AU2008101213B4

AU2008101213B4 - Method for Leaching Nickel

Info

Publication number: AU2008101213B4
Application number: AU2008101213A
Authority: AU
Inventors: Michael Rodriguez
Original assignee: Murrin Murrin Operations Pty Ltd
Current assignee: Murrin Murrin Operations Pty Ltd
Priority date: 2008-09-10
Filing date: 2008-12-11
Publication date: 2009-07-02
Anticipated expiration: 2016-12-11
Also published as: AU2008101213A4; AU2008101213B8; AU2008101213A8

Description

Regulation 3.2 ORIGINAL AUSTRALIA Patents Act 1990 INNOVATION SPECIFICATION Invention Title: Method for Leaching Nickel The invention is described in the following statement: 1 -2 "Method for Leaching Nickel" Field of the Invention The present invention relates to a method for leaching nickel. More particularly, the method of the present invention is intended to provide a single process for the 5 leaching of nickel from a variety of nickel ore compositions. Background Art To date, high grade nickel sulphide ores have been treated pyrometallurgically via smelting, in order to recover nickel. These ores are generally unsuited to hydrometallurgical treatments such as High Pressure Acid Leach (HPAL), as their 10 highly reducing nature lowers the oxidation potential which in turn may result in damage to the autoclave lining. Traditionally, an operator must be very selective about any sulphide material entering a HPAL autoclave. In particular, the Fe/Mg ratio, together with the oxidation potential, would need to be carefully monitored. Alternatively, the treatment of ores via pyrometallurgical methods requires 15 significant capital expenditure as a result of the plant infrastructure required to support the conditions required for such processes. Low grade nickel sulphides typically contain high quantities of Mg. If the MgO content of the slag produced in smelting is too high, it becomes very viscous and can be difficult to remove from the furnace. Further, these ores contain arsenic at 20 levels which render them unsuitable to smelting. Australian Innovation Patent 2008100563 discloses a method for the combined treatment of sulphide and oxide ores in a high pressure acid leach circuit in the presence of an oxidant, wherein the oxidant is preferably oxygen. The use of oxygen readily enables a much higher oxidation/reduction potential or ORP 25 (approximately 800mV or greater) to be achieved. High ORP has been -3 understood to be beneficial to ensure that no degradation of the titanium oxide lining in HPAL autoclaves occurs as a result of low ORP. The present method has as one objective thereof to substantially overcome the problems associated with the hydrometallurgical treatment of smeltable and/or 5 non-smeltable nickel sulphide ores, by providing treatment of same via a hydrometallurgical circuit, or to at least provide a useful alternative to prior art methods. Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be 10 understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part 15 of the common general knowledge as at the priority date of the application. Disclosure of the Invention In accordance with the present invention there is provided a hydrometallurgical method for leaching nickel, said method comprising the method steps of: i) directing a nickel laterite feed material to a high pressure acid leach 20 (HPAL) circuit; and ii) adding a sulphide ore or concentrate feed material to an autoclave of the HPAL circuit, wherein an oxidant is added to the autoclave to maintain an oxidation/reduction potential (ORP) within the range of 300mV to 600mV (Ag/AgCI reference).

-4 More preferably, the ORP in the cooled autoclave discharge is within the range of about 350 to 450mV. Still preferably, the oxidant includes, but is not limited to, one or more of ferric iron and manganese dioxide (MnO 2 ). 5 More preferably, the oxidant is ferric iron added in the form of a pregnant leach solution (PLS) resulting from a heap leach. The sulphide ore or concentrate may comprise a smeltable sulphide ore or concentrate, a non-smeltable ore or concentrate, or a blend thereof. The PLS from the heap leach circuit preferably has a ferric iron concentration 10 within the range of about 5 to 30 g/L. More preferably, the PLS from the heap leach circuit has a ferric iron concentration within the range of about 5 to 10 g/L. Preferably, the laterite feed material has a free acid concentration within the range of 10 to 50 g/L. 15 More preferably, the free acid concentration in the laterite feed material is within the range of 10 to 20 g/L. Preferably, the laterite feed material has a nickel concentration within the range of 2 to 8 g/L. More preferably, the laterite feed material has a nickel concentration within the 20 range of 3 to 5 g/L. The sulphide ore or concentrate preferably has a nickel content within the range of about 2 to 30% Ni.

- 5 More preferably, the sulphide ore or concentrate has a nickel content within the range of about 10 to 20%. Preferably, the nickel laterite feed material comprises a slurry of nickel containing ore with water and/or sulphuric acid. 5 Preferably, the sulphide ore or concentrate is combined with the laterite feed material to form a blended ore material prior to addition to the autoclave. The presence of the oxidant enables the addition of substantially any ratio of sulphide ore or concentrate to laterite feed material. However, it is preferable for operating purposes that the content of sulphide ore or concentrate in the blended 10 ore material is within the range of about 1 to 50%. More preferably, the content of the sulphide ore or concentrate in the blended ore material is within the range of about 2 to 20%. Preferably, the iron content in the sulphide ore or concentrate is sufficient to stabilise any arsenic present in the form of iron arsenate. 15 Preferably, the free acid concentration in the autoclave is within the range of about 20 to 100 g/L (measured in the cooled autoclave discharge). More preferably, the free acid concentration in the cooled autoclave discharge is within the range of about 40 to 80 g/L. The ferric iron concentration within the cooled autoclave discharge is preferably 20 within the range of about 0.5 to 30 g/L. More preferably, the ferric iron concentration within the cooled autoclave discharge is within the range of about 1 to 5 g/L.

