Construction of OTAB/Bt/TiO₂ Composite Photocatalysts to Improve the Adsorption and Photocatalytic Performance for SCN^- Removal

The widespread use of cyanidation in gold beneficiation leads to a large amount of SCN- in the gold extract tail solution, which poses a threat to the environment and human health. The present study successfully synthesized octadecyltrimethylammonium bromide/bentonite/titanium dioxide (OTAB/Bt/TiO2) photocatalysts through a sol-gel hydrothermal approach. Evaluation of the BET specific surface area, X-ray diffraction (XRD) analysis, UV-vis diffuse reflectance spectroscopy, and zeta potential experiments unveiled the beneficial impact of incorporating OTAB. This inclusion led to an enlargement of the pore size and layer spacing of Bt, broadening the range of photoresponses. Additionally, it effectively neutralized the negative charge residing on the surface of Bt. Consequently, these enhancements contributed to the improved performance of the photocatalytic material in terms of adsorption and catalytic degradation of SCN-. The degradation rate of SCN- reached 98.78% under the reaction conditions of initial SCN- concentration of 50 mg/L, OTAB/Bt/TiO2 dosage of 0.8 g/L, pH = 8, and reaction time of 300 min. The degradation of the SCN- composite through the OTAB/Bt/TiO2 photocatalytic process followed a zero-order kinetic model with a calculated rate constant (k value) of 0.1148 min(-1). Notably, this rate constant was 1.9 times greater than the degradation rate observed in the pure TiO2 system. The free radical quenching test showed that h(+), center dot OH and center dot O2- were the main oxidizing substances for photocatalytic degradation. The identification of intermediates proved that the complete mineralization of SCN- could be achieved by OTAB/Bt/TiO2 adsorption and photocatalytic degradation without generating the highly toxic intermediate CN-. Overall, this study provides guidance for the development of more photocatalysts with strong adsorption properties and more effective removal of SCN- from gold extraction tailings.