Study and mechanism of formation of phosphorus production waste in Kazakhstan

: This article contains information about the accumulated industrial waste from phosphorus production and methods for its recycling and disposal to produce market-able products. Monitoring of cottrel dust ’ s impact on the environment, namely, ground and surface water, soil, and atmosphere was carried out. The mechanism of formation of cottrel dust was studied. The dispersed, chemical, and phase compositions of the dust in furnace gases during the electrothermal smelting of phosphorites were determined. The sequence of chemical reactions during the formation of cottrel dust was elucidated. The ratios of initial components entering the chemical reaction and the thermodynamic parameters (Gibbs energy) were determined using the Chemistry HSC-6 software package. IR spectral and elemental analyses were carried out for determining cot-trel dust ’ s functional groups and elemental composition. Based on modern instrumental studies, it was found that the total content of phosphorus( V ) oxide in cottrel dust was 30.7%. This content of phosphorus( V ) oxide is su ﬃ cient to use cottrel dust as an initial raw material for producing phosphorus-containing fertilizers. This method was proposed for processing cottrel dust to produce monocalcium phosphate on a production scale. The chemical composition of the resulting monocalcium phosphate was determined and con ﬁ rmed by analytical methods. The proposed technology for producing monocalcium phosphate from cottrel dust is recommended for use in the agro-industrial complex.


