CA2113039C - Process for biolixiviating copper sulfides by indirect contact with separation of effects - Google Patents
Process for biolixiviating copper sulfides by indirect contact with separation of effectsInfo
- Publication number
- CA2113039C CA2113039C CA002113039A CA2113039A CA2113039C CA 2113039 C CA2113039 C CA 2113039C CA 002113039 A CA002113039 A CA 002113039A CA 2113039 A CA2113039 A CA 2113039A CA 2113039 C CA2113039 C CA 2113039C
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- lixiviation
- primary
- copper
- accordance
- liquor
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/18—Extraction of metal compounds from ores or concentrates by wet processes with the aid of microorganisms or enzymes, e.g. bacteria or algae
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B15/00—Obtaining copper
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Biochemistry (AREA)
- Biotechnology (AREA)
- Microbiology (AREA)
- Environmental & Geological Engineering (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Electrolytic Production Of Metals (AREA)
- Preparation Of Compounds By Using Micro-Organisms (AREA)
Abstract
Process for biolixiviating minerals from copper sulfides and also from their flotation concentrates, characterized by the use of biolixiviation through indirect contact as well as separation and improvement of the chemical and biological steps of the biolixiviation process. In the chemical step, a low concentration of ferric sulfate is used as the lixiviating agent. In the biological step, bacterial films of Thiobacillus ferrooxidans attached to an inert solid are used to regenerate the lixiviating agent by converting the ferrous ion into ferric ion through oxidation. The regenerated agent is then recycled to the lixiviation reactor. The biolixiviation process permits complete extraction of the copper contained in the ore and results in a lixiviation liquor which contains all the copper charge and a low concentration of ferric sulfate similar to the low concentration of ferric sulfate used initially. The copper obtained can be treated without difficulty by means of extraction with solvents and electrolysis in order to obtain cathode copper.
Description
- 2 ~ 3 ~
SPECIFICATION
The present invention pertains to a process for biolixiviating minerals from copper sulfides and from their flotation concentrates, characterized by the use of biolixiviation by indirect contact with separation and improvement of the chemical and biological effects. For the chemical stage, low-concentration ferric sulfate is used as the lixiviating agent.
Bacterial films of Thiobacillus ferrooxidans carried on an inert solid are used for the biological stage, the objective of which is the oxidation and regeneration of the lixiviating liquor for converting the ferrous ion into ferric ion and recycling the said liquor to the lixiviation reactor. The process permits the complete extraction of the copper contained in the ore, with a lixiviating liquor being obtained with all the copper charge and a concentration of ferric sulfate as low as that initially used, such that it can be treated without difficulty by means of extraction with solvents and electrolysis in order to obtain a copper cathode.
The increasing legal restrictions in the matter of contamination, the exhaustive saturation of the market with sulfuric acid, the toughpenalties which the sale of flotation concentrates experiences, the high cost of energy of the traditional pyrometallurgical treatment processes, as well as the limited flexibility of such processes with respect to the composition of the raw material have been the reasons, among others, that have, during the last few decades, given rise to a growing interest in hydrometallurgy as an alternative for the treatment of the flotation concentrates of copper sulfides. The main difficulty is focused on the selection of a ~ ~ ~3~3~
suitable method of lixivi-ation which is economical, effective and flexible, and this is where biolixiviation may be considered as a suitable alternative.
Biolixiviation can be defined as a hydrometallurgical operation, in which various components of a metallic ore disintegrate thanks to the action of certain chemolithotrophic microorganisms which obtain the energy necessary for their growth from processes of intracellular oxidation of inorganic substances. The species Thiobacillus ferro-oxidans, which uses, as energy substrates, ferrous ion in solution and any reduced form of sulfur, including the metallic sulfides, merits standing out.
The principal disadvantage, into which the biolixiviation of sulfurated metallic ores runs, is the slow kinetics of this type of process, which must operate with very high reaction times. This deter-mines to a considerable extent the industrial device to be used and, in its turn, the type of mineral to be treated. Thus, we are faced with the fact that, nowadays, it [biolixiviation] is only used for the benefit of low-grade or even marginal-grade minerals and refractory minerals, using installations of lixiviation by percolation in heap or dump leaching systems.
The biolixiviation of sulfurated ores can take place through two different mechanisms, called indirect contact and direct contact. According to the first of the two mechanisms, the ferric ion oxidizes with the metallic sulfide producing ferrous sulfate and elemental sulfur which, in their turn, are reoxidized by the bacteria regenerating the ferric ion with the production of acid. According to the mechanism of direct contact, the bacterial action is independent of the presence of Fe3+, and only an intimate physical contact between the bacteria and the surface of the mineral is required. These two mechanisms have very different kinetics.
