Method and system for the beneficiation of very low-grade chromite ores

Abstract

The present invention relates to the beneficiation of low-grade chromite ores in the mining industry. Specifically, the invention addresses the prevention of waste of ores having a chromite content of less than 5%, particularly those comprising olivine, and the economic recovery of such resources. As per the invention, the method steps and system equipment employed accordingly comprise subjecting the powdered ore particles to magnetic pre-separation at a field intensity of 9,000-10,000 Gauss before gravity separation, thereby ensuring that at least 30% of the gangue minerals, primarily comprising olivine, are discarded as a dense, clean residue, resulting in a pre- concentrate with a chromite grade of at least 7% suitable for gravity-based separation. The process can then continue with gravity-based separation and, if necessary, additional magnetic separation.

Description

[0001] DESCRIPTION

[0002] METHOD AND SYSTEM FOR THE BENEFICIATION OF VERY LOW-GRADE CHROMITE ORES

[0003] TECHNICAL FIELD

[0004] The present invention relates to ore preparation and beneficiation processes in the mining industry. More specifically, the invention relates to the beneficiation of low-grade chromite ores.

[0005] PRIOR ART

[0006] Chromium, a metallic element with a shiny, silver-like appearance, is one of the natural components of the earth's crust, belonging to group VI.A. It is generally found in solidified lava formations within dense rocks in crystal form. Chromium is critically important to various industries, serving as a fundamental element in metallurgy, chemistry, and refractory industries.

[0007] Although there exists about 25 known minerals containing chromium, the richest and most widespread in terms of chromium content is the mineral chromite. Theoretically, its chemical formula is FeC^C ; however, in nature, the formula of chromite is given as (Mg,Fe)(Cr,Al,Fe)2O4. Chromite ore can be characterized as massive, disseminated, nodular, orbicular, banded, and disseminated-banded. While Mg, Cr, Fe, and Al elements constitute the chromite mineral, silica from gangue minerals is also an integral part of chromite ore analyses. Chromite ore is essential in producing ferrochrome, which is used in manufacturing stainless steel in the metallurgy field; in the refractory field, it is used in the manufacture of refractory bricks and mortars; and in the chemical industry, chromite is used as a pigment, in leather tanning, and in the manufacture of dry cells. A significant portion of the world's chromite ore production is dedicated to producing ferrochrome for stainless steel manufacturing.

[0008] The world's total chromite resources are approximately 7.6 billion tons, with 3.6 billion tons classified as reserves. A large portion of the world's chromium resources belong to stratiform deposits. These deposits, characterized by small particle size, regular crystal shape, low Cr / Fe ratio, and high iron content, are mostly found in South Africa, Canada, Finland, and Madagascar. In contrast, podiform type deposits, which have larger particle size, irregular crystal shape, higher Cr / Fe ratio, and higher chromium content, are mainly found in Kazakhstan, Turkiye, and Albania. In Turkiye, where most of the chromite deposits are podiform with high Cr / Fe ratios and high chromium content, only 5% (13,087,000 tons) of the known 242,341,000 tons of chromite resources have directly marketable grades, making it necessary to beneficiate and concentrate the chromite ores. In Turkiye, chromite mining has generally been conducted through surface or open-pit mining methods. However, due to the gradual depletion of chromite ores accessible via open-pit mining, the production of chromite ores through underground mining methods has been increasing since 1960 to the present day.

[0009] The produced ore is generally beneficiated using physical and / or physicochemical methods. The most suitable method is selected based on the liberation particle size of chromite and the gangue minerals in the ore composition, ore mineralogy, and the physical and physicochemical differences between the chromite mineral and gangue minerals. Mostly, beneficiation methods based on specific gravity differences are applied.

[0010] The chromite mineral to be recovered from an ore composition generally has a specific gravity of 4.1-4.9 g / cm3, a hardness of 5.5, a bright black color, and a streak color of brown. Considering that the mass magnetic susceptibility of the magnetite mineral is 1156 x10-6m3 / kg and that of the hematite mineral is 0.60-2.16 x10-6m3 / kg, with a mass magnetic susceptibility of 0.63- 0.88 x10-6m3 / kg, the chromite mineral has very low magnetic susceptibility and can only be attracted at very high magnetic field intensities. However, chromite ore can have higher magnetic susceptibility due to the presence of iron minerals and Fe in its spinel structure, as found in the Bursa Harmancik ore.

