X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
339–348
OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION:
TARGETED ENRICHMENT AND STABILIZATION OF VANADIUM
THROUGH NON-EQUILIBRIUM SOLIDIFICATION
OPTIMIRANJE UPORABE VANADIJEVE KONVERTERSKE
@LINDRE: CILJANA OBOGATITEV IN STABILIZACIJA
S POMO^JO NERAVNOTE@NEGA STRJEVANJA
Xiao-Pei Zhang, Jian-Bao Zhang, Li-Jie Peng, Ya-Jun Wang
*
, Jun-Guo Li
School of Metallurgy and Energy, North China University of Science and Technology, 063210 Tangshan, P. R. China
Prejem rokopisa – received: 2023-10-01; sprejem za objavo – accepted for publication: 2024-04-10
doi:10.17222/mit.2023.984
The objective of this research was to optimize the comprehensive utilization of vanadium converter slag through targeted enrich-
ment and stabilization of heavy metal vanadium. Employing the non-equilibrium solidification theory and FactSage software,
we investigated the potential of modifying vanadium converter slag. When the original slag failed to generate vanadium-rich
spinel with usable V elements, introducing modifying agents Fe and Al proved effective. Fe facilitated the enrichment of Cr
within spinel, while Al significantly promoted the V enrichment. Expanding on this, we systematically examined the influence
of Fe2O3,Al 2O3 and MgO contents on spinel phase precipitation during vanadium slag solidification. The addition of Al resulted
in the precipitation of corundum, hematite, spinel, olivine and diopside phases. With an increase in the Fe2O3 content, the pre-
cipitation of FeV2O4 and MgV2O4 initially increased, peaking at 9.67 % before subsequently decreasing. Maintaining the Fe2O3
content within a range of 25–30 % proved optimal for enhancing vanadium precipitation and enrichment. In contrast, variations
in the Al2O3 content had minor impacts on SP-V phase precipitation, with slight effects on FeV2O4 reaching 10.34 %. Further-
more, the incorporation of MgO facilitated the precipitation of MgV2O4 while concurrently suppressing the FeV2O4 precipita-
tion. By judiciously controlling the MgO content at approximately 20 %, vanadium enrichment in the form of FeV2O4 and
MgV2O4 spinel phases reached a remarkable 94.46 %.
Keywords: vanadium, converter slag, enrichment, stabilization, non-equilibrium solidification
V ~lanku avtorji opisujejo raziskavo optimizacije sestave vanadijeve konverterske `lindre za splo{no uporabo s pomo~jo ciljane
obogatitve in stabilizacijo vanadija kot te`ke in okolju {kodljive kovine. Z uporabo teorije neravnote`nega strjevanja in
programskega orodja FactSage so raziskali potencialne mo`nosti za modifikacijo vanadijeve konverterske `lindre. Ker se v
originalni `lindri ne tvori na vanadiju bogati {pinel, ki porabi ves raspolo`ljivi vanadij, se z uvedbo modificiranja z dodatki kot
sta `elezo (Fe) in aluminij (Al) le tega u~inkovito porabi. @elezo (Fe) pospe{i obogatitev {pinela s kromom (Cr), medtem ko
aluminij mo~no pospe{i njegovo obogatitev z vanadijem. Na osnovi tega so avtorji sistemati~no raziskali vplive vsebnosti Fe2O3,
Al2O3 in MgO na izlo~anje {pinelne faze med strjevanjem vanadijeve `lindre. Dodatek Al je povzro~il izlo~anje (tvorbo)
korunda, hematita, {pinela, olivina in diopsidne faze. Pove~anje vsebnosti Fe2O3 je v za~etku pove~alo nastajanje FeV2O4 in
MgV2O4 do maksimalne vrednosti 9,67 %, nato pa je koncentracija obeh za~ela strmo upadati. Da bi pospe{ili izlo~anje in
obogatitev {pinela z vanadijem je potrebno ohranili koncentracijo Fe2O3 v mejah med 25% in 30%. Nasprotno pa ima variranje
vsebnosti Al2O3 zanemarljiv vpliv na izlo~anje SP-V faze z rahlim u~inkom na obogatitev z FeV2O4 do 10,34 %. Nadalje
dodatek MgO pospe{i nastanek in izlo~anje MgV2O4, kar pa takoj zavre izlo~anje FeV2O4. Z natan~no kontrolo vsebnosti MgO
pri pribli`no 20 % so avtorji te raziskave dosegli pomembno 94,46 % vezavo vanadija in tako obogatitev `lindre s {pinelnima
fazama v obliki FeV2O4 in MgV2O4.
Klju~ne besede: vanadij, konverterska `lindra, obogatitev, stabilizacija, neravnote`no strjevanje
1 INTRODUCTION
Vanadium, as a rare metal element, finds wide appli-
cation due to its high melting point, hardness, and tough-
ness, in fields such as materials, steel production, aero-
space, and petrochemicals, and is crucial for strategic
resources worldwide.
