Continuous ore processing system

Abstract

The system according to the present application involves the processing of ore containing the lanthanide series and the production of rare earth carbonate, which involves receiving and conditioning the raw material, separating fine solids and precipitating the rare earth salt, and involves a spent solution tank that feeds back into the process as a whole and the use of flocculant prior to the seeding process and final filtration. The process according to the present application begins with material being extracted from a mine (ROM), transported by lorries and stacked in a specific location, a stockpile, and involves the following successive stages: first screening, second screening, third screening, fourth screening, leaching / ion exchange, and precipitation, sodium chloride, sodium carbonate and a flocculant solution being used as reagents during the process.

Description

[0001] "Continuous Mineral Processing System"

[0002] FIELD OF THE INVENTION

[0003]

[0001] The present invention applies to the field of lanthanide extraction and processing. In particular, the present invention relates to a continuous process of screening, leaching / ion exchange, filtration, precipitation, concentration and filtration for the extraction, purification and production of oxides of elements from the lanthanide series, with the aim of improving ore recovery efficiency and reducing environmental impact, as well as dispensing with the use of ammonium salts.

[0004] BACKGROUND OF THE INVENTION

[0005]

[0002] Extracting elements from the lanthanide series can be considered relatively complex, especially because these elements are usually found mixed with other geological materials, making their selective extraction difficult.

[0006]

[0003] The extraction of elements from the lanthanide series is carried out, in the state of the art, mainly by two methods: in-situ desorption and heap leaching. In the in-situ desorption method, a series of wells is drilled directly into the reservoir, through which a desorbing agent is injected, which is subsequently captured at the base of the wells. In the heap leaching process, piles are constructed with the material of interest, which are irrigated with the desorbing agent, which penetrates and is then captured at the base of the pile.

[0007]

[0004] Document BR102020021851, for example, discloses a system for concentrating and drying ores consisting of tanks with different configurations, designed to combine the functions of concentrating and drying ores, thus providing greater particle size classification with separation of grains with different particle sizes and weights.

[0005] Document BR112017002928, in turn, discloses a method for extracting and separating rare earth elements comprising providing an ore or mining tailings containing rare earths; grinding the ore containing rare earths to form powdered ore; leaching with at least one mineral acid, forming a leaching solution comprising at least one metal ion, rare earth elements and a solid material; separating the solid material from the leaching solution to form an aqueous metal concentrate;Precipitate the aqueous metal concentrate to selectively remove the metal ion from the leaching solution and obtain a precipitate of rare earth elements; heat the precipitate of rare earth elements in air to form oxide of rare earth elements; mix oxide of rare earth elements with an ammonium salt and heat in dry air / nitrogen; form a mixture of anhydrous rare earth salts in an aqueous solution and separate the rare earth elements from the aqueous solution by means of an electrolytic extraction process.

[0008]

[0006] Document BR112019002095 discloses a method for extraction, enrichment and recovery of rare earths from a low concentration rare earth solution, using a non-saponification organic extractor to perform centrifugal extraction, obtaining an organic phase containing rare earths and a raffinate; using an inorganic acid to perform centrifugal extraction on the organic phase containing rare earths, obtaining a liquid enriched with rare earths.Single or double coupling centrifugal extraction is performed according to the actual concentration of the rare earth solution, allowing all rare earths or light rare earths and medium-heavy rare earths to be respectively enriched in the organic phase containing rare earths, and then centrifugal re-extraction is performed through inorganic acid, thus obtaining the rare earth-enriched liquid containing all rare earths or containing mainly light rare earths or medium-heavy rare earths.

