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Article

Initial Characterization of Titanium and Vanadium-Rich Magnetite from the Manastir Heights in Southeast Bulgaria Aiming at Future Environmentally Friendly Beneficiation

by
Marinela Panayotova
1,*,
Ivan Dimitrov
2 and
Angelika Sofronieva
1
1
Department of Mineral Processing and Recycling, University of Mining and Geology, Boyan Kamenot Str. 1, 1700 Sofia, Bulgaria
2
Department of Geology and Geoinformatics, University of Mining and Geology, Boyan Kamenot Str. 1, 1700 Sofia, Bulgaria
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(9), 964; https://doi.org/10.3390/min15090964
Submission received: 17 July 2025 / Revised: 8 September 2025 / Accepted: 8 September 2025 / Published: 11 September 2025
(This article belongs to the Special Issue Advances in Physical Separation of Gold, Iron Ore and Rare Earth Minerals)
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Abstract

Titanium (Ti) and vanadium (V) are metals critical for the sustainable development of our society. Their growing demand and the depletion of ores rich in these metals along with technological development lead to a reconsideration of sources that were previously considered unpromising. The present work is devoted to the study of an iron (Fe) ore from southeastern Bulgaria, containing Ti and V in low but potentially recoverable concentrations. The aim was to check whether it is possible to obtain an iron concentrate containing Ti and V in concentrations comparable to those in similar market products. The material was examined by optical microscopy, XRD, SEM-EDS, and ICP MS. Magnetic separation was applied with and without predating gravity separation. By applying wet gravity beneficiation followed by a low-intensity magnetic field, an iron concentrate (40%–65% Fe) bearing 3%–5% Ti and 0.4%–0.59% V was obtained. Using only a low-intensity magnetic field, without gravity separation, an iron concentrate (59.4% Fe) containing 3.5% Ti and 0.44% V was obtained. Vanadium was extracted in the highly magnetic material, while a significant amount of Ti was left in the weak magnetic fraction. An additional 1.5% may be recovered by applying a high-intensity magnetic field. The main processing challenge appears to be the recovery, without flotation beneficiation, of magnetite that is oxidized to non-magnetic hematite and maghemite. Using magnetic separation (with or without preliminary wet gravity beneficiation) avoids pollution of the processing waste with reagents. Thus, the waste from the beneficiation of the studied type of ore can be used as a soil improver. As a result, the extraction of critical metals using a practically waste-free technology may be achieved.

