AU2008217468B2

AU2008217468B2 - A process for extracting metals from laterite

Info

Publication number: AU2008217468B2
Application number: AU2008217468A
Authority: AU
Inventors: Tong Deng
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-02-15
Filing date: 2008-02-15
Publication date: 2011-02-03
Anticipated expiration: 2028-02-15
Also published as: AU2008217468A1; CN101245414A; WO2008101414A1; CN101245414B

Description

A PROCESS FOR EXTRACTING METALS FROM LATERITE TECHNICAL FIELD The invention generally relates to a process for extracting metals from ores. More specifically, 5 the invention relates to a process of extracting Ni, Co and other metals from laterite ores. BACKGROUND OF THE INVENTION Laterite ores are mixtures of hydrated ferric oxide with hydrated magnesium silicate formed fi-om ultramafic rocks such as olivine and serpentine by long-term and large-scale weathering, eluviation. alteration and enrichment. They are loose, clay-like oxidized nickel ores containing a 10 large amount of water, and thus are easy to be mined but difficult to be processed. The currently available laterite ores are generally composed by three layers: a limonite layer, a saprolite layer, and a transient layer between them. Laterite ores have varying chemical composition, depending on not only the deposit, but the depth of the deposit, which makes the contents of Ni, Co, Fe, Mg and the like even in the same deposit vary with the depth. These further increase the difficulty i5 and cost for the processing of laterite ores. Laterite ores can be treated by pyrometallurgical or hydrometallurgical processes, depending on their chemical composition. For the hydrometallurgy, leaching is the key step, which not only efficiently dissolves valuable metals such as Ni and Co, but prevents impurities, especially iron, firom being taken into the solution in large amounts. Currently, commercially available 20 hydronetallurgical processes for treating laterite ores only include the Caron process (Reductive Roasting - Ammoniacal Leaching) and the HPAL process (High Pressure Acid Leaching), both of which allow for the well-controlled dissolution of iron during leaching of Ni and Co. The Caron process combines the pyrometallurgical and hydrometallurgical processes, in which ores are firstly roasted under reductive atmosphere, to selectively reduce nickel therein to metallic Ni 25 and iron to Fe 3 0 4 as much as possible, and the calcine is then leached in an ammoniacal medium to avoid the introduction of iron and magnesium into the solution. However, this process renders relatively large losses of Ni and Co owing to their adsorption with leaching residues, so that the recovery ratios of the metals are reduced to generally only 70% - 80% for Ni and even less than 40% for Co. Moreover, the Caron process involves ore drying before roasting, which needs high energy consumption owing to 30-50% of adsorptive water contained in laterite ores. For these reasons, the Caron process is less competitive now, though it is the earliest commercially 5 available hydrometallurgical process for laterite ores. Sulphuric acid can be used to directly leach Ni and Co from laterite ores, which eliminates the energy-intensive drying and reductive roasting operations; further, it has relatively low cost. However, direct leaching with sulphuric acid under atmospheric pressure has no selectivity, such that nearly all the iron in ores is also taken into the solution. To improve leaching selectivity so 10 as to control the dissolution of iron, the HPAL process is carried out at a temperature between 250-270'C (corresponding vapor pressure up to approximately 50 atm) by using dilute sulphuric acid. in which iron is hydrolyzed at high temperature to precipitate as hematite while sulphuric acid is released. In this way, iron can be removed from the solution, with reduced acid consumption. The HPAL process had thus once become a preferred technology for treating is laterite ores during a period. However, the process is disadvantageous owing to its high investment and energy consumption: it requires a reactor being made by a material with good resistance to corrosion and pressure and sealing performance at high temperature, and also being manufactured and operated under strict conditions with high skill and cost; the process involves the use of steam during leaching to heat all the ore slurry above 270'C, which is also energy 20 consumptive; and especially, there may occur troublesome scaling in the reactor, which requires frequent shutting down for cleaning, significantly reducing the operating availability and increasing the running cost of the HPAL process. Thus, difficulties may be present in adopting this process in a large-scale project for laterite ores to achieve desirable effect, or even normal running. 