AU2022287623A1

AU2022287623A1 - A process for treating refractory sulphide ore and a solids-gas reactor therefor

Info

Publication number: AU2022287623A1
Application number: AU2022287623A
Authority: AU
Inventors: David BUDGE
Original assignee: Goldtec Ip Pty Ltd
Current assignee: Goldtec Ip Pty Ltd
Priority date: 2021-12-21
Filing date: 2022-12-15
Publication date: 2023-07-06

Abstract

A process for treating a refractory metal sulphide ore comprises the steps of comminuting the refractory metal sulphide ore to obtain a particle size in a range of about 10-70 pm, and contacting said comminuted ore with an oxidising agent, steam, and an oxide, a hydroxide compound or a carbonate compound under low pressure at a temperature above 400 °C, optionally in the presence of a carbonaceous material or hydrocarbon. The metal sulphide undergoes at least partial oxidation in a first solid-gas reaction to produce a metal oxide and sulphur dioxide. The sulphur dioxide produced in the first solid-gas reaction further reacts with the carbonate compound in a second solid-gas reaction to produce a sulphate compound and carbon dioxide. The second solid-gas reaction thereby shifts the position of equilibrium of the first solid-gas reaction to favour increased production of metal oxide and sulphur dioxide. 1/3 El2 70 -- r --,>0 0>M %0, < >, < >< T~ Fi-.

Description

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"A process for treating refractory sulphide ore and a solids-gas reactor therefor"

Technical Field

[0001] The disclosure relates to a process for treating refractory sulphide ore and a solids-gas reactor therefor.

Background

[0002] The discussion of the background to the disclosure is intended to facilitate an understanding of the disclosure. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0003] Gold may be commonly associated with iron sulphides or a refractory ore body but the gold extraction rates can be as low as 0.3%, requiring these gold-bearing refractory ores to be treated to convert the sulphide phase (at least partially) to a different mineral phase to liberate the gold.

[0004] There are several processes for converting sulphides to oxides but they are typically capital intensive, occupy a large footprint on site, and provide environmental management and sustainability challenges.

[0005] Conventionally, high pressure oxidation (HPOX) has been used to liberate gold from gold-bearing refractory sulphide ore. HPOX is performed in an autoclave at high pressure and temperature, where high-purity oxygen is mixed with a slurry of ore and the sulfide minerals are oxidised, liberating the trapped gold. This process has a high gold recovery rate, typically at least 10% higher than from ore roasting. The oxidation of the iron sulfide minerals produces sulfuric acid, soluble compounds such as ferricsulfate, and solids such as iron sulfate or jarosite. The key disadvantage to this technology is its high complexity and major capital costs. Current capital costs are over AUD 100m for a small plant.

[0006] More recently, the Albion process and bio-oxidation have become viable alternatives to HPOX.

[0007] The Albion process is an atmospheric leaching process for processing zinc sulphide concentrates, refractory copper sulphide concentrates and gold-bearing refractory ores. The Albion process is not sensitive to the concentration grade and gives favourable recovery with both low and dirty concentrates. The primary chemical process is as follows:

MS 2 (s) + O2(aq) 0 + H2 SO4 -- MSO4 (aq) + 2S 0 + H20(aq) (1)

[0008] In the Albion process, milled ore is placed under strain which causes an increase in the number of grain boundary fractures and lattice defects which activate the mineral, facilitating leaching. Oxygen is introduced to the leaching process to assist oxidation. The downside to this method is that ore needs to be milled to a very fine particle size which is energy expensive and requires a special mill. Current capital costs are over AUD 50 million.

[0009] Bio-oxidation is an oxidation process caused by microbes where the valuable metal remains (but becomes enriched) in the solid phase. Bio-oxidation leaves the metal values in the solid phase and the resulting solution may be discarded. This contrasts with bioleaching where the valuable metal is solubilized. If the valuable metal in the ore is hosted by, but not bound to, a surrounding undesired mineral matrix which is blocking the valuable metal from further chemical treatment, the matrix can be degraded by selective dissolution of the undesired mineral matrix. Here the microbes causing the selective dissolution may enrich the valuable metal and facilitate metal extraction by selective dissolution of the undesired mineral matrix. The major disadvantages of employing bio-oxidation is the low extraction rate, the need for controlled temperature regulation and further treatment of the ore is required

[0010] The present disclosure seeks to overcome at least some of the aforementioned disadvantages.

Summary

[0011] The disclosure provides a process for treating a refractory suIphide ore and a solids-gas reactor therefor.

