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WO2008061310A1 - Régénération de lixiviant - Google Patents

Régénération de lixiviant Download PDF

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Publication number
WO2008061310A1
WO2008061310A1 PCT/AU2007/001796 AU2007001796W WO2008061310A1 WO 2008061310 A1 WO2008061310 A1 WO 2008061310A1 AU 2007001796 W AU2007001796 W AU 2007001796W WO 2008061310 A1 WO2008061310 A1 WO 2008061310A1
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WO
WIPO (PCT)
Prior art keywords
lixiviant
anode
cathode
cell
stream
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/AU2007/001796
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English (en)
Inventor
Marcus Worsley Richardson
James Andrew Davidson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Heathgate Resources Pty Ltd
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Heathgate Resources Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2006906581A external-priority patent/AU2006906581A0/en
Application filed by Heathgate Resources Pty Ltd filed Critical Heathgate Resources Pty Ltd
Publication of WO2008061310A1 publication Critical patent/WO2008061310A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
    • C22B3/10—Hydrochloric acid, other halogenated acids or salts thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/0204—Obtaining thorium, uranium, or other actinides obtaining uranium
    • C22B60/0217—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes
    • C22B60/0221—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes by leaching
    • C22B60/0226—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes by leaching using acidic solutions or liquors
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/24—Halogens or compounds thereof
    • C25B1/26—Chlorine; Compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/045—Leaching using electrochemical processes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to a method and apparatus for the regeneration of lixiviant used, for instance, in the leaching of a metal such as uranium.
  • Leaching of uranium ore involves circulating leach fluid through a bed of the ore.
  • the leach fluid, or lixiviant is acidified for instance with sulphuric acid and an oxidising agent is added to cause oxidation of the ore.
  • the action of the oxidising agent is to cause conversion to 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 operation.
  • the acid in- situ leach (ISL) method 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 cause oxidation of the ore.
  • the action of the oxidising agent is to cause conversion to 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.
  • the oxidising agents usually used in ISL mining are oxygen, sodium chlorate or hydrogen peroxide. These oxidising agents regenerate the oxidising capacity of the depleted lixiviant.
  • Sodium chlorate has the disadvantage that its use adds sodium chloride to the lixiviant which is a drawback when ion exchange resins are used to capture the uranium from the pregnant lixiviant (chloride ions compete with the uranium compound for active sites on the resin therefore a larger quantity of resin is required to extract the uranium).
  • Hydrogen peroxide is relatively costly and requires special handling precautions in its concentrated form.
  • a method for regenerating a depleted lixiviant used to recover a metal from a metal ore including the step of: passing a feed lixiviant stream containing chloride ions into an electrolytic cell assembly to form an anolyte and a catholyte; oxidising chloride ions in the anolyte to chlorine in the anode cell; combining the anolyte including chlorine with the catholyte from the cathode cell to form a regenerated lixiviant capable of oxidising ferrous ions to ferric ions.
  • a method for regenerating a depleted lixiviant used to recover a metal from a metal ore including the step of: separating a feed lixiviant stream containing chloride ions into at least two streams; causing a first stream to pass through an anode cell of an electrolytic cell assembly to form a anolyte and a second stream to pass though a cathode cell of an electrolytic cell assembly to form a catholyte; oxidising the chloride ions in the first stream to chlorine in the anode cell; combining the anolyte including chlorine from the anode cell with the catholyte from the cathode cell to form a regenerated lixiviant capable of oxidising ferrous ions to ferric ions.
  • the anode cell and cathode cell are separated from one another in the electrolytic cell assembly by a separating means which assists in preventing the chlorine formed at the anode from reaching the cathode.
  • the regenerated lixiviant is used to recover a metal from a metal ore in an in-situ leach process.
  • the ore may be a milled ore.
  • the metal recovered from a metal ore is preferably uranium.
  • a chemical species oxidised in the anode cell are ferrous ions which are oxidised to ferric ions.
  • the dissolved chlorine in the anolyte can oxidise ferrous ions to ferric ions in the combined catholyte and anolyte steams or with further untreated lixiviant which is not passed through the electrolytic cell assembly.
  • the separating means is a membrane or diaphragm. More preferably, the membrane or diaphragm defines a plurality of micropores which inhibit bulk fluid flow across the diaphragm in the electrolytic cell.
