Dissolution of finely ground limestone particles in acid solutions

Batch dissolution of fine limestone particles in HCl solutions was studied in a baffled tank reactorstirred with a Rushton turbine using a pH-drift technique. The effects of both acid strength andstirring rate were analyzed by varying the initial pH in the range of 3.7-5 and the impellerReynolds number in the range of 104-105. The main experimental result is that, after a veryfast step that leads to a quick rise of the solution pH, the dissolution rate is strongly affected byCO2 gas-liquid mass transfer, the intensity of which depends on the rate of stirring. A diffusionalmodel based on film theory was used to analyze the data. The model confirmed that, for theoperating conditions considered, a very short time is necessary for the first step of the dissolutionprocess to take place. Furthermore, by taking into account the two limiting cases of the absenceof CO2 gas-liquid transport and of infinitely fast transport, it was possible to identify lowerand upper bounds for the experimental Ca2+ concentration.