| Solvent impregnated resin(SIR)combines the advantages of solvent extraction and ion exchange,including good selectivity,simple operation and high efficiency.However,since the extractant in the SIR is not firmly bound to the support of SIR,the extractant is easy to ran away and the capacity of the SIR will decline.In this study,the effect of support properties on the preparation process and the properties of vanadium adsorption of SIR were investigated.The P204 impregnated resin(P204-SIR)was prepared by the suitable support,and then coated by polyvinyl alcohol(PVA)cross-linked with vapor-phase glutaraldehyde.Then the adsorption characteristics of the uncoated and coated SIR for vanadium were comparatively studied.The main conclusions of this study are as follows:(1)The support resin with abundant micropores can quickly achieve the impregnation balance,and the extractant is preferentially impregnated in the small pores through wall-spreading to form monolayer films,which result in the relatively high utilization efficiency of extractant and strong stability of the SIR with abundant micropores.However,the extractant is more easily accumulated in the big pores by means of pore-filling to form multilayer films than in the small pores,which leads to the higher amount of extractant and pore-filling percentage in the SIR,but lower utilization efficiency of extractant and weaker stability of the SIR with abundant macropours and/or mesopores.Among those support resins studied,XAD-7HP resin is a special case.Its total pore volume is the smallest,but the amount of extractant,pore-filling percentage,adsorption capacity and utilization efficiency of extractant is the highest,because of its matrix where the P204 extractant molecules can form hydrogen bonds.Thus,the extractants not only exist in the channel,but also on the resin surface.(2)Although the adsorption capacity of XAD-7HP based SIR is the highest,the stability is poor.In order to reduce the loss of the extractant,the semipermeable film which is prepared by the glutaraldehyde vapor cross-linked polyvinyl alcohol(PVA)is adopted to coat the P204-SIR.The effects of PVA concentration and steam crosslinking time on the adsorption stability of the coated P204-SIR were investigated.It was found that the higher the concentration of PVA is,the better the adsorption stability for vanadium but the worser ion mass transfer can be acheived.The longer the crosslinking time is,the better the adsorption stability can be obtained,but the worse ion mass transfer also is found.In consideration of the adsorption stability and the ion mass transfer,the PVA concentration of 3wt% and the crosslinking time of 30 min were selected to prepare the coated SIR.It was found that the coated film is a cross-linked and reticular film by scanning electron microscopy,and the presence of coated film does not affect the structure and thermal stability of the SIR through infrared analysis and thermogravimetric analysis.(3)The static adsorption test showed that the adsorption capacity of uncoated and coated P204-SIR for vanadium reached the high value when the pH of solution is 1.5~2.0 and the adsorption process of the two kinds of SIRs for vanadium is consistent with the Langmuir isothermal adsorption.The saturated adsorption capacity of them for vanadium are 34.25 mg/g and 37.88 mg/g,respectively.The adsorption capacity of them for vanadium increase with the time,and the uncoated P204-SIR does not reach the adsorption equilibrium until 16 h,but the coated P204-SIR needs more than 20 h to achieve adorption equilibium,indicating that the presence of the coated film has impact on the mass transfer of ions in the solution.The results of the column adsorption test showed that the slower flow rate of the feed liquid or the larger bed volume of the SIR is,the larger breakthrough volume of the uncoated and coated P204-SIR is obtained,which means that the adsorption capacity of them is higher.The coated P204-SIR has bigger breakthrough volume than the uncoasted resin under the same conditions,indicating that the coated film on the SIR can retard effectively the lose of the extractant form the SIR.(4)Kinetic studies showed that the adsorption of vanadium on uncoated and coated P204-SIR is both controlled by chemical reaction but the adsorption rate of vanadium on the coated P204-SIR is smaller than that on the uncoated P204-SIR,suggesting that the presence of the coated film does not affect the rate-controlling step of the adsorption,but affect the adsorption rate. |
