RU2165990C1 - Method of processing magnesium slags containing metallic magnesium, magnesium oxide and chlorides - Google Patents

Abstract

FIELD: foundry; applicable in production of magnesium-containing alloying composition from magnesium slags containing metallic magnesium, magnesium oxide and chlorides, and in production of castings from spherulitic iron. SUBSTANCE: method includes preparation of special melt based on silicon and/or copper; maintenance of melt temperature in its combination with slag between melting temperature of chloride salts and temperature of their volatizing; filling of space in which melt is combined with magnesium slag with protective gas; combination of melt with magnesium slag. EFFECT: higher economic efficiency of method due to combination of magnesium recovery from magnesium slag, and preparation of alloying compositions for production of castings from spherulitic iron. 4 cl, 1 dwg, 4 tbl

Description

 The invention relates to foundry and can be used to obtain a magnesium-containing ligature based on silicon or (and) copper and magnesium dissolved in them from magnesium slags containing magnesium metal, chloride salts and magnesium oxide. The magnesium-containing ligature is then used to produce nodular iron castings.

 At present, in enterprises producing castings of magnesium alloys by injection molding, the problem of processing the resulting magnesium slag containing chloride salts is very urgent. So, at one of the well-known enterprises of magnesium slag several hundred tons have already accumulated. Slag of this enterprise have the composition shown in table. 1.

 Magnesium-containing slag is formed during the smelting of the charge in the CAT-0.15 electric furnace due to oxidation of magnesium and the precipitation of magnesium oxide particles to the bottom of the crucible during refining of the finished alloy by flux from chloride salts.

 The amount of flux used for smelting is 2.8-3.0% of the weight of the alloy in the furnace. Magnesium-containing slag formed at the bottom of the crucible of the furnace is recovered through the thickness of the liquid alloy. It is a conglomerate of entangled magnesium alloy in a flux oxide mixture and structurally consists of a framework (skeleton) of a magnesium alloy, as well as small and large inclusions of a flux oxide mixture, in which inclusions of metal particles of various sizes can be found.

 Goskomekologiya does not allow the removal of these slags for disposal, in particular, due to the high content of magnesium in them.

 Known solutions for the processing and use of these magnesium slags do not find practical implementation for several reasons.

 In the table. 2 presents technical solutions for the processing of magnesium slag, selected as analogues.

According to the technical nature of the prototype, the method should be adopted, which consists in melting an aluminum alloy, coating it with flux and introducing magnesium waste under a melt level having a temperature of 660-720 ^o C (M. B. Altman and others. Melting and casting of light alloys. M. , Metallurgy, 1960, p. 317).

 The purpose of the invention is to dissolve magnesium from magnesium slags containing magnesium metal, chloride salts and magnesium oxide in molten metals based on silicon and / or copper to obtain alloys for the production of nodular iron castings.

The proposed method for the processing of magnesium slag containing metallic magnesium, chloride salts and magnesium oxide, to obtain alloys for the production of iron castings with spherical graphite includes:
preparation of a molten metal based on silicon or copper;
maintaining the temperature of the melt when combined with magnesium slag within the range between the maximum melting point of chloride salts and the minimum boiling point;
filling the space in which the melt and magnesium slag are connected with a protective gas, in particular nitrogen;
the connection of the melt and magnesium slag containing magnesium metal, chloride salts and magnesium oxide.

The main difference between the proposed method and the prototype is that, firstly, the melt is prepared not on the basis of aluminum, but silicon or copper, and secondly, the temperature of the melt when combined with slag is maintained between the maximum melting temperature of chloride salts ( 960 ^o C) and a minimum boiling point (1413 ^o C), thirdly, a protective gas, in particular nitrogen, is supplied into the space in which the melt and magnesium slag are connected.

 The first two distinguishing features are of fundamental importance. It is their combination that allows the processing of magnesium slag containing metallic magnesium, chloride salts and magnesium oxide, with the formation of ligatures for the production of castings from cast iron with spherical graphite.

