM. The results of this study indicate evident advantages of the novel EGM process over the traditional SLM by showing higher flux and operating stability.