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Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds
Materials Today: Proceedings xxx (xxxx) xxx
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Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds Alsu Yusupova a, Rizeda Ahmetova a, Alexander Bobrishev b,⇑ a b
Kazan National Research Technological University, K. Marksa Street 68, Kazan, Republic Tatarstan 420015, Russian Federation Kazan Federal University, Sjujumbike Street 10a, 1Naberezhnye Chelny, Republic Tatarstan 420008, Russian Federation
a r t i c l e
i n f o
Article history: Received 16 May 2019 Received in revised form 8 July 2019 Accepted 24 July 2019 Available online xxxx Keywords: Sulfur Aluminum chloride Silicate Polysulfides Waste
a b s t r a c t The method was developed to produce sulfur concrete from sulfur waste of petrochemical plants and silica containing compounds with high strength, performance properties, and resistance to aggressive environments. The composite materials were studied using the methods of X-ray analysis, electron paramagnetic resonance analysis, electron microscopy. Aluminum chloride has an activating effect on sulfur melt and its interaction with the surface of silicate, and formation of aluminum silicate polysulfides. Usage of aluminum chloride enables sulfur activation to encourage the chemical interaction between the components and formation of a compact structure of sulfur materials with high physical mechanical properties. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
1. Introduction
2. Experimental
One of the key aspects of resource efficiency is the effective use of production waste. Rehabilitation of man-made deposits will solve the important problems in the Russian mineral resources sector and improve the ecological situation. The sustainable multipurpose use of feedstock reduces the quantity of underused substances, increases a range of end products, makes it possible to manufacture new products from the portion of the feedstock which has been gone to waste earlier. All the above indicates the urgency and importance of the waste disposal and recycling problem for various industry sectors. This paper discusses the production of sulfur concrete from sulfur waste of petrochemical plants and silica containing compounds. As a modifier, aluminum chloride powder is used, which is a sulfur electrophilic activator [1,2]. A tight contact between the modified silicate, filler, and sulfur, i.e. after heating and pressing, may lead to the appearance of new interatomic bonds and phase interaction forces to ensure the optimum structure formation in a system at the microscale and macroscale level [3–5].
For production of inorganic sulfides based on sulfur and silica containing raw materials, the following components were used: sulfur (S), which was the waste from the Nizhnekamsk oil refinery with 99.98% wt. of base material (GOST 127-93); titanium chloride TiCl4, (TU 6-09-2118-77); silica-containing rock from the Dobrinskoe site, Saratov oblast (mineral composition, % wt.: 78 ± 7 of opal-cristobalite, 7 ± 2 of zeolite, 5 of montmorillonite). The composite materials were studied using the methods of physical chemical analysis. The X-ray studies were carried out with a DRON 3 diffractometer using monochromatic Cu K-alpha radiation. The electron paramagnetic resonance studies were performed with a RE-1306 radio spectrometer (at frequencies of 9100 and 9370 MHz) at 77 and 300 K, respectively. Single-crystal ruby with Cr3+ was used as an internal standard. The spectra were recorded in three scanning ranges of the external magnetic field. The photomicrograms of the samples were taken using an EMMA 4 transmission electron microscope-microanalyzer with 250 magnification.
