WO2008061309A1

WO2008061309A1 - Modifying a lixiviant

Info

Publication number: WO2008061309A1
Application number: PCT/AU2007/001795
Authority: WO
Inventors: Marcus Worsley Richardson
Original assignee: Heathgate Resources Pty Ltd
Current assignee: Heathgate Resources Pty Ltd
Priority date: 2006-11-24
Filing date: 2007-11-22
Publication date: 2008-05-29
Anticipated expiration: 2009-05-24

Abstract

A method and apparatus for reducing the concentration of chloride ions in a lixiviant. The method includes the steps of treating a lixiviant stream in an electrolytic cell assembly (10) thereby forming dissolved chlorine from the chloride ions in the treated lixiviant, sparging (22) the treated lixiviant to remove at least some of the dissolved chlorine to reduce the concentration of the dissolved chlorine in the lixiviant. By this arrangement the concentration of the chloride ions in the treated lixiviant is reduced. The lixiviant may be used in an in situ uranium leaching process (24).

Description

MODIFYING A LIXIVIANT

DESCRIPTION

FIELD OF THE INVENTION

This invention relates to a method and apparatus for modifying a lixiviant in order, for instance, to improve the efficiency of the recovery of metal during an leaching process, in particular, the recovery of uranium during an in-situ leach process although the invention is not restricted to this application.

BACKGROUND OF THE INVENTION

Mining underground deposits of uranium ore by the acid in-situ leach (ISL) method (also referred to as solution mining) involves circulating leach fluid through the ore using a pattern of wells in the well-field. The leach fluid, or lixiviant, is acidified for instance with sulphuric acid and an oxidising agent is added to facilitate oxidation of the ore. The action of the oxidising agent is to assist in the conversion of the lower oxidation states of uranium in the ore to the hexavalent uranyl ion, which together with the complexing action of the sulphuric acid dissolves the ore to produce a pregnant lixiviant. The uranium in this pregnant lixiviant is then extracted using an ion exchange or solvent extraction process, and in either case, the captured uranium is further chemically processed to produce a solid uranium oxide product ("yellowcake") which is the valuable product of the mining operation.

An ion exchange process for recovering uranium drawn from the well-field in the lixiviant can require that the pregnant lixiviant is passed through one or more ion exchange columns or beds before a sufficient amount of the uranium is extracted from the lixiviant. This can be time consuming and expensive, particularly since the ion exchange resin must be regenerated by eluting the uranium once it has reached a certain concentration of captured uranium (an equilibrium concentration, or more usually, less than this). Chloride in the lixiviant preferentially attaches to sites in the ion exchange resin and thereby reduces the extraction of uranium from the lixiviant.

An object of this invention is to provide a process to reduce chloride concentration from a solution such a lixiviant whereby the lixiviant can be more efficient.

In the case of in situ uranium extraction it is an object of the present invention to provide a method which increases the capacity of the ion exchange process to capture uranium and thereby reduces the number of elutions of the ion exchange column or columns during an in-situ leach process. The process also increases the capacity of the capture and subsequent uranium precipitation processes. This is important for capital and operating costs of the processes. Also, if there is too much chloride in the lixiviant, the more costly solvent exchange capture process must be used.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method for reducing the concentration of chloride ions in a lixiviant including the step of: treating a lixiviant stream in an electrolytic cell assembly thereby forming dissolved chlorine from the chloride ions in the treated lixiviant; sparging the treated lixiviant to remove at least some of the dissolved chlorine to reduce the concentration of the dissolved chlorine in the lixiviant; whereby the concentration of the chloride ions in the treated lixiviant is reduced.

The treated lixiviant can be used to recover a metal from a metal ore in an leaching process. Preferably, the metal recovered from a metal ore is uranium.

The treated lixiviant can be collected from the electrolytic cell and the step of sparging the treated lixiviant can be performed at a later point in time.

The concentration of chloride ions in the treated lixiviant is preferably reduced to a level which permits the extraction of uranyl ions in the treated lixiviant by an ion exchange process.

