Adsorption Experimental Study On Removing Cr(â…¥) Fromsimulated Wastewater By Walnut And Peanut Shells

The thesis adopted agricultural and forestry waste walnut shells and peanut shells asadsorbent, chromium-containing simulated wastewater was treated with these adsorbents. Bystatic and dynamic adsorption experiment, adsorption characteristics on Cr（VI） fromsimulated wastewater was studied.The static adsorption experiment results show that:（1） Treating50mL wastewater whoseconcentration of Cr（VI） is20mg·L^-1, when the producing area of walnut is Xinjiang, thetemperature is25℃, the diameter is1.0^-1.6mm, the adsorbent dosage is1.0g, the optimumcondition is pH=1.0, oscillation speed is200r/min, adsorption time is about180minutes, theadsorption rate of Cr（VI） can be up to98.68%, the concentration of Cr（VI） is0.184mg·L^-1after adsorption, which meets the Integrated wastewater discharge standard GB8978^-1996standards for a class of pollutants.（2） Treating50mL wastewater whose concentration ofCr（VI） is20mg·L^-1, when the producing area of peanut is Guangdong、the temperature is25℃,the diameter is1.6-2.5mm, the adsorbent dosage is1.0g, the optimum condition is pH=1.0,oscillation speed is200r/min, adsorption time is about180minutes, the removal rate ofCr（VI） can be up to99.08%, the concentration of Cr（VI） is0.144mg·L^-1after adsorption,which meets the Integrated wastewater discharge standard GB8978^-1996standards for aclass of pollutants.（3）The adsorption of Cr（VI） rises as the temperature rises. Theiradsorption isotherm are type I, and the result shows the Freundlich model can reflect theprocess of adsorption better than the Langmuir model.（4）After walnut and peanut shellsreused ten times, the removal rate of Cr（VI） is still more than86%and90%, and the walnutand peanut shells after regeneration whose adsorbability has little reduced, they can at leastrecycle six times.（5）From the kinetics equations we can see: the fitting related coefficient R²of the pseudo-second-order model is0.9993, it is better than the R²of the pseudo-first-ordermodel and Elovich model.The dynamic adsorption experiment results show that:（1） Treating wastewater whoseconcentration of Cr（VI） is20mg·L^-1, when the producing area of walnut is Xinjiang, thediameter is1.0^-1.6mm, the adsorbent dosage is5.0g, the optimum condition is pH=1.0, theflow rate is3.0mL·min^-1, the removal rate of Cr（VI） can be up to98.88%, the concentration ofCr（VI） is0.224mg·L^-1after adsorption, which meets the Integrated wastewater dischargestandard GB8978^-1996standards. From the dynamic adsorption break through curve ofwalnut shells, penetrative point on142min, failure point on810min, Thomas model canreflect the characteristics of the adsorption process well, the dynamic saturated adsorption capacity of walnut shells is6.1mg/g. The desorption completed within60min, the highestpoint of concentration was found at about9min.（2） Treating wastewater whose concentrationof Cr（VI） is20mg·L^-1, when the producing area of peanut is Guangdong, the diameter is1.6-2.5mm, the adsorbent dosage is5.0g, the optimum condition is pH=1.0, the flow rate is3.0mL·min^-1, the removal rate of Cr（VI） can be up to99.08%, the concentration of Cr（VI） is0.184mg·L^-1after adsorption, which meets the Integrated wastewater discharge standardGB8978^-1996standards. From the dynamic adsorption break through curve of peanut shells,penetrative point on219min, failure point on1312min, Thomas model can reflect thecharacteristics of the adsorption process well, the dynamic saturated adsorption capacity ofpeanut shells is9.4mg/g. The desorption completed within90min, the highest point ofconcentration was found at about10min.The modified adsorption experiment results show that:（1）Walnut shells wereimpregnated24hours with phosphoric acid whose concentration（） is50%, removing theliquid part after mix well, drying at50℃, and further to200℃heating for90min, thenremoving phosphate ion with distilled water, drying at50℃in the end, the adsorption effectof modified walnut shells is the best under these conditions. The modified walnut shellsadsorbed50mL wastewater whose concentration of Cr（VI） is200mg·L^-1, removal rate maycome up to95.60%, but only77.60%for unmodified walnut shells.（2） when the peanut/modifier ratio is1:5, ethanol/ZnSO₄ratio is1:5(concentration of ZnSO₄is0.1mg·L^-1), wasperformed at80℃in constant water bath for4hours,the adsorption effect of modified peanutshells is the best under these conditions. The modified peanut shells adsorbed50mLwastewater whose concentration of Cr（VI） is200mg·L^-1, removal rate may come up to92.89%, but only88%for unmodified peanut shells. Relatively speaking, the adsorptioneffect on Cr（VI） of modified walnut shells is better than modified peanut shells’.Finally, the residues of the walnut and peanut shells were studied by using SEM andFTIR, it indicated that we can’t explain and describe it properly by single chemical orphysical adsorption, the process of Cr（VI） adsorption on walnut and peanut shells was a verycomplicated process include the redox reaction and adsorption.