The use of zeolite-based geopolymers as adsorbent for copper removal from aqueous media

Copper has been proven to have hazardous effects on human beings depending on its concentration levels. Recently, there has been a growing interest in developing geopolymers using local industrial minerals and by-products. However, research on the adsorption of heavy metals by geopolymer based on mordenite-rich tuffs is still limited. The geopolymer adsorbents have been synthesized using natural Ecuadorian zeolite-rich tuffs containing quartz, mordenite calcite and amorphous content with 20.8%, 28.5%, 4.2% and 46.4%, respectively. The geopolymers showed a maximum compressive strength of 26.86 MPa for 28 d of curing time. In the present study, an Ecuadorian zeolite-based geopolymer's removal capacity on copper ions in aqueous solutions, varying concentration and contact time were tested. Kinetic models were developed using pseudo first-order, pseudo second-order and the Elovich model. The adsorption data, using Cu²⁺ concentrations from 20 to 160 ppm, at 25°C were described by the Langmuir and Freundlich isotherms. Linear coefficient of determination (R ²) results show that the Langmuir model fits the best. The attained adsorption capacity of 52.63 mg g^-1 demonstrates the low-cost geopolymer's effectiveness for this study and its competitiveness compared with other studies. Adsorption kinetics follows the pseudo second-order kinetics model at the lower initial concentration of Cu²⁺.