A method for producing magnesium by carbothermal reduction and co-producing calcium carbide

Abstract

The present invention relates to a method for producing magnesium by carbothermal reduction with co-production of calcium carbide, which is particularly suitable for carbothermal reduction of magnesium using a mixture of magnesium oxide and calcium oxide as raw materials and carbon as a reducing agent. Prepare a mixed powder containing magnesium oxide, calcium oxide and a carbon reducing agent; form the mixed powder into pellet furnace charge and put it into a reactor provided with a heat source; set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P ≤ atmospheric pressure or slightly positive pressure, and the reaction temperature T within the range of 11lg²P + 71lgP + 1210 °C < T < 98lg²P - 129lgP + 1300 °C, and carry out the smelting reaction. Liquid magnesium is obtained by condensation through a condenser connected to the reactor. After the smelting reaction is completed, calcium carbide is obtained in the reactor. By this method, the safety hazard of explosion caused by the easy formation of magnesium powder when the magnesium vapor and CO gas in carbothermal reduction of magnesium are cooled together can be completely avoided, and the cost of magnesium smelting can be significantly reduced. This method has good application prospects in industry.

Description

[0001] This application is a divisional application of the following application: Application date: December 17, 2020; Application number: 202080087519.1; Invention title "A method for producing magnesium by carbothermal reduction and co-producing calcium carbide". Technical Field

[0002] The present invention relates to the field of smelting, and in particular to a method for producing magnesium by carbothermal reduction and co-producing calcium carbide. Background Art

[0003] Currently, the industrial production of magnesium generally uses the silicothermal method or the electrolytic method. Among them, in the silicothermal method for producing magnesium, calcined dolomite (referred to as calcined white, with the active ingredient MgO·CaO) is used as the raw material, and ferrosilicon (with the active ingredient Si) is used as the reducing agent. At high temperature and under vacuum, the following reduction reaction occurs: 2(MgO·CaO) (s) +Si (s) →2Mg (g) +2CaO·SiO 2(s) The generated waste residue 2CaO·SiO2 has little application value and is usually landfilled; in the electrolytic method for producing magnesium, molten magnesium chloride is used as the raw material, and the following reaction occurs in the electrolytic cell: MgCl 2(l) →Mg (l) +Cl 2(g) The generated waste gas Cl2 is a toxic and harmful gas, and a complex and lengthy process is required for the comprehensive utilization (harmless treatment) of chlorine gas.

[0004] The carbothermal method uses calcined white (MgO·CaO) or calcined magnesite (MgO) as the raw material and carbon as the reducing agent. At high temperature and under vacuum, the following reduction reaction occurs: MgO·CaO (s) +C (s) →Mg (g) +CO (g) +CaO (s) Or MgO (s) +C (s) →Mg (g) +CO (g) The cost of the carbon reducing agent is significantly lower than that of the ferrosilicon reducing agent in the silicothermal method for producing magnesium, and the generated CO waste gas can be used as fuel. Especially when calcined magnesite is used as the raw material, no waste residue is generated, and when calcined white is used as the raw material, the generated CaO waste residue has certain utilization value. Therefore, it is generally believed that the carbothermal method for producing magnesium has obvious economic advantages.

[0005] However, the carbothermal method for producing magnesium has two fatal weaknesses: one is that when the generated magnesium vapor and CO gas are cooled together, they will condense into magnesium powder, and the high-temperature magnesium powder will explode violently when encountering air, posing a great safety hazard; the other is that during the co-cooling process of magnesium vapor and CO gas, the reverse reaction of the smelting process will occur: Mg (g) +CO (g) →MgO(s) +C (s) , this reverse reaction not only reduces the smelting reduction rate, but also significantly reduces the purity of crude magnesium.

[0006] For a long time, researchers at home and abroad have been studying to solve the above two problems of magnesium smelting by the carbothermal method, but no effective solution has been found so far. Therefore, the carbothermal method has not been industrialized. The Commonwealth Scientific and Industrial Research Organization of Australia announced a new technology for magnesium smelting by the carbothermal method in July 2016. The mixed gas of magnesium vapor and CO passes through a specially designed "supersonic nozzle" (Laval nozzle) at a speed of 4 times the speed of sound. After passing through the nozzle, the magnesium vapor "instantly" condenses into solid crystalline magnesium. While preventing the formation of magnesium powder, it can reduce the degree of the reverse reaction in smelting. However, no industrial application reports have been found so far.

[0007] The Chinese patent "A process for simultaneously producing metallic magnesium and calcium carbide by the carbothermal method" with the application number 201710320876.8 uses calcined dolomite as the raw material. By combining the magnesium smelting reaction by the carbothermal method MgO·CaO + C → Mg + CO + CaO and the calcium carbide (CaC2) smelting reaction CaO + 3C → CaC2 + CO, calcium carbide is produced while smelting magnesium. However, the magnesium vapor in this patent still coexists with CO gas, and the two main problems of magnesium smelting by the carbothermal method, namely the safety hazard of generating magnesium powder and the reverse reaction in smelting, have not been solved. And a large number of experiments by Zhengzhou University and many researchers have proved that in the range of absolute pressure (hereinafter referred to as absolute pressure or pressure) of 10 - 100 Pa and temperature of 1500 - 1800 °C given in the application number 201710320876.8, the reaction rates of MgO·CaO + C → Mg + CO + CaO and CaO + 3C → CaC2 + CO are very slow and basically have no industrial application value. Experiments have found that for a single pellet charge weighing dozens of grams, after reacting for several hours at 1500 - 1600 °C, only a very small amount of calcium carbide (even sometimes hardly detectable) can be detected in the solid-phase product; after reacting for several hours at a higher temperature above 1700 °C, although calcium carbide is generated in the solid-phase product, the amount of Ca atoms in the smelting products (CaO and CaC2) is significantly less than the content in the raw materials, indicating that part of the Ca in the raw materials evaporates and is lost in the gaseous form. Some literature reports on similar phenomena can be seen in: (1) Research on the reaction and catalytic mechanism of low-temperature synthesis of calcium carbide, He Yantao et al., "Petrochemical Industry Application", Vol. 29, No. 10; (2) Thermodynamic analysis and experimental verification of low-temperature synthesis of calcium carbide, Liu Siyuan et al., "Coal Conversion", Vol. 40, No. 5. Summary of the Invention

[0008] Therefore, the inventor of the present invention has conducted a large number of experiments and calculations, and the results show (see Figure 1 ), a series of reactions will occur when the mixture of calcined dolomite (MgO.CaO) and C is in a high-temperature vacuum reactor as follows:

[0009] 1. First, when the temperature is higher than curve (1), MgO·CaO (s) +C (s) →Mg (g) +CO (g) +CaO (s) reacts (referred to as "Reaction 1") to produce Mg vapor and CaO. The relationship between the temperature T (°C) and the absolute pressure P (Pa) of curve (1) is T = 20lg 2 P + 60lgP + 1050;

[0010] 2. Second, if the temperature is higher than curve (2), the CaO generated by "Reaction 1" continues to react with C, CaO (s) +3C (s) →CaC 2(s) +CO (g) (referred to as "Reaction 2"), consuming CaO and generating CaC2. The relationship between the temperature T (°C) and the absolute pressure P (Pa) of curve (2) is T = 11lg 2 P + 71lgP + 1210;

[0011] 3. Then, if the temperature is higher than curve (3), the CaC2 generated by "Reaction 2" will react with the calcined dolomite remaining from "Reaction 1", MgO·CaO (s) +CaC 2(s) →Mg (g) +2C (s) +2CaO (s) reacts (referred to as "Reaction 3"). While consuming CaC2 to generate Mg vapor, CaO is generated again, and "Reaction 3" is much easier to react than "Reaction 1" and "Reaction 2", that is, before all the magnesium oxide in the calcined dolomite is reduced to Mg vapor, there is basically no CaC2 in the reaction system. The relationship between the temperature T (°C) and the absolute pressure P (Pa) of curve (3) is T = 51lg 2 P - 38lgP + 800;

[0012] 4. After all the magnesium oxide in the calcined dolomite is reduced to Mg vapor, if the temperature is still higher than curve (2), CaC2 will continue to be generated through "Reaction 2"; if the temperature is also higher than curve (4) at the same time, the generated CaC2 will react with the remaining CaO in the system, 2CaO (s) +CaC 2(s) →3Ca (g) +2CO (g) reacts (referred to as "Reaction 4"), further consuming CaC2 while generating Ca vapor. The relationship between the temperature T (°C) and the absolute pressure P (Pa) of curve (4) is T = 30lg 2 P + 58lgP + 1215;

[0013] 5. Finally, if the Ca vapor generated by "Reaction 4" encounters C with a temperature lower than (note: not higher than) the curve (5) in the reaction system, an exothermic reaction Ca (g) + 2C (s) → CaC 2(s) (referred to as "Reaction 5") will occur, and CaC2 will be generated again; if the Ca vapor does not encounter C with a temperature lower than the curve (5), "Reaction 5" cannot occur, and the Ca vapor can only be discharged from the reaction system. The relationship between the temperature T (°C) and the absolute pressure P (Pa) of the curve (5) is T = 98lg 2 P - 129lgP + 1300.

