HEAT TECHNOLOGY
SINTERING K.
K.
CAUSTIC Strelov
MAGNESITE and
K.
V.
DUST
Simonov
UDC 666.762.32.046.4
The amount of caustic dust r e m o v e d f r o m flue g a s e s in the burning of magnesite is about 800,000 tons a y e a r , including 600,000 tons which is e x t r a c t e d by cyclones, and 200,000 tons by electric filters. About 100,000 tons taken f r o m cyclones is r e t u r n e d directly to the u s e r s ; the r e m a i n d e r mixed with raw magnesite is burned in r o t a r y kilns to obtain m e t a l l u r g i c a l powders that a r e used to make and r e p a i r the bottom and slopes of o p e n - h e a r t h and electric steel furnaces. The use of caustic dust for making fettling powders is i r r a t i o n a l , since it has a high content of magnesia, and in its p r o p e r t i e s is suitable for the production of the s c a r c e r f i n e - g r a i n e d powders on whose basis we can make special and effective r e f r a c t o r y a r t i c l e s [1-5]. Investigations of the p r o p e r t i e s and sintering of caustic magnesite dust extracted f r o m the waste flue g a s e s in firing m a g n e s i t e in r o t a r y kilns [6-10] established that the caustic dust is badly sintered; to improve its sintering we r e c o m m e n d fine grinding, the introduction of sintering additives, and pelletizing before burning. The dust contained a l a r g e amount of g r a n u l a r anhydride, alkalis, and f l u o r i n e - f o r m i n g simple and complex alkaline sulfates and alkaline earths, and also m a g n e s i u m fluoride [11], whose influence on the sintering of the dust and the production of powders was not taken into consideration in the previous work. This article gives the r e s u l t s of a study of the sintering of caustic dust* containing alkali sulfates, a l k a l i n e - e a r t h sulfates and m a g n e s i u m fluoride. The p r o p e r t i e s of the four samples are shown in Table 1. The p r o p e r t i e s of the dust depend on the f o r m of the original m a t e r i a l fed to the furnace and the type of dust extracting equipment. The dust was slaked with water and mixed on runner mills. The m o i s t u r e content of the compound was 7-10%. Cylindrical s p e c i m e n s 12-15 m m thick were p r e s s e d (close in dimensions to briquet obtained on the industrial flat r o l l e r p r e s s e s ) at p r e s s u r e s of 80-100 MPa [10]. They were fired in tunnel kilns at 1620, 1650, 1750, 1840, and 1850~ in l a b o r a t o r y e l e c t r i c f u r n a c e s with z i r c o n h e a t e r s at 1500~ and in a vacuum e l e c t r i c furnace ( 1 . 1 0 - 2 - 5 9 10 -2 Pa) at 1800, 1900, and 2000~ and also in a 90-m r o t a r y furnace at 1750~ The r e s u l t s are shown in Tables 2 and 3 and in Figs. 1-3. The dust extracted with the cyclones is poorly sintered without p r e l i m i n a r y activation for all burning t e m p e r a t u r e s , which c a u s e s it to be c o a r s e l y grained and gives it a low specific surface (see Tables 1-3). 9 With the participation of O. V. Krasnova, R. S. Polovinkina, and L. D. Bocharov. TABLE i.
C h a r a c t e r i s t i c s of Caustic Dust i dlC~
E e
I. Loo.sr
i
.•
~l tlons), m~ithout)with ',~5 9
Cyclone 1 73 i~5 1 , ] 0 Natural 97 a I 0,52 magnesir~ Electric filter Mixture of Cyclon 84 4~51i ,,0 natural Electric 3 99 0,47 and caustic mag- filter
siqaK-
1,45 0.84
Content,* ~o
Content,* % (calcined weight) o
~ SiO~
2.0 7.5
1,4 2,8 0,80 10,5
AltOs Fe)O)
CaO
KtO+ MgO I SO, +Na,O
F..
