Deactivation mechanism of Fe/Al2O3 catalyst during the ozonation of reverse osmosis concentrates (ROCs): Effect of silicate

Abstract

Catalytic ozonation is regarded as a promising process for the treatment of heavily contaminated industrial wastewater, but has not been widely implemented at full-scale due to the high expense of catalyst. In this paper, the catalysts from a fix-bed catalytic ozonation reactor were collected and analyzed after the consecutive operation of three and a half years. The reactor was fed with 200 m3/h of Reverse osmosis concentrates (ROC) from a coal refinery plant located in mid-west China. The deactivation mechanism of the Fe/Al2O3 catalyst is revealed. It was found that the deposition of Si on the catalyst surface (an increase of about 40 times) was the main cause of deactivation. Herein, the role of typical functional sites of Fe/Al2O3 formed under various physicochemical conditions, for the silicate adsorption was studied based on the adsorption isotherms and theoretical analyses using density functional theory (DFT) calculation. The sites associated with catalytic activation of ozone: Fe-OOH (-0.66 eV) and Fe-O-Al (-0.49 eV) sites have much higher binding energy of silicate than non-reactive Fe-OH (-0.05 eV) sites. As a relatively strong Brönsted acid, silicic acid preferentially interacts with Fe-O-Al and Fe-OOH to reduce the abundance of Lewis acidity on the catalyst surface, which leads to the catalyst poisoning. This work points out the deactivation mechanism of the ozonation catalyst when treating wastewater with high salinity or alkalinity, and will lead to the new direction on the design of heterogenous ozonation catalysts.

Keywords

• Catalytic ozonation
• Fe/Al2O3
• Reverse osmosis concentrate (ROC)
• Deactivation
• Zero liquid discharge(ZLD)
• Silicate