AU754715B2

AU754715B2 - Upgrading of nickel laterite ores

Info

Publication number: AU754715B2
Application number: AU23544/99A
Authority: AU
Inventors: Jacobus Cornelius Gideon Kotze Van Der Colf
Original assignee: BHP Billiton SA Ltd
Current assignee: BHP Billiton SA Ltd
Priority date: 1998-04-06
Filing date: 1999-04-01
Publication date: 2002-11-21
Anticipated expiration: 2019-04-01
Also published as: CU22821A3; AU2354499A; ID23254A; FR2777022A1

Description

Page 1 BACKGROUND OF THE INVENTION This invention relates to a method for upgrading nickel laterite ores.

Nickel laterite ores are a well known source of nickel and nickel is recovered from such ores in many parts of the world. Nickel occurs in these ores in oxidised form.

Nickel laterite ores are treated without prior upgrading because the oxidised forms of nickel in the ore are not amenable to concentration.

g o" Attempts have been made to increase the grade of nickel in the ore by converting the nickel to another form. This enables the nickel to be concentrated and the ore to be upgraded.

One such method is called segregation. The segregation process has been used :20 more specifically for copper oxide ores and, in this case, relies on the presence a. 0 o• during roasting of chloride compounds which cause copper to be volatilised.

Carbon particles are provided onto which the copper is reduced. Subsequent separation of the carbon particles provides a means of upgrading the ore for the metal. The process is also effective for nickel oxide ores, although the temperature must be higher. To the applicant's knowledge, this process has not P.18156/au Page 2 been commercialised for nickel.

Conventional pyrometalurgical processes involve the reduction of the nickel content of the ore. In most of these processes the ore is smelted with carbonaceous reductants such as coal or coke. This is most often carried out in an electric furnace.

The reduction process is normally preceded by a heating process which is used to dry the ore and raise the temperature of the ore. It is commonplace to use a rotary kiln to heat the ore because readily available fuels such as oil or coal can be used. Some pre-reduction of the nickel may also take place in the rotary kiln, and even some smelting if the temperature is high enough. All these actions are °e designed to reduce the cost of the electrical energy used in the electric furnace.

S.The process of partial reduction in a rotary kiln and reduction of nickel and some iron in the electric furnace produces a ferro-nickel with more or less iron depending on the degree of iron reduction. Typically a molten ferro-nickel with to 25% nickel is produced.

However, the cost of the process is high because, although the ore may contain from 1% to 2% nickel, all the ore must be dried, heated and melted.

P.18156/au It is evident that it would be advantageous if the nickel grade could be increased by concentrating nickel into a higher grade fraction.

Summary of the Invention According to a first aspect, the present invention consists in a method of upgrading nickel laterite ore which includes the steps of adding a chloride salt to the ore such that the ratio of the chloride salt to the ore, on a weight basis, lies in the range of from 5:1000 to 20:1000, reducing at least some of the nickel in the ore, in the presence of the salt, to nickel metal in a magnetic form, and magnetically separating the ore into high grade and low grade fractions.

According to a second aspect, the present invention consists in a method of upgrading nickel laterite ore which includes the steps of adding calcium chloride and a reductant to the ore, roasting the ore, the calcium chloride being present in a quantity which is insufficient to cause substantial transfer of nickel to a carbon phase but sufficient to promote the formation of reduced nickel in a magnetic form, recovering the reduced nickel as a magnetic fraction by means of magnetic separation, and smelting the magnetic fraction in a DC electric arc furnace to produce a ferro-nickel product.

According to a third aspect, the present invention consists in nickel laterite ore upgraded by the method of the first or second aspect.

The invention provides a method of upgrading nickel laterite ore which includes the steps of adding a chloride salt to the ore, reducing at least some of the nickel in the ore, in the presence of the salt, to nickel metal in a magnetic form, and magnetically separating the ore into high grade and low grade fractions.

•The chloride salt may be calcium chloride.

S• The quantity of chloride salt which is added to the ore is insufficient to cause substantial transfer of the metal to a carbon phase.

