Kinetic Features of the Hydrogen Sulfide Sorption on the Ferro-Manganese Material

Abstract

The kinetics of hydrogen sulfide sorption by the surface of a ferromanganese material containing in its composition a mixture of iron (II) and (III) oxides FeO × Fe₂O₃, takanelite (Mn, Ca) Mn₄O₉ × 3H₂O and quartz SiO₂, and which is samples of unrefined ferromanganese ore, was studied in this work. Sorption rate constant and activation energy constant values were calculated. The catalytic effect of iron (III) oxide was established, the presence of which in natural material contributes to a decrease in the H₂S sorption activation energy. Based on the results of X-ray phase and chromatographic analysis methods, a chemical (redox) reaction of the conversion of hydrogen sulfide into elemental sulfur and H₂O was revealed. The overall process rate is expressed in terms of the physical sorption stage and chemical transformation of the components; the influence of the rate of the third stage—reaction products desorption—on the overall rate of the process is taken into account. The limiting stage of the process is determined—a chemical reaction. The relation between the heat and the activation energy of the chemical transformation is used according to the Bronsted—Polanyi rule for catalytic processes. It was found that with an increase in the chemisorption heat, the activation energy of the chemisorption stage decreases and, as a consequence, its rate increases. The sorption process parameters were calculated—the Fe₂O₃ coverage degree with the initial substances and reaction products providing the maximum sorption rate, which can be a criterion for evaluating the catalytically active sites of the catalyst surface for carrying out catalytic reactions.

1. Introduction

The emission of waste gases containing toxic substances, including sulfur-containing compounds, is a serious environmental problem of the metallurgical industry [1,2,3,4,5,6]. Sorption methods are still effective in the field of the air environment cleaning process. Considering the volume of evolved gaseous substances, porous inorganic materials containing substances possessed with oxidative properties to a number of gaseous compounds can be used as promising and inexpensive sorbents [7]. Manganese oxides are widely used in gas cleaning technologies as oxidizing agents. There exist various artificial sorption materials with the manganese oxide film coated surface. Oxidative destruction of phenols and cyanide compounds, sorption of hydrogen sulfide and sulfur (IV) oxide, as well as organic compounds, is taking place on the surface of manganese oxide.

The use of both products and raw materials of metallurgy plants during the gas cleaning process can be cost-effective. Their application will ensure low or even waste-free main production technologies due to the full engagement of the mentioned materials. Reducing the ecological impact on the environment caused by metallurgical enterprises is possible by involving unrefined ferromanganese ores in the technological cycle. Providing high sorption characteristics comparable to the properties of synthesized sorbents based on manganese oxide [8], ferromanganese ores can be used in the process of sulfur-containing gas clearing.

The authors of this work investigate the sorption properties of ferromanganese material—unrefined ferromanganese ore samples of the Ulu-Telyaksky deposit (Republic of Bashkortostan), which is the raw material for manganese and iron oxide production. The presence of manganese (IV) and iron (III) compounds in ore samples provides oxidizing properties in relation to gaseous compounds, which contain reducing elements. Iron and manganese oxides can also exhibit catalytic properties. Accordingly, in the process of heterogeneous catalysis, the interaction of the reactant with the surface of the solid catalyst will have a dominant role. Consequently, the nature of physical and chemical interactions with the surface of the ferromanganese material will determine the kinetics of the hydrogen sulfide sorption process, the study of which is the subject of this work.

Since catalysis is a specific phenomenon, only a specific (individual) catalyst can be used for each chemical reaction or process. Zhuravskiy et al. investigated the process of hydrogen sulfide sorption on active coals [9], which comes with the oxidation of hydrogen sulfide to elemental sulfur and water due to the presence of nitrogen and oxygen atoms in the coals. Oxidized nitrogen-modified activated carbons were used as a sorbent. As a result of the study, the authors determined the presence of elemental sulfur traces and made a conclusion about the mechanism of electronic catalysis.