[0012] One aspect of the disclosure provides a process for treating a refractory metal sulphide ore, the process comprising the steps of: a) comminuting the refractory metal sulphide ore to obtain a particle size in a range of about 10-70 pm; and, b) contacting said comminuted ore with an oxidising agent, steam, and a metal oxide, hydroxide or carbonate compound under low pressure at a temperature above 400 °C,

optionally in the presence of a carbonaceous material or hydrocarbon, whereby the metal sulphide undergoes at least partial oxidation in a first solid-gas reaction to produce a metal oxide and sulphur dioxide, the sulphur dioxide produced in the first solid-gas reaction further reacting with the carbonate compound in a second solid-gas reaction to produce a sulphate compound and carbon dioxide, the second solid-gas reaction thereby shifting the position of equilibrium of the first solid-gas reaction to favour increased production of metal oxide and sulphur dioxide.

[0013] In one embodiment, the oxidising agent may comprise oxygen, an oxygen containing gas such as air, ozone, hydrogen peroxide, or potassium permanganate. In one embodiment, the oxidising agent may be gaseous under low pressure above 400 °C. In an alternative embodiment, the oxidising agent may be an atomised aqueous solution of potassium permanganate, fuming nitric acid, ammonium perchlorate, potassium nitrate or any other suitable oxidising agent.

[0014] In one embodiment, the carbonate compound may comprise a metal carbonate salt, in particular an alkali metal carbonate salt such as sodium carbonate or potassium carbonate, even more particular an alkaline earth metal carbonate salt such as calcium carbonate or magnesium carbonate. The oxide or hydroxide compound may also be an alkali metal oxide or hydroxide salt, or an alkaline earth metal oxide or hydroxide salt. It will be appreciated that the metal oxide, hydroxide or carbonate compound comprises a finely divided solid, in particular having a particle size of 10 pm to 70 pm . Alternatively, the metal oxide, hydroxide or carbonate compound may be an atomised aqueous solution of the metal oxide, hydroxide or carbonate compound.

[0015] In one embodiment, said process maybe performed at a low pressure of about 1.0 to about 3 atmospheres.

[0016] In one embodiment, the process is performed in a temperature range of about 500 °C to 1350 °C.

[0017] In one embodiment, the process may be performed in the presence of a carbonaceous or hydrocarbon to maintain the temperature of said process above 400 °C when the metal sulphide content of the ore is less than about 5 to 7 wt%.

[0018] In one embodiment the carbonaceous material may comprise pulverised coal, pulverised coke, or pulverised char. It will be appreciated that other pulverised or powdered carbonaceous materials may be used.

[0019] In another embodiment, the hydrocarbon may comprise natural gas, reformed gas, syngas, methane, ethane, propane or a combination thereof. Alternatively, the hydrocarbon may be partially or entirely replaced with hydrogen.

[0020] In one embodiment, the comminuted ore, the carbonate compound and optionally the carbonaceous material may be contacted with the oxidising agent and steam as a free-falling stream or curtain of solid particles. In one embodiment, the free-falling stream or curtain of solid particles has a particle density of from about 0.1 to about 5.8 kg. m 3 . In another embodiment, the free-falling stream or curtain of solid particles has a flow rate of from about 100 mm/s to about 10,000 mm/s.

[0021] In one embodiment, the oxidising agent and the steam flow concurrently with the free-falling stream or curtain of solid particles. The oxidising agent and the steam may be separate streams or combined as a single stream. In one embodiment, the oxidising agent and steam have a flow rate directly proportional to the mass flow rate where the oxygen provided by the oxidising agent is between 0.1 to 5 times the molar quantity of the sulphide in the comminuted sulphide ore. The steam flow rate is also directly proportional to the mass flow rate where the steam is provided between 0 to 8 times the molar quantity of the comminuted sulphide ore.

[0022] In one embodiment, the oxidising agent and/or the steam may be injected into the free falling curtain of solid particles in a manner to disrupt their path and to break up any clumps of material that may have formed during the feeding process. Jets of either oxidising agent and/or steam may be configured to divert the free falling curtain of solid particles to an angle from the vertical. The diverted free falling curtain may potentially impact a side wall of a reactor or an impact plate (for that purpose). The free falling curtain may be diverted from the vertical continuously or intermittently.

[0023] In one embodiment, the free-falling stream or curtain of solid particles flows into a continuous flow of liquid thereby producing a slurry of at least partially oxidised metal sulphide and metal oxide particles. In one embodiment, the slurry may undergo ultrasonic cavitation. The resulting slurry may undergo further processing upstream to extract or recover the metal values of interest more readily or under less robust conditions.

[0024] In another aspect of the disclosure there is provided a solid-gas reactor, said reactor comprising: a vessel having a base, outer side walls extending upwardly from the base, and inner side walls spaced apart from the outer side walls in parallel alignment therewith, wherein respective lower ends of the inner side walls are spaced apart from the base, the inner side walls thereby defining an upper reactor portion therebetween, a cavity between the outer and inner side walls, and a lower reactor portion disposed between the outer side walls and the base; a solids distribution means in communication with a hopper, wherein the solids distribution means is arranged to deliver a free-falling stream or curtain of solid particles into the upper reactor portion of the vessel; one or more inlets disposed in the upper portion of the vessel in fluid communication with a plurality of laterally extending gas distribution tubes, each gas distribution tube having a series of apertures disposed in a lowermost surface therein to direct a reactant gas in concurrent flow with the free-falling stream or curtain of solid particles into the upper reactor portion of the vessel; an inlet disposed in the outer side wall arranged, in use, to allow ingress of liquid to the lower reactor portion via the cavity; a gas outlet disposed in the outer side wall arranged, in use, to allow egress of gas from the lower reactor portion via the cavity; and, an outlet disposed in the lower reactor portion of the vessel for removal of a slurry of reacted solid particles therefrom.

[0025] In one embodiment, the vessel may be provided with one or more further gas inlets in fluid communication with the gas outlet to recycle gas from the lower reactor portion to the upper reactor portion of the vessel.

[0026] In one embodiment, the plurality of laterally extending gas distribution tubes are arranged in two rows of regularly spaced gas distribution tubes, wherein a first row of distribution tubes is offset from the second row of distribution tubes thereby providing a serpentine pathway for the free-falling stream or curtain of solid particles. In some embodiments, the gas distribution tubes may have a circular cross-section. In other embodiments, the gas distribution tubes may have a diamond-shaped cross section. The diamond-shaped cross-section may have acute angles at the upper and lower apices of said cross-section.

[0027] In one embodiment, the solids distribution means comprises a vibratory feeder. The vibratory feeder comprises an apron having a plurality of adjacent tapered fingers, wherein the apron is configured so that the plurality of adjacent tapered fingers are disposed in perpendicular alignment to the plurality of gas distribution tubes.

[0028] In one embodiment, respective facing sides of the inner side walls are provided with a refractory lining.

[0029] In one embodiment, a liquid level in the lower reactor portion is coincident or proximal to the lowermost end of the inner side walls.

[0030] In one embodiment, the base of the vessel and/or lower portions of the outer side walls are provided with one or more sonic transducers arranged, in use, to generate and direct sufficient ultrasonic energy into the lower portion of the vessel to cavitate a slurry contained therein.

Brief Description of Drawings

[0031] Notwithstanding any other forms which may fall within the scope of the process as set forth in the Summary, specific embodiments will now be described with reference to the accompanying figures below:

[0032] Figure 1 is a schematic side view representation of one embodiment of a solids-gas reactor as disclosed herein;

[0033] Figure 2 is a schematic perspective view representation of the solids-gas reactor shown in Figure 1;

[0034] Figure 3 is a schematic representation of a detail of a solids distribution means and a gas distributor as configured in the solids-gas reactor shown in Figure 2; and

[0035] Figure 4 is a schematic representation of a cross-section of one element of the gas distributor as shown in more detail in Figure 3.

Description of Embodiments

[0036] The disclosure relates to a process for treating a refractory sulphide ore and a solids-gas reactor therefor.

GENERALTERMS

[0037] Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e. one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. For example, reference to "a" includes a single as well as two or more; reference to "an" includes a single as well as two or more; reference to "the" includes a single as well as two or more and so forth.

[0038] Each example of the present disclosure described herein is to be applied mutatis mutandis to each and every other example unless specifically stated otherwise. The present disclosure is not to be limited in scope by the specific examples described herein, which are intended for the purpose of exemplification only. Functionally-equivalent products, compositions and methods are clearly within the scope of the disclosure as described herein.

[0039] The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0040] When an element or layer is referred to as being "on", "engaged to", "connected to" or "coupled to" another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0041] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0042] Reference to positional descriptions, such as lower and upper, are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[0043] Spatially relative terms, such as "inner," "outer," "beneath", "below", "lower", "above", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0044] The term "and/or", e.g., "X and/or Y" shall be understood to mean either "X and Y" or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

[0045] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

[0047] The term "about" as used herein means within 5%, and more preferably within 1%, of a given value or range. For example, "about 3.7%" means from 3.5 to 3.9%, preferably from 3.66 to 3.74%. When the term "about" is associated with a range of values, e.g., "about X% to Y%", the term "about" is intended to modify both the lower (X) and upper (Y) values of the recited range. For example, "about 20% to 40%" is equivalent to "about 20% to about 40%".

PROCESS FOR TREATING REFRACTORY ORE

[0048] Various embodiments as disclosed herein provide a process for treating a refractory ore, in particular metal sulphide ores. The term 'refractory' as used herein refers to a metal value-bearing ore, such as a gold-bearing ore, that has ultra-fine particles of the metal value disseminated and occluded throughout a mineral that is unreactive and impervious to leaching. Consequently, the recovery of the metal value when subjected to convention extraction processes, such as cyanidation and carbon adsorption processes, may be very low. Suitable examples of refractory ores include, but are not limited to, pyrites (i.e. iron sulphides), chalcopyrites and bornites (i.e. copper iron sulphides), and iron sulphides containing lead, zinc, cobalt, nickel, molybdenum and silver.

