The method of construction of the remedial geochemical barrier in the underground environment

 

The invention relates to mining and can be used in the design, construction and operation located on the surface or directly in the unsaturated zone storage of toxic solid and liquid waste, including radioactive, as well as in undertaking rehabilitation of contaminated territories and activities related to the protection of groundwater from other sources of contamination that can be attributed plots heap leaching, waste dumps, tailings and other industrial objects of mining companies. The technical result is to provide a very efficient protection of groundwater from contamination with localization at the initial site of penetration into the underground environment. In the method of construction of the remedial geochemical barrier in a subterranean environment, comprising applying to the area formed by the barrier inhibiting materials-reducing agents, the specified barrier is formed in the unsaturated zone, at the same time as inhibiting materials-reducing agents use gas-reducing agent. And as a reducing gas using the hydrogen sulfide, the gas supply of the reducing agent is performed by pumping it through the hole,stenopetalum its upper boundary of the feature is below the lower limit of the maximum amplitude of oscillations of an air column aeration zone, occurring in it when the atmospheric pressure changes. In some cases, in the area formed by the barrier additionally served solution containing iron salts, in particular the sulphate of iron. 5 C.p. f-crystals, 1 Il.

The invention relates to mining and can be used in the design, construction and operation located on the surface or directly in the unsaturated zone storage of toxic solid and liquid waste, including radioactive ones. The invention can also be used in undertaking rehabilitation of contaminated territories, and related to the protection of groundwater from other sources of contamination that can be attributed plots heap leaching, waste dumps, tailings and other industrial objects of mining companies.

There are various ways to protect groundwater against pollution from land-based sources [1, 2] from the most simple, is based on the concept of controlled (regulated) contamination of groundwater and associated with the natural process of their self-purification, to the most complex, consisting of pumping contaminated groundwater, leaching of contaminated sites and clean otkachivaetsya, when the possibility of natural self-purification are quickly exhausted, and the second is their low efficiency and high cost.

Closest to the technical essence is a way to create an oxidizing geochemical barrier against dioxin contamination of groundwater [3]. According to this method is the increased oxidative properties of the host rocks of the aquifer at the site before approaching the front of contaminated groundwater. This strengthening is achieved by the processing section kislorodozawisimae water from the same horizon. The disadvantage of this method is the limitation of its action mainly against the contamination of groundwater by organic compounds.

Also known restorative barriers in the form of trenches (slits) with different fillers [2, T. 3, page 62]. For example, the University of Waterloo (Canada) actively promotes artificial chemical barrier on the basis of aggregates of metal (steel, brass, aluminum) chips and 90% of the sand to clean filtered water through it from the chlorine-carbon pollutants. Cleanup occurs due to the establishment of the necessary restoration of the environment at the same time is possible, small life, etc.

Also known a method of creating a permeable reactive barrier of granular iron for treatment of contaminated groundwater [4]. This barrier became operational in 1996, the Center support of the coast guard, Elizabeth city, North Carolina, USA, for the treatment and cleanup of pollution plumes chromates and hydrocarbon, chlorinated solutions. The barrier is a trench width of 0.6 m, a length of 46 m and a depth of 7.3 m, filled with granular iron (280 t) with a grain size of 0.4 mm

The main disadvantages of slotted barriers is their high cost, shallow depth, inefficient use of material-reducing agent due to its surface oxide film, which hinders the contact of the reducing agent with pollutants. A significant drawback is the inability to create them for cleaning vertical flows of polluted water, common in the unsaturated zone (zone of aeration) directly under the source of contamination.

Closest to the claimed is a method of construction of the remedial geochemical barrier in the underground environment, including operations on the construction of the geochemical barrier, applying the HHS made of acid rock, mainly sulphides (RF patent 2075125, G 21 F 9/20, 10.03.1997).

The technical result of the invention is to provide a very efficient protection of groundwater from contamination with localization at the initial site of penetration into the underground environment.

This is achieved in that in the method of construction of the remedial geochemical barrier in a subterranean environment, comprising applying to the area formed by the barrier inhibiting materials-reducing agents, the specified barrier is formed in the unsaturated zone, at the same time as inhibiting materials-reducing agents use gas-reducing agent. This gas may be hydrogen, carbon monoxide, mixtures between them (generator, coal gas) and other

As a reducing gas in some cases the use of hydrogen sulfide. It is advisable to supply a reducing gas injection through hole, a filter which is installed in the lower part of the aeration zone.

It is advisable when filling zone formed by the barrier gas by reducing its upper boundary of the feature is below the lower limit of the maximum amplitude of oscillations of an air column aeration zone, resulting in him when the atmospheric pressure changes. In nekotorye iron.

