Modification Of D201 Resin Intensified By High Gravity And Its Performance For Cr(Ⅵ) Removal

With the rapid development of in our country,the problem of heavy metal contamination in waters has attracted widespread attention.Hexavalent chromium is toxic,easy to accumulate and difficult to degrade,which poses a serious threat to human health and ecological security.At present,ion exchange adsorption is considered to be one of the most economical and effective methods to treat wastewater containing Cr（Ⅵ）.In this method,the key factor is the mass transfer effect and adsorption efficiency of ion exchange process.As a new process intensification technology,high gravity has shown excellent performance in enhancing mass transfer and mixing between phases.Based on this,high gravity technology was applied to the liquid-solid mass transfer process of D201 resin modification and adsorption of heavy metal Cr（Ⅵ）.The adsorption behavior of D201 resin on Cr（Ⅵ）removal were systematically investigated by using high gravity rotating packed bed（RPB）as process intensification equipment.In order to improve the adsorption selectivity and adsorption capacity of D201 resin,D201 resin loaded nano metal-oxide composites were prepared by modifying the resin fillers with high gravity enhanced micro-mixing characteristics.From the perspectives of adsorption equilibrium,adsorption thermodynamics and adsorption kinetics,the mechanism of D201 resin modified material on Cr（Ⅵ）removal was investigated,which determined the rate control steps,explored the internal factors of high gravity enhanced ion exchange mass transfer process,and analyzed the fundamental reasons for improving Cr（Ⅵ）adsorption efficiency of modified composite.The main research contents and results are as follows:（1）Using D201 resin as a filler,the adsorption behavior of D201 resin for Cr（Ⅵ）in high gravity field was investigated.The results showed that the adsorption equilibrium of D201 resin conformed to the Langmuir isotherm adsorption model.The maximum equilibrium adsorption capacity was 169.56 mg/g and the adsorption heat was 3.425 k J/mol,indicating that the adsorption process was a monolayer endothermic reaction.The adsorption process of D201resin for Cr（Ⅵ）was in accordance with the pseudo-first-order kinetics model,and the intra-particle diffusion was the rate control step.The adsorption rate constant of D201 resin for Cr（Ⅵ）in RPB was 0.0547 min^-1,which was 1.68 times of that in the magnetic stirrer（STR）under the same experimental conditions,indicating that the high gravity field could effectively improve the adsorption rate of Cr（Ⅵ）.（2）In order to improve the adsorption selectivity and adsorption capacity of D201 resin,D201 resin supported nano hydrated iron oxide composite（D201-HFO）was prepared by high gravity ion exchange-surface deposition method.The results showed that the Fe loading and reactivity of D201-HFO firstly increased and gradually decreased with the increase of high gravity factor and liquid flow rate.The optimum condition parameters were high gravity factor of 72.23 and liquid flow rate of 80 L/h.Under these conditions,the average particle size of D201-HFO composites was 10.34 nm,the specific surface area was 17.31 m²/g,and the Fe content was 4.21%.（3）The adsorption process of Cr（Ⅵ） under high gravity field was investigated by using D201-HFO as filler,Cr（Ⅵ）solution as ion exchange object and RPB as process intensification means.The kinetic study showed that the adsorption process was dominated by external diffusion and internal diffusion.The external diffusion rate constant in RPB was 8.554 mg·g^-1·min^-0.5,which was 2.14 times of that in STR.The internal diffusion rate constant was 8.958mg·g^-1·min^-0.5,which was 1.15 times of that in STR,indicating that RPB could enhance the adsorption rate of Cr（Ⅵ）by strengthening the surface diffusion process.Besides,it was found that the presence of co-existing ions NO₃^-and SO₄^2-had an inhibitory effect on the removal of Cr（Ⅵ）by D201-HFO.Compared with D201 resin,D201-HFO had higher Cr（Ⅵ）removal rate and interference resistance of coexisting ions.The maximum adsorption capacity of D201-HFO was 179.14 mg/g.（4）In order to further improve the chemical stability and adsorption capacity of D201-HFO,the supported iron-zirconium oxide nanocomposite（D201-Fe-Zr）was prepared in RPB with hydrated zirconia as the second metal oxide and D201 resin as the carrier.The adsorption behavior of D201-Fe-Zr on Cr（Ⅵ）removal was investigated.At the same p H,the dissolution rate of iron in D201-Fe-Zr was higher than that of zirconium.When the p H value was higher 3,the zirconium basically did not dissolve in D201-Fe-Zr,indicating that the loading of zirconium oxide could improve the chemical stability of D201-Fe-Zr composite.Under optimal conditions,the equilibrium adsorption capacity of D201-Fe-Zr for Cr（Ⅵ）was 193.05 mg/g.XPS analysis showed that the loading of iron-zirconium oxide had stronger coordination with Cr（Ⅵ）,which promoted the adsorption of Cr（Ⅵ）.After five adsorption-regeneration cycles,the removal rate of Cr（Ⅵ）still remained at 90.81%.Thus,D201-Fe-Zr composite had good reusability.