 Silicon and / or copper, on the basis of which the melt is prepared, dissolve magnesium well and do not reduce the casting and strength properties of cast iron, but, on the contrary, have a positive modifying and alloying effect on cast iron. Aluminum cannot be used as the basis for preparing the melt and obtaining a ligature for the modification of ordinary cast irons, since its ingress into cast iron in amounts of more than 0.15% leads to defects in castings and is therefore unacceptable.

It is also important to maintain the temperature of the melt at the time of its connection with the slag between the maximum melting point of chloride salts and the minimum boiling point. Maintaining the melt temperature above the maximum melting point of chloride salts (960 ^o C) contributes to the rapid melting of chloride salts and the establishment of direct contact between the melt and magnesium in the slag and accelerate its dissolution in silicon or copper. Maintaining the melt temperature below the minimum boiling point of chloride salts (1413 ^o C) reduces the bubbling, emissions of the melt and the smoke of the atmosphere of the melting site.

The combination of the melt and slag at a temperature below the maximum boiling point of chloride salts is achieved by introducing other elements into silicon or (and) copper that lower the melting point (solidification) of the melt. For example, the introduction of 8-10% Si into copper reduces the melting point (solidification) from 1089 ^° C (for copper) to 875 ^° C and makes it possible to melt and magnesium slag at a temperature of 960 ^° C and higher. The introduction of silicon 40-50% iron allows you to reduce the melting point (solidification) of the melt from 1423 ^o C [1] to 1220 ^o C and to connect the melt and magnesium slag at a temperature below the minimum boiling point of chloride salts - at a temperature of 1300-1400 ^o C In addition, iron and copper perform another important function - weighting of the melt, due to which there is an accelerated floating (separation) of the flux-oxide mixture. Of course, the melt-slag compound temperature is most preferred between the melting point of chloride salts (960 ^° C.) and the boiling point of magnesium (1120 ^° C.). In this case, due to the exclusion of boiling magnesium, the pyroeffect and bubbling are even more reduced. The aforementioned can practically be realized when using copper-based melts, in particular, with a silicon content of 6 - 12% and, unfortunately, is not possible when using silicon-based melts. For this reason, copper-based melts are more preferable, but due to the high price of copper compared to silicon, copper-based alloys are about two times more expensive than silicon-based alloys. It is economically feasible to use copper-based ligatures to produce castings from cast iron, which should be alloyed with copper. For ordinary (unalloyed) cast irons, the use of silicon-based alloys is economically preferable. In this case, it is necessary to connect the melt and magnesium slag at a temperature above the boiling point of magnesium.

 The introduction of a protective gas, in particular nitrogen, into the space in which the melt and magnesium slag are connected increases the degree of absorption of magnesium from magnesium slag, and reduces the pyroelectric effect and the amount of smoke emissions.

 The description deliberately uses the expression "compound of the melt and magnesium slag" instead of, for example, the expression "input of magnesium slag into the melt." This is due to the fact that the connection of the melt and magnesium slag can be carried out by introducing magnesium slag into the melt located in the furnace (ladle, other vessel), or by filling the vessel with the melt (furnace crucible, ladle, mold, etc.) with it located magnesium slag. The choice of the method of combining the melt and magnesium slag depends on a number of circumstances: in particular, the type of melting furnace available, the requirements for the ligature, in particular, the quantity and limits of the magnesium content in it; other possibilities and specific conditions in the foundry.

 For example, when preparing a melt in an arc furnace and a relatively low magnesium content in the ligature (up to 5-7%), it may be more acceptable to pour the melt onto solid magnesium slag located in a ladle or in another special container. In this case, the space in the bucket or other container, with magnesium slag located in them, must be filled with nitrogen before the melt is poured into them. The advantages of this method of connection should include its mobility and performance; the disadvantages are the difficulty of obtaining a ligature with a strictly defined magnesium content due to possible fluctuations in the magnesium content in the slag.

 With a relatively high content of magnesium in the ligature (10-15%), narrow limits on the deviation in the magnesium content in the ligature and the presence of an induction furnace in the workshop, the introduction of solid magnesium slag into the melt located directly in the furnace, for example, using a bell, will be more acceptable. The advantage of this method is the possibility of obtaining a ligature with the required magnesium content; the disadvantage is the need for bells. In this case, after carrying out an express analysis for magