1. Patent Search
  2. Details

Method Of Carbothermic Process Of Magnesium Production And Co-Production Of Calcium Carbide

20230049604 · 2023-02-16

    Inventors

    Cpc classification

    International classification

    Abstract

    This invention relates to a method of carbothermic process of magnesium production and co-production of calcium carbide, which is particularly suitable for carbothermic process of magnesium production with a mixture of magnesium oxide and calcium oxide as a raw material and carbon as a reducing agent. A mixed powder containing magnesium oxide, calcium oxide and a carbon reducing agent is prepared. The mixed powder is processed into a pelletized furnace feed material, which is placed into a reactor equipped with a heat source. With an absolute pressure P in the reactor being set within the range of 1000 Pa≤P≤atmospheric pressure or to a slightly positive pressure and a reaction temperature T within the range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P-129 lgP+1300° C., a smelting reaction is run. Liquid magnesium is obtained through condensation by a condenser connected to the reactor, and after the smelting reaction has finished, calcium carbide is obtained within the reactor. With this method, a potential safety hazard in that a magnesium vapor produced during carbothermic magnesium production, when co-cooled with a CO gas, tends to give rise to a magnesium powder and cause an explosion can be completely avoided, and magnesium production cost can be significantly reduced. This method has a good prospect of industrial application.

    Claims

    1. A method of carbothermic process of magnesium production and co-production of calcium carbide, characterized in comprising steps of: S1: preparing a mixed powder containing magnesium oxide, calcium oxide and a carbon reducing agent; S2: processing the mixed powder into a pelletized furnace feed material and placing it into a reactor equipped with a heat source; and S3: with an absolute pressure P in the reactor being set within a range of 1000 Pa≤P≤atmospheric pressure or to a slightly positive pressure and a reaction temperature T within a range of 11 lg.sup.2P+71 lgP+1210° C.<T≤98 lg.sup.2P−129 lgP+1300° C., running a smelting reaction, and obtaining liquid magnesium through condensation by a condenser connected to the reactor and calcium carbide within the reactor.

    2. The method of claim 1, characterized in that, in the mixed powder, a molar content M.sub.C of the carbon reducing agent, a molar content M.sub.MgO of the magnesium oxide and a molar content M.sub.CaO of the calcium oxide are in a relationship of: M.sub.C≈M.sub.MgO+3M.sub.CaO.

    3. The method of claim 1, characterized in that the mixed powder has a degree of fineness of 80 mesh or greater.

    4. The method of claim 1, characterized in that the pelletized furnace feed material has an equivalent diameter of 20 mm to 40 mm.

    5. The method of claim 1, characterized in that: an outer layer of the reactor is a hermetic container provided therein with a smelting chamber, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber; and the pelletized furnace feed material is placed within the smelting chamber.

    6. The method of claim 5, characterized in that the smelting chamber is constructed from components of a high-temperature resistant material that is resistant to a temperature not lower than 1700° C.

    7. The method of claim 6, characterized in that the high-temperature resistant material is graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature resistant ceramic.

    8. The method of claim 1, characterized in that the carbon reducing agent is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    9. The method of claim 1, characterized in that a heating manner of the heat source is electric heating.

    10. A method of carbothermic process of calcium production and co-production of calcium carbide, characterized in comprising steps of: S1: preparing a mixed powder containing calcium oxide and a carbon reducing agent; S2: pressing the mixed powder into a pelletized furnace feed material and placing it into a reactor equipped with a heat source; and S3: with an absolute pressure P in the reactor being set within a range of 10000 Pa≤P≤atmospheric pressure or to a slightly positive pressure and a reaction temperature as T>30 lg.sup.2P+58 lgP+1215° C., running a smelting reaction, and obtaining liquid calcium through condensation by a condenser connected to the reactor and calcium carbide within the reactor.

    11. The method of claim 10, characterized in that a molar ratio of the calcium oxide to the carbon reducing agent contained in the mixed powder is CaO:C≈1:3-1:1.

    12. The method of claim 10, characterized in that the mixed powder has a degree of fineness of 80 mesh or greater.

    13. The method of claim 10, characterized in that the pelletized furnace feed material has an equivalent diameter of 20 mm to 40 mm.

    14. The method of claim 10, characterized in that: an outer layer of the reactor is a hermetic container provided therein with a smelting chamber, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber; and the pelletized furnace feed material is placed within the smelting chamber.

    15. The method of claim 14, characterized in that the smelting chamber is constructed from components of a high-temperature resistant material that is resistant to a temperature not lower than 1700° C.

    16. The method of claim 15, characterized in that the high-temperature resistant material is graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature resistant ceramic.

    17. The method of claim 10, characterized in that the carbon reducing agent is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    18. The method of claim 10, characterized in that a heating manner of the heat source is electric heating.

    19. A method of carbothermic process of magnesium production and co-production of calcium carbide using solid-phase calcium carbide as a catalyst, characterized in comprising steps of: S1: preparing a mixed powder containing magnesium oxide, calcium oxide, a carbon reducing agent and a calcium carbide catalyst; S2: processing the mixed powder into a pelletized furnace feed material and placing it into a reactor equipped with a heat source; S3: with an absolute pressure P in the reactor being set within a range of 1000 Pa≤P≤atmospheric pressure and a reaction temperature T within a range of 51 lg.sup.2P−38 lgP+800° C.<T<20 lg.sup.2P+60 lgP+1050° C., running a smelting reaction for magnesium, and obtaining liquid magnesium through condensation by a condenser connected to the reactor; and S4: after the smelting reaction for magnesium in S3 has finished, with an absolute pressure P in the reactor being set within a range of 1000 Pa≤P≤atmospheric pressure or to a slightly positive pressure and a reaction temperature T within a range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P−129 lgP+1300° C., running a smelting reaction for calcium carbide, and obtaining calcium carbide within the reactor.

    20. The method of claim 19, characterized in that, in the mixed powder, a molar content M.sub.MgO of the magnesium oxide, a molar content M.sub.CaO of the calcium oxide, a molar content M.sub.CaC2 of the calcium carbide and a molar content M.sub.C of the carbon reducing agent are in relationships of: M.sub.MgO≈M.sub.CaC2 and M.sub.C≈M.sub.MgO+3M.sub.CaO.

    21. The method of claim 19, characterized in that the mixed powder has a degree of fineness of 80 mesh or greater.

    22. The method of claim 19, characterized in that the pelletized furnace feed material has an equivalent diameter of 20 mm to 40 mm.

    23. The method of claim 19, characterized in that the carbon reducing agent is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    24. The method of claim 19, characterized in that a heating manner of the heat source is electric heating.

    25. The method of claim 19, characterized in that: an outer layer of the reactor is a hermetic container provided therein with a smelting chamber, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber; and the pelletized furnace feed material is placed within the smelting chamber.

    26. The method of claim 25, characterized in that the smelting chamber is constructed from components of a high-temperature resistant material that is resistant to a temperature not lower than 1700° C.

    27. The method of claim 26, characterized in that the high-temperature resistant material is graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature resistant ceramic.

    28. A method of carbothermic process of magnesium production and co-production of calcium carbide using liquid-phase calcium carbide as a catalyst, characterized in comprising steps of: S1: preparing a granular raw material containing magnesium oxide and calcium oxide and a granular carbon reducing agent; S2: placing a calcium carbide catalyst into a reactor equipped with a heat source and heating and melting the calcium carbide so that it in a molten state forms a catalyst melt pool; S3: a) mixing the granular raw material containing the magnesium oxide and the calcium oxide with the granular carbon reducing agent and adding them to the catalyst melt pool to form a solid-phase material layer with a certain thickness over a surface of the catalyst melt pool; or b) first, laying a layer of the granular raw material containing the magnesium oxide and the calcium oxide over a surface of the catalyst melt pool to form a first raw material layer, then laying a layer of the granular carbon reducing agent over the first raw material layer to form a first reduction layer, and following this order to stack sequentially a number of such layers; and S4: with an absolute pressure P in the reactor being set within a range of 1000 Pa≤P≤atmospheric pressure or to a slightly positive pressure and a melt pool temperature T within a range of 1900° C.≤T≤30 lg.sup.2P+58 lgP+1215° C., running a smelting reaction, during the reaction, through adjusting thickness of the material layer in S3, causing a magnesium vapor to continually pass through the material layer and leave the material layer at a cooled temperature higher than a condensation temperature of the magnesium vapor T.sub.b=21.4 lg.sup.2P+18.4 lgP+437° C., and obtaining liquid magnesium through condensation by a condenser connected to the reactor.

    29. The method of claim 28, characterized in that in all the material layer in S3, a molar content M.sub.C of the carbon reducing agent, a molar content M.sub.MgO of the magnesium oxide and a molar content M.sub.CaO of the calcium oxide are in a relationship of: M.sub.C≈M.sub.MgO+3M.sub.CaO.

    30. The method of claim 28, characterized in that the granular raw material and the granular carbon reducing agent have sizes of 5 mm to 100 mm.

    31. The method of claim 28, characterized in that: an outer layer of the reactor is a hermetic container provided therein with a smelting chamber, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber; and the calcium carbide catalyst melt pool is placed within the smelting chamber.

    32. The method of claim 31, characterized in that the smelting chamber is constructed from components of a high-temperature resistant material that is resistant to a temperature not lower than 1900° C.

    33. The method of claim 32, characterized in that the high-temperature resistant material is graphite.

    34. The method of claim 28, characterized in that the carbon reducing agent is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    35. The method of claim 28, characterized in that a heating manner of the heat source is electric heating.

    36. A method of carbothermic process of metal production using solid-phase calcium carbide as a catalyst, characterized in comprising steps of: S1: preparing a mixed powder containing a metal oxide M.sub.mO, a carbon reducing agent and the calcium carbide catalyst, wherein a metal M in the metal oxide M.sub.mO is Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo or V, and m is an atomic number ratio of metal element M to oxygen element O and m≤1; S2: processing the mixed powder into a pelletized furnace feed material and placing it into a reactor equipped with a heat source; S3: with an absolute pressure P in the reactor being set within a low vacuum range higher than a triple-point pressure of the metal M and a reaction temperature T to be higher than a temperature at which a reaction ##STR00013## begins at the absolute pressure P and lower than a temperature at which a reaction ##STR00014## begins at the absolute pressure P, running a smelting reaction for the metal M, and obtaining a simple substance of the metal M through condensation by a condenser connected to the reactor; and S4: after the smelting reaction for the metal M in S3 has finished, with the absolute pressure P in the reactor being set within a low vacuum range higher than the triple-point pressure of the metal M or to atmospheric pressure or a slightly positive pressure and a reaction temperature T within a range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P−129 lgP+1300° C., running a smelting reaction for calcium carbide, and after the reaction has finished, obtaining calcium carbide within the reactor.

    37. The method of claim 36, characterized in that a molar ratio of the metal oxide M.sub.mO to the calcium carbide to the carbon reducing agent contained in the mixed powder is M.sub.mO:CaC.sub.2:C≈1:1:1.

    38. The method of claim 36, characterized in that: when the metal oxide is magnesium oxide, in S3, with the absolute pressure P in the reactor being set within a low vacuum range of 1000 Pa≤P<atmospheric pressure and the reaction temperature T within a range of 51 lg.sup.2P−38 lgP+800° C.<T<20 lg.sup.2P+60 lgP+1050° C., a smelting reaction for magnesium is run; and in S4, with the absolute pressure P in the reactor being set within a range of 1000 Pa≤P≤atmospheric pressure or to a slightly positive pressure and the reaction temperature T within a range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P−129 lgP+1300° C., a smelting reaction for calcium carbide is run.

    39. The method of claim 36, characterized in that the mixed powder has a degree of fineness of 80 mesh or greater.

    40. The method of claim 36, characterized in that the pelletized furnace feed material has an equivalent diameter of 20 mm to 40 mm.

    41. The method of claim 36, characterized in that: an outer layer of the reactor is a hermetic container provided therein with a smelting chamber, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber; and the pelletized furnace feed material is placed within the smelting chamber.

    42. The method of claim 41, characterized in that the smelting chamber is constructed from components of a high-temperature resistant material that is resistant to a temperature not lower than 1700° C.

    43. The method of claim 42, characterized in that the high-temperature resistant material is graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature resistant ceramic.

    44. The method of claim 36, characterized in that the carbon reducing agent is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    45. The method of claim 36, characterized in that a heating manner of the heat source is electric heating.

    46. A method of carbothermic process of metal production using liquid-phase calcium carbide as a catalyst, characterized in comprising steps of: S1: preparing a granular raw material containing a metal oxide M.sub.mO and a granular carbon reducing agent, wherein a metal M in the metal oxide M.sub.mO is Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo or V, and m is an atomic number ratio of metal element M to oxygen element O and m≤1; S2: placing a calcium carbide catalyst within a reactor equipped with a heat source, heating and melting the calcium carbide so that it in a molten state forms a catalyst melt pool, and maintaining the melt pool at a temperature of 1900-2300° C.; S3: a) mixing the granular raw material containing the metal oxide M.sub.mO with the granular carbon reducing agent and adding them to the catalyst melt pool to form a solid-phase material layer with a certain thickness over a surface of the melt pool; or b) first, laying a layer of the granular raw material containing the metal oxide M.sub.mO over a surface of the catalyst melt pool to form a first raw material layer, then laying a layer of the granular carbon reducing agent over the first raw material layer to form a first reduction layer, and following this order to stack sequentially a number of such layers; and S4: with an absolute pressure P in the reactor being set to a low vacuum pressure higher than a triple-point pressure of the metal M, atmospheric pressure or a slightly positive pressure, running a smelting reaction, during the reaction, through adjusting thickness of the material layer in S3, causing a vapor of the metal M produced by the reaction to continually pass through the material layer and leave the material layer while remaining in a gaseous state, and obtaining a liquid simple substance of the metal M through condensation by a condenser connected to the reactor.

