Separation method

Abstract

A process for recovering metal from a process material comprising the metal and a component that is more volatile than the metal, which process comprises: transporting the process material in a retort provided in a furnace, the retort being operated under vacuum and at a temperature sufficient to cause sublimation of the component from the process material thereby producing purified metal; depositing the component that has been sublimed on a cool surface; removing purified metal from the retort; and removing deposited component from the cool surface.

Claims

1. A process for recovering a metal from a process material comprising the metal and at least one component that is more volatile than the metal, which process comprises: transporting the process material in a retort provided in a single furnace, the retort being operated under vacuum and at a temperature sufficient to cause sublimation of the at least one component from the process material thereby producing purified metal as a solid, the process material comprising the metal and the at least one component which includes one or more volatile salts of another metal; depositing via deposition the at least one component that has been sublimed on a cool surface that is in continuous direct communication with the retort; removing the purified metal from the retort; and removing the at least one component that has been deposited on the cool surface from the cool surface, wherein the process is operated on a continuous basis with fresh process material being supplied to the retort and furnace, with the purified metal being removed continuously and with the at least one component deposited on the cool surface being removed continuously.

2. The process of claim 1, wherein the metal is selected from titanium, zirconium and hafnium and the process material is a reduction reaction product including the metal reduction reaction by-products.

3. The process of claim 1, wherein the metal is titanium and the process material is produced by reduction of titanium tetrachloride with magnesium.

4. The process of claim 1, wherein the process material is transported in the retort using a rotating screw.

5. The process of claim 1, wherein a temperature gradient is provided so that process material transported in the retort is transported into a hot zone where sublimation of the at least one component from the process material takes place.

6. The process of claim 1, wherein multiple components that are more volatile than the metal are removed from the process material via sublimation and deposition.

7. The process of claim 1, wherein the process material is in particulate form.

8. The process of claim 7, wherein temperature and pressure is controlled to avoid formation of liquid phases.

Description

(1) Embodiments of the invention are illustrated in the accompanying non-limiting figures in which:

(2) FIG. 1 is a schematic illustrating a reactor in accordance with the present invention; and

(3) FIGS. 2 and 3 are schematics illustrating componentry that may be used in a reactor in accordance with the present invention.

(4) The figures are schematics only and are not limiting with respect to relative proportions and dimensions.

(5) The figures will be discussed for the purposes of illustration only with reference to the processing of titanium-containing process material produced by the reduction of titanium tetrachloride with magnesium. The process material may be produced as described in Applicant's published International patent application WO2006/042360 entitled Low temperature industrial process. The process material takes the form of composite particles in which titanium particles are embedded in a matrix of MgCl.sub.2. The invention is not restricted to implementation using this type of product however.

(6) FIG. 1 illustrates a reactor including a cannister/hopper (1) for feeding the process material onto the surface of a sublimation screw (2) via an inlet port. Feeding of the composite particles may be metered using valves. The sublimation screw (2) is provided within a sublimation retort (3) that takes the form of an elongated tube. Rotation of the sublimation screw (2) will have the effect of transporting the process material. The sublimation screw (2) is a shaftless screw rotated by a drive (4) located at one end of the screw.

(7) The sublimation retort (3) extends into a furnace (5) that has a maximum temperature (at a zone remote from the location at which process material is delivered onto the sublimation screw (2)) of about 1050 C. The sublimation retort (3) may be subjected to a vacuum via vacuum line (6) and is typically operated between 0.01 and 0.015 kPa. The apparatus is typically flushed with a purge gas (argon, for example) to keep air out of the apparatus during operation.

(8) At the end of the sublimation screw (2) remote from the end that receives process material there is provided a canister (7) for collection of titanium that has been purified due to the sublimation of volatiles.

(9) The reactor also includes a deposition screw (8) and deposition retort (9). The deposition retort may extend into the sublimation screw (2). In this case the sublimation screw (2) may be shaftless. The deposition screw (8) may also be shaftless. It also follows that if an internal deposition retort is used the internal diameter of the deposition retort (9) is less than that of the sublimation retort (3). FIG. 1 shows the arrangement of the deposition screw (8) and deposition retort (9) and the sublimation screw (2) and sublimation retort (3) where external deposition retorts are employed.

(10) An independent drive unit (10) is used to rotate the deposition screw (8) within the deposition retort (9). A vacuum line (6) connects with the deposition retort (9), and in turn is linked to a vacuum pump. The deposition retort (9) also includes a discharge outlet for collection of deposited material into a canister (11)

(11) In use the apparatus is evacuated using vacuum pumps and purged with argon. The pressure in the system is generally 0.01 to 0.015 kPa. The retort (5) component of the apparatus is brought up to temperature (about 800 C.) using heating elements or the like. The sublimation screw (2) and deposition screw (8) are rotated. Process material is metered onto the sublimation screw (2) and is transported into the furnace portion of the apparatus. Under the prevailing pressure and temperature conditions volatiles present in the process material (primarily MgCl.sub.2) are sublimed off thereby leaving purified titanium metal particles. These particles are transported the length of the sublimation retort and are discharged at the end of the retort and collected in a canister (7). The titanium particles may be used as is or subjected to further processing in accordance with the invention to enhance the purity by driving off further volatile species that may be present. Some light sintering of the titanium particles may occur and if it does this may actually be beneficial to reduce the reactivity of the ultrafine titanium particles.

