Kinetics and synthesis of formation of phosphate composites from low-grade phosphorites in the presence of phosphate–siliceous shales and oil sludge

Zhunisbek Turishbekov; Saltanat Tleuova; Dana Pazylova; Ayaulym Tileuberdi; Mariyam Ulbekova; Nurila Sagindikova

doi:10.1515/gps-2025-0070

Article Open Access

Kinetics and synthesis of formation of phosphate composites from low-grade phosphorites in the presence of phosphate–siliceous shales and oil sludge

Zhunisbek Turishbekov , Saltanat Tleuova , Dana Pazylova , Ayaulym Tileuberdi , Mariyam Ulbekova and Nurila Sagindikova

Published/Copyright: August 8, 2025

Published by

Become an author with De Gruyter Brill

Submit Manuscript Author Information

From the journal Green Processing and Synthesis Volume 14 Issue 1

Abstract

The purpose of this work is to study the kinetic features of the formation of phosphate agglomerates from low-grade phosphorites in the presence of phosphate–siliceous shales (PSSs), coke, and oil sludge. The selection of the Yerofeyev–Kolmogorov equation characterizing heterogeneous processes is justified by a comparative analysis of the Aravi equation used for the crystallization processes. The PSS/coke–oil sludge system has been studied in the temperature range of 1,073–1,373 K in the air environment, typical for agglomeration firing. Thermogravimetric analysis, X-ray fluorescence analysis, scanning electron microscopy, and IR spectrometry were used to study the features of oil sludge and the physicochemical characteristics of the phase composition and mineralogical structure of the firing products. The effect of the modulus of acidity and temperature on the strength parameters of phosphate agglomerate was studied for charges of 0.7–0.83, providing mechanical strength of 3.3–3.4 MPa at temperatures of 1,313–1,318 K of the onset of deformation. The calculation results of the apparent energy corresponding to 4.15–22.99 kJ·mol⁻¹ indicate complex diffusion–reaction characteristics of the agglomeration process in the presence of PSS and oil sludge.

Keywords: phosphate–siliceous shales; oil sludge; kinetics of decarbonization; Yerofeyev–Kolmogorov equation; synthesis

1 Introduction

Efficient processing of phosphate raw materials is one of the urgent needs of the chemical industry, particularly the low-quality phosphorous ores with a high content of carbonate and silica impurities. The issue of intensifying the thermal treatment of phosphorites while involving industrial waste in the process is acute against the background of limited natural resources and increasing requirements for the environmental friendliness of the processes (including minimizing CO₂ emissions). The use of phosphate–siliceous shales (PSSs) and oil waste (including oil sludge) as additional fuel and flux opens up prospects for resource conservation and environmental safety, as well as increasing technological flexibility [1,2,3,4,5,6,7].

Traditionally, the agglomeration process (sintering) of phosphorous fines provides dehydration, decarbonization, and partial defluorination, as well as hardening of the agglomerate due to high-temperature treatments [8,9,10,11,12,13,14].

The literature review included an analysis of key publications from 2015 to 2023. However, none of these studies used the poor phosphorite–PSS–coke–oil sludge complex. Unlike the work of Bobkov et al. [8], where the kinetics of carbonate decomposition was modeled exclusively through a system of equations of thermal and mass transfer in a spherical grain without taking into account experimental verification of strength and phase composition, our study additionally includes direct measurements of mechanical properties and quantitative phase analysis. Elgharbi et al. [10] used a highly sensitive combination of thermogravimetry differential thermal analysis (TG/DTA) and Raman spectroscopy for a deep understanding of the molecular and crystalline transformations of pure phosphorite, but the study lacked both kinetic calculations of the mechanism and an assessment of the effect of fluxes and carbon additives. Meshalkin et al. [14] successfully combined thermogravimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analysis with compression tests, which allowed us to establish optimal sintering temperatures for pure phosphorites, but their approach does not cover ecotoxicological aspects and dynamics of hydrocarbon fuel combustion. This research combines TGA methods with the Yerofeyev–Kolmogorov model performed with digital processing of kinetic parameters.

At the same time, the key stage is the kinetically complex process of forming a promising multicomponent phosphate material with the characteristics of a composite with a phosphate matrix and a dispersed phase [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]. The total rate of thermal degradation largely determines the formation of the microstructure of the sinter, its porosity and strength, similar to composite materials in the construction industry [31,32,33]. The addition of silicon-containing rocks and hydrocarbon waste affects the physical and chemical properties of the softened charge, the reaction flow mechanism, and the nature of gas exchange [4,5,6,7].

The complex kinetics of agglomeration in the presence of PSSs and hydrocarbon industrial waste have not been sufficiently studied, despite significant developments in the thermal decomposition of phosphorites. The aim of this research is to investigate the quantitative assessment of the rate of transformations of carbonate and phosphate–siliceous fractions to identify the effect of oil sludge on sinter formation and phase composition and to determine the optimal agglomeration conditions to ensure high strength with minimal fuel consumption. The scientific novelty of the research carried out lies in the complex use of low-grade phosphate ores with the addition of PSSs and oil sludge as a fluxing and enriching component. At the same time, the use of oil sludge to partially replace the fuel component provides a solution for the disposal of technogenic refinery waste.

