CZ3295A3 - Process of wasteless liquidation of waste water, product being formed during this process and its use for recultivation - Google Patents

Description

The invention relates to a process for the waste-free disposal of waste water containing, in particular, heavy metals and water-soluble salts, to the product formed in this process and to the use of this product for reclamation purposes.

Prior art

Many methods of wastewater treatment from municipal and industrial activities are known. In known water purification and treatment processes, the waste water is freed of undesired components by mechanical treatment, the action of chemicals, biological or other processes. Water treated in these ways, which is discharged into a public watercourse or possibly reused (recycled), contains residues of the chemical compounds used, often in the form of water-soluble salts, which degrades its quality and has an adverse effect on the environment.

Wastewater treatment methods are also known, in which the wastewater is treated mechanically and then with the aid of chemicals, after which it is treated by special technological processes such as electrodrodialysis, osmosis or ultrafiltration. In this way, treated water with a reduced salt content is obtained, as well as a salt concentrate which can be further used as such or, if appropriate, further processed by crystallization. If no use is found for said concentrate or crystalline salt, these materials must be stored as waste. The disadvantages of the described procedure are high costs and often problematic use of the final product.

A method for disposing of industrial waste water with a high salt content by evaporation technologies is also known. Here, the waste water is pretreated in various ways and then evaporation technology is applied. Soluble salts are obtained from the distillation residue by crystallization. This process produces a usable condensate and a solid crystalline fraction of inorganic salts, the commercial use of which determines the economics of the process.

The described known methods have a number of disadvantages, the investment and operating costs are considerable. It requires the construction of expensive buildings and / or the purchase of expensive equipment, the mastery of complex technology, the operation is demanding in terms of energy consumption, auxiliary chemicals and operation. An environmental assessment is also important in those cases where water-soluble salts remain intact in treated water or pose a potential hazard when wastewater treatment products are disposed of in insufficiently secured landfills.

Known methods of reclamation of old ecological burdens, especially sludge ponds and especially sludge ponds remaining after the completion of hydrometallurgical treatment of uranium ores (hereinafter sludge ponds), are associated with a number of serious problems, some of which can be solved only at very high cost. solved at all.

In the case of sludge tanks, the procedure is usually such that, after pumping out the salt water, the disposal of which is very difficult, the unfilled free volume of the sludge tank is gradually filled with various types of waste suitable for reclamation. For example, demolition building material, sewage sludge, excavated soil, etc. are used. However, these materials are suitable when they are spread on a solid stationary substrate. However, on a thixotropic incoherent substrate, their higher weight and low bonding increase the risk of the used mechanisms and vehicles falling into the muddy substrate. The strong thixotropic centers of the sludge tanks cannot be recultivated practically at all by this procedure.

In the treatment of uranium ores by a hydraulic process, the ore is finely ground and the uranium component is chemically separated in the form of a concentrate. The ground waste materials are transported to a repository (sludge tank), where the solid particles settle and separate. Coarser particles settle faster and settle on the edge of the aquifer, fine particles settle very slowly in the aquifer and form a bottom that has thixotropic properties. Water, which usually contains a high percentage of salts due to the chemical processing of the ore, is recycled during operation, which constantly increases the salt content. After the termination of the original function of the repository, it is first necessary to dispose of the residual salt water very expensively and then to recultivate the irrigated swampy centers and swampy beaches using suitable material.

During the processing of uranium ores, the sludge tanks show increased radiation emanation and therefore it is necessary to create a shielding layer with a thickness of at least 1 meter. The materials hitherto used for this purpose are heavy and incoherent, which causes the layer to form to sink into the swampy subsoil and push the bottom material over the structural material. This movement endangers the travel of the mechanization on the surface.

Another problem with the disposal of these repositories is that after the salt water has been pumped out, the thixotropic substrate is exposed, which dries out in some places and increases the dustiness and thus the entrainment of the active material into the air.

It can be stated that currently there is no reliable method available that would allow technically and economically to solve the reclamation of irrigated parts of sludge tanks, especially sludge tanks in uranium ore processing plants.

