This study investigates the adsorption of heavy metals (Cd²⁺, Pb²⁺, and Cr³⁺) from wastewater using a newly synthesized cobalt-diphenylamine (Co-DPA) complex. The Co-DPA complex was synthesized by reacting cobalt nitrate hexahydrate with diphenylamine in a water-ethanol solution. The synthesized Co-DPA was characterized using XRD and FTIR, revealing its crystalline structure and functional groups. The complex was then used to treat real wastewater samples collected from the Akamuj River in Ethiopia. The adsorption capacity and efficiency of Co-DPA were evaluated under various conditions, including pH, adsorbent dose, initial metal concentration, and contact time. The results showed that Co-DPA effectively removed Cd²⁺, Pb²⁺, and Cr³⁺ from wastewater, with removal efficiencies of 95.6%, 99.5%, and 99.5%, respectively, after 80 minutes of treatment. The adsorption process was found to fit the Freundlich isotherm model, indicating multilayer adsorption on a heterogeneous surface. The kinetic data followed the pseudo-second order model for Cd²⁺ and Cr³⁺, and the pseudo-first order model for Pb²⁺. The Co-DPA complex demonstrated good reusability, with the ability to be regenerated by adjusting the pH of the solution. The study concludes that Co-DPA is a promising adsorbent for the removal of heavy metal ions from wastewater due to its high adsorption capacity, efficiency, and reusability. The results suggest that Co-DPA could be a viable alternative to conventional adsorbents for the treatment of industrial wastewater containing heavy metals.This study investigates the adsorption of heavy metals (Cd²⁺, Pb²⁺, and Cr³⁺) from wastewater using a newly synthesized cobalt-diphenylamine (Co-DPA) complex. The Co-DPA complex was synthesized by reacting cobalt nitrate hexahydrate with diphenylamine in a water-ethanol solution. The synthesized Co-DPA was characterized using XRD and FTIR, revealing its crystalline structure and functional groups. The complex was then used to treat real wastewater samples collected from the Akamuj River in Ethiopia. The adsorption capacity and efficiency of Co-DPA were evaluated under various conditions, including pH, adsorbent dose, initial metal concentration, and contact time. The results showed that Co-DPA effectively removed Cd²⁺, Pb²⁺, and Cr³⁺ from wastewater, with removal efficiencies of 95.6%, 99.5%, and 99.5%, respectively, after 80 minutes of treatment. The adsorption process was found to fit the Freundlich isotherm model, indicating multilayer adsorption on a heterogeneous surface. The kinetic data followed the pseudo-second order model for Cd²⁺ and Cr³⁺, and the pseudo-first order model for Pb²⁺. The Co-DPA complex demonstrated good reusability, with the ability to be regenerated by adjusting the pH of the solution. The study concludes that Co-DPA is a promising adsorbent for the removal of heavy metal ions from wastewater due to its high adsorption capacity, efficiency, and reusability. The results suggest that Co-DPA could be a viable alternative to conventional adsorbents for the treatment of industrial wastewater containing heavy metals.