[0049] While the disclosure is generally made in the context of treating a gold bearing iron sulphide ore, it will be appreciated that the disclosure has general application for treating other metal-bearing sulphide ores or concentrates of said ore. In particular, the process as described herein may be used as a pre-treatment for metal-bearing sulphide ores or concentrates which may subsequently undergo further processing upstream to extract or recover the metal values of interest with conventional recovery processes, where said processes can be performed under less robust condition and/or which result in improved metal value recovery rates.

[0050] The refractory metal sulphide ore may be comminuted to obtain a particle size in a range of about 10-70 pm in any suitable grinding mill. Suitable examples of grinding mills include, but are not limited to, an autogenous mill, a semi-autogenous mill, a ball mill, or high pressure grinding rolls and tower mills.

[0051] The comminuted metal sulphide ore is then contacted with an oxidising agent and a carbonate compound at a temperature above 400 °C, whereupon said sulphide ore undergoes at least a partial oxidation in a first solid-gas reaction to produce a metal oxide and sulphur dioxide in accordance with Equation (2):

2FeS2 (s) + 5 2 02 (g) -- Fe203 (s) + 4SO2(g) (2)

[0052] While not being bound by theory, the inventor opines that the first solid-gas reaction may additionally induce a mineral phase change from pyrite to pyrrhotite which oxidises significantly faster than pyrite at standard atmospheric oxygen.

[0053] The sulphur dioxide produced in the first solid-gas reaction is subsequently consumed by reacting with the carbonate compound in a second solid-gas reaction to produce a sulphate compound and carbon dioxide in accordance with Equation (3):

CaCO3(s)+ S02(g)+ 2 02(g) -> CaSO4 (aq)+ C02(g) (3)

[0054] The second solid-gas reaction shifts the position of equilibrium of the first solid-gas reaction to favour increased production of metal oxide and sulphur dioxide. It is beneficial to consume sulphur dioxide via the second solid-gas reaction because sulphur dioxide converts readily to sulphuric acid in the presence of water, and removal of S02 will reduce corrosion in the reactor and associated pipework.

[0055] Preferably, steam is also contacted with the comminuted metal sulphide ore, the oxidising agent and the carbonate compound. Steam may provides a source of heat and pressure and a mechanism for controlling the temperature of the chamber for the first and second solid-gas reactions. Additionally, the presence of steam also shifts the position of equilibrium of the first-solid gas reaction to favour increased production of metal oxide and sulphur dioxide by converting the sulphur dioxide to sulphurous acid and/or sulphuric acid.

[0056] The oxidising agent may comprise oxygen, an oxygen-containing gas such as air, ozone, hydrogen peroxide, nitric acid, perchloric acid or potassium permanganate. Generally, the oxidising agent is a gas under the first solid-gas reaction conditions. Alternatively, solid oxidising agents, such as potassium permanganate may be employed as an atomised aqueous solution of potassium permanganate, optionally co mixed with steam.

[0057] The carbonate compound may comprise a solid metal carbonate salt, in particular an alkali metal carbonate salt or an alkaline earth metal carbonate salt.

Suitable examples include, but are not limited to sodium carbonate, potassium carbonate, calcium carbonate or magnesium carbonate, although calcium carbonate is preferred. It will be appreciated that the carbonate compound comprises a finely divided solid, in particular having a particle size of 10 pm to 70 pm Alternatively, an atomised aqueous solution of the carbonate compound, optionally mixed with steam, may be employed. Alternatively, a suitable metal oxide or metal hydroxide may replace the carbonate compound.

[0058] The first and second solid-gas reactions may be performed above atmospheric pressure, in particular at a pressure of about 1.5 to about 3 atmospheres. The process may be performed in a temperature range above 400 °C, above 500 °C,

above 600C, above 700C, above800C, above 900C, above 1000C, above 1100 °C, above 1200 °C, or above 1300 °C. In particular, the first and second solid gas reactions may be performed in a range of about 500 °C to 1350 °C.

[0059] The oxidation of the metal sulphide to the metal oxide and sulphur dioxide is an exothermic reaction. Accordingly, in some embodiments the heat generated by the first solid-gas reaction may be sufficient to maintain the temperature of said process above 400 °C. When the metal sulphide content of the ore is less than about 5 to 7 wt%, however, additional thermal energy may be required. In these particular embodiments, the process may be performed in the presence of the carbonaceous material or hydrocarbon to maintain the temperature of said process above 400 °C.

Sufficient carbonaceous material or hydrocarbon may be supplied and consumed in a combustion reaction with oxygen to generate the required additional thermal energy.