[0014] Through Figure 1 it can be known that within the working range of the absolute pressure of 10 - 100 Pa and the temperature of 1500 - 1800 °C given in the application number 201710320876.8, the above "Reaction 1" to "Reaction 4" can all occur, but "Reaction 5" cannot occur. That is to say, the CaC2 generated by "Reaction 2" will be consumed by "Reaction 3" and "Reaction 4", and the more complete the reaction, the more thoroughly CaC2 is consumed. Especially since the Ca vapor generated by "Reaction 4" cannot be converted back into CaC2 by "Reaction 5", ultimately Ca is lost in the form of vapor and discharged from the reaction system in vain (from Figure 4 it can be known that when the absolute pressure is 10 - 100 Pa, the gasification temperature of Ca is about 500 - 600 °C). And from Figure 1 it can be known that when the absolute pressure is 10 - 100 Pa, the curve (2) and the curve (4) are very close, that is, the starting temperatures of "Reaction 2" and "Reaction 4" are quite similar, and it is very difficult to make only "Reaction 2" that generates CaC2 occur without making "Reaction 4" that reduces CaC2 to generate Ca vapor occur. Moreover, the curve (5) is also very close to the curve (4), that is to say, after CaC2 is reduced to generate Ca vapor, it is also very difficult to make the Ca vapor react with C to generate CaC2 in "Reaction 5", and only the Ca vapor can flow out of the reaction system. The result is equivalent to the combined (overall) reaction of "Reaction 2" and "Reaction 4" CaO (s) + C (s) → Ca (g) + CO (g) . Finally, when the reaction proceeds sufficiently, there is no obvious generation of CaC2, and only when the reaction is not sufficient, there will be a small amount of CaC2 coexisting with CaO.

[0015] In view of the above defects of the prior art, the present invention provides a method for producing magnesium by carbothermal reduction and co-producing calcium carbide to partially or completely solve the above problems.

[0016] On the one hand, the present invention provides a method for producing magnesium by carbothermal reduction and co-producing calcium carbide, comprising the following steps:

[0017] S1. Prepare a mixed powder containing magnesium oxide, calcium oxide, and a carbon reducing agent;

[0018] S2. Make the mixed powder into pelletized furnace charge and put it into a reactor equipped with a heat source;

[0019] S3. Set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P ≤ atmospheric pressure or as a slightly positive pressure, and the reaction temperature T within the range of 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C, carry out a smelting reaction, and obtain liquid magnesium by condensing through a condenser connected to the reactor, and obtain calcium carbide in the reactor.

[0020] In some embodiments, preferably, the molar content M of the carbon reducing agent, the molar content M of magnesium oxide, and the molar content M of calcium oxide in the mixed powder satisfy the following relationship: M C ≈ M MgO + 3M CaO C MgO CaO .

[0021] In some embodiments, preferably, the fineness of the mixed powder is above 80 mesh, and more preferably, the fineness of the mixed powder is 100 mesh.

[0022] In some embodiments, preferably, the equivalent diameter of the pelletized furnace charge is 20 mm to 40 mm.

[0023] In some embodiments, preferably, the outer layer of the reactor is a closed container, with a smelting chamber inside. There is a heat insulation layer between the closed container and the smelting chamber. The closed container is not directly heated, and its function is to seal and isolate the internal smelting environment of the reactor from the outside air; the pelletized furnace charge is placed in the smelting chamber, and the smelting chamber is composed of high-temperature resistant material components. The heat-resistant temperature of the high-temperature resistant material is at least higher than 1700 °C, preferably graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy, or high-temperature resistant ceramics, etc.

[0024] In some embodiments, preferably, the heat source for heating the smelting chamber in the reactor adopts an electric heating method, and heating methods such as electromagnetic induction heating, resistance heating, and arc heating can be used. And, preferably, the smelting chamber itself can also be electrified as an electric heating element.

[0025] In some embodiments, optionally, the reducing agent carbon is one of carbonaceous materials such as coke, semi-coke, coal, petroleum coke, coal tar, graphite, asphalt, etc., or a mixture of any two or more of the foregoing in any proportion.

[0026] ​​​In some embodiments, optionally, the mixed powder can be directly prepared from calcined dolomite and a carbon reducing agent.

[0027] In some embodiments, optionally, the ratio of magnesium oxide to calcium oxide in the mixed powder is different, and the ratio of magnesium and calcium carbide produced is different.

[0028] Second, the present invention also provides a method for producing calcium by carbothermal reduction and co-producing calcium carbide, comprising the following steps:

[0029] S1. Prepare a mixed powder containing calcium oxide and a carbon reducing agent;

[0030] S2. Press the mixed powder into pelletized furnace charge and place it in a reactor equipped with a heat source;

[0031] S3. Set the absolute pressure P in the reactor within the range of 10000 Pa ≤ P ≤ atmospheric pressure or to a slightly positive pressure, and the reaction temperature T > 30lg 2 P + 58lgP + 1215 °C, carry out the smelting reaction, and liquid calcium can be obtained by condensation through a condenser connected to the reactor, and calcium carbide is obtained in the reactor.

[0032] In some embodiments, optionally, the molar ratio of calcium oxide to carbon reducing agent in the mixed powder is CaO:C ≈ 1:3 to 1:1. Different ratios of CaO and C result in different production ratios of calcium and calcium carbide. Optionally, the mixed powder is prepared according to the molar ratio CaO:C ≈ 1:1. After sufficient smelting reaction, the products are only liquid calcium and CO, and basically no calcium carbide is generated except for impurity residues. Optionally, the mixed powder is prepared according to the molar ratio CaO:C ≈ 1:3. In step S3, the reaction temperature T is set within the range of 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C. After sufficient smelting reaction, the products are only calcium carbide and CO, and basically no liquid calcium is generated.

[0033] Third, the present invention also provides a method for producing magnesium by carbothermal reduction and co-producing calcium carbide using solid-phase calcium carbide as a catalyst, comprising the following steps:

[0034] S1. Prepare a mixed powder containing magnesium oxide, calcium oxide, a carbon reducing agent, and a calcium carbide catalyst;

[0035] S2. Make the mixed powder into pelletized furnace charge and place it in a reactor equipped with a heat source;

[0036] S3. Set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P < atmospheric pressure, and the reaction temperature T is within the range of 51lg 2 P - 38lgP + 800 °C < T < 20lg 2In the range of P + 60lgP + 1050 °C, carry out the magnesium smelting reaction, and obtain liquid magnesium by condensing through a condenser connected to the reactor;

[0037] S4. After the magnesium smelting reaction in S3 above, set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P ≤ atmospheric pressure or to a slightly positive pressure, and the reaction temperature T within 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C, carry out the calcium carbide smelting reaction, and obtain calcium carbide in the reactor.

