AU8077698A - Leaching of a nickel sulphide concentrate - Google Patents

Description

AUSTIRALIA

Patents Act 1990 COMPLETE

SPECIFICATION

sTANDARD PATENT Applicant: W14C RESOURCES LIMITED 004 184 598) invention Title: Leaching of a Nickel Sulphide Concentrate The following statement is a full description of this invention, including the best method of performing it known to

US:

2 LEACHING OF A NICKEL SULPHID

CONCENTRATE

FIELD OF THE INVENTION The present invention relates generally to a method for oxidative leaching of nickel and other valuable metals from a nickel sulphide concentrate.

BACKGROUND TO THE INVENTION Nickel sulphide concentrates primarily contain the sulphide minerals pentlandite and pyrrhotite together with some violarite, chalcopyrite and pyrite, but may also contain various gangue oxide minerals containing iron, silica and magnesium. The only commercially proven method of leaching these concentrates is by pressure oxygen leaching in 15 ammonia solution at 80 0 C, as in the Sherritt-Gordon Process, which selectively leaches nickel, cobalt and copper from the iron, silica and magnesium minerals.

Unfortunately this process is energy intensive and produces large quantities of ammonium sulphate as well as iron oxide 20 residues, and is no longer used for nickel concentrates.

Pressure oxygen leaching of mineral sulphides in dilute sulphuric acid solution has been commercialised for many years as typified by the Sherritt Process for treating refractory sulphide gold ores or zinc sulphide concentrates. However investigations are continuing with nickel and copper sulphide concentrates.

Generally in the pressure leaching of sulphide minerals it is found that below 120 0 C the rate of leaching is slow, and oxidation of the sulphide produces mostly solid elemental sulphur which can inhibit the diffusion of oxidant to the Smineral surface. At temperatures between 120 to 160 0 C the Srate of leaching is fast, but the elemental sulphur melts and can encapsulate the remaining sulphide minerals to prevent complete recovery. Some sulphur slowly oxidises to

~T~T~T~T~T~T~T~T~T~T~T~T~T~T~T~T~T~

3 sulphuric acid under these conditions. At temperatures above 200 0 C all the sulphur is oxidised to sulphuric acid and complete leaching of the metal is achieved, but the cost of oxygen and base to neutralise the acid formed is high.

When the concentrate contains significant amounts of iron, as in pyrrhotite, pentlandite and chalcopyrite concentrates, it is preferable to pressure oxygen leach at temperatures below 160 0 C in order to hydrolyse the iron as it is leached and precipitate iron oxides in the weakly acidic leach liquor. However, the abovementioned problems associated with leaching at this temperature still have to be overcome.

Vezina in The Canadian Mining and Metallurgical Bulletin, May, 1973 reported that by fine grinding a chalcopyrite-pentlandite-pyrrhotite concentrate to a size of P80 less than 20 microns, almost complete extraction of 20 nickel and cobalt was achieved in 8 hours at 110 0 C. Copper extraction was only partially complete under these conditions. However 8 hours leaching is considered too long for economic benefit.

Subramanian and Ferrajuolo in Elsevier's Hydrometallurgy, 2(1976)reported that the addition of chloride ion to a similar finely ground Fe-Ni-Cu sulphide concentrate significantly enhanced the recovery of copper and precipitation of iron, without affecting nickel extraction.

Up to 95% Ni and 79% Cu were extracted in about 2 hours under the optimum conditions where 68% of the concentrate was less than 11 microns in size. However, to achieve a ground mineral size of less than 11 microns requires ultra-fine milling which is energy intensive and relatively expensive. tr F 4 -4- Several papers have since reported the benefit of chloride icn addition to sulphate solutions to specifically enhance the rate of reaction and copper recovery in the pressure oxygen leaching of copper sulphides.

Tn_Elsevier's Hydrometallurgy, 29(1992) Nyman et al described the Outokumpu HIKO Process in which a nickel-copper-iron sulphide concentrate was leached by oxygen pressure at 1100C in dilute sulphuric acid. A temperature below the melting point of sulphur was advocated as being enough provided the slurry was intensively mixed. However, no details of the leach conditions, time or required particle size were given.

Extraction yields of 96% Ni, 94% Co and 66% Cu were 15 reported.

