Hydrom 42 1996 Kinetics low-grade scheelite.pdf

7/25/2019 Hydrom 42 1996 Kinetics low-grade scheelite.pdf

1/17

See discussions, stats, and author profiles for this publication at:https://www.researchgate.net/publication/238372934

Kinetics of soda ash leaching of

low-grade scheelite concentrates

ARTICLE in HYDROMETALLURGY SEPTEMBER 1996

Impact Factor: 1.93 DOI: 10.1016/0304-386X(95)00099-3

CITATIONS

14

READS

42

1 AUTHOR:

J.I. Martins

University of Porto

49PUBLICATIONS 734CITATIONS

SEE PROFILE

Available from: J.I. Martins

Retrieved on: 06 February 2016
https://www.researchgate.net/profile/JI_Martins?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_4https://www.researchgate.net/?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_1https://www.researchgate.net/profile/JI_Martins?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_7https://www.researchgate.net/institution/University_of_Porto?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_6https://www.researchgate.net/profile/JI_Martins?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_5https://www.researchgate.net/profile/JI_Martins?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_4https://www.researchgate.net/?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_1https://www.researchgate.net/publication/238372934_Kinetics_of_soda_ash_leaching_of_low-grade_scheelite_concentrates?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_3https://www.researchgate.net/publication/238372934_Kinetics_of_soda_ash_leaching_of_low-grade_scheelite_concentrates?enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ%3D%3D&el=1_x_2


2/17

E L S E V I E R

Hydrometallurgy42 (1996) 221-236

hydrometaUurgy

Kinet ics o f soda ash leaching of low-grade schee l i te

concentrates

J .P . Martins

Departam ento de Engenha ria Qufmica , L aborat6r io de Cat6l ise e Mater ia is , FEUP, Rua dos Bragas, 4099

Porto , Por tugal

Received 7 July 1995; accepted 14 October 1995

A b s t r a c t

Th e react ion kinet ics for the leaching of low-grad e scheel ite concentrates with sodium

carbon ate have bee n s tudied to establ ish the effect of the mo st important process variables, such as

st i rr ing, sol id / l iquid ra t io , sodium carbonate concentrat ion, temperature and part ic le s ize . The

leaching residues w ere chem ical ly and s tructurally character ize d by X-ray diffract ion. Th e

experimental resul ts conform with the shrinking core model and they show that the scheel i te

leaching is un der diffusion con trol for about 30 min af ter the s tart o f the react ion in the range

100-250 C. Go od tungs ten reco very can be ob ta ined.

1 . I n t r o d u c t i o n

D r e s s i n g t e c h n i q u e s , s u c h a s g r a v i t y c o n c e n t ra t i o n , f r o t h f lo t a ti o n , m a g n e t i c a n d

e l e c t r ic f i e l d s , a r e g e n e r a l l y e f f e c t i v e i n t h e s e p a r a t i o n o f s c h e e l i te f r o m a s s o c i a t e d

g a n g u e , b u t s o m e o f t h e t u n g s t e n c o n c e n t r a t e s p r o d u c e d s t il l c o n t a i n o n l y 5 - 2 0 w t %

W O 3. It is t h u s n e c e s s a r y t o t r ea t t h e s e c o n c e n t r a t e s i f w e w a n t t o r a i se t h e t u n g s t e n

r e c o v e r y . T a k i n g i n t o a c c o u n t t he c o m m o n m i n e r a l o g i c a l c o m p o s i t i o n o f s c h e e li t e o re s ,

h y d r o m e t a l l u r g i c a l a l k a l in e p r o c e s s e s a r e a d v i s a b l e t o m i n i m i z e l e a c h i n g o f im p u r i t ie s .

