Method and system for removing lead impurity in magnesium steam based on metal calcium filter material

Abstract

The invention relates to a method and system for removing lead impurities in magnesium steam based on a metal calcium filter material, and the method comprises the following steps: heating a magnesium raw material, and reacting to generate magnesium steam; and placing the metal calcium filter material or the carrier containing the metal calcium on a flowing channel of the magnesium steam, so that the magnesium steam passes through the metal calcium filter material or the carrier containing the metal calcium to remove lead-containing impurities, and condensing and crystallizing to obtain low-lead crude magnesium. The filter material and the process provided by the invention have the characteristics of low cost and high efficiency, and can be directly linked with the existing silicothermic magnesium production process, and under industrial conditions, the metal calcium filter material reduces the lead content in crude magnesium by 50.5% and reduces the impurity Pb content to 10 ppm or below. In addition, the method is also suitable for a vacuum distillation method. By applying and popularizing the technology, high-purity and low-lead raw materials can be provided for the field of magnesium.

Description

Technical Field

[0001] The invention relates to the technical field of primary magnesium smelting, and in particular to a method and system for removing lead impurities in magnesium vapor based on a metallic calcium filter material. Background Art

[0002] Magnesium metal is known as a "new generation" of biomedical degradable implant materials because of its excellent biocompatibility, moderate biodegradability, good mechanical properties and special biofunctionality. However, the application of magnesium and magnesium alloy implantable devices is not as expected. At present, only a very small number of high-purity magnesium implant devices in China have been approved by the State Food and Drug Administration. One of the reasons is that the role of alloying elements in the human body is still unclear, and a large number of long-term cell, tissue, and human compatibility experiments are required for safety assessment. Studies have shown that impurity lead can be toxic to the nervous system, blood system, digestive system, etc., so the lead content of biomedical magnesium needs to be strictly controlled. The group standard "T / CSBM 0041-2023 Medical High-Purity Magnesium Extruded Round Bars" stipulates that the impurity Pb ​​content in the high-purity magnesium products used shall not exceed 10 ppm.

[0003] At present, the main methods for removing lead impurities from magnesium are flux refining and vacuum distillation. The former mainly uses the replacement effect of flux (KCl, MgCl2, CaCl2) on metal element impurities to remove impurities, and has good affinity with oxide inclusions (MgO, etc.) and can be separated by static separation. The main impurities removed are Ca, K, and Na, and the removal effect on Pb is limited. The impurity removal principle of vacuum distillation is mainly to use the difference in saturated vapor pressure between magnesium and impurities to separate magnesium from impurities during evaporation and condensation. However, since the saturated vapor pressure of Pb is similar to that of magnesium, lead impurities can easily enter magnesium. In addition, the existing purification technology also uses Fe, Ni, Si, CaO and other filter materials (CN201911178561.X, CN201911178325.8, CN201911178562.4, CN202310084209.X), but Fe, Ni, Si filter materials mainly play the role of providing heterogeneous nucleation sites and physically intercepting particulate impurities. CaO filter materials are mainly used for magnesium vapor in the silicon thermal method, mainly forming mineral salts with aluminum fluoride impurities in magnesium in the silicon thermal method to selectively remove aluminum. The impurity Pb ​​has low binding energy and poor affinity with substances such as Fe, Ni, Si, and CaO. The solubility of Pb in metals such as Fe, Ni, and Si is low, and it will not form a solid solution, and it will not react with the above-mentioned Fe, Ni, Si, CaO and other filter materials to form compounds. The above-mentioned filter materials have no impurity removal effect on lead impurities.

[0004] In view of this, it is urgent to find a low-cost and efficient method to remove lead impurities in magnesium vapor. Summary of the invention

[0005] The object of the present invention is to provide a method and system for removing lead impurities in magnesium vapor based on metallic calcium filter material to solve the above-mentioned problem.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for removing lead impurities in magnesium vapor based on a metal calcium filter material, comprising: The magnesium raw material is heated to generate magnesium vapor by reaction; A metallic calcium filter material or a carrier containing metallic calcium is placed on a flow channel of magnesium vapor, so that the magnesium vapor passes through the metallic calcium filter material or the carrier containing metallic calcium to remove lead impurities, and then condenses and crystallizes to obtain low-lead crude magnesium.

[0007] Optionally, the lead-containing impurity is elemental lead.

[0008] Optionally, the working temperature of the metal calcium filter material for removing lead impurities is 450 ~ 800 ℃.

[0009] Optionally, the metallic calcium filter material is any one of refined calcium ingots and crystalline crude calcium.

