Removal of copper and cobalt ions by fly ash-based geopolymer from solutions-equilibrium study

Fly ash-based geopolymer was used for removal of copper and cobalt ions from aqueous solutions by a batch technique. The experimental data were obtained at constant geopolymer particles size (0.071-0.090mm) for the different initial concentrations (in the range from 3.881 to 39.390mmolL(-1)) of copper and cobalt solutions, respectively, and at various temperatures (T=298, 308 and 318K). For characterization of synthesized geopolymer, before and after sorption of heavy metals, FTIR, XRD, and SEM/EDS analyses were used to confirm the dissolution of geopolymer structure. SEM/EDS analysis also confirmed that sorption process occurred, as well as the fact that Na ions are outgoing ions. Various types of isotherm models, two-parameter isotherms: Langmuir, Freundlich, Jovanovic, and Dubinin-Radushkevich and three-parameter isotherms: Hill, Redlich-Peterson, and Sips were fitted to the experimental data obtained. In order to calculate parameters of the isotherms a nonlinear regression method was used. According to the results obtained, the most appropriate models for describing equilibrium data were Langmuir, Jovanovic, Hill, and Redlich-Peterson isotherm models. Thermodynamic parameters indicated endothermic (positive values of Delta H degrees) and spontaneous nature (negative values of Delta G degrees) of sorption process.