Article pubs.acs.org/IECR
Combined Carboreduction−Iodination Reaction of TiO2 and FeTiO3 as the Basic Step toward a Shortened Titanium Production Process Philipp Schlender† and Arnold E. W. Adam* Faculty of Nature and Materials Science, Institute of Inorganic and Analytical Chemistry, Clausthal University of Technology, Paul-Ernst-Straße 4, D-38678 Clausthal-Zellerfeld, Germany ABSTRACT: Although recent research has concentrated on optimizing steps in the common process or developing electrochemical methods, there remains a need for cost- and energy-efficient methods of titanium production. In this study, a combined carboreduction−iodination (“carboiodination”) reaction as a promising step toward a shortened titanium production process is introduced and examined. Experiments were conducted with pelletized mixtures of various titanium oxide and carbonaceous reactants in a tube furnace under a gentle flow of argon or argon/iodine atmosphere. Pellet residues were analyzed by X-ray powder diffraction and iodide precipitates by either absorption spectrometry or emission spectrometry. A reaction between nanoscale anatase and thermolytic carbon leads to TiI4 at 900 °C. Carboreduction and carboiodination results compare well with similar studies and thermochemical modeling, respectively. The carboiodination reaction could pave the way to a shortened overall process by substituting sulfate process, carbochlorination, and metallothermic reduction. Future work will concentrate on increasing the scale of the process.
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INTRODUCTION Titanium and titanium alloys are beneficial materials for aeroand astronautics, turbine blade manufacturing, and chemical plant construction. They provide high corrosion and oxidation resistance and low density and have outstanding mechanical properties.1 However, the use of titanium and titanium alloys is limited to several niche applications because of their high manufacturing costs. Although titanium is the tenth most abundant element in the lithosphere, it is still difficult to obtain from its ores. Because of its high oxygen affinity, titanium mainly occurs in oxides like anatase, rutile, or ilmenite but never in its elemental form. Additionally, the resources are widely distributed and either have a low titanium concentration or contain several impurities, which makes preliminary enrichment and purification steps necessary.2 The most common titanium-producing process was developed in the first half of the 20th century and involves several batch-like and energy-intensive steps.1,3 Because of this, the production costs of titanium are comparatively high and there is a great demand for developing new, energy-saving and cost-effective production routes for high-purity titanium and titanium alloys. In the most recent decades, much research has focused on developing electrolytic processes as well as optimizing the common process steps. Overviews of common and new processes to produce titanium are given by Cheng and coworkers and Fray.4,5 While there has been some improvement in the preliminary enrichment and leaching steps, all steps followed and mentioned above offer only little potential for major improvements with regard to energy-consumption and cost-efficiency. © 2017 American Chemical Society
None of the new processes are used on an industrial scale, and the major issues of titanium production, the high energy consumption and processing costs, have still not been settled. In the present study, we developed an alternative approach and investigated the carboiodination reaction as the basic step toward shortening the process of titanium production from crude titanium dioxide (anatase or rutile) or iron titanium oxide (ilmenite).6,7 Our concept derives from the carbochlorination step used in the common process. Possible benefits of our concept are a shortened process, the recycling of iodine and hydrogen, and omission of electrolytic steps. Although carbochlorination and carbobromination of titanium dioxide are familiar reactions,8 carboiodination has attracted no attention and has so far remained unstudied. Nevertheless, our own thermochemical calculations promise this reaction to be feasible. In this article, carboiodination is described for the first time.
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BACKGROUND, CONCEPT, AND THEORETICAL SECTION Common Process Steps. The common process is composed of several single steps, specifically sulfate process,9 carbochlorination, fractionated distilling, metallothermic reduction with magnesium (Kroll process)10 or sodium (Hunter Received: Revised: Accepted: Published: 6572
March 21, 2017 May 10, 2017 May 11, 2017 May 31, 2017 DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
Article
Industrial & Engineering Chemistry Research process or Armstrong process),11,12 van Arkel−de Boer process,13 and ultrapurification (Figure 1). After titanium-
Figure 1. Common process steps for titanium production.
