<p>The purity of magnetite recovered from steel pickling waste liquor (SPWL) via electrochemical technology remains low. This study developed a three-dimensional multi-physics field coupling model and optimized the structural parameters of the electrochemical reactor to achieve high-purity magnetite from steel pickling waste liquor. The regulatory mechanism of electrode arrangement on the electrochemical field was revealed through numerical simulations. Compared to parallel electrodes, the alternating electrode arrangement increased electric field strength by 13.4% and current density by 20.1%. Experimental validation showed that this electrode arrangement enhanced magnetite purity to 97.62%. Additionally, a quantitative relationship between stirring parameters and flow field uniformity was established through computational fluid dynamics simulation. The optimal mixing conditions were found to be 60&#xa0;mm blade diameter, 10&#xa0;mm blade installation height, and 400&#xa0;rpm rotation speed. Flow field optimization improved Fe²⁺/Fe³⁺ mass transfer efficiency, promoted lattice orientation coordination, and raised magnetite purity to 98.01%. The dynamic mechanism of magnetite electrosynthesis was further elucidated through electrode surface pH monitoring, video frame capture, and X-ray diffraction characterization. It was found that Fe²⁺ is electro-oxidized to Fe³⁺ at the anode, while OH⁻ is generated through water reduction at the cathode. These species undergo electromigration-diffusion-convection transport, forming Fe(OH)₂/Fe(OH)₃ mixed colloids, which ultimately assemble into a spinel structure with a Fe²⁺: Fe³⁺ molar ratio of 1:2. This study provides a novel solution for the resource-based high-value utilization of acidic heavy metal wastewater. </p> Graphical Abstract <p></p>