US20220003100A1

US20220003100A1 - Method and facility for operating an in-situ leach mine

Info

Publication number: US20220003100A1
Application number: US17/294,024
Authority: US
Inventors: Adrien DEBERGÉ; Violet Jerome
Original assignee: Orano Mining SA
Current assignee: Orano Mining SA
Priority date: 2018-11-14
Filing date: 2019-11-13
Publication date: 2022-01-06
Also published as: AU2019382091A1; WO2020099514A1; FR3088364B1; FR3088364A1

Abstract

An operating method for an in situ leach mine comprises a routine phase implemented at the end of life of a block (3) of cells (5) of the mine, including collecting the leachate produced by at least one cell being recycled (5) in the block (3), the leachate forming the recycled leachate; and injecting the recycled leachate into at least one cell (5) of said block (3).

Description

The present disclosure relates in general to the operation of a mine by in-situ leaching, particularly the operation of a uranium mine.

BACKGROUND

In-situ leaching of a chemical component, also called “In-situ Leaching” or the ISL method, is a mining method that consists of:

- establishing a circulation of a leaching solution in the base of the deposit capable of selectively dissolving the chemical component to be mined;
- pumping the leached solution loaded with the desired mineral element to surface treatment facilities, where the valuable mineral element is separated and concentrated into a marketable product;
- recycling the leaching solution to the deposit, after reconditioning.

The ISL method is particularly applied to low-grade uranium, copper or gold deposits. It has the advantage that the selective dissolution of the mineral element from its gangue is done without physically moving the mineral and without significantly modifying the host rock (generally a 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 for a progressive and fairly selective dissolution. In a variant, the leach liquor is an acid solution, usually sulfuric, for a more aggressive and faster but less selective dissolution.
The leaching solution, also called the leach liquor, is injected under pressure into the permeable horizon containing the chemical component, through a network of injector wells that descend 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, called producer wells, inserted in above network, pumps the mineralized leaching solution and sends it to the plant installed on the surface. A conventional treatment allows for extraction of the chemical component in the liquid phase.
After treatment, the leaching power of the solution is regenerated so that it can be re-injected as a leach liquor into the injector well network a large number of times, for example between ten and more than fifty times.
The mine is typically divided into blocks, with each block having a plurality of production cells served by a single mining facility.
At the end of their life, the cells are mined until the concentration of the chemical component in the extracted leachate reaches a minimum cut-off value or the tonnage produced on a block or multi-cell basis is no longer sufficient to complete the desired annual production under economically viable conditions (production constraint and hydraulic capacity constraint of the existing systems).
Such an approach has the shortcoming that significant reserves of the chemical component can be left in the ground and are not extracted.

SUMMARY

In this context, an operating method and an operating facility that do not have the above defect are provided.
A method is provided for operating an in-situ leach mine of at least one chemical component, the mine comprising a plurality of production cells, each equipped with at least one injection well configured for injection of a leach liquor into said cell and at least one production well configured for collecting a leachate containing the at least one chemical component moving upwards from said cell, the method comprising, when a block of cells is at the end of its life, a routine phase during which the following operations are carried out:

- collecting the leachate produced by at least one cell being recycled in said block, the leachate forming the recycled leachate;
- injecting the recycled leachate into at least one cell of said block.

Thus, the leachate produced by the cells being recycled is not directed to the treatment plant for separation of the chemical component. Instead, it is recycled directly into one or more cells of the block.
This first has the effect of partially or totally reducing the flow of leachate from the block to the treatment plant. The solutions sent to the treatment plant are more charged than in the state of the art, which enables optimization of the use of the transfer networks to the treatment plant. In addition, this treatment plant treats more concentrated leachates, so that the specific consumption of chemical reagents is lower.
As a result, it becomes cost-effective to continue operating the cells even if the chemical component concentration in the leachate decreases below the usual cut-off threshold or annual production targets. Thus, more of the chemical component can be recovered from the cells, which increases the profitability of the operation.
The method of the present disclosure is scalable for the area mined it is incorporated early in the design of the mining facility. It has a significant effect on the capacity of the infrastructure to be built.
Typically, 50% of the production blocks in an ISL mine are at the end of their life, producing leachate having a content of the said chemical component of about 60% of the average content of the other production blocks. The end-of-life blocks provide about 30 to 40% of the total throughput. The method of the present disclosure is applied to half of the end-of-life blocks, for example, and results in a reduction in managed throughput of about 20%. This results in a significant reduction in the capacity required for the transport and treatment facilities.
The method further comprises one or more of the following features, considered alone or according to all technically possible combinations:

- the method comprises a treatment operation of the recycled leachate before the injection operation, for example by acidification of the recycled leachate;
- said routine phase comprises an operation of collecting the leachate produced by at least one production cell of said block and of transferring the leachate to a treatment plant, said leachate forming the transferred leachate, the at least one chemical component being separated from the leachate transferred to the treatment plant;
- during the injection operation, the recycled leachate is injected into the at least one production cell;
- during said routine phase, the leach liquor is injected into the cell being recycled concomitantly with the collection of the recycled leachate;
- during said routine phase, the leach liquor is injected into the production cells concomitantly with the collection of the transferred leachate;
- at the end of said routine phase, the operation of the at least one cell being recycled is stopped, and a new phase starts:
- the at least one cell into which the recycled leachate is injected in the said routine phase becomes the at least one cell being recycled 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 operation of the cells of the block being progressively stopped according to said direction of underground flow;
- said routine 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 of time 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 of the block are recycled and the recycled leachate is reinjected into all the cells of the block.

A facility is also provided for operating an in-situ leach mine of at least one chemical component, the mine comprising at least one block having a plurality of cells, the operating facility comprising:

- for each cell of said block, at least one injection well configured for the injection of leach liquor into said cell;
- for each cell of said block, at least one production well configured to collect a leachate containing the at least one chemical component moving upwards from said cell; and
- a recycle manifold;
- a plurality of collection pipes, each fluidly connecting one of the production wells to the recycle manifold, each collection pipe being equipped with a collection cut-off device capable of selectively authorizing or prohibiting the circulation of collected leachate in the corresponding collection pipe;
- an injection well supply assembly configured to selectively place the recycle manifold in fluid communication with one or more of the injection wells.

The facility may further comprise one or more of the following features, considered alone or according to all technically possible combinations:

- the operating facility comprises a unit for treating the recycled leachate before injection into the or each injection well, for example by acidifying the recycled leachate;
- the operating facility comprises:
- a production manifold adapted 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 pipes, each fluidly connecting one of the production wells to the production manifold, each production pipe being equipped with a production cut-off device capable of selectively authorizing or prohibiting the circulation of leachate in the corresponding production pipe;
- the operating facility comprises a separation module arranged upstream of the injection well supply assembly and configured to separate a phase concentrated in the at least one chemical component of the recycled leachate;
- the operating facility comprises in-situ storage of the concentrated phase, and a module for transferring the concentrated phase from the separation module to a treatment plant, with the at least one chemical component being separated from the concentrated phase in the treatment plant;
- the supply assembly comprises:
- a plurality of recycle pipes, each fluidly connecting the recycle manifold to one of the supply wells, each recycle pipe being equipped with a recycle cut-off device capable of selectively allowing or preventing flow through the corresponding recycle pipe;
- the supply assembly comprises:
  - a supply manifold, intended to be connected to a leach liquor supply unit;
  - a plurality of supply pipes, each fluidly connecting the supply manifold to one of the supply wells, each supply pipe being equipped with a supply cut-off device capable of selectively authorizing or prohibiting the circulation in the corresponding supply pipe.

