Selective Oxidation Control for Synchronous Vanadium Extraction and Chromium Retention from Vanadium- and Chromium-Bearing Hot Metal

Abstract

To address the technical challenges involved in the resource utilization of hot metal containing high levels of vanadium (V: 2–5%) and chromium (Cr: 1–5%), this study proposes a novel method based on pyrometallurgical selective oxidation for simultaneously extracting vanadium and retaining chromium. Through thermodynamic analysis and high-temperature smelting experiments, the competitive oxidation behaviors of carbon, vanadium, and chromium were revealed, and the synergistic control mechanism of temperature and oxygen partial pressure was clarified. The results indicate that within a temperature range of 1693–1753 K, adjusted over 1 h, vanadium preferentially oxidizes over carbon and chromium, while carbon effectively suppresses chromium oxidation. By optimizing ω(FeO) (10.0–15.7%), we achieved a vanadium oxidation efficiency (η_V) of 72.5–82.2% and maintained a chromium retention efficiency (100−η_Cr) exceeding 57.1%. Compared to traditional methods, which rely on high-oxygen blowing (oxygen supply: 43–195 kg/tFe), multi-stage roasting, and hydrometallurgical refining, this approach eliminates roasting and hydrometallurgical steps (such as sodium/calcium roasting and the associated leaching–precipitation units), shortens the process chain, reduces oxygen consumption (>80 kg/tFe), and lowers environmental risks (Cr oxidation reduced > 40%). This study establishes a theoretical framework for achieving sustainable V/Cr separation, enhancing resource efficiency and minimizing pollution (e.g., Cr(VI)-containing wastewater, high-salinity NH₄⁺/Na⁺ wastewater).

1. Introduction

Vanadium- and chromium-bearing hot metal is a product generated from the reduction and smelting of vanadium-extracted chromium-containing residues. Typically, its vanadium (V) content ranges from 2 to 5 mass%, while its chromium (Cr) content ranges from 1 to 5 mass% [1,2,3,4]. In this manuscript, ω denotes mass fraction, and all percentage compositions for elements and compounds are given in mass% unless otherwise specified. Due to the high contents of V and Cr, there is still no effective way of achieving resource utilization. The traditional V and Cr separation process involves oxidative enrichment, roasting, pretreatment, and wet separation. Although this process is highly industrialized, it can only be applied to hot metal with low vanadium and chromium contents (V: 0.15–0.35%, Cr: 0.2–0.6%) [4,5,6]. However, the availability of relevant research and experimental data remains severely limited for high-vanadium and high-chromium hot metal (V > 2%, Cr > 1%), and the applicability of traditional processes in this context has yet to be fully validated. Furthermore, traditional processes are characterized by long flowsheets, with a progressive decrease in metal recovery rates at each stage. Consequently, the overall recovery rate of vanadium and chromium from hot metal to final products typically reaches only 60–80% [6,7]. During converter oxidation, the high oxygen potential leads to excessive chromium oxidation (Cr₂O₃ accounts for 5–10% of the slag phase) [8,9,10], significantly reducing the efficiency of chromium recovery. During the roasting step, sodium roasting produces high-salt wastewater containing Na⁺ (5–10 g/L) and NH₄⁺ (2–3 g/L) [8,11,12], as well as toxic wastewater containing Cr(VI) (0.5–1.2 kg/t) [13,14]. Calcium roasting generates a by-product of CaSO₄ slag containing 12–15% sulfur [15,16,17], which is difficult to utilize as a resource. Moreover, the roasting process consumes 10–15% of the slag weight in Na₂CO₃ or CaCO₃ [18], with energy consumption reaching 200–300 kWh/t of slag [11,19], significantly increasing costs. Additionally, the subsequent hydrometallurgical leaching–precipitation process is time-consuming (12–16 h), achieving vanadium leaching rates of only 33–85%, leaving a portion of vanadium in the slag [16,20]. Therefore, traditional processes exhibit significant shortcomings regarding economic efficiency and environmental sustainability.

To address these issues, this study proposes a novel and efficient method for separating vanadium and chromium based on pyrometallurgical selective oxidation. This method targets high-vanadium and high-chromium hot metal (V: 2–5%, Cr: 1–5%), achieving vanadium–chromium separation during the converter oxidation stage via the selective oxidation of vanadium to slag, while retaining chromium in the hot metal (as shown in Figure 1). Thus, the subsequent roasting and wet processing processes are completely eliminated. This method provides a new technical path for the resource utilization of high-vanadium and high-chromium hot metal, as well as for reducing the production cost and environmental pollution. To achieve these objectives, this study combines thermodynamic calculations with experimental verification. The analysis, based on the intersections of their standard Gibbs free energy of oxidation values, proposed a fundamental thermodynamic window (1517–1704 K) and chemical potentials for selective oxidation. Based on these findings, high-temperature smelting experiments were designed to investigate the effects of temperature and oxygen chemical potential on vanadium–chromium separation efficiency. The results demonstrate that this method maximizes vanadium oxidation while significantly reducing chromium oxidation. This study not only overcomes the technical bottleneck of selective oxidation in pyrometallurgical separation but also provides theoretical and practical guidance for developing efficient and environmentally friendly metallurgical processes.

2. Thermodynamic Analysis for Oxidative Vanadium Extraction and Chromium Retention in Hot Metal

2.1. Optimal Temperature Control Strategy

Under standard conditions (1 atm pressure and pure substances in their standard state), the oxidation reactions of vanadium, chromium, and carbon in vanadium- and chromium-bearing hot metal can be described by the below reaction equations. Their corresponding Gibbs free energy changes (${\mathsf{\Delta }G}^{ѳ}$), denoting the standard Gibbs free energy of formation for the respective oxides [21], are also shown:

$$2[\mathrm{O}]+{\displaystyle \frac{4}{3}}[\mathrm{V}]={\displaystyle \frac{2}{3}}{\mathrm{V}}_2{\mathrm{O}}_3\left(\mathrm{s}\right) \mathsf{\Delta }{G}_1^{ѳ}=-541.57+0.21T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(1)

$$2[\mathrm{O}]+{\displaystyle \frac{4}{3}}[\mathrm{Cr}]={\displaystyle \frac{2}{3}}{\mathrm{Cr}}_2{\mathrm{O}}_3\left(\mathrm{s}\right) \mathsf{\Delta }{G}_2^{ѳ}=-463.03+0.20T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(2)

$$2[\mathrm{O}]+2[\mathrm{C}]=2\mathrm{CO}(\mathrm{g}) \mathsf{\Delta }{G}_3^{ѳ}=30.70-0.12T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(3)

where $\mathsf{\Delta }{G}_{\mathrm{i}}^{ѳ}$ denotes the standard Gibbs free energy change for reaction (i) (kJ/mol); i denotes the index of the chemical reaction, with T being the reaction temperature (K); and the element symbol enclosed in [ ] denotes the element dissolved in the hot metal.

