Environmental friendly management of CRT glass by foaming with waste egg shells, calcite or dolomite

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CERAMICS INTERNATIONAL

Ceramics International 40 (2014) 13371–13379 www.elsevier.com/locate/ceramint

Environmental friendly management of CRT glass by foaming with waste egg shells, calcite or dolomite Hugo R. Fernandesa, Diana D. Ferreiraa, Fernanda Andreolab, Isabella Lancellottib, Luisa Barbierib, José M.F. Ferreiraa,n b

a Department of Materials and Ceramics Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, via Vignolese 905/a, 41125 Modena, Italy

Received 19 February 2014; received in revised form 22 April 2014; accepted 8 May 2014 Available online 16 May 2014

Abstract Panel (P) and funnel (F) glasses from Cathode Ray Tube (CRT) have been used to obtain glass foams by a simple and economic processing route, consisting of direct heating the glass powders at relatively low temperatures (650–750 1C) using different foaming agents (FA) such as egg shells, calcite, dolomite. Mixtures in different proportions of P and F glass powders were tested and the effects of composition and heat treatment temperature on the foaming behaviour were evaluated. Glass foams featuring apparent density and compressive strength values of 0.29 g/cm3 and 2.34 MPa, respectively, could be produced from a P/F ratio ¼1 with added 3 wt% of egg shells upon heat treating at 700 1C for 15 min. The P/F ratio was found to strongly influence the foaming behaviour and, consequently, the physical properties of the final foam glass. The relative performance of other foaming agents under a given set of experimental conditions revealed to be dependent on the type of glass (composition and thermal properties). & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: CRT glass; Recycling; Glass foams; Egg shells

1. Introduction Once electronic devices reach the end of their useful life, they become electronic waste [1]. Cathode ray tubes (CRTs) are used in televisions and computer display screens, which represent about two-thirds of the weight of a television set or a computer monitor and include 50–85% glass materials [2–5]. The CRT glasses comprise [2,6–8]: (1) Panel (the front part) – a homogeneous barium strontium glass, whose weight is about two-thirds of the whole CRT; (2) cone or funnel – a lead glass whose weight is about one-third of the whole CRT used for shielding the radiation produced by the gun; (3) neck – a glass with a very high lead content enveloping the electron gun, (source of the signal leading to the display); and (4) frit (the connection between the panel and the cone) – a low-melting n

Corresponding author. Tel.: þ351 234 370242; fax: þ 351 234 370204. E-mail address: [email protected] (J.M.F. Ferreira).

http://dx.doi.org/10.1016/j.ceramint.2014.05.053 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

temperature lead glaze. This last one is a kind of glass solder used to join the panel and cone sections, which contains from  15 to nearly 100 g of lead per CRT, depending on the size. The lead from the frit is in a soluble form, primarily lead oxide as compared to the insoluble lead in the glass matrix of the funnel and faceplate. Although the Directive 2002/95/EC [9] restricts the use of certain hazardous substances in electrical and electronic equipment, including Pb, some applications are exempted from those requirements, such as lead in glass of cathode ray tubes. Thus, the management of this kind of WEEE (Waste Electrical and Electronic Equipment) both as matter recovery and landfill disposal become problematic. So, CRTs from TV sets or computers can become a significant source of lead in municipal solid wastes (e.g., lead content can be as high as 0.6–2.7 kg, depending on the size and year of manufacture) [6,7,10]. Human exposure to lead can result in damage to the central and peripheral nervous systems, blood system, kidney