[0038] In some embodiments, preferably, the molar content M of magnesium oxide MgO in the mixed powder, the molar content M of calcium oxide CaO , the molar content M of calcium carbide CaC2 and the molar content M of the carbon reducing agent C have the following relationship: M MgO ≈ M CaC2 , M C ≈ M MgO + 3M CaO .

[0039] In some embodiments, optionally, the mixed powder can be directly prepared from calcined dolomite, calcium carbide catalyst and carbon reducing agent.

[0040] In some embodiments, optionally, different ratios of magnesium oxide and calcium oxide in the mixed powder result in different output ratios of magnesium and calcium carbide.

[0041] Fourthly, the present invention also provides a method for producing magnesium by carbothermal reduction and co-producing calcium carbide using liquid-phase calcium carbide as a catalyst, comprising the following steps:

[0042] S1. Prepare granular raw materials containing magnesium oxide and calcium oxide, and granular carbon reducing agent;

[0043] S2. Place the calcium carbide catalyst into a reactor provided with a heat source, and heat and melt the calcium carbide into a molten state to form a catalyst molten pool;

[0044] S3. a) Mix the granular raw materials containing magnesium oxide and calcium oxide with the granular carbon reducing agent, and add them to the catalyst molten pool to form a solid-phase material layer with a certain thickness on the liquid surface of the catalyst molten pool; or b) First spread a layer of the granular raw materials containing magnesium oxide and calcium oxide on the liquid surface of the catalyst molten pool to form a first raw material layer, and then spread a layer of the granular carbon reducing agent on the first raw material layer to form a first reduction layer, and stack the layers in sequence;

[0045] S4. Set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P ≤ atmospheric pressure or to a slightly positive pressure, and set the molten pool temperature T within the range of 1900 °C ≤ T ≤ 30lg 2 P + 58lgP + 1215 °C, and carry out the smelting reaction; during the reaction process, adjust the thickness of the material layer in S3 so that the magnesium vapor continuously passes through the material layer and cools to a temperature higher than the condensation temperature T b =21.4lg 2 P + 18.4lgP + 437 °C when leaving the material layer, and obtain liquid magnesium by condensation through a condenser connected to the reactor.

[0046] In some embodiments, preferably, the molar content M C of the carbon reducing agent, the molar content M MgO of magnesium oxide, and the molar content M CaO of calcium oxide in all the material layers of S3 satisfy the relationship: M C ≈M MgO + 3M CaO .

[0047] In some embodiments, preferably, the sizes of the granular raw material and the granular carbon reducing agent are 5 mm to 100 mm.

[0048] In some embodiments, preferably, the outer layer of the reactor is a closed container, with a smelting chamber arranged inside. There is a heat insulation layer between the closed container and the smelting chamber. The closed container is not directly heated, and its function is to seal and isolate the internal smelting environment of the reactor from the outside air; the calcium carbide catalyst molten pool is in the smelting chamber, and the smelting chamber is composed of high-temperature resistant material components with a heat-resistant temperature of at least higher than 1900 °C. The high-temperature resistant material is preferably graphite.

[0049] In some embodiments, optionally, the raw material containing magnesium oxide and calcium oxide can be directly made from calcined dolomite.

[0050] In some embodiments, optionally, different ratios of magnesium oxide and calcium oxide in the granular raw material result in different production ratios of magnesium and calcium carbide.

[0051] Fifth aspect, the present invention also provides a method for carbothermal reduction of metals using solid-phase calcium carbide as a catalyst, including the following steps:

[0052] S1. Prepare a mixed powder containing metal oxide M m O, a carbon reducing agent, and a calcium carbide catalyst; the metal M in the metal oxide M m O is Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo or V, and m is the atomic ratio of the metal element M to the oxygen element O, where m ≤ 1;

[0053] S2. Make the mixed powder into pelletized furnace charge and put it into a reactor equipped with a heat source;

[0054] S3. Set the absolute pressure P in the reactor within a low vacuum range higher than the triple point pressure of metal M, and the reaction temperature T is higher than the temperature at which the reaction starts under the absolute pressure P and lower than the temperature at which the reaction starts under the absolute pressure P (The pressure of the triple point of the relevant metal and the temperature at which the relevant reaction starts can be calculated according to the method given on pages 1 - 25 of the second edition of "Practical Inorganic Thermodynamic Data Handbook" written by Ye Dalun and the relevant data in this handbook), and carry out the smelting reaction of metal M. Condense through a condenser connected to the reactor to obtain elemental metal M;

[0055] S4. After the smelting reaction of metal M in S3 ends, set the absolute pressure P in the reactor within a low vacuum range higher than the triple point pressure of metal M or under normal pressure or slightly positive pressure, and the reaction temperature T is within 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C, and carry out the calcium carbide smelting reaction. After the reaction ends, calcium carbide is obtained in the reactor.

[0056] In some embodiments, preferably, the molar ratio of the metal oxide M m O, calcium carbide, and carbon reducing agent in the mixed powder is M m O:CaC2:C ≈ 1:1:1.

[0057] In some embodiments, preferably, when the above metal oxide is magnesium oxide, in S3, set the absolute pressure P in the reactor within a low vacuum range of 1000 Pa ≤ P < normal pressure, and the reaction temperature T is within 51lg 2 P - 38lgP + 800 °C < T < 20lg 2 P + 60lgP + 1050 °C, and carry out the magnesium smelting reaction; in S4, set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P ≤ normal pressure or slightly positive pressure, and the reaction temperature T is within 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C, and carry out the calcium carbide smelting reaction.

[0058] Sixth aspect, the present invention also provides a method for carbothermal reduction of metals using liquid - phase calcium carbide as a catalyst, including the following steps:

[0059] S1. Prepare granular raw materials containing metal oxide M m O, and granular carbon reducing agent; the metal oxide M mIn O, the metal M is Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo or V, m is the atomic ratio of the metal element M to the oxygen element O, and m ≤ 1;

[0060] S2. Place the calcium carbide catalyst into a reactor equipped with a heat source, heat the calcium carbide to a molten state to form a catalyst molten pool, and maintain the temperature of the molten pool at 1900 - 2300 °C;

[0061] S3. a) Mix the granular raw material containing the metal oxide M m O and the granular carbon reducing agent, add them to the catalyst molten pool, and form a solid-phase material layer with a certain thickness on the liquid surface of the catalyst molten pool; or b) First spread a layer of the granular raw material containing the metal oxide M m O on the liquid surface of the catalyst molten pool to form a first raw material layer, and then spread a layer of the granular carbon reducing agent on the first raw material layer to form a first reduction layer, and stack the layers in sequence;

[0062] S4. Set the absolute pressure P in the reactor under low vacuum, normal pressure or slightly positive pressure higher than the triple point pressure of the metal M, and carry out the smelting reaction; during the reaction, by adjusting the thickness of the material layer in S3, make the vapor of the metal M generated by the reaction continuously pass through the material layer and still remain gaseous when leaving the material layer, and obtain the liquid metal element M by condensation through the condenser connected to the reactor.

[0063] In some embodiments, preferably, the molar ratio of the total content of the metal oxide and the carbon reducing agent contained in the S3 material layer is M m O:C ≈ 1:1.

[0064] In some embodiments, preferably, when the oxide is magnesium oxide, set the absolute pressure P in the reactor in the range of 1000 Pa ≤ P ≤ normal pressure or as slightly positive pressure in S4, and carry out the smelting reaction; by adjusting the thickness of the material layer in S3, make the magnesium vapor generated by the reaction continuously pass through the material layer and cool to a temperature higher than the magnesium vapor condensation temperature T b = 21.4lg 2 P + 18.4lgP + 437 °C, and obtain liquid magnesium by condensation through the condenser connected to the reactor.

