Crystallization of Boric Acid through Reactive Dissolution of Oxalic Acid Crystals in Aqueous Borax Solution

Abstract In the reaction between solid oxalic acid and aqueous borax solution, product boric acid precipitates in the solution phase after complete dissolution of oxalic acid crystals. This makes it possible to measure the dissolution and precipitation kinetics independently. The oxalic acid dissolution process was found to be diffusion controlled. Nucleation rates of product boric acid were influenced by heterogeneous primary nucleation and secondary nucleation, while growth rates were affected by both the bulk diffusion and surface integration processes. Dissolution of oxalic acid ctystals was described by a surface reaction model, and overall nucleation and growth rates were correlated in terms of the influencing process variables. Simulation analysis was carried out by linking the two processes of dissolution and precipitation in series. The trends of the predicted supersaturation profiles, number concentration, magma density and mean size of the product crystals are in good agreement with measured values.