A method for co-production of calcium carbide and magnesium by carbothermic process

Abstract

The present application relates to a kind of carbon thermal method smelting magnesium and calcium carbide co-production method, especially suitable for carbon thermal method smelting magnesium with magnesium oxide and calcium oxide mixture as raw material, carbon as reducing agent.The mixed powder containing magnesium oxide, calcium oxide and carbon reducing agent is prepared;Mixed powder is made into pellet feed, and is placed in the reactor provided with heat source;The absolute pressure P in the reactor is in the range of 1000Pa≤P≤atmospheric pressure or is slightly positive pressure, and the reaction temperature T is in the range of 111lg 2 P+71lgP+1210℃<T<98lg 2 P‑129lgP+1300℃, smelting reaction is carried out, and liquid magnesium is obtained by condenser connected to the reactor, after smelting reaction, calcium carbide is obtained in the reactor.By this method, the safety hazard of magnesium powder explosion caused by magnesium vapor and CO gas cooling together in carbon thermal method smelting magnesium can be completely avoided, and the cost of magnesium smelting can be significantly reduced, and the method has good application prospect in industry.

Description

[0001] This application is a divisional application of the following application: Application Date: December 17, 2020; Application Number: 202080087519.1; Invention Name: "Method for co-production of calcium carbide in carbon thermal method of magnesium smelting". TECHNICAL FIELD

[0002] The present application relates to the field of smelting, in particular to a method for co-production of calcium carbide in carbon thermal method of magnesium smelting. BACKGROUND

[0003] At present, the silicon thermal method or electrolytic method is generally used in industry for magnesium smelting. Among them, the silicon thermal method uses calcined dolomite (referred to as calcined white, effective component MgO·CaO) as raw material and ferrosilicon (effective component Si) as reducing agent to occur 2(MgO·CaO) (s) +Si (s) →2Mg (g) +2CaO·SiO 2(s) reduction reaction at high temperature and vacuum, and the generated waste slag 2CaO·SiO2 has no application value and is usually landfilled; the electrolytic method uses molten magnesium chloride as raw material to occur MgCl 2(l) →Mg (l) +Cl 2(g) reaction in an electrolytic cell, and the generated waste gas Cl2 is a toxic and harmful gas, which needs a complex and lengthy process for comprehensive utilization (harmless treatment) of chlorine.

[0004] The carbon thermal method uses calcined dolomite (MgO·CaO) or calcined magnesite (MgO) as raw material and carbon as reducing agent to occur MgO·CaO (s) +C (s) →Mg (g) +CO (g) +CaO (s) or MgO (s) +C (s) →Mg (g) +CO (g) reduction reaction at high temperature and vacuum. The cost of carbon reducing agent is significantly lower than that of silicon thermal method of magnesium smelting, and the generated CO waste gas can be used as fuel, especially when using calcined magnesite as raw material, no waste slag is generated, and when using calcined white as raw material, the generated CaO waste slag has certain utilization value, so the carbon thermal method of magnesium smelting is generally considered to have obvious economic advantages.

[0005] However, the carbon thermal method of magnesium smelting has two fatal weaknesses: first, the generated magnesium vapor and CO gas will condense into magnesium powder when cooled together, and high-temperature magnesium powder will explode violently when exposed to air, which has great safety hazards; second, during the cooling process of magnesium vapor and CO gas, the reverse reaction of the smelting process Mg (g) +CO (g) →MgO(s) +C (s) , the 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 researching to solve the above two problems of carbon thermal method smelting magnesium, but so far no effective solution has been found, so the carbon thermal method has not entered industrial application. In July 2016, the Commonwealth Scientific and Industrial Research Organization of Australia announced a new technology for smelting magnesium by carbon thermal method. The magnesium vapor and CO mixed gas is passed through a specially designed "supersonic nozzle" (Laval nozzle) at 4 times the speed of sound. The magnesium vapor is "instantly" condensed into solid crystalline magnesium after passing through the nozzle, which can prevent the formation of magnesium powder and reduce the degree of smelting reverse reaction, but so far no industrial application report has been found.

[0007] The Chinese patent "A process for simultaneously producing metallic magnesium and calcium carbide by carbon thermal method" with application number 201710320876.8 uses calcined lime as raw material, and combines the magnesium smelting reaction MgO·CaO+C→Mg+CO+CaO and the calcium carbide smelting reaction CaO+3C→CaC2+CO to produce calcium carbide while smelting magnesium. However, the magnesium vapor is still in a coexistence state with CO gas, and the two main problems of carbon thermal method smelting magnesium, the safety hazard of magnesium powder formation and smelting reverse reaction, have not been solved. And a large number of experiments by Zhengzhou University and many researchers have proved that the reaction MgO·CaO+C→Mg+CO+CaO and CaO+3C→CaC2+CO at an absolute pressure (hereinafter referred to as absolute pressure or pressure) of 10-100 Pa and a temperature of 1500-1800℃ is very slow, and basically has no industrial application value. Experiments have found that a single ball of dozens of grams of ball material, after reacting for several hours at 1500-1600℃, only a small amount of calcium carbide (even sometimes almost undetectable) can be detected in the solid phase product; after reacting for several hours at a higher temperature of 1700℃ or above, although calcium carbide is generated in the solid phase product, the amount of Ca atoms in the smelting product (CaO and CaC2) is significantly less than the content in the raw material, indicating that part of the Ca in the raw material evaporates and is lost in gaseous form. Some literature reports of similar phenomena can be found in: (1) Study on Low-temperature Synthesis of Calcium Carbide and Its Catalytic Mechanism, He Yantao et al., Petroleum and Chemical Applications, 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

[0008] Therefore, the inventors have conducted a large number of experiments and calculations, and the results show (see Figure 1 ) that the mixture of calcined lime (MgO·CaO) and C will undergo a series of reactions in a high-temperature vacuum reactor as follows:

[0009] 1. First, MgO-CaO in the calcined lime (s) + C (s) → Mg (g) + CO (g) + CaO (s) reacts (called "Reaction 1") to form 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 produced by "Reaction 1" continues to react with C CaO (s) + 3C (s) → CaC 2(s) + CO (g) (called "Reaction 2") to consume CaO and produce 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 produced by "Reaction 2" reacts with the remaining calcined lime in the system MgO-CaO (s) + CaC 2(s) → Mg (g) + 2C (s) + 2CaO (s) (called "Reaction 3") to consume CaC2 to form Mg vapor again, and to produce CaO, and "Reaction 3" is much easier than "Reaction 1" and "Reaction 2", i.e. before all the MgO in the calcined lime is reduced to Mg vapor, there is essentially no CaC2 in the 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 MgO in the calcined lime is reduced to Mg vapor, if the temperature is still higher than curve (2), CaC2 will continue to be produced by "Reaction 2"; and if the temperature is also higher than curve (4), the CaC2 produced will react with the remaining CaO in the system 2CaO (s) + CaC 2(s) → 3Ca (g) + 2CO (g) (called "Reaction 4") to consume CaC2 further and to produce 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 in "reaction 4" encounters a temperature lower than (note: not higher than) C in the reaction system than that of curve (5), an exothermic reaction Ca will occur. (g) +2C (s) →CaC 2(s) (Referred to as "Reaction 5"), CaC2 is generated again; if the Ca vapor does not come into contact with the C at a temperature lower than that of curve (5), then "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 curve (5) is T = 98lg 2 P-129lgP+1300.

