WO2001018265A1

WO2001018265A1 - Method and device for continuous treatment of copper sulphide containing ore by biological leaching

Info

Publication number: WO2001018265A1
Application number: PCT/FR2000/002471
Authority: WO
Inventors: Dominique Morin; Paul Norris; Dietger KÖPPL; Werner Schwab; Christopher Bonney
Original assignee: B.R.G.M. - Bureau De Recherches Geologiques Et Minieres; Universite De Warwick; Henkel
Priority date: 1999-09-07
Filing date: 2000-09-07
Publication date: 2001-03-15
Also published as: AU7299800A; PL354138A1; FR2798144A1; PL195976B1; FR2798144B1

Abstract

The invention concerns a method and a device for treating copper sulphide containing ore, comprising a step of biological leaching whereby the minerals are subjected in reactors (1) in cascade arrangement, wherein the temperature is maintained between 75 °C and 85 °C to the action of a bacterial culture, which comprises a thermophilic bacterium of the Sulfolobus type, leading to solution heat treating of the copper. The method is characterised in that, during said biological leaching step, the treatment is uninterrupted, the medium containing the bacterial culture being continuously mechanically agitated to ensure oxygenation thereof, and suspension of the solid elements, and the solid mass proportion of the culture medium is maintained above 10 %.

Description

PROCESS AND DEVICE FOR THE CONTINUOUS TREATMENT OF SULFIDATED COPPER MINERALS BY BIOLIXIVIATION

The present invention relates to a process and a device for the continuous treatment of copper sulphide minerals with a view to recovering the latter.

Many metals, such as copper, silver, gold or palladium, exist in nature in association with other minerals. In order to recover them, processes have been abundantly described, in the prior art, consisting of, during a first bioleaching step, acting on minerals, bacteria of various types which ensure the destruction of the sulfur matrix trapping a specific metal, by dissolving this matrix, which has the effect of dissolving the metal concerned. In a second treatment step, the metal contained in this solution is recovered by working on it, in particular chemically and / or electrochemically. US Pat. No. 4,571,387 has thus proposed a process for leaching sulfurous copper ores, for example chalcopyrite (CuFeS ₂ ), in which the copper ores are brought into contact with strains of the bacterium Thiobacillus ferrooxydans in measurement of oxidizing sulphides, in an acidic aqueous solution and Cu ²⁺ ions as well as sulfur and sulphate or sulfuric acid are formed by oxidation of the ore. The Cu ²⁺ ions can then be treated by liquid / liquid extraction. A similar process is described in US Patent 4,729,788 which describes the use of bacteria Sulfolobus type thermophiles to ensure the leaching of sulfurous ores of gold and silver.

US Pat. No. 5,919,674 has also proposed a method for implementing, on the one hand, the first step of continuous bioleaching of copper ores by means of a bacterium, in particular of the Sulfolubus type. However, it appears that such a process hardly lends itself to implementation on an industrial level.

The object of the present invention is to propose a process aimed at recovering the copper contained in sulphide minerals, comprising a step of continuous bioleaching, and this by using a new thermophilic bacterial culture, of the Sulfolobus type.

The present invention thus relates to a process for the treatment of copper sulphide minerals comprising a bioleaching step during which the minerals are subjected, in reactors arranged in cascade, in which a temperature between 75 ° C. and 85 is maintained. ° C, to the action of a bacterial culture, which comprises a thermophilic bacterium of the so-called Sulfolobus type, leading to the dissolution of copper, characterized in that, during this bioleaching step:

- the treatment is carried out continuously,

- the medium containing the bacterial culture is subjected to continuous mechanical stirring, so as to ensure its oxygenation and a suspension of the solid elements,

- A mass solid content of the culture medium greater than 10% is maintained. The bacterial culture used is a new culture that is in. makes a mixture of bacteria capable of catalyzing the oxidation of sulphides and which has an optimal growth temperature of between 75 ° C and 85 ° C. This bacterial culture has been gradually adapted to improve its tolerance to copper. Such an adaptation was carried out by successive subcultures on a chalcopyrite substrate, during which the concentrations of copper in solution were gradually and artificially increased. Such an adaptation has made it possible to make these bacteria capable of growing in environments with a copper concentration of the order of 50 g / l.