When the bacteria uses the metallic sulfide directly as an energy substrate, its mean generation time is on the order of days or even weeks, while when ferrous ion is used, said time ranges between 4 and 8 hours. Even in spite of this difference, the kinetics of indirect biolixiviation continues to be slow, and this is the reason which prevents its use in the treatment of high-grade minerals or flotation concentrates.
The possibilities of improved kinetics in the biolixiviation processes by direct contact are based on the establishment of more active pieces, easily by means of the discovery of new natural species or by modification of those already used by means of adaptation techniques or even genetic manipulation, although, certainly, the implantation of these cultures will run into serious difficulties, especially that of preventing said prepared strains from losing their identity after a short operating time.
With respect to the biolixiviation processes by the mechanism of indirect contact, the possibilities of improved kinetics are much greater in the short term. It is only necessary to separate the two processes which take place simultaneously in the lixiviation reactor: the chemical attack on the metallic sulfide by the ferric ion and the bacterial oxidation of the ferrous ion produced. This separation permits the improvement of both processes.
The attack of the ferric ion on the metallic sulfides takes place through a mechanism of an electrochemical nature, which is based on the semiconductor properties of these materials. The kinetics of these reactions is greatly affected by the temperature. At ambient temperature, the reactions are very slow; however, at moderately high temperatures, even a great deal below the boiling point of water, they are considerably faster. This is due to the fact that, unlike normal conductors, an increase in the temperature increases the conductivity of the semiconductors.
The mesophilic character of the bacteria normally used prevents the use of the recourse to the increase in temperature for accelerat-ing the lixiviation process; however, the physical separation of the chemical and biological effects effectively permits the use of this recourse.
During the chemical reaction stage, the ferric ion, which acts as a depolarizer, is depleted, converting into ferrous ion. In order to prevent the reaction from stopping, it is necessary to oxidize the ferrous ion formed in order to regenerate the primary lixiviating agent, and this is where the help of the bacteria plays a fundamental role, by catalyzing said oxidation process.
When the biolixiviation is carried out in a simple stage in a single reactor, a series of phenomena occur which considerably limit the speed of this oxidation process. When mixed reactors are used, a significant abrasive effect takes place on the bacteria by the mineral particles, which [effect]
leads to their partial destruction, producing two negative effects on the kinetics of the process: at the half-way point, there appear organic substances which come from the rupture of the cellular membrane and bring about disintegration of the cyto-plasma, and which have a pronounced inhibitory effect on the bacterial growth. On the other hand, this abrasive effect makes the active bacterial count decrease.
After several days of operation, the oxidative activity of the bacterial suspension succeeds in being up to twenty times less than that of the inoculation from which it originates.
On the other hand, the bacteria, in addition to being autotrophs, are aerobes, that is, they require an adequate supply of CO2 and ~2/ the former as an exclusive source of carbon for the synthesis of the cellular material and the latter as a final acceptor of the pairs of electrons generated in the oxidation processes, in which they take part.
It is necessary, then, to use a device that permits a continuous supply of these two gases, in amounts as high as permitted by the saturation conditions of the liquid medium, in which they are dis-solved.
The bacterial oxidation of the ferrous ion can be carried out with two types of essentially different devices: the model of bacterial suspension and that of the carried bacterial film. As their own names indicate, in the first of these [devices], the bacteria are dispersed in a liquid medium, which is mixed or not mixed; in the second [device], they [bacteria] are fixed on a film formed by the bacteria themselves and a binding cement consisting of basic iron sulfates. Said film is carried, in general, on an inert solid.
Numerous studies, which make it possible to draw an irrefutable conclusion, have been conducted on this topic: the carried film model is much more effective than that of the bacterial suspension for two basic reasons: when the bacteria are dispersed in a liquid medium, it consumes a certain amount of energy in carrying out locomotion work; on the contrary, when they [bacteria] form part of the film, this energy is completely spent in the bacterial growth, which causes the coefficient of performance to be considerably greater. On the other hand, the supply ~f ~2 and CO2 contained in the air is much more direct and therefore more effective in the carried bacterial film model.
The ferric sulfate operates according to the following reactions:
SCu + 2Fe3+ S~ + 2Fe++ + Cu++
SCu2 + 4Fe3+ ---------- S~ + 2Cu++ + 4Fe++
S2CuFe + 4Fe3+ 2S~ + Cu++ + 5Fe++
However, its direct use according to the stoichiometry of the above reactions would imply that the lixiviating liquor obtained has a ferrous ion concentration between two and five times greater than Cu, which would considerably complicate the subsequent treatment stages.
This problem can be solved by using amounts of ferric sulfate which are much less than the stoichiometry required; once the ferric [ion] has been depleted and has been converted into ferrous [ion], it is sent to a reoxidation stage and is recirculated to the reactor. In this manner, the same lixiviating liquor leaves the reactor, is reoxidized and recirculated continuously before leaving the circuit.
