[0001] THIS INVENTION relates to the production of ferronickel from nickel containing laterite and, more
particularly, is concerned with a process whereby it may be possible to utilise laterite
fines and dust, large quantities of which have been stockpiled over the years as feedstock.
Possibly more importantly, the invention relates to a process in which production
costs can be decreased with the added consequence that processing of previously uneconomical
ore bodies may become viable.
[0002] The 'oxidised' ores of nickel constitute by far the world's largest known reserves
of this metal. The term 'oxidised' is meant to include not only the true laterites,
in which the nickel oxide is intimately associated with limonitic iron oxide, but
also the silicate ores which often contain the mineral garnierite. These oxidised
ores are found in regions of the world where tropical weathering occurs, or where
at least sub-tropical conditions have prevailed in geological times.
[0003] Mined laterite ore, being of a porous nature, can hold a large content of free moisture,
commonly 25 to 30 percent H
2O, although it can contain as much as 40 percent or more. Moreover, combined water,
which is not driven off until a temperature of 700 to 800°C is reached, can amount
to up to 15 per cent based on the dry ore weight. This indicates the necessity of
drying and preferably calcining the ore before smelting.
[0004] Because of the friable nature of laterites, run-of-mine ore is normally screened
as the first step of a ferronickel operation. In the screening operation alone, up
to 50 percent undersize particles may be screened out because of the difficulties
in effecting a physical separation of wet laterite at a lower size than 6 to 8mm.
This material would then require some form of agglomeration (e.g. sintering or pelletising)
before further processing. It is conceivable that the material could be dried before
screening to say 1 or 2mm prior to calcining.
[0005] Lateritic Ni-ferrous ores or garnierite are typically treated by preheating and/or
calcination and/or prereduction before they entered into the electric furnace or arc
furnace for final reduction (US-A-3535105, FR-A-508 508 or Handbook of Extractive
Metallurgy pp. 759-763, WILEY 1997).
[0006] However, fines and dust are generated in the drying process and dust generation in
the calcining step is also increased. In the drying/calcining step large amounts of
fines/dust are generated which are unsuitable for smelting in a conventional electric
arc furnace. Once again, these fines need to be extracted and, if they are to be utilised,
need to be agglomerated at considerable expense. If dusts are captured in a wet scrubber
and returned with the fresh ore to the drier, the dust recycle load in the circuit
would increase with a consequent increase in the energy requirements for drying.
[0007] Waste dusts, in particular AOD or other dusts, containing oxides of metals are normally
treated in light-arc or plasma-arc furnaces together with a reductant, in order to
recover the metal values (SE-A-447996, WO-A- 92/03896.
[0008] Added to previously mentioned problem is one of the chemical composition of the laterite.
The composition usually varies considerably and often one body of ore will have an
undesirably high Si:Mg ratio. A normal electric furnace is difficult to operate with
a Si:Mg ratio of greater than 2.0. Also, some ore bodies have an iron content of greater
than 20% by weight, and such high iron contents are unworkable in a normal furnace
as it tends to cause slag foaming.
[0009] The solution employed at present to the problems associated with the chemical composition
of the ore is to blend different ores to provide an acceptable feedstock for a normal
furnace. This is, to say the least, inconvenient and costly.
[0010] It is an aim of this invention to provide a process for the thermal reduction and
smelting of nickel-containing laterites in which the disadvantages outlined above
are, at least to a significant extent, obviated.
[0011] In accordance with this invention there is provided a process for the reduction and
smelting of nickel containing laterite ore fines, said fines having a SiO
2/MgO ratio of from 1.2:1 to 3:1, being calcined, preheated and being screened to a
particle size of less than 2mm, the process comprising continuously feeding said fines
simultaneously with sufficient carbonaceous reductant to achieve a desired degree
of reduction of the nickel oxide present, into the central region of the molten bath
of a cylindrical furnace of a DC transferred arc plasma furnace having one or more
electrodes situated in the roof acting as cathode and the molten bath acting as an
anode; and periodically or continuously with-drawing nickel depleted slag and unrefined
ferronickel from the furnace.
[0012] Preferred features of the invention provide for a frozen lining to be maintained
between the molten bath and the refractory lining by controlling the power and feedrate
supplied to the furnace and optionaly water-cooling the furnace sidewalls; for the
electrodes situated in the roof of the furnace to be graphite electrodes; for there
to be only one such electrode which is located centrally; for the one or more electrodes
to be hollow in which case reactants are preferably introduced into the furnace by
way of the bore of such hollow electrode or electrodes; and for air to be substantially
excluded from the interior of the furnace in which case enhancement of the exclusion
of air may be achieved by operating the furnace at a slightly positive pressure.
[0013] Preferably, the feed material is dried, calcined, preheated, or pre-reduced, in any
combination thereof.
