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)

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• 1982
  • 1982-12-21 WO PCT/US1982/001776 patent/WO1983002266A1/en not_active Application Discontinuation
  • 1982-12-21 AU AU11505/83A patent/AU1150583A/en not_active Abandoned
  • 1982-12-21 EP EP19830900397 patent/EP0096075A4/de not_active Withdrawn

Non-Patent Citations (2)

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