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Pergamon Minerals Engineering, Vol . 9 , No. 3, pp. 357-366, 1996Copyr i gh t 1~ 1996 P ub l i she d by E l se v i e r S c ie nc e L i dPr inted in Grea t Br i ta in. Al l r ights r eservedPII: S0892--6875(96)00020-9 0 8 9 2 ~ g 7 5 / 9 6 $ 1 5 . 0 0 + 0 . 0 0

T E C H N I C A L N O T EA D S O R P T I O N O F O L E A T E A N D O C T Y L - H Y D R O X A M A T E

O N T O R A R E - E A R T H S M I N E R A L SO . P A V E Z , P . R . G . B R A N D A O t a n d A . E . C . P E R E S t

Dept. of Metallurgy, Universidad de Atacama, Casilla 240--Copiapo, Chilet Dept. of Mining Engineering, UFMG, Rua Espirito Santo, 35/702,

30160-030 Belo Horizonte, MG, Brazil(Received 16 Jun e 1995; accepted 18 Oc tober 1995)

ABSTRACTThe adsorpt ion o f sodium o lea te and potass iu m octy l -hydroxamate onto the rare-earthsm inerals mo nazite and bastnaesite wa s invest igated through microflotation experiments,ze ta po ten t ia l de terminat ions and in frared spectroscopy.The m onazi te an d bastnaesi te samp les w ere puri f ied in the laboratory reaching ,respective ly , f ina l grade s o f 68 . 7 and 45 .3% RE2 03 + ThO 2.The resu l t s confi rm that sodium o lea te chemisorbs onto bastnaesi te an d suggest a physica ladsorpt ion m echanism o f th i s reagent on to monazite. Despi te the lack o f a fu l lconfirmation fro m F TIR spectrometry, there is a poss ibil i ty of oleate chem isorption on tomo nazi te in the p H range above the i soe lec tr ic po in t .A chem ical adsorpt ion m echanism was es tabl ished fo r the in teract ion be tween octy l-hydroxamate and both minerals .KeywordsFlotation reagents; flotation collectors; industrial minerals

INTRODUCTIONBastnaesite and monazite are the most important rare-earths bearing minerals in the world. Sodium oleateadsorption onto these minerals has been reported in the literature. Gerdel and Smith [1] observed thatsodium oleate abstraction by basmaesite is significant above the isoelectric point--IEP, indicatingchemisorption of the reagent onto the mineral surface. Viswanathan and Majumdar [2] investigated, viainfrared spectroscopy, oleate adsorption onto monazite, arriving at the conclusion that a chemisorbed layeris formed on the mineral surface. Zakharov et al. [3] suggested that monazite flotation with sodium oleatedepends on the reactions between the collector and thorium and rare-earths elements, with the formationof the corresponding metal oleate.Hydroxamic acids adsorption has been attributed to their ability of complexing metallic cations. Accordingto Bogdanov [4], they form stable complexes with the cations of rare-earths elements. Fuerstenau andPradip [5] presented a model based on equations to explain the chemical interaction between potassiumoctyl-hydroxamate and bastnaesite. A similar model was proposed by Jiake and Xiangyong [6] for thechemisorption of hydroxamic acid onto bastnaesite and monazite.

Poster presentation at Minerals Engineering '95 , St. Ires, Cornwall, England, June 1995

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358 Technical NoteT h e p r e s e n t i n v e s t i g a t i o n s t u d i e s t h e m e c h a n i s m s o f s o d i u m o l e a t e a n d p o t a s s i u m o c t y l - h y d r o x a m a t ea d s o r p t i o n o n t o t h e r a r e - e ar t h s b e a r i n g m i n e r a l s m o n a z i t e a n d b a s t n a e s it e .

