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Biomass fly ash and aluminium industry slags-based geopolymers
Materials Letters 229 (2018) 6–12
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Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Biomass fly ash and aluminium industry slags-based geopolymers L. Pérez-Villarejo a,⇑, E. Bonet-Martínez a, D. Eliche-Quesada a, P.J. Sánchez-Soto b, J.Mª. Rincón-López c, E. Castro-Galiano a a
Department of Chemical, Environmental, and Materials Engineering, University of Jaén, Campus Las Lagunillas, s/n, 23071 Jaén, Spain Materials Science Institute of Sevilla (ICMS), Joint Center Spanish National Research Council (CSIC)-University of Sevilla, c/Américo Vespucio, 49, 41092 Sevilla, Spain c Research Group GLASSCErinCON+T, Department of Agrochemistry and Environment, University Miguel Hernández, UMH, Elche, Alicante, Spain b
a r t i c l e
i n f o
Article history: Received 1 February 2018 Received in revised form 3 June 2018 Accepted 23 June 2018 Available online 25 June 2018 Keywords: Geopolymers Alkali-activation Biomass fly ash Aluminium industry slag
a b s t r a c t Geopolymers are a new class of non-Portland cements produced using an alumino-silicate material and an activating solution, which is mainly composed of sodium or potassium and waterglass to be subsequently cured at relatively low temperatures. Those can be formulated by adding natural minerals, waste and/or industrial by-products. The study investigates the microstructural properties of geopolymers synthesized from metakaolin (MK) and the admixture of fly ash (FBA) and aluminium industry slags (AIS) at different ages of curing. Five different geopolymer compositions were prepared and characterized by XRD, ATR-FTIR and SEM/EDS. The study revealed that geopolymeric gels are identified, which show mainly glassy microstructures, in agreement with the X-ray amorphous diffraction patterns, broad FTIR features and confirmed by SEM/EDS, with promising results prior to an industrial scale. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Geopolymers are described as a wide variety of inorganic and composite materials with limited restrictions on alumina and silica content [1]. Chemically geopolymers are formed of tetrahedral alumina and silica units condensed at room temperature, yielding to three-dimensional network structure [2]. Geopolymers are a class of alkali-activated materials that use an aluminosilicate source that produces a cementitious binder. Since the 90’s of 20th century, alkali activation research has grown dramatically in all corners of the globe [3]. However, much research has been focused on the development of geopolymers as Portland cement substitute from coal fly ashes, slags and another industrial wastes [4], while investigations regarding the production of geopolymers using biomass ashes have been scarce. Fly ash from biomass combustion is composed mainly of amorphous silica and alumina, which makes it a suitable material for the production of geopolymers reducing the environmental impact of its production [5]. In the recycling process of the waste generated in the secondary aluminium industry, there is a by-product whose main component is aluminium oxide and whose characteristics closely resemble bauxite.
⇑ Corresponding author. E-mail address: [email protected] (L. Pérez-Villarejo). https://doi.org/10.1016/j.matlet.2018.06.100 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
In this work, metakaolin and biomass fly ash, as precursor of aluminosilicates, and aluminium industry slag (AIS) as source of alumina, were examined as raw materials to obtain geopolymers using NaOH solution and sodium silicate solution (water glass) as activating agent. The geopolymers obtained were studied after curing for 60 days at room temperature, with a previous treatment at 60 °C for 24 h. The samples were subjected to characterization assays by attenuated total reflectance (ATR-FTIR) and X-ray diffraction (XRD). Finally, samples were subjected to microstructural and microchemical SEM/EDS analysis after 28 and 60 days. In this paper, a preliminary advance of the main results is presented. 2. Materials and methods 2.1. Materials The raw materials used to synthesize geopolymers are metakaolin (MK), biomass fly ash (FBA) provided by the Aldebarán Energía del Guadalquivir S.L. located in Andújar (Jaén, Spain), a plant that generates renewable energy using olive-pruning and forest pruning (pine) biomass. Aluminium industry slag (AIS) was supplied by the company Befesa Aluminio S.L. located in Valladolid, Spain. They were used without any pre-treatment. For alkaline activation, a mixture of sodium silicate ‘‘water glass” (Panreac S.A.; 8.9 wt% Na2O, 29.2 wt% SiO2 and 61.9 wt% H2O) and NaOH (reactive grade, 98 wt%, Panreac S.A) was used. The NaOH solution (5 M) was prepared in distilled water. The weight
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ratio between NaOH solution and water glass (NaOH/water glass) was 0.20 and the ratio between liquid and solid (L/S) used for all geopolymeric mixtures was 2.85.