Introduction
Currently, environmental problems related to the interaction of phosphorus plants with the environment, spread of soluble phosphorus compounds, and formation of a significant amount of phosphorus-containing waste and harmful emissions are relevant in Kazakhstan [1][2][3].Environmental degradation is especially evident in places where industrial enterprises are concentrated, and these industrial regions are turning into focal zones of profound changes in the lithosphere and biosphere [4][5][6].
It is noted that the fluorine concentration in zones of influence of enterprises producing phosphorus and phosphorus-containing fertilizers sometimes reaches 100-200 mg•m −3 .Such emissions reduce photosynthesis, suppress vegetation, etc.According to the qualitative composition and harmfulness of production emissions, phosphorus production enterprises relate to industries that pollute the atmosphere with gases containing carcinogenic and toxic substances [7,8].
At the international congress on mineral resources and metallurgy, the President of Kazakhstan said that the country has accumulated more than 30 billion tonnes of industrial waste, much of which is toxic.He emphasized that now industrial waste must be considered as an independent raw material base [9].
In order to process the accumulated industrial waste, scientists and technological engineers have developed various recycling methods to produce commercial multi-purpose products [10].
The work of Besterekov et al. [11] presents the results of studies on the production of a nitrogen-phosphoruspotassium (NPK) fertilizer with an ammonium nitrate/cottrel dust mass ratio equal to 1:0.73 by introducing heat-treated cottrel dust into ammonium nitrate solution.Cottrel dust, which is dehydrated cottrel milk, was used as an inorganic additive that stabilizes ammonium nitrate.As a result of the research, a complex water-soluble NPK fertilizer with improved agrochemical properties was obtained.
Duisembiev et al. [12] show the possibilities of using cottrel milk for producing PK-containing fertilizers and phosphorite agglomerate, which will improve the environmental situation in the area of a phosphorus plant and dispose of hazardous waste accumulated during the operation of the plant.
Scientists [13] also studied the thermodynamic probability of the formation of PK fertilizers during the processing of cottrel milk and the formation of double pyro-and metaphosphates from compounds that are components of furnace gas.
Lisitsa [14] proposed a method allowing the recycling of phosphorus-containing industrial wastes and producing a new NPK fertilizer, which is an ameliorant with improved chemical, physical, and mechanical properties.
All these developed technologies have not yet found full-scale practical application due to their incomplete scientific and technical validity, complexity of technological processes, need for expensive equipment, and low economic efficiency.
It is known that the electrothermal production of phosphorus is characterized by the formation of a significant amount of gaseous harmful substances in the atmosphere and fugitive gas emissions accounting for 20-25% of their total amount.Sources of fugitive emissions are very diverse: phosphorus storage facilities, open raw material warehouses, sludge storage facilities, dumps, etc.The fugitive emissions contain the same polluting components as the emissions provided by the technology.The formation of hazardous solid and liquid wastes and intermediate products occupying industrial sites is significant.Technological conditions for the production of phosphorus and its compounds are also characterized by the release of harmful fumes, wastewater, and pasty and solid wastes.All of these are sources of technogenic environmental pollution [15,16].
Industrial phosphorus-containing waste accumulated at the New-Dzhambul phosphorus plant is stored in open areas.Phosphorus production wastes, especially cottrel dust, have the following negative environmental impacts: -Pollution of ground and surface water.Compounds containing fluorine and phosphorus pose a great danger to water bodies.Groundwater in the waste storage area is contaminated with fluorine, sulfates, and phosphates.The fluorine content in the groundwater exceeds the maximum permissible concentration by 3.17-7.5times and that of sulfates and phosphates by 1.8-2.33 and 5.5-6.5 times, respectively.-Negative impact on the state of land resources.Currently, phosphorus-containing waste covers an area of about 200 hectares; insoluble metals cause soil erosion and deterioration of soil structure.-Air pollution.The source of pollution is fluorine and phosphorus compounds, which spread in the form of dust and gases [17].
An effective solution for environmental problems associated with phosphorus production waste is identifying causes for the release of waste, their analysis, and development of new waste-free technologies that meet the requirements of modern ecology.
Production operation of electrothermal furnaces has shown that the processing of phosphorite raw materials into phosphorus is characterized by a significant amount of by-products and waste: phosphate slag, phosphogypsum, phosphorus-containing sludge, and cottrel dust.Processing of phosphorus production wastes is a complex and laborintensive work in terms of their chemical and granulometric composition [18][19][20].
One of the main reasons for the formation of hazardous waste is the low quality of initial raw materials and the heterogeneity of phosphate ores.This is explained not only by the heterogeneity of initial raw materials with a complex material composition but also by the lack of perfect methods for the preliminary preparation of raw materials for the electrothermal sublimation of phosphorus.
Cottrell dust is formed in electric precipitators as a result of the reduction electric smelting of phosphate rock during the production of phosphorus.About 150-160 kg of cottrel dust is formed per tonne of yellow phosphorus upon the reduction electric smelting of phosphate raw materials at the New-Dzhambul phosphorus plant.The dust is discharged into evaporation basins in the form of a suspension cottrel milk [21][22][23].The appearance of the New-Dzhambul phosphorus plant is shown in Figure 1.
Cottrel dust is considered a secondary raw material; it can be used to produce phosphorus-containing fertilizers since cottrel dust contains phosphorus and other useful components.
The element phosphorus is an integral part of all biological and physiological processes in the body of plants and animals.In addition, phosphate minerals are a valuable natural resource widely used as agricultural fertilizers [24].
The scientific novelty of this work lies in the study of the mechanism of cottrel dust formation and the possibility of its processing to produce a commercial productmonocalcium phosphate in the form of phosphorus-containing fertilizers on a production scale for the country's agroindustrial complex.
2 Methods and methodology

Instrumental methods of analysis
The following installations were used to carry out instrumental physicochemical analysis methods: 1. Thermodynamic analysis of the mechanism of cottrel dust formation was carried out using a multifunctional software package Chemistry HSC-6, based on the principle of maximum entropy and enthalpy values with Gibbs energy values.For chemical reactions occurring in a heterogeneous system, calculation of the change in the enthalpy ΔH, entropy ΔS, and Gibbs energy ΔG values was implemented in accordance with Eqs.1-3, respectively: where T is the temperature and ν i are stoichiometric coefficients.2. To study the change in cottrel dust's mass depending on the time and temperature, a thermogravimetric analysis (TGA) of the dust was carried out using a TGA/DSC 1HT/ 319 analyzer.
3. A JEOL JSM-6490 LV electron scanning microscope (Japan) was utilized to determine the element-weight composition of the sample under study by obtaining micrographs of various materials of inorganic nature and energy dispersion analysis.4. The infrared spectral analysis of cottrel dust was carried out using an IR Fourier spectrometer, Shimadzu IR Prestige-21, with a frustrated total internal reflection device, Miracle (Pike Technologies Kyoto, Japan).The IR Prestige-21 uses a bright ceramic light source, a highsensitivity DLATGS detector, and high-throughput optical elements.Optimization of optical/electronics/signal systems minimizes noise and maximizes the S/N ratio (40,000:1 and better).

