WO2020099514A1

WO2020099514A1 - Method and facility for operating an in-situ leach mine

Info

Publication number: WO2020099514A1
Application number: PCT/EP2019/081232
Authority: WO
Inventors: Adrien DEBERGÉ; Violet JEROME
Original assignee: Orano Mining
Priority date: 2018-11-14
Filing date: 2019-11-13
Publication date: 2020-05-22
Also published as: US20220003100A1; FR3088364B1; AU2019382091A1; FR3088364A1

Abstract

The operating method comprises a routine phase implemented at the end of life of a block (3) of cells (5) of a mine, during which the following operations are carried out: - collecting the leachate produced by at least one cell (5) being recycled in the block (3), the leachate forming the recycled leachate; - injecting the recycled leachate into at least one cell (5) of the block (3).

Description

Method and installation for operating a mine by in situ leaching

The invention generally relates to the operation of a mine by in situ leaching, including the operation of a uranium mine.

The in situ leaching of a chemical component, called "In Situ Leaching" in English or ISL method, is a mining method which consists of:

- to establish in the base of the deposit a circulation of a leaching solution capable of selectively dissolving the chemical component that we want to exploit;

- pumping the leached solution loaded with the desired mineral element in surface treatment installations, where the valuable mineral element is separated and concentrated in a commercial product;

- to recycle the leaching solution to the deposit, after reconditioning.

The ISL method is notably applied to deposits with a low content of uranium, copper or gold. It has the advantage that the selective dissolution of the mineral element of its gangue is done without physical displacement of the ore and without significant modification of the host rock (generally sandy and porous medium).

For uranium, depending on the composition of the gangue, the solution injected to dissolve the chemical component is for example an alkaline solution of sodium carbonate or bicarbonate, which allows a progressive and fairly selective solution. Alternatively, the attack liquor is an acid solution, usually sulfuric, for a more aggressive and faster dissolution, but less selective.

The leaching solution, also called attack liquor, is generally injected under pressure into the permeable horizon containing the chemical component, by a network of injector wells which descends to the permeable horizon. In this way, the leaching solution is brought into contact with the chemical component to be dissolved.

A second network of wells known as producing wells, inserted in the previous network, pumps the mineralized leaching solution and returns it to the plant installed on the surface. A conventional treatment allows the extraction of the chemical component in the liquid phase.

After treatment, the leaching power of the solution is regenerated so that it can be reinjected as an attack liquor in the network of injector wells a large number of times, for example between ten and more than fifty times.

The mine is generally divided into blocks, each block comprising a plurality of production cells served by the same operating facility.

At the end of their life, the cells are exploited until the concentration of chemical component in the leachate extracted reaches a minimum cut-off value or that the tonnage produced on the scale of the block or several cells is no longer sufficient to complete the desired annual production under economically viable conditions (production constraint and hydraulic capacity constraint of existing networks).

Such an approach has the drawback that significant reserves of the chemical component can be left in the ground and are not extracted.

In this context, the invention aims to propose an operating method and an operating installation which do not have the above defect.

According to a first aspect, the invention relates to a method of operating a mine by in situ leaching of at least one chemical component, the mine comprising a plurality of production cells each equipped with at least one well. injection configured for the injection of an attack liquor into said cell and of at least one production well configured to withdraw a leachate containing the at least one chemical component rising from said cell, the method comprising, when a block of cells is at the end of its life, a current phase during which the following operations are implemented:

collecting the leachate produced by at least one cell for recycling said block, said leachate forming the recycled leachate;

- injection of the recycled leachate into at least one cell of said block.

Thus, the leachate produced by the cells in recycling is not sent to the treatment plant for separation of the chemical component. On the contrary, it is recycled directly into one or more cells in the block.

This first has the effect of partially or completely reducing the flow of leachate sent from the block to the treatment plant. Solutions sent to the processing plant are more loaded than in the prior art, which optimizes the use of transfer networks to the processing plant. In addition, this treatment plant processes more concentrated leachate, so that the specific consumption of chemical reagents is lower.

As a result, it becomes profitable to continue operating the cells even if the concentration of chemical component in the leachate decreases and becomes below the usual cut-off threshold or the annual production targets. It is thus possible to recover a greater quantity of chemical component in the cells, which increases the profitability of the operation.

