RECOVERY OF PHOSPHORIC ACID FROM WASTE ACID MIXTURE WITH SOLVENT EXTRACTION

By applying a solvent extraction method for the etching waste solution discharged \nfrom the manufacturing process of liquid crystal display, the removal of acetic acid \nand nitric acid were carried out from the waste acid mixture containing phosphoric, acetic and nitric acids to obtain phosphoric acid as the raffinate. Fundamental studies on the recovery of phosphoric acid were conducted by using Tri-octyl phosphate (TOP) as the extractant for acetic acid and nitric acid. From the results, demonstration tests using a mixer-settler equipment were carried out to obtain crude phosphoric acid. Acetic and nitric acids were selectively extracted by TOP from the waste acid mixture, which contains phosphoric acid as a main component. From the McCabe Thiele analysis, almost all of the acetic and nitric acids were removed by a countercurrent multi-extraction operation of phase ratio(A/O) 0.4 and 6-stage. When TOP loading acids was contacted with the water under the countercurrent operation \nconditions of phase ratio (0/A) 1.0 and 4-stage, 99% of acetic acid and 99.5% of nitric acid were stripped from the organic phase, respectively. From these results obtained by the fundamental studies, a demonstration test was carried out for the extraction of acetic and nitric acids by using a mixer-settler equipment. Consequently, the extractions of acetic and nitric acids in the waste acid mixture were about 95% and 98%, respectively, and crude phosphoric acid can be obtained as a raffinate after the solvent extraction.