Coated Slag

Abstract

The invention relates to coated slag, which is coated with a layer of a hydrophobic polyurethane.

Description

The invention relates to slag coated with a hydrophobic polyurethane.

Slags are obtained in many processes, in particular in metallurgy. Depending on the production process, a distinction is made in the case of slags between blast furnace, smelting and steel mill slag. Depending on the process, these are produced from metal ores, coke, limestone and dolomite as byproducts in the actual production process. Blast furnace slag is generally used as cement raw material and in road construction and in isolated case also as fertilizer. The steel furnace slag obtained in a slightly smaller amount is predominantly used in the building material sector and to lesser extents as fertilizer. A small part, generally about 10%, is disposed of in landfills.

A part of the steel furnace slag is also used in hydraulic engineering in addition to road construction. The substantial requirements with regard to hydraulic engineering stones are specified in “Technische Lieferbedingungem für Wasserbausteine” and include requirements with regard to the rock density, the classification by dimensions and weight, the stone shape, the compressor strength, the frost resistance and the constancy of volume. Slag used in hydraulic engineering now often replaces constructions which were previously produced from lattice work. In general, the slag stones are no longer set in a complicated manner but are randomly dumped.

A disadvantage of the use of slag is firstly insufficient mechanical stability. Thus, it has been found that, for example, 10-20% of the slag disintegrates to a very fine particle size on use in hydraulic engineering. This comminution process leads in the course of time to cementing which is virtually water-impermeable and thus constitutes potential rupture points of the top layers.

Furthermore, it is necessary to avoid the release of toxic substances from the slag into the environment or, in the case of hydraulic engineering, into the water. An adverse effect on the biocoenosis and at the same time on the self-purifying capacity of the body of water are feared as a result.

The prior art discloses the use of slag in combination with a plastic for civil engineering and hydraulic engineering.

Thus, DE 1 946 469 describes a sealing layer for inclined surfaces, in particular in hydraulic engineering, which layer consists of stones, slag and a binder. Binders used are in particular asphalt and a thermoplastic. By the addition of the plastic to the binder, the sealing layer is prevented from flowing away.

U.S. patent application—please insert the number—and KR 2002008805 describe the use of slag and a polymer resin as material in road construction. This is said to increase the strength of the material.

JP 2001163649 describes a mixture comprising an inorganic material, for example, industrial wastes which are coated with a sulfur-containing melt. This gives a construction material of <44 mm which can be used in road construction but also in the coastal region. The elution of toxic material is prevented by the coating so that the mixture can also be used as construction material.

JP 53137222 describes the provision of porous material, for example slag, with a photocurable coating. Hardness, heat resistance and chemical stability of the material are improved as a result.

KR 2002001916 describes a water-curable coating for surrounding silica, glass or slag. The coating consists of sodium-polyacrylate. The composite has good resistance to sea water.

JP 2004236546 describes the coating of slag with calcium carbonate. The slag provided with the coating is applied to the coast or to the bottom of the water and is said to regulate the pH of the sea water and to reduce the construction costs.

JP 7048187 describes the recycling of waste slag in the construction sector by coating with a liquid resin, in particular an epoxy resin or a fiber-reinforced resin.

A disadvantage of the solutions mentioned is in particular that they generally have insufficient resistance to environmental influences. This may result in the coating being destroyed and its advantages no longer being effective.

It was an object to treat slag stones so that they have high mechanical stability and are environmentally compatible. The process for the treatment of the slag stones should be simple and reliable.

The object could surprisingly be achieved by coating the slag with a layer of a hydrophobic polyurethane.

The invention accordingly relates to slag coated with a layer of a hydrophobic polyurethane.

The invention furthermore relates to a process for the production of coated slag, wherein the slag is coated with the liquid starting components of a hydrophobic polyurethane which cure on the surface of the slag.

Slag used may be all types known in industry. In particular, it may be blast furnace, smelting and steel mill slag. The slag is generally present in the form of pieces having a diameter in the range of from 0.5 to 50 cm, preferably from 0.5 to 20 cm, particularly preferably from 2 to 15 cm, in particular from 2.5 to 6.5 cm. A small proportion of smaller pieces down to fine dust can be tolerated since this can be incorporated into the coating. However, the amount of dust should not exceed 10% by weight, based on the slag, since otherwise disturbances in the polyurethane may occur.

The layer of the polyurethane on the stone is generally only a few millimeters, preferably not more than 5 mm, in particular from 0.1 to 5 mm, thick. The slag is substantially completely coated.