[0014] Further preferred features of the invention provide for the recovery of energy by
using the thermal calorific value of the off-gases from the furnace, optionally after
cleaning, to dry, calcine, preheat or pre-reduce the feed material; and for the feed
material to include recycled slag produced in a downstream converter for purifying
the unrefined ferronickel product produced in the process of the invention.
[0015] Preferably, the laterite feed material is dried and calcined prior to being fed to
the furnace.
[0016] The invention still further provides, as one alternative thereof, for the laterite
to be pre-reduced to meet a required final ferronickel specification, prior to introduction
into the furnace. Preferably, the feed material is milled prior to or following calcining
and the milled feed material is subjected to pre-reduction prior to being fed to the
furnace.
[0017] Preferably, the prereduction is carried out in a fluidised reduction reactor using
gaseous reductants or gases generated from solid reductants combusted in the reactor.
[0018] In such a case the laterite ore is preferably dried first followed by dry milling;
and calcining at about 700 to 800°C in a fluidised calciner. The calcined laterite
is then pre-reduced in a fluidised reduction reactor at about 800-850°C prior to feeding
to the furnace bath as defined above.
[0019] In one particularly preferred embodiment, drying is carried out at a temperature
of about 150°C; calcining at about 700 - 800°C, and prereduction at a temperature
of about 800 - 850°C.
[0020] This variant of the process of the invention has even greater advantages in cases
where the SiO
2:MgO ratio is what would normally be regarded as excessively high. No SiO
2 would be reduced in the pre-reduction step and accordingly does not appear in the
molten metal produced in the furnace. Also, by selective pre-reduction of NiO and
Fe
2O
3 in the pre-reduction step the ratio of Ni to Fe in the metal can be effectively controlled.
A smaller furnace, by comparison, is thus foreseen in such a variant of the invention
since melting requires less energy than smelting, especially if SiO
2 were also to be reduced to some extent in the smelting process.
[0021] Clearly, in all cases the feed rate of materials and the energy input into the furnace
are adjusted to achieve and maintain desired bath and tapping temperatures of both
slag and molten metal as well as, where required, the protective freeze lining to
protect the furnace lining against excessive wear. Such a protective lining is regarded
as essential to the protection of the furnace in all cases where the SiO
2 to MgO ratio is greater than 1,5.
[0022] Preferably, the carbonaceous reductant is employed in such quantities that the nickel
content of the slag is below 0,1 percent and to ensure that oxygen in the off-gases
is substantially in the form of carbon monoxide and the temperature of the furnace
is controlled to between 1500 and 1600°C.
[0023] The most important advantage of the process is the fact that a wide range of laterite
ores can be processed. This is due to the fact that in the d.c. transferred arc plasma
furnace the electrical resistance is mainly in the arc and to a lesser extent in the
open-bath slag. In particular the advantages are illustrated in the examples below.
Example 1 demonstrates the smelting of laterite ore fines and dusts (even 100%<100µm);
the smelting of partially calcined laterite ores; and, the smelting of nickel-containing
slags; which can be recycled from a subsequent converter or refining step.
[0024] In example 2, there is illustrated the smelting of laterite types over a wide range
of SiO
2/MgO ratios, ie. 1,2 to 3,0; and, the smelting of laterite types over a wide range
of Fe contents ie. 14 to 20%. Additional advantages with respect to the open bath
smelting technology include i) the control of the bath temperature to control slag
foaming with high iron containing slags, and ii) effective control of the reductant
requirement since there is no contact between the graphite electrode and the melt.
[0025] Although, in the examples mentioned above, feed materials were not pre-reduced, the
above features would make it possible to conduct a final reductant trimming addition
to the furnace if pre-reduced materials were to be smelted. Since the d.c. plasma
furnace can smelt fine materials, a fluid bed reactor can be linked up with the plasma
furnace as in the case of example 2. Although in the example feed materials were only
preheated with liquid petroleum gas, one could conduct pre-reduction using a carbonaceous
reductant (solid or gaseous) or alternatively, and preferably, furnace off gases to
effect preheating/pre-reduction. Preferably, the carbonaceous reductant is employed
in such quantities that the nickel content of the slag is below 0,1%.
[0026] In order that the invention may be more fully understood, examples thereof will now
be described in greater detail. In the description of example 2 reference will be
made to the accompanying drawings.
[0027] In the drawings:-
- FIG. 1
- is a schematic sectional elevation of a furnace; and,
- FIG. 2
- is a similar view of a fluidised bed.
EXAMPLE 1
[0028] In this example tests were conducted in a 100 kVA furnace manufactured by the applicant.
The furnace was of a known d.c. plasma-arc furnace type employing a single graphite
electrode located centrally above the furnace bath. A direct current power supply
was employed in which the molten bath formed, in use, the anode, while the graphite
electrode formed the cathode.
