The method of refining magnesium scrap

 

(57) Abstract:

The invention relates to ferrous metallurgy and can be used in the processing of magnesium scrap. The method of refining magnesium scrap includes the melting of scrap in the environment of the molten flux certain density and sedimentation, and the melt before settling further treated by air under pressure in the range of 0.03-0.6 MPa and served under a layer of melt in dispergirovannom, supporting the specific air flow rate in the range of 0.1 to 100.0 cm3/(kgf), and the density of the molten flux is kept lower than the density of solid scrap, but higher than the density of secondary molten metal with respect to the mass of molten flux to the mass of recycled scrap in the range of 0.08 to 3.5. In addition, the melting is carried out at a temperature of melt 700-780C in the molten flux of the following composition, wt.%: 45-58 KS1, 8-19 NaCI, 18-31 MgCl2, 4-12 BaCl2, 0-2,0 l2, 0-5,0 CaF2, 0-1,5 gF2. The melt is treated with metallic magnesium in an amount of 0-3% of its mass, is achieved by increasing the degree of extraction of the metal. 8 C.p. f-crystals.

The invention relates to ferrous metallurgy and can be used in the processing of magnesium RCDs.with ang. M: Metallurgy. - 1972. - S. 488) the number of ways to extract the metal from various forms of magnesium scrap.

Large magnesium scrap is processed by melting, and in any ratio. This technology is obvious and does not require improvement.

Scrap covered by corrosion, by direct fusion gives a dry crucible residue, which reduces the degree of extraction and degrades the quality of the secondary metal.

Small chips, it is recommended to add together with flux in continuously stir the bath at a temperature close to the liquidus temperature. After melting of the entire chip temperature raise and produce clean flux. However, experimental validation of the method showed that the thus obtained secondary metal is extremely dirty magnesium oxide, and its output is low due to heavy smoke in the first stage of processing. The same applies to the melting of sawdust and powder. Therefore, these types of scrap, usually buried in the ground or destroyed by burning.

For crucible residues proposed the following processing methods:

a) melting the "rich" residues with a protective flux and mixing for sintering metal;

b) raznogo alloy;

C) mechanical disintegration with sorting of waste rock;

g) wet disintegration by flushing flux and release of metal;

d) centrifuging crucible residues.

However, all these methods have significant drawbacks. For example, the method "a" allows for the melting of partially removing the metal, which is then usually broken into small drops under stirring of the melt. In addition, the mixing leads to resuspension of magnesium oxide, which is adsorbed on the droplet surface, weight and forces them to fall in the slurry zone. Methods "b", "C" and "d" allow to extract the metal in the form of a coated oxide-salt film granules of very low quality. Method "d" can be extracted, usually not more than 50% of the metal contained in the waste. This is because the metal in the waste is mainly in the form of fine drops (diameter less than 2 mm), covered with a durable oxide film. Given that the density of magnesium oxide (3.6 g/cm3in two and a half times greater than the density of molten magnesium (~ 1.56 g/cm3and about twice the flux density (1.6 to 1.8 g/cm3), the formal density drops (weight of magnesium oxide and magnesium in the droplet volume) becomes comparable with Y.

The closest and most effective way to the same destination to the claimed invention, a combination of traits, selected as a prototype, is a method (U.S. Pat. N 1480360, action, 28.07.94) metallurgical processing of magnesium-containing waste, including smelting waste in the environment of flux and sedimentation. And smelting waste is carried out at 730-760oC in an environment of flux density lower than the density of the melt waste at the rate of flux 8-10% by weight of the waste and subsequent processing of calcium fluoride when the flow rate of 1-2% by weight of waste. The method is very effective, cheap and allows you to extract up to 70-74% of the metal contained in the waste. The resulting metal fully complies with the technical requirements for secondary magnesium alloy and can be used without further processing as a charge component in the production of standard magnesium alloys.

The main disadvantage of the prototype is not a high degree of extraction of the metal, due to the impossibility of removing it from the small, covered with a durable oxide film of metal drops.

The task on which the invention is directed, is to increase the degree of extraction of the metal due to the inclusion in ne is in the method of refining magnesium scrap, including the melting of scrap in the environment of the molten flux certain density with a melt and defending, what's new is that the melt before settling further treated by air under pressure.

In addition, the excess pressure is maintained within the range of 0.03-0.6 MPa.

In addition, the air supplied under a layer of melt in dispergirovannom.

In addition, the specific flow rate of air is maintained within the range of 0.1 to 100.0 cm3/(kg).

In addition, the density of the molten flux is kept lower than the density of solid scrap, but higher than the density of secondary molten metal.

In addition, the ratio of the mass of molten flux to the mass of processed scrap is maintained within the range of 0.08 to 3.5.

In addition, the melting is carried out at a temperature of melt 700-780oC.

In addition, the melting lead in a molten flux of the following composition, wt. %: KCl 45-58, NaCl 8-19, MgCl218-31, BaCl24-12, CaCl2- not more than 2.0, CaF2- not more than 5.0, MgF2- not more than 1.5.

In addition, the melt is treated with metallic magnesium in an amount of not more than 3% of its mass.

The choice of these terms of refining magnesium sadamasa on the metal surface as in the solid scrap, and small drops of molten metal in the scrap, there is always a silicide of magnesium (Mg2Si), which falls into the metal at the stage of electrolytic production of magnesium by its interaction with silicon oxide, which is part of fireclay pot lining

SiO2+ 4Mg = Mg2Si + 2 MgO (1)

In some special studies, we experimentally proved that the presence of magnesium silicide promotes the oxide film, which is not destroyed even in the presence in the melt of such well-known depassivation as CaF2and MgF2. As a consequence, there are ways to recycle scrap, including the way the prototype, allow to extract from the waste only metal in the melt in the form of relatively large units ("pots"), not covered with the oxide film. Such a metal in liquid metallurgical wastes, as a rule, is about 70%. This explains the corresponding degree of metal extraction from liquid metallurgical wastes in the method of the prototype. About 30% of the material placed in such waste in the form of small (diameter less than 2.0 mm), covered with an oxide film of metal drops, unable to extract. The same result is almost always education, or digging in the earth.

We experimentally found that to extract the metal from the small, covered with a durable oxide film drops can be used for a treatment of the melt with air. This is because the silicide of magnesium in the interaction with air moisture intensively decomposed:

Mg2Si + 2H2O = SiH4+ 2MgO (2)

with the formation of magnesium oxide and silane.

The latter, in turn, decomposes into silicon oxide and water:

SiH4+ 2O2= SiO2+ 2H2O (3)

which is partly re-involved in the interaction with magnesium silicide by reaction (2), and partially consumed by the decomposition of silane:

SiH4+ 2H2O = SiO2+ 4H2. (4)

As a result of this rapidly flowing process of the oxide film on the surface of droplets of the metal is destroyed, and the released droplets of metal in the coalescence merge into a compact mass, suitable for its separation from oxide molten salt known methods.

It is shown that, depending on the thickness of the metal-oxide-salt melt and the viscosity of the air should flow at a pressure of 0.03-0.6 MPa.

When this lower limit is due to neobjevena melt.

For a more uniform flow of process depassivation of metal drops in the volume of the melt, the air must be submitted under a layer of melt in dispergirovannom the form of, for example, through various spray devices.

The specific flow rate of air should be maintained in the range of 0.1 to 100.0 cm3/(kgf). It was established experimentally that at a flow rate below the lower limit of the process of depassivation drops proceeds slowly and the released droplets of metal, unable to merge, covered with a new oxide film - a compact mass of metal is not formed.

When the air flow is above the upper limit, the process proceeds very rapidly, as a consequence, the fused metal is again divided into small granules.

To create conditions favorable for metal recovery from scrap, melting is carried out in the molten flux, the density of which is lower than the density of solid scrap, but higher than the density of secondary molten metal. In this case, the loaded waste pass through a layer of molten refining flux, cleaned of excess oxides, and the initial stage of their melting takes place under the flux layer, which reduces metal loss on the fumes in the furnace. After melting and release from oxt, forming a compact mass.

It is found experimentally that for the successful completion of the separation of melting a mass of molten flux to the mass of recyclable scrap must be maintained in the range of 0.08-3,50. When the ratio below the lower limit of the amount of flux is insufficient for cleaning metal and the latter are heavily polluted with non-metallic impurities (oxides, chlorides, fluorides, and so on). The increase in the ratio over 3,50 not economically feasible, because it does not increase the purity of the metal, or to increase the degree of extraction from scrap.

It was established experimentally that the heat should be carried out at a temperature of melt 700-780oC in the molten flux of the following composition, wt.%: 45-58 KCl, 8-19 NaCl, 18-31 MgCl2, 4-12 BaCl2, 0-2,0 CaCl2, 0-5,0 CaF2, 0-1,5 MgF2. In the specified temperature range the flux of this compound provides good cleaning of metal from non-metallic inclusions, primarily from fragments of the oxide film. In addition, in this temperature range the flux has good fluidity and the desired density. When drops of metal after they depassivation converge very slowly, which is possible when bol is TBE "seed" in the melt add magnesium metal in an amount up to 3% by weight of the melt.

Conducted by the applicant's analysis of the prior art, including searching by the patent and scientific and technical information sources and identify sources that contain information about the equivalents of the claimed invention, has allowed to establish that the applicant had not discovered analogues characterized by signs, identical all the essential features of the invention. The definition from the list of identified unique prototype, as the most similar set of features analogue, has allowed to establish the essential towards perceived by the applicant to the technical result of the distinctive features in the proposed method, set forth in the claims. Therefore, the claimed invention meets the condition of "novelty."

