Enhancement of coal waste slurry flocculation by CTAB combined with bioflocculant produced by Azotobacter chroococcum

A bioflocculant produced by Azotobacter chroococcum, a natural polymer containing sugar and protein, can be used to flocculate coal waste slurry, but electrostatic repulsion impacts the flocculation of quartz attached to the solid coal particles. In this work, cetyltrimethylammonium bromide (CTAB) combined with this bioflocculant were used to flocculate coal waste slurry. The adsorption and zeta potential of CTAB on quartz, kaolinite, and organic matter were investigated in aqueous media. The results show that the data for CTAB adsorption fit the typical Langmuir adsorption model, and that the CTAB adsorption level is higher in an alkaline medium than in an acidic medium. The electrostatic interaction and formation of at-complexes contributed to the adsorption of CTAB on minerals and organic matter. Zeta potential measurements demonstrated that the point of zero charge values shifted to higher pH values after CTAB adsorption on mineral and organic matter surfaces. Furthermore, the behavior of the bioflocculant with the addition of CTAB was investigated to determine the effect of CTAB on the flocculation of coal waste slurry; quartz, kaolinite, and organic matter were used for comparison. Flocculation tests indicated that the optimum CTAB dosage for obtaining higher flocculation rates and clearer suspension of organic matter, quartz, and kaolinite was 50, 100, and 40 mg/L, respectively. A higher flocculation rate and clearer suspension of quartz were obtained in a very acidic medium, while organic matter suspension continued to increase in the pH range of 2.2-6.2 and remained almost constant in an alkaline medium. In addition, there were no significant changes in the flocculation rate or turbidity of kaolinite with an increase in pH. CTAB exhibited significant enhancement in terms of flocculation of coal waste slurry when the bioflocculant was used as a flocculant. Finally, surface tension measurements were taken to confirm the interaction between the bioflocculant and CTAB. The results show that CTAB could bind to the bioflocculant and form complexes.