The purpose of research is a comprehensive study of the kinetics of agglomeration of low-grade phosphorites in the presence of PSSs, coke, and oil sludge (P-PSS-C-OS).

The scientific novelty of the research performed is to study the kinetic patterns of formation of mechanically strong phosphate agglomerate from low-grade phosphorites in the presence of PSSs, coke, and oil sludge. At the same time, PSS is used as a flux component, and OS as a multifunctional fuel, pore forming agent, and reducing agent. This ensures the expansion of the raw material base and the disposal of man-made oil refining waste.

2 Materials and methods

2.1 Materials

Low-grade fine-grained phosphorites (fraction 10-0 mm) from two deposits of Janatas and Akzhar in the Karatau basin were used as the main phosphate component. The difference in the content of P₂O₅ (19–22%) and fluorocarboapatites, dolomite, and calcium carbonates was up to 60–62%. Silicicoluminate inclusions are represented by hydrosludges and feldspar compounds. An additional fluxing component was PSS with an insoluble residue content of up to 40–46%, P₂O₅ of up to 5–16%, and a CO₂ content of up to 5%.

The fuel and carbon base of the charge consisted of coke fines (0–3 mm) with a fixed carbon content of 78–86% and oil sludge from the treatment facilities of the PetroKazakhstan Oil Products Limited Liability Partnership (LLP) refinery, containing 10–15% water, 20–45% heavy hydrocarbons, and the mineral part of up to 20–40%.

2.2 Methods

2.2.1 Sample preparation

All components were ground to a grain size of 90% < 0.07 mm in a laboratory ball mill. Mixing was carried out with a variation of (a) the proportion of PSS in the range of 20–40% (of the total weight); and (b) the ratio of coke fines: oil sludge from 1:0.2 to 1:0.4 at a coke consumption of 8% of the total weight of the charge. The resulting powdered charge was pelletized on a plate granulator (diameter 800 mm, tilt angle 45°), adjusting the humidity to 7–9%. The granules (8–15 mm) were dried at 110°C to a humidity of less than 1%.

2.2.2 Agglomeration firing conditions

Laboratory studies were performed in an agglomeration bowl (diameter 0.4 m, layer height 250 mm) with a grate and a fan to create a vacuum (700–1,800 Pa) at an excess of 1.3–1.5. The upper layer was ignited with air heated in a gorenje to 1,073–1,373 K for 3–5 min, and then the sintering process was maintained by burning fuel inside the layer. The heating rate was 10–15 min at 1,073–1,373 K. The temperature was measured with a thermocouple. The relative error of the experimental data does not exceed 2.1%. The exhaust gases of agglomeration firing are cleaned of dust and chemical contaminants sequentially in battery cyclones and hollow scrubbers irrigated with lime solution before being released into the atmosphere. The dust trapped in cyclones is returned to the agglomeration process or to obtain complex mineral fertilizers with trace elements. The gas phase of firing in cyclones is 99% dust-free. After wet scrubbing, the residual concentrations of emissions are as follows: SO₂ ≤ 1 mg·m⁻³ at a rate of 300 mg·m⁻³, VOC ≤ 15 mg·m⁻³ at a rate of 50 mg·m⁻³, and CO < 1 mg·m⁻³ at a rate of 20 mg·m⁻³, which is significantly below the limits of CH 1.02-07-2015.

2.2.3 Degree of decarbonization

Three-fold firing was carried out for all temperatures and durations to analyze the decarbonization process. The samples were taken from the firing zone at different time points (10, 20, 40, and 60 min) to analyze the changes in the carbonate phase after heat treatment. The degree of decarbonization α was found as the ratio of the remaining CO₂ to its initial content:

(1) α = C O 2 ( begin . ) − C O 2 ( end . ) C O 2 ( begin . ) × 100 %

or through the mass fraction of unbound CaO, determined by complexometric titration. The decarbonization results were calculated by averaging the data obtained. The standard deviation is ±0.01.

2.2.4 Physical and chemical analysis

The analysis methods are based on an integrated approach, including physical and chemical analyses of the obtained phosphate composite. Thermogravimetric analysis (TGA) is performed on a BAXI device (B-TGA-103) from room temperature to 1,473 K. The heating speed was 353 K·min⁻¹ (adjustable), and the accuracy of mass measurement was ±0.01 mg. The microstructure, element-wise composition, and quantitative phase composition were determined by X-ray fluorescence analysis (EDX-7000P; Shimadzu, Japan) and a scanning electron microscope (JEOL JSM-6490 LV; JOEL, Japan), with energy dispersive microanalysis systems INCA Energy and structural analysis HKL-Basic, IR Fourier spectrometer IRPrestige-21 (Shimadzu, Japan).