[0010] Optionally, the shape of the metal calcium filter material is any one of block, spherical, and filamentary.

[0011] Optionally, when the metal calcium filter material is in block or spherical shape, the equivalent diameter is 3 to 30 mm; when the metal calcium filter material is in filamentary shape, the filament diameter is 1 to 5 mm.

[0012] Optionally, the calcium content of the metallic calcium filter material is between 95 wt.% and 99.5 wt.%.

[0013] Optionally, the magnesium raw material is a silicothermic raw material or a magnesium ingot, and the source of the magnesium vapor is any one of magnesium vapor generated by silicothermic method or magnesium vapor generated by vacuum distillation method.

[0014] A system for removing lead impurities from magnesium vapor based on a metal calcium filter material, comprising: A magnesium vapor generation module is used to heat the magnesium raw material to generate magnesium vapor through reaction; The impurity removal module is used to place a metallic calcium filter material or a carrier containing metallic calcium on the flow channel of magnesium vapor, so that the magnesium vapor passes through the metallic calcium filter material or the carrier containing metallic calcium to remove lead impurities, and then condenses and crystallizes to obtain low-lead crude magnesium.

[0015] The invention discloses an application of a system for removing lead impurities in magnesium vapor based on a metallic calcium filter material, which is used for the preparation of low-lead crude magnesium.

[0016] Compared with the prior art, the present invention has the following technical effects: The lead removal effect of the present invention is excellent. In view of the situation that the deposition temperatures of magnesium vapor and lead impurities are similar and difficult to separate in the traditional method, the present invention uses metallic calcium and impure lead to form Ca2Pb, so that the deposition temperature of lead impurities is increased, and the difference in deposition temperature between lead impurities and magnesium vapor is increased, thereby achieving magnesium-lead separation.

[0017] The invention has wide applicability and can be applied to a variety of magnesium vapor sources, including silicon thermal magnesium vapor sources and vacuum distillation magnesium vapor sources; The metal calcium filter material proposed by the present invention can be produced in the existing equipment of the metal magnesium plant by replacing the magnesium smelting raw material with the calcium smelting raw material, thereby realizing local material acquisition and independent supply of the filter material.

[0018] In addition to removing lead, the metal calcium filter material of the present invention can also provide heterogeneous nucleus sites for impurity condensation and physically intercept dust particles, thereby further reducing other major impurities in magnesium vapor.

[0019] The filter material and process provided by the present invention have the characteristics of low cost and high efficiency, and can be directly connected with the existing silicon thermal magnesium production process. Under industrial conditions, the metal calcium filter material reduces the lead content in crude magnesium by 50.5%, and the impurity Pb ​​content is reduced to below 10ppm. In addition, the method is also applicable to vacuum distillation. The application and promotion of this technology can provide high-purity, low-lead raw materials for the magnesium field. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 The thermodynamic calculation diagram of the deposition behavior of magnesium vapor with temperature before and after using the metal calcium filter material in the present invention; Figure 2 Schematic diagram of the change of lead impurity content in magnesium before and after use in Example 2 of the present invention and Comparative Example 2; DETAILED DESCRIPTION To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0022] Example 1 The present embodiment provides a method for removing lead impurities in magnesium based on a metal calcium filter material. Based on the silicothermic magnesium smelting process, the metal calcium filter material is used to purify and remove lead impurities in magnesium vapor, comprising the following steps: heating the raw materials for silicothermic magnesium smelting to react and generate magnesium vapor, allowing the magnesium vapor to pass through the metal calcium filter material to remove lead impurities, and then condensing and crystallizing to obtain low-lead crystalline magnesium.

[0023] In this embodiment, the silicon thermal method for magnesium smelting includes the following steps: placing the raw materials for magnesium smelting by silicon thermal method in a closed container, evacuating the closed container so that the vacuum degree of the closed container is 10 Pa; heating the closed container so that the magnesium vapor passes through the metal calcium filter material arranged in the closed container to remove lead impurities, and then crystallizes to obtain low-lead crystalline magnesium.