[0011] In addition, chromite ore is accompanied by serpentine group minerals, which are magnesium hydrosilicates in structure, as gangue rock. These are found in nature as chrysotile, lizardite, and antigorite. Its density is between 2.5-27 g / cm3. It is softer than granite and generally harder than most marble, with a hardness of 3 on the Mohs scale. The most commonly accepted mineral formula of serpentine is (Mg.Fe.Ni.Mn.Znh-BfSi.Al.FehOsfOH Depending on their iron content, serpentine minerals belong to the class of paramagnetic minerals and can be recovered at high magnetic field intensities.

[0012] Another gangue rock found as an accompanying mineral is olivine, which is most commonly found in ultrabasic (peridotite) rocks, especially in dunites. Olivine minerals, which crystallize in the orthorhombic system, are mainly composed of Mg+2and Fe+2silicates and belong to the orthosilicate group. The dominant end members, where Mg+2and Fe+2are predominant, are named Mg2SiO4 (forsterite) and Fe2SiO4 (fayalite). Olivine minerals other than forsterite and fayalite, which fall between said end members, are not very common in nature. Olivine is generally green to dark green in color and is a quite hard mineral (6.5-7 on the Mohs scale). Its density varies between 3.22 and 4.40 g / cm3, depending on its iron content.

[0013] The chromite ores, in which said minerals accompany each other in pairs or triples, are beneficiated based on the properties of both the gangue and chromite minerals. As observed, when olivine, which has a specific gravity close to that of chromite, is present in the ore structure, there is no highly selective separation with gravity methods, and the obtained Cr2Oa percentages remain low.

[0014] In the presence of serpentine, which has lower hardness and specific gravity, effective beneficiation can be achieved through gravity separation, reaching high Cr2Oa contents (over 46%) and higher recovery efficiencies. Due to the fact that Turkish ores, for instance, generally have said composition, almost all chromite beneficiation plants operate using a classical process where the ores are crushed and ground, screened, and then fed in powdered form into hydraulic classifiers and subsequently onto shaking tables.

[0015] However, in some regions, the rock accompanying the chromite ore is dunite, which contains very high amounts of olivine minerals. Additionally, iron compounds that appear as spots and / or streaks on the surface of the chromite mineral in these ore structures cause significant differences in the ore's magnetic susceptibility. While chromite concentrate production in the country has mostly been from classic ore deposits, these types of ore formations have been considered problematic and relegated to secondary importance

[0016] In today's world, the rising population and technological advancements have led to an increased demand for various raw materials, while the availability of easily beneficiated ores is steadily declining. Consequently, the development and optimization of processes for treating these challenging ores have become crucial. Additionally, although the economic beneficiation grade for chromite ore is 5% CT2O3, ores with lower grades are regrettably not included in the reserves.

[0017] However, if an ore deposit contains an average of 5% C^Chwith a reserve of 1 million tons, and the ore to be produced has an average grade of 3% C^Ch, it becomes feasible to incorporate even very low-grade ores into the reserve and effectively recover thereof. In this scenario, preventing the waste of national resources and ensuring the efficient utilization of the country's resources would be recognized as a significant achievement.

[0018] In conclusion, there exists a requirement to operate mining deposits with the most appropriate and efficient technologies, ensuring sustainable and responsible mining practices that respect both the environment and society, and minimize negative impacts on natural resources and water systems. It is imperative to use all raw materials and water resources efficiently and effectively in ore beneficiation processes. The principle of minimizing waste and maximizing added value requires reasonable and environmentally friendly approaches that prevent or minimize environmental damage, thereby contributing to the national economy through value-added innovative studies in mining enrichment and operations. OBJECTIVES AND BRIEF DESCRIPTION OF THE INVENTION

[0019] The primary objective of the present invention is to provide an innovative and sustainable alternative method to existing practices in the mining industry by addressing the challenges frequently encountered in processing low-grade chromite ores.

[0020] Another significant objective of the invention is to provide a value-added method for economically processing low-grade chromite ores comprising less than 5% chromite, using distinctive processing techniques.

[0021] Another objective of the present invention is to provide a method for efficiently separating gangue minerals such as olivine and other undesirable mineral components from the ore with minimal loss.

[0022] Yet, another objective is to provide a system that maximizes the purity of the chromite concentrate obtained through the newly-developed processing methods, producing a high-quality product suitable for industrial use.

[0023] Furthermore, one of the significant objectives of the invention is to provide a system that effectively manages energy consumption and operational costs throughout the process, enhancing overall efficiency and economic sustainability while minimizing environmental impact and implementing sustainable waste management and water usage practices.

[0024] In order to achieve the aforementioned objectives, the present invention provides a unique method and system for processing very low-grade chromite ores comprising olivine, featuring the process steps defined in Independent Claim 1 and the structural components and characteristics defined in the independent system claim, further supported by the subsequent dependent claims.

[0025] The primary focus of the method is to economically process low-grade ores with less than 5% chromite content, particularly those comprising olivine, thereby preventing waste and contributing to the economy. The method comprises reducing the ore to a particle size below 500 microns, applying a relatively moderate magnetic field for pre-separation, followed by gravity separation, and optionally, a subsequent magnetic separation.

[0026] Said low-grade ore is initially reduced to the reported liberation particle size. At this stage, the high iron content on the chromite surface not only increases its specific gravity but also enhances its magnetic susceptibility. In such a case, a material that would typically exhibit very low magnetic susceptibility due to being solely comprising chromite mineral attains medium-level magnetic susceptibility because of said structural characteristic and can be attracted as a magnetic product at a magnetic field intensity of 9,000-10,000 Gauss. On the other hand, gangue minerals comprising olivine, having much lower magnetic susceptibility, are obtained as non-magnetic products at said magnetic field intensities. This process results in a pre-concentrate with higher C^Ch content from the magnetic product, while a clean residue with low C^Ch content (<0.5% Cr2Oa) is obtained from the non-magnetic product. Consequently, approximately 35-40% of the ore fed into the process can be discarded as residue before entering gravity beneficiation.

[0027] This phenomenon, which is not encountered in classic ore deposits, provides a significant advantage and unexpected success for these types of ore deposits within the scope of the invention. The adverse effects created by the iron surfaces on the chromite ore have been transformed into a beneficial outcome, enabling pre-beneficiation through magnetic separation. This also contributes to the beneficiation of lower-grade ores and their inclusion in the reserves.

[0028] In a preferred first aspect of the invention, a method is provided for the beneficiation of low-grade chromite ores comprising olivine and having a chromite grade / content of less than 5%, which comprises reducing the ore to a suitable particle size and performing gravity-based separation. This method comprises the following process steps; reducing the ore particles to a size below 500 microns through grinding, subjecting the ore, reduced to said particle sizes, to a magnetic pre-separation at a field intensity of 9,000-10,000 Gauss, thereby separating at least 30% of gangue minerals predominantly comprising olivine as a clean residue and obtaining a chromite-rich magnetic intermediate product as a pre-concentrate, and subjecting the pre-concentrate, which is richer in chromite from the magnetic preseparation step, to gravity separation after being classified into narrower size ranges.

[0029] As a result of said magnetic pre-separation step, the chromite content in the pre-concentrate is at least 5%, and at least 0.5% in the clean residue. Additionally, at least two-thirds of the total feed in the pre-concentrate obtained here has a Cr2Oa content of more than 8%, while the remaining one-third residue is removed from the process with a C^Ch content of 0.4%. Furthermore, the magnetic pre-separation process is a wet process to be carried out after wet grinding, and thus no drying procedure is required beforehand.

[0030] In the method according to the invention, the magnetic pre-separation step involves separating the ground chromite ore at a moderate magnetic field intensity of 9,000 to 10,000 Gauss, typically generated by strong magnets with natural magnetic properties such as neodymium, or provided by a generator. Following the magnetic pre-concentration carried out during said magnetic pre-separation step, the magnetic minerals / pre-concentrate are retained on the belt, then classified into narrower size ranges using hydraulic classifiers in the subsequent step, and finally subjected to gravity separation, resulting in a concentrate with at least 40% chromite content.

[0031] The chromite-rich concentrate obtained from said gravity separation step is subjected to a cleaning and beneficiation step using magnetic separators at a field intensity of 6,000-7,000 Gauss in the subsequent step, resulting in the production of a concentrate with more than 45% Cr2Oa content.