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and reproductive system [11]. Directive WEEE 2002/96/EC [12] for the recovery and recycling of waste from electric and electronic equipment and the recast of the WEEE Directive (exacting the newest WEEE Directive 2012/19/EU) in particular aim at minimising the impact of EE goods on the environment, by increasing re-use and recycling and reducing the amount of WEEE going to landfill. Reusing heavy metal-containing glasses might also raise concerns. Yot and Méar [13] studied the leaching ability of lead, barium and strontium from foamed CRT glasses. They followed the leaching procedure described in the AFNOR X 31-210, which is widely used to determine the degree of inertization of either materials to be re-used or wastes to be disposed in landfill. The method is comparable to other procedures used in Europe [14–16] and is similar to the Italian leaching procedure (UNI EN 12457-2). Foaming of glasses may be caused by an oxidation process of C-based foaming agents (graphite, coal, carbon black, SiC), or a decomposition of minerals like carbonates (Na2CO3, CaCO3, MgCO3, etc.) or sulphates (CaSO4, i.e. gypsum) [17]. Decomposition processes are more suitable for glasses containing remarkable amounts of heavy metals since they prevent (i) the formation of toxic easily reducible oxides of these metals and (ii) the use of higher temperatures for gas evolving [13]. These drawbacks can be overcome by using carbonates [18]. The egg shell itself is about 95% CaCO3; the remaining 5% includes calcium phosphate and magnesium carbonate and soluble and insoluble proteins. The disposal methods for waste egg shells are: 26.6% as fertilizer, 21.1% as animal feed ingredients, 26.3% discarded in municipal landfill, and 15.8% used in other ways [19]. Among the innovative ways for egg shells recovery, the Japanese company Green Techno 21, developed a technology able to obtain a coating for wall using egg shells with good insulating properties [20]. In Italy the egg shells waste produced are around 250,000 ton/year deriving from pasta and confectionery industries. In this context, recycling has emerged as a very important environmental issue nowadays, also due to the diminishing natural resources and the increasing amount of solid wastes. Glasses are among the materials which attract great interest in the recycling concept. The recycling of CRT wastes has recently been the research subject of some investigations in diverse fields such as porcelain stoneware production, tableware glass, glass-ceramics, glazes, clay bricks and roof tiles, and insulating glass fibre or glass foams [21–27]. In a previous paper we reported on the feasibility of producing glass foams using waste egg shells as an alternative calcium carbonate-based (  95 wt%) foaming agent derived from food industry [18]. The glass foams were prepared using separately two types of CRT glass wastes (panel and funnel) foamed by different added amounts of egg shells upon heating the powder mixtures at relatively low temperatures (600– 800 1C). The present work aims at investigating the possibility of obtaining foamed glasses from waste materials at lower temperatures. The performance of a fixed amount (3 wt%) of different foaming agents (egg shells, calcite and dolomite) and

its relation with the chemical/thermal properties of the waste glasses was also compared.

2. Experimental procedure Panel (P) and funnel (F) glass wastes were first crushed in a crushing machine, and then dry-milled to obtain powders with mean particle size about 10 mm as determined by laser scattering technique (Coulter LS 230, CA USA; Fraunhofer optical model). The egg shell waste (E) was also milled ( 8 mm) and used as foaming agent (FA). In order to evaluate the effect of different FA, powder mixtures containing calcite (C, CaCO3, technical grade – 99.5%) or dolomite (D, CaMg (CO3)2, technical grade – 99.5%, containing 45.7 wt% MgCO3 and 54.3 wt% CaCO3 [28], in good agreement with the theoretical value [29]) were also tested under a set of experimental conditions. The chemical compositions of CRT glass were determined by XRF spectroscopy (XRF – sequential spectrometer, ARL ADVANT’XP, ThermoTechno, Switzerland), the data are reported in Table 1. The real carbonate content in waste egg shells (95.2 wt%) was determined using a Dietrich-Fruhling-calcimeter. The remaining material is a organic matrix [30]. The X-ray diffraction analysis (XRD) of powdered egg shell samples (particle size o 025 μm) was carried out by using a Ni-filtered Cu Kα radiation (PW 3710, Philips) diffractometer in the 5–70º 2θ range. Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) of foaming agents were carried out in air (DTA-TG, Labsys Setaram, Caluire France; heating rate 5 K/min). Table 2 shows all the batch compositions of the investigated glass foams with the general formula [P100  xFx]97FA3 (wt%). The powders (P, F and foaming agent) were dry mixed in a cylindrical rotary mixer for 30 min. Cylindrical pellets (∅ ¼ 20 mm) were prepared by uniaxial pressing (40 MPa). The green samples were heat treated in air in the temperature range of 650–750 1C. True density was measured using a He pycnometer (Micromeritics Accupyc 1330, USA) on powdered samples and the apparent density of glass foams was determined by measuring the weight and the dimensions of the Table 1 Chemical compositions of glass wastes (wt%). Oxide

