DE3909060A1 - Process for the making inert (inerting) of combustion residues and also natural and industrial sediments - Google Patents

Abstract

According to the invention, a process is provided for converting contaminated, in particular by heavy metals, combustion residues and also natural and industrial sediments into a form which can be landfilled (dumped). In this process, the materials to be treated and, in particular, the reactive pollutants contained therein are made inert by reaction with an alkali metal silicate solution, in particular a sodium or potassium silicate solution, and by subsequent reaction with a calcium hydroxide or magnesium hydroxide slurry or an alkaline earth metal salt solution, in particular a calcium or magnesium chloride solution, and also immobilised by the silica gel precipitating in the process. The material obtained is preferably solidified by addition of a cement to give a fine concrete capable of ultimate storage or use.

Description

The invention relates to a method for transferring burning contaminated especially with heavy metals residues as well as natural and industrial se dimen in a landfillable form.

Every year growing amounts of fall through worldwide Heavy metals contaminated combustion residues and Dredged material. In order to be able to dispose of such masses, you need an Un impermeable to leachate background. A suitable surface in dense be settled areas with a high discharge of harm Masses containing substances are hardly available anymore.

Methods have therefore already been developed that on the one hand with the sealing of the substrate for new burden or with the isolation of contaminated sites or themselves on the other hand with the precautionary treatment of the depo deal no good.  

For masses of the type in question here a precaution to undergo treatment or such masses You can convert it into a landfill-ready form in Principle to use two different methods, namely ceramization or solidification through binders.

A ceramization process is, for example, that one can be converted into a landfill form Mass sinters. For this you dry these masses and then plasticizes them according to their composition either without additives or together with an or several additives, e.g. B. clay, clay or organic Substances. Then the masses are preformed, at 400 pre-fired to 600 ° C and then at 1100 to 1300 ° C depending on the process control to ceramic small grain sintered from the desired structure and surface.

DE-OS 36 12 381 describes a process for the preparation waste materials (e.g. filter dust, dredging sludge) described in which the waste materials with z. B. clay or mixing clay; this mixture is made with a capillarity and catalytic ion exchange the water binding forces of the cohesive material set additional material and ge to form presses. The moldings can be at a temperature heat treated from 400 ° C to 1400 ° C.

A lot of energy is used in these known methods used, both for drying, for pre-burning and for high temperature sintering as well as for through leadership of the diverse mechanical, the use of Machine-related work stages. The corresponding Comprehensive systems need wear and corrosion be stable, especially with regard to the Installa tion for the separation of dusts and for absorption  environmentally damaging or nuisance components of the Exhaust gas flow.

Ceramization processes are also known for which use silt as a secondary raw material for example for brick burning and for production of glass fibers for insulating materials while melting 1400 to 1500 ° C. (Free and Hanseatic City of Hamburg, Be auditor for power and port construction, dredging seminar, 27.2 - 1.3. 1984, Hamburg 1984, G. M. Dörr, dredged material as Secondary raw material for the production of building materials, p. 389-403).

In the ceramization processes or in the associated sintering, they are not ver burned pollutants ceramized together with the matrix.

In the likewise known methods for solidification of pollutant-containing masses by means of binders the former by adding an organic polymer or bound by water and cement and then by pouring to blocks or by pressing to strands, pellets, etc. to form deformable and solidifying products works. However, polymers cannot be used for Solidification of always water-containing silt but only for dry slags, ashes and fly dusts for use be brought. Anthology VGB conference "Kraftwerk and environment 1987 "S. 205-209, J. Ernst, G. Hagedorn, Investigation of the elutability of fly ash products.

With the fine to fine-grained masses, with the help are solidified by polymers, the particles including the pollutants from the organic binder tel just wrapped and cemented together without using the latter a chemical, water-insoluble compound enter into.  