The use of these operations causes the appearance of the next number of new positive merits of the claimed invention: 1. According to the foregoing the invention to the first and its main difference concerns the creation of a geochemical barrier in the unsaturated zone using gases with reducing properties. This approach to the construction of the barrier determines the appearance of several new positive properties.

1.1. The possibility of its facilities under direct sources of subsurface contamination, which can significantly reduce the volume of contaminated rocks and to prevent the spread of this contamination with groundwater.

1.2. The absence of any significant constraints to economic, technical or technological nature to create barriers over a large area when the areal location of sources of pollution, which is associated with gases, the property of which is high mobility.

1.3. The possibility of building a barrier in the unsaturated zone, composed of the rocks of different lithological composition, including consisting of soft porous sedimentary sandy-clayey rocks or from a firm capacity of the host rocks to clean contaminated water and delay dirt rock-forming minerals. This property is caused by reactions between gas-reducing agent and oxidized forms of the minerals of the host rocks. As a result of these reactions is the recovery of oxidized elements to ferrous or neutral forms. The recovered minerals then in contact with pollutants become reductants for them in the reducing conditions result in the precipitation of the most famous of contaminants, including heavy and radioactive, as well as the destruction of a number of organic compounds.

1.5. Highly efficient use of space of the unsaturated zone (pore - sandy rocks and fractured the rocks) to almost 100% for accumulation and reliable delay in this space by repeated and repeated submission in the area of barrier gas-reducing agents as to the exhaustion of it resilience from the previous submission. In this respect, there are no theoretical and practical obstacles to achieve such concentrations of impurities in the barrier, which are characteristic of ore deposits formed in reducing conditions, in particular deposits of uranium, copper, gold and other metals.

You who with her natural retention capacity. For example, in the publication [5] presented the results of the simulation of flow and mass transfer in fractured environment aeration zone rocks, it is specified that the unsaturated zone at Yucca mountain region, Nevada, USA) is a potential radioactive waste repository and to the active zone includes only from 18 to 27% of interstitial space rocks.

2. Use as a reducing gas of hydrogen sulfide provides additional positive effects in localization technology of contaminants in the vadose zone. This is due to the nature of the hydrogen sulfide related to strong reducing agents, and the characteristics of its interaction with common contaminants of groundwater and minerals of the host rocks. Possible reactions of this interaction occurring in the aquatic environment, even at room temperatures and atmospheric pressure, is known from General chemistry [6], from theory and practices of hydrometallurgical processes for the beneficiation of ores of nonferrous metals [7] and other sources. The main of these reactions include: Me2++H2S(p-p)=MeS(TV)+2H+(1) Me2+H2S(p-p)+S(e)=MeS2(TV)+2H+(2) 3H2S+H2SO>5S(e)+H2About=2FeS2(TV)+H2SO4(5) H2S+1/2O2=H2O+S (6) from the properties of hydrogen sulfide and reactions with contaminants and minerals of the host rocks, additional advantages of the claimed process from the use of this gas are expressed in the following terms: 2.1. The high solubility of hydrogen sulfide relative to other gases and component in 10o3.44 volume of gas to 1 volume of water or 5,28 g/l [6, T. 1, page 703] that determines the relative ease of deposition of contaminants from the water moving through the unsaturated zone. The deposition may occur in the form insoluble sulphides (copper, Nickel, iron, and others) by the type of reactions (1, 2) or in the form of insoluble oxides (chromium, aluminum, strontium, and others) for resultsarray in the aquatic environment of the metals on the type of reaction (3).

2.2. The ability to significantly enhance the cleaning ability of the unsaturated zone, mainly due to the reaction with iron, it is almost always contained in rocks of any origin in appreciable quantities (0.5% and more). As a result of these reactions, passing by the type of reactions (4, 5, 6), iron from oxidized forms is recovered in the sulfide form, forming artificial sulphide geochemic osstanavlivayuschaya the ability of the unsaturated zone increases in this case is proportional to the amount of absorbed hydrogen sulfide. Without these reactions healing ability of the medium in the feed area of hydrogen sulfide was determined only by its number, located in the adsorbed state on the surface of solid particles, dissolved in water and gas in the free space of the unsaturated zone;
2.3. High degree of purification of polluted water from the metals recovery sulfide barrier, proof of which is found on the barriers, resulting in a natural way. An example would be the ability to clean groundwater from uranium contamination, common areas storage of liquid radioactive waste, uranium mining methods underground and heap leaching, where the concentration of uranium in the groundwater reaches tens or hundreds of mg/l, in particular in groundwater near lake Karachay, which is the storage of liquid radioactive waste, uranium content is 41 mg/l [2, T. 3, page 674].

