<p>The sustainable management and conservation of water treatment residuals (WTRs) are crucial for advancing resource-efficient and environmentally friendly practices. This study investigates the performance of WTRs loaded hydroxyapatite (HAP) in the remediation of aqueous lead (Pb²⁺) and cadmium (Cd²⁺). By integrating HAP into the WTRs, the resultant HAP-WTRs exhibit significantly enhanced capacities for removing Pb²⁺ and Cd²⁺, with an optimal HAP to WTRs ratio of 3:2. In monometallic systems, the HAP-WTRs demonstrated adsorption capacities of 84.85&#xa0;mg/g for Pb²⁺ and 34.25&#xa0;mg/g for Cd²⁺. However, in bimetallic systems, competitive adsorption was observed, with a higher affinity for Pb²⁺ over Cd²⁺. The adsorption kinetics and isotherms align with the pseudo-second-order kinetic model and the Langmuir isotherm model, suggesting that the process is predominantly driven by monolayer chemical adsorption. Microscopic analyses reveal that the adsorption mechanisms of HAP-WTRs involve ion exchange with Al²⁺, Fe²⁺, and Ca²⁺, electrostatic interactions, surface complexation with functional groups such as -OH and -COOH, and co-precipitation with phosphates and carbonates.</p> Graphical Abstract <p></p>