Experimental procedure
Determination of phosphates and phosphorus in mineral fertilizers and other wastes was carried out in accordance with the State Standard 20851.2-75(ISO 5316-77, ISO 6598-85, ISO 7497-84).This standard applies to mineral fertilizers and industrial wastes with a mass fraction of P 2 O 5 from 3 to 55% and establishes methods for determining the content of total, assimilable, and water-soluble phosphates with their preliminary extraction from fertilizers, as well as free acidity.
1. Extraction of total phosphates using a mixture of acids.
The method was based on dissolving a sample in a mixture of nitric and hydrochloric acids at the boiling temperature.About 2 g of the investigated substance was weighed accurate to the fourth decimal place and placed in a 250 cm 3 glass; then 15 cm 3 of nitric acid solution and 5 cm 3 of hydrochloric acid solution were added.The mixture was heated to its boiling point and boiled in the glass covered with a watch glass until the sample completely dissolved; then water was added to a volume of 50 cm 3 , and the mixture was boiled for 5 min.
The solution was transferred quantitatively into a 250 cm 3 volumetric flask, cooled, diluted with water to the mark, mixed thoroughly, and filtered through a dry filter into a dry flask; the first portion of the filtrate was removed.2. Extraction of total phosphates with citric acid.About 2 g of the investigated substance was weighed accurate to the fourth decimal place and placed in a Shtokhman flask (or volumetric flask) with a capacity of 250 cm 3 .Then, 200 cm 3 of citric acid solution was added into the flask, and the mixture was mixed immediately to avoid the formation of lumps.The flask was stoppered, placed in a rotary apparatus, and mixed for 30 min.After that time, the mixture was diluted with a citric acid solution, the volume was made up to the mark, mixed, and filtered through a dry filter into a dry container, removing the first 30-50 cm 3 of the filtrate.Water was used instead of citric acid when bringing the volume to the mark.3. Extraction of assimilable phosphates with a Trilon B solution.About 1 g of the investigated substance was weighed accurate to the fourth decimal place and placed in a conical or volumetric flask through a dry funnel, washing off the sample with a Trilon B solution preheated in a glass to a temperature of 93 ± 3°C, and the mixture was shaken using a mechanical shaker or mixed by means of a magnetic stirrer.4. Determination of mobile phosphorus compounds in soil.
The test was carried out in accordance with the State Standard 26207-91.Determination of mobile phosphorus and potassium compounds was implemented using the method of Kirsanov modified according to the CINAO/ 26207-91.This Standard establishes a method for determining mobile phosphorus and potassium compounds in podzolic, soddy-podzolic, gray forest, and other types of soils.The method was based on the extraction of mobile phosphorus (P 2 O 5 ) and potassium (K 2 O) compounds from the soil with a hydrochloric acid solution (extracting solution) with a molar concentration of 0.2 mol•dm −1 and subsequent quantitative determination of mobile phosphorus compounds using a photoelectrocolorimeter and potassium ones using a flame photometer.
5. Determination of phosphorus-containing substances in water.The test was carried out in accordance with the State Standard 18309-2014.The method used was based on the hydrolysis of polyphosphates into orthophosphates, with the formation of a phosphorus-molybdenum complex colored blue, and subsequent photometric analysis of the resulting colored compound at a wavelength of 690-720 nm.The content of orthophosphates initially present in the sample was preliminarily determined; their content should be subtracted from the result obtained when determining polyphosphates.This standard applies to drinking (including packaged in containers), natural (ground and surface), and waste water and establishes the following photometric methods for the determination of phosphorus compounds.