[0014] pass Figure 1 It is known that within the operating range of 10–100 Pa absolute pressure and 1500–1800 °C given in application number 201710320876.8, reactions 1–4 can occur, but reaction 5 cannot. In other words, the CaC2 generated in reaction 2 will be consumed by reactions 3 and 4, and the more complete the reaction, the more thoroughly CaC2 is consumed. In particular, since the Ca vapor generated in reaction 4 cannot be converted back into CaC2 by reaction 5, Ca is ultimately lost as vapor and discharged from the reaction system. Figure 4 It is known that at an absolute pressure of 10–100 Pa, the vaporization temperature of Ca is approximately 500–600 °C. Furthermore, from… Figure 1 It can be seen that when the absolute pressure is 10-100 Pa, curves (2) and (4) are very close, that is, the starting temperatures of "reaction 2" and "reaction 4" are similar, making it difficult to ensure that only "reaction 2" which generates CaC2 occurs without "reaction 4" which reduces CaC2 to produce Ca vapor. Moreover, curve (5) is also very close to curve (4), meaning that after CaC2 is reduced to produce Ca vapor, it is also difficult to ensure that Ca vapor reacts with C to generate CaC2 in "reaction 5". Only Ca vapor can be allowed to flow out of the reaction system, which is equivalent to the combined (overall) reaction of "reaction 2" and "reaction 4" CaO. (s) +C (s) →Ca (g) +CO (g) Ultimately, when the reaction proceeds fully, no significant CaC2 is generated; only when the reaction is incomplete will a small amount of CaC2 coexist with CaO.

[0015] In view of the above-mentioned deficiencies of the prior art, the present invention provides a method for co-producing calcium carbide by carbothermic magnesium smelting, so as to partially or completely solve the above problems.

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

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

[0018] S2, preparing the mixed powder into briquettes, and placing the briquettes into a reactor provided with a heat source;

[0019] S3, setting the absolute pressure P in the reactor to be in the range of 1000 Pa≤P≤atmospheric pressure or to be slightly positive, and setting the reaction temperature T to be in the range of 111lg 2 P+71lgP+1210℃<T<98lg 2 P-129lgP+1300℃, carrying out a smelting reaction, condensing liquid magnesium through a condenser connected to the reactor, and obtaining calcium carbide in the reactor.

[0020] In some embodiments, preferably, the molar content M C of the carbon reducing agent in the mixed powder, the molar content M MgO of the magnesium oxide, and the molar content M CaO of the calcium oxide satisfy the following relationship: M C ≈M MgO +3M 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 briquettes is 20 mm to 40 mm.

[0023] In some embodiments, preferably, the outer layer of the reactor is a sealed container, and a smelting chamber is arranged inside the sealed container. A heat insulation layer is arranged between the sealed container and the smelting chamber, and the sealed container is not directly heated, so as to seal and isolate the smelting environment inside the reactor from the outside air. The briquettes are placed in the smelting chamber, and the smelting chamber is composed of high-temperature-resistant material components, and the heat-resistant temperature of the high-temperature-resistant material is at least higher than 1700°C, and preferably, the high-temperature-resistant material is graphite, silicon carbide, molybdenum disilicide, tungsten, tungsten alloy, molybdenum, molybdenum alloy or high-temperature-resistant ceramic.

[0024] In some embodiments, preferably, the heat source for heating the smelting chamber in the reactor adopts an electric heating mode, and can adopt electromagnetic induction heating, resistance heating, arc heating and the like. In addition, preferably, the smelting chamber itself can also be electrified to serve as an electric heating element.

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

[0026] In some embodiments, the mixed powder is optionally prepared by mixing calcined lime and carbon reductant.

[0027] In some embodiments, the mixed powder has different ratios of magnesium oxide and calcium oxide, and different ratios of magnesium and calcium carbide are produced.

[0028] In a second aspect, the present application further provides a method for producing calcium and calcium carbide by carbothermal reduction, comprising the following steps:

[0029] S1, preparing a mixed powder containing calcium oxide and carbon reductant;

[0030] S2, pressing the mixed powder into a pelletized charge and placing it into a reactor provided with a heat source;

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

[0032] In some embodiments, the mixed powder has a molar ratio of calcium oxide to carbon reductant of CaO:C≈1:3~1:1, and different ratios of calcium oxide and carbon reductant result in different ratios of calcium to calcium carbide; the mixed powder is optionally prepared according to a molar ratio of CaO:C≈1:1, and after sufficient smelting reaction, the product is only liquid calcium and CO, and basically no calcium carbide is generated except for impurity residues; the mixed powder is optionally prepared according to a molar ratio of CaO:C≈1:3, and the reaction temperature T is set to be in the range of 11lg 2 P+71lgP+1210℃<T<98lg 2 P-129lgP+1300℃, and after sufficient smelting reaction, the product is only calcium carbide and CO, and basically no liquid calcium is generated.

[0033] In a third aspect, the present application further provides a method for producing magnesium and calcium carbide by carbothermal reduction using solid-phase calcium carbide as a catalyst, comprising the following steps:

[0034] S1, preparing a mixed powder containing magnesium oxide, calcium oxide, carbon reductant and calcium carbide catalyst;

[0035] S2, preparing a pelletized charge from the mixed powder and placing it into a reactor provided with a heat source;

[0036] S3, setting the absolute pressure P in the reactor to be in the range of 1000 Pa≤P<atmospheric pressure, and the reaction temperature T to be in the range of 51lg 2 P-38lgP+800℃<T<20lg 2P+60lgP+1050℃ range, magnesium smelting reaction is carried out, and liquid magnesium is obtained by condensation through a condenser connected to the reactor;

[0037] S4, after the magnesium smelting reaction in S3 ends, the absolute pressure P in the reactor is set to be in the range of 1000 Pa≤P≤atmospheric pressure or slightly positive pressure, and the reaction temperature T is set to be in the range of 11lg 2 P+71lgP+1210℃<T<98lg 2 P-129lgP+1300℃ range, calcium carbide smelting reaction is carried out, and calcium carbide is obtained in the reactor.

