Crystallization Kinetics of High Purity Boric Acid in Preparation Process

High purity boric acid was prepared by HCl acidification of borax combined with recrystallization and ion resin exchange. Some influential factors on the crystallization process of H3BO3-NaCl-H2O system such as supersaturation, crystallization temperature and time, stirring speed, and impurity in the solution were studied. The results show that with the solution concentration at 18.26%, and final crystallization temperature 10℃ held for 480 min, stirring speed 300 r/min, and proper cooling, the formation of boric acid crystals has been optimally achieved. The rate of crystallization can be over 83%, and the crystals are fine granules. NaCl can accelerate boric acid crystallization in the system. Based on the experimental data, the curve of crystallization kinetics is gained and kinetics equation formed with the reaction order of 2.