Study On Preparation Of Geopolymer From Low-calcium Coal Gangue In Hengshan Mining Area

Coal gangue is the main solid waste produced in the process of coal mining and washing.Its large accumulation not only takes up valuable land resources,but also causes serious environmental pollution and potential safety hazards.The Hengshan mining area is one of the main coal producing areas in the energy and chemical base of northern Shaanxi.It produces a large amount of gangue every year.The realization of the use of coal gangue materials in the area is the key to achieving low-carbon,green and sustainable development of the regional economy,and it is also the realization of carbon neutrality.With the inevitable requirement of carbon peak,the market prospect is extremely broad.This article takes Jurassic coal gangue from Hengshan mining area as the object,and on the basis of understanding its basic properties,systematically analyzes the influencing factors,optimal preparation conditions,performance characteristics and formation mechanism of geopolymers from coal gangue.Research on the basic properties of coal gangue in the area found that it has the characteristics of high ash(ash yield of 91.86%)and low calcium(CaO content of 0.67%).The main mineral sources of ash are mainly quartz and kaolinite,and it contains mica,calcite,siderite,anorthite,dolomite,etc.The coal gangue is suitable as a raw material for preparing geopolymers.The thermal activation method is used to activate the mineral activity of coal gangue,and it is found that the optimal activation temperature range of the coal gangue is 700?800?;using the pozzolan activity test method to study the activity of calcined coal gangue lime in this temperature range shows 750? is the optimal activation temperature of the coal gangue.The total content of active SiO2,Fe2O3 and Al2O3 in the coal gangue after calcination at 750? for 120 min is 11.93%.Research on the main factors of geopolymer performance found that the raw material aluminum-silicon ratio,raw material calcium-based component content,water glass content and other parameters are the key factors that restrict the geopolymer performance.The results show that when the ratio of aluminum to silicon is close to 0.5,most beneficial to the condensation and forming of geopolymers;when the calcium-based component of the raw material is quicklime or gypsum,with the increase of the calcium-based component,the compressive strength of the geopolymer continues to increase However,when the content of quicklime exceeds 4%,the prepared geopolymer mortar test block will crack and lose its strength.When the calcium-based component is slag,as the content of calcium-based component increases,the compressive strength of the geopolymer mortar test block gradually increases;the addition of water glass provides a suitable alkaline environment for the formation of geopolymers.Research on the calcium-based component in the geopolymer raw material found that when the calcium-based component in the local polymer raw material is quicklime or gypsum,the geopolymer mortar test block prepared with quicklime as the calcium-based component has greater compressive strength.Metakaolin corrects the ratio of aluminum to silicon in raw materials.Calcined coal gangue accounts for a minimum of 74%,but its strength is lower than the compressive strength of cement-made mortar,so it is considered to be compared with ordinary silicon with a compressive strength of 42.5.Salt cement is mixed to improve the overall performance and maximize the use of coal gangue.The orthogonal test shows that when the geopolymer raw material is mixed with cement 1:1,its compressive strength meets the requirements of cement with a compressive strength grade of 42.5.The local polymer raw material has an aluminum-silicon ratio of 0.55,and the cement content is 50%and 2%quicklime content,the 28-day compressive strength of the prepared mortar test block can reach 48.80 MPa,of which the calcined coal gangue can replace 37%of the cement;the raw materials used to prepare the mortar test block are prepared by adding water The finished test cake is tested for setting time and stability according to GB/T1346-2011 Water consumption,setting time,and stability test method for cement standard consistency.The initial setting time is 119 min,and the final setting time is 247 min,and its stability is good.When slag is used as the calcium-based component of the geopolymer raw material,the calcined coal gangue content is 70%,the water glass content is 20%,and the slag content is 20%,the prepared geopolymer mortar test block is 28 d resistant the compressive strength can reach 34.09 MPa;the raw material is made into a test cake and the setting time and stability test are carried out.The initial setting time is 145 min,and the final setting time is 310 min.The initial setting time is greater than 45 min,and the final setting time is greater than 45 min.The setting time is less than the requirement of 390 min,and its stability is good,and there is no obvious cracking and deformation.The prepared geopolymer meets the standard of ordinary Portland cement with a compressive strength grade of 32.5.At the same time,the cost estimate is obtained.The preparation cost is about 215?265 ?/t.