MXPA96003459A - Process for the treatment of contaminate material - Google Patents

Abstract

A process for decontaminating a medium, comprising a particulate material contaminated with one or more metallic species, the process is characterized in that it comprises the steps of treating a body of the microbially produced sulfuric acid medium, to solubilize the metal species as a sulphate metal, treat leached metal sulphate, by a process of bioprecipitation, which converts the sulfate to insoluble sulphide, separate the hydrogen sulfide produced during the bioprecipitation of the insoluble metal sulfide, and oxidize the separated hydrogen sulfide to form a reusable source of an ingredient that contains sulfur

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 removal of metal contaminants, especially heavy metals, from bulky particulate material such as soil or topsoil using biochemical processes. Throughout the world, substantial amounts of land have become contaminated with metals as a result of waste disposal, industrial and other activities. Examples of such contaminants include: mercury, cadmium, barium, • chromium, manganese and lead, radionuclides such as actinides and fission products. Such contaminants can 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 cleaning, if they do not act responsibly towards their waste. Therefore, there is a growing need for technologies, which can help solve problems caused by 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 biological processes currently used; c) The generation of a high volume, or difficult to control secondary waste, for example land stabilization and incineration; d) Lack of selectivity of options in if your or ex if your according to is 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 contaminated metal, not specifically the earth. According to the present invention, a process for decontaminating a medium, comprising a particulate material contaminated with one or more metal species, comprising the steps of treating a body of the medium with sulfuric acid produced microbially to solubilize and leach the metallic species as a metal sulfate; treat leached metal sulphate by a bioprecipitation process, which converts the sulfate to an insoluble sulphide; separating the hydrogen sulfide produced during the bioprecipitation of the insoluble metal sulfide; and oxidizing the hydrogen sulfide separated to the form of a reusable source of a sulfur-containing ingredient. The means to be decontaminated may consist of a particulate material such as soil, rock particles, dredging, sediments, sludges, process residues, slag from pyrolytic processes, kiln dusts and the like. Contaminants can be contaminated on the surface of the particulate material or they can be bound within their particles. Various metal species may be present in the medium and these may be converted to various metal sulfates and subsequently bioprecipitated as various metal sulfides. The term "metallic species" as used, in the present, 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; 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 selenium to cerium range. The 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 and cobalt and other common contaminants. 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. As described in the following, the process of the present invention can be extended to include steps in which organic contaminants in the medium to be treated are also removed or detoxified.

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. Where the earth or other particulate material, for example, process residues or slag, is to be treated ex if you can be treated in one or more known, suitable reactors. The ingredients mentioned in the above can be added to promote acid production. Where the bioconversion to produce sulfate ions is carried out on 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 tana neapoli These organisms, for example, can be present as a consortium. 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 'ground 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, the sulfuric acid required for the leaching stage in the process exemplifying the present invention can be produced chemically or biochemically in a separate bioreactor and added to the soil or other particulate material after production. During the beginning 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 from the body of particulate material and can be collected. 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 step of the process.

The bioprecipitation step employed in the process of the present invention may be similar to the known sulfate reduction processes. Such processes, for example, are used in the prior art to treat both sulfates and heavy metals, either alone or in combination, removed from the wastewater. For example, the process described in EP 426254A which employs both ethanol as a substrate and methanogenic organisms to anaerobically convert produced acetate to methane is suitable. Additionally, such processes occur naturally within many anaerobic environments. The bioprecipitation process in the present invention can employ a consortium that naturally occurs from 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 of the above ground. 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, the sulfatoe are reduced to sulfides and water. As the sulfides of many heavy metals have low solubilities in aqueous solution, they precipitate along with some biomass like a sludge inside the 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 reactor of the phase that dissolves the metal, will result in the production of hydrogen sulfide and the consequent reduction in the concentration of sulfuric acid. This will result in maintaining a pH close to neutrality within the bioprecipitation reactor 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, i.e. < -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) sludge containing precipitated metal sulfides and biomass; (b) aqueous hydrogen sulfide, soluble metal and sulfides together with some biomass; (c) gaseous hydrogen sulfide. The gaseous hydrogen sulfide can be extracted by means of ventilation, 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. The sludge can be dehydrated and recycled to recover the metal or it can be 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 opcion of the metal leaching stage of the process according to the present invention, the leachate that enters the bioprecipitation, will possess a substantially 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 the bioprecipitation can be used separately or in combination and can be oxidized within a closed bioreactor. The bioreactor system may contain 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 trificane and Thiomicrospira. Two routes are possible for the oxidation of sulfur: (a) direct oxidation to sulfuric acid and / or sulfates; (b) oxidation to elemental sulfur, which can, if appropriate, then be added to, for example, sprayed on 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. The process of the present invention can be extended to include one or more steps for the removal of organic contaminants from the contaminated medium and this can be done by a biodegradation process employed in conjunction with the metal removal process as described in the Requests U.S. Patents Nos. 9402975.8 and 9414425.0 co-pending (which process is the subject of a co-pending PCT application of the same date as the present one). 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. (3) It allows the simultaneous treatment of metal and organic contaminants. (4) In situ and ex situ treatment systems may be available and selected as appropriate. (6) The size of secondary waste streams and therefore the cost of dealing with them is minimized. (2) The use of harsh chemicals, which could harm the environment, is minimized. (5) 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 to provide by a recovery process, which exemplifies 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. The layer 1 incorporates a region 4 contaminated with metal, which has been produced by the migration of pollutants from a waste sink 5 provided on the surface of layer 1. Region 4 extends into the aquifer 3. Control well 6 projects down through region 4 to allow the measurements on the extent of contamination in region 4 that is going to be determined. The depth and dimensions of the contaminated region 4 have been previously determined using known, appropriate analytical techniques. The level of the soil is indicated by the number 18. Nutrients from a nutrient and acid source 22, 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 and promote the. acidification of the earth. Elemental sulfur can also be added to and mixed in deep contamination areas, such as the base of sink 5 to further promote bioleaching in itself as described above. 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 speed of addition of the nutrient can be varied to avoid or create anoxic conditions within the contaminated region 4. The plume or region in layer 1 and aquifer 3 supplied with nutrients and acid is indicated by reference 20. This plume covers region 4 contaminated in layer 1 and aquifer 3. This treatment produces leaching of acid metal 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 metals as determined from time to time by the proper analysis. The products of the. Metal leaching treatment are collected within a portion of the aquifer mantle 3, either occurring naturally or artificially created in an X direction and being received 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 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: (a) a buffer tank 12 for aeration and addition of appropriate nutrients prior to 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 upwards through the reactor 13. In doing so, the sulphate reducing organisms present in the reactor 13 convert the sulphates inlet to sulfides in the manner described above. 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 bioleaching process or additionally 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 produced acidic liquor is then transferred to the buffer tank or bioreactor 12, where more elemental sulfur can be added from a source 23, if required and oxidized to sulfuric acid by microorganisms brought from the reactor 17 prior to readmission to the contaminated material in the reactor. land 1 in the manner described above (by means of wells 8 and gallery 9 and sprinkler 7). 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, leached gradually by the leached solution containing sulfuric acid formed biochemically 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 decontaminating a medium, comprising a particulate material contaminated with one or more metallic species, the process is characterized in that it comprises the steps of treating a body of the medium with microbially produced sulfuric acid, to solubilize the metal species as a metal sulfate; treat the leached metal sulphate, by a process of bioprecipitation, which converts the sulphate to an insoluble sulphide; separating the hydrogen sulfide produced during the bioprecipitation of the insoluble metal sulfide; and oxidizing the separated hydrogen sulfide to form a reusable source of a sulfur-containing ingredient.

2. The process according to claim 1, characterized in that several metal species are present in the medium and these are converted to various metal sulfates and subsequently bioprecipitated as various metal sulfides.

3. The process according to claim 1 or claim 2, characterized in that the metal or metals include radioactive species.

. The process according to any of claims 1 to 3, characterized in that the medium to be decontaminated comprises a particulate material selected from soil, rock particles, dredging, sediment, mud, process residues, slag from a process Pyrolytic and kiln dust, contaminants may be contaminated on the surface of the particulate material or be bound within their particles.

5. The process according to any of the preceding claims, characterized in that the particulate material is treated by leaching with sulfuric acid produced microbially using an aqueous leaching solution.

6. The process according to claim 5, characterized in that the sulfuric acid is produced microbially in itself in the material comprising the particulate material.

7. The process according to claim 5, characterized in that the sulfuric acid is produced in a separate bioreactor and is added to the material comprising the particulate material.

8. The process according to claim 5 or claim 6, characterized in that the process is applied to treat land or land in the same.

9. The process according to any of the preceding claims, characterized in that the insoluble sulfides or sulphides produced in the bioprecipitation process are extracted and encapsulated.

10. The process in accordance with the claim 1, characterized in that the process is operated cyclically, the reusable source of the sulfur-containing ingredient that is reapplied to the medium being decontaminated, to additionally provide metal leaching of sulfuric acid.