DE19858004A1 - Non-alkaline gel-forming mixture for sealing ground, waste heaps and dumps against ground water penetration consists of waterglass, water, acidic reagent, anionic polyelectrolyte and additives - Google Patents

Abstract

Non-alkaline gel-forming mixture consists of waterglass, water, acidic reagent, anionic polyelectrolyte and additives. Preferred Features: The additives are, e.g., inorganic and organic salts, buffers, alcohols, nonionic polymers, wetting agents or foam inhibitors.

Description

The invention relates to a non-alkaline, gel-forming mixture for sealing and Solidification of soils against the flow of water in construction and civil engineering objects, for Sealing of engineering objects built into the floor and for encapsulating Contaminated sites and landfills to protect groundwater.

Under civil engineering objects there are preferably construction pits, under engineering objects manholes, Understand storage, basins and tunnels. Under the soil are fine to coarse sand or these soils or fillings that are comparable in terms of grain sizes.

It is known that for the purpose of sealing and consolidating soil Water glasses, usually soda water glass, can be used as gel formers. For the production of sealing measures, common soft gels are used Water glass solutions water and reactive, the latter added in such doses that gel formation is delayed and compression (injection) of the mixture into the So floor is made possible. Acids can be used as reactive agents to trigger gel formation and salts, preferably salts of polyvalent metals, as well as cationic colloids (Literature: Cambefort, H .: Bodeninjektionstechnik, Bauverlag GmbH, 1969). Soft gels are also made by adding a reactive combination consisting of a tri- Alkoxi-alkyl-silane and monosodium dihydrogen monophosphate, obtained (literature: Hass, H.-J., All-round encapsulation of pollutants in the underground by means of pollutant-resistant Injection gels and sealants, Federal Environment Agency, Materials 1/85, pp. 357-408).

To achieve sufficiently long gel times of at least 30, better 45-60 minutes, the enable the agents to be injected into the soil, it is common for the reactive agents mentioned above to dose that the pH of the water glass / water / reactive mixture in alkaline Area remains and there is delayed and incomplete gel formation. This The approach is particularly important in soils next to or under landfills and contaminated sites high levels of acids and acids which act as reactive for the gel formation of water glass Salts, but also in pollutant-free soils with naturally high salt levels and interchangeably bound proportions of polyvalent metallic cations, the Disadvantage that strong reductions that change with the reactive potential of the soils the gel time and spread of the injection mixtures that may occur Question the applicability of the injection procedure. The constant adjustment of the Recipes of the alkaline agents to the given soil load with reactive active substances required effort for sampling and analytical Exploration is not feasible.

By washing out and under the influence of what is known as syneresis Shrinkage process, these gels separate water and non-gelled alkali silicates and Silicas, which leads to a reduction in the strength and the sealing effect of the generated gels in the pores and voids of the soil leads.

The disadvantage of incomplete gel formation can be found in U.S. Patent No. 4,226,556 be avoided if so much acid is added to a water glass that a pH Set a value of 5 or less. To make such a non-alkaline mixture it is required according to the cited patent specification to put water glass in an aqueous solution of the acid reactives at high speed to prevent premature precipitation of To avoid silicas. Stir is not enough to make a homogeneous injectable To get mixture. The acidic mixture can be used to fine-tune the pH weak acids or acid salts, but also alkaline compounds can be added.  

A characteristic of non-alkaline water glass brine that can be injected for sealing is that they have very low viscosities at the beginning and slowly change to a gel. The combination of low viscosity and long gel time involves risks for the too Sealing purposes required the production of uniformly structured injection bodies.

Injection agents with the properties mentioned can under the influence of Gravity drains down into crevices and cavities or through flowing Groundwater from the injection and thus destination are shipped. The making of a closed sealing layer is very due to this spreading behavior at risk. This is particularly critical because there are no sophisticated procedures to check the tightness of sealing walls made by injection.

The with the reactive combination of tri-alkoxy-alkyl-silane and monosodium di Hydrogen monophosphate soft gels are made by using the silane component very expensive. In addition, the silane component is for the user in the processing process toxic as well as fire and explosion hazard during storage.