J~
1,99 2.22 92,50 1,0 0,47 0,35 4,6 2.35 2,35 87,82 3.0 1,0 0,34 0,5 1,60 6,1 I,! 0,32 1,70 1,60 92,20 1,9 l , l 1,4 0,53 1,82 2,03 8|,41 7,3 4.9 2,40 6,4
1,4 0,47
2,1
1,12
~
~o
lff
,h
~'~
32 47 22 i 56
10 ll
17 i 53 14 45
16 20
),02.~ 1,5 [,5i3,C 4.0 1,52,~ 3,0 ),52,[ 1,0
carbon substance Ibrueite, ilime
0,5 0,5
2,0 1,5
2,5 3,5
2,o 1,5
nesite
* Here and subsequently, we state the weight proportions. The size of the c r y s t a l s of p e r i c l a s e and active MgO (mainly caustic magnesite) is 3-10 t i m e s less than in the high fired MgO (nonactive to sintering MgO). $ Here and subsequently, the mixture contains 10-14 tons of natural magnesite and 19-22 tons caustic.
U r a l s S. M. Kirov Polytechnic Institute. 15-21, J a n u a r y , 1981.
Magnezit Combine.
0034-3102/81/0102-0007507.50
T r a n s l a t e d f r o m Ogneupory, No. 1, pp.
9 1981 Plenum Publishing Corporation
7
~', g / c m ~
2,8 3O 28 26
3t
22~ ZO
25 84
0
20
z~O 60
80 lO0
0
20
r
80
80 100
Amount of milled dust,%
Amount of dust from electric filters, Fig. i
Fig. 2
Fig. 1. Change in the bulk density 7 of dust with shaking (1) and without shaking (2) and the open p o r o s i t y Pop of briquet h e a t - t r e a t e d at different t e m p e r a t u r e s (indicated on curves) as a function of the amount of dust taken f r o m e l e c t r i c filters, added to the dust f r o m the cyclones. Fig. 2. Change in the a p p a r e n t density p app of g r e e n b r i c k m a d e of dust f r o m cyclones (1) and e l e c t r i c f i l t e r s (2) and the open p o r o s i t y P a p of the briquet, f i r e d in tunnel kiln at 1850"C, f r o m dust taken f r o m cyclones (3), e l e c t r i c f i l t e r s (4), and f r o m a m i x t u r e of 60% cyclone dust and 40% filter dust (5) as a function of the amount of milled dust. The i n c r e a s e in firing t e m p e r a t u r e in the tunnel kiln f r o m 1650 to 1850~ and in the vacuum furnace f r o m 1800 to 2000~ facilitates a reduction in the open p o r o s i t y of the briquet amounting in total to 2.9-6.9~1o (see Table 2). The dust taken f r o m the e l e c t r i c f i l t e r s s i n t e r s b e t t e r than that f r o m the cyclones. F o r example, the p o r o s i t y of the briquet m a d e f r o m filter dust fired in a tunnel kiln is 1.2-2.9 t i m e s l e s s than the p o r o s i t y of briquet made f r o m cyclone dust (see Table 2). It should be noted that the sintering of dust f r o m the f i l t e r s largely depends on the type of m a t e r i a l s fed for firing; dust taken f r o m the f i l t e r s during the burning of natural m a g n e s i t e s i n t e r s b e t t e r (open p o r o s i t y of briquet 15.8 and 10.0%) than in firing a m i x t u r e of caustic and d,~m i
#0:
2
4 "60
sol
50
zo ~
40
70 75oo
t 770o
~ ~0 79oo-t,"c
Fig. 3. Change in open p o r o s i t y of briquet Pop (i, 2) and size of the p e r i e l a s e c r y s t a l s d (3, 4) with r i s e in firing t e m p e r a t u r e , t: i, 4) briquet f r o m dust taken f r o m cyclones; 2, 3) f r o m e l e c t r i c filters.
