Patent Application
20160265080
The present invention generally relates to methods and apparatuses for extracting desired components, such as metals, from ores. In particular, the present invention is related to methods and apparatuses for increasing the porosity of a metal bearing ore to enhance the extraction of the metal(s) contained in the ore.
Gold deposits are often found in silica-based deposits where the gold is in the form of small, microscopic or nanoscale particles that are entrained and/or encapsulated within layers of silica quartz. The gold contained in the ores mined from these types of deposits is generally difficult to extract using conventional methods and processes known in the art.
A common process for extracting gold from a metal bearing ore is cyanidation and heap leaching followed by the Merrill-Crowe process. During heap leaching, crushed ore containing gold is dosed with a leaching solution such as sodium cyanide (NaCN) or potassium cyanide (KCN). Gold and other metals dissolve into such leaching solutions, known as lixiviants, by forming soluble metal-cyanide complexes. The gold “pregnant” leachate is then drained from the heaped ore in a leaching pit, filtered, and then is subjected to the Merrill-Crowe process, wherein zinc is added to the leachate to precipitate dissolved gold out of solution. The precipitated gold is then filtered and further purified as needed.
During heap leaching, the cyanide leaching solution must come into contact with the metals contained in the ore in order for the metals to be dissolved into solution. However, ores containing very small microscopic or nanoscale metal particles that are encapsulated by layers of silica quartz will generally remain un-wetted by the leaching due to the relatively low porosity of the ores because the ore morphology lacks capillary pathways to allow adequate diffusion of the leaching solution to the metal surfaces contained therein. Examples of capillary pathways include, for example, fractures and fissures. Thus, the low “aqueous” porosity caused by the lack of capillary pathways in these ores generally limits gold recovery using the heap leaching process, whether or not followed by the Merrill-Crowe process.
Some attempts have been made at destabilizing the silica matrix surrounding the metals to effectively increase the porosity of the ores. These attempts include heating the ores using microwave radiation or radiant heat, such as with an oven, as well as mechanical crushing of the ores to increase the surface area of the ore material. In one example, U.S. Pat. No. 3,988,036 to Fisher et al. describe inductively heating ore deposits while still in the ground for purposes of metal extraction.
In U.S. Pat. No. 7,459,006 to Ridler, a method is provided for enhancing the extraction of an element from an ore, the method comprising subjecting the ore to pyrolysis using electromagnetic radiation.
In Canadian Patent No. 2,277,383, a method is provided for enhancing the extraction of an element from an ore by subjecting the element bearing material to thermal shock.
In addition, irradiating gold containing ores with high-power electromagnetic pulses for increasing the precious metal recovery is also known and described by Chanturiya et al. (Chanturiya, V. A. et al. (2005); “Application of High-Power Electromagnetic Pulses to Desintegration of Gold-Containing Mineral Complexes”, Pulsed Power Conference, 2005 IEEE: 361-365).
Some of the known methods and processes are generally difficult to implement due to the relatively large energy requirements associated with heating or pyrolyzing the ore in addition to fine particle cone crushing and subsequent handling of the fines.
Thus, there exists a need for a method, process and/or apparatus for increasing the porosity, or “aqueous porosity”, of an ore material that alleviates at least one of the problems known in the art.
In one aspect, the present invention provides a method and/or apparatus for increasing the porosity of a metal bearing ore. In one aspect, the invention provides a method wherein a metal bearing ore is exposed to an oscillating magnetic field at an exposure rate sufficient to cause an increase in the porosity thereof. In another aspect, the metal bearing ore is subjected to a magnetic field oscillating at a frequency greater than about 0.1 MHz, and preferably of about 0.1 to about 1 MHz. In another aspect, the exposure rate of the metal bearing ore to the oscillating magnetic field is greater than about 0.1 T/kg/min.
In another aspect, an apparatus for increasing the porosity of a metal bearing ore is provided, the apparatus comprising a magnetic field source configured to generate an oscillating magnetic field, and a conveyor adapted to transport the metal bearing ore through the oscillating magnetic field with an exposure rate sufficient to cause an increase in the porosity thereof. In one aspect, the oscillating frequency of the magnetic field is greater than about 0.1 MHz, and preferably about 0.1 MHz to 1 MHz. In another aspect, the exposure rate of the metal bearing ore to the oscillating magnetic field is greater than about 0.1 T/kg/min.
The features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings, wherein:
The terms “comprise”, “comprises”, “comprised” or “comprising” may be used in the present specification. As used herein (including the disclosure and/or the claims), these terms are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not as precluding the presence of one or more other feature, integer, step, component or a group thereof as would be apparent to persons having ordinary skill in the relevant art.