There are a number of ways to influence the properties of gels based on water glass chemical substances as additives to the basic recipes for the production of water glass gels, consisting of water glass, water and reactive have been proposed. In the Hungarian Patent No. 186,586 describes the addition of organic polymers to Water glass solutions with gaseous fluorides as reactive the elasticity of the resulting Gels increased. This procedure is because of the high toxicity of those used as reactive Fluorides such as hydrogen fluoride, silicon tetrafluoride and hydrogen silicon fluoride hardly applicable. In the German patent DE 44 25 314 the application nonionic organic polymers to increase the viscosity of aqueous Metal salt solutions described that are injected into the soil as the first solution and to aqueous in a second injection process for the purpose of gel formation Silica sol is added. According to British Patent GB 2,186,879, the Rapidly increasing viscosity of the injection mixtures for the production of water glass gels when adding organic polymers as disadvantageous for influencing the Gel properties considered because of the deterioration in injectability the mixtures preclude an optimization of the polymer content. That is why proposed to add gels by adding polycarboxylic acids from water glass solutions generate and at the same time to increase their elasticity monomers organic Polymers, together with these cross-linking substances and required for this Catalysts to add to the water glass solutions to reduce the content of To increase polymer in the resulting gel.

For the sealing of contaminated sites and landfills by encapsulation with silica-containing, only slightly water-permeable soil layers, but also for the introduction of the necessary injection mixtures in soils with a high proportion of naturally occurring components that trigger the gel formation of water glass, preparations based on the components water glass / Water / reactive needed that:

• - The influence of gelling agents in the soil such as acids, salts and interchangeable multivalent metallic cations at the time of injection exclude,
• Cause a high rate of conversion of the water glass sol to silica gel,  
• - Have a spreading behavior that, by influencing the viscosity and the gel time or tipping time of the injection mixture, which is dependent on this, can be regulated can be designed
• - can be produced with simple technology,
• - Form gels, the low losses of silicate due to leaching as well as low Volume shrinkage due to syneresis and thus a high sealing Have an effect
• - produce gels resistant to contaminants from contaminated sites and landfills,
• - are inexpensive to use,
• - largely exclude dangers for users and the environment,
• - due to the totality of their properties favorable conditions for the Show applicability under practical conditions.

The object of the invention is to achieve the stated object.

It was found that non-alkaline water glass / water / acid mixtures as ge prove the requirements regarding the exclusion of the gel-forming effect to ensure reactive in the ground at the time of injection and a effect complete conversion of the water glass to silica gel. The spread such injection mixtures in the soil is only of its geological structure, especially the porosity, and the quantitative relationships of the starting materials in the Injection mixture dependent.

It was also found that the very low viscosity of the non-alkaline Injection agent advantageous depending on the dose by adding anionic polyelectrolytes can be raised, not only due to the higher viscosity of these substances themselves, but also on interactions between the polyelectrolytes and the silica particles is due. As a result, the spread of the agents according to the invention in injectable soils controllably reduced and drift restricted, but on the other hand also a good fusion of the injection body to a uniform sealing Layer can be achieved by setting sufficiently long gel times. Will continue by adding the anionic polyelectrolyte, the sealing effect of the resulting mixture according to the invention improved gel.

A simplified preparation of non-alkaline injection mixtures is possible if one exact control of the pH value takes place. This is achieved when the quantities used water-diluted water glass and water-diluted acid preferably equal volumes via dosing pumps of a slightly acidified aqueous receiver be added with stirring. This mixture is mixed in with further stirring anionic polyelectrolyte present in aqueous solution or emulsion. At Ensuring adequate mechanical mixing of the for the production of Soft gels dosed individual components in the pH range ≦ 4, is a premature Gel formation excluded.

Produced on the basis of the non-alkaline injection mixtures according to the invention Soft gels are characterized by extremely low leaching of silicate as well as by low syneresis. This is due to the addition of the acidic reactive in  Dosages that cause a high gelation rate of the water glass, as well as by the Silica particle cross-linking properties of the polyelectrolyte.

Fine to medium-sandy mica sands solidified with mixtures according to the invention proved to be effective over a test period of 250 days in a highly inorganic and organic contaminated groundwater of a landfill (pH 3.8; conductivity 14.9 mS / cm; chemical oxygen requirement 1077 mg / l) resistant. Long-term tests with this groundwater in uniaxial permeability measuring cells for the penetration of such injection bodies under the action of a hydraulic gradient of 10 showed that permeability coefficients of <1.10 ^-9 m / s can be reliably achieved.

All recipe components of the mixtures according to the invention are on an industrial scale manufactured. The high gelation rate of these mixtures enables savings of Water glass compared to alkaline injection mixtures or the manufacture higher quality, denser and therefore more impermeable gels. The necessary Mixing processes can be implemented with simple technology. These factors are the basis for the cost-effective solution of the inventive objective.

Water glass is a completely non-toxic product. The in the injection mixtures and gels The silica contained is inert in the soil and groundwater. From the Water glass released by ion exchange as well as from the preferably Anions released as reactive mineral acids are not foreign substances in the Groundwater, but naturally occur there. Only the proportion of these ions will temporarily increased in the vicinity of the applied sealing layers. The The polymers used are based on their ability to interact with the Silicas held in the gel. Your application in aqueous media, e.g. B. as Flocculant is allowed and common. Biodegradation of chemical substances in Water glass gels can have a maximum of 60 Å due to the narrow pore spaces Make the ingress of bacteria and fungi impossible, be excluded. It is also possible to use polymers that are not biodegradable, such as z. B. applies to the polyacrylamides.

The properties of the agents according to the invention described above are documented animals achieve the inventive goal and are the basis for usability of the result.

Water glass solutions with an SiO ₂ / Na ₂ O weight ratio of greater than 3, preferably from 3.2 to 4.0, are preferably used in the agents according to the invention, the viscosity of which in the undiluted state is between 10-1000 mPa.s, expediently between 10 150 mPa.s.

The addition of water, based on the amount of water glass used in the mixtures, can in a volume ratio of 1: 1 to 6: 1, preferably in a ratio of 2: 1 to 5: 1, respectively.

The SiO ₂ content relevant for gel formation in 100 ml of the mixture of the components water glass, water, acidic reactive and anionic polyelectrolyte is 5-18 g, preferably 6-12.5 g. When using high SiO ₂ proportions, very solid injection bodies are created in the injected soils, while with decreasing SiO ₂ contents they become increasingly soft.

Strong inorganic and organic acids as well as acid salts can be used as reactants strong acids, but preferably strong mineral acids such as sulfuric acid, hydrogen chloride or phosphoric acid can be used. The pH of the mixture of water glass, Water, acidic reactive and anionic polyelectrolyte should preferably be in the range of 2-4 can be set.  

In order to increase the viscosity of the injection mixtures consisting of water glass, water and reactive and to influence the properties of the gels resulting from these, organic and anionic polyelectrolytes which are harmless to health and their behavior towards the environment are added in such an amount that their initial viscosity is reduced to a maximum of 10 mPa.s is increased. Examples include polymers with alkali salts of copolymers containing acrylic, methacrylic and maleic acid. The molar mass of the polyelectrolytes which can be used is advantageously between 5.10 ⁴ and 2.10 ⁷ , in particular above 1.10 ⁵ . Those with a high charge density are preferred.

If necessary, the injection mixtures according to the invention can be further Additives that influence their properties or the resulting gels, such as various inorganic or organic salts, buffers, alcohols, non-ionic polymers, surfactants or foam inhibitors can be added.  

example 1

In comparative laboratory tests are as test samples

• - an alkaline mixture of water glass, water and acidic reactive,
• - a non-alkaline mixture of water glass, water and acid reactive,
• - a non-alkaline mixture of water glass, water, acid reactive and one anionic polyelectrolytes based on polyacrylamide,

regarding the parameters

• - viscosity development,
• - tipping times,
• - syneresis of the gels,
• - Spread in unpolluted mica sand as well as in mica sand from one Landfill base,
• - permeability coefficients of solidified test specimens,
• - Resistance of solidified specimens made of mica sand and gel in distilled and in contaminated groundwater from a landfill,

been examined.

The viscosities were determined using a viscometer at 20 ° C. in each case 30, 60 and 120 minutes after the mixtures were made.

The tipping times are over at the same temperature conditions in closed bottles visual assessment of the flow behavior was determined. The period was noted after which the mixture was no longer flowable when the bottle was inclined by 45 °.

To determine the syneresis, 125 ml of a gel-forming mixture are in each closable glass bottles have been filled. These approaches were done in triplicate Repetition. The resulting cylindrical gel body had a diameter of 5 cm. 20 days after the start of the experiment, the volume of the gel excreted Amount of liquid has been determined.