Chung Lau L. et al. studied the absorption of H₂S on activated carbon, which was impregnated with a solution of cerium (III) nitrate, washed with sodium hydroxide, filtered, and dried at 80 °C [10]. Kinetic studies were carried out in the temperature range of 30–70 °C. The calculation of kinetic parameters was carried out using pseudo-first and pseudo-second order models according to the equations:

Pseudo-first order

$$n\left(Q_e-Q_t\right)=-k_1+\ln Q_e,$$

(1)

Pseudo-second order

$$\frac{t}{Q_t}=\frac{1}{k_2{Q}_e^2}+\frac{t}{Q_e},$$

(2)

where Q_t—adsorption capacity at time t; Q_e—full sorbent capacity, calculated based on thermodynamic data; k₁—pseudo-first order reaction rate constant; k₂—pseudo-second order reaction rate constant.

Based on the results of linear dependencies plotting, the authors have chosen a pseudo-second-order calculation model. The calculated values of the reaction rate constants at temperatures of 30, 40, 50, 60, and 70 °C are: (2.39; 2.73; 3.98; 3.64 and 4.07) × 10⁻⁶ g/mg × min, the activation energy value was 11.7 kJ/mol.

Aslam Z. et al. investigated the oil fly ash (OFA) collected during the utilization of power plants, which was processed by the method of physicochemical activation to improve the surface properties [11]. The synthesized activated carbon from oil fly ash was used for the adsorption of hydrogen sulfide. The sorbent was obtained by adding a mixture of acids (20% nitric acid and 80% phosphoric acid) to OFA, after which the sorbent was treated with 2 M potassium hydroxide to increase the surface affinity. As a result of the treatment, the sorption capacity of the material in relation to H₂S was increased.

To describe the kinetics of H₂S adsorption on the alkali-modified activated carbon, Thomas, Yoon–Nelson, and Clark models were used, which made it possible to establish the partial dependencies of the flow rate and concentration of H₂S on the adsorption value.

The desulfurization kinetics of hot coal gas (H₂S 0.25%, H₂ 10.6%, CO 18%, and carrier gas N₂) is described by an improved deactivation kinetic model based on the use of the chemical stoichiometric Equation (3) by the authors of [12]:

H₂S + ⅔LaFeO₃ + ⅓H₂ = ⅓La₂O₂S + ⅔FeS + 1⅓H₂O,

(3)

The mesoporous zeolite (M41) based sorbent containing LaFeO₃ with a molar ratio of elements La/Fe = 1:2 (LF₂) and their different percentages (LF₂ 40, 50, 60 and 100%) was used in the mentioned research. According to the percentage, the obtained reaction rate constants were k × 10³ min⁻¹ × g⁻¹ 8.89; 8.52; 7.61 and 2.52. Despite the obvious chemical (redox) interactions between hydrogen sulfide and LaFeO₃, the calculated value of the activation energy did not exceed 25.1 kJ/mol.

Thus, the kinetic dependencies of sorption processes on zeolite and carbonaceous materials impregnated with substances exhibiting oxidizing properties are approximated by the equations of formal kinetics [13]. However, the contribution of physical and chemisorption to the main sorption process, as well as the effect of desorption of reaction products, remains unclear. A quantitative assessment of the catalytic effect of sorption of hydrogen sulfide on the covalent or ionic surfaces of solids has not been given. There is no understanding of the amount of the active surface of the solid phase responsible for the physical sorption effects. This work was carried out in order to determine the kinetic dependencies of the hydrogen sulfide sorption by solid sorbents exhibiting obvious oxidizing properties. Another purpose of this study was to determine the mechanism and to reveal a number of specific features of the heterogeneous process sorption.

2. Materials and Methods

The kinetics of H₂S sorption on ferromanganese ore of the Ulu-Telyaksky deposit was investigated in this work. Samples with a fraction of 1 to 1.6 mm, having a specific surface area of 110 m²/g and a pore size of 1.36∙10⁻⁸ m were selected for the experiment. Sample parameters were determined by thermal nitrogen desorption using a Nova 1000e surface area and pore size analyzer (Quantachrome Instruments, Boynton Beach, FL, USA). The chemical composition of the ore shown in

Table 1. Elemental composition of ferromanganese ore.

Element	MnO	SiO2	Al2O3	Fe2O3	CaO	MgO	K2O	Na2O	SO3	Impurities
Content, %	48.24	24.57	8.61	7.50	7.08	1.88	1.54	0.20	0.07	0.31

is mainly represented by manganese, silicon, aluminium, and iron. Elemental analysis was carried out by X-ray fluorescence using Shimadzu XRF-1800 spectrometer (Shimadzu Corporation, Kyoto, Japan).