bearing ores such as ilmenite are enriched via the sulfate process, the titanium oxide rich slags are dried and carbochlorinated at 700−1000 °C. Fractionated distilling of the carbochlorination products leads to pure titanium(IV) chloride which is reduced in liquid magnesium or sodium to obtain titanium sponge (Kroll process and Hunter process) or titanium powder (Armstrong process). Alternatively, the reduction can be done with CaH2 (Hydrimet process)14 or electrochemically (FFC-Cambridge process15,16). High-purity titanium is achieved via Van Arkel−de Boer process, electromigration, or zone melting.4 The whole process route involves several energy-intensive steps, above all the recycling of magnesium chloride or sodium chloride. Carboiodination. Using iodine instead of chlorine in a carbohalogenation reaction is advantageous. Iodine and carbon can react directly with raw ilmenite, anatase, or rutile to give titanium(IV) iodide. In the same step, a separation via distillation or sublimation results in pure titanium(IV) iodide. This intermediate product is decomposed thermally at high temperatures via the Van Arkel−de Boer process to give crystalline titanium bars. As a variation, this concept proposes to treat TiI4 with hydrogen to achieve titanium hydride powder. Titanium hydride results in high-purity titanium powder after thermal decomposition at medium temperatures (Figure 2).17 Carbohalogenation. In contrast to many other metals, titanium oxide cannot be reduced to elemental titanium by carbon at acceptable temperatures. In combination with chlorine, carbon converts titanium dioxide to titanium tetrachloride. Two general reaction paths can be proposed for the carbohalogenation: either a one-step reaction (eq 1) or a two-step-reaction, where the carboreduction-step is followed by the halogenation step (eqs 2a and 2b) TiO2 + 2C + 2X 2 → TiX4 + 2CO
Figure 2. Comparison of the common process steps and the carboiodination concept.
Carboreduction. The carboreduction of titanium dioxide takes place at temperatures of 900−1300 °C, whereas the reaction between partly reduced titanium oxides (e.g., Ti2O3) and iodine runs at ambient temperatures of about 700 °C. With respect to the reaction temperature, carboreduction is the critical step. The purpose of the carboreduction experiments was to find a mixture of educts containing titanium dioxide and carbonaceous educts. This mixture would result in the formation of reduced titanium oxides at the lowest possible temperature. Ti2O3 was chosen as the target compound. Further reduction to TiO would also lead to the simultaneous formation of TiC, which is an undesired byproduct because of its inert character. Numerous studies present results of reduction experiments conducted with various kinds of titanium oxides and carbons and different maximum temperatures, reaction times, particle sizes, and atmospheres.24−29 Chou and Lin give an extensive overview of all influences on the reaction, supplemented by the results of their own experiments. They state that the rate of reaction is accelerated by increasing the sample thickness, reaction temperature, and initial bulk density and decreasing the inert gas flow rate. Additionally, a high carbon content and smaller TiO2 grains are beneficial.30 Den Hoed and co-workers investigated the carboreduction of ilmenite.31,32 They presented a three-step reaction mechanism in which present Fe(III) is reduced to Fe(II) at first, followed by a partial reduction of 2FeTiO3 to FeTi2O5 and Fe(0); at last FeTi2O5 is reduced to Fe(0) and a Ti-rich solid solution phase of M3O5-form. Further reduction, especially of titanium, does not happen until all iron content is reduced to its elemental state. Wang and Yuan confirmed den Hoed’s studies and indicated in their publication that the formation of reduced titanium oxides like Ti3O5 is possible at temperatures of 1200 °C.33 Apart from that, Williams and Welham observed a
(1)
2TiO2 + C → Ti 2O3 + CO
(2a)
2Ti 2O3 + 2X 2 → TiX4 + 3TiO2
(2b)
Numerous studies addressed the mechanism of carbochlorination.18−20 Both phosgene and carbon tetrachloride are said to be reactive intermediates of carbochlorination. In three studies the iodine homologues of phosgene and carbon tetrachloride were investigated and found to be very unstable compounds, which hardly exist above room temperature.21−23 It is unlikely that they would be part of a reaction that requires elevated temperatures. While there is much evidence that carbochlorination is a one-step reaction, carboiodination will most likely be a combined carboreduction−iodination step. 6573
DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
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Industrial & Engineering Chemistry Research starting TiO2 reduction at 800 °C in a ground mixture of ilmenite and graphite.24 Our own experiments were run in a tube furnace with TiO2 of different grain sizes, reactive-ground and synthetic ilmenite powders, and three different kinds of carbon (graphite, charcoal, and thermolytic carbon). Furthermore, a very slow argon flow rate and both a loosely packed powder and stamppressed pellets were used. Carboiodination. A carboiodination reaction has never been reported before. In this study, we suppose that the driving force of this reaction is the formation of gaseous reaction products such as TiI4, FeI2, and CO. Thermochemical calculations using FactSage were performed to get a first impression as to whether the reaction is feasible and which temperatures render desired products (Figure 3).
