Preparation Of Semi-coke-based Activated Coke And Its Adsorption Performance On Divalent Pb And Cd Ions In Aqueous Solution

When heavy metal wastewater is treated by adsorption way,granular activated carbon based on coal and biomass is widely used as adsorbent.Coal-based granular activated carbon has the advantages of high output,while its preparation cost is high due to the high price of coal.Biomass-based activated carbon has the advantages of low cost,while it can not meet the market demand for very small production scale.Therefore,it is eager to develop high-yield and low-cost activated carbon to meet the huge demand in the field of sewage treatment.Therefore,we try to prepare columnar activated coke,a special activated carbon,with low price and wide source semi-coke powder as the main raw material and carbon dioxide and steam as activator.The main studies include the optimization of the preparation process of activated coke,the evaluation of activated coke removing the Cd²⁺ and Pb²⁺ in aqueous solution,and the adsorption mechanism and kinetics.The specific research contents and results are as follows:（1）In the preparation of activated coke,the time used for microwave carbonization was only 1/35 of the time used for conventional electric heating carbonization.Mercury injection pressure（MIP）analysis shows that the pore permeability of carbon obtained by microwave carbonization is over three times higher than that obtained by electric heating。（2）When the activated coke is prepared bysteam activation（activated coke obtained is marked H₂O-AC）,the optimum conditions are as follows: activation temperature is 850℃,steam flow rate is 2 m L? min-1,activation time is 240 min.Under this condition,the iodine adsorption value of the active coke obtained reaches725 mg?g^-1,the yield is 41.06%,the compressive strength is 43.10 da N,the wear resistance is 82.51%,the specific surface area is 667 m2?g^-1,and the volume percentage of the micropore volume to the total pore volume is 31.76%.The results of FTIR analysis show that the active coke surface contains abundant OH 、-C=O functional groups,and the Boehm titration results show that the content of basic functional groups is 2.0008 mmol?g^-1;and the content of phenolic hydroxyl,inner lipid,and carboxylic acid groups of acid functional groups is 0.4530 mmol?g^-1、0.1923mmol?g^-1 and 1.3961?g^-1,respectively.When activated coke is prepared by carbon dioxide activation（activated coke obtained is marked H₂O-AC）,the optimal process conditions are as follows: the activation temperature is 950°C,the carbon dioxide flow rate is 0.75 L·min-1,and the activation time is 180 min.under this condition,the iodine adsorption value of theactivated coke obtained is 584 mg·g^-1,the yield is 38.33%,the compressive strength is48.53 dan,the wear resistance is 85.15%,the specific surface area is 505 m2·g^-1,and the percentage of micropore volume to the total pore volume is 48.26%.The results of Boehm titration showed that the content of alkaline functional groups was 2.0236mmol·g^-1;the contents of acid functional groups phenolic hydroxyl,internal lipid,and carboxylic acid groups were 0.1968 mmol·g^-1,0.7213 mmol·g^-1 and 1.1233 mmol·g^-1,respectively.（4）The study of adsorption experiments illustrates that the saturated the saturated adsorption capacity of H₂O-AC for Cd²⁺and Pb²⁺is 3.98mg·g^-1and20.90mg·g^-1,respectively.The saturated adsorption capacity of CO₂-AC for Cd²⁺ and Pb²⁺ is 9.8 mg·g^-1 and 48.70 mg·g^-1.The results of FTIR,XRD,TEM,SEM,EDS and XPS analysis show that the adsorption of activated coke for Cd²⁺ and Pb²⁺ is based mainly on physical adsorption and little complex chemical adsorption.（5）The investigation of adsorption kinetics studies show that the adsorption process of H₂O-AC and CO₂-AC for Cd²⁺ and Pb²⁺ is better described by the quasi-second order model.Adsorption data of H₂O-AC and CO₂-AC for Cd²⁺ and Pb²⁺can be fitted well by Langmuir isothermal model.