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
  • C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
  • C22B26/20—Obtaining alkaline earth metals or magnesium
  • C22B26/22—Obtaining magnesium
• • 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
  • C22B5/00—General methods of reducing to metals
  • C22B5/02—Dry methods smelting of sulfides or formation of mattes
  • C22B5/06—Dry methods smelting of sulfides or formation of mattes by carbides or the like
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• ABSTRACT A method of producing magnesium by the reduction of magnesium oxide by means of a metallic reducing agent, in the presence of a molten oxidic slag, wherein the system contains an inert gas to obviate at least in part the need of a high vacuum.
• This invention is concerned with the production of metallic magnesium by the metallothermic reduction of magnesium oxide at elevated temperature, and it relates to an improved process wherein magnesium oxide, usually in the form of calcined dolomite or calcined magnesite or mixturesthereof, is caused to react with a metallic reducing agent, such as silicon, aluminum, calcium or mixtures or alloys thereof, .-in the presenceof a molten slag bath in a furnace at temperatures in excess of 1300C., to release magnesium vapor which may be condensed and collected.
• a metallic reducing agent such as silicon, aluminum, calcium or mixtures or alloys thereof
• the commercial process of this type is operated under very high vacuum. It is the purpose of this invention to provide means whereby operation under high vacuum may be avoided, and the process operated more nearly at atmospheric pressure or at least under lower vacuum, thereby improving the technology and economics of the process.
• the equipment in which such a process has beencarried out comprises in sequence: feed bins in which the raw materials are stored and from which they arefed to the furnace through ducts or tubes; the furnaceproper in which the reducing reaction takes place; a throat or duct through which magnesium vapor released in the reaction zone passes; a condenser in which the magnesium vapor is condensed to. molten metal; and a pot or crucible attached to the condenserin which the molten magnesium is collected.
• a vacuum system removes such gasses as may appear in the system, and maintains a'.-high vacuum, usually corresponding-to an. absolute pressure ofless than about one-twentiethatmosphere.
• the operation of such an extensive system. under very high vacuum at elevatedtemperatures involves design, engineering, construction and operating problems, the alleviation of which is the objectof the present invention.
• Magnesium vapor is the only gaseous product of the'desired reactionthe other products being molten slag .and spent alloy-and this vapor is condensed to molten metal as rapidly as it is formed.
• the absolute pressure. in theMagnetherm system is essentially that corresponding to the vapor pressure of magnesium at or somewhat above its melting point, namely less than about one-twentieth atmosphere.
• inxeffect magnesium formed in the reaction zone is distilled from-the furnace under very high vacuum, condensed,.and collected in the crucible as molten (or solid) metal.
• theu'present inventions may bev characterized as the reduction of magnesium oxide by means of a metallic reducing agent in the presence of a molten oxidic slag at a temperature above 1300C. wherein the magnesium vapor is evolved and condensed in an atmosphere at an absolute pressure of at least one-tenth atmosphere and comprising an inert gas at a partial pressure of at least about one-tenth atmosphere.
• the present invention provides a process of the Magnetherm type which produces magnesium vapor under a relatively high absolute pressure, due in part at least to the presence of an inert gas. This added pressure may be utilized to decrease or eliminate the pressure differential between the interior of the system and the atmosphere.
• the term high vacuum refers to an absolute-pressure of less than one-twentieth atmosphere, and a relatively high pressure is one-tenth atmosphere or higher.
• an absolute pressure of up to at least about 1 atmosphere including the partial pressure of both magnesium and an inert gas, will not inhibit the reaction to a serious extent; and under normal conditions gaseous diffusion .alone will provide a mass transfer rate of magnesium vapor from furnace to condenser sufficient to keep pace with the rate of production in the furnace.
• gaseous diffusion .alone will provide a mass transfer rate of magnesium vapor from furnace to condenser sufficient to keep pace with the rate of production in the furnace.
• the partial pressure of the magnesium ,in the furnace depends, of course, upon other conditions, primarily the temperature of .the slag-bath,;but alsothe concentration of magnesium oxide, the composition of the reducing agent,.the temperature of the condenser. and the production rate.
• the partial pressure oftheinertgas also is dependent on other factors, but
• the partial pressure of the inert gas need not be higher than 1 atmosphere (or slightly less) inorder that the absolute pressure of the system be about 1 atmosphere. But, if desired, the absolute pressure may be higher,.and the partial pressure of the inert, gas may be corv. 5.
• inert gas includesthose gaseous materials thatare non-reactivewith the components ofthe .system under, the conditions of operation. Becauseof theshighchemicalactivityof magnesium at elevated temperature, few gases can be considered inert in the present process. Suitable inert gases include the literally inert gases, such as helium, neon, argon and the like. Another non-reactive gas is hydrogen, which is in certain respects desirable. Hydrogen is cheap and easily available, it provides excellent characteristics for heat transfer in the condenser, and it provides a relatively high specific rate of diffusion. If for some reason air leaks into the system, its oxygen should react with magnesium in preference to the hydrogen. If the hydrogen leaks out of the system, it should either burn or otherwise be dissipated innocuously. Any other gas with equivalent inertness may be used in this invention.
• the magnesium oxide reactant may comprise magnesia, usually derived from magnesite by calcination, or calcined dolomite, an equimolar combination of magnesium oxide and calcium oxide, or mixtures of both.
• magnesia usually derived from magnesite by calcination, or calcined dolomite, an equimolar combination of magnesium oxide and calcium oxide, or mixtures of both.
• the magnesium oxide content of the system should be maintained relatively high, above 5 percent and preferably between about 10 and 20 percent, measured as a fraction of the oxidic slag.
• the metallic reducing agent may be silicon, aluminum, aluminum-silicon, ferrosilicon-aluminum, calcium-silicon, calcium-aluminum-silicon or the like.
• an aluminum-silicon alloy containing silicon and aluminum in a ratio of at least 0.8: l is employed. High utilization of the silicon is possible with such alloys.
• the presence of aluminum in close physical association with the silicon stimulates the reductant synergistically, and a major fraction of the silicon may be utilized to reduce the magnesium oxide.
• Scrap aluminum may be used, and it may be added to provide part of the reducing agent.
• aluminum silicon
• aluminum-silicon alloy include those reductants which, when added to the molten slag in the reaction zone of a reducing furnace, as herein described, provide metallic aluminum, silicon or both.
• a ferrosilicon alloy for example a ferrosilicon-aluminum alloy containing about -25 percent iron, 40-65 percent silicon and 25-50 percent aluminum, particularly in view of the ready availability of such aluminum-silicon alloys.
• Such alloys can be manufactured by electric furnace smelting procedures, which are well known. As the aluminum content of the alloy increases, a small proportion of iron is desirable or, at times, even necessary in order to prevent excessive volatilization of aluminum and silicon from the furnace. It is generally considered that the aluminum content of these alloys is for practical reasons limited to about 60 percent maximum. In such cases the iron content is generally greater than about percent.
• the oxidic slag generally contains a mixture of calcium, aluminum and silicon oxides, sometimes called a calcium-aluminum-silicate or lime-alumina-silica slag, in combination with the magnesium oxide reactant.
• a calcium-aluminum-silicate or lime-alumina-silica slag in combination with the magnesium oxide reactant.
• One or more of these oxides may of course be a product of the reaction, depending on the reductant used, which could, along with the consumption of magnesium oxide, vary the slag composition as the reaction proceeds.
• the composition of the slag in any case is about 10-60 percent calcium oxide, 10-35 percent aluminum oxide,
• a typical slag might contain 50 percent calcium oxide, 20 percent aluminum oxide, 25 percent silica and 5 percent magnesium oxide.
• a preferred slag composition is about 25-30 percent silica, 20-25 percent alumina, 35-40 percent calcium oxide and 10-15 percent magnesium oxide; another is about 30-45 percent silica, 25-30 percent alumina, 10-20 percent calcium oxide and 10-20 percent magnesium oxide.
• the temperature of the slag, and hence of the system depends primarily on the slag composition (i.e., it must be molten), but the temperature is usually at least l300C., and preferably about l400-l700C.
• a temperature of at least about l400C. to promote good reaction conditions, but temperatures higher than about l700C. are undesirable because they create difficult engineering and operating problems. It is therefore desirable to employ a slag whose melting point is not higher than about 1600C. in order that enough superheat may be applied to impart sufficient fluidity to the slag without the necessity of excessively high temperature.
• a temperature of about l400-l700C. in the reaction zone is preferred, although in certain instances higher or lower temperatures are suitable and may be desired.
• slags of relatively high viscosity can be used in the present process because there is in the furnace no bed of solid material through which the slag must find its way in order to reach the tap hole for removal from the furnace.
• slag viscosity is not as great as it is in most metallurgical processes, but it is still a factor requiring attention.
• the composition of the slag is determined in the present process by the ratio of aluminum to silicon fed as the reducing agent; the degree of utilization of silicon as reductant, which for reasons of economy should be as high as feasible; the relative proportions of magnesium oxide fed as magnesia and as dolomitic lime; and the amount of alumina (if any) as a flux.
• a stream of the inert gas may be introduced into the furnace and fed through the condenser, in order to augment the magnesium flow to the condenser, in which case a recycle system may be utilized to recover the inert gas.
• a recycle system may be desired in any case to recover inert gas, especially if a vacuum system is employed.
• small amounts of impurities in the raw materials fed to the system may find their way into the furnace and produce reactive gases, such as CO and N which should be vented from the system.
• reactive gases such as CO and N which should be vented from the system.
• gases may be removed as required by bleeding off the inert gas, in which they will be present as impurities, in order to prevent the buildup of reactive gas on the one hand, or, alternatively, to prevent an increase of pressure.
• the operation of the present process under relatively high absolute pressure significantly decreases the leakage of air into the system. This decrease is advantageous, since the presence of air results in the reaction of oxygen and nitrogen with the magnesium product not only to decrease yield but also to form accretions of solid matter on the system walls. In particular the decrease of solids deposited on the heat transfer surfaces substantially increases the condenser efficiency and extends the period between shutdowns.
• a high absolute pressure particularly as atmospheric pressure is approached, makes it possible to operate the process as a continuous or semicontinuous process, with attendant benefits, such as facilitating removal of spent slag and magnesium product. Further, even if a batch process is used, the need for a hermetically sealed reaction-condensation system may be eliminated-and problems, such as vacuum breaking, may be avoided-completely, or at least in part.
• a metallothermic process for the production of magnesium in a reaction-condensation system having a reducing furnace reaction zone and a condenser which comprises charging a metallic reducing agent and magnesium oxide to the reaction zone, containing a molten oxidic slag bath at a temperature of at least about l300C., evolving magnesium vapor from the reaction zone to the condenser and condensing and recovering the magnesium as a product, wherein said evolving and condensing is done in the presence of an inert gas at a partial pressure of between about 1/10 and 5 atmospheres in said reaction-condensation system.
• the inert gas is selected from the group consisting of helium, neon, argon and hydrogen.
• molten oxidic slag comprises -60 percent calcium oxide, 10-35 percent aluminum oxide, -50 percent silica and 5-25 percent magnesium oxide.
• the metallic reducing agent is selected from the group consisting of aluminum, silicon and aluminum-silicon alloys.
• a metallothermic process for the production of magnesium in a reaction-condensation system including a reducing furnace reaction zone and a condenser, which comprises charging a reducing agent, selected from the group consisting of aluminum, silicon and aluminum-silicon alloys, and an oxidant comprising magnesium oxide to the reaction zone, containing a molten oxidic slag comprising about 10-60 percent calcium oxide, 10-35 percent aluminum oxide, 20-50 percent silica and 5-25 percent magnesium oxide at a temperature of about 1400 to 1700C., and, in an atmosphere containing an inert gas at a partial pressure of between about 1/10 and 5 atmospheres, evolving magnesium vapor from the reaction zone to the condenser and condensing the magnesium.
• a reducing agent selected from the group consisting of aluminum, silicon and aluminum-silicon alloys
• an oxidant comprising magnesium oxide to the reaction zone, containing a molten oxidic slag comprising about 10-60 percent calcium oxide, 10-35 percent aluminum oxide, 20-50 percent silica
• inert gas is selected from the group consisting of helium, neon, argon and hydrogen.

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Citations (5)

• 1969
  • 1969-02-03 US US3658509D patent/US3658509A/en not_active Expired - Lifetime
• 1970
  • 1970-01-21 DE DE19702002544 patent/DE2002544B2/de not_active Ceased
  • 1970-01-22 YU YU14970A patent/YU33212B/xx unknown
  • 1970-01-28 GB GB1290921D patent/GB1290921A/en not_active Expired
  • 1970-02-03 FR FR7003666A patent/FR2033876A5/fr not_active Expired

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