Alpha gypsum hemihydrate is obtained by calcining calcium sulfate dihydrate, generated with flue-gas desulfurization of power plants or by chemical process, e.g. in the production of phosphoric acid. The calcining process comprises producing initially a dispersion from calcium sulfate dihydrate and diluted, sulfuric acid solution and ...

The report gives results of a theoretical and experimental study to characterize the coprecipitation of calcium sulfate with calcium sulfite hemihydrate. A coprecipitation product had been suggested to explain the mechanism by which sulfate could be preci...

The work reported here shows excellent scaling threshold improvement in natural sea water concentrates enriched with magnesium chloride. Scaling thresholds of calcium sulfate hemihydrate and anhydrite were evaluated from solubility measurements under equi...

The report gives results of a theoretical and experimental study to characterize the coprecipitation of calcium sulfate with calcium sulfite hemihydrate. A coprecipitation product had been suggested to explain the mechanism by which sulfate could be precipitated from a scrubber solution subsaturated with respect to calcium ...

The objective of this report is to document laboratory testing of blended calcium aluminate - calcium hemihydrate grouts for P-Reactor vessel in-situ decommissioning. Blended calcium aluminate - calcium hemihydrate cement-based grout was identified as can...

A novel utilization way of the sludge from wet calcium-based flue gas desulfurization (FGD) processes has been developed in this paper. This study focused on the conversion of the FGD gypsum into alpha-hemihydrate calcium sulfate by a hydrothermal salt solution method at atmospheric pressure. Experimental study has been carried out in a batch reactor. ...

The formation of calcium sulfate scales is a persistent problem. At high ambient temperatures, the mineral phases exhibit reduced solubility, and hydrate phase changes may take place. In this study, the growth and dissolution of the ..cap alpha..-hemihydrate and anhydrite phases of calcium sulfate have been investigated at temperatures ...

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The precipitation of calcium sulfate dihydrate (CaSO/sub 4/.2H/sub 2/O) and calcium sulfite hemihydrate (CaSO/sub 3/.1/2H/sub 2/O) from high, up to 240,000 mg/L, total dissolved solids (TDS) solutions was studied at 50/sup 0/C. The solutions were selected to cover a range of solution compositions of magnesium, calcium, sodium, chloride, and ...

A wet process for producing phosphoric acid and phosphohemihydrate by acidulation of phosphate rock. A strong phosphoric acid is obtained with concomitant production of an improved calcium sulfate that is extremely low in radioactivity by operation in Region II for shorter time so as to produce small sized hemihydrate particles, then hydration of a ...

The report gives results of a theoretical and experimental study to characterize the coprecipitation of calcium sulfate with calcium sulfite hemihydrate. A coprecipitation product had been suggested to explain the mechanism by which sulfate could be precipitated from a scrubber s...

... 3 2011-04-01 2011-04-01 false Calcium sulfate. 184.1230 Section 184.1230 Food...Specific Substances Affirmed as GRAS § 184.1230 Calcium sulfate. (a) Calcium sulfate (CaSO4 , CAS Reg. No....

Hydration reactions of C[sub 3]A with C[sub 4]AF with calcium sulfate hemihydrate and gypsum were investigated and the kinetics of the reactions compared. The rates of C[sub 3]A and C[sub 4]AF hydration, as determined by heat evolution, vary depending on whether the sulfate-containing reactant is gypsum or calcium ...

Diverse large-scale sources of FGD gypsum, the plentiful waste by-product from SO/sub 2/ emissions cleanup in major industrial countries, are characterized in terms of properties including crystal form and contained impurities that affect commercial usability. New technology to expand FGD gypsum usage by economical conversion to alpha hemihydrate of calcium ...

Diverse large-scale sources of FGD gypsum, the plentiful waste by-product from SO/sub 2/ emissions cleanup in major industrial countries, are characterized in terms of properties including crystal form and contained impurities that affect commercial usability. New technology to expand FGD gypsum usage by economical conversion to alpha hemihydrate of calcium ...

Phosphoric acid and gypsum are produced from phosphate rock by digesting same with sulfuric acid to produce a high concentration of phosphoric acid and calcium sulfate hemihydrate. The solubilized uranium in the rock is rendered recoverable by reducing same from the +6 valence state to the +4 valence state during the digestion step followed by oxidizing ...

A method of disposing of wastes, especially wastes containing radioactive or toxic substances, such as the wastes generated in the water associated with nuclear power production is described. A feature of the invention is to incorporate the waste into a hardenable setting mass when mixed with water, comprising calcium sulfate hemihydrate, water soluble ...

Samples of plasters (i.e., calcium sulfate hemihydrate, CaSO4.1/2H20) from six sources and one plaster retarder from a different source were obtained and characterized by a combination of chemical and physical testing and by petrographic examination. The ...

This patent describes a method of cementing a casing in a wellbore. It comprises pumping a cement slurry into the annulus between the casing and the wellbore, the cement slurry containing from 0.2 to 2.0 percent by weight, based on the weight of cement solids in the slurry, of an additive consisting essentially of from 30 to 80 percent by weight of partially hydrolyzed high molecular weight vinyl ...

The objective of this report is to document laboratory testing of blended calcium aluminate - calcium hemihydrate grouts for P-Reactor vessel in-situ decommissioning. Blended calcium aluminate - calcium hemihydrate cement-based grout was identified as candidate material for filling (physically stabilizing) the 105-P Reactor vessel (RV) because it is less ...

A method of treating final products from a flue gas desulfurization. The flue gas desulfurization is carried out by the absorption of sulfur oxide in a spray dryer with a suspension which contains lime, or in a reactor with a dry, fine-grained, absorbent which contains lime. Prior to desulfurization, the fly ash carried along by the flue gas which is to be desulfurized is separated entirely, ...

Calcium sulfate hydrates receive significant attention due to numerous large scale industrial applications. There has been a long debate on the possible existence of two gypsum hemi-hydrate polymorphs, denoted alpha- and beta-CaSO(4).0.5H(2)O. In this work, a new crystal structure of calcium sulfate hemi-hydrates ...

In wet-process phosphoric acid plants, both previous and recent test results show that uranium dissolution from phosphate rock is significantly higher when the rock is acidulated under oxidizing conditions than under reducing conditions. Excess sulfate and excess fluoride further enhance the distribution of uranium to the cake. Apparently the U(IV) present in the crystal ...

This study examined the thermal behavior of cast gypsum specimens, with and without additives, by means of simultaneous differential thermal analysis-thermogravimetry (DTA-TG) and dilatometry. Specimens were prepared from wet-calcined hemihydrates (Hydrocal and Densite). The additives studied were boric acid (H3BO3) and sodium chloride (NaCl), and these were added to the ...

Abstract Regeneration and preservation of bone after the extraction of a tooth is necessary for the placement of a dental implant. The goal is to regenerate alveolar bone with minimal postoperative pain. Medical grade calcium sulfate hemihydrate (MGCSH) can be used alone or in combination with other bone grafts; it improves graft handling characteristics ...

Superplasticizers (SPs), namely sulfonated melamine formaldehyde (SMF) and polycarboxylate (PC), were independently admixed with alpha-calcium sulfate hemihydrate based plaster to improve the material's performance. SMF and PC gave, respectively, 38% and 25% increases in the 2 h bending strength at the optimum dosages of 0.5 wt.% and 0.3 wt.%, ...

The influence of addictives on the hydrothermal formation of hemi-hydrate calcium sulfate (CaSO4.0.5H2O) whiskers were discussed in this paper, using CaCl2 and Na2SO4 as the reactants. The presence of NaCl, CaCl2 or Na2SO4 increased the concentrations of Ca2+ and SO42-, leading to the formation of CaSO4.0.5H2O whiskers with aspect ratio lower than 50. The ...

Samples of plasters (i.e., calcium sulfate hemihydrate, CaSO4.1/2H/sup 2/0) from six sources and one plaster retarder from a different source were obtained and characterized by a combination of chemical and physical testing and by petrographic examination. The petrographic examination included x-ray diffraction, optical microscopy, differential thermal ...

A novel injectable bone cement based on mineralized collagen was reported in this paper. The cement was fabricated by introducing calcium sulfate hemihydrate (CaSO(4).1/2H(2)O, CSH) into nano-hydroxyapatite/collagen (nHAC). The workability, in vitro degradation, in vitro and in vivo biocompatibility of the cement (nHAC/CSH) were studied. The comparative ...

The bone-repairing composite material CS/PLLA was fabricated by mixing poly-L-lactic acid (PLLA) and calcium sulfate hemihydrate (CSH). The structure of the composite was analyzed with Infrared spectroscope, X-ray diffraction, and scanning electron microscope. The results indicated that the crystal pattern of calcium sulfate was ...

Three-dimensional printing (3DP) is a CAD/CAM built-up using ink-jet printing technique. Commercially available 3DP system can form only gypsum model and not for bioceramics. On the other hand, transformation of hardened gypsum into hydroxyapatite (HA) by treatment in ammonium phosphate solution was found lately. In the present study, transformation of the 3DP gypsum block to HA was attempted. ...

Predicting potential scaling problems can be difficult, and numerous saturation indices and computer algorithms have been developed to determine if, when, and where scaling will occur. The Langelier, Stiff-Davis, and the Oddo-Tomson saturation indices, all widely used in the oil field, are compared and contrasted relative to calcium carbonate scale. New saturation indices for barium, strontium, ...

This essay is to present an improvement on the concentration assay for hemihydrate gypsum in plaster of Paris bandage-Viscose form. PMID:19459355

The emergence of resistant strains of Gram-positive organisms in osteomyelitis creates treatment challenges. Daptomycin is an antibiotic that shows promise for treating some resistant strains of Gram-positive infections; however, it has not been widely used clinically for the treatment of osteomyelitis. We determined whether daptomycin eluted from calcium sulfate�a local ...