BRIEF SUMMARY OF THE DRAWINGS

Other features and advantages of the present disclosure will be apparent from the detailed description given below, by way of indication and not in any way limiting, with reference to the appended figures, among which:

FIG. 1 is a simplified schematic representation the operation of an in-situ leach mining facility according to the present disclosure;

FIG. 2 is a view similar to that of FIG. 1, when this mining facility is operated according to a first embodiment of the operating method of the present disclosure; and

FIG. 3 is a view similar to that of FIG. 1, when the operating facility is operated according to a second embodiment of the method of the present disclosure.

DETAILED DESCRIPTION

The facility 1 shown in FIG. 1 is intended for the operation of a mine by in-situ leaching, particularly the operation of a uranium mine.
As illustrated in FIG. 1, the mine comprises at least one block 3 having a plurality of cells 5.
The operating facility 1 comprises:

- for each cell 5 of the block 3, at least one injection well 7, configured to inject a leach 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 moving upwards from said cell 5.

Typically, the injection wells 7 are arranged in a determined, generally regular mesh, each mesh defining one of the cells.
For example, the injection wells 7 are arranged in a square mesh, with the production well serving the corresponding cell placed in the center of the square. The injection wells 7 are generally spaced from fifteen to fifty meters apart, the distance between an injection well and a production well being between eleven and thirty-three meters.
The term block is used here to refer to 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 manifolds.
In FIG. 1, only three cells have been shown. However, the block typically has a higher number of cells. The block 3 typically comprises about 15 cells, with a minimum of 6 and a maximum of 24.
The operating facility 1 comprises a recycle manifold 11 and a plurality of collection pipes 13 each fluidly connecting one of the production wells 9 to the recycle manifold 11.
Each collection pipe 13 is equipped with a collection cut-off device 15, capable of selectively authorizing or prohibiting the circulation of leachate collected in the corresponding collection pipe 13.
In the present description, all the cut-off devices are preferably valves. In a variant, the cut-off devices are of any other suitable type.
In the present description, a cut-off device is said to be open when it authorizes the circulation of fluid in the corresponding pipe. A cut-off device is said to be closed when it prohibits the circulation of fluid in the corresponding pipe.
Thus, the facility comprises as many collection ducts 13 as production wells 9.
The facility 1 also comprises a production manifold 17, adapted to be connected to a treatment plant 19. As mentioned above, in the treatment plant, the chemical component of interest is separated from the leachate, so as to produce a marketable product.
The facility 1 further comprises a plurality of production pipes 21, each fluidly connecting one of the production wells 9 to the production manifold 17.
Each production pipe 21 is equipped with a production cut-off device 23 capable of selectively authorizing or prohibiting the circulation of leachate in the corresponding production pipe 21.
The facility 1 comprises as many production pipes as producing wells.
The facility 1 further comprises an assembly 25 to supply the injection wells 7, configured to selectively place the recycle manifold 11 in fluid communication with one or more of the injection wells 7.
In other words, the supply assembly 25 allows the collected leachate to be recycled by injection into one or more of the injection wells 7, without first sending the collected leachate to the treatment plant 19.
The supply assembly 25 comprises:

- a supply manifold 27, adapted to be connected to a leach liquor supply unit 29;
- a plurality of supply pipes 31, each fluidly connecting the supply manifold 27 to one of the supply wells 7.