Dominion Mining Ltd has recently described, in Australian patent application No. 663525, its so-called ACTIVOX Process for leaching mineral sulphides including nickel 20 sulphides whereby the mineral is first "activated" by ultra-fine milling to a size of between 2 to 20 microns equal to 15 microns). The "activated" mineral Ssulphide is then pressure oxygen leached in dilute sulphuric acid at a temperature of 110 0 C. Complete leaching is achieved in 15 to 150 minutes according to the mixing conditions or mineral used. However the capital cost and energy cost associated with ultra-fine milling is high and efficient solid-liquid separation and washing is difficult.

Cominco Ltd has also recently described, in a paper presented by David L. Jones in October 1996 at a Alta Copper Hydrometallurgy Forum, its so-called CESL Copper Process for treating chalcopyrite concentrate. The concentrate is ball milled to a size of 30 to 40 microns and then pressure oxygen leached in dilute sulphuric acid at 150-C for 1 hour in the presence of about 12 grams per litre chloride ion- The presence of chloride ion is necessary to improve the recovery of copper from copper sulphides Thus;~~~ teporatteaches that -to- pressurre- leach nickel suiphide concentrates in a reasonable time, it is necessary to either ultra-fine grind the concentrate prior to leaching, each at a temperature above the melting point of sulphur. it also teaches that the addition of chloride ion enhances the recovery of copper from the concentrate but not the recovery of nickel.

SUNMARY OF THE INVENTION An intention of the present invention is to provide a method for oxidative leaching of a nickel sulphide a concentrate, said method being relatively quick and inexpensive in recovering a high percentage of nickel and other valuable metals.

C According to one aspect of the present invention there is provided a method of preparing a leach solution for oxidative leaching of a nickel sulphide concentrate, said method comprising the step of: a) adding copper ion, readily leachable copper salts compounds, or copper metal to the leach solution or the nickel sulphide concentrate so that said copper catalyses the oxidative leaching of the nickel sulphide concentrate whereby a relatively high percentage of nickel and other valuable metals can be recovered from said nickel sulphide concentrate over a relatively short period of time.

According to another aspect of the present invention there is provided a method for oxidative leaching of a nickel -6sulphide concentrate, said method comprising the st~eps Of: a) adding copper ion,, readily leachlable copper salts compounds, or copper metal to a leach-scflljtiof or the nickel sulphide concentrate in preparation for leachinlg of the nickel sulphide concentrate; andainiklslhd b) oxidatJively leaching sai nicke cpper concentrate in the presence ofsadcpe whereby said copp~er catalyses the oxidative leaching Of said concentrate so that a relatively high percentage of nickel and other valuable metals can be recovered from said concentrate over a relatively short period of time.

15 Generally,~ the nickel sulphide concentrate includes a relatively low level of copper minerals. Typically, the nickel sulphide concentrate has levels of copper minerals which would ordinarily provide less then approximately 5 gramsllitr copper ion to a conventional leach solution- However, it should be appreciated that the invention extends to nickel sulphide concentrates having higher levels Of copper minerals where the addition of copper acts so as to improve leaching kinetics and the recovery of nickel and other valuable metals- PreferablY, said method includes the step of adding acid to the leach solution prior to oxidative leaching of the nickel sulphide concentrate. Typically, sufficient acid is F C> added to the leach solution so that during oxidative leaching the pH remains below approximately 3 and thus the precipitation of the copper from solution as basic copper sulphate (2Cu(OH)2 .CUSO41 is avoided. The required amount of acid to be added will depend largely upon the amount Of acid consuminlg gangue minerals in the nickel sulphide concentrate and on the degree of sulphur oxidation during the oxidative leach. Generally, acid is added to the leach 7 solution in the form of sulphuric acid.

Typically, the addition of copper in step involves the addition of between approximately 1 to 20 g/1 copper ion to the leach solution- More typically, the copper is added such that a concentration of between approximately 5 to g/l. Copper ion is present in solution during leaching.

Generally, the addition of copper in step involves the addition of a copper (II) salt such as copper sulphate, a readily leachable copper compound such as precipitated copper sulphide, or copper metal, added either to the leach solution or nickel concentrate.

Preferably, said method further comprises the step of recovering the copper subsequent to oxidative leaching of the nickel sulphide concentrate, and thereafter recycling said copper for addition to the leach in step Typically, the recovery of copper for recycle to the leach solution involves one of several known methods including solvent extraction, cementation onto iron or nickel sulphide, or precipitation with sodium sulphide.

Typically, said method also comprises the step of adding i chloride ion to the leach solution or the nickel sulphide concentrate. It has been discovered that the addition of chloride ion maintains the copper in solution avoiding precipitation of some copper sulphide to a residue.

Typically, the chloride ion is added at a concentration of between approximately 2 to 50 g/l. Preferably, the chloride ion is added at a concentration of between approximately 10 to 20 g/l.

It has been observed that, with chloride ion concentrations in excess of approximately 20 gl/, copper ion concentration in solution decreased thereby slowing the oxidative leach kinetics. The decrease in copper ion concentration in 8 solution is believed to occur because chloride ion inhibits the formation of sulphuric acid and precipitation of an intermediate basic copper sulphate [2Cu(OH).CuSOj occurs until sufficient acid is generated to re-dissolve the precipitate.

Typically, said method may include the step of fine grinding the nickel sulphide concentrate prior to oxidative leaching in step Generally, the fine grind is achieved in a conventional ball mill. More typically, said nickel sulphide concentrate is finely ground to a particle size of between approximately 30 to 70 microns with a preferred particle size of between approximately to 50 microns. Advantageously, this avoids ultra-fine milling to a P80 of less than approximately 30 microns which is relatively expensive to achieve.

Typically, oxidative leaching of the nickel sulphide concentrate in step is conducted at a temperature below the melting point of elemental sulphur. Thus, generally the oxidative leach is performed at a temperature of less than approximately 120 0 C being the melting point of -elemental sulphur. More typically, the oxidative leach is conducted at a temperature of approximately 110 0

C.

Leaching at a temperature in excess of approximately 120 0

C

can cause the formation of molten sulphur balls which can lower the recovery of nickel and other valuable metals and also present difficulties in residue handling.

Typically, the oxidative leach is conducted at an oxygen pressure of between 500 to 2500 kPa. More typically, the oxidative leach is at an oxygen pressure of between 1500 to 2000 kPa.

Typically, said process achieves recoveries of nickel and cobalt in excess of approximately 90%. Typically, this recovery of nickel and cobalt is obtained over ac period of less than approx atel ore tcoer of the nickel and other valuabe met i rcovered within approxim ateT-2to 3 hurs- BRIE DESC RIPTION O E E S of the nature in order to facilitate a better derstandine nat of the present invention several preferred e diments methods for oxidative leaching of a nickel sulphide b by wa of example only, concentrate will ow be described, b whicha of exaple onl with reference to the fol ing graphs in which Figure 1 is a base plot of nickel extraction versus grind size for a blended nickel sulphid concentrate grind oize tor- a Mt Kith (BuKO) and without copper addition using t Kith and Leinster (LNO) process water; SFigure 2 is a base pot of copper extraction versus grind size for the blended concentrate without copper ^addition; me or Figure 3 is a base plot of extraction versus time for the blended concentrate without copper addition; Figure 4 is another base plot of extraction versus time for the blended concentrate without copper versus time for the blended concentrate with copper ion addition; r t Figure 6 is a plot of extraction versus time for the blended concentrate with copper ion addition; Figure 7 is a plot of nickel extraction versus time for a nickel sulphide concentrate with copper ion addition at different temperatures and pressures; Figure 8 is a plot of nickel extraction versus time for the nickel sulphide concentrate with the addition of less copper ion; Figre 9 is a plot of nickel extraction versus time for the nickel sulphide concentrate with copper ion 10 addition at different oxygen pressures; Figure 10 is a plot of nickel. extraction versus time for the nickel sulphide concentrate with copper ion addition at various oxygen pressures and at a lower temperature; Figure 11 is a plot of nickel extraction versus time for the nickel sulphide concentrate with copper ion addition at elevated oxygen overpressures; Figure 12 is a plot of nickel extraction versus time for the nickel sulphide concentrate with copper ion addition together with various levels of chloride ion addition; Figure 13 is a plot of copper distribution versus time for the nickel sulphide concentrate with copper ion addition at various levels of chloride ion addition: Figure 14 is a plot of residual sulphuric acid versus time for the nickel sulphide concentrate with copper ion addition at various levels of chloride ion addition; Figure 15 is a plot of nickel extraction versus time for the nickel sulphide concentrate with copper ion addition with and without acid addition; Figure 16 is a plot of copper distribution versus time for the nickel sulphide concentrate with copper ion addition with and without acid addition; Figure 17 is a plot of nickel extraction versus time at 1400C for the nickel sulphide concentrate with copper ion addition at various concentrate P80 grind sizes; and Figure 18 is a plot of nickel extraction versus time at 110°C for the nickel sulphide concentrate with copper ion addition at two fine concentrate P80 grind sizes.

D :ALD DESCRIPTION OF THE PREERRD

EBD~T

Base trials were performed on a blended nickl 5 lhd concentrate from Kanlbalda, Leinster and M4t Kihi etr Austali hainga Sze of p80 equalto7mirn ad 0 taifling 14-7% Ni, 39Co 45Cu 3.7 Fe 3.%lg and 29.2% S- spesr oye ece The "as received' concentrate Was.ye pressure aneahd for 2 hours at 110 0 C and 150WC, 500 kPa oye resr n 8.9% solids pulp density usingwae frmtKih .9 Soai i d 8 gan per litre (g total dissolved solids (TDS) and water from.Leinster containing less than1gl TDS. This provided base results in the asneo de copper and without fin gatalyse 1 eCT Xnd2 sulhurc aid ereadded initially tocaayeogn utansfri and toenre th ial leach solution remained slightly acidic.

Thebas reult inTable 1 below show thatol ata Te as e of s lt Ni iC n d Cu s a h ed in 2 hours, even at 150Wand that the presence of about 4 g/l1hoieini the pro0Ces ae hda r significant effect On Cu.

reoYtac nN n orcv~Y The effect Of cord ion wa o incease the recovery of Ni and Co atJ 110Wbut dcreae the recovery at 1500. Ithabec o chlrideionrather more acid and iron entered h leach solution.

Wate Sorce Temperature Recovery% oefttil(g) Ni Co CU Fe S0 MtKit 100 659 58.4 64.3 1.3 3.6 71.8 62.99 51.3 7.6 43.2 Lentr100 56.7 52.6 44.6 54 (n cloid)1500 4. 8. 50.6 42.9 40.5 Bass trials Without copper additi=f 12 Further base trials were conducted on the blended nickel sulphide concentrate without copper addition but with grinding of the concentrate to various sizes. The results of these further base trials are shown in the graphs of Figures 1 and 2.

The base test results in Figure 1 indicated a significant increase in nickel extraction with a decrease in particle size (P80) for each leaching time assessed. The response of cobalt extraction to variations in grind size was essentially identical to that of nickel. Figure 1 also indicated that nickel extraction improved with increased salinity or chloride ion concentration.

Figure 2 indicated that copper extraction was less affected by grind size (especially after 180 minutes of leaching) than nickel or cobalt. Additionally, increased salinity or chloride ion concentration significantly improved the leaching response of copper. However the concentration of copper ion in solution was less than 1 g/l, and 30 times less than the concentration of nickel.

Sulphur oxidation (which manifests as increased sulphuric acid concentration) also increased as particle size decreased. Coincident with the increased acid concentration was an increase in solution iron tenor.

However, as illustrated in Figures 3 and 4 the extraction of nickel and cobalt was still less than 90% after a 3 hour leach. Figures 3 and 4 represent leaching of the blended nickel sulphide concentrate using water from Leinster, having negligible salinity and Mt Keith, having some salinity, respectively. Leaching with the saline water which provides a source of chloride ion achieved a significant increase in copper extraction without greatly affecting the extraction of Ni and Co.

