WO2015147330A1

WO2015147330A1 - Method for pre-treating gold ore

Info

Publication number: WO2015147330A1
Application number: PCT/JP2015/060302
Authority: WO
Inventors: Kazuhiro Hatano; Takeshi Nakamura
Original assignee: Jx Nippon Mining & Metals Corporation
Priority date: 2014-03-26
Filing date: 2015-03-25
Publication date: 2015-10-01
Also published as: AU2015234654B2; JP6263422B2; CL2016002167A1; JP2015187286A

Abstract

To provide a method for pre-treating gold ore in order to recover gold from gold ore containing pyrite by means of hydrometallurgy, wherein the generation of sulfur dioxide is suppressed and the rate of recovery of the gold can also be improved. A method for pre-treating by means of hydrometallurgy in order to recover gold included in gold ore that contains 30 mass% or more pyrite (FeS₂), said method including a step for heating the gold ore in a non-oxidizing atmosphere in such a manner that the gold ore after the pre-treatment has a smaller particle size (D80) at which the cumulative weight becomes 80% on a distribution curve of the cumulative weight-particle size, versus the D80 of the gold ore before the pre-treatment.

Description

Title of Invention

Method for Pre-Treating Gold Ore

Technical Field

[0001]

The present invention relates to a method for pre-treating gold ore by means of hydrometallurgy in order to recover gold from gold ore containing pyrite, and to a treatment method including a step for subsequently leaching out gold by means of hydrometallurgy.

Background Art

[0002]

One known method for recovering gold from sulfide minerals that contain gold is a technique where a wet method is used. Traditionally, the leaching of gold in sulfide minerals out into a solution has been carried out by using chemicals such cyanide, thiourea, thiosulfate, and halogen gas. Recently, as less toxic leaching agents, there have been proposals to use gold leachates that utilize chloride ions, iron ions, copper ions, and bromide ions, such as are disclosed in Japanese laid-open patent publication no. 2008- 106347 (patent document 1 ) and Japanese laid-open patent publication no. 2009-235525 (patent document 2).

[0003]

A method of oxidizing roasting sulfide mineral has been known as a pre-treatment for enabling the leaching of gold from sulfide minerals, and a pre-treatment that

incorporates other steps into oxidizing roasting has also been proposed in recent years. For example, Japanese laid-open patent publication 2010-235999 (patent document 3) discloses leaching out a copper sulfide mineral at a temperature not higher than the melting point of sulfur, and making use of the differences in hydrophobicity from other iron oxides and gangue components to float particles of sulfur which have taken the form of fine granules and any sulfides that remained instead of being leached out from the resulting leach residue, but separating the iron oxides, gangue components, and the like as sediment or precipitate, thereby concentrating the gold that is included in the leach residue. Thereafter, the concentrated components containing gold undergo oxidizing roasting after removal of the sulfur, making the iron components into iron oxide

(hematite), followed by dissolution using sulfuric acid, whereby a residue in which the gold has been concentrated is recovered.

[0004]

Alternatively, but only for pyrite, it has been known that upon heating to 550°C or above in a non-oxidizing atmosphere, there is decomposition into an acid readily-soluble pyrrhotite and sulfur; Japanese laid-open patent publication 2005-042155 (patent document 4) proposes a method of concentrating by making use of this reaction to remove pyrite from a pyrite-containing copper sulfide ore leaching residue, thus raising the content ratio of the noble metals contained therein.

Citation List

Patent Literature

[0005]

Patent document 1 : Japanese laid-open patent publication no. 2008-106347

Patent document 2 : Japanese laid-open patent publication no. 2009-235525

Patent document 3 : Japanese laid-open patent publication no. 2010-235999

Patent document 4 : Japanese laid-open patent publication no. 2005-042155

Summary of Invention

Technical Problem

[0006]

The method disclosed in Japanese laid-open patent publication 2009-235525 (patent document 2) makes it possible to easily leach out gold without employing highly toxic chemicals such as cyanide, thiourea, thiosulfate, or halogen gas, and therefore has extremely high practicability for leaching gold from copper sulfide mineral. However, when the method is applied to pyrite, the gold leaching speed is unsatisfactory.

[0007]

Therefore, thought has also been given to methods of removing sulfur beforehand and making it easier to leach out iron by performing a pre-treatment making use of oxidizing roasting performed by supplying oxygen, such as described in Japanese laid-open patent publication 2010-235999 (patent document 3).

[0008]

However, when methods of oxidizing and roasting sulfide mineral are employed, including even the method disclosed in patent document 3, then chemical reactions as per 2CuS + 30₂→ 2CuO + 2S0₂, or 4CuFeS₂ + 130₂→ 4CuO + 8S0₂ + 2Fe₂0₃ and 4FeS₂ + 1 10₂→ 2Fe₂0₃ + 8S0₂ occur preferentially, and the result is the generation of sulfur dioxide (S0₂₎, known as a contaminant for environment. In particular, when the gold ore contains a large amount of pyrite, then an enormous amount of sulfur dioxide is generated, so problems still remain in terms of practicality.

