WO1985001750A1

WO1985001750A1 - Smelting nickel ores or concentrates

Info

Publication number: WO1985001750A1
Application number: PCT/AU1984/000205
Authority: WO
Inventors: William Thomas Denholm; Robert Norton Taylor
Original assignee: Commonwealth Scientific And Industrial Research Or
Priority date: 1983-10-19
Filing date: 1984-10-17
Publication date: 1985-04-25
Also published as: ZA848065B

Abstract

Sulphidised nickel silicate and/or sulphidic nickel ores and/or concentrates in the form of dry and/or wet pellets or filter cake, wetted down material or slurries mixed with fluxes, to avoid dust, are added to, or as powder, pneumatically injected into, a turbulent bath consisting mainly of matte and slag, which is agitated by a stream of combustion gas, derived from natural gas, fuel oil or powdered coal, with a measured excess of oxygen. Nickel ores and concentrates are associated with iron to a greater or lesser extent, and may also be associated with one or more of cobalt, copper and the noble metals. Oxidation of the molten bath, which takes place at about 1250oC is selective and controllable, and the iron sulphide in the matte is oxidised to iron oxide and forms a silicate slag, with silicates already present in the ores and/or concentrates, or silica added as a flux. This leaves an enriched nickel (cobalt, noble metal) matte, in which the nickel content may range from 45 to 75%, from which nickel may be readily and economically recovered as a useful nickel matte product, (2% max. S), by partial conversion with available free and/or combined oxygen, under conditions of a mildly oxidising gas flush or substantially reduced pressure, at 1450oC and upwards. Any nickel reporting in the slag may be recovered by carbonaceous or gaseous reduction, and recycled to the charge. The process may be carried out in a known crucible-type furnace, as exemplified in the drawing.

Description

"SMELTING NICKEL ORES OR CONCENTRATES"

This invention relates to a new process for smelting nickel ores or concentrates.

Traditionally, the recovery of nickel from its ores or concentrates has been characterized by a multiplicity of sequential steps involving sintering and/or roasting, smelting to produce a nickel sulphide matte and various converting operations. In more recent years, flash smelting techniques have been introduced to reduce the number of process steps involved and to utilize the heat available from the combustion of sulphides present in the feed. This technique involves the use of separate oxidising and reducing regions in a comparatively large furnace to produce a slag phase and an enriched nickel matte suitable for the recovery of nickel.

Conventional pneumatic-based nickel smelting processes cannot be operated to produce nickel mattes of grades above 45% Ni because of excessive losses of nickel to the slag phase. Costly electrical furnaces are therefore needed to produce matte grades above 45% Ni.

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^2^.o_^ It is an object of the present invention to provide a smelting process which is capable of producing matte grades above 45% Ni and up to 70% Ni or more, thus providing a product from which it is much more economical to recover nickel by conventional processes.

Also in accordance with the recent trends in the industry the invention seeks to provide a process which utilises a comparatively small furnace in which combustion of the unwanted sulphides occurs and which is accompanied by the production of a high grade nickel matte suitable for further processing.

These and other objects are achieved by the nickel smelting process described below which permits simpler and cheaper furnace construction than existing commercial processes, is easier to operate and is more economically viable.

According to one aspect of the present invention, a nickel smelting process is characterised by the following step:

(i) adding the ore or concentrate to a turbulent molten bath which consists essentially of matte and slag and which is agitated and heated by the gases released by combustion of a fuel burned below the surface of the matte layer with an oxidizing gas injected into the bath; (ii) injecting sufficient oxidizing gas, in excess of that required for combustion of the fuel, to cause oxidation of the iron sulphide contained in the ore or concentrate to iron oxide, thereby to form a slag by combination of the iron oxide with silica present in ore or concentrate, or added as a flux, and an enriched nickel-containing matte; and

(iii) separating the slag from the matte product.

The liquid nickel matte phase produced by the above-described process typically contains 45% to 70% Ni. This can be treated for recovery of nickel by methods well known in the art.

Fluxes, ores or concentrates, or carbon or carbonaceous materials may also be incorporated into the bath within the furnace region.

