DE10238957B4 - Method for reducing uranium (VI) concentration in flowing waters - Google Patents

Abstract

method to reduce the uranium (VI) concentration in running waters, at which the uranium (VI) predominantly is present as a carbonate, sulfate or hydroxy complex and element-specific Filter materials are used in a geochemical barrier, wherein the uranium contained in the water (VI) by means of a chicken faeces feldspar mixture converted into uranium (IV) oxide and uranium (VI) phosphate and both substances be precipitated in the geochemical barrier.

Description

The The invention relates to a method for the purification of waters with high uranium (VI) concentrations, in particular the removal of high uranium from contaminated waters, such as the waters flooded pits of uranium mining.

Based on mining activities for the extraction of uranium, methods are known according to which uranium from concentrated solutions, which often result from previous leaching processes of the uranium ores, is sorbed and enriched in ion exchange resins ( JP58161926 . JP600011224 ). These methods are also proposed for the removal of uranium from wastewater ( JP2000246243 . JP62191094 ).

Furthermore, it is known that with suitable organic ligands, such as calixarenes ( JP62136242 ) or activated carbon ( JP11094994 ), Uranium can be removed or recovered from aqueous solutions.

Another technical possibility to remove metals from contaminated waters represents the use of iron (III) hydroxides for the sorption of metals and subsequent separation of the iron (III) hydroxides with the sorbed heavy metals from the water to be purified ( US4481087 ). Disadvantage of these methods is that mostly iron (III) salts are used and the formed iron (III) hydroxide to transform over time.

Described is a method for fixing the radioactive decay products of uranium, which are released in the uranium production, by precipitation of the decomposition products with aluminum, aluminates and silica and sintering of the radionuclide-containing precipitates ( JP11295485 ). A similar process is based on the fixing of radionuclides by water glass ( JP6308292 ). A disadvantage of this method is the use of industrial recyclables and the use of partially soluble, hazardous aluminum compounds.

In order to achieve a cost-effective and natural cleaning of heavy metals contaminated waters, methods based on geochemical barriers have been developed. Such geochemical barriers are usually natural substances or material systems which, when used according to the method, considerably reduce the migration of heavy metals, such as, for example, the transport of uranium with the water. Described is the use of ashes from industrial combustion processes (WO9315831) and concrete and mortar demolition ( DE4307468 ) for pollutant fixation. The high fixation potential of clay minerals for heavy metals is generally known, which is used, for example, in landfill sealing ( EP0081403 . US4344722 . CH682502 . EP0412630 ). However, the sorption of uranium on clay minerals, especially in carbonate-rich waters, is weak due to the stable uranium (VI) carbonate complexes.

"Wetlands", which usually Wetlands, such as Ponds with reed belt represent are one alternative possibility heavy metals polluted waters to clean. However, these methods are safe storage the heavy metal-containing sediments are not provided and an erosion and release of heavy metals by flood events not ruled out what the applicability of Wetlands to purify uranium waters severely limits long-term vision.

The use of metallic iron to purify uranium-contaminated waters has been described in the literature (Morrison, SJ et al., 2001: Uranium precipitation in a permeable reactive barrier by progressive irreversible dissolution of zerovalent iron. Environ. Sci. Tech. 35: 385-390). , Also known are processes based on a geochemical barrier introduced in flow paths, consisting of fractions of metallic iron and lignite or matte coal ( DE10033162 ). According to the method described in the patent US5514279 metallic iron or organic substance is introduced as a geochemical barrier in situ in the contaminated aquifer for uranium fixation, due to the unspecified organic substance, the applicability of the method is not given, since the uranium solubility in water of certain organic substances can be greatly increased. In these methods ( DE10033162 . US5514279 ) it comes to the electrochemical reduction and precipitation of tetravalent uranium. The formation of poorly water-soluble uranium phosphate compounds and the removal of the uranium from the water with separation of these uranium phosphate compounds is known (US Pat. US4410497 . US4476099 . US 4536034 . DE4313127 ), as well as the use of poorly water-soluble phosphates as reactive barriers ( US6290637 ). The phosphate source used in these processes are orthophosphates, such as phosphoric acid, sodium hydrogen phosphate, used.

adversely however, the use of industrial processes is described in the processes described Recyclables as barrier material. Besides that is in use metallic iron the release of toxic alloying constituents, such as, in particular, allergenic nickel.

