STUDY AND PRODUCTION OF FIREFIGHTING SUBSTANCES BASED ON ACID PROCESSING OF LOW-GRADE PHOSPHORITE

ABSTRACT

The paper presents the results of the study of methods for obtaining fire retardants based on the products of acid processing of low-grade phosphorite by the method of IR spectroscopy. Data and discussions of diffraction patterns of initial phosphorite and products of its processing are given. Based on the research results, depending on the composition of both phases, the possibility of using special-purpose inorganic materials for obtaining inorganic materials has been established in the future.

АННОТАЦИЯ

В работе приводится результаты изучение способов получения антипиренов на основе продуктов кислотной переработки низкосортных фосфорита методом ИК спектроскопии. Приводятся данные и обсуждения дифрактограмм исходного фосфорита и продуктов его переработки. По результатам исследований в зависимости от состава обеих фаз в перспективе установлена возможность использования для получения неорганических материалов специального назначения.

Keywords: low-grade phosphorites, silicate-aluminate, phosphate, carbonate groups, IR spectroscopy, diffraction patterns, flame retardant, flame retardants.

Ключевые слова: низкосортные фосфориты, силикатно-алюминатные, фосфатные, карбонатные группы, ИК-cпектроскопии, дифрактограммы, возгование, антипирены.  

Introduction

To date, Western European countries are increasing the demand for flame retardants. Fire retardants are used in buildings and structures where combustible materials are used for fire safety purposes. Flame retardants are substances that protect wood, fabrics, plastics and other materials of organic origin from ignition and self-burning.

According to the mechanism of protection of materials from ignition, fire retardants are divided into various groups. There may be a flame retardant having a low melting point, which, when attempting to ignite, forms a dense film on the surface that blocks the access of oxygen to the material. When heated, the fire retardant may decompose with the release of inert gases or vapors that make it difficult to ignite the gaseous decomposition products of the protected material.

To further deepen and develop methods for the effective and non-traditional use of low-grade phosphorites, we are researching obtaining a special-purpose substance. Such substances include reducing the flammability of various materials, i.e. phosphate fire retardants. To obtain such substances based on silicate-phosphate, silicate-aluminate and phosphate-aluminate additives, in our opinion, the natural sources of the above components - low-grade phosphorites of the Central Kyzylkum - are the most suitable with economic and environmental feasibility.

On the other hand, noteworthy is the fact that in the scientific literature there are almost no data on the involvement of natural raw materials and, therefore, little attention has been paid to these studies to obtain products with fire retardant properties. There are no scientific works on the study of the involvement of mineral waste containing phosphates, silicates, aluminates and other compounds accumulated in large volumes during the extraction of phosphate raw materials.

When developing methods for processing phosphate raw materials (FS) to obtain a particular product, the main approach is to select conditions that are functions of changing the pH of the medium, varieties and quantitative ratios of reagents. By choosing acidic (pH < 7) or alkaline (pH > 7) processing methods, depending on the composition of the initial API sample, you can get different end products.

In this regard, for the partial practical implementation of all of the above, we conducted preliminary studies on the production of flame retardant substances based on the acid processing of low-grade phosphorites (selection from the 1-layer), accumulated as waste in the Kyzylkum phosphorite complex, which opens up opportunities in the future for obtaining inorganic materials for special purposes [1].

Experimental part

For research, a sample of low-grade phosphorite (LPh) was selected with the content of the main components (%): SiO₂ - 10.5, P₂O₅ - 13.6, Al₂O₃ - 1.42, CaO - 45.4, Na₂O - 2.7, K₂O - 0.3, MgO - 1.7, Fe₂O₃ - 2.1, CO -16, 30. Analyzes were carried out in the Central Laboratory of Geological Exploration JSC method of emission semi-quantitative spectral analysis in the range of contents from 1*10-5% to n%. Measuring instruments: Diffraction spectrograph PGS-2 (Germany) with a diffraction grating 600 lines/mm; - microscope type MBS-9).

According to the results of the experimental studies, the following results were obtained:

Acid processing was carried out at a ratio of T:L = 1:3 (50 g LPh : 137 ml 20% HCl solution, ρ = 1.098 g/cm³ and 50 g LPh : 142.3 ml 10% HNO₃ solution, ρ = 1.054 g/cm³) with stirring at 70-80°C for 2 hours. After acid processing of the LPh sample, solutions were obtained containing (on average): SiO₂ - 0.1542 g/l, P₂O₅ - 35.66 g/l, and Al₂O₃ - 2.073 g/l. Solutions in composition are phosphate-aluminate with an insignificant silicate fraction.

To establish compound changes depending on the pH of the medium during the processing of inorganic raw materials, one of the most informative methods is IR spectroscopy. Therefore, we undertook to study the IR spectra of solid samples of phosphorite before and after acid processing, which were taken on an IR Tracer-100 spectrometer (Shimadzu, Japan) in the range of 4000 - 500 cm^-1 (Fig.1-2).

