WO2012156894A2 - Membrane solvent extraction process - Google Patents

Membrane solvent extraction process Download PDF

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Publication number
WO2012156894A2
WO2012156894A2 PCT/IB2012/052391 IB2012052391W WO2012156894A2 WO 2012156894 A2 WO2012156894 A2 WO 2012156894A2 IB 2012052391 W IB2012052391 W IB 2012052391W WO 2012156894 A2 WO2012156894 A2 WO 2012156894A2
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WIPO (PCT)
Prior art keywords
metal
leach
permeate
retentate
solution
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PCT/IB2012/052391
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French (fr)
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WO2012156894A3 (en
Inventor
Johannes Petrus Willem VAN DER WESTHUYSEN
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Synexus (Pty) Ltd
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Publication of WO2012156894A2 publication Critical patent/WO2012156894A2/en
Publication of WO2012156894A3 publication Critical patent/WO2012156894A3/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/24—Dialysis ; Membrane extraction
    • B01D61/246—Membrane extraction
    • B01D61/2461—Membrane extraction comprising multiple membrane extraction steps
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/58—Multistep processes
    • 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
    • C22B60/0252—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes treatment or purification of solutions or of liquors or of slurries
    • C22B60/026—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes treatment or purification of solutions or of liquors or of slurries liquid-liquid extraction with or without dissolution in organic solvents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/027—Nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/145—Ultrafiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/147—Microfiltration

Definitions

  • the present invention relates to a membrane solvent extraction process.
  • the present invention relates to a membrane solvent extraction process for extracting metals in particular uranium.
  • uranium Whilst uranium has been used since the early 1940's up to the end of the Cold War almost exclusively for the production of nuclear weapons, the direct use of uranium for military is currently depleted uranium, for armour-piercing projectiles, ballast for missile re-entry vehicles, etc. Almost all the uranium mined today is used as enriched uranium as the thermal power source in nuclear power plants.
  • Uranium recovery involves both open pit (shallow orebodies) and underground (deeper orebodies) mining methods. Ore preparation involves crushing and grinding of the ore and/or agglomeration, often with radiometric pre-sorting, or other pre-concentration methods like flotation of gravity concentration methods.
  • uranium is extracted by heap leach, and for unconsolidated ores, by in-situ leaching.
  • Slurry leach for high grade ores, is conducted at ambient or elevated temperatures, at atmospheric conditions in cascading tanks or at elevated pressure in autoclaves.
  • the leach solution can be alkaline or acidic.
  • barren rock and other undissolved minerals from the leach process are separated from the uranium-rich solution (or pregnant liquor solution (PLS)) in a solid :liquid separation circuit, washed and discarded as tailings.
  • PLS pregnant liquor solution
  • Solid:liquid separation typically uses high rate gravity thickeners, often in a multi-stage counter- current decantation layout, or filtration systems like belt, drum or disk filters.
  • IX ion-exchange
  • SX solvent-exchange
  • IX and SX can be used either as standalone extraction technologies, or (and often) in combination.
  • the flow configurations for IX include resin-in-pulp (RIP), fixed-bed ion exchange (FBIX), continuous counter-current ion exchange (CCIX), etc.
  • solvent extraction SX includes variations like pulsed columns or mixer settler designs.
  • Uranium bearing ore contain impurities such as iron, manganese, magnesium, zinc, aluminium, silicon, chromium, chloride, copper, barium, vanadium, cadmium, etc.. These impurities are usually taken up into the PLS with the uranium value metal. While IX and/or SX are relatively selective in extracting uranium from the PLS, a percentage of these impurities are co-extracted and impacts on the final uranium oxide quality. Therefore, IX and/or SX extraction processes are often followed by a purification sequence to remove impurities. Uranium is recovered from the uranium rich solution produced by IX and/or SX processes by chemical precipitation often as an ammonium di-uranate. The precipitate is thickened, washed and de-watered and calcined to produce a mixed uranium oxide product, referred to as yellowcake of ⁇ 99% U 3 0 8 or 85% uranium by mass.
  • impurities such as iron, manga
  • IX and/or SX processes are not without their problems.
  • the hydraulic flow rates for PLS, especially for heap leach operations, are very high requiring large IX and/or SX plants with associated high CAPEX and OPEX to treat these flows.
  • plant CAPEX (and OPEX) is further affected by the highly corrosive environment.
  • Clarified leach liquors containing less than 40ppm of suspended solids, are essential to minimise crud formation in SX circuits.
  • a membrane solvent extraction process includes the steps
  • the leach solution may be a heap leach, atmospheric leach, pressure other leach or pregnant leach solution or mother liquor, and/or a washate or wash solution (from a ripios circuit).
  • the leach solution may be acidic or alkaline.
  • the metal may be uranium, base, precious or other energy metals.
  • the first extractant may comprise a mixture of an active organic extractant such as a tertiary amine (such as Alamine), with or without an organic diluent (such as Shellsol), with or without a phase modifier (such as isodecanol).
  • the first extractant is recirculated. It is bled off and replenished as needed to maintain reactivity.
  • the first scrub solution may be a weak (sulphuric) acid solution at pH ⁇ 2.8. It is recirculated, with bled off and replenishment as needed to maintain reactivity.
  • the first strip solution may be a sulphuric acid solution at ⁇ 40% strength, or a sodium carbonate solution at ⁇ 1.6M. It is recirculated, with bled off and replenishment as needed to maintain reactivity.
  • the first retentate may be returned to the pregnant leach solution or to the leach process.
  • the second permeate may be fortified with leach reagents and returned to leach.
  • the third retentate may be returned to leach (and that from the ripios back to wash/ripios or leach) or both may be returned to leach.
  • the arrangement may include both the first and second pre-treatment steps, only the first pre-treatment step or only the second pre-treatment step, or none at all.
  • the arrangement may include one or more membrane solvent extraction units, one or more membrane scrub units and one or more membrane strip units.
  • All of the membrane solvent extraction units, membrane scrub units and membrane strip units include internal recirculation, at a ratio specific to the leach stream chemistry and type of metal.
  • the feed pump arrangement of all the membrane solvent extraction units, membrane scrub units and membrane strip units may include internal recirculation, at a ratio specific to the leach stream chemistry and type of metal and very high impeller tip speeds to improve mass transfer (and thus extraction, scrub and strip kinetics).
  • the membranes of the membrane solvent extraction units, membrane scrub units and membrane strip units may include polymeric or ceramic membranes or a combination thereof.
  • the metal recovering unit may be a uranium recovering unit.
  • the process may be used to extract and concentrate uranium from a pregnant leach stream and to provide a clean concentrated feed solution to a downstream uranium product recovery circuit.
  • the process may be used to extract and concentrate uranium from a pregnant leach stream as well as a washate (from ripios circuit) providing a means for both leach solution and uranium recovery from the pregnant leach and the washate.
  • a metal extraction process arrangement includes
  • a microfiltration plant for removing suspended solids from a pregnant leach solution including at least one metal and to form a first retentate including the solids and a first permeate including the metal;
  • an acid recovering unit for recovering acid from the fourth permeate in to form a fifth permeate and a fifth retentate including the metal which is treated in a metal recovering unit.
  • the metal may be uranium.
  • the metal recovering unit may be a uranium recovering unit.
  • the metal may be base, precious and/or other energy metals from similar or other leach or mother liquors.
  • the process may be used to extract and concentrate uranium from a pregnant leach stream and to provide a clean concentrated feed solution to a downstream uranium product recovery circuit.
  • the first retentate may be returned to the pregnant leach solution.
  • the second permeate may be fortified with acid and returned to leach.
  • the arrangement may include two or more membrane solvent extraction units.
  • the aqueous phase may contain traces of organic compounds.
  • Figure 1 A conceptual design for a typical membrane solvent extraction process in accordance with the invention
  • FIG. 1 A conceptual design for a typical membrane solvent extraction process in accordance with the invention without flow of a washate (ripios) circuit;
  • FIG. 1 A conceptual design for a typical membrane solvent extraction process in accordance with the invention with flow of a washate (ripios) circuit.
  • the drawing illustrates a conceptual process flow diagram (PFD) of a conceptual design for a typical membrane solvent extraction process plant properly integrated for the recovery and concentration of uranium from a conventional acid heap leach uranium operation.
  • PFD process flow diagram
  • the flow diagram also show how the process in integrated with acid from the final washate (ripios) circuit, but these stream have been assigned zero hydraulic flow values.
  • a sulphuric acid solution of ⁇ 50g 6 is used for the heap leach operation.
  • the pregnant leach solution (PLS) from the heap leach pond with a uranium concentration of ⁇ 200mg 6 is pumped (pump not shown) at a rate of ⁇ l,000m 3 /hr to a microfiltration plant (MF01).
  • the purpose of the MF01 is to remove suspended solids to pre-treat the PLS to the desired NTU prior to acid recovery in the acid recovery nano- filtration plant (NFOl).
  • MF01 is designed with special acid stable high flux membranes.
  • the molecular weight cut-off (MWCO) of these membranes is ⁇ 0.1 ⁇ allowing fluxes of some ⁇ 50 to 100LMH.
  • MF01 recovers ⁇ 97% or ⁇ 970m 3 /hr of the PLS feed as permeate.
  • the retentate of ⁇ 30m 3 /hr is returned to the PLS pond (or could be returned to the heap).
  • NFOl is designed with special acid stable high flux membranes.
  • the MWCO of these membranes is in the ⁇ 200 to 600Da range allowing average fluxes of some ⁇ 10 to 25LMH.
  • the hydraulic recovery in NFOl is ⁇ 80% (to ⁇ 95%), thus from a feed of ⁇ 970m 3 /hr, the flow rate of the permeate is ⁇ 776m 3 /hr with a uranium concentration of ⁇ lmg 6 and an acid concentration ⁇ 40g 6.
  • the permeate (recovered acid reagent) is returned to the heap leach circuit. Because of the quality of acid so recovered, the leach kinetics are enhanced compared to similar leach operations.
  • Sulphuric acid recovery by NF01 is ⁇ 80% (to ⁇ 92%) (wt/wt).
  • UF01 is designed with acid stable membranes.
  • the MWCO of these membranes is in the ⁇ 1,000 to 50kDa range allowing average fluxes of some ⁇ 40 to 300LMH.
  • the flow rate of the retentate stream 31from UF01 is ⁇ 175m 3 /hr with a uranium concentration of ⁇ lg 6 and an acid concentration ⁇ 40g 6 which proceeds to the MSX circuit.
  • the retentate of ⁇ 19m 3 /hr is returned to the heap.
  • the MSX circuit comprises two membrane uranium solvent extraction units MSX1 and MSX2.
  • the MSX units function as a two-stage high rate solvent extraction system. These units are operated in counter-current flow with the organic solvent or extractant (where relevant) referred to as the organic phase.
  • this organic phase comprises a mixture of an active organic extractant like a tertiary amine, modifiers like iso-decanol (to assist in phase break) and a diluent like paraffin (about 20% aromaticity).
  • this organic phase comprises a mixture of an active organic extractant like a tertiary amine, with paraffin like Shellsol as diluent, but a modifier is not necessarily required,.
  • Stream 31 (plus stream 29 from the ripios circuit), referred to as the aqueous phase with a flow rate of ⁇ 175m 3 /hr, and the partially loaded organic phase from MSX1, stream 6 with a flow rate of ⁇ 388m 3 /hr, enters a pump (not shown).
  • This pump is a high speed device designed to function as both a pump and a high rate mass transfer device. This arrangement realises very high extraction kinetics of dissolved uranium from the aqueous PLS phase to the organic phase, within seconds, achieved by crating a high shear within the pump volute, high impeller tips speeds and recirculation to achieve the desired organic to aqueous ratio..
  • stream 7 with a flow rate of ⁇ 563m 3 /hr is mixed with the organic phase recirculation stream to MSX2, stream 9, before entering MSX2 at a combined flow rate of ⁇ 951m 3 /hr (stream 8).
  • MSX2 is operated with internal organic phase recirculation of some 100% (vol/vol) (of the organic phase feed), variable to suit the specific extraction conditions. MSX2 achieves separation of the organic (now loaded with uranium) from the aqueous phase. MSX2 is designed with special acid stable hydrophilic membranes. The molecular weight cut-off of these membranes (MWCO) is in the ⁇ l,500Da to 25kDa range, allowing high fluxes.
  • MWCO molecular weight cut-off of these membranes
  • MSX2 Permeate from MSX2 passes to a second membrane solvent extraction unit in series with MSX1 and operated in similar fashion to MSX2.
  • MSX2 is the second and final uranium extraction step from the aqueous phase (PLS). For certain applications, less or more extraction steps may be necessary.
  • MScrb membrane scrub circuit
  • a weak acid solution at pH ⁇ 2.8 a weak acid solution at pH ⁇ 2.8.
  • species such as iron, zirconium, molybdenum, etc. partially load with uranium and have to scrubbed, in at least a single scrub stage. Weak acid at pH ⁇ 2.8 is typically used.
  • This pump is a high shear rate pump arrangement similar to the feed pumps to MSX1/2. This pump together with high recirculation (variable to optimise scrubbing), realises very high scrub efficiencies.
  • MScrb is designed with special acid stable high flux membranes. The MWCO of these membranes is in the ⁇ 200 to 600Da range allowing average fluxes of some ⁇ 10 to 25LMH.
  • the hydraulic separation efficiency of separation in MScrb is almost 100%, thus from the organic phase feed of ⁇ 388m 3 /hr, a final retentate stream 19 with a flow rate of ⁇ 388m 3 /hr is recovered.
  • the permeate stream 35 is bleed, based on contamination levels and recirculated to leach.
  • the retentate from MScrb i.e. the uranium loaded scrubbed organic phase, is then stripped in a separate membrane strip circuit (MStrp) using sulphuric acid solution at ⁇ 40% strength, alternatively (depending on downstream uranium recovery as either ADU or SDU), using sodium carbonate solution at ⁇ 1.6M.
  • MStrp membrane strip circuit
  • This pump is a high shear rate pump arrangement similar to the feed pumps to MSX1/2.
  • MStrp This pump together with high recirculation (variable to optimise stripping), realises very high strip efficiencies.
  • the exit from the feed pump stream 20 enters MStrp at a combined flow rate of ⁇ 563m 3 /hr.
  • MStrp is designed with special acid stable high flux membranes.
  • the MWCO of these membranes is in the ⁇ 200 to 600Da range allowing average fluxes of some ⁇ 10 to 25LMH.
  • MRec is designed with special acid stable high flux membranes.
  • the MWCO of these membranes is in the ⁇ 200 to 600Da range allowing fluxes of some ⁇ 10 to 25LMH.
  • the hydraulic recovery in MRec is ⁇ 87.5%, thus from a feed of ⁇ 29m 3 /hr, the flow rate of the permeate is ⁇ 25m 3 /hr with a uranium concentration of ⁇ lmg 6 and an acid concentration ⁇ 40g 6.
  • the permeate is returned to the heap leach circuit.
  • the flow rate of the retentate stream 23 from MAR1 is ⁇ 4m 3 /hr with a uranium concentration of ⁇ 995mg 6 and an acid concentration of ⁇ 35g 6 which proceeds downstream to the uranium recovery/precipitation circuit.
  • Sulphuric acid recovery by MRec is ⁇ 80% (to ⁇ 95%) (wt/wt).
  • the invention has its application in the mining sector, in its current form, the extraction of dissolved uranium from leach liquors.
  • the invention is almost certain to have application for the extraction of base, precious and other energy metals from similar or other leach or mother liquors, using perhaps different extractants or configuration, yet the same principle of this invention.
  • the membrane solvent extraction process according to the invention thus provides a new method to extract and concentrate uranium from leach liquor, to provide a clean concentrated feed solution to the downstream uranium product recovery circuit, while at the same time provide a means to recovery both uranium, and, acid from a final washate or ripios circuit, and compared to other known methods:
  • Acid (reagent) recovered is cleaner and thus offer more effective leach characteristics when returned/reused in leach; ⁇ A significantly smaller plant footprint with its associated cost benefits;
  • This invention offers an alternative for a more cost effective uranium extraction process, while at the same time reducing reagent usage (through recovery) and thus impacts on the environment, higher product quality and thus less intensive downstream purification, minimising process hazards, etc.
  • the first extractant comprises a mixture of an active organic extractant such as a tertiary amine (such as Alamine), with or without an organic diluent (such as Shellsol), with or without a phase modifier (such as isodecanol), the issue is that the invention does not need as much diluent compared to conventional SX) or modifier (for phase separation), as separation is achieved by membrane and not the organic aqueous interface (gravity separation). This is also the reason that an emulsion may be created, which is strictly avoided in conventional SX due to the inability to separate the emulsion (containing the metal) from the aqueous phase).
  • an active organic extractant such as a tertiary amine (such as Alamine)
  • an organic diluent such as Shellsol
  • phase modifier such as isodecanol

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Abstract

The invention discloses a metal extraction process and arrangement therefore which includes a microfiltration plant for removing suspended solids from a pregnant leach solution including a metal to form a first retentate including the solids and a first permeate including the metal; a nanofiltration plant for recovering acid from the first permeate to form a second retentate including the metal and a second permeate; a membrane solvent extraction unit for extracting the metal from the second permeate to form a third retentate being an organic phase including the metal and third permeate being an aqueous phase; a membrane acid strip unit for stripping the third retentate to form a fourth retentate and a fourth permeate including the metal; an acid recovering unit for recovering acid from the fourth permeate to form a fifth permeate and a fifth retentate including the metal which is treated in a metal recovering unit.

Description

Membrane solvent extraction process
FIELD OF INVENTION
The present invention relates to a membrane solvent extraction process.
More particularly, the present invention relates to a membrane solvent extraction process for extracting metals in particular uranium.
BACKGROUND TO INVENTION
Whilst uranium has been used since the early 1940's up to the end of the Cold War almost exclusively for the production of nuclear weapons, the direct use of uranium for military is currently depleted uranium, for armour-piercing projectiles, ballast for missile re-entry vehicles, etc. Almost all the uranium mined today is used as enriched uranium as the thermal power source in nuclear power plants.
The World Nuclear Organisation reported that the global uranium mining production in 2010 was the equivalent of 63,285 tonne triuranium octaoxide. This is about 78% of world demand, mostly for reactor fuel requirements. The shortfall in demand is mostly met from highly enriched uranium declared surplus to military requirements by the USA and Russia that is being converted into fuel for commercial nuclear reactors. In 1993, the USA agreed to purchasing from Russia a minimum of 500t (the equivalent of ±140,000 to 150,000 tonne natural uranium from mines) of this material over a 20 year period. When this contract expires in 2013 a further increase in the uranium demand supply gap could be expected.
The above, plus a proliferation in nuclear power to meet the world's growing energy demands, for example, according to the World Nuclear Organisation, by 1 April 2011, 440 nuclear power plants were in operation, 61 were under construction, 158 were approved with funding and major commitments in place, while another 326 are being proposed (specific programs or site proposals in place), equating to a world uranium demand of some 68,971 tonne uranium from mines or 81,338 tonne triuranium octaoxide, would see a further impact on the shortfall in uranium supply from mining. As a result, there has been growing activity in preparing to open new mines in many countries. Notwithstanding that growing demand, technology development, particularly more cost effective uranium extraction and recovery technologies, has been lagging behind. The present mining steps include:
• Mining and ore/feed preparation;
• Leaching;
• Solid liquid separation; and
• Uranium recovery. Uranium mining involves both open pit (shallow orebodies) and underground (deeper orebodies) mining methods. Ore preparation involves crushing and grinding of the ore and/or agglomeration, often with radiometric pre-sorting, or other pre-concentration methods like flotation of gravity concentration methods.
There are various ways to extract or liberate uranium from uranium containing ores, the choice of which is dependent on the type and grade of ore. Generally, for low grade ores uranium is extracted by heap leach, and for unconsolidated ores, by in-situ leaching. Slurry leach, for high grade ores, is conducted at ambient or elevated temperatures, at atmospheric conditions in cascading tanks or at elevated pressure in autoclaves. The leach solution can be alkaline or acidic. Following slurry leaching, barren rock and other undissolved minerals from the leach process are separated from the uranium-rich solution (or pregnant liquor solution (PLS)) in a solid :liquid separation circuit, washed and discarded as tailings. Solid:liquid separation typically uses high rate gravity thickeners, often in a multi-stage counter- current decantation layout, or filtration systems like belt, drum or disk filters. There are mainly two technologies used for the extraction of uranium from the PLS, namely ion-exchange (IX) and solvent-exchange (SX). Depending on a number of factors, IX and SX can be used either as standalone extraction technologies, or (and often) in combination. The flow configurations for IX include resin-in-pulp (RIP), fixed-bed ion exchange (FBIX), continuous counter-current ion exchange (CCIX), etc. and for solvent extraction (SX) includes variations like pulsed columns or mixer settler designs. By enlarge, these processes are aimed at selective extraction and concentration of the dissolved uranium from the PLS, to provide a relatively clean, low volume, high uranium concentration stream as feed to final uranium recovery circuit.
Uranium bearing ore contain impurities such as iron, manganese, magnesium, zinc, aluminium, silicon, chromium, chloride, copper, barium, vanadium, cadmium, etc.. These impurities are usually taken up into the PLS with the uranium value metal. While IX and/or SX are relatively selective in extracting uranium from the PLS, a percentage of these impurities are co-extracted and impacts on the final uranium oxide quality. Therefore, IX and/or SX extraction processes are often followed by a purification sequence to remove impurities. Uranium is recovered from the uranium rich solution produced by IX and/or SX processes by chemical precipitation often as an ammonium di-uranate. The precipitate is thickened, washed and de-watered and calcined to produce a mixed uranium oxide product, referred to as yellowcake of ±99% U308 or 85% uranium by mass.
IX and/or SX processes, are not without their problems. The hydraulic flow rates for PLS, especially for heap leach operations, are very high requiring large IX and/or SX plants with associated high CAPEX and OPEX to treat these flows. Where acidic leach solutions are used, plant CAPEX (and OPEX) is further affected by the highly corrosive environment.
In both alkaline and acidic leach solutions, impurities such as chloride, etc. taken up into the PLS with uranium, compete with uranium for adsorption by IX resins, some times to the extent where significantly larger resin inventories, hydraulic capacity, unnecessary large reagent use (e.g. for elution or reactivation), etc need to be provided for, again affecting both CAPEX and OPEX, and final product quality. Design parameters for SX extraction plants are constrained by the organic extractant to aqueous flow ratio, an upper mass transfer rate of uranium transport from the dissolved aqueous solution (PLS) to the organic extractant beyond which a further increase in the mass transfer rate leads to emulsions and downstream phase separation problems, etc. Due to its solubility, organic solvent is lost via the aqueous phase. While organic losses cannot be eliminated altogether, current SX technology, does not provide any means to lower organic losses below that of the solubility concentration.
Conventional SX plants are prone to fires, that could cause significant plant damage and environmental pollution. Clarified leach liquors, containing less than 40ppm of suspended solids, are essential to minimise crud formation in SX circuits.
Both conventional IX and SX plant does not allow for the recovery of a purified leach solution (or leach reagent), not the simultaneous recovery of both leach reagent and uranium, from a washate (tailings) or ripios circuit It is an object of the invention to suggest a membrane solvent extraction process method which will assist in overcoming the aforesaid and other obstacles to provide a more economical and safer process flowsheet or method for extracting uranium from leach liquors prior to final recovery
SUMMARY OF INVENTION According to the invention, a membrane solvent extraction process includes the steps
(a) of a first pre-treatment step of a leach solution including at least one target metal species by means of a microfiltration plant to form a first retentate including the unwanted suspended solids and other matter and a first permeate at the desire NTU or SDI and including the metal; (b) of recovering leach solution (leach reagent) from the first permeate by means of a nano-filtration plant to form a second retentate including the metal and a second permeate including the reagent solution; (c) of, depending on the propensity of crud formation in the MSX circuit, an optional second pre-treatment step of the second retentate by means of a ultra-filtration plant, removing silica (and other crud forming species) to form a third retentate including the unwanted species and a third permeate including the metal;
(d) of extracting the metal from the third permeate by means of a first extractant in at least one membrane solvent extraction unit to form a fourth retentate being an organic phase including the metal and fourth permeate being an aqueous phase; (e) of scrubbing the fourth retentate by means of a first scrub solution in at least one membrane scrub unit to form a fifth retentate being an organic phase including the extractant and the metal and a fifth permeate being an aqueous phase solution;
(f) of stripping the metal from fifth retentate by means of a first strip solution in at least one membrane strip unit to form a sixth retentate and a sixth permeate including the metal;
(g) of recovering the first strip solution (reagent) from the sixth permeate in a membrane recovering unit to form a seventh retentate including the metal and a seventh permeate; and (h) of recovering the seventh retentate in a metal recovering unit.
The leach solution may be a heap leach, atmospheric leach, pressure other leach or pregnant leach solution or mother liquor, and/or a washate or wash solution (from a ripios circuit).
The leach solution (leach reagent) may be acidic or alkaline. The metal may be uranium, base, precious or other energy metals. The first extractant may comprise a mixture of an active organic extractant such as a tertiary amine (such as Alamine), with or without an organic diluent (such as Shellsol), with or without a phase modifier (such as isodecanol).
The first extractant is recirculated. It is bled off and replenished as needed to maintain reactivity.
The first scrub solution may be a weak (sulphuric) acid solution at pH ±2.8. It is recirculated, with bled off and replenishment as needed to maintain reactivity.
Depending on downstream uranium recovery as either ADU or SDU, the first strip solution may be a sulphuric acid solution at ±40% strength, or a sodium carbonate solution at ±1.6M. It is recirculated, with bled off and replenishment as needed to maintain reactivity.
The first retentate may be returned to the pregnant leach solution or to the leach process.
The second permeate may be fortified with leach reagents and returned to leach. The third retentate may be returned to leach (and that from the ripios back to wash/ripios or leach) or both may be returned to leach.
The arrangement may include both the first and second pre-treatment steps, only the first pre-treatment step or only the second pre-treatment step, or none at all.
The arrangement may include one or more membrane solvent extraction units, one or more membrane scrub units and one or more membrane strip units.
All of the membrane solvent extraction units, membrane scrub units and membrane strip units, include internal recirculation, at a ratio specific to the leach stream chemistry and type of metal.
The feed pump arrangement of all the membrane solvent extraction units, membrane scrub units and membrane strip units, may include internal recirculation, at a ratio specific to the leach stream chemistry and type of metal and very high impeller tip speeds to improve mass transfer (and thus extraction, scrub and strip kinetics).
The membranes of the membrane solvent extraction units, membrane scrub units and membrane strip units may include polymeric or ceramic membranes or a combination thereof.
The metal recovering unit may be a uranium recovering unit.
The process may be used to extract and concentrate uranium from a pregnant leach stream and to provide a clean concentrated feed solution to a downstream uranium product recovery circuit. The process may be used to extract and concentrate uranium from a pregnant leach stream as well as a washate (from ripios circuit) providing a means for both leach solution and uranium recovery from the pregnant leach and the washate.
Also according to the invention, a metal extraction process arrangement includes
(a) a microfiltration plant for removing suspended solids from a pregnant leach solution including at least one metal and to form a first retentate including the solids and a first permeate including the metal;
(b) a nanofiltration plant for recovering acid from the first permeate to form a second retentate including the metal and a second permeate;
(c) at least one membrane solvent extraction unit for extracting the metal from the second permeate to form a third retentate being an organic phase including the metal and third permeate being an aqueous phase;
(d) at least one membrane acid strip unit for stripping the third retentate to form a fourth retentate and a fourth permeate including the metal; and
(e) an acid recovering unit for recovering acid from the fourth permeate in to form a fifth permeate and a fifth retentate including the metal which is treated in a metal recovering unit. The metal may be uranium.
The metal recovering unit may be a uranium recovering unit.
The metal may be base, precious and/or other energy metals from similar or other leach or mother liquors. The process may be used to extract and concentrate uranium from a pregnant leach stream and to provide a clean concentrated feed solution to a downstream uranium product recovery circuit.
The first retentate may be returned to the pregnant leach solution. The second permeate may be fortified with acid and returned to leach. The arrangement may include two or more membrane solvent extraction units. The aqueous phase may contain traces of organic compounds. BRIEF DESCRIPTION OF DRAWINGS
The invention will now be described by way of example with reference to the accompanying schematic drawings. I n the drawings there is shown in
Figure 1: A conceptual design for a typical membrane solvent extraction process in accordance with the invention;
Figure A conceptual design for a typical membrane solvent extraction process in accordance with the invention without flow of a washate (ripios) circuit; and
Figure A conceptual design for a typical membrane solvent extraction process in accordance with the invention with flow of a washate (ripios) circuit. DETAILED DESCRIPTION OF DRAWING
Referring to the drawings, a membrane solvent extraction process in accordance with the invention is shown.
The drawing illustrates a conceptual process flow diagram (PFD) of a conceptual design for a typical membrane solvent extraction process plant properly integrated for the recovery and concentration of uranium from a conventional acid heap leach uranium operation. For illustration purposes, the flow diagram also show how the process in integrated with acid from the final washate (ripios) circuit, but these stream have been assigned zero hydraulic flow values. A sulphuric acid solution of ±50g 6 is used for the heap leach operation.
Acid recovery from leach
The pregnant leach solution (PLS) from the heap leach pond with a uranium concentration of ±200mg 6 is pumped (pump not shown) at a rate of ±l,000m3/hr to a microfiltration plant (MF01). The purpose of the MF01 is to remove suspended solids to pre-treat the PLS to the desired NTU prior to acid recovery in the acid recovery nano- filtration plant (NFOl). MF01 is designed with special acid stable high flux membranes. The molecular weight cut-off (MWCO) of these membranes is ±0.1μιη allowing fluxes of some ±50 to 100LMH.
MF01 recovers ±97% or ±970m3/hr of the PLS feed as permeate. The retentate of ±30m3/hr is returned to the PLS pond (or could be returned to the heap).
The permeate from MF01 is then pumped (pump not shown) as feed to NFOl for acid recovery. NFOl is designed with special acid stable high flux membranes. The MWCO of these membranes is in the ±200 to 600Da range allowing average fluxes of some ±10 to 25LMH. The hydraulic recovery in NFOl is ±80% (to ±95%), thus from a feed of ±970m3/hr, the flow rate of the permeate is ±776m3/hr with a uranium concentration of ±lmg 6 and an acid concentration ±40g 6. The permeate (recovered acid reagent) is returned to the heap leach circuit. Because of the quality of acid so recovered, the leach kinetics are enhanced compared to similar leach operations. Sulphuric acid recovery by NF01 is ±80% (to ±92%) (wt/wt).
Depending on the propensity of crud formation in the MSX circuit, the retentate from NF01 is then pumped (pump not shown) as feed to an UF01 as pre-treatment for (mainly) silica (and other crud forming species) removal. UF01 is designed with acid stable membranes. The MWCO of these membranes is in the ±1,000 to 50kDa range allowing average fluxes of some ±40 to 300LMH.
The flow rate of the retentate stream 31from UF01 is ±175m3/hr with a uranium concentration of ±lg 6 and an acid concentration ±40g 6 which proceeds to the MSX circuit. The retentate of ±19m3/hr is returned to the heap.
The MSX circuit - extraction
The MSX circuit comprises two membrane uranium solvent extraction units MSX1 and MSX2. The MSX units function as a two-stage high rate solvent extraction system. These units are operated in counter-current flow with the organic solvent or extractant (where relevant) referred to as the organic phase.
In conventional SX, this organic phase comprises a mixture of an active organic extractant like a tertiary amine, modifiers like iso-decanol (to assist in phase break) and a diluent like paraffin (about 20% aromaticity). Other than in conventional SX, this organic phase comprises a mixture of an active organic extractant like a tertiary amine, with paraffin like Shellsol as diluent, but a modifier is not necessarily required,.
Stream 31 (plus stream 29 from the ripios circuit), referred to as the aqueous phase with a flow rate of ±175m3/hr, and the partially loaded organic phase from MSX1, stream 6 with a flow rate of ±388m3/hr, enters a pump (not shown). This pump is a high speed device designed to function as both a pump and a high rate mass transfer device. This arrangement realises very high extraction kinetics of dissolved uranium from the aqueous PLS phase to the organic phase, within seconds, achieved by crating a high shear within the pump volute, high impeller tips speeds and recirculation to achieve the desired organic to aqueous ratio.. As a result, a complete emulsion is formed (which incidentally is exactly what is avoided with conventional SX). The exit from the pump, stream 7 with a flow rate of ±563m3/hr is mixed with the organic phase recirculation stream to MSX2, stream 9, before entering MSX2 at a combined flow rate of ±951m3/hr (stream 8).
MSX2 is operated with internal organic phase recirculation of some 100% (vol/vol) (of the organic phase feed), variable to suit the specific extraction conditions. MSX2 achieves separation of the organic (now loaded with uranium) from the aqueous phase. MSX2 is designed with special acid stable hydrophilic membranes. The molecular weight cut-off of these membranes (MWCO) is in the ±l,500Da to 25kDa range, allowing high fluxes.
Permeate from MSX2 passes to a second membrane solvent extraction unit in series with MSX1 and operated in similar fashion to MSX2. MSX2 is the second and final uranium extraction step from the aqueous phase (PLS). For certain applications, less or more extraction steps may be necessary.
The hydraulic separation efficiency in both MSX2 and MSX is almost 100%, thus from a feed to the MSX process train of ±175m3/hr, a final permeate steam 15 with a flow rate of ±175m3/hr is recovered with a uranium of less than lmg 6 and an acid concentration ±40g 6. Uranium extraction is thus ±99.5%. Because of the fairly open membranes being used in MSX2 and MSX1, dissolved impurities in the aqueous phase are is not reject by the membranes, and thus do not accumulate or create problems leading to crud formation. The permeate or raffinate is returned to the leach circuit. Using membrane as the separation step, loss of organic is with the aqueous phase is significantly reduce with organic in the <5ppm in the final permeate (stream 15). The MSX circuit - scrub
The retentate from MSX2, i.e. the uranium loaded organic phase, is then scrubbed in a separate membrane scrub circuit (MScrb) using a weak (sulphuric) acid solution at pH ~2.8. Using a tertiary amine as extractant, species such as iron, zirconium, molybdenum, etc. partially load with uranium and have to scrubbed, in at least a single scrub stage. Weak acid at pH ~2.8 is typically used.
The retentate from MSX2, stream 16 with a flow rate of ±388m3/hr and a weak acid solution at pH ~2.8, stream 18 with a flow rate of ±175m3/hr, enters Mscrb feed pump (not shown). This pump is a high shear rate pump arrangement similar to the feed pumps to MSX1/2. This pump together with high recirculation (variable to optimise scrubbing), realises very high scrub efficiencies. The exit from the feed pump stream 17 enters MScrb at a combined flow rate of ±563m3/hr. MScrb is designed with special acid stable high flux membranes. The MWCO of these membranes is in the ±200 to 600Da range allowing average fluxes of some ±10 to 25LMH.
The hydraulic separation efficiency of separation in MScrb is almost 100%, thus from the organic phase feed of ±388m3/hr, a final retentate stream 19 with a flow rate of ±388m3/hr is recovered. The permeate stream 35 is bleed, based on contamination levels and recirculated to leach. The MSX circuit - strip
The retentate from MScrb, i.e. the uranium loaded scrubbed organic phase, is then stripped in a separate membrane strip circuit (MStrp) using sulphuric acid solution at ±40% strength, alternatively (depending on downstream uranium recovery as either ADU or SDU), using sodium carbonate solution at ±1.6M. The retentate from MScrb, stream 19 with a flow rate of ±388m3/hr and a clean acid solution, stream 21 with a flow rate of ±175m3/hr, enters the feed pump (not shown) to MStrp. This pump is a high shear rate pump arrangement similar to the feed pumps to MSX1/2. This pump together with high recirculation (variable to optimise stripping), realises very high strip efficiencies. The exit from the feed pump stream 20 enters MStrp at a combined flow rate of ±563m3/hr. MStrp is designed with special acid stable high flux membranes. The MWCO of these membranes is in the ±200 to 600Da range allowing average fluxes of some ±10 to 25LMH.
The hydraulic separation efficiency of separation in MStrp is almost 100%, thus from the organic phase feed of ±388m3/hr, a final retentate stream 11 with a flow rate of almost ±388m3/hr is recovered with a uranium of less than lmg/β. This retentate, i.e. the stripped organic phase, is fed in recirculation mode back to MSX1. Uranium strip efficiency is ±99.5%.
Reagent recovery (MRec)
The MStrp permeate or strip solution, stream 22 with a flow rate of ±293/hr, advances to MRec, an acid (or alkaline) reagent recovery circuit.
MRec is designed with special acid stable high flux membranes. The MWCO of these membranes is in the ±200 to 600Da range allowing fluxes of some ±10 to 25LMH.
The hydraulic recovery in MRec is ±87.5%, thus from a feed of ±29m3/hr, the flow rate of the permeate is ±25m3/hr with a uranium concentration of ±lmg 6 and an acid concentration ±40g 6. The permeate is returned to the heap leach circuit.
The flow rate of the retentate stream 23 from MAR1 is ±4m3/hr with a uranium concentration of ±995mg 6 and an acid concentration of ±35g 6 which proceeds downstream to the uranium recovery/precipitation circuit. Sulphuric acid recovery by MRec is ±80% (to ±95%) (wt/wt).
The invention has its application in the mining sector, in its current form, the extraction of dissolved uranium from leach liquors. The invention is almost certain to have application for the extraction of base, precious and other energy metals from similar or other leach or mother liquors, using perhaps different extractants or configuration, yet the same principle of this invention. The membrane solvent extraction process according to the invention thus provides a new method to extract and concentrate uranium from leach liquor, to provide a clean concentrated feed solution to the downstream uranium product recovery circuit, while at the same time provide a means to recovery both uranium, and, acid from a final washate or ripios circuit, and compared to other known methods:
• Provides a more cost effective uranium extraction and concentration method;
• Acid (reagent) recovery from the leach liquor;
• Acid (reagent) recovered is cleaner and thus offer more effective leach characteristics when returned/reused in leach; · A significantly smaller plant footprint with its associated cost benefits;
• As it is a completely isolated/sealed process, does not pose fire hazards;
• Renders a purer uranium oxide product;
• Decreases organic inventory and thus "first fill" costs;
• Offers almost zero organic losses; · Permits simultaneous recovery of uranium and acid from a ripios circuit;
• Less environmental impact (ripios, organic losses, etc.).
This invention offers an alternative for a more cost effective uranium extraction process, while at the same time reducing reagent usage (through recovery) and thus impacts on the environment, higher product quality and thus less intensive downstream purification, minimising process hazards, etc.
Where the first extractant comprises a mixture of an active organic extractant such as a tertiary amine (such as Alamine), with or without an organic diluent (such as Shellsol), with or without a phase modifier (such as isodecanol), the issue is that the invention does not need as much diluent compared to conventional SX) or modifier (for phase separation), as separation is achieved by membrane and not the organic aqueous interface (gravity separation). This is also the reason that an emulsion may be created, which is strictly avoided in conventional SX due to the inability to separate the emulsion (containing the metal) from the aqueous phase).

Claims

PATENT CLAIMS
1. A membrane solvent extraction process, which includes the steps
(a) of a first pre-treatment step of a leach solution including at least one target metal species by means of a microfiltration plant to form a first retentate including the unwanted suspended solids and other matter and a first permeate at the desire NTU or SDI and including the metal;
(b) of recovering leach solution (leach reagent) from the first permeate by means of a nano-filtration plant to form a second retentate including the metal and a second permeate including the reagent solution;
(c) of, depending on the propensity of crud formation in the MSX circuit, an optional second pre-treatment step of the second retentate by means of a ultra-filtration plant, removing silica (and other crud forming species) to form a third retentate including the unwanted species and a third permeate including the metal;
(d) of extracting the metal from the third permeate by means of a first extractant in at least one membrane solvent extraction unit to form a fourth retentate being an organic phase including the metal and fourth permeate being an aqueous phase;
(e) of scrubbing the fourth retentate by means of a first scrub solution in at least one membrane scrub unit to form a fifth retentate being an organic phase including the extractant and the metal and a fifth permeate being an aqueous phase solution;
(f) of stripping the metal from fifth retentate by means of a first strip solution in at least one membrane strip unit to form a sixth retentate and a sixth permeate including the metal; (g) of recovering the first strip solution (reagent) from the sixth permeate in a membrane recovering unit to form a seventh retentate including the metal and a seventh permeate; and
(h) of recovering the seventh retentate in a metal recovering unit.
2. A process as claimed in claim 1, in which the leach solution is at least one selected from the group comprising a heap leach, an atmospheric leach, a pressure leach, a pregnant leach solution, a mother liquor, a washate and a wash solution from a ripios circuit.
3. A process as claimed in claim 1 or claim 2, in which the leach solution (leach reagent) is acidic or alkaline.
4. A process as claimed in any one of the preceding claims, in which the metal is uranium, base, precious and/or other energy metals.
5. A process as claimed in any one of the preceding claims, in which the first extractant comprises a mixture of an active organic extractant with or without an organic diluent and with or without a phase modifier.
6. A process as claimed in claim 5, in which the organic extractant is a tertiary amine.
7. A process as claimed in any one of the preceding claims, in which the first extractant is recirculated.
8. A process as claimed in claim 7, in which the first reactant is bled off and replenished as needed to maintain reactivity.
9. A process as claimed in any one of the preceding claims, in which the first scrub solution is a weak acid solution at pH ±2.8.
10. A process as claimed in claim 9, in which the first scrub is recirculated.
11. A process as claimed in claim 10, in which the first scrub is bled off and replenishment as needed to maintain reactivity.
12. A process as claimed in any one of the preceding claims, in which depending on downstream uranium recovery as either ADU or SDU, the first strip solution is a
5 sulphuric acid solution at ±40% strength, or a sodium carbonate solution at
±1.6M.
13. A process as claimed in claim 12, in which the first strip solution is recirculated.
14. A process as claimed in claim 13, in which the first strip solution is bled off and replenished as needed to maintain reactivity.
10 15. A process as claimed in any one of the preceding claims, in which the first retentate is returned to the pregnant leach solution or to the leach process.
16. A process as claimed in any one of the preceding claims, in which the second permeate is fortified with leach reagents and returned to leach.
17. A process as claimed in any one of the preceding claims, in which the third 15 retentate is returned to leach and that from the ripios back to wash/ripios or leach or both may be returned to leach.
18. A process as claimed in any one of the preceding claims, which is used to extract and concentrate uranium from a pregnant leach stream and to provide a clean concentrated feed solution to a downstream uranium product recovery circuit.
20 19. A process as claimed in any one of the preceding claims, which is used to extract and concentrate uranium from a pregnant leach stream as well as a washate from ripios circuit providing a means for both leach solution and uranium recovery from the pregnant leach and the washate.
20. A metal extraction process arrangement, which includes
(a) a microfiltration plant for removing suspended solids from a pregnant leach solution including at least one metal and to form a first retentate including the solids and a first permeate including the metal;
5 (b) a nanofiltration plant for recovering acid from the first permeate to form a second retentate including the metal and a second permeate;
(c) at least one membrane solvent extraction unit for extracting the metal from the second permeate to form a third retentate being an organic phase including the metal and third permeate being an aqueous phase;
10 (d) at least one membrane acid strip unit for stripping the third retentate to form a fourth retentate and a fourth permeate including the metal; and
(e) an acid recovering unit for recovering acid from the fourth permeate in to form a fifth permeate and a fifth retentate including the metal
15 which is treated in a metal recovering unit.
21. An arrangement as claimed in claim 20, in which the metal is uranium, base, precious and/or other energy metals from similar and/or other leach or mother liquors.
22. An arrangement as claimed in claim 20 or claim 21, in which the metal recovering
20 unit is a uranium recovering unit.
23. An arrangement as claimed in any one of claims 20 to 22, in which the first retentate is returned to the pregnant leach solution.
24. An arrangement as claimed in any one of claims 20 to 23, in which the second permeate is fortified with acid and returned to leach.
25 25. An arrangement as claimed in any one of claims 20 to 24, which includes two or more membrane solvent extraction units.
26. An arrangement as claimed in any one of claims 20 to 25, which includes both the first and second pre-treatment steps as claimed in claim 1, only the first pre- treatment step or only the second pre-treatment step, or none at all.
27. An arrangement as claimed in any one of claims 20 to 26, which includes at least 5 one membrane solvent extraction unit, at least one membrane scrub units and at least one membrane strip units.
28. An arrangement as claimed in claim 27, in which the membrane solvent extraction units, membrane scrub units and membrane strip units include internal recirculation at a ratio specific to the leach stream chemistry and type of
10 metal.
29. An arrangement as claimed in claim 27 or claim 28, in which the feed pump arrangement of all the membrane solvent extraction units, membrane scrub units and membrane strip units, includes internal recirculation at a ratio specific to the leach stream chemistry and type of metal and very high impeller tip
15 speeds to improve mass transfer.
30. An arrangement as claimed in any one of claims 27 to 29, in which the membranes of the membrane solvent extraction units, membrane scrub units and membrane strip units includes polymeric or ceramic membranes or a combination thereof.
20 31. An arrangement as claimed in any one of claims 20 to 30, in which the aqueous phase contains traces of organic compounds.
32. A membrane solvent extraction process substantially as hereinbefore described with reference to the accompanying drawings.
33. A metal extraction process arrangement substantially as hereinbefore described 25 with reference to the accompanying drawings.
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