Table 1 XRF of raw materials: metakaolin (MK), aluminium industry slags (AIS) and biomass fly ash (FBA). Oxide content (wt. %)
MK
AIS
FBA
SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 SO3 SrO LOI
66.50 25.66 0.54 0.01 0.12 0.14 0.07 3.10 0.26 0.02 – – 0.28
8.60 56.22 1.81 0.19 5.75 1.90 3.88 1.41 0.54 0.03 0.19 – 18.47
41.2 8.05 2.78 0.18 4.63 22.10 – 6.78 0.45 1.99 0.28 0.05 –
2.2. Preparation of geopolymers The geopolymers were prepared with five different compositions: pure MK and four other compositions such that GP1 (50% MK, 25% AIS, 25% FBA with a ratio Si/Al = 2.30), GP2 (50% MK, 33% AIS, 17% FBA, Si/Al = 1.95), GP3 (40% MK, 35% AIS, 25% FBA, Si/Al = 1.85) and GP4 (40% MK, 25% AIS, 35% FBA, Si/Al = 2.35). The synthesis was carried out by mixing the raw materials for 10 min. Subsequently the activating solution was added and stirred for 15 min. Then, the generated slurry was transferred to plastic molds. The samples were cured under controlled conditions
Q
MK 14 days MK 28 days MK 60 days
a) Q Intensity (a.u.)
Q
K
Q
Q Q
K K
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
2 Theta (º)
GP 2-2 14 days
b)
GP 2-2 28 days
Intensity (a.u.)
GP 2-2 60 days
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
2 Theta (°) Fig. 1. XRD diffractograms of a) MK; b) GP2; c) GP3 and d) GP4 geopolymers evolution at different curing ages (Q: Quartz; K: Kaolinite).
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GP 3-2 14 days
c)
GP 3-2 28 days
Intensity (a.u.)
GP 3-2 60 days
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
2 Theta (º) GP 4-2 14 days
d)
GP 4-2 28 days
Intensity (a.u.)
GP 4-2 60 days
5
10
15
20
25
30
35 40 45 2 Theta (º)
50
55
60
65
70
75
80
Fig. 1 (continued)
(60 °C) for 24 h. The specimens were demolded and kept at ambient conditions for 60 days of curing.
Transform Infrared spectroscopy Vertex 70 equipment from Bruker was used to characterize the geopolymers.
2.3. Techniques of characterization
3. Results and discussion
To characterize the AIS, FBA, MK powders and the designed geopolymers, scanning electron microscopy (SEM) JEOL SM 840 equipment, with energy dispersive spectroscopy, EDS, was used. Crystalline phases of RHA, DFD and geopolymers were evaluated with X-ray diffractometry (XRD) with an X’Pert Pro MPD automated diffractometer (PANalytical) equipped with a Ge (1 1 1) primary monochromator, using monochromatic Cu Ka radiation and an X’Celerator detector. Chemical composition was determined by X-ray fluorescence (XRF) using a Philips Magix Pro (PW-2440). An equipment of attenuated total reflectance (ATR-FTIR) Fourier
3.1. Raw materials The chemical composition of the raw materials is shown in Table 1, and they show that the source of aluminium is provided by AIS and silica is provided by both MK and FBA. The XRD pattern of AIS shows the results of phase quantification: corundum (a-Al2O3), aluminium hydroxide Al(OH)3, quartz (SiO2), magnesium aluminium iron oxide (MgAl1.9Fe1O4), sodium aluminium iron oxide Na2(Al,Fe)12O19 and aragonite (CaCO3). XRD patterns of biomass fly ash (FBA) shows a large number of tiny diffraction
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peaks matched with calcium oxide and aluminosilicates, with composition as Al0.5Ca2Mg0.75O7Si1.75 and Al0.83Ca3.027Fe1.17O12Si3. 3.2. Geopolymer XRD patterns of pure MK and GP geopolymers and the results of phase identification are reported in Fig. 1at different ages of curing. Fig. 1a shows the evolution of pure metakaolin after alkaline activation. It can be see a large broad peak between 18 and 40° 2h centered at 29° h (broad hump structure), which typical of an amorphous geopolymer, in accordance with previous findings [6]. In Fig. 1b (sample GP 2 at different ages of curing) this structure seems greater for the samples of 28 and 60 days, which could be
related to the formation of the geopolymer network in these samples. In these samples, the peaks increase considerably in intensity at advanced stages that barely appear at early stages, such as those located at 2h = 20.8; 23.3; 33.8; 50.1; 59.9 and 68.1, which indicates the development of the geopolymeric network. Fig. 1c and b include the results of geopolymerization experiments of samples GP3 and GP4 after 14, 28 and 60 days. In all the cases, these results indicate the formation of geopolymers as in the precedent samples (Fig. 1a, b). The ATR-FTIR spectra during the evolution of ages of curing of the geopolymers manufactured with metakaolin and the two residues are shown in Fig. 2. It can be observed absorption bands characteristic of the geopolymers, like that centered at 1430 cm 1
1
a)
0.9
0.7
1640 1
3400
0.6
685 1450
0.5
945
0.4 0.5
MK 7 days
0.3
MK 14 days
Transmittance (a.u.)
