Preparation Of Magnetic Hydroxylated Chitosan (MHKCTS) And Its Adsorption Performance And Mechanism For U (Ⅵ) And Cr (Ⅵ)

In recent years, with the development of nuclear industry, the uranium miningand processing industry is increasingly prosperous，which producing more and moreuranium-bearing wastewater. Due to the special dangers of uranium-bearingwastewater, its treatment method makes much attention on the one hand, on the otherhand, how to recycle uranium become a hot topic of many researchers because of thegrowing shortage of uranium resources. Compared with uranium contamination,chromium pollution has no radioactivity, but the high toxicity, carcinogenicity andmutagenicity of hexavalent chromium has aroused people’s wide attention, andsolving the problem of chromium pollution is imminent.Chitosan was transformed into hydroxamated chitosan by α-ketoglutarate andhydroxylamine hydrochloride, then glutaraldehyde was used as crosslinker to developa novel sorbent—cross-linked magnetic hydroxamated chitosan (MHKCTS) forremoving U(VI) from radioactive wastewater and Cr(VI) from heavy metalwastewater after soaking in alkali liquor. The adsorption experiments were carried outin batch systems，and different factors such as pH, reaction time, initial concentrationwere considered. The kinetic and thermodynamic of the adsorption process wereanalyzed respectively, and explored their adsorption mechanism through a variety ofmeans.The results showed that the optimum pH was6.0of adsorption uranium. Theremoval rate of uranium was improved by the extended period of time and increasedamount of adsorbent, however, was decreased by the increased initial concentration.The removal of uranium was less affected by cations of calcium and magnesium ions,but great influence by anions of sulfate and carbonate ions. The kinetics of adsorptionprocess followed better the pseudo-second-order model. The adsorption process fittedLangmuir isotherm model better than the Freundlich equation, which indicated theprocess belonged to monolayer adsorption. The thermodynamic parameters (△H,△G and△S) demonstrated that the adsorption of U(VI) on MHKCTS was anendothermic, spontaneous process, the uranium (VI) was adsorbed by coordinated action of hydroxamic group with uranium (VI).The adsorption of chromium experimental results showed that optimum pH was4.0and equilibrium was established90min. The kinetics of adsorption processfollowed well the pseudo-first-order model (R2=0.9975) and pseudo-second-ordermodel (R2=0.9999), indicating that there were both physical and chemical action. Thethermodynamic parameters demonstrated that the adsorption of Cr(VI) on MHKCTSwas an endothermic, spontaneous process too, the chromium (VI) was adsorbed byelectrostatic forces of hydroxamic group protonation and dichromate ions.