WO1983002266A1 - Conversion of fluoroanhydrite to plaster - Google Patents

Conversion of fluoroanhydrite to plaster Download PDF

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Publication number
WO1983002266A1
WO1983002266A1 PCT/US1982/001776 US8201776W WO8302266A1 WO 1983002266 A1 WO1983002266 A1 WO 1983002266A1 US 8201776 W US8201776 W US 8201776W WO 8302266 A1 WO8302266 A1 WO 8302266A1
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WO
WIPO (PCT)
Prior art keywords
fluoroanhydrite
fluorogypsum
gypsum
water
calcium sulfate
Prior art date
Application number
PCT/US1982/001776
Other languages
French (fr)
Inventor
States Gypsum Company United
Robert Byron Bruce
John C. Gaynor
Jay W. Palmer
Original Assignee
United States Gypsum Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by United States Gypsum Co filed Critical United States Gypsum Co
Priority to AU11505/83A priority Critical patent/AU1150583A/en
Publication of WO1983002266A1 publication Critical patent/WO1983002266A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates
    • C01F11/466—Conversion of one form of calcium sulfate to another
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B11/00—Calcium sulfate cements
    • C04B11/02—Methods and apparatus for dehydrating gypsum
    • C04B11/024—Ingredients added before, or during, the calcining process, e.g. calcination modifiers
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B14/02—Granular materials, e.g. microballoons
    • C04B14/04—Silica-rich materials; Silicates

Definitions

  • This invention relates to a process for transforming fluoroanhydrite into gypsum plaster and gypsum wallboard products.
  • Fl ⁇ ororanhydrite is a by-product in the manufacture of hydrogen fluoride from the sulfuric acid treatment of fluorite (calcium fluoride).
  • fluorite calcium fluoride
  • the fluoroanhydrite which is contaminated with sulfuric acid, is neutralized with lime or calcium carbonate additions and allowed to hydrate naturally over a several year period of time while weathering in waste heaps. It had been hoped that upon weathering such materials would then be usable in the industrial manufacture of various products. This has not proven to be the case. Description of the Prior Art
  • fluoroanhydrite contains other impurities.
  • Fluoroanhydrite or fluorogypsum can contain up to 2-3% fluoride, probably derived from unreacted calcium fluoride, together with smaller quantities of unreacted soluble and insoluble silicofluorides.
  • fluorine impurity species probably a fluoroaluminum complex anion such as [AlF-H 2 O -2 ] impede the practical commercial conversion of the stockpiled material into calcium sulfate hemihydrate.
  • these impurities inhibit the hydration
  • a part of the findings of the present invention is that while some of the fluorine and aluminum species contamination in by-product fluoroanhydrite can bo removed by careful washing during the various conversion stages, complex species are trapped in the growing calcium sulfate crystal. By including reactive silicates during various stages of the processing, the crystallized species can either be inhibited in their growth and/or removed from the calcium sulfate crystals.
  • the starting material is a residue from the process of manufacturing hydrofluoric acid from fluorospar.
  • Fluoroanhydrite fresh from the reactor may be treated by the process of this invention and then stored for gradual conversion.
  • weathered stockpile material containing fluorogypsum as well as fluoroanhydrite may be treated.
  • treatment may be carried out during calcination of the fluorogypsum to fluorostucco.
  • hot fluoroanhydrite directly from the reactor may be blended with the reactive siliceous material and passed to briquetting or pelletizing apparatus for mixing with a suitable binder while being formed into briquettes or pellets.
  • the briquettes may then be warehoused or stockpiled while the conversion to fluorogypsum occurs. Thereafter, the fluorogypsum is calcined to fluorostucco for use as plaster products or subsequent rehydration in gypsum board manufacture.
  • Suitable active siliceous materials preferably include Portland cement, finely ground expanded perlite, diatomaceous earth, reactive colloidal silica such as Cab-O-Sil® silica or Aerosil® fumed pyrogenic silica and alkaline earth metal silicates such as sodium, potassium and calcium silicate. These are all siliceous products having high surface areas (greater than about 10,000 square centimeters per gram) and having chemically reactive sites due to surface deformaties, such as chemically incomplete silicon dioxide surfaces, missing oxygen atoms in the alkali metal silicates and Portland cement, or stressed crystal configurations in expanded perlite sintered or fumed silicas and diatomaceous earth. Other reactive siliceous products suitable for use in this invention will be evident from this description.
  • siliceous material Generally inclusion of about 1-10% by weight of the active siliceous material based on the weight of calcium sulfate present in the fluoroanhydrite will produce satisfactory results. Preferred amounts of siliceous material are dependent upon the time at which the material is added in the process and the particular siliceous material.
  • the difficult contaminant species are co-crystalline or occluded, i.e., as the fluoroanhydrite is undergoing the transformation to fluorogypsum, contaminant ions in the surrounding solution crystallize on the growing gypsum phase and are occluded or co-crystallized in the gypsum matrix. It has now been found that these contaminating ions can be rendered inactive in the solution phase, and then the gypsum which re-crystallizes is relatively free of impurities and has properties similar to those of natural gypsum.
  • the preferred first step for fresh or weathered fluoroanhydrite material is a water or dilute acid wash.
  • washing the weathered material twice with water, with a light grinding in between washings drammatically increased the surface area from about 6,000 cm 2 /g to 15,900 cm 2 /g; and reduces the set time with a standard amount of accelerator from approximately 12 minutes without washing to 6.3 minutes after the double washing.
  • the light grinding and second wash released some of the impurities.
  • the same treatment steps using 32% sulfuric acid instead of water gave an even better accelerated set time response of 4 minutes.
  • neither of these treatments provided sufficient strength or the dispersion disintegration characteristics of natural gypsum.
  • active siliceous materials may be added to the mixing (gauging) water of fluorostucco.
  • the following were evaluated as slurry additives to fluorostucco obtained by calcining different weathered fluorogypsum samples without any adjustments. The samples were from different locations in the fluorogypsum pile and analysis indicated widely varying degrees of hydration and chemicals content:
  • active siliceous materials may be added to the fluorogypsum at the stage of calcination to fluorostucco.
  • the additives were mixed with weathered fluorogypsum and then kettle calcined under standard conditions. Since kettle calcination itself is a topatactic dehydration, the additives at this point should have a surface effect rather than a crystallographic effect.
  • the difficult-to-remove contaminant species are co-crystalline.
  • the fluoroanhydrite is undergoing the transformation to fluorogypsum, contaminant ions in the surrounding solution crystallize on the growing gypsum phase and are occluded in the gypsum matrix.
  • the high drag temperature of the fluorogypsum demonstrates the adverse effect of even low concentrations of the impurities in the gypsum lattice.
  • the impurity species probably a fluoroaluminum ion complex such as [A1F 5 (H 2 O)] -2 , desensitizes the calcined fluorostucco to the presence of accelerators in the mixing water.
  • Fluoroanhydrate Hydration Additive The additives listed below were mixed with fluoroanhydrite and neutralized gypsum pond water and allowed to weather hydrate over time. When the samples had hydrated to an appreciable extent above 70% gypsum they were kettle calcined without further additive addition to fluorostucco and the Vicat and temperature rise set times of the materials with and without 10 pounds per ton setting accelerator and gauging water without further additive addition were determined:

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Civil Engineering (AREA)
  • Curing Cements, Concrete, And Artificial Stone (AREA)
  • Glass Compositions (AREA)

Abstract

Gypsum plaster and gypsum wallboard products can be made from fluoroanhydrite by contacting the fluoroanhydrite with a reactive silica selected from the group consisting essentially of Portland cement; perlite; calcium, sodium or potassium silicates; pyrogenic colloidal silica and diatomaceous earth; and after gradual conversion of the fluoroanhydrite to substantially pure fluorogypsum, the purified gypsum is processed in customary fashion in the industrial manufacturing of plaster products. The reactive silica may be added to the fluoroanhydrite during the gradual aging conversion in water to fluorogypsum; or it may be added during water calcination of the fluorogypsum to stucco; or to the gauging water during gypsum plaster or wallboard product formation from the fluorostucco.

Description

Conversion of Fluoroanhydrite to Plaster
Background of the Invention Field of the Invention
This invention relates to a process for transforming fluoroanhydrite into gypsum plaster and gypsum wallboard products.
Flύororanhydrite is a by-product in the manufacture of hydrogen fluoride from the sulfuric acid treatment of fluorite (calcium fluoride). Historically, the fluoroanhydrite, which is contaminated with sulfuric acid, is neutralized with lime or calcium carbonate additions and allowed to hydrate naturally over a several year period of time while weathering in waste heaps. It had been hoped that upon weathering such materials would then be usable in the industrial manufacture of various products. This has not proven to be the case. Description of the Prior Art
Some early attempts to utilize the naturally weathered materials looked at the relationship of this material to Keenes cement (U.S. 1,304,148) and attempted to convert the weathering anhydrite material directly to the dihydrate form by the inclusion of various hydration catalysts and accelerators. Such proposed means to convert this waste product into an industrially usable product have focused upon the quick setting or hardening of the anhydrite content into a dihydrate material in the presence of reactive silica compounds coupled with pozzolonic materials and lime. See for example U.S. Patent Nos. 2,060,127; 2,606,128; 2,608,491 and the like. There is little demand for such inorganic binders; the primary commercial usage for calcium sulfate materials being in the formation of gypsum wallboard.
In addition to residual acids, fluoroanhydrite contains other impurities. Fluoroanhydrite or fluorogypsum can contain up to 2-3% fluoride, probably derived from unreacted calcium fluoride, together with smaller quantities of unreacted soluble and insoluble silicofluorides. These fluorine impurity species, probably a fluoroaluminum complex anion such as [AlF-H2O-2], impede the practical commercial conversion of the stockpiled material into calcium sulfate hemihydrate. First, these impurities inhibit the hydration
of the fluoroanhydrite to gypsum. Secondly, they raise the calcining temperature for conversion of the fluorogypsum to stucco. Thirdly, they inhibit the setting of the stucco to a degree unreasonable for present day commercial wallboard formation and result in producing gypsum products of poor quality. Some of the residual fluoride species in the weathering stockpile material form compounds which are water soluble and may be washed away; while other species form water insoluble compounds that tend to co-crystallize with the dihydrate crystals being formed on weathering. These latter impurities, on attempts to convert the fluorogypsum to hemihydrate, cause extreme difficulties in the calcination conversion to hemihydrate and inhibit response of the formed stucco to set control agents. Further the stucco exhibits slow disintegration when mixed with gauging water. These are significant problems because all gypsum board lines employ set control agents as being critical in production rate and cost of production. Finally, stucco from such material exhibits low maximum rate of hydration and slow disintegration upon mixing with gauging water. This is critical in determining the strength of the set product. Natural gypsum, immediately after being calcined, characteristically
disintegrates to a large degree upon dispersion in water. This disintegration may be measured as a large increase in the particle surface area. When fluoroanhydrite is neutralized with lime and hydrated, the resulting fluorogypsum it has been found, after being calcined to a fluorostucco, disintegrates only to a small degree upon dispersion, and the degree of disintegration is further reduced upon exposure to humidity such that an aged fluorostucco approaches the unpredictable, erratic dispersion properties of aged natural stucco unsuitable for building plaster or gypsum wallboard usage. Summary of the Invention
It has now been found that by allowing a controlled gradual weathering of stockpiled waste fluoroanhydrite materials and calcination to calcium sulfate hemihydrate in the presence of a reactive silica, a truly industrially usable stucco is obtained. The impurities in fluorogypsum are present on the surfaces as well as throughout the crystal. Acid or water washing, particularly with grinding in between washings, is effective to remove the surface exposed impurities. Coupling this with calcination and hydration additives to remove co-crystalline impurities gives a combined effect making the material usable. The obtained fluorostucco has satisfactory calcination characteristics, rheological and physical properties customary to plaster made from natural gypsum rock when mixed with water and is suitable for formation into gypsum wallboard.
