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    International Journal of Mineral Processing, 5 ( 1 9 7 8 ) 1 8 3 - - 1 9 7 1 8 3 E l s ev i e r S c i e n t i f ic P u b l i s h i n g C o m p a n y, A m s t e r d a m - - P r i n t e d i n T h e N e t h e r l a n d s

    F L U I D I Z E D - B E D T H E R M A L T R E A T M E N T O F P H O S P H A T E R O C K :E F F E C T O F O P E R A T I N G VA R I A B L E S

    M . A . D O H E I M , M . M . TA R S H A N a n d M .M . E L - G E N D Y

    Mining and Metallurgical Engineering Department, Faculty of Engineering, Assiut Uni-versity, Assiut (Egypt)

    ( R e c e i v e d J u n e 9 , 1 9 7 7 ; re v i s ed a n d a c c e p t e d D e c e m b e r 3 0 , 1 9 7 7 )

    ABSTRACT

    D o h e i m , M . A . , Ta r s h a n , M . M . a n d E 1 - G e n d y, M . M . , 1 9 7 8 . F l u i d i z e d - b e d t h e r m a l t r e a t -m e n t o f p h o s p h a t e r o c k : e f f e c t o f o p e r a t i n g v a r i a b le s . In t . J. M i ne r. P r o ce s s ., 5 : 1 8 3 - - - 1 9 ' 7

    T h e p r e s e n c e o f h u ge a m o u n t s o f l ow - a n d i n t e rm e d i a t e - g r a d e p h o s p h a t e o r e a n d t h en e e d f o r h i g h - g ra d e o r e f o r i n d u s t r y, n e c e s s i t a t e s th e a v a i l a b il i ty o f e c o n o m i c a n d e f fi -c i e n t u p g r a d i n g t e c h n i q u e s . T h e f l u i d i z e d - b e d t e c h n i q u e i s m o s t s u i t a b l e f o r u p g r a d i n g ,b y t h e r m a l t r e a t m e n t , o f o r e s h a v in g h ig h p e r c e n t a g e s o f o r g a n ic m a t t e r , c a r b o n a t e s ,a n d m o i s t u r e . I n t h i s w o r k , s t u d ie s w e r e c a r r ie d o u t o n t h e p r o c e s s o f t h e r m a l u p g r a d i n go f p h o s p h a t e r o c k i n a f l u i d i z e d - b e d fu r n a c e o f 1 0 - c m d i a m e t e r. T h e s t u d i e s in v o l ve th ee f f e c t o f t h e i m p o r t a n t o p e r a t i n g v a r ia b l e s s u ch a s p ro c e s s t e m p e r a t u r e , a i r - f l o w r a t e ,c a l c i n e q u e n c h i n g t e m p e r a t u r e , a n d t h e a t t r i t i o n o f p h o s p h a t e p a r t i c l e s. A r u n - o f - m i n ei n t e r m e d i a t e - g r a d e p h o s p h a t e o r e w a s u s e d . B a t c h a n d c o n t i n u o u s r u n s w e r e c a r r i e d o u ta n d t h e o r e w a s c a lc i n e d a n d w a s h e d .

    I t w a s f o u n d t h a t t h e i n c r e a s e i n p r o c e s s t e m p e r a t u r e f a v o u r a b l y a f f e c t s t h e % u p -g r a d in g o f t h e o r e , b u t t h i s s h o u l d b e s t u d i e d i n c lo s e c o n n e c t i o n w i t h t h e e c o n o m i ca s p e c ts , e s p e c i a l ly i n t h e c a se o f o r e s w i th l o w c a r b o n a c e o u s m a t t e r c o n t e n t s . T h e f l u id -i z in g a i r - fl o w r a t e , a n d t h u s , t h e h y d r o d y n a m i c c o n d i t i o n o f t h e b e d , s l i g h t ly a ff e c t s t h eu p g r a d i n g p r o c e s s. T h e u s e o f h i g h a ir - f lo w r a t e s in c r e a s es t h e e x t e n t o f a t t r i t i o n o f p h o s -p h a t e p a r t i c le s . T h e q u e n c h i n g t e m p e r a t u r e o f t h e c a l c in e w a s f o u n d t o h a v e n o e f f e c t o nt h e p r o c e s s p r o d u c t , w i t h i n t h e r a n g e i n v e s t i g a te d .

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

    T h e w i d e u s e o f p h o s p h o r o u s a n d p h o s p h a t i c c o m p o u n d s ( A n o n y m o u s ,1 9 7 4 ; B a s t a a n d K a m m a r , 1 9 7 4 ) a s f e r t i l i z e r s , a n d i n c h e m i c a l , m e t a l l u r g i c a la n d o t h e r i n d u s t r i e s , n e c e s s i t a t e s t h e a v a i l a b i l i t y o f h i g h - g r a d e p h o s p h a t e o r ef o r p r o c e s s i n g . P r o d u c t i o n o f P i n a n e l e c t r i c a l f l u i d i z e d - b e d f u r n a c e h a s b e e nr e p o r t e d ( D o r n , 1 9 7 3 ) , w i t h t h e r e a c t i o n o c c u r r i n g b e t w e e n p h o s p h a t e o r e ,c o k e , a n d q u a r t i z i t e . T h e p y r o m e t a l l u r g i c a l t h e r m a l - t r e a t m e n t p r o c e s s e s o f

    o r e s a n d m i n e r a l s a r e v e r y e f f e c t i v e in u p g r a d i n g a n d b e n e f i c i a t i n g t h e o r e so r c o n v e r t i n g t h e m t o c o m p o u n d s f r o m w h i c h t h e m e t a l c a n b e e a s i l y e x -t r a c t e d . A m o n g t h e s e p r o c e s s e s , r o a s t i n g a n d c a l c i n i n g a r e t h e m o s t i m p o r -t a n t . R o a s t i n g i s u s u a l l y c a r r i e d o u t a t a t e m p e r a t u r e b e l o w t h a t o f c a l c i n a t i o n