Preferably, the concentration of chlorine ions in the treated lixiviant is reduced to below approximately 5g of chlorine per litre (g/L). More preferably, the concentration of chlorine is reduced to about 2 g/L.

Optionally, the anode cell and cathode cell of the electrolyser may be separated from one another in the electrolyser assembly by a separating means which restricts mixing and transport to the other electrode of the chemical species formed at either the anode or the catihode

There can be a plurality of anode and cathode cells. For example, there may be up to 150 cells arranged alternately in a stack or stacks.

Preferably, the electrodes used in the electrolysers are bipolar.

Preferably, the bipolar electrodes consist of titanium, bare on the cathode side and coated with a mixed metal oxide on the anode side.

According to another aspect of the present invention, there is provided a method for reducing the concentration of chloride ions in a lixiviant including the step of: separating a feed lixiviant stream including chloride ions into at least two streams; causing a first stream to pass through an anode cell of an electrolytic cell assembly to form an anolyte and a second stream to pass though a cathode cell of an electrolytic cell assembly to form a catholyte; oxidising some of the chloride ions in the anolyte to chlorine in the anode cell; sparging the anolyte with air or another gas to reduce the concentration of chlorine; combining the anolyte including chlorine from the anode cell with the catholyte from the cathode cell to form a treated lixiviant wherein, the concentration of chloride ions in the treated lixiviant is reduced.

The electrolyser according to the present invention may be used to treat all of the flow of lixiviant or may be used to treat part of the flow as a side stream whereby the electrolysed lixiviant side stream will contain dissolved chlorine capable of oxidising ferrous in the main stream to the required extent as well as enabling removal of some chlorine by sparging.

Alternatively a side stream of the lixiviant of an in situ uranium extraction plant may be treated according to the present invention to remove substantially all of the chlorine in that stream and then the side stream returned to the main lixiviant stream.

As they oxidises the uranium ore, ferric ions in the lixiviant are reduced to ferrous ions and the uranium becomes a soluble uranium ion (uranyl sulphate sulfato complexes) which can be subsequently extracted by ion exchange as a valuable mining product. Uranyl sulphate is absorbed from the lixiviant onto an ion exchange resin, however, depending on the concentration of chloride ions in the lixiviant in relation to the concentration of uranyl sulphate, the chloride ions will be absorbed in preference to the uranyl ions into the ion exchange resin and reduce its useful capacity to capture the uranium . Accordingly, as the concentration of the chloride ions in the lixiviant increases and its capacity for uranium capture decreases, a larger quantity of ion exchange resin will be required and the resin will have to be eluted more often to recover the captured uranium. In a preferred embodiment of the present invention, chlorine is formed electrochemically from chloride ions in solution which react at an anode of an electrolyser to form free chlorine. This chlorine is used to regenerate ferrous to ferric ions. Excess chlorine can then be removed from the lixiviant by passing the lixiviant though the dechlorinator of the present invention during the in-situ leach process to produce a modified lixiviant stream having reduced chlorine levels. The dechlorinator removes a portion of the chlorine as chlorine gas (by sparging the lixiviant with air or other suitable gas). Once the concentration of chloride ions is reduced, it is relatively easier to remove the uranium from the lixiviant which represents a significant time and cost saving in the industry. The sparged chlorine can be collected or suitably disposed off.

In an alternative form the invention comprises a lixiviant containing chloride ions modification apparatus comprising; an electrolytic cell assembly in which a lixiviant is electrolytically reacted to produce chlorine; means to withdraw the reacted lixiviant from the electrolytic cell assembly; means to sparge air through the withdrawn lixiviant ; and means to vent the sparged air along with at least a portion of the chlorine.

