GB2032896A - Upgrading nickel ores - Google Patents

Abstract

A process for upgrading the nickel content of a nickeliferous ore of lateritic origin comprises subjecting the ore to controlled attrition to liberate the friable portions in the ore particles without breaking the harder portions, such that the d90:d10 ratio of the ore (where d90 is the smallest size of mesh passing 90% by weight of the ore and d10 is the smallest size of mesh passing 15% by weight of the ore) subjected to attrition is at least twice the d90:d10 ratio of the original ore, and classifying the ore particles according to their size, those having a size below a certain value being recovered as the upgraded ore of higher nickel content.

Description

SPECIFICATION Process for upgrading nickeliferous oxide ores of lateritic origin This invention relates to a process for upgrading nickeliferous ores of lateritic origin and is a development of that described and claimed in the Specification of our Patent No. 1 542901 (hereinafter referred to as "the earlier Specification"), Claim 1 of which is in the following terms: 1.A process of upgrading the nickel content of a nickeliferous oxide ore containing, by weight, 2 to 43% iron, 8 to 46% silica, 2 to 36% magnesia and 1.20 to 3.20% nickel, wherein: a) the ore is subjected to a controlled attrition as herein defined, so as to separate the particles of the ore without appreciable breakage thereof, and b) the separated particles of ore are classified according to their size and those having a dimension smaller than 50 microns are selected as the upgraded ore of higher nickel content.

Controlled attrition is defined in the earlier Specification as a process which "wears away and shakes the particles of ore without breaking them".

This definition of attrition should be emphasized because the term is sometimes used in error to designate mild grinding or simply washing. Hereinafter in this specification, the expression "controlled attrition" will not be used to refer to either of these two operations. The operation of washing, disintegration or de-sliming, consists essentially in separating from one another the fine particles which already exist in the ore or the by-product, while the object of attrition is to create new particles. It should also be pointed out that a washing operation takes only a few minutes, while controlled attrition takes some tens of minutes (at least ten minutes and preferably at least twenty minutes).

In contrast to harsh fragmentation, attrition as stated above wears down and shakes the particles of ore without breaking them. The wear and shaking movements are produced by inter-particulate friction and collisions. Attrition therefore depends on a moderate mechanical action to liberate the friable portions in the ore particles without breaking the harder portions.

On a Rosin-Rammler granulometric diagram, therefore, the successive curves comparable to straight lines corresponding to the particle sizes produced by successive attritions tend to become horizontal, while those which correspond to the particle sizes produced with successive grinding operations remain parallel to one another or have a slight tendency to become vertical.

However, this definition of attrition is qualitative and is unsuitable for quantifying the conditions which will give a controlled character to attrition. That is why, during research resulting in the present invention, secondary attrition criteria were examined in order to discover numerically and accurately the preferred conditions of controlled attrition which, hereinafter, will be referred to either as attrition or controlled attrition without discrimination.

According to this invention, to this end, the controlled attrition stage (b) is so carried out that the d90 to d10 ratio of the ore subjected to attrition (where d90 is the smallest mesh passing 90% by weight of the product and d10 is the smallest mesh passing 10% by weight of the product) is at least twice the d90:d10 ratio of the initial ore.

This criterion is not the only one that can be selected in order quantitatively to define the preferred attrition conditions.

Reference to the Rosin-Rammler diagrams will show that in the case of grinding the straight lines representing the particle size move parallel to one another, the d100 (defined as the smallest mesh passing 100% by weight of the product) moving like the other points of the straight line. In the case of attrition, however, the slope of the successive straight lines diminishes while the d100 varies only slightly, if at all. Generally, the "d" of high index vary little while those of low index vary considerably with the total attrition time.

It should be noted that the straight lines representing the successive attritions cannot in any case have a smaller slope than that of the straight line passing through the initial d100 and a d10 corresponding to the molecular size of the most fragile phase.

Although study of Rosin-Rammler diagram is the finest and the most suitable criterion for distinguishing controlled attrition from grinding, it is difficult to quantify. For this reason other criterion are applied, which may be designated as secondary criteria.

