Extractive Metallurgy of Zirconium—1945 to the Present

Stephens, W. W.

doi:10.1520/stp34458s

Cited by 12 publications

(6 citation statements)

References 26 publications

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“…[1][2][3][4] The current commercial production method of zirconium is the Kroll process. [5][6][7] This process is classified into two main stages; zircon sand is firstly converted to zirconium dioxide, which subsequently treated through many hydrometallurgical processes in order to obtain pure zirconium oxide. In the second stage, the later is reconvert to zirconium tetrachloride and then reduced by liquid magnesium to zirconium metal.…”

Section: Introductionmentioning

confidence: 99%

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Calciothermic Reduction of Zirconium Oxide in Molten CaCl2

Abdelkader

El-Kashif

2007

ISIJ Int.

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The reduction of zirconium dioxide using liquid calcium and molten calcium chloride was investigated. The study focusing on the influence of reductant amount, reaction time, CaCl 2 amount, and temperature on the reduction process. Zirconium powder with oxygen content less than 800 ppm was obtained at 1 100°C after 3 h and by using two times the theoretical amount of Ca and four times that of CaCl 2 . The reduction reaction of ZrO 2 was found to be multi steps process through the formation of intermediate phase CaZrO 3 . The morphology of the obtained zirconium was observed to be highly affected by the reaction temperature.KEY WORDS: zirconium; calciothermic reduction; calcium; calcium chloride. 25© 2007 ISIJ common reductant, was reported in their work. It is clearly seen that only calcium may be expected to produce pure zirconium from oxides.The third criterion is the ability to separate the pure metal from other reduction byproducts. For example, if magnesium used as a reductant the removal of the ignited magnesia (MgO) by acid leaching without attacking the formed zirconium would be a difficult task. 22,23) The fourth important requirement in the reducing agent is that it must be cheap and available commercially and that it must satisfy the environmental requirements. Rare earths are expensive and cannot be used as economic reductant. Radioactive or noxious elements are excluded as zirconium reductants.Calcium is the only candidate that satisfies all the above requirements. At 400°C, DG°of formation for ZrO 2 is Ϫ970.92 kJ/mol corresponding to an oxygen partial pressure P O 2 ϭ5ϫ10 Ϫ76 atm at the equilibrium of the reaction, ZrϩO 2 ↔ZrO 2 . The DG°of formation for 2CaO is Ϫ1062.6 kJ/mol. At the equilibrium of the reaction 2CaϩO 2 ↔2CaO, P O 2 is lowered to 3ϫ10 Ϫ83 atm i.e. by a factor of 2ϫ10 7 less than its value with zirconium. 24,25) From the O-Zr phase diagram, the solubility of O in Zr at equilibrium with ZrO 2 is 5 wt%. 26,27) Reducing the oxygen partial pressure by a factor of 2ϫ10 7 brings the dissolved oxygen below the ppm level. Calcium has no recognized intermetallic compounds with zirconium, and it has low solubility in b-Zr and a-Zr. Also it may be produced commercially through direct electrolysis of calcium chloride.Practically, Kroll 22,23) reported the presence of thousands ppm oxygen remained in the produced Zr after reducing with calcium. The slow mass transfer through the by-product CaO attached to the surface of Zr particles and hindered further reduction. Also, CaO that precipitated on the metal surface was trapped inside the particles when sintering took place. This CaO could not be eliminated during leaching by HCl and as a result, calcium and oxygen contents in the Ti powders could not be lowered to sufficient degree.Molten CaCl 2 can dissolve about 20 % mole CaO. [28][29][30] Threadgill 30) used this principle to precipitate electrolyticaly calcium metal from calcium oxide dissolved in molten calcium chloride bath. He also reported that the presence of CaO decrease the freezing point...

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Section: Introductionmentioning

confidence: 99%

“…24,25) From the O-Zr phase diagram, the solubility of O in Zr at equilibrium with ZrO 2 is 5 wt%. 26,27) Reducing the oxygen partial pressure by a factor of 2ϫ10 7 brings the dissolved oxygen below the ppm level. Calcium has no recognized intermetallic compounds with zirconium, and it has low solubility in b-Zr and a-Zr.…”

Section: Introductionmentioning

confidence: 99%

Calciothermic Reduction of Zirconium Oxide in Molten CaCl2

Abdelkader

El-Kashif

2007

ISIJ Int.