The process of the invention is dimensioning for the mining field if it is integrated from the start of the design of the mine's operating installation. It has a significant effect on the capacity of the infrastructure to be built. Typically, 50% of the production blocks of an ISL mine are at the end of their life, and produce a leachate having a content of said chemical component of approximately 60% of the average content of the other production blocks. The blocks at the end of their life supply approximately 30 to 40% of the total flow. The method of the invention is for example applied to half of the blocks at the end of their life, and allows a reduction in the managed throughput of around 20%. This results in a significant reduction in the capacity required for the transport and processing installations.

The process can also have one or more of the characteristics below, considered individually or in all technically possible combinations:

the method comprises an operation for treating the recycled leachate before the injection operation, for example by acidification of the recycled leachate;

said current phase comprises an operation of collecting the leachate produced by at least one cell for producing said block and of transferring the leachate into a treatment plant, said leachate forming the leachate transferred, the at least one chemical component being separated from the leachate transferred to the processing plant;

- during the injection operation, the recycled leachate is injected into at least one production cell;

- during said current phase, the attack liquor is injected into the cells for recycling concomitantly with the collection of the recycled leachate;

- during said current phase, the attack liquor is injected into the production cells concomitantly with the collection of the transferred leachate;

- at the end of said current phase, the operation of the at least one recycling cell is stopped, and a new phase starts:

• the at least one cell into which the leachate recycled in said current phase is injected becoming the at least one cell in recycling during the new phase;

• the leachate recycled during the new phase being injected into at least one new cell of said block;

- the block of cells is traversed by an underground flow flowing in a determined direction, the exploitation of the cells of the block being gradually stopped according to said direction of the underground flow;

- Said current phase comprises a separation operation during which a phase concentrated in the at least one chemical component is separated from the recycled leachate; - The concentrated phase is stored in situ for a determined period and then transferred to a treatment plant, the at least one chemical component being separated from the concentrated phase in the treatment plant;

- all the cells in the block are being recycled and the recycled leachate is reinjected into all the cells in the block).

According to a second aspect, the invention relates to an installation for operating a mine by in situ leaching of at least one chemical component, the mine comprising at least one block having a plurality of cells, the operating installation including:

- for each cell of said block at least one injection well configured for the injection of an attack liquor into said cell;

- for each cell of said block at least one production well configured to take a leachate containing the at least one chemical component rising from said cell;

- a recycling collector;

a plurality of collection conduits, each fluidly connecting one of the production wells to the recycling collector, each collection conduit being equipped with a collection cut-off member capable of selectively authorizing or prohibiting the circulation of leachate collected in the corresponding collection conduit;

- an injection well supply assembly, configured to selectively put the recycling manifold into fluid communication with one or more of the injection wells.

The installation can also have one or more of the characteristics below, considered individually or in all technically possible combinations:

the operating installation comprises a unit for treating the leachate recycled before injection into the or each injection well, for example by acidification of the recycled leachate;

- the operating installation includes:

• a production collector intended to be connected to a treatment plant, the at least one chemical component being separated from the leachate in the treatment plant;

• a plurality of production conduits, each fluidly connecting one of the production wells to the production collector, each production conduit being equipped with a production cut-off member capable of selectively authorizing or prohibiting the circulation of leachate in the corresponding production duct;

the operating installation comprises a separation module arranged upstream of the supply assembly for the injection wells and configured to separate a concentrated phase into the at least one chemical component of the recycled leachate; the operating installation comprises an in situ storage of the concentrated phase, and a module for transferring the concentrated phase from the separation module to a treatment plant, the at least one chemical component being separated from the concentrated phase in the processing plant;

- the power supply includes:

• a plurality of recycling conduits, each fluidly connecting the recycling collector to one of the supply wells, each recycling conduit being equipped with a recycling cut-off member capable of selectively authorizing or prohibiting circulation in the corresponding recycling conduit;

- the power supply includes:

• a supply manifold, intended to be connected to a supply unit for attack liquor;

• a plurality of supply conduits, each fluidly connecting the supply manifold to one of the supply wells, each supply duct being equipped with a supply cut-off member capable of selectively authorizing or d '' prohibit circulation in the corresponding supply duct.

