DE102004051673A1 - Binder for a waste material that contains heavy metals, comprises using ash material from fossil fuels - Google Patents

Abstract

A process for producing a binder for waste material that contains heavy metals, comprises using ash material from fossil fuels. The solubility or concentration of the phase forming CaO, Al2O3 and solid SO3 is achieved according to the formula 3CaO + Al2O3 + 3CaSO4 + 32H2O = C3A.3Cs.32H, where the pH is 11-13. The ratios of CaO:Al2O3:SO3 are 1:0.25-0.35:0.65-0.75. The components are mixed with 20-40% water. The layer thickness is 150-300mm.

Description

The The invention relates to a method for producing a landfill binder for the immobilization of heavy metal waste in a landfill, wherein As a dumpster primarily different ashes, residues and pollutant-containing waste products are used.

Known is a process for the energetically favorable generation of reactive Components for the storage mineral formation from ashes and water-containing substances in a reactor (DE-PS 197 19 684 C1). Here are one or several ashes and hydrous substances with possibly calcium oxide mixed and heated at a temperature of 100 to 600 ° C. The method refers to the use of a variety of different Ashes and mud. Decisive disadvantage of this solution is the elaborate and expensive heat treatment of the mixture and the complexity of the process of manufacture a product with reasonably consistent quality and to Control of impermissible Propellant phenomena. A permanent pollutant immobilization could can not be reached in this way.

Also known is a process for improving the transportability, processability and incorporation of a slurry by altering its consistency, adding an additive to the sludge and spreading it in the sludge, thereby increasing the processability descriptive curve of the mixture of sludge and additives compared to that of US Pat Proctor curve of the sludge is shifted towards higher water contents, wherein the sludge added as an additive a lime-containing power plant filter ash in a proportion between 2 and 7 wt .-% based on the dry mass of the sludge, and the additive and the sludge in volume constant proportions taking into account the change The bulk density of the power plant filter ash is forcibly mixed in the presence of water and thus the additive in the sludge is homogeneously distributed ( EP 0 934 906 B1 ). The method is limited to the processability and transport of mixtures of power plant ashes and sludges, whereby no statement is made on the hydraulic setting of the mixture and a permanent immobilization of pollutants.

Furthermore is a method of making a structural and / or sealant hydratationsfähigen Mass known using filter bag in which the filter ash stirred with the addition of water and further processed the mass to the building and / or sealant is, where for Mixtures of at least two filter ashes and / or filter ash components, which have different granulation bands, the respective water claim for the preparation of dispersions corresponding to the respective mixing ratio is determined and the filter ash and / or filter ash components in a mixing ratio, the outside of the maximum or a relative maximum of the curve of the A / W value in the range of a relative minimum of the A / W value or a range with relatively low A / W value change is, mixed and stirred to a dispersion (DE-PS 41 03 412 C2). This method is not reproducible in its complicated drafting and not executable.

A method is known for the disposal of pollutant-laden materials, soils or liquids, wherein the addition of an at least latent hydraulic ash under adjustment of sufficient for complete hydration water / solid ratio is carried out in order to dispose of these substances better ( DE-OS 36 34 650 A1 ). The aim is the disposal of different types of pollutants with the same procedure. However, with this known method, the pollutants are not permanently and completely involved in the set ash. Drifting and swelling phenomena of latent hydraulic ash are not avoided.

From the DE-OS 196 12 513 A1 a binder is known for immobilizing pollutants in and / or for solidifying soils, soil-like mixtures, sludges, production and other residues containing blast furnace flour and fly ash. The fly ash can come from hard coal and / or lignite power plants or from fluidized bed furnaces. The binder should cause the pollutants are incorporated and harden. Again, there are similar disadvantages that have not been resolved. The experience in dealing with such mixtures and elution experiments show that a permanent immobilization of pollutants does not take place.

DE-PS 196 10 075 C2 shows a method for the immobilization of pollutants, acidic waste products of petrochemicals where waste is mixed with hydraulically reacting fly ash or a fly ash-cement mixture such that the pH of the mixture> 7.5 is set and blistering due to existing or during the mixing process by temperature control Forming water is prevented and the resulting stabilizer has a rollable consistency, the stabilizer hardens in the course of compressing under internal swelling pressure and so forms an immobilizate. However, in practice, the swelling pressure described here has had such a lasting negative impact on the hardening process that the effects already described have again occurred here.