A s i s w e l l k n o w n [ 1 ] , t h e i n a b i l it y t o d i s s o l v e s c h e e l i t e i n c a u s t i c s o l u t i o n s i s a r e s u l t o f

t h e r m o d y n a m i c s r a th e r th a n k in e t ic s . O t h e r w i s e , t h e P o u r b a i x d i a g r a m f o r t h e C a - W -

C O 3 + H 2 0 s y s t e m a t 2 5 C s h o w s t h a t c a l c i u m t u n g s t a te i s r e l a ti v e l y u n s t ab l e t o t h e

c a r bo n a te . U s i n g t h e r m o d y n a m i c d at a [ 2 - 4 ] a t 2 5 C , t h e r e a c t i o n :

Ca W O4 ( s ) + Na 2 CO3 ( a q ) ~ Na 2W O4 ( aq ) + Ca CO 3 ( s ) ( 1 )

h a s a s t a n da r d e n t h a l p y a n d fr e e e n e r g y o f 3 7 . 6 k J / m o l a n d 5 6 .5 k J / m o l , r e s p ec t iv e l y ,

w h i c h m e a n s t h a t i t i s e s s e n t i a l t o o p e r a t e a t h i g h t e m p e r a t u r e s .

0304-386X /96/$15.00 Copy right 1996 Elsevier Science B.V . All rights reserved.

S S D I

0 3 0 4 - 3 8 6 X ( 9 5 ) 0 0 0 9 9 - 2
https://www.researchgate.net/publication/261362104_Oxidation_Potentials?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/261362104_Oxidation_Potentials?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==


3/17

222 J.P. Martins / Hydrom etallurgy 42 (1996) 221-2 36

T h e f i r s t r e p o r t o f t h e u s e o f s o d i u m c a r b o n a t e t o d i g e s t s c h e e l i t e w a s b y H a m i l t o n

[5 ]. H o w e v e r , o n l y w i t h t h e w o r k o f M a s l e n i s k i i [ 6] w a s t h e d e c o m p o s i t i o n o f s c h e e l i te

u n d e r p r e s s u r e d i s c u s s e d . F o l l o w i n g t h i s p i o n e e r i n g w o r k , M a s l e n i s k i i [ 7 , 8 ] , P e r l o v

[ 8 - 1 0 ] a n d Z e l i k m a n a n d R a d o v a [ 11 ] c a r r i e d o u t f u r t h e r i n v e s t ig a t i o n s . A b o u t a d e c a d e

a g o , B e l i k o v a n d M a s l e n i s k i i [1 2] a n d Q u e n e a u [13]s t u d i e d t h e k i n e t ic s o f d i s so l u t i o n o f

s c h e e l i t e i n a l k a l i n e s o l u t io n s . T h e y c o n c l u d e d t h a t t h e d i f f u s i o n o f c a l c i u m o r c a r b o n a t e

i o n s t h r o u g h t h e c a l c i t e l a y e r f o r m e d d u r i n g t h e l e a c h i n g m a y b e t h e r a t e - c o n t r o l l i n g

s t e p . M o r e r e c e n t l y , Z e l i k m a n a n d M e e r s o n [ 1 4 ] h a v e c o n s i d e r e d t h a t t h e l e a c h i n g i s

c o n t r o l l e d b y t h e r a t e o f c h e m i c a l r e a c t i o n . A s t h i s p r o c e s s i s u s e f u l it c o n t i n u e s t o

a t t ra c t th e a t t e n t i o n o f re s e a r c h e r s ; i m p r o v e m e n t s , s u c h a s t h e s i m u l t a n e o u s a c t i o n o f

o t h e r a l k a li n e c o m p o u n d s w i t h s o d i u m c a r b o n a t e [ 1 5 ,1 6 ] , c o u n t e r - c u r r e n t e x t r a c t i o n o f

c o n c e n t r a te s [ 1 7] a n d o t h e r m e a n s o f i n c r e a si n g p r o c e s s e f f i c i e n c y [ 1 8 - 2 0 ] h a v e b e e n

p r o p o s e d .

T h e a i m o f t h i s w o r k i s to e s t a b l i sh t h e e f f e c t o f th e p r o c e s s v a r i a b l e s o n t h e r e a c t io n

r a t e o f s o d a a s h l e a c h i n g o f l o w - g r a d e s c h e e l i t e c o n c e n t r a t e s a n d t h e u s e o f a

c o u n t e r - c u r re n t e x t ra c t i o n p r o c e s s t o i m p r o v e t u n g s te n r e c o v e r y .

2 . N o n - c a t a l y t i c s o l i d - f l u i d r e a c t i o n m o d e l s

T h e r e a r e s e v e r a l k i n e t i c s m o d e l s t o d e s c r i b e n o n - c a t a l y t i c s o l i d - f l u i d r e a c t i o n s

[ 2 1 - 2 7 ] . T h e m e a s u r e m e n t o f t h e s p e c i f ic s u r f ac e a r e a o f t he l o w - g r a d e c o n c e n t r a te a f t e r

g r i n d i n g t o < 1 0 0 tx m i n d i c a t e d a s u r f a c e a r e a o f < 0 . 0 5 m 2 / g . T h i s s u g g e st s t h a t t h e

s o l id p a r t ic l e s a r e p r a c t i c a l l y n o n - p o r o u s . T h e c h e m i s t r y a n d p h y s i c a l e x a m i n a t i o n o f th e

p e l le t a f te r l e a c h i n g s h o w t h e p r e s e n c e o f c a l c i u m c a r b o n a t e s u r r o u n d in g a n u n r e a c t e d

s c h e e li te c o r e . T h e r e f o r e , t h e u n r e a c t e d s c h e e l i te c o r e d u r i n g l e a c h i n g m o v e s f r o m t h e

o u t s i d e t o w a r d s t h e c e n t r e ; w i t h o u t a n y c r a c k i n g o r s w e l l i n g o f t h e p r o d u c t f il m t h e s i z e

o f th e p e l l e t is m a i n t a i n e d . T h e s h r i n k i n g c o r e m o d e l [23] s e e m s t o b e a s u i t a b l e

m a t h e m a t i c a l m o d e l t o d e s c r i b e t h e k i n e t ic s o f th e p r o c e s s .

2 .1 . C o n v e r s i o n e x p r e s s i o n s f o r t h e s h r i n k i n g c o r e m o d e l

C o n s i d e r i n g t h e a p p r o x i m a t i o n t o t h e p s e u d o - s t a t i o n a r y s ta t e , th e e v o l u t i o n o f t h e

u n r e a c t e d c o r e w i t h t i m e f o r f i r s t a n d z e r o r e a c t i o n o r d e r s , r e s p e c t i v e l y , t o t h e l e a c h i n g

a g e n t a n d t o t h e s c h e e l i t e , i s g i v e n b y t h e r e l a t io n :

R s [ 1 R ) , R ]

t= CA---- K m A D eA 1 - - r a / R 3 ) + - -p s K s 1 - + ~ ( 1 - r 2 / R 2 )

(2)

w h i c h f o r t h e t o t a l c o n v e r s i o n , t = -r a n d r e = 0 , b e c o m e s :

R p s ( 1 1 R )

r = ~ A 3Km- -'~+ ~ + ~ ( 3 )

K s P s 6 D e A
https://www.researchgate.net/publication/279514478_The_Kinetics_of_the_Dissolution_of_Scheelite_in_Alkaline_Aqueous_Solutions?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/256139996_The_Cracking_Core_Model_for_the_Reaction_of_Solid_Particles?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/232325431_Fluidized_Solid_Reactors_with_Continuous_Solid_Feed?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/256139996_The_Cracking_Core_Model_for_the_Reaction_of_Solid_Particles?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/250793548_Non-Catalytic_Heterogeneous_Solid-Fluid_REaction_Models?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/216834127_Chemical_Reaction_Engineering_Eq_23?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/244112269_A_Structural_Model_for_Gas-Solid_Reactions_with_a_Moving_Boundary-II?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/279514478_The_Kinetics_of_the_Dissolution_of_Scheelite_in_Alkaline_Aqueous_Solutions?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/232325431_Fluidized_Solid_Reactors_with_Continuous_Solid_Feed?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==https://www.researchgate.net/publication/232325431_Fluidized_Solid_Reactors_with_Continuous_Solid_Feed?el=1_x_8&enrichId=rgreq-daf49e85-e29b-4211-b7f5-1861b1b2bb1a&enrichSource=Y292ZXJQYWdlOzIzODM3MjkzNDtBUzoyNjE1OTA4NzIyMjc4NDBAMTQzOTM3OTUzMjI0MQ==


