Hydrofluoric Acid Recovery from Waste Semiconductor Acid Solution by Ion Exchange

Recovery of hydrofluoric acid (HF) from waste semiconductor acid solution by ion exchange was investigated. Strong base anionic and strong acid cationic ion exchange resins were involved in the recovery process. The former was used to capture the fluoride in the waste acid solution while the latter was employed for exchanging hydrogen ion for sodium in the NaF solution resulting from regeneration of the anion exchanger with NaOH. The ion exchange process consisted of two ion exchange steps and two regeneration steps. Batch experiments were conducted to determine the equilibrium ion exchange capacities and to develop ion exchange isotherms. Column tests were made to examine the performances of continuous ion exchange operations under conditions of different feed flow rates and inlet acid concentrations. A simplified model based on the general logistic function was adopted and tested for describing the solute breakthrough behaviors of the exit aqueous solution. Regeneration of exhausted ion exchange resins was also examined to test their effectiveness for repeated use. The hydrofluoric acid recovered by the ion exchange process would be available for reuse. It could also be converted by calcium chloride to high-purity calcium fluoride.