AU2010225450C1

AU2010225450C1 - Impurity removal from hydrated minerals

Info

Publication number: AU2010225450C1
Application number: AU2010225450A
Authority: AU
Inventors: Michael John Fisher-White; Roy Randall Lovel; Graham Jeffery Sparrow
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 2009-03-16
Filing date: 2010-03-15
Publication date: 2013-11-21
Anticipated expiration: 2030-03-15
Also published as: CN102395692A; AU2010225450A1; AU2010225450B2; WO2010105292A1

Abstract

A method for the removal of a impurity element from an iron ore, the method including the steps of heating the ore to a temperature not exceeding about 500 °C and subsequently contacting the ore with an acid or alkaline leach solution to leach the impurity element from the ore.

Description

WO 2010/105292 PCT/AU2010/000302 1 Impurity removal from hydrated minerals Field of the invention The present invention relates to the removal of impurities from mineral resources and in particular, the invention relates to the removal of phosphorous from oxidic iron ores. 5 Background of the invention There is a need for iron oxide bearing materials (generally referred to herein as iron ore for simplicity) used in certain industrial processes to meet strict specifications with respect to impurities. For instance, iron ore used as a feedstock for blast furnace smelting to produce iron is often desired to have a low phosphorous content. While 10 methods for removing phosphorous from molten iron exist, a number of factors such as financial penalties and market access make it attractive to ensure that phosphorous is removed from the iron ore prior to its use in smelting. Thus, processes that reduce the amount of phosphorous present in an iron ore are commercially attractive, particularly in regard to the treatment of ores naturally high in 15 phosphorous (such as limonitic and goethitic ores). In some applications a phosphorous reduction to 0.1 weight % may be commercially acceptable, but a reduction to less than 0.08 weight % is more desirable. Most desirable is a reduction to less than 0.07 weight Processes exist for the removal of phosphorous from iron ores where the phosphorous 20 is present as apatite (eg Forssberg, E. and Adolfsson, G., 1981. Entphosphorung von hochphosphorhaltigen eisenerzen durch saure laugung, Erzmetall, 34 (6), 316-322. (in German)). An example of such a process is physical beneficiation and chemical leaching with an acidic or alkaline solution. However, the existing methods for removing phosphorous from iron ores where the phosphorous is associated with an iron oxide 25 phase (ie oxidic iron ores such as goethitic and limonitic ores) suffer from a number of disadvantages and there is no process to remove phosphorous from goethitic iron ores in common use.

WO 2010/105292 PCT/AU2010/000302 2 In International Patent Application no. PCT/BR91/00030, it was shown that heating an iron ore at 1200 *C, and then leaching with 2.5M (10%) hydrochloric acid, reduced its P, A1 2 0 3 , CaO and MgO levels appreciably. It is known that heat treatment of an iron ore at such high temperatures can alter the iron oxide phase (eg from goethite to hematite) to 5 decrease its dissolvability, while at the same time promoting migration of the impurities to the surface to increase their accessibility and dissolvability. In Australian patent 457,026, a heat treatment at 1000-1300 0 C followed by a leach with hydrochloric acid or sulphuric acid is claimed to reduce the phosphorous levels in an Australian iron ore. 10 In U.S. Patent 3,402,041, an iron ore and a roasting additive (such as an alkali earth metal halide) is subjected to a roasting step of from 500-12000C, prior to a leaching step conducted with an inorganic acid (such as hydrochloric acid), in order to remove phosphorous from the iron ore. In U.S. Patent 3,928,024, it is stated that roasting of ores in a rotary kiln at temperatures 15 above about 800 *C, and in conjunction with alkali metal hydroxides, is known to lower the sulphur and phosphorous content. The patent relates to a process for lowering the sulphur and phosphorous content of an oxidic iron ore by mixing the ore with an inorganic base (such as an alkali metal hydroxide), heating the mixture at temperatures of up to 650 *C, but preferably from 250 0C to 350 *C, for a period of about 1 hour, and 20 then leaching with water. The inorganic base is added to the ore at about 0.1 to 1.5 parts by weight base per part by weight ore. More recently, Fisher-White, Lovel and Sparrow (Iron Ore Conference 2009, Australasian Institute of Mining and Metallurgy, Carlton, pp. 249-254) have reported similar results but with much lower additions of the alkali metal hydroxide in the heating treatment. 25 While reducing the phosphorous content increases the inherent value of the ore, the use of high temperatures carries with it a high economic penalty. Furthermore, roasting additives are an additional expense and the use of corrosive chemicals at high temperatures enhances their corrosivity and reduces the operation life of processing equipment.

