ES2204340A1 - A method of operating a bioleach process with control of redox potential - Google Patents

Abstract

A method of operating a bioleach process for the leaching of a sulfide bearing oreor concentrate includes subjecting a bioleach slurry which includes dissolved oxygen, dissolved carbon dioxide, sulphide and microorganisms to a bioleach stage, and controlling the redox potential of the bioleach slurry within a predetermined range.

Description

Procedure to operate a process bioleaching with redox potential control.

The present invention relates to a procedure to operate a bioleaching process. In In particular, it refers to a procedure to operate a process of  bioleaching for leaching of a mineral that contains sulfide or a concentrated suspension.

At present it is generally accepted that a primary mechanism for leaching sulfide ores in processes Bioleaching is ferric (chemical) oxidation, in which the bacteria act as a catalyst promoting oxidation of ferrous iron to ferric by oxygen. Mineral leaching of sulphide in liquor or acid sulfate suspensions is strongly influenced by the redox potential of the liquor or suspension. In bioleaching processes, the redox potential of the suspension or leaching solution is largely determined by the concentration ratio of Fe 3+ / Fe 2+. A Sulfide ore such as pyrite (FeS2) has a potential to high rest and oxidation is therefore extremely slow to redox potentials below 450 mV (versus electrode reference Ag / AgCl), but increases rapidly as increases redox potential to approximately 650 mV. This is can compare with the copper sulfide ore, chalcocite (Cu 2 S) which has a low resting potential and will be leached quickly even at low redox potentials of approximately 400 mV Chalcopyrite leaching (CuFeS2) is more complex. Leaching of this mineral is enhanced at low redox potentials (380 to 480 mV), but it is inhibited at high redox potentials due to passivation of the surface of the mineral.

Bioleaching processes employ mixed cultures of microorganisms or bacteria. These microorganisms may include low temperature types (mesophiles) that prefer temperatures in the range of 30 to 45 ° C, moderate thermophilic types that prefer temperatures in the range of 45 to 60 ° C and extreme thermophilic types that prefer temperatures in the range of 60 to 90 ° C Low temperature bacterial cultures, for example, are composed of Thiobacillus ferro-oxidants, Thiobacillus thio-oxidans and Leptospirillum ferro-oxidans . These individual bacteria also exhibit optimal activity at different redox potentials. Thus, Leptospirillum has an optimal activity at redox potentials of 600 to 650 mV, while Thiobacillus ferro-oxidans has an optimal activity at redox potentials of approximately 450 to 500 mV.

In a bioleaching process that operates continuously and treats finely ground sulfur concentrate in agitated tanks, the conditions are normally adjusted so that the optimal conditions for bacterial activity are provided. Under these conditions, the bacterial growth rate and the oxidizing activities will be maximum and the sulfide leaching rate observed represents a condition in which the bacterial ferric iron production rate and the ferric iron consumption rate for the equilibrium are balanced. sulfur oxidation. For bioleaching processes that treat a pyrite-based food, it is usually found that a relatively high redox potential is observed and that the bacteria that predominate in the process are Leptospirillum ferro-oxidans . For a pyrite bioleaching process, this could be referred to as the normal or "natural" operating conditions for the process. In fact, a commercial process would be designed to ensure that these conditions are provided. For minerals with lower resting potentials, such as chalcocite, ferric ion oxidation will occur at lower redox potentials. For chalcocite, it has been speculated that normal operating conditions will be of relatively low redox potential and that under these conditions, Thiobacillus ferro-oxidans bacteria may predominate (this is frequently observed in practice).

All bioleaching bacteria live and they reproduce using only inorganic nutrients. The bacteria use the oxidation of ferrous iron and sulfur (or sulfur) by the oxygen as sources of energy that allows them to grow and survive In addition to oxygen, other essential nutrients required by bacteria are carbon dioxide, the nitrogen and phosphorus When all these are present individual nutrients (in solution) in excess, bacteria they can grow at a maximum speed and present the maximum oxidation rates of ferrous iron and sulfur.

In the process engineering design of bioleaching, a fundamental consideration is to ensure that the oxygen and carbon dioxide intake are sufficient, and the usual design criterion is to ensure that these will be always present in excess. The primary contribution of these nutrients Bacterial comes from the air supplied to the process. In the case of leaching in sulfide concentrate reservoir, the air is bubbles in the tank and has to be transferred or dissolved in solution, so that it is available to bacteria, by mass transfer process. The demand for oxygen by the process is high, for example, the oxidation of a kilogram of Pyrite requires the contribution of one kilogram of oxygen. However, oxygen and carbon dioxide are poorly soluble in water at ambient temperature and atmospheric pressure and therefore the mass transfer of these nutrients becomes a key design variable and a factor in cost.

