Investigating the effect of acid erosion on degradation and brittle fractures in coal using etching solutions

Abstract

ABSTRACT With an increase in the application of deep coal mining, there has been a significant increase in the risk of rock bursts due to increased mine pressures. Thus, research is required on more effective methods of preventing and controlling rock bursts. In this study, three types of solutions were used to study the brittle fracture degradation of coal by acid leaching. The principle of acid leaching and the microscopic mechanical behavior characteristics of brittle fracture degradation were analyzed. The quantitative laws governing different acid leaching times and unloading values were then obtained. The results were as follows. (1) The iron ions in the coal were replaced by a citric acid solution. The scanning electron microscope (SEM) results of the damaged coal sample indicated slight bending of the coal surface, accompanied by the shedding of small coal particles. After immersion, the failure strain increased by 63.6%, and the failure response time increased by 324.1%. (2) After soaking the coal sample in a phosphoric acid solution, numerous bubbles were observed on the coal surface, and the permeability was significantly enhanced. The SEM results of the damaged coal revealed that the coal surface was divided into blocks after soaking, and the minerals in the coal precipitated and accumulated. After immersion, the failure stress decreased by 24.5%. (3) A mixed acid solution, comprising citric and phosphoric acids, resulted in the most significant corrosion effect. The SEM results of the damaged coal revealed that chemical reactions occurred after the soaking process, and minerals were precipitated. Furthermore, uniaxial failure was the most complete. In particular, the failure stress decreased by 49.8%, the failure strain increased by 81.8%, and the failure response time increased by 77.7%. The mixed acid solution enhanced the plastic characteristics of the coal, reduced its strength, and demonstrated favorable characteristics for coal pressure relief. Thus, the results of this study provide significant engineering advancements for chemical pressure reduction technology, which can be applied to deep coal mining.