Since experience has shown that polymers are influenced by the reverse exercise one associated with dismantling and structural change Aging process can be bound in such a way Masses permeable to leachate and thus elutable will. Such masses are also in mixed landfills not only susceptible to being covered and touched by domestic and industrial landfill goods, but also against alkaline building rubble and oily substances. At use as a bedding surcharge in road construction its wear down by liquid fuels or Lö liquid from leaks and damaged tankers and thus not leaching out an environmentally hazardous leaching shut down.

In the known methods for solidifying harm Substance-containing masses are largely outweighed by cement portion of the skin that is insensitive to hydration appropriate masses embedded in concrete, while the on the so-called cement paste corresponding components into the chemical processes of the setting process fen. In contrast to the gravel contained in the usual building concrete extremely fine-grained combustion residues or Silt a high proportion of capillary and adsorptive bound water. This leads to a corresponding bottom Rosity of a herge by this known method made fine concrete. In addition, they are also in garbage slag, fly ash and flue gas cleaning sludge contained, harmful concrete salts leachability and vulnerability and thus the disintegration of such "infi graced "concrete body favor, even if specialty elements are used and the mixing regulations be strictly observed.

This has the consequence that the concrete tears open and that the leaching pollutants that are no longer covered are exposed. In particular, this applies to the during of setting due to increasing alkalinity  emerging, easily soluble and thus easily washable hydroxyl compounds of lead and zinc. They are also present as sulfides under these conditions heavy metals due to oxidation in an alkaline medium converted to sulfates and are then also light washable or leachable.

Further, which concern the problem in question here The literature is listed at the end of the examples.

The object of the present invention is a method for transferring contaminated, especially with Heavy metals contaminated combustion residues and Provide dredging sludge in a landfillable form len, this method being free from the disadvantages of is previously known processes and leads to end products, that can be safely disposed of.

This task is solved by the teaching of Claim 1.

The inventive method thus in Containing combustion residues and dredging sludge, environmentally harmful components chemically and physically inerted. To the Ver with the help of the invention machinable combustion residues and bag sludges include, for example, silt, garbage slag, Fly ash, flue gas cleaning sludge and garbage combustion residues. The method according to the invention is therefore universally applicable; with its help thus the usual contaminated residues of any kind will be brought into a landfill-compatible form.

In the method according to the invention, they are processed tending masses in a first stage with an alkali likate solution added, expediently under constant Revolution. The alkali silicate solution is preferably used  a concentrated alkali silicate solution, for example as a sodium or potassium silicate solution. The amount the alkali silicate solution to be used depends on the treating masses. It is expedient to set it Alkali silicate solution in such an amount that the contained in the masses to be treated, environmentally harmful components can react with it. Expedient the alkali silicate solution is sometimes put in one Excess one. It is preferable to use a concentrated one Alkali silicate solution in such an amount that the contained solids 2 to 12 wt .-% of that at the end of the end product obtained according to the invention settlement (total cementitious mass). The turned set amount of concentrated alkali silicate solution depends of course on the composition of the treated Masses.

Conveniently, you allow them by moving the treated masses obtained with the alkali silicate solution React mixture 2 to 30 min., In particular 15 min., preferably preferably circulating. During this Those react to time at ambient temperature cationic constituents of the masses to be treated, the respond to the alkali silicate solution.

If, for example, a sodium silicate solution (pH 11 to 13) is used, the following conditions are present. A sodium silicate solution of the type mentioned contains an SiO₂ content exceeding the stoichiometric ratio of 1 Na₂O to 1 SiO₂ in the metasilicate Na₂SiO₃. For 1 Na₂O there are therefore n SiO₂ (n = 3 to 4). By the reaction of the silicate anion (SiO₃ ^2- ) with the oxides, oxyhydrates, carbonates, chlorides, fluorides and sulfates of the heavy and alkaline earth metals present in the masses to be treated in various quantities, these are meta- and orthosilicates (MeSiO₃ and Me₂SiO₄ ) transferred. Me stands for example for Ca, Cd, Cu, Fe, Mg, Mn, Ni, Pb and Zn. Al is precipitated as Al₂O₃ × 3 SiO₂ X n H₂O and Cr as Cr (OH) ₃.

By using an alkali silicate according to the invention the contaminating heavy metals in solution Silicates transferred, all as minerals in the Na tur and occur against chemical influences are extremely resistant. Such silicates are we that is due to exceptionally aggressive leachate leachable by acid rain.

It is also advantageous to adjust to pH 9.5 to 11 ling alkalinity of the fully reacted composition. There through are in a landfill by oxidation of Sulfides or acid that is constantly produced by organisms neutralized including carbon dioxide.

In the second stage of the method according to the invention you bind the unreacted or excess Alka lisilikat by mixing the masses to be treated with a Calcium hydroxide or magnesium hydroxide slurry or an alkaline earth salt solution, more appropriate wise with upheaval. It is preferable to use the second stage the calcium hydroxide or magnesium hydro xid slurry or the alkaline earth salt solution in one such an amount that the solid of the calcium hydroxide or magnesium hydroxide slurry or the alkaline earth salt solution 1 to 6% by weight of the final composition (total cementitious mass).

You can also use calcium hydroxide or magnesium hydroxide use in "baked form", ie as CaO or MgO. However, quicklime (CaO) is dangerous to handle; MgO reacts slowly.  

In this second stage of the method according to the invention a calcium hydroxide slurry is preferably used and / or a calcium chloride solution.

If, for example, a calcium chloride solution or a calcium hydroxide slurry is used according to the invention, then the precipitated calcium silicate (CaO × SiO₂ to 3 × CaO × SiO₂) and the excess silica released in the process, which is a voluminous and water-binding silica gel (SiO₂ × n H₂O) fails, not only the silicates precipitated in the first stage of the process according to the invention but also all of their particles of the mass to be treated, including the organic constituents, in an insoluble layer filling pores and capillaries.

You get at the end of the two procedures described above a slurry-like mass (cementitious mass), whose environmentally harmful ingredients have been "rendered inert" the. Through the going on at ambient temperature Inertization are thus the z. B. in combustion back as well as in natural and industrial sediments contained reactive pollutants by reacting with an alkali silicate, especially sodium or Ka liumsilicate with a stoichiometric ratio nis content of insoluble in insoluble Silicates transferred and then after adding a Calcium hydroxide or magnesium hydroxide slurry or an alkaline earth metal salt solution, especially one Calcium or magnesium chloride solution, both through the due to the reaction with excess alkali silicate precipitating alkaline earth silicate, especially calcium or Magnesium silicate, as well as by this outgoing silica gel immobilized.

The immobilized masses obtained can now be dispose of this form of disposal and deposit it.  

However, it is preferably solidified according to the invention inert, pulp-like mass obtained by metered Mix cement and water. By choosing the Ze mentes, e.g. B. Portland, trass or alumina cement, and by dosing the amount still required the consistency, setting, of hydration water time, the solidification process and the strength of the resulting molded body on a repository or on a certain use can be discontinued.

The inertization described above takes place Ambient temperature. The method according to the invention runs thus without supplying thermal energy. Are also for the Implementation of the method according to the invention no com plicated furnaces and wear-prone grinding and Pelleting plants are required, as is the case with the ceramization processes mentioned at the beginning and Solidification process with the help of binders Case is. Also, no dust removal measures are required during the work phases and to prevent damage substances in the exhaust gases are hit, u. a. the ther mixed volatile Cd and Hg compounds as well as the um troublesome combustion products.

Compared to the known method with solidification with The process according to the invention has the aid of polymers the advantage that only inorganic substances be applied. Instead of the indifferent, unsuitable for water-containing masses and only those Particle-fixing polymers react to the pollutants in the process according to the invention with inerting the leachable heavy metal compounds to aging resistant and insoluble silicates that don't like that Polymers in a mixed landfill due to alkaline seepage water and rotting are vulnerable or depending on the ver application by oily substances or solvents be decomposed.  

Due to the inertization achieved according to the invention, a Leaching the silicated heavy metals from the after consolidation (the process stage of consolidation represents a preferred embodiment of the fiction method) obtained, very fine-grained and depending on the type of mass involved, more or less fine-cracked concrete is prevented because even in the non- ertized concrete due to alkalinity of soluble heavy tallhydroxo complexes used as alkali-resistant silicates be bound.

Which may occur in the known methods gradual increase in volume of fine concrete by the so-called gypsum drive in the after The inertized process obtained according to the invention Masses through the formation of silicate, especially Cal cium silicate prevented. This is particularly important in the With regard to the solidification of sulfate-containing slags, Fly ash and flue gas cleaning sludge. Also the Resistance to acid chemicals or agents cien through the alkalinity of the non-inert Buffer capacity going beyond concrete increases for a long time.

The method according to the invention thus represents a station wagon nation of two process stages. In the first stage the contaminated masses to be treated with an alkali silicate, preferably with sodium silicate in Form of water glass offset. The second stage is then with calcium hydroxide or magnesium hydroxide slurry and / or a water-soluble alkaline earth salt, preferably treated with potassium chloride. The fiction moderate process stages cause heavy metal ions to Silicates and hydrated oxides are bound and then be immobilized in the excreted silica gel.

The method according to the invention is described below examples of the preferred embodiments  explained in more detail, with substantially different masses were used, which then with the help of fall suitable cements have been solidified.

In order to carry out the investigations explained in more detail in the following four examples, cylindrical test specimens with a height of 100 mm, a diameter of 56.4 mm, a volume of 250 cm 3 and a surface area of 227 cm 2 were produced. These test specimens had the composition given below in the examples mentioned. After 21 days of hardening, each test specimen was leached with 500 ml of distilled water, that is to say with a total of 3.5 l, under complete coverage, for seven days, in order to compare the runability for 14 days. For the quantitative determination of the low heavy metal contents, the 3.5 l obtained was concentrated to 200 ml. The heavy metal ions enriched in this way were determined spectrally photometrically. The detection ^limit was 0.002 for Cd ²⁺ , 0.01 for Cr ³⁺ , 0.01 for Cu ²⁺ , 0.005 for Pb ²⁺ and 0.04 mg / l for Zn ²⁺ .

For the implementation of the method and the following were thus used for the inertization:

1. Water glass solution (D = 1.34 g / cm³) with 36% Na₂O × n SiO₂ - solid, n = 3.5; abbreviated WglF.

2. Calcium hydroxide slurry with 50 wt .-% Ca (OH) ₂ - Solid, abbreviated Ca (OH) ₂F.

The following were used for consolidation:

1. Portland cement (PZ)
2. Alumina cement (TSZ)
3. Road cement (TrZ).

The test specimens were made in accordance with the Swiss standard SN 640 509a (stabilization with hydraulic binders, Switzerland, road specialists Zurich, Zurich, 1985) to so-called called proctor bodies compressed.

In terms of leachability is because of the sub differences in the context and weight of the test specimens not the direct comparison of the leached quantities (Tab. 1.1, 2.1, 3.1, 4.1) decisive, but their order Calculated values per thousand plus the formation of quotients (Tab. 1.2, 2.2, 3.2, 4.2). The cementless test specimens (K 1.1, 2.1, 3.1, 4.1) were used to delay decay 1% alginate added during leaching. The details in percent (%) and in parts per thousand (‰) are weight% respectively. -‰.

Example 1 Waste incineration slag

The process according to the invention was carried out using Carried out slag that came from incineration. The slag freed from metallic iron (Schl.) D = 1.93 g / cm³, contained 22% water after grinding and sieving. Grain size <0.5 mm.

Contents in kg dry matter (TS): Cd 0.045 g, Cr 0.63 g, Cu 1.15 g, Pb 1.16 g, Zn 2.27 g.

Composition of the test specimen (PK)

Table 1.1

Leaching values

Table 1.2

Evaluation of table 1.1

Example 2 Fly ash from waste incineration

The grain size of the screened, dry fly ash (FlA) was less than 0.1 mm, the density was 0.95 g / cm³.

Composition of the test specimen (PK)

Table 2.1

Leaching values

Table 2.2

Evaluation of table 2.1

Example 3 Fly ash, washed

The fly ash washed with water (pH 9.5) for about 10 min (FlAg) was dried at 110 ° C. The grain size of the closing screened fly ash was less than 0.1 mm, the Density at 1.66 g / cm³.

Contents in kg dry matter (TS): Cd 0.16 g, Cr 0.62 g, Cu 1.14 g, Pb 7.14 g, Zn 19.63 g.

Composition of the test specimen (PK)

Table 3.1

Leaching values

Table 3.2

Evaluation of table 3.1

Example 4 Port silt, puncture-proof, free of gravel and sand

The harbor silt (HS) contained 60% water, the density was 1.35 g / cm³. After partial drying to 30% Moisture and sieving using a vibrating sieve was the Density at 1.80 g / cm³, the grain size below 0.06 mm. Ge hold in kg dry matter (TS): Cd 0.017 g, Cr 0.18 g, Cu 0.38 g, Pb 0.26 g, Zn 1.16 g.

Composition of the test specimen (PK)

Table 4.1

Leaching values

Table 4.2

Evaluation of table 4.1

Based on the accumulated content of Cd, Cr, Cu, Pb and Zn in non-inertized and not with cement strengthened test specimens, the leachability decreased inertized and distilled by distilled water test specimens on the one hand and on the other hand not inertized, only solidified with the same type of cement test specimens when used

• - on low chloride and sulfate, only with Portland cement solidified, e.g. T. sintered and glazed slags from waste incineration from 2 to 5 times to 8 up to 12 times;
• - on chloride and sulfate rich, only with alumina melt cemented fly ash from waste incineration from 7 to 10 times 65 to 83 times;
• - on fly ash from waste incineration after extensive Wash out the chlorides and sulfates, also with Alumina cement hardened, from 4 to 9 times 25 to 35 times;
• - at port silt, solidified only with cement, from 6- up to 11 times 29 to 34 times.

further reading

1. BMFT research report Z 85-012, Janura 1985 "Pilot development of a process for the production of a lightweight material from fine-grained river and lake sediments"
2. Hansa 125 (1988) pp. 1051-1066, H. Krönig, "Process engineering treatment of contaminated port silt"
3. Federal Institute for Environmental Protection, Bern, April 1987, Environmental Protection Publication No. 62 "Treatment and solidification of residues from waste incineration plants"

Claims (9)

1. Process for converting combustion residues and natural and industrial sediments contaminated in particular with heavy metals into a landfill-compatible form, characterized in that the residues or sediments

• a) with an alkali silicate solution and
• b) subsequently mixed with a calcium hydroxide or magnesium hydroxide slurry and / or an alkaline earth metal salt solution.

2. The method according to claim 1, characterized in that the mass obtained after carrying out stage b) mixed with a cement. 3. The method according to claim 1 or 2, characterized in that one uses as alkali silicate solution based on sodium or potassium silicate of the composition Na₂O × n SiO₂ or K₂O × n SiO₂ with n <1 and in particular a water glass solution. 4. The method according to any one of claims 1 to 3, characterized characterized in that the alkali silicate solution in kon centered form and in such an amount that the solids content of alkali silicate be 2 to 12% by weight contributes to the final composition. 5. The method according to any one of the preceding claims, characterized in that in step b) the calcium hydroxide or magnesium hydroxide slurry or the Alkali salt solution is used in such an amount that the Calcium hydroxide or magnesium hydroxide content substance or alkaline earth salt solid is 1 to 6% by weight, based on the final composition obtained. 6. The method according to claim 1 or 5, characterized records that in step b) a calcium hydroxide on slurry and / or a calcium chloride solution. 7. The method according to any one of the preceding claims, characterized in that for stages a) and b) un constant circulation of the combustion residues or Carries out sediments. 8. The method according to any one of the preceding claims, characterized in that after the implementation of the Step a) a period of 2 to 30 minutes. and particularly from 15 min. let pass before going up the step b) carries out. 9. The method according to any one of claims 2 to 8, characterized characterized in that Portland, Trass or Alumina cement.