powder diffraction analysis, atomic absorption, and atomic emission spectrometry. Further information is provided within the analytics subsection. Materials. The reactive-ground compounds were provided by a collaborating workgroup at the Institute of Mineral and Waste Processing, Waste Disposal and Geomechanics, Clausthal University of Technology (abbreviated as IMWP). All other listed compounds are commercially available. Every substance was used as supplied (Table 1). Table 1. Chemical Compounds Used in Experiments abbreviation
source (grade)
anatase anatase, reactive-ground nano-anatase ilmenite ilmenite, natural, reactiveground graphite
substance
TiO2 TiO2 TiO2 FeTiO3 FeTiO3
formula
TiO2 rm-TiO2 n-TiO2 FeTiO3 rm-FeTiO3
Merck (p.a.) IMWP Alfa Aesar (p.a.) Alfa Aesar (p.a.) IMWP
C
G
sucrose (thermolytic carbon) charcoal iodine
C12H22O11
TC
Riedel-de Haën (p.a.) Südzucker
C I2
HK I2
IMWP Sigma-Aldrich (p.a.)
Experimental Setup and Methods. Preparation of Educt Mixtures. Carboreduction experiments were carried out with mixtures of one titanium-bearing mineral and one carbonaceous educt. Five different titanium-bearing minerals and three different carbonaceous educts were available (Figure 4).
Figure 3. Mole fractions of relevant phases in a mixture of TiO2, C, I2, and Ar.
FactSage is an enhanced free Gibbs energy minimizer and calculates thermodynamically stable phases at a chosen temperature in a closed system. It provides no predictions about the reaction mechanism and does not admit any assumptions about the reaction course. The starting mixture employed consisted of 1 mol of TiO2, 10 mol of C, and 5 mol of I2. To overcome the incompatibility between a closed system calculation and open system experiments, an excess of a gaseous reaction atmosphere, namely 10 mol of Ar, was allowed for. All gas and solid phases of the system Ti−C−I−O−Ar contained in the pure substance database FactPS were included in the calculation. The calculations were performed for a temperature range of 100−1500 °C.34 Obviously, TiI4 is a relevant part of the chemical equilibrium from 500 °C on. Its molar fraction increases from 600 °C to reach a maximum of nearly 1 at 900 °C. At higher temperatures, the formation of TiI3, TiI2, and TiC becomes more favorable and the equilibrium molar fraction of TiI4 decreases to 0.8 at 1200 °C and 0.2 at 1400 °C. The calculations promise good experimental results in a temperature range between 900 and 1000 °C.
Figure 4. Overview of titanium-bearing and carbonaceous starting materials.
Mixtures with graphite were thoroughly mixed in an agate mortar from the powders in a molar ratio of TiO2:C = 1:4 or FeTiO3:C = 1:6. In most cases, the mixtures were pelletized in a stamp press. Reactive-ground educts (rm-TiO2 and rm-FeTiO3) were ground in a vibratory mill using steel balls. One mixture of FeTiO3 charcoal was ground together in the same manner (rmFeTiO3 + HK series) Mixtures with thermolytic carbon were produced by heating a 6:1 molar ratio mixture of TiO2 with sucrose. TiO2-powder and sucrose were ground in an agate mortar to yield a homogeneous mixture and filled into a corundum or quartz crucible. The crucible was put into a fused silica tube (30 × 300 mm) and placed in the hot zone of a tube furnace of our own design and construction (Figure 5). After the tube was flushed with argon, the mixture was heated in graduated steps to 500 °C under a slow argon stream to allow slow thermolysis and prevent heavy bubbling and splashing. After cooling, the crucible was taken out and the dark gray charcoal-like solid was transferred into an agate mortar and crushed to a fine powder. The resulting O:C ratio is 1:1.
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EXPERIMENTAL DETAILS This study consists of two series of experiments. In the first stage, the reduction of titanium oxide-bearing minerals with carbonaceous educts was investigated to discover promising mixtures with a low reduction temperature. In the second stage, carboiodination experiments were conducted by annealing promising mixtures in pelletized form in iodine-containing argon atmosphere. The main analytic methods are X-ray 6574
DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
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Figure 5. Thermolysis apparatus.