0.8
0.2
MK 28 days
0 1350
MK 60 days
1150
950
750
0.1
550
0 4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
1 0.9
b)
0.8
0.6
1390 3400
0.5 0.4
GP 1-1 7 days
0.3
GP 1-1 14 days
0.2
GP 1-1 28 days
0.1
GP 1-1 60 days
0 4000
3500
3000
2500 2000 1500 Wavenumber (cm-1)
1000
500
Fig. 2. FTIR analysis of a) MK; b) GP1; c) GP3 and d) GP4 geopolymers evolution at different curing ages.
Transmittance (a.u.)
0.7 1650
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1 0.9
c)
0.7 0.6
0.5 0.4 GP 3-1 7 days
0.3
GP 3-1 14 days
0.2
GP 3-1 28 days
0.1
GP 3-1 60 days 4000
Transmittance (a.u)
0.8
0
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
1 0.9
d)
0.8
0.6 0.5 0.4 0.3
GP 4-1 7 days GP 4-1 14 days
0.2
GP 4-1 28 days
0.1
GP 4-1 60 days 4000
3500
3000
Transmittance (a.u.)
0.7
0 2500
2000
1500
1000
500
Wavenumber (cm-1) Fig. 2 (continued)
which is barely visible for 7 and 14 curing days, but of great intensity for 28 and 60 days, as well as the 1390 cm 1 band. This band is associated with O-C-O stretching due to atmospheric carbonation. These bands suggest the formation of carbonated species in the mixture [7]. In the range between 600 and 800 cm 1 (Fig. 2a) appear several weak bands, especially one centered at 685 cm 1 that indicates polymerization of oligomers during polymerization [8]. Another phenomenon that indicates that the geopolymerization reaction is being generated is the displacement towards longer wavenumbers observed in the band centered at 945 cm 1 in the metakaolin samples (Fig. 2a). The band at 1640 cm 1 which is associated with dOH [9] is reduced from early ages until it disappears, which reveals a polycondensation reaction, as well as the broad band centered at 3400 cm 1 attributable to tOH which is reduced
as water is consumed during the different reaction stages [10]. Similar results can be deduced studying the samples GP3 and GP4. Fig. 3 shows the SEM micrographs of the fractured surfaces of all the obtained geopolymers to investigate the changes in morphology and physical properties of formulated geopolymers at different stages. The geopolymeric gels are identified, which shows mainly as glassy microstructures, in agreement with the X-ray amorphous diffraction patterns and broad FTIR features. The EDS analysis of needle like crystals in Fig. 3e shows the presence of Si, Na, Ca and Al. However the amount of Si in this type of structures is relatively lower than that detected in the matrix (see EDS analysis in Fig. 3b). The appearance of pores, as can be seen in Fig. 3a and c, may be due to trapped air during the agitation stage of the slurry [11]. Further studies are in progress to a deep
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b
a 1
1
1
1
c
d 2
2
1
1
1
1
2
2
e
f
1
1
Fig. 3. SEM micrographs and EDS analysis of obtained geopolymers: a) MK; b) GP3; c) GP4; d) GP2 and e)-f) GP1.
