Synthesis of porous volcanic tuff-based geopolymer for nickel and cobalt removal

This study investigates the synthesis and application of porous volcanic tuff-based geopolymers for the efficient removal of Ni²⁺ and Co²⁺ ions from aqueous solutions. The geopolymer was prepared using volcanic tuff as the primary aluminosilicate source, activated with sodium hydroxide, and foamed with hydrogen peroxide to enhance porosity. The synthesized geopolymer was characterized using SEM and XRD. Batch adsorption studies were conducted to assess the effects of pH, contact time, initial metal concentration, and geopolymer dose on removal efficiency. Results indicated that the geopolymer exhibited superior adsorption capacity compared to raw volcanic tuff, with maximum removal efficiencies of 86.72 % for Co²⁺ and 81.27 % for Ni²⁺ at optimal conditions (pH 6, 180 min contact time). Adsorption data were best fitted to the Langmuir isotherm model, indicating monolayer adsorption on a homogeneous surface, with maximum adsorption capacities of 3.19 mg/g for Ni²⁺ and 2.40 mg/g for Co²⁺. The thermodynamic parameters ΔG°, ΔH°, and ΔS° suggest that the geopolymer adsorption is favorable, and the process is endothermic and significantly more effective at higher temperatures.