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Synthesis of zeolite type analcime from industrial wastes
Microporous and Mesoporous Materials xxx (xxxx) xxx
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Synthesis of zeolite type analcime from industrial wastes Raquel Vigil de la Villa Mencía a, Eunate Goiti b, Marta Ocejo b, Rosario García Gim�enez a, * a b
Geomateriales. Asso, Un. CSIC. Deparatmento de Geología y Geoquimica. Fac. Ciencias. UAM. 28049 Madrid, Spain Building Technologies Division, TECNALIA R&I, Astondo Bidea, Derio, 48160, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords: Analcime Industrial waste Hydrothermal synthesis Cement paste
A range of industrial wastes (recycled glass, silica fume, siliceous concrete waste aggregates, sterile coal and foundry sand from the steel industry) are employed in the formation of secondary raw materials following their hydrothermal treatment. Composed mainly of zeolites, these secondary materials, in almost all cases, formed analcime. The sterile coal yielded the best defined analcime crystals. In addition, the secondary raw materials are incorporated as an addition in cement paste formulations, to evaluate their effect at early stages of the hydration process. The secondary materials from the siliceous concrete waste aggregates and recycled glass produced a 23% increase in the compressive strength of the paste after 1 day of curing (in comparison with the cement paste reference).
1. Introduction Zeolite is a generic name for a range of porous aluminosilicate ma terials with three-dimensional crystalline structures, often referred to as molecular sieves [1]. They consist of three-dimensional open structures of silicon and aluminium tetrahedrons the cavities of which are filled with water molecules and cations that compensate the charge difference and that are responsible for their Cation Exchange Capacity (CEC). A generally accepted formula of a zeolite is Mx/n [(AlO2) x (SiO2) and] wH2O, where (M) is an alkaline-earth element and (n) is the valence of that cation. The number of water molecules per cell unit contained in intracrystalline channels is represented as (w), x, and y are the total number of tetrahedral cells per structural unit. One of the most frequently occurring and well-defined forms of ze olites is analcime, with relatively structured unit cells based on nonintersecting channels with four, six, and eight members of oxygen rings and 16 sites occupied by sodium in the smallest 24 cavities and by water molecules, located in the 16 largest channels. The crystal structure of analcime is isometric. Analcime (Hydrous sodium aluminum silicate) is a member of the zeolite group, and often occurs together with other zeolites. However, it is closely related in structure to the feldspathoid group, and is occasionally also classified as a feldspathoid together with the similar mineral leucite. The name analcime is derived from the Greek term “an alkimos”, meaning “not strong, in allusion to the weak pyroelectricity exhibited by this mineral.
Zeolite can be synthesized from kaolinite (K), a source of alumina and silica [2], through subsequent calcination between 700 � C and 1000 � C to achieve dehydroxylation, leading to the formation of meta kaolinite (MK) [3]. The MK is then subjected to hydrothermal treatment with NaOH, to generate zeolite. According to Chang and Bell [4], the process is a reversible mechanism. Commercial synthetic zeolites are more frequently employed than natural zeolites, due to their higher purity [5] and uniform particle size, of greater suitability for most industrial applications [6,7]. However, the preparation of synthetic zeolites from silica and alumina is a rather costly process. Numerous studies in the literature have been performed in the search for affordable alternative raw materials for the synthesis of zeolites [8,9] such as rice husk ash [10–12]; fly ash [10,13,14]; bagasse ash [15–17]; silicon ash [18]; paper sludge [19,20]; sandstones [21,22]; residual porcelain [23,24]; and, kaolinite [25–28]. Johnson and Arshad [29] highlighted the advantages of using economical natural materials for the synthesis of kaolinite-based zeolite. There are two essential steps in the production of zeolites from K: 1) metakaolinitization - which in volves the transformation of kaolin to MK by activation of kaolin; and, 2) zeolitization – the treatment of MK with aqueous alkaline solution to form zeolite materials. However, according to Dion et al. [30], metakaolinitization occurs through dehydroxylation (the water is linked to two adjacent hydroxyl groups) and diffusion (furthering water transport) processes. The met akaolin will then have to be subjected to a hydrothermal process in an
* Corresponding author. E-mail addresses: [email protected] (R. Vigil de la Villa Mencía), [email protected] (E. Goiti), [email protected] (M. Ocejo), rosario.garcia@ uam.es (R.G. Gim�enez). https://doi.org/10.1016/j.micromeso.2019.109817 Received 31 July 2019; Received in revised form 26 September 2019; Accepted 21 October 2019 Available online 1 November 2019 1387-1811/© 2019 Elsevier Inc. All rights reserved.
Please cite this article as: Raquel Vigil de la Villa Mencía, Microporous and Mesoporous Materials, https://doi.org/10.1016/j.micromeso.2019.109817
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Table 1 Industrial wastes. Material
Name
Industrial origin
Silica fume Recycled glass Siliceous concrete waste aggregates Sterile coal
MSN G SCW SC
Alkaline phenolic-based chemically bonded sand Silicate-based chemically bonded sand Alkaline phenolic-based chemically bonded sand Furan-based chemically bonded sand Silicate-based chemically bonded sand
AF1
Electric arc furnace Construction and demolition waste Construction and demolition waste Coal mine from La Robla, Le� on Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain
AF3 AF6 AF7 AF9
Fig. 1. Hydrothermal treatment procedure followed in this paper.
aqueous NaOH solution to synthesise the zeolite. Hydrothermal synthesis is the most common strategy for zeolite synthesis. It can be performed at either subcritical or supercritical con ditions, depending on the reaction temperature. In the first, the tem perature range of the reaction is 100� - 240 � C, while under supercritical conditions, the temperature can reach up to 1000 � C with pressures as high as 3000 bar [31]. Under supercritical conditions, the water acts as a solvent; it changes the physical and chemical properties of the reactants and products; it accelerates the reaction; it participates in the reaction; and, it transfers pressure [32]. In general, the most important advantages of a hydrothermal process are the high reactivity of the reagents, its low energy consumption, the low air pollution, easy control of the solution and the formation of metastable phases and unique condensed phases [33]. The synthesis of zeolite during the hydrothermal process is not only affected by the temperature and pressure, but also by many other vari ables such as Si/Al ratio (must be less than 5), alkalinity, the presence of inorganic cations, the aging process, and the formation of crystallization nuclei [34]. The synthesis of zeolites through the hydrothermal process is therefore a multi-phase process [35] which, in general, covers at least one liquid phase and other crystalline and amorphous solid phases. Zeolites are of great versatility, due to their physical properties, with regard to the number of applications in which they are incorporated. They are principally used in chemical engineering as catalysts, molec ular sieves, and adsorbents. Another important area of application is the construction sector. In this area, several research works have shown that due to the pozzolanic character of zeolites, they can be incorporated in cement mixtures and mortars resulting in the improvement of their properties: increased mechanical strength and durability [36], resis tance to alkali-silica reactions [37], concrete sulphate corrosion [38], and resistance to chloride diffusion [39]. Various aspects can influence the pozzolanic activity of zeolites, amongst which: their purity, chemical composition, mineralogical structure, surface area, and ion exchange capacity. If any of those parameters vary, the final properties of the zeolites will also change. In view of the above, the objective of this paper is the preparation of zeolites from different industrial waste sources, through a hydrothermal treatment, transforming them into secondary raw materials of interest in different applications. Moreover, the influence of this secondary raw material in the hydration of cement pastes at early ages will be also evaluated.
2.1. Materials The industrial wastes employed in the present study are listed in Table 1: silica fume, recycled silica glass, foundry sands from different locations, construction and demolition waste, and coal waste. 2.2. Hydrothermal treatment The hydrothermal reactor (Büchiglasuster bll150) that has been used is a stirrer autoclave of 2L capacity that operates up to 350 � C and up to 350 MPa. The same hydrothermal treatment procedure has been followed for all industrial wastes (Fig. 1) they were treated with a NaOH solution (of 10 M concentration) in the hydrothermal reactor at 225 � C for 2 h. After this time, the reaction mixture was cooled and then filtered. The filtered solid was then washed in water and dried in the oven to a constant weight, obtaining the different solids under study (secondary raw materials). 2.3. Preparation of cement pastes with secondary raw material The cement pastes were prepared using Ordinary Portland cement type I 52.5 R and maintaining a constant water/cement ratio equal to 0.4. The concentration of secondary raw material was established at 5 wt % with respect to cement. No secondary material was added to the reference material, which maintained the same w/c ratio. The pastes were prepared in moulds of 1 cm � 1 cm x 6 cm dimensions. The mix tures were cured at 1, 7, and 28 days in a humid chamber. The secondary raw material selected for the preparation of the pastes was formed from the following industrial waste: glass, sterile coal, and recycled aggregate of siliceous concrete. 2.4. Methods Both the industrial waste and the secondary raw materials were characterized, as described below: The mineralogical composition of the bulk samples was determined using random powder X-ray diffraction (XRD) on a Siemens D-5000 (Munich, Germany) X-ray diffractometer fitted with a Cu anode. The operating conditions were 30 mA and 40 kV with a divergence slit ¼ 2 mm and a receiving slit ¼ 0.6 mm, respectively. The samples were scanned in (2θ) 0.041 steps with a 3-s count time. X’Pert High Score Plus software Ver. 4.1 was used for qualitative determination of the spectra by X-ray powder diffraction equipped with the PDF-2 data base, Release 2008 (International Centre for Diffraction Data, Newtown Square, PA). Quantification of the phases with the Rietveld method was done with the Match 3.5.2. program using internal rutile as a standard, for the quantification of the amorphous phase.
2. Materials and methods Different industrial wastes were hydrothermally treated with the aim of transforming them into secondary raw material of use in other ap plications. The waste products are from different industrial activities such as electric arc furnace, foundry, coal industry and construction. 2
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Table 2 Major elements (by % in weight oxides) of the industrial wastes under analysis. Material
SiO2
Al2O3
Fe2O3 total
MnO
Mg0
CaO
Na2O
K2O
TiO2
P2O5
Cr2O3
LOI
MSN G SCW SC AF1 AF3 AF6 AF7 AF9
91.83 70.49 78.95 56.63 75.90 85.65 88.99 86.55 69.98
0.72 1.83 3.51 25.29 0.64 2.40 2.96 1.43 0.45
0.35 0.53 1.54 4.64 0.60 3.74 0.94 0.13 3.26
0.02 0.02 0.05 0.08
0.45 2.53 0.87 0.77 1.34 1.21 0.28 0.20 21
0.27 9.79 8.19 4.20 0.10
0.15 12.06 0.27 0.17 1.89 0.77 0.28 0.21 0.50
0.99 0.81 0.63 3.09 0.33 0.20 1.32 0.75 0.07
0.02 0.07 0.23 1.17 0.05 0.15 0.04 0.02 0.02
0.10 0.02 0.05 0.14
n.d. n.d. n.d. n.d. 0.23 5.53 0.99 0.01 0.08
3.55 0.28 5.71 3.09 16.19 1.13 0.87 5.24 0.84
n.d. ¼ not detected. L.D. ¼ Limit of Detection. LOI ¼ Loss On Ignition. Table 3 Major elements (by % in weight oxides) of the materials obtained from hydrothermal treatment (secondary raw materials). Material
SiO2
Al2O3
Fe2O3 total
MnO
MgO
CaO
Na2O
K2O
TiO2
P2O5
Cr2O3
LOI
MSN G SCW SC AF1 AF3 AF6 AF7 AF9
55.83 48.96 50.90 47.75 31.75 60.17 58.74 73.52 42.06
2.24 2.99 7.74 25.44 3.15 8.84 14.14 5.92 0.418
2.190 1.020 2.900 4.010 2.060 10.590 6.920 0.315 6.510
0.1960 0.0378 0.1030 0.0570 0.0400 0.0900 0.0850 0.0090 0.1080
7.340 4.890 1.950 0.747 4.650 3.460 2.360 0.126 48.060
2.520 17.780 16.410 2.190 0.641 0.175 0.407 0.201 0.080
9.920 15.040 8.660 8.730 5.760 2.000 3.770 3.980 0.851
0.296 0.110 0.758 2.18 0.508 0.370 1.970 1.210 n.d.
0.0174 n.d. n.d. 0.9480 0.2540 0.5110 0.2020 0.0810 n.d.
n.d. n.d. n.d. 0.118 0.040 0.010 0.051 0.028 n.d.
0.0196 0.0599 n.d. 0.0200 0.6980 12.2800 6.7600 0.0240 0.1670
18.83 8.73 9.61 7.60 49.38 0.82 3.98 14.15 1.10
n.d. ¼ not detected.
The morphological observations and microanalysis of the samples were performed with SEM/EDX, by using an Inspect FEI Company Electron Microscopy (Hillsboro, OR), equipped with energy dispersive X-ray analyzer (W source, DX4i analyzer and Si/Li detector). The chemical composition was established with an average value of ten analyses for each sample, expressed in this case alongside the standard deviation. The results were expressed in oxides (wt %) adjusted to 100%. Chemical composition of the samples was determined by X-ray fluorescence using a sequential wavelength fluorescence X-ray spec trometer of the PANalytical brand; model AXIOS, equipped with an Rh tube and three detectors. Loss on Ignition (LOI) for the samples was at 1050 � C for 1 h. The granulometry of the secondary raw materials was determined by analysis in a Malvern Mastersizer. The cement pastes were characterized by evaluating the setting heat, by means of a conduction calorimeter for pastes (TA equipment, model TAM AIR). The base temperature for the measurements was 25 � C and the records were completed during the first 48 h of hydration. The me chanical properties of the pastes were studied by means of compression tests in an IBERTEST ELIB-10 unit with a loading cell of 10 kN. 3. Results and discussion
Fig. 2. XRD patterns from the initial waste and the secondary raw material (silica fume, MSN).
3.1. X-ray fluorescence analysis
described below.
The elemental compositions of the major elements of the industrial wastes under study are shown in Table 2. All the industrial wastes had silica percentages of over 55%. Sterile coal (SC) presented high levels of Al2O3. The chemical composition of the materials obtained from the hy drothermal treatment of each industrial waste was also evaluated (Table 3). 3.2. X-ray diffraction analysis
3.2.1. Silica fume (MSN) Silica fume, microsilica or active silica is a product composed of spherical particles obtained in the reduction of quartz by coal [40]. The original material presents a strong degree of amorphousness (Fig. 2), with a very wide peak in the region of the spectrum corresponding to the quartz. It can therefore be identified as a silica glass. When this waste is subjected to hydrothermal treatment, a reorganization of the vitreous network occurs; modifying the bonds and an analcime phase trans formation occurs (Fig. 2, Table 4).