  • the separating means can be formed from a porous polypropylene material.
  • the separating means can be a porous poly tetrafluoroethylene PTFE membrane or a porous polyvinylchloride PVC membrane.
  • the chemical species restricted from passing through the separating means include chlorine and ferric ions so that these do not reach the cathode.
  • anode and cathode cells there can be a plurality of anode and cathode cells.
  • the electrodes used in the electrolytic cell are bipolar.
  • the electrodes consist of titanium, bare on the cathode side and coated with a mixed metal oxide on the anode side.
  • ferric ions become ferrous ions as they oxidise the uranium ore to provide a soluble uranium ion which can be subsequently extracted as a valuable mining product.
  • the present invention provides a means for re-oxidizing ferrous ions back to ferric ions, quickly, and without the use of expensive oxidizing agents.
  • ferrous ions in the lixiviant are oxidized by dissolved chlorine in the lixiviant.
  • the chlorine is formed electrochemically from chloride ions in the lixiviant solution which react at the anode of the electrolytic cell assembly to form free chlorine.
  • the dissolved, free chlorine oxidizes the ferrous ions to ferric ions and both species are separated from the cathode by a diaphragm to restrict reduction of them back to the component chloride ions or ferrous ions.
  • the concentration of ferric ions in the lixiviant is optimized thereby enhancing the recovery of uranium once the lixiviant is re-circulated into the well-field.
  • a method for generating dissolved chlorine in a lixiviant used to recover a uranium metal from a uranium ore in an in-situ leach process including the step of: separating a feed lixiviant stream containing chloride ions into at least two streams; causing a first stream to pass through an electrolytic cell assembly and a second stream to bypass the electrolytic cell assembly; allowing the chloride ions in the first stream to be oxidised to form chlorine in an anode cell of the electrolytic cell assembly; combining the anolyte including chlorine produced from the anode cell with the bypassed feed lixiviant stream to form a regenerated lixiviant used to recover a uranium metal from a uranium ore in the in-situ leach process.
  • a lixiviant regeneration apparatus comprising; an electrolytic cell assembly including a plurality of alternate anode cells and cathode cells; alternate cells being separated by a bipolar electrode and the other alternate cells being separated by an electrolytically conductive separating means which prevents bulk transport of chemical species formed in the anode cell reaching the cathode cell; a depleted lixiviant supply; separation means to separate the depleted lixiviant into at least a cathode side stream and an anode side stream and to supply the cathode side stream to respective cathode cells and the anode side stream to the anode cells; withdrawal means to withdraw catholyte from the cathode cells and to withdraw anolyte from the anode cells; and mixing means to mix the withdrawn anolyte and catholyte.
  • the lixiviant supply includes a bypass and further including a further mixing means to mix the withdrawn anolyte and catholyte with
  • the invention is said to comprise a lixiviant regeneration apparatus comprising an electrolytic cell comprising an upstream metal mesh cathode and a downstream anode, a depleted lixiviant supply and means to flow the depleted lixiviant through the electrolytic cell through the cathode and then through the anode.
  • FIGURE 1 is a schematic of the process according to a preferred embodiment of the present invention.
  • FIGURE 2 is a schematic of the process according to a preferred embodiment of the present invention for in situ leaching
  • FIGURE 3 is a schematic of the process according to a preferred embodiment of the present invention for countercurrent leaching;
  • FIGURE 4 shows detail on one form of electrolytic cell useful for the present invention.
  • FIGURE 5 shows an alternative embodiment of an electrolytic cell useful for the present invention.
  • FIGURE 6 shows an alternative embodiment of an electrolytic cell useful for the present invention.
  • FIGURE 7 shows schematic flow chart for use of the electrolytic cell of
  • ferric ions Fe 3+
  • Ferric ions may be naturally present in the acidified leach fluid and/ or may be deliberately added to it (in the form of ferric ions or ferrous ions or both). The reaction is as follows:
  • U IV O2 can here can more generally represent the uranium contained in leachable ores such as coffinite
  • the sulfato complex ion [UO 2 (SO ⁇ s] 4 - is also formed by a reaction similar to reaction (3).
  • the uranyl sulphato anions including [(UO 2 ) (SO 4 ) 2 ] 2 ' and [(UO 2 ) (SO 4 )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.
