Preparation Of Activated Carbon Modified By Iron Nitrate And Study On Its Adsorption Capacity Of Cu²⁺ And Pb²⁺

Water pollution caused by heavy metal has always been a study hotspot by domestic and foreign experts and scholars, and so far varieties of methods have also been taken for the wastewater treatment containing heavy metal, of which adsorption by activated carbon is widely used. In this study, the modified granular activated carbon was prepared by iron nitrate using immersion-heating technique and then applied to increase the adsorption capacity of Cu2+and Pb2+.The physicochemical properties of granular activated carbon (GAC) and iron nitrate modified granular activated carbon (Fe-GAC) were characterized by analysis methods of specific surface area test (BET), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectroscope, Boehm functional group titration, and X-ray diffraction (XRD), etc. The results showed that the specific surface area and the total pore volume of Fe-GAC were decreased by10.83%and15.53%, respectively, and the average pore size of Fe-GAC increased a little. While the oxygen acidic functional groups increased by17.8%, the polarity enhanced, and iron oxide was coated on GAC. After the modification by iron nitrate, the physical and chemical properties of GAC surface were all changed with a direct effect on its adsorption capacity. We found that the change of chemical properties was the dominating factor for GAC adsorption capacity improvement of Cu2+and Pb2+The influences of adsorption time, dosage, pH, temperature and initial concentration on Cu2+and Pb2+adsorption by GAC and Fe-GAC were investigated, respectively. It was found that when the initial concentration of Cu2+solution was10mg/L and the dosage of Fe-GAC was2g/L, the removal rate of Cu2+reached95.4%, which was27.3%more than that of GAC. As to the Pb2+solution with the same concentration of10mg/L, the optimal dosage of Fe-GAC was2g/L, and the removal rate of Pb2+was98.73%, which was30.15%more than that of GAC. The adsorption process could be divided into three steps:fast adsorption, slow adsorption and dynamic equilibrium. The adsorption equilibrium time of Cu2+and Pb2+by Fe-GAC were180min and120min, respectively.Within pH range of4-10, the removal of Cu2+and Pb2+increased with the increase of pH values, and the adsorption capacity of Fe-GAC was less affected by pH variations than GAC. When the dosage of adsorbents was the same, the removal of Cu2+and Pb2+decreased with the increase of initial metal concentration. Within temperature range of10℃-30℃, the removal of Cu2+and Pb2+increased a little with the increase of temperature, which suggested that the absorption reactions were endothermic reactions.According to the adsorption results of Cu2+and Pb2+, the mechanism and the adsorption isotherm of heavy metal adsorption were studied. The adsorption isotherms using GAC and Fe-GAC both conformed to Langmuir adsorption equation, and the correlation coefficients R2were all more than0.99. The adsorption data of Cu2+and Pb2+could be well described by pseudo second-order reaction kinetics model with R2above0.99.