Preferably the electrolytic cell assembly comprises a plurality of cathode cells and a plurality of anode cells, wherein the lixiviant is electrolytically reacted in the anode cells to produce the chlorine and the means to withdraw the reacted lixiviant from the electrolytic cell assembly comprises means to withdraw from the anode cells. Throughout this specification unless the context requires otherwise, the words 'comprise' and 'include' and variations such as 'comprising' and 'including' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

A specific embodiment of the invention will now be described in some further detail with reference to and as illustrated in the accompanying drawings. This embodiment is illustrative, and is not meant to be restrictive of the scope of the invention. Suggestions and descriptions of other embodiments may be included within the scope of the invention but they may not be illustrated in the accompanying figures or alternatively features of the invention may be shown in the figures but not described in the specification.

While the invention is generally discussed in relation to the leaching of uranium ore, it is not so limited and other metal ores which can be extracted using the present method and apparatus are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative embodiment of the present invention will be discussed with reference to the accompanying drawings and examples wherein:

Figure 1 is a schematic of the process according to a preferred embodiment of the present invention;

Figure 2 is a close-up view of the electrolytic cell of Figure 1; and Figure 3 is a schematic of the process for the in situ leaching of uranium ore incorporation the modification process according to a preferred embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

It is recognized that the chemical species responsible for oxidizing the uranium ore in the leach fluid (or lixiviant) is ferric iron (Fe³⁺). Ferric iron cations may be naturally present in the acidified leach fluid and/ or may be deliberately added to it (in the form of ferric iron or ferrous iron or both). The reaction is as follows:

Leaching of uranium ore:

2Fe³⁺ + 2e- = 2Fe²⁺ (1)

U^IVO₂ = U^VIO₂ ²⁺ + 2e- (2)

(U^IVO2 can here can more generally represent the uranium contained in leachable ores such as coffinite)

(UO₂)²⁺ + 2(SO₄)²- = [(UO₂)(SO₄):.]²- (3)

The sulfato complex ion [(UO2) (SO₄)S]⁴' is also formed during reaction (3).

Preferably, the uranyl sulfato anions, including [(UO₂) (SO₄^]²" and [(UO₂) (SO₄)3]⁴" , are absorbed onto cationic ion exchange resin in a uranium recovery plant and the uranium eluate from the ion exchange columns is treated (with hydrogen peroxide) to precipitate uranium peroxide (studtite and/ or metastudtite), which is the valuable product produced at the mine.

In some locations the leach fluid may also naturally contain high levels of chloride ions. For example, in Australia, the salinity of the in-situ leach liquor may be relatively high due to the naturally high occurrence of salt in the groundwater saturating the ore zones. Alternatively, chloride ions may have been added to the leach fluid, for example, some oxidizing agents such as sodium chlorate add chloride ions to the system. Where there are high levels of chloride ions, these ions may compete with the uranyl sulfato ions for active sites on the ion exchange resin.

If the concentration of uranyl ions is sufficiently in excess of the chloride ions in the lixiviant then the ion exchange process will not be substantially affected by the chloride ions. However, if the chloride ions are in excess of the uranyl ions then the capacity of the ion exchange resin may be decreased to the point that it may be necessary to use a substantial amount of it to capture the uranium from a pregnant lixiviant and elute it more often to recover the uranium in the subsequent processing stages. This can be both time consuming and expensive.

More concerning is that if the chloride ion concentration is too great, ion exchange is not a feasible option and instead solvent extraction must be undertaken to capture and concentrate the uranium. Solvent extraction involves the use of kerosene and a complexing agent. Ion exchange is preferable compared to solvent extraction for a number of reasons, including cost and hazards associated with handling large quantities of a flammable solvent. The present invention provides a method for reducing the concentration of chloride ion in the lixiviant and furthermore, provides a means of reducing those levels such that the capacity of the ion exchange resin to capture the uranium from the lixiviant and the number of elutions required to produce a concentrated uranium solution for the recovery of the solid uranium peroxide product is minimised.