25 Sulphation roasting, or known as selective oxidizing roasting, is an effective pretreatment process in hydrometallurgy for ores difficult to be leached, in which sulphide ores are roasted at a controlled temperature under oxidizing atmosphere so as to convert reluctantly leachable compounds of non-ferrous metals such as Cu, Co and Ni into their water-soluble sulphates and Fe into water-insoluble iron oxides. Thus, the resulting sulphates of Ni, Co and Cu can be easily 2 3 taken in the pregnant liquor during subsequent leaching, while Fe is left behind in the leaching residues. Such process is successful in treating sulphide ores. However, it cannot be simply copied for oxidized ores owing to lack of sulphur in their composition. Effort has been made to adopt sulphation roasting in the treatment of laterite ores 5 according to literature. For example, N. Zubryckyj et al. (N Zubryckyj, D. J. I. Evans and V. N. Mackiw, Preferential sulphation of nickel and cobalt in lateritic ores, Journal of Metals, 17(5): 478-486 (1965)) and Y. V. Swamy et al. (Y. V. Swamy, B. B. Kar and J. K. Mohanty, Physico-chemical characterization and sulphation roasting of low-grade nickeliferous laterites, Hydrometallurgy 69: 89-98 (2003)) reported sulphation roasting of io laterite ores by blending with concentrated sulphuric acid. J. H. Canterford (J. H. Canterford, The sulphation of oxidized nickel ores, Paper presented at the International Laterite Symposium, New Orleans, Louisiana, Feb. 19-21, 1979) reported sulphation roasting of laterite ores by blending with concentrated sulphuric acid or by introducing a mixture of sulphur dioxide and air. Either of the processes can realize is sulphation roasting of laterite ores with selective leaching of Ni and Co and controlled dissolution of Fe. However, both require additional fuel during roasting, to heat all the materials generally up to 600*C or above, which is undesirably energy-consumptive especially in view of the fact that energy sources are shortage and fuel price increases. Further, the blending with sulphuric acid requires the acid to be supplied in situ or from a 20 self-built plant, while the use of sulphur dioxide requires an adjacent plant to produce stack gas of sulphur dioxide from sulphide ores through pyrometallurgy, both of which are inconvenient and difficult to implement. Moreover, the two processes require a downstream device for the collection and absorption of stack gas discharged from the roaster furnace to treat sulfur oxides contained therein. 25 SUMMARY OF THE INVENTION A first aspect of the invention provides for a process of extracting metals from laterite ore containing Ni and Co, comprising: (1) mixing laterite ores with at least one sulphur-bearing material selected from elemental sulphur and metal sulphides, roasting the obtained mixture in an oxidizing 30 atmosphere to convert non-ferrous metals therein into sulphates and convert iron into oxides; and (2) leaching the roasted materials with water to extract non-ferrous metals, especially Ni and Co, therein into the leach liquor, 3a wherein the sulphur-bearing material selected from elemental sulphur and metal sulphides has the total content of sulphur between 5 and 35 wt.%, based on the total weight of the mixture to be roasted by dry basis. A second aspect of the invention provides for a process for roasting laterite ores 5 containing Ni and Co, comprises mixing laterite ores with a sulphur-bearing material selected from elemental sulphur and metal sulphides, and roasting the obtained mixture in an oxidizing atmosphere, wherein the sulphur-bearing material selected from elemental sulphur and metal sulphides has the total content of sulphur between 5 and 35 wt% based on the total weight i0 of the mixture to be roasted by dry basis. A third aspect of the invention provides for metals extracted from laterite ore containing Ni and Co by the process as defined in the first aspect of the invention. DISCLOSURE OF THE INVENTION Disclosed herein is a process for extracting metals from laterite ores containing is Ni and Co, comprising (1) mixing laterite ores with a sulphur-bearing material selected from elemental sulphur and metal sulphides, roasting the obtained mixture in an oxidizing atmosphere to convert non-ferrous metals therein into sulphates and convert iron into oxides; (2) leaching the roasted materials with water to extract Ni and Co therein into the leach liquor. The invention further relates to a process for roasting laterite ores containing Ni and Co, comprising mixing the laterite ores with a sulphur-bearing material selected from elemental sulphur and metal sulphides, and roasting the obtained mixture in an oxidizing atmosphere. 