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P e r g a m o nMineralsEngineering,Vol. 10, No. 12, pp. 1395-1404, 1997 1997 Published by Elsevier Science LtdAll fights reserved. Printed n Great Britain0 8 9 2 - 6 8 7 5 ( 9 7 ) 0 0 1 2 9 - 5 0 89 2 -6 8 75 /9 7 $ 17 .0 0+ 0.00

A N E W ' C O L L E C T O R F O R R A R E E A R T H M I N E R A L F L O T A T I O N

J . R E N ~*, S . L U t , S . S O N G * a n d J . N I U ~ Un ivers i ty of Science and Tech nology B eij ing, Col lege o f Resources Engineering,

30 College Road, Beijing 100083, China. E-mail: l icylxj@public.bta.net.cnv Ba oto u Iron and Steel Corporation, Bao tou, Innermongolian 014010, Ch inaUnivers idad A utono ma d e San L uis Potos i, Inst ituto de M etal lurgia ,

San Lius Potos i , S.L.P, C.P. 78240, MexicoM inis try o f Meta llurgical Industry of P.R. China, B ei j ing 100044, Ch ina

(Received 29 September 1996; accepted 16 June 1997)

A B S T R A C TA new c oU ecto rfor bastnaesite f lotation - modified hydroxamic a cid (MO HA) has beendev elope d through several years laboratory research. The experimental results of lotationo f pu re b astnaesite mineral an d rare earth ore s, and the application experience inflotation plants showed that MOHA is an eff icient collector for bastnaesite f lotation.M OH A .lugs stronger collector abil ity a nd higher selectivity compared to the othe rcomm only used collectors. Throu gh the measurements o f zeta-potential, adsorption a ndinfrared adsorption spectrum and in terms o f the electronegativity theory o f reagentgroups, the f lotation mechanism has been discussed. I t was concluded tha t the adsorptiono f M OH A on bastnaesite surfaces is chemical adsorption in nature through three oxygenatoms in the polar group of MO HA chelat ing the surface C e( l l l) o f bastnaesi te to for ma pentago n-cycle chelate: O-C--N-O -Ce(III)-O. Add itionally, the chem isorption isaccompanied wi th the mul ti layer a nd non-homogeneous ph ysical adsorption of the MOH Amolecules, The MO HA adsorption equation at the surfaces o f bastnaesite can be expressedas: I" = 6.76x 10-2C /1.02, wh ile the adsor ption rate cons tant k is: k = 2.64x10 5min-lmot"lm 2. 1997 Published by Elsevier Science LidK e y w o r d sFlotation collectors; froth flotation

I N T R O D U C T I O N

D ue to the rapid de velo pm ent o f superconducting, magnetic, functional and fluorescent materials the dem andfor rare earth materials in the world is continuously increasing. B astnaesite (CeCO3F ) is one o f the mainrare earth minera ls, wh ich conta ins approximate ly 75% C e. At the present time, abou t 60 -70 % of the rareearth (RE203) in the world is extracted from bastnaesite.Th ere is li tt le literatures con cerne d with the flotation of bastnaesite [1-8]. V arious reagents, su ch as oleicac id, o xidized OP -100, a lkylhydroxamic ac id, naphthenic ac id, sodium do decylsulfa te , N-hy droxy lphthalicimide and styrophosphonic acid have been investigated as collectors for bastnaesite flotation.

Presented a t Minerals Engineering '96 ,Brisbane, Australia, August 26-28, 19961 3 9 5