Other characteristics and advantages of the invention will emerge from the detailed description which is given below, by way of indication and in no way limitative, with reference to the appended figures, among which:

- [Fig 1] Figure 1 is a simplified schematic representation of a mine operating installation by in situ leaching according to the invention;

- [Fig 2] Figure 2 is a view similar to that of Figure 1, when this operating installation is operated according to a first embodiment of the operating method of the invention; and

- [Fig 3] Figure 3 is a view similar to that of Figure 1, when the operating installation is operated according to a second embodiment of the method of the invention.

The installation 1 shown in FIG. 1 is intended for the exploitation of a mine by in situ leaching of a chemical component, in particular the exploitation of a uranium mine.

As illustrated in FIG. 1, the mine comprises at least one block 3 having a plurality of cells 5.

Operating installation 1 includes:

- For each cell 5 of block 3, at least one injection well 7, configured for the injection of an attack liquor into said cell 5; - for each cell 5 of said block 3, at least one production well 9, configured to take a leachate containing the at least one chemical component rising from said cell 5.

Typically, the injection wells 7 are arranged in a determined mesh, generally regular, each mesh defining one of the cells.

For example, the injection wells 7 are arranged in a square mesh, the production well serving the corresponding cell being placed in the center of the square. The injection wells 7 are generally spaced fifteen to fifty meters apart, the distance between an injection well and a production well being between eleven and thirty-three meters.

Here we call all the cells served by the same operating facility. In other words, the block corresponds to all the cells that can be served from the same collectors.

In Figure 1, only three cells have been shown. However, the block typically has a higher number of cells. Block 3 typically includes about 15 cells, with a minimum of 6 and a maximum of 24.

The operating installation 1 comprises a recycling collector 1 1 and a plurality of collection conduits 13 each fluidly connecting one of the production wells 9 to the recycling collector 1 1.

Each collection conduit 13 is equipped with a collection cut-off member 15, capable of selectively authorizing or prohibiting the circulation of leachate collected in the corresponding collection conduit 13.

In the present description, all the cut-off members are preferably valves. As a variant, the cut-off members are of any other suitable type.

In the present description, it will be said that a cut-off member is open when it authorizes the circulation of fluid in the corresponding conduit. It will be said that a cut-off device is closed when it prevents the circulation of fluid in the corresponding duct.

Thus, the installation comprises as many collection conduits 13 as production wells 9.

The installation 1 also includes a production collector 17, intended to be connected to a treatment plant 19. As indicated above, in the treatment plant, the chemical component of interest is separated from the leachate, so as to produce a marketable product.

The installation 1 also comprises a plurality of production conduits 21, each one fluidly connecting one of the production wells 9 to the production collector 17. Each production conduit 21 is equipped with a production cut-off member 23 capable of selectively authorizing or prohibiting the circulation of leachate in the corresponding production conduit 21.

Installation 1 has as many production conduits as there are producer wells.

The installation 1 also includes an assembly 25 for supplying the injection wells 7, configured to selectively put the recycling manifold 1 1 into fluid communication with one or more of the injection wells 7.

In other words, the supply assembly 25 makes it possible to recycle the leachate collected by injection into one or more of the injection wells 7, without prior sending of the leachate collected to the treatment plant 19.

The power supply 25 includes:

- A supply manifold 27, intended to be connected to a unit 29 for supplying attack liquor;

- a plurality of supply conduits 31, each fluidly connecting the supply manifold 27 to one of the supply wells 7.

The attack liquor supply unit is typically the leachate treatment plant 19.

Indeed, after separation of the chemical component, the leachate has a composition suitable for being recycled and forming, possibly after correction of its composition, the attack liquor.

Each supply duct 31 is equipped with a supply cut-off member 33, capable of selectively authorizing or prohibiting the circulation of fluid in the corresponding supply duct.

Thus, there are as many supply conduits 31 as injection wells 7.

The supply assembly 25 also includes a plurality of recycling conduits 35, each fluidly connecting the recycling manifold 1 1 to one of the injection wells 7.

Each recycling conduit 35 is equipped with a recycling cut-off member 37, capable of selectively authorizing or prohibiting circulation in the corresponding recycling conduit 35.

There are as many recycling pipes as there are injection wells.

In the example shown, the recycling conduits 35 connect the recycling collector 1 1 indirectly to the injection wells 7.

Thus, the recycling conduits 35 start from a branch 39 connected in bypass to the supply manifold 27. The recycling collector 1 1 is directly connected to the supply collector 27, upstream of the branch 39.

The term upstream is understood here relative to the normal direction of flow of the attack liquor.