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investigation of the present preliminary results, in particular the texture properties of the geopolymers.
4. Conclusions The evolution of the species through XRD and ATR-FTIR at different ages of curing of geopolymers shows that the geopolymerization reaction occurs in the designed materials obtained using metakaolin and non-conventional precursors treated with alkaline solution (NaOH 5 M) and waterglass, being corroborated by SEM/EDS. According to the present results, it was demonstrated the feasibility of the use of biomass fly ash (FBA), as well as, industrial by-products of the aluminium industry (AIS) as a raw material as partial substitutes for metakaolin, to generate geopolymers substitutes of Portland cement.
Acknowledgement This work has been funded by the Project ‘‘Valuation of various types of ash for the obtaining of new sustainable ceramic materials” (UJA2014/06/13), Own Plan University of Jaen, sponsored by Caja Rural of Jaén.
References [1] P. Benito, C. Leonelli, V. Medri, A. Vaccari, Geopolymers: a new and smart way for a sustainable development, Appl. Clay Sci. 73 (2013) 1. [2] J.L. Provis, P. Duxson, J.S.J. Van Deventer, G.C. Lukey, The role of mathematical modelling and gel chemistry in advancing geopolymer technology, Chem. Eng. Res. Des. 83 (2005) 853–860. [3] J.L. Provis, Introduction and Scope, in: John L. Provis, Jannie S.J. van Deventer (Eds.), Alkali Activated Materials, State-of-the-Art Report, RILEM TC 224-AAM, Springer, New York, 2014, pp. 1–9. [4] H. Xu, J.S.J.V. Deventer, Effect of source materials on geopolymerization, Ind. Eng. Chem. Res. 42 (2003) 1698–1706. [5] N. Toniolo, A.R. Boccaccini, Fly ash-based geopolymers containing added silicate waste. A review, Ceram. Int. 43 (2017) 14545–14551. [6] M. Zhang, T. El-Korchi, G. Zhang, J. Liang, M. Tao, Synthesis factors affecting mechanical properties. Microstructure and chemical composition of red mudfly ash based geopolymers, Fuel 134 (2014) 315–325. [7] M. Cyr, R. Pouhet, Carbonation in the pore solution of metakaolin based geopolymer, Cem. Concr. Res. 88 (2016) 227–235. [8] E. Kamseu, M.C. Bignozzi, U.C. Melo, C. Leonelli, V.M. Sglavo, Design of inorganic polymer cements: Effects of matrix strengthening on microstructure, Constr. Build. Mater. 38 (2013) 1135–1148. [9] R.L. Frost, A.M. Vassalo, The dehydroxylation of kaolinite clay minerals using infrared emission spectroscopy, Clay Clays Miner. 44 (1996) 636–651. [10] J. Peyne, J. Gautron, J. Doudeau, E. Joussein, S. Rossignol, Influence of calcium addition on calcined brick clay based geopolymers: a thermal and FTIR spectroscopy study, Const. Build. Mater. 152 (2017) 794–803. [11] E. Papa, V. Medri, E. Landi, B. Ballarin, F. Miccio, Production and characterization of geopolymers based on mixed composition of metakaolin and coal ashes, Mater. Des. 56 (2014) 409–415.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Biomass fly ash and aluminium industry slags-based geopolymers L. Pérez-Villarejo a,⇑, E. Bonet-Martínez a, D. Eliche-Quesada a, P.J. Sánchez-Soto b, J.Mª. Rincón-López c, E. Castro-Galiano a a
Department of Chemical, Environmental, and Materials Engineering, University of Jaén, Campus Las Lagunillas, s/n, 23071 Jaén, Spain Materials Science Institute of Sevilla (ICMS), Joint Center Spanish National Research Council (CSIC)-University of Sevilla, c/Américo Vespucio, 49, 41092 Sevilla, Spain c Research Group GLASSCErinCON+T, Department of Agrochemistry and Environment, University Miguel Hernández, UMH, Elche, Alicante, Spain b
a r t i c l e
i n f o
Article history: Received 1 February 2018 Received in revised form 3 June 2018 Accepted 23 June 2018 Available online 25 June 2018 Keywords: Geopolymers Alkali-activation Biomass fly ash Aluminium industry slag