The influence of microorganisms on the electrochemical reduction of uranium (VI) to poorly water-soluble uranium (IV) is described by Lovley DR et al. 1991: Microbial reduction of uranium. Nature 350, 413-416 and in WO200039035. Furthermore, methods are known ( DD225415 . US4293334 ), in which metals are obtained by means of biosorption on bacteria from aqueous solutions. Disadvantages of these processes are the high costs for the cultivation of the microorganism strains to be used.

Of the Invention has for its object to develop a method the uranium (VI) from heavily polluted mining wastewater, Haldensicker-, and contaminated groundwaters economical and environmentally friendly in big Quantities removed, using a barrier material for uranium fixation which has a texture which is long-term stable, safe disposal or recovery of enriched uranium allows.

The Task is achieved by a method according to claim 1 solved. Advantageous embodiments are in the subclaims explained.

The Waters contaminated with uranium (VI) are passed through a two-part, reactive biogeochemical barrier, dried in the Anstrombereich the water from a mixture Hühnerkots as a waste product of poultry farming, which is preferably granulated, in a ratio of 1: 1 to 3: 1 mixed with naturally occurring Feldspar as a reactive carrier material wherein the feldspar preferably contains calcium and in a suitable grain size is present, the one to grant the permeability and contact time can be varied, and preferably between 63 and 2000 um. In the discharge area, this barrier consists exclusively of Feldspar. The quantity ratio chicken-fox-feldspar mixture in the Anstrombereich and the Feldspats in the Abstrombereich of the to be cleaned Water is between 1: 2 and 1: 5, preferably this ratio is 1: 3. Other accumulating, uranbelastete sewage sludge can by admixing with the dried chicken droppings be recycled up to a maximum of 20%, as the organic component of sewage sludge similar to the dried chicken droppings acts. As beneficial turns out, the purified water from the uranium after passing through this reactive biogeochemical barrier oxidatively to clarify, being the quality the water is further improved so that it is cleaned again into the water network can be fed. To the inventive cleaning of the loaded To reach water, the contact time of the water should be in the reactive biogeochemical barrier at least 4 hours.

in the Contact with the chicken faeces feldspar Mixture occurs, associated with the lowering of the electrochemical Redox potential, to a microbially catalyzed uranium (VI) reduction through the chicken feces contained reactive organic substance and precipitation of heavy in water soluble Uranium (IV) oxide and, in part, uranium (IV) silicate, the silicon from the slowly dissolving in contact with water Feldspar originates. By the very high phosphate content of the dried chicken drop forms with the calcium the feldspar also difficult to dissolve calcium phosphates or Uranium (VI) phosphate, which is the uranium (VI) dissolved in water and its decomposition products fix. The reactive carrier material Feldspar causes in addition to the release of silicon and calcium and the grant the permeability the barrier, a carrier function for catalytic effective as well as for Uranium sorbed microorganisms. In the downstream area of the feldspar to be purified water primarily serves as a filter for restraint the particular Ingredients of chicken droppings. In the following clarifiers becomes the electrochemical redox potential of the purified water raised again, and still contained, water-soluble, organic Ingredients of chicken droppings oxidatively degraded. In this process step, it comes to oxidation in the water contained iron (II) shares, which are called amorphous iron (III) hydroxide residual trace amounts of uranium and other heavy metals as well Fix arsenic.

The implementation of the process leads to an effective separation of uranium from heavily polluted waters, as they occur in uranium mining. This effectiveness of the method is realized by the fixation of the uranium within the biogeochemical barrier material, the combination of multiple retardation Mechanisms, such as bioelectrochemical reduction to uranium (IV) and precipitation of poorly soluble uranium (IV) oxide and uranium (IV) silicate, sorption on calcium phosphate or formation of uranium (VI) phosphates and sorption on biomass, of process engineering importance. The advantage of the invention over known methods and methods for heavy metal separation from waters is that it provides a method which is especially suitable for eliminating the uranium from the waters. It uses materials that are significantly less expensive than conventional sorbents such as ion exchange resins or calixarenes and are particularly available in rural areas with underdeveloped infrastructure, such as in developing countries with uranium mining available. The calcium phosphate apatite that forms in the biogeochemical barrier in this process is able to bind large divalent cations in its structure and thus represents a good fixation option in addition to uranium (VI) sorption for the uranium decay products radium and lead especially phosphate-containing (7.5 to 11% P) natural substance and feldspar as calcium source (up to 14% Ca) are combined very reactive starting materials for apatite formation according to the invention. This is advantageous over the known use of industrially produced phosphate sources such as phosphoric acid or sodium hydrogen phosphate.