According to the results of X-ray phase analysis presented in Figure 1 (X-ray diffractometer Shimadzu XRD-7000 manufactured by Shimadzu Corporation, Kyoto, Japan), the natural material contains few crystalline phases, which are a mixture of iron (II) and (III) oxides FeO × Fe₂O₃, takanelite (Mn,Ca)Mn₄O₉ × 3H₂O and quartz SiO₂ [14]. The JCPDS-ASTM international X-ray database was used to correlate the peaks with the composition.

Both standard samples of hydrogen sulfide with a H₂S content of 125 ppm and samples of hydrogen sulfide synthesized in a Wurtz flask were used for the experiment. An excess of Na₂S (reagent grade) and phosphoric acid solution at a concentration of 3 mol/L was added to the Wurtz flask. A part of the synthesized hydrogen sulfide was passed through a 6 mol/L NaOH solution (Figure 2a), from the other part a 10–20 mL aliquot of H₂S was taken to a gas syringe. An aliquot was transferred in an air-proof glass vessel with a capacity of 260 mL, after preliminary removal of 10–20 mL of air from the vessel, then 1 mL of a gas sample was taken. One gas sample was placed in a 260 mL vessel with 50 ± 2 mg of ore charge, and another gas sample was placed in a vessel of the same volume without ore charge, taking the gas concentration as the initial value. The experimental set-up scheme is shown in Figure 2b.

The studies were carried out at temperatures of 252, 280, 298 K. To reach the equilibrium concentration, the phase contact time was up to 3 h. At certain time intervals from the beginning of the experiment, aliquots of H₂S were sampled with a gas syringe, for hydrogen sulfide content determination by chromatography method using a Thermo Trace GC Ultra gas chromatograph manufactured by Thermo Scientific, Waltham, MA, USA, using the ratio of the peak areas of standard samples (125 ppm H₂S, 134 ppm CH₃SH, and 149 ppm C₂H₅SH in a helium atmosphere). To measure the thermal effect of the sorption process of hydrogen sulfide on ferromanganese material, a calorimetric unit was assembled using an IKA C2000 basic thermochemical gas analyzer (IKA WERKE, 79219 Staufen im Breisgau, Germany).

3. Results and Discussion

As a result of the experiment, the kinetic dependencies of the hydrogen sulfide concentration (C) change on the sorption time were obtained, as shown in Figure 3.

The kinetic parameters were calculated using the laws of formal kinetics. The reaction order was determined by a graphical method of plotting linear forms of kinetic dependencies. The rate constants of the sorption process were calculated using linear forms of the dependence of the H₂S concentration logarithm on the sorption time on ferromanganese ore at temperatures of 252, 280, 298 K, which is presented in Figure 4.

Approximation equations, correlation values, and rate constants of the sorption process are presented in

Table 2. Results of processing linear forms of kinetic dependencies.

T, K	Approximation Equation	Correlation Value R2	Rate Constant k	lnk
252	lnC = −0.0023 × t − 9.4254	0.98	0.0023 ± 0.0001	−6.03 ± 0.30
280	lnC = −0.0029 × t − 9.6098	0.99	0.0029 ± 0.0001	−5.84 ± 0.29
298	lnC = −0.0032 × t − 9.6039	0.97	0.0032 ± 0.0002	−5.74 ± 0.29

.

To confirm the first order of the reaction, the periods of half-conversion (sorption) of hydrogen sulfide were determined at various initial concentrations. The obtained kinetic dependencies of the H₂S concentration on time are shown in Figure 5.

According to the calculations based on Equation (3):

$$n=1+\frac{\ln \left(\frac{t_{1/2}^i}{t_{1/2}^{i+1}}\right)}{\ln \left(\frac{c_{1/2}^{i+1}}{c_{1/2}^i}\right)},$$

(4)

where $t_{1/2}^i$, $t_{1/2}^{i+1}$—half-conversion time at initial concentrations, sec, C ¹ = 1.06∙10⁻² mol/L, C ² = 1.35∙10⁻² mol/L and C ³= 2.89∙10⁻³ mol/L; $c_{1/2}^i$, $c_{1/2}^{i+1}$—half-conversion concentration at initial concentrations C ¹, C ² and C ³, the reaction order within the error tolerance was 1.