  • ferric ions Once ferric ions have oxidized the uranium ore, they become ferrous ions.
  • the present invention provides a means for re-oxidizing the ferrous ions back to ferric ions, quickly, and without the addition of oxidizing reagents to the lixiviant solution. Instead of adding oxidizing agents to the lixiviant, the ferrous ions are indirectly oxidized by dissolved chlorine (or free chlorine) in the lixiviant in accord with the following reaction:
  • the chlorine is produced by an electrochlorination process i.e. a process where chlorine is generated electrolytically at an anode cell of an electrolytic cell assembly from chloride ions in solution.
  • the chloride ions are already present in the lixiviant (this may be the case in areas having highly saline water in the aquifer containing the ore). It is an option, that chloride ions can be added to the lixiviant.
  • the flow rate of the solution through the electrolytic cell assembly can be controlled (at the same cell current) in order to control the concentration of chlorine in the anolyte. For example, a slower flow rate (at the same cell current) 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.
  • Figure 1 is a schematic diagram of the electrolytic process 10 in a flowing cell type arrangement and Figure 4 shows detail of the electrolytic cell.
  • 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 a substantial portion of the valuable constituents from the lixiviant (i.e. uranium).
  • Part of the barren lixiviant is separated into at least two side streams to undergo electrolytic treatment in an electrolytic cell assembly.
  • Side streams 16 and 18 are shown separated from the circulating barren lixiviant stream 12.
  • Side stream 16 is a feed lixiviant directed through a manifold towards cathode cells 21 (hereinafter the catholyte side stream) and side stream 18 is a feed lixiviant directed through a manifold towards anode cells 17 (hereinafter the anolyte side stream).
  • the anode and cathode cells are more clearly shown in Figure 4.
  • the anolyte is the liquid which flows through the anode cell and is chemically changed by the electrolytic process(es) at the anode.
  • the catholyte is the liquid which flows through the cathode cell and is chemically changed by the electrolytic process(es) at the cathode.
  • Dissolved chlorine is produced in the anolyte side stream 18 by electrolytic oxidation of chloride ions in the anode cell 17 of the electrolytic cell assembly 19.
  • Hydrogen is evolved at the cathode by reduction of hydrogen ions in the acidic lixiviant solution and discharged from surge tank 13 at 33.
  • sulphuric acid 15 is added to the catholyte surge tank 13 from which lixiviant is circulated in the electrolytic cell assembly 19.
  • the hydrogen gas 33 can be recovered if desired.
  • more lixiviant is separated into the anolyte side stream 18 than to the catholyte side stream 16.
  • the efficiency of the process is improved if any ferric ions which exist in the lixiviant are kept from the cathode (since they will be reduced to ferrous ions).
  • the flow rate of the anolyte side stream may be approximately 20 L/ s.
  • the lixiviant flows into anolyte surge tank 23 and from there is passed into electrolyser or electrolytic cell 19.
  • the flow rate of side stream 16 may be approximately 2 L/s, the lixiviant flows into catholyte surge tank 13 and from there is passed into electrolyser or electrolytic cell 19.
  • Electrolytic cell assembly 19 comprises a number of cells, in Figure 1 there are four cathode cells and four anode cells shown, however, there are preferably 150 cells in three stacks of 50.
  • Figure 4 shows more detail of the electrolytic cell assembly 19.
  • Each cell has a pair of bipolar titanium electrodes 28 with a mixed metal oxide coating on the anode side 28a (the right-hand side of the electrodes as shown schematically in Figure 1).
  • the cathode side 28b of the electrode is the left- hand side of electrode 28 as shown schematically in Figure 1 and may be bare metal.
  • 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.
  • ferric ions in the lixiviant are used to oxidize the uranium ore in the well-field, however, before they are able to oxidize the ore it is possible that the cations will move to the cathode of the electrolytic cell assembly and be reduced back to ferrous ions. Furthermore, it is also possible that the free chlorine produced in solution will be reduced back to its composite ions at the cathode before it has been able to oxidize ferrous ions. In order to prevent his from occurring and to thereby increase the likelihood that uranium is efficiently oxidized, the ferric ions and the free chlorine are restricted from moving to the cathode by a separating means.
  • Figures 1 and 4 show a porous separating means or diaphragm 30 separating the anode cell from the cathode cell.