[0029] The furnace which had an outside diameter of 600mm and a refractory lining thickness
of 114mm, was lined with a refractory material wherein the MgO content was approximately
96 percent. The hearth was lined with a chrome-magnesite rammable material to a thickness
of 310mm and a number of mild steel rods were used to make the d.c. (anode) electrical
connection from the molten bath through the hearth refractory to the anode cable.
The molten bath in the furnace was heated to the desired operating temperature, with
an initial metal charge.
[0030] The feed materials consisted of calcined laterite dust (<100µm) from an industrial
rotary kiln calciner (Tests A and C), -6mm laterite ore fines calcined at 250°C (Tests
B and D) and -4mm charcoal (all four tests), having the compositions detailed in Table
1. The feed materials were passed through a feed port in the furnace roof into the
reaction zone and the liquid products were tapped intermittently from the furnace.
For Test D a somewhat smaller furnace shell, with water-cooling of the sidewalls,
was used on the 100 kVA power supply, to increase the number of samples obtainable
at the scale of operation.
[0031] Results of the smelting tests showing metal, and slag compositions are given in Table
2.
TABLE 1
CHEMICAL ANALYSIS OF THE FEED MATERIALS (MASS %) |
Component |
Laterite fines (calcined @ 250° C) |
Laterite dust |
Charcoal |
NiO |
1,96 |
2,45 |
- |
Fe2O3 |
39,1 |
36,8 |
- |
MgO |
12,2 |
17,5 |
0,2 |
SiO2 |
30,7 |
34,4 |
4,3 |
Al2O3 |
5,60 |
3,83 |
0,8 |
CaO |
0,50 |
0,25 |
0,4 |
MnO |
0,69 |
0,58 |
- |
Cr2O3 |
2,51 |
1,15 |
- |
Fixed Carbon |
- |
0,79 |
64,0 |
Moisture |
9,17 |
2,0 |
5,6 |
Volatiles |
- |
- |
23,3 |
TABLE 2A
SMELTING OF FERRONICKEL FROM LATERITE FINES AND DUST |
Test Series |
Batch |
Mild Stell % |
Laterite Fines % |
Dust % |
Charcoal (kg) |
Slag (kg) |
Ferronickel (kg) |
Slag (kg) |
A |
Start |
1.50 |
|
|
|
|
|
|
|
1 |
|
|
5.90 |
0.51 |
|
|
|
|
2 |
|
|
7.00 |
0.52 |
|
|
4.30 |
|
3 |
|
|
7.00 |
0.44 |
|
0.22 |
9.50 |
|
4 |
|
|
7.00 |
0.44 |
|
0.12 |
8.30 |
|
5 |
|
|
7.00 |
0.37 |
|
1.86 |
16.60 |
B |
1 |
|
7.00 |
|
0.60 |
|
|
|
|
2 |
|
7.00 |
|
0.52 |
|
|
|
|
3 |
|
7.00 |
|
0.44 |
|
|
5.10 |
|
4 |
|
7.00 |
|
0.44 |
|
|
4.20 |
|
5 |
|
10.00 |
|
0.63 |
|
|
8.60 |
|
6 |
|
7.00 |
|
0.37 |
|
|
27.50 |
C |
Start |
6.00 |
1.00 |
|
|
|
|
|
|
1 |
|
|
10.00 |
0.63 |
|
|
|
|
3 |
|
|
10.00 |
0.63 |
|
0.08 |
21.40 |
Furnace Contents |
|
|
|
|
|
|
7.00 |
8.60 |
D |
Start |
47.5 + 1.5Ni |
|
|
|
|
|
|
|
1 |
|
|
|
0.11 |
4.90 |
0.20 |
2.30 |
|
2 |
|
|
|
0.11 |
4.00 |
0.78 |
2.50 |
|
3 |
|
|
|
0.12 |
5.00 |
|
2.10 |
|
4 |
|
5.00 |
|
0.70 |
|
|
3.30 |
|
5 |
|
5.00 |
|
0.70 |
|
0.27 |
2.60 |
|
6 |
|
5.00 |
|
0.84 |
|
8.00 |
4.90 |
TABLE 2B
METAL ANALYSES (MASS %) |
Test |
Tap # |
Ni |
Fe |
Si |
Cr |
P |
S |
C |
A |
3 |
0.06 |
99.10 |
0.15 |
0.08 |
|
|
|
|
4 |
0.21 |
99.60 |
0.11 |
0.05 |
|
|
|
|
5 |
14.70 |
84.30 |
0.05 |
0.06 |
0.02 |
0.10 |
0.05 |
C |
3 |
7.82 |
90.50 |
0.18 |
0.04 |
|
|
0.10 |
Digout |
|
8.43 |
90.90 |
0.02 |
0.05 |
|
0.22 |
0.02 |
D |
5 |
23.30 |
72.80 |
0.75 |
0.20 |
|
|
|
|
6 |
16.60 |
83.10 |
0.05 |
0.40 |
|
|
|
TABLE 2C
SLAG ANALYSES (MASS %) |
Test |
Tap # |
NiO |
FeO |
SiO2 |
Cr2O3 |
MgO |
CaO |
MnO |
Al2O3 |
A |
2 |
0.11 |
43.10 |
20.30 |
5.45 |
27.60 |
0.21 |
0.52 |
4.67 |
|
3 |
0.06 |
42.08 |
21.40 |
4.98 |
27.00 |
0.02 |
0.53 |
3.99 |
|
4 |
0.04 |
41.90 |
23.20 |
4.88 |
27.00 |
0.02 |
0.53 |
4.05 |
|
5 |
0.19 |
40.20 |
17.70 |
6.23 |
30.90 |
0.02 |
0.47 |
4.72 |
B |
3 |
1.37 |
36.70 |
25.40 |
4.74 |
26.50 |
0.40 |
0.57 |
5.89 |
|
4 |
1.35 |
37.90 |
24.90 |
4.69 |
24.80 |
0.46 |
0.60 |
5.80 |
|
5 |
1.04 |
38.50 |
26.80 |
3.70 |
24.30 |
0.49 |
0.63 |
6.14 |
|
6 |
1.18 |
37.30 |
28.00 |
4.12 |
25.30 |
0.40 |
0.59 |
5.55 |
C |
3 |
0.15 |
29.90 |
29.30 |
4.09 |
28.30 |
0.39 |
0.65 |
4.73 |
D |
1 |
0.24 |
32.30 |
25.00 |
3.73 |
29.30 |
0.55 |
0.96 |
7.10 |
|
2 |
0.88 |
33.10 |
24.80 |
4.21 |
29.80 |
0.55 |
0.72 |
6.43 |
|
3 |
0.01 |
33.40 |
26.50 |
3.13 |
28.30 |
0.64 |
0.74 |
6.93 |
|
4 |
0.03 |
23.00 |
34.10 |
3.83 |
28.40 |
0.70 |
1.12 |
8.51 |
|
5 |
0.71 |
26.00 |
34.30 |
2.85 |
27.40 |
0.76 |
1.00 |
8.16 |
|
6 |
0.19 |
16.50 |
36.70 |
3.55 |
32.90 |
0.70 |
0.95 |
8.83 |
[0032] From the above it will be seen that even extremely fine (<100 µm) nickel-containing
laterite can be utilised effectively in a d.c. plasma-arc furnace. Nickel levels could
be stripped from the produced slag to less than 0,1%, when laterite fines and dusts
were smelted as well as when nickel-containing slags were processed.
EXAMPLE 2
[0033] A 200 kVA d.c. transferred arc plasma facility was used in this example. The furnace,
as shown in Fig. 1 comprised a water-cooled refractory lined shell 1 and conical roof
2, a graphite electrode and an anode configuration comprising various pins 3 protruding
the hearth refractory 4. Sidewall and hearth refractories were of a high quality magnesite
type. The internal diameter of the furnace was 760mm. There were two tapholes ie.
a bottom taphole 5 for metal product and a top taphole 6 for slag drainage. The two
taphole system ensured efficient metal/slag separation. Four ports 7 were located
in the furnace roof, namely an electrode entry port 7a a view port (not shown), a
gas extraction port 7b and a feed port 7c. Not shown are ancillaries namely the power
supply, control system, gas cleaning system and water circuits. Fig. 2 shows the LPG
heated fluid bed reactor which had been used to preheat the calcined laterite feed
to about 600°C prior to smelting the preheated materials in a few cases in test 2
(FBR). The FBR had an inlet 8 for laterite, and an outlet 9 opposite the inlet, a
lower inlet 10 for fluidising air and liquid petroleum gas (LPG) and an off gas outlet
11. A change in diameter of the interior of the reactor and located between the material
inlet 8 and outlet 9, forms the region in which the solids become less fluidised,
to limit fines carry over to the off gas 11.
[0034] The laterites, when dried, had a loss on ignition (LOI) value of 11,5%. Prior to
the smelting testwork, the laterite ores were calcined to a residual LOI of 6,5%.
[0035] The smelting campaign was conducted on a continuous basis over a period of 7 days,
and about 7,2 tons total material was smelted. Table 3 summarises on a tap-to-tap
basis, the Ni content of the metal and slag, as well as the SiO
2/MgO ratios and iron contents in the laterite and the slag.
[0036] For the purposes of all tests that were conducted by feeding the laterite directly
to the furnace, the laterite was screened to a particle size of minus 8mm. In the
case of heating at 600C (in a fluidised bed reactor (see tests indicated by FBR in
Table 3)) prior to feeding to the furnace the feed material was screened to minus
2mm.