[0009]

[0007] Finally, document BR112019018463 discloses a system and a method for processing minerals containing the lanthanide series and producing rare earth oxides, which allow for a completely closed and continuous treatment of the different materials and desorbing agents involved in the process, thus improving extraction efficiency and avoiding associated environmental risks.The method comprises the following steps: receiving and conditioning the raw material; desorption of valuable product through a plurality of mixing and reaction stages in which the raw material is contacted in countercurrent with a stream of desorbing solution; separation of fine solids; precipitation of secondary minerals through the use of a first reactive solution; precipitation of rare earth carbonates through the use of a second reactive solution; and drying and roasting of the rare earth carbonates to obtain rare earth oxides; wherein the method further comprises a secondary process that allows for the further processing of the residual mineral, and a dehydration and washing step in which the residual mineral from the desorption step is washed and a liquid containing lanthanide is recovered.

[0010]

[0008] It is clear that the search, in the state of the art, is for increasingly efficient processes with less environmental impact for the processing of minerals containing the lanthanide series and for the production of rare earth oxides.

[0011] SUMÁRIO DA INVENÇÃO

[0012]

[0009] The present invention relates to a continuous process of screening, leaching / ion exchange, filtration, precipitation, concentration and filtration for the extraction, purification and production of oxides of lanthanide series elements, with the aim of improving the efficiency of ore recovery and reducing the environmental impact. The process according to the present application begins with material being removed from a mine (ROM), transported by trucks and stockpiled in a specific location, a stockpile, and involves the successive steps of:

[0013] - peneiramento,

[0014] - lixiviação / troca iônica, e

[0015] - precipitation; in which the sieving stage actually corresponds to four sieving processes that occur simultaneously, each independent of the other.

[0016]

[0010] In other words, in the screening stage there are four screening systems operating simultaneously, in different locations in the mine.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018]

[0011] The drawings accompanying this descriptive report reflect an exemplary and non-limiting embodiment of the process that is the subject of this application, in which:

[0019] Figure 1 shows a flowchart of the process for processing rare earth carbonate according to the present invention;

[0020] Figures 2a to 2d show a flowchart of the consecutive sieving steps within the process according to the present invention;

[0021] Figure 3 shows a flowchart of the leaching / ion exchange step within the process according to the present invention;

[0022] Figure 4 shows a flowchart of the precipitation step within the process according to the present invention;

[0023] - Figure 5 shows a flowchart of the pH adjustment and flocculant addition step that precipitates rare earth elements in the form of carbonates, within the process according to the present invention; and - Figure 6 shows a flowchart of the flocculant solution preparation within the process according to the present invention.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025]

[0012] The process according to the present application involves processing a mineral containing the lanthanide series and producing rare earth carbonate which involves receiving and conditioning the raw material, separating fine solids, precipitating the rare earth salt, and involves a wastewater tank that feeds back into the process as a whole and the use of flocculant before the seeding process and final filtration.

[0026]

[0013] The process according to this application begins with material being removed from a mine (ROM), transported by trucks and stockpiled in a specific location, a stockpile, and involves the successive steps of:

[0027] - screening, in four simultaneous sections,

[0028] - leaching / ion exchange, and

[0029] - precipitation.

[0030]

[0014] As illustrated in Figure 1, the ROM material is transported by a front-end loader that feeds two silos operating in parallel equipped with a grate and removes materials larger than 100mm. The material larger than 100mm is piled near the silo, and the front-end loader itself breaks up this material and returns it to the silos. The passing material is conveyed, via a conveyor belt, to the pulpers, each of which receives a stream of spent solution.

[0031]

[0015] The four screening units, with the same processing capacity, were designed to be located as close as possible to the mine. These screening areas are distributed across three extraction zones. Two screening areas are located in the central zone, one in the eastern zone, and one in the northern zone. The distinction between each of these areas is based on the distance to the rare earth processing unit and also aims to balance production throughout the mine's lifespan. The leaching area separates the rare earth elements through solubilization and filtration. Thus, the solubilized rare earth elements are separated by filtration, and the leaching / ion exchange cake is sent to the waste disposal area.In the precipitation area, the soluble material passing through leaching is subjected to a pH adjustment process and the addition of flocculant, which precipitates the rare earth elements in the form of carbonates. These carbonates are concentrated in the thickener and separated from the liquid by filtration. The resulting cake is called Mixed Rare Earth Carbonate (or MREC), which is the product of interest.