  • the chemical species in the anolyte and catholyte are therefore separated which minimises the extent of undesirable reactions (described above) that reduce the efficiency of the system.
  • the separating means may be a membrane or a diaphragm, or the like, which permits fluid communication throughout the electrolytic cell assembly but which reduces or eliminates the transport of ferric ions and chlorine chemical species from the vicinity of the anode to the vicinity of the cathode.
  • the separating means is a material which defines a plurality of micropores and which inhibit bulk flow within the electrolytic cell but does not substantially reduce the electrolytic conductivity of the electrolytic cell.
  • the separating means should have the mechanical strength to withstand conditions in the cell and should be durable in the acidic and chlorinated conditions that exist.
  • the separating means is a polypropylene felt material.
  • the separating means can be a porous polytetrafluoroethylene (PTFE) membrane or a porous polyvinylchloride (PVC) membrane.
  • Anolyte side stream 16 having increased levels of dissolved chlorine (and associated hypochlorite ions in equilibrium) and catholyte side stream 18 are recombined with barren circulating lixiviant stream 12 at location 20.
  • the chlorine in the lixiviant rapidly oxidises ferrous ions in the lixiviant stream.
  • the treated or regenerated lixiviant stream 22, which is rich in ferric ions, circulates through a leach step 24 for the extraction of uranium from a uranium containing ore.
  • the anolyte which is combined with circulating lixiviant 12 at location 20 preferably contains dissolved chlorine at a concentration of around 2g/L.
  • the oxidation of the ferrous ions 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.
  • the lixiviant including the dissolved uranium (referred to as the pregnant lixiviant) 26 flows from 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 plant if this is preferred or necessary).
  • the barren lixiviant 12 is again released as stream 12 which is circulated as described above and the process continues.
  • FIG 2 is a schematic diagram of the electrolytic process 10 in a flowing cell type arrangement for use with in situ leaching.
  • the embodiment shown in Figure 2 is similar to that of Figure 1 in many respects 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 a substantial portion of the valuable constituents from the lixiviant (i.e. uranium).
  • Part of the barren lixiviant is separated into at least two side streams to undergo electrolytic treatment in an electrolyser or electrolytic cell assembly.
  • Side streams 16 and 18 are shown separated from the circulating barren lixiviant stream 12.
  • Side stream 16 is a feed lixiviant directed through a manifold towards cathode cells 21 (hereinafter the catholyte side stream) and side stream 18 is a feed lixiviant directed through a manifold towards anode cells 17 (hereinafter the anolyte side stream).
  • the anolyte is the liquid which flows through the anode cell and is chemically changed by the electrolytic process(es) at the anode.
  • the catholyte is the liquid which flows through the cathode cell and is chemically changed by the electrolytic process(es) at the cathode.
  • Dissolved chlorine is produced in the anolyte side stream 18 by electrolytic oxidation of chloride ions in the anode cell 17 of the electrolytic cell assembly or electrolyser 19.
  • Hydrogen is evolved at the cathode by reduction of hydrogen ions in the acidic lixiviant solution and discharged from surge tank 13 at 33.
  • sulphuric acid 15 is added to the catholyte surge tank 13 from which lixiviant is circulated in the electrolytic cell assembly 19. The hydrogen gas 33 can be recovered if desired.
  • more lixiviant is separated into the anolyte side stream 18 than to the catholyte side stream 16.
  • the efficiency of the process is improved if any ferric ions which exist in the lixiviant are kept from the cathode (since they will be reduced to ferrous ions).
  • the flow rate of the anolyte side stream may be approximately 20 L/ s.
  • the lixiviant flows into anolyte surge tank 23 and from there is passed into the electrolytic cell assembly 19.
  • the flow rate of side stream 16 may be approximately 2 L/s, the lixiviant flows into catholyte surge tank 13 and from there is passed into the electrolytic cell assembly 19.
  • Anolyte side stream 16 having increased levels of dissolved chlorine (and associated hypochlorite ions in equilibrium) and catholyte side stream 18 are recombined with barren circulating lixiviant stream 12 at location 20.
  • the chlorine in the lixiviant rapidly oxidises ferrous ions in the lixiviant stream.
