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Production of Anhydrous Zirconium Tetrafluoride from Plasma Dissociated Zircon and Ammonium Bifluoride

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Production of Anhydrous Zirconium Tetrafluoride from Plasma Dissociated Zircon and Ammonium Bifluoride International Conference on Chemical, Mining and Metallurgical Engineering (CMME'2013) Nov. 27-28, 2013 Johannesburg (South Africa) Production of Anhydrous Zirconium Tetrafluoride from Plasma Dissociated Zircon and Ammonium Bifluoride Milton M. Makhofane, Johann T. Nel, Johan L. Havenga, and Ayo S. Afolabi methods are that the starting materials are expensive and Abstract—Zirconium tetrafluoride is used as a catalyst for hydrogen fluoride is extremely hazardous to work with. the production of chlorofluoro-hydrocarbons and to In 2010, Nel, et al. [11] registered a patent for the manufacture zirconium tetrafluoride based glass. The production of zirconium tetrafluoride by reacting plasma traditional methods of producing zirconium tetrafluoride dissociated zircon with ammonium bifluoride. In 2011, involve fluorinating zirconium oxide, chlorides, etc. with Makhofane et al. [12] presented a paper on the production of aqueous or anhydrous hydrogen fluoride. In this work, zirconium tetrafluoride from the method patented by Nel et al. zirconium tetrafluoride was manufactured from plasma [11] at the ZrTa2011 New Metals Development Network dissociated zircon and ammonium bifluoride in a batch reactor Conference. This paper was a follow up on the paper system. It was confirmed by XRD analysis that zirconium presented at this conference and presents the details on the tetrafluoride was produced with a purity of 82.87%. The batch purity of the synthesized zirconium tetrafluoride and efficiency reactor system was 93.85% efficient. of the batch reactor system used. The production of zirconium tetrafluoride in the batch reactor system follows the reactions Keywords—ammonium bifluoride, Plasma dissociated zircon, in Equations 1-4. batch reactor, efficiency. ZrO2.SiO2 + 8NH4HF2→ (NH4)3ZrF7 + (NH4)2SiF6 + 3NH4F + I. INTRODUCTION 4H2O (1) IRCONIUM tetrafluoride together with zirconium oxide (NH4)3ZrF7 → (NH4)2ZrF6 +NH3 + HF (2) Z and partially fluorinated zirconium oxide are being used as (NH4)2ZrF6 → NH4ZrF5 + NH3 + HF (3) a catalyst for the fluorination of chloro-hydrocarbon to NH4ZrF5 → ZrF4 + NH3 +HF (4) chloro-fluoro hydrocarbons [1-3]. Other uses of zirconium tetrafluoride include the synthesis of zirconium fluoride based II. PROCEDURE glass, where this glass exhibit high optical transparency from the near ultraviolet (0.20 μm) to the mid-infrared (8 μm) in the A. Reagents electromagnetic wavelength spectrum. These zirconium Plasma dissociated zircon (ZrO2.SiO2) with a purity ≥ 95% fluoride based glasses are used in the production of laser was manufactured at The South African Nuclear Energy windows, fiber optic elements and Faraday rotators [4-6]. Corporation SOC Ltd. (Necsa) by subjecting zircon to high The traditional methods of producing zirconium temperatures, approximately 2500°C, in the flame of a non- tetrafluoride involve fluorination of zirconium compounds transferred arc plasma reactor. This process was followed by (oxides, chlorides, oxychlorides, hydroxides and nitrates) with rapid quenching of the product to form the plasma dissociated aqueous or anhydrous hydrogen fluoride. These methods have zircon [13]. The plasma dissociated zircon was used without been well documented in the US Patent office since 1953 [7- further treatment. Ammonium bifluoride (NH4HF2) of 10]. However, the major drawbacks to these traditional analytical grade (Sigma-Aldrich, South Africa) was used without further treatment. Milton M. Makhofane is with Plasma Technology, Applied Chemistry, Research and Development, South African Nuclear Energy Corporation SOC B. Process and equipment description Ltd, P O Box 582, Pretoria, 0001, South Africa and Department of Civil and The production equipment consists of a reactor, a cold trap, Chemical Engineering, College of Science, Engineering and Technology, a cyclone, a Fourier Transform Infrared spectrometer (FTIR) University of South Africa, P/Bag X6, Florida 1710, Johannesburg, South Africa. Tel: +27721367377; E-mail: [email protected]. and utilities (Figure 1). The utilities consist of hydrofluoric Johann Nel, Plasma Technology, Applied Chemistry, Research and acid scrubber, potassium hydroxide scrubber, a vacuum pump Development, South African Nuclear Energy Corporation SOC Ltd, PO Box and a cooling water circuit (not shown in the Figure). The 582, Pretoria, 0001, South Africa reactor is heated externally with a ceramic band heater having Johan Havenga, Plasma Technology, Applied Chemistry, Research and Development, South African Nuclear Energy Corporation SOC Ltd, PO Box a maximum power output of 2 kW. The reactor has a height of 582, Pretoria, 0001, South Africa 200 mm, a diameter of 100 mm and is fabricated using a 316 Ayo Afolabi is with the Chemical Engineering Department, University of stainless steel. The lid of the reactor is fitted with a type K South Africa, P/Bag X6, Florida 1710, Johannesburg, South Africa. 