To verify compliance of the claimed invention the term "inventive step", the applicant conducted an additional search of the known solutions to identify signs that match the distinctive features of the prototype of the characteristics of the claimed method. The search results showed that the claimed invention not apparent to the expert in the obvious way from the prior art because the prior art defined by the applicant, not to identify the Oia technical result. Therefore, the claimed invention meets the condition of "inventive step".

Experimental validation of the proposed method were carried out in industrial conditions on the existing technological equipment.

Example 1. Clean scrap crucible installed in a shaft furnace CMT-2, melted 400 kg flux of the following composition, wt.%: 50 KCl, NaCl 15, 20 MgCl2, 8 BaCl2, 2 CaCl2, 4 CaF2, 1 MgF2. The flux of such composition at a temperature of 700-750oC has a density 1,68-1.66 g/cm3. The melt was heated to 750oC and portions of 100-200 kg in the crucible loaded 1500 kg briketirovannogo chip magnesium alloy MA-1. Solid chips alloy MA-1 has a density of approximately 1.77 g/cm3so after you download it fell under the layer of the melt, the metal melted and the temperature was raised to 750oC. the density of the alloy at this temperature is approximately 1.64 g/cm3, i.e., the metal became easier flux and was able to float on its surface. However, the "apparent" density drops of metal (mass of metal and oxide films in the droplet volume) is comparable with the density of the flux (rate of 1.67 g/cm3), and therefore the bulk of the metal in the form of droplets coated with oxide film, stuck in tol the VA was not detected. Attempts to extract the metal by mechanical stirring of the melt and further processing fluorides of calcium and magnesium did not lead to success. Then the crucible was installed a steel tube connected to the compressed air and equipped with device for spraying. Spent processing the melt for 20 min, feeding compressed air to the bottom of the crucible under a pressure of 0.1 MPa at specific discharge 1.65 cm3/(kgf). The metal after treatment were merged into a compact mass, and separated from the oxide molten salt using the wall for flow of metal. Weighing showed that the extracted 1365 kg of recycled magnesium alloy, i.e., the degree of recovery was 91%.

Example 2. The experiment was carried out as described in example 1. The difference was that the ratio of the mass flux to the metal experience was 3,79, because the mass flux of 1500 kg, weight briketirovannogo, strongly oxidized chip - 400 kg After melt processing compressed air metal on the surface of the melt in the CD was missing. In the crucible was added 50 kg of magnesium raw and processed melt compressed air for 3 minutes After 10 min of sludge from the crucible learned 420 kg of recycled metal, i.e., the total degree of izvlecheny the ri 700oC in a crucible steel download portions at 70-150 kg metallurgical waste from the production of magnesium alloys ("bottom remainders"). During the filling of the crucible (uploaded 1700 kg of waste) the melt was heated to 750oC, was treated with calcium fluoride in the amount of 25 kg (1.35% of the mass of the melt), advocated for 40 min and extracted fused metal - 440 kg. Given that the metal content in the waste about 40%, the degree of extraction of metal from a waste at this amounted to 64.7%. After that, remaining in the crucible, the melt was treated with air at a pressure of 0.15 MPa for 30 min at specific discharge 2.2 cm3/(kgf) and further extracted with 200 kg of recycled metal. The total recovery of metal from waste was 94,1%.

Thus, the experimental verification of the proposed method shows that it helps to increase the degree of extraction of metal from scrap and waste up to 90-94%.

1. The method of refining magnesium scrap, including the melting of scrap in the environment of the molten flux certain density with a melt and sedimentation, characterized in that the melt before settling further treated by air under pressure.

2. Ways is .1, characterized in that the air supplied under a layer of melt in dispergirovannom.

4. The method according to p. 1, characterized in that the specific flow rate of air is maintained within the range of 0.1 to 100.0 cm3/(kg).

5. The method according to p. 1, characterized in that the density of the molten flux is kept lower than the density of solid scrap, but higher than the density of secondary molten metal.

6. The method according to p. 1, characterized in that the ratio of the mass of molten flux to the mass of processed scrap is maintained within the range of 0.08 to 3.5.

7. The method according to p. 1, wherein the melting is carried out at a melt temperature of 700 - 780oC.

8. The method according to p. 1, characterized in that the melting lead in a molten flux of the following composition, wt.%: KCl - 45 - 58; NaCl - 8 - 19; MgCl2- 18 - 31; BaCl2- 4 - 12; CaCl2- not more than 2.0; CaF2- not more than 5.0; MgF2- not more than 1.5.

9. The method according to p.,1 characterized in that the melt is treated with metallic magnesium in an amount of not more than 3% of its mass.

 

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