3. Results and discussion ⇑ Corresponding author. E-mail address: [email protected] (A. Bobrishev).
The samples of sulfur concrete with aluminum chloride were made in two stages. First, the silicate was modified with aluminum
https://doi.org/10.1016/j.matpr.2019.07.682 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
2
A. Yusupova et al. / Materials Today: Proceedings xxx (xxxx) xxx
chloride by mixing reagents while being heated (200–500 °C), and then the modified silicate was added to molten sulfur. As shown in Fig. 1, the relationship between strength of the samples and quantity of AlCl3 modifier is of an extreme nature. The samples had the highest compressive strength when they were pre-calcinated at 500 °C and when they contained 5% wt. of aluminum chloride. The composite material with such composition had a strength of 70 MPa. When the modification temperature of silicate lowered down to 200 °C the strength of the samples decreased by a factor of two. A higher content of aluminum chloride (5–8%) at a temperature of 200–400 °C increased the strength insignificantly. An increase in the modification temperature higher than 500 °C did not provide a qualitative improvement of strength properties in the composite material. It appears to be related to sintered silicate and changed crystalline structure. Apparently, aluminum chloride could not modify silicate at low temperatures, or did not modify it fully, so there was not a sufficient quantity of electrophilic centers of sulfur activation on the surface of silicate. We believe that 5% wt. of aluminum chloride and a modification temperature of 500 °C are optimum conditions for activation of the silicate surface, and they can give a significant increase in strength of the composite materials with this binderfiller ratio. With a higher filler content (ratio of 1:1.5), a decrease in strength of the sulfur composite material was observed (Fig. 2), mainly, as a result of insufficient amount of binder. Maximum strength of the samples did not exceed 42 MPa. The higher the amount of powdery modifier was, the lower the strength of the samples was (at any temperature of heat pre-treatment). The samples had maximum strength at a binder-filler ratio of 1:1, and it equaled to 70 MPa. The relationship between strength of the composite materials and time of aluminum chloride modification is shown in Fig. 3. At a modification temperature of 400–500 °C, strength of the composite materials increased steadily and became stable within 30 min. Thus, the optimum modification time at 500 °C is 30 min. The optimum modification time is 30 min (500 °C). The relationships between water absorption of the resulting samples and content of aluminum chloride in the binder and temperature of modification at different binder-filler ratios are shown in Figs. 4 and 5. As shown in Fig. 4, the lowest water absorption of the samples (1.68%) was observed at a binder-filler ratio of 1:1, a silicate modification temperature of 500 °C, and 10% wt. of silicate. It can be assumed that ‘‘molecular sorption” of aluminum chloride with
Fig 2. Relationship between compressive strength of the sulfur composite samples and content of aluminum chloride at different temperatures of pre-calcination. The binder-filler ratio is 1:1.5.
Fig. 3. Relationship between compressive strength and modification time at different temperatures of pre-calcination. The binder-filler ratio is 1:1.
Fig. 4. Relationship between water absorption of the sulfur composite samples and content of aluminum chloride at different temperatures of pre-calcination. The binder-filler ratio is 1:1.
Fig. 1. Relationship between compressive strength of the sulfur composite samples and content of aluminum chloride at different temperatures of heat pre-treatment. The binder-filler ratio is 1:1.
vacant d-orbitals was the basis for sulfur activation and retention on the silicate surface with the formation of a monolayer. The formation of a compact nonporous structure under these conditions lowered sorption properties of the silicate. A higher amount of modifier (15%) at this temperature increased the water absorption of the samples by 40%. It is likely that the structure of the samples was loosened by an excessive amount of the modifier. Also, a lower modification temperature (200 °C) increased water absorption of the samples (up to 4%). It is possible that silicate was not modified fully at lower temperatures, and chemically
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
A. Yusupova et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 5. Relationship between water absorption of the sulfur composite samples and content of aluminum chloride at different temperatures of pre-calcination: 500 °C (1); 400 °C (2); 300 °C (3); 200 °C (4). The binder-filler ratio is 1:1.5.