Result and discussion

An analysis of the spectra of the original sample shows that in the high-frequency region there are several bands with frequencies of 3734.19 and 3647.39 cm^-1, characteristic of ν (OH) hydroxyl groups of the bound HO-M (M = Al⁺³, Mg⁺², Fe^+3/+2) and silicate constituents contained in phosphorite. The band at 3566.38 cm^-1 refers to ν(OH) of the crystallization water molecule in the interplanar layers of rock-forming components [2].

Figure 1. IR spectrum of the original LPh (Fosmuka 1-layer I)

In the middle region of the spectrum at 1417.69 cm^-1 there is a wide band characteristic of νas(CO) of the carbonate group, which corresponds to the results of chemical analysis of phosphorites 16-19% CO₂. Judging by the manifestation of a narrowly intense band at 871.82 cm^-1, a very weak band at 728.5 and an average intensity at 711.73 cm^-1, characteristic of the vibrations of the carbonate group, it can be concluded that carbonate rock-forming components in the composition of phosphorite are in in the form of dolomitic limestone (calcite) [3, 4].

Figure 2. Comparison of the IR spectra of the samples: the original LPh (Fosmuka 1-layer) (green lines), the product after processing with 20% HCl solution (black lines) and the product after processing with 10% HNO₃ solution (red lines)

In this part of the spectrum, the intensely wide band at 1030 cm^-1 is due to νas(SiO) of the silicate group. The remaining low-frequency bands, manifested at 522.71, 507.28, 472.56 and 462.92 cm^-1, are related to bending vibrations of Si-O-Al(M) and O-Si-O bonds in tetrahedral structures.

It is appropriate to note that the main component in the composition of phosphorites is the presence of phosphate ions, but their characteristic bands in the studied spectra do not appear in their inherent region of the IR spectrum in the range of 950-1200 cm^-1, the marked bands overlap with a wide intense band in the indicated frequency interval.

According to the data of chemical analysis and IR spectroscopic study, it was established that the studied LPh sample consists of carbonate, phosphate, silicate-aluminate anions and cations neutralizing their charges (Na⁺, Mg⁺², K⁺, Ca⁺², Fe^+3/+2), as well as from compounds of other metals in trace amounts.

To establish the ongoing compound changes after the acidic (pH = 2) processing of LPh with a 20% HCl solution and a 10% HNO₃ solution, IR spectral studies of the solid phases obtained after processing was carried out. It is known that carbonate and phosphate groups are the most acidically decomposed components of phosphorites, silicate-aluminate groups are little exposed to the action of H₃O⁺ ions in acid solutions. Consequently, a comparison of the IR spectra of the original and processed images shows the existence of noticeable differences in their characteristic areas.

Thus, in the high-frequency range of the spectrum of samples processed with HNO₃ and HCl solutions, band conservations were found, but with a lower intensity at 3734, 3647 cm-1, attributed to v(OH) HO-M (M= Al⁺³, Mg⁺², Fe^+3/+2) fragments.Along with them, new broad bands with average intensity appear in the spectra with doublet maxima at 3500, 3446.79 cm^-1 in the case of a recycled sample with HNO₃ and a band in the range of 3000-3579 cm^-1 with a maximum of 3390.86 cm^-1 in the spectrum of a sample processed with HCl. The appearance of these bands is caused by a valence oscillation of v(OH) bound water, and possibly due to the penetration of H₃O⁺ into the cavities of aluminate-silicate groups, as well as partial substitution of M⁺ⁿ cations (Na⁺, K⁺, Ca⁺², Mg⁺², Fe⁺³, Al⁺³) associated with phosphate and silicate groups on H3O+ ions of acid solutions [2-4].

In addition, the presence of bound water molecules is evidenced by the appearance of new bands with medium intensities at 1614.42 cm^-1 and a doublet at 1645.28, 1622.19 cm^-1, related to δ(Н₂О). In the lower frequency part in this region of the spectra, the positions of the doublet (in the range of 1558.48-1556.4 cm^-1) bands remained almost unchanged. This is due to the presence of hydroxyl groups remaining out of reach from the action of H₃O⁺ of the above-mentioned OH groups in densely packed intercrystalline layers of phosphorite after acid processing [3, 4].

It should be noted that in the spectra of the acid processed samples, the characteristic absorption bands of the νas(CO) vibration of carbonate groups disappear (Fig. 2), but a more high-frequency shifted weak band in the spectra of both products at 1456 cm^-1 is assigned to νas(CO). This is apparently due to the incomplete decomposition of the existing more stable modification of the carbonate constituents in phosphorite. In addition, the complete decomposition of dolomite-calcite and limestone carbonate components of phosphorites is indicated by the absence of a trinity of bands at 870, 728, and 711 cm^-1, found in the spectrum of the original phosphorite [4].

