Preparation Of Extraction Gel Film And Its Properties

To enhance the stability of the supported liquid membrane(SLM)process,the polydimethylsiloxane-tetraethyl orthosilicate-di(2-ethylhexyl)phosphoric acid(PDMS-TEOS-D2EHPA)extraction gel membrane(EGM)combining the gel techniques and SLM process was prepared base on the PVDF hollow fiber ultrafiltration membrane.In this study,Ni(?)was used as a representative metal ion to be separated.The basic physical and chemical properties of the prepared EGM were studied via a series of characterization and analytical techniques.The influences of the EGM preparation and coating parameters on its extraction efficiency and mass transfer performance were investigated through a group of simultaneous extraction and stripping experiments.The optimal extraction efficiency and stability of EGM were achieved as the EGM was prepared from the ratio of 10:8.0:0.20 for PDMS/TEOS/DBTL.PDMS concentration of 24 wt.%.coating time of 40 min and a low level relative humidity around 15%-25%.In addition,the influences of the feed phase concentration,flow rates of the two aqueous phases as well as module packing density on the operation stability and Ni(?)mass transfer flux of the EGM prepared from the optimal condition were explored.Results from 9 h experiments show that the optimal extraction efficiency and stability of EGM were achieved in the condition of feed phase flow rate of 1250 mL/min,stripping flow rate of 93 mL/min and module packing density of 14%,respectively.Finally,based on the above findings,the operation stability of the EGM process were investigated and compared with the conventional SLM based on data from 120 h continuous running experiments.The results show that the conventional SLMs suffered 100%flux loss within only 45 h,while the flux attenuation of EGM was merely 34.1%at the end of 120 h.Simultaneously.the initial flux of EGM was found to be conspicuously improved,which was 7.1 times higher than that of the traditional SLM.These results show that the EGM have dual advantages in improving both mass transfer efficiency and long-term operation stability.Furthermore,the facilitated mass transfer mechanism of the EGM for target solute was analyzed and the fixed-site jumping carrier mechanisms were confirmed.This mass transfer mechanism avoids the resistance induced by viscous polymers and the complex membrane structure on mass transfer and therefore,it is benefit for directional migration of the target solutes.