uncombined aluminum chloride with high hygroscopic properties loosened the structure of the samples. The relationship of water absorption of the sulfur composite samples with a binder-filler ratio of 1:1.5 has a quite different nature (Fig. 5). With a higher amount of modifier (aluminum chloride), the water absorption of the samples increased steadily at any temperature of heat pre-treatment. Moreover, even the starting samples without aluminum chloride did not meet the requirements of the GOST standard. It can be explained by an insufficient amount of binder and, hence, a loose structure of the samples and resulting voids. As the samples with the optimized composition were selected, further tests were performed on the best samples. Table 1 shows the results of physical mechanical tests of the samples which were made in the optimum conditions and contained 5% wt. of aluminum chloride. As shown in the table, the samples made by the proposed formula with an optimum component ratio have high coefficient of resistance to HCl, H2SO4, CaCl2, NaCl, MgSO4 solutions, high compressive strength (62 MPa). The properties of sulfur composites are much influenced by the filler geometry: first of all, by powder fineness [6]. The analysis with the electron microscope-microanalyzer showed that the smaller sulfur crystals were responsible for not only higher strength of the sulfur binder, optimum film thickness around the filler, but stronger adhesive bonds between sulfur and filler surface (Si–O–S). Much higher strength of the sample with sand (binder-filler ratio is 40–60% wt.) can be explained by the formation of a more compact structure where the fine filler particles (fraction of less than 0.5 mm) fill the intergranular aggregate space in the sample evenly and provide additional intermolecular bonds in the binder-filler phase boundary. A higher sand fraction in the filler (more than 20%) makes density of the composite material decrease by 0.3 g/cm3, which is likely due to the lower
3
intensity of the bond between binder and filler. The samples with optimum composition have a compact homogeneous nonporous material structure. In order to explain changes in the structure of the samples, physical mechanical and quantum chemical studies were performed. The X-ray diffraction analysis showed that crystallinity of the sulfur samples with aluminum chloride was 61 per cent, and without it – 69 per cent (Fig. 6). A lower crystallinity of the sample with the modified silicate indicates that a portion of crystalline sulfur was used to form a covalent bond with aluminum, silicon, and oxygen of the filler, and create X-ray amorphous compounds. The samples of silicate were studied using the method of electron paramagnetic resonance (EPR). The electron-hole centers detected with EPR method represented the defects of the crystalline structure of the studied objects. In general, electron-hole centers can be described as special electron configurations of atom clusters, which are associated with defective areas in the atomic structure that have taken over an electron or electron hole. The EPR spectrum for paramagnetic centers (in this case, for electronhole centers) had the form of a single line with g-factor 2.00. The shape, width, and position of the line in a magnetic field scale (H = 3300 Gs, g 2.036) corresponded to those for paramagnetic centers (free radical type) formed due to broken chemical bonds. Table 2 shows a number of electron-hole centers (in arbitrary units) in the samples of initial and modified silicates. The maximum number of electron-hole centers (19 arb. un.) was recorded in sample no. 2. As for the other samples (nos 1, 3, 4), the number of electron-hole centers decreased to ‘‘trace amounts of electronhole centers”. The chemical modification with aluminum chloride resulted in an intended change in the chemical properties of a silicate surface. The vacant d-orbitals in the resulted silicate-aluminum chloride system were electron-hole centers of the surface. As shown in Table 2, the modification with aluminum chloride (AlCl3 5%) led to a higher number of electron-hole centers (up to 19 arb.
Table 1 Physical mechanical and performance properties of sulfur concrete with aluminum chloride as an activator. Property
Value
Amount of aluminum chloride (binder), % wt. Binder-filer ratio, weight fractions Quantity of freeze-thaw cycles Water absorption, % Density, g/cm3
5 1:1 240 2.32 1.80
Coefficient of resistance to aggressive environments (GOST 25881-83)
5% 5% 5% 5% 5%
HCl H2SO4 MgSO4 CaCl2 NaCl
0.972 0.963 0.968 0.969 0.983
Fig. 6. X-ray diffraction analysis of the sulfur composite samples with aluminum chloride (2) and without it (1).
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
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A. Yusupova et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 2 EPR-measurements of silicate containing materials. No
Sample
Number of electron-hole centers (arb. un.)