The essence of the invention

The subject of the invention is a method for waste-free disposal of waste waters containing water-soluble inorganic salts with

a significant proportion of heavy metals, distinguishing se that waste water (hereinafter always liquid folder) (k) se mixes with an inert solid component (t) and a lime component (in) in mass ratio k: t: v = (0.1 to 1.5): 1: (0.01 to 0.3) and the mixture is left, optionally after the previous one pretreatment,

solidify to the desired consistency.

The invention is based on the finding that when mixing the above-mentioned components, water with a high content of water-soluble salts is mineralogically firmly bound to the final product, from which the original water-soluble salts leach only to a very limited extent after solidification.

The process according to the invention is particularly suitable for the disposal of waste water from mining and processing activities and in particular for the waste-free disposal of radioactive high-salt waters, which represent a significant economic and environmental burden in mining, mining and hydrometallurgical processing of uranium and polymer ore. According to the method of the invention, it is possible to ecologically dispose of salt waste over-balance water, which is collected at the repositories of residues from ore processing and, after costly pretreatment, discharged into a public recipient (for example in the locality of Mydlovary to Vltava). For the sake of completeness, it should be added that it is of course possible to use any other technological water or, if necessary, drinking water for the given purpose.

As an inert solid phase, fly ash trapped in the purification of flue gases from the combustion of solid fossil fuels can be advantageously used. As the lime component it is possible to use calcium oxide, calcium hydrate, calcium sulphate, calcium carbonate or mixtures thereof, optionally with the addition of cement. Advantageously, the product lost during flue gas desulphurisation can be used by various technological processes, such as dry additive limestone technology, wet limestone washes or semi-dry lime processes. It is also possible to use wastes generated by fluidized bed combustion of solid fossil fuels with the addition of lime, limestone, etc. to the fluidized bed or directly to the fuel.

The process according to the invention is carried out in such a way that the waste water to be disposed of (optionally freed of solid impurities, leaves, wood, etc.) is mixed in a mixing device with a solid component and a lime component. It is also possible to add to the mixture various types of dusts containing iron, aluminum or aromatic derivatives such as foundry sands, oils from metallurgical production, construction materials, etc. After homogeneous mixing, the resulting product is either transported directly to the storage site or prepared to the desired location. consistency and allowed to solidify. The setting time depends on the ratio of the raw materials in carrying out the process according to the invention and on the temperature.

By suitable choice of the mutual ratio of the individual components, it is possible to achieve different forms of the final product. In principle, it is a free-flowing state or a form of a thick suspension to a paste. For example, when the liquid (k), solid (t) and lime (v) components are mixed in a weight ratio

k: t: v = (0, 1 to 0.6): 1: (0.01 to 0.3) has the final product loose consistency, while at ratio ' k; t; v = (0.6 to 1.5): 1: (0.01 to 0.3)

the product results in a thick suspension to a paste.

The ability to adjust the consistency of the resulting product in various ways is particularly advantageous because a product can be obtained whose consistency is optimal for its further desired applications or storage.

The product in bulk form can be transported over long distances in a simple manner, for example on the body of a truck, because it solidifies more slowly than the product in the form of a suspension or paste. After storage and possible compaction, this loose product then solidifies in about 24 to 75 hours and the resulting mass further increases its strength. The setting time depends on the temperature, the water content of the mixture and the amount and type of additive added.

The product according to the invention, i.e. solidified fly ash, can be layered in moist bulk form directly on a thixotropic swamp surface in a layer thickness of 0.1 to 5.0 m and preferably further mechanically compacted. The bulk solidify can also be loaded by a suitable mechanism directly into the waterlogged part of the sludge tank and allowed to solidify there. It is also possible to form a layer of sewage sludge, often waterlogged, and to coat it with a solidate with a layer thickness of 0.1 to 5.0 m.

The product in the form of a suspension or paste should be transported to the application site by a suitable technique, for example in closed containers or automixes. Since the solidification time of the suspension or paste varies between 5 and 20 hours, depending on the temperature, this procedure can be used for transport over shorter distances. The advantage of the product here is that it can be used to fill various hard-to-reach cavities, joints, etc. In this case, therefore, the solidified is deposited at the application site in the same way as the liquid concrete mixture is deposited. This material can also be cast into preforms where, after solidification, a product with high compressive strength ranging from 2.0 to 12.0 MPa and low water permeability in the range of about 10 ' ^s to 10' ⁹ cm is obtained. / s.