3 Although this invention is predominantly illustrated in relation to the reduction of phosphorous content, it is also applicable to the reduction of other impurities in iron ore such as silica and alumina. Other sample specific elements may also be removed. Thus, the object of the invention is to increase the economic viability of the process for 5 removing elements, particularly phosphorous, from mineral ores, particularly hydrated oxidic iron ores. Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could 0 reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. Summary of the invention The inventors have discovered that the heating step of the prior art is unduly complex. In particular, the high temperatures and additives used during the heating step are not 5 necessary in order to remove impurities to the requisite degree. This invention removes impurity elements from iron ores by heating the ore without any additives, followed by a leaching step to remove impurity elements. Accordingly, in one aspect of the invention there is provided a method for the removal of elements from an iron ore, the method including the steps of heating the ore to a 20 temperature less than 400 *C and subsequently contacting the ore with an acid or alkaline leach solution to remove the impurity elements from the ore. The step of heating the ore is conducted without the presence of roasting additives or leaching solutions. That is, the iron ore is heated in air or in an atmosphere that may be varied as discussed below. 25 The step of heating the iron ore may be conducted at a temperature above about 225 *C. Preferably the step of heating the iron ore is conducted at a temperature of above about 250 *C. The step of heating the iron ore may be conducted at a temperature as 4 high as about 500 0 C. Preferably the step of heating the iron ore is conducted at a temperature of below about 350 0 C in air. More preferably, the step of heating the iron ore is conducted at a temperature of about 300 0 C. In another aspect of the invention there is provided a method for the removal of a 5 impurity element from an iron ore, the method including the steps of heating the ore to a temperature less than 300 0 C and subsequently contacting the ore with an acid or alkaline leach solution to leach the impurity element from the ore. The step of heating the iron ore may be carried out with conventional furnaces (eg a rotary furnace, a fluidized bed furnace, a travelling grate furnace or a flash furnace) with 10 direct or indirect heating in an appropriate gas atmosphere. Preferably, the atmosphere is air, but heating in atmospheres other than air (eg combustion gases) is also effective. The element requiring removal (the impurity element) from an iron ore may be, for instance, phosphorous, silica, or alumina. Other sample specific elements (eg sulphur) may also be removed. In one specific case, the element requiring removal is 15 phosphorous. In these embodiments, the phosphorous that is removed from the iron ore may be present in a goethitic and/or limonitic phase in the iron ore, but may also be present in any non-oxidic apatitic phase of the ore. The leach solution may be an acidic or alkaline aqueous solution. The acidic leaching solution may be an inorganic or organic acid. Examples of acidic leach solutions include 20 HCI, HNO 3 , H 2

SO

4 , and citric acid. Preferably, the leach solution is alkaline. Examples of alkaline leach solutions include NaOH, KOH and NH 4 0H. More preferably, the leach solution is NaOH. The step of contacting the iron ore with a leach solution may be conducted at ambient temperature or at an elevated temperature up to the boiling point of the leaching 25 solution. Preferably, the step of contacting the iron ore with a leach solution is conducted at an elevated temperature. In another aspect of the invention there is provided a purified ore prepared according to the above method and having reduced impurity content.

WO 2010/105292 PCT/AU2010/000302 5 Detailed description of the embodiments The nature of phosphorous (and other elements) containment in mineral samples is ore specific. In goethitic samples the inventors believe that it is possible that phosphorous was originally adsorbed onto the surface of growing iron ore crystals at the time of 5 deposition, that the adsorbed phosphorous was covered over (encapsulated) with iron ore and over geological time (and through geological processes) became part of the mineral structure. The inventors also believe that during the heating, dehydroxylation of the goethite to a deformed hematite (as opposed to a dense hematite phase) occurs. In this deformed 10 hematite, impurity elements in the goethite (originally), such as phosphorous, are rejected from the mineral structure. As a result, these impurity elements are able to be leached from the mineral. In contrast, Apatite (Ca 5

(PO

4

)

3 0H) is a common, familiar accessory mineral in iron ores that is known to be soluble in acid. It is not possible to remove phosphorous associated 15 with goethite under the conditions used to remove phosphorous associated with apatite because untreated high phosphorous goethitic ores are not greatly affected by acid leaching. Apatite (and its phosphorous) in ores treated by the process of the invention is expected to be leached along with the more difficult phosphorous associated with goethite. 20 The temperature and time of heating, the time of leaching, and the concentration of the leachant depend on the iron ore and on the final desired product specification. It is believed that the heat treatment causes the de-hydroxylation of the goethite phase to hematite that then makes the impurities available for removal in the leach. Consequently the heating temperature, and the time at temperature, should be chosen 25 to achieve this phase transformation. The step of heating the iron ore can be conducted for a time as little as 0.25 hr or less. Heating times of up to about 24 hrs are not detrimental but may not be cost efficient. Preferably, the heating time is from about 0.25 hr to about 4 hours. More preferably, the heating time is about 1 hour.