5 SPECIFIC EMBODYMENT OF THE INVENTION In the process of extracting metals from laterite ores containing Ni and Co according to the invention, the laterite ores are first mixed with a sulphur-bearing material selected from elemental sulphur and metal sulphides, and the obtained mixture is then roasted in an oxidizing atmosphere. such that the metals in the obtained calcine are converted to sulphates thereof and 10 iron is converted to oxides. In a preferred embodiment of the invention, the laterite ores may be limonite, saprolite, or a combination thereof. In a preferred embodiment of the invention, the said sulphur-bearing material selected from elemental sulphur and metal sulphides is selected from sulphur, and an ore or concentrate of 15 sulphide minerals containing Ni, Co or other ferrous and non-ferrous metals, or the like, such as precipitates containing Ni and Co sulphides and matte from ore processing. The sulphide minerals containing Ni, Co or other metals are, for example, chalcopyrite, chalcocite, covellite, pyrrhotite, cobaltiferous pyrite, pentlandite, pyrite and sphalerite and the like metal sulphide ores. Elemental sulphur and metal sulphides can be used in combination or alone. 20 In a particularly preferred embodiment, the mixture of laterite ore and a sulphur-bearing material selected from elemental sulphur and metal sulphides further comprises one selected from alkali and alkali earth metal sulphates, particularly one of sodium sulphate and magnesium sulphate, especially sodium sulphate. In a preferred embodiment of the invention, the mixture of laterite ore and a sulphur-bearing 25 material selected from elemental sulphur and metal sulphides further comprises sulphuric acid. In a preferred embodiment of the invention, the sulphur-bearing material selected from 4 elemental sulphur and metal sulphides has the total content of sulphur between 5 and 35 wt.% (weight percent), preferably below 30 wt.%, especially preferably between 10 and 20 wt.%, based on the total weight of the mixture to be roasted by dry basis (including laterite ore, the sulphur-bearing material selected from elemental sulphur and metal sulphides, and optionally, 5 alkali and alkali earth metal sulphates and sulphuric acid). The specific total content percentage of sulphur by weight depends on the amount of acid-consuming materials, such as magnesium and non-ferrous metals, present in the materials to be roasted, and can be readily determined by a person skilled in the art in light of the disclosure of the invention. In a preferred embodiment of the invention, the roasting temperature is 400-850"C, preferably 10 450-750C., especially 600-700'C. In the process according to the invention, the sulphur-bearing material selected from elemental sulphur and metal sulphides is admixed into laterite ores. During roasting, such material acts as both sulphating agent and fuel. On the one hand, as sulphating agent, the sulphur-bearing material provides sulphur to convert Ni and Co oxides in laterite ores to sulphates thereof, while 15 excess sulphur becomes stack gas, which can be formed in situ into sulphuric acid for recycle. On the other hand, the sulphur-bearing material can also serve as fuel, which provides heat, for example up to 12884 kJ/kg in the case of pyrite, for roasting of ores through the oxidation of sulphur or sulphides, with no addition of additional fuel necessary. This not only allows for the self-heating of roasting operation, but provides residual heat for generating electricity by a waste 20 heat boiler. Thus, compared with the method of separately roasting a sulphur-bearing material selected from elemental sulphur and metal sulphides to produce SO 2 or converting it into sulphuric acid, which is in turn then used to roast laterite ores so as to convert Ni and Co therein into sulfates and iron into oxides, the process according to the invention is more economic and convenient. 25 The roasting of the mixture of laterite ores and sulphur-bearing material selected from elemental sulphur and metal sulphides is conducted in an oxidizing atmosphere. The oxidizing atmosphere may be composed by an oxygen-containing mixture, especially air, or an air mixture with increased oxygen content. Preferably, oxygen is present in the gas mixture at an amount of 20-35 vol.%. preferably 20-30 vol.%, particularly preferably 20-25 vol.%, especially 20 vol.