The basic common feature of all the forms described above is that both heavy metals and water-soluble salts are firmly bound in them and cannot endanger the environment.

The substantial advantages of the process according to the invention over the processes known to date can be summarized as follows:

1) Waste materials are preferably used as input components. These are wastewater, fly ash from the combustion of solid fossil fuels, dust from gas cleaning and a product that falls off during the desulphurisation of flue gases by various technologies. This solves the problem of simultaneous disposal of all three waste materials.

2) The method is quite investmentable and technologically manageable, not demanding on energy consumption and operation.

3) The process according to the invention produces a material which can be expediently used for reclamation purposes.

By using the material formed in the process according to the invention for the reclamation of old ecological burdens, in particular irrigated parts of sludge tanks and in particular sludge tanks from uranium ore processing plants, the basic problems associated with this reclamation can be avoided. It has been found that the solids resulting from the process according to the invention are particularly suitable for the construction of the cover and support layers required for the reclamation work.

4) By a suitable choice of the ratio and type of input raw materials, materials can be obtained which are characterized by low water permeability, high degree of radiation shielding and optimal weight, ensuring the formation of a solid layer over the thixotropic substrate. Very good mechanical properties (compressive strength) allow the travel of even heavy mechanisms on the surface of the formed covering and shielding layer.

5) The material obtained during the application of the method according to the invention can also be used for reclamation of other types of repositories, such as municipal waste landfills, etc. The material can also be used as a base construction material in the construction of landfills.

The invention is illustrated by the following examples, which do not limit the scope of the invention in any way.

Examples of embodiments of the invention

Example 1

Water from the sump containing 16 000 mg of SO _4/1, 980 mg of NH _4/1, 276 mg NO _3/1, 140 mg NO. / 1, 400 mg Mn / 1, 2.05 mg U / 1, 2.1 mg V / 1, 3.71 mg Cr / 1, 5.05 mg Ni / 1, 60 mg Cl / 1 and combustion ash of brown coal were mixed in a weight ratio of k: t = 0.8: 1

Calcium hydrate was further added to the mixture in an amount of 5.1% by weight, based on the weight of the mixture. The resulting ternary mixture was stirred for 5 minutes. Then, the mixture in the form of a thick paste was filled into a plastic mold, where. within 24 hours it solidified to a solid state.

After removal from the mold, the material was subjected to a compressive strength test and a strength of 6 MPa was found. After crushing the material, a water leachability test was performed according to the prescribed methodology (Government Regulation No. 513/92 Coll.) With the following result:

Composition of the aqueous extract:

Component S0 ₄ nh ₄ No. ₃ No. ₂ Mn U V Cr total. Ni Cl Leaching telnost (mg / 1) 240.0 0.5 20.0 18.0 0.3 0.01 0.04 0.03 0.02 21.0

Example 2

The procedure was as in Example 1, except that the flue gas desulphurisation product was used instead of the lime hydrate by the semi-dry lime method. Weight ratios of fly ash: desulphurisation product = 1: 1

Composition of the aqueous extract:

Component S0 ₄ nh ₄ no ₃ NO. Mn U V Cr Ni Cl total. Leachate telnost 210, 0 0.45 28.0 26.0 0.2 0.04 0.04 0.03 0.02 28.0 (mg / 1)

Example 3

The procedure was as in Example 1, except that the waste water was mixed with the solids collected in a separator downstream of a fluidized bed boiler in which brown coal was burned with the addition of 12% by weight. calcium carbonate. No additive was added to the mixture. The mixture was prepared by mixing one part of said solid phase and 0.8 part of waste salt water.