1 2 3 4
Silicate dried at T = 500 °C Modified silicate (AlCl3 10%) Modified silicate (AlCl3 5%+S 50%) Silicate
Trace amounts 19 Trace amounts Trace amounts
un.). Therefore, we got the material with catalytic properties. The presence of lone sulfur pairs defined its activating ability under the influence of electrophiles of the modified silicate surface. After opening of sulfur rings, the polysulfide radicals were formed, and they interacted with the active surface of the modified silicate by the donor-acceptor mechanism. It resulted in a dramatic decrease in the number of electron-hole centers on the surface of silicate (Table 2) – quenching of active sites Si–AlCl2. The results of physical chemical studies allow us to presume that the chemical interaction between sulfur and aluminum (attached to the surface of silicate), as well as oxygen and silicon (a part of silicate itself) proceeded using the donor-acceptor mechanism, with the formation of aluminum silicate polysulfide [7]. Therefore, modification of silicate with aluminum chloride led to increase in an amount of active sites on the surface of silicate and opening of sulfur rings. The chemical interaction between sulfur and atoms of oxygen and silicon of the silicate surface resulted in the formation of solid material with high density, strength, and resistance to aggressive environments. Aluminum chloride which modified the silicate surface initiated opening of sulfur rings and formation of aluminum silicate polysulfide. In the view of the above, the approximate stoichiometry was performed for sulfur concrete made from silicate and aluminum
chloride with an optimum sulfur-silicate ratio of 1:1 and 10% wt. of aluminum chloride in the filler (mol %): sulfur chemically combined with silicon and oxygen was 28, sulfur combined with aluminum chloride was 10, sulfur inside the globules was 28, chemically uncombined sulfur was 22. 4. Conclusions 1. The method was developed to produce aluminum silicate polysulfides and sulfur concrete from it, the compositions and process conditions were optimized. 2. The physical chemical studies confirmed the chemical interaction between sulfur and silicate with the formation of polysulfides, which defined the formation of a compact homogeneous structure and high physical mechanical properties of sulfur concrete based on them.
References [1] M.G. Voronkov, N.S. Vyazankin, E.H.N. Deryagina, Sulfur Reactions with Organic Compounds, Nauka, Novosibirsk, 1979 (in Russian). [2] A.A. Ysupova, A.G. Shamov, R.T. Ahmetova, V.A. Pervushin, A.I. Hatsrinov, Titanium tetrachloride as electrofilic activator in technology of inorganic polysulfides, J. Quantum Chem. 111 (11) (2011) 2575–2578. [3] E.V. Korolev, A.P. Proshin, V.I. Solomatov, Sulfur Binder and Compositions Based On It, PGASA, Penza, 2001 (in Russian). [4] A.N. Volgushev, Sulfur binder and compositions based on it, Concr. Reinf. Concr. 5 (1997) 46–48 (in Russian). [5] V.I. Solomatov, A.N. Bobryshev, A.P. Proshin, Clusters in the structure and technology of composite building materials, news of universities, Building 4 (1983) 51–56 (in Russian). [6] V.I. Solomatov, Elements of the general theory of composite materials, news of universities, Building 8 (1980) 61–70 (in Russian). [7] R.T. Ahmetova, L.R. Baraeva, A.A. Yusupova, A.I. Hacrinov, T.Z. Lygina, Activation of components in low-waste technologies of silicate sulfides and materials based on them, Basic Res. 2 (2015) 4855–4860 (in Russian).
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds Alsu Yusupova a, Rizeda Ahmetova a, Alexander Bobrishev b,⇑ a b
Kazan National Research Technological University, K. Marksa Street 68, Kazan, Republic Tatarstan 420015, Russian Federation Kazan Federal University, Sjujumbike Street 10a, 1Naberezhnye Chelny, Republic Tatarstan 420008, Russian Federation
a r t i c l e
i n f o
Article history: Received 16 May 2019 Received in revised form 8 July 2019 Accepted 24 July 2019 Available online xxxx Keywords: Sulfur Aluminum chloride Silicate Polysulfides Waste
a b s t r a c t The method was developed to produce sulfur concrete from sulfur waste of petrochemical plants and silica containing compounds with high strength, performance properties, and resistance to aggressive environments. The composite materials were studied using the methods of X-ray analysis, electron paramagnetic resonance analysis, electron microscopy. Aluminum chloride has an activating effect on sulfur melt and its interaction with the surface of silicate, and formation of aluminum silicate polysulfides. Usage of aluminum chloride enables sulfur activation to encourage the chemical interaction between the components and formation of a compact structure of sulfur materials with high physical mechanical properties. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
1. Introduction
2. Experimental
One of the key aspects of resource efficiency is the effective use of production waste. Rehabilitation of man-made deposits will solve the important problems in the Russian mineral resources sector and improve the ecological situation. The sustainable multipurpose use of feedstock reduces the quantity of underused substances, increases a range of end products, makes it possible to manufacture new products from the portion of the feedstock which has been gone to waste earlier. All the above indicates the urgency and importance of the waste disposal and recycling problem for various industry sectors. This paper discusses the production of sulfur concrete from sulfur waste of petrochemical plants and silica containing compounds. As a modifier, aluminum chloride powder is used, which is a sulfur electrophilic activator [1,2]. A tight contact between the modified silicate, filler, and sulfur, i.e. after heating and pressing, may lead to the appearance of new interatomic bonds and phase interaction forces to ensure the optimum structure formation in a system at the microscale and macroscale level [3–5].
