Synthesis of zeolite from sugarcane bagasse fly ash and its application as a low-cost adsorbent to remove heavy metals

Abstract

A new clean and sustainable procedure to synthesize low-cost zeolites from sugarcane bagasse fly ash (BFA), an industrial waste, is presented. BFA is used as source of Al and Si to obtain aluminosilicates with distinguished ion exchange capacity, confirmed by copper uptake. After the fly ash has been calcined and submitted to hydrothermal treatment employing NaOH as mineralizing agent, the XRD patterns of the as-synthesized samples revealed the formation of zeolite Na-A. Temperature and calcination time are key parameters affecting the ion-exchange capacity (q) of the zeolitic materials. Calcination at 600 °C for 8 h, under oxygen atmosphere, ensures that all carbon from fly ash has been removed and optimizes the ion-exchange properties. As a strategy to further improve q, Al isopropoxide was added to the synthesis medium, reducing the Si/Al ratio in the zeolite and generating more ion exchange sites. The hydrothermal treatment and addition of Al modify the structure and morphology of the zeolitic material, leading to a maximized adsorption capacity (142 mg Cu2+ g-1) at 1.71 Si/Al, which is much higher than the observed for a commercial polymeric resin (46.6 mg g-1).