[0032] In a preferred second aspect of the invention, a system is provided for the beneficiation of low- grade chromite ores comprising olivine and having a chromite content of less than 5%, which comprises an ore preparation unit with crushers and size classification devices to reduce the ore to a suitable particle size, and a gravity-based separation unit. Said system comprises the following components; at least one grinder to reduce the ore to a particle size below 500 microns, at least one wet magnetic pre-separation unit operating at a field intensity of 9,000- 10,000 Gauss to separate at least 30% of the gangue material comprising olivine and obtain a chromite-rich magnetic intermediate product, following said grinder, and gravity separation means following said magnetic pre-separation unit.

[0033] Said magnetic pre-separation unit comprises at least two rotating drums, one of which is motor- driven, a moving conveyor belt surrounding said drums, and high-intensity electromagnets or permanent magnets, such as neodymium, arranged either on the surface of one of said drums or in a geometric plane between the drums, over which the conveyor belt passes in contact. Additionally, the magnetic pre-separation unit comprises a belt tensioning mechanism, a belt inclination adjustment mechanism, a drive cylinder, and product channels. Optionally, the conveyor belt surface can be provided with strip elevations of at least 0.5 mm at intervals perpendicular to the belt rotation direction.

[0034] The method and system of the present invention represent a significant step forward in economically utilizing such problematic low-grade ores, other than classic chromite ores. As a result of the process, high-purity chromite concentrate can be obtained, olivine and other gangue minerals can be effectively separated, and an environmentally friendly chromite beneficiation method that enhances process efficiency can be provided

[0035] The features, applications, and advantages of the present invention will become more apparent and better understood from the following detailed description and examples. BRIEF DESCRIPTION OF THE FIGURES

[0036] Figure 1: A conventional process flow diagram for the beneficiation of chromite ore comprising olivine as an example of prior art.

[0037] Figure 2: A flow diagram of the method according to the present invention for the beneficiation of very low-grade chromite ore comprising olivine.

[0038] Figure 3: A partial schematic view of a preferred embodiment of the method according to the present invention.

[0039] Figure 4: A front view of a magnetic pre-separation unit in a preferred embodiment according to the system of the present invention.

[0040] REFERENCE NUMBERS IN THE FIGURES

[0041] 1a-b : Primary-Secondary (Jaw-Cone) Crushers

[0042] 2 : Tertiary Crushers

[0043] 3a-b : Ball / Rod Mills / Grinders

[0044] 4a-b : Magnetic Pre-Beneficiation / Separation Units

[0045] 5a-c : Hydraulic Classifiers

[0046] 6a-c : Shaking Tables

[0047] 7a-b : Magnetic Separators-Cleaning Circuit

[0048] 40 : Magnets

[0049] 41 : Ground Material (Chromite Ore)

[0050] 42 : Drive Drum (or Magnetic Drum)

[0051] 43 : Standard Drum

[0052] 44 : Conveyor Belt

[0053] 45 : Partition

[0054] 46 : Magnetic Valuable Minerals

[0055] 47 : Non-Magnetic (Residual) Materials

[0056] 48 : Feed Hopper

[0057] 49 : Water Sprays

[0058] 50 : Inclination Adjustment Mechanism

[0059] 51 : Drive Cylinder

[0060] 52 : Motor

[0061] 53 : Tension Mechanism

[0062] A1-2 : Residual Products

[0063] AU : Intermediate Residual Product

[0064] OK : Pre-Concentrate

[0065] K : Concentrate DETAILED DESCRIPTION OF THE INVENTION

[0066] Ore preparation and beneficiation processes are applied to transform various minerals within an ore into the most suitable raw material needed by the industry without altering their chemical structure, and to separate economically valuable (precious) minerals from those that do not hold economic value. Here, the process of separating valuable and non-valuable minerals / elements that make up a run-of-mine ore is referred to as "beneficiation (concentration)," and the product obtained, which mostly comprises valuable minerals / elements, is called "concentrate," while the remaining non-valuable product is termed "tailings (gangue)."