[0009]

As regards pre-treatments for increasing the leaching speed of gold, in terms of safety and environmental concerns it is desirable to reduce the sulfur dioxide that is generated in the mineral treatment process for gold leaching, to enhance the safety and lower the impact on the environment. A pre-treatment that could be applied even to gold ore containing large amounts of pyrite, which has thus far proven difficult to adapt to practical use, would be a major contribution to the advancing of the development of gold mining.

[0010]

Regarding this matter, patent document 4 is a process predicated on recovering noble metals by pyrometallurgy, in view of the fact that there are problems with methods of recovering noble metals with hydrometallurgy; a leaching treatment for noble metals with a wet technique is not envisioned (see patent document 4 paragraphs [0007]-[0008], [0078], etc.). There is likewise no suggestion whatsoever regarding what kind of effects would be obtained by hydrometallurgy.

[001 1]

The present invention has been made in view of the above circumstances, and addresses the problem of providing a method for pre-treating gold ore by means of

hydrometallurgy in order to recover gold from gold ore containing pyrite, wherein the generation of sulfur dioxide is suppressed and the rate of recovery of the gold can also be improved.

Solution to Problem

[0012]

In intensive studies aimed at solving the aforementioned problems, the present inventors have discovered regarding gold ore that contains large quantities of pyrite that when the gold ore is heated in a non-oxidizing atmosphere under certain conditions, then a reduction in particle size is advanced. The present inventors have also discovered that the speed at which gold is leached out from the gold ore is improved by the advance in the reduction in particle size. The present invention has been completed on the basis of these findings.

[0013]

One aspect of the present invention is a method for pre-treating in order to recover gold included in gold ore containing 30 mass% or more pyrite (FeS₂)by means of

hydrometallurgy , wherein the pre-treatment method comprises a step for heating the gold ore in a non-oxidizing atmosphere in such a manner that the gold ore after the pre- treatment has a smaller particle size (D80) at which the cumulative weight becomes 80% on a distribution curve of the cumulative weight-particle size, versus the D80 of the gold ore before the pre-treatment.

[0014]

In one embodiment of the pre-treatment method as in the present invention, the D80 of the gold ore after the pre-treatment is 50 to 90 μηι.

[0015]

In another embodiment of the pre-treatment method as in the present invention, the D80 of the gold ore before the pre-treatment is 100 to 200 μπι.

[0016]

In yet another embodiment of the pre-treatment method as in the present invention, the ratio of the D80 of the gold ore after the pre-treatment with respect to the D80 of the gold ore before the pre-treatment is 0.7 or lower. [0017]

In yet another embodiment of the pre-treatment method as in the present invention, the heating step comprises heating the gold ore to 600 to 850°C.

[0018]

In yet another embodiment of the pre-treatment method as in the present invention, the heating step is performed in a rotary kiln.

[0019]

In yet another embodiment of the pre-treatment method as in the present invention, the heating step is performed under such conditions that the cumulative pore volume for a pore diameter 3 to 5 μιη increases by at least two-fold as compared to before the pre- treatment.

[0020]

In yet another embodiment of the pre-treatment method as in the present invention, the pre-treatment method comprises a step for sampling the gold ore and finding the particle size distribution thereof in the midst of the heating step and determining an end point of the heating step on the basis of the measurement result.

[0021]

In yet another embodiment of the pre-treatment method as in the present invention, the heating step is ended when the particle size has been reduced to such an extent that the D80 of the gold ore according to the sampling reaches the range of 50 to 70 μπι.

[0022]

Another aspect of the present invention is a method of treating gold ore, the method comprising performing a step where gold is leached out by hydrometallurgy on gold ore that has been subjected to the pre-treatment method as in the present invention.

Advantageous Effects of Invention

[0023]

Performing the hydrometallurgy after having carried out the pre-treatment method as in the present invention on gold ore containing pyrite makes it possible to obtain a significantly improved gold recovery rate even while also suppressing the generation of harmful sulfur oxides. That is to say, according to the present invention, it is possible to provide an extremely highly practical method of leaching gold out that excels in safety and environmental friendliness.

