US3579326A - Process for the production of magnesium - Google Patents

Process for the production of magnesium Download PDF

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US3579326A
US3579326A US648856A US3579326DA US3579326A US 3579326 A US3579326 A US 3579326A US 648856 A US648856 A US 648856A US 3579326D A US3579326D A US 3579326DA US 3579326 A US3579326 A US 3579326A
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magnesium
slag
percent
silicon
aluminum
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Julian M Avery
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JULIAN M AVERY
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JULIAN M AVERY
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    • 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

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  • This invention is concerned with the production of magnesium metal by the metallothermic reduction of magnesium oxide at elevated temperatures. More particularly, it relates to an improved process of the type, in the prior art, wherein metallic silicon, customarily in the form of a ferrosilicon alloy, and magnesium oxide, customarily in the form of calcined dolomite, are caused to react in an electric furnace-condenser system, customarily maintained under a high vacuum.
  • the object of the present invention is to provide an improved metallothermic process which is fully competitive with known methods for the production of magnesium.
  • the present invention may be characterized as a continuous or batch process operable at or about atmospheric pressure, in which: an aluminumsilicon alloy is used as the metallic reducing agent; a major portion of the magnesium oxide required is supplied as magnesia, rather than dolomitic lime; a relatively high concentration of magnesium oxide is maintained in the slag at all times; and the proportions of metallic aluminum and silicon and the slag composition are mutually coordinated and maintained in such manner that all, or nearly all, of the alumina and silicon dioxide required for slag formation are derived by the reduction of magnesium oxide to metallic magnesium.
  • an aluminumsilicon alloy is used as the metallic reducing agent
  • a major portion of the magnesium oxide required is supplied as magnesia, rather than dolomitic lime
  • a relatively high concentration of magnesium oxide is maintained in the slag at all times
  • the proportions of metallic aluminum and silicon and the slag composition are mutually coordinated and maintained in such manner that all, or nearly all, of the alumina and silicon dioxide required for slag formation are derived by the reduction of magnesium
  • an aluminumsilicon alloy containing silicon and aluminum in a ratio of at least about 0.8:1 is used for the reduction of magnesium oxide, from an oxidant containing a major proportion of magnesia, in the presence of a molten slag of a certain composition at temperatures above about l400 C.
  • magnesium vapor can be released, even at atmospheric pressure, in quantities corresponding to very high utilization of the silicon content of the alloy.
  • the presence of aluminum as a reactant, in close physical association with silicon and the molten slag as defined herein stimulates the reductant synergistically to react, to such an extent that magnesium vapor evolves even at atmospheric pressure, thus obviating the necessity of maintaining a high vacuum on the system.
  • aluminum-silicon alloys of suitable composition thus provides very important advantages over the use of ferrosilicon.
  • a clear advantage is the possibility of carrying out the reaction at or about atmospheric pres sure.
  • a major fraction of the silicon content of the reducing alloy may be utilized to reduce magnesium oxide.
  • the aluminum oxide as required in the slag may be derived as a side-product of the reaction, whereby the ratio of slag to magnesium metal produced may be beneficially reduced.
  • magnesium oxide content of the slag is maintained at a relatively high concentration, above about 5 percent and preferably between about 10 and about 20 percent, the tendency of silicon to react with magnesium oxide to produce magnesium is greatly enhanced.
  • the increased rate of reaction of magnesium oxide with both aluminum and silicon substantially increases the productive capacity of a furnace of given size.
  • the high concentration of magnesium oxide in the slag thus plays a vital role in the process of the present invention.
  • the process of the present invention is characterized by the utilization of an aluminum-silicon alloy to reduce magnesium oxide in the reaction zone of a reducing furnace, at temperatures above about 1400" C. and in the presence of a molten slag bath of the general composition:
  • Percent Broad Preferable Component range range An optimum composition of the molten slag appears to be about 20 percent calcium oxide, about 15 percent magnesium oxide, about 30 percent aluminum oxide and about percent silicon dioxide.
  • the composition of the molten slag may be defined by the curves shown in FIG. 1.
  • the broad range of composition of the molten slag covers those having about 5-25 percent magnesium oxide, and calcium oxide, silicon dioxide and aluminum oxide in proportions represented by curve 10 of FIG. 1.
