RU2366521C1 - Method of toxic waste disposal - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method excludes toxicant migration in geological environment and can be used as in new construction of land disposals as well as at recuperation and liquidation of the existing ones. The claimed method allows to enhance the geotechnical performance of the constructions foundation soils and provides protection of the environment from contamination. Method of toxic wastes disposal includes excavation of the foundation pit, installation of the protective covering on its walls and bottom, packed laying of the disposal layer by layer, bridging of every layer with separative insulating layer of the low-permeability material; after laying of the upper separative insulating layer the geochemical barrier in the form of the contour multilayer labyrinth curtain is carried out. The disposal layer of every level is bound by the way of pumping under pressure of the foamed solidifying soil cement slurry at component ratio dangerous waste: foamed soil cement = 2:1.

EFFECT: enhancing of the reliability of toxic waste disposal and excluding of the toxicant migration from disposal zone to the subsoil, underground water and atmosphere.

3 dwg, 1 tbl, 1 ex

Description

The invention relates to the field of construction of landfills for waste, in particular to technologies that increase the reliability of the disposal of toxic waste, and methods of binding them by injection methods. The method eliminates the migration of toxicants in the geological environment and can be used both in the new construction of landfills, and in the recovery and liquidation of existing ones. The method allows to improve the geotechnical characteristics of the soils of the base of the foundations of structures constructed at the sites of former landfills, and also provides environmental protection from pollution.

A known method of disposing of solid household waste, including excavating a pit, layering waste with packing and overlapping layers of low-permeable material (see "Instructions for the design, operation and reclamation of landfills for disposal of solid household waste." Moscow. 1996 t.) / 1 /

The disadvantage of this method is the poor compaction of the layers and their poor waterproofing, which leads to the formation of voids, dips on the surface, the migration of harmful substances into the environment and, as a result, pollution of the soil, groundwater and air.

A known method of protecting the environment, including the installation of a protective barrier in the soil around the perimeter of the contaminated area from anti-filter material (for example, clay) according to the type “wall in soil”, in which a trench is first arranged, which is subsequently filled with clay mortar, or in the form of a sheet pile flat elements connected to the lock and preventing the spread of pollution (see "The way to protect the environment from pollution by household and industrial waste." RU No. 2294245, B09B 1/00, 2007-02-27) / 2 /

The disadvantage of this method is that when creating a barrier, it is necessary to build a trench, fill it with a clay solution or erect a sheet pile from flat elements, which significantly increases the cost and complexity of the work, and does not exclude the possibility of environmental pollution during their implementation.

A known method of neutralizing liquid toxic waste (RU application No. 93003297, C02F 1/12, 1995.06.19) / 3 / by pre-mixing them with a natural diatomite sorbent at the rate of not less than 500 kg per 1 m ^{3 of} waste. After stirring, the mixture is buried.

The disadvantage of this method is the need to transport diatomite from the place of its extraction, significant costs for mixing and laying the mixture at the burial site with the device of protective screens.

Injection methods for strengthening soils are known, which allow improving the properties of soils of the base of foundations, as well as filling voids and creating curtains in the form of geochemical barriers, including through directional breaks (SU 1444473, E02D 3/12, 1988-12-15) / 4 /, (SU 1227787, 4E05B 37/12, 1986-04-30) / 5 /, (RU 2122068, E02D 3/14, 1999-11-20) / 6 /, (see 50-306-2005 "Reasons and foundations of increased bearing capacity. ”Ministry of Construction, Architecture and Housing and Public Utilities of the RO, 2005) / 7 /.

A disadvantage of the known methods is the lack of information about the possibility of their use for binding toxic waste and reducing the migration of toxicants in the soil environment.

The closest known solutions to the technical nature and the achieved effect to the proposed invention (prototype) is a method for the disposal of toxic waste, including excavation of a pit, a protective layer on its sides and bottom, layer-by-layer waste packing with a seal, overlapping of each layer with a separating insulating layer of low-permeable material (see SNiP 2.01.28-85. "Landfills for the neutralization and disposal of toxic industrial waste. The main provisions for the design." Moscow. 1985) / 8 /.

The disadvantage of this method is the impossibility of high-quality compaction of the waste layers, poor waterproofing and the possibility of migration of toxicants when exposed to the aqueous phase (rain, snow). This leads to the formation of voids, dips on the surface, the migration of harmful substances into the environment and, as a result, pollution of the soil, groundwater and air.

The technical result and the objective of the invention is to increase the reliability of the disposal of toxic waste and the exclusion of the possibility of migration of toxicants from them into soils, groundwater and the atmosphere from the disposal zone.

The essence of the invention lies in the fact that in the known method for the disposal of toxic waste, including excavation of a pit, the device of a protective layer along its sides and bottom, layer-by-layer stacking of waste with a seal, overlapping of each layer with a separating insulating layer of low permeability material, after laying the upper separating insulating layer, a geochemical a barrier in the form of a contour multilayer labyrinth curtain, and a layer of waste of each level is connected by injection of foamed hardening cement under pressure to soil solutions to obtain a volume ratio of components 2: 1 in the array (hazardous waste: foamed cement soil).