1,2
P r e s e n t l y ,o v e r9 0%o fv a n a -
dium resources are sourced from vanadium-titanium
magnetite, with vanadium slag (V
2
O
5
) being obtained
through iron reduction processes.
3
Depending on iron
smelting methods, production stages, and slag treatment
approaches, the chemical composition of vanadium slag
varies. Common oxide components in most vanadium
slags include Fe
2
O
3
,V
2
O
5
, SiO
2
, MgO, MnO, and TiO
2
,
along with minor amounts of CaO, Cr
2
O
3,
and P
2
O
5
. The
diverse chemical composition of vanadium slag influ-
ences its phase composition, which in turn affects subse-
quent processes for vanadium and chromium extrac-
tion.
4–6
Common phases in the low-calcium vanadium
slag from converters include spinel, olivine and pyro-
xene, characterized as follows.
Chromium in vanadium slag mainly exists in forms
such as Cr
2
O
3
, MgCr
2
O
4
, FeCr
2
O
4
, CrAl
2
O
4
and CrFe
2
O
4
,
while vanadium is primarily present in forms like
FeV
2
O
4
, MgV
2
O
4,
and V
2
O
3
. When chromium and vana-
dium exist as AB
2
O
4
spinels, they exhibit enhanced oxi-
Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348 339
UDK 546.881:625.821.4 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(3)339(2024)
*Corresponding author's e-mail:
wangyj@ncst.edu.cn (Ya-Jun Wang)

dation resistance, reduced susceptibility to acid-base cor-
rosion, and effective suppression of chromium
leaching.
7–11
Al
2
O
3
in vanadium slag reacts with MgO
and Cr
2
O
3
to form solid solutions like Mg(CrxAl
1-x
)O
4
,
aiding in lowering the Cr
2
O
3
content and positively influ-
encing chromium enrichment and stabilization.
12,13
Moreover, spinel precipitation is closely related to tem-
perature, with higher temperatures promoting spinel for-
mation.
14–16
Tang et al.
17
found that at temperatures below
1540 °C, the slag contains an amorphous material and
iron-aluminum spinel, while at 1580 °C, enriched chro-
mium iron-aluminum spinel begins to precipitate, vali-
dating the above viewpoint. Wang
20
studied the effects of
B
2
O
3
on vanadium slag, observing that the spinel phase
size increased with a higher B
2
O
3
content, with most
chromium enriched in the spinel phase. Engstrom et al.
21
indicated that higher masses of MgO and Fe
2
O
3
in slag
favor increased chromium spinel phase precipitation, un-
derscoring the significant influence of the MgO and
Fe
2
O
3
content on chromium spinel precipitation in vana-
dium slag. Additionally, researchers like Cao and Pan
18–20
investigated the impact of alkalinity on chromium en-
richment in vanadium slag, finding that an alkalinity of
1.5 was beneficial for chromium enrichment in the spinel
phase, with a nearly 100 % enrichment observed at a
temperature of 1300 °C.
Consequently, investigating the selective enrichment
and stabilization of vanadium-chromium elements in
spinel phases within vanadium slag holds critical signifi-
cance for enhancing resource utilization and promoting
green metallurgical manufacturing.
22–26
This study, based
on the vanadium slag composition and thermodynamic
principles, employs the FactSage 8.2 thermodynamic
software to simulate the solidification process of the
Fe
2
O
3
-SiO
2
-TiO
2
-V
2
O
5
-Al
2
O
3
-Cr
2
O
3
-MgO slag system.
The analysis explores the influence of the Fe
2
O
3
content
on the spinel phase precipitation behavior, thereby pro-
viding a theoretical foundation for the enrichment of va-
nadium-chromium elements and efficient resource utili-
zation in steel slag.