The used reactive biogeochemical barrier material is strong after use according to the method uranhaltig, which requires conditioning for safe disposal or elution of the uranium for production purposes. Due to the mixing ratio of feldspar has the barrier material a chemical composition that is easier, industrial produced glasses is similar. This similarity is caused by the chicken feces contained components potassium and phosphate even stronger. It It is therefore appropriate that barrier material was made according to the procedure Uranium fixation to glaze or sinter by known methods and to immobilize uranium and its decay products over the long term. Economically In doing so, the carbonate contents, which are advantageous for the Decomposition of the chicken droppings used arise because they use the melting point in the glazing process as a flux reduce. Is the extraction of uranium of interest, is the possibility by known elution methods, such as leaching with sulfuric acid Solutions, To extract uranium from the barrier material used. The remaining one Feldspar can again be used in accordance with the procedure. Especially the vitrifiability of the spent, uranium-containing barrier material is a clear advantage over the previously known method for the purification of uranbelasteten Water. This applies above all to the use of metallic iron and lignite as well as the use of microorganisms in which the long-term Behavior of uranium-containing materials in the final disposal not is known.

The The invention will be explained in more detail below with reference to two exemplary embodiments.

1st embodiment

The ability of the material used in the biogeochemical barrier, uranium in high concentrations from water to remove, was in shaking attempts examined. To this was dried at room temperature 0.5 g each chicken droppings and 0.5 g of feldspar of particle size 63-200 μm in 40 ml solution dispersed and the uranium concentration at intervals of one week increased by 2.38 mg / l. The uranium levels determined with ICP-MS in solution after one week Contact time are shown in Table 1.

Table 1: Uranium retardation by biogeochemical barrier in the shaking test

As can be seen in Table 1, the barrier material used in the process has a high potential to remove uranium from water. The advantage of the method lies in the reduction of very high uranium concentrations concentrations, in particular in the range from 2 to 20 mg / l at high carbonate concentrations, to values which are close to the introduction limit values and associated therewith the fixation of the largest quantities of uranium.

2nd embodiment

In a column experiment, which largely met the conditions of underground mining, was at 20 to 25 ° C the effectiveness of the procedure. This was a loaded with 5 mg / l uranium (VI) Water, characterized by high concentrations of alkaline earths (Ca 309 mg / l, Mg 299 mg / l), alkalis (Na 528 mg / l, K 38 mg / l) and Total carbonate (1160 mg / l) and sulphate (1880 mg / l) - similar to one Flooding water, as released from uranium mines passed a two-part biogeochemical barrier. The flow of the water and thus the residence time were varied in two stages, wherein the residence time in the biogeochemical barrier at a Flow of about 20 ml per day for about 12 hours corresponded. In the first Part of the biogeochemical barrier, which consists of 2 parts dried Hühnerkots and a fraction of feldspar, uranium is almost completely out the water to be purified (Table 2), while the second part of the barrier in the outflow area primarily for retention or filtration is used. The relationship between the reactive chicken faeces feldspar Mixture and the passive filtration portion of the barrier was 2: 1.

Table 2: Uranium retardation by biogeochemical barrier in the column experiment

Claims (10)

Method for reducing the uranium (VI) concentration in fluent Water, in which the uranium (VI) predominantly is present as a carbonate, sulfate or hydroxy complex and element-specific Filter materials are used in a geochemical barrier, wherein the uranium contained in the water (VI) by means of a chicken faeces feldspar mixture converted into uranium (IV) oxide and uranium (VI) phosphate and both substances be precipitated in the geochemical barrier. Method according to claim 1, characterized in that that the process is carried out at a temperature between 8 and 40 ° C. Method according to claim 1, characterized in that that the chicken droppings is mixed in a dried form with the feldspar and the chicken faeces feldspar mixture between 3: 1 and 1: 1 is applied. Method according to claim 1, characterized in that that the waters immediately after passage of the chicken faeces feldspar mixture by feldspar in granular Be directed. Method according to claim 1, characterized in that that the residence time of the flowing waters in the geochemical barrier is between 4 and 12 hours. Method according to one of the claims 1, 3 or 4, characterized in that the feldspar in a Grain size between 63 and 2000 microns is used. Method according to claim 1 or 3, characterized that the dried chicken droppings is used in granulated form. Method according to claim 1, characterized in that that the chicken droppings uranium loaded sewage sludge up to added to 20%. Method according to claim 1, characterized in that that the waters be cleared oxidatively after passing the barrier. Method according to claim 1 or 3, characterized that the uranium-containing chicken feces-feldspar mixture glazed after use.