213 International Conference on Chemical, Mining and Metallurgical Engineering (CMME'2013) Nov. 27-28, 2013 Johannesburg (South Africa) thermocouple, a nitrogen inlet and a pressure gauge. The cold for thermogravimetric analysis (TGA) and x-ray powder trap is fitted with a water cooled copper coil. The temperature diffraction analysis (XRD). The cold trapped and the cyclone of cooling water was maintained at 18°C by cooling water were also opened and the waste product was collected, mixed, circuit. weighed and taken for XRD analysis. Nitrogen V-11 inlet III. RESULTS AND DISCUSSION V-10 Water inlet Water outlet The X-ray powder diffraction analysis confirmed that the PI P01 I-5 P03 reactor product contained anhydrous zirconium tetrafluoride FI I-4 P-1 with a monoclinic crystal structure. The spectrum of the x-ray Temperature readout powder diffraction of the reactor product is depicted in Fig. 2. V-7 TI PI P05 I-2 I-3 35000 34000 33000 32000 31000 30000 P02 29000 28000 27000 ZrF4 pattern 26000 25000 Cold 24000 V-8 23000 V-9 Trap Cyclone 22000 21000 P06 P04 20000 19000 18000 17000 TC V-6 V-5 01 16000 15000 Lin (Counts) 14000 Reactor 13000 12000 11000 10000 9000 8000 7000 6000 5000 P07 4000 3000 2000 PI To 1000 I-1 atmosphere 0 Orifice 01 P13 10 20 30 40 50 60 70 80 90 100 110 120 130 140 HF KOH 2-Theta - Scale P10 P11 P12 P08 File: ZrF4_Run2 product_b.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 144.991 ° - Step: 0.020 ° - Step time: 94.5 s - Temp.: 25 °C (Room) - Time Started: 17 s - 2-Theta: 10.000 ° - Theta: 5.000 ° - Chi: 0.00 ° - Scrubber Scrubber Operations: Strip kAlpha2 0.500 | Background 0.014,1.000 | Import P09 00-033-1480 (*) - Zirconium Fluoride - ZrF4 - Y: 61.47 % - d x by: 1. - WL: 1.5406 - Monoclinic - a 9.55850 - b 9.95120 - c 7.70710 - alpha 90.000 - beta 94.520 - gamma 90.000 - Body-centered - I2/a (15) - 12 - 730.8 E-1 Outside V-4 V-2 Utilities Fig. 2 Powder XRD diffraction pattern of the reactor product overlaid V-1 V-3 with zirconium tetrafluoride pattern IR Cell Nitrogen purge The x-ray powder diffraction analysis of the mixed waste product from the cold trap and the cyclone confirmed that the Fig 1 Schematics of zirconium tetrafluoride production system waste product contains ammonium fluoride, as shown in Figure 3, and the ammonium hexafluorosilicate bounded with C. Manufacturing of zirconium tetrafluoride ammonium fluoride, as revealed in Fig. 4. In a typical experiment for the manufacturing of zirconium 27000 tetrafluoride, 100 g of plasma dissociated zircon and 200 g of 26000 25000 ammonium bifluoride were mixed together. The mixture was 24000 23000 NH4F pattern placed in the reactor and the latter was closed. The reactor was 22000 -1 21000 first purged with nitrogen at 0.25 g.s and then the system was 20000 19000 evacuated to a pressure of 78.8 kPa (atmospheric pressure = 18000 17000 86.8 kPa) and maintained at that pressure. The flow of the 16000 15000 cooling water, at room temperature, for the cold trap was 14000 -5 3 -1 13000 maintained at 8.33x10 m .s . The temperature of the reactor 12000 Lin (Counts) 11000 was slowly increased to reach an internal temperature of 10000 9000 150°C and maintained at that temperature for thirty minutes to 8000 7000 allow the fluorination of plasma dissociated zircon to take 6000 5000 place. The temperature was increased so that the internal 4000 3000 temperature reached 280°C and maintained at that temperature 2000 1000 for thirty minutes to sublime the ammonium fluorosilicate. 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Lastly, the temperature was increased to reach an internal 2-Theta - Scale File: ZrF4_Run2 cold finger_a.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 144.991 ° - Step: 0.020 ° - Step time: 94.5 s - Temp.: 25 °C (Room) - Time Started: 20 s - 2-Theta: 10.000 ° - Theta: 5.000 ° - Chi: 0.00 ° temperature of 380°C and maintained at that temperature for Operations: Strip kAlpha2 0.500 | Background 0.145,1.000 | Import 00-035-0758 (*) - Ammonium Fluoride - NH4F - Y: 18.16 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 4.44080 - b 4.44080 - c 7.17260 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63mc (186) - 2 - 122.4 thirty minutes to decompose the formed ammonium fluorozirconate compounds. After the experiment, the reactor was allowed to cool to room temperature over a period of 12 Fig. 3 XRD powder diffraction pattern of cold trap product overlaid hours. with ammonium fluoride pattern The product was collected after the reactor has cooled to room temperature. The reactor product was weighed and sent 214 International Conference on Chemical, Mining and Metallurgical Engineering (CMME'2013) Nov. 27-28, 2013 Johannesburg (South Africa) 27000 26000 25000 24000 23000 22000 21000 20000 19000 18000 17000 (NH4)2SiF6.NH4F pattern 16000 15000 14000 13000 12000 Lin (Counts) 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 2-Theta - Scale File: ZrF4_Run2 cold finger_a.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 144.991 ° - Step: 0.020 ° - Step time: 94.5 s - Temp.: 25 °C (Room) - Time Started: 20 s - 2-Theta: 10.000 ° - Theta: 5.000 ° - Chi: 0.00 ° Operations: Strip kAlpha2 0.500 | Background 0.145,1.000 | Import 00-003-0097 (I) - Ammonium Silicon Fluoride - (NH4)2SiF6·NH4F - Y: 14.69 % - d x by: 1.
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