The temperature-dependent ${\mathsf{\Delta }G}^{ѳ}$ of these reactions are plotted in Figure 2, where the oxidation curve of carbon intersects with those of chromium and vanadium at points A (1517 K) and B (1704 K), respectively. By drawing vertical lines at these intersection points parallel to the Y-axis, the temperature domain is divided into three distinct regions: I (T < 1517 K), II (1517 K < T < 1704 K), and III (T > 1704 K).

• Region I (T < 1517 K):

Oxidation priority follows [V] > [Cr] > [C]. However, the minimal separation between the vanadium and chromium oxidation curves (${\mathsf{\Delta }G}^{ѳ}$ = 57.9–64.1 kJ/mol) leads to the simultaneous oxidation of chromium during vanadium extraction, resulting in suboptimal chromium retention.

• Region II (1517 K < T < 1704 K):

The oxidation propensity of carbon is intermediate between those of vanadium and chromium, thereby allowing it to function as a redox mediator that promotes vanadium extraction while preserving chromium in the metallic phase. The carbon-mediated reactions involved in this process are given by Equations (4) and (5). For the system to achieve concurrent vanadium extraction and chromium retention, both reactions must proceed spontaneously in the forward direction. This dual role is essential for selectively extracting of vanadium while maintaining chromium in the metallic state.

$${\displaystyle \frac{2}{3}}{\mathrm{Cr}}_2{\mathrm{O}}_3(\mathrm{s})+2[\mathrm{C}]={\displaystyle \frac{4}{3}}\left[\mathrm{Cr}\right]+2\mathrm{CO}(\mathrm{g}) \mathsf{\Delta }{G}_4^{ѳ}=493.73-0.32T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(4)

$${\displaystyle \frac{4}{3}}\left[\mathrm{V}\right]+2\mathrm{CO}(\mathrm{g})={\displaystyle \frac{2}{3}}{\mathrm{V}}_2{\mathrm{O}}_3(\mathrm{s})+2[\mathrm{C}] \mathsf{\Delta }{G}_5^{ѳ}=-572.27+0.33T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(5)

• Region III (T > 1704 K):

Oxidation priority reverses to [C] > [V] > [Cr], where premature carbon oxidation depletes oxygen availability, severely limiting vanadium extraction efficiency.

While all three regimes satisfy the basic requirement of [V] > [Cr] oxidation priority, Regime II (1517–1704 K) uniquely balances vanadium extraction efficiency and chromium retention. The intermediate temperature range ensures the following: (1) Maximized vanadium oxidation—the dominance of $\mathsf{\Delta }{G}_1^{ѳ}$ over $\mathsf{\Delta }{G}_3^{ѳ}$ maintains thermodynamic favorability for vanadium extraction. (2) Effective chromium protection—carbon acts as a sacrificial agent, oxidizing before chromium and reducing oxygen activity in the melt.

2.2. Oxygen Partial Pressure Control

The typical chemical composition of vanadium–chromium-containing hot metal obtained through the reduction of vanadium-extracted residues is shown in

Table 1. The typical composition of vanadium–chromium-containing hot metal/mass%.

Element	C	Si	Mn	Cr	V
Content	4.0	0.5	0.5	3.8	3.6

. The chemical compositions were determined using X-ray fluorescence (XRF) spectroscopy (model ZSX Primus II, Rigaku, Tokyo, Japan). Specifically, the Cr, V, and C contents are 3.8%, 3.6%, and 4.0%, respectively, along with trace amounts of Si and Mn.

The oxygen partial pressure required to achieve equilibrium for vanadium extraction while preserving chromium in the hot metal of this composition is calculated using the below equation. The reaction for oxygen dissolution in hot metal and its corresponding Gibbs free energy change is expressed as [22]

$${\mathrm{O}}_2=2[\mathrm{O}] \mathsf{\Delta }{G}_6^{ѳ}=-234.3-0.00578T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(6)

By linearly combining Equations (1) and (2) with Equation (6), the following equilibrium reactions and their Gibbs free energy changes are obtained:

$${\mathrm{O}}_2(\mathrm{g})+{\displaystyle \frac{4}{3}}[\mathrm{V}]={\displaystyle \frac{2}{3}}{\mathrm{V}}_2{\mathrm{O}}_3(\mathrm{s}) \mathsf{\Delta }{G}_7^{ѳ}=-775.87+0.21T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(7)

$${\mathrm{O}}_2(\mathrm{g})+{\displaystyle \frac{4}{3}}\left[\mathrm{Cr}\right]={\displaystyle \frac{2}{3}}{\mathrm{Cr}}_2{\mathrm{O}}_3(\mathrm{s}) \mathsf{\Delta }{G}_8^{ѳ}=-697.33+0.20T (\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l})$$

(8)

Considering only the interaction of C, V, and Cr, the interaction coefficients of C-Cr, Cr-Cr, C-V, and V-V, based on the Wagner’s formalism for dilute solutions, are shown in

Table 2. The interaction coefficients of C-Cr, Cr-Cr, C-V, and V-V.

${\mathit{e}}_{\mathbf{Cr}}^{\mathbf{C}}$	${\mathit{e}}_{\mathbf{Cr}}^{\mathbf{Cr}}$	${\mathit{e}}_{\mathbf{V}}^{\mathbf{C}}$	${\mathit{e}}_{\mathbf{V}}^{\mathbf{V}}$
−0.12	−0.0003	−0.16	0.015

.