P

F

SiO2 Al2O3 Na2O K2O CaO MgO BaO SrO PbO Fe2O3 TiO2 LoI Total

67.25 2.76 7.89 7.56 1.34 0.36 11.31 0.26 0.13 0.04 0.49 0.61 100.00

58.84 3.73 6.60 7.33 3.24 1.47 1.80 0.09 16.02 0.12 0.14 0.62 100.00

H.R. Fernandes et al. / Ceramics International 40 (2014) 13371–13379 Table 2 Batch compositions of prepared foams with general formula [P100  xFx]97FA3 (wt%), with FA (foaming agent)¼E, C or D. Compositions

P

F

E

C

D

0 0 0 25 50 75 100 100 100

[P100F0]97E3 [P100F0]97C3 [P100F0]97D3 [P75F25]97E3 [P50F50]97E3 [P25F75]97E3 [P0F100]97E3 [P0F100]97C3 [P0F100]97D3

97 97 97 72.8 48.5 24.2 – – –

– – – 24.2 48.5 72.8 97 97 97

3 – – 3 3 3 3 – –

– 3 – – – – – 3 –

– – 3 – – – – – 3

D

780 ºC 844 ºC

Heat flow (µV)

x

13373

C

880 ºC

E 870 ºC Endo

produced materials. The porosity was evaluated according to the Eq. (1), where P0 is porosity (%), da is the apparent density and dt is the true density.   da P0 ¼ 1   100 ð1Þ dt

0

E

-10

TG (%)

The compression strength of cubic samples was measured in a Shimadzu machine (Trapezium 2, Japan, displacement 0.5 mm/min). Five different samples from each composition were tested. A side-view hot-stage microscope (HSM, Leitz Wetzlar, Germany) equipped with a Pixera video-camera and a image analysis system was used at a heating rate of 5 K/min to investigate the foaming behaviour of glass powder compacts. The crystalline phase assemblage was detected by X-ray diffraction analysis (XRD, Rigaku Geigerflex D/Mac, C Series, Cu Kα radiation, Japan) and microstructure observations were done by scanning electron microscopy (SEM, Hitachi SU-70, Japan).

10

-20 -30

C D

-40 -50 600

700

800

900

Temperature (ºC)

3. Results and discussion 3.1. Thermal DTA/TGA analysis of foaming agents Thermal analyses are an effective way to predict the thermal decomposition of the foaming agents. The DTA and TGA curves of these materials are presented in Fig. 1a and Fig. 1b, respectively. It can be seen that the thermal decomposition of dolomite took place in two typical stages: (1) CaMg(CO3)2MgO þ CO2 þ CaCO3 (at around 700–800 1C) and (2) CaCO3-CaO þ CO2 (at around 900 1C) [31,32]. These two distinct stages are easily identified by the two discrete endothermic peaks centred at 780 and 844 1C. On the other hand, calcite and egg shell both consisting mostly of CaCO3, presented similar DTA curves, with the egg shell one only slight shifted to lower temperatures. This small difference can be understood considering the organic content ( 4.8 wt%) of E, and the expected less organised crystallite structure either before or especially after the burning out of organic matter. Fig. 1b shows that calcite has undergone a weight loss of  43 wt%. This weight change is consistent with the theoretically expected value of  44 wt% for pure CaCO3 and is therefore attributed to the release of CO2. The lower weight loss experienced by egg shell, in comparison to calcite, is also