TABLE 2. Material being fired
R e s u l t s of Sintering C a u s t i c Dust
Sample
INo.(~ee
;
Cyclone
Natural magnesitr
Electric filter Cyclone
Mixture of natural magnesite and caustiemagnesite
Pressin~ ~pparent [ Firing IdensityofL
IS.ampunglforce.
Ig~e~n l~emp", ~ri=2, I'C Icm~ t
In tunnel kiln I00 1,95 I00
1,84
80
2,15
100
2,12 2,04
Electric filter
80
2,12
100
2,18 2,06
Mixture of natural and caustic magnesite
3 4 P$
1620 1840 1620 1840 15007 1650 1750 1850 1620 1840 1650 1850 1500T 1650 1750 1850 1620 1840 1650 1850
in vacuum furnace 100 2,05 1800 1900 2000 100 2,06 1800 Elec~ic 1900 filter 2000 Cyclone 100 2,06 1800 1900 andelee2000 ~ic ill-I
Cyclone
Iu ~age
tApparentlOpenporosity
ng. e itY o lof briquo
1 f;> I, 34 38 52 53 21 22 23 25 22 29 31 33 35 41 44 46 34 40 37 38
2,35 2,55 2,99 3,14 2,17 2,24 2,28 2,37 2,33 2,54 2,54 2,66 2,52 2,62 2,65 2,88 2,51 2,77 2.63 2 ,~0
34,3 29,0 15,8 10,0 40,2 37,4 36,4 33,4 34,3 29,7 28,4 24,3 29,O 26,5 25,7 18,6 29,6 23,1 25,8 20,9
17
2,53 2,56 2,63 2,77 2,75 2,90 2,57 2,55 2,61
29,4 28,4 26,5 21,8 21,9 17,8 28,7 28,4 27,0
19~3 Not det. 61,0
~ter
*When f i r i n g in vacuum f u r n a c e i n d i c a t e s l o s s in weight, %. F i r i n g in e l e c t r i c f u r n a c e with z i r c o n h e a t e r s . $ P -- the s a m p l e c o n t a i n s 80% dust f r o m c y c l o n e s and 20% f r o m e l e c t r i c filters.
n a t u r a l dust (open p o r o s i t y of b r i q u e t 29.6 and 23.1). With a r i s e in the f i r i n g t e m p e r a t u r e the open p o r o s i t y of the b r i q u e t d i m i n i s h e s by 5-11%. The b e t t e r s i n t e r i n g of dust f r o m the f i l t e r s c o m p a r e d with c y c l o n e s i s due to the g r e a t e r s u r f a c e a r e a of the p a r t i c l e s . At high burning t e m p e r a t u r e s in a vacuum e l e c t r i c f u r n a c e the b r i q u e t m a d e f r o m the c y c l o n e dust s i n t e r s badly; f r o m the e l e c t r i c f i l t e r s -- much b e t t e r , but the open p o r o s i t y of the b r i q u e t r e m a i n s r e l a t i v e l y high (17.8-21.9%). This is due to the r e m o v a l of v o l a t i l e s and the s u b s t a n t i a l e v a p o r a t i o n of the m a g n e s i a in vacuum, e s p e c i a l l y at 2000~ the l o s s in weight r e a c h e s 61%. The s i n t e r i n g r e s u l t s for m i x t u r e s a r e shown in F i g . 1. A m a r k e d i m p r o v e m e n t in s i n t e r i n g at above 1650~ i s noted f o r m i x t u r e s containing m o r e than 50% dust f r o m the e l e c t r i c f i l t e r s . The i n c r e a s e d p o r o s i t y of the b r i q u e t h e a t e d at 1000~ with m o r e than 50% f i l t e r dust in it i s due to the i n c r e a s e in the amount of p o r e f o r m i n g v o l a t i l e c o m p o n e n t s in the b r i q u e t ( s u l f a t e s and f l u o r i d e s of m a g n e s i u m ) and the a b s e n c e of s i n t e r i n g of m a t e r i a l at such low t e m p e r a t u r e s . The s t r e n g t h of the g r e e n b r i q u e t i s i n c r e a s e d 1.5 t i m e s with a mi:ature content of 20% f i l t e r dust, so the b r i q u e t should be p r e s s e d f r o m the c y c l o n e dust and the e l e c t r i c f i l t e r dust in a r a t i o of 4: 1, i . e . , in the