881~-r~ P~ I _i -13- Examle 13 al ee then perfored on the blended nickel sulphide entra te under similar leach conditions to the base concentrials except with the aditin f 10 /1 copper ion and 17tals xcet wh te As illustrated in Figures 5 and 6 17 g/1 chloride ion. extraction was achieved approximately 95% Ni and 90% Co etraction was achieved after leaching the ground concentrate at 1100C and 500 kPa Stoxrleaching the r y 2 to 3 hours. Although there was Soxyen pressure e on Ni and Co extraction between the a marked difference nconcentrate and the "as received" (p80 of 106 micron) concenthe difference in 10p8 of 28 microri concentrate ground to P8 le significant between extraction of both Ni and Co was le iniican e en the p80 of 14 and 28 micron tests- After 3 hours leaching Sthe p80 of 1 an d 2 8 m i c r o n teextraction of Ni and Co there was little difference in ra n in u l tra-fi n e i 15 between the P80 of 14 and 28 m and fine grinding, respectively- Exasmple o nickel sulphide concentrate from A sample of rougher tralia, which assayed at 10.8% Ni, 0.30% Co, 0.04% Cu, 19.1% Fe, 12.9% Mg and 16.3% S and was 0.30% CO, 0.04% Cu, 19.1 (p80 equal to 28 micron) ground to 100% passing 38 microns on80 eqal t 28 micron) in a ball mill. The nickel sulphide concentrate ures then pressure leached for up to a4 hous in the presence of 500 kPa and 1500 kPa at 0 and 140 in the presence of 2 5 500 addition of either 2,S NaC (18 g/l CI and with the addition of either 2, or 10 g/l Cu(II) as copper sulphate.

Sn Figure 7 to 10 show that at the lower The results given in Figurethe extraction of '*copper concent 5 ation' oxygen pressure and copper concentrationickel was extracted nickel was slow at 11C and only 50% nickel wasching was after hours However, significantly faster leaching was after 4 ho u r s H o w e v e r, s g in the presence of obtained with 1500 kPa oxygen pressure it at least 5 g/1 Cu(II) so that abut 9 Ni wa extrate of after 3 hours eachig at 110C At 140 0 C the rate of l35 afer 3 hours le a oxygen I leaching was faster than at 110C. but -CI-li- achI 14 pressure and copper addition was not so pronounced.

After 2 hours leaching at 140 0 C a small decrease in nickel extraction was observed, possibly due to some re-adsorption of nickel into the iron oxide and silica residue.

Subsequent tests showed that the decrease in nickel concentration with time was greater if the concentrate was ground even finer to P80 of 14 microns. However this effect was not observed at 110°C. Thus, there appears to be an advantage to leaching at 110 0 C rather than 140 0 C in obtaining higher overall nickel recoveries despite slightly longer leach times.

,A single leach test was then conducted to assess the effect S. s 15 of an elevated (2000 kPa) oxygen overpressure at 110 0 C on leaching response. The results were compared to a similar test conducted at 1500 kPa oxygen overpressure and the nickel extraction kinetics are plotted in Figure 11. With the exception of increased sulphur oxidation, 39% at 1500 kPa compared to 48% at 2000 kPa, increasing oxygen pressure had negligible effect on valuable metal leaching kinetics and impurity deportment.

Example 3 The nickel sulphide concentrate of Example 2 having been ground to a size of P80 equals 28 microns was pressure leached at 110 0 C and both 500 and 1500 kPa oxygen pressure in the presence of 10 g/l Cu(II) for up to 4 hours with various chloride ion concentrations ranging from 0.25M to 2.0M Cl (9 to 73 g/1 Cl). The results are included in Table 2 below and Figure 12.

Test Conditions Extraction Residue Cu(%) Test Conditions 40- minute- 120 240 Test 02 Cu C 120 minute 240 minute o m te No. kPa AI M Ni Co Ni Co Mg S minute minute 1 OO 2 0 7.3 6.4 37.8 35.8 16.1 28.0 0.74 079 2 500 2 0.5 18.3 17.0 55.2 50.7 18.2 35.8 0.78 0.83 3 1500 10 0.25 96.4 98.5 97.5 98.5 25.5 43.6 0.43 0.42 4 1500 10 0.5 97.1 97.0 98.0 9.0 24.1 39.1 0.52 0.40 1500 10 1.0 97.3 97.4 97.7 98.5 20.2 39.6 0.55 0.43 6 1500 10 2.0 92.1 92.2 95.3 96.2 19.0 36.0 1.48 0.36 TABLE 2 Summary of Valuable Metal Extractions (Effect of Chloride) Note: 1. S extraction represents oxidation of sulphide sulphur to soluble sulphate.

2. All leach tests conducted at 110 0

C.

3. H2S04 added for test Nos.3 to 5 but not for test Nos.l and 2.

As well illustrated in Figure 12 the chloride ion 10 concentration had little effect on nickel extraction.

Indeed, with chloride ion concentrations in excess of a small decrease in nickel extraction and final acid concentration was evident. f *a n 15 Figure 13 shows the results of monitoring copper concentration with time. A significant decrease in copper concentration was experienced during the initial hour of leaching when in excess of 0.5M chloride ion concentration was used. It is believed that this is a consequence of copper being precipitated onto the nickel sulphide initially as copper sulphide (CuS) and then being releached. That is, Cu(II) NiS CuS Ni(II) This reaction is well known in the processing of nickel matte (Ni 3

S

2 in chloride media.

Alternatively, it is possible that copper is precipitated at a pH of 3 to 4 as basic copper sulphate [2Cu(OH) 2 .CuS04].

l 16 Figure 14 illustrates another effect of chloride ion concentration. Higher concentrations of residal sulphuric acid in the leach solution are achieved with lower concentrations of chloride ion. Accordingly, the pH is maintained at a relatively low value, preferably below about 3.0, so as to avoid the precipitation of copper as described in the preceding paragraphs.

Thus, there appears to be an optimum level of chloride ion concentration of between 0.25 to 0.5M so as to ensure that Cu(II) remains in solution and catalyses the leaching of the nickel sulphide concentrate.

Example4 Under otherwise similar conditions, the nickel sulphide Sconcentrate was leached at both 0C and 1400

C

and 1500 kPa oxygen pressure in the presence of 10 g/lCu() and 18 g/1 Cl (0.5M) but with the prior addition of ulphuric acid to the leach solution.

Figure 15 shows that the initial presence of acid enhanced the rate of extraction of nickel both at 110 0 C and 140 0

C.

A plot of the copper distribution with time in Figure 16 shows that in the absence of acid initially, nearly all of the added copper was precipitated within 10 minutes presumablY as basic copper sulphate due to the presence of basic gangue minerals in the concentrate and the acid consumption by oxygen. However, it was subsequently releached as acid was produced from the oxidation of sulphur during leaching.

As further depicted in Figure 16 the addition of acid maintained copper in solution throughout the leach and improved nickel leaching was obtained The amount of acid required will depend largely on the concentrate used and autoclave leach conditions. It is also necessary to 'i 17 ensure that the concentration of acid in the final leach liquor is not high enough to cause iron oxide to redissolve from the residue.

Example Trials were also conducted on the nickel sulphide concentrate under similar conditions to Example 3 at 110 0

C

and 140 0 C. The results are illustrated in the graphs of Figures 17 and 18, respectively. The leach tests were otherwise conducted with 1500 kPa oxygen overpressure, g/l copper ion addition, and 100 kg/tonne (kg/t) sulphuric acid addition at grind sizes of P80 between 14 to 150 microns.

Leach tests kinetics clearly indicate that ultra fine grinding to a P80 of 14 microns has a detrimental effect on nickel extraction at 140 0 C. A net reduction in nickel Sextraction with respect to increasing time was observed.

No such effect was observed for leaching at 110 0 C. Two proposed mechanisms for the effect are as follows: reaction of iron oxide minerals produced by leaching and precipitation adsorbing nickel ions from solution; and ii) reaction of silicate minerals being leached and reprecipitating as silica which adsorbs nickel ions from solution.

Now that several examples of the present invention have been described it will be apparent to those skilled in the relevant art that the method for oxidative leaching of a nickel sulphide concentrate has at least the following advantages over the admitted prior art: i) the oxidative leach achieves relatively high nickel and other valuable metal recoveries over a relatively short period of time; 18 ii) the oxidative leach does not necessitate an ultra-fine grind of the concentrate but rather is suited to fine milling which is relatively inexpensive; iii) the oxidative leach can be conducted over a range of temperatures between 100-150 0 C but preferably at a temperature of less than 120 0 C thereby avoiding problems associated with handling of molten sulphur; and iv) the oxidative leach is suited to the addition of chloride ion and/or acid so as to optimise the recovery of nickel and other valuable metals.

