Process and system for concentrating supergene iron ore into a high-content concentrate (>67% fe(t)) and converting it into metamorphic iron ore

Abstract

The present invention relates to a process and a system for concentrating iron ore, particularly suited to the concentration of supergene iron ores, said process comprising the steps of (i) drying; (ii) disaggregation / attrition / grinding; (iii) air classification; (iv) roasting; (v) magnetisation; (vi) grinding and (vii) magnetic separation, and said system comprising a modified impact crusher and a modified ball mill equipped with a burner. The process described herein enables the obtainment of a concentrated product with an iron content > 67%, which, following agglomeration, is suitable for use in direct reduction.

Description

PROCESS AND SYSTEM FOR CONCENTRATING SUPERGENIC IRON ORE INTO HIGH-GRADE CONCENTRATE (>67% Fe(T)) AND TRANSFORMING IT INTO METAMORPHIC IRON ORE. FIELD OF THE INVENTION

[0001] The present invention relates to a process and system for concentrating iron ore. The process in question is particularly suitable for concentrating supergene iron ores, which present difficulties in metal recovery. The process proposed here allows obtaining a product with an iron content > 67% which, after agglomeration, is suitable for use in direct reduction. FUNDAMENTALS OF THE INVENTION

[0002] In the field of iron ore beneficiation, and aiming to maximize the use of mineral resources, the recovery of iron ores that present difficulties in metallic recovery presents a technological challenge. In this context, it is important to highlight supergene ores, which are associated with the reconcentration of mineralizations from a primary ore. Supergene alteration of minerals refers to transformation processes that occur in minerals due to interaction with environmental agents, which can result in changes in the chemical composition, structure, and properties of the minerals.

[0003] In general, supergene iron ores exhibit a high concentration of ferruginous fines, composed essentially of iron hydroxide (mainly in the form of goethite [FeO.OH]), aluminum hydroxide (mainly in the form of gibbsite [Al(OH)3]), and silica. In the supergene alteration process, goethite and gibbsite are formed by oxidation and hydration of iron minerals and aluminum-bearing minerals (Al₂O₃). Goethite and gibbsite, both paramagnetic, are associated with the decrease in magnetization of supergene ores. Furthermore, goethite and gibbsite precipitate onto the iron-bearing minerals (hematite and magnetite) of the ore, forming a coating and cementing the iron ore particles.

[0004] In this context, the present invention proposes a process for beneficiating supergene iron ore comprising the separation of ferruginous fines that is economically viable. For the separation of ferruginous fines, the present invention promotes improved ore disaggregation by means of a modified impact crusher. Furthermore, the proposed process enables the transformation of supergene ores into metamorphic ores by transforming goethite into hematite through roasting heat treatment and includes subsequent magnetic concentrations. To promote the improved dehydroxylation of goethite, the present invention includes a roasting step using a ball mill modified with a burner. Thus, the proposed process allows for the maximization of thermal efficiency.

[0005] In summary, the proposed process comprises the following steps: (i) drying; (ii) disintegration / attrition / grinding; (iii) air classification; (iv) roasting; (v) magnetization; (vi) grinding and (vii) magnetic separation.

[0006] State-of-the-art technologies propose solutions related to the beneficiation of supergene ores, including the transformation of goethite into hematite through heat treatment. However, the state of the art does not contemplate an economically viable and energy-efficient process for transforming supergene iron ore into metamorphic iron ore in the manner described in the present invention.

[0007] Brazilian patent document BR 102020009196-4 A2 refers to a recycling process for tailings, waste rock, and marginal ores resulting from iron mining, through the transformation of these materials into hematite, quartz, and pozzolan. According to this document, the goethite present in the mining waste undergoes a dehydroxylation process, loses molecular water, and transforms into hematite, allowing its metallurgical use. This document mentions that the process may include magnetic concentration, obtaining products with iron contents above 65%. However, this document describes a heat treatment step consisting of flash calcination at temperatures between 300 and 830°C, unlike the roasting step of the present invention. Furthermore, this document is silent on a hematite magnetization step and also on an improved ore disaggregation using an impact crusher as described in the present invention.

[0008] Document IN 397649 B, in turn, discloses a selective fragmentation method to improve the liberation and beneficiation of low-grade iron ores, such as goethite-rich hematite iron ores of different compositions, where goethite can be transformed into hematite during pretreatment processes, such as microwave heating or thermal heating followed by quenching. In fact, this document teaches a heat treatment step different from the roasting step of the present invention, involving the consecutive tempering of the heat-treated material and subsequent concentration by means of flotation (and not magnetic concentration). Furthermore, this document is silent on a hematite magnetization step and also on the improved ore disaggregation by means of an impact crusher in the manner of the present invention.