WO 2010/105292 PCT/AU2010/000302 6 The step of contacting the iron ore with a leach solution may be conducted for a time of up to about 5 hours. Longer leaching times are not detrimental but are not as cost efficient. Preferably, the leaching time is about 3 hr. More preferably, the leaching time is about 0.25 to 1 hr. 5 The concentration of the leach solution may be from about 0.001 M to about 5.0 M. Higher concentrations are not detrimental but are not likely to be as cost efficient or safe. The step of contacting the iron ore with a leach solution may be carried out in a reaction vessel with suitable agitation to ensure good contact between the iron ore and the 10 leaching solution. Single or multiple stages of leaching may be carried out as required to achieve a satisfactory impurity element removal. Alternatively, the heated ore could be contacted with the leach solution under conditions used in heap leaching operations. Examples Examples 1 to 11 illustrate the method of the present invention on two Australian 15 Brockman high phosphorous iron ores. Both samples were crushed to less than 1.2 mm to improve sample homogeneity. Phosphorous removal from coarse samples is more favourable in industrial applications but difficult to demonstrate in a reproducible manner. X-Ray Fluorescence spectroscopy (XRF) analyses showed that the iron ore sample 1 contained 62.0 wt% Fe, 0.146 wt% P, 3.07 wt% SiO 2 , and 2.27 wt% A1 2 0 3 20 while iron ore sample 2 contained 62.1 wt% Fe, 0.123 wt% P, 3.22 wt% SiO 2 , and 2.18 wt% A1 2 0 3 , Following each test, the leach solids were collected by filtration, washed with water and dried at 60 *C. The leach solutions were collected as required. The amount of the elements removed by the various test conditions was assessed using the XRF assays of the leach residues and Inductively Coupled Plasma-Optical Emission 25 Spectroscopy (ICP-OES) assays for solution samples. To allow the effects of the heat treatment on the removal of phosphorous in a subsequent leach to be assessed in the examples, the two ore samples were leached WO 2010/105292 PCT/AU2010/000302 7 with different leaching solutions without a heat treatment and the results are shown in Table A. Table A Ore sample Leaching XRF assay data (wt%) solution* Fe P SiO 2 A1 2 0 3 Iron ore 1 n/a 62.0 0.146 3.07 2.27

H

2 0 65.2 0.147 3.03 2.26 1.OM NaOH 62.8 0.134 2.64 2.08 5.OM NaOH 65.3 0.112 1.03 0.89 Iron ore 2 n/a 62.1 0.123 3.22 2.18

H

2 0 61.7 0.117 3.26 2.10 0.1M NaOH 63.6 0.098 1.94 0.87 1.OM NaOH 63.8 0.093 1.76 0.78 5.OM NaOH 64.7 0.080 1.49 0.62 1M H 2

SO

4 62.0 0.112 3.21 2.19 * Leaches were at boiling point with 0.5 wt% solids for 3 hours. 5 t Sulphuric acid leach was at 60 0 C with 25 wt% solids for 3 hours. n/a not applicable. Leaching either ore sample directly with boiling water resulted in the removal of virtually no impurity elements. Leaching iron ore sample 1 with sodium hydroxide solution did remove a small amount of phosphorous, along with some alumina and silica. With iron 10 ore sample 2, leaching with sodium hydroxide also resulted in removal of phosphorous, silica and alumina with the amounts removed increasing with higher concentrations of sodium hydroxide in the leaching solution. Leaching iron ore sample 2 with sulphuric acid resulted in dissolution of some phosphorous but virtually none of the silica or alumina. There was a 1.2% weight loss in the leach. 15 Comparing the results in Table A with the appropriate data in the following examples shows that better phosphorous removal is achieved with a heat treatment before the leach with a caustic or acidic leaching solution.