The diffractograms of the initial and secondary raw material samples (the industrial wastes and their respective materials obtained from hy drothermal treatment) revealed the mineralogical compositions that are
3.2.2. Recycled glass (G) The initial recycled glass showed traces in XRD similar to those of silica fume, possibly with a greater degree of amorphousness, which 3
Olivine (%)
A nd nd nd nd nd nd nd nd nd B nd nd nd 27 nd nd nd nd nd A nd nd nd nd 9 nd nd nd 30 A nd nd 18 24 3 nd nd nd nd
A nd nd 8 2 13 nd nd nd nd
Calcite (%)
B nd nd 6 2 nd nd nd nd nd
Mica (%)
B nd nd 15 28 9 nd nd nd nd A nd nd 5 Nd 4 nd 32 9 nd
Feldspar (%)
B nd nd 20 9 7 nd 2 1 22 A nd 5 nd nd nd nd nd nd nd
Pyroxene (%)
B nd nd nd nd nd nd nd nd nd A nd 4 nd nd nd nd nd nd nd
Ilmenite (%)
B nd nd nd nd nd nd nd nd nd A nd 16 38 11 18 49 34 47 70
Quartz (%)
B nd nd 30 32 72 89 92 99 65 A nd 12 nd nd nd nd nd nd nd
Fig. 4. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-1.
B nd nd nd nd nd nd nd nd nd
Anhydrite (%)
Fig. 3. XRD patterns from the initial waste and the secondary raw material (recycled glass, G).
A 3.2 9.3 7.8 9.0 7.2 8.5 9.8 9.1 9.5 G SCW SC AF1 AF3 AF6 AF7 AF9
after hydrothermal treatment was converted into a mixture of crystalline phases such as pyroxene, analcime, quartz, anhydride, and ilmenite (Fig. 3, Table 4).
nd ¼ not detected; B ¼ initial waste; A ¼ secondary raw material. χ2, is the setting value in the Rietveld method.
B 8.5 9.3 8.9 9.9 9.5 7.0 7.0 10.1 8.7 A 68 17 24 55 21 27 10 9 nd B nd nd nd nd nd nd nd nd nd A 32 46 7 8 32 24 24 34 nd B 100 100 5 2 12 11 6 nd nd MSN
Х2 Analcime (%) Amorphous material (%) Material
Table 4 Mineralogical composition of the all-industrial waste before and after hydrothermal treatment.
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B nd nd nd nd nd nd nd nd 13
Kaolinite (%)
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3.2.3. Siliceous concrete waste aggregates (SCW) Waste from construction and demolition is rich in silicate minerals such as quartz, mica and feldspars, which are accompanied by a small amount of calcite. After the hydrothermal treatment, the same mineral species are conserved and analcime is formed in a new phase (Table 4). 3.2.4. Sterile coal (SC) Sterile coal from tailings is characterized by the presence of micas, kaolinite, quartz, calcite and feldspars. After the hydrothermal treat ment, mica, quartz, and calcite remain, while no feldspar signal is detected and kaolinite disappears, observing the analcime formation as the crystalline product of the reaction (Table 4). 3.2.5. Foundry sands Within this group, five foundry sands from different sources were studied. In its initial phase, the AF1 foundry sand was composed of quartz and 4
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Fig. 5. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-3. Fig. 8. XRD results for the AF-9 foundry sand: initial waste and secondary raw material.
a small amount of feldspars and mica. Following its hydrothermal treatment, the quartz remained, the feldspars recrystallized (a more powerful signal) and new crystalline phases appeared; analcime and olivine (Fig. 4, Table 4). The AF3 foundry sand was composed of quartz and feldspar. The latter disappeared after the hydrothermal treatment, generating an analcime as phase of neoformation (Fig. 5, Table 4). The mineralogical composition of the AF6 foundry sand was basi cally quartz and feldspar. Following the hydrothermal treatment, quartz remained, and the Na–K feldspars recrystallized, showing a very strong signal, and very well crystallized analcime formations appeared as a new solid phase (Fig. 6, Table 4). As an initial and secondary raw material, the AF7 foundry sand showed a similar composition (Fig. 7, Table 4). Finally, the AF9 foundry sand was formed of quartz, olivine, and feldspars (Fig. 8). Following the hydrothermal treatment of the sample, the feldspars had disappeared, leaving the other two minerals, quartz and olivine. Fig. 6. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-6.
3.3. SEM/EDX The general behavioural trend of the different wastes, once subjected to hydrothermal treatment, in all cases resulted in analcime phases, except for the AF9 foundry sand sample, where the new material was olivine. Polycrystalline analcime has been prepared from hydrogels under hydrothermal conditions [35,41] for a long time [32] up until the present [42]. AF6, following hydrothermal treatment was converted into analcime and Na–K feldspar (composition 4.26% Na2O, 30.29% Al2O3, 57.59% SiO2, 7.31% K2O; 0.56% CaO) (Fig. 9A and B), as described by Goodwin [43]. Concerning AF9 material, its treatment lead to the neoformation of the olivine phase with a composition of 50.05% MgO, 43.77% SiO2, 6.18% Fe2O3), which corresponds to a forsterite. (Fig. 9C and D). Following hydrothermal treatment of AF3, a new analcime phase formation was observed, with poorly defined crystalline faces, which indicates that an incipient formation has occurred (Fig. 9A and B). A similar phenomenon is observed for AF7; the neoformed analcime (composition 15.05% Na2O, 22.33% Al2O3, 62.62% SiO2) also presents poorly formed faces that coexist with silica aggregates (Fig. 10A and B). The opposite situation was observed in AF1, as showed in Fig. 9C and D the analcime particles present good defined faces and angles (isolated trapezohedrons). When using silica fume (SMN) as raw material, incipient analcime crystals with silica are formed (composition 15.46% Na2O, 23.12%
Fig. 7. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-7.
5
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Fig. 9. SEM images of AF – 6 foundry sand: A) analcime and waste glass B) prismatic feldspars. SEM images of AF – 9 foundry sand: C) and D) olivine crystals.
Fig. 10. SEM images of AF – 3: A) and B) incipient faces of analcime crystals. SEM images of AF – 1: C) and D) analcime trapezohedrons.
Al2O3, 61.42% SiO2) (Fig. 10C and D). The analcime crystals that presented the best-defined faces and an gles were obtained from the sterile carbon’s (SC) treatment. Here the analcime had a composition of 15.75% Na2O, 24.19% Al2O3 and 60.06% Si2O and showed trapezoidal trigonal trisoctahedral faces (Fig. 11A and B). The hydrothermal reaction of recycled glass (G) generated the neo formation of analcime crystals with their faces coated by fibres of Ca–Na
pyroxenes (15.34% Na2O; 5.56% MgO; 0.99 Al2O3; 58.37% SiO2; 1.27, SO3; 17.63% CaO and 0.83% Fe2O3 (Fig. 11C and D). 3.4. Cement pastes with secondary raw material As indicated in the introduction, zeolites can have various applica tions. Here, the effects of zeolites, which are integrated into the sec ondary raw materials, in the hydration of cement pastes is evaluated. 6
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Fig. 11. SEM images of AF – 7: A) Analcime B) silica. SEM images of SMN: C) Incipient analcime crystal formation.
Fig. 12. SEM images of SC: A) and B) perfect crystals of analcime. SEM images of G: C) Analcime covered by pyroxenes; D) Pyroxene fibres.