    47. The method of claim 46, characterized in that a molar ratio of the metal oxide to the carbon reducing agent contained in all the material layer in S3 is M.sub.mO:C≈1:1.

    48. The method of claim 46, characterized in that: when the metal oxide is magnesium oxide, in S4, with the absolute pressure P in the reactor being set within a range of 1000 Pa≤P≤atmospheric pressure or a slightly positive pressure, the smelting reaction is run; through adjusting thickness of the material layer in S3, a magnesium vapor produced by the reaction is caused to continually pass through the material layer and leave the material layer at a cooled temperature higher than a condensation temperature of the magnesium vapor T.sub.b=21.4 lg.sup.2P+18.4 lgP+437° C., and liquid magnesium is obtained through condensation by the condenser connected to the reactor.

    49. The method of claim 46, characterized in that the granular raw material and the granular carbon reducing agent have sizes of 5 mm to 100 mm.

    50. The method of claim 46, characterized in that: an outer layer of the reactor is a hermetic container provided therein with a smelting chamber, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber; and the calcium carbide catalyst melt pool is placed within the smelting chamber.

    51. The method of claim 50, characterized in that the smelting chamber is constructed from components of a high-temperature resistant material that is resistant to a temperature not lower than 1900° C.

    52. The method of claim 51, characterized in that the high-temperature resistant material is graphite.

    53. The method of claim 46, characterized in that the carbon reducing agent is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    54. The method of claim 46, characterized in that a heating manner of the heat source is electric heating.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0066] FIG. 1 shows curves representing temperature T (° C.)-absolute pressure P (Pa) relationships of relevant chemical reactions in a mixture of magnesium oxide, calcium oxide and carbon with calcium carbide, in which Curves (1) to (4) represent reactions that can occur at temperatures higher than the respective curves and Curve (5) represents a reaction that can occur at a temperature lower than the curve;

    [0067] FIG. 2 shows a curve indicating transitions between three phases experienced by a magnesium vapor being cooled, which is given by existing literature;

    [0068] FIG. 3 shows a curve indicating transitions between three phases experienced by a magnesium vapor being cooled, which is plotted based on thermodynamic calculations;

    [0069] FIG. 4 shows a curve indicating transitions between three phases experienced by a calcium vapor being cooled, which is plotted based on thermodynamic calculations;

    [0070] FIG. 5 shows curves representing temperature T (° C.)-absolute pressure P (Pa) relationships of relevant chemical reactions involved in a carbothermic process for smelting an oxide M.sub.mO of a metal M using CaC.sub.2 as a catalyst to produce a simple substance of the metal M according to a preferred embodiment, in which Curves (1) and (3) are schematic qualitative curves of reduction reactions of the metal oxide M.sub.mO, Curves (1) to (4) represent reactions that can occur at temperatures higher than the respective curves and Curve (5) represents a reaction that can occur at a temperature lower than the curve.

    DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

    [0071] Below, the accompanying drawings of this specification are referenced to introduce several technical contemplations and preferred embodiments of the present invention so that the techniques thereof become more apparent and readily understood. The present invention may be embodied in many different forms of technical contemplation and embodiment, and the protection scope of the invention is not limited only to the technical concepts and embodiments mentioned herein.

    I. Technical Contemplation 1—Carbothermic Process of Magnesium Production and Co-Production of Calcium Carbide

    [0072] As shown in FIG. 1, at an absolute pressure P<100 Pa, i.e., when lgP<2, Curve (2) of the reaction CaO.sub.(s)+3C.sub.(s).fwdarw.CaC.sub.2(s)+CO.sub.(g) is very close to Curve (4) of the reaction 2CaO.sub.(s)+CaC.sub.2(s).fwdarw.3Ca.sub.(g)+2CO.sub.(g), indicating that it is difficult to enable, through reaction temperature control, only the CaC.sub.2-producing reaction but not the Ca vapor-producing reaction to occur. Similarly, Curve (5) of the reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) that occurs between vaporous Ca and C and produces CaC.sub.2 is also very close to Curve (4), while the exothermic reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) can occur only at a temperature lower than Curve (5), indicating that, in practice, once the Ca vapor-producing reaction 2CaO.sub.(s)+CaC.sub.2(s).fwdarw.3Ca.sub.(g)+2CO.sub.(g) has started, it would become difficult to trigger the reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) at a temperature lower than Curve (5). Consequently, the Ca vapor has to be lost in vain and is difficult to react with carbon to produce CaC.sub.2. However, at an absolute pressure P≥1000 Pa, i.e., when lgP≥3, the distances between Curves (2), (4) and (5) are both expanded, making it relatively easy to control a reaction temperature within the range higher than Curve (2) and lower than Curve (4) and thus ensure that only the CaC.sub.2-producing reaction occurs, but not the Ca vapor-producing reaction, takes place. Moreover, it also becomes relatively easy to control a reaction temperature within the range higher than Curve (2) and Curve (4) and lower than Curve (5) and thus ensure the occurrence of not only the CaC.sub.2-producing reaction but also the subsequent reaction of the resulting Ca vapor with C. As a result, CaC.sub.2 is produced, and the vapor will not be just lost. Of course, at this point, as the temperature is significantly higher than both Curves (1) and (3), there is no problem for vaporous magnesium to be produced.

    [0073] FIG. 1 shows mathematical equations representing temperature T-absolute pressure P relationships of the reactions which have been regressed from experimental data and validated by thermodynamic calculations, in which the regression equation of Curve (2) for the reaction CaO.sub.(s)+3C.sub.(s).fwdarw.CaC.sub.2(s)+CO.sub.(g) is approximated as T=11 lg.sup.2P+71 lgP+1210° C., and the regression equation of Curve (5) for the reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) is approximated as T=98 lg.sup.2P−129 lgP+1300° C. At an absolute pressure P≥1000 Pa, as long as a reaction temperature T lies within the range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P−129 lgP+1300° C., it can be ensured to produce vaporous magnesium and CaC.sub.2 without a decrease in the yield of calcium carbide due to evaporative loss of calcium.