a b s t r a c t Geopolymers are a new class of non-Portland cements produced using an alumino-silicate material and an activating solution, which is mainly composed of sodium or potassium and waterglass to be subsequently cured at relatively low temperatures. Those can be formulated by adding natural minerals, waste and/or industrial by-products. The study investigates the microstructural properties of geopolymers synthesized from metakaolin (MK) and the admixture of fly ash (FBA) and aluminium industry slags (AIS) at different ages of curing. Five different geopolymer compositions were prepared and characterized by XRD, ATR-FTIR and SEM/EDS. The study revealed that geopolymeric gels are identified, which show mainly glassy microstructures, in agreement with the X-ray amorphous diffraction patterns, broad FTIR features and confirmed by SEM/EDS, with promising results prior to an industrial scale. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Geopolymers are described as a wide variety of inorganic and composite materials with limited restrictions on alumina and silica content [1]. Chemically geopolymers are formed of tetrahedral alumina and silica units condensed at room temperature, yielding to three-dimensional network structure [2]. Geopolymers are a class of alkali-activated materials that use an aluminosilicate source that produces a cementitious binder. Since the 90’s of 20th century, alkali activation research has grown dramatically in all corners of the globe [3]. However, much research has been focused on the development of geopolymers as Portland cement substitute from coal fly ashes, slags and another industrial wastes [4], while investigations regarding the production of geopolymers using biomass ashes have been scarce. Fly ash from biomass combustion is composed mainly of amorphous silica and alumina, which makes it a suitable material for the production of geopolymers reducing the environmental impact of its production [5]. In the recycling process of the waste generated in the secondary aluminium industry, there is a by-product whose main component is aluminium oxide and whose characteristics closely resemble bauxite.
⇑ Corresponding author. E-mail address: [email protected] (L. Pérez-Villarejo). https://doi.org/10.1016/j.matlet.2018.06.100 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
In this work, metakaolin and biomass fly ash, as precursor of aluminosilicates, and aluminium industry slag (AIS) as source of alumina, were examined as raw materials to obtain geopolymers using NaOH solution and sodium silicate solution (water glass) as activating agent. The geopolymers obtained were studied after curing for 60 days at room temperature, with a previous treatment at 60 °C for 24 h. The samples were subjected to characterization assays by attenuated total reflectance (ATR-FTIR) and X-ray diffraction (XRD). Finally, samples were subjected to microstructural and microchemical SEM/EDS analysis after 28 and 60 days. In this paper, a preliminary advance of the main results is presented. 2. Materials and methods 2.1. Materials The raw materials used to synthesize geopolymers are metakaolin (MK), biomass fly ash (FBA) provided by the Aldebarán Energía del Guadalquivir S.L. located in Andújar (Jaén, Spain), a plant that generates renewable energy using olive-pruning and forest pruning (pine) biomass. Aluminium industry slag (AIS) was supplied by the company Befesa Aluminio S.L. located in Valladolid, Spain. They were used without any pre-treatment. For alkaline activation, a mixture of sodium silicate ‘‘water glass” (Panreac S.A.; 8.9 wt% Na2O, 29.2 wt% SiO2 and 61.9 wt% H2O) and NaOH (reactive grade, 98 wt%, Panreac S.A) was used. The NaOH solution (5 M) was prepared in distilled water. The weight
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ratio between NaOH solution and water glass (NaOH/water glass) was 0.20 and the ratio between liquid and solid (L/S) used for all geopolymeric mixtures was 2.85.
Table 1 XRF of raw materials: metakaolin (MK), aluminium industry slags (AIS) and biomass fly ash (FBA). Oxide content (wt. %)
MK
AIS
FBA
SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 SO3 SrO LOI
66.50 25.66 0.54 0.01 0.12 0.14 0.07 3.10 0.26 0.02 – – 0.28
8.60 56.22 1.81 0.19 5.75 1.90 3.88 1.41 0.54 0.03 0.19 – 18.47
41.2 8.05 2.78 0.18 4.63 22.10 – 6.78 0.45 1.99 0.28 0.05 –
2.2. Preparation of geopolymers The geopolymers were prepared with five different compositions: pure MK and four other compositions such that GP1 (50% MK, 25% AIS, 25% FBA with a ratio Si/Al = 2.30), GP2 (50% MK, 33% AIS, 17% FBA, Si/Al = 1.95), GP3 (40% MK, 35% AIS, 25% FBA, Si/Al = 1.85) and GP4 (40% MK, 25% AIS, 35% FBA, Si/Al = 2.35). The synthesis was carried out by mixing the raw materials for 10 min. Subsequently the activating solution was added and stirred for 15 min. Then, the generated slurry was transferred to plastic molds. The samples were cured under controlled conditions
Q
MK 14 days MK 28 days MK 60 days
a) Q Intensity (a.u.)