Fig. 1. Thermal analysis curves of foaming agents: (a) DTA and (b) TGA.

consistent with its lower purity (95.2%). As expected, dolomite was the foaming agent that undergone the highest weight loss ( 46 wt%). This can be easily inferred considering the lower molecular mass of magnesium in comparison to calcium. For a stoichiometric dolomite, a total amount of CO2 released during thermal decomposition per unity of mass would be 47.7 wt%. The difference between this value and the experimentally measured one is small and might be attributed to deviations from stoichiometry and/or any experimental error. 3.2. Thermal behaviour of CRT glass wastes with added 3 wt% E The thermal behaviours of glasses P and F are shown in Fig. 2a through the HSM curves. The typical temperatures corresponding to the beginning of deformation and to the maximum shrinkage are also indicated for each glass. It can be seen that glass F (x ¼ 100) begins deforming at a temperature that is  40 1C below that observed for glass P (x¼ 0). With increasing temperatures the samples undergo shrinkage due to the sintering effect up to maxima values, with the curves running almost parallel. The maximum shrinkage for F is also

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564 ºC

1.0

525 ºC P (x = 0)

A/A0

0.9

F (x = 100)

0.8

0.7

619 ºC 667 ºC 0.6 400

500 600 Temperature (ºC)

700

P F 25

675

700

725

Fig. 2. Hot stage microscopy measurements for glass-powders P (x¼ 0) and F (x ¼100): (a) variation in the relative area of the glass-powder compacts (A/A0) vs temperature, and (b) images of glass powder compacts on alumina substrates at different temperatures.

consistently attained at a temperature that is  50 1C below that observed for P. These results indicate glass F as being more prone to foam at lower temperatures because of its lower refractoriness in comparison to glass P. Moreover, glass F underwent immediate expansion after the maximum shrinkage was attained due to the entrapment of CO2/air inside the melt, while expansion was delayed for glass P, which maintained a slight shrinkage trend within the analysed range of temperatures. This interpretation is well supported by the sequences of HSM images shown in Fig. 2b. At 700 ºC glass F has undergone a noticeable expansion, while the expansion process seems to not have yet started in the case of glass P. These different thermal behaviours of glasses P and F are in good agreement with their chemical compositions (Table 1). Both glasses comprise similar contents of modifier oxides (Na2Oþ K2Oþ CaOþ MgO), but F presents a lower content of SiO2 than P. Furthermore, F is rich in PbO while P is a BaO-rich glass. These differences in the chemical composition are responsible for the lower refractoriness of glass F in comparison to glass P. 3.3. Influence of the type of foaming agent on foaming behaviour A fixed heat treatment schedule (700 1C, 15 min) was selected based on preliminary foaming results at different temperatures and times (not shown). The sequence of HSM images for P glass shown in Fig. 2b suggests that this temperature is insufficient to promote foam formation in the

case. However, one should consider that the HSM analysis was performed at a heating rate of 5 K/min, while a holding time of 15 min was allowed in the foaming experiments. This can be understood considering that the extension of thermal processes depends on both time and temperature. The foaming behaviour of P and F CRT glasses with a fixed added amount (3 wt%) was evaluated separately under these conditions. Fig. 3 shows that for both glasses, the C-containing foams featured the lower values of apparent density (0.32 and 0.27 g/cm3, for P and F glasses, respectively), while the highest value (0.49 g/cm3) was obtained for D-containing foams derived from P glass. These results might be explained by the different decomposition behaviours of C, D and E at 700 1C. For expanding, the glass should attain enough low viscosity (107–108 poise) to allow the sample to expand under the internal pressure produced by gas releasing from the decomposition process of the foaming agent. However, excessively low viscosity can lead to the collapse of the foam structure under the gravity effect, hindering a high porosity to be obtained. Besides viscosity, a suitable foaming ability also requires the generation of enough amount of gas from the decomposition of the foaming agent at the optimal foaming temperature. The results presented in Fig. 3 suggest that C is the most effective foaming agent at 700 1C, which leads to the lowest apparent density foams independently of the kind of glass. Since the attained viscosity at a certain time–temperature conditions is the same for compositions containing a given glass, the dominant factor for the foaming process will be the decomposition behaviour of the foaming agent, namely the matching between the gas releasing event and the closing of open pores. In the present case, it seems that although D releases a higher amount of CO2 than C, its earlier decomposition of the MgCO3 component seems to have occurred when the glass powder beds were still permeable letting some gas to escape before causing expansion and foam formation. The same reasoning helps explaining why E exhibits a better foaming ability that D does. The intermediate foaming ability of E is also supported by its lower degree of purity of E (95.2 wt%) [30] in comparison to C. In accordance with the above referred lower refractoriness of glass F, Fig. 3 confirms that for a fixed added amount of the different FA, the F-derived 0.60

