<p>Copper arsenic residue is a common hazardous waste in nonferrous metallurgical industries. Owing to the economic value of copper and the environmental toxicity of arsenic, efficient separation of copper and arsenic in sulfide arsenic residue represents a critical step for copper resource recovery and environmental protection. Focusing on the Cu-As filter cake and employing a sodium sulfide (Na₂S) leaching process, this study explored the displacement reaction between As₂S₃ and Cu²⁺, and investigated the effects of Na₂S dosage, addition time, reaction time, and temperature on copper–arsenic separation efficiency. The results indicate that the prepared Cu-As filter cake achieves optimal copper–arsenic separation under the following conditions: a Na₂S(theoretical) to Na₂S(actual) molar ratio of 1:3, a reagent addition time of 10&#xa0;min, a reaction time of 60&#xa0;min, and a reaction temperature of 20&#xa0;°C. Under these optimum conditions and after leaching with the specified reagent, the copper enrichment extent reached 97.1%; arsenic removal extent achieved 70.5%; and the copper content in the residue measured 32.4% after leaching. This work provides valuable insights into the treatment of Cu-As-containing filter cake in nonferrous metal smelting processes.</p> Graphical Abstract <p></p>