WO2022190147A1

WO2022190147A1 - Process for making mineral wools from metallurgical slag

Info

Publication number: WO2022190147A1
Application number: PCT/IT2022/050022
Authority: WO
Inventors: Giacomo BOUABDALI
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-03-10
Filing date: 2022-02-08
Publication date: 2022-09-15
Anticipated expiration: 2023-09-10
Also published as: EP4304999A1

Abstract

Described is a process for obtaining mineral wools and, in particular, rock wool products starting from metallurgical slag deriving from an electric arc furnace (EAF) or from a converter. The process comprises adding EAF slag or converter slag ground and screened with soda carbonate (Na2CO3) to the mixture normally used in the production of mineral wools.

Description

PROCESS FOR MAKING MINERAL WOOLS FROM METALLURGICAL

SLAG

This invention generically refers to a process for obtaining mineral wools and, specifically, rockwool products starting from metallurgical slag.

More specifically, the invention relates to the use of metallurgical slag deriving from an electric arc furnace (EAF) or from a converter for the production of mineral wool; in practice, the innovation is that of adding EAF slag or converter slag ground and screened with sodium carbonate (Na₂C0₃) to the mixture normally used in the production of mineral wools.

The solidified foamy product which is deposited above the fusion baths during the production of metals is commonly called "slag"; after cooling it is an agglomerate of uniform and solid mass (solidified foam) of non-volatile mineral impurities (solid non-metallic parts), consisting mainly of aluminium and calcium silicates, which are normal components of the rock.

The lower density slags are removed by overflow and are often used as raw materials for ancillary productions, typically for the production of cements. Therefore, according to the prior art, the majority of the metallurgical slags are no longer reused and contributes to an increase in atmospheric pollution.

Within the scope of the above-mentioned requirements, therefore, the main aim of the invention is to overcome the drawbacks of the prior art and, in particular, to provide a process for the production of mineral wool starting from metallurgical slag, which allows the atmospheric pollution deriving from the removal of metallurgical slags and their minimal re-use in production to be limited.

Another aim of the invention is to provide a process for the production of mineral wools starting from metallurgical slag in an efficient and safe manner and with high yields. A further aim of the invention is to provide a process for the production of mineral wools starting from metallurgical slag, which has a low manufacturing cost with respect to known techniques and by virtue of the advantages achieved. These and other aims, which will be described in more detail below, are achieved according to the invention by means of a process for the production of mineral wools starting from metallurgical slag, according to the accompanying claims 1 and 5; further detailed technical specifications of the process are reported in the subsequent dependent claims.

Further aims and advantages of the invention will be more evident from the following description, referring to a preferred but non-limiting embodiment of the process in question.

In practice, according to the invention, metallurgical slags deriving from an electric arc furnace (EAF) or from a converter are used for the production of mineral wools.

The process according to the invention comprises adding EAF metallurgical slag or metallurgical slag from a converter ground and screened with soda carbonate (Na₂C0₃) to the mixture normally used in the production of mineral wools.

The chemical composition of the EAF slag, determined by X-ray fluorescence spectrometry (WDXRF), is shown in the following Table 1.

Table 1 - EAF slag

The chemical composition of the converter slag, determined by X-ray fluorescence spectrometry (WDXRF), is shown in the following Table 2 and on the basis of this the use of the resulting product was tested as raw material for the production of glass for rock wool.

Table 2 - Converter slag

According to a first embodiment of the invention, the process of producing mineral wools and, in particular, rock wool takes place starting from metallurgical converter slag.

Rock wool belongs to the group of products called Artificial Glass Fibres (AGF) and is used as a thermal and acoustic insulator in building constructions (walls, roofs, floors, etc.), in industrial technical installations (pipes, chemical plants, etc.) and in agriculture as a substrate in soilless cultivation techniques (hydroponic cultivation).

The chemical compositions of industrial products made of rock wool have fairly wide ranges of oxide concentrations (as shown in Table 3 below).

Table 3 Indicative ranges of the oxide concentrations of industrially produced rock wool

The compositions must however guarantee two fundamental parameters, such as the insulating capacity linked to the type of short fibre produced during the spinning process and an adequate level of bio-solubility of the material.

The diffusion of these materials is due to the particular properties of the AGF, which are highly resistant, inextensible, but very flexible, non- flammable and poorly attacked by humidity and corrosive chemical agents; moreover they are not degradable by microorganisms.

As already noted, the indicative ranges of the oxide concentrations of industrially produced rockwool, expressed in % by weight, are those shown in Table 2 above. Table 4 below shows the composition of the vitrifiable mixture prepared for the fusion, according to the process of the invention, in which the raw material has been used in a quantity equal to 29.3% by weight.

Table 4

As shown in T able 4, in order to obtain a composition of glass for rock wool, the following raw materials have been added to the converter slag: silica sand (Si0₂), hydrated alumina or aluminium hydroxide, (Al (OH)₃), dolomite or double carbonate of calcium and magnesium (MgCa (C0₃)₂) and soda or sodium carbonate (Na2C0₃).

Again according to the process of the first embodiment of the invention, the mixture (with a mass equal to approximately 800 g.) is loaded into an electric furnace inside a silico-alumina crucible at a temperature of 1200°C, gradually increased to 1400°C and kept fused at this temperature for approximately four hours.

The molten glass is then poured onto a metal plate, annealed at 650 °C and left to cool inside the furnace to room temperature. Advantageously, it is possible to produce a plate (according to preferred embodiments with dimensions equal to approximately 16 cm x 8.5 cm x 1 cm and with a mass equal to approximately 500 g) of opaque black glass, which is homogeneous and macroscopically free of defects. Advantageously, a smaller amount of glass is cast separately and used for the preparation of a sample for chemical analysis performed by wavelength dispersion X-ray fluorescence spectrometry (WDXRF); the quantitative chemical composition determined is shown in Table 5 below, where a comparison is also made with the theoretical composition calculated on the basis of the vitrifiable mixture.

Table 5

The laboratory tests performed made it possible to verify that the raw material sample is potentially suitable for use as a raw material in the production of glass for rock wool, after verification on an industrial scale. According to a further embodiment of the invention, the process for production of mineral wools can also take place starting from EAF metallurgical slag.

Table 6 below shows the composition of the vitrifiable mixture prepared for the fusion in which the EAF slag is used in a % by weight equal to 22%.

Table 6

As shown in the table, in to obtain a vitrified composition for the production of rock wool, silica sand, dolomite or double carbonate of calcium and magnesium (MgCa(CC>3)2), hydrated alumina or aluminium hydroxide (AI(OH)3) and sodium carbonate (Na2CC>3) are used, in addition to the EAF slag.

Advantageously, the mixture (with a mass of approximately 500 g) is loaded into an electric furnace inside an alumina crucible at a temperature of 1300°C, brought to 1350°C and kept fused at this temperature for approximately four hours. The molten glass is then poured onto a metal plate, annealed at 700 °C and left to cool inside the furnace to room temperature. According to the embodiment of the invention, two plates (of dimensions equal to approximately 10 cm x 5 cm and 5 cm x 5 cm and thickness of approximately 8 mm) of homogeneous black glass and macroscopically free of defects were obtained.

The chemical composition of the glass, determined by fluorescence spectrometry of the X-rays available at wavelength (WDXRF), is shown in Table 7 below, in comparison with the theoretical composition calculated on the basis of the vitrifiable mixture.

Table 7

Based on the tests performed, it is concluded that the EAF metallurgical slag can also be used as a raw material in the production of rock wool products. Furthermore, the glass sheet obtained according to the embodiments described also has characteristics suitable for use as tiles, mosaics, etc.

It was thus found that it is possible, in a fast, simple and practical way, to obtain mineral wool products and, in particular, rock wool with optimal characteristics starting from metallurgical slag, which, in this case, are not scrapped, but they can be reused in an advantageous manner, also limiting the increase in atmospheric pollution. The characteristics of the process for the production of mineral wools starting from metallurgical slag, according to the invention, clearly emerge from the description, as do the advantages thereof.

In particular, the above-mentioned advantages include:

- reduction of energy demand during the production step; - reduction of maintenance of the furnace used;

- possible recycling of slag;

- reduction of the use of natural resources;

- reduction of CO2 emissions;

- reduction of the bio-persistence of the finished product. Lastly, it is clear that numerous other variants might be made to the process in question, without forsaking the principles of novelty of the inventive idea of the accompanying claims, while it is clear that in the practical actuation of the invention, the materials, the shapes and the dimensions of the illustrated details can be of any type according to requirements, and can be replaced by other technically equivalent elements.

Claims

1. Process for making mineral wools from metallurgical slag, by using a mixture of the following components

and wherein said mixture is - loaded into an electric furnace inside a silico-allumina crucible at a temperature of 1200°C,

- the temperature is gradually increased to 1400°C,

- said mixture is fused and kept fused at 1400^ for about four hours,

- said mixture, after being fused, is cast on a metal plate and then placed in annealing at 650^QC, then is cooled inside said electric furnace up to room temperature.

2. Process as claimed in claim 1 , characterised in that, after said mixture is cast, annealed and cooled up to room temperature, an opaque black glass plate is obtained, said plate being homogeneous and macroscopically free of defects.

3. Process as claimed in claim 2, characterised in that said opaque black glass plate comprises the following oxides

4. Process as claimed in at east one of the previous claims, characterised in that said opaque black glass plate is used as a raw material in the production of glass for mineral wools and, in particular, for rockwool and/or as a tile or mosaic.

5. Process for making mineral wools from metallurgical slag, by using a mixture of the following compounds

and wherein said mixture is loaded into an electric furnace inside an allumina crucible at a temperature of 1300°C,

- the temperature is gradually increased to 1350 °C,

- said mixture is fused and kept fused at 1400^ for about four hours,

- said mixture, after being fused, is cast on a metal plate and then placed in annealing at 700^QC, then is cooled inside said electric furnace up to room temperature.

6. Process as claimed in claim 5, characterised in that, after said mixture is cast, annealed and cooled up to room temperature, an homogeneus black glass plate is obtained, said plate being macroscopically free of defects.

7. Process as claimed in claim 6, characterised in that said homogeneus black glass plate comprises the following oxides

8. Process as claimed in at least one of the claims from 5 to 7, characterised in that said homogeneus black glass plate is used as a raw material in the production of glass for mineral wools and, in particular, for rock wool and/or as a tile or mosaic.