Study on influence factors and mechanism of Floc-Bubble interaction in the flotation treatment of drilling wastewater

The increasing environmental burden of drilling wastewater calls for more efficient and mechanistically informed treatment strategies to support the sustainable development of oil and gas operations. This study systematically compares the performance of three flocculants—polyaluminum chloride (PAC), polyaluminum ferric silicate (PSAF), and aluminum sulfate (Al₂(SO₄)₃)—in the flocculation-flotation treatment of drilling wastewater, with an emphasis on elucidating floc–bubble interaction mechanisms. Flotation experiments demonstrated that PAC achieved the highest suspended solids (SS) removal efficiency (80.58 % at 1.0 g/L), followed by PSAF and Al₂(SO₄)₃. Comprehensive characterization, including FTIR, zeta potential, contact angle analysis, and floc size measurement, revealed that PAC formed large, moderately hydrophobic flocs with strong structural integrity and stable bubble adhesion. In contrast, Al₂(SO₄)₃ generated smaller, highly hydrophobic flocs with low interfacial energy barriers, leading to poor aggregate stability. The EDLVO theory was applied to calculate interaction energy profiles, demonstrating that floc–bubble adhesion is governed by the combined effects of van der Waals, electrostatic, and hydrophobic interactions. PAC presented the most balanced profile, combining high adhesion potential with strong post-attachment stability. These findings provide novel mechanistic insights for optimizing flocculation-flotation processes in complex wastewater systems, offering a theoretical basis for practical engineering applications.