Highly efficient low-cost zeolite for cobalt removal from aqueous solutions: Characterization and performance

Cobalt is considered to be a strategic metal, with a high market value due to its scarcity and difficulty of extraction. Its concentration in wastewater is much higher than that recommended by environmental agencies. In this work, adsorption is the selected process for cobalt removal and recovery and the adsorbent, a commercial natural zeolite, was chosen because of its wide availability, low price, and adequate particle size. The zeolite employed was clinoptilolite according to XRD and FTIR results. Other techniques like XRF have helped to show that the zeolite treated with acid has suffered dealumination process while the zeolite treated with sodium has kept its Si/Al ratio and it has incorporated sodium into its structure. The optimization of the adsorption process has allowed to enhance the removal of cobalt up to a 21%, exchanging the bare zeolite with NaCl 1 M, and up to a 42%, increasing the temperature to 333 K. In relation to the mechanism, adsorption of cobalt on clinoptilolite is an endothermic and spontaneous process where both external and intraparticle diffusion take place. A pseudo-second-order model can adequately describe the adsorption kinetics. Regarding to adsorption equilibrium, it is better described by Double Langmuir isotherm model. (c) 2018 American Institute of Chemical Engineers Environ Prog, 38: S352-S365, 2019