WO 2010/105292 PCT/AU2010/000302 8 Example 1 The effect of the temperature of the heat treatment on the amount of phosphorous and other impurities removed in a subsequent leach with sodium hydroxide is shown when the iron ore sample 1 is either: 5 1. subjected to a heating step for a period of 1 hour in air at a temperature of 225 *C, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution; 2. subjected to a heating step for a period of 1 hour in air at a temperature of 250 *C, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution; 3. subjected to a heating step for a period of 1 hour in air at a temperature of 275 *C, 10 followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution; 4. subjected to a heating step for a period of 1 hour in air at a temperature of 300 *C, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution; 5. subjected to a heating step for a period of 1 hour in air at a temperature of 350 *C, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution, or 15 6. subjected to a heating step for a period of 1 hour in air at a temperature of 500 *C, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution. Assay data for leach products from leaches for 3 hours at a pulp density of 0.5 wt% solids are shown in Table 1. 20 WO 2010/105292 PCT/AU2010/000302 9 Table 1 Test Heating Heating Leaching XRF assay data (wt%) condition temp. time solution (*C) (h) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a 62.0 0.146 3.07 2.27 iron ore 1 225 1.0 5.0M NaOH 64.8 0.112 1.12 0.82 2 250 1.0 5.0M NaOH 65.8 0.097 1.03 0.70 3 275 1.0 5.OM NaOH 66.6 0.081 1.04 0.54 4 300 1.0 5.0M NaOH 66.9 0.067 1.07 0.56 5 350 1.0 5.OM NaOH 67.2 0.065 1.05 0.58 6 500 1.0 5.OM NaOH 66.6 0.069 1.14 0.72 n/a not applicable A heating temperature of 250 *C is sufficient to obtain removal of some of the impurities with a sodium hydroxide leach. However, better impurity element removal is achieved 5 with higher heating temperatures of 275-350 *C. Heating above 350 *C does not significantly improve the removal of the impurities. It is believed that the heat treatment causes the goethite to undergo phase changes that then makes the impurities available for removal in the sodium hydroxide leach. Consequently the heating temperature should be chosen to achieve the required 10 impurity element removal. Example 2 The effect of the time at temperature of the heat treatment on the amount of phosphorous and other impurities removed in a subsequent leach with sodium hydroxide is shown when the iron ore sample 1 is either: 15 1. subjected to a heating step at a temperature of 300 *C in air for a period of 0.25 hour, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution; 2. subjected to a heating step at a temperature of 300 0C in air for a period of 0.5 hour, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution; WO 2010/105292 PCT/AU2010/000302 10 3. subjected to a heating step at a temperature of 300 'C in air for a period of 1.0 hour, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution, or 4. subjected to a heating step at a temperature of 300 *C in air for a period of 2 hours, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution. 5 Assay data for leach products from leaches for 3 hours at a pulp density of 0.5 wt% solids are shown in Table 2. Table 2 Test Heating Heating Leaching XRF assay data (wt%) condition temp. time solution (OC) (h) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a 62.0 0.146 3.07 2.27 iron ore 1 300 0.25 5.0M NaOH 66.2 0.078 1.03 0.52 2 300 0.5 5.OM NaOH 66.8 0.070 1.07 0.54 3 300 1.0 5.OM NaOH 66.9 0.067 1.07 0.56 4 300 2.0 5.0M NaOH 66.9 0.065 1.05 0.55 n/a not applicable For a heating temperature of 300 *C, a heating time as short as 15 minutes has been 10 shown to be sufficient to achieve appreciable impurity element removal with a sodium hydroxide leach and a heating time of more than 1 hour does not have any further significant beneficial effects. It is anticipated that a flash heating treatment of less than 15 minutes may be a practical embodiment of this invention. It is believed that the heat treatment causes the goethite to undergo phase changes that 15 then makes the impurities available for removal in the sodium hydroxide leach. Consequently the heating temperature, and the time at temperature, should be chosen to achieve the required impurity element removal. Example 3 The effect of the concentration of sodium hydroxide in the leach on the amount of 20 phosphorous removed after a heat treatment is shown when the iron ore sample 1 is either: WO 2010/105292 PCT/AU2010/000302 11 1. subjected to a heating step of 300 0C for a period of 1 hour in air, followed by being contacted with a boiling water leach solution; 2. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 0.1 M NaOH leach solution; 5 3. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 1.0 M NaOH leach solution; 4. subjected to a heating step of 300 0C for a period of 1 hour in air, followed by being contacted with a boiling 2.5 M NaOH leach solution, or 5. subjected to a heating step of 300 0C for a period of 1 hour in air, followed by being 10 contacted with a boiling 5.0 M NaOH leach solution. Assay data for leach products from leaches for 3 hours at a pulp density of 0.5 wt% solids are shown in Table 3. Table 3 Test Heating Heating Leaching XRF assay data (wt%) condition temp. time solution (OC) (h) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a 62.0 0.146 3.07 2.27 iron ore 1 300 1.0 H 2 0 63.7 0.149 2.88 2.19 2 300 1.0 0.1M NaOH 65.3 0.097 1.93 1.03 3 300 1.0 1.OM NaOH 66.0 0.086 1.39 0.77 4 300 1.0 2.5M NaOH 66.3 0.083 1.20 0.77 5 300 1.0 5.OM NaOH 66.7 0.075 1.22 0.70 n/a not applicable 15 Leaching with boiling water after a heat treatment at 300 0C for 1 hour removes little of the impurities, but greater levels of impurity element removal can be achieved in a leach with boiling 0.1 M NaOH after a heat treatment at 300 0C for 1 hour. Greater amounts of impurity element removal are achieved when higher concentrations of sodium hydroxide are used in the leach.

WO 2010/105292 PCT/AU2010/000302 12 Example 4 The effect of the concentration of sodium hydroxide in the leach on the amount of phosphorous and other impurities removed after a heat treatment is shown when the iron ore sample 2 is either: 5 1. subjected to a heating step of 300 0 C for a period of 1 hour in air, followed by being contacted with a boiling water leach solution; 2. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 0.001 M NaOH leach solution; 3. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being 10 contacted with a boiling 0.01 M NaOH leach solution; 4. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 0.1 M NaOH leach solution; 5. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 1.0 M NaOH leach solution; 15 6. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 2.5 M NaOH leach solution, or 7. subjected to a heating step of 300 *C for a period of 1 hour in air, followed by being contacted with a boiling 5.0 M NaOH leach solution. Assay data for leach products from leaches for 3 hours at a pulp density of 0.5 wt% 20 solids are shown in Table 4.

WO 2010/105292 PCT/AU2010/000302 13 Table 4 Test Heating Heating Leaching solution XRF assay data (wt%) condition temp. time (*C) (h) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a 62.1 0.123 3.22 2.18 iron ore 1 300 1.0 H 2 0 63.3 0.127 3.25 2.32 2 300 1.0 0.001M NaOH 63.3 0.091 3.15 2.14 3 300 1.0 0.01M NaOH 63.3 0.081 3.42 1.52 4 300 1.0 0.1M NaOH 65.6 0.071 2.10 0.83 5 300 1.0 1.0M NaOH 65.8 0.063 1.81 0.67 6 300 1.0 2.5M NaOH 62.9 0.053 1.66 0.56 7 300 1.0 5.0M NaOH 60.4 0.040 1.36 0.40 n/a not applicable Leaching with boiling water after a heat treatment at 300 *C for 1 hour removes little of the impurities, but significantly greater levels of impurity element removal can be 5 achieved in a leach with boiling 0.001 M NaOH after a heat treatment at 300 0 C for 1 hour. Greater amounts of impurity element removal are achieved when higher concentrations of sodium hydroxide are used in the leach. Compared with the results for iron ore sample 1 in Table 3, the results for iron ore sample 2 in Table 4 indicate that a lower concentration of sodium hydroxide in the leach 10 is required to achieve a similar removal of impurities. This difference presumably reflects differences in the mineralogy of the samples. Example 5 The effect of the temperature of the sodium hydroxide leach on the amount of phosphorous removed after a heating treatment is shown when the iron ore sample 1 is 15 either: 1. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a 5.0 M sodium hydroxide leach solution at a leach temperature of 21 *C; WO 2010/105292 PCT/AU2010/000302 14 2. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a 5.0 M sodium hydroxide leach solution at a leach temperature of 40 *C; 3. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, 5 followed by being contacted with a 5.0 M sodium hydroxide leach solution at a leach temperature of 60 *C; 4. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a 5.0 M sodium hydroxide leach solution at a leach temperature of 80 *C, or 10 5. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution. Assay data for leach products from leaches for 3 hours at a pulp density of 0.5 wt% solids are shown in Table 5. Table 5 Test Heating Heating Leaching Leaching XRF assay data (wt%) condition temp. time solution temp. (OC) (h) (OC) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a n/a 62.0 0.146 3.07 2.27 iron ore 1 300 1.0 5.OM NaOH 21 62.4 0.113 3.56 2.04 2 300 1.0 5.0M NaOH 40 63.7 0.109 2.52 1.99 3 300 1.0 5.OM NaOH 60 64.2 0.098 2.08 1.53 4 300 1.0 5.OM NaOH 80 65.8 0.088 1.21 0.84 5 300 1.0 5.OM NaOH B.Pt. 66.9 0.067 1.07 0.56 15 n/a not applicable The extent of the removal of impurities in a sodium hydroxide leach after a heat treatment increases with the temperature of the leach liquor. The extent of the removal of impurities also depends on the time of the leach. Consequently the leaching conditions should be chosen to achieve the required impurity element removal. 20 WO 2010/105292 PCT/AU2010/000302 15 Example 6 The effect of the time of the sodium hydroxide leach on the amount of phosphorous removed after a heating treatment is shown when the iron ore sample 2 is either: 1. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, 5 followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a pulp density of 0.5 wt% solids with a sample taken at 0.25 hour; 2. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a pulp density of 0.5 wt% solids with a sample taken at 0.50 hour; 10 3. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a pulp density of 0.5 wt% solids with a sample taken at 1.0 hour; 4. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at 15 a pulp density of 0.5 wt% solids with a sample taken at 2.0 hours; 5. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a pulp density of 0.5 wt% solids with a sample taken at 3.0 hours; 6. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, 20 followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a pulp density of 0.5 wt% solids with a sample taken at 5.0 hours, or 7. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at a pulp density of 25 wt% solids with a sample taken at 0.25 hour; WO 2010/105292 PCT/AU2010/000302 16 8. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at a pulp density of 25 wt% solids with a sample taken at 0.50 hour; 9. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, 5 followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at a pulp density of 25 wt% solids with a sample taken at 1.0 hour; 10. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at a pulp density of 25 wt% solids with a sample taken at 2.0 hours; 10 11. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at a pulp density of 25 wt% solids with a sample taken at 3.0 hours, or 12. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at 15 a pulp density of 25 wt% solids with a sample taken at 5.0 hours. Assay data for solutions from the leaches are shown in Table 6. Table 6 Test Leaching Leaching Leaching Solution assay data (mg/L) condition solution pulp time density (wt %) (h) Fe P Si Al 1 O.1M NaOH 0.5 0.25 <1.0 1.3 24 6.0 2 0.1M NaOH 0.5 0.50 <1.0 1.5 25 6.0 3 0.1M NaOH 0.5 1.0 <1.0 1.7 30 8.0 4 0.1M NaOH 0.5 2.0 <1.0 1.9 40 10 5 0.1M NaOH 0.5 3.0 <1.0 2.0 49 13 6 0.1M NaOH 0.5 5.0 <1.0 2.1 63 17 7 2.5M NaOH 25' 0.25 0.6 132 * 458 8 2.5M NaOH 25 0.50 0.6 134 * 644 9 2.5M NaOH 25 1.0 0.6 118 * 868 10 2.5M NaOH 25 2.0 0.6 124 * 1290 11 2.5M NaOH 25 3.0 0.6 118 * 1414 12 2.5M NaOH 25 5.0 0.6 102 * 1252 Initially 3.2 g ore in 600 mL of lixiviant.

