Adsorption kinetics and equilibrium of Ni2+, Cu2+, Co2+, and Ag+ on geopolymers derived from ashes: application to treat effluents from the E-Coat printing process

Geopolymers were obtained from ashes through an alternative geopolymerization process and applied to remove Ni²⁺, Cu²⁺, Co²⁺, and Ag⁺ from synthetic aqueous media and real effluents. The study in synthetic solutions revealed that pseudo-second-order and general order models were the best to fit the kinetic curves. To represent the equilibrium curves, Langmuir and Freundlich were the most adequate. The geopolymer derived from bottom ash (GHA) was superior to adsorb Cu⁺², Co⁺², and Ag⁺¹ than the geopolymer derived from fly ash (GFA). GHA reached adsorption capacities of 279.5, 288.2, and 462.8 mg g^-1 for Co⁺², Cu⁺², and Ag⁺¹, respectively. Otherwise, GFA was the best for Ni⁺² removal, with an efficiency of 95% in low concentrations. In treating real effluents of the E-coat printing process, both GHA and GFA were efficient, with the removal of higher than 85% for all the metals. In brief, it can be stated that GFA and GHA prepared are promising materials to remove metals from aqueous media (synthetic and real), presenting fast adsorption kinetics, high adsorption capacity, and high metal removal percentage.