Síntese de zeólita de baixa razão Si/Al a partir de cinza de carvão mineral para adsorção de iões de cobre

Abstract

Ash is one of the residues generated after the combustion of mineral coal and is employed in the construction industry. However, the rate of generation of this residue is higher than the rate at which it is used, thereby causing environmental and economic problems. In this study, low Si/Al ratio zeolites were synthesized from coal ash for the adsorption of copper ions, thus adding value to the residue and minimizing environmental pollution. Coal ash generated by CDM was used, and characterization results showed that this ash is a mixture of fly ash and bottom ash, and it also has an ideal composition (about 94% Si and Al) for zeolite synthesis. Two zeolite synthesis routes were followed (zeolite synthesis with and without the addition of sodium aluminate) using a two-step method (fusion); the synthesis variables were temperature and synthesis time. The copper ion removal test results showed that the zeolites synthesized at 100°C and a synthesis time of 16 hours had the highest removal rate for both synthesis routes, and the temperature of 80°C had less effect on the dissolution of the zeolite precursors. It was also observed that there was not a significant difference in the amounts removed by both zeolites synthesized using the two routes. Two zeolites (A1 and B1) were chosen to proceed with adsorption isotherm studies (the choice was based on the removal percentage). Zeolite A1 fitted the Langmuir model with (R 2 = 0.892 and q max = 34.24 mg/g), while zeolite B1 had an R 2 less than 0.70 for both the Langmuir and Freundlich models, likely due to measurement difficulties. The same zeolites (A1 and B1) were used to study adsorption kinetics. The results showed that equilibrium was reached in 100 minutes, indicating that both zeolites had the same efficiencies; however, at equilibrium, the amount adsorbed by zeolite B1 was higher than that of zeolite A1, which is attributed to the lower Si/Al ratio presented by zeolite B1. The correlation coefficients (R 2 ) and calculated adsorption capacities (q e ) showed that the pseudo-second-order kinetic model better describes the adsorption process of the synthesized zeolites. The copper ion removal percentage by zeolite A1 was 94%, thus it can be concluded that this zeolite can be used for copper ion removal.