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    a n d i t in v o lv e s t h e r e m o v a l o f p h y s i c a l ly a n d c h e m i c a l l y b o u n d w a t e r , o r g a n i cm a t t e r , a n d e a s il y v o l a t i li z e d s u b s t a n c e s . T h e c a l c i n i n g p r o c e s s is u s u a l l yc a r ri e d o u t a t a h i g h er te m p e r a t u r e s o th a t t h e c a r b o n a t e s i n th e p h o s p h a t ea r e d e c o m p o s e d . T h e p h o s p h a t e a f t e r r o a s ti n g is m o r e l ia b le t o f l o t a t i o n ,w h e r e a s a f t e r c a lc i n a ti o n , w i t h f o r m a t i o n o f C a a n d M g o x i d e s , t h e p H o ft h e p u l p w o u l d b e t o o h i g h f o r fl o t a t io n . P o o r p h o s p h a t e r o c k , h a v i n g h i g hp e r c e n t a g e s o f c a r b o n a c e o u s m a t e r i a ls ( o r g a n i c c a r b o n ) , c a l c a r e o u s m a t e r ia l s( c a lc i te , d o l o m i t e ) , a n d m o i s t u r e , is b e s t t h e r m a l l y t r e a t e d i n f lu i d i z e d - b e df u r n a c e s . T h is t r e a t m e n t , a t t h e c a l c i n a t i o n t e m p e r a t u r e , is s u f f i c i e n t f o rh i g h l y u p g r a d i n g t h e o r e , e s p e c i a l ly lo w - s i li c a o r e s. F l u i d i z e d - b e d c a l c i n i n g isa ls o u s e d t o d e f l u o r i n a t e p h o s p h a t e r o c k a t a t e m p e r a t u r e o f a b o u t 1 3 0 0 Ct o m a k e i t s u i t a b l e f o r a n i m a l f e e d .

    T h e p r e s e n t w o r k i s c o n c e r n e d w i t h t h e t h e r m a l t r e a t m e n t o f a n in t e r m e d i -a t e - g ra d e p h o s p h a t e o r e in a f l u i d iz e d - b e d f u r n a c e . T h e i n t e r m e d i a t e - g r a d eo r e is i n t e n d e d t o b e p r o c e s se d a t i n t e r m e d i a t e c o n d i t i o n s s o t h a t t h e d a t ao b t a i n e d c a n b e m o r e r e p r e s e n t a ti v e . T h e s t u d y i n vo lv e s t h e e f f e c t o f t h ei m p o r t a n t o p e r a t i n g v a r ia b le s s u c h a s p r o c e s s t e m p e r a t u r e , a i r - fl o w ra t e , a n dt h e c a l c i n e q u e n c h i n g t e m p e r a t u r e o n t h e p r o c e s s . T h e e f f e c t o f a i r- f lo wr a t e o n t h e p h o s p h a t e a t t r it i o n w a s a ls o st u d i e d . B a t c h a n d c o n t i n u o u s r u n sw e r e c a r r i e d o u t .

    PREVIOUS WORK

    T h e b e n e f i c ia t i o n o f p h o s p h a t e r o c k c a n b e a c c o m p l i s h e d b y s i m p l e p r o-c e ss e s a s w e l l a s b y c o m p l i c a t e d o n e s , d e p e n d i n g o n t h e o r e a n d t h e e x t e n to f u p g r a d i n g r e q u i r e d . T h e s i m p l e s t a n d l o w e s t - c o s t m e t h o d s i n v o l v e g r i n d i n ga n d s iz in g , w h i c h a r e m o r e s u i t a b l e f o r c l a y e y o re s . C r u s h i n g , s c r e e n i n g , a n dw a s h in g m a y b e i n v o lv e d ( A n o n y m o u s , 1 9 7 0 ). M o r e c o m p l i c a t e d f lo ws h e e ts i n c l u d i n g c r u s h in g , f l o t a t i o n , a n d r o a s t in g p l a n t s h a v e b e e n r e p o r t e d( A n o n y m o u s , 1 9 6 0 ) . T h e f l o t a t i o n p l a n t i n c l u d e s w a s h i n g , d e s li m i n g , g r in d i n g ,c o n d i t i o n i n g , f l o t a t i o n , f i l tr a t io n , a n d d r y i n g . F l o t a t i o n is t h e u s u a l p r a c t i c ef o r p h o s p h a t e w i t h h i g h si li ca c o n t e n t s . M a n y i n v e s ti g a ti o n s ( To w n e t a l.,1 9 6 7 ; O r p h y e t a l . , 1 9 6 8 a , b ; B i b a w y, 1 9 6 9 ; H a n n a , 1 9 6 9 ) h a v e b e e n c a r r i e do u t t o s t u d y t h e d i f f e r e n t f a c to r s i n v o lv e d in t h e f l o t a t i o n p r o c e s s . T h e f lo -t a t i o n t e c h n i q u e h a s t h e a d v a n t a g e o f b e in g a p p li e d to t h e b u l k m a t e r i a lw i t h o u t t h e n e c e s s i t y o f p r i o r s c re e n i n g .

