RU2398035C1 - Procedure for extraction of magnesium out of wastes of foundry conveyor - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to procedure for extraction of magnesium out of wastes produced at magnesium casting on foundry conveyor. The procedure consists in crucible melt of wastes in flux medium containing magnesium, sodium and potassium chlorides. After melt magnesium is settled, tapped and treated with calcium fluoride. Also as flux, there is used electrolyte of electrolytic cells for production of magnesium with carnallite feeding circuit; carnallite is heavier, than liquid magnesium at 0.03-0.05 g/cm³ and contains 5-15% of MgCl₂, 18-20% of NaCl, 0.1-0.3% of F, KCl - the rest. Melt is carried out at ratio electrolyte - wastes: (0.7-1.5):1 at the temperature 700-730°C, also bottom layers are stirred-up manually. The rest of melt upon magnesium tapping is treated with calcium fluoride at manual mixing. Upon treatment magnesium is settled and tapped.

EFFECT: increased extraction of magnesium from wastes produced at magnesium tapping at foundry conveyor and simplification of salt medium composition.

1 tbl, 1 ex

Description

The proposed solution relates to non-ferrous metallurgy, specifically to the production of magnesium.

In the production of commercial magnesium in pigs at various redistribution processes, waste is generated, the cause of which is mainly due to the tendency of magnesium to oxidize with atmospheric oxygen. Waste is generated as part of crucible residues (when refining magnesium in crucibles) and when casting on a casting conveyor in the form of so-called splashes. Sples is a top film of oxidized magnesium taken from a ingot (ingot) by a worker manually. Its composition depends on the technology of metal protection during casting (for example, sulfur or gas) and the qualifications of the worker.

The structure and composition of magnesium-containing wastes (MSOs) formed during casting processes are not constant and depend on many factors: process temperature, metal protection method, the presence of flux and its composition, type of process, personnel qualifications. Methods of additional extraction of magnesium from waste are worked out for each type of waste separately in accordance with their composition and structure.

The present invention provides a method for extracting magnesium from waste foundry conveyor - splas. The usual composition of splashes: magnesium (50-98%); magnesium oxide (2-35%); flux used to prevent burning of stored splits (1-10%). The structure of the collected splashes is a crystallized shapeless ingot weighing 5-20 kg with developed porosity. Magnesium in splashes is in the form of large drops with a diameter of more than 10 mm.

Known methods for processing magnesium-containing sludge by centrifugation (ed. St. USSR 1002384 and ed. St. 1396617), including centrifugation of the sludge-salt mixture, followed by separation of the solid phases of the metal, oxides and salt. The methods are intended for the processing of melts containing magnesium, including in the form of small droplets with a diameter of less than 10 mm, are quite complex and time-consuming, require special sophisticated equipment and high labor costs.

A known method of processing waste light metals and alloys (ed. St. 1287604), including the melting of the metal in the flux melt, mixing and settling with additional treatment with a refining agent containing calcium fluoride and / or molten magnesium. The method is intended for use in the processing of scrap magnesium and magnesium alloys in salt furnaces with a volume of 12-15 m ³ . For turbulization of flows, compressed air is used. Such furnaces were operated at the Solikamsk Magnesium Plant until the end of the 20th century, and are now liquidated. To apply the method for crucible melting foundry splays of a different composition and structure than scrap, in the declared form is impossible and inappropriate. In addition, air additionally oxidizes and crushes magnesium, increasing losses.

The closest in terms of characteristics and adopted as a prototype is a method for processing metallurgical magnesium-containing waste according to auth. 1480360, including melting of waste in a flux medium at 730-760 ° C with a density lower than the density of the waste melt at a flux consumption of 8-10 wt.% From the waste mass, followed by treatment with calcium fluoride at its flow rate of 1-2 wt% from the waste mass. The method is used for waste with a density above 1.75 g / cm ³ and a molten flux density of less than 1.7 g / cm ³ . Melting is carried out in the crucible furnace SMT-2. Waste contains 25-52 wt.% Magnesium, 4-25% of magnesium oxide. Metal recovery reaches 74%.

The disadvantages of the prototype method in relation to the remelting of splash casting conveyor are:

- insufficient amount of flux in the crucible, because at the same time, the splash immersed in the crucible “lump” will not be covered by salt and will be intensively oxidized;

- high melting temperature, also contributing to the burning of magnesium;

- the need for a special composition of the flux;

- insufficient extraction of magnesium.

The aim of the proposed technical solution is to increase the extraction of magnesium from foundry splits during remelting in a crucible and to simplify the salt environment.

