Study On The Preparation And Properties Of Chitosan Adsorbent

Heavy-metal ions are often toxicity at low concentrations, so they must be removed from the waste water. Most of studies focus on Cd(II) absorbent-chitosan, a material containing a high level of amine functions. In this study, I have investigated the dissociation constants of chitosan in aqueous solutions, fabricated porous chitosan beads, synthesed cross-linked adsorbent and studied the Cd(II) adsorption behaviors and mechanisms by chitosan adsorbent.Some conclusions are obtained:(1) Potentionmetric behavior of chitosan was well described by the Katchalsky s equation. The dissociation constant varied with the ionic strength and depended on the extra salts, and its corresponding value was 6.17(K 6.382 (O.lmol ?L/'NaClX 6.390 (O.lmol ?I/'KCIX 6.592 (0.5mol ?I/'NaClX 6.725 (0.5mol ?I/'KCl) .respectively.(2) The compositions and bonding energies of elements C, O and N in the surfaces of chitosan and Cd2+-chitosan chelate have been investigated by XPS. An adsorption mechanism was proposed that the adsorption occured through a chelating reaction between Cd2+ and -NH2 on the surface of chitosan.(3) The method of preparing porous chitosan beads was: chitosan was dissolved in 4wt% acetic acid to produce a viscous solution with approximatly 4wt%, and dropped into NaOH aqueous solution from 0.5 to 2.5mol/L.(4) Synthesis of cross-linked chitosan beads was devided into 2 steps:firstly the wet chitosan beads were reacted with epichlorohydrin, which enhanced rifidity of chitosan beads; secondly the mid-products cross-linked with polyethylenemine, which improve the adsorption power.(5) FTIR was used to study the structure of chitosan beads, mid-products of chitosan and cross-linked chitosan adsorbent.(6) The experimental results showed pH and salt ions seriously influenced the adsorption properties. Its adsorption efficiency was optimal when pH during 5.5-7.0, the maximum adsorption capacities for Cd ( II ) was 213mg/g . Under the concentration of 0.0 to l.Omol/L, adding salts improved the abilities to adsorb Cd ( II) .(7) Fixed bed column systems showed that cross-linked chitosan column systems was fit for remove Cd (II) . This simplified approach offers an easy prediction of cross-linked chitosan adsorbent for further industrial applications.