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

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

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

[0041] In a fourth aspect, the present application further provides a method for preparing magnesium and co-producing calcium carbide by using liquid-phase calcium carbide as a catalyst in a carbothermic process, comprising the following steps:

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

[0043] S2, placing calcium carbide catalyst into a reactor provided with a heat source, and heating and melting the calcium carbide into a molten state to form a catalyst pool;

[0044] S3, a) mixing the granular raw materials containing magnesium oxide and calcium oxide with the granular carbon reducing agent, and adding them into the catalyst pool to form a solid-phase material layer with a certain thickness on the liquid surface of the catalyst pool; or b) first laying a layer of the granular raw materials containing magnesium oxide and calcium oxide on the liquid surface of the catalyst pool to form a first raw material layer, and then laying a layer of the granular carbon reducing agent on the first raw material layer to form a first reducing layer, and sequentially stacking layers in order;

[0045] S4, setting the absolute pressure P in the reactor in the range of 1000 Pa≤P≤atmospheric pressure or a slightly positive pressure, and setting the temperature T of the molten pool in the range of 1900℃≤T≤30lg 2 P+58lgP+1215℃, and the thickness of the material layer in S3 is adjusted to make the magnesium vapor continuously pass through the material layer and cool down to a temperature higher than the condensation temperature T of the magnesium vapor when leaving the material layer. b =21.4lg 2 P+18.4lgP+437℃, and the liquid magnesium is obtained by condensation through a condenser connected to the reactor.

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

[0047] In some embodiments, preferably, the size of the granular raw material and the granular carbon reducing agent is 5mm-100mm.

[0048] In some embodiments, preferably, the outer layer of the reactor is a sealed container, and a smelting cavity is arranged inside the sealed container. A heat insulation layer is arranged between the sealed container and the smelting cavity, and the sealed container is not directly heated, which plays a role of sealing and isolating the smelting environment inside the reactor from the outside air. The molten pool of the calcium carbide catalyst is arranged in the smelting cavity, and the smelting cavity is composed of high-temperature-resistant material components with a heat-resistant temperature of at least 1900℃. 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 of calcined lime.

[0050] In some embodiments, optionally, the ratio of the magnesium oxide and the calcium oxide in the granular raw material is different, and the output ratio of the magnesium and the calcium carbide is different.

[0051] In a fifth aspect, the present application further provides a method for smelting metal by using solid-phase calcium carbide as a catalyst, comprising the following steps:

[0052] S1, preparing a mixed powder containing metal oxide M m O and carbon reducing agent, and 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, and m≤1;

[0053] S2, the mixed powder is made into a pelletized charge, and is put into a reactor provided with a heat source;

[0054] S3, the absolute pressure P in the reactor is set to be in a low vacuum range higher than the three-phase point pressure of the metal M, and the reaction temperature T is higher than the reaction starting temperature at the absolute pressure P and lower than the reaction starting temperature at the absolute pressure P of the metal M, and is condensed by a condenser connected to the reactor to obtain the metal element M; S3, the absolute pressure P in the reactor is set to be in a low vacuum range higher than the three-phase point pressure of the metal M, and the reaction temperature T is higher than the reaction starting temperature at the absolute pressure P and lower than the reaction starting temperature at the absolute pressure P

[0055] S4, after the metal M smelting reaction in S3 ends, the absolute pressure P in the reactor is set to be in a low vacuum range higher than the three-phase point pressure of the metal M or is at normal pressure or micro-positive pressure, and the reaction temperature T is in the range of 11lg 2 P+71lgP+1210℃<T<98lg 2 P-129lgP+1300℃, a calcium carbide smelting reaction is carried out, and calcium carbide is obtained in the reactor after the reaction ends.

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

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

[0058] In a sixth aspect, the present application further provides a method for smelting a metal by a carbothermal method using liquid-phase calcium carbide as a catalyst, which comprises the following steps:

[0059] S1, preparing a granular raw material containing a metal oxide M m O, and a granular carbon reducing agent; the metal oxide M mM 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, placing the calcium carbide catalyst into a reactor provided with a heat source, heating the calcium carbide to melt into a molten state to form a catalyst pool, and keeping the pool temperature at 1900-2300℃;

[0061] S3, a) mixing the particulate raw material containing the metal oxide M m O and the particulate carbon reducing agent, and adding them into the catalyst pool to form a solid phase material layer with a certain thickness on the liquid surface of the catalyst pool; or b) first laying a layer of the particulate raw material containing the metal oxide M m O on the liquid surface of the catalyst pool to form a first raw material layer, and then laying a layer of the particulate carbon reducing agent on the first raw material layer to form a first reducing layer, and sequentially stacking layers in order;

[0062] S4, setting the absolute pressure P in the reactor to be lower than the triple-point pressure of the metal M, and performing a smelting reaction; during the reaction, the thickness of the material layer in S3 is adjusted so that the vapor of the metal M generated by the reaction continuously passes through the material layer and remains in a gaseous state when leaving the material layer, and the liquid metal element M is obtained by condensation through a 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 material layer in S3 is M m O:C≈1:1.

[0064] In some embodiments, preferably, when the oxide is magnesium oxide, the absolute pressure P in the reactor in S4 is set to be in the range of 1000Pa≤P≤atmospheric pressure or to be slightly positive, and a smelting reaction is performed; the thickness of the material layer in S3 is adjusted so that the magnesium vapor generated by the reaction continuously passes through the material layer and cools down to a temperature higher than the condensation temperature T b =21.4lg 2 P+18.4lgP+437℃ when leaving the material layer, and the liquid magnesium is obtained by condensation through a condenser connected to the reactor.

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

[0066] 1. The method disclosed in the present application can produce liquid magnesium, completely solving the safety hazard of explosion caused by the generation of magnesium powder in the carbon thermal method for smelting magnesium, and the liquid magnesium can be directly refined or ingot-cast, saving the cost of smelting magnesium again;

[0067] 2. The present application can significantly improve the economic benefits of magnesium smelting by co-producing calcium carbide (calcium carbide) by-product, and has no waste residue generation, and the environmental benefits are also very superior, and has good application prospect in industry;

[0068] 3. Using the solid phase calcium carbide in the present application as a catalyst for magnesium and other metal smelting can completely solve the problem of reverse reaction of carbothermic smelting; when using the liquid phase calcium carbide in the present application as a catalyst for magnesium and other metal smelting, the reverse reaction of carbothermic smelting mainly occurs in the process of metal vapor and CO mixed gas passing through the solid phase material layer, and the macro efficiency of smelting reverse reaction is greatly weakened, which can basically solve the problem of reverse reaction of carbothermic smelting;

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

[0070] 5. Compared with solid phase calcium carbide catalyst smelting, the process route is simplified and the cost is saved by using liquid phase calcium carbide catalyst for magnesium and other metal smelting, and the process route is simplified and the cost is saved; in addition, the liquid phase reaction speed is obviously faster than the solid phase reaction speed, and the production efficiency is improved;

[0071] 6. The carbothermic process of the calcium carbide catalyst in the present application can smelt various metals, such as lead, tin, zinc, iron, manganese, nickel, cobalt, chromium, molybdenum, vanadium and other metal oxides, which can first be reacted with calcium carbide catalyst to generate metal elements and calcium oxide, and then the calcium oxide reacts with carbon to generate calcium carbide, which has wide application range and low smelting cost.

