I
JUMPEI A N D 0 Faculty of Engineering, Chuo University, Tokyo, Japan
Simultaneous Production of Nickel Matte and Calcium Magnesium Phosphate A unique approach to a problem of unwanted slag and the need for a fertilizer for acid soils
IN
THE production of nickel matte from garnierite (nickel magnesium silicate), the ore is usually fused with limestone, silica, gypsum, and coke. Recently in Japan, production of nickel matte together with fused calcium magnesium phosphate was begun on a commercial scale by using rock phosphate instead of limestone and silica. The advantage of this modification lies in the simultaneous production of phosphate fertilizer instead of the usual slag. The two processes are compared below :
Standard Process Parts
Charge (fusion temp., 1320-70° C.) Garnierite" Limestone Silica Gypsum Coke
100 35-40 0-10 10 30
Products Nickel matteb Nickel slap
I n the standard process materials are charged in a blast furnace, to which hot or cold air is introduced, and then fused. An electric furnace with three graphite electrodes can also be used, with 4 or 5 parts of coke added for reduction. I n the modified process, garnierite is sintered with phosphate rock followed by fusion with gypsum and coke. Part of the phosphorus is reduced and introduced into the matte. Although it is subsequently removed in a converter and does not affect nickel quality, it is desirable to suppress phosphorus reduction without decreasing nickel yield and phosphate solubility. Blast furnace operation is often more difficult in the modified process than in the standard process because of the higher fusion temperature of the charge. The difficulty increases if higher grade phosphate (containing more phosphorus pentoxide) is produced because a higher fusion temperature is required, promot-
Coke
Experimental Chemical composition of raw materials is shown in Table I. All materials were ground to 50 mesh. Garnierite, phosphate rock, and gypsum were blended with coke, placed in clay crucibles, and fused in an electric furnace. Raw mixes melted in 15
13-15 100
Modified Process Charge (fusion temp., 1370-400° C.) Garnierite Phosphate rock Gypsum
ing phosphorus reduction. Nickel output decreases when a higher proportion of phosphate rock is used to produce higher grade phosphate. The most efficient scheme should produce a phosphate which is easily fused at a lower temperature and which can be rendered soluble, along with acceptable nickel yield. Phosphorus reduction should be kept to a minimum. This study was undertaken to determine the optimum combination of phosphate composition and nickel yield and to establish the conditions under which this can be achieved.
Table 1. 100 120 10-15 50
Products Nickel matted 13-15 Calcium magnesium phosphate' 180 a Nickel magnesium silicate ore. 2023% Ni; 1617% S; 60-66% Fe. 1720% MgO; 19-24% CaO; 4447% SiOz; 6-10% FeO; 5 6 % AlzOs; 0.1-0.2% Ni. 3-8% P ; 20-23% Ni; 10-15% 9; 60-65% Fe. * 17-18% PzOs; 0.1% Ni.
Code A B C S A' B' C'
D E F G
Material
Garnierite Garnierite Garnierite Serpentine Phosphate rock Phosphate rock Phosphate rock Gypsum Gypsum Coke Coke
Raw Materials Came from World-Wide Sources Chemical Composition, % Ignition Source loss Si02 FezO: AlzOs MgO Ni CaO PzOs F
New Caledonia 17.6 New Cdedonia 14.4 New Caledonia 8.9 Ogose, Japan 13.7 Macatea 9.5 Florida 7.8 Florida 6.9 Wakamatsu, Japan Wakamatsu, Japan
..(....
34.4 16.5 3.0 35.6 22.5 4.9 46.5 21.3 4.1 38.4 8.0 1.9 0.1 1.9 1.2 3.5 1.4 1.3 9.4 1.6 1.4 17.3 2.0 6.0 7.2 1.4 1.0 [ash 30.01 [ash 19.81
VOL. 51, NO. 10
... .., ... ... ... ... .,. ... ... ... ...
