Study On Adsorption Of Aqueous Cd(?)by A Granular 4A Molecular Sieve/Attapulgite Composite

Recently,Heavy metal pollution have been becoming more and more serious.There have been studies on the development of new adsorbent for heavy metal ions.Natural clays have received much attention on heavy metals sorption from contaminated water due to its abundant sources,low cost,and high removal efficiency.However,powdered clay was hard separated from the treated water after adsorption.Therefore,in this study,with attapulgite and 4A molecular sieve having excellent adsorption performance being uesed as raw material,the two granular adsobent was prepared successfully after mixing,shaping and roasting.The preparation process and the Cd(?)adsorption of 4A/ATP were discussed,and the dynamic adsorption experiment was conducted.Then,4A/ATP was modified by sodium carboxymethyl cellulose(CMC),and the adsorption of CMC-4A/ATP for Cd(?)which existed in the mixed heavy metal wastewater was investstigated.The main results ale listed in the following:1)The 4A/ATP was analyzed by XRD and BET characterization.The results indicated that there existed the characteristic peaks of A type molecular sieve when it was calcinated at 400?-700?.The characteristic diffraction peaks of A type molecular sieve disappeared almostly over 800?.Moreover,with the increase of the calcination temperature,material surface the area and the pore volume decreases gradually.2)Adsorption kinetics was found to follow the pseudo second-order model better than the pseudo-first order.The adsorption data fitted best to the Langmuir isotherm model and and the maximum sorption capacity of Cd(?)was 212.8 mg/g.The main adsorption mechanism could be explained to the cation exchange and precipitation.3)The column test results of 4A/ATP showed that when the concentration of Cd(?)in influent was 20 mg/L,the breakthrough and saturation time of 4A/ATP was 22 h and120 h,respectively.Cadmium in saturated 4A/ATP reached 4.63%,which can be recycled by separation and smelting techniques.4)Compared with 4A/ATP,the adsorption capacity of Cd(?)by CMC-4A/ATP was enhanced.The maximum sorption capacity of Cd(?)reached 251.9 mg/g.The breakthrough and saturation time of CMC-4A/ATP was 30 h and 150 h,respectively.Cadmium in saturated 4A/ATP reached 14.01% after column test.5)The ranking of adsorption preference of those three metals on CMC-4A/ATP was Pb(?)>Cd(?)>Zn(?).Competitive adsorption data showed that the presence of Pb(?)or Zn(?)greatly inhibits adsorption of Cd(?)on CMC-4A/ATP.