Based on Equations (7) and (8), the oxygen partial pressure required to establish equilibrium between the slag phase and the hot metal with mass fractions ω[V] and ω[Cr] can be obtained as follows:

$${(\lg p_{{\mathrm{O}}_2})}_{\mathrm{v}}={\displaystyle \frac{2}{3}}\lg {\alpha }_{{\mathrm{V}}_2{\mathrm{O}}_3}+0.21\omega [\mathrm{C}]+0.02\omega [\mathrm{V}]-{\displaystyle \frac{4}{3}}\lg \omega [\mathrm{V}]-{\displaystyle \frac{\mathrm{40,521.30}}{T}}+10.75$$

(9)

$${(\lg p_{{\mathrm{O}}_2})}_{\mathrm{Cr}}={\displaystyle \frac{2}{3}}\lg {\alpha }_{{\mathrm{Cr}}_2{\mathrm{O}}_3}+0.16\omega \left[\mathrm{C}\right]+0.0004\omega [\mathrm{Cr}]-{\displaystyle \frac{4}{3}}\lg \omega [\mathrm{Cr}]-{\displaystyle \frac{\mathrm{36,419.33}}{T}}+10.19$$

(10)

In Equations (9) and (10), ${\alpha }_{{\mathrm{V}}_2{\mathrm{O}}_3}$ and ${\alpha }_{{\mathrm{Cr}}_2{\mathrm{O}}_3}$ represent the activities of V₂O₃ and Cr₂O₃ in the slag, respectively. ${\lg p}_{{\mathrm{O}}_2}$ denotes the equilibrium oxygen partial pressure, while ω[C], ω[V], and ω[Cr] correspond to the mass fractions of [C], [V], and [Cr], respectively.

Assuming that ${\alpha }_{{\mathrm{V}}_2{\mathrm{O}}_3}$ = 1 and ${\alpha }_{{\mathrm{Cr}}_2{\mathrm{O}}_3}$ = 1, the following equations are obtained when $\omega [\mathrm{C}]=4\%$:

$${(\lg p_{{\mathrm{O}}_2})}_{\mathrm{v}}=0.02\omega [\mathrm{V}]-{\displaystyle \frac{4}{3}}\lg \omega [\mathrm{V}]-{\displaystyle \frac{\mathrm{40,521.30}}{T}} + 11.59$$

(11)

$${(\lg p_{{\mathrm{O}}_2})}_{\mathrm{Cr}}=0.0004\omega [\mathrm{Cr}]-{\displaystyle \frac{4}{3}}\lg \omega [\mathrm{Cr}]-{\displaystyle \frac{\mathrm{36,419.33}}{T}}+10.83$$

(12)

It is important to note that in the actual slag system, vanadium and chromium predominantly form stable spinel solid solutions (e.g., (Fe, Mn) V₂O₄ and (Fe, Mg) Cr₂O₄). The assumption that ${\alpha }_{{\mathrm{V}}_2{\mathrm{O}}_3}$ = 1 and ${\alpha }_{{\mathrm{Cr}}_2{\mathrm{O}}_3}$ = 1 is a simplification made for this theoretical calculation. The formation of spinels lowers the activity of V₂O₃ and Cr₂O₃, meaning that the actual equilibrium oxygen partial pressures would be higher than those plotted here. However, this simplified model remains valid for establishing the relative thermodynamic priorities and the critical operational window for selective oxidation.

Taking $\lg p_{{\mathrm{O}}_2}$ as the vertical axis and ω[Cr] and ω[V] as the horizontal axes, Equations (11) and (12) are plotted in Figure 3.

As demonstrated in Figure 3, the equilibrium oxygen partial pressures for vanadium oxidation ($(\lg p_{{\mathrm{O}}_2})$_V) and chromium oxidation ($(\lg p_{{\mathrm{O}}_2})$_Cr) exhibit distinct dependencies on their respective solute concentrations (ω[V] and ω[Cr]) in the melt. Both $(\lg p_{{\mathrm{O}}_2})$_V and $(\lg p_{{\mathrm{O}}_2})$_Cr increase monotonically with decreasing ω[V] and ω[Cr], respectively. Notably, the rate of increase diverges significantly across concentration regimes: (1) At high solute concentrations (ω[V] > 1.0% and ω[Cr] > 1.0%), the oxygen partial pressures show gradual variations with composition. (2) Below the critical threshold of ω[V] < 1.0% or ω[Cr] < 1.0%, both $(\lg p_{{\mathrm{O}}_2})$_V and $(\lg p_{{\mathrm{O}}_2})$_Cr increase rapidly, indicating enhanced thermodynamic driving forces involved in oxidation at dilute concentrations.

Importantly, a consistent hierarchy of oxygen partial pressure is observed across all temperatures: $(\lg p_{{\mathrm{O}}_2})$_V < $(\lg p_{{\mathrm{O}}_2})$_Cr. This thermodynamic hierarchy establishes an optimal oxygen partial pressure window ($(\lg p_{{\mathrm{O}}_2})$_V < lg$p_{{\mathrm{O}}_2}$ < $(\lg p_{{\mathrm{O}}_2})$_Cr) for selective oxidation processes. Within this window, vanadium extraction can be prioritized while suppressing chromium loss, as exemplified by the 1723 K system: (1) The lower upper bound (${\lg p}_{{\mathrm{O}}_2}$ > −11.91) ensures that sufficient vanadium oxidation occurs when ω[V] < 1.0%. (2) The upper bound ($\lg p_{{\mathrm{O}}_2}$ < −10.94) prevents chromium oxidation at ω[Cr] > 3.0%. Setting 3.0% as the lower limit ensures that the oxygen partial pressure window remains sufficiently wide for experimental control. (3) The resultant operational window of −11.91 < $\lg p_{{\mathrm{O}}_2}$ < −10.94 demonstrates the feasibility of achieving concurrent vanadium extraction and chromium preservation through precise oxygen potential control.

In practical experiments, the oxygen partial pressure could be controlled by adjusting either the CO-CO₂ gas ratio in the furnace atmosphere or the FeO content in slag.

The thermodynamic calculations used in this study are based on the stability of V₂O₃ (s) rather than V₂O₅ (l). This approach is justified by the prevailing conditions of our process. Our process operates under conditions of low oxygen partial pressure. Under these weakly oxidizing conditions, vanadium predominantly exists in a trivalent state (V³⁺) as V₂O₃, which is a stable solid phase [23]. Forming pentavalent vanadium (V⁵⁺) in V₂O₅ requires a significantly higher oxygen potential, which is deliberately avoided in our selective oxidation strategy to prevent chromium oxidation. Therefore, considering V₂O₃ as the primary oxidation product is thermodynamically sound for our system.

