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REVIEW ON APPLICATIONS.The industry of metallic rare earths (R.E.)
P. Poirier
To cite this version:
P. Poirier. REVIEW ON APPLICATIONS.The industry of metallic rare earths (R.E.). Journal de Physique Colloques, 1979, 40 (C5), pp.C5-269-C5-272. �10.1051/jphyscol:19795100�. �jpa-00218883�
JOURNAL DE PHYSIQUE Colloque C5, supplkment au no 5 , Tome 40, Mai 1979, page C5-269
REVIEW O N A PPL ICA TIONS.
The industry of metallic rare earths (R.E.)
P. Poirier
RhBne-Poulenc, 21, rue J.-Goujon, 75360 Paris, Cedex 08, France
RBsumC. - 1. Les ressources en terres rares : abondance naturelle, les reserves mondiales, principaux minerais.
2. SCparation et purification industrielles des terres rares : Cchange d'ions et extraction liquide-liquide. 3. Fabri- cation des mktaux des terres rares : I'Clectrolyse en sels fondus : applicable uniquement aux terres rares Iegtres.
RCductions mCtallothermiques des oxydes ou des fluorures ; procedks de CO-rkduction. 4. Applications indus- trielles des mCtaux des terres rares : - applications traditionnelles : pierres a briquet, fontes nodulaires, aciers, magnksium : - applications au dCveloppement : aimants permanents terres rares-cobalt, composCs LaNi, pour stockage de I'hydrogtne, alliages magnCtostrictifs, alliages rkfractaires. 5. Probl6mes Cconomiques liCs a l'abon- dance relative des diffkrentes terres rares, aux methodes de production des mCtaux et a I'tquilibre de vente des diffkrentes terres rares par rapport a la composition des minerais. (Version franqaise disponible.)
Abstract. - 1. Rare earths resources : rare-earths abondance and world reserves, main ores. 2. Rare earths separation and purification : ionic exchange, solvent extraction. 3. Metallic rare earths and their mixtures, metallothermic reduction of oxides or fluorides (Ca, Mg, AI, Si or rare earth metals), CO-reduction process for intermetallic compounds (SmCo,). 4. Industrial applications of metallic rare earths : traditional applications : flints, nodular cast iron, steel refining, magnesium industrie ; - applications under development : rare earths/
cobalt magnets, LaNi, for hydrogen storage, special alloys (automotive post combustion), magnetostrictive alloys.
5. Economical problems : rare earth are elements relatively abundant and often at easily accessible prices. Howe- ver, this group of 15 elements are liable to certain economical restraints. It is difficult to crack ore for only one rare earth. Availability of one given rare earth must be associated with the other corresponding rare earths to absorb all the other rare earths in other applications. Rare-earth industry has a strong expanding rate. 20 % per year average for 6 years with RhBne-Poulenc. Thanks to their exceptional, specific characteristics rare earths have a bright future particularly for their metals.
The development of a particular R.E. for an indus- trial application of large volume involves different parameters and processes caracteristic of R.E. industry taken as a whole :
- Availability of this R.E. : some of the R.E.
are abondant, others are quite rare.
- If the application needs a separated R.E., R. E. producers will have to undergo the separation between the R.E. and the purification at the level suitable for the application. These chemical processes give R.E. salts (chloride, nitrate ...) or oxides.
- Reduction of R.E. to the metallic state : the electrolysis in molten salts or metallothermic reduction will be gpplied.
- The economical parameters will become essen- tial if the application involves large amounts of R.E.
The potential resources of R.E. is not the only factor to be taken into consideration, on the one hand, other applications can absorb a part of the availability (oxide salt or metal) on the other hand, the economy of one R.E. is trongly connected to the whole R.E.
economy. One element cannot be extracted for itself if most of the remaining R.E. are not sold for other applications. In addition to the potential resource concept, the actual availability must be considered.
- The price of the final R.E. metal will be affected by all these factors. If you have the choice for a new application between different R.E., or if you have the possibility of using mixtures of R.E., then these factors will have to be evaluated at the initial stage of your study.
Let us have a look at these parameters.
1. R.E. resources. The ores. - It is well known that R.E. are relatively abondant elements. The relative abondance of some elements in the earth's crust is as follows :
It is true that R.E. are often quite diluted in the rocks. However, some ores are rich in R.E. elements.
The composition o f the main ores is
Bastnaesite is an ore for light R.E. the heavy fraction is only about 1 X .
Monazites are also ores for light R.E. but it contains 7 of the heavies. Monazites are the main sources for Sm, Gd, Tb, Y and for Thorium.
Xenotime is only an Yttrium ore.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19795100
P POIRIER
Monazite Bastnaesite Xenotime
The world resources are estimated by the US Bureau of Mine to be 10 million tons of R.E.O. only in Bastnaesite and Monazite. The actual level of extraction is as follows :
Bastnaesite . . . 15 000 t/y R.E.O.
Monazite . . . 12 000 t/y R.E.O.
27 000 t
At this present rate of extraction, the resources correspond to 350 years of consumption, without taking into account the important deposits located in the Soviet Union and China for which we have no data, not to mention the ores with a lower R.E.
content which could be extracted if needed.
2. Separation and purification. - We shall not emphasize the old processes now outdated which were based on the fractionated precipitation or cristalli- sation.
2.1 PROCESS BASED ON THE VALENCY STATE OF SOME R.E. - R.E. are trivalent elements. Some of these elements can take anormal valency state, four for Cerium or two for Europium. The di- or tetravalent have chemical properties quite different from those of trivalent elements. It can be used for separations.
2.2 ION EXCHANGE ON RESINS. - This process is in fact a chromotography on resins. It is based on the small difference of the repartition coefficient of the different R.E. between the solution used for the elution and the resin.
This process can give separated R.E. of high purity but it is a slow, discontinuous and expensive process.
It is used less and less for industrial separation but it retains some interest for the preparation of small quantities of elements of high purity.
2.3 SOLVENT EXTRACTION. - This process which is both continuous and easy to automatize can assure production of industrial tonnage of R.E. with a purity higher than 99.999 if needed.
This process is based on the difference of affinity (repartition coefficient) of the different R.E. elements between a solution of R.E. in water and a chelating agent in an organic solvent. Mixing of the two solu- tions and decantation leads to an equilibrium of repartition of R.E. between the two phases. The element having the highest affinity for the chelating agent being enriched in the solvent. This elementary effect is very small. The repetition of such an equi- librium in a multi-stage counter current battery can assure the total separation of two R.E. elements or two R.E. groups. A battery is needed for each cut carried out.
For example, the R.E. plant of Rh6ne-Poulenc in La Rochelle which is, by far, the largest plant in the world for these separations is equipped with more than 1 000 mixers/settlers which are used to separate and purify the different individual R.E. elements and also for the removal of the non R.E. elements from the solution coming from the attack of the ores.
3. Production of R.E. metals. - 3 . 1 PRODUCTION.
3.1.1 Electrowinning. - This process can only be applied to light R.E. from Lanthanum to Neodymium.
The electrolysis is generally achieved on anhydrous chlorides with the addition of non R.E. chlorides used to decrease the meking point of the mixture.
The anode is made of carbon. The crucible can be used as cathode.
The electrowinning may be also achieved through a fluoride medium using R.E. oxide. However, the solubility of R.E. oxide in fluorides is poor and it seems that the industrial adjustment of the process has caused some problems to the users.
Electrolysis is mainly applied for production of Mischmetal. MM is the alloy of the light R.E. with a natural composition without the heavy fraction which is not electrolysed, the heavy R.E. are concen- trated in the slags if this fraction, have not been separated chemically before electrolysis.
Electrolysis can also be used for the production of the individual R.E. metals La, Ce, Pr, Nd. Nd alone is more difficult to get through this process because of the high melting point of this metal.
It is also possible to get any particular mixture of this light R.E. metal.
3 . 2 METALLOTHERMIC REDUCTIONS. - Oxides or fluorides can be used in the reduction. This process is suitable for all the R.E. elements. In fact for industrial production it is mainly used for heavy R.E. which cannot be obtained through electrowinning. The choice of metals able to reduce R.E. is limited because of the high thermodynamic stability of the R.E.
compounds. The general formula for this reduction in the case of oxide is
R.E.O. + M
-
R.E. + M OM = metal used for the reduction
THE INDUSTRY OF METALLIC RARE EARTHS (R.E.) C5-271
It is difficult to get the pure R.E. metal without M.
M will be chosen in order to have a good possibility to separate M from R.E. This separation is often achieved by vacuum distillation.
3.2.1 Reduction by MM. - MM can reduce heavy R.E. In the case of Sm for instance Sm203 is reduced by MM. Sm is purified by distillation. Sm has a vapour pressure higher than the vapour pressure of the R.E.
metals of the MM.
3.2.2 Calcium reduction. - This process is the most common for the heavies. It is sometimes difficult to operate because of bad coalescence of the R.E.
metals. This is why some researchers have set up a system with three components in which an auxiliary metal is added. This metal is not active on the reduction but is able to give an alloy with the R.E. metal, easy to separate. It is the so-called CO-reduction process used for Sm-CO Magnets production [G.E. (USA), Goldschmidt (Germany)].
In this case CO is added, Sm/Co alloy in powder form is directly produced, ready after milling to be pressed for Magnet production.
The CO-reduction could be used for the production of LaNi,. However, it should not be competitive against electrolysis.
3.2.3 Reduction by Aluminium. - The yield is poor and the R.E. metals is difficult to recover.
This process is used for Y production or more exactly to get an YlAl alloy to be used directly as an additive in special alloys for high temperature.
3.2.4 Reduction by Silicon. - This method is employed industrially for the preparation of Silicol Mischmetal used in foundery, and gives an alloy SiIMM.
3.2.5 Reduction by Magnesium. - Rarely used.
Alloys are obtained with this method.
4. Main industrial applications of R.E. metals. -
4.1 TRADITIONAL APPLICATIONS. -, 4.1 . l Flints. -
From a historical point of view it is one of the first industrial applications for R.E.
Flints are made from an alloy of 75 % MM and 25 % iron called Ferrocerium. Some additives are usually added Mg, Cu.. .
The development of disposable cigarette lighters has stimulated this activity.
About 700 t per year of Flints are produced world- wide. As you have roughly 5 000 pieces per kg the world consumption is about 3.5 billion Flintslyear.
4.1.2 Cast iron. - MM and Mg are added to cast iron to get nodular cast iron. These additives help the graphit to take the shape of microspheres. MM alone could achieve this nodulisation. To save on the price Mg is used and MM is added mainly to protect Mg against metalloids especially oxygen.
in steel in the form of sulfides (Manganese sulfide) which are liquid at the rolling temperature.
These sulfides cristallize when cooling after rolling in the shape of a loup giving special fragility.
The R.E. metals added in the steel give nodules of refractory R.E. sulfides with isotrop mechanical properties. The R.E. increase the resilience of steel which is mainly used today for pipe line steel. The development of this kind of steel in other applications (car and building industries) could involve very large volumes of R.E. metals.
The MM consumption, worldwide, for all these applications is in the range of 3 500 t/y. It is the second application of R.E. following petroleum cracking catalysts.
4.1 .4 Magnesium industry. - R.E. and Th metals are added to Magnesium in order to increase the mechanical properties of this metal. The R.E. cris- tallize at the surface of the Mg grains and thus limit their size. The treated Mg is mainly used in aircraft industry.
4.1.5 R.E./Cobalt permanent magnets. - This application is just approaching the industrial scale.
It could be, in the future, one of the major applications for R.E.
The first compositions developped have been SmCo, and Sm2Co,,. RhBne-Poulenc is, today, the main source for Sm. We should sell more than 150 t of Sm203 in 1978 (55 t in 1977).
The development of the Sm/Co compositions will be limited by the Sm availability. The annual potential availability is about 400 t/y today. However, the substitution of a part of the Sm by other R.E. metals especially by the abondant elements as La, Ce, Pr, Nd or their mixtures could lead to a very large deve- lopment of these magnets in mass applications (small motors for car industry for instance). For such deve- lopment, the Sm1R.E. ratio must be as low as possible (below 10 X). A very active research is being done all around the world by all the magnet manufacturers to win this bet.
4.2 HYDROGEN STORAGE LaNi, . - This appli- cation is at the preliminary development stage. The cheapest way to produce this alloy seems today to use a melting process starting from Lanthanum prepared by electrolysis.
Lanthanum is an abondant element 25 to 30 %
R E 0 depending on the ores. This element is in excess 'compared to the actual applications (optical glasses, ceramic capacitors, catalyst...). It could allow an important development of new applications. More than 7 000 t of La203 are mined each year. Onry 300 to 400 t are used as separated elements for specific properties of Lanthanum.
Taking into account the cheap price of Lanthanum metal (under 100 F/kg for industrial quantities) and 4.1.3 Steel. - MM is used to get a metalloid its availability, it should not be profitable to use MM epuration is steel (mainly sulphur) Sulphur is found which gives, by far, lower performances. In any case
CS-272 P. POIRIER
Cerium is to be avoided and it should be more inte- is expensive. It is obvious that if the market was large resting to use a Cerium depleted alloy La, Pr, Nd enough to allow an industrialisation of the production with an intermediary price between that of MM and the price would drop lower. It has been the case for
Lanthanum. Samarium for which the price has been cut by 3 within
4 . 3 OTHER APPLICATIONS UNDER DEVELOPMENT. -
R.E. metal should find industrial applications in refractory alloys (car industry, alloy for turbine).
Some of the heavy R.E. metals will be used in magneto- strictives alloys.
5. Economy. - The development of a R.E. metal for a new application will depend on the performance of this metal compared to the performance of other R.E. metals or non R.E. metals. Eventually, it will be the ratio Performance/Price which will guide the final decision.
We have seen that the price of a R.E. metal will depend on :
- Price of the R.E. in the form of salt or oxide. -
This price is related to the natural relative abondance in the ores. It is also related to the annual tonnage prepared by a plant and of the level of purity needed.
- Cost of transformation into metal. - The pro- duction of a metal through electrolysis seems today the cheapest method. We have seen that this method can be used only for the first elements of the serie. The metallothermic reduction is an interesting process from an economical point of view if the alloy between the R.E. metal and the metal used for reduction can be used directly without trying to get the pure R.E.
metal or if a CO-reduction process can be applied.
a few years.
The concept of availability for a R.E. is only valid for a given moment. R.E. industry is progressing rapidly. Rh6ne-Poulenc has acquired a rate of increase of 20 %/year in the past 6 years.
Some of the R.E. especially among the heavies have no industrial use. From the current production Rh6ne-Poulenc can put on the market the following quantities of heavy R.E.
We think that the development of a new application can only be achieved by means of a dialogue between the research people, the industry and the R.E. pro- ducers. How many of you wereaware that for instance : 26 t of Dy203 are available each year from Rh6ne- Poulenc alone, that the world production of R.E.
metals is in the range of 4 000 t/y and the production The production of pure R.E. metals will remain capacity is far from being saturated, that some quite expensive not only because of the price of the mixtures of light R.E. metals are about the same price raw materials but also because of the cost of processes as nickel, that Lanthanum metal has today a lower to be used (reduction, distillation.. .). price than cobalt and it is more available.
However, besides Sm and Y, the heavy R.E. metals R.E. industry would appreciate this dialogue and have no industrial applications. Their production in acknowledges today's opportunity to continue in small quantities on a laboratory or small pilot scale this line.
