Sustainable treatment of HF wastewaters from semiconductor industry with a fluidized bed reactor

Within the semiconductor industry, large volumes of hydrogen fluoride (HF) containing wastewaters need to be treated. This paper describes a technique that makes it possible to treat HF wastewater with virtually no waste production. A method based on crystallization of CaF₂ on sand particles in a fluidized bed reactor, with trade name Crystalactor, was assessed for the first time with real wastewater originating from a semiconductor prototyping line. Several process parameters were investigated such as influent fluoride concentration, calcium reagent excess, pH, single versus multiple calcium reagent dosing, etc. It can be concluded that the performance of the reactor is greatly dependent on the initial concentrations of calcium and fluoride at the bottom of the reactor (referred to as local saturation). The original hardware design was changed from a single reagent dosing to a multiple reagent dosing to prevent too high local supersaturation values of fluoride and calcium and thus obtain higher CaF₂ crystallization efficiencies. Fluoride loads up to 7 kg/m²·h were still possible with multiple reagent dosing, compared to a maximum treatable load of 3.5 kg/m²·h for single reagent dose. Additionally, an alternative post-treatment process based on replacement of calcite by fluorite in a granular calcite column is demonstrated.