The amount of chloride salt which is added may be such that the ratio of the chloride salt to the ore, on a weight basis, lies in the range of from 5:1000 to 20:1000. A suitable ratio is of the order of 10:1000.

The nickel laterite ore may be limonite ore or saprolite ore or a blend of these.

The ore may be dried and it may be pelletised prior to roasting.

9 o• [R:\LIBFF] 10598speci.doc:njc Page 4 Use may be made of any appropriate reductant but preferably a carbonaceous reductant such as coke or charcoal is used.

The reducing step may take place at a temperature of between 1000 0 C and 1100 0 C but preferably takes place at a temperature of the order of 1050 0

C.

Sufficient reductant may be added to cause all the nickel present to be converted to the metal phase.

a. a.

a.

a a a a a a a a a a.

a The reduced material may be cooled before being subjected to the magnetic separation step.

The magnetic fraction, which is the high grade fraction, may be smelted in a DC electric arc furnace.

The ore, prior to the reduction step, may be comminuted so that a fine product is produced in the magnetic separation step which is suitable for directly feeding to the DC arc furnace through a hollow electrode.

The furnace may be operated at a temperature of about 1600 0

C.

BRIEF DESCRIPTION OF THE DRAWING P.18156/au Page The invention is further described by way of example with reference to the accompanying drawing which illustrates in block diagram form a method of upgrading nickel laterite ore according to one form of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT The invention is based on the recognition that it is possible to take advantage of the fact that some nickel is reduced to metal in a pre-reduction kiln. If metal is formed it can be separated from the ore because nickel is magnetically susceptible.

It has been established that the conditions for successful development of a more magnetic fraction are favoured by adding a very small amount of a chloride salt :such as calcium chloride to the ore before roasting. The amount of calcium chloride used is far less than the amount of chloride salts added to the so-called segregation process. There is insufficient chloride salt added to cause substantial transfer of the metal to a carbon phase. The amount of chloride salt, which typically is about 10 grams of calcium chloride per kilogram of ore, is sufficient to promote the formation of reduced nickel in a magnetic form which responds to magnetic separation of the ore into a high grade fraction and a low grade fraction.

P.18156/au Page 6 It is to be noted that the process of segregation, referred to hereinbefore, aims to achieve a very high degree of separation of nickel from the waste ore. The method of the present invention is not intended to achieve this result. In the process of segregation, the cost of adding large amounts of chloride salts is high and produces a high grade of nickel concentrate with very little iron. The method of the present invention is not intended to achieve this result and a typical ratio of iron to nickel would be about 4 to 1. This ratio is similar to the ratio of iron to nickel in the final ferro-nickel product.

It has been established that the method of the invention can be successfully applied to nickel laterite ore in the limonite form or the saprolite form or to a °°blend of the two ore types.

The accompanying drawing illustrates the method of the invention. Limonite ore 10 and saprolite ore 12 are optionally blended in a step 14. The ore blend is comminuted to a suitable fine form in a step 16 and thereafter is dried in a step .18.

'a The dried ore blend is fed to a rotary kiln 20 and a carbonaceous reductant 22 and calcium chloride 24 are added to the kiln.

The reductant may be coke or charcoal and it is added in a quantity which is P.18156/au Page 7 sufficient to cause all the nickel present to be converted to the metal phase.

Some of the iron must also be converted.

The calcium chloride is added to the kiln in the proportion of 10 kilograms per ton of dry ore, as CaCI 2 .2H 2 0.

The kiln is heated to a temperature of from 1 000 0 C to 1100 0 C with a suitable temperature being of the order of 10500C.

The product of the rotary kiln is cooled in a suitable system 26. The cooled product is then sent to a wet magnetic separator 28 which separates the product S. into a magnetic fraction 30 containing from 90% to 95% of the nickel, and a nonmagnetic fraction 32.