    [0074] Further, among the two major problems associated with carbothermic magnesium production, the safety problem arising from the formation of a magnesium powder during co-cooling of a magnesium vapor and a CO gas is the culprit that inhibits its industrial application (the reverse reaction problem that leads to a lower reduction rate and more impurities in the produced crude magnesium may be overcome by extending the reduction time, refining the crude magnesium or other supporting technical measures, so it is not considered as the primary factor that inhibits industrial application). Existing literature (see FIG. 2) and thermodynamic calculations (see FIG. 3) both suggest that, at an absolute pressure P≥1000 Pa, a magnesium vapor, when cooled, will directly condense into a solid phase without undergoing a liquid phase. Moreover, during the cooling, when co-existing with CO or another gas that does not condense, it is easy for the magnesium vapor to transition into a magnesium powder. However, at an absolute pressure P≥1000 Pa, cooling a magnesium vapor will first covert it into liquid magnesium which, when further cooled, will become crystalline magnesium in the form of a block rather than a magnesium powder. As graphite, silicon carbide and similar high-temperature resistant non-metallic materials are not able to maintain vacuum, traditional magnesium production techniques relying on thermal reduction all employed a reduction tank made of heat-resistant steel as a reactor. A service temperature of heat-resistant steel is typically not higher than 1200° C. Under such a temperature, an absolute pressure that allows effective smelting does not exceed 10-100 Pa. Therefore, in the traditional magnesium production techniques, a magnesium vapor cannot be cooled into liquid magnesium.

    [0075] When an electric heating reactor is employed, a furnace feed material is held and smelted in a smelting chamber made of a high-temperature resistant material, and the smelting chamber is in turn contained in a hermetic container, with a thermal insulation layer being disposed between the hermetic container and the smelting chamber. An electric heating element directly or indirectly heats the smelting chamber and the furnace feed material within the thermal insulation layer, whilst the hermetic container is not subject to the high temperature and serves mainly to seal and isolate the inside of the reactor from outside air. As the high-temperature resistant material from which components of the smelting chamber are fabricated can resist a temperature up to 1500° C. or higher, a magnesium vapor is allowed to be present at an absolute pressure of 1000 Pa or higher, which enables the production of liquid magnesium. Thus, the safety problem arising from the generation of a magnesium powder can be totally circumvented, and the produced liquid magnesium can be directly refined or cast into ingots, saving the energy, labor and other cost involved in magnesium re-melting. The high-temperature resistant material may be selected from, among others, graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature resistant ceramic.

    [0076] Therefore, if a smelting chamber reactor made of a high-temperature resistant material is electrically heated in a hermetic container, and an absolute pressure P in the reactor is maintained in the range of 1000 Pa≤P≤atmospheric pressure or at a slightly positive pressure for carbothermic magnesium production, not only the energy consumed by a vacuum pump can be saved with efficient magnesium and CaC.sub.2 production being achieved, but also the danger of an explosion caused by a magnesium powder during carbothermic magnesium production is completely avoided. Moreover, the produced liquid magnesium can be directly refined or cast into ingots, saving the cost of magnesium re-melting. In the context of the present invention, the “slightly positive pressure” refers to a positive pressure not 1000 Pa higher than the local atmospheric pressure.

    [0077] The carbon reducing agent used in carbothermic magnesium production is coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt or a mixture of any two or more of the above.

    Example 1

    [0078] Anthracite with a fixed carbon content of 90% was obtained from a coal mine, and dolomite (MgCO.sub.3.CaCO.sub.3) obtained from an ore mine was chemically analyzed. The results are shown in the table below.

    TABLE-US-00001 Chemical Compositions of Dolomite Samples (w %) Sample Burning No. MgO CaO SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 Loss Rest 1 20.28 33.87 0.34 0.07 0.12 44.93 0.39 2 20.42 34.17 0.26 0.06 0.10 44.87 0.21 Average 20.35 34.02 0.30 0.07 0.11 44.90 0.30

    [0079] In S1, after the dolomite was calcined into dolime in a rotary kiln, 100 kg of the dolime was weighed, which contained 36.93 kg of magnesium oxide (MgO) and 61.74 kg of calcium oxide (CaO), and 56.31 kg of anthracite was then weighed. The two were mixed and ground into 156.31 kg of a 100 mesh powder.

    [0080] In S2, in a pellet mill, the aforementioned powder was pressed into a furnace feed material in the form of pillow-shaped pellets with dimensions of 50 mm (length)×30 mm (width)×20 mm (height). The material was placed into a graphite smelting chamber contained in a steel hermetic container. An electromagnetic induction coil was provided as a heat source outside the graphite smelting chamber, and a thermal insulation layer was disposed between the induction coil and the graphite smelting chamber. A shell and tube condenser was connected in series between an interface for a vacuum pipe on the top of the steel container and a vacuum pump, and a lower portion of the condenser was connected to a hermetic liquid magnesium reservoir.

    [0081] In S3, through continuous vacuumization, an absolute pressure in the steel container was maintained at P≈3000 Pa, and the smelting chamber was heated to and maintained at a temperature T=1800±20° C. by electromagnetic induction. A smelting reaction carried on, and through an observation window in the liquid magnesium reservoir, liquid magnesium could be seen flowing from the condenser into the liquid magnesium reservoir. After 4 hours of the reaction, as indicated by a meter, electric heating power had undergone a significant decrease and showed a tendency toward a constant level. This indicated that the smelting reaction had substantially ended. Argon was introduced to eliminate the vacuum until a vacuum pressure meter on the reactor read zero. A waste discharge port at the bottom of the reactor was opened, and calcium acetylide pellets were discharged.

    [0082] After being collected and weighed, 18.89 kg of crude magnesium and 89.05 kg of calcium acetylide pellets were produced. Chemical analysis results showed that the produced crude magnesium had a magnesium content of 98.5% and the calcium acetylide had a gas production capacity of 236 l/kg, which was equivalent to a calcium carbide content of 63%.

    II. Technical Contemplation 2—Carbothermic Process of Calcium Production and Co-Production of Calcium Carbide

    [0083] As can be seen from FIG. 1, in the phase of the calcium carbide-producing reaction between carbon and calcium oxide: (1) if the temperature is in the range of 11 lg.sup.2P+711 lgP+1210° C.<T<30 lg.sup.2P+58 lgP+1215° C., then only the reaction CaO+3C.fwdarw.CaC.sub.2+CO will take place to produce CaC.sub.2. (2) If the temperature is in the range of 30 lg.sup.2P+58 lgP+1215° C.<T<98 lg.sup.2P−129 lgP+1300° C., then following the CaC.sub.2— producing reaction CaO+3C.fwdarw.CaC.sub.2+CO, the reaction 2CaO+CaC.sub.2.fwdarw.3Ca+2CO will further occur to produce a calcium vapor. However, if a C/CaO molar ratio of the reaction system is ≥3, then the reaction CaO+3C.fwdarw.CaC.sub.2+CO will first proceed completely, and there will be no CaO left to undergo the calcium-producing reaction 2CaO+CaC.sub.2.fwdarw.3Ca+2CO with CaC.sub.2. As a result, the product of the system is CaC.sub.2, and there will be no calcium vapor released from the reaction system. If the C/CaO molar ratio is <3, as the amount of carbon is not sufficient to support the adequate completion of the reaction CaO+3C.fwdarw.CaC.sub.2+CO, CaO will partially remain. The CaO remainder will undergo the calcium-producing reaction 2CaO+CaC.sub.2.fwdarw.3Ca+2CO with CaC.sub.2. Consequently, there will be a reduced amount of CaC.sub.2 in the system and a calcium vapor released from the reaction system. If the C/CaO molar ratio of the reaction system is ≤1, due to a too small amount of carbon in the system, the reaction CaO+3C.fwdarw.CaC.sub.2+CO will be more inadequate, and the produced CaC.sub.2 will be completely consumed in 2CaO+CaC.sub.2.fwdarw.3Ca+2CO. Moreover, the produced calcium will be completely released from the reaction system due to the absence of carbon being left to undergo with it the reaction Ca+2C.fwdarw.CaC.sub.2. Finally, there will be no calcium carbide produced, and the only product is calcium. (3) If the temperature T is >98 lg.sup.2P−129 lgP+1300° C., only the two reactions CaO+3C.fwdarw.CaC.sub.2+CO and 2CaO+CaC.sub.2.fwdarw.3Ca+2CO will occur successively. Due to the excessively high temperature, the reaction Ca+2C.fwdarw.CaC.sub.2 will not take place. In this case, even when there is a sufficient amount of carbon in the reaction system and the reaction proceeds adequately, finally only calcium but no calcium carbide will be produced.