The coating of the slag is effected, as mentioned above, by applying the liquid starting components of the polyurethanes to the slag, where they cure. The slag stones can be laid out and wetted with the liquid starting components of the polyurethanes. The wetting can be effected, for example, by pouring or spraying, but also by simple mechanical mixing, but preferably by spraying.

The process can be designed so that the coated slag is present in the form of individual pieces.

Preferably, the coated slag is present in the form of a composite body, i.e. the individual pieces are bonded to one another by the polyurethane. The individual pieces of the slag are firmly bonded by the polyurethane, the bonding taking place only at the points of contact. As a result, cavities form in the interior of the molding.

The composite bodies can be produced by introducing the slag into a mold and adding the liquid starting components of the polyurethanes thereto, preferably by pouring or spraying as stated above. The size of the mold is not critical but should only be so large that the liquid starting components of the polyurethane can wet the entire slag before they cure. Preferably, the moldings have a size of 100+50×100+50×15+10 cm.

In a further embodiment of the process according to the invention, the slag is applied where it is to be used, for example on embankments, dams, dykes or traffic routes, and wetted on site with the liquid starting components of the polyurethanes, where they cure.

In a further embodiment of the invention, the slag is mixed with the liquid starting components of the polyurethane in a mixer. The mixture is then discharged from the mixer and the polyurethane cures.

The mixers used for mixing the slag with the starting components of the plastic can in principle be all types of mixers with which substantially complete wetting of the slag with the starting components of the plastic is possible. Mixers which consist of an open container, for example a drum, which is preferably provided with internals, have proven particularly suitable. For the mixing, either the drum can be rotated or the internals can be moved.

Such mixers are known and are used, for example, in the construction industry for the production of concrete mixes.

If the mixture is applied directly to the surface to be consolidated, it may be advantageous to mount the mixer on a vehicle, for example a tractor, a front loader or a truck. In this embodiment of the process according to the invention, the mixture can be trans-ported in each case to the place where it is to be applied. After the mixer has been emptied, the mixture can be distributed manually, for example by means of raking.

In an embodiment of the process according to the invention, the mixing of the slag with the liquid starting components of the polyurethane is effected continuously. For this purpose, the slag and the liquid starting components of the polyurethane are introduced continuously into the mixer and the wetted stones are discharged continuously. In this procedure, it must be ensured that the starting materials remain in the mixer until sufficient wetting of the slag can take place. Expediently, such a mixing apparatus can be moved along the sections to be consolidated at a speed such that the slag wetted with the liquid starting components of the plastic are discharged from the mixer in an amount required for consolidation. It is also possible to operate the continuous mixing apparatus while stationary and to transport the wetted slag discharged from the mixture to the desired location.

In a further embodiment of the continuous design of the process according to the invention, the mixer may be a rotating drum into which slag is introduced continuously. This drum is equipped with nozzles which continuously distribute the starting components of the plastic over the stones. Here, the rotation of the drum ensures thorough mixing of plastic and stones. Plastic/slag composites are then discharged continuously through the opening at the end of the drum. The rotating drum may be horizontal but may also be inclined at various angles in order to promote the discharge.

In a further embodiment of the continuous process, the slag is transported continuously onto a conveyer belt which is moved through a tunnel. This has openings via which the starting materials of the plastic are discharged continuously onto the slag. At the end of the conveyer belt, the slag then falls into an open mixing drum which discharges the composite at a conveying speed which can be set.

The following may be stated with regard to the hydrophobic polyurethanes.

In the context of the present invention, components of the polyurethanes are understood very generally as meaning compounds having free isocyanate groups and compounds having groups which are reactive with isocyanate groups. Groups which are reactive with isocyanate groups are generally hydroxyl groups or amino groups. Hydroxyl groups are preferred since the amino groups are very reactive and the reaction mixture therefore has to be processed rapidly. The products formed by reaction of these components are generally referred to below as polyurethanes.

Polyurethanes used may be the conventional and known compounds of this type. The polyurethanes are prepared by reacting polyisocyanates with compounds having at least two active hydrogen atoms. Polyisocyanates used can in principle be all polyisocyanates, mixtures and prepolymers which are liquid at room temperature and have at least two isocyanate groups.

Aromatic polyisocyanates are preferably used, particularly preferably isomers of toluoylene diisocyanate (TDI) and of diphenylmethane diisocyanate (MDI), in particular mixtures of MDI and polyphenylenepolymethylene polyisocyanates (crude MDI). The polyisocyanates may also be modified, for example, by the incorporation of isocyanurate groups and in particular by the incorporation of urethane groups. The last-mentioned compounds are prepared by reacting polyisocyanates with less stoichiometric amount of compounds having at least two active hydrogen atoms and are usually referred to as NCO prepolymers. Their NCO content is in general in the range from 2 to 29% by weight.

In general, polyfunctional alcohols, so-called polyols, or less preferably, polyfunctional amines are generally used as compounds having at least two hydrogen atoms reactive with isocyanate groups.

In a preferred embodiment of the process according to the invention, compact polyurethanes used are those which have been rendered hydrophobic. The hydrophobicity can be produced in particular by addition of hydroxyl-functional components known in fat chemistry to at least one of the starting components of the polyurethane system, preferably to the polylol component.

A number of hydroxyl-functional components are known in fat chemistry and may be used. Examples are castor oil, oils modified with hydroxyl groups, such as grapeseed oil, black cumin oil, pumpkin seed oil, borage seed oil, soybean oil, wheatgerm oil, rapeseed oil, sunflower oil, peanut oil, apricot kernel oil, pistachio kernel oil, almond oil, olive oil, macadamia nut oil, avocado oil, sea buckthorn oil, sesame oil, hazelnut oil, evening primrose oil, wild rose oil, hemp oil, safflower oil, walnut oil, fatty acid esters modified with hydroxyl groups and based on myristoleic acid, palmitoleic acid, oleic acid, vaccenic acid, petroselinic acid, gadoleic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, stearidonic acid, arachidonic acid, timnodonic acid, clupanodonic acid and cervonic acid. Castor oil and its reaction products with alkylene oxides or ketone-formaldehyde resins are preferably used here. The last-mentioned compounds are sold, for example, by Bayer AG under the name Desmophen® 1150.

A further preferably used group of polyols known in fat chemistry can be obtained by ring opening of epoxidized fatty acid esters with simultaneous reaction with alcohols and, if appropriate, subsequent further transesterification reactions. The incorporation of hydroxyl groups into oils and fats is effected in the main by epoxidation of the olefinic double bonds present in these products, followed by the reaction of the epoxide groups formed with a monohyrdric or polyhydric alcohol. A hydroxyl group or, in the case of polyfunctional alcohols, a structure having a larger number of OH groups is obtained from the epoxide ring. Since oils and fats are generally glyceryl esters, parallel trans-esterification reactions also take place in the case of the abovementioned reactions. The compounds thus obtained preferably have a molecular weight in the range from 500 to 1500 g/mol. Such products are available, for example, from Henkel.

In a particularly preferred embodiment of the process according to the invention, the compact polyurethane used is one which can be prepared by reacting polyisocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups, wherein the compounds having at least two reactive hydrogen atoms comprise at least one polylol known in fat chemistry and at least one phenol-modified aromatic hydrocarbon resin in particular an indene/cumarone resin. These polyurethanes and their components have such a high hydrophobicity that they can in principle cure even under water.

Preferably used phenol-modified aromatic hydrocarbon resins having a terminal phenol group are phenol-modified indene/cumarone resins, particularly preferably industrial mixtures of aromatic hydrocarbon resins, in particular those which comprise, as a substantial constituent, compounds of the general formula (I)

where n is from 2 to 28. Such products are commercially available and are offered, for example, by Rütgers VTF AG under the trade name NOVARES®.

The phenol-modified aromatic hydrocarbon resins, in particular the phenol-modified indene/cumarone resins, generally have an OH content of from 0.5 to 5.0% by weight.

The polylol known in fat chemistry and the phenol-modified aromatic hydrocarbon resin, in particular the indene/cumarone resin, are preferably used in a weight ratio from 100:1 to 100:50.

Together with said compounds further compounds having at least two active hydrogen atoms may be used. Because of their high stability to hydrolysis, polyether alcohols are preferred. They are prepared by conventional and known processes, generally by an addition reaction of alkylene oxides with H-functional starter substances. The concomitantly used polyether alcohols preferably have a functionality of at least 3 and a hydroxyl number of at least 400 mg KOH/g, preferably at least 600 mg KOH/g, in particular in the range from 400 to 1000 mg KOH/g. They are prepared in a conventional manner by reacting at least trifunctional starter substances with alkylene oxides. Starter substances which may be used are preferably alcohols having at least three hydroxyl groups in the molecule, for example glycerol, trimethylolpropane, pentaerythritol, sorbitol or sucrose. A preferably used alkylene oxide is propylene oxide.

Further conventional constituents, for example catalysts and conventional assistants and additives, may be added to the reaction mixture. In particular, drying agents, for example zeolites, should be added to the reaction mixture in order to avoid accumulation of water in the components and hence foaming of the polyurethanes. The addition of these substances is preferably effected to the compounds having at least two hydrogen atoms reactive with isocyanate groups. This mixture is frequently referred to in industry as polyol component. For improving the long-term stability of the composites, it is furthermore advantageous to add agents for preventing attack by microorganisms. Moreover, the addition of UV stabilizers is advantageous for avoiding embrittlement of the moldings.

The polyurethanes used can in principle be prepared without the presence of catalysts. For improving the curing, catalysts may be concomitantly used. Catalysts chosen should preferably be those which result in as long a reaction time as possible. As a result, it is possible for the reaction mixture to remain liquid for a long time. As described, it is also possible in principle to work entirely without a catalyst.

The combination of the polyisocyanates with the compounds having at least two hydrogen atoms reactive with isocyanate groups should be effected in a ratio such that a stoichiometric excess of isocyanate groups, preferably of at least 5%, in particular in the range from 5 to 60%, is present.

The preferably used hydrophobic polyurethanes are distinguished by particularly good processability. Thus, these polyurethanes exhibit particularly good adhesion, in particular to moist substrates, such as wet rock, in particular granite rubble. The curing of the polyurethanes takes place in virtually compact form in spite of the presence of water. The compact polyurethanes used exhibit completely compact curing even in the case of thin layers.

The preferably used polyurethanes are therefore outstandingly suitable for the consolidation of embankments, in particular dams and dykes. The bond between rock and polyurethane is very strong. Furthermore, particularly with the use of very hydrophobic polyurethanes, there is virtually no hydrolytic degradation of the polyurethanes and hence very long durability of the embankments consolidated by the process according to the invention.

For carrying out the process according to the invention, the polyisocyanates are preferably mixed with the compounds having at least two active hydrogen atoms and this mixture is mixed with the stones. In principle, it would also be possible for both starting components of the polyurethane to be added separately to the stones and mixed together with them. In this case, however, nonuniform mixing and hence inadequate mechanical properties of the polyurethane may occur.

The mixing of the starting components of the polyurethane can be effected in a known manner. In the simplest case, the components can be introduced in the desired ratio into a vessel, for example a bucket, mixed by simple stirring and then mixed with the stones in the mixing apparatus. It is also possible to mix the starting components of the polyurethane in a mixing member customary in polyurethane chemistry, for example a mixing head, and to bring this mixture into contact with the stones.

By means of the hydrophobic treatment of the polyurethanes, their hydrolytic decomposition can be suppressed. The coating thus has a virtually unlimited life.

As a result of the coating with the hydrophobic polyurethanes, there is no emission of soluble metal compounds from the slag. The coated slag can therefore be used for all applications, in particular for hydraulic engineering.

The coated slag according to the invention has high strength and can be widely used. It can be used both in the form of individual stones and in the form of composite bodies.

The advantage of the composite bodies in hydraulic engineering is in particular their high strength. Furthermore, owing to the cavities in their interior and the resulting water permeability, they can absorb the energy of the waves and therefore provide effective protection of the banks.

Claims

1. A coated slag, which is coated with a layer of a hydrophobic polyurethane.

2. The coated slag according to claim 1, wherein the layer of the polyurethane is not more than 5 mm thick.

3. The coated slag according to claim 1, wherein the layer of the polyurethane is from 0.1 to 5 mm thick.

4. The coated slag according to claim 1, wherein the particles of the slag are bound by the polyurethane to give a molding.

5. The coated slag according to claim 1, wherein the preparation of the polyurethanes is effected by reacting polyisocyanates with compounds having at least two active hydrogen atoms.

6. The coated slag according to claim 5, wherein the compounds having at least two active hydrogen atoms comprise at least one hydroxy-functional component known from fat chemistry.

7. The coated slag according to claim 5, wherein the compounds having at least two active hydrogen atoms comprise at least one phenol-modified indene/cumarone resin.

8. A process for the production of coated slag, wherein the slag is wetted with the liquid starting components of a hydrophobic polyurethane which cure on the surface of the slag.

9. The process according to claim 8, wherein the wetting of the slag with the liquid starting components of the hydrophobic polyurethane is effected by spraying.

10. The process according to claim 8, wherein the wetting of the slag with the liquid starting components of the hydrophobic polyurethane is effected by pouring.

11. The process according to claim 8, wherein the wetting of the slag with the liquid starting components of the hydrophobic polyurethane is effected in a mixer.