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Title:
RECOVERY OF YTTRIUM AND EUROPIUM COMPOUNDS
Document Type and Number:
WIPO Patent Application WO/2014/167534
Kind Code:
A1
Abstract:
A recovery process includes contacting a powder comprising an admixture of yttrium oxide and europium oxide with an inorganic acid to form an acidic solution containing yttrium ions and europium ions. In a first multiple plate liquid-liquid extraction stage, the acidic solution (aqueous phase) is contacted with an organic solvent (organic phase) by countercurrent extraction, to extract, into the organic phase, yttrium ions, while the europium ions remain in the aqueous phase. The yttrium-rich organic phase (extract) is treated to recover a yttrium compound. The europium-rich aqueous phase (raffinate) is treated in a second multiple plate liquid-liquid extraction stage, where it is contacted with an organic solvent (organic phase) thereby to extract by means of countercurrent extraction europium ions into the organic phase. The europium-rich organic phase is treated to recover a europium compound.

Inventors:
RAMJUGERNATH DERESH (ZA)
WILLIAMS-WYNN MARK (ZA)
CARSKY MILAN (ZA)
HEYBERGER ALES (CZ)
GRUBER VACLAV (CZ)
Application Number:
PCT/IB2014/060642
Publication Date:
October 16, 2014
Filing Date:
April 11, 2014
Export Citation:
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Assignee:
UNIV KWAZULU NATAL (ZA)
CESKOSLOVENSKA AKADEMIE VED (CZ)
International Classes:
C22B3/26; C22B7/00; C22B59/00
Domestic Patent References:
WO2006058508A12006-06-08
Foreign References:
JP2004285467A2004-10-14
CZ302854B62011-12-14
EP1817437A12007-08-15
CZ302854B62011-12-14
Other References:
INFORMATION ON COMPACT FLUORESCENT LIGHT BULBS (CFLS) AND MERCURY, 2009, Retrieved from the Internet
RABAH, M. A.: "Recyclables recovery of europium and yttrium metals and some salts from spent fluorescent lamps", WASTE MANAGEMENT, vol. 28, 2008, pages 318 - 325, XP022370796
SHIMIZU R.; SAWADA K.; ENOKIDA Y., YAMAMOTO: "Supercritical fluid extraction of rare earth elements from luminescent material in waste fluorescent lamps", J. SUPERCRITICAL FLUIDS, vol. 33, 2005, pages 235 - 241, XP025336934, DOI: doi:10.1016/j.supflu.2004.08.004
"Rare Earth Materials in the Defence Supply Chain", 2010, UNITED STATES GOVERNMENT ACCOUNTABILITY OFFICE
Attorney, Agent or Firm:
KOTZE, Gavin, Salomon et al. (PO Box 101, 0001 Pretoria, ZA)
Download PDF:
Claims:
CLAIMS

1 . A process for the recovery of yttrium and europium compounds from a powder comprises an admixture of at least yttrium oxide and europium oxide, the process including

in a leaching stage, contacting the powder with an inorganic acid, thereby to dissolve the yttrium oxide and the europium oxide, with an acidic solution containing yttrium ions and europium ions thus being formed;

in a first multiple plate liquid-liquid extraction stage, contacting the acidic solution, which is hence an aqueous phase, with an organic solvent, which is hence an organic phase, by means of countercurrent extraction, thereby to extract, into the organic phase, yttrium ions, while the europium ions remain in the aqueous phase;

treating the yttrium-rich organic phase or extract from the first extraction stage, to recover a yttrium compound;

treating the europium-rich aqueous phase or raffinate from the first extraction stage in a second multiple plate liquid-liquid extraction stage, where it is contacted with an organic solvent, which is hence an organic phase, thereby to extract from the aqueous phase and into the organic phase, and by means of countercurrent extraction, europium ions;

treating the europium-rich organic phase or extract from the second extraction stage, to recover a europium compound; and

withdrawing spent aqueous phase from the second extraction stage as a raffinate.

2. The process according to Claim 1 , wherein the powder is an impure powder which contains mercury as an impurity, with the mercury being removed as a component of the raffinate from the second extraction stage. 3. The process according to Claim 2, wherein the powder is luminophorous powder recovered from compact fluorescent light bulbs (CFLs).

4. The process according to any one of Claims 1 to 3 inclusive, wherein the first and second extraction stages are provided by the same vibrating plate column, with the passing of the europium-rich aqueous phase to the vibrating plate column being effected after contacting of the acidic solution with the organic solvent to extract the yttrium ions into the first extraction stage extract has been completed.

5. The process according to any one of Claims 1 to 3 inclusive, wherein the first and second extraction stage is each provided by a separate vibrating plate column. 6. The process according to any one of Claims 1 to 5 inclusive, wherein the inorganic acid used in the leaching stage is nitric acid.