Based on the graphical dependence of the reaction rate constant logarithm value on the reciprocal temperature (lnk = −470.55 (1/T) − 4.1644, R ² = 0.99) the value of the activation energy of the sorption process was calculated, which was E_a = 3.9 ± 0.2 kJ/mol (Figure 6).

The results of the chemical analysis of the studied ore samples after contact with H₂S, obtained by the X-ray fluorescence analysis method (

Table 3. Chemical composition of the ore after sorption of hydrogen sulfide (relative percentages).

Element	MnO	SiO2	Al2O3	Fe2O3	CaO	MgO	K2O	SO3	Impurities
Content, %	10.19	21.67	6.47	2.36	3.74	1.34	1.48	52.48	0.27

), indicate a significant increase in the sulfur content in the ore, and, as a consequence, a decrease in the relative content of manganese, iron and other elements.

The data on the elemental composition before and after sorption are presented in

Table 4. Elemental composition of ore before and after contact with hydrogen sulfide.

Element	Mg	Al	Si	K	Ca	Mn	Fe	S	Σ
Mass Content Before Sorption, %	1.61	7.51	20.08	2.16	8.09	53.66	6.89	-	100
Mass Content After Sorption, %	-	4.72	7.43	0.90	3.95	65.57	6.32	11.11	100

.

According to the results of X-ray phase analysis of ore samples, after contact with gas, there are no crystalline sulfur-containing phases, while along with quartz hydrated silicate H₂Si₂O₅ and iron (III) oxide, a new phase MnO (OH) appears, which is a hydrated form of manganese (III) oxide Mn₂O₃ 2H₂O. Takanelite (Mn,Ca)Mn₄O₉ × 3H₂O was not found in the ore (Figure 7).

The formation of elemental sulfur in the composition of ore samples is indicated by the chromatographic analysis results of samples obtained by dissolving with toluene a sulfur-containing substance, which was removed from the surface of the ore after contact with H₂S. Based on the phase analysis, it can be assumed that, along with the process of physical adsorption of gas, a chemical redox reaction occurs:

2MnO₂ + H₂S = S + Mn₂O₃ + H₂O,

(5)

Physical sorption is caused by the presence of uncompensated interatomic interaction forces on the surface, due to which hydrogen sulfide molecules are attracted. Generally, physical adsorption proceeds at a high rate without activation energy and leads to equilibrium coverage of the active surface of the solid substance.

Temperature range of physical sorption cannot significantly exceed the hydrogen sulfide condensation temperature equal to 212.7. Therefore, with the increasing temperature, the equilibrium coverage will decrease, while there is no such limitation for chemisorption, it can occur both at low (less than 273 K) and at higher temperatures (more than 273 K). Chemisorption of the reactant, opposed to physical sorption, is proceeding with the involvement of an activated complex characterized by a certain activation energy. The presence of iron (III) oxide in the ore composition can affect the chemical sorption process, contributing to its acceleration due to the generated catalytic effect [15,16].

To determine the effect of iron (III) oxide on the chemical reaction rate, a series of hydrogen sulfide sorption experiments were carried out on iron (III) oxide with a specific surface area of 31 m²/g and a pore size of 4.84 × 10⁻⁸ m and on a model sample consisting of SiO₂, Al₂O₃ and MnO₂ oxides mixture, which does not contain Fe₃O₄ and quantitatively represents the composition of the studied ore. The specific surface area of 75 m²/g and the pore size of 3.33 × 10⁻⁸ m of the model sample are practically commensurable with those of real ore samples, which makes it possible to compare their kinetic sorption characteristics. According to the experimental results, iron (III) oxide showed no sorption tendency to hydrogen sulfide. During the experiment phase and H₂S concentration changes were not observed. The dependencies of the H₂S concentration change on time during sorption on model samples containing manganese (IV) oxide and the rate constant logarithm on reciprocal temperature are shown in Figure 8 and Figure 9.

The calculated value of the hydrogen sulfide sorption activation energy on model samples containing manganese (IV) oxide was 18.6 ± 0.9 kJ/mol. The increase in the activation energy is probably caused by the absence of iron (III) oxide in the composition of the sorption material.

