Microbubble catalytic ozonation of refractory organic flotation reagents with steel slag and degradation pathways

Advanced oxidation processes for treating flotation wastewater suffer from low oxidation efficiency and secondary pollution. Here, the novel microbubble catalytic ozonation, combining steel slag as a cost-effective and efficient catalyst with microbubbles as an advanced form of aeration, was proposed to treat simulated flotation wastewater containing butyl xanthate (BX), O-isopropyl-N-ethyl thionocarbamate (Z-200), terpineol, and sodium humate. The chemical oxygen demand (COD) removal efficiency and mineralization rates of organic flotation reagents were compared by macrobubble/microbubble ozonation, macrobubble/microbubble catalytic ozonation. The employing of microbubbles increased the removal efficiency of COD in ozonation from 31.45 % to 50.42 %, followed by the mineralization rates of C, S, and N increasing from 19.57 % to 33.45 %, 28.90 % to 48.16 %, and 21.80 % to 31.82 %, respectively. Importantly, the addition of steel slag (0.5 g/L) further enhanced COD removal efficiency (58.34 %) and C (41.56 %), S (53.76 %), N (37.88 %) mineralization rates. Both EPR and dissolved ozone concentration variations demonstrated that steel slag effectively promoted ozone decomposition and hydroxyl radical (•OH) generation, confirming its catalytic role. The degradation pathways of organic flotation reagents with microbubble catalytic ozonation were proposed, mainly relying on the oxidation of organic flotation reagents by the products generated from ozone decomposition. The combined application of steel slag and microbubbles effectively overcame the low ozone solubility and slow •OH generation rate associated with ozonation alone, presenting a powerful strategy for enhancing organic flotation reagents degradation.