The technical result is achieved by using an electrolyte of electrolysis cells for producing magnesium with a ratio of electrolyte: waste (0.7-1.5): 1 as a flux, and melting is carried out at a temperature of 700-730 ° C with manual stirring of the bottom layers.

The electrolyte of electrolyzers is always available in the production of magnesium by electrolysis, and it is 0.03-0.05 g / cm ³ heavier than liquid magnesium, i.e. magnesium in it floats on the surface. The ratio in the crucible of electrolyte: splits (0.7-1.5): 1 ensures complete immersion of solid splashes in the molten salt, preventing oxidation. A temperature of 700-730 ° C is sufficient for a stable melting process of magnesium contained in the splits, without bringing it to combustion. Lowering the temperature to less than 700 ° C increases the melting time. Manual stirring of the bottom layers during melting contributes to the emergence of drops of magnesium that have fallen into the bottom layers during melting, giving the drops the necessary vertical acceleration.

The electrolyte composition of electrolyzers with a carnallite power scheme: 5-15% MgCl ₂ , 18-20% NaCl, 0.1-0.3% F ^- , KCl - the rest.

An example implementation of the method:

In the crucible of the SMT-2 furnace, 1 ton of electrolyte, which was brought to the foundry from the electrolysis section by a vacuum ladle, was poured, heated to 725 ° С, 700 kg of the splice of the casting conveyor previously warmed up on the furnace lid were loaded, the splash was melted for 2 hours, the bottom layers were processed with a manual stirrer, it was left for 20 min under the protection of a coating flux (~ 10 kg), transferred to another crucible to prepare alloys of 620 kg of magnesium, 10 kg of CaF ₂ were added to the remaining melt, mixed with a hand stirrer, stood for 10 minutes, another ~ 10 kg of magnesium was drained . Thus, ~ 630 kg of magnesium was recovered from 700 kg of splays. A sample of bottom crucible sludge showed that the amount of magnesium in it is ~ 6 kg.

We assume that ~ 30 kg of flux was loaded into the splits at the foundry conveyor to protect magnesium from burning during the collection of splashes, ~ 700 kg of magnesium and ~ 670 kg of magnesium and magnesium oxide were in splashes.

Extraction of magnesium was 630/670 = 94%.

Casting was carried out from a large-capacity furnace by an electromagnetic pump. When casting from crucibles, the oxidation of magnesium is more significant and experimental melts showed that the extraction of magnesium is from 74 to 80%.

The table shows the results of experimental swimming trunks justifying the values given in the claims.

Parameter The amount of salt, kg The number of splits, kg Received magnesium, kg Smelting time, hour Extraction of magnesium,% Note Temperature 600 ° C 700 600 420 4,5 73.0 Long time. low recovery 700 ° C 1000 800 616 3,5 80.0 715 ° C 1000 750 670 3.0 92.0 730 ° C 900 700 650 2,8 94.0 750 ° C 1000 800 570 2.5 75.0 Low recovery Salt: splash ratio 0.5: 1 500 1000 700 4.2 72.0 Long time, low recovery 0.7: 1 600 855 620 3.8 76.0 1.0: 1 800 800 650 3.6 86.0 1.3: 1 900 690 580 3.3 87.0 1.5: 1 1000 667 580 3.0 90.0 1.7: 1 1200 705 620 3.0 91.0 Net crucible volume decreases

At temperatures below 700 ° C, the melting time increases significantly, and hence the energy consumption, and in proportion to the loss of magnesium during combustion. At temperatures above 730 ° C, magnesium losses during combustion in a crucible increase.

With a salt: splash ratio of less than 0.7: 1, magnesium losses during combustion increase and melting time increases, with a ratio of more than 1.5: 1 the furnace’s magnesium output decreases.

It should be noted that the effectiveness of the method increases with automated monitoring and control of the process, i.e. minimize the "human factor".

Thus, the proposed technical solution provides an increase in magnesium extraction to 76-94% with a fairly simple technology and available salt.

Claims (1)

A method of extracting magnesium from waste generated during casting of magnesium on a casting conveyor, including crucible melting of waste in a flux containing magnesium, sodium and potassium chlorides, settling, draining of magnesium, treatment with calcium fluoride, characterized in that the electrolyte for producing electrolysers is used as a flux magnesium in the carnallite diet, which is 0.03-0.05 g / cm ³ heavier than liquid magnesium and contains 5-15% MgCl ₂ , 18-20% NaCl, 0.1-0.3% F ^- , KCl - the rest, they are melted with the ratio of electrolyte: waste (0.7-1.5): 1 and at a temperature of 7 00-730 ° C with manual stirring up of the bottom layers, the residue of the melt is subjected to treatment with calcium fluoride after draining the magnesium, and it is carried out with manual stirring, settling and draining of magnesium.