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“…Nicholas [18], ground zircon with MgO for up to 100 h, in a procedure that resulted in a solid-state reaction leaching ZrO 2 . ZrC can be formed by carbonization in an electric furnace (2000-2200 °C), followed by chlorination at 350-450 °C [19]. The chlorination method refers to the chlorination of zircon sand with coal in a blast furnace at 900-1000 °C [20].…”

Section: Introductionmentioning

confidence: 99%

Controlling the formation of Na2ZrSiO5 in alkali fusion process for zirconium oxychloride production

Liu

Song

et al. 2016

Advanced Powder Technology

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In the alkali fusion process for the production of zirconium oxychloride, the formation of the water-insoluble by-product, Na 2 ZrSiO 5 , largely affects NaOH recovery and results in the formation of silicon slags. Thus, controlling Na 2 ZrSiO 5 formation is necessary. In this paper, we studied the effects of roasting temperature, NaOH/zircon mole ratio, and particle size of zircon sand on Na 2 ZrSiO 5 formation. The optimum reaction parameters, when the roasting time was 1 h, were as follows: ≥ 95 μm average particle size of zircon sand, 6:1 NaOH/zircon mole ratio, and 750 °C roasting temperature. To avoid an uneven roasting temperature during alkali fusion, the use of a rotary kiln reactor is recommended. The amount of Na 2 ZrSiO 5 was significantly decreased under these optimum conditions, and the content of Na 2 O was reduced from 7.049% to only 2.21% after three water-leaching cycles.

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“…4 As the standard free energy of formation of zircon is very high (ΔG f,1400K o = −1 489 100 kJ/Kmol), and its structure consists of high coordinated bisdisphenoid ZrO 8 in a tetragonal structure and SiO 4 tetrahedra, a drastic condition is required to decompose it. 5,6 Among the various methods used to decompose ZrSiO 4 , (i) the thermal dissociation in the presence of carbon within a plasma arc furnace, 7−9 (ii) chlorination, 10 (iii) fluorosilicate fusion, 11 (iv) substoichiometric Na 2 CO 3 fusion, 12 (v) slight excess NaOH or Na 2 CO 3 fusion, 13,14 (vi) high stoichiometric NaOH fusion, 15−21 (vii) alkaline earth metal oxide or carbonate fusion, 22−26 (viii) formation of ZrC in an electric furnace (2273−2473 K) followed by chlorination at 623−723 K, 27 (ix) mechano-chemical treatment followed by acid attack 28−34 etc. are mentionable.…”

Section: Introductionmentioning

confidence: 99%

Preparation of Some Useful Compounds of Zirconium from Bangladeshi Zircon

Biswas

Habib

Karmakar

et al. 2012

Ind. Eng. Chem. Res.

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A number of useful zirconium compounds, such as hydrated zirconyl chloride, hydrated zirconium sulfate, zirconium dioxide, γ-zirconium ammonium phosphate, γ-zirconium phosphate, γ-zirconium phosphate phosphite, and γzirconium phosphate hypophosphite have been prepared from Bangladeshi zircon following the NaOH-fusion, acid (HCl and H 2 SO 4 )-leaching, precipitation, calcination/pyrolysis, condensation polymerization, ion exchange and the tap tactic reaction methods. The products have been characterized by chemical and thermogravimetric analyses in all cases, together with the XRD patterns and sodium exchange capacities in some cases.

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Extractive Metallurgy of Zirconium—1945 to the Present

Cited by 12 publications

References 26 publications

Calciothermic Reduction of Zirconium Oxide in Molten CaCl2

Calciothermic Reduction of Zirconium Oxide in Molten CaCl2

Controlling the formation of Na2ZrSiO5 in alkali fusion process for zirconium oxychloride production

Preparation of Some Useful Compounds of Zirconium from Bangladeshi Zircon

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