26.5 3.16 21.4 2.80 17.1 3.72 38.2 0.11 1.3 49.135.52.8 49.8 34.7 3.7 44.2 31.4 3.7 3.3 29.1(SOa 41.3) 2.1 31.5(50~43.8)
... ... ... ... ... ... ....
OCTOBER 1959
1267
minutes, reached 1350' C. 10 minutes later, and were maintained at that temperature for 30 minutes. Temperature was measured by observing the melt surface n i t h an optical pyrometer. TYhile the melt \cas at 1350' C.. temperature outside the crucible. measured by a platinum-platinum-rhodium thermocouple was 1350' to 1360' C. T h e melt was poured into \cater to quench. Most of the matte cohered into a feiv lumps. and the remainder formed small pellets. 'Those largrr than 1 mm. were gathered. Icrighed. and analyzed. Plow Length. For resting proprrties of the phosphate melt. ra\v mixes \vrre fused in graphite crucibles. Other crucibles were corroded severely by the phosphate melt, thus changing the composition of rhe phosphate considerably. Because graphite of the crucible reduced the raw materials. less coke \cas added. Each 90 to 110 grams of ra\c mix was fused in a n electric furnace so that the amount of fused phosphate resulting \vas 75 to 80 grams. Raw mixes melted and reached temperatures sholcn in Figure 3 after 30 minutes and icere maintained a t those temperatures for 20 minutes. Then the melt \cas poured onto a triangular metal trough 110 cm. long placed at a n inclination of 30' and allowed to cool. The length of the cooled. hardened phosphate (flow length) \cas measured. Softening Point. Ra\v mix or fused phosphate \\.as shaped into a cone ( 7 ) and heated at a rate of 5' C. per minute in an electric furnace. T h e temperature a t n.hich the cone fell \vas measured by a thermocouple. Citric Solubility. Raw mixes ivere fused in graphire crucibles for 20 minutes in an electric or gas furnace. Quenched products icere passed through a 10-mesh sieve! and the sieved material was powdered to 100 mesh. Citric solubility was measured by the official .Japanese method (150-ml. method) in \chich 150 ml. of 2yLcitric acid is added to 1 gram of powdered sample and shaken for an hour. Citric solubility measured by the international method (100-ml. method), in nhich 100 ml. of acid is used and the shaking period is 0.5 hour! was usually 0.5 to 3% lower.
Table II.
Materials Used, Grama Phosphate Garnierite rock Gyp.un1
L x p t No
H-1 H-2 L-1 L-2
50 50 50 50
60
5
60
7.5 5 5
22.5 22.5
raiv materials; when 15 to 20 parts Lvere added about SO% reacted. Nickel and sulfur irere reduced more easily than iron and phosphorus. \Vhrn 7 to 10 parts of coke \cere added. nickel yield rate \cas 88 to 9257%phosphorus content of t h r inaite \vas 3.5 to :.OS;, and nickel content of the fused phosphate \vas 0.10 to 0.205,. Addition of more coke raised both nickel yield and phosphorus content of the matte. Phosphorus pentoxide Content of the phosphate \cas 16 to 17c;. A considerable amount of the crucible \cas fused into the phosphate. Nickel Yield and Phosphorus Content. Garnierite B: phosphate rock C', and gypsum D were blended with various amounts of coke and fused a t 1320' or 1350' C. (.I'able 11). The relationship between nickel yield rate and phosphorus content uf the matte is illustrated in Figure 2. Phosphorus content was lower in sample H-2 (Figure 2), to Lvhich more gypsum \vas added. I t promoted apatite formation in the phosphate product, ivith consequent depression of citric acid solubility. \Vhen less g p u m was used, phosphorus content of the matte was raised, but highly soluble phosphate fertilizer was easily obtained (Table 111).
100
I 11>1011 Temp, O ( '
softeilillg
Pomt, 1240 1250 1235 1235
c.