Carboreduction Setup. The carboreduction experiments were carried out in a tube furnace (Carbolite STF 15/180, 60 × 600 mm mullite tube, Eurotherm 3216 temperature controller) with water-cooled flanges (Figure 6). The maximum temper-
Figure 6. Tube furnace setup. Figure 8. Carboiodination apparatus.
ature of the furnace is 1500 °C, which is sufficient for all conducted experiments. The flanges allow the use of an inert gas atmosphere to prevent reoxidation. About 200−500 mg of the powdery or pelletized mixtures were put into either 10 × 100 mm corundum or quartz crucibles. They were placed exactly in the hot zone of the tube. Both materials are inert against all used educts. After the powdery or pelletized mixtures were placed in the tube furnace, the tube was flushed with a moderate argon stream of 2 L/min for 30 min. Then, the flow rate was reduced to gentle 0.5 L/min, the temperature program was started, and the mixture was annealed at a chosen maximum temperature for 3 h. The slow cooling to 700 °C was meant to keep the mullite reaction tube and the SiC heating rods from breaking because of thermal stress (Figure 7).
filled into a glass capillary and measured via Debye−Scherrer geometry with a linear wire PSD or the powder was prepared between two zero scattering foils, fitted into a thin-layer transition sample holder, and measured via transition geometry and an image plate PSD. In most cases, the capillary method was chosen. Phase analysis was carried out with the software package WinXPOW and the ICDD database (Table 2).35,36 Table 2. ICDD-Sets Used for Phase Analysis by X-ray Powder Diffraction
Figure 7. General temperature program (RT = room temperature, TT = target temperature).
Carboiodination Setup. The carboiodination experiments were carried out in a glass apparatus shown in Figure 8. All parts were connected via cone and socket joints. The reaction tube (30 × 300 mm) consisted of fused silica and was placed vertically into a smaller, locally designed and constructed tube furnace. The tube was half filled with predried charcoal granules so that the pelletized TiO2/carbon or FeTiO3/carbon mixture could be placed in the hot zone. At the lower end of the tube, the iodine reservoir, a U-shaped glass tube with frit-inlay, filled with iodine shots, was placed and slightly heated with the infrared lamp (approximately 80 °C). Gaseous iodine was transported through the reaction tube with a slow argon stream of 0.2 L/min. At the top end of the reaction tube gaseous reaction products like FeI2, TiI4, or residual I2 resublimed on the mounted water-cooled glass finger. Analytics. After cooling to room temperature, the carboreduction products were ground in an agate mortar. The resulting phases were analyzed via X-ray powder diffraction on a Stoe Stadi-P diffractometer with a Cu Kα radiation source (λ = 1.5406 Å, U = 40 kV, I = 30 mA). Either the powder was
formula
name
TiO2 TiO2 FeTiO3 C CaTiO3 Ti9O17 Ti4O7 Ti3O5 Ti2O3 TiC Fe
anatase rutile ilmenite graphite perovskite
khamrabaevite iron
ICDD no. 21-1276 21-1272 29-733 41-1487 22-153 50-791 50-787, 77-1392 11-217 10-63, 43-1033, 74-2277 32-1383 6-696
The pellet residues resulting from the carboiodination experiment were treated in the same way as the carboreduction reaction products and analyzed via X-ray powder diffraction. The resublimed reaction products on the cooling finger were not suitable for X-ray powder analysis. Because of the fast precipitation caused by the significant temperature difference between the argon atmosphere and the cooling finger, the crystallinity of the resublimed products was very low. Therefore, the diffraction patterns would have been of low quality. As an improvised method of obtaining information whether iron or titanium iodides precipitated on the cooling finger, the precipitates were rinsed off completely with a small amount of sulfuric acid immediately after the finger was taken out of the reaction tube. The solutions obtained were analyzed via atomic absorption spectrometry (flame-AAS, analyticJena novAA 350) or atomic emission spectroscopy (ICP-AES, 6575
DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
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Industrial & Engineering Chemistry Research Table 3. Phase Compositions of the Mixtures Annealed in the Temperature Range 900−1400 °Ca TiO2 T [°C]
G
900
rm-TiO2 TC
TiO2 (s)
TiO2 (s)
TiO2 (s)
1050
1100
TiO2 (s)
TiO2 (s) Ti4O7 (m)
1150
TiO2 (s)
TiO2 (s)
TiO2 (w) Ti4O7 (w)
TiO2 (m) Ti2O3 (s) TiC (s) TiO2 (w) Ti2O3 (m) TiC (s) TiO2 (w) Ti2O3 (w) TiC (s) Ti2O3 (w) TiC (s)
TiO2 (m) Ti4O7 (w)
1300
TiO2 (m) Ti2O3 (m)
Ti2O3 (m) TiC (m) Ti2O3 (w) TiC (m)
1400
Ti2O3 (m) TiC (s)
1250
a
G
TiO2 (w) Ti2O3 (m) TiC (s) TiC (s)
FeTiO3 TC
TiO2 (s)
TiO2 (s)
G
TiO2 (s)
FeTiO3 (s)
TiO2 (s) Ti2O3 (s)
FeTiO3 (m) TiO2 (w) Fe (s) FeTiO3 (w) TiO2 (m) Fe (s) TiO2 (m) Fe (s)
TiO2 (s)
TiO2 (s)
Ti4O7 (w) Ti2O3 (w) TiC (w) Ti2O3 (s) TiC (m)
1200
n-TiO2 TC
TiO2 (s)
950
1000
G
TiO2 (s) Ti2O3 (s)
TiO2 (m) Ti4O7 (m)
Ti2O3 (w) TiC (s)
TiO2 (w) Ti2O3 (m) TiC (s) Ti2O3 (w) TiC (s)
Ti2O3 (w) TiC (s)
TiO2 (w) Fe (s) TiO2 (w) Ti2O3 (m) Fe (s) TiO2 (w) Ti2O3 (w) Fe (s)
rm-FeTiO3 TC
TiO2 (m) Fe (s) TiO2 (m) Fe (s) TiO2 (m) Fe (s) FeTiO3 (w) TiO2 (m) Fe (s) FeTiO3 (w) TiO2 (m) Fe (s) FeTiO3 (w) TiO2 (m) Fe (s) FeTiO3 (m) TiO2 (m) Fe (s)
HK FeTiO3 (w) Fe (s) Ti2O3 (w) TiC (w) Fe (s) Ti2O3 (m) TiC (m) Fe (s) Ti2O3 (m) TiC (m) Fe (s) Ti2O3 (w) TiC (m) Fe (s)
TiC (s)
The letters in parentheses correspond to the peak intensity: s, strong; m, medium; w, weak.
reduction temperatures are somewhat higher than 1000 °C, which is the target temperature for the proposed process. The comparison between the different titanium dioxidecontaining educts in their reduction behavior toward thermolytic carbon at varying temperatures indicates that a smaller particle size promotes the reduction. Especially nanoscale anatase shows a noticeably lower reduction temperature of 1000 °C compared to 1100 °C for standard anatase. The reaction between synthetic ilmenite and thermolytic carbon does not produce reduced titanium oxide under 1200 °C. While between 900 and 1000 °C iron is reduced, higher temperatures enable iron and titanium dioxide to form ilmenite again. The lowest reduction temperature is achieved when a reactive-ground mixture of natural ilmenite and charcoal is used. Ti2O3 occurs after annealing at 950 °C. Overall, this is the best result of all the experiments. In general, the carboreduction results of this study are well in accord with other studies which deal with the influence of particle size on carboreduction of TiO2 and FeTiO3.24,30 The evaluation of Langmuir isotherms for the three types of anatase employed indicates that the specific surface area of both nanoscale anatase (114.1 m2/g) and reactive-ground anatase (122.5 m2/g) is much higher than that of standard anatase (9.4 m2/g). With an increasing specific surface area the required reduction temperatures decrease for the reaction series with thermolytic carbon. However, no correlation can be found for the reaction series with graphite. The specific surface area seems to have an influence only when carbon is directly interfacing with TiO2, as when thermolytic carbon is used.
Spectroflame Spectro). The results of these cation analyses gave indications as to whether iron iodide or titanium iodide or both together occurred in the experiment. Additionally, the specific surface area (Langmuir) of the three different TiO2 samples was calculated from a partial nitrogen adsorption isotherm measured with a Micromeritics ASAP 2020 system. The results were related to the carboreduction experiments to find a correlation between the specific surface area and the reduction temperature.