[0032]

[0016] The alternative proposed in this application considers the first start-up feeding the plant with exhausted solution at a concentration of 75 g / L, considering that under this condition the process parameters are more easily achieved than if the plant were started with water only. Therefore, initial preparation involves producing a 5M NaCl solution, diluting this solution to the exhausted solution concentration, and connecting auxiliary lines to carry out the operations necessary for the first start-up. With the plant operating under exhausted solution conditions, the start-up procedure with the ROM begins with the screening areas.

[0033]

[0017] Four consecutive screening stages are illustrated in Figures 2a to 2d.

[0034]

[0018] As shown in Figure 1, the material is initially removed from the mine (ROM), transported by trucks, and stacked in the stockpile located at each screening unit. This material is then transported by a front-end loader that feeds two silos operating in parallel, equipped with screens, and removes materials larger than 100mm. The material larger than 100mm is stacked near the silo, and the front-end loader itself breaks up this material and returns it to the silos. The passing material is conveyed, via a conveyor belt, to the pulpers, each of which receives a stream of spent solution. Due to the addition of this spent solution, the material that entered the pulpers with an average of 87% solids now exits with 60% solids by weight.

[0035]

[0019] Each pulper feeds a sieve which in turn also receives a flow of exhausted solution to maximize separation efficiency. The sieves are designed to separate materials larger than 1 mm. The two sieves discharge the undersize material with 40% solids into a single tank which is pumped to the next stage of the process.

[0036]

[0020] The oversize material from the screens is directed to the waste area, and the liquid drained from this material is pumped via a well pump from the stockpile yard to the spent solution tank (tag). The solid returns to the mine with approximately 10% moisture for pit replenishment.

[0037]

[0021] As can be seen from the flowcharts in Figures 2a to 2d, what differentiates the screening areas is the distance of each one to the leaching area. This distance impacts the need for different pumps in each screening area, with specific manometric heights for the effective pumping of the pulp to the leaching area. In case of stoppages in the screening area, the pulp can clog the piping that connects the screening area to the leaching area. To avoid this type of problem, a spent solution tank with sufficient volume is provided to wash the entire line in case of such stoppages. In summary, what differentiates each screening area in terms of equipment are the pulp pumps and the volume of the spent solution tank.

[0022] After four screening stages, leaching and precipitation stages follow.A leaching area, in the process according to the present application, separates the rare earth elements by means of solubilization and filtration and is illustrated in Figure 3. Figure 4 illustrates the precipitation stage. Thus, the solubilized rare earth elements are separated by filtration and the leaching cake is sent to a waste disposal area.

[0038]

[0023] As shown in Figure 3, the leaching area receives the streams from the four screening areas, which are directed to a transfer box with a volume of 3m³. 3 This box discharges the pulp into a 440m³ agitated tank. 3In this process, a 5 molar sodium chloride solution is also added to solubilize the rare earth elements in the form of chlorides. The resulting solution has a pH of approximately 4.2, and under these conditions, some impurities, notably aluminum and iron, are also solubilized. The pulp then flows into a stirred tank with a volume of 363 m³ via overflow. 3 The process involves adjusting the pH to 4.7 by adding sodium carbonate to precipitate impurities, mainly aluminum and iron. The pulp is then transferred to an agitated tank with a volume of 363 m³ via overflow. 3 , which feeds, by pumping, a subsequent filtration stage.

[0039]

[0024] In filtration, the solid material is retained in press-type filters with automated operation. The passing material goes to the precipitation stage and the filtered bolo (cake) is conveyed, by conveyor belts or dump trucks, to a bean pile, and subsequently transported to the reject pile, where it will be disposed of and compacted.

[0040]

[0025] Under normal conditions, the operating flow rate from each screening area is 681.6 t / h, equivalent to 506.2 m³. 3 / h with a density of 1.35 and 40% solids.

