Process for the preparation of stable coarse grain with compact structure of different calcium sulfate phases

Abstract

The present invention is concerned with a process for the processing of gypsum powder, wherein gypsum powder having a bulk density of 990 g / L or less is subjected to compression treatment at a pressure of at least 0.1 N / mm2 and a stabilization treatment, wherein, when a gypsum powder is processed, the gypsum powder is subjected to a calcination treatment before the stabilization treatment. By such processing, it is possible to significantly reduce the water demand of stucco powder having a low bulk density, as is often the case for recycled stucco, which improves the processing speed and reduces the energy demands for respective gypsum powders. The present application is further concerned with a respective use of the inventive process for reducing the water demand of stucco made from recycled gypsum and the use of the produced recycled stucco for the production of gypsum articles.

Description

[0001] Knauf Gips KG

[0002] P-KGI-363-WO

[0003] 5 Process for the preparation of stable coarse grain with compact structure of different calcium sulfate phases

[0004] The present invention is concerned with a process for the processing of gypsum powder, wherein gypsum powder having a bulk density of 990 g / L or less is subjected to compression treatment at a pressure of at least 0.1 N / mm2, a calcination treatment and a stabilization treatment, which is applied to the gypsum after the compression treatment. By such processing, it is possible to significantly reduce the water demand of gypsum powder having a low bulk density, as is often the case for recycled gypsum, which improves the processing speed and reduces the energy demands for respective gypsum powders. The present application is further concerned with a respective use of the

[0005] 15 inventive process for reducing the water demand of recycled gypsum and the use of the product recycled gypsum for the production of gypsum articles.

[0006] State of the art

[0007] Recycled gypsum-based binders such as stucco or thermal anhydrite have a significantly increased water demand and a low bulk density compared to gypsum-based binders

[0008] 20 made from natural raw or FGD gypsum (i.e., gypsum obtained from the residues of flue gas desulphurisation plants). This is due to the tendency of gypsum to form aggregates or agglomerates with a significant proportion of voids (when the gypsum is initially processed), whereas natural raw gypsum or FDG gypsum is predominantly present as compact individual particles. This problem does not exclusively apply to recycled gypsum but is also observed for phosphogypsum and the fine fraction of FGD and natural gypsum.

[0009] The increased water demand, for example in the production of plasterboards, leads to greater drying efforts and thus to high energy costs. In addition, the low bulk density leads to a reduction in the conveying capacity in the existing gypsum transport routes in production (e. g. limiting the conveying in a dosing screw that can only convey a certain

[0010] 30 volume). Also, the low bulk density leads to a reduction of capacity during calcination (e. g. because the calcination device is filled with less material at the same volume) and to

[0011] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0012] P-KGI-363-WO

[0013] - 2 - reduced heat transfer in the gypsum fill and thus also to higher energy consumption. For this reason, for example recycled gypsum is currently only used in minor quantities together with FGD or natural stone gypsum.

[0014] On the other hand, FGD gypsum is obtained from the combustion of coal by reacting the

[0015] 5 waste gases from the combustion with a calcium oxide or calcium carbonate suspension, whereby the sulphur dioxide (SO2) contained in the flue gas is first converted to sulphur trioxide (SO3) in the presence of oxygen and then bound as calcium sulfate (CaSO4). Given the fact that many governments have decided to phase out coal-fired power generation in the coming years, it is to be expected that FGD gypsum will become an increasingly scarce raw material. Also, natural gypsum faces problems in the approval of mining sites by the local population, as gypsum is often produced in open pit mining, which is a concern with population which lives in the vicinity of the site.

[0016] Whereas recycled gypsum or the use of fine fractions of gypsum is an obvious substitute for these declining gypsum sources, for the reasons as given above they are not

[0017] 15 economically competitive with the use of natural or FGD gypsum.

[0018] However, in order to still be able to meet the existing demand for gypsum building materials, it can be assumed that the recycling of gypsum products will play an increasingly important role over time.

[0019] In the prior art, some methods have been described, by which the calcium sulfate

[0020] 20 (including calcium sulfate dihydrate, hemihydrate and anhydrite) is compacted. E. g. DE 26 58 915 A1 describes a process for the production of lumpy calcium sulfate from finely divided calcium sulfate using roller pressing. In DE 26 58 915 A1 , the starting material calcium sulfate can be from a natural source or a synthetic source and it can be a dihydrate as well as a hemihydrate or anhydrite. For the processing, the free water content of the finely divided calcium sulfate is adjusted to a value between greater than 0 and 4% and the resulting mixture is pressed into a lumpy form at temperatures of between 0 and 600C under a contact pressure of 1 to 5 Mp per cm (about 9.81 to 49.05 kN / cm) of roller width. The aim of the process of DE 26 58 915 A1 was to improve the handling (dosing) and to reduce the tendency of the material to form dust.

[0021] 30 EP 0 534458 A1 describes a similar process to DE 26 58 915 A1 , which differs therefrom in that the free water content of the finely divided calcium sulfate is adjusted to between

[0022] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0023] P-KGI-363-WO

[0024] - 3 - greater than 5 to 12% and the starting material is calcium sulfate dihydrate from flue gas desulfurization.

