CN109136993B - Post-treatment method of regenerated cryolite obtained by wet-method treatment of electrolytic aluminum carbon slag - Google Patents

Post-treatment method of regenerated cryolite obtained by wet-method treatment of electrolytic aluminum carbon slag Download PDF

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CN109136993B
CN109136993B CN201811115145.0A CN201811115145A CN109136993B CN 109136993 B CN109136993 B CN 109136993B CN 201811115145 A CN201811115145 A CN 201811115145A CN 109136993 B CN109136993 B CN 109136993B
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intermediate frequency
graphite crucible
furnace
melt
electrolyte
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CN109136993A (en
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杨鹏鸿
张维民
铁国泰
李建胜
曹国强
郑冬
丁少华
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Aluminum Corp of China Ltd
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Aluminum Corp of China Ltd
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    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25CPROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/18Electrolytes

Abstract

The invention discloses a post-treatment method of regenerated cryolite obtained by wet processing of electrolytic aluminum carbon slag, which comprises the following steps of 1) manufacturing a graphite crucible inner container medium-frequency induction furnace; 2) drying the manufactured graphite crucible inner container intermediate frequency induction furnace; 3) putting the regenerated cryolite into a graphite crucible, electrifying to heat and melt the regenerated cryolite into a melt, fishing out carbon slag, injecting the electrolyte melt into a mold, cooling, solidifying and demolding to obtain the product. The invention has the beneficial effects that: the electrolyte block produced by the technology has various index contents meeting the standard, can meet the requirement of electrolyte block production by electrolysis while consuming excessive regenerated cryolite, and is environment-friendly, economic and good in benefit.

