Analysis Of Macro-Micromechanical Characteristics And Kinetics Dissolution Mechanism Of Acid-Corroded Sandstone

With the increasing scale of human engineering activities and the rapid development of industrial modernization,the problem of environmental pollution has become increasingly aggravated,which in turn has led to the problem of acid rain that greatly affects the long-term stability of rock engineering.The paper takes feldspathic sandstone as the research object,carries out a series of rock macrofabrication tests under acidic solution corrosion,analyzes the physical,chemical and mechanical properties and microfabrication structural characteristics of rock samples under the action of different acidic environments;establishes the chemical damage variables of sandstone fine structure based on porosity change and the kinetic model of acid-rock reaction based on chemical reaction principle.The main research contents are as follows:(1)With the help of static immersion accelerated corrosion test,the mass of rock samples,the cation concentration of acid solution and the pH change law during the immersion process of pH=2,5 HCl and H₂SO₄solutions were analyzed.The results showed that:with the weakening of acidity and the extension of corrosion time,the mass growth rate of wet rock samples showed a trend of decreasing,then increasing and then decreasing,and the mass loss rate of drying rock samples showed a trend of gradually increasing;the dissolution rate of Na⁺,K⁺,Mg²⁺and Ca²⁺in the solution at each stage showed a trend of gradually decreasing;the pH value of acidic solution showed a trend of gradually increasing in general,and the acidic solution with pH=5solution,showing a trend of conversion to neutral;pH=2 HCl solution showing a trend of conversion to weak acid;pH=2 H₂SO₄solution showing a trend of conversion to medium to strong acid.(2)The microstructural characteristics of sandstone were investigated by electron microscopy and energy spectrum analysis,which showed that the roundness of mineral particles gradually increased,the connection between mineral particles gradually evolved into a loose porous state,and the pore connectivity gradually increased after the sandstone was corroded and soaked in acidic solution.The weight percentages and atomic percentages of Na,K,Mg,Ca,Al,Fe,etc.of the rock samples gradually decreased with the enhancement of the acidity of the solution and the extension of the soaking time.(3)The analysis of the uniaxial test results shows that the stress-strain curve of sandstone subjected to acid corrosion can be divided into four stages:compression-density,elasticity,plasticity and damage.As the pH of corrosion solution decreases and the immersion time increases,the compressive dense phase of the curve gradually grows,the elastic phase becomes shorter,the axial peak stress and elastic modulus gradually decrease,and the axial peak point strain gradually increases.Under the effect of acid solution dissolution,the brittle characteristics of sandstone gradually weakened with the prolongation of corrosion time,while the ductile characteristics gradually increased.(4)Based on the variation of porosity,the chemical damage variables were constructed to reflect the microstructure of acid corroded rocks,and the calculation equation of damage measurement parameters based on longitudinal wave velocity was given.The damage variables were analyzed as a function of uniaxial compressive strength and elastic modulus,and it was concluded that the uniaxial compressive strength and elastic modulus of sandstone rock samples showed a decreasing trend with the increase of damage variables.(5)The dissolution characteristics of sandstone in different acidic solutions were analyzed,and the study showed that the dissolution rate constant k of sandstone increased with the decrease of solution pH,that is,the stronger the acidity,the greater the dissolution rate,and the reaction rates in HCl solution were all faster than those in H₂SO₄solution.Based on the principle of acid-rock chemical reaction and the kinetic model of acid-rock reaction,the kinetic model of sandstone acid-rock reaction is constructed,and the established model better responds to the mass loss rate of sandstone under chemical corrosion as a function of time.