CONTINUOUS FLOW SEPARATION, AN APPLICATION OF SELECTIVE MAGNETOSEDIMENTATION

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CONTINUOUS FLOW SEPARATION, AN APPLICATION OF SELECTIVE

MAGNETOSEDIMENTATION

R. van Kleef, H. Myron, P. Wyder, M. Parker

To cite this version:

R. van Kleef, H. Myron, P. Wyder, M. Parker. CONTINUOUS FLOW SEPARATION, AN APPLI- CATION OF SELECTIVE MAGNETOSEDIMENTATION. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-763-C1-766. �10.1051/jphyscol:19841155�. �jpa-00223628�

J O U R N A L DE PHYSIQUE

Colloque C l , suppl6ment au no I, Tome 45, janvier 1984 page C1-763

CONTINUOUS FLOW SEPARATION, AN APPLICATION OF S E L E C T I V E MAGNETOSEDIMENTATION

R.P.A.R. van K l e e f , H.W. Myron, P . Wyder and M.R. ~ a r k e r *

Research I n s t i t u t e for Materials and High F i d d Magnet Laboratory, University of Nijmegen, 6525 ED Nijmegen, The NetherZands

* ~ e p a r t m e n t of Pure and Applied Physics, University of Salford, SaZford M5 4WT, U . K .

R6sumb - Une technique de s 6 p a r a t i o n P f l u x c o n t i n u (CFS), q u i marche de fason ininterrompue s a n s l ' u s a g e d'une m a t r i c e pour l a f i l t r a t i o n magnbtique, e s t d6- c r i t e i c i . C e t t e technique s e base s u r une magn6tosbdimentation s 6 l e c t i v e . Un systOme P f l u x c o n t i n u P l ' b c h e l l e du l a b o r a t o i r e a S t 6 c o n s t r u i t e t expbrimen- t 6 avec p l u s i e u r s genres de suspension de p a r t i c u l e s dans un l i q u i d e .

A b s t r a c t - A Continuous Flow S e p a r a t i o n (CFS) technique i s i n t r o d u c e d , which o p e r a t e s u n i n t e r r u p t e d l y , without t h e use of a magnetic f i l t e r matrix. CFS i s based on s e l e c t i v e magnetosedimentation, i n a f i e l d g r a d i e n t introduced by t h e processing magnet i t s e l f . A l a b o r a t o r y s c a l e continuous flow system h a s been developed and t e s t e d f o r s e v e r a l t y p e s o f s l u r r i e s . R e s u l t s w i l l be given f o r a v a r i e t y of experimental parameters using a t e s t suspension.

1 - INTRODUCTION - ^Magnetic

t h a t a ferromagnetic bodv.

-

c e r t a i n f i e l d g r a d i e n t s , whi

s e p a r a t i o n techniques such a s HGMS a r e based on t h e f a c t placed i n an e x t e r n a l l y a p p l i e d magnetic f i e l d g e n e r a t e s ch tend t o a t t r a c t magnetic p a r t i c l e s towards t h e sur- f a c e . S i n c e l o a d i n g of t h e m a t r i x reduces t h e c a p t u r e e f f i c i e n c y , t h e magnetic f i e l d h a s t o be switched o f f p e r i o d i c a l l y i n o r d e r t o r e g e n e r a t e t h e m a t r i x and t o c o l l e c t t h e magnetic f r a c t i o n . This not only reduces t h e p r o c e s s r a t e c o n s i d e r a b l y , b u t a l s o d i s c o u r a g e s t h e a p p l i c a t i o n of superconducting magnet systems. These problems a r e overcome by a c l a s s of m a t r i x l e s s s e p a r a t o r s i n which t h e magnetic f o r c e i s generated by t h e e x t e r n a l f i e l d only. However, t h e a p p l i c a b i l i t y of much of t h e s e d e v i c e s i s d i r e c t e d towards d r y s e p a r a t i o n of g r a v i t y - f e d p a r t i c l e s .

I n t h i s paper we p r e s e n t a magnetic s e p a r a t i o n d e v i c e , capable o f handling s l u r - r i e s and o p e r a t i n g i n a t r u l y continuous mode. The s e p a r a t i o n e f f i c i e n c y i s demon- s t r a t e d under v a r i o u s o p e r a t i n g c o n d i t i o n s .

