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

The precipitation kinetics of calcium oxalate CaC2O4, are studied at the la boratory scale using a 300 mi draft tube baffled (DTB) precipitation reacto r. The vessel is operated continuously at 37 degrees C at different residen ce 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, gr owth, agglomeration and disruption from the particle size distribution. Cry stal 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 th erefore suggest a mixing-controlled nucleation process. The disruption rate s obtained account for breakage due to both particle splitting and attritio n, and increase linearly with power input. The agglomeration rates, in cont rast, 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.