An injectable and self-setting bone repair materials (nano-hydroxyapatite/collagen/calcium sulfate hemihydrate, nHAC/CSH) was developed in this study. The nano-hydroxyapatite/collagen (nHAC) composite, which is the mineralized fibril by self-assembly of nano-hydrocyapatite and collagen, has the same features as natural bone in both main hierarchical ...

The retarding influence of polyacrylate and polyphosphate on the nucleation of calcium sulphate was investigated. SEM analyses show that these inhibitors didn�t only influence the nucleation kinetics but also the precipitate morphology by adsorption onto crystal growth sites. The influence of different concentrations of the additives on the mineralogy of solid precipitated was also examined. ...

Craters and earth voids are quickly filled with a high-strength, quick-setting cement composition comprising a mixture of cement material consisting essentially of from about 9.5 to about 4 Pt. by wt of calcium sulfate hemihydrate to about 0.5 to about 6 Pt. by wt of Portland cement and water which is present in a quantity of from about 22% to about 70% by ...

In this work, the technology of using pressurized fluidized-bed combustor ash to produce a heat insulator by curing with steam at low temperature was studied and developed. It was found that (1) the produced heat insulator mainly consists of calcium silicate hydrates, calcium aluminate sulfate, and hemihydrate gypsum, (2) the produced heat insulator has ...

Nanoparticles of calcium sulfate (nCS) have potential advantages as a ceramic matrix, scaffold and/or vehicle for delivering growth factors for osseous regeneration in a variety of clinical situations. The objectives of this study were to synthesize and characterize nanoparticles of hemihydrate calcium sulfate (nCS) and to develop a ...

Flue gas desulfurization (FGD) gypsum mainly composed of calcium sulfate dihydrate (DH) was used as a raw material to obtain alpha-calcium sulfate hemihydrate ({alpha}-HH) through dehydration in a Ca-Mg-K-Cl-solution medium at 95{sup o}C under atmospheric pressure. The effects of potassium sodium tartrate and sodium citrate on the ...

pH is one of the most important parameters that determine the crystallization process, but it is always neglected in the preparation of {alpha}-calcium sulfate hemihydrate ({alpha}-HH) from calcium sulfate dihydrate (DH) with the hydrothermal method. Flue gas desulfurization (FGD) gypsum, which is mainly composed of DH, was used as raw ...

A process for removing, from spent electroless metal plating bath solutions, accumulated byproducts and counter-ions that have deleterious effects on plating. The solution, or a portion thereof, is passed through a selected cation exchange resin bed in hydrogen form, the resin selected from strong acid cation exchangers and combinations of intermediate acid cation exchangers with strong acid ...

A process is described for removing, from spent electroless metal plating bath solutions, accumulated byproducts and counter-ions that have deleterious effects on plating. The solution, or a portion thereof, is passed through a selected cation exchange resin bed in hydrogen form, the resin selected from strong acid cation exchangers and combinations of intermediate acid cation exchangers with ...

Starting from calcium sulfate (gypsum) as fermentation byproduct of lactic acid production process, high-performance composites have been produced by melt-blending polylactide (PLA) and beta-anhydrite II (AII) filler, i.e., calcium sulfate hemihydrate previously dried at 500 degrees C. Characterized by attractive properties due to good ...

This study was aimed to create strontium-calcium sulfate compounds for making a new bioactive material with osteoconductive and osteoinduceable activity for bone repairing. Its mechanics and degradation features were assessed in vitro. Powders of alpha-calcium sulfate hemihydrate (alpha-CSH) and SrCl2 were mixed completely to make ...

The conversion of newly developed three dimensionally printed calcium sulfate hemihydrate (70-90% wt/wt CaSO(4).0.5.H(2)O) based materials to calcium phosphate bioceramics by phosphorization in di-sodium hydrogen phosphate solution at 80 degrees C for 4, 8, 16 and 24 h was studied. It was found that transformation rate, phase composition and mechanical ...

PURPOSE: The aim of this investigation was to evaluate clinical and histological outcome of using medical grade calcium sulfate hemihydrate (MGCSH) mixed with platelet-rich plasma (PRP) for extraction socket preservation graft prior to implant placement. MATERIALS AND METHODS: This study was a single-site, randomized and controlled investigation. Sixteen ...

In the present study new calcium sulfate-based nanocomposite bone cement with improved physicochemical and biological properties was developed. The powder component of the cement consists of 60�wt% ?-calcium sulfate hemihydrate and 40�wt% biomimetically synthesized apatite, while the liquid component consists of an aqueous ...

Daptomycin is a new antibiotic active against many resistant Gram-positive organisms and seems an appropriate candidate for local delivery for severe musculoskeletal infections. Calcium sulfate dihydrate as a delivery vehicle is readily resorbable, allows new bone formation, and can be combined with therapeutic agents. We compared the elution of daptomycin and tobramycin in ...

A process for reducing radioactive contamination of phosphogypsum. Phosphogypsum containing radioactive material is calcined to form hemihydrate crystals carrying the radioactive contaminants, and a portion of the crystals is converted to substantially radiation-free gypsum crystals which are readily separated from the hemihydrate crystal relics containing ...