Adsorption Of Cr(?) In Water By Polyethyleneimine Modified Activated Carbon

Heavy metals are directly discharged without treatment,causing pollution of surrounding water and soil,which seriously threatens human health.At present,there are various methods for treating heavy metal wastewater.The adsorption method is an efficient and economical physical and chemical treatment method,the performance of the adsorbent directly affects the adsorption effect.In this paper,the activated carbon modification treatment improves the adsorption performance of activated carbon on hexavalent chromium(Cr(?)).In this paper,rice hull powder activated carbon(DC)and coal powder activated carbon(MC)were used as raw materials,and modified by polyethyleneimine(PEI)by ultrasonic method,Cr(?)wastewater was simulated by potassium dichromate solution,the adsorption of Cr(?)in potassium dichromate solution by modified activated carbon was studied.The influence Law of PEI quality ratio,wastewater pH value,adsorption time,initial Cr(?)concentration of wastewater and dosage of modified activated carbon on the adsorption performance of modified activated carbon were discussed.The activated carbon was characterized by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and specific surface area and pore size analyzer(BET),the morphology,surface chemical composition,main constituent elements,specific surface area and pore structure of activated carbon were observed.The kinetics,thermodynamics and regeneration properties of Cr(?)in wastewater adsorbed by modified activated carbon were studied.The main results are as follows:(1)The PEI mass ratio has a great influence on the adsorption performance of modified rice hull powder activated carbon,and has little influence on the modified coal powder activated carbon.The adsorption performance of the modified coal powder activated carbon is better than that of the modified rice hull powder activated carbon.With the increase of PEI mass ratio,the adsorption performance of modified rice hull powder activated carbon increased first and then decreased.The modified rice hull powder activated carbon with the PEI mass ratio of 30%(DC-30)had the largest adsorption capacity(5.12mg/g).With the increase of PEI mass ratio,the adsorption performance of modified coal powder activated carbon is almost the same,the modified coal powder activated carbon with a PEI mass ratio of 50% has the largest adsorption capacity(5.71 mg/g);The pH value of wastewater has a great influence on the adsorption of Cr(?)on two kinds of modified activated carbons [DC-30,modified coal powder activated carbon with the PEI mass ratio of 20%(MC-20)].With the increase of pH value,the adsorption performance of the two kinds of modified activated carbons both increased first and then decreased.The difference is that the optimal pH range of MC-20 is wider than DC-30,the optimum pH value of DC-30 is 3.0,and the optimal pH value of MC-20 is between 2.0 and 3.0;The dosage of modified activated carbon and the initial Cr(?)concentration of wastewater will affect the adsorption performance of modified activated carbon.With the increase of dosage,the removal rate of Cr(?)by the two kinds of modified activated carbons increased gradually,and the adsorption capacity decreased gradually.With the increase of initial Cr(?)concentration in wastewater,the adsorption capacity of Cr(?)by modified coal powder activated carbon is getting larger and larger,and the removal rate is getting smaller and smaller.(2)The experimental results show that the initial Cr(?)concentration of wastewater is 20mg/L,the pH value is 3.0,the adsorption temperature is 25°C,the dosage of modified rice hull powder activated carbon is 0.5g/L,and the adsorption time is 3h,the adsorption capacity of modified rice hull powder activated carbon to Cr(?)can reach 19.54mg/g;In the initial Cr(?)concentration of wastewater is 20mg/L,pH value is 3.0,adsorption temperature is 25°C,the dosage of modified coal powder activated carbon is 0.4g/L,and the adsorption time is 4h,the adsorption capacity of modified coal powder activated carbon to Cr(?)can reach 34.43mg/g;According to the results of the characterization,after the modification of the two kinds of activated carbon,the number of holes was reduced,and the surface of the rice hull powder activated carbon was smooth and uniform.After the modification of the two kinds of activated carbon,the presence of surface PEI significantly increased the proportion of nitrogen on the surface.After the modification of the coal powder activated carbon,its surface is loaded with more PEI,which blocks the pores of the activated carbon,so that the specific surface area and pore volume are greatly reduced,and the pore diameter is increased;Through adsorption kinetic experiments,it was found that the quasi-secondary kinetic model can well describe the adsorption process of the two kinds of modified activated carbons,and the intraparticle diffusion model can also describe their adsorption kinetics.According to the adsorption isotherms of modified coal powder activated carbon on Cr(?),the Langmuir and Freundlich isotherm adsorption models were used to linearly fit the experimental data,the results show that the Freundlich isotherm adsorption model has a high degree of fit to the isothermal adsorption data,belongs to the multi-molecular layer adsorption.The adsorption thermodynamics and regenerability of modified coal powder activated carbon were studied,it was found that its adsorption reaction on Cr(?)is a spontaneous endothermic process,and the cycle regeneration was very good.