    T h e t h e r m a l t r e a t m e n t o f p h o s p h a t e o r e s m a y in v o lv e o n e o r all o f t h ef o l lo w i n g p r o c e ss e s: d r y i n g , ro a s ti n g , a n d c a l c in a t io n . U p g r a d e d p h o s p h a t em a y b e p r o d u c e d ( A n o n y m o u s , 1 9 6 7 ) w i th j u s t sc r e en i n g a n d d r y i n g to g iv e7 5 % T C P, w h i l e a 7 8. 5% g r a d e o r e m a y b e p r o d u c e d f r o m t h e m o i s t - s c r e e n e dp h o s p h a t e b y c a l c i n a t i o n a t 9 5 0 C . T h e c a l c in i n g is c a r r i e d o u t i n r o t a ti n gk il ns f ir e d b y f u e l o il. A h ig h - g r a d e p h o s p h a t e ( 8 0 - - 8 2 % ) m a y b e p r o d u c e db y m o r e c o m p l i c a t e d p r o c e ss e s. B e n e f i c i a t i o n s t u d ie s ( R a m b a b u e t al., 1 9 7 3 )o n l o w - g r a d e ( 1 6 .4 % P 2O s) c al c it e -b e a r i n g p h o s p h a t e r o c k h a v e b e e n r e p o r t e du s in g c a l c in a t i o n a t a t e m p e r a t u r e o f 9 60 C . T h e c a r b o n a c e o u s m a t e r ia l s i n

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    the phosphatic beds, which may amount to 3.5%, interfere with the produc-tion of triple superphosphate and they are now successfully removed by

    roasting in fluidized beds at temperatures below 760C (Priestly, 1967). A5-m diameter thr ee-compartment Fluosolids reactor is used. This percentageof carbonaceous material furnishes most of the fuel required for the process.

    Batch and continuous-circuit beneficiation of western phosphate ore hasbeen reported (Town et al., 1967). Two flow sheets were developed; thefirst involved roasting, attrition scrubbing, sizing to remove a concentrate,grinding of the oversize, desliming, and flotation; in the other flow sheetthe roasting step was eliminated. Roasting was carried out in fluidized beds.Fluidized-bed roasting o f phosphate rock at 700 C to obtain A1 and Fe phos-phate has been reported (Anonymous, 1966). Calcining of phosphate ores

    in a fluidized bed at higher temperatures than 760C converts the carbonatesto oxides which can be leached out in a washing process (Priestly, 1967).Studies on the upgrading of the ca rbonaceous Nile Valley phosphate by cal-cination of the calcitic samples have been reported by Orphy et al. (1969}.At the Eleventh International Mineral Processing Congress (Semi nar ... , 1975)several authors tackled the beneficiation problems of calcareous phosphat eores using flotation, leaching, and calcination. No concern was given to thefluidized phosphate particle attrition and its consequent effect on bed behav-iour and process performance.

    The present study provides data on the important operating variables ofthe thermal treatment process for upgrading the phosphate rock, particular-ly on the attrition behaviour of the fluidized phosphate particles. Thesedata should be useful and essential in designing and operating larger-scaleunits.

    E X P E R I M E N T A L

    Materials

    A run-of-mine SIBAIYA phosph ate rock was used. A detailed mineralogicalstudy may be foun d elsewhere (Phillobos, 1969). A limited mineralogicalstudy through microscopical examination indicated that the phosphoritesconsisted mainly of phosphatic material and of carbonates, together withminor proporti ons of detritic quartz. These are embedded in a scanty chemi-cal cement consisting mainly of collophane and subordina te calcite, to-gether with minor chalcedony. The bone apatite contains parallel streaks andfine points of organic matter. Some of the carbonates include minut e granulesof iron oxide. The chemical compos ition of the ore is shown in Table I, andthe loss on ignition amounted to about 19%. The ore, containing about 20%

    P2Os, is considered to be of an intermediate grade. The minimum fluidizationv e l o c i t i e s , U m f , for the different sizes of phosphate rock were determinedby pressure-drop--fl ow rate measurements. These velocities were determinedat room temperature. Most of the work was carried out on a run-of-mine

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    TABLE I

    Chemical analysis of phosphate rock

    Component Weight%

    CasP20 s 45.93Carbonates 30.34Insolubles 11.24Oxides 2.29Chlorides 0.70Sulphates 1.96Moisture 1.83

    TABLE II

    Umf values for phosphate rock at room temperature

    Size (mesh) --4 --6 -- 8 --10 --14Umf (cm/sec) 14.6 12.2 9.7 7.3 6.3

    --8 mesh p hos pha te ore and t he Umf values are given in Table iI. The Vmfvalues at higher temperat ures were obta ined from the values at roo m tem-peratures t hrough the use of a factor a ccount ing for the change in air vis-cos ity (Singh et al., 1973). Air was used as the f luidi zing gas.

