Porous Glass-Ceramics from Alkali Activation and Sinter-Crystallization of Mixtures of Waste Glass and Residues from Plasma Processing of Municipal Solid Waste
Total Page：16
File Type：pdf, Size：1020Kb
Journal of Cleaner Production 188 (2018) 871e878 Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro Porous glass-ceramics from alkali activation and sinter-crystallization of mixtures of waste glass and residues from plasma processing of municipal solid waste * Patricia Rabelo Monich a, Acacio Rincon Romero a, Daniel Hollen€ b, Enrico Bernardo a, a Dipartimento di Ingegneria Industriale, Universita Degli Studi di Padova, Via Marzolo 9, 35131 Padova, Italy b Chair of Waste Processing Technology and Waste Management, Montanuniversitat€ Leoben, Franz-Josef-Str. 18, 8700 Leoben, Austria article info abstract Article history: Alkali-activated aqueous slurries of fine glass powders, mostly deriving from the plasma processing of Received 11 December 2017 municipal solid waste (‘Plasmastone’), were found to undergo progressive hardening at low temperature Received in revised form (75 C) owing to the formation of CeSeH (calcium silicate hydrate) gels. Before complete setting, slurries 27 February 2018 could be easily foamed by vigorous mechanical stirring, with the help of a surfactant; finally, the Accepted 16 March 2018 resulting open-celled structure could be ‘frozen’ by a subsequent sintering treatment, with crystallization Available online 6 April 2018 of CaeFe silicates. The densification of the struts upon firing was enhanced by mixing Plasmastone with up to 30 wt% recycled glasses and increasing the firing temperature from 800 to 1000 C. A total porosity Keywords: Alkali activation exceeding 75 vol%, comprising both well-interconnected macro- and micro-sized pores on cell walls, was Gel casting accompanied by good compressive strength, well above 1 MPa. The stabilization of pollutants generally Glass-ceramic foams increased with increasing firing temperature and glass content, with some exceptions; no practical Waste glasses leaching was observed from samples deriving from Plasmastone combined with 30 wt% boro-alumino- Upcycling silicate glass from the recycling of pharmaceutical vials. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction the firing atmosphere could not reach C-containing foaming agents, so that further additives (‘oxidizers’, such as MnO2 and CaSO4)are Glass foams represent a very interesting class of materials due to needed for optimizing the gas release. In addition, in the case of high surface area and permeability, low density and specific heat, glass-ceramic foams, the situation is even more delicate, since glass high thermal and acoustic insulation and high chemical resistance. sintering and gas evolution must be combined with crystallization In addition, unlike polymeric foams, glass foams are non- (Rincon et al., 2016). flammable and flame resistant, chemically inert and not toxic In an effort to reduce the costs of glass foams processing, a new (Rincon et al., 2016). Therefore, cellular glass materials have the technique was developed by Rincon et al. (2017). The distinctive potential to replace polymeric foams as building insulation mate- character of the new technique is the separation between foaming rials, thus aiding in minimizing damages in case of fire. and sintering. The approach, applied to soda-lime glass, combined Compared to polymer foams, glass foams are currently far more alkali activation and firing. More specifically, suspensions of fine expensive, owing to the specific processing. The most established glass powders in alkaline aqueous solutions exhibited a marked method consists of the mixing of glass powders with a foaming pseudoplasticity, according to partial dissolution of glass and gel- agent, followed by firing. During the heat treatment, glass powders ification of the corrosion products. Air bubbles, incorporated by soften and form a ‘pyroplastic’ mass, foamed as an effect of gas intensive mechanical stirring (with the help of surfactants), at high evolution from the additive, in turn depending on decomposition shear rates and low viscosity, remained ‘frozen’ when stirring or oxidation reactions. The control of viscous flow sintering and stopped, at low shear rate and high viscosity, configuring an foaming phenomena is quite delicate: as an example, oxygen from ‘inorganic gel casting’. A cellular structure was thus available at low temperature, in samples in ‘green’ state. Firing treatments were applied after a drying step, at only 700 C, instead of 850e1000 C * Corresponding author. (necessary for the usual foaming reactions to occur), used for E-mail address: [email protected] (E. Bernardo). conventional glass foams. https://doi.org/10.1016/j.jclepro.2018.03.167 0959-6526/© 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 872 P.R. Monich et al. / Journal of Cleaner Production 188 (2018) 871e878 The low temperature foaming, after alkali activation, was