Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B34/00—Obtaining refractory metals
  • C22B34/10—Obtaining titanium, zirconium or hafnium
  • C22B34/12—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08
  • C22B34/1218—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by dry processes
  • C22B34/1222—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by dry processes using a halogen containing agent

Definitions

• This invention relates to the chlorination of titaniferous materials using porous carbon reductants. Titaniferous materials are often subjected to chlorination as chlorination is an efficient and economical way to obtain a high purity source of titanium for making titanium alloys, titanium compounds, and especially pigmentary titanium dioxide.
• Several processes have been described in the art for the chlorination of titaniferous materials. Such processes generally react a titanium-containing raw material such as rutile ore or ilmenite ore, with a chlorine-providing material and a carbon reductant at an elevated temperature according to one or both of the following equations:
• the carbon reductants utilized by the various processes are from divergent sources such as coal, coke, charcoal, and carbon-containing gases, and the particle size of the carbon typically is determined by other process parameters or desired economic conditions.
• divergent sources such as coal, coke, charcoal, and carbon-containing gases
• the particle size of the carbon typically is determined by other process parameters or desired economic conditions.
• the carbon used in the chlorination of a titaniferous material can have a substantial effect on the completeness of said chlorination reaction and under some conditions render the vanadium impurities readily separable from the chlorinated product.
• One embodiment of the present invention is to chlorinate titanium-containing materials and ores in a fluid bed at a temperature of at least about 600°C. using a porous carbon reductant.
• a second embodiment of the present invention is to chlorinate powdered titanium-containing materials and ores in a down-flow chlorination reactor.
• a third embodiment of the present invention is to chlorinate titanium- and iron-containing materials and ores producing titanium chlorides and by-products metallic iron in a laminar flow process. Additionally, an object and advantage of the present invention is that the present chlorination process can be more selective relative to impurity oxides in the materials and ores being chlorinated resulting in greater reactor efficiency and ease of operation due to the absence of normally liquid or sticky chlorides produced during high-temperature chlorination processes which adhere to reactor surfaces.
• a still further object and advantage of the present invention is that vanadium impurities in the titaniumcontaining reactants can be rendered readily separable from the titanium-containing products if the reaction temperature is maintained at greater than about 800°C.
• the present invention is a process for the chlorination of titaniferous materials.
• a mixture of titaniferous material and porous carbon reductant having internal surface due to micropores of less than 20 ⁇ is reacted with a chlorine-providing material in a chlorination reaction zone at a temperature of at least about 600°C.
• the present process has been found effective and efficient for substantially chlorinating the titanium values of most titanium-bearing ores. Additionally, at temperatures greater than about 800°C. vanadium impurities in the titanium-containing materials can be rendered readily separable from the titanium—containing products.
• the present invention is a chlorination process.
• Porous carbon reductants useful in the present invention contain micropores having a pore diameter of less than about 20 ⁇ . Typically such porous carbon reductants will have at least about 10m 2 /g. of surface area in such micropores, advantageously at least about 100m 2/g. of surface area in such micropores and preferably about 500m 2 /g. of such internal surface.
• Non-porous carbons and carbons having exclusively large pores, e.g. charcoal, are not useful in the present process.
• the preferred carbons used in the present invention have less than about 1500m 2 /g internal surface area and preferably less than about 1000m 2 /g of internal surface area m said micropores.
• the carbon particles can be any size useful in a chlorination process.
• such particles must be small enough to be fluidized by the fluidizing gas and yet be large enough such that they are not carried out of the fluid bed by the off-gas stream.
• Granular materials of about -8 mesh are typical.
• the average particle size can range from about 4 mesh to about 200 mesh and be useful in a fluid-bed process.
• the carbon particles will have an average particle size greater than about 100 mesh and will be substantially retained on a 140-mesh screen.