    Apparatus

    An arran gement involving a perspex c olu mn was used to determ ine themin imum fluid ization velocities at room temperature. A sketch o f the ther-ma lt re at me nt apparatus is shown in Fig.1. It consists mainly of a fluidized-bed steel furnace o f 10-cm diamet er and 100-cm height. The fluidized-bedcolumn is terminated with an expanded section with double its diameter,to inhibi t the en trai nme nt of solids and the elutriation of fine materials. Thefluidized phosp hate bed was heated electrically throug h the use of a 1.25-mm Kanthal wire. Variac transformers were used to regulate the t empera turewhich was measured by Chromel/A lumel thermoco uples. On t he average,temperature adjustments within + 5--10C were obtained. The furnace wasprovided with facilities for carrying ou t t he c onti nuou s runs. A belt orefeeder was used for feeding the ph osph ate rock and the discharge was con-trolled throu gh a gate on the discharge opening.

    Procedure

    The work rep orted in this paper involves batch and cont inu ous runs. Inbatch runs a weighed charge of abo ut 1 kg was droppe d slowly into the fur-

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    solids flow rate. Af ter reaching steady-state conditi ons, th e calcined ore wasquench ed in water at high te mperature , and samples were taken for deter-

    mining the P2Os co nt en t of the initial, calcined , and washed ores.A volumetric method (Vogel, 1961; E1-Shahat, 1964) was used for thedeterm inatio n of the P205 con ten t of the phosphate ore samples.

    RESULTS AND DISCUSSION

    The reported investigation includes studies on the fluidized-bed roastingand calcining of run-of-mine phosphate rock. The studies mainly involve theeffect of the im port ant operat ing variables on the the rmal-tre atment process.The attrition of phosphate particles was also observed. Certain design con-

    siderations will be discussed later in the paper.

    Effect of temperature

    In studying the effect of temperature, a --8 mesh ore was used with a bedweight of about 1 kg giving an H/D ratio of about 2.0 for the static bed (H=height of bed, D = diameter of bed}. The durat ion of the thermal t r eatm entwas about 15 minutes at the different tempera tures of 500, 600, 700, 800and 900C. The runs at 500, 600, and 700C may be considered as roastingand those at 800 and 900C as mainly calcining. The results are given in

    TABLE III

    Thermal trea tment of phosphate rock at d i f f e r e n t t e m p e r a t u r e s

    Temperature Umf Vf 1 Assay p e r c e n t( C) (cm/sec) (i/rain.)

    P 2 0 s c o r r e s p o n d i n g

    T.C.P.

    500 5.0 30 20.10 *~ 43.87

    24.88 *~ 54.3125.34 *4 55.32

    600 4.6 40 19.93 43.5125.34 55.3226.65 58.17

    700 4.3 42 19.90 43.4425.88 56.5127.39 59.79

    800 4.0 45 19.90 43.4426.65 58.1729.05 63.41

    900 3.8 47 20.01 43.8'727.45 59.9228.19 61.54

    , l V f = f l u i d i z i n g - g a s - f l o w ~ " "a t e ; , 2 l ~ lt l a l o r e ; * ~ c a l c i n e d o r e ; , 4 c a l c in e d a n d w a s h e d o r e .

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    1 9 0

    Effect of fluidizing-gas-flow rate

    T h e - - 8 m e s h p h o s p h a t e r o c k w a s c a l c i n e d a t d i f f e r e n t f l o w r a te s c o rr e -s p o n d i n g t o Uf/Umf v a l u e s o f 1 , 2 , 4 , 6 , a n d 8 , ( U f = f l u i d iz i n g - g a s v e l o c i t y )a t a p r o c e s s t e m p e r a t u r e o f a b o u t 8 0 0 C a n dH/D o f a b o u t 2 . T h e r e s u l t sa r e g iv e n i n Ta b l e I V. I t c a n b e n o t i c e d t h a t t h e P : O s c o n t e n t o f th e p h o s -p h a t e i n c r e a s e d f r o m 2 0 t o a b o u t 3 0 % , in s o m e ru n s , b y t h e r m a l t r e a t m e n ta n d w a s h i n g . A m e t a l l u r ig c a l b a l a n c e o f s o m e r u n s a t d i f f e r e n t f l o w r a te s isg iv e n i n Ta b l e V I I . T h e d a t a i n t h e t a b l e i n d i c a te s t h a t t h e P 2 O s c o n t e n t o ft h e e l u t r i a t e d f i n es i s m u c h l e ss t h a n t h e i n i ti a l p h o s p h a t e , i n d i c a t i n g t h a te l u t r ia t i o n o f fi n e s c o n t r i b u t e s t o t h e u p g r a d i n g p r o c e s s . T h e e f f e c t o f f l o wr a te c a n b e s t b e s h o w n b y p l o t t in g A P 2 O s a g a in s tUf/Umf a s given in F ig .3 .I t ca n b e s e e n t h a t t h e r e i s o n l y a sl ig h t i m p r o v e m e n t i n t h e P 2 O s c o n t e n to f th e c a l c in e . T h i s m a y p r o b a b l y b e d u e t o t h e p a r t i c le / p a r t ic l e i n t e r a c t io nw h i c h c a u s e s a t t r i t i o n a n d s iz e d e g r a d a t i o n o f t h e f l u i di z e d p h o s p h a t e . T h ee x t e n t o f t h is e f f e c t i n c re a s e s w i t h f l o w - r a t e i n c re a se . T h i s e f f e c t i m p r o v e st h e d e g r e e o f l i b e r a ti o n a n d m a k e s t h e t h e r m a l - t r e a t m e n t p r o c e s s m o r e e f fi -c i e n t .

