- Email: [email protected]
Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions
Accepted Manuscript Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions
Piotr Izak, Longin Ogłaza, Włodzimierz Mozgawa, Joanna Mastalska-Popławska, Agata Stempkowska PII: DOI: Reference:
S1386-1425(18)30133-1 https://doi.org/10.1016/j.saa.2018.02.022 SAA 15826
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received date: Revised date: Accepted date:
3 November 2017 30 January 2018 6 February 2018
Please cite this article as: Piotr Izak, Longin Ogłaza, Włodzimierz Mozgawa, Joanna Mastalska-Popławska, Agata Stempkowska , Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Saa(2017), https://doi.org/10.1016/j.saa.2018.02.022
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions Piotr Izak1, Longin Ogłaza2, Włodzimierz Mozgawa1, Joanna Mastalska-Popławska1*, Agata Stempkowska3 AGH University of Science and Technology, Faculty of Materials Science and Ceramics, 30-059 Krakow; *corresponding author: [email protected] 2 Rudniki S.A. Chemical Plant, 42-240 Rudniki by Częstochowa 3 AGH University of Science and Technology, Faculty of Mining and Geoengineering, 30-059 Krakow
PT
1
Abstract
RI
To avoid agglomeration and sedimentation of grains, ceramic slurries should be modified by
SC
stabilizers in order to increase the electrostatic interactions between the dispersed particles. In this study we present the spectral analysis of aqueous sodium silicates obtained by different synthesis methods and their influence on the rheological properties of kaolin based slurries.
NU
Infrared and Raman spectra can be used to describe the structure of silicate structural units present in aqueous sodium silicates. It was confirmed that the best stabilization results possess
MA
aqueous sodium silicates of the silicate moduli of about 2 and the optimal concentration of the used fluidizer is 0.3 wt% to the kaolin clay dry mass. One of the most important conclusions is that the synthesis method of the fluidizer has no significant effect on its stabilization
D
properties but used medium does create adequate stabilization mechanism depending on the
PT E
silicate structures present in the sodium silicate solution.
1. Introduction
CE
Keywords: Aqueous sodium silicates, Kaolin, Rheology, Silicate modulus, Stabilization.
AC
Aqueous solutions of alkali silicates, because of their good water solubility, are called soluble silicates or more often water glasses. They are the basic raw materials inter alia for ceramics, glasses, cements and moulds in foundry industries. Because of their lack of toxicity, they can be also used as corrosion inhibitors, cleaning agents or components of ceramic paints. However, due to the low stability of the silicate ions and their varying degree of condensation, they are difficult to investigate. Previous studies indicate that their properties largely depend on their synthesis method [1-3]. In this article, aqueous sodium silicates of different silicate moduli (molar ratio of silica to sodium oxide) and various methods of preparation were investigated for their use as fluidizers of ceramic slurries.
1
ACCEPTED MANUSCRIPT In the case of inorganic ceramic fluidizers such as aqueous solutions of sodium silicates, the main fluidization mechanism is the ion exchange which causes the change of the electrokinetic potential on the surface of the grain (electrostatic stabilization). Their fluidization efficiency depends on their silicate modulus and the type of ceramic suspension [4-7]. Other fluidization mechanisms that may be present in the ceramic slurry are: electrostatic, polymeric, electro-spatial and depleted. They occur mainly when organic stabilizers are used. Typically, these phenomena occur simultaneously and produce more or
PT
less stable effects (synergy effect) [8-9].
Researchers investigating the problem of stabilization of ceramic slurries focus mainly
RI
on the rheological properties of the tested mixtures [10-13]. In this article we are trying to
SC
answer the question whether and how the method of synthesis of the aqueous sodium silicate stabilizers influences the fluidization of kaolin ceramic suspensions. In addition, a thorough
NU
analysis of the results of oscillation spectroscopy was carried out and silicate units present in the slurries have been assigned to the suitable fluidization mechanism. These studies could be helpful in the design of new casting slurries used in the ceramic industry, as well as in
MA
understanding of the silicate fluidizers structure and their mechanisms of stabilization of the
2. Materials and Methods
PT E
2.1. Aqueous sodium silicates
D
ceramic slurries.
Five different types of aqueous sodium silicates were used as the inorganic stabilizers for kaolin KOC clay ( Surmin-Kaolin, Poland; white-burned raw material enriched in quartz
CE
and low in titanium and iron, use in ceramic industry because if its stable rheological properties) slurries (Table 1). They differed not only in the content of individual oxides and
AC
silicate modulus, but also in the methods of preparation. Samples 1 and 3-5 were synthesized by dissolving a sodium enamel, while aqueous sodium silicate labeled as Sample 2 (R-150z) was synthesized from the silicic acid sol. In addition, for the synthesis of aqueous sodium silicate labeled as Sample 1 (R-150D), instead of distilled water used in R-150, heavy water D2O was used. After preparation, all samples were purified by filtration and then subjected to chemical analysis according to the factory standards [14]. All synthesis and composition analysis were performed at Rudniki S.A. Chemical Plant (Poland).
2
ACCEPTED MANUSCRIPT
Viscosity (20oC) [mPas] NA 270 157 189 114
PT
Table 1. Physicochemical analysis of the aqueous sodium silicates used in this work [14]. Specific Sample Na2O Silicate Type SiO2 [wt.%] gravity number [wt.%] modulus [g/cm3] 1 R-150D 8.3 17.3 2.08 1.373 2 R-150z 13.2 26.4 2.06 1.465 3 R-150 13.8 27.4 2.05 1.484 4 R-145 12.1 29.3 2.50 1.472 5 R-137 9.2 28.9 3.25 1.381
2.2. Preparation of the kaolin KOC slurries
RI
Kaolin KOC slurries consisted of 60 wt% of kaolin KOC, 40 wt% of distilled water and inorganic stabilizer, i.e. aqueous sodium silicate selected from Table 1, which was added
SC
to the slurry in the amount of 0.1-0.5 wt% calculated vs the kaolin KOC dry mass. The mixture was stirred at medium rotation speed (about 50 RPM) for 5 minutes to obtain a
NU
homogenous slurry. After that, it was aged for 10 minutes and again stirred before the
MA
rheological measurements for 1 minute to destroy possible thixotropic structure.
