Study On The Utilization Of Coal Gasification Fine Slag In Soil Improvement And Water Pollution Control

Coal gasification slag is a kind of bulk solid waste discharged in the field of coal chemical industry which has a large annual output and low comprehensive utilization rate.The stack treatment of coal gasification slag will not only occupy land,but also cause harm to the environment.At the same time,China is facing serious problems of land impoverishment and water environment pollution,which have a great negative impact on the national economy and social development.As a kind of coal gasification slag,coal gasification fine slag is characterized by fine and loose structure,rich amorphous carbon content,high reactivity and developed pores,etc.,which has high research value and application prospect in soil improvement and water pollution control.In this paper,the physical and chemical properties of coal gasification fine slag were deeply explored.By selecting reasonable disposal technology,it was applied to soil improvement and water pollution treatment,which provided research methods and theoretical basis for the resource utilization of coal gasification fine slag and the low-cost treatment of ecological environment.The research content of this paper can be summarized as the following aspects:1.The coal gasification fine slag can be used to improve the physical and chemical properties of soil by using its excellent physical and chemical properties such as large specific surface area,rich pore structure and high carbon content.The coal gasification fine slag was mixed with sandy soil in Inner Mongolia for cultivation,pot planting and field experiments to explore the influence of coal gasification fine slag on the physical and chemical properties of the soil and the effect on the emergence rates as well as the yields of crops.The results showed that the mixing of 20%coal gasification fine slag reduces the soil bulk density to 1.05 cm³/g,p H to 8.23,carbon content to increase by10.4 times,cation exchange capacity to 4.68 cmol/kg,saturation water absorption increase by 52.5%and the evaporation rate is significantly reduced.In addition,coal gasification fine slag increased the emergence rates of maize and wheat in pot experiments to 100%on the seventh day,in the field experiment,the growth of maize in the two years improved group was excellent,the grain quality was improved and the yield increased by 18%.2.Based on the characteristics of high activity of non-crystalline siliceous components in coal gasification fine slag,it was applied to increase the available Si content in soil.By testing the content of available Si in coal gasification fine slag under different treatment conditions,comparing the difference of available Si content between coal gasification fine slag with other Si containing materials,it is found that the available Si content of coal gasification fine slag has a stable release under different conditions,about 57.96-62.86 g/kg,and the available Si content of coal gasification fine slag is higher than other Si containing materials（fly ash and steel slag,etc.）.In addition,the results of rice pot experiment showed that coal gasification fine slag could improve the available Si content in soil and promote the absorption of available Si by rice.The total Si content in rice stalk of 5%treatment group was increased by 22%compared with blank control group.3.The abundant pore structure of coal gasification fine slag was used as a sustained-release agent for soil organic fertilizer humic acid.The fixation and slow release of coal gasification fine slag to humic acid was studied by adsorption-desorption-resorption experiment.The results showed that:when the temperature is 293K,p H=7,and the amount of adsorbent added is 2.5 g/L,the maximum adsorption capacity of coal gasification fine slag for humic acid reaches 60.67 mg/g.The adsorption of humic acid by coal gasification fine slag is in accordance with the pseudo-second-order kinetic equation,intra-particle diffusion model and Langmuir isotherm adsorption equation.In addition,the desorption rate of humic acid from coal gasification fine slag was up to 75%,and it had certain recycling characteristics.It is a kind of good humic acid sustained release agent.4.Based on the characteristics of high reactivity of inorganic components and rich carbon content in coal gasification fine slag,carbon-silica mesoporous composite with adsorption characteristics of nitrate was prepared by using coal gasification fine slag as raw material.An in-situ acid leaching method was used to dissolve part of the oxides in the non-crystalline silica microspheres of coal gasification fine slag to leave pores,and the residual carbon components with mesoporous structure in the coal gasification fine slag were retained.The carbon-silica mesoporous composite was prepared successfully.The sample CSMC-O with a specific surface area of 337.51 m²/g was prepared by Box-Behnken experimental design with the maximum specific surface area as the objective.CSMC-O showed adsorption characteristics for nitrate pollutants in water,and the adsorption process was consistent with Langmuir adsorption isotherm equation,intra-particle diffusion model and pseudo-second-order kinetic equation.Adsorption is greatly affected by internal diffusion and adsorbent surface adsorption site.5.A TiO₂/HSAM adsorption-photocatalytic composite was prepared by using the HCl leaching silica amorphous microspheres（HSAM）with mesoporous structures in coal gasification fine slag as the supported substrate for the removal of organic dye pollutants Rh B from water.Through the characterization and performance study of the composites prepared under different conditions,the optimal synthesis conditions were optimized as follows:TiO₂:HSAM load ratio 1:3,p H=2,calcination temperature 500°C.Under this condition,the composite material 1:3-TiO₂/HSAM-2-500 has good removal rate and photocatalytic ability for Rh B,and the total removal rate reaches 88%after 8h of visible light irradiation.In addition,1:3-TiO₂/HSAM-2-500 has better adsorption-photocatalysis ability than 1:3-TiO₂/SAM-2-500 which was prepared with unacid-treated silica amorphous microspheres（SAM）from coal gasification fine slag as supporting substrate and pure TiO₂.