Stability optimization of iron-based catalysts: Application of Cr-enriched alloy steel catalyst in ozonation pharmaceutical wastewater
Catalytic ozonation for advanced treatment of industrial wastewater has proved to be effective, and the stability of the catalyst is crucial for the long-term application of the ozonation process in practical engineering. In this study, the electrochemical characteristics of four iron (Fe) shavings: alloy steels (38CrMoAl and 40Cr) and carbon steels (A3 and 45#) were investigated, and a new citric acid-optimized H 2 O 2 modification method was proposed. The low open circuit potential (OCP) of carbon steels indicated that they were more likely to be oxidized therefore required shorter modification times. The higher the OCP of alloy steels, the higher H 2 O 2 concentration was required to enhance modification efficiency. By adding citric acid, the rapid modification of alloy steel was achieved, and the catalysts exhibited lower passivation current (I p ), indicating a lower rate of substrate loss and a longer lifetime of alloy steel catalysts. Furthermore, chromium (Cr) enrichment occurred in the oxide layer of alloy steel catalysts. The Cr/Fe (atomic ratio) in oxide layer for 38CrMoAl and 40Cr increased from 0.018 to 0.040 and from 0.010 to 0.037, respectively. The presence of CrOOH and Cr 2 O 3 within the oxide layer reinforced the layer’s overall structural integrity and enhanced its protection for the internal substrate, making the catalysts more resistant to adapt to high-salinity wastewater. Through laboratory tests, it was found that among the four catalysts, 38CrMoAl showed the highest stability and good catalytic activity with low Fe loss concentration. Therefore, the pilot-scale application effect of 38CrMoAl catalyst was evaluated. In the advanced treatment of pharmaceutical wastewater, chemical oxygen demand (COD) and total organic carbon (TOC) removals were 56.3% and 32.4%, respectively. These results showed that the stability of catalyst can be improved by optimizing the selection of steel, and the introduction of citric acid achieved Cr enrichment effect and amplified the potential stability advantage of alloy steel. The research provides guidance on raw material selection for catalyst preparation to different industries' wastewater treatment, especially in high-salinity wastewater ozonation treatment, which can realize the long-term stable application of catalyst.
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