Out DE 199 15 134 A1 is a method for producing a landfill body for the deposition of mechanically or mechanically-biologically treated waste, sludges from municipal or industrial wastewater treatment or mineral residues known with harmful or organic contaminants, where waste with a hydraulically active lignite filter ash and a liquid are mixed so that After the chemical setting reaction has subsided, an excess of hydraulically active ash remains in the mixture, which converts to a new mineral over the course of 5 to 10 months with infiltrated precipitation water and the entire percolated water is thereby permanently incorporated ( DE 199 15 134 A1 ). Under hydraulically active brown coal filter ash are after DE 199 15 134 A1 lime-rich BFA to understand. The reaction of lime with water is erroneously referred to as [CaO + H ₂ O ⇒ Ca (OH ₂ )] - (limescale reaction and formation of hydrated lime) as a hydraulic reaction and ettringite formation by [6Ca + + 3SO ₄ ^2- + Al ₂ O ₃ + 36H ₂ O ⇒ Ca ₆ Al ₂ [(OH) ₄ SO ₄ ] ₃ 24H ₂ O - (crystal formation from supersaturated solution phase) as a pozzolanic reaction.

Of course, when calcareous BFA reacts with water, hydrated lime and vanishing ettringite are always produced. Both phases should be in accordance with the DE 199 15 134 A1 in the initial reaction does not drain completely, so that later penetrating water can be bound. This is a pure water binding and can not be compared to complete ettringite formation as a "pozzolanic reaction".

It is the same with the DE 44 17 012 C3 , which describes a method for producing a material with high water storage capacity, in which dewatered organic sewage sludge having a dry matter content between 20 and 35% and mixed in intensive mixer with lime-rich hydraulic Westelbischer brown coal filter ash in an amount of> 60%, based on the dry matter of the mixture becomes. The first claim corrects that the mixture also contains ettringite. About the amount may be speculated. An optimized and controlled Ettringitbildung can not be spoken. The lime hydrate formation is not discussed. Sense of the whole is a high water binding from the sewage sludge, to make it compactable. At best, therefore, a change in the consistency by dehydration (the ettringite binds 32 molecules of water) and no involvement of pollutants.

In the DE 36 43 345 For example, polluted sludge is pelletized and subsequently rolled (powdered) in limestone ash, which is intended to form a protective layer that physically packs the pollutants. It is clear to the person skilled in the art that a hardened ash layer in the micrometer range does not provide sufficient protection against subsequent leaching of only physically bound pollutants. The ettringite, which initially forms on the surface, converts to sulfate by sulfate deficiency. The further development - disintegration of the non-stabilized monosulfate by carbonation - is not given for a good reason.

The DE 43 37 789 C2 describes a method of incinerating refuse incineration ash for use in road construction wherein the refuse incineration ash is stored to exclude monocarbonate under exclusion of air. This process appears to be very problematic in terms of the duration of ettringite formation under water or air occlusion and the associated plant bonding. Additives such as lime, aluminate, cement or ash are added to the water trough without mixing. How this should set the necessary for an Ettringitbildung optimal concentrations is incomprehensible. Another problem is that, of course, the ettringite formed will also carbonate after treatment under water or in the absence of air if it is not sufficiently stabilized by an excess of sulfate. Thus, the entire pretreatment is called into question and ineffective.

In DE 198 27 540 A1 a method for producing a covering or profiling material for covering landfills or contaminated sites or for the production of mono-landfills is described in which a low-calorific, prepared and separated fraction of household and commercial waste with hydraulically-responsive and ettringite-capable ashes and water in a specific Mixing ratio are mixed together. It is a hydraulically reactive and capable of ettringite BFA from caloric power plants in central Germany used for the mixture. It is known from extensive known experiments that these BFA are subject to considerable fluctuations in the chemical composition and thus the reactivity, depending on the coaling. However, since the stoichiometry of the solution phase is constantly changing and can not be corrected according to the method, is a stable implementation according to the claims not guaranteed.