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RESULTS AND DISCUSSION Carboreduction Experiments. Several experiments with various compositions of titanium oxide-bearing compound and carbonaceous educts were conducted. With the majority of compositions, the temperatures required to yield Ti2O3 were much higher than 1000 °C. Nevertheless, two compositions met the target of only 950 and 1000 °C as the reduction temperature (Table 3). Both reactive-ground TiO2 and ilmenite powder give Ti2O3 when graphite is used as the carbonaceous reactant after annealing at 1150 °C. In reactions between nanoscale anatase powder and graphite, at least 1300 °C are required to produce Ti2O3. This is contrary to our expectations, because nanoscale anatase should react quicker because of its greater surface area. Most likely, both the distracted structure and the high-energy entry during the reactive-grinding process cause an increased reactivity of the anatase powder used. During ilmenite reduction with graphite, iron, and highly amorphous TiO2 are formed, while the latter is readily reduced to Ti2O3 at comparatively low temperatures. At 1150 °C the required 6576
DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
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Industrial & Engineering Chemistry Research Carboiodination Experiments. Both the experiments with TiO2 and with FeTiO3 resulted in the formation of titanium(IV) iodide. While in the reaction with TiO2 a substantial amount of red-brown TiI4 powder precipitated at the cooling finger, the amount of precipitated TiI4 in the experiment with FeTiO3 was very low. Additionally, the iodination of titanium carbide surprisingly resulted in the formation of TiI4, too. The experiments with TiO2 were carried out between 900 and 950 °C, and red-brown titanium(IV) iodide powder precipitated on the cooling finger while holding the maximum temperature. X-ray analysis of the residual pellet indicated partly reduced titanium dioxide, e.g., Ti4O7 or Ti9O17, besides TiO2. On the one hand, this result proves a reduction at temperatures as low as 900 °C, which is well in accord with the thermochemical modeling. On the other hand, the partly reduced TiO2 should have reacted with iodine. It is obvious that iodine reacted superficially only and did not diffuse into the pellet. Carboiodination experiments with ilmenite were carried out at 980 °C. On the cooling finger, a small amount of red-brown powder of TiI4 precipitated as well as numerous wine red flat crystals of FeI2. An ICP-AES analysis revealed that almost all of the substance rinsed off the cooling finger was iron iodide. This observation can be explained with the reaction mechanism of ilmenite reduction. The reduction of iron is advantageous compared with the reduction of titanium. That is why iron enriches in the outer sphere of the ilmenite particle, while the core enriches with TiO2.31,37 Because iodine reacts only on the particle surface, a lot of iron iodide is formed but almost no TiI4. Additionally, one iodination experiment with TiC was performed. In this case, TiC was also pelletized together with graphite as the binding compound. Although TiC is known to be very unreactive, a substantial amount of TiI4 was formed at a reaction temperature of 900 °C.
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CONCLUSION
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AUTHOR INFORMATION
Zellerfeld, Germany. E-mail:
[email protected]. Phone: +49 (0) 5323 72-2227. ORCID
Philipp Schlender: 0000-0003-4624-8733 Present Address †
P.S.: School of Science, Faculty of Chemistry and Food Chemistry, Chair of Inorganic Chemistry II, TU Dresden, Bergstraße 66, D-01062 Dresden, Germany. Funding
The authors thank the German Research Foundation (DFG) for supporting this work6,7 within the research unit FOR1372, Grant Number Ad 122/4.1. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully thank German Research Foundation (Deutsche Forschungsgemeinschaft) for the financial support provided. Thanks also to Dr. Milan Hampl and Prof. Rainer Schmid-Fetzer (Institute of Metallurgy, Clausthal University of Technology) for their thermochemical calculations and helpful discussions; to Petra Lassen (Institute of Inorganic and Analytical Chemistry, Clausthal University of Technology) for the AAS and ICP-AES analyses; as well as to Rafael Kuwertz and Nadine Kruse (Institute of Chemical and Electrochemical Process Engineering, Clausthal University of Technology) for the specific surface area calculations. We acknowledge with thanks the provision of reactive-ground educts by Dr. Marcela Achimovicova and Prof. Eberhard Gock (Institute of Mineral and Waste Processing, Waste Disposal and Geomechanics, Clausthal University of Technology).
