US3589988A - Process for the production of chromium of low carbon content by means of fused electrolytic extraction and chromium alloy obtained thereby - Google Patents

Process for the production of chromium of low carbon content by means of fused electrolytic extraction and chromium alloy obtained thereby Download PDF

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Publication number
US3589988A
US3589988A US728594A US3589988DA US3589988A US 3589988 A US3589988 A US 3589988A US 728594 A US728594 A US 728594A US 3589988D A US3589988D A US 3589988DA US 3589988 A US3589988 A US 3589988A
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chromium
electrolyte
electrolysis
metal
cell
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US728594A
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English (en)
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Rene Winand
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Universite Libre de Bruxelles ULB
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Universite Libre de Bruxelles ULB
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/32—Electrolytic production, recovery or refining of metals by electrolysis of melts of chromium
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/36—Alloys obtained by cathodic reduction of all their ions
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts

Definitions

  • the present invention relates to a process for the production of chormium of low carbon content by means of fused electrolytic extraction.
  • ferrochrome of low carbon content may be obtained by different means, depending on the carbon content it is desired to attain.
  • carbon contents of about 1%
  • carburized ferrochrome with 6 or 10% carbon
  • part of the carbon thereof being oxidised either by blowing air into the liquid metal or by the reaction of the latter with a slag rich in Cr O
  • lower carbon contents of about 0.1% it is necessary to make use of more complicated and more costly methods.
  • the Swedish cyclical process which comprises first the preparation of a carburized ferrochrome, followed by the elimination of the carbon therefrom by saturating the metal with silicon and, lastly, to make this metal react with a slag rich in Cr O
  • the Ugine-Perrin process comprises the direct preparation of a ferrosilicon chromium and to make the latter react in two stages with a slag rich in Cr O
  • the electrolyte comprises a mixture of oxides containing boron oxide.
  • the impurities which might possibly be present, would produce emission of corrosive vapors.
  • the charge ofthe furnace be damp, there might even be formation of gaseous hydrofluoric acid in the furnace, with all the serious consequences resulting therefrom.
  • the problem of the refractory material to be used as a crucible is substantially unsoluble from an economic point of view, carbon having to be ruled out, as it would carburize the chromium produced.
  • the aim of the present invention is to overcome the disadvantages of the said methods and to provide a process for the production of metallic chromium by means of fused electrolysis, on an industrial scale, starting with electrolyte of well specified composition so as to produce an industrially pure chromium at a very interesting cost rice.
  • the process according to the invention includes the use of an electrolytic bath deriving from a ternary system selected among the group comprising the Systems Cr O CaO-Al O CI'203-MgOAl203, Cr O -CaO-MgO', Cr O SiO CaO and as well as the complex systems derived from compounds of the said ternary systems.
  • the process comprises maintaining the quantity of silica in the electrolytic bath at a value below 50% by weight of the electrolyte.
  • the process comprises adjusting the total of the quantity of lime and magnesia with reference to the total of the quantity of silica and alumina in the electrolytic bath in a ratio by weight which shall not be less than .75.
  • the process according to the invention may also be advantageously used to prepare a chromium based alloy.
  • At least one or more metals having an afiinity for oxygen less than, equal to, or slightly in excess of that of chromium are introduced in the electrolytic bath so that said metal or metals are deposited at the cathode alongside with the chromium and form an alloy with the latter.
  • the aflinity of the said metal or metals for oxygen is superior to that of chromium, it will be sufiicient to maintain a cathodic current density sufliciently high or to exhaust the bath partially of chromium in order to achieve this.
  • the fusion point of the added metal is lowerthan the temperature of the electrolyte and of the melted cathodic metal, it is possible to introduce it directly in metal form in the electrolysis cell.
  • the invention also relates to an electrolysis cell to be used for working the said process.
  • Said cell comprises a container above which is mounted at least one carbon anode and the bottom thereof is provided with a cavity wherein terminates one lead of cathodic current, said cavity being intended to contain the metal, such as chromium, to be extracted, providing the cathode, an electrolyte being located above the latter and comprising said metal in the shape of an oxide compound, characterized in that the lead of cathodic current is effected 'by means of a cooled conductor so as to coat it with a protective layer of said solidified metal, a layer of the said liquid metal floating on top of the solidified metal.
  • FIG. 1 is an elevational view, partially broken away, of a first form of embodiment of the object of the invention.
  • FIG. 2 is an elevational view, partially broken away, of a second form of embodiment of the object of the invention.
  • the electrolysis shown in FIG. 1 was used to carry out large scale laboratory tests.
  • an outer casing 1 made from ordinary steel sheet, surrounded by a cooling pipe 2, a watercooled hollow bottom 3, a carbon free magnesia concrete inside lining 4, a cathodic current lead comprising a copper tube 5 internally cooled by a circulation of water supplied through a pipe 6 and carried away through a pipe 7, a steel component 8 screwed in the top end of the tube 5, a chromium layer 9 providing the cathode, a graphite anode 10, an electrolyte 11, wherein dips the anode 10, floating on the chromium layer 9, a thermal screen 12 of heat-resisting steel, wherein are provided openings 13 permitting the progressive charging of the cell, three angles 14 mounted radially and carrying, on the one hand, the screen 12 and, on the other hand, a tubular sleeve 15 guiding the anode 10 and lastly removable steel lids 16 protected on their bottom faces by a layer of asbestos.
  • the lids 16 are partially supported by the angles 14 and are used to maintain a a
  • the component 8 is covered with a solidified protective layer 17 of chromium, the remainder of the layer 9 being in the liquid condition.
  • a solidified protective layer 17 of chromium the remainder of the layer 9 being in the liquid condition.
  • the cell is carried on a tripod 19, a tap hole 20 is provided for removing the metal 9 and another hole 21, provided above the first tap hole 20 is provided to remove exhausted electrolyte.