[0072] The concept, specific structure and technical effects of the present application will be further described in combination with the accompanying drawings to fully understand the purpose, features and effects of the present application. BRIEF DESCRIPTION OF DRAWINGS

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

[0074] Figure 2 The three-phase change curve of the existing data given magnesium vapor cooling process 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 4The three-phase change curves of the calcium vapor cooling process, plotted based on thermodynamic calculations, are shown.

[0077] Figure 5 The oxide M of metallic element M, as shown in the preferred embodiment, is... m The relationship curves between the chemical reaction temperature T (°C) and absolute pressure P (Pa) of metal element M smelted by carbothermal method using CaC2 as catalyst; wherein: curves (1) and (3) are the metal oxide M m Qualitative schematic curves of the O reduction reaction: curves (1) to (4) indicate that the reaction can proceed when the temperature is higher than the corresponding curve, and curve (5) indicates that the reaction can proceed when the temperature is lower than the corresponding curve. Detailed Implementation

[0078] The following description, with reference to the accompanying drawings, illustrates several technical approaches and preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied through many different technical approaches and embodiments, and the scope of protection of the present invention is not limited to the technical approaches and embodiments mentioned herein.

[0079] I. Technical Approach 1 – Carbothermic process for magnesium smelting and co-production of calcium carbide

[0080] Depend on Figure 1 It can be seen that when the absolute pressure P < 100 Pa, i.e., lgP < 2, CaO (s) +3C (s) →CaC 2(s) +CO (g) The reaction curve (2) and 2CaO (s) +CaC 2(s) →3Ca (g) +2CO (g) The reaction curves (4) are very close together, indicating that it is difficult to control the reaction temperature to allow the reaction that produces CaC2 to occur while preventing the reaction that produces Ca vapor from occurring. Furthermore, the Ca vapor reacts with C to produce CaC2. (g) +2C (s) →CaC 2(s) The reaction curve (5) is also very close to the curve (4), while the exothermic reaction Ca (g) +2C (s) →CaC 2(s) This reaction only occurs at temperatures below curve (5), indicating that the reaction 2CaO produces Ca vapor in practical applications. (s) +CaC 2(s) →3Ca (g) +2CO (g) Once this occurs, it becomes very difficult to achieve Ca at temperatures below curve (5). (g) +2C (s) →CaC 2(s)The reaction occurs when Ca vapor is lost and cannot react with carbon to form CaC2. However, when the absolute pressure P ≥ 1000 Pa, i.e., lgP > 3, the distance between curves (2), (4), and (5) increases sequentially. It is relatively easy to control the reaction temperature within the range higher than curve (2) but lower than curve (4), ensuring that only the reaction to form CaC2 occurs and not the reaction to form Ca vapor. It is also relatively easy to control the reaction temperature within the range higher than both curves (2) and (4) but lower than curve (5), ensuring that after the reaction to form CaC2 occurs, the generated Ca vapor can react with C to form CaC2 again without evaporating and being lost. Of course, at this time, the temperature is significantly higher than curves (1) and (3), and there is no problem with the formation of magnesium vapor.

[0081] Figure 1 The mathematical equations relating temperature T to absolute pressure P for the relevant reaction, based on regression from experimental data and verified by thermodynamic calculations, are presented, where 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℃, reaction Ca (g) +2C (s) →CaC 2(s) The regression equation of curve (5) is approximately T = 98lg 2 P-129lgP+1300℃, when the absolute pressure P≥1000Pa, as long as the reaction temperature T is within 11lg 2 P + 71lgP + 1210℃ <T<98lg 2 Within the range of P-129lgP+1300℃, it is possible to ensure the generation of magnesium vapor and CaC2, without reducing the yield of calcium carbide due to calcium evaporation loss.

[0082] In addition, among the two main problems of carbothermic magnesium smelting, the safety issue of magnesium powder generated when magnesium vapor and CO gas are co-cooled is the main factor restricting industrial application (the problem of reduced reduction rate and high impurity content in crude magnesium caused by the reverse reaction in smelting can be solved by auxiliary technologies such as extending the reduction time and refining crude magnesium, and is not the main factor restricting industrial application). Existing literature (see...) Figure 2 ) and thermal calculations (see Figure 3)indicate that the magnesium vapor is condensed directly into solid phase without passing through liquid phase when cooled at absolute pressure P≥1000 Pa, and the magnesium powder is easily generated during the cooling process when the magnesium vapor coexists with non-condensable gas such as CO; but when the absolute pressure P≥1000 Pa, the liquid magnesium is first generated when the magnesium vapor is cooled, and the further cooling of the liquid magnesium can only get the blocky crystalline magnesium but not the magnesium powder. Since the high-temperature-resistant non-metallic materials such as graphite and silicon carbide cannot maintain vacuum, the reduction tank made of heat-resistant steel is used in the reactor of the traditional magnesium smelting technology, and the working temperature of the heat-resistant steel is generally not more than 1200℃, and the absolute pressure at which the smelting reaction can be effectively carried out is not more than 10-100 Pa at this temperature, so the magnesium vapor of the traditional magnesium smelting technology cannot be cooled into liquid magnesium.

[0083] When the electric heating reactor is used, the furnace charge is placed in the smelting chamber made of high-temperature-resistant material for smelting, the smelting chamber is arranged in the closed container, the heat insulation layer is arranged between the closed container and the smelting chamber, the electric heating element directly or indirectly heats the smelting chamber and the furnace charge in the heat insulation layer, and the closed container is not subjected to high-temperature heat and mainly plays the 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 component constituting the smelting chamber can reach 1500℃ or even higher, the corresponding absolute pressure of the magnesium vapor can be increased to 1000 Pa or higher to produce liquid magnesium, which can completely avoid the safety problem of generating magnesium powder, and the produced liquid magnesium can be directly refined or ingot-cast, thereby 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 ceramic, etc.

[0084] It can be seen that if the smelting chamber made of high-temperature-resistant material in the closed container is used for electric heating, and the carbon thermal reduction magnesium smelting is carried out at the absolute pressure P in the range of 1000 Pa≤P≤atmospheric pressure or under micro-positive pressure, not only can the CaC2 be efficiently produced in the case of saving the energy consumption of vacuum pump, but also the danger of magnesium powder explosion in the carbon thermal reduction magnesium smelting can be completely avoided; and the produced liquid magnesium can be directly refined or ingot-cast, thereby saving the cost of secondary magnesium melting. The micro-positive pressure referred to in the present application means that the positive pressure is not higher than 1000 Pa of the local atmospheric pressure.

[0085] The carbon reducing agent used in the carbon thermal reduction magnesium smelting is coke, semicoke, 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 the anthracite produced by a certain coal mine is 90%, and the assay results of the dolomite (MgCO3·CaCO3) produced by a certain mine are shown in the following table.