    B e s i d e s p a r t i c l e / p a r t i c l e i n t e r a c t i o n , t h e f l o w - r a t e i n c re a s e a f f e c t s , p a r-t i c u l a r l y, t h e h e a t - t r a n s f e r c h a r a c t e r i s t i c s o f t h e b e d . T h e i n c r e a s e in f l o wr a te i n c r e a se s t h e m i x i n g o f s o li d s ( B a e y e n s a n d G e l d a r t , 1 9 7 4 ) a n d t h i si m p r o v e s h e a t t r an s f e r an d le a d s t o t e m p e r a t u r e u n i f o r m i t y t h r o u g h o u t t h e

    T A B L E I V

    T h e r m a l t r e a t m e n t o f p h o s p h a t e r o c k a t d i f f e r e n t f l o w r a t e s a t 8 0 0 C

    Vf UflUmf A s s a y p e r c e n t( l / r a i n . )

    P 2 0 s c o r r e s p o n d i n gC a 3 P i O s

    2 0 1 . 0 2 1 9 . 9 0 . 1 4 3 . 4 4

    2 5 . 11 *= 5 4 . 8 12 6 . 2 4 * 3 5 7 . 3 0

    4 0 2 . 0 2 1 9 . 9 0 4 3 . 4 42 5 . 8 9 5 6 . 5 22 9 . 0 5 6 3 . 4 1

    8 0 4 . 0 8 1 9 . 9 0 4 3 . 4 42 6 . 5 9 5 7 . 8 72 6 . 7 1 5 8 . 2 9

    1 2 0 6 . 1 2 1 9 . 9 0 4 3 . 4 42 6 . 8 2 5 8 . 5 52 6 . 8 2 5 8 . 5 5

    1 6 0 8 . 1 6 1 9 . 9 0 4 3 . 4 42 6 . 6 5 5 8 . 1 72 6 . 8 2 5 8 . 5 4

    * ' I n i t i a l o r e ; , 2 c a l c i n e d o r e ; * 3c a l c i n e d a nd w a s h e do r e .

  • 8/8/2019 Nung quang

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    vL~

    0

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    TA B L E V

    Coarse and f ine f rac t ions of t rea ted phospha te rock a t d i ffe ren t f low ra tes and d i ffe ren t

    s ize cuts

    Size of Umf Vf Star t ingpho spha te (cm /sec) (1/min.) pho sph a teb a t c h(mesh )

    Trea t ed phospha t e a t d i f f e ren tf l ow cond i t i ons

    2 .1 4 6 8

    - 4 6.1 90 30.24 *2 28.08 24.19 19.64 16.3469.64 *3 71.91 75.81 80.39 83.66

    --6 5.0 75 29.22 24.37 21.00 16.77 12.7870 .71 75 .60 79 .00 83 .26 86 .70

    - -8 4 .0 60 28 .80 22 .75 19 .92 16 .46 13 .2171 .70 76 .80 80 .02 83 .46 86 .73

    -10 3 .0 45 26 .45 22 .36 18 .59 16 .05 12 .9774 .25 78 .11 81 .38 83 .87 86 .88

    - -14 2 .6 40 18 .33 16 .50 15 .20 14 .00 13 .3081 .63 83 .60 84 .80 86 .60 86 .70

    *' Uf/Umfvalues., 2 The coa rse f r a c t ion ( f rom +3 .15 t o - 1 . 0 + 0.63 r am) ., 3 The f ine f ra c t i on ( f rom - -0 .63 + 0 .5 t o - - 0 . 20 r am) .

    o f th i s e f f e c t d ec r e a s es a s t h e s iz e o f t h e p h o s p h a t e b a t c h d e c r e a se s f r o m - - 4t o - - 1 4 m e s h . T h i s m a y b e a t t r i b u t e d t o t h e d e c r e a s e d a v e r a g e p a r t i c le s i zea n d t h e i n c r e a s e d a m o u n t o f o ri g in a l f i n e s w h i c h s e rv e a s a l u b r i c a n t b e t w e e nt h e c o a r s e r p a r t i c le s a n d g iv es m o r e u n i f o r m f lu i d iz a t io n . T h e p r e s e n c e o ff in e s r e d u c e s p a r t i c le a t t r i t io n ( Z a b r o d s k y , 1 9 6 6 ) .

    A m o r e r e p r e s e n t a t i v e p i c t u r e o f t h e b e h a v i o u r c a n b e o b t a i n e d b y p l o t t i n gt h e t o t a l p a r t i c l e si ze d i s t r i b u t i o n s a t t h e d i f f e r e n t f l o w c o n d i t i o n s . E x a m p l e so f s u c h p l o t s a r e g i v e n i n F ig s . 4 a n d 5 f o r - - 4 a n d - - 6 m e s h s iz e s.