At the end, said liquor contains all the corresponding Cu charge and a Fe concentration that is as low as that initially used.
If the circuit is purged after the reoxidation stage, the content of ferrous salts will be zero. In this manner, the desired objective can be achieved by using ferric sulfate concentrations of less than 10 g/L, some 10 times less than the stoichiometry required for a 10% pulp density.
The present invention will be able to be better understood from the detailed description below, in combination with the attached drawings, in which:
Figures 1 and 2 show the flow diagrams of the process of the present invention.
Figure 3 represents arrangement of the biooxidation dump.
Figure 4 shows the typical results of this stage operating on a continuous basis.
Figures 5 and 6 show the results obtained in actual tests.
As can be seen in Figure 1, the process consists of a primary lixiviation stage 1 in a reactor provided with mechanical agitation, in which the mineral M or concentrate reacts, at ambient temperature (between 5 and 30~C), with a disintegration of ferric sulfate having a concentration that is much less than the stoichiometric amount. To supply all the ferric [sulfate] required, it is necessary to continuously regenerate the lixiviating agent as it is being depleted. For this reason, a pulp flow is continuously extracted from the reactor and is sent to the settling tank 2. On the upper part of this [tank], the clear phase free from solids emerges via an overflow, and the thickened phase, which mostly returns to the primary lixiviation reactor 1, is extracted by means of a pump on the lower part [of said tank].
The clear phase leaving from the settling tank 2, which is partly depleted of ferric ion and charged with ferrous ion, is sent to the biooxidation stage on the carried film 3. This point constitutes the real novelty of the process, and it lends originality and great possi-bilities for development when permitting the lixiviation with low-concentration ferric [sulfate], with the tremendous advantages that it implies in the treatment of the final liquor obtained.
After it passes through this stage and is recharged with ferric ion, most of the liquor returns to the primary lixiviation stage 1, in which, in addition to the mineral M or concentrate, water, which is outside of the circuit, is introduced.
To completely finish the extraction of copper from the thickened pulp from the outlet of the settling tank 2, the mass fraction corresponding to the mineral feed is separated and is introduced into a secondary lixiviation reactor 4, which has characteristics similar to those of the primary lixiviation reactor 1, although of smaller size, together with a fraction of the liquor from the outlet of the biooxidation [stage] and an external solution of ferric sulfate. The extraction of copper is completed in this reactor 4, which operates at a temperature ranging between 50 and 85~C.
The pulp from the outlet of same [reactor 4] is filtered in a filter 5 in order to separate the solid residue R, and the filtrate, which contains a significant charge of ferrous ion, is sent to the biooxidation stage 3.
In order to minimize heat losses, the fraction of liquor coming from the biooxidation [stage] 3, which enters the secondary lixiviation stage 4, is heated in a liquid-pulp heat exchanger at the expense of the pulp from the outlet of said stage.
The rich liquor L, containing all of the dissolved copper charge and an iron concentration as low as that initially used, is purged at the outlet of the biooxidation stage 3. Said liquor L, after a purification and concentration by extraction with solvents in 6, is electrolyzed in 7, in order to obtain a commercial copper cathode of high purity.
The depleted electrolyte is used as a reextraction agent, and the watery, refined fraction from the extraction stage is used for feeding outside water to the biolixiviation process.
In the specific case of chalcopyritic sulfides, silver is added as a catalytic agent for the lixiviation of chalcopyrite, in order to guarantee the complete extraction of the copper contained [therein].
For this reason, the concentrate from the inlet to the primary lixiviation stage 1 is saturated with a solution of Ag+, which remains deposited on the surface of the mineral, exercising its catalytic effect on both lixiviations (primary and secondary) 1 and 4.
Figure 2 shows a similar circuit with recirculation of solids in both lixiviation stages:
primary and secondary 1 and 4.
The biooxidation stage 3 is formed by a heap or dump, similar to the lixiviation heaps. As can be seen in Figure 3, it consists of a bed of carrier material 8, which is ceramic, natural or artificial, or a polymer type (plastic), with a particle size ranging between 1 and 5 mm, arranged on an inclined and waterproofed surface 9, lined on its lower part with pipes for the supply of air 10. On the bottom is placed a first layer of aggregates (1-2 cm particle size) to prevent the clogging-of vents and to improve the percolation capacity, and on this layer is placed the layer of carrier material (inert solid), with a layer height ranging between 0.5 and 1 meter. The liquid percolates through the layer, and it is collected in one of the vertices of the dump 11.