According to the Bronsted–Polanyi equation for catalytic processes, the difference between the activation energy of the process in the absence (E₀) and in the presence (E) of the catalyst is determined by the heat effect of H₂S chemisorption by the catalyst, where α is a constant coefficient for a given reaction and catalyst, varying from 0 to 1:

E = E₀ − α × ΔH.

(6)

The catalytic conversion of H₂S includes the following stages: physical adsorption, chemisorption, chemisorption of reaction products, physical adsorption of reaction products and proceeds according to the scheme:

(1) H2S + [] → H2Sads.

(2) H2Sads. + 2[MnO2] → [Mn2O3] + Sads. + H2Oads.

(3) Sads. + H2Oads. → S + H2O + [],

where []—free for chemisorption area on the active surface. Therefore, the energy path of the hydrogen sulfide sorption and oxidation process will include three peaks corresponding to three stages of the process. Consequently, for each individual process, the values of the activation energies can be expressed in accordance with the Bronsted–Polanyi rule:

E₁ = E₀₁ − α × ΔH₁

(7)

E₂ = E₀₂ + (1 − α) × ΔH₁ − α × ΔH₂

(8)

E₃ = E₀₃ + (1 − α) × ΔH₂

(9)

where E_1,2,3—is the activation energy of the first, second and third stages of the process with the catalyst participation, ΔH₁ and ΔH₂—chemisorption heats of the initial material H₂S_ads. and reaction products S_ads. + H₂O_ads, α—coefficients for the corresponding reaction (5) and catalyst.

According to the Bronsted–Polanyi rule, the activation energy of the first stage will decrease by the hydrogen sulfide chemisorption heat amount of ΔH₁, while the activation energy of the second stage should increase by the chemisorption heat value of the initial substance H₂S due to the formed bonds of adsorbed H₂S with the catalyst and decrease with an increase in the chemisorption heat of the reaction products S_ads. + H₂O_ads. The energy of the third stage will increase with an increase in the products chemisorption heat. Therefore, according to the first reaction the hydrogen sulfide sorption rate can be expressed by the equation:

$${\upsilon }_1=K_{01}\exp \left(-\frac{E_{01}-\alpha \mathsf{\Delta }{H}_1}{RT}\right)\left(1-{\theta }_1-{\theta }_2\right)=k_1\exp \left(\frac{\alpha \mathsf{\Delta }{H}_1}{RT}\right)\left(1-{\theta }_1-{\theta }_2\right)$$

(10)

and the chemical reaction rate is expressed by Equation (11):

$${\upsilon }_2=K_{02}\exp \left(-\frac{E_{02}-\left(1-\alpha \right)\mathsf{\Delta }{H}_1-\alpha \mathsf{\Delta }{H}_2}{RT}\right){\theta }_1=k_2\exp \left(\frac{\alpha \mathsf{\Delta }{H}_2-(1-\alpha )\mathsf{\Delta }{H}_1}{RT}\right){\theta }_1$$

(11)

and thus, the hydrogen sulfide desorption rate is expressed by Equation (12):

$${\upsilon }_3=K_{03}\exp \left(-\frac{E_{03}-\left(1-\alpha \right)\mathsf{\Delta }{H}_2}{RT}\right){\theta }_2=k_3\exp \left(\frac{(1-\alpha )\mathsf{\Delta }{H}_2}{RT}\right){\theta }_2$$

(12)

where ${\theta }_1$ and ${\theta }_2$ are the sections of Fe₃O₄ surface, occupied by the chemisorption components of H₂S, S_ads and H₂O_ads; $K_{01}$, $K_{02}$, $K_{03}$—rate constants of first, second and third process stages; $k_1$, $k_2$, $k_3$—coefficients independent of H₂S, S_ads and H₂O_ads chemisorption heat.

