Study On The Mechanism And Properties Of Ecological Cementitious Materials Prepared From High-salt Wastewater And Low-carbon Gasification Slag In Coal Chemical Industry

Coal gasification technology is one of the core technologies for the development of coal industry chain,which has greatly improved the utilization rate of coal.However,coal gasification technology will produce a large number of new wastes,mainly including low-carbon gasification slag and high-salt wastewater from coal chemical industry.The new waste emissions are large,occupying land,polluting the environment,causing waste of resources and other problems,restricting the sustainable development of coal gasification industry.The new type of ecological cementitious material is a kind of green and environment-friendly cementitious material,which is made of silicon aluminum waste as raw material,supplemented by a certain amount of alkaline activator,and adopting a suitable molding process.It has a good application prospect.At present,there are few reports about low-carbon gasification slag and high-salt wastewater in the field of preparing ecological cementitious materials at home and abroad.Therefore,this paper studies the basic properties of low-carbon gasification slag and high-salt wastewater and the mechanical properties and hydration mechanism of low-carbon gasification slag assisted by high-salt wastewater to prepare ecological cementitious materials.The specific research contents and results are as follows:（1）The main chemical components of low-carbon gasification slag were Si O₂,Al₂O₃,Ca O,Fe₂O₃,and so on.The low-carbon gasification slag is mainly amorphous glass,and there is also a small amount of quartz phase crystal mineral phase;in addition,the low-carbon gasification slag is in irregular morphology,with flakes,lumps,and a small number of spherical particles.The surface structure is very dense.The steam-dried high-salt wastewater of coal chemical industry is mainly composed of sodium chloride,sodium sulfate and a small amount of sodium silicate.The high salt wastewater is light yellow and p H value is 9.6 and weak alkaline.（2）The selected activators can stimulate the activity of low-carbon gasification slag to a certain extent,and improve the compressive strength of low-carbon gasification slag based cementitious materials.Among them,sodium hydroxide,cement,calcium oxide and calcium hydroxide play a significant role in promoting the strength of low-carbon gasification slag based cementitious materials,while the effect of sodium silicate is weak.（3）The compressive strength of eco cementitious materials prepared from gasification slag stimulated by coal chemical high-salt wastewater and cement,calcium hydroxide and sodium hydroxide respectively increased first and then decreased.When the content of high-salt wastewater reaches 25%,the excitation effect of cement activated low-carbon gasification slag is the best,and the compressive strength reaches16.7 MPa at 28 days;when the content of high-salt wastewater reaches 75%,the excitation effect of calcium hydroxide activated low-carbon gasification slag is the best,and the compressive strength reaches 14.0 MPa at 28 days;when the content of high-salt wastewater reaches 75%,the activation effect of the system of ecological cementitious materials prepared by low-carbon gasification slag excited by sodium hydroxide is the best,and the compressive strength reaches 19.3 MPa at 28 days.When the content of high-salt wastewater exceeds the optimal content,the development of mechanical properties of low-carbon gasification slag based cementitious materials has a restraining effect.（4）The mechanical properties of high-salt wastewater from coal chemical industry combined with cement or calcium hydroxide and sodium hydroxide to excite low-carbon gasification slag to produce ecological cementitious materials are superior to the effect of the single excitation agent.The compressive strength of high-salt wastewater in cooperation with cement and sodium hydroxide to stimulate the gasification slag to produce ecological cementitious materials gradually increases.When pure high-salt wastewater is mixed,the maximum compressive strength of ecologically cemented materials is 32.6 MPa.The compressive strength of high-salt wastewater combined with calcium hydroxide and sodium hydroxide to stimulate the gasification slag to produce ecological gelling materials first increases and then decreases.When 50%high salt wastewater is mixed,the maximum compressive strength of eco cementitious materials is 61.1 MPa.Compared with the single mixing,the compressive strength of the composite mixing can be increased by 44%.（5）Cement,calcium hydroxide and sodium hydroxide alone can stimulate the hydration of low-carbon gasification slag.When cement and calcium hydroxide are added alone,a small amount of silica gel can be formed by hydration.When sodium hydroxide is added,low-carbon gasification slag will be hydrated to form a small amount of faujasite zeolite phase and aluminum gel.When the cement,calcium hydroxide and sodium hydroxide are mixed together,the hydration of low-carbon gasification slag is further promoted.When the cement and sodium hydroxide are mixed together,the hydration of low-carbon gasification slag is stimulated to generate calcium silicate,while when the calcium hydroxide and sodium hydroxide are mixed together,a large number of faujasite zeolite phases are generated,and the ecological cementitious materials are easy to carbonize.When the high-salt wastewater is added to activate the low-carbon gasification slag,the degree of hydration is further intensified,more hydration products are generated,the connection between the hydration products is closer,and the density of the system is higher.