TABLE 3
Test No |
Tap No |
Laterite Batch kg |
Coal Batch kg |
Fixed carbon * |
% Ni in Metal |
% NiO in Slag |
Desgn SiO2/ MgO Ratio |
Actual SiO2/ MgO Ratio |
% Fe in Laterite |
% Fe in Slag |
Warm up* |
Warm up |
50 |
|
|
|
|
|
|
|
|
1 |
1 |
96.2 |
2.10 |
0.96 |
4.34 |
0.04 |
1.51 |
1.56 |
17.25 |
78.60 |
1 |
2 |
62.6 |
10.00 |
6.22 |
6.10 |
0.04 |
1.51 |
1.44 |
17.25 |
21.80 |
1 |
3 |
100 |
10.00 |
4.10 |
5.69 |
0.13 |
1.51 |
1.44 |
17.25 |
11.90 |
1 |
4 |
100 |
10.00 |
4.10 |
|
0.52 |
1.51 |
1.41 |
18.37 |
16.90 |
1 |
5 |
26.2 |
10.00 |
12.47 |
|
0.17 |
1.51 |
1.31 |
18.37 |
16.10 |
1 |
6 |
100 |
10.00 |
4.10 |
7.82 |
0.04 |
1.51 |
1.47 |
17.80 |
7.50 |
1 |
7 |
100 |
10.00 |
4.10 |
9.07 |
0.09 |
1.51 |
1.45 |
17.31 |
10.20 |
1 |
8 |
100 |
10.00 |
4.10 |
1.78 |
0.09 |
1.51 |
1.51 |
17.56 |
10.00 |
1 |
9 |
100 |
7.00 |
2.95 |
12.50 |
0.22 |
1.51 |
1.51 |
16.91 |
10.20 |
1 |
10 |
100 |
5.00 |
2.15 |
|
0.86 |
1.51 |
1.52 |
16.82 |
20.00 |
1 |
11 |
100 |
5.00 |
2.15 |
|
0.80 |
1.51 |
1.46 |
16.77 |
28.90 |
1 |
12 |
100 |
7.00 |
2.95 |
|
0.26 |
1.51 |
1.36 |
16.85 |
29.80 |
1 |
13 |
100 |
7.00 |
2.95 |
3.58 |
0.11 |
1.51 |
1.39 |
17.15 |
30.80 |
1 |
14 |
100 |
8.50 |
3.54 |
1.23 |
0.16 |
1.51 |
1.52 |
17.56 |
21.30 |
1 |
15 |
100 |
8.50 |
3.54 |
0.90 |
0.07 |
1.51 |
1.66 |
17.56 |
17.80 |
1 |
16 |
100 |
7.00 |
2.95 |
|
0.04 |
1.51 |
1.32 |
17.74 |
17.10 |
1 |
17 |
100 |
7.50 |
3.15 |
19.90 |
0.04 |
1.51 |
1.41 |
15.95 |
15.40 |
1 |
18 |
100 |
7.50 |
3.15 |
|
0.06 |
1.51 |
1.38 |
16.57 |
26.40 |
2 |
19 |
100 |
7.50 |
3.15 |
|
1.21 |
|
14.47 |
18.90 |
|
2 |
20 |
50 |
3.75 |
3.15 |
|
|
1.21 |
|
14.61 |
|
2 |
21 |
50 |
3.75 |
3.15 |
20.70 |
0.04 |
1.21 |
1.13 |
15.03 |
|
2 |
22 |
200 |
15.00 |
3.15 |
|
|
1.21 |
|
15.03 |
16.50 |
2 |
23 |
100 |
7.50 |
3.15 |
17.90 |
0.04 |
1.21 |
1.25 |
15.83 |
|
2 |
24 |
100 |
7.50 |
3.15 |
|
|
1.21 |
|
14.94 |
13.50 |
2 |
25 |
150 |
11.25 |
3.15 |
|
0.07 |
1.21 |
1.20 |
14.94 |
|
2 |
26 |
50 |
3.75 |
3.15 |
17.80 |
0.04 |
1.21 |
1.20 |
14.92 |
11.30 |
2 |
27 |
100 |
7.30 |
3.07 |
|
|
1.21 |
|
14.96 |
10.90 |
2 |
28 |
150 |
10.95 |
3.07 |
|
0.04 |
1.21 |
1.21 |
15.00 |
|
2 |
29 |
50 |
3.65 |
3.07 |
16.40 |
0.04 |
1.21 |
1.21 |
14.65 |
15.30 |
2 |
30 |
100 |
7.30 |
3.07 |
|
|
1.21 |
|
14.72 |
13.50 |
2 |
31 |
150 |
10.95 |
3.07 |
|
0.04 |
1.21 |
1.14 |
14.49 |
|
2 |
32 |
50 |
3.65 |
3.07 |
16.30 |
0.07 |
1.21 |
1.19 |
14.69 |
9.80 |
2 |
33 |
100 |
7.00 |
2.95 |
|
|
1.21 |
|
14.87 |
12.90 |
2 |
34 |
150 |
10.50 |
2.95 |
|
0.07 |
1.21 |
1.20 |
14.77 |
|
2 |
35 |
50 |
3.50 |
2.95 |
|
|
1.21 |
|
14.53 |
13.10 |
2 |
36 |
50 |
3.50 |
2.95 |
15.70 |
0.12 |
1.21 |
1.14 |
14.63 |
|
FBR |
37 |
250 |
16.25 |
2.76 |
16.80 |
0.08 |
1.21 |
1.36 |
14.61 |
13.5 |
FBR |
38 |
250 |
16.25 |
2.76 |
16.40 |
0.51 |
1.21 |
1.24 |
15.03 |
17.9 |
FBR |
39 |
250 |
16.25 |
2.76 |
18.10 |
0.36 |
1.21 |
1.32 |
14.98 |
17.80 |
FBR |
40 |
169.3 |
9.29 |
2.35 |
18.90 |
0.65 |
1.21 |
1.25 |
14.99 |
22.30 |
3 |
41 |
100 |
6.50 |
2.76 |
|
|
1.50 |
19.05 |
21.60 |
|
3 |
42 |
150 |
9.75 |
2.76 |
|
0.11 |
1.50 |
1.29 |
19.60 |
|
3 |
43 |
50 |
3.25 |
2.76 |
16.10 |
0.11 |
1.50 |
1.31 |
19.54 |
14.90 |
3 |
44 |
100 |
6.50 |
2.76 |
22.60 |
0.51 |
1.50 |
1.40 |
19.56 |
16.40 |
3 |
45 |
150 |
9.00 |
2.56 |
|
|
1.50 |
|
19.49 |
24.20 |
3 |
46 |
100 |
6.00 |
2.56 |
|
0.10 |
1.50 |
1.52 |
19.22 |
|
3 |
47 |
50 |
3.00 |
2.56 |
19.90 |
0.11 |
1.50 |
1.51 |
19.71 |
24.50 |
3 |
48 |
100 |
6.00 |
2.56 |
|
|
1.50 |
|
19.12 |
26.80 |
3 |
49 |
150 |
9.00 |
2.56 |
|
0.09 |
1.50 |
1.41 |
19.07 |
|
3 |
50 |
50 |
3.00 |
2.56 |
21.30 |
0.16 |
1.50 |
1.44 |
19.31 |
26.00 |
3 |
51 |
100 |
6.00 |
2.56 |
|
|
1.50 |
|
20.62 |
26.60 |
3 |
52 |
150 |
9.00 |
2.56 |
|
0.15 |
1.50 |
1.40 |
18.97 |
|
3 |
53 |
50 |
3.00 |
2.56 |
23.30 |
0.27 |
1.50 |
1.43 |
19.01 |
27.00 |
4 |
54 |
100 |
6.00 |
2.56 |
|
|
1.71 |
|
14.80 |
27.70 |
4 |
55 |
150 |
9.00 |
2.56 |
|
0.06 |
1.71 |
1.52 |
14.77 |
|
4 |
56 |
50 |
3.00 |
2.56 |
22.10 |
0.18 |
1.71 |
1.56 |
14,84 |
19.90 |
4 |
57 |
100 |
6.00 |
2.56 |
|
|
1.71 |
|
14.93 |
19.20 |
4 |
58 |
150 |
9.00 |
2.56 |
|
0.10 |
1.71 |
1.71 |
14.82 |
|
4 |
59 |
50 |
3.00 |
2.56 |
23.20 |
0.07 |
1.71 |
1.69 |
15.96 |
20.50 |
4 |
60 |
100 |
6.00 |
2.56 |
|
|
1.71 |
|
15.29 |
20.90 |
4 |
61 |
150 |
9.00 |
2.56 |
|
0.06 |
1.71 |
1.54 |
15.00 |
|
4 |
62 |
50 |
3.00 |
2.56 |
21.50 |
0.25 |
1.71 |
1.59 |
15.29 |
16.10 |
5 |
63 |
100 |
6.00 |
2.56 |
|
|
3.00 |
|
19.83 |
17.10 |
5 |
64 |
150 |
9.00 |
2.56 |
|
0.09 |
3.00 |
218 |
19.61 |
|
5 |
65 |
50 |
3.00 |
2.56 |
21.70 |
0.10 |
3.00 |
2.14 |
20.69 |
20.20 |
5 |
66 |
100 |
6.00 |
2.56 |
|
|
3.00 |
|
20.69 |
18.20 |
5 |
67 |
150 |
9.00 |
2.56 |
|
|
3.00 |
|
20.69 |
|
5 |
68 |
50 |
3.00 |
2.56 |
20.20 |
0.43 |
3.00 |
2.37 |
20.69 |
|
* kg Carbon/ 100 kg feed material |
[0037] It is envisaged that an extremely effective and economic process is provided by this
invention in that in addition to the smelting of a wider range of conventional laterite
blends, laterite ores (crushed or uncrushed, dried or undried, calcined or uncalcined)
and dusts can also be utilised directly in the production of ferronickel.
[0038] It is also envisaged that the process of this invention can be combined with various
other processes or operations to form a variety of combined processes. These include
processes in which a fraction or all of the reductant in added in a reactor and any
remainder is added to the furnace; processes in which a conventional process applied
to coarse laterites and the process of the invention is applied in parallel, to the
fines which may even be constituted by a waste stream (eg. kiln dust); and processes
in which the invention is included in to a conventional arrangement having conventional
upstream processing steps as well as downstream refining steps (drying, calcining/prereduction)
to lower P,S,C and Si, and Cr contents of the ferronickel produced.
1. A process for the reduction and smelting of nickel containing laterite ore fines,
said fines having a SiO2/MgO ratio of from 1.2:1 to 3:1, and being calcined, preheated and screened to a particle
size of less than 2 mm; the process comprising continuously feeding said fines simultaneously
with sufficient carbonaceous reductant to achieve a desired degree of reduction of
the nickel oxide present, into the central region of the molten bath of a cylindrical
furnace of a DC transferred arc plasma furnace having one or more electrodes situated
in the roof acting as cathode and the molten bath acting as an anode; and periodically
or continuously with-drawing nickel depleted slag and unrefined ferronickel from the
furnace.
2. A process as claimed in claim 1 in which a frozen lining is maintained between the
molten bath and the refractory lining by controlling the power and feedrate supplied
to the furnace, and optionally by water cooling the furnace sidewalls.
3. A process as claimed in any one of the preceding claims in which the feed material
is dried, calcined, preheated, or pre-reduced, in any combination thereof.
4. A process as claimed in any one of the preceding claims in which the feed material
includes recycle slag produced in a downstream converting or refining step for upgrading
the unrefined ferronickel product produced by this process.
5. A process as claimed in any one of the preceding claims in which the laterite feed
material is dried and calcined prior to being fed to the furnace.
6. A process as claimed in claim 5 in which the feed material in milled prior to or following
calcining and the milled feed material is subjected to pre-reduction prior to being
fed to the furnace.
7. A process as claimed in claim 6 in which the prereduction is carried out in a fluidised
reduction reactor using gaseous reductants or gases generated from solid reductants
combusted in the reactor.
8. A process as claimed in any one of claims 5 to 7 in which drying is carried out at
a temperature of about 150°C; calcining at about 700 - 800°C, and prereduction at
a temperature of about 800 - 850°C.
9. A process as claimed in any one of the preceding claims in which the electrodes situated
in the roof of the furnace are graphite electrodes.
10. A process as claimed in any one of the preceding claims in which there is only one
centrally located electrode in the roof of the furnace.
11. A process as claimed in any one or the preceding claims in which air is excluded in
the interior of the furnace and the furnace is operated at a slight positive pressure
to enhance such exclusion.
1. Verfahren zur Reduktion und zum Schmelzen von nickelhaltigen Lateriterz-Feinstoffen,
die ein SiO2/MgO-Verhältnis von 1,2:1 bis 3:1 haben und kalziniert, vorerhitzt und auf eine Teilchengröße
von weniger als 2 mm gesiebt werden, wobei man in diesem Verfahren, um einen erwünschten
Reduktionsgrad des vorhandenen Nickeloxids zu bekommen, kontinuierlich die Feinstoffe
gleichzeitig mit genügend kohlenstoffhaltigem Reduktionsmittel in den Mittelbereich
des geschmolzenen Bades eines zylindrischen Ofens eines Gleichstromübertragungs-Lichtbogenplasmaofens
mit einer oder mehreren Elektroden, die in der Decke angeordnet sind und als Kathode
wirken, während das geschmolzene Bad als eine Anode wirkt, einspeist und periodisch
oder kontinuierlich nickelverarmte Schlacke und nicht raffiniertes Ferronickel aus
dem Ofen abzieht.
2. Verfahren nach Anspruch 1, bei dem man eine gefrorene Schicht zwischen dem geschmolzenen
Bad und der hitzebeständigen Auskleidung aufrechterhält, indem man die Stärke und
Beschickungsgeschwindigkeit zu dem Ofen steuert und gegebenenfalls die Ofenseitenwände
mit Wasser kühlt.
3. Verfahren nach einem der vorausgehenden Ansprüche, bei dem das Beschickungsmaterial
in irgendeiner Kombination getrocknet, kalziniert, vorerhitzt oder vorreduziert wird.
4. Verfahren nach einem der vorausgehenden Ansprüche, worin das Beschickungsmaterial
zur Verbesserung des nach diesem Verfahren erzeugten ungereinigten Ferronickelprodukts
Rückführschlacke enthält, die in einer Abstromumwandlungs- oder -reinigungsstufe hergestellt
wurde.
5. Verfahren nach einem der vorausgehenden Ansprüche, bei dem das Laterit-Beschickungsmaterial
vor dem Einspeisen in den Ofen getrocknet und kalziniert wird.
6. Verfahren nach Anspruch 5, in welchem das Beschickungsmaterial vor oder nach der Kalzinierung
vermahlen und das vermahlene Beschickungsmaterial vor dem Einspeisen in den Ofen einer
Vorreduktion unterzogen wird.
7. Verfahren nach Anspruch 6, in welchem die Vorreduktion in einem fluidisierten Reaktionsreaktor
unter Verwendung gasförmiger Reduktionsmittel oder Gase, die aus festen Reduktionsmitteln,
die in dem Reaktor verbrannt werden, erzeugt wurden, durchgeführt wird.
8. Verfahren nach einem der Ansprüche 5 bis 7, in welchem Trocknung bei einer Temperatur
von etwa 150°C, Kalzinieren bei etwa 700-800°C und Vorreduzieren bei einer Temperatur
von etwa 800-850°C erfolgt.
9. Verfahren nach einem der vorausgehenden Ansprüche, worin die in der Decke des Ofens
angeordneten Elektroden Graphitelektroden sind.
10. Verfahren nach einem der vorausgehenden Ansprüche, in welchem nur eine mittig angeordnete
Elektrode in der Decke des Ofens vorhanden ist.
11. Verfahren nach einem der vorausgehenden Ansprüche, in welchem Luft im Inneren des
Ofens ausgeschlossen wird und der Ofen bei einem leicht positiven Druck, um einen
solchen Ausschluß zu verbessern, betrieben wird.
1. Procédé pour la réduction et la fusion de particules fines d'un minerai consistant
en latérite contenant du nickel, lesdites particules fines ayant un rapport SiO2/MgO compris dans l'intervalle 1,2:1 à 3:1 et étant calcinées, préchauffées et tamisées
à un diamètre de particule inférieur à 2 mm ; procédé comprenant l'introduction continue
desdites particules fines simultanément avec un agent réducteur carboné suffisant
pour parvenir à un degré désiré de réduction de l'oxyde de nickel présent, dans la
région centrale du bain fondu d'un four cylindrique d'un four à plasma à arc à transfert
à courant continu comprenant une ou plusieurs électrodes situées dans la voûte jouant
le rôle de cathode, et le bain fondu jouant le rôle d'anode ; et à décharger de manière
périodique ou continue des scories appauvries en nickel et du ferronickel non raffiné
du four.
2. Procédé suivant la revendication 1, dans lequel un revêtement figé est maintenu entre
le bain fondu et le revêtement réfractaire en régulant la puissance et la vitesse
d'alimentation fournies au four, et éventuellement en refroidissant par eau les parois
latérales du four.
3. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la matière
d'alimentation est séchée, calcinée, préchauffée ou pré-réduite, suivant n'importe
laquelle de leurs associations.
4. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la matière
d'alimentation comprend les scories recyclées produites dans une étape de conversion
ou d'affinage en aval pour valoriser le produit consistant en ferronickel non raffiné
produit par ce procédé.
5. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la matière
d'alimentation consistant en latérite est séchée et calcinée avant d'être introduite
dans le four.
6. Procédé suivant la revendication 5, dans lequel la matière d'alimentation est broyée
avant ou après calcination et la matière d'alimentation broyée est soumise à une préréduction
avant d'être introduite dans le four.
7. Procédé suivant la revendication 6, dans lequel la préréduction est effectuée dans
un réacteur de réduction fluidisé en utilisant des corps réducteurs gazeux ou les
gaz engendrés à partir de corps réducteurs solides soumis à une combustion dans le
réacteur.
8. Procédé suivant l'une quelconque des revendications 5 à 7, dans lequel le séchage
est effectué à une température d'environ 150°C; la calcination est effectuée à une
température d'environ 700 à 800°C et la préréduction est effectuée à une température
d'environ 800 à 850°C.
9. Procédé suivant l'une quelconque des revendications précédentes, dans lequel les électrodes
situées dans la voûte du four sont des électrodes en graphite.
10. Procédé suivant l'une quelconque des revendications précédentes, dans lequel il existe
une seule électrode en position centrale dans la voûte du four.
11. Procédé suivant l'une quelconque des revendications précédentes, dans lequel l'air
est exclu de l'intérieur du four et le four est soumis à un fonctionnement à une pression
légèrement positive pour accroître cette exclusion.