WO 2010/105292 PCT/AU2010/000302 17 * Initially 40.32 g ore in 121 mL of lixiviant. * Silica had precipitated from the solutions before they were analysed. A significant amount of the impurities are removed within the first 15 minutes with 5 further impurities being removed with increasing leaching time. The extent of the removal of impurities in a sodium hydroxide leach after a heat treatment increases with the time and temperature of the leach. Consequently the leaching conditions should be chosen to achieve the required impurity element removal. Example 7 10 The effect of the solids pulp density of the sodium hydroxide leach on the amount of phosphorous removed after a heat treatment is shown when the iron ore sample 1 is either: 1. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution 15 with a solids pulp density of 0.5 wt% solids; 2. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution with a solids pulp density of 10 wt% solids; 3. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, 20 followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution with a solids pulp density of 25 wt% solids, or 4. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution with a solids pulp density of 50 wt% solids. 25 Assay data for leach products from leaches for 3 hours are shown in Table 7.

WO 2010/105292 PCT/AU2010/000302 18 Table 7 Test Heating Heating Leaching Leaching XRF assay data (wt%) condition temp. time solution pulp density (*C) (h) (wt %) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a n/a 62.0 0.146 3.07 2.27 iron ore 1 300 1.0 2.5M NaOH 0.5 66.3 0.083 1.20 0.77 2 300 1.0 2.5M NaOH 10 62.4 0.089 3.38 2.41 3 300 1.0 2.5M NaOH 25 62.7 0.092 3.28 2.30 4 300 1.0 2.5M NaOH 50 62.8 0.101 3.36 2.32 n/a not applicable For the same leaching conditions the extent of impurity element removal is lower with increasing solids pulp density in the leach, in particular for the removal of silicon and 5 aluminium species which are anticipated to have saturated the liquor at the higher pulp densities. However, phosphorous removal is less affected by increasing solids pulp density in the leach. Example 8 The effect of the solids pulp density and the concentration of sodium hydroxide leach on 10 the amount of phosphorous removed after a heat treatment is shown when the iron ore sample 2 is either: 1. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a solids pulp density of 0.5 wt% solids; 15 2. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M sodium hydroxide leach solution at a solids pulp density of 0.5 wt% solids; 3. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at 20 a solids pulp density of 0.5 wt% solids; WO 2010/105292 PCT/AU2010/000302 19 4. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution at a solids pulp density of 0.5 wt% solids; 5. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, 5 followed by being contacted with a boiling 0.1 M sodium hydroxide leach solution at a solids pulp density of 25 wt% solids; 6. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M sodium hydroxide leach solution at a solids pulp density of 25 wt% solids; 10 7. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 2.5 M sodium hydroxide leach solution at a solids pulp density of 25 wt% solids, or 8. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 5.0 M sodium hydroxide leach solution at 15 a solids pulp density of 25 wt% solids. Assay data for leach products from leaches for 3 hours are shown in Table 8. Table 8 Test Heating Heating Leaching Leaching XRF assay data (wt%) condition temp. time solution pulp density (OC) (h) (wt %) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a n/a 62.1 0.123 3.22 2.18 iron ore 1 300 1.0 0.1M NaOH 0.5 65.6 0.071 2.10 0.83 2 300 1.0 1.OM NaOH 0.5 65.8 0.063 1.81 0.67 3 300 1.0 2.5M NaOH 0.5 62.9 0.053 1.66 0.56 4 300 1.0 5.0M NaOH 0.5 60.4 0.040 1.36 0.40 5 300 1.0 0.1M NaOH 25 63.6 0.086 3.49 2.17 6 300 1.0 1.OM NaOH 25 62.4 0.088 3.88 2.48 7 300 1.0 2.5M NaOH 25 61.7 0.064 3.60 2.11 8 300 1.0 5.OM NaOH 25 57.0 0.055 3.33 1.92 n/a not applicable WO 2010/105292 PCT/AU2010/000302 20 The extent of impurity element removal is lower with increasing solids pulp density in the leach, in particular for the removal of silicon and aluminium species which are anticipated to have saturated the liquor at the higher pulp densities. Phosphorous removal is affected by increasing solids pulp density to a lesser degree. However, 5 phosphorous removal can be maintained at an appropriate level by increasing the concentration of the sodium hydroxide in the leach to off-set an increase in the solids pulp density of the leach. Example 9 The effect of alternate alkaline leaching solutions such as aqueous ammonia 10 (ammonium hydroxide) and potassium hydroxide is shown when the iron ore sample 2 is either: 1. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M ammonium hydroxide leach solution; 15 2. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 5.3 M ammonium hydroxide leach solution; 3. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M potassium hydroxide leach solution, 20 or 4. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 5.0 M potassium hydroxide leach solution; Assay data for leach products from leaches for 3 hours at a pulp density of 0.5 wt% solids are shown in Table 9. 25 WO 2010/105292 PCT/AU2010/000302 21 Table 9 Test Heating Heating Leaching Leaching XRF assay data (wt%) condition temp. time solution pulp density

(

0 C) (h) (wt %) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a n/a 62.1 0.123 3.22 2.18 iron ore 1 300 1.0 1.OM NH 4 0H 0.5 63.6 0.095 3.21 2.04 2 300 1.0 5.3M NH 4 0H 0.5 60.8 0.089 4.98 2.22 3 300 1.0 1.OM KOH 0.5 66.0 0.070 1.84 0.65 4 300 1.0 5.OM KOH 0.5 66.0 0.062 1.59 0.55 n/a not applicable Significant levels of impurity element removal can be achieved in a leach with boiling ammonium hydroxide and potassium hydroxide after a heat treatment at 300 *C for 1 5 hour. Greater amounts of impurity element removal can be achieved when higher concentrations of the alkaline leaching solutions are used in the leach. Example 10 The effect of acid leaching solutions such as an inorganic acid, sulphuric acid, and an organic acid, citric acid, is shown when the iron ore sample 2 is either: 10 1. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sulphuric acid leach solution at a solids pulp density of 0.5 wt% solids; 2. Subjected to a heating step at a temperature of 300 0 C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M sulphuric acid leach solution at a 15 solids pulp density of 0.5 wt% solids; 3. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 0.1 M sulphuric acid leach solution at a solids pulp density of 10 wt% solids; WO 2010/105292 PCT/AU2010/000302 22 4. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M sulphuric acid leach solution at a solids pulp density of 25 wt% solids, or 5. Subjected to a heating step at a temperature of 300 0 C in air for a period of 1 hour, 5 followed by being contacted with a 1.0 M citric acid leach solution at 77-80 0 C under reflux at a solids pulp density of 0.5 wt% solids. Assay data for leach products from leaches for 3 hours are shown in Table 10. Table 10 Test Heating Heating Leaching solution Leaching XRF assay data (wt%) condition temp. time pulp density (OC) (h) (wt %) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a n/a 62.1 0.123 3.22 2.18 iron ore 1 300 1.0 0.1M H 2