  • the electrolysis cell shown in FIG. 2. may be used on an industrial scale. It comprises substantially an outer casing 1 made from ordinary steel sheet cooled, if need be, by a water circulation not shown, walls 22 and a bottom 23 made from refractory bricks, a carbon free magnesia concrete inside lining 4, cathodic current leads comprising copper tubes 5 on the top of each of which is provided a mild or stainless steel component 8 and cooled internally by a water circulation, a layer of chromium 9 providing the cathode, a plurality of anodes 10 made from, for example Soderberg quality, carbon,
  • a vault 16 made from silica provided with bores 25 connected to pipes, not shown in the figure, for exhausting the gases released at the anode 10, bores 25 connected to feed hoppers, also not shown in the FIG, 2, and lastly sight bores 26.
  • a tap hole 20 enables the removal of the metal built up on the cathode while another hole 21 is used to remove exhausted electrolyte.
  • the leak tightness is provided by means of an appropriate device 27.
  • the vault 16 maintains a reducing atmosphere inside the furnace in order to prevent the surface oxidization of the electrolyte. However, in certain cases where a slight surface oxidization of the bath is permissible, said vault need not be provided.
  • the current intensity mounted to 1,050 amps for a terminal voltage of 25 v., while, the anode dipping in the electrolyte 11, the distance between such anode and the chromium layer 9 providing the cathode exceeded 5 cm., these conditions being maintained for five hours.
  • the anode was withdrawn from the electrolyte 11 and the cell was left to cool slowly. When the cell had reached substantially ambient temperature, the exhausted electrolyte and the metal produced were withdrawn. The electrolyte still contained about 4% of Cr O while the collected metal met the following analysis.
  • the remainder comprised substantially iron.
  • the cathodic current efliciency was about 60%, which may be considered as very satisfactory, considering the fairly small scale at which the test was carried out.
  • the current intensity used for this test corresponded to an average current density of about 350 amps/dmP.
  • the remainder comprised mainly iron which could originate from pieces of oxide fallen from the thermal screen in heat-resisting steel.
  • the cathode current efficiency was about 50%, which may be considered a success, considering the scale at which the test was carried out.
  • the current intensity used for this test corresponded to an average current density of about 600 amps/dm.
  • the cathodic liquid chromium is carried on a solid layer formed by one or more refractory 'oxides which do not react with the chromium.
  • the electric cathodic contact between the liquid chromium and the feed of cathodic current is effected by means of a conductor cooled so as to become coated with a layer of solidified chromium. This has for its aim to prevent any contamination of the chromium produced at the cathode by the metal or metals comprising the cathodic current feed.
  • the electrolyte may comprise three or a plurality of the following compounds: Cr O CaO, SiO A1 and MgO.
  • Cr O CaO Cr O CaO
  • SiO A1 MgO
  • a mixture of oxides comprising 46% of CaO, 6.3% of MgO and 47.7% of A1 0 by weight may dissolve up to 30% of Cr O by weight while maintaining all the time a melting temperature below 1600 C.
  • Mixtures of this kind when subjected to electrolysis, have revealed themselves extremely interesting. Indeed, for anodic and cathodic current densities close to 250 amps/dm.
  • the anode used in the electrolysis cell for working the process according to the invention may be of amorphous carbon, of graphite or more currently of Sd'derberg type.
  • the metal produced by electrolysis is essentially characterized by a very low carbon content (less than 1%) and a low silicon content (generally less than 2%).
  • the content of other impurities is conditioned by the purity of the electrolyte.
  • all of the iron contained in the electrolyte passes into the chromium deposited at the cathode.
  • the silicon content of the metal produced at the cathode is essentially conditioned by the index of basicity of the electrolyte, by its silica content and by its degree of final exhaustion. If said index is maintained at a value equal to or higher than unity, that the silica content is less than 25% and the electrolysis is stopped at the time when about 5% Cr O remain in the electrolyte, it is possible to achieve silicon contents of less than 1%. Under those conditions, and insofar as the electrolyte does not contain inpurities more reductible than Cr O it is possible to produce a chromium of about 99% or more.
  • a chromium with a higher silicon content it will be sufficient to maintain the index of basicity of the electrolyte sufficiently low, for example below .75 and/or a silica content exceeding 25% and to continue the electrolysis until a high rate of exhaustion of the electrolyte is reached.
  • the chromium ore mixture contains iron, it is possible to produce by electrolysis a chromium with a low iron content by carrying out beforehand an operation to remove the iron.
  • the ore is then subjected to an electrolysis similar to that permitting to achieve a chromium with little impurities, without, however, proceeding as far as to exhaust the chromium from the electrolyte.
  • an electrolyte containing 20% or more of Cr O for example but the iron of which has been removed, which is afterwards subjected to an exhaustion electrolysis in another electrolysis cell of the type hereinbefore described and, on the other hand, a ferrochrome of low carbon and silicon content, having a high commercial value compared with heavily carburized chromium pig iron produced by a conventional iron removal method, such as a reducing melt in an electric furnace.
  • the electrolyte could contain minute additions of other oxides or salts than those comprised in the ternary systems hereinbefore cited such as BaO, B 0 NaF, CaF and having for their object to reduce the melting temperature thereof or to increase the electric conductivity thereof.
  • a process for the production of chromium of low carbon content by means of fused electrolytic extraction including the use of an electrolytic bath deriving from a ternary system selected among the group comprising the systems Cr O CaOAl O CI O MgO--Al O and Cr -O MgO-SiO as well as the complex systems derived from compounds of the said ternary systems.
  • a process as claimed in claim 1 comprising using a cathode formed by the metal to be extracted, such as chromium or a chromium alloy with another metal present in the electrolyte in the form of oxide.
  • a preliminary electrolysis in order to remove from the bath the metals which are more easily reductible than the chromium such as iron for example, to remove also the alloy, such as ferrochrome, deposited on the cathode, as well as to subject the electrolyte purified in this manner to a second electrolysis so as to produce the chromium.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Secondary Cells (AREA)
US728594A 1967-05-19 1968-05-13 Process for the production of chromium of low carbon content by means of fused electrolytic extraction and chromium alloy obtained thereby Expired - Lifetime US3589988A (en)

