Method for smelting magnesium through silicothermic method by using suspended calcined dolomite and photovoltaic silicon sludge

Abstract

The invention belongs to the technical field of magnesium metal refining, and relates to a method for smelting magnesium through a silicothermic method by using suspended calcined dolomite and photovoltaic silicon sludge, which comprises the following steps: step 1, crushing dolomite, and carrying out suspension calcination by using suspension calcination equipment to obtain calcined dolomite; 2, heating and drying the photovoltaic silicon sludge to obtain dried silicon sludge; 3, mixing the calcined dolomite obtained in the step 1, the dried silicon sludge obtained in the step 2 and fluorite powder to obtain a mixed raw material; step 4, carrying out compression molding on the mixed raw material obtained in the step 3, heating under a vacuum condition, collecting magnesium steam, and condensing to obtain metal magnesium; the suspension calcined dolomite is combined with the silicon sludge, so that the step of integral ball milling adopted by a magnesium factory at present can be avoided, the energy consumption of the ball milling step can be saved, and the defect that the reducing capacity of the silicon sludge is reduced due to the fact that the silicon sludge is oxidized due to easy heating of ball milling is overcome; according to the method, the high-silicon component in the photovoltaic waste silicon sludge is effectively utilized, the problem of waste disposal is solved, and the additional value of the photovoltaic waste silicon sludge is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal magnesium refining, and relates to a method for siliothermic magnesium refining by using suspended calcined dolomite and photovoltaic silicon mud. Background Art

[0002] At present, the silicon thermal method of magnesium smelting generally uses dolomite obtained by calcining in a rotary kiln as raw material, and uses ferrosilicon as a reducing agent. During the calcination process of the rotary kiln, the block dolomite accumulates in the kiln and is calcined by contacting the high-temperature flue gas through the continuous rotation of the kiln body. Ferrosilicon is crushed and mixed with calcined white and fluorite in a ball mill. The role of ferrosilicon is to react with magnesium oxide in the dolomite calcination product at high temperature to generate metallic magnesium. In addition, the silicon mud waste generated by the photovoltaic industry contains a high silicon content and usually needs to be disposed of or landfilled. The reuse of these wastes has important economic and environmental value.

[0003] However, the existing silicon thermal method of magnesium smelting has the following disadvantages: High energy consumption: Rotary kiln calcination requires calcination at 1200-1300℃ for several hours. At the same time, the hardness of ferrosilicon is between 40-50HRC. When ball-milled with calcined white block and fluorite, the loss of ferrosilicon can reach 1.5%, and the energy consumption of the crusher can be as high as 720 degrees / day, which seriously reduces the economic benefits. Unstable product quality: Due to the heat exchange of the accumulated block stone in the rotary kiln, the problems of "overburning" and "underburning" are prone to occur, affecting product quality. Waste of resources: Photovoltaic waste silicon mud is usually landfilled or disposed of, and is not effectively utilized, resulting in waste of resources.

[0004] Therefore, a method or device with low energy consumption and high recovery rate is needed to solve the above technical problems. Summary of the invention

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud, comprising the following steps:

[0006] Step 1, crushing the dolomite and then calcining it in a suspended calcination device to obtain calcined dolomite;

[0007] Step 2, heating and drying the photovoltaic silicon mud to obtain dry silicon mud;

[0008] Step 3, mixing the calcined white obtained in step 1, the dry silicon mud obtained in step 2 and the fluorite powder to obtain a mixed raw material;

[0009] Step 4: Press the mixed raw material obtained in step 3 into a shape, then heat it under vacuum conditions, collect magnesium vapor, and condense it to obtain metallic magnesium.

[0010] Preferably, in step 1, dolomite is first crushed to a particle size of no more than 200 μm to obtain dolomite powder; and then the dolomite powder is suspended calcined using a suspension calcination device to obtain calcined dolomite.

[0011] Preferably, in step 1, the temperature of the suspension calcination is about 900-1000° C., and the suspension calcination time is less than 10 s.

[0012] Preferably, in step 2, the photovoltaic silicon mud includes: elemental silicon, water-based cutting fluid, additives, metallic impurities and non-metallic impurities.

