AU2009201837A1 - Atmospheric Leach of Laterite with Iron Precipitation as Hematite - Google Patents

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Atmospheric Leach of Laterite with Iron Precipitation as Hematite Applicant: BHP Billiton SSM Development Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: 1 ATMOSPHERIC LEACH OF LATERITE WITH IRON PRECIPITATION AS HEMATITE 5 Introduction The present invention resides in the process for the atmospheric pressure acid leaching of laterite ores to recover nickel and cobalt products. 10 More specifically, the invention resides in the sequential and joint acid leaching of the low magnesium ore fraction and high magnesium ore fraction of a lateritic ore to recover nickel and cobalt while disposing of iron as hematite. In one embodiment, a hematite seed is added to the leach process in order to initiate hematite precipitation. The hematite seed itself may be sourced from 15 any available source. One particular source may be from recycling a part of the hematite residue in the resultant discharge slurry following the high magnesium ore leach. Another source may be the residue following a high pressure leach of part of the low magnesium ore fraction. 20 Whereas the process is particularly applicable to processing the limonite and saprolitic fractions of laterite ore deposits, the process can also be applied to explore nickel containing smectitic or nontronitic ores, which typically contain high aluminium content and have iron and magnesium contents between those of typical limonite and saprolite ores or with comparable magnesium content to 25 the limonitic and saprolitic ores. Background of the Invention Laterite ores are oxidised ores and their exploitation requires essentially whole ore processing as generally there is no effective method to beneficiate the ore 30 to concentrate the valuable metals nickel and cobalt. As shown in Table 1, the iron/nickel ratio is variable being high in the limonite fraction, lower in the saprolite fraction and mediate in nontronite ore, therefore 2 the separation of solubilized nickel and cobalt from dissolved iron is a key issue in any recovery process. Ore Type Fe wt.% Mg Ni Co Fe/Ni ratio wt.% wt.% wt.% Indonesia limonite 40.8 1.30 1.53 0.10 27 Indonesia saprolite 8.5 14.60 3.37 0.03 3 Indonesia saprolite with 18.5 11.10 2.18 0.14 9 high Fe content ________ 0 41.3.63 New Caledonia limonite 47.1 0.40 1.33 0.16 35 New Caledonia saprolite 7.7 23.3 1.00 0.02 8 Western Australian low-Mg 25.4 4.90 2.50 0.07 10 ore Western Australian high-Mg 10.0 16.6 1.38 0.02 7 ore Cuban low-Mg nontronite 21.6 2.60 1.80 0.05 12 ore I I _ I Cuban high-Mg nontronite 18.8 8.30 1.17 0.04 16 ore _ 5 Table 1 Iron, Nickel and Cobalt Content in Various Laterite Ore Sample In the acid leaching of lateritic ore, the high pressure acid leaching (HPAL) process was developed to dissolve nickel and cobalt and convert the major portion of solubilized iron to insoluble hematite. This was achieved in 10 autoclaves operated at high temperatures (250-300 0 C) and associated pressures (around 50 bar). HPAL methods recover high percentages of nickel and cobalt but require expensive, sophisticated equipment to withstand the high pressure and temperature operating conditions. 15 In order to avoid the use of expensive equipment, alternatives to the HPAL process have been disclosed. These generally operate at temperatures up to 110 0 C at atmospheric pressure. One such disclosure is US Patent 6,261,527, which describes the sequential leaching of limonite and saprolite fractions of laterite ore with sulfuric acid at atmospheric pressure and temperatures below 20 the boiling point, discarding most of the dissolved iron as insoluble jarosite solids. 3 There are environmental concerns with this iron removal process as the jarosite compounds are thermodynamically unstable. Jarosite may decompose slowly to iron hydroxides releasing sulfuric acid. The released acid may redissolve traces of precipitated heavy metals, such as Mn, Ni, Co, 5 Cu and Zn, present in the leach residue tailing, thereby mobilizing these metals into the ground or surface water around the tailings deposit. Another disadvantage of this process is that jarosite contains sulfate, and this increases the acid requirement for leaching significantly. Sulfuric acid is 10 usually the single most expensive input in acid leaching processing, so there is also an economic disadvantage in the jarosite process. Australian application 2003209829 in the name of QNI Technology Pty Ltd describes a process where a lateritic ore is separated into its low magnesium 15 containing ore fraction and its high magnesium ore fraction where the low magnesium containing ore fraction is leached at atmospheric pressure, and the high magnesium containing ore fraction is introduced to the resultant discharge slurry. The addition of the high magnesium containing ore fraction releases sulphuric acid which assists in completing the leaching of the high 20 magnesium ore fraction and results in the iron being precipitated as goethite. US Patent 6,379,637 in the name of Walter Curlook describes an atmospheric acid leach process for leaching nickel and cobalt from highly serpentinized saprolitic fractions of nickel laterite ores. This process involves the leaching of 25 the highly serpentinized saprolitic ore by the direct addition of sulfuric acid solutions to the ore at atmospheric pressure. The acid consumption in this process is suggested to be 800 to 1000 kg per tonne of dry ore. UK Patent GB 2086872 in the name of Falconbridge Nickel Mines Ltd, relates 30 to an atmospheric leaching process of lateritic nickel ores whereby nickel and cobalt are solubilized from high-magnesia nickelferous serpentine ores by leaching the ore with an aqueous solution of sulfuric acid. A reducing agent is also added to the solution in large quantities to maintain the redox potential of 4 the solution at a value of between 200 and 400 mV measured against the saturated calomel electrode. Such processes utilize direct addition of acid in the leaching process where 5 acid is used to leach the whole content of the ore being processed. With sulfuric acid being an expensive input in the acid leaching process there are economic as well as environment disadvantages to such processes. The present invention aims to overcome or alleviate one or more of the 10 problems associated with prior art processes by developing an atmospheric leach process where a hematite seed is added to the process to precipitate iron predominantly as hematite. This has the advantage of avoiding precipitating iron as jarosite or goethite and therefore improving the settling behaviour of leach residue and lowering the volume of residue (tailings) to be 15 disposed due to the higher density of hematite. Further, there is reduced nickel loss due to co-precipitation of nickel with iron as hematite does not incorporate nickel into its lattice structure. Hematite is also a more stable residue than jarosite and so is more environmentally sound. 20 The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia 25 before the priority date of each claim of this application. Brief Outline of the Invention The present invention resides in the process for the atmospheric acid leaching of lateritic ores to recover nickel and cobalt products. In particular, the present 30 invention resides in the acid leaching of separate fractions of the lateritic ore sequentially and/or jointly to recover nickel and cobalt at atmospheric pressure and at temperatures up to the boiling point of the acid. 5 The present invention is particularly applicable to processes where iron is removed substantially as a hematite residue following the addition of a hematite seed during the leach process. 5 Accordingly, the present invention resides in an atmospheric leach process for the recovery of nickel and cobalt from lateritic ores, said process including the steps of: a) separating the lateritic ore into its low magnesium ore fraction and its high magnesium ore fraction, or separately providing such 10 fractions; b) leaching the low magnesium ore fraction with sulfuric acid in a primary leach step; and c) introducing the high magnesium ore fraction to the resultant discharge slurry from the primary leach step in a secondary leach 15 step; wherein a hematite seed is added together with the high magnesium ore fraction or during the secondary leach step to assist in precipitating iron as a hematite residue. 20 The term "low magnesium containing ore fraction" is intended to define the fraction of a lateritic ore that includes those ore fractions that predominantly have less than 6% by weight magnesium content. It includes limonitic type ore together with the clay type fractions, namely the low or medium magnesium (containing less than 6%) smectite and/or low or medium magnesium 25 (containing less than 6%) nontronite type ores or combinations thereof. The term "high magnesium containing ore fraction" is intended to define the fraction of a lateritic ore that includes those ore fractions that predominantly have greater than 6% by weight magnesium content. It includes saprolitic type 30 ore together with the clay type fraction, namely the high or medium magnesium (containing greater than 6%) smectite or the high or medium magnesium (containing greater than 6%) nontronite ore or combinations thereof. 6 The clay type fractions, namely the smectite and nontronite ores may generally be considered to be either high or low in magnesium and processed together with the saprolite or limonite respectively. However, the mineral content of the ores, such as iron and magnesium content, will often fall between typical 5 limonite and saprolite ores and for the purposes of the process defined herein, could be processed with either the high or low magnesium ore fraction. The high and low magnesium containing ore fractions are generally prepared by separating the lateritic ore into its various fractions by selective mining or 10 post-mining separation. Alternatively, the process is also applicable to simply providing both the high and low magnesium containing ore from alternative sources. The low magnesium containing ore fraction and the high magnesium 15 containing ore fraction are separately slurried using available fresh waters. The hematite seed may be sourced from an external source and added directly to the saprolite leach step. That is, the hematite may be imported from a different source, such as the residue from a laterite pressure leach process. 