1. Introduction

Titanium (Ti) is a high-strength, low-density, corrosion-resistant metal possessing superconductivity. It is used in aerospace applications (major use in the USA in 2024), marine hardware, power generation, high-tech equipment, information technology, armor, chemical processing, biomedical applications for medical implants, and other fields [1,2,3]. Titanium dioxide (TiO2), the most used titanium compound, is included in paints, as a filler for paper and plastic, in cosmetics, in solar batteries, as an ingredient in formulations of coatings, sealants, and adhesives, and included in catalysts, ceramics, coated fabrics, and textiles [3,4].
Traditional methods for titanium extraction and the production of titanium products have been mainly concentrated on the use of ilmenite-containing raw materials.
The demand for titanium is expected to rise in the future and this is accompanied by the uncertainty of supply and a practical lack of substitute materials and recycling. Owing to these facts, titanium is listed among critical minerals by the United States as the third strategic metal for development after iron and aluminum [5]. The European Union included titanium in its lists of critical materials starting from 2020 [6,7]. Even more, in China, Ti has also been listed as a priority metal in the “Made in China 2025” and “New Materials Industry Development Guide” policies [2].
Vanadium (V) is used in the steel industry for enhancing the mechanical properties of steel (hardness, tensile strength, ductility, and fatigue resistance). It is applied in advanced aerospace engineering and as catalysts in the chemical industry. Owing to its high-temperature strength, vanadium is used in super alloys for crafting jet engines, turbine blades, and other moving parts working under overheating conditions. Vanadium compounds are applied as catalysts in petroleum product cracking and in controlling the exhaust fumes in diesel engines [8]. Vanadium is used in renewable energy sources, mainly in vanadium redox flow batteries that are a promising technology for safe, large-scale, and environmentally friendly energy storage. It is also applied in permanent magnets and small rechargeable batteries [9].
The main vanadium-containing mineral is vanadium titaniferous magnetite (VTM) [9], which is the source of 88% of V produced worldwide nowadays [10]. Uranium-bearing sandstone, phosphate rock, bauxite, crude oil deposits, tar sands, and oil shales also hold traces of vanadium [9,11]. China is the worldwide leader of vanadium production. It is considered that comprehensive recovery of vanadium can be achieved when the ore contains at least 0.08%–0.1% V [12].
The increasing worldwide demand for vanadium and the concentration of its sources and production in a few unreliable supplier counties have resulted in vanadium’s inclusion on the EU’s and the USA;s lists of critical raw materials [5,6,7].
The exhaustion of high-grade and easily processed placer deposits, containing titanium and vanadium, brings up the need to utilize low-grade ores from magmatic deposits for the future supply of raw materials [13,14]. The beneficiation technologies generally used include wet gravity separation, magnetic separation, flotation, and electrostatic separation [15,16,17,18,19]. Even though the separation and metal recovery effects of flotation and electrostatic separation are good, there will be high consumption of reagents in the flotation process, generation of flotation tailings bearing residual reagents, and a need for further handling and high energy consumption in the electrostatic separation process, especially when the content of the target minerals in raw ore is low [20,21,22].
Magnetic separation manifests itself as a low cost, environmentally friendly, and high-efficiency technology [23]. Titanium and vanadium distribution in ore particles with different sizes [24,25] and different magnetic properties [24,26,27], and magnetic field strengths [28,29,30] has been highlighted in the literature as the most important factor affecting the effectiveness of the production of sellable concentrates bearing Ti and V.
Ore roasting [31], oxidation [32], and reduction [33] prior to magnetic separation are proposed with the aim of magnetizing the surface of weakly magnetic ilmenite particles and improving the magnetic beneficiation process. Another approach is to use a high-pressure grinding roller (HPGR) and parallel separation of Fe–Ti for the HPGR product instead of a jaw crusher and stage separation [26]. Combining the use of high-intensity dry magnetic separation with shaking table beneficiation with an appropriate frequency and amplitude is proposed for processing titanomagnetite with the aim of obtaining an iron concentrate bearing V2O5 in concentrations high enough to be used for vanadium extraction using hydro-metallurgical processes [25]. However, those and similar approaches require additional energy, equipment, and funds and are subject of environmental and economic evaluation.
In order to reduce its dependence on imports of critical raw materials, the European Parliament and Council adopted Regulation (EU) 2024/1252 [34]. Increasing the domestic capacity for the production of critical and strategic raw materials is among the measures envisaged. New geological exploration projects, re-evaluating the exploration of deposits considered unpromising in the past, and the development of new environmentally friendly technologies are foreseen as possible solutions to the critical material problem.
Historically, magmatic deposits of iron (Fe) ore have been prospected in Bulgaria. They were concluded to be unpromising at that time and the possibility of containing critical metals has not been investigated.
The first dedicated study of titanium-rich magnetite from the Manastir intrusion in Southeast Bulgaria, Yambol district, dates from 1941, when Dimitrov and Kamenov [35] presented petrological studies of the titanium–magnetite–ilmenite mineral intergrowth in the gabbro of the Manastir intrusion. Their paper was based on optical microscopic work and was supported by incomplete classical chemical analysis of the ore minerals. Although some of their conclusions are still valid and significant, the detailed nature of the titanium-bearing minerals was not known. This was because of the lack of XRD studies and the overall low level of understanding of these minerals at the time. The presence of a significant amount of vanadium in this mineral paragenesis was not uncovered. However, the above authors turned their attention to the martitisation of the magnetite, expressed in the formation of secondary hematite and maghemite, and commented that some domains of the gabbro are non-magnetic or partially magnetic because of this process.
The next level of understanding was the petrologic paper of Kamenov (1969) [36], who described the petrological varieties of the Manastir multiphase intrusion and defined a special type of “ore-bearing gabbro”, which is the host of titanium mineralization. The “ore gabbro” of the Manastir heights is usually represented by a common gabbro, olivine gabbro, hypersthene gabbro, and hornblende gabbro. Transitions exist as in some varieties a significant amount of hypersthene is found but in others the diopside is predominant over the hypersthene. In all cases, diopside and labradorite can be found as well as alteration products on the pyroxenes. Apatite is the main accessory mineral and the alteration products are serpentine, chlorite, and uralite. The earliest to crystallize was the labradorite and after that hypersthene, diopside, titanomagnetite (which is synonymous for ulvöspinel), and amphibole. The ulvöspinel crystallized in a relatively early stage of the crystallization process as some grains filled the space between the pyroxenes and rather large inclusions were found only in the diopside and hornblende. The vanadium was still undetectable at that time. The emphasis on vanadium was due to Kanurkov’s publication in the eighties of the last century [37] which was not dedicated entirely on the Manastir intrusion but on several Upper Cretaceous basic intrusions in Bulgaria, all of which carry titanium-rich magnetite. Kanurkov also turned his attention to the global geological aspects of this mineralization and its important role for providing both titanium and vanadium for the world markets. He emphasized one significant problem in the development of these deposits: the fact that a huge amount of waste rock in a finely grinded state will be released after the beneficiation process. It was thought that the piles of rock powder would present a pollution challenge to the environment. However, recent studies have indicated that the rock dust might be utilized as a fertilizer, so the concentrate produced might be waste-free [38].
The aim of the present work was to carry out an initial assessment of the magmatic iron ore from the gabbro Manastir intrusion in the Yambol district of Southeast Bulgaria. The idea was to check (i) whether Ti and V are present in this domestic for Europe ore field, (ii) to identify to what extent V and Ti are deported in fractions with different particle sizes and different magnetic properties, and (iii) to elucidate whether in principle Ti and V may be recovered in an environmentally friendly way, without a flotation stage, in an iron concentrate containing Ti and V in concentrations that are similar to marketable concentrates (of Bushveld type).
The results from the chemical analysis of the ore concentrates, the XRD and microscopic studies, and the results from the magnetic separation are presented. This paper presents the initial minimum information on the actual level of prospecting of the deposit in order to indicate its likely significance as a domestic source for the supply of critical raw materials—titanium and vanadium—in Europe.

