AU593061B2

AU593061B2 - Method for the removal of lead chlorides from rare earths

Info

Publication number: AU593061B2
Application number: AU68786/87A
Authority: AU
Inventors: Alain Rollat; Jean-Louis Sabot
Original assignee: Rhone Poulenc Chimie SA
Current assignee: Rhodia Chimie SAS
Priority date: 1986-02-14
Filing date: 1987-02-13
Publication date: 1990-02-01
Anticipated expiration: 2007-02-13
Also published as: EP0233121A1; JPS62253739A; AU6878687A; ATE58398T1; MY101053A; DE3766119D1; FR2594429A1; KR870007846A; EP0233121B1; BR8700668A

Abstract

Process for removing lead from rare earths in the form of chlorides in aqueous solution, consisting in: - performing a liquid-liquid extraction between an aqueous phase containing at least one rare earth and the lead in the form of chlorides, and an organic phase containing an extraction agent consisting of an alkyl monoester of an alkylphosphonic acid: the aqueous phase brought into contact with the organic phase having at the time of the extraction a chloride ion concentration of at least 2 moles/litre and a pH higher than or equal to 2 and lower than or equal to 4, - then recovering the rare earth(s) from the organic phase.

Description

Gl1 1 593061 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION FOR OFFICE USE: Class Int. Class Application Number: Lodged: 9 I 99 68786/7 t I GComplete Specification Lodged:

I

9 t A Accepted: Published: ,Priority:

V

Related Art: This document contains the amendments made und r Section 49 and is correct for printing.

Name of Applicant: Address of Applicant: RHONE-POULENC CHIMIE 25, quai Paul Doumer, 92408 Courbevoie, France Actual Inventor: Alain ROLLAT and Jean-Louis SABOT Address for Service: Shelstor: Waters, I9 Clarence Street, Sydney Complete Specification for the Invention entitled: "METHOD FOR THE REMOVAL OF LEAD CHLORIDES FROM RARE EARTHS" The following statement is a full description of this invention, including the best method of performing it known to me/us:- 1 -1 METHOD FOR THE REMOVAL OF LEAD FROM RARE-EA RTHS This invention relates to a method for the removal of lead from rare-earths. More particularly, it deals with a process for the removal of lead from rare-earth chlorides in an aqueous solution.

In industrial processes providing rare-earths by p treating rare-earth ore to produce a mixture of rare-earth hydroxides, the recovery of the hydroxides in an acid medium and the subsequent separation of the rare-earths, lead is one of the elements found after the separation, as well as at least one of the rare-earths.

When rare-earths are processed in the form of 4 chlorides, it is known that the lead can be removed by adding alkaline sulphides or sulferetted hydrogen to an aqueous solution of the chlorides so as to precipitate the lead as a sulphide. The precipitation is slow and the removal of the lead incomplete.

4 JP-A-58 185729 proposed an improvement to this method by adding hydrozine or hydroxylamine. However, the drawbacks associated with the use of sulphides remain.

The aim of this invention is to provide a new method for the removal of lead and producing purer rare earths.

To this end, this invention aims at a method for the elimination of lead impurities from an aqueous solution of rare earth chlorides, comprising liquid/liquid extracting such aqueous solution with an organic phase which comprises a phosphonic monoester extractant having the formula

RZ

2 0 OH ~ALI~, 2wherein R 1 and R 2 which may be identical or different, are each a linear, branched or cyclic alkyl radical having from 4 to 20 carbon atoms, said aqueous solution having, at the time of extraction thereof, a chloride ion concentration of at least 2 moles/liter and a pH ranging from 2 to 4, and whereby rare earth values are transferred into said organic phase and said lead impurities remain in said aqueous solution, and (ii) recovering rare earth values from said organic phase.

The term rare-earths used in relation to this invention refers to elements name lanthanides with atomic numbers from 57 to 71 inclusive, also yttrium with the atomic number 39.

The extractant is a compound of formula in which R1 and R 2 are alkyl groups containing 8 carbon atoms, in particular the hexylic ethyl-2 monoester of hexylphosphonic ethyl-2 acid, hexylic ethyl-2 monoester of S n-octylphosphonic acid, the n-octylic monoester of ethyl-2 hexylic acid, n-octylic monoester of n-octylphosphonic acid. These esters have previously been suggested as extractants for lanthanides (Peppard Col. notably J Inorg. Nucl. Chem 1965, 27, 2065). However, their use for the removal of lead in a liquid-liquid extraction process has not previously been considered.