2.3. Rheological measurements
Brookfield RV DV-III rotary viscometer with the chamber SC4-13RPY and spindle
D
SC4-29, where the gap is 5.7 mm, was used for the rheological measurements. Flow curves,
PT E
i.e. dependence of viscosity on the shear rate, were made for increasing and decreasing shear rates in the range of 2.5-50 s-1 (records made every 30 s). Each flow curve measurement was followed by the thixotropy test; rotation was stopped for 10 minutes and then viscosity was
CE
measured at fixed shear rate of 5.6 s-1 after 1 s, 2 s, 3 s, 4 s, 5 s, 10 s, 20 s and 30 s. The temperature during the measurements was 23 °C.
AC
2.4. Vibrational spectroscopy Vibrational spectroscopy measurements have been used to determine whether infrared and Raman spectra can be used to describe the structure of silicate structural units present in aqueous sodium silicates used as fluidizers of ceramic suspensions. Infrared spectra were collected using the Bio-Rad FTS-60 spectrometer. Spectra were collected in mid infrared region after 256 scans and 2 cm-1 resolution. The Raman spectra were made with the use of Horiba LabRam HR spectrometer equipped with 1800 and 600 diffraction gratings. At the beginning, the spectra of the fluidizers were measured using a transmission technique and KBr pellets in the range of 4000-400 cm-1. However, the shape of the spectra
3
ACCEPTED MANUSCRIPT can be disturbed by such a measurement method, since potassium bromide partially dissolved in the alkaline medium of the fluidizers during recording of the spectra. For this reason, IR spectra measurements were repeated using an Attenuated Total Reflection (ATR) technique with the use of zinc selenide prism as an optical element in the range of 4000-550 cm-1. On the other hand, the disadvantage of ATR measurements was the narrowed spectrum range (as the transmission limit for the applied zinc selenide is about 550 cm-1) and the change of the
PT
position of the bands in the spectra caused by the phenomenon of infrared beam reflection.
3.1. Vibrational spectra of the aqueous sodium silicates
RI
3. Results and Discussion
SC
Figures 1 and 2 summarize the spectra of the fluidizers measured by the transmission technique and KBr pellets in the range of 4000-400 cm-1 and with the use of ATR technique.
NU
The bands in the spectra can be divided into two basic groups: bands connected to the vibrations of OH-groups and water molecules and bands related to silico-oxygene vibrations
AC
CE
PT E
D
MA
in silicate anions with different degrees of polymerization.
Fig. 1. Comparison of the MIR transmission spectra of the aqueous sodium silicate fluidizers.
4
RI
PT
ACCEPTED MANUSCRIPT
SC
Fig. 2. Comparison of the ATR spectra of the aqueous sodium silicate fluidizers.
NU
The first group is in the range of about 3200-3450 cm-1 and is associated with the stretching vibrations of hydroxyl groups. These vibrations take place both in water molecules and in OH groups linked to silicate structural units (eg. tetrahedrons terminal groups). The
MA
second band associated with the presence of molecular water is the band at about 1640 cm -1, which is associated with bending vibrations of H-O-H. The high intensity of these bands is understandable because all tested fluidizers were aqueous solutions. The most visible change
D
in band position is related to the effect of isotope substitution ( i.e. spectra of the R-150D
PT E
fluidizer). The use of heavy water in the preparation of the fluidizers causes nearly double change in mass due to H→D substitution (without changing the corresponding force constants), what significantly changes the wavenumber of the vibrating molecular oscillators.
CE
And so, the bands from stretching vibrations change the position in the spectra to 2540 cm-1 (2470 cm-1 in the ATR spectra), and from the bending vibration of the water to 1440 cm-1. 1
AC
Among the bands of the second group, the most intense are the bands at about l000 cmassociated with asymmetric stretching vibrations of Si-O. Position of this band depends on
the degree of polymerization of the silicate anions. With the increase of this degree, the band appears at increasing wavenumbers. For the most polymerized silicate structure, i.e. SiO 2, this band is located at about 1100 cm-1. In the discussed spectra, the position of this band varies between 1028-1006 cm-1 in transmission spectra and between 1005-980 cm-1 in ATR spectra. It means that there is no polyanions with the highest unrestricted degree of polymerization, i.e. 2D and 3D. It is also unlikely that chain anions with unrestricted polymerization are also present (this band usually occurs at around 1070 cm-1). The possible anions are those consisting of single SiO4 tetrahedrons or those built of countable number of SiO4 tetrahedrons 5
ACCEPTED MANUSCRIPT (including both cyclic and chain systems). It was also noticed that the position of the main band changes with the SiO2/Na2O ratio. When this ratio decreases, the position of the band moves to lower wavenumbers. This leads to a conclusion that the increase of the silicate modulus prefers the presence of lower polymerized silicate units in the tested fluidizers [1517]. Another, less intense, band related to the silicate vibrations observed in the spectra is the band coming from the symmetrical stretching vibrations associated with the existence of
PT
Si-O-Si bridges (860-880 cm-1). The presence of this band indicates the formation of overtetrahedric units and may indicate the presence of pyrosilicate anions (two linked
RI
tetraehedrons) and / or anions consisting of more tetrahedrons. This band is not present in the
SC
spectra of R-137 aqueous sodium silicate, what means that for the silicate modulus of 3.2 only isolated SiO4 tetrahedrons are present in the samples. By contrast, silico-oxygene bridges
NU
occur for the silicate modulus of 2.5 (spectra of the R-145 aqueous sodium silicate). In addition, there is a band in the so-called pseudo-lattice region at 615-640 cm-1, indicating occurrence of rings composed of tetrahedrons closed in cyclic system (cyclosilicates). The
MA
relatively low value of the wavenumbers of this band indicates the formation of 6-membered rings, although the presence of 4-membered rings can not be excluded [18]. The last band of
D
this group comes from O-Si-O bending vibrations and occurs at about 460 cm-1. Because
over-tetrahedric units.