The preparation of the pastes was performed with three of the ma terials obtained from the hydrothermal treatment of the recycled glass, sterile coal, and the SCW, respectively. The size distribution of these materials was evaluated by means of a granulometric analysis in a Malvern Mastersizer. In all three cases, 95% by volume of the particles had a size below 100 μm. The mechanical tests performed after 1 day of curing showed that the compressive strength is increased a 23%, with respect to the reference material, for the cement pastes prepared with the secondary raw
material coming from the recycled glass and the SCW. In the case of using the secondary raw material from the sterile coal waste, the value of the compressive strength remains equal to the reference material. After 7 and 28 curing days, the value of the compressive strength was basically equal in all the samples (see Fig. 12). In the literature, the improvement of mechanical properties is asso ciated with two phenomena: i) the micro or nano size effect of the particle (added in the cement paste formulation), which produces a nucleation effect resulting in an acceleration of hydration; and, ii) a 7
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Moreover, because of the hydrothermal treatment the presence of feldspars and micas, as well as some silicate minerals is observed. However, in some cases, the analcime neoformation phase was total, leaving only the analcime as the reaction product. Finally, the results pointed to the possibility of using the secondary raw materials as accelerators in the hydration of cement pastes. The secondary raw materials obtained from the SCW and recycled glass produced a 23% increase in the compressive strength compared to the reference material after 1 day of curing. Acknowledgements This research has been founded by The Spanish Ministry of the Economy and Competitiveness under coordinated project BIA201565558-C3-1-2-3R (MINECO/FEDER) and The Spanish Ministry of Sci ence Innovation and Universities under a coordinated project RTI2018097074-B-C21 (MICINN/FEDER).
Fig. 13. Compressive strength after 1, 7, and 28 days of curing.
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Fig. 14. Normalized heat flow during hydration at early ages.
pozzolanic reaction. If we observe the curves (Fig. 13) that correspond to the evolution of the hydration heat (obtained in the calorimetry tests), an acceleration occurs in those cement pastes where the secondary raw material from the recycled glass and the SCW had been added. On the contrary, this acceleration phenomenon was not observed in the case of the material from the sterile coal waste (see Fig. 14). It therefore appears that the increase in the compression strength was due to the nucleation effect of the particles of the secondary raw material obtained from the SCW and Glass treatment. Lending attention to the chemical composition of the three materials (Table 3), we can see that they all have a composition of around 50% silica, however, the secondary raw materials formed from recycled glass and SCW presented a high percentage of calcium (around 17%), while the secondary raw material produced from the sterile coal had around 2% [44-46]. These results contribute to the hypothesis that the acceleration that occurs during the early hydration ages may not only be derived from the seed effect, but also from the effect of the composition of the particles added. 4. Conclusions In this work, the use of different waste streams for the formation of zeolites following hydrothermal treatment has been validated. The treatment applied to these silica-rich wastes leads to analcime phase neoformation except in the case of AF9 in which an olivine phase neo formation was noted. The analcime crystals that have the best-defined faces and angles were obtained from the AF1 and sterile coal waste materials. 8
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Microporous and Mesoporous Materials xxx (xxxx) xxx [35] C.S. Cundy, P.A. Cox, The hydrothermal synthesis of zeolites: history and development from the earliest days to the present time, Chem. Rev. 103 (2003) 663–702. [36] M. Najimi, J. Sobhani, B. Ahmadi, M. Shekarchi, An experimental study on durability properties of concrete containing zeolite as a highly reactive natural pozzolan, Constr. Build. Mater. 35 (2012) 1023–1033. [37] B. Ahmadi, M. Shekarchi, Use of natural zeolite as a supplementary cementitious material, Cement Concr. Compos. 32 (2010) 134–141. [38] I. Janotka, L. Krajci, Sulfate resistance and passivation ability of the mortar made from pozzolan cement with zeolite, J. Therm. Anal. Calorim. 94 (2008) 7–14. [39] S.Y.N. Chan, X. Ji, Comparative study of the initial surface absorption and chloride diffusion of high performance zeolite, silica fume and PFA concretes, Cement Concr. Compos. 21 (1999) 293–300. [40] Humo de sílice Cedex, Cat� alogo de residuos utilizables en construcci� on, Ficha 2.4 (2012). [41] C.S. Cundy, P.A. Cox, The hydrothermal synthesis of zeolites: precursors, intermediates and reaction mechanism, Microporous Mesoporous Mater. 82 (1–2) (2005) 1–78. [42] J. Chen, H. Ma, C. Liu, J. Yuan, Synthesis of analcime crystals and simultaneous potassium extraction from natrolite syenite, Adv. Mat. Sci. Eng. (2017) 2617597–2617606. [43] J.H. Goodwin, Analcime and K-feldspar in tutfs of the green river formation, Wyoming, Am. Mineral. 58 (1973) 93–105. [44] E. Berodier, K. Scrivener, Understanding the filler effect on the nucleation and growth of C-S-H, J. Am. Ceram. Soc. 97 (2014) 3764–3773. [45] M. Valipour, F. Pargar, M. Shekarchi, S. Khani, Comparing a natural pozzolan, zeolite, to metakaolin and silica fume in terms of their effect on the durability characteristics of concrete: a laboratory study, Constr. Build. Mater. 41 (2013) 879–888. [46] J. Stark, B. Moser, F. Bellmann, Nucleation and growth of C-S-H phases on mineral admixtures, Adv. Constr. Mat. (2007) 531–538.
[22] T. Wajima, K. Munakata, Material conversion from waste sandstone cake into cation exchanger using alkali fusion, Ceram. Int. 38 (2012) 1741–1744. [23] T. Wajima, Y. Ikegami, Zeolitic adsorbent synthesized from powdered waste porcelain, and its capacity for heavy metal removal, Ars Separat. Acta 4 (2006) 86–95. [24] T. Wajima, Y. Ikegami, Synthesis of crystalline zeolite-13X from waste porcelain using alkali fusion, Ceram. Int. 35 (2009) 2983–2986. [25] A. De Lucas, M.A. Uguina, I. Covi� an, L. Rodríguez, Synthesis of 13X zeolite from calcined kaolins and sodium silicate for use in detergents, Ind. Eng. Chem. Res. 31 (1992) 2134–2140. [26] C. Covarrubias, R. García, R. Arriagada, J. Y� anez, M.T. Garland, Cr (III) exchange on zeolites obtained from kaolin and natural mordenite, Microporous Mesoporous Mater. 88 (2006) 220–231. [27] A. Kovo, O. Hernandez, S. Holmes, Synthesis and characterization of zeolite Y and ZSM-5 from Nigerian Ahoko kaolin using a novel, lower temperature, metakaolinization technique, J. Mater. Chem. 19 (2009) 6207–6212. [28] D. Georgiev, B. Bogdanov, Y. Hristov, I. Markovska, Synthesis of NaA zeolite from natural kaolinite, Oxid. Commun. 34 (2011) 812–819. [29] E. Johnson, S.E. Arshad, Hydrothermally synthesized zeolites based on kaolinite: a review, Appl. Clay Sci. 97 (2014) 215–221. [30] P. Dion, J.-F. Alcover, F. Bergaya, A. Ortega, P. Llewellyn, Kinetic study by controlled-transformation rate thermal analysis of the dehydroxylation of kaolinite, Clay Miner. 33 (1998) 269–276. [31] T. Abdullahi, Z. Harun, M. Hafiz, D. Othman, A review on sustainable synthesis of zeolite from kaolinite resources via hydrothermal process, Adv. Powder Technol. 28 (8) (2017) 1827–1840. [32] H. Mimura, T. Tezuka, K. Akiva, formation of analcime film under hydrothermal conditions, J. Nucl. Sci. Technol. 3 (2) (1995) 1250–1258 [12]. [33] A. Julbe, D. Farrusseng, J. Jalibert, C. Mirodatos, C. Guizard, Characteristics and performance in the oxidative dehydrogenation of propane of MFI and V-MFI zeolite membranes, Catal. Today 56 (2000) 199–209. � [34] Y. Jihong, Chapter 3 synthesis of zeolites, in: Cejka Ji�rí, v.B. Herman, C. Avelino, S. Ferdi (Eds.), Studies in Surface Science and Catalysis, vol. 168, Elsevier, Amsterdam, 2007, pp. 39–103.
