Adsorption Mechanism Of Organic Pollutants In Coking Wastewater On Coke Powder

Coal chemical industry,a new way to realize coal from single fuel to both fuel and material,has been developed rapidly in China.As an important part of coal chemical industry,coking industry shows great significance in development of steel and its downstream industry.However,high pollution in coking industry not only limits its further development,but also takes negative effects on our living environment,especially in coking wastewater.Adsorption is widely used in coking wastewater treatment,and common adsorbents include activated carbon,resin,fly ash,and so on.But these adsorbents have not been widely used because of its high adsorbent cost,poor adsorption efficiency and secondary pollution.Therefore,it is necessary to find new green and efficient adsorbent.Coke powder（CP）is a kind of porous coal-based material,which is produced after high temperature pyrolysis of coking coal in dry quenching process.Adsorption mechanism of pyridine,quinoline and indole,typical NHCs in coking wastewater on CP,was studied in this paper.CPs,prepared by different modification methods,was characterized by surface morphology,physical-chemical properties.Adsorption isotherm,adsorption rate control process and spontaneous spontaneity of CP were highlighted in this paper.The main conclusions are:（1）The structure of CP is mainly composed of graphite sheets,rimmed with fundamental groups（i.e.C-C,C=O,C-O,π-π*）,on the edge for ming connected mesoprous network.The micropore capacity of CP is only about 10 % of its total pore volume.The specific surface area（SSA）of CP-Raw was 25.36 m2/g,which would increased by 16.84%-28.08% with modification.HNO₃ will dissolve some minerals containing Ca and Mg in CP,resluting in the smooth surface of CP-HNO₃.Otherwise,HNO₃ will increase the content of C-O on CP-HNO₃ by oxidation.CP modified by H2SO4 is similar to CP-HNO₃,but its content of oxygen-containing functional group is lower than of CP-HNO₃.NaOH could react with some alu minumsilicate minerals in CP,and the dissolve-precipitation process resulted in more developed SSA and rich composition than CP-HNO₃ and CP-H2SO4.Microwave treatment makes the decomposition of oxygen-containing organic matter in CP,resulting in more abundant pore and graphite structure.（2）Adsorption behavior of NHCs on CP can be well fittered by Freundlich model,but adsorption of pyridine is better fittered by Langmuir model.Adsorption of pyridine on pyridine was do minated by surface-adsorption,while the adsorption behaviors of quinoline and pyridine were do minated by layer-adsorption with surface-adsorption.CP has significant adsorption effect on NHCs,and its maximum adsorption capacity of pyridine,quinoline and indole reached 15.56 mg/g,9.26 mg/g and 15.28 mg/g,respectively.The analysis of four interaction mechanism shows that the hydrophobic force may contribute to the adsorption process,but there are also van der,electrostatic interaction and π-π EDA interaction.CP physical adsorption and chemical adsorption existed in this adsorption,and their contributions need to be further studied.（3）Adsorption process of NHCs on CP can be well fittered by lagergren second-order dynamic model comparing with lagergren first-order model and Weber diffusion model.Adsorption process mainly involves surface diffusion and diffusion of pores,do minanted by surface diffusion.The adsorption rate of NHCs on CP is fast.The first stage（0-1 min）is do minanted by surface diffusion,and the adsorption content of NHCs can reach 72-94% of equilibrium adsorption.The second stage（1-10 min）is do minanted by the diffusion stage of the pores,and the adsorption amount of NHCs reaches 4-17 %.（4）CP-MW has the best adsorption effects in CPs.Heating helps increase the adsorption content of pyridine on CP,but decrese that of quinoline and indole.The average activation energy on adsorption of pyridine,quinoline and indole are 12.55 kJ/mol,22.51 kJ/mol,12.52 kJ/mol,respectively.NHCs can be adsorbed on CP easily,resulted by physical adsorption.△G0 of pyridine,quinoline and indole are all positive,which implys adsorption process of NHCs is non-spontaneous.The adsorption of pyridine on pyridine is an endothermic reaction,which increases the degree of thermodynamic confusion.The thermodynamic behavior of indole and quinoline on CP is the opposite of pyridine,belonging to the exothermic reaction and decreasing degree of thermodynamic confusion.