    T h e b e h a v i o u r e x p l a i n e d a b o v e m a y b e a t t r i b u t e d t o a t t r i t i o n e f f e c t sw h i c h a r e e n h a n c e d w i t h f r i a b l e o r e s. I n v o l v e d in t h e c a u s e s o f a t t r i t i o n a r et h e p a r t i c l e / p a r t i c l e i n t e r a c t i o n a n d p a r t i c l e c o ll i s i o n w i t h t h e w a ll s o f t h ec o n t a i n e r . T h i s a t t r i t i o n is n o t a c o n t r o l l e d a t t r i t i o n a n d i t w a s n o t t a k e n i n-t o c o n s i d e r a t i o n in d e s ig n i n g t h e f l u id i z e d - b e d u n i t f o r t h e r m a l t r e a t m e n t .T h e i n c re a s e d d e g r e e o f l i b e r a t i o n a n d t h e i n c re a s e d a m o u n t o f f i n e s d u e t oa t t r i t i o n a r e a c c o m p a n i e d b y i n c r e a s e d e l u t r i a t i o n e f f e c t s , p a r t i c u l a r l y a t h i g hg a s - f lo w ra te s . T h e a b o v e a t t r i t io n b e h a v i o u r a n d e x t e n t i n d i c a t e t h a t a t t r i t i o ne f f e c t s c a n n o t b e i g n o r e d i n t h e d e s ig n a n d o p e r a t i o n o f f l u i d i ze d - b e d u n i t sf o r t h e r m a l t r e a t m e n t o f p h o s p h a t e r o c k .

    E f f e c t o f q u e n c h i n g t e m p e ra t u re

    T h e e f f e c t o f q u e n c h i n g t e m p e r a t u r e w a s s t ud i e d d u r in g t h e c o n t i n u o u so p e r a t i o n o f t h e ca l c in i n g f u r n a c e . T h e q u e n c h i n g o f t h e c a lc i n e d p h o s p h a t ein w a t e r c o n v e r t s th e c a l c iu m a n d m a g n e s i u m o x i d es , f o r m e d f r o m c a r b o -

  • 8/8/2019 Nung quang

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    o i n i t i a l r un

    zL p roce s sed; to tes 'U / U m f

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    F ig .4 . E f f e c t o f ga s f l o w o n t h e a t t r i t i o n o f p h o s p h a t e r o c k ( - - 4 m e s h ) .

    I

    0.~4 O. 2

    n a t e d e c o m p o s i t i o n , i n t o h y d r o x i d e s . T h e q u e n c h i ng t e m p e r a t u r e is im -p o r t a n t w i t h r e g a rd t o r e c a r b o n a t i o n a n d i t s h o u l d b e h i g ho e n o ug h t o m i ni -m i z e r e c a r b o n a t i o n o f th e c a l c in e d p h o s p h a t e . T h e e f f e c t o f q u e n c h i n g t e m -p e r a t u r e w a s s t u d i e d a t t h r e e t e m p e r a t u r e l ev e ls : 4 5 0, 6 0 0 a n d 8 0 0 C . T h ec a l c i n a t io n w a s c ar r ie d o u t a t a t e m p e r a t u r e o f a b o u t 8 0 0 C a n d a f l o w r a teo f a b o u t d o u b l e t h a t f o r m i n i m u m f l u id i z a t io n . T h e r e s u l ts a r e g i ve n i nTa b l e V I a t t w o v a l u e s o f t h eH/D r a ti o . A s c a n b e s ee n f r o m t h e t a b l e , t h eq u e n c h i n g t e m p e r a t u r e h a s n o e f f e c t o n t h e p r o ce s s p r o d u c t w i t h in t h e r an g ei n v e s t i g a te d , a n d t h u s t h e r e i s n o f e a r o f r e c a r b o n a t i o n .

    Design considerations

    I n d e s ig n in g fl u i d i z e d - b e d u n it s f o r t h e r m a l t r e a t m e n t o f p h o s p h a t e r o c k ,t h e f ri a b le n a t u r e o f m a n y p h o s p h a t e o r e s r ai se s s o m e p r o b l e m s . T h e m o s ti m p o r t a n t o f th e s e is t h e i n c r e a s e d a t t r i t i o n o f su c h o r e s w i t h t h e g e n e r a t i o no f a p p r e c i a b l e a m o u n t s o f f in e s a n d i ts c o n s e q u e n c e s . E v e n w i t h l e ss f ri a b lea n d m o r e d e n s e o r e s , t h e s o l i d d e c o m p o s i t i o n r e a c t i o n s o c c u r r i n g w e a k e n

    t h e so l id s s t r e n g t h a n d e n h a n c e a t t r it i o n . T h e c o n s e q u e n c e s o f a t t r i t i o n a n df in e s g e n e r a t i o n i n c l u d e t h e n e e d f o r c o m p l i c a t e d h e a v y - d u t y d u s t se p a ra -t i on e q u i p m e n t t o a v o id a n y e n v ir o n m e n t a l p o l l u t i o n p r o b l e m s , a n d t h ed i s t u rb a n c e o f t h e s y s t e m p e r f o r m a n c e . T h e e x t e n t o f a tt r i t i o n o f so li ds

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    15

    in i t i a l run o f mine o re

    v 1 Proces sed = 2

    a I ore s a t = 4x / U f l U m f = 6

    J v a l u e s o f = 8

    of s i ze - 6 mesh

    cu

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    [ I l L2 . 6 2 1 4 2 1 2 2 1 0 II+ 8 I ] 6 11 .4 1 . 2 1 , 0 O , B 0 1 . 6

    p c lr ti c le s i z e , m mF i g . 5 . E f f e c t o f g a s f l o w o nt h e a t t r it i o n o f p h o s p h a t er o c k ( - - 6 m e s h ) .

