# Synergistic effects of surfactants and compound acids on the mechanical and microscopic properties of coal

## TL;DR

This study explores how combining surfactants and acids affects coal's strength and structure, showing that the combination significantly weakens coal and improves permeability, which could help prevent mining disasters.

## Contribution

The novelty lies in demonstrating the synergistic effect of surfactants and acids on coal properties, revealing enhanced permeability and reduced strength with implications for disaster prevention.

## Key findings

- Acid treatment weakens coal strength, and adding SDS further reduces it.
- SDS modifies coal's chemical structure, reducing aromatic and fat content significantly.
- Synergistic treatment enhances water diffusivity and coal permeability, aiding in stress mitigation.

## Abstract

This study examines the effects of synergistic treatment with surfactants and compound acids on the mechanical properties (e.g., strength and deformation characteristics) and microscopic features (e.g., pore structure, surface wettability, and chemical composition) of coal. The results indicate that acid treatment weakens coal strength, and the addition of sodium dodecyl sulfate (SDS) further exacerbates this effect. Acidification significantly reduces acoustic emission energy, electromagnetic radiation energy, and infrared radiation temperature released by coal. Moreover, SDS modifies the chemical structure of coal, reducing aromatic content by ~ 30% and fat content by ~ 50% compared to untreated coal. Under the synergistic effect of SDS, acid-induced erosion reaches its maximum. The decrease in fractal dimensions DW and DS indicates that SDS promotes coal pore connectivity. Furthermore, molecular dynamics simulations reveal that the synergistic interaction between surfactants and compound acids enhances water molecule diffusivity, improving coal wettability and promoting pore and fracture network development. This synergistic effect not only further reduces coal strength but also significantly enhances permeability, which is vital for mitigating stress accumulation in coal seams. This provides critical theoretical and technical guidance for the effective prevention and control of dynamic disasters such as rock bursts.