The term “conveyor” as used herein is intended to mean a device or apparatus that serves to transfer a material from one location to another. In one example, the conveyor may be a conveyor belt, which transports material on a surface thereof. In another example, the conveyor may be a conduit, such as a pipe or the like, through which material is moved. The movement of the material through the conduit may be effected using any force, including pumps and/or gravity.
The term “aqueous porosity” as used herein is intended to mean a porosity that is sufficient to allow penetration and diffusion of a liquid solution.
In one aspect, the present invention provides a method for increasing the porosity, or “aqueous” porosity, of a metal bearing ore, the method comprising exposing the metal bearing ore to an oscillating magnetic field. The magnetic field preferably oscillates at a frequency of greater than about 0.1 MHz, and preferably about 0.1 MHz to about 1 MHz. The exposure rate of the metal bearing ore to the magnetic field is preferably greater than about 0.1 T/kg/min. More preferably, the magnetic field oscillates at a frequency of about 250 to about 350 kHz. In one embodiment, the magnetic field oscillates at a frequency of about 330 kHz. In one aspect, the invention provides a “non-thermal” method of increasing the aqueous porosity of the metal bearing ore, in that the method does not require heating of the metal bearing ore.
The method according to one embodiment of the invention is illustrated in
As illustrated in
It is generally well known that some metals, such as iron, display ferromagnetism, and as such, are affected by changes in the external magnetic field. It has also been shown by Luo et al. (Weidong Luo et al. (2007); “s-Electron Ferromagnetism in Gold and Silver Nanoclusters”, Nano Letters, 7(10): 3134-3137) that nanoclusters of gold also exhibit ferromagnetic behaviour, and are therefore responsive to changes in the external magnetic field. It has been observed that iron particles as well as gold nanoclusters can be present in ores mined from some silica-based deposits. Based on these previous findings, the inventors postulated that exposure of these metal-containing ores to a magnetic field, in particular an oscillating, or reversing magnetic field, will induce vibration of the metal particles 12, which would in turn apply a force against the surrounding mineral component of the ore. This force would be generated as a result of the metal particles 12 vibrating in response to the oscillation of the magnetic field, such as would be expected in accordance with the Lorentz force law. It will be appreciated that, unlike the metal particles 12, the minerals surrounding the metal particles 12 (e.g. silica quartz matrices) are not magnetic, and therefore will not respond to the externally applied magnetic field. The vibration of the metal particles would thereby generate fractures and/or fissures in the surrounding mineral component, thereby increasing the aqueous porosity of the latter. In such state, the ore would be more effectively treated with a leaching solution to dissolve and extract the metal or metals contained therein.
It will be appreciated that in an oscillating magnetic field, the polarity of the magnetic field is reversed every half-cycle. For greater clarity, a half-cycle is understood to be a time period that is half of the period of oscillation of the magnetic field. As explained above, the oscillating magnetic field causes the metal particles 12 to periodically apply vibratory forces against the minerals surrounding the metal particles 12. The vibratory forces applied by the metal particles 12 stress the surrounding minerals, and over time, lead to formation of micro-fractures and/or fissures in the surrounding minerals. The formation of micro-fractures and/or fissures increase the overall porosity of the metal bearing ore, thus enhancing the effectiveness of the metal extraction processes. For example, creation of the aforementioned fractures and/or fissures will allow more of the metal to be exposed to leaching solutions, thereby improving the metal recovery efficiency. The micro-fractures and fissures formed according to the method of the present invention are schematically illustrated in comparing
Preferably, the exposure rate of the metal bearing ore to the oscillating magnetic field is greater than about 0.1 T/kg/min. In other words, as will be understood, the magnetic flux density of the oscillating magnetic field would be adjusted in accordance with the mass flow rate of the gold bearing ore passing through the field. It will be understood that, for example, 1 kilogram of gold bearing ore may be exposed to an oscillating magnetic field having a magnetic flux density of about 0.1 Tesla for approximately 1 minute in accordance with the methods and/or apparatuses of the present invention to increase the porosity of the metal bearing ore. For greater clarity, the exposure time as used herein will be understood to be the time period for which the metal bearing ore is exposed to the oscillating magnetic field.
