| Summary: | 碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系碩士在職專班 === 102 === CaF2 powders can be produced rapidly by reacting waste crystalline calcium (crystalline CaCO3 is primary) collected form purification plants with high concentration waste hydrofluoric acid solution discharged from the electro-optical, semiconductor or hydrochlorofluorocarbons (HCFCs) industry. Therefore, in this study, the effects of operating parameters, including the particle size of crystalline calcium (0.34~1 mm, < 0.34 mm), initial F/Ca molar ratio, initial hydrofluoric acid concentration ([HF]i), reaction temperature (25℃, 50℃), reaction time (0~60 min), and mixing conditions (stirring method, stationary method) on the removal efficiency of HF solution and conversion of crystalline calcium (expressed as CaCO3), were demonstrated.
The results showed that stirring the small particle of crystalline calcium (< 0.34 mm), at a lower F/Ca ratio and a higher reaction temperature could enhance the removal efficiency, while at a higher feeding F/Ca ratio could result in a higher conversion of CaCO3. In order to accomplish a higher conversion of CaCO3 with preprocessing a high concentration of waste HF solution, a two-stage processes were proposed in this study. The first stage is to simulate the continuous stirred-tank reactor (CSTR) via stirring the reactants at 25℃ and inlet F/Ca ratio = 5 conditions. After reacting 40 mins/cycle for 3 cycles, the residual concentration of HF discharged reduced to 26,900 mg/L from a high concentration of [HF]i (100,000 mg/L), with the conversions of CaCO3 were between 71.1% ~ 80.8%. Afterwards, to simulate a packing bed reactor (PBR) by stationary method at second stage, an initial concentration of HF, 30,000 mg/L could be decreased to 4,580 mg/L with a conversion of CaCO3 of 84.3% at 25℃ and F/Ca ratio = 5 condition. It can be concluded that conversion of CaCO3 could raise to over 90% with a HF concentration of less than 3,000 mg/L ([HF]in = 100,000 mg/L) by reasonably increasing the reaction temperature.
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