Chloride ions are removed by firstly forming free chlorine (also referred to as dissolved or elemental chlorine) in the lixiviant. The chlorine is produced by an electrochlorination process i.e. a process where chlorine is generated electrolytically from chloride ions in solution at an anode in an electrolytic cell. As described above, the chloride ions may already be present in the lixiviant (this may be the case in areas having highly saline water). Alternatively, chloride ions may have been added to the lixiviant. The flow rate of the solution through the electrolytic cell assembly can be controlled in order to control the amount of chlorine generated at the anode. For example, a slower flow rate will allow more contact time with the anode and therefore create a higher concentration of free chlorine in the anolyte. The dissolved chlorine in solution will exist as free, elemental chlorine and hypochlorite ions in equilibrium with the water molecules and the acid added to the lixiviant.

Figure 1 is a schematic diagram of an electrolytic process 10 in a flowing cell type arrangement. A barren lixiviant stream 12, flows from uranium recovery plant 14 at a rate of approximately 300 litres per second (L/ s). The lixiviant is referred to as 'barren' because the uranium recovery plant 14 has extracted all (or a at least a substantial portion of) the valuable constituents from the lixiviant (i.e. uranium).

AU or part of the barren lixiviant is separated into at least two side streams to undergo electrolytic treatment. Side streams 16 and 18 are separated from the circulating barren lixiviant stream 12. Side stream 16 is a feed lixiviant directed through a manifold into cathode cells 21 (hereinafter the catholyte side stream) of an electrolytic cell assembly 19. Side stream 18 is a feed lixiviant directed through a manifold into anode cells 17 (hereinafter the anolyte side stream) of an electrolytic cell assembly 19. The anode and cathode cells are shown in more detail in Figure 2. The anolyte is the liquid which flows from the anode cell and is chemically changed by the electrolytic process(es) at the anode. The catholyte is the liquid which flows from the cathode cell and is chemically changed by the electrolytic process(es) at the cathode cell 21.

Preferably, more lixiviant is separated into side stream 18 than to side stream 16. The efficiency of the process is improved if any ferric ions which exist in the lixiviant entering the electrolyser are kept from the cathode (since they will be reduced to ferrous ions and decrease the efficiency of the electrolytic process). The flow rate of side stream 18 is approximately 20 L/s, the lixiviant flows into anolyte surge tank 26 and from there is passed into the anode cells 17 of the electrolyser or electrolytic cell 19. The flow rate of side stream 16 is a approximately 2 L/s, the lixiviant flows into catholyte surge tank 13 and from there is passed into the cathode cells 21 electrolyser or electrolytic cell 19.

In order to produce sufficient chlorine in the anolyte stream, the flow rate of the lixiviant through the anode cell is adjusted accordingly.

The anolyte rich in chlorine is then passed by pipe 23 to dechlorinator 22. Dechlorinator 22 removes the unwanted chlorine by bubbling air (or another gas) though the anolyte as it flows through a column (bubbling air though the anolyte is referred to as sparging). Air sparging is the process of injecting air directly into the lixiviant; the air is supplied at 27 and strips the chlorine, in gaseous form, from the anolyte through vent 25. Stripped chlorine and air are separated in separator 35 into chlorine 37 and air 39. The dechlorinated anolyte is then remixed with the catholyte stream at location 20 to provide a lixiviant having reduced levels of chloride ions.

In Figure 1, dechlorinator 22 is shown arranged in series in the anolyte stream 23. However, the dechlorinator 22 can form part of the anolyte surge tank 26 or can be at any other location provided chlorine is removable.

The more air sparged and the flow rate of the air through the anolyte will affect the amount of chlorine removed. The chlorine 37 removed can be passed through a scrubber or collected. By controlling the flow rate of the lixiviant and air during the sparging process, the desired level of chloride can be removed from the lixiviant. It has been found that when there is 5 grams per litre (g/L) of chloride in the lixiviant, there is required twelve ion exchange column elutions per day. When chlorine levels are reduced to about 2 g/L there are required only five or six elutions per day.

Effectively, the reduction of chloride ion concentration increases the capacity of the ion exchange resin and therefore more uranium can be extracted. Less elutions represents a significant cost and time saving.