Description

Post-treatment method of regenerated cryolite obtained by wet-method treatment of electrolytic aluminum carbon slag
Technical Field
The invention belongs to the field of waste residue recycling in the electrolytic aluminum industry, and relates to electrolytic aluminum carbon residue, in particular to a further treatment method of regenerated cryolite obtained by wet treatment of the electrolytic aluminum carbon residue.
Background
The electrolytic aluminum carbon slag is a solid hazardous waste substance, and mainly comprises carbon, fluoride salt, aluminum oxide, iron compound and other trace elements. Once a large amount of carbon slag exists in the electrolytic cell, the electrolytic cell can be seriously damaged, for example, the voltage of electrolyte is increased, the power consumption is increased, the service life of the electrolytic cell is shortened, and the comprehensive economic indexes of the electrolytic production slide down, so the carbon slag in the electrolytic cell needs to be timely salvaged out.
The carbon slag is subjected to harmless treatment, so that the pollution to the environment can be avoided, more than half of electrolyte can be recycled, and the method is an important cost-reducing and efficiency-improving measure. At present, the general treatment methods for carbon slag by aluminum electrolysis production enterprises mainly comprise two methods: one is a pyrogenic process and the other is a wet process. The pyrogenic process is to directly heat the carbon slag to a molten state, so that most of carbon substances and oxygen react and are discharged into the atmosphere in a gas form. The liquid electrolyte is recycled through the working procedures of casting, slag dragging, cooling, demoulding and the like; the pyrogenic process production has the defects of poor production field environment condition, high production cost, short furnace life, high overhaul cost, large carbon emission and the like; the wet processing is that the carbon slag is ground into mixed powder with the particle size of 0.15mm by a ball mill, a flotation reagent is added into a charging port and a discharging port of the ball mill according to the proportion requirement while grinding the carbon slag, then stirring, flotation and separation are carried out in a flotation machine, the recycled regenerated cryolite can be used for electrolytic production, and the recycled carbon powder can be used for manufacturing an anode protection ring or used for producing other carbon products after harmless treatment; the wet production has the advantages of good production environment, stable yield and the like, but the regenerated cryolite produced by the wet production is mainly used for starting the electrolytic cell, has small daily demand and low market price, so how to produce the regenerated electrolyte block with large demand and high market price by using the surplus regenerated cryolite is the problem to be researched and solved on the premise of environmental protection, economy and small carbon emission.
Disclosure of Invention
The invention aims to provide a post-treatment method of regenerated cryolite obtained by wet-method treatment of electrolytic aluminum carbon slag, so as to expand the application range of the regenerated cryolite, improve the product value and protect the environment.
The technical scheme of the invention is as follows: a post-processing method of regenerated cryolite obtained by wet processing of electrolytic aluminum carbon residue, 1) manufacturing a special intermediate frequency induction furnace with a graphite crucible liner, specifically laying refractory bricks at the bottom for bottoming, arranging induction coils above the refractory bricks, smearing daub on the turns and the inner wall of the induction coils, coating asbestos cloth on the surface and the upper surface of the refractory bricks after the daub is dried in the air, building a furnace bottom by furnace burden, placing a graphite crucible above the furnace bottom, ensuring that the center of the graphite crucible is coincident with the center of the induction coils (the upper part of the graphite crucible can be fixed by a clamp and is stable), and placing and tamping the building burden in an area between the graphite crucible and the asbestos cloth; 2) baking the manufactured graphite crucible inner container intermediate frequency induction furnace: filling regenerated cryolite in the graphite crucible, connecting an induction coil to an intermediate frequency control system, then electrifying, adjusting the intermediate frequency power to 50KW in one stage, heating for 2h, adjusting the intermediate frequency power to zero, keeping the temperature for 1h, adjusting the intermediate frequency power to 100KW in two stages, heating for 1.5h, adjusting the intermediate frequency power to zero, keeping the temperature for 0.5h, adjusting the intermediate frequency power to 150KW in three stages, heating for 0.5h, adjusting the intermediate frequency power to zero, keeping the temperature for 0.5h, and finishing baking the furnace; 3) putting the regenerated cryolite into a graphite crucible, raising the power of an intermediate frequency control system to 400KW within 2 minutes, heating and melting the regenerated cryolite into a melt after 10-15 minutes, fishing out carbon slag on the surface of the melt, stirring electrolyte melt in the graphite crucible after fishing out the carbon slag, controlling the total time of fishing out the carbon slag and stirring within 2 minutes, continuing intermediate frequency heating for 1 minute after stirring, then reducing the intermediate frequency power to zero within 20 seconds, injecting the electrolyte melt into a mold and standing for 2 minutes, fishing out a small amount of carbon slag floating on the surface of the electrolyte melt in the mold, cooling and solidifying the electrolyte melt to obtain an electrolyte block, and demolding to obtain a product.
The graphite mass fraction of the graphite crucible is not less than 50%, the external diameter of the crucible body is 600 mm-700 mm, and the wall thickness is 80 mm-100 mm.
The graphite crucible preferably has a graphite mass fraction of 55 to 60%.
The invention has the beneficial effects that: the electrolyte block produced by the technology has various indexes (C, LiF, KF and AL)2O3、SiO2Etc.) the contents meet the standard, and the electrolyte block can meet the requirements of electrolytic production while consuming excessive regenerated cryolite, thereby being one of effective measures for reducing cost and improving efficiency; the technology has the advantages of low investment, quick response, simple and flexible operation, low requirement on production site, low production cost, low carbon emission, stable and safe production and the like, more than 95 percent of tailings exist in a solid state form, and the tailings can also be used for producing the anode protection ring, so the technology is environment-friendly, economic and good in benefit.