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1396 J. Ren e t a l .Hydroxam ic ac id i s a che la t ing agen t com m only used in chem ica l ana lys i s . Due to i t s h igh s e lec t iv i ty tora re ea r th e lem en t ions in the weak a lka l ine r eg ion , hydroxam ic ac id has been used as the co l l ec to r in r a reear th m inera l f lo ta tion . In ou r p rev ious paper s [9 ,10 ] , we descr ibed exp er im en ta l s tud ies on the f lo ta t ion o fm o n a z i t e a n d b a s t n a e si t e f r o m r a r e e a r th o r e s b y u s i n g a c o m b i n a t i o n o f m o d i f i e d h y d r o x a m i c a c i d ( M O H A )a n d p r o p e r m o d i f i e r s. M O H A ( R - O H C O O N H 2 ) i s c h a r a c t e ri z e d b y i ts t w o p o l a r g r o u p s ; i n a d d i ti o n t o t h eh y d r o x a m i c g r o u p a h y d r o x y l g r o u p i s i n tr o d u c e d , b o t h p o l a r g r o u p s b e i n g c o n n e c t e d t o t h e n o n - p o l a r c h a i no f t h e r e a g e n t m o l e c u l e . T h e s t ru c t u re o f M O H A i s s im i l a r t o s a l ic y l ic h y d r o x a m i c a c i d, b u t i n s t e a d o f ab e n z e n e r i n g t h e n o n - p o l a r p a rt i n t h e M O H A m o l e c u l e i s a n a p h t h a le n e r i ng .In th is paper , the co l l e c to r behav iour s o f MO HA in bas tnaes it e f lo ta tion and i ts com m erc ia l app l ica t ion inth ree f lo ta tion p lan t s a r e desc r ibed . Fu r therm o re , the co l l ec to r m ec han ism o f MO HA is d i scus sed in t e rm sof the da ta ob ta ined th rough ze ta -po ten t ia l , adso rp t ion and in f r a red abso rp t ion spec t rum m easurem en ts andf r o m t h e p o i n t o f v i e w o f e l e c t r o n e g a ti v i ty t h e o r y o f r e a g e n t g r o u p s.

M A T E R I A L S A N D E X P E R IM E N T A L M E T H O D S

T h e pure bas tnaes i t e s am ple used in th i s s tudy is taken f rom Ma on iup ing m ine , S ichuan P rov . , Ch ina . T h es p e c i m e n w a s c u t b y h a m m e r a n d p u r i fi e d b y h a n d - s o r ti n g , t h e n w i t h g r a v i t y c o n c e n tr a t i o n a n d m a g n e t i cs epara t ion in de io n ized wate r . A f te r tha t, the pu r i f ied s am ples w ere g roun d and c las s if i ed in to s evera l s i zef r ac t ions , and the s i ze f r ac t ion 37 - 10 0 larn was used fo r the tes t s. T be p u r i ty o f the bas tnaes i t e s am ple was98 . 13%, and i t s spec i f i c su r f ace a rea the 0 . 2011 m 2/g .T h e b a s t n a e si t e o r e s a m p l e s u s e d f o r t h e f lo t a ti o n t e st s w e r e f r o m M a o n i u p i n g ( M N P ) m i n e , W e i s h a n ( W S )m i n e a n d B e i y u n e b o ( B Y E B ) m i n e , C h i n a . T h e m a i n c o m p o s i t io n o f t h e s a m p l es i s g i v e n in T a b l e 1 . T h e-7 41 am f r a c t io n i n t h e o r e s a m p l e s w a s 6 7 % f o r M N P o r e a n d 7 1 % f o r W S o r e , r e s p e c t iv e l y . T h e g a n g u em inera l s a r e bar i t e , f luo r i te and s i l ica te m inera l s .

T A B L E 1 T h e c o m p o s i t i o n o f t h e r a re e a r t h o r e s (% )o r e s s a o F F e , , t S i O z c o 2 p 3, PbM N p 9 . 5 O 2 8 . 7 3 I I . 8 9 6 . 7 l 1 2 . 5 4 4 . 5 O 1 3 . 7 4 7 . 3 7 O . 3 5 0 . 7 8W S 6.14 22.25 10 .11 1.06 9.84 2.30 30.63 7.93 0.20 6-53 0.053