• the carbon particles In a down-flow process the carbon particles must be small enough to fall at a rate similar to the titaniferous material particles, such rate of fall being sufficiently slow to allow an adequate time within the reactor for chlorination to take place.
• Powdered materials of about -200 mesh are generally adequate here; however, various sizes, generally -140 mesh and finer, may be useful.
• the carbon particles In a laminar flow process the carbon particles must also be appropriately sized; however, in this case they must be so sized as to pass through the chlorination reactor in substantially laminar flow with the titaniferous material. Suitable materials are predominantly less than about 40 microns and substantially all will pass through a 325-mesh sieve.
• a preferred high surface area carbon is a appropriately sized coal treated to increase its internal surface area by making it porous.
• Coal is an inexpensive source of carbon and can be obtained relatively free of undesirable impurities. It is readily available in various sizes and size distribution useful in the present invention. Coal is also an amorphous form or carbon and this attribute has been found to be advantageous in the present invention.
• the titaniferous material useful in the present invention can be any titanium-containing compound or raw material such as rutile ore, ilmenite ore, or other.
• a particularly advantageous embodiment of the present invention is that the present chlorination process can be carried out at low temperature in a fluid-bed utilizing naturally occurring titanium-bearing sand such as naturally occurring sand-size rutile ore exemplified by certain Australian sands. Such sand-sized rutile ore is typically -40 mesh and +140 mesh.
• titaniferous materials having various particle sizes can be used in this and other embodiments of the present invention.
• the titaniferous material will be similarly sized to the carbon reductant with which it reacts. Various sizes from about -4 mesh to about -325 mesh can be useful.
• the titaniferous material can be substantially pure or contain a wide variety of impurities.
• the titaniferous material should contain at least about 90% TiO 2 ; however,other embodiments will operate with lesser amounts of TiO 2 in the titaniferous material.
• the titaniferous material in the laminar flow embodiment of the present invention, must contain a substantial proportion of iron for practical commercial scale operation, most often utilizing an Fe/Ti ratio of about 0.5 to 1.5. Impurities present in the titaniferous raw materials will chlorinate along with titanium values; however, the problem created by such impurity chlorination can be minimized by operating certain embodiments of the present process within preselected temperature ranges as described herein.
• the chlorine-providing material can be chlorine gas, HCl, an organo-chloride and mixture thereof.
• the chlorine-providing material is used as the fluidizing gas in the process.
• the gas contain a high percentage of chlorine such that a minimum volume of fluidizing gas can be used and maximum reaction rates obtained.
• Chlorine gas (Cl 2 ) is preferred; however, other organo-chlorides can be used. Highly reactive chlorine sources such as NOCl and selective chlorination agents such as FeCl 2 are not within the scope of the present invention.
• titaniferous material and the porous carbon reductant are intimately mixed within the chlorination reaction zone.
• Discrete particles of titaniferous material and carbon reductant are utilized in the present invention. Preagglomeration of titaniferous material and carbon together into larger granules is not practiced; however, some preagglomeration of titaniferous fines into larger titaniferous material granules or of carbon fines into larger carbon granules, may be practiced within the scope of the present invention.
• Such agglomerates of titaniferous materials or of carbon reductant are considered to be discrete particles for present purposes so long as any given agglomerate contains only titaniferous material or only carbon reductant and not both,
• the temperature is maintained greater than about 600°C.
• the off-gas stream is then collected and cooled to condense the products and facilitate collection.
• granular porous carbon reductant and granular titaniferous material are blended together and charged into the fluid-bed reactor.
• the reactor temperatur is raised to a chlorination reaction temperature of at least about 600°C. and chlorine-providing gas is introduced into the bottom of the reactor to fluidize the bed and an off-gas product stream is withdrawn from the top of the bed.
• powdered porous carbon and powdered titaniferous material are entrained in a stream of chlorine providing gas and introduced into a chlorination reaction zone wherein they proceed in a substantially downward path.
