Abstract:
The present work examines the chemical absorption of carbon dioxide (CO2) gas in aqueous calcium hydroxide (Ca(OH)(2)) slurries, which leads to the precipitation of calcium carbonate. Carbonation of the Ca(OH)(2) slurry is an important method for the industrial manufacture of precipitated calcium carbonate (PCC), wherein the hydroxide particles are gradually converted to carbonate. Experimental data have been generated by contacting CO2 with an aqueous Ca(OH)(2) suspension in a model gas-liquid, stirred contactor, under different operating conditions. It is not possible to distinguish between the different types of particles present in the system (hydroxide, carbonate, mixed particles) "visually". Therefore, the particle size distribution of all the particles present has been obtained using microscopy and optical image analysis techniques. The conversion of hydroxide-to-carbonate is determined by titration. A modeling approach that assumes that the hydroxide particles get converted by the diffusion of dissolved CO2 into its internal parts (as is observed in a "shrinking core" scenario), coupled with a population balance to describe the size distribution of the unreacted particle cores has been formulated. The experimental and theoretical conversions agree reasonably well.