One of the first secondary criteria is to define controlled attrition by the fact that the d100 does not decrease by more than 50% and, preferably, 25% during attrition, no matter how long. However, this criterion is not very satisfactory, since the d100 corresponds to the largest particle size. This specific feature makes this secondary criterion relatively unreliable.

As another secondary criterion it is also possible to define controlled attrition by the fact that the do and the d80 during this attrition do not decrease by more than 75 and 100% respectively, and preferably by more than 20 and 30% respectively.

For this reason, the most satisfactory criterion is defined by the fact that the d90:d10 or d80:d20 ratio increases during successive attritions. This condition indicates the preferred attrition zone to be given, by the fact that the d90:d10 ratio is multiplied by 2 during the attrition. If the d90:d10 ratio is difficult to calculate or if, for any other reason, it is not possible to obtain this ratio easily, another substantially equivalent criterion is that the d80:d20 ratio increases by at least a factor of 1.5 during attrition. The d90:d10 ratio must preferably increase at least 10 times during attrition.

Although attrition techniques are relatively unknown, if known at all, grinding techniques are very well known and it is possible to define the attrition conditions by contrast with the grinding conditions.

The mills conventionally used in the ore industry are constructed to fragment mineral particles by producing an impact between the latter and grinding members provided for this purpose. The frictional wear between the different members present in the mill is only an accessory, if not a parasitic, phenomenon, since the fines are always considered as a source of difficulty in the subsequent minerallurgical processes. Thus in the case of grinding with rotary mills, the speed of rotation and the size of the grinding members are controlled to ensure that all the particles are broken. The speed of rotation is generally between 60 and 80% of the critical speed, the latter being defined as the speed from which the charge starts to be centrifuged and can no longer exert its cataract effect on the mineral particles.

The optimum dimensions of the grinding members can also be determined by means of substantially empirical formulae, e.g. those of Rittinger (Ritter von Rittinger P. Lehrbuch der Aufbereitungskunde P 1922 Berlin 1867), Coghill (Coghill W. H. De Vaney F. D. Bull Mo Sch Min Tech Ser Sept 1938) and Bond (Bond F. C. AIME Trans 19, P 484 1952).

This optimization of grinding has been the subject of numerous publications summarized in the work by P. Blazy "La valorisation des Minerais"-Presses Universitaires de France, Paris 1970more particularly pages 42 to 44.

Thus the skilled addressee familiar with the parameters which play an important part in grinding, and the conditions which give good fragmentation, can by contrast define the conditions for a satisfactory controlled attrition, e.g. by selecting a speed of 90% of the critical speed.

Advantageously, the grinding members used may be the ore particles of a dimension between 1 and 5 mm produced in a previous operation.

To obtain the best results during pulp attrition, the proportion of solids in the pulp should be between 60 and 80%, and preferably between 65 and 75%.

To avoid the fragmentation of the original ore particles, the attrition stage (b) is preferably so conducted that when two particles collide the relative speed thereof is less than 5 metres per second and is preferably between 2 and 4 metres per second.

The pulp attrition operation can be carried out by agitating the pulp in a tank by means of a moving agitator. In that case the operating conditions are preferably so selected that the pulp passes through the moving agitator between 1 000 and 10 000 times per hour, and preferably between 3 000 and 5 000 times per hour, the speed of the pulp on passing through the moving agitator advantageously being between 0.9 and 2.4 m per second.

The time of an attrition operation is preferably between 20 minutes and two hours.

When the process according to the present invention is re-started as many times as is necessary to extract the nickel from the rejected particles, it is preferable for the number of treatments to be between 1 and 5, and preferably between 1 and 3.

The time required for each attrition operation generally increases with the,order of the treatments.

Irrespective of the number of treatments, it is advantageous that the total attrition time should be between 30 minutes and 5 hours, and preferably, between 1 and 3 hours.

It was stated in the earlier Specification that it is sometimes desirable to grind the initial ore before carrying out the actual attrition operation. According to this invention, it has been found that it is advantageous so to carry out grinding that the d80 of the ground ore is between 100 and 5 000 microns and, preferably, between 200 and 1 000 microns.

