  The hydrothermal carbonation of calcium hydroxide (Ca(OH)2) at high pressure
of CO2 (initial PCO2 1/4 55 bar) and moderate to high temperature (30 and 90
1C) was used to synthesize fine particles of calcite. This method allows a high
carbonation efficiency (about 95% of Ca(OH)2-CaCO3 conversion), a significant
production rate (48 kg/m3 h) and high purity of product (about 96%). However,
the various initial physicochemical conditions have a strong influence on the
crystal size and surface area of the synthesized calcite crystals. The present
study is focused on the estimation of the textural properties of synthesized
calcite (morphology, specific surface area, average particle size, particle
size distribution and particle size evolution with reaction time), using
Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer-Emmett-Teller
(BET) measurements, and scanning electron microscope (SEM) and transmission
electron microscope (TEM) observations. This study demonstrate that the
pressure, the temperature and the dissolved quantity of CO2 have a significant
effect on the average particle size, specific surface area, initial rate of
precipitation, and on the morphology of calcium carbonate crystals. In
contrast, these PTx conditions used herein have an insignificant effect on the
carbonation efficiency of Ca(OH)2. Finally, the results presented here
demonstrate that nano-calcite crystals with high specific surface area (SBET
1/4 6-10m2/g) can be produced, with a high potential for industrial
applications such as adsorbents and/or filler in papermaking industry.