Applicants know the US document 5,397,380 which refers to a process for the treatment of Materials based on complex metal sulfide and recovery of the metallic values of such materials. The process implies subject the material first to a leaching process in conditions such that sulfur sulfur is oxidized to sulfate and in such a way that oxidized iron and impurities such as Ace become in solution, after which, the leaching residue for pyrometallurgical recovery Conventional metal values. The applicants too know the document JP-A-10265864 for a sulfur-containing copper leaching procedure using bacteria in conditions of high redox potential in the interval from 550 to 750 mV. A relatively acid concentration is used strong at a redox potential of 550 to 750 mV to increase the leaching speed. Applicants also know a article by P d'HUGUES et al., entitled "Bioleaching of a cobaltiferous pyrite: a continuous laboratory-scale study at high solids concentration "(Bioleaching of a pyrite  Cobaltiferrosa: a continuous scale study at high laboratory solids concentration), published in Minerals Engineering, Vol. 10, No. 5, pages 507 to 527 in 1997. This reference refers to the bioleaching of a cobaltiferrosa pyrite that has 20% of solids in a continuous laboratory scale unit of four stirred reactors arranged in series, and investigates the optimization of the bioleaching process using stirred reactors mechanically and aerated. Finally, applicants know the US 5,007,620, which refers to the mechanical design and the operation of a bioleaching reactor used for suspension bioleaching that provide, in particular, the provision of a specific low power consumption mechanism for aeration of the suspension and to maintain the suspension. This involves the injection of air as a source of air in the reactor through porous membrane diffusers specially arranged and that operate at the base of the reactor.

In accordance with the invention, a procedure to operate a bioleaching process for the leaching of a sulfide-containing mineral or concentrate, including the procedure

submit a bioleaching suspension that includes dissolved oxygen, dissolved carbon dioxide, sulfur and microorganisms at a bioleaching stage; and

control the redox potential of the suspension of bioleaching in a previously determined interval.

The procedure may include ensuring that both the concentration of dissolved oxygen and the concentration of carbon dioxide dissolved in the bioleaching suspension they remain above their lower concentration limits respective, selecting their lower limits of respective concentration to ensure that the growth of microorganisms is not limited by too much concentration low dissolved oxygen or dissolved carbon dioxide, in the bioleaching suspension.

The redox potential of the suspension of bioleaching can be controlled in the interval previously determined by controlling the concentration of at least one of the two, dissolved oxygen and dissolved carbon dioxide in the bioleaching suspension.

In a preferred embodiment of the invention, the redox potential of the bioleaching suspension is controlled in the previously determined interval controlling the concentration of carbon dioxide dissolved in the suspension of bioleaching.

Typically, at least part of the dioxide carbon and oxygen are contributed to the bioleaching suspension like air The process may also include providing carbon dioxide. carbon and oxygen to the bioleaching suspension in the form of air enriched in carbon dioxide. On the contrary, the Carbon dioxide can be supplied as a separate gas stream.  In another embodiment, the bioleaching suspension may be acidic and the procedure may include providing carbon dioxide to the bioleaching suspension in the form of calcium carbonate. In a further embodiment, the bioleaching suspension can include microorganisms with enzymes in their cells that can react with urea releasing carbon dioxide, and may include the procedure then contribute the carbon dioxide to the urea bioleaching suspension.

When the redox potential is controlled by controlling the concentration of dissolved oxygen in the suspension of bioleaching, the dissolved oxygen concentration can be control by controlling the speed of air supply to the bioleaching suspension or controlling the contribution rate of a separate oxygen gas stream.

In an embodiment of the invention, the concentration of dissolved carbon dioxide or dissolved oxygen in the bioleaching suspension is controlled by maintaining a constant feed rate of carbon dioxide or oxygen to the bioleaching suspension, and manipulating time of medium residence of the ground product at the stage of bioleaching. The growth rate of microorganisms and, therefore, the oxidation rate of sulfur changes with the residence time, usually increasing as Residence time decreases.