The aqueous phase placed in contact with the extractant can be an aqueous solution from the redissolution with hydrochloric acid of hydroxides obtained from the sodic attack of the ores containing rare-earths such as monazite, bastnaesite and xenotime.

Any other solution of rare-earth salt may be used after the anion present has been changed to a chloride anion.

For example, this solution can have been previously treated for removal of thorium according to the usual methods. The aqueous solution could also be a ceric earth solution such as lanthane, cerium, praseodyme, neodyme resulting from an initial separation of the rare-earths.

3 The method of the invention applies to solutions as they are or after they have been concentrated.

Usually the liquid-liquid extraction process carried out with rare-earth chloride solutions with concentrations expressed in rare-earth oxides which vary between 20 g/l and 500 g/l the figures given are in no way critical. For preference the concentration should be between 50 g/l and 200 g/l.

The acidity normally varies between 0.01 N and 3.0 N.

In accordance with the method of this invention, the organic phase, as well as the extractant contain an organic diluent. Diluents to be used are those usually employed for liquid-liquid extraction. Among these: aliphatic hydrocarbons such as hexane, heptane, dodecane and petroleum diluents of the kerosene type aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene and petroleum diluents composed of a mixture of alkylbenzene, particularly the SOLVESSO solvents marketed *4 by EXXON (SOLVESSO is a trade mark of EXXON) and finally the halogen derivatives such as chloroform and carbon tetrachloride. A mixture of these may also be used.

The concentration of the extractant in the organic phase is not a critical factor of this invention and can vary considerably. It can vary from 5% of the volume of the organic phase when the extractant is in solution in a diluent, up to 100% when the extractant is used pure.

When the extractant used is the hexylic ethyl-2 monoester of hexylphosphonic ethyl-2 acid, the preferred extractant, the concentration in the organic phase can S30 usefully be 0.5 to 3 moles/litre and preferably still 1 to ,2 moles/litre.

In accordance with the invention, the organic phase may also contain various modifying agents to improve the hydro-dynamic properties of the method without altering the chelating properties of the organophosphonic compound. Suitable compounds are those with an alcohol function, particularly heavy alcohols where the number of -4w i I~ *y EXN(OVSS satae ako XON n ial I m a carbon atoms is between 4 and 15 and heavy phenols as well as various other compounds e.g. phosphoric esters like tri-butylphosphate, phosphonic esters like diakyl-phosphonates, dibutylbutylphosphonates or bis (ethyl-2 hexyl) ethyl-2 hexylphosphonate, phosphine oxides or sulphoxides. A ratio between 3 and 20 by volume in relation to the organic phase is usually satifactory.

When formulating the extraction process, the hydrogen H+ ion concentration and the concentration of chloride ions in the aqueous phase are important.

For the extraction to take place satisfactorily, the aqueous phase in contact with the organic phase at the time of extraction should have an ion chloride concentration of at least 2 moles/litre and a pH of from 2 to 4.

The aqueous phase must contain a concentration of chloride ions of at least 2 moles/litre and preferably between 2 and 4 moles/litre. If the concentration of chloride ions in the aqueous phase is insufficient, the chloride ions may be increased by the addition of hydrochloric acid or a salt in the form of ammonium chloride.

This may be added as a solid or as an aqueous solution.

The quantity of acid or salt to be added is determined so that the desired concentration of chloride ions is obtained. When using aqueous solutions it is preferable, although not critical, to use concentrated solutions so as not to excessively dilute the aqueous phase.

Because the aqueous solutions of rare-earth chlorides used in the first place are relatively acid, it is often necessary to adjust the concentration of H ions in the aqueous phase by adding an alkaline base e.g. soda or ammonium hydroxide. For preference an aqueous solution of diluted or concentrated ammonium hydroxide is used the concentration may vary widely, between 1 and 10 N but a concentrated solution of ammonium hydroxide is preferable.

The quantity of alkaline base to be added corresponds to some extent to the stoechiometric quantity of the rare- 5 I i II~ I Ir t t t It I t i4 earths to be extracted in the organic phase to which the required quantity of base has been added to neutralise the free acidity until the desired pH has been obtained, this should be from 2 to 4 and preferably from 2.5 to During the extracting phase, the organic and aqueous phase are placed in contact at a temperature which is not critical it is usually selected between 100C and but more often between the ambient temperature and 40 0

C.

The extraction can be done in the usual way, by trickling, preferably counter to the aqueous and organic phase. The number of levels and the flow of the two phases is determined in accordance with the usual calculations known to scientists.