PT E
these vibrations are performed within tetraehedrons, this band can not be used to identify the
Figure 3 shows the Raman spectra of the fluidizers measured with the use of diffraction grating 1800. In the case of the diffraction grating 600, these spectra were less 1
CE
intense. The bands related to asymmetric stretching vibrations of Si-O groups (1035-1050 cm) and the bands in the pseudo-lattice region of 600-400 cm-1 were analyzed.
AC
The weak bands at around 595 cm-1 indicate the presence of 4-membered ring systems, whereas bands at about 437 cm-1 denote the presence of 6-membered rings systems. A number of "additional" bands in this region should be associated with the possible rings deformation that occur in cyclic systems, especially in the case of 6-membered rings. Ring deformation can also be a reason for the relatively low intensity of the bands in this region, because usually a strong band
corresponds to fully symmetrical character of the pore opening
vibrations. It can be also noticed that in the case of R-137 aqueous sodium silicate spectra there is no band at 435 cm-1, it has low intensity in the R-145 aqueous sodium silicate spectra, and in the case of R-150 aqueous sodium silicate spectra it is already quite noticeable. This may mean that the favorable rheological properties of the fluidizers with a silicate modulus of 6
ACCEPTED MANUSCRIPT about 2 (R-150 samples) may be due to the presence of units built of the 6-membered rings
NU
SC
RI
PT
[19-24].
MA
Fig. 3. Comparison of Raman spectra of the silicate fluidizers using 1800 diffraction grating.
3.2. Thixotropic properties of kaolin KOC slurries fluidized with aqueous sodium silicates
D
Figures 4 and 5 show that the kaolin slurries modified with the tested aqueous sodium
PT E
silicates have thixotropic properties, i.e. their apparent viscosity decreases with duration of applied shear. This means that shear stress values at decreasing shear rates are smaller than with the increasing shear rates because as a result of decreasing shear rate (which immediately
CE
follows an increase in the shear rate), the formation of the thixotropic structure begins, but since this is not an immediate phenomena, the read stress is lower than the "equilibrium";
AC
therefore, the curve for decreasing shear rates is below the curve for the increasing shear rates. These properties do not depend on the method of preparation of the tested fluidizer (results not presented here).
7
SC
RI
PT
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
Fig. 4. Flow curves of the kaolin slurry modified with 0.1 wt% of aqueous sodium silicate.
Fig. 5. Flow curves of the kaolin slurry modified with 0.3 wt% of aqueous sodium silicate.
Thixotropy phenomenon consists in transforming sol into gel with time and is caused by electrostatic interactions between the grains and stabilizing molecules [8, 9]. Other rheological calculations, i.e. work of the thixotropic structure destruction, confirmed that D2O produces stronger hydrogen bonds and reduces ion exchange than normal water. This leads to increase in the amount of silicate micelles with polymeric structures that form a separate dispersed fraction. For example, thixotropy index (measured during the thixotropy test; value of apparent viscosity measured after 1 s (η1) at shear rate of 5.6 s-1 divided by the value of apparent viscosity measured after 30 s (η30) at the same shear rate) determined in the
8
ACCEPTED MANUSCRIPT suspension in D2O for Mk= 2.08 was 1.165 and for identical composition in H2O, it was 0.967; Table 2 [10, 11, 29].
Table 2. Thixotropy index of the ceramic slurries modified with aqueous sodium silicates.
Silicate modulus 2.06
2.08
2.50
3.25
0.967 0.970 0.909 0.932 0.951
1.089 0.985 0.964 0.982 0.983
1.165 0.974 0.947 0.967 0.984
1.100 1.066 0.967 0.947 0.927
1.089 1.059 0.937 0.984 0.982
RI
PT
2.05
SC
Fluidizer concentration [wt%] 0.1 0.2 0.3 0.4 0.5
3.3. Viscosity of kaolin KOC slurries fluidized with aqueous sodium silicates
NU
Figure 6 presents the fluidization curves of the kaolin slurries modified with the aqueous sodium silicates of the silicate moduli in the range of 2.05-3.25. The best fluidization
MA
properties show sodium silicate solutions of the silicate moduli of about 2 and there is no significant difference in the apparent viscosity values in terms of the way of preparation of the fluidizer. With a fluidizer content of 0.3 wt% the apparent viscosity value is the lowest and
D
above this concentration there is no significant improvement in stabilization of the kaolin
PT E
slurry. Therefore, it can be assumed that the best stabilization properties poses aqueous sodium silicates with the silicate moduli of about 2 and the optimum concentration of 0.3 wt% relative to the kaolin dry mass. These conclusions were confirmed by the spectroscopic
CE
studies presented in the previous chapter. Higher silicate modulus, above 2.5, indicates independent silicate structures that don't affect the kaolinite grains and because of that the
AC
dominant fluidization mechanism is depleted stabilization, in which the macromolecules are dispersed in a suspension and constitute a separate dispersed fraction. For the lower values of the silicate modulus the main fluidization mechanism is ion exchange [15, 25-28].
9
RI
PT
ACCEPTED MANUSCRIPT
NU
SC
Fig. 6. Fluidization curves of the kaolin KOC slurries modified with aqueous sodium silicates.
4. Conclusions
The main purpose of the work was to explain the phenomena occurring during
MA
stabilization of ceramic slurries based on kaolin using several types of aqueous sodium silicates with the silicate moduli in the range of 2.05-3.25. Analysis of MIR and Raman
D
spectroscopic studies enabled to link the stabilization mechanisms with the silicate structures
PT E
occurring in different aqueous sodium silicates. For example, the increase of the silicate modulus prefers the presence of lower polymerized units what causes worse fluidization. Based on the rheological measurements, it was also determined which aqueous sodium silicate possessed the best fluidization properties. Additionally, the influence of the type of the
CE
medium on the fluidization properties was investigated. Analysis of the research results showed that the best fluidization properties characterize aqueous sodium silicate of silicate
AC
modulus of about 2, where the dominant fluidization mechanism is ion exchange. Those with the modulus larger than 2.5 created independent silicate micelles, mainly isolated SiO4 tetrahedrons. Changing the medium from H2O to D2O, which produces stronger hydrogen bonds, results in a stronger thixotropic structure.
Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
10
ACCEPTED MANUSCRIPT References [1]. R.K. Iler, The chemistry of silica, first ed., Wiley, New York, 1979. [2]. J.G. Vail, Soluble Silicates, first ed., Reinhold, New York, 1952. [3]. D. Hoebbel, K. Endres, T. Reinert, I. Pitsch, Inorganic-organic polymers derived from functional silicic acid derivatives by additive reaction, J. Non Cryst. Solids 176 (1994) 179188. [4]. F. Bergaya, G. Lagaly, Surface modification of clay minerals, Appl. Clay Sci. 19 (2001)
PT
1-3.
[5]. P. Mpofu, J. Addai-Mensah, J. Ralston, Investigation of the effect of polymer structure
RI
type on flocculation, rheology and dewatering behaviour of kaolinite dispersions, Int. J. Min.
SC
Process 71 (2001) 247-268.
[6]. J.E. Otterstedt, D.A. Brandreth, Small particles technology, Springer Science, fourth ed.,
NU
New York, 1998.
[7]. M. Chi, R. Eggleton, Cation exchange capacity of kaolinite, Clays Clay Miner. 47 (1999) 174-180.
MA
[8]. D. R. Dinger, Rheology for Ceramists, Morris Publishing, second ed., New York, 2002. [9]. P. Izak, Rheology in Ceramics AGH Publishing House, first ed., Krakow, 2015.
D
[10]. D. Penner, G. Lagaly, Influence of anions on the rheological properties of clay mineral dispersions, Appl. Clay Sci. 19 (2001) 131-142.
PT E
[11]. N. Yildiz, Y. Sarikaya, A. Calimli, Modification of rheology and permeability of Turkish ceramic clays using sodium silicate, Appl. Clay Sci. 13 (1998) 65-77. [12]. F. Pacheco-Torgal, J. Castro-Gomes, S. Jalali, 2008. Alkali-activated binders: A review.
CE
Part 2. About materials and binders manufacture, Con. Build. Mat. 22 (2008) 1315-1322. [13]. V. Penkavova, M. Guerreiro, J. Tihon, J.A.C. Teixeira, Deffloculation of kaolin
AC
suspensions- the effect of various electrolytes, Appl. Rheol. 25 (2014) 1-9. [14]. Factory standard, 2016. ZN-02/Z.Ch. Rudniki SA/257. http://www.zchrudniki.com.pl/ download/show/97/szklo-wodne-sodowe.pdf (accessed 25 September 2017). [15]. J.S. Falcone, J.L. Bass, , M. Angelella, M.R. Schenk, K.A. Brensinger, Characterizing the infrared bands of aqueous soluble silicates, J. Phys. Chem. A 114 (2010) 2438-2446. [16]. M. Handke, W. Mozgawa, Model quasi-molecule Si2O as an approach in the IR spectra description glassy and crystalline framework silicates, J. Mol. Struct. 348 (1995) 341–344. [17]. K. M. Davis, M. Tomozawa, An infrared spectroscopic study of water-related species in silica glasses. J. Non Cryst. Solids 201 (1996) 177–198.
11
ACCEPTED MANUSCRIPT [18]. M. Sitarz, W. Mozgawa, M. Handke, Rings in the structure of silicate glasses, J. Mol. Struct. 511 (1999) 281-285. [19]. J. Nordström, A. Sundblom, G. Vestergaard Jensen, J. Skov Pedersen, A. Palmqvist, A. Matic, Silica/alkali ratio dependence of the microscopic structure of sodium silicate solutions, J. Colloid Interface Sci. 397 (2013) 9–17. [20]. X. Yang, P. Roonasi, A. Holmgren, A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy, J. Colloid Interface Sci.
PT
328 (2008) 41–47.
[21]. W.R. Taylor, Application of infrared spectroscopy to studies of silicate glass structure:
RI
Examples from the melilite glasses and the systems Na2O-SiO2 and Na2O-Al2O3-SiO2, Proc.
SC
Indian Acad. Sci. 99 (1990) 99-117.
[22]. E.F. Medvedev, A.S. Komarevskaya, IR spectroscopic study of the phase composition
NU
for sodium silicate synthesized in aqueous medium, Glass Ceramics 64 (2007) 7-11. [23]. J. L. Bass, G. Turner, Anion distributions in sodium silicate solutions. Characterization by 29Si NMR, Infrared Spectroscopies, and Vapour Phase Osmometry, J. Phys. Chem. B 101
MA
(1997) 10638-10644.
[24]. G. Lagaly, W. Tufar, A. Minihan, A. Lovel, Silicates, in: B. Elvers, Ulmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012, pp.509-572.
D
[25]. A. Stempkowska, J. Mastalska-Popławska, P. Izak, L. Ogłaza, M. Turkowska,
PT E
Stabilization of kaolin clay slurry with sodium silicate of different silicate moduli, App. Clay Sci. 146 (2017) 147-151.
[26]. A. Papo, L. Piani, R. Ricceri, Sodium tripolyphosphate and polyphosphate as dispersing
CE
agents for kaolin suspensions: rheological characterization. Colloids Surf. 201 (2002) 219-230. [27]. N.J. Garcia, M.D. Ingram, J.C. Bazan, Ion transport in hydrated sodium silicates (water
AC
glasses) of varying water content, Solid State Ionics 146 (2002) 113-122. [28]. D.C.H Cheng, Characterization of thixotropy revisited, Rheol. Acta 42 (2003) 372-382. [29]. E.J. Teha, Y.K. Leonga, Y. Liua, A.B. Fourieb, M. Fahey, Differences in the rheology and surface chemistry of kaolin clay slurries: The source of the variations, Chem. Eng. Sci. 64 (2009) 3817-3825.
12
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
SC
RI
PT
Graphical abstract
13
ACCEPTED MANUSCRIPT Highlights
CE
PT E
D
MA
NU
SC
RI
PT
Aqueous sodium silicates of silicate moduli 2.05-3.25 were tested as fluidizers. Fluidizer synthesis method has a low impact on its fluidization properties. IR and Raman spectroscopy can be used for analysis of aqueous sodium silicates. The best fluidization properties show fluidizers of silicate moduli of about 2.