Drawings
FIG. 1 is a schematic view of a graphite crucible inner container medium frequency induction furnace; in the figure: 1-graphite crucible, 2-daub covering layer, 3-firebrick, 4-casting material, 5-asbestos cloth and 6-induction coil.
Detailed Description
The medium frequency induction furnace is a power supply device which converts power frequency 50Hz alternating current into medium frequency (more than 300Hz to 1000Hz), three-phase alternating current is converted into direct current after rectification, the direct current is converted into adjustable medium frequency current through inversion, the adjustable medium frequency current is supplied to a capacitor and an induction coil, the medium frequency alternating current generates high-density magnetic lines in the induction coil and cuts a conductor to enable the conductor to generate heat, and regenerated cryolite cannot be directly heated and melted through the medium frequency furnace, so that a graphite crucible inner container (the content of graphite is more than 50 percent) arranged in the induction coil enables the graphite crucible to generate large eddy current and generate heat. The temperature of the regenerated cryolite gradually rises along with the rise of the temperature of the crucible, when the temperature reaches about 900 ℃, the cryolite begins to melt into liquid electrolyte, about 13 percent of carbon powder contained in the cryolite floats on the liquid surface of the electrolyte in a solid state due to high melting point (between 3500 ℃ and 3770 ℃), and only a small amount of carbon slag reacts with oxygen to be discharged into the atmosphere. After the liquid electrolyte is continuously heated for a certain time, the carbon residue tailings in the liquid electrolyte are almost completely separated from the electrolyte liquid, the liquid electrolyte has casting conditions, and after the cast electrolyte liquid is subjected to slag dragging, cooling and demolding procedures, the finally produced qualified electrolyte block can meet the daily production requirements of electrolytic aluminum. The treatment method has the advantages of low investment amount and low carbon emission, mainly solves the problem of air pollution caused by carbon emission in the carbon slag treatment process, and has good environmental protection and economic benefits.
The graphite mass percentage of the used graphite crucible liner reaches 55-60% best, the carbon powder is 30-35%, the adhesive mainly comprises petroleum coke and needle coke (the ratio is about 10%), the outer diameter of the crucible is 600-700%, the wall thickness is 80-100% best, the crucible graphite content is too low, the heating performance of the crucible is poor, the service life of the crucible is short, the crucible is very easy to crack when the crucible is heated due to too large outer diameter, and the service life of the crucible is very short. After the basic size of the graphite crucible is determined, the size of the induction coil is determined, and then an intermediate frequency system is selected according to data such as the pipe section size of the induction coil, the number of turns of the coil, the turn pitch and the like. Mounting the manufactured induction coil on a production station after insulation treatment and pressing detection; the specific furnace building process mainly comprises the following steps: firstly, after the installation position of an induction coil is determined, daubing is daubed between turns and around the coil according to requirements, and the daubing in the inner ring of the coil is required to be smooth and flat; secondly, after the daub is air-dried for a certain time, carrying out heat insulation treatment on the inner side of the coil by using asbestos cloth; thirdly, after building a furnace bottom by using a building material, installing a graphite crucible inside the induction collar, wherein the crucible and the induction coil are required to be in the same central position during installation; and fourthly, the region between the outer side surface of the crucible and the inner surface of the induction coil is a key process for building the furnace, the quantity of the furnace charge which is put into each time is required to be certain, the tamping force is reasonable, the position of the crucible is ensured to be unchanged, and the crucible is not damaged. And finally finishing the furnace building process after multiple times of feeding and tamping.
Before a new graphite crucible is put into production, baking is carried out according to a specified baking curve, the crucible is required to be filled with regenerated cryolite before baking, and the baking time is 6 hours optimally.
A furnace baking process: the medium frequency power is 50KW, the heating time is 2h,
the medium-frequency power is 0, the temperature is kept for 1h,
medium frequency power of 100KW, heating time of 1.5h,
the intermediate frequency power is 0, the temperature is kept for 0.5h,
the medium frequency power is 150KW, the heating time is 0.5h,
and (5) keeping the intermediate frequency power at 0 ℃ for 0.5 h.
The method comprises the following steps of finishing a furnace baking process according to a furnace baking curve, then feeding materials for production, gradually increasing the medium-frequency power to 400KW within 2 minutes, wherein the smelting time of the regenerated cryolite in each furnace is about 12 minutes, when the regenerated cryolite heated to the liquid state in a graphite crucible is heated, most carbon slag floats on the liquid level, the first slag removal treatment is carried out at the moment, the electrolyte solution is stirred after the slag removal, the raw materials are ensured to be completely melted, and the slag removal and stirring time is controlled within 2 minutes. The electrolyte solution is stirred and heated for 1 minute, then casting conditions are achieved, and the medium frequency power is reduced to zero within 20 seconds. And (3) injecting the electrolyte solution into the die and standing for 2 minutes, then carrying out secondary deslagging operation, and fishing out a small amount of carbon slag floating on the surface of the electrolyte solution in the die to produce an electrolyte block with low carbon content.
When an emergency power failure condition is met, an emergency water source is required to be quickly opened, the electrolyte in the crucible is strictly forbidden to move out of the crucible, otherwise, the crucible cracks and the furnace is scrapped due to the rapid temperature drop, so that the production cost is additionally increased.
TABLE 1 technical indices, mass fractions, of electrolyte blocks produced according to the invention
C LiF KF Al2O3 SiO2
Index of the product of the invention 0.8% 5.5% 2.3% 3.7% 0.18%
Minimum standard for electrolytic production of electrolyte blocks <1.0% <6.0% <2.8% <3.8% <0.36%