As can be seen in Figure 4, the oxidative capacity of the dump remains high after a prolonged operating time, with no percolation problems nor aging phenomena of the bacterial films being detected. The percentage of oxidation Fe(II) is shown on the ordinates, and time expressed in days is shown on the abscissas. The dotted line corre-sponds to the extraction to the right, and the solid line corresponds to the extraction to the left.
EXAMPLE No. 1 For a refined concentrate with a 6% copper grade, the completeoperating data for each ton/hour of concentrate would be as follows:
Total demand of ferric [sulfate]: 80 kg Demand of ferric [sulfate] in cold: 20 kg Demand of ferric [sulfate] in heat to 70~C: 60 kg Mean residence time in cold: 3 hours Density of pulp in cold: 40% (W/V) Volume of reaction in cold: 7.5 m3 Mean residence time in heat: 3 hours Density of pulp in heat: 30% (W/V) Volume of reaction in heat: 10 m3 No recirculation of solids in heat - 12 ~ 3 ~ 3 ~
Composition of liquor from outlet: 13 g/L Fe and 20 glL Cu Volume of liquor from outlet: 2.9 m3 Figure S shows how the copper concentration at the outlet varies as a function of the iron concentrations used in each of the circuits. Line A
reflects the hot circuit, and line B reflects the biological circuit.
EXAMPLE No. 2 For a final concentrate with a 50% copper grade, the complete operating data for each ton/hour of concentrate would be as follows:
Total demand of ferric [sulfate]: 700 kg Demand of ferric [sulfate] in cold: 200 kg Demand of ferric [sulfate] in heat to 70~C: 500 kg Mean residence time in cold: 3 hours Density of pulp in cold: 25% (W/V) Volume of reaction in cold: 12 m3 Mean residence time in heat: 4 hours Density of pulp in heat: 25% (W/V) Volume of reaction in heat: 16 m3 Recirculation of solids in heat: 5/6 Composition of liquor from outlet: 14 g/L Fe and 20 gtL Cu Volume of liquor from outlet: 24.5 m3 Figure 6 shows how the copper concentration at the outlet varies as a function of the iron concentrations used in each of the circuits. Line A
reflects the hot circuit, and line B reflects the biological circuit.
SPECIFICATION
The present invention pertains to a process for biolixiviating minerals from copper sulfides and from their flotation concentrates, characterized by the use of biolixiviation by indirect contact with separation and improvement of the chemical and biological effects. For the chemical stage, low-concentration ferric sulfate is used as the lixiviating agent.
Bacterial films of Thiobacillus ferrooxidans carried on an inert solid are used for the biological stage, the objective of which is the oxidation and regeneration of the lixiviating liquor for converting the ferrous ion into ferric ion and recycling the said liquor to the lixiviation reactor. The process permits the complete extraction of the copper contained in the ore, with a lixiviating liquor being obtained with all the copper charge and a concentration of ferric sulfate as low as that initially used, such that it can be treated without difficulty by means of extraction with solvents and electrolysis in order to obtain a copper cathode.
The increasing legal restrictions in the matter of contamination, the exhaustive saturation of the market with sulfuric acid, the toughpenalties which the sale of flotation concentrates experiences, the high cost of energy of the traditional pyrometallurgical treatment processes, as well as the limited flexibility of such processes with respect to the composition of the raw material have been the reasons, among others, that have, during the last few decades, given rise to a growing interest in hydrometallurgy as an alternative for the treatment of the flotation concentrates of copper sulfides. The main difficulty is focused on the selection of a ~ ~ ~3~3~
suitable method of lixivi-ation which is economical, effective and flexible, and this is where biolixiviation may be considered as a suitable alternative.
Biolixiviation can be defined as a hydrometallurgical operation, in which various components of a metallic ore disintegrate thanks to the action of certain chemolithotrophic microorganisms which obtain the energy necessary for their growth from processes of intracellular oxidation of inorganic substances. The species Thiobacillus ferro-oxidans, which uses, as energy substrates, ferrous ion in solution and any reduced form of sulfur, including the metallic sulfides, merits standing out.
The principal disadvantage, into which the biolixiviation of sulfurated metallic ores runs, is the slow kinetics of this type of process, which must operate with very high reaction times. This deter-mines to a considerable extent the industrial device to be used and, in its turn, the type of mineral to be treated. Thus, we are faced with the fact that, nowadays, it [biolixiviation] is only used for the benefit of low-grade or even marginal-grade minerals and refractory minerals, using installations of lixiviation by percolation in heap or dump leaching systems.
The biolixiviation of sulfurated ores can take place through two different mechanisms, called indirect contact and direct contact. According to the first of the two mechanisms, the ferric ion oxidizes with the metallic sulfide producing ferrous sulfate and elemental sulfur which, in their turn, are reoxidized by the bacteria regenerating the ferric ion with the production of acid. According to the mechanism of direct contact, the bacterial action is independent of the presence of Fe3+, and only an intimate physical contact between the bacteria and the surface of the mineral is required. These two mechanisms have very different kinetics.
