MXPA97003049A - Methods to improve the bioxidation in battery of sulfide refractory mineral particles that are bioxided using a recircul biolixiviate solution - Google Patents

Abstract

The present invention relates to a method for improving the rate of bioxidation in a sulfide refractory mineral particle stack that at least partially bio-oxidates using the recirculated biolixiviate spent solution, the method includes the steps of bioxidizing a battery (10) of refractory sulfide mineral particles with a solution of biolixiviate: to collect, from the stack, a spent solution of biolixiviate that includes a multitude of inhibitory materials dissolved therein, the concentration of each individual inhibitory material being below the individual inhibitory concentration, but being sufficient in the combined concentration of at least two of the inhibiting materials to inhibit the rate of bioxidation of sulfide refractory mineral particles, condition (20) the spent solution of biolixiviate to reduce the inhibitory effect caused by the combined concentration of at least two inhibitor materials is to recirculate the reconditioned biolixiviate solution (22) to the stack, and bioxidize the refractory sulfide mineral particles in the stack with the biolixiviato solution recondition

Description

METHOD FOR BlOXIDflTION OF A PILE OF MINERAL This application is a continuation in part of the copending application Serial No. 08 / 329,002, filed on October 25, 1994. Application 08 / 329,002 is incorporated herein by reference.

CQMPO DE Lft INVENTION The present invention relates to the recovery of values of refractory sulfide metal and refractory carbonaceous sulphide minerals. More particularly, the present invention relates to the bioxidation of a stack of sulphide refractory minerals using an effluent solution of recirculated biolixiviate.

BACKGROUND PE INVENTION Gold is one of the rarest metals on earth. Gold minerals can be divided into categories of two types: easy to grind and refractory. The minerals of easy grinding are those that can be treated by means of simple gravity or direct cyanidation techniques. Refractory minerals, on the other hand, are not susceptible to conventional cyanide treatment. Deposits that have gold are considered refractory if they can not be economically treated using conventional cyanide leaching techniques, because the gold is solubilized in insufficient quantity. These minerals are frequently refractory due to their excessive content of metal sulphides (for example, pyrite and arsenopy ita) and / or organic carbonaceous matter. A large number of refractory minerals consist of minerals with a precious metal such as gold, occluded in iron sulphide particles. The iron sulfide particles consist mainly of pyrite and arsenopyrite. If the gold or other precious metal remains occluded within the sulfide, even after grinding, then the sulfides must be oxidized to release the encapsulated precious metal values and make them susceptible to a leaching agent (or leach); In this way, the oxidation process of sulfur reduces the refractory nature of the mineral. A number of treatments are known in the art for oxidizing sulfide minerals to release precious metal values. These methods can generally be divided into two types: milling operations and pile operations. Milling operations are typically expensive procedures that have high operating and capital costs. As a result, even though the total recovery regime is typically superior for milling-type processes, milling operations are not applicable to low-grade minerals, that is, minerals that have a gold concentration of less than about 2.2 gr / ton. , and still as low as approximately 0.62 g / ton. Two well-known methods for oxidizing sulfides in grinding operations are oxidation under pressure in an autoclave, and calcination. Oxidation of sulfides in refractory gold minerals can also be effected using autotrophic acidophilic microorganisms such as Thiobacillus ferrooxidans. SulfQlp and s, species of flcidianus and facultative thermophilic bacteria, in a microbial pretreatment. These microorganisms can use the oxidation of sulfide minerals as a source of energy during metabolism. During the oxidation process, the above microorganisms oxidize the iron sulfide particles to cause the solubilization of iron as ferric iron, and sulfur, as ion sulfate. Oxidation of sulphide refractory minerals using microorganisms, or, as it is often called, bioxidation, can be carried out in a mill process or a pile process. Compared to pressure oxidation and calcination, bioxidation procedures are simpler to operate, require less capital, and have lower operating costs. In fact, bioxidation is often chosen as the procedure for oxidizing sulphide minerals in sulphide refractory minerals, as it is economically favored over other methods to oxidize the mineral. Nevertheless, due to the lower oxidation rates associated with microorganisms, when compared with chemical and mechanical methods to oxidize sulphide refractory minerals, bioxidation is often the limiting step in mine exploitation. A mill type bioxidation process includes pulverization of the ore, followed by treatment of a suspension of the ore in a bioreactor where the microorganisms can use the finely ground sulfides as a source of energy. This milling process was used on a commercial scale at the Tonkin Springs mine. However, the mining industry has generally considered the Tonkin Springs bioxidation operation a failure. A second mill-type bioxidation process includes separating sulfides that carry gold from the ore using conventional sulfide concentration technologies, such as flotation, and then oxidizing the sulfides in a stirred bioreactor to mitigate its refractory nature. Commercial operations of this type are in use in Africa, South America and Australia. Bioxidation in a stack process typically involves the formation of a stack of sulphide-refractory mineral particles and then inoculating the stack with a microorganism capable of bio-oxidizing the sulfide minerals in the ore. After the bioxidation has reached a desired end point, the pile is drained and washed by repeated flooding. The values of precious metal released are at that moment ready to be leached with an adequate leach. Typically, minerals containing precious metal are leached with cyanide since it is the most efficient leach for the recovery of precious metal values from the ore. However, if cyanide is used as a leach, the stack must be neutralized first. Because bioxidation occurs at a low pH, acid, while cyanide treatment must occur at a high, basic pH, the bioxidation of the stack followed by conventional cyanide treatment is inherently a two-step procedure. As a result, treatment options that use heap bioxidation must separate the two steps of the procedure. This is done conventionally by separating the steps temporarily. For example, in pile bioxidation, first the battery is bioxide and then rinsed, neutralized and treated with cyanide. To do this economically and practically, most battery bioxidation operations use a permanent cell pad in one of several mineral-free mineral configurations. Of the different bioxidation procedures available, battery bioxidation has the lowest operating and capital costs. This makes the pile bioxidation process particularly applicable to low grade or depleted type minerals, that is, minerals having a gold concentration (or equivalent precious metal value) of less than about 2.2 g / ton. However, pile bioxidation has very low kinetics compared to milling bioxidation procedures. Stack bioxidation can take many months to sufficiently oxidize the sulfide minerals in the ore to allow gold or other precious metal values to be recovered in sufficient quantities by means of subsequent leaching with cyanide for the process to be considered economical. Therefore, battery bioxidation operations become limited by the extension of the time required for sufficient bioxidation to occur to allow economic recovery of gold. The longer the time required for bioxidation, the permanent pad installations will be greater and the capital investment needed will be greater. At mine sites where the amount of soil suitable for construction of pile pads is limited, the size of the permanent pad may become a limiting factor in the amount of ore treated in the ina and thus, in the use of the mine. In these circumstances, the limiting conditions of the speed of the bioxidation process become even more important. Conditions that limit the speed of the pile bioxidation process include inoculant access, nutrient access, air or oxygen access, and carbon dioxide access, which are required to make the process more efficient and thus an option of attractive treatment. In addition, induction times with respect to bio-oxidants, growth cycles, bicidal activities, the viability of bacteria and the like are important considerations for bioxidation because variables such as accessibility, particle size, sedimentation, compaction and the like are economically irreversible once the stack has been built. As a result, batteries can not be prepared once formed, except on a limited basis. The methods described in U.S. Patent No. 5,246,486, issued September 21, 1993, and U.S. Patent No. 5,431,717, issued on August 11, 1995, by one of the aforementioned inventors, both of which are incorporated in the present as a reference, are aimed at increasing the efficiency of the pile bioxidation process by ensuring good flow of fluid (both gas and liquid) throughout the pile. However, the solution of the invention and the handling of the solution also have important speed limiting considerations for the pile bioxidation process. The solution drained from the bioxidation cell is acid and contains bacteria and ferric ions. Therefore, this solution can be used advantageously in the agglomeration of the new ore or recirculating it back to the top of the pile. However, toxic or inhibitory materials can be formed in this depleted solution. For example, ferric ions that are generally a useful aid in pyrite leaching, are inhibitory to the growth of bacteria when their concentration exceeds about 30 g / 1. Active biocide metals can also be formed in this solution, delaying the bioxidation process. The active biocide metals that are frequently found in sulphide refractory minerals include arsenic, antimony, cadmium, lead, mercury and molybdenum. Also, other toxic metals, bio-oxidation byproducts, dissolved salts and bacterially produced material can be inhibitors for the speed of bioxidation. When these inhibitory materials are formed in the spent solution at a sufficient level, the recirculation of the spent solution becomes detrimental to the rate at which the bioxidation process is carried out. In , the continuous recirculation of an exhausted solution that has a sufficient formation of inhibitory materials, will completely stop the process of bioxidation. Previously, to avoid excessive formation of inhibitor materials in the spent effluent solution of biolixiviate collected from the stack, the operations of the mine simply replace, or dilute the effluent of the stack with fresh inoculant solution. This is expensive as it increases the consumption of fresh water and also increases the need for waste water treatment. In US Patent No. 5,246,486, a method is described for removing inhibitory concentrations of arsenic or iron from the exhausted solution of the cell, which is defined in that reference as concentrations exceeding approximately 14 g / 1 and 30 g / 1. , respectively. The method described in this patent covers increasing the pH of the solution exhausted effluent of biolixiviate above 3, so that the arsenic ions in solution coprecipitate with ferric ions in solution. However, there are several shortcomings with the method described in this patent. First, as described above, there is a multitude of potential inhibitory materials that can be leached from the ore or that can be formed as a result of the biolivixed process; in this way, simply following the formation of arsenic or ferric ion in the spent solution of biolixiviate does not solve the problem of inhibitory concentrations of other metals or formation materials in the spent solution. In addition, the depleted solution in most cases does not contain inhibitory concentrations of any specific inhibitory material. However, the bioxidation process will be delayed by the formation of a combination of a number of inhibiting materials in the recirculated exhausted solution. Therefore, the combined concentration of at least two inhibitory materials may be sufficient to inhibit the rate of bioxidation of refractory sulfur mineral particles in the cell, even when not a single material has a concentration above its inhibitory concentration. Consequently, there is a need in the stack bioxidation methods of a method for removing inhibitory concentrations of a group of inhibitory materials within the spent cell solution. Such a method would reduce the time required for battery bioxidation procedures and concomitantly reduce the capital required to construct the battery bioxidation facility. In addition, such a method would reduce the stack bioxidation shrinkage that typically occurs in mine operations.

BRIEF DESCRIPTION OF Lft INVENTION An object of the present invention is to provide a stack bioxidation process of the type described above, wherein the spent solution of biolixiviate can be recirculated with little or no reduction in the rate of bioxidation of the refractory sulfide mineral particles within the pile due to the formation of an inhibitory concentration of a group of inhibitory materials within the exhausted solution of the cell. For this purpose, a battery bioxidation process is provided in which particles of sulphide refractory ore are bio-oxidated with an effluent solution of biolixiviate. The exhausted effluent solution of biolixiviate is collected from the cell. If this solution is inhibitory to the bioxidation process due to the combined concentration of a group of inhibitory materials, then the exhausted effluent solution of biolixiviate is conditioned to reduce the inhibitory effect caused by these materials. The effluent solution of conditioned biolixiviate is then recirculated to the top of the pile with little or no reduction in the rate of bioxidation. Alternatively, the effluent solution of conditioned biolixiviate can be applied to a second stack of sulfide refractory particles or used to agglomerate refractory sulfide mineral particles prior to stack formation. A preferred method of conditioning the spent effluent solution of biolixiviate includes increasing the pH of at least a portion of the spent solution to a pH within the range of about 5.0 to 6.0, preferably at a pH within the range of about 5.5 to 6.0. This can be done continuously as a prophylactic measure, or only after it is specifically determined that the solution is inhibitory. In this way, by increasing the pH of the solution exhausted effluent of biolixiviate, the inhibiting materials that cause the reduction in the rate of bioxidation are typically precipitated. Then, the precipitated solids are separated from the effluent solution of biolixiviate and the pH of the solution is lowered to an optimum pH for the bioxidation process. The effluent solution of conditioned biolixiviate is then recirculated to the cell or used to agglomerate new mineral. The objects, features, and prior and other advantages will become apparent to those skilled in the art from the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic of a bioxidation process with a solution management system in accordance with one embodiment of the present invention. Figure 2 is a schematic of the prior art bioxidation process, "race track" type, which can be used with the solution handling system according to the present invention. Figure 3 is a graph of the iron% leached from a mineral as a function of time. Figure 4 is a graph of Eh of a spent effluent solution of biolixiviate from a sulphide refractory mineral and a corresponding concentrate of the mineral sulfides as a function of time. Figure 5 is a graph illustrating the Fe% leached as a function of time for a mineral in which the exhausted effluent solution of biolixiviate was recirculated without treatment. Figure 6 is a graph that illustrates the% Fe leached as a function of time from a mineral in which only fresh solution was applied to the ore. Figure 7 is a graph illustrating Eh of different effluent solutions of biolixiviate at time 0 and after the course of 24 hours. Figure 8 is a graph comparing Eh of an original effluent of a mineral with that of the effluent that has been adjusted to a pH of 6.0 and then readjusted to a pH of 1.8 without removal of the precipitates formed during the first pH adjustment. Figure 9 is a graph illustrating the extent of pyrite bioxidation as a function of time for a pilot stack bioxidation process. Figure 10 is a graph illustrating the amount of ferrous ion converted to ferric ion for different samples. Figure 11 is a graph illustrating the mg ferric ion in different solutions as a function of time. Figure 12 is a graph illustrating the amount of ferrous ion converted to ferric ion for several samples; Y Figure 13 is a flow chart of a solution management system in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In accordance with a first embodiment of the present invention, there is provided a method for improving the bioxidation rate of a stack of refractory sulfide mineral particles, which are at least partially bioxidated using a recycled effluent solution of recirculated biolixiviate. The process comprises the steps of bioxidizing refractory sulfur mineral particles with an effluent solution of biolixiviate; collecting an exhausted effluent solution of biolixiviate from the stack including a plurality of inhibitor materials dissolved therein, the concentration of each inhibitor material in the exhausted solution of biolixiviate effluent is below its individual inhibitory concentration, and the combined concentration of at least two of the inhibiting materials are suffit to inhibit the rate of bioxidation of the refractory sulfur mineral particles in the ore; conditioning the spent effluent solution of biolixiviate to reduce the inhibitory effect caused by the combined concentration of at least two inhibitory materials; recirculating the effluent solution of biolixiviate conditioned to the same cell or to a second cell; and bioxidizing refractory sulphide mineral particles, in the same or second stack, with the effluent solution of conditioned biolixiviate. The starting material in which the present invention can operate includes sulfide refractory minerals and carbonaceous sulfide refractory minerals. As used herein, therefore, sulfur refractory mineral is also understood to encompass carbonaceous sulphide refractory minerals.

In figure 1 a schematic illustration of a means to practice the present modality is provided. Referring to Figure 1, stack 10 of refractory sulfur particles is formed in a reusable leach pad. After the stack 10 is bioxidized according to a target amount, the stack 10 becomes the stack 12, which is allowed to drain. The drained stack 12 is then made into the washed pile 14. After the stack 14 is washed, the refractory sulfur particles in the stack 14 are typically removed from the permanent leach pad and the gold is recovered in a cyanidation process of pile, as is well known in the art. If the refractory material to be treated is a carbonaceous sulfide mineral, then additional treatment steps may be necessary after microbial pretreatment to avoid loss by impregnation of the aurocyanide complex, or other precious metal-leaching complexes, with the material carbonaceous by treatment with a leaching agent. In U.S. Patent No. 5,127,942, issued July 7, 1992, which is incorporated in the present reference, a known method of carbonaceous sulphide minerals for pile biolixiviate is disclosed. In accordance with this method, after the ore undergoes an oxidative bioleaching to oxidize the sulfide component of the ore and release the precious metal values, then the mineral is inoculated with a bacterial association in the presence of nutrients to promote growth of the bacterial association; The bacterial association is characterized by the property of deactivating in the mineral the tendency of the loss by impregnation of the carbonaceous matter. In other words, the bacterial association functions as a biological blocking agent. After treatment with the microbial association, which deactivates the precious metal adsorbent carbon, the mineral is leached with an appropriate leach to cause the dissolution of the precious metal in the ore, as is known in the art. The first step of the biolixiviato process is to obtain sulphide refractory ore particles of an appropriate size for heap leaching. This can be done by grinding the ore to the desired size scale. Preferably, the sulphide refractory ore is crushed to a maximum size white on the scale of approximately 0.63 to 2.54 cm. Appropriate targets of maximum particle sizes include 0.63, 0.95, 1.27, 1.90 and 2.54 crn. If the ore passes any of these targets of particle sizes, it would be suitable for pile leaching. The smaller the particle size, however, the greater the surface area of the sulfide particles in the ore will be, and of course, the sulfide particles will biodegrade faster. There is also an increase in the recovery of precious metal values. However, this must be considered against the additional cost of crushing the ore to a smaller particle size. The additional amount of precious metal recovered may not justify the added cost. In gold pile leaching, minerals are frequently crushed to approximately 1.90 cm, which is a good compromise between reducing the size of the rock to minimize the leaching time required and the cancellation of the production of too many particles thin, which cause low permeability in the ore pile and impede the flow of the effluent solution of biolixiviate, and subsequently, the flow of the cyanide solution, which is percolated down through the ore pile. The particle size must be selected so as to achieve the highest bioxidation rate, concomitantly with the most economical crushing of the particular mineral. In this way, for easy to crush minerals, the size is less than, eg, 1.27 cm less than ten mesh size, but for minerals difficult to crush is more typical from 2.54 to 0.63 cm. Appropriate crushing and particle size are achieved by means well known in the art. Of course, if the sulphide refractory mineral body to be bioxided is already of an appropriate size for pile bioleaching, no additional grinding is required. In the event that the concentration of acid consumable mineral components, which are well known in the art, is significant, or that the mineral contains excessive concentrations of inhibitory materials, a pre-treatment of the mineral with acid may be necessary to condition the mineral appropriately for bioxidation. The conditioning of the mineral typically includes adjusting the pH of the mineral, washing out soluble inhibitory components, and adding microbial nutrients, followed by aging the ore. Conditioning should be started as soon as possible. If feasible, conditioning must begin with the mineral in situ within the mineral body. Subsequent conditioning must be carried out during hauling, crushing, agglomeration and / or stacking of the ore. Bioxidation of sulphide refractory minerals is especially sensitive to percolation channels blocked by loose clay and fine material, since bacteria need large amounts of air or oxygen to develop and bioxidize the iron sulfide particles in the ore. Also important is the air flow to dissipate the heat generated by the exothermic bioxidation reaction, since excessive heat can kill the bacteria that develop in a large pile, poorly ventilated. Therefore, if the ore is high in fine particles and loose clay material, the agglomeration of the mineral may be necessary to avoid plugging the flow channels in the pile. Alternatively, good fluid flow can be ensured within the stack by removing fine and / or clay materials from the refractory sulfide ore prior to stack formation, as taught in U.S. Patent 5,431,717, to W. Kohr, which was previously incorporated as a reference. Preferably, the initial inoculation of the refractory sulfide mineral particles with bio-oxidant bacteria is carried out during the agglomeration step, as taught in U.S. Patent 5,246,486, which was previously incorporated as a reference; or immediately after stacking the ore on the pile. Although other means of stack construction can be used, conveyor stacking is preferred. The conveyor stack minimizes the co-location of the ore within the stack. Other means of stack construction, such as unloading at the end with bulldozer scraper or top discharge, may result in regions of reduced fluid flow within the stack. Once the stack 10 is formed, the stack 10 is inoculated with additional biolixiviate effluent solution supplied from the tank 18 through line 16 based on what is required. The effluent solution of biolixiviate delivered through line 16 contains at least one microorganism capable of bioxidizing refractory sulphide mineral particles in stack 10. A solution of microbial nutrients is also applied to the stack 10, as required. Nutrient additions are monitored throughout the course of the bioxidation process and are performed on selected performance indicators such as the rate of solubility of arsenic or iron in the pyrites or the oxidation rate of sulfides, which can be calculated from it. Other performance indicators of bioxidation that can be used include pH measurement, titratable acidity and Eh of solution. The following bacteria can be used in the practice of the present invention: Group A. Thiobacillus. ferrPOX.Í4ans; T iohacilluR + .hipp? .i'Jflns7 ThiQfraciiius, organobarus; Thiobaciiiim anirln-n ilusT Group B. Let QSPirillUffl ferroqx. j < Jans; Group C. Sulfgbacjllus, therrnosulfidooxyurea? Group D. BulbolohuB acidocaldariuB: Sul olohus ££; ' Sul faith 1 howitzer solfataricus and flcidianus brißrl vi and the like.

These bacteria are available from the "American Type Culture Collection "or similar culture collections or have been made available for them and / or will be made available to the public prior to the publication of this description as a patent. B are mesophilic, that is, the bacteria are capable of developing at medium-scale temperatures (eg, about 30 ° C.) Group C consists of facultative thermophiles since the bacteria are capable of developing on the temperature scale Finally, group D bacteria are obligate thermophiles, which can develop only at high temperatures (thermophilic) (eg, greater than about 50 ° C). that the bacteria of groups A and B remain useful, the temperature of the cell should not exceed about 35 ° C, for bacteria of group C, the temperature of the cell should not exceed about 5 ° C. 5 ° C, and for group D bacteria, the temperature of the pile should not exceed approximately 80 ° C. As is well known in the art, the temperature in a bioleaching pile is not uniform and frequently the bacteria are unable to survive if the temperature is improperly controlled or if the appropriate bacteria are not used. Accordingly, based on a temperature profile of the stack when the oxidation of the refractory particles of sulfide ore is at its most advanced stage and the exotherm of the sulfide oxidation is the highest, the stack can be bathed with a bioleaching agent cooled, a recirculated and cooled biolixiviante or a cooled maintenance solution, that is, a nutritive solution. In addition, the stack can be constructed with provisions of 0 7 cooling (and / or heating). In addition, the pile can be inoculated with the appropriate bacteria to meet the temperature limits of the mineral. In this way, if the ore is a mineral with a high sulfur content, preferably ternophilic bacteria should be used. After the bioxidation reaction has reached an economically defined end point, the stack can then be drained and subsequently washed by repeated jets with water. The number of wash cycles that is required is typically determined by an appropriate marker element such as iron and by the pH of the wash effluent. After the wash cell 14 is suitably jetted, it is separated, neutralized and treated in a traditional process of heap leaching by cyanidation, as is well known in the art. The inventory and the handling of the solution are an important part of the bioxidation process. Figure 1 illustrates a solution management system according to an inclusion of the present invention for the complete sequence of bioxidation, drainage and washing. From figure 1, it can be seen that according to this inclusion, all the values of the solution are reused. This minimizes the amount of fresh water that is required in the bioxidation process. According to Figure 1, the biolixiviate solution q? E that has been filtered through the stack 10 is collected and reapplied to the top of the stack 10. This solution is acidic and contains ferric ion and, therefore, it can be used advantageously recirculating it to the top of the pile or using it for the agglomeration of new ore. However, the effluent solution generated initially in the bioxidation process will also contain significant concentrations of base and heavy metals, including the components that produce the microbial inhibition. As the inhibitor materials accumulate in the spent solution, the bioxidation process is delayed. For example, ferric ions, which are generally a useful component in the leaching of pyrite, inhibit the growth of bacteria when their concentration exceeds almost 30 g / 1. Biocidically active metals can also accumulate in this solution, delaying the bioxidation process. The biocide-active metals that are frequently found in sulphide refractory minerals include arsenic, antimony, cadmium, lead, mercury, molybdenum and silver. Other inhibitory metals (including copper and aluminum), bio-oxidation byproducts, dissolved salts and material produced by bacteria can also inhibit the rate of bioxidation. Anions such as Cl-, N0a- and L "S0] s.- may also need to be reduced before the solution is recirculated back to the stack.When these inhibitory materials accumulate in the depleted solution to a sufficient level , the recirculation of the spent solution becomes detrimental to the rate at which the bioxidation process runs its course.In addition, the continuous recirculation of an exhausted solution having a sufficient accumulation of inhibitory materials will stop the bioxidation process altogether. , the normal adjustment of the pH of the exhausted solution of biolixiviate to the optimal scale of pH for the bioleaching is unsuitable for removing the inhibitor materials from the solution, thus, if the pH of the spent solution is only adjusted to the optimal scale before the recirculation of the solution to the top of the stack, the rate of bioxidation will be suppressed, nor is it simply monitoring the accumulation of arsenic or ferric ions in the spent solution of biolixiviate and then treating the spent solution when one of these compounds is present in excessive concentrations suitable to solve the problem of the accumulation of inhibitory concentrations of other metals or materials in the spent solution. More importantly, the spent solution in most cases will not contain inhibitory concentrations of any specific inhibitory material. However, rather, the bioxidation process will be delayed from the accumulation of a combination of a number of inhibitory materials in the recirculated exhausted solution. Therefore, in most cases, the combined concentration of at least two inhibitory materials will be sufficient to inhibit the bioxidation rate of the refractory particles of the sulfide ore in the stack. In addition, typically, the bioxidation rate of the depleted solution of biolixiviate will be inhibited due to the combined concentration of a group of inhibitory materials long before the concentration of any inhibitory material in the group even approaches its inhibitory concentration. As is well known in the art, different bacteria and different strains of the same bacteria have varying sensitivities to the inhibitory materials. Thus, the inhibitory concentration of individual inhibitory materials will vary with different bacteria and with different strains of the same bacteria. In addition, some strains will be highly resistant to one metal, while others will be highly sensitive to it. For this reason, it is useful to test the bacteria that are being used in a bioxidation procedure in terms of s? sensitivity to metals in the ore and in the effluent or in the spent solution. To determine the individual inhibitory concentration of a specific inoculum of bacteria, as illustrated in Example 1 below, a simple bioxidation test can be carried out using a biolixiviate solution containing a known concentration of the inhibitor material, preferably in the form of sulfate, and a known concentration of bacteria. The concentration of the inhibitor material is then increased gradually until an inhibitory effect on the biolixiviato bioxidation rate is observed. The point at which an inhibitory effect is observed is the inhibitory concentration for the material. The observed inhibitory effect is determined by comparing the sample with a positive control. According to the present invention, the depleted solution of biolixiviate is treated in a conditioning circuit 20 to reduce the inhibitory effect caused by the combined concentration of a group of inhibitory materials before any specific inhibitory material in the group reaches its level. inhibitory concentration. Treatment options for conditioning the depleted solution of biolixiviate include lime softening, limestone softening, ion exchange, electrodeposition, iron cementing, reverse osmosis or a combination of these technologies. In some cases, the concentration of an inhibitory metal may be high enough to justify the economic recovery of the value of the metals. For example, if the concentration of copper is sufficiently high in the solution depleted of biolixiviato, the extraction with solvent or the electrolytic extraction could be used to recover this metal. According to the present invention, the preferred conditioning method of the depleted solution of biolixiviate is the softening with lime or the softening with limestone. This is accomplished by using lime or limestone to raise the pH of the spent biolixiviate solution to a pH of at least 5.0, preferably at a pH within the range of about 5.0 to 6.0, and more preferably at a pH within the range of scale of almost 5.5 to 6.0. The resulting precipitates are then removed from the exhausted solution of biolixiviate. After the precipitates are removed, the pH of the solution is reduced again to the optimal scale of 1.2 to 2.6 for bioxidation using concentrated acid or using acid in the wash water 24 and / or in the drainage solution 26. More preferably, the pH of the solution is reduced to the scale of 1.7 to 1.9, and more preferably the pH is reduced to a pH of almost 1.8. Although lime or limestone is the preferred means of raising the pH to a value greater than 5.0, other strong bases may also be used, as would be recognized by one of ordinary skill in the art. If the spent solution of treated biolixiviate remains too inhibitory after being softened with lime or limestone, then the spent solution may require further purification by some of the other conditioning techniques mentioned above. Whether another conditioning technique is used will depend on whether the additional improvement in the rate of bioxidation, which is achieved through the removal of additional inhibitory materials, is justified by the added cost of removing the inhibitory materials. After the pH of the depleted solution of biolixiviate is again adjusted to the pH appropriate for bioxidation, the conditioning of the depleted solution of biolixiviate ends and the conditioned solution 22 can be reapplied to the top of the stack 10 to promote the Additional bioxidation inside the stack. In addition, the bioxidation rate will be higher than that for the exhausted solution of recirculated and unconditioned biolixiviate and, in some cases, higher than that by means of a fresh solution. Alternatively, the conditioned biolixiviate solution can also be used to agglomerate the mineral as it is placed on the pile. Since ferric ions promote the bioxidation process, it would be beneficial to include almost 5 to 20 g / 1 of ferric ion in the conditioned solution 22. A potential source of ferric ions is the depleted solution of biolixiviate that comes from the battery 10 Before conditioning, the depleted solution of biolixiviate from stack 10 will typically have a high concentration of ferric ions. In a variation to the present inclusion, the conditioning circuit 20 is separated into a preliminary softening stage and a final softening stage. This two-step precipitation process allows the recovery of ferric ions from the spent solution for subsequent addition to the conditioned solution 22. Thus, in the present variation, instead of raising the pH of the spent solution of biolixiviate at least at 5.0, an intermediate pH adjustment is carried out first, in which the pH of the exhausted solution of biolixiviate is adjusted to the scale of about 3.0 to 4.0. Within this scale, most of the ferric ion in solution must precipitate, while at the same time it must minimize, to the greatest extent possible, the amount of inhibitory metals and other materials precipitated from the spent solution. The amount of inhibiting materials precipitated during the preliminary softening step is minimized because many of the inhibiting materials present in the spent solution will not precipitate, unless the pH of the spent solution is adjusted to a higher pH than when minus 5.0 After the pH of the depleted solution of biolixiviate is adjusted to the scale of 3.0 to 4.0, any precipitate that forms is separated from the spent aqueous solution. This precipitate will have a high concentration of precipitated ferric ion and can be redissolved in conditioned biolixiviate solution 22. After removing the precipitate formed during the preliminary softening stage, the spent solution is subjected to a final softening stage, in which the pH of the solution is raised as described above to a pH of at least 5.0, and preferably at a pH of about 5.5 to 6.0 to precipitate the volume of the remaining inhibitory components in the spent solution. The freshly formed precipitates are then removed and the pH of the solution is reduced again to the optimal scale of 1.2 to 2.6 for bioxidation. More preferably, the pH of the solution is reduced back to the scale of about 1.7 to 1.9. The conditioning of the spent solution of biolixiviato is now complete. The ferric ion concentration of the conditioned depleted solution can now be adjusted to the preferred scale of 5 to 20 g / 1 using an appropriate amount of the ferric ion precipitate formed during the preliminary softening step. The conditioned depleted solution is now able to be added to the pile 10 or used to agglomerate the mineral as it is placed on the pile. It is economically preferred for the flow rate of the biolixiviate solution through the ore, which is as low as possible. In the case of minerals that require purification or conditioning of the effluent solution before it can be reapplied, the preferred flow rate of the biolixiviate through the pile ranges from 0.0005 to 0.003 gpm / piee2. If the solution of biolixiviate applied to the pile contains almost 5 to 20 g / 1 of ferric ion, then the flow rate of the biolixiviate through the pile can rise to approximately 0.01 gpm / ft58. In the case of minerals that produce toxic materials while they are being leached, the movement of fresh or purified solution through the pile will allow the development of bacteria at least at the top of the pile. The bacteria will grow in the pile as fast as the elution of the toxic materials allows. This intensity of bacterial penetration may vary, and may be difficult to determine. However, the ferric ions produced by bacteria in the upper part of the pile, or those added to the solution of biolixiviato antee of the application to the pile, will migrate to the bottom of the pile, where bacterial growth can be inhibited. This will allow bioxidation to run its course even when the growth of bacteria is not favored. By this method, ore that contains toxic elements or that produces any toxic material as it oxidizes, can biodegrade in a pile by recirculating detoxified solution back to the top of the pile, rather than simply reusing the draining solution without treatment. Based on the teachings included herein, in many cases, those skilled in the art will recognize from just the ore test, that the refractory sulfide ore they are processing poses a problem with respect to the accumulation of a metalworking combination. inhibitors in the exhausted biolixiviato solution. Based on this knowledge, a decision will be made to simply treat the depleted solution of biolixiviate on a continuous basis in a liming or lime-softening circuit of the type noted above, before recirculating the biolixiviate solution. Alternatively, those skilled in the art may decide to treat the biolixiviate solution after each step through the stack in the liming or limestone softening circuit simply as a prophylactic measure. Both procedures would be included within the teachings of the present invention. The present invention also contemplates processes in which the conditioning of the spent solution of biolixiviate is carried out in response to an affirmative determination that the spent solution is inhibitory to the bioxidation process. Those skilled in the art will readily recognize that there are nurnerosae techniques that can be used to determine whether the depleted solution of biolixiviate is inhibitory. Many of the techniques may not specifically determine the concentration of individual inhibitory materials. In addition, it is preferred that techniques be used that simply contemplate whether the bioxidation in the solution deteriorates when compared to a positive control. This is because the concentration of inhibitor materials present in a solution exhausted from biolixiviato will change continuously, depending on factors such as where the mineral was obtained in the body of the mineral and how far the process of bioxidation has advanced. Therefore, it would be very difficult, if not impossible, to try to determine whether a particular combination of inhibitory materials at a given concentration is inhibitory simply by observing the concentrations of the inhibitory materials in the spent solution. On the other hand, by comparing the performance of the spent solution with a positive control, it can be easily determined whether the combined concentration of the inhibitory materials in the spent solution is inhibitory. In addition, such proof does not need to be carried out on a continuous basis. Rather, during the pilot or mineral column test, the typical period in which the inhibitory concentrations of toxins or inhibitory matter can be leached from the mineral can be determined. From this knowledge, those skilled in the art can easily determine how much the bioxidation process should proceed in its course before the exhausted biolixiviate solution can safely be recycled without conditioning to remove the inhibitory materials. Preferably, however, the toxicity of the spent solution of biolixiviate for the bioxidation microorganism is tested on a continuous basis. In this way, it can be determined whether the depleted solution of biolixiviate is inhibitory, the degree to which it inhibits the bioxidation process and which methods of treatment suppress inhibition more adequately. The two following test techniques are preferred to determine the toxicity of the solution towards the bioxidation microorganism. The first, a test of spectrophotometric activity, is based on the absorbance of the ferric ion (Fe3 *) at 304 nm. This procedure is a modification of the method described by Steiner and Lazaroff, Applied Microbioloov. 28: 872-880, 1974, incorporated herein by reference, to determine the concentration of ferric ion in a solution. According to this test, samples containing a known number of bacteria, the test solution and ferrous sulfate, are monitored over time (often 5 to 20 minutes) by measuring their absorbance at 304 nm. These absorbances are compared with time with a standard curve that relates the aberration with the concentration of the ferric ion. As a result, a curve is obtained that describes the rate of ion oxidation by bacteria. The oxidation rates of the ion by the bacteria in different solutions can be compared deep directly, giving an indication of the ability of the solution to inhibit this activity. Solutions that delay the rate of oxidation of the ion by bacteria are considered toxic or inhibitory. A plate test is the second preferred method to measure the toxicity of the spent solution of biolixiviate. The spectrophotometric test is very sensitive to the ferric ion concentration. It has only a useful concentration scale of almost 0.1-1000 ppm ferric ion. The micro-label plate test was developed to show high concentrations of ferric ion. As in the previous test, the test mixtures include a known number of bacteria, test solution and ferrous sulfate. However, in this test, the redox potential (Eh) of the sample is measured with respect to time (often 24 to 48 hours). The redox potential is a measure of the ratio of ferric ion to ferrous ion in solution, where the higher redox potentials indicate a high percentage of ferric ion. By knowing the percentage of ferrous ion in the starting material, the percentage of ferrous ion at the end of the test, the total amount of iron (ferrous and ferric combined), and the milligrams of ferrous ion converted to ferric ion can be calculated. The activities of the bacteria in the different solutions are compared with a positive control on the basis of the milligrams of ferrous ion converted to ferric ion at the end of the test, which is when all the ferrous ion is converted to ferric ion in the Positive control sample. An advantage of the spectrophotometric and microtitre tests is that they allow rapid determination of the toxicity of specific substances. By using these tests, two types of toxicities to bacteria have been observed. They are known as "acute" and "chronic". The "acute" toxicity describes the inhibition of the ferrous ion oxidation with respect to the ferric ion, while the bacteria are in the spent solution; "Chronic" toxicity describes the ability of an exhausted solution to inhibit bacterial oxidation by bacteria that have been removed from the solution, washed and placed in a fresh medium of ferrous sulfate. The spectrophotometric test can be used to test the "chronic" toxicity of the solutions and the "acute" toxicity of the solutions that do not contain large amounts of ferric ion (ie, solutions containing <1000 pprn Fe). The microtiter test can be used to measure the "acute" and "chronic" toxicities of the solutions. These tests can also be used in combination, to test the "chronic" and "acute" toxicities of a solution. The microtiter plate test is carried out first, for 24 to 48 hours, during which the time in which the oxidation of the ion by bacteria in solution is measured ("acute" toxicity test). The bacteria are then removed from the test plate, pelleted, washed and resuspended in a ferrous sulfate solution. This suspension is monitored at 304 nm to observe the increase in ferric ion over time ("chronic" toxicity test). By combining these two tests, the ability of a solution to produce immediate and / or lasting toxicity can be determined. In a preferred variation of the present invention, instead of conditioning the total volume of the spent solution, only a portion of the spent solution is treated to remove the inhibitory materials. The conditioned portion is then replenished with the non-conditioned portion to dilute the inhibitor materials therein present prior to recirculation. This variation is particularly preferred when softening with lime or limestone is used as the conditioning method, since less lime or limestone is required. After the precipitates have been removed from the conditioned depleted solution, the unconditioned portion of the spent solution can be used to reduce the pH of the conditioned portion back to the optimal scale for bioxidation. Preferably almost 70% to 85%, more preferably almost 70% to 80% of the solution exhausted from biolixiviate, are conditioned by softening with lime or limestone. In this way, approximately the same amount of lime or limestone is required to raise the pH of the treated volume of solution to the preferred conditioning pH scale of 5.5 to 6.0, as required to raise the pH of the entire depleted solution of biolixiviate up to the preferred bioxidation pH of almost 1.7 to 1.9. This is due to the buffering capacity of the biolixiviato solution. Thus, when the treated and untreated portions are recombined, the final pH of the whole depleted solution of conditioned biolixiviate should be within the optimum range of about 1.7 to 1.9 for bioxidation. If this is not the case, minor adjustments can be made using concentrated acid or acid from the drainage and washing circuit. Even though only 70 to 85% of the spent solution is actually treated in this variation, sufficient inhibitory materials are removed from this portion of the spent solution, so that when it is recombined with the remaining 15 to 30% of the solution spent untreated, the bioxidation rate of all the conditioned depleted solution substantially improves. Aei, this variation has the advantage of removing a substantial portion of the inhibitor materials from the depleted solution of biolixiviate, while using almost the same amount of lime or limestone as is required to adjust the pH again from the entire spent solution to the optimal scale for bioxidation. Instead of applying the conditioned biolixiviate solution 22 to the top of the stack 10, it can alternatively be applied to the top of the stack 28. And, to maintain an appropriate level of activity within the stack., as needed, biolixiviato solution can be added from tank 18 through line 32 to complement the conditioned biolixiviate solution applications 22 from stack 10. Pile 28, like stack 10, It is a pile of refractory particles of sulfide ore. However, compared to stack 10, stack 28 is in a more advanced stage of bioxidation. Because the stack 28 is in an advanced stage of bioxidation, most of the inhibitor materials have already been washed out of the stack 28. Thus, the effluent from this stack will have a high acidity (pH of almost 1), a high concentration of ferric ion and few inhibitory components. Therefore, the depleted solution of biolixiviate 30 in the cell 28 can be advantageously applied to the cell 10 which is in the first stages of the bioxidation process, since the high ferric ion concentration and the high acidity coupled with the Low levels of inhibitory components will accelerate the initiation of bioxidation. Also, the depleted solution of conditioned bioleaching 22 of the stack 10 can be applied to the more fully bioxided mineral of the stack 28. Since the more fully bioxided mineral of the stack 28 is very acidic, the biolixiviate solution applied should not be as acid when applied to a mineral that is less completely bioxidized. In addition, because the stack 28 contains fewer toxins, the rate of application of the biolixiviate solution to this stack can be reduced. Preferably, the pH of the solution that is applied to the stack 28 is on the scale of almost 2 to 3, instead of 1.7 to 1.9. Thus, acidic rnenoe is required to lower the pH of the exhausted solution of biolixiviate from cell 10 to the optimum scale of bioxidation for cell 28 after which it passes through softening with lime or with limestone in the cell circuit. conditioning 20. This means that a greater percentage of the spent solution can be treated in the conditioning process with lime or with limestone. To reiterate, the acidity of the effluent, the content of ferric ion and the content of inhibitor material from different bioxidation stacks (corresponding to minerals that have been biooxidated to different degrees), will be different. Any effluent that has a high combined concentration of inhibitory materials must be treated to remove the inhibitory components. Solutions applied to the different piles should be formed from mixtures of the existing effluent solutions. Optimal mixtures can be obtained, so that the solution applied to the stack at the beginning in the bioxidation process has a high content of ferric ion, high acidity and few inhibitory components. The solutions applied to piles more completely biooxidades can have a lower acidity. By using these optimal mixtures, the initiation of bioxidation should occur more rapidly, and the level of neutralization required should be less with a corresponding reduction in the costs associated with neutralization. In addition, acid additions will be reduced to a minimum. Minerals that have a high natural level of carbonate may require an excessive amount of acid to condition the mineral at the desired pH level for bioxidation. Waste acid generated from the drainage stack 12 or the bioxidation stack 28 is preferably used in such circumstances to condition this mineral. Waste acid should be used as much as possible to reduce the pH of the mineral, in order to minimize the neutralization requirements of the exhausted solution of biolixiviate. The system for handling the solution described in relation to figure 1 can also be used in conjunction with the process of bioxidation of the "racetrack" type battery illustrated in figure 2. The use of the "track" type battery "runs" of Figure 2 allows the present invention to be practiced in a more restricted area, when the space available for bioxidation is limited. According to FIG. 2, a circular stack 40 of the "race track" type is constantly being formed and reformed. Thus, the expansion zone of the stack 42, which represents the empty surface area, is gradually moving around the circle formed by the stack 40 of the "race track" type. As new layers of ore 44 are added on face 46, the agglomerated and preferably inoculated refractory sulfide particles approach the new face 45 of the newly inoculated mineral 44. From a front 43 removal part moves from similarly, the ore is taken to a cyanide leach pile as is known in the art. Also, a front wash portion 47 and its corresponding new wash front 48 illustrate the moving wash section 49 that is being treated to reduce the acidity of the biooxidized mineral in the "race track" type stack. The bioxidation in the stack 40 occurs in the bioxidation zone 41 between the front part of the washing in motion and the front part of the mineral in motion. In the following examples, various aspects of the invention are extended and used as illustration, but are not limiting of the invention described herein.

EXAMPLE 1 The strain of Thiohacillus ferroo irianp. used in the present example was initially harvested from a culture consisting of a consortium of ATCC 14119, ATCC 19859, ATCC 23270 and ATCC 33020. However, the culture currently used by the inventor is no longer pure. Over time, this crop has been contaminated with wild strains. A deposit of this culture was made on October 25, 1995, with ATCC 55718. The present experiment was conducted to test the senebility of the modified strain of T. ferrooxi ans to individual metals found in the effluent from a column that It contains particles of refractory sulfide ore from a sample of ore from the Gilt Edge Mine, which is located in South Dakota. The effluent of biolixiviate or spent solution as a whole was found to be inhibitor-for the bioxidation process.

The ore sample from the Gilt Edge Mine within the bioxidation column consisted of 8 kg of -95cm ore. An inductively coupled plasma emission spectroscopy ("ICP") analysis of the biolixiviate effluent solution of this mineral was conducted to determine the concentration of inhibitory metals therein. Individual tests were then prepared with metal concentrations identical to or slightly higher than those determined by the ICP analysis of the effluent. The metals were added to the analysis as metal salts, mainly as sulfate salts. The individual metals were then tested for their ability to inhibit the oxidation of ferrous sulfate by T. ferrooxidans. To determine if there was any inhibitory effect observed as a result of the concentration of the individual metal, each test was compared against a positive control. Table 1 below lists the metals that are present in the effluent, the concentration of each metal in the effluent and in the individual tests, and if an inhibitory effect was observed in the test.

TABLE i Based on these results, additional tests were conducted for aluminum and zinc to determine the minimum toxic levels for metals. In addition, tellurium, molybdenum and copper were tested to determine the minimum concentration at which these metals inhibit the bioxidation process. With respect to aluminum and zinc, the sulfate salts of these metals were used for this test in place of the chloride salts. In this test, no inhibitory effect was observed at the maximum tested concentration, which was 5000 ppm for aluminum and 2000 ppm for zinc. The chlorine salts of this and other metals showed slight inhibition of iron oxidation at 0.2% chlorine, which increased to full toxicity at approximately 1% chloride ion. Therefore, the inhibitory effect observed for aluminum and zinc in the first test was due to the chloride ion and no inhibitory effect due to the metals themselves. The inhibitory effect observed in the manganese test was determined to be the result of an unknown artifact. This was concluded from the fact that when the original effluent was conditioned by increasing its pH to a value within the range of 5.0 to 6.0, the conditioned solution showed no inhibitory effect after readjustment of the pH for bioxidation. In fact, the conditioned effluent had an action as good or better than the positive control. However, solubilized manganese is a very difficult metal to leach out of the effluent. In fact, raising the pH of the effluent to a pH of 6.0 will not precipitate manganese from the biolixiviato solution. Therefore, although the conditioned effluent still contained the same amount of manganese as before conditioning, after the conditioning the effluent was no longer inhibitory. This means that an artifact of some kind caused the manganese test to show a minimal level of inhibition, and the inhibition was not due to manganese itself. Subsequent testing has indicated that the inhibitory effect observed in the manganese solution was due to the N03 counter-ion in the solution used and not to the manganese ion itself.

In summary, although the mineral effluent solution from the Gilt Edge Mine was an inhibitor for the bioxidation process, the concentration of non-individual rnetal contained within the solution was inhibitory. A summary of the individual metal toxicity tests made after the initial study are included in Table 2.

TABLE 2 As seen in Table 2, Mo inhibited the bioxidation rate of the modified T. ferrooxidans strain when its concentration reached > 50 ppm in the test solutions. In addition to the metals listed in Table 2, the sodium inhibitory effect was also tested using solutions containing various concentrations of Nasa O *. As a result of these tests, it was determined that Na was not toxic to the modified strain of T. ferrooxidans up to a concentration of approximately 1.2 m (Na).

EXAMPLE 2 Doe ore samples obtained from the Gilt Edge Mine in South Dakota were prepared for a biolixiviato shale flask test. The two mineral samples were milled for 20 minutes in a ball mill. A sample was mixed with janthate and floated in a laboratory flotation cell to form a pyrite concentrate. A portion of the pyrite concentrate was used to grow and acclimatize a culture mixed in a laboratory of bacteria Thiobacillus ferrQQXjcjans, to this mineral. The mineral was inoculated with 5 x 10ß cells / milliliter in a 9K salee medium at a concentration of 0.5 at a pH of 2.2 and a pulp density of approximately 10% (5g / 50 ml). The slightly larger pH was used to obtain a better growth of the cells. The composition of the normal 9K salts medium for T. ferrooxidans is listed below. The concentrations are provided in grams / liter. After the medium was prepared, the pH of the medium was adjusted to 2.2 using Hi2S0 *.

After 13 days of stirring at 250 rpn at 30 ° C, the bacteria solution was divided into two fractions. A fraction was used to inoculate the entire sample of ore that had been milled but not floated. The other fraction was used to inoculate the pyrite flotation concentrate. The pulp densities were 25% (250 g / 1000 ml) for the whole ore and 10% (70 g / 630 rnl) for the pyrite concentrate. The starting pH was 1.9 for each sample and the starting pH was approximately 460 mV for each. The samples were shaken at 250 rpm and kept at 3 ° C. Before the inoculation, a small sample of each was sent for metal analysis. The percentages of both iron and copper were used to calculate the total amount of iron and copper in each experiment. As the digestion proceeded, a small volume of liquid was removed and checked for soluble iron and copper. This was used to determine the total amount of iron and copper in solution. The total amount of iron and copper in solution was then used to calculate the percentage of each leached metal as the reaction proceeded. The time in days that these samples were taken as well as the iron and copper levels in pprn and the percentage lixiadiate and the Eh and pH are listed in table 3. On day 28, both ore samples were allowed to stand-to provide a supernatant that could be removed. The removed solution was replaced by 9K salts at a concentration of 0.5 to a pH of about 1.8. The bioxidation continued with the fresh solution. Shortly after the removal of this solution, which was high in inhibitory metals, the pH and the rate of leaching were increased. This effect can be seen graphically in Figures 3 and 4, which were prepared from the data in Table 3. After several weeks, the Eh and the speed of iron bidding were slow again. This indicated that toxic or inhibitory elements were again leached to the leach solution, and that the removal of these elements was important for the rapid bioxidation of this mineral or similar minerals.

TABLE 3 % Fe leached / H% Fe leached from all ore Fe X Fe decontaminated concentrate % of Cu leached / H% of Cu leached from all ore Cu% Cu% leached from the concentrate Eh H The Eh of the solution from a sample of complete mineral Eh ce The Eh of the solution from a sample of pyrite concentrate EXAMPLE 3 A second test was conducted with the mineral used in Example 2 to simulate a pile bioxidation process. The sample provided by Dakota Mining Corporation was crushed to -635cm material. To achieve a good air flow, the fine material (passing a 30 mesh screen) which represents approximately 20% by weight of this sample of 16 Kg was removed. A sample of 7.8 Kg of the mesh + 30 ee mineral mixed with sulfuric acid and 9K salts at a concentration of 0.5 to moisten the mineral and reduce the pH below 2.0. The wet mineral was placed in a 7.62 cm column. by 1.82 meters. The air was introduced into the bottom and the liquid (salts of 9K at the concentration of 0.2, pH 1.8) and bacteria (~ 10't cell / g of mineral) were applied to the top of the column. The solution from the bottom of the column was analyzed for iron and copper, and the concentration of rnetalee in the solution samples removed from the column was used to calculate the total percentage of iron and leached copper. After 34 days, the solution from the column was applied directly to the top of the column without treatment. This was done to see if high ferric levels of recirculated solution would accelerate the leaching of pyrite. The leaching proceeded but very slowly. After 91 days, the column was changed back to a one-step system. Shortly after switching back to a seventh of a one-step solution, the leaching rate increased. The effects of this change are shown in Figure 5. The pH, Eh, Fe concentration and% Fe leached for the various test times of the effluent solution from the column are reported in Table 4.

EXAMPLE 4 Another column test was performed with the ore from the Gilt Edge Mine of Example 2. In this example, the -10 mesh material was removed from the ore, and the ore was only crushed at -952 cm. The ore was prepared as before and placed in a 7.62 cm by 1.82 m column with air from the bottom and liquid from the top as in example 3. In addition, only fresh solution was introduced from the top of the column. column. The leaching rate was determined by the amount of metal removed as before. The percentage of leached iron is plotted in figure 6 for comparison with figure 5, which represents the column of whole ore in example 3. From this comparison, it can be seen that the recirculation of leaching solution was inhibitory at the speed of bioxidation. The pH, Eh and% of Fe leached at the different times of testing the effluent solution are reported in table 5.

TABLE R AXIS? PLQ 5 The effluent from the stack bioxidation field test using 4,750 dry short tons of refractory sulfide ore from the Gilt Edge Mine mine near Dead? Ood, South Dakota was collected 63 days into the test. This mineral contained approximately 5.5% sulfides such as sulfur and 1.78 g. of Au / ton of ore. The bioxidation rate as measured by changes in sulfate concentration in the effluent solution was lower than desired due to the concentration of inhibitor components in the effluent solution. In the effluent solution. The effluent solution was recirculated and applied to the test stack without conditioning. The samples of the effluent were adjusted to several pH to evaluate the minimum pH for the removal of the toxic components. The effluent had a pH of 2.0. Aliquots of the effluent were adjusted to 3.0, 3.5, 4.0, 4.5, 5.0, and 5.5, with lime, in separate tubes. The supernatant of aliquotua tin was collected for inhibition tests with Thiobacill.ua ferrooxidans. Ferrous sulfate heptahydrate was added to each supernatant at a concentration of 30 ° per liter, and the pH was adjusted to 1.7-1.9 with sulfuric acid. The electrochemical potential (Eh) of each solution was recorded (time 0), the solutions were inoculated with T. ferrooxidans. and were stirred at 34 ° C overnight. The change in Eh was monitored as an indication of bioxidation of the ferrous iron. The results are tabulated in table 6 below. The highest pH supernatant, at 5.5, consistently produced the highest Eh (highest ferric concentration), and flying or surpassing the positive control. The lower pH supernatants showed a lower increase in the Eh of the sample, indicative of a lower level of bacterial activity, suggesting incomplete removal of the toxins from the solution as illustrated in Figure 7. Adjusting the fluent solution to a pH of 5.5 or higher, however, was necessary and sufficient to precipitate all the inhibitory components in the effluent solution for this mineral. A further sample of the effluent solution was adjusted to pH 6, with lime, producing a sludge. Without removing the mud, the pH became adjusted to 1.8. The liquid resulting from this mixture was tested for toxicity to L. ferro ida s. The toxicity of the readjusted mixture was the same as that of the original effluent solution, indicating that all the toxic components were precipitated in the mud at a pH >; 5.5. and then dr again sulubilized during the adjustment back to a pH of 1.8 as illustrated in figure 8 this example shows the need to remove the metal precipitates during softening with lime or limestone before the pH of the solutions Re-adjust TABLE 6 EXAMPLE 6 A pile bio-oxidation field test that used 4,750 dry short tons of refractory sulfide ore from the GiH mine: Edge Mine near Deadwood, South Dakota was carried out. The test mineral contained 5.5% sulfides, such as sulfur and 1.78 grams of gold per ton of gold. The extraction by means of conventional cyanidation tests by roller in bottle gave a recovery of 56%. After the pile was built, it was inoculated with T. ferrooxidans and bioxidation was initiated. During the pile bioxidation test, the degree of bioxidation was determined by examining the concentration of sulfate ions in the effluent solution. Graph 9 shows the degree of bioxidation as the% sulfides oxidized against time in the test. Approximately the first 60 days of the bioxidation test are depicted in Figure 9. All effluent from the stack was collected in containment tanks, and except as noted below, the effluent solution was recirculated to the top of the pile without conditioning. The effluent was recirculated to the top of the pile through drip emitters placed just below the surface of the ore. After the water inventory levels in the basin were established, a constant water inventory was maintained, establishing steady-state water circulation, achieved using a fixed application rate and supplementing with additional water to maintain a constant level in the tanks of containment. Initially, the field test showed a fast bio-oxidation rate, which quickly became slow. Deceleration corresponds to an increase in the solubilized metals observed including copper in the effluent solution. The initial bioxidation rate was 0.133% per day (day 3 to 13). During this time, the water inventory was established in the bioxidation pile and the fresh water was applied. With this continuous addition of fresh water the inhibitory components were kept diluted and did not affect the speed of bioxidation. After the fresh water was no longer added to the surface of the pile, on day 13 the bioxidation rate became slow. At about day 23, a charge neutralization of a portion of the cell effluent was conducted by raising the pH of the solution to about 5.5, removing the solid precipitates and then reducing the pH of the solution back to about 1.8. After this charge neutralization was performed, the bioxidation rate increased until about day 35 when leveled due to increased concentrations of solubilized metals. On day 38 approximately 10% of the effluent solution was adjusted to approximately pH 5.5, removing the inhibitory components. The bioxidation rate after the removal of these inhibitory components was improved until day 42 when the concentration of inhibitory metals suppressed the bioxidation rate. A small inflection point is also observed approximately on day 51 in Figure 9. This is due to the dilution of the inhibitory components in the effluent with fresh water. Seventy-one days in the pile operation a significant amount of fresh water in the form of rainfall was added to the pile. The rain represented approximately 50% increase in the solution inventory. The recirculation was maintained, producing a dilution of the circulating inhibitory components during a limited period. During the two weeks prior to rain, the concentration of the soluble sulphate in the recirculating solution increased linearly. After the rain, it took 8 days to re-establish a recirculation of steady state solution. For the next 2 weeks there was an increase in the speed of bioxidation. After the speed of bio-oxidation r-discharge to the levels seen before The rain. The timeline that illustrates important events and the speed of concentration of soluble sulfate increases during the previous weeks and after the first precipitation event is shown below: Day 57-71- Speed of increase in sulfate concentration was 168.4 ppm / di Day 72-80- 27.94 cm of fluvial precipitation Day 81-88- The stable state of recirculation is re-established. Day 89-96- The rate of increase of sulphate concentration was 223.5 pp / day Day 97.117- The speed the increase in sulfate concentration was 168.0 ppm / day.

Temporary dilution of the recirculating solution associated with the precipitation caused a decrease in the concentration of inhibitory materials. As a result, the rate of increase in the concentration of sulfate ion in the exhausted solution was accelerated. However, as the additional inhibitory components were leached from the ore and the solution inventory returned to its pre-precipitation levels, the bioxidation rate also returned to its pre-rain level. Later in the stack operation, a second major precipitation event occurred. This rain was 22.86 cm for 3 days. During this time, no recirculation of the effluent solution was conducted, so that the rain produced a runoff of the inhibitory components of the test cell. All the effluent that drained from the pile was discarded. The ion sulfate concentration, the total liquid discharged and the total kilograms of sulphate discarded during the previous periods, during and after the rain are shown in table 7.

PICTURE. 7 The concentration and total amount of sulfate discarded from the test stack increased as a result of the rain wash, which indicates that the inhibitor compounds were removed from the pile and that the velocity of bioxidation increased during the rest of the test. .

EXAMPLE 7 A three-column system was constructed to simulate a large-scale pile bioxidation process. Three loads of crushed and agglomerated ore of .952 cm that had been sprayed with bacteria, each of approximately 8 kg, was placed in three different columns having a diameter of 7.62 crn and a height of 1824 meters. Only the first three columns were provided with airflow. The other two columns were closed to stimulate the air limitation that could occur in a large pile. The test was started by applying fresh 9 K salts at a concentration of 0.2 which had a pH of 1.8 at the upper part of the first column at the rate of approximately 200 rnl / day or 0.029 1 / m2 / min. After about 3 days, the solution eluted from the bottom of the first column was pumped onto the second column without any treatment. After another 3 days, the solution eluted from the second column was pumped into the third column. The solution eluted from the third column was collected until the volume was one liter. Deepuée of 15 days of operation, the first liter was treated with limestone powder to raise the pH to approximately 5.5. The precipitate was removed by filtration. The treated solution was then mixed again with spent solution untreated at the rate of 85% tr-linked solution (approximately pH 5.5) and 15% untreated solution (pH 1.6 or lower). If the resulting mixture was about pH 2.0 then sulfuric acid was used to adjust the pH back to 2.0 or lower. After 18 days from the start of the operation, the mixture of spent and untreated spent solution was used to replace the addition of fresh solution of pH 1.8 to the first column. Over time, the volume of liquid decreased to the point where the fresh solution had to be added to the system to compensate for the water removed in the process of precipitation and loss to evaporation. This system was intended to mimic a field operation where as much water as possible was recirculated. This system also used the acid generated from the bioxidation process to adjust the pH back to a value below 2 after treatment with lime or limestone. The first recirculated solution required approximately 10 days to move through the tree columns. A small drop in the rate of bioxidation was noted between the period between day 29 and day 31. The recirculated solution was first used on day 18 and required 1.0 days to pass through the three columns. This meant that it would be day 28 when a change would show up in the speed of bioxiation. The rate of iron leaching fell from 0.132% / day to 0.103% / day. This change was considered small enough for the system to be functioning in the removal of the toxic metal accumulation in the solution exhausted from biolixiviato. further, the reuse of most of the water in the system was considered of sufficient economic value to justify the small drop in the speed of bioxidation with respect to the speed obtainable using only fresh solution. The pH, Eh, Fe concentration and leached Fe% are reported in the following quad-8 for several times in the bioxiviation procedure. These values were determined by testing the battery effluent at the times indicated in the table.

TABLE 8 EXAMPLE 8 This test was conducted to determine the acute and chronic toxicity of the modified strain T. ferrooxidans used by the inventors. Dilutions of a source produced in the early stages of a column biooxidation were tested using the microtitre plate assay for their ability to inhibit the oxidizing activity of the iron of T. ferrooxidans ("acute" toxicity). As shown in Figure 10, when compared to a positive control sample of T. ferrooxidans in a ferrous sulfate medium, only the 1:10 and 1: 5 dilutions allowed adequate oxidation of the iron. Minor dilutions (1: 2 and undiluted) inhibited most of the iron oxidizing activity in the cells. The "chronic" toxicity of the effluent dilutions was immediately tested with the spectrophotometric activity assay. The test cells with microtitre plates were pooled, washed and resuspended in a medium of 9K salts and 0.2 resistance to which 2 rng / ml of ferrous sulfate was added. The concentration of ferric ion produced with respect to time was measured and plotted in figure 11. Activity ratios were calculated from the curves resulting from Figure 11. These values are given in Table 9. The activities of the Cells exposed to the effluent, in fresh medium, were similar to the activities of the cells in the effluent. Similar results were obtained when the spectrophotometric activity assay was repeated after overnight incubation of the cells in a ferrous sulfate medium. The results suggest that the effluent can inhibit the cells for some time after they are removed from direct contact with the inhibitory effluent.

TABLE g EXAMPLE 9 As discussed above, a method to treat a bio-oxidation effluent that is inhibitory to T.

Ferrooxidans is raising the pH enough to precipitate the inhibitory substances and then readjusting the pH to the optimal scale for biooxidation after extracting the precipitates. This procedure was performed with the effluent of example 8, and the resulting supernatant solutions were tested and as for s? ability to inhibit bacteria in the assay with rnicrotitulación plate. The results, shown in Figure 12, indicate that the inhibition is eliminated with a pH between 5 and 6. The partial activation of a supernatant solution with pH 5 is seen and the complete activity is established with a pH of 6.

EXAMPLE 10 The present example is described in connection with Figure 13, which illustrates a preferred system for controlling the solutions according to the present invention to produce a spent solution of conditioned biolixiviate 66 that can be recirculated to a sulfide refractory unit stack for promote biooxidation with little or no inhibitory effect.

According to the present example, an exhausted solution of biolixiviate containing a multitude of inhibitory metals is gathered in a storage tank 50. The spent biolixiviate solution of one or more piles is assembled in biooxidation and, in addition to having a multitude of inhibitory metals , the spent solution will characteristically contain approximately 10-30 g / 1 of ferric ion and will have a pH of 1.0 to 1.5. In addition, due to the combined consentration of at least doe of the inhibitory metals, the biooxidation ratio in the stack of the depleted solution of biolixiviate is inhibited compared to a positive control. To minimize the amount of alkaline material required to condition the spent solution, approximately 70 to 90% of the spent bioleaching solution pooled is pumped to a preliminary softening tank 52 and the other 10 to 30% of the spent solution is pumped. of biolixiviate collected directly to the mixer tank 54. The spent solution of biolixiviate pumped into the preliminary softening tank 52 is subjected to a preliminary softening. This is achieved by raising the pH of the spent biolixiviate solution to a pH sufficient to precipitate the ferric ion in solution while minimizing the amount of precipitated inhibitory metals. Characteristically? PH in the scale of approximately 3.0 to 4.0 will be sufficient to achieve this goal.

The pH of the spent biolix solution can be elevated or sent to the preliminary softening tank 52 using any strong base, including powdered limestone, lime or sodium hydroxide.

The precipitate 58 formed during the preliminary softening is separated from the previously treated depleted solution 56. The precipitate 58, which will be high in ferric ion, is then pumped in slurry form to the mixing tank 54 and the spent pretreated solution 56 is pumped to the softening tank 60. It rises after the pH of the previously treated solution 56 to a pH of at least 5.0 and preferably to a pH within the range of about 5.5 to 6.0, in the softening tank 60 using limestone or lime. The precipitate 62 formed during this final softening step is removed and sent to waste treatment for disposal. The precipitate 62 should contain most of the inhibitory metals remaining in the pretreated depleted solution 56. The aqueous supernatant solution 64 produced in the softening tank 60 is pumped to the mixing tank 54. The pH of the aqueous supernatant solution 64 will depend on the pH that is used to continue to soften the previously spent depleted solution 56 in the softening tank 60. However, it will characteristically be on the scale of about 5.5 to 6.0. The aqueous supernatant solution 64 should be substantially free of inhibitory metals at this point.

The spent solution of untreated biolixiviate pumped from the storage tank 50 to the mixing tank 54, the precipitate 58 and the aqueous supernatant solution 64 are combined in the mixing tank 54. The acid in the spent solution of untreated biolixiviate will be sufficient to decrease the pH of the whole solution in the mixing tank 54 to the scale of approximately 1.5 to 2.0 and concordantly to redissolve the ferric precipitate 58 in the mixture. If the final pH of the solution in the mixing tank 54 is reached outside the desired scale for biooxidation, appropriate adjustments can be made by subsequent acid or base additions. The final concentration of ferric ion in the solution of the mixing tank 54 should be in the range of about 5 to 20 g / 1. In this way, only enough ferric precipitate 58 needs to be added to mixer tank 54 to result in a final concentration within this scale. Excess precipitate 58 can be stored or sent to waste treatment for disposal.

Once the pH of the solution is adjusted within the mixer-54 tank at an appropriate pH for biooxidation, and the ferric ion concentration of the solution is within the preferred range of 5 to 20 g / 1, the conditioning of the exhausted biolixiviate solution is complete and the conditioned biolixiviato 66 solution is conditioned and pumped to the storage tank 68 from which it can be pumped to a sulfide refinery mineral pile to promote biooxidation. Alternatively, the spent conditioned biolixiviate solution 66 can be used to agglomerate the sulfide refractory ore particles during the stack formation process.

Although the invention has been described with reference to the preferred embodiments and specific examples, it will be immediately appreciated by those of ordinary skill in the art that many modifications and adaptations of the invention are possible without departing from the spirit and scope of the invention as it is claimed below.

Claims (46)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for improving the rate of bioxidation in a sulfide refractory mineral particle stack that is at least partially bioxidated using a recirculated biolixiviate depleted solution, comprising the procedure of: a) bioxidizing a stack consisting of refractory mineral particles of sulfur with the biolixiviato solution and thus producing a spent solution of biolixiviate which includes a multitude of inhibitory materials dissolved therein, wherein the concentration of each individual inhibitory material in the spent solution of biolixiviate is below its individual inhibitory concentration and the combined concentration of at least two of the inhibitory materials is sufficient to inhibit the rate of bioxidation of sulfide refractory ore particles in the ore; b) collecting the spent solution of biolixiviato from the cell; c) conditioning the spent solution of biolixiviate to reduce the inhibitory effect caused by the combined concentration of at least two inhibitory materials; d) recirculate the exhausted solution of biolixiviate to the cell; and e) bioxidizing the refractory sulfide mineral particles in the stack with the exhausted solution of recirculated biolixiviate.

2. - A method for improving the rate of bioxidation in sulfur refractory mineral particle stack according to claim 1, further characterized in that the method for conditioning the exhausted solution of biolixiviate is at least one selected from the group consisting of softening with lime, softening with limestone, ion exchange, electrodeposition, iron cementation and reverse osmosis.

3. A method for improving the rate of bioxidation in a particle stack in sulfide refractory ore according to claim 1, further characterized in that the method of conditioning the spent solution of biolixiviate is at least one selected from the group consisting of of softening with lime and softening with limestone.

4. A method for improving the rate of bioxidation in a sulfur refractory mineral particle stack according to claim 3, further characterized in that the pH of the spent solution of biolixiviate is raised to a pH of at least 5.0 during the conditioning step.

5. A method for improving the rate of bioxidation in a sulfur refractory mineral particle stack according to claim 3, further characterized in that the pH of the spent solution of biolixiviate is raised to a pH in the range of 5.5 to 6.0. during the conditioning step.

6. A method for improving the rate of bioxidation in a pile of refractory sulfide mineral particles that are at least partially bioxided by using a solution that is depleted of biolixiviate or recirculated, comprising the procedure of: a) bioxidizing a battery composed of particles of refractory sulfur mineral with a solution of biolixiviato and thus producing a solution exhausted of biolixiviato that includes a multitude of inhibitory materials dissolved therein; b) collecting the spent solution of biolixiviato from the cell; c) raising the pH of the spent solution of biolixiviate to a pH higher than 5.0 and thus forming a precipitate; d) separating the precipitate from the exhausted solution of biolixiviate; e) to use the pH of the spent solution of the bioloxibiate at a pH suitable for bioxidation following the separation of the precipitate; f) recirculating the spent solution of biolixiviato to the cell; and g) bioxidizing the refractory sulfide mineral particles in the stack with the recirculated biolixiviate spent solution.

7. A method for improving the rate of bioxidation in a sulfur refractory mineral particle stack according to claim 6, further characterized in that the pH of the spent solution of biolixiviate is raised to a pH in the range of 5.5 to 6. "0.

8.- A method for improving the rate of bioxidation in sulfur refractory ore particle stack according to one of claims 6-7, further characterized in that the pH after the exhausted solution of biolixiviate is adjusted to a scale of 1.2 to 2.6 following the separation of the precipitate.

9. A method for improving the speed of bioxidation in sulfur refractory mineral particle stack according to claim 6, characterized in that the spent solution of biolixiviate is recirculated to the cell by means of a) Agglomerate the particles of refractory sulfide mineral with the spent solution of biolixiviato; and b) Add the agglomerated particles of the sulphide refractory ore to the pile.

10. A method to at least partially bioxide a stack consisting of sulphide refractory mineral particles using an exhausted solution of biolixiviate that includes a multitude of inhibitory materials dissolved therein, further characterized by the concentration in each inhibitory material individual in the depleted solution of biolixiviate is below its individual inhibitory concentration, yet the combined concentration of at least two of the inhibitory materials is sufficient to inhibit the rate of bioxidation of refractory sulfide mineral particles in the mineral, constant of the procedure of: a) Condition the spent solution of biolixiviate to reduce the inhibitory effect caused by the combined consideration of at least two inhibitory materials; b) Recirculate the exhausted solution of biolixiviato to the battery; and c) Bióxidar the particles of sulfide refractory ore in the pile with the solution exhausted of biolixiviato.

11.- A method in accordance with the claim 10, further characterized in that the conditioning of the spent solution of biolixiviate consists of: a) raising the pH of the spent solution of biolixiviate with pH of at least 5.0 to form a precipitate; b) separating the precipitate from the spent solution of biolixiviate; and c) adjusting the pH of the spent solution of biolixiviate to a pH suitable for bioxidation following the separation of the precipitate.

12.- A method according to the claim 11, further characterized in that the pH of the spent solution of biolixiviate is raised to a pH of at least 5.5.

13. A method according to one of claims 11-12, further characterized in that the pH of the spent solution of biolixiviate is adjusted to a scale of 1.2 to 2.6 following the separation of the precipitate.

14. A method according to one of claims 11-1.2, characterized in that the pH of the spent solution of biolixiviate is adjusted on a scale of 2 to 3 following the separation of the precipitate.

15. A method according to claim 10, further characterized in that the spent biolixiviato solution is obtained from the cell.

16. - A method in accordance with the claim 10, further characterized in that the exhausted biolixiviate solution is obtained from a second stack consisting of refractory sulfide mineral particles that are bio-oxidating.

17. A method for improving the speed of bioxylation in a sulfur refractory mineral particle stack according to claim 10, further characterized in that the exhausted solution of biolixiviate is circulated to the pile by a) agglomerating the refractory mineral particles. of sulfur with the spent solution of biolixiviate; and b) add the agglomerated particles of sulfide refractory ore to the pile.

18. A method for at least partially bioxidizing a stack consisting of refractory sulfide mineral particles using a spent solution of biolixiviate that includes a multitude of inhibitory materials dissolved therein, costing the procedure of: a) raising the pH of the depleted solution of biolixiviate with pH greater than 5.0 and thus forming a (precipitate; b) separating the precipitate from the solution exhausted from biolixiviate; c) adjusting the pH of the spent solution of biolixiviate to a pH suitable for bioxidation following the separation of the precipitate; d) recirculate the exhausted solution of biolixiviate to the cell; and e) bioxidizing the refractory sulfide mineral particles in the stack with the spent solution of biolixiviate.

19. - A method according to claim 18, characterized in that the pH of the spent solution of biolixiviate is raised to a pH of at least 5.5.

20. A method according to one of claims 18-19, characterized in that the pH of the spent solution of biolixiviate is adjusted to the scale of 1.2 to 2.6 following the separation of the precipitate.

21. A method according to one of claims 18-19, characterized in that the pH of the exhaustion of biolixiviate is adjusted to the scale of 2 to 3 following the separation of the precipitate.

22. A method according to claim 18, further characterized in that the exhausted solution of biolixiviate is obtained from the cell.

23.- A method in accordance with the claim 18, further characterized in that the exhausted solution of biolixiviate is obtained from a second stack consisting of refractory sulfide mineral particles that are being bio-oxidated.

24.- A method for improving the speed of bioxylation of a battery consisting of sulfide-refractory mineral particles which at least partially bioxide erases an exhausted biolixiviate solution which includes a multitude of inhibitory materials dispersed therein , further characterized in that the concentration of each individual inhibitory material in the depleted solution of biolixiviate is below its individual inhibitory concentration, yet the combined concentration of at least two of the inhibitory materials is sufficient to inhibit the bioxylation rate of the particles of sulfide refractory mineral in the ore, costing the procedure of: a) collecting the spent solution of biolixiviato; b) dividing the spent solution of biolixiviate into a first portion and a second portion; c) treating the first portion of the exhausted solution of biolixiviate to separate at least some of the inhibitory materials dislented therein; d) combining the first and second portions of the depleted solution of biolixiviate to thereby form a depleted solution of conditioned biolixiviate; e) recirculate the exhausted solution of biolixiviate conditioned to the cell; and f) bioxidizing sulfur refractory ore particles in the stack with the depleted solution of conditioned biolixiviate.

25. A method according to claim 24, further characterized in that the treatment method is selected at least within the group consisting of softening with lime, softening with limestone, ion exchange, electrodeposition, iron cementation and osmose inverea.

26. A method according to claim 24, further characterized in that the first portion comprises 70 to 90% of the spent biolixiviate solution pooled.

27. A method according to claim 24, further characterized in that the method for treating the first portion consists of: a) raising the pH of the first portion or a pH of at least 5.0 and thereby forming a precipitate; and b) separating the precipitate from the first portion.

28. A method in accordance with the claim 27, further characterized in that the pH of the first portion of the spent solution of biolixiviate is raised to a pH of at least 5.5.

29. A method according to claim 24, further characterized in that the method for treating the first portion consists of: a) raising the pH of the first portion to a pH in the range of 3.0 to 4.0 and thus forming a first precipitate that includes ferric ion; b) separating the first precipitate from the first portion; c) raising the pH of the first portion or a pH of at least 5.0 after separation of the first precipitate and thus forming a second precipitate; d) separating the second precipitate from the first portion.

30. A method according to claim 29, further comprising adding at least a portion of the first precipitate to the exhausted solution of biolixiviate conditioned to increase the ferric ion content.

31. A method according to claim 30, further characterized in that a sufficient quantity of the first precipitate is added to the exhausted conditioned biolixiviate solution to raise the ferric ion concentration of the conditioned bioleaching exhausted solution within the range of 5 to 20. g / 1.

32. A method according to claim 29, further characterized in that the first portion consists of 70 to 90% of the spent biolixiviato solution pooled.

A method according to one of claims 27-32, which further comprises the step of using the pH of the spent biolixiviate-depleted solution or a pH suitable for bioxidation.

34. A method in accordance with the claim 33, further characterized in that the pH of the conditioned solution of conditioned biolixiviate is adjusted to a pH in the range of 1.2 to 2.6.

35. A method for improving the bioxidation rate of a stack of refractory ore or sulfide particles that at least partially bio-oxidates using a depleted solution of biolixiviate, comprising the procedure of: a) raising the pH of the depleted solution of biolixiviato at a pH in the scale approximately 3.0 to 4.0 and thus form a first precipitate that includes ferric ions; b) separating the first precipitate from the solution exhausted from biolixiviate; c) raising the pH of the spent solution of biolixiviate to a pH of at least 5.0 following the separation of the first precipitate and thus forming a second precipitate; d) separating the second precipitate from the solution exhausted from biolixiviate; e) adjusting the pH of the spent solution of biolixiviate to a pH suitable for the bioxidation immediately after the separation of the second precipitate and thus forming a solution exhausted of conditioned biolixiviate; f) adding at least a portion of the first precipitate to the exhausted solution of conditioned biolixiviate; g) recirculate the exhausted solution of bioliquiviate conditioned to the cell; h) bioxidize the sulfur-refractory mineral particles in the pile with the exhausted solution of conditioned biolixiviate.

36. A method according to claim 35, further characterized in that the pH of the spent solution of biolixiviate is raised to a pH of at least 5.5 in step c).

37. A method according to claim 35, further characterized in that a sufficient quantity of the first precipitate is added to the exhausted solution of conditioned biolixiviate to raise the concentration of ferric ion of the spent solution of biolixiviate conditioned within the scale of 5 to 20 g / 1.

38. A method according to one of claims 35-37, further characterized in that the pH of the spent solution of biolixiviate is adjusted to the scale of 1.2 to 2.6 following the separation of the second precipitate.

39. A method for improving the bioxidation rate of a sulfide refractory ore particle stack that at least partially bio-oxidates using a depleted solution of biolixiviate, comprising the procedure of: a) collecting the spent biolixiviate solution; b) dividing the spent solution of biolixiviate into a first portion and a second portion; c) raising the pH of the first portion to a pH of at least 5.0 and thus forming a precipitate; d) separating the precipitate from the first portion; e) combining the first and second portions of the depleted solution of biolixiviate to thereby form a depleted solution of conditioned biolixiviate; f) recirculate the exhausted solution of biolixiviate conditioned to the cell; and g) bioxidizing the particles of sulphide refractory ore in the stack with the solution exhausted from conditioned biolixiviate.

40. A method according to claim 39, further characterized in that the first portion consists of 70 to 90% of the spent biolixiviato solution pooled.

41. A method in accordance with the claim 39, which further comprises the following steps, which are carried out before the step of raising the pH of the first portion to a pH of at least 5.0; a) raising the pH of the first portion to a pH scale of 3.0 to 4.0 and thus forming a precipitate containing ferric ion; and b) separating the precipitate containing ferric ion from the first portion.

42. A method according to claim 41, further comprising adding at least a portion of the precipitate that contains ferric ion to the exhausted solution of biolixiviate conditioned to increase its ferric ion content.

43. A method according to claim 42, further characterized in that a sufficient amount of the precipitate containing ferric ion is added to the exhausted solution of biolixiviate conditioned to raise the concentration of ferric ion of the spent solution of conditioned biolixiviate within the scale of 5 to 20 g / 1.

44. A method according to claim 41, further characterized in that the first portion consists of 70 to 90% of the spent biolixiviato solution pooled.

45. A method according to one of claims 39-44, further comprising the step of adjusting the pH of the exhausted solution of biolixiviate conditioned to a pH suitable for bioxidation.

46. A method according to claim 45, further characterized in that the pH of the conditioned biolixiviate-depleted solution is adjusted to a pH in the range of 1.2 to 2.6.