Dissolution of Finely Ground Limestone Particles in Acidic Solutions

Batch dissolution of fine limestone particles in HCl solutions was studied in a baffled tank reactor stirred with a Rushton turbine using a pH-drift technique. The effects of both acid strength and stirring rate were analyzed by varying the initial pH in the range of 3.7−5 and the impeller Reynolds number in the range of 10 4 −10 5 . The main experimental result is that, after a very fast step that leads to a quick rise of the solution pH, the dissolution rate is strongly affected by CO 2 gas−liquid mass transfer, the intensity of which depends on the rate of stirring. A diffusional model based on film theory was used to analyze the data. The model confirmed that, for the operating conditions considered, a very short time is necessary for the first step of the dissolution process to take place. Furthermore, by taking into account the two limiting cases of the absence of CO 2 gas−liquid transport and of infinitely fast transport, it was possible to identify lower and upper bounds for the experimental Ca 2+ concentration.