An HBC–CaO hybrid was prepared from KOH-activated coconut-stem biochar and calcined calcium carbide residue (CCR) and evaluated for Fe and Zn removal in single-metal and binary aqueous systems. Batch removal experiments were conducted in triplicate, and results are reported as mean ± standard deviation (SD; n = 3). Biochar activated at 750 °C was combined with CCR calcined at 900 °C at a 3:1 mass ratio. We characterised the material using N₂ adsorption (BET), SEM–EDX, FTIR, and XRD. After contact with the binary Fe–Zn solution, the BET surface area decreased from 350.31 to 249.84 m² g⁻¹. In single-metal kinetic tests, the operational capacities at 240 min were 9.008 mg g⁻¹ for Fe introduced as Fe(II) and 8.364 mg g⁻¹ for Zn(II). The pseudo-second-order model gave the best kinetic fit on the original qₜ scale (R²qₜ = 0.9913 for Fe and 0.9887 for Zn). The Freundlich model best described the Fe isotherm (R²qₑ = 0.9758), whereas the Temkin model best described the Zn isotherm (R²qₑ = 0.9473). In the binary system, the total operational capacity reached 68.80 mg g⁻¹, and the Fe/Zn selectivity coefficient ranged from 1.447 to 1.556. After five reuse cycles, the adsorbent maintained about 69% of its initial removal performance. The mean final pH was 8.7; because we did not run adsorbent-free controls, we could not separate adsorption and precipitation contributions. Accordingly, we interpret removal as removal from the aqueous phase during operation.