Study On Active Composite Supported Liquid Membrane Based On NI(II)-P204 Extraction System

A hydrophilic polyamide layer was formed on the outer surface of the hydrophobic PVDF hollow fiber microporous membranes by interfacial polymerization method.The organic extractant Di-(2-ethylhexyl)phosphoric acid(P204)was added into the composite layer to prepare the activated composite membrane(ACM).Formation of the hydrophilic polyamide layer reduced the emulsion effect which induced by shear force in the system operation process and,immobilized the membrane liquid effectively.The existence of extractant in the composite layer established an effective channel for the extraction and mass transfer of Ni(II).With the ACM,the stability of supported liquid membrane process was improved and simultaneously,the mass transfer efficiency was promoted.Four different aqueous monomers,m-phenylenediamine(MPD),piperazine(PIP),lysine(Lys),histine(His),as well as the mixture of Lys and His(L+H)were tested to study the influence on activated composite layer.Finally the optimal aqueous monomers L+H were selected.With the carboxyl group of Lys/His,their high hydrophilicity and negatively charged properties,as well as the low organic permeation rate of activated composite layer were beneficial to immobilize the membrane liquid.With an effective membrane area of 1.2×10-2m2,working at a condition as feed flow rate of 0.2 m·s-1,stripping flow rate of 0.05 m·s-1,5hrs extraction rate of Ni(II)by activated composite supported liquid membrane(ACSLM)is 41.0%.The initial mass transfer flux is 308.3mg·m-2·h-1,and the flux attenuation is 15.2%lower than unmodified membrane.Therefore,L+H was considered as the optimal aqueous monomers for the preparation of ACSLM with advantages both in good stability and in mass transfer flux improvement.In addition,the existence mechanism of extractant P204 in the composite layer was investigated systematically in this paper.The chemical reaction based existence mechanism of P204 was proposed based on the data from the analysis of variation of N/P contents using XPS.This hypothesis is verified primairily using FTIR analysis.The new extractant A formed by P204 and aqueous monomers was presented by acid-base reaction.The mass transfer of the extractant A was investigated primarily through a group of experiments.The experimental data indicated that the extractant A can fulfill the extraction of Ni(II),whereas,the Ni(II)-A complex could not be transfer effectively to the stripping solution.