Coral Skeleton-Alginate-Biochar Bead: A Modified Adsorbent for Cu(II) Removal

We developed a Ca-Alginate-Biochar adsorbent utilizing calcium derived from waste coral skeleton for the adsorption of copper ions (Cu 2+ ). The coral skeleton underwent calcination at 850°C to remove organic compounds, yielding CaO with a purity of approximately 88.15%. This was subsequently reacted with HCl to produce CaCl 2 , serving as a crosslinking agent for sodium alginate. Biochar, obtained via pyrolysis of coconut shell, was activated and incorporated into a 1% sodium alginate solution. The resulting mixture was then added dropwise to CaCl 2 solutions of varying concentrations (0.25, 0.50, 0.75, and 1.00 M) to form Ca-Alginate-Biochar beads. Optimization studies examined the effects of contact time (30-240 minutes) and temperature (25-65°C) on adsorption performance. Kinetic analyses were conducted using pseudo-first and second-order models, while thermodynamic parameters were determined via the Van't Hoff equation. The adsorbent's efficacy was evaluated using Cu 2+ standard spike solutions and industrial electrolysis wastewater. Results indicated the optimal CaCl 2 concentration was 0.5 M, yielding an adsorption capacity of 1.92 mg/g. The optimal contact time was 150 minutes (3.57 mg/g), and the opti mal temperature was 50°C, achieving a capacity of 6.97 mg/g and 70.1% efficiency. Application to industrial electrolysis waste demonstrated an adsorption capacity of 85.5 mg/g and 81.1% efficiency. Kinetic studies revealed conformity with the pseudo-second-order model (R 2 = 0.9499), suggesting a chemisorption mechanism. Thermodynamic analysis indicated an endothermic process (ΔH° = 33.17 kJ/mol) with increased entropy (ΔS° = 92.2 J/mol·K), exhibiting a tendency towards spontaneity at elevated temperatures despite positive ΔG° values. These findings demonstrate the efficacy of coral skeleton-based Ca-Alginate-Biochar for Cu 2+ removal from industrial waste, highlighting its potential for scalable applications. • Ca-Alginate-Biochar adsorbent utilizes calcium derived from waste coral skeleton. • The optimized bead adsorbent was recorded at 0.50M CaCl 2 , 150 minutes, and 50°C. • The pseudo-second-order model of the bead adsorbents revealed a chemisorption mechanism. • ΔH° = 33.17 kJ/mol and ΔS° = 92.2 J/mol·K exhibited a spontaneity of Cu(II) adsorption. • This novel bead adsorbent could be applied to the electrolysis waste industry.