The leach liquor supply unit is typically the leachate treatment plant 19.
Indeed, after separation of the chemical component, the leachate has a composition suitable for recycling and forming, possibly after correction of its composition, the leach liquor.
Each supply pipe 31 is equipped with a supply cut-off device 33, capable of selectively authorizing or prohibiting the circulation of fluid in the corresponding supply pipe.
Thus, there are as many supply pipes 31 as there are injection wells 7.
The supply assembly 25 further comprises a plurality of recycling pipes 35, each fluidly connecting the recycling manifold 11 to one of the injection wells 7.
Each recycling pipe 35 is equipped with a recycling cut-off device 37, capable of selectively authorizing or prohibiting the circulation in the corresponding recycling pipe 35.
There are as many recycling pipes as injection wells.
In the example shown, the recycling pipes 35 connect the recycling manifold 11 indirectly to the injection wells 7.
Thus, the recycling pipes 35 branch off from a branch 39 connected to the supply manifold 27.
The recycle manifold 11 is directly connected to the supply manifold 27, upstream of the branch 39.
The term upstream is understood here to refer to the normal flow direction of the leach liquor.
A bypass pipe 41 directly connects a point 43 of the recycle manifold 11 to a point 45 of the branch 39. The bypass pipe 41 is equipped with a cut-off device 46.
A cut-off device 47 is interposed along the recycle manifold 11 between the point 43 and the supply manifold 27.
A cut-off device 49 is interposed on the branch 39 between the supply manifold 27 and the point 45. The supply manifold 27 is also equipped with a cut-off device 51, located for example between the inlet of the recycle manifold 11 and the outlet of the branch 39.
The operating facility 1 further comprises a unit 53 for treating the recycled leachate before injection into the or each injection well 7.
The treatment unit 53 is arranged to inject a treatment product into the recycled leachate, before it is injected into the or each injection well 7.
Typically, the treatment unit 53 is arranged to acidify or basify the recycled leachate.
It is configured to increase the acidity or basicity of the recycled leachate. For example, when the ISL method implements an acid leach liquor, the acidity can be adjusted up to a value of 30 grams of acid per liter of recycled leachate, typically 30 grams of H₂SO₄per liter of recycled leachate.
The treatment unit 53 is fluidly connected to a point 55 on the branch 39 by a pipe 57 equipped with a cut-off device 59. The point 55 is located downstream of the point 45, with a cut-off device 61 interposed between the points 45 and 55. The recycling ducts 35 branch off from points located downstream of the point 55.
Preferably, the operating facility comprises a separation module 63, arranged upstream of the assembly 25 for supplying injection wells 7 and configured to separate a phase concentrated in the at least one chemical component from the recycled leachate.
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 into the concentrated phase.
The separation module 63 comprises, for example, ion exchange resins, of the type adapted to bind the chemical component when the ion exchange resins are traversed by the recycled leachate. The ion exchange resins then constitute the concentrated phase.
In a variant, the separation module 63 is configured to perform an extraction or liquid/liquid separation operation (by resins, membranes, fluid bed, etc.), using a solvent of a type adapted to recover the chemical component. The collected leachate is brought into contact with the solvent in the separation module 63, the chemical component being transferred in the solvent. The solvent constitutes the concentrated phase.
In a variant, the separation module 63 is of any other suitable type.
In this case, the operating facility 1 preferably comprises an in-situ storage of the concentrated phase, and a module for transferring the concentrated phase from the separation module to an operating plant.
This operating plant is typically the operating plant 19.
The in-situ storage is sized to store a quantity of concentrated phase corresponding to a given production time, for example one month.
The storage is a function of the type of separation method used. For example, the storage is a tank storage. In the case of resins, the storage is 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, for example, is removably connected to the recycle manifold 11. It constitutes the in-situ storage. In effect, the separated 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 recycle manifold 11, and transported, together with the ion exchange resins, to the treatment plant.
In a variant, the resins are eluted on site and only the eluate is transported by a mobile tank to the treatment plant.
In another embodiment, a part of the resins is discharged from the separation module 63 and transported by a mobile tank to the operating plant.
Thus, in some cases, the transfer module is a mobile tank, into which the ion exchange resins, the eluate, or the chemical component-laden solvent is transferred.
In the example shown, the separation module 63 is connected by an upstream pipe 65 to a point 66 on the recycle manifold 11, and by a downstream pipe 67 to a point 68 on the recycle manifold 11. The upstream and downstream pipes are equipped with respective cut-off devices 69 and 71. A cut-off device 73 is interposed between the points 66 and 68. A cut-off device 75 is placed upstream of point 66 and a cut-off device 75 between points 68 and 43.
The in-situ leach mining method according to the present disclosure will now be described, with reference to FIGS. 2 and 3. In these figures, the lines in use are shown in solid lines, and the inactive lines in dashed lines. The open cut-off devices are shown as hollowed out, and closed cut-off devices are shown as filled in.
A method using an acid leach liquor will be described below.
The operating facility 1 is designed for the implementation of this operating method.
Conversely, the operating method is particularly suitable for implementation with the operating facility 1. However, it could be implemented with a different operating facility.
The method is especially designed to allow for optimized operation when the cell block 3 is at the end of its life.
The method comprises a routine operation phase, during which the following operations are implemented:

- collecting the leachate produced by at least one cell being recycled 5 of the block 3, said leachate forming the recycled leachate;
- injecting the recycled leachate into at least one cell 5 of said block 3.

Thus, in the following description, the leachate coming from the at least one cell being recycled 5 is referred to as recycled leachate.
According to a first embodiment of the method shown in FIG. 2, the current operating phase also comprises an operation of collecting the leachate produced by at least one production cell 5 of the block 3, and of transferring said leachate to a treatment plant. This leachate is referred to here as transferred leachate.
During the injection operation, the recycled leachate is injected into the at least one production cell 5.
The production cell(s) is/are different from the cell(s) being recycled.
Typically, during the routine phase, 5 cells are cells being recycled, and 10 cells are production cells. This is the case especially at the beginning 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 being recycled. The third cell 5, located above, is the production cell.
During the routine phase, the leach liquor is injected into the or each recycle cell 5, concomitantly with collecting the recycled leachate.
Similarly, during the routine phase, the leach liquor is injected into the or each production cell concomitantly with the collection of the transferred leachate.
The leach liquor is for example a solution containing 2 grams of acid per liter.
Injecting the leach liquor into the cells being recycled 5 enables the natural process of pH increase in these cells to slow down, and thus the residual operating time of these cells increases.
The transferred leachate is sent to the treatment plant 19. It is collected separately, the recycled leachate never being mixed with the transferred leachate.
Preferably, the method comprises a treatment operation of the recycled leachate, performed before the injection operation. This operation is typically an acidification operation of the recycled leachate, coming from the or each cell being recycled. The recycled leachate is acidified typically to a value of 30 grams of acid per liter.
The configuration of the operating facility 1 during the routine phase is shown in FIG. 2.
The collection cut-off devices 15 of the collection pipes 13 associated with the or each cell being recycled are open. In contrast, the production cut-off devices 23 of the production pipes 21 associated with the or each recycling cell are closed.
For the or each production cell 5, the associated production cut-off device 23 is open, and the collection cut-off device 15 is closed.
The cut-off device 51 located on the supply manifold 27 is open. Similarly, the supply cut-off devices 33 associated with the or each cell being recycled 5 and the or each production cell 5 are open.
The recycling cut-off device 37 of each recycling pipe 35 associated with the or each production cell 5 is open. The recycling cut-off devices 37 of the recycling lines 35 associated with the other cells 5 are closed.
The cut-off devices 75, 73, 77 interposed along the recycle manifold 11 are open. The treatment unit 53 is operational, and supplies the branch 39 via the pipe 57. The cut-off devices 46 and 61 are open. The cut-off devices 47 and 49 are closed.
Thus, the transferred leachate produced by the or each production cell 5, is directed to the production manifold 17 via the or each corresponding production pipe 21. It is then directed to the treatment plant 19. The recycled leachate, from the or each recycling cell 5, is collected by the recycle manifold 11, via the collection pipes 13. The recycled leachate is acidified by the treatment module 53 which is configured to make an acid top-up.
The recycled acidified leachate is injected into the or each production cell 5 via the or each corresponding recycling pipe 35.
It mixes with the leach liquor from the supply manifold 27 via the corresponding supply pipe 31.
Concurrently, the cells being recycled 5 are fed with the leach liquor via the corresponding supply pipes 31.
The recycled leachate contains the chemical component extracted from the or each cell being recycled. It is re-injected into the or each production cell 5, so that the leachate coming from the or each production cell 5 has a significantly higher concentration of chemical component than the leachate coming from the or each cell being recycled 5.
At the end of the routine phase, the operation of the or each cell being recycled is stopped.
This operation is typically stopped when the pH increases in the cells clog the corresponding production wells 9 or when the economic cut-off points of the method have been reached.
A new phase then starts in which:

- the at least one cell 5 into which the leachate recycled was injected in the routine phase becomes the at least one cell being recycled 5 during the new phase;
- the leachate recycled during the new phase is injected into at least one new cell 5 of the block 3.

The new phase implements the same operations as those described for the routine phase. Only the circulation of the leachate and the leach liquor is modified.
This change in the circulation of the leachate and of the leach liquor is easily carried out, since it is sufficient to modify the position of the cut-off devices to switch from the routine phase to the new phase.
An underground flow traverses the cell 5 block 3 in a certain direction. This underground flow corresponds to the non-potable groundwater or an underground river running through the mine. Neither of these waters has any other application than mining. The direction of the groundwater flow within the block 3 is known. It is typically determined by hydrogeological studies, prior to the start of mining operations. The flow direction of the flow is represented by an arrow F on FIG. 2.
According to the operating method of the present disclosure, the operation of the cells 5 of the block 3 is stopped progressively, according to said flow direction.
This means that the first cells 5 to be stopped will be the cells located upstream of the flow. The last cells 5 to be stopped will be the cells located downstream of the flow.
Thus, for a given operating phase, the cell or cells 5 being recycled will be located relatively upstream, and the cell or cells 5 in production will be located relatively downstream.
At the time of the transition 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 dashed lines in FIG. 2.
The operating method thus comprises several successive operating phases. At the end of each operating phase, one or more cells are shut down, typically those located furthest upstream in the flow direction. The operating method ends when all the cells in the block have been shut down.
The method described above has multiple advantages.
It enables a reduction in the volume of leachate produced by the block 3 at the end of the production, that is, at the end of mining the block. The volume of leachate sent to the treatment plant via the supporting hydraulic networks, usually conveying the solutions produced, is thus reduced.
This enables networks operators to not saturate the supporting hydraulic networks, while optimizing the global production at the mine level. It also enables the average chemical concentration of the solutions sent to the treatment plant not to decrease. As a result, specific overconsumption of reagents at the treatment plant is avoided.
The method also enables the recovery percentage of the reserves of the block 3 to increase, and thus the economic production cut-off point of the block 3 to be lowered.
This potentially enables the recovery of resources not classified as reserves, in the case where it is possible to significantly lower the value of the economic production cut-off of a block 3.
The method described also enables preparation for the remediation of hydraulic mining reservoirs used during a mining operation by in-situ leaching. The rise in pH is monitored until it is impossible to operate the cells hydraulically, due to the precipitation of certain compounds that clog the pores of the cell and the strainers of the producing wells.
A second embodiment of the operating method of the present disclosure 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 elements performing the same function will be designated by the same references.
The second embodiment has only one operating phase.
Thus, all the cells 5 of the block are cells being recycled. This means that the leachate produced by each cell 5 of the block 3 is directed to the recycle manifold 11. The production manifold 17 does not receive any leachate from the cells of the block. Thus, all leachate is recycled.
The recycled leachate is re-injected into all the cells 5 of the block. In other words, each cell 5 of the block receives a portion of the recycled leachate.
The cells 5 in the block 3 are fed only with the recycled leachate, and do not receive any leach liquor.
The single operation phase comprises 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, the at least one chemical component is separated from the recycled leachate and transferred to a concentrated phase.
The concentration of the chemical component of interest of the recycled leachate 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 the chemical component of interest of 40% of the average concentration produced in the mining area. The method of the present disclosure is only economically viable if the recycled leachate, before the separation operation, has a concentration of chemical component of interest typically higher than 10% of the average concentration produced in the mining area. Below this value, the method 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 solvent extraction method.
The concentrated phase is stored in-situ for a specified time. 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 treatment plant 19, where the 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 that is, for example, uncoupled from the recycle manifold 11 and then transported to the plant 19. In a variant, the resins are eluted and the eluate is transferred to a mobile tank. In another variant, a portion of the resins is transferred to a mobile tank and transported in the mobile tank to the treatment plant.
When the separation operation involves a solvent, the spent solvent containing the chemical component is transferred into a mobile tank, the tank then being transported to the treatment plant.
The recycled leachate is preferably subjected to a treatment operation before injection. Typically, this treatment is an acidification treatment of the recycled leachate.
The acidification of the recycled leachate is carried out, for example, by adding an acid solution with 30 grams of acid per liter, typically 30 grams of H₂SO₄per liter.
The collected leachate, after acidification, has an acid concentration 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 H₂SO₄per 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 facility 1 during the second embodiment of the present disclosure will now be described. The production cut-off devices 15 are all open. The production cut-off devices 23 are all closed. The leachate from the individual cells 5 is thus directed via the collection pipes 13 to the recycle manifold 11. It forms the recycled leachate.
The recycled leachate is directed from the recycle manifold 11 to the separation module 63. To do this, the cut-off device 73 located between points 66 and 68 is closed. In contrast, the cut-off devices 75, 69, 71 and 77 are open. The recycled leachate is thus directed from the recycle manifold 11 via the upstream pipe 65 to the separation module 63, then from the separation module 63 via the downstream pipe 67 to the downstream part of the recycle manifold 11.
The cut-off devices 47 and 49 are closed. In contrast, the cut-off devices 46 and 61 are open. The recycled leachate, after passing through the treatment module 63, therefore flows via the bypass pipe 41 to the branch 39. The treatment unit 53 injects a quantity of acid at 30 g/l into the recycled leachate, via the pipe 57. The cut-off device 59 is opened.
Then, the recycled and acidified leachate is injected into the cells 5 through the recycling pipes 35. The recycling cut-off devices 37 are open.
The supply manifold 27 is inactive, the cut-off device 51 being closed. The supply cut-off devices 33 are also closed.
This operating method also has multiple advantages.
This method allows the operation of an isolated cell block that is not fluidly connected to the hydraulic networks under load. More specifically, block 3 is separated from the hydraulic networks in charge connecting block 3 to the treatment plant 19. It is also separated from the hydraulic networks in charge supplying the leach liquor.
Because the end-of-production block 3 is separated from the on-load hydraulic systems that convey the produced solutions to the operating plant, the operators of these hydraulic systems can avoid saturating the on-load lines with highly diluted leachate and optimize the overall production at the mine.
Again, the method according to the present disclosure maintains the average concentration of leachate sent to the treatment plant, and avoids specific overconsumption of reagents in this plant.
The percentage recovery of the block reserves can be increased. The economic production cut-off value of the block is lowered, which makes it possible to recover resources not classified as reserves in case of a significant lowering of the economic production cut-off value of a block.
In the exemplary embodiment described above, the block is totally separated from the supporting hydraulic networks. In a variant, some cells are supplied with leach liquor derived from the treatment plant. These cells are production cells, the leachate moving upwards from these cells being directed to the treatment plant and not recycled through a separation module.