Apparent density (g/cm3)

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Glass P

0.50

Glass F

0.40 0.30 0.20 0.10 0.00 E

C

D

E

C

D

Type of foaming agent Fig. 3. Values of apparent density of samples heat treated at 700 ºC and foamed with 3 wt% of each foaming agent tested.

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1 mm Fig. 4. Microstructural (SEM) analysis of foams obtained from batches with different foaming agents after being heat treated at 700 1C for 15 min: (a) [P0F100]97C3; (b) [P100F0]97C3; (c) [P0F100]97D3; and (d) [P100F0]97D3.

foams formed at 700 1C exhibit lower apparent density in comparison with those derived from P glass [18]. The microstructures of foams obtained at 700 1C for 15 min from P and F glasses with added 3 wt% of C and D shown in Fig. 4 are very consistent with different thermal properties of the glasses. The bubbles are larger for F foams (Fig. 4a,c) irrespective of the foaming agent used, although the largest pores are observed for C-containing foams, probably for the reasons referred above (earlier decomposition of magnesium carbonate when the porosity of powders compacts was not yet completely closed) letting some gas to escape and resulting in less foaming power (Fig. 4b,d). These observations are in accordance with the results of apparent density reported in Fig. 3. Thus, for foams prepared under the same experimental conditions, the samples could be ordered by their apparent density according to the following general trend: P4F, and D4E4C. In other words, the most refractive glass P, and the early decomposition of D, are the factors that favour denser foams to be obtained. From the huge density difference between the glasses (P ¼ 2740 kg/m3, F ¼ 2960 kg/m3) and air (1.225 kg/m3 at sea level and at 15 1C [33]), the air bubbles are expected to raise and coalesce along the foaming period and lead to some porosity gradients in the vertical direction. As a matter of fact, the SEM micrographs presented in Fig. 5 for the [P100F0]97C3 glass foam formed at 700 1C for 15 min confirm that the size of the pores increases from the bottom to the top. Possible temperature/viscosity gradients within the glass powder

top a b c bottom

1 mm Fig. 5. Microstructures of the [P100F0]97C3 glass foamed at 700 1C for 15 min evidencing the pore structures at different levels of the sample: (a) top; (b) main part (centre); and (c) bottom.

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compacts are also likely to contribute for a less homogeneous distribution of pore sizes in foamed glasses. 3.4. Influence of glass mixture and temperature on foaming ability The same fixed heat treatment schedule (700 1C, 15 min) was selected for evaluating the foaming behaviour of (P þ F) glass mixed in different proportions with a fixed added amount of E as the foaming agent. In a second set of experiments a given glass mixture (P/F ¼ 1) was also heat treated at different temperatures for 15 min. The SEM microstructures for the first and second set of experiments are presented in Figs. 6 and 7, respectively, while the related apparent density and porosity data are reported in Fig. 8. It can be seen that the changes in porous structure of the samples were not homogeneous. In the first set of experiments the size of the pores increased for glass mixtures with x 450, likely due to a gradual decrease of viscosity and the smaller internal pressure required for foam deformation or to pore coalescence. The possible bursting of the larger bubbles and the consequent partial collapse of the foams is also likely to occur, leading to an overall increase in their apparent density [34], as suggested by Fig. 6 and confirmed by the data plotted in Fig. 8a. The following interesting aspects can be highlighted from the apparent density and porosity data reported in Fig. 8a–b: 1. A good foaming behaviour was observed for all CRT (P and F) glass mixtures upon heat treating at 700 1C for 15 min. The