9
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Microporous and Mesoporous Materials journal homepage: http://www.elsevier.com/locate/micromeso
Synthesis of zeolite type analcime from industrial wastes Raquel Vigil de la Villa Mencía a, Eunate Goiti b, Marta Ocejo b, Rosario García Gim�enez a, * a b
Geomateriales. Asso, Un. CSIC. Deparatmento de Geología y Geoquimica. Fac. Ciencias. UAM. 28049 Madrid, Spain Building Technologies Division, TECNALIA R&I, Astondo Bidea, Derio, 48160, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords: Analcime Industrial waste Hydrothermal synthesis Cement paste
A range of industrial wastes (recycled glass, silica fume, siliceous concrete waste aggregates, sterile coal and foundry sand from the steel industry) are employed in the formation of secondary raw materials following their hydrothermal treatment. Composed mainly of zeolites, these secondary materials, in almost all cases, formed analcime. The sterile coal yielded the best defined analcime crystals. In addition, the secondary raw materials are incorporated as an addition in cement paste formulations, to evaluate their effect at early stages of the hydration process. The secondary materials from the siliceous concrete waste aggregates and recycled glass produced a 23% increase in the compressive strength of the paste after 1 day of curing (in comparison with the cement paste reference).
1. Introduction Zeolite is a generic name for a range of porous aluminosilicate ma terials with three-dimensional crystalline structures, often referred to as molecular sieves [1]. They consist of three-dimensional open structures of silicon and aluminium tetrahedrons the cavities of which are filled with water molecules and cations that compensate the charge difference and that are responsible for their Cation Exchange Capacity (CEC). A generally accepted formula of a zeolite is Mx/n [(AlO2) x (SiO2) and] wH2O, where (M) is an alkaline-earth element and (n) is the valence of that cation. The number of water molecules per cell unit contained in intracrystalline channels is represented as (w), x, and y are the total number of tetrahedral cells per structural unit. One of the most frequently occurring and well-defined forms of ze olites is analcime, with relatively structured unit cells based on nonintersecting channels with four, six, and eight members of oxygen rings and 16 sites occupied by sodium in the smallest 24 cavities and by water molecules, located in the 16 largest channels. The crystal structure of analcime is isometric. Analcime (Hydrous sodium aluminum silicate) is a member of the zeolite group, and often occurs together with other zeolites. However, it is closely related in structure to the feldspathoid group, and is occasionally also classified as a feldspathoid together with the similar mineral leucite. The name analcime is derived from the Greek term “an alkimos”, meaning “not strong, in allusion to the weak pyroelectricity exhibited by this mineral.
Zeolite can be synthesized from kaolinite (K), a source of alumina and silica [2], through subsequent calcination between 700 � C and 1000 � C to achieve dehydroxylation, leading to the formation of meta kaolinite (MK) [3]. The MK is then subjected to hydrothermal treatment with NaOH, to generate zeolite. According to Chang and Bell [4], the process is a reversible mechanism. Commercial synthetic zeolites are more frequently employed than natural zeolites, due to their higher purity [5] and uniform particle size, of greater suitability for most industrial applications [6,7]. However, the preparation of synthetic zeolites from silica and alumina is a rather costly process. Numerous studies in the literature have been performed in the search for affordable alternative raw materials for the synthesis of zeolites [8,9] such as rice husk ash [10–12]; fly ash [10,13,14]; bagasse ash [15–17]; silicon ash [18]; paper sludge [19,20]; sandstones [21,22]; residual porcelain [23,24]; and, kaolinite [25–28]. Johnson and Arshad [29] highlighted the advantages of using economical natural materials for the synthesis of kaolinite-based zeolite. There are two essential steps in the production of zeolites from K: 1) metakaolinitization - which in volves the transformation of kaolin to MK by activation of kaolin; and, 2) zeolitization – the treatment of MK with aqueous alkaline solution to form zeolite materials. However, according to Dion et al. [30], metakaolinitization occurs through dehydroxylation (the water is linked to two adjacent hydroxyl groups) and diffusion (furthering water transport) processes. The met akaolin will then have to be subjected to a hydrothermal process in an
* Corresponding author. E-mail addresses: [email protected] (R. Vigil de la Villa Mencía), [email protected] (E. Goiti), [email protected] (M. Ocejo), rosario.garcia@ uam.es (R.G. Gim�enez). https://doi.org/10.1016/j.micromeso.2019.109817 Received 31 July 2019; Received in revised form 26 September 2019; Accepted 21 October 2019 Available online 1 November 2019 1387-1811/© 2019 Elsevier Inc. All rights reserved.
Please cite this article as: Raquel Vigil de la Villa Mencía, Microporous and Mesoporous Materials, https://doi.org/10.1016/j.micromeso.2019.109817
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Microporous and Mesoporous Materials xxx (xxxx) xxx
Table 1 Industrial wastes. Material
Name
Industrial origin
Silica fume Recycled glass Siliceous concrete waste aggregates Sterile coal
MSN G SCW SC
Alkaline phenolic-based chemically bonded sand Silicate-based chemically bonded sand Alkaline phenolic-based chemically bonded sand Furan-based chemically bonded sand Silicate-based chemically bonded sand
AF1
Electric arc furnace Construction and demolition waste Construction and demolition waste Coal mine from La Robla, Le� on Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain Foundry industry located in the North of Spain
AF3 AF6 AF7 AF9
Fig. 1. Hydrothermal treatment procedure followed in this paper.
aqueous NaOH solution to synthesise the zeolite. Hydrothermal synthesis is the most common strategy for zeolite synthesis. It can be performed at either subcritical or supercritical con ditions, depending on the reaction temperature. In the first, the tem perature range of the reaction is 100� - 240 � C, while under supercritical conditions, the temperature can reach up to 1000 � C with pressures as high as 3000 bar [31]. Under supercritical conditions, the water acts as a solvent; it changes the physical and chemical properties of the reactants and products; it accelerates the reaction; it participates in the reaction; and, it transfers pressure [32]. In general, the most important advantages of a hydrothermal process are the high reactivity of the reagents, its low energy consumption, the low air pollution, easy control of the solution and the formation of metastable phases and unique condensed phases [33]. The synthesis of zeolite during the hydrothermal process is not only affected by the temperature and pressure, but also by many other vari ables such as Si/Al ratio (must be less than 5), alkalinity, the presence of inorganic cations, the aging process, and the formation of crystallization nuclei [34]. The synthesis of zeolites through the hydrothermal process is therefore a multi-phase process [35] which, in general, covers at least one liquid phase and other crystalline and amorphous solid phases. Zeolites are of great versatility, due to their physical properties, with regard to the number of applications in which they are incorporated. They are principally used in chemical engineering as catalysts, molec ular sieves, and adsorbents. Another important area of application is the construction sector. In this area, several research works have shown that due to the pozzolanic character of zeolites, they can be incorporated in cement mixtures and mortars resulting in the improvement of their properties: increased mechanical strength and durability [36], resis tance to alkali-silica reactions [37], concrete sulphate corrosion [38], and resistance to chloride diffusion [39]. Various aspects can influence the pozzolanic activity of zeolites, amongst which: their purity, chemical composition, mineralogical structure, surface area, and ion exchange capacity. If any of those parameters vary, the final properties of the zeolites will also change. In view of the above, the objective of this paper is the preparation of zeolites from different industrial waste sources, through a hydrothermal treatment, transforming them into secondary raw materials of interest in different applications. Moreover, the influence of this secondary raw material in the hydration of cement pastes at early ages will be also evaluated.