% 5 (i.e. using air directly). The roasting lasts 0.5-5 hr, preferably 1-3 hr. However, the specific roasting time varies with the mixture of laterite ores and sulphur-bearing material selected from elemental sulphur and metal sulphides, which can be easily determined by a person skilled in the art in light of the disclosure 5 of the invention. In the process according to the invention, once mixed uniformly, laterite ores and any roasting adjuvants can be directly introduced into a roaster furnace without predrying. In view of the fact that laterite ores generally contains 30-50% of moisture, such characteristic makes the process according to the invention with significantly decreased energy consumption, in comparison with 10 other treatments lor laterite ores, such as by pyrometallurgical processes or the Caron process, which involves an indispensable predrying. In the process according to the invention, after the mixture of laterite ores and sulphur-bearing material selected from elemental sulphur and metal sulphides is roasted, a calcine is obtained, in which non-ferrous metals such as Ni, Co and Cu are mainly present in the form of sulphates, and 15 iron is mainly present as oxides. This is advantageous to the leaching of Ni, Co and Cu and controlled dissolution of iron in the leach liquor during subsequent leaching operation. Ni and Co may be extracted at a ratio exceeding 90%, while the dissolved iron can be controlled at an amount below 3%. In the process according to the invention, when Ni, Co, Cu or Fe sulphides are used as 20 sulphur-bearing material, Ni, Co or Cu contained therein is also converted into sulphates, which are subsequently leached together with Ni and Co in laterite ores during the leaching of calcine, and then recovered from the leach liquor. In the process according to the invention, the calcine obtained from the roasting step is leached with water to extract Ni, Co and other non-ferrous metals, such as Cu, into the leach liquor. In a 25 preferred embodiment of the invention, the calcine obtained is leached by water at a temperature between 30-95'C for a time of 0.5-3 hr. An acid such as sulphuric acid, hydrochloric acid and the like is optionally added into water for leaching, but preferably sulphuric acid is added. In the case where sulphuric acid is added, the amount of the free sulphuric acid remaining in the leach 6 liquor is preferably less than 30 g/L. After the calcine obtained from the roasting according to the invention is leached with water, the resulting leach slurry is separated to a solution, i.e. leach liquor, which is then treated to recover N i and Co. as well as other non-ferrous metals such as Cu. The recovery of Ni, Co and Cu from 5 the leach liquor can be carried out by a method selected from precipitation, solvent extraction or ion exchange. all of which per se are well known to one skilled in the art. The invention further provide a process of roasting laterite ores containing Ni and Co, comprising mixing laterite ores and a sulphur-bearing material selected from elemental sulphur and metal sulphides, and roasting the obtained mixture in an oxidizing atmosphere. The 10 sulphur-bearing material and roasting condition are as mentioned for the roasting step in the foregoing present process, and will not be described in detail here. It is obvious that the product of the present process, i.e. calcine, can be further treated to extract metal values and so on, or used for other applications. The invention will be illustrated through the following examples. However, it is not limited to I5 these examples. Those skilled in the art can make various modifications and alternations to the invention without departing from the spirit of the invention. EXAMPLES Example I A laterite ore containing (dry basis) 1.43% of Ni, 0.041% of Co, 21.43% of Fe, 9.06% of Mg, 20 and 35.43% of moisture was finely ground until 90% passed through 74 lim mesh and then divided into two portions. One portion was admixed uniformly with sulphur in the ratio of 4:1 by weight and then introduced into a roaster furnace directly (test 1). The other was mixed in the same way, except that 5 wt.% (based on the weight of the ore) of concentrated sulphuric acid was also blended; the resulting mixture was then introduced into a roaster furnace (test II). Both 25 samples for tests I and 11 were roasted at 500"C for 1 hr in an air atmosphere, and the calcine was then directly discharged into an agitated leaching tank containing water and leached for 2 h. The leaching temperature in the tank reached above 80"C without additional heat being applied. 