It should be pointed out that the research resulting in this invention has also shown that the critical character of the 10 micron cut-off. Reference to the following Examples will clearly show that depending on whether the cut-off mesh is 7 or 1 5 microns, the increase in the content of the concentrate with respect to the initial ore varies considerably. Generally, it may be stated that in practically all the ores as defined in the earlier Specification it is possible to obtain a concentrate with a content in excess of at least 1% of the initial content of the ore with cut-off between 5 and 1 5 microns and with a nickel recovery ratio of 70%. The cut-off mesh selected depends on the ore being treated and is easily determined by the skilled addressee by routine tests.

It is possible to obtain even better concentrations with a cut-off below 5 microns. However, it is no longer possible to use hydrocyclones for such classification. Centrifugation techniques must be used to obtain such fine cut-off. It should be noted that there is no point in a cut-off below a value of 0.1 microns. Finally, if nickel recovery ratios of about 80% are required, they can be obtained by a cut-off of about 30 or 40 microns. In that case, however, the content increase is only about 0.5%, although it may be more than that in some cases.

It should also be pointed out that the present upgrading technique enables MgO/SiO2 ratios (between 0.45 and 0.7) to be obtained which are very favourable for reducing the concentrates to ferronickels.

The following non-limitative Exampies are intended to show the skilled addressee how the operating conditions suitable for each specific case can readily be determined.

EXAMPLE 1: Grinding and attrition of an ore from the Bonini deposit A sample of this ore having a 1.5% nickel content was processed by the following sequence of operations: De-sliming of the initial material and recovery of the fine particles; Reduction of the d80 of the de-slimed ore from a value of 40 mm to 1 mm by grinding; Processing the resulting material by attrition.

Four attrition operations were carried out lasting 10, 50, 60 and 1 20 minutes respectively, each being followed by centrifugation allowing the particles below 1 0 microns to be recovered.

The solids concentration of the pulp was 70%.

Ni recovery Product by weight % Ni ratio% Washing fines (1) 10.70 3.36 23.80 Preliminary grinding fines (2) 2.00 2.78 3.68 Fines obtained after attrition (3) 24.04 2.93 46.72 Concentrate (1) + (2) + (3) 36.74 3.06 74.20 Feed 100.00 1.51 100.00 This Example clearly shows that the fine particles produced from preliminary grinding represent only a very small fraction of the fines subsequently produced by attrition.

This Example also shows that a very low nickel content ore is very highly upgraded since a concentrate is obtained which contains 3.6% of nickel with a 74% nickel recovery rate.

EXAMPLE 2: Comparative test between grinding and attrition A Si Reis ore having the following composition: 2.30% nickel, 10.3% iron, 28.4% MgO and 46.5% SiO2 was processed to compare attrition and grinding.

In a first stage it was de-slimed to remove the fines (less than 10 microns) and then subjected to a preliminary grinding to give a d80 of 1 500 microns.

Grinding conditions: Grinding was carried out in a ball mill rotating at 78% of its critical speed and containing 0.5 kg of ore, 0.5 kg of water and 28 balls of 40 mm diameter.

Three tests were carried out with grinding times of 20, 40 and 60 minutes respectively.

Attrition conditions: The conditions are defined below in Example 3.

The following Table shows different means of drawing a comparison according to the different slopes of the particle-size curves. It also enables very clear histograms to be obtained.

Grinding Attrition Feed 20 min 40 min 60 min 20 min 40 min 60 min Particle size % by in microns weight % by weight % by weight 1 - 2 0 2,6 4,0 5,0 1,2 2,3 2,5 2 4 0 4,4 7,0 10,3 1,9 2,5 3,0 4- 8 0 7,8 12,0 13,5 1,6 4,0 4,0 8 16 0 12,0 17,5 21,5 3,8 5,0 6,0 16 - -32 3,8 18,0 22,5 23,0 5,0 6,0 6,0 32 - 64 9,2 22,0 20,0 14.5 8,5 7,0 8,0 64- 128 12,5 19,5 11,5 4,6 10,0 10,0 9,0 128 - 256 14,5 8,8 2,0 0,4 11,5 10,0 10,0 256 - 512 15,5 12,5 13,0 11,5 512 - 1024 17,0 17,5 12,0 10,5 1024 - 2048 14,5 14,5 11,0 9 2048 - 4096 8,0 1 8,0 7,0 6

It should be noted that after the first grinding there was no particle left of a size above 256 microns It is particularly significant that even after 2 hours of controlled attrition the particle size of the ore is still comparable to that of the initial ore, the only exception being the occurrence of particles of less than 16 microns.