Ultimately is from DE-PS 196 07 081 C2 discloses a method for immobilizing one or more pollutants with or with which a material (in particular building rubble or soil material) is contaminated, known the contaminated material being colloidally dispersed in water Aluminum hydroxide and latent hydraulic binder to a a pH of 6 to 13 having mixtures are mixed. Electrofilter ash, which contains high amounts of chloride, is used be added. As einzumischende pollutants are almost all named known substances. The solubility the phase former of the mixture components is not investigated. The addition of aluminum hydroxide in amounts of 50 to 500 mol% preferably 200 mol% of the sum of the pollutants to be added achieve that in particular calcium aluminate hydrates with platelet-shaped habit be formed, which are able to adsorptive the pollutants or to bind chemically. The additional formation of calcium aluminate trisulfate hydrates Of the Ettringittyp is admittedly acceptable, procedural steps however, the preferred formation of these phases is not indicated. As the proof of a crystal chemical integration of heavy metals in calcium aluminate hydrate phases so far failed a practical implementation of the procedure for permanent immobilization heavy metal contaminants based on environmental legislation Requirements can not be realized.

• 1. Einbindung von Schadstoffe aufbauende Kationen oder Anionen in die Kristallstruktur von sogenannten Speichermineralen.
• 2. Einbindung der Schadstoffe in den Gelporenraum einer Feststoffmatrix. Hierzu müssen die Schadstoffe nicht zwingend gelöst werden, es muss sich jedoch eine Matrix entwickeln, deren Poren nicht eluierbar sind.
• 3. Dauerhafte Stabilisierung einer Feststoffmatrix durch Dichtigkeitserhöhung, um die spezifische Oberfläche und damit die Durchströmbarkeit (Permeabilität) zu verringern.

A permanent inclusion of pollutants is only given if 3 mechanisms work together:

• 1. Incorporation of harmful substances cations or anions in the crystal structure of so-called storage minerals.
• 2. Integration of the pollutants into the gel pore space of a solid matrix. For this purpose, the pollutants do not necessarily have to be solved, but it must develop a matrix whose pores are not elutable.
• 3. Permanent stabilization of a solid matrix by increasing the density in order to reduce the specific surface area and thus the flowability (permeability).

In the large number of materials to be incorporated and in the wide pH ranges of the DE 196 07 081 C2 The emphasis of the mechanism of this intellectual property right is on a physical stabilization (point 2 and 3). It is known that Al hydroxide in a pH range between 5 and 10 is almost insoluble (see HENNING, KNÖFEL - chemistry in construction) and formation of corresponding aluminates can take place only in very, very small amounts. Since the solubility is a thermodynamic term and does not depend on the particle size of the material - depending on the reaction rate or rate of dissolution - it does not matter if the Al hydroxide has particle sizes in the micrometer or nanometer range. Accordingly, mechanism 1 - if it takes place here at all - is of subordinate importance, especially as the concretization specifies a pH range between 5 and 9.

The Controlled ettringite formation is described for cement and fly ash and shown as unfit. This is understandable, as procedurally simple Cements and flyashes hydrate and no specific mixtures from different components - including the pollutant component - under Attention to the material characteristics takes place.

At long last is in o. a. Patent cement or lime as a binder component added to in a further step a molding with certain strength and durability. In order to A multi-stage process is carried out that is tedious and cumbersome.

Of the Invention is based on the object, based on suitable Filter ashes to develop a dumpster capable of heavy metal waste elution-proof into a hydrated binding building block matrix of a multibarrier model permanently and safely involved.

• a) die jeweiligen Löslichkeiten bzw. Konzentrationen c_i [g/l] der Phasenbildner CaO(c_CaO), Al₂O₃ (c_Al2O3) und SO₄ (c_SO4) für eine Ettringitbildung nach der Formel 3CaO + Al₂O₃ + 3CaSO₄ + 32 H₂O ⇒ Ettringit (C₃A·3Cs·32H) an allen Ausgangsstoffen in wässriger Lösung im pH-Wertebereich von 11 bis 13 ermittelt
• b) die Ergebnisse zur Berechnung der Stoffanteile im Hinblick auf eine bevorzugte Ettringitbildung so verwendet werden, das im Gemisch die Teilkonzentrationen c_i [g/l] in folgendem Verhältnis stehen c_CaO : c_Al2O3 : c_SO4 = 1 : 0,25–0,35 : 0,65–0,75
• c) die ermittelten Anteile zu einem Gemisch mit einem Wasseranteil von 20 bis 40 M.-gemischt sowie als Schicht in einer Dicke von 150 bis 300 mm auf die vorhandene Deponieoberfläche aufgebracht, verdichtet und als eine sich selbst verfestigende Schicht mit hohen Anteilen eines feinkristallinen, siliciumhaltigen Ettringits ausgebildet wird.

This has been inventively achieved by the content of claims 1 to 5, wherein

• a) the respective solubilities or concentrations c _i [g / l] of the phase former CaO _(CaO c), Al ₂ O ₃ (c _Al2O3) and SO ₄ (c _SO4) for a ettringite formation according to the formula 3CaO + Al ₂ O ₃ + 3CaSO ₄ + 32H ₂ O ⇒ Ettringite (C ₃ A · 3Cs · 32H) determined on all starting materials in aqueous solution in the pH range from 11 to 13
• b) the results for the calculation of the proportions of substances with regard to a preferred ettringite formation so ver be used, which are in the mixture, the partial concentrations c _i [g / l] in the following ratio c _{CaO: Al2O3} c: c _SO4 = 1: 0.25-0.35: 0.65-0.75
• c) the determined proportions are mixed to a mixture with a water content of 20 to 40 M. and applied as a layer in a thickness of 150 to 300 mm on the existing landfill surface, compacted and as a self-consolidating layer with high levels of finely crystalline, silicon-containing ettringite is formed.

According to the invention was found that the formation of ettringite as a storage mineral targeted by mixtures of different starting materials, including the material to be immobilized, can be controlled when the Boundary conditions according to claim 1 are observed. this happens in a one-step process.

When new mechanism of action has been found to be a permanent contaminant not on the failures of heavy metal hydroxides in the alkaline environment, but on the formation of storage minerals of the type silicon-containing ettringite, possibly also of zeolite. For the former requires sulphate, with no sulphate in ettringite occupied, which can be occupied by heavy metal cations. Here plays the calcium, but also the aluminum a crucial role. It could be demonstrated for the first time that according to the invention The aluminum also silicon as exchange in the Ettringitgitter can be installed. This idea is also important because since the heavy metal ions can be 2-, 3- or higher. Appropriate Space variations in the ettringit or storage mineral structure are therefore present. An integration of heavy metal cations in channels in Ettringit is unknown.

It was further found to be a crystal chemical incorporation exclusively via the solution phase can work. Exactly this point is in the inventive solution the reference point to the solved Amount of aluminum, sulphate and CaO (lime) accounted for.

Ettringit can carbonate, convert to monosulfate in sulfate deficiency or dissolve. Crucial according to the invention is a corresponding supply of sulphate. Aims at this point the solution according to the invention, the ettringite is to be stabilized, in which the available sulphate quantity exceeds the for a stoichiometric Ettringitbildung necessary quantity lies. As in inventive samples after over a year of ettringite no signs of decay by carbonation showed, it can be assumed that by the incorporation of silicon in place of aluminum the ettringite lattice in a special way is stabilized. The same effect apparently have the built-in Heavy metals chromium, cadmium and zinc.

In the solution according to the invention is controlled ettringite formed and stabilized by a sulfate surplus. additionally forms the same matrix in which the ettringite originated, a very dense structure, around the environmental influences to minimize.

Of the Landfillers according to the invention will be complete made of ashes and / or residues and / or waste products and works without cement additions. He is primarily made of a mixture of water, calcareous ash (s) (preferably from power plants with Desulfurization by the limestone additive process), more aluminate Ash and / or an aluminate carrier from other waste products and sulphate portions (preferably from Coal power plant or refuse incineration ash) together. These proportions are mixed according to claim 1, wherein in a surprise A very fine crystalline, silicon-containing and a high Microporous distribution Ettringitphase as storage mineral out forms. The heavy metals are predominantly crystal chemical built into the Ettringitgitter, creating a permanent immobilization is reached.

When special inventive effect has been found that after the installation of a layer on the landfill with this binder immobilisate produced is able to cover pollutant inputs from Contain landfill material and crystal chemical to neoplasms of ettringite or adsorption to bind existing phases.

One Another advantage of this landfill construction material is that special waste scraps by the mixture according to the invention in the landfill building so sure chemically in the crystal lattice be involved in this mixture in a landfill of the class II can be spent.

• I. Einlagerung von Schadstoffbestandteilen (Ionen, Moleküle, Molekülgruppen) in die Kristallstruktur der sich bei der Hydratation bildenden Hydratphasen vom Ettringittyp, wobei zwischen einem diadochen Ersatz von Kristallbausteinen und der Fixierung auf Zwischengitterplätzen unterschieden werden muss.
• II. Sorption von Schadstoffen an der sehr großen Oberfläche des sich ausbildenden Gelporenraumes der feinkristallinen AFt-Phasen. Bei Porengrößen < 10 nm wirkt das Porenwasser auf Grund der Adhäsionskräfte wie ein Dichtungsmittel und ist demzufolge nicht auslaugbar.
• III. Fixierung von in Wasser unlöslichen Schadstoffen im Kapillarporenraum der Feststoffmatrix durch Ausbildung einer dichten Gefügestruktur, wobei die Schadstoffe sowohl durch den hohen pH-Wert der Porenlösung als auch durch die hohe Gefügedichtigkeit (geringer Durchlässigkeitsbeiwert k) dauerhaft immobilisiert werden.

The following is also realized according to the invention:

• I. incorporation of pollutant constituents (ions, molecules, molecular groups) into the crystal structure of the hydrate-forming hydrate phases of the ettringite type, it being necessary to distinguish between a diadochic replacement of crystal building blocks and the fixation on interstitial sites.
• II. Sorption of pollutants on the very large surface of the developing gel pore space of the fine crystalline AFt phases. For pore sizes <10 nm, the pore water acts as a sealant due to the adhesion forces and is therefore not leachable.
• III. Fixation of water-insoluble pollutants in the capillary pore space of the solid matrix by forming a dense microstructure, the pollutants are permanently immobilized both by the high pH of the pore solution and by the high structural density (low permeability coefficient k).

in the Regarding the long-term stability of the binder comes the mechanisms I. and II. A special role, as in a mechanical Preparation of the building material, the bound heavy metals not leached and thus bioavailable again can be.

in the With regard to a landfill construction, the mechanism III. a additional and not, as in a pure solidification, the main barrier against a pollutant leaching.

Out Preliminary tests as well as the developed model conceptions showed, that the investigations concentrate on the production of a binder have to, in the hydrate phase as ettringite predominantly with regard to on the chemical / adsorptive binding of pollutants as well as regarding the Performance characteristics as landfill construction like pressure resistance, Tightness and room stability is formed.

For reaching This objective was initially the for an ettringite formation of suitable ashes with the appropriate phase formers - calcium oxide, Alumina and sulphate - comprising to characterize chemical-mineralogical. To the stoichiometry the solution phase for the To be able to stop ettringit formation, was found after extensive experiments that one solubility the phase former in the pH range 11 to 13 from the starting materials to determine optimal yields of these for the structural properties of a landfill construction material important phase.

embodiments

Based of exemplary embodiments the invention will be described in more detail below explained become.

To In each case, 2 available lignite (BFA) - or Coal filter ash (SFA) in terms of expected solubility the phase former examined.

The results are shown below:
In their chemical composition (Table 1), the filter ashes differ both in terms of the fuel used - brown or hard coal - as well as in relation to the desulfurization used - limestone addition in the fuel dust or Kalkwäsche the flue gases.

The Ashes 1 as well as 3 and 4 can a silicate and aluminate-rich, the ash 2 a calcareous ash type be assigned with regard to the coaling. The partly high Lime and free lime content Ashes 1 and 3 are not coal-related, but result from the limestone additive process for flue gas desulphurisation.

Tab. 1: Chemical composition of the ashes (data in% by mass)

To determine the water-soluble fractions of Al ₂ O ₃ , SiO ₂ and the pH, mixtures were prepared with 1 g of ash and 100 ml of distilled water. After mixing, pH values of> 12.5 are already established in the solution phase after 1 to 2 min. The solubility of Al ₂ O ₃ or SiO ₂ is different and does not correspond directly to the chemical composition (Table 2).

Tab. 2: Solubility of SiO ₂ and Al ₂ O ₃ in aqueous solution

With regard to the possibilities of ettringite formation from the solution phase, a structural chemical characterization of the dissolved aluminum was carried out by means of 27 Al NMR spectroscopy. In the corresponding diagrams, the spectrum of an aluminate sample is plotted for comparison ( 1 - 27 Al NMR spectroscopy of the solution phase). The x-axis indicates the chemical shift that contains information on the coordination of the ligands around the aluminum. The y-axis can be interpreted as relative intensities, thus as contents of the individual coordination polyhedra.

It is important for the formation conditions of the ettringite that the alkaline ash solutions do not contain any free aluminate, either in 6-coordination or in 4-coordination with oxygen or OH ions. This statement is clear in comparison with the Al sample. The sharp peak in this sample represents aluminum coordinated with 4 OH ^- ions. Such pure aluminate structures (Al (OH) ₄ - tetrahedra) are not formed in the alkaline solutions of the ashes. Instead, the relatively broad peaks indicate that the AlO ₄ tetrahedra coordinate with silicon instead of hydrogen. Al-O-Si bonds are formed in the solutions, and the number of silicon ions can vary between 1 and 2. Thus, in the alkaline ash solution according to the invention before solution conditions that allow a first time permanent incorporation of silicon in the Ettringitgitter.

• – Verbindungen des Calciums -Calciumsulfat (Anhydrit), Calciumaluminataluminatferrit (Brownmillerit), Calciumsilicatlalumosilicat (Gehlenit), Calciumoxid, Calciumaluminatsulfat (Yeelimit), teilweise Calciumcarbonat (Calcit)
• – Verbindungen des Eisen und Magnesiums – Eisenoxide, Magnesiumoxide/-ferrit
• – Quarz
• – Glasphase – Aktivglas (Kalksilikatglas mit aluminatischen Anteilen – Melilithglas) Inertglas (aufgeschmolzene Tonminerale kaolinitischer Zusammensetzung)

To determine the quantitative mineral content of the ashes, the equivalent standard method is used to calculate an actual mineral composition from chemical analysis and qualitative mineral analysis. The investigated ashes were of the following mineral population go:

• Compounds of calcium-calcium sulphate (anhydrite), calcium aluminate aluminate ferrite (brownmillerite), calcium silicate-lalumosilicate (gehlenite), calcium oxide, calcium aluminate sulphate (yeelimite), partly calcium carbonate (calcite)
• - Iron and magnesium compounds - Iron oxides, magnesium oxides / ferrite
• - Quartz
• - Glass phase - Active glass (silicate glass with aluminate content - melilite glass) Inert glass (molten clay minerals of kaolinitic composition)

• 1. Ermittlung des Sulfatgehaltes und Abstimmung mit der röntgenographisch ermittelten Anhydritmenge in den untersuchten Aschen
• 2. Bestimmung des Gesamt-CaO-Gehaltes und Zuordnung des Kalkes zu den entsprechenden kalkhaltigen Aluminaten, Silicaten und eventuell Aluminatsulfaten
• 3. Röntgenographische Bestimmung des Freikalkes und Vergleich dieses Wertes mit dem im Ergebnis der Zuordnung des Kalkes nach Punkt 2 übrigbleibenden "Rest- CaO-Gehaltes"
• 4. Zuordnung eines dann noch verbleibenden Restes an freiem CaO zu Aluminat und Silicat zur Ermittlung des Aktivglasanteils unter Berücksichtigung der Reaktivität (Anteil der Korngruppe < 0,035 mm)
• 5. Berechnung des aluminatisch-silicatischer Inertglasanteils aus einer Differenzbildung zwischen den Gesamtaluminat- bzw. -silicatanteilen und den bisher zugeordneten Aluminat- und Silicatanteilen zum Kalk

Since a clear complete characterization of all constituents of ashes is difficult, the following approach was chosen according to the invention for the purpose of optimizing the ettringite yield:

• 1. Determination of the sulphate content and coordination with the X-ray-determined anhydrite amount in the investigated ashes
• 2. Determination of the total CaO content and assignment of the lime to the corresponding calcareous aluminates, silicates and possibly aluminate sulfates
• 3. X-ray determination of the free lime and comparison of this value with the "residual CaO content" remaining as a result of the assignment of the lime to point 2
• 4. Assignment of a remaining amount of free CaO to aluminate and silicate for determining the proportion of active glass, taking into account the reactivity (proportion of the grain group <0.035 mm)
• 5. Calculation of the aluminosilicate inert glass portion from a difference between the total aluminate or -silicatanteilen and the previously assigned aluminate and silicate to lime

in the Result of this description can be for the investigated ashes Balance sheet with regard to ettringit formation. In this case, the determined amount of aluminate of the respective ashes taken as a basis and then the existing / required quantities based on sulfate and lime (Table 3).

Tab. 3: Ettringit balance of the investigated ashes

Legend:

gl

- glassy structure

kr

- crystalline structure

The Ash 1 and 2 are of chemical-mineralogical and granulometric View (share <0.035 mm) as Ettringitbildner suitable. In addition, however, mixtures are between the ashes sensible and necessary, thereby reducing the ettringit balance by itself or by suitable additions of sulphate (hemihydrate) and Aluminate (amorphous aluminum hydroxide) are compensated.

On this basis were various mixtures with a water / binder value of 0.5 and after 14 d the hydration products by X-ray and under the scanning electron microscope on the live state and studied the structure.

By way of example, the results of binder series 5 are presented below, which serve as the basis for Further investigations according to the invention for heavy metal incorporation served.

Tab. 4: Composition of binder series 5 (proportions in% by mass)

The mineral phase balance of the hydrated samples with increasing sulfate content shows the 2 Ettringit formation depending on the addition of sulphate.

The Ettringitmenge goes through dependent on from the added amount of sulfate a maximum value of 28% by mass, which sets at about 3 wt .-% sulfate. In an addition area of sulphate up to 7.5% by weight, the amount of gypsum formed remains with it 5 to 7% by weight relatively low. Anhydrite and limestone become extensive consumed.

When Water addition is necessary in an amount of 20 to 40 M .-%.

• – Bildung fasriger, feinkristalliner Ettringitstrukturen auf den Aschepartikeln
• – Neben Ettringit wird Gips in größer ausgebildeten Kristallen vorgefunden
• – Andere Mineralaggregate können nicht eindeutig identifiziert werden

The radiographic results are confirmed by scanning electronic investigations. In the 3 (SEM image of fine crystalline ettringite structures on the surface of the ash particles) visible structures of the invention can be described as follows:

• - Formation of fibrous, fine-crystalline ettringite structures on the ash particles
• In addition to ettringite, gypsum is found in larger crystals
• - Other mineral aggregates can not be clearly identified

at conducted EDX analyzes on the ettringite crystals were next to the typical Composition S, Al, Ca, O in surprising Way also considerable Proportions of silicon found.

Due to the micro- to nanocrystallinity of these sample areas, the surface and pore distribution of the binder matrix was investigated by gas adsorption. For the binder 5.1, BET surface areas of about 30 m ² / g were obtained with a microporous radii distribution between 1 and 5 nm and an average pore radius of 2.7 nm.

The binders are resistant to space after storage in water. Mortar test specimens produced according to DIN EN 196 or DIN 18127 achieve average compressive strengths after 28 d of> 10 N / mm ² and permeability coefficients according to Darcy of> 8 · 10 ^-8 m / s. Thus, the requirements for landfill construction materials are also met with regard to the requirements for the stability of Immobilisaten.

investigations for pollutant immobilization

The investigations were carried out on pastes and mortars of binder 5.1 with a view to use as landfill builder / binder. Soluble heavy metals were added to the mixtures with the mixing water in the following concentrations: - 187 mg / l K ₂ CrO ₄ corresponds to 50 mg chromium / l - 78 mg / l ZnCl ₂ corresponds to 37.5 mg zinc / l - 59 mg / l cd-acetate corresponds to 25 mg cadmium / l

at heavy metal selection and concentration was determined to be the crystal chemical integration in the order chromium, zinc, Cadmium decreases.

DCA studies show that the course of hydration and the heat of hydration when the reaction is complete or the reaction conversion in the form of ettringite formation are not significantly affected by the heavy metal incorporation. The inventive crystal chemical incorporation of heavy metals Mechanism I was able to be detected by means of EDX on ettringite crystallites.

As Binding technical investigations have been made, also the compressive strength and room stability not significantly affected by the heavy metals.

The Elution experiments were carried out by means of modified DEV-S4 or trough method. According to DEV-S4, the sample bodies are crushed to a particle size <10 mm. The trough process becomes cubes with an edge length eluted from 100 mm. The heavy metal contents in the eluates were determined by AAS (atomic adsorption spectroscopy) (Table 5).

Tab. 5: Results of elution experiments on the binder 5.1

in the Result cadmium and zinc are completely immobilized by the binder, wherein the contents in the eluates correspond to the O-samples and in the Range of determination limit of ASS (all specified values are marked with < Limit of quantification of AAS, d. H. smaller values can not distinguished from each other or metrologically resolved) lie. For chromium, immobilization rates of 96% after DEV-S4 or 99.5% by trough method achieved, which in terms of Initial concentration is very positive.

These Results formed the basis for immobilization studies of heavy metals containing substances from pyrolysis or incineration of waste. Tab. 6 shows by way of example the results for a soot cake (RK) and a waste incineration ash (MVA) at a mixing ratio Binder / waste of 3: 1.

Tab. 6: Immobilization of waste (eluates according to DEV-S4)

The soluble heavy metal contents could be completely immobilized and thus the classification characteristics for landfill classes I and II could be undercut. At higher admixtures (MV 1: 1) u. U. Problems with ettringite formation and room stability of the binder due to chloride levels of the MVA of> 20000 mg / l. As ongoing investigations according to the invention show, these problems can be controlled by a substantial increase in the amount of aluminate in the solution phase. In this case the chloride is bound as Friedel's salt (3 CaO · Al ₂ O ₃ · CaCl ₂ · 10 H ₂ O).

According to the invention was found that an immobilization of soluble heavy metal compounds waste by chemical / adsorptive binding to Ettringitphasen possible and auslaugsicher feasible is. The proven mechanisms according to the invention of a multibarrier model ensure one long-term stable pollutant integration.

Claims (5)

A method for producing a landfill binder for immobilization and solidification of waste containing heavy metals in a landfill, being used as landfillers various ashes of fossil-fueled power and / or heating plants, residues and contaminated waste products, characterized in that a) the respective solubilities or concentrations c _i [g / l] of the phase former CaO _(CaO c), Al ₂ O ₃ (c _Al2O3) and solid SO ₃ (c _SO3) for ettringite formation according to the formula 3CaO + Al ₂ O ₃ + 3CaSO ₄ + 32H ₂ O ⇒ Ettringite (C ₃ A · 3Cs · 32H) determined on all starting materials in aqueous solution in the pH range from 11 to 13 b) the results for the calculation of the substance proportions with regard to a preferred ettringite formation are used so that in the mixture the partial concentrations c _i [g / l] are in the following ratio c _{CaO: Al2O3} c: c _SO3 = 1: 0.25-0.35: 0.65-0.75 c) the determined proportions mixed to a mixture with a water content of 20 to 40 M .-% and applied as a layer in a thickness of 150 to 300 mm on the existing landfill surface, compacted and as a self-consolidating layer with high levels of finely crystalline , silicon-containing ettringite is formed. Method according to claim 1, characterized in that that the dry starting materials are premixed and after a water addition in height from 20 to 40% by mass before being applied to the landfill surface become. Method according to claims 1 and 2, characterized by lime-rich lignite filter bags (BFA) and / or as ash Hard coal filter ash (SFA) from limestone additive process and / or alumi natreiche BFA and / or SFA with reactive glass phase and / or sulphate-containing BFA and / or SFA and / or filter ash from waste incineration plants be used with high proportions of chloride. Method according to claims 1 to 3, characterized by free-lime-rich constituents from the cement industry as residues such as by-pass or fine flour, clay products from the ceramic, Glass or aluminum industry and sulfate hemihydrate and / or anhydrite from the gypsum industry be used. Method according to claims 1 to 4, characterized by that as waste products dry and / or moist and / or muddy scraps with high levels of pollutants, such as sulphate and / or chlorides and / or Heavy metals are used.