[0024] In this embodiment, a reaction zone, a temperature transition zone and a crystallization zone are sequentially arranged in a closed container in the silicon thermal magnesium smelting process, and the movement path of magnesium vapor under vacuum is sequentially the reaction zone, the temperature transition zone and the crystallization zone; The reaction zone is used to load raw materials for magnesium smelting by silicon thermal process, and the raw materials for magnesium smelting by silicon thermal process loaded in the reaction zone are heated, so that the raw materials react at 1250-1300°C to generate magnesium vapor, and the magnesium vapor contains lead impurities, and the main existence form of lead is simple substance; The composition of raw material balls (calcined white, ferrosilicon, fluorite mixture) of the silicothermic method is usually MgO 32.74 wt.%, CaO 46.15 wt.%, Al2O3 0.29 wt.%, Fe2O3 0.46 wt.%, MnO 0.08 wt.%, PbO 0.0021 wt.%, SiO21.05 wt.%, ZnO 0.0013 wt.%, Si 13.75 wt.%, Fe 3.68 wt.%, Al 0.32 wt.%, Ca 0.17wt.%, Mn 0.02 wt.%, Pb 0.0002 wt.%, Zn 0.0004 wt.%, CaF2 1.30 wt.%, etc. Thermodynamic calculation of the raw materials with the above composition shows that the main form of lead impurities in magnesium vapor is elemental lead; The raw material magnesium ingot composition of vacuum distillation method is usually Al 0.0053 wt.%, Ca 0.0021 wt.%, Cu 0.0003wt.%, Fe 0.0024 wt.%, Mg99.9735 wt.%, Mn 0.0031 wt.%, Ni 0.0003 wt.%, Pb 0.0016wt.%, Si 0.0039 wt.%, Zn 0.0045 wt.%. Thermodynamic calculation of the raw materials of the above composition shows that the existence form of lead vapor in magnesium is also single lead. In the thermodynamic equilibrium state, in the common service pressure range of 10 ~ 100 Pa, the deposition temperature of Pb gas phase impurities in magnesium vapor is about 552 ~ 605 ℃, and the temperature of complete deposition of Mg vapor is about 498 ~ 587 ℃, and the temperature difference between the two is relatively small. Under industrial conditions, the deposition behavior of gaseous substances often deviates far from the thermodynamic equilibrium state, so lead impurities are more likely to co-deposit with Mg, making it difficult to separate Mg-Pb. In the presence of metallic calcium, in the range of 10~100 Pa, the affinity of metallic calcium with impurity Pb ​​is stronger than that of magnesium in this range. Impurity Pb ​​will form Ca2Pb compounds with metallic calcium, which increases the deposition temperature of impurity Pb ​​to 608~676℃, while the complete deposition temperature of magnesium vapor is still 498~587℃. The difference between the deposition temperature of Pb vapor and the deposition temperature of magnesium vapor increases, which can avoid the co-deposition of impurity Pb ​​and magnesium, and then realize the separation of magnesium and lead. In addition, it should be noted that at this temperature, metallic calcium may enter magnesium due to partial evaporation, but whether it is the silicon thermal method or the vacuum distillation method, the subsequent refining process can significantly reduce the Ca content, which has almost no effect on the purity of magnesium. In addition, the equipment used in the aluminothermic smelting process of metallic calcium is the same as the equipment used in the silicothermic smelting process of metallic magnesium, and the process operations are similar. By replacing the raw materials in the existing silicothermic magnesium smelting equipment with calcium smelting raw materials, the calcium filter material can be directly produced in the magnesium plant.

[0025] A metal calcium filter material is arranged in the temperature transition zone, and the magnesium vapor generated by the reaction in the reaction zone moves to the temperature transition zone under the action of vacuum, and the magnesium vapor contacts the metal calcium filter material, thereby removing the lead-containing impurities in the magnesium vapor and obtaining purified magnesium vapor; A crystallizer is arranged in the crystallization zone, and the purified magnesium vapor is condensed and crystallized in the crystallization zone, thereby obtaining low-lead crystalline magnesium.

[0026] In this embodiment, the following steps are specifically followed: (1) The amount of silicon thermal magnesium smelting raw material (pellets) placed is 250 g, the heating temperature of the first reaction zone is 1250 °C, the heating temperature of the second temperature transition zone is controlled at 450 ~ 1250 °C, and the temperature of the third zone is controlled at 450 °C.

