Study on the Effect of Modified Vanadium–Titanium Slag Explosion Suppressant on the Explosion Characteristics of Polyacrylonitrile Dust

Abstract

In this study, a composite powder explosion suppressant (MVTS–NaHCO₃) was prepared via the wet coating method of the solution–crystallization (WCSC) process, using modified vanadium–titanium slag (VTS) as the carrier and NaHCO₃ as the active suppressive component. A 20 L spherical explosion apparatus and a transparent pipeline explosion propagation test system were employed to investigate the effects of the composite powder explosion suppressant with different mass fractions (0%, 10%, 20%, 30%, 40%, 50%) on the explosion pressure and micro-mechanism of polyacrylonitrile (PAN) dust. The experimental results indicated that the MVTS–NaHCO₃ composite powder exhibited a significant suppression effect on PAN dust explosions. In the confined 20 L vessel, complete suppression was achieved when the mass fraction of the composite powder explosion suppressant exceeded 30%, with a maximum explosion pressure reduction of 53.2%. In the semi-open pipeline, 40% composite powder explosion suppressant reduced the maximum explosion pressure to 0.08 MPa (a reduction rate of 82.6%), and complete suppression was achieved at a mass fraction of 50%. Microstructural analysis revealed that the suppression performance of the composite powder explosion suppressant is attributed to the synergetic effects of physical and chemical mechanisms. Physically, NaHCO₃ decomposes endothermically (100 kJ/mol), releasing CO₂ and H₂O and thereby diluting the oxygen concentration, while the porous structure of MVTS enhances dispersibility. Chemically, the hydroxyl groups on the surface of MVTS bond with NaHCO₃, delaying its decomposition, while metal hydroxides (e.g., Al(OH)₃) decompose thermally to form Al₂O₃, which adsorbs and quenches free radicals (e.g., ·OH, ·H), thereby inhibiting chain reactions. This study provides new insights for the resource utilization of VTS and the prevention and control of industrial dust explosions. The findings have important reference value for optimizing explosion suppressant formulations and improving the intrinsic safety.

1. Introduction

Dust explosions are a common and highly hazardous type of industrial accident that greatly threatens production safety and human life and property [1]. Dust explosions occur in the concurrent presence of all the following: (a) combustible dust particles of a sufficiently fine size and appropriate concentration; (b) an oxidizing gas with adequate oxygen concentration; and (c) an ignition source with sufficient energy [2,3]. Polyacrylonitrile (PAN) dust is a highly active organic dust that is prone to explosion upon exposure to electrostatic discharge or high temperature, leading to catastrophic hazards [4,5]. Conventional explosion suppression measures are frequently challenged by high cost and environmental concerns. Therefore, developing new, high-efficiency, low-cost explosion suppressants becomes an urgent task. Vanadium–titanium slag (VTS) is a bulk solid waste from ilmenite smelting with an annual output of over ten million tons. Composed of TiO₂, FeO, and Al₂O₃, VTS features good thermal stability and adsorptivity, but a low recycling rate (less than 30%) [6]. Extensive stockpiling poses environmental risks. Utilizing this material to prepare explosion suppressants promotes the resource utilization of solid wastes, offering both environmental and economic benefits.

Regarding the preparation of explosion suppressants from solid wastes, most studies have focused on compounding two or more materials into composite suppressants. Wang et al. [7,8] prepared Ca(HPO₄)₂/RM composite powders with a core–shell structure to suppress aluminum dust explosions. The NaHCO₃ also developed high-efficiency powder suppressants by blending shell powder with active powders to further enhance the suppression of coal dust explosions. Wang et al. [9] reported the excellent performance of a diatomite composite powder in suppressing aluminum dust explosions. These studies have provided valuable inspirations on solid waste utilization and dust control. Regarding the preparation of explosion suppressants from solid wastes, most studies have focused on compounding two or more materials into composite suppressants. Wang et al. [7,8] prepared Ca(HPO₄)₂/RM composite powders with a core–shell structure to suppress aluminum dust explosions. They also developed high-efficiency powder suppressants by blending the shell powder with active powders to further enhance the suppression of coal dust explosions. Wang et al. [9] reported the excellent performance of a diatomite–NaHCO₃ composite powder in suppressing aluminum dust explosions. These studies have provided valuable inspirations in solid waste utilization and dust control. However, most of the existing studies have focused on red mud, diatomaceous earth and other carriers, and the study of vanadium–titanium slag (VTS) as an inhibitor carrier has not been reported. In particular, the key scientific question is whether the unique chemical composition of VTS (including FeO, Al₂O₃, etc.) can produce synergistic effects with active inhibitory components (such as NaHCO₃) after modification, so as to effectively inhibit PAN dust explosion. Considering the widespread presence of PAN dust in the chemical fiber industry and its high explosion risk, exploring an efficient and low-cost inhibitor based on VTS has both academic value and practical significance.