From this Table the following Table can be prepared, which shows the d, d80, d20 and dto, and also the d90:d10 and d80:d20 ratios.

Grinding Attrition Characteristic point Feed 20 min 40 min 60 mien 20 min 40 min 60 min d90 2400 130 70 48 2400 2400 2400 d80 1500 80 50 37 1400 1350 1200 d20 90 10 5,4 3,8 69 24 11 52 52 3,7 2,3 1,6 24 6 2,5 d90/d10 46 35 30 30 100 600 960 d,,/d;;, 16,5 8 9 9 24 60 110 The results of this Table are sufficiently clear for no commentary to be necessary.

EXAMPLE 3:Attrition of the Si Reis ore This Example, and those which follow, were carried out with Si Reis ore and clearly show that it is possible to recover an at least 1% upgraded nickel concentrate with a 70% recovery ratio.

An ore sample having a nickel content of 2.30% and containing different phases such as peridotite, with little serpentinisation, if any, while the hardest parts correspond to harzburgite of varying weathering, was treated as follows: d80 reduced to a value of 20 mm in a jaw crusher; grinding to 2.5 mm; de-sliming and recovery of the fraction below 10 microns; at the end this fraction will be added to the attrition product to form the concentrate: the fraction above 10 microns was subjected to attrition in three operations separated from one another by a centrifugation operation to recover the fine particles produced on each treatment.

The attrition feed had an initial particle size characterised by a 1000 micron d80.

Each attrition took 20 minutes. The solids concentration of the pulp during each of these operations was about 65%. The conditions and equipment were otherwise the same as in Example 4.

The attrition concentrate consisted essentially of serpentines and limonites.

The following Table shows the results of these operations: Ni % by Composition recovery MgO/ weight Ni Fe MgO SiO2 ratio % SiO2 Concentrate 52.3 3.36 12.0. 23.1 43.9 76.7 0.53 (fraction - 10) Rejection 47.7 1.12 8.4 34.3 49.4 23.3 0.69 (fraction + 10) Feed 100.0 2.29 10.3 28.4 46.5 100.0 0.61 This Example clearly shows a significant upgrading and a good nickel recovery. Although the MgO/SiO2 ratio decreases, it is quite suitable for ferro-nickel smelting of the concentrate.

The following three Examples use the same ores as the present Example and the attrition technique is substantially identical to that of this Example. Any different conditions are indicated wherever they arise.

EXAMPLE 4 Volume of pulp: 500 litres Speed of pulp on passing through moving agitator: 1.6 m/s.

Diameter of screw (moving agitator): 0.55 m The pulp passed through the moving agitator 5400 times per hour.

The pulp had a solids content of 70%.

d80 day of Yield Duration Feed in concentrate as % by % Nickel Nickel in min. microns (microns) weight Concentrate Rejection Feed yield % 0 14 30 3.34 1.76 2.23 45 20 300 16 43 3.28 1.44 2.23 63 60 300 16 '51 3.22 1.18 2.23 74 120 300 16 59 3.11 0.94 2;23 83 240 300 16 65 3.00 0.82 2.23 87 EXAMPLE 5 Volume of pulp: 5000 litres.

Speed of pulp on passing through moving agitator: 2.4 m/s.

The pulp passed through the moving agitator between 3000 and 4000 times per hour.

The pulp had a 70% solids content.

The d80 of the ore before attrition was 300 microns.

d80 of Yield as Duration concentrate % by % Nickel Nickel in min. (microns) weight Concentrate Rejection Feed yield % 0 10 28 3.58 1.88 2.36 42 45 18 42 3.52 1.61 2.36 63 135 12 49 3.49 1.51 2.36 72 270 12 55 3.43 1.34 2.36 -80 EXAMPLE 6 Different tests were carried under the same conditions as the previous example but the d, of the concentrate varied as did also the d80 of the ore for attrition and the solids content of the pulp.