7. The process according to any one of Claims 1 to 6 inclusive, wherein the organic solvent used in the first and the second extraction stages is the same, and is bis-(2-ethylhexyl) phosphoric acid in an organic diluent.

8. The process according to any one of Claims 1 to 7 inclusive, which includes passing an inorganic acid countercurrently through the organic phase in each of the extraction stages, thereby to entrain any undesired substances present in the organic phase.

9. The process according to any one of Claims 1 to 8 inclusive, wherein the treatment of the extract from the first extraction stage to recover the yttrium compound includes

in a re-extraction stage, contacting the yttrium-rich organic phase with an inorganic acid, to obtain an yttrium salt;

in a separating stage, separating an aqueous phase containing the yttrium salt, from the organic phase;

recycling the organic phase from the separating stage to the first extraction stage;

passing the aqueous phase of the separating stage to a neutralizing stage, to neutralize any residual inorganic acid present therein by means of a base; passing the neutralized aqueous phase of the neutralizing stage to a reaction/precipitation stage to which is added oxalic acid which causes the yttrium to precipitate as yttrium oxalate; and

calcining the yttrium oxalate to obtain yttrium oxide.

10. The process according to any one of Claims 1 to 9 inclusive, wherein the treatment of extract from the second extraction stage to recover the europium compound includes

in a re-extraction stage, contacting the europium-rich organic phase with an inorganic acid, to obtain an europium salt;

in a separating stage, separating an aqueous phase containing the europium salt, from the organic phase;

recycling the organic phase from the separating stage to the second extraction stage;

passing the aqueous phase of the separating stage to a neutralizing stage, to neutralize any residual inorganic acid present therein by means of a base;

passing the neutralized aqueous phase of the neutralizing stage to a reaction/precipitation stage to which is added oxalic acid which causes the europium to precipitate as europium oxalate; and

calcining the europium oxalate to obtain europium oxide.

Description:
RECOVERY OF YTTRIUM AND EUROPIUM COMPOUNDS

THIS INVENTION relates to the recovery of yttrium and europium compounds. In particular, it relates to a process for the recovery of yttrium and europium compounds from a powder comprising an admixture of at least yttrium oxide and europium oxide.

Background of the invention

Compact fluorescent light bulbs (CFLs) require substantially less electricity than incandescent light bulbs to provide a similar lighting level, and have therefore become a preferred alternative to incandescent light bulbs. They operate by using electricity to excite mercury vapour, which in turn radiates ultraviolet light, which causes phosphorescent (luminescent) materials to fluoresce. This produces visible light. The phosphorescent materials comprise of solid inorganic materials, including oxides of rare earth metals, such as yttrium (II) oxide and europium (II) oxide (Rabah, 2008). In 2009, 97 % of the world production of rare earth metal oxides occurred in China (United States Government Accountability Office, 2010). Due to the restriction of trade by China in these metals, their prices have increased dramatically.

The presence of mercury in the CFLs means that the disposal of the CFLs in landfill sites is not an environmentally viable option, due to the subsequent mercury emissions (Energy Star, 2009). Other means of disposing of the CFLs therefore need to be developed.

With the rapid increase in the price of these rare earth metal oxides, it has become a viable option to recycle the rare earth metal oxides from CFLs alongside the glass, mercury and other components. Up until now, the glass and mercury have been recovered from the CFLs, with the phosphorescent materials being sent to landfill sites (Shimizu et al., 2005). It is hence an object of the present invention to provide a process for recovering yttrium and europium values from CFLs.

A process for the recovery of the yttrium and europium oxides from phosphorescent materials similar to those obtained from CFLs was developed by the Institute of Chemical Process Fundamentals at the Czech Academy of Sciences in the Czech Republic (Gruber, 2009). This process can be applied as an intermediate step in the current process for recovery of the rare earth metals from CFLs.

Disclosure of the invention

Thus, according to the invention, there is provided a process for the recovery of yttrium and europium compounds from a powder comprising an admixture of at least yttrium oxide and europium oxide, the process including

in a leaching stage, contacting the powder with an inorganic acid, thereby to dissolve the yttrium oxide and the europium oxide, with an acidic solution containing yttrium ions and europium ions thus being formed;

in a first multiple plate liquid-liquid extraction stage, contacting the acidic solution, which is hence an aqueous phase, with an organic solvent, which is hence an organic phase, by means of countercurrent extraction, thereby to extract, into the organic phase, yttrium ions, while the europium ions remain in the aqueous phase;

treating the yttrium-rich organic phase or extract from the first extraction stage, to recover a yttrium compound;

treating the europium-rich aqueous phase or raffinate from the first extraction stage in a second multiple plate liquid-liquid extraction stage, where it is contacted with an organic solvent, which is hence an organic phase, thereby to extract from the aqueous phase and into the organic phase, and by means of countercurrent extraction, europium ions;

treating the europium-rich organic phase or extract from the second extraction stage, to recover a europium compound; and

withdrawing spent aqueous phase from the second extraction stage as a raffinate. The powder may be an impure powder which contains mercury as an impurity. The mercury may then be removed as a component of the raffinate from the second extraction stage. In particular, the powder may be luminophorous powder recovered from compact fluorescent light bulbs (CFLs). The luminophorous powder is typically obtained from the compact fluorescent light bulbs by crushing the glass of the light bulbs, and thereafter removing the powder from the glass fragments by mechanical means. This powder consists of yttrium oxide and europium oxide, as well as other less valuable phosphorescent materials and mercury.

The rare earth oxides, i.e. the yttrium oxide and the europium oxide, are thus separated, in the leaching stage, from the luminophorous material by leaching with the inorganic or mineral acid. This mineral acid may have a concentration of about 1 M to about 8M, typically about 5M. The mineral acid can advantageously be nitric acid. In the leaching stage, the mineral acid is thus contacted with the luminophorous powder. Most of the yttrium oxide, europium oxide and mercury are dissolved by the mineral acid, with the acidic solution forming. The remainder of the solids are insoluble and remain as solids, possibly in suspension in the acidic solution. The remaining solids may be removed from the acidic solution by mechanical or gravitational separation. The mechanical separation, when used, may be filtration; the gravitational separation, when used, may involve using a settling tank. The process may include rinsing the solids recovered from the mechanical or gravitational separation, in order to improve the yields of yttrium and europium, as well as to reduce the contamination of the solids with the mineral acid. The wash water from the washing of the solids can be used for the dilution of the mineral acid where required in the process.

The first extraction stage may comprise, or be provided by, a vibrating plate column. Similarly, the second extraction stage may comprise, or be provided by, a vibrating plate column. The vibrating plate columns will thus naturally have a multiple or plurality of spaced vibrating plates. In a first embodiment of the invention, the first and second extraction stages may be provided by the same vibrating plate column, with the passing of the europium-rich aqueous phase to the vibrating plate column being effected after contacting of the acidic solution with the organic solvent to extract the yttrium ions into the first extraction stage extract has been completed. In the first embodiment, the same column as is used for the first extraction step is thus used to extract the europium from the diluted or partially neutralised raffinate of the first extraction stage, but at a later time. The first extraction stage thus makes use of the counter current vibrating plate extraction column in order to extract the yttrium from the acidic solution or aqueous mineral acid phase, which, as indicated comprises europium and mercury, along with the yttrium. The extraction stages may utilise the method patented by Gruber et al. (201 1 ) in so much as it uses the same process to separate the yttrium from the aqueous phase.

The extraction column may have three feed points: two aqueous phase feed points and one organic phase feed point. The one aqueous phase feed point may then be located between the upper and lower ends of the column, e.g. at about the middle of the column, with the acidic solution entering the column through this feed point; the other aqueous phase feed point may be located at or near the upper end of the column, with fresh mineral acid entering through this feed point; and the organic phase feed point may be located at or near the bottom of the column, with the organic solvent entering the column through this feed point. The column operates continuously in a counter current manner. The extraction column thus consists of two sections - a stripping section and an enrichment section. In the enrichment section, fresh mineral acid which enters from the top of the column entrains any undesired components as it moves down the column. The extraction process is controlled by the pH of the aqueous phase. The metals to be extracted by the organic solvent can be controlled by altering the pH of the acid solutions entering the column. In the extraction column, even though the two phases are mutually immiscible, one phase is dispersed as droplets in the other phase, which is thus a continuous phase, with a controlled drop size distribution achieved by the vibration of the plates in the column. The separation effect is enhanced by this vibrating action of the plates in the column. Such arrangement ensures high process efficiency in the case of the extraction of the yttrium from the aqueous phase into the organic phase. Each vibrating plate has holes of two different sizes which allows for the movement of the continuous phase and the dispersed phase. Depending on which phase is dispersed, i.e. either the phase with a lesser density (the organic phase) or the phase with the greater density (the aqueous phase), the interface is maintained either in an upper or in a lower calming section of the column respectively. The phase that is dispersed may be determined, amongst others, by the materials of construction of the column.

The fresh mineral acid fed into the top of the column may have a concentration of about 1 M to about 2 M. This mineral acid should be the same as the acid utilised for the leaching step, and is therefore also most advantageously nitric acid. The extraction column may have calming sections on both of its ends. The aqueous acidic solution feed for the first extraction step may be diluted or neutralised to between about 1 M and about 2 M prior to being added to the extraction column.

The ratio of the feeds to the column may vary from 1 : 10 to 10: 1 volumetric parts organic solvent to acidic solution and about 0.2 parts fresh mineral acid. The ratio of organic solvent to acidic solution to fresh acid feed may typically be about 25 to 5 to 1 .

In a second embodiment of the invention, each of the first and second extraction stage may be provided by a different vibrating plate column.

In the second embodiment, a second extraction column is thus used to perform this extraction. This second extraction column, when used, operates in exactly the same manner as the first extraction column. This second embodiment naturally requires the duplication of the entire process utilised for the recovery of the yttrium and europium, with one recovery step being used for the recovery of yttrium, and the duplicate being used for the recovery of the europium. The mineral acid added to the top of the second extraction column may have an acid concentration of between about 0.1 M and about 1 M. The raffinate from the first extraction column may be diluted or partially neutralised to between about 0.1 M and about 1 M prior to entering the second extraction column, by the addition of a base.

The ratio of the feeds to the second extraction column may be between 1 : 10 to 10: 1 volumetric parts organic solvent to parts feed solution and to about 0.2 parts fresh mineral acid. The ratio of organic solvent to feed solution to fresh acid feed acid may typically be about 5 to 10 to 1 .

The process thus preferably includes passing an inorganic acid countercurrently through the organic phase in each of the extraction stages, thereby to entrain any undesired substances present in the organic phase.

The organic solvent used in both extraction stages may be the same, and may be bis-(2-ethylhexyl) phosphoric acid in an organic diluent, such as octane decane or xylene, to improve the physical properties of the solvent.

The treatment of the extract from the first extraction stage to recover the yttrium compound may include

in a re-extraction (stripping) stage, contacting the yttrium-rich organic phase with an inorganic acid, to obtain an yttrium salt;

in a separating stage, separating an aqueous phase containing the yttrium salt, from the organic phase;

recycling the organic phase from the separating stage to the first extraction stage;

passing the aqueous phase of the separating stage to a neutralizing stage, to neutralize any residual inorganic acid present therein by means of a base;

passing the neutralized aqueous phase of the neutralizing stage to a reaction/precipitation stage to which is added oxalic acid which causes the yttrium to precipitate as yttrium oxalate; and calcining the yttrium oxalate to obtain yttrium oxide (Y2O3).

The treatment of extract from the second extraction stage to recover the europium compound may include

in a re-extraction (stripping) stage, contacting the europium-rich organic phase with an inorganic acid, to obtain an europium salt;

in a separating stage, separating an aqueous phase containing the europium salt, from the organic phase;

recycling the organic phase from the separating stage to the second extraction stage;

passing the aqueous phase of the separating stage to a neutralizing stage, to neutralize any residual inorganic acid present therein by means of a base;

passing the neutralized aqueous phase of the neutralizing stage to a reaction/precipitation stage to which is added oxalic acid which causes the europium to precipitate as europium oxalate; and

calcining the europium oxalate to obtain europium oxide (EU2O3).

The inorganic acid used in the re-extraction stages may, in one embodiment of the invention, be hydrochloric acid with the salt that is formed thus being yttrium chloride or europium chloride. The hydrochloric acid may be used in excess. The process may then include, in a concentration stage, evaporating the hydrochloric acid, thereby increasing the concentration of the yttrium chloride or the europium chloride present in the acidic aqueous phase. The hydrochloric acid used for the recovery of the rare earth metals may have an H + concentration of between about 3 M and about 5 M. About 80 volumetric % of the hydrochloric acid solution may be evaporated.

The yttrium or europium present in the organic phase reacts with the hydrochloric acid to form yttrium chloride (YCI3) or europium chloride (EuC ). These chlorides are soluble in the aqueous phase, and are therefore removed with the aqueous phase after the two immiscible phases are separated.

In another embodiment of the invention, the inorganic acid used in the re- extraction stages may be sulphuric acid, with the salt that is formed thus being yttrium sulphate or europium sulphate, which precipitates. The sulphuric acid may be added in excess of stoichiometric requirements. The process may then include a filtration and dissolution stage where yttrium sulphate or europium sulphate is filtered from the sulphuric acid solution. The sulphate may then, if desired, be redissolved in cold water. Sufficient water may be used to re-dissolve all of the precipitated sulphates that remain after filtration.

The sulphuric acid used for the recovery of the rare earth metals may have an H + concentration of between about 3 M and about 10 M.

The yttrium or europium present in the organic phase reacts with the sulphuric acid to form yttrium sulphate [Y2(S0 4 ) 3 ] or europium sulphate [Eu 2 (S0 4 ) 3 ].

Solubility of the products [Y 2 (S0 4 )3 and Eu 2 (S0 4 )3] in a solution of H 2 S0 4 of this concentration is limited and precipitation of these salts therefore occurs. Equilibrium of the re-extraction reaction is not affected by the solid phase, and there is therefore a shift towards a more complete re-extraction of the Y and Eu metals from the organic phase. The precipitated solid sulphates can be separated from the sulphuric acid by mechanical means. An example of this mechanical separation could be filtration. The filtered sulphates are thereafter re-dissolved with water, in which they have a higher solubility.

The recovery of the yttrium or europium from the organic phase is thus performed in re-extraction stages. The recovery in the re-extraction or reaction stages may be performed batch-wise in mixer-settler vessels.

The mineral acid (sulphuric acid or hydrochloric acid) that remains in the solution after filtration (when sulphuric acid is used to recover the yttrium or europium) or after evaporation (when hydrochloric acid is used to extract the yttrium or europium) must be neutralised with the base prior to precipitation of the yttrium oxalate or the europium oxalate. Some non-limiting examples of bases that can be used to neutralise the mineral acid are ammonia or ammonium hydroxide solution. In the reaction/precipitation stages, the precipitation of the yttrium or europium oxalates is achieved by the addition of oxalic acid to the solution. In one embodiment of the invention, the oxalic acid is added in its crystalline form. However, in a more elegant embodiment of the invention, the oxalic acid is first dissolved in water, and thereafter added to the solution containing the yttrium sulphate or europium sulphate. Approximately 2kg of oxalic acid is required per kilogram of resulting rare earth oxide. The second embodiment is preferred, as it gives a more uniform size distribution of the resulting precipitate.

Mechanical separation is required at this point, to separate the precipitated product from the liquid. This mechanical separation can be filtration, or centrifugal separation. Centrifugal separation is required if the precipitate is very fine.

The final products of the process of invention are high purity yttrium oxide and europium oxide, which are formed by the calcination, e.g. in a furnace, of the yttrium oxalate or europium oxalate at temperatures in excess of about 600°C, e.g. at about 800°C.

The process may include a mercury removal stage, where mercury present in the raffinate from the second extraction step may be precipitated out by reaction with sulphide anions. The sulphide anions may be provided by the addition of a sodium sulphide solution or an ammonium sulphide solution to the raffinate from the second extraction step.

To allow for the disposal of a mercury free aqueous solution after the second extraction stage, the invention thus includes the mercury removal stage for the removal of the mercury from the second raffinate. The mercury present in the solution reacts with added sulphide anions, allowing the precipitation of mercury sulphide. Two non-limiting examples of solutions that can be used to provide the sulphide anions for the reaction with the raffinate are ammonium sulphide and sodium sulphide. To prevent the disposal of any mercury compounds into the environment, the solid mercury sulphide is separated from the liquid effluent by mechanical means. This mechanical separation may be a filtration unit, which removes the precipitated mercury sulphite in a filter cake, with the mercury free solution being the filtrate.

The invention will now be described in more detail hereunder, with reference to the following schematic drawings. In the drawings,

FIGURE 1 shows a flow diagram of a process in accordance with a first embodiment of the invention, in which a vibrating plate column is used firstly for the extraction of yttrium, and then, after a time, for the extraction of the europium from the raffinate of the first extraction process; sulphuric acid is used to recover the yttrium or europium from the organic solvent;

FIGURE 2 shows a flow diagram of a process in accordance with a second embodiment of the invention, in which two vibrating plate columns are used; the first thereof is used to extract yttrium from an aqueous solution, and the second thereof is used to extract the europium from the raffinate from the first column; sulphuric acid is used to recover the yttrium or europium from the organic solvent;

FIGURE 3 again shows the flow diagram of the process in accordance with the first embodiment of the invention, in which the vibrating plate column is used firstly for the extraction of yttrium, and then, after a time, for the extraction of the europium from the raffinate of the first extraction process; however, hydrochloric acid is now used to recover the yttrium or europium from the organic solvent; and

FIGURE 4 again shows the flow diagram of the process in accordance with the second embodiment of the invention, in which two vibrating plate columns are used; the first thereof is used to extract the yttrium from an aqueous solution, and the second thereof is used to extract the europium from the raffinate from the first column; however, hydrochloric acid is used to recover the yttrium or europium from the organic solvent. In Figures 1 to 4, the same reference numerals refer to the same or similar processing units (and the same or similar functioning thereof) or streams, unless otherwise indicated. Referring to FIGURE 1 , reference numeral 10 generally indicates a process according to a first embodiment of the invention, for recovery of yttrium and europium compounds from a powder comprising an admixture of at least yttrium oxide, europium oxide and mercury. In the process 10, stream 12 comprises a luminophorous powder, from which yttrium oxide and europium oxide are to be recovered, in accordance with the process of the invention. This powder has been separated from glass shards obtained by crushing of CFL bulbs. In a leaching stage or unit 14, a nitric acid solution (stream 16) is mixed with the luminophorous powder, leaching yttrium oxide, europium oxide and mercury from the powder. The resultant slurry is fed by means of a flow line 18 through a filter (unit 20), where residual solids (stream 22) are separated from the filtrate (stream 24). The acid solution is then diluted, in a vessel 26, to a concentration of about 1 M for the extraction of the yttrium, by the addition of water as stream 27.

In this first embodiment of the invention, the process up to this stage is continuous, while after this step, it becomes a batch-wise process. In a first extraction step, the diluted solution is fed from the dilution vessel 26, by means of flow lines or streams 28, 32 and a pump 30, to a feed point near to the middle of a vibrating plate extraction column 34.

Stream 36 is added to the top of the extraction column 34. The volumetric ratio of stream 36 to stream 32 is approximately 0.2 to 1. The stream 36 comprises nitric acid having a concentration of about 1 M. This flows downwards to the bottom of the column. The aqueous acidic feed 32 to the central section also flows in a downward direction, with the yttrium being stripped from this phase by an organic phase as it moves downwards. The yttrium depleted raffinate exits the column as stream 38. The organic phase, comprising approximately 25 v/v % bis-(2-ethylhexyl) phosphoric acid, is added through the bottom calming or quiescent section of the column 34 as stream 40. The volumetric ratio of stream 40 to stream 32 is about 5 to 1 . The organic phase moves in an upward direction, i.e. countercurrently to an aqueous phase comprising the acidic feed (stream 32) and the fresh acid (stream 36), and exits as stream 42, impregnated with the yttrium.

The raffinate from the first extraction step in column 34 is recovered as stream 44, diluted further with water or partially neutralised (stream 46) to a concentration of about 0.4 M and at a later time, i.e. after intermediate storage (not shown) until yttrium extraction has been completed, fed to column 34 via streams 48, 28 and 32 for europium extraction. In this second extraction step, the flow rates of the various feeds and products, as well as the ratios of the various feeds to one another and the concentrations of the feeds are altered. Naturally, during this second extraction of europium, feeding of fresh acidic solution containing both yttrium and europium values to the column 34 as hereinbefore discussed, is ceased.

The volumetric ratio of stream 36 to stream 32 is approximately 0.1 to 1 for the second extraction step. Stream 36 has a concentration of approximately 0.4 M for the second extraction step. The volumetric ratio of stream 40 to stream 32 for the second extraction is about 1 to 2.

The raffinate from the second extraction step is contaminated with mercury. This raffinate, leaving the column as stream 38, flows, via a flow linear stream 50, to a reaction precipitation stage or vessel (unit 52). Stream 54 delivers a sulphide anion containing solution in a stoichiometric ratio to the reaction vessel 52. The sulphide anions react with the mercury present in the raffinate to form mercury sulphide, which precipitates out of the solution. The solution and the precipitate flow as stream 56 to a filter (unit 58), where the precipitate (stream 60) is separated from the filtrate (stream 62).

In this first embodiment of the invention, as shown in Figure 1 , the first and second extracts are treated in exactly the same manner. In this embodiment, the rare earth metal recovered during the first extraction is yttrium, while the rare earth metal recovered during the second extraction is europium. The process, and the stream and unit numbers discussed below, apply equally to the recovery of the yttrium and of the europium. The extract from the column 34 (stream 42) is collected batch-wise in a vessel or unit 64, and the required amount of sulphuric acid is added to the vessel as stream 66. The two immiscible liquids are well mixed and then allowed to separate. An aqueous phase is withdrawn from the vessel as stream 68, while an organic phase, free from the rare earth metals, is recycled to the column 34 as streams70, 40 using a pump 72. The aqueous phase, i.e. stream 68, passes through a filter (unit 72), where the precipitated yttrium sulphate or europium sulphate is removed from the filtrate (stream 74). Water via stream 76 is then used to dissolve the filtered sulphates. The sulphate solution is sent to a unit 78, as stream 80. In unit 78, an ammonium hydroxide solution (stream 82) is used to neutralise any residual sulphuric acid present in the sulphate solution.

The neutralized solution flows via stream 84 to a final precipitation reactor, unit 86. Oxalic acid is added to the solution in unit 86, via a stream 87, and the rare earth metal is precipitated out of the solution in its oxalate form.

The solution and the oxalates exit the precipitation reactor 86 as stream 88, and pass through a filter (unit 89). The filtrate from this filtration is discarded as stream 90, while the precipitated solids (stream 92) are sent to a furnace (unit 94), where they are calcined into the oxide, which exits the furnace as stream 96, while any off-gases from the calcination exit as stream 98.

Referring to FIGURE 2, reference numeral 100 generally indicates a process according to a second embodiment of the invention, for recovery of yttrium and europium compounds from a powder comprising an admixture of at least yttrium oxide, europium oxide and mercury.

The process 100 remains the same as for the process 10 of the first embodiment of the invention up until the end of the first extraction step. In the process 100, however, a second column 102 is used to perform the second extraction step, and the process downstream of the first extraction, used to recover the yttrium, is replicated for the recovery of europium from the second extraction. Streams and units 12 to 72 remain the same as for Figure 1 . However, the raffinate from column 34 (stream 102), in the process 100, is diluted to the required acid concentration of 0.4 M for the second extraction by the addition of water along stream 104 or else is neutralised to the required acid concentration by the addition of ammonium hydroxide solution along stream 104. Stream 102 is then fed into a second vibrating plate extraction column 106. Nitric acid, with a concentration of 0.4 M, is added to the top of the extraction column as stream 108. An organic solvent comprising of 25 wt. % bis-(2- ethylhexyl) phosphoric acid is added to the bottom of the column as stream 1 10. The europium laden solvent exiting the column leaves the top calming or quiescent section as stream 1 12. The aqueous phase, devoid of europium, leaves the bottom calming or quiescent section as stream 1 14.

This stream, i.e. stream 1 14, is fed into a precipitation reactor 1 16, where mercury present in the stream is reacted with a sulphide solution, which is fed into the reactor 1 16 through stream 1 18. The liquid, along with the precipitate, is transferred via a stream 120 to a filter (unit 122), where the precipitated mercury sulphide (stream 124) is removed from the liquid, which exits in stream 126. The extract from the column 106 (stream 1 12) is collected batch-wise in a vessel 128, and the required amount of sulphuric acid is added to the vessel 128 as stream 130. The two immiscible liquids are well mixed and then allowed to separate. The aqueous phase is withdrawn from the vessel as stream 132, while the organic phase, free from the rare earth metal, is recycled to the column 106 as streams 134, 1 10 using a pump 136.

The yttrium bearing aqueous phase from the first extraction stage, in stream 68, passes through a filter (unit 138); where the precipitated yttrium sulphate is removed from the filtrate (stream 140). Water via stream 142 is then used to dissolve the filtered sulphates. The sulphate solution passes to a unit 144 as stream 143. In unit 144, an ammonium hydroxide solution (stream 146) is used to neutralise any residual sulphuric acid present in the solution.

The neutralized solution flows, as a stream 148, to a precipitation reactor, unit 150. Oxalic acid is added, as a stream 152, to the solution in unit 150, and the yttrium is precipitated out of the solution in its oxalate form.

The solution and the oxalates exit the precipitation reactor 150 as stream 154, and pass through a filter (unit 156). The filtrate from this filtration is discarded as stream 158, while the precipitated solids (stream 160) are sent to a furnace (unit 162), where they are calcined into the oxide, which exits the furnace as stream 164, while any off-gases from the calcination exit as stream 166.

The europium bearing aqueous phase from the second extraction stage, as stream 132, passes through a filter (unit 168) where the precipitated europium sulphate is removed from the filtrate (stream 170). Water, as a stream 172, is then used to dissolve the filtered europium sulphate. The sulphate solution passes to a unit 174 as a stream 176. In unit 174, an ammonium hydroxide solution (stream 178) is used to neutralise any residual sulphuric acid present in the solution.

The neutralized solution flows, as a stream 180, to a precipitation reactor, unit 182. Oxalic acid is added, as a stream 184, to the solution in unit 182, and the europium is precipitated out of the solution in its oxalate form.

The solution and the oxalates exit the precipitation reactor 182 as stream 186, and pass through a filter (unit 188). The filtrate from this filtration is discarded as stream 190, while the precipitated solids (stream 192) are sent to a furnace (unit 194), where they are calcined into the oxide, which exits the furnace as stream 196, while any off-gases from the calcination exit as stream 198.

Referring to FIGURE 3, reference numeral 200 generally indicates a process (similar to the process 10 of Figure 1 ) for recovery of yttrium and europium compounds from a powder comprising an admixture of at least yttrium oxide, europium oxide and mercury. As also hereinbefore indicated, units or streams of the process 200, which are the same or similar to those of the process 10 hereinbefore described, are indicated with the same reference numerals. Also, the operating parameters of the process 10 of Figure 1 apply to the process 200 of Figure 3, unless otherwise indicated.

In this embodiment of the invention, the first and second extracts are thus also produced by the same column. In this embodiment, the rare earth metal recovered during the first extraction is yttrium, while the rare earth metal recovered during the second extraction is europium. The process and the stream and unit numbers discussed below, apply equally to the recovery of the yttrium and of the europium. As in the process 10 of Figure 1 , the extract from the column 34 (stream 42) is collected batch-wise in the unit or vessel 64, and the required amount of hydrochloric acid is added to the vessel 64 as stream 202. The two immiscible liquids are mixed well and then allowed to separate. An aqueous phase is withdrawn from the vessel 64 as a stream 204, while an organic phase, free from the rare earth metals, is recycled to the column 34 as streams 70, 40 using the pump 72. The aqueous phase (stream 204) passes through an evaporator (unit 206); where up to 80 v/v % of the liquid (hydrochloric acid) is evaporated, with the vapor exiting as stream 208. The concentrated liquid exits the evaporator as stream 210, and enters another reaction vessel (unit 212). In unit 212, the remaining hydrochloric acid is neutralized by the addition of an ammonia solution (stream 214). The neutralized solution flows as stream 216 to a last precipitation reactor, unit 218. Oxalic acid is added, as a stream 220, to the solution in unit 218, and the rare earth metal is precipitated out of the solution in its oxalate form.

The solution and the oxalates exit the precipitation reactor 218 as a stream 222, and pass through a filter (unit 224). The filtrate from this filtration is discarded as stream 226, while the precipitate (stream 228) is sent to a furnace (unit 230), where it is calcined into the oxide, which exits the furnace as a stream 232, while any off-gases from the calcination exit as stream 234.

Referring to FIGURE 4, reference numeral 300 generally indicates a process (similar to the process 100 of Figure 2) for recovery of yttrium and europium compounds from a powder comprising an admixture of at least yttrium oxide, europium oxide and mercury.

As also hereinbefore indicated, units or streams of the process 300, which are the same or similar to those of the processes 10, 100 hereinbefore described are indicated with the same reference numerals. Also, the operating parameters of the processes 10, 100 apply to the process 300 of Figure 4, unless otherwise indicated. The extract from the column 106 (stream 1 12), is fed to the vessel 128, to which hydrochloric acid with a concentration of between about 3 M to about 5 M is also added, through stream 302. Good contact between the aqueous and organic phases in vessel 128 is ensured by vigorous stirring, after which, the two phases are allowed to separate. The organic solvent is recycled to the column 106 as streams 134, 1 10 using the pump 136, while the aqueous phase, bearing the europium, is sent to a europium recovery section of the process.

The yttrium bearing aqueous (hydrochloric acid) phase from the first extraction stage (stream 304) passes to an evaporator 306. In the evaporator 306, up to 80 volumetric % of the liquid (hydrochloric acid) is evaporated, with the vapor exiting as stream 308.

The concentrated liquid exits the evaporator 306 as a stream 310, and enters a reaction vessel or reactor 312. In the reactor 312, any remaining hydrochloric acid is neutralized by the addition of an ammonia solution (stream 314). The neutralized solution flows as a stream 316 to a further precipitation reactor 318. Oxalic acid is added, as a stream 320, to the solution in reactor 318, and the yttrium is precipitated out of the solution in its oxalate form. The solution and the oxalates exit the precipitation reactor 318 as a stream 322, and pass through a filter 324. The filtrate from this filtration is discarded as a stream 325, while the precipitate (stream 326) is sent to a furnace 328, where it is calcined into the oxide, which exits the furnace as stream 330, while any off-gases from the calcination exit as stream 332.

The europium bearing aqueous phase from the second extraction stage passes from the vessel 128 to an evaporator 334 as a stream 336. In the evaporator 334, up to 80 volumetric % of the liquid (hydrochloric acid) is evaporated, with the vapor exiting as a stream 338.

The concentrated liquid exits the evaporator as stream 340, and enters a reactor 342. In reactor 342, any remaining hydrochloric acid is neutralized by the addition of an ammonia solution as a stream 344. The neutralized solution flows as a stream 346 to a further precipitation reactor 348. Oxalic acid is added, as a stream 350, to the solution in reactor 348, and the europium is precipitated out of the solution in its oxalate form.

The solution and the oxalates exit the precipitation reactor as a stream 352, and pass through filter 354. The filtrate from this filtration is discarded as a stream 356, while the precipitate (stream 358) is sent to a furnace 360, where it is calcined into the oxide, which exits the furnace in stream 362, while any off-gases from the calcination exit as a stream 364.

References

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