Mechanism of formation of cottrel dust
The reaction gas leaving a phosphorus furnace contains up to 200 g•cm −3 of solid particles in the form of dust.Processes associated with dust entrainment take place in various zones of the phosphorus furnace.These processes include the following: -Mechanical entrainment of dust by a gas flow; -Evaporation of low-boiling components of charge, the condensation of which leads to the formation of dust; -Chemical processes in the gas phase leading to the formation of solid particles; -Filtration of gases through a charge layer and condensation of sublimates on it.The latter process results in a reduction in dust content.The dispersed composition of dust in furnace gases is shown in Figure 2 and that with mechanical entrainment is given in Table 1.
It follows from Table 1 that 90% of the dust particles have a size of at least 20 µm, and therefore they cannot be the result of mechanical entrainment.The small proportion (10%) of mechanical entrainment is explained by the following reasons: first, the gas velocity in the furnace above the charge layer (under the furnace roof) is small, and for furnaces of this type it is about 0.035 m•s −1 ; therefore, this part of the furnace is actually a settling chamber.Second, the first zone of the furnace, the height of which is about 2.5 m, has a porosity of 36-39%, and it is a filter zone for the reaction gas.Calculations have shown that the capture coefficient for particles up to 6 µm is insignificant (about 0.1), but particles larger than 10 µm are captured with high efficiency in the temperature range of 327-673°C, that is, over the entire height of the zone [25][26][27].

Thermodynamic patterns of the formation of cottrel dust
The sequence of processes and the contribution to the formation of cottrel dust are presented in Figure 3. Experiments were carried out to determine the ratio of initial components and thermodynamic parameters using the Chemistry HSC-6 software package in the temperature interval of 0-2,000°C with an increase in temperature for every 200°C during the formation of cottrel dust which enters the chemical reaction 1 between silicon(IV) oxide and carbon (Table 2) and reaction 2silicon(II) oxide decomposition (Table 3).
Experiments were carried out to determine the ratio of the initial components and thermodynamic parameters in the range of 50-100°C with an increase in temperature for every 10°C during the formation of cottrel dust, which enters into chemical reactions 3 (between silicon(IV) oxide, potassium oxide, and calcium oxide), 4 (interaction of silicon fluoride with water), and 5 (interaction of phosphorus with water) (Tables 4-6).

Chemical and phase analyses of furnace gases
The chemical composition of dust formed in the furnace during the electrothermal smelting of phosphorites is shown in Table 7.
It follows from Table 7 that the dust is enriched in alkali metal oxides (especially K 2 O), silicon(IV) oxide, and phosphates.For the charge's acidity modulus of 0.85, the SiO 2 /CaO ratio in the dust reaches 2.30.As we can see, the bulk   of the dust is a consequence of the evaporation of sodium and potassium metaphosphates and silicon monoxide.
To study the change in cottrel dust's mass depending on the time and temperature, TGA of the dust was carried out using a TGA/DSC 1HT/319 analyzer (Mettler Toledo).The results of the analysis are shown in Figure 4.
In conclusion, we present the phase composition of dust in the furnace gas in Table 8.

Results of thermodynamic study of cottrel dust
It follows from Table 9 that with an increase in temperature from 0 to 2,000°C, the Gibbs energy for reaction (1) decreases from 602.5 to −77.5 kJ•mol −1 and becomes negative, and the possibility of this chemical reaction is explained by the negative value of Gibbs energy.The given chemical reaction is possible at a temperature of 1,800°C, when the Gibbs energy value is -13.7 kJ•mol −1 .For reaction (2), the Gibbs energy at temperatures from 0 to 2,000°C increases from -614.0 to 36.43 kJ•mol −1 .The critical temperature for both reactions is 1,800°C.Data of Table 10 show that at a temperature of 50-100°C, the Gibbs energy for reaction 3 decreases from 196.6 to 132.1 kJ•mol −1 ; thus, this reaction does not occur.For reaction 4, the Gibbs energy at a temperature of 50-100°C decreases from −233.0 to −346.4 kJ•mol −1 , and for reaction 5 the Gibbs energy in the same temperature interval decreases from −402.4 to −439.2 kJ•mol −1 .

IR spectrum and elemental analysis of cottrel dust
To determine the functional groups in cottrel dust, spectral studies were carried out using an IR spectrometer (Shimadzu IR Prestige-21).The results of studies are shown in Table 11 and Figure 5.
Figure 5 shows the IR spectrum of cottrel dust, from which it follows that: -The absorption peak at the wavelength of 1,620.21cm −1 characterizes the presence of silicate Si-O-Si and Si-O-C groups in cottrel dust; -The absorption peak at the wavelength of 1,442.75cm −1  characterizes the presence of a silicate Si-O-Na with carbon valence bonds; -The absorption peak at the wavelength of 1,288.45cm −1 is characteristic of phosphorus-containing compounds with silicon functional groups (Si 2 P 2 O 7 ); -The absorption peak at the wavelength in the range of 1,222.87cm −1 is characteristic of phosphorus and potassium-containing compounds (KH 2 PO 4 ); -The absorption peak at the wavelength in the range of 1,095.57cm −1 is characteristic of phosphorus compounds containing sodium (NaH 2 PO 4 ); -The absorption peak at the wavelength of 1,053.13cm −1  shows the presence of phosphorus compounds containing calcium (CaHPO 4 ) and magnesium (MgHPO 4 ); -Absorption peak at the wavelength of 968.27 cm −1 is characteristic of phosphorus compounds containing potassium and calcium (KCaPO 4 ) and fluorine (P-F); -Absorption peak at the wavelength of 864.11 cm −1 characterizes the presence of phosphorus compounds containing sulfur (P]S);  -Absorption peaks at wavelengths in the range of 748.22-478.35cm −1 are characteristic of compounds containing Al 3+ , Fe 3+ , Mg 2+ , and Fe 2+ .
The results of IR spectral studies confirm the presence of functional groups in cottrel dust's components.Cottrel dust's elemental and phase composition, determined using modern instrumental and analytical methods, confirms the correctness of decoding its IR spectra.Based on the research carried out, it can be concluded that cottrel dust is a phosphorus-containing waste and is suitable for producing monocalcium phosphate, which can be used in the production of phosphorus-containing fertilizers.
The elemental composition and micrograph of coal waste (Table 12 and Figure 6) were determined using scanning microscopy (JSM-6490lV, JEOL, Tokyo, Japan).From Figure 4, it follows that the microstructure of potassium humate has mainly an amorphous structure with the addition of potassium, since potassium combines with the functional groups of humic acids.The scale of this microstructure is 40 times the increase from the actual state (600 µm; spectral range: 0-12 keV).Study and mechanism of formation of phosphorus production waste in Kazakhstan  9 It follows from Figure 6 that the surface of cottrel dust is characterized by imperfect cohesion of minerals with the formation of cracks and chips.The main mineralogical phases of the sample are silicophosphates and silicofluorophosphates, which have colorless lamellar crystal structures.Small inclusions of potassium phosphates are characterized by soldered crystals of small elongated irregularly shaped plates.An accumulation of fine-grained chain structures of calcium silicate crystals is observed around phosphate minerals.Intermediate spaces and cracks are filled with the carbonaceous phase [28,29].
When studying the chemical composition of cottrel dust, it was determined that the main part of dust is a consequence of the evaporation of sodium, potassium, calcium metaphosphates, and silicon monoxide.This is evidenced by the elemental and phase compositions of cottrel dust.When yellow phosphorus is produced by the electrothermal method, the dust is formed periodically, although the chemical composition of the starting materials does not change much.For this reason, electrostatic precipitators are purified at the end of each production cycle to remove dust.Regardless of the furnace conditions and the chemical composition of the initial material, the volume of cottrel dust formed varies from 150 to 160 kg per tonne of the resulting yellow phosphorus.
According to the results (Table 12) of instrumental studies, it was found that the chemical composition of cottrel dust contains metals such as Na, Mg, Al, K, Ca, Fe, and Zn.These metals are light and in small amounts.Moreover, the necessary element phosphorus (P) is 13.4%.This phosphorus content is enough to process this waste and then obtain mineral fertilizers.
In addition to elemental analysis, chemical analysis for total and assimilable forms of phosphorus in cottrel dust was carried out.Chemical analysis was performed using

