Application of reutilization technology to calcium fluoride sludge from semiconductor manufacturers

Optimization of Calcium Fluoride Crystallization Process for Treatment of High-Concentration Fluoride-Containing Semiconductor Industry Wastewater

This study utilized a fluidized bed reactor (FBR) for fluoride removal from high-concentration fluoride-ion-containing simulated semiconductor industry wastewater and recovered high-purity CaF2 crystals. The effects of hydraulic retention time (HRT), pH, Ca2+ to F- ratio, upflow velocity, seed size and seed bed height were investigated by performing lab-scale batch experiments. Considering fluoride removal and CaF2 crystallization efficiency, 5 h HRT, pH 6, seed height of 50 cm and [Ca2+]/[F-] ratio of 0.55 (mol/mol) were found to be optimum. The effect of the interaction between the important process parameters on fluoride removal was further analyzed using response surface methodology (RSM) experimental design. The results showed that all the individual parameters have a significant impact (p = 0.0001) on fluoride removal. SEM-EDX and FTIR analysis showed the composition of the crystals formed inside FBR. HR-XRD analysis confirmed that the crystalline structure of samples was mainly CaF2. The results clearly demonstrated the feasibility of silica seed material containing FBR for efficient removal and recovery of fluoride as high-purity calcium fluoride crystals.

Recycle of synthetic calcium fluoride and waste sulfuric acid to produce electronic grade hydrofluoric acid

An innovative method for utilizing synthetic calcium fluoride (CaF₂), recovered from fluoride-containing semiconductor wastewater, and waste sulfuric acid (H₂SO₄) to produce hydrofluoric acid (HF) was investigated. The research was set to study the low-temperature production of HF via reaction of synthetic CaF₂ and waste H₂SO₄. The impact of four factors, including H₂SO₄ concentration, total volume (H₂SO₄ + H₂O)/CaF₂ ratio, drying temperature of synthetic CaF₂, and reaction carried out under different temperature, on HF productivity was investigated in this study. HF yield increased with increasing H₂SO₄ concentration and total volume/CaF₂ ratio under room temperature. Generally, reactions carried out under low-temperature (< 100 °C) had a positive impact on HF yield. The higher temperature led to an increase in absorbed-HF but a decrease in total-HF. The reaction of commercial CaF₂ and 70% H₂SO₄ had a higher absorbed-HF yield of 61.7% than synthetic CaF₂ and 70% waste H₂SO₄, which had a yield of 36%. This was due to the higher purity of the commercial CaF₂ and fewer interference ions in H₂SO₄. HF productivity was lowered by CaSO₄, which hindered the reaction of reactants and also the generation of fluorosulfuric acid.

Efficient Removal of Fluoride by Complexation Extraction: Mechanism and Thermodynamics

A complexation extraction system was designed to develop a new process for the efficient removal of fluoride from solutions, such as zinc or copper electrolytes or wastewater derived from flue gas. The effects of the boron fluoride molar ratio, organic phase composition, initial pH, temperature, and phase volume ratio on the extraction efficiency were investigated. The extraction efficiency was found to increase with the increase in the boron fluoride molar ratio, Alamine336 concentration, and phase volume ratio, whereas it decreased with the increase in temperature. For the simulated electrolyte or wastewater derived from flue gas, the majority of metallic ions were insensitive to the extraction, with the exception of Al³⁺ and Fe³⁺. Fluoride decreased from 5 g/L to 0.05 g/L after two-stage cross-flow extraction alone; with an extraction efficiency of 99%. Both the stripping and cycling properties were excellent when sodium hydroxide was employed as the stripping reagent. Furthermore, the loading capacity was 43.4 g/L, and increased by four times, when boric acid was added. This novel process implies a wide range of potential applications, such as the removal of unwanted fluoride ions from various high-fluoride polluted solutions and the simplification of brine phase diagram.

The Prospective Approach for the Reduction of Fluoride Ions Mobility in Industrial Waste by Creating Products of Commercial Value

In this work, we present the possibility to reduce the amount of fluoride ions in silica gelwaste by using different techniques or to immobilize these ions by creating products ofcommercial value. The leaching of fluoride ions from silica gel waste to the liquid medium wasdone under static and dynamic conditions. It was determined that the removal of fluoride ionsfrom this compound depends on various factors, such as dissociation, solubility, the w/s ratio,reaction temperature, leaching conditions, the adsorption properties of silica gel waste, and others.The obtained results showed that, by applying different techniques, the quantity of fluoride ionscan be reduced by 60%, while obtained water was neutralized by calcium hydroxide.Additionally, it was determined that silica gel waste is a promising raw material for thehydrothermal synthesis of a stable compound containing fluoride ions – cuspidine.