Hydrogen is evolved at the cathode by reduction of hydrogen ions in the acidic lixiviant solution and discharged from surge tank 15 at 33. To prevent the pH from increasing, sulphuric acid 15 is added to the catholyte surge tank 13 from which lixiviant is circulated to electrolyser 19. The sulphuric acid 15 compensates for the removal of hydrogen ions and, in addition to this, the sulphate ions replace the chloride ions. The sulphate ions do not compete with the uranyl species for active sites on the ion exchange resin to the same extent as chloride. The hydrogen gas can be recovered if desired.

An electrochemical cell assembly or electrolyser comprises a number of cells, in Figure 1 there are four cells shown, however, there are preferably 150 cells in three stacks of 50 comprising each electrolyser.

The at least partially dechlorinated lixiviant is combined with circulating lixiviant 12 at location 20. Remaining dissolved chlorine at a concentration of around 2g/L causes the oxidation of the ferrous ions in the recirculating lixiviant and re- reduces the free chlorine back to chloride ions. Accordingly, the concentration of chloride ions remains unchanged and the process can be referred to as autogenous other than that chlorine removed by the dechlorinator. The regenerated lixiviant is then passed through the leach step 24 to extract uranium and the lixiviant including the dissolved uranium (referred to as the pregnant lixiviant) 26 flows from the leach step 24 and into the uranium recovery plant 14. The uranium product is removed by ion exchange methods in recovery plant 14 (or solvent extraction if it is preferred or necessary). The barren lixiviant 12 is again released as stream 12 which is circulated as described above and the process continues.

Figure 2 is a close-up view of the electrolytic cell assembly. Each cell has a pair of bipolar titanium electrodes 28 with a mixed metal oxide coating on the anode side 28a (the left-hand side of the electrodes as shown schematically in Figure 1).

The cathode side 28b of the electrode is the right-hand side of electrode 28 as shown schematically in Figure 1. Each bipolar electrode 28 is therefore shared by an adjacent electrolytic cell, except for the electrodes at the end of each stack. The end electrodes have current connections to the external circuit which includes DC power supply 29. Internal manifolds and flow-directors are part of the internal structure of electrolyser 19 (not shown).

An advantage of using bipolar electrodes is that they do not have external current conductors to provide a current path between the anode side and the cathode side. This leads to simplification of the cell design. Recirculation pumps 31 and 32 (see Figure 1) increase the flow velocity of the side stream 16 and 18 electrolyte across the electrode surfaces, which increases the efficiency by reducing concentration gradients at the electrode surfaces.

The dissolved chlorine is formed as the chloride ions contact the anode. It is preferable that the chlorine produced at the anode is prevented from diffusing to the cathode by a separating means 30 in the form of a membrane or diaphragm which permits fluid communication throughout the electrolytic cell assembly but which restricts the migration of the formed chlorine by fluid transport between the anode and cathode parts of a cell, or is substantially impermeable to it in the case of an ion selective membrane.

If the chlorine levels are still undesirably high (either because insufficient chlorine has been removed at dechlorinator 22 or more chlorine has been added to the system), the lixiviant can be re-passed through the dechlorinator to either further reduce or maintain the levels of chlorine in the system 10.

Figure 3 shows an alternative embodiment of leach process incorporating the chlorine removal of the present invention. This embodiment is similar to the embodiment shown in Figure 1 and the same reference numerals are used for corresponding items.