In a preferred embodiment of the invention, the process is carried out using sulphidic nickel ores or concentrates, without prior roasting or sintering, and/or nickel silicate ores or concentrates containing a source of sulphur for producing the nickel matte. This may be done by feeding the raw materials into a refractory-lined stationary vessel in which liquid matte and slag phases are maintained in a highly turbulent bath, by means of gas injection through a lance submerged in the bath. The injection process is operated to produce a rain of liquid droplets in a splashing region above the bath. As indicated above, the apparatus requirements for the process are simple and the process may be carried out in a furnace of compact and simple design which, by way of example, is preferably cylindrical in shape, is refractory lined, and may be water-jacketed, e.g. above the level of the matte layer which is formed during operation of the process. The process is usually carried out at about 1250°C, although higher temperatures may be used. The feed requirements are not onerous and the raw materials may take any suitable physical form which does not allow their loss as dust. Thus dry and/or wet pellets or filter-cake or wetted-down concentrates may be used or wet filter cake or slurries mixed with appropriate fluxes may also be used as top additions. The incorporation of these materials within the bath results from their rapid collection in the splashing region. Dry powdered concentrate may also be injected through the lance into the bath if desired.

Oxygen, either as air or as an oxygen-enriched or oxygen-depleted air stream, is preferably injected vertically downwards below the surface of the bath by means of one or more lances, preferably using a "Sirosmelt" lance such as is described in U.S. patent 4,251,271. The gases injected in this manner maintain the vigorous agitation and splashing action characteristic of this lance and ensures high rates of mass and heat transfer and thus yields the high overall rates of the chemical reactions concerned.

Smelting rates exceeding 0.7 tonne/hour cubic metre of the smelting vessel can be readily achieved. The concentrates are thereby oxidised substantially to yield an oxide slag and a nickel matte which may contain copper, cobalt and precious metals if these elements were originally present in the ore, concentrates, or fluxes used. Control of the oxygen potential and temperature required to obtain the high grade nickel matte product are readily achieved by varying the flows or air, oxygen and fuel through the lance in relation to the feeding of concentrate. Any values in the fume obtained during the operation of this process is collected and may be recycled with the feed material.

Although in laboratory experiments matte grates of 45% Ni could be achieved using air/nitrogen mixtures, or air alone, using a single alumina tube (typically 2mm I.D.) as a lance, the production of higher grades of nickel matte was associated with blockages of the tube or tubes and this led to complete failure of the smelting operation.

Surprisingly however, it was discovered that the lance blockages could be prevented, when operating with nickel matte grades from 45 to 70% Ni, by using a lance consisting of two concentric alumina tubes in which a fuel gas, or oil, or pulverised carbon, was injected through one of the concentric passages of the lance and air with or without additional nitrogen, was injected through the other. Any suitable fuel gases can be used, for example, hydrogen, carbon monoxide, methane or natural gas or mixtures of any two or more of such gases. In an industrial installation the preferred fuels would be natural gas, fuel oil or pulverized coal. The small quantities of nickel remaining in the slag produced in the process of the invention may be removed by the addition of sulphidizing agents, such as pyrites, preferably in a separate furnace, followed by a lancing procedure as described above. This procedure yields a very low grade nickel slag suitable for discard, and a low nickel content matte suitable for admixture with feed during the treatment described in the preceding paragraphs. Alternatively, a slag reduction step may be used in which coal or other solid, liquid or gaseous reductants are added while operating in a submerged lance mode.

If desired lump coal (-50 mm) can be added with the concentrate feed to provide a cheap source of heat, if required, for the smelting and slag treatment stages, additionally or alternatively to part of the fuel addition described above.

The process of the invention, may also be operated under reduced pressure, which aids the removal of sulphur (as sulphur dioxide) from the melt and results in the production of a matte product of very low sulphur content. Such a product on cooling, will contain a substantial amount of metallic nickel. For example, by carrying out the process at about 30 Torr (4 kPa) a sulphidized nickel product containing 2% or less of sulphur is obtained.