Recycling of cottrel dust
Recycling of cottrel dust using a 10% concentration of sulfuric acid and a temperature of 90°C yields a phosphorus concentration of 11.10%; this phosphorus content is sufficient for its use as a phosphorus-containing component.
The filtration properties and moisture content of the sediment were determined by standard methods.The sediment and filtrate were analyzed for the content of P 2 O 5 water and P 2 O 5 assimilable by double titration.On the finished product, the content of total and assimilable phosphorus oxide was calculated taking into account that transferred to the filtrate and sediment [7,28,30].Scanning microscopy (JSM-6490lV, JEOL, Tokyo, Japan) revealed the chemical composition of samples of a phosphorus-containing compound, monocalcium phosphate, extracted from cottrel dust from the wastes of the New-Jambul phosphorus plant.The results of the study are given in Table 13.
According to the results of elemental analysis of monocalcium phosphate (Table 13), it was determined that at a sulfuric acid solvent concentration of 10% and a temperature of 90°C, the phosphorus oxide yield is P 2 O 5 (total) -25.42% and P 2 O 5 (assimilable) -22.43%.Such a content of phosphorus obtained from waste can be used in medium fertile soils as a phosphorus-containing fertilizer [7,31].
In addition to phosphorus, monocalcium phosphate contains metals such as calcium, magnesium, iron, and aluminum.These metals do not affect the function of phosphorus.Some of the metals remained undissolved in the precipitate.The solubility of phosphorus in monocalcium phosphate was determined to be 96% in Trilon B buffer solutions and 95-96 in 2% citric acid.
The optimal parameters of a phosphorus-containing compound from cottrel dust were determined, and the process of crystallization of monocalcium phosphate was studied depending on the duration of the process and the yield of P 2 O 5 with the product [7,32,33] (Figure 7).