Preferably, the sulphide minerals are supplied to the culture medium in the form of a sulphide concentrate having a particle size d80 of less than one hundred micrometers.

According to the invention, a pH of between 1.2 and 1.6 is maintained in the bioleaching reactors, in particular by adding calcium carbonate. The bioleaching step will be followed by a second step during which, in a first phase, the pulp from the bioleaching reactors is admitted into precipitation reactors in which the iron is removed by causing jarosite precipitation, by adding of calcite, and keeping the solution at a pH below 3, and the neutralized pulp is admitted to a decanter and part of the solids are recirculated at the top of the precipitation reactors.

In a second phase of this embodiment, the liquid from the decanter is admitted into reactors of neutralization in which a pH of about 3.5 is maintained, in particular by adding calcite, so as to cause only a minimum of copper, and the pulp obtained is filtered. In a third phase of this embodiment, the aqueous phase of the liquid coming from the filtration is admitted into an organic solvent extraction unit in which it is subjected to the action of an extractant product, so as to transfer the copper of the aqueous phase in the organic phase, the operating conditions are modified so as to transfer the copper of the organic phase of the extractant product into a pure aqueous phase.

In a variant implementation of the invention, the output of the extraction unit will be placed in communication with the input of the precipitation reactors, so as to recirculate part of the raffinate collected at this output by passing it through. again said reactors with a high flow rate relative to the flow rate of the pulp coming from the bioleaching reactors, so as to cause a dilution of the aqueous solution subjected to extraction, up to a copper concentration of the order of about 10 g / l, that is to say up to a value corresponding to the possible extraction of copper in an extraction unit.

The present invention also relates to a device for the continuous treatment of copper sulphide minerals of the type comprising bioleaching means in which the minerals are subjected to the action of a bacterial culture leading to the dissolution of copper, to a high concentration, of the order of 40 g / l, followed by the means of precipitating the iron contained in this solution, by adding calcium carbonate, followed by means of extraction by organic solvent characterized in that the outlet of the means d solvent extraction is in communication with the inlet of the precipitation means, so as to recirculate a part of the raffinate collected at this outlet by making it again pass through the precipitation means with a high flow rate relative to the flow rate of the solution at the outlet of the bioleaching means, so as to cause a dilution of the aqueous solution subjected to extraction, up to a copper concentration lower than that existing at the outlet of the bioleaching means and preferably of the order of 10 g / l.

According to the invention, the reactors used during the bioleaching stage include means making it possible to channel the gaseous fluid which passes through them towards condensing means. An embodiment of the present invention will be described below, by way of non-limiting example, with reference to the appended drawing in which:

The single figure schematically represents the different stages of the method according to the invention. According to the invention, the bacteria are cultured in agitated and aerated reactors 1 which are continuously supplied with sulphide minerals put in the pulp state. This pulp is transferred from one reactor to another by overflow. The culture medium, which consists of the sulphide minerals and the culture bacterial, is supplied with nutrients, which are essential for the growth of microorganisms in the culture, the concentrations of which have been optimized in order to allow good growth of the latter. Of course, the reactors can be arranged in another configuration than in cascade, and the transfer of the pulp from one reactor to another can be carried out by means other than an overflow, and in particular by pumping means. whether mechanical or carrier gas effect (so-called "air lift" systems)

It is also known, from the prior art, that the biological constitution of the outer membranes of thermophilic bacteria is such that these bacteria prove to be relatively fragile as regards the physical constraints of attrition that they are likely to have to undergo and which are linked to the presence of solid particles in solution when the solid levels (expressed as a percentage by mass) are greater than 1%.

It is also known that these bacteria are sensitive to the shear stresses which they undergo, in particular when they are in the presence of mechanical stirring means. According to the invention, the bacterial culture was also subjected to an adaptation intended to increase the percentage of solid content used. To do this, the levels of solid of the solution brought into contact with the bacterial culture were increased, in successive stages, and the bacteria were able to withstand solid mass of. in the range of 10% to 15%.