Composition of the aqueous extract:

Component S0 ₄ nh ₄ No. ₃ NO ₂ Mn U V Cr Ni Cl total. Leachate telnost 412.0 0.3 18.0 21.0 0.1 0.04 0.02 0.02 0.01 31.0 (mg / 1)

Example 4

A mixture of fly ash and flue gas desulphurisation product obtained from an electrostatic precipitator downstream of a fluidised bed boiler in which coal was burned with the addition of 12% by weight. calcium carbonate (based on the weight of the fuel burned) was mixed with process water in the mixing plant in the ratio t of the fly ash mixture: 300 kg of process water

The resulting moistened mixture was transported from the mixing plant, installed at the producer, by truck in bulk up to a distance of 50 km to the storage location. At the storage site, it was used to recultivate the area of the decommissioned sludge tank of the plant, which hydraulically processed uranium ore into a chemical concentrate and transported the leached ore to the sludge tank by hydraulic means.

The mixture was deposited partly directly on the thixotropic surface of the displaced precipitated material, partly directly in the over-balancing process water above the thixotropic material in a layer thickness of about 0.5 m to 1.5 m. This overlay layer was compacted by traveling mechanisms and then overcoated with a 20 cm layer. excavated soils. The surface created in this way proved to be suitable for the biological remediation of the building. A reclamation layer on an area of 0.1 ha was made from one thousand tons of moistened material in the manner described above.

Example 5

Reclamation of a swampy beach

Fly ash obtained from fluidised bed combustion of brown coal additive of 3% by weight of calcium hydroxide trapped in the separation device was solidified in the mixing device with the addition of 28.5% by weight. technical water) A moist mixture with a bulk density of 890 kg / m ³ was obtained.

The mixture was transported by truck * to the sludge tank space and stored in an amount of 2000 t in a layer of thickness

1.5 m on a typical transition bed of a sludge tank with thixotropic properties and subsequently compacted by a dozer. After storage, no changes were observed at the edge of the deposited material. After compaction, even heavily loaded vehicles could be driven along the edges of the compacted material in 24 hours without shifting the stored material.

After deposition, the shielding efficiency of the radioactivity was measured with a solidate layer with a thickness of 1.5 m. The reduction of radioactivity by 93.6% was measured.

Example 6

Reclamation of the irrigated part

In the lagoon of the sludge tank, after loading the edge parts, a swamp was formed, covered by a water surface. This part could not be recultivated by simple introduction of soil due to the fall of the soil into the thixotropic bottom. The lagoon had an area of 0.5 ha, of which the aquifer part 0.2 ha. The solidified composition in the composition given in Example 5 was applied. The solidified composition was transported to the paved edge by trucks, and the swampy area, including the water surface, was covered with unconsolidated solidificate and compacted by a dozer.

When the water surface was covered with solidification, there was an intensive infiltration of water into the material. The sampled material increases its water content from the original 28.5% by weight. on

86.2% by weight The solidate after contact with water shows strong hydrating properties, which is manifested by an increase in temperature by 4.1 ° C. After covering the irrigated area of the lagoon with solidification and compaction with a dozer, the surface was covered with recultivation soil with a layer thickness of 0.25 m. After 48 hours despite the thus recultivated part of the irrigated sludge tank, no negative reactions of the subsoil occur.

Measurements of radioactivity showed a reduction of the radioactive background by 93% of the original value of the subsoil.

Example 7

Combination with brown coal slag

In rainy weather, the soil was soaked on the driveway in the area of the sludge tank, which was originally recultivated by excavated soil, sewage sludge, etc. Wetting of the surface completely ruled out the possibility of transporting the solidificate to the place of application in the dedicated part of the sludge tank.

The dozer created a corridor of the access road to the place of application, this corridor was introduced by solidification and compacted by a dozer. The compacted surface was covered with fossil fuel slag. After compaction, this crossing corridor was used as a road by heavy mechanisms, transporting solidification to the central part of the sludge tanks without any problems, even in very rainy weather. In the case of the original areas reclaimed with soil, on the other hand, it was necessary to significantly reduce the reclamation work or temporarily stop it completely.

Example 8

Combination with dust from steel mills

In the dedicated part of the municipal waste landfill, a space of 2.5 x 3.0 m was excavated and filled with solidification made from fly ash generated during the combustion of black coal, steelworks dust, limestone dust containing 52% lime hydrate and service water.

Dust from steel mills contained 24.3% by weight. zinc,

6.2% by weight of lead, 0.3 wt. cadmium and 22 wt. ferric oxide.