In another embodiment of the invention, it is controlled the concentration of dissolved carbon dioxide or the concentration of dissolved oxygen in the bioleaching suspension while maintaining a constant feed rate of carbon dioxide or oxygen to the bioleaching suspension, and a time of average residence of the constant ground product at the stage of bioleaching, and adding mineral or concentrate, in the form of dry solids, to the bioleaching suspension. The contribution of Additional sulfide solids acts creating a greater demand for oxygen and carbon dioxide, thereby providing a medium to control the concentration of carbon dioxide or oxygen in the bioleaching suspension.

The bioleaching suspension can be agitated. Thus, in a further embodiment of the invention, the concentration of dissolved carbon dioxide or dissolved oxygen in the bioleaching suspension is controlled by maintaining constant a feed rate of carbon dioxide u oxygen in the bioleaching suspension and, manipulating the agitation of the bioleaching suspension, controlling this mode the dissolution rate of carbon dioxide or oxygen in the suspension For a given impeller type, the coefficient of gas-liquid mass transfer for dioxide carbon or oxygen depends mainly on the speed of the agitator.

The mineral or concentrate may include pyrite as an undesirable component, in which case the redox potential is It can control in the range of 380 mV to 450 mV, with respect to of the Ag / AgCl reference electrode, thereby inhibiting the leaching of pyrite, selectively leaching the sulphide minerals present in the mineral or concentrated with a resting potential that is less than the resting potential of the pyrite.

The mineral or mineral concentrate may include  chalcopyrite as the predominant suitable component, in which case, the redox potential can be controlled in the 380 mV range at 480 mV with respect to the Ag / AgCl reference electrode thereby promoting the speed and extent of the chalcopyrite oxidation.

Microorganisms can be selected from mesophiles such as Thiobacillus ferro-oxidants, Thiobacillus thio-oxidans, Thiobacillus caldus and Leptospirillum ferro-oxidans , moderate thermophiles such as Sulfobacillus and Acidimicrobium species, extreme thermophiles such as Sulfolobus and Acid mixtures of the same.

The lower limit of dioxide concentration of dissolved carbon in the bioleaching suspension can be at least 0.15 ppm. Typically, the concentration of dioxide of dissolved carbon in the bioleaching suspension is maintained at or above at least 0.2 ppm for a culture of bacteria moderately thermophilic The lower limit of the concentration of dissolved oxygen in the bioleaching suspension may be at minus 0.2 ppm for a moderately bacterial culture thermophilic The lower concentration limit of the dioxide of dissolved carbon in the bioleaching suspension can be at minus 0.6 ppm, typically at least 0.7 ppm, for a culture of  Extremely thermophilic bacteria Lower oxygen limit dissolved in the bioleaching suspension can be at least 0.5 ppm, typically at least 0.7 ppm for a crop of Extremely thermophilic bacteria However, it will be appreciated that the lower limits for the concentration of dissolved oxygen and of dissolved carbon dioxide depend on factors such as used microorganisms and suspension conditions of bioleaching (pH, temperature) and that the lower limits appropriate can be established for each bioleaching process through routine experimentation.

The invention is described below by means of the following non-limiting examples and of the drawings companions

In the drawings:

Figure 1 shows a graph of the consumption of carbon dioxide (r_ {CO2}) versus the mass concentration of dissolved carbon dioxide (C CO2) in a suspension of bioleaching of a first sulfide mineral concentrate, resulting from the test work set forth in Example 1 plus ahead;

Figure 2 shows a graph of the consumption of carbon dioxide (r_ {CO2}) versus the mass concentration of dissolved carbon dioxide (C CO2) in a suspension of bioleaching of a second sulfide mineral concentrate, resulting from the test work set forth in Example 1 plus ahead;

Figure 3 shows a graph of the consumption of oxygen (r O2) versus mass oxygen concentration dissolved (C2) in the bioleaching suspension of the second sulphide mineral concentrate, which results from the work of test set forth in Example 1 below;

Figure 4a shows a graph of the potential redox and air flow versus time, which results from test work set forth in Example 2 below;

Figure 4b shows a graph of the potential redox and mass concentration of dissolved carbon dioxide versus time, resulting from the test work exposed in the Example 2 below;

Figure 4c shows a graph of the potential redox and the mass concentration of dissolved oxygen against the time, resulting from the test work set forth in Example 2 later;

Figure 4d shows a graph of the potential redox and oxygen absorption over time, resulting from test work set forth in Example 2 below;

Figure 4e shows a graph of the potential redox and copper concentration versus time, resulting from test work set forth in Example 2 below;

