Water-quenched blast furnace slag (WBFS) has been assessed regarding its capacity to remove Cu2+, Cd2+, and Zn2+ from aqueous solutions. The physicochemical properties of the slag were characterized by ICP, SEM, and XRD. Batch experiments were conducted to study the effects of the adsorbent dosage, pH, initial concentration of heavy metal ions, temperature, and contact time on the removal of Cu2+, Cd2+, and Zn2+. The results showed that the removal efficiency increased with increasing adsorbent dosage and the optimum conditions for the removal of Cu2+, Cd2+, and Zn2+ were obtained in the dosage of 12, 16, and 16 g/L, respectively. The removal efficiency and adsorption amount of Cu2+, Cd2+, and Zn2+ onto WBFS increased on increasing the solution pH from 1 to 9, while the values decreased slightly as the pH further increased above 9. The adsorption process could fit the pseudo-second-order kinetic and Langmuir isotherm models. Various thermodynamic parameters were calculated and the results indicated the adsorption of Cu2+, Cd2+, and Zn2+ onto WBFS was feasible and endothermic in nature. These results have significant implications for the treatment of heavy metal wastewater using low-cost adsorbents.