• the chlorination reaction temperature is maintained at a temperature from about 800°C. to about 1200°C. and the reaction zone is sufficiently long so that the falling carbon and titaniferous material experience a retention time of between about 1 and 10 seconds within the chlorination reaction zone.
• a mixture of powdered porous carbon reductant and titaniferous material is passed in substantially laminar flow through a chlorination reaction zone maintained at about 1350°C. to about 1950°C, the atomic ratio of carbon in said mixture to the oxygen content in said mixture being greater than 1:1 for formation of CO, the ratio of the moles of chlorine in said chlorinating agent to said titanium in said titaniferous materials being not substantially above about 2 and the ratio of iron to titanium (Fe/Ti) in the titaniferous material passed into said zone being not substantially above 2.
• the present process increases the selectivity of the chlorination reaction for titanium values over impurities such as aluminum, zirconium, and silicon oxides.
• impurities such as aluminum, zirconium, and silicon oxides.
• AlCl 3 and ZrCl 4 tend to condense on the titanium chloride condensation chamber surfaces which results in eventual plugging and shutdown.
• the production of impurity chlorides consumes chlorine and thereby reduces the overall efficiency of the process and also creates a pollution and disposal problem for such impurity chlorides.
• a further benefit of low-temperature fluid-bed operation of the present process is that no liquid metal chloride impurities are formed in the fluid bed itself.
• the fluidized bed and the off-gas products would be below the melting points of normally troublescnre calcium, magnesium, and iron chlorides.
• liquid chlorides of calcium and magnesium tend to cause bed defluidization.
• FeCl 2 vapor tends to condense on the off-gas product pipeline wall as a liquid and cause dusty solids in the off-gas to stick. This collection of liquid and dusty materials will eventually plug the apparatus and cause a shutdown.
• these troublesome impurity chlorides are solid and are removed from the bed as a fine dust in the off-gas stream and therefore do not cause plugging or defluidization.
• the above-described low temperature capability of the present process enables the use of particularly impure titaniferous materials containing high levels of calcium, magnesium, and iron impurities that previously had to be avoided in conventional fluid-bed chlorination processes.
• ilmenite can be chlorinated at low temperatures in the present process without the extreme plugging problems encountered at conventional temperatures in fluid-bed chlorination processes.
• the nonfluid bed embodiments can effectively chlorinate impure titaniferous materials.
• a further advantage realized from the use of low temperatures in the present process is the ability to increase the TiCl 4 production rate or alternatively decrease the carry-over losses of ore and carbon. The gases in the fluid bed expand when heated to reaction temperature. This expension is considerably less at low temperatures.
• the velocity of the gases in the fluid bed would be lower and entrain less ore and carbon in the off gas.
• more chlorine could be used during low temperature operation of the present process compared to conventional temperature operation and increase the production of TiCl 4 without any increase in the gas velocity.
• the present process is operated in a fluidbed reactor at conventional chlorination temperatures of greater than about 800°C. to about 2000°C, other benefits can be realized. Vanadium values present as impurities in the titaniferous raw materials chlorinate along with the titanium values; however, instead of being very difficult to separate from the titanium values, the chlorinated vanadium values produced are in a different physical form from the chlorinated titanium values and therefore easily separable.
• the chlorinated titanium values (primarily TiCl 4 ) are gaseous whereas the chlorinated vanadium values produced (believed to be VCl 3 ) are solid, and below about 136°C. to about -25°C. the chlorinated titanium values are liquid, while the chlorinated vanadium values remain solid. Furthermore, the chlorinated vanadium values are insoluble in both the gaseous and the liquid chlorinated titanium values. Therefore, below about 450°C, a conventional solid-gas separation or solid-liquid separation is effective to remove the vanadium values contained in the chlorinated titaniferous material.
