Recovery of rare earth elements from phosphorites in the USSR

Journal of AUoys and Compounds, 180 (1992) 71-76 JAL 8014

71

Recovery of rare earth elements from phosphorites in the USSR J. I. S k o r o v a r o v , V. D. Kosynkin, S. D. M o i s e e v a n d N. N. R u r a All-Union Research Institute of Chemical Technology, 33 Kashirskoe Shosse, 115230 Moscow (Russia)

Abstract Data on the main rare earth compositions in the USSR are presented, showing that the most promising sources are phosphorites and apatites. The rate earth oxide content in the above ore concentrates reaches 1%. Technological schemes for recovering the total and individual rare earth oxides as byproducts have been developed. Extraction methods are used for recovering rare earths from nitrate solutions, with individual oxides more than 99.9% pure being obtained. Apatites are decomposed by nitric acid, yielding apart from fertilizers, strontium carbonate, sodium fluorosilicate, chalk and oxides of rare earth elements.

1. I n t r o d u c t i o n T h e m i n e r a l o g y o f the r a r e e a r t h e l e m e n t s in t h e USSR differs c o n s i d e r a b l y f r o m t h a t of the m a i n p r o d u c i n g c o u n t r i e s , w h e r e t h e m a j o r w o r k a b l e m i n e r a l s a r e m o n a z i t e , bastnfisite a n d x e n o t i m e [1 ]. P r o c e s s i n g o f t h e s e m i n e r a l s yields r a r e e a r t h s , w h i c h c o n s t i t u t e t h e v a l u a b l e c o m p o n e n t o f t h e s t a r t i n g material. T h e r a r e e a r t h m i n e r a l s in t h e USSR h a v e a c o m p l e x c o m p o s i t i o n a n d c o n t a i n s e v e r a l v a l u a b l e c o m p o n e n t s . T h e m a i n r e s e r v e s a r e confined to p h o s p h a t e s (apatite, p h o s p h o r i t e ) a n d t i t a n o t a n t a l o n i o b a t e s (loparite). In addition t o r a r e earths, l o p a r i t e c o n t a i n s s u c h v a l u a b l e c o m p o n e n t s as titanium, t a n t a l u m a n d n i o b i u m [2 ]; similarly, p h o s p h o r i t e s c o n t a i n p h o s p h o r u s , fluorine a n d u r a n i u m [3], a n d a p a t i t e s c o n t a i n p h o s p h o r u s , s t r o n t i u m a n d fluorine [41. P h o s p h o r i t e s a n d a p a t i t e s h a v e h i g h e r c o n t e n t s of m e d i u m a n d h e a v y r a r e e a r t h s t h a n o t h e r m i n e r a l s ; h o w e v e r , t h e i r t o t a l c o n t e n t in c o n c e n t r a t e s is less t h a n 1% a n d t h e i r r e c o v e r y w o u l d b e profitable o n l y as b y p r o d u c t s while m a n u f a c t u r i n g p h o s p h o r i c fertilizers. It follows t h a t t h e m a j o r r e q u i r e m e n t f o r t h e r a r e e a r t h r e c o v e r y p r o c e s s is t h a t it s h o u l d n o t cut d o w n the r e c o v e r y of t h e p h o s p h o r u s p r o d u c t s . T h e p o t e n t i a l i n c r e a s e in. the,fertilizer p r o d u c t i o n c o s t w o u l d b e c o m p e n s a t e d b y s o m e additional p r o d u c t i o n of r a r e earths. As well as t h e a b o v e m i n e r a l s , t h e r a r e e a r t h s of the USSR a r e r e c o v e r e d f r o m y t t r o s y n c h i s i t e , b u t the s c a l e o f t h e o p e r a t i o n is n o t large.

0925-8388/92/$5.00

© 1992 - Elsevier Sequoia. All rights reserved

72

Because of the peculiar composition of phosphorites and the need to recover other valuable components, we have developed new complex technological schemes, which will be described below.

2. Phosphorite processing technology The compositions of the main rare earth minerals in the USSR are given in Table 1. Apatite and loparite are processed as enrichment concentrates only. Phosphorites (clay-pyrite ores) are treated according to a technology developed for the valuable components being recovered from both the ore and the concentrates. After phosphorite enrichment, the concentrate (generally francolite) contains 25% of P205, up to 1% of rare earth oxide (REO) and a few tenths of a per cent of uranium. Table 2 presents the contents of individual rare earth elements in the main minerals [5]. The phosphorite rare earths have an optimal composition, since they are rich in the medium elements (samarium, europium, gadolinium, terbium) and yttrium at the same time. Originally, rare earths in the USSR were recovered from loparite only. After the deposits of uranium-containing phosphorites had been introduced into production, the rare earth content there became quite important in view of their recovery as byproducts [6]. The technology for recovering the main products via phosphorite processing is presented in Fig. 1. The extractional processes above utilize ethers of phosphororganic acids and amines as extractants. The obtained rare earth solution is generally contaminated with radionuclides (the products of the uranium and thorium series) to an insignificant TABLE 1 Compositions of major rare earth minerals in the USSR Loparite [ 1 ] (concentrate) Component

Phosphorite [2 ] (ore) Contents

Component

(%) TiO2 Nb205 Ta205 ThO2 NazO K20 CaO SrO SiO2 REO

~ J

39.24 11.48 0.67 9.06 0.75 5.26 0.62 0.27 32.29

Apatite [3 ]

Contents

Component

(%) P205 U S(total) CaO Fe C(total) C(organic) CO2 Rare earth Ni Mo Co

3.0-6.0 < 0.1 11.7 7.5 11.6 4.6 3.5 3.9 0.1-0.2 < 0.1 <0.1 <0.1

Contents

(~) P205 CaO F SrO REO Al2Oa Fe203 TiO2 SiOg.

39.5 50.9 3.31 2.79 0.98 0.45 0.79 0.71 1.93

73 TABLE 2 Rare earth contents in the concentrates (per cent)

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y

Loparite

Apatite

Phosphorite

25 53 6 14 0.9 0.08 0.56 0.37 0.12 0.08 0.016 0.003 0.008 0.002 0.008

27.4 42.8 4.9 13.9 2.1 0.7 1.7 0.1 1.1 0.1 0.4 0.1 4.8

18.9 30.8 2.8 18.6 3.3 0.6 4.7 0.5 2.4 0.2 1.4 0.1 1.1 0.2 14.2

d e g r e e ; h o w e v e r , t h e t e c h n o l o g i c a l f l o w s h e e t i n c l u d e s d e c o n t a m i n a t i o n operations. T h e light e l e m e n t s , o b t a i n e d in t h e t r e a t m e n t p r o c e s s , are utilized as i n t e g r a t e d p r o d u c t s in t h e p e t r o l e u m i n d u s t r y f o r f a b r i c a t i n g c r a c k i n g catalysts. T h e m e d i u m a n d h e a v y e a r t h c o n c e n t r a t e is s e p a r a t e d into g r o u p s b y e x t r a c t i o n . All t h e c o m p o n e n t s o f the m e d i u m e l e m e n t s c o n c e n t r a t e h a v e to b e e x t r a c t e d , since t h e y a r e s c a r c e a n d find w i d e u s e in m a n u f a c t u r i n g p h o s p h o r s , g a r n e t s , m a g n e t s etc. Yttrium is e x t r a c t e d f r o m t h e y t t r i u m c o n c e n t r a t e in a s i n g l e - s t a g e o p e r a t i o n . T h e a b o v e p r o c e s s i n g o f p h o s p h o r i t e s yields o x i d e s o f individual r a r e e a r t h e l e m e n t s m o r e t h a n 9 9 . 9 9 % p u r e . The u r a n i u m - c o n t a i n i n g p h o s p h o r i t e p r o c e s s i n g is e s p e c i a l l y viable for r e c o v e r i n g yttrium, e u r o p i u m a n d individual h e a v y e l e m e n t s . T h e d e m a n d f o r y t t r i u m a n d e u r o p i u m will g r o w in t h e n e a r f u t u r e a n d t h e r e f o r e it will b e n e c e s s a r y to i n t r o d u c e s o m e n e w k i n d s of r a w m a t e r i a l s . As a l r e a d y m e n t i o n e d , s u c h a r a w m a t e r i a l in the USSR is u n d o u b t e d l y a p a t i t e . H o w e v e r , t h e g r e a t e r p a r t o f t h e a p a t i t e is t r e a t e d in t h e s u l p h u r i c a c i d circuit, the r a r e e a r t h s b e i n g d u m p e d t o g e t h e r w i t h c a l c i u m in p h o s p h o g y p s u m . A b o u t 1.5 million t o n s p e r y e a r o f a p a t i t e is p r o c e s s e d u s i n g nitric acid, a n d in this c a s e the g r e a t e r p a r t o f t h e r a r e e a r t h s p a s s e s into t h e n i t r a t e - - p h o s p h a t e s o l u t i o n to b e p r e c i p i t a t e d f r o m t h e r e as p h o s p h a t e s . A c o m p l e x nitric a c i d f l o w s h e e t f o r a p a t i t e p r o c e s s i n g is p r e s e n t e d in Fig. 2 [7]. T h e a p a t i t e c o n c e n t r a t e is d e c o m p o s e d b y 5 4 % nitric acid. T h e o b t a i n e d p u l p o f the s t r o n t i u m - c o n t a i n i n g r e s i d u e is s u b j e c t e d t o t h i c k e n i n g a n d filtration. T h e filtrate is t r e a t e d f o r c a l c i u m n i t r a t e e x t r a c t i o n , a n d t h e s t r o n t i u m - c o n t a i n i n g r e s i d u e is l e a c h e d w i t h water, yielding s t r o n t i u m nitrate, f r o m w h i c h pelletized s t r o n t i u m c a r b o n a t e , a p p l i c a b l e in c o l o u r t e l e v i s i o n s c r e e n p r o d u c t i o n , is o b t a i n e d . T h e nitric acid e x t r a c t is f r o z e n out, a n d the

74

Enrichmentconcentrate lr J,

HNO3' H2'SO4

Decomposition by nitric and sulphur c acids, f itration Nitrate-phosphate

NH3

Phosphogypsum

solution t ~ I Precipitationof the collective concentrate, f itrat on Nitrato-phosp ate solution

+

To the dump

Collective concentrate of U and rare earths

For fertilizers

|and e-extraction of rare earths

li' i' JDissolutionin HNO3 I extraction-separation I e-extraction of Sc

FeY

~(/ I Cleaning from radioactive impurities

reprocessing

e-extractien Ra inate of U /

Ferv 7

Fe

reprocessing

fertilizers

Medium and heav,/"rare earths

Light

rare earth

,k IExtraction and separation into groups I Concentrate of Eu

Concentrate of Y

JSeparation of the middle I greup elements ,~. J Sm203

HN03

Gd203

Tb4O7

Eu2O3

JRecevery by extraction I

~

Y203

, Concentrateof heavy rare earths

Fig. 1. Diagraxn f o r rare e a r t h recover3" f r o m p h o s p h o r i t e s .

calcium nitrate is crystallized. The crystals are converted by ammonium carbonate, yielding the commercial products: chalk and ammoniacal saltpetre. NA2SiF8 is precipitated from the mother liquor after calcium extraction, yielding a commercial product which can alternatively be reprocessed into hydrofluoric acid. Extraction of calcium and fluorine is a precondition for the rare earth phosphate precipitation, since with the decreased viscosity the filtration values become viable for production use. The nitrate--phosphate solution has the following composition [8]: REO 8.1 g 1-1; P~Oa, 330 g 1-1; CaO, 420 g 1-1; F, 0.5 g 1-I; density, 1.4 g cm -a. The rare earth precipitation is performed by gaseous ammonia, and the residue, recalculated as dry mass, contains the following: REO, 24.0 mass%; P205, 36.8 mass%, CaO, 8.9 mass%; F, 1.28 mass°; Fe20~, 4.54 mass%; A1208, 5.48 mass%; N(nitrate), 0.56 mass%; N(ammonia), 2.3 mass%; SiO2, 4.0 mass%. The degree of recovery of rare earth elements, from the nitrate--phosphate solution is 85% of the rare earth elements contained in apatite.

75

Apatiteconcentrate ~,

Nitric acid

Decomposition with nitric acid S-containing residue

Nitrate-phosphate solution

ToS-~'-~ 3 extraction

Crystalli~'zationof

calcumnirate

Mother solution

Ca(NO3)2.4H20

NH3

CO2

~.

Nitrogen salts

--"~l

F extraction I iothe~ solution

a2SiF

Precipitation of

To CaF 2 manulacture

liareearths jl Nitratephosphate solution

Chalk

Nitre

Phosphate concentrate of rare earths

To fertilizer

manufacture

Fig. 2. C o m p l e x n i t r i c acid p r o c e s s i n g o f apatite.

The t e c h n o l o g y described leaves practically neither liquid nor solid wastes, since nitric acid, ammonia and all apatite c o m p o n e n t s are utilized as useful products: fertilizers, chalk, strontium carbonate, sodium silicofluoride and rare earth phosphates. Of all the variants for cleaning the rare earth concentrate the most viable has proved to be the extraction method based on the recovery of rare earth elements from nitrate-phosphate solutions by tributylphosphate or phosphonates dissolved in kerosene [9]. The extraction takes place in a countercurrent system in which the organic phase is washed with an ammonium nitrate solution in order to separate completely phosphorus from the rare earth elements. At the same time here the rare earths are cleared from calcium and iron. The purification process has yielded REOs with the following composition: REO, more than 98.0%; P205, less than 0.05%; Ca, less than 0.01%; Fe, less than 0.01%. The total degree of recovery from a phosphate concentrate into a ready product is c a . 95%.

3. C o n c l u s i o n The Soviet Union p o s s e s s e s large resources of phosphorites with rare earths, uranium, scandium, fluorine and strontium. The technology developed makes it possible to obtain on a production scale in addition to fertilizers

76 all t h e v a l u a b l e c o m p o n e n t s demand.

in q u a n t i t i e s sufficient for m e e t i n g the c o u n t r y ' s

References 1 A. I. Mikhallichenko, E. B. Mikhlin and Y. B. Patrikeev, Rare Earth Elements, Metallurgija, Moscow, 1987. 2 J. G. Gorostchenko, Physical and Chemical Study on Processing of Rare Earth Titanoniobates by Sulphuric Acid, USSR Academy of Sciences, Moscow, Leningrad, 1960. 3 A. P. Zefirov, J. I. Skorovarov, B. N. Nevski, A. A. Matveev, V. F. Burlachkin, G. A. Mjasnikova, G. I. Farutina and N. M. Tikhomirova, Proc. Syrup. on the Recovery of Uranium, Sd~o Paulo, International Atomic Energy Authority, Vienna, 1971. 4 V. A. Masloboev, I. P. Smirnova and V. I. Belokoskov, Complex processing of apatite from the Kola Peninsula. In Physical, Chemical and Technological Studies on Processing minerals, USSR Kolar Academy of Sciences, Apatity, 1989, pp. 59-63. 5 D. A. Mineev, Lanthanoids in the Ores of Rare Earths and Complex Deposits, Publishing House NAUKA, Moscow, 1974. 6 A. P. Zefirov, G. E. Kaplan, S. D. Moiscev and I. I. Anufriev, Prospects for large-scale application of rare earth metals in industry. In Rare Earth Metals, Alloys and Compounds, Publishing House NAUKA, Moscow, 1973. 7 A. L. Goldinov and B. A. Kopylev, Complex Nitric Acid Processing f o r Phosphate Ores, Publishing House CHIMIJA, Leningrad, 1982. 8 A. L. Goldinov, S. D. Moiseev, F. I. Novoselov, G. L. Shelekhova, O. B. Abramov, E. V. Afanasenko and V. A. Semenov, Khim. Promst. (Moscow), 4 (1980) 33. 9 S. D. Moiseev, V. A. Semenov and G. L. Shelekhova, Khim. Promst. (Moscow), 8 (1981) 24.