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

[0089]

[0090] S1, the dolomite is calcined into calcined dolomite by a rotary kiln, 100 kg of the calcined dolomite is weighed, wherein MgO = 36.93 kg, CaO = 61.74 kg; 56.31 kg of anthracite is weighed, and the two are mixed to form 156.31 kg of powder with a mesh size of 100;

[0091] S2, the powder is pressed into a pillow-shaped ball with a size of 50*30*20 mm by a ball press, and is placed in a graphite smelting chamber in a steel sealed container, an electromagnetic induction coil heating source is arranged outside the graphite smelting chamber, a heat preservation layer is arranged between the induction coil and the graphite smelting chamber, a shell and tube condenser is connected in series between a vacuum pipeline interface at the upper part of the steel container and a vacuum pump, and a sealed magnesium liquid tank is connected to the lower part of the condenser;

[0092] S3, the absolute pressure in the steel container is maintained at P≈3000 Pa by continuous vacuum pumping, the smelting chamber is heated by electromagnetic induction and maintained at T=1800±20℃, and smelting reaction is carried out, and liquid magnesium can be seen flowing from the condenser into the magnesium liquid tank through the observation hole of the magnesium liquid tank. After 4 hours of reaction, the instrument shows that the electric heating power is significantly reduced and tends to be stable, indicating that the smelting reaction is basically completed, the vacuum is broken by argon until the pressure displayed by the vacuum pressure gauge of the reactor is zero, the bottom discharge hole of the reactor is opened, and the ball-shaped carbide is discharged.

[0093] After collection and weighing, 18.89 kg of crude magnesium and 89.05 kg of ball-shaped carbide are obtained. After analysis and testing, the crude magnesium prepared contains 98.5% of magnesium, and the prepared carbide has a gas emission of 236 l / kg and a calcium carbide content of 63%.

[0094] II. Technical idea 2 - carbon thermal method for producing calcium and calcium carbide

[0095] 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℃<T<30lg 2 P+58lgP+1215℃<T<98lg 2 P+58lgP+1215℃<T<98lg 2P-129lgP+1300℃, then the reaction CaO+3C→CaC2+CO occurs first to generate 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 is ≥3, the reaction CaO+3C→CaC2+CO occurs first and fully, and there is no residual CaO to react with CaC2 to produce calcium vapor; if the molar ratio of C / CaO is <3, the reaction CaO+3C→CaC2+CO cannot fully complete due to insufficient carbon, and the residual CaO reacts with CaC2 to produce calcium vapor; if the molar ratio of C / CaO is ≤1, the reaction CaO+3C→CaC2+CO cannot fully complete due to insufficient carbon, and the generated CaC2 is completely consumed by the reaction 2CaO+CaC2→3Ca+2CO, and the generated calcium is completely discharged from the reaction system without residual carbon to react with the calcium to produce calcium carbide. 2 P-129lgP+1300℃, then the reaction CaO+3C→CaC2+CO occurs first to generate 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 is ≥3, the reaction CaO+3C→CaC2+CO occurs first and fully, and there is no residual CaO to react with CaC2 to produce calcium vapor; if the molar ratio of C / CaO is <3, the reaction CaO+3C→CaC2+CO cannot fully complete due to insufficient carbon, and the residual CaO reacts with CaC2 to produce calcium vapor; if the molar ratio of C / CaO is ≤1, the reaction CaO+3C→CaC2+CO cannot fully complete due to insufficient carbon, and the generated CaC2 is completely consumed by the reaction 2CaO+CaC2→3Ca+2CO, and the generated calcium is completely discharged from the reaction system without residual carbon to react with the calcium to produce calcium carbide.

[0096] The current mainstream calcium smelting method is the aluminum thermal method, which uses calcium oxide powder as raw material and aluminum powder as reducing agent. After mixing and pressing into a ball, calcium vapor is generated by the reduction reaction 6CaO+2Al→3Ca+3CaO·Al2O3 under the conditions of vacuum and 1050-1200℃, and crystalline calcium is obtained after condensation. Smelting 1 ton of calcium consumes about 3 tons of calcium oxide and 0.5 tons of aluminum powder, and generates about 2.5 tons of calcium aluminate waste slag, which has high smelting cost and the aluminum powder is explosive.

[0097] If carbon is used as a reducing agent for calcium smelting, the relevant reactions are as follows:

[0098]

[0099]

[0100] The above second formula is added to obtain:

[0101]

[0102] Theoretically, smelting 1 ton of calcium only consumes 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, and the smelting cost is about half of that of the aluminum thermal method. The economic benefit, environmental benefit and safety production level are all significantly improved.

[0103] The ratio of calcium to calcium carbide produced after full smelting reaction is different when the ratio of CaO to C in the mixed powder is different. When the molar ratio CaO:C is about 1:1, only calcium and CO are generated without calcium carbide; when the molar ratio CaO:C is about 1:3 and the reaction temperature T is in the range of 1100-1300°C, only calcium carbide and CO are generated without calcium; when the molar ratio CaO:C is between 1:1 and 1:3, both calcium and calcium carbide can be generated. 2 P+71lgP+1210℃<T<98lg 2 P-129lgP+1300℃ range, only calcium carbide and CO are generated without calcium; when the molar ratio CaO:C is between 1:1 and 1:3, both calcium and calcium carbide can be generated.

[0104] Example 2

[0105] S1, the chemical composition of limestone produced by a mine is CaO=54.0%, MgO=3.0%, SiO2=1.5%, burn loss 41.4%, and the rest is impurities 0.1%; the carbon fixed carbon content of coke produced by a coking plant is 85%. Take 100 kg of calcined lime from the limestone as raw material, which contains 92.15 kg of calcium oxide; when only calcium is produced without co-production of calcium carbide, 23.23 kg of coke reducing agent is added according to the molar ratio CaO:C≈1:1, and after mixing, 123.23 kg of 100 mesh mixed powder is obtained;

[0106] S2, the above powder is pressed into a pillow-shaped ball by a ball press to form a pillow-shaped ball with a length×width×height=50×30×20mm, which is placed in a graphite smelting chamber in a steel sealed container, an electromagnetic induction coil heating source is provided outside the graphite smelting chamber, a heat preservation layer is provided between the induction coil and the graphite smelting chamber, a shell and tube condenser is connected in series between the vacuum pipe interface at the upper part of the steel container and the vacuum pump, and a sealed liquid calcium collection tank is connected below the condenser;

[0107] S3, the absolute pressure P in the steel container is maintained at about 10000 Pa by continuous vacuum pumping, the smelting chamber is heated by electromagnetic induction and the temperature is maintained at T=2000±20°C, and the smelting reaction is carried out, from which it can be seen that liquid calcium flows from the condenser into the liquid calcium collection tank through the observation hole of the liquid calcium collection tank. After 2.5 hours of reaction, the instrument shows that the electric heating power is significantly reduced and tends to be stable, indicating that the smelting reaction is basically completed. When the pressure gauge of the reactor shows zero, the pressure in the reactor is broken by argon, and when the pressure in the reactor is zero, the residue hole at the bottom of the reactor is opened, and a small amount of residue is generated. Although the residue contains a small amount of calcium carbide, it has no industrial value as a carbide.

[0108] The collection of weighing, production of crude calcium 63.07 kg, residue 13.35 kg. Analysis of crude calcium content of calcium 99.53%, the main impurity elements are Mg, Fe, etc.; the main elements of the residue are C, Ca, Si, Al, etc.

[0109] Three, technical idea 3-solid phase catalyst carbon thermal method of magnesium production calcium carbide

[0110] The above "technical idea 1" through the condenser connected to the reactor to obtain liquid magnesium, no magnesium powder is generated, which solves the major safety hazard of industrial production of carbon thermal method. But "technical idea 1" only significantly weakens the smelting reverse reaction of magnesium vapor and CO, and does not completely avoid the occurrence of smelting reverse reaction, so the reduction rate and product purity of "technical idea 1" are still low.

[0111] Experimental studies have found that the carbon thermal method of magnesium production reaction The magnesium production rate in the system with CaC2 is much faster than that without CaC2. Theoretical studies have shown that when there is enough CaC2 in the system, under certain conditions, the magnesium production reaction Composed of two steps And CaC2 acts as a catalyst in the reaction. And in the reaction of MgO and CaC2, only one gas, magnesium vapor, is generated, and in the reaction of CaO and C, only one gas, CO, is generated. Therefore, under the condition of timely discharge of generated gas, magnesium vapor and CO cannot exist in the reactor at the same time, and the smelting reverse reaction Mg (g) +CO (g) →MgO (s) +C (s) cannot occur, and liquid magnesium cannot be generated. And theoretically, the generated CaC2 is equal to the catalyst CaC2 added in the raw materials, which can be recycled as a catalyst for the next smelting cycle, and the use of catalyst does not increase the smelting cost. Similarly, when using calcined white (MgO·CaO) as raw material, the reaction Can be decomposed into And Two steps, and the generated CaC2 is twice as much as when MgO is used as raw material, half of which can be reused as a catalyst, and the other half can be sold as calcium carbide, greatly improving the economic benefits of magnesium smelting.

[0112] As can be seen from Figure 1 In the reaction system of magnesium oxide and calcium oxide with C, if there is enough amount of CaC2, if the reaction temperature is first maintained below curve (1), but higher than curve (3), then the reaction MgO·CaO (s) +C (s) →Mg (g) +CO(g) + CaO (s) will not occur, only the reaction of curve (3) MgO-CaO (s) + CaC 2(s) → Mg (g) + 2C (s) + 2CaO (s) , i.e. only Mg vapor, C and CaO are produced, without CO; since Ca (g) + 2C (s) → CaC 2(s) The exothermic reaction occurs only at temperatures below curve (5), so if after the completion of the magnesium smelting reaction of curve (3) the temperature is raised to a temperature above curve (2) but below curve (5) and the smelting is continued, 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) and the reaction of curve (5) Ca (g) + 2C (s) → CaC 2(s) will occur, CaC2and CO are produced, and there is no problem of loss of calcium in the form of vapor. That is, if sufficient CaC2is added to the system of carbothermic magnesium smelting reaction of MgO and CaO with C, and the reaction process is divided into two steps of magnesium smelting and calcium carbide smelting, i.e.

[0113] (1) first, the reaction temperature is kept in the range of 51 lg 2 P - 38 lg P + 800°C < T < 20 lg 2 P + 60 lg P + 1050°C for magnesium smelting, only Mg vapor is produced, and the reverse reaction of magnesium smelting with CO cannot occur, and if the pressure is kept at P≥1000 Pa, liquid magnesium is produced, and there is no danger of magnesium powder explosion;

[0114] (2) then, the temperature is kept in the range of 11 lg 2 P + 71 lg P + 1210°C < T < 98 lg 2 P - 129 lg P + 1300°C for CaC2smelting and CO production, and there is no problem of loss of calcium in the form of vapor, which causes a decrease in the yield of CaC2.

[0115] Example 3

[0116] S1, select the same anthracite and dolomite as in example 1, gas production 300 l / kg (CaC2 content 80%) of carbide, fixed carbon content 80% of high temperature pitch; after calcining dolomite with a rotary kiln, 100 kg of calcined dolomite is weighed, containing MgO = 36.93 kg, CaO = 61.74 kg; the theoretical requirement of pure carbon is 50.69 kg, for the convenience of ball pressing, 80% of carbon is anthracite, 20% is pitch; 45.06 kg of anthracite, 12.67 kg of pitch and 73.31 kg of carbide are weighed. After mixing 100 kg of calcined dolomite with anthracite, pitch and carbide, 231.45 kg of powder with 100 mesh is ground;

[0117] S2, the above powder is pressed into a pillow-shaped ball with length x width x height = 50 x 30 x 20 mm by a ball press, and is placed in a graphite smelting chamber in a steel sealed container, an electromagnetic induction coil heating source is provided outside the graphite smelting chamber, a heat preservation layer is provided between the induction coil and the graphite furnace chamber, a shell and tube condenser is connected in series between the vacuum pipe interface on the upper part of the steel container and the vacuum pump, and a sealed magnesium liquid tank is connected below the condenser;

[0118] S3, the absolute pressure in the steel container is maintained at P≈2000 Pa by continuous vacuum pumping, the smelting chamber is heated by electromagnetic induction and the temperature is maintained at T=1450±20℃, and magnesium smelting reaction is carried out, and liquid magnesium can be seen flowing from the condenser into the magnesium liquid tank through the observation hole of the magnesium liquid tank.

[0119] S4, after the above reaction is carried out for about 1 hour, the instrument shows that the electric heating power is significantly reduced and tends to be stable, which indicates that the magnesium smelting reaction has basically ended. Then the pressure in the steel container is kept unchanged, the temperature of the smelting chamber is increased to T=1750-1800℃, and calcium carbide smelting reaction is carried out. After about 2 hours of reaction, the heating power is reduced again and tends to be stable, which indicates that the calcium carbide smelting reaction is basically completed. When the pressure of the reactor vacuum pressure gauge is zero by breaking the vacuum with argon, the bottom slag discharge hole of the reactor is opened, and the ball carbide is discharged.

[0120] The device has a production cycle of about 3 hours, and produces 20.96 kg of crude magnesium and 89.9 kg of carbide (excluding the input calcium carbide catalyst) per cycle. After analysis and testing, the crude magnesium contains 99.93% magnesium, the ball carbide has a gas production of 241 l / kg, and the calcium carbide content is about 64% after conversion. The average production of magnesium is about 7 kg / h and the average production of pure calcium carbide (excluding the input catalyst) is about 15 kg / h per hour.

