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

Abstract The precipitation kinetics of calcium oxalate CaC 2 O 4 are studied at the laboratory scale using a 300 ml draft tube baffled (DTB) precipitation reactor. The vessel which is operated continuously at 37°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, and agglomeration 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.

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