| Summary: | 碩士 === 元培科技大學 === 環境工程衛生研究所 === 101 === Fluorite (CaF2) sludge generated by the semiconductor industries is becoming a heavy environmental loading. In 2010, the Taiwan Environmental Protection Administration (Taiwan EPA) estimated that the annual amount of the waste fluorite sludge was more than 38,000 tonnes. Partially due to over-dosage in operation, the fluorite slurry bearing a high calcium chemical has led to be treated as industrial waste by landfill process. In recent years both of the limited land space and environmental awareness have gradually reduced the landfill process in Taiwan. This study developed a purifying process to increase the CaF2 content by adding hydrofluoric acid (HF) to the calcium-bearing fluorite sludge. Results from the precipitation experiments indicate that through the adjustment of HF amount, the CaF2 content in the fluorite can be increased from 30% to 80% as expected. The resulting fluorite products were characterized by the energy dispersive X-ray (EDX) and Scanning Electron Microscopy (SEM). Spectra analysis confirms that the obtained product is CaF2. HF containing H3PO4 and H2SO4, respectively, was also investigated in this study. Experimental results show that as the mole ratio of [H3PO4]/[HF] or [H2SO4]/[HF] increases, from 0.05 to 0.5, the CaF2 content in fluorite gradually decreases, up to 15 %. The decrease of the CaF2 purity in the fluorite products can be attributed to the increase of calciumproducts such as Ca3(PO4)2 and CaSO4. This study concludes that adding HF to the fluorite sludge is a feasible waste reuse technology. In addition, the HF containing acid that may react with calcium should be taken into account to avoid the loss of CaF2 purity.
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