[0065] The technical effects achieved by the present invention are as follows:

[0066] 1. Through the method disclosed by the present invention, liquid magnesium can be produced, completely solving the safety hazard that magnesium powder is easily generated and explodes in the carbothermal reduction method for producing magnesium, and the liquid magnesium can be directly refined or ingoted, saving the cost of remelting magnesium;

[0067] 2. The present invention can significantly improve the economic benefits of magnesium smelting by co-producing calcium carbide (calcium carbide) as a byproduct, and does not generate any waste slag, and has excellent environmental benefits, and has a good application prospect in industry;

[0068] 3. The use of the solid phase calcium carbide in the present invention as a catalyst for smelting magnesium and other metals can completely solve the reverse reaction problem of carbothermal smelting; when the liquid phase calcium carbide in the present invention is used as a catalyst for smelting magnesium and other metals, the reverse reaction of carbothermal smelting mainly occurs in the process of metal vapor and CO mixed gas passing through the solid phase material layer, and the macroscopic efficiency of the smelting reverse reaction is greatly reduced, which can basically solve the reverse reaction problem of carbothermal smelting;

[0069] 4. Compared with the traditional aluminothermic calcium smelting process, the calcium smelting cost is significantly reduced by using the carbon thermal calcium smelting method of the present invention, and the carbon thermal calcium smelting method does not produce waste slag, and the by-products calcium carbide and carbon monoxide can be effectively utilized, which has obvious economic value;

[0070] 5. The use of liquid calcium carbide as a catalyst for smelting magnesium and other metals, compared with solid calcium carbide catalyst smelting, omits the grinding, ball pressing and other processes, simplifies the process route, and saves costs; in addition, the liquid phase reaction speed is significantly faster than the solid phase reaction speed, which improves production efficiency;

[0071] 6. The calcium carbide catalyst carbon thermal method of the present invention can be used to smelt a variety of metals, such as oxides of lead, tin, zinc, iron, manganese, nickel, cobalt, chromium, molybdenum, vanadium and other metals. The calcium carbide catalyst can first react to generate metal elements and calcium oxide, and then the calcium oxide reacts with carbon to generate calcium carbide. It has a wide range of applications and low smelting costs.

[0072] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 The relationship curve between temperature T (°C) and absolute pressure P (Pa) of the chemical reaction of magnesium oxide, calcium oxide and carbon and the mixture of calcium carbide is shown; wherein: curves (1) to (4) are the reaction that can proceed when the temperature is higher than the corresponding curve, and curve (5) is the reaction that can proceed when the temperature is lower than the curve;

[0074] Figure 2 The three-phase change curve of magnesium vapor cooling process given in existing data is shown;

[0075] Figure 3 The three-phase change curve of the magnesium vapor cooling process drawn according to the thermodynamic calculation is shown;

[0076] Figure 4Shows the three-phase change curve of the calcium vapor cooling process drawn according to the thermal calculation;

[0077] Figure 5 Shows the oxide M of the elemental metal M in the preferred embodiment m O, the relationship curve of the relevant chemical reaction temperature T (°C) and the absolute pressure P (Pa) for smelting the elemental metal M by carbothermal reduction using CaC2 as a catalyst; where: Curves (1) and (3) are the qualitative schematic curves of the reduction reaction of the metal oxide M m O. When the temperature is higher than the corresponding curve, the reaction can proceed for curves (1) to (4), and when the temperature is lower than this curve, the reaction can proceed for curve (5). Specific embodiments

[0078] The following introduces several technical ideas and preferred embodiments of the present invention with reference to the accompanying drawings of the specification to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of technical ideas and embodiments, and the protection scope of the present invention is not limited to the technical ideas and embodiments mentioned in the text.

[0079] I. Technical idea 1 - Magnesium smelting by carbothermal reduction with co-production of calcium carbide

[0080] From Figure 1 it can be seen that when the absolute pressure P < 100 Pa, that is, lgP < 2, for the reaction of CaO (s) + 3C (s) → CaC 2(s) + CO (g) the curve (2) of the reaction is very close to the curve (4) of the reaction 2CaO (s) + CaC 2(s) → 3Ca (g) + 2CO (g) indicating that it is very difficult to control the reaction temperature to make the reaction for generating CaC2 occur while the reaction for generating Ca vapor does not occur. Moreover, for the reaction curve (5) of Ca (g) + 2C (s) → CaC 2(s) reacting with C to form CaC2 is also very close to curve (4), and the exothermic reaction Ca (g) + 2C (s) → CaC 2(s) occurs only when the temperature is lower than curve (5), indicating that in practical applications, once the reaction 2CaO (s) + CaC 2(s) → 3Ca (g) + 2CO (g) for generating Ca vapor occurs, it is very difficult to make Ca (g) + 2C (s) → CaC 2(s)The reaction occurs, that is, the Ca vapor can only be lost in vain and it is difficult to react with carbon to form CaC2. However, when the absolute pressure P≥1000Pa, that is, lgP>3, the distances between curves (2), (4), and (5) are successively widened. It is possible to relatively easily control the reaction temperature in the range higher than curve (2) but lower than curve (4) to ensure that only the reaction to form CaC2 occurs and the reaction to form Ca vapor does not occur. It is also possible to relatively easily control the reaction temperature in the range higher than both curve (2) and curve (4) but lower than curve (5) to ensure that after the reaction to form CaC2 occurs, the generated Ca vapor can react with C to form CaC2 again without evaporating and losing. Of course, at this time, the temperature is significantly higher than curves (1) and (3), and there is no problem with the generation of magnesium vapor.

[0081] Figure 1 The mathematical equations for the relationship between the temperature T and the absolute pressure P of the relevant reactions, which are regressed based on experimental data and verified by thermodynamic calculations, are given. Among them, for the reaction CaO (s) +3C (s) →CaC 2(s) +CO (g) The regression equation of curve (2) is approximately T = 11lg 2 P + 71lgP + 1210°C. For the reaction Ca (g) +2C (s) →CaC 2(s) The regression equation of curve (5) is approximately T = 98lg 2 P - 129lgP + 1300°C. When the absolute pressure P≥1000Pa, as long as the reaction temperature T is in the range of 11lg 2 P + 71lgP + 1210°C < T < 98lg 2 P - 129lgP + 1300°C, it can ensure the generation of magnesium vapor and CaC2, and the yield of calcium carbide will not be reduced due to the evaporation and loss of calcium.

[0082] In addition, among the two main problems in the carbothermal reduction of magnesium, the safety problem of the formation of magnesium powder when magnesium vapor and CO gas are co-cooled is the main factor restricting industrial application (the problems of reduced reduction rate and high impurity content in crude magnesium caused by the reverse reaction of smelting can be solved by auxiliary technical means such as extending the reduction time and refining crude magnesium, and they are not the main factors restricting industrial application). Existing literature (see Figure 2 ) and thermodynamic calculations (see Figure 3)All indicate that when the absolute pressure P of magnesium vapor is ≥ 1000 Pa, during cooling, it directly condenses into a solid phase without passing through the liquid phase. When magnesium vapor coexists with non-condensable gases such as CO, magnesium powder is easily formed during the cooling process. However, when the absolute pressure P ≥ 1000 Pa, liquid magnesium is first formed during the cooling of magnesium vapor, and further cooling of the liquid magnesium can only obtain massive crystalline magnesium and cannot become magnesium powder. Since high-temperature non-metallic materials such as graphite and silicon carbide cannot maintain a vacuum, the reactors of traditional magnesium smelting technology by thermal reduction method all use heat-resistant steel reduction tanks. The working temperature of heat-resistant steel generally does not exceed 1200 °C. At this temperature, the absolute pressure at which the smelting reaction can effectively proceed does not exceed 10 - 100 Pa. Therefore, magnesium vapor in traditional magnesium smelting technology cannot be cooled into liquid magnesium.

[0083] When using an electric heating reactor, the furnace charge is placed in a smelting cavity made of high-temperature resistant material for smelting. The smelting cavity is arranged inside a closed container, and there is a heat insulation layer between the closed container and the smelting cavity. The electric heating element directly or indirectly heats the smelting cavity and the furnace charge inside the heat insulation layer. The closed container is not affected by high temperature and mainly plays a role of sealing and isolating the inside of the reactor from the outside air. Since the heat-resistant temperature of the high-temperature resistant material components constituting the smelting cavity can reach above 1500 °C or even higher, the corresponding absolute pressure of magnesium vapor can be increased to above 1000 Pa to produce liquid magnesium, which can completely avoid the safety problem of magnesium powder generation. Moreover, the produced liquid magnesium can be directly refined or ingoted, saving the energy consumption, labor and other costs of secondary magnesium melting. The high-temperature resistant material can be selected from graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature resistant ceramics, etc.