[0121] Four, technical idea 4 —— liquid phase catalyst carbothermic process for smelting magnesium and co-producing calcium carbide

[0122] The above "Technical Idea 3" must first grind the raw materials, reducing agent, catalyst into powder, then press into pellets, and then load the pellets into the reactor to complete the smelting process by solid phase reaction. Generally, the solid phase reaction speed is much slower than the liquid phase reaction speed, and the grinding and balling process makes the process route longer and the production cost higher.

[0123] 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. Tests have found that when bulk MgO is put into the molten calcium carbide pool, a large amount of magnesium vapor and CO gas will be produced soon; when bulk MgO·CaO is put into the calcium carbide pool, a large amount of magnesium vapor and CO gas will be produced soon, and a small amount of calcium vapor will also be produced, and the amount of liquid CaC2 in the pool will gradually increase. If the surface of the calcium carbide pool is layered with MgO·CaO raw material chunks and coke chunks (or mix coke with raw material chunks), and the layer is layered on the liquid surface (part of it will be submerged below the liquid surface, and part of it will float above the liquid surface), when the layer above the liquid surface is thick, only magnesium vapor and CO are discharged from the upper part of the chunk layer; when the layer above the liquid surface is thin, a large amount of magnesium vapor and CO gas is discharged from the upper part of the chunk layer, and a small amount of calcium vapor is also discharged, and by changing the thickness of the layer, the amount of calcium vapor discharged can be adjusted.

[0124] Analysis Figure 1 It can be seen that when bulk MgO·CaO and bulk C are put into molten CaC2, the following reactions occur 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 some extent, but the last two reactions (especially the last one) are weaker, and the amount of calcium vapor and CO produced (compared with magnesium vapor) is less, and when passing through the bulk material layer, calcium vapor will react with C on the surface of the bulk carbon Ca (g) +2C (s) →CaC 2(s) When the bulk carbon layer is thick enough, there is no calcium vapor discharged from the upper part of the layer; after the MgO in the pool is consumed, CaO and C begin to react CaO (l) +3C (s) →CaC 2(l) +CO (g)CaC2in the molten pool will increase with the reaction. Because of the high temperature and fast diffusion of reactants in molten CaC2, especially CaO and CaC2are in eutectic state, the reaction CaO (l) + 3C → CaC2+ CO (s) is much faster than the solid phase reaction CaO 2(l) + 3C → CaC2+ CO (g) , i.e. (s) + 3C → CaC2+ CO (s) + 3C → CaC2+ CO 2(s) + 3C → CaC2+ CO (g) , i.e. The carbon reduction of magnesium smelting in liquid phase catalysis is much faster than that in solid phase catalysis.

[0125] From Figure 1 and Figure 3 , Figure 4 , it can be seen that when CaC2is in molten state, i.e. the molten pool temperature T > 1900℃, the pressure P is in the range of 1000Pa ≤ P < 10000Pa, by setting a reasonable layer thickness (adjusted according to the specific reaction temperature and absolute pressure), the temperature T of magnesium vapor leaving the layer is controlled to be lower than T = 98lg 2 P - 129lgP + 1300℃, slightly higher than the condensation temperature T b = 21.4lg 2 P + 18.4lgP + 437℃, i.e. the temperature T of magnesium vapor leaving the layer is in the range of 7812.6 / (11.8-lgP) - 273℃ < T < 98lg 2 P - 129lgP + 1300℃, when liquid magnesium can be obtained by condensing magnesium vapor, but at this time a small amount of calcium vapor may be lost with CO gas; if the pressure P ≥ 10000Pa, while controlling the molten pool temperature T ≤ 30lg 2 P + 58lgP + 1215℃, the temperature T of magnesium vapor leaving the layer is slightly higher than T = 21.4lg 2 P + 18.4lgP + 437℃, liquid magnesium can be obtained by condensing magnesium vapor, and the smelting reverse reaction can be basically eliminated, and there is no calcium vapor loss. Similarly, when the pressure P ≥ 10000Pa, if the molten pool temperature T > 30lg 2 P + 58lgP + 1215℃, the temperature T of magnesium vapor leaving the layer is > 37lg 2 P - 73lgP + 580℃ (condensation temperature of calcium vapor), then liquid magnesium and a small amount of liquid calcium can be obtained by condensation, without calcium vapor loss.

[0126] Example 4

[0127] S1, the same particle size of 20-50mm dolomite is selected, and is calcined into calcined dolomite in a rotary kiln. Each ton of calcined dolomite contains 369.3kg of magnesium oxide and 617.4kg of calcium oxide. A certain type of coal is selected, which is produced by a certain coal plant and has a particle size of 10-20mm and a fixed carbon content of 82%. A certain type of calcium carbide is selected, which is produced by a certain calcium carbide plant and has a gas evolution of 300l / kg (CaC2 content of 80%). It is calculated that 618.2kg of coal is needed for each ton of calcined dolomite, i.e. the mass ratio of calcined dolomite to coal is 1:0.6182.

[0128] S2, the calcium carbide is placed in the graphite smelting cavity of the resistance-heated sealed steel reactor and heated to melt, forming a calcium carbide pool about 300mm deep.

[0129] S3, the calcined dolomite particles and coal particles are mixed uniformly according to the mass ratio of 1:0.6182 and then added to the pool until the un-submerged material layer above the pool surface is about 500mm thick.

[0130] S4, the absolute pressure P≈20000Pa in the reactor is set, the smelting reaction is carried out by adjusting the electric heating power to keep the pool temperature at T=2000±20℃, and at the same time, the material layer thickness is adjusted by feeding to make the temperature of magnesium vapor leaving the material layer about 1000℃, and the magnesium vapor enters the condenser connected in series to the reactor to obtain liquid magnesium by condensation. During the smelting process, when the pool liquid surface rises above the control liquid surface, it is discharged through the reactor liquid discharge port, and the discharged liquid calcium carbide is condensed and sold as a byproduct calcium carbide.

[0131] The method produces about 13kg / h of pure magnesium and about 33kg / h of pure calcium carbide per hour, and the production efficiency is about twice that of the solid-phase catalyst method. The crude magnesium after direct condensation of magnesium liquid contains about 95% magnesium, and the calcium carbide obtained after cooling of the liquid calcium carbide has a gas evolution of 270l / kg, which is equivalent to a calcium carbide content of about 72%. The quality of crude magnesium is lower than that of the solid-phase method, but the quality of calcium carbide is higher than that of the solid-phase method.

