Evolution Of Glauberite Microstructure Under THC Coupling Action

Glauberite is a kind of soluble rock,the mechanical properties and chemical composition of glauberite will be changed under interaction between groundwater and rock in nature,it will affects the stability of rock engineering,such as landslide,earthquake,dam failure,ground subsidence and earthen materials damage.So the interaction between groundwater and rock is a basic research subject.It affords a new method for estimate of stability of rock engineering,geological disaster prevention and corresponding parameters selection.Glauberite deposits whose value in use is very high are exploited mainly to extract their dissolvable component called sodium sulphate,a kind of very important material of chemical industry.It plays an increasingly important role in social life and civil economy.Therefore,the investigation on the theories and methods about glauberite in situ solution mining can ensure the rational exploitation of mineral resources.In fact,glauberite in-situ solution mining is a process of solid deformation distortion,fluid migration and multi-field coupling of mineral dissolution.So the study on theory of glauberite's solution mining is of great significance on the technology of solution mining.Glauberite dissolution will cause its internal structure change,which will result in the change of the permeability.Focusing on internal structure evolution of glauberite under synthetical coupling reaction as water,heat and chemistry and dissolution permeability,this context makes a number of theory analysis,experimental investigation,and numerical simulation.The main context and results are as follows:(1)In this context,an experimental analysis is made to study the influence of temperature on the internal structure of the inorganic mineral(calcium sulfate)and organic minerals(coal).Furthermore,physical and chemical change mechanism and their affected factors of the main elements of glauberite internal are expounded with a large number of data.The test results show that:when affected by the single temperature field,glauberite internal structure change subtly,when by synthetic reactions as multi-field coupling function,the glauberite internal structure changed will change obviously.(2)Affected by great complexity,the crack evolution of glauberite is totally a complex issue.To begin with,the internal structure of rock samples is important factors that cause the glauberite crack to come into being and expand.Secondly,the temperature plays a paradoxical role in the experiments.On one side,the thermal expansion effect of mineral particles from the temperature will make part of the fissures density,inhibit the crack coming into being and expanding.On the other side,the temperature will influence the thermal cracking depth of mineral particles,which promotes the dissolution of glauberite and the expansion of its fissure.Last,the solution concentration is also a control over the dissolution of glauberite.If the time of solution is extended,the crack will come into being and expand more easily.Synthetically,it is the above multi-factors that cause the glauberite internal crack.In this paper,the experimental study is carried out on the glauberite from salt solution,different in temperature and concentrations,by using the advanced CT technology.At the same time,different crack length and density are analyzed.Test results show that:in the salt solution of different concentration,with the increasing of temperature(18 ??95 ?),small cracks grow and connect to form larger cracks,resulting in a tendency and law in which small cracks decrease,while the larger cracks increase in the overall numbers.It shows that the temperature can promote the internal cracks to grow and connect in glauberite.At different temperature in solution,with the increase of concentration,the number change rate of fissures in various length tends to 0 as the concentration rises.It shows that concentration inhibits the crack coming into being and expanding,or more exactly,the dissolution of soluble mineral in glauberite's internal structure.Therefore,the solubility is an important factor affecting its internal structure.In fresh water,with the increase of temperature,the increasing speed of fissures density reduces from 8/(m2-h)to 4/(m2·h),which shows that temperature help cracks grow and connect.With the increase of concentration,the change rate of crack density tends to 0.It is mainly because that the concentration gap makes the soluble mineral dissolve quickly,which lead to the appearance,growth and connection of cracks.With the increase of concentration,the concentration gap decreases;finally,the decrease for dissolution of soluble mineral inhibits the change of crack density.