Study On Microwave-assisted Manganese/magnesium Oxide Modified Activated Carbon For The Treatment Of Heavy Metal Wastewater

In recent years,water pollution events caused by heavy metal wastewater occur frequently.Activated carbon adsorption method is one of the most promising methods to deal with metal pollution.However,ordinary activated carbon has poor selective adsorption capacity and low adsorption capacity for heavy metals.The results show that the metal oxides have many adsorption sites,complex structure,high surface activity and good adsorption performance for heavy metal ions.However,it is difficult for particles such as manganese dioxide and magnesium oxide to precipitate from water,which limits their use.Due to the large amount of agricultural waste in China,the cost of wastewater treatment will be greatly reduced by preparing agricultural waste into usable activated carbon.In this paper,the modified activated carbon（AC）and manganese dioxide（Mn O₂）and magnesium oxide（Mg O）were prepared successfully by microwave heating of oil tea shell.In the experiment,the method of"impregnation-co-precipitation-microwave heating"was used to prepare manganese dioxide-doped activated carbon,magnesium oxide-doped activated carbon,and mixed-doped activated carbon.The adsorption targets were Pb²⁺and Cd²⁺.Orthogonal experiments and discussion of the main influencing factors determine phosphoric acid as the best chemical activator.In the experiment,divalent lead ions and divalent cadmium ions were selected as static adsorption objects.The composite adsorbents were compared with each other.The results showed that the manganese dioxide-doped activated carbon had a Pb²⁺concentration of 50mg/L,a solution volume of 200ml,and an adsorbent mass of 20mg.Under the conditions of oscillating adsorption for 2 hours,the removal efficiency is 99.96%,which meets the national emission standards.Magnesium oxide-doped activated carbon has a Cd²⁺concentration of 50 mg/L,a solution volume of 200 ml,and an adsorbent mass of 20 mg.The adsorption efficiency is 99.94%,which meets the national emission standards.Adsorption under high concentration conditions,the maximum adsorption amount of lead ions by manganese dioxide-doped activated carbon is 364.14 mg/g;the maximum adsorption amount of cadmium ions by magnesium oxide-doped activated carbon is 313.15mg/g.The experiment also studied that the adsorption is worthy of ph.Among them,manganese dioxide-doped activated carbon has the best adsorption effect when the water ph is 6;magnesium oxide-doped activated carbon has the best adsorption effect when the water ph is 7.In order to enable the material to adapt to more complex water bodies and explore the effect of mixed doping,experimentally,co-precipitation method and high-temperature thermal decomposition method were used to prepare mixed-doped materials.When the mixed-doped materials were Mn:Mg=4:1,The maximum adsorption of lead ions is 384.77 mg/g;when Mg:Mn=3:1,the maximum adsorption of cadmium ions is 345.37 mg/g.Experiments show that proper mixed doping can promote adsorption,and excessive doping can inhibit adsorption.