Figure 5a shows a graph of the potential redox and oxygen absorption over time, resulting from test work set forth in Example 2 below;

Figure 5b shows a graph of the mass concentration of dissolved oxygen and mass concentration of carbon dioxide dissolved against time, resulting from test work set forth in Example 3 below;

Figure 5c shows a graph of the leaching copper concentration and iron concentration leached against time, resulting from the test work set forth as shown in Example 3 below;

Figure 6 shows a graph of the consumption of oxygen (r O2) versus mass oxygen concentration dissolved (C2) in the bioleaching suspension of the second sulphide mineral concentrate, which results from the work of test set forth in Example 4 below;

Figure 7 shows a graph of the consumption of carbon dioxide (r_ {CO2}) versus the mass concentration of dissolved carbon dioxide (C CO2) in a suspension of bioleaching of a second sulfide mineral concentrate, resulting from the test work set forth in Example 4 plus ahead;

A series of trials were carried out in a small-scale continuous pilot plant trying concentrates of copper sulfide For the purposes of the tests described in the Examples, the plant was operated as a 2 or 25 reactor liters of volume in a single stage. Normally, they were made operate three of these facilities as a series of reactors operating in series The 25 liter reactors are design conventional with a variable speed stirrer that provides the mixture of the ground product in the reactor through a turbine Rushton flat pallets and 6 conventional pallets on the part bottom of a stirring shaft combined with an axial impeller of 45º of 6 pallets located above. The 2 liter reactor is similar, but with a Rushton turbine with flat blades of 6 Single blades at the bottom of the stirring shaft. The aeration was performed by a bubbling duct located by under the Rushton turbine. The tank was completely full of baffles. The control of the operating temperature in the reactor was achieved using a temperature controller through of a temperature probe and immersion heater in the reactor. For continuous operation, a suspension of finely ground concentrate to the reactor from a tank feeding through a peristaltic pump. Overflow of the ground product of the 25 liter reactor was produced through from a gravity overflow to a receiving tank. For the 2 liter reactor, the overflow of the ground product is pumped from the reactor at the same flow rate as the suspension of feeding through a peristaltic pump. The air supplied to the deposit was supplemented, if necessary, with carbon dioxide additional gas. The inlet gas to the reactor and the Exhaust gas above the ground product in the reactor is analyzed to determine the oxygen and dioxide content of Carbon using gas analyzers. This allows to calculate the speed at which these gases were consumed in the reactor at from simple material balances. Oxygen content Dissolved in the mass was measured using a dissolved oxygen probe. The redox potential and the pH of the ground product were determined using probes immersed in the ground product. Concentrations Copper (and iron) were obtained by analyzing samples of liquor extracted from the reactor.

Example 1

In this example, a first test group to determine the effect of levels of dissolved oxygen and dissolved carbon dioxide in the sulphide oxidation and bacterial growth rates for a culture of moderately thermophilic bacteria at 45 ° C. He They used two concentrates in these trials. The first concentrate consisted of a polymetallic sulfide concentrate containing (by mass) 42% chalcopyrite, 24.5% sphalerite (ZnS), 16% galena (PbS), 4% pyrite, 2% bornite (Cu 5 FeS 4), 2% Covelite (CuS), comprising the rest of the dough mainly Bargain minerals. The second concentrate (concentrate 2) comprised mainly chalcopyrite concentrate that contained (by mass) 60% chalcopyrite (CuFS2) and 20% pyrite (FeS_ {2}), comprising the rest of the mass fundamentally bargain metals

The 25 liter reactor was used in this series of essays. The concentrates fed to the reactor had been ground giving a d_ {90} = 10 to 12 µm. The concentrated suspension fed to the bioleaching reactor from the tank feed contained 10% (based on mass) of concentrate in an inorganic nutrient solution. This nutrient solution contained (NH 4) 2 SO 4, 3 g / l, K 2 HPO 4, 0.5 g / l MgSO 4, 0.2 g / l and Ca (NO 3) 2), 0.05 g / l.

Initially, the reactor was operated bioleaching under conditions in which it was estimated that the dioxide of carbon and oxygen would be present in concentrations in excess, in other words, than the oxidation rates of sulfide and bacterial growth would not be limited by concentrations of these components. The contribution of oxygen and carbon dioxide from the air supply to the reactors in the leaching solution was produced by the transfer process of gas-liquid mass. Under operating conditions stationary, mass transfer speeds gas-liquid oxygen and carbon dioxide will be equal to the speeds at which these are consumed components by bacteria to displace the reactions of oxidation and growth that occur in the reactor.

Mass transfer speeds gas-liquid for oxygen follow this equation:

r_ {O2} = K_ {LO2} (C ^ * O2} - C_ {02}) \ eqnum {(1)} where r_ {02} = the rate of oxygen transferred and consumed (kgO2 / m3 \ day), K_ {LO2} = the total gas-liquid mass transfer coefficient for oxygen, C * O2 = oxygen concentration that would be in equilibrium with the partial pressure of oxygen in the gas phase in the reactor (kg / m3) and C2 = mass oxygen concentration measured in the suspension in the reactor (kg / m 3). The mass transfer coefficient, K_ {LO2}, will depend fundamentally on the type, size and design of the impeller system used, the agitation speed of the impeller and the air flow. The term (C * 02 - C 02) in equation (1) represents a driving force by difference in concentration, in which the magnitude of this driving force can be increased by increasing the partial pressure of oxygen in the gas supplied to the reactor, since this will in turn increase the value of C * O2.

For the consumption of carbon dioxide you can write a similar equation:

r_ {CO2} = K_ {LCO2} (C ^ * O2 - C_ {CO2}) \ eqnum {(2)} In the case of carbon dioxide, the difficulty is that, unlike dissolved oxygen, the carbon dioxide dissolved in the suspension, C_ {CO2}, cannot be measured directly. However, it has been found that:

K_ {LCO2} = 0.89 K_ {LO2} \ eqnum {(3)} Equations (1), (2) and (3) can be combined by giving:

C_ {CO2} = C ^ * O2 - [1, 124 (r_CO2 / r / o2) (C ^ * O2 -C_ {02})] \ eqnum {(4) } Since r_ {CO2} and r_ {O2} are estimated from the carbon dioxide and oxygen matter balances, the values of C * CO2 and C * O2 are estimated from the analysis of the output gases, and the C_ {2} is measured, equation (4) allows an estimate of the C_ {CO2}. This was the procedure used to estimate CO2 in all results of the described trials.

Once the operation has been achieved stationary in these trials, the supply of oxygen mass transfer by varying the air flow and maintaining the rest of constant operating conditions. He carbon dioxide mass transfer supply to reactor was changed by means of changes in the air flow and in the Carbon dioxide content in the intake air. It was left that the reactor will reach stationary operating conditions a  again and then the rates of oxygen and of carbon dioxide from balances of matter in oxygen and carbon dioxide through the reactor. The results of these tests are shown in Figures 1 and 2 in terms of r_ {CO2} against C_ {CO2} (concentrates 1 and 2, respectively) and in the Figure 3 in terms of r_ {O2} versus C_ {2} (concentrate 2). It is evident from Figures 1 and 2 that for both concentrated r_ {CO2} is not affected by the decrease in C_ {CO2} until the concentration drops to a value of 0.15 at 0.2 ppm. Below this critical value, a decrease occurs approximately linear in r_ {CO2}.

For oxygen in Figure 3 a type can be seen of similar tendency. In this case, r_ {O2} is not affected by the decrease in C2 to approximately 0.2 ppm. This brings the lowest concentration that can be determined using precisely the dissolved oxygen probe that is used. As conclusion can be said from this result that the value Critical for CO2 is less than 0.2 ppm for culture bacterial used and the conditions used in the test. He you will appreciate however that at the concentration of dissolved oxygen below the critical level the process was relatively unstable. Therefore, the preferred control procedure is the based on the control of the contribution of carbon dioxide, in which the  process presents a higher level of stability.

Critical values for C_ {CO2} and C_ {O2} identified above will be considered characteristic of the crop moderately thermophilic bacterial for bioleaching of copper concentrates used under leaching conditions specific used. These critical concentrations can be identify for different bacterial cultures and the processes of Specific bioleaching used in each case.

