Experimental study on the preparation of Sodium Alginate-Chitosan microcapsules for mining applications and the mechanism of their inhibition of coal spontaneous combustion

Sodium Alginate-Chitosan capsule for aerobic microorganisms (SA-CS-AMC) was prepared. • The SA-CS-AMC achieved an optimal oxygen consumption rate of 96.26%. • The SA-CS-AMC demonstrated good environmental adaptability. • SA-CS-AMC demonstrated excellent effectiveness in suppressing the spontaneous combustion of coal. Free aerobic microorganisms are prone to inactivation under harsh conditions in mine shafts, exhibit weak reproductive capacity, and have a short effective period, resulting in poor suppression of coal spontaneous combustion. Therefore, the research utilized Sodium Alginate (SA) and Chitosan (CS) to encapsulate aerobic microorganisms, resulting in the preparation of microbial capsules (SA-CS-AMC) with high oxygen consumption capacity and strong environmental tolerance. Using the Box-Behnken response surface design, SEM, environmental stress tests, physical property evaluations, programmed temperature experiment, and FTIR, we investigated the influence patterns and interactions of SA concentration, CS concentration, and second crosslinking time on the oxygen consumption performance of SA-CS-AMC. This revealed the mechanism by which SA-CS-AMC suppresses coal spontaneous combustion. Research findings indicated that when the SA concentration was 1.4%, the CS concentration was 0.8%, and the second crosslinking time was 37 min, the SA-CS-AMC exhibited the highest oxygen consumption rate of 96.26% after 48 h. Under the protection of the capsule, the aerobic microorganisms' tolerance ranges for temperature and pH were expanded to 25–40°C and 6.0–8.0, respectively. The SA-CS-AMC-treated coal sample exhibited a delayed crossing point temperature of 38.2°C compared with raw coal during combustion, demonstrating superior suppression effects compared to the free microbial treatment group. SA-CS-AMC effectively deactivated active functional groups in coal, with the peak areas for hydroxyl and oxygen-containing functionalities decreasing by 52.80% and 46.09%, respectively, thereby significantly reducing the coal's tendency toward spontaneous combustion. This paper presents a novel, highly effective microbial technology solution for preventing and controlling coal spontaneous combustion. Download: Download high-res image (165KB) Download: Download full-size image First, the optimal preparation parameters for Sodium Alginate-Chitosan aerobic microbial capsules(SA-CS-AMC) were determined through response surface design. Subsequently, SEM observations revealed the three-dimensional network structure and microbial loading within the capsules. Environmental stress and physical property tests confirmed their excellent environmental adaptability, mass transfer efficiency, and water retention capacity. Furthermore, programmed temperature-gas chromatography and FTIR analyses elucidated the microscopic mechanisms by which these capsules inhibit coal spontaneous combustion. In summary, this study provides a theoretical basis for the application of SA-CS-AMC in the prevention and control of coal spontaneous combustion.