BY EB 7.91 6.58 14.88 9.56 - 24.28 9.18 - 5.12 1.02

T h e m o d i f i e d h y d r o x a m i c a c id ( M O H A ) u s e d i n th i s s tu d y w a s p r e p a r e d i n o u r l a b o r a t o r y , a n d w a s 9 0 . 1 6 %pure . Modi f ie r s -wate r g las s and H103 a re indus t r i a l p roduc t s . Reagen t H03 , wh ich cons i s t s m ain ly o f ana l c o h o l i c o r g a n i c c o m p l e x , i s a b y - p r o d u c t o f th e s y n t h e s is o f M O H A .T h e exp er im en t w i th pu re bas tneas i t e was cond uc ted in a 50 m l XFG -36 f lo ta t ion ce l l. I n i ti a l ly 2 .0g o f thep u r e s a m p l e w a s c o n d i t i o n e d w i t h d i st i ll e d w a t e r f o r 1 m i n , t h e n M O H A w a s a d d e d a n d a g i t at e d f o r 5 m i nbefo re f lo ta tion fo r 5 m in . T he f lo ta t ion resu l t s were r ep roduc ib le , the abso lu te e r ro r be ing be twe en + 1 . 5%of f lo ta t ion r ecovery . T he o re f lo ta t ion t es t s were conduc ted in a l abora to ry 500 m l XJK f lo ta t ion ce l l .I n i ti a l ly 1 5 0 g o f t h e o r e s a m p l e w a s c o n d i t i o n e d w i t h t ap w a t e r f o r 1 m i n , t h e n N a 2 S i O 3 , M O H A a n d H 1 0 3wer e adde d in s equ ence an d ag i t a ted fo r 5 m in , 5 m in , 1 r a in , r espec t ive ly , f lo ta t ion be ing fo r 6 m in . B o thlabora to ry f lo ta t ion ce l l s were m echan ica l ly ag i t a ted . T he XJK f lo ta t ion ce l l i s a type o f s e l f - ae ra t ing andm echan ica l ly ag i t a ted f lo ta t ion m ach ine , wh ich has a f l a t b laded im pel le r w i th 6 b lades , pe rpend icu la r tothe d i r ec t ion o f ro ta t ion , and a s t a to r w i th 18 b lades , in s ta l led underne a th a ho r izon ta l round p la te w i thsevera l c i r cu la t ing ho les and a t an ang le to the d i r ec t ion o f ro ta t ion . T h e X JK f lo ta t ion ce l l i s w ide ly u sedin the f lo ta t ion p lan ts in C h ina .Z e t a - p o t e n t ia l w a s m e a s u r e d w i t h a M R K m i c r o - e l e c tr o p h o r e t ic m e t e r , m a d e i n Ja p a n . T h e M O H Aadsorp t ion was m easured w i th a UV-3000 u l t r a -v io len t spec t ropho tom ete r , Sh im azu Co . , J apan . T hes t ruc tu re o f adso rp t ion p roduc t a t the m inera l su r faces were es t im ated w i th a 74 -F I - IR in f r a red - spec t rom e te r ,N i c o l e t C o . , U S A . T h e p r o c e d u r e o f m e a s u r e m e n t c o n s is t e d o f th e f o l l o w i n g s te p s :f i rs t a d d M O H A t o t h em inera l s am p le o f -21am and ag i ta te fo r ha l f an hour , then s epara te the so l id f rom l iqu id by cen t r i fuga t ion ,

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F L O T A T I O N R E S U L T SF l o t a t i o n T e s t s o f P u r e B a s t n a e si t e

10 0

T h e f l o ta t i on r e c o v e r y o f b a s tn a e s it e w i t h M O H A v s. t h e p H v a l u e a n d t h e c o n c e n t r a t io n o f M O H A i sshow n in F igure s 1 a and b , r espec t ive ly . As s een in F igu re 1 , w i th inc rease in pH f lo ta tion r ecove ry sharp lyr i s es un t i l pH= 8 . 5 . A t p H 8 . 5 - 9 . 5 , the f lo ta t ion r eco very r eaches i t s m a x im um and then de creases in s t ronga l k a l in e m e d i a . T h e f l o t a ti o n re c o v e r y i n c r e a se s w i t h i n c r e a s e o f c o n c e n t r a t io n o f M O H A . F l o t a t i o n r e c o v e r yr e a c h e d 9 0 % a t 1 . 0 x l 0 3 m o l / 1 o f M O H A , a n d 9 5 % a t 5 .0 x1 0" 3m o l/ 1 o f M O H A .

l e

i "m

6 . -

8

a

1 N

U o

N -

40-

m -

A new collector or rare earth mineral flotation 1397then d ry the s e d im e n t a t a t em pera tu re low er than 30 C, then p res s the d r ied s am ple in to sm al l ca ke fo r IRana lys i s .

