Effects of Impurities on CaSO₄ Crystallization in the Ca(H₂PO₄)₂–H₂SO₄–H₃PO₄–H₂O System

Abstract

Wet-process phosphoric acid is a fundamental process in the fertilizer industry. The influence of impurities on crystallization kinetics of CaSO 4 was investigated in the Ca(H 2 PO 4 ) 2 –H 2 SO 4 –H 3 PO 4 –H 2 O system using a mixed suspension mixed product removal crystallizer. Effects of Si, Al, Fe, Mg, K, and Na on crystal morphology and structure were examined in the highly acidic system through scanning electron microscopy and high-resolution transmission electron microscopy. Results show that the increase of Mg, K, and Na content facilitates crystal growth. Si, Al, and Fe are beneficial to CaSO 4 crystal growth at a certain concentration range. Impurities also affect the crystal morphology, and the addition of Si, Fe, and Na promotes the formation of needle-like crystals compared with other impurities. X-ray diffraction results show that the preferred crystal growth direction is (020), and the interplanar spacing of the crystals is affected by the element radius of the impurities.

Bone Healing and Regeneration Potential in Rabbit Cortical Defects Using an Innovative Bioceramic Bone Graft Substitute

“…The dehydration method is prone to creating certain impurities like β-calcium sulfate hemihydrate and anhydrite as the byproduct since this method is unable to control the variations in temperature and pressure [30]. These impurities will affect the crystal size and morphology with elongated crystals that eventually reduce the mechanical and biological properties [31,32]. On the other hand, the microwave-irradiation treatment can synthesize high-purity bone graft substitute without sacrificing any useful mechanical or biological properties with controllable temperature and pressure, a great heating rate, and a homogeneous reaction temperature of volume [33].…”

Rapid Micelle-Mediated Size-Controlled Fabrication of Calcium Sulfate Nanorods Using Silver Nanoparticles

“…In view of previous reports that the morphology of calcium sulfate materials can be altered or manipulated by careful variation of pH or acid concentration, ,− the effects of pH and nitric acid addition were briefly examined.…”

Gamma‐CaSO4 With Abnormally High Stability From a Hyperarid Region on Earth and From Mars

“…There are some laboratory experimental studies about the effect of impurity on the morphological appearance of precipitated Ca‐sulfates, especially of bassanite. The tested additive impurities include Poly(acrylic acid), Poly(sodium‐4‐styrene sulfonate), sodium triphosphate, magnesium chloride hexahydrate (Wang & Meldrum, 2012), and Si, Al, Fe, Mg, K, Na, $${\mathrm{P}\mathrm{O}}_{4}^{3-}$$ (Mu et al., 2019). Their observations revealed the changes in microscopic morphology of the formed nanocrystals of bassanite.…”