A part of the findings of the present invention is that while some of the fluorine and aluminum species contamination in by-product fluoroanhydrite can bo removed by careful washing during the various conversion stages, complex species are trapped in the growing calcium sulfate crystal. By including reactive silicates during various stages of the processing, the crystallized species can either be inhibited in their growth and/or removed from the calcium sulfate crystals. Employing about 1-10% by weight of an active siliceous material in some manner frees the calcium sulfate from the poisonous fluoro and aluminum complex impurities that inhibit hydration of the fluoroanhydrite to gypsum, that inhibit subsequent calcination of the fluorogypsum to fluorostucco, that inhibit the setting action and strength development of the fluorostucco product. Description of the Preferred Embodiments
The starting material is a residue from the process of manufacturing hydrofluoric acid from fluorospar. Fluoroanhydrite fresh from the reactor may be treated by the process of this invention and then stored for gradual conversion. Alternatively, or in addition, weathered stockpile material containing fluorogypsum as well as fluoroanhydrite may be treated. Alternatively, or in addition, treatment may be carried out during calcination of the fluorogypsum to fluorostucco. Thus, in one preferred embodiment, hot fluoroanhydrite directly from the reactor may be blended with the reactive siliceous material and passed to briquetting or pelletizing apparatus for mixing with a suitable binder while being formed into briquettes or pellets. The briquettes may then be warehoused or stockpiled while the conversion to fluorogypsum occurs. Thereafter, the fluorogypsum is calcined to fluorostucco for use as plaster products or subsequent rehydration in gypsum board manufacture.
Suitable active siliceous materials preferably include Portland cement, finely ground expanded perlite, diatomaceous earth, reactive colloidal silica such as Cab-O-Sil® silica or Aerosil® fumed pyrogenic silica and alkaline earth metal silicates such as sodium, potassium and calcium silicate. These are all siliceous products having high surface areas (greater than about 10,000 square centimeters per gram) and having chemically reactive sites due to surface deformaties, such as chemically incomplete silicon dioxide surfaces, missing oxygen atoms in the alkali metal silicates and Portland cement, or stressed crystal configurations in expanded perlite sintered or fumed silicas and diatomaceous earth. Other reactive siliceous products suitable for use in this invention will be evident from this description. Generally inclusion of about 1-10% by weight of the active siliceous material based on the weight of calcium sulfate present in the fluoroanhydrite will produce satisfactory results. Preferred amounts of siliceous material are dependent upon the time at which the material is added in the process and the particular siliceous material.
Extensive studies on a partially hydrated fluoroanhydrite-fluorogypsum stockpile material showed the material to be northomogeneous, and calcination to stucco resulted in very slow setting even when accelerators were used. The slow setting properties were caused by poor disintegration of the stucco upon dispersion in water, and by a chemical interference to the growth of calcium sulfate crystals in the gypsum phase. In comparison to natural gypsum, calcination of the stockpile materials exhibited higher drag and dump temperatures. The resultant fluorostucco upon mixing with water had a smaller particle size initially, but a larger particle size upon dispersion. While having a surface area initially comparable to natural gypsum, the fluorostucco exhibited a lower surface area upon dispersion with water in a board machine mixer.
It is now believed that while some of the contaminant species are water and/or acid soluble and may be washed off the surfaces of the fluoroanhydrite or fluorogypsum, the difficult contaminant species are co-crystalline or occluded, i.e., as the fluoroanhydrite is undergoing the transformation to fluorogypsum, contaminant ions in the surrounding solution crystallize on the growing gypsum phase and are occluded or co-crystallized in the gypsum matrix. It has now been found that these contaminating ions can be rendered inactive in the solution phase, and then the gypsum which re-crystallizes is relatively free of impurities and has properties similar to those of natural gypsum.
The preferred first step for fresh or weathered fluoroanhydrite material is a water or dilute acid wash. For example, it has been found that washing the weathered material twice with water, with a light grinding in between washings, drammatically increased the surface area from about 6,000 cm2/g to 15,900 cm2/g; and reduces the set time with a standard amount of accelerator from approximately 12 minutes without washing to 6.3 minutes after the double washing. Apparently, the light grinding and second wash released some of the impurities. The same treatment steps using 32% sulfuric acid instead of water gave an even better accelerated set time response of 4 minutes. However, neither of these treatments provided sufficient strength or the dispersion disintegration characteristics of natural gypsum. Further, during calcination these materials were difficult to stir, had a high drag temperature and the calcination temperature was difficult to maintain and not uniform throughout the kettle. Coupling this step with active siliceous material addition to inhibit co*-crystalline impurities gives a combined effect making the fluoroanhydrite material usable for building plaster and gypsum wallboard production.
As one alternative, active siliceous materials may be added to the mixing (gauging) water of fluorostucco. For example, the following were evaluated as slurry additives to fluorostucco obtained by calcining different weathered fluorogypsum samples without any adjustments. The samples were from different locations in the fluorogypsum pile and analysis indicated widely varying degrees of hydration and chemicals content:
Slurry Addition Alone
Untreated Slurry Vicat 1 Temperature
Fluorostucco Additive Amount Set Time Rise Set Time
Control — — 10.5 minutes 17.0
Na2SiO3 1 gram 8.8 14.0
Elapsed time from mixing 50 g. plaster with gauging water to when a 300 g. Vicat needle will not penetrate more than half way (20 + 2mm) into the setting slurry.
From the results it is clear this addition rendered the co-crystalline impurity, non-interfering in the through solution setting of stucco recrystallizing as dihydrate.
As another alternative, active siliceous materials may be added to the fluorogypsum at the stage of calcination to fluorostucco. The additives were mixed with weathered fluorogypsum and then kettle calcined under standard conditions. Since kettle calcination itself is a topatactic dehydration, the additives at this point should have a surface effect rather than a crystallographic effect. Calcination Addition
Additive Amt. Amt. Drag Dump Hydration Analysis
Added Cal. TempºF TempºF Hem. Dihyd.Anh. other
Untreated - 4 kg 268 293 B3.6 3.7 2.8 9.9 Control
Na2 40g 4.04kg 273 302 86 2.1 1.7 10.2 siO3
Diatomaceous earth 80g 4.08kg 262 293 79 3.2 2.8 15
Portland cement 80g 4.08kg 266 293 81.5 2.8 2.9 12.8
From the table it may be seen that the additives did not significantly affect the calcination properties. Diatomaceous earth reduced the drag temperature by a slight amount, but still significantly above that of natural gypsum. Following calcination, the materials were evaluated for setting and disintegration properties of the fluorogypsum calcined with the additives: Setting & Disintegration Properties of Calcination Addition
Additive Accelerator Vicat Temp/Rise Set
Control
Untreated 10 lb/ton 17.0 min 23.5 (w/o accel.) 11.5 18.5 (w/acceler.)
Na2SiO3 10 lb/ton 13.8 18.5 10.8 15.0
Diatomaceous 10 lb/ton 19.0 25.0 earth 12.0 19.0
Portland 10 lb/ton 16.2 23.0 cement 10.3 18.0
The subsequent rehydration of stucco when mixed with gauging water is a through solution process thus the additives having only a surface effect during calcination when cairied through the rehydration also have a crystal lographic effect. From the table it may be seen that sodium silicate and Portland cement shortened the with accelerator sotting timcs and were thus found to increase accelerator response of the calcined fluorogypsum. Thus, it seems that the silicate active ion appears to have a beneficial effect. The diatomaceous earth increased the disintegration of the treated stucco to a level equal to that of natural land plaster; however, the set time was not affected.
Thus, while some of the contaminant species are water and/or acid soluble and may be washed off the surfaces of the fluoroanhydrite or fluorogypsum, the difficult-to-remove contaminant species are co-crystalline. As the fluoroanhydrite is undergoing the transformation to fluorogypsum, contaminant ions in the surrounding solution crystallize on the growing gypsum phase and are occluded in the gypsum matrix. The high drag temperature of the fluorogypsum demonstrates the adverse effect of even low concentrations of the impurities in the gypsum lattice. The impurity species, probably a fluoroaluminum ion complex such as [A1F5(H2O)]-2, desensitizes the calcined fluorostucco to the presence of accelerators in the mixing water.
Fluoroanhydrate Hydration Additive The additives listed below were mixed with fluoroanhydrite and neutralized gypsum pond water and allowed to weather hydrate over time. When the samples had hydrated to an appreciable extent above 70% gypsum they were kettle calcined without further additive addition to fluorostucco and the Vicat and temperature rise set times of the materials with and without 10 pounds per ton setting accelerator and gauging water without further additive addition were determined:
Figure imgf000013_0001
The above shows Portland cement and perlite additions at this one processing step lowered calcination temperature of the treated materials. The long unaccelerated set times of treated fluorostucco with some of the materials is not a significant problem because virtually all commercial gypsum, board lines employ set control agents.
It has now been found that these contaminating ions can be rendered inactive in the solution phase, and then the gypsum which crystallizes out would be relatively free of impurities and have properties similar to natural gypsum. With sufficient treatment, the occlusion of these fluorine and aluminum ion species as the fluoroanhydrite is undergoing transformation to fluorogypsum can bo prevented completely, and treatment in the calcination and/or gauging water hydration stages may not be necessary.

Claims

WHAT IS CLAIMED IS:
1. A process for the conversion of fluoroanhydrite to a hydrated calcium sulfate product which comprises mixing a form of calcium sulfate from hydrogen fluoride manufacture with water and about 1-10 weight % of active siliceous material and recrystallizing a hydrated calcium sulfate.
2. The process of Claim 1 in which the hydrogen fluoride manufacture calcium sulfate is fluoroanhydrite, and it is recystallized to fluorogypsum.
3. The process of Claim 1 in which the hydrogen fluoride manufacture calcium sulfate is fluorogypsum, and it is recrystallized to fluorostτιcco .
4. The process of Claim 1 in which the hydrogen fluoride manufacture calcium sulfate is fluorostucco, and it is mixed with gauging water to recrystallize a gypsum product.
5. The process of Claim 1 in which said siliceous material is Portland cement.
6. The process of Claim 1 in which said siliceous material is calcium silicate.
7. The process of Claim 1 in which said siliceous material is potassium silicate.
8. The process of Claim 1 in which said siliceous material is sodium silicate.
9. The process of Claim 1 in which said siliceous material is perlite.
10. The process of Claim 1 in which said siliceous material is pyrogenic colloidal silica.
11. The process of Claim 1 in which said siliceous material is diatomaceous earth.
12. The process of Claim 1 in which the hydrogen fluoride manufacture calcium sulfate is washed before being mixed with water and siliceous material.
13. The process of Claim 12 in which the calcium sulfate is washed with water.
14. The process of Claim 12 in which the calcium, sulfate is washed with sulfuric acid.
PCT/US1982/001776 1981-12-21 1982-12-21 Conversion of fluoroanhydrite to plaster WO1983002266A1 (en)

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US332,579811221 1981-12-21

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Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1756637A (en) * 1927-04-09 1930-04-29 Rumford Chemical Works Method of preparing by-product calcium sulphate for plaster
US1969449A (en) * 1931-10-17 1934-08-07 Rumford Chemical Works Process of producing by-product calcium sulphate
US2606127A (en) * 1949-03-25 1952-08-05 Weber Herman Light-weight building materials and their manufacture from synthetic anhydrous calcium sulfate
CA590594A (en) * 1960-01-12 Calligaris Giuseppe Process for de-acidifying anhydrous gypsum produced from fluorspar
US3042537A (en) * 1961-06-23 1962-07-03 W J Newell Gypsum plaster
GB983204A (en) * 1962-05-26 1965-02-10 Bayer Ag A process for the neutralisation of calcium sulphate containing hydrofluoric acid and sulphuric acid
GB1174512A (en) * 1967-04-07 1969-12-17 Chemie Linz Ag Process for Purifying Gypsum.
GB1248037A (en) * 1968-01-13 1971-09-29 Fisons Ltd Calcium sulphate
US3847634A (en) * 1973-03-12 1974-11-12 R Vickery Synthetic lightweight building material
US4026990A (en) * 1974-12-11 1977-05-31 Chemie Linz Aktiengesellschaft Production of low-fluorine gypsum as a by-product in a phosphoric acid process
DD129772A1 (en) * 1976-05-31 1978-02-08 Chemie Linz Ag PROCESS FOR PREPARING FLUORARM CALCIUM SULFATE
JPS5369225A (en) * 1976-12-02 1978-06-20 Nissan Chemical Ind Ltd Method for increasing flow value of slurry of plaster paris

Patent Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA590594A (en) * 1960-01-12 Calligaris Giuseppe Process for de-acidifying anhydrous gypsum produced from fluorspar
US1756637A (en) * 1927-04-09 1930-04-29 Rumford Chemical Works Method of preparing by-product calcium sulphate for plaster
US1969449A (en) * 1931-10-17 1934-08-07 Rumford Chemical Works Process of producing by-product calcium sulphate
US2606127A (en) * 1949-03-25 1952-08-05 Weber Herman Light-weight building materials and their manufacture from synthetic anhydrous calcium sulfate
US3042537A (en) * 1961-06-23 1962-07-03 W J Newell Gypsum plaster
GB983204A (en) * 1962-05-26 1965-02-10 Bayer Ag A process for the neutralisation of calcium sulphate containing hydrofluoric acid and sulphuric acid
GB1174512A (en) * 1967-04-07 1969-12-17 Chemie Linz Ag Process for Purifying Gypsum.
US3547581A (en) * 1967-04-07 1970-12-15 Chemie Linz Ag Process for removing fluorine and phosphate from gypsum produced in the manufacture of phosphoric acid
GB1248037A (en) * 1968-01-13 1971-09-29 Fisons Ltd Calcium sulphate
US3847634A (en) * 1973-03-12 1974-11-12 R Vickery Synthetic lightweight building material
US4026990A (en) * 1974-12-11 1977-05-31 Chemie Linz Aktiengesellschaft Production of low-fluorine gypsum as a by-product in a phosphoric acid process
DD129772A1 (en) * 1976-05-31 1978-02-08 Chemie Linz Ag PROCESS FOR PREPARING FLUORARM CALCIUM SULFATE
JPS5369225A (en) * 1976-12-02 1978-06-20 Nissan Chemical Ind Ltd Method for increasing flow value of slurry of plaster paris

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0096075A4 *

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EP0096075A4 (en) 1984-06-13
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