A bypass duct 41 directly connects a point 43 of the recycling collector 11 to a point 45 of the branch 39. The bypass duct 41 is equipped with a cut-off member 46.

A cutoff member 47 is interposed along the recycling collector 11 between point 43 and the supply collector 27.

A cut-off member 49 is interposed on the branch 39 between the supply collector 27 and the point 45. The supply collector 27 is also equipped with a cut-off member 51, located for example between the arrival of the collector recycling 1 1 and departure from branch 39.

The operating installation 1 also includes a unit 53 for processing the leachate recycled before injection into the or each injection well 7.

The treatment unit 53 is provided for injecting a treatment product into the recycled leachate, before it is injected into the injection well (s) 7.

Typically, the treatment unit 53 is provided for acidifying or basifying the recycled leachate.

It is configured to increase the acidity or basicity of the recycled leachate. For example, when the ISL process uses an acid attack liquor, the acidity can be adjusted up to a value of 30 grams of acid per liter of recycled leachate, typically 30 grams of H ₂ SO ₄ per liter of recycled leachate.

The processing unit 53 is fluidly connected to a point 55 of the branch 39 by a conduit 57 equipped with a cut-off member 59. The point 55 is located downstream of the point 45, a cut-off member 61 being interposed between the points 45 and 55. The recycling conduits 35 start from points located downstream from point 55.

Preferably, the operating installation comprises a separation module 63, arranged upstream of the assembly 25 for supplying the injection wells 7 and configured to separate a phase concentrated in the at least one chemical component of the leachate recycled.

The separation module 63 is thus configured to separate the at least one chemical component from the recycled leachate and transfer the at least one chemical component to the concentrated phase.

The separation module 63 comprises for example ion exchange resins, of the type suitable for fixing the chemical component when the exchange resins ions are crossed by the recycled leachate. The ion exchange resins then constitute the concentrated phase.

As a variant, the separation module 63 is configured to carry out an extraction or liquid / liquid separation operation (by resins, membranes, fluid bed, etc.), using a solvent of the type suitable for recovering the chemical component. The collected leachate is brought into contact with the solvent in the separation module 63, the chemical component being transferred to the solvent. The solvent constitutes the concentrated phase.

As a variant, the separation module 63 is of any other suitable type.

In this case, the operating installation 1 preferably comprises an in situ storage of the concentrated phase, and a module for transferring the concentrated phase from the separation module to a processing plant.

This treatment plant is typically the treatment plant 19.

The in situ storage is sized to store a quantity of concentrated phase corresponding to a determined production duration, for example one month.

Storage depends on the type of separation process used. For example, storage is tank storage. In the case of resins, storage takes place on the resin contained in the separation module 63 ..

The transfer module is of any suitable type.

When the separation module 63 contains ion exchange resins, this module is for example detachably connected to the recycling collector 1 1. It constitutes in situ storage. Indeed, the separate chemical component is stored in the resins. The module 63 also constitutes the transfer module. It is configured so that it can be disconnected from the recycling collector 1 1, and transported, with the ion exchange resins, to the treatment plant.

Alternatively, the resins are eluted on site and only the eluate is transported by a mobile tank to the processing plant.

According to another variant, part of the resins is discharged from the separation module 63 and transported by a mobile tank to the processing plant.

Thus, in some cases, the transfer module is a mobile tank, into which the ion exchange resins, the eluate, or the solvent loaded with chemical component are transferred.

In the example shown, the separation module 63 is connected by an upstream conduit 65 to a point 66 of the recycling collector 1 1, and by a downstream conduit 67 to a point 68 of the recycling collector 1 1. The upstream conduits and downstream are equipped with respective cut-off members 69 and 71. A cut-off member 73 is interposed between points 66 and 68. A cut-off member 75 is placed upstream of point 66 and a cut-off member 75 between points 68 and 43.

The method of operating the mine by in situ leaching according to the invention will now be described, with reference to FIGS. 2 and 3. In these figures, the lines in service are shown in solid lines, and the inactive lines in broken lines. . The open cut-off members are shown hollowed out, and the closed cut-off members are shown filled.

A method using an acid attack liquor will be described below.

The operating installation 1 is designed for the implementation of this operating process.

Conversely, the operating method is particularly suitable for being implemented using the operating installation 1. It could however be implemented with a different operating installation.

