Study On Preparation And Properties Of Coal Slime-Spontaneous Combustion Coal Gangue Ceramsite

For a coal resource-exhausted city,due to the concentration of resources in the past led to a large number of solid waste emissions,the formation of a hundred million tons of coal-based solid waste,encroach on a large amount of land,seriously polluting the environment.At present,there is an urgent need for an independent innovation technology system to transform the hidden dangers of solid waste into resource advantages and achieve resource utilization.Sintered ceramsite is a kind of artificial sand aggregate,which can be used in concrete members to reduce the weight,facilitate the transportation and installation of components,and give it excellent characteristics such as thermal insulation,sound absorption and sound insulation.Traditional ceramsite is mostly fired from natural resources such as clay and shale.As the country’s constraints on resources and environment continue to increase,non-renewable resources have been restricted to exploitation.Therefore,it is the current research trend to gradually replace natural resources with industrial solid waste with similar chemical composition to prepare ceramsite.In this paper,a scheme of preparing ceramsite by using coal slime and spontaneous combustion coal gangue as main materials and adding pore-forming agent is proposed.Firstly,the chemical composition and thermal stability of coal slime and spontaneous combustion coal gangue were analyzed.Secondly,the mixing ratio of raw materials for pottery making was determined by single factor test.Thirdly,the response surface Box-Behnken design(BBD)test was used to optimize the calcination temperature,preheating temperature and calcination time.Finally,the phase change and microstructure of ceramsite were described by XRD,TG-DSC and SEM.The main work carried out and results achieved are as follows:(1)Firstly,the raw material properties of coal slime-spontaneous combustion coal gangue ceramsite were tested,and the chemical composition and mineral composition of coal slime and spontaneous combustion coal gangue were analyzed.Based on the pre-test,the proportion range of ceramsite prepared from coal slime and spontaneous combustion coal gangue was determined.The coal slime was selected as the main raw material,and the spontaneous combustion coal gangue was selected as the auxiliary material.Stearic acid(analytically pure)was used as the pore-forming agent.Through single factor test,the optimum mix ratio of coal slime-spontaneous combustion coal gangue ceramsite was determined,and the reasonable range of firing process parameters such as preheating temperature,preheating time,roasting temperature and roasting time was determined.(2)The response surface Box-Behnken(BBD)design was used to design 17 groups of experiments.The roasting temperature,preheating temperature and roasting time were used as the preparation process factors,and the ceramsite bulk density,1h water absorption and cylinder compressive strength were used as the response values.The response surface model was constructed to reveal the correlation between various factors and interaction terms and response values,and the optimal firing process with the best comprehensive performance was obtained.The R~2 of each quadratic regression model was greater than 0.96,indicating that the model was reasonable and well fitted.When the preheating temperature is 345°C,the preheating time is 15min,the roasting temperature is 1083°C and the roasting time is 23min,the performance indexes of the prepared 500 density grade ceramsite meet the national standard requirements.(3)X-ray diffraction analysis shows that the phase of coal slime-spontaneous combustion coal gangue ceramsite is mainly quartz and vitreous phase,containing a small amount of anorthite and hematite.SEM observation showed that the surface of coal slime-spontaneous combustion coal gangue ceramsite was rough and had no obvious glaze layer,and there were a large number of uniform and less connected honeycomb micropores inside,which ensured the excellent performance of ceramsite.There are 47 figures,25 tables and 80 references in this paper.(4)The benefit analysis shows that the use of coal slime and spontaneous combustion coal gangue as raw materials,in addition to reducing the cost of raw materials and enjoying the preferential tax policies of the state,the by-product waste heat recovery in the process of making ceramsite from high calorific value coal-based solid waste raw materials can generate electricity and heat.The calorific value of coal-based solid waste is not included in carbon emissions and comprehensive energy consumption,which can achieve significant carbon emission reduction.The paper has 47 figures,25 tables and 80 references.