Study On Adsorption Of Two Typical Industrial Wastewater By Modified Coal Gangue Adsorbent

Coal gangue is a kind of rock associated and symbiotic with coal in the process of formation,and it is a solid waste generated in the process of coal production and processing.China is a large coal country,with coal production accounting for about 50%of global production,while coal gangue emissions account for about 15%of coal production,making it the second largest industrial solid waste in China.The massive accumulation of coal gangue will cause problems such as air,soil and water pollution.Therefore,research on the comprehensive utilization of coal gangue is an urgent difficulty and hot spot in the coal industry.Methyl orange（MO）and malachite green（MG）are widely used in the printing and dyeing industry,producing a large amount of printing and dyeing wastewater containing MO and MG.MO and MG have light stability,thermal stability,resistance to biodegradation and long-lasting retention.Moreover,MO and MG have the effect of"three coherence",which will cause serious harm to the environment.At present,the common methods of treating printing and dyeing wastewater containing MO and MG include biological treatment,chemical treatment and physical treatment.The main inorganic pollutants and organic pollutants in coking wastewater are ammonia and phenolic substances,respectively,which will lead to excessive ammonia nitrogen and COD in the wastewater,and the wastewater cannot meet the Coking Chemical Industry Pollutant Discharge Standard（GB16171-2012）through pretreatment.Therefore,advanced treatment is required.Common advanced treatment methods include:advanced oxidation method,reverse osmosis treatment technology and adsorption method.Among the two typical industrial wastewater treatment methods,the adsorption method is widely used due to its advantages of simple operation and recyclability,but the existing adsorption materials（such as activated carbon,resin,etc.）have the problems of high regeneration cost and limited adsorption capacity.To sum up,the preparation of cost-effective adsorption materials with good adsorption performance is very important for the treatment of printing and dyeing wastewater and coking wastewater.In this study,the modified coal gangue adsorbent（MCGA）was prepared by the zinc chloride modification method using coal gangue as the raw material,and various characterization methods were used to characterize the MCGA to analyze the physical and chemical properties of the MCGA.It was used to adsorb two common main pollutants in typical industrial wastewater,and the adsorption mechanism was studied.Realize the high value-added resource utilization of solid waste,and achieve the purpose of"using waste to treat waste".The main research contents and results are as follows:1.Preparation of MCGA.The main components and loss on ignition of CG were determined by EDTA titration,copper sulfate back titration and ignition subtraction method.The optimum preparation conditions of MCGA were determined by the adsorption effect of MO and MG,TG/DTG,XRD and other characterization analysis as follows:calcination temperature 600℃,calcination time 2 h,impregnation ratio(m _CG:m _{Zn Cl2})2:1.BET,SEM,FT-IR characterization results show that MCGA has a higher specific surface area and a slit-like mesoporous structure（compared with unmodified coal gangue,the specific surface area,total pore volume and average pore size are increased by 51.66%,118.85%and44.38%,respectively）,and its surface has a variety of oxygen-containing functional groups,which is conducive to the adsorption of pollutants in wastewater.Zeta potential analysis and characterization showed that the zero-point potential of MCGA was about 4.68.When p H<4.68,the surface of MCGA carried positive charges,and when p H>4.68,the surface of MCGA carried negative charges.2.MCGA adsorbs MO and MG.Under the optimal preparation conditions of MCGA,when the initial concentrations of MO and MG were both 30 mg·L^-1 and the dosage of MCGA was 4 g·L^-1,the removal rates of MO and MG reached 98.88%and 99.92%,respectively.The adsorption kinetics fitting results show that the adsorption of MO and MG by MCGA conforms to the pseudo-second-order kinetic model;the adsorption isotherm fitting results show that the adsorption of MO by MCGA is more in line with the Temkin adsorption isotherm model,while the adsorption of MG is more in line with the Freundlich adsorption isotherm model.The results of adsorption thermodynamic analysis showed that the adsorption of MO and MG by MCGA was a spontaneous endothermic reaction,and it was an entropy-increasing process.The adsorption mechanism of MCGA to MO and MG includes:diffusion of adsorbate in the pore structure of MCGA,electrostatic interaction,hydrogen bonding,π-πconjugation and cation-πinteraction.3.MCGA adsorbs ammonia nitrogen and COD.The optimum dosage of MCGA in the adsorption process of ammonia nitrogen and COD was 10 g·L^-1 and 24 g·L^-1,respectively,and the optimum p H values were 5 and 9,respectively.The fitting results of adsorption kinetics and adsorption isotherms show that the adsorption process of ammonia nitrogen and COD by MCGA is more in line with the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model.The adsorption process of ammonia nitrogen by MCGA reaches the plateau earlier than the adsorption process of COD,and the adsorption is multi-layer heterogeneous adsorption;the adsorption thermodynamic fitting results show that the adsorption of ammonia nitrogen and COD by MCGA is a spontaneous endothermic reaction,and the solution system tends to be disordered during the adsorption process.The adsorption mechanism of MCGA to ammonia nitrogen and COD includes:diffusion of adsorbate in the pore structure of MCGA,electrostatic interaction,hydrogen bonding,π-πconjugation and cation-πinteraction.4.MCGA treats actual coking wastewater.In order to evaluate the adsorption capacity of MCGA for ammonia nitrogen and COD in the advanced treatment process of actual coking wastewater,the actual biochemical treatment coking wastewater effluent was used for adsorption experiments.When the dosage of MCGA was 36 g·L^-1 and the p H value of the solution was adjusted to 7,the coking wastewater after adsorption can meet the standard of Coking Chemical Industry Pollutant Discharge Standard（GB16171-2012）.