Study on Mechanical Properties and Weakening Mechanism of Acid Corrosion Lamprophyre

In order to study the weakening mechanism and mechanical behaviors of hard lamprophyre of Carboniferous Permian coal-bearing strata in China's mining area, lamprophyre samples were subjected to static rock dissolution experiments with pH values of 0, 2, and 4. The acid corrosion mechanism of lamprophyre was revealed from the weight changes of samples, characteristics of solution ion concentration, and macro-mechanical properties. The experimental results show that reaction occurred between lamprophyre and acid solution. With the increasing concentration of H⁺, the reaction was more intense, the degree of acid etching was higher, and the weight loss was greater. The internal damage induced by acid etching results in the slow extension of the compaction stage of stress-strain curve of uniaxial compression, and the obvious deterioration of mechanical properties of the lamprophyre. The uniaxial compressive strength of the lamprophyre in the dry state is 132 MPa, which decreased to 39 MPa under the acid etching condition, showing significant mudding characteristics. Dolomite (CaMg(CO₃)₂ with 19.63%) and orthoclase (KAlSi₃O₈ with 31.4%) in lamprophyre are the major minerals constituents involved in acidification reaction. Photomicrograph recorded from SEM studies reveals that the dissolution effect was directly related to the concentration of H⁺ in the solution. The dissolution effect was from the surface to the inside. The small dissolution pores became larger and continuously expanded, then finally formed a skeleton structure dominated by quartz. The content of K⁺, Ca²⁺, and Mg²⁺ in the solution after acid etching reaction indicates that the acidified product of orthoclase is colloidal H₂SiO₃, which adhered to the surface of samples during acid etching and hinders the further acidification of minerals. The dissolution of dolomite and orthoclase under acidic conditions directly leads to the damage of their structure and further promotes the water-rock interaction, which is the fundamental reason for the weakening of the mechanical properties of lamprophyre.