• a preferred solid-gas separation is the use of a cyclone separator at a temperature of about 140°C. to about 300°C. and preferably about 175°-200°C.; such separation is used in conventional chlorination processes to collect particulates in the TiCl 4 gas stream, but does not remove vanadium values during conventional processing.
• Tail gases are those gases that accompany the product as it leaves the chlorinator and must be disposed of as an effluent of the process.
• the CO 2 :CO ratio in the tail gases of a conventional fluid-bed chlorination process is about 1 or 2:1.
• Such tail gas must be treated before being expelled into the environment because of the high CO level (about 33-50%). This gas cannot support combustion; therefore , treatment by mere burning is precluded and other effective treatments are costly.
• the CO 2 :CO ratio is reduced to about 0.01 or 0.02:1 (about 98 or 99 percent CO).
• this tail gas contains substantially more CO than does the tail gas from conventional processes, this tail gas can be burned directly before expelling into the atmosphere as a means of treatment and thus is substantially easier and less expensive to treat than the tail gas of conventional processes.
• the CO-rich tail gas can be used for its fuel value by burning it in a boiler, kiln, or other.
• the tail gases produced by the non-fluid-bed embodiments of the present invention are believed to be similarly enhanced in CO values, however, not to the extent of the fluid-bed tail gases,
• a still further benefit of the case of porous carbon in the present chlorination proces is a surprising increase in reaction rates and degree of completion. In the case of low-temperature chlorination and down-flow chlorination it is this feature which makes these processes feasible,.
• the porous carbon reductant useful in the present invention can be produced from non-porous carbon by reacting in a fluidized bed at an elevated temperature with air, CO 2 , and/or steam until micropores are produced. Typically about 5% or more of the carbon will be burned off during such treatment.
• the coal introduced into the treatment process can be either wet or dry. Dry coal is actually preferred; however, wet granular coal is a much more readily available commercial product. Water is present in such wet coals to hold down dusting during transportation, as a remnant from washing, flotation or other processing or from unprotected storage.
• Other processes for making high internal surface area carbons are readily available, Any available process for increasing the internal surface area of carbon can be used for making a porous carbon reductant useful in the present invention, so long as a sufficient amount of the internal micropores are produced. Such processes are typically used for producing activated carbon. Commercially available activated carbons have surface areas of about 3000m 2 /g. and are effective in the instant process. However, such materials are substantially more expensive at this time than the above-described treated coals. Also, it has been found that the commercially available activated carbons are not as effective and efficient in the present process as the above-described treated coal.
• EXAMPLE 1 Australian rutile ore containing about 96% TiO 2 and having a particle size such that substantially all of it would pass through a 40-mesh screen and be retained on a 140-mesh screen was chlorinated by blending with a porous carbon reductant and reacting with chlorine in a fluid-bed reactor.
• the reactor consisted of a 3-inch diameter quartz tube with a porous quartz gas distributor plate near one end.
• the porous carbon reductant was prepared by treat ing granular anthracite coal having a particle size such that it would substantially pass an 18-mesh screen and be retained on a 100-mesh screen.
• the treatment consisted of heating the coal in a fluid bed in air at about 450°C. until about 15% of the coal burned off and about 163m 2 /g. of internal surface had formed.
• Surface area as expressed here and throughout this specification is "effective surface area" as determined from the N 2 adsorption isotherm at -195°C. and application of the standard Brunauer, Emmett, and Teller (BET) procedure.
• Granular anthracite coal is substantially amorphous with very little carbon crystallinity.
• the rutile ore and porous carbon were then blended together in a ratio of about 3 : 1 and charged into the reactor to form a bed of about 12 inches deep.
• the bed was fluidized by passing N 2 gas through it, and the reactor was heated to about 575°C. After heat up, the fluidizing gas was switched to Cl 2 with a small measured amount of N 2 added to provide a standard for offgas analysis.
• the Cl 2 feed rate was predetermined to provide a Cl 2 flow of about 35 feet per second and thus a contact time of 3 to 3.5 seconds with the materials in the fluid bed.