- 6 Preferably, the temperature within the autoclave is maintained between about 200 and 2800C. The residence time within the autoclave is within the range of about 15 to 90 minutes. 5 More preferably, the residence time within the autoclave is within the range of about 30 to 90 minutes. The pressure of within the autoclave is preferably maintained within the range of about 3500kPa to 6500kPa. More preferably, the pressure within the autoclave is maintained within the range 10 of 4000kPa to 5500kPa. Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawing, in which; Figure 1 is a diagrammatic representation of a flow sheet depicting a 15 hydrometallurgical method for leaching nickel in accordance with the present invention. Best Mode(s) for Carrying Out the Invention In Figure 1 there is shown a hydrometallurgical method 10 for the leaching of nickel in accordance with the present invention. 20 A nickel sulphide ore 12, comprising a smeltable sulphide ore or non-smeltable ore, or a blend thereof, undergoes a concentration step 14 to produce a nickel sulphide concentrate 16. The nickel sulphide concentrate 16, having a nickel content within the range of about 2 to 30%, for example 10 to 20%, is then -7 combined with a nickel laterite feed material 18 to form a blended ore material 20. The nickel laterite feed material 18 comprises either a pregnant leach solution (PLS) exiting an atmospheric leach, for example a heap leach, or a slurry of nickel containing ore with water and/or sulphuric acid. The free acid concentration of the 5 nickel laterite feed material 18 is within the range of about 10 to 50 g/L, for example 10 to 20 g/L. The concentration of nickel within the nickel laterite feed material is within the range of about 2 to 8g/L, for example 3 to 5g/L. The sulphide ore 12 or concentrate 16 and nickel laterite feed material 18 are combined such that the sulphide ore 12 or concentrate 16 comprises about 1 to 10 50% of the blended ore material, for example 2 to 20%. The blended ore material 20 is then directed to an autoclave 22 of a HPAL circuit. An oxidant 24, for example manganese dioxide and/or ferric iron is added to the autoclave 22. Where the oxidant 24 is in the form of ferric iron, it can be added in the form of a PLS from an atmospheric leach, which has a ferric iron 15 concentration within the range of about 5 to 30 g/L, for example 5 to 10 g/L. Manganese dioxide occurs naturally in the ore material and is therefore also a readily available oxidant that does not incur significant expense. The blended ore material 20, in the presence of the oxidant 24 is then leached in the autoclave 22 at a temperature within the range of about 200 to 280 0 C, and a pressure within 20 the range of about 3500kPa to 6500kPa, for example about 4000kpa to 5500kPa, for a residence time within the range of about 15 to 90 minutes, for example, 30 to 90 minutes. The presence of the oxidant 24 ensures that the oxidation/reduction potential (ORP) is maintained within the range of about 300 to 600mV (Ag/AgCI reference, and measured in the cooled autoclave discharge), for example 350 to 25 450mV (Ag/AgCl). The resulting leach slurry 26 exiting the autoclave 22 is then subjected to known recovery processes. The addition of the oxidant 24 ensures that the ORP can be maintained within the desired limits specified above. ORP within these limits allows for ferrous iron - 8 (produced as a result of the oxidation of sulphide in the ore) to be re-oxidised to ferric iron. This in turn generates further acid, helping to maintain acid levels within the process. It should also be noted that maintaining the ORP ensures sufficient iron remains in solution to stabilise arsenic in the form of iron arsenate, 5 enabling the relatively safe treatment of non-smeltable sulphide ores. The Applicant has also surprisingly discovered that higher extractions, in the order of 2 to 3%, are obtained when the ORP is maintained within this lower range. Further, the oxidising conditions minimises any potential damage to the autoclave lining, particularly in cases where the autoclave lining comprises titanium dioxide 10 (TiO 2 ). That is, the oxidising conditions prevent TiO 2 from undergoing a reduction reaction resulting in the dissolution of Ti into solution. Thus, by adding an oxidant and ensuring that the ORP is maintained within the desired limits, there is theoretically no limit to the amount of sulphide that can be added to the autoclave. It is understood that the sulphide ore 12 need not necessarily undergo a 15 concentration step 14 in order to be utilised in the method of the present invention. It is also understood that the sulphide ore 12 or concentrate 16, and the laterite feed material 18 could be added directly to the autoclave 22, without the requirement of blending first. The present invention is further illustrated by way of the following non-limiting 20 examples: Example I High Pressure Acid Leach of Blends of Laterite HPAL feed, High Grade Sulphide Ore Two high pressure acid leaches were conducted, one on each of two blends, 5% 25 and 10% (w/w) nickel sulphide ore.