2.2.5 Kinetic studies

For kinetic studies of agglomeration firing of low-grade phosphorites in the presence of PSS, coke, and oil sludge, Yerofeyev–Kolmogorov (Y-K) equation is chosen, characterizing a heterogeneous high-temperature process [34,35,36]. The choice of this equation is justified by the peculiarities of the decarbonization of a granular complex charge, which characterizes the multiple nucleation of CACO₃ → CaO + CO₂, followed by propagation of the reaction region through a porous matrix. This structure of mineral formation satisfies the assumptions of the Y-K on the origin and statistical overlap of growing transformation regions, characterized by the linearity of the graphs (Eq. 2). However, the Aravi formula, which formally coincides in mathematics, is mostly used for the homogeneous processes, where all germs are formed under the same conditions. The “shrinking core” model is effective when a dense, impenetrable crust of the product is formed, and the rate is limited either by a chemical reaction or by diffusion through the layer. In our case, nucleation depends on the degree of decarbonization of carbonate constituents and binding to SiO₂ of PSS in a heterogeneous system. At the same time, the high porosity of the resulting product is ensured by burning the hydrocarbon component of the oil sludge.

The Yerofeyev–Kolmogorovequation was used to process experimental data and dependences of kinetic curves obtained by heat treatment of the phosphate raw materials in the presence of oil sludge [34,35,36]. This equation is quite flexible, describing a large number of upward curves depending on the degree of decarbonization, the temperature, and duration of various formulations. The obtained curves have an ascending linear dependence on the experimental data, without taking into account the state of the initial components:

(2) α = 1 − e − k τ n

converted from a power law to a linear law:

(3) ln [ − ln ( 1 − α ) ] = lnk + n ln τ

where α is the degree of decarbonization, fractions of one; n and k are the kinetic parameters; and τ is the time of the process, min.

The value of the kinetic constant K determined by G.V. Sakovich’s correction [34] is most acceptable to establish the apparent activation energy when studying the interaction in the formation of intergranular bonds in complex heterogeneous processes:

(4) K = n × k 1 n

The process of processing experimental data by Eq. 2 is reduced to determining the parameters n and K at each temperature. The parameter n was determined as tg φ of the angle of inclination of the straight line on the abscissa axis in the coordinates of Eq. 2, depending on the power part of the logarithm of time.

The apparent activation energy was determined using the following formula [35]:

(5) E apparent = 1.98 × tg φ × 4.19

where 1.98 and 4.19 are empirical coefficients that take into account the linear approximation of the dependence of the logarithm of the velocity constant from the inverse temperature.

3 Results and discussion

The results of the chemical and physicochemical analysis of the raw materials and the ratio of the charge components for sintering are presented in Table 1.

Table 1

Chemical composition of the starting materials

Materials	Content of components, mass %
Materials	CaO	MgO	P₂O₅	Fe₂O₃	SiO₂	Al₂O₃	CO₂	C/C_nH_m	SO₃	R₂O
Phosphorous fines of the Janatas deposit	40.7	3.31	19.11	1.61	23.32	2.91	8.74	—	0.3	—
Phosphorous fines of the Akzhar deposit	42.4	3.71	21.1	0.68	21.0	2.3	8.3	—	0.51	—
PSS	26.04	1.80	12.03	1.42	46.49	2.7	4.92	—	0.5	4.1
Oil slag	2.8	3.0	—	6.9	28.3	5.2	4.12	46.48	3.2	—
Petroleum coke	1.52	0.3	—	0.56	0.51	0.71	—	96.0	0.4	—
Coke fines	0.82	0.69	—	1.31	1.31	0.40	—	86.64	—	8.83

Thermogravimetric analysis of oil sludge carried out in an air atmosphere with a heating rate of 283 K·min⁻¹ at 1,373 K revealed three main temperature ranges accompanied by significant mass loss (Figure 1). In the range of 333.1–404.7 K, a decrease in mass of 2.57% is observed, which corresponds to the removal of physically adsorbed moisture and low-molecular-weight volatile compounds. This process proceeds without significant thermal decomposition and is primarily a physical desorption.

Figure 1

Thermogravimetric analysis of oil sludge.

In the second temperature range, from 698.5 to 929.2 K, a loss of 9.33% of the mass occurs. This interval corresponds to the thermal decomposition of high-molecular-weight organic components of petroleum sludge – asphaltenes, resins, and polycondensed aromatic hydrocarbons. In the presence of oxygen, their partial oxidative degradation and the beginning of burning out of coke structures are possible. This is accompanied by pronounced exothermic activity and weight loss at a high rate.

The total mass loss in the range of 333.1–1,369 K is 31.95%, which indicates the presence of a significant proportion of thermolabile organic substances. The remaining ∼68% of the mass is a thermally stable residue, which is typical for ash inorganic components. Mass losses in the range above 929 K to the final heating temperature can be because of the burning of residual coke, the decomposition of carbonates (e.g., CaCO₃), as well as the possible elimination of volatile sulfur components (SO₂).

Thus, the nature of the thermogravimetric curve indicates the presence of both volatile low-molecular-weight compounds and a stable coke-forming organic component accompanied by a significant inorganic ash residue in the oil sludge.

3.1 Influence of the modulus of acidity and temperature on the strength parameters of the phosphate composite

The effect of the modulus of acidity (SiO₂ + Al₂O₃/(CaO + MgO) in the charge composition under sintering conditions is shown in Table 2. The melting point of silicate eutectic decreases from 1,543 to 1,513 K with modulus ranging from 0.70 to 0.75, which creates favorable conditions for sintering. The results show that the addition of 10–15% PSS (with a high SiO₂ content of up to 46%) accelerates the onset of melt formation, improves contact sintering of granules, and increases mechanical strength up to 3.4 MPa. At the same time, excess silica (modulus > 0.83) has no significant changes in the temperature of the onset of softening and strength.

Table 2

Influence of the modulus of acidity and temperature on the strength parameters of the phosphate composite

Initial ore	Fluxing additive (%)	Modulus of acidity	Temperature (K)		Strength (MPa)
Initial ore	Fluxing additive (%)	Modulus of acidity	Beginning of deformation	Softening	Strength (MPa)
Unfluxed agglomerate	—	0.7	1,398	1,543	3.1
Phosphorous fines of the Janatas deposit	PSS-10	0.75	1,333	1,513	3.2
Phosphorous fines of the Janatas deposit	Oil slag/coke fines (1:0.2)	0.8	1,313	1,503	3.4
Phosphorous fines of the Akzhar deposit	PSS-15	0.76	1,323	1,523	3.3
Phosphorous fines of the Akzhar deposit	Oil slag/coke fines (1:0.3)	0.81	1,303	1,508	3.1
Phosphorous fines of the Janatas and Akzhar deposit (1:1)	PSS-20	0.78	1,328	1,518	3.3
Phosphorous fines of the Janatas and Akzhar deposit (1:1)	Oil slag/coke fines (1:0.4)	0.83	1,318	1,513	3.3

It should be noted that Janatas phosphorites have a lower temperature of the onset of deformation and softening compared to the Janatas and Akzhar composition (1:1).

For determining the degree of decarbonization and mechanical properties of the obtained phosphate composite, the firing mode of the specified charge composition was adopted, corresponding to continuous production processes of agglomeration firing along the entire length of the grate at 1,073–1,373 K with a duration of 10–60 min.

Compressive strength studies have shown that samples with oil sludge accounting for 15–20% of the total mass of the fuel and acidity modulus of 0.7–0.8 reach a strength of 3.3–3.4 MPa with a porosity of 25–30%, which indicates the composite nature of the material. The comparative mechanical strength of the Janatas and Akzhar compound (1:1) does not differ from the other listed compounds. This makes it possible to use low-grade phosphorites from these deposits in specified charge composition ratios.

3.2 “Apparent” activation energy

The dependence of the degree of decarbonization (α, %) on the duration (10–60 min) and temperature (1,073–1,373 K) for charges with different fractions of oil sludge (0.2–0.4) in coke was studied (Figures 2–7). The results of the experimental data of the firing process showed the dependence of the degree of decarbonization (α, %) on the duration (τ) and temperature (T, K) (Figures 2 and 5). As the temperature increases, the rate of fuel burnout and CO₂ release increases, which leads to a rapid increase in the degree of decarbonization. For compositions containing 0.1 and 0.4 oil sludge (from the mass of coke), the process proceeds most intensively with immersion in the transition region. Under these conditions, the degree of decarbonization reaches 76–86% in 40 min at 1,273–1,373 K.

Figure 2

Dependence of the degree of decarbonization (α, %) on the duration (τ, min) and temperature (T, K) at a coke/oil sludge ratio of 1:0.2.

$Figure 3 Dependence of the decarbonization ln [ − ln ( 1 − α ) ] \mathrm{ln}[\left-\mathrm{ln}(1\left-\alpha \left)] = f (ln τ) at a coke/oil sludge ratio of 1:0.2.$

Figure 3

Dependence of the decarbonization ln [ − ln ( 1 − α ) ] = f (ln τ) at a coke/oil sludge ratio of 1:0.2.

$Figure 4 Dependence of ln K = ƒ 1 T \mathrm{ln}K=ƒ\left(\phantom{\rule[-0.75em]{}{0ex}},\frac{1}{T}\right) at a coke/oil sludge ratio of 1:0.2.$

Figure 4

Dependence of ln K = ƒ 1 T at a coke/oil sludge ratio of 1:0.2.

Figure 5

Dependence of the degree of decarbonization (α, %) on the duration (τ, min) and temperature (T, K) at a coke/oil sludge ratio of 1:0.4.

$Figure 6 Dependence of the decarbonization ln [ − ln ( 1 − α ) ] \mathrm{ln}[\left-\mathrm{ln}(1\left-\alpha \left)] = f (ln τ) at a coke/oil sludge ratio of 1:0.4.$

Figure 6

Dependence of the decarbonization ln [ − ln ( 1 − α ) ] = f (ln τ) at a coke/oil sludge ratio of 1:0.4.

$Figure 7 Dependence of ln K = ƒ 1 T \mathrm{ln}K=ƒ\left(\phantom{\rule[-0.75em]{}{0ex}},\frac{1}{T}\right) at a coke/oil sludge ratio of 1:0.4.$

Figure 7

Dependence of ln K = ƒ 1 T at a coke/oil sludge ratio of 1:0.4.