4/17

J.P. Martins/Hydrometallurgy 42 (1996) 221-236

223

I f t h e f l u id f i lm r e s i s t a n c e c o n t r o l s t h e r e a c t i o n r a t e , K m a


5/17

224

J.P. M artins Hydrometallurgy 42 (1996) 221 -236

Table 2

Sieve analysis of three lots o f low-grade scheelite concentrate

Size, mesh Fraction (%)

Lot A Lot B Lot C

140 21.3 - -

200 22.8 - -

325 23.7 22.1 30.3

400 6.4 21.1 17.5

< 400 25.8 56.8 52.2

Me dian size (ixm) 60 40 40

3 . 2 . L e a c h i n g t r i a l s

T h e l e a c h i n g t r i a ls a t a t m o s p h e r i c p r e s s u r e w e r e c a r r i e d o u t i n P y r e x Q u i c k f i t v e s s e l s

t h e r m o s t a t i c a l l y c o n t r o l l e d a t 1 0 0 + I C a n d u n d e r p r e s s u r e i n a 1 1 P a r r m o d e l 4 5 3 1

a u t o c l a v e , u s i n g 2 0 - 8 0 g o f sa m p l e . T h e t i m e o f e x p e r i m e n t w a s t a k e n a f t e r a t t a in i n g

t h e r e q u i r e d t e m p e r a t u r e . A t t h e e n d o f a r u n, t h e h e a t i n g w a s s t o p p e d a n d t h e a u t o c l a v e

a l l o w e d t o c o o l t o 7 0 C .

E x t r a c t i o n w a s c a r r i e d o u t u s i n g t w o t y p e s o f s y s t e m s : a c o n t i n u o u s c o u n t e r - c u r re n t

s y s t e m - - I ( F i g . 1 ) - - a n d a s e m i - c o n t i n u o u s c o u n t e r - c u r r e n t s y s t e m - - I I ( F i g . 2 ) .

F r o m e a c h o f t h e p r o c e s s e s u n d e r s t e a d y - s t a t e c o n d i t i o n s w e c a n c o n c l u d e t h at t h e

n u m b e r o f s o l i d a n d f l u i d i n t e r a c t i o n s a r e f i v e f o r s y s t e m I I a n d t h r e e f o r s y s t e m I . T h e

N a 2 C O 3 u s e d i n t h e e x p e r i m e n t s w a s o f re a g e n t g r a d e .

A t t h e e n d o f e a c h e x p e r i m e n t t h e m i x t u r e w a s f i l t e r e d a n d t h e r e s i d u e s w a s h e d ,

u s i n g a b o u t t w i c e t h e v o l u m e o f t h e f i l t ra t e . A l i q u o t s w e r e c o l l e c t e d a n d a n a l y s e d f o r

t u n g s te n b y t h e m e r c u r o u s m e t h o d a n d a v o l u m e t r i c m e t h o d w a s u s e d f o r c ar b o n a t e .

4 . R e s u l t s a n d d i s c u s s i o n

4 . 1 . E f f e c t o f s t i r r i n g

T h e s t i r r e r u s e d w a s t h e p i t c h e d b l a d e t u r b i n e ; o t h e r d e t a i l s a re : s t i rr e r s y s t e m a r e :

i m p e l l e r / v e s s e l d i a m e t e r r a t io 0 .6 ; n u m b e r o f s t a g e s 2 , w i t h a s p a c i n g o f 0 . 0 4 m ; a n d

h e i g h t / d i a m e t e r i m p e l l e r r a t i o 0. 1. T h e r e s u lt s , p r e s e n t e d i n T a b l e 3 , in d i c a t e t h a t t h e