The invention is illustrated by the drawings depicted in figure 1 ÷ 3.

Figure 1 shows a cross section of a pit with a protective layer along its sides and bottom; layers of toxic waste and separation insulating layers of low permeability material.

Figure 2 - device geochemical barrier in the form of a contour multilayer labyrinth curtain.

Figure 3 - binding of the layer of waste at each level by injection under pressure of foamed hardening cement-soil solutions with obtaining in the array the volume ratio of components 2: 1 (toxic waste: foamed cement).

The method is carried out in the following sequence.

First, excavate a pit 1, arrange a protective layer 2 along its sides and bottom, layer-by-layer waste packing 3 with a seal, cover each layer 3 with a separating insulating layer of low-permeability material 4. Then, after laying the upper separating insulating layer 5, a geochemical barrier 6 with contour multilayer elements is performed labyrinth curtain 7 through the injector with a cutter 8.

In the next step, the layer 3 of waste of each level is bonded from bottom to top by injection under pressure through injectors 9 foamed hardening cement soil solutions to obtain in the array of fixing zones 10 with a volume ratio of components 2: 1 (hazardous waste: foamed cement soil).

When creating a geochemical barrier 6 in the form of a contour multilayer labyrinth curtain with elements 7, for example, methods of sequential injection of two components through a directed discontinuity are used (SU 1444473, 1227787). Moreover, a feature of the invention is the injection of the first solution, for example sodium silicate, with properties that provide sorption of toxic waste in layers 6, that is, to form an element of the geochemical barrier. The second solution (for example, based on cement) is a hardening solution, which serves to create a multilayer labyrinth curtain of elements 7.

When aqueous solutions of sodium silicate are injected into the soil (for example, through an injector with a cutter 8), an instant reaction occurs between the injected solution and the absorbing complex of the soil with the formation of calcium oxide hydrate. Calcium oxide hydrate is an amorphous mass with a large specific surface on which silicic acid gel is adsorbed. In parallel with these processes of ion exchange and sorption, sodium silicate also interacts with gypsum, calcium carbonate and other salts on the surface of particles and aggregates with the formation of thin films of silicic acid gel.

Physico-chemical processes that occur during the interaction of aqueous solutions of sodium silicate and loess rocks can be represented in the form of reactions where the soil itself plays the role of hardener

[PC] Ca + Na ₂ O nSiO ₂ + mH ₂ O = [PC] Na + nSiO ₂ (m-1) H ₂ O + Ca (OH) ₂

CaSO ₄ + Na ₂ O nSiO ₂ + mH ₂ O = Na ₂ SO ₄ + nSiO ₂ (m-1) H ₂ O + Ca (OH) ₂

CaCO ₃ + Na ₂ O nSiO ₂ + mH ₂ O = Na ₂ CO ₃ + nSiO ₂ (m-1) H ₂ O + Ca (OH) ₂

The reaction products provide significant hardening of the soil, reduce its permeability, increase the bearing capacity and water resistance. As is known, the exchange capacity of loess rocks in an alkaline medium increases sharply, because of this, the main role in the fixing process is played by exchange reactions between calcium cations of the colloidal-mineral part of the soil and sodium silicate solution. This reaction is presented as:

Depending on the activity of the soil, its structural strength and physico-mechanical characteristics, as well as the density of the injected solution and its volume, a geochemical barrier is obtained from the fixed soil. Excess hydrate of calcium oxide and sodium silicate provide physico-chemical sorption of the toxic components of the waste and prevent its migration to the environment.

During migration, the toxicant must overcome not only the labyrinth of elements 7, but also be repeatedly filtered through the elements of the geochemical barrier 6. When using these methods and this design of the curtain, not only the permeability of the sides of the foundation pit is sharply reduced, but also the migration of toxicants into the environment due to chemical processes is excluded , ion exchange and sorption. In addition, the curtain improves the conditions for the binding of toxicants by foamed cement mortar, as it eliminates the possibility of the solution leaving the treated layer.

The injection of hardening foamed cement mortar solutions to bind toxicants in layers 3 is carried out under pressure using one of the methods specified in TSN 50-306-2005, through injectors 9 or previously drilled wells. In this case, first the filling of voids, loose zones and other violations and defects in the waste layer occurs. Then, when the pressure rises to 0.3-0.6 MPa, the rest of the waste layer is impregnated (including through micro-fractures) with compaction and binding of the bulk.