• the CO 2 /CO ratio was used to determined carbon consumption and thus additions required to maintain the fluid-bed depth.
• the present carbon was prepared by heating similarly sized granular coal in a fluidized bed in the presence of super-heated steam at a temperature of about 890°C. until about 40% of the coal burned off.
• the steam-treated coal had a surface area of about 680m 2 /g.
• Example 2 In the procedure of Example 1 similarly sized untreated granular anthracite coal was used in place of the porous carbon reductant. This granular coal had a surface area of about 0.1m 2 /g.
• bituminous char In the procedure of Example 1 similarly sized granular bituminous char was used in place of the porous carbon reductant.
• the bituminous char is not porous and thus has only external surface; however, it is substantially amorphous with very little carbon crystallinity.
• the sur face area of the bituminous char was about 0.3m 2 /g.
• EXAMPLE 5 In the procedure of Example 1 calcined petroleum coke having a particle size such that it would substantially pass through a 10-mesh screen and be retained on a 40-mesh screen was used in place of porous carbon reductant.
• the petroleum coke was nonporous and had a surface area of about 0.3mm 2 /g.
• the petroleum coke was substantially crystalline having about 58% crystalline carbon and about 42% amorphous carbon.
• EXAMPLE 6 Wet, granular (-18 mesh), anthracite coal was placed in a fluid-bed reactor and fluidized by introduction of hot steam at a superficial velocity of 0.8 feet per second at a temperature of 890oC. A plot of surface area versus carbon burn-off is shown in Figure 2. Coal treated according to this example is effective in the present process.
• EXAMPLE 7 In the procedure of Example 6, CO 2 at 950°C. was used in place of steam. A plot of surface area versus percent of carbon burn-off is shown in Figure 2. Coal treated according to this example is effective in the present process.
• EXAMPLE 8 In the procedure of Example 6, air at 450oC. was used in place of steam. A plot of surface area versus percent of carbon burn-off is also shown in Figure 2. Coal treated according to this example is effective in the present process.
• Rutile ore containing about 96.1% TiO 2 , 1.2% Fe 2 O 3 , and 0.4% V 2 O 5 was chlorinated in a fluid-bed chlorinator at 1000°C. Chlorine gas and a coal treated in accordance with Example 6 having a 5% carbon burn-off were used. A fluidbed depth of 14-15 inches was maintained by continuously feeding fresh ore and treated coal. The chlorination was run for a period of 3 hours, and the CO 2 :CO ratio in the chlorinator tail gas was measured about every 10 minutes via gas chromatography. The gaseous product stream was allowed to cool partially and was passed through a solid-gas cyclonetype separator.
• the temperature of the gas stream passing through the separator was controlled at about 175oC, how ever, the actual temperature varied between 150° and 200°C.
• the solids collected in this separator include fluid-bed blow-over, FeCl 2 and most of the vanadium values (believed to be VCl 3 ).
• TiCl 4 was then condensed from the product gas stream and solid were allowed to settle. These solids are present mainly due to the inefficiency of the cyclone separator, and contain essentially the same components as the cyclone solids.
• the clear sample of supernatant TiCl 4 was poured off and analyzed for vanadium. The surface area of the carbon source, the average CO 2 :CO ratio, and the vanadium impurity level in the TiCl 4 product are shown in Table I.
• EXAMPLE 15 In order to further characterized the carbons useful in the present invention, three high surface area carbons were selected. Using the BET technique, surface area in ⁇ 20 ⁇ diameter pores were measured and then surface area in >20 ⁇ diameter pores were measured. The total surface area is the sum of these two measurements.
• the examples show the improved chlorination achieved when porous carbon reductants are used in place of conventional nonporous carbons.
• the examples further indicate that the nearly complete removal of vanadium impurities that can be easily accomplished at conventional chlorination temperatures when porous carbon reductant is utilized.

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