The outcome of gas-liquid precipitation in industrial reactors, such as bubble columns, is determined by the interplay between multiphase fluid dynamics; gas-liquid reaction engineering; and crystallization mechanisms such as nucleation, growth, and agglomeration. In this work, a modeling approach that takes the above phenomena into account is proposed and applied to investigate the semibatch precipitation of CaCO3. The main elements of the approach are a dynamic population balance equation including nucleation, growth, and agglomeration, discretized with a finite element method; a phenomenological model of interfacial mass transfer and reaction based on penetration theory; and rigorous prediction of gas holdup via an Eulerian-Eulerian multiphase CFD code. Experiments on CaCO3 precipitation via reaction of CO2 and Ca(OH)(2) in a 21-L bubble column are conducted and simulated with the aid of the model. The evolution of the process is adequately reproduced, and qualitative comparisons with the product CSD are possible, but more fundamental work on precipitation kinetics in the gas-liquid hydrodynamic environment is required to obtain quantitative agreement.