Purification of phosphoric acid from waste acid etchant using layer melt crystallization

Spent acid etchant is the corrosive waste coming from the etching process of semiconductor manufacturing plants. This waste solution consists of phosphoric acid, nitric acid and acetic acid, and includes various toxic metallic impurities. In this work, the recovery of phosphoric acid from the waste etchant was conducted by removal of metallic impurities, nitric acid, and acetic acid, using static melt crystallization. The effect of cooling rate, amount of seeds, subcooling, and sweating on the distribution coefficient was investigated. Nitric acid and acetic acid were successfully removed by single-stage layer crystallization. The quantity of metallic impurities of the purified phosphoric acid was 1/1000 times smaller than that of the crude etchant.