Discussion
The results of experimental studies are confirmed by the results of analytical studies.This is evidenced by the data obtained during the determination of total phosphates using various acids and buffer solutions (Section 2).
Based on the results of experimental and analytical studies, it was determined that the phosphorus(V) oxide content in cottrel dust reaches 30.7%.As is follows from the studies, cottrel dust contains sufficient amount of assimilable P 2 O 5 in its composition.So, cottrel dust can be used as a fertilizer after its chemical processing in order to oxidize phosphorus to its salts.In addition, to improve cottrel dust's physical properties when using it as a fertilizer, it should be possible to granulate it to obtain granules with sufficient strength to prevent their destruction at the stages of transportation and application to the soil.
The most acceptable ways are the following: Way 1decomposition of cottrel dust with sulfuric acid solutions to produce monocalcium phosphate in the form of granules for their use as a phosphorus-containing fertilizer to increase the yield of agricultural crops; Way 2producing superphosphate with various compositions by mixing cottrel dust, phosphogypsum, and clarified water to produce a pulp, which is then ammoniated with ammonia; Way 3producing superphosphate with various compositions by adding phosphogypsum and cottrel dust in different ratios to the extraction pulp, followed by neutralization of the resulting mixture with ammonia.
Of the proposed options, way 1 is the most optimal.This method allows us to produce monocalcium phosphate extracting phosphorus from cottrel dust, and the remaining components can be used in construction and other areas.
This method (way 1) for processing cottrel dust is more economically viable and technologically feasible on a commercial scale.The proposed technology does not have potential environmental risks since it is aimed at reducing accumulated phosphorus-containing industrial waste with the subsequent production of fertilizers for their application in the country's agro-industrial complex.
The authors provide comparative analyses and examples of producing monocalcium phosphate from cottrel dust.The technical and economic indicators of the developed technologies are determined using the example of amorphous production technology.The approximate cost of the proposed production is shown in Table 14.A method for producing a phosphorus-containing fertilizermonocalcium phosphatefrom cottrel dust by recycling technogenic phosphorus production waste has been developed, and it is recommended to be introduced during production at the Mineral Fertilizers Plant, Kazphosphate LLP.
According to the calculations, the production cost to produce 1 tonne of monocalcium phosphate is $330.In the mineral fertilizer market, 1 tonne of monocalcium phosphate costs $1,800-2,000.
In accordance with the given calculations, it is clear that the price of monocalcium phosphate produced from cottrel dust is 5-6 times cheaper than other analogs.Therefore, the processing of cottrel dust using sulfuric acid followed by the production of monocalcium phosphate is economically profitable and technologically feasible.In addition, this technology is aimed at reducing industrial waste, which in turn helps to improve the environmental situation in the region.

Conclusions
This article contains information about accumulated industrial waste from phosphorus production and methods for its recycling and disposal to produce marketable products.The monitoring of cottrel dust's impact on the environment, namely, ground and surface water, soil, and atmosphere, was carried out.
The mechanism of formation of cottrel dust was studied.The dispersed, chemical, and phase composition of dust in the furnace gases formed at the electrothermal smelting of phosphorites was determined.The sequence of chemical reactions occurring during the formation of cottrel dust is given.The ratios of initial components entering the chemical reaction and the thermodynamic parameters (Gibbs energy) were determined using the Chemistry HSC-6 software package.IR spectral and elemental analyses were implemented for determination of the functional groups and elemental composition of cottrel dust.Based on the results of elemental and chemical analyses, it was found that the total content of phosphorus(v) oxide in cottrel dust is 30.7%.This content of phosphorus(v) oxide is sufficient to use cottrel dust as an initial raw material for producing mineral phosphorus-containing fertilizers [32,33].This method was proposed for processing cottrel dust to produce monocalcium phosphate on a production scale.The chemical composition of the resulting monocalcium phosphate was determined and confirmed by analytical methods.Calculations of the project costs for the production of monocalcium phosphate in the conditions of Kazphosphate LLP are given.The proposed technology for producing monocalcium phosphate from cottrel dust is recommended for use in the agro-industrial complex.

Figure 2 :
Figure 2: Dispersed composition of dust in furnace gases.

Table 1 : 5 Figure 3 :
Figure 3: Sequence of chemical processes and reactions during the formation of cottrel dust.

Table 2 :
Chemical parameters of starting and final substances for reaction 1

Table 3 :
Chemical parameters of starting and final substances for reaction 2

Table 4 :
Chemical parameters of starting and final substances for reaction 3

Table 5 :
Chemical parameters of starting and final substances for reaction 4

Table 6 :
Chemical parameters of starting and final substances for reaction 5

Table 7 :
Chemical composition of dust formed in the furnace during electrothermal smelting

Table 8 :
Phase composition of dust in the furnace gas

Table 9 :
Change in the Gibbs energy in the temperature interval of 0-2,000°C for reactions 1 and 2

Table 11 :
Spectral data of cottrel dust

Table 12 :
Elemental composition of cottrel dust

Table 14 :
Calculation of project costs for monocalcium phosphate (1 tonne) productionNote: cost of cottrel dust is not determined, since it is a secondary industrial waste; calculations were made using reporting data from Kazphosphate LLP.