2 EXPERIMENTAL PART
2.1 FactSage simulation conditions
The Sheil-Gulliver solidification model is an approxi-
mate model for complex melt solidification processes,
assuming infinite-fast element diffusion in the liquid
phase and zero diffusion rate in the solid phase. During
the cooling process, the solid-liquid interface always
maintains the local equilibrium state. The liquid and
solid phase compositions at the interface can be calcu-
lated based on the system phase equilibrium, and the
composition of the solid phase remains constant after its
formation, while the liquid phase maintains a uniform
composition. Based on the non-equilibrium solidification
theory of the melt, i.e., the Sheil-Gulliver equation, using
the thermodynamic software FactSage 8.2 and relevant
databases, the Fe
2
O
3
-SiO
2
-TiO
2
-V
2
O
5
-Al
2
O
3
-Cr
2
O
3
-MgO
slag system’s phase equilibrium during solidification was
simulated. The influence of the Fe
2
O
3
content on the pre-
cipitation behavior of the spinel phase during slag cool-
ing was investigated. The simulation calculation em-
ployed the following database, compound and
precipitation phase settings
13
: (1) Databases: FToxide,
FactPS; (2) Compound settings: ideal gas, pure solid; (3)
Liquid phase settings: FToxide-SLAGA, FToxide-
SPINA, FToxide-MeO_A, FToxide-aC2SA, FToxide-
bC2SA, FToxide-Mel_A, FToxide-OlivA, FToxide-Cord,
FToxide-Mull, FToxide-CORU, FToxide-SP-V,
FToxide-TiO
2
, with the cooling calculation set to
Sheil-Gulliver cooling in FToxide-SLAGA. The simula-
tion calculation was performed in a temperature range of
1000–2000 °C with a step size of 10 °C, and the system
calculation pressure was set to 1.013 × 10
5
Pa. To vali-
date the thermodynamic calculation results, a compari-
son was conducted between experimental outcomes of
the SP-V generation in vanadium slag. This was per-
formed to corroborate the effects of Fe
2
O
3
,A l
2
O
3
and
MgO on the vanadium enrichment behavior within the
slag.
3 RESULTS AND DISCUSSION
3.1 Simulation of S0 slag
In accordance with the compositional range of vana-
dium slag from steel plants, a base vanadium slag mate-
rial with a mass of 100 g was designed. The composition
is as follows: w(Fe
2
O
3
)=5 5% ,w (SiO
2
)=1 5% ,
w (TiO
2
)=10%,w (V
2
O
5
)=10%,w (Al
2
O
3
)=4%,
w (Cr
2
O
3
)=3%,andw (MgO)=3%,asshowninFig-
ure 1. The non-equilibrium solidification process of the
S0 base slag was simulated using the Sheil-Gulliver so-
lidification model.
Table 1: Composition of S0 slag mixture (g)
ID Fe2O3 SiO
2 TiO
2 V2O5 Al2O3 Cr
2O3 MgO
S0 55 15 10 10 4 3 3
From Figure 1, it can be observed that SPINA is a
spinel phase containing chromium (Cr) elements, while
SP-V is a spinel phase containing vanadium (V) ele-
ments. In the SPINA phase, the main constituents are
FeCr
2
O
4
, MgCr
2
O
4
, FeAl
2
O
4
, MgAl
2
O
4
, and MgFe
2
O
4
.
However, there is no precipitation of the SP-V phase. In
the SP-V phase, the main constituents are FeV
2
O
4
,
MgV
2
O
4
, FeAl
2
O
4
, MgAl
2
O
4
, and MgFe
2
O
4
. The precipi-
tation of chromium-rich spinel is very low, at 3.39 %.
Within the SPINA phase, precipitation fractions of
MgCr
2
O
4
and FeCr
2
O
4
containing Cr are 0.0013 % and
0.000708 %, respectively, which is almost negligible.
Similarly, within the SP-V phase, the precipitation frac-
tions of MgV
2
O
4
and FeV
2
O
4
are both 0, which can be
attributed to the lack of FeO generation in the S0 slag
system. This phenomenon is supported by the studies by
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
340 Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348

Su et al.
13
and Yu et al.
27
To address the issue of vana-
dium not precipitating in the form of a spinel phase and
to increase the precipitation of spinel with larger and
more concentrated growth, we introduced Fe and Al ele-
ments into the slag system as the reducing agents. Ther-
modynamic simulations were conducted for this combi-
nation of slag systems.
3.2 Simulation with Fe and Al additions in S0 slag
Based on the composition range of steel mill vana-
dium slag, the basic vanadium slag with a mass of 100 g
was designed. Fe and Al elements were separately added
to the slag to investigate the influence of different com-
positions on the precipitation behavior of the SP-V
phase. The goal was to identify effective reducing agents
to enhance the yield of vanadium precipitation in the
slag. The simulated slag compositions are presented in
Table 2.