[0025] US 2016 / 0214895 A1 describes a recycling process for plasterboards. In this process, after the plates are broken and ground into small particles, the material is sieved to remove

[0026] 5 paper residue. The different gypsum size fractions, which are thereby obtained, are then mixed in a defined manner in order to obtain a constant gypsum quality. After mixing, the gypsum mixture is compacted in a roller press to increase the density.

[0027] Whereas a compaction step may contribute to better processing efficiency for e.g. later converting the gypsum to gypsum hemihydrate in a calcination device, stucco, which is processed accordingly (similar to stucco, which is not processed by compaction processing), still suffers from the problem of a high water demand (i.e. the stucco requires a higher quantity of added water to provide the same processing characteristics such as fluidity of a gypsum slurry than is required for the processing of FGD or natural stone gypsum).

[0028] 15 In the prior art, there have been some attempts to increase the grain size of the gypsum which involve a partial recrystallization thereof. E. g. EP 2305605 B1 describes a process for continuously modifying dihydrate gypsum, wherein the gypsum is subjected to a first dehydration step and a subsequent “recrystallization” in an aqueous environment at elevated temperature. This method is effective to increase the average particle size of the

[0029] 20 gypsum dihydrate from e. g. about 28 pm to 86 pm and also provides a reduced water demand for a gypsum hemihydrate, which is obtained after calcination of the thus produced gypsum dihydrate.

[0030] EP 3 984 977 A1 discloses a process for the preparation of recycled gypsum in an alpha gypsum process using a process, where the gypsum hemihydrate is produced under elevated pressure (also known as Nitto process). The product obtained in this process is an alpha hemihydrate, which, as is usual with alpha gypsum, consists of compact gypsum crystals.

[0031] Whereas the processes of both of the above patents provide compact gypsum crystals with a coarser grain size, which are associated with a reduced water demand, the process

[0032] 30 of EP 2 305 605 B1 requires the use of a very large amount of energy (the material has to be calcined twice to obtain a hemihydrate with the desired properties) and the process

[0033] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0034] P-KGI-363-WO

[0035] - 4 - of EP 3 984 977 A1 has very high process costs, especially for the processing of the gypsum under increased pressure. Accordingly, these processes are hardly feasible for the processing of large gypsum quantities.

[0036] Accordingly, there is a demand for a process for the reprocessing of recycled gypsum and

[0037] 5 other gypsum types, which suffer from higher water demands on processing to gypsum articles such as gypsum board or plaster, wherein the process has improved economic feasibility and is associated with less costs and minimal adaptation of existing processing equipment for gypsum.

[0038] The present application addresses these needs.

[0039] Detailed description of the invention

[0040] In the investigations which are underlying the present invention it has unexpectedly been found that the water demand of gypsum hemihydrate, which is produced from a gypsum dihydrate starting material with a low bulk density (as an indication of a higher content of void volume in the gypsum dihydrate due to agglomerate and aggregate formation of

[0041] 15 smaller initial gypsum grains) via a compression treatment at a pressure of at least 0.1 N / mm2and which is subsequently subjected to a stabilization treatment, provides a product, which as gypsum hemihydrate has a water demand similar or even better (i.e. less water is required) compared to the water demand of a gypsum hemihydrate obtained from conventional FGD or natural stone gypsum. Thereby, the process allows for an

[0042] 20 economic use of recycled gypsum for the production of respective new gypsum articles, which may even be constituted from 100 % recycled gypsum after processing of the same via the herein described process.

[0043] Compared to the prior art processes as discussed above, the process of the invention solves the problems with significantly lower energy and process expenditure and provides a raw material (in the form of compact individual particles) that is comparable to stucco made from natural stone or FGD.

[0044] Accordingly, in a first aspect the present invention concerns a process for the processing of gypsum or stucco powder, wherein gypsum or stucco powder having a bulk density of 990 g / L or less is subjected to compression treatment at a pressure of at least 0.1 N / mm2

[0045] 30 and a stabilization treatment, wherein, when a gypsum powder is processed, the gypsum powder is subjected to a calcination treatment before the stabilization treatment.

[0046] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0047] P-KGI-363-WO

[0048] - 5 -

[0049] As noted above, the bulk density of 990 g / L or less is a result of the gypsum or stucco material (e.g. gypsum powder or stucco powder) having a constitution of aggregates or agglomerates with a larger internal gas volume, which in turn influences the behavior of the stucco (or stucco obtained from respective gypsum) during the hardening / curing

[0050] 5 process. In addition, more water is required to convert the stucco into a slurry with the required fluidity for a given processing, when the stucco has a larger internal gas volume. As gypsum hemihydrate in stucco on conversion into gypsum dihydrate takes up 1 .5 water molecules, it is desired to add water in an amount which does not significantly exceed the amount of water that is bound to the gypsum hemihydrate, as such excess water later has to be removed from the product by conventional drying. This drying results in higher energy demands.

[0051] Further, in case of use for gypsum blocks, screeds, jointing compounds, finishing compounds, wall plaster or molding plaster, shorter drying times can result due to using less water.

