AU601998B2

AU601998B2 - Oxygenated rare earth derivatives

Info

Publication number: AU601998B2
Application number: AU76784/87A
Authority: AU
Inventors: Claire Gourlaouen; Bertrand Latourrette; Jean-Luc Le Loarer; Claude Magnier
Original assignee: Rhone Poulenc Specialites Chimiques
Current assignee: Rhone Poulenc Specialites Chimiques
Priority date: 1985-07-11
Filing date: 1987-08-11
Publication date: 1990-09-27
Anticipated expiration: 2006-07-11
Also published as: AU7678487A

Description

60 1 98 COMMONWEALTH OF AUSTRALIA 9 FORM PATENTS ACT 1952 C OM P L E TE S P E C I F I C A 'p To w S P E C I F I C A T 1 0 M FOR OFFICE USE: Class Int.Cla .3 Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name of Applicant: Address of Applicant: Actual Inventor: RHONE-POULENC SPECIALITES CHIMIQUES "Les Miroirs", 18 Avenue d'Alsace, 92400, Courbevoie PARIS CLAUDE MAGNIER CLAIRE GOURLAOUEN, JEAN-LUC LE LOARER and BERTRAND LATOURRETTE tp Address for Service: SHELSTON WATERS, 55 Clarence Street, Sydney Complete Specification for the Invention entitleda "OXYGENATED RARE EARTH DERIVATIVES" The following statement is a full description of this invention, including the best method of performirg it known to me/us:- 1 This invention relates to a modification in, or improvement to, the invention described in our co-pending application 60076/86, the disclosure of which is incorporated herein by reference.

That application (hereinafter called "the parent application") describes a procedure for obtaining precursors of oxides of rare earths and to products obtained according to the procedure.

It has now been found that a modification of the above procedure consist3 in using the precursors of the parent for the manufacture of oxygenated derivatives of rare earths especially for manufacture of rare earth oxides and carbonates.

SUMMARY OF THE INVENTION The present invention provides a method comprising the steps of: reacting an aqueous solution of at least one salt of a trivalent rare earth with a base, at a temperature in the range of 100 to 50 0 C, under conditions such that the molar ratio of the concentration of the OH~ ions from the base to the concentration 'f the salt of rare earth of the solution, expressd in rare earth cations, is smaller than -4 separating and drying the precipitate obtinr d, and calcinating thpa cried precipitate to produce an oxygenated derivative of tha rare earth, wherein said i oxygenated derivative is a rare earth oxide or rate earth carbonate.

4 A-2- To THE COMMISSIONER OF PATENTS.

SHELSTON WATERS PATENT ATTORNEYS CLARENCE STREET. SYDNEY

AUSTRALIA

Cables: 'Vald' Sydney Telex: 24422 In preferred embodiments of the present modification the rare earth oxides are obtained by calcination of the precursors of the parent application preferably at from 650 1300 0 C. The resulting rare earth oxides are characterized by their appearance which, like their precursor, is in the form of microballs. The microballs usually vary between 2 and 50 micrometers in diameter.

In the first step of the procedure, the aqueous solution of a salt of a trivalent rare earth is mixed with 10 the base.

The aqueous solution of the salt of a trivalent rare earth has to be soluble under the conditions of the invention.

Among the salts well suited to the invention are the nitrates of rare earths, the double salt of rare earths -2a- A 1' nitrates and ammonium or the chlorides of rare earth such as yttrium or lauthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lucetium.

A solution containing one or several rare earths can be used: in particular, a solution of salts of rare earths obtained directly or indirectly from the treatment of the minerals of rare earths can be used.

The purity of the one or several salts of rare earths employed is chosen according to the demands of their application.

o o. The concentration of the solution of one or several 0ao salts of rare earths is not a critical factor and can vary Swithin large limits; it should nevertheless be in the af s range 0.1 to 2 moles per litre, and is optimally chosen between 0.3 and 1.5 moles per litre.

The acidity of the aforesaid solution is not critical according to the invention.

The base used in the invention procedure is usually in the form of an aqueous solution. An aqueous solution of bases such as ammonia, sodaf potash, ammonium *it carbonate, urea, hexamethylenetetramine, etc. can be used.

S so Gaseous ammonia can also be used.

According to the invention, a solution of ammonia is preferentially used.

The normality of the basic solution used is not a critical factor according to the invention: It can vary within large limits, for instance, between 0.1N and 11N, -3- 1 ,4 but it is preferable to use solutions whose concentration varies between 2 and 11N.

The proportion between the basic solution and the solution of at least one salt of trivalent rare earth is 3+ 3 is preferably such that the molar ratio (OH-)/(RE 3 is greater than 0.2 and smaller than 5. However, the productivity or the precipitation is optimum when this ratio is greater or equal to 2 and smaller than The mixing of the above mentioned reactants can be i0 achieved in several ways. For instance, simultaneous mixing, under agitation of the aqueous solution of at least one salt of trivalent rare earth and of the basic solution can be achieved, or the base can be added, continuously or all at once, into the aqueous solution of at least one salt of trivalent rare earth or inversely.

The rates at which the solutions of reactants are added are adjusted so that the molar ratio

(OH-)/(RE

3 defined above is respected.

It is also possible to control the rates by adjusting the pH which usually varies between 6.5 and 9.5. The aforesaid pH depends upon the nature of the salt of rare earth and upon the agitation.

The temperature of the reaction medium should be in the range of about 10OC to about 50°C, and optimally between 10 and 30 C. The upper limit presents a critical aspect with reFpect to productivity: since at temperatures greater than 50 C, it has been noticed that the filtration of the obtained precipitate is not as good.

1 i iThe duration of the incubation of the mixture in the reaction medium can vary between one minute and several hours, for instance 48 hours or more: the upper limit is not a critical factor; however a duration of five minutes to thirty minutes is usually satisfactory.

The conditions of agitation have to be relatively vigodfrous. The speed of agitation depends upon the type of agitation and upon the ratio of the diameter of the agitator and of the reactor.

For example, for a four bladed agitator which goes past very close to the wall of a 15cm diameter reactor o0 0 3 oou (effective volume: 730 cm the speed is fixed between 200 and 1000 rotations/minute, but optimally between ,00 and 400 rotations/minute.

U The second step of the procedure consists of separating the precipitate so obtained, which is in suspension in the reaction mass, and appears under some 0, o0 conditions as microballs.

o o The precipitate can be separated from the reaction hb medium using the current techniques of solid-liquid separation, more particularly decantion or filtration, the f latter being easily conducted. This separation is usually o0 .j achieved at room temperature, most often 15 to 25 C.

The decanted precipitate or the filter cake can eventually be washed so as to eliminate any anions adsorbed onto the precipitate. Water, preferably distilled or "deionised", the temperature of which can vary between 5 and 90 C, is used for the wash.

One to several washes, most often one to three, are usually performed.

An organic solvant can also be used for washing, for instance aliphatic, cycloaliphatic or aromatic hydrocarbons or aliphatic or cycloaliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, neobutanol.

One to several washes, most often one to three, are usually performed.

After the wash, the water content of the cake is between 20 and 80%, usually 20 and The precipitate obtained after separation and washes can then be subjected to thermal treatment. It can be dried, and this can be done either under normal atmosphere -2 or under low pressure conditions of the order of 10 to 100mm of mercury (1,33 to 1,33 x 10 Pa), The drying temperature can vary between room temperature and 200°C. The duration of the drying process is a function of the temperature: it is not critical and can range from j 30 minutes to 48 hours, but is optimum between 2 and 8 hours.

The procedure of the invention can be achieved using classical apparatus. The mixing step of the solutions of reactants is achieved in a reactor equipped with a reliable heating system, for instance, hot water circulation within the double wall of the reactor, or via thermal exchangers (coils). The reactor also has to be equipped wit' the usual devices for controlling temperature (thermometer) and agitation (agitation via pales, brace, screw or turbine) as well as a device to introduce one or two of the reactants in the form of aqueous solutions, for instance, a metering pump.

The devices to be used to achieve the separation and the drying steps do not require any particular characteristics, The filtration of the suspension obtained can be achieved using an inert gas (nitrogen) pressure filter, a low-pressure filter (Buchner, Nutche) or using a continous filtration device such as a rotary filter (Vermay type) or a filtration column.

o. The precipitate is placed in silica, porcelain or alumina baskets, then subjected to the drying operation, which can be achieved in any kind of drying device, for instance, a ventilated or low pressure drying cupboard or else in a dessicator usually under low pressure, maintained via a water pump.

In accordance with the invention procedure, a i precursor of an oxygenated derivative of rare earth is obtained, which always filters easily, and which takes the form of an hydroxide of rare earth, of which some of the hydroxil groups have been partially substituted by the anion brought by the salt of rate earth.

An examination with the scanning electron microscope reveals the morphological aspect of the invention product. It shows the presence of agglomerate., the dimensions of which range from 2 to 100 micrometers, -7- When the molar ratio (OH 3 is greater than or equal to 1 and smaller than or equal to 3 the existence of particularly well rounded microballs is noticed. In this case, the mean diameter of the microballs varies between 50 and 60 micrometer. The mean diameter is defined as the diameter such that 50% in weight of the microballs have a diameter greater or smaller than the mean diameter.

r The precursor obtained can, according to the invention, be used as an intermediate to the fabrication particularly of oxides or carbonates of rare earths.

A particular application of the precursor of oxygenated derivative of the invention resides in the preparation of an oxide of rare earth by the calcination of the dried precursor.

The operation of calcination is preferably performed at a temperature ranging between about 650 and about 1300 0

C.

The duration of the calcination process is not critical and is optimum between 1 and 4 hours.

An oxide of rare earth is obtained which, like its precursor, appears as microballs. The size of the microballs usually varies between 2 and 50 micrometers.

To better illustrate the protocol of the invention, different examples are given further on. These examples are, of course, not restricting.

Before detailing the aforesaid examples, we shall describe the test of filtrability which enables an appreciation of the filtration qualities of the -8- C> S'*a precipitate obtained.

For the test, the filtration is achieved using a Buchner Filter, the sintered glass of which is covered with 12.5 cm 2 Millipore filter paper, the porosity of which is 0.45 micrometer.

The aforesaid Buchner is connected to a water pump via a tube along which are interposed a pair of Mohr forceps, an air entry valve and a manometer.

The procedure is as follows:- The water pump is started while the Mohr forceps is kept closed.

When the manometer indicates that the pressure equilibrium is reached, a loss of pressure P=j20mm of mercury (0.42-10 Pa) is produced by opening the "air-entry" valve, the Mohr forceps still closing the circuit.

The solution of the precursor of an oxygenated derivative of rare earth is then rapidly poured into the filter and the Mohr forceps are removed.

S- The time for the outflow of 100cm 3 of suspension is measured.

An index of filtrability expressed in cm 3 /h/cm 2 S is defined, and represents the numeral expression of the behavior of the precipitate upon filtration.

The test is considered satisfactory when the value obtained for the index is at least equal to 100.

The following examples 1-11 illustrate the preparation of precursors of oxygenated derivatives of -9- L neodymium, samarium, praseodymium and cerium III.

Examples 12-13 illustrate calcination of the precursors.

EXAMPLE 1 In a 2 litre reactor with a double wall within which circulates thermostated water at 20 0 C, and equipped with a thermometer, a device to introduce the reactants and a device for agitation (quadripale), the following are introduced simultaneously at rates of 1300cm 3/h nd 800cm 3 respectively: a solution of neodymium nitrate containing mole/litre of Nd 3 a solution of ammonia 2N, te ratio OH /Nd being equal to I The temperature of the reaction medium is The duration of the incubation of the mixture in the reaction medium is 20 minutes.

The speed of agitation is 500 rotations/min.

After 20 minutes, the reaction mass is filtered at room temperature using a Buchner Filter as previously described for the best.

The index of filtrability is 1100cm /h/cm 2 The J quantity of neodymium remaining in the original waters is S* assessed by chelation with a titrated solution of ethylenediamine totracetic acid sodium salt, which shows that the productivity of precipitation is 100%.

The precipitate obtained is then subjected to drying in a drying cupboard at 50 C for 2 hours.

The product prepared according to the invention shows a morphology illustrated in Fig. 1, which is a scanning electronmicroscope photograph (G=300). It shows microballs, the apparent diameter of which varies between and 50 micrometers.

The granulometric analysis achieved by means of sedimentation, confirms the apparent diameter. The results are given below: Particles Diameter Cumulated in weight 1 micrometer micrometer 13 6 micrometer 8 micrometer micrometer 33 micrometer 61 20 micrometer 83 micrometer 96 mean diameter 13 micrometers.

Example 2 In relation to example 1, the rate of addition of the solution of ammonia is modified to become 1300cm3/hour, so that the ratio OH-/Nd3+ now equals 4.

The index of filtrability obtained is decreased to 400cm /h/cm 2 which is not as good, but still satisfactory.

Example 3 In this example, the influence of the concentration of the solution of rieodymium nitrate is shown. The -11i .i operative conditions of example 1 are repeated except for the concentration of the aforesaid solution which is now 1.4 moles/litre instead of 0.5 moles/litre.

3 2 The index of filtrability is now 200cm /h/cnV Example 4 This example illustrates this influence of the duration of the incubation.

Example I is repeated except for the fact that the duration of the incubation of the mixture in the reaction medium is now 10 minutes.

In this case, the index of filtrability is 3 2 700cm /h/cm Examples 5 and 6 The preparation of the precursor of an oxygenated derivative of neodymiumi is performod under the cond it ion,,; described in example 1, however, the temperature of the reaction is modified to 30 0 C in example 3 and to 0C in example 6.

The results are summarized in table Por comparison, the index of Eiltrobilit-,imt 1 is .'so included in the table Eamle~ 4b I T 0 MC 20 30 Tr (am 3/h/cMW 2 100 800 3.000 Examples 7 and.8 These two examples i1lu:state the inflztme nf.

speed of aqitatidon of the roaction mod~iura, Ia- The procedure is the same as in example but for the speeds of agitation.

The results are summarized in Table II Example nb 1 5 6 Speed of agitation 500 100 800 (rotations/min) I (cm/h/cm 2 1100 500 800 Example 9 The preparation of a precursor of an oxygenated derivative of samarium is achieved under the same conditions as in example 1, The filtration of the precipitate is very good since 3 2 the index of filtrability is 700ct /h/cm Figure 2 represents a scanning electron microscope photograph (G=300) which shows the morphology of the product obtained.

It can be observed that the microballs obtained have an apparent diameter which varies from 10 to 40 micometer.

Example In this example, the preparation of a precursor of an oxygenated derivative of praseodymium is illustrated.

The procedure is as in example 1.

The index of filtrability obtained is 500cm 3 /h/cm 2 The product obtained has a morphology similar to that illustrated in figure 2.

Example 11 Example 1 is repeated but for the replacement of the solution of neodymium nitrate by a solution of cerium -13- -U 3+ nitrate, containg 0.5 mole/litre of Ce 3 The precipitate obtained filters very well since its index of filtrability is 900cm3/h/cm 2 The morphology and the dimensions of the particles from the precursor of the oxygenated derivative of cerium are similar to those of the product from example 9.

Example 12 lOg of the product prepared in example 1 is weighed out. It is placed in a basket then placed in a tubular oven. The temperature is raised by 9 C per minute up to 0 C, and maintained at this level for one hour. It is let to cool down with the oven.

of calcinated product is obtained, of structure type Nd 2 03 (ASTM21-579). It appears as microballs the size of which varies from 4 to 40 micrometer.

Example 13 Following the same operative procedure as in example 12, 10g of the precursor of the oxygenated derivative of prasoidymium prepared according to example 10 are calcinated.

An oxide of praseodymium presenting as microballs, the size of which ranges between 10 and 45 micrometer, is obtained.

In other embodiments of the invention microballs having a size of from 2 to 50 micrometers have been obtained.

-14-

Claims

1. A method comprising the steps of: reacting an aqueous solution of at least one salt of a trivalent rare earth with a base, at a temperature in the range of 10' L.o 50 0 C, under conditions such that the molar ratio of the concentration of the OH ions from the base to the concentration of the salt of rare earth of the solution, expressd in rare earth cations, is smaller than separating and drying the precipitate obtained, and calcinating the dried precipitate to produce an oxygenated derivative of the rare earth, wherein said oxygenated derivative is a rare earth oxide or rare earth carbonate.

2. A method according to claim 1 characterised in that the salt of a trivalent rare earth is a rare earth nitrate or a double salt of nitrates of rare earth and of ammonium. or a chloride of rare earth.

3. A method according to claims 1 and 2 wherein the concentration of the solution of one or several salts of rare e-rths varies between 0.1 and 2 moles per litre.

4. A method according to claim 3 wherein the concentratio;l of the solution of one or several salts from rare earths is optimum between 0.3 and 1.5 moles per litre. A method according to any one of claimsi 1 to 4 wherein the base is chosen within the group formed by T 7-T -i ammonia, soda, potash, ammonium carbonate, urea, hexamethylenetetramine and ammonia.

6. A method according to any one of claims 1 to wherein thp normality of the basic solution varies between 0.1 and 11N.

7. A method according to claim 6 is wherein the normality of the basic solution is optimum between 2 and 11N.

8. A method according to any one of claims 1 to 7 wherein the molar ratio (OH 3 is greater than 0.2 and smaller than

9. A method according to any one of claims 1 to 8 wherein the molar ratio (OH-)/(RE 3 is greater than or equal to 2 and smaller than A method according to any one of claims 1 to 9 wherein the molar ratio is greater than or equal to 1 and smaller than or equal to 3.

11. A method according to any one of claims 1 to wherein mixing is achieved simultaneously, under agitation of the aqueous solution of at least one salt of trivalent rare earth and of the basic solution, or wherein the base is added continuously or all at once, into the aqueous solution of at least one salt of trivalent rare earth or inversely.

12. A method according to claim 11 wherein the rate at which the reactants are added is controlled so that the molar ratio (OH-)/(RE 3 defined in one of the claims 8 to 10 is obtained. k -16-

13. A method according to claim 11 wherein the rate at which the reactants are added is controlled by regulation of the pH between 6.5 and

14. A method according to any one of claims 1 to 13 wherein the temperature of the reaction medium is optimum between 10 and 30 0 C, A method according to any one of claims 1 to 14 wherein the duration of the incubation of the mixture in the reaction medium varies between 1 minute and 48 hours.

16. A method according to claim 15 wherein the duration of the incubation of the mixture in the reaction medium is optimum between 5 minutes and 30 minutes.

17. A method according to any one of claims 1 to 16 wherein the speed of agitation is between 200 and 1000 rotations/minute.

18. A method according to any one of claims 1 to 17 0 wherein the speed of agitation is optimum between 300 and 400 rotations/minute.

19. A method according to any one of claims 1 to 18 wherein the separation of the precipitate is achieved by filtration or by decantation. A method according to any one of claims 1 to 19 wherein one to several washes are performed, using water or an organic solvent.

21. A method according to any one of claims 1 to wherein the drying step is performed at a temperature 1 between room temperature and 200 C. -17-. V" ^y

22. A method according to any one of claims 1 to 21 wherein the duration of the drying process is between minutes and 48 hours.

23. A method according to claim 22 wherein the duration of the drying process is between 2 hours and 8 hours.

24. A method according to any one of claims 1 to 23 wherein the precipitate is calcined at from 650 C to 1300 C. A method according to any one of claims 1 to 24 wherein the died precipitate appears as agglomerates ranging in dimension from 2 100 micrometers.

26. A method according to Claim 25 wherein the dried precipitate appears as microballs.

27. A method according to Claim 26 wherein the mean diameter of the microballs varies between 50 and micrometers.

28. A rare earth oxide produced in accordance with the method defined by any one of claims 1 to 27 characterized in that it has a microspherical appearance.

29. A rare earth oxide according to Claim 28 having a size of from 2 to 50 micrometers. A rare earth oxide according to Claim 29 wherein the rare earth is praseodymium.

31. A rare earth oxide according to Claim 29 wherein the rare earth is Neodymium. -18-

32. A method substantially as herein described with reference to Example 12 or 13. DATED this 6th day of June, 1990 RHONE-POULENC SPECIALITES CHIMIQUES Attorney: IAN T. ERNST Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS 01 -19-