Claims (3)

1. A post-processing method of regenerated cryolite obtained by wet processing of electrolytic aluminum carbon residue, 1) manufacturing a special intermediate frequency induction furnace with a graphite crucible liner, specifically laying refractory bricks at the bottom for bottoming, arranging induction coils above the refractory bricks, smearing daub between turns and on the inner wall of the induction coils, coating asbestos cloth on the surface and the upper surface of the refractory bricks after the daub is dried in the air, building a furnace bottom by furnace burden, placing a graphite crucible above the furnace bottom, ensuring that the center of the graphite crucible coincides with the center of the induction coils, and placing the furnace burden in an area between the graphite crucible and the asbestos cloth and tamping the furnace burden; 2) baking the manufactured graphite crucible inner container intermediate frequency induction furnace: filling regenerated cryolite in the graphite crucible, connecting an induction coil to an intermediate frequency control system, then electrifying, adjusting the intermediate frequency power to 50KW in one stage, heating for 2h, adjusting the intermediate frequency power to zero, keeping the temperature for 1h, adjusting the intermediate frequency power to 100KW in two stages, heating for 1.5h, adjusting the intermediate frequency power to zero, keeping the temperature for 0.5h, adjusting the intermediate frequency power to 150KW in three stages, heating for 0.5h, adjusting the intermediate frequency power to zero, keeping the temperature for 0.5h, and finishing baking the furnace; 3) putting the regenerated cryolite into a graphite crucible, raising the power of an intermediate frequency control system to 400KW within 2 minutes, heating and melting the regenerated cryolite into a melt after 10-15 minutes, fishing out carbon slag on the surface of the melt, stirring electrolyte melt in the graphite crucible after fishing out the carbon slag, controlling the total time of fishing out the carbon slag and stirring within 2 minutes, continuing intermediate frequency heating for 1 minute after stirring, then reducing the intermediate frequency power to zero within 20 seconds, injecting the electrolyte melt into a mold and standing for 2 minutes, fishing out a small amount of carbon slag floating on the surface of the electrolyte melt in the mold, cooling and solidifying the electrolyte melt to obtain an electrolyte block, and demolding to obtain a product.
2. The method for post-treating regenerated cryolite obtained by wet processing of carbon residue of electrolytic aluminum according to claim 1, wherein: the graphite mass fraction of the graphite crucible is not less than 50%, the external diameter of the crucible body is 600 mm-700 mm, and the wall thickness is 80 mm-100 mm.
3. The method for post-treating the regenerated cryolite obtained by the wet processing of the carbon residue of the electrolytic aluminum according to claim 2, which is characterized in that: the graphite mass fraction of the graphite crucible is 55-60%.
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