Claims

What is claimed is:

1-18. (canceled)

19. A method of exploiting a mine comprising at least one chemical component by in-situ leaching, the mine comprising a plurality of cells each equipped with at least one injection well configured for injection of a leach liquor into said cell and at least one production well configured for collecting a leachate containing the at least one chemical component moving upwards from said cell, the method comprising:

when a block of the cells is at the end of its life, a routine phase comprising:

collecting the leachate produced by at least one of the cells being recycled in said block, said leachate forming the recycled leachate; and

injecting the recycled leachate into at least one of the cells of said block.

20. The method according to claim 19, further comprising treating the recycled leachate before the injecting of the recycled leachate into the at least one cell of said block.

21. The method according to claim 20, wherein the treating of the recycled leachate before the injecting of the recycled leachate into the at least one cell of said block includes acidifying the recycled leachate.

22. The method according to claim 19, wherein said routine phase comprises collecting the leachate produced by at least one production cell of the cells of said block and transferring the leachate to a treatment plant, said leachate forming the transferred leachate, the at least one chemical component being separated from the leachate transferred in the treatment plant.

23. The method according to claim 22, wherein during the injecting of the recycled leachate into at least one cell of said block, the recycled leachate is injected into the at least one production cell.

24. The method according to claim 22, wherein during said routine phase, the leach liquor is injected into the cells being recycled concomitantly with the collection of the recycled leachate.

25. The method according to claim 22, wherein during said routine phase, the leach liquor is injected into the at least one production cell concomitantly with the collection of the transferred leachate.

26. The method according to claim 22, wherein at the end of said routine phase, the operation of the at least one cell being recycled is stopped, and a new phase starts in which:

the at least one cell into which the leachate recycled is injected in said routine phase becomes the at least one cell being recycled during the new phase, and

the leachate recycled during the new phase is injected into at least one new cell of said block.

27. The method according to claim 26, wherein the block of cells is traversed by an underground flow flowing in a determined direction, the operation of the cells of the block being stopped progressively according to the said determined direction of the underground flow.

28. The method according to claim 19, wherein said routine phase comprises a separation operation during which a phase concentrated in the at least one chemical component is separated from the recycled leachate.

29. The method according to claim 28, wherein the concentrated phase is stored in-situ for a period of time and then transferred to a treatment plant, with the at least one chemical component being separated from the concentrated phase in the treatment plant.

30. The method according to claim 28, wherein all of the cells of the block are being recycled and the recycled leachate is reinjected into all of the cells of the block.

31. An operating facility for operating a mine by in-situ leaching for at least one chemical component, the mine comprising at least one block having a plurality of cells, the operating facility comprising:

at least one injection well for each cell of said block configured for injection of a leach liquor into said cell;

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

a recycle manifold;

a plurality of collection pipes each fluidly connecting one of the production wells to the recycle manifold, each collection pipe being equipped with a collection cut-off device configured for selectively authorizing or prohibiting the circulation of leachate collected in the corresponding collection pipe; and

a supply assembly for supplying the injection wells, configured to selectively place the recycle manifold in fluid communication with one or more of the injection wells.

32. The operating facility according to claim 31, further comprising a unit for treating the recycled leachate before injection into the or each injection well.

33. The operating facility according to claim 32, wherein the unit for treating the recycled leachate before injection into the or each injection well is configured for acidifying the recycled leachate.

34. The operating facility according to claim 31, further comprising:

a production manifold configured to be connected to a treatment plant, the at least one chemical component being separated from the leachate in the treatment plant; and

a plurality of production pipes, each fluidly connecting one of the production wells to the production manifold, each production pipe being equipped with a production cut-off device configured for selectively authorizing or prohibiting the flow of leachate in the corresponding production pipe.

35. The operating facility according to claim 31, further comprising a separation module arranged upstream of the supply assembly of the injection wells and configured to separate a phase concentrated in the at least one chemical component from the recycled leachate.

36. The operating facility according to claim 35, further comprising in-situ storage of the concentrated phase, and a module for transferring the concentrated phase from the separation module to a treatment plant, with the at least one chemical component being separated from the concentrated phase in the treatment plant.

37. The operating facility according to claim 31, further comprising a plurality of recycling pipes, each fluidly connecting the recycle manifold to one of the supply wells, each recycle pipe being equipped with a recycle cut-off device configured for selectively authorizing or prohibiting the circulation in the corresponding recycle pipe.

38. The operating facility according to claim 31, further comprising:

a supply manifold, configured to be connected to a leach liquor supply unit;

a plurality of supply pipes, each fluidly connecting the supply manifold to one of the supply wells, each supply pipe being equipped with a supply cut-off device configured for selectively authorizing or prohibiting the circulation in the corresponding supply pipe.