1350 1350 1350 1320
Phosphorus in the matte can be removed together with iron as a citricsoluble slag by oxidizing treatment in a converter and does not affect the quality of refining nickel. Addition of 10 to 1.5 parts of gypsum to 100 parts o f garnierite is suitable as in the standard treatment of the ore with limestone. \Vhen Irss phosphate rock \cas used (Table 11. IA-l). phosphorus content of the matte \cas lower than in H-1. but reduction rate of phosphorus (ratio of phosphorus in the matte t o that in the raw material) \cas higher. \\:hen fused at a lower temperature. (I2-2) r~hosphorus reduction \cas lo\vrr. '1'0 deprcss phosphorus rrduction it is desirable to kerp the mrlting point or thc raw mix lo\ver and to fuse it a t a lower temperature. Fusion at higher temperatures promotrs considerable volatilization of phosphorus, a s described later. Flow Length. Onc hundrcd parts of garnierite :\. R. o r C, lS parts of gypsum E. and 2 parts uf coke G were blended with various amounts o f phosphate rock A'. B': or C:'. Chphite crucibles were usrd. as described. Fluw length is an indication of fluidity or viscosity, and the ease of tapping the melt from thr furnace is relatrd tu its fluidity. Chemical reactions are apt to be rnore rapid i n a fluid melt than i n a viscous one. Flo\c length is also related t o citric acid solubility of t h c phosphate product? as dcscribed latcr.
90
60 IO0
70 60
50
Results and Discussion
40
Influence of Coke Addition. FifLy grams of garnierite B. 60 grams of phosphate rock C', and S grams of gypsum D \vere used in the raw mix. Figure 1 sho\vs the relation between amount of coke added and yield rate of each component, as \sell as chemical composition of the matte. Some of the added coke was burned by air. Calculation showed that when less than 10 parts of coke were added, about 60% was involved in reducing
30
1268
Conditions of Preparation Were Varied to Determine Optimum Procedure
/'
20 10 88
0.
3
5
7
10
15
Figure 1 . Effect of coke addition on chemical composition of the matte and yield rate of each component Addition of more coke raised both nickel yield and phosphorus content in the matte
INDUSTRIAL AND ENGINEERING CHEMISTRY
2
4
6
8
IO
20
Figure 2. Relationship between nickel yield rate and phosphorus content of matte under various conditions Addition of gypsum prevented phosphorus reduction, but too much gypsum promoted formation of apatite in the phosphate
N I C K E L MATTE Table 111.
No. AA'-11 AA'-17 AA'-19 BA'-10 BA'-14 BC'-10-1 BC'-10-2 BC'-13 BC'-18 CCf-12 CC'-15 AC'-17 AC'-18 AC'-19-1 AC'-19-2 AC'-19-3 AC'-19-4 AB'-lQ-l AB'-19-2 BB'-19
Many Combinations of Raw Materials Were Tested to Obtain the Most Satisfactory Products
Raw Materials Blended, Grams Phosphate Garnierite rock Gypsum Coke A 100 A' 40 15 2 A 100 A' 75 15 2 A 100 A'100 15 2 B 100 A' 30 15 2 B 100 A' 55 15 2 B 100 C' 45 10 2 20 2 B 100 C' 48 B 100 C' 65 10 2 B 100 C'120 12 3 c 100 C' 55 15 2 c 100 C' 80 15 2 A 100 C'110 12 3 A 100 C'120 12 3 A 100 (2'130 12 3 A 100 C'130 8 2.5 A 100 (2'130 4 2 0 2 A 100 C'130 A 100 B'110 15 2 10 2 A 100 B'llO B 100 B'110 12 2
Electric furnace.
Solubility, % 150 100 ml. ml
Yield - ._._
Matte, grams 8.8 14.0 15.0 9.8
Fusion
Temp., O C. 1350" 1350' 1380' 1350b 1350b 1370b 1370b 1370b 1360a 1350b 1350b 1360" 1360" 1370' 1370" 1370' 1370a 1380" 1380' 1380"
Phosphate, grams
PZOS, % 11.2 17.2 19.0 9.6 14.4 9.9 10.3 12.6 18.4 12.0 14.8 17.3 18.2 18.9 18.8 18.9 18.8 19.4 19.1 19.6
118
145 166
.*.
