Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4–NaCl–H2O system

Synthesis of zeolite Y from diatomite as silica source

“…The acid leaching step was also successful in decreasing the iron and magnesium contents five to ten fold. Sulfur was almost completely washed away by the acid treatment in sample aD3, which can be attributed to the dissolution of the gypsum crystals [33]. The fact that the SO 3 content remained unchanged in aD1 and even increased almost five fold in aD2 can most probably be related to insufficient washing to strip the sulfate ions originated from the sulfuric acid away.…”

Preparation of Anhydrous Calcium Sulfate Whiskers from Phosphogypsum in H₂O-H₂SO₄ Autoclave-Free Hydrothermal System

“…The formation of whiskers underwent threestage process. First of all, crystal nucleus of AH formed; secondly, self-assembly of AH possibly aggregated co-oriented along their c axes; in the end, the crystals grown along their c axes and formed acicular crystals 13) . AH usually crystallizes in the one-dimensional (1D) shape in free condition because the crystal lattice of AH are consisted of calcium and sulfur oxygen tetrahedron chains (-Ca-SO 4 -Ca-SO 4 -).…”

“…Anhydrous calcium sulfate whiskers (AH) can be used as reinforcers in friction materials because the whiskers do not fail at high work temperature (above 150 C) 9,11,12) . Wang et al 13) prepared HH whiskers by using ue-gas desulfurization (FGD) gypsum as raw materials in the H 2 O-H 2 SO 4 -NaCl system at 130 C for 60 min. Luo et al 14) explored results indicated that DH plates, HH whiskers and AH spindles were obtained in CaCl 2 -Na 2 SO 4 system at ≤100 C, 130-160 C and ≥170 C, respectively.…”

Effect of CuCl2 on hydrothermal crystallization of calcium sulfate whiskers prepared from FGD gypsum

“…Recently, much attention has been paid to calcium sulfate whiskers (CSWs), prepared from flue‐gas desulfurization (FGD) gypsum or phosphogypsum in hydrothermal solution . However, compared to CSWs prepared from high quality natural gypsum, the aspect ratio of these CSWs which were prepared from industrial byproduct was smaller (i.e., less than 120), and their diameters were non‐uniform.…”

“…However, compared to CSWs prepared from high quality natural gypsum, the aspect ratio of these CSWs which were prepared from industrial byproduct was smaller (i.e., less than 120), and their diameters were non‐uniform. Moreover, defects could be readily observed by scanning electron microscopy (SEM) images . When CSWs are applied in materials such as rubber and binder, defects and lower aspect ratios of CSWs would weaken the effect of enhancing strength and toughness of the composites .…”