A barren lixiviant stream 12, flows from uranium recovery plant 14 at a rate of approximately 300 litres per second (L/ s). The lixiviant is referred to as 'barren' because the uranium recovery plant 14 has extracted all (or a at least a substantial portion of) the valuable constituents from the lixiviant (i.e. uranium). All or part of the barren lixiviant is separated into at least two side streams to undergo electrolytic treatment. Side streams 16 and 18 are separated from the circulating barren lixiviant stream 12. Side stream 16 is a feed lixiviant directed through a manifold into cathode cells 21 (hereinafter the catholyte side stream) of an electrolytic cell assembly 19. Side stream 18 is a feed lixiviant directed through a manifold into anode cells 17 (hereinafter the anolyte side stream) of an electrolytic cell assembly 19. The anode and cathode cells are shown in more detail in Figure 2. The anolyte is the liquid which flows from the anode cell and is chemically changed by the electrolytic process(es) at the anode. The catholyte is the liquid which flows from the cathode cell and is chemically changed by the electrolytic process(es) at the cathode cell 21. Preferably, more lixiviant is separated into side stream 18 than to side stream 16. The efficiency of the process is improved if any ferric irons which exist in the lixiviant entering the electrolyser are kept from the cathode (since they will be reduced to ferrous ions and decrease the efficiency of the electrolytic process). The flow rate of side stream 18 is approximately 20 L/s, the lixiviant flows into anolyte surge tank 26 and from there is passed into the anode cells 17 of the electrolyser or electrolytic cell 19. The flow rate of side stream 16 is a approximately 2 L/s, the lixiviant flows into catholyte surge tank 13 and from there is passed into the cathode cells 21 electrolyser or electrolytic cell 19.

The anolyte rich in chlorine is then passed by pipe 23 to dechlorinator 22. Dechlorinator 22 removes the unwanted chlorine by bubbling air (or another gas) though the anolyte as it flows through a column (bubbling air though the anolyte is referred to as sparging). Air sparging is the process of injecting air directly into the lixiviant; the air is supplied at 27 and strips the chlorine, in gaseous form, from the anolyte through vent 25. Stripped chlorine and air are separated in separator 35 into chlorine 37 and air 39. The dechlorinated anolyte is then remixed with the catholyte stream at location 20 to provide a lixiviant having reduced levels of chlorine/ chloride ions.

The more air sparged and the flow rate of the air through the anolyte will affect the amount of chlorine removed. The chlorine 37 removed can be passed through a scrubber or collected.

By controlling the flow rate of the lixiviant and air during the sparging process, the desired level of chloride can be removed from the lixiviant. It has been found that when there is 5 grams per litre (g/L) of chloride in the lixiviant, there is required twelve ion exchange column elutions per day. When chlorine levels are reduced to 2 g/L there are required only five or six elutions per day. Effectively, the reduction of chloride ion concentration increases the capacity of the ion exchange resin and therefore more uranium can be extracted. Less elutions represents a significant cost and time saving.

The at least partially dechlorinated lixiviant is combined with circulating lixiviant 12 at location 20. Remaining dissolved chlorine at a concentration of around 2g/L causes the oxidation of the ferrous ions in the recirculating lixiviant and re- reduces the free chlorine back to chloride ions. Accordingly, the concentration of chloride ions remains unchanged and the process can be referred to as autogenous other than that chlorine removed by the dechlorinator.

The regenerated lixiviant is then directed to a well field where 40 where it is injected into the well field by pipe 42 to extract uranium by leaching and the lixiviant including the dissolved uranium (referred to as the pregnant lixiviant) is extracted by pipe 44 and flows in line 46 flows from the leach step into the uranium recovery plant 14. The uranium product is removed by ion exchange methods in recovery plant 14 (or solvent extraction if it is preferred or necessary). The barren lixiviant 12 is again released as stream 12 which is circulated as described above and the process continues. Chloride reduction test

A synthetic lixiviant was made up by dissolving sodium chloride, sodium sulphate, ferrous sulphate and sulphuric acid in water. Electrolysis was carried out in an arrangement where 93 ml of the synthetic lixiviant containing 1.6 g added concentrated sulphuric acid was used as catholyte. The catholyte was placed in a porous ceramic pot in the centre of a 500 ml beaker, and surrounded by 275 ml of synthetic lixiviant as anolyte. The cathode and anode were rectangular sheets of perforated titanium, coated with mixed metal oxide in the case of the anode and uncoated in the case of the cathode.

After electrolysing the combination for one hour at a current of 1 amp and a voltage of 7.4 volts, the anolyte containing dissolved chlorine was placed in a measuring cylinder and air bubbled through it using a ceramic aquarium bubbler and air pump. At the end of three minutes, the smell of chlorine was no longer evident in the anolyte sparged with air in this way. After chemical analysis by XRF, the treated anolyte and catholyte were combined, and showed a reduction of the chloride concentration of 2.6 g/L.