2 - OPERATING PRINCIPLES - I t i s w e l l known t h a t f l o c c u l a t i o n of p a r t i c l e s r e s u l t s i n an i n c r e a s e i n s e t t l i n g v e l o c i t y , because i n most c a s e s t h e mass of t h e c l u s t e r i s i n c r e a s i n g more r a p i d l y than i t s hydrodynamic diameter. Hencl and Svoboda [ I ] have shown t h a t magnetic - f l o c c u l a t i o n can be used t o s e p a r a t e magnetic p a r t i c l e s from non-magnetic ones. The enhanced s e t t l i n g r a t e of t h e f l o c c u l a t e d magnetic p a r t i c l e s e n a b l e s them t o s e t t l e by g r a v i t y i n a f l u i d stream d i r e c t e d upwards, while t h e non- f l o c c u l a t e d , non-magnetic p a r t i c l e s a r e c a r r i e d away by t h e f l u i d . Unfortunately, f o r paramagnetic p a r t i c l e s i n a homogeneous magnetic f i e l d , t h e f l o c c u l a t i o n causes only a very l i m i t e d enhancement i n s e t t l i n g r a t e and t h e r e f o r e t h e s e p a r a t i o n process i s very s e n s i t i v e t o changes i n s l u r r y c h a r a c t e r i s t i c s . I n a d d i t i o n , t h e t h r e s h o l d f i e l d f o r f l o c c u l a t i o n i s i n v e r s e l y dependent upon p a r t i c l e s i z e and s u s c e p t i b i l i t y , which means t h a t t h e maximum f i e l d a v a i l a b l e determines a lower l i m i t f o r both quan- t i t i e s .

Previous experiments [ 2 , 3 ] have demonstrated t h a t p a r t i c l e s with i n t e r m e d i a t e sus- c e p t i b i l i t i e s and even diamagnetic p a r t i c l e s can be f l o c c u l a t e d i n high magnetic f i e l d s , b u t moreover i t h a s become c l e a r t h a t a s u i t a b l e g r a d i e n t i n t h e f i e l d , t o - Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841155

Cl-764 JOURNAL DE PHYSIQUE

g e t h e r with f l o c c u l a t i o n r e s u l t s i n a d r a s t i c i n c r e a s e i n s e t t l i n g v e l o c i t y . T h i s p r o c e s s o f magnetosedimentation can be d e s c r i b e d by a force-balance e q u a t i o n of t h e form

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

x t h e e f f e c t i v e s u s c e p t i b i l i t y of t h e p a r t i c l e , B t h e e x t e r n a l magnetic f i e l d , q t h e v i s c o s i t y of t h e f l u i d and v t h e s e t t l i n g v e l o c i t y . Magnetic f l o c c u l a t i o n , i . e . t h e formation of b i n a r y c l u s t e r g mainly a f f e c t s t h e volume-terms i n t h e L.H.S. of equa- t i o n ( I ) , l e a d i n g t o a n i n c r e a s e i n t h e p r o p o r t i o n a l i t y c o n s t a n t between s e t t l i n g v e l o c i t y and magnetic f o r c e d e n s i t y .

These c h a r a c t e r i s t i c s form t h e b a s i s of t h e Con- t i n u o u s Flow S e p a r a t i o n d e v i c e a s presented i n t h i s paper. A schematic p i c t u r e i s g i v e n i n Fig. 1 . I n p r i n c i p l e , t h e system i s s i m i l a r t o I t h e one d e s c r i b e d i n r e f e r e n c e [ I ] , but i n o r d e r

Fig.1 - Schematic p i c t u r e of t h e Continuous Flow S e p a r a t i o n de- v i c e . D e t a i l s a r e explained i n

t o improve i t s f u n c t i o n i n g i t ^now i s placed i n a high and inhomogeneous f i e l d of a B i t t e r magnet (1). The s e p a r a t i o n tube (2) i s p o s i t i o n e d i n t h e bore of t h e magnet i n such a way t h a t i t i s completely above t h e p o i n t o f maximum f i e l d . S l u r r y i s fed i n t o t h e s e p a r a t i o n tube through a feed p i p e ( 3 ) . This pipe i s p e r f o r a t e d a t t h e lower end i n o r d e r t o make t h e s l u r r y e n t e r t h e tube i n a r a d i a l d i r e c t i o n . The p a r t i c l e s ex- p e r i e n c e a magnetic f o r c e p r o p o r t i o n a l t o BVB, which p u l l s t h e f e r r o - and paramagnetic p a r t i - c l e s downwards i n t h e d i r e c t i o n o f o u t l e t ( 4 ) . The magnetic f o r c e a c t i n g on diamagnetic p a r t i - c l e s i s small b u t , anyhow, d i r e c t e d upwards and so t h e y a r e c a r r i e d away with t h e f l u i d stream and l e a v e t h e d e v i c e v i a an o ~ e r f l o w ( 5 ) . .- . Maa-