[0009] The scientific document entitled “Chemical and mineral transformation of a low grade goethite ore by dehydroxylation, reduction roasting and magnetic separation” refers to chemical and mineral transformations of goethite ore through dehydroxylation, roasting, and magnetic separation. In this context, the document mentions that roasting transforms goethite into hematite and, eventually, magnetite, which can be recovered through magnetic separation, thus allowing for a higher concentration of iron. However, the document describes a heat treatment at around 450°C for transforming goethite into hematite and around 700°C for transforming hematite into magnetite, unlike the roasting step of the present invention. Furthermore, this document is silent on a hematite magnetization step and also on the improved ore disaggregation using an impact crusher as described in the present invention.

[0010] As explained above, there are state-of-the-art efforts dedicated to the beneficiation of supergene ores, including the transformation of goethite into hematite through heat treatment. Furthermore, the state of the art also envisions solutions concerning increasing the magnetic susceptibility of iron minerals and changing the crystallographic phase for concentrating iron ore that presents difficulties in metal recovery. However, there remains a need for a process route that is economically viable and energy-efficient for transforming supergene iron ore into metamorphic iron ore. It is worth noting that the state of the art does not mention a modified ball mill with a burner to promote the enhanced dehydroxylation of goethite in the manner of the invention discussed here.Furthermore, the prior art does not appear to achieve the technical effect concerning the enhanced disaggregation of the ore with removal of the ferruginous fines covering the hematite and the ferruginous cement between the hematite particles, as achieved in the disaggregation / attrition / grinding step by means of the modified impact crusher in the form of the invention discussed herein.

[0011] As will be detailed below, the present invention aims to solve the problems of the prior art described above in a practical and efficient manner. SUMMARY OF THE INVENTION

[0012] The present invention relates to a process and system for concentrating supergene iron ore. In summary, the proposed process comprises the following steps: (i) drying; (ii) disaggregation / attrition / grinding; (iii) air classification; (iv) roasting; (v) magnetization; (vi) grinding; and (vii) magnetic separation.

[0013] Furthermore, the present invention relates to a supergene iron ore concentration system served by a modified impact crusher for conducting the disaggregation / attrition / grinding stage, and by a modified ball mill, with a burner, for the roasting stage.

[0014] The present invention aims to provide a route and system for concentrating supergene iron ore, comprising the separation of compound ferruginous fines, that is economically viable and has maximized energy efficiency.

[0015] The aforementioned objectives and other advantages of the present invention will become clearer from the description that follows. BRIEF DESCRIPTION OF THE FIGURES

[0016] Figure 1 illustrates the essential components of the ball mill of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] In order to achieve the objectives described above, the present invention provides a process and a system for concentrating supergene iron ore, said system being served by a modified impact crusher and a modified ball mill with a burner. The proposed process comprises the following steps: (i) drying; (ii) disaggregation / attrition / grinding; (iii) air classification; (iv) roasting; (v) magnetization; (vi) grinding; and (vii) magnetic separation.

[0018] In this context, a combined process is proposed that integrates traditional wet rotation with dry rotation for concentrating supergene iron minerals, using the steps of (i) drying, (ii) disaggregation / attrition / grinding, and (iii) air classification. The iron concentrate obtained by the conventional wet process undergoes a drying step, followed by disaggregation / attrition / grinding and, subsequently, air classification, with the aim of exclusively removing the superfine particles, known as ferruginous fines. These fines are rich in goethite (FeO.OH), aluminum oxide (Al2O3), silica (SiO2), and often phosphorus (P), an element that has a high affinity for ferruginous fines.

[0019] According to the present invention, the raw material for the process in question consists of supergene iron ore rich in hematitic and goethite iron minerals, with high Fe contents (about 60% to about 65%), significant SiO2 contents (about 1% to about 10%) and alumina (about 1% to about 4%), with high loss on ignition (LOI) (> 2.5%) and a brittle and porous granular morphology.

[0020] The drying stage aims to reduce the moisture content of the ore to less than about 0.5% and is conducted in rotary dryers, rapid dryers, or fluidized bed dryers at a temperature between about 90°C and about 110°C.

[0021] Next, the material is conveyed to a disaggregation / attrition / grinding stage, in which an impact crusher is used to promote enhanced attrition and disaggregation of the ore, in order to remove the ferruginous fines that cover the hematite (which are rich in goethite) and the ferruginous cement between the hematite particles (which is rich in silica and alumina and represents between approximately 15% and approximately 30% of all the processed material). Furthermore, the impact crusher promotes partial grinding of particles smaller than 1.0 mm.

[0022] Traditional iron ore concentration routes, such as flotation and the combination of magnetic separation plus flotation, do not include the disaggregation / attrition process. This step is extremely important for releasing ferruginous fines, which often carry aluminum oxide (Al2O3), silica (SiO2), and phosphorus (P). These ferruginous fines usually coat the hematite grains or act as cement between the hematite grains.