2.1. Materials The industrial wastes employed in the present study are listed in Table 1: silica fume, recycled silica glass, foundry sands from different locations, construction and demolition waste, and coal waste. 2.2. Hydrothermal treatment The hydrothermal reactor (Büchiglasuster bll150) that has been used is a stirrer autoclave of 2L capacity that operates up to 350 � C and up to 350 MPa. The same hydrothermal treatment procedure has been followed for all industrial wastes (Fig. 1) they were treated with a NaOH solution (of 10 M concentration) in the hydrothermal reactor at 225 � C for 2 h. After this time, the reaction mixture was cooled and then filtered. The filtered solid was then washed in water and dried in the oven to a constant weight, obtaining the different solids under study (secondary raw materials). 2.3. Preparation of cement pastes with secondary raw material The cement pastes were prepared using Ordinary Portland cement type I 52.5 R and maintaining a constant water/cement ratio equal to 0.4. The concentration of secondary raw material was established at 5 wt % with respect to cement. No secondary material was added to the reference material, which maintained the same w/c ratio. The pastes were prepared in moulds of 1 cm � 1 cm x 6 cm dimensions. The mix tures were cured at 1, 7, and 28 days in a humid chamber. The secondary raw material selected for the preparation of the pastes was formed from the following industrial waste: glass, sterile coal, and recycled aggregate of siliceous concrete. 2.4. Methods Both the industrial waste and the secondary raw materials were characterized, as described below: The mineralogical composition of the bulk samples was determined using random powder X-ray diffraction (XRD) on a Siemens D-5000 (Munich, Germany) X-ray diffractometer fitted with a Cu anode. The operating conditions were 30 mA and 40 kV with a divergence slit ¼ 2 mm and a receiving slit ¼ 0.6 mm, respectively. The samples were scanned in (2θ) 0.041 steps with a 3-s count time. X’Pert High Score Plus software Ver. 4.1 was used for qualitative determination of the spectra by X-ray powder diffraction equipped with the PDF-2 data base, Release 2008 (International Centre for Diffraction Data, Newtown Square, PA). Quantification of the phases with the Rietveld method was done with the Match 3.5.2. program using internal rutile as a standard, for the quantification of the amorphous phase.
2. Materials and methods Different industrial wastes were hydrothermally treated with the aim of transforming them into secondary raw material of use in other ap plications. The waste products are from different industrial activities such as electric arc furnace, foundry, coal industry and construction. 2
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Table 2 Major elements (by % in weight oxides) of the industrial wastes under analysis. Material
SiO2
Al2O3
Fe2O3 total
MnO
Mg0
CaO
Na2O
K2O
TiO2
P2O5
Cr2O3
LOI
MSN G SCW SC AF1 AF3 AF6 AF7 AF9
91.83 70.49 78.95 56.63 75.90 85.65 88.99 86.55 69.98
0.72 1.83 3.51 25.29 0.64 2.40 2.96 1.43 0.45
0.35 0.53 1.54 4.64 0.60 3.74 0.94 0.13 3.26
0.02 0.02 0.05 0.08
0.45 2.53 0.87 0.77 1.34 1.21 0.28 0.20 21
0.27 9.79 8.19 4.20 0.10
0.15 12.06 0.27 0.17 1.89 0.77 0.28 0.21 0.50
0.99 0.81 0.63 3.09 0.33 0.20 1.32 0.75 0.07
0.02 0.07 0.23 1.17 0.05 0.15 0.04 0.02 0.02
0.10 0.02 0.05 0.14
n.d. n.d. n.d. n.d. 0.23 5.53 0.99 0.01 0.08
3.55 0.28 5.71 3.09 16.19 1.13 0.87 5.24 0.84
n.d. ¼ not detected. L.D. ¼ Limit of Detection. LOI ¼ Loss On Ignition. Table 3 Major elements (by % in weight oxides) of the materials obtained from hydrothermal treatment (secondary raw materials). Material
SiO2
Al2O3
Fe2O3 total
MnO
MgO
CaO
Na2O
K2O
TiO2
P2O5
Cr2O3
LOI
MSN G SCW SC AF1 AF3 AF6 AF7 AF9
55.83 48.96 50.90 47.75 31.75 60.17 58.74 73.52 42.06
2.24 2.99 7.74 25.44 3.15 8.84 14.14 5.92 0.418
2.190 1.020 2.900 4.010 2.060 10.590 6.920 0.315 6.510
0.1960 0.0378 0.1030 0.0570 0.0400 0.0900 0.0850 0.0090 0.1080
7.340 4.890 1.950 0.747 4.650 3.460 2.360 0.126 48.060
2.520 17.780 16.410 2.190 0.641 0.175 0.407 0.201 0.080
9.920 15.040 8.660 8.730 5.760 2.000 3.770 3.980 0.851
0.296 0.110 0.758 2.18 0.508 0.370 1.970 1.210 n.d.
0.0174 n.d. n.d. 0.9480 0.2540 0.5110 0.2020 0.0810 n.d.
n.d. n.d. n.d. 0.118 0.040 0.010 0.051 0.028 n.d.
0.0196 0.0599 n.d. 0.0200 0.6980 12.2800 6.7600 0.0240 0.1670
18.83 8.73 9.61 7.60 49.38 0.82 3.98 14.15 1.10
n.d. ¼ not detected.
The morphological observations and microanalysis of the samples were performed with SEM/EDX, by using an Inspect FEI Company Electron Microscopy (Hillsboro, OR), equipped with energy dispersive X-ray analyzer (W source, DX4i analyzer and Si/Li detector). The chemical composition was established with an average value of ten analyses for each sample, expressed in this case alongside the standard deviation. The results were expressed in oxides (wt %) adjusted to 100%. Chemical composition of the samples was determined by X-ray fluorescence using a sequential wavelength fluorescence X-ray spec trometer of the PANalytical brand; model AXIOS, equipped with an Rh tube and three detectors. Loss on Ignition (LOI) for the samples was at 1050 � C for 1 h. The granulometry of the secondary raw materials was determined by analysis in a Malvern Mastersizer. The cement pastes were characterized by evaluating the setting heat, by means of a conduction calorimeter for pastes (TA equipment, model TAM AIR). The base temperature for the measurements was 25 � C and the records were completed during the first 48 h of hydration. The me chanical properties of the pastes were studied by means of compression tests in an IBERTEST ELIB-10 unit with a loading cell of 10 kN. 3. Results and discussion
Fig. 2. XRD patterns from the initial waste and the secondary raw material (silica fume, MSN).
3.1. X-ray fluorescence analysis
described below.
The elemental compositions of the major elements of the industrial wastes under study are shown in Table 2. All the industrial wastes had silica percentages of over 55%. Sterile coal (SC) presented high levels of Al2O3. The chemical composition of the materials obtained from the hy drothermal treatment of each industrial waste was also evaluated (Table 3). 3.2. X-ray diffraction analysis
3.2.1. Silica fume (MSN) Silica fume, microsilica or active silica is a product composed of spherical particles obtained in the reduction of quartz by coal [40]. The original material presents a strong degree of amorphousness (Fig. 2), with a very wide peak in the region of the spectrum corresponding to the quartz. It can therefore be identified as a silica glass. When this waste is subjected to hydrothermal treatment, a reorganization of the vitreous network occurs; modifying the bonds and an analcime phase trans formation occurs (Fig. 2, Table 4).
The diffractograms of the initial and secondary raw material samples (the industrial wastes and their respective materials obtained from hy drothermal treatment) revealed the mineralogical compositions that are
3.2.2. Recycled glass (G) The initial recycled glass showed traces in XRD similar to those of silica fume, possibly with a greater degree of amorphousness, which 3
Olivine (%)
A nd nd nd nd nd nd nd nd nd B nd nd nd 27 nd nd nd nd nd A nd nd nd nd 9 nd nd nd 30 A nd nd 18 24 3 nd nd nd nd
A nd nd 8 2 13 nd nd nd nd
Calcite (%)
B nd nd 6 2 nd nd nd nd nd
Mica (%)
B nd nd 15 28 9 nd nd nd nd A nd nd 5 Nd 4 nd 32 9 nd
Feldspar (%)
B nd nd 20 9 7 nd 2 1 22 A nd 5 nd nd nd nd nd nd nd
Pyroxene (%)
B nd nd nd nd nd nd nd nd nd A nd 4 nd nd nd nd nd nd nd
Ilmenite (%)
B nd nd nd nd nd nd nd nd nd A nd 16 38 11 18 49 34 47 70
Quartz (%)
B nd nd 30 32 72 89 92 99 65 A nd 12 nd nd nd nd nd nd nd
Fig. 4. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-1.
B nd nd nd nd nd nd nd nd nd
Anhydrite (%)
Fig. 3. XRD patterns from the initial waste and the secondary raw material (recycled glass, G).
A 3.2 9.3 7.8 9.0 7.2 8.5 9.8 9.1 9.5 G SCW SC AF1 AF3 AF6 AF7 AF9
after hydrothermal treatment was converted into a mixture of crystalline phases such as pyroxene, analcime, quartz, anhydride, and ilmenite (Fig. 3, Table 4).
nd ¼ not detected; B ¼ initial waste; A ¼ secondary raw material. χ2, is the setting value in the Rietveld method.
B 8.5 9.3 8.9 9.9 9.5 7.0 7.0 10.1 8.7 A 68 17 24 55 21 27 10 9 nd B nd nd nd nd nd nd nd nd nd A 32 46 7 8 32 24 24 34 nd B 100 100 5 2 12 11 6 nd nd MSN
Х2 Analcime (%) Amorphous material (%) Material
Table 4 Mineralogical composition of the all-industrial waste before and after hydrothermal treatment.
Microporous and Mesoporous Materials xxx (xxxx) xxx
B nd nd nd nd nd nd nd nd 13
Kaolinite (%)
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3.2.3. Siliceous concrete waste aggregates (SCW) Waste from construction and demolition is rich in silicate minerals such as quartz, mica and feldspars, which are accompanied by a small amount of calcite. After the hydrothermal treatment, the same mineral species are conserved and analcime is formed in a new phase (Table 4). 3.2.4. Sterile coal (SC) Sterile coal from tailings is characterized by the presence of micas, kaolinite, quartz, calcite and feldspars. After the hydrothermal treat ment, mica, quartz, and calcite remain, while no feldspar signal is detected and kaolinite disappears, observing the analcime formation as the crystalline product of the reaction (Table 4). 3.2.5. Foundry sands Within this group, five foundry sands from different sources were studied. In its initial phase, the AF1 foundry sand was composed of quartz and 4
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Fig. 5. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-3. Fig. 8. XRD results for the AF-9 foundry sand: initial waste and secondary raw material.
a small amount of feldspars and mica. Following its hydrothermal treatment, the quartz remained, the feldspars recrystallized (a more powerful signal) and new crystalline phases appeared; analcime and olivine (Fig. 4, Table 4). The AF3 foundry sand was composed of quartz and feldspar. The latter disappeared after the hydrothermal treatment, generating an analcime as phase of neoformation (Fig. 5, Table 4). The mineralogical composition of the AF6 foundry sand was basi cally quartz and feldspar. Following the hydrothermal treatment, quartz remained, and the Na–K feldspars recrystallized, showing a very strong signal, and very well crystallized analcime formations appeared as a new solid phase (Fig. 6, Table 4). As an initial and secondary raw material, the AF7 foundry sand showed a similar composition (Fig. 7, Table 4). Finally, the AF9 foundry sand was formed of quartz, olivine, and feldspars (Fig. 8). Following the hydrothermal treatment of the sample, the feldspars had disappeared, leaving the other two minerals, quartz and olivine. Fig. 6. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-6.
3.3. SEM/EDX The general behavioural trend of the different wastes, once subjected to hydrothermal treatment, in all cases resulted in analcime phases, except for the AF9 foundry sand sample, where the new material was olivine. Polycrystalline analcime has been prepared from hydrogels under hydrothermal conditions [35,41] for a long time [32] up until the present [42]. AF6, following hydrothermal treatment was converted into analcime and Na–K feldspar (composition 4.26% Na2O, 30.29% Al2O3, 57.59% SiO2, 7.31% K2O; 0.56% CaO) (Fig. 9A and B), as described by Goodwin [43]. Concerning AF9 material, its treatment lead to the neoformation of the olivine phase with a composition of 50.05% MgO, 43.77% SiO2, 6.18% Fe2O3), which corresponds to a forsterite. (Fig. 9C and D). Following hydrothermal treatment of AF3, a new analcime phase formation was observed, with poorly defined crystalline faces, which indicates that an incipient formation has occurred (Fig. 9A and B). A similar phenomenon is observed for AF7; the neoformed analcime (composition 15.05% Na2O, 22.33% Al2O3, 62.62% SiO2) also presents poorly formed faces that coexist with silica aggregates (Fig. 10A and B). The opposite situation was observed in AF1, as showed in Fig. 9C and D the analcime particles present good defined faces and angles (isolated trapezohedrons). When using silica fume (SMN) as raw material, incipient analcime crystals with silica are formed (composition 15.46% Na2O, 23.12%
Fig. 7. XRD patterns from the initial waste and the secondary raw material for the foundry sand AF-7.
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Fig. 9. SEM images of AF – 6 foundry sand: A) analcime and waste glass B) prismatic feldspars. SEM images of AF – 9 foundry sand: C) and D) olivine crystals.
Fig. 10. SEM images of AF – 3: A) and B) incipient faces of analcime crystals. SEM images of AF – 1: C) and D) analcime trapezohedrons.
Al2O3, 61.42% SiO2) (Fig. 10C and D). The analcime crystals that presented the best-defined faces and an gles were obtained from the sterile carbon’s (SC) treatment. Here the analcime had a composition of 15.75% Na2O, 24.19% Al2O3 and 60.06% Si2O and showed trapezoidal trigonal trisoctahedral faces (Fig. 11A and B). The hydrothermal reaction of recycled glass (G) generated the neo formation of analcime crystals with their faces coated by fibres of Ca–Na
pyroxenes (15.34% Na2O; 5.56% MgO; 0.99 Al2O3; 58.37% SiO2; 1.27, SO3; 17.63% CaO and 0.83% Fe2O3 (Fig. 11C and D). 3.4. Cement pastes with secondary raw material As indicated in the introduction, zeolites can have various applica tions. Here, the effects of zeolites, which are integrated into the sec ondary raw materials, in the hydration of cement pastes is evaluated. 6
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Fig. 11. SEM images of AF – 7: A) Analcime B) silica. SEM images of SMN: C) Incipient analcime crystal formation.
