Visible-light-driven Photodegradation of Xanthate in a Continuous Fixed-Bed Photoreactor: Experimental Study and Modeling

Photocatalysis has been widely employed as a promising method for wastewater treatment. However, existing studies are primarily conducted in batch reactors. To the best of our knowledge, a continuous reactor has not been used to degrade xanthate residual in mineral beneficiation wastewater. In this work, a continuous fixed-bed photoreactor (CFPR) was first designed, and Bi2WO6 photocatalysts coated on silica sands were used to degrade sodium isobutyl xanthate (SIBX) under visible light irradiation. The effects of various parameters, including catalyst loading, pH level, initial SIBX concentration, wastewater flow rate, calcium ion (Ca2+) concentration, magnesium ion (Mg2+) concentration, and zinc ions (Zn2+), on the degradation efficiency, were systematically investigated. The results show that the photodegradation percentage of SIBX increases with increasing catalyst loading, decreasing initial concentration, and decreasing flow rate within the scope under investigation. Addi-tionally, low concentrations (30 mg center dot L-1) of Ca2+ and Mg2+ ions favor the photodegradation of SIBX, whereas excessive Ca2+ and Mg2+ ions (240 mg center dot L-1) inhibit photocatalytic activity. The presence of Zn2+ ions inhibits photodegradation percentage. Furthermore, the photodegradation percentage is slightly higher at alkaline than at acidic pH. The maximum degradation percentage reached 95.40 % after 70 min of visible light irradiation under optimal conditions. In addition, a fixed bed reactor model considering surface reaction kinetics and mass transfer constraints was established by combining the Langmuir-Hinshelwood (L-H) kinetic equations and the series resistance theory. This model can accurately estimate the intrinsic kinetic parameters and can well predict degradation efficiency with a root-mean-square-error (RMSE) of 4.24 %. Finally, the bottleneck for improving the performance of the reactor can be identified under different conditions.