s a m e r a t i o as they a r e e x t r a c t e d at the Magnezit Combine. F i n e m i l l i n g of c a u s t i c dust r e d u c e s the open p o r o s i t y of the f i r e d b r i q u e t m a d e f r o m c y c l o n e dust by 7%, and f r o m f i l t e r dust by 3%. The m i n i m u m p o r o s i t y i s c h a r a c t e r i s t i z e d by b r i q u e t containing 20-25% unground m a t e r i a l and 75-80% m i l l e d dust (see Fig. 2), and so in obtaining dense p o w d e r s it i s i r r a t i o n a l to m i l l the dust in i t s e n t i r e t y . In i t s d e g r e e of s i n t e r i n g the m i l l e d dust f r o m the c y c l o n e s i s c l o s e to the u n m i l l e d dust f r o m the e l e c t r i c f i l t e r s . The s i n t e r i n g :results f o r b r i q u e t in the r o t a r y kiln a r e c l o s e to those obtained in [10]. B r i q u e t s for f i r i n g in r o t a r y k i l n s w e r e p r e p a r e d on the r o l l e r p r e s s e s f r o m c a u s t i c dust containing 1.59o SiO2, 0.9% A1203, 1.8% Fe203, 2.090 CaO, 82.4% MgO, 6.1% SOn, 5.1% Na20 + K20 and 8.6% c a l c i n a t i o n l o s s . The a p p a r e n t d e n s i t y of the g r e e n b r i q u e t i s 1.86-2.10 g / c m 3. The open p o r o s i t y of the p o w d e r a f t e r f i r i n g i s 9.2%, the a p p a r e n t d e n s i t y 3.18 g / c m a ; the MgO content i s 91.1%.
T A B L E 3. E f f e c t of P r e l i m a r y H e a t P r o c e s s e d (1000~ and B r i q u e t on the M a t e r i a l ' s S i n t e r i n g *
Sampling site
5amp1: No. (see Tables 1 and 2
Cyclone
3
Apparenl Ope___n porosity of briquet, ~. density ofgreen after heat [.afterfiring in tunnel brick,g / eeatment at .~In at$ (~
Dustr
erlqs
]
[ Unground U8%)
$@
J
Electric
fiker
4
2,04
2-m
, Ground (98%) **
2,12
[Mixture of 69~q0unground and 40~. ground Unground
2.19
9Ground
I ,82
l '82
I
Electric filter
Caustic Dust
iMixturc of 60o~.un] ground and 4C~.ground
1,84
~,4T 2,17
~Ungreund
2,26
50,9 38,6 49,1 37,6 46,3 38,4 52,5 31,9 52,3 30,7 52,9 37 Y. 45,5 36,7
44,3 35,3
@
iMixture of 60~ unground and 40~ogxound
iO00*C
2,19 36,3
|
1780
1840
32,3
30,3 2l ,8 24,0 18,8 26,4 19,2 24,7 22,7
27,i
2_2,_C
2t ,0 25,1 22,5 29,0 23,9 26,9 16,4 26,4 21,1
* T h e n u m e r a t o r i n d i c a t e s t h e f a c t o r s f o r t h e b r i q u e t m a d e of o r i g i n a l dust, not preheated; the denominator -- from dust that had first been heated. t T a k e n f r o m a f u r n a c e f i r i n g a m i x t u r e of n a t u r a l (35%) and c a u s t i c (65%) m a g n e s i t e . $ T h e s a m e s p e c i m e n s w e r e f i r e d a s h a d b e e n p r e h e a t e d a t 1000~ ** I n d i c a t e s c o n t e n t of f r a c t i o n s m i n u s 63 # m . T h e output of t h e r o t a r y k i l n w a s l i m i t e d by t h e output of the r o l l e r p r e s s e s and e q u a l e d 7 t o n s / h . W i t h an i n c r e a s e in the f u r n a c e output, the p o w d e r ' s p o r o s i t y i n c r e a s e d (e. g . , with the o r d i n a r y output of 1 1 - i 2 t o n s / h i t c a m e within the r a n g e 11-14%). T h e s i n t e r a b i l i t y of one and the s a m e m a t e r i a l with i d e n t i c a l t e m p e r a t u r e s in r o t a r y k i l n s i s b e t t e r than in tunnel. T h u s , the open p o r o s i t y of b r i q u e t with an a p p a r e n t d e n s i t y of 1.86 g / c m ~ f i r e d in a t u n n e l k i l n at 1730~ w a s 32.6%, the a p p a r e n t d e n s i t y 2.4 g / c m ~. T h e m o r e i n t e n s e s i n t e r i a g of the m a t e r i a l in t h e r o t a r y k i l n c o m p a r e d with t u n n e l i s e x p l a i n e d by t h e c o n t i n u o u s m o v e m e n t of the m a t e r i a l a c c o m p a n i e d by the i m p a c t of t h e g r a i n s on e a c h o t h e r and on the lining, and a l s o the p r e s s u r e of t h e a b o v e - l y i n g p o w d e r on the l o w e r l a y e r s . S p e c i m e n s f r o m d u s t c o n t a i n i n g m o r e v o l a t i l e s a r e s i n t e r e d w o r s e t h a n t h o s e with s m a l l a m o u n t s of v o l a t i l e s . In o r d e r to s t u d y t h e e f f e c t of r e m o v i n g v o l a t i l e s on the s i n t e r i n g , we c o m p l e t e d e z p e r i m e n t s with the p r e l i m i n a r y h e a t p r o c e s s i n g of the m a t e r i a l s at 1000~ f o r t h e d u s t i t s e l f , and with the g r e e n b r i q u e t s p r e s s e d f r o m it. A s s e e n f r o m T a b l e 3, t h e d u s t p r e s s e d into b r i q u e t w i t h o u t p r e h e a t i n g s i n t e r e d b a d l y , w h i c h i s due to the p r e s e n c e of f i l m s of v o l a t i l e s ( a l k a l i n e s u l f a t e s and a l k a l i n e e a r t h s and m a g n e s i u m f l u o r i d e ) on t h e p a r t i c l e s of dust. T h e f i l m s p r e v e n t c o n t a c t b e t w e e n p a r t i c l e s at the p r e s s i n g s t a g e s and s i n t e r i a g and do not yield dense green articles or dense fired briquet. M i c r o s c o p i c s t u d i e s e s t a b l i s h e d t h a t p o r e s a r e f o r m e d in t h e b r i q u e t p r e s s e d f r o m n o n h e a t - p r o c e s s e d d u s t (and t h e n h e a t e d to 1000~ to r e m o v e t h e f i l m s f r o m the p a r t i c l e s ) and t h e s e p o r e s p r e v e n t e d p a r t i c l e c o n t a c t and s i n t e r i n g . A f t e r p r e l i m i n a r y h e a t t r e a t m e n t of t h e o r i g i n a l d u s t a t 1000~ and r e m o v a l of p a r t of t h e f i l m s of v o l a t i l e s t h e d e n s i t y of t h e p r e s s i n g s and the f i r e d b r i q u e t i n c r e a s e d s i g n i f i c a n t l y {see T a b l e 3). T h e h i g h e s t d e n s i t y i s r e c o r d e d f o r f i r e d b r i q u e t p r e p a r e d f r o m p r e h e a t e d d u s t t a k e n f r o m the f i l t e r s , c o n t a i n i n g t h e m a x i m u m q u a n t i t y of a l k a l i s u l f a t e s and a l k a l i n e e a r t h s and m a g n e s i u m f l u o r i d e ( s e e T a b l e s i and 3). W i t h an i n c r e a s e in the p r e l i m i n a r y h e a t i n g t e m p e r a t u r e to I I 0 0 ~ t h e r e i s a c o n t i n u a t i o n of t h e r e m o v a l of t h e r e m a i n i n g p a r t s of t h e v o l a t i l e s , but in t h i s c a s e t h e r e i s a r e d u c t i o n in the s i n t e r i n g a c t i v i t y of the m a g n e s i a i t s e l f ; and a s a r e s u l t of t h i s , no c o n s i d e r a b l e i n c r e a s e in d e n s i t y of t h e b r i q u e t a f t e r f i r i n g i s o b s e r v e d .