AC
14
Piotr Izak, Longin Ogłaza, Włodzimierz Mozgawa, Joanna Mastalska-Popławska, Agata Stempkowska PII: DOI: Reference:
S1386-1425(18)30133-1 https://doi.org/10.1016/j.saa.2018.02.022 SAA 15826
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received date: Revised date: Accepted date:
3 November 2017 30 January 2018 6 February 2018
Please cite this article as: Piotr Izak, Longin Ogłaza, Włodzimierz Mozgawa, Joanna Mastalska-Popławska, Agata Stempkowska , Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Saa(2017), https://doi.org/10.1016/j.saa.2018.02.022
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions Piotr Izak1, Longin Ogłaza2, Włodzimierz Mozgawa1, Joanna Mastalska-Popławska1*, Agata Stempkowska3 AGH University of Science and Technology, Faculty of Materials Science and Ceramics, 30-059 Krakow; *corresponding author: [email protected] 2 Rudniki S.A. Chemical Plant, 42-240 Rudniki by Częstochowa 3 AGH University of Science and Technology, Faculty of Mining and Geoengineering, 30-059 Krakow
PT
1
Abstract
RI
To avoid agglomeration and sedimentation of grains, ceramic slurries should be modified by
SC
stabilizers in order to increase the electrostatic interactions between the dispersed particles. In this study we present the spectral analysis of aqueous sodium silicates obtained by different synthesis methods and their influence on the rheological properties of kaolin based slurries.
NU
Infrared and Raman spectra can be used to describe the structure of silicate structural units present in aqueous sodium silicates. It was confirmed that the best stabilization results possess
MA
aqueous sodium silicates of the silicate moduli of about 2 and the optimal concentration of the used fluidizer is 0.3 wt% to the kaolin clay dry mass. One of the most important conclusions is that the synthesis method of the fluidizer has no significant effect on its stabilization
D
properties but used medium does create adequate stabilization mechanism depending on the
PT E
silicate structures present in the sodium silicate solution.
1. Introduction
CE
Keywords: Aqueous sodium silicates, Kaolin, Rheology, Silicate modulus, Stabilization.
AC
Aqueous solutions of alkali silicates, because of their good water solubility, are called soluble silicates or more often water glasses. They are the basic raw materials inter alia for ceramics, glasses, cements and moulds in foundry industries. Because of their lack of toxicity, they can be also used as corrosion inhibitors, cleaning agents or components of ceramic paints. However, due to the low stability of the silicate ions and their varying degree of condensation, they are difficult to investigate. Previous studies indicate that their properties largely depend on their synthesis method [1-3]. In this article, aqueous sodium silicates of different silicate moduli (molar ratio of silica to sodium oxide) and various methods of preparation were investigated for their use as fluidizers of ceramic slurries.
1
ACCEPTED MANUSCRIPT In the case of inorganic ceramic fluidizers such as aqueous solutions of sodium silicates, the main fluidization mechanism is the ion exchange which causes the change of the electrokinetic potential on the surface of the grain (electrostatic stabilization). Their fluidization efficiency depends on their silicate modulus and the type of ceramic suspension [4-7]. Other fluidization mechanisms that may be present in the ceramic slurry are: electrostatic, polymeric, electro-spatial and depleted. They occur mainly when organic stabilizers are used. Typically, these phenomena occur simultaneously and produce more or
PT
less stable effects (synergy effect) [8-9].
Researchers investigating the problem of stabilization of ceramic slurries focus mainly
RI
on the rheological properties of the tested mixtures [10-13]. In this article we are trying to
SC
answer the question whether and how the method of synthesis of the aqueous sodium silicate stabilizers influences the fluidization of kaolin ceramic suspensions. In addition, a thorough
NU
analysis of the results of oscillation spectroscopy was carried out and silicate units present in the slurries have been assigned to the suitable fluidization mechanism. These studies could be helpful in the design of new casting slurries used in the ceramic industry, as well as in
MA
understanding of the silicate fluidizers structure and their mechanisms of stabilization of the
2. Materials and Methods
PT E
2.1. Aqueous sodium silicates
D
ceramic slurries.
Five different types of aqueous sodium silicates were used as the inorganic stabilizers for kaolin KOC clay ( Surmin-Kaolin, Poland; white-burned raw material enriched in quartz
CE
and low in titanium and iron, use in ceramic industry because if its stable rheological properties) slurries (Table 1). They differed not only in the content of individual oxides and
AC
silicate modulus, but also in the methods of preparation. Samples 1 and 3-5 were synthesized by dissolving a sodium enamel, while aqueous sodium silicate labeled as Sample 2 (R-150z) was synthesized from the silicic acid sol. In addition, for the synthesis of aqueous sodium silicate labeled as Sample 1 (R-150D), instead of distilled water used in R-150, heavy water D2O was used. After preparation, all samples were purified by filtration and then subjected to chemical analysis according to the factory standards [14]. All synthesis and composition analysis were performed at Rudniki S.A. Chemical Plant (Poland).
2
ACCEPTED MANUSCRIPT
Viscosity (20oC) [mPas] NA 270 157 189 114
PT
Table 1. Physicochemical analysis of the aqueous sodium silicates used in this work [14]. Specific Sample Na2O Silicate Type SiO2 [wt.%] gravity number [wt.%] modulus [g/cm3] 1 R-150D 8.3 17.3 2.08 1.373 2 R-150z 13.2 26.4 2.06 1.465 3 R-150 13.8 27.4 2.05 1.484 4 R-145 12.1 29.3 2.50 1.472 5 R-137 9.2 28.9 3.25 1.381
2.2. Preparation of the kaolin KOC slurries
RI
Kaolin KOC slurries consisted of 60 wt% of kaolin KOC, 40 wt% of distilled water and inorganic stabilizer, i.e. aqueous sodium silicate selected from Table 1, which was added
SC
to the slurry in the amount of 0.1-0.5 wt% calculated vs the kaolin KOC dry mass. The mixture was stirred at medium rotation speed (about 50 RPM) for 5 minutes to obtain a
NU
homogenous slurry. After that, it was aged for 10 minutes and again stirred before the
MA
rheological measurements for 1 minute to destroy possible thixotropic structure.
2.3. Rheological measurements
Brookfield RV DV-III rotary viscometer with the chamber SC4-13RPY and spindle
D
SC4-29, where the gap is 5.7 mm, was used for the rheological measurements. Flow curves,
PT E
i.e. dependence of viscosity on the shear rate, were made for increasing and decreasing shear rates in the range of 2.5-50 s-1 (records made every 30 s). Each flow curve measurement was followed by the thixotropy test; rotation was stopped for 10 minutes and then viscosity was
CE
measured at fixed shear rate of 5.6 s-1 after 1 s, 2 s, 3 s, 4 s, 5 s, 10 s, 20 s and 30 s. The temperature during the measurements was 23 °C.
AC
2.4. Vibrational spectroscopy Vibrational spectroscopy measurements have been used to determine whether infrared and Raman spectra can be used to describe the structure of silicate structural units present in aqueous sodium silicates used as fluidizers of ceramic suspensions. Infrared spectra were collected using the Bio-Rad FTS-60 spectrometer. Spectra were collected in mid infrared region after 256 scans and 2 cm-1 resolution. The Raman spectra were made with the use of Horiba LabRam HR spectrometer equipped with 1800 and 600 diffraction gratings. At the beginning, the spectra of the fluidizers were measured using a transmission technique and KBr pellets in the range of 4000-400 cm-1. However, the shape of the spectra
3
ACCEPTED MANUSCRIPT can be disturbed by such a measurement method, since potassium bromide partially dissolved in the alkaline medium of the fluidizers during recording of the spectra. For this reason, IR spectra measurements were repeated using an Attenuated Total Reflection (ATR) technique with the use of zinc selenide prism as an optical element in the range of 4000-550 cm-1. On the other hand, the disadvantage of ATR measurements was the narrowed spectrum range (as the transmission limit for the applied zinc selenide is about 550 cm-1) and the change of the
PT
position of the bands in the spectra caused by the phenomenon of infrared beam reflection.
3.1. Vibrational spectra of the aqueous sodium silicates
RI
3. Results and Discussion
SC
Figures 1 and 2 summarize the spectra of the fluidizers measured by the transmission technique and KBr pellets in the range of 4000-400 cm-1 and with the use of ATR technique.
NU
The bands in the spectra can be divided into two basic groups: bands connected to the vibrations of OH-groups and water molecules and bands related to silico-oxygene vibrations
AC
CE
PT E
D
MA
in silicate anions with different degrees of polymerization.
Fig. 1. Comparison of the MIR transmission spectra of the aqueous sodium silicate fluidizers.
4
RI
PT
ACCEPTED MANUSCRIPT
SC
Fig. 2. Comparison of the ATR spectra of the aqueous sodium silicate fluidizers.
NU
The first group is in the range of about 3200-3450 cm-1 and is associated with the stretching vibrations of hydroxyl groups. These vibrations take place both in water molecules and in OH groups linked to silicate structural units (eg. tetrahedrons terminal groups). The
MA
second band associated with the presence of molecular water is the band at about 1640 cm -1, which is associated with bending vibrations of H-O-H. The high intensity of these bands is understandable because all tested fluidizers were aqueous solutions. The most visible change
D
in band position is related to the effect of isotope substitution ( i.e. spectra of the R-150D
PT E
fluidizer). The use of heavy water in the preparation of the fluidizers causes nearly double change in mass due to H→D substitution (without changing the corresponding force constants), what significantly changes the wavenumber of the vibrating molecular oscillators.
CE
And so, the bands from stretching vibrations change the position in the spectra to 2540 cm-1 (2470 cm-1 in the ATR spectra), and from the bending vibration of the water to 1440 cm-1. 1
AC
Among the bands of the second group, the most intense are the bands at about l000 cmassociated with asymmetric stretching vibrations of Si-O. Position of this band depends on
the degree of polymerization of the silicate anions. With the increase of this degree, the band appears at increasing wavenumbers. For the most polymerized silicate structure, i.e. SiO 2, this band is located at about 1100 cm-1. In the discussed spectra, the position of this band varies between 1028-1006 cm-1 in transmission spectra and between 1005-980 cm-1 in ATR spectra. It means that there is no polyanions with the highest unrestricted degree of polymerization, i.e. 2D and 3D. It is also unlikely that chain anions with unrestricted polymerization are also present (this band usually occurs at around 1070 cm-1). The possible anions are those consisting of single SiO4 tetrahedrons or those built of countable number of SiO4 tetrahedrons 5
ACCEPTED MANUSCRIPT (including both cyclic and chain systems). It was also noticed that the position of the main band changes with the SiO2/Na2O ratio. When this ratio decreases, the position of the band moves to lower wavenumbers. This leads to a conclusion that the increase of the silicate modulus prefers the presence of lower polymerized silicate units in the tested fluidizers [1517]. Another, less intense, band related to the silicate vibrations observed in the spectra is the band coming from the symmetrical stretching vibrations associated with the existence of
PT
Si-O-Si bridges (860-880 cm-1). The presence of this band indicates the formation of overtetrahedric units and may indicate the presence of pyrosilicate anions (two linked
RI
tetraehedrons) and / or anions consisting of more tetrahedrons. This band is not present in the
SC
spectra of R-137 aqueous sodium silicate, what means that for the silicate modulus of 3.2 only isolated SiO4 tetrahedrons are present in the samples. By contrast, silico-oxygene bridges
NU
occur for the silicate modulus of 2.5 (spectra of the R-145 aqueous sodium silicate). In addition, there is a band in the so-called pseudo-lattice region at 615-640 cm-1, indicating occurrence of rings composed of tetrahedrons closed in cyclic system (cyclosilicates). The
MA
relatively low value of the wavenumbers of this band indicates the formation of 6-membered rings, although the presence of 4-membered rings can not be excluded [18]. The last band of
D
this group comes from O-Si-O bending vibrations and occurs at about 460 cm-1. Because
over-tetrahedric units.
PT E
these vibrations are performed within tetraehedrons, this band can not be used to identify the
Figure 3 shows the Raman spectra of the fluidizers measured with the use of diffraction grating 1800. In the case of the diffraction grating 600, these spectra were less 1
CE
intense. The bands related to asymmetric stretching vibrations of Si-O groups (1035-1050 cm) and the bands in the pseudo-lattice region of 600-400 cm-1 were analyzed.
AC
The weak bands at around 595 cm-1 indicate the presence of 4-membered ring systems, whereas bands at about 437 cm-1 denote the presence of 6-membered rings systems. A number of "additional" bands in this region should be associated with the possible rings deformation that occur in cyclic systems, especially in the case of 6-membered rings. Ring deformation can also be a reason for the relatively low intensity of the bands in this region, because usually a strong band
corresponds to fully symmetrical character of the pore opening
vibrations. It can be also noticed that in the case of R-137 aqueous sodium silicate spectra there is no band at 435 cm-1, it has low intensity in the R-145 aqueous sodium silicate spectra, and in the case of R-150 aqueous sodium silicate spectra it is already quite noticeable. This may mean that the favorable rheological properties of the fluidizers with a silicate modulus of 6
ACCEPTED MANUSCRIPT about 2 (R-150 samples) may be due to the presence of units built of the 6-membered rings
NU
SC
RI
PT
[19-24].
MA
Fig. 3. Comparison of Raman spectra of the silicate fluidizers using 1800 diffraction grating.
3.2. Thixotropic properties of kaolin KOC slurries fluidized with aqueous sodium silicates
D
Figures 4 and 5 show that the kaolin slurries modified with the tested aqueous sodium
PT E
silicates have thixotropic properties, i.e. their apparent viscosity decreases with duration of applied shear. This means that shear stress values at decreasing shear rates are smaller than with the increasing shear rates because as a result of decreasing shear rate (which immediately
CE
follows an increase in the shear rate), the formation of the thixotropic structure begins, but since this is not an immediate phenomena, the read stress is lower than the "equilibrium";
AC
therefore, the curve for decreasing shear rates is below the curve for the increasing shear rates. These properties do not depend on the method of preparation of the tested fluidizer (results not presented here).
7
SC
RI
PT
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
Fig. 4. Flow curves of the kaolin slurry modified with 0.1 wt% of aqueous sodium silicate.
Fig. 5. Flow curves of the kaolin slurry modified with 0.3 wt% of aqueous sodium silicate.
Thixotropy phenomenon consists in transforming sol into gel with time and is caused by electrostatic interactions between the grains and stabilizing molecules [8, 9]. Other rheological calculations, i.e. work of the thixotropic structure destruction, confirmed that D2O produces stronger hydrogen bonds and reduces ion exchange than normal water. This leads to increase in the amount of silicate micelles with polymeric structures that form a separate dispersed fraction. For example, thixotropy index (measured during the thixotropy test; value of apparent viscosity measured after 1 s (η1) at shear rate of 5.6 s-1 divided by the value of apparent viscosity measured after 30 s (η30) at the same shear rate) determined in the
8
ACCEPTED MANUSCRIPT suspension in D2O for Mk= 2.08 was 1.165 and for identical composition in H2O, it was 0.967; Table 2 [10, 11, 29].
Table 2. Thixotropy index of the ceramic slurries modified with aqueous sodium silicates.
Silicate modulus 2.06
2.08
2.50
3.25
0.967 0.970 0.909 0.932 0.951
1.089 0.985 0.964 0.982 0.983
1.165 0.974 0.947 0.967 0.984
1.100 1.066 0.967 0.947 0.927
1.089 1.059 0.937 0.984 0.982
RI
PT
2.05
SC
Fluidizer concentration [wt%] 0.1 0.2 0.3 0.4 0.5
3.3. Viscosity of kaolin KOC slurries fluidized with aqueous sodium silicates
NU
Figure 6 presents the fluidization curves of the kaolin slurries modified with the aqueous sodium silicates of the silicate moduli in the range of 2.05-3.25. The best fluidization
MA
properties show sodium silicate solutions of the silicate moduli of about 2 and there is no significant difference in the apparent viscosity values in terms of the way of preparation of the fluidizer. With a fluidizer content of 0.3 wt% the apparent viscosity value is the lowest and
D
above this concentration there is no significant improvement in stabilization of the kaolin
PT E
slurry. Therefore, it can be assumed that the best stabilization properties poses aqueous sodium silicates with the silicate moduli of about 2 and the optimum concentration of 0.3 wt% relative to the kaolin dry mass. These conclusions were confirmed by the spectroscopic
CE
studies presented in the previous chapter. Higher silicate modulus, above 2.5, indicates independent silicate structures that don't affect the kaolinite grains and because of that the
AC
dominant fluidization mechanism is depleted stabilization, in which the macromolecules are dispersed in a suspension and constitute a separate dispersed fraction. For the lower values of the silicate modulus the main fluidization mechanism is ion exchange [15, 25-28].
9
RI
PT
ACCEPTED MANUSCRIPT
NU
SC
Fig. 6. Fluidization curves of the kaolin KOC slurries modified with aqueous sodium silicates.
4. Conclusions
The main purpose of the work was to explain the phenomena occurring during
MA
stabilization of ceramic slurries based on kaolin using several types of aqueous sodium silicates with the silicate moduli in the range of 2.05-3.25. Analysis of MIR and Raman
D
spectroscopic studies enabled to link the stabilization mechanisms with the silicate structures
PT E
occurring in different aqueous sodium silicates. For example, the increase of the silicate modulus prefers the presence of lower polymerized units what causes worse fluidization. Based on the rheological measurements, it was also determined which aqueous sodium silicate possessed the best fluidization properties. Additionally, the influence of the type of the
CE
medium on the fluidization properties was investigated. Analysis of the research results showed that the best fluidization properties characterize aqueous sodium silicate of silicate
AC
modulus of about 2, where the dominant fluidization mechanism is ion exchange. Those with the modulus larger than 2.5 created independent silicate micelles, mainly isolated SiO4 tetrahedrons. Changing the medium from H2O to D2O, which produces stronger hydrogen bonds, results in a stronger thixotropic structure.
Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
10
ACCEPTED MANUSCRIPT References [1]. R.K. Iler, The chemistry of silica, first ed., Wiley, New York, 1979. [2]. J.G. Vail, Soluble Silicates, first ed., Reinhold, New York, 1952. [3]. D. Hoebbel, K. Endres, T. Reinert, I. Pitsch, Inorganic-organic polymers derived from functional silicic acid derivatives by additive reaction, J. Non Cryst. Solids 176 (1994) 179188. [4]. F. Bergaya, G. Lagaly, Surface modification of clay minerals, Appl. Clay Sci. 19 (2001)
PT
1-3.
[5]. P. Mpofu, J. Addai-Mensah, J. Ralston, Investigation of the effect of polymer structure
RI
type on flocculation, rheology and dewatering behaviour of kaolinite dispersions, Int. J. Min.
SC
Process 71 (2001) 247-268.
[6]. J.E. Otterstedt, D.A. Brandreth, Small particles technology, Springer Science, fourth ed.,
NU
New York, 1998.
[7]. M. Chi, R. Eggleton, Cation exchange capacity of kaolinite, Clays Clay Miner. 47 (1999) 174-180.
MA
[8]. D. R. Dinger, Rheology for Ceramists, Morris Publishing, second ed., New York, 2002. [9]. P. Izak, Rheology in Ceramics AGH Publishing House, first ed., Krakow, 2015.
D
[10]. D. Penner, G. Lagaly, Influence of anions on the rheological properties of clay mineral dispersions, Appl. Clay Sci. 19 (2001) 131-142.
PT E
[11]. N. Yildiz, Y. Sarikaya, A. Calimli, Modification of rheology and permeability of Turkish ceramic clays using sodium silicate, Appl. Clay Sci. 13 (1998) 65-77. [12]. F. Pacheco-Torgal, J. Castro-Gomes, S. Jalali, 2008. Alkali-activated binders: A review.
CE
Part 2. About materials and binders manufacture, Con. Build. Mat. 22 (2008) 1315-1322. [13]. V. Penkavova, M. Guerreiro, J. Tihon, J.A.C. Teixeira, Deffloculation of kaolin
AC
suspensions- the effect of various electrolytes, Appl. Rheol. 25 (2014) 1-9. [14]. Factory standard, 2016. ZN-02/Z.Ch. Rudniki SA/257. http://www.zchrudniki.com.pl/ download/show/97/szklo-wodne-sodowe.pdf (accessed 25 September 2017). [15]. J.S. Falcone, J.L. Bass, , M. Angelella, M.R. Schenk, K.A. Brensinger, Characterizing the infrared bands of aqueous soluble silicates, J. Phys. Chem. A 114 (2010) 2438-2446. [16]. M. Handke, W. Mozgawa, Model quasi-molecule Si2O as an approach in the IR spectra description glassy and crystalline framework silicates, J. Mol. Struct. 348 (1995) 341–344. [17]. K. M. Davis, M. Tomozawa, An infrared spectroscopic study of water-related species in silica glasses. J. Non Cryst. Solids 201 (1996) 177–198.
11
ACCEPTED MANUSCRIPT [18]. M. Sitarz, W. Mozgawa, M. Handke, Rings in the structure of silicate glasses, J. Mol. Struct. 511 (1999) 281-285. [19]. J. Nordström, A. Sundblom, G. Vestergaard Jensen, J. Skov Pedersen, A. Palmqvist, A. Matic, Silica/alkali ratio dependence of the microscopic structure of sodium silicate solutions, J. Colloid Interface Sci. 397 (2013) 9–17. [20]. X. Yang, P. Roonasi, A. Holmgren, A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy, J. Colloid Interface Sci.
PT
328 (2008) 41–47.
[21]. W.R. Taylor, Application of infrared spectroscopy to studies of silicate glass structure:
RI
Examples from the melilite glasses and the systems Na2O-SiO2 and Na2O-Al2O3-SiO2, Proc.
SC
Indian Acad. Sci. 99 (1990) 99-117.
[22]. E.F. Medvedev, A.S. Komarevskaya, IR spectroscopic study of the phase composition
NU
for sodium silicate synthesized in aqueous medium, Glass Ceramics 64 (2007) 7-11. [23]. J. L. Bass, G. Turner, Anion distributions in sodium silicate solutions. Characterization by 29Si NMR, Infrared Spectroscopies, and Vapour Phase Osmometry, J. Phys. Chem. B 101
MA
(1997) 10638-10644.
[24]. G. Lagaly, W. Tufar, A. Minihan, A. Lovel, Silicates, in: B. Elvers, Ulmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012, pp.509-572.
D
[25]. A. Stempkowska, J. Mastalska-Popławska, P. Izak, L. Ogłaza, M. Turkowska,
PT E
Stabilization of kaolin clay slurry with sodium silicate of different silicate moduli, App. Clay Sci. 146 (2017) 147-151.
[26]. A. Papo, L. Piani, R. Ricceri, Sodium tripolyphosphate and polyphosphate as dispersing
CE
agents for kaolin suspensions: rheological characterization. Colloids Surf. 201 (2002) 219-230. [27]. N.J. Garcia, M.D. Ingram, J.C. Bazan, Ion transport in hydrated sodium silicates (water
AC
glasses) of varying water content, Solid State Ionics 146 (2002) 113-122. [28]. D.C.H Cheng, Characterization of thixotropy revisited, Rheol. Acta 42 (2003) 372-382. [29]. E.J. Teha, Y.K. Leonga, Y. Liua, A.B. Fourieb, M. Fahey, Differences in the rheology and surface chemistry of kaolin clay slurries: The source of the variations, Chem. Eng. Sci. 64 (2009) 3817-3825.
12
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
SC
RI
PT
Graphical abstract
13
ACCEPTED MANUSCRIPT Highlights
CE
PT E
D
MA
NU
SC
RI
PT
Aqueous sodium silicates of silicate moduli 2.05-3.25 were tested as fluidizers. Fluidizer synthesis method has a low impact on its fluidization properties. IR and Raman spectroscopy can be used for analysis of aqueous sodium silicates. The best fluidization properties show fluidizers of silicate moduli of about 2.
AC
14