O $ 6 7 O 11 13 4 -6 .4 4 -42 .4

C aF i g . 1 T h e e f f e c t s o f p H v a l u e a n d M O H A c o n c e n t r a ti o n o n t h e f l o ta t io n r e c o v e r y o f b a s t n a e s i te

F l o t a t i o n t e s t o f B a s t n a e s i t e o r e sT h e e f f e c t s o f p H v a l u e a n d M O H A d o s a g e o n t h e f lo t a ti o n r e s ul ts o f th r e e b a s tn a e s it e o r e s a r e s h o w n i nF igures 2a and 2b , r espec t ive ly . I t can be s een tha t the bes t f lo ta t ion r esu l t s were ob ta ined a t pH 8 . 5 -9 . 5 .T h r e e o r e s a m p l e s w e r e t h e n t e s t e d u n d e r t h e o p t i m u m p H c o n d i t io n i n a c l o s e d f l o t a ti o n c ir c u i t w i t h o n es t ep r o u g h e r f l o ta t i o n a n d o n e s t ep c l e a n i n g , re a g e n t s a d d e d b e i n g M O H A , N a 2 S i O 3 a n d H 1 0 3 . T h e r e s u lt so f the c losed f lo l: at ion c i r cu i t a r e show n in T ab le 2 .

T A B L E 2 F l o t a t io n p e r f o r m a n c e o f t h r e e b a s t n a e s it e o r e sOres

M N P

W SB Y E B

Coneea l r a teT e i l i ~

F e e dConcen t r a te

l"ailingsF e e dC o n c e n l n t eMiddlinss

Tai l iassF e e d

Ye %

13.878 6 . 1 3I 0 0 . 0 09.05

90.95100.007.913.3188.78100.00

R E O63.780.759.5156.131.316.2760.1319.512 .5 87.70

~ %B aO2.13

33.0128.73 i3 .9 62 4 . 0 722.251.89

6.58

C aO7.75

12.581 1 .8 99 . 0 410.22

10.119.04

1 4 .8 8

R e e o v e ~ %R E O B a O C a O93.12 1.03 8.836 . 8 8 9 8 . 9 7 91.17

1 0 0 . 0 0 1 0 0 . 0 0 1 00 .0 081.01 1 .61 8 .091 8 . 9 9 9 8 3 9 9 1 . 9 11 0 0 .0 0 1 0 0 . 0 0 1 0 0 .0 061.82 2.27 2.578 . 4 4

2 9 . 7 41 0 0 . 0 0 1 0 0 . 0 0 1 00 .0 0

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1398 J. Ren e t a l .

8

i .I 'Q

- - 6 - - ~ a

- - ~ - - M- - i l . - I I I- - O - - M- - O - - M

$ J ~ 4 l e 12

1W

Mi -[ .1E

m

b ~ A 2- - A - - m- - D - M- - n - - B 1- - O - - A 1

0L 5 1 1.S 2 ~ 3 ~LS 4u c x ~

Fig.2 Flota tion results of bastnaesite ores as a function o f (a) pH and (b) collecto r concentration (A-Rec overy , B-Grade, 1-MNP ore , 2-W S ore, 3-BYEB o re)

I ndus t r i a l A pp l i c a t i onOn the bas is of the labora tory tes ts, the reagent combinat ion mentioned abov e has been appl ied in the plantsof Maoniuping (M NP) mine and Be iyunebo (BYEB) mine wi th 2 .8m 3 X3K flotation cells. W ith o ne-steproug her flotation and on e-step cleaning flotation, high quality b astnaesite concentrates are obtained. T heflotation parameters and results in the plants are listed in Table 3 and Table 4.

T A B L E 3 T h e o p e ra t in g p a r a m e t e r s o f b a s t n a e s i t e f l o t a t i o n i n p l a n t s

~ , t / dS iz e o f F e e d ( - 7 4 p r o ) , %Solid dmm ity, %T ~ o f P u lp , Cp Hv o m s e o f N . ~ . ]qr/tv o s ~ o f M O H ~ ~S/tH I 03 , I ~ / t

~ , , p ~ a t B Y E n l~ at7 5 ' 3 0 07 2 . 7 8 9 5 . 6 64 , ~ M 4 ~ - , ~28-32 30- ,358 - 9 8 . 5 - - 9 . 53.76 3.19O.68 1 .34o.2~ o~1

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A new collect or for rate earth mineral flotation 1399

MNP Coneenerateplant TailingFeedB Y ~ B C o n ~plant Teil~18Feed

TABLE 4 The results of bastnaes it e flotation in plantsY e ed G n U %

14.9285.08100.00il.9788.03100.00

mxMy,%m oaaoc s io Fe aa0 s io Fe

, , , ,

60.81 2.33 7.97 2.10 - 92.77 1 .37 14 .2 6 1 .560.83 29.488 .41 23.26 - 7.23 98.63 85.74 98.449.78 25.43 8.34 20.10 - !00.00 100.00 100.00 100.0050.190.98 9.53 1.14 6.842.91 7.71 15.39 10.35 27.818.64 6 .9 1 14.6 9 9 .25 25.30

70.37 1.74 7.76 1.51 3.2429.63 ~ . ~ 92.24 98.49 96.76100.00 100.00 100.00 100.00 100.00

The data obtained in the industrial practice and from the laboratory tests demonstrate that MOHA is anefficient collector for bastnaesite flotation.