It is known that the implementation of such a process requires oxygenation of the culture medium which, in the present case, will be ensured by an injection of air at the bottom of the tank. In the event that during the process the concentration of dissolved oxygen becomes insufficient, the injected air could be enriched with pure oxygen so as to improve the transfer of oxygen to the solution and thus promote oxidation. of the sulphide mineral substrate. This injected air can also be enriched with carbon dioxide which constitutes the carbon substrate of this type of bacteria.

The agitation to which the bacterial culture is subjected during the reaction is a mechanical agitation which is obtained using an electric motor connected to a vertical rotary axis provided with so-called “mobile agitation” elements. A first stirring mobile called a "turbine" is disposed in the lower position of the shaft and is made up in a known manner of a disc, the lower face of which comprises multiple radial plates which, during the rotation of the disc, ensure an action shear causing the dispersion of the air injected into the bacterial culture. The second mobile element is arranged in the upper part of the reactor and consists of a propeller. This mobile element has good pumping characteristics and thus promotes mixing and homogenization of the culture medium. Those skilled in the art will know how to optimize such means of agitation, so as to ensure optimal development of the bacterial culture. It was found that, surprisingly, the thermophilic bacterial culture used was thus able to withstand relatively vigorous stirring means and with a high shearing effect. Furthermore, depending on the nature of the mineral substrate used, we will ensure that the pH of the culture medium is maintained at a value preferably between 1.2 and 1.6, and this by good control of the various operating conditions. Note, however, that the pH value can be regulated, in particular in the event of the pH falling, to values less than 1.2, by controlled addition of calcium carbonate, the dissolution of which will also provide carbon dioxide.

In order to reduce the water losses due to evaporation in the reactors, which can result in an uncontrolled increase in the concentration of the elements in solution likely to disturb the development of the culture, closed reactors will be used in which the flow of the exhaust air will pass through means of condensation. If these losses are not reduced sufficiently enough, either a one-off water addition or a supply of nutritive solution can be carried out without adding a concentrate, for a period of time adapted to the loss of water observed. In a particularly advantageous embodiment of the invention, it is possible to use a condensation system intended to direct the air flow in order to set up means for on-line analysis of the gases leaving the reactors. These means will thus make it possible to obtain, in real time, information on the state of the culture bacterial and thus ensure complete monitoring of the treatment device.

The first stage of the treatment process according to the invention, namely the bioleaching stage, being completed, a pulp is obtained at the outlet of the reactors which contains, in addition to the copper in solution which it is desired to isolate, at a concentration about 40g / l, various chemicals, which are either dissolved in the liquid phase or in solid form and in particular the residue of undegraded ore, gypsum and ferric iron hydroxides.

The following stages of the process will therefore consist first of all, during an intermediate stage, of separating these various components in order to extract, during a subsequent stage of electrolysis, the copper metal from the purified solution.

During this intermediate stage, the iron will first be eliminated. For this, the pulp, taken from battery 1 of bioleaching reactors, is admitted into a battery 5 of several reactors into which calcite is introduced at 6. It is known in fact that the iron which is mainly available in its oxidized form Fe ³⁺ is neutralized by calcite which causes precipitation of jarosite type compounds (that is to say a precipitate containing iron, sulphate, and a counter cation possibly being H ₃ 0 ⁺ , Na ⁺ , K ⁺ , or NH ₄ ⁺ ) of hydroxides and gypsum.

We know that the precipitation of jarosite, which is particularly interesting, since on the one hand it allows a lower consumption of calcite and on the other hand the solid precipitates obtained have much more advantageous filtration facilities than the hydroxide type compounds, is greatly favored by a relatively high temperature (which is the case for the pulp obtained from the bioleaching) and that this type of precipitate is stable to low pH (less than 3). The pH in the reactors will therefore be controlled in order to maintain it at a value below 2.8 and this by controlling the addition of calcite. The installation will include, downstream of the battery 5, in the reactors from which the jarosite precipitates, a decanter 7 which has an outlet 8 connected to the inlet 4 of the battery 5 and which makes it possible to recirculate part of the solids " at the head of neutralization "so that, by germination, we will promote the growth of crystals. This not only improves the growth rates of the minerals but also the characteristic of good capacity for filtration of solids. These are particularly interesting parameters in an industrial installation because they directly affect the dimensioning and therefore the cost thereof.