127
11.0
... ...
9.1 10.9 9.5 15.2 9.8 9.6 16.4 15.0 14.6 14.7 14.5
135
183
... ...
'
...
172 178 190 189
...
...
15.5 15.5 16.4
171 170 167
.
99.5 99.3 83.6 96.7 99.5 99.1 99.4 99.6 94.6 88.4 96.9 99.0 96.7 89.5 90.5 96.9 98.9 80.5 85.3 95.4
99.3 99.1 82.5 95.5 97.0
...
97.1 97.3 92.6
... ... 98.0 ...
... . . a
96.0 97.5
... ... ...
Gas furnace.
Figure 3 shows the effect of phosphorus pentoxide content on flow length of the phosphate produced with various raw materials. Product samples are identified by the code for garnierite and phosphate rock raw materials (Table I). Products identified by S were fused phosphates prepared from serpentine (Table I) and phosphate rock without gypsum or coke. The basicity of the melts, as indicated by the mole ratio of magnesia to silica, was highest for the AA' melts and lowest for the CC' melts. Thus the more basic the melt, the longer its maximum flow length and the steeper the curve of Figure 3. Also, the more basic the melt, the higher the phosphorus pentoxide content a t maximum flow length. Furnace operation in the standard
process is satisfactory when the flow length of the slag is 50 to 70 cm. a t the usual operating temperature of 1350' to 1370' C. O n this basis, the fluidity of the experimental melts AA', BA', and BC' would be adequate a t 1350' C. when their phosphorus pentoxide contents are 13 to 18%) 9 to 17%, or 8 to 17%, respectively. Softening Point. The more acidic sample (Figure 4) had a lower softening point. This explains why the melt of the more acidic sample was more viscous, had a shorter flow length, and showed a more gentle slope than in Figure 3. Softening point of each sample was lowest when it contained about 2% less phosphorus pentoxide than the sample with maximum flow length. Correlation of the data from flow length
experiments showed the melts were sufficiently fluid a t 1350' C. when their composition was in the range of 6 to 9% iron(I1) oxide, 3 to 5% alumina, 12 to 17% phosphorus pentoxide, 43 to 47% phosphorus pentoxide plus silica, 16 to 19% magnesia, and 24 to 29% calcium oxide. Citric Acid SolubLity. I n a largescale plant phosphate melt is usually quenched and crushed by a jet of water into small grains almost all of which pass a 10-mesh seive ( 5 ) . However, as laboratory products contained much larger grains which were not sufficiently quenched, it was necessary to powder the material for the citric solubility tests as described. Citric acid solubility results are shown in Table I11 and Figure 5. Samples B.4' and C C '
lllll-
I4-
I1
r
b
,,,\ $ 8 Id--II I1 Ik I6 I1 II
22
I,'';
I1
11
14
I I
1I
10
II
12
11
I8
~
II
__
28
21
2(1
Figure 3. Effect of phosphorus pentoxide content on flow length of phosphate
Figure 4. Effect of phosphorus pentoxide content on softening point of phosphate
More bask phosphates had longer Row lengths
Acidic samples had lower softenlng painh
Figure 5. Effect of phosphorus pentoxide content on citric solubility of phosphate Somples containing more than 19% phosphorus pentoxide were less than 95% soluble
VOL. 51, NO. 10
OCTOBER 1959
1269