For production of inorganic sulfides based on sulfur and silica containing raw materials, the following components were used: sulfur (S), which was the waste from the Nizhnekamsk oil refinery with 99.98% wt. of base material (GOST 127-93); titanium chloride TiCl4, (TU 6-09-2118-77); silica-containing rock from the Dobrinskoe site, Saratov oblast (mineral composition, % wt.: 78 ± 7 of opal-cristobalite, 7 ± 2 of zeolite, 5 of montmorillonite). The composite materials were studied using the methods of physical chemical analysis. The X-ray studies were carried out with a DRON 3 diffractometer using monochromatic Cu K-alpha radiation. The electron paramagnetic resonance studies were performed with a RE-1306 radio spectrometer (at frequencies of 9100 and 9370 MHz) at 77 and 300 K, respectively. Single-crystal ruby with Cr3+ was used as an internal standard. The spectra were recorded in three scanning ranges of the external magnetic field. The photomicrograms of the samples were taken using an EMMA 4 transmission electron microscope-microanalyzer with 250 magnification.
3. Results and discussion ⇑ Corresponding author. E-mail address: [email protected] (A. Bobrishev).
The samples of sulfur concrete with aluminum chloride were made in two stages. First, the silicate was modified with aluminum
https://doi.org/10.1016/j.matpr.2019.07.682 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
2
A. Yusupova et al. / Materials Today: Proceedings xxx (xxxx) xxx
chloride by mixing reagents while being heated (200–500 °C), and then the modified silicate was added to molten sulfur. As shown in Fig. 1, the relationship between strength of the samples and quantity of AlCl3 modifier is of an extreme nature. The samples had the highest compressive strength when they were pre-calcinated at 500 °C and when they contained 5% wt. of aluminum chloride. The composite material with such composition had a strength of 70 MPa. When the modification temperature of silicate lowered down to 200 °C the strength of the samples decreased by a factor of two. A higher content of aluminum chloride (5–8%) at a temperature of 200–400 °C increased the strength insignificantly. An increase in the modification temperature higher than 500 °C did not provide a qualitative improvement of strength properties in the composite material. It appears to be related to sintered silicate and changed crystalline structure. Apparently, aluminum chloride could not modify silicate at low temperatures, or did not modify it fully, so there was not a sufficient quantity of electrophilic centers of sulfur activation on the surface of silicate. We believe that 5% wt. of aluminum chloride and a modification temperature of 500 °C are optimum conditions for activation of the silicate surface, and they can give a significant increase in strength of the composite materials with this binderfiller ratio. With a higher filler content (ratio of 1:1.5), a decrease in strength of the sulfur composite material was observed (Fig. 2), mainly, as a result of insufficient amount of binder. Maximum strength of the samples did not exceed 42 MPa. The higher the amount of powdery modifier was, the lower the strength of the samples was (at any temperature of heat pre-treatment). The samples had maximum strength at a binder-filler ratio of 1:1, and it equaled to 70 MPa. The relationship between strength of the composite materials and time of aluminum chloride modification is shown in Fig. 3. At a modification temperature of 400–500 °C, strength of the composite materials increased steadily and became stable within 30 min. Thus, the optimum modification time at 500 °C is 30 min. The optimum modification time is 30 min (500 °C). The relationships between water absorption of the resulting samples and content of aluminum chloride in the binder and temperature of modification at different binder-filler ratios are shown in Figs. 4 and 5. As shown in Fig. 4, the lowest water absorption of the samples (1.68%) was observed at a binder-filler ratio of 1:1, a silicate modification temperature of 500 °C, and 10% wt. of silicate. It can be assumed that ‘‘molecular sorption” of aluminum chloride with
Fig 2. Relationship between compressive strength of the sulfur composite samples and content of aluminum chloride at different temperatures of pre-calcination. The binder-filler ratio is 1:1.5.