THEORETICAL STUDYFigure 3 illustrates the relationship between zeta potential of bastnaesite and pH.The iso-electde~l point of bastnaesite in pure water is pH 8.0. However, in the presence of MOHA the zetapotential curve of bastnaesite shifts left, and the i.e.p, becomes pH 5.9. Moreover, a peak of negative zetapotential appears at pH 9.0.

4e

l

Z 4 | | 4111 12

Fig.3 Relationship between zeta potential and pH (A2-In water, B2-In MOHA)

Figures 5 and 6 illustrate the adsorption ( F) of MOHA at the surface of bastnaesite as a function of MOHAconcentration ( C ) as well as adsorption time (t), respectively. The relationships between the adsorptionof MOHA at the surfaces of bastnaesite and the pH value is given in Figure 4. It can be seen that themaximum adsorption occurs in the range of pH 8.0 - 10.0, and when the pH value becomes greater than11, the adsorption dramatically reduces, being in agreement with the flotation results' dependence on pHvalue (Figure la).The infrared absorption spectra of MOI-IA, untreated bastnaesite and bastnaesite treated with MOHA areshown in Figure '7. It can be seen that the infrared absorption bands of the active groups of MOHA are at

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140o J. Ren e t a l .1 6 1 0 c m "~, 1 1 5 0 c m .1 a n d 1 0 5 0 c m ~ , r e s p e c t i v e l y , t h e i n f r a r e d a b s o r p t i o n b a n d s o f b a s t n a e s i t e a r e i n t h er e g i o n o f 1 5 5 0 - 1 3 5 0 c m m a n d 9 5 0 - 8 0 0 c m . A f t e r a d s o rp t i o n o f M O H A , t h e i nf r a re d a b s o r p t i o n b a n d sa t 1 5 5 0 c m "1 a n d 1 1 0 0 c m "l w e r e m u c h e n h a n c e d a n d b e c o m e w i d e r.

'12

! .S

2 4 I | ' IB '12p H

F i g . 4 R e l a t io n s h i p b e t w e e n p H a n d t h e a d s o r p t io n o f M O H A o n b a s tn a e s it e s u r fa c e

.4 ,

.4 ,

t 4j 4

4

4 .7 4 ~ l c i 4 . 4 4F i g . 5 T h e a d s o r p t i o n o f M O H A o n s u r fa c e v s . t h e c o n c e n t r a t i o n o f M O H A

D I S C U S S I O N SO r i g i n o f S u r f a c e C h a r g e s o il B a s tu a e s i t eI n a q u e o u s s o l u t i o n , C e ( I I I ) i o n i s h y d r o l y s c d , t h e h y d r o l y s i s e q u a t i o n s b e i n g a s f o l l o w s :

k iCe 3+ + H 2 0 = Ce ( O H ) 2+ + H + k ! = 1 0s'9 (1 )

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A new collector for rare earth mineral flotation 1401

C e ( O H ) 2+ + H 2 0

C e ( O H ) 2 + + H 2 0

C e ( O H ) 3 + H 2 0

, , C e ( O H ) 2 + + H + k2 = 105-8k3

= C e ( O H ) 3 + H + k 3 = 1 04.3k4

= C e ( O H ) 4 + H k4=103-1t 6

(2 )

(3 )

(4 )

I $

'114

I I

X5

3

I0 4 $ $ 2 t S 2 9t n i

F i g . 6 T h e a d s o r p t i o n o f M O H A a t b a st n a e s it e s u r f a c e v s . a d s o r p ti o n t i m e

I

1

t m mw m m w t o t a l m

F i g . 7 T h e i n l~ a re d s p e c t r a o f M O H A , b a s t n a e si t e a n d b a s t n a es i te t r e a te d M O H A ( 1 - M O H A ,2 - b a s t n a e s i t e , 3 - a d s o r b e d M O H A o n b a s t n a e s i t e )