-

t h e t e x t . n e t i c f l o c c u l a t i o n f u r t h e r improves t h e s e p a r a - t i o n e f f i c i e n c y .

The s e p a r a t i o n p r o c e s s can be d e s c r i b e d by e q u a t i o n ( I ) , where v h a s t o be r e - placed by t h e v e l o c i t y v of t h e p a r t i c l e with r e s p e c t t o t h e & n o u n d i n g f l u i d . A f t e r d e f i n i n g pM = xBVB / 1.1 g and a = 2g / 9q, e q u a t i o n ( 1 ) can be r e w r i t t e n a s

A p a r t i c l e with r a d i u s a , d e n s i t y p and magnetic d e n s i t y p w i l l be c o l l e c t e d i n t h e magnetic f r a c t i o n i f i t s v e l o c i t y according t o equation

(9)

3 - EXPERIMENT - Our l a b o r a t o r y - s c a l e s e p a r a t i o n device was completely made o f non- magnetic m a t e r i a l , with a 40 mm ( i n n e r ) diameter s e p a r a t i o n tube and a 10 mm ( o u t e r ) diameter feed pipe. The o u t l e t of t h e feed p i p e was p o s i t i o n e d 100 mm above t h e mid- p o i n t of t h e 60 mm diameter bore of t h e B i t t e r magnet, a t a p l a c e where t h e magnetic f o r c e d e n s i t y i s l a r g e . S l u r r y v e l o c i t y was c o n t r o l l e d by a p e r i s t a l t i c pump i n com- b i n a t i o n with a v a l v e on o u t l e t ( 5 ) , which a l s o served t o p r e s s u r i z e t h e system. I n o r d e r t o c o l l e c t t h e magnetic f r a c t i o n i t h a s t o be removed from t h e e n e r g e t i c a l l y f a v o u r a b l e p o i n t a t t h e c e n t r e of t h e magnet. I t t h e r e f o r e i s n e c e s s a r y t o c r e a t e a hydrodynamic f o r c e which i s l a r g e r t h a n t h e competing magnetic f o r c e . T h i s was done by u s i n g an o u t l e t ( 4 ) with a s m a l l i n n e r diameter - high f l u i d v e l o c i t y - , c u t o f f by a magnetic v a l v e a t a p l a c e o u t s i d e t h e magnet. T h i s v a l v e was opened p e r i o d i c a l - l y , where t h e open-period was such a s t o allow a s m a l l q u a n t i t y o f magnetic m a t e r i a l t o l e a v e t h e magnet without d i s t u r b i n g t h e flow i n t h e r e s t of t h e system. The hy- drodynamic p r e s s u r e ensured a high enough flow through t h e o u t l e t t o avoid blocking

a t high f i e l d s .

Systematic experiments t o i n v e s t i g a t e t h e performance of t h e s e p a r a t i o n d e v i c e were c a r r i e d o u t u s i n g mixtures o f paramagnetic MnC03 and diamagnetic SiO a3 t e s t suspensions. 5The volume s u s c e p t i b i l i t i e s of t h e s e compounds a r e xV ^{= 4.3-70- and} xV ^{= -1.6010-} (SI-units) r e s p e c t i v e l y . A l l p a r t i c u l a t e m a t e r i a l used i n t h e experi- ments was pre-sieved t o a s i z e s m a l l e r t h a n 38 pm and suspended i n tapwater, without pH-adjustment o r a d d i t i o n of d i s p e r s a n t s . The s l u r r i e s were u l t r a s o n i c a l l y shaken b e f o r e being fed i n t o t h e s e p a r a t i o n device.