It will be appreciated that the method for oxidative leaching of a nickel sulphide concentrate is not limited to the examples described herein but may also extend to other embodiments which are considered to be within the scope of the present invention. For example, the invention would include mixtures of nickel sulphide concentrate with the addition of readily leachable copper salts or compound or minerals (such as copper oxide, hydroxide, sulphide or chloride) recovered from the leach solution or from other sources.

S 25 All such embodiments are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

a-

Claims (7)

1. A method of preparing a leach solution for oxidative leaching of a nickel sulphide concentrate, said method comprising the step of: a) adding copper ion, readily leachable copper salts compounds, or copper metal to the leach solution or the nickel sulphide concentrate so that said copper catalyses the oxidative leaching of the nickel sulphide concentrate whereby a relatively high percentage of nickel and other valuable metals can be recovered from said nickel sulphide concentrate over a relatively short period of ,..time.

2. A method for oxidative leaching of a nickel sulphide concentrate, said method comprising the steps of: a) adding copper ion, readily leachable copper salts compounds, or copper metal to a leach solution or the nickel sulphide concentrate in preparation for leaching of the nickel sulphide concentrate; and b) oxidatively leaching said nickel sulphide concentrate in the presence of said copper whereby said copper catalyses the oxidative leaching of said concentrate so that a relatively high percentage of nickel and other valuable metals can be recovered from said concentrate over a relatively short period of time.

3. A method for preparing a leach solution or a method of oxidative leaching as defined in claims 1 or 2 including the step of adding acid to the leach solution prior to oxidative leaching of the nickel i sulphide concentrate. Ip~P-D-- I 20 A method for preparing a leach solution or a method of oxidative leaching as defined in claim 3 wherein sufficient acid is added to the leach solution so that during oxidative leaching the pH remains below approximately 3 and thus the precipitation of the copper from solution as basic copper sulphate [2Cu(OH)2.CuS04] is avoided. A method for preparing a leach solution or a method of oxidative leaching as defined in any one of the preceding claims wherein the addition of copper in step involves the addition of between approximately 1 to 20 g/l copper ion to the leach solution.

6. A method for preparing a leach solution or a method of oxidative leaching as defined in any one of the preceding claims wherein the addition of copper in Sstep involves the addition of a copper (II) salt such as copper sulphate, a readily leachable copper compound such as precipitated copper sulphide, or copper metal, added either to the leach solution or nickel concentrate.

7. A method for preparing a leac solution or a method of oxidative leaching as defined in any one of the preceding claims further comprising the step of recovering the copper subsequent to oxidative leaching of the nickel sulphide concentrate, and thereafter recycling said copper for addition to the leach in step

8. A method for preparing a leach solution or a method of oxidative leaching as defined in any one of the preceding claims also comprising the step of adding chloride ion to the leach solution or the nickel 1

21- sulphide concentrate. 9. A method for preparing a leach solution or a method of oxidative leaching as defined in claim 8 wherein the chloride ion is added at a concentration of between approximately 2 to 50 g/l. A method for oxidative leaching as defined in claim 2 but in addition including the step of further grinding the nickel sulphide concentrate prior to oxidative leaching in step 11. A method for oxidative leaching as defined in claim wherein said nickel sulphide concentrate is finely ground to a P80 particle size of between approximately to 70 microns- 12. A method for oxidative leaching as defined in claims 10 or 11 wherein oxidative leaching of the nickel sulphide concentrate in step is conducted at a temperature below 120*C being the melting point of elemental sulphur. 1:13. A method for oxidative leaching as defined in any one of claims 10 to 12 wherein the oxidative leach is conducted at an oxygen pressure of between 500 to 2500 IrPa. 14. A method for preparing a leach solution or a method of oxidative leaching as defined in any one of the preceding claims wherein recoveries of nickel and cobalt in excess of approximately 90% are obtained over a leaching period of less than approximately 4 hours. -22- A method for preparing a leach solution or a method of oxidative leaching substantially as herein described with reference to Figures 5 to 1S inclusive. Dated this 182- day of August 1998 tWMC RSURCES LIMIjTED By his patent Attorneys GRIFFITH HACK -NBC