The thermodynamic calculations reveal that the addi-
tion of Fe and Al to the S0 original slag can achieve a
high proportion of the SP-V phase, including types like
FeV
2
O
4
and MgV
2
O
4
. However, we need to further inves-
tigate the influence of different Fe and Al contents on the
enrichment of vanadium in the spinel phase. Figure 2
presents the impact of a varying Fe content on the pre-
cipitation of the SP-V phase in the S0 slag system. It is
observed that with the Fe content below 10 %, the pre-
cipitation fraction of the SP-V phase gradually increases,
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348 341
Figure 1: Mineral phase composition and SPINA phase precipitation fraction during solidification of S0 base slag system
Table 2: Slag compositions with Fe and Al additions (g)
ID Fe2O3 SiO2 TiO2 V2O5 Al2O3 Cr2O3 MgO Fe Al
F e 15 51 51 01 04335–
Fe2 55 15 10 10 4 3 3 10
Fe3 55 15 10 10 4 3 3 15
Fe4 55 15 10 10 4 3 3 20
Fe5 55 15 10 10 4 3 3 25
A L 15 51 51 01 0433–1 0
AL 2 55 15 10 10 4 3 3 12.5
AL 3 55 15 10 10 4 3 3 13.5
A L 45 51 51 01 0433 1 5
A L 55 51 51 01 0433 2 0

X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
342 Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348
Figure 3: Precipitation fractions of spinel phases after adding Fe and Al to S0 slag
Figure 2: Precipitation fractions of the SP-V phase after the addition of Fe and Al to the S0 slag

and the critical precipitation temperature also rises, indi-
cating a positive correlation. However, when the Fe con-
tent exceeds 10 %, the precipitation fraction of the SP-V
phase decreases, and the critical precipitation tempera-
ture reduces, revealing a negative correlation. Hence,
controlling the Fe content within a range of 10–15 %
during the vanadium extraction process could effectively
enhance the vanadium yield. Furthermore, the addition
of Al to the S0 slag also promotes the precipitation of va-
nadium in the spinel phase. The data in Figure 2 demon-
strate that when Al is below 13.5 %, the precipitation
fraction of the SP-V phase continues to increase with the
increasing Al content, along with a rise in the critical
precipitation temperature, indicating a positive correla-
tion. However, when the Al content surpasses 13.5 %,
the precipitation fraction of the SP-V phase decreases,
and the critical precipitation temperature also decreases,
showing a negative correlation. Therefore, restricting the
Al content within a range of 13.5–15 % during the vana-
dium extraction process could enhance the vanadium
yield. The precipitation process of the SP-V phase is
generally completed at around 1050 °C.
From Figure 3, it can be observed that the FeV
2
O
4
precipitation fraction gradually increases as the Fe con-
tent rises from5%to25%,with a notable increment
when Fe reaches 25 %, resulting in a precipitation frac-
tion of approximately 5.5 %. This is concurrent with a
significant enrichment of vanadium within the FeV
2
O
4
phase. Similarly, with the addition of Al to the S0 slag,
the precipitation fraction of FeV
2
O
4
initially increases
and then decreases as Al increases. The maximum pre-
cipitation fraction of FeV
2
O
4
is achieved at an Al content
of 13.5 %, reaching around 9.86 %. This also leads to a
pronounced enrichment of vanadium in the FeV
2
O
4
spinel phase. For MgV
2
O
4
, when the Fe content exceeds
10 %, some vanadium starts to be present in the FeV
2
O
4
phase, causing a decrease in its precipitation fraction.
This consequently results in a slight reduction in the
overall SP-V phase precipitation, accounting for approxi-
mately 50 % of the total precipitation. The enrichment of
vanadium within the FeV
2
O
4
phase also experiences a
slight decrease. When Al is added to the S0 slag, with
the Al content below 15 %, the precipitation fraction of
MgV
2
O
4
gradually increases with an increasing Al con-
tent, peaking at 1.87 % when Al reaches 15 %. However,
with further increases in the Al content, the precipitation
fraction of MgV
2
O
4
diminishes. This behavior is attrib-
uted to the partial presence of vanadium in the FeV
2
O
4
spinel phase, causing a decrease in the precipitation frac-
tion of the MgV
2
O
4
spinel phase.
3.3 Summary
(1) When adding Al to S0 slag with an Al content of
12.5 g, the mass of MgV
2
O
4
and FeV
2
O
4
containing V
elements increased from0gto1.338 g and 9.9587 g, re-
spectively. The precipitation rate of V in spinel reached
94.46 %, indicating a significant role of Al in promoting
the V enrichment in spinel during industrial vanadium
recovery processes. (2) When adding Fe to S0 slag with
a Fe content of 25 g, the mass of MgCr
2
O
4
and FeCr
2
O
4
containing Cr elements increased from 0.000708 g and
0.00103 g to 3.25 g and 0.47 g, respectively. The precipi-
tation rate of Cr in spinel reached 86 %. This highlights
the importance of the Fe content in enhancing the enrich-
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348 343
Figure 4: Mineral phase composition and the fraction of precipitated spinel phases during the solidification of base slag system S0 after the Al
addition

ment of Cr in spinel, particularly in the growth of
MgCr
2
O
4
and FeCr
2
O
4
, during industrial chromium re-
covery processes. (3) Based on (1) and (2), it is evident
that the reducing agent Fe is more favorable for increas-
ing the precipitation fraction of chromite and promoting
the growth of MgCr
2
O
4
and FeCr
2
O
4
, leading to the en-
richment of Cr in spinel. On the other hand, the reducing
agent Al significantly enhances the growth of the SP-V
phase, resulting in superior precipitation of MgV
2
O
4
and
FeV
2
O
4
and promoting the enrichment of V in spinel.