    [0084] The aluminothermic method is the current mainstream calcium production method, which involves using a calcium oxide powder as a raw material and an aluminum powder as a reducing agent, mixing and pelletizing them, producing a calcium vapor by carrying out the reduction reaction 6CaO+2Al.fwdarw.3Ca+3CaO.Al.sub.2O.sub.3 under vacuum at 1050-1200° C. and condensing the calcium vapor into crystalline calcium. Producing 1 ton of calcium consumes about 3 tons of calcium oxide and 0.5 tons of the aluminum powder and leads to the generation of about 2.5 tons of calcium aluminate as solid waste. This method is associated with high smelting cost and a risk of explosion due to the aluminum powder used.

    [0085] If carbon is used as a reducing agent for calcium production, the reactions involved will be:

    ##STR00002##

    [0086] Combining these equations, we obtain

    ##STR00003##

    [0087] In theory, producing 1 ton of calcium consumes only 1.4 tons of calcium oxide and 0.3 tons of carbon, and no solid waste will be generated. Estimated power consumption is about 5000 kWh/t. The smelting cost is approximately half that of the aluminothermic approach. Significant increases can be achieved in terms of economic benefits, environmental benefits and production safety.

    [0088] Different ratios of CaO to C in the mixed powder will lead to different ratios of calcium to calcium carbide produced by the adequate smelting reaction. When the molar ratio CaO:C is ≈1:1, only calcium and CO will be produced, and there is substantially no calcium carbide produced. When the molar ratio CaO:C is ≈1:3, and at a reaction temperature Tin the range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P−129 lgP+1300° C., only calcium carbide and CO will be produced, and there is substantially no calcium produced. When the molar ratio CaO:C is within the range of 1:1 to 1:3, both calcium and calcium carbide will be produced.

    Example 2

    [0089] In S1, limestone was obtained from an ore mine, with a chemical composition as follows: CaO=54.0%, MgO=3.0%, SiO.sub.2=1.5%, burning loss=41.4%, rest impurities=0.1%. Coke with a fixed carbon content of 85% was obtained from a coking plant. After the limestone was calcined into lime, 100 kg of the lime was weighed and used as a raw material, which contained 92.15 kg of calcium oxide. In case of only calcium to be produced without co-production of calcium carbide, 23.23 kg of the coke is added as a reducing agent resulting in a molar ratio CaO:C≈1:1. The two were mixed and ground into 123.23 kg of a 100 mesh mixed powder.

    [0090] In S2, in a pellet mill, the aforementioned powder was pressed into a furnace feed material in the form of pillow-shaped pellets with dimensions of 50 mm (length)×30 mm (width)×20 mm (height). The material was placed into a graphite smelting chamber in a steel hermetic container. An electromagnetic induction coil was provided as a heat source outside the graphite smelting chamber, and a thermal insulation layer was disposed between the induction coil and the graphite smelting chamber. A shell and tube condenser was connected in series between an interface for a vacuum pipe on the top of the steel container and a vacuum pump, and a lower portion of the condenser was connected to a hermetic liquid calcium reservoir.

    [0091] In S3, through continuous vacuumization, an absolute pressure in the steel container was maintained at P≈10000 Pa, and the smelting chamber was heated to and maintained at a temperature T=2000±20° C. by electromagnetic induction. A smelting reaction carried on, and through an observation window in the liquid calcium reservoir, liquid calcium could be seen flowing from the condenser into the liquid calcium reservoir. After 2.5 hours of the reaction, as indicated by a meter, electric heating power had undergone a significant decrease and showed a tendency toward a constant level. This indicated that the smelting reaction had substantially ended. Argon was introduced to eliminate the vacuum until a vacuum pressure meter on the reactor read zero. After a waste discharge port at the bottom of the reactor was opened, a small amount of solid waste was seen. Although the solid waste contained an insignificant amount of calcium carbide, it was of no value in terms of industrial use as calcium acetylide.

    [0092] After being collected and weighed, 63.07 kg of crude calcium and 13.35 kg of solid waste were produced. Chemical analysis results showed that the produced crude calcium had a calcium content of 99.53% and the main impurity elements were Mg, Fe, etc. The main element components of the solid waste were C, Ca, Si, Al, etc.

    III. Technical Contemplation 3—Carbothermic Process of Magnesium Production and Co-Production of Calcium Carbide Using Solid-Phase Catalyst

    [0093] In “Technical Contemplation 1” above, liquid magnesium is obtained through condensation by a condenser connected to the reactor without the formation of a magnesium powder, thereby eliminating the severe potential safety hazard in industrial carbothermic production. However, “Technical Contemplation 1” can only significantly suppress, but not totally prevent, the reversing of the smelting reaction between vaporous magnesium and CO. Therefore, “Technical Contemplation 1” still suffers from relatively low reduction rate of the magnesium production reaction and product purity.

    [0094] Experimental research has found that the carbothermic magnesium production reaction

    ##STR00004##

    obviously has a much higher magnesium production rate in the presence of CaC.sub.2 than in the absence of CaC.sub.2 in the system. Theoretical research shows that, when there is sufficient CaC.sub.2 in the system, under certain conditions, the magnesium production reaction

    ##STR00005##

    consists of two steps:

    ##STR00006##

    in which CaC.sub.2 serves as a catalyst. The reaction between MgO and CaC.sub.2 in the first step produces a magnesium vapor as the only gas product, and the reaction between CaO and C in the second step produces CO as the only gas product. Therefore, when these gases are released immediately after being produced, co-existence of the magnesium vapor and CO in the reactor will not take place, thus avoiding the occurrence of the reverse reaction Mg.sub.(g)+CO.sub.(g).fwdarw.MgO.sub.(s)+C.sub.(s). Moreover, it is not possible for a magnesium powder to be formed during the production of the liquid. Further, theoretically, the produced CaC.sub.2 is equal in amount to the CaC.sub.2 catalyst added to the raw material, and can be recycled as the catalyst for the next smelting cycle. Therefore, the use of the catalyst will not increase the smelting cost. Similarly, when dolime (MgO.CaO) is used as a raw material, the reaction

    ##STR00007##

    can be decomposed into two steps:

    ##STR00008##

    and the produced CaC.sub.2 is twice as much as that produced with MgO being used as a raw material. Accordingly, one half of it can be reused as a catalyst, and the other half can be sold as calcium acetylide. This can greatly increase economic benefits from magnesium production.

