Preparation Of Coal-based Activated Carbon Foam And Preliminary Study On Its Adsorption Performance Of Organic Pollutants In Coking Wastewater

Coking wastewater is a kind of industrial wastewater with complex composition,various kinds of pollutants,high organic concentration and low biodegradability.The treatment process of coking wastewater with biochemical method as the core is considered to be the most economic and effective method,but a large number of dilution water is needed in the biochemical process due to the characteristics of high organic concentration,poor biodegradability,and big toxicity of the coking wastewater,which results in an increase in the scale of the wastewater treatment facilities,as well as the extension of treatment cycle of wastewater.Thus it is of great theoretical significance and practical value to reduce the high organic load and shorten the treatment cycle by adsorption pretreatment for coking wastewater.This work used Liulin coal as the raw material to prepare carbon foam by atmospheric pressure foaming method,and activated carbon foam was prepared with water vapor as activator.The activated carbon foam with overall structure,better mechanical property,higher porosity and certain specific surface area was further used to adsorb organic matter in coking wastewater to effectively reduce the high organic concentration and improve the biodegradability of coking wastewater,and ultimately,reduce the pressure on subsequent treatment of coking wastewater.The main results are as follows:(1)The effects of foaming temperature on the apparent morphology,bulk density,porosity and compressive strength of green carbon foam were investigated.The results show that with the increase of foaming temperature,the overall pore size,apparent density and porosity of green carbon foam increase first and then decrease,the carbon skeleton structure of green carbon foam becomes denser,the effective stress area,the thickness of ligament structure,and the compressive strength all increase.The effects of carbonization temperature on the apparent morphology,volume density,porosity and compressive strength of carbon foams,as well as the specific surface area and compressive strength of activated carbon foams were investigated.The results show that with the increase of carbonization temperature,the condensation polymerization is more sufficient,the overall pore size of the carbon foam decreases gradually,the bulk density and compressive strength increase,and the porosity decreases.The specific surface area of activated carbon foam first increases and then decreases,while the compressive strength first decreases and then increases.When the carbonization temperature is 750 ~oC,the specific surface area of activated carbon foam reaches the maximum value,which is 443.5 cm~2/g,and the compressive strength is 3.50 MPa.(2)The effects of activation temperature,water vapor flow rate and activation time on the compressive strength,combustion loss rate,porosity,specific surface area and pore structure of activated carbon foam were investigated.The results show that with the increase of activation temperature,water vapor flow rate,activation time,and the compressive strength of activated carbon foams decreases,the loss rate and porosity increase,and the micropore volume first increases and then decreases.When the micropore volume reaches the maximum value,the activation reaction rate is accelerated by further increasing the activation intensity,and the carbon atoms in the pore wall of the activated carbon foam are excessively consumed,resulting in the decrease of the number of micropores in the activated carbon foam.The apparent morphology,specific surface area,pore structure and surface chemical properties of the four kinds of carbonaceous adsorbents were analyzed.Compared with AC,CF-A1,CF-A2 and CF-A3 have pore bubble structures of several hundred microns and higher porosity.The order of specific surface area of the four carbonaceous adsorbents is:CF-A2>AC>CF-A3>CF-A1,among which CF-A2 has the largest number of micropores at 0.8～2 nm.Except for CF-A1,the other three carbonaceous adsorbents all have abundant mesopores,among which CF-A3 has the largest number of mesopores.There is no significant difference in the types of surface functional groups among the four carbonaceous adsorbents,and the order of the relative content of surface oxygen-containing functional groups is:CF-A3>CF-A2>AC>CF-A1.(3)The effects of the four carbonized adsorbents on COD removal rate and biodegradability of coking wastewater were studied.The results show that,compared with AC,activated carbon foam can reduce the resistance of organic matter diffusion in coking wastewater,and has a faster adsorption rate.CF-A2 has the largest number of micropores of0.8～2 nm,which has the highest COD removal rate for coking wastewater.CF-A3 has a larger pore size and a larger number of oxygen-containing functional groups on the surface,which can significantly improve the biodegradability of coking wastewater.When the adsorption time is 120 min,the adsorption process of activated carbon foam has reached equilibrium.The adsorption kinetics of organic compounds in coking wastewater by CF-A2 was analyzed,and the adsorption process is suitable to be described by the quasi-second-order adsorption kinetics equation.By analyzing the composition of organic matter in coking wastewater before and after CF-A2 adsorption,it is found that the relative content of easily degradable organic matter in coking wastewater increases after adsorption,which further verifies that CF-A2 can improve the biodegradability of coking wastewater.