When the bacteria uses the metallic sulfide directly as an energy substrate, its mean generation time is on the order of days or even weeks, while when ferrous ion is used, said time ranges between 4 and 8 hours. Even in spite of this difference, the kinetics of indirect biolixiviation continues to be slow, and this is the reason which prevents its use in the treatment of high-grade minerals or flotation concentrates.
The possibilities of improved kinetics in the biolixiviation processes by direct contact are based on the establishment of more active pieces, easily by means of the discovery of new natural species or by modification of those already used by means of adaptation techniques or even genetic manipulation, although, certainly, the implantation of these cultures will run into serious difficulties, especially that of preventing said prepared strains from losing their identity after a short operating time.
With respect to the biolixiviation processes by the mechanism of indirect contact, the possibilities of improved kinetics are much greater in the short term. It is only necessary to separate the two processes which take place simultaneously in the lixiviation reactor: the chemical attack on the metallic sulfide by the ferric ion and the bacterial oxidation of the ferrous ion produced. This separation permits the improvement of both processes.
The attack of the ferric ion on the metallic sulfides takes place through a mechanism of an electrochemical nature, which is based on the semiconductor properties of these materials. The kinetics of these reactions is greatly affected by the temperature. At ambient temperature, the reactions are very slow; however, at moderately high temperatures, even a great deal below the boiling point of water, they are considerably faster. This is due to the fact that, unlike normal conductors, an increase in the temperature increases the conductivity of the semiconductors.
The mesophilic character of the bacteria normally used prevents the use of the recourse to the increase in temperature for accelerat-ing the lixiviation process; however, the physical separation of the chemical and biological effects effectively permits the use of this recourse.
During the chemical reaction stage, the ferric ion, which acts as a depolarizer, is depleted, converting into ferrous ion. In order to prevent the reaction from stopping, it is necessary to oxidize the ferrous ion formed in order to regenerate the primary lixiviating agent, and this is where the help of the bacteria plays a fundamental role, by catalyzing said oxidation process.
When the biolixiviation is carried out in a simple stage in a single reactor, a series of phenomena occur which considerably limit the speed of this oxidation process. When mixed reactors are used, a significant abrasive effect takes place on the bacteria by the mineral particles, which [effect]
leads to their partial destruction, producing two negative effects on the kinetics of the process: at the half-way point, there appear organic substances which come from the rupture of the cellular membrane and bring about disintegration of the cyto-plasma, and which have a pronounced inhibitory effect on the bacterial growth. On the other hand, this abrasive effect makes the active bacterial count decrease.
After several days of operation, the oxidative activity of the bacterial suspension succeeds in being up to twenty times less than that of the inoculation from which it originates.
On the other hand, the bacteria, in addition to being autotrophs, are aerobes, that is, they require an adequate supply of CO2 and ~2/ the former as an exclusive source of carbon for the synthesis of the cellular material and the latter as a final acceptor of the pairs of electrons generated in the oxidation processes, in which they take part.
It is necessary, then, to use a device that permits a continuous supply of these two gases, in amounts as high as permitted by the saturation conditions of the liquid medium, in which they are dis-solved.
The bacterial oxidation of the ferrous ion can be carried out with two types of essentially different devices: the model of bacterial suspension and that of the carried bacterial film. As their own names indicate, in the first of these [devices], the bacteria are dispersed in a liquid medium, which is mixed or not mixed; in the second [device], they [bacteria] are fixed on a film formed by the bacteria themselves and a binding cement consisting of basic iron sulfates. Said film is carried, in general, on an inert solid.
Numerous studies, which make it possible to draw an irrefutable conclusion, have been conducted on this topic: the carried film model is much more effective than that of the bacterial suspension for two basic reasons: when the bacteria are dispersed in a liquid medium, it consumes a certain amount of energy in carrying out locomotion work; on the contrary, when they [bacteria] form part of the film, this energy is completely spent in the bacterial growth, which causes the coefficient of performance to be considerably greater. On the other hand, the supply ~f ~2 and CO2 contained in the air is much more direct and therefore more effective in the carried bacterial film model.
The ferric sulfate operates according to the following reactions:
SCu + 2Fe3+ S~ + 2Fe++ + Cu++
SCu2 + 4Fe3+ ---------- S~ + 2Cu++ + 4Fe++
S2CuFe + 4Fe3+ 2S~ + Cu++ + 5Fe++
However, its direct use according to the stoichiometry of the above reactions would imply that the lixiviating liquor obtained has a ferrous ion concentration between two and five times greater than Cu, which would considerably complicate the subsequent treatment stages.
This problem can be solved by using amounts of ferric sulfate which are much less than the stoichiometry required; once the ferric [ion] has been depleted and has been converted into ferrous [ion], it is sent to a reoxidation stage and is recirculated to the reactor. In this manner, the same lixiviating liquor leaves the reactor, is reoxidized and recirculated continuously before leaving the circuit.
At the end, said liquor contains all the corresponding Cu charge and a Fe concentration that is as low as that initially used.
If the circuit is purged after the reoxidation stage, the content of ferrous salts will be zero. In this manner, the desired objective can be achieved by using ferric sulfate concentrations of less than 10 g/L, some 10 times less than the stoichiometry required for a 10% pulp density.
The present invention will be able to be better understood from the detailed description below, in combination with the attached drawings, in which:
Figures 1 and 2 show the flow diagrams of the process of the present invention.
Figure 3 represents arrangement of the biooxidation dump.
Figure 4 shows the typical results of this stage operating on a continuous basis.
Figures 5 and 6 show the results obtained in actual tests.
As can be seen in Figure 1, the process consists of a primary lixiviation stage 1 in a reactor provided with mechanical agitation, in which the mineral M or concentrate reacts, at ambient temperature (between 5 and 30~C), with a disintegration of ferric sulfate having a concentration that is much less than the stoichiometric amount. To supply all the ferric [sulfate] required, it is necessary to continuously regenerate the lixiviating agent as it is being depleted. For this reason, a pulp flow is continuously extracted from the reactor and is sent to the settling tank 2. On the upper part of this [tank], the clear phase free from solids emerges via an overflow, and the thickened phase, which mostly returns to the primary lixiviation reactor 1, is extracted by means of a pump on the lower part [of said tank].
The clear phase leaving from the settling tank 2, which is partly depleted of ferric ion and charged with ferrous ion, is sent to the biooxidation stage on the carried film 3. This point constitutes the real novelty of the process, and it lends originality and great possi-bilities for development when permitting the lixiviation with low-concentration ferric [sulfate], with the tremendous advantages that it implies in the treatment of the final liquor obtained.
After it passes through this stage and is recharged with ferric ion, most of the liquor returns to the primary lixiviation stage 1, in which, in addition to the mineral M or concentrate, water, which is outside of the circuit, is introduced.
To completely finish the extraction of copper from the thickened pulp from the outlet of the settling tank 2, the mass fraction corresponding to the mineral feed is separated and is introduced into a secondary lixiviation reactor 4, which has characteristics similar to those of the primary lixiviation reactor 1, although of smaller size, together with a fraction of the liquor from the outlet of the biooxidation [stage] and an external solution of ferric sulfate. The extraction of copper is completed in this reactor 4, which operates at a temperature ranging between 50 and 85~C.
The pulp from the outlet of same [reactor 4] is filtered in a filter 5 in order to separate the solid residue R, and the filtrate, which contains a significant charge of ferrous ion, is sent to the biooxidation stage 3.
In order to minimize heat losses, the fraction of liquor coming from the biooxidation [stage] 3, which enters the secondary lixiviation stage 4, is heated in a liquid-pulp heat exchanger at the expense of the pulp from the outlet of said stage.
The rich liquor L, containing all of the dissolved copper charge and an iron concentration as low as that initially used, is purged at the outlet of the biooxidation stage 3. Said liquor L, after a purification and concentration by extraction with solvents in 6, is electrolyzed in 7, in order to obtain a commercial copper cathode of high purity.
The depleted electrolyte is used as a reextraction agent, and the watery, refined fraction from the extraction stage is used for feeding outside water to the biolixiviation process.
In the specific case of chalcopyritic sulfides, silver is added as a catalytic agent for the lixiviation of chalcopyrite, in order to guarantee the complete extraction of the copper contained [therein].
For this reason, the concentrate from the inlet to the primary lixiviation stage 1 is saturated with a solution of Ag+, which remains deposited on the surface of the mineral, exercising its catalytic effect on both lixiviations (primary and secondary) 1 and 4.
Figure 2 shows a similar circuit with recirculation of solids in both lixiviation stages:
primary and secondary 1 and 4.
The biooxidation stage 3 is formed by a heap or dump, similar to the lixiviation heaps. As can be seen in Figure 3, it consists of a bed of carrier material 8, which is ceramic, natural or artificial, or a polymer type (plastic), with a particle size ranging between 1 and 5 mm, arranged on an inclined and waterproofed surface 9, lined on its lower part with pipes for the supply of air 10. On the bottom is placed a first layer of aggregates (1-2 cm particle size) to prevent the clogging-of vents and to improve the percolation capacity, and on this layer is placed the layer of carrier material (inert solid), with a layer height ranging between 0.5 and 1 meter. The liquid percolates through the layer, and it is collected in one of the vertices of the dump 11.
