MX2007011920A - Use of mining waste and concentrates containing pyrite, in the culture of iron-oxidizing and sulfer-oxidizing microorganisms as an energy source for bacterial growth. - Google Patents

Abstract

The invention publishes the use of mining products and sub-products that contain pyrite, such as copper concentrates, and waste from the process in which these concentrates are obtained, known as scavenger tail, as an energy source for the large-scale culture of an association of microorganisms that are useful for ore bioleaching, and that includes both isolated microorganisms, and native microorganisms from the worked ores. In particular, the invention publishes the use of mining waste known as scavenger tail from the flotation process, in the culture of an association of isolated microorganisms of the Acidithiobacillus ferrooxidans y Acidithiobacillus thiooxidans type together, with or without other native microorganisms from the worked ores.

Description

USE OF CONCENTRATES AND MINING WASTE CONTAINING PIRITE, IN THE CULTIVATION OF OXIDIZING IRON AND SULFOOXIDANT MICROORGANISMS AS AN SOURCE OF ENERGY FOR GROWTH BACTERIAL.

FIELD OF THE INVENTION The invention discloses the use of mining products and by-products that contain pyrite, such as copper concentrates, and the residue of the process for obtaining said concentrates, known as "tail scavenger", as an energy source. for the large scale cultivation of a consortium of microorganisms useful in the bioleaching of minerals, and which comprises both isolated microorganisms and microorganisms native to the minerals that are exploited. In particular, the invention discloses the use of a mining residue known as "tail scavenger" of the flotation process, in the cultivation of a consortium of isolated microorganisms of the type Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans together, with or without other native microorganisms of the minerals that are exploited.

BACKGROUND OF THE INVENTION Typically, in the cultivation of microorganisms, artificial culture media, or preparations, are used. expressly, frequently from high purity organic and / or inorganic chemicals. This usually aims to control to the maximum the variables related to the requirements of microorganisms, and to avoid all potential sources of contamination and inhibition of microbial growth. For example, the growth of At. ferrooxidans and At. thiooxidans at laboratory scale has been respectively described by Silverman, M.P. & Lundgren D.G. 1959. "Studies on the chemoautotrophic iron bacterium ferrobacillus ferrooxidans I. An Improved Medium and a Harvesting Procedure for Securing High Cell Yields". Journal of Bacteriology. 77: 642-647, and Cook, T.M. 1964. "Growth of Thiobacillus thiooxidans in shaken culture". Journal of Bacteriology. 88: 620-623. The previous approach is very suitable for the cultivation of microorganisms on a laboratory scale, and sometimes even on a pilot scale, but due to economic considerations it may become impractical, especially if it involves the production of biomass on a large scale. A common solution to this problem is to use reagents of technical industrial grade, which reduces the cost of the medium, but the potential sources of contamination increase, besides adding impurities that can inhibit the growth of microorganisms. Thus, for the cultivation of microorganisms under industrial conditions, formulations based on ammonium sulfate and potassium phosphate of technical grade have been described (Hackl et al, U.S. Patent No. 5,089,412). In the same sense, Chilean patent applications CL 2731-2004 and CL 2101-2005 respectively use culture media known as modified 9K (3.0 g / L of (NH4) 2S04, 0.5 g / L of K2HP04, 0.5 g / L of MgSO4 * 7H20, 0.1 g / L of KCl and 0.1 g / L of Ca (N03) 2, 30 g / L of FeS04-7H20) and 9KS (3 , 0 g / L of (NH4) 2S04, 0.5 g / L of K2HP04, 0.5 g / L of MgSO4 * 7H20, 0.1 g / L of KCl, 0.1 g / L of Ca (N03) ) 2, 1% elemental sulfur or other reduced sulfur compound). It is known that in cultures of microorganisms in media such as those indicated, the final concentration of biomass is limited by the concentration of the substrate used as an energy source and by the inhibition of growth exerted both by said substrate and by the metabolism products of that, generated during microbial growth [LaCombe, J., Lueking, D. 1990. "Growth and maintenance of Thiobacillus ferrooxidans cells". Applied and Environmental Microbiology. 56: 2801-2806; Nagpal, S. 1997. "A structured odel for Thiobacillus ferrooxidans growth on ferrous Iron. "Biotechnology and Bioengineering 53. 310-319.] On the other hand, the type of microorganisms obtained depends on the type of energy source used., iron in the form of Fe2 + compounds for iron oxidizing microorganisms, and sulfur compounds - in oxidation state -2, 0 and +4 - for sulfur oxidizing microorganisms. This is a limitation for the design of a mixed biomass production process (iron and sulfur oxidant), by imposing different production conditions - substrates and pH - for each strain. In the case that it is desired to cultivate two or more species of microorganisms, it is attractive to use the same culture medium, or even more, to cultivate the microorganisms together. In this way, the number of stages of the process is reduced, the complexity of the operation is simplified, and in some cases the characteristics of the underlying biochemistry can be taken advantage of.