[0023] According to the present invention, the impact crusher used is provided with a dynamic or static air classifier, coupled to its discharge, through which the air classification stage is conducted. In this stage, the processed ore is separated into a coarse fraction (greater than about 150 microns), a natural fine fraction (between about 5 microns and about 150 microns), and a superfine fraction (smaller than about 5 microns).

[0024] It is worth noting that the superfine fraction (less than about 5 microns) of ore has a higher quantity of gibbsite [Al(OH)3] and, due to the random (Brownian) movement of these superfine particles, they tend to remain inside the impact crusher and tend to exit through the feed opening. Therefore, the impact crusher according to the present invention also includes a superfine collector positioned at the feed opening, through a slight depression. The superfine fraction can be used in other processes (such as raw material for the production of geopolymers, for example).

[0025] The roasting stage, in turn, is conducted in a ball mill with a burner only for the natural fine fraction (< than about 0.15 mm), which contains a high content of goethite. In this stage, the aforementioned natural fine fraction is subjected to a heat treatment at a temperature of about 350°C, sufficient to promote the dehydroxylation of goethite. Through the heat treatment, the goethite loses hydroxyl groups (OH) and releases water vapor (H2O), resulting in the formation of hematite (Fe2O3) according to equation (I) below. 2FeO(OH) -> Fe2O3 + H2O (I)

[0026] In the dehydroxylation process, with the removal of the OH radical, the Fe ions +3 They realign in the same direction, creating conditions for them to be magnetized when exposed to an electromagnetic field, thus increasing their magnetic susceptibility.

[0027] According to the present invention, the ball mill in which the roasting stage is conducted promotes an enhanced dehydroxylation of goethite. Figure 1 illustrates the essential components of said ball mill, which comprises a burner (1) with a structure adjusted to maximize the exposure of the material to the flame (2) - increasing the flame tongue, achieved through modifications in the fuel flow, the amount of air and the fuel pressure; internal fins (3) to continuously lift the material during the rotation of the mill, ensuring that it is constantly exposed to the flame; a discharge baffle (4) for heat retention (baffle with a conical design and ring inclined at approximately 45° at the mill discharge point, creating a flame return effect to the interior of the mill); and a modified discharge system comprising lifters (5) that collect the ore at the bottom and lift it, discharging it from the mill.Furthermore, the modified ball mill according to the present invention comprises a truncated cone with a larger diameter at the final discharge. Said truncated cone comprises an off-gas outlet at the top and an outlet for the calcined ore at the bottom.

[0028] The ball mill configuration according to the present invention ensures continuous and uniform movement of the material, effectively exposing it to the flame. Furthermore, this configuration is crucial for maintaining heat within the mill, maximizing the thermal efficiency of the roasting process and reducing energy consumption. In addition, the modified ball mill according to the present invention incorporates further advantages to the process, such as shorter dehydroxylation time, mechanical transport without the use of large volumes of air, reduced equipment size for dehydroxylation, and fewer steps (for example, there is no need to separate air from solids).

[0029] The calcined ore from the roasting stage is then conveyed to a magnetization stage of the transformed hematite, in which the hematite obtained in the roasting stage is subjected to a pulsed magnetization process, conducted in a pulsed electromagnetizer at the outlet of the ball mill. This pulsed electromagnetizer applies high-intensity electric current pulses to generate a strong and temporary magnetic field, which magnetizes the target material, also temporarily.

[0030] According to the present invention, the grinding step is carried out in an impact mill only for the coarse fraction (greater than about 150 microns) from the air classification step, aiming to achieve a P95 particle size of about 1.0 mm (referred to as the fine ground fraction).

[0031] Finally, the magnetic separation stage is conducted in moderate-intensity magnetic roller separators. In this stage, the material from the magnetization stage is fed in, as well as the finely ground fraction from the grinding stage. More specifically, this stage comprises a first stage of low intensity (between approximately 700 and approximately 3,500 gauss), a second stage of medium intensity (between approximately 3,500 and approximately 10,000 gauss), and a third stage of high intensity (between approximately 10,000 and approximately 15,000 gauss or higher). The combination of different intensities allows for increased selectivity, in addition to contributing to a reduction in the overall process cost.

[0032] Furthermore, the present invention provides a system for concentrating supergene iron ore through the process described above, being served by a modified impact crusher and a modified ball mill with a burner as defined above.

[0033] In light of the above, it is highlighted that the process proposed here allows for the production of an iron ore concentrate with a high iron content (>67%) and low loss on ignition (LOI) due to the pre-calcination of goethite. This allows for the production of a more resistant and reducible agglomerate, and therefore, much more suitable for use in direct reduction furnaces for obtaining high-grade metallization DRI (Direct Reduction Iron).