Brief Description of Drawings

[0024]

[FIG. 1] Fig. l is a graph illustrating a change in the particle size distribution of Lihir concentrate before and after oxidizing roasting and non-oxidizing roasting;

[FIG. 2] Fig.2 is a graph illustrating a change in particle size distribution of a

concentrate produced in Papua New Guinea before and after oxidizing roasting and non- oxidizing roasting;

[FIG. 3] FIG. 3 is a graph illustrating a change in particle size distribution of a pyrite reagent before and after oxidizing roasting and non-oxidizing roasting;

[FIG. 4] FIG. 4 is a graph illustrating a change in particle size distribution of a

Kensington concentrate before and after non-oxidizing roasting;

[FIG. 5] FIG. 5 is a graph illustrating a change in particle size distribution of a pyrite reagent when the holding temperature has been changed in non-oxidizing roasting;

[FIG. 6] FIG. 6 is an SEM image of iron sulfide (pyrite) in gold ore before pre-treatment;

[FIG. 7] FIG. 7 is an SEM image of iron sulfide in gold ore after pre-treatment; and

[FIG. 8] FIG. 8 is a result of a gold leaching test done on raw ore and on gold ore after non-oxidizing roasting 1.

Description of Embodiments

[0025]

The present invention shall be described in greater detail below.

[0026]

1. Pre-treatment

One embodiment of a method for pre-treating gold ore containing pyrite (FeS₂) as in the present invention comprises a step for heating gold ore in a non-oxidizing atmosphere in such a manner that the gold ore after the pre-treatment has a smaller particle size (D80) at which the cumulative weight becomes 80% on a distribution curve of the cumulative weight-particle size, versus the D80 of the gold ore before the pre-treatment. When the heating step reduces the particle size, there is an increase in the exposed portions of gold present in the pyrite interior, and therefore the speed at which the gold leaches out when hydrometallurgy is performed after the pre-treatment is improved.

[0027]

(1) Gold ore

The present invention is directed toward gold ore that contains 30 mass% or more pyrite. The reason for this is that the purpose of the present invention is to increase the leaching rate of gold in pyrite, which is refractory and has a low gold leaching rate. The effects of reducing the particle size become increasingly prominent as the content ratio of pyrite increases, so the gold ore preferably contains at least 50 mass% pyrite, more preferably at least 60 mass%, even more preferably at least 70 mass%. There is, however, no limitation to other requirements, e.g., the magnitude of concentration of gold in the ore. The gold ore to which the treatment of the present invention is directed can also be understood to be gold ore after a conventional beneficiation treatment, such as flotation beneficiation or gravity separation. It would also be possible to crush and grind the ore for reducing the particle size of the ore, thus making it easier for a gold leachate to come into contact with the gold that is inside the ore. The concentration of gold in the gold ore is typically about 0.1 to 100 ppm by mass, more typically about 1 to 20 ppm by mass.

[0028]

The gold ore may contain substances other than pyrite, such as chalcopyrite, galena, sphalerite, arsenopyrite, stibnite, pyrrhotite, or the like, but in the present invention, gold ore containing 30 mass% or more pyrite is used. In such gold ore, the concentration of sulfur versus the gold content in the ore (S/Au) is higher, and it is generally difficult to efficiently recover the gold. Therefore, using such gold ore having a high concentration of pyrite causes the effects of the pre-treatment according to the present invention to be prominently exhibited.

[0029]

(2) Reducing the particle size In the prior art, oxidizing roasting has been done in the presence of oxygen or air, and therefore the sulfur in the sulfide minerals combines with oxygen to produce oxidized sulfur. Oxidizing roasting also fails to produce a significant effect in reducing the particle size of the gold ore. According to results of investigations by the present inventors, when gold ore that has not yet been pre-treated is subjected to heat treatment in a non-oxidizing atmosphere, the ore has been found to become smaller in the heat treatment, depending on the operating conditions. Performing this heat treatment under the appropriate operating conditions therefore makes it possible to reduce the particle size of the gold ore.

[0030]

Specifically, the ratio of the D80 of the gold ore after the pre-treatment versus the D80 of the gold ore before the pre-treatment can be made to be 0.7 or lower, preferably 0.6 or lower, more preferably 0.5 or lower, e.g., 0.3 to 0.6.

[0031]

The D80 of the gold ore after the pre-treatment is preferably 50 to 90 μηι, more preferably 50 to 80 μιη, even more preferably 50 to 70 μηι. Having the D80 of the gold ore after the pre-treatment be 90 μη or lower significantly improves the speed at which the gold is leached out during a subsequent leaching step. A longer heating time results in a higher particle size-reducing effect, but further advances in reducing the particle size are less likely to occur when thermal decomposition of pyrite into pyrrhotite (described below) is completed. According to results of investigations by the present inventors, the limit of the reduction in particle size is approximately 50 μηι in D80. A D80 that is 50 μιη or higher is also advantageous in suppressing the excessive generation of dust and making handling easier in subsequent steps.