This process is specially designed to optimize operation when block 3 of cells 5 is at the end of its life.

The method includes a current operating phase, during which the following operations are implemented:

collecting the leachate produced by at least one cell 5 for recycling the block 3, said leachate forming the recycled leachate;

injection of the recycled leachate into at least one cell 5 of said block 3.

Thus, in the description which follows, the leachate from the at least one recycling cell 5 is called recycled leachate.

According to a first embodiment of the method represented in FIG. 2, the current operating phase also comprises an operation of collecting the leachate produced by at least one production cell 5 of block 3, and of transferring said leachate to a treatment plant . This leachate is called here transferred leachate.

During the injection operation, the recycled leachate is injected into at least one production cell 5.

The production cell (s) are different from the recycling cell (s).

Typically, during the current phase, 5 cells are recycling cells, and 10 cells are production cells. This is particularly the case at the start of the partial recycling operation at the end of life.

In the example shown in FIG. 2, the two cells 5 located at the bottom are the cells in recycling. The third cell 5, located above, is the production cell. During the current phase, the attack liquor is injected into the or each recycling cell 5, concomitantly with the collection of the recycled leachate.

Likewise, during the current phase, the attack liquor is injected into the or each production cell concomitantly with the collection of the transferred leachate.

The attack liquor is for example a solution containing 2 grams of acid per liter.

Injecting the attack liquor into the recycling cells 5 slows down the natural process of raising the pH in these cells, and therefore increases the residual operating time of these cells.

The transferred leachate is sent to treatment plant 19. It is collected separately, the recycled leachate, never being mixed with the transferred leachate.

Preferably, the method comprises an operation for treating the recycled leachate, carried out before the injection operation. This operation is typically an operation of acidification of the recycled leachate, coming from the or from each cell in recycling. The recycled leachate is typically acidified to a value of 30 grams of acid per liter.

The configuration of operating installation 1 during the current phase is illustrated in Figure 2.

The collection cut-off members 15 of the collection conduits 13 associated with the or each recycling cell are open. On the other hand, the production cut-off members 23 of the production conduits 21 associated with the or each cell being recycled are closed.

For the or each production cell 5, the associated production cut-off member 23 is open, and the collection cut-off member 15 is closed.

The cut-off member 51 interposed on the supply manifold 27 is open. Likewise, the supply cut-off members 33 associated with the or each recycling cell 5 and with the or each production cell 5 are open.

The recycling cut-off member 37 of each recycling duct 35 associated with the or each production cell 5 is open. The recycling cut-off members 37 of the recycling lines 35 associated with the other cells 5 are closed.

The cut-off members 75, 73, 77 interposed along the recycling collector 1 1 are open. The processing unit 53 is functional, and supplies the branch 39 via the conduit 57. The cut-off members 46 and 61 are open. The cut-off members 47 and 49 are closed.

Thus, the transferred leachate produced by the or each production cell 5, is directed to the production collector 17 via the or each production conduit 21 corresponding. It is then sent to the treatment plant 19. The recycled leachate, coming from the or each recycling cell 5, is collected by the recycling collector 1 1, via the collection conduits 13. The recycled leachate is acidified by the treatment module 53 which is configured to make an acid make-up.

The acidified recycled leachate is injected into the or each production cell 5 via the or each corresponding recycling conduit 35.

It mixes with the attack liquor from the supply manifold 27 via the corresponding supply duct 31.

Concomitantly, the cells 5 in recycling are supplied with the attack liquor via the corresponding supply conduits 31.

The recycled leachate contains the chemical component extracted from the or each cell being recycled. It is reinjected into the or each production cell 5, so that the leachate coming from the or each production cell 5 has a concentration of chemical component much higher than the leachate coming from the or each cell in recycling 5.

At the end of the current phase, the operation of the or each recycling cell is stopped.

This exploitation is typically stopped when the pH rises in the cells clog the corresponding production wells 9 or when the economic cut-off thresholds of the process have been reached.

A new phase then begins in which:

- the at least one cell 5 in which the leachate recycled in the current phase was injected becomes the at least one cell in recycling 5 during the new phase;

- the leachate recycled during the new phase is injected into at least one new cell 5 in block 3.

The new phase implements the same operations as those described for the current phase. Only the circulation of the leachate and the attack liquor is modified.

This change in circulation of the leachate and the attack liquor is easily carried out, since it suffices to modify the position of the cut-off members to switch from the current phase to the new phase.

