Adsorption And Separation Of Gallium And Vanadium By Macroporous Amidoxime Chelating Resin And Its Mechanism

Gallium is rare-scattered metals,which is widely used in high-tech fields due to its unique physical and chemical properties.At present,90%of gallium comes from Bayer liquor,and vanadium is also leached into Bayer liquor together with Ga,which would have a great influence on extracting high quality Ga metals.When amidoxime resin is used to adsorb gallium from Bayer liquor,vanadium is aslo adsorbed and it is difficult to desorb,resulting in a decrease in the adsorption capacity of the resin for gallium.Therefore,how to efficiently recycle and produce high quality gallium and vanadium has become a hot topic.Aiming at the separation and recovery of gallium and vanadium,a macroporous amidoxime chelating resin was used as adsorbent.The adsorption performance,kinetic and isotherm characteristics of the resin for gallium and vanadium were systematically investigated by static adsorption experiments.The influence of coexisting ions on the adsorption of gallium by the resin was analyzed.On the basis of static optimal experiment,the influence of flow rate and NaOH concentration on the breakthrough curve of gallium and vanadium was investigated by column experiment,which provided theoretical basis for the separation of gallium and vanadium in practice,and adsorption mechanisms was conducted by FT-IRand XPS analysis.The conclutions can be drawn as following:(1)The effects of initial ion concentration,resin particle size,adsorption temperature,sodium hydroxide concentration and adsorption time on the adsorption of gallium and vanadium by amidoxime chelating resin were discussed.The results show that chelating resin had good adsorption selectivity for gallium.When NaOH concentration was lmol/L,the concentration of gallium ion was 200?g/mL,the reaction temperature was 25 ?,the adsorption time was 120min,the resin diameter was 0.3?0.6mm,the resin adsorbent had the best adsorption for gallium,the adsorption capacity of gallium was 1.8 mg/g,the adsorption capacity of vanadium was 0.9mg/g;the saturated adsorption capacity of gallium and vanadium was 27.59mg/g and 20.16mg/g,respectively,indicating that the affinity of resin to gallium was stronger than that of vanadium.The adsorption of vanadium on the resin was obviously inhibited at high alkalinity and low temperature.The optimum separation conditions were NaOH concentration 5-10mol/L,equilibrium adsorption capacity of gallium and vanadium were 1.75-1.82mg/g and 0.18-0.71mg/g,respectively.(2)The analysis of results show that the adsorption process of the resin for gallium and vanadium was well described by the pseudo-second-order model(R2=0.99),which indicated chemical adsorption on resin and the theoretical value was close to the experimental data.The fitting results of intraparticle diffusion model showed that the adsorption process of the resin for gallium and vanadium was controlled by both external diffusion and internal diffusion.The adsorption process of gallium and vanadium were well fitted by Langmuir linear model(R2=0.99),indicating that the adsorption process of gallium and vanadium was monolayer isotropic adsorption;the thermodynamic fitting degree was good,indicating that the adsorption process of resin is an endothermic process and can be carried out spontaneously.(3)On the basis of static optimization,column experiment was carried out and the results show that the optimum separation conditions of gallium and vanadium was temperature 25 ?,NaOH concentration 5mol/L and flow rate 0.05mL/min,the breakthrough curve of gallium appeared "S" shape,the breakthrough curve of vanadium appeared no-idea "S" shape,and the dynamic saturated adsorption capacity of gallium was 18mg/g,the dynamic saturated adsorption capacity of vanadium was 4.69mg/g.The above results show that the resin has stronger affinity for gallium and the separation of gallium and vanadium can be achieved.(4)The results of FT-IR and XPS showed that the adsorption mechanism of the adsorbents for gallium and vanadium was different.The gallium ions in the solution interact with oxime group(C=NOH)in resin.Vanadium ion interacts with oxime group(C=NOH)and amino group(C-NH2)of amidoxime group.Gallium and vanadium combined with oxime group(C=NOH),so a competitive adsorption would happen betwenn gallium and vanadium.