[0013] Preferably, in step 2, the drying temperature of the heating and drying is 200-300° C., and the heating and drying time is 50-650 min.

[0014] Preferably, in step 4, the pressing pressure of the pressing molding is 60 to 150 MPa, and the holding time is 20 to 40 s.

[0015] Preferably, in step 4, the vacuum conditions for heating under vacuum conditions are vacuum degree <10 Pa, heating rate is 1-5°C / min, and the temperature is heated to 1050-1350°C.

[0016] Preferably, in step 4, the purity of the metallic magnesium is > 99.95%.

[0017] Preferably, in step 3, the mixing ratio of calcined white and dried silicon mud ranges from 3:1 to 5:1.

[0018] More preferably, in step 3, the mixing ratio of calcined white and dried silicon mud ranges from 4:1 to 4.7:1.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention effectively reduces the energy consumption of magnesium smelting by silicon thermal method; the present invention combines suspension calcination of calcined white with silicon mud, which can avoid the overall ball milling step currently used in magnesium plants. The advantage of suspension calcination is that the suspension calcination technology allows dolomite powder to fully contact with high-temperature hot air in a suspended state, achieving instant heat exchange, and its heat exchange efficiency is much higher than the piled heat exchange of traditional rotary kilns. During the suspension calcination process, dolomite can be quickly heated to the required reaction temperature (such as 900-1000°C) within a few seconds, and the temperature distribution is uniform, avoiding the "overburning" and "underburning" problems caused by local overheating or overcooling, thereby obtaining highly active calcined white. The hydration activity of the obtained calcined white can reach an average of more than 30%. Taking the compound swing jaw crusher (Y225M-8 type) used in the magnesium plant as an example, the power is 30KW, and it consumes at least 720 degrees of electricity for one day of work. The use of silicon mud can save the energy consumption of this step. Therefore, the present invention can reduce the energy consumption of magnesium smelting by silicon thermal method.

[0021] 2. The present invention can effectively reduce the oxidation of silica mud and ensure the uniformity of the mixture. Currently, if calcined white block and silica mud are used in industry and the calcined white block and silica mud are ball-milled together, in addition to the problem of uneven mixing, there is also the problem of heat generated by ball milling, which makes the silica mud easy to oxidize and leads to a decrease in its reducing ability. The present invention can avoid the above defects because it does not require mixed ball milling.

[0022] 3. The present invention can significantly improve the magnesium recovery rate of silicothermic magnesium refining; the silicon mud and calcined dolomite in the present invention are both in powder state, are evenly mixed and have better reaction effect, and the magnesium recovery rate is increased to more than 92%.

[0023] 4. The present invention can improve the resource recycling of photovoltaic waste silicon mud: The present invention effectively utilizes the high silicon content in photovoltaic waste silicon mud, solves the waste disposal problem, and improves the added value of photovoltaic waste silicon mud. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of the finished product of magnesium metal in a method of siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] refer to Figure 1 As shown, this embodiment uses high-activity calcined dolomite prepared by suspension calcination and photovoltaic waste silicon mud to perform silicon thermal magnesium smelting. The specific steps are as follows:

[0027] Step 1: crush the dolomite and perform suspension calcination using a suspension calcination device to obtain calcined dolomite.

[0028] Step 2: Heat and dry the photovoltaic silicon mud to obtain dry silicon mud.

[0029] Step 3: Mix the calcined white obtained by suspension calcination, dry silicon mud and fluorite powder to obtain a mixed raw material.

[0030] Step 4: Press the mixed raw material into a shape, then heat it under vacuum conditions, collect magnesium vapor, and condense it to obtain metallic magnesium.

[0031] Furthermore, in step 1, the preparation method of calcined white is: crushing dolomite to a particle size of at least 150 μm to obtain dolomite powder, and calcining the dolomite powder in a suspended state using a suspended calcining device to obtain calcined white.

[0032] Furthermore, in step 1, the temperature of suspension calcination is about 950° C., and the residence time at high temperature is less than 10 seconds; the reaction temperature can be adjusted between 1050° C. and 1350° C. to adapt to different production conditions.