Q
K
Q
Q Q
K K
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
2 Theta (º)
GP 2-2 14 days
b)
GP 2-2 28 days
Intensity (a.u.)
GP 2-2 60 days
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
2 Theta (°) Fig. 1. XRD diffractograms of a) MK; b) GP2; c) GP3 and d) GP4 geopolymers evolution at different curing ages (Q: Quartz; K: Kaolinite).
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GP 3-2 14 days
c)
GP 3-2 28 days
Intensity (a.u.)
GP 3-2 60 days
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
2 Theta (º) GP 4-2 14 days
d)
GP 4-2 28 days
Intensity (a.u.)
GP 4-2 60 days
5
10
15
20
25
30
35 40 45 2 Theta (º)
50
55
60
65
70
75
80
Fig. 1 (continued)
(60 °C) for 24 h. The specimens were demolded and kept at ambient conditions for 60 days of curing.
Transform Infrared spectroscopy Vertex 70 equipment from Bruker was used to characterize the geopolymers.
2.3. Techniques of characterization
3. Results and discussion
To characterize the AIS, FBA, MK powders and the designed geopolymers, scanning electron microscopy (SEM) JEOL SM 840 equipment, with energy dispersive spectroscopy, EDS, was used. Crystalline phases of RHA, DFD and geopolymers were evaluated with X-ray diffractometry (XRD) with an X’Pert Pro MPD automated diffractometer (PANalytical) equipped with a Ge (1 1 1) primary monochromator, using monochromatic Cu Ka radiation and an X’Celerator detector. Chemical composition was determined by X-ray fluorescence (XRF) using a Philips Magix Pro (PW-2440). An equipment of attenuated total reflectance (ATR-FTIR) Fourier
3.1. Raw materials The chemical composition of the raw materials is shown in Table 1, and they show that the source of aluminium is provided by AIS and silica is provided by both MK and FBA. The XRD pattern of AIS shows the results of phase quantification: corundum (a-Al2O3), aluminium hydroxide Al(OH)3, quartz (SiO2), magnesium aluminium iron oxide (MgAl1.9Fe1O4), sodium aluminium iron oxide Na2(Al,Fe)12O19 and aragonite (CaCO3). XRD patterns of biomass fly ash (FBA) shows a large number of tiny diffraction
9
L. Pérez-Villarejo et al. / Materials Letters 229 (2018) 6–12
peaks matched with calcium oxide and aluminosilicates, with composition as Al0.5Ca2Mg0.75O7Si1.75 and Al0.83Ca3.027Fe1.17O12Si3. 3.2. Geopolymer XRD patterns of pure MK and GP geopolymers and the results of phase identification are reported in Fig. 1at different ages of curing. Fig. 1a shows the evolution of pure metakaolin after alkaline activation. It can be see a large broad peak between 18 and 40° 2h centered at 29° h (broad hump structure), which typical of an amorphous geopolymer, in accordance with previous findings [6]. In Fig. 1b (sample GP 2 at different ages of curing) this structure seems greater for the samples of 28 and 60 days, which could be
related to the formation of the geopolymer network in these samples. In these samples, the peaks increase considerably in intensity at advanced stages that barely appear at early stages, such as those located at 2h = 20.8; 23.3; 33.8; 50.1; 59.9 and 68.1, which indicates the development of the geopolymeric network. Fig. 1c and b include the results of geopolymerization experiments of samples GP3 and GP4 after 14, 28 and 60 days. In all the cases, these results indicate the formation of geopolymers as in the precedent samples (Fig. 1a, b). The ATR-FTIR spectra during the evolution of ages of curing of the geopolymers manufactured with metakaolin and the two residues are shown in Fig. 2. It can be observed absorption bands characteristic of the geopolymers, like that centered at 1430 cm 1
1
a)
0.9
0.7
1640 1
3400
0.6
685 1450
0.5
945
0.4 0.5
MK 7 days
0.3
MK 14 days
Transmittance (a.u.)