s t i r ri n g r a t e h a s l i t t l e e f f e c t o n t h e d i s s o l u t i o n r a t e o f s c h e e l i t e w h e n t h e s p e e d i s

c h a n g e d f r o m 3 0 0 m i n - l t o 8 0 0 m i n - 1 . I t i s th e r e f o r e r e a s o n a b l e t o c o n c l u d e t h a t

b e y o n d 7 5 0 m i n - t t h e s o l i d p a r t ic l e s a r e n o t k i n e t i c a l ly li a b l e to d i f f u s i o n c o n t r o l b y t h e

a d h e r e n t f l u i d f i l m .

S o = f e s h s o l .u io n Sl 2 S 3 = # i n a (.( o tu t i o n

~ l l g S t a g e j - - J 2 e S t a g e j - = J 3 a S t a g e j -

n ~ = L e a ch e d o r e m 2 m o r e

o o = f r e s h

Fig. 1. Scheme of a continuous countercurrent system.


6/17

J.P. Martins/Hydro metallurgy 42 (1996) 221-236 225

x t ~

1a Stage: initially, rea cto rs A and B in

operation and C discharge

l - t o set the fresh or e inside C

2-change the leaching solution fi-om B to C

3-change the leaching solution from A to B

4-t o bring fresh leaching solution to C

2 ~ Stage:

1-separation o f solids and liquids at C and

leave of a solution with two stages o f

leaching

2-change the leaching solution from B to C


4-removal of steri le leached ore from A

3~d Stage :

1- to

set the fresh ore inside A

2-change the leaching solution from C to A

3-change the leaching solution from B to C

4- to bring fresh leaching solution to B

3 = Lk,.~

- 1 ~ 2 ~ $ t

4 h Stage:

l-sep aratio n o f solids and l iquids at A and

leave of a solution with three stages

of leaching


3-change the leaching solution fi 'om B to C

4-removal o f leached ore from B

5 h Stage:

1-to set the f lesh o re inside B



4-t o bring fresh leaching solution to C

6~ Stage:

1-separation o f solids and liquids at B and

leave o f a solution with f ive stages

of leaching



4-removal o f leached ore from C

Fig. 2. Schem e of a sem i-continuous countercurrent system.

4 .2 . E f f e c t o f s o l i d / l i q u i d r a ti o

T h e i n f l u e n c e o f s o l i d / l i q u i d ra t i o w a s s t u d i e d a t 1 0 0 C f o r a le a c h i n g t i m e o f 3 h

u s i n g d i f f e r e n t c o n c e n t r a t io n s o f N a 2 C O 3. F i g . 3 s h o w s t h at , f o r t h e s a m e s t o i c h i o m e t r i c


7/17

226 J .P. Ma rt ins / H ydrometal lurgy 42 (1996) 2 21 -23 6

Table 3

Influence of stirring rate on the convers ion of the scheelite

Time Na2CO 3 /W O 3 Stirring rate (rai n- 1

(h) (mo l/ mol ) 300 500 750 800

1.00 2 14.01 14.66 18.42 18.30

1 .0 0 4

35.22 34.18

3 5 . 1 8

35.20

1 . 0 0 8 4 1 . 1 9 42.80 43.32 43.12

2.25 2 18.36 19.05 23.04 23.15

2.25 4 43.71 44.22 43.81 44.20

2.25 8 52.98 53.75 52.52 53.05

4.50 2 18.84 20.95 23.43 23.12

4.50 4 50.26 53.10 53.40 53.30

4.50 8 67.24 67.24 67.85 67.60

Experimental conditions: p = 1 atm; T = 100+ IC; solid/liquid ratio = 1/5; ore = lot A ( < 100 Ixm).