The dependence of the degree of decarbonization (α, %) on the duration (τ, min) and temperature (T, K) at a coke/oil sludge ratio of 1:0.2 is shown in Figure 2.

The analysis of the graphical dependence of the degree of decarbonization (α, %) on the firing duration at a coke/oil sludge ratio of 1:0.2 is characterized by a linear relationship. The maximum degree of decarbonization is achieved at a temperature of 1,373 K and a duration of 60 min.

The linear dependence of the degree of decarbonization of the Eq. 2 at a coke/oil sludge ratio of 1:0.2 is shown in Figure 3.

The graphical dependence of the logarithm of the velocity constant from the inverse temperature at a coke/oil sludge ratio of 1:0.2 for calculating the apparent activation energy is shown in Figures 3–7.

For coke formulations C:OS = 1:0.2, the apparent activation energy ranges from 4.15 to 5.02 kJ·mol⁻¹; with an increase in oil sludge to 1:0.3. 0.4, the energy barrier increases to 19.5–22.99 kJ·mol⁻¹. The increase in the apparent activation energy with an increase in the amount of oil sludge is explained by the simultaneous thermal decomposition of carbonates with the combustion of the hydrocarbon component of oil sludge and ensures the formation of both internal and external pores due to gaseous components.

The dependence of the degree of decarbonization (α, %) on the duration (τ, min) and temperature (T, K) at a coke/oil sludge ratio of 1:0.4 differs from the first composition by increasing α to 96% in 40 min, as shown in Figure 4.

The data in Table 3 illustrate that for the temperature range 1,073–1,373 K, the values of n lie within 0.45–0.65, and the constant k increases exponentially with increasing temperature.

Table 3

Parameters of the Yerofeyev–Kolmogorov equation

Charge composition (%)			T (K)	n	k	К = n·k ^1/n	ln K	E _apparent (kJ·mol⁻¹)
Phosphorite	PSS	Oil sludge coke ratio	T (K)	n	k	К = n·k ^1/n	ln K	E _apparent (kJ·mol⁻¹)
70	30	—	1,073	0.44	0.142	0.045	–1.420	4.15
			1,173	0.47	0.181	0.017	–4.110
			1,273	0.48	0.210	0.028	–3.631
			1,373	0.5	0.346	0.031	–3.112
80	10	1:0.2	1,073	0.52	0.171	0.0069	–2.674	5.02
			1,173	0.52	0.220	0.020	–4.423
			1,273	0.51	0.336	0.035	–3.352
			1,373	0.51	0.450	0.0426	–3.155
75	15	1:0.25	1,073	0.45	0.390	0.0320	–3.440	5.13
			1,173	0.47	0.556	0.0890	–2.542
			1,273	0.56	0.573	0.121	–2.112
			1,373	0.62	0.660	0.266	–1.324
70	20	1:0.30	1,073	0.44	0.446	0.055	–2.920	8.16
			1,173	0.47	0.632	0.1037	–2.270
			1,273	0.53	0.694	0.333	–1.099
			1,373	0.62	0.782	0.71	–0.034
65	25	1:0.35	1,073	0.59	0.237	0.0406	–3.204	19.5
			1,173	0.62	0.400	0.088	–2.430
			1,273	0.65	0.532	0.234	–1.452
			1,373	0.68	0.674	0.478	–0.738
60	30	1:0.4	1,073	0.60	0.439	0.0409	–3.196	22.99
			1,173	0.62	0.584	0.214	–1.542
			1,273	0.67	0.627	0.274	–1.295
			1,373	0.70	0.674	0.582	–0.541

Considering this in the Yerofeyev– Kolmogorov equation, the parameter K is not a velocity constant in each curve of Figures 4–5.

As the temperature increases, the rate of fuel burnt out and CO₂ release increases, which leads to a rapid increase in the degree of decarbonization. For formulations containing 10% and 40% oil sludge (by weight of coke), the process proceeds most intensively with immersion in the transition region. The degree of decarbonization reaches 80–85% in 20 min at 1,273 K under these conditions.

3.3 Phosphate composite structure

The results of the IR spectra of the charge firing product low-grade phosphorite–PSS–coke–oil sludge at a temperature of 1,373 K and a duration of 60 min are shown in Figure 8, which is characterized by a number of absorption bands associated with changes in the main functional groups formed during high-temperature firing.

Figure 8

IR spectra of the batch firing product low-grade phosphorite–PSS–coke–oil sludge.

The IR spectra of the absorption band at 470–590 cm⁻¹ (Si–O), 700–800 cm⁻¹ (Si–O–P), 1,000–1,100 cm⁻¹ (P–O), 1,444 cm⁻¹ (CO₃ ²⁻), 2,800–3,000 cm⁻¹ (C–H), 3,478–3,627 cm⁻¹ (–OH) confirm the multicomponent nature of silicate inclusions and calcium phosphates, with carbonaceous residues (Figure 8).