In natural conditions at the entrance to the natural geochemical barrier, which is formed uranium Deposit, the uranium content in the groundwater is n10-5to n10-6g/l, at the exit of the barrier, the uranium content in this water shigechika substance, the iron sulfides and hydrogen sulfide. To the same concentration here reduces the content of molybdenum is a frequent companion of uranium on its deposits. You can expect the decline to the same concentrations of artificial geochemical barriers and such a radioactive element of the unknown in nature, but common in the storage of liquid wastes radiochemical enterprises as technetium-99, which in its properties chemical analogue of molybdenum.

Another example of a high cleansing ability sulfide barriers are data monitoring groundwater contaminated as a result of copper mining in the mines of Burgas in Bulgaria [9]. Revealed that groundwater aquifers are in the process of water self-purification from heavy metals (cu, Pb, Mo, MP) under the action of hydrogen sulfide resulting from the activity of sulphate-reducing bacteria. The hydrogen sulfide converts hexavalent uranium to insoluble condition, and heavy metals thus precipitate as sulphides, as a result, the concentration of pollutants is reduced to the level of the MPC.

2.4. The influence of hydrogen sulfide and the products of its reaction with the host rocks at the contaminated water is osmolyte. Indicative monitoring of groundwater at the site biofeedback (Department of the Vienne, France). In publications in this area [10] it is shown that the natural denitrification, i.e., the recovery of nitrogen from nitrates to molecular States occurs in the presence of the rocks pyrite (FeS2or organic compounds. Calculations established that when filtering on the distance 250-500 m nitrate content will be reduced from 100 to 0.1 mg/L.

2.5. It should be noted relatively high resistance of artificial sulfide barrier against the natural process of destruction. The natural destruction of the barrier to the return of the unsaturated zone in original condition, is likely to occur under the action dissolved in water infiltration of oxygen. For the approximate calculation of the rate of destruction will accept that it will happen according to the reactions [3, 4, 6], considering the first two of them are reversible, in the rock with a volumetric weight of 2 t/m3, a content of iron of 0.5%, when the rate of supply of water in the unsaturated zone of 50 mm/year and the content in water of dissolved oxygen 10 mg/l For these source data duration of destruction 1 m barrier will be 22,9 thousand years or destruction of the barrier will occur with the panorama and practically unlimited in time localization of contaminants in artificial barrier;
2.6. The use of hydrogen sulfide, aqueous solution which possesses a weak acid properties, determine the possibility of a significant increase of the sorption capacity of the rock is relatively even pattern of elements, such as radioactive cesium-137 and strontium-90. This ability is determined by analogy with the use for the same purpose of solution of carbon dioxide [11] , the processing which translates exchange capacity of the rocks in the hydrogen cation form. The experimental data of the Institute of IPC RAS processing of sandy-argillaceous carbonate solution increases their sorption capacity coefficient of interphase distribution for strontium-90 in 2-5 times.

3. When the supply of gas to the aeration zone through the well, the filter which is located near the groundwater level, there are such positive properties of how low the cost of construction of underground utilities and increased the size distribution of gas from one well. The increase in the area of gas distribution is achieved by lowering the filter to the zone of water saturation to the groundwater level.

When equal to the height of the fill gas aeration zone and the location of the filter well in the middle part of the height of a horizontal square is osphere. This will give ceteris paribus, in particular at the same level and the same permeability of the unsaturated zone in all directions, a fourfold increase in the area occupied by the gas.

4. The application of the method with the restriction of the gas flow in the unsaturated zone so that its upper limit was below the limit of maximum oscillations of a gas column in this area, ensures the full use of the gas for the purpose, without losses due to release on the day surface. If we denote the surface of the air phase of the unsaturated zone at the minimum atmospheric pressure at the earth's surface, the air trapped below the surface, with a maximum atmospheric pressure will be compressed and the surface will sink to a depth proportional to the difference between the maximum and minimum atmospheric pressure.

The flow of reducing gas in the unsaturated zone without exceeding this depth provides in addition to the full of its use to create a geochemical barrier still safe and ecologically intact environment on the earth's surface. This is especially important when using such a relatively toxic gas such as hydrogen sulfide.

5. The use of pic is her iron, preferably solutions of sulphate of iron, provides the possibility of increasing the number of detained therein pollutants. This feature is implemented, in particular, in the reaction solution with hydrogen sulfide and precipitation of iron in the form of sulphides, which in further precipitating contaminants.

This operation is particularly effective in the absence of sufficient natural iron in the unsaturated zone. The use of sulfate solutions has the advantage relative to other salts, such as nitrate, which, together with the iron sulfides occurs the precipitation of elemental sulfur according to reaction (1, 3), as well as contributing to the formation of a long recovery environment in the treated part of the unsaturated zone.

The invention is illustrated in the drawing, which shows: water-saturated rocks 1; groundwater level 2; filter 3 gas supply wells; cased part 4 gas supply hole; aeration zone 5; border 6 distribution of reducing gas in the unsaturated zone; border 7 maximum amplitude of oscillations of an air column in the unsaturated zone; flow line 8 of polluted water; near-surface source of contamination 9; top 10 gas supply wells.