3. Materials and Methods

3.1. Raw Materials

The initial melt was prepared using blast furnace (BF) powder, Ferrovanadium-50 (FeV50), and high-carbon Ferrochrome (HC FeCr), all supplied by Shanxi Taisteel Stainless Steel Co., Ltd. (Taiyuan, China).

Table 3. The chemical compositions of raw materials used for initial melt preparation/wt.%.

Materials	Fe	V	Cr	C	Si	Mn	S	P
BF iron powder	88.50			4.00	0.5	0.5	0.005	0.005
FeV50 powder	47.10	50.00		0.65	1.45	0.48	0.03	0.04
HC FeCr powder	42.50		49.53	7.45

summarizes the chemical compositions of these materials. The initial slag consisted of reagent-grade FeO, CaO, and SiO₂ powders (purity > 99%).

3.2. Experimental Apparatus

Experiments were conducted in a molybdenum-lined muffle resistance furnace (Model BFS-16, Beijing Fiame Temperature Technology Co., Ltd., Beijing, China) equipped with MoSi₂ heating elements. The furnace operates up to 1873 K with a temperature control accuracy of ±5 K (Figure 4).

3.3. Experimental Design

As discussed in Section 2.1, the optimal temperature range for vanadium extraction while preserving chromium under standard conditions is 1517–1704 K. However, the temperatures corresponding to points A and B in Figure 1 are typically higher than those recorded under standard conditions due to the influence of the hot metal composition. To ensure effective slag-metal separation during the experiments, the temperature range was set with a lower limit of 1633 K, an upper limit of 1753 K, and an interval of 30 K.

In this study, FeO was selected as the oxidizing agent. The required amount of FeO had two components: one for oxidizing Si, Mn, and V, and another as an additional component for maintaining the oxygen potential equilibrium necessary to balance residual V and Cr. Based on calculations, for 100 g of hot metal, the theoretical FeO consumption for oxidizing Si, Mn, and V is 10.9 g. The quantity of FeO required to maintain equilibrium for residual V and Cr is determined through the below equations.

The relationship between the solubility of oxygen in hot metal and temperature is expressed as [24]

$$\lg \omega [\mathrm{O}]=-{\displaystyle \frac{6320}{T}}+2.734+\lg \alpha (\mathrm{FeO})$$

(13)

where α(FeO) is the activity of FeO in the slag. ω[O] can be derived from the equilibrium constant for dissolving O₂ in hot metal, as shown in Equation (6). The equilibrium constant K₆ is expressed as

$$K_6={\displaystyle \frac{{{(p}_{{\mathrm{O}}_2})}^{\frac{1}{2}}}{\alpha [\mathrm{O}]}}$$

(14)

Since the dissolved oxygen in hot metal can be considered a dilute solution of [O], its activity relative to the 1% standard state was approximately equal to its mass percentage, i.e., α[O] = ω[O]. Substituting Equations (6) and (14) into Equation (13) yields

$$\lg \omega [\mathrm{O}]={\displaystyle \frac{1}{2}}\mathrm{l}\mathrm{g} p_{{\mathrm{O}}_2}+{\displaystyle \frac{\mathrm{117,150}+2.89T}{2.303\mathrm{R}T}}$$

(15)

Substituting Equation (15) into Equation (13) yields

$$\lg \alpha (\mathrm{FeO})={\displaystyle \frac{1}{2}}\mathrm{l}\mathrm{g}{ p}_{{\mathrm{O}}_2}+{\displaystyle \frac{\mathrm{117,150}+2.89T}{2.303\mathrm{R}T}}+{\displaystyle \frac{6320}{T}}-2.73$$

(16)

At a temperature of 1723 K and an oxygen partial pressure ${\lg p}_{{\mathrm{O}}_2}$ ranging from −11.91 atm to −10.94 atm (calculated in Section 2.2), α(FeO) was determined to be between 0.048 and 0.147 according to Equation (16). For simplicity, the final slag was assumed to behave as an ideal solution, with α(FeO) equal to its mole fraction. The final slag consisted of CaO, SiO₂, FeO, V₂O₃, and MnO with their molar quantities denoted as n(CaO), n(SiO₂), n(FeO), n(V₂O₃), and n(MnO), respectively. Thus, α(FeO) can be expressed as

$$\alpha (\mathrm{FeO})={\displaystyle \frac{n(\mathrm{FeO})}{n(\mathrm{CaO}) + n(\mathrm{Si}{\mathrm{O}}_2) + n(\mathrm{FeO}) + n({\mathrm{V}}_2{\mathrm{O}}_3) + n(\mathrm{MnO})}}$$

(17)

Considering a 100 g sample of vanadium–chromium-containing hot metal and 40 g of initial slag with a fixed basicity of (R₂: ω(CaO)/ω(SiO₂)) 1.8, n(FeO) was found via Equation (17) to range from 0.026 mol to 0.086 mol, corresponding to an FeO mass of approximately 2.23 g to 8.95 g, in turn corresponding to a ω(FeO) content in final slag of 5.6–17.0%. Incorporating FeO consumed during oxidation reactions, the total FeO requirement is estimated to be between 13.13 g and 19.85 g.

In this paper, a two-stage single-factor experimental design was adopted to systematically analyze the effects of temperature and FeO content on vanadium–chromium separation: (1) Temperature gradient experiment (Heat No. 1–5)—The fitting of ω(FeO) in final slag was 10.0%. We systematically varied the temperature from 1633 K to 1753 K at 30 K intervals. This design isolated temperature as the sole variable to determine the thermal window for optimal vanadium oxidation and chromium retention. (2) FeO content gradient experiment (Heat No. 6–9)—The fixed temperature identified at the optimal value in stage 1 (1723 K) and systematically varied in ω(FeO) in the final slag is 3.0–20.0%. This stage focuses on optimizing FeO dosage to achieve the desired oxygen potential for selective oxidation. Each experimental condition (Heat No. 1–9) was conducted in triplicate, resulting in 27 samples (9 heats × 3 replicates) for statistical reliability.

The experimental plan was designed as shown in

Table 4. The experimental scheme.

