Preparation of α-Calcium Sulfate Hemihydrate by Reaction of Sulfuric Acid with Lime

Abstract

Direct preparation of R-calcium sulfate hemihydrate out of sulfuric acid solution by reaction with lime under atmospheric pressure conditions is systematically investigated. Two preparation methods are investigated: one involving addition of dry lime to sulfuric acid solution (standard procedure) and the other involving addition of sulfuric acid solution to slaked lime (reverse procedure). On the basis of the standard procedure, the operating window is first determined, followed by thorough examination of preparation conditions such as acidity, retention time and CaO/H 2 SO 4 molar ratio. Dihydrate was found to form as intermediate phase that converts to hemihydrate under all tested conditions. The typical morphology of R-hemihydrate crystals produced by the standard procedure is needle-shaped with 50-100 µm length and 1-3 µm thickness. However, when the reverse procedure was used, a different growth mechanism apparently applied yielding shorter (∼60 µm) but thicker (5-10 µm) column-shaped crystals within otherwise the same operating window.

The crystal growth kinetics of alpha calcium sulfate hemihydrate in concentrated CaCl2–HCl solutions

“…Differential Scanning Calorimetry for the identification of α-HH was done on a Netzsch STA 449 F3 Jupiter thermal analyzer setting the heating rate to 10 K/min under inert gas atmosphere with an Argon flow of 30 mL/min. This technique has shown to be capable of differentiating between α-HH and β-HH [37]. Finally, filtrates were analyzed for calcium and sulfate with a Dionex ICS 5000 ion chromatograph.…”

Calcium Sulfate Hemihydrate Powders with a Controlled Morphology for Use as Bone Cement

“…6 So far, a number of manufacturing methods have been developed for the preparation of CSH, including heat treatment of CSD using water, inorganic acids, or condensed inorganic salt solutions under high or atmospheric pressure. [7][8][9] From the viewpoint of its practical use as bone cement, it is preferred that the CSH powder has a spherical shape (or a low aspect ratio) for the purpose of enhancing its injectability and mechanical properties. 10,11 However, only a few attempts have been made to modify the shape of the CSH particle by varying the salt concentration during heat treatment in the presence of surfaceactive substances.…”

Preparation of High Percentage <i>α</i>-Calcium Sulfate Hemihydrate via a Hydrothermal Method

“…Nowadays, the management and utilization of FGD gypsum have become a significant issue [1]. Preparation of calcium sulfate hemihydrate (HH, CaSO 4 ·0.5H 2 O) utilizing DH as raw material is one of the most promising alternatives to recycle DH and also manufacture HH which is a very useful material especially in the building industry [2] [3] [4]. There are two types of HH: α-form and β-form.…”

“…[3] [7]. Due to α-HH's better paste workability and higher mechanical strength of the hardened material, it exhibits a notably advantageous performance over β-HH in a wide range of fields, such as modern construction industry, molding, binder system, orthopedic and other medical applications [2] [6].…”

“…Commercial production of α-HH involves converting FGD gypsum to α-HH at elevated temperature (100˚C -150˚C) under elevated pressure (138 -414 KPa) in an atmosphere of saturated vapor in an autoclave, which is known as Autoclave Method [2] [4]. It has been widely reported that α-HH can also be prepared by heating FGD gypsum in various salt or acid solutions near boiling point under atmospheric pressure, which is termed as Hydrothermal Method [2] [13] [14] [15].…”