In one embodiment, the method may be performed by transporting the metal bearing ore through the oscillating magnetic field as schematically illustrated in
In one aspect, the invention provides an apparatus for increasing the porosity of a metal bearing ore. The apparatus comprises a magnetic field source configured to generate an oscillating magnetic field and a conveyor adapted to transport the metal bearing ore through the oscillating magnetic field. As will be understood, such a configuration of the apparatus provides a continuous treatment process. It also be understood that the method of the invention may equally be conducted in a batch manner, in which case the conveyor may be omitted. In a further aspect, the frequency of oscillation of the oscillating magnetic field is about 0.1 MHz to about 1 MHz. Generally, the apparatus of the invention is adapted to expose the metal bearing ore to an oscillating magnetic field at a rate of at least about 0.1 T/kg/min.
One embodiment of the apparatus of the invention is illustrated in
In the preferred embodiment, each magnetic field generator 60 is configured to generate an oscillating magnetic field. The purpose or advantage of using an oscillating magnetic field was described above. The apparatus is arranged such that the metal bearing ore is transported by the conveyor, such as the conveyor belt 140, through the oscillating magnetic field. Thus, the conveyor allows untreated ore to pass through a treatment zone where the ore is exposed to the magnetic field and converted to a treated ore. In
One embodiment of a magnetic field generator 60 for use in the methods and/or apparatuses described herein is shown in
Although the electrical conductor 20 is generally shown as being a planar or plate conductor, it will be appreciated that the conductor may take on any other shapes or configurations. For example, the conductor may be wounded to form a solenoid. However, it will be understood that increasing the number of turns or loops in such conductor configurations will result in increased inductance and therefore greater resistivity. As such, in order to minimize the resistivity and power loss, the electrical conductor 20 preferably only forms one loop as shown in
According to one embodiment, in operation, the metal bearing ore is positioned on the conveyor belt 140 upstream from the magnetic field generators 60. The metal bearing ore is then transported downstream in the direction indicated by the arrow 59 through the oscillating magnetic field generated by the magnetic field generators 60. In the embodiment shown in
The interactions between the magnetic field created by the current flowing through the electrical conductors 20 and the metal bearing ore 10 are schematically illustrated in the
It will be appreciated that the conveyor belt 140 may generally comprise non-conductive components to avoid inductive coupling and thereby avoid heating thereof. For example, the conveyor belt 140 may be made of a conventional fiberglass woven material.
As will be understood, due to the current flowing through the conductor 20, heat will be generated. In situations where the ambient conditions may result in overheating of the conductors 20, the apparatus of the invention provides a cooling system, which is illustrated in
In one aspect, the magnetic field generator 60 may further comprise at least one capacitive component and at least one inductive component. These circuit components may be connected in parallel and/or series configuration. By way of example, a tuning capacitor 84 and a coupling capacitor 86 are shown in
It will be appreciated that the method as described above may be performed as a continuous process, wherein a crushed metal bearing ore is continuously fed onto the moving conveyor belt 140 to be transported through the oscillating magnetic field, at a predetermined speed, and collected downstream. It will also be appreciated that the speed at which the conveyor belt 140 transports the metal bearing ore and/or the magnetic flux density of the oscillating magnetic field generated by the magnetic field generator 60, may be varied appropriately to obtain the desired exposure rate. Preferably, the exposure rate of the metal bearing ore to the oscillating magnetic field is greater than about 0.1 T/kg/min.
Although the apparatus has been described and shown as generally transporting the metal bearing ore in a substantially horizontal direction, it will be appreciated that the treatment may be performed while transporting the metal bearing ore in any other orientation, such as in an inclined or declined orientation. The invention is not limited to any orientation of the conveyor.
As mentioned above, in one embodiment, the metal bearing ore may be transported through a conduit instead of by a conveyor belt.
As also shown in
In the embodiment shown in
As will be understood, the mandrel 240 serves to prevent blockage of the ore material as it passes through the conduit 230. In one aspect of the invention, the mandrel 240 is adapted to vibrate or shake while the hollow conduit 230 remains stationary. The movement of the mandrel 240 results in agitation of the ore stream and thereby reduces the likelihood of the material becoming jammed within the conduit 230. The mandrel 240 may be connected to, for example, a hydraulic control system 242 as shown in
According to one embodiment of the invention as illustrated in
As shown in
Although various aspects and embodiments have been described with reference to iron and gold as examples, it will be understood that the methods and apparatuses described herein may be similarly applied to metal bearing ores comprising various other metals and/or metal complexes.
It will be appreciated that the metal bearing ore may be crushed prior to being exposed to the magnetic field in various aspects and embodiments described herein. As such, the metal bearing ore as used herein may comprise a plurality of metal bearing ore fragments. Furthermore, it would be apparent to persons skilled in the art that the metal bearing ore may be crushed in any number of ways.