Heat No.	Design Stage	Temperature/K	ω(FeO) in Final Slag (Set Value), %	Initial Slag, g
				FeO	CaO	SiO2	R2
1	1 (Temp)	1633	10.0	14.9	19.8	9.9	1.8
2	1 (Temp)	1663	10.0	14.9	19.8	9.9
3	1 (Temp)	1693	10.0	14.9	19.8	9.9
4	1 (Temp)	1723	10.0	14.9	19.8	9.9
5	1 (Temp)	1753	10.0	14.9	19.8	9.9
6	2 (FeO)	1723	3.0	12.1	21.6	10.9
7	2 (FeO)	1723	5.0	12.9	21.0	10.6
8	2 (FeO)	1723	15.0	17.1	18.3	9.1
9	2 (FeO)	1723	20.0	19.1	17.1	8.4

. CaO and SiO₂ were added to improve the fluidity of the resultant slag. To reduce interactions with the corundum crucible, the slag’s basicity was set at 1.8. This promoted the creation of a protective layer of 2CaO·SiO₂ at the interface, minimizing Al₂O₃ dissolution [25,26]. The hot metal mass was fixed at 100 g, and its composition is detailed in Table 1.

3.4. Experimental Procedure

All raw materials were thoroughly mixed and loaded into a corundum crucible. Once the furnace reached the predetermined experimental temperature, the crucible containing the sample was then placed into the closed chamber of the molybdenum-lined muffle resistance furnace at the predetermined experimental temperature. The furnace was then shut, and the timing process started. This setup, while not actively purged, provided a confined environment that minimized extensive air exchange. After being held at the target temperature for 1 h, the crucible was removed and cooled to room temperature. Then, the crucible walls were visually inspected after the experiment and showed no significant signs of corrosion or slag penetration. The crucible was then carefully broken using a chisel. A clear interface between the metal phase (bottom) and the slag phase (top) was observed in all samples, confirming effective phase separation. Representative samples were collected separately from the metal and slag phases for subsequent chemical and microstructural analyses.

The experiments were conducted in a semi-closed system provided by a corundum crucible within a muffle furnace. Although no external protective gas was used, the oxygen potential was effectively controlled by two primary factors. First, the FeO added to the slag served as the dominant and controlled oxygen source. Second, and more critically, the high carbon content (4.0%) in the charge generated a protective local CO atmosphere upon heating. This in situ generated CO effectively minimized the influence of ambient air, ensuring that the oxygen potential was governed by the intended FeO/C/V/Cr equilibria.

3.5. Calculation Methods

The oxidation rate η_M, representing the percentage of vanadium, chromium, and carbon that was successfully oxidized, was calculated using the following formula:

$${\eta }_{\mathrm{M}} = {\displaystyle \frac{\omega {[\mathrm{M}]}^0- \omega [\mathrm{M}]}{\omega {[\mathrm{M}]}^0}} \times 100\%$$

(18)

where ω[M]⁰ is the initial mass fraction of the element in the hot metal (%), and ω[M] is the mass fraction in the hot metal after oxidation (%), with ω[V] set below 1%, that is, η_V > 72.22%.

To achieve our goal of maximizing vanadium oxidation (η_V) while minimizing chromium oxidation (η_Cr) in hot metal, this study introduces the vanadium–chromium separation index (SI_V-Cr) to quantify the degree of separation between vanadium and chromium. The calculation formula for SI_V-Cr is provided in Equation (19):

$${SI}_{\mathrm{V}\text{-}\mathrm{Cr}} = \sqrt{{\displaystyle \frac{{\eta }_{\mathrm{V}} \times (100-{\eta }_{\mathrm{Cr}})}{100}}}$$

(19)

where η_V represents the extent of vanadium oxidized, and (100–${\eta }_{\mathrm{Cr}}$) represents the degree of chromium retained. Both are dimensionless quantities derived from Equation (18). As a composite index, SI_V-Cr evaluates the separation performances of vanadium and chromium through a geometric mean approach, emphasizing the simultaneous optimization of vanadium extraction and chromium retention. Specifically, a high SI_V-Cr value indicates effective separation, characterized by high vanadium oxidation and low chromium oxidation. Conversely, a low SI_V-Cr value suggests poor separation, with either low vanadium oxidation or high chromium oxidation occurring.

The slag–metal distribution ratios of vanadium (L_V) and chromium (L_Cr) were calculated using the following equations:

$$L_{\mathrm{V}}={\displaystyle \frac{\omega ({\mathrm{V}}_2{\mathrm{O}}_3)}{\omega [\mathrm{V}]}}$$

(20)

$$L_{\mathrm{Cr}}={\displaystyle \frac{\omega ({\mathrm{Cr}}_2{\mathrm{O}}_3)}{\omega [\mathrm{Cr}]}}$$

(21)

where ω(V₂O₃) and ω(Cr₂O₃) are the mass fractions of V₂O₃ and Cr₂O₃ in the slag (%), respectively.

4. Results and Discussion

4.1. Effect of Temperature on Vanadium Extraction and Chromium Retention

4.1.1. Temperature-Dependent Oxidation and Separation of [V] and [Cr] in Hot Metal

The oxidation behaviors of [V], [Cr], and [C] in hot metal were systematically investigated under a fixed ω(FeO) (10%) in the final slag. The individual contents of carbon, vanadium, and chromium were fitted with temperature, as shown in Equations (22)–(24) and Figure 5a. While all three elements decreased in content as the temperature increased, the behavior of vanadium diverged from those of chromium and carbon above 1693 K, where its rate of decline attenuated. This divergence may be attributed to carbon’s relatively higher susceptibility to oxidation compared to vanadium at high temperatures. The determined operational window for achieving ω[V] ≤ 1%, as derived from Equation (23) and the experimental data, is 1693 K to 1753 K. Beyond this range, the vanadium content increases, confirming that these extreme temperatures inhibit effective vanadium oxidation:

$$\omega [\mathrm{Cr}]=3.49\times {10}^{-5}{T}^2-0.12T+113.33$$

(22)

$$\omega [\mathrm{V}]=7.45\times {10}^{-5}{T}^2-0.26T+231.54$$

(23)

$$\omega [\mathrm{C}]=3.97\times {10}^{-5}{T}^2-0.15T+134.25$$

(24)

Figure 5b illustrates the temperature-dependent oxidation rates (η_V, η_Cr, and η_C). η_C demonstrates the steepest positive correlation, increasing linearly from 55% to 89% across the temperature range. η_V peaked at 82.2% at 1723 K (the optimal temperature for vanadium extraction), while η_Cr increased monotonically from 24.74% (1633 K) to 42.89% (1753 K), exhibiting near-linear progression above 1693 K. Across the entire temperature range, η_V consistently exceeded η_Cr, with a steeper increase in η_V (55.56% to 82.22%) compared to η_Cr (24.74% to 42.89%). This divergence stemmed from two factors: thermodynamic preference (Section 2.1) and the mediating role of carbon (detailed in Section 4.1.2).

Below 1723 K, η_V and η_C followed similar trends; however, above 1723 K, η_C surpassed η_V (Figure 5b). This inversion reflects intensified competition between [C] and [V] for oxygen at elevated temperatures [27,28].

The separation efficiency of [V] and [Cr], quantified by SI_V-Cr, is shown in Figure 5c. The fitting curve exhibits an upward convex characteristic and attains its peak at approximately 1723 K. The initial increase in SI_V-Cr was driven by the rapid increase in η_V (50.56% to 82.22%), while η_Cr increased modestly (24.74% to 41.84%). Beyond 1723 K, SI_V-Cr declined slightly, primarily due to the reduction in η_V (82.22% to 79.17%) and marginal increase in η_Cr (41.84% to 42.89%). Considering the quadratic fitting relationship, the following equation was used:

$${SI}_{\mathrm{V}\text{-}\mathrm{Cr}}=-7.55\times {10}^{-5}{T}^2+0.03T-21.87$$

(25)

where within a temperature range of 1693 K ≤ T ≤ 1753 K, SI_V-Cr can be maintained within a range from 0.67 to 0.69. These results underscore the adverse effects of excessive temperatures on vanadium oxidation selectivity, thereby reducing the separation efficiency.

The optimal process window was determined to be 1693–1753 K, where SI_V-Cr exceeded 0.67, η_V remained above 73.06%, and η_Cr was suppressed below 42.89%. At the same time, ω[V] was reduced to <0.97%, while ω[Cr] remained >2.17%. These results indicate that the effective separation of vanadium and chromium in hot metal was achieved under the specified conditions.

It should be noted that the discussion on the influence of temperature in this section is based on the condition of a fixed ω(FeO) content (10%). The boundaries of this optimal temperature window (1693–1753 K) are essentially the result of competition between the thermodynamics of the oxidation of V and Cr for this specific oxygen potential. We predict that when the initial oxygen potential (such as FeO content) changes, the oxidation behavior of carbon and the oxidation competition between V and Cr will also change, leading to a shift in the optimal temperature range. For example, at a higher FeO dosage, to avoid the excessive oxidation of Cr, the upper limit of the optimal temperature may need to be appropriately reduced.

4.1.2. Carbon-Mediated Vanadium Extraction and Chromium Retention

To systematically assess the role of carbon as a medium of vanadium extraction and chromium protection, we introduced two empirical indices: the vanadium extraction efficiency per unit carbon oxidation rate (η_V/η_C) and the protected chromium per unit residual carbon content ((100–η_Cr)/ω[C]); these measures are illustrated in Figure 6. The value of ω[Cr]/ω[C] monotonically increases with the increase in temperature, growing from 1.59 at 1633 K to 4.93 at 1753 K, which suggests that carbon has an enhanced protective effect on chromium at higher temperatures. In contrast, η_V/η_C demonstrates less temperature sensitivity than (100–η_Cr)/ω[C], with an initial increase followed by a decline. Above 1723 K, the efficiency of carbon in extracting vanadium decreases. The overall effect of carbon is responsible for the significantly greater temperature sensitivity observed during the oxidation of vanadium compared to chromium.

4.1.3. Temperature-Dependent Migration Behavior of Vanadium and Chromium

The migration behaviors of vanadium and chromium oxides in the slag phase were critically influenced by temperature variations, as summarized in Figure 7.

The V₂O₃ content in the slag initially increased with increasing temperature, peaking at 14.01% (1723 K), followed by a slight decline to 13.46% at 1753 K (Figure 7a). In contrast, the Cr₂O₃ content gradual decreased from 6.30% (1623 K) to 4.65% (1753 K). Correspondingly, L_V increased significantly from 4.10 (1623 K) to 21.89 (1723 K), then decreased to 17.95 (1753 K), while L_Cr remained relatively stable within a narrow range (1.68–3.14) across the tested temperatures (Figure 7b). These results demonstrate that moderate temperature increase (<1723 K) significantly enhances vanadium partitioning into the slag, whereas chromium migration is minimally affected.

Within the optimized temperature window (1693–1753 K), V₂O₃ content stabilized between 12.91% and 14.01%, while Cr₂O₃ content varied from 4.58% to 4.75%. Notably, despite the temperature-dependent increase in the chromium oxidation rate (Section 4.1.1), oxidized chromium exhibited incomplete migration to the slag phase.

4.2. Effect of FeO Content on Vanadium Extraction and Chromium Retention

4.2.1. FeO-Dependent Oxidative Separation of [V] and [Cr]

The oxidative separation of [V] and [Cr] in hot metal was systematically investigated under varying ω(FeO) contents at 1723 K, as summarized in Figure 8.

Figure 8a illustrates the equilibrium between the slag oxygen potential and residual element content of hot metal. Both ω[V] and ω[Cr] exhibit pronounced decreasing trends with increasing ω(FeO) content. The empirical relationship between ω[V] and ω(FeO) was established using Equation (26):

$$\omega [\mathrm{V}]=0.01{\omega (\mathrm{FeO})}^2-0.36\omega (\mathrm{FeO})+3.52$$

(26)

Based on Equation (26) and the experimental data, we determined that ω[V] dropped below the critical threshold of 1.0% only when ω(FeO) exceeded 10%, with the corresponding oxygen partial pressure $\lg p_{{\mathrm{O}}_2}$ = −11.42. This value exceeds the theoretical prediction ($\lg p_{{\mathrm{O}}_2}$ = −11.91) due to idealized assumptions in the model and competitive FeO consumption by carbon oxidation. Thus, efficient vanadium extraction requires higher oxygen potential than theoretically projected.

Figure 8b plots η_V and η_Cr against ω(FeO). Although both efficiencies increase with ω(FeO) content, their response curves differ significantly—η_V exhibits a convex upward trend, in contrast to the concave downward trend of η_Cr. These distinct behaviors form the basis for defining the three characteristic regions listed in

Table 5. Characteristic regions defined by η_V and η_Cr oxidation behavior versus ω(FeO).

Region	Name	ω(FeO) Range	Dominant Process	ηV/ηCr
I (O)	V-Dominant Zone	3–10%	Vanadium Preferential Oxidation	2.5–3.1
II (O)	Cr-Activation Zone	10–15%	Chromium Oxidation Activation	1.8–2.4
III (O)	Cr-Runaway Zone	>15%	Chromium Massive Oxidation	<1.1

.

The three regions’ behaviors are summarized in more detail below:

• Region I(O) (V-Dominant Zone, ω(FeO) = 3–10%): η_V increases sharply due to preferential vanadium oxidation (thermodynamically favored; Section 2.2), while η_Cr increases marginally;
• Region II(O) (Cr-Activation Zone, ω(FeO) = 10–15%): η_Cr oxidation accelerates;
• Region III(O) (Cr-Runaway Zone, ω(FeO) > 15%): η_Cr undergoes rapid escalation, exceeding chromium’s oxidation threshold.

This divergence underscores the core mechanism of selective oxidation: Vanadium oxidizes readily at low oxygen potentials, whereas chromium requires significantly higher potentials for massive oxidation. Precise oxygen potential control, thus, enables targeted vanadium extraction at a temperature of 1723 K and a holding time of 1 h with chromium retention.

Figure 8c reveals a non-monotonic trend in SI_V-Cr, which peaks then declines with increasing ω(FeO) content. The relationship is fitted by

$${SI}_{\mathrm{V}\text{-}\mathrm{Cr}}=-0.004{\omega (\mathrm{FeO})}^2+0.084\omega (\mathrm{FeO})+0.268$$

(27)

Maximizing dSI_V-Cr/dω(FeO) = 0 yields a distinct selectivity peak (SI_V-Cr = 0.74) at ω(FeO) = 10.5%. Suboptimal oxidation occurs at ω(FeO) < 10.5%, while ω(FeO) > 15.7% promotes excessive Cr oxidation, degrading selectivity.

Thus, effective V/Cr separation (SI_V-Cr ≥ 0.67) requires an operational window of ω(FeO) = 10.0–15.7%, corresponding to $\lg p_{{\mathrm{O}}_2}$ = −11.4 to −10.9. This range spans “Region II(O)” and early “Region III(O)”. Although chromium begins to oxidize at an FeO concentration of 15%, the practically feasible range is extended to 15.7%. This indicates that FeO can vary by ±0.35% without compromising process stability. Such tolerance not only enhances operational flexibility but also guarantees the efficient extraction of vanadium, highlighting its critical role in process control.

Within this window, the following is true: (1) η_V > 72.22%, η_Cr < 41.58%; (2) ω[V] < 1.0%, ω[Cr] > 2.3%. The requisite oxygen supply (33.1–38.2 kg/tFe) is 27.7–81.1% lower than that for conventional converter-based vanadium extraction (43.0–195.0 kg/tFe, accounting for 70–90% utilization efficiency [29]). This demonstrates the feasibility of low-oxygen-potential vanadium extraction with minimal chromium loss—this represents a significant advance toward the sustainable refining of high-chromium hot metal.

The optimal operating window of FeO (10–15.7%) determined in this study was obtained at a fixed temperature of 1723 K. Temperature plays a crucial role, as it directly affects the equilibrium constant and kinetic rate of the reaction. At higher temperatures, the reducing power of carbon increases, which may enable the same V oxidation efficiency with a lower FeO dosage while better suppressing the oxidation of Cr. Conversely, at lower temperatures, a higher FeO content may be required to compensate for the insufficient reaction kinetics, but this significantly increases the risk of Cr oxidation. Therefore, the control range of FeO is not constant but closely related to temperature.

4.2.2. FeO-Dependent Migration of Vanadium and Chromium

The migration behavior of vanadium and chromium oxides into the slag phase under varying ω(FeO) contents is illustrated in Figure 9. As ω(FeO) increased, both the V₂O₃ and Cr₂O₃ contents in the slag increased (Figure 9a), driven by its enhanced oxidative capacity. L_V increased significantly from 1.22 (3.0% FeO) to 22.28 (15% FeO), with no obvious bending point (Figure 8b). In contrast, chromium migration L_Cr exhibited a milder increase (1.68–4.58), with a distinct inflection at 15% ω(FeO) (Figure 9b). This indicates that FeO promotes vanadium migration to slag, while low dose ω(FeO) (15%) has no significant effect on chromium migration.

Within the optimized ω(FeO) range of 10–15.7% identified in Section 4.2.1, the vanadium–chromium slag achieves ω(V₂O₃) values of 8.04–10.88% and ω(Cr₂O₃) values of 3.46–4.58%.

4.3. Comprehensive Discussion on the Synergistic Control of Temperature and Oxygen Potential

The experimental design of this study adopted the single-factor variable method, which separately revealed the independent influence laws of temperature and FeO dosage on the separation of V-Cr. However, the success of industrial applications relies on achieving coordinated control of these two key parameters.

A more scientific process control strategy should be regarded as a dynamic optimization process: higher operating temperatures create favorable thermodynamic and kinetic conditions for achieving “low oxygen potential extraction of V”, allowing for the use of lower FeO dosages, thereby achieving the efficient extraction of V while maximizing the utilization of carbon’s protective effect on Cr; while operating at lower temperatures, the system is forced into “high oxygen potential extraction of V” mode, significantly increasing the risk of Cr loss.

Therefore, the temperature window (1693–1753 K) and FeO window (10–15.7%) determined in this study should be understood as a guiding parameter space. The core value of these concepts is that they reveal that the combination of “high temperature–medium-low FeO” is a more optimal path for selective oxidation. Future research can further precisely quantify this coupling relationship. Using advanced thermodynamic software (e.g., FactSage 8.2) with appropriate databases is recommended to build a more accurate thermodynamic model as a first approximation. This can be combined with experimental designs such as response surface methodology (RSM) to construct a comprehensive mathematical model for guiding industrial production.

4.4. Comparative Analysis of the Vanadium Extraction and Chromium Retention (VECR) Process with Conventional Methods

A systematic comparison between the proposed VECR process and traditional vanadium extraction methods is summarized in

Table 6. A comparison of process parameters and results of VECR process with traditional process.