  • the preferred composition of the molten slag comprises about 10-20 percent magnesium oxide and the remaining components in the proportion shown by curve 12 of FIG. 1. It should be noted that the percentages given in FIG. 1, for simplicity, relate to the molten slag without its magnesium oxide content, that is, 5-25 percent and preferably 1020 percent of the total slag. Thus the total of the three components adds up to 100 percent but represents that part of the slag excluding magnesium oxide.
  • the molten slag composition is such that the ratio of aluminum and magnesium oxides to silicon dioxide is less than 1.611; the total aluminum and magnesium oxides is less than 50 percent of the slag; and the ratio of calcium and magnesium oxides to silicon dioxide is less than 1.6:1.
  • metallurgical slags have a high content of CaO-at least percent and usually on the order of 50 percent, sometimes even higher.
  • Such slags are known as basic slags, and they are characterized by a relatively sharp melting point and form a fluid slag of low viscosity with little superheat.
  • Slags of the above range of composition are classed as acidic, and are characterized by a somewhat vague melting point, and form rather viscous, glassy slags which require considerable superheat to achieve lower viscosity.
  • the range of the composition given above covers a wide range of melting points. Within this range, many combinations are possible, but they must be carefully selected, because it is necessary to produce a slag in which the mixture of oxides is such that a suitable combination of melting point and viscosity is obtained. To this end, a flux such as fluorspar can be added to the slag if desired.
  • the oxidant charged to the reaction zone is suitably a mixture of oxides such as magnesium oxide and calcium oxide.
  • a major proportion of the oxidant is magnesia, that is, magnesium oxide ore.
  • a minor proportion of the oxidant may be calcined dolomite, an equimolar combination of magnesium oxide and calcium oxide, derived from CaMg(CO)
  • the molar ratio of magnesium oxide to calcium oxide in the oxidant is at least 2: 1.
  • magnesitic dolomite stone having a relatively high ratio of magnesium oxide to calcium oxide content
  • dolomitic lime is unavailable or not desired, it is evident that lime produced from limestone may be used to provide such calcium oxide as may be necessary for formation of a suitable slag.
  • a temperature of at least about 1400 C. to promote good reaction conditions, but temperatures higher than about 1700 C. 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 1600 C. 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 1400-1700 C. 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; and the relative proportions of magnesium oxide fed as magnesia and as dolomitic lime.
  • aluminum-silicon alloy includes those reductants which, when added to the molten slag in the reaction zone of a reducing furnace, as herein described, provide metallic aluminum and silicon.
  • Al-Si-Fe alloys as the reductant of this invention may be desirable, particularly in view of the ready availability of such aluminum-silicon alloys.
  • Aluminum in the form of 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 percent maximum. In such cases the iron content is generally greater than about 5 percent.
  • the ratio of silicon to aluminum is at least 0.8:1, desirably greater than 121 and preferably at least 1.4: 1.
  • the composition of the aluminum-silicon reductant of the present invention may be represented by the three-component graph of FIG. 2.
  • the reductant composition falls within the area bounded ⁇ by curve 20 on FIG. 2.
  • the reductant composition falls within the area bounded by curve 22 of FIG. 2.
  • EXAMPLES The following operations are conducted in an electric reducing furnace coupled with a condensing chamber.
  • the procedure is to charge the furnace with a slag and to supply heat until a proper viscosity is reached at a temperature above about 1400 C., whereupon the oxidant and reductant are charged in small batches.
  • the molten slag and ferrosilicon alloy, if any, are tapped.
  • the addition of oxidant and reductant and the tapping of slag and spent ferrosilicon are conducted in such manner that the composition of the slag is maintained substantially constant.
  • the operation is conducted substantially continuously.
  • the oxidant and reductant charged to the furnace and the tapped slag has the compositions shown in Table I.
  • the reactions takes place at temperatures also shown in Table I, and magnesium vapor may be evolved and condensed at atmospheric pressure.
  • the slag compositions are also shown in Table I.
  • the temperature of the molten slag is higher than desirable, e.g., Examples 2, 5 and 6. In such cases a flux can be added to improve viscosity without requiring excessively high temperatures.
  • the furnace is maintained at or about atmospheric pressure, although vacuum operation is feasible and may in certain instances be preferred.
  • magnesium condense the magnesium under a lower pressure say down to 0.5 atmosphere
  • an inert gas such as helium, argon or hydrogen to maintain in the closed furnacecondenser system a total pressure of about one atmosphere.
  • titanium and other metallic oxides are sometimes present in raw materials used for the production of an aluminum-silicon alloy, and the corresponding metal is therefore sometimes present in the alloy produced.
  • the presence of such tramp metals does not interfere with the operation of the process of this invention, and may be tolerated or remedied by suitable metallurgical procedures.
  • a metallothermic process for the production of magnesium which comprises charging a reductant and an oxidant to the reaction zone of a reducing furnace, maintaining the reaction zone of the furnace at a temperature of at least 1400 C., evolving magnesium vapor from the reaction zone, and condensing and recovering the magnesium as a product; wherein said reductant is a metallic alloy comprising about 25-30 percent by weight aluminum, about 40-65 percent silicon and about -20 percent iron, and having a ratio of silicon to aluminum of at least 0.8: 1, said oxidant comprises at least a major proportion by weight of magnesium oxide and has a molecular ratio of magnesium oxide to calcium oxide of at least 2: l, and said reaction zone contains a molten slag which comprises, on a weight basis exclusive of other components, about 5-25 percent magnesium oxide, about 15-35 percent aluminum oxide, about 25-50 percent silicon dioxide, and less than 30 percent calcium oxide, wherein the ratio of aluminum and magnesium oxides to silicon dioxide in the slag is less than 1.6, the aluminum and magnesium oxides comprise less than 50
  • a metallothermic process for the production of magnesium which comprises charging a reductant and an oxidant to the reaction zone of a reducing furnace, maintaining the reaction zone of the furnace at a temperature of at least about 1400 C., evolving magnesium vapor from the reaction zone, and condensing and recovering the magnesium as a product;
  • said reductant is a metallic alloy comprising about 30-40 percent aluminum, about 50-60 percent silicon and about percent iron, and having a ratio of silicon to aluminum of at least 0.8:1
  • said oxidant comprises at least a major proportion by weight of magnesium oxide and has a molecular ratio of magnesium oxide to calcium oxide of at least 2:1
  • said reaction zone contains a molten slag which comprises, on a weight basis exclusive of other components, about 5-25 percent magnesium oxide, about -35 percent aluminum oxide, about -50 percent silicon dioxide, and less than about percent calcium oxide.
  • molten slag comprises about 10-20 percent calcium oxide, about 10-20 percent magnesium oxide, about 25-30 percent aluminum oxide, and about 30-45 percent silicon dioxide.
  • a metallothermic process for the production of magnesium which comprises charging to the reaction zone of a reducing furnace a reductant comprising aluminum, silicon and iron in proportions such that its composition falls within the the area defined by curve 22 of FIG. 2;
  • an oxidant comprising at least a major proportion of magnesium oxide and having a molecular ratio of magnesium oxide to calcium oxide of at least 2:1;
  • reaction zone contains a molten slag comprising about 5-25 percent magnesium oxide and, as the remainder,
  • reaction zone contains a molten slag comprising about 10-20 percent magnesium oxide and, as the remainder, calcium oxide, aluminum oxide and silicon dioxide in proportions such that the composition of the slag exclusive of magnesium oxide falls within the area defined by curve 12 of FIG. 1.
  • a metallothermic process for the production of magnesium which comprises charging a reductant and an oxidant to the reaction zone of a reducing furnace, maintaining the reacting zone of the furnace at a temperature of at least 1400 C., evolving magnesium vapor from the reaction zone, and condensing and recovering the magnesium as a product; wherein said reductant is a metallic alloy comprising about 25-50 percent by weight aluminum, about 40-65 percent silicon and about 0-20 percent iron, and having a ratio of silicon to aluminum of at least 0.811, said oxidant comprises at least a major proportion by weight of magnesium oxide and has a molecular ratio of magnesium oxide to calcium oxide of at least 2: 1, and said reaction zone contains a molten slag comprising about 10-20 percent calcium oxide, about 10-20 percent magnesium oxide, about 25-30 percent aluminum oxide, and about 30-45 percent silicon dioxide.
  • said reductant is a metallic alloy comprising about 25-50 percent by weight aluminum, about 40-65 percent silicon and about 0-20 percent iron, and having a ratio of silicon to aluminum of at least
  • a metallothermic process for the production of magnesium which comprises charging to the reaction zone of a reducing furnace a reductant comprising aluminum silicon and iron in proportions such that its composition falls within the area defined by curve 20 of FIG. 2;
  • an oxidant comprising at least a major proportion of magnesium oxide and having a molecular ratio of magnesium oxide to calcium oxide of at least 2:1;
  • reaction zone contains a molten slag comprising about 10-20 percent magnesium oxide and, as the remainder, calcium oxide, aluminum oxide and silicon dioxide in proportions such that the composition of the slag exclusive of magnesium oxide falls within the area defined by curve 12 of FIG. 1; and

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US648856A 1967-06-26 1967-06-26 Process for the production of magnesium Expired - Lifetime US3579326A (en)

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FR (1) FR1580990A (enrdf_load_stackoverflow)
IN (2) IN141344B (enrdf_load_stackoverflow)
NO (1) NO124001B (enrdf_load_stackoverflow)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3994717A (en) * 1970-04-06 1976-11-30 Julian Avery Metallothermic production of magnesium in the presence of a substantially static atmosphere of inert gas
US4204860A (en) * 1978-09-20 1980-05-27 Reynolds Metals Company Magnesium production
US4478637A (en) * 1983-03-10 1984-10-23 Aluminum Company Of America Thermal reduction process for production of magnesium
US4498927A (en) * 1983-03-10 1985-02-12 Aluminum Company Of America Thermal reduction process for production of magnesium using aluminum skim as a reductant
US4572736A (en) * 1983-12-21 1986-02-25 Shell Internationale Research Maatschappij B.V. Process for producing magnesium
WO1989000613A1 (en) * 1987-07-10 1989-01-26 The University Of Manchester Institute Of Science Magnesium production
US20120097653A1 (en) * 2008-10-28 2012-04-26 Electra Holdings Co., Ltd. Laser Refining Apparatus and Laser Refining Method

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3698888A (en) * 1970-04-06 1972-10-17 Julian Miles Avery Metallothermic production of magnesium
US4582532A (en) * 1985-05-02 1986-04-15 Aluminum Company Of America Thermal reduction process for production of calcium using aluminum as a reductant

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3994717A (en) * 1970-04-06 1976-11-30 Julian Avery Metallothermic production of magnesium in the presence of a substantially static atmosphere of inert gas
US4204860A (en) * 1978-09-20 1980-05-27 Reynolds Metals Company Magnesium production
US4478637A (en) * 1983-03-10 1984-10-23 Aluminum Company Of America Thermal reduction process for production of magnesium
US4498927A (en) * 1983-03-10 1985-02-12 Aluminum Company Of America Thermal reduction process for production of magnesium using aluminum skim as a reductant
US4572736A (en) * 1983-12-21 1986-02-25 Shell Internationale Research Maatschappij B.V. Process for producing magnesium
WO1989000613A1 (en) * 1987-07-10 1989-01-26 The University Of Manchester Institute Of Science Magnesium production
US20120097653A1 (en) * 2008-10-28 2012-04-26 Electra Holdings Co., Ltd. Laser Refining Apparatus and Laser Refining Method

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IN141341B (enrdf_load_stackoverflow) 1977-02-19
FR1580990A (enrdf_load_stackoverflow) 1969-09-12
NO124001B (enrdf_load_stackoverflow) 1972-02-14
IN141344B (enrdf_load_stackoverflow) 1977-02-19

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