X-ray fluorescence analysis showed significant quantitative content of CaO – 37.9%, SiO₂ – 24%, P₂O₅ – 19–23%, and impurities of MgO, Al₂O₃, Fe₂O₃, as well as heavy metals (MnO, CuO, ZnO, PbO) in trace amounts (Figure 9).

Figure 9

IR spectra of the batch firing product low-grade phosphorite PSS– coke–oil sludge.

The microstructure and element-by-element composition of the firing product of the charge composition at the ratios phosphorite–PSS–coke – oil sludge 65-25-10 (1:0.35) is shown in Table 4 and Figure 10. The analysis of the element composition and microstructure of the sample is characterized by the predominance of oxides of calcium, silicon, phosphorus, iron, and fluorine. As a result, the total area of the sample is characterized by the predominance of a calcium phosphate matrix in the form of irregular, fragmented, rhombic, lamellar minerals. The silicate components in the intermediate space are characterized by rounded, colorless crystals of rankinite. Insignificant dark-brown accumulations of small oval crystals are characteristic of ferritic calcium minerals and residual carbon of coke fines.

Table 4

Elemental composition of the firing product of the charge composition of phosphorite–PSS–coke–oil sludge ratios 65–25–10 (1:0.35)

Element	C	O	F	Na	Mg	Al	Si	P	S	Cl	K	Ca	Fe
Weight (%)	3.89	42.30	0.39	0.80	1.13	1.46	7.27	10.35	0.71	0.24	0.53	28.45	2.47

Figure 10

Micrograph (a) and microstructure (b) of the firing product of the charge composition of phosphorite–PSS–coke – oil sludge ratios 65–25–10 (1:0.35).

Thus, the product under study appears to be a phosphate–silicate composite in which the “matrix” (Ca–P) is combined with a glassy phase (Si–O–Al) and partially burned hydrocarbons, forming an increased strength of the composite (3.3–3.4 MPa).

4 Conclusions

The results of the conducted studies of agglomeration firing of phosphorite–PSS–coke–oil sludge have shown that the presence of these additives significantly improves the quality of phosphate agglomerate. With an increase in the amount of the PSS additive from 10 to 15% and a coke-to-oil sludge ratio of 1:0.3, the acid modulus of the charge is 0.8–0.81. In this case, the temperature of the onset of deformation and softening decreases to 1,303 and 1,508 K. At the same time, the mechanical strength of the agglomerate increases to 3.3–3.4 MPa. The analysis of graphical dependences of the degree of decarbonization on the ratio of coke/petroleum sludge from 1:02 to 1:0.4 and the firing duration increases to 76–86%.

An analysis of the nature of the thermogravimetric curve of the oil sludge indicates the presence of volatile low-molecular-weight organic compounds and components in the form of inorganic and ash residues.

The IR spectra confirm that as a result of the firing of the charge phosphorite–PSS–coke–oil sludge, a complex multicomponent structure with phosphate and silica bonds is formed. The presence of wide bands in the range of 590–1,346 cm⁻¹ shows silicate and aluminosilicate bonds.

X-ray fluorescence analysis of the firing product showed a high intensity of the calcium base while maintaining the proportion of phosphates. A significant amount of SiO₂ characterizes the presence of a phosphate–silicon matrix. Low-intensity diffraction peaks of inclusions of MgO, Al₂O₃, Fe₂O₃, and metallic phases reflect the complex mineral composition of aluminosilicates and calcium ferrites.

The results of the element-by-element composition and microstructure also confirm the basic phosphate–calcium matrix of crystals with inclusions of silicate and aluminosilicate crystals.

The multicomponent composition of the obtained phosphate agglomerate characterizes its improved specific physicochemical and mechanical properties, which are important for further use in phosphorus production.

Of significant interest is the variation of the composition of PSS in terms of MgO and K₂O content for the targeted synthesis of low-melting silicate–phosphate eutectic with increased acid resistance. In addition, studies of alternative types of oil sludge (drilling, catalytic) and biocarbon wastes are of practical importance in order to assess the effect of their chemical composition on the kinetics of decarbonization and the formation of microstructure.

Funding information: This research was funded by Committee on Science and Higher Education of the Republic of Kazakhstan, grant number BR21882181.
Author contributions: Dana Pazylova and Ayaulym Tileuberdi: conceptualization. Saltanat Tleuova: methodology. Zhunisbek Turishbekov: software. Ayaulym Tileuberdi and Mariyam Ulbekova: validation. Zhunisbek Turishbekov and Nurila Sagindikova: formal analysis. Mariyam Ulbekova: investigation. Dana Pazylova: resources and data curation. Saltanat Tleuova: writing – original draft preparation. Saltanat Tleuova: writing – review and editing. Ayaulym Tileuberdi: visualization. Ayaulym Tileuberdi: supervision. Saltanat Tleuova: project administration. Ayaulym Tileuberdi: funding acquisition.
Conflict of interest: The authors state no conflicts of interest.
Data availability statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

References

[1] Tleuova S, Tileuberdi A, Pazylova D, Ulbekova M, Sagyndykova N, Lavrov B, et al. Investigation of the process of agglomeration of phosphorites using phosphate-siliceous shales and oil sludge. Open Chem Eng J. 2024;18:e18741231331231. 10.2174/0118741231331231240731153013.Search in Google Scholar

[2] Tleuov A, Tleuova S, Pazylova D, Tileuberdi A, Ulbekova M, Turishbekov Zh. The method of agglomeration of phosphate raw materials. Republic of Kazakhstan, Astana city: The National Institue of Intellectula Property. Utility Model Patent of the Republic of Kazakhstan. No. 9772 dated 11.15.2024.Search in Google Scholar

[3] Tleuov A. Kinetics of phosphorus reduction from pre-melted phosphate-siliceous shales. In Proceeding of the Collection of scientific papers of the Kazakh Scientific and Technical University, Almaty, Republic of Kazakhstan. Vol. 5, 5.12.2001.Search in Google Scholar

[4] Tleuov A. Kinetics of decarbonization of phosphorites during agglomeration using oil sludge. In Proceeding of the Collection of scientific papers of the Problems of natural sciences at the present stage, Bishkek, Republic of Kyrgyzstan; 03. 02. 2002.Search in Google Scholar

[5] Tleuov A, Shevko V, Tleuova A. The use of hydrocarbon raw materials in the processes of decarbonization of phosphate ore. In Proceeding of the Collection of materials of the Republican scientific and practical conference. Institute of General and Inorganic Chemistry of the Academy of Sciences of the Republic of Uzbekistan, Tashkent, Republic of Uzbekistan; 15. 05. 2003.Search in Google Scholar

[6] Tleuov A, Shevko V, Tleuova A. Kinetic patterns of decarbonization of phosphate raw materials in the presence of hydrocarbon compounds. J Integr Use Miner Raw Mater. 2003;6(231):66–9.Search in Google Scholar

[7] Bishimbayev V, Tleuov A, Shevko V, Tleuova A. Pilot industrial tests of coke replacement for oil sludge during the fumigation of phosphorous fines. Collect Sci News Kaz. 2003;5:44–8.Search in Google Scholar

[8] Bobkov V, Borisov V, Dli M. Thermally activated chemical technology processes of agglomeration of phosphorites. Theor Found Chem Eng. 2018;52:35–41. 10.1134/S0040579518010025.Search in Google Scholar

[9] Lv X, Yu B, Zhang J, Xiang S. Sintering behaviour and sinter properties of phosphorite. Miner Process Extr Metall. 2015;124(1):16–26. 10.1179/1743285514Y.0000000072.Search in Google Scholar

[10] Elgharbi S, Horchani-Naifer K, Ferid M. Investigation of structural and mineralogical changes of Tunisian phosphorite during calcination. J Therm Anal Calorim. 2015;119(1):265–71. 10.1007/s10973-014-4132-5.Search in Google Scholar

[11] Panchenko S, Shirokih T. Investigation of structural and mineralogical changes of Tunisian phosphorite during calcination. Theor Found Chem Eng. 2014;48(1):77–81. 10.1134/S0040579514010096.Search in Google Scholar

[12] Yang H. Sintering behavior of the sinter of phosphrite from Leshan, China. Metalurgia Int. 2014;19(2/3):461–7.Search in Google Scholar

[13] Guo E. Sintering process of phosphorite from Leshan, China. In Proceedings of the 4th International Symposium on High‐Temperature Metallurgical Processing, Hoboken, USA; 20.2.2013. 10.1002/9781118663448.ch56.Search in Google Scholar

[14] Meshalkin V, Bobkov V, Dli M. Experimental studies of the physicochemical process of heating ore phosphorites. Russ J Gen Chem. 2023;93:686–93. 10.1134/S1070363223030234.Search in Google Scholar

[15] Pazylova D, Shevko V, Tleuov A, Lavrov B, Saidullayeva N, Abzhanova A. Kinetics of extraction of inorganic chlorides from lead production slags in the presence of distiller liquid. Rasayan J Chem. 2020;13(4):2646–52. 10.31788/RJC.2020.1345862.Search in Google Scholar

[16] Naktiyok J, Bayrakceken H, Ozer A, Gulaboglu M. Kinetics of thermal decomposition of phospholipids obtained from phosphate rock. Fuel Process Technol. 2013;116:158–64. 10.1016/j.fuproc.2013.05.007.Search in Google Scholar

[17] Rui L, Weilong H, Jiangfei D, Shengxia F, Yu Zh. Thermal properties and pyrolysis kinetics of phosphate-rock acid-insoluble residue. Waste Manag. 2022;146(1):77–85. 10.1016/j.wasman.2022.04.039.Search in Google Scholar PubMed

[18] Eroglu H, Sahin G, Kadir M, Oumlzer A. Calcination kinetics of phosphate rock in CO2 atmosphere. Asian J Chem. 2014;26(27):39–44. 10.14233/ajchem.2014.19009.Search in Google Scholar

[19] Bobkov V. Mathematical model for the kinetics of heterogeneous reaction of carbonates dissociation in the process of roasting in the presence of temperatures gradients in phosphate raw material. Solid State Phenom. 2021;316:610–8. 10.4028/www.scientific.net/SSP.316.610.Search in Google Scholar