2. Geological Position of the Fe-Ti-V Magnetite Deposit of the Monastir Intrusion

The surface exposure of the Manastir intrusion in Southeast Bulgaria is around 55 km2 but because some parts of its periphery are covered by thin Neogene and Quaternary sediments, it can be speculated that the total area of the intrusion is around 70 km2 (Figure 1). It is elongated in the E-W direction and its maximum exposed width is around 6 km.
The intrusion is located in the Eastern Srednogorie area of the Late Cretaceous island-arc in Bulgaria that includes numerous larger or smaller hypabyssal and subvolcanic bodies [39]. The isotopic data indicate subduction-related mantle magmatism with minor crustal contamination for these bodies [40]. K-Ar dating for a few plutons in the Eastern Srednogorie vary in the range of 90–72 Ma (Turonian-Campanian). U-Pb zircon data are available for the Manastir pluton, giving an age of 86 ± 1.3 Ma for the intrusion [41]. Since this intrusion clearly has undergone pronounced magmatic differentiation, the period of injection, separation, and settlement of the magmatic domains may have taken a rather protracted amount of time. In this sense, the above numbers regarding the age of the intrusion should be considered only relatively accurate. The following main rock varieties are found to compose this magmatic body [36]: (1) for the main magmatic body—pyroxene-olivine gabbro, gabbro-norite, normal gabbro, anorthosite, pyroxenite, amphibole gabbro, gabbro-diorite, diorite, and quartz containing diorite; (2) for the satellite bodies, which crop around the intrusion—quartz, diorite, plagiogranite, plagioaplite, and aplite; (3) in and around the intrusion, a variety of dykes are found, which postdate the main magmatic event and they include hornblendites, gabbro porphyrites, diorite porphyrites (very common), quartz diorite porphyrites, plagiogranite porphyry, plagioaplites, gabbro porphyrites, micro gabbro diorites, and granite aplite. The granitic dykes are in fact very rare [36]. The magnetite deposit is an enriched domain located in the southern part of the intrusion [37].
The Manastir intrusion was displaced by a NE-striking wrench fault, so the ore-rich magmatic domain remains in the western part of the intrusion, which was moved to SW [42]. The northern part of the intrusion was also displaced by a normal fault [43] together with magnesium and calcium skarn deposits that have been formed on the contact of Upper Cretaceous gabbroic magma and Triassic carbonates. These skarn deposits have been mined consistently throughout time as they provide magnetite and copper mainly from chalcopyrite. The skarn magnetite and the magmatic magnetite are very different from a geochemical point of view, and in this work, the skarn magnetite of the Manastir heights will not be examined.
This paper is devoted only to the magmatic magnetite from the domain described by Kanurkov [37], named here as the Manastir deposit, that carries close resemblance to the Bushveld magmatic magnetite from South Africa, a commercial source of titanium and vanadium [44,45,46].

3. Materials and Methods

In order to assess the titanium and vanadium content in the ore and the beneficiation effectiveness of magnetic separation on a laboratory level, the Manastir deposit was split into two domains—western and eastern. Here, the western domain is named Kopanica (sampling point 1—SP 1) and the eastern domain is named Rock Chapel (sampling point 2—SP 2). Around 20 kg of rock chips were collected from the Kopanica domain and around 20 kg from the Rock chapel domain by sampling the surface gabbro exposures with a geological hammer. The material was subjected to processing and analysis procedures, as presented in Figure 2.
Initially, a thin section of gabbro samples was studied optically under a polarizing microscope, model Meiji Techno MT9430, Saitama, Japan. The natural occurrence of the ore minerals was evaluated in four polished samples, two for each locality, by using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The JEOL/EO 6510 (LA) device (Tokyo, Japan) version 2.01 was used, operated at a beam energy of 20 kV.
The rock chips were crushed using a laboratory jaw crusher and grinded in a laboratory ball mill, model GR/B-REV (Ceramic Instruments, Fiorano, Italy), until 95% of the material size was below 2 mm. The material thus prepared was subjected to gravity beneficiation using a laboratory shaking wet gravity table (LY1000x450, ZJH Minerals, Zhengzhou, China). Thus, the mass and volume of materials to be subjected to further processing were reduced. Since previous studies [24,25] pointed to the deportment of different amounts of Ti and V in fractions of different particle sizes, the resulting gravity concentrate was divided into different grain size fractions using a laboratory sieve shaker, BA200N Compact (CISA Cedaceria Industrial, Lliçà de Vall, Spain). The goal was to determine which fractions contained the largest amounts of the targeted metals and thus assess the necessary degree of grinding in further studies. Each of the resulting fractions was subjected to magnetic separation with a SALA—LIMS (Metso Minerals Sweden AB, Sala, Sweden) laboratory magnetic separator at 0.2 T (one pass, fraction sizes < 0.25, 0.25–0.50, 0.50–0.80 mm) with the aim of determining the presence of the targeted metals in the fractions that differ in particle size.
In order to reveal the presenting ore minerals, equal amounts of fractions less than 0.80 mm were subjected to XRD analysis. The fraction > 0.80 mm was not analyzed due to the fact that the ore minerals were not completely liberated from their non-valuable and non-magnetic matrix and this fraction usually represents mineral aggregates that include rock-forming minerals. For the XRD analysis, samples were used after magnetic separation. Strongly magnetic and non-magnetic fractions, separated at 0.2 T, were analyzed. The analysis was conducted with Bruker D2 Phaser, Cu Kα (Bruker, Berlin, Germany) radiation at λ = 1.54184, and a 2θ interval from 5° to 90° with a step of 0.02° and counting time of 0.41 s per step. The instrument uses DIFFRAC.SUITE software, v.3.1, including tools such as EVA, for search/match and structure databases.
The magnetic and non-magnetic fractions (for each particle size range) were subjected to chemical analysis with the aim of finding the most suitable particle size range for the studied metals’ concentrations. For this purpose, Inductively Coupled Plasma Mass Spectrometry (ICP MS)—method IMS40B—with the digestion of four acids was used. Data were processed with the Excel program. Sample designation is presented in Table 1.
Additionally, magnetic fractions were designated with the letter M and non-magnetic with NM. For example, SP1-1 M means a sample from the Kopanica sampling point with a magnetic fraction of particles of 0–0.25 mm.
Since the gravity beneficiation in water of a large amount of rock mass will impose a significant environmental load, the possibility of magnetic enrichment without any predating gravity separation of gangue minerals was studied on a laboratory scale. For this study, a small magnetite vain formation was sampled from the Rock chapel domain, which was previously interpreted by Dimitrov and Kamenov [35], as a formation of mineralized thermal joints. In this domain, richer subdomains of “ore gabbro” can be found containing around 20% magnetite. For dry magnetic separation, around 7.5 kg of grinded rock mass from the magnetite veins was used. It contained 16.85% iron, 0.89% titanium, and 383 ppm vanadium. The material (fraction with particles < 0.25 mm) was subjected initially to a low-intensity magnetic field (0.2 T, one pass) and then to a high-intensity magnetic field (0.6 T, one pass) to obtain iron concentrates enriched with titanium and vanadium. The choice of magnetic field intensity was based on experience with iron ore magnetic separation and the findings and conclusions of other authors [23,28]. Concentrations of iron, titanium, and vanadium were determined by ICP MS.
The enrichment ratio (ER) for vanadium and titanium is calculated as the ratio of the grade of the concentrate (c) to the grade of the feed (f), i.e., ER = c/f, following Han et al. [28].
All of the above procedures were performed at the Department of Mineral Processing and Recycling and at the Department Geology and Geoinformatics at the University of Mining and Geology, Sofia.

4. Results

4.1. Observations in Thin Sections

Photographs of thin sections are presented in Figure 3. The views are shown in plane polarized light (PPL) and in crossed polarizers (XPLs). The thin sections are from rocks that are moderately enriched with magnetite, and they were taken from the sampling sites. All views show evidence of mechanical deformation expressed in sub-grain formation and the development of alteration products. The magnetite grains appear to corrode the labradorite grain but they are found as inclusions in the hornblende.
The ilmenite formed lamellas, plates, needles, or grains inside or alongside the magnetite grains. Sometimes, it appears as a fine lamella parallel to the (111) or (100) faces in the magnetite. The martitisation of the magnetite [47], which is expressed in the formation of maghemite and hematite as pedomorphosis on the magnetite, appears to progress from fractures in the magnetite grains. The percentage of the hematite pseudo morphoses (in the scale of deposit) that are not susceptible to magnetic beneficiation is yet to be studied. From a pure geological reason, an irregular intensity of alteration and fracturing is expected. We assume that the intensity of this process in the deposit is very irregular and will be revealed only by detailed prospecting and pilot-scale magnetic separation studies.

4.2. SEM-EDS Investigation

The SEM image and ESD spectra of the Kopanica sample (SP1) are shown Figure 4, as an illustration, and the results on the sample’s composition, obtained by SEM-EDS analysis, are given in Table 2. The SEM image and concentrations of studied elements obtained by SEM-EDS analysis for a sample from Rock Chapel (SP2) are presented in Figure 5. In this figure, points 5, 6, and 8 denote rock-forming minerals. The main constituents in point 5 are MgO 32.51%, Al2O3 23.88%, and SiO2 33.54%. The FeO concentration is 10.07%. The main constituents in point 6 are MgO 22.95%, Al2O3 1.70%, SiO2 58.49%, and CaO 11.36%. The FeO concentration in this point is 5.50%. The main constituents in point 8 are Na2O 2.45%, MgO 14.89, Al2O3 16.34%, SiO2 43.28%, and CaO 11.42%. The FeO concentration in this point is 11.02% and the TiO2 concentration is 0.60%. In Figure 5, points 1, 2, 3, and 4 represent ilmenite and point 7 is clearly magnetite.
The SEM results clearly demonstrate that the ilmenite is found inside the larger magnetite crystals, as obviously the original ulvöspinel was broken into ilmenite and magnetite as the rock cooled, forming lamellar or needle-like intergrowths between the two phases. The size of the ilmenite lamellas varies widely from a quarter of a millimeter to a portion of micron-wide needle-like spikes, which will present a significant challenge to any attempt to separate the two mineral phases via grain size reduction. The majority of the probed ilmenite contains between 31 and 33% Ti and around 34 to 35% Fe. It is interesting that ilmenite lamellas usually contain vanadium in amounts varying between 0.15% and 0.4%, although the majority of the vanadium in the magnetite reaches or exceeds 1%. The titanium content of the magnetite grains varies, although it is usually around 1%. Titanium was also found in a Ca-Mg hornblende at a concentration of approximately 0.4%. Obviously, the titanium from the major rock-forming minerals will not be targeted for extraction in future mining initiatives.

4.3. X-Ray Diffractograms

The results of the XRD analysis are presented in Figure 6. It should be noted that the XRD analyses of samples with a huge iron content presented challenges to mineral identification due to the high density of Fe, which can lead to artifacts or reduced image quality. This is because the iron absorbs or reflects X-ray beams. The XRD analysis was performed after magnetic separation of the sample at 0.2 T with the yield of strongly magnetic minerals. The residual assemblage of weakly magnetic or non-magnetic minerals (denoted in Figure 6 as non-magnetic) was also studied.
At present, no ulvöspinel was found by X-ray diffraction. In this work, it is assumed that the primary crystallized phase was indeed ulvöspinel and, later in the magmatic consolidation, it was transformed to magnetite and ilmenite by nearly complete exsolution of the ilmenite phase from the original ulvöspinel (Fe2TiO4). This process is known as oxy-exsolution [48]. Such is the case in many other deposits of similar genesis [49].
The purpose of this study was three-fold: (1) to evaluate if some portion of ilmenite remains in the non-magnetic faction, (2) to assess the occurrence of secondary oxidized non-magnetic phases that might have developed at the expense of the original magnetite, and (3) to see what are the main gangue minerals that persisted through gravitational beneficiation. The high iron content and the resemblance of the spinel structures from the magnetite mineral group did not allow for the identification of coulsonite, even if it exists in the samples. The fraction less susceptible to magnetic beneficiation contains labradorite, diopside, tremolite, and ilmenite. The fraction susceptible to magnetic beneficiation contains magnetite, maghemite, ilmenite, tremolite, and hematite. The fact that ilmenite, maghemite, tremolite, and hematite were found in the strongly magnetic fraction can be explained by the intergrowth between the magnetite and ilmenite and with incomplete secondary oxidation of the original magnetite to maghemite and hematite. The intergrowth is not only between the magnetite and ilmenite but also between some gangue minerals such as hornblende that have inclusions of magnetite which facilitate their attraction by the magnetic field. The hornblende as well as the clinopyroxenes such as diopside were later altered, which is why tremolite shows in the diffractograms as it is not a primary magmatic mineral but an alteration product. Regarding the maghemite and hematite, they formed via the process of martitisation and can be found in the magnetic susceptible and magnetic insusceptible fractions.
It appears that some magnetic domains of the original magnetite crystals remain in the mineral particles, so they show a crystal structure of maghemite or hematite but can still be attracted to a magnetic field. The XRD study confirms that part of the titanium might be lost in the form of weakly magnetic ilmenite that has fallen into the non-magnetic fraction. Part of the titanium and vanadium included in the oxidized non-magnetic iron phases will also be lost, so 100% extraction of the valuable metals by magnetic separation might be impossible no matter how fine the grinding is.

4.4. Gravity Concentration and Particle Size Distribution

Shaking table use allowed for each of the primary samples to be separated a gravitational concentrate of around 1500 g. The obtained materials were subjected to separation into fractions with different particle sizes. The results are presented in Figure 7.
As can be seen from Figure 7, over 50% of the material falls into the finer fractions and almost 80% of the material is in fractions with sizes below 0.8 mm. This indicates that the raw material in both cases does not contain heavy rock-forming minerals in large quantities.

4.5. Magnetic Separation Studies and ICP MS Analyses

Each of the fractions with a different size range was subjected to magnetic separation at 0.2 T and the results are presented in Figure 8.
As can be seen from Figure 8, for all three fractions, over 80% of them possess magnetic properties, regardless of particle size. The quantity of particles with magnetic properties decreases slightly with increasing particle size. Our findings are in line with the results of Han and coauthors who found that the magnetite content in samples increased with increasing grinding time, i.e., decreasing particle size [28]. The positive effect of particle size decrease on the liberation and recovery of iron and titanium by magnetic separation from vanadium–titanium magnetite ore is also pointed out by Chen and coauthors [50].
Magnetic and non-magnetic fractions were subjected to chemical analysis, and Table 3 presents the concentrations of some metals that are characteristic for the studied materials. Each value given in Table 3 is an average of two parallel samples.
The data from the ICP MS analysis show that vanadium is completely associated with iron, most likely through isomorphic substitution in the magnetite. The correlation coefficient between the concentrations of the two metals for the samples from both localities is r = 0.999. This is in agreement with findings of other authors who found that in titanomagnetite and high-magnetite-content ores, vanadium is closely associated with magnetite, whereas ilmenite contains a relatively negligible amount of vanadium [23,51].
Vanadium is definitely concentrated in the highly magnetic samples and it is predominantly found in samples with a particle size less than 0.5 mm. This is in line with the results of Yan and coauthors who found increased vanadium concentration and recovery in finer particles [51].
Titanium is also mainly associated with iron, as the correlation coefficient between the two metals is r = 0.759 for the first locality and r = 0.967 for the second. Higher amounts of titanium are determined in highly magnetic fractions with a particle size less than 0.5 mm. However, significant concentrations are determined in the fraction behaving as non-magnetic at 0.2 T, most probably containing mainly ilmenite, with a particle size lower than 0.25 mm. Rahman et al. also found higher Ti concentrations in ilmenite magnetic concentrates with a particle size in the range 0.125–0.50 mm [52]. This indicates (i) the need for relatively fine grinding to increase titanium recovery in possible future technologies, and (ii) the necessity to apply a high-intensity magnetic field in order to recover more titanium. The need to apply a more intensive magnetic field to recover titanium is also pointed out by other authors [51].

4.6. Test on Magnetic Beneficiation Without Predating Gravity Separation

The applied simple beneficiation scheme and the results are presented in Figure 9. The goal was to determine whether and to what extent titanium and vanadium can be efficiently concentrated without gravity beneficiation in iron-containing fractions with different magnetic properties.
The mineralogical study of the raw samples showed that vanadium and titanium are mainly distributed in iron minerals. Due to the fact that non-oxidized iron minerals with a low degree of oxidation are strongly magnetic minerals, it is practicable to separate them by using a low-intensity magnetic field.
A major part of vanadium and a significant part of titanium available in the ore are separated in the iron concentrate by applying a weak magnetic field. However, the separation is imperfect. Chen et al. also pointed out the incomplete extraction of titanium (58.44%) by using a weak magnetic field (0.25 T) [50].
Our results on concentrating titanium in iron concentrates are comparable but higher than the results of Maldybayev et al. who used a magnetic field of 0.2 T with a tubular magnetic analyzer 298-CE (Davis tube) for preliminary separation of a magnetic fraction containing concentrated titanomagnetite [29]. We achieved an ER of 4.4 for Ti and 11.5 for V, compared to 6.45 and 2.12, respectively, by Maldybayev. At the same time, for a high-V-content VTM ore, Han and coauthors [28] found an ER of 3.64 for V and 1.64 for Ti for the applied magnetic field in the range 0.05–0.8 T. Our higher ER value for V may be attributed to the fact that in our case vanadium is entirely bound to magnetite.
In an attempt to further recover titanium, a stronger magnetic field was applied. Additional amounts of titanium and vanadium were extracted in the low magnetic iron concentrate. Still, some titanium was left in the non-magnetic fraction, confirming assumptions based on the results from the XRD and EDS analyses and pointing out the need for separation optimization.
A number of authors point out the significant influence of the size of the mineral particles subjected to separation and the intensity of the applied magnetic field on the efficiency of vanadium and titanium extraction and propose different optimal conditions, mainly depending on the mineralogical characteristics of the ores [23,26,28,51]. After establishing the presence of vanadium and titanium in the investigated ores and the principal possibility of obtaining iron concentrate rich in vanadium and titanium, further studies are needed to optimize the grinding and magnetic separation processes in order to maximize magnetite and ilmenite recovery.

5. Discussion

5.1. The Effect of the Oxy-Exsolution and Martitisation on Magnetic Enrichment

As it appears, the largest concentrations of Ti and V were found in samples SP1-1,2 and SP2-1,2. These are the samples processed on shaking tables and ground to 0–0.25 and 0.25–0.5 mm. Especially high are the concentrations of Ti and V in SP2-2. The fact that a higher concentration is found in the 0.25–0.5 mm rock and not in the finer grinded rock has important implications on the future strategy of sample processing. It appears that the two post-deposition processes affecting the primary titanomagnetite—the oxy-exsolution—which is the exsolution of lamellar or needle-shaped ilmenite, and the martitisation that forms non-magnetic hematite and intermediate maghemite play a critical role in the separability of titanium and vanadium. First of all, the ilmenite is a weekly magnetic mineral. So, it makes more sense for it to be recovered in a magnetic field included in the larger magnetite crystals. If these crystals are grinded to finer fractions, the released weakly magnetic or non-magnetic ilmenite may not be attracted by the magnetic field. However, if it is included in the magnetite lattice all of it will be separated by a magnetic field. Consequently, too fine grinding may not be beneficial for titanium extraction in the concentrate. For example, Xu et al. found that the recovery of vanadium, titanium, and iron decreased with increased grinding fineness, i.e., increased fraction of particles with a size less than 0.074 mm. With decreasing particle size, the grade of titanium decreased a little. The grade of V2O5 decreased when the quantity of particles with a size less than 0.074 mm was over 85.2% [23].
The SEM and XRD studies show that separate vanadium phases do not exist but most of the vanadium is included in the magnetite and only a minor amount is in the ilmenite and the gangue minerals. In this sense, the extraction of the magnetite without breaking out the ilmenite domains may be beneficial for V extraction. On the other hand, optical microscopy and SEM studies show that some smaller magnetite crystals are included in the hornblende as inclusions, and for these inclusions to be released, grinding to under 0.25 mm might be beneficial. Martitisation also imposes ambiguous or opposing dilemmas as to how the ore should be prepared for beneficiation. First of all, maghemite and hematite are found in both the magnetic and non-magnetic fractions, which suggests that martitisation is not complete. It is very likely that some of the magnetite particles have been only partially oxidized so they have a core that can be attracted by the magnetic field and the exterior coating of hematite, which is non-magnetic. Such particles might be attracted by the magnetic field even if parts of them are non-magnetic. Increasing grinding intensity may lead to particle splitting and a loss of ability of valuable non-magnetic parts of former bigger particles to be attracted by the magnetic field. At this moment, we do not have a critical mass of studies in order to indicate the level of particle size reduction needed to optimize the extraction of Ti and V from the point of view of the martitisation processes in the ore but it is obvious that more work needs to be carried out in this direction.
Detailed prospecting of the deposit might indicate that there are domains inside the deposit that are more oxidized than others. The share of the hematite and maghemite pseudo morphoses in this deposit that are not susceptible to magnetic beneficiation may be responsible for the incomplete recovery of Ti and V host minerals. Future detailed prospecting is needed that should include denser drilling to (i) split the deposit in domains of higher or lesser content of magnetite, (ii) determine the domains of more or less intense martitisation, (iii) map the internal distribution of titanium and vanadium in the deposit, (iv) as a result, determine the reserves and resources of the deposit.

5.2. Economic Validation of the Featured Fe-Ti-V Concentrate

If the deposit is considered within the dimensions given by Kanurkov [37] and given the Ti and V concentrations provided in Table 3, assuming a conservative 7% uniformly distributed magnetite content in the “ore gabbro” [37], the deposit has at least 66,000,000 million metric tons of magnetite, containing between 3 and 5% titanium and 0.4%–0.59% vanadium. However, the percentage of the marketable, industrially recovered-for-profit concentrate will depend on the mining and enrichment losses. A brief review of published certificates of titanium and vanadium concentrates, especially from the Bushveld complex in South Africa, indicates that the above concentrations (Table 3) are actually worth attention. For example, open internet sources show that a Ti-V concentrate containing Fe 21.98%, Ti 2.98%, and V 3763 ppm from Bushveld is successfully marketed outside Africa for up to 3300 ZAR or 187 USD per ton of concentrate [53]. The metallurgical extraction of metals can raise the value of the deposit. With a lack of the well-developed titanium and vanadium metallurgy in the EU, the deposit can still be mined to produce a Ti and V concentrate that is exported to other countries. In this case, the environmental complications are minimal. Such environmental problems might arise from using flotation, which will also prohibit the use of the gangue minerals in agriculture. Although not so significant, the gravity water beneficiation will also present environmental complications, because the studied region lacks abundant water resources. It is also significant to mention that this deposit is not the only Bushveld-type titanium mineralization in Bulgaria. The country has at least three other deposits of a similar type, as reported by Kanurkov [37]. All of them may serve as a base for the titanium industry. The ideal scenario is the development of modern metallurgical methods in the EU and the development of critical element recovery. This might contribute to a solution in the best interest of EU citizens.

5.3. Opportunity for Rock Waste Material Handling

Recent research and market developments indicate that in this particular case, the perceived “waste problem” due to redundant rock dust might turn out to be the greatest asset of this deposit. A dedicated study on carbonate subsoils and soil degradation in Southeast Bulgaria has found that around 11% of the highly productive agricultural soils of Yambol district are affected by soil erosion [54], leading to exposure on the surface of a non-fertile calcareous soil matter known as calcrete [55]. This requires remediation [56] by adding agents like rock dust, which upon weathering will serve as a matrix for humus formation [56,57] with the added benefits of the rich micronutrients found in the grinded gabbro. Rock dust from some of the Bulgarian quarry sites is already in demand and exported to destinations outside Bulgaria. This modern development indicates that “ore gabbro” mining and magnetic beneficiation can be waste-free as practically all products will be used in the economy, creating added value. A very important aspect to stress is that this is valid only if the rock can be processed by magnetic separation only, without flotation, and thus the rock particles should be clean from flotation agents and in their natural state. It is important to point out that rock fertilization works better if the rock dust is finer. The finer the particle, the faster the weathering to clay minerals [58]. This is complemented by the fact that a large wheat-producing region of Bulgaria, Yambol district, is located immediately to the north of the Manastir heights. In practice, the patches of infertile soil calcrete exposed in this land that need amelioration by humus introduction [59] affect the agricultural operators much more than the global strive to mediate carbon emissions, so real economic interest in gabbro waste is expected to materialize among local farmers.
Numerous scientific studies on rock dust of a similar composition have been performed, addressing the weathering problems from a climatic point of view, where the rate of weathering is measured in tons of CO2 neutralized per hectare of land per year. For example, Reershemius, et al. [60] assessed that the carbon dioxide removal (CDR) rate is around 2.24 t CO2/(ha. yr.)—with column experiments (50 t basalt/ha) using mass balance-based methods. Since the Manastir gabbro is of a similar composition, comprising mainly labradorite, orto- and clinopyroxene, and olivine, its composition is expected to adhere to a similar CDR rate. This CDR rate implies an opportunity for an additional environmental benefit.

6. Conclusions

The gabbro from the Manastir heights, Southeast Bulgaria, carries magnetite containing Ti and V. Application of magnetic separation with the aim of producing a marketable concentrate appears feasible. Wet gravity beneficiation followed by using low-intensity magnetic field, applied in an open cycle, results in obtaining a magnetite concentrate (containing 40%–65% Fe) bearing 3%–5% Ti and 0.4%–0.59% V. Using only a low-intensity magnetic field, without preliminary gravity separation, produces a concentrate containing 59.4% Fe, 3.5% Ti, and 0.44% V. Vanadium is concentrated in the highly magnetic material. A significant amount of Ti is left in the weakly magnetic fraction (primary ilmenite but also hematite and maghemite). Application of a high-intensity magnetic field may recover a substantial amount of Ti from that material.
The waste material from the magnetic beneficiation can be used to ameliorate the calcareous agricultural soil in the region. Thus, in the best-case scenario, the mining and magnetic separation of the described ore can be green, i.e., an environmentally friendly and waste-free process.
Although this study is very preliminary and much future work is needed, its positive result is the indication that in Europe, a source exists of two critical raw metals that could be obtained using environmentally friendly technologies.

Author Contributions

Conceptualization, I.D.; methodology, I.D. and M.P.; investigation, A.S.; writing—original draft preparation, I.D. and M.P.; writing—review and editing, I.D., M.P. and A.S.; visualization, A.S.; project administration, M.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Science Program “Critical and strategic raw materials for a green transition and sustainable development”, approved by the Resolution of the Council of Ministers No. 508/18.07.2024 and funded by the Ministry of Education and Science (MES) of Bulgaria.

Data Availability Statement

The research data are available in the text.

Acknowledgments

The authors are thankful to Raicho Donchev for his help with the magnetic separation tests.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
CDRcarbon dioxide removal
EDSenergy-dispersive X-ray spectroscopy
ERenrichment ratio
ICP MSInductively Coupled Plasma Mass Spectrometry
PPLplane polarized light
SEMscanning electron microscopy
SPsampling point
VTMvanadium titaniferous magnetite
XPLcrossed polarizer
XRDX-ray diffractometry