[0026] After the leaching inlet flow meter, the pulp passes through the densimeter which, through density, analyzes the percentage of solids in the mixture. If the density is below, with an equivalent percentage less than 15% solids, the flow will be automatically directed to an 88m³ tank. 3 until the density condition is re-established.

[0041]

[0027] Leach filtration occurs with six filters operating in parallel, with approximately 34% solids. The feed from the high-flow pump is responsible for filling the chamber, and the high-pressure pump is responsible for supplying the operating pressure. The time for each filtration cycle is 28 minutes, and the operating pressure is 10 kgf / cm². 2 .

[0042]

[0028] A conductivity meter and a turbidimeter are installed in the outlet line of each filter.

[0043]

[0029] The conductivity meter controls the second washing time of the cakes with water until a desired salt concentration of 60 g / L is reached, however the washing will be automatically interrupted after a time limit if the maximum volume of water has been reached, according to the moisture content of the ore at the entrance of the screening process, even if the conductivity has not reached a defined set point.

[0044]

[0030] The turbidimeter's function during the production process is to analyze the turbidity of the filtrate (rich solution) and activate a set of valves via a controller, releasing the flow to the appropriate tank according to the measured turbidity. The tank has a capacity of 300m³. 3 The product will only be dispensed when the turbidimeter detects turbidity in the rich solution below 7 NTU. For values ​​above 7 NTU, the flow is automatically directed to a tank with a capacity of 125 m³. 3 , which uses a pump to recycle the turbid material back into the tank.

[0031] The PLS tank sends, via pumps, a flow rate of 1,834.5 t / h equivalent to 1,761 m 3 / h, the clarified rich solution is sent to the precipitation area via a line leading to a tank.

[0045]

[0032] The normal shutdown of operations, in this section, involves suspending the feed of pulp from the screening areas to the leaching plant. The leaching plant operator requests the shutdown of the screening areas and informs the precipitation area operator about the shutdown and the period during which the plant will be inoperative.

[0046]

[0033] The leaching area can stop when the tanks are full or when the entire unit is depleted. If the tanks are full, the agitators must remain on to prevent the solids from settling and causing subsequent problems. If the plant is completely depleted, the tanks can be emptied by operating valves through the pumps that feed the leaching filters.

[0047]

[0034] The precipitation area is the area that receives the solution from the leaching area and has the function of precipitating and concentrating the rare earth elements (REEs) that were previously soluble in the leaching area into carbonate form. This precipitation is done by adding sodium carbonate and flocculant. Concentration is achieved using a thickener to increase the percentage of solids in the outflow stream. The final stage of this area is filtration to extract the REEs in the form of insoluble carbonates, collected in the filter cake. This concentrate is packaged in bags and stored in a warehouse for shipment and sale.

[0048]

[0035] As shown in Figure 5, in the precipitation area, the soluble material passing through leaching (discussed previously) is subjected to a pH adjustment process and the addition of flocculant, which precipitates the rare earth elements in the form of carbonates. These carbonates are concentrated in a thickener and separated from the liquid by filtration. The cake is called Mixed Rare Earth Carbonate (or MREC), which is the product of interest in this process.

[0049]

[0036] The solution rich in rare earth elements, exiting the leaching circuit through a tank, pumped at a flow rate of 1623 t / h, enters the precipitation system in a 3 m junction box. 3capacity. In this same tank, two more solution / pulp streams are added: one coming from the thickener underflow, called "seeding," which under normal conditions has 10% solids and a flow rate of 137.7 t / h through one line; and the other, a sodium carbonate solution with a concentration of 150 g / L, transferred by a pump with a flow rate of 7.4 t / h.

[0050]

[0037] The transfer case has two motorized dart-type valves at the bottom of the case. Under normal conditions, these valves direct a flow of approximately 1,767 t / h through a line to an agitated tank, with one section open and the other closed.

[0051]

[0038] A tank with 240m 3With a capacity and residence time of approximately 7 minutes, it is equipped with a pH meter and conductivity meter. The pH meter is connected to a control loop that acts on the pump motor's rotation, controlling the sodium carbonate flow rate in the transfer box in order to maintain the pH at values ​​close to 7.5.

[0052]

[0039] A U-shaped chute transfer tank measuring 500x500mm (width and depth) transfers the rich solution at a flow rate of 1,768.9 t / h, equivalent to 1,694.2 m³. 3 / h for a stirred tank with a volume of 240m³ 3and a residence time of approximately 7 minutes. In this tank, under normal conditions, 0.42 t / h of flocculant solution is dosed by a pump through a line. The pH and conductivity can also be checked in the tank. Therefore, in case of unavailability of the tank, the precipitation process will start in an appropriate section.

[0040] In each of the tanks, level gauges are installed, interconnected and interlocked by an operational logic to the motor, preventing it from starting without a safety level in the selected tank. Automated shut-off valves are also part of this control logic that acts on the operational safety of the pump. Similarly, the valves are opened before the pump is activated.

[0053]

[0041] At nominal flow rate, the two pumps feed the thickener transfer box 3m 3through a collector at a flow rate of 1,773.10 t / h with approximately 1% solids, this flow rate being checked by a meter and density by the appropriate instrument.

[0054]

[0042] The transfer box feeds the thickener by gravity at a flow rate of 1,774.5 t / h through a line. The feed is made in a zone of hydraulic turbulence, physically separated from the thickener's separation bed by only an opening at the bottom through which, via communicating vessels, the separation bed receives the material to be thickened. Under normal conditions, the thickener also receives flocculant solution at a flow rate of 1.4 t / h through a line.

[0055]

[0043] In the upper collection trough, called the overflow, the turbidimeter and pH meter analyze the exhausted solution together. Turbidity indicates the presence of dissolved REEs in the collected exhausted solution and consequently a loss of productivity. pH values ​​below 7.5 indicate that there may be a decrease in precipitation efficiency, keeping some REEs in solution, also causing a loss of productivity.

[0056]

[0044] The exhausted solution, collected in the thickener overflow, flows by gravity through a line with a flow rate of 1621.4 t / h equivalent to 1,560.7 m³. 3 / h for a tank with 600m³ 3 capacity.

[0045] In the heavy stage of the thickener, called underflow, the product has as its main characteristic a solids percentage greater than or equal to 10%. The thickener underflow feeds a collector with a flow rate of 153.03 t / h equivalent to 138.9 m 3 / h through two pipelines. The seeding recirculation pumps and the underflow transfer pumps are connected to this collector.

[0057]

[0046] A hydrometer, installed in the pump discharge line (seeding), acts on valves. In normal operation, the density read by the instrument is approximately 1.1 t / m³. 3 .

[0058]

[0047] In the recirculation (seeding) circuit, the densitometer acts by opening and closing valves, automatically directing the flow of 137.7 t / h equivalent to 125 m 3 / h through a line to the transfer box. This flow can eventually be recirculated back to the thickener through a line to the transfer box to promote bed formation in the thickener. The seeding flow rate corresponds to 90% of the total underflow rate of the thickener.

[0059]

[0048] In the underflow transfer circuit, the densimeter acts by opening and closing valves, automatically directing the flow of 15.3 t / h equivalent to 13.9 m 3 / h through a line to tank 06-TK-1580 which will feed the precipitation filters. If the density is below 1.1 t / m³ 3 The valve status is reversed, and the pulp flow is recirculated back to the thickener through a line to the transfer box. Under normal conditions, the underflow transfer rate represents 10% of the total underflow rate of the thickener.

[0060]

[0049] The next step within the precipitation area is filtration, which occurs with two filters. Each of them has the capacity to filter the entire production, that is, 15.3 t / h of pulp with a density of 1.1 t / m³. 3These filters do not operate in parallel, dividing the flow; they operate sequentially so that while one piece of equipment is filtering, another is washing the cake or filter cloth, or blowing the cake for unloading. Each filtration cycle lasts 30 minutes and the operating pressure is 15 kgf / cm². 2 .

