Microstructural and thermal properties of coal measure sandstone subjected to high temperatures

To study the microscopic structure,thermal and mechanical properties of sandstones under the influence of temperature,coal measure sandstones from Southwest China are adopted as the research object to carry out high-temperature tests at 25℃-1000℃.The microscopic images of sandstone after thermal treatment are obtained by means of polarizing microscopy and scanning electron microscopy(SEM).Based on thermogravimetric(TG)analysis and differential scanning calorimetric(DSC)analysis,the model function of coal measure sandstone is explored through thermal analysis kinetics(TAK)theory,and the kinetic parameters of thermal decomposition and the thermal decomposition reaction rate of rock are studied.Through the uniaxial compression experiments,the stress‒strain curves and strength characteristics of sandstone under the influence of temperature are obtained.The results show that the temperature has a significant effect on the microstructure,mineral composition and mechanical properties of sandstone.In particular,when the temperature exceeds 400℃,the thermal fracture phenomenon of rock is obvious,the activity of activated molecules is significantly enhanced,and the kinetic phenomenon of the thermal decomposition reaction of rock appears rapidly.The mechanical properties of rock are weakened under the influence of rock thermal fracture and mineral thermal decomposition.These research results can provide a reference for the analysis of surrounding rock stability and the control of disasters caused by thermal damage in areas such as underground coal gasification(UCG)channels and rock masses subjected to mine fires.

Pore structure characterization and seepage analysis of ionic rare earth orebodies based on computed tomography images

Pore network structure of ore body is a diffusion channel of leaching agent solution that exerts a significant influence on seepage.The ore body structure,pore distribution,pore and throat size,and pore network characteristics of topsoil,weathered,and semiweathered layers of ionic rare earth ore in southern Jiangxi Province were explored in this study.The effect of leaching operation on the pore structure was investigated,and main factors affecting the seepage were analyzed.Results showed that the semiweathered layer presents a dense structure and a small number of unconnected pores.Pores of topsoil and weathered layers are mainly long and narrow column openings with some planar fractures.Even pore distribution and large size span were observed.Compared with the weathered layer,the topsoil layer demonstrates larger voids,smaller average pore volume and equivalent radius,and fewer coordination throats;however,the average equivalent radius of the throat in the topsoil layer is larger and largescale channels exist through ore body vertically.Hence,permeability of the topsoil layer is significantly higher than that of the weathered layer.Colloidal clay minerals migrate easily and the occurrence of silting in the small porosity blocks the throat and significantly decreases the permeability of the ore body in the leaching process.The equivalent radius of the throat is the key to the seepage.Reducing the migration of fine particles is an effective measure to protect the throat and shorten the leaching period.