7 Afterward, the leach slurry was subjected to solid-liquid separation, and both the leach residues and the leach liquor were analyzed to determine their respective metal contents. Based on these contents, the leaching ratios for these two tests were calculated as Ni 90.32%, Co 93.33%, Fe 3.13% (test I): and Ni 90.48%, Co 93.60%, Fe 2.99% (test II), respectively. It shows that the 5 process according to the invention allows for the efficient extracting of Ni and Co from laterite ore and the controlled dissolution of Fe. It also reveals that whether sulphuric acid is blended into laterite ore has no significant effect on the leaching yields Example 2 A laterite ore in example I was mixed with a cobalt-copper concentrate containing 1.62% of Cu, 10 0.58% of Co. 0.36% of Ni and 28.55% of S and sulphur, in the weight ratio of 4: 1:1, wherein the metal minerals in the Co-Cu concentrate mainly include chalcopyrite, pyrite and cobaltiferous pyrite. The obtained mixture was roasted at a temperature of 650"C in an air atmosphere for 2 h, and the calcine was treated according to the process in example 1. The thus obtained leaching ratios were Ni 89.95%. Co 94.02% and Cu 95.67%, respectively. 15 Example 3 A laterite ore containing 1.85% of Ni, 0.053% of Co and 48.2% of moisture was finely ground until 90% passed through 74 pm mesh and divided into two portions. Each portion was separately admixed with a pyrrhotite concentrate containing 1.26% of Ni, 0.50% of Cu, 0.033% of Co. 22.76% of S and 46.68% of Fe in the weight ratio of 1:1. Then, one portion was 20 introduced into a roaster furnace directly (test 1), while the other was fed into a roaster furnace after addition of 5 wt.% (based on the weight of the mixture as described above) of sodium sulfate (test 11). The useful minerals contained in the pyrrhotite concentrate comprise pyrrhotite, pentlandite, chalcopyrite and pyrite. Both test samples were roasted and leached according to example 1, with the result that the leaching ratios were Ni 89.73%, Co 91.27%, Cu 93.16% (for 25 test I): and Ni 90.34%, Co 93.18%, Cu 93.99% (for test 11), respectively. The tests show that the addition of sodium sulphate increases the leaching yield, compared with that without sodium sulphate. 8

Claims

2. The process according to claim 1, wherein the laterite ores include limonite, saprolite, or a combination thereof. 15 3. The process according to claim 1, wherein the sulphur-bearing material selected from elemental sulphur and metal sulphides is selected from sulphur, and an ore or concentrate of sulphide minerals containing Ni, Co or other metals, or the like, such as Ni and Co sulphides precipitates and matte produced from ore processing, wherein the sulphide minerals containing Ni, Co or other metals are, for example, chalcopyrite, 20 chalcocite, covellite, pyrrhotite, cobaltiferous pyrite, pentlandite, pyrite and sphalerite.
4. The process according to claim 1, wherein the mixture of laterite ores and sulphur-bearing material selected from elemental sulphur and metal sulphides further comprises one selected from alkali and alkali earth metal sulphates, especially sodium sulphate. 25 5. The process according to claim 1, wherein the mixture of laterite ores and sulphur-bearing material selected from elemental sulphur and metal sulphides further comprises sulphuric acid.
6. The process according to claim 1, wherein the sulphur-bearing material selected from elemental sulphur and metal sulphides has the total content of sulphur 30 between 10 and 30 wt.%, based on the total weight of the mixture to be roasted by dry basis. 10
7. The process according to claim 1, wherein the roasting is carried out at a temperature of 400-850'C.
8. The process according to claim 1, wherein the oxidizing atmosphere is composed by a free oxygen-containing gas mixture, especially air, or an air mixture with 5 increased oxygen content.
9. The process according to claim 8, wherein oxygen is present in the oxidizing atmosphere at an amount of 20-35 vol.%, preferably 20-30 vol.%, particularly preferably 20-25 vol.%, especially 20 vol.%.
10. A process for roasting laterite ores containing Ni and Co, comprises io mixing laterite ores with a sulphur-bearing material selected from elemental sulphur and metal sulphides, and roasting the obtained mixture in an oxidizing atmosphere, wherein the sulphur-bearing material selected from elemental sulphur and metal sulphides has the total content of sulphur between 5 and 35 wt% based on the total weight of the mixture to be roasted by dry basis. is 11. Metals extracted from laterite ore containing Ni and Co by the process as defined in claim 1.
12. A process of extracting metals from laterite ore containing Ni and Co as defined in claim I as substantially as hereinbefore described with reference to any one of the Examples. 20 Dated 7 January, 2011 Tong Deng Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON