Abstract
This study investigated the one-pot hydrothermal synthesis of mixed-phase ion-exchangers from waste amber container glass and three different aluminium sources (Si/Al = 2) in 4.5 M NaOH(aq) at 100 °C. Reaction products were characterised by X-ray diffraction analysis, Fourier transform infrared spectroscopy, 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy and scanning electron microscopy at 24, 48 and 150 h. Nitrated forms of cancrinite and sodalite were the predominant products obtained with reagent grade aluminium nitrate (Al(NO3)3∙9H2O). Waste aluminium foil gave rise to sodalite, tobermorite and zeolite Na-P1 as major phases; and the principal products arising from amorphous aluminium hydroxide waste were sodalite, tobermorite and zeolite A. Minor proportions of the hydrogarnet, katoite, and calcite were also present in each sample. In each case, crystallisation was incomplete and products of 52, 65 and 49% crystallinity were obtained at 150 h for the samples prepared with aluminium nitrate (AN-150), aluminium foil (AF-150) and amorphous aluminium hydroxide waste (AH-150), respectively. Batch Pb2+-uptake (~100 mg g−1) was similar for all 150-h samples irrespective of the nature of the aluminium reagent and composition of the product. Batch Cd2+-uptakes of AF-150 (54 mg g−1) and AH-150 (48 mg g−1) were greater than that of AN-150 (36 mg g−1) indicating that the sodalite- and tobermorite-rich products exhibited a superior affinity for Cd2+ ions. The observed Pb2+- and Cd2+-uptake capacities of the mixed-product ion-exchangers compared favourably with those of other inorganic waste-derived sorbents reported in the literature.
Highlights
It is estimated that approximately 200 Mt of waste soda-lime-silica container glass are landfilled per annum [1]
Nitrated forms of cancrinite and sodalite were the predominant products obtained with reagent grade aluminium nitrate (Table 2)
This study has demonstrated that mixed-phase cation-exchangers can be prepared from amber container glass and solid waste aluminium sources by a one-step hydrothermal reaction (Si/Al = 2 in 4.5 M NaOH(aq) at 100 ◦C)
Summary
It is estimated that approximately 200 Mt of waste soda-lime-silica container glass are landfilled per annum [1]. In order to conserve energy and natural resources, it is theoretically possible to recycle up to 90% of waste container glass, this potential is undermined by a range of geographical, economic and technical challenges [2,3,4]. Irrespective of colour, the principal oxide components of soda-lime-silica container glasses are SiO2 (66–75 wt%), Na2O (12–16 wt%), CaO (6–12 wt%), Al2O3 (0.7–7 wt%), MgO (0.1–5 wt%) and K2O (0.1–3 wt%), with trace chromophores (Fe2O3, SO3 and Cr2O3) below 0.5 wt% [16]. The reactivity of the amorphous silica species in container glass under mild hydrothermal conditions has been exploited in several studies to produce a range of technologically relevant mineral phases including tobermorite (Ca5Si6O16(OH)2·4H2O) [3,17,18,19], lithium metasilicate (Li2SiO3) [9,15,20] and various zeolites [6,7,8,9,14,21,22,23,24]
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