In recent years, composite powder suppressants have drawn increasing attention from researchers [10,11,12]. However, no study has been reported on the suppression performance of VTS-based composite suppressants on PAN dust explosions. In this study, a MVTS–NaHCO₃ composite powder explosion suppressant was prepared using modified VTS as the carrier and loading it with NaHCO₃ via the wet coating method of solution–crystallization (WCSC), involving carrier pretreatment, NaHCO₃ solution preparation, solution–crystallization loading, filtration and drying, and post-treatment. The effect and suppression mechanism of MVTS–NaHCO₃ powder with different mass fractions on PAN dust explosions were systematically investigated in a 20 L spherical explosion vessel and a transparent pipeline system. The findings provide a useful reference for VTS utilization and industrial dust control. The research results aim to open up new paths for the high-value-added utilization of VTS and to provide theoretical support and technical references for the prevention and control of industrial dust explosions.

2. Materials and Methods

2.1. Preparation and Testing of the Composite Powder Explosion Suppressant

The VTS sample was sourced from Pangang Group Vanadium Titanium Resources Co., Ltd. According to the X-ray fluorescence (XRF) analysis result, as summarized in

Table 1. Chemical composition of raw VTS determined by XRF analysis.

Sample	TiO2	FeO	Fe2O3	Al2O3	SiO2	CaO	MgO	V2O5
Slag	28.3	10.1	20.5	17.2	8.5	4.1	2.8	1.2

, the main constituents included TiO₂, FeO, Fe₂O₃, Al₂O₃, SiO₂, CaO, MgO, and V₂O₅.

Metal oxides were converted into metal hydroxides via an acid–base treatment method—metal hydroxides and metal ions possess explosion suppression activity. This was achieved by the following procedure: (1) carrier pretreatment—grind VTS to particle size ≤ 100 μm and remove impurities by magnetic or flotation separation to improve purity; (2) acid dissolution—add the pretreated VTS powder into 1–3 mol/L hydrochloric or sulfuric acid solution (solid-to-liquid ratio 1:5), and stir at 70 °C for 2 h to dissolve metal oxides (e.g., FeO, Al₂O₃, TiO₂) into metal ion solutions.

Example reactions:

$$\mathrm{FeO} + 2\mathrm{HCl} \to {\mathrm{FeCl}}_2+ {\mathrm{H}}_2\mathrm{O}$$

(1)

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

(2)

TiO₂ + 2H₂SO₄ → Ti(SO₄)₂ + 2H₂O

(3)

(3) Filtration to remove impurities—separate undissolved residues (e.g., SiO₂) by pressure filtration or centrifugation. Add hydrogen peroxide (H₂O₂) to the filtrate to oxidize Fe²⁺ to Fe³⁺ for subsequent precipitation control; (4) alkaline neutralization precipitation—while stirring, add 2–4 mol/L ammonia water (NH₃·H₂O) to adjust the pH to 8 and maintain at 70 °C to precipitate metal ions as hydroxides.

Example reactions:

Fe³⁺ + 3OH⁻ → Fe(OH)₃↓

(4)

Ti⁴⁺ + 4OH⁻ → Ti(OH)₄↓ (or dehydrated to TiO(OH)₂)

(5)

(5) Filtration and washing—separate hydroxide precipitates by vacuum or pressure filtration and wash repeatedly with deionized water until the filtrate becomes neutral to remove residual Cl⁻ or SO₄²⁻; and (6) dry the wet filter cake at 105 °C to constant weight to yield modified vanadium–titanium slag (MVTS).