The rest of the iron in solution is then eliminated, in the form of hydroxides, by means of a battery 11 consisting of neutralization reactors, disposed downstream of the decanter 7, in which a pH of 3.5 is maintained by addition at 12 of calcite, so as to cause by coprecipitation only a minimum of copper. A belt filter system 13 collects the pulp at the outlet 10 of the battery 11 and makes it possible to ensure a solid / liquid separation. Such a filtration system consists in known manner of a band on which the pulp is admitted and which is stretched between drums which ensure its drive in rotation. Suction means are applied through the strip and a cake of increasing thickness is obtained during the movement of these, which is extracted at 14 after it has undergone one or more washing operations.

This solution is then sent at 16 to an organic solvent extraction unit 17. It is known that such a unit is formed by several mixers / decanters into which the solution to be treated is introduced, a mixture consisting of specific extractants and a diluent. Due to the different affinity of copper for the aqueous phase and for the organic phase which depends on the operating conditions, it is possible (under determined operating conditions) to transfer the copper into the organic phase and then, by changing the operating conditions ( bringing the organic phase into contact with an aqueous solution rich in sulfuric acid), bringing the copper back into a pure aqueous solution so that the copper metal can then be recovered by electrolysis. During this operation, the impurities which could pollute the cathodes during electrolysis were removed.

Use will preferably be made, as an extractant, of a reagent sold by the company HENKEL under the brand "LIX".

Note however that the selective extraction of copper with the extractants being a reaction chemical exchange between proton and cation, it follows that, for each copper ion extracted, two protons are released by the extractant. This production of acid leads to a decrease in pH in the aqueous phase (raffinate). However, due to the high solid levels of the pulp from the bioleaching stage, the quantity of copper in solution is high and the mass of acid thus generated during the extraction induces a decrease in pH to values that hinder extraction, or even that make it impossible. It is therefore necessary to ensure that the pH is maintained at a value compatible with that allowing the extraction.

Furthermore, it has been found that the first stage of the process, namely the bioleaching stage, delivers a pulp having a significant copper concentration, close to 40 g / l, and it is known that the extraction operation does not allow extract only copper concentrations of the order of 10g / l at these pH values.

It would of course be possible to work at lower solid levels during the bioleaching stage, but such treatment means would then require, for an identical quantity of copper produced, to have bioleaching reactors of much larger volume, which which would have the disadvantage of increasing the complexity, size and cost of the installation.

A mode of implementation of the invention will be described below with reference to the single figure, which represents a first solution making it possible to overcome these drawbacks.

In this embodiment, the output 19 of the extraction unit 17 is placed in communication with the inlet 4 of the battery 5, so as to recirculate a part of the raffinate collected at this outlet 19 by making it pass through the battery 5 again. Thus, when passing through it, the addition of calcite, which is carried out in 6, has the effect of increasing the pH of the solution, so as to compensate for the drop in the latter due to the emission of H ⁺ ions during extraction. Furthermore, by adjusting the recirculation rate Q2, which is important with respect to the rate Ql of the pulp admitted into the battery 5 coming from the bioleaching battery 1, a dilution of the aqueous solution subjected to extraction is brought about, up to at a concentration of the order of approximately 10 g / l, that is to say up to a value corresponding to the possible extraction in an extraction unit 17. This embodiment is particularly advantageous in to the extent that it makes it possible to ensure the extraction of copper from a pulp with a high copper concentration using a single extraction unit and without additional use of devices intended to raise the pH.

In a second embodiment of the invention, part of the raffinate will not be recirculated, and successive means will be available, on the one hand, for raising the pH of the solution after extraction, and on the other hand to extract this solution of modified pH, and this until having extracted the 40g / l of copper contained in the starting solution.

It will then remain to implement the last step of the method according to the invention during which, in an electrolytic cell 20, one will carry out electrolysis of the raffinate recovered at the end of extraction in order to recover the copper metal.

