Influence of surfactant adsorption on coal oxidation and wettability: Experimental discussion and model development

To further investigate the physicochemical properties and wettability changes of surfactant-modified coal after oxidation, the contact angle, industrial composition, and functional groups of the surfactant-modified coal were measured. The experimental data were analyzed using a ridge regression prediction model to explore the relationship between the physicochemical properties and the wettability. The results indicate that the oxidated-modified coal has a worse wettability at room temperature. The adsorption of SL and CDEA surfactants effectively impedes the increase in the contact angle of the oxidized coal. The hydrophilic functional group (2#CO, C–O–C, RHCCH2) in coal demonstrates higher sensitivity to surfactants, while the hydrophobic functional group (2# Free OH, 1#CC) exhibits greater reactivity. There is a strong correlation between the industrial composition, structural parameters, and the contact angle. The quantitative influence of the parameters on the contact angle is as follows: FCad > Vad > P1 ≥ P4 ≥ Mad ≥ P3 ≥ P2. A coal wetting model is established that considers the combined action of surfactants and coal quality. These findings suggest that wettability is determined by multiple parameters, providing a basis for discovering new reagents that significantly enhance coal wettability and reduce coal oxidation activity.