Synergistic effects of surfactant-flocculant mixtures on ultrafine coal dewatering and their linkage with interfacial chemistry

Flocculants are widely used in ultrafine coal dewatering to improve the particles settling rate. However, water entraps inside flocs that consequently increase generated filter cake moisture. In this paper, we report the effectiveness of a chemically enhanced approach to effectively increase particles settling rate and reducing filter cake moisture by taking advantage of the synergistic effect of dewatering chemicals. The effect of the dewatering chemicals on centrifugal dewatering performance, filter cake structure were studied. Applied anionic surfactant did not show a significant effect on dewatering rate and the filter cake structure, but it reduced solid recovery from 89% to 70% and filter cake moisture 19%–13% through strong attribution to decrease in liquid phase surface tension. However, cationic surfactant revealed a slight expansion in solid recovery to 94%, dewatering rate, and the filter cake permeability while there was a decrease in the filter cake moisture to 15% due to the increased coal particles hydrophobicity. Anionic flocculant also improved dewatering rate and filter cake permeability with an increase in solid recovery to 96%, but with the sacrifice of increased filter cake moisture to 24%. Mixed anionic surfactant/flocculant did not show a positive effect on dewatering parameters. However, cationic surfactant-flocculant mixtures led to a higher dewatering rate and solid recovery of 97% with lower moisture (22%) in comparison with single flocculant condition. X-ray Computed Tomography (XCT) results confirmed improved filter cake porosity in the cationic surfactant/flocculant mixture conditions. In agglomerate structure studies, flocculation and agglomeration of ultrafine particles with the cationic surfactant, flocculant, and mixed flocculant-cationic surfactant were observed. Nevertheless, the structure of the agglomerates in the mixed anionic surfactant/flocculant condition was loosened. The financial analysis confirmed using cationic surfactant or its mixture with the flocculant has an economic benefit in comparison with single flocculant condition.