M A T E R I A L S A N D M E T H O D ST h e m o n a z i t e s a m p l e w a s s u p p l i e d b y S A M I T R I - - S A M i n e r a c a o d a T r i n d a d e , f r o m S a o G o n c a l o d oS a p u c a i , M G , B r a z il i n t h e si z e r a n g e - 2 1 0 + 1 0 5 / ~ m . T h e s a m p l e w a s p u r if i e d b y u s i n g a F r a n t zi s o d y n a m i c m a g n e t i c s e p a r a t o r , w a s h e d w i t h d i s ti l le d w a t e r a n d d r i e d a t 8 0 C .B a s m a e s i t e w a s e x t r a c t e d f r o m a s a m p l e o f t h e ra r e - e a r th s o r e o b t a in e d f r o m P o c o s d e C a l d a s , M G , B r a z i l,s u p p l i e d b y M I N E G R A L S A . A f t e r c ru s h i n g ( ro l l s c r u s h e r ) , a h a n d p i c k i n g o p e r a t i o n , u n d e r a s t e r e o s c o p i cm i c r o s c o p e , p r o v i d e d g ra i n s r ic h in b a s t n a e si t e . A f ra c t i o n - 2 1 0 + 7 4 / z m w a s p r o d u c e d b y g ri n d i n g a n df u r t h e r p u r i fi e d i n a F r a n t z i s o d y n a m i c m a g n e t i c s e p a r a t o r an d i n a M a g s t r e a m a p p a r a t u s . T h e m a t e r ia l w a sg r o u n d t o 1 0 0 % - 3 7 / ~ m , w a s h e d w i t h d i s t i l l e d w a t e r a n d d r i e d a t 8 0 C .T h e c h e m i c a l a n a l y s e s o f t h e t w o s a m p l e s w a s a s f o ll o w s :

S a m p l e

m o n a z i t eb a s tn a e s i t e

R e 2 0 3 +T h O 2 % S iO 2%6 8 . 7 1 . 1 545 . 3 1 1 . 6 4

A1203 P %% C a O F e %%0 . 9 2 1 2 . 1 0 . 9 69 . 8 3 1 5 . 1 2

T h e r e a g e n t s u t il i s e d w e r e :i . p o t a ss i u m o c t y i h y d r o x a m a t e - - C H 3 ( C H 2 ) 6 C O N H O K - - s y n t h e t i s e d ac c o r d in g t o a m e t h o d r e p o r te db y F u e r s t e n a u a n d P r a d i p [ 5 ] ;i i. s o d i u m o l e a t e- - C H 3 ( C H 2 ) 7 C H = C H ( C H 2 ) T C O O N a - - a n a ly t i c a l g r ad e ;i ii . p o t a s s i u m h y d r o x i d e a n d h y d r o c h l o r i c a c i d , a n a l y ti c a l g r a d e , f o r p H c o n t r o l ;iv . p o ta s s iu m c h lo r id e , a n a ly t i c a l g r a d e , a s in d i f f e r e n t e l e c t r o ly te ;v . n i t r o g e n , a s g a s in th e m ic r o f lo t a t io n e xp e r im e n t s .M i c r o f l o t a t i o n t e s ts w i t h m o n a z i t e ( - 2 1 0 + 7 4 t x m ) w e r e p e r f o r m e d in a m o d i f i e d H a l l i m o n d t u b e s i m i l a rt o t h a t d e s c r i b e d b y F u e r s t e n a u , M e t z g e r a n d S e e l e [7 ] . A t u b e s i m i l a r to t h a t d e s c ri b e d b y S i w e k , Z e m b a l aa n d P o m i a n o w s k i [8 1 w a s u t i l is e d f o r t h e f in e r ( - 3 7 # m ) b a s t n a e s it e s a m p l e .Z e t a p o t e n t i a l d e t e r m i n a t i o n s w e r e c a r r i e d o u t u si n g a R a n k B r o t h e r s M a r k I I a p p a r a tu s w i t h a 1 m m f la tm i c r o e l e c t r o p h o r e t i c ce l l . E a c h p o i n t r e p r e s e n t e d a n a v e r a g e o f 2 0 d e t e r m i n a t i o n s . T h e m i n e r a l s a m p l e sw e r e g r o u n d t o - 3 7 t zm i n a p o r c e l a i n m o r ta r . A l x l 0 - 3 M K C 1 s o l u t io n w a s e m p l o y e d a s in d i f f e r e n te l e c t r o l y t e a nd p H w a s c o n t r o l l e d w i t h 5 % w / v H C 1 a nd K O H s o l u t io n s .T h e i n f r a r e d a b s o r p t i o n s p e c t r a w e r e o b t a i n e d t h r o u g h t h e K B r p e l l e t m e t h o d i n a F o u r i e r t r a n s f o r mi n f r a r e d s p e c t r o m e t e r P e r k i n E l m e r F T - I R 1 7 6 0 X , c o n t r o l l e d t h r o u g h a n i n t e r f a c e c o n n e c t e d t o aP r o f e s s i o n a l C o m p u t e r P e r k i n E l m e r 7 7 0 0 . T h e d a t a a c q u i s i t i o n a n d s p e c t r a p r o c e s s i n g a n d d i s p l a y i n gp r o g r a m m e s w e r e t h e r e g u l a r o n e s ( C D S p a c k a g e ) , s u p p l i e d b y P e r k i n E l m e r . T h e m o n a z i t e a n d b a s t n a e s it es a m p l e s w e r e p r e v i o u s l y g r o u n d i n a n a g a t e m o r t a r f o r e i g h t h o u r s . T h e s p e c i f i c s u r f a c e a r e a s , a sd e t e r m i n e d b y B E T t e c h n i q u e , u s i n g a Q u a n t a s o r b i n s t r u m e n t , w e r e 5 . 0 5 m 2 / g f o r m o n a z i t e a n d 8 . 4 7 m 2 / gf o r b a s t n a e s it e .

