Preparation of high purity boric acid and its influencing factors

Boric acid with high purity of 99.99% was prepared from borax with modified traditional techniques,including adopting HCl gas instead of chlorhydric acid solution to acidize borax,thereby reducing the introduction of impurities,ion exchange adsorption resin method and recrystallization process.The related effects of the three procedures on the purity and crystallization ratio of boric acid were investigated.The results show that the optimal experimental parameters during neutralization reaction are as follows: acidolysis temperature is 90 ℃,pH is 3-4,crystallization is under the condition of 8 ℃ for 8 h.During ion exchange adsorption,the volume ratio of anion versus cation is 3-1,the current velocity of boric acid solution is 8-10 mL/min.During recrystallization process,the concentration of boric acid solution is 28.5%-31.0%,and crystallization is at 10 ℃ for 15 h associated with slow stirring.Using scanning electronic microscope the final boric acid crystals are observed to be granular and fine.The impurity contents of ferrum,chloride and sulphate in the finished product meet the index of high purity boric acid.