(Figure 5) were prepdred with 100 grams of garnierite B or C. 1 5 grams of gypsum E, 2 grams of coke G, and 25 to 100 grams of phosphate rock .4 or C’; SC’ was prepared with 100 grams of serpentine S and 85 to 170 grams of phosphate rock C’. Fused phosphates containing 8 to 17vL8 phosphorus pentoxide were easily rendered as glasses soluble in 27:, citric acid. Moreover, yield rate of these samples was high (Table I\-). The maximum solubility of products B.4’ and CC’ of the garnierite process was obtained when the phosphorus pentoxide content was about 15Yc. Products made from serpentine had maximum solubilities a t about l8YC. Increasing the fusion temperature from 1350’ to 1370’ C. increased the solubility somr\\.hat. X-ray examination of several of the experimental products led to rhr folloLving results: Products that had very high citric acid solubilities consisted almost entirely of a glass Ivith very little crystalline material, similar to the usual calcium magnesium phosphate (3, 4 ) . In samples that contained 19°C or more phosphorus pentoside. considerable amounts of crystalline apatite were present. This accounts for the low citric acid solubility of these products. Products that contained less than 13 phosphorus pentoxide consisted p i marily of glass, often containing crystalline silicates or tridymite. Forsterite (2MgO,SiO?), observed in one sample (AA’-l l ) , \vas possibly formed from calcined garnierite that was not assiniilated in the melt (2). T h e citric acid solubility of the phosphorus pentoxide component of these samples usually \vas high, but in one case (CC’-l?) it \vas below 90%. This was due to the siliceous character of the glass; highsilica glass dissolves slowly in citric acid
(4.
In Table I-j0,’N.F. ratio relates the total number of oxygen atoms to the total number of network-forming ions such as phosphorus, silicon. and aluminum. Samples with a ratio of 3.3 to 3.6 were most easily rendered as soluble glasses similar to phosphates prepared by the standard method (,5). Sample A.4’19, with a ratio of 3.7, \\.as too basic and thus crystallized promptly. Samples with a ratio less than 3.3 dissolved in 2% citric acid slowly. Phosphorus Loss. Loss of phosphorus (Table IV) was caused by loss in experimental procedure a n d volatilization during fusion. At 1350’ C. less than lY0 and at 1380” C. 2 to 3% of this phosphorus volatilized. In the large-scale plant less volatilization of phosphorus occurs because the melt is usually covered by raw materials. For the production of fused calcium
1270
Table IV.
No.
AA‘-11 AA‘-17 AA’-19 BA‘-10 BA‘-14 BC‘-10-1 BC’-10-2 BC‘-13 CC‘-12 CC‘-15 AC’-19-1 AC’-19-2 AC’-19-3
Table V.
AA’-11 AA’-17 AA’-19 BA‘-10 BA‘-14 BC’-10-1 BC’-10-2 BC’-13 CC‘-12 CC’-15 AC’-19-1
Under Opiimum Conditions, Nickel and Phosphorus Pentoxide Yields Are High and Phosphorus Loss Is Low Chemical C(otiij)obitioii of Matte. % Kl Fe S 26.5 22.3 20.1 26.3 23.0 26.5 22.7 25.3 27.0 26.6 20.4 20.5 20.4
56.8 58.3 58.3 56.9 55.4 56.9 57.2 58.3 52.0 52.0 58.6
14.1 12.7 10.0 14.2 11.6 9.3 14.5 10.3 13.0 12.0 9.5
...
...
*..
...
~
s i 111
P
73.8 98.7 95.4 90.1 90.3 85.7 88.6 85.8 70.8 68.5 94.3 95.5 93.5
5.5
5.5 8.4 5.5 4.9 7.7 5.8 4.1 9.0 7.0 8.3 10.4 10.2
93.0 93.4 89.0
1.5 1.5 2.6
93.8
1.3
... ... 92.2 ... ... ...
87.4 85.1
...
...
... ... ... ...
2.0
4.3 4.5
...