The system will remain a stationary state if some of its essential characteristics do not change over time or if the formation rate of a system component is equal to its decay rate. When the stationary state of the hydrogen sulfide sorption process is reached, the total speed of the system will be equal to the speed of each of the conjugate stages:

$$\begin{gathered} \upsilon ={\upsilon }_1={\upsilon }_2={\upsilon }_3= \\ =k_1\exp \left(\frac{\alpha \mathsf{\Delta }{H}_1}{RT}\right)\left(1-{\theta }_1-{\theta }_2\right)=k_2\exp \left(\frac{\alpha \mathsf{\Delta }{H}_2-\left(1-\alpha \right)\mathsf{\Delta }{H}_1}{RT}\right){\theta }_1=k_3\exp \left(-\frac{\left(1-\alpha \right)\mathsf{\Delta }{H}_2}{RT}\right){\theta }_2 \end{gathered}$$

(13)

from the equality of which we find the values of ${\theta }_2$ and ${\theta }_1$ by Equations (14) and (15):

$${\theta }_2={\theta }_1\frac{k_2}{k_3}\exp \left(\frac{\mathsf{\Delta }{H}_2-\left(1-\alpha \right)\mathsf{\Delta }{H}_1}{RT}\right)$$

(14)

$${\theta }_1=\frac{1}{1+\frac{k_2}{k_1}\exp \left(\frac{\alpha \mathsf{\Delta }{H}_2-\mathsf{\Delta }{H}_1}{RT}\right)+\frac{k_2}{k_3}\exp \left(\frac{\mathsf{\Delta }{H}_2-\left(1-\alpha \right)\mathsf{\Delta }{H}_1}{RT}\right)}$$

(15)

and express the overall process rate:

$$\upsilon =\frac{k_2\exp \left(\frac{\alpha \mathsf{\Delta }{H}_2-(1-\alpha )\mathsf{\Delta }{H}_1}{RT}\right)}{1+\frac{k_2}{k_1}\exp \left(\frac{\alpha \mathsf{\Delta }{H}_2-\mathsf{\Delta }{H}_1}{RT}\right)+\frac{k_2}{k_3}\exp \left(\frac{\mathsf{\Delta }{H}_2-\left(1-\alpha \right)\mathsf{\Delta }{H}_1}{RT}\right)}.$$

(16)

From the conditions $\frac{d\upsilon }{d\mathsf{\Delta }{H}_1}=0$ at $\mathsf{\Delta }{H}_2=const$ and $\frac{d\upsilon }{d\mathsf{\Delta }{H}_2}=0$ at $\mathsf{\Delta }{H}_1=const$ we find the solutions of this equation:

$$\mathsf{\Delta }{H}_1=RT\ln \left(\frac{k_2}{k_1}\frac{\alpha }{1-\alpha }\right)+\alpha \mathsf{\Delta }{H}_2\mathrm{and}\mathsf{\Delta }{H}_2=RT\ln \left(\frac{k_3}{k_2}\frac{\alpha }{1-\alpha }\right)+\left(1-\alpha \right)\mathsf{\Delta }{H}_1,$$

the substitution of which in Equations (14) and (15) allows to obtain expressions for the section of the catalyst surface ${\theta }_1$ and ${\theta }_2$, optimally covered with chemisorbed substances:

$${\theta }_1=\frac{\alpha \left(1-\alpha \right)}{1-\alpha -{\alpha }^2}\mathrm{and}{\theta }_2=\frac{{\alpha }^2}{1-\alpha -{\alpha }^2},$$

(17)

If we assume that the free surface of the catalyst is evenly distributed between H₂S_ads, S_ads and H₂O_ads, then the values of ${\theta }_1$ and ${\theta }_2$ are equal, which is observed at α = 0.5 and corresponds to the maximum catalytic reaction rate. To assess the uniform distribution degree of the reactants and reaction products on the Fe₃O₄ surface, the heat of hydrogen sulfide sorption on the surface of ferromanganese ore was measured. The heat value of the sorption process was: ΔH = −69.44 ± 1.39 kJ/mol.

If the calculated activation energy of sorption on ore samples is taken as the total value of the activation energies of the chemisorption stage, chemical transformation stage, and desorption stage, then the coverage degree of the iron (III) oxide surface with chemisorbed substances can be estimated. According to the calculations by Formulas (6) and (17), the coverage degree values were: ${\theta }_1$ = 0.23 and ${\theta }_2$ = 0.07. With these values of the coverage degree, the rate constant ratio of physical sorption and chemical reaction $\left(\frac{k_1}{k_2}\right)$ was estimated, which was 1.25 × 10⁻¹⁴, which characterizes chemisorption (redox reaction) as the limiting stage of the process. The Fe₃O₄ role as a catalyst resides in the electronic conductivity presence due to the element existence in two different valence states, in equivalent positions of the crystal lattice, and the possibility of electron exchange between iron ions (2+) and (3+). The general mechanism of catalyst action in oxidation reactions reside in the simplification of electronic transitions in reacting molecules due to their own electrons. The process begins with the interaction of the solid body electrons with the reacting molecules of hydrogen sulfide, which leads to deformation of the adsorbed molecule and weakening of intramolecular bonds.