  • the treated or regenerated lixiviant stream 22, which is rich in ferric ions, circulates through the in-situ leach well-field pattern 24a for the extraction of uranium from the underground ore deposit.
  • the lixiviant including the dissolved uranium (referred to as the pregnant lixiviant) 26 flows from leach step 24a and into the uranium recovery plant 14.
  • the uranium product is removed by ion exchange methods in recovery plant 14 (or solvent extraction plant if this 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 3 shows an alternative embodiment of metal recovery process utilising the regeneration process of the present invention.
  • the embodiment shown in Figure 3 is similar to that of Figure 1 in many respects 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 a substantial portion of the valuable constituents from the lixiviant (i.e. uranium).
  • Part of the barren lixiviant is separated into at least two side streams to undergo electrolytic treatment in an electrolyser or electrolytic cell assembly.
  • Side streams 16 and 18 are shown separated from the circulating barren lixiviant stream 12.
  • Side stream 16 is a feed lixiviant directed through a manifold towards cathode cells 21 (hereinafter the catholyte side stream) and side stream 18 is a feed lixiviant directed through a manifold towards anode cells 17 (hereinafter the anolyte side stream).
  • the anolyte is the liquid which flows through the anode cell and is chemically changed by the electrolytic process(es) at the anode.
  • the catholyte is the liquid which flows through the cathode cell and is chemically changed by the electrolytic process(es) at the cathode.
  • Dissolved chlorine is produced in the anolyte side stream 18 by electrolytic oxidation of chloride ions in the anode cell 17 of the electrolytic cell assembly or electrolyser 19.
  • Hydrogen is evolved at the cathode by reduction of hydrogen ions in the acidic lixiviant solution and discharged from surge tank 13 at 33.
  • sulphuric acid 15 is added to the catholyte surge tank 13 from which lixiviant is circulated in the electrolytic cell assembly 19. The hydrogen gas 33 can be recovered if desired.
  • more lixiviant is separated into the anolyte side stream 18 than to the catholyte side stream 16.
  • the efficiency of the process is improved if any ferric ions which exist in the lixiviant are kept from the cathode (since they will be reduced to ferrous ions).
  • the flow rate of the anolyte side stream may be approximately 20 L/s. the lixiviant flows into anolyte surge tank 23 and from there is passed into electrolyser or electrolytic cell 19.
  • the flow rate of side stream 16 may be approximately 2 L/s, the lixiviant flows into catholyte surge tank 13 and from there is passed into electrolyser or electrolytic cell 19.
  • the anolyte which is combined with circulating lixiviant 12 at location 20 preferably contains dissolved chlorine at a concentration of around 2g/L.
  • the oxidation of the ferrous ions 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.
  • Anolyte side stream 16 having increased levels of dissolved chlorine (and associated hypochlorite ions in equilibrium) and catholyte side stream 18 are recombined with barren circulating lixiviant stream 12 at location 20.
  • the chlorine in the lixiviant rapidly oxidises ferrous ions in the lixiviant stream.
  • the treated or regenerated lixiviant stream 22, which is rich in ferric ions, circulates through the counter-current leaching process for the extraction of uranium from milled ore.
  • the counter-current leaching process comprises a plurality of leach tanks 25 with ore 27 progressing between tanks in one direction and the lixiviant 22 passing in the other direction.
  • the lixiviant including the dissolved uranium (referred to as the pregnant lixiviant) 26 flows from leach step 25 and into the uranium recovery plant 14.
  • the uranium product is removed by ion exchange methods in recovery plant 14 (or solvent extraction plant if this is preferred or necessary).
  • the barren lixiviant 12 is again released as stream 12 which is circulated as described above and the process continues.
  • FIG. 5 shows an alternative embodiment of electrolyser useful for the present invention.
  • the electrolytic cell assembly 40 comprises a flow tube 42 having a plurality of alternate anodes and cathodes 43 spaced across the flow path through the flow tube 42.
  • First anode 46 and last cathode 48 are connected to a DC power supply 50.
  • Each cathode and anode 43 is preferably combined as a titanium plate having an anode side 44 and a cathode side 45.
  • FIGS 6 and 7 show an alternative embodiment of electrolytic cell, suitable for the present invention.
  • a flow through electrolytic cell 50 comprises a tube 62 with an upstream cathode 64 and a downstream anode 66.