[0067] Figure 1 illustrates a process flow diagram commonly used in conventional applications for the beneficiation of chromite ore comprising olivine, as an example of prior art. In these applications, during the beneficiation process of chromite ore, the ore is initially reduced to millimeter-sized particles using primary, secondary, and tertiary crushers (1a, 1b, 2) available in the market. For example, after being subjected to a 500 mm screen, a jaw crusher (1a) is used to further reduce the size of the particles remained on the screen. The material is then directed to a 100 mm screen for further size reduction. A cone crusher (1b) is used to further reduce the size of the particles remained on the screen, and the crushed material is fed back to the screen. Thus, the material is refined and subjected to a 20 mm screen, and finally, the screened material is directed to a two- layer screen with 10 mm and 5 mm sizes for further separation. After this screening process, the oversize materials are further reduced using jigs to obtain heavy and light products. The heavy product is taken as coarse concentrate and fed back to the beginning of the process. The light products are further refined in a ball mill (3a, 3b) and passed through a 0.5 mm screen. The material reduced to a size below 0.5 mm is sent to a hydraulic classifier (5a-c). Material sizes ranging from 0.038 to 0.212 mm, 0.212 to 0.5 mm, and 0.5 to 1 mm from the hydraulic classifier are subjected to a two-stage triple-series shaking table (6a-c) application, separating them to finally obtain chromite concentrate (K) as a heavy product. In this final process, intermediate products (A) are fed back to the hydraulic classifier, while slimes and tailings are removed.

[0068] In studies reported in the literature, high-field magnetic separation methods using shaking tables (6a-c) followed by magnetic separators (7a-b) have been tested for the beneficiation of chromite tailings. Additionally, high-field magnetic separation and flotation methods (not shown in the figure) have also been used to obtain chromite concentrate from chromite plant tailings. As a result of these applications, it is possible to obtain final concentrates comprising 35-40% and 43-48% Cr2C>3, respectively, from chromite tailings with a high Cr2Os content of about 25%. However, considering the installation and operational costs of methods such as magnetic separation and flotation, gravity separation is deemed the most suitable circuit design for chromite ore beneficiation. On the other hand, these applications do not offer a solution for chromite ores with a content of less than 5% Cr2O3, whether as raw material or tailings. Figures 2 and 3 schematically illustrate a preferred embodiment of the method according to the present invention for the beneficiation of very low-grade chromite ore comprising olivine. This method is particularly applied to obtain high-efficiency chromite concentrate from very low-grade chromite ore with less than 5% chromite content and comprising olivine.

[0069] The primary objective here is to prevent the wastage of said economically low-value ores, which are commonly encountered in the mining industry, and to reintroduce them into the economy. The method of the present invention ensures that powdered ore particles are subjected to relatively moderate magnetic pre-separation before commencing the gravity separation process, thereby allowing gangue minerals such as olivine to be discarded as a dense and clean residue. As a result, it becomes possible to obtain a high-chromite-content pre-concentrate, preferably with a grade of more than 7% C^Ch, suitable for subsequent gravity-based separation.

[0070] According to the method of the invention, low-grade chromite ore is initially subjected to size reduction processes known from conventional applications until the liberation particle size is achieved. This process comprises primary crushing (1a-b), secondary and tertiary crushing (2) steps according to the beneficiation particle size, and rod and / or ball mills (3) may be used depending on the target particle size. The crushing, grinding, and size classification unit to be created will vary depending on the ore characteristics, size, mineralogy, and liberation particle size. The sample content ratios of the ore being processed are reported in Table 1 below:

[0071] Table 1: Composition of incoming ore (by weight):

[0072] Due to the high bond work index of the ore, the rate of transition to fine particle size (slime) (- 100 microns) after size reduction (crushing-grinding) processes is quite low. The proportion of material passing below 100 microns in the material below the beneficiation particle size of 500 microns is approximately 8-9%. Therefore, chromite losses in fine particle size during magnetic separation (4a-b) and gravity-based beneficiation (6a-c) remain at very low levels. In this process, magnetic separation (pre-beneficiation) carried out at a magnetic field intensity of 9,000 to 10,000 Gauss ensures very low chromite losses in fine particle size, leading to more selective separation. As is known, the most important parameters affecting separation in a magnetic separation process are the mineralogy of the ore, grinding properties, the intensity of the magnetic field to be applied, and the structural characteristics of the device. Therefore, optimization studies related to the beneficiation process are carried out depending on all these properties. The magnetic separation process for pre-beneficiation according to the invention is a wet process to be carried out after wet grinding, eliminating the need for any drying process beforehand.

