Recovery of Effective Acid from Waste Generated in the Anodic Oxidation Polishing Process

The high treatment costs associated with wastewater and waste solutions produced by the anodic oxidation polishing section significantly limit industry development. To address this challenge, the present study investigates the characteristics of polishing wastewater and waste solutions, employing extraction and ion exchange combined with diffusion dialysis to recover effective acids. For waste tank solutions, single and dual solvent extraction experiments were conducted to determine the optimal extraction system. Electrostatic potential and interaction region indicator (IRI) analyses were performed to provide theoretical justification. Regarding cleaning wastewater, resin adsorption was applied to selectively remove aluminium ions from waste acid solutions, facilitating effective acid recovery. Static and dynamic adsorption–desorption experiments were initially performed to identify suitable resins. Subsequently, optimised parameters—including adsorption and desorption concentrations, volumes, and flow rates—were systematically established through conditional experiments, and diffusion dialysis was applied to recover acids from the desorbed solutions. The experimental results indicate that tributyl phosphate (TBP) emerged as the optimal single extractant, achieving an effective acid extraction rate of 88.67% under a solvent ratio of 4:1 at a room temperature of 28 °C. A binary solvent system, composed of TBP with 20% sulfonated kerosene, demonstrated superior engineering feasibility due to its reduced viscosity and satisfactory extraction rate of 82.19%. Moreover, adsorption–desorption tests confirmed that the resin-based method effectively recovered acids from cleaning wastewater. Specifically, under optimal operational conditions—downstream adsorption at 0.3–0.5 bed volumes (BV) and 1.0 BV/h, coupled with counter-current desorption at 2 BV and 2.4 BV/h—the acid recovery rate reached ≥95% while removing ≥90% of aluminium ions. Additionally, employing 20% sulfuric acid solution for desorption in diffusion dialysis enabled cyclic desorption. Consequently, this study successfully achieved acid reuse and substantially lowered wastewater treatment costs, representing a promising advancement for anodic oxidation polishing processes.