[0052] 15 While the inventors do not want to be bound to any particular theory it is believed that during setting of gypsum hemihydrate to the respective dihydrate in the production of e.g. gypsum boards or plaster, a fine-pored sponge structure forms as a result of the excess water that is necessary to achieve the desired consistency; this excess water evaporates and leaves behind fine-pored cavities and is found in all recycled stuccos. This sponge

[0053] 20 structure is believed to be the cause of the high water demand and the low bulk density of recycled stucco. To reduce the water demand and increase the bulk density, this sponge structure has to be destroyed and coarse compact stucco grains have to be produced. Such particles require less water for wetting and the bulk density increases due to the loss of void volume in the particles.

[0054] For the inventive process, it is not of relevant importance if the gypsum is calcined prior to the compression treatment or after this treatment (in terms of the resulting water demand in the product). On the other hand, since a compressed gypsum has a higher bulk density than prior to compression it is preferred that in the inventive process the compression is conducted as a first treatment on a gypsum starting material, the

[0055] 30 calcination is conducted as a second treatment and the stabilization is conducted as a third treatment.

[0056] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0057] P-KGI-363-WO

[0058] - 6 -

[0059] In the inventive process, the “stabilization treatment” designates a processing of calcined gypsum or stucco, where after calcination the stucco reacts with a small amount of water (which is either added in fluid form or via moisture in the atmosphere, to which the stucco is exposed). This process is also known as "forced aging" of stucco. In “stabilization”,

[0060] 5 anhydrite III contained in the stucco after calcination is transformed to calcium sulfate hemihydrate, crystal defects in the stucco are healed, which in turn reduces the need for water when forming a slurry.

[0061] “Gypsum”, as this term is used in the present invention designates the chemical compound with the formula CaSCM ■ 2 H2O, I. e. calcium sulfate dihydrate. When gypsum is heated at elevated temperature, the dihydrate loses water and provides an active form as calcium sulfate with 1 / 2 units of crystal water as “CaSO4-1 / 2 H2O” (also designated as calcium sulfate hemihydrate or CaSCM ■ 0.5 H2O or hemihydrate) or without crystal water as “CaSC ” (also designated as calcium sulfate anhydrite or anhydrite). The “gypsum” for use in this invention may comprise at least 60 wt.-% of calcium sulfate dihydrate (CaSCM

[0062] 15 ■ 2 H2O), preferably at least 80 wt.-%. Further, gypsum may contain other calcium sulfate phases (hemihydrate (CaSC ■ 0.5 H2O (“hemihydrate”) or anhydrite (CaSC without H2O)) as well as carbonates or other minerals in small amounts.

[0063] “Stucco”, as this term is used in the context of this invention, is gypsum, which has been heat treated to convert at least a portion of the calcium sulfate dihydrate in the gypsum to

[0064] 20 calcium sulfate hemihydrate, e. g. at least 40 wt.-% and preferably at least 60 wt.-%. Stucco, next to the gypsum, which has not been converted to calcium sulfate hemihydrate, usually contains minor amount of anhydrite and carbonates or other minerals. Stucco for use in the inventive process is regularly stucco, which has not (yet) been subjected to a stabilization treatment.

[0065] For the compression treatment in the inventive process, the pressure, to which the gypsum or stucco powder is exposed is not subject to any relevant restrictions as long as the pressure is above 0.1 N / mm2as noted above. For practical reasons, it is however preferred that the pressure is not excessive (for cost reasons), and in most cases a pressure of up to 30 N / mm2will be sufficient to provide the desired compression and

[0066] 30 morphology change of the gypsum. Accordingly, in a preferred embodiment of the inventive process the gypsum powder is subjected to compression treatment at a pressure in the range from 0.1 to 30 N / mm2and preferably in the range 0.5 to 20 N / mm2.

[0067] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0068] P-KGI-363-WO

[0069] - 7 -

[0070] The compression treatment in the invention can in principle be affected by any means, which is available to compress a powdery material, i.e., by extrusion or processing in a stamp press. In a preferred embodiment, the compression treatment is effected by compacting the gypsum between two counter-rotating rolls (similar to a rolling process in

[0071] 5 steel production, where the roll may be rolls with or without recesses), as this is a very simple and cheap means for such processing. To this end, the gypsum or stucco mass to be compressed can be continuously fed to the rolls, where the mass is drawn in by the rolling movement of the rolls and compressed as a result of the space becoming less and less when the material gets right between the middle of the rolls.

[0072] The compression can involve a single pass of the gypsum or stucco to be compressed through a respective compression apparatus, or the compression can be conducted as multiple passes of the gypsum to be compressed through a respective apparatus, where the respective passes can be conducted with the same or different compression pressures. In one embodiment, the compression pressure is lower in a first pass of the

[0073] 15 gypsum or stucco through the compression apparatus and higher (e. g. by at least 1 N / mm2and preferably at least 3 N / mm2) in a second pass of the gypsum or stucco through the compression apparatus.