[20] Bobkov V. Analysis of chemical-metallurgical agglomeration processes during charge sintering. CIS Iron Steel Rev. 2020;20:7–11. 10.17580/cisisr.2020.02.02.Search in Google Scholar

[21] Bayrakceken H, Naktiyok J, Okur H, Ozer A. Non isothermal calcination kinetics of phosphate rock. J Eng Sci. 2014;20(7):266–71. 10.5505/pajes.2014.67044.Search in Google Scholar

[22] Gezzaz H. Thermodynamic and kinetic modeling of thermal decarbonization of low-grade phosphate ore. Diss. Polytechnique Montréal. Canada: PolyPublie, Polytechnique Montreal Institute; 2021. https://publications.polymtl.ca/9960/.Search in Google Scholar

[23] Bazhirova K, Zhantasov K, Bazhirov T, Kolesnikov A, Toltebaeva Z, Bazhirov N. Acid-free processing of phosphorite ore fines into composite fertilizers using the mechanochemical activation method. J Compos Sci. 2024;8:165. 10.3390/jcs8050165.Search in Google Scholar

[24] Azeez R, Tonsuaadu K, Kaljuvee T, Trikkel A. Kinetics of Estonian phosphate rock dissolution in hydrochloric acid. Minerals. 2024;14:322. 10.3390/min14030322.Search in Google Scholar

[25] Brown M, Maciejewski M, Vyazovkin S, Nomen R, Sempere J, Burnham A, et al. Computational aspects of kinetic analysis: Part A: The ICTAC kinetics project-data, methods and results. Thermochim Acta. 2000;355(1–2):125–43. 10.1016/S0040-6031(00)00443-3.Search in Google Scholar

[26] Roduit B. Computational aspects of kinetic analysis.: Part E: The ICTAC Kinetics Project – numerical techniques and kinetics of solid state processes. Thermochim Acta. 2000;355(1–2):171–80. 10.1016/S0040-6031(00)00447-0.Search in Google Scholar

[27] Rayimbekov Y, Abdurazova P, Nazarbek U. Dissolution kinetics of carbonates in low-grade microgranular phosphate ore using organic acids as leaching agents. Mining. 2024;4:766–76. 10.3390/mining4040043.Search in Google Scholar

[28] Kareeva A, Besterekov U, Abdurazova P, Nazarbek U, Pochitalkina I, Rayimbekov Y. Synthesis of NPK fertilizer from low-grade phosphate raw material. Int J Chem React Eng. 2022;20(8):805–14. 10.1515/ijcre-2021-0246.Search in Google Scholar

[29] Smailov B, Zakirov B, Beisenbayev O, Tleuov A, Issa A, Azimov A, et al. Thermodynamic-kinetic research and mathematical planning on the obtaining of phosphorus-containing components based on Cottrell dust from phosphorus production waste. Rasayan J Chem. 2022;15(4):2274–9. 10.31788/RJC.2022.1547022.Search in Google Scholar

[30] Smailov B, Ismailov B, Zakirov B, Turakulov B, Tursynbay L, Aimenova Zh. Study and mechanism of formation of phosphorus production waste in Kazakhstan. Green Process Synth. 2024;13:20240023. 10.1515/gps-2024-0023.Search in Google Scholar

[31] Musa C, Zaidi M, Depriester M, Allouche Y, Naouar N, Bourmaud A, et al. Development of foam composites from flax gum-filled epoxy resin. J Compos Sci. 2024;8:244. 10.3390/jcs8070244.Search in Google Scholar

[32] Martin S, Milickovic TK, Charitidis CA, Moisan S. Ready-to-use recycled carbon fibres decorated with magnetic nanoparticles: Functionalization after recycling process using supercritical fluid chemistry. J Compos Sci. 2023;7:236. 10.3390/jcs7060236.Search in Google Scholar

[33] Fang C, Xiao H, Zheng T, Bai H, Liu G. Organic solvent free process to fabricate high performance silicon/graphite composite anode. J Compos Sci. 2021;5:188. 10.3390/jcs5070188.Search in Google Scholar

[34] Cherepanov V, Aksenova T. Chemical kinetics. Ural: Ural Federal University; 2016. p. 132.Search in Google Scholar

[35] Arnaut L. Chemical kinetics. 2nd edn. Amsterdam, Netherlands: Elsevier; 2021. p. 5–9. 10.1016/B978-0-444-64039-0.00028-5.Search in Google Scholar

[36] Li Q, Jun Y. The apparent activation energy and pre-exponential kinetic factor for heterogeneous calcium carbonate nucleation on quartz. Commun Chem. 2018;1:56. 10.1038/s42004-018-0056-5.Search in Google Scholar

Received: 2025-03-31

Accepted: 2025-06-25

Published Online: 2025-08-08

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/gps-2025-0070

Keywords for this article

phosphate–siliceous shales; oil sludge; kinetics of decarbonization; Yerofeyev–Kolmogorov equation; synthesis

Creative Commons

BY 4.0