*

An aqueous extract of dust was prepared by the prescribed methodology with the following result:

Component Zn Pb CD Fe pH Leachability (mg / 1) 120.0 86.0 32.0 41.0 6.8

The high solubility of the components was reduced by solidification. The solidate was experimentally applied as an overlay to the substrate formed by compacted municipal waste, as follows:

1.5 t of fly ash from hard coal combustion separators were mixed with a truck mixer with 240 kg of waste lime hydrate, 4.78 t of steelworks waste and 1.45 t of service water. The mixture was stirred for 20 minutes, the resulting slurry was then placed in a dredged space. After thirty, sixty and ninety days, control samples were taken to determine the leachability of the components that provided

these results: after 30 days: - Component Zn _ Pb CD Fe pH Leachability (mg / 1) 0.37 0.08 less than 0.005 less than 0.1 11.3

after 60 days:

Component Zn Pb CD Fe pH Leachability 0.27 0.08 less than less than 11.4 (mg / 1) 0.005 0.1

after 90 days:

Component Zn Pb CD Fe pH Leach eInos t 0.20 0.06 less than less than 11.4 (mg / 1) 0.005 0.1

After three months, the surface was covered with soil and it was possible to drive on it without any problems.

Example 9

Solidified in combination with sewage sludge

The procedure was as in Example 5, except that the thixotropic radioactive surface was covered with a 0.5 m thick sewage sludge layer by simply spreading the material without compaction, and then this layer was covered with a 1.5 m thick layer solidified and compacted with a dozer. After compaction, it was possible to drive on the surface without any problems even in heavy rainy weather with fully loaded trucks with a total tonnage of 32 t.

On the other hand, movement on pedestrians, even in the dry season, was not possible on a substrate covered only with a layer of sewage sludge.

Industrial applicability

The process according to the invention can be used for the ecologically extremely suitable waste-free disposal of in particular waste water at the same time as the disposal of waste ash and slag from the combustion of solid fossil fuels and flue gas desulphurisation products. The resulting product can be used for safe and environmentally friendly reclamation of ecological burdens, especially swampy parts of water lilies.

Claims (10)

PATENT CLAIMS A process for the waste-free disposal of waste waters containing, in particular, heavy metals and water-soluble salts, characterized in that the liquid component is mixed with an inert solid particulate and lime component in a weight ratio (0.1 to 1.5): 1 (0.01 to 0.3) and the mixture is allowed to solidify to the desired consistency, if necessary after previous application. Method according to claim 1, characterized in that waste water from mining and treatment operations, in particular radioactive high-salt water, is used as the liquid component. Method according to claims 1 and 2, characterized in that fly ash entrapped in solid particle separators is used as the solid component, in particular fly ash from the combustion of solid fossil fuels, optionally mixed with a slag of the same fossil fuel. Method according to claims 1 to 3, characterized in that either the lime hydrate, calcium sulphate, calcium oxide, calcium carbonate or a mixture thereof, or a mixture thereof with the addition of cement, preferably their various waste forms. Method according to claim 4, characterized in that the lime product is a lime product from the desulphurization of the flue gas by the semi-dry lime method, in particular the product from the desulphurisation of the flue gas resulting from the combustion of solid fossil fuels. Method according to claims 1 to 5, characterized in that the liquid, solid and lime component are mixed in a weight ratio (0.1 to 0.6): 1: (0.01 to 0.3) to form a product. loose consistency. Method according to claims 1 to 5, characterized in that the liquid, solid and lime component are mixed in a ratio of (0.6 to 1.5): 1: (0.01 to 0.3) to form a product in in the form of a thick suspension to a paste. A free-flowing, pasty or suspension product resulting from the disposal of wastewater according to claim 1, formed by mixing the wastewater with a particulate solid component and a lime component, in a weight ratio (0.1 to 1.5): 1: : (0.01 to 0.3). Use of the material according to claim 8 for the reclamation of ecological burdens, in particular sludges and tailings ponds, preferably sludges, in uranium ore treatment plants. Use according to claim 9, characterized in that the free-flowing mixture according to claim 6 is applied to the aquifer part of the sludge and optionally metallurgical.