Preparation And Characterization Of Geopolymer Bricks For Low-silica Tailings

The problem of tailings storage is harmful to the environment.With the increase of stacking quantity,potential safety hazards have increased significantly.Under the combined effects of rainfall,groundwater,and earthquake,it is easy to cause tailings dams to break,thus inducing landslides,debris flow and other geological disasters.The tailings have a chemical composition similar to clay and can be used as potential raw materials for the preparation of geopolymers.Recycling tailings waste can reduce the adverse impact on the ecological environment.However,for most low-silica tailings,the content of Si and Al is low,is not conducive to the formation of geopolymer structure.This research aims to improve the comprehensive utilization rate of low-silica tailings,and explores the possibility of producing environmentally friendly building materials with low-silica slate tailings and basalt tailings as the matrix.By adding fly ash and metakaolin two silica-alumina calibration materials,the tailings-based geopolymer brick samples were prepared under the action of alkali solution,and with the help of compression test,X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),Scanning electron microscopy(SEM)and Atomic force microscopy(AFM)and other analytical testing methods were employed to study the influence of tailings content,alkali solution content and curing time on the macro and micro mechanical properties of geopolymer bricks.The main research achievements are outlined as follows:(1)The compressive strength of geopolymer bricks is controlled by adjusting the content of tailings and alkali solution and the length of curing time.Among them,when the content of slate tailings and basalt tailings are both 50%,and the content of alkali solution is 14% and 16%respectively,and the curing time is 28 days,the geopolymer brick has the best mechanical properties.The compressive strengths are respectively 20.47 MPa and 20.63 MPa,which meet the requirements of MU20 grade in JC/T 422-2007 "Non-fired rubbish gangue brick".Combined with microscopic characterization,the increase of alkali solution content causes crystal such as quartz,clinochlore and diopside to dissolve,and the depolymerization of siliconoxygen tetrahedra and aluminum-oxygen tetrahedron participates in the geopolymerization.The amorphous gel phase increases significantly,and the porosity decreases.The structure becomes denser,so the strength of the geopolymer bricks is significantly improved.(2)The geopolymer gel mainly exists in the form of flocculent particles,and the distribution of the surface stiffness of the sample is different from that of the adhesion energy.The adhesion energy on the higher surface is much higher than the adhesion energy at the edge of the test area.The measured stiffness of the geopolymer gel is about 14～16 n/m,the adhesion energy is about 150～160 fj,and the microscopic Young’s modulus is about 22 GPa.(3)The durability of the geopolymer bricks is verified by testing the water absorption,acid corrosion resistance,freeze-thaw cycle resistance and high temperature resistance of the test sample.The water absorption rates of the geopolymer brick samples based from slate tailings and basalt tailings are 13.4% and 11.9%,respectively.After 20 freeze-thaw cycles,the sample mass loss rates are 1.42% and 0.92%,respectively.The strength loss rates are 7.56% and 7.95%respectively,and the water resistance and frost resistance meet the requirements of the specification JC/T 422-2007 " Non-fired rubbish gangue brick ".After the samples are immersed in a 5% dilute sulfuric acid solution for 7 days,the mass loss rates are 8.29% and2.68%,and the strength loss rates are 25.0% and 9.55% respectively.The acid resistance of the basalt tailings brick sample is better than that of the slate tailings.At a high temperature of800℃,the mass loss rates of the slate tailings and basalt tailings brick samples are 5.82% and5.11%,respectively,and the strength loss rates are 38.90% and 32.90%,which are much lower than the OPC under the same conditions.The mass loss rate of OPC is 30% and the strength loss rate is 80%,indicating that these two tailings-based bricks have better high temperature resistance than OPC.(4)Combined with the microscopic analysis results of high temperature resistance test,it is known that the increase of calcination temperature leads to the partly decomposition of geopolymer gels.The crystal diffraction peak height of the crystal in the matrix decreases first,and then increases.The characteristic peak band broadens and the wavelength becomes shorter,and the porosity increases inside the sample.Evaporation of water and dehydroxylation lead to the formation of a large number of interconnected irregular pores.The microscopic characterization results correspond to the changes in mass and strength change rates at the macroscopic scale.