Bands characteristic of silicate fragments were found in the spectrum of the sample processed with HNO₃ at 1029.99 (strong) and with an average intensity of 576.72, 547.78, 513.7 cm^-1. In the spectrum of a sample of processed phosphorite with a solution of hydrochloric acid, νas(Si-O) is high-frequency shifted to 1078.21 cm^-1, the remaining bands appear at 798.53, 597.93, 518.85, 505.35 and 489.92 cm^-1, that characteristic ring vibrations of Si-O-Si groups in silicon-oxygen tetrahedra Si-O-Al (silicates) and bending vibrations of O-Si-O bonds [3].

It should be noted that the bands of vas(P=O) and vas(P-O) phosphate groups were detected only in the spectrum of nitric acid of the processed sample at 1215.15 (weak), 1100 (shoulder) and 950.91 (medium) cm^-1 (Fig. 2). In the spectrum of hydrochloric acid of the processed sample the sample shows only a weak band at 950.91 cm^-1, the remaining strong ones are covered by a wide absorption band in the range of 850-1300 cm^-1 [2-4].

The absence of absorption bands in the spectrum of the nitric-acid-processed sample in the region of 1300-450 cm^-1, characteristic of the valence vibrations of the vas(N-O) and vs(N-O) nitro groups, indicates the absence of NO₃^-ions in the solid phase [2].

To determine the phase composition of phosphorite and products of its processing, X-ray phase analysis was carried out. The phase composition of the initial and processed sample of phosphorite raw materials was studied using a Bruker AXS X-ray diffractometer (Germany). The diffraction patterns were interpreted automatically using the EVA software package of a Bruker AXS X-ray diffractometer. Diffractograms of the original and processed sample of phosphorite raw materials are shown in Figures 3,4 and 5.

Figure 3 shows a diffraction pattern of a sample of the original LPh; the diffraction pattern contains lines of quartz and dolomite, characterized by 2θ angles of reflections of diffraction lines (angular degrees). Quartz: 29.38; 20.82; 2.62; 50.2. Dolomite: 31.98; 33.18; 39.39; 41.2; 50.4; 51.3.

Rice. 3. X-ray diffraction pattern of the original LPh (Fosmuka 1-layer)

Figure 4 shows the X-ray diffraction pattern of LPh processing (Fosmuka 1-layer) with 10% HNO₃ solution. Quartz is present as impurities in the fluorocarbonate apatite phase (2θ are the angles of diffraction reflections, angular degrees: 20.9; 20.47; 26.7; 49.68; 49.61; 60.72), perixiglas (magnesium oxide) (2θ – angles of diffraction reflections, angular degrees: 35.94; 42.9; 62.3; 78.5), calcium oxide (2θ – angles of diffraction reflections, angular degrees: 25.9; 25.88; 26.73; 28 .18; 29.87; 30.34; 48.43; 47.07), silicon oxide (2θ - angles of diffraction reflections, angular degrees: 57.47; 64.73; 72.99; 23.02).

Figure 4. X-ray diffraction pattern of the LPh processing product (Plast I) with 10% HNO₃ solution

A comparison of the diffraction patterns shows that in Fig. 5 there are no most intense peaks characteristic of dolomitic carbonate components, and in Fig. 4 there are only weak reflections at 50.4; 51.3. This corresponds to the fact that carbonates are not completely decomposed in the IR spectrum of the nitric acid-treated sample, while complete decarbonization occurs in the hydrochloric acid-treated sample [5].

Figure 5. X-ray diffraction pattern of the LPh processing product (Plast I) with 20% HCl solution

Another feature of the conducted acid processing of phosphorites is that, theoretically, with this method of processing, the silicate components should not be subjected to decomposition. However, the results of the analysis of the liquid phase indicate a sufficient content of SiO2 in the solution. In addition, a comparison of the diffraction patterns indicates a significant decrease in the intensity of the main reflection of quartz at 29.84 (1430, Fig. 4.), 29.84 (5900, Fig. 5) relative to a similar reflection of 29.38 (~14500, Fig. 3) in the diffraction pattern original sample of phosphorite.

The reason for the facts is the presence of up to 2.0% F in the original phosphorite. In our opinion, due to the presence of fluorine in the original phosphorite during acid processing, the decomposition of fluoride salts occurs with the formation of HF. Further, under the action of HF, the silicates are converted into [SiF₆]^-2, which contributes to their transition into solution. Following this, in the diffraction patterns of acid-processed products, the intensities of the peaks characteristic of quartz constituents of phosphorite are reduced.

Conclusion

Based on the results of the studies carried out, it can be concluded that low-grade phosphorites (< 15% P₂O₅) can be processed under the action of strong acids, with the production of liquid and solid phases. The liquid phase is dominated by phosphate, chloride, and nitrate ions, respectively, depending on the acid used, as well as metal cations. The solid phases mainly consist of activated aluminosilicates and phosphates. Depending on the composition, both phases formed can be used in the future to obtain inorganic materials for special purposes, to which the results of our next studies will be devoted.

References:

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