Fig. 3. Relationship between compressive strength and modification time at different temperatures of pre-calcination. The binder-filler ratio is 1:1.
Fig. 4. Relationship between water absorption of the sulfur composite samples and content of aluminum chloride at different temperatures of pre-calcination. The binder-filler ratio is 1:1.
Fig. 1. Relationship between compressive strength of the sulfur composite samples and content of aluminum chloride at different temperatures of heat pre-treatment. The binder-filler ratio is 1:1.
vacant d-orbitals was the basis for sulfur activation and retention on the silicate surface with the formation of a monolayer. The formation of a compact nonporous structure under these conditions lowered sorption properties of the silicate. A higher amount of modifier (15%) at this temperature increased the water absorption of the samples by 40%. It is likely that the structure of the samples was loosened by an excessive amount of the modifier. Also, a lower modification temperature (200 °C) increased water absorption of the samples (up to 4%). It is possible that silicate was not modified fully at lower temperatures, and chemically
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
A. Yusupova et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 5. Relationship between water absorption of the sulfur composite samples and content of aluminum chloride at different temperatures of pre-calcination: 500 °C (1); 400 °C (2); 300 °C (3); 200 °C (4). The binder-filler ratio is 1:1.5.
uncombined aluminum chloride with high hygroscopic properties loosened the structure of the samples. The relationship of water absorption of the sulfur composite samples with a binder-filler ratio of 1:1.5 has a quite different nature (Fig. 5). With a higher amount of modifier (aluminum chloride), the water absorption of the samples increased steadily at any temperature of heat pre-treatment. Moreover, even the starting samples without aluminum chloride did not meet the requirements of the GOST standard. It can be explained by an insufficient amount of binder and, hence, a loose structure of the samples and resulting voids. As the samples with the optimized composition were selected, further tests were performed on the best samples. Table 1 shows the results of physical mechanical tests of the samples which were made in the optimum conditions and contained 5% wt. of aluminum chloride. As shown in the table, the samples made by the proposed formula with an optimum component ratio have high coefficient of resistance to HCl, H2SO4, CaCl2, NaCl, MgSO4 solutions, high compressive strength (62 MPa). The properties of sulfur composites are much influenced by the filler geometry: first of all, by powder fineness [6]. The analysis with the electron microscope-microanalyzer showed that the smaller sulfur crystals were responsible for not only higher strength of the sulfur binder, optimum film thickness around the filler, but stronger adhesive bonds between sulfur and filler surface (Si–O–S). Much higher strength of the sample with sand (binder-filler ratio is 40–60% wt.) can be explained by the formation of a more compact structure where the fine filler particles (fraction of less than 0.5 mm) fill the intergranular aggregate space in the sample evenly and provide additional intermolecular bonds in the binder-filler phase boundary. A higher sand fraction in the filler (more than 20%) makes density of the composite material decrease by 0.3 g/cm3, which is likely due to the lower
3
intensity of the bond between binder and filler. The samples with optimum composition have a compact homogeneous nonporous material structure. In order to explain changes in the structure of the samples, physical mechanical and quantum chemical studies were performed. The X-ray diffraction analysis showed that crystallinity of the sulfur samples with aluminum chloride was 61 per cent, and without it – 69 per cent (Fig. 6). A lower crystallinity of the sample with the modified silicate indicates that a portion of crystalline sulfur was used to form a covalent bond with aluminum, silicon, and oxygen of the filler, and create X-ray amorphous compounds. The samples of silicate were studied using the method of electron paramagnetic resonance (EPR). The electron-hole centers detected with EPR method represented the defects of the crystalline structure of the studied objects. In general, electron-hole centers can be described as special electron configurations of atom clusters, which are associated with defective areas in the atomic structure that have taken over an electron or electron hole. The EPR spectrum for paramagnetic centers (in this case, for electronhole centers) had the form of a single line with g-factor 2.00. The shape, width, and position of the line in a magnetic field scale (H = 3300 Gs, g 2.036) corresponded to those for paramagnetic centers (free radical type) formed due to broken chemical bonds. Table 2 shows a number of electron-hole centers (in arbitrary units) in the samples of initial and modified silicates. The maximum number of electron-hole centers (19 arb. un.) was recorded in sample no. 2. As for the other samples (nos 1, 3, 4), the number of electron-hole centers decreased to ‘‘trace amounts of electronhole centers”. The chemical modification with aluminum chloride resulted in an intended change in the chemical properties of a silicate surface. The vacant d-orbitals in the resulted silicate-aluminum chloride system were electron-hole centers of the surface. As shown in Table 2, the modification with aluminum chloride (AlCl3 5%) led to a higher number of electron-hole centers (up to 19 arb.