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Minerals 15 00964 g001
Figure 1. A location map of the Manastir intrusion showing the roads and the adjacent villages in Southeast Bulgaria. The exposed boundaries of the intrusion around the village Golyam manastir are shown with a pink raster over the green geographic map. The sampling locations, SP1—Kopanica and SP 2—Rock Chapel, are shown with a black circle and a black square. The red frame represents the detailed Figure with the road network of the area.
Figure 1. A location map of the Manastir intrusion showing the roads and the adjacent villages in Southeast Bulgaria. The exposed boundaries of the intrusion around the village Golyam manastir are shown with a pink raster over the green geographic map. The sampling locations, SP1—Kopanica and SP 2—Rock Chapel, are shown with a black circle and a black square. The red frame represents the detailed Figure with the road network of the area.
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Figure 2. Flow sheet of processing and analysis procedures carried out with samples SP1 and SP2.
Figure 2. Flow sheet of processing and analysis procedures carried out with samples SP1 and SP2.
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Figure 3. Two views of opaque grains of magnetite included in gabbro—in plane polarized light (PPL) and in crossed polarizers (XPLs). The magnification is 10X for all views. Top row—Kopanica (SP1); bottom row—Rock Chapel (SP2).
Figure 3. Two views of opaque grains of magnetite included in gabbro—in plane polarized light (PPL) and in crossed polarizers (XPLs). The magnification is 10X for all views. Top row—Kopanica (SP1); bottom row—Rock Chapel (SP2).
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Figure 4. SEM image (a) and ESD spectra of different elements in sample SP1: (a) detail of sampled crystal; (b) point 1; (c) point 2; (d) point 3; (e) point 4; (f) point 5.
Figure 4. SEM image (a) and ESD spectra of different elements in sample SP1: (a) detail of sampled crystal; (b) point 1; (c) point 2; (d) point 3; (e) point 4; (f) point 5.
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Figure 5. SEM image (a) and concentrations of elements characteristic for specific points in raw SP2 sample (b).
Figure 5. SEM image (a) and concentrations of elements characteristic for specific points in raw SP2 sample (b).
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Minerals 15 00964 g006aMinerals 15 00964 g006b
Figure 6. X-ray diffractograms of studied samples. (a) Kopanica sampling point—magnetic fraction; (b) Kopanica sampling point—non-magnetic fraction; (c) Rock Chapel sampling point—magnetic fraction; (d) Rock Chapel sampling point—non-magnetic fraction.
Figure 6. X-ray diffractograms of studied samples. (a) Kopanica sampling point—magnetic fraction; (b) Kopanica sampling point—non-magnetic fraction; (c) Rock Chapel sampling point—magnetic fraction; (d) Rock Chapel sampling point—non-magnetic fraction.
Minerals 15 00964 g006aMinerals 15 00964 g006b
Minerals 15 00964 g007
Figure 7. Results from sieving analysis.
Figure 7. Results from sieving analysis.
Minerals 15 00964 g007
Minerals 15 00964 g008
Figure 8. Results from magnetic separation: M—magnetic; NM—non-magnetic fraction.
Figure 8. Results from magnetic separation: M—magnetic; NM—non-magnetic fraction.
Minerals 15 00964 g008
Minerals 15 00964 g009
Figure 9. A simple flowsheet for iron ore magnetic separation and the results obtained: α—iron content in the raw material, β—iron content in the iron concentrate, γ—yield, ε—iron recovery in products, and θ—iron content in the waste.
Figure 9. A simple flowsheet for iron ore magnetic separation and the results obtained: α—iron content in the raw material, β—iron content in the iron concentrate, γ—yield, ε—iron recovery in products, and θ—iron content in the waste.
Minerals 15 00964 g009
Table 1. Sample designation.
Table 1. Sample designation.
Sampling PointParticle Size, mmDesignation
Kopanica sampling point
SP 1		0–0.25SP1-1
0.25–0.50SP1-2
0.50–0.80SP1-3
>0.80SP1-4
Rock Chapel sampling point SP 20–0.25SP2-1
0.25–0.50SP2-2
0.50–0.80SP2-3
>0.80SP2-4
Table 2. Concentrations of elements characteristic for raw SP1 sample determined by SEM-EDS in different points.
Table 2. Concentrations of elements characteristic for raw SP1 sample determined by SEM-EDS in different points.
Point; Element, wt. %OMgFeAlTiVMnNbTa
00131.521.1734.51 31.120.311.38
00231.061.2534.31 32.030.211.14
00340.508.5419.1630.98 0.090.73
00425.93 70.090.912.210.86
00524.94 71.360.601.300.81
Table 3. Concentrations of metals in studied material samples, as determined by ICP MS.
Table 3. Concentrations of metals in studied material samples, as determined by ICP MS.
Metal; SampleSP1-1 MSP1-2 MSP1-3 MSP1-1 NMSP1-2 NMSP1-3 NM
Al, %1.951.732.194.123.503.32
Ca, %2.682.296.859.0011.410.9
Fe, %40.242.720.57.716.785.92
K, %0.070.070.090.120.120.12
Mg, %1.972.185.545.116.576.10
Mn, ppm286325342261290922972049
Na, %0.300.320.460.740.650.61
Ti, %3.312.971.392.680.870.57
V, ppm402143901960311357310
Zn, ppm320.9318.0168.0180.0128.593.6
Metal; SampleSP2-1 MSP2-2 MSP2-3 MSP2-1 NMSP2-2 NMSP2-3 NM
Al, %1.392.422.313.873.233.07
Ca, %0.361.403.448.3510.211.2
Fe, %51.665.234.710.37.357.43
K, %0.030.070.090.100.130.14
Mg, %0.651.893.215.076.496.75
Mn, ppm201229982096255220191956
Na, %0.060.210.240.580.520.50
Ti, %3.314.982.761.700.750.43
V, ppm465358433031360359381
Zn, ppm371.6527.8283.5105.066.358.5
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Panayotova, M.; Dimitrov, I.; Sofronieva, A. Initial Characterization of Titanium and Vanadium-Rich Magnetite from the Manastir Heights in Southeast Bulgaria Aiming at Future Environmentally Friendly Beneficiation. Minerals 2025, 15, 964. https://doi.org/10.3390/min15090964

AMA Style

Panayotova M, Dimitrov I, Sofronieva A. Initial Characterization of Titanium and Vanadium-Rich Magnetite from the Manastir Heights in Southeast Bulgaria Aiming at Future Environmentally Friendly Beneficiation. Minerals. 2025; 15(9):964. https://doi.org/10.3390/min15090964

Chicago/Turabian Style

Panayotova, Marinela, Ivan Dimitrov, and Angelika Sofronieva. 2025. "Initial Characterization of Titanium and Vanadium-Rich Magnetite from the Manastir Heights in Southeast Bulgaria Aiming at Future Environmentally Friendly Beneficiation" Minerals 15, no. 9: 964. https://doi.org/10.3390/min15090964

APA Style

Panayotova, M., Dimitrov, I., & Sofronieva, A. (2025). Initial Characterization of Titanium and Vanadium-Rich Magnetite from the Manastir Heights in Southeast Bulgaria Aiming at Future Environmentally Friendly Beneficiation. Minerals, 15(9), 964. https://doi.org/10.3390/min15090964

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