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Technical Note 359

In this infrared study the following spectra were compared: (a) mineral exposed to water at the desired pH;(b) mineral exposed to the collector solution at the desired pH.

RESULTSFloatability curves as a function of pH for monazite and bastnaesite in the presence of sodium oleate andpotassium octyl-hydroxamate are presented in Figure 1.In the presence of 152 mg/l sodium oleate, monazite showed high floatability at pH=3 and the rangebetween 6 and 10, showing a minimum around pH=4.

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3 6 0 T e c h n i c a l N o t e

A h i g h f l o a ta b i l it y o f b a s t n a es i t e w i t h o l e a t e a t p H = 8 w a s r e p o r t e d b y G e r d e i a n d S m i t h [ 1 . T h e m a x i m u ma r o u n d p H = 9 ( t h e p K a r a n g e r e p o r t e d f o r h y d r o x a m i c a c id s i s 8 . 5 t o 9 . 5 ) i s c h a ra c t e r i s ti c f o rh y d r o xa m a te s in a d s o r p t io n a n d f lo t a t io n s tu d ie s , a c c o r d in g to F u e r s t e n a u a n d P r a d ip [5 ] .Z e t a p o t e n t i a l c u r v e s o f m o n a z i t e a n d b a s t n a e s it e a s a f u n c t i o n o f p H , i n t h e a b s e n c e o f b o t h c o l l e c t o r s a n di n t h e p r e s e n c e o f s o d i u m o l e a t e a n d p o t a s s i u m o c t y l - h y d r o x a m a t e , a r e p r e s e n t e d i n F i g u r e 2 . T h ei s o e l e c t ri c p o i n t s t a y s a t p H = 5 . 2 f o r m o n a z i te an d p H = 4 . 9 f o r b a s t na e s i te . T h e p re s e n c e o f c o l l e c t o rd i s p l ac e s t h e I E P t o w a r d s t h e m o r e a c i d i c re g i o n . I n t h e p H r e g i o n a b o v e t h e I E P t h e c o l l e c t o r s h if t s t h ez e ta p o te n t i a l t o m o r e n e g a t iv e v a lu e s .

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