2.2. Preparation of the Composite Powder Explosion Suppressant

According to the literature [13,14,15], materials are generally compounded either by reverse osmosis or mechanical means. In this study, the WCSC process was employed to prepare slag-based composite powder explosion suppressants (Figure 1). This involved the following procedure: (1) carrier pretreatment—grind MVTS to particle size ≤ 50 μ and ultrasonically disperse MVTS powder into deionized water to form a 10–20 wt% suspension; (2) NaHCO₃ solution preparation—weigh a certain amount of analytical pure NaHCO₃ (purity ≥ 99%) and dissolve it in deionized water to form a 0.5–1.0 mol/L solution, then add 0.2 wt% surfactant sodium dodecyl sulfate into the solution; (3) solution–crystallization loading—Step 1: mix MVTS suspension with NaHCO₃ solution at a mass fraction of 1:3 and stir magnetically at 30–50 °C for 30 min to achieve full contact between the carrier and solute; Step 2: slowly add precipitant anhydrous ethanol at a volume ratio of 1:2 to initiate NaHCO₃ oversaturation and precipitation; Step 3: stir for another 1–2 h so that NaHCO₃ crystals are uniformly loaded over the surface of MVTS to form a composite powder with a core–shell structure; (4) filtration and drying—separate composite powder by vacuum or pressure filtration, wash alternately with deionized water and ethanol three times to remove residual impurities, dry the wet filter cake in an oven at 60–80 °C for 12 h; (5) post-treatment—the dried powder was calcined at 100–150 °C for 1 h. At this temperature, the loaded NaHCO₃ undergoes thermal decomposition into Na₂CO₃, accompanied by the release of CO₂ and H₂O. The resulting Na₂CO₃ may interact with the surface hydroxyl groups of MVTS, forming the final MVTS-Na₂CO₃ composite powder. For consistency in terminology throughout this paper, we continue to refer to this product as the “MVTS-NaHCO₃ composite powder,” with the understanding that the active component exists primarily as Na₂CO₃ after calcination. (Note: The calcination step (100–150 °C) during preparation likely causes partial or complete decomposition of NaHCO₃ to Na₂CO₃. Thus, the term “MVTS-NaHCO₃ composite powder” in this paper refers to the inhibitor prepared using NaHCO₃ as a precursor, with the actual active component possibly being Na₂CO₃.)

2.3. Microstructural Analysis of MVTS–NaHCO₃ Composite Powder Explosion Suppressant

As illustrated in Figure 2, the prepared MVTS–NaHCO₃ composite powder exhibited a particle size of approximately 20 μm. Compared with raw MVTS, the MVTS–NaHCO₃ composite powder prepared by the WCSC process was more adequately coated, with NaHCO₃ filling up MVTS pores.

As illustrated in Figure 3, the nitrogen adsorption–desorption isotherm of raw MVTS corresponded to a type IV–H2(a) hysteresis loop under the IUPAC classification, indicating a uniform mesoporous structure. The isotherm of MVTS–NaHCO₃ composite powder, in contrast, corresponded to a type III profile, suggesting a nonporous material.

As shown in

Table 2. Specific surface area and pore volume of MVTS and MVTS–NaHCO₃ composite powder.

Sample	Specific Area (m2/g)	Pore Capacity (cm3/g)
MVTS	567.6	0.417
MVTS–NaHCO3 composite powder explosion suppressant	68.4	0.198

Note: Data are presented as mean ± standard deviation (SD) from three replicate measurements.

, after NaHCO₃ loading, the specific surface area and pore volume of MVTS–NaHCO₃ composite powder reduced significantly compared with raw MVTS.

2.4. Explosion Suppression Experiment of MVTS-NaHCO₃ Composite Powder

Polyacrylonitrile (PAN) is an important precursor polymer for acrylic fiber production. Its molecular formula is (C₃H₃N)_n, formed via free-radical polymerization of acrylonitrile monomers, with acrylonitrile units connected in a head-to-tail configuration in the macromolecular chain.