Ba s e d on t he s t a b l e c ons t a n t s o f hyd ro l ys i s o f Ce ( I I I ) i n Equ a t i ons 1 , 2 , 3 , 4111], t he pC -p H d i a g ra m f o rCe 3+ hyd ro l yse s i in a que o us so l u t i on ha s be e n c a l c u l a t e d a nd t he r e su l t s a re show n i n F i gu re 8 . I t c a n bes e e n f r o m t h e c o m p a r i s o n o f F i g u r e 3 w i t h F i g u r e 8 t h a t th e n e g a t i v e e l e c tr o k i n e t ic p o t e n t i a l o f b a s t n a e s i tei n w a t e r i s p r o b a b l y d u e t o t h e a d s o r p ti o n o f O H a n d C e ( O H ) 4 - o n t h e s u r f a ce o f b a s t n a e s i t e in t h e h i g hp H r e g i o n ; w h e r e a s t h e p o s i t i v e z e ta - p o t e n ti a l o f b a s tn a e s i te o b s e r v e d i n t h e r e g i o n o f p H < 8 . 0 i s d u e t o

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1402 J. Ren e t a l .t he adsorp t ion o f H and C e 3 +. Af te r the adsorp t ion o f M OHA, the ~ -pH curve moves toward a nega t iveva lue ( the i . e.p , mov es f rom pH 8 .0 to pH 5 .9 ), t h i s t r end be ing in good accordance w i th the F - pH curve .Th i s i s obv ious ly caused by the adsorp t ion o f M OH A an ions a t t he bas tnaes i te su r f aces . The exper ime n ta lresul t show that even i f the pH > i .e .p . , M OH A, a n anionic col lector , can st i l l adsorb on b astnaesi te sur faceregard less o f i ts nega t ive charges and the bas tnaesi t e su rf ace becomes m ore nega t ive because o f the M OH Aadsorp t ion . Accord ing ly , i t i s r easonab le to p ropose tha t M OHA an ions a r e chemica l ly adsorbed onbastnaesi te s ur faces, or i t i s esse nt ia l ly the speci f ic adsorpt ion.

-3

..4

I ,6

g 4-7

.40 2 4 tt 12

i

8 lO

Fig .8 Logar i thmic concen t r a t ion d iag ram o f C e 3+ hyd rolysa te (10 -4 mol /1)(1-Ce3 , 2 -Ce (OH ) 2 , 3-Ce(OH)2 + , 4 -Ce (OH ) 3, 5-C e(O H)4 -)

A d s o r p t i o n E q u a t i o nThe adsorp t ion cu rve lgF- lgC shown in F igure 5 i s a l i near one , and can be s imula ted by the fo l lowingequat ion:

1I ' - - 6 . 7 6 x 1 0 - 2 C 1.02 ( 5 )

Obvious ly , t he adsorp t ion o f M OHA on the bas tnaes i t e su r f aces obeys the F reund ich adsorp t ion fo rmula1

F = k C n . Thus , t he M OH A adsorp t ion a t t he bas tnaes it e su r f ace can be cons idered as a mul t i l ayer andnon-homogeneous adsorp t ion . An adsorbed l ayer i s chemica l ly connec ted wi th the su r f ace and d i r ec t lys i tua ted on i t, f u r ther the re ex i s ts a phys ica l ly adsorbed M OH A mul t i l ayer , wh ich i s assoc ia t ed wi th thechemisorbed l ayer . I n Equa t ion 5 , n = 1 .02 , ind ica t ing tha t t he adsorp t ion o f M OH A a t bas tnaes it e su r f acesis re lat ively s table .F rom the adsorp t ion k ine t i c cu rve shown in F igure 6 , t he adsorp t ion r a t e o f M OHA a t t he bas tnacs i t esu r f aces can be descr ibed by the fo l low equa t ion:

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A new co l lecto r fo r rare ear th mineral f lota tion 1403

t 1 t- 2 . tM x l O S x ( 1 .6 4 x 1 0 _ 6 ) 2 + 1 . 6 4 x 1 0 ~ ( 6 )

E vide n t ly , i t is a s eco nd o rde r equa t ion w i th a genera l fo rm such as : t 1 tP k l -,2 P . .r a te cons tan t o f M OH A, ob ta ined f rom equa t ion (6 ) is : k = 2 .64x105 m in lm ol4m 2 .

T hu s the a dso rp t ion

P r o p e r t ie s o f M O H A C h e l a te d w i t h S u r f a ce C e ( I H )T h e c h e l a t i n g a c t i o n o f M O H A t o C e ( I II ) m a i n l y d e p e n d s o n t h e c h a r a c t e r o f i ts a c t i v e g r o u p s. B a s e d o nthe th eo ry o f e leA:t ronega tivi ty o f r eagen t ac t ive g roups , an a t t em p t has been m ade to f ind the bond ing a tom so f M O H A . I n o u r c o n s i d e ra t i o n s, t h e P a u l i n g s t a n d a rd i z a ti o n o f e l e c t r o n e g a ti v i ty a n d a c a l c u l a t i n g m e t h o dsugges te d by W . 'm g [12] w ere used , and on ly the fi r st a tom C w hich d i r ec t ly connec t s w i th po la r g roup inthe naph tha lene r ing was t aken in to accoun t .

X s = 0 . 3 1 ( n * + l ) + 0 . 5 ( 7 )?.

Xt+lX tn*=(N-P)+E mo ~+xa~-~" oXn+XXn-X~tE 2 m , + S , ( ~ ) a , (8 )w h e r e , X g i s the e lec t ronega t iv i ty o f g roup ; r i s the cova len t r ad ius; n* i s the num ber o f cov a len t e lec t rons ;P i s the num ber o f e lec t rons bonded by ne ighbour a tom s ; X i s the a tom e lec t ronega t iv i ty ; i i s o rd ina lnum ber o f the a tom in g roup ( 0 , 1 , 2 . .. . . i = 0 fo r a tom A , i = 1 fo r a tom B) ; m i i s t h e n u m b e r o f e l e c t r o nc o u p l e s w i t h a s e p a r a t io n d i s t a n c e i f r o m t h e b o n d e d a t o m A ; m o i s t h e n u m b e r o f e l e c t ro n c o u p l e s a t A - Bbond; S i i s t h e n u m b e r o f n o n - b o n d e d e l e c t r o n s w i t h a s e p a r a ti o n d i s ta n c e i f r o m t h e b o n d e d a t o m A ; S oi s th e n u m b e r o f n o n - b o n d e d e l e c t ro n s o f a to m B ; a i i s the coef f i c ien t o f pa r t it ion , aF 2 . 7 in ou r case .T h e ca lcu la ted e lec t ron ega t iv i t i e s o f a tom s N and O a re no ted in the r eagen t s t ruc tu ra l fo rm ula as fo l lows :

H ( 3 . s o )--OH 3 . s 5 )N - - O H ( 3 . 6 9 )

( 4 . 0 3 )I t i s c lea r tha t a tom N in the naph tha lene r ing has a h igher e lec t ron a ff in i ty than a tom O , so a tom O losese l e c t r o n s m o r e e a s i l y t h a n a t o m N . T h e r e f o r e , b a s e d o n t h e t h e o r y o f c o o r d in a t e c h e m i s t ry , t w o a t o m s Oi n t h e h y d r o x a m i c g r o u p o f M O H A m o l e c u l e d o n a t e e l e c tr o n s t o s u r fa c e C e ( II I ), f o r m i n g s t a b le p e n t a g o n -c y c l e c h e l a te :

I

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1404 J. Ren et al.on the bas tnaes i te surface , therefore making the surface hydrophobic.The infrared spectrum shown in Figure 7 have fur ther proved tha t the bonds C-O-Ce and N-O-Ce indeedexis t on the bas tnaes i te surfaces t rea ted with MOHA.

C O N C L U S I O N SM O H A is a selectiv e and efficien t collec tor for bastnaesite flotation d ue to its specific affinity to the surfa ceCe(III ) of bas tnaesi te . The o pt imu m pH value of bastnaes ite f lotat ion with M O H A is in the pH range 8 -9.5.M OH A, ch emical adsorb ed on the bas tnaes i te surfaces through i ts ox ygen a toms to chela te surface Ce(II I )of bas tnaesi te , can form a pentagon -cycle chela te on i t. The chem ical ly adso rbed layer is accomp anied w iththe non-ho mo geneo us and phy sica l ly adsorbed M OH A multi layer. I t is the surface Ce(III ) of bas tnaes i tewh ich dom inates the f lota tion behav ior of bas tnaesi te with M O HA as a collector.

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2.3.

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5.

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7.8.9.10.11.12.

REFERENCES

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