US3374163A

US3374163A - Cell for electrolysis with molten salt electrolyte

Info

Publication number: US3374163A
Application number: US322106A
Authority: US
Inventors: Meier Edwin; Schweizer Erich
Original assignee: Ciba AG
Current assignee: BASF Schweiz AG
Priority date: 1962-11-15
Filing date: 1963-11-07
Publication date: 1968-03-19
Anticipated expiration: 1985-03-19
Also published as: NL300517A; SE324657B; AT242378B; GB1048090A; DE1184965B; CH439766A; BE639899A

Description

March 1968 E. MEIER ETAL CELL FOR ELECTROLYSIS WITH MOLTEN SALT ELECTROLYTE Filed Nov. 7, 1963 SUPPLY FEED DUCT FOR METAL HALIDE 6 W m we EE .l. M m P E OF PD G RR 0 E F um X M NA E0 E6 NH LZ F FF E i l w N n A CATHODE EVAPORATING cmmasn ORIFICE m ANODE VESSEL/ w w Edw/h Meier and Er/ch 5chwe/Zer INVENTOR ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE An electrolytic cell is provided for the manufacture of metals of the 4th, 5th and 6th sub-groups-of the Periodic Table from the halide of the metal in a molten salt electrolyte. The cell has a hollow cylindrical anode and a rod-shaped cathode. The cathode is positioned within and coaxially aligned with the anode. The anode is characteriz ed by havinga plurality of annularly-arranged holes which extenddownward from the inner wall of the anode to the outer wall of the anode. The cell has a downward-opening annular chamber positioned'about the outer wall of the anode. In operation the cell is filled with a molten salt electrolyte to a level-at which the surface of the electrolyte is slightly above the holes in the anode and in commu nica t ion with the opening of. theannular r. A. PQ ZQ me a ha id i e in the annular chamber from where it is introduced into the elec-" trolyte. The holes in the anode assist the circulation of the electrolyte and facilitate the removal ofthehalide gases from the electrolyte in the cell.

Several electrolysis cells are. known for the production of heavy metals, by electrolysis by the. continuousaddition of a metal halide toa moltensalt electrolyte. In some cases it has been proposed to supply thernetal halide bya special supply feed directly to the cathode, or to introduce it into the melt bath through a hollow cathode. There are also known cells. with a cylindrical anode and a rod-shaped cathode arranged coaxially thereto. r

\ One of the main difficulties in the manufacture of heavy metals by electrolytic means is to discover conditions under which metal separates in as pure a state as possible.

I Special 'diificulties halide is added in vaporous state. The composition ofthe bath, the electrolysis temperature, the-material of cathode, anode, vessel and diaphragm .and the arrangement of the individual elements of the cell'influence the electrolysis and, consequently, the quality and quantity of the metal separated. The arrangement-and constitution 'ofthe cell present invention conis of particular importance. The cerns this problem and provides possible to manufacture especially It-has been found puremetals sub-group of the Periodic Table the corresponding metal halide if the cell has thefollowa cell which makes it pure; metal. 7 of the'4th,- 5th and 6t ing features:

(l) The cell has no supply duct for the-metal halide vapour intothe melt, but only an arrangement whereby the metal halide is supplied to the surface of the melt".

Thus, the metal halide is not introduced but ifiows on to the surface where it is absorbed bytthe molten salt bath on account of convection. The elimination of a duct submerged into the melt also eliminates the .difiiculty of having to introduce the metal halide under pressure. In duct also prevents any addition, the elimination of the additional contamination of'the-melt.

(2) An essential feature of the invention; is that the condensing chamber for the metal halide, i.e., the place are encoun ter ed, when the metal 1 may be produced from where the halide is absorbed by the molten bath, is outside the zone of the electrolysis. According to the invention, it is arranged concentrically around electrolytic zone. This arrangement avoids losses of metal halide, such as occur during the condensation of the halide vapour in the electrolytic zone by discharge with the anode gas. Condensing chamber and electrolytic zone correspond to the principle of communicating vessels so that the level of the bath is the same in both parts of the cell.