Example 2

In this example, an assay was carried out using the concentrate 1 described in Example 1 above. The concentrate fed to the reactor had been ground giving a d 90 = 10 µm. The concentration of the feed suspension was 10% and the Average residence time of the ground product in the reactor was 2 days. The moderately thermophilic bacterial culture was used at a temperature of 45 ° C and the inorganic nutrient solution used was the same as for Example 1. In this test the reactor of 25 was used liters

After it was put into operation, it was allowed to the test will reach stationary operation in conditions in which neither dissolved oxygen nor dissolved carbon dioxide limited the speed of bioleaching. In the figures 4A-E data is shown for this test during A period of 25 days. Data for days 20 to 28 represent the initial period of stationary operation in which the potential Redox is high (575 to 625 mV). Figures 4B, 4C, 4D and 4E show the corresponding data for C_ {CO2}, C_ {02}, r_ {O2} and copper concentration during the period of high redox potential initial. The air flow rate was maintained from 200 to 230 liters / hour with the carbon dioxide content in the fixed inlet air at 1800 ppm During this period, the dissolved oxygen was high, with concentrations greater than 2 ppm. The dioxide concentration of dissolved carbon was also generally high in the range of 0.15 to 0.44 ppm.

On day 27, the air flow rate was reduced to 140 liters / hour and then up to 90 liters / hour on day 30. The objective was manipulate the air flow as a base to control the supply mass transfer of carbon dioxide in order to reduce the redox potential to approximately 430 to 440 mV. He you can see that the C_ {CO2} remained at an equal value or exceeds its critical value. This guarantees that the speed of bacterial growth was never limited by C_ {CO2} by what the maximum bioleaching speed was always maintained. He used this low redox potential range since the results Preliminary laboratory work has indicated that this provides the optimal conditions for copper leaching to from a chalcopyrite component in this concentrate.

The results of the Figures 4A-E show that on the 30th the redox potential fell up to approximately 410 mV, which is considered too low and the air flow rate was increased again. On day 33, and until day 43, the air flow could be set at a stationary value of 170 liters / hour, with the stationary redox potential in the range of 430 to 460 mV. During this period, the C_ {CO2} was averaged at approximately 0.15 ppm (its critical value), while the C_ {O2} was always 0.3 ppm (above its critical value of 0.2 ppm). Also during this period, it can be seen that the sulphide oxidation rate, measured by r O2 (Figure 4D) and the concentration of leached copper (Figure 4E) had significantly decreased both compared to the period Initial high redox potential. This is achieved with a C_ {CO2} maintained at or above its critical value.

The data in Figure 4A shows that on day 43, the air flow rose to 185 liters / hour. This showed to be An increase too large. It can be seen that C_ {CO2} increased significantly (well above its critical value; Figure 4B) and therefore the redox potential increased above of the set value, r_2 decreased (Figure 4D) and the concentration Copper decreased (Figure 4E).

Example 3

In this example, an assay was also carried out.  using the concentrate 1 described above. The objective of this essay was to assess in more detail the optimal redox potential for bioleaching of this concentrate using bacterial culture moderately thermophilic

In this test the 2 liter reactor was used. He concentrate fed to the reactor had been ground giving a d 90 = 10 µm. The concentration of the food suspension was 10% and the average residence time of the ground product in the reactor It was 1.25 days. The inorganic nutrient solution used was as the one described in Example 1. The purpose of this test was to control the redox potential at different setpoints controlling the transfer of mass in the dioxide supply of carbon, while maintaining the maximum speed of possible bioleaching to the specific redox potential. In this test, a platinum electrode was permanently immersed and one of Ag / AgCl reference in the reactor and connected to a meter and to a controller. The controller output adjusted the stirring speed of the impeller controlling the supply of mass transfer of carbon dioxide, keeping this mode the redox potential at the set point. When obtained considerable changes in bioleaching speed, changes were also made in the air flow, but it They performed manually. The carbon dioxide content in the Air intake remained constant at 2000 ppm.

The results of this test are shown in the Figure 5A-C The redox potential was modified in a way  staggered in the range of 420 to 520 mV. The data in Figure 5A show that the bioleaching rate (oxygen consumption or absorption rate) changed when the redox potential It changed in this interval. The maximum bioleaching speed it was obtained in the range of redox potential from 460 to 470 mV, as was indicated by the rate of oxygen consumption (Figure 5A) and the leached copper and iron concentrations (Figure 5C). The oxidation rate (oxygen consumption) observed in these Leaching conditions was very high. The values of C_ {CO2} and C_ {O2} shown in Figure 5B are daily measurements. Without However, a more detailed analysis showed that the values of C_ {CO2} and C_ {O2} presented considerable cyclic changes (for several hours) despite the operating conditions in nominal steady state. This was related to changes in the agitator speed needed for the controller maintain the redox potential in the setpoint value associated with the high air flow rates required to maintain the high oxidation rate obtained. The C_ {CO2} values shown in Figure 5B they indicate, however, that the CO2 was always in excess of the critical concentration. The values of C_ {O2} always remained well above the value critical.