3.4 Vanadium spinel precipitation behavior in vana-
dium slag
To explore the detailed impact of adding Fe and Al to
S0 slag on the precipitation behavior of vanadium spinel,
and based on the conclusions drawn earlier, the effect of
adding Al is examined. The Sheil-Gulliver solidification
model is used to simulate the non-equilibrium solidifica-
tion of S0 basic slag with an addition of 12.5 g Al. The
slag composition includes w(Fe
2
O
3
) = 55 %, w(SiO
2
)=
15 %, w(TiO
2
)=1 0% ,w ( V
2
O
5
) = 10 %, w(Al
2
O
3
)=
4 %, w(Cr
2
O
3
)=3%,w(MgO)=3%,and12.5 g Al.
The results are presented in Figure 4. During the slag so-
lidification process, the main precipitated phases include
corundum, hematite, spinel, olivine, and diopside. Both
chromite and SP-V phases, which contain chromium, are
high-temperature precipitates. In the solidification of the
S0 basic slag, the starting temperature for the precipita-
tion of these two phases slightly differs by 1460 °C for
chromite and 1340 °C for SP-V. As the temperature de-
creases, the chromite phase reaches its maximum precip-
itation fraction of 20.4 % when the temperature drops to
1160 °C. On the other hand, the SP-V phase achieves its
maximum precipitation fraction of approximately 42.5 %
at 1090 °C. The Al
4
FeSi
5
O
18
and Al
4
MgSi
5
O
18
phases
start to precipitate at around 1230 °C, with precipitation
fractions increasing from0%t o0.10 and 0.56 %, re-
spectively. When the temperature drops to 1190 °C, the
precipitation fraction of Al
4
MgSi
5
O
18
no longer in-
creases, reaching a maximum value of 9.8 %. Finally, at
1150 °C, the precipitation fraction of Al
4
MgSi
5
O
18
stops
increasing, with the maximum value being 1.88 %.
The SPINA phase consists of solid solutions, primar-
ily composed of FeAl
2
O
4
, MgFe
2
O
4
, MgCr
2
O
4
, FeCr
2
O
4
,
and minor amounts of CrAl
2
O
4
and CrFe
2
O
4
. After the
completion of solidification, the total precipitation frac-
tion of the SPINA phase is 16.59 %, with the FeAl
2
O
4
content of 6.35 %, MgFe
2
O
4
content of 2.04 %, FeCr
2
O
4
content of 3.96 %, and MgCr
2
O
4
content of 1.09 %. In
contrast, the SP-V phase has a slightly different compo-
sition, primarily replacing MgCr
2
O
4
and FeCr
2
O
4
with
FeV
2
O
4
and MgV
2
O
4
. The composition of the SP-V
phase includes FeAl
2
O
4
at 13.56 %, MgFe
2
O
4
at 2.38 %,
FeV
2
O
4
at 10.12 %, and MgV
2
O
4
at 2.67 %. Addi-
tionally, the SPINA phase contains trace amounts of
spinel-type CrO·Cr
2
O
3
chromite (0.05 %), Fe
3
O
4
inverse
spinel (0.21 %), and minor amounts of MgFe
2
O
4
,
CrFe
2
O
4
, and CrAl
2
O
4
spinel phases. In this study, a con-
trolled variable method was employed (keeping other
variables constant except for the Fe
2
O
3
content varia-
tion). Thus, the primary focus is on investigating the im-
pact of the Fe
2
O
3
content on the precipitation of SPINA
and SP-V phases in the slag system. Therefore, the fol-
lowing sections will primarily analyze the changes in
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
344 Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348
Figure 5: Changes in V and Cr contents in each phase during the solidification after adding Al to the base slag system S0 and the standard Gibbs
free energy of spinel phase formation

precipitation fractions and onset temperatures of spinel
phases, including MgCr
2
O
4
, FeCr
2
O
4
,F e V
2
O
4
,a n d
MgV
2
O
4
.
Figure 5 shows the changes in the Cr and V contents
in the slag and spinel phases during the solidification of
the basic slag system S0, and the standard Gibbs free en-
ergy of formation for four types of spinel phases. As the
temperature drops to 1550 and 1350 °C, respectively, the
contents of Cr and V in the spinel phase begin to in-
crease; upon complete solidification of the S0 base slag
at 1000 °C, the mass fraction of Cr in the spinel phase is
1.46 %. Calculations show that the mass fraction of Cr in
the base slag with 3-% Cr
2
O
3
is 2.05 %, indicating that
the precipitation rate of Cr in the chromite phase is 71.4
%. The mass fraction of chromium in the oxide (CrO
x
)is
also 2.05 %, suggesting that in theoretical conditions,
chromium is entirely present in the chromite phase.
