This work presents a detailed description of urea decomposition during direct coagulation processing of alumina suspensions. We report on the chemical equilibria involved in the decomposition of urea in an aqueous environment with and without alumina particles. The model uses the logarithm of the concentrations as variables to ensure fast convergence and nonnegativity of the solutions, and is able to give a semiquantitative description of the experimentally observed development of pH and ionic strength (specific conductivity) during the decomposition of urea in a 30 vol % solid loading alumina suspension. Assuming local equilibrium, and a homogeneous distribution of the catalyst urease and the evolving educts, the results show an increasing solubility of CO2, with increasing pH. As a consequence the production of gaseous CO2, during the urea decomposition (direct coagulation casting (DCC) process), shifting the pH from 4 to 9 occurs only when a strong buffer is present at low and medium pH. This is advantageous for the preparation of defect-poor ceramic green bodies using this internal gellation reaction in the DCC process.