[0074] In the inventive process, the form, into which the gypsum or stucco is processed by the compression treatment, is not subject to any relevant restrictions. For example, the

[0075] 20 material can be processed by rolls which have a flat surface, where the form, in which the gypsum material exits the rolls is irregular as a result of the material breaking at uneven spots. On the other hand, it is also possible to produce compression processed gypsum and stucco by using rolls, which are shaped such that the gypsum produced by the processing of the gypsum or stucco is in the form of strips or briquettes (e. g. with a thickness of up to 50 mm). However, the result of the compression treatment with the rolls which have a flat surface can be better than the result of the compression treatment with the rolls which are shaped.

[0076] For the compression treatment, the gypsum can be either a dry gypsum (i. e. a gypsum with a moisture content of less than 1% and preferably less than 0.5 % by weight), but it

[0077] 30 is also possible that the gypsum can have residual moisture, or moisture which has deliberately been added. In most cases, however, the gypsum powder will have a moisture content of at most 12 wt.-%. In one preferred embodiment, the gypsum powder used as starting material in the process of the invention has a moisture content of from 0 to 12 wt.-

[0078] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0079] P-KGI-363-WO

[0080] - 8 -

[0081] %. In a particularly preferred embodiment, the gypsum powder has a moisture content of 1 to 10 wt.-% and especially 3 to 8 wt.-%.

[0082] In one preferred embodiment, it is envisaged that the compression treatment and calcination is performed in a single step, e. g. by performing the compression in a heated

[0083] 5 environment (e.g. by heating rolls, which are used in the compression treatment). Such processing is in particular suitable for the production of gypsum hemihydrate, which relative to the respective anhydrite is produced at much lower temperatures.

[0084] As noted above, the bulk density of the starting material gypsum or stucco is 990 g / L or less, which results from the gypsum being present as small grains, which form aggregates or agglomerates. In most cases, the gypsum or stucco powder will have a bulk density of 900 g / L or less, preferably 800 g / L or less, in particular in the range of 400 to 750 g / L and especially in the range of 550 to 710 g / L.

[0085] The gypsum material, which is used as the starting material for the inventive process, can be any gypsum material having the properties as indicated above, e.g. gypsum or stucco

[0086] 15 powder. However, the main gypsum materials, which have these properties, and which are therefore preferred for use in the context of this invention encompass recycled gypsum, citro gypsum, phosphogypsum or gypsum grinding dust. In a particularly preferred embodiment, the starting material is recycled gypsum from used gypsum boards (e. g. plasterboards, gypsum fiber boards) and / or gypsum plaster. In general, the recycled

[0087] 20 gypsum may contain at least 60 wt.-% of calcium sulfate dihydrate (CaSCM ■ 2 H2O), preferably at least 80 wt.-%. Further, recycled gypsum may contain other calcium sulfate phases (hemihydrate (CaSC ■ 0.5 H2O (“hemihydrate”) or anhydrite (CaSC without H2O)) as well as carbonates or other minerals in small amounts. Also, very small contents organic constituents or other materials used in drywall construction may be contained.

[0088] The process of the invention can be conducted without the addition of any additives, or it is possible that additives are added to the gypsum or stucco starting material to adjust its processing properties. In a preferred embodiment, an additive to slightly dissolve the gypsum on the surface and promote the formation of stable gypsum grains is added to the gypsum or stucco starting material before the material is subjected to compression

[0089] 30 treatment. Such additive is suitably selected from the group comprising formic acid or sulfuric acid. Alternatively, or in addition thereto one or more additives for enhancing the solubility of stucco in water at ambient or higher temperatures and / or for modulating the

[0090] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0091] P-KGI-363-WO properties of an end product can be added, which are known to the skilled practitioner. Such additives may be selected from one or more foaming agents, one or more accelerators, one or more thickeners, one or more defoamers, one or more retarders, and one or more liquefiers. Suitable foaming agents may be surface-active, amphiphilic

[0092] 5 substances, preferably tensides (also called surfactants), surface-active, amphiphilic polymers or surface-active, amphiphilic proteins. Suitable accelerators may be fine ground gypsum (also called ball mill accelerator (BMA)), potassium sulfate or ammonium sulfate. Suitable thickeners may be a starch, polysaccharides or a polyacrylamide. Suitable defoamers may be unipolar silicon-components. Suitable retarders may be hydroxycarboxylic acids, preferably tartaric acid, citric acid or malic acid, phosphates or degraded and / or modified proteins. Suitable plasticizers may be melamine resins, polycarboxylates or cellulose partial hydrolysates.

[0093] The compression treatment can be conducted at ambient temperature, decreased temperature or elevated temperature. Mostly, however, the compression treatment will be

[0094] 15 conducted at a temperature of from 0 to 80°C, where a range of 15 to 50°C and in particular 20 to 40°C will be employed in most cases.

[0095] After the compression treatment, it is expedient in the process according to the invention, that the compacted gypsum or stucco from the compression treatment is converted into smaller parts, as in most cases the compression treatment will provide a size of the

[0096] 20 product, which is too large for regular calcination processing. Material, which has not or not sufficiently been compacted (e. g. because it has passed the compaction apparatus in the edge area of the rolls), may suitably be separated from the mixture and reintroduced into the compression processing. While in principle the larger compressed pieces of the processed gypsum or stucco can be reduced to smaller pieces by any means which is available to the skilled practitioner in the art, a particularly suitable means for this processing is grinding, preferably with a device selected from a condux mill, a ball mill, a hammer mill, a cross beater mill, a roller mill, a pendulum roller mill, a cutting mill, a bowl mill crusher or by grinding drying, wherein the grinding can be before and / or after the stabilization treatment.