[0084] It can be seen that if an electric heating high-temperature resistant material smelting cavity reactor is used inside a closed container and the absolute pressure P inside the reactor is maintained within the range of 1000 Pa ≤ P ≤ atmospheric pressure or under slightly positive pressure for carbothermal magnesium smelting, not only can magnesium be efficiently smelted and CaC2 be efficiently produced while saving the energy consumption of the vacuum pump, but also the risk of magnesium powder explosion in carbothermal magnesium smelting can be completely avoided. Moreover, the produced liquid magnesium can be directly refined or ingoted, saving the cost of remelting magnesium. The slightly positive pressure mentioned in the present invention refers to the situation where the positive pressure does not exceed 1000 Pa of the local atmospheric pressure.

[0085] The carbon reducing agent used in carbothermal magnesium smelting is coke, semi-coke, coal, petroleum coke, coal tar, graphite, pitch or a mixture of any two or more of the foregoing.

[0086] Example 1

[0087] The fixed carbon content of anthracite produced by a certain coal mine is 90%. The test results of dolomite (MgCO3·CaCO3) produced by a certain mine are shown in the following table.

[0088] Chemical composition (w%) of dolomite sample

[0089]

[0090]

[0091] S1. After calcining the dolomite into calcined dolomite in a rotary kiln, weigh 100 kg of the calcined dolomite, which contains 36.93 kg of magnesium oxide (MgO) and 61.74 kg of calcium oxide (CaO); weigh 56.31 kg of anthracite, and grind the two into 156.31 kg of powder with a mesh size of 100.

[0092] S2. Use a briquetting machine to press the above powder into pillow-shaped pellet furnace charge with a length × width × height of 50 × 30 × 20 mm, and place it in the graphite smelting cavity of a steel closed container. There is an electromagnetic induction coil heating heat source outside the graphite smelting cavity, and there is a heat insulation layer between the induction coil and the graphite smelting cavity. The vacuum pipeline interface at the upper part of the steel container is connected in series with a shell-and-tube condenser between the vacuum pump, and the lower part of the condenser is connected with a closed magnesium liquid tank.

[0093] S3. Keep the absolute pressure in the steel container at P≈3000 Pa by continuous vacuum pumping, heat the smelting cavity by electromagnetic induction and maintain the temperature at T = 1800 ± 20 °C for smelting reaction. It can be seen from the observation hole of the magnesium liquid tank that liquid magnesium flows into the magnesium liquid tank from the condenser. After the reaction proceeds for 4 hours, the instrument shows that the electric heating power decreases significantly and tends to be stable, indicating that the smelting reaction is basically over. When the vacuum of the reactor is broken with argon until the pressure shown on the vacuum pressure gauge of the reactor is zero, open the slag discharge hole at the bottom of the reactor to discharge the pellet calcium carbide.

[0094] After collection and weighing, 18.89 kg of crude magnesium and 89.05 kg of pellet calcium carbide are produced. After analysis and testing, the crude magnesium contains 98.5% magnesium, and the gas generation amount of the calcium carbide produced is 236 l / kg, and the calcium carbide content is 63% after conversion.

[0095] II. Technical idea 2 - Calcium production by carbothermal method with co-production of calcium carbide

[0096] From Figure 1 it can be seen that in the stage of producing calcium carbide by the reaction of carbon and calcium oxide: (1) If the temperature is in the range of 11lg 2 P + 711lgP + 1210 °C < T < 30lg 2 P + 58lgP + 1215 °C, then only the reaction of CaO + 3C → CaC2 + CO occurs, and CaC2 is smelted. (2) If the temperature is in the range of 30lg 2 P + 58lgP + 1215 °C < T < 98lg 2In the range of P - 129lgP + 1300 °C, the reaction CaO + 3C → CaC2 + CO occurs first to produce CaC2, and then the reaction 2CaO + CaC2 → 3Ca + 2CO occurs to produce calcium vapor. However, if the molar ratio of C / CaO in the reaction system ≥ 3, since the reaction CaO + 3C → CaC2 + CO occurs first and fully, there is no remaining CaO to react with CaC2 in the reaction 2CaO + CaC2 → 3Ca + 2CO to produce calcium, so the system product is CaC2 and no calcium vapor flows out of the reaction system; if the molar ratio of C / CaO < 3, since there is not enough carbon to fully complete the reaction CaO + 3C → CaC2 + CO, there is remaining CaO, and the remaining CaO will react with CaC2 in the reaction 2CaO + CaC2 → 3Ca + 2CO to produce calcium, resulting in less CaC2 in the system and calcium vapor flowing out of the reaction system; if the molar ratio of C / CaO in the reaction system ≤ 1, since there is too little carbon in the system, the reaction CaO + 3C → CaC2 + CO cannot be fully completed, and the generated CaC2 will be completely consumed by 2CaO + CaC2 → 3Ca + 2CO, and the generated calcium will finally flow out of the reaction system completely because there is no remaining carbon to react with it in the reaction Ca + 2C → CaC2, and finally no calcium carbide is produced but only calcium is produced. (3) If the temperature T > 98lg 2 P - 129lgP + 1300 °C, only the two reactions CaO + 3C → CaC2 + CO and 2CaO + CaC2 → 3Ca + 2CO can occur successively. Because the temperature is too high, the reaction Ca + 2C → CaC2 cannot occur. Even if there is enough carbon in the reaction system and the reaction is sufficient, finally only calcium can be produced and no calcium carbide.

[0097] The current mainstream calcium smelting method is the aluminothermic method. Using calcium oxide powder as the raw material and aluminum powder as the reducing agent, after mixing and pelletizing, under vacuum and at 1050 - 1200 °C, calcium vapor is produced through the reduction reaction 6CaO + 2Al → 3Ca + 3CaO·Al2O3, and crystalline calcium is obtained after condensation. Smelting 1 ton of calcium consumes about 3 tons of calcium oxide and 0.5 ton of aluminum powder, producing about 2.5 tons of calcium aluminate waste residue. The smelting cost is high, and aluminum powder has an explosion risk.

[0098] If carbon is used as the reducing agent for calcium smelting, the relevant reactions are as follows:

[0099]

[0100]

[0101] Adding the above second formula, we get:

[0102]

[0103] Theoretically, smelting 1 ton of calcium only requires consuming 1.4 tons of calcium oxide and 0.3 tons of carbon, and no waste residue is generated. The estimated power consumption is about 5000 kWh / t. The smelting cost is about half of that of the aluminothermic process, and the economic benefits, environmental benefits, and safety production level are all significantly improved.

[0104] When the ratios of CaO and C in the mixed powder are different, the ratios of calcium and calcium carbide produced after sufficient smelting reaction are different. When the molar ratio CaO:C ≈ 1:1, only calcium and CO are generated, and basically no calcium carbide is generated; when the molar ratio CaO:C ≈ 1:3 and the reaction temperature T is within the range of 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C, only calcium carbide and CO are generated, and basically no calcium is generated; when the molar ratio CaO:C is between 1:1 and 1:3, both calcium and calcium carbide can be produced.

