Preparation Of Buckwheat Shell-based Activated Carbon And Its Adsorption Properties For Hexavalent Chromium

The wastewater containing heavy metals will not only seriously pollute water resources,harming aquatic organisms,but also threaten people’s domestic water and endanger human health.Activated carbon has good effect in the treatment of heavy metal wastewater.Buckwheat shell of biomaterials was selected as raw material in this paper.The buckwheat shell-based activated carbon was prepared by the two-step method of carbonization and KOH activation,and the structure and properties of the activated carbon were studied.1.The industrial analysis of the buckwheat hull material was conducted and the content of each component was analyzed.The buckwheat shell-based activated carbon was prepared by pretreatment of buckwheat husks,carbonization,KOH activation,pickling and drying.Scanning electron microscopy(SEM),energy spectrum analysis(EDS)and Fourier-transform infrared spectroscopy(FTIR),X ray diffraction(XRD),Raman spectroscope(Raman),specific surface area instrument were used to analysis the micro morphology,main elements,surface groups,crystalline morphology,specific surface area and pore structure of the buckwheat shell based activated carbon.2.The effects of carbonization time,carbonization temperature,alkali-to-carbon ratio,activation time and activation temperature on the specific surface area,The specific surface area and iodine adsorption value of buckwheat shell-based activated carbon first increase to the maximum and then decrease with the increase of the carbonization time,carbonization time,carbonization temperature,alkali-carbon ratio,activation time and activation temperature,and the yield decreases.The optimum preparation conditions were:carbonization time 3h,carbonization temperature 400℃,alkali to carbon ratio 3:1,activation time 1h,and activation temperature 800℃,pore structure,iodine adsorption value and yield of prepared buckwheat shell-based activated carbon were studied.The buckwheat shell-based activated carbon with a specific surface area of 2578.23 m2/g was prepared.3.The effects of solution pH and initial concentration of hexavalent chromium solution on the adsorption of hexavalent chromium by buckwheat shell-based activated carbon were studied.At low pH value,adsorption amount is larger,with the increase of pH value,the adsorption quantity decreased gradually,When the initial solution concentration is 50 mg/g,the adsorption amount is 49.72 mg/g.When the concentration is low,the adsorption amount varies.The initial concentration of hexavalent chromium solution increases,and when the solution concentration increases to a certain extent,the adsorption capacity no longer increases,and the maximum adsorption capacity is 142.28 mg/g.The Langmuir isothermal adsorption equation and the Freundlich isotherm adsorption equation were fitted to the adsorption of hexavalent chromium solution with buckwheat shell-based activated carbon.The results showed that the Langmuir isotherm model could illustrate effectively the adsorption of buckwheat shell-based activated carbon.According to the Langmuir isotherm adsorption model,the maximum adsorption of hexavalent chromium by buckwheat shell-based activated carbon can reach 142.86 mg/g.Based on the adsorption kinetics study of buckwheat shell-based activated carbon,it was found that the adsorption process conformed to the pseudo-second-order kinetic model.