-9 The compositions of the laterite and sulphide ores are provided in Table 1 below: Table 1 Sample Unit Analysis Ni Co Fe Fe(II) S(t) S2- so FA Sulphide % 3.25 0.099 19.4 - 3.12 2.85 0.3 HPAL Feed % 1.12 0.132 28 - - - - The results from the leach tests are provided in Table 2 hereinafter. The main 5 observations from these tests were: " The ORP values during the leach were significantly lower for the 10% sulphide blend " The 10% blend generated higher residual free acid concentrations e There were significantly higher Fe(II) concentrations in the product 10 liquor when leaching the 10% blend. " Nickel and cobalt recoveries were greater at the beginning of the leach for the 10% blend. However, with increasing leach time, these differences became insignificant. * The nickel concentration in the PLS after 120 minutes was much 15 higher in the 10% blend test than in the 5% blend test (7640 mg/L compared with 6080 mg/L). This is believed to be due to the fact that more nickel is added to the system as a result of the increased % of nickel sulphide added. The overall extractions were very similar for both tests 1 and 2, being 97.1% and 97%, respectively.

U, > ) r. CV) OLL U co 0 No-v C)C CN - 'D C) o) >0< qC) < CD I C)C) C) U) 0 f f C) Z -0~- C) C) >)~ >0 C)0 CD U-co E U 0 N 0> C N- C) 0 N > LI) O) 0 < co cc N- N cc U) CD CC4 - 11 Example 2 High Pressure Acid Leach of High Grade Sulphide and Laterite blend in the presence of Column PLS Four tests (Test 3 to 6) were conducted in the presence of column leach PLS, 5 simulating the flowsheet of the present invention in which PLS from a heap leach is also added to the HPAL circuit. The composition of each of the ore streams is provided in Table 3 below: Table 3 Sample Unit Analysis Ni Co Fe Fe(II) S(t) S2- so FA Sulphide % 3.25 0.099 19.4 - 3.12 2.85 0.3 HPAL Feed % 1.12 0.132 28 - - - - Column mg/L 4,520 277 47,000 123 - - - 36,230 PLS 10 The conditions used are provided in Table 4 below: [the remainder of this page is intentionally blank] -12 Table 4 Test No. % (w/w) Sulphide Vol. % of Column Acid Addition, Ore PLS kg/t 3 10 10 384 4 10 10 295 5 15 10 295 6 20 10 295 Results from each of the tests are provided in Table 5 hereinafter. The following observations were made after comparing the results from Test 3 5 with those of Test 4: " Slightly higher nickel and cobalt recoveries were obtained with the higher acid addition leach. After 90 minutes nickel recoveries were 96.5% for Test 3 and 94.6% for Test 4. * Higher residual free acid concentrations were obtained when higher 10 acid addition was used. " Slightly higher redox values were recorded in Test 3, after 90 minutes of leaching the values obtained were 483mV for Test 3 and 451 mV (Ag/AgCI) for Test 4. * Even at the lower acid addition of Test 4, the residual free acid 15 concentration after 120 minutes of leaching was 58.3 g/L.

-13 The following observations were made when a comparison was made between Test 5 and Test 6: * A relatively low acid addition was used in Test 5 and Test 6. However, the free acid concentration decreased to less than 50g/L 5 only in the 20% sulphide ore test (Test 6). Furthermore, higher Fe(II) concentrations were generated in Test 6 and the ORP values correspondingly lower. " Analysis of the leach residues showed that essentially all of the sulphide sulphur (originally present in the sulphide ore) was oxidised 10 to the sulphate condition. Conclusions: As is observed from examples 1 and 2, significant quantities of sulphide ore or concentrate can be treated, as the ORP can be maintained within desirable limits by the addition of an oxidant. 15 The results of these tests further indicated that significant increases in the nickel concentration of the product leach liquor were possible by blending high grade sulphide ore with the HPAL feed material (laterite feed). Savings on acid additions appear to be possible as a result of the oxidation of the sulphide component in the high grade sulphide ore. That is, the oxidising 20 conditions promote acid regeneration. Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

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Claims

1. A hydrometallurgical method for leaching nickel, said method comprising the method steps of: i) directing a nickel laterite feed material to a high pressure acid 5 leach (HPAL) circuit; and ii) adding a sulphide ore or concentrate feed material to an autoclave of the HPAL circuit, wherein an oxidant is added to the autoclave to maintain an oxidation/reduction potential (ORP) within the range of about 300mV to 10 600mV (Ag/AgCI reference).

2. A hydrometallurgical method according to claim 1, wherein the ORP is maintained within the range of about 300mV to 450mV.

3. A hydrometallurgical method according to claim 1 or 2, wherein the oxidant comprises one or more of ferric iron or manganese dioxide. 15

4. A hydrometallurgical method according to claim 3, wherein the ferric iron is added via the addition of a pregnant leach solution (PLS) resulting from a heap leach.

5. A hydrometallurgical method according to any one of the preceding claims, wherein the temperature in the autoclave is maintained within the range of 20 about 2000C to 2800C and the pressure is maintained within the range of about 3500kPa and 6500kPa.