[0132] Five, technical idea 5-solid phase calcium carbide catalyst carbon thermal method smelting multiple metals

[0133] It is found that not only the mixture of magnesium oxide and calcium oxide can be smelted by carbon thermal method with calcium carbide as catalyst to produce magnesium, but also the oxides of many metals (hereinafter collectively referred to as M) such as Mg, Pb, Sn, Zn, Fe, Mn, Ni, Co, Cr, Mo, V can react with calcium carbide to produce metal elements and calcium oxide, and the calcium oxide produced in the reaction can also react with carbon to produce calcium carbide again. The smelting reaction can be uniformly represented by the following formula: m

[0134]

[0135] ​

[0136] The above two formulas are added together to obtain:

[0137]

[0138] It can be seen that CaC2 acts as a catalyst in the reaction. The thermodynamic law of the chemical reaction is qualitatively described by Figure 5

[0139] Therefore, using the same method of refining magnesium as described above, i.e., using carbon as a reducing agent and calcium carbide as a catalyst, the oxides of magnesium, lead, tin, zinc, iron, manganese, nickel, cobalt, chromium, molybdenum, vanadium, etc. can also be smelted to produce the corresponding elemental metals. The amount of calcium carbide produced in each production cycle is basically equal to the amount of catalyst calcium carbide added, which can be fully reused as a catalyst.

[0140] Example 5

[0141] S1, a certain mine produces magnesite first-class product, the chemical composition is MgO = 46%, CaO = 0.6%, SiO2 = 1.0%; a certain calcium carbide plant produces calcium carbide first-class product, the CaC2 content is 80%; a certain chemical plant produces high-temperature pitch, the fixed carbon content is 80%. Take 100 kg of calcined magnesite, containing effective component MgO = 96.64 kg, add 191.84 kg of calcium carbide, and add 35.97 kg of pitch. After mixing, grind the mixed powder into 100 mesh mixed powder 327.81 kg.

[0142] S2, the above mixed powder is pressed into a pillow-shaped ball with length x width x height = 50 x 30 x 20 mm, and is placed in a graphite smelting chamber in a steel sealed container. The graphite smelting chamber is heated by resistance, and a heat preservation layer is provided between the smelting chamber and the steel container. A shell and tube condenser is connected in series between the vacuum pump and the vacuum pipe interface at the upper part of the steel container, and a sealed magnesium liquid tank is connected below the condenser.

[0143] S3, set the absolute pressure P ≈ 1000 Pa in the reactor, adjust the heating electric power to keep the smelting chamber temperature T = 1400 ± 20 ℃ for magnesium smelting. From the observation hole of the magnesium liquid tank, it can be seen that the liquid magnesium flows from the condenser into the magnesium liquid tank.

[0144] S4, after about 2 hours of the above magnesium smelting reaction, the heating electric power is significantly reduced and tends to be stable, indicating that the magnesium smelting reaction has basically ended. Then set the absolute pressure P ≈ 3000 Pa in the reactor, increase the smelting chamber temperature to T = 1750 ± 20 ℃, and carry out calcium carbide smelting reaction. After about 1 hour of reaction, the heating power is reduced again and tends to be stable, indicating that the calcium carbide smelting reaction has basically ended. When the pressure displayed by the vacuum pressure gauge of the reactor is zero, open the bottom slag discharge hole of the reactor, and discharge the generated calcium carbide, which is used as a reducing agent for the next production cycle.​

[0145] The method is about 3 hours for a production cycle, and each cycle produces 68.56 kg of crude magnesium, with an average of about 22 kg / h of magnesium per hour, and the crude magnesium contains 99.96% magnesium.

[0146] Sixth, technical idea 6 - liquid phase calcium carbide catalyst carbothermic smelting of various metals

[0147] If the above "technical idea 5" carbothermic smelting of various metals method is changed to use liquid phase CaC2 as catalyst, not only can significantly improve the smelting reaction speed, but also can save the grinding, ball pressing and other processes, so as to improve the production efficiency, shorten the process flow and reduce the product cost.

[0148] Example 6

[0149] S1, select the same particle size of 20-50mm magnesite as in example 5, after calcination, each ton of calcined magnesite contains 966.4kg of magnesium oxide; select the particle size of 10-20mm, fixed carbon content of 85% of the coke produced by a certain coke plant, and the gas production of 300l / kg(CaC2 content 80%) of the calcium carbide produced by a certain calcium carbide plant. Each ton of calcined magnesite needs to be mixed with 338.5kg of coke, that is, the mass ratio of calcined magnesite to coke is 1:0.3385.

[0150] S2, put the calcium carbide into the graphite smelting cavity of the resistance heated closed steel reactor and heat it to melt, and form a calcium carbide pool about 300mm deep.

[0151] S3, according to the above mass ratio of calcined magnesite to coke 1:0.3385, mix the calcined magnesite particles and coke particles uniformly, and add them to the catalyst pool in the smelting cavity, until the thickness of the material layer above the molten pool is about 500mm.

[0152] S4, set the absolute pressure P≈20000Pa in the reactor, adjust the electric heating power to keep the pool temperature at T=2000±20℃, and carry out smelting reaction; at the same time, adjust the material layer thickness by feeding, so that the temperature of magnesium vapor leaving the material layer is about 1000℃, and the magnesium vapor enters the condenser connected in series on the reactor to condense liquid magnesium.

[0153] The method can produce about 40kg / h of pure magnesium on average per hour, and the production efficiency is close to twice that of the solid phase catalyst method. The magnesium liquid directly condensed contains about 95% magnesium, and the quality of the crude magnesium is lower than that of the solid phase method.

[0154] The technical ideas and preferred embodiments of the present application are described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations without creative effort based on the concept of the present application. Therefore, any technical solutions obtained by logical analysis, reasoning or limited experiments based on the concept of the present application in the prior art should be within the protection scope defined by the claims.

Claims

1. A method for co-producing calcium carbide through carbothermic calcium refining, characterized in that, Includes the following steps: S1. Prepare a mixed powder containing calcium oxide and carbon reducing agent; the molar ratio of calcium oxide and carbon reducing agent in the mixed powder is CaO:C≈1:3~1:1; S2. Press the mixed powder into pellets and place them into a reactor equipped with a heat source; S3. Set the absolute pressure P inside the reactor to 10000 Pa ≤ P ≤ slight positive pressure, where slight positive pressure refers to a positive pressure not exceeding 1000 Pa above the local atmospheric pressure; the reaction temperature T > 301g. 2 P+58lgP+1215℃, a smelting reaction is carried out, and liquid calcium is obtained by condensation through a condenser connected to the reactor, and calcium carbide is obtained in the reactor.

2. The method as described in claim 1, characterized in that, The fineness of the mixed powder is above 80 mesh.

3. The method as described in claim 1, characterized in that, The equivalent diameter of the pellet furnace charge is 20mm~40mm.

4. The method as described in claim 1, characterized in that, The outer layer of the reactor is a sealed container, and the interior is provided with a smelting chamber. An insulation layer is provided between the sealed container and the smelting chamber. The pellet furnace charge is placed in the smelting chamber.

5. The method as described in claim 4, characterized in that, The smelting chamber is made of high-temperature resistant material components, and the heat resistance temperature of the high-temperature resistant material is not lower than 1700℃.

6. The method as described in claim 5, 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.

7. The method as described in 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 foregoing.

8. The method as described in claim 1, characterized in that, The heat source is heated electrically.

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