Solids content Pulp Yield d80 of of pulp- Attrition speed by concentrate % do feed time m/s weight % Ni 7 64 550 30 1,35 4,7 4,0 7 73 650 30 1,35 12,7 4,2 7 63,8 550 60 1,35 7,4 4,2 7 58,3 550 30 1,35 4,8 4,4 7 61,3 900 60 1,35 5,8 4,5 7 61,3 300 60 1,07 3,9 4,2 10 65,5 200 60 1,07 9,2 3,4 10 56,2 300 60 1,07 7,7 3,4 10 59,7 500 60 1,35 5,5 3,9 7 61,3 400 60 1,50 5,0 4,2 10 56 200 60 1,50 13,5 3,4 10 63,5 300 60 2,23 5,8 3,2 10 59,7 500 60 1,35 6,4 3,6 It will be seen from this table that the finer the d80 of the concentrate the richer the concentrate even after several attritions.

EXAMPLE 7: Tiebaghi Facies M ore A Tiebaghi ore having the following characteristics: 2.48% nickel, 1 7.43% iron, 14.85% MgO and 39.27% SiO2 was treated by the process according to the invention: Reduction to 20 mm in a jaw crusher; Grinding to 2.5 mm of the fraction above 2.5 mm; De-sliming to recover the fraction below 10 microns, which constitutes the first concentrate: Processing of fraction above 1 0 microns by three attritions lasting one hour and separated from one another by centrifugation to recover the fines produced during attrition.

The solids content of the pulp was 70%.

Results of operation: Ni recovery Product weight % Ni ratio % MgO/SiO2 Primary fines 31.13 3.83 48.08 Primary fines and first and second 41.74 3.78 63.61 attrition particle fines Primary fines and 1sot, 2nd and 3rd attrition 48.24 3.68 71.65 particle fines Feed 53.77 3.58 77.56 0.45 100.00 2.48 100.00 0.38 In this operation, if all the particles below 40 microns are recovered after 3 hours' attrition, the resulting concentrate has the following characteristics: 71.67% by weight; 3.10% nickel; nickel recovery ratio 89.5%.

It should be noted that in the case of the Tiebaghi ore the quantity of primary fines was abnormally high and the MgO/SiO2 ratio -- which does not allow the Tiebaghi ore to be smelted to ferro-nickels under conventional conditions - was sufficiently high to aliow smelting of the concentrate.

EXAMPLE 8: Attrition of an ore from the Poro deposit A Poro ore having the following characteristics: 2.45% nickel, 10.6% iron, 29.2% MgO and 43.4% SiO2 was processed by the method according to the invention: Reduction to 20 mm in a jaw crusher.

Grinding to 2.5 mm of the fraction above 2.5 mm; De-sliming to recover the fraction below 1 0 microns, which constitutes the first concentrate; Processing of fraction above 10 microns having a d80 of 1200 microns by four attrition operations lasting 20, 25, 30 and 30, minutes respectively, each being followed by recovery of the fine fraction below 10 microns, while the fraction above 10 microns was re-trented in the next attrition.

The solids content of the pulp was 65%.

MgO % by Composition % Ni recovery Product weight Ni Fe SiO2 MgO ratio % SiO2 Washing fines 11.7 3.93 21.9 33.9 17.9 18.8 0.53 Washing and attrition fines 47,0 3.81 15,7 38.7 21.9 73.2 0.57 Rejection 53.0 1.24 6.1 47.3 35.7 26.8 0.75 Feed 100.0 2.45 10.6 43.4 29.2 100.0 0.67 The MgO/SiO2 ratio decreases slightly but is still suitable for smelting of the concentrate to ferronickels.

EXAMPLE 9: Processing of an acidic ore by attrition A highly acidic ore with the following characteristics: 1.60% nickel, 1 6.3% MgO, 67.0% SiO2 and 7.8% Fe2O3 was processed by the method according to the invention.

Reduction to 20 mm and then to 2.5 mm; De-sliming and recovery of the particles below 10 microns; Processing of fraction above 10 microns by three attrition operations lasting 5, 1 5 and 30 minutes respectively, each being followed by recovery of the fine fraction below 10 microns, while the fraction above 1 0 microns was re-treated in the next attrition.