The spreading behavior of the injection mixtures in mica sand, which is not contaminated and contaminated by anthropogenic chemical inputs, the latter comes from the soil under a former landfill site of a chemical company, has been investigated in glass tubes 30 cm high and with an inner diameter of 2.8 cm. The tubes were filled 25 cm high with sand, the moisture of which was set at 15% by mass. The permeability coefficient of the unpolluted, compacted sand was in the order of approx. 10 ^-4 m / s, that of the loaded at approx. 10 ^-5 m / s. The injection mixture was filled into the columns from above. Below the sand column was a thin layer of glass wool. The sand-filled glass tubes were placed on suction bottles with a vacuum of 40 mm Hg column, which sucked the injection mixture into the sands. The trials were repeated three times. The time required for penetration of the sand column or the thickness of the penetrated layer when the spread stopped prematurely was determined.

The tests for determining the permeability with the injection mixtures of solidified sands were carried out in uniaxial permeability measuring cells. The sand samples were compacted in several layers. The diameter per solidified body was 5.3 cm. 327 g of mica sand were compressed to a height of 8.3 to 8.8 cm per test sample. Before the injection mixture was introduced, initial permeability values were determined in order to be able to identify and rule out cavities in the outer edge region. Contaminated groundwater from the area of a landfill with chemical waste has been used for this, in order to have a saturated test specimen with reactive constituents when the injection mixture is subsequently introduced. After the permeability determination on the installed test specimen had ended, this groundwater was drained off to the level of the surface of the sand and the injection mixture was introduced over the sand. This mixture was then sucked into the sand using a constant vacuum of 40 mm Hg column. As soon as the front of the mixture reached the lower boundary layer of the sand, the suction was stopped. An excess of the injection mixture was removed from the surface of the sand after 24 hours at the latest, and the penetrated body was then covered with contaminated groundwater. The cell has been covered to prevent water loss through evaporation. The contaminated groundwater had the following measurements and ingredients.

10 days after the injection mixtures have been introduced into the permeability measuring cells was carried out with the investigations of the permeability of the penetrated sands in each case hydraulic gradient started from 10. The examinations were carried out in triplicate Repetition.  

To determine the resistance of the gels in penetrated mica sand, they are cylindrical Test specimens 7 cm high and 7 cm in diameter each in 0.5 l distilled or contaminated groundwater characterized above was stored for a long time. In They were assessed visually at intervals of several days. Decay of the test specimen the test is terminated. The examinations are repeated in triplicate been made.

Test results

Example 2

The proof that anionic polyelectrolytes in no way influence the spread of the injection mixtures only by their viscosity was obtained in the following test setup:
A non-alkaline injection mixture with and without anionic polyelectrolytes was sucked in up to 260 minutes after mixing in mica sand which was not contaminated by chemicals according to the method described in Example 1 for investigating the spreading behavior of the injection mixtures and the time for the penetration of the 25 cm high sand column was determined.

In a second test, the same injection mixtures were used immediately after Mixing process sucked into sand pillars, 30 and 120 minutes earlier with the same, freshly prepared agents have been penetrated. Also in this one Experimental arrangement were the times for sucking in the injection mixtures until Bottom of the sand column.

Test results

Claims (7)

1. Non-alkaline, gel-forming mixture for sealing and solidifying soils against Flow of water in construction and civil engineering objects, for sealing in the ground built-in engineering objects as well as for encapsulation of contaminated sites and landfills, consisting of water glass, water, acid reactive, anionic polyelectrolyte and Additives. 2. Mixture according to claim 1, characterized in that diluted with water Water glass and acidic reactive dissolved in water at preferably equal volumes fed to a weakly acidified aqueous receiver with stirring via metering pumps be and this mixture with further stirring the in aqueous solution or in aqueous emulsion is added polyelectrolyte. 3. Mixture according to claim 1, characterized in that water glass with a molar ratio SiO ₂ / Na ₂ O <3 is used. 4. Mixture according to claim 1, characterized in that as a reactive for gel formation of the Water glass acids or acidic salts of strong acids serve to adjust the pH of the injectable mixture ≦ 4 and the mixture delayed gel formation having. 5. Mixture according to claim 1, characterized in that the volume fraction of the Mixture of added water, based on the volume of the water glass in the Mixture, at least the same size and a maximum of six times larger. 6. Mixture according to claim 1, characterized in that the viscosity of the injection mixture is increased to a maximum of 10 mPa.s by adding anionic polyelectrolytes, the molar mass of which should be between 5.10 ⁴ and 2.10 ⁷ . 7. Mixture according to claim 1, characterized by additives such as inorganic and organic salts, buffers, alcohols, nonionic polymers, surfactants or Foam inhibitor to influence the properties of the injection mixtures and the these resulting gels.