F i g . 2 shows t h e grade ( c o n c e n t r a t i o n o f MnCO ) of t h e Grade s e p a r a t i o n products a s a f u n c t i o n of magnetic ? i e l d f o r a 2.0 %-vol s l u r r y c o n t a i n i n g 47 % MnC_T The f l u i d v e l o c i t y i n t h e s e p a r a t i o n tube was 16 mms

?'

s t a g e non-magnetic p a r t i c l e s can be c o l l e c t e d i n t h e mags, e i t h e r because t h e y a r e swept downwards a l o n g with t h e magnetic ones o r trapped i n t h e f l o c s . On t h e o t h e r hand, t h e recovery of magnetic ma-

- t e r i a l i n t h e mags, a s d e p i c t e d i n

Fig. 3 , keeps r i s i n g u n t i l a t a

0.2 - f i e l d of about 6 T a l i m i t of 0.93

i s reached. I n c o n t r a s t t o t h e mags, t h e overflow product i n F i g 2

0 ^{1 1 1 1} shows no s i g n of s a t u r a t i o n .

0 2 4 6 8 0 2 4 6 8 Fig. 4 shows t h e grade of t h e

B ( T I B ( T ) s e p a r a t i o n products a s a f u n c t i o n of f l u i d v e l o c i t y i n t h e s e p a r a t i o n Fig.2 - Grade of t h e ~ i ~ . 3 - R~~~~~~~ of tube a t an a p p l i e d magnetic f i e l d s e p a r a t i o n products magnetic material in of 6 T. The s l u r r y c o n s i s t e d of a a s a f u n c t i o n of t h e t h e mags vs. f i e l d 1.5 %-'01 suspension of MnCOj and magnetic f i e l d . f o r t h e same exper.- ^SiO c o n t a i n i n g 17 % ^MnC03. A s 0 : Mags; ment a s i n Fig.2. c o u h be expected, t h e grade of t h e

0 : Overflow product overflow i n c r e a s e s with i n c r e a s i n g

f l u i d v e l o c i t y because, s t a r t i n g with t h e s m a l l e s t p a r t i c l e s , t h e m a g n e t i c a l l y induced p a r t of t h e s e t t l i n g v e i o c i t y i s n o t s u f f i c i e n t t o prevent them from being c a r r i e d away by t h e f l u i d . On t h e o t h e r hand, s i n c e g r a v i t a t i o n a l s e t t l i n g _- i s l e s s f o r h i g h e r f l u i d v e l o c i t i e s , t h e amount o f nonlmagnetics i n t h e mags w i l l d e c r e a s e , . r e s u l t i n g i n a n i n c r e a s e i n grade. I t i s obvious t h a t a h i g h e r f l u i d v e l o c i t y l e a d s t o a worse recovery o f magnetic m a t e r i a l i n t h e mags, a s i s confirmed by Fig. 5.

y-

t

-1

4 - DISCUSSION

-

Recovery I

Fig.4 - Grade of t h e s e p a r a t i o n products a s a f u n c t i o n of f l u i d v e l o c i t y . 0 : mags; 0 : Overflow.

Fig.5 - Recovery of mag- n e t i c m a t e r i a l i n t h e mags vs. f l u i d v e l o c i t y f o r t h e same experiment a s Fig.4

velocity (cmls) velocity (cmls)

C1-766 JOURNAL DE PHYSIQUE

" &

Fig.6 - Grade of B ( T ) p r e s e n t e d i n t h i s paper i s t h e

s e p a r a t i o n p r o d u c t s shape o f t h e magnetic f i e l d pro-

v s . f i e l d , w i t h t h e f i l e . I n t h e B i t t e r magnet used s e p a r a t o r p o s i t i o n e d Fig.7 - Recovery of d u r i n g t h e experiment, we measured u p s i d e down i n t h e magnetic materal in a magne IC f o ce d e n s i t y of about lower h a l f o f t h e t h e mags f o r t h e same 2.0 10" Nm-' a t t h e o u t l e t of t h e magnet. @ : Mags; experiment a s i n ~ i ~ . 6 . feed p i p e f o r a f i e l d of 7 T. A

0 : Overflow p r o d u c t . propably more f a v o u a b l e f i e l d pro-

f i l e w i l l b e one w i t h a n isodynamic f i e l d a t t h e p l a c e s where t h e s e p a r a t i o n a c t u a l l y o c c u r s , i . e . t h e r e g i o n of s p a c e d i r e c t l y above t h e o u t l e t of t h e f e e d p i p e . The f i e l d a t o t h e r p l a c e s may have d i f - f e r e n t c h a r a c t e r i s t i c s a s l o n g a s t h e magnetic f o r c e p o i n t s i n t h e r i g h t d i r e c t i o n .