Table 1 Physical mechanical and performance properties of sulfur concrete with aluminum chloride as an activator. Property
Value
Amount of aluminum chloride (binder), % wt. Binder-filer ratio, weight fractions Quantity of freeze-thaw cycles Water absorption, % Density, g/cm3
5 1:1 240 2.32 1.80
Coefficient of resistance to aggressive environments (GOST 25881-83)
5% 5% 5% 5% 5%
HCl H2SO4 MgSO4 CaCl2 NaCl
0.972 0.963 0.968 0.969 0.983
Fig. 6. X-ray diffraction analysis of the sulfur composite samples with aluminum chloride (2) and without it (1).
Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682
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A. Yusupova et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 2 EPR-measurements of silicate containing materials. No
Sample
Number of electron-hole centers (arb. un.)
1 2 3 4
Silicate dried at T = 500 °C Modified silicate (AlCl3 10%) Modified silicate (AlCl3 5%+S 50%) Silicate
Trace amounts 19 Trace amounts Trace amounts
un.). Therefore, we got the material with catalytic properties. The presence of lone sulfur pairs defined its activating ability under the influence of electrophiles of the modified silicate surface. After opening of sulfur rings, the polysulfide radicals were formed, and they interacted with the active surface of the modified silicate by the donor-acceptor mechanism. It resulted in a dramatic decrease in the number of electron-hole centers on the surface of silicate (Table 2) – quenching of active sites Si–AlCl2. The results of physical chemical studies allow us to presume that the chemical interaction between sulfur and aluminum (attached to the surface of silicate), as well as oxygen and silicon (a part of silicate itself) proceeded using the donor-acceptor mechanism, with the formation of aluminum silicate polysulfide [7]. Therefore, modification of silicate with aluminum chloride led to increase in an amount of active sites on the surface of silicate and opening of sulfur rings. The chemical interaction between sulfur and atoms of oxygen and silicon of the silicate surface resulted in the formation of solid material with high density, strength, and resistance to aggressive environments. Aluminum chloride which modified the silicate surface initiated opening of sulfur rings and formation of aluminum silicate polysulfide. In the view of the above, the approximate stoichiometry was performed for sulfur concrete made from silicate and aluminum
chloride with an optimum sulfur-silicate ratio of 1:1 and 10% wt. of aluminum chloride in the filler (mol %): sulfur chemically combined with silicon and oxygen was 28, sulfur combined with aluminum chloride was 10, sulfur inside the globules was 28, chemically uncombined sulfur was 22. 4. Conclusions 1. The method was developed to produce aluminum silicate polysulfides and sulfur concrete from it, the compositions and process conditions were optimized. 2. The physical chemical studies confirmed the chemical interaction between sulfur and silicate with the formation of polysulfides, which defined the formation of a compact homogeneous structure and high physical mechanical properties of sulfur concrete based on them.
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Please cite this article as: A. Yusupova, R. Ahmetova and A. Bobrishev, Sulfur concrete made from sulfur waste of petrochemical plants and silica containing compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.682