    L 0*.20 4

    TABLE VI

    P~O 5 c ont ent of c a l c i n e q u e n c h e d a t d i f f e r e n t t e m p e r a t u r e s

    H/D Q u e n c h i n g t e m p e r a t u r e ( C)

    450 600 800

    4.0 20.10 .1 20.10 20.1025.59 *2 25.59 25.5928.81 *3 28.93 28.98

    6.0 20.10 20.10 20.1026.36 26.36 26.3628.87 28.98 29.04

    , i Ini tia l ore; ,2 calcined ore; ,3 c a l c i n e d a n d w a s h e d ore.

    m a y b e d e c r e as e d t h r o u g h t h e c o n s i d e r a t i o n o f c e r ta i n d e s ig n a n d o p e r a t in g

    a s p e c t s ( D o h e i m e t a l . , 1 9 7 6 ) .A n o t h e r i m p o r t a n t d e s ig n a s p e c t i s t h e n e c e s s i t y o f m u l t i- s t a g in g f o r, a tl e a s t , e n e rg y e c o n o m y. T h e t h e r m a l e f f i c i e n c y o f t h e f l u i d i z e d - b e d t r e a t -m e n t o f p h o s p h a t e o r es i n c r ea s e s w i t h m u l t i -s t a g in g . I n d e s i g n i n g m u l t i -s t a g e

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    1 9 6

    fluidized-bed systems, there are many problems which include: gas distribu-tor plates, solid transfer system from a bed to a lower one, and the workingstability (Lago et al., 1967). A design pro cedure for multi-stage systems ofindustrial application is given by Toei and Akao (1968). Their fluidized-bedapparatus is characterised by having perforated plates instead of the conven-tional overflow pipes (down-comers). Improved stability is expected withthe system having perfor ated plates.

    C O N C L U S I O N S

    The fluidized bed technique is very efficient in the thermal tre atment o fphosphate ores having high contents of carbonaceous and calcareous matter,

    giving an appreciable degree of upgrading. The upgrading ef ficiency of thetechnique increases as the degree of liberat ion o f the ore increases. The in-crease in process temper ature favourably affects the % upgrading of the orebut this should be studied in close connect ion with the economic aspects,especially with ores with low carbonaceous mat ter contents. The fluidizinggas-flow rate and thus the hyd rod ynamic condition of the bed slightly af-fects the thermal upgrading process. However, the use of high air-flow rateswas foun d to affec t the particle-size distribution of the bed greatly throughincreasing the ex ten t of attrition. The attri tion generates an appreciable amou ntof fines.

    The quenching temperat ure is an import ant parameter with regard to re-carbonation but it was found to have no effec t on the process product with-in the investigated range. The washing of the calcined ore was ineff icien twith the fine sizes and at low temperatures.

    R E F E R E N C E S

    A n o n y m o u s , 1 9 60 . P r o d u c i n g q u a li t y p h o s p h a t e f r o m l o w - g r a d e c a r b o n a c e o u s o r e. E n g.Min . J . , 161 (5 ) : p . 86 .

    A n o n y m o u s , 1 9 66 . C h r i st m a s I s la n d p h o s p h a t e c o m m i s s io n " D e v i c e f or t h e h e a t t re a t -m e n t o f p a r t i c u l a t e m a t t e r " . A u s t r a l i a n A p p l . 0 2 F e b . , 5 p p .

    A n o n y m o u s , 1 9 6 7 . P h o s p h a t e p r o d u c t i o n i n M o r o c c o . M in . M i n e r. E n g ., 3 ( 1 ): p . 2 1 .A n o n y m o u s , 1 9 7 0 . M i n e c o n s t r u c t i o n o v e r s e as ( K O P E X ) s ta t e e n t e r p r is e - p o l a n d . A

    Feasibili ty r e p o r t f o r t h e e r e c t i o n o f t h e A b u - S h a g a l a m i n i n g c o m p l e x , K o s s ei r,A n o n y m o u s , 1 9 7 4. P h o s p h a t e d e p o s i t s a n d a s s o c i a t e d e l e m e n t s in t h e A r a b c o u n t r i es .

    I n : T h e 2 n d A r a b C o n f e r e n c e f o r M i n e r a l R e s o u r c e s , J e d d a h , C o n f e r e n c e D o c u m e n t s ,D i s c u s s i o n P a p e r s , p . 2 0 .

    B i b a w y, T.M . , 1 9 6 9 . B e n e f i c i a t i o n o f t h e N i l e - Va l l e y P h o s p h a t e O r e s . T h e s i s , C a i r oU n i v e r s i t y.

    B a s ta , E .Z . a n d E l K a m m a r , A . M . , 1 97 4 . R a r e e a r t h e l e m e n t s d i s t r i b u t i o n in s o m e E g y p -t i a n p h o s p h o r i t e s . I n : T h e 2 n d A r a b C o n f e r e n c e f o r M i n e r a l R e s o u r c e s , J e d d a h , C o n -f e r e n c e D o c u m e n t s , B a c k g r o u n d P a p e r s , P h o s p h a t e , p ~ 151 .

