MXPA96003461A - . process for the treatment of materialcontamin - Google Patents

Abstract

The present invention relates to a process for decontaminating a medium, comprising a material contaminated with one or more organic species and one or more metallic species, the process comprising the steps of: treating a body of the medium by one or more microbial agents that split the contaminant or organic contaminants by or through the action of one or more microbial agents, the microbial agents are provided under aerobic conditions and a substantially neutral pH, followed by treating the body of sulfuric acid produced microbially, under aerobic conditions and a Substantial pH, in order to solubilize and leach the metal species as a metal sulfate, and treat the leached metal sulfate by a bioprecipitation process, under anaerobic conditions, which converts the sulfate to one or more insoluble metal sulphides

Description

PROCESS FOR THE TREATMENT OF CONTAMINATED MATERIAL DESCRIPTION OF THE INVENTION The present invention relates to a process for the treatment of contaminated material, in particular to a process for the treatment of organic and metallic contaminants, especially heavy metals, in a bulky, particulate material such as soil or topsoil using processes biochemical Throughout the world, substantial amounts of land have been contaminated with both organic and inorganic substances as a result of waste disposal, industrial and other activities. Examples of such pollutants include: toxic heavy metals that include mercury, cadmium, barium and lead, radionuclides such as y-actinides and fission products and organic pollutants such as btex (benzene, toluene, ethylbenzene and xylene), PAHs (polyaromatic hydrocarbons), PCBs (PCB) and dioxins. Such contaminants may pose a significant threat to groundwater and therefore supplies of drinking water in many still limit, or prevent reuse of the land. Additionally, as a result of recent legislation in the United States of America and probably similar legislation within the European Community and elsewhere, waste producers are becoming increasingly subject to prosecution and to cover the costs of recovery and cleanup, if they do not act responsibly towards their waste. Therefore, there is a growing need for technologies, which can solve the problem of contaminated land or land. To date, many techniques have been developed to remedy contaminated soil. Examples include: soil stabilization, electromigration, vitrification, volatilization, incineration, land washing, pumping and treatment systems, land agriculture, bioremediation in the suspension phase, etc. Many of these known techniques have several limitations, including: a) Lack of a permanent solution to the problem, for example transfer of the material to a toxic public landfill, or entrapment within matrices that have a limited duration; b) The impropriety to treat a wide range of pollutants, for example land contaminated with metal in the case of current biological processes; c) The generation of a high volume, or difficult to control secondary waste, for example land stabilization and incineration; d) Lack of selectivity of in situ or ex situ options as appropriate for a particular site, for example as in the case of incineration or washing of the land; e) High costs, for example incineration, vitrification and pumping and injection systems; f) Limited capacity to reuse pollutants, for example soil stabilization systems when applied to metals. The present invention seeks to solve these problems by allowing biological systems to recover the metal and organic contaminated media such as not specifically the earth. According to the present invention, a process for decontaminating a medium, comprising a material contaminated with one or more organic species and one or more metal species, comprising the steps of treating a body of the medium by a process which divides or unfolds the contaminant or organic contaminants by or through the action of microbial agents, followed by treatment of the same body with microbially produced sulfuric acid to solubilize and leach the metal species as a metal sulfate; and treating leached metal sulfate by a bioprecipitation process, which converts the sulfate to one or more insoluble metal sulphides. Advantageously, the process also includes the following steps: a) separation of hydrogen sulphide from insoluble metal sulphides. 5 b) Subsequent oxidation of the separated hydrogen sulfide to form a reusable source of the sulfur-containing ingredient. In the process of organic pollutants, They can also be split or divided by the action of 0 sulfuric acid produced microbially in the second stage of the process (elimination of the metallic species). In the first or stage of organic degradation of the process, the pH of the medium being treated, advantageously is in the range of 4 to 9. The microorganisms which unfold the organic compounds, can be present in the medium as species that are presented in natural form, for example as bacteria present in the soil or crops of them can be added to the environment. In any case, the nutrients are advantageously fed to promote the activity of the appropriate species. The microbial consortium used will depend on the type of organic contaminant present, which can be determined by the previous analysis of the environment and the nutrients will be selected accordingly. The enrichment of the medium by the addition of 5 different types of microorganisms to unfold the organic contaminants present is further described in the following. The organic contaminants may consist, for example, of benzene, toluene, other aromatics, PAHs or any of the other common organic contaminants mentioned above. The means to be decontaminated may consist of a particulate material such as soil, rock particles, dredging, sediments, sludge, process residues, slag from pyrolytic processes, kiln dust and the like. Contaminants can be contaminated on the surface of the particulate material or they can be bound within their particles. Several metallic species may be present in the medium and these can be. converted to various metal sulfates and subsequently bioprecipitated as diverse / f "metal sulfides" The term "metal species" as used herein, includes metals, alloys, metal salts, metalloids and metal-containing compounds and complexes Contaminants of the metallic species may include: i) actinides or their products of radioactive degradation or their compounds; 25 ii) fission products; iii) heavy metals or their compounds. Actinides are elements that have periodic numbers in the range of 89 to 104 inclusive. The term "fission product" as used herein, refers to those elements formed as direct products (or so-called "fission fragments") in the fission of nuclear fuel and the products formed from such direct products by beta decay. or internal transitions. Fission products include elements in the range of selenium to cerium in the Table Periodic Non-radioactive heavy metals that wish to be separated by the process of the present invention include toxic metals such as nickel, zinc, cadmium, copper, mercury and cobalt. These are commonly found as contaminants in the soil or in aquatic sediments near industrial plants, which have used chemical agents that contain these elements and in waste disposal sites. The metal contaminants separated by the process of the present invention can include a mixture of radioactive and non-radioactive metal contaminants. The particulate material is advantageously treated by leaching with biologically produced sulfuric acid using an aqueous leachate solution.

Where the environment that is going to be decontaminated includes land or land, this can be treated in if you or ex if you. In the latter case, the earth can be pretreated, for example to remove or crush large objects such as large stones, stones and the like. A suitable mixture of an aqueous solution containing biologically produced sulfuric acid and / or a source of bioconvertible sulfur material to sulfuric acid can be injected into or mixed with the soil. Other ingredients such as nitrogen-rich materials or materials rich in phosphorus and air can optionally be added. Bioconversion can be carried out in a known way by microbial agents present in the soil. The sulfur material may consist of either elemental sulfur or another reduced form of sulfur. Some addition of nutrients may be required to promote the microbial action necessary for the degradation of organic materials. The precise nature of these additions will be specific site and therefore selected. Where the earth or other particulate material, for example, process residues or slag, will be treated ex situ, can be treated in one or more known, suitable reactors. The ingredients mentioned in the above can be added to promote the elimination of organic materials and acid production.

Where the bioconversion to produce sulfate ions is carried out in the land to be treated, it can be brought about by the action of organisms that oxidize sulfur that occurs naturally, including: Thiobacillus ferooxidans, Thiobacillus thiooxidans and Thiobacillus neapoli tanue These organisms obtain the energy necessary for their growth by the oxidation of the reduced forms of sulfur, which produces sulfates and sulfuric acid or by the oxidation of ferrous iron to ferric iron. If the soil is deficient in appropriate microorganisms, or if the particulate material to be treated in a separate bioreactor, then these microorganisms can be added as a mixed consortium obtained from similar soil environments. In addition to the acid leaching mentioned above, the release of the metal can occur by one or more of the following mechanisms: a) direct attack of metal sulphides; b) by electrochemical processes (galvanic conversion), which results from contact between two different metal species immersed in suitable electrolytes, for example sulfuric acid; or c) by the oxidizing effect of ferric sulfate.

As an alternative to the production of biological acid in itself, the sulfuric acid required for the leaching process can be produced chemically or biochemically in a separate bioreactor and added to the soil or other particulate material after production. During the start of the process, elemental sulfur or sulfuric acid (production of biological acid in itself by derivation), can be used as the source of acid for leaching. Then, elemental sulfur or a combination of elemental sulfur and sulfuric acid, can be the main acid source. Elemental sulfur or sulfuric acid can be added to replace the loss of sulfur available from the system, such as metal sulphides. The leached solution can be allowed to percolate through and drain out of the body of particulate material. The leached solution thus collected can then either be recirculated through the particulate material or be pumped into a reactor to carry out the bioprecipitation process. The bioprecipitation step in the process of the present invention may be a per se known step, which may employ a consortium that occurs naturally of sulfate-reducing bacteria (SRB), to convert aqueous metal sulfates to metal sulphides. The microorganisms responsible for this transformation include: Desulfovibrio and Desulfomonas species and can be cultured in a closed bioreactor system. These organisms oxidize simple organic compounds such as lactic acid and ethanol, to derive the energy necessary for their growth. However, more complex carbon sources may be used occasionally, for example phenolic compounds, or possibly organic materials leached from the earth during bioleaching. As a consequence of this oxidation, sulfates are reduced to sulfides and water. As the sulphides of many heavy metals have low solubilities in aqueous solution, they precipitate along with some biomass such as a sludge inside the bioprecipitation reactor. The metal sulphides will normally be separated as mud and can be recovered and sold for the recovery of the metal, or in the case of toxic or radioactive metals, further immobilized in a subsequent process. The reduction of sulfuric acid entering the bioprecipitation stage, for example the reactor, of the metal leaching stage, will result in the production of hydrogen sulfide and the consequent reduction in the concentration of sulfuric acid. This results in maintaining a pH close to neutrality within the bioprecipitation stage and thus, an optimum pH for SRB activity. Additionally, the substantially neutral pH will cause the hydrogen sulfide to remain in the solution, thus maintaining a sufficiently low redox potential for the viability of SRB, ie <-300mV. The maintenance of an adequate redox potential by this method is common. Although the process has previously been used to maintain a suitable pH reactor (for example as in EP 436254A), it had not previously been used to buffer against incoming acid flows having a pH as low as pH 1.0 as it should be. from the acid leaching stage, described herein. As a result of the production of hydrogen sulphide and metal sulphides during bioprecipitation, three different product streams can be produced from the bioprecipitation process: (a) precipitated metal salts (eg sulphides and hydroxides) and some biomass; (b) aqueous hydrogen sulfide, soluble metal and sulfides together with some biomass; (c) gaseous hydrogen sulfide and carbon dioxide. The gaseous hydrogen sulfide can be extracted by a venting means, provided at or near the top of the reactor. The aqueous hydrogen sulfide and other soluble sulfides can be separated from the sludge. The metal sulphide sludge can be removed separately by means of adequate drainage in the reactor. Then the sludge can be dehydrated, collected and transported to another site, treated for metal recycling or treated by a suitable encapsulation process, for example fixation of the biologically enhanced metal. The gaseous and aqueous extracted hydrogen sulphide is a valuable source of reusable sulfur, which can be used by the biochemical oxidation process described in the following. During the initial stages of operation of the metal leaching stage of the process according to the present invention, the. leachate that enters the bioprecipitation, will possess a neutral pH. Therefore, a portion of this liquor can be used to dissolve the gaseous hydrogen sulfide effluent produced from the bioprecipitation. The two streams of aqueous hydrogen sulfide derived from bioprecipitation can be used separately, or preferably combined and oxidized within a closed bioreactor. The bioreactor may consist of a known system containing a consortium of organisms that oxidize sulfur, which occur naturally. Examples of microorganisms known to oxidize soluble sulfides include: Thiobacillus thioparus, T. neapoli tanus, T. doni trificans and Thiomicrospira. Two routes are possible for the oxidation of sulfur: (a) direct oxidation to sulfuric acid and sulfates; (b) oxidation to elemental sulfur, which can, if appropriate, be introduced into contaminated soil to produce sulfuric acid. Oxidation to elemental sulfur requires a limited oxygen environment, but has the advantage of providing a sulfur-free neutral pH liquor that can be used to dissolve hydrogen sulfide gas effluent from bioprecipitation. Sulfuric acid liquor produced by direct oxidation is more versatile for use in subsequent contact with contaminated soil. As noted in the above, the process of the present invention includes one or more stages for the elimination of organic contaminants from the contaminated medium and this may be by a recovery process deployed in a manner similar to that used for the elimination process. of metal. In general, different microorganisms are known to degrade different species of the organic compound and the appropriate microbial consortium can be selected according to the type or types of compounds to be degraded, but will generally be present within the contaminated material. The contaminated material is preferably analyzed before treatment to ensure an appropriate consortium already present or added to be present. Examples of the degradative strategies which can be selected are given as follows. As a result of the interest in and research carried out in the prior art, to investigate the microbiological degradation of organic pollutants, several known key strategies have emerged. The strategies employed are greatly influenced by oxygen, which can function either as a preferred electron acceptor or can be incorporated enzymatically into the molecule. Alkanes - can be degraded aerobically by microorganisms belonging to several genera including: Pseudomonas, Nocardia, Mycobacteria and Flavobacteria The degradation of such compounds initially involves the introduction of oxygen into the molecule by a monooxygenase enzyme. The subsequent conversion of the resulting fatty acids to aldehydes and carboxylic acids further allows oxidation through the beta oxidation path (Gottschalk, 1986). Alkenes and alkynes - can be degraded either aerobically or anaerobically. Aerobic degradation occurs by a mechanism similar to that for alkanes. However, the more reactive nature of the double and triple bonds also allows the initial degradation of the molecule under anaerobic conditions either by hydration or epoxidation reactions. Then the subsequent oxidation proceeds by means of beta oxidation. Halogenated aliphatic compounds - are susceptible to both aerobic and anaerobic degradation. Generally, however, the more highly halogenated compounds are more susceptible to anaerobic degradation. Cyclic and aromatic compounds - are once again susceptible to both aerobic and anaerobic degradation.

Under aerobic conditions, the initial attack involves the insertion of a series of oxygen atoms in the molecule by the oxygenase enzymes. Subsequent degradation occurs either by ortho or meta fission involving another dioxygenase enzyme to achieve ring breaking. The halogenated compounds are degraded by a similar mechanism. The microorganisms involved in such degradations include: species of Alcaligenes, Pseudomonas and Corynebacteria, which are capable of degrading the polychlorinated biphenyls (Unter an et al 1988) and the Flavobacteria species which are also capable of degrading pentachlorophenol (Frick et al 1988 ).

Under anaerobic conditions, the substituted aromatic compounds are reduced to cyclohexanone. The unfolding of the ring is achieved by hydration. Aromatic compounds with more than one chlorine atom are dehalogenated reductively before conversion to cyclohexanone. Halogenated compounds - particularly those that possess more than one functional halogen group, are also subject to reductive dehalogenation. This implies that the compounds that act as electron receptors and chlorine atoms that are removed from the molecule to be replaced by the hydrogens. Highly halogenated compounds, for example hexachloroethane, are strongly oxidized and possess greater affinities for electrons than molecular oxygen. As successive rounds of dehalogenation occur and affinities for electrons diminish, the use of alternative electron receptors such as oxygen and nitrate becomes probable, thus governing the conditions and groups of organisms that are capable of effecting degradation. Examples of organisms involved in reductive dechlorination include: Pseudomonas, Alcaligenes and Clostridia sp. On the contrary to the elimination of the metal, the mechanisms used to degrade organic earth or soil contaminants, will be very specific site, since these will need to be adapted to the particular contaminants present within a site. However, some generalizations can be made: 1. The degradative process will be optimized to reduce and / or eliminate a range of organic compounds, particularly VOCs (volatile organic compounds) and PAHs under aerobic or anaerobic conditions. These compounds will be mineralized at C02 and H20. 2. With the exception of a sulphate source and possibly an anaerobic environment, the nutrients required to promote the growth of degradative organisms will be the same as during the metal bioleaching and will be required in similar concentrations. 3. Almost neutral pH conditions will be required to maximize the numbers and types of degradative organisms, which can be grown. 4. Similar types of ground handling equipment, will be required for the degradation of organic materials, as required during the elimination of metals. In some cases, the organic contaminants present together with metal contaminants are advantageously treated before significant acidification, or mobilization within the contaminated material, since this could have a harmful effect on the microorganisms required in the degradation stage of the organic materials. Therefore, the organic materials can initially be degraded during the operation of the process, according to the present invention prior to the leaching of the metal. Another degradation of the organic materials can occur during the leaching of the metal. Depending on the degradative requirement of the organic contaminants, the system can be operated aerobically, anaerobically or a combination of the two. However, the anaerobic operation could delay the acidification of the contaminated material. Additionally, if large amounts of organic material contaminants are present, it may be necessary to delay the acidification process until sufficient organic degradation has occurred. For example, for a halogenated compound such as trichlorethylene, the anaerobic conditions can be maintained to allow reductive dechlorination to vinyl chloride, which subsequently can be mineralized under anaerobic conditions. After the degradation of most of the organic material, then the metal removal system can be initiated. Additionally, some of the organisms used for metal removal may be able to degrade particular contaminants, for example phenolic compounds may be degraded by the Desulfobacteria species. The treatment step of the organic materials, when applied to the soil and the like, can be carried out either in if or ex if it as appropriate and as determined by the requirements of the metal leaching stage. In the ex processes, if a nutrient solution is in contact with the earth after excavation, on an impermeable base, the leached solution is collected and recirculated after aeration if necessary. The processes themselves for the treatment of soil or soil contaminated with organic materials, may involve either injecting or spraying nutrients onto the contaminated area, thus avoiding excavation. Where the aeration of the nutrient solution is necessary for the degradation of the contaminant, the air can be injected into the contaminated area, or an oxidizing agent, for example hydrogen peroxide can be added to the nutrient solution. The leachate can be collected either in trenches or using a well recovery and recirculation system. Therefore, the present invention beneficially allows metal and organic contaminants to be removed from a contaminated medium, using a single multi-stage biotreatment system. Since the sulfur source can be at least partially recycled, this allows the reuse of the liquor of the process, the process can be conveniently operated as a cyclic system. The present invention offers the following additional advantages over the processes of the prior art: (1) It provides a permanent solution to the problem of contamination. (2) It allows the simultaneous treatment of metal and organic contaminants. (3) In-and-out treatment systems may be available and selected as appropriate. (4) The size of secondary waste streams and therefore the cost of dealing with them is minimized. (5) The use of harsh chemicals, which could harm the environment, is minimized. (6) An opportunity is offered to reuse certain metallic contaminants. The embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional, diagrammatic view of a region of land that is treated in itself by a recovery process exemplifying the present invention, together with the equipment used in the process. As shown in Figure 1, a region of land to be treated comprises a layer 1 of soil on an underground aquifer 3 below a level 2.

Layer 1 incorporates a region 4 contaminated with metal, which has been produced by the migration of contaminants from a waste sink 5 provided on the surface of layer 1. Region 4 extends into the aquifer 3. Well 6 Control is projected down through region 4 to allow measurements on the extent of contamination in region 4 to be determined. The depth and dimensions of the contaminated region 4 have been determined previously using known, appropriate analytical techniques, the level of the soil is indicated by point 18. The nutrients from a nutrient source 22 and at a suitable stage in the acidic process, the which can be carried out in a suitable carrier liquid, for example aerated water, are applied to the base of the vacuum sump 5. This application is carried out by a sprinkler 7. This liquid is also applied by means of the injection walls 8 placed appropriately and through an infiltration gallery 9, to permeate through the material in the contaminated region 4. Nutrients are selected initially to promote the growth of appropriate microorganisms to provide degradation of organic materials under substantially neutral pH conditions, using one or more of the methods described above. The addition of the nutrient is subsequently modified to promote acidification of the soil. During this secondary treatment phase, the elemental sulfur can also be added to and mixed in deep contamination areas, such as the base of the sink 5 to further promote the bioleaching of the metal species itself. To allow aerobic conditions to be developed and maintained within the contaminated region 4, air is blown by an air bellows 21 attached to a series of ventilation wells 10, (one of which is shown) either to draw air into the air. through contaminated region 4 in layer 1 or to inject air into groundwater in aquifer 3 or both. Additionally, the rate of addition of the nutrient can be varied to avoid or create anoxic conditions within the contaminated region 4, as appropriate. The boom or -region in layer 1 and aquifer 3 supplied with nutrients and ingredients in an aqueous medium is indicated by reference 20. This plume 20 covers region 4 contaminated in layer 1 and aquifer 3. This The treatment degrades the organic materials and subsequently also produces metal leaching, acid in region 4 in the manner described in the foregoing. This may continue for weeks or months until the soil in the contaminated region 4 is substantially free of contaminating organic materials and metals as determined from time to time by the proper analysis. The products of both the organic material degradation and metal leaching are collected within a portion of a water flow in the earth in an X direction, either occurring naturally or artificially created and being collected by and returned to the surface above layer 1, by means of a series of recovery wells 11 (one shown) using appropriate pumps (not shown). Level 2 of the water table 3 can be adjusted by the addition of water by means of an infiltration gallery 24 to assist the flow of water in the X direction. The collected liquor is then supplied to a selected location of three locations, viz .: (a) a buffer tank 12 for aeration and addition of appropriate nutrients before reapplication to the contaminated area. This is the main route during the initial operation of the process; (b) a bioprecipitation reactor 13; (c) a gas-liquid contactor 14 for washing the hydrogen sulfide from the gaseous effluent of the bioprecipitation. The liquor enters the reactor 13 at its base and flows up through the reactor 13. By doing so, the organisms that reduce the sulfate present in the reactor 13, convert the sulphates inlet to sulfides in the manner described in the foregoing. The gaseous effluent produced during the bioprecipitation in the reactor 13 is passed through the gas-liquid contactor 14 connected to the reactor 13. The contactor 14 allows the recovery of hydrogen sulphide. The gas stream leaving the contactor 14 is passed through a secondary washing machine unit 19 and discharged into the atmosphere. The bioprecipitated sludge containing insoluble sulphides is collected at the base of the reactor 13 and transferred via a pipe 15 to a separate treatment process, for example biologically enhanced metal fixation, or is dehydrated and collected and supplied to another site for metal recovery. The liquor obtained by the dehydration of the sludge can be either returned for reuse in the metal bioleaching step of the process exemplifying the invention, or further treated and discharged. The effluent liquor containing dissolved sulfides that are produced from the bioprecipitation is extracted and combined with the aqueous sulfide stream that is produced from the gas / liquid contactor. The combined aqueous sulfide stream is then pumped through a gas / liquid contactor 16 and into a sulfide oxidation reactor 17. The contactor 16 ensures that any gaseous hydrogen sulfide released by the acid in the reactor 17 is redissolved by the alkaline inlet liquor. Within the oxidation reactor 17, the sulfur-containing liquor is intimately mixed with suitable microorganisms and oxidized to sulfate in the manner described above. The acid liquor produced then is transferred to the - «- buffer tank or bioreactor 12, where 0 or more elemental sulfur can be added from a source 23, if required and oxidized to sulfuric acid by the microorganisms brought from the reactor 17 before the readmission to the contaminated material on the ground 1 in the described in the above (by means of wells 8 and gallery 9 and the sprinkler 7). The added sulphurous material and nutrients form a plume 20. Therefore, the metal removal treatment process is cyclic and the metal contaminants in portion 3 of layer 1 of earth are, during several cycles of the metal removal process, gradually leached by the incoming solution containing biochemically formed sulfuric acid and recovered as an insoluble sulphide formed in the bioprecipitation reactor 13.

A proportion of the sulfur is recovered by oxidation of sulfides in the oxidation reactor 17 and is reused in the acid leaching of the soil from the metal contaminants. Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. A process for the decontamination of a medium, comprising a material contaminated with one or more organic species and one or more metallic species, characterized in that it comprises the steps of treating a body of the medium by a process, which unfolds the contaminant or organic contaminants by or through the action of microbial agents followed by the treatment of the same body with microbially produced sulfuric acid, to solubilize and leach the metal species as a metal sulfate and treat the leached metal sulphate, by a bioprecipitation process, which converts the sulfate to one or more insoluble metal sulfides.

2. The process in accordance with the claim 1, characterized in that the hydrogen sulphide produced during bioprecipitation is separated from the insoluble metal sulphides.

3. The process in accordance with the claim 2, characterized in that the hydrogen sulfide is oxidized to form a reusable source of a sulfur-containing ingredient.

4. The process according to any of the preceding claims, characterized in that in a first stage of the process, in which the organic pollutants are biodegraded by microbial agents before the acid treatment, the pH of the contaminated medium is maintained in the range of 5 to 9 .

5. The process according to claim 4, characterized in that the organic contaminants are also split by the action of the sulfuric acid produced microbially in the second stage of the process.

6. The process according to any of the preceding claims, characterized in that the medium comprises a particulate material selected from soil, rock particles, dredging, sediments, sludges, process residues, slag and kiln dusts.

7. The process according to any of the preceding claims, characterized in that the metal species comprises a kind of radioactive metal or a toxic heavy metal.

8. The process according to claim 6 or claim 7, characterized in that the medium comprises earth, which is treated in itself.

9. The process according to any of the preceding claims, characterized in that part of the process of the treatment of the metal species is cyclic, the reusable source of the sulfur-containing ingredient that is converted microbially to sulfuric acid to be reused in the medium.

10. The process according to claim 9, characterized in that the microbial conversion to sulfuric acid is carried out in itself in the medium to be treated.