[0027] The raw material for silicothermic magnesium smelting is pellets, which contain MgO 32.74 wt.%, CaO 46.15 wt.%, Al2O30.29 wt.%, Fe2O3 0.46 wt.%, MnO 0.08 wt.%, PbO 0.0021 wt.%, SiO2 1.05 wt.%, ZnO0.0013 wt.%, Si 13.75 wt.%, Fe 3.68 wt.%, Al 0.32 wt.%, Ca 0.17 wt.%, Mn 0.02wt.%, Pb 0.0002 wt.%, Zn 0.0004 wt.%, CaF2 1.30 wt.%, etc. Through thermodynamic calculations of the pellets with the above components, it can be seen that when the silicon thermal reduction reaction occurs, the main form of impurity lead is gas phase elemental lead, and the molar ratio of gas phase impurity lead to magnesium vapor is about 0.00001:1. This ratio is used as an input parameter to calculate the phase diagram of the two at 1 ~ 100 Pa and 450 ~ 1250 ℃, and only the phase lines of complete deposition of Pb and complete deposition of Mg are presented. It can be seen that the complete deposition temperature of impurity Pb ​​is about 552 ~ 605 ℃, and the temperature of complete deposition of Mg vapor is about 498 ~ 587 ℃ ( Figure 1 ).

[0028] (2) The present invention selects metallic calcium as the filter material and calculates the phase diagram under the addition of 0.001 molCa, which also only presents the phase lines of complete deposition of Pb and complete deposition of Mg. It can be seen that the deposition temperature of impurity Pb ​​increases to 608 ~ 676 ℃, while the complete deposition temperature of magnesium vapor is still 498 ~ 587 ℃ ( Figure 1 , in order to show the local changes, the horizontal axis is adjusted to 450~700℃).

[0029] In this embodiment, 5 g of crystalline bulk metal calcium with an equivalent diameter of 10-20 mm is placed in the second temperature transition zone, more specifically in the temperature range of 600-700° C.

[0030] According to the above description, after 120 min of silicon thermal reduction reaction, the crystalline magnesium in the crystallizer was collected and weighed to obtain 49.0 g of low-lead crystalline magnesium.

[0031] The content of each element in the crystalline magnesium was analyzed according to the national standard GB / T 3499-2021, as shown in Table 1.

[0032] Table 1

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that in step (2), no metal calcium filter material is placed in the second temperature transition zone.

[0034] After 120 min of silicon thermal reduction reaction, the crystalline magnesium in the crystallizer was collected and weighed to obtain 48.4 g of low-lead crystalline magnesium.

[0035] The content of each element in the crystalline magnesium was analyzed according to the national standard GB / T 3499-2021, as shown in Table 2.

[0036] Table 2

[0037] According to Example 1 and Comparative Example 1, after the magnesium vapor was purified by using the metal calcium filter material, the impurity lead content decreased from 56.6 to 25, with a decrease of 55.8%.

[0038] Example 2 (1) The difference between this embodiment and embodiment 1 is that the implementation device is an industrial silicon thermal reduction furnace. The industrial silicon thermal reduction furnace is a double-sided single-row furnace, each row of which contains 13 sealing devices with the same basic functions as embodiment 1 as basic production units; each sealing device contains a high-temperature reaction zone, a temperature transition zone and a crystallization zone.

[0039] (2) The difference from Example 1 is that 250 kg of silicothermal raw materials are placed in the high-temperature reaction zone of each basic production unit; (3) The difference from Example 1 is that a carrier containing a metal calcium filter material is placed in the temperature transition zone of each basic production unit; the metal calcium filter material is placed on the vapor flow channel of the carrier; the equivalent diameter of the metal calcium filter material is 20 to 30 mm; (4) Another difference from Example 1 is that the reaction time is 12 hours; after weighing the produced crystalline magnesium, the average output of a single sealed device is 39 kg.

[0040] The crystalline magnesium from each production unit was mixed and remelted, and the content of each element in the crystalline magnesium was shown in Table 3.

[0041] Table 3

[0042] Comparative Example 2 The difference between this comparative example and Example 2 is that in step (2), a carrier containing a metal calcium filter material is placed at 550-650° C. in the temperature transition zone according to the distribution of the temperature transition zone; however, no metal calcium filter material is placed in the carrier.

[0043] After 12 hours of silicon thermal reduction reaction, the crystalline magnesium in the crystallizer was collected and weighed to obtain 38.9 kg of low-lead crystalline magnesium.

[0044] The crystallized magnesium of each production unit was mixed and remelted, and the content of each element in the crystallized magnesium was shown in Table 4. According to Example 2 and Comparative Example 2, after the magnesium vapor was purified by using the metal calcium filter material, the impurity lead content decreased from 10.1 to 5.0, a decrease of 50.4% (such as Figure 2 ). At the same time, the impurity Ca content in Example 2 is 7 ppm, which is lower than the impurity Ca content of 18.5 ppm in Comparative Example 2, indicating that the placement of the metal calcium filter material will not cause pollution to the system.

[0045] Table 4

[0046] Example 3 The difference between this embodiment and embodiment 1 is that in step (2), the placement temperature of the metal calcium filter material is 550-650°C.