SO

4 0.5 64.8 0.062 3.31 1.87 2 300 1.0 1.OM H 2

SO

4 0.5 63.8 0.012 5.17 2.42 3 300 1.0 0.1M H 2

SO

4 10 64.0 0.123 3.15 1.94 4 300 1.0 1.OM H 2

SO

4 25 64.2 0.066 3.55 1.79 5 300 1.0 1.OM citric acid 0.5 64.2 0.062 3.20 1.81 n/a not applicable 10 Significant levels of impurity element removal can be achieved in a leach with sulphuric acid and citric acid. However, dissolution of the acid soluble iron-containing minerals also occurs with an associated weight loss during the leaching. For the test that gave a leach product with 0.012% P, the weight loss of the sample was around a 70%. Weight losses of 10-20% were associated with good phosphorous removal in the leach. 15 Example 11 The effect of leach temperature with an inorganic acid leaching solution, sulphuric acid, is shown when the iron ore sample 2 is either: 1. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a 1.0 M sulphuric acid leach solution at 21 *C 20 (room temperature); WO 2010/105292 PCT/AU2010/000302 23 2. Subjected to a heating step at a temperature of 300 *C in air for a period of 1 hour, followed by being contacted with a 1.0 M sulphuric acid leach solution at 40 *C; 3. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a 1.0 M sulphuric acid leach solution at 60 *C; 5 4. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a 1.0 M sulphuric acid leach solution at 80 *C, or 5. Subjected to a heating step at a temperature of 300 0C in air for a period of 1 hour, followed by being contacted with a boiling 1.0 M sulphuric acid leach solution. Assay data for leach products from leaches for 3 hours at a pulp density of 25 wt% 10 solids are shown in Table 11. Table 11 Test Heating Heating Leaching Leach Weight XRF assay data (wt%) condition temp. time solution temp. loss (*C) (h) (OC) (wt %) Fe P SiO 2 A1 2 0 3 Untreated n/a n/a n/a n/a 62.1 0.123 3.22 2.18 iron ore 1 300 1.0 1.OM H 2

SO

4 21 0 63.2 0.114 3.16 2.08 2 300 1.0 1.OM H 2

SO

4 40 3.5 63.0 0.097 3.14 2.04 3 300 1.0 1.OM H 2

SO

4 60 9.6 63.3 0.078 3.26 1.92 4 300 1.0 1.OM H 2

SO

4 80 10.9 63.7 0.074 3.22 1.83 5 300 1.0 1.OM H 2

SO

4 B.Pt. 13.7 64.2 0.066 3.55 1.79 n/a not applicable Significant levels of impurity element removal can be achieved in a leach with sulphuric acid. The extent of impurity element removal, and the associated weight loss, increase 15 with an increase in the leach temperature. However, a weight loss of at least 10 wt% solids is associated with good removal of the phosphorous. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various 20 alternative aspects of the invention.

Claims

1. A method for the removal of a impurity element from an iron ore, the method including the steps of heating the ore to a temperature less than 400 0 C and subsequently contacting the ore with an acid or alkaline leach solution to leach the 5 impurity element from the ore.

2. The method of claim 1 wherein the step of heating the ore is conducted at a temperature is below about 350 *C.

3. The method of claim 1 or 2 wherein the step of heating the ore is conducted at a temperature of about 300 *C. 10

4. A method for the removal of a impurity element from an iron ore, the method including the steps of heating the ore to a temperature less than 300 0 C and subsequently contacting the ore with an acid or alkaline leach solution to leach the impurity element from the ore.

5. The method of any one of the preceding claims wherein the step of heating the 15 ore is conducted at a temperature as low as about 225 *C.

6. The method of any one of the preceding claims wherein the step of heating the ore is conducted without the presence of roasting additives or leaching solutions.

7. The method of any one of the preceding claims wherein the step of heating the ore is conducted for about 0.25 hours or more. 20

8. The method of claim 7 wherein the step of heating the ore is conducted for a period of about 1 hour.

9. The method of claim 7 or 8 wherein the step of heating the ore is conducted for a period of less than about 4 hours. 25

10. The method of any one of the preceding claims wherein the impurity element is phosphorous, silica or alumina.

11. The method of any one of the preceding claims wherein the impurity element is phosphorous. 5

12. The method of any one of the preceding claims wherein the leach solution is selected from the group consisting of NaOH, H 2 SO 4 , NH 4 0H, KOH, HCI, HNO 3 and citric acid.

13. The method of claim 10 wherein the leach solution is NaOH.

14. The method of any one of the preceding claims wherein the leach solution is at a 10 concentration of from about 0.001 M to about 5.0 M or more.

15. The method of any one of the preceding claims wherein the leach solution is at a temperature of from 40 0 C to the boiling temperature.

16. The method of any one of the preceding claims wherein the step of contacting the ore with a leach solution is conducted for a period of about 0.25 hours or longer. 15

17. The method of claim 15 wherein the step of contacting the ore with a leach solution is conducted for a period of about 3 hours.

18. The method of removal of elements from iron ore substantially as hereinbefore described with reference to the preferred embodiment and examples.