[0073] As a result of the magnetic pre-beneficiation process employed according to the invention, a preconcentrate with more than 7% CX2O3 content and a clean residue with less than 0.5% C^O; content can be obtained. In this way, at least 30%, preferably 35-40%, of the ore fed can be discarded as residue without entering the gravity beneficiation, thus reducing the process load from the outset. The effectiveness of this separation is confirmed through mineralogical analysis and density measurements in field tests. The analysis results for a field application are reported in Table 2.

[0074] Table 2: Distribution and content of ore beneficiation products

[0075] Subsequently, the pre-concentrate obtained from the pre-beneficiation is classified into narrow size ranges using hydraulic classifiers (5a-c) and then subjected to gravity separation (6a-c). This process further beneficiates the ore by utilizing density differences. For example, shaking tables or spirals are used to separate chromite, with higher specific gravity, from lighter gangue minerals. As a result of gravity separation, a chromite concentrate with up to 40% C^Ch content can be obtained due to the presence of olivine minerals with specific gravity close to that of chromite in the ore. The Cr2Os content in the clean tailing is below 0.5%.

[0076] Afterwards, a magnetic separation process can be performed in order to bring the concentrate with 40% Cr2O3 content to a marketable grade. A magnetic separator (900) operating at a magnetic field intensity of 6,000-7,000 Gauss is used for selective separation, and a magnetic product with approximately 46-47% C^O; content can be obtained as a concentrate.

[0077] According to a second embodiment of the invention, the system configuration comprises a magnetic pre-separation unit (4a / 4b) as a critical part of the beneficiation process, precisely processing the ground chromite ore (41) (Figure 3). Following said size reduction processes, the material (41) ground to below 500 microns is preferably fed into the magnetic pre-separation unit (4a and / or 4b) via a feed hopper (48) of a certain height. Within this unit (4a), there are at least two rotating drums (42, 43), one of which is motor-driven (52), a moving conveyor belt (44) surrounding said drums, and magnets (40) arranged either on the surface of one of the drums (46) or in a geometric plane between the drums (42, 43), over which the conveyor belt (44) passes in contact. Additionally, a feed mechanism designed according to the granulometric properties of the ore particles can be used to ensure the homogeneous distribution of the ground ore onto the belts (44).

[0078] In said unit configuration, a moderate magnetic field intensity of 9,000-10,000 Gauss is typically generated using strong magnets with natural magnetic properties, such as neodymium, or electromagnets, causing the magnetic mineral (46) to adhere to the relevant belt surface. In the preferred first embodiment, the surface of the drum (42) is generally covered with arrays of rotating magnets / ferromagnetic material (40) that are rotated in the magnetic field. For example, magnets with a thickness of at least 1 mm, preferably 5-10 mm, are provided on the outer surface of the magnetic drum (42) in a ring-like form, either continuously, stepwise, or intermittently. As the magnetic drum (42) rotates, non-magnetic materials (47) are washed away by water jets and / or thrown off the drum due to falling and swerving effects, while magnetic valuable minerals (46) adhere to the drum (42) and are separated with the aid of a partition (45) towards the end of the drum, directed to the collection area (OK) as pre-concentrate. Meanwhile, non-magnetic materials (47) are directed to a separate residue collection point (A1).

[0079] In a preferred second embodiment, as shown in Figure 4, the wet pre-magnetic separation unit (4a) comprises plate-type magnets (40) arranged in a geometric plane inclined between the drums (42, 43) instead of being placed on the drum surface. Said unit comprises a durable conveyor belt (44), drums (42, 43), and a plate-type magnet assembly (40), as well as a motor (52), and preferably a belt tensioning mechanism (53), a belt inclination adjustment mechanism (50), a drive cylinder (51), and product channels.

[0080] Said belt (44) is at least 1 mm, preferably 1.5-2.5 mm thick, and at least 1 meter wide, configured to form a slight U-shaped trough with raised edges for the ground material (41) laden with water to flow downward. Optionally, the belt (44) surface can have strip elevations of at least 0.5 mm, preferably 1.0-2.5 mm, at intervals perpendicular to the belt rotation direction to help capture magnetic particles by the magnetic poles beneath the belt.

[0081] Magnets (40) are preferably made of NdFeB (Neodymium Iron Boron) blocks, aligned along the belt rotation and width with sequentially aligned polarities. Narrow magnetic poles placed between the NdFeB rows generate high magnetic fields and gradients, thereby providing strong magnetic force to capture fine magnetic particles from the material (41) fed onto the belt surface. This arrangement acts as a magnetic matrix, producing a magnetic field of 9,000-10,000 Gauss.

[0082] When the magnetic pre-concentration unit (4a) is in operation, the slurry of ground material (41) supplied to the feed hopper (48) enters the U-shaped belt (44) and flows downward evenly in a layer several centimeters thick. The magnetic particles (46) adhere to the belt (44) and are carried upward (with the aid the transverse elevations on the belt). Under the rinsing water sprays (49), the direct impact of the washing water completely disintegrates the magnetic deposits, removing the accompanying non-magnetic particles from the deposits. The magnetic particles are then transported to the upper drum (43) end of the belt, where they fall off, completely separating from the belt and are directed to the magnetic product (OK) chute with the support of water sprays. Meanwhile, the non-magnetic particles (47) flow downward along the belt's inclination as a slurry and are removed as a non-magnetic product (Al).

[0083] During the operation of the unit (4a), the magnetic force required to capture magnetic valuable minerals (46) on the surface of the belt (44) is related to the properties of the particles, such as permeability and density, the operating parameters of the belt, such as rotation speed and inclination angle, and the characteristics of the slurry, such as flow rate. The technical parameters for a pilot application according to the invention are reported in Table 3.

[0084] Table 3: Operating parameters of the wet pre-magnetic separation unit

[0085] Through the magnetic pre-separation process according to the invention, undesirable materials (A1) predominantly composed of olivine minerals, referred to as gangue minerals, are successfully separated. For simplicity in the figures, detailed secondary components such as skeletal structures, material direction mechanisms, partitions, and beds, which a person skilled in the art can easily foresee, are not shown. Naturally, all processes can be managed by a control unit equipped with appropriate sensors that monitor operational efficiency and make continuous adjustments. For example, the efficiency of this process is optimized through careful control of various parameters such as material quantity and flow rate, drum rotation speed, waterjet pressure if applicable, and magnetic field strength. The adjustment of said parameters, based on the characteristics of the ore and the type of mineral to be processed, ensures the effective separation of ore particles entering the magnetic field.

[0086] After magnetic separation, the pre-concentrate comprising enriched chromite is classified by size and subjected to gravity separation. This stage further purifies the chromite, making it suitable for use.

[0087] Although certain examples and applications of the present invention have been described so far, it is evident that various other changes and modifications can be made by those skilled in the art without departing from the essence and scope of the invention. Therefore, such changes and modifications are also included within the protection scope of the present invention, as defined by the appended claims.

Claims

CLAIMS1. A method for the beneficiation of ores comprising olivine and having a chromite content of less than 5%, which comprises the steps of reducing the ore to a suitable particle size and performing gravity-based separation, comprising the following steps; reducing the ore particles to a size below 500 microns through grinding; subjecting the ore, reduced to said particle sizes, to a magnetic pre-separation at a field intensity of 9,000-10,000 Gauss, thereby separating at least 30% of gangue minerals predominantly comprising olivine minerals as a dense clean residue and obtaining a chromite-rich magnetic intermediate product as a pre-concentrate; and subjecting the pre-concentrate, which is richer in chromite from the magnetic preseparation step, to gravity separation after being classified into narrower size ranges.

2. The method according to claim 1, characterized in that the chromite content in the preconcentrate obtained from said magnetic pre-separation step is at least 5%, and at least 0.5% in the clean residue.

3. The method according to claim 1, characterized in that at least two-thirds of the total feed in the pre-concentrate obtained from said magnetic pre-separation step has a C^Ch content of more than 8%, while the remaining one-third residue is removed from the process with a C^Ch content of about 0.4%.

4. The method according to claim 1, characterized in that the ground chromite ore in the magnetic pre-separation step is separated at a moderate magnetic field intensity of 9,000-10,000 Gauss, typically generated by strong magnets with natural magnetic properties such as neodymium.

