Determination of nucleation, growth, agglomeration and disruption kinetics from experimental precipitation data: the calcium oxalate system

The precipitation kinetics of calcium oxalate CaC(2)O(4), are studied at the laboratory scale using a 300 mi draft tube baffled (DTB) precipitation reactor. The vessel is operated continuously at 37 degrees C at different residence times, feed concentrations, stirrer speeds and with feed point locations inside and outside the draft tube. A new procedure is introduced to solve the inverse problem and determine the kinetic parameters for nucleation, growth, agglomeration and disruption from the particle size distribution. Crystal growth rates indicate a surface-integration-controlled mechanism with a second-order dependence on absolute supersaturation, while the nucleation rates are dependent on the power input and the feed point position, and therefore suggest a mixing-controlled nucleation process. The disruption rates obtained account for breakage due to both particle splitting and attrition, and increase linearly with power input. The agglomeration rates, in contrast, exhibit a maximum with increasing power inputs. Thus, it is inferred that both decreased agglomeration efficiency and increased breakage lead to a decrease in the number of agglomerates observed at higher stirrer speeds. (C) 2000 Elsevier Science Ltd. All rights reserved.