    B a e y e n s , J. a n d G e l d a r t , D . , 1 9 7 4 . P a r t i c l e m i x i n g in a g a s f l u i d i z e d b e d . P r o c . I n t . S y m p .F l u i d i z a t i o n a n d i t s A p p l i c a t io n s . S t ~ C h i m i e I n d u s t r i e ll e , To u l o u s e , p . 1 8 2 .D o r n , F. W. , 1 9 7 3. P r o d u c t i o n o f P i n a n e l e c t r i c a l f l u i d i z e d b e d f u r n a c e . C h e m . I n g.

    Te c h n o l . , 4 5 ( 1 6 ) : 1 0 1 3 - - 1 0 1 9 .

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    19 7

    D o h e i m , M . A . , G h a n e y a , A . A . a n d R a s s o u l , S . A . , 1 9 7 6 . T h e a t t r i t i o n b e h a v i o u r o f ir o no r e s i n fl u i d i z e d b e d r e a c t o r s . C h i m . I n d . , 5 8 ( 1 2 ) : 8 3 6 - - 8 4 0 .

    E I - S h a h a t, R .M . , 1 9 6 4 . N o t e s o n th e " A n a l y s i s o f p h o s p h a t e r o c k " , C h e m i s t r y D e p a r t -m e n t , M i n i s t r y o f I n d u s t r y, E g y p t .

    H a n n a , H . S ., 1 9 6 9 . C o n t r i b u t i o n t o t h e F l o t a t i o n o f P h o s p h a t e O r es . T h e s is , A i n S h a m sU n i v e r s i t y.

    L a g o , E . C ., O t e r o , A . R . a n d R o f , J .S . , 1 9 6 7. D e v e l o p m e n t o f a c o u n t e r c u r r e n t m u l t i-s t a g e f lu i d i z e d b e d r e a c t o r f o r s o l i d - - g a s s y s t e m s . P r o c . I n t . S y r u p . F l u i d i z a t i o n , E i n d -h o v e n , N e t h e r l a n d s U n i v. P r e ss , A m s t e r d a m , p . 7 59 .

    O r p h y, M . K ., Yo u s e f , A . A . a n d H a n n a , H . S . , 1 9 6 8 a . B e n e f i c i a t io n o f lo w - g r a d e p h o s p h a t eo res . Min . Mine r. Eng . , 4 (5 ) : 44 .

    O r p h y, M . K . , Yo u s e f , A . A . a n d H a n n a , H . S ., 1 9 6 8 b . B e n e f i c i a ti o n o f l o w - g r a d e p h o s -pha te o re s . Min . Mine r. Eng . , 4 (10 ) : 48 .

    O r p h y, M . K . , Yo u s e f , A . A . a n d B i b a w y , T. A ., 1 9 6 9 . C a l c i n a t i o n o f c a l c a r e o u s p h o s p h a t e

    o res . Mine ra l Mag . , 121 : p . 195 .P r i e s t l y, R . J . , 1 9 6 7 . H i g h t e m p e r a t u r e r e a c t i o n s i n f l u i d i z e d b e d s. P r o c . I n t . S y m p . o nF l u i d i z a t i o n , N e t h e r l a n d s U n iv. P re ss , A m s t e r d a m , p . 7 0 1 .

    P h i l o b b o s , E . R . , 1 9 6 9 . G e o l o g y o f t h e P h o s p h o r i t e s o f t h e N i le Va ll y. T h e s is , A s s i u tU n i v e r s i t y, E g y p t .

    R a m b a b u , C h . I. , M a j u m d a r , K . K . J . a n d P h a d n i s , A . N . , 1 9 7 3. B e n e f i c i a t i o n s t u d i e s o nc a l c i te - b e a r i n g p h o s p h a t e r o c k f r o m K a n p u r. I n d i a n Te c h n o l ., 11 ( 2 ) : 7 8 - - 8 2 .

    S i ng h , B , R i g b y, G .R . a n d C a l l e o tt , T. G . , 1 9 7 3 . M e a s u r e m e n t o f m i n i m u m f l u i d i z a t i o nv e l o c i t i e s a t e l e v a t e d t e m p e r a t u r e s . Tr a n s . I n s t . C h e m . E n g . , 5 1 ( 2 ) : p . 9 3 .

    S e m i n a r o n b e n e f i c i a t i o n o f l e a n p h o s p h a t e s w i t h c a r b o n a t e g a n g u e , 1 9 7 5 . E l e v e n t h I n te r -n a t i o n a l M i n e r a l P r o c e s s i n g C o n g r e s s , C a g l ia r i , I t a l y, A p r i l 2 3 - - 2 4 .

    To w n , J .W. e t al ., 1 9 6 7. B a t c h a n d c o n t i n u o u s - c i r c u i t b e n e f i c i a t i o n o f w e s t e r n p h o s p h a t e

    o res . U .S . Bur. Mines Rep . Inves t . No . 6930 .To e i , R . a n d A k a o , T. , 1 9 68 . M u l t i - st a g e f l u i d i z e d b e d a p p a r a t u s w i t h p e r f o r a t e d p l a t e s ,

    I n t . C h e m . E n g . S y m p o s . S e r. N o . 3 0 : p . 3 4 .Vo g e l, A . , 1 9 6 1 . A T e x t B o o k o f Q u a n t i t a t iv e I n o r g a n i c A n a ly s i s . L o n g m a n ' s G r e e n ,

    L o n d o n .Z a b r o d s k y, S .S . , 1 9 6 6 . H y d r o d y n a m i c s a n d H e a t t ra n s f e r in F l u i d i z e d b e d s . T h e M . I. T.

    Press , p . 306.