  • Each of the anode and cathode are formed from an electrically conductive mesh such as a pressed metal mesh which have the advantage of high surface area and angles to induce turbulence for good mixing and for good electrical contact.
  • a DC power supply 68 is connected between the anode and cathode.
  • the flow rate of lixiviant through the cell is preferably greater than the drift velocity of ions from the anode to the cathode such that ferric ions produced adjacent to the anode from reaction with chlorine produced at the anode cannot drift under the electric field between the anode and cathode to the cathode and be reconverted back to ferrous ions again.
  • electrolytic cells 60 there may be a plurality of electrolytic cells 60 arranged in parallel with a flow of barren lixiviant 70 split between them.
  • the electrolytic cells are arranged electrically in series with the anode of the first electrolytic cell assembly and the cathode of the last electrolytic cell assembly connected to the power supply and the intermediate cathodes connected to the anode of the next cell by electrical connection 73.
  • Oxidation of ferrous iron in acid in situ leaching barren lixiviant by dissolved chlorine Oxidation of ferrous iron in acid in situ leaching barren lixiviant by dissolved chlorine.
  • the replacement of hydrogen peroxide as oxidant for the barren lixiviant at an in situ leaching mine was tested by adding a solution of chlorine water (water containing dissolved chlorine, prepared by bubbling chlorine gas through water- dissolved chlorine is taken to mean the amount of chlorine gas taken up in solution and available for oxidation, as shown by iodimetric titration) to 400 ml of unoxidised barren lixiviant taken from the uranium recovery plant.
  • the chlorine water was added in increments to the stirred solution and the oxidation process monitored by the use of an oxidation/ reduction potential (ORP) electrode.
  • ORP oxidation/ reduction potential
  • the barren lixiviant had a total iron concentration of 0.366 g/L as determined by X-ray fluorescence, and a residual uranium concentration of 13 mg/L.
  • the oxidation/ reduction potential increased from 475 mV (Pt electrode and AgCl/ saturated KCL reference electrode) to 550 mV on addition of 9.5 ml of chlorine water containing 4.7 g/L dissolved chlorine.
  • An ORP of 550 mV corresponds to the value normally maintained in the oxidised barren lixiviant by the addition of hydrogen peroxide.
  • the reaction with the chlorine water added was very fast such that a time delay between the addition of the chlorine water and the rise in ORP measured with the electrodes could not be observed.
  • 'barren lixiviant is meant the lixiviant used in the in-situ mining process from which uranium has been extracted and which is recirculated through the underground mineralised uranium deposit to react with and extract the uranium.
  • the electrolytic production of dissolved chlorine was demonstrated in cells where a porous ceramic diaphragm was used to separate the cell into an anode and a cathode compartment.
  • the anodes comprised titanium sheet or mesh coated with a mixed metal electrocatalytic coating
  • the cathodes comprised bare titanium metal sheet or mesh.
  • Positive displacement peristaltic pumps were used to provide flows of electrolyte through the anode and the cathode compartments to form separate streams of treated anolyte and catholyte, respectively.
  • the electrolyte treated in this manner was unoxidised barren lixiviant obtained from an in situ leaching mine. Additional sulphuric acid was added to the catholyte stream to maintain the pH of the treated lixiviant and to prevent the formation of precipitates in the cathode compartment of the cells. To simulate the electrochemical process whereby the ferrous iron in the lixiviant is oxidised the anolyte and catholyte was combined after the two separate streams had passed through the electrolytic cell assembly.
  • Flow-through cell tests with mesh electrodes and no diaphragm were made with coaxial, tubular anodes and cathodes.
  • the central cathode was made from titanium mesh and had a diameter of 70 mm and a length of 250 mm. It was separated from the outer tubular anode by silicone rubber spacers.
  • the anode was a tube of titanium metal mesh of diameter 85 mm with a mixed metal oxide coating.
  • the bottom of the coaxial tubular electrode assembly was closed off by a plastic cup, causing the lixiviant introduced through the central axial plastic distributor tube to pass first through the spaces in the mesh cathode then through the mesh anode.
  • Untreated barren lixiviant (unoxidised by hydrogen peroxide) was introduced to the coaxial electrode arrangement through a 20 mm diameter PVC tube closed at the bottom end and having 66 holes of 5 mm diameter evenly spaced along the submerged length. The whole arrangement was placed in a vertical plastic tube closed at the bottom and with an arrangement that enabled overflow and collection of the treated electrolyte that had flowed through the electrodes from inside to outside.
