Adsorption of Cu(II), Pb(II), Cd(II), and Cr(III) from aqueous solutions using modified coffee grounds biochar

To address the issue of heavy metal contamination in water, K400 biochar (K400), K600 biochar (K600), and K800 biochar (K800) were prepared from agricultural waste—spent coffee grounds—via pyrolysis at 400 °C, 600 °C, and 800 °C, respectively. Among them, K800 was selected and chemically modified with potassium hydroxide to produce K-K800 biochar (K-K800). The adsorption performance of K-K800 for Copper (Cu(Ⅱ)), Plumbum (Pb(Ⅱ)), Cadmium (Cd(Ⅱ)), and Chromium (Cr(Ⅲ)) ions was systematically investigated under varying conditions. Experimental results demonstrated that the optimal adsorption occurred at a dosage of 2 g·L⁻¹ and initial solution pH of 6, with maximum adsorption capacities of 75.02 mg·g⁻¹ for Cu(Ⅱ), 229.67 mg·g⁻¹ for Pb(Ⅱ), 45.17 mg·g⁻¹ for Cd(Ⅱ), and 51.68 mg·g⁻¹ for Cr(Ⅲ). Adsorption equilibrium was attained at 360 minutes. The maximum adsorption capacities of K-K800 were determined to be 112.3 mg·g -1 for Cu(Ⅱ), 428.6 mg·g -1 for Pb(Ⅱ), 198.8 mg·g -1 for Cd(Ⅱ), and 63.1 mg·g -1 for Cr(Ⅲ), respectively. These enhancements significantly improved its adsorption capability. K-K800 is thus a green, eco-friendly, and highly efficient adsorbent for removing multiple heavy metals from aqueous environments.