A METHOD FOR LONG-TERM MINE MANAGEMENT AND A SYSTEM FOR LONG-TERM MANAGEMENT OF TAILINGS GENERATED DURING THE BAUXITE MINING PROCESS

Abstract

METHOD FOR LONG-TERM MANAGEMENT OF A MINE, AND SYSTEM FOR LONG-TERM MANAGEMENT OF TAILINGS GENERATED DURING THE BAUXITE MINING PROCESS. This application relates to a method and a system for the long-term management of tailings generated during bauxite mining. Bauxite ores are frequently found under a shallow layer (usually less than 15 meters) of soil (called overburden). The mining process comprises the following main operations, performed sequentially: vegetation suppression, overburden removal, bauxite removal and transport, bauxite beneficiation, and land rehabilitation.The present invention relates to a method and a system that, by re-landfilling the tailings generated during the beneficiation stage essentially back to the same location where the material was originally mined, significantly reduces the environmental footprint, operational risk, and capital intensity of bauxite mining activity.

Description

/ 9 A METHOD FOR LONG-TERM MINE MANAGEMENT AND A SYSTEM FOR LONG-TERM MANAGEMENT OF TAILINGS GENERATED DURING THE BAUXITE MINING PROCESS Technical Field

[001] The present invention relates to a method and a system for long-term management of tailings generated during the bauxite mining process. According to the method and the system, the tailings can be permanently replaced at the same location where they were mined as part of the ore.

[002] Bauxite ores contain alumina and are commonly mined from the ground. Such ores are often found under a shallow layer (usually less than 15 meters) of soil (called overburden). The mining method considered most suitable for this type of bauxite deposit is the strip mining method. This mining method comprises cyclical operations performed sequentially: vegetation suppression, overburden removal, ore removal and transport, ore beneficiation, and land rehabilitation. Since it allows rehabilitation to occur soon after ore mining, the strip mining method will typically have a low environmental and visual impact.

[003] Figure 1 illustrates the main operations of a commonly known bauxite mining method. During the beneficiation stage, as the ore is enriched in alumina in a beneficiation plant, tailings with a high liquid content are generated and commonly stored in dams or reservoirs. A problem for mining companies is that these dams or reservoirs can increase in size year after year due to difficulties in finding sustainable disposal solutions.

[004] The present invention relates, in particular, to improving the Petition 870260009464, dated 01 / 30 / 2026, page 17 / 42 / 9 state of the art mentioned above for mine tailings management, by implementing a new method and system for backfilling tailings, and, by this method and system, essentially returning the tailings to the same location where they were originally mined in a sustainable and permanent manner. Fundamentals of the technique

[005] The present invention is particularly suitable for operation with the specific ore from the Applicant's Paragominas mine in the state of Pará in Brazil, but may also be applicable to other ores.

[006] The present invention relates to the disposal of tailings which are by-products of bauxite ore beneficiation, involving grinding and particle size classification. These are mechanical and non-chemical processes and, as a result, the by-product is inert bauxite tailings.

[007] Preferably, mechanical beneficiation of bauxite ore can occur near the mine, before transporting the beneficiated product to an alumina refinery. The distance between the mine and the refinery can sometimes be one hundred kilometers or more. Red mud is a byproduct of the refinery. Inert bauxite tailings versus 'red mud'

[008] Bauxite tailings (inert materials) describe the byproduct generated in the mining and beneficiation processes of bauxite ore through the continuous comminution stages associated with the desliming process. In short, bauxite tailings are the byproduct of a mining process.

[009] While bauxite tailings are inert, that is, they do not pose a risk to human health or the environment, red mud is environmentally hazardous due to its alkalinity. Summary of the invention Petition 870260009464, dated 01 / 30 / 2026, page 18 / 42 / 9

[0010] The object of the present invention is a more efficient and environmentally friendly method for the long-term management of tailings generated during the mining of bauxite ore and a corresponding system for implementing the method. By the present invention, the environmental impact of mining activity is significantly reduced.

[0011] These and other advantages that can be achieved by the present invention are detailed in the appended claims.

[0012] According to claim 1, a method is provided for the long-term management of a mine where bauxite ore is mined in a continuous, steady-state manner, comprising steps related to the mining part which include vegetation suppression, overburden removal, removal of bauxite ore from a mine pit and transportation of ore to a processing facility; - where bauxite ore is beneficiated into an enriched bauxite fraction for alumina production in a refinery, and a tailings fraction, which tailings fraction must be stored or disposed of, - and in which a portion of the land reclamation is carried out in the mined area and includes rehabilitation through the following steps, - the aforementioned tailings fraction is dried to a solids content of 80% or more using exclusively solar energy, - and in which the dry tailings fraction is backfilled into the mined pit on a permanent basis, - before or in connection with the aforementioned land reclamation phase. Brief description of the figures

[0013] The invention will now be further described by examples and figures, in which; Figure 1 illustrates the main operations of the state-of-the-art strip mining process. Petition 870260009464, dated 01 / 30 / 2026, page 19 / 42 / 9 Figure 2 shows a photo of the RP1 tailings dam, Figure 3 shows the tailings desiccation process, Figure 4 shows the final configuration of the Paragominas Main Tailings Plan before the Tailings Dry Backfill Project, Figure 5 shows the proposed approach in the mine pits. Detailed description

[0014] With reference to Figure 1, a mining method comprises cyclical operations, performed in sequence: vegetation suppression, overburden removal, ore removal and transport, beneficiation, land rehabilitation.

[0015] The crushed raw ore (ROM) produced in Paragominas, which feeds the beneficiation plant, will typically have a moisture content between 9% and 12%, and the following particle sizes and chemical characteristics: Particle Size

[0016] 81% to 90% passing through sieve 3 (76 mm) 32% to 38% passing through a 20# sieve (0.85 mm) 25% to 32% passing through a 400# sieve (0.038 mm) Chemical quality

[0017] Usable A12O3 — ranging from 36.90% to 41.38 Reactive SiO2 — ranging from 7.77% to 10.67% Total A12O3 — ranging from 48.12% to 50.68% Total SiO2 — ranging from 9.78% to 12.76% Total Fe2O3 — ranging from 9.60% to 12.69% Total TiO2 — ranging from 1.79% to 2.06% Loss on ignition — ranging from 24.27% to 26.27%.

[0018] The Paragominas bauxite beneficiation circuit includes three main classification stages to separate the coarser fraction, with the highest gibbsite content, from the finer fraction, in which most of the Petition 870260009464, dated 01 / 30 / 2026, page 20 / 42 / 9 kaolinite is present. The first stage is carried out in sieves, where the coarser fraction becomes product after grinding. The passing fraction feeds a pair of cyclone batteries in series. The overflow (portion of finer particles) from the cyclones feeds a ball mill (bali mill) and becomes product, while the fines are pumped to the third classification stage, with 2 cyclones. The coarser fraction from this last stage also becomes product, while the underflow (portion of coarser particles) are the tailings.

[0019] The tailings from Paragominas will typically exhibit the following particle sizes and chemical characteristics: Particle size

[0020] 100% passing through sieve #20 (0.85 mm) 90% to 98% passing through a 400# sieve (0.038 mm) Chemical quality

[0021] Usable A12O3 — ranging from 18.02% to 19.83% Reactive SiO2 — ranging from 20.29% to 21.97% Total A12O3 — ranging from 38% to 42% Total SiO2 — ranging from 21.69 to 23.69% Total Fe2O3 — ranging from 12.10% to 14.94% Total TiO2 — ranging from 1.90% to 2.10%; loss on ignition — ranging from 18% to 20%.

[0022] As ore beneficiation basically consists of particle size classification and does not include any chemical process, it can be noted that, in addition to being finer, the tailings do not differ much chemically from the ROM. Therefore, the Paragominas tailings are classified as chemically inert. Furthermore, after desiccation in the dams, the tailings can reach a moisture content between 18% and 40%.

[0023] Prior to the Tailings Dry Backfill Project, the Paragominas Master Tailings Plan established the final and permanent disposal of Petition 870260009464, dated 01 / 30 / 2026, page 21 / 42 / 9 tailings in dams. Figure 2 shows a photo of RP1 in Paragominas, the tailings storage dam currently in operation.

[0024] The RP1 dam was designed so that the geometry of the quadrants, the positioning of its 5 settling systems and the spacing between spillways allow for adequate drying of the tailings. The total area of ​​RP1 is approximately 300 ha and contains 142 spillways spaced between 75 and 100 meters from each other.