(12) Volatiles that sublime off the process material are drawn under vacuum into the deposition retorts (9) where the temperature is controlled to cause deposition. In this regard the deposition retort, or at least a part of it, may include a cooling sleeve (12). Typically, the temperature along the length of the deposition retort (9) will decrease away from the furnace (5). A temperature gradient ranging from 750 C. to 350 C. along the length of the deposition retort (9) may be suitable. Deposited solids on the inner surface of the deposition retorts (9) will be transported along the retort by the action of the deposition screws (8). At one end of the screws the deposited solids are discharged through a port provided in the retorts and collected in a canister (7).

(13) FIGS. 2 and 3 illustrate a portion of a sublimation retort in the form of a tubular member. The sublimation retort (1) will include a sublimation screw but this is not illustrated in FIGS. 2 and 3. The interior of the sublimation retort (1), is connected to a deposition retort (2) via a port (3). The deposition retort takes the form of a tubular member. Typically, the deposition retort (2) meets the sublimation retort (1) at 90 but this is not essential. The deposition retort (2) includes a discharge outlet (4).

(14) In FIG. 2 the deposition retort (2) includes a deposition screw (5) comprising a shaft (6) and screw threads (7).

(15) In FIG. 3 the deposition retort (2) includes a central tubular member (9) that is fixed. In the annular space (10) between the tubular member (9) and the inner surface of the deposition retort (2) is provided a shaftless deposition screw (11) that rotates around the tubular member (9).

(16) In use in the sublimation retort (1) volatiles are sublimed at high temperature and they are drawn into the deposition retort (2). If the temperature in the deposition retort is suitably low, volatiles will deposit as solids on surfaces within the retort (2). In FIGS. 2 and 3 deposited volatiles are identified by referent numeral 8. Rotation of the screw (5) will have the effect of scraping deposited volatiles (8) off the inside surface of the deposition retort (2) and transport it along the deposition retort (2) where the purified metal (8) will be discharged through outlet (4) for collection.

(17) In FIG. 3 deposition will take place on the inner surface of the deposition retort (2) and the surface of the central tubular member (9). Deposited volatiles (8) will be scraped from the surfaces of the deposition retort (2) and tubular member (9) by the deposition screw (10) and transported along the deposition retort (2) for discharge at outlet (4).

(18) The embodiments shown in FIGS. 2 and 3 will include the same additional componentry as shown in FIG. 1the main difference between the embodiment of FIGS. 1-3 lies in the type of the deposition retort and deposition screw(s) employed. The mode of operation for the embodiments in FIGS. 2 and 3 essentially the same as in FIG. 1, subject of course to design modification for the deposition retort/deposition screw(s).

(19) The apparatus used in the invention and components thereof are made of materials having suitable properties, and one skilled in the art would be familiar with materials to be used.

(20) The following non-limiting example illustrates an embodiment of the present invention.

EXAMPLE

(21) The apparatus used was a cylindrical sublimation retort made of 253MA stainless steel, 2.2 m in length with an internal diameter of 153 mm. The central section of the sublimation retort was placed in a 1300 mm long 14.4 kW, 3 zone, split furnace and heated to 870 C. The hot zone of the sublimation retort (a section above 750 C.) was 700 mm long. The feed section of the sublimation retort comprised a 50 mm port attached to a single auger powder feeder. The feed process material, a composite material containing Ti particles in a magnesium chloride matrix (20.1% Ti, 79.7% MgCl.sub.2), sub 400 microns, was fed into the sublimation retort at a rate of 250 g/hr taking 8 minutes to pass through the hot zone.

(22) At the outlet end of the sublimation retort was a 70 mm discharge pipe, allowing the Ti rich metal powder to fall through a ball and knife gate valve into a sealed metal tube. After a single pass, the metal power consisted of 99.3% Ti, 0.10% Mg and 0.30% Cl.

(23) The sublimation retort was designed to operate under medium vacuum with minimal air ingress. The composite material was moved through the sublimation retort by a shaftless screw with a 90 mm pitch driven from the feed end at 1 to 10 rpm. The drive train consisted of an electric motor connected to a high ratio gear box and passing through a 3 chamber mechanical seal to ensuring minimal air ingress. The pressure within the sublimation retort was operated between 0.01 and 0.015 kPa. A purge gas of Ar was added at 5 mg/min as a barrier gas.

(24) Magnesium chloride from the composite material that has sublimed within the hot zone is then removed from the sublimation retort through a 136 mm ID internal deposition retort running from the feed end of the sublimation retort through the centre of the shaftless screw to a point close to the hot zone where its entry point was located. The magnesium chloride sublimed in the hot zone in the sublimation retort was then pulled into the deposition retort via a vacuum pump connected to the end of the deposition retort. The magnesium chloride deposited rapidly on entry into the deposition retort. The deposition screw was used to transport the solid magnesium chloride powder through the deposition retort to a 50 mm discharge port and into a metal canister. The deposition screw was extended slightly past the entry point to prevent build-up of accretion on the entry to the deposition retort.

(25) The apparatus was operated continuously over a 20 hour period generating approximately 0.9 kg of purified metal.

(26) Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention

(27) The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

(28) Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.