Patent Application
20230167525
The technical field generally relates to methods for recovering at least one precious metal from ores including refractory ores, ore concentrates, or ore tailings which include at least one of arsenic, carbon, and sulfur and ores which are refractory to the recovery of precious metals.
Refractory gold ores have increasingly been an important source of gold production with the exhaustion of free-milling gold deposits.
Gold ores are classified “free-milling” and “refractory” based on their response to cyanide dissolution. For instance, a gold recovery of 90% or more can be readily achieved with a conventional direct cyanidation and/or gravity concentration of free-milling ores. In contrast, ores whose gold recovery performances are below 90% are called refractory ores (Zhou, J., et al. “Establishing the process mineralogy of gold ores.” Technical bulletin (2004): 03).
Gold recovery is negatively affected by the presence of arsenic, organic carbon, and/or sulfur. For example, the gold in refractory ores can be associated with and encapsulated within oxidizable gangue such as sulfide minerals, carbonaceous materials and/or non-oxidizable matrix (silicates), or associated with carbonaceous matter capable of adsorbing gold from alkaline cyanide solution (e.g. heavy hydrocarbons, humic acid, or elemental carbon) via a phenomenon known as preg-robbing, and/or can be a solid solution with highly reactive minerals (e.g. pyrrhotite, arsenopyrite, or copper oxide). It is often referred to the presence of two or three of the above-mentioned categories in the same ore as double or triple refractory ores. For example, double refractory ores can include gold encapsulated within sulfide minerals and gold preg-robbing due to the presence of organic carbon.
It is a well known that refractory ores can be challenging to process, for instance, they can require treatment processes for the cyanidation process to be effective in recovery of the gold. Various treatment processes have been proposed increase gold recovery from refractory ores. These treatment processes can include, for example, mechanical pre-treatments (e.g., grinding), oxidative pre-treatments (e.g., pressure oxidation, wet pressure oxidation, roasting oxidation, and biological oxidation, and chemical oxidation), gravity separation, carbon flotation, roasting, carbon-in-leach separation, carbon-in-pulp separation and passivation or deactivation of the preg-robbing material.
Although these treatments generate a great deal of interest because of their efficiency when compared to more conventional gold cyanidation, they are still limited by several factors, such as extraction efficiency, the need for high pressure and/or high temperature equipment, energy consumption, costs, and negative environmental impacts.
Accordingly, many challenges still exist and there is a need for new methods that can overcome one or more of the disadvantages encountered with the use of conventional methods for recovering precious metals from refractory ores.
According to one aspect, the present technology relates to a method for recovering gold from a refractory gold ore, the method comprising the steps of:
In one embodiment, the method further comprises mixing at least the gold-containing leachate with the gold complexing agent
In another embodiment, the refractory gold ore includes a sulfide mineral, or an arsenic sulfide mineral selected from the group consisting of arsenopyrite, pyrite, tetrahedrite, pyrrhotite, marcasite, chalcopyrite, stibnite, and a combination of at least two thereof.
In another embodiment, the alkaline reagent is selected from the group consisting of calcium carbonate, sodium carbonate, calcium hydroxide, sodium hydroxide, and a mixture of at least two thereof.
In another embodiment, the oxidant is selected from the group consisting of air, oxygen, ozone, peroxide, iron oxide, perchlorates, and a mixture of at least two thereof.
In another embodiment, the leaching step is carried out at ambient temperature.
In another embodiment, the leaching step is carried out at a temperature in the range of from about 10° C. to about 100° C., or from about 10° C. to about 95° C., or from 10° C. to about 90° C., or from about 10° C. to about 85° C., or from about 10° C. to about 80° C., or from about 10° C. to about 70° C., or from about 10° C. to about 60° C., or from about 40° C. to about 100° C., or from about 40° C. to about 95° C., or from about 40° C. to about 90° C., or from about 40° C. to about 85° C., or from about 40° C. to about 80° C., or from about 40° C. to about 70° C., or from about 40° C. to about 60° C.
In another embodiment, the step of separating the gold-containing leachate from the gold-unlocked solid residue is performed by thickening or filtration.
In another embodiment, the method further comprises adding a surfactant to the gold-unlocked solid residue prior to the mixing step.
In another embodiment, the gold complexing agent is selected from the group consisting of cyanide salts, thiocyanate salts, thiourea salts, thiocyanate salts, ammonium salts, halide salts, and a combination of at least two thereof.
In another embodiment, the method further comprises recovering the gold-containing complex by adsorption on an absorbent.
In another embodiment, the method further comprises comminuting the refractory gold ore to obtain refractory gold ore particles having a predetermined size.
According to another aspect, the present technology relates to a method for recovering gold from a refractory gold ore being subject to sulfide locking, the method comprising the steps of:
In one embodiment, the method further comprises separating the gold-containing leachate from the gold-unlocked solid residue.
In another embodiment, the method further comprises mixing at least the gold-containing leachate with the gold complexing agent.