In the preferred embodiment, in order to produce a metallic nickel product, a final operation is performed, in which the temperature is raised to at least 1450°C and conditions are adjusted to permit SO-,

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^Ϊ£s£mo* $$ at a pressure of approximately 30 Torr to pass into the product gas stream as it passes through the bath.

These conditions may be achieved in practice at an adequate rate, either by treatment under reduced pressure or by passing a large volume of hot gas through the natte to transport the sulfur dioxide into the gas stream. In the latter case, at about the melting point of nickel (i.e. 1452°C) the gas is preferably a reducing combustion gas with a low oxygen

__7 partial pressure, typically 10 atmosphere (e.g. with

CO/CO- ratio of about 1/5) , which prevents significant formation of nickel oxide but permits sulfur dioxide to enter the gas stream.

The following Examples further illustrate the invention and indicate preferred operating conditions of the process for producing high grade mattes containing 45% to 70% nickel.

The experimental apparatus used is shown diagrammatically in Figure 1.

Experiments were conducted in consumable reactors made from a lidded aluminous porcelain crucible (1) (supplied by Nilsen Porcelains (Aust) . Pty. Ltd., Melbourne, Australia) . A lid (2) and a porcelain extension tube (3) were cemented (4) to each crucible with "Fraxset Assembly Cement" as shown in the Figure. The reactor assembly was entirely contained in an induction heated clay-graphite enclosure consisting of two machined "Morganite" size A10 crucibles (5,6) housed within a refractory insulating brick enclosure (7) which in turn was surrounded by a copper sheet

1 _.WTO .^J induction coil (8) provided with copper cooling tubes (9) . Temperature was sensed by a noble metal thermocouple in an alumina sheath (10) placed inside the graphite crucible (6) , and control was achieved by switching the induction heater via a grid-switching circuit with a time proportioning indicating controller (not shown) .

The lance consisted of a 2mm I.D. alumina tube (11) inserted through the extension tube (3) almost to the base of the crucible (1) . A fume hood (12) was also provided to carry off gaseous products and fume to a cooler and fume filter (not shown) .

In each experiment the starting matte and starting slag were added to the weighed reactor and melted under a cover of nitrogen, then heated to the reaction temperature (usually 1250°C) . The pelletized charge was added at a uniform rate by dropping down the vertical extension tube (3) commencing at the same time as the blowing of air through a submerged lance (11) , and the addition of pellets was timed to end when about 90% of the total air had been blown. After completion of blowing, the lance was withdrawn and the reactor space purged with nitrogen during a settling period of 10 minutes at the reaction temperature followed by rapid cooling to below the solidification temperature.

After cooling to room temperature the reactor with its contents was reweighed and broken open to separate matte and slag. EXAMPLE 1

Pellets were first prepared from a nickel concentrate (14.4% Ni, 30.7% Fe, 0.7% Cu, 30.4%S) and a calculated amount of silica flux (14% by weight of 99+% Si0₂ in this case) and binding was achieved by the addition of 2% of methyl cellulose.

In the first two experiments, the aim was to produce a final matte grade of 46% Ni. 200 grams of a previously prepared nickel matte (46.3% Ni) and 50 grams of slag (36% Fe, 38% SiO-) were melted under nitrogen in the aluminous crucible (1) at 1250°C by means of the induction heater (8) . 300 grams of the low grade nickel concentrate pellets were then added to the bath at a uniform rate by dropping these through the extension tube (3) . An air/nitrogen mixture (15% N, 85% air) was then blown at the rate of 10 litres/minute through the lance (11) , the blowing being commenced simultaneously with the commencement of pellet addition and continued until the calculated air requirements for the experiment were satisfied. At the end of this procedure, the crucible and contents were cooled quickly under nitrogen and the slag and the matte phases were separated by breaking and sorting.

For the first experiment, analysis showed that the matte grade was 45.9% Ni in good agreement with the target value of 46% Ni and that the slag phase contained only 0.77% Ni. In a second experiment, similar to the first, matte and slag phases containing 42.4% Ni and 1.4% Ni , respectively, were obtained.

