EP3645759A1 - Séparation d'actinium à partir de liqueurs de traitement - Google Patents

Séparation d'actinium à partir de liqueurs de traitement

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Publication number
EP3645759A1
EP3645759A1 EP18823055.1A EP18823055A EP3645759A1 EP 3645759 A1 EP3645759 A1 EP 3645759A1 EP 18823055 A EP18823055 A EP 18823055A EP 3645759 A1 EP3645759 A1 EP 3645759A1
Authority
EP
European Patent Office
Prior art keywords
ions
actinium
solution
sulfate
precipitate
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.)
Pending
Application number
EP18823055.1A
Other languages
German (de)
English (en)
Other versions
EP3645759A4 (fr
Inventor
Chris Griffith
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.)
Australian Nuclear Science and Technology Organization
Original Assignee
Australian Nuclear Science and Technology Organization
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 AU2017902476A external-priority patent/AU2017902476A0/en
Application filed by Australian Nuclear Science and Technology Organization filed Critical Australian Nuclear Science and Technology Organization
Publication of EP3645759A1 publication Critical patent/EP3645759A1/fr
Publication of EP3645759A4 publication Critical patent/EP3645759A4/fr
Pending 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
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates
    • C01F11/462—Sulfates of Sr or Ba
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G21/00—Compounds of lead
    • C01G21/20—Sulfates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G99/00—Subject matter not provided for in other groups of this subclass
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C02F1/5245—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using basic salts, e.g. of aluminium and iron
    • 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
    • C22B3/12—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic alkaline solutions
    • 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
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical 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
    • C22B59/00—Obtaining rare earth metals
    • 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
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5209—Regulation methods for flocculation or precipitation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/006—Radioactive compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/10—Nature of the water, waste water, sewage or sludge to be treated from quarries or from mining activities

Definitions

  • the present invention relates to the separation of actinium from process liquors.
  • Actinium-227 is frequently present in mineral processing circuits. Its presence is the result of the decay of uranium-235, which may be associated, for example, with rare earth mineral deposits, either occurring in the rare earth mineral itself or otherwise associated with the process feed.
  • Actinium-227 is radioactive, with a half-life of approximately 22 years. It decays through ⁇ emission to thorium-227, which gives rise to further decay products.
  • Actinium contamination is a problem in mineral processing. While standard processing methods remove the majority of the sources of radioactivity present in mineral process feeds, due to its chemical similarity to, for example, the rare earth elements, actinium is not easily removed. Furthermore, regulatory authorities set restrictive limits on the amount of actinium activity that may be present in materials (for example the International Atomic Energy Agency sets a limit of 0.1 Bq/g (or 1.0 Bq/g), depending on the circumstances) for actinium activity, see e.g. IAEA Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards, Series No. GSR Part 3, 19 July 2014).
  • rare earth processing feeds may be processed either into individual rare earth products, which typically requires the use of solvent extraction, or into a mixed mineral concentrate, which typically does not require solvent extraction.
  • Solvent extraction can be used to remove actinium from rare earth process streams, however, as it is a costly step and involves extensive additional processing, it is best avoided if possible.
  • solvent extraction can be used to remove actinium from rare earth process streams, however, as it is a costly step and involves extensive additional processing, it is best avoided if possible.
  • solvent extraction can be used to remove actinium from rare earth process streams, however, as it is a costly step and involves extensive additional processing, it is best avoided if possible.
  • solvent extraction Using previously available technology, if a mixed concentrate is to be produced from a feedstock that is contaminated with actinium, it must be processed using solvent extraction, which would not otherwise be required for the production of a mixed concentrate.
  • An object of the present invention is the provision of a method of at least partially removing actinium from a feed solution which does not require solvent extraction.
  • a method of removing actinium from a solution comprising actinium ions and ions of interest comprising adding metal ions to said solution, a sulfate salt of which has a solubility in water at 20 °C of less than about 0.3 g/100 mL; wherein if the sulfate concentration of the solution is insufficient to cause the sulfate salt of the metal ions to precipitate, a water soluble source of sulfate ions is added to said solution until the sulfate salt of the metal ions precipitates; whereby a precipitate comprising actinium and the sulfate salt of the metal ions is formed and wherein a sufficient amount of metal ions is added to cause at least 40% of the actinium ions to precipitate.
  • the metal ions may be added in an amount of 0.01-100 mmol per Bq/L of activity of the solution. This may therefore be considered to be a sufficient amount of the metal ions.
  • the ions of interest may be rare earth ions.
  • the concentration of the ions of interest in the solution may be essentially unchanged by the method.
  • the actinium ions may be Ac-227 ions.
  • the actinium activity of the total dissolved ions of interest contained in said solution may be greater than about 1.0 Bq/g.
  • the metal ions may be divalent metal ions.
  • the metal may be selected from the group consisting of calcium, strontium, barium or lead. It may be strontium, or it may be lead, or it may be barium.
  • the metal ions may comprise a mixture of different metal ions, such as a mixture of barium ions and strontium ions.
  • the solution comprising actinium ions and ions of interest may be produced as a result of the processing of an ore or mineral concentrate containing the ions of interest.
  • the ions of interest may be of one or more rare earth elements selected from the group consisting of Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
  • the ore may comprise, or may be, monazite, xenotime, or a mixture thereof.
  • the ore or mineral concentrate may be such that if a mixed rare earth concentrate were to be produced from it without the removal of actinium, the actinium activity of the mixed rare earth concentrate would be greater than 1.0 Bq/g.
  • the ions of interest may not be rare earth ions, in this case, the ore or mineral concentrate may be, for example, an ore containing uranium.
  • the method may comprise a step of processing an ore or mineral concentrate using an acid cracking process so as to produce the solution comprising actinium ions and ions of interest.
  • the metal ions may be lead(II).
  • the lead(II) may be in the form of lead(II) chloride or lead(II) nitrate.
  • the method may alternatively comprise a step of processing an ore or mineral concentrate using an alkaline cracking process so as to produce the solution comprising actinium ions and ions of interest.
  • the metal ions may be strontium or barium, or a mixture thereof, which may be in the form of barium chloride and/or strontium chloride.
  • a water soluble source of sulfate ions may be added to said solution until the sulfate salt of the metal ions precipitates.
  • the water soluble source of sulfate ions may be selected from the group consisting of sulfuric acid, sodium sulfate, magnesium sulfate, or a combination of any two or all of these.
  • the molar ratio of sulfate ions to metal ions may be in the range of about 1 : 1 to about 1000: 1.
  • the solution may further comprise radium ions.
  • the metal ions are barium ions, or a mixture of strontium and barium ions. Strontium ions and barium ions may also be added sequentially, in either order.
  • the metal ions may be in the form of barium chloride and/or strontium chloride, and a precipitate comprising actinium ions, radium ions, and barium sulfate and/or strontium sulfate, may be formed.
  • a sufficient amount of metal ions may be added to cause at least 40% of the actinium ions to precipitate and at least 99% of the radium ions to precipitate.
  • the metal ions may be added to the solution in the form of a solid. They may be added in the form of an aqueous solution.
  • the water soluble source of sulfate ions may be added to the solution in the form of a solid. It may be added in the form of an aqueous solution.
  • the method may further comprise separating the precipitate from the solution.
  • the solution may have a reduced concentration of actinium or its actinium activity may be reduced or both.
  • the method may further comprise obtaining a solid mixed rare earth concentrate from the solution.
  • the solid rare earth concentrate may have an actinium activity of less than or equal to 1.0 Bq/g.
  • a method of removing actinium from a solution comprising actinium-227 ions and rare earth ions comprising adding to the solution lead chloride or strontium chloride; wherein if the sulfate concentration of the solution is insufficient to cause the sulfate salt of the lead or strontium to precipitate, a water soluble source of sulfate ions such as sodium sulfate, sulfuric acid, magnesium sulfate, or a combination of any two or all of these, is added to the solution until the sulfate salt of the lead or strontium precipitates; whereby a precipitate comprising actinium and the sulfate salt of the metal ions is formed.
  • a sufficient amount of metal ions is added to cause at least 40% of the actinium ions to precipitate.
  • a method of removing actinium from a solution comprising actinium-227 ions and rare earth ions comprising processing an ore or mineral concentrate using an acid cracking process so as to provide the solution comprising actinium ions and rare earth ions and adding to the solution lead(II) chloride, whereby a precipitate comprising lead(II) sulfate and actinium is formed.
  • a sufficient amount of metal ions is added to cause at least 40% of the actinium ions to precipitate.
  • the method may further comprise separating the precipitate from the solution. Following said separation, the solution may have a reduced actinium activity and the concentration of rare earth ions in said solution may be essentially unchanged.
  • a method of removing actinium from a solution comprising actinium-227 ions and rare earth ions comprising processing an ore or mineral concentrate using an alkaline cracking process so as to provide the solution comprising actinium ions and rare earth ions; adding to the solution strontium chloride and, a water soluble source of sulfate ions such as sodium sulfate, sulfuric acid or magnesium sulfate; whereby a precipitate comprising strontium sulfate and actinium is formed.
  • a sufficient amount of metal ions is added to cause at least 40% of the actinium ions to precipitate.
  • the method may further comprise separating the precipitate from the solution. Following said separation, the solution may have a reduced actinium activity and the concentration of rare earth ions in said solution may be essentially unchanged.
  • a method of removing actinium and radium from a solution comprising actinium-227 ions, radium ions and rare earth ions comprising processing an ore or mineral concentrate using an alkaline cracking process so as to provide the solution comprising actinium ions, radium ions and rare earth ions; adding to the solution barium chloride and a water soluble source of sulfate ions, such as sulfuric acid, sodium sulfate, magnesium sulfate, or a combination of any two or all of these; whereby a precipitate comprising barium sulfate, radium and actinium is formed, and wherein a sufficient amount of metal ions is added to cause at least 40% of the actinium ions to precipitate and at least 99% of the radium ions to precipitate.
  • the method may further comprise separating the precipitate from the solution. Following said separation, the solution may have a reduced actinium activity, a reduced
  • a solid mixed rare earth concentrate obtained by the method of the first aspect of the invention wherein the ions of interest are rare earth ions.
  • the solid mixed rare earth concentrate may have an actinium activity of less than 1.0 Bq/g.
  • a metal ion the sulfate salt of which has a solubility in water at 20 °C of less than about 0.3 g/100 mL, for removing actinium from a solution comprising actinium ions and ions of interest.
  • a precipitate comprising a sulfate salt of a metal ion and further comprising actinium-227, said precipitate being obtained by the method of the first aspect of the invention.
  • a method of preparing a radioisotope comprising: obtaining a precipitate according to the fourth aspect of the invention; separating the actinium-227 from the precipitate; purifying the actinium-227; allowing a portion of the actinium-227 to decay to a decay product, which is the radioisotope, and purifying the radioisotope.
  • the radioisotope may be thorium-227 or radium-223.
  • the present specification relates to a method for removing actinium from process liquors comprising ions of interest (which may be, for example, rare earth ions) and actinium ions.
  • ions of interest which may be, for example, rare earth ions
  • actinium ions become associated with the precipitate causing them to be removed from the solution.
  • the method allows actinium to be removed from the solution selectively i.e. without the concurrent removal of substantial amounts of the ions of interest present in the solution.
  • the inventors have discovered that if the process liquors derive from an alkaline cracking process and contain radium and/or lead ions as well as actinium ions, the method of the invention may result in actinium, radium and lead ions becoming associated with the precipitate of the metal sulfate salt. In this way, it is possible to remove a proportion of actinium, radium and lead from process liquors in a single process step. If the removal of radium and/or lead, as well as actinium, is desired, the amount of metal ions required (and
  • the solution which is used as a feed to the method of the invention comprises water, however it may in some instances also comprise one or more non-aqueous co-solvents, or other organic or inorganic additives. In some instances, there may be no co-solvents or additives. In the event that co-solvents or additives, e.g. organic solvents, are present, they may be in a proportion of less than about 20% by volume of the solution, or less than about 15%, 10%, or 5%, or in a proportion of about 0-10, 10-20, 5-15, 0-5, 5-10, 10-15, 15-20% by volume of the solution. The co-solvents or additives may be present in an amount of about 5, 10, 15 or 20% by volume.
  • the solution may be provided as a result of the processing of an actinium-containing material, which may be an ore or mineral concentrate containing ions of interest, such as rare earth elements.
  • an actinium-containing material which may be an ore or mineral concentrate containing ions of interest, such as rare earth elements.
  • Two methods which may be used in the processing of an ore or mineral concentrates are acid cracking and alkaline cracking.
  • the process of acid cracking comprises a step of treating the ore or mineral concentrate with concentrated sulfuric acid at elevated temperature.
  • the resulting mixture may be leached with water.
  • sulfate ions which are subsequently precipitated to remove actinium, are present in the process liquor from the sulfuric acid.
  • the process of alkaline cracking comprises a step of treating the ore or mineral concentrate with a concentrated solution of a base such as sodium hydroxide at elevated temperature. This is followed by solubilisation of the caustic residue in an acid, such as hydrochloric acid, adjusting the pH of the solution to 3-4. As no sulfate is provided during this process, it is commonly necessary to add a source of sulfate ions in order to form a precipitate so as to remove actinium.
  • a base such as sodium hydroxide
  • Actinium is present in the feed solution.
  • the actinium may be present as a result of the decay of uranium-235 or it may occur as a result of any natural or artificial process.
  • the actinium may be actinium-227.
  • Other isotopes of actinium may also be present.
  • the method of the invention may be used to successfully remove all isotopes of actinium present in the solution.
  • actinium includes elemental actinium as well as actinium ions in any oxidation state. Commonly the actinium will be present as Ac 3+ ions.
  • Radium may also be present in the feed solution.
  • the radium may be present as a result of any natural or artificial process.
  • the radium may be radium-226 or radium-228.
  • Other isotopes of radium may also be present.
  • the method of the invention may be used to
  • the feed solution will typically contain ions of interest.
  • the ions of interest are non- actinium ions present in the solution which the operator of the method of the invention may wish to separate from the actinium ions.
  • a goal of the method may be to obtain the ions of interest free from undesirable levels of actinium activity or with reduced actinium activity.
  • a goal of the method may equally be to obtain actinium ions and, optionally, discard the ions of interest.
  • the ions of interest may be rare earth ions.
  • Rare earth ions present in the solution may be ions (of any oxidation state) of one or more of the following elements: Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
  • the solution may contain no rare earth ions.
  • Another example of an ion of interest may be a uranium ion.
  • the ions of interest may comprise both rare earth ions and non-rare earth ions.
  • Other organic or inorganic components may also be present in the solution.
  • the concentration of the ions of interest may be about 1 to about 200 g/L, or about 1-100, 100-200, 50-150, 1-25, 25-75, 75-100, 100-125, 125-150, 150-175 or 175-200 g/L.
  • metal ions are added to the feed solution.
  • the metal ions may be of any metallic element in any oxidation state, provided that the solubility of a sulfate salt of the metal ions in water at 20 °C is less than about 0.3 g/100 mL.
  • the solubility of the sulfate salt of the metal ions in water at 20 °C may be less than about 0.25, 0.2, 0.15, 0.1, 0.05, 0.02, 0.005, 0.002, 0.001, 0.0005 or 0.0001 g/100 mL.
  • the metal ions are divalent metal ions such as lead, barium or strontium, or combinations thereof. Where a combination of different divalent metal ions is added, the metal ions may be added simultaneously or sequentially.
  • the feed solution may comprise sulfate ions.
  • the sulfate ions may be present in a sufficient concentration to cause at least some of a sulfate salt of the metal ions to precipitate on addition of the metal ions.
  • a sufficient concentration of sulfate ions is such that, for the given metal ion concentration, the solubility product of the metal sulfate salt is exceeded by the product of the metal ion and sulfate concentrations.
  • addition of the metal ions may result in formation of at least some precipitate which comprises actinium and the sulfate salt of the metal ions.
  • the concentration of sulfate ions in the solution may be insufficient to cause at least some of the sulfate salt of the metal ions to precipitate.
  • concentration of sulfate ions in the solution may be insufficient to cause at least some of the sulfate salt of the metal ions to precipitate.
  • an insufficient concentration of sulfate ions is one at which the solubility product of the sulfate salt of the metal ions is not exceeded by the product of the metal ions and sulfate concentrations.
  • a water soluble source of sulfate ions Any water soluble source of sulfate ions may be used, such as sodium sulfate, magnesium sulfate, potassium sulfate, sulfuric acid, or any mixture of these. Sulfuric acid, magnesium sulfate, or a combination thereof, are preferred.
  • the water soluble source of sulfate ions may be added, continuously, intermittently or as a single bolus, until at least some of a precipitate comprising the sulfate salt of the metal ions forms. Once a sufficient concentration of sulfate ions is achieved, at least some of a precipitate comprising the sulfate salt of the metal ions and further comprising actinium forms.
  • the method of the invention is at least partially selective, and in some circumstances, substantially or essentially completely, for the removal of actinium over ions of interest from the feed solution.
  • concentration of ions of interest in the solution may be essentially the same before and after applying the method of the invention.
  • “essentially the same” means the concentration of ions of interest is not reduced by more than about 1%, or not reduced by more than about 2, 5, 10 or 15%.
  • the concentration may be reduced by about 0-15%, or about 0-10, 0-5, 5-10, 5-15 or 10-15%.
  • the term "essentially unchanged" has a corresponding meaning.
  • the term "the concentration of ions of interest” may refer either to the total concentration of ions of interest or it may refer to the concentration of any or each ion of interest individually.
  • the selectivity of the method is sensitive to the amount of metal ions added. If an excessive amount of metal sulfate is caused to precipitate, the concentration of ions of interest may be unacceptably reduced. If an insufficient amount of the metal ions is added, it may not be effective in removing the desired quantity of actinium. In the method of the invention, the metal ion is added in a sufficient amount so as to remove actinium to an acceptable level, and no more.
  • the amount of metal ions added will be greater than that required for the removal of radium alone.
  • a sufficient amount of the metal ions is in the range of about 0.01-100 mmol per Bq/L of actinium activity of the feed solution, or about 0.01-0.1, 0.01-1, 0.01-10, 0.01-50, 1-10, 1-50, 50-100, 0.1- 1 , 1 -10, 10-25, 25-50, 50-75, 75-100 mmol per Bq/L of actinium activity of the feed solution.
  • the amount of metal ions which is sufficient to remove actinium without unacceptably reducing the concentration of ions of interest will depend on the identity of the metal ions.
  • a sufficient amount of the metal ions is about 0.01-5 mmol per Bq/L, or about 0.01 -0.5, 0.01 -1 , 0.01 -2, 1 -5, 2-5, 0.01 -0.05, 0.05-0.1 , 0.1 -0.5, 0.5-1 , 1 -2, 2-3, 3-4, or 4-5 mmol per Bq/L.
  • metal ion are Sr 2+ ions
  • a sufficient amount of the metal ions is about 0.1-15 mmol per Bq/L, or about 0.1-1, 0.1-5, 0.1-10, 0.1-0.2, 0.2-0.5, 0.5-1, 1-5, 1-10, 1-15, 5-10, or 5- 15 mmol per Bq/L.
  • the metal ions are Ca 2+ ions
  • a sufficient amount of the metal ions is about 10-100 mmol per Bq/L, or about 10-50, 50-100, 10-20, 20-30, 30-40, 40-50, 50-60, 60-70, 70- 80, 80-90, or 90-100 mol per Bq/L.
  • metal ions are Ba 2+ ions
  • a sufficient amount of the metal ions is about 0.1-15 mmol per Bq/L, or about 0.1-1, 0.1-5, 0.1-10, 0.1-0.2, 0.2-0.5, 0.5-1, 1-5, 1-10, 1-15, 5-10, or 5-15 mmol per Bq/L.
  • activity refers to radioactivity.
  • Actinium activity refers to the radioactivity of actinium-227,. Activity is measured in Bq/g or Bq/L, depending on the context. The activity of Ac-227 is typically determined by gamma spectroscopy of in-growth of Th-227.
  • a sufficient amount of the metal ion that is added to the solution must be caused to precipitate as a sulfate salt. It may be titrated into the solution to a desired actinium activity endpoint. This may be achieved by adjusting the relative amounts of metal ions and sulfate ions such that the stoichiometry allows a sufficient amount of the metal ions to form a sulfate salt.
  • the processing of the ore or mineral concentrate comprises an alkaline cracking step and thus the metal ions are strontium ions and a water-soluble source of sulfate ions is required, typically an at least equimolar amount of sulfate ions, relative to the amount of strontium or barium ions, will be added.
  • an excess of sulfate ions is added relative to the strontium or barium ions.
  • the molar ratio of sulfate ions to the total amount of metal ions may be in the range of about 1 : 1 to 1000: 1, or about 1 : 1 to 2: 1, 5: 1, 10: 1, 100: 1, 200: 1, 300: 1 ; 400: 1, 500: 1, 600: 1, 700: 1, 800: 1 or 900: 1, or about 10: 1 to 100: 1, 200: 1, 300: 1 ; 400: 1 , 500: 1 , 600: 1 , 700: 1 , 800: 1 , 900: 1 or 1000: 1 , or about 100: 1 to 200: 1 , 300: 1 ;
  • the ratio of sulfate ions to metal ions may be about 1 : 1, 1.5: 1, 2: 1, 5: 1, 10: 1, 50: 1, 100: 1, 200: 1, 300: 1 ; 400: 1, 500: 1, 600: 1, 700: 1, 800: 1, 900: 1 or 1000: 1.
  • the skilled person will be able to determine, by routine trial and error guided by the information disclosed herein, a ratio of sulfate to metal ions which is appropriate to remove actinium from particular process liquors.
  • the total dissolved ions of interest for example total dissolved rare earths, contained in the solution may originate from an ore or from a mineral concentrate.
  • the ore or mineral concentrate is processed, resulting in the formation of the solution used as a feed to the method of the invention.
  • the dissolved ions of interest may derive from various salts such as carbonates or oxides.
  • the total dissolved ions of interest contained in the solution may be radioactive.
  • the radioactivity may originate from actinium-227. Other radioactive elements may be present.
  • the actinium activity of the total dissolved ions of interest may be greater than about 0.1 Bq/g, or about 1, 10, 100 or 500 Bq/g.
  • the actinium activity may be in the range of about 0.1-500 Bq/g, or about 0.1-100, 0.1-10, 0.1-1, 1-10, 10-100 or 100-500 Bq/g.
  • the actinium activity of the total dissolved ions of interest may be about 0.1 Bq/g, or about 1, 10, 100 or 500 Bq/g.
  • the actinium activity may be expressed per unit volume of the feed solution.
  • the actinium activity may be in the range of about 1 -500 Bq/L, or about 1 -100, 1 -250, 100-250, 250-500, 1 - 100, 1-200, 1-300, 1-400 Bq/L.
  • the actinium activity may be about 1 Bq/L or about 2, 5, 10, 20, 50, 100, 150, 200, 250, 300, 350, 400, 450 or 500 Bq/L.
  • the precipitate may be separated from the solution by any method known to the skilled person. Methods of separation include, but are not limited to, filtration, gravitational settling, centrifugation or flotation and skimming, or any combination of these.
  • the precipitate may comprise a single chemical species, or may comprise multiple species.
  • the word 'precipitate' is intended to refer to the totality of species caused to precipitate out of solution as a result of carrying out the method of the invention.
  • the solution may have a reduced concentration of actinium when compared to the concentration of actinium prior to carrying out the method of the invention.
  • the actinium concentration may be reduced by up to 100%, or up to about 95, 90, 85, 80, 70, 60, 50, 40, 30 or 20%.
  • the reduction may be in the range of about 100-20%, or about 100-60, 100-85, 85-20, 60-20, 20-40, 40-60, 60-85, 85-90, 90-95 or 95-100%.
  • concentration may be reduced by about 100%, or about 95, 90, 85, 80, 70, 60, 50, 40, 30 or 20%. Equivalently, up to 100%, or up to about 95, 90, 85, 80, 70, 60, 50, 40, 30 or 20% of the actinium ions may be caused to precipitate.
  • the proportion of actinium ions caused to precipitate may be in the range of about 100-20%, or about 100-60, 100-85, 85-20, 60-20, 20- 40, 40-60, 60-85, 85-90, 90-95 or 95-100%.
  • the amount of actinium ions caused to precipitate may be about 100%, or about 95, 90, 85, 80, 70, 60, 50, 40, 30 or 20%.
  • the degree of reduction (amount of precipitation) may be controlled in part by the quantity of the metal ion, which may be determined with reference to the measured actinium activity of the solution.
  • the method may therefore further comprise measuring the actinium activity of the solution and determining from the measured actinium activity the required quantity of the metal ions to be added.
  • the method may also comprise adding to the solution metal ions, a sulfate salt of which has a solubility in water at 20 °C is less than about 0.3 g/100 mL and, if required, a source of water soluble sulfate, whereby a precipitate to form comprising actinium and the sulfate salt of the metal ions is formed; measuring the actinium activity of the solution, and determining from the measured actinium activity if further addition of the metal ions (and water soluble source of sulfate, if required) is needed. This step may be repeated as often as required until an acceptable level of actinium activity is reached.
  • the actinium activity may be measured by gamma spectroscopy of in-growth of thorium-227.
  • the actinium activity of the solution is reduced when compared to its actinium activity prior to carrying out the method of the invention.
  • the actinium activity may be reduced by up to or about 100%, or about 95, 90, 85, 60, 40 or 20%.
  • the reduction may be in the range of about 100-20%, or about 100-60, 100-85, 85-20, 60-20, 20-40, 40-60, 60-85, 85-90, 90-95 or 95-100%.
  • the actinium activity may be reduced by about 100%, or about 95, 90, 85, 60, 40 or 20%. The same proportional reductions apply,
  • a mixed rare earth concentrate is a solid comprising a mixture of rare earth elements intended for further processing.
  • a mixed rare earth concentrate produced by the method of the invention may have an actinium activity of less than or equal to about 1.0, 0.75, 0.5, 0.25, 0.1, or 0.05 Bq/g.
  • the actinium activity may be in the range of about 0-0.05, 0-0.1 , 0-0.5, 0-1.0, 0.05-0.1, 0.1 -0.25, 0.25-0.5, or 0.5-1 Bq/g.
  • the actinium activity may be about 0.05, 0.1, 0.25, 0.5, 0.75, or 1.0 Bq/g.
  • the invention also encompasses a method of preparing a radioisotope from the precipitate comprising the sulfate salt of the metal ion and further comprising actinium-227, obtained by the method of the invention.
  • Actinium-227 may be separated from the precipitate by any method known to the skilled person.
  • a suitable method involves treating the precipitate with hydrochloric acid.
  • the liberated actinium-227 may then be purified by any suitable method, e.g. ion exchange or solvent extraction.
  • the resulting purified actinium compound may then be allowed to decay, resulting in the formation of decay products which may be the radioisotope.
  • the decay product may be thorium-227 or radium-223.
  • actinium-227 decays to thorium-227, which decays to radium-223
  • selection of the desired radioisotope may be accomplished by selecting a suitable time for which the actinium-227 is allowed to decay.
  • Thorium-227 or radium-223 produced by the above method may be used in medical imaging or radiotherapy.
  • Example 1 To sulfate containing process liquor containing about 8 Bq/L Ac-227 and rare earths, mainly as yttrium, was added strontium. Strontium chloride was dissolved in a minimal amount of water, added to the actinium containing sulfate liquor at room temperature, and agitated for 20 hours. The sulfate precipitate was filtered off and the Ac-227 removal determined by gamma spectrometry analysis of the liquor. Test ID A-2-13 A-2-1 1 A-2-12
  • Example 2 To sulfate-containing process liquor containing ⁇ 8 Bq/L Ac-227 and rare earths, mainly as yttrium, was added lead(Il) chloride. Lead chloride was dissolved in a minimal amount of water, added to the actinium containing sulfate liquor at room temperature, and agitated for 20 hours. The sulfate precipitate was filtered off and the Ac-227 removal determined by gamma spectrometry analysis of the liquor. The Ac-227 removal was
  • Example 3 To a chloride containing process liquor containing -70 Bq/L Ac-227 and minimal radium was added strontium. The radium had been previously removed by co- precipitation with barium sulfate by addition of barium chloride and sulfuric acid. Strontium chloride solid was added to the process liquor and dissolved in it. Magnesium sulfate was added as a 250 g/L solution to induce the precipitation of strontium sulfate at room temperature. The mixture was agitated for 20 hours at room temperature. The sulfate precipitate was filtered off and the Ac-227 removal determined by gamma spectrometry analysis of the liquor. There was approximately 50% removal of Ac-227 with 2% precipitation of rare earths. Test ID 61-2
  • Example 4 To a chloride containing process liquor containing -90 Bq/L Ac-227 and minimal radium was added lead. The radium had been previously removed by co -precipitation with barium sulfate by addition of barium chloride and sodium sulfate. Lead chloride solid was added to the process liquor and lead chloride that had not dissolved was filtered off (0.98 g PbCh/L feed dissolved). Sodium sulfate was added as a 150 g/L solution and the mixture agitated for 20 hours at room temperature. The precipitate was filtered off. There was 41% removal of Ac-227. The relatively high precipitation of rare earths is attributed to sodium sulfate addition and precipitation of a sodium sulfate rare earth double sulfate salt.
  • Example 5 To a chloride containing process liquor containing >100 Bq/L Ac-227 and >10,000 Bq/L Ra-228 was added barium. Barium chloride solid was added to the process liquor and dissolved. Sulfuric acid solution was added as the sulfate source to induce precipitation of barium sulfate. The mixture was agitated for 20 hours at room temperature. The precipitate was filtered off. Results are presented in the table below. Test ID 56-1 56-2 56-3
  • Barium chloride was dissolved in the process liquor and sulfuric acid added to initiate barium sulfate precipitation. Without filtration of the barium sulfate, strontium chloride was dissolved in the slurry and more sulfuric acid was added to initiate strontium sulfate precipitation.
  • the Ac-227 removal was slightly higher when precipitation of barium sulfate and strontium sulfate occurred sequentially rather than simultaneously. Radium removal was >99.9% in both cases.

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Abstract

La présente invention concerne un procédé d'élimination d'actinium à partir de liqueurs de traitement comprenant des ions d'intérêt (qui peuvent être, par exemple, des ions de terres rares) et des ions actinium. Dans ce procédé, un sel de sulfate métallique à faible solubilité est amené à précipiter dans une solution comprenant des ions d'intérêt et des ions actinium. Les ions actinium deviennent associés au précipité, ce qui conduit à leur élimination de la solution. Le procédé permet d'éliminer l'actinium de la solution de façon sélective, c'est-à-dire sans l'élimination concomitante de quantités importantes des ions d'intérêt présents dans la solution.
EP18823055.1A 2017-06-27 2018-06-26 Séparation d'actinium à partir de liqueurs de traitement Pending EP3645759A4 (fr)

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