[0061]

[0050] The filter cake undergoes a blowing process to reduce moisture. After this process, a filter discharges the cake into the chute, which in turn directs the material to screw conveyors that operate in series. The two lines from each filter join in the loading system, which is done in 2-ton bags. Forklifts organize these bags following an internal inventory management procedure within the warehouse.

[0062]

[0051] The precipitation area may stop when the vessels are full or exhaust the entire area.

[0063]

[0052] In case of shutdown with full tanks, the agitators must remain on to prevent clogging of solids and subsequent problems during restart. The seeding pump can remain on, recirculating through the system. In this case, the dosage of flocculant solution in the tank should occur according to the turbidity parameters in the thickener overflow; however, the dosage of flocculant solution should be interrupted if there is no pulp flow entering the tank through the piping.

[0064]

[0053] In case of total depletion of the precipitation area, the tanks can be emptied by operating valves via the pumps that feed the thickener transfer box. Similarly, the operator should only stop dosing the flocculant solution into the box when there is no more pulp flow through the piping.

[0065]

[0054] In the process according to the present application, a reagent area includes the preparation of sodium chloride solution for consumption in the leaching / ion exchange area and the preparation of flocculant and sodium carbonate solutions, both for use in the precipitation area.

[0055] It is important to highlight that the carbonate here is sodium carbonate and that the necessary elements for pH adjustment and flocculant addition are carried out as illustrated in Figure 6.

[0066]

[0056] The flocculant solution prepared in the tank is transferred by pump, under level control, through a line to the tank.

[0067]

[0057] The flocculant solution is consumed at two points in the precipitation process. A pump doses the flocculant solution into the precipitation circuit in the tank. During the startup of the process, the flocculant dosage adjustment should be directed 75% of the flow rate to precipitation and 25% to thickening.

[0068]

[0058] The total amount of flocculant required by the process is determined by the turbidimeter installed in the thickener overflow, and this signal is sent to two pumps.

[0069]

[0059] The prepared solution, contained in the tank, is at a concentration of 2.5 g / L, however the ideal concentration for the flocculant to perform its function properly is 0.25 g / L. In this context, at the pump outlet, a flow meter sends a signal to a controller that acts on the control valve, adjusting the necessary amount of exhausted solution for dilution according to the manufacturer's instructions.

[0070]

[0060] For the other line, a similar process occurs; at the pump outlet, the flow meter sends a signal to the controller, which acts on the control valve, adjusting the required amount of solution.

[0071]

[0061] It is important to note that, when the present invention is put into practice, modifications may be made with respect to certain details of construction and form, without departing from the fundamental principles that are clearly set forth in the context of the claims, it being understood that the terminology employed is not intended to limit the invention.

Claims

CLAIMS 1. Continuous process for the extraction, purification, and production of rare earth element salts, characterized by the fact that it operates with the reception and conditioning of raw materials, separation of fine solids, precipitation of rare earth salts, and involves a spent solution tank that feeds back into the process as a whole, and the use of flocculant before a seeding and final filtration process, which begins with material being removed from a mine (ROM), transported by trucks, and stockpiled in a specific location, involving the successive steps of: - sieving, - leaching / ion exchange, and - precipitation.

2. Process, according to claim 1, characterized in that the four screening stages take place in four different screening units, with the same processing capacity, successively located as close as possible to the mine, where the distinction of each of these areas is given by the distance to the rare earth processing unit.

3. Process, according to claim 1, characterized in that the leaching / ion exchange area separates the rare earth elements by means of solubilization and filtration, wherein the leaching / ion exchange cake is sent to a waste disposal area.

4. Process, according to claim 1, characterized in that, in the precipitation area, the soluble material passing through leaching / ion exchange is subjected to a pH adjustment process and the addition of a flocculant that precipitates the rare earth elements in the form of carbonates.

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