10
Caustic dust from cyclones
Caustic dust from electric fikcrs
I
]
Moistening, mixing (double shaft mixer Or runner mill) Briqueting under pressure of 50-80 MPa on roller press /
Firing at 1650-170~*C in rotary kilns Grinding. to fractions 4-0 mm Classification into fractions 3-1 and 1-0 mm Batch preparation Pressing under prew /
of 90-150 MPa
Firing products (16~0-1700 far magnesite, 1700-1840 "C for periclase spinel Fig. 4. Production scheme for obtaining a r t i c l e s based on caustic dust. Thus, the sintering of the p a r t i c l e s of caustic dust depends on the degree of "contamination" of their surface by volatiles, the evaporation of the m a g n e s i a itself and impurities, and also on the dust' s fineness. F r o m the caustic dust which is difficult to sinter and contaminated with volatiles it is possible to obtain a c o m p a r a t i v e l y dense fired briquet with an open p o r o s i t y of 10-167o by including the following operations in the technology: p r e l i m a r y t h e r m a l p r o c e s s i n g of the dust at 1000-1100~ for p a r t i a l r e m o v a l of volatiles, fine grinding, briqueting, and firing the briquet at elevated t e m p e r a t u r e s . In view of the negative effect of the "contamination" of the s u r f a c e s of the p a r t i c l e s by the volatiles with r e g a r d to the d u s t ' s sintering, it became n e c e s s a r y to make a deeper study of this p r o c e s s . It is established that during the firing of magnesite products with a high t e m p e r a t u r e , there is a considerable i n c r e a s e in the pore sizes, and to a l e s s e r extent t h e r e is a reduction in the overall p o r o s i t y [12]. The c o a l e s c e n t nature of the i n c r e a s e in pore size during the firing of r e f r a c t o r i e s was described p r e v i o u s l y [113]. The ratio of the probability of the sintering p r o c e s s e s AF C and c o a l e s c e n c e AF K is e ~ p r e s s e d by the equation [14] AF.__~= (l__n_l/3)_l AFK where n is the n u m b e r of p o r e s in unit volume. In caustic magnesite (briquet after firing) the pore s i z e s are 10-6-10 -3 ram, n > 104. * With this value for n the p r o c e s s e s of c o a l e s c e n c e and sintering are equally probable. Simultaneously with sintering and c o a l e s c e n c e , there o c c u r s the p r o c e s s of r e c r y s t a l l i z a t i o n , a c cornpanied by a reduction in free energy. As a result of the movement of c r y s t a l s during r e c r y s t a l l i z a t i o n , the p o r e s tend to c o a l e s c e [14l. The kinetics of all three p r o c e s s e s in a f i r s t approximation is proportional to ~ i / 3 , where r is the sintering time. However, according to [15], the degree factor for r e c r y s t a l l i z a t i o n of p e r i c l a s e c e r a m i c s 'varies in the range 0.32-0.28, diminishing with an i n c r e a s e in porosity, i . e . , with a c e r t a i n reduction in p o r o s i t y the p r o c e s s of r e c r y s t a l l i z a t i o n will o c c u r to a g r e a t e r degree (see Fig. 3). F u r t h e r m o r e , for MgO the apparent energy of activation of r e c r y s t a l l i z a t i o n (293 k J / m o l e [15]) is less than the app a r e n t energy of sintering (326 k J / m o l e [16]). Consequently, m e r e l y by i n c r e a s i n g the sintering t e m p e r a t u r e of caustic dust it is impossible to achieve a high density. The production of a c o m p a r a t i v e l y dense powder from caustic dust is attained by fine grinding, briqueting, firing in r o t a r y kilns at t e m p e r a t u r e s above 1750~ [10], and in some c a s e s additionally by t h e r m o activation and i n c o r p o r a t i o n of sintering additives [8]. 9 The concentration of p o r e s in 1 c m 3 is determined with the use of m e r c u r y p o r o m e t r i c data according to the known method [13, p. 84].