5. The method according to claim 1, characterized in that the ground chromite ore in the magnetic pre-separation step is separated by passing over magnetic belts at an electromagnetic field intensity of 9,000-10,000 Gauss provided by a generator.

6. The method according to claim 1, characterized in that the pre-concentrate obtained after the pre-concentration in the magnetic pre-separation step is classified into narrower size ranges by hydraulic classifiers and then subjected to gravity separation.

7. The method according to claim 1, characterized in that the chromite content in the concentrate obtained from said gravity separation step is at least 40%.

8. The method according to claim 1, characterized in that the chromite-rich concentrate obtained from said gravity separation step is subjected to a cleaning beneficiation step with magnetic separators at a field intensity of 6,000-7,000 Gauss in the subsequent step, resulting in the production of a concentrate with more than 45% C^Ch content.

9. The method according to anyone of the preceding claims, characterized in that the magnetic minerals are retained on the belt during the magnetic pre-separation step and transferred to the subsequent process step, while the non-magnetic minerals are directed to a waste collection hopper.

10. The method according to anyone of the preceding claims, characterized in that the magnetic pre-separation process for obtaining pre-concentration is a wet process carried out after wet grinding, thus eliminating the need for any drying procedure beforehand.

11. A system for the beneficiation of ores comprising olivine and having a chromite content of less than 5%, which comprises an ore preparation unit with crushers and size classification devices to reduce the ore to a suitable particle size, and a gravity-based separation unit, comprising; at least one grinder to reduce the ore to a particle size below 500 microns; at least one wet magnetic pre-separation unit providing a field intensity of 9,000- 10,000 Gauss to separate at least 30% of the gangue material comprising olivine and obtain a chromite-rich magnetic intermediate product, following said grinder; and gravity separation means following said magnetic pre-separation unit.

12. The system according to claim 11, characterized in that said magnetic pre-separation unit comprises at least two rotating drums, one of which is motor-driven, a moving conveyor belt surrounding said drums, and magnets arranged either on the surface of one of said drums or in a geometric plane between the drums, over which the conveyor belt passes in contact.

13. The system according to claim 11, characterized by further comprising a wet magnetic separation circuit for removing non-chromite minerals in the gravity concentrate obtained from the gravity separation means and for cleaning the concentrate.

14. The system according to anyone of claims 11 to 13, characterized in that the magnetic preseparation unit comprises high-intensity electromagnets or permanent magnets such as neodymium.

15. The system according to anyone of claims 11 to 14, characterized in that the magnetic preseparation unit comprises magnets with a thickness of at least 1 mm, arranged in a ringlike form, either continuously, stepwise, or intermittently on said magnetic drum.

16. The system according to anyone of claims 11 to 15, characterized in that the width of the conveyor belt in the magnetic pre-separation unit is at least 1 meter.

17. The system according to anyone of claims 11 to 16, characterized in that the magnetic preseparation unit comprises a belt inclination adjustment mechanism and / or a belt tensioning mechanism.

18. The system according to anyone of claims 11 to 17, characterized in that the magnetic preseparation unit comprises a drive cylinder.

19. The system according to anyone of claims 11 to 18, characterized in that the magnetic preseparation unit comprises water sprays and product channels.

20. The system according to anyone of claims 11 to 19, characterized in that the magnetic preseparation unit comprises strip elevations of at least 0.5 mm at intervals perpendicular to the belt rotation direction on the surface of said conveyor belt.

21. The system according to anyone of claims 11 to 20, characterized in that the magnetic preseparation unit comprises a speed control mechanism for said conveyor belt.

22. The system according to anyone of claims 11 to 21, characterized in that the magnetic preseparation unit comprises at least one feed hopper.

23. The system according to anyone of claims 11 to 22, characterized in that it further comprises a control unit to optimize the magnetic separation process based on ore characteristics.

24. The system according to claim 11, characterized in that the size reduction means comprise mechanical crushing and grinding devices such as hammer mills, ball mills, or rod mills, and cone crushers.

25. The system according to claim 11, characterized in that the gravity separation means comprise shaking tables, spiral separators, or similar density-based separation devices.

26. The system according to claim 11, characterized in that the control unit further comprises advanced algorithms and sensor technologies that continuously monitor and analyze process data and adjust magnetic separation parameters in real-time.

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