(3) The cylindrically shaped anode contains in its upper portion, slightly below the level of the melt, several orifices in annular arrangement. These orifices produce a continuous circultion 0f the bath. In the inner part of the anode cylinder, the bath rises, flows through the orifices and down along the-outside of the anode. In the inner part of the cylindrical anode, the halide is produced and the formed gas bubbles support the upward movement of the circulation in this zone.

(4) A special advantage of the arrangement of the invention is that no diaphragm is necessary. The supply of the metal halide vapour outside the electrolytic zone and the described circulation of the molten bath result in optinum conditions for the electrolysis so that no diaphragm is necessary.

The present invention relates to a cell for the electrolysis of halides of metals of the 4th, 5th and 6th subgroups of the Periodic Table in a molten salt electrolyte, equipped with a feed duct for the vaporous metal halide and with a rod-shaped cathode, arranged coaxially within a cylindrical anode, characterized in that the condensing chamber for the metal halide is located outside the electrolytic zone, that the anode has preferably cylindrical holes in annular arrangement, slightly below the horizontal plane forming the upper defining line of the effective partof the rod cathode, and that there is arranged on the outside of the anode cylinder a downwardly open bath is at the same time the upper limit of the active.

part of the cathode rod. Below this limit there are the openings in the anode and, above, there is the non-irnmersed part of the annular channel, i.e., the socalled condensing chamber.

-. is shown at 6, a delivery duct at 7, and the outlet of the halogengases formed at the anode at 8. Reference numeral 9 indicates a hinged cover. The vaporous metal halide enters at 10 and passes through 11 into the annular channel 12.'The bath 13 circulates as indicated by the arrows. -14 is'an orifice in the cylindrical anode. These v orifices 14- are preferably of cylindrical shape, the longitudinal axisof the cylinder sloping downwardly toward the outside. This arrangement prevents the anode gas from being carried along into the condensing chamber. The supply feed duct 11 for the metal halide vapour terminates conveniently in the top of the annular channel 12.

Preferably a' hollow cathode is used, with a watercooled holder, and made of nickel. The cylindrical anode,

as well as the vessel, are made of graphite. The top of r the cell is closed so that access of foreign gases, such as air, is prevented.

above which horizontal plane The melts consist of mixtures of alkaline and alkaline earth halides, such as KCl, NaCl, KF, NaF, CaClor CaF Preferably mixtures are used which produce, after addition of the metal halide, stable double salts of the metal to be separated with the fluorides present in the bath.

The cell is suitable for producing titanium, zirconium, vanadium, chromium, molybdenum, tungsten, and especially tantalum and niobium. The metal halides supplied as vapours are especially metal chlorides, such as TiCl VCl VOCl NbCl TaCl and WCI and WOCL EXAMPLE 1 In an electrolytic cell according to FIG. 2, about 40 kg. of a salt mixture, consisting of 40% sodium chloride, potassium chloride and 30% potassium fluoride, are molten at about 800 C. Into this melt, about 7 kg. tantalum pentachloride are added as vapour by convection through conduit 11 and annular channel 12. Electrolysis is effected at a bath temperature of 800 C. to 900 C. with 1500 amps. In order to maintain the concentration of tantalum chloride in the melt, 3.6 kg. TaCl are introduced in the course of one hour. After one hour, the separated metal is removed from the cell and further electrolysis is carried out with a second cathode. 1710 grams of tantalum are separated during this time. The yieldrelated to TaCl is 95% and the mean current yield is 83%. The metal produced has a uniform, metallic appearance and consists of dendrites of 100 to 500 microns. An analysis shows the following impurities:

Percent, below Carbon 0.02 Oxygen 0.02 Hydrogen 0.002 Nitrogen 0.005 Silicon 0.001 Tungsten 0.003 Molybdenum 0.001 Niobium 0.005 Chromium 0.005 Nickel 0.01 Iron 0.005 Titanium 0.001

EXAMPLE 2 A cell as shown in FIG. 2 is used. 2.5 kg. of titanium tetrachloride are added as vapour through annular channel 12 and absorbed in kg. of a basic melt consisting of percent by weight of sodium chloride, 40 percent by weight of potassium chloride and 20 percent by weight of potassium fluoride; electrolysis is carried out for 1 hour at 1000 amps. and at a bath temperature of 800 C. A further 2.5 kg. of titanium tetrachloride are added as vapour during electrolysis. The Separated metal on the cathode is cooled in an atmosphere of argon; after washing, the weight of the metal is 327 grams which corresponds to a current yield of 72.6% and a metal yield of 89%. An analysis shows the following values:

Percent, below Carbon 0.02 Oxygen c 0.02 Hydrogen 0.005 Silicon 0.001 Molybdenum 0.001 Chromium 0.01 Nickel 0.03 Iron 0.02 Tungsten 0.003

EXAMPLE 3 In each case a cell as shown in FIG. 2 is used.