Chemical Composition of Phosphate Determines Its Flow Length, Softening Point, and Citric Solubility
30.8 25.0 21.8 34.6 30.4 34.0 33.6 31.2 37.7 36.4 27.3
3.0 2.8 2.5 5.1 4.0 4.7 4.7 4.2 4.1 3.8 3.8
10.3 8.6 7.1 11.9 8.7 10.5 10.5 9.5 9.5 8.2 3.5
Total nuinlwr of oxygen utoiiis’total
23.0 18.4 15.6 19.4 16.8 18.4 18.0 16.0 12.8 12.4 15.5
21.3 29.1 32.2 19.0 24.3 20.9 21.5 24.8 20.3 24.4 32.0
iiiitiilier
magnesium phosphate togrthcr Xvitli nickel matte, optimum composition of the fused phosphate is as follows: 12. to 17YGphosphorus pentoxide; 16 to 19% magnesia; niagnvsia I O silica inole ratio, 0.8 to 1.1; O/S.I.’.ratio. i.? to 3.6 The best blending ratio of gypsum is 10 to 15 parts 10 100 parts o f garnierite to produce fused phosphate containine; more than 15(% phosphorus penroxide and a little more for fused phosphates containing lrss phosphorus pentoxide. Coke should be blended such that the amount of carbon involved in reducing raw materials is betxveen 3.5 to 4 parts to 100 parts of garnieritr. Fusion at 1350’ C. produces about 90% of the nickel in garnierite as matte, together with more than 927, of thc phosphorus pentoxide in phosphate rock as fused phosphate fertilizer Xvhich is more than 97y0 soluble to 2f% citric acid. T o produce fused phosphate containing more than 18% phosphorus pentoxide, a higher temperature is required and reduction of phosphorus increases. Although the use of garnierite containing a high proportion of magnesia is best, the use of magnesium sulfate instead of gypsum may improve results still more. Garnierite C (‘Table I ) is not suitable for producing fused phosphate containing more than 15% phosphorus pentoxide because its magnesia content is too lo\\.. It may he uscd to
INDUSTRIAL AND ENGINEERING CHEMISTRY
IllnitP
3.9 4.1 8.7 2.6 3.8 5.2 3.5 3.8 6.9 8.0 9.7 11.2 10.7
Yield ltate, Yo_ _ _ _ . __ __ I,n+ C,f P in P2OS 111 niat t v phosphnte I’, c/b
i,f
11.2 17.2 19.0 9.6 14.4 9.9 10.3 12.6 12.0 14.8 18.9
1.1 1.1 1.1 0.82 0.83 0.80 0.80 0.76 0.51 0.51 0.85
3.5 3.6 3.7 3.2 3.3 3.2 3.3 3.3 3.0 3.1 3.4
i i r t a r ~ r 6 - f i ~ r m i 1I iOgI I ~
producc. low q a d e fused phosphate il blended with phosphate rock containing a high calcium oxide content anti less silica or if tilore gypsum or i n > i ~ nesium sulfate is acldcd. In producing higher grade phosphatc. the ratio o f phosphate fertilizrr to nickel produced is higher than in production of lo\ver grade fusrd phosphate. Phosuhorus pentoxide content of the fuscd phosphatt: to be produced should hc detrrmined hg cur’rent prices and dc.mand !or both nickrl and phosphate, fertilizer. Acknowledgment
Thanks are cxtcnded to Shimurakako Co., Ltd., Tokyo, for samples of garnieritr. and to H. Shimada of that company for assistance with chernical analyses. literature Cited (1 I . l n i , Soc. .I’esting Materials: Philadelphia, Pa., C2 24-46. (2) Ando: J., k’u~yyo K q a k u %asshi 60,
1101 (1957).
( 3 ) Hill, W. I,., LVard, F’. N.: ArInigci., W. H., Jacob, K. I]., J . Asruc. (@c. A g r . Chemists 31, 381 (19481. (4) Nagai, S., Ando, J., Kogyo K R , ~ O X I I Za.rshi 54, 495 (1951). ( 5 ) Ibid., 55, 433 (1952).
RECEIVED for review September 22, 1958 Accee~ImDrccinhrr 15. l(l.58