r e l a ti o n o f N a 2 C O 3 / W O 3 ( s o l id l in e s ), t h e c o n v e r s i o n i n c re a s e s w h e n t h e s o l i d / l i q u i d

r a t i o i n c r e a s e s , w h i c h s h o w s a k i n e t i c d e p e n d e n c e o n t h e c o n c e n t r a t i o n o f th e l e a c h i n g

a g e n t . I t is a l s o c l e a r f o r t h e s a m e c o n c e n t r a t i o n o f s o d i u m c a r b o n a t e ( d a s h e d l i n es ) , t h a t

t h e r e i s a n i n c r e a s e i n t h e c o n v e r s i o n w i t h a d e c r e a s e i n t h e s o l i d / l i q u i d r a t i o . T h e

m a i n t e n a n c e o f s o d i u m c a r b o n a t e c o n c e n t ra t i o n w i t h a d e c r e a s e i n t h e s o l i d / l i q u i d r a t i o

d e m a n d s a l a r g e r e x c e s s o f t h e r e a g e n t o v e r t he s t o ic h i o m e t r ic r e q u ir e m e n t s . T h e r e f o r e ,

t h e b u l k c o n c e n t r a t i o n c a n b e c o n s i d e r e d u n c h a n g e a b l e w i t h t im e , w h i c h c o n f i r m s t h e

h y p o t h e s i s o f t h e p s e u d o - s t a t i o n a r y s t a t e .

4.3. Effect of sodium carbonate and temperature

T h e p l o t t i n g o f t h e c o r r e l a t i o n c o n v e r s i o n s a g a i n s t ti m e , X = f i t ), s h o w s t w o d i s t i n c t

z o n e s ( F i g s . 4 - 7 ) : i n th e f i r s t f e w m i n u t e s , t h e s l o p e o f th e f u n c t i o n i s c o n s t a n t a n d

i n c r e a s e s w i t h t h e t e m p e r a t u r e ; f o r l o n g e r l e a c h i n g t i m e s t h e r e a c t i o n r a t e d e c r e a s e s a n d

5

~

[ 3

0

u 1l

h l f l

1/3 1/5 117 111(

s o l i d / l i q u i d r a t i o

Fig. 3. Correlation between the yield o f WO 3 leaching and soli d/li quid ratio for different concentrations of

Na2CO 3. Experimental conditions: time = 3 h; stirring rate = 750 m in -t ; ore = lot A( < 100 mesh); tempera-

ture = 100C.


8/17

J.P.

Martins Hydrometallurgy

2 (1996) 221-236 2 2 7

1 0 0

~ 9 G e = ~

E

3 _

~ / *0 / # ~ l te r n p er a tu r e .100Z lO C

~

s t i r r i n g ? 5 0 m i n I

2 0 . I ,. I o r e = t o t A

I I I 1

0 1 2 3 l , 5 6 ? 8 9 10 11

t i m e h )

F ig . 4 . E f f e c t o f s o d i u m c a r b o n a te c o n c e n t r a t io n o n t h e p e r c e n ta g e o f W O 3 e x tr a c t e d a t 1 0 0 C f o r l o t A .

at ta ins a cons tant va lue . I t i s poss ib le

t

s a y t ha t a m a x i m um reco v ery o f a bo ut 80 wt %

W O 3 is ga ined ab ou t 2 h a f ter the s tart o f the react ion a t 10 0C , a f ter 1 h a t 15 0C , a f ter

3 0 m i n a t 2 0 0 C a nd a f t er 1 5 m i n a t 2 50 C . T he ca l cu l a t i o n o f a p p a rent a c t i v a t i o n

energ y wi t h t he A rrhen i us equa t i o n p ro v i des a f ur t her cr i t er i o n f o r de t erm i n i ng t he

co nt ro l l i ng s t ep o f t he rea c ti o n . T he A rrhen i us p l o t co ns t ruc t ed fo r t he f ir s t 1 5 m i n a nd

