Anugrah Ricky Wijaya, Ulia Nur Roiniah, Rahadian Zainul, Nor Kartini Binti Abu Bakar
We developed a Ca-alginate-biochar adsorbent utilizing calcium derived from waste coral skeleton for the adsorption of copper ions (Cu2+). 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 CaCl2, 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 CaCl2 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 min) 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 Cu2+ standard spike solutions and industrial electrolysis wastewater. Results indicated the optimal CaCl2 concentration was 0.5 M, yielding an adsorption capacity of 1.92 mg/g. The optimal contact time was 150 min (3.57 mg/g), and the optimal 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 (R2 = 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 Cu2+ removal from industrial waste, highlighting its potential for scalable applications. © 2026 The Authors.
Department of Chemistry, Faculty of Sciences and Mathematics, Universitas Negeri Malang (UM) or State University of Malang, Semarang 5, Malang, 65145, Indonesia; Department of Chemistry, Faculty of Mathematics and Sciences Education, Universitas Negeri Padang, Jalan Prof. Dr. Hamka, Air Tawar, Sumatera Barat, Padang, 25173, Indonesia; Department of Chemistry, Faculty of Science, Universiti Malaya, Kuala Lumpur, 50603, Malaysia
