Separation and recovery of acids from waste acid mixture mainly containing phosphoric acid discharged in liquid crystal display manufacturing process

A separation process of acids from waste etching acid mixture discharged in a liquid crystal display manufacturing process was established by using solvent extraction. Acetic and nitric acids were extracted from the waste acid mixture, and phosphoric acid, which was the main components, was left in the raffinate. Tri-octyl phosphate (TOP) was used as an extractant to extract acetic and nitric acids. Fundamental studies were carried out for extraction and stripping of acetic, nitric and phosphoric acids, and a demonstration test was conducted using a mixer-settler equipment. TOP selectively extracts acetic and nitric acids from the waste acid mixture mainly containing phosphoric acid. Extraction of acetic and nitric acids is approximately 100% by applying the continuous countercurrent extraction with a phase ratio (A/O) of 0.4 and 6-stage extraction using TOP as an extractant. Acetic and nitric acids extracted in TOP are stripped with water as a stripping agent at 99 % and 99.5% under the conditions of a phase ratio (O/A) of 1.0 and 4-stage stripping. In the demonstration test using a mixer-settler equipment, 95% of acetic acid and 98% of nitric acid in the waste acid mixture were extracted, and phosphoric acid was left in the raffinate to give crude phosphoric acid as a product.