(3)In order to analyze the glauberite internal structure under THC coupling effects from microscopic view,this part makes a comprehensive analyze on CT scan two-dimensional pictures by experiments.At the same time,a statistics is made on the porosity,pore size,and changing laws about the specific surface area of pores in glauberite microstructure.The change regularity of glauberite damage CT number is tallied up to represents the rupture process of glauberite by the 3D reconstruction of two-dimensional image.Through the statistical analysis of glauberite pore parameters,the paper shows that the porosity,pore size,and the specific surface area of pores in glauberite of different temperature increase with the corrosion time increasing.There exists an obvious gap of glauberite porosity reacted by solution leaching under the condition of different concentration.Setting the common temperature(18?)and the porosity(1.1?1.8%)as the initial conditions,when the glauberite dipped in fresh water for 48h,the porosity will reach 16.62%.It increases nearly 10 times,compared with an initial porosity.Meanwhile,when the glauberite dipped in half saturated and saturated salt solution,the porosity is 3.21%and 1.85%respectively.It increases only 1?2 times compared with an initial porosity.The higher the concentration is,the more obvious the inhibition of salt solution on glauberite pore evolution is.In different temperature water solution,it takes 48h for the glauberite porosity to reach 16.62%;when the temperature is above 65 °C,the porosity is up to 17.89%in 23h leaching;when temperature 95 ?,the porosity will be up to 17.89%in 10h leaching.Temperature whose increase can greatly shorten the dissolution time plays an important role in promoting the glauberite dissolution and pore structure evolution.The CT number shows that:in solution of the same temperature,with corrosion time increasing,average values of CT number are reducing,which indicates that the increase of corrosion time deepen the extent of damage of rock samples;The average values of CT number first change dramatically,then they become more and more slowly with the increase of concentration.It shows that the increase of concentration will strengthen the inhibitory effect on the rupture process of glauberite.The average values of CT number change more and more dramatically with the increase of temperature.It indicates that temperature promotes the rupture process of rock samples.(4)Solubility is the basic characteristics of salt minerals,and permeability is a very important transport characteristic of porous media.As for salt rock of glauberite,the solubility difference between sodium sulfate and calcium sulfate makes the permeability change with the shift of solubility.Therefore,the experimental study on permeability and solubility of glauberite is so important that a profound understanding of mineral characteristics will carry out the in-situ solution mining method for glauberite.In this paper,the dissolution speed and rate of glauberite are experimentally studied and statistically analyzed by using two kinds of test methods as PXSJ-226 ion and CT scan data.Furthermore,this paper studies the permeability of glauberite by using calculation method of fine permeability.Testing results by using ion meter show that different as the temperature of salt solution is,the rules of influence of solution time on soluble mineral dissolution characteristics is the same.With corrosion time increasing,the concentration of sodium ion,calcium ion increases gradually;while the dissolution rate of tested ion reduces gradually.The reason is that with corrosion time increasing,the concentration gap decreases gradually,finally whose gradient inhibit the minerals dissolving.Dissolution rate of calcium sulfate in the solution process also reduces gradually,but the variation is very small.With the increase of concentration(0?3mol/L),the rate of permeability change declines sharply in solution with different temperature.It indicates that the increase of concentration inhibits fissures and pores inside the glauberite from growing,which decreases the rate of permeability change.With concentration increasing,the permeability changes subtly.(5)Because the microscopic pore structure of glauberite determines its physical mechanics macroscopic properties,it is important to study the evolution law of rock pore structure.In this paper,the mathematical model of glauberite porosity's dynamic derivative under the reaction of chemical solutions is established.Setting corrosion test in which 5×5×10mm glauberite specimen are put in freshwater with three kind of temperature as an example,this paper calculates the porosity evolution process of glauberite in different temperature,and studies the change law of the concentration field.The results show that sodium ion,sulfate ion is separate out in the solution.With the increase of reaction time,concentration of ions on the specimen increases first then decreases.And glauberite porosity gradually increases,finally,tend to balance.The higher the temperature is,the less time porosity takes to reach the equilibrium values,which tallies with the experimental results.It indicates that the identity between numerical calculation results and experimental results can simulate factually the change law of mineral corrosion rate changing caused by chemical reaction.It is also true of the dynamic evolution of porosity.