3 0 m i n o f t he rea c t io n , F i g . 8 , g i v es , re s p ec t i v e l y, a n a p p a rent energ y a c t i v a ti o n o f 4 1

kJ / m o l a nd 1 8 kJ / m o l . T hes e v a l ues i nd i ca t e k i ne t i c co nt ro l a t t he s t a r t o f t he rea c t i o n ,

whi ch cha ng es t o d i f f us i o n co nt ro l . T here f o re , t he a s h l a y er o f t he ca l c i um ca rbo na t e ,

associa ted wi th the s tructure o f the so l id part ic les , has a part icular ro le in the l eaching

process . The X-ray powder di f f ract ion pat tern on the externa l surface o f a gra in a f ter

l ea ch i ng i s rep ro duced i n F i g . 9 . T he ca l c i t e de t ec t ed co nf i rm s t he p res ence o f a n

1 0 0

_ , 0

o

O

o/;

o

u

2 0

I

f

I

r . . - 1

f

J

r

I

t e m p e r a t u r e = l S 0 ~ 5 0 C i

s o t i d / l iq u i d r a t i o = l l l O i

s t i r r i n g

= 7 5 0 m i n - t

3 ~ 5

t i m e h I

Fig. 5 . E f f e c t o f s o d i u m c a r b o n a t e c o n c e n t r a t io n o n t h e p e r c e n t a g e o f W O 3 e x t r a ct e d a t 1 5 0 C f o r l o t A .


9/17

228

J.P. Martins / Hydrometallurgy 42 (1996) 221-236

1 0 0

8 O

o+

60

o

g

20

f

f

F

1 =2

11.5

I

I

I

p

_ _ _ _ - - - - 4 -

P

I

l

f ~ ' ~ t 11m pllra tur11= 200.+5+C

/ s o t i d / | i q u i d r a t i 0 = 1 11 0

r

s t i r r i n g = 7 5 0 m i n - I

i I

0 1 2 3 & 5

t i m e [ h )

Fig. 6. Effect of sodium carbonate concentration on the percentage of W O3 extracted at 200 C for lot A.

i n s o l u b l e f i l m o n t h e u n r e a c t e d c o r e d u r i n g l e a c h i n g , a s h a s a l s o b e e n d e s c r i b e d i n t h e

l i t e r a tu r e [ 8 ,2 8 ] .

T h e a n a l y s i s o f t h e i m p u r i ti e s i n s o m e l e a c h l i q u o r s, T a b l e 4 , s h o w s t h e p u r i f y i n g

e f f e c t o f a lk a l i n e l e a c h i n g s o l u t i o n s o n l o w - g r a d e s c h e e l it e c o n c e n t r a te s . Y i e l d c a n b e

d e f i n e d a s t h e m o l e s o f a p a r t ic u l a r p r o d u c t p e r m o l e o f i ni ti al l e a c h i n g r e a c t a n t.

T h e r e f o r e , t h e r a ti o o f t h e u s e f u l p r o d u c t t o t h e y i e l d o f s e c o n d a r y p r o d u c t s i s t h e

s e l e c t i v i ty , w h i c h i s t h e r a t i o o f c o - o r d i n a t e y a x i s t o th e c o - o r d i n a t e x a x i s i n F i g . 1 0 .

100

. ~ 8 0

C

~6

f

S

I

e = 4

e = 3

I r - - - " - ' -

f ~

t 11mp'11rature 250~ 5%

20 olid/tiquid ratio= 1/10

s t i r r l n g = ? 5 0 r a i n - +

0 2 :~ ~,

t i m e ( h )

Fig. 7. Eff ect of sodium carbonate concentration on the percentage of WO 3 extracled at 250C for lot A.


10/17

J .P . M a r t i n s / H y d r o m e t a l l u r g y 4 2 1 9 96 ) 2 2 1 - 2 3 6

2 2 9

0

e.

-

e.

o

0

.=,

< ~ -

v

,O

o

o

e

z

e.

.o

a

0

o

o

~'=

< .=.

e.

o

o . o

e~

o

) ~ 'q

c 5 i o d , : S d ~

t ,i I ~ ~ ~ 0 e,'~ 0

0

V

Documents

Hydrom 42 1996 Kinetics low-grade scheelite.pdf