HK1188808B - Flame protection - Google Patents

Abstract

The present invention relates to an inorganic halogen-free flame retardant made from improved rehydrated red mud (MR2S),Rehydrated red mud (MR2S) contains the following mineral components: 10% -50% (weight percentage) of iron compounds,12% -35% (weight percentage) aluminum compound,5% -17% (weight percentage) of silicon compounds,2% -21% (weight percentage) TiO2,0.5% -6% (weight percentage) calcium compound,Among them,Compared with the oxide composition of iron compounds,Iron compounds have hydroxides and oxide hydrates greater than or equal to 50% by weight,Preferably greater than or equal to 80% (weight percentage),And,Compared with the oxide composition of aluminum compounds,Aluminum compounds have hydroxides and oxyhydrates greater than or equal to 50% by weight,Preferably greater than or equal to 80% (weight percentage);The present invention further relates to a fire-resistant material structure comprising a combustible material and the aforementioned inorganic halogen-free flame retardant, and its manufacturing method.

Description

Flame-retardant protective body

Technical Field

The present invention relates to the field of inorganic flame retardants (AFM).

Background

A flame retardant is a fire retardant used to limit, slow or stop the spread of a fire.

Flame retardants are used in places where there is a potential source of fire or where the use of flammable materials can pose a safety risk.

The demand for flame retardants has increased due to the increasing demand for safety in building, aircraft and automobile manufacture, and in interior decoration, and the increasing use of high-performance synthetic materials in place of metal and metal alloy materials.

The working principle of flame retardants is based on different reactions:

-interrupting the radical chain reaction of the gases produced during pyrolysis of the material;

-forming a protective layer from the charring material (expanding) so as to prevent the ingress of oxygen and heat;

-cooling the combustion process by stimulating endothermic decomposition or by evaporating the water of hydration;

-diluting the combustible gas by means of an inert gaseous substance;

liquefaction, that is to say the formation of a solution which can flow out of the combustion zone, with a reduction in the surface area.

Most flame retardants can initiate one or more of the chemical-physical reactions mentioned above.

Therefore, flame retardants can be classified into the following four types:

-an additive flame retardant, a flame retardant that may be added to the combustible material;

reactive flame retardants, flame retardants which become part of the material itself by polymerization into the synthetic material;

natural flame retardants, flame retardants whose material itself is flame retardant;

coating type flame retardants, flame retardants that can be applied externally to combustible materials.

Inorganic flame retardants are becoming increasingly important because of their toxicity (i.e., the formation of toxic gases during decomposition), as well as natural and additive flame retardants, have been criticized and are currently being subjected to rigorous risk assessment.

Reference may be made to the Danish environmental protection agency's report on global production rates (brominated flame retardants. Mass flow analysis and evaluation of candidate materials (1999)). The classification of flame retardants is as follows:

50% of an inorganic flame retardant (AFM), for example: ATH (Al (OH)₃) And MDH (Mg (OH)₂)，

-25% of a halogenated flame retardant,

-20% of an organophosphorus compound,

-5% of a nitrogen-based flame retardant.

Aluminum hydroxide (ATH) is the most important inorganic flame retardant in terms of quantity. In the bayer process, aluminum hydroxide (ATH) can be extracted from bauxite while simultaneously producing spent red mud (RS). Hereinafter, red mud (RS) is understood as a residue generated when aluminum hydroxide (ATH) is extracted from bauxite by the bayer process.

Red mud (RS), sometimes also called bauxite with aluminium hydroxide (ATH) removed, is a substance that is very heterogeneous in terms of chemical and mineral composition, endothermic properties, pH (see table 1). The reason for this heterogeneity depends on the one hand on the various constituents of the bauxite employed, but on the other hand also on whether the bayer process uses an autoclave digestion process or a tube digestion process. In the autoclaving digestion process, digestion can be carried out at 170-180 ℃ using a sodium hydroxide solution with a concentration of 30% -35%, so that the pressure can be adjusted to 6-8 bar, while the tube digestion process is designed with the aim of shortening the reaction time from 6 to 8 hours to less than 1 hour by increasing the temperature to 270 ℃. However, at this temperature the pressure of the water vapour at the end of the reactor will reach 60 bar. Such high temperatures of the tube digestion process also affect the red mud composition. For example: in the tube leaching process, Fe-O₂-H₂The O will be out of balance and almost completely converted to hematite.

Due to this inhomogeneity of red mud (RS), there has not been significant economic use to date. In this connection, red mud (RS) is disposed of almost exclusively as waste residues in the yard.

Disclosure of Invention

The object of the present invention was to avoid the disadvantages mentioned above by preparing a new, economically usable inorganic flame retardant.

This object is achieved by the independent claims. Advantageous developments and embodiments of the invention are defined in the dependent claims.

The invention relates to an inorganic halogen-free non-toxic flame retardant, which comprises the following mineral components in percentage by weight: 10-50% of iron compound, 12-35% of aluminum compound and 5-17% of SiO₂2-21% of TiO₂0.5-6% of CaO and 3-10% of Na₂O。

Wherein, in the inorganic flame retardant according to the present invention, the ratio of aluminum hydroxide/alumina hydrate to alumina is 1 or more (that is, at least 50% by weight, preferably 80% by weight of aluminum hydroxide/alumina hydrate), and the ratio of iron oxide hydrate to iron oxide is 1 or more (that is, at least 50% by weight, preferably 80% by weight of iron oxide hydrate). In addition, the inorganic flame retardant is modified rehydrated red mud (MR 2S).

In addition, it is advantageous that Na is soluble in the modified rehydrated red mud (MR2S)₂The proportion of O is 0.03% by weight or less, the average particle diameter (d50) is 50 μm or less, preferably 0.5 to 10 μm, and the residual moisture is 0.4% by weight or less. By the method, economic use of the red mud (RS) can be developed, and the problem of garbage treatment of expensive special waste of the red mud (RS) can be solved.

In addition, the invention relates to a fire-protection material structure comprising a combustible material, the flame retardant according to the invention and a process for producing a fire-protection material structure, the process having the following steps: a combustible material is prepared and mixed with the flame retardant according to the present invention or coated on the combustible material, thereby obtaining a fire-retardant material structure.

Among them, a modified rehydrated red mud (MR2S) was prepared, which has proven to be a good inorganic flame retardant. Furthermore, it has been surprisingly found that improved rehydrated red mud (MR2S) used as an inorganic flame retardant (AFM) in combustible materials (e.g., polymers) can sinter or vitrify the ash scale in the event of a fire. The combustible material using the inorganic flame retardant (AFM) of the present invention is not only not melted in the case of a fire, but also fly ash does not appear after combustion, by sintering or vitrification. In contrast, the soot deposit also has certain mechanical properties, in particular a particular stability. This is particularly advantageous in avoiding fly ash that may be inhaled by humans. It is also particularly advantageous that no liquefaction of the combustible structure occurs, thereby preventing the spread of a fire. Furthermore, it is particularly advantageous that the amount of oxygen entering the core of the combustible structure can be reduced in this way, thereby preventing further combustion or burn-through. It is particularly advantageous that the vitrification of the soot can have the effect of insulating the cable in such a way that the functionality of the cable can be maintained even in the event of a fire.

After modification of red mud (RS), it has proven to be an excellent halogen-free inorganic flame retardant. The improvement can be understood as the following aspects:

-preparing the red mud (RS),

-analyzing the composition of the prepared red mud (RS),

-rehydrating the red mud,

physical processing of rehydrated red mud.

Further improvements can also be made in the following respects:

washing the prepared red mud (RS) with water,

rinsing the rehydrated red mud with water,

-drying the rehydrated red mud,

physical processing of the rehydrated red mud, in order to advantageously obtain a desired granular structure, such as: by milling and screening.

-mixing the dried and physically processed rehydrated red mud with a plastic matrix.

Incorporation of endothermically reactive species, such as: ATH (gibbsite, boehmite), magnesium hydroxide (MDH) or goethite, etc., in order to optimize the thermal properties and, if necessary, to enlarge the temperature range in which the inorganic flame retardant reacts.

During rehydration, oxides (e.g., aluminum or iron oxides) are converted to hydroxides: boehmite (hydrated alumina) is converted into gibbsite (Al (OH)₃)，Al₂O₃Will convert to gibbsite and hematite (iron oxide) will convert to goethite (iron oxide hydrate). That is, substances with the greatest possible endothermic potential are produced from substances with no or only a lower effect in the desired range of action from 180 ℃ to 350 ℃. By this process, the chemical and mineral composition of the red mud (RS) can be changed, thereby increasing the enthalpy of heat absorption and ultimately increasing the flame-retardant effect, i.e. an inorganic flame retardant (AFM) is produced which is well-defined within its scope of effect, irrespective of whether the red mud (RS) originates from an autoclave digestion process or from a tube digestion process.

The modified rehydrated red mud (MR2S) thus produced can be used as an inorganic flame retardant (AFM) in a variety of material structures with defined properties. The higher the enthalpy of endotherm after rehydration, the lower must be the degree of packing in the material structure.

Since the endothermic reaction coverage of the modified rehydrated red mud (MR2S) is in the range of approximately 180 ℃ to 350 ℃, ATH and/or MDH can be replaced partially or completely by the modified rehydrated red mud (MR2S), i.e. only one single substance is used.

Modified rehydrated red mud (MR2S) may also be modified in its surface area for ease of incorporation into the material structure.

In particular, modified rehydrated red mud (MR2S) can be coated with nanoclay. In this way, the vitrification of the soot can be further increased in the event of a fire. Moreover, the clay-type bonds contained in the modified rehydrated red mud (MR2S) also produce a vitrification effect of the ash scale.

In particular, fine-grained modified rehydrated red mud (MR2S) is prone to sintering at high temperatures, which can lead to the formation of the glassy limescale.

In conclusion, the improved rehydrated red mud (MR2S) not only covers the application range of ATH and MDH, but also has fireproof effect. Coating with nanoclay also improves vitrification and thus solves the problem of soot. Since there is a large amount of red mud (RS) as the starting raw material for the modified rehydrated red mud (MR2S), all large-scale products can be provided with a low-priced inorganic flame retardant (AFM).

In order to add inorganic flame retardants (AFM) to combustible substances, for example polymers, it is necessary to reduce as far as possible the amount of water-soluble sodium carbonate (as Na)₂Expressed as a percentage by weight of O) in order to improve the water resistance of the polymer, which is particularly suitable for the insulation of cables.

The invention relates to a fireproof material structure, which comprises a combustible material and a flame-retardant substance (hereinafter referred to as a flame retardant or a fireproof agent), and is characterized in that the flame retardant comprises a mineral component, and the mineral component comprises the following components:

10-50% by weight of an iron compound,

12-35% by weight of an aluminum compound,

5-17% (weight percent) SiO₂，

2-10% by weight of TiO₂，

0.5-6% by weight of CaO, with

3-10% (weight percent) of Na₂O。

The mineral component is preferably modified rehydrated red mud (MR 2S). It is important that the iron compound and the aluminum compound are mainly present in the form of hydroxide or oxide hydrate, not in the form of oxide. Most of all aluminum compounds and iron compounds are converted to hydroxides or oxide hydrates by the rehydration process. In the aluminum compound,. gamma. -Al₂O₃And boehmite are converted into gibbsite, and hematite is converted into goethite among iron compounds. This makes it possible to achieve as high a level of endothermic enthalpy as possible and thus to achieve as high a flame-retardant performance as possible.

The material structure may be a building material, a plastic product, a rubber product, a cardboard, a cable insulation or a cable insulation sheath consisting of one or more polymers.

The material structure may contain 3-95% by weight of flame retardant.

The flame retardant may contain 30 to 100% by weight of the mineral component (MR2S), the remaining 0 to 70% by weight being made up by other flame-retardant components or flame-retardant additives.

Other flame retardant ingredients or flame retardant additives may include an inorganic, non-toxic endothermic reactive material.

Other flame retardant ingredients or flame retardant additives may preferably include salt hydrates, hydroxides and carbonates.

Soluble Na₂The content of O is adjusted to less than 0.03% by weight, or 0.003% by weight or 0.003 to 0.03% by weight.

The invention relates to the use of the flame retardant substance as a flame retardant for combustible material structures, combustible building materials, plastics, rubber, cardboard materials or cable insulation sheaths.

The invention also relates to a process for producing a fire-resistant material structure, comprising the following steps:

a. preparing a combustible material

b. Mixing the combustible material with the flame retardant or coating the flame retardant on the combustible material,

c. and thus a fire-resistant material structure is obtained.

The mineral component of the flame retardant in step b may be fine particles having an average particle diameter (d50) of 0.5 to 50 μm, preferably 0.5 to 10 μm.

The flame retardant may be subjected to a physical treatment, preferably milling, before the mixing or coating work of step b.

The flame retardant may be surface-treated, preferably coated, with a substance which improves its compatibility with the polymeric matrix or improves the vitrification of soot, which in the event of a fire prevents the diffusion of the combustion-supporting (pyrolysis) gas to the flame front or insulates the surface, and which in the case of a cable construction ensures a functional continuity as long as possible in the event of a fire.

The surface of the flame retardant is preferably coated using silanes, fatty acids and plasticizers and known processes. It is preferred to use nanoclays, boric acid and its metal derivatives and zinc stannate and/or zinc hydroxystannate and mixtures of the above compounds to enhance the vitrification of the soot scale. In this way, possible afterfires can be prevented.

Drawings

FIG. 1 shows the thermal analysis curves (DTA) of boehmite (FIG. 1a), gibbsite (FIG. 1b) and goethite (FIG. 1 c);

FIG. 2 shows the DTA curve and TG curve of an autoclaved and digested red mud (RS) sample after washing. Recording the endothermic reaction of the gibbsite and the boehmite residual component and not recording the endothermic reaction of the goethite residual component at the temperature of between 220 and 280 ℃;

fig. 3 shows a DTA curve and a TG curve of a pipe-eluted red mud (RS) sample after washing. Recording the endothermic reaction of the gibbsite and the boehmite residual component and not recording the endothermic reaction of the goethite residual component at the temperature of between 220 and 280 ℃;

FIG. 4 shows DTA and TG curves of filter residue (undissolved components) after acidic digestion of an autoclaved digested red mud (RS) sample. No endothermic reaction was found. On acidic dissolution, all endothermically reactive components, including oxides, are dissolved away (see x-ray analysis);

FIG. 5 shows DTA and TG curves of filter residue (undissolved components) after acidic digestion of a pipe-digested red mud (RS) sample. No endothermic reaction was found. On acidic dissolution, all endothermically reactive components, including oxides, are dissolved away (see x-ray analysis);

FIG. 6 shows the DTA curve and TG curve of the precipitate obtained from the autoclave digestion red mud filtrate (pH 10.9). Again, a significant endothermic reaction occurred between 214 c and about 350 c. The reason for this is that it contains gibbsite, boehmite and goethite, which are generated by precipitation from a sulfuric acid solution after re-alkalization, but do not precipitate in the form of crystals.

FIG. 7 shows the DTA curve and TG curve of the precipitate obtained from the tube-leached red mud filtrate (pH 11.1). Again, a significant endothermic reaction occurred between 268 ℃ and 350 ℃. The reason for this is mainly goethite, because under the harsh conditions (270 ℃/60 bar) in the tube digestion process, the aluminum is completely dissolved, under which conditions goethite is converted to hematite. After rehydration, the hematite again appears as endothermically reactable goethite;

fig. 8 shows the DTA curve versus TG curve for goethite, referenced against bayside E99163. The endothermic reaction occurs between 236 ℃ and about 350 ℃. Which is comparable to the endothermic reaction of the precipitate obtained in the leaching of red mud filtrate from the pipeline.

Detailed Description

[ DEFINITIONS ]

By "fire-resistant construction material" is meant a device in which a combustible material can be joined together with a fire retardant, thereby preventing or slowing the ignition of the combustible material in such a device by fire or heat. Such flame retardants are preferably fixedly attached to the combustible material, for example: by mixing or coating.

"flame-retardant substance" means in the context of the present invention a flame retardant, preferably a non-toxic, halogen-free, inorganic flame retardant, in particular a modified rehydrated red mud (MR 2S).

By "combustible or combustible material" is meant a material that can be burned or readily burned, particularly polymers and non-volatile hydrocarbons such as: acrylic latex, acrylic resin, synthetic rubber, epoxy resin, latex, melamine resin, Polyamide (PA), Polyethylene (PE), polyethylene copolymer, thermoplastic polyethylene copolymer, reticulated polyethylene copolymer, phenolic resin, polyester resin (UP), polyurethane, polypropylene (PP), polyvinyl chloride (PVC), PVC plastisol, Thermoplastic Polyurethane (TPU), vinyl ester resin, asphalt, and others. Combustible and combustible may be considered synonyms herein.

"Red mud (RS)" refers to waste residue produced when ATH is extracted from bauxite by the Bayer process. "modified rehydrated red mud (MR 2S)" refers to the product of rehydrating, drying, milling, mixing with other materials, coating surfaces, etc. red mud (RS). The modified rehydrated red mud (MR2S) has: water content of 0.4 wt% or more and Na soluble in water of less than 0.03 wt% or less₂O, particle diameter (d50) of 0.5 to 50 μm, preferably 0.5 to 10 μm.

[ objects of the invention ]

In the present invention, the modified rehydrated red mud (MR2S) is used as an inorganic flame retardant (AFM).

Red mud is produced in the production of alumina according to the bayer process. In the bayer process, suitable bauxite is dried and milled, mixed with liquid concentrated sodium hydroxide in a calculated ratio, and subjected to digestion under elevated temperature and pressure in an autoclave digestion process or in a pipeline digestion process. The sodium aluminate solution produced is separated off. After dilution, the ATH was completely precipitated from the slurry by stirring with freshly precipitated ATH as seed crystals. Aluminum oxide and Al can be prepared from aluminum hydroxide (ATH)₂O₃And thus aluminum metal.

Separating, washing and concentrating the residue which is not dissolved in the autoclaving digestion process or the pipeline digestion process, and piling the residue as red mud in a 'yard'. Red mud is named from its red color, which is due to the high iron content.

Depending on the quality of the bauxite ore used, it is inevitable to produce 1-2 tons of red mud with a water content of about 50% per ton of aluminium produced, millions of tons being produced each year, which together with the large amount of red mud already stacked in the yard cause serious problems. Since red mud has not been successfully introduced into the relevant economic sector so far, it has been regarded as waste residue and also subjected to waste disposal. The garbage disposal mode of the red mud mainly comprises the step of piling the red mud in a sealed yard. This form of storage is expensive and wasteful because of the large yards required and the high cost of transporting these red mud. In addition, the long term costs incurred by the yard (primarily monitoring the yard) is also an economic issue. Therefore, the development of the economic value of the red mud is urgently needed.

The composition of the dried red mud is determined mainly by the composition of the bauxite used. The pressure digestion of the Bayer process NaOH also has great influence in the pressure digestion process or the pipeline digestion process. Typical compositions and average bandwidths are given in table 1 as weight percentages. Since the bayer process has not been effectively treated, red mud having a different composition is found in the yard.

TABLE 1

Composition of red mud

Component (A)	Typical content%	Bandwidth (%)
			Fe2O3	40	10-50
Al2O3	25	10-30
			SiO2	15	3-25
TiO2	7	2-24
			CaO	1	0.5-10
Na2O	9	2-20
			Others	3	0-3

Mineralogically, red mud (RS) is a mixture of different minerals and oxides (as described above) determined mainly by the composition of the bauxite ore used and the pressure digestion process. The red mud (RS) comprises gibbsite, boehmite and gamma-Al₂O₃Goethite, hematite, rutile, anatase, quartz, kaolinite, hydroxysodalite, calcite, and others.

The results of the particle structure measurements show that the red mud (RS) is precipitated as a very fine powder.

Other tests (e.g.by means of Differential Thermal Analysis (DTA)) show that red mud (RS) has an endothermic reaction. The reason is that red mud (RS) also contains residues of aluminum hydroxide or alumina hydrate (gibbsite and boehmite) and iron hydroxide or iron oxide hydrate (goethite), which react endothermically and separate water. However, the heat absorption performance varies greatly, from very weak to very strong. This property is present both in newly produced red mud (RS) and in red mud (RS) piled up to the yard. Extensive analytical studies can explain this phenomenon: the above endothermic properties, including dehydration, are only obtained when the hydroxides and oxide hydrates (e.g. gibbsite, boehmite or goethite) in the red mud (RS) are in the temperature range of about 180 c to 350 c. This residue is critically dependent on the bauxite used, but also on the pressure digestion process and the temperature and pressure at which the pressure digestion is carried out. The higher the temperature at which the pressure digestion is carried out, the more the aluminium compound and the iron compound change from hydroxide to oxide hydrate to pure oxide, which does not undergo any endothermic reaction in the preferred temperature range of 180 ℃ to 350 ℃. Therefore, there is a large fluctuation in the endothermic performance and the desired dehydration performance. The red mud (RS) precipitated during production without treatment cannot be used as defined inorganic flame retardant (AFM).

According to the invention, red mud (RS) is modified, preferably rehydrated, in order to significantly improve its endothermic and dehydration properties, thus giving the opportunity to produce it as an efficient, renewable and to a certain extent standardized inorganic flame retardant. In the case of aluminum compounds, the aluminum oxide hydrate can be converted into aluminum hydroxide by this conversion, i.e. from γ -Al₂O₃Converted to ATH (gibbsite), and converted from boehmite to ATH (gibbsite). In iron compounds, iron oxide (hematite) can be changed into iron oxide hydrate (goethite) by this conversion. After rehydration, the aluminum and iron compounds are mainly present in the form of hydroxides/oxihydrates, which can be used as modified rehydrated red mud (MR2S) products and, to the greatest extent, as inorganic flame retardants (AFM), because only hydroxides and oxihydrates have endothermic reaction and dehydration properties.

The modified rehydrated red mud (MR2S) is chemically and minerally equivalent to the red mud (RS) which is waste residue in the bayer process, and is completely different in that it is a product obtained from the red mud (RS) by a chemical reaction. The modified rehydrated red mud (MR2S) mainly contains hydroxides and hydrates oxides. Only by the improvement as described above, a non-toxic, halogen-free, inorganic fire-retardant product that can be marketed can be produced.

Production of MR2S

The production of modified rehydrated red mud (MR2S) is in principle achieved by treating red mud (RS) with mineral acids, preferably with sulfuric acid or hydrochloric acid.

For example: the red mud (RS) may be mixed with concentrated sulfuric acid (e.g., 96 or 70% strength). The optimal temperature and the optimal acid concentration are adjusted by adding water, so that the optimal red mud solubility is achieved. Among them, aluminum hydroxide (e.g., gibbsite) is predominant) Alumina hydrate (e.g.: boehmite) and gamma-Al₂O₃And iron oxide hydrates (e.g., goethite) and iron oxides (e.g., hematite) dissolve to aluminum sulfate and iron sulfate.

By the rehydration process, the aluminum and iron salts are recovered as hydroxides or as oxide hydrates. The conversion of oxides and oxide hydrates into hydroxides/oxide hydrates by this leads to an increase in the endothermic enthalpy of the chemical constituents of the red mud (RS) used as starting material. The ratio of hydroxide/oxide hydrate to oxide will favor hydroxide/oxide hydrate after rehydration.

After treatment of the red mud (RS) with acid, the acid filtrate is separated from the undissolved residue, and the hydroxide or oxide hydrate is precipitated separately from the undissolved residue.

Rehydration can also be achieved by placing the alkaline red mud (RS) in an acidic environment, basifying again after dissolution of the oxides and hydroxides/oxide hydrates. In this case, the metal salts, particularly the metal sulfates, will precipitate as hydroxides or as oxide hydrates. In this way, the oxide content can be greatly reduced or the oxide can be completely converted into the hydroxide/oxide hydrate.

In the case of conventional inorganic flame retardants (e.g.ATH), production is carried out only in alkaline conditions, so that the Na dissolution must be optimized by flushing₂O content and pH value, and in the production of modified rehydrated red mud (MR2S), the thermal and chemical properties (such as Na-solubility) of the product can be improved by changing the alkaline environment into acidic environment, then into neutral environment, and then into alkaline environment₂O content) and can be tailored to the respective use, for example: the solution is titrated from acidic to alkaline to adjust the amount of soluble Na present to less than 0.003 wt%₂O。

A general description of the production process of modified rehydrated red mud (MR2S) is: the improved rehydrated red mud (MR2S) obtained by the modification, in particular rehydration, of the red mud (RS) allows to extract a new material, different in composition from the original red mud, which is new both in chemical and mineral composition and in its thermal and physical characteristics, which can be specifically adjusted and reproduced according to its respective use and the characteristics required for this use.

In red mud (RS), mainly aluminum hydroxide/alumina hydrate (gibbsite and boehmite) and iron hydroxide/iron oxide hydrate (goethite) are responsible for the endothermic reaction. Fig. 1 shows the thermal analysis curves (taken from g.liptay, graph set of thermal analysis curves, Heyden & Son ltd., london, 1973) for boehmite (fig. 1a), gibbsite (fig. 1b) and goethite (fig. 1 c).

Depending on the residual amounts of aluminum and iron hydroxides/oxide hydrates and oxides in the red mud (RS) precipitated by the bayer process, almost all aluminum and iron salts are obtained in the form of hydroxides/oxide hydrates after the rehydration process. Chemical analysis of red mud (RS) showed that the hydroxide/oxide hydrate content after rehydration could be maximized. Therefore, the heat absorption effect can also be defined.

The higher endothermic effect obtained by rehydrating the hydroxides/oxide hydrates and oxides present in red mud (RS) can only be achieved by adding hydroxides/oxide hydrates of aluminium, iron or magnesium.

Example 1+2

About 50g of each red mud sample obtained by autoclaving and tube leaching is added to 200ml of 70% H₂SO₄The solution was suspended and stirred for 1 hour. To accelerate the dissolution process, 600ml of distilled water were added to each of the two suspensions. In addition to the thermal effects which occur at this time, the suspension was placed on a heating plate and heated to 80-90 ℃. The dissolution process is ended after the red colour of the suspension has disappeared and the undissolved residue has become grey. In separating residues by means of a vacuum filtration deviceAfter the residue was washed with a small amount of water, the residue was dried in a drying oven at 105 ℃.

The two acidic filtrates obtained from the red mud (RS) of the autoclaving digestion process and the tube digestion process, respectively, are neutralized by careful addition of NaOH solution. By further adding NaOH, iron salt and aluminum salt can be precipitated in the form of hydroxide or oxidized hydrate in the alkaline range (pH 10-11). The precipitate turns reddish brown due to the higher iron content. The suspension is then filtered and the filter residue is rinsed with distilled water at elevated temperature in order to rinse at least part of the sodium sulphate and caustic soda from the filter residue. The filter residue was then dried in a drying oven at 105 ℃.

The two samples obtained from the autoclaving and tube digestion processes were subjected to x-ray analysis and thermal analysis, respectively.

Results of x-ray analysis

Since the rapid precipitation is unseeded, the hydroxide and the oxidized hydrate have substantially no crystalline precipitate. Whereas in terms of mineral composition half of the contents were measured as iron compounds and aluminum compounds (see table 2).

TABLE 2

Results of x-ray analysis

Figures 2-8 show the conversion of aluminum oxide to hydroxide or oxide hydrate and the conversion of oxide hydrate to hydroxide. DTA-measurements (differential thermal analysis), TG-measurements (thermogravimetry) and DTG-measurements (differential thermogravimetry) are shown

Discussion of the related Art

The red mud may also be packaged according to different pressure digestion methods, i.e. pressure digestion process and pipeline digestion processAluminum-containing compounds and iron compounds. The aluminium compound may be aluminium hydroxide (gibbsite), alumina hydrate (boehmite) or alumina (gamma-Al)₂O₃). The iron compounds are mainly present as hematite in the autoclaving process and almost exclusively as hematite in the tube digestion process.

According to the process, that is to say after acidic digestion, almost all of the iron and aluminium hydroxides/oxide hydrates and oxides are dissolved. After reprecipitation, for example: in an alkaline environment, the aluminum compound and the iron compound almost completely precipitate again in the form of hydroxide/oxide hydrate. The content of oxides is significantly reduced or eliminated.

According to records, oxides can be converted to hydroxides/oxide hydrates, or oxide hydrates (in aluminum) to hydroxides, by rehydration processes. In this way, the aluminum compounds and iron compounds contained in the initial red mud (RS) can be almost completely converted into endothermically reactable substances. Regardless of its origin, that is to say whether it comes from the initial bauxite or from the selected digestion process, the red mud (RS) can maintain in its endothermic reaction the chemical content of aluminium compounds and iron compounds in the initial red mud at a maximum. A new material can thus be produced which is particularly suitable for use as an inorganic flame retardant (AFM). In addition to this, all reactions and processes can be carried out with the substance according to the invention (MR 2S).

[ examples ] A method for producing a compound

The invention relates to a fireproof material structure, which comprises a combustible material and a flame retardant, and is characterized in that the flame retardant comprises a mineral component, and the mineral component comprises the following components:

10-50% by weight of an iron compound,

12-35% by weight of an aluminum compound,

5-17% (weight percent) SiO₂，

2-10% by weight of TiO₂，

0.5-6 wt% CaO,

3-10% (weight percent) of Na₂O。

The invention relates to the fact that in MR2S, the ratio of iron hydroxide (goethite) to iron oxide (hematite) is almost exclusively biased towards goethite. The invention also relates to the use of aluminum hydroxide (gibbsite) and aluminum oxide hydrate (boehmite) and aluminum oxide (gamma-Al) in MR2S₂O₃) The ratio of (A) is strongly biased towards aluminium hydroxide/alumina hydrate.

Wherein the mineral component may comprise 10-45%, 30-50% or 40% (by weight) Fe₂O₃。

Wherein the mineral component may comprise 12-30%, 20-35% or 25% (by weight) Al₂O₃。

Wherein the mineral component may comprise 5-17%, 10-17% or 15% (by weight) SiO₂。

Wherein the mineral component may comprise 5-21%, 2-15%, 5-10% or 7% (by weight) TiO₂。

Wherein the mineral component may contain 0.5-6%, 0.5-2.5%, 0.5-1.5% or 1% (by weight) CaO.

Wherein the mineral component may contain 5-10%, 3-6%, 8-10% or 0.02% (by weight) of Na₂O。

Among them, the above various ranges may be combined, and the following combinations are preferable:

40% by weight of an iron compound,

25% by weight of an aluminum compound,

15% by weight of SiO₂，

7% by weight of TiO₂，

1% (by weight) of CaO,

0.02% (by weight) of Na₂O。

Among them, in the iron compound and the aluminum compound, the ratio of hydroxide and oxide hydrate to oxidation is significantly biased toward hydroxide/oxide hydrate.

The mineral component may be modified rehydrated red mud (MR 2S). The red mud made from MR2S can be made from bayer process alumina or ATH extracted from domestic or imported bauxite in an autoclave digestion process or pipeline digestion process, the most important industrial countries in various continents, in particular germany, australia, iceland, china, india, the usa or jamaica, can provide bauxite as a raw material.

The material structure may be a building material, a plastic product, a rubber product, cardboard or a cable insulation cover. Preferred material structures are a canvas shed, carpet backing, floor covering, roofing, conveyor belts, cables, profiles (plastic for windows and doors), pipes, gaskets, cardboard, injection molded, laminated, printed circuit board, hoses, filled resins, foams or others.

The material structure may contain 3-95% by weight of flame retardant.

The proportion of flame retardant in the material structure depends on the combustible material or material structure used. In this context, the highest possible fire protection effect is to be taken into account when optimizing the physical and technical properties of the combustible material and the material structure (e.g. processability, stability and flexibility). In an inorganic flame retardant (AFM) having a high endothermic enthalpy, the degree of filling can be lowered, so that the physical properties of the combustible structure can be less changed.

In particular, the material structure may comprise 3 to 90%, 3 to 80%, 3 to 70%, 3 to 60%, 3 to 50%, 3 to 40%, 3 to 30%, 3 to 20%, 3 to 15%, 3 to 10%, 3 to 4% (by weight) of flame retardants. The material structure preferably comprises 10 to 90%, 20 to 90%, 30 to 90%, 40 to 90%, 50 to 90%, 60 to 90%, 70 to 90%, 80 to 90% (weight percent) of flame retardants. In addition, each of the limits of these ranges may be combined with other range limits. Thus, a range of from 3 to 90% and 3 to 80% by weight may constitute a range of from 80 to 90% by weight, or a range of from 5 to 70% and 30 to 90% by weight may constitute a range of from 70 to 90% by weight. In addition, the material structure may also contain 3-95% by weight of a flame retardant, where each of these values in these ranges is considered to be within the scope of the present invention.

The flame retardant may contain 3 to 100% by weight of the mineral component (MR2S), the remaining 0 to 70% by weight being constituted by a further flame-retardant component.

The flame retardant may also contain 40-100%, 50-100%, 60-100%, 70-100%, 80-100%, 90-100%, 30-90%, 30-80%, 30-70%, 30-60%, 30-50% or 30-40% by weight of a mineral component, and the remaining 0-70% by weight may be constituted by one other flame retardant component. As mentioned above, these ranges are combinable, such as combining the ranges 40-100% and 30-70% (weight percent) into 40-70% (weight percent). In addition, the flame retardant may contain 30 to 100% by weight of mineral components, wherein each value in these ranges is considered to be within the scope of the present invention.

Other fire-retardant ingredients may include an inorganic, non-toxic, endothermic reactive substance.

Other fire-retardant ingredients are preferably water of hydration, hydroxides and carbonates. Hydroxides, for example: aluminium hydroxide, goethite or magnesium hydroxide, either with a specific (BET) surface (2-50 m)²/g) and average particle diameter (d50) < 1 μm (named nano magnesium hydroxide), or natural milled particlesBrucite having a particle size (average particle diameter) (d50) of less than 50 μm, preferably less than 10 μm, which comprises or may comprise hydromagnesite or basic magnesium carbonate, and the proportions may vary. The water of hydration may be sodium silicate hydrate or calcium silicate hydrate, calcium aluminum sulfate hydrate, etc. The carbonate can be calcium carbonate, heavy calcium carbonate, magnesium carbonate, etc.

MR2S has a maximum of 0.03% (by weight) soluble Na2O, preferably 0.003-0.03% (by weight).

The particle size of MR2S is 0.5-50 μm, preferably 0.5-10 μm. The invention relates to a flame retardant which uses the flame retardant substance in combustible material structures, combustible building materials, plastics, rubber, cardboard materials or cable insulation sleeves.

The invention also relates to a method for producing a fire-protection material structure, comprising the following steps:

a. preparing a combustible material

b. Mixing the combustible material with the flame retardant or coating the flame retardant on the combustible material,

c. and thus a fire-resistant material structure is obtained.

The mineral component of the flame retardant in step b is fine-grained, and the average particle diameter (d50) is preferably 0.5 to 10 μm, 0.5 to 9 μm, 0.5 to 8 μm, 0.5 to 7 μm, 0.5 to 6 μm, 0.5 to 5 μm, 0.5 to 4 μm, 0.5 to 3 μm, 0.5 to 2 μm, 0.5 to 1 μm, 1 to 9 μm, 2 to 9 μm, 3 to 9 μm, 4 to 9 μm, 5 to 9 μm, 6 to 9 μm, 7 to 9 μm, 8 to 9 μm, and the ranges obtained by combining the limits of these ranges are also considered to be the ranges according to the present invention.

The flame retardant may also be subjected to a physical treatment, preferably milling, before the mixing or coating work of step b. Milling can bring the flame retardant to any average particle size. The particle size achieved may be any value between 0 and 10 μm. If MR2S precipitates as particles larger than > 10 μm, then for special applications MR2S with particle diameters larger than > 10 μm can also be used without milling.

In addition, to improve the compatibility of the flame retardant with the combustible materials disclosed herein, particularly polymers or polymeric substrates, the flame retardant may be modified by coating with substances or by surface treatment.

The surface of the flame retardant may be coated with a coupling agent according to the prior art, preferably with a silane, a fatty acid and a plasticizer. These coatings are, on the one hand, easy to process in a polymeric matrix and, on the other hand, they are elastic, thermosetting or thermoplastic. In addition, the performance characteristics of the inorganic flame retardant (AFM) structures of the present invention can be specifically influenced in accordance with the desired performance characteristics. MR2S may be mixed alone or with the potentiators of the present invention, for example: nanoclays, afterglow inhibitors (zinc borate and boric acid derivatives, zinc stannate/zinc hydroxystannate) are mixed with other halogen-free inorganic flame retardants (AFM) and then surface modified together. Alternatively, MR2S can also be used in the form of a masterbatch in admixture with a synergist.

It is achieved by surface coating and/or preferably mixing with nanoclays (Cloisites von S C P Inc, Gonzales, Texas, USA) that the resulting gray scale will have considerable residual elasticity in case of fire and polymorphic glass firmness.

Examples of the invention

In order to determine the effect of the modified rehydrated red mud on the fire and mechanical properties of different materials, some specific tests were performed. The purpose of the experiment was to confirm whether the common ATH and MDH could be partially and/or completely replaced with MR 2S.

Tests were performed on two polar plastics (PVC with Ethylene Vinyl Acetate (EVA)) and two non-polar plastics (PE with PP) and each compared to pure ATH or MDH.

The following examples are given solely for the purposes of illustration and description, and are not intended to be limiting, except as set forth in the appended claims.

Example 1PVC

As starting raw materials were used:

standard PVC-U for window profiles,

substances for comparison with MR2S (reference sample), the ATH component of aluminum hydroxide martinal (Martineol 104// LEO, manufactured by Albemarle corporation of Begadham),

MR2S used as an inorganic flame retardant (AFM) had the following composition:

dry powders were first produced in a mixing vessel (CM80, Mixaco). The dry powder was produced into profiles by means of twin screw extruders (model DS7.22 from Weber masschinenfabrik) running in opposite directions. The extrusion temperature is 180 ℃ to 190 ℃.

From the profiles produced, test specimens for carrying out tensile tests (DIN EN ISO527, type lB) and flame tests (DIN4102, method B) were worked out.

The following formulation was produced:

PVC-U formula containing 4% of inorganic flame retardant for window profile

The inorganic flame retardant comprises the following components:

the following tests were performed:

tensile test [ MPa ]]Reference DIN EN ISO527

Tensile modulus [ MPa ]]DIN EN ISO527

Fire protection performance, see DIN4102, method B

To test the fire behavior, the test specimens were subjected to a fire test (cf. DIN4102, method B). In the test, the ignition of the edge of the test piece, the burning rate and the burning dripping of the building material were evaluated.

In the combustion test, the flame front of all the formulation combustion specimens did not reach the topmost measurement mark and the combustion specimens extinguished themselves earlier, so all the specimens had a fire rating of K1.

The fire behavior of method B with reference to DIN4102 will remain unchanged by partial or complete replacement of ATH by AFM.

Example 2EVA

In the production of EVA formulations, ZSE27Mxx was used as a mixing machine. The temperature is between 145 ℃ and 160 ℃. A continuous granulator was used to produce the granules. AFM was found to have better loosening properties than ATH upon mixing, and was significantly easier to process and disperse. The EVA mixtures were sprayed into test specimens for carrying out impact tensile tests (DIN EN IS08256), tensile tests (DIN ISO527) and oxygen index tests (LOI, DIN ISO 4589-2).

Starting material

EVA containing 1.2% adhesion promoter and 0.4% stabilizer

Martinal OL104/LEO (ATH component)

MR2S as inorganic flame retardant (AFM)

Formulation of

EVA containing 60% of flame retardant

Composition of flame retardant

The following tests were performed:

tensile test [ MPa ]]Reference DIN EN ISO527

Tensile modulus [ MPa ]]DIN EN ISO527

Elongation at break [% ]]Reference DIN EN ISO527

Impact toughness [ KJ/m ² ]Reference DIN EN ISO8256

Fire-proof performance

Example 3PE

The formulation on the PE substrate was plasticized and homogenized in a co-operating twin screw extruder ZSE18 HPE. The temperature in the mixer is between 190 ℃ and 220 ℃. The PE mixtures were produced by injection molding to give test specimens for tensile tests (DIN EN ISO527, type lB), impact tests (DIN EN ISO179) and fire tests (UL 94).

Starting materials:

PE magnesium oxide 7287/Brenntag, pure chemical magnesium hydroxide (MDH-component, zero sample)

MR2S as inorganic flame retardant (AFM)

Formulation of

PE containing 50% flame retardant

The components of the flame retardant are as follows:

the following tests were carried out

Tensile test [ MPa ]]Reference DIN EN ISO527

Tensile modulus [ MPa ]]DIN EN ISO527

Elongation at break [% ]]Reference DIN EN ISO527

Charpy impact toughness, [ KJ/m ] ² ]DIN EN ISO179

Fireproof performance [ mm/min ]]UL94 level test

Example 4PP

The formulation on the PP matrix was plasticized and homogenized in a co-operating twin screw extruder Z SE18 HPE. The temperature in the mixer is between 190 ℃ and 220 ℃. The PP mixtures were produced by injection molding to give test specimens for tensile tests (DIN EN ISO527, type 1B), impact tests (DIN EN ISO179) and fire tests (UL 94).

Starting material

PP MgO 7287/Brenntag, pure chemical magnesium hydroxide (MDH-component, zero specimen)

MR2S as inorganic flame retardant (AFM)

Formulation of

PP containing 50% of flame retardant

The components of the flame retardant are as follows:

the following tests were performed:

tensile test [ MPa ]]Reference DIN EN ISO527

Tensile modulus [ MPal DIN EN ISO527 ]

Elongation at break [% ]]Reference DIN EN ISO527

Charpy impact toughness, [ KJ/m ] ² ]DIN EN ISO179

Fireproof performance [ mm/min ]]UL94 level test

Discussion of the related Art

All formulations can meet DIN4102 method B or the level test referred to UL94 (requirement: burning velocity less than 40 mm/min), the measured burning velocity being significantly lower than the required value.

According to the invention, it was possible to demonstrate, by means of targeted tests on PVC-, EVA-, PE-and PP-mixtures, that modified rehydrated red mud (MR2S), which is comparable to ATH and MDH in terms of both fire-proofing and mechanical properties, can be used successfully without any auxiliary treatment (for example, surface treatment with vinylsilane) in the tests.

In terms of the fire-retardant property of MR2S, it is not important which endothermic reaction components (e.g., goethite, gibbsite, boehmite, etc.) of MR2S contribute in which temperature ranges, nor is it important whether the components react synthetically with each other. Importantly, the fire-retardant effect of the endothermically reactive substance contained in MR2S is comparable to that of ATH and MDH.

Decisive for the fire protection effect is the endothermic reaction of the fire-protecting substance, which can be produced by separating off water and evaporating off water. The measurement standard is the enthalpy of absorption, which is given in units of: j/g.

The endothermic enthalpy can be measured by Thermogravimetry (TG), Differential Thermal Analysis (DTA), and differential thermal analyzer (DSC).

Specific measurement proves that red mud generated in the Bayer process has smaller endothermic enthalpy and larger fluctuation if not treated. In contrast, modified rehydrated red mud (MR2S) has a significantly higher endothermic enthalpy and less fluctuation, because iron oxide and aluminum oxide are converted into iron and aluminum hydroxides/oxide hydrates by the rehydration process, which react endothermically. MR2S can therefore be produced as a unified inorganic flame retardant (AFM), which can also be tailored to various material structures.

In a targeted test using MR2S as an inorganic flame retardant (AFM), the fire performance and mechanical properties of the material structure containing this flame retardant were comparable to those of the material structure containing ATH and MDH. The results show that MR2S has the same results as ATH and MDH. Because MR2S can exert an endothermic enthalpy between 180 ℃ and 350 ℃, MR2S can partially or completely replace ATH as well as MDH. Compared to red mud (RS), MR2S, which is produced from red mud by means of an improved, in particular rehydrated, process, is a completely different substance in terms of chemical, mineralogical and endothermic properties. In contrast to red mud (RS), MR2S is comparable to ATH and MDH used as AFM. Measurement by roentgen ray diffractometer, DTA, TG and DSCThe amount indicates that modifying, in particular rehydrating, the ratio of hydroxide/oxide hydrate to oxide can be altered to favor hydroxide/oxide hydrate, which equates to a higher endothermic enthalpy. It is important to determine the relationship between the specific enthalpy (in J/g) measured and the degree of filling in the various material structures. The endothermic enthalpy of gibbsite is about 1000J/g, the endothermic enthalpy of boehmite is about 500J/g, and the endothermic enthalpy of goethite is about 260J/g. If gibbsite is considered to have a density of p =2.4 g/cm³The density of boehmite is p =2.98 g/cm³Goethite having a density of p =4.17 g/cm³Then the endothermic effects of the three most important endothermic reaction components in MR2S are close. While goethite is more effective.

The degree of filling multiplied by the specific enthalpy is equal to the "value" which can affect the flame-retardant effect. The higher the specific enthalpy, the lower the filling degree required, which is of great importance both from the point of view of the economy of the material structure and from the point of view of its mechanical properties. The smaller the degree of filling, the less the mechanical properties of the material structure change.

No toxic or corrosive gases are produced in terms of the thermal performance of MR 2S.

The mechanical properties measured in the tests of the mixtures made from MR2S show a similarity to the results of the mixtures made from ATH or MDH. If the fire-retardant substance is surface-treated with silanes, fatty acids or plasticizers, the compatibility of the filling substance with the polymeric matrix is more favorable and the mechanical properties of the mixture can be improved. The surface treatments used in ATH and MDH can also be used in MR2S and can optimize performance.

The particle size and the particle distribution of the inorganic flame retardants (AFM) used play a very important role in the mixture properties. The prior art is the ATH and MDH based products that were used in the market before to adjust particle size and particle distribution. Although ATH can be produced by a fine particle settling reaction, in MR2S, it is necessary to perform refinement using a milling process and a screening process due to its insolubility in water. Advantageously, the precipitated red mud (RS) is very fine as in MR 2S.

The ATH product may have a thermal stability of 225 ℃ and the MDH may have a thermal stability of 340 ℃. In this regard, in practice, ATH products are commonly used if the processing temperature is less than <200 ℃, and MDH products are commonly used if the processing temperature is greater than >200 ℃. According to the invention, MR2S can be used both at processing temperatures <200 ℃ and >200 ℃.

Inorganic flame retardants (AFM) based on ATH, MDH and MR2S according to the invention are particularly suitable for use in polymers, but also in other combustible material structures.

For example: the polymers are: acrylic latex, acrylic resin, synthetic rubber, epoxy resin, latex, melamine resin, Polyamide (PA), Polyethylene (PE), polyethylene copolymer, thermoplastic polyethylene copolymer, reticulated polyethylene copolymer, phenolic resin, polyester resin (UP), polyurethane, polypropylene (PP), polyvinyl chloride (PVC), PVC plastisol, Thermoplastic Polyurethane (TPU), vinyl ester resin, and others. The application is as follows: canvas sheds, carpet backcoatings, floor coverings, roofing, conveyor belts, cables, profiles, pipes, cardboard, injection molded, laminated, printed circuit boards, hoses, resin filled, foams, or others.

The digestion-digested red mud or tube-digested red mud (RS) settled in the Bayer process can also be produced by means of the invention by chemical reaction (for example by rehydration or by other improved processes) into a new material, namely MR2S, which can be used as halogen-free, inorganic and non-toxic flame retardants in various forms of material structures. Because of the wide temperature range over which MR2S can react, MR2S can replace ATH and/or MDH, either partially or completely.

Claims (30)

1. An inorganic halogen-free flame retardant made from a modified rehydrated red mud comprising the following mineral components:

10-50% by weight of an iron compound,

12-35% by weight of an aluminum compound,

5-17% by weight of a silicon compound,

2-21 wt% of TiO₂，

0.5-6% by weight of a calcium compound,

wherein the iron compound has a hydroxide and an oxide hydrate in an amount of 50% by weight or more as compared with the oxide component of the iron compound,

the aluminum compound has a hydroxide and an oxide hydrate of 50% by weight or more, as compared with the oxide component of the aluminum compound.

2. The improved rehydrated red mud of claim 1 wherein the iron compound has greater than or equal to 80% by weight hydroxide and hydrated oxide compounds relative to the oxide component of the iron compound.

3. The improved rehydrated red mud of claim 1 wherein the aluminum compound has greater than or equal to 80% by weight hydroxide and hydrated oxide compounds relative to the oxide component of the aluminum compound.

4. The inorganic halogen-free flame retardant of claim 1 made from improved rehydrated red mud, characterized by soluble Na₂The content of O is less than or equal to 0.03 percent (weight percentage).

5. The inorganic halogen-free flame retardant of improved rehydrated red mud according to any one of claims 1 to 4, wherein the average particle size d50 is less than or equal to 50 μm.

6. The inorganic halogen-free flame retardant of improved rehydrated red mud according to claim 5, wherein the average particle size d50 is 0.5 μm to 10 μm.

7. The inorganic halogen-free flame retardant of improved rehydrated red mud according to any one of claims 1 to 4, wherein the residual moisture content is 0.4% or less (wt%).

8. The inorganic halogen-free flame retardant of any of claims 1-4 wherein the surface of the modified red mud is treated with at least one substance that improves the compatibility of the modified red mud with the polymeric matrix.

9. The inorganic halogen-free flame retardant of improved rehydrated red mud according to claim 8, wherein the substance comprises silanes, fatty acid derivatives, plasticizers, boric acid and its metal salts, zinc stannate, zinc hydroxystannate or mixtures of these substances.

10. The inorganic halogen-free flame retardant of improved rehydrated red mud according to any one of claims 1 to 4, wherein the surface of the inorganic flame retardant is coated with a substance to improve vitrification of the soot.

11. The inorganic halogen-free flame retardant of improved rehydrated red mud according to claim 10, wherein the substance is nanoclay.

12. The inorganic halogen-free flame retardant of any one of claims 1 to 4, wherein the flame retardant is mixed with 0 to 70 wt.% of another flame retardant additive.

13. The inorganic halogen-free flame retardant of improved rehydrated red mud according to claim 12, wherein the another flame retardant additive is an endothermically reactable material.

14. The inorganic halogen-free flame retardant of improved rehydrated red mud according to claim 13, wherein the endothermically reactable substance is aluminum hydroxide, gibbsite, boehmite, magnesium hydroxide, goethite or a mixture of these substances.

15. A fire-retardant material structure comprising a combustible material and a fire retardant as claimed in any one of claims 1 to 14.

16. The material structure according to claim 15, characterized in that said material structure is a building material, plastic, rubber, cardboard or a cable insulation sheath.

17. The material structure according to claim 15 or 16, characterized in that it has 3-95% (weight percentage) of flame retardant.

18. A material structure according to claim 15 or 16, characterized in that the fire retardant comprises 30-100% by weight of said mineral component, while the remaining 0-70% by weight is constituted by an additional fire-retardant component.

19. The material structure of claim 18 wherein said other fire-protecting component comprises an inorganic non-toxic endothermically reactive substance.

20. A material structure as claimed in claim 18, wherein the other fire retardant components include salt hydrates, hydroxides and carbonates.

21. A flame retardant according to any one of claims 1 to 14 for use as a flame retardant in combustible material structures.

22. A process for producing a fire-barrier material structure according to any one of claims 15 to 20, comprising the steps of:

a. a combustible material is prepared which is capable of being burnt,

b. mixing the combustible material with the flame retardant according to any one of claims 1 to 14 or applying the flame retardant onto the combustible material,

c. this results in a fire-resistant material structure.

23. The process of claim 22, wherein the flame retardant is physically treated prior to the mixing or coating operation of step b.

24. The process of claim 23, wherein the physical treatment is milling.

25. The process of claim 23, wherein the physical treatment is used with a synergist.

26. The process of claim 25, wherein the synergist is a nanoclay, a boric acid derivative, zinc stannate, and/or zinc hydroxystannate.

27. A process according to any one of claims 22 to 26, wherein the surface of the flame retardant in step b is coated with a firestop material.

28. The process of claim 27, wherein a coating agent is used to coat the surface of the flame retardant to optimize and control the fire-retardant function and processing characteristics.

29. The process of claim 28, wherein the coating agent is a silane, a fatty acid derivative, mixtures thereof and a plasticizer, or nanoclay, boric acid and its metal salts, zinc stannate, zinc hydroxystannate and mixtures thereof.

30. A process according to any one of claims 22 to 26, wherein the synergist is added in the form of small particles when used in the form of a masterbatch with the flame retardant in the elastomeric and thermoplastic structures.