11
It is established [1-5] that r e f r a c t o r i e s with a low t h e r m a l conductivity, e . g . , linings of r o t a r y kilns, walls, slopes and bottoms of open-hearth furnaces, can be obtained on the basis of porous powders from caustic dust, which is economically m o r e favorable than making dense powders and a r t i c l e s on t h e i r basis. The production scheme for making magnesite M and p e r i c l a s e - - s p i n e l PShTsK r e f r a c t o r i e s on the basis of caustic dust is shown in Fig. 4. The batch for r e f r a c t o r i e s M included 30-4070 porous powder fractions 3-1 m m from caustic dust, 30-40~ of the same powder fraction 1-0 m m and 27-35?0 finely milled constituent made of dense magnesite powder; the batch for making r e f r a c t o r i e s PShTsK -- 30-40% porous powder f r a c tions 3-1 ram f r o m caustic dust, 28-36% dense powder fractions 1-0 m m f r o m magnesite, 32-38% finely milled m i x t u r e of c h r o m i t e (70%) and dense magnesite powder (3~o). Thus, it was established that the sintering of p a r t i c l e s of e x t r a c t e d caustic dust largely depends on the degree of "contamination r' of their surface by volatile components (sulfates, selait), the volatilization of the magnesia, andthe fineness of the dust. A technology was developed for obtaining porous powders f r o m extracted caustic dust containing sulfates and selait, by m e a n s of briqueting a mixture of unground dust taken from cyclones and e l e c t r i c f i l t e r s in a certain ratio, and firing the briquet at m o d e r a t e t e m p e r a t u r e s in r o t a r y or shaft Mlns. The above justifies the introduction of a production technology for magnesite a r t i c l e s with the use of porous grains of filler f r o m e x t r a c t e d caustic dust using the proposed method. LITERATURE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
12
CITED
K . K . Strelov et a l . , Ogneupory, No. 7 (1979). Inventor's Certificate No. 336310, A. P. P a n a r i n et aL, Otkrytiya, Izobret. P r o m . Obraztsy, Toy. Zn., No. 14 (1972). V . I . Shubin et al., T s e m e n t , No. 7 (1970). N . F . Bugaev et al., Ogneupory, No. 3 (1970). A . I . Uzberg et al., Ogneupory, No. 1 (1973). N. !~. Bugaev et aL, Ogneupory, No. 2 (1967). V . A . P e r e p e l i t s y n et al., Ogneupory, No. 9 (1970). V . A . Bron e t a l . , Tr. VostlO, No. 11 (1971). L. Ya. Osipova e t a l . , in: P r o b l e m s of the Technology for Producing Magnesia P r o d u c t s [in Russian], Leningrad (1973). K . V . Simonov et al., Ogneupory, No. 3 (1974). K . V . Simonov et al., Ogneupory, No. 4 (1979). K . S . Nazarov, Ogneupory, No. 3 (1963). K . K . Strelov, Structure and P r o p e r t i e s of R e f r a c t o r i e s [in Russian], Moscow (1972). Ya. E. Geguzin et al., P h y s i c s of Sinterlng [in Russian], Moscow (1967). N . T . Andrianov et al., T h e r m a l Aging of C e r a m i c s [in Russian], Moscow (1979). F,. V. Degtyareva, in: The C h e m i s t r y of H i g h - T e m p e r a t u r e Materials [in Russian], Moscow (1967).