[0105] Example 2

[0106] S1. The chemical composition of the limestone produced by a certain mine is CaO = 54.0%, MgO = 3.0%, SiO2 = 1.5%, loss on ignition 41.4%, and the remaining impurities 0.1%; the fixed carbon content of the coke produced by a certain coking plant is 85%. Weigh 100 kg of the lime after calcining the limestone as raw material, which contains 92.15 kg of calcium oxide; when only producing calcium without co-producing calcium carbide, 23.23 kg of coke reductant is added according to the molar ratio CaO:C ≈ 1:1. After mixing and grinding, 123.23 kg of 100-mesh mixed powder is obtained;

[0107] S2. Use a briquetting machine to press the above powder into a pillow-shaped pellet charge with length × width × height = 50 × 30 × 20 mm, and put it into the graphite smelting cavity in a steel sealed container. There is an electromagnetic induction coil heating heat source outside the graphite smelting cavity, and there is a heat insulation layer between the induction coil and the graphite smelting cavity. The vacuum pipeline interface at the upper part of the steel container is connected in series with a shell-and-tube condenser between the vacuum pump, and the lower part of the condenser is connected with a sealed liquid calcium collection tank;

[0108] S3. Keep the absolute pressure P ≈ 10000 Pa in the steel container by continuous vacuum pumping, heat the smelting cavity by electromagnetic induction and maintain the temperature at T = 2000 ± 20 °C for smelting reaction. It can be seen from the observation hole of the liquid calcium collection tank that the liquid calcium flows from the condenser into the liquid calcium collection tank. After the reaction proceeds for 2.5 hours, the instrument shows that the electric heating power decreases significantly and tends to be stable, indicating that the smelting reaction is basically over. When the vacuum of the reactor is broken with argon until the pressure shown on the vacuum pressure gauge of the reactor is zero, open the slag discharge hole at the bottom of the reactor and find that a small amount of residue is generated. Although the residue contains a small amount of calcium carbide, it has no industrial value for use as calcium carbide.

[0109] Collect and weigh, producing 63.07 kg of crude calcium and 13.35 kg of residue. The analysis shows that the crude calcium contains 99.53% calcium, and the main impurity elements are Mg, Fe, etc.; the main elements in the residue are C, Ca, Si, Al, etc.

[0110] III. Technical Idea 3 - Carbothermal Reduction of Magnesium with Solid Catalyst and Coproduction of Calcium Carbide

[0111] In the above "Technical Idea 1", liquid magnesium is obtained by condensation using a condenser connected to the reactor, and no magnesium powder is generated, solving a major safety hazard in industrial carbothermal reduction. However, "Technical Idea 1" only significantly weakens the reverse reaction of magnesium vapor and CO during smelting, and does not completely avoid the occurrence of the reverse reaction. Therefore, the magnesium reduction rate and product purity of "Technical Idea 1" are still relatively low.

[0112] Experimental research found that in the carbothermal reduction of magnesium in the system where CaC2 exists the magnesium production rate is significantly faster than when there is no CaC2. Theoretical research shows that when there is enough CaC2 in the system, under certain conditions, the magnesium reduction reaction consists of and two steps, and CaC2 acts as a catalyst in the reaction. And in the first step of the reaction between MgO and CaC2, only magnesium vapor is generated as a gas, and in the second step of the reaction between CaO and C, only CO is generated as a gas. Therefore, when the generated gases are discharged in a timely manner, magnesium vapor and CO will not coexist in the reactor, and it is impossible for the reverse reaction Mg (g) +CO (g) →MgO (s) +C (s) to occur, and there is no possibility of generating magnesium powder when producing liquid. And theoretically, the generated CaC2 is equal in amount to the catalyst CaC2 added in the raw materials and can be recycled as a catalyst for the next smelting cycle, and using the catalyst does not increase the smelting cost. Similarly, when using calcined dolomite (MgO·CaO) as the raw material, the reaction can be decomposed into and two steps, and the produced CaC2 is twice that when using MgO as the raw material. Half of it can be recycled as a catalyst, and the other half can be sold as calcium carbide, greatly improving the economic benefits of magnesium smelting.

[0113] From Figure 1 it can be seen that in the reaction system of magnesium oxide and calcium oxide with C, if there is enough CaC2 present, if the reaction temperature is first maintained at a state lower than curve (1) but higher than curve (3), then the reaction of curve (1) MgO·CaO (s) +C (s) →Mg (g) +CO(g) +CaO (s) will not occur. Only the reaction of curve (3), MgO·CaO, will occur (s) +CaC 2(s) →Mg (g) +2C (s) +2CaO (s) , that is, only Mg vapor, C, and CaO are generated, and there is no CO. Since Ca (g) +2C (s) →CaC 2(s) the exothermic reaction occurs only when the temperature is lower than curve (5). Therefore, if after completing the magnesium smelting reaction of curve (3), the temperature is raised to a temperature higher than curve (2) but lower than curve (5) for continuous smelting, then the reaction of curve (2), CaO (s) +3C (s) →CaC 2(s) +CO (g) and the reaction of curve (4), 2CaO (s) +CaC 2(s) →3Ca (g) +2CO (g) as well as the reaction of curve (5), Ca (g) +2C (s) →CaC 2(s) will occur, generating CaC2 and CO, and there will be no problem of calcium loss in the form of vapor. That is to say, if enough CaC2 is added to the carbothermal reduction magnesium smelting reaction system of magnesium oxide, calcium oxide and C, and the reaction process is divided into two steps: magnesium smelting and calcium carbide smelting, namely:

[0114] (1) First, keep the reaction temperature in the range of 51lg 2 P - 38lgP + 800℃ < T < 20lg 2 P + 60lgP + 1050℃ for magnesium smelting, then only magnesium vapor is produced as a gas, and it is impossible for the reverse smelting reaction of magnesium vapor and CO to occur. If the pressure is simultaneously kept at an absolute pressure P ≥ 1000 Pa to produce liquid magnesium, there is also no danger of magnesium powder explosion;

[0115] (2) Then, keep the temperature in the range of 11lg 2 P + 71lgP + 1210℃ < T < 98lg 2 P - 129lgP + 1300℃ for calcium carbide smelting to generate CO, and there will also be no problem of calcium loss in the form of vapor resulting in a reduction in the output of CaC2.

[0116] Example 3

[0117] S1. Select the same anthracite and dolomite as in Example 1, calcium carbide with a gas generation of 300 l / kg (CaC₂ content 80%), and high-temperature pitch with a fixed carbon content of 80%. After calcining dolomite in a rotary kiln, weigh 100 kg of calcined dolomite, which contains 36.93 kg of magnesium oxide (MgO) and 61.74 kg of calcium oxide (CaO). Theoretically, 50.69 kg of pure carbon is required. For convenience of pelletizing, 80% of the carbon is anthracite and 20% is pitch. Weigh 45.06 kg of anthracite, 12.67 kg of pitch, and 73.31 kg of calcium carbide. Mix 100 kg of calcined dolomite with anthracite, pitch, and calcium carbide and grind them into 231.45 kg of 100-mesh powder;

[0118] S2. Use a pellet press to press the above powder into pillow-shaped pellet furnace charge with a length × width × height of 50 × 30 × 20 mm, and place it in a graphite smelting cavity inside a steel closed container. There is an electromagnetic induction coil heating heat source outside the graphite smelting cavity, and there is a heat insulation layer between the induction coil and the graphite furnace cavity. A shell-and-tube condenser is connected in series between the vacuum pipeline interface at the upper part of the steel container and the vacuum pump, and a closed magnesium liquid tank is connected to the lower part of the condenser;

[0119] S3. Keep the absolute pressure in the steel container at P ≈ 2000 Pa by continuously pumping vacuum, heat the smelting cavity through electromagnetic induction and maintain the temperature at T = 1450 ± 20 °C to carry out the magnesium smelting reaction. It can be seen from the observation hole of the magnesium liquid tank that liquid magnesium flows into the magnesium liquid tank from the condenser.

[0120] After about 1 hour of the above reaction, the instrument shows that the electric heating power decreases significantly and tends to be stable, indicating that the magnesium smelting reaction has basically ended. Then keep the pressure in the steel container unchanged, raise the temperature of the smelting cavity to T = 1750 - 1800 °C, and carry out the calcium carbide smelting reaction. After about 2 hours of the reaction, the heating power decreases again and tends to be stable, indicating that the calcium carbide smelting reaction has basically ended. Use argon to break the vacuum until the pressure shown on the vacuum pressure gauge of the reactor is zero, and then open the slag discharge hole at the bottom of the reactor to discharge the pellet calcium carbide.