The block 3 of cells 5 is traversed by an underground stream flowing in a determined direction. This underground flow corresponds to the non-potable water table, or to an underground river running through the mine. None of these waters has other applications than mining. The direction of flow of the underground flow inside block 3 is known. It is typically determined by hydrogeological studies, before the start of mine operations. The direction of flow flow is represented by an arrow F in FIG. 2. According to the operating method of the invention, the operation of cells 5 of block 3 is gradually stopped, according to said direction of flow.

By this is meant that the first cells 5 to be stopped will be the cells located upstream of the flow. The last 5 cells to be stopped will be the cells located downstream of the flow.

Thus, for a given operating phase, the cell or cells 5 in recycling will be located relatively upstream, and the cell or cells 5 of production will be located relatively downstream.

When moving to the next phase, the new cell or cells, in which the leachate is recycled, will be located downstream of the production cell or cells of the previous phase. One of these new cells is shown in broken lines in Figure 2.

The operating process thus comprises several successive operating phases. At the end of each operating phase, one or more cells are shut down, typically those which are located furthest upstream from the direction of flow. The operating process ends when all the cells in the block have been shut down.

The process just described has multiple advantages.

It makes it possible to reduce the volume of leachate produced by block 3 at the end of production, that is to say at the end of mining of the block. The volume of leachate sent to the treatment plant via the hydraulic networks in charge, usually conveying the solutions produced, is thus reduced.

This allows network operators not to saturate the hydraulic networks under load, while optimizing overall production at the mine level. This also makes it possible not to decrease the average concentration of chemical component of the solutions sent to the treatment plant. This therefore avoids specific overconsumption of reagents at the treatment plant.

The method also makes it possible to increase the percentage of recovery of the reserves of block 3, and therefore to lower the economic cut-off threshold for production of block 3.

This makes it possible to potentially develop resources that are not classified as reserves, in the event that it is possible to significantly lower the value of the economic cut-off threshold for production of a block 3.

The described method also makes it possible to prepare the remediation of the hydraulic mine reservoirs used during an in situ leaching operation. The rise in pH is supervised until it is impossible to hydraulically operate the cells, due to the precipitation of certain compounds clogging the pores of the cell and the strainers of the producing wells.

A second embodiment of the operating method of the invention will now be described with reference to FIG. 3. Only the points by which the second embodiment differs from the first will be detailed below.

Identical elements or ensuring the same function will be designated by the same references.

The second embodiment has only one operating phase.

Thus, all of the cells in the block are recycling cells. By this is meant that the leachate produced by each cell 5 of block 3 is directed to the recycling collector 1 1. The production collector 17 receives no leachate from the cells of the block. Thus, all the leachate is recycled.

The recycled leachate is reinjected into all of the cells in the block. In other words, each cell 5 in the block receives part of the recycled leachate.

The cells 5 of block 3 are fed only with recycled leachate, and do not receive attack liquor.

The single exploitation phase includes a separation operation during which a phase concentrated in the at least one chemical component is separated from the recycled leachate

In other words, during the separation operation, at least one chemical component is separated from the recycled leachate and transferred to a concentrated phase.

The concentration of chemical component of interest in the leachate recycled at the end of the separation operation depends on the nature of the chemical component. For uranium, it is less than 25 milligrams per liter, generally less than 15 milligrams per liter, or even less than 5 milligrams per liter.

The recycled leachate, before the separation operation, typically has a concentration of chemical component of interest of 40% of the average concentration produced on the mining field. The process of the invention is economically viable only if the recycled leachate, before the separation operation, has a concentration of chemical component of interest typically greater than 10% of the average concentration produced on the mining field. below this value, the process is not economically viable because of the reagents consumed at the treatment plant and the investment cost.

The separation operation is carried out as described above with reference to FIG. 1. It is for example carried out using ion exchange resins, or a liquid / liquid extraction process by solvent.

The concentrated phase is stored in situ for a determined period. For example, a quantity of concentrated phase corresponding to one month of production is stored in situ.

This concentrated phase is then transferred to the processing plant 19, where at least one chemical component is separated from the concentrated phase.