The magnetic fraction 30 is dewatered and dried in a step 34 and then fed to a DC arc furnace 36.

oThe typical electric furnace used in a conventional rotary kiln/electric furnace process requires that pellets or miniballs are fed to the rotary kiln and hot transfer of the kiln product to the electric furnace takes place. In the present invention the fine product of the rotary kiln and the magnetic separator would not be a suitable feed for a conventional electric furnace.

P.18156/au Page 8 The DC arc furnace 36 can therefore be used to advantage in that the fine magnetic fraction 30 can be fed to the arc furnace through its hollow electrode directly into the reaction zone for smelting.

Smelting takes place at a temperature of about 1600 0 C and produces a molten ferro-nickel product 38 which typically contains from 20% to 25% nickel in iron.

In one example of the invention a blend of four parts of saprolite ore to one part of limonite ore was made. The analysis of the ores and the blend is given in Table 1. The ore was treated in a rotary kiln at a temperature of 1050 0 C with coke of the composition given in the Table.

The magnetic product was about 40% of the dry weight of the original blend.

The electrical energy consumption to implement the method of the invention, as described, is approximately 136 kilowatt hours per ton wet ore. On the other S-hand if the original blend were to be treated in a rotary kiln and smelted the total energy consumption would be of the order of 920 kilowatt hours per ton wet ore.

In the method of the invention about 93% of the nickel present was found in a magnetic fraction of 40,5% by mass at a grade of 4.28%. The grade of nickel in the blend was 1,86%. The iron content was increased from 15,66% to 27,3% at P.18156/au Page 9 a recovery of 72~3%.

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a a a a a a. a a a a a P.18156/au Page Table 1

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Claims

1. A method of upgrading nickel laterite ore which includes the steps of adding a chloride salt to the ore such that the ratio of the chloride salt to the ore, on a weight basis, lies in the range of from 5:1000 to 20:1000, reducing at least some of the nickel in the ore, in the presence of the salt, to nickel metal in a magnetic form, and magnetically separating the ore into high grade and low grade fractions.

2. A method according to claim 1 wherein the chloride salt is calcium chloride.

3. A method according to claim 2 wherein the ratio is of the order of 10:1000.

4. A method according to any one of claims 1 to 3 wherein the nickel laterite ore is limonite ore or saprolite ore or a blend of these. A method according to any one of claims 1 to 4 wherein the ore is dried prior to the reduction step.

6. A method according to any one of claims 1 to 5 wherein a carbonaceous reductant is used in the reducing step.

7. A method according to any one of claims 1 to 6 wherein the reducing step takes place at a temperature of between 1000 0 C and 1100 0 C.

8. A method according to claim 7 wherein the reducing step takes place at a temperature of the order of 1050 0 C.

9. A method according to any one of claims 1 to 8 wherein the ore is cooled 20 before being subjected to the magnetic separation step. :o 10. A method according to any one of claims 1 to 9 which includes the step of smelting the high grade fraction in a DC electric arc furnace.

11. A method according to claim 10 wherein the furnace is operated at a temperature of about 1600 0 C.

12. A method according to claim 10 or 11 wherein the furnace produces a ferro- nickel product which contains from 20% to 25% nickel in iron.

13. A method according to any one of claims 1 to 12 which includes the step of comminuting the ore prior to the reducing step.

14. A method of upgrading nickel laterite ore which includes the steps of adding 30 calcium chloride and a reductant to the ore, roasting the ore, the calcium chloride being S present in a quantity which is insufficient to cause substantial transfer of nickel to a carbon phase but sufficient to promote the formation of reduced nickel in a magnetic form, recovering the reduced nickel as a magnetic fraction by means of magnetic T q separation, and smelting the magnetic fraction in a DC electric arc furnace to produce a S 35 ferro-nickel product. [R:\LIBFF] 10598speci.doc: njc 12 A method of upgrading nickel laterite ore substantially as hereinbefore described with reference to the accompanying drawing and/or any one of the examples.

16. Nickel laterite ore upgraded by the method of any one of claims 1 to Dated 21 August, 2002 Billiton S.A. Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON **o C [R:\LIBFF] 10598speci.doc:njc