The catalytic oxidation of hydrogen sulfide is of interest, first of all, as an effective method for purifying industrial gas emissions from it. In addition, the study of this process is important for the development of the catalysts selective action theory, since the formation of three sulfur-containing products is possible during the oxidation of hydrogen sulfide: S, SO₂ and SO₃. The use of ferromanganese materials for the sulfur-containing gases purification, for which unrefined ferromanganese ore was used in this work, makes it possible to eliminate any losses of H₂S and provide the waste-free process. The adsorbed sulfur is recovered during ore reprocessing into iron and manganese compounds. The method, based on selective catalytic oxidation of hydrogen sulfide from hydrocarbon and metallurgical industrial gases, makes preliminary gas purification from hydrogen sulfide, its concentration and oxidation to sulfurous anhydride unnecessary. The use of manganese and iron (III) oxides has a technological advantage over the currently used titanium and aluminum oxides, which require a constant composition and high specific surface area: the oxidation process of H₂S with manganese oxide is characterized by one-stage and continuous operation, unlike the known Claus method, and mild temperature conditions for the implementation of the process.

The obtained quantitative regularities of the direct catalytic oxidation process of hydrogen sulfide made it possible to estimate the contribution of physical and chemical sorption to the main process of the elemental sulfur formation. The mathematical description of the desorption process, taking into account the conjugated stages of sorption and desorption of all participants of the hydrogen sulfide oxidation process, based on the Bronsted–Polyani theory, can be used to describe any catalytic processes in order to determine the catalytic activity of the catalyst and the fraction of its active surface. Foresight of the catalytic action is the most important task of the catalysis theory.

4. Conclusions

In this work, the kinetic features of the sorption process of hydrogen sulfide, possessed by reducing properties on an inorganic natural ferromanganese material containing crystalline phases of FeO × Fe₂O₃, takanelite (Mn,Ca)Mn₄O₉ × 3H₂O and quartz SiO₂ are determined. The fundamental possibility of effective gas purification process from hydrogen sulfide with the use of inorganic materials with oxidizing properties based on iron and manganese oxides, is shown.

The catalytic effect of the iron (III) oxide presence in ferromanganese samples on the hydrogen sulfide sorption process was revealed. The activation energy values of H₂S sorption by ore samples and model samples simulating the composition of ferromanganese material without Fe₂O₃ content, were calculated and amounted to 3.9 ± 0.2 and 18.6 ± 0.9 kJ/mol. The Fe₂O₃ presence increases the energy compensation degree of the antibonding bonds by the energy of the formed ones.

The sulfur (IV) and (IV) oxides absence in the gas mixture after sorption and the appearance of elemental sulfur in solid samples were determined by the chromatographic method. The results of X-ray phase analysis demonstrate the appearance of a new hydrated crystalline phase Mn₂O₃ × 2H₂O, which is absent in the initial samples. Based on the analysis of the hydrogen sulfide sorption products, the process is expressed by a chemical redox reaction:

2MnO₂ + H₂S = S + Mn₂O₃ + H₂O.

According to the results, the measured heat of the H₂S sorption process was ΔH = −69.44 ± 1.39 kJ/mol, and a limiting stage was established, which is a chemical reaction. The hydrogen sulfide and reaction products distribution degree on the Fe₃O₄ surface was estimated. An unequal coverage degree of the catalyst surface by the chemical reaction components was revealed: the section ${\theta }_1$ occupied by the chemisorption initial component H₂S was 0.23, while the section of the chemisorption reaction products S_ads H₂O_ads was only 0.07. The optimum or maximum rate of the hydrogen sulfide sorption process corresponds to the coverage degrees equality ${\theta }_1$ and ${\theta }_2$, which can be achieved by changing the structure of the catalyst, creating the optimal size and shape of its grains.

Thus, the established features of the catalytic process of H₂S sorption by ferromanganese materials contribute to the development of an optimal catalyst for carrying out catalytic reactions on an industrial scale.