The transfer method is as described above with reference to FIG. 1. When the separation operation is carried out using ion exchange resins, it is the treatment unit itself which is for example uncoupled from the recycling collector 1 1, then transported to the factory 19. As a variant, the resins are eluted and the eluate is transferred to a mobile tank. According to another variant, part of the resins is transferred to a mobile tank and transported in this mobile tank to the processing plant.

When the separation operation uses a solvent, the spent solvent containing the chemical component is transferred to a mobile tank, the tank then being transported to the treatment plant.

The recycled leachate is preferably the subject of a treatment operation before injection. Typically, this treatment is an acidification treatment for recycled leachate.

The acidification of the recycled leachate is carried out for example by adding an acid solution to 30 grams of acid per liter, typically to 30 grams of H2SO4 per liter.

The leachate collected, after acidification, has an acid concentration of between 2 and 10 grams of acid per liter, depending on the acid saturation of the mining reservoir. This concentration is for example between 2 and 10 grams of H ₂ SO4 per liter.

In the second method, the operation of each cell 5 is stopped when the rise in pH in said cell clogs the or each producing well 9 associated with the cell.

The configuration of the operating installation 1 during the second embodiment of the invention will now be described. The collection cut-off members 15 are all open. The production cut-off members 23 are all closed. The leachate from the different cells 5 is therefore directed via the collection pipes 13 to the recycling collector 11. It forms the recycled leachate.

The recycled leachate is directed from the recycling collector 11 to the separation module 63. To do this, the cut-off member 73 located between the points 66 and 68 is closed. On the other hand, the cut-off members 75, 69, 71 and 77 are open. Leachate recycled is thus directed from the recycling collector 1 1 via the upstream conduit 65 to the separation module 63, then from the separation module 63 via the downstream conduit 67 as far as the downstream part of the recycling collector 1 1.

The cut-off members 47 and 49 are closed. On the other hand, the cut-off members 46 and 61 are open. The recycled leachate, after passing through the treatment module 63, therefore flows via the bypass duct 41 to the branch 39. The treatment unit 53 injects an amount of acid at 30 g / l into the leachate recycled, via the conduit 57. The cut-off member 59 is open.

Then, the recycled and acidified leachate is injected into the cells 5 through the recycling conduits 35. The recycling cut-off members 37 are open.

The supply manifold 27 is inactive, the cut-off member 51 being closed. The supply cut-off members 33 are also closed.

This operating process also has multiple advantages.

This process allows the operation of an isolated cell block and not fluidly connected to the hydraulic networks under load. More precisely, the block 3 is isolated from the hydraulic networks under load connecting the block 3 to the treatment plant 19. It is also isolated from the hydraulic networks under load supplying the attack liquor.

Because block 3 at the end of production is isolated from the loaded hydraulic networks which convey the solutions produced to the treatment plant, the operators of these hydraulic networks may not saturate the loaded pipes with very dilute leachate and optimize overall production at the mine level.

Again, the process according to the invention makes it possible to maintain the average concentration of leachate sent to the treatment plant, and to avoid specific overconsumption of reagents in this plant.

The percentage of recovery of block reserves can be increased. The economic production cut-off threshold value of the block is lowered, which makes it possible to valorize resources not classified as reserves in the event of a significant lowering of the economic production cut-off threshold value of a block.

In the embodiment described above, the block is completely isolated from the hydraulic systems under load. Alternatively, some cells are supplied with attack liquor from the processing plant. These cells are production cells, the leachate rising from these cells being directed to the treatment plant and not recycled through a separation module.

Claims

1.- Method for operating a mine of at least one chemical component by in situ leaching, the mine comprising a plurality of production cells (5) each equipped with at least one configured injection well (7) for the injection of an attack liquor into said cell (5) and at least one production well (9) configured to take up a leachate containing the at least one chemical component rising from said cell (5), the method comprising, when a block (3) of cells (5) is at the end of its life, a current phase during which the following operations are implemented:

collecting the leachate produced by at least one cell (5) by recycling said block (3), said leachate forming the recycled leachate;

- injection of the recycled leachate into at least one cell (5) of said block (3).

2.- The method of claim 1, wherein the method comprises an operation of treating the leachate recycled before the injection operation, for example by acidification of the recycled leachate.

3.- Method according to claim 1 or 2, wherein said current phase comprises an operation of collecting the leachate produced by at least one cell (5) for producing said block (3) and transferring the leachate in a treatment plant ( 19), said leachate forming the leachate transferred, the at least one chemical component being separated from the leachate transferred to the treatment plant.

