The invention relates to processing gold-containing ores that contain reactive sulphide minerals.
The invention relates more particularly, although by no means exclusively, to recovering gold from gold-containing ores that contain reactive sulphide minerals and there is preferential deportment of gold to the reactive sulphide minerals.
One known method for recovering gold from gold-containing sulphide minerals in ores includes:
Carbon-in-pulp is one but not the only known gold recovery option from oxidized ores.
The applicant has developed an improvement to the known method.
The above description is not an admission of the common general knowledge in Australia or elsewhere.
The applicant has realized that selecting processing conditions for gold-containing ores that are optimized to facilitate liberating gold only from reactive sulphide minerals in the ores is an effective option.
The term “reactive” sulphide minerals in an ore means sulphide minerals that react earlier than other sulphide minerals in the ore when heated under oxidizing conditions at a given temperature or react at lower temperatures than other minerals in the ore and have preferential deportment of gold in the minerals compared to the concentrations of gold in other less reactive sulphide minerals in the ore. The other less reactive sulphide minerals are described herein as “barren” minerals.
Examples of minerals that may be reactive sulphide minerals include iron-containing sulphide minerals, such as pyrite, arsenopyrite, chalcopyrite and all secondary copper sulphide minerals, pentlandite, and arsenian pyrite.
The reactive sulphide minerals may be reactive, by way of example only, as a consequence of distortion of the crystalline lattice, for example as a result of elements such as arsenic in the lattice.
The reactive sulphide minerals may be reactive for other reasons.
In situations where a method for recovering gold from gold-containing sulphide minerals in ores includes an oxidation step, such as a pressure oxidation step (or any other oxidation technology, such as but not limited to atmospheric tanks, bio-oxidation systems, heap leach systems, and nitric acid systems), the applicant has realized that it is not necessary to oxidize all of the sulphur in sulphide minerals in gold-containing ores to economically recover gold from the ores. Australian provisional application 2019900350 entitled “Processing Ores Containing Precious Metals” lodged on 5 Feb. 2019 in the name of the applicant and International application PCT/AU2020/050086 lodged on 5 Feb. 2020 in the name of the applicant describe an invention in this regard. The disclosure in the specifications of the provisional and International applications are incorporated herein.
The invention goes beyond the teaching of the provisional and International applications.
In particular, the applicant has realized that preferential deportment of gold to reactive sulphide minerals means that, where there are reactive sulphide minerals and “barren” minerals in an ore, it is sufficient to oxidize only the sulphur in reactive sulphide minerals and thereby liberate gold in the reactive sulphide minerals to obtain cost effective gold recovery and it is not necessary to oxidize sulphur in “barren” minerals.
In the context of the invention, where the method includes (a) an oxidation step and (b) a feed ore to the oxidation step has reactive sulphide minerals and “barren” minerals in the ore, the focus is on supplying sufficient oxygen within a reaction time period and subject to other processing conditions in an oxidation unit, such as an autoclave, to oxidize sulphur in reactive sulphide minerals only in the ore.
The invention has a beneficial impact on gold recovery steps on a discharge stream from the oxidation step.
In broad terms, the invention provides a method of processing a gold-containing ore that contains reactive sulphide minerals that includes selecting processing conditions to optimize liberating gold in reactive sulphide minerals and processing the ore in accordance with the selected processing conditions and liberating gold in the reactive sulphide minerals. In other words, in broad terms, when there are reactive sulphide minerals and “barren” minerals in an ore, the invention focuses on liberating gold in the reactive sulphide minerals only.
In addition, in broad terms, the invention provides a method of processing a gold-containing ore that contains reactive sulphide minerals, the method including:
Where there is a mixture of different sulphide minerals in an ore, typically, iron-containing sulphide minerals are more reactive than other sulphide minerals and contain higher concentrations of gold than less reactive sulphide minerals, i.e. “barren” minerals.
Iron-containing sulphide minerals may include by way of example any one or more than one of pyrite, arsenopyrite, chalcopyrite and all secondary copper sulphide minerals, pentlandite, and arsenian pyrite.
It is noted that not all iron-containing sulphide minerals are reactive sulphide minerals.
For example, at the Lihir mine of the applicant there are pyrites that are not reactive and have low concentrations of gold, typically 2-3 g/t of pyrite. There is also pyrite at Lihir that contains high concentrations of gold, typically 100-150 g/t of pyrite.
Where the method is a continuous method, step (a) may include assessing the effectiveness of actual processing conditions in processing step (b) at a given point in time and using this information to inform the selection of processing conditions for ore supplied to processing step (b) a later point in time.
In addition, or alternatively, where the method is a continuous method, step (a) may include assessing the proportion of the total sulphur that is in reactive sulphide minerals in the ore before the ore is supplied to processing step (b) to inform the selection of processing conditions for step (b).
The method may include periodically or continuously assessing the proportion of the total sulphur that is in reactive sulphide minerals in the ore, selecting processing conditions for step (b) to optimize processing the reactive sulphide minerals in the ore based on the assessments and, as required, varying the processing conditions in response to variations in selected processing conditions based on the ongoing assessments over time to continue to optimize processing of the reactive sulphide minerals.
The processing step (b) may include an oxidation step, such as a pressure oxidation step.
In that event, step (a) of the method may include selecting processing conditions for the oxidation step so that there is sufficient oxygen to oxidize at least substantially all of the sulphur in reactive sulphide minerals in the ore to liberate gold in the reactive sulphide minerals and not preferentially oxidize sulphur in “barren”, i.e. less reactive, sulphide minerals to thereby optimize processing of the reactive sulphide minerals.
It is noted that, in the method of the invention, it is not necessary to supply additional oxygen to the oxidation step or change other processing conditions to change oxidation because there is comparatively little value in oxidizing sulphur in “barren” minerals in the ore.
The applicant has found that complete oxidation of sulphur in reactive sulphide minerals is important because carry-over of reactive sulphide minerals in a discharge stream from the oxidation step to downstream processing steps, such as a downstream cyanide leach circuit, can interfere with gold recovery from the stream.
In one embodiment, the method may include:
The use of ORP is based on a realization that, if the ORP drops during the oxidation step, this can be a good indication whether the oxygen supplied to the step and the other process conditions (such as reaction time) are sufficient to oxidize all of the sulfur in the reactive sulphide minerals and there are no reactive sulphide minerals in the discharge stream from the step.
Depending on the ORP and other information on the mineralogy of the feed ore to the oxidation step, it is possible to determine the oxygen and other process requirements for processing the feed ore in the oxidation step.
It is noted that where there is a constant oxygen rate to an oxidation step and variation of oxidation is required based on ORP monitoring of the discharge stream, it is necessary to vary other processing conditions, such as ore feed rate to achieve complete oxidation of sulphur in reactive sulphide minerals in the oxidation step.
In another embodiment, the method may include:
The method may include periodically or continuously assessing the proportion of the total sulphur that is in reactive sulphide minerals in an ore feed to the oxidation step, selecting the amount of oxygen and other processing conditions in the oxidation step to oxidize at least substantially all of the sulphur in the reactive sulphide minerals and not preferentially oxidize sulphur in “barren” sulphide minerals based on the assessments and, as required, varying the processing conditions in the oxidation step in response to variations in selected processing conditions based on ongoing assessments over time to continue to optimize processing of the reactive sulphide minerals.
The processing step (b) may include a gold leaching step, such as a cyanide leach step, to recover gold from the oxidized ore or concentrates of the ore in a discharge stream from the processing step.
In a situation where processing step (b) includes an oxidation step, such as a pressure oxidation step, the adverse consequences of not adding enough oxygen to oxidize all of the reactive sulphide minerals are potentially substantial.
The adverse consequences apply to all oxidation technologies for reactive sulphide minerals, such as but not limited to autoclaves, atmospheric tanks, bio-oxidation systems, heap leach systems, and nitric acid systems. The invention is not limited to a particular oxidation technology.
The adverse consequences include by way of example:
1. As the reactive sulphide minerals such as pyrite contain the bulk of the gold, then not oxidizing all of the sulphur in the reactive sulphide minerals will lead to lower gold recovery. The amount of oxygen required to oxidize at least substantially all of the sulphur in the reactive sulphide minerals is a “tipping point” in terms of gold recovery vs oxidation for the gold-containing ores shown in
2. The reactive sulphide minerals that are not oxidized or are only partly oxidized and therefore have at least some gold that has not been liberated in an oxidation step and are carried over to downstream processing steps may interfere with the downstream processing steps. For example, these carry-over reactive sulphide minerals will consume oxygen and cyanide in a cyanide leach step. The presence (with or without gold) of these carry-over reactive sulphide minerals will seriously reduce the extraction efficiency and should not be present in a cyanide leach step as they will reduce overall gold recovery for the liberated gold present. It is noted that the oxidation step may be carried out in equipment such as but not limited to autoclaves, atmospheric tanks, bio-oxidation systems, heap leach systems, and nitric acid systems.
The method may include processing an ore that has a recovery-oxidation curve in a graph of % recovery of gold versus % oxidation of the minerals that has a slope of less than 1:1 in a higher % oxidation part of the curve and a slope of greater than 1:1 in a lower % oxidation section of the curve in a processing plant, with the processing steps including:
The method may include allowing variations of the amount of oxygen and other processing conditions in the oxidation unit over time.
The invention is not limited to a particular oxidation technology.
Different oxidation technologies, such as but not limited to autoclaves, atmospheric tanks, bio-oxidation systems, heap leach systems, and nitric acid systems, are all options.
The method may include recovering gold from a discharge stream from the oxidation unit.
The gold recovery step may be based on the use of any one or more than one of cyanide, halides (including chloride), thiosulphate to achieve gold recovery or any other means for final gold recovery, noting that oxidation step (d) is essentially a pre-treatment technology for gold recovery by any known method.
In broad terms, the invention also provides a processing plant for recovering gold from a gold-containing ore that contains reactive sulphide minerals, the plant including:
In more particular terms, the invention also provides a processing plant for recovering gold from a gold-containing ore that contains reactive sulphide minerals, the plant including:
Typically, the plant includes a sulphide concentration unit, such as a sulphide flotation unit, for producing a concentrate output from at least a part of the ore preparation unit output.
With this arrangement, the oxidation unit may be used for oxidizing sulphur in the concentrate output of the flotation unit.
In more particular terms, the invention also provides a processing plant for recovering gold from a gold-containing ore that contains reactive sulphide minerals, the plant including:
(a) an ore preparation unit that includes, for example, comminution and size separation units, such as crushing and milling units, for processing a mined ore and producing an ore preparation unit output from a mined ore,
(b) a sulphide concentration unit, such as a sulphide flotation unit, for producing a concentrate output from at least a part of the ore preparation unit output;
(c) at least one oxidation unit, such as an autoclave unit, for oxidizing sulphur in gold-containing sulphide minerals in the ore;
(d) a metal recovery unit for recovering gold from the oxidation unit output of at least one oxidation unit and/or concentrate output from the sulphide concentration unit; and
(e) a control system for controlling operation of one or both of the oxidation unit and the metal recovery unit, the control system being operable to control the operation of the oxidation unit and/or the metal recovery unit to optimize recovery of gold from the reactive sulphide minerals.
The invention is equally applicable to a greenfield plant and a brownfield plant.
The invention is described further below with reference to the accompanying drawings, of which:
As described above, the invention provides a method of processing gold-containing ores that contain reactive sulphide minerals, with the method including:
As noted above, the applicant has realized that selecting processing conditions for gold-containing ores that are optimized to facilitate liberating gold only from reactive sulphide minerals in the ores and not preferentially from “barren”, i.e. less reactive, sulphide minerals in the ores is an effective option.
The following description focuses on selecting processing conditions to optimize oxidizing reactive sulphide minerals in an ore in a pressure oxidation unit, such as a series of autoclaves, to liberate gold in the reactive sulphide minerals to facilitate recovering the gold in downstream processing unit operations, such as a carbon in pulp operation. It is noted that the invention is not confined to this application.
The following description focuses on reactive pyrite as the reactive sulphide mineral, noting that the invention is not confined to reactive pyrite and is applicable to other reactive sulphide minerals.
The following description also focuses on gold-containing minerals of the type illustrated in
The graph of % recovery of gold from gold-containing sulphide ores versus the % oxidation of sulphur in the ores in
With reference to
The curves shown in the section of the graph of
The curve sections 5a are in a lower oxidation part of the Figure and have a slope of greater than or equal to 1:1. The curve sections 5b are in a higher oxidation part of the Figure and have a slope of less than 1:1.
The transition between the lower and higher curve sections 5a, 5b is typically approximately 45% oxidation for the curves shown in
It can be appreciated from the curves that changing the % oxidation of sulphur in the minerals in these ores in the higher curve sections 5b that have a slope of less than 1:1, i.e. above approximately 45% oxidation in
It is noted that, reactive sulphide minerals, such as reactive pyrite, are being burnt across all oxidation values in the upper curve sections 5b shown in
The slopes of the curves in sections 5b reflect the gold associated with the “barren”, i.e. less reactive pyrite and any other less reactive sulphide minerals.
Going from 60 to 80% oxidation along a selected upper curve section 5b means that, at both 60% and 80%, substantially all of the sulphur in the high-gold containing reactive pyrite has already been burnt and that going from 60 to 80% oxidation is burning “barren” pyrite for incremental gold recovery and loss of mass throughput due to increased residence time in oxidation units.
The tipping point between curve sections 5a, 5b is reached when substantially all of the sulphur in the reactive pyrite has been burnt.
One embodiment of the invention includes a control system that monitors the amount of oxidation of reactive pyrite and any other reactive sulphide minerals in ores upstream of oxidation units and controls operating conditions in the oxidation units to ensure that the amount of oxidation is above the tipping point for each ore. This ensures that the sulphur in at least substantially all of the reactive pyrite and any other reactive sulphide minerals has been oxidized and therefore gold in these minerals has been liberated.
The control system is described further below in the context of the embodiment of the of a plant and a method for recovering gold from an ore that contains gold-containing reactive and “barren”, i.e. less reactive, sulphide minerals.
With reference to the flow sheet of
The mill output from the milling unit 7 is split and supplied via separate transfer lines to a flotation unit 11 and to three autoclave units 13.
The split between the amount of ore preparation unit output transferred to the flotation unit 11 and the amount of ore preparation unit output transferred directly to the autoclave units 13 may vary depending on operational requirements, including the sulphur and other characteristics of feed ore to the units 11, 13.
The flotation unit 11 produces a concentrate slurry. The concentrate slurry is transferred via a transfer line to the autoclave units 13.
The flotation unit 11 also produces a tails slurry. This is transferred via a transfer line for downstream processing (not shown in the Figure).
The flotation unit 11 may be any suitable unit.
The autoclave units 13 operate under high pressure and high temperature, with oxygen being supplied to the units 13, to oxidize sulphur in the ore preparation unit output and sulphur in the concentrate slurry from the flotation unit 11 and produces an autoclave output slurry.
It is noted that the invention is not confined to the use of autoclave units and extends to any suitable oxidation units for oxidizing sulphur in the feed ore and concentrate slurry to the units. The sulphur oxidation liberates gold in the gold-containing minerals.
The autoclave output slurry is returned to atmospheric conditions. This is accomplished through one or two or more than two letdown/flash stages (not shown).
The autoclave output slurry is transferred to a metal recovery unit 23 for recovering gold. The metal recovery unit 23 may be any suitable unit. One example of a suitable gold-recovery operation is a carbon-in-pulp (CIP) process. Other examples include thiosulphate or glycine or chloride leaching processes.
The autoclave units 13 may be any suitable units operating at suitable elevated pressure and temperature conditions, with an oxygen plant (not shown) supplying an oxygen-containing gas, typically pure oxygen, to the autoclaves of the autoclave units 13 and a holding tank (not shown) that stores the concentrate slurry to be supplied to the autoclaves of the autoclave units 13.
By way of example, typical operating conditions in the autoclave units are as follows:
The target oxidation conditions for the autoclave units 13 are selected to oxidize sulphur to a % oxidation value for the ore that is at or close to the tipping point 7 between the curve sections 5a, 5b in
More particularly, the oxidation conditions in the autoclave units 13 are selected so that at least substantially all of the sulphur in reactive pyrite and any other reactive sulphide minerals in the ore is oxidized and sulphur in other minerals, i.e. “barren” minerals, is not preferentially oxidized.
In this context, the reference to “preferentially oxidized” herein is a recognition that there may be some oxidation of “barren” minerals, but that the conditions are such that this will not occur in preference to oxidation of reactive sulphide minerals.
The oxidation conditions, such as oxygen flow rate and residence time, may be a fixed or variable in each autoclave unit 13, and there may be differences in and variations of oxidation values in different autoclave units 13 depending on operational factors.
The method makes it possible to maximize ore sulphur mass feed rate to the autoclave units 13 at all times irrespective of equipment availability (upstream and downstream of the autoclave units 13) and ore type variability and without being dependent on a target sulphur % oxidation in each of the autoclave units 13. The reason for this is that the method is not dependent on operating to completely oxidize all of the sulphur in gold-containing minerals in the ore.
In the context of
The control system includes:
In one embodiment of the invention, described below in relation to
In another embodiment of the invention, described below in relation to
The conventional LECO SC632 instrument produces data on Total S and Total C in test samples. The LECO SC632 instrument heats samples to a constant temperature and analyses the decomposition of the samples over time. In the case of S, the LECO SC632 instrument monitors the decomposition of sulphur compounds in the samples, noting that different sulphur compounds decompose at different temperatures or at different times when heating is at a constant temperature. The LECO SC632 instrument uses IR detectors to produce IR intensity data over time. The intensity data is a measure of the sulphur compounds. The standard LECO SC632 instrument produces a visual display in the form of a graph of intensity versus time for sulphur (and another graph for C).
The applicant realized that the standard graph can be used as a basis to provide valuable information on the amount of reactive sulphide minerals in ore for use for controlling autoclave operation.
LECO was retained by the applicant to modify the software of the standard LECO SC632 instrument to include an algorithm of the applicant and to produce a new graph that provides information on the sulphur (and C) species in ores.
The peaks and troughs within the graph of
The sulphide reactivity index is a control parameter for the Lihir autoclaves.
Understanding the amounts of more reactive sulphide minerals and “barren”, i.e. less reactive sulphide, minerals makes it possible to optimize oxygen supply and this is beneficial for autoclave costs and downstream cyanide consumption.
It is noted that determination of reactive sulphide minerals can also have direct benefits in non-oxidation processes, e.g. where ores (and concentrates of ores) containing different sulphide species. Specifically, determining the amounts of reactive sulphide sulphur can be used to predict plant performance and allow prior adjustment of operating parameters to optimize economic gold recovery.
As noted above,
The graph of
The region of the graph between the 1st and 2nd vertical lines from the left hand side of the graph indicates reactive sulphide minerals, the region between the 2nd and 3rd vertical lines indicates less sulphide minerals, and the area to the right of the 3rd vertical line indicates sulphate sulphur. The thermal decomposition of these three forms of sulphide/sulphate mineral overlap to an extent on the X axis and, hence, the absence of clearly defined separate peaks. The location of the boundaries was determined having regard to analysis of pure specimen samples of different sulphide and sulphate minerals and interpretation by the applicant.
Calculating the areas within the three regions defined by the boundaries provides an indication of the amount of reactive sulphide minerals in the ore as a proportion of the total sulphur in the sample.
The applicant has found that the modified LECO SC632 instrument can generate data on the sulphide reactivity index for ore samples sufficiently quickly for the information to be considered and taken into account by autoclave operators to make adjustments to operative conditions in the autoclaves.
Each Figure plots the amount of oxygen supplied to the autoclave units 13 versus time, with the oxygen expressed as a ratio of the amount of oxygen supplied and the amount of oxygen required to oxidize all of the sulphur in the reactive pyrite and other reactive pyrites in the ore in the autoclave units 13.
The straight line at a value of 1 in each Figure indicates 100% oxidation of reactive sulphide minerals versus time, based on information generated by the modified LECO SC632 instrument on ore samples collected upstream of the autoclaves.
It is evident from
Therefore, typically 20% of the reactive sulphide minerals were carried over to the metal recovery unit 23, with a resultant loss of recovery and increased use of reagents to compensate for reagent consumption for the reactive sulphide minerals.
The information in
It is evident from
Therefore, the processing conditions in
It is evident from
The embodiment shown in
It is possible to infer the amount of reactive pyrite and other reactive sulphide minerals remaining in the discharge stream from the ORP data shown in the graph.
Lower ORP values indicate higher amounts of non-oxidized reactive pyrite.
More particularly, If the ORP values are low, this shows that reactive pyrite is still present and has not been burnt, and the autoclave operators must slow down the throughput in a situation where the oxygen rate is constant in order to ensure complete oxidation of the sulphur in reactive pyrite and other reactive sulphide minerals only.
With reference to
The ORP values at the end of the monitored period were >380 mV, indicating an opportunity to increase the sulphur mass throughput for the autoclave (in a situation where the autoclave operates with a constant oxygen rate) for similar feed ore.
It follows from the above that the ORP data, together with information on the mineralogy of incoming feed ore, makes it possible to make adjustments, if required, to the oxygen rate (if this is variable) and/or other autoclave processing conditions to achieve complete oxidation of sulphur in reactive sulphide minerals in the feed ore and not oxidize sulphur in barren sulphide minerals, with the beneficial impact on cost effective gold recovery in downstream processing steps.
By way of summary:
Many modifications may be made to the invention described above without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2019902382 | Jul 2019 | AU | national |
Filing Document | Filing Date | Country | Kind |
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PCT/AU2020/050692 | 7/2/2020 | WO |