In another embodiment, the refractory gold ore includes a sulfide mineral or an arsenic sulfide mineral selected from the group consisting of arsenopyrite, pyrite, tetrahedrite, pyrrhotite, marcasite, chalcopyrite, stibnite, and a combination of at least two thereof.
In another embodiment, the alkaline reagent is selected from the group consisting of calcium carbonate, sodium carbonate, calcium hydroxide, sodium hydroxide, and a mixture of at least two thereof.
In another embodiment, the oxidant is selected from the group consisting of air, oxygen, ozone, peroxide, iron oxide, perchlorates, and a mixture of at least two thereof.
In another embodiment, the method further comprises adding a surfactant to refractory gold ore mixture or to the gold-unlocked solid residue prior to the mixing step.
In another embodiment, the step of separating the gold-containing leachate from the gold-unlocked solid residue is performed by thickening or filtration.
In another embodiment, the gold complexing agent is selected from the group consisting of cyanide salts, thiocyanate salts, thiourea salts, thiocyanate salts, ammonium salts, halide salts, and a combination of at least two thereof.
In another embodiment, the method further comprises recovering the gold-cyanide complex by adsorption on an absorbent.
In another embodiment, the method further comprises comminuting the refractory gold ore to obtain refractory gold ore particles having a predetermined size.
According to another aspect, the present technology relates to a method for recovering gold from a refractory gold ore, the method comprising the steps of:
In one embodiment, the method further comprises separating the gold-containing leachate from the gold-unlocked solid residue.
In another embodiment, the method further comprises mixing at least the gold-containing leachate with the gold complexing agent.
In another embodiment, the refractory gold ore includes a sulfide mineral or an arsenic sulfide mineral selected from the group consisting of arsenopyrite, pyrite, tetrahedrite, pyrrhotite, marcasite, chalcopyrite, stibnite, and a combination of at least two thereof.
In another embodiment, the concentrating step is performed by flotation.
In another embodiment, the gold ore concentrate comprises at least 5 wt. % of organic carbon or arsenic.
In another embodiment, the alkaline reagent is selected from the group consisting of calcium carbonate, sodium carbonate, calcium hydroxide, sodium hydroxide, and a mixture of at least two thereof.
In another embodiment, the oxidant is selected from the group consisting of air, oxygen, ozone, peroxide, iron oxide, perchlorates, and a mixture of at least two thereof.
In another embodiment, the method further comprises adding a surfactant to refractory gold ore mixture or to the gold-unlocked solid residue prior to the mixing step.
In another embodiment, the step of separating the gold-containing leachate from the gold-unlocked solid residue is performed by thickening or filtration.
In another embodiment, the gold complexing agent is selected from the group consisting of cyanide salts, thiocyanate salts, thiourea salts, thiocyanate salts, ammonium salts, halide salts, and a combination of at least two thereof.
In another embodiment, the method further comprises recovering the gold-cyanide complex by adsorption on an absorbent.
In another embodiment, the method further comprises comminuting the refractory gold ore to obtain refractory gold ore particles having a predetermined size.
In another embodiment, the method further comprises comminuting the refractory gold ore concentrate to obtain refractory gold ore concentrate particles having a predetermined size.
According to another aspect, the present technology relates to a method for recovering gold from a refractory gold ore, the method comprising the steps of:
In one embodiment, the method further comprises separating the gold-containing leachate from the gold-unlocked solid residue.
In another embodiment, the method further comprises mixing at least the gold-containing leachate with the gold complexing agent.
In another embodiment, the refractory gold ore includes a sulfide mineral or an arsenic sulfide mineral selected from the group consisting of arsenopyrite, pyrite, tetrahedrite, pyrrhotite, marcasite, chalcopyrite, stibnite, and a combination of at least two thereof.
In another embodiment, the gold-containing leachate comprises arsenic.
In another embodiment, the concentrating step is performed by flotation.
In another embodiment, the refractory gold ore concentrate comprises at least 0.1 wt. % of organic carbon or arsenic.
In another embodiment, the alkaline reagent is selected from the group consisting of calcium carbonate, sodium carbonate, calcium hydroxide, sodium hydroxide, and a mixture of at least two thereof.
In another embodiment, the oxidant is selected from the group consisting of air, oxygen, ozone, peroxide, iron oxide, perchlorates, and a mixture of at least two thereof.
In another embodiment, the method further comprises adding a surfactant to refractory gold ore mixture or to the gold-unlocked solid residue prior to the mixing step.
In another embodiment, the gold complexing agent is selected from the group consisting of cyanide salts, thiocyanate salts, thiourea salts, thiocyanate salts, ammonium salts, halide salts, and a combination of at least two thereof.
In another embodiment, the method further comprises recovering the gold-cyanide complex by adsorption on an absorbent.
According to another aspect, the present technology relates to a method recovering gold from a refractory gold ore including sulfide mineral or an arsenic sulfide mineral, the method comprising the steps of:
In one embodiment, the method further comprises separating the gold-containing leachate from the gold-unlocked solid residue.
In another embodiment, the method further comprises mixing at least the gold-containing leachate with the gold complexing agent.
In another embodiment, the refractory gold ore includes a sulfide mineral or an arsenic sulfide mineral selected from the group consisting of arsenopyrite, pyrite, tetrahedrite, pyrrhotite, marcasite, chalcopyrite, stibnite, and a combination of at least two thereof.
In another embodiment, the metal of the metal hydroxide is selected from the group consisting of alkali metals and alkaline earth metals. In some example, the metal hydroxide is sodium hydroxide or calcium hydroxide.
In another embodiment, the amount of hydroxide is in the range of from about 1 equivalent to about 4 equivalents, or from about 1 equivalent to about 3 equivalents, or from about 1.5 equivalents to about 2.5 equivalents per equivalent of sulfur contained in the refractory gold ore.
In another embodiment, the oxidant is selected from the group consisting of air, oxygen, ozone, peroxide, iron oxide, perchlorates, and a mixture of at least two thereof.
In another embodiment, the oxidant is added at a flow rate inferior to about 132 L/h/kg, or inferior to about 120 L/h/kg, or inferior to about 108 L/h/kg, or inferior to about 96 L/h/kg, or inferior to about 84 L/h/kg, or inferior to about 72 L/h/kg, or inferior to about 60 L/h/kg, or inferior to about 48 L/h/kg.
In another example, the leaching step is carried out at a temperature in the range of from about 45° C. to about 75° C., or from about 50° C. to about 70° C., or from about 55° C. to about 65° C.
In another embodiment, the method further comprises adding a surfactant to refractory gold ore mixture or to the gold-unlocked solid residue prior to the mixing step.
In another embodiment, the gold complexing agent is selected from the group consisting of cyanide salts, thiocyanate salts, thiourea salts, thiocyanate salts, ammonium salts, halide salts, and a combination of at least two thereof.
In another embodiment, the method further comprises recovering the gold-cyanide complex by adsorption on an absorbent.
The following detailed description and examples are illustrative and should not be interpreted as further limiting the scope of the invention. On the contrary, it is intended to cover all alternatives, modifications and equivalents that can be included as defined by the present description. The objects, advantages and other features of the methods will be more apparent and better understood upon reading the following non-restrictive description and references made to the accompanying drawings.
Where applicable, although process flow diagrams may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with steps, reactants and/or products, not all figures contain all the steps, reactants and/or products. Some steps, reactants and/or products may be found in only one figure, and steps, reactants and/or products of the present disclosure which are illustrated in other figures can be easily inferred therefrom.
All technical and scientific terms and expressions used herein have the same definitions as those commonly understood by the person skilled in the art when relating to the present technology. The definition of some terms and expressions used herein is nevertheless provided below for clarity purposes.
When the term “about” is used herein, it means approximately, in the region of, or around. When the term “about” is used in relation to a numerical value, it modifies it; for example, by a variation of 10% above and below its nominal value. This term can also take into account the rounding of a number or the probability of random errors in experimental measurements; for instance, due to equipment limitations.
When a range of values is mentioned in the present application, the lower and upper limits of the range are, unless otherwise indicated, always included in the definition. When a range of values is mentioned in the present application, then all intermediate ranges and subranges, as well as individual values included in the ranges, are intended to be included.
When the term “equilibrium” is used herein, it refers to a steady state in which the stated variable has no observable impact (or no net impacts) on the properties of the system, although the ongoing process strives to change it.
As used herein, the expression “refractory ore” refers to an ore which is less than 90% amenable to gold extraction by standard cyanidation leaching techniques. The expression “refractory ore” encompass mildly, moderately, and highly refractory ores which are respectively between 80% and 90%, between 50% and 80%, and less than 50% amenable to gold extraction by standard cyanidation leaching techniques. The expression “refractory ore” also includes ore concentrates and ore tailings which are less than 90% amenable to gold extraction by standard cyanidation leaching techniques.
As used herein, the expression “gold complexation” refers to the conversion of gold comprised in a leachate to a gold-containing complex. The expression “cyanide complexation” refers to the conversion of gold comprised in a leachate to a gold-cyanide complex, or to a common gold cyanidation process also referred to as a cyanide process or a MacArthur-Forrest process.
It is worth mentioning that throughout the following description when the article “a” is used to introduce an element, it does not have the meaning of “only one” and rather means “one or more”. It is to be understood that where the specification states that a step, component, feature, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature or characteristic is not required to be included in all alternatives. When the term “comprising” or its equivalent terms “including” or “having” are used herein, it does not exclude other elements. If a group is defined hereinafter to include at least a certain number of embodiments, it is also to be understood to disclose a group, which preferably consists only of these embodiments.
The present technology relates to methods for recovering at least one precious metal from refractory ores and refractory concentrates, and more particularly, to methods for recovering gold from refractory gold ores and refractory concentrates. The method includes an alkaline oxidative leaching pre-treatment step followed by a gold complexation step.
The refractory gold ore can be, for example, a simple, double, or even a triple refractory gold ore. For example, a double refractory gold ore includes gold particles locked within sulfide minerals and preg-robbing due to the presence of organic carbon. The refractory gold ore can include at least one of sulfide minerals, a carbonaceous material, a non-oxidizable matrix, and reactive minerals. The refractory gold ore can include sulfide minerals and/or arsenic sulfide minerals.
For example, the sulfide mineral and/or arsenic sulfide minerals can be selected from the group consisting of arsenopyrite, pyrite, tetrahedrite, pyrrhotite, marcasite, chalcopyrite, stibnite, and combinations thereof. In one variant of interest, the refractory gold ore includes pyrite, arsenopyrite and pyrrhotite. In another variant of interest, the refractory gold ore includes pyrite, pyrrhotite, arsenopyrite, stibnite, and chalcopyrite.
The refractory gold ore can have a grade of at least about 0.1 gram of gold per ton of dry refractory gold ore. For example, the refractory gold ore can have a gold grade in the range of from about 0.1 g/t to about 30 g/t, limits included.
For a more detailed understanding of the disclosure, reference is first made to
As illustrated in
The alkaline oxidative leaching step can be performed in order to completely or partially oxidize sulfur and/or dissolve the arsenic present in the refractory gold ore in order to render the gold substantially more amenable to complexation, thereby substantially improving the gold-containing complex leaching rate.
In some examples, the alkaline oxidative leaching step can be substantially free of added gold complexing agent (e.g., cyanide) to substantially reduce or completely avoid preg-robbing at this stage of the process. In one variant of interest, the alkaline oxidative leaching step is completely free of added gold complexing agent.
The alkaline oxidative leaching step is performed by mixing the refractory gold ore with at least one alkaline reagent (or alkaline lixiviant) in the presence of at least one oxidant to obtain a refractory gold ore mixture including a gold-containing leachate and a gold-unlocked solid residue.
For example, any compatible alkaline reagent is contemplated. Non-limiting examples of alkaline reagent include alkali and alkali earth metal basic salts, oxides and hydroxides, and mixtures thereof. For example, the alkaline reagent includes at least one of calcium carbonate (CaCO3), sodium carbonate (Na2CO3), calcium hydroxide (Ca(OH)2), and sodium hydroxide (NaOH). In one variant of interest, the alkaline reagent is sodium hydroxide (NaOH).
Any compatible oxidant is also contemplated. Examples of suitable oxidant include, but are not limited to air, oxygen, ozone, peroxide, iron oxide, perchlorates, and combinations thereof. In one variant of interest, the oxidant is oxygen.
In some examples, the oxidant is added at a flow rate inferior to about 144 L/h/kg. For example, the oxidant is added at a flow rate inferior to about 132 L/h/kg, or inferior to about 120 L/h/kg, or inferior to about 108 L/h/kg, or inferior to about 96 L/h/kg, or inferior to about 84 L/h/kg, or inferior to about 72 L/h/kg, or inferior to about 60 L/h/kg, or inferior to about 48 L/h/kg. In one variant of interest, the oxidant is added at a flow rate inferior to about 48 L/h/kg.
The alkaline reagent can be added in an amount sufficient to obtain a pH in the range of from about 8 to about 14, preferably a pH of at least 12, or more preferably a pH of at least 13. For example, the pH is maintained during the gold complexation step. In one variant of interest, the alkaline reagent is added in an amount sufficient to obtain a pH of about 10.5.
In some examples, the refractory gold ore mixture includes less than about 30 wt. %, or less than about 25 wt. %, or less than about 20%, or less than about 15 wt. % of the alkaline reagent. For example, the refractory gold ore mixture includes from about 0.5 wt. % to about 30 wt. %, or from about 0.5 wt. % to about 25 wt. %, or from about 0.5 wt. % to about 20 wt. %, or from about 0.5 wt. % to about 15 wt. %, or from about 0.5 wt. % to about 10 wt. %, or from about 1 wt. % to about 10 wt. %, or from about 2 wt. % to about 10 wt. %, or from about 3 wt. % to about 10 wt. %, or from about 4 wt. % to about 10 wt. %, or from about 5 wt. % to about 10 wt. %, or from about 6 wt. % to about 10 wt. % of the alkaline reagent, limits included.
In some examples, the refractory gold ore can include a sulfide mineral or an arsenic sulfide mineral and the alkaline reagent is a metal hydroxide added so that the amount of hydroxide is up to about 4 equivalents per equivalent of sulfur contained in the refractory gold ore. For instance, the amount of hydroxide is in the range of from about 1 equivalent to about 4 equivalents per equivalent of sulfur contained in the refractory gold ore, limits included. For example, the amount of hydroxide is in the range of from about 1 equivalent to about 3.5 equivalents, or from about 1 equivalent to about 3 equivalents, or from about 1 equivalent to about 2.5 equivalents, or from about 1.5 equivalents to about 2.5 equivalents per equivalent of sulfur contained in the refractory gold ore, limits included. In one variant of interest, the amount of hydroxide is of about 2 equivalents per equivalent of sulfur contained in the refractory gold ore. The metal of the metal hydroxide can be an alkali and alkali earth metal, for example, the metal hydroxide can be sodium hydroxide or calcium hydroxide. In one variant of interest, the refractory gold includes pyrite or arsenopyrite and the metal hydroxide is added so that the amount of hydroxide is of about 2 equivalents per equivalent of sulfur contained in the refractory gold ore.
The alkaline oxidative leaching step is carried out under atmospheric pressure or near-atmospheric and under either ambient or near-ambient conditions (i.e., at atmospheric pressure, and either at ambient temperature or a near-ambient temperature).
In some example, the alkaline oxidative leaching step is a near-ambient alkaline oxidative (NAAO) leaching step (i.e. carried out at atmospheric pressure, and at a near-ambient temperature). The NAAO leaching step can be carried out at a temperature at ambient temperature or at a moderately elevated temperature (below the boiling point of the refractory gold ore mixture). For example, the NAAO leaching step can be carried out at a temperature in the range of from about 10° C. to about 100° C., or from about 10° C. to about 95° C., or from 10° C. to about 90° C., or from about 10° C. to about 85° C., or from about 10° C. to about 80° C., or from about 10° C. to about 70° C., or from about 10° C. to about 60° C., or from about 40° C. to about 100° C., or from about 40° C. to about 95° C., or from about 40° C. to about 90° C., or from about 40° C. to about 85° C., or from about 40° C. to about 80° C., or from about 40° C. to about 70° C., or from about 40° C. to about 60° C., limits included. In one variant of interest, the NAAO leaching step is carried out at a temperature in the range of from about 40° C. to about 80° C.
In some examples, the alkaline oxidative leaching step is carried out until the system reaches equilibrium. For instance, the alkaline oxidative leaching step is carried out for a time period of less than about 96 hours. For example, the alkaline oxidative leaching step is carried out for a time period in the range of from about 8 hours to about 96 hours, or from about 12 hours to about 96 hours, or from about 24 hours to about 96 hours, or from about 48 hours to about 96 hours, or from about 72 hours to about 96 hours, limits included.
In some example, the gold-unlocked solid residue has a percentage of solid in the range of from about 35 wt. % to about 85 wt. %, or from about 40 wt. % to about 85 wt. %, or from 50 wt. % to about 85 wt. %, or from about 60 wt. % to about 85 wt. %, or from about 70 wt. % to about 85 wt. %, limits included.
In some example, the method optionally includes at least one concentration step which can be performed, for example, by flotation or by gravity separation.
In some examples, the method optionally includes a comminution step or a size reduction step (not shown in
In some examples, the refractory gold ore particles are substantially uniform in size. For instance, the refractory gold ore particles have a size suitable to facilitate liberation of gold from the refractory gold ore. For example, the refractory gold ore particles can have a diameter in the range of from about 1 μm to about 300 μm, or from about 1 μm to about 100 μm, or from about 1 μm to about 75 μm, or from about 1 μm to about 60 μm, or from about 1 μm to about 50 μm, or from about 1 μm to about 40 μm, or from about 1 μm to about 30 μm, or from about 1 μm to about 25 μm, limits included.
In cases where the method includes a comminution step, the comminution and alkaline oxidative leaching steps can be performed sequentially, simultaneously, or partially overlapping in time with each other.
In some examples, the comminution and alkaline oxidative leaching steps are performed sequentially, and the comminution step is performed before the alkaline oxidative leaching step.
In some other examples, the comminution and alkaline oxidative leaching steps are performed partially overlapping in time with each other. For instance, a first amount of the alkaline reagent can be added to the refractory gold ore particles during the comminution step and a second amount of the alkaline reagent can be added in a subsequent alkaline oxidative leaching step. For example, from about 0.5 wt. % to about 10 wt. % of the alkaline reagent can be added during the comminution step and a second amount can be added during the following alkaline oxidative leaching step. Preferably, the first and second amounts are substantially similar. It is to be understood that the alkaline reagent is added in the presence of an oxidant as defined herein.
The method optionally includes mixing the refractory gold ore particles or the gold-unlocked solid residue with water (not shown in
Now referring to
In some example, the refractory gold ore mixture can include a solid content in the range of from about 25 wt. % to about 60 wt. %, limits included. For example, the refractory gold ore mixture can include a solid content of less than 60 wt. %, or less than 50 wt. %, or less than 40 wt. %, or less than 30 wt. %, or less than 25 wt. %. In one variant of interest, the oxidized refractory gold ore can be thickened to obtain a solid concentration of about 25 wt. %.
Referring back to
Any known compatible gold complexing agent is contemplated, for example, compatible gold complexing agents include cyanides, thiocyanates, thioureas, thiocyanates, ammonia, halide (e.g., chloride, bromide, and iodide), a salt thereof, a combination of at least two thereof when applicable and other similar complexing agents. For example, the gold complexing agent can be a cyanide salt. Non-limiting examples of cyanide salts include sodium cyanide, potassium cyanide and calcium cyanide. In one variant of interest, the gold complexing agent is sodium cyanide.
In some examples, the gold complexation step is performed under alkaline conditions, for example, at a pH as defined above.
The gold complexation step can be carried out until the system reaches equilibrium. For instance, the gold complexation step can be carried out for a time period of less than about 96 hours. For example, the gold complexation step can be carried out for a time period in the range of from about 8 hours to about 96 hours, or from about 12 hours to about 96 hours, or from about 24 hours to about 96 hours, or from about 48 hours to about 96 hours, or from about 72 hours to about 96 hours limits included.
Still referring to
In some example, a surfactant can be optionally added to the gold-unlocked solid residue prior to the gold adsorption step. For instance, the surfactant can be any compatible carbon blanking reagent used in gold leaching processes to prevent preg-robbing by carbonaceous or graphitic material. For example, the surfactant can be Dehscofix™ DG 30.
In some example, gold can be recovered by desorbing the gold-containing complex from the adsorbent, for example, at elevated temperature and pH.
In cases where the refractory gold ore includes arsenic, at least a portion of the arsenic can be dissolved in the alkaline oxidative leaching step and thereby be included in the gold-containing leachate. For instance, the gold-containing leachate can also comprise arsenic. In such cases, extractive recovery and valorisation of arsenic can be performed, for example, via precipitation or crystallization by the addition of ferric salts, calcium oxide, or any other compatible chemical compounds known in the field.
In some example, the method can also optionally include recycling and/or reusing at least a portion of the alkaline reagent, the gold complexing agent, and/or the adsorbent.
In some example, the method can also optionally include detoxifying the tailing from the gold complexation step. The detoxification step can be performed to substantially reduce the concentration of residual gold complexing agent, for instance, to reduce the concentration of residual cyanide.
In at least one embodiment, the refractory ore is a double or a triple refractory ore including arsenic and/or gold being subject to sulfide locking, and reference is now made to
In some example, the refractory ore is a double or a triple refractory ore can include carbonaceous matter which can lead to gold adsorption on carbonaceous matter.
As illustrated in
As illustrated in
As illustrated in
The following non-limiting examples are illustrative embodiments and should not be construed as limiting the scope of the present invention. These examples will be better understood with reference to the accompanying Figures.
(a) Gold Recovery from Gold-Arsenic-Bearing Refractory Carbon Concentrates
For a more detailed understanding of the disclosure, reference is now made to
As illustrated in
The mineralogical composition of the gold-arsenic-bearing carbon concentrate samples was also determined, and the main sulfide minerals identified were pyrite, arsenopyrite and pyrrhotite.
A near-ambient alkaline oxidative (NAAO) leach was performed for 48 hours at different temperatures and NaOH concentrations in an oxidative medium supplied by an oxygen flow. The solid percentage in the NAAO was determined to be up to about 60 wt. %. However, optimal results were obtained at a lower solid percentage of about 25 wt. %. A solid percentage of about 25 wt. % was implemented for the results presented in Table 2 below.
Results were also obtained by a direct cyanidation and a CIL process for comparative purposes. They respectively showed no and substantially low gold recovery, and this even in presence of considerably elevated amounts of activated carbon in the CIL process.
The results obtained with the method as described herein including the NAAO leaching step yield to an arsenic dissolution of up to about 86%, and to a gold dissolution of up to about 50%.
The mechanism by which arsenic dissolves is presented in Equation 2.
6FeAsS+22NaOH+13O2↔6Fe(OH)3+2Na3AsO3S+4Na3AsO4+2Na2S2O3+2H2O (eq.2)
Equation 2 shows the formation of sodium thiosulfate and sulfides that can react with oxidized gold to form complexes as presented in Equations 4 and 5 below. These gold complexes cannot be preg-robbed and remain soluble and persistent in the leached solution.
Au++S2−↔AuS− (eq.4)
Au++S2O32−↔Au(S2O3)23− (eq.5)
The gold complexes obtained by the process as described herein were recovered by a solid-liquid separation method. Gold was first converted in gold cyanide by cyanide addition and then recovered on activated carbon. The arsenic was precipitated or crystallized using salts addition with or without temperature adjustment and with or without seeding and was then separated from the liquid stream.
The cyanide containing arsenic-gold-depleted stream was sent to a CIL circuit. The solid residue from the NAAO leaching step was also sent to the CIL circuit with or without conditioning with a surfactant. The CIL was optimized with a sufficient amount of activated carbon to substantially decrease or completely inhibit preg-robbing with a residence time of 48 hours. The use of a surfactant mainly impacted the amount of activated carbon required to achieve optimal gold recovery. Gold recoveries in the range of from about 32% to about 47% were achieved at the gold complexation step (cyanidation step). The effect of the temperature and the NaOH concentration were also evaluated. The maximum arsenic and gold recovery were achieved at a temperature of about 60° C. and a NaOH concentration of about 8% and tantamount to 85.7% and 85.6%, respectively. Finally, the residual cyanidation stream was routed to the detoxification for cyanide destruction and residual arsenic precipitation.
As can be seen in Table 2, in cases without surfactants preconditioning the concentration of activated carbon is increased to avoid preg-robbing. In cases with surfactant preconditioning, the concentration of activated carbon can be decreased while maintaining the gold recovery.
For a more detailed understanding of the disclosure, reference is now made to
As illustrated in
The mineralogical composition of the refractory arsenic-carbonaceous sulfide gold ore samples was also determined, and the main sulfide minerals identified were pyrite, pyrrhotite, arsenopyrite, stibnite, and chalcopyrite.
The NAAO leach was initiated during a grinding step by adding 1 wt. % of NaOH in a ball mill set at a pH=10.5, and at a solid percentage of 60 wt. %. The heat generated during the grinding step improved substantially the dissolution of both arsenic and gold. The absence of cyanide during the grinding step is essential to avoid preg-robbing. The NAAO leaching of the ground material was continued in a pre-cyanidation tank for about 24 hours where an additional 1 wt. % of NaOH was introduced. The leachate thus obtained was then separated from the solid residue prior to a cyanidation step. The leachate was separated from the solid residue by a solid-liquid separation method.
Gold was first converted in gold cyanide by cyanide addition, and then recovered on activated carbon. The arsenic was precipitated or crystallized using salts addition with or without temperature adjustment and with or without seeding, and then separated from the liquid stream.
The cyanide containing arsenic-gold-depleted stream was sent to a CIL circuit. The solid residue from the NAAO leaching step was also sent to the CIL with or without conditioning with a surfactant. The CIL was optimized with a sufficient amount of activated carbon to substantially decrease or completely inhibit preg-robbing with a residence time of either 24 hours or 48 hours. The use of a surfactant mainly impacted the amount of activated carbon required to achieve optimal gold recovery. The maximum arsenic and gold recovery were 50.5% and 94.6%, respectively. Finally, the residual cyanidation stream was routed to the detoxification for cyanide destruction and residual arsenic precipitation. The results are presented in Table 4.
Optimization and validation tests were performed in order to maximize the economic profit obtained from the gold recovery processes described herein.
(a) Optimization of the Kinetics of Sulfur Oxidation and Arsenic Dissolution Under Controlled Laboratory Conditions
The effect of the temperature and the NaOH concentration on the kinetics of formation of thiosulfate and arsenic dissolution during the first six hours (i.e., initial kinetics) of the NAAO leaching step was determined. The progress of the system's physicochemical parameters was also monitored. The test was carried out on a carbon flotation concentrate sample comprising gold embedded in an arsenopyrite matrix. The elemental composition of the sample is summarized in Table 5.
A three-level factorial design was employed, with reference to midpoints tested during preliminary work. Temperatures of 40° C., 60° C. and 80° C. as well as NaOH concentrations of 6 wt. %, 8 wt. % and 10 wt. % with respect to the ore were tested.
For a constant oxygen flow, an increase in pre-treatment temperature or an increase of the NaOH concentration resulted in an increase in the formation of thiosulfate. This can be attributed to an increase kinetics of sulfur oxidation in these conditions. As can be seen on
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(b) Metallurgical Performances
The metallurgical performances were evaluated for a carbon flotation concentrate sample (1 kg). The elemental composition of the sample is presented in Table 6.
The NAAO leaching step was carried out for about 48 hours followed by a cyanidation step also carried out for about 48 hours. The tests were performed under controlled laboratory conditions with different NaOH concentrations varying between about 39 kg/t and about 154 kg/t as well as different oxygen flow rates, varying from 2.1 L/min (126 L/h/kg) to <0.8 L/min (<48 L/h/kg). The temperature was kept constant at about 60° C. from the NAAO leaching step to the cyanidation step. Table 7 summarizes the metallurgical performance obtained for the sample presented in Table 6.
As can be seen in Table 7, by direct cyanidation of the flotation concentrate (test #0), the gold recovery reached 46.6%. With the addition of an NAAO leaching step, the gold recovery after cyanidation reached up to 82.6%.
Similar to the results obtained over 6 hours, the oxidized sulfur quantified after 48 hours is proportional to the NaOH concentration and thus to the NaOH stoichiometry in the NAAO leaching step. Table 7 also shows a direct correlation between the oxidation of sulfides by NAAO and the gold recovery after cyanidation. A correlation can therefore be established between the NaOH consumption and stoichiometry during the NAAO leaching step and the gold recovery after cyanidation.
The presence of oxygen also plays a role in the oxidation of sulfides. Tests carried out at a lower oxygen flow rate (<0.8 L/min) show that the presence of dissolved oxygen was not only limited to the addition or not of the reagent. Indeed, the dissolved oxygen measured remains above 0 despite the decrease in the oxygen flow rate to values <0.8 L/min. For a constant NaOH concentration, a lower oxygen flow rate leads to a substantial decrease in the oxidation of sulfides (about 20%), and this, without significantly affecting the gold recovery. This can be explained by the presence of the oxidation of sulfur limiting value required to allow an optimal accessibility to gold surfaces for cyanidation, ensuring that a gold recovery ceiling is reached. Despite a decrease in the oxygen flow rate, the oxidation of sulfides was still sufficient after 48 hours to allow an average gold recovery of about 80%.
The differences in the kinetics of formation of thiosulfate and of dissolved gold in the NAAO leaching step as a function of the oxygen flow rate were also evaluated. The nature of the by-products resulting from the oxidation of sulfides during the NAAO leaching step is significantly influenced by the oxygen flow rate. Indeed, for a constant NaOH concentration, the distribution of thiosulfate formed during the NAAO leaching step increases by about 30% with a lower oxygen flow rate. However, the formation of thiosulfate eventually decreases to zero after 48 hours of NAAO leaching step. This greater formation of thiosulfate with a lower oxygen flow rate is consistent with oxidation conditions less conducive to the total and rapid oxidation of sulfides to sulfates. Even if thiosulfates were measured after 6 hours of NAAO leaching with an oxygen flow rate of about 2.1 L/min, maintaining this flow rate for 48 hours makes it possible to rapidly complete the oxidation of residual thiosulfates, the completion the oxidation of thiosulfates to sulfates, although slower, is also fully completed after 48 hours with a lower oxygen flow rate. Thiosulfates can therefore be considered as a reaction intermediate in the NAAO leaching process.
The gold dissolution during the NAAO leaching step is also favored with a lower oxygen flow rate.
(a) Pilot-Scale NAAO Leaching Circuit
The NAAO pre-treatment pilot tests were carried out in a circuit consisting of four tanks in a series, each tank having a volume between 40 and 45 L. The pulp, process water and NaOH were fed into the first tank by peristaltic pumps, the transfer to the second to the fourth tanks was performed by overflow. The feed rate of the pilot unit was 1 kg/h for the ore or 2.33 kg/h for the pulp, considering a pulp comprising 25 wt. % of solids. The calculated residence time was 12 hours per tank, for a total of 48 hours over the entire circuit.
After the fourth tank, the pulp was filtered through a filter pan to collect solids and filtrates for analysis, or later use if necessary, to recirculate any potentially residual NaOH. Each reactor was supplied with oxygen using a mass flow controller to allow a constant oxygen supply over time. The tanks were covered with an external insulation and their contents were kept at a temperature of 60° C. using a steam heating element. Each tank was also equipped with a motor with a stirring rod to promote the dispersion of oxygen in order to promote mass transfer.
The cyanidation process was carried out in close reactors on samples taken every 12 hours at the discharge of the fourth tank and before filtration.
Prior to the addition of cyanide, the samples taken at the discharge of the fourth tank were conditioned with a surfactant (Dehscofix™ DG 30) without oxygen for 30 minutes to prevent preg-robbing by carbonaceous material. The conditioning and cyanidation steps were carried out at 60° C. The reactors were also fitted with a gas condenser to limit the loss of water vapor and maintain a constant percentage of solids throughout the tests.
(b) Pilot Test Operating Conditions
The operating conditions tested during the pilot testing of the NAAO leaching process and the cyanidation step are summarized in Tables 8 and 9, respectively.
The objective of each operating condition of the NAAO leaching process was:
Feed and discharge samples from all tanks from the NAAO circuit were taken every 12 hours to assess the metallurgical performances of the process and to validate the solid percentages. The physicochemical parameters were monitored every 6 hours in each of the four tanks of the circuit.
The cyanide concentration was readjusted frequently after titration to assess the total cyanide consumption. The pH was maintained between 10.5 and 11 using an automatic pH controller allowing the addition of limewater. Samples were taken after 24 and 48 hours to follow the metallurgical performances and the formation of cyanidation by-products (cyanates, sulfates, thiosulfates, and thiocyanates).
(c) Pilot Testing of the Process Under Real-Time Operating Conditions
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The gold leached during the NAAO leaching step was monitored and measured in all the process tanks and the results are presented in
During the pilot-scale test of the NAAO leaching step, cyanidation was initiated every 12 hours on samples from the discharge of the fourth tank to evaluate the metallurgical performances of the process.
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This application claims priority under applicable laws to U.S. provisional application No. 63/018,882 filed on May 1, 2020, the content of which is incorporated herein by reference in its entirety for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2021/050605 | 4/30/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63018882 | May 2020 | US |