[0033] Furthermore, in step 2, the photovoltaic silicon mud includes elemental silicon, water-based cutting fluid, metallic impurities and non-metallic impurities.

[0034] Furthermore, in step 2, the drying temperature is 200-300° C., and the heating drying time is 50-650 min.

[0035] Furthermore, in step 4, the pressing pressure is 60-150 MPa, and the holding time is 20-40 s.

[0036] Furthermore, in step 4, the vacuum condition is a vacuum degree of <10Pa, and the heating rate is a maximum increase of 5°C per 1min, and the temperature is heated to 1250-1350°C.

[0037] Furthermore, in step 4, the purity of the magnesium metal is greater than 99.95%.

[0038] Furthermore, in step 3, the mixing ratio is adjusted to: the mixing ratio of silicon mud and suspended calcined dolomite ranges from 3:1 to 5:1, such as 80:20 or 70:15, etc., to optimize the reaction effect.

[0039] Compared with the traditional method, the present invention first utilizes the highly active calcined powder prepared by suspension calcination, and secondly uses photovoltaic silicon mud, saving the energy consumed in the traditional crushing of ferrosilicon. The suspension calcination technology enables the dolomite powder to be in full contact with high-temperature hot air in a suspended state, achieving instantaneous heat exchange, and its heat exchange efficiency is much higher than the stacked heat exchange of the traditional rotary kiln. During the suspension calcination process, the dolomite can be rapidly heated to the reaction temperature (such as 900 - 1000 °C) within seconds, and the temperature distribution is uniform, avoiding the problems of "overburning" and "underburning" caused by local overheating or overcooling, thereby obtaining highly active calcined white. The average hydration activity of the obtained calcined white can reach over 30%. When this highly active calcined white is combined with photovoltaic silicon mud, a unique reaction microenvironment can be formed. The silicon in the silicon mud and the magnesium oxide in the calcined white are in more sufficient contact at the microscopic level, and the number of reactive sites increases, significantly improving the initial rate and overall efficiency of the reduction reaction. Experimental data show that within the same reaction time, the magnesium production rate of the reaction system using suspension-calcined dolomite and silicon mud can be increased by over 30% compared to the traditional system. The obtained material-magnesium ratio can reach 5.7 and the purity of the obtained magnesium can reach over 99.95%.

[0040] Through research, the optimal mixing ratio range of silicon mud and suspension-calcined dolomite was determined, such as 80:12, etc. During the mixing process, the mixing time was flexibly set to ensure uniform mixing of the two, which can not only ensure sufficient mixing of the materials but also avoid problems such as material heating and sticking or other adverse effects caused by too long mixing time. In addition, the mixed materials were monitored in real time, such as through particle size analysis, composition uniformity detection, etc., to ensure the stable quality of each batch of mixed materials, providing a reliable guarantee for the subsequent stable silicon thermal reduction reaction. Currently, in industry, if calcined white blocks and silicon mud are mixed and used, they still need to be ball-milled together. In addition to the problem of uneven mixing, there is a more important problem that ball-milling will generate heat, which causes the oxidation of silicon mud and the reduction ability to decline. The method of the present invention can avoid this defect in the prior art.

[0041] Example

[0042] In this example, the dolomite was crushed to a particle size of less than 150 μm and calcined at a temperature of about 950 °C for about 10 s using a suspension calcination device to obtain calcined white. Then the photovoltaic silicon mud was heated and dried to obtain dried silicon mud; the dried silicon mud, calcined white, and fluorite were mixed to obtain a mixed raw material; then the mixed raw material was first pressed into shape and then heated under vacuum conditions to collect magnesium vapor, and after condensation, metallic magnesium was obtained.

[0043] For this technology, the particle size of silicon mud is required to be below 200μm, and the dryness requires that the water content per kilogram of silicon mud does not exceed 5%. When mixing, the mixing time can be flexibly adjusted according to the amount of material. If the total mass of the raw materials is less than 500g, the mixing time is 10-15min; if the total mass of the raw materials is greater than 500g, the mixing time is 15-30min. The overall mixing time is controlled between 10-30min, preferably to mix completely without stratification and adhesion. When pressing the ball, the prepared ball is required to fall from a height of 1m and break into at most three petals.

