Effects of emulsified asphalt on the mechanical properties of granulation of calcium fluoride sludge
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ORIGINAL ARTICLE
Effects of emulsified asphalt on the mechanical properties of granulation of calcium fluoride sludge Keng‑Ta Lin1 · Ya‑Fen Wang2 · Bo‑Shng Jhng3 · Cheng‑Hsien Tsai3 Received: 7 June 2020 / Accepted: 18 September 2020 © Springer Japan KK, part of Springer Nature 2020
Abstract To reduce the landfill volume of waste CaF2 sludge, artificial fluorite bulk (AFB) is granulated by blending CaF2 sludge and emulsified asphalt (EA) for the use of flux in this study. Results showed that high stability of micron-sized EA can be successfully prepared and used to granulate CaF2 powders to form AFB. EA has high-dispersivity with the particle size being measured in the range of 1–8 μm by optical microscope examination from an optimal emulsifiers ratio (CTAB (cetrimonium bromide)/OP-10 (commercial surfactant mixtures) = 75/25), and a high rotational speed in the homogenizer (20,000 rpm). Moreover, with the optimal addition of 12.5% asphalt, the prepared AFB pellets present the highest mechanical strength, reaching 9.88 kgf/cm2 and 4.06 kgf/cm2 for the uniaxial compressive strength and flexural strength, respectively. The optimal 12.5% addition also satisfies the requirement of the steelmaking process by passing the tumble-test quality examination. The analyses also infer that the cohesiveness of AFB is mainly combined through physical combination forces, including Van der Waals force, bridging action, and mechanical mosaic force. This occurs without triggering new chemical bonding. Keywords Calcium fluoride sludge · Emulsified asphalt · Flux · Granulation · Adhesion force
Introduction Hydrofluoric acid (HF) is commonly used for surface treatment, cleaning and etching in semiconductor, solar panel, and photovoltaic cell manufacturing processes. However, waste hydrofluoric acid solution is still harmful and should be converted into stable and harmless calcium fluoride (CaF2) sludge through a fluorine industrial wastewater treatment process. The quantity of C aF2 sludge from wastewater treatment in high technical industry is enormous, reaching more 30 thousand tons/year in Taiwan. The chemical precipitation method of adding calcium salts [1] was often adopted to remove fluorine-containing species. The removal
* Cheng‑Hsien Tsai [email protected] 1
Office of General Affairs, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan
2
Department of Environmental Engineering, Chung Yuan Christian University, Chung‑Li, Taiwan
3
Department of Chemical and Materials Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan
of fluoride also was proposed using a fluidized-bed crystallizer [2, 3] or cryolite crystallization [4]. Natural fluorite minerals (fluorspar) are an important source of fluorine chemicals and are widely used in the steelmaking, ceramics and glass industries [5]. Fluorspar is mainly composed of Ca and F ( CaF2) with trace amounts of Fe, Pb, Cl, U, Zn, and rare earth elements. It also divided into chemical, ceramic, and metallurgic
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