Furthermore, it will be appreciated that different features of various embodiments of the method and apparatus, as described herein, may be combined with one another in any number of ways. In other words, for example, different frequencies and device configurations described in relation to one embodiment may similarly be applied to other embodiments described herein, although not specifically stated.
Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art. Any examples provided herein are included solely for the purpose of illustrating the invention and are not intended to limit the invention in any way. Any drawings provided herein are solely for the purpose of illustrating various aspects of the invention and are not intended to be drawn to scale or to limit the invention in any way. The scope of the claims appended hereto should not be limited by the preferred embodiments set forth in the above description, but should be given the broadest interpretation consistent with the present specification as a whole. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.
Aspects of the invention will now be illustrated with reference to the following examples. It will be understood that the scope of the invention is not to be limited by the examples.
A number of tests were conducted to determine the effectiveness of the method for increasing the porosity of the metal bearing ore. The tests were generally performed by taking crushed metal bearing ore samples having an average diameter of approximately 32 mm and exposing the crushed metal bearing ore samples to an oscillating magnetic field. As shown in Table 1 below, factors such as the exposure time, the frequency of oscillation of the magnetic field, as well as the power of the current used to generate the oscillating magnetic field were varied between each sample.
Table 1 summarizes the results obtained from a series of direct bottle roll cyanide leaching tests that was performed on Veladero™ Type I metal bearing ore samples. As previously mentioned, the metal bearing ore samples were first prepared by mechanically crushing the ore until an average diameter of approximately 32 mm was reached. The crushed ore samples were then each exposed to the oscillating magnetic field in accordance with the parameters noted in Table 1. It is noted that the crushed ore samples were all treated by placing each metal bearing ore sample in a 500 mL Pyrex® beaker and subjecting it to an oscillating magnetic field generated by an alternating current flowing through a conductor wrapped around the beaker.
The treated metal bearing ore samples were then placed in a container along with sodium cyanide (NaCN) solution. It is also noted that for each sample, the pulp density was adjusted to 35% solids with water. Furthermore, 200 g/L lime slurry was used to maintain the pH of the solution at approximately 11. The level of cyanide was maintained at 1 g/L. All bottle roll leaching tests were performed at ambient temperature, and the samples were all rolled for a period of 13 days to determine the leaching kinetics and the final gold recovery percentages.
During the tests, samples of leached solution were taken every 24 hours from each bottle for the purpose of analysing the leaching kinetics. At the end of the testing, the contents of each bottle were filtered to obtain a filtrate and a retentate. The filtrate and the washings (i.e. the retentate) were collected from each bottle and analyzed separately. In particular, the washed retentate was dried, weighed and crushed until the average diameter was approximately 2 mm, and then further pulverized until 90% of the pulverized retentate had a diameter of less than approximately 75 μm. The pulverized retentate was then analyzed for metal content.
In Table 1, treatment parameters including the exposure time in seconds, the frequency of oscillation of the magnetic field in kHz, and the power of the current used to generate the magnetic field in kW are listed for each sample. Additionally, the calculated head grade of gold and the residue grade of gold, which represent the amount of gold in grams present per one ton of ore before leaching and after leaching, respectively, are shown for each sample. Percentage recovery of gold was calculated by dividing the amount of gold recovered from each sample using the Merrill-Crowe process by the total amount of gold contained in the control sample (i.e. the calculated head grade of the control sample). Furthermore, the temperature gain observed in each sample following the exposure to the magnetic field was recorded. The temperature gain for each sample was determined by taking the difference between the temperatures of the ore surface before the treatment and immediately after the treatment. The surface temperatures of the treated ore samples were measured using an IR laser thermometer.
In total, 19 samples were subjected to the cyanide leaching tests. The mass of each sample ranged from about 400 to 640 grams. It is noted that ore sample 1 is a control sample, meaning that it was not subjected to a magnetic field treatment.
Furthermore, it is apparent from comparing the gold recovery percentage of the exposed samples to that of the control sample (i.e. sample 1) that gold recovery was increased by up to about 17% when the metal bearing ore was subjected to 332 kHz magnetic field. Similarly, gold recovery was increased by up to about 15% and 13% for samples exposed to 332 kHz magnetic field and 3339 kHz magnetic field, respectively.
The above observations are further supported by the leaching kinetics data shown in the plot of
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/CA2013/050815 | Oct 2013 | CA | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2013/050815 | 10/28/2013 | WO | 00 |