Iron sulfides, such as pyrite (FeS2), or the materials that contain them, are reduced iron and sulfur sources, and therefore, constitute an interesting alternative for the production of mixed leaching biomass.

Schippers, A., Jozsa, P.G., Sand, W. 1996. "Sulfur chemistry in bacterial leaching of pyrite". Applied and Environmental Microbiology. 62: 3424-3431, propose the formation of thiosulfate (S2032"") during the pyrite degradation cycle. Said compound can follow a series of abiotic reactions, or be used as an energy source by sulfur-oxidizing bacteria, which gives rise to the joint culture of ferrooxidant and thiooxidant microorganisms on materials containing pyrite. Finally, regarding the use of pyrite or materials that contain it, existing works raise different approaches, for example, in the patents WO0136693, WO0071763 and WO2004027100 its use as a source of sulfuric acid is proposed. In WO0136693 pyrite is associated to leaching systems in which sulfuric acid is not added; in WO0071763 its use is related to the replacement of the acid when the mineral presents a high demand for it; and in document O2004027100, its use is for the replacement of part of the necessary acid. In other documents such as US Pat. No. 6,110,253 and application US2005103162, pyrite is used as a mechanism for increasing the temperature of the cell, since it is biooxidated and generates heat that According to said text, it allows to practice bioleaching with thermophilic microorganisms. Other uses of pyrite are found, for example, in the works of Bacelar-Nicolau, P. & Jonson, B. 1999. "Leaching of pyrite by acidophilic heterotrophic iron-oxidizing bacteria in puree and mixed cultures". Applied and Environmental Microbiology. 65: 585-590, and Chong,. , Karamanev, D.G., Margaritas, A. 2002. "Effect of particle-particle shearing on the bioleaching of sulfide minerals". Biotechnology and Bioengineering. 80: 349-357, the growth of microorganisms such as At is demonstrated at a laboratory scale. ferrooxidans on pyrite as an energy source. However, the growth rate in this material seems to be affected by the friction between the solid particles. Therefore, as far as we know, the lack of lower-cost culture media that make viable large-scale production of microorganisms useful in bioleaching is maintained, and we are not aware of processes in which pyrite is effectively used as an energy source for biomass growth.

SUMMARY OF THE INVENTION For a better understanding of the processes, understand: a) ATCC: "American Type Culture Collection", American collection of cultures of microorganisms type. b) Bioleaching of minerals in rafts: a process carried out in a pond with a false bottom where the mineral is loaded by flooding it with the leaching solution which is circulated through the mineral particles, in the presence of acidophilic microorganisms, extracting the copper dissolved in an acid solution. c) Bioleaching of minerals in dumps: The minerals that are located under the cut-off law, which are extracted from an "open-pit" farm, are collected "run of mine" or with a primary crushing, in ravines that have appropriate characteristics for control the infiltration of solutions or surfaces where an impermeable folder has been previously installed and the leaching solution is irrigated on the surface, in the presence of acidophilic microorganisms, extracting copper dissolved in an acid solution at the base. d) Bioleaching of minerals in piles: In this process, the crushed ore at a defined granulometry is collected on a waterproof, low surface slope and the leaching solution is irrigated on the surface, in the presence of acidophilic microorganisms, extracting copper dissolved in an acid solution at the base. e) Bio-leaching of minerals "in si tu": Mineral deposits in the natural state or that have been fractured, due to previous mining operations, are leached directly in their place, irrigating the leaching solution on the surface, in the presence of acidophilic microorganisms, extracting by the base the copper dissolved in an acid solution. f) Biolixiviation of minerals in agitated tanks or reactors: the bioleaching process is carried out in a mechanically agitated pond where the finely divided mineral is mixed with the leaching solution, forming a pulp with a solids content of up to 20%, with the presence of Acidophilic microorganisms, extracting dissolved copper in an acidic solution. g) Biolixiviation of tailings dams: Tails coming from the flotation process and containing smaller amounts of the metal present in the ore are collected in dams, from where they are extracted to leach them either in piles or by agitation, in presence of acidophilic microorganisms, extracting the copper dissolved in an acid solution. Biomass: mass of living organisms produced in a given area or volume. Scavenger tail: Sands resulting from a float cell circuit of the sands of the main mineral cleaning circuit. DSM: "Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH" German collection of cultures of microorganisms type. Inoculum: pure or mixed bacterial culture that will act as an active biological material during the bioleaching process. Passivation: Decrease in the leaching rate of a mineral as a consequence of the accumulation of layers of sulfur and poly-sulfides on its surface. PLS: Aqueous solution generated in the bioleaching process that contains the metal ions leached from the ore. This solution constitutes the feeding of the solvent extraction plant. Refining: Aqueous acid solution exhausted in copper resulting from the solvent extraction process. o) Mixed energy source: substrate that allows the simultaneous growth of iron and sulfur oxidizing microorganisms. p) Mixed biomass: mass of microorganisms with the capacity to oxidize reduced iron and sulfur compounds.

BRIEF DESCRIPTION OF THE FIGURES Figure 1: The growth curve in batch mode of a consortium of microorganisms in culture medium modified with the incorporation of tail scavenger, according to what is described in Example 1, is presented in this figure. Figure 2: They are presented in this figure the content of At. Ferrooxidans Wenelen DSM 16786 (black bars) and At. Thiooxidans Licanantay DSM 17318 (white bars) in a continuously operated biomass propagation Zirreactor, using culture medium modified with the incorporation of scavenger tail, according to what is described in Example 2.

DETAILED DESCRIPTION OF THE INVENTION In order to produce on a large scale isolated microorganisms useful in the bioleaching of sulphided metal ores, a process has been developed, based on the use of bioreactors, in which it is possible to reduce the costs of culture media for the growth of said microorganisms. Said cost reduction is based on the use of concentrates, or a waste of the mineral flotation process that contains pyrite, such as the residue known as tail scavenger, to replace a part of the standard culture medium, as a source of energy of two microorganisms of different types that grow together, namely, Acidíthíobacíllus ferrooxidans and Acidithiobacillus thiooxidans. This process also provides advantages related to the quantity of microorganisms, their adaptation to the solid phase, and also provides advantages related to the recovery of copper and obtaining the iron to the +3 oxidation state. One of the possible residues to be used, the tail scavenger of the flotation process has a typical composition that is presented in Table 1. According to this composition, it has a content not less than pyrite, which reaches around 20% , and which can be advantageously used for the joint culture of indicated microorganisms.

Table 1: Mineralogical composition of the scavenger tail considering 100% opaque minerals Mineral%%% Mo is Weight Vol.% S% Cu% Fe% Zn Calcopir ita 2, 08 1, 51 0, 73 0, 72 0, 63 Calcosin at 0.53 0.29 0, 11 0.43 Covelin 0.62 0.41 0.21 0.41 Bornita 1.37 0, 82 0, 35 0.86 0, 15 Pyrite 19, 28 11, 76 10, 30 8, 98 Molibden ita 0, 94 0, 61 0.38 0.57 Sphalerite 0, 05 0, 04 0, 02 0, 04 Magnetit at 0, 21 0, 12 0, 15 Limonite 0.20 0, 16 0, 13 Rutile 0, 17 0, 12 Ganga 74, 54 84, 16 100, 0 100, 0 Total 0 0 12, 08 2.42 10, 05 0, 57 0, 04 As it has been known for some time, pyrite can be used as an energy source by microorganisms of the type Acidithiobacillus ferrooxidans, whose activity can be represented by the following formula FeS2 + 6Fe3 + + 3H20? 7Fe2 + + S2032 ~ + 6 H + 7Fe2 + + 7/4 02 + 7H? 7Fe3 + + 7/2 H20 + At. ferrooxidans FeS2 + 7/4 02 + H +? Fe3"+ S2032 '+ 1/2 H20 + At. Ferrooxidans reaction (i) As can be seen in reaction (i), one of the products is thiosulfate, which contemplates sulfur in an intermediate oxidation state, and which is useful as a source of energy for microorganisms of the Acidithiobacillus thiooxidans type, according to the following reaction : S2032"+ H20 + 202? 2S042" + 2H + + At. thiooxidans reaction (ii) Therefore, the simultaneous cultivation of microorganisms of the Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans type together with other microorganisms, takes advantage of the presence and formation of Suitable species as an energy source, respectively iron (II) and thiosulfate. Taking into account that part of the conventional culture medium has been replaced by a residue, such as the tail scavenger, which has no cost, it is obvious that this crop is less expensive than the crop using conventional means. In addition, by cultivating two microorganisms simultaneously, there are also cost reductions related to facilities, reactors, control systems, etc., which otherwise would have to be duplicated. Furthermore, the joint culture using the scavenger tail residue allows to obtain a higher concentration of microorganisms than is normally obtained when the same microorganisms are grown separately. This is of economic importance, which can be evaluated by reducing the equipment needed to obtain a certain target concentration when new installations are projected, or by a greater production capacity in facilities that are in operation.

From the studies carried out, which are presented later in the examples, it is possible to affirm that the consortium of microorganisms that contemplates isolated microorganisms mixed with microorganisms native to the minerals normally grows in the medium modified with tail residue scavenger. This constitutes an advance with respect to the state of the art, since it reduces the costs of cultivation by reducing the costs of the culture medium.

On the other hand, according to the reactions stated above, a higher concentration of the species Acidithiobacillus thiooxidans will naturally occur, or equivalently, a greater relative growth of the species Acidithiobacillus thiooxidans. This may or may not be advantageous, depending on considerations about the subsequent processes in which the generated biomass is used. However, if desired or if necessary, the growth of the microorganisms can be balanced by the incorporation of Fe + 2 in the ferrous sulfate form (FeS04-7H20). As noted, in practice the invention is verified by replacing a part of the standard culture medium of the microorganisms with a residue containing pyrite, for example, the scavenger tail of the mineral flotation process. The fraction of the culture medium that is replaced is that corresponding to the iron and sulfur species, being possible to replace it in a wide margin, for example, in a modified culture medium of According to the invention, between 1 and 100 g / L of tail scavenger can be used. On the other hand, and because the residues such as the scavenger glue contain solids, an adaptation of the microorganisms to the oxidation of sulfides in solid phase is achieved. This adaptation is useful, and it is also a step forward in the technique, since the microorganisms are adapted to the solid phase, they will quickly populate the materials stored in piles, dumps, tailings dams or other operations "in si tu", in the which are used, decreasing the times associated with the leaching of them. Additionally, copper present in the pyrite-containing waste, in particular in the tail scavenger, in which copper constitutes about 2.5%, will be released to the solution, remaining free to be recovered through the usual processes of copper recovery, increasing the overall performance of the process. Again this constitutes an advance, since in the state of the art the copper present in these residues is lost. Finally, and in accordance with the reactions presented above, an enrichment of iron to the +3 oxidation state in the culture medium occurs. As is known in the art, the presence of Fe3 + favors the leaching of secondary minerals, by which also represents an advantage over other processes.

EXAMPLE 1 In order to determine the growth kinetics and biomass yield of the Wenelen DSM 16786 and Licanantay DSM 17318 microorganism consortium using modified medium with the addition of scavenger tail, an experiment is performed using the following protocol.

PROTOCOL The bacterial growth was carried out in a reactor of 6 m3 of useful volume.

The culture medium used in the propagation of the microorganisms was prepared by suspending tail scavenger (at a pulp density of 1.25%) in a nutrient solution of the following composition: 75 g FeS04 / L, 0.99 g (NH4) 2S04 / L, 0.128g NaH2P04 | H20 / L, 0.0525g KH2P04 / L, 0, lg MgSO4 · 7H20 / L, 0.021g CaCl2 / L. The pH of the culture medium was adjusted to 1.8.

To start the culture, 5,400 L of culture medium were mixed with 600 L of bacterial inoculum, carrier of the microorganisms Wenelen DSM 16786 and Licanantay DSM 17318. To allow the growth of the microorganisms in the reactor, air enriched with 0 was supplied. 5% of C02. The temperature of the reactor was controlled at 30 ° C. The pH in the reactor was controlled by the addition of H2SO4. The reactor was operated in batch mode for 15 days. During the operation of the reactor, the growth of microorganisms was monitored by microscopic counting using a Petroff-Hausser chamber.

RESULTS As seen in Figure 1, there was a rapid increase in the concentration of microorganisms in the culture medium modified with scavenger tail, reaching a maximum concentration of microorganisms of l, 7xl09 cells / ml in 6 days. From the data obtained during the exponential growth phase it was possible to determine a specific growth rate of 0.069 h "1.

EXAMPLE 2 In order to demonstrate that the microorganism consortium Wenelen DSM 16786 and Licanantay DSM 17318 can effectively be propagated continuously using a modified medium with the addition of tail scavenger, an experiment is performed using the following protocol.

PROTOCOL Bacterial growth was carried out in a 50 m3 industrial reactor. The culture medium used in the propagation of microorganisms was prepared by suspending tail scavenger (at a pulp density of 0.125%) in a nutrient solution of the following composition: 8 g FeS04 / L, 0.99 g (NH4) 2S04 / L, 0.128 g NaH2P04 · H20 / L, 0.0525 g H2P04 / L, 0, lg MgSO4 · 7H20 / L, 0.021 g CaCl2 / L. The pH of the culture medium was adjusted to 1.8. To start the culture, 44 m3 of culture medium was mixed with 6 m3 of bacterial inoculum, carrier of the microorganisms Wenelen DSM 16786 and Licanantay DSM 17318. To allow the growth of the microorganisms in the reactor, air enriched with 0 was supplied. 5% of C02. The temperature of the reactor was controlled at 30 ° C. The pH in the reactor was controlled by the addition of H2SO4.

During the operation of the reactor, the growth of microorganisms was monitored by microscopic counting using a Petroff-Hausser chamber. The characterization of the microorganisms present in the reactor was performed by the quantitative PCR technique (qPCR). The reactor was operated in batch mode for 7 days, at the end of which the continuous operation of said reactor was started, by feeding the culture medium of the indicated composition at a rate of 360 L / h. During the continuous operation phase of the reactor, samples were taken for characterization by qPCR.

RESULTS As can be seen in Figure 2, the continuous operation of a bioreactor, using a modified medium with the addition of tail scavenger, effectively allows the spread of microorganisms of the At species. ferrooxidans and At. thiooxidans.

Advantages of the present invention: In order to evaluate the decrease in costs of the culture medium resulting from the incorporation of scavenger glue, a stack of 2,000 tons is considered; irrigated with a flow of 480 L / h for 365 days; with continuous inoculation at a concentration of 1-108 cells / mL.

The conditions indicated determine a need for microorganism production of 360 L / h at a concentration of 1.3 · 108 cells / ml. If a value of US $ 350.- per tonne of ferrous sulphate is considered, at a concentration of 8 g / 1 of ferrous sulphate, the total substitution of said reagent by tail scavenger would result in a saving of 8,830 dollars per year, since the tail scavenger has no cost. Typical tasks of copper mining involve the biolixivation of more than 2 million tons of ore per year (for example the Cerro Colorado site in Chile), so the savings associated with the use of pyrite instead of ferrous sulfate and a source of sulfur separately are more than US $ 8 million per year, making the continuous inoculation of bacteria to the process sustainable. In the case of using copper concentrates containing pyrite as an energy source for bacterial growth, the biolixed copper fraction is incorporated into the biolixivation solution together with the microorganisms, while the copper remaining in the concentrate can be sent to the casting in the form of a higher grade copper concentrate, by eliminating a much of the pyrite in the bacterial growth process.

Claims (4)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the content of the following CLAIMS is claimed as property. Use of concentrates and mining residues containing pyrite, CHARACTERIZED because they are used in the cultivation of iron oxidizing and sulfooxidant microorganisms as an energy source for bacterial growth in the process of bioleaching of minerals in reactors. Use of concentrates and mining residues containing pyrite, according to claim 1, CHARACTERIZED because the pyrite-containing residue used in the cultivation of microorganisms is tail scavenger corresponding to sands resulting from a mineral cleaning circuit of flotation cells. Use of concentrates and mining residues containing pyrite, according to claim 1 or 2, CHARACTERIZED because the iron oxidizing and sulfooxidant microorganisms are mixtures of microorganisms isolated with microorganisms native to the minerals that are exploited. 4. Use of concentrates and mining residues containing pyrite, according to claim 3, CHARACTERIZED because the isolated microorganisms that are used are Wenelen DSM 16786 and Licanantay DSM 17318