20 Alternatively, the hematite seed may be recycled from the hematite residue following the secondary leach step or sourced from a hematite residue following pressure leaching of at least a part of the low magnesium ore fraction as part of the overall process. As only part of the low magnesium ore fraction is subjected to a high pressure leach, this has the advantage of enabling the 25 leach to be conducted within a small autoclave. Both the primary leach step and the secondary leach step are conducted at atmospheric pressure and temperatures up to the boiling point of the acid. Where only atmospheric leaching is involved, a convenient source of the 30 hematite seed is to recycle some of the hematite residue that follows the secondary leach step. 7 An alternative means in order to provide a source of the hematite seed, is to subject at least a portion of the low magnesium ore fraction to a pressure acid leach which will leave hematite as a residue. The remaining low magnesium ore fraction is subjected to an atmospheric leach. The resultant discharge 5 slurry from both the pressure acid and the atmospheric leach of the low magnesium ore fractions are combined to form a combined discharge slurry. This slurry is transferred to a second reactor where the high magnesium ore fraction is introduced to the combined discharge slurry. This slurry is then subjected to an atmospheric leach in the secondary leach step. The hematite 10 residue newly formed with the pressure acid leach functions as a hematite seed to promote precipitating iron as a hematite residue during the secondary atmospheric leach step. The primary leach step is generally carried out in a first reactor or group of 15 reactors at a temperature of up to 105 0 C or the boiling point of the leach reactants at atmospheric pressure. The sulfuric acid is preferably in a concentration of from 100% to 160% of stoichiometric proportions. The secondary leach step is completed in a second reactor or group of 20 reactors at a temperature of up to 105 0 C or the boiling point of the leach reactants at atmospheric pressure, following addition of the hematite seed. The dose of hematite seed added is in an amount of up to 500 wt% of the high magnesium ore fraction by weight. 25 The redox potential during the primary leach step is controlled to be between 800mV and 10OOmV (SHE). Preferably, the redox potential is controlled to be about 835mV (SHE). During the secondary leach step, the redox potential is preferably maintained to be between 700mV and 900mV (SHE). The redox 30 potential itself is controlled by injecting suitable agents such as sulfur dioxide gas, or sodium and potassium free metabisulfite or sulfite such as lithium sulfite into the slurry. 8 The dry ore ratio between the high magnesium containing ore and the low magnesium containing ore is preferably within the range of from about 0.5:1.3 depending on the distribution of ore resource. 5 Following the secondary ore leach step, a portion of the discharge slurry, which includes the residue containing predominantly hematite, may be recirculated back to the secondary leach step to act as hematite seed. Alternatively the discharge slurry may undergo solid/liquid separation techniques with the residue is simply disposed of to tailings. Any discharge 10 slurry not recirculated may then be treated to remove residual iron and other impurities such as aluminium prior to undergoing solid/liquid separation. The nickel and cobalt is then recovered from the resultant solution. Nickel and cobalt may be recovered by any conventional means such as sulfide 15 precipitation using hydrogen sulfide or other sulfide source, mixed hydroxide precipitation, ion exchange, or solvent extraction. Detailed Description of the Invention The invention will now be described with reference to the accompanying 20 drawings. Figure 1 illustrates a proposed flowsheet for lateritic atmospheric leach with hematite seed and residue recycle. 25 Figure 2 shows a proposed flowsheet wherein a portion of the low magnesium containing ore fraction is pressure leached where hematite residue is produced as part of this pressure leach step. This hematite residue is subsequently used as a hematite seed in the secondary leach step. 30 It should be understood that these drawings are illustrative of preferred embodiments of the invention, and that the invention should not be seen as limited to the embodiments shown in these figures. 9 Figure 1 illustrates a process where the laterite ore has first been separated into its low magnesium containing ore fraction and high magnesium containing ore fraction. This may have been done by selective mining or post-mining separation, or the ore fractions supplied in this manner. 