Corrosion effect of hydrochloric acid on the granite : insights from electrical conductivity, mineral composition, and tensile behavior

Abstract

Hydrochloric acid (HCl) extensively exists in deep underground projects, arising from the transportation of industrial raw materials or fracturing fluids of petroleum engineering. It results in corrosion, which can significantly impact the stability of surrounding rock structures. Therefore, in-depth analysis of the degradation of rock corroded by the HCl solution is an essential task for underground engineering. In this study, the granite specimens are initially treated with the HCl solution with various concentrations. Then, the tests and analyses, such as electrical conductivity (EC) measurements, mineral composition assays, and Brazilian splitting tests, are employed to investigate the corrosion mechanism of the HCl solution. Our results and findings are generally as follows: (1) As the immersion time increases, the EC exhibits a relatively high level at pH value of 1, a decreasing trend at pH value of 3, and an increasing trend at pH value of 5 and 7. (2) The HCl solutions with various concentration have different effect on mineral composition, characterized by an increase in proportion of SiO2 and a reduction in proportion of Na2O, Al2O3, K2O, MgO, and CaO, as the solution pH value decreases. (3) After immersion in the solutions with pH values of 1, 3, and 5, the tensile strength of the granite decreases by 23.85%, 20.84%, and 20.24%; the average stiffness of the specimen decreases by 29.29%, 23.43%, and 11.97%; the proportion of releasable energy increases by 6%, 4%, and −2%; the releasable energy decreases by 54.96%, 26.09%, and 14.52%; and the dissipated energy decreases by approximately 68.85%, 41.39%, and 5.41%, respectively. (4) The evolution of physical and mechanical properties of the immersed granite specimen can be analyzed from a chemical aspect. The corrosive action of HCl cleaves Si–O and Al–O chemical bonds within the granite, particularly altering the tetrahedral structures of its silicate components. This process involves breaking existing chemical bonds and the formation of new ones, ultimately destroying the silicate molecular structures. As the concentration of HCl increases, the rate of these reactions accelerates, progressively weakening the chemical bonds and consequently deteriorating the mechanical characteristics of the granite. These findings can deepen our knowledge about the corrosion effect of HCI solutions on natural surrounding rocks and serve as references for further research on rock corrosion mechanisms in underground engineering.