EXAMPLE 2

A pellet feed, prepared as described in Example l_r was used in conjunction with molten matte and slag phases. • In this case, the matte contained 61% Ni, 1.6% Fe and 21%S_r and the smelting temperature used was 1300°C. The slag composition was the same as that used for Example 1.

To overcome the lance blocking problems encountered during preliminary runs when using the 60% Ni matte, a lance consisting of two concentric tubes (not shown in Figure 1) was found to operate successfully. The concentric lance consisted of an inner tube of 1 mm I.D. and 2mm O.D. and an outer tube of 5 mm I.D. A gaseous fuel (hydrogen) was introduced through the inner tube at 1 litre per minute. Air was introduced at a rate of 9 litres per minute through the annulus between the inner tube and the outer tube.

The operating procedure outlined in Example 1 was then followed and this resulted in a product matte containing 60.2% Ni and a slag of 1.0% Ni.

EXAMPLE 3

This experiment consisted of a repeat of Example 2 but using a molten matte containing 69% Ni instead of 60% Ni. The product matte and slag phases obtained

OMPI ^τio_≤ ^J at the end of the experiment contained 70% Ni and 3% Ni respectively. The slag layer was gently stirred with nitrogen at 1 litre per minute for 3 minutes then allowed to settle for 10 minutes before cooling. The settled slag contained 0.8% Ni. Subsequent microscopic examination showed that the first slag contained a large number of fine prills of matte, whereas the settled slag contained fewer prills of larger size.

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Claims

CLAIMS :

1. A process for the smelting of a nickel sulphide ore or concentrate to produce a high grade matte, characterized by the steps of:

(i) .adding the ore or concentrate, and if necessary a suitable flux, to a turbulent molten bath which consists essentially of matte and slag and which is agitated and heated by the gases released by combustion of a fuel burned below the surface of the matte layer with an oxidizing gas injected into the bath;

(ii) injecting sufficient oxidizing gas, in excess of that required for combustion of the fuel, to cause oxidation of the iron sulphide contained in the ore or concentrate to iron oxide, thereby to form a slag by combination of the iron oxide with silica present in ore or concentrate, or added as a flux, and an enriched nickel-containing matte; and

(iii) separating the slag from the matte product.

2. A process as claimed in Claim 1, characterized in that the oxidizing gas is injected into the bath by means of a submerged injector.

3. A process as claimed in Claim 1 or Claim 2, characterized in that the fuel is gas, fuel oil or powdered coal which is injected with the air or other oxidizing gas.

4. A process as claimed in Claim 1 or Claim 2, characterized in that the fuel is solid coal, coke or char which is dropped onto the surface of the bath.

5. A process as claimed in any one of Claims 1 to 4, characterized in that the oxidizing gas is air or oxygen enriched air.

6. A process as claimed in any one of Claims 1 to 5, characterized in that nickel contained in the separated slag is recovered by treating the slag with a sulphidizing agent and a reductant in a submerged combustion vessel to produce a low-nickel slag for discard and a low-nickel matte for recycle to step (i) with the ore or concentrate feed.

7. A process as claimed in any one of Claims 1 to 6, characterized in that the high grade matte produced is treated under conditions of reduced partial pressure of sulphur dioxide to produce a metallic nickel product containing two percent or less of sulphur.

8. A process as claimed in Claim 6, characterized in that the slag treatment is carried out in batch mode in the vessel used for the smelting operation after tapping the matte.

9. A process as claimed in Claim 6, characterized in that the slag is tapped into a separate vessel before treatment.

10. A process as claimed in Claim 7, characterized in that the matte is treated in the vessel used for the smelting operation, after tapping the slag, and by continued submerged injection of combustion gases which are neither oxidizing nor reducing, to lower the partial pressure of sulfur dioxide and remove sulfur thereby to form a sulphidized nickel product.

11. A process as claimed in Claim 7, characterized in that the matte is tapped into a separate vessel for treatment under reduced pressure.

12. A process as claimed in Claims 1, 6 and 7, characterised in that the production and treatment of the matte and slag are carried out continuously in three separate vessels.