[0097] 30 In one embodiment, the milling will be such that the predominant part of the resulting product will have a particle size less than 1 mm, preferably, at least 60 wt.-% of the product will have such particle size, more preferably at least 70 wt.-%. The milling is usually done to provide a particle size according to needs of the end product, and may be different for

[0098] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0099] P-KGI-363-WO

[0100] - 10 - a floor screed, plaster, gypsum board, gypsum fiber board. The skilled practitioner will regularly choose respective milling conditions resulting in particle size distributions according to the product needs. In the context of the application the particle size in the range of 1 mm (as well as the ratio of particles having a particle size of less than 1 mm is

[0101] 5 determined by sieve analysis, where the length designates the mesh size of the sieve, i.e., a sieve to retain particle having a particle size of larger than 1 mm has holes of 1 mm x 1 mm).

[0102] As it will in most cases not be possible to avoid the formation of larger particles (i.e., particle with a particle size of more than 1 mm) the share of particles in the desired range can be increased by sieving off the particles of the desired size. Smaller particles (which may alternatively be designated as fines), which are also obtained after the grinding, are likewise suitably removed by sieving and are then reintroduced into the gypsum compression treatment (where they are reprocessed to larger particles).

[0103] In a preferred embodiment, the compacted gypsum or stucco from the compression

[0104] 15 treatment may be ground, and preferably fractions with undesired particle size, which are obtained after the grinding, may be separated. Fractions finer than desired may be reintroduced into the gypsum or stucco compression treatment and / or fractions larger than desired may be reintroduced into the grinding treatment.

[0105] The product produced in the compression treatment and subsequent grinding differs

[0106] 20 significantly in the properties for the product before this treatment. For example, it is preferred if the product of the compression and grinding treatment exhibits a bulk density of at least 950 g / L, and preferably in the range of from 1000 to 1200 g / L. Alternatively, or in addition it is preferred that the respective product has a tamped density of at least 1050 g / l and preferably in the range from 1100 to 1400 g / L. In the context of this invention, the bulk density is determined according to DIN EN 459-2:2021 -09. The tamping density is determined by DIN EN ISO 787-11 :1995-10 and the measurement is done based on said DIN. Due to the fact, that some materials have quite a low bulk density the procedure differs from DIN EN ISO 787-11 :1995-10 in the amount of sample that is used, here 100 g unsieved material, and the number of stamps performed by the device, here 1000. The

[0107] 30 volume of the sample after stamping was read to + / - 1 ml. Alternatively, or in addition thereto, it is preferred that the product produced in the compression treatment has a bulk or tamping density, which is higher by at least 10% preferably at least 15% and even more

[0108] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0109] P-KGI-363-WO

[0110] - 11 - preferably at least 20% than the bulk or tamping density of the non-compressed starting material, where increases of up to about 120% have been observed.

[0111] The gypsum powder, which is to be processed to stucco in the calcination step is subjected to temperatures where the calcium sulfate dihydrate is converted to the

[0112] 5 respective calcium sulfate hemihydrate which in most cases will be temperatures above 100°C. In this respect, the skilled practitioner is aware that a calcination at a higher temperature provides a higher conversion rate, but on the other hand, if the temperature is too high there is a risk that also more significant quantities of calcium sulfate anhydrite may form. In terms of a good compromise between conversion rate and avoidance of the formation of undesirable amounts of anhydrite, the heating during the calcination is preferably at a temperature of at least 110°C, more preferably at least 130°C, even more preferably in the range of 160°C to 240°C and even more preferably to a temperature in the range of 170°C to 220°C. If the gypsum is exposed to temperatures of above 200°C, the skilled practitioner will be aware that it must be ensured that the material is evenly

[0113] 15 exposed to this temperature (and hotter / colder areas are avoided) as otherwise undesirable quantities of anhydrite may form in the process.

[0114] The stabilization treatment as noted above has the purpose that the stucco material reacts with a small amount of water, whereby anhydrite III contained in the stucco material after calcination is transformed to calcium sulfate hemihydrate, crystal defects in the stucco are

[0115] 20 healed. In one embodiment, which is preferred in the context of this invention, the stabilization treatment involves the exposure of the stucco to a moisture containing atmosphere for at least 4 h, preferably for from 8 h to 48 h and more preferably for from 12 h to 30 h. For the moisture content of the atmosphere there are no relevant restrictions, whereby the skilled practitioner will be aware however, that a lower moisture content can possibly result in a very long stabilization time. Preferably, thus, the moisture content of the atmosphere will be in the range of 40 to 95% and more preferably 50 to 91%. The temperature for such kind of stabilization treatment is preferably in the range of 15°C to 40°C and more preferably in the range of 20°C to 30°C.

[0116] An alternative stabilization treatment, which can be employed in the practice of the

[0117] 30 invention, includes a stabilization, which is provided by adding water to the stucco, preferably fresh stucco, which predominantly contains gypsum hemihydrate, to obtain moistened stucco, and the moistened stucco is maintained at a temperature of at least 30 °C for a time interval of at least 30 Min to obtain a stabilized stucco. A corresponding

[0118] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0119] P-KGI-363-WO

[0120] - 12 - stabilization treatment is described in detail in the international application WO 2019 / 024971 A1 . In such treatment, the free moisture (i.e. , the moisture due to water, which is not bound as crystal water in the gypsum) is preferably in the range of 0.2 to 5 wt.-%, and more preferably in the range of 0.5 to 1 .5 wt.-%. In some cases, it may also

[0121] 5 be sufficient if the ..maintaining step” at a temperature of at least 30 °C is conducted even for less than 30 Min, e. g. for a time interval of at least 1 Min, at least 3 Min, at least 8 Min, at least 10 Min or at least 15 Min.

[0122] A yet alternative stabilization treatment, which can be employed in the practice of the invention, is described in EP 1 547 984 A1. In this process, beta-calcium sulfate hemihydrate is introduced with a temperature of above 100°C into an apparatus, and water and / or steam are subsequently injected into the beta-calcium sulfate hemihydrate. The walls of the apparatus, which is used in the process described in EP 1 547 984 A1 , also have a temperature of at least 100°C. The injection takes place in such a way that the entire surface of the hemihydrate can get into contact with the water and / or steam.

[0123] 15 The atmosphere in the apparatus is kept at the dew point level in a temperature range of 75 - 99°C. The moistened hemihydrate is then transferred to a storage container in which the temperature is above 75°C and stored there in this atmosphere for at least 3 minutes. The moistened and deposited hemihydrate is then dried in a dryer.

[0124] The product, which is obtained after the stabilization treatment, preferably has a water

[0125] 20 gypsum value of less than 0.7, and more preferably in the range from 0.69 to 0.40, and even more preferably from 0.65 to 0.45. The water gypsum value in the context of this invention is determined according to the sprinkling quantity in accordance with DIN EN 13279-2:2014-03.

[0126] In a further aspect, the present invention pertains to the use of a process as noted above for reducing the water demand of stucco obtained via calcination of gypsum, wherein the gypsum is preferably selected from recycled gypsum, citro gypsum, phosphogypsum or gypsum dust, wherein the gypsum is more preferably selected from recycled gypsum, where the water demand, which is assessed on the basis of the water gypsum value as noted above.

[0127] 30

[0128] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0129] P-KGI-363-WO

[0130] - 13 -

[0131] In a yet further aspect, the present invention pertains to the use of stabilized stucco, which is produced according to the process as described above, for the production of building boards, as well as for gypsum blocks, screeds, jointing compounds, finishing compounds, wall plaster, molding plaster or any other gypsum-based product.

[0132] 5 In relation to the prior art, the inventive process in particular provides the following advantages:

[0133] Compared to a process which only involves a compression treatment the inventive processing provides a product, which has a significantly reduced water demand, so that, for example, stucco on the basis of recycled gypsum can be produced, which has an equivalent water demand to stucco on the basis of natural or FGD gypsum. Also, a compression treatment of grinding dust of gypsum cannot produce the advantageous properties that can be achieved with the inventive process.

[0134] Compared to a process, which only involves a stabilization treatment, also, the water demand of the product can be significantly reduced to obtain an equivalent water demand

[0135] 15 to stucco on the basis of natural or FGD gypsum. In addition, by subjecting the gypsum to a compression step, the bulk density increases to a relevant degree, which leads to further advantages as explained above, in particular for a calcination step.

[0136] In comparison to the process described in EP 2 305 605 B1 the process of the invention requires significantly less energy for the same or an even better result. As an example,

[0137] 20 approximately 160 kWh / t of recycled gypsum must be used for the additional calcination process required in the process of EP 2 305 605 B1 alone, where the energy required for additional process steps is not yet even taken into account. In comparison, the compression processing of the invention only requires an energy input of a maximum of about 14 kWh / t of recycled gypsum.

[0138] In addition, the implementation of the process of the invention requires significantly lower investment costs (e.g. low expenditure on equipment, small space requirement), since only an appropriately sized compression / compacting machine and simple stabilization through deposition (e.g. gassed silo) are required. The other process steps mentioned in the description of the process of the invention above, comminution and calcination, are

[0139] 30 mostly already components of stucco production.

[0140] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0141] P-KGI-363-WO

[0142] - 14 -

[0143] In comparison to the above-described process for the production of alpha- calcium sulfate hemihydrate, the product of the invention is mainly stucco on the basis of beta-calcium sulfate hemihydrate, which can universally be used and is equivalent to stucco from natural gypsum or FGD gypsum.

[0144] 5 The present invention is further described with reference to a number of examples of embodiments which, however, are intended solely to illustrate the invention and are not in any way to be construed as limiting the scope of protection of the application.

[0145] Example 1

[0146] Recycled gypsum (RCG) and stucco obtained from calcination of recycled gypsum (RCS) were compacted in an apparatus with two counter-rotating rolls, where the gypsum / stucco was compressed by passing the space between the two rolls. The recycled gypsum was used with either a moisture content of 4,5 % to 6,8 % or in dry form. During the processing the gypsum / stucco was compressed with different forces in the range of from 100 kN (specific pressure 6.85 N / mm2) to 200 kN (specific pressure 13.71 N / mm2) as shown in

[0147] 15 the below table 1 .

[0148] After the respective compression processing, the gypsum / stucco was processed in a condux mill to a maximum particle size of 5 mm, and thereafter sieved to obtain the particle fraction with a particle size of less than 1 mm (1 x 1 mm sieve). The thus obtained gypsum was calcined for 2 h at a temperature of 180°C and subsequently stored under controlled

[0149] 20 conditions (ambient temperature (23°C) under regular atmosphere).

[0150] The gypsum / stucco samples obtained in this way were investigated for their particle size distribution, bulk and tamping density and water gypsum value. The bulk and tamping densities were determined according to DIN EN 459-2:2021 -09 and based on DIN EN ISO 787-11 :1995-10 as mentioned above, respectively. The particle size of the respective powders was determined by the laser diffraction method. The water gypsum value was determined according to the sprinkling method in accordance with DIN EN 13279-2:2014-03 (SQ indicates “sprinkled quantity”). The respective results of these tests are given in the below table 1 .

[0151] 30

[0152] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0153] P-KGI-363-WO

[0154] - 15 -

[0155] Table 1 : n.c. = not compressed - n.a. = not applicable; 1 = determined before stabilization treatment

[0156] As is apparent from the above table 1 , the compression treatment provides a bulk and 5 tamping density, which is significantly increased over the respective densities of the starting materials. The respective densities are similar to FGD gypsum with a bulk and tamping density of 1095 / 1282 g / L and FGD stucco with 1017 / 1141 g / L.

[0157] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0158] P-KGI-363-WO

[0159] - 16 -

[0160] Example 2: Effect of stabilization

[0161] Moist RCG was processed with different compression strength, calcined at 180 °C for 2 h and subsequently stabilized as described in the above Example 1 . The respective water gypsum values of the samples were determined for each of the samples before and after

[0162] 5 the stabilization treatment. The results of these investigations are given in the below table 2.

[0163] Table 2

[0164] As is apparent from the above table, the stabilization treatment significantly reduces water

[0165] 10 gypsum values both relative to the non-stabilized gypsum and the non-compressed starting material (WGV of 0.99).

[0166] Example 3: Effect of stabilization time

[0167] The effect of the stabilization time was assessed by investigation of the sprinkled quantity for a stucco obtained from moist gypsum, which had been compressed at 70 kN and calcined at 180°C for 2h. The stabilization was performed at ambient temperature in regular atmosphere. The results of these tests are given in the below table 3. The sprinkled quantity is the amount of stucco in grams that is moistened when sprinkled in 100 ml of water.

[0168] 20

[0169] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0170] P-KGI-363-WO

[0171] - 17 -

[0172] Table 3

[0173] As is apparent from the above table, an optimum stabilization time is about 24h, as a further stabilization for an additional 6h did not provide a relevant further increase in the 5 sprinkled quantity.

[0174] Example 4: comparison of different gypsum starting materials

[0175] Different gypsum starting materials were compacted in an apparatus with two counterrotating rolls with a pressure of 200 kN (13.71 N / mm2), where the gypsum / stucco was compressed by passing the space between the two rolls as described in Example 1 . io After the respective compression processing, the gypsum / stucco was processed in a condux mill to a maximum particle size of 5 mm, the particles having a particle size of 1 mm or less were separated. The thus obtained gypsum material (< 1 mm fraction) was calcined for 2h at a temperature of 180°C and subsequently stored under controlled conditions (ambient temperature (23°C) under regular atmosphere). The respective

[0176] 15 densities, sprinkled quanties and curing times (start and end of stiffening) for the thus produced materials are given in the below table 5.

[0177] The same procedure has been done for stucco, phospho stucco and moist RCG with a pressure of 100 kN (6.85 N / mm2) and with a further step of sieving off smaller particles directly after the compression. This removes particles, which have been obtained from

[0178] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0179] P-KGI-363-WO

[0180] - 18 - material, which has not or not sufficiently been compacted. The smaller particles were sieved off with a sieve having a mesh size of 1 mm. The respective results are also given in the below table 4 and show even better values.

[0181] Table 4

[0182] Received at EPO via Web-Form on Dec 20, 2024 Knauf Gips KG

[0183] P-KGI-363-WO

[0184] As is apparent from the above table, the processing according to the invention provides significantly higher bulk densities and also higher sprinkled quantities compared to respective samples which have not been processed by compression treatment.

[0185] Received at EPO via Web-Form on Dec 20, 2024

Claims

Knauf Gips KGP-KGI-363-WO- 20 -5 Claims1 . Process for the processing of gypsum or stucco powder, wherein gypsum or stucco powder having a bulk density of 990 g / L or less is subjected to compression treatment at a pressure of at least 0.1 N / mm2and a stabilization treatment, wherein, when a gypsum powder is processed, the gypsum powder is further subjected to a calcination10 treatment before the stabilization treatment.

2. Process according to claim 1 , wherein the gypsum or stucco powder is subjected to compression treatment at a pressure in the range from 0.1 to 30 N / mm2and preferably in the range 0.5 to 20 N / mm2.

3. Process according to claim 1 or 2, wherein the gypsum or stucco obtained after15 compression treatment is subjected to grinding, preferably with a device selected from a ball mill, a condux mill, a hammer mill, a cross beater mill, a roller mill, a pendulum roller mill, a cutting mill, a bowl mill crusher or by grinding drying, wherein the grinding can be before and / or after the stabilization treatment.

4. Process according to any one of claims 1 to 3, wherein the gypsum or stucco powder in the compression treatment is processed by rolls which have a flat surface or by rolls which are shaped, preferably processed by flat rolls.

5. Process according to any one of the preceding claims, wherein the gypsum powder used as starting material in the process has a moisture content of from 0 to 12 wt.-%.

6. Process according to any one of the preceding claims, wherein the gypsum or stucco25 powder has a bulk density of 900 g / L or less, preferably 800 g / L or less, in particular in the range of 400 to 750 g / L and especially in the range of 550 to 710 g / L. ceived at EPO via Web-Form on Dec 20, 2024Knauf Gips KGP-KGI-363-WO- 21 -7. Process according to any one of the preceding claims, wherein an additive to promote the formation of stable gypsum grains, preferably selected from formic acid and sulfuric acid, and / or one or more additives to enhance the solubility of stucco in water at ambient or higher temperatures and / or to modulate the properties of a slurry or an5 end product, preferably selected from one or more foaming agents, one or more retarders, one or more accelerators, one or more liquefiers, one or more thickeners and / or one or more defoamers, is added in the compression treatment.

8. Process according to any one of the preceding claims, wherein gypsum or stucco material, which has not been compacted into larger parts during the compression treatment is separated from the compacted gypsum or stucco and is reintroduced in the compression treatment.

9. Process according to any one of the preceding claims, wherein the compression treatment is affected by compacting the gypsum or stucco between two counterrotating rolls and / or wherein the compression treatment is conducted at a temperature15 of from 0 to 80°C.

10. Process according to any one of the preceding claims, wherein the compacted gypsum or stucco from the compression treatment is ground, and wherein preferably fractions with undesired particle size, which are obtained after the grinding, are separated and wherein fractions finer than desired are reintroduced into the gypsum or stucco compression treatment and / or wherein fractions larger than desired are reintroduced into the grinding treatment.11 . Process according to claim 10, wherein the ground gypsum or stucco exhibits a bulk density of at least 950 g / L and preferably in the range of from 1000 to 1200 g / L and / or a tamped density of at least 1050 g / l and preferably in the range from 1100 to 140025 g / L.

12. Process according to any one of the preceding claims, wherein the stucco after the stabilization treatment exhibits a water gypsum value of less than 0.7, preferably in the range from 0.69 to 0.4, and more preferably from 0.65 to 0.

45. ceived at EPO via Web-Form on Dec 20, 2024Knauf Gips KGP-KGI-363-WO- 22 -13. Process according any one of the preceding claims, wherein the gypsum powder is subjected to calcination treatment to produce stucco, preferably by heating to a temperature of at least 110°C, more preferably in the range of 125°C to 240°C and even ore preferably to a temperature in the range of 150°C to 220°C.5 14. Process according to claim 13, wherein the stabilization treatment involves the exposure of the calcined gypsum to a moisture containing atmosphere for at least 4 h, preferably for from 8 h to 48 h and more preferably to from 12 h to 30 h.

15. Process according to claim 14, wherein the stabilization is provided by adding water to the stucco, preferably fresh stucco to obtain moistened stucco, and the moistened10 stucco is maintained at a temperature of at least 30 °C for a time interval of at least 30 Min to obtain a stabilized stucco.

16. Process according to claim 14, wherein the stabilization is provided by adding water to the stucco, preferably fresh stucco to obtain moistened stucco, and the moistened stucco is maintained at a temperature of at least 30 °C for a time interval of at least 1 Min, at least 3 Min, at least 8 Min, at least 10 Min or at least 15 Min.

17. Process according to any one of the preceding claims, wherein recycled gypsum, citro gypsum, phosphogypsum or gypsum dust, in particular in the form of gypsum grinding dust, fine natural gypsum and fine gypsum residues from gypsum product production processes, is used as a starting material.20 18. Process according to claim 17, wherein the recycled gypsum is recycled gypsum from gypsum boards and / or gypsum plaster.

19. Use of a process according to any one of claims 1 to 18 for reducing the water demand of stucco obtained via calcination of gypsum, wherein the gypsum is preferably selected from recycled gypsum, citro gypsum, phosphogypsum or gypsum dust,25 wherein the gypsum is more preferably selected from recycled gypsum. ceived at EPO via Web-Form on Dec 20, 2024Knauf Gips KGP-KGI-363-WO- 23 -20. Use of stabilized stucco produced according to any one of claims 1 to 18 for the production of building boards, as well as for gypsum blocks, screeds, jointing compounds, finishing compounds, wall plaster, molding plaster or any other gypsumbased product. ceived at EPO via Web-Form on Dec 20, 2024

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