[0025] The RP1 dam's settling system consists of 4 spillways, which are designed to expel rainwater and water released from the tailings, thus aiding in the drying of the tailings. The spillways are connected to transfer channels, which in turn will flow into clarification basins.

[0026] The RP1 dam was designed based on the following geotechnical characteristics of the tailings: Specific gravity of tailings (Gs) = 2.68; average solids content at disposal (by weight) = 35%; final solids content (by weight) = 60%; tailings density at disposal = 1.27 t / m3; tailings density after desiccation = 1.60 t / m3.

[0027] Currently, the disposal method used at RP1 consists of disposing of thickened tailings, with an average solids content of 35%, in layers of approximately 50 cm which are subsequently exposed to solar drying, allowing the tailings to reach 60% solids content. The disposal alternates between the four quadrants to allow sufficient time for sun exposure for the tailings to desiccate. Figure 3 shows the tailings desiccation process.

[0028] At the end of its useful life, projected for 2021, an expansion in storage capacity would occur. This would happen continuously through the construction of new storage quadrants — designated RP2 a Petition 870260009464, dated 01 / 30 / 2026, page 22 / 42 / 9 RP8 — and by the additional elevation of the dikes. Figure 4 shows the final configuration of the Paragominas Main Tailings Plan before the Tailings Dry Backfill Project.

[0029] The Master Tailings Plan was divided into 11 construction stages – of which the construction of the initial RP1 dam dike was the first and therefore completed. The remaining 10 construction stages would be built over a period of 20 years and would provide approximately 126 Mm3 for tailings disposal in an area of ​​854 ha. The dikes would be raised to heights of up to 14 m. The estimated capital cost to build the remaining 10 stages was US$ 800 million.

[0030] The main concept proposed for the Tailings Dry Backfill project in Paragominas is to use the RP1 of the current tailings storage facility for tailings drying - reaching at least 60% solids - and from there mechanically remove and transport the tailings for final disposal in the mine pits.

[0031] The RP1 dam is perfect for this task. The internal separation of the dam into four large quadrants will allow the removal and disposal of tailings to happen simultaneously, without having a major impact on normal operations.

[0032] The minimum solids content of 60% was defined to increase productivity in the mechanical removal of tailings from dams and also in disposal in mine pits. In addition, this solids content optimizes volume utilization in the pits.

[0033] The removal of tailings is carried out using mine operating equipment, such as loaders, excavators, and trucks. Once removed from the dams, the tailings are transported for disposal in existing pits in a manner similar to what is currently done for overburden disposal. This approach completely eliminates the need to build new dams or further increase existing dam capacity. Petition 870260009464, dated 01 / 30 / 2026, page 23 / 42 / 9 existing dams. Figure 5 shows the proposed approach in mine pits.

[0034] As can be seen in Figure 5, a displacement of 5 meters was allowed between one layer of tailings and the next to allow rainwater to infiltrate between the layers of tailings - since the tailings have very low permeability - and therefore do not affect groundwater recharge.

[0035] According to the present invention, it is shown that it is possible to obtain very low moisture contents from inert bauxite tailings using only solar energy, i.e., where no filtration or separate drying is required.

[0036] With this, more viable mining can be achieved and, in addition, less energy will be needed for drying and transportation.

[0037] The present method allows the backfilling of tailings with moisture as low as 15%. Low moisture makes it possible to return the mined area to its original topography - high moisture levels will not allow this method and will therefore result in changes in the topography of the reclaimed land compared to the original situation. Volumetric expansion

[0038] When excavating natural terrain (such as a mine), the soil, which was previously in a certain state of compaction, will undergo volumetric expansion. Therefore, it is difficult to fit everything that has been removed back into a 'hole'.

[0039] Since the overburden layer can be considerably larger than the original bauxite layer, this would represent a problem for the tailings backfill, i.e., the overburden occupies almost all the available volume.

[0040] The solution proposed by the Applicant addresses this problem by desiccating the tailings to extremely high solids (or moisture) contents. Petition 870260009464, dated 01 / 30 / 2026, page 24 / 42 / 9 extremely low). Although a minimum solids content of 60% was established at one of the Applicant's mines, the solution was able to provide a solids content exceeding 80%.