glasses, such as soda-lime glass and boro-alumino-silicate glass conceptually close to that of geopolymer foams (Strozi Cilla et al., from disposed pharmaceutical vials, is discussed as a fundamental 2014). However, it must be noted that the activation was much tool for improving the sintering and the chemical stability of the weaker and the nature of the developed gels was completely developed foams. different. While in true geopolymers the hardening is associated to the formation of a three-dimensional network structure, from the 2. Experimental procedure polymerization of smaller units (in turn provided by the complete dissolution of alumino-silicate raw materials), glass suspensions Plasmastone (PS) was gently provided by Scanarc (Sweden) were stabilized by the formation and interlocking of calcium sili- (Scanarc, 2017). The chemical composition of this residue (deter- e e cate hydrates (C S H) at the surface of powders (Cyr et al., 2012; mined by X-Ray fluorescence) is reported in Table 1. Received in Garcia-Lodeiro et al., 2016; Rincon et al., 2017). form of granules with a mean particle size of 10 m, it was ground e e C S H are well known products of alkaline attack, in general, of into fine powders, below 75 mm, by dry ball milling. Soda-lime glass any CaO-rich silicate glass. As a consequence, the successful (SLG) powders (medium particle size equal to 30 mm) were gently e extension of the approach, from soda-lime glass, to Ca Mg silicate provided by SASIL SpA (Brusnengo, Biella, Italy), as the fraction bioglass, was not surprising (Elsayed et al., 2017). Interestingly, the obtained from glass cullet after colour selection and removal of open-celled structure available after low temperature foaming, in metallic and polymeric residues (essentially not employed due to e this case, was maintained with the precipitation of Ca and Ca Mg the presence of ceramic contaminations) (Rincon et al., 2017). Boro- fi silicate crystals (wollastonite and diopside), impeding signi cant alumino-silicate glass (BSG), from disposed pharmaceutical vials, fl fi viscous ow upon ring. was finally provided by Nuova OMPI (Piombino Dese, Padova, Italy); The present paper aims at further extending the approach to received in form of coarse fragments, it was ground into powders inorganic residues from municipal solid waste (MSW). Plasma below 45 mm, again by ball milling. The composition of the two heating has distinctive advantages in resource recovery from waste, recycled glasses is also reported in Table 1 (Ponsot et al., 2014). fi since it provides both gasi cation of organics, by pyrolysis, and Differential thermal analysis (DTA/TGA, STA409, Netzsch metal separation upon melting (owing to reducing conditions) Geratebau€ GmbH), with heating rate of 10 C/min) was done on (Scanarc, 2017). This approach is not attractive only with respect to Plasmastone, in form of coarse fragments as well as of fine powders the treatment of fresh MSW, but also with respect to the treatment of Plasmastone in order to determine the chemical reactions and of excavated MSW, which has been disposed of during the last physical changes which would occur during a sintering process. “ fi ” decades ( Land ll Mining , LFM). Material recovery from LFM is Plasmastone and soda-lime glass (quantities of 0e30 wt%) e limited to metals which are present only in amounts of 3 5 wt% powders were cast in an alkaline activating solution of 2.5 M NaOH/ (Krook et al., 2012; Wolfsberger et al., 2015b). Consequently, energy KOH (ratio 1:1), for an overall solid loading of 68 wt%, under me- recovery is the key technology in LFM projects. However, co- chanical stirring at 400 rpm. After 3 h of alkaline activation, the incineration in cement kilns is limited by high concentrations of suspension was poured in a closed polystyrene mould (60 mm heavy metals (Wolfsberger et al., 2015a). diameter) and cured at 75 C to undergo gelification (4 h for foams Incineration using grate furnace technology represents the state with only Plasmastone, and 3 h for foams from SLG-containing of the art for energy recovery of MSW and fractions thereof, which mixtures). Partially gelified suspension were added to 4 wt% fi do not ful l the requirements for co-incineration. However, this Triton X-100 (polyoxyethylene octyl phenyl ether e yields to the formation of large amounts of bottom ashes, which are C H O(C H O) ,n¼ 9e10, Sigma-Aldrich, Gillingham, UK) sur- fi 14 22 2 4 n even higher for land lled MSW than for fresh MSW, considering factant and then subjected to intensive mechanical stirring at the degradation of organics and the relative enrichment of the 2000 rpm. The resulting ‘green’ foams were then dried at 40 C, for fi fi mineral fraction in the land ll. Re-land lling of bottom ashes, due 48 h, before being demoulded. Finally, a sintering treatment was to the high total and leachable contents of heavy metals, is rec- applied to stabilize the foams at 800e1000 C, using a heating rate ommended (e.g.