    [0095] As can be seen from FIG. 1, in the reaction system of magnesium oxide and calcium oxide with C, if there is a sufficient amount of CaC.sub.2, then when the reaction temperature is kept lower than Curve (1) but higher than Curve (3), the reaction MgO.CaO.sub.(s)+C.sub.(s).fwdarw.Mg.sub.(g)+CO.sub.(g)+CaO.sub.(s) of Curve (1) will not take place, and only the reaction MgO.CaO.sub.(s)+CaC.sub.2(s).fwdarw.Mg.sub.(g)+2C.sub.(s)+2CaO.sub.(s) of Curve (3) will occur. Consequently, only vaporous Mg, C and CaO but no CO will be produced. Since the exothermic reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) only occurs at a temperature lower than Curve (5), after the smelting reaction of Curve (3) for magnesium production has completed, if the smelting process is continued with the temperature being raised to a value higher than Curve (2) but lower than Curve (5), then the reaction CaO.sub.(s)+3C.sub.(s).fwdarw.CaC.sub.2(s)+CO.sub.(g) of Curve (2), the reaction 2CaO.sub.(s)+CaC.sub.2(s).fwdarw.3Ca.sub.(g)+2CO.sub.(g) of Curve (4) and the reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) of Curve (5) will occur to produce CaC.sub.2 and CO, without the problem of loss of calcium in the form of a vapor. In other words, if enough CaC.sub.2 is added to the carbothermic magnesium production reaction system of magnesium oxide and calcium oxide with C and the reaction process is decomposed into two steps respectively for producing magnesium and calcium carbide, i.e.,

    [0096] (1) the initial magnesium production step run at a temperature maintained within the range of 51 lg.sup.2P−38 lgP+800° C.<T<20 lg.sup.2P+60 lgP+1050° C., then only one gas, i.e., a magnesium vapor, will be produced, without the occurrence of the reverse reaction between the magnesium vapor and CO, and liquid magnesium will be produced when an absolute pressure P is further maintained ≥1000 Pa, without a hazard of explosion due the formation of a magnesium powder;

    [0097] (2) the subsequent CaC.sub.2 production step run at a temperature maintained within the range of 11 lg.sup.2P+71 lgP+1210° C.<T<98 lg.sup.2P−129 lgP+1300° C. and producing CO, then loss of calcium in the form of a vapor and hence a decrease in the yield of CaC.sub.2 will not happen.

    Example 3

    [0098] In S1, the same anthracite and dolomite as Example 1, calcium acetylide with a gas production capacity of 300 l/kg (a CaC.sub.2 content of 80%) and high-temperature pitch with a fixed carbon content of 80% were used. After the dolomite was calcined into dolime in a rotary kiln, 100 kg of the dolime was weighed, which contained 36.93 kg of magnesium oxide (MgO) and 61.74 kg of calcium oxide (CaO). Theoretically, 50.69 kg of pure carbon was needed, in order to facilitate palletizing, 80% of which was provided by the anthracite and 20% by the pitch. 45.06 kg of the anthracite, 12.67 kg of the pitch and 73.31 kg of the calcium acetylide were weighed. The 100 kg of dolime was mixed with the anthracite, the pitch and the calcium acetylide, and the mixture was then ground into 231.45 kg of a 100 mesh powder.

    [0099] In S2, in a pellet mill, the aforementioned powder was pressed into a furnace feed material in the form of pillow-shaped pellets with dimensions of 50 mm (length)×30 mm (width)×20 mm (height). The material was placed into a graphite smelting chamber in a steel hermetic container. An electromagnetic induction coil was provided as a heat source outside the graphite smelting chamber, and a thermal insulation layer was disposed between the induction coil and the graphite smelting chamber. A shell and tube condenser was connected in series between an interface for a vacuum pipe on the top of the steel container and a vacuum pump, and a lower portion of the condenser was connected to a hermetic liquid magnesium reservoir.

    [0100] In S3, through continuous vacuumization, an absolute pressure in the steel container was maintained at P≈2000 Pa, and the smelting chamber was heated to and maintained at a temperature T=1450±20° C. by electromagnetic induction. A smelting reaction for magnesium production carried on, and through an observation window in the liquid magnesium reservoir, liquid magnesium could be seen flowing from the condenser into the liquid magnesium reservoir.

    [0101] In S4, after about 1 hour of the aforementioned reaction, as indicated by a meter, electric heating power had undergone a significant decrease and showed a tendency toward a constant level. This indicated that the smelting reaction for magnesium production had substantially ended. After that, with the pressure in the steel container being maintained, the temperature in the smelting chamber was increased to T=1750-1800° C. to allow a smelting reaction for calcium carbide production to proceed. After about 2 hours of this reaction, heating power again experienced a decrease and showed a tendency toward a constant level, indicating the smelting reaction for calcium carbide production had substantially ended. Argon was introduced to eliminate the vacuum until a vacuum pressure meter on the reactor read zero. A waste discharge port at the bottom of the reactor was opened, and calcium acetylide pellets were discharged.

    [0102] This apparatus operated in production cycles of about 3 hours. In each cycle, 20.96 kg of crude magnesium and 89.9 kg of calcium acetylide (not including the calcium carbide added as a catalyst) were produced. Chemical analysis results showed that the crude magnesium has a magnesium content of 99.93% and the calcium acetylide pellets had a gas production capacity of 241 l/kg, which was equivalent to a calcium carbide content of about 64%. In average, per hour, about 7 kg/h of magnesium and about 15 kg/h of pure calcium carbide (not including that added as a catalyst) were produced.

    IV. Technical Contemplation 4—Carbothermic Process of Magnesium Production and Co-Production of Calcium Carbide Using Liquid-Phase Catalyst

    [0103] In “Technical Contemplation 3” above, it is necessary to first grind the raw material, the reducing agent and the catalyst into a powder and press the powder into pellets and then to feed the pellets into the reactor so that smelting is accomplished by a solid-phase reaction. In general terms, a solid-phase reaction proceeds much more slowly than a liquid-phase reaction. In addition, the pulverizing and pelletizing steps extend the process and raise its cost.

