Abstract: Calcium fluoride fines or residues comprising calcium fluoride fines, e.g. residues from treating waste water or waste gas, e.g. originating from HF or fertilizer production, with calcium oxide or calcium carbonate to remove HF or fluorides can be converted to HF and calcium sulfate by reaction with sulfuric acid in the form of a suspension. Unreacted calcium oxide or calcium carbonate generates sufficient heat to the endothermic reaction between calcium fluoride and sulfuric acid so that no external heat is needed.

Abstract: The invention relates to a method for reducing or eliminating the soluble content of pollutants in gypsum or in compounds containing gypsum, wherein the gypsum or gypsum-containing compound is mixed with additives that contain or can generate aluminium oxide. More specifically, the gypsum originates from gas desulphurisation and the pollutant is fluorine.

Abstract: The invention provides a process for preparing ?-calcium sulfate hemihydrate which comprises the following steps: adding aqueous solutions containing sulfate ions and calcium ions to calcium chloride solution with a range of concentration; reacting the mixture of a) at a range of temperature for an appropriate time; filtering and washing the reaction products of b) with a rising solvent to isolate the solid and liquid phases; and d) collecting and drying the solid phase to obtain ?-calcium sulfate hemihydrate with high purity; wherein the relationship between the range of the concentration of calcium chloride (y) and the range of the reaction temperature (x) is shown as the following formula: ?0.4x5+7.33x4?52.83x3+187.17x2?328.27x+316<y<1.2x5?22x4+158.5x3?561.5x2+984.8x?588 (2<X<5).

Abstract: Disclosed is an improved alpha-type calcium sulfate hemihydrate. Methods of producing an improved powdered calcium sulfate hemihydrate (CaSO4.½H2O) [alpha-type] compound are disclosed, at least one method including forming calcium sulfate dihydrate (CaSO4.2H2O) into a briquette, calcining the briquette to transform the calcium sulfate dihydrate to calcium sulfate hemihydrate [alpha-type], drying the calcium sulfate hemihydrate [alpha-type] briquette, and optionally grinding the briquette. Also disclosed are methods of producing an improved gypsum plaster including producing the disclosed powdered calcium sulfate hemihydrate [alpha-type] and mixing the powdered calcium sulfate hemihydrate [alpha-type] with water.

Abstract: The invention provides a process for preparing ?-calcium sulfate hemihydrate which comprises the following steps: adding aqueous solutions containing sulfate ions and calcium ions to calcium chloride solution with a range of concentration; reacting the mixture of a) at a range of temperature for an appropriate time; filtering and washing the reaction products of b) with a rising solvent to isolate the solid and liquid phases; and d) collecting and drying the solid phase to obtain ?-calcium sulfate hemihydrate with high purity; wherein the relationship between the range of the concentration of calcium chloride (y) and the range of the reaction temperature (x) is shown as the following formula: ?0.4x5+7.33x4?52.83x3+187.17x2?328.27x+316<y<1.2x5?22x4+158.5x3?561.5x2+984.8x?588(2<X<5).

Abstract: The invention relates to a gypsum product which consists of essentially intact crystals having a size of between 0.1 and below 2.0 ?m. The product is especially suitable as a coating pigment or filler in paper manufacture. The invention also relates to a process for the preparation of a gypsum product, wherein calcium sulphate hemihydrate and/or calcium sulphate anhydrite, water and a crystallization habit modifier are contacted so that the calcium sulphate hemihydrate and/or calcium sulphate anhydrite and the water are reacted with each other and form a crystalline gypsum product. The calcium sulphate hemihydrate and/or calcium sulphate anhydrite is/are used in such an amount that the reaction mixture formed from the calcium sulphate hemihydrate and/or calcium sulphate anhydrite, the water and the crystallization habit modifier has a dry matter content of between 50 and 84% by weight. Then, said gypsum product can be formed which consists of essentially intact crystals having a size of between 0.