PAN appears as a white powder with a density of 1.14–1.15 g/cm³, softening and decomposing at 220–300 °C. In this study, high-purity PAN dust with a molecular weight of 150,000 was used for experiments. The powder particles were 2–30 μm in size, as illustrated in Figure 4, and spherical in shape, with rough, cracked surfaces, as illustrated in Figure 5.

Following the Chinese national standard GB/T16425, a 20 L spherical explosion vessel was used for explosion suppression characterization. As illustrated in Figure 6, this test apparatus comprised a main spherical chamber, a control system, and a data acquisition system. A dust dispersion device was installed at the bottom of the vessel and connected to a dust storage chamber via a pipeline equipped with a solenoid valve. The compressed air reservoir had a capacity of 0.6 L. The explosion pressure was collected by a piezoelectric pressure sensor installed on the container wall, with a measurement range of 0–2 MPa and a sampling frequency set at 10 kHz. The data were transmitted to a computer via a data acquisition card. Throughout the experiment, a 10 kJ chemical igniter connected to the ignition wires was used, with two firing wires connected to the ignition electrode. Prior to the experiment, a 10 kJ igniter was installed and the vessel was sealed. The dust mixture was placed in the chamber and vacuumed to 0.06 MPa; the dispersion pressure was set to 2.0 MPa. After the solenoid valve was started, the dust mixture was injected into the explosion chamber. Ignition was initiated after a delay time of 60 ms.

Experiments began with the baseline PAN dust concentration of 500 g/m³ (maximum explosibility). The 10 g PAN was mixed with MVTS, MVTS–NaHCO₃, and NaHCO₃ at the mass fractions shown in

Table 3. Mass fractions and experimental parameters for PAN dust explosion tests in the 20 L spherical vessel.

Mass Fraction	Mass/g
	PNA	MVTS–NaHCO3	MVTS	NaHCO3
0	10.0	0	0	0
10%	10.0	1.0	1.0	1.0
20%	10.0	2.0	2.0	2.0
30%	10.0	3.0	3.0	3.0
40%	10.0	4.0	4.0	4.0
50%	10.0	5.0	5.0	5.0
60%	10.0	6.0	6.0	6.0
70%	10.0	7.0	7.0	7.0
80%	10.0	8.0	8.0	8.0
90%	10.0	9.0	9.0	9.0
100%	10.0	10.0	10.0	10.0

Note: Mass fraction is defined as the mass percentage of the inhibitor, relative to the PAN dust (i.e., [mass of inhibitor/mass of PAN] × 100%). The PAN dust mass was kept constant at 10.0 g for all tests, corresponding to a nominal dust concentration of 500 g/m³. For each mass fraction, tests were conducted with the MVTS-NaHCO₃ composite powder, MVTS and pure NaHCO₃ separately, as indicated in the table.

. Each test was repeated three times. The maximum explosion pressure (Pmax) and maximum rate of pressure rise ((dP/dt)max) were analyzed.

A transparent pipeline test system was used for explosion propagation characterization, as illustrated in Figure 7. The pipeline measured 0.15 m in diameter and 3 m in total length (six sections, each 0.5 m), consisting of injection, ignition, and data acquisition functions. The process of flame propagation during an explosion inside a transparent tube was recorded using a high-speed camera (Phantom V711, Vision Research, Wayne, NJ, USA), with the frame rate set to 2000 fps and an image resolution of 1024 × 512 pixels. Five piezoelectric pressure sensors (model: PCB 113B24, USA) were evenly installed along the tube axis to measure pressure variations during the blast wave propagation. The sensors had a range of 0–1 MPa and a sampling frequency of 50 kHz. The ignition system used a 20 J electric spark igniter with an electrode gap of 3 mm, and the ignition delay time was set to 20 ms, according to

Table 4. Mass fractions and experimental parameters for PAN dust explosion propagation tests in the transparent pipeline system.

Mass Fraction	Mass/g
	PNA	MVTS–NaHCO3	MVTS	NaHCO3
0	9.0	0	0	0
10%	9.0	0.9	0.9	0.9
20%	9.0	1.8	1.8	1.8
30%	9.0	2.7	2.7	2.7
40%	9.0	3.6	3.6	3.6
50%	9.0	4.5	4.5	4.5
60%	9.0	5.4	5.4	5.4
70%	9.0	6.3	6.3	6.3
80%	9.0	7.2	7.2	7.2
90%	9.0	8.1	8.1	8.1
100%	9.0	9.0	9.0	9.0

Note: Mass fraction is defined as the mass percentage of inhibitor, relative to the PAN dust. The ignition delay time was optimized for each test to ensure proper dust dispersion.

. Prior to the experiment, the powder was placed in the chamber and charged with compressed air to 1 MPa. The ignition energy was set to E = 20 J and the delay time to t = 25 m. After the test system started, dust was uniformly injected into the pipeline from the dust chamber by compressed air and ignited after the set delay time.

PAN was mixed with MVTS, MVTS–NaHCO₃, and NaHCO₃ at the mass fractions and experimental parameters shown in Table 4. Each test was repeated three times. The maximum flame length was analyzed.

3. Result and Discussion

3.1. Suppression of PAN Dust Explosion Pressure in a Confined 20 L Vessel

MVTS, NaHCO₃, and MVTS–NaHCO₃ composite powder were experimentally used to suppress the PAN dust explosion. Each suppressant was mixed at the set mass fractions, ground, and sieved to <75 μm before it was tested at a temperature of 27 °C, a humidity of 67%, and an atmospheric pressure of 99.1 kPa.

As illustrated in Figure 8, when the mass fraction of MVTS–NaHCO₃ composite powder reached 30%, the explosion of PAN dust was significantly suppressed, with the maximum explosion pressure reduced by 53.2% compared to pure PAN. A mass fraction of 30% achieved higher maximum pressure reduction (53.2%) than NaHCO₃ (50.6%) and MVTS (47.8%). Among the three suppressants, the explosion suppression performance followed this order: MVTS–NaHCO₃ composite powder > NaHCO₃ > MVTS.

3.2. Suppression of PAN Dust Explosion Propagation in a Semi-Open Pipeline

Explosion suppression tests were conducted in a transparent pipeline system by mixing PAN with each of the three suppressants. The maximum pressures from each sensor were plotted into discrete curves, as illustrated in Figure 9.

After PAN was ignited, a large amount of products were generated, forming a pressure wave. Pressure reached the maximum of 0.46 MPa at 0.2 m (sensor 1). As the explosion propagated, the pressure dropped to 0.13 MPa at 2.2 m (sensor 5). Adding suppressants reduced both the combustion speed and the participating mass, leading to a reduction in pipeline pressure. Data showed that 40% MVTS–NaHCO₃ composite powder reduced the maximum pressure to 0.08 MPa (reduction rate 82.6%); complete suppression was achieved at 50%.

Using images obtained from a high-speed camera, we analyzed the longest continuous flame during the explosion process [16]. As shown in Figure 10, before adding the MVTS-NaHCO₃ composite powder flame suppressant, the flame of the pure PAN dust explosion was the longest and fullest, with a continuous flame contour, indicating that the combustion was vigorous and complete. After adding the flame suppressant, the flame height and propagation speed were significantly reduced, the volume noticeably decreased, and the continuity and integrity of the flame were disrupted, indicating that the combustion reaction was locally interrupted and the stability of flame propagation decreased.

3.3. Analysis of Gaseous and Solid Explosion Products

To characterize the generation of explosion reactants, the gas and solid products from explosion suppression tests in the 20 L spherical test apparatus were analyzed [17]. To characterize the formation features of explosive reactants, the gaseous and solid products generated during explosion suppression tests in a 20 L spherical test device were analyzed. After each explosion test, the sphere’s vent valve was quickly opened within 30 s (or your actual time), and the mixed gases produced by the explosion were drawn into aluminum foil composite film gas sampling bags (specifications: 1 L, Dalian Haide Technology Co., Ltd., Dalian, China) through a PTFE tube connected to the sampling port, using a vacuum sampling pump. Before sampling, the gas sampling bags were flushed three times with high-purity nitrogen and evacuated to avoid contamination from residual gases. The collected gas samples were sent to the analysis and testing center within 24 h. The gas components were qualitatively and quantitatively analyzed, using a gas chromatograph–mass spectrometer (GC-MS-QP2010 Ultra, Shimadzu, Japan). After the explosion test, once the sphere cooled to room temperature, it was opened, and the solid residues deposited on the inner wall and bottom of the container were carefully collected using a stainless steel scraper. The collected solid samples were ground in an agate mortar until they could pass through a 200-mesh sieve (<75 μm), mixed evenly, and then sealed and stored in a desiccator for testing. The chemical composition of the solid residues was analyzed using an X-ray fluorescence spectrometer (EDX 4500H, Tianrui Instruments, China). The analysis results are summarized in

Table 5. Composition of gaseous and solid products generated from PAN dust explosion with and without MVTS–NaHCO₃ composite powder.

GCMS analysis	Sample	Relative Content
		CO2	NO2	CO	SO2
	100% PAN	63.5	7.2	8.4	0.23
	20% MVTS–NaHCO3 + PAN	78.7	1.4	8.58	0.11
XRF analysis		SiO2	Fe2O3	Al2O3	CaO	Na2O	TiO2	MgO	MnO
	20% MVTS–NaHCO3 + PAN (pre–combustion)	66.5	16.1	10.4	3.82	1.56	1.47	0.09	0.08
	20%MVTS–NaHCO3+PAN (post-combustion)	66.5	17.3	13.4	1.35	1.31	1.5	0.01	0.05

.

The analysis results are summarized in Table 5.

Gas chromatography–mass spectrometry (GC–MS) analysis indicated that for PAN and its mixtures with suppressants, the main gases from explosion are CO₂, NO₂, CO, and SO₂. Adding 20% MVTS–NaHCO₃ increased the relative contents of CO₂ and CO by 5.2% and 2.2%, respectively. This occurred because adding suppressants reduces PAN reactions and inhibits combustion. The suppression of complete oxidation and the reduction in flame temperature promote incomplete combustion pathways, resulting in an increased proportion of CO while maintaining CO₂ as the dominant gaseous product.

$${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{\mathrm{m}}+2{\mathrm{O}}_2\underset{\mathrm{Underreaction}}{\to }{\mathrm{C}}_{\mathrm{n}-2}{\mathrm{H}}_{\mathrm{m}-2}+\mathrm{CO}\uparrow +\mathrm{C}{\mathrm{O}}_2\uparrow +{\mathrm{H}}_2\mathrm{O}$$

(6)

Also, as NaHCO₃ in the suppressant generates CO₂ in an explosion environment, the increase in CO₂ content in the explosion products was modest.

$$2{\mathrm{NaHCO}}_3\underset{\mathrm{Pyrolysis}}{\to }\mathrm{N}{\mathrm{a}}_2\mathrm{C}{\mathrm{O}}_3+{ \mathrm{H}}_2\mathrm{O}\uparrow +\mathrm{C}{\mathrm{O}}_2\uparrow$$

(7)

XRF analysis of solid products indicated that adding 20% MVTS–NaHCO₃ composite powder slightly increased Fe₂O₃ and Al₂O₃. This occurred because metal hydroxides like Fe₂O₃ and Al₂O₃ were endothermically decomposed to generate corresponding oxides, contributing to the observed increase in Fe₂O₃ and Al₂O₃ content.

Microstructural analysis revealed the synergistic effects of physical and chemical mechanisms in the composite powder. Physically, NaHCO₃ absorbs approximately 100 kJ/mol of the heat, releasing CO₂ and H₂O and diluting the oxygen concentration to reduce flammability. The porous structure of MVTS also enhances dispersibility. Chemically, hydroxyl groups bond with NaHCO₃ to delay its decomposition. Metal hydroxides like Al(OH)₃ thermally decompose to generate Al₂O₃, which adsorbs and quenches key free radicals in chain reactions such as OH· and H·, inhibiting their generation and propagation, thus interrupting the combustion chain reaction and inhibiting explosion.

3.4. Suppression Mechanism of MVTS–NaHCO₃ Composite Powder on PAN Dust Explosion

As illustrated in Figure 11, MVTS–NaHCO₃ composite powder exerts synergistic physical and chemical suppression effects on PAN dust explosion.

Physical suppression involves three aspects. ① Physical coating: The energy wave generated by PAN dust under external energy causes the composite powder to break. Broken particles coat the surface of the combustible dust, reducing and isolating external heat and oxygen. Additionally, Al₂O₃, Fe₂O₃, and SiO₂ also adhere to the surface of dust particles involved in explosion, adding to the coating effect. ② Physical heat absorption: NaHCO₃, Al (OH)₃, and Fe (OH)₃ absorb the heat generated during the explosion. NaHCO₃ decomposes endothermically to generate CO₂ and H₂O, with the latter absorbing heat to become steam, and Al (OH)₃ and Fe (OH)₃ thermally decompose into corresponding oxides Al₂O₃ and Fe₂O₃, effectively lowering the ambient temperature. ③ Gas inserting: CO₂ generated by NaHCO₃ thermal decomposition occupies part of the explosion space. Gasified steam competes with oxygen for space in a confined environment, reducing the oxygen concentration in the explosion environment.

Chemical suppression involves the following reactions. Upon entry into the combustion explosion flame zone, NaHCO₃, Al(HO)₃, and Fe(HO)₃ solid particles undergo homogeneous and heterogeneous chemical reactions, including multiple chain reactions with free radicals participating in combustion chain reactions. These reactions consume key free radicals H· and OH· that sustain combustion chain reactions and reduce exothermic reactions between free radicals and O·, thus inhibiting combustion reactions.

4. Conclusions

This study focuses on the prevention and control of polyacrylonitrile (PAN) dust explosions and the challenge of reutilizing industrial solid waste vanadium–titanium slag (VTS). It aims to develop an efficient composite powder explosion suppressant based on modified VTS, and to elucidate its mechanism for inhibiting PAN dust explosions. Using the wet solution–crystallization coating (WCSC) method, sodium bicarbonate (NaHCO₃) was loaded onto modified vanadium–titanium slag (MVTS) as a carrier to prepare the MVTS-NaHCO₃ composite powder. Through a 20 L spherical explosive device and a transparent pipeline explosion propagation test system, the system evaluated the suppression performance of compound powders with different mass fractions on PAN dust explosion pressure and flame propagation, and the explosion products were analyzed using GC-MS and XRF. The research results indicate the following:

(1)

MVTS-NaHCO₃ composite powder has a significant inhibitory effect on PAN dust explosions. In a 20 L closed container, adding 30% of the composite powder can achieve effective suppression, reducing the maximum explosion pressure by 53.2%. In a semi-open transparent pipeline, adding 50% of the composite powder achieves complete suppression, and a 40% addition can reduce the maximum explosion pressure by 82.6%.

(2)

The porous structure of MVTS enhances the dispersion of the inhibitor, while the endothermic decomposition of NaHCO₃ (100 kJ/mol) releases CO₂ and H₂O, diluting the oxygen concentration.

(3)

In terms of chemical inhibition mechanisms, the hydroxyl groups on the surface of MVTS combine with NaHCO₃ to slow its decomposition, while the thermal decomposition of metal hydroxides such as Al(OH)₃ produces Al₂O₃, which can effectively adsorb and quench key radicals (such as ·OH and ·H) in the combustion chain reaction, interrupting the propagation of the reaction.

In summary, this study successfully demonstrated the feasibility of using industrial solid waste VTS to prepare an efficient composite explosion suppressant, achieving the dual objectives of “solid waste resource utilization” and “dust explosion prevention.” The MVTS-NaHCO₃ composite powder exhibited superior suppression performance compared to single components through a synergistic mechanism of physical heat absorption, gas-phase dilution, and chemical radical quenching. The results provide a theoretical basis and technical reference for the high-value utilization of VTS and the prevention and control of industrial dust explosions. Further research can explore the applicability of this composite powder in other combustible dusts, such as coal dust and aluminum powder.