Preparation Of Quaternary Ammonium Modified Sawdust And Its Adsorption Performance Of Cr(?) In Water

Hexavalent chromium(Cr(VI)) can cause various and different environmentalproblems as a common pollutant in water. The disadvantages of the traditional treatmenttechnologe for wastewater with chromium are low efficiency and high cost. Adsorptionof Cr(VI) in wastewater with the advantages of high efficiency and low cost depends onselecting excellent adsorbent with high adsorption capacity and low cost. Agriculturalresidues that are rich in cellulose are the main resorce of low-cost adsorbent.In the paper, the modified sawdust with amidogen was pepared by amine reactionwith raw sawdust using N, N dimethyl formamide(DPM) as dissolvent,epichlorohydrin(EPC) as etherifying agent, diethylenetriamine(DETA) as cross-linkingagent, triethylamine as grafting agent. Factors of preparing the modified sawdust suchas DETA dosage, triethylamine dosage, contact time and tempepature of graftingreaction, were optimized by Cr(VI) removal efficiency and production yield. Sawdustsamples before and after modification were characterized by FT-IR, SEM, BET. Theexperiments show that the optimal preparation conditions of modified sawdust were asfollows:3.0g sawdust, DPM20mL, EPC15mL, DETA5mL, triethylamine10mL,grafting temperature80?, grafting time180min. With FT-IR spectra analysis, theamino group was introduced onto the surface of raw sawdust. BET results showed thatspecific surface area of sawdust after modification was raised to0.7507m2/g from0.1224m2/g.In order to test the adsorption property of modified sawdust for Cr(VI), static anddynamic column experiments were conducted. In the static tests, sorption factorsincluding pH, modified sawdust dosage, initial Cr(VI) concentration, contact time,temperature and coexistence of anion were investigated and regenetation test wasconducted. Column test in different flow rate was carried out in the dynamic experiment.The static experiment showed that the Cr(VI) adsorption capacity on the raw sawdustwas only around6.25mg/g, while after modification to212.5mg/g. The optimalmodified sawdust dosage was2g/L during pH3~6in60mins, and the adsorptioncapacity inproved with temperature increasing and decreased with existence of coexistanions, CO32-> SO42-NO3-> Cl-. The stability of Cr(VI) adsorption capacity inregeneration test indicated the synergy of ion exchange and redox. In the dynamic test,breaking point went down with high flow rate. The mechanism of Cr(VI) adsorption by modified sawdust was studied. Kineticmodels including pseudo-first-order, pseudo-second-order and intraparticle diffusionmodels were used to fitting the adsorption kinetics data. The results showed that theadsorption process was consistent with pseudo-second-order kinetic equation anddetermined to be chemisorptions by activation energy of38.46kJ/mol. The adsorptionisotherms fitting of adsorption process of Cr(VI) on the modified sawdust which wasfound to be fitted well to the Langmuir isotherm model was described by Langmuir andFreundlich adsorption models. The thermodynamic parameters was abtained. Thenegative standard Gibbs free energy and positive standard enthalpy change indicated itsspontaneous and endothermic nature of adsorption.