In the aeration zone, with a capacity of 70 meters the Flow of waste in this area is performed through the trench evenly distributed throughout the area. Waste storage in the unsaturated zone is based on the natural inhibiting properties forming it rocks. However, the natural retention capacity of the rocks was exhausted, it was discovered the penetration of contaminants into the groundwater and there was a danger of pollution of nearby watercourses.

The unsaturated zone at this site is composed of sandy-clayey rocks with a bulk density of 1.7 t/m3, moisture content of 20-25% and a content of the air phase 10-15%. The maximum difference between the highest and lowest atmospheric pressure in this area is 25% of the amount of low pressure. This means that the upper boundary of the air column aeration zone, coinciding with low atmospheric pressure with the surface of the earth at high pressure due to the compression of the air column will descend to a depth of approximately 17.5 m (see border 7 in the drawing).

To enhance the inhibiting properties of the unsaturated zone and reliable localization of pollution are drilling in the Central part of the well at a depth of 70 m, equipped at the bottom of the filter 2 m, casing pipes with comentariovuena in the unsaturated zone the hydrogen sulfide thus, to the upper boundary of this gas would not be above the depth of 20 m from the ground surface. When the total quantity of gas approximately 75 t he extends throughout the area, creating in the vadose zone remedial environment and conditions for the deposition of impurities in the form of insoluble compounds.

Such quantities of hydrogen sulfide enough, for example, for deposition of at least 200 tons of uranium in the achievement of its content in the unsaturated zone approximately 0,025-0,03%. This content exceeds 2.5-3 times extremely low uranium content in the ore, suitable for practicing the method of underground leaching [8] . Note for comparison that the published data [2, ie 3] about 200 tons of uranium dispersed in groundwater within a radius of 2-3 km around the lake Karachay, this uranium is caught in these waters by filtering from the lake for 45 years of liquid radioactive waste.

Another indicator of the effectiveness of such artificial geochemical barrier is a significant time delay dirt. For example, if the pollution of the underground environment salts of copper observed in the squares heap leaching, tailings and dumps mining enterprises with the intensity of the volume pumped into hydrogen sulphide 75 t able to clear from copper flowing water for about 150 years.

In this example, additional processing zone formed by the barrier of iron-containing solutions were not required because of the rather high content of natural iron, more than 0.5%, in the unsaturated zone. If necessary, this treatment could be carried out through an additional supply of iron salts directly into the liquid waste is placed in the zone of aeration.

References
1. Boochever F. M., David N. N., Oradovskaya A. E. Protection of groundwater against pollution. M., Nedra, 1979, 254 S.

2. Mironenko C. A., Romania Century, the problem of hydrogeologie. Monograph in 3 volumes. M., Moscow state University press, 1999.

3. D. Yu. Kultin, O. K. Lebedeva, N. V. Sokolov, Yu. V. Kultin, A. J. Rybalchenko. Oxidative-geochemical barrier against dioxin-pollution of ground-water. International conference on Groundwater Research, Copenhagen, Denmark, June 2000.

4. Abstract journal "Geology", 7, 1999, abstract E.

5. Abstract journal "Mining", 1, 2000, summary 00.01 - 10V.253.

6. Remy, the Rate of inorganic chemistry. M., publishing house of the World, so 1, 1972, T. 2, 1974.

7. Laptev Y. C., Sarkis A. L., Kolonin, P Sulphur and sulfadiazine in hydrometallurgical processes. Novosibirsk: Nauka, 1987, 160 S.

8. Exploration for uranium mining by underground leaching. Shumilin M. C., Muromtsev N. N., Brovin K. G., and others, M Depths, 198 is at A.

11. Kultin Y. C., Rybalchenko, A. I. Method of localization of contaminants in aquifers. Description of the invention to the patent of the Russian Federation 2039230, 1995.


Claims

1. The method of construction of the remedial geochemical barrier in a subterranean environment, comprising applying to the area formed by the barrier inhibiting materials-reducing agents, characterized in that said barrier is formed in the unsaturated zone, at the same time as inhibiting materials-reducing agents use gas-reducing agent.

2. The method according to p. 1, characterized in that as a reducing gas using hydrogen sulfide.

3. The method according to p. 1, characterized in that the supply of a reducing gas are injected through a borehole, a filter which is installed in the lower part of the aeration zone.

4. The method according to p. 1, characterized in that when filling zone formed by the barrier gas by reducing its upper boundary of the feature is below the lower limit of the maximum amplitude of oscillations of an air column aeration zone, resulting in him when the atmospheric pressure changes.

5. The method according to p. 1, characterized in that the area formed by the barrier additionally submit a solution containing salts of iron.

6. The method according to p. 5, the

 

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