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JP (1) JPS4945205B1 (en)van)
BE (1) BE698705A (en)van)
GB (1) GB1190679A (en)van)
NL (1) NL6807140A (en)van)
NO (1) NO123729B (en)van)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4243502A (en) * 1978-04-07 1981-01-06 Swiss Aluminium Ltd. Cathode for a reduction pot for the electrolysis of a molten charge
US4287045A (en) * 1978-11-10 1981-09-01 Institut De Recherches De La Siderurgie Francaise Cooled electrode adapted to contact molten metal

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITTO970080A1 (it) * 1997-02-04 1998-08-04 Marco Vincenzo Ginatta Procedimento per la produzione elettrolitica di metalli

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4243502A (en) * 1978-04-07 1981-01-06 Swiss Aluminium Ltd. Cathode for a reduction pot for the electrolysis of a molten charge
US4287045A (en) * 1978-11-10 1981-09-01 Institut De Recherches De La Siderurgie Francaise Cooled electrode adapted to contact molten metal

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Publication number Publication date
NO123729B (en)van) 1972-01-03
JPS4945205B1 (en)van) 1974-12-03
GB1190679A (en) 1970-05-06
NL6807140A (en)van) 1968-11-20
BE698705A (en)van) 1967-11-03
DE1758334B1 (de) 1975-09-25

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