composition containing equal parts of F and P (x¼ 50) featured the minimum and the maximum values of apparent density (0.29 g/cm3) and porosity (89.8%), respectively, (Fig. 8a). These values are similar to the typical ones presented by commercial glass foam products, which are within 0.1–0.3 g/ cm3 and 85–95% for apparent density and porosity, respectively [35]. 2. The compressive strength of the glass foams decreased monotonically with the increasing F contents (x), as shown in Fig. 8b. This tendency is in good agreement with the variation of apparent density and porosity up to P/F ¼ 1 (x ¼ 50 wt%) as shown in Fig. 8a. However, the decreasing trend of compressive strength observed for x 450 appears as counterintuitive, as mechanical properties would be enhanced with the apparent density increasing. For x ¼ 50 wt%, Fig. 8c shows that both composition and temperature affect the foaming behaviour.

For the second set of experiments performed with the [P50F50]97E3 (x ¼ 50) glass mixture, significant microstructural changes with the heat treatment temperature can be observed in the SEM micrographs of Fig. 7a–d. At 650 1C the microstructure is characterised by very small and homogeneous dispersed pores (Fig. 7a). An almost similar structure is observed for the sample sintered at 675 1C (Fig. 7b). A further 25 1C increment in temperature resulted in pore coalescence and the appearance of large pore sizes separated by struts containing smaller pores, as well evidenced by the sample

500 µm Fig. 6. Microstructural (SEM) analysis of glass foams obtained from different batch compositions with a fixed added amount of 3 wt% E after being heat treated at 700 1C for 15 min: (a) x ¼0; (b) x ¼25; (c) x¼ 75; and (d) x¼100.

H.R. Fernandes et al. / Ceramics International 40 (2014) 13371–13379

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300 µm Fig. 7. Microstructural (SEM) analysis of the [P50F50]97E3 glass foams heat treated for 15 min at: (a) 650 1C; (b) 675 1C; (c) 700 1C; and (d) 750 1C.

sintered at 700 1C (Fig. 7c). The larger pores observed are consistent with the measured minimum density values for foams sintered at this temperature (Fig. 8c). Further increasing the temperature to 750 1C has apparently enhanced the volume fraction and size of pores at the foam cell walls (struts) [36], and to the concomitant partial collapse of larger ones as seen in Fig. 7d, an observation that is consistent with findings reported elsewhere [34,37]. This partial collapse of larger pores is consistent with the concomitant slight increase in apparent density (Fig. 8c). Fig. 7d also reveals that the struts became more porous with the temperature increasing, suggesting that the slight increase in overall apparent density is not likely to compensate the expected loss in mechanical properties derived from the more porous pore walls. The results presented in Figs. 6–8 show that both composition and temperature affect the foaming behaviour. The apparent density of glass P samples is very temperature dependent due to its higher refractoriness, while the corresponding values for glass F tend to converge within the whole temperature range tested. The enlargement of cell size with rising temperature for the [P50F50]97E3 (x=50) glass mixture, due to a decreasing glass viscosity and an increasing gas pressure is followed by the partial collapse of the foams, a weakening of the struts that become more porous, while the overall apparent density increases. It was already found that mechanical properties of glass foams could be affected by the type of porous structure (pore size, pore size distribution) and crystalline phase assemblage

