The characteristics of nucleation and the crystal growth of aragonite-precipitated calcium
carbonate in Ca(OH)2 – MgCl2 – CO2 system by a carbonation process is investigated. MgCl2, in
this study, was added in order to increase the formation yield of aragonite precipitated calcium
carbonate. Optimum conditions of the concentration of the reactants, the temperature and the
amount of additives were studied. The formation yield of calcite gradually decreased, and the
formation yield of aragonite increased with the addition of MgCl2. A higher formation yield of
above 98% for aragonite is obtained by the adding of the Mg2+ ion in a 0.2M Ca(OH)2 – 0.6M
MgCl2 – CO2 system at 80. The nucleation rate increased as the temperature decreased and as the
CO2 gas flow rate increased. The particle size and aspect ratio increased at a high temperature, a
low flow rate of gas, and a high concentration of Ca(OH)2 slurry. Small-sized aragonite was
obtained at a low temperature. The increase in crystal size with the decrease in the CO2 gas flow
rate can be explained by the decrease in the nucleation rate, in addition to the increase in the crystal
growth rate resulting from the decrease in the dissolution rate to CO3
2- ion.
Characteristics of nucleation and crystal growth of aragonite precipitated calcium carbonate in Ca(OH)2 – MgCl2 – CO2 system via a carbonation process is investigated. Aragonite precipitated calcium carbonate with high aspect ratio was synthesized at high reaction temperature and concentration of Ca(OH)2 slurry. The increase in crystal size with decreased in CO2 gas flow rate can be explained by a decrease in the nucleation rate and an increase in the crystal growth rate caused by a decrease in the dissolution rate to CO3 2- ion. In this study, crystal growth of aragonite was investigated by adding aragonite seed. It was found that crystal growth of aragonite precipitated calcium carbonate could be controlled by three-step carbonation process using reactants as the Ca(OH)2. Aragonite with an aspect ratio from 5 to 27 and diameter from 3μm to 24μm was thereby grown at a reaction temperature of 80°C and a CO2 flow rate of 50ml/min. It was also found that MgCl2 aqueous solution can be used again in the carbonation process for the synthesis of aragonite precipitated calcium carbonate.
The objective of this study is to synthesize the single phase aragonite precipitated calcium carbonate by the carbonation process in the Ca(OH)2-MgCl2-CO2 system. Many researchers reported the influence of Mg2+ ion on the synthetic properties. The inhibition of calcite nucleation and crystal growth, distortion of calcite lattice, and change of surface electrification were investigated. Variety of particle size and aspect ratio were observed according to changes in the concentration of Ca(OH)2 slurry, temperature, and CO2 gas flow rate. The nucleation rate increased when decreasing the temperature and increasing the CO2 gas flow rate. Particle size and aspect ratio increased at high temperature, low CO2 gas flow rate, and high concentration of Ca(OH)2 slurry, however small-sized aragonite was obtained at low temperature.
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