[0047] After 120 min of silicon thermal reduction reaction, the crystallized magnesium in the crystallizer was collected and weighed to obtain 49.2 g of low-lead crystallized magnesium. The crystallized magnesium was remelted, and the lead impurity content in the remelted magnesium ingot was 23.5 ppm. Compared with Comparative Example 1, the lead impurity decreased by 58.48%.

[0048] Example 4 The difference between this embodiment and embodiment 1 is that the raw material used to generate magnesium vapor is a primary magnesium ingot weighing 100 g; the first stage reaction zone is heated to 850°C; Example 5 The difference between this embodiment and embodiment 4 is that the metal calcium filter material used is spherical metal calcium particles with an equivalent diameter of 3 to 5 mm; The above description is only a preferred embodiment of the present invention. In some embodiments, the operating temperature of the above-mentioned metal calcium filter material for removing lead impurities in magnesium vapor is 450~800℃; in order to ensure that the metal calcium filter material is at the optimal working temperature, one optional method is to place the metal calcium filter material in the temperature transition zone to purify and remove lead impurities in magnesium vapor; another optional method is to place the metal calcium filter material in an area corresponding to a specific temperature range in the temperature transition zone based on the temperature distribution area in the temperature transition zone.

[0049] In some embodiments, the above-mentioned metal calcium filter material is naturally filled with metal calcium raw material on the movement path of magnesium vapor, and the metal calcium raw material is any one of block, spherical, and filamentary; in some examples, when the metal calcium filter material is block or spherical, the diameter is 3~30mm; in some examples, when the metal calcium filter material is filamentary, the wire diameter is 1~5 mm.

[0050] In some instances, the above-mentioned metallic calcium filter material is placed on the channel through which magnesium vapor flows in the carrier, and the carrier is placed on the movement path of the magnesium vapor; in some instances, metallic calcium can also be blended with other filter materials that are beneficial to the purification of magnesium vapor, such as the pure iron filter material disclosed in CN201911178561.X, the elemental silicon filter material disclosed in CN201911178325.8, the nickel-based filter material disclosed in CN201911178562.4, the CaO filter material disclosed in CN202310084209.X, etc. Of course, the dosage ratio is adjusted according to the adaptability to the impurity removal effect of magnesium vapor.

[0051] The above embodiments are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing lead impurities in magnesium vapor based on a metal calcium filter material, characterized in that: include: The magnesium raw material is heated to generate magnesium vapor by reaction; A metallic calcium filter material or a carrier containing metallic calcium is placed on a flow channel of magnesium vapor, so that the magnesium vapor passes through the metallic calcium filter material or the carrier containing metallic calcium to remove lead impurities, and then condenses and crystallizes to obtain low-lead crude magnesium.

2. A method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 1, characterized in that: The lead impurity is elemental lead.

3. The method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 1, characterized in that: The working temperature of metal calcium filter material for removing lead impurities is 450 ~ 800 ℃.

4. The method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 1, characterized in that: The metallic calcium filter material is any one of refined calcium ingot and crystalline crude calcium.

5. The method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 1, characterized in that: The shape of the metal calcium filter material can be any one of block, spherical, and filamentary.

6. The method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 5, characterized in that: When the metal calcium filter material is in block or spherical shape, the equivalent diameter is 3 ~ 30 mm; when the metal calcium filter material is in filamentary shape, the wire diameter is 1 ~ 5 mm.

7. The method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 1, characterized in that: The calcium content of metallic calcium filter material is between 95 wt.% and 99.5 wt.%.

8. The method for removing lead impurities in magnesium vapor based on a metal calcium filter material according to claim 1, characterized in that: The magnesium raw material is a silicothermic raw material or a magnesium ingot, and the source of the magnesium vapor is any one of magnesium vapor generated by silicothermic method and magnesium vapor generated by vacuum distillation method.

9. A system for removing lead impurities from magnesium vapor based on metal calcium filter material, characterized in that: include: A magnesium vapor generation module is used to heat the magnesium raw material to generate magnesium vapor through reaction; The impurity removal module is used to place a metallic calcium filter material or a carrier containing metallic calcium on the flow channel of magnesium vapor, so that the magnesium vapor passes through the metallic calcium filter material or the carrier containing metallic calcium to remove lead impurities, and then condenses and crystallizes to obtain low-lead crude magnesium.

10. An application of the system for removing lead impurities in magnesium vapor based on a metal calcium filter material as claimed in claim 9, characterized in that: Used for the preparation of low-lead crude magnesium.

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