Parameter	Traditional Process	VECR Process	Improvement
Temperature/K	1623–1693 [29,30]	1693–1753	+65 K (optimized oxidation)
Oxygen supply/kg·(tFe)−1	43.0–195.0	33.1–38.2	>80 kg/tFe reduction
ηV/%	75.0–90.0 [29]	72.5–82.2	Comparable efficiency
ηCr/%	50.0–70.0 [31]	28.2–42.9	>40% reduction
ω(V2O3)/%	8.2–16.5 [32,33]	10.9–14.0	Higher purity
ω(Cr2O3)/%	5.0–10.0	3.5–7.3	Meets low-Cr standards

. The primary differences between these two processes lie in the control of temperature and oxygen potential, as well as the differences in the oxidation rate and composition of vanadium chromium slag caused by these factors.

The VECR process is about 65 K higher than that of the traditional process. In traditional processes, the temperature is typically maintained below the C-V oxidation transition temperature. In contrast, the VECR process requires the temperature to be controlled at a nearly C-V oxidation temperature to ensure maximum SI_V-Cr.

Traditional processes involve a relatively high oxygen supply (43.0–195.0 kg/tFe) (as described in Section 4.2.1) to create a high-oxygen-potential environment, which promotes vanadium oxidation. However, such conditions also significantly increase the chromium oxidation rate (50–70%), leading to a higher chromium content in the vanadium slag (5–14%). This not only reduces the recovery value of the vanadium slag but also complicates subsequent chromium recovery. Furthermore, the high oxygen potential and elevated temperatures accelerate equipment wear and increase maintenance costs. In comparison, the VECR process reduces the oxygen supply to 33.1–38.2 kg/tFe, achieving effective vanadium oxidation (η_V: 72.5–82.2%) under low-oxygen-potential conditions while significantly lowering η_Cr (<42.9%).

The VECR process significantly reduces oxygen consumption and chromium oxidation losses. Compared to conventional processes, the oxygen consumption of the VECR process is reduced by more than 80 kg/tFe, while that of η_Cr is reduced by over 40%. This improves the purity of the vanadium slag. In the vanadium slag formed via the VECR process, ω(V₂O₃) is 10.88–14.01% and ω(Cr₂O₃) is 3.5–7.3%. These values satisfy the requirements for the recycling and utilization of low-chromium vanadium–chromium slag. Specifically, vanadium slag is considered to have industrial extraction value only when the V₂O₅ content exceeds 10% [34,35] (equivalent to V₂O₃ content 8.2%). Additionally, the Cr₂O₃ content in low-chromium vanadium–chromium slag is typically required to be less than 8% [36].

It is important to note that the higher operational temperature of the VECR process compared to some traditional methods (Table 6) implies an increase in energy input at the oxidation stage. However, this cost must be evaluated against the significant energy savings achieved by completely eliminating the subsequent roasting and hydrometallurgical units. A full life-cycle assessment and techno-economic analysis are recommended for future research to comprehensively evaluate the net energy and cost benefits of the integrated VECR route. Furthermore, the reaction kinetics under the controlled low-oxygen-potential conditions might be slower than for high-oxygen blowing, potentially requiring careful optimization of stirring and mass transfer for industrial-scale implementation.

Overall, the VECR process demonstrates significant advantages in terms of chromium retention and cost-effective production. By reducing the chromium oxidation rate, this process not only minimizes chromium resource waste but also achieves efficient resource utilization. Moreover, the lower oxygen supply significantly reduces energy consumption and carbon emissions, aligning with the principles of green metallurgy. From an industrial application perspective, the VECR process is particularly suitable for production scenarios with high demand for vanadium and chromium resource utilization efficiency, especially in regions where chromium resources are scarce or environmental regulations are stringent. In the future, this process is expected to achieve broader applications in the steel and metallurgical industries and provide valuable insights for developing green metallurgical technologies.

5. Conclusions

This study successfully developed and validated a novel pyrometallurgical strategy for the synchronous extraction of vanadium and retention of chromium from high-V-Cr hot metal through the precise control of selective oxidation. The combined thermodynamic and experimental investigation produced the following key findings:

• The thermodynamic analysis established that the temperature window of 1517–1704 K is critical, as it enables carbon to function as an effective redox mediator. Within this regime, the oxidation priority of [V] > [C] > [Cr] creates a thermodynamic pathway for selective V extraction. Furthermore, there is a hierarchy of oxygen partial pressure required for oxidizing vanadium and chromium. An optimal oxygen partial pressure window of −11.91 to −10.94 (logarithmic scale) at 1723 K was identified to achieve high V oxidation while suppressing Cr loss. This theoretical prediction provides a key parameter window for optimizing experimental conditions, and its core conclusion is directly verified in subsequent experiments.
• Temperature-dependent experiments demonstrate the differential responses of η_V and η_Cr: vanadium oxidation exhibits higher temperature sensitivity than chromium, a phenomenon attributed to the stronger protective effect of carbon on chromium compared to its promoting effect on vanadium extraction. The optimal temperature range is 1693–1753 K (SI_V-Cr > 0.67). In the low-temperature region (<1693 K), vanadium oxidation is incomplete, whereas in the high-temperature region (>1753 K), the separation efficiency deteriorates.
• Both η_V and η_Cr increase upon adding FeO, with η_V consistently exceeding η_Cr. [V] oxidation occurs preferentially at lower FeO dosages. The optimal FeO dosage range is 10.0–15.7%. FeO contents exceeding this range lead to the over-oxidation of [Cr], while insufficient FeO additions result in incomplete [V] oxidation.
• Under optimized process conditions, η_V exceeds 72.5%, while η_Cr remains below 42.9%. These conditions result in a reduction of ω[V] to less than 1%, while ω[Cr] remains above 2.17%. Additionally, ω(V₂O₃) and ω(Cr₂O₃) are 10.88–14.01% and 3.46–7.31%, respectively, meeting the criteria for recycling low-chromium vanadium slag. These results demonstrate the effectiveness of the process for selectively oxidizing vanadium while minimizing chromium oxidation losses.
• Compared to traditional processes, the proposed VECR method demonstrates significant advantages. It reduces oxygen consumption by over 80 kg/tFe and Cr oxidation losses by more than 40%, directly translating to lower operational costs and enhanced resource utilization. The resulting V-Cr slag, with 10.88–14.01% V₂O₃ and 3.5–7.3% Cr₂O₃, meets the industrial standard for low-Cr feedstock. Most importantly, this process completely eliminates the need for the energy-intensive roasting and complex hydrometallurgical steps, offering a shorter, cleaner, and more economical flowsheet.