A leaching stage is sometimes necessary after the extraction in order to eliminate the lead which can be removed in small quantities in the organic phase.

At the leaching stage, the organic phase is leached with an aqueous solution containing chloride ions at a concentration of at least 1 mole/litre the upper figure is not critical and is limited only by solubility.

A solution with this concentration can therefore be used and be an aqueous solution of hydrochloric acid, an aqueous solution of a salt in the form of a chloride, in particular ammonium chloride with a pH diminished to 1 or less by the addition of an acid such as hydrochloric acid or an aqueous solution of rare-earth chlorides of the same kind as the rare earths to be extracted and composed of a fraction of the aqueous phase obtained in the following operation of counter extraction of the rare-earths from 30 the organic phase.

This operation should preferably, as before, be done at a counter flow. The number of levels and the flow are calculated to extract almost all the lead present in the organic phase.

After extraction and leaching followed by separation of the aqueous and organic phases a counter extraction of

LI

-6- I It r. I 1 9 *.itr

I

4611 I~c~ Ua*l~ the rare earths contained in the extractant is usually carried out.

The rare-earths present in the organic phase are separated by placing this phase in contact with an acid aqueous solution, e.g. a hydrochloric acid solution with a concentration of from 0.5 N up to very high concentrations such as 10 N, but preferably 5 to 8 N.

The counter extraction may be done counter to the current as previously described, the number of levels and the flows are determined according to the method of calculation familiar to scientists.

The rare-earths extracted are removed in an aqueous solution but the extraction solvent can be recycled to the extraction stage. This recycling is not essential to the invention but is desirable for economic reasons.

o" The various stages of contact and leaching can take place in the usual liquid-liquid extraction equipment S which operates with a counter flow. These elements r' usually include several levels of mixer-decanting vessels trr 20 or line and/or agitated columns intended for extraction, selective leaching, recovery of rare-earths in an aqueous

I

phase and for the recuperation of extracting solvents.

The following examples are given only for guidance and in no way limit either the field or the concept of the invention.

In these examples, the percentages are expressed by weight.

EXAMPLE 1 Figure 1 illustrates this example The equipment used includes in series and counter-current flows section A for liquid-liquid extraction composed of a mixer-decanting vessel i section B for leaching, composed of 3 mixer-decanters section C for counter-extraction of the rare-earths, composed of 3 mixr-decanters.

7 The aqueous solution to be treated is an aqueous solution of rare-earth chlorides with a concentration of rare-earth oxides of 120 g/l. It also contains 0.5% lead in relation to the weight of rare earth oxides.

The concentration of chloride ions is 2.8 moles/litre and that of H ions is 0.5 mole/litre.

The extractant used is ethyl-2 hexylic monoester of ethyl-2 hexylphosphonic acid. It is used in it's marketed form under the name of PC 88 A.

This extractant is placed in solution in kerosene at 2 moles/litre and the mixture thus obtained is the extraction solvent.

Before detailing the various operations it should be stated that for the entry and exit of the extraction leaching counter-extraction units, the direction of flow of the organic phase is used.

The aqueous solution of rare-earths to be refined is introduced at 1 in extraction section A at a flow rate of 1000 litres per hour.

At the same time a solution of ammonium hydroxide N is introduced at 2 with a flow of 255 litres per hour.

Thus the pH of the aqueous solution 2.4 N hydrochloric acid is introduced in the reverse direction of flow at a rate of 150 litres/hour.

At the entry of extraction section A, the organic phase composed of the extracting solvent is introduced at 3 at a flow rate of 3000 litres/hour.

This phase then goes into leaching section B and at 4 an aqueous solution of 2.4 N hydrochloric acid is V 30 introduced in the reverse direction of flow at a rate of 150 litres/hour.

The separated aqueous phase goes to extraction section A where it is added to the aqueous phase and evacuated at 5 after the extraction. l The organic phase from leaching section B is placed in the counter extraction section C where at 6, cocnter to the flow an aqueous solution of hydrochloric acid 7 N at a 8-

A

r I- -I Il__y L-IOI-LUI i-~CViRii rate of 360 litres/hour is introduced.

At 7, the entry to counter-extraction section C, an aqueous solution of chlorides of rare-earths, with a concentration of rare-earth oxides of 350 g/l is recovered the rare earths are determined by gravimetry of the oxides which results from the calcination of the earth oxalates precipitated from the aqueous solution of rare-earth chlorides treated with oxalic acid.

The lead content in the aqueous solution of rare-earth chlorides is less than 0.001 which is the limit of detection for measurement, i.e. atomic absorption o 0 V It, Vi t V tI'V

II

*L

spectometry.

The regenerated organic phase is drained off at 8 and recycled at the exit of counter-extraction section C, in extraction section A, at the same rate of flow.

EXAMPLE 2 Figure 1 illustrates this example and the characteristics for the solution of rare earth chlorides are the same as those given for Example 1.

The aqueous solution of rare-earths to be treated are introduced into extraction section A at a flow rate of 1000 litres/hour.

Simultaneously at 3, an aqueous solution of ammonium hydroxide 10 N is introduced at a rate of 240 litres/hour. This maintains the pH of the resulting aqueous solution at 3.2.

At 3 of extraction section A, the organic phase composed of the extraction solvent is introduced. This is the same as that used in example 1, at a rate of 3000 litres/hour.

This phase then passes into leaching section B and at 4, an aqueous solution of hydrochloric acid 1.0 N is introduced counter to the flow at a rate of 180 litres/hour.

The separated aqueous phase goes to extraction section A where it is added to the aqueous phase which is removed at 5 after the extraction.

9 The organic phase from leaching section B is introduced into counter-extraction section C where, at 6 at counter-current is introduced an aqueous solution of hydrochloric acid 7 N at a rate of 360 litres/hour.

At 7 of counter-extraction section C, an aqueous solution of rare-earth chlorides, with a concentration expressed in rare-earth oxides of 350 g/l is recovered.

The lead content in the aqueous solution of rare-earth chlorides is less than 0.001 The regenerated organic phase is evacuated at 8 and is recycled at the exit of counter-extraction section C in extraction section A at the same rate of flow.

EXAMPLE 3 The equipment for this example is identical to that for example 1 except that leaching section B is composed of 4 mixer-decanting vessels instead of 3.

The aqueous solution to be processed is an aqueous solution of rare-earth chlorides with a concentration of rare-earth oxides of 127 g/l containing 0.5 lead expressed in relation to the weight of rare-earth oxides.

The ion chloride concentration is 2.8 moles/litre and of SH ions is 0.5 mole/litre.

The aqueous solution of rare-earths to be refined is introduced at 1 of extraction section A at a rate of 1000 litres/hour.

Simultaneously an aqueous solution of ammonium i hydroxide 10 N with a flow of 250 litres/hour is introduced at 2. This addition maintains the pH of the K resulting aqueous solution at 3.2.

At the entry 3 of the extraction section A, an organic phase composed of the ethyl-2 hexylic monoester of ethyl-2 hexyl-phosphonic acid is introduced at a flow rate of 8000 litres/hour, it is in solution ii, kerosene at a rate of one mole per litre.

This phase then goes to leaching section B where at 4, counter to the flow an aqueous solution of hydrochloric acid 2.4 N is introduced at 300 litres/hour.

10 The separated aqueous phase is sent to extraction section A where it is added to the aqueous phase which is removed after extraction at The organic phase from leaching section B is introduced into counter-extraction section C, where at 6, counter to the flow, an aqueous solution of hydrochloric acid 7 N is introduced at a rate of 380 litres/hour.

At the entry to counter-extraction section C, at 7, an aqueous solution of rare-earth chlorides with a concentration expressed in rare earth oxides of 350 g/l is recovered.

The lead content in the aqueous solution of rare-earth chlorides is less than 0.001 .The regenerated organic phase is removed at 8 and 9o- recycled at the exit to the counter-extraction section C Oh in section A at the same flow rate.

Vr EXAMPLE 4 0 One part of the solution of chlorides of rare earth has a concentration of rare earth oxides of 135 g/l and contains 0,5% of lead.

The distribution of rare earths in this solution is Sas follows: La 2 03 CeO 2 Pr 6 0 11 Nd 2 0 S24,7% 50,0% 5,5% 19,8% 3 3 Mixing 100 cm of this solution with 600 cm 3 of a solvant constituted of the monoester ethyl-2-hexyl of the acid ethyl-2-hexylphosphonate in a kerosene solution, results in a concentration of 1 mol/liter.

If 10 N of ammonia is added to this mixture, the resulting pH value is as shown in the following table.

After decanting, an amount of rare earths and of lead remains in each phase. The table also depicts separating factors for the different rare earths containing lead: 11 PH% of %of %f f %f pH rare La 6ef Tro f d pI Of FaP hF b r~/P earthi extr. extr. extr. extr. F~/bFc P F /P extra cted 87,% 64,3 94,1 97,1 98,1 85 750 1570 2430 2,2 92,7% 78,3 96,9 98,5 99,0 155 1360 2860 4440 2,4 95,7% 90,0 98,7 99,4 99,6 290 2550 75000 >5000 It II f 'fit I Li

I

One notices that the separating increasing pH values.

factor increases with 12

Claims

1. Method for the elimination of lead impurities from an aqueous solution of rare earth chlorides, comprising (i) liquid/liquid extracting such aque as solut_' i with an organic phase which comprises a phosphonic monoester extractant having the formula R 2 0 OH wherein R and R 2 which may be identical or different, are each a linear, branched or cyclic alkyl radical having from 4 to 20 carbon atoms, said aqueous •solution having, at the time of extraction thereof, a *4t" chloride ion concentration of at least 2 moles/liter and a I, °pH ranging from 2 to 4, and whereby rare earth values are transferred into said organic phase and said lead impurities remain in said aqueous solution, and (ii) recovering rare earth values from said organic phase.

2. Method according to claim 1 characterised by the phosphonic monoester complying with formula in which R and R 2 are alkyl groups containing 8 carbon atoms.

3. Method according to claim 2 characterised by the I, phosphonic monoester being hexylic ethyl-2 monoesters of hexyl-nhosphonic ethyl-2 acid. o 44 4. Method according to one of claims 1 to 3 characterised by the concentration of chloride ions in the aqueous phase being from 2 to 4 moles/litre. Method according to one of the claims 1 to 4 characterised by the pH of the aqueous base being 2.5 to -13- I .4 6# trr F I: 1

6. Method according to one of the claims 1 to characterised by the aqueous solution of rare-earth chlorides having a concentration, expressed in rare-earth oxides, between 20 and 500 g/l.

7. Method according to claim 6 characterised by the aqueous solution of rare-earth chlorides having an acidity between 0.01 N and 3.0 N.

8. Method according to one of the claims 1 to 7 characterised furthermore, by the organic phase having at least one organic diluent selected from the group made up of aliphatic hydrocarbons, kerosene type petroleum diluents or composed of a mixture of alkyl-benzenes, aromatic hydrocarbons,, halogenated hydrocarbons.

9. Method according to claim 1 characterised by the concentration of phosphonic monoester in the organic phase being between 5 and 100 of the volume of the organic phase. Method according to claim 1 characterised by the concentration of the hexylic ethyl-2 monoester of hexylphosphonic ethyl-2 acid in the organic phase being from 0,5 to 3 moles/litre.

11. Method according to claim 10 characterised by the concentration of the hexylic ethyl-2 monoester of hexylphosphonic ethyl-2 acid in the organic phase being from 1 to 2 moles/litre.

12. Method according to one of the claims 1 to 11 characterised by the organic phase having at least one modifying agent selected from the group composed of the compounds with an alcohol function, phosphoric esters, phosphonic esters, phosphine oxides, sulphoxides.

13. Method according to claim 12 characterised by the concentration of the modifying agent in the organic phase being between 3 and 20 of the volume of the organic phase.

14. Method according to one of the claims 1 to characterised by the concentration of H+ ions in the aqueous phase being adjusted by the addition of ammonium hydroxide. *1 I 14 c-- Method according to one of the claims 1 to 14 characterised by the extraction temperature being between 0 C and 50 0 C.

16. Method according to one of the claims 1 to characterised by proceeding, after the extraction to a leaching of the organic phase with an aqueous solution containing ion chlorides at a concentration of at least 1 mole/liitre.

17. Method according to claim 16 characterised by the leaching solution being a hydrochloric aqueous solution.

18. Method according to claim 16 characterised by the leaching solution being an aqueous solution of ammonium chloride with a pH of 1 or less.

19. Method according to claim 16 characterised by the leaching solution being an aqueous solution of rare-earth chlorides. Method according to one of the claims 1 to 19 characterised by proceeding, after the extraction process and the successive leachings, followed by a separation of the aqueous and organic phase, to a counter-extraction of the rare-earths from the extraction solvent by placing the organic phase in contact with an acid aqueous solution.

21. Method according to claim 20 characterised by the acid aqueous solution being a hydrochloric acid aqueous solution.

22. Method according to claims 20 and 21 characterised by the concentration of the acid aqueous solution being between 0.5 N and 10 N.

23. Method according to claim 22 characterised by the concentration of the acid aqueous solution being between and 8 N. DATED this 13th day of February, 1987. RHONE-POULENC CHIMIE Attorney: ROBERT G. SHELSTON Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS 15