[0034] The invention proposed here, as explained above, in one embodiment, consists of a process that has advantages related to maximizing thermal efficiency and reducing associated costs. These advantages are associated with the separation of ferruginous fines from supergene ore, improved roasting in a modified ball mill (with effective dehydroxylation of goethite), increased magnetic susceptibility of the processed ore, and the consequent possibility of magnetic separation at moderate intensities.

[0035] The description given so far of the object of the present invention should be considered only as one possible embodiment or embodiments, and any particular features introduced therein should be understood only as something written to facilitate understanding. Therefore, they should not be considered as limiting the invention, which is limited to the scope of the claims.

Claims

CLAIMS 1. Supergene iron ore concentration process, characterized by comprising the following steps: (i) drying; (ii) disaggregation / attrition / grinding; (iii) air classification; (iv) roasting; (v) magnetization; (vi) grinding; and (vii) magnetic separation.

2. Process according to claim 1, characterized in that the (i) drying step is carried out in rotary dryers, flash dryers or fluidized bed dryers at a temperature between about 90°C and about 110°C.

3. Process according to claim 2, characterized in that, after the (i) drying step, the moisture content of the ore is reduced to less than about 0.5%.

4. Process according to claim 1 or 2, characterized in that the (ii) disaggregation / attrition / grinding step is carried out in an impact crusher.

5. Process according to claim 4, characterized in that, in the (ii) disaggregation / attrition / grinding step, the impact crusher promotes partial grinding of particles below 1.0 mm.

6. Process according to any of the preceding claims, characterized in that the (iii) air classification step is carried out in a dynamic or static air classifier coupled to the impact crusher, wherein the ore is separated into a coarse fraction (greater than about 150 microns), a natural fine fraction (between about 5 microns and about 150 microns) and a superfine fraction (less than about 5 microns).

7. Process according to claim 6, characterized in that the surface fraction is collected in the impact crusher.

8. Process according to claim 6, characterized in that the natural fine fraction is conveyed to the (iv) roasting step.

9. Process according to claim 6, characterized in that the coarse fraction is conveyed to the (vi) grinding step.

10. Process according to any of the preceding claims, characterized in that the (vi) grinding step is carried out in an impact mill.

11. Process according to any of the preceding claims, characterized in that the (iv) roasting step is carried out in a ball mill with a burner, at a temperature of about 350°C.

12. Process according to claim 11, characterized in that the (iv) roasting step is conducted at a temperature of about 300°C to about 400°C.

13. Process according to any of the preceding claims, characterized in that the (v) magnetization step is conducted in a pulsed electromagnetizer at the outlet of the ball mill.

14. Process according to any of the preceding claims, characterized in that, after the (vi) grinding step, the P95 particle size of the ore is reduced to about 1.0 mm.

15. Process according to any of the preceding claims, characterized in that the (vii) magnetic separation step is carried out in moderate-intensity magnetic roller separators for the ore from the (v) magnetization and (vi) grinding steps.

16. Process according to claim 15, characterized in that the (vii) magnetic separation step comprises a first low-intensity stage between about 700 and about 3,500 gauss, a second medium-intensity stage between about 3,500 and about 10,000 gauss and a third high-intensity stage between about 10,000 and about 15,000 gauss or higher).

17. System for concentrating supergene iron ore by means of the process as defined in claim 1, characterized in that it is served by an impact crusher and a ball mill.

18. System according to claim 17, characterized in that the impact crusher comprises a dynamic or static air classifier coupled to its discharge.

19. System according to claim 17, characterized in that the impact crusher further comprises a superfines collector positioned at the feed opening, through a slight depression.

20. System according to claim 17, characterized in that the ball mill comprises a burner (1).

21. System according to claim 20, characterized in that the burner (1) has a structure adjusted so as to maximize the exposure of the material to the flame (2).

22. System according to claim 20, characterized in that the ball mill further comprises internal fins (3), a discharge baffle (4) and discharge lifters (5).

23. System according to claim 22, characterized in that the discharge baffle (4) has a conical design and a ring inclined at approximately 45° at the mill discharge point.

24. System according to claim 20, characterized in that the ball mill further comprises a truncated cone with a larger diameter at the final discharge, said truncated cone comprising an off-gas outlet at the top and an outlet for the calcined material at the bottom.

25. Integration process of the stages of (i) drying, (ii) disaggregation / attrition / grinding and (iii) air classification, applied to iron concentrates obtained by traditional wet beneficiation processes, such as flotation and / or the combination of magnetic separation with flotation, resulting in a higher purity iron concentrate, in addition to promoting the selective elimination of ferruginous fines.

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