Abstract: The invention relates to a process for the preparation of a gypsum product wherein calcium sulphate hemihydrate and/or calcium sulphate anhydrite and water are contacted so that the calcium sulphate hemihydrate and/or calcium sulphate anhydrite and the water react with each other and form a gypsum product. The reaction mixture has a dry matter content of 34-84% by weight in order to obtain a gypsum product which consists of crystals that are small, flat and of as equal size as possible. The invention also relates to a product prepared by this process. A gypsum product is formed which consists of essentially intact crystals having a size of between 0.1 and below 2.0 ?m. The products are applicable e.g. as fillers or coating pigments in e.g. paper industry.

Abstract: The invention relates to a method for stabilising a metastable soluble anhydrite III, to a method for producing a hydraulic binder based thereon, to the thus obtainable hydraulic binder, to a method for the use thereof in the cement industry and to an industrial plant for carrying out the inventive method. The method consists in stabilising a metastable soluble anhydrite III by mechanically stressing the particles thereof in such a way the crystal structure of the particles is modified and the metastable phase thereof is stabilised. Said invention makes it possible to stabilise the metastable soluble anhydrite III particles without using current steps for heating and quenching said particles.

Abstract: The invention pertains to a method of inertising free soluble impurities of phosphates and/or fluoride ions, in phosphogypsum, for use in commercial and industrial applications. The Phosphogypsum is pre-conditioned over an extended period of time separately or treated along with standard constituents by spraying, interblending or intergrinding during the process of manufacture, with alkyl, alkenyl and/or alkanol derivatives of ammonia, either individually or in combination with one another, to form stable intermediary phosphates and/or fluoride salts of the derivatives of ammonia.

Abstract: A method for calcining gypsum in a pressurized reactor by injecting combustion gases and air into the pressurized reactor to create a fluidized bed of gypsum, and heating the fluidized bed of gypsum in the pressurized reactor sufficiently to form a calcined hemihydrate.

Abstract: A process is disclosed for making a blend of alpha- and beta-stucco including a slurry calcination step to produce alpha calcium sulfate hemihydrate followed by a fluidized bed calcination step to produce beta calcium sulfate hemihydrate. The process starts with 50-75% gypsum-containing solids slurry, and then steam calcines the slurry in a first reactor to form partially calcined gypsum slurry which contains calcium sulfate dihydrate and alpha calcium sulfate hemihydrate. The partially calcined slurry is then dewatered. Then the filter cake is fed into a kettle to complete the calcination process by converting the calcium sulfate dihydrate of the filter cake material into beta calcium sulfate hemihydrate.

Abstract: The present invention is based on solid-state reaction or reactions in the presence of small amounts of water, between phospho gypsum and agglutinating-neutralizing agents, principally though the application of oxy and hydroxy compounds, without discounting use of the respective carbonates of magnesium, aluminum and principally calcium, in addition to mixtures of these, and the subsequent preparation of self-hardening pellets which facilitate transport and handling. The technological process associated with the invention notably simplifies both the number and type of individual operations, and the preparation of pellets from mixtures of phosphor gypsum; it also reduces energy costs by operating at low temperatures (150°C.) during short periods (1-2 hours), while reducing the quantity of neutralizing agents, and minimizing the volume of water required for the process.

Abstract: Methods and systems for generating sulfuric acid (102) are disclosed. In some embodiments, the method includes combusting a sulfur-containing material (114) with a gas including oxygen (116) to produce a first stream of sulfur dioxide (118), mixing water with the first stream of sulfur dioxide to produce a mixed stream, using an energy, electrolytically converting (108) the mixed stream of sulfur dioxide and water into sulfuric acid (102) and hydrogen (122), generating a source of energy (126) from the hydrogen, and providing the source of energy as at least a portion of the energy for electrolytically converting the first stream of sulfur dioxide and water into sulfuric acid and hydrogen. In some embodiments, the system includes a first chamber for combusting a sulfur-containing material to produce a first stream of sulfur dioxide, an electrolytic cell (108) for converting the first stream into sulfuric acid and hydrogen, and a fuel cell (112) for generating an energy source from the hydrogen.

Abstract: A process for producing alpha-hemihydrate gypsum from dihydrate gypsum includes feeding a slurry comprising the dihydrate gypsum and water into a heating tube, heating the heating tube at a temperature effective to generate steam and pressure from the water, wherein the steam and pressure are effective to convert the dihydrate gypsum to the alpha-hemihydrate gypsum, and withdrawing the alpha-hemihydrate gypsum from the heating tube.