(a) 6 kg. of tungsten hexachloride are added as vapour into a basic melt of the same composition as described in Example 2 and electrolyzed as described in Example 2.

- 4 I Y The washed metal Weighs 784 grams. The current yield is 68.4%, the metal yield 83%. a

(b) 4 kg. of tungsten oxychloride are added as vapour into the above melt and subjected to electrolysis at 1000 amps for 1 hour to yield 724 grams of metal. The current yield is 63%, the metal yield 85%.

An analysis shows the following values:

' Percent, below Carbon 0.03 Oxygen 0.03 Hydrogen 0.005 Silicon -2 0.001 Molybdenum 0.001 Chromium 0.01 Nickel 0.03 Iron 0.02 Titanium 0.001

, EXAMPLE 4 A'cell as shown in FIG. 2 is used. A total of 3 kg. of niobium pentachloride is added as vapour through annular channel 12 into a basic melt of 17.1 kg. of sodium chloride, 9.8 kg. of potassium chloride and 13.0 kg. of potassium fluoride. The bath temperature is 900 C. Electrolysis is carried out for 1 hour with 1200 amps. The weight of the metal separated during this time amounts, after washing, to 310 grams, which corresponds to a current yield of 37.2%. After analysing the niobium remaining in the melt, a material yield of 89.5% was found.

An analysis shows the following values:

- Percent, below Carbon 0.03 Oxygen 0.03 Hydrogen 0.005 Silicon 0.001 Tungsten 0.003 Molybdenum 0.001 Tantalum 0.01 Chromium 0.01 Nickel 0.03 Iron 0.02 Titanium 0.001

What is claimed is:

1. Cell for the electrolysis of halides of metal of the 4th, 5th and 6th sub-groups of the Periodic System, in a molten salt electrolyte, having a supply feed for the vaporous metal halide and a rod-shaped cathode, arranged coaxially within a cylindrical anode, characterized in that the condensing chamber for the metal halides is outside the electrolytic zone; that the anode has cylindrical holes in annular arrangement slightly below the horizontal plane forming the upper defining line of the eifective part of the rod cathode the remainder of said anode being non-fora-minous, said holes having a cylindrical shape and their longitudinal axis sloping downwardly and outwardly, and that a downwardly open annular channel is arranged on the outside of the cylindrical anode, extending from said holes upwardly to above the horizontal plane forming the upper definition of the effective part of the rod cathode, above which horizontal plane there terminates at least one supply duct for the vaporous metal halide in this annular channel.

2. A cell as claimed in claim 1, characterized in that the supply duct for the metal halide terminates in the top of the annular channel.

3. An electrolytic cell for the manufacture of the metals of the 4th, 5th and 6th sub-groups of the Periodic Chart from a-halide of said metals using a molten salt electrolyte, said electrolytic cell comprising in combination 1' downwardextending apertures from the inner wall to the outer wall arranged annularly about said anode at a position which is only slightly below the surface of the electrolyte when the anode is emersed to said predetermined level, the remainder of said anode being non-foraminous said annular chamber being positioned about the outer wall of the anode so that it is in communication with the surface of the electrolyte when the anode is emersed to the predetermined level, and said supply duct being in communication with the annular chamber and adapted to feed said metal halide, in vaporized form, to the annular chamber.

References Cited UNITED STATES PATENTS 2,898,276 8/1959 Snow 204246 X 2,908,619 10/ 1959 Barnett 204-246 X 3,079,324 2/1963 Allen et a1. 204-246 HOWARD S. WILLIAMS, Primary Examiner. JOHN H. MACK, Examiner.

l D. R. VALENTINE, Assistant Examiner.