[0044] Mixing ratio adjustment of this embodiment: The mixing ratio of silicon mud and suspended calcined dolomite can be adjusted according to actual needs, such as 80:20 or 70:15, etc., to optimize the reaction effect. Reaction temperature range of this embodiment: The reaction temperature can be adjusted between 1050°C and 1350°C to adapt to different production conditions.

[0045] Example 1

[0046] The dried photovoltaic waste silicon mud (water content of 4%, particle size of 80μm) and the suspended calcined calcined dolomite (particle size of 60μm) were mixed in a mass ratio of 1:1 for 15 minutes. The mixture was sent to the reactor for silicon thermal reduction reaction at 1200℃ for 120 minutes. The final magnesium metal purity was above 99.95%, with high reaction efficiency and low energy consumption, which met the requirements of industrial production.

[0047] Example 2

[0048] Silicon mud (3% moisture content, 90 μm particle size) and calcined dolomite (50 μm particle size) were mixed at a mass ratio of 1:1.5 for 12 minutes, followed by a silicothermic reduction reaction at 1250°C for 120 minutes. The final magnesium recovery rate reached 92%. ， The purity of the obtained metallic magnesium is above 99.95%, the output is stable, and photovoltaic waste silicon mud is utilized to achieve green production.

[0049] Example 3

[0050] The dried photovoltaic waste silicon mud (water content of 2%, particle size of 100μm) and the suspended calcined calcined dolomite (particle size of 150μm) were mixed in a mass ratio of 1:1 for 20 minutes. The mixture was sent to the reactor and subjected to silicon thermal reduction reaction at 1200℃ for 120 minutes. The final magnesium metal obtained has a purity of more than 99.95%, high reaction efficiency, low energy consumption, and meets industrial production requirements.

[0051] In summary, the present invention combines suspended calcined magnesia with silicon mud, which can avoid the overall ball milling step currently adopted by magnesium factories, thus saving the energy consumption of the ball milling step; the present invention effectively utilizes the high-silicon component in photovoltaic waste silicon mud, solves the problem of waste disposal, and improves the added value of photovoltaic waste silicon mud.

[0052] It should be emphasized that the above are only the preferred embodiments of the present invention, and there is no limitation in any form to the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud, characterized in that: The following steps are involved: Step 1, crushing the dolomite and then calcining it in a suspended calcination device to obtain calcined dolomite; Step 2, heating and drying the photovoltaic silicon mud to obtain dry silicon mud; Step 3, mixing the calcined white obtained in step 1, the dry silicon mud obtained in step 2 and the fluorite powder to obtain a mixed raw material; Step 4: Press the mixed raw material obtained in step 3 into a shape, then heat it under vacuum conditions, collect magnesium vapor, and condense it to obtain metallic magnesium.

2. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 1, dolomite is first crushed to a particle size of no more than 200 μm to obtain dolomite powder; and then the dolomite powder is suspended calcined using a suspension calcination device to obtain calcined dolomite.

3. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 1, the temperature of the suspension calcination is about 900-1000° C., and the suspension calcination time is less than 10 seconds.

4. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In step 2, the photovoltaic silicon mud includes: elemental silicon, water-based cutting fluid, additives, metal impurities and non-metal impurities.

5. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 2, the drying temperature of the heating and drying is 200 to 300° C., and the heating and drying time is 50 to 650 minutes.

6. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 4, the pressing pressure of the pressing molding is 60 to 150 MPa, and the holding time is 20 to 40 seconds.

7. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 4, the vacuum conditions for heating under vacuum conditions are vacuum degree <10Pa, heating rate of 1-5°C / min, and heating to 1050-1350°C.

8. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 4, the purity of the metallic magnesium is greater than 99.95%.

9. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 1, characterized in that: In the step 3, the mixing ratio of calcined white and dried silicon mud ranges from 3:1 to 5:

1.

10. The method for siliothermic magnesium smelting using suspended calcined dolomite and photovoltaic silicon mud according to claim 9, characterized in that: In the step 3, the mixing ratio of calcined white silicon mud and dried silicon mud ranges from 4:1 to 4.7:1.

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