A copper–cobalt ore processing enterprise in the Democratic Republic of the Congo (DRC) generates a substantial volume of post-cobalt-precipitation effluent during production. To prevent environmental risks associated with the discharge of this alkaline wastewater, the company plans to reuse it as flotation process water. However, industrial-scale flotation results have shown that using this effluent reduces the copper recovery from oxidized copper–cobalt ore by approximately 15%. This study focuses on optimizing flotation performance under such conditions to help achieve the company’s quality and efficiency goals. The effect of using post-cobalt-precipitation effluent as flotation water was first evaluated through laboratory experiments. Based on the ore’s mineralogical characteristics, the study then investigated the influence of different proportions of recycled process water on flotation recovery and determined a suitable flotation process. A high-efficiency collector system composed of ammonium dibutyl dithiophosphate (ADD) and butyl xanthate in a mass ratio of 1 to 1 was developed. Under optimized conditions, this collector combination achieved a copper recovery of 80.13%, which is 5.87% higher than the control group, and a cobalt recovery of 69.15%, an increase of 6.96% points. It also reduced acid consumption to 4,152.42 kg per tonne of copper produced, a decrease of 1,758 kg compared to the control. The proposed technical solution is suitable for industrial application and provides a valuable reference for optimizing the flotation performance of similar oxidized copper–cobalt ores.