Synthesis of zeolites from waste container glass and scrap aluminium Nichola Coleman , Kelly M. Fox, Victoria K. Elmes, Andrew P. Hurt School of Science, Faculty of Engineering &Science, University of Greenwich, Chatham Maritime, ME4 4TB, UK Throughout the past few decades, increasing efforts have been made to prepare zeolites and other technologically significant silicate minerals from a range of industrial, agricultural and municipal wastes [1]. Current interest in the facile and economical synthesis of potassium-bearing ion-exchangers, such as zeolite K-F (K 2 Al 2 Si 3 O 10 .xH 2 O), chabazite-K (K 2 Al 2 Si 4 O 12 .6H 2 O) and phillipsite-K ((K,Na,Ca 0.5 ) 4-7 Al 4-7 Si 12-9 O 32 .16H 2 O), arises from their applications in soil fertilisation and conditioning [2]. In this study, the hydrothermal formation of mineral products from a mixture of waste flint container glass and scrap aluminium (Al:Si molar ratio = 1.0 or 0.3) in 4 M KOH (aq) at 100 °C was monitored at 3, 24 and 72 h by X-ray diffraction analysis with Rietveld refinement, Fourier transform infrared spectroscopy and scanning electron microscopy (after Taylor et al. [1]). The equimolar Al:Si mixture gave rise to zeolite K-F and minor quantities of katoite (Ca 3 Al 2 SiO 4 (OH) 8 ) with a total crystallinity of 48% within 72 h. Lowering the Al:Si reagent ratio to 0.3 resulted in a chabazite-rich product and minor proportions of zeolite K-F and katoite with a total crystallinity of 35% at 72 h. A potential strategy to improve zeolitisation kinetics and yield is to employ a reaction medium comprising a two- component mixture of alkali metal hydroxides rather than pure KOH (aq) [3]. In this respect, a binary reaction liquor of 2 M KOH (aq) and 2 M NaOH (aq) markedly improved the yield of zeolite K-F from the equimolar Al:Si reagents and increased the crystallinity to 76% at 72 h. Conversely, the binary metal hydroxide solution had little impact on the zeolitisation rate of the mixture with the Al:Si ratio of 0.3, although it did alter the phase assembly to yield a zeolite K-F-rich product with minor quantities of phillipsite and katoite. In conclusion, the slow zeolitisation rate of soda-lime-silica container glass and aluminium in potassium hydroxide solution can be enhanced by using a binary mixture of potassium and sodium hydroxides, although this effect is not universal. References 1. J.H. Taylor, V.E. Elmes, A.P. Hurt, N.J. Coleman, Synthesis of feldspathoids and zeolite K-F from waste amber container glass. Mater. Chem. Phys. 2020, 246, 122805. 2. J. Yuan, J. Yang, H. Ma, Q. Chang, Preparation of zeolite F as slow release fertilizers from K-feldspar powder, ChemistrySelect 2017, 2, 10722-10726. 3. T. Wajima, K. Munakata, Effect of alkali species on synthesis of K-F zeolitic materials from paper sludge ash for soil amendment, Chem. Eng. J. 2012, 207, 906-912.
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