0.8
0.2
MK 28 days
0 1350
MK 60 days
1150
950
750
0.1
550
0 4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
1 0.9
b)
0.8
0.6
1390 3400
0.5 0.4
GP 1-1 7 days
0.3
GP 1-1 14 days
0.2
GP 1-1 28 days
0.1
GP 1-1 60 days
0 4000
3500
3000
2500 2000 1500 Wavenumber (cm-1)
1000
500
Fig. 2. FTIR analysis of a) MK; b) GP1; c) GP3 and d) GP4 geopolymers evolution at different curing ages.
Transmittance (a.u.)
0.7 1650
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1 0.9
c)
0.7 0.6
0.5 0.4 GP 3-1 7 days
0.3
GP 3-1 14 days
0.2
GP 3-1 28 days
0.1
GP 3-1 60 days 4000
Transmittance (a.u)
0.8
0
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
1 0.9
d)
0.8
0.6 0.5 0.4 0.3
GP 4-1 7 days GP 4-1 14 days
0.2
GP 4-1 28 days
0.1
GP 4-1 60 days 4000
3500
3000
Transmittance (a.u.)
0.7
0 2500
2000
1500
1000
500
Wavenumber (cm-1) Fig. 2 (continued)
which is barely visible for 7 and 14 curing days, but of great intensity for 28 and 60 days, as well as the 1390 cm 1 band. This band is associated with O-C-O stretching due to atmospheric carbonation. These bands suggest the formation of carbonated species in the mixture [7]. In the range between 600 and 800 cm 1 (Fig. 2a) appear several weak bands, especially one centered at 685 cm 1 that indicates polymerization of oligomers during polymerization [8]. Another phenomenon that indicates that the geopolymerization reaction is being generated is the displacement towards longer wavenumbers observed in the band centered at 945 cm 1 in the metakaolin samples (Fig. 2a). The band at 1640 cm 1 which is associated with dOH [9] is reduced from early ages until it disappears, which reveals a polycondensation reaction, as well as the broad band centered at 3400 cm 1 attributable to tOH which is reduced
as water is consumed during the different reaction stages [10]. Similar results can be deduced studying the samples GP3 and GP4. Fig. 3 shows the SEM micrographs of the fractured surfaces of all the obtained geopolymers to investigate the changes in morphology and physical properties of formulated geopolymers at different stages. The geopolymeric gels are identified, which shows mainly as glassy microstructures, in agreement with the X-ray amorphous diffraction patterns and broad FTIR features. The EDS analysis of needle like crystals in Fig. 3e shows the presence of Si, Na, Ca and Al. However the amount of Si in this type of structures is relatively lower than that detected in the matrix (see EDS analysis in Fig. 3b). The appearance of pores, as can be seen in Fig. 3a and c, may be due to trapped air during the agitation stage of the slurry [11]. Further studies are in progress to a deep
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b
a 1
1
1
1
c
d 2
2
1
1
1
1
2
2
e
f
1
1
Fig. 3. SEM micrographs and EDS analysis of obtained geopolymers: a) MK; b) GP3; c) GP4; d) GP2 and e)-f) GP1.
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investigation of the present preliminary results, in particular the texture properties of the geopolymers.
4. Conclusions The evolution of the species through XRD and ATR-FTIR at different ages of curing of geopolymers shows that the geopolymerization reaction occurs in the designed materials obtained using metakaolin and non-conventional precursors treated with alkaline solution (NaOH 5 M) and waterglass, being corroborated by SEM/EDS. According to the present results, it was demonstrated the feasibility of the use of biomass fly ash (FBA), as well as, industrial by-products of the aluminium industry (AIS) as a raw material as partial substitutes for metakaolin, to generate geopolymers substitutes of Portland cement.
Acknowledgement This work has been funded by the Project ‘‘Valuation of various types of ash for the obtaining of new sustainable ceramic materials” (UJA2014/06/13), Own Plan University of Jaen, sponsored by Caja Rural of Jaén.
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