[0121] The device has a production cycle of about 3 hours. Each cycle produces about 20.96 kg of crude magnesium and 89.9 kg of calcium carbide (deducting the input calcium carbide catalyst). After analysis and testing, the crude magnesium contains 99.93% magnesium, and the gas generation of the pellet calcium carbide is 241 l / kg, and the converted calcium carbide content is about 64%. On average, about 7 kg / h of magnesium and about 15 kg / h of pure calcium carbide (deducting the input catalyst) are produced per hour.

[0122] IV. Technical Idea 4 - Liquid Phase Catalyst Carbothermal Reduction Method for Magnesium Smelting with Co-production of Calcium Carbide

[0123] The above "Technical Idea 3" must first grind the raw materials, reducing agent, and catalyst into powder and then press them into pellets. Then, the pellets are loaded into the reactor, and the smelting process is completed through solid-phase reaction. Generally speaking, the solid-phase reaction rate is much slower than the liquid-phase reaction rate, and the processes of grinding and pelletizing lengthen the process route and increase the production cost.

[0124] The melting point of pure CaC2 is about 2300 °C, and the melting point of calcium carbide containing different proportions of CaO can be reduced to about 1800 - 1900 °C at the lowest. Experiments have found that when lumpy MgO is put into the molten calcium carbide bath, a large amount of magnesium vapor and CO gas will be produced quickly; when lumpy MgO·CaO is put into the calcium carbide bath, while a large amount of magnesium vapor and CO gas are produced quickly, a small amount of calcium vapor will also be generated, and the amount of liquid CaC2 in the bath will gradually increase. If a layer of crushed MgO·CaO raw materials and a layer of crushed coke are laid layer by layer (or the coke and raw material fragments are mixed) on the surface of the calcium carbide bath (part will be submerged below the bath surface and part will float above the bath surface), when the upper layer of the material above the bath surface is thick, the gases discharged from the upper part of the fragmented material layer are only magnesium vapor and CO; when the upper layer of the material above the bath surface is thin, a large amount of magnesium vapor and CO gas are discharged from the upper part of the fragmented material layer, and a small amount of calcium vapor will also be discharged. Moreover, by changing the thickness of the material layer, the discharge amount of calcium vapor can be adjusted.

[0125] Analysis Figure 1 It can be seen that when lumpy MgO·CaO and lumpy C are put into molten CaC2, the reaction occurs first. At the same time, as free C is generated in the melt, the reaction MgO·CaO (s) +C (s) →Mg (g) +CO (g) +CaO (s) and 2CaO (s) +CaC 2(s) →3Ca (g) +2CO (g) will also occur to a certain extent, but the latter two reactions (especially the last one) are weaker, and the amount of calcium vapor and CO generated (compared with the generation of magnesium vapor) is relatively small. When passing through the lumpy material layer, it will react with C on the surface of the lumpy carbon to form Ca (g) +2C (s) →CaC 2(s) . When the lumpy carbon layer is thick enough, no calcium vapor is discharged from the upper part of the material layer; after the MgO in the bath is consumed, CaO and C start to react to form CaO (l) +3C (s) →CaC 2(l) +CO (g)During the reaction, the amount of CaC2 in the molten pool will increase as the reaction proceeds. Due to the high temperature and the fast diffusion of reactants in molten CaC2, especially when CaO and CaC2 are in a eutectic state, the reaction in the molten pool CaO (l) +3C (s) →CaC 2(l) +CO (g) is much faster than the solid-phase reaction CaO (s) +3C (s) →CaC 2(s) +CO (g) That is, the reduction of magnesium by carbon is much faster under liquid-phase catalysis than under solid-phase catalysis.

[0126] From Figure 1 and Figure 3 、 Figure 4 it can be seen that when CaC2 is in a molten state, that is, the temperature of the molten pool T > 1900 °C and the pressure P is in the range of 1000 Pa ≤ P < 10000 Pa, by setting a reasonable thickness of the material layer (adjusted according to the specific reaction temperature and absolute pressure), controlling the temperature T of the magnesium vapor leaving the material layer to be lower than T = 98lg 2 P - 129lgP + 1300 °C and slightly higher than the condensation temperature T b = 21.4lg 2 P + 18.4lgP + 437 °C, that is, when the temperature T of the magnesium vapor leaving the material layer is in the range of 7812.6 / (11.8 - lgP) - 273 °C < T < 98lg 2 P - 129lgP + 1300 °C, liquid magnesium can be obtained by condensing the magnesium vapor, but there may be a small amount of calcium vapor lost with the CO gas at this time; if the pressure P ≥ 10000 Pa, while controlling the temperature T of the molten pool T ≤ 30lg 2 P + 58lgP + 1215 °C, controlling the temperature T of the magnesium vapor leaving the material layer to be slightly higher than T = 21.4lg 2 P + 18.4lgP + 437 °C, liquid magnesium can be obtained by condensing the magnesium vapor, and the reverse smelting reaction can be basically eliminated, and there is no loss of any calcium vapor. Similarly, when the pressure P ≥ 10000 Pa, if the temperature T of the molten pool T > 30lg 2 P + 58lgP + 1215 °C and the temperature T of the magnesium vapor leaving the material layer T > 37lg 2 P - 73lgP + 580 °C (calcium vapor condensation temperature), then liquid magnesium and a small amount of liquid calcium can be obtained by condensation, and there is no loss of calcium vapor.

[0127] Example 4

[0128] S1. Select dolomite with the same particle size of 20 - 50 mm as in Example 1 and calcine it into calcined dolomite in a rotary kiln. Each ton of calcined dolomite contains 369.3 kg of magnesium oxide and 617.4 kg of calcium oxide. Select semi-coke with a particle size of 10 - 20 mm and a fixed carbon content of 82% produced by a certain semi-coke factory, and calcium carbide with a gas generation of 300 l / kg (CaC₂ content of 80%) produced by a certain calcium carbide factory. Calculate that 618.2 kg of semi-coke needs to be added per ton of calcined dolomite, that is, the mass ratio of calcined dolomite to semi-coke is 1:0.6182.

[0129] S2. Put the calcium carbide into the graphite smelting cavity of a closed steel reactor heated by electricity and heat it to melt, forming a calcium carbide molten pool about 300 mm deep.

[0130] S3. After mixing the calcined dolomite particles and semi-coke particles evenly according to the above mass ratio of calcined dolomite to semi-coke of 1:0.6182, add them to the molten pool until the thickness of the unmelted material layer not submerged above the molten pool surface is about 500 mm.

[0131] S4. Set the absolute pressure P in the reactor to be approximately 20000 Pa, and keep the temperature of the molten pool at T = 2000 ± 20 °C by adjusting the electric heating power to carry out the smelting reaction; at the same time, adjust the thickness of the material layer by feeding to make the temperature of the magnesium vapor about 1000 °C when it leaves the material layer, and the magnesium vapor enters the condenser connected in series to the reactor and is condensed to obtain liquid magnesium. During the smelting process, when the molten pool surface rises above the control liquid level, it is discharged through the liquid discharge port of the reactor, and the discharged liquid calcium carbide is condensed and sold as a by-product calcium carbide.

[0132] This method produces about 13 kg / h of pure magnesium and about 33 kg / h of pure calcium carbide on average per hour, and the production efficiency is about 2 times that of the solid-phase catalyst method. The crude magnesium after direct condensation of the magnesium liquid has a magnesium content of about 95%, and the gas generation of the calcium carbide obtained after cooling the liquid calcium carbide is 270 l / kg, and the converted calcium carbide content is about 72%. The quality of the crude magnesium is lower than that of the solid-phase method, but the quality of the calcium carbide is higher than that of the solid-phase method.