Fig. 12. SEM images of SC: A) and B) perfect crystals of analcime. SEM images of G: C) Analcime covered by pyroxenes; D) Pyroxene fibres.
The preparation of the pastes was performed with three of the ma terials obtained from the hydrothermal treatment of the recycled glass, sterile coal, and the SCW, respectively. The size distribution of these materials was evaluated by means of a granulometric analysis in a Malvern Mastersizer. In all three cases, 95% by volume of the particles had a size below 100 μm. The mechanical tests performed after 1 day of curing showed that the compressive strength is increased a 23%, with respect to the reference material, for the cement pastes prepared with the secondary raw
material coming from the recycled glass and the SCW. In the case of using the secondary raw material from the sterile coal waste, the value of the compressive strength remains equal to the reference material. After 7 and 28 curing days, the value of the compressive strength was basically equal in all the samples (see Fig. 12). In the literature, the improvement of mechanical properties is asso ciated with two phenomena: i) the micro or nano size effect of the particle (added in the cement paste formulation), which produces a nucleation effect resulting in an acceleration of hydration; and, ii) a 7
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Moreover, because of the hydrothermal treatment the presence of feldspars and micas, as well as some silicate minerals is observed. However, in some cases, the analcime neoformation phase was total, leaving only the analcime as the reaction product. Finally, the results pointed to the possibility of using the secondary raw materials as accelerators in the hydration of cement pastes. The secondary raw materials obtained from the SCW and recycled glass produced a 23% increase in the compressive strength compared to the reference material after 1 day of curing. Acknowledgements This research has been founded by The Spanish Ministry of the Economy and Competitiveness under coordinated project BIA201565558-C3-1-2-3R (MINECO/FEDER) and The Spanish Ministry of Sci ence Innovation and Universities under a coordinated project RTI2018097074-B-C21 (MICINN/FEDER).
Fig. 13. Compressive strength after 1, 7, and 28 days of curing.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.micromeso.2019.109817. References � [1] M. Theo, The zeolite scene — an overview. Chapter 1. In: Ji�rí Cejka, H. v B.A.C., Ferdi, S. (Eds.), Elsevier, Amsterdam, pp. 1–12, 2007.. [2] R.M. Barrer, Hydrothermal Chemistry of Zeolites, Academic Press, London, 1982. [3] E.I. Basaldella, R. Bonetto, J.C. Tara, Synthesis of NaY zeolite on preformed kaolinite spheres. Evolution of zeolite content and textural properties with the reaction time, Ind. Eng. Chem. Res. 32 (1993) 751–752. [4] C.D. Chang, A.T. Bell, Studies on the mechanism of ZSM-5 formation, Catal. Lett. 8 (5–6) (1991) 305–316. [5] J.C. Buhl, J. L€ ons, Synthesis and crystal structure of nitrate enclathrated sodalite Na8[AlSiO4]6(NO3)2, J. Alloy. Comp. 235 (1996) 41–47. [6] L. McCusker, F. Liebau, G. Engelhardt, Nomenclature of structural and compositional characteristics of ordered microporous and mesoporous materials with inorganic hosts IUPAC Recommendations 2001, Pure Appl. Chem. 73 (2001) 381–394. [7] I. Petrov, T. Michalev, Synthesis of zeolite A: a review, Sci. Tech. Rep. 51 (2012) 30–35. [8] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Reticular synthesis and the design of new materials, Nature 423 (2003) 705–714. [9] J. Lee, S. Han, T. Hyeon, Synthesis of new nanoporous carbon materials using nanostructured silica materials as templates, J. Mater. Chem. 14 (2004) 478–486. [10] M. Chareonpanich, T. Namto, P. Kongkachuichay, J. Limtrakul, Synthesis of ZSM-5 zeolite from lignite fly ash and rice husk ash, Fuel Process. Technol. 85 (2004) 1623–1634. [11] D. Prasetyoko, Z. Ramli, S. Endud, H. Hamdan, B. Sulikowski, Conversion of rice husk ash to zeolite beta, Waste Manag. 26 (2006) 1173–1179. [12] H. Katsuki, S. Furuta, T. Watari, S. Komarneni, ZSM-5 zeolite/porous carbon composite: conventional-and microwave-hydrothermal synthesis from carbonized rice husk, Microporous Mesoporous Mater. 86 (2005) 145–151. [13] H. Tanaka, S. Furusawa, R. Hino, Synthesis, characterization, and formation process of Na-X zeolite from coal fly ash, J. Mater. Synth. Process. 10 (2002) 143–148. [14] H. Tanaka, A. Fujii, Effect of stirring on the dissolution of coal fly ash and synthesis of pure-form Na-A and-X zeolites by two-step process, Adv. Powder Technol. 20 (2009) 473–479. [15] M. Ahmaruzzaman, A review on the utilization of fly ash, Prog. Energy Combust. Sci. 36 (2010) 327–363. [16] C.W. Purnomo, C. Salim, H. Hinode, Synthesis of pure Na–X and Na–A zeolite from bagasse fly ash, Microporous Mesoporous Mater. 162 (2012) 6–13. [17] M.P. Mois�es, C.T.P. da Silva, J.G. Meneguin, E.M. Girotto, E. Radovanovic, Synthesis of zeolite NaA from sugarcane bagasse ash, Mater. Lett. 108 (2013) 243–246. [18] H. Kazemian, Z. Naghdali, T.G. Kashani, F. Farhadi, Conversion of high silicon fly ash to Na-P1 zeolite: alkaline fusion followed by hydrothermal crystallization, Adv. Powder Technol. 21 (2010) 279–283. [19] T. Wajima, T. Shimizu, Y. Ikegami, Synthesis of zeolites from paper sludge ash and their ability to simultaneously remove NH4 þ and PO4 3_, J. Environ. Sci. Health, Part A 42 (2007) 345–350. [20] T. Wajima, K. Munakata, Material conversion from paper sludge ash in NaOH solution to synthesize adsorbent for removal of Pb2 þ, NH4 þ and PO3_ 4 from aqueous solution, J. Environ. Sci. 23 (2011) 718–724. [21] T. Wajima, K. Munakata, Y. Ikegami, Conversion of waste sandstone cake into crystalline zeolite X using alkali fusion, Mater. Trans. 51 (2010) 849–854.
Fig. 14. Normalized heat flow during hydration at early ages.
pozzolanic reaction. If we observe the curves (Fig. 13) that correspond to the evolution of the hydration heat (obtained in the calorimetry tests), an acceleration occurs in those cement pastes where the secondary raw material from the recycled glass and the SCW had been added. On the contrary, this acceleration phenomenon was not observed in the case of the material from the sterile coal waste (see Fig. 14). It therefore appears that the increase in the compression strength was due to the nucleation effect of the particles of the secondary raw material obtained from the SCW and Glass treatment. Lending attention to the chemical composition of the three materials (Table 3), we can see that they all have a composition of around 50% silica, however, the secondary raw materials formed from recycled glass and SCW presented a high percentage of calcium (around 17%), while the secondary raw material produced from the sterile coal had around 2% [44-46]. These results contribute to the hypothesis that the acceleration that occurs during the early hydration ages may not only be derived from the seed effect, but also from the effect of the composition of the particles added. 4. Conclusions In this work, the use of different waste streams for the formation of zeolites following hydrothermal treatment has been validated. The treatment applied to these silica-rich wastes leads to analcime phase neoformation except in the case of AF9 in which an olivine phase neo formation was noted. The analcime crystals that have the best-defined faces and angles were obtained from the AF1 and sterile coal waste materials. 8
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