Abstract
Spent fluorescent lamps (SFL) are classified as hazardous materials in the European Waste Catalogue, which includes residues from various hi-tech devices. The most common end-of-life treatment of SFL consists in the recovery of rare earth elements from the phosphor powders, with associated problems in the management of the glass residues, which are usually landfilled. This study involves the manufacturing of porous ceramics from both the coarse glass-rich fraction and the phosphor-enriched fraction of spent fluorescent lamps. These porous materials, realizing the immobilization of Rare Earth Elements (REEs) within a glass matrix, are suggested for application in buildings as thermal and acoustic insulators. The proposed process is characterized by: (i) alkaline activation (2.5 M or 1 M NaOH aqueous solution); (ii) pre-curing at 75 °C; (iii) the addition of a surfactant (Triton X-100) for foaming at high-speed stirring; (iv) curing at 45 °C; (v) viscous flow sintering at 700 °C. All the final porous ceramics present a limited metal leaching and, in particular, the coarse glass fraction activated with 2.5 M NaOH solution leads to materials comparable to commercial glass foams in terms of mechanical properties.
Highlights
The sustainability of glass recycling is delicate
The material had been pretreated by the company to remove mercury. It was sieved at 20 μm to separate the thinnest part in which Rare Earth Elements (REEs) are present in higher concentrations, according to Belardi et al [9]. Both glass and phosphor-enriched fractions were characterized by means of Environmental Scanning Electron Microscopy–Energy Dispersive X-Ray (ESEM–EDX) for elemental semi-quantification (Table 1), X-Ray Diffraction (XRD) to determine the crystalline phases present, and Fourier Transform Infrared (FTIR) spectroscopy to identify the functional groups of the samples
The main differences between the two fractions are represented by the presence of calcite (CaCO3, PDF#72-1652), known as the minor phase within the phosphors for fluorescent lamps [26] and a substantial amount of glass in the coarse fraction
Summary
The sustainability of glass recycling is delicate. The saving in embodied energy by using recycled material instead of mineral raw materials is lower than 25%, definitely scarce in comparison with aluminum (nearly 90%) [1]. This is caused by the need to separate the glass fractions from impurities and other materials during sorting [2]. There are several difficulties in re-melting end-of-life glasses to produce the original articles (closed-loop recycling) [3,4]: contaminations may degrade the chemical stability or the optical properties (e.g., in pharmaceutical vials, LCD panels, etc.) or even determine the release of noxious emissions, as in the case of fluorine [5]
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