Optimal Preparation Of Activated Carbon Modified By Manganese Oxide And Its Adsorption Of Cd(?)

In recent years,water pollution incidents caused by cadmium(Cd(II))have occurred frequently.Activated carbon adsorption method is one of the most promising methods to treat heavy metal pollution.However,ordinary activated carbon has poor adsorption performance for heavy metals.The results show that MnO2 has many adsorption sites,good surface activity and good adsorption properties for heavy metal ions,but MnO2 particles are difficult to precipitate from water,limiting their application.In this subject,activated carbon loaded with manganese oxide was modified by potassium permanganate impregnated-roasting method.,and the preparation process of modified activated carbon(MOAC)was optimized by orthogonal experiment.It is expected to improve the sedimentation performance of manganese oxide particles while improving the adsorption performance of activated carbon The MOAC was characterized by SEM,BET,XRD,EDX,FTIR and XPS.Through static adsorption experiment,the adsorption effect of Cd(?)was researched as a function of various factors such as pH value,initial concentration,dosage of adsorbent,adsorption time and coexisting ions.Besides these,the regeneration studies of MOAC after saturation adsorption was carried out and the mechanism of adsorption was analyzed..The results indicated that the optimized conditions were as follows:impregnation time of 7h,KMnO4 mass fraction of 2.7%,roasting temperature of 470?,roasting t-ime of 2.5h..The adsorption capacity of activated carbon before and after modification was 3.37mg/g and 84.15mg/g,and the adsorption performance of modified activated carbon was improved greatly.The characterization results show that the zero-charge point of the activated carbon decreases and the electronegativity increases,and the surface roughness increases and the specific surface area suddenly decreases.The manganese oxide is loaded on the surface of MOAC by ?-MnO2 with a large number of hydrocarbyl functional groups.The static adsorption results show that pH value has a significant effect on the adsorption of Cd(?)by MOAC.When the pH value is between 2 and 4,the removal rate increases rapidly.When the pH value is between 4 and 6,the rate increases slowly.the pH value is between 6 and 7,the rate basically remain the same.While the initial concentration solution is 50mg/L and the optimum dosage of adsorbent is 0.5g/L,the removal rate of Cd(?)is 82.52%.The adsorption process of Cd(?)by MOAC included a rapid adsorption in early period,a slow adsorption in medium process and a equilibrium adsorption in later stage;the interfering effect of coexisting anions followed the order:Al3+>Ca2+>K+>Na+.with the decrease of coexisting ion radius and the increase of charge number,the inhibition of adsorption is enhanced.The regeneration results showed that HCl was better for the adsorption saturation activated carbon.In the concentrationt of 0.1mol/L,the regeneration rate was 72.47%.The regeneration rate was still 46.29%after four adsorption and regeneration.The study on adsorption kinetics and thermodynamics indicated the adsorption process of Cd(?)by MOAC are in accordance with pseudo-second-order equation and Langmuir isothermal model well.The adsorption rate of Cd(?)by MOAC is controlled by chemical adsorption,which means the existence of electrons sharing or transferring between adsorbate and adsorbent.Thermodynamic parameters reveal that low temperature is conducive to the adsorption reaction,and adsorption is exothermic,spontaneous process.The characterization of MOAC before and after adsorption demonstrates that Cd(?)is adsorbed onto the surface of MOAC,which mainly exists in the form of-Cd-O on the surface of adsorbent.It is concluded that the oxygen atoms in the-OH group have lone pair electrons,which are easily shared with heavy metal ions electronic.Therefore,the adsorption mechanism of Cd(?)by MOAC includes ions exchange,electrostatic attraction and coordination complexation.