  • the lixiviant Prior to the test, the lixiviant was acidified with 2 ml of concentrate sulphuric acid per litre. The flow rate of lixiviant through the electrolytic cell assembly was set to 1 L/ minute.
  • So-called surface milling processes are known in which crushed and ground uranium ore is leached using a lixiviant containing sulphuric acid and dissolved iron, and to which an oxidant is added to maintain the dissolved iron in the ferric state as it oxidises the ore.
  • oxidants are hydrogen peroxide, sodium chlorate and manganese dioxide.
  • chlorine can fulfil the role of oxidant, in which case it could be added to the leaching process as gaseous chlorine obtained by the evaporation of liquid chlorine transported to the mine and held in pressurised vessels.
  • Oxidant addition Started after 30 minutes, to allow for decomposition of any sulphides or calcite present. Subsequently added during leach test to maintain an ORP of 528 mV (Pt electrode against Ag/ AgCl/ satd KCl reference electrode).

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Abstract

Procédé et dispositif de régénération de lixiviant appauvri utilisé pour la récupération de métal à partir de minerai métallique en tant qu'opération minière de lixiviation in situ. Le procédé consiste à injecter une flux de lixiviant d'alimentation (12) qui contient des ions chlorure et des ions ferreux dans un ensemble cellule électrolytique (19 à anode (28a) et cathode (28b), à oxyder les ions chlorure en chlore et à permettre au chlore d'oxyder les ions ferreux en ions ferriques pour former un lixiviant régénéré. La cellule électrolytique peut être une3 cellule bipolaire ou une cellule de flux (40, 60).
PCT/AU2007/001796 2006-11-24 2007-11-22 Régénération de lixiviant Ceased WO2008061310A1 (fr)

Applications Claiming Priority (2)

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AU2006906581A AU2006906581A0 (en) 2006-11-24 Regeneration of a lixiviant
AU2006906581 2006-11-24

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WO2008061310A1 true WO2008061310A1 (fr) 2008-05-29

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015000002A1 (fr) * 2013-07-04 2015-01-08 Pureox Industrieanlagenbau Gmbh Procédé d'oxydation électrochimique de solutions de chlorure de fe2+

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1528207A (en) * 1923-04-02 1925-03-03 William E Greenawalt Metallurgical process
US2894804A (en) * 1949-03-02 1959-07-14 Carl W Sawyer Process of extracting uranium and radium from ores
US3901776A (en) * 1974-11-14 1975-08-26 Cyprus Metallurg Process Process for the recovery of copper from its sulfide ores
US4061552A (en) * 1975-02-14 1977-12-06 Dextec Metallurgical Proprietary Limited Electrolytic production of copper from ores and concentrates
US4272341A (en) * 1980-01-09 1981-06-09 Duval Corporation Process for recovery of metal values from lead-zinc ores, even those having a high carbonate content
US4734171A (en) * 1984-04-10 1988-03-29 In-Situ, Inc. Electrolytic process for the simultaneous deposition of gold and replenishment of elemental iodine

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1528207A (en) * 1923-04-02 1925-03-03 William E Greenawalt Metallurgical process
US2894804A (en) * 1949-03-02 1959-07-14 Carl W Sawyer Process of extracting uranium and radium from ores
US3901776A (en) * 1974-11-14 1975-08-26 Cyprus Metallurg Process Process for the recovery of copper from its sulfide ores
US4061552A (en) * 1975-02-14 1977-12-06 Dextec Metallurgical Proprietary Limited Electrolytic production of copper from ores and concentrates
US4272341A (en) * 1980-01-09 1981-06-09 Duval Corporation Process for recovery of metal values from lead-zinc ores, even those having a high carbonate content
US4734171A (en) * 1984-04-10 1988-03-29 In-Situ, Inc. Electrolytic process for the simultaneous deposition of gold and replenishment of elemental iodine

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015000002A1 (fr) * 2013-07-04 2015-01-08 Pureox Industrieanlagenbau Gmbh Procédé d'oxydation électrochimique de solutions de chlorure de fe2+

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