Adsorption kinetics, equilibrium, and thermodynamics of Cu2+on pristine and alkali activated steel slag

Two adsorbents, pristine electric arc furnace slag (EAFS) and alkali activated slag (AAS) were used for Cu2+ removal from aquatic solutions. Batch adsorption tests were conducted at various temperatures and initial Cu2+ concentrations, while solid to liquid ratio and pH of solution were kept constant. Pseudo-first-order and pseudo-second-order (PSO) kinetics models, Langmuir and Freundlich isotherm models, as well as intraparticle and Boyd's diffusion models were applied in order to investigate the adsorption process. It has been found that alkali activation of EAFS leads to an increase in the specific surface of slag and thus improves the sorption properties of EAFS. The adsorption of Cu2+ onto both adsorbents proceeds via PSO adsorption mechanism, film diffusion mainly controls the adsorption process, and Langmuir isotherm model fits well the experimental data. Results indicated a fast adsorption process which is spontaneous and endothermic in nature. Microstructural investigation of EAFS and AAS revealed morphological changes in metal loaded EAFS and AAS samples in comparison to unloaded adsorbents. X-ray powder diffraction analysis indicated that adsorption of Cu2+ onto both adsorbents occurs through formation of a Cu-complex.