5 The low magnesium containing ore fraction, which is illustrated in Figure 1 as limonite (1), but may be a low or medium magnesium smectite or nontronite ore, is subjected to a primary leach (3) which is done in a suitable reactor. Sulfuric acid (5) is used to leach the limonite ore fraction. The sulfuric acid 10 itself is preferably in a concentration of from 100% to 160% of stoichiometric proportions. The resultant discharge slurry from this atmospheric leach includes nickel and cobalt, together with impurities such as aluminium, magnesium, manganese, 15 copper, zinc and iron amongst other impurities. The iron will exist predominantly as ferric ions in solution. The high magnesium containing ore, which is illustrated in Figure 1 as saprolite (7), but may be a high or medium magnesium smectite or nontronite ore, is then combined with the discharge slurry from a primary leach step in a secondary leach step at atmospheric 20 pressure (9). A hematite seed (11) is added to the secondary leach step. This seed may be added at the same time or following the addition of the saprolite ore fraction. Sulfuric acid will generally be released during iron precipitation following the 25 addition of the saprolite ore which will assist in leaching nickel and cobalt from the saprolite ore fraction. The addition of the hematite seed will promote the precipitation of the iron as hematite in the residue (13). This hematite residue may be recycled (15) for 30 use as a hematite seed in the process, or removed as tailings (16). Figure 2 illustrates a similar process, however the limonite ore fraction is first separated into two portions, such that one portion is leached by a pressure 10 acid leach step (17), while the other portion is subjected to an atmospheric leach step (18) as part of the primary leach step. The pressure acid leach step will produce a hematite residue which may act as the hematite seed in the subsequent secondary atmospheric leach step. The size of the autoclave may 5 be relatively small for this step as only a portion of the low magnesium containing ore fraction is subjected to the pressure leach. The discharge slurry from both the pressure and the atmospheric primary leach step are combined to form a combined discharge slurry. This discharge 10 slurry is then transferred to a second reactor and the saprolite ore fraction is then added to the discharge slurry from the primary leach step in a secondary atmospheric leach step (19). The iron will precipitate predominantly as hematite during the secondary atmospheric leach step which is then disposed of to tailings (20) together with other solid impurities. 15 Following solid/liquid separation of the discharge slurry from the secondary leach step, the nickel and cobalt may then be recovered from the product leach solution by any standard recovery process, such as sulfide precipitation using hydrogen sulfide or other sulfide source, mixed hydroxide precipitation, 20 ion exchange or solvent extraction. The solid residue is disposed of to tailings. Examples Example 1 In these tests the weight ratios of sulphuric acid/limonite, saprolite/limonite and 25 sulphuric acid/ore ratio were 1.40, 1.0 and 0.7 respectively. These ratios remained constant and the type and amount of hematite seed was varied. Initially, limonite slurry (12170 g, 25 wt%) was leached with 98 wt% H 2 SO4 (4281 g) at 100 0 C for 3 hours. The redox potential was controlled to 830mV (SHE) by the addition of lithium sulphite. The limonite leachate was transferred 30 into reactors and reheated to 100 0 C. Saprolite slurry (25 wt%) was added followed by the hematite seed. The saprolite atmospheric leach was performed at 95 to 105 0 C for 11 hours. The hematite seed was added as high pressure 11 acid leach (HPAL) slurry, HPAL residue or hematite powder. The redox potential was 800 mV to 700 mV without further addition of lithium sulphite. The residues at the end of the saprolite leach were analysed by XRD and 5 contained predominantly hematite with some other species present. Test 1 2 3 HPAL residue Hematite Source of hematite seed HPAL slurry (solid only) powder Mass Limonite Leachate (25.1 wt %) 524 785 786 Mass Saprolite Slurry (25.8 wt%) 400 600 603 Overall Nickel Extraction (%) 78.9 79.6 79.5 Overall Cobalt Extraction (%) >98 >98 >98 Hematite Seed (/100 g saprolite) 219 146 184 Residue Analysis (XRD) Hydronium Jarosite 2 9 5 Hydronium alunite 2 1 3 Enstatite/pyroxene 9 7 4 Forsterite 8 5 2 Goethite 3 4 2 Hematite 84 65 80 Lizardite 0 0 0 'Amorphous' 0 9 5 Total 100 100 100 The invention described herein is acceptable to variations, modifications 10 and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description. 12 Further patent applications may be filed in Australia or overseas on the basis of, or claiming priority from, the present application. It is to be understood that the following provisional claims are provided by use of example only and are not intended to limit the scope of what may be claimed in any such future 5 applications. Features may be added to or omitted from the provisional claims at a later date so as to further define or redefine the invention or inventions. 13

Claims (22)

1. An atmospheric leach process for the recovery of nickel and cobalt from 5 lateritic ores, said process including the steps of: a) separating the lateritic ore into its low magnesium ore fraction and its high magnesium ore fraction, or separately providing such fractions; b) leaching the low magnesium ore fraction with sulfuric acid in a 10 primary leach step; and c) introducing the high magnesium ore fraction to the resultant discharge slurry from the low magnesium ore fraction in a secondary leach step; wherein a hematite seed is added together with the high magnesium ore 15 fraction or during the secondary leach step to assist in precipitating iron as a hematite residue.

2. A process according to claim 1 wherein the low magnesium ore fraction includes laterite ore fractions that predominantly have less than 6% 20 magnesium and the high magnesium ore fraction includes laterite ore fractions that predominantly have greater than 6% magnesium content.

3. A process according to claim 1 wherein the low magnesium ore fraction is either limonite, low or medium magnesium smectite and/or low or 25 medium magnesium nontronite or combinations thereof.

4. A process according to claim 1 wherein the high magnesium ore fraction is either saprolite, high or medium magnesium smectite and/or high or medium magnesium nontronite or combinations thereof. 30

5. A process according to claim 1 wherein the low magnesium ore fraction and the high magnesium ore fraction are selectively mined or separated by post-mining separation. 14

6. A process according to claim 1 or 2 wherein the low magnesium ore fraction and the high magnesium ore fraction are separately slurried. 5

7. A process according to any one of the preceding claims wherein the hematite seed is sourced from an external source and added directly to the secondary leach step.

8. A process according to claim 1 wherein at least a portion of the hematite 10 residue is recycled to the secondary leach step to act as the hematite seed.

9. A process according to claim 1 wherein the primary leach step is conducted at atmospheric pressure. 15

10. A process according to claim 1 wherein the secondary leach step is conducted at atmospheric pressure.

11. A process according to claim 1 wherein the primary leach step includes 20 subjecting: a) a portion of the low magnesium ore fraction to a pressure acid leach to produce a discharge slurry containing a hematite residue as seeds; and b) a further portion of the low magnesium ore fraction to an 25 atmospheric leach; the process including the further steps of: c) combining the discharge slurry from both the pressure acid and atmospheric primary leach to form a low magnesium ore discharge slurry; and 30 d) introducing the high magnesium ore fraction to the low magnesium ore discharge leach slurry; wherein the hematite residue from the pressure acid leach acts as a hematite seed during the secondary leach step to promote precipitating iron as a hematite residue. 15

12. A process according to claim 11 wherein the pressure acid leach takes place in a small autoclave. 5

13. A process according to claim 1 wherein the primary leach step is carried out in a first reactor at a temperature of up to 1050C or the boiling point of the leach reactants.

14. A process according to claim 1 wherein the sulfuric acid is preferably in a 10 concentration of from 100% to 160% of stoichiometric proportions.

15. A process according to claim 1 wherein the high magnesium ore fraction is introduced in a second reactor for completion of the secondary leach step at a temperature of up to 105"C or boiling point of the leach 15 reactants.

16. A process according to claim 1 wherein the dose of hematite seed added is in an amount of up to 500wt% of the total weight of both the low and high magnesium containing ore. 20

17. A process according to claim 1 wherein the redox potential during the limonite leach step is controlled to between 800mV and 10OOmV (SHE).

18. A process according to claim 13 wherein the redox potential in the 25 limonite leach step is about 835 mV (SHE).

19. A process according to claim 1 wherein the redox potential in the saprolite leach step is between 700mV and 900mV (SHE). 30

20. A process according to any one of claims 13 to 15 wherein the redox potential is controlled by injecting either sulfur dioxide gas, or lithium metabisulfite or sulfite into the slurry. 16

21. A process according to claim 1 wherein the dry ratio between the high magnesium ore fraction and the low magnesium ore fraction is from about 0.5 tol.3. 5

22. A process according to claim 1 wherein the following the secondary leach step the discharge slurry is subjected to a solid/liquid separation step and the nickel and/or cobalt is recovered from the resultant product leach solution by way of either sulfide precipitation using hydrogen sulfide or other sulfide source, mixed hydroxide precipitation, ion exchange or solvent 10 extraction. 15 20 25 30 17