    [0104] Pure CaC.sub.2 has a melting point of about 2300° C. By containing various percentages of CaO, the melting point of calcium acetylide can drop up to about 1800-1900° C. Experiments have found that, when MgO blocks are put into a calcium acetylide melt pool in a molten state, a large amount of vaporous magnesium and gaseous CO will be produced soon. When MgO.CaO blocks are put into a calcium acetylide melt pool, in addition to a large amount of vaporous magnesium and gaseous CO that will be produced soon, a small amount of vaporous calcium will also be produced, and liquid CaC.sub.2 will gradually grow in amount in the melt pool. If small blocks of MgO.CaO raw material and small coke blocks that are alternately laid in layers (or mixed coke and raw material blocks) are laid over a surface of a calcium acetylide melt pool surface (part of which will be submerged below the surface, while the rest will remain above the surface), in case of a large thickness of the material layers above the surface, gases discharged from the top of the material layers of blocks will be only vaporous magnesium and CO. In case of a small thickness of the material layers above the surface, in addition to a large amount of vaporous magnesium and CO, a small amount of vaporous calcium will be also discharged from the top of the material layers of blocks. Further, the amount of the discharged vaporous calcium can be adjusted by changing the thickness of the material layers.

    [0105] As can be found from an analysis of FIG. 1, when MgO.CaO blocks and C blocks are put into molten CaC.sub.2, the reaction

    ##STR00009##

    will first take place. With free C being formed in the melt, the reactions MgO.CaO.sub.(s)+C.sub.(s).fwdarw.Mg.sub.(g)+CO.sub.(g)+Cao.sub.(s) and 2CaO.sub.(s)+CaC.sub.2(s).fwdarw.3Ca.sub.(g)+2CO.sub.(g) will also occur to certain extents. However, the latter two reactions (especially the last one) are mild and provide a small amount of vaporous calcium and CO (compared to the amount of vaporous magnesium produced). When passing through the material layers of blocks, the vaporous calcium will undergo the reaction Ca.sub.(g)+2C.sub.(s).fwdarw.CaC.sub.2(s) with C at the surface of carbon blocks. When the carbon layers of blocks are thick enough, no vaporous calcium will be discharged from the top of the material layers. After MgO in the melt pool is completely consumed, the reaction CaO.sub.(l)+3C.sub.(s).fwdarw.CaC.sub.2(l)+CO.sub.(g) between CaO and C will start, and as this reaction proceeds, an increasing amount of CaC.sub.2 will be present in the melt pool. Because of a higher temperature and faster diffusion of reactants in molten CaC.sub.2, especially when both CaO and CaC.sub.2 are in a molten state, the reaction CaO.sub.(l)+3C.sub.(s).fwdarw.CaC.sub.2(l)+CO.sub.(g) in the melt pool proceeds much faster than the solid-phase reaction CaO.sub.(s)+3C.sub.(s).fwdarw.CaC.sub.2(s)+CO.sub.(g). That is, the carbon reduction reaction

    ##STR00010##

    for magnesium production proceeds much faster under liquid-phase catalysis than under solid-phase catalysis.

    [0106] As can be seen from FIGS. 1, 3 and 4, at a molten state of CaC.sub.2, i.e., at a melt pool temperature T>1900° C. and a pressure P in the range of 1000 Pa≤P<10000 Pa, through properly configuring the thickness of the material layers (according to specific values of the reaction temperature and absolute pressure), the magnesium vapor can be controlled so as to leave the material layers at a temperature T lower than T=98 lg.sup.2P−129 lgP+1300° C. and slightly higher than a condensation temperature of the magnesium vapor, T.sub.b=21.4 lg.sup.2P+18.4 lgP+437° C. That is, the magnesium vapor is controlled so as to leave the material layers at a temperature T in the range of 7812.6/(11.8−lgP)−273° C.<T<98 lg.sup.2P−129 lgP+1300° C. As a result, liquid magnesium can be obtained by condensation of the magnesium vapor. However, in this case, there may be a small amount of vaporous calcium lost together with gaseous CO. In contrast, at a pressure P≥10000 Pa, through controlling the melt pool temperature as T≤30 lg.sup.2P+58 lgP+1215° C. and causing the magnesium vapor to leave the material layers at a temperature T slightly higher than T=21.4 lg.sup.2P+18.4 lgP+437° C., liquid magnesium can be obtained by condensation of the magnesium vapor and reversing of the smelting reaction can be substantially eliminated, without any loss of vaporous calcium. Similarly, at a pressure P≥10000 Pa, if the melt pool temperature T is >30 lg.sup.2P+58 lgP+1215° C. and the magnesium vapor leaves the material layers at a temperature T>37 lg.sup.2P−73 lgP+580° C. (condensation temperature of vaporous calcium), both liquid magnesium and a minor amount of liquid calcium can be obtained through condensation, without loss of vaporous calcium.

    Example 4

    [0107] In S1, the same dolomite as Example 1 with a particle size of 20-50 mm was used and calcined into dolime in a rotary kiln. Each ton of the dolime contained 369.3 kg of magnesium oxide and 617.4 kg of calcium oxide. Semi-coke with a particle size of 10-20 mm and fixed carbon content of 82% was obtained from a semi-coke plant. Calcium acetylide with a gas production capacity of 300 l/kg (a CaC.sub.2 content of 80%) was obtained from a calcium acetylide plant. According to a calculation, each ton of the dolime was added with 618.2 kg of the semi-coke. That is, a mass ratio of the dolime to the semi-coke was 1:0.6182.

    [0108] In S2, the calcium acetylide was placed into a graphite smelting chamber of a resistively heated hermetic steel reactor and then heated and melted therein, resulting in the formation of a calcium acetylide melt pool with a depth of about 300 mm.

    [0109] In S3, dolime particles and semi-coke particles were homogenously mixed according to the aforementioned dolime/semi-coke mass ratio, i.e., 1:0.6182, and added to the melt pool, until an about 500 mm thick unsubmerged material layer emerged above a surface of the melt pool.

    [0110] In S4, with an absolute pressure P in the reactor being set as ≈20000 Pa and a temperature of the melt pool being maintained at T=2000±20° C. through adjusting electric heating power, a smelting reaction was run. Meanwhile, the thickness of the material layer was adjusted by material addition so that a magnesium vapor produced left the material layer at a temperature of about 1000° C. The magnesium vapor entered a condenser connected in series to the reactor and condensed there into liquid magnesium. During the smelting process, once the surface of the melt pool rose beyond a control level, it was discharged from a liquid discharge port in the reactor. After the discharged liquid calcium carbide condensed, it could be sold as a co-product.

    [0111] In average, per hour, this method produced about 13 kg/h of pure magnesium and about 33 kg/h of pure calcium carbide. The production efficiency was about twice that of the solid-phase catalysis approach. The crude liquid magnesium immediately from condensation had a magnesium content of about 95%, the calcium acetylide obtained after the liquid calcium carbide was cooled had a gas production capacity of 270 l/kg, which was equivalent to a calcium carbide content of about 72%. The quality of the crude magnesium was lower than that obtained by the solid-phase approach, but the quality of the calcium acetylide was higher than that obtained by the solid-phase approach.

    V. Technical Contemplation 5—Carbothermic Process of Production of Multiple Metals Using Solid-Phase Calcium Carbide Catalyst

    [0112] Studies have found that, not only carbothermic magnesium production from a mixture of magnesium oxide and calcium oxide using calcium carbide as a catalyst is possible, oxides M.sub.mO (m represents a ratio of metal atoms to oxygen atoms) of many metals such as Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo and V (hereinafter, collectively denoted as M) can react with calcium carbide to produce simple substances of the metals and calcium oxide, and the produced calcium oxide can also further react with carbon to again produce calcium carbide. These smelting reactions can be collectively expressed as the following equations:

    ##STR00011##

    [0113] Combining the above two equations, we obtain

    ##STR00012##

    [0114] It can be seen that CaC.sub.2 serves as a catalyst in the reactions. The thermodynamic laws of the chemical reactions are qualitatively described in FIG. 5.

    [0115] Thus, using the same method as described above, which uses a mixture of magnesium oxide and calcium oxide as a raw material, carbon as a reducing agent and calcium carbide as a catalyst for magnesium production, oxides of metals such as magnesium, lead, tin, zinc, iron, manganese, nickel, cobalt, chromium, molybdenum and vanadium can be smelted to produce simple substances of the metals. In each production cycle, substantially the same amount of calcium carbide as that of the added calcium carbide catalyst can be produced and reused in its entirety as a catalyst.

    Example 5

    [0116] In S1, first-grade magnesite was obtained from an ore mine, with a chemical composition as follows: MgO=46%, CaO=0.6%, SiO.sub.2=1.0%. First-grade calcium acetylide with a CaC.sub.2 content of 80% was obtained from a calcium acetylide plant, and high-temperature pitch with a fixed carbon content of 80% was obtained from a chemical plant. To 100 kg of calcined magnesite containing 96.64 kg of the active ingredient MgO, 191.84 kg of the calcium acetylide and 35.97 kg of the pitch were added. They were then mixed and ground to 327.81 kg of a 100 mesh mixed powder.

    [0117] In S2, the aforementioned mixed powder was pressed pillow-shaped pellets with dimensions of 50 mm (length)×30 mm (width)×20 mm (height), and the pellets were placed into a graphite smelting chamber contained in a steel hermetic container. The graphite smelting chamber was resistively heated, and a thermal insulation layer was disposed between the smelting chamber and the steel container. A shell and tube condenser was connected in series between an interface for a vacuum pipe on the top of the steel container and a vacuum pump, and a lower portion of the condenser was connected to a hermetic liquid magnesium reservoir.

    [0118] In S3, with an absolute pressure P in the reactor being set as P≈1000 Pa and a temperature in the smelting chamber being maintained at T=1400±20° C. through adjusting electric heating power, a smelting reaction for magnesium production was run. Through an observation window in the liquid magnesium reservoir, liquid magnesium could be seen flowing from the condenser into the liquid magnesium reservoir.

    [0119] In S4, after about 2 hours of the aforementioned smelting reaction for magnesium production, electric heating power had undergone a significant decrease and showed a tendency toward a constant level, indicating that the smelting reaction for magnesium production had substantially ended. After that, with the absolute pressure P in the reactor being set as ≈3000 Pa, the temperature in the smelting chamber was increased to T=1750±20° C. to allow a smelting reaction for calcium carbide production to proceed. After about 1 hour of this reaction, heating power again experienced a decrease and showed a tendency toward a constant level, indicating the smelting reaction for calcium carbide production had substantially ended. Argon was introduced to eliminate the vacuum until a vacuum pressure meter on the reactor read zero. A waste discharge port at the bottom of the reactor was opened, and the produced calcium acetylide was discharged and used as a reducing agent for the next production cycle.

    [0120] This method operated in production cycles of about 3 hours. In each cycle, 68.56 kg of crude magnesium was produced. In average, per hour, about 22 kg/h of magnesium was produced. The crude magnesium had a magnesium content of 99.96%.

    VI. Technical Contemplation 6—Carbothermic Process of Production of Multiple Metals Using Liquid-Phase Calcium Carbide Catalyst

    [0121] In the method as described above in “Technical Contemplation 5” for carbothermic production of multiple metals, if liquid-phase CaC.sub.2 is instead used as the catalyst, not only much faster smelting reaction speeds can be achieved, but also the pulverizing, pelletizing and other steps can be saved, resulting in increased production efficiency, a shortened process flow and reduced product cost.

    Example 6

    [0122] In S1, the same magnesite as Example 5 with a particle size of 20-50 mm was used and calcined. Each ton of the calcined magnesite contained 966.4 kg of magnesium oxide. Coke with a particle size of 10-20 mm and a fixed carbon content of 85% was obtained from a coke plant, and calcium acetylide with a gas production capacity of 300 l/kg (a CaC.sub.2 content of 80%) was obtained from a calcium acetylide plant. Each ton of the calcined magnesite was added with 338.5 kg of the coke. That is, a mass ratio of the calcined magnesite to the coke was 1:0.3385.

    [0123] In S2, the calcium acetylide was placed into a graphite smelting chamber of a resistively heated hermetic steel reactor and then heated and melted therein, resulting in the formation of a calcium acetylide melt pool with a depth of about 300 mm.

    [0124] In S3, calcined magnesite particles and coke particles were homogenously mixed according to the aforementioned calcined magnesite/coke mass ratio, i.e., 1:0.3385, and added to the catalyst melt pool in the smelting chamber, until an about 500 mm thick unsubmerged material layer emerged above a surface of the melt pool.

    [0125] In S4, with an absolute pressure P in the reactor being set as P≈20000 Pa and a temperature of the melt pool being maintained at T=2000±20° C. through adjusting electric heating power, a smelting reaction was run. Meanwhile, the thickness of the material layer was adjusted by material addition so that a magnesium vapor produced left the material layer at a temperature of about 1000° C. The magnesium vapor entered a condenser connected in series to the reactor and condensed there into liquid magnesium.

    [0126] In average, per hour, this method produced an equivalent amount of about 40 kg/h of pure magnesium. The production efficiency was about twice that of the solid-phase catalysis approach. The liquid magnesium immediately from condensation had a magnesium content of about 95%. The quality of the crude magnesium was lower than that obtained by the solid phase approach.

    [0127] Technical contemplations and preferred specific embodiments have been described in detail above. It is to be understood that, those of ordinary skill in the art, without the need for creative effort, can make various modifications and changes, based on the concept of the present invention. Accordingly, all the technical solutions that can be obtained by those skilled in the art by logical analysis, inference or limited experimentation in accordance with the concept of the invention on the basis of the prior art are intended to fall within the protection scope as defined by the claims.