[0041] Tailings with 80% solids will occupy approximately 4 times less space than tailings with 35% solids (the original solids content in the disposal). This volumetric reduction of tailings - caused by their desiccation - will allow the tailings to be backfilled in the mine pits occupying very little space.

[0042] Therefore, even considering the volumetric expansion of the overburden layer, backfilling can occur and return the land to its original topography. Returning the land to its original topography makes the mining method more sustainable, as it facilitates environmental rehabilitation and reduces the aesthetic impact of the mine. Additional benefits of the invention

[0043] Although this method may seem obvious to those skilled in the art, the large volumes of tailings generated in mining — in the mine mentioned, approximately 4.5 million tons of tailings per year — make it extremely difficult to find a solution for drying, transporting, and backfilling the tailings in the pits, and the tailings are commonly deposited in dams or similar structures.

[0044] By the present method, savings in logistics operations can be achieved, for example, by exploiting the free capacity of trucks returning from the bauxite processing plant to the mine, for the transport of tailings to the landfill. This will also reduce the CO2 footprint of the operations.

[0045] Furthermore, the present method allows for the backfilling of large quantities of tailings. This is related to the low moisture content of the tailings due to drying by solar energy. Petition 870260009464, dated 01 / 30 / 2026, page 25 / 42

Claims

1 / 3 CLAIMS 1. A method for the long-term management of a mine, where bauxite ore is mined from a mine pit in a continuous, steady-state manner, characterized in that it comprises the following steps: a) vegetation suppression, b) overburden removal, c) removal of bauxite ore and transport to an ore processing facility, d) beneficiation of bauxite ore into an enriched bauxite fraction for alumina production in a refinery and a tailings fraction to be stored or disposed of, e) land reclamation carried out in the mined area, f) rehabilitation carried out in the mined area, wherein: g) said tailings fraction from step d) is dried to a solids content of 80% or more using exclusively solar energy, and h) tailings dried according to step g) are backfilled in the mine pit in a permanent manner before or in connection with step e).

2. Method according to claim 1, characterized in that the tailings fraction of step g) may have a moisture content as low as 18%.

3. Method according to claim 1, characterized in that the reject fraction from step d) will normally have the following particle sizes and chemical characteristics: Particle size 100% passing through sieve 20# (0.85 mm) 90% to 98% passing through sieve 400# (0.038 mm) Chemical quality Usable A12O3 — ranging from 18.02% to 19.83% Petition 870260009464, dated 01 / 30 / 2026, page. 26 / 42 2 / 3 Reactive SiO2 — ranging from 20.29% to 21.97% Total Al2O3 — ranging from 38% to 42% Total SiO2 — ranging from 21.69% to 23.69% Total Fe2O3 — ranging from 12.10% to 14.94% Total TiO2 — ranging from 1.90% to 2.10% Loss on ignition — ranging from 18% to 20%.

4. Method according to claim 1, characterized in that the tailings fraction from step d) is chemically inert and is chemically unchanged relative to the ore from a mined raw ore production (ROM).

5. Method according to claim 1, characterized in that the tailings fraction from step d) is finer in terms of particle size distribution than the raw ore production (ROM) ore.

6. Method according to claim 1, characterized in that the backfilling in step h) is done with a displacement of a few meters for drainage purposes.

7. Method according to claim 1, characterized in that the bauxite is mined in strips in a section that is 25 meters wide, and that the backfilling in step h) is done with an offset of 5 (five) meters, and that the backfilling of the tailings is done in a section that is 20 meters wide.

8. System for long-term management of tailings generated during the bauxite mining process by continuous steady-state strip mining of bauxite ore according to steps a) to h) of the method as defined in claim 1, characterized in that the system comprises a tailings drying plant that allows tailings fractions to be dried according to step d) to a solids content of 80% or more.

9. System according to claim 8, characterized by the fact that the tailings fraction of step d) is dried to achieve a moisture content of 20% or less.

10. System according to claim 8, characterized in that the tailings fraction is chemically inert and dried to a certain level for sustainable backfilling and storage in the mined pit. Petition 870260009464, dated 01 / 30 / 2026, pp. 28 / 42

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