[0032]

In view of this, one embodiment of the pre-treatment method as in the present invention comprises a step for sampling the gold ore and finding the particle size distribution thereof in the midst of the heating step and determining an end point of the heating step on the basis of the measurement result. For example, on the basis of the facts set forth above, it would be possible to deem that the particle size has been adequately reduced and to end the heating step when the particle size has been reduced to the point that the D80 of the gold ore is in the range of 50 to 70 μιη, preferably 50 to 60 μηι. It suffices for the heating step to be implemented to such an extent that the particle size is reduced to the point that the D80 of the gold ore reaches this range; further continuation of the heating would constitute energy loss.

[0033]

On the other hand, the size of the gold ore before the pre-treatment is not particularly limited; typically, though, the heating treatment can be efficiently performed when the D80 is in the range of 100 to 200 μιυ.

[0034]

(3) Pore volume

The particles of pyrite included in the gold ore (concentrate) before the heating treatment will be such that pores are not observed, as is illustrated in the SEM image in FIG. 6. Focusing on this state, the present inventors have inferred that in the leaching out of ore, the leaching speed might be improved in the event that the particles, including iron, that have undergone the pre-treatment possess pores; as a result of intensive study, the present inventors have been able to obtain particles that have pores, as illustrated in FIG. 7 regarding iron compounds.

Upon using mercury intrusion porosimetry to find the pore volume distributions for gold ore before and after pre-treatment, the present inventors have discovered that a characteristic change is observed when the pore diameter is in the range of 3 to 5 μπι, and have discovered that performing pre-treatment remarkably increases the cumulative pore volume of this pore diameter range.

[0035]

The measurement of pore volume distribution by mercury intrusion porosimetry is performed for the ore as a whole, and therefore the measurement is done not solely with the altered pyrite particles in the ore but also with the other gangue as well. However, in light of the research of the present inventors, it has been discovered that the change in cumulative pore volume for this pore diameter range is prominent in pyrite, and a desirable change in pyrite has taken place to an adequate extent, irrespective of the ore, provided that the change in cumulative pore volume is double or more in terms of the ratio before and after the pre-treatment. Then, in combination with the above-described reduction in particle size, the increase in pore volume is believed to produce an advantage in making it easier for the gold leachate to penetrate to the interior of the gold ore.

[0036]

Preferably, the cumulative pore volume for a pore diameter 3 to 5 μπι is 2.5-fold or greater than before the pre-treatment; more preferably, the cumulative pore volume for a pore diameter 3 to 5 μηι is 3-fold or greater than before the pre-treatment. However, this ratio is also affected by the amount of pyrite that is contained in the gold ore before the pre-treatment, and is even about 20-fold in cases where the amount of pyrite contained is close to 100 mass%. The ratio would not be so high for gold ore that contains less pyrite than this. As such, the ratio is typically 15-fold or lower, more typically ten-fold or lower, even more typically 5-fold or lower.

[0037]

Performing a heat treatment that is in a non-oxidizing atmosphere as a pre-treatment not only reduces the particle size and increases the pore volume, but also makes it possible to thermally decompose the pyrite (FeS₂) in the gold ore into a hydrochloric acid-soluble iron sulfide - specifically, into pyrrhotite, represented by Fe_!-xS (where x = 0 to 0.2). Typically, the chemical reaction at this time is represented by FeS₂→ FeS + S.

Pyrrhotite designates a sulfide of iron, which has a stoichiometric ratio of Fe:S = 0.8 to 1 : 1 . Pyrite (FeS₂) is refractory in hydrochloric acid, and therefore conversion to an iron sulfide that is soluble in hydrochloric acid can be expected to improve the recovery rate when the gold is recovered by a subsequent hydrometallurgy. That is to say, in addition to the effect of reducing the size of the particles and exposing the gold inside when the non-oxidizing roasting is performed as a pre-treatment, conversion of the pyrite to a hydrochloric acid-soluble material makes it possible to synergistically raise the speed at which the gold is leached out when a leaching step is carried out thereafter.

[0038]

(4) Heating conditions

In the present invention, references to a "non-oxidizing atmosphere" indicate that the molar ratio of the oxygen supply with respect to the pyrite is oxygen:pyrite = 1 :5 or lower; preferably, the molar ratio of the oxygen supply with respect to the pyrite is oxygen:pyrite = 1 : 10 or lower, more preferably 1 :20 or lower.

[0039]

Examples of the non-oxidizing atmosphere for when the heating step is being performed include a reducing atmosphere of ammonia, carbon monoxide, hydrogen sulfide, or the like, as well as a noble gas atmosphere such as argon or helium, an inert atmosphere such as a nitrogen atmosphere or a carbon dioxide atmosphere, or a water vapor atmosphere; an inert atmosphere is preferable in terms of preventing unanticipated reactions from taking place. Alternatively, an exhaust gas used for thermal decomposition may be circulated and used.

[0040]

Provided that the heat treatment is done under conditions where admixture of oxygen is suppressed, then the amount of sulfur oxides generated is reduced and there is no need to install separate sulfuric acid manufacturing equipment in order to treat the same. The sulfuric oxides can be fully removed with a shower tower. A non-oxidizing atmosphere may even obviate the need to install a shower tower.

[0041]

Having gone through the heating step, the gold ore possesses greatly improved solubility to a gold leachate (described below) as compared to when the gold ore does not undergo the heating step, and the speed at which the gold is leached out can be elevated by as much as approximately ten-fold.

[0042] In the heating step, the temperature of the gold ore is desirably held at 600°C or higher, preferably 700°C or higher, more preferably 750°C or higher in order to accelerate the reduction in particle size and thermal decomposition of the pyrite. For similar reasons, the holding temperature of the heating step is preferably continued for five minutes or longer, more preferably for 15 minutes or longer. However, when the temperature of the gold ore is raised excessively, then a greater amount of energy is needed to raise the temperature, sintering takes place and the fluidity is lowered, and there is the risk that the handleability will deteriorate; therefore, the holding temperature is preferably not greater than 850°C, more preferably not greater than 800°C. Similarly, the duration during which the holding temperature is maintained is preferably not longer than 120 minutes, more preferably not longer than 60 minutes.

[0043]

Though the type of heating furnace used to carry out the heating step is not particularly limited, a reduction in particle size can be efficiently achieved by using, for example, a tube furnace, and especially a rotary kiln.

[0044]

Elemental sulfur generated by the thermal decomposition of pyrite is gasified inside a high-temperature furnace, and therefore it is possible to implement a solid-gas separation from the gold ore. The sulfur gas can then be sent to an exhaust system along with the atmosphere gas. However, when elemental sulfur is sent to the exhaust system, the sulfur precipitates as the temperature drops, producing problems such as clogging of the gas path, and therefore the elemental sulfur is desirably recovered with a condenser or the like.

[0045]

2. Hydrometallurgical treatment step

The gold ore after the pre-treatment allows for the gold to be recovered in

hydrometallurgy. Examples of hydrometallurgy can include leaching out of the gold by cyanide bath combined with autoclave treatment, or leaching out of the gold by acidic bath, but there is no limitation thereto. [0046]

In leaching out of the gold by cyanide bath, generally gold ore that contains pyrite is reacted with water and oxygen at high temperature and high pressure (ex.: 200°C, 30 atm) in a pressure-resistant vessel, to make the iron sulfide into iron oxide, following which the gold is leached out. This is referred to as autoclave treatment, because an autoclave is used for the pressure-resistant vessel.

In the case of gold ore that has not undergone the pre-treatment, the oxidation reaction of the iron sulfide is represented by the following formula.

4FeS₂ + 150₂ + 8H₂0→ 2Fe₂0₃ + 8H₂S0₄ - (1)

In the case of gold ore that has been subjected to the pre-treatment, however, then the oxidation of the sulfides generates sulfuric acid, and the sulfuric acid makes it possible to leach out the iron compounds that are soluble in acid, therefore making it possible to shorten the reaction time.

[0047]

In leaching out of the gold by acidic bath, also, it is generally important to bring a leachate into contact with the gold that is locked in the iron sulfides. In a case where the pre-treatment as in the present invention has been performed, the gold that is inside the gold ore is more readily exposed due to the reduction of particle size and the increase in the pore volume, and also the pyrite can be converted to iron sulfide that is soluble in acid; accordingly, the leachate can be more quickly brought into contact with the gold in the iron sulfide.

[0048]

Both hydrometallurgical treatments can reduce the time for the hydrometallurgical treatment after the pre-treatment, but leaching the gold out using an acidic leachate is more advantageous due at least in part to the fact that the hydrometallurgy can be implemented under milder operating conditions (atmospheric pressure, less than 100°C) and highly toxic cyanide is not used.

[0049] There are no limitations to the step nor to the type of acid for when the gold is being leached out by acidic bath with respect to the gold ore after the pre-treatment, but one very effective gold leaching step would comprise a step for bringing the gold ore into contact with a gold leachate containing halide ions, copper ions and iron ions under a supply of oxidizing agent, to leach out the gold component present in the gold ore.

[0050]

It would also be possible to carry out a variety of treatments for removing impurities in the gold ore after the pre-treatment has been performed and before the gold leaching step has been performed. For example, regarding the elemental sulfur, the gold ore after the pre-treatment step could be heated to a high enough temperature for the elemental sulfur to melt, then filtered off to separate the gold and the elemental sulfur.

[0051]

After the gold leaching reaction, a solid-liquid separation can be used to obtain a gold solution from which the gold can be recovered. The method for recovering the gold is not particularly limited, but it would be possible to use activated carbon adsorption, electrowinning, solvent extraction, reduction, cementation, ion exchange, or the like. The sulfur component is present in the post-leaching solution in the form of sulfate, sulfides, elemental sulfur and the like, but it can be separated by a solid-liquid separation or during the gold recovery operation after the leaching reaction of gold is over.

[0052]

The recovery of the gold in the course of the leaching reaction lowers the gold

concentration in the leaching reaction solution, and raising the gold leaching rate would also be an effective technique. This could be performed by, for example, feeding activated carbon or activated carbon and lead nitrate to the gold leachate undergoing the leaching reaction.

Examples

[0053]

The present invention shall be described in a more specific manner below through working examples. The present shall not be limited thereto, however. The method of analyzing the metals that is used in the working examples is inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0054]

Pyrite concentrate (Lihir concentrate) was prepared as the gold ore. The amount of pyrite contained in this pyrite concentrate (raw ore) was determined to be 16 mass% by XRD and chemical analysis. A laser diffraction-type particle size distribution measurement device (the SALD2100 model from Shimadzu Corp.) was used to obtain a distribution curve of the cumulative weight-particle size for the raw ore. According thereto, the particle size (D80) at which the cumulative weight reached 80% was 62.4 μηι (the mean value for when measurements were taken three times).

[0055]

(Non-oxidizing roasting: comparative example)

The raw ore (200 g) was fed to a rotary kiln and heated for 30 minutes at 700°C in a nitrogen atmosphere (where the molar ratio of the oxygen supply with respect to the pyrite was oxygen:pyrite = 1 :20 or lower; the same applies hereinbelow). Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 99.5 μηι (the mean value for when measurements were taken three times).

[0056]

(Oxidizing roasting: comparative example)

The raw ore (200 g) was fed to a rotary kiln and heated for 60 minutes at 600°C in an air atmosphere (where the molar ratio of the oxygen supply with respect to the pyrite was at least oxygen:pyrite = 1 : 1 ; the same applies hereinbelow). Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 95.9 μπι (the mean value for when measurements were taken three times).

[0057] Table 1 and FIG. 1 show the changes in particle size distribution at this time. Numerical values are all mean values for when measurements were taken three times, and the units for particle size are μπι.

[Table 1 ]

[0058]

A change before and after heating treatment in the cumulative pore volume for a pore diameter of 3 to 5 μιη in the pyrite concentrate was also observed using mercury intrusion porosimetry. The pore volume distribution was determined under the following conditions.

Measurement device: Pore Master 60-GT (made by Quantachrome)

Sample quantity: 0.5 to 1.0 g

Sample cell: Small cell (l Ocp χ 30 mm)

Measurement range: high-pressure measurement

Measurement scope: pore diameter 0.0036 to 10 μιη

Mercury purity: top-grade (99.9999 mass%)

Mercury contact angle: 140 deg

Mercury surface tension: 480 dyn / cm

Table 2 shows the results. Numerical values are all mean values for when measurements were taken three times, and the units for cumulative pore volume are cc/g.

[Table 2]

[0059]

<Example 2 (Concentrate produced in Papua New Guinea)> Pyrite concentrate (concentrate produced in Papua New Guinea) was prepared as the gold ore. The amount of pyrite contained in this pyrite concentrate (raw ore) was determined to be 64 mass% by XRD and chemical analysis. A laser diffraction-type particle size distribution measurement device (the SALD2100 model from Shimadzu Corp.) was used to obtain a distribution curve of the cumulative weight-particle size for the raw ore. According thereto, the particle size (D80) at which the cumulative weight reached 80% was 122.3 μιη (the mean value for when measurements were taken three times).

[0060]

(Non-oxidizing roasting: Inventive example)

The raw ore (50 g) was fed into a rotary kiln and heated for 30 minutes at 700°C in a nitrogen atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 61.8 μηι (the mean value for when measurements were taken three times).

[0061]

(Oxidizing roasting: comparative example)

The raw ore (50 g) was fed into a rotary kiln and heated for 60 minutes at 600°C in an air atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 123.4 μηι (the mean value for when measurements were taken three times).

[0062]

Table 3 and FIG. 2 show the changes in particle size distribution at this time. Numerical values are all mean values for when measurements were taken three times, and the units for particle size are μιη. Performing the heat treatment in a non-oxidizing atmosphere was found to have promoted the reduction in particle size.

[Table 3 ] Concentrate produced Raw ore Non-oxidizing Oxidizing

in Papua New Guinea Mean Mean Mean

Median diameter 64.0 30.3 67.7

Mode diameter 93. 1 54.4 82.6

Mean value 44. 1 24. 1 57.9

Standard deviation 0.6 0.5 0.4

D 10 6.0 4.9 1 9.9

D50 64.0 30.3 67.7

D 80 122.3 61 .8 123.4

D80 ratio (vs . raw ore) - 0.47 1 .06

[0063]

A change before and after heating treatment in the cumulative pore volume for a pore diameter of 3 to 5 μηι in the pyrite concentrate was also observed using mercury intrusion porosimetry. The pore volume distribution was determined under similar conditions to those for example 1. Table 4 shows the results. Numerical values are all mean values for when measurements were taken three times, and the units for cumulative pore volume are cc/g.

[Table 4]

[0064]

A pyrite reagent was prepared. The amount of pyrite contained in this reagent (raw ore) was determined to be 95 mass% by XRD and chemical analysis. A laser diffraction-type particle size distribution measurement device (the SALD2100 model from Shimadzu Corp.) was used to obtain a distribution curve of the cumulative weight-particle size for the raw ore. According thereto, the particle size (D80) at which the cumulative weight reached 80% was 184.1 μηι (the mean value for when measurements were taken three times).

[0065]

(Non-oxidizing roasting: Reference example)

The raw ore (30 g) was fed into a rotary kiln and heated for 30 minutes at 700°C in a nitrogen atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 67.3 μιη (the mean value for when measurements were taken three times).

[0066]

(Oxidizing roasting: Reference example)

The raw ore (30 g) was fed into a rotary kiln and heated for 60 minutes at 600°C in an air atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 167.0 μιη (the mean value for when measurements were taken three times).

[0067]

Table 5 and FIG. 3 show the changes in particle size distribution at this time. Numerical values are all mean values for when measurements were taken three times, and the units for particle size are μηι. Performing the heat treatment in a non-oxidizing atmosphere was found to have promoted the reduction in particle size.

[Table 5]

[0068]

A change before and after heating treatment in the cumulative pore volume for a pore diameter of 3 to 5 μηι in the pyrite concentrate was also observed using mercury intrusion porosimetry. The pore volume distribution was determined under similar conditions to those for example 1. Table 6 shows the results. Numerical values are all mean values for when measurements were taken three times, and the units for cumulative pore volume are cc/g.

[Table 6]

Pyrite reagent Raw ore Non-oxidizing Oxidizing

Mean Mean Mean

Cumulative pore vo lume 0.003 0.055 0.01 5

for pore diameter 3 to 5 μπι [0069]

Kensington concentrate was prepared as the gold ore. The amount of pyrite contained in this pyrite concentrate (raw ore) was determined to be 74 mass% by XRD and chemical analysis. A laser diffraction-type particle size distribution measurement device (the SALD2100 model from Shimadzu Corp.) was used to obtain a distribution curve of the cumulative weight-particle size for the raw ore. According thereto, the particle size (D80) at which the cumulative weight reached 80% was 140.7 μηι (the mean value for when measurements were taken three times).

[0070]

(Non-oxidizing roasting 1 : Inventive example)

The raw ore (40 g) was fed into a rotary kiln and heated for 30 minutes at 700°C in a nitrogen atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 64.5 μηι (the mean value for when measurements were taken three times).

[0071]

(Non-oxidizing roasting 2: Inventive example)

The raw ore (40 g) was fed to a rotary kiln and heated for 30 minutes at 700°C in a water vapor atmosphere (where the molar ratio of the oxygen supply with respect to the pyrite was oxygenrpyrite = 1 :20 or lower). Cooling was allowed to proceed to room

temperature, and the particle size distribution curve was obtained again. The D80 was 63.2 μπι (the mean value for when measurements were taken three times).

[0072]

Table 7 and FIG. 4 show the changes in particle size distribution at this time. Numerical values are all mean values for when measurements were taken three times, and the units for particle size are μιη. Performing the heat treatment in a non-oxidizing atmosphere was found to have promoted the reduction in particle size. It was also found that there was no significant difference in the particle size-reducing effect between the nitrogen atmosphere and the water vapor atmosphere. [Table 7]

[0073]

(Gold leaching test)

Next, raw ore and the gold ore that had undergone the non-oxidizing roasting 1 were subjected to a gold leaching test at a liquid temperature of 85°C using a gold leachate acidified with hydrochloric acid, which possesses a composition set forth in Table 8. During the leaching treatment, air was continuously blown in (at 0.1 L/min, with respect to 1 L of leachate), and stirring was continuously performed. During leaching, hydrochloric acid was added as appropriate so as to maintain the pH of the gold leachate at 1.1. Leaching was performed in a plurality of stages. Namely, a solid-liquid separation was implemented at after each stage ended, with division into residue and filtrate, following which fresh leachate was used in a subsequent stage on the residue to repeat the leaching. Table 9 sets forth the results for the raw ore and Table 10 sets forth the results for the gold ore that had undergone the non-oxidizing roasting 1. FIG. 8 also sets forth the results. In the Table, the leaching rate (%) = (weight of Au dissolved in the leachate) ÷ (weight of Au contained the gold ore being subjected to the leaching treatment) ^χ 100.

[0074]

[Table 8]

[0077]

A pyrite reagent was prepared. The amount of pyrite contained in this reagent (raw ore) was computed by XRD and chemical analysis and found to be 95 mass%. A laser diffraction-type particle size distribution measurement device (the SALD2100 model from Shimadzu Corp.) was used to obtain a distribution curve of the cumulative weight- particle size for the raw ore. According thereto, the particle size (D80) at which the cumulative weight reached 80% was 184.1 μιη (the mean value for when measurements were taken three times).

[0078]

(Non-oxidizing roasting 1 : Reference example)

The raw ore (30 g) was fed into a rotary kiln and heated for 30 minutes at 600°C in a nitrogen atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 127.1 μηι (the mean value for when measurements were taken three times).

[0079] (Non-oxidizing roasting 2: Reference example)

The raw ore (30 g) was fed into a rotary kiln and heated for 30 minutes at 700°C in a nitrogen atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 67.3 μηι (the mean value for when measurements were taken three times). This test is the same as the non- oxidizing roasting in Example 3.

[0080]

(Non-oxidizing roasting 3 : Reference example)

The raw ore (30 g) was fed into a rotary kiln and heated for 30 minutes at 850°C in a nitrogen atmosphere. Cooling was allowed to proceed to room temperature, and the particle size distribution curve was obtained again. The D80 was 71.2 μηι (the mean value for when measurements were taken three times).

[0081]

Table 1 1 and FIG. 5 show the changes in particle size distribution at this time.

Numerical values are all mean values for when measurements were taken three times, and the units for particle size are μπι. Performing the heat treatment in a non-oxidizing atmosphere was found to have promoted the reduction in particle size. A difference was also observed in the particle size-reducing effect, depending on the temperature conditions; heat treatment at 700°C or 850°C was found to be more effective than heat treatment at 600°C.

[Table 1 1 ]

[0082]

A change before and after heating treatment in the cumulative pore volume for a pore diameter of 3 to 5 μηι in the pyrite concentrate was also observed using mercury intrusion porosimetry. The pore volume distribution was measured under similar conditions to those for example 1 . Table 12 shows the results. Numerical values are all mean values for when measurements were taken three times, and the units for cumulative pore volume are cc/g.

[Table 12]

Pyrite reagent Raw ore Non-oxidizing Non-ox idizing 2 Non-oxidizing 3

Mean Mean Mean Mean

Cumulative pore volume 0.003 0.025 0.055 0.01 0 for pore diameter 3 to 5 μπι

Claims

[Claim 1]

A method for pre-treating in order to recover gold included in gold ore containing 30 mass% or more pyrite (FeS₂) by means of hydrometallurgy, the pre-treatment method comprising a step for heating the gold ore in a non-oxidizing atmosphere in such a manner that the gold ore after the pre-treatment has a smaller particle size (D80) at which the cumulative weight becomes 80% on a distribution curve of the cumulative weight-particle size, versus the D80 of the gold ore before the pre-treatment.

[Claim 2]

The method of pre-treating gold ore according to claim 1 , the D80 of the gold ore after the pre-treatment being 50 to 90 μηι.

[Claim 3]

The method of pre-treating gold ore according to claim 1 or 2, the D80 of the gold ore before the pre-treatment being 100 to 200 μπι.

[Claim 4]

The method of pre-treating gold ore according to any of claims 1 to 3, the ratio of the D80 of the gold ore after the pre-treatment with respect to the D80 of the gold ore before the pre-treatment being 0.7 or lower.

[Claim 5]

The method of pre-treating gold ore according to any of claims 1 to 4, the heating step comprising heating the gold ore to 600 to 850°C.

[Claim 6]

The method of pre-treating gold ore according to any of claims 1 to 5, the heating step being performed in a rotary kiln.

[Claim 7]

The method of pre-treating gold ore according to any of claims 1 to 6, the heating step being performed under such conditions that the cumulative pore volume of a pore diameter 3 to 5 μηι increases by at least two-fold as compared to before the pre-treatment.

[Claim 8] The method of pre-treating gold ore according to any of claims 1 to 7, comprising a step for sampling the gold ore and finding the particle size distribution thereof in the midst of the heating step and determining an end point of the heating step on the basis of the measurement result.

[Claim 9]

The method of pre-treating gold ore according to any of claims 1 to 8, the heating step being ended when the particle size has been reduced to such an extent that the D80 of the gold ore according to sampling reaches the range of 50 to 70 μιη.

[Claim 10]

A method of treating gold ore, the method comprising performing a step where gold is leached out by hydrometallurgy on gold ore that has been subj ected to the pre-treatment method according to any of claims 1 to 9.