Abstract: The present invention includes pure single-crystalline metal oxide and metal fluoride nanostructures, and methods of making same. These nanostructures include nanorods and nanoarrays.

Abstract: A process is disclosed for making dead burn calcium sulfate anhydrite. The process includes a slurry calcination step to produce calcium sulfate anhydrite followed by removing free water from the anhydrite while avoiding substantial rehydration. Also disclosed are dead burn calcium sulfate anhydrite particles with high aspect ratios, e.g. fibers having an average aspect ratio of at least 4:1, or very fine particle size, e.g., at or below 2 micrometers average, combined with very low water content, e.g., less than 0.5, preferably less than 0.3, wt. % water. These particles are typically useful as fillers.

Abstract: A process for treating organic material, separating calcium and recovering phosphorus and to utilization of the obtained products and their use as a soil conditioner and a fertilizer as well as for providing carbon dioxide traps in gas cleaning. In the process, organic ingredients are separated from calcium-phosphate-containing ingredients, the calcium-phosphate-containing ingredients are dissolved in an acid-containing solution and/or the calcium is precipitated as a salt corresponding to the acid, and optionally phosphoric acid formed from a phosphate ion is separated. The invention also relates to a calcium-carbonate-containing product and a phosphoric-acid containing product, which are prepared by the process of the invention.

Abstract: The present invention relates to a system and associated method for the production of gypsum in manufacturing plant. More specifically, the invention relates to the production of alpha-type gypsum in a gypsum board manufacturing plant. The system yields increased efficiencies by capturing heat given off during processing steps and using that heat to reduce the energy needed for calcination. The invention finds particular application in the production alpha-type gypsum. The present invention is described in greater detail hereinafter in conjunction with the following specific embodiments.

Abstract: A method for reducing acid gases in a flue gas, the method comprising reacting biosolids comprising a scrubbing agent with a flue gas comprising an acid gas, thereby reducing the amount of acid gas in the flue gas is disclosed. Also disclosed is a flue gas scrubbing process comprising: combusting a fossil fuel and biosolids comprising a scrubbing agent, thereby producing a flue gas comprising an acid gas, wherein the flue gas has a reduced amount of acid gas compared with flue gas produced from the combustion of the fossil filet alone. A flue gas scrubbing process comprising providing a stream of biosolids that includes a hydroxide or an oxide of a Group IA or IIA element, providing a flue gas comprising an acid gas, and reacting the biosolids stream with the flue gas so as to reduce the amount of acid gas in the flue gas is also disclosed.

Abstract: A pretreatment agent for a sample to be subjected to Limulus assay comprising an alkali metal sulfate and/or an alkaline earth metal sulfate wherein the sulfate(s) has a final concentration of 20 mM or more when the sulfate(s) is allowed to contact with the sample, or an alkali metal halide and/or an alkaline earth metal halide wherein the halide(s) has a final concentration of from 0.4 M to 1.2 M or less when the halide(s) is allowed to contact with the sample, or a kit for Limulus assay reagent comprising thereof as a composing article.

Abstract: This invention provides a production process, which can stably produce high-quality satin white (calcium trisulfoaluminate) having very small and homogeneous particulate shapes suitable for incorporation into coated paper for printing, and an apparatus for use in said process. In this process for producing calcium trisulfoaluminate, a calcium hydroxide suspension (A) is reacted with an aqueous aluminum sulfate solution (B) to produce calcium trisulfoaluminate (C). The aqueous aluminum sulfate solution (B) is added in plurality of stages to the calcium hydroxide suspension (A). At least any one stage of the plurality of stages addition, addition of the aqueous aluminum sulfate solution (B) to the calcium hydroxide suspension (A) is carried out in such a manner that the aqueous aluminum sulfate solution (B) is continuously added to the calcium hydroxide suspension (A) being continuously transferred.

Abstract: The preparation of gypsum parts (dihydrate calcium sulfate) with high mechanical resistance is obtained with the aid of water layers with nanometric thickness. Calcium sulfate is used, dihydrate as well as hemihydrate, to obtain parts from these two materials, pure or mixed, especially to use in construction work, where the parts are prepared by compressing their slightly humidified powders.

Abstract: A method of reducing sulfur dioxide emissions of a circulating fluidized bed boiler. Sulfur-containing carbonaceous fuel is fed to a furnace of the boiler, and calcium carbonate is fed to the furnace at a rate relative to the first stream such that the molar ratio of calcium in the second stream to sulfur in the first stream is at most about 1.0. The fuel is combined so that the sulfur is oxidized to form sulfur dioxide. The calcium carbonate is calcined to form calcium oxide and the calcium oxide is used to sulfate the sulfur dioxide to form calcium sulfate. Flue gas particles are separated using a hot loop separator, and the separated particles are returned to the furnace. A sulfur-reduction stage downstream of the furnace further reduces the sulfur content of the flue gases.

Abstract: The present invention relates to a composition comprising water, more than 30% w/w of calcium hydroxide, and >0.2% w/w dispersant. A process for preparing such a composition is also disclosed. The composition which can be in the form of a 45-55% concentration lime slurry is particularly useful for converting concentrated ammonium lignosulfonate into calcium lignosulfonate, for converting ammonium lignosulfonate into low sulfate calcium, potassium, sodium, or magnesium lignosulfonate and mixtures thereof, for removing soluble sulfate from concentrated sodium, potassium, ammonium or magnesium lignosulfonate or for treating a weak liquor obtained from the pulp and paper industry.

Abstract: A process for treating beta calcium sulfate hemihydrate is disclosed. The process comprises exposing beta calcium sulfate hemihydrate to steam at a pressure above atmospheric pressure.

Abstract: Disclosed is an improved alpha-type calcium sulfate hemihydrate. Methods of producing an improved powdered calcium sulfate hemihydrate (CaSO4.½H2O) [alpha-type] compound are disclosed, at least one method including forming calcium sulfate dihydrate (CaSO4.2H2O) into a briquette, calcining the briquette to transform the calcium sulfate dihydrate to calcium sulfate hemihydrate [alpha-type], drying the calcium sulfate hemihydrate [alpha-type] briquette, and optionally grinding the briquette. Also disclosed are methods of producing an improved gypsum plaster including producing the disclosed powdered calcium sulfate hemihydrate [alpha-type] and mixing the powdered calcium sulfate hemihydrate [alpha-type] with water.

Abstract: A process is disclosed for making dead burn calcium sulfate anhydrite. The process includes a slurry calcination step to produce calcium sulfate anhydrite followed by removing free water from the anhydrite while avoiding substantial rehydration. Also disclosed are dead burn calcium sulfate anhydrite particles with high aspect ratios, e.g. fibers having an average aspect ratio of at least 4:1, or very fine particle size, e.g., at or below 2 micrometers average, combined with very low water content, e.g., less than 0.5, preferably less than 0.3, wt. % water. These particles are typically useful as fillers.

Abstract: A method for removing impurities accumulated in a scrubbing fluid in a flue gas scrubber and effluents from the scrubber. The flue gases are scrubbed with a scrubbing fluid that includes a calcium-containing absorbent. The scrubbing fluid containing gypsum and other impurities and produced in the scrubber is discharged from the scrubber. The gypsum is separated from the scrubbing fluid. To the scrubbing fluid is added an auxiliary agent, by the effect of which the impurities accumulated in the scrubbing fluid are removed with the gypsum and the moisture content of the gypsum to be separated from the scrubbing fluid is increased.

Abstract: A process is disclosed for making a blend of alpha- and beta-stucco including a slurry calcination step to produce alpha calcium sulfate hemihydrate followed by a fluidized bed calcination step to produce beta calcium sulfate hemihydrate. The process starts with 50-75% gypsum-containing solids slurry, and then steam calcines the slurry in a first reactor to form partially calcined gypsum slurry which contains calcium sulfate dihydrate and alpha calcium sulfate hemihydrate. The partially calcined slurry is then dewatered. Then the filter cake is fed into a kettle to complete the calcination process by converting the calcium sulfate dihydrate of the filter cake material into beta calcium sulfate hemihydrate.

Abstract: The present invention concerns the application of a novel process for the physical and chemical conditioning of chemical gypsum or phospho gypsum, derived from the production of phosphoric acid, and its use as a retarding agent in the setting of Portland type cements or in the preparation of other construction materials. This conditioning is based on solid-state reactions or reactions in the presence of small amounts of water, between phospho gypsum and agglutinating-neutralizing agents, principally through the application of oxy and hydroxy compounds, without discounting use of the respective carbonates of magnesium, aluminum and principally calcium, in addition to mixtures of these, and the subsequent preparation of self-hardening pellets which facilitate transport and handling.

Abstract: A method for processing flue gas scrubber material flows. The flue gas is scrubbed with a calcium-based absorbent containing washing fluid for absorbing sulphur oxides from the flue gases, and the formed gypsum slurry is directed from the flue gas scrubber to the separator. At the separating point of the separator, gypsum is separated from the washing fluid and the gypsum and washing fluid are taken out of the separator as separate material flows. From the flue gas scrubber the washing fluid is directed to a tank located before the separating point of the separator or after the separating point of the separator, in which tank foam is separated from the washing fluid as its own phase and taken out of the tank.

Abstract: The invention relates to synthesis of nanoparticles, in particular to methods for producing nanoparticles with networks consisting of Z sulphate (Z=magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) or the binary mixtures thereof). The inventive method consists in synthesising the nanoparticles by crystal growth from an ion Z source and a sulphate ion source in a liquid phase mixture. The invention produces Z sulphate nanoparticles having a small diameter and uniformly dispersible in water or other solvents in a simple way. Co-ordinating solvents like glycerine, glycol ethylene and other polyethylene glycols, polyalcohols or dimethylsulphoxide (DMSO) are used for the synthesis mixture.

Abstract: Method of synthesis for a material made of particles having a core and a coating and/or being connected to each other by carbon cross-linking, the core of these particles containing at least one compound of formula LixM1?yM?y(XO4)n, in which x,y and n are numbers such as 0?x?2, 0?y?0.6 and 1?n?1.5, M is a transition metal, M? is an element with fixed valency, and the synthesis is carried out by reaction and bringing into equilibrium the mixture of precursors, with a reducing gaseous atmosphere, in such a way as to bring the transition metal or metals to the desired valency level, the synthesis being carried out in the presence of a source of carbon called carbon conductor, which is subjected to pyrolysis. The materials obtained have excellent electrical conductivity as well as very improved chemical activity.

Abstract: A process to regenerate wet flue gas scrubber purge liquid into NaOH caustic suitable for make-up caustic for the scrubber is disclosed. Further, sulfur is removed from waste effluent in the form of gypsum with the process described herein. Lime is added to the spent, sodium sulfate-containing purge liquid to result in the formation of gypsum and sodium hydroxide.

Abstract: A method is described for the manufacture of hydrotalcites by using at least one compound of a bivalent metal (Component A) and at least one compound of a trivalent metal (Component B), wherein at least one of these components is not used in the form of a solution, characterized in that a) at least one of the Components A and/or B which is not used in the form of a solution, shortly before or during mixing of the components, and/or b) the mixture containing the Components A and B is subjected to intensive grinding until an average particle size (D50) in the range of approx. 0.1 to 5 ?m is obtained, and optionally, after aging treatment or hydrothermal treatment, the resulting hydrotalcite product is separated, dried, and optionally calcinated.

Abstract: The present invention provides methods and apparatus for treating flue gas containing sulfur dioxide using a scrubber, and more particularly relates to recovering gypsum and magnesium hydroxide products from the scrubber blowdown. The gypsum and magnesium hydroxide products are created using two separate precipitation reactions. Gypsum is crystallized when magnesium sulfate reacts with calcium chloride. Magnesium hydroxide is precipitated when magnesium chloride from the gypsum crystallization process reacts with calcium hydroxide. The process produces a high quality gypsum with a controllable pH and particle size distribution, as well as high quality magnesium hydroxide.

Abstract: A process for reducing a level of radionuclei in a phosphogypsum material having a radioactive contaminant is provided, wherein the process includes the steps of: (a) mixing the phosphogypsum material with an acid decontamination solution to form a mixture; (b) separating the mixture into a liquid stream having a large portion of the radioactive contamination and a solid stream having a residual component of the acid decontamination solution; and (c) removing the residual component of the acid decontamination solution from the solid stream, thus providing a gypsum material that meets or exceeds federal standards for level of radioactive nuclei and providing a process that is environmentally friendly and capable of avoiding the generation of phosphogypsum stacks, as well as eliminating existing or abandoned phosphogypsum stacks, further providing for recovery of the radioactive nuclei if desired.

Abstract: Disclosed is an improved alpha calcium sulfate hemihydrate. Methods of producing an improved powdered calcium sulfate hemihydrate (CaSO4·½H2O) [alpha-type] compound are disclosed, at least one method including forming calcium sulfate dihydrate (CaSO4·2H2O) into a briquette under high pressure, calcining the briquette to transform the calcium sulfate dihydrate to calcium sulfate hemihydrate [alpha-type], drying the calcium sulfate hemihydrate [alpha-type] briquette, and optionally grinding the briquette. Also disclosed are methods of producing an improved gypsum plaster including producing the disclosed powdered calcium sulfate hemihydrate [alpha-type] and mixing the powdered calcium sulfate hemihydrate [alpha-type] with water.

Abstract: A flue gas desulfurization apparatus includes at least one activated carbon fiber board 20 provided in a catalyst unit 6, the board being formed by alternatingly juxtaposing one or more plate-like activated carbon fiber sheets and one or more corrugated activated carbon fiber sheets so as to provide vertically extending conduits, wherein water for producing sulfuric acid is supplied, through a capillary phenomenon, to the activated carbon fiber board 20 provided in the catalyst unit 6. The flue gas desulfurization apparatus attains removal of sulfur oxides (SOx) by adding a minimum required amount of water to the activated carbon fiber board 20 so as to attain uniform water distribution and can reduce the amount of water required for removing sulfur oxides (SOx).

Abstract: A calcium hydroxide slurry is injected into the off gases in the exhaust duct of an industrial plant which burns sulfur containing fuels. The calcium hydroxide slurry reacts with SO3 produced as a result of the combustion process and forms a primary solid calcium sulfate reaction product. The calcium sulfate can then be removed in a particulate removal station in the plant.

Abstract: A wet type exhaust gas desulfurization method includes sucking liquid in a liquid reservoir containing a sulphur compound formed from sulphur dioxide contained in exhaust gas so as to form a flow of the liquid, reducing the flow of the liquid in diameter to form a depressurized region in the flow, the reducing including passing the liquid through a reduction section which includes a reduction section plate having a reduction section hole and a peripheral portion surrounding the reduction section hole, the peripheral portion protruding toward the upstream side of the flow, introducing air into the depressurized region so as to generate a mixture stream of the air and the liquid, and spouting the mixture stream into the liquid reservoir. The reducing includes forming cavities in the flow, the forming cavities includes shearing the flow, and the shearing includes bringing the flow into contact with the peripheral portion.

Abstract: A gas refining method for adsorbing a reducing gas obtained by pressure gasification of coal or oil comprises introducing a reducing gas stream into an adsorbing and removing zone where it contacts an adsorbent. Sulfur-containing compounds are adsorbed onto the adsorbent and a first oxygen-containing gas stream is introduced into the adsorbing and removing zone in order to form a regeneration gas containing sulfur dioxide. The regeneration gas is contacted with a second oxygen-containing stream and a calcium-containing liquid slurry to effect absorption of sulfur dioxide by the slurry and precipitation of a gypsum compound. The temperature of the slurry is varied to cause selective precipitation of 60 -gypsum hemihydrate or gypsum dihydrate.

Abstract: A flue gas processing apparatus for removing sulfur oxide contained in a gas, including a desulfurization tower through which the gas flows, the desulfurization tower including a catalyst unit having at least one activated carbon fiber board which adsorbs the sulfur oxide and a water-supply device configured to supply water to the catalyst unit so as to form sulfuric acid from the sulfur oxide adsorbed to the at least one activated carbon fiber board, the water-supply device being positioned above the catalyst unit in the desulfurization tower, and a pressurizing device configured to apply pressure to the gas supplied to the desulfurization tower so as to flow the gas through the catalyst unit by the pressure.

Abstract: A method for treating and upgrading effluents containing at least a metallic sulphate comprising adding at least a base to the effluent to precipitate the metallic ions in the form of iron oxy-hydroxides Fe(OHx) wherein x=2 and/or 3; separating the precipitated hydroxide calcium sulphate CaSO4; and separating the calcium sulphate CaSO4 precipitated during the preceding step. Said method enables obtainment of calcium sulphate (white gypsum) substantially free of metals and therefore capable of being upgraded and iron oxy-hydroxides likewise capable of being upgraded.

Abstract: Calcium sulfate is regenerated to lime at a relatively low temperature and in a short time. In a method of regenerating lime by reducing calcium sulfate by flowing a reducing gas containing 0.5 to 20% by volume of CO and 0.03 to 30% by volume of CO2, the reduction is carried out in the presence of an aid selected from the group consisting of Fe2O3, MgSO4 and mixtures thereof at a temperature of 900 to 1000° C. In cases where the aid is Fe2O3, the amount thereof is 0.2 to 10% by weight based on the weight of the calcium sulfate in terms of anhydrous calcium sulfate. In cases where the aid is MgSO4, the amount thereof is preferably 10 to 50% by weight based on the weight of the calcium sulfate in terms of anhydrous calcium sulfate.

Abstract: A chemical process for the purification of CaSO4 utilizes the ability of an aqueous solution of a chelating agent to selectively dissolve CaSO4 in that the initial extraction can be carried out at certain pH and CaSO4 can be recovered by titration to a different pH (usually a a lower pH) following a mechanical treatment, such as centrifugation or filtration, to separate the aqueous chelate solution from insoluble material. Also claimed are an apparatus and the use of chelating agents therefor.

Abstract: The suspension of needle-shaped (acicular) calcium sulfate dihydrate particles is prepared by mixing freshly calcined calcium sulfate hemihydrate (CaSO4112?O), having an average particle size between 1 and 100 micrometers, and water in a reactor at medium to high shear rate, with either no additives or together with acids or with calcium or sulfate containing additives. The average length and width of the resulting calcium sulfate dihydrate particles are then about 5 to 35 micrometers and 1 to 5 micrometers, respectively. The calcium sulfate dihydrate particles of reduced solubility are obtained using a calcium chelating agent, with or without the addition of a weak acid. The resulting product is a suspension of calcium sulfate dihydrate particles that can be used as a filler in papermaking. The particles have a high retention and provide improved optical properties with minimal filler losses due to solubility.

Abstract: A method of producing surgical grade calcium sulphate suitable for use as resorbable osteoconductive bone void filler material. The method comprising forming an initial calcium sulphate di-hydrate from synthetic constituents; dehydrating the initial calcium sulphate di-hydrate to form calcium sulphate anhydrite; and subsequently rehydrating the calcium sulphate anhydrite and allowing subsequent calcium sulphate di-hydrate to crystallize out.

Abstract: The present invention relates to an apparatus and a process for producing zinc oxide from an acid soluble zinc-bearing material. The process according to the present invention comprises the steps of leaching the zinc oxide material with sulphuric acid; precipitating iron and silica from the leach solution using calcium oxide; removing copper, cadmium and cobalt from the leach solution by cementation with zinc dust; precipitating zinc oxide from the leach solution using calcium oxide; and upgrading zinc content in zinc oxide precipitates by separating zinc oxide from gypsum using a flotation or granulometric sizing technique.

Abstract: A process for synthesizing a hydraulic binder based on natural calcium sulfate (gypsum), the process consisting in heating the calcium sulfate to obtain a large proportion of anhydrite III or &agr; anhydrite, and then in quenching. The process consists in: completely dehydrating the calcium sulfate, and suddently cooling the matter thus dehydrated. The present invention finds a preferred application in the construction industry in obtaining a hydraulic binder that can be used as cement.