28
Ad-
ditionally, the mass fraction of V in the spinel phase is
5.2 %. Calculations reveal that the mass fraction of V in
the base slag with 10-% V
2
O
5
is 5.6 %, indicating that
the precipitation rate of V in the SP-V phase is 94.46 %.
Hence, it can be concluded that, in theoretical circum-
stances, vanadium is exclusively present in the SP-V
phase.
From Figure 5, it is evident that at a certain tempera-
ture, MgCr
2
O
4
is the most stable phase. Furthermore,
previous studies demonstrated that the contents of Fe
2
O
3
,
Al
2
O
3
, and MgO can influence the solubility of the
FeCr
2
O
4
spinel phase in slag.
13
To enhance the enrich-
ment of Cr and V elements in stable spinel phases within
vanadium slag, providing favorable conditions for vana-
dium and chromium extraction from the original slag,
adjustments in the slag’s elemental composition are nec-
essary. These adjustments aim to promote the precipita-
tion of chromium as MgCr
2
O
4
and FeCr
2
O
4
spinel phases
while facilitating the precipitation of vanadium as the
FeV
2
O
4
spinel phase.
3.4 Vanadium slag composition design
Table 3: Designed slag formulations (g)
ID Fe2O3 SiO2 TiO2 V2O5 Al2O3 Cr2O3 MgO Al
S0 55 15 10 10 4 3 3 12.5
F1 32 15 10 10 4 3 3
F2 35 15 10 10 4 3 3
F3 37 15 10 10 4 3 3
F4 40 15 10 10 4 3 3
F5 45 15 10 10 4 3 3
F6 50 15 10 10 4 3 3
A1 55 15 10 10 4 3 3
A2 55 15 10 10 6 3 3
A3 55 15 10 10 8 3 3
A4 55 15 10 10 10 3 3
A5 55 15 10 10 15 3 3
A6 55 15 10 10 20 3 3
M1 55 15 10 10 4 3 8
M2 55 15 10 10 4 3 10
M3 55 15 10 10 4 3 12
M4 55 15 10 10 4 3 15
M5 55 15 10 10 4 3 20
M6 55 15 10 10 4 3 25
According to the composition range of steel mill va-
nadium slag, when adding 12.5 g of Al, a basic vana-
dium slag mass of 100 g is designed. On this basis, the
Fe
2
O
3
,Al
2
O
3
, and MgO contents of the steel slag are var-
ied to study the effect of different components on the
phase separation behavior of SP-V. This provides a theo-
retical basis for a comprehensive utilization of vanadium
slag. The simulated slag formulations are shown in Ta-
ble 3.
3.5 Effects of three oxide contents on SP-V phase pre-
cipitation
Figure 6 shows the influences of Fe
2
O
3
,Al
2
O
3
, and
MgO contents on the behavior of SP-V phase precipita-
tion and the proportions of various spinel phases after so-
lidification in vanadium slag. As depicted in Figure 6a,
with an increase in the Fe
2
O
3
content from 32 % to 50 %,
the starting precipitation temperature of the SP-V phase
gradually increases, with a precipitation temperature
range of 1200–1400 °C. During slag solidification, the
amount of SP-V phase precipitation increases with the
increasing Fe
2
O
3
content, showing a positive correlation.
The maximum precipitation amount is achieved with a
Fe
2
O
3
content of 50 %, reaching 30.82 %. This indicates
a significant influence of the Fe
2
O
3
content on the pre-
cipitation of the SP-V phase. From Figure 6a, showing
the proportion of each component in the spinel phase, it
is evident that FeV
2
O
4
and FeAl
2
O
4
constitute the highest
proportion in the SP-V phase. With an increase in the
Fe
2
O
3
content, the proportion of MgV
2
O
4
spinel in the
SP-V phase initially increases and then decreases. When
the Fe
2
O
3
content is between 37 and 40 %, the proportion
of MgV
2
O
4
spinel in the SP-V phase reaches its maxi-
mum value of 15 %. Meanwhile, the proportion of
FeV
2
O
4
spinel in the SP-V phase decreases with the in-
crease in the Fe
2
O
3
content, declining from 48 to 34 %.
The increased proportion of MgV
2
O
4
spinel is attributed
to the decreased proportion of FeV
2
O
4
spinel. The pro-
portion of FeAl
2
O
4
also follows the pattern of initial de-
creasing and then increasing. As previously analyzed,
under certain temperatures, FeV
2
O
4
is more stable than
FeAl
2
O
4
.F e V
2
O
4
and MgV
2
O
4
spinels are preferable
solid chromium phases. Therefore, maintaining Fe
2
O
3
at
37–40 % (minimizing the proportion of FeAl
2
O
4
)iscon -
ducive to the precipitation of vanadium in the form of
FeV
2
O
4
spinel. As indicated in Figure 6b, an increase in
the Al
2
O
3
content slightly raises the starting precipitation
temperature of the SP-V phase to a range of 1350–1410
°C. During solidification, the precipitation of the SP-V
phase increases with an increase in the Al
2
O
3
content,
showing a positive correlation. However, the precipita-
tion amount of the SP-V phase remains between 29.02 %
and 31.43 %, suggesting a minor influence of the Al
2
O
3
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348 345

content on the precipitation of the SP-V phase. Figure
6b includes a diagram showing the proportions of com-
ponents in the spinel phase. With an increase in the
Al
2
O
3
content, the proportions of FeV
2
O
4
and MgV
2
O
4
spinels in the SP-V phase after solidification remain rela-
tively unchanged. This implies that the changes in the
Al
2
O
3
content have a minimal impact on the proportions
of various spinels in the SP-V phase. According to Fig-
ure 6c, when the MgO content increases from 8 % to
25 %, the precipitation proportion of the SP-V phase ini-
tially increases, then decreases, and increases again. This
indicates that a moderate MgO content promotes the for-
mation of the SP-V phase. Thus, maintaning the MgO
content at 10 % can facilitate the generation of the SP-V
phase. According to Figure 6c, the proportion of each
component in the spinel phase is plotted; with an in-
crease in the MgO content, the proportion of MgV
2
O
4
spinel in the spinel phase increases from 12 % to 25 %,
while the proportion of FeV
2
O
4
spinel decreases from
39 % to 26 %. This implies that an increased MgO con-
tent favors the enrichment of vanadium in the form of
MgV
2
O
4
spinel. Additionally, the content and proportion
of MgAl
2
O
4
spinel will also experience a substantial in-
crease. In conclusion, a higher MgO content promotes
the precipitation of MgV
2
O
4
while inhibiting the precipi-
tation of FeV
2
O
4
, making MgO an effective regulator of
the composition of the SP-V phase.
3.6 Fe
2O
3,Al 2O
3, and MgO content effects on FeV2O4
and MgV
2
O
4
spinel phase precipitation in slag
The influences of Fe
2
O
3
,Al
2
O
3
, and MgO contents on
the precipitation behavior of FeV
2
O
4
and MgV
2
O
4
spinel
phases in the slag are depicted in Figure 7. As shown in
Figure 7a, the precipitation fraction of the FeV
2
O
4
spinel
phase in the slag increases with a higher Fe
2
O
3
content.
When the Fe
2
O
3
content reaches 50 %, the precipitation
fraction of the FeV
2
O
4
spinel phase reaches its maximum
value of 9.668 %. This is due to a substantial reduction
of Fe
2
O
3
to FeO in the slag, leading to the reaction of
FeO with V
2
O
3
to form the FeV
2
O
4
spinel phase. An in-
creased FeO content enhances the enrichment of the
SP-V phase, further increasing the precipitation of the
FeV
2
O
4
spinel phase. According to the figure, the precip-
itation fraction of the MgV
2
O
4
spinel phase initially in-
creases and then decreases with the rising Fe
2
O
3
content.
The MgV
2
O
4
spinel phase content increases from 0.08 %
to 3.06 % as the Fe
2
O
3
content rises to 40 %, and then
decreases to 1.72 % with further increases in the Fe
2
O
3
content. This suggests that the addition of Fe
2
O
3
gener-
ally promotes the precipitation of the SP-V phase, espe-
cially the main component FeV
2
O
4
, and controlling the
Fe
2
O
3
mass fraction within a range of 40–50 % is favor-
able for the precipitation of the FeV
2
O
4
spinel phase and
enrichment of vanadium in the spinel phase. Conse-
quently, it can be inferred that the FeO content is also a
crucial factor influencing vanadium extraction in the slag
system.
As illustrated in Figure 7b, the precipitation fraction
of the FeV
2
O
4
spinel phase increases with a higher Al
2
O
3
content, showing a positive correlation. When the Al
2
O
3
content reaches 20 %, the precipitation fraction of the
FeV
2
O
4
spinel phase reaches its maximum value of
10.347 %. This is attributed to Al
2
O
3
promoting the gen-
eration of FeO, leading to an increase in the FeO content
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
346 Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348
Figure 6: Influence of Fe
2
O
3
,Al
2
O
3
, and MgO contents on crystalli-
zation of the SP-V phase: a) effect of Fe
2
O
3
on SP-V phase, b) effect
of Al
2
O
3
on SP-V phase, c) effect of MgO on SP-V phase

in the slag, and subsequently enhancing the precipitation
of the FeV
2
O
4
spinel phase. The content of the MgV
2
O
4
spinel phase increases and then decreases with the rising
Al
2
O
3
content. When the Al
2
O
3
content increases to 8 %,
the MgV
2
O
4
spinel phase content increases from the
original 1.15 to 1.23 %. Overall, the addition of Al
2
O
3
plays a role in promoting the enrichment of vanadium in
the SP-V phase, but its effect is not substantial. As the
MgO content increases, the precipitation temperature for
FeV
2
O
4
increases while its precipitation fraction de-
creases, showing an inverse relationship. When the addi-
tion of MgO increases from 8 to 25 %, the precipitation
temperature of FeV
2
O
4
rises from 1350 °C to 1520 °C,
and its precipitation fraction decreases from 8.16 % to
5.72 %, which is a significant reduction. At the same
time, the precipitation temperature of MgV
2
O
4
increases
with the increase in MgO, and its precipitation amount
also increases with the increase in the MgO content. Es-
pecially in the high-temperature region (>1200 °C), the
rate of increase in the precipitation of MgV
2
O
4
is consid-
erable. At 1150 °C, when the MgO addition increases
from 8 % to 25 %, the precipitation fraction of MgV
2
O
4
increases from 2.55 % to 4.79 %, which is a moderate in-
crease. Therefore, the promotion of MgV
2
O
4
spinel pre-
cipitation by MgO comes at the expense of a reduction in
the FeV
2
O
4
precipitation, but overall, the enrichment of
vanadium in the SP-V phase is still beneficial, so main-
taining MgO at around 20 % is favorable for the enrich-
ment of vanadium in the form of FeV
2
O
4
and MgV
2
O
4
spinel phases.
4 CONCLUSIONS
In the process of vanadium slag treatment, the pres-
ence of the S0 original slag alone does not facilitate a
substantial precipitation of high-content SPINA and
SP-V phases, thus failing to achieve the enrichment of
vanadium and chromium elements within spinel struc-
tures. Nevertheless, by introducing Al into the S0 slag,
with an Al content of 12.5 g, the mass of V-containing
MgV
2
O
4
and FeV
2
O
4
increases from0gto1.338 g and
9.9587 g, respectively. This results in the precipitation
rate of V in spinel rising from0%toaremarkable
94.46 %. Simultaneously, an addition of Fe to the S0
slag, with a Fe content of 25 g, causes the mass of
Cr-containing MgCr
2
O
4
and FeCr
2
O
4
to rise from their
original values of 0.000708 g and 0.00103 g to 3.25 g
and 0.47 g, respectively, leading to a Cr precipitation rate
within spinel structures of 86 %. Furthermore, during the
solidification of vanadium slag with added Fe and Al,
prominent phases that form include Al
4
FeSi
5
O
18,
Al
4
MgSi
5
O
18
, and spinel phases. The SP-V phase pre-
dominantly comprises MgV
2
O
4
and FeV
2
O
4
, while the
SPINA phase is primarily composed of MgCr
2
O
4
and
FeCr
2
O
4
.In general, the Fe
2
O
3
content significantly af-
fects the precipitation behavior of the SP-V phase. A
moderate increase in Fe
2
O
3
promotes the precipitation of
FeV
2
O
4
and MgV
2
O
4
. However, excessive Fe
2
O
3
sup-
presses the precipitation of MgV
2
O
4
. The Al
2
O
3
content
influences the overall precipitation of the SP-V phase,
with a moderate Al
2
O
3
content facilitating the precipita-
tion of FeV
2
O
4
spinel, especially at an Al
2
O
3
content of
20 %, where the precipitation rate of FeV
2
O
4
reaches a
maximum of 10.347 %. Nonetheless, the impact on the
proportions of different spinel phases within the SP-V
phase is minimal. With an increase in the MgO content,
the proportion of MgV
2
O
4
rises, while that of FeV
2
O
4
de-
creases. Controlling the MgO content at around 20 % is
advantageous for the enrichment of vanadium in the
form of both FeV
2
O
4
and MgV
2
O
4
spinel phases. In con-
clusion, these interrelated factors collectively contribute
X.-P. ZHANG et al.: OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348 347
Figure 7: Influences of Fe
2
O
3
,Al
2
O
3
, and MgO contents on the precipitation of the SP-V phase: a) Effects of Fe
2
O
3
on FeV
2
O
4
and MgV
2
O
4
,b)
effects of Al
2
O
3
and MgO on FeV
2
O
4
and MgV
2
O
4
, respectively

to an effective enrichment of vanadium and chromium
elements within spinel structures in vanadium slag.
Acknowledgments
The authors gratefully acknowledge the support of
the Postgraduate Innovation Project of North China Uni-
versity of Science and Technology (2024S11), the Cen-
tral-Guided Local Science and Technology Development
Funding Project of Hebei Province (236Z3803G), and
the Science and Technology Plan Project of Tangshan
City (23130205E).
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348 Materiali in tehnologije / Materials and technology 58 (2024) 3, 339–348