[0060] The carbonaceous material may comprise pulverised coal, pulverised coke, or pulverised char. It will be appreciated that other pulverised or powdered carbonaceous materials may be used. In some embodiments, the carbonaceous material may be mixed with the comminuted metal sulphide ore and/or the solid carbonate compound prior to reacting with the oxidising agent. Alternatively, the carbonaceous material, the comminuted metal sulphide ore and the solid carbonate compound may be fed separately to a reactor where the first and second solid-gas reactions take place.

[0061] The hydrocarbon may comprise natural gas, reformed gas, syngas, methane, ethane, propane or a combination thereof. In some embodiments, the hydrocarbon may be mixed with the gaseous oxidising agent and/or steam prior to combustion.

[0062] In some embodiments an ignition source may be provided in the reactor to at least initiate combustion of the carbonaceous material or the hydrocarbon.

[0063] It will be appreciated that the sulphide content of the ore supplied to the reactor in a continuous process may vary temporally, and the relative proportions of ore, oxidising agent, carbonate compound and carbonaceous material (or hydrocarbon) supplied to the reactor may need to be varied accordingly. In use, the refractory metal sulphide ore may be scanned, either before but preferably after comminution, by a sensor capable of determining sulphide content therein. For example, the comminuted refractory metal sulphide ore may be scanned by an XRF detector in real time to determine sulphide content. The XRF detector may be arranged in operative communication with a controller which is arranged to vary the relative proportions of ore, oxidising agent, carbonate compound and carbonaceous material (or hydrocarbon) that are supplied to the reactor, said relative proportions being controlled to ensure that sufficient carbonaceous material (or hydrocarbon) is supplied to augment thermal requirements in the reactor. In embodiments where the sulphide content is higher, there will be a decreased demand for carbonaceous material or hydrocarbon and an increased demand for carbonate compound, whereas in embodiments where the sulphide content is lower, there will be an increased demand for carbonaceous material or hydrocarbon and a decreased demand for carbonate compound.

[0064] The process described herein may be distinguished from many prior art processes for treating refractory sulphide ores in that the first and second solids-gas reactions as described above proceed with no or minimal solid particle-particle contact. In this regard, the comminuted ore, the carbonate compound and optionally the carbonaceous material may be contacted with the oxidising agent and steam as a free-falling stream or curtain of solid particles. In one embodiment, the free-falling stream or curtain of solid particles has a particle density of from about 0.1 to about 5.8 kg. m-. In another embodiment, the free-falling stream or curtain of solid particles has a flow rate of from about 100 mm/s to about 10,000 mm/s.

[0065] Contacting the oxidising agent and steam with the free-falling stream or curtain of solid particles has several benefits. Firstly, the solid particles have a relatively high surface area for increased solid-gas interactions resulting in an increased reaction rate. Secondly, as the free-falling stream or curtain of solid particles enter the reactor, the solid particles rapidly achieve temperature equilibrium and radiate heat uniformly from the surface thereof to establish a uniform temperature gradient across the reactor. Consequently, although the residence time of the solid particles of ore in the reactor may be relatively short compared to prior art processes, oxidation (or at least partial oxidation) of the solid particles of sulphide ore occur much more rapidly than prior art processes.

[0066] The oxidising agent and the steam may be arranged to flow concurrently with the free-falling stream or curtain of solid particles, so as not to increase solid-solid particle interactions. The oxidising agent and the steam may be separate streams or combined as a single stream. In one embodiment, the oxidising agent and steam have a flow rate that is directly proportional to the mass flow rate where the oxygen provided by the oxidiser is between 0.1 and 5 times the molar quantity of the comminuted sulphide ore. The steam flow rate is also directly proportional to the mass flow rate where the steam is provided between 0 and 8 times the molar quantity of the comminuted sulphide ore.

[0067] The resulting products in the free-falling stream or curtain of solid particles may flow into a continuous flow of liquid, typically water, thereby producing a slurry of at least partially oxidised metal sulphide and metal oxide particles. In one embodiment, the slurry may undergo ultrasonic cavitation. Ultrasonic cavitation may beneficially further fracture partially oxidised metal sulphide particles, producing 'fresh' surfaces for further reaction. The resulting slurry may undergo further processing upstream to extract or recover the metal values of interest more readily or under less robust conditions.

REACTOR

[0068] Referring to the Figures, wherein like numerals refer to like features throughout, there is shown a solid-gas reactor 10. The solid-gas reactor 10 may be particularly suitable for performing the process as described herein, in particular the first and second solid-gas reactions as described above.

[0069] The solid-gas reactor 10 includes a tank 12 having a base 14, opposing outer side walls 16 and opposing end walls 18 extending upwardly from a periphery of the base 14. As shown in the Figures, the tank 12 is generally an elongate rectangular tank and may take the form of a sea container (or replicate the dimensions thereof) so that the tank 12 may be conveniently transported to site on a flatbed haulage vehicle. It will be appreciated by those skilled in the art that the tank 12 may take other forms, such as a cylindrical tank in alternative embodiments.

[0070] The tank 12 is also provided with opposing inner side walls 20 that are spaced apart from the opposing outer side walls 16 in parallel alignment therewith. The opposing inner side walls 20 extend between the opposing end walls 18 from an upper edge thereof, respective lower ends 22 of the inner side walls 20 being spaced apart from the base 14.

[0071] The lower ends 22 of the inner side walls 20 maybe provided with respective flanges 24 which extend laterally toward the adjacent outer side wall 16. The upper ends 26 of the inner side walls 20 may be provided with respective web members 28 to interconnect the upper end 26 of the inner side wall 20 with the adjacent outer side wall 16. The web members 28 help to rigidify the inner side walls 20 and prevent solid particulates from entering a cavity 30 extending between the outer and inner side walls 16,20.

[0072] Facing surfaces 32 of the inner side walls 20 may be provided with a refractory lining 34. The refractory lining 34 may extend substantially over the entire facing surfaces 32 of the inner side walls 20. The refractory lining 34 may be fabricated from any suitable refractory material that is resistant to decomposition by heat and retains strength and form at high temperatures (i.e. < 1400 °C). Suitable refractory materials include, but are not limited to, refractory fire bricks or castables rated to over 1500 °C, oxides of aluminium, silicon, magnesium, zircon, titanium, binary compounds such as tungsten carbide or boron nitride, aluminosilicates, or ceramics.

[0073] As shown in the Figures, the opposing inner side walls 20 define an upper portion 36 of said reactor 10 configured for solid-gas reactions therebetween and a lower portion 38 of said reactor 10 disposed between the outer side walls 16 and the base 14. The upper portion 36 may occupy from about 55% to about 85% volume of the tank 12.

[0074] The solid-gas reactor 10 also includes a solids distribution means 40 in communication with a hopper 42 for solid particles. The hopper 42 has an elongate outlet 44 spaced above and extending along the length of one of the web members 28a. The solids distribution means 40 may be in the form of a vibratory feeder having an apron 46 extending along the length of said web member 28a beneath the elongate outlet 44. The apron 46 includes a plurality of tapered fingers 48 in the form of adjacent triangular sections 50 which laterally extend toward opposing web member 28b in a manner whereby respective apices 50a of the triangular sections 50 are disposed above web member 28b. As shown in Figures 2 and 3, the adjacent triangular sections define complimentary triangular gaps 52 therebetween.

[0075] The vibratory feeder is operatively associated with a motor (not shown) and a variable frequency drive (not shown) that are configured to provide the apron 46 and the tapered fingers 48 with a broad range of stroke/frequency combinations. Typically, the motor will cause the apron 46 and the tapered fingers 48 to vibrate by sequentially translating the apron 46 and the tapered fingers 48 in alternating vertical and horizontal planes in a square cycle at a frequency controlled by the variable frequency drive. In this way, solid particulates may be continuously dispensed by the hopper 42 onto the apron 46 and caused to flow in a direction from one web member 28a to the opposing web member 28b along the tapered fingers 48. In this particular direction the triangular sections 50 progressively narrow towards their respective apices 50a and the triangular gaps 52 therebetween progressively widen. Consequently, as the solid particles flow across the surface of the tapered fingers 48, the solid particles are caused to progressively fall into the triangular gaps 52, thereby delivering a free-falling stream or curtain of solid particles into the upper portion 36 of the tank 12. It will be appreciated that the stroke and frequency combinations of the motor and variable frequency drive may be varied to control the desired volume of solid particles, flow rate and particle density of the free-falling stream or curtain of solid particles delivered to the upper portion 36 of the tank 12.

[0076] As shown in Figure 2, the upper portion 36 may be provided with one or more inlets 54a, 54b for ingress of reactant gas and/or steam. The inlets 54a, 54b may be disposed in one of the end walls 18a. The inlets 54a, 54b are in fluid communication with a plurality of tubes 56 that extend laterally into the upper portion 36 in parallel longitudinal alignment with the inner side walls 20. The tubes 56 may extend to the opposing end wall 18b.

[0077] Each tube 56 has a plurality of apertures 58 disposed along the length thereof. The apertures 58 may be regularly spaced and disposed in a lowermost surface 60 of the tube 56. In this way, the reactant gas and/or steam may be directed into the upper portion 36 in concurrent flow with the free-falling stream or curtain of solid particles.

[0078] As shown in the Figures, the plurality of tubes 56 may be regularly spaced and arranged in two rows of tubes 56a, 56b. A first row of tubes 56a may be laterally offset from a second row of tubes 56b, thereby providing a serpentine pathway for the free-falling stream or curtain of solid particles. It will be appreciated that in other embodiments there may be more than two rows of tubes 56 or, alternatively, only one row of tubes 56.

[0079] The tubes 56 may have any suitably shaped cross-section. For example, the tubes 56 may have a circular cross-section or a diamond-shaped cross-section, as shown in the Figures. The diamond-shaped cross-section may have acute angles at the upper and lower apices of said cross-section to reduce the possibility of solid particle build up on an upper surface 62 of the tubes 56.

[0080] The reactor 10 may also include an inlet 64 disposed in the outer side wall 16b to allow ingress of a liquid, such as water, to the lower portion 38 of the reactor 10 via the cavity 30. Two outlets 66, 68 are disposed in the opposing outer side wall 16a. Outlet 66 is disposed in fluid communication with the cavity 30 in an upper portion 70 of the outer side wall 16a and outlet 68 is disposed in fluid communication with the lower portion 38 in a lower portion 72 of the outer side wall 16a.

[0081] In use, a continuous flow of liquid is introduced into the lower portion 38 of the reactor 10 via inlet 64 and the cavity 30, so that a liquid level is coincident with or proximal to the lower ends 22 and flanges 24 of the inner side walls 20. The free falling stream or curtain of solid particles collects in the lower portion 38 of the reactor thereby forming a slurry of reacted solid particles therein. The continuous flow of liquid into the lower portion 38 urges removal of said slurry from the lower portion 38 of the reactor 10 via the outlet 68.

[0082] Gas, such as carbon dioxide, generated in the slurry may egress via outlet 66. In some embodiments, gas outlet 66 may be in fluid communication with one or more gas inlets 74 via conduit 76 to recycle gas from the lower portion 38 to the upper reactor portion 34 of the reactor 10.

[0083] In some embodiment, the base 12 and/or lower portions 72 of the outer side walls 16 and end walls 18 are provided with one or more sonic transducers (not shown) arranged, in use, to generate and direct sufficient ultrasonic energy into the lower portion 38 to cavitate a slurry contained therein.

[0084] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

[0085] In the claims which follow and in the preceding description except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS:

1. A process for treating a refractory metal sulphide ore, the process comprising the steps of: a) comminuting the refractory metal sulphide ore to obtain a particle size in a range of about 10-70 pm; and, b) contacting said comminuted ore with an oxidising agent, steam, and an oxide, a hydroxide compound or a carbonate compound under low pressure at a temperature above 400 °C, optionally in the presence of a carbonaceous material or hydrocarbon, whereby the metal sulphide undergoes at least partial oxidation in a first solid-gas reaction to produce a metal oxide and sulphur dioxide, the sulphur dioxide produced in the first solid-gas reaction further reacting with the carbonate compound in a second solid-gas reaction to produce a sulphate compound and carbon dioxide, the second solid-gas reaction thereby shifting the position of equilibrium of the first solid-gas reaction to favour increased production of metal oxide and sulphur dioxide.

2. The process according to claim 1, wherein the oxidising agent comprises oxygen, an oxygen-containing gas such as air, ozone, hydrogen peroxide, or potassium permanganate.

3. The process according to claim 1 or claim 2, wherein the oxidising agent is gaseous under low pressure above 400 °C.

4. The process according to claim 1 or claim 2, wherein the oxidising agent comprises an atomised aqueous solution of potassium permanganate.

5. The process according to any one of claims 1 to 4, wherein the carbonate compound, hydroxide compound or oxide comprises a metal carbonate salt, a metal hydroxide salt or a metal oxide, respectively.

6. The process according to any one of claims 1 to 5, wherein the carbonate compound comprises a finely divided solid having a particle size of X pm to Y pm.

7. The process according to any one of claims 1 to 5, wherein the carbonate compound comprises an atomised aqueous solution of the carbonate compound.

8. The process according to any one of claims 1 to 7, wherein the process is performed at a low pressure of up to 3 atmospheres.

9. The process according to any one of claims 1 to 8, wherein the process is performed in a temperature range of about 700 °C to 1350 °C.

10. The process according to any one of claims 1 to 9, wherein the process is performed in the presence of a carbonaceous or hydrocarbon to maintain the temperature of said process above 400 °C when the metal sulphide content of the ore is less than about 5 to 7 wt%.

11. The process according to claim 10, wherein the carbonaceous material comprises pulverised coal, pulverised coke, or pulverised char.

12. The process according to claim 10, wherein the hydrocarbon comprises natural gas, reformed gas, syngas, methane, ethane, propane or a combination thereof.

13. The process according to claim 10, wherein the hydrocarbon is partially or entirely replaced with hydrogen.

14. The process according to any one of claims 1 to 13, wherein the comminuted ore, the carbonate compound and optionally the carbonaceous material may be contacted with the oxidising agent and steam as a free-falling stream or curtain of solid particles.

15. The process according to claim 14, wherein the free-falling stream or curtain of solid particles has a particle density of from about 0.1 to about 5.8 kg. m 3 .

16. The process according to claim 14 or claim 15, wherein the free-falling stream or curtain of solid particles has a flow rate of from about 100 mm/s to about 10,000 mm/s.

17. The process according to any one of claims 14 to 16, wherein the oxidising agent and the steam flow concurrently with the free-falling stream or curtain of solid particles.

18. The process according to any one of claims 14 to 16, wherein the oxidising agent and/or the steam are injected into the free falling stream or curtain of solid particles in a manner to disrupt said stream or curtain.

19. The process according to claim 18, wherein one or more jets of oxidising agent and/or steam is configured to divert said stream or curtain of solid particles to an angle from the vertical.

20. The process according to claim 19, wherein the diverted stream or curtain impacts a side wall of a reactor or an impact plate.

21. The process according to claim 19 or claim 20, wherein the free falling stream or curtain is diverted from the vertical continuously or intermittently.

22. The process according to any one of claims 17 to 21, wherein the oxidising agent and steam have a flow rate that is proportional to the mass flow rate of the sulphide ore where the oxygen provided by the oxidising agent is between 0.1 and 5 times the molar quantity of the comminuted sulphide ore and/or the steam flow rate is directly proportional to the mass flow rate where the steam provided is between 0 and 8 times the molar quantity of the comminuted sulphide ore.

23. The process according to any one of claims 14 to 22, wherein the free-falling stream or curtain of solid particles flows into a continuous flow of liquid thereby producing a slurry of at least partially oxidised metal sulphide and metal oxide particles.

24. The process according to claim 23, wherein the slurry may undergoes ultrasonic cavitation.

25. The process according to claim 23 or claim 24, wherein the slurry undergoes further processing upstream to extract or recover the metal values of interest.

26. A solid-gas reactor, said reactor comprising: a vessel having a base, outer side walls extending upwardly from the base, and inner side walls spaced apart from the outer side walls in parallel alignment therewith, wherein respective lower ends of the inner side walls are spaced apart from the base, the inner side walls thereby defining an upper reactor portion therebetween, a cavity between the outer and inner side walls, and a lower reactor portion disposed between the outer side walls and the base; a solids distribution means in communication with a hopper, wherein the solids distribution means is arranged to deliver a free-falling stream or curtain of solid particles into the upper reactor portion of the vessel; one or more inlets disposed in the upper portion of the vessel in fluid communication with a plurality of laterally extending gas distribution tubes, each gas distribution tube having a series of apertures disposed in a lowermost surface therein to direct a reactant gas in concurrent flow with the free-falling stream or curtain of solid particles into the upper reactor portion of the vessel; an inlet disposed in the outer side wall arranged, in use, to allow ingress of liquid to the lower reactor portion via the cavity; a gas outlet disposed in the outer side wall arranged, in use, to allow egress of gas from the lower reactor portion via the cavity; and, an outlet disposed in the lower reactor portion of the vessel for removal of a slurry of reacted solid particles therefrom.

27. The reactor according to claim 26, wherein the vessel is provided with one or more further gas inlets in fluid communication with the gas outlet to recycle gas from the lower reactor portion to the upper reactor portion of the vessel.

28. The reactor according to claim 26 or claim 27, wherein the plurality of laterally extending gas distribution tubes are arranged in two rows of regularly spaced gas distribution tubes, wherein a first row of distribution tubes is offset from the second row of distribution tubes thereby providing a serpentine pathway for the free-falling stream or curtain of solid particles.

29. The reactor according to any one of claims 26 to 28, wherein the gas distribution tubes have a circular cross-section.

30. The reactor according to any one of claims 26 to 28, wherein the gas distribution tubes have a diamond-shaped cross-section.

31. The reactor according to claim 30, wherein the diamond-shaped cross-section has acute angles at the upper and lower apices of said cross-section.

32. The reactor according to any one of claims 26 to 31, wherein the solids distribution means comprises a vibratory feeder.

33. The reactor according to claim 32, wherein the vibratory feeder comprises an apron having a plurality of adjacent tapered fingers, the apron being configured so that the plurality of adjacent tapered fingers are disposed in perpendicular alignment to the plurality of gas distribution tubes.

34. The reactor according to any one of claims 26 to 34, wherein respective facing sides of the inner side walls are provided with a refractory lining.

35. The reactor according to any one of claims 26 to 34, wherein a liquid level in the lower reactor portion is coincident or proximal to the lowermost end of the inner side walls.

36. The reactor according to any one of claims 26 to 35, wherein the base of the vessel and/or lower portions of the outer side walls are provided with one or more sonic transducers arranged, in use, to generate and direct sufficient ultrasonic energy into the lower portion of the vessel to cavitate a slurry contained therein.