The composition of the foamed cement mortar can be taken depending on the hazard class of the waste, the type and amount of toxic components contained in it (for example, with different cement contents, according to the invention patent No. 2122068). In this case, for supertoxicants of hazard class 1-2, the solution should have at least 50-70% cement, and for the rest in the range of 10-45%. A feature of the application of the above methods in the present invention is that, as laboratory studies have shown, the highest binding efficiency of toxic wastes (e.g. pesticides, copper and iron sulfate, etc.) is achieved when the volume ratio of the components is 2: 1 in the array (hazardous waste: foamed cement soil) and below. Moreover, the recoverability of toxic components from cement stone is 20–25 times less than from the initial waste.

As an example of a specific implementation of the method, we consider proposals for the destruction (conservation) of a landfill for the disposal of hazardous waste-pesticides, salts of copper sulfate and other pesticides in the area of Bataisk, Rostov Region.

The disposal of hazardous waste was carried out in 1977-78. in compliance with the basic requirements for the selection of the site, geological conditions, etc. in camouflage cavities obtained by the explosion at a depth of 25-30 m in low-permeable clay soils. 120-150 tons of pesticides and other pesticides were put into each container. The waste was supplied in bulk, in containers and without containers, through a “pipe” with a diameter of 1.0 m, which, after completion of work, was filled with clay soil with the creation of an earth cork in the upper part. Considering that groundwater was opened at a depth of 49.5 m, and the underlying soil with waste was represented by low-permeable clays, a decision was made to arrange a geochemical barrier in the form of a contour multilayer labyrinth curtain and to bind toxicants in the camouflage cavity with foamed cement-soil solutions obtaining in the array a volume ratio of components 2: 1 (hazardous waste: foamed cement soil).

During the operation of the landfill, due to poor compaction of the waste during installation, surface dips with a diameter and depth of 4-5 m occurred. In view of this, before the start of the injection work, it was proposed to fill up the dips and lay a clay pillow on top of 1.5-2.0 m. Then it was proposed to create a geochemical barrier with elements of a contour multilayer labyrinth curtain (through an injector with a cutter according to author certificate No. 1444473) by first injecting through a directed gap 600 l / l.m solution of sodium silicate with a density of 1.13 g / cm ³ and then after flushing hoses and injectors with a water cutter of 150 l / l.m foamed cement mortar with 20% cement content. At the same time, a combined element of a geochemical barrier with a thickness of 20 cm was formed, inside of which (at the second injection stage), an element of a labyrinth curtain of cement-soil stone with a thickness of 5.0 cm and a length of 3.0 m was formed. Of these combined elements with a thickness of 25 cm along the contour of each cavity a two-layer curtain was laid (2 layers of 25 cm) with a total length of 18.0 m in plan and 10 m high.

After the geochemical barrier with the elements of the contour multilayer labyrinth curtain was completed, wells with a diameter of 127 mm were drilled, equipped with injection pipes for injection work to bind waste in the camouflage cavity. The total number of injections was 12 pcs. with an injection radius of 1.0 m and an entry height of 4 m. Based on the ratio of hazardous waste: foamed cement in a 2: 1 array, 6.0 m ^{3 of} foamed cement and mortar was injected per injection. The parameters of the solution at 50% cement and 50% loam with a ductility number of 0.11-0.14 are shown in the table.

Table Component consumption per 1000 l of working solution % soda cement in tv phases. Cement, kg Amount of soil, kg Number of surfactants, kg The amount of water, l Parameters of soil suspension for cement for soil Total acc. G: B Volume l γ, g / cm ³ fifty 530 530 0.6 250 450 700 1.18 740 1.38

To prepare a soil suspension, use loams with a plasticity number of not more than 0.14. Cement grade should be at least 400.

Thus, due to the creation of a geochemical curtain barrier and the binding of waste in the cavity, the possibility of environmental pollution is sharply reduced, and the toxic waste disposal area is surrounded by a “sarcophagus” of cement soil.

Information sources

1. Instructions for the design, operation and reclamation of landfills for the disposal of municipal solid waste. Moscow. 1996 year

2. RU No. 2294245, B09B 1/00, 2007-02-27.

3. RU application No. 93003297, C02F 1/12, 1995.06.19.

4. SU 1444473, E02D 3/12, 1988-12-15.

5. SU 1227787, 4 E05B 37/12, 1986-04-30.

6. RU 2122068, E02D 3/14, 1999-11-20.

7. TSN 50-306-2005 "Foundations and foundations of increased bearing capacity." Ministry of Construction, Architecture and Housing and Public Utilities of the RO, 2005

8. SNiP 2.01.28-85. “Landfills for the disposal and disposal of toxic industrial waste. Design Guidelines. ” Moscow. 1985 - prototype.

Claims (1)

A method for the disposal of toxic waste, including excavation of a pit, arranging a protective layer along its sides and bottom, layer-by-layer waste packing with compaction, overlapping each layer with a separating insulating layer of low permeability material, characterized in that after laying the upper separating insulating layer, a geochemical barrier in the form of a contour multilayer a labyrinth curtain, and a layer of waste of each level is connected by injection under pressure of foamed hardening cement-soil solutions to obtain in the array of the volumetric ratio of components hazardous waste: foamed cement soil = 2: 1.

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