As can be seen in Figure 4, the oxidative capacity of the dump remains high after a prolonged operating time, with no percolation problems nor aging phenomena of the bacterial films being detected. The percentage of oxidation Fe(II) is shown on the ordinates, and time expressed in days is shown on the abscissas. The dotted line corre-sponds to the extraction to the right, and the solid line corresponds to the extraction to the left.
EXAMPLE No. 1 For a refined concentrate with a 6% copper grade, the completeoperating data for each ton/hour of concentrate would be as follows:
Total demand of ferric [sulfate]: 80 kg Demand of ferric [sulfate] in cold: 20 kg Demand of ferric [sulfate] in heat to 70~C: 60 kg Mean residence time in cold: 3 hours Density of pulp in cold: 40% (W/V) Volume of reaction in cold: 7.5 m3 Mean residence time in heat: 3 hours Density of pulp in heat: 30% (W/V) Volume of reaction in heat: 10 m3 No recirculation of solids in heat - 12 ~ 3 ~ 3 ~
Composition of liquor from outlet: 13 g/L Fe and 20 glL Cu Volume of liquor from outlet: 2.9 m3 Figure S shows how the copper concentration at the outlet varies as a function of the iron concentrations used in each of the circuits. Line A
reflects the hot circuit, and line B reflects the biological circuit.
EXAMPLE No. 2 For a final concentrate with a 50% copper grade, the complete operating data for each ton/hour of concentrate would be as follows:
Total demand of ferric [sulfate]: 700 kg Demand of ferric [sulfate] in cold: 200 kg Demand of ferric [sulfate] in heat to 70~C: 500 kg Mean residence time in cold: 3 hours Density of pulp in cold: 25% (W/V) Volume of reaction in cold: 12 m3 Mean residence time in heat: 4 hours Density of pulp in heat: 25% (W/V) Volume of reaction in heat: 16 m3 Recirculation of solids in heat: 5/6 Composition of liquor from outlet: 14 g/L Fe and 20 gtL Cu Volume of liquor from outlet: 24.5 m3 Figure 6 shows how the copper concentration at the outlet varies as a function of the iron concentrations used in each of the circuits. Line A
reflects the hot circuit, and line B reflects the biological circuit.
Claims (14)
1. A process for biolixiviating minerals from copper sulfides or flotation concentrates thereof, said method comprising the steps of:
(a) subjecting said copper sulfides or flotation concentrates thereof to a chemical lixiviation, said chemical lixiviation being performed in two stages, (i) a first stage comprising primary lixiviation in pulp at a temperature ranging between 5 and 40°C in a primary lixiviation reactor with mechanical agitation, and (ii) a second stage comprising secondary lixiviation in pulp at a temperature ranging between 50 and 90°C in a secondary lixiviation reactor with mechanical agitation, said primary lixiviation comprising treating said copper sulfides or flotation concentrates with a lixiviating agent comprising ferric ions at an initial concentration ranging between 5 and 15 g/L and resulting in the formation of a mineral pulp comprising said minerals and a primary lixiviation liquor which comprises extracted copper and ferrous ions produced by reduction of said lixiviating agent, a fraction of the pulp from said primary lixiviation being recirculated to said first stage, and said secondary lixiviation comprising treating the non-recirculated fraction of pulp from said primary lixiviation with a lixiviating agent comprising ferric ions at an initial concentration ranging between 20 and 70 g/L and resulting in the formation of a pulp comprising a solid residue and a secondary lixiviation liquor which comprises the extracted copper and the ferrous ions;
(b) separating said primary lixiviation liquor from said mineral pulp and transporting the separated primary lixiviation liquor to a biooxidation vessel;
(c) separating said secondary lixiviation liquor from the pulp comprising said solid residue, and transporting the separated secondary lixiviation liquor to a biooxidation vessel and recirculating the pulp comprising the solid residue to said secondary lixiviation reactor;
(d) regenerating said lixiviating agent by contacting said primary and secondary lixiviation liquor, containing ferrous ions, with a ferrooxidant microorganism immobilized on a solid support in said biooxidation vessel, said contacting resulting in conversion of said ferrous ions to ferric ions, thereby producing a regenerated lixiviation agent comprising said extracted copper and said ferric ions;
and (e) returning said regenerated lixiviation agent to said primary and secondary lixiviation reactors.