4.- Method according to claim 3, wherein during the injection operation, the recycled leachate is injected into the at least one production cell (5).

5.- Method according to claim 3 or 4, wherein during said current phase, the attack liquor is injected into the cells (5) in recycling concomitantly with the collection of recycled leachate.

6.- Method according to any one of claims 3 to 5, wherein during said current phase, the attack liquor is injected into the production cells (5) concomitantly with the collection of the transferred leachate.

7.- Method according to any one of claims 3 to 5, wherein at the end of said current phase, the operation of the at least one cell (5) in recycling is stopped, and a new phase starts:

- the at least one cell (5) into which is injected the leachate recycled in said current phase becoming the at least one cell (5) in recycling during the new phase;

- the leachate recycled during the new phase being injected into at least one new cell (5) of said block (3).

8.- Method according to claim 7, wherein the block (3) of cells (5) is traversed by an underground flow flowing in a determined direction, the operation of the cells (5) of the block (3) being stopped gradually according to said direction of the underground flow.

9.- Method according to claim 1 or 2, wherein said current phase comprises a separation operation during which a phase concentrated in the at least one chemical component is separated from the recycled leachate.

10.- Method according to claim 9, wherein the concentrated phase is stored in situ for a determined period and then transferred to a treatment plant (19), the at least one chemical component being separated from the concentrated phase in the factory. treatment (19).

1 1 .- Method according to claim 9 or 10, wherein all the cells (5) of the block (3) are being recycled and the recycled leachate is reinjected into all the cells (5) of the block (3).

12.- Installation for operating a mine of at least one chemical component by in situ leaching, the mine comprising at least one block (3) having a plurality of cells (5), the operating installation (1 ) including:

- For each cell (5) of said block (3) at least one injection well (7) configured for the injection of an attack liquor in said cell (5);

- for each cell (5) of said block (3) at least one production well (9) configured to take a leachate containing the at least one chemical component rising from said cell (5);

- a recycling collector (1 1);

- A plurality of collection conduits (13), each fluidly connecting one of the production wells (9) to the recycling collector (1 1), each collection conduit (13) being equipped with a collection cut-off member (15) capable of selectively authorizing or prohibiting the circulation of leachate collected in the corresponding collection conduit (13);

- An assembly (25) for supplying the injection wells (7), configured to selectively put the recycling manifold (11) in fluid communication with one or more of the injection wells (7).

13.- Installation according to claim 12, wherein the operating installation (1) comprises a unit (53) for treating the leachate recycled before injection into the or each injection well (7), for example by acidification of the recycled leachate.

14.- Installation according to claim 12 or 13, wherein the operating installation (1) comprises:

- a production collector (17) intended to be connected to a treatment plant (19), the at least one chemical component being separated from the leachate in the treatment plant (19); - a plurality of production conduits (21), each one fluidly connecting one of the production wells (9) to the production collector (27), each production conduit (21) being equipped with a production cut-off member ( 21) capable of selectively authorizing or prohibiting the circulation of leachate in the corresponding production conduit (21).

15.- Installation according to any one of claims 12 to 14, wherein the operating installation (1) comprises a separation module (63) arranged upstream of the assembly (25) supplying wells injection (7) and configured to separate a concentrated phase into the at least one chemical component of the recycled leachate.

16.- Installation according to claim 15, wherein the operating installation (1) comprises an in situ storage (63) of the concentrated phase, and a transfer module (63) of the concentrated phase from the separation module at a treatment plant (19), the at least one chemical component being separated from the phase concentrated in the treatment plant (19).

17.- Installation according to any one of claims 12 to 16, in which the supply assembly (25) comprises:

- A plurality of recycling conduits (35), each fluidly connecting the recycling collector (1 1) to one of the supply wells (7), each recycling conduit (35) being equipped with a cut-off member recycling (37) capable of selectively authorizing or prohibiting circulation in the corresponding recycling conduit (35).

18.- Installation according to any one of claims 12 to 17, in which the supply assembly (25) comprises:

- a supply manifold (27), intended to be connected to a supply unit of attack liquor (29);

- a plurality of supply conduits (31), each fluidly connecting the supply manifold (27) to one of the supply wells (7), each supply conduit (31) being equipped with a member power cut (33) selectively capable of authorizing or prohibiting circulation in the corresponding supply conduit (31).