Untreated, synthetic lixiviant: SO₄ ²" concentration 1.4 g/L

Q- concentration 5.3 g/L

Fe²⁺ concentration 420 mg/L pH 2.0 (25 C)

Anolyte, after electrolysis and air sparging: SO₄ ²- concentration 2.9 g/L

Cl" concentration 2.8 g/L

Catholyte, after electrolysis: SO4²" concentration 8.9 g/L Cl- concentration 1.97 g/ L

Mixed catholyte and sparged anolyte after electrolysis: SO4²" concentration 4.7 g/ L Cl- concentration 2.7 g/ L

ORP after electrolysis 505 mV pH 2.0

Although a preferred embodiment of the apparatus of the present invention has been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention. Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Co-pending Patent Application entitled "Regeneration of a Lixiviant" filed concurrently with this application provides details of regeneration processes for lixiviants for uranium extraction processes and the teaching therein is incorporated herein in its entirety.

Claims

THE CLAIMS

1. A method for reducing the concentration of chloride ions in a lixiviant including the step of: treating a lixiviant stream in an electrolytic cell assembly thereby forming dissolved chlorine from the chloride ions in the treated lixiviant; sparging the treated lixiviant to remove at least some of the dissolved chlorine to reduce the concentration of the dissolved chlorine in the lixiviant; whereby the concentration of the chloride ions in the treated lixiviant is reduced.

2. A method according to claim 1, wherein the treated lixiviant is used to recover a metal from a metal ore in a leaching process.

3. A method according to claim 2, wherein, the metal recovered from a metal ore is uranium.

4. A method according to claim 1, wherein the treated lixiviant is collected from the electrolytic cell and the step of sparging the treated lixiviant is performed at a later point in time.

5. A method according to claim 1 wherein the concentration of chloride ions in the treated lixiviant reduced to a level which permits the extraction of uranyl ions in the treated lixiviant by an ion exchange process.

6. A method according to claim 5, wherein the concentration of chlorine in the treated lixiviant is reduced to below 5g per litre (g/L).

7. A method according to claim 5, wherein, the concentration of chlorine in the treated lixiviant is reduced to below 2 g/L.

8. A method according to claim I₁ wherein the electrolytic cell assembly comprises an anode cell and a cathode cell.

9. A method according to claim 8, wherein the anode cell and cathode cell are separated from one another by a separating means.

10. A method according to claim 8, wherein there are 150 anode and cathode cells arranged alternately in a stack or stacks.

11. A method according to claim 8, wherein the electrodes used in the electrolytic cells are bipolar.

12. A method for reducing the concentration of chloride ions in a lixiviant including the step of : separating a feed lixiviant stream including chloride ions into at least two streams; causing a first stream to pass through an anode cell of an electrolytic cell assembly to form an anolyte and a second stream to pass though a cathode cell of an electrolytic cell assembly to form a catholyte; oxidising some of the chloride ions in the anolyte to chlorine in the anode cell; sparging the anolyte with air or another gas to reduce the concentration of chlorine; combining the anolyte including chlorine from the anode cell with the catholyte from the cathode cell to form a treated lixiviant, wherein the concentration of chloride ions in the treated lixiviant is reduced.

13. A lixiviant modification apparatus comprising; an electrolytic cell assembly in which a lixiviant is electrolytically reacted to produce a gaseous species; means to withdraw the reacted lixiviant from the electrolytic cell assembly; means to sparge air through the withdrawn lixiviant ; and means to vent the sparged air along with at least a portion of the gaseous species.

14. A lixiviant modification apparatus as in Claim 14 wherein the electrolytic cell assembly comprises a plurality of cathode cells and a plurality of anode cells, wherein the lixiviant is electrolytically reacted in the anode cells to produce the gaseous species and the means to withdraw the reacted lixiviant from the electrolytic cell assembly comprises means to withdraw the reacted lixiviant from the anode cells.