The solids content of the pulp was 60%.

by Composition % Ni recovery MgO Product weight Ni SiO2 MgO Foe203 ratio % SiO2 Concentrate: fraction -10 after attrition and washing 41 3.08 43.3 28.4 12.1 77.34 0.66 Fraction 10-40 after treatment 15.8 0.86 8.44 Fraction + 40 after treatment 43.2 0.53 14.22 Feed 100.0 1.61 67.0 16.3 7.8 100.00 0.24 If all the 40 micron fraction obtained after three attritions is recovered, a concentrate is obtained which has a nickel content of 2.48% and which represents 85.78% of the metal, the concentrate corresponding to 58.4% of the initial weight of the ore.

The Mg9iSiO2 ratio was 0.66, which is extremely favourable forferro-nickel smelting, particularly by comparison with the value of the same ratio in the initial ore. This proves that it is possible to treat acidic ores, i.e. those having a silica content between 46 and 70%, by the method according to the invention, but that the total attrition time can be less than that required for conventional garnierite ores.

Claims (27)

1. A process for upgrading the nickel content of a nickeliferous ore of lateritic origin comprising subjecting the ore to controlled attrition as herein defined such that the d9o:d,0 ratio of the ore subjected to attrition is at least twice the d0:d10 ratio of the original ore, and classifying the ore particles according to their size, those having a size below a certain value being recovered.

2. A process according to Claim 1, wherein the attrition is conducted such that the c:d,, ratio of the ore subjected to attrition is at least ten times the d9o:d,0 ratio of the initial ore.

3. A process according to Claim 1, wherein the attrition is conducted such that the d,:d, ratio of the ore subjected to the attrition is at least one and a half times the d80:d20 ratio of the initial ore.

4. A process according to any of Claims 1 to 3, wherein the ore is subjected to attrition in the form of a pulp having a solids content between 60 and 80%.

5. A process according to Claim 4, wherein the solids content of the pulp is between 65 and 75%.

6. A process according to any of Claims 1 to 5, wherein the relative speed of colliding particles during the attrition is less than 5 metres per second.

7. A process according to Claim 6, wherein the relative collision speed is between 2 and 4 metres per second.

8. A process according to any one of Claims 1 to 7, wherein the ore is agitated in pulp form during attrition by a moving agitator.

9. A process according to Claim 8, wherein the pulp passes through the agitator between 1,000 and 10,000 times per hour.

10. A process according to Claim 9, wherein the pulp passes through the agitator between 3,000 and 5,000 times per hour.

11. A process according to any one of Claims 8 to 10, wherein the speed of the pulp through the agitator is between 0.9 and 2.4 metres per second.

12. A-process according to any preceding claim, wherein the ore is subjected to attrition for between 20 minutes and 2 hours.

13. A process according to any preceding claim, wherein rejected particles having a size above said value are subjected to at least one further treatment as defined in any one of Claims 1 to 12.

14. A process according to Claim 13, wherein the total number of treatments is between 1 and 5.

15. A process according to Claim 14, wherein the total number of treatments is between 1 and 3.

1 6. A process according to any one of Claims 13 to 1 5, wherein the duration of the attrition is increased with successive treatments.

17. A process according to any preceding claim, wherein the total duration of attrition is between 30 minutes and 5 hours.

1 8. A process according to Claim 17, wherein the total duration is between 1 and 5 hours.

1 9. A process according to Claim 18, wherein the total duration of attrition is between 1 and 3 hours.

20. A process according to any preceding claim, wherein the nickeliferous ore is subjected to a preliminary grinding such that the d80 of the ground ore is between 100 and 5.000 microns.

21. A process according to Claim 20, wherein the d80 of the ground ore is between 200 and 1,000 microns.

22. A process according to any preceding claim, wherein the silica content of the nickeliferous ore is between t and 46%.

23. A process as claimed in Claim 1 and substantially as herein described.

24. A process for upgrading the nickel content of a nickeliferous ore, substantially as herein described with reference to any one of Examples 1 to 9 of the invention.

25. Ore when processed according to any preceding claim.

26. Ferro-nickel when produced by reduction smelting ore as claimed in Claim 25.

27. The features as herein disclosed, or their equivalents, in any novel selection.