S i n c e t h e s e p a r a t o r , a s can be s e e n i n F i g . 1 , i s o n l y p o s i t i o n e d i n t h e upper h a l f o f t h e magnet, a l a r g e f i e l d r e g i o n s t a y s unused. I n o r d e r t o examine t h e pos- s i b i l i t y o f a l s o t a k i n g advantage o f t h i s p a r t o f t h e f i e l d we p l a c e d t h e whole s e p a r a t i o n d e v i c e u p s i d e down i n t h e lower p a r t of t h e B i t t e r magnet. Fig. 6 and 7 show t h e r e s u l t s o f s e p a r a t i o n r u n s with t h e d e v i c e i n t h i s p o s i t i o n . The experiment was i d e n t i c a l t o t h e one of Fig. 2 and 3 , w i t h o n l y t h e g r a v i t a t i o n a l f o r c e r o t a t e d o v e r 180'. I n o t h e r words, t h e d e n s i t y p i n e q u a t i o n ( 2 ) h a s changed s i g n . C l e a r l y , t h e s e p a r a t i o n performances a r e s i m i l a r , which, i n f a c t , can be expected i n c a s e s when t h e g r a v i t a t i o n a l f o r c e s a r e s m a l l compared with t h e magnetic ones.

One t h e r e f o r e may conclude t h a t a s o l e n o i d - t y p e magnet, h a v i n g a s u i t a b l e f i e l d p r o f i l e , c a n c o n t a i n , above and below i t s m i d p o i n t , l i k e m i r r o r images, two CFS- d e v i c e s s i m i l a r t o t h e one drawn i n Fig. 1 . T h i s sytem w i l l t h e n be a b l e t o o p e r a t e w i t h t h e same e f f i c i e n c y and a t r o u g h l y t h e same c o s t s , b u t w i t h a s l u r r y throughput t w i c e a s l a r g e .

S e p a r a t i o n e f f i c i e n c i e s f o r h i g h e r s l u r r y d e n s i t i e s and f o r s l u r r i e s with l e s s pronounced composition a r e b e i n g i n v e s t i g a t e d a t p r e s e n t i n t h i s l a b o r a t o r y .

Grade

Acknowledgement

-

magnetic ones. The i n f l u e n c e o f t h e magnetic f i e l d i s two- f o l d . F i r s t , s u i t a b l e f i e l d g r a d i e n t s produce a magnetic f o r c e which w i l l enhance t h e s e t t l i n g v e l o c i t y and second, s e l e c t i v e magnetic f l o c c u l a t i o n e n l a r g e s t h e a p p a r e n t par- t i c l e s i z e and t h e r e f o r e t h e i n f l u e n c e o f t h e f i e l d g r a - d i e n t s . Furthermore, we have shown t h a t t h e s e p a r a t i o n

References

J., 1 3 t h I n t . Mineral P r o c e s s i n g Congress, Warsaw (1 979) 209.

KLEEF R.P.A.R., MYRON H.W. and WYDER P., J. Magn. Magn. Mater.

27 (1982) 250. . - . -

[ 3 ] E n KLEEF R.P.A.R., MYRON H.W., WYDER P. and PARKER M.R., J. Appl. Phys. 54

(1983) 4223.

1 1

~ K r ~ ~ ~ ~ ~

i t p o s s i b l e t o s c a l e up t h e s e p a r a - t o r and m a i n t a i n o p e r a t i n g c o s t s a t a r e a s o n a b l e l e v e l .

A f l u i d v e l o c i t y of 16 mms-' a s used i n o u r experiments c o r r e s p o n d s tfj a s l u r r y rou.zhuut o f 57.4 m /hour p e r

L9

0.4

0.2

0 2 4 6 8 c l i n e i n s e p a r a t i o n e f f i c i e n c y .

B(T) 0 C e r t a i n l y t h e most i m p o r t a n t a s -

0 2 4 6 8 p e c t o f t h e t v ~ e o f s e v a r a t i o n -

- -

-

0 - " ' I