Claims

1.- Process for treating copper sulphide minerals comprising a bioleaching step during which the minerals are subjected, in reactors (1) arranged in cascade, in which a temperature between 75 ° C and 85 ° C is maintained , to the action of a bacterial culture, which comprises a thermophilic bacterium of the so-called Sulfolobus type, leading to the dissolution of copper, characterized in that, during this bioleaching step:

- the treatment is carried out continuously,

- A mass solid content of the culture medium greater than 10% is maintained.

2.- Method according to claim 1 characterized in that the sulphide minerals are supplied to the culture medium in the form of a sulphide concentrate having a particle size d80 of less than one hundred micrometers.

3.- Method according to one of the preceding claims, characterized in that the bacterial culture used has been previously subjected to an adaptation, by successive subcultures on a substrate, in particular of chalcopyrite, by progressively and artificially increasing the concentrations of copper in solution, in order to bring it to be able to develop in environments whose mass concentrations of copper are of the order of 50g / l.

4.- Process. according to one of the preceding claims, characterized in that a pH of between 1.2 and 1.6 is maintained in the bioleaching reactors (1).

5.- Method according to claim 4 characterized in that maintaining the pH at the desired value is obtained by adding calcium carbonate.

6.- Method according to one of the preceding claims, characterized in that, throughout the bioleaching phase, the physiological state of the bacterial culture is checked, using on-line analysis means of the gases leaving the reactors.

7.- Method according to one of the preceding claims characterized in that the bioleaching step is followed by a second step during which, in a first phase: the pulp from the bioleaching reactors (1) is admitted into precipitation reactors (5) in which the iron is removed by causing jarosite precipitation by adding calcite and keeping the solution at a pH below 3,

- the neutralized pulp is admitted to a decanter (7) and part of the solids are recirculated at the top of the precipitation reactors (5).

8.- Method according to claim 7 characterized in that, in a second phase:

- the liquid from the decanter (7) is admitted into neutralization reactors (11) in which a pH of about 3.5 is maintained, in particular by adding calcite, so as to cause only one minimum copper, - the pulp obtained is filtered.

9.- Method according to claim 8 characterized in that, in a third phase:

- the aqueous phase of the liquid from the filtration is admitted into an organic solvent extraction unit (17) in which it is subjected to the action of an extractant product, so as to transfer the copper from the aqueous phase into the organic phase,

- The operating conditions are modified so as to transfer the copper from the organic phase of the extractant product into a pure aqueous phase.

10.- Method according to one of claims 7 to 9 characterized in that the outlet (19) of the extraction unit (17) is placed in communication with the inlet (4) of the precipitation reactors ( 5), so as to recirculate a part of the raffinate collected at this outlet (19) by making it again pass through said reactors (5) with a high flow rate (Q2) relative to the flow rate (Ql) of the pulp coming from the reactors bioleaching (1), so as to cause a dilution of the aqueous solution subjected to extraction, up to a copper concentration of the order of about 10 g / 1, that is to say up to a value corresponding to the possible extraction of copper in an extraction unit (17).

11.- Device for continuous treatment of copper sulphide minerals of the type comprising bioleaching means (1) in which the minerals are subjected to the action of a bacterial culture leading to the dissolution of copper, at a concentration significant, of the order of 40 g / l, followed by the means of precipitation (5) of the iron contained in this solution, by adding calcium carbonate, followed by organic solvent extraction means (17) characterized in that the outlet (19) of the solvent extraction means (17) is in communication with the inlet (4) of the precipitation means (5), so as to recirculate a portion of the raffinate collected at this outlet (19) by making it again pass through the precipitation means (5) with a high flow rate (Q2) relative to at the flow rate (Ql) of the solution at the outlet of the bioleaching means (1), so as to cause a dilution of the aqueous solution subjected to extraction, up to a copper concentration lower than that existing at the outlet of the bioleaching means ( 1) and preferably of the order of 10 g / l.

12.- Device according to claim 11 characterized in that the reactors used during the bioleaching step include means for channeling the gaseous fluid which passes through them to condensing means.