Example 4

In this example an assay was carried out using an extremely thermophilic bacterial culture at 70 ° C. Essay used 2 milled concentrate until d 90 = 25 µm. A 25 liter reactor with the same nutrient solution as described for Trial 1. The average residence time of the ground product in the reactor was 1.8 days. The concentration of solids in the food was 5%.

At the beginning of this trial, the reactor for a sufficient period of time (several weeks) until a stationary operation was achieved in the conditions under which the transfer of oxygen mass and of Carbon dioxide did not limit speed. Once there was achieved this, the effect of the changes in the C_ {O2} and C_ {CO2} on oxidation rates and increase. In the case of C_ {O2}, this was done only due to changes in the air flow to the reactor, maintaining the agitator speed and carbon dioxide content in the constant input air. In the case of C_ {CO2}, this is performed by a combination of changes in air flow at reactor and the concentration of carbon dioxide in the air of input, again keeping the stirrer speed constant. The technique was to carry out these changes for short periods. of time (non-stationary state technique). However, the periods of time remained short enough (less than one hour) so that changes in cell concentrations in steady state were virtually negligible.

The results of these tests are shown in Figures 6 and 7 for oxygen and carbon dioxide, respectively. Figure 6 indicates that the critical value of C_2 for the extremely thermophilic culture used is in the 0.5 to 0.7 ppm range. Figure 7 indicates that the critical value of C_ {CO2} for the extremely thermophilic culture used is in the range of 0.6 to 0.7 ppm.

After the previous tests, it was operated the reactor under conditions in which the supply of dioxide of carbon and oxygen were again sufficient to maintain the C_ {CO2} and C_ {O2} well above their critical values respective. Under these conditions a high was maintained in the process redox potential After this initial phase, it was done again operate the reactor again under conditions in which the supply of carbon dioxide was limited in mass transfer with the in order to control and maintain the redox potential at a low value. In Table 1 presents a summary of the results obtained. He objective of these trials was to assess the effect of these operating conditions on oxidation levels of Chalcopyrite and pyrite components in the concentrate.

During the initial "non-limited" phase, the conditions used allowed to maintain the C_ {CO2} and the C_ {O2} above its critical values. The data shown in the Table 1 show that this was achieved, and that the redox potential was high (578 mV). Under these conditions, high levels of oxidation for both chalcopyrite and pyrite (76 and 83%, respectively). During the second phase with the transfer of mass of limited carbon dioxide, the CO2 was maintained at, or close to the critical value (0.6 to 0.7 ppm) and the potential was maintained redox at 437 mV. It was observed that at the lowest redox potential there was a lower increase in the level of leached chalcopyrite compared to the observed to greater redox potential. If the redox potential is lower It has a potentiating effect on the bioleaching of chalcopyrite at 70 ° C, it does not appear to be as pronounced as that observed at lower temperature The greatest effect of the minor redox potential is in the bioleaching of pyrite. The pyrite leached at 437 mV was only 35% compared to 83% at 578 mV. For a process that treat the present concentrate (concentrate 2), the ability to control the redox potential and, therefore, the amount of pyrite oxidized, it would provide a better process advantage. For the complete oxidation of all chalcopyrite and pyrite sulfide, the process would produce an excess of acid that would be necessary neutralize with a neutralizing agent such as calcium carbonate. He they can avoid the added power costs to promote the oxygen mass transfer supply required for the pyrite oxidation and for the corresponding cooling load additional using the method of the invention.

TABLE 1

       \ nobreak \ vskip.5 \ baselineskip \ centering \ begin {tabular} {| l | c | c |} \ hline
  \ + CO2 supply \ + Limited CO2 supply \\
\ + in excess \ + in mass transfer \\\ hline Potential
redox (mV, \ + 578 \ + 437 \\ Ag / AgCl) \ + \ + \\\ hline pH \ + 1.55
\ + 1.77 \\\ hline C O2 (ppm) \ + 2.11 \ + 1.8 \\\ hline
C CO2 (ppm) \ + 0.9 \ + 0.6 - 0.7 \\\ hline
Leached sulfide: \ + \ + \\\ hline Chalcopyrite (%) \ + 76 \ + 84
\\\ hline Pyrite (%) \ + 83 \ + 35
\\\ hline \ end {tabular} \ par \ vskip.5 \ baselineskip
    

The examples described above show how to you can use the gas-mass transfer control of carbon dioxide advantageously to maintain the concentration of dissolved carbon dioxide at or above a critical lower limit as a means of controlling redox potential of the suspension at a chosen value. Advantageously, this is can perform while maintaining the speed of bioleaching at its maximum. Thus, the process of the invention allows an efficient manipulation of a bioleaching process to achieve a desired level of redox potential.

