Hydrothermal synthesis of zeolites from green container glass

Abstract

Landfilling and stockpiling unrecycled colored container glass represents a considerable failure in sustainability with respect to the conservation of energy and mineral resources. In this study, the single-step hydrothermal synthesis of low-silica zeolites from a mixture of waste green container glass and aluminum foil (Al:Si = 1) in 4 M NaOH(aq) at 125 °C was followed at 1, 3, 7 and 14 days. The principal phases, sodalite and cancrinite, appeared within 1 day accompanied by minor quantities of hydrogarnet and tobermorite arising from a stoichiometric excess of calcium ions in the parent glass. Products of 63, 67, 71 and 72% crystallinity were obtained at 1, 3, 7 and 14 days, respectively, with partial successive conversion of sodalite to cancrinite over time. Ion-exchange and catalytic applications of sodalite and cancrinite arise from the high anionic charge of the 1:1 ratio of alternating SiO44- and AlO45- units within their aluminosilicate frameworks. In this respect, the uptake capacity of the 14-day zeolitic product for Cu2+ and Cd2+ ions (1.58 meq g-1 and 1.66 meq g-1, respectively) was within the expected range for zeolites and compared favorably with those reported for other inorganic sorbents derived from industrial and municipal wastes. The 14-day product was also found to be an effective basic heterogeneous catalyst for the Knoevenagel condensation reaction.