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REFERENCES
(1) Sibum, H.; Güther, V.; Roidl, O.; Habashi, F.; Wolf, H. U. Titanium, Titanium Alloys, and Titanium Compounds. In Ullmann’s Encyclopedia of Industrial Chemistry; Elvers, B., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2012; Vol. 37, pp 51−82. (2) Sibum, H. Titanium and Titanium Alloys − From Raw Material to Semi-finished Products. In Titanium and Titanium Alloys: Fundamentals and Applications; Leyens, C., Peters, M., Eds. WileyVCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2003; pp 231−244. (3) Auer, G.; Woditsch, P.; Westerhaus, A.; Kischkewitz, J.; Griebler, W.-D.; De Liedekerke, M. Pigments, Inorganic, 2. White Pigments. In Ullmann’s Encyclopedia of Industrial Chemistry; Elvers, B., Ed.; WileyVCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2012; Vol. 27, pp 257−291. (4) Zhang, W.; Zhu, Z.; Cheng, C. Y. A Literature Review of Titanium Metallurgical Processes. Hydrometallurgy 2011, 108, 177. (5) Fray, D. J. Novel Methods for the Production of Titanium. Int. Mater. Rev. 2008, 53, 317. (6) Schlender, P. Untersuchungen zur Carboreduktion und Carboiodierung titanoxidhaltiger Edukte sowie zur Trennung von Iodidgemischen durch Sublimation. Doctoral Thesis, Clausthal University of Technology, Clausthal-Zellerfeld, Germany, 2014. (7) Rempel, H. Untersuchungen zur Reaktion von Titan(IV)-iodid mit Wasserstoff. Doctoral Thesis, Clausthal University of Technology, Clausthal-Zellerfeld, Germany, 2014. (8) Wiberg, N. Verbindungen des Titans. Lehrbuch der Anorganischen Chemie; Walter de Gruyter: Berlin, 2007; Vol. 102, p 1524. (9) Farup, P. Process for Precipitating Titanium Compounds. U.S. Patent 1,773,727, August 28, 1930. (10) Kroll, W. The Production of Ductile Titanium. Trans. Electrochem. Soc. 1940, 78, 35.
Fundamental reactions of a carboiodination process were investigated. Carboreduction experiments indicated optimal mixtures of titanium dioxide-containing starting materials and carbonaceous educts. A mixture of reactive-ground natural ilmenite with charcoal led to the formation Ti2O3 at 950 °C. A mixture of nanoanatase and thermolytic carbon resulted in the formation of Ti2O3 at 1000 °C. With all other mixtures, temperatures above 1100 °C were required. In the presence of iodine, partly reduced titanium oxides occur at temperatures of 900 °C with a starting mixture of nanoscale anatase and thermolytic carbon. TiI4 is formed as expected. Mixtures of ilmenite required slightly higher temperatures and produced iron iodide primarily. Overall, the experimental results indicate that carboiodination of titanium oxide-containing minerals results in titanium iodide, which can either by thermally decomposed or reduced by hydrogen. This discovery could pave the way to a shorter, less energy consuming, and therefore more cost-effective process of titanium production.
Corresponding Author
*Clausthal University of Technology Institute of Inorganic and Analytical Chemistry, Paul-Ernst-Straße 4, D-38678 Clausthal6577
DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
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Industrial & Engineering Chemistry Research
databases − recent developments. CALPHAD: Comput. Coupling Phase Diagrams Thermochem. 2009, 33, 295. (35) WinXPOW, version 3.02; Stoe & Cie: Darmstadt, Germany, 2014. (36) PDF-2. International Centre for Diffraction Data: Newtown Square, PA, 2014. (37) Dewan, M. A. R.; Zhang, G.; Ostrovski, O. Phase Development in Carbothermal Reduction of Ilmenite Concentrates and Synthetic Rutile. ISIJ Int. 2010, 50, 647.
(11) Hunter, M. A. Metallic Titanium. J. Am. Chem. Soc. 1910, 32, 330. (12) Armstrong, D. R.; Borys, S. S.; Anderson, R. P. Method of Making Metals and Other Elements from Halide Vapor of the Metal. U.S. Patent 5,958,106, September 28, 1999. (13) Van Arkel, A. E.; De Boer, J. H. Darstellung von reinem Titanium-, Zirkonium-, Hafnium- und Thoriummetall. Z. Anorg. Allg. Chem. 1925, 148, 345. (14) Alexander, P. P. Production of Titanium Hydride. U.S. Patent 2,427,338, September 16, 1947. (15) Chen, G. Z.; Fray, D. J.; Farthing, T. W. Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride. Nature 2000, 407, 361. (16) Fray, D. J.; Farthing, T. W.; Chen, Z. Removal of Oxygen from Metal Oxides and Solid Solutions by Electrolysis in a Fused Salt. World Patent 9,964,638, December 16, 1999. (17) Rittmeyer, P.; Wietelmann, U. Hydrides. In Ullmann’s Encyclopedia of Industrial Chemistry; Elvers, B., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2012; Vol. 18, pp 103− 132. (18) Yang, F.; Hlavacek, V. Carbochlorination Kinetics of Titanium Dioxide with Carbon and Carbon Monoxide as Reductant. Metall. Mater. Trans. B 1998, 29, 1297. (19) Sohn, H. Y.; Zhou, L.; Cho, K. Intrinsic Kinetics and Mechanism of Rutile Chlorination by CO + Cl2 Mixtures. Ind. Eng. Chem. Res. 1998, 37, 3800. (20) Yang, F.; Hlavacek, V. Effective Extraction of Titanium from Rutile by a Low-Temperature Chloride Process. AIChE J. 2000, 46, 355. (21) Barnes, I.; Becker, K.; Stracke, J. The Gas-Phase Infrared Spectra of Formyl Iodide and Carbonyl Iodide. Chem. Phys. Lett. 1995, 246, 594. (22) Parkington, M. J.; Ryan, T. A.; Seddon, K. R. Carbonyl Dihalides: Synthesis and Spectroscopic Characterization. J. Chem. Soc., Dalton Trans. 1997, 251. (23) Phosgene and Related Carbonyl Halides. In Topics in Inorganic and General Chemistry Vol. 24; Ryan, T. A., Ryan, C., Seddon, E. A., Seddon, K. R., Eds. Elsevier Ltd: Amsterdam, 1996; pp 679−683. (24) Welham, N. J.; Williams, J. S. Carbothermic Reduction of llmenite (FeTiO3) and Rutile (TiO2). Metall. Mater. Trans. B 1999, 30, 1075. (25) Lefort, P.; Maitre, A.; Tristant, P. Influence of the Grain Size on the Reactivity of TiO2/C Mixtures. J. Alloys Compd. 2000, 302, 287. (26) Maitre, A.; Lefort, P. Carbon Oxidation at High Temperature During Carbothermal Reduction of Titanium Dioxide. Phys. Chem. Chem. Phys. 1999, 1, 2311. (27) Maitre, A.; Tetard, D.; Lefort, P. Role of Some Technological Parameters During Carburizing Titanium Dioxide. J. Eur. Ceram. Soc. 2000, 20, 15. (28) Berger, L.-M. Investigations of the Carbothermal Reduction of Ti2O3 in Argon and Nitrogene Atmospheres. J. Mater. Sci. Lett. 2001, 20, 1845. (29) Kwon, H.; Kang, S. Carbothermal Reduction of Titanium Monoxide (TiO). J. Ceram. Soc. Jpn. 2008, 116, 1154. (30) Chou, C.; Lin, C. Reaction between Titanium Dioxide and Carbon in Flowing Helium Stream. Br. Ceram. Trans. 2001, 100, 197. (31) Hoed, P. d.; Edwards, R. I. Perspectives on a Process: Kinetics of Ilmenite Reduction. In Heavy Minerals; Robinson, R. E., Ed; The Symposium Series S17; The South African Institute of Mining and Metallurgy: Johannesburg, 1997; pp 49−59. (32) den Hoed, P.; Luckos, A. Oxidation and Reduction of IronTitanium Oxides in Chemical Looping Combustion: A PhaseChemical Description. Oil Gas Sci. Technol. 2011, 66, 249. (33) Wang, Y.; Yuan, Z. Reductive Kinetics of the Reaction between a Natural Ilmenite and Carbon. Int. J. Miner. Process. 2006, 81, 133. (34) Bale, C. W.; Bélisle, E.; Chartrand, P.; Decterov, S. A.; Eriksson, G.; Hack, K.; Jung, I.-H.; Kang, Y.-B.; Melançon, J.; Pelton, A. D.; Robelin, C.; Petersen, S. FactSage thermochemical software and 6578
DOI: 10.1021/acs.iecr.7b01170 Ind. Eng. Chem. Res. 2017, 56, 6572−6578