In the case of leaching chalcopyrite, the method of the invention provides a control strategy of mass transfer that maintains the concentration of carbon dioxide dissolved at all times in, or above its critical lower limit, thereby reducing redox potential from its normally high level (600 mV) to a lower level (430 mV), advantageously achieving a stable operation. It will also be appreciated that, since the leaching rate of chalcopyrite significantly improved to potential levels minor redox, the level of final control for the supply of carbon dioxide mass transfer that is necessary maintain is significantly higher than required at levels of high redox potential.

Copper Sulfide Concentrates contain frequently significant amounts of pyrite (FeS2). TO high redox potentials (> 500 mV), the pyrite component is will leach quickly and contribute significantly to the level general oxidation (ferric iron consumption) observed. In low redox potential conditions (<450 mV), the level of Pyrite oxidation is negligible. Control of the potential redox therefore provides an effective procedure to control the oxidation of this sulfide. The pyrite component is not normally a valuable component of copper concentrates and the advantage obtained by avoiding the oxidation of pyrite would be a reduction in process power costs for supply of air and cooling. Also, if the pyrite is allowed to leach, the process can produce an excess of acid and would be a cost added neutralize and discard this acid. On the other hand, others copper concentrates can be acid deficient and the ability to control the leaching of pyrite producing acid "fair enough" is advantageously a benefit economic.

Claims (7)

1. A procedure to operate a process of bioleaching for the leaching of a mineral or concentrate that contains sulfur, including the procedure submit a bioleaching suspension that includes dissolved oxygen, dissolved carbon dioxide, sulfur and microorganisms at a bioleaching stage; and control the redox potential of the suspension of bioleaching in a previously determined interval, controlling the concentration of at least one of dissolved oxygen and carbon dioxide dissolved in the bioleaching suspension, making sure that both the concentration of dissolved oxygen and the concentration of dissolved carbon dioxide in the suspension of bioleaching remain above their respective limits of lower concentration, selecting the respective limits of lower concentration to ensure that the growth of microorganisms is not limited by too much concentration low dissolved oxygen or dissolved carbon dioxide in the bioleaching suspension, controlling the redox potential in the interval 380 to 450 mV with respect to a reference electrode of Ag / AgCl when the mineral or mineral concentrate includes pyrite as an undesirable component, thereby inhibiting leaching of pyrite and leaching sulfide minerals selectively Desirable present in the mineral or mineral concentrate with a resting potential that is less than the resting potential of the pyrite, and in the range of 380 to 480 mV with respect to a reference electrode of Ag / AgC1 when the mineral or ore concentrate includes chalcopyrite as a component of predominant sulfide, thereby promoting speed and extension of chalcopyrite oxidation. 2. A method according to claim 1, in  which microorganisms comprise a bacterial culture moderately thermophilic and the lower concentration limit for the dissolved carbon dioxide and the dissolved oxygen in the Bioleaching suspension is 0.2 ppm. 3. A method according to claim 1, in  which microorganisms comprise a bacterial culture extremely thermophilic, the concentration limit being lower for the carbon dioxide dissolved in the suspension of 0.6 ppm bioleaching and lower concentration limit for dissolved oxygen in the 0.5 bioleaching suspension ppm. 4. A procedure according to any one of the previous claims, wherein the redox potential of the bioleaching suspension is controlled in an interval previously determined by controlling the dioxide concentration of carbon dissolved in the bioleaching suspension. 5. A procedure according to any one of the previous claims, including supplying dioxide of carbon and oxygen to the bioleaching suspension in the form of air enriched in carbon dioxide. 6. A procedure according to any one of the claims 1 to 4 inclusive, wherein the suspension of Bioleaching is acidic and that includes supplying dioxide from carbon to the limestone bioleaching suspension. 7. A procedure according to any one of the claims 1 to 4 inclusive, wherein the suspension of bioleaching includes microorganisms with enzymes in their cells that can react with urea releasing carbon dioxide, including the procedure supplying carbon dioxide to the urea bioleaching suspension.