(a) subjecting said copper sulfides or flotation concentrates thereof to a chemical lixiviation, said chemical lixiviation being performed in two stages, (i) a first stage comprising primary lixiviation in pulp at a temperature ranging between 5 and 40°C in a primary lixiviation reactor with mechanical agitation, and (ii) a second stage comprising secondary lixiviation in pulp at a temperature ranging between 50 and 90°C in a secondary lixiviation reactor with mechanical agitation, said primary lixiviation comprising treating said copper sulfides or flotation concentrates with a lixiviating agent comprising ferric ions at an initial concentration ranging between 5 and 15 g/L and resulting in the formation of a mineral pulp comprising said minerals and a primary lixiviation liquor which comprises extracted copper and ferrous ions produced by reduction of said lixiviating agent, a fraction of the pulp from said primary lixiviation being recirculated to said first stage, and said secondary lixiviation comprising treating the non-recirculated fraction of pulp from said primary lixiviation with a lixiviating agent comprising ferric ions at an initial concentration ranging between 20 and 70 g/L and resulting in the formation of a pulp comprising a solid residue and a secondary lixiviation liquor which comprises the extracted copper and the ferrous ions;
(b) separating said primary lixiviation liquor from said mineral pulp and transporting the separated primary lixiviation liquor to a biooxidation vessel;
(c) separating said secondary lixiviation liquor from the pulp comprising said solid residue, and transporting the separated secondary lixiviation liquor to a biooxidation vessel and recirculating the pulp comprising the solid residue to said secondary lixiviation reactor;
(d) regenerating said lixiviating agent by contacting said primary and secondary lixiviation liquor, containing ferrous ions, with a ferrooxidant microorganism immobilized on a solid support in said biooxidation vessel, said contacting resulting in conversion of said ferrous ions to ferric ions, thereby producing a regenerated lixiviation agent comprising said extracted copper and said ferric ions;
and (e) returning said regenerated lixiviation agent to said primary and secondary lixiviation reactors.
2. Process in accordance with claim 1, characterized in that the regenerating of the lixiviation agent is carried out on bacterial films carried on said inert solids arranged as a fixed bed or revolving biological contactors.
3. Process in accordance with claim 2, characterized in that the fixed bed, comprises a particulate material selected from the group consisting of: ceramic material, natural or artificial material, and polymer material.
4. Process in accordance with claim 3 in which said particulate material comprises a particle size range from about 1 mm to about 15 mm.
5. Process in accordance with claim 4 in which the particle size is about 4 mm.
6. Process in accordance with claim 1, characterized in that the copper sulfides or flotation concentrates thereof are selected from the group of materials consisting of:
run-of-mine coal minerals, refined concentrates, aggregates, semi-aggregates and concentrates.
run-of-mine coal minerals, refined concentrates, aggregates, semi-aggregates and concentrates.
7. Process in accordance with claim 1 in which the secondary lixiviation is carried out at 65°C.
8. Process in accordance with claim 1, characterized in that between 80% and 90% of the ferric ions for said chemical lixiviation are produced in the regenerating step and between 10% and 20% of the ferric ions for the chemical lixiviation are provided from an external source.
9. Process in accordance with claim 1, characterized in that the combined concentration of iron in the primary lixiviation and biooxidation vessel is 5 to 15 g/L, and the concentration of iron in the secondary lixiviation is 20 to 70 g/L.
10. Process in accordance with claim 9 in which the combined concentration of iron in the primary lixiviation and the biooxidation vessel is about 12 g/L and the concentration of iron in the secondary lixiviation is about 35 g/L.
11. Process in accordance with claim 1, characterized in that the copper sulfide comprises concentrates of chalcopyritic copper and silver is added as a catalytic agent to the primary lixiviation.
12. Process in accordance with claim 1, characterized in that the primary lixiviation and secondary lixiviation produce a final residue that comprises elemental sulfur and a rich liquor that comprises the extracted copper.
13. Process in accordance with claim 12, characterized in that the rich liquor is treated by extraction with solvents and electrolysis in order to obtain a cathode copper of high purity.
14. Process according to claim 1, wherein said ferrooxidant microorganism is Thiobacillus ferrooxidans.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002113039A CA2113039C (en) | 1994-01-07 | 1994-01-07 | Process for biolixiviating copper sulfides by indirect contact with separation of effects |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002113039A CA2113039C (en) | 1994-01-07 | 1994-01-07 | Process for biolixiviating copper sulfides by indirect contact with separation of effects |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2113039A1 CA2113039A1 (en) | 1995-07-08 |
| CA2113039C true CA2113039C (en) | 1999-04-06 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002113039A Expired - Fee Related CA2113039C (en) | 1994-01-07 | 1994-01-07 | Process for biolixiviating copper sulfides by indirect contact with separation of effects |
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| CA2353002C (en) | 2001-07-13 | 2009-12-01 | Teck Cominco Metals Ltd. | Heap bioleaching process for the extraction of zinc |
| US7455715B2 (en) | 2001-07-13 | 2008-11-25 | Teck Cominco Metals Ltd. | Heap bioleaching process for the extraction of zinc |
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