[27,35,36]. Therefore, XRD data were gathered in order to identify any eventual crystalline phase formed during the heat treatment. The XRD patterns (Fig. 9) collected for both sets of experiments reveal that glass foams are essentially amorphous, exhibiting only broad and weak XRD peaks of quartz (ICDD card 070-2538). This phase tends to gradually disappear either with increasing contents of F glass at 700 1C (Fig. 9a), or with increasing sintering temperatures (650–750 1C) for the composition containing equal parts of F and P (x¼ 50) (Fig. 9b). These observations suggest that the trace amounts of quartz tend to dissolve in the glassy matrix either by using lower melt temperature batches or by increasing the heat treatment temperature. Besides the light porous materials obtained at a moderate temperature, which might find a number of practical applications, the results presented show that this approach could also be regarded as an interesting waste treatment/management solution. Moreover, the viability of recycling of CRT glass mixtures offers a further advantage of avoiding the actual careful separation of these glasses with different chemical compositions. The leaching behaviour of foamed CRT glasses is out of the scope of this paper. Concerning these aspects, the readers are advised to consult the references [13–16]. In any case, leaching tests performed for lead on as-received panel and funnel glasses according to UNI EN 12457-2 showed values of 0.003 and 0.070 mg/L, respectively, which are lower than the Italian regulation limit (D.M 27/9/2010-Table 5) for

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Compres. strength (MPa)

92 700 ºC

[P100−x Fx]97E3

700 ºC 90

0.40 0.35

88

0.30

86

0.25

84

Porosity (%)

Apparent dens. (g/cm3)

0.45

100 75 50 25 0

4.5 700 ºC

4.0

Quartz

3.5 3.0

x = 50

2.5

750 ºC

2.0 1.5

725 ºC

1.0

700 ºC

Apparent density (g.cm-3)

1.0

675 ºC

650 ºC

0.8 675 ºC

650 ºC

0.6 750 ºC

0.4 0.2

Quartz 10

700 ºC

725 ºC

25

30

40

50

60

2θ (º)

0.0 0

20

50

75

100

x (wt.%)

Fig. 9. XRD spectra of glass foams: (a) compositions with different P/F ratios heat treated at 700 1C for 15 min; (b) composition containing x¼ 50 heat treated at different temperatures within the range of 650–750 1C (quartz: ICDD card 070-2538).

Fig. 8. Evolution of foam properties vs composition: (a) apparent density and porosity of samples heat treated at 700 1C; (b) compressive strength of samples heat treated at 700 1C; (c) apparent density of samples heat treated at different temperatures within the range of 650–750 1C.

different foaming agents (egg shell wastes, calcite and dolomite). The following specific conclusions can be drawn from results obtained: landfilling of both non-dangerous (1 mg/L) and dangerous waste (5 mg/L). Pb leaching could be further reduced by devitrification of funnel glass based compositions [38]. The use in our study of carbonate-based foaming agents that decompose at relatively low temperatures, coupled with the absence of reduction agents is likely to drastically decrease the risk of heavy metals reduction upon the foaming process of panel and funnel glasses.

4. Conclusions The present work proved the feasibility of producing glass foams from waste CRT glasses (panel and funnel glass) at relatively low temperatures (650–750 ºC) by heat treating powder mixtures containing a fixed amount (3 wt%) of

1. The used of egg shells as foaming agent enables obtaining glass foams from 100% industrial wastes. 2. Heat treating at 700 1C for 15 min a mixture containing equal amounts of P and F glasses resulted in glass foams featuring apparent density and compressive strength values of 0.29 g/cm3 and 2.34 MPa, respectively, which are similar to the values featured by commercial glass foams. 3. Using mixtures of P and F has some extra advantages since F enhances the foaming ability, while P enhances the compressive strength of the foams. This might be also an alternative approach for the separation of the two types of glasses derived from WEEE wastes. 4. The chemical/thermal characteristics of the starting glasses and their mixtures dictate the foaming behaviour of the powder batches and the physical properties of the foams.

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Acknowledgements Hugo R. Fernandes is grateful for the financial support of CICECO (PEst-C/CTM/LA0011/2013) and for the Post doc grant (SFRH/BPD/86275/2012) from the FCT, Portugal.

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