[0133] V. Technical Idea 5 - Carbothermal Reduction of Calcium Carbide Catalyst for Smelting Multiple Metals

[0134] It is found that not only the mixture of magnesium oxide and calcium oxide can be used to smelt magnesium by carbothermal reduction with calcium carbide as a catalyst, but also oxides of many metals such as Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo, V, etc. (hereinafter uniformly represented by M) m O (m represents the ratio of the number of metal atoms to the number of oxygen atoms) can react with calcium carbide to form metal elements and calcium oxide, and the calcium oxide generated by the reaction can also react with carbon to regenerate calcium carbide again. The smelting reaction can be uniformly represented by the following formula:

[0135]

[0136]

[0137] Adding the above two equations gives:

[0138]

[0139] It can be seen that CaC₂ acts as a catalyst in the reaction. The thermodynamic laws of chemical reactions are qualitatively described by Figure 5 qualitative description.

[0140] Thus, using the same method of smelting magnesium with the aforementioned mixed raw materials of magnesium oxide and calcium oxide, carbon as the reducing agent, and calcium carbide as the catalyst, it is also possible to smelt metal oxides such as magnesium, lead, tin, zinc, iron, manganese, nickel, cobalt, chromium, molybdenum, and vanadium to produce the corresponding elemental metals. The amount of calcium carbide produced in each production cycle is basically equal to the amount of calcium carbide used as the catalyst added, and can all be reused as the catalyst.

[0141] Example 5

[0142] S1. A certain mine produces first-grade magnesite with chemical components MgO = 46%, CaO = 0.6%, and SiO₂ = 1.0%; a certain calcium carbide factory produces first-grade calcium carbide with a CaC₂ content of 80%; a certain chemical plant produces high-temperature pitch with a fixed carbon content of 80%. Take 100 kg of calcined magnesite containing 96.64 kg of the active ingredient MgO, add 191.84 kg of calcium carbide, and add 35.97 kg of pitch. After mixing, grind it into 327.81 kg of mixed powder with a mesh size of 100.

[0143] S2. Press the above-mentioned mixed powder into a pillow-shaped pellet with a length × width × height = 50 × 30 × 20 mm, and place it in the graphite smelting cavity of a steel closed container. The graphite smelting cavity is heated by resistance, and there is a heat insulation layer between the smelting cavity and the steel container. A shell-and-tube condenser is connected in series between the vacuum pipeline interface at the upper part of the steel container and the vacuum pump, and a closed magnesium liquid tank is connected to the lower part of the condenser.

[0144] S3. Set the absolute pressure P in the reactor to be approximately 1000 Pa, adjust the heating electric power to keep the temperature T of the smelting cavity at 1400 ± 20 °C for magnesium smelting. It can be seen from the observation hole of the magnesium liquid tank that liquid magnesium flows into the magnesium liquid tank from the condenser.

[0145] S4. After about 2 hours of the above magnesium smelting reaction, the heating electric power decreases significantly and tends to be stable, indicating that the magnesium smelting reaction has basically ended. Then set the absolute pressure P in the reactor to be approximately 3000 Pa, and raise the temperature of the smelting cavity to T = 1750 ± 20 °C for the calcium carbide smelting reaction. After the reaction proceeds for about 1 hour, the heating power decreases again and tends to be stable, indicating that the calcium carbide smelting reaction has basically ended. Use argon to break the vacuum until the pressure shown on the vacuum pressure gauge of the reactor is zero, and then open the slag discharge hole at the bottom of the reactor to discharge the generated calcium carbide for use as the reducing agent in the next production cycle.

[0146] This method has a production cycle of approximately 3 hours. In each cycle, 68.56 kg of crude magnesium is produced, with an average magnesium production rate of approximately 22 kg / h. The magnesium content rate of the crude magnesium is 99.96%.

[0147] VI. Technical Idea 6 - Carbothermal Reduction of Multiple Metals with Liquid-Phase Calcium Carbide Catalyst

[0148] If the method of carbothermal reduction of multiple metals in the above "Technical Idea 5" is modified to use liquid-phase CaC2 as the catalyst, not only can the smelting reaction rate be significantly increased, but also processes such as grinding and briquetting can be omitted, resulting in increased production efficiency, shortened process flow, and reduced product cost.

[0149] Example 6

[0150] S1. Select magnesite with the same particle size of 20 - 50 mm as in Example 5. After calcination, each ton of calcined magnesite contains 966.4 kg of magnesium oxide. Select coke with a particle size of 10 - 20 mm and a fixed carbon content of 85% produced by a certain coke plant, and calcium carbide with a gas generation of 300 l / kg (CaC2 content of 80%) produced by a certain calcium carbide plant. Each ton of calcined magnesite requires 338.5 kg of coke, that is, the mass ratio of calcined magnesite to coke is 1:0.3385.

[0151] S2. Place the calcium carbide into the graphite smelting chamber of a resistance-heated sealed steel reactor and heat it to melt, forming a calcium carbide molten pool about 300 mm deep.

[0152] S3. According to the mass ratio of calcined magnesite to coke of 1:0.3385 described above, mix the calcined magnesite particles and coke particles evenly and add them to the catalyst molten pool in the smelting chamber until the thickness of the unmelted material layer not submerged above the molten pool surface is about 500 mm.

[0153] S4. Set the absolute pressure P in the reactor to be approximately 20000 Pa, and maintain the molten pool temperature at T = 2000 ± 20 °C by adjusting the electric heating power to carry out the smelting reaction. At the same time, adjust the thickness of the material layer by feeding to make the temperature of the magnesium vapor leaving the material layer about 1000 °C. The magnesium vapor enters the condenser connected in series to the reactor and is condensed to obtain liquid magnesium.

[0154] The average hourly conversion of pure magnesium production by this method is about 40 kg / h, and the production efficiency is nearly twice that of the solid-phase catalyst method. The magnesium content rate of the directly condensed magnesium liquid is about 95%, and the quality of the crude magnesium is lower than that of the solid-phase method.

[0155] The technical concept and preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A method for producing magnesium by carbothermal reduction and co-producing calcium carbide, using solid-phase calcium carbide as a catalyst, characterized in that, It includes the following steps: S1. Prepare a mixed powder containing magnesium oxide, calcium oxide, a carbon reducing agent, and a calcium carbide catalyst; S2. Make the mixed powder into pelletized furnace charge and put it into a reactor equipped with a heat source; S3. Set the absolute pressure P in the reactor within the range of 1000 Pa ≤ P < atmospheric pressure, and the reaction temperature T within the range of 51lg 2 P - 38lgP + 800 °C < T < 20lg 2 P + 60lgP + 1050 °C, and conduct the magnesium smelting reaction. Condense the obtained product through a condenser connected to the reactor to obtain liquid magnesium; S4. After the magnesium smelting reaction in S3 above, set the absolute pressure P in the reactor to be 1000 Pa ≤ P ≤ slightly positive pressure, and the reaction temperature T to be within the range of 11lg 2 P + 71lgP + 1210 °C < T < 98lg 2 P - 129lgP + 1300 °C, and carry out the calcium carbide smelting reaction to obtain calcium carbide in the reactor; Among them, the slightly positive pressure means that the positive pressure is not higher than 1000 Pa of the local atmospheric pressure.

2. The method according to claim 1, characterized in that The molar content M of magnesium oxide in the mixed powder MgO , the molar content M of calcium oxide CaO , the molar content M of calcium carbide CaC2 and the molar content M of the carbon reducing agent C are related as follows: M MgO ≈M CaC2 , M C ≈M MgO + 3M CaO .

3. The method according to claim 1, characterized in that The fineness of the mixed powder is above 80 mesh.

4. The method according to claim 1, characterized in that The equivalent diameter of the pelletized furnace charge is 20 mm to 40 mm.

5. The method according to claim 1, wherein 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 foregoing.

6. The method according to claim 1, wherein The heating method of the heat source is electric heating.

7. The method according to claim 1, characterized in that, The outer layer of the reactor is a closed container, and a smelting cavity is arranged inside. A heat insulation layer is provided between the closed container and the smelting cavity; the pelletized furnace charge is placed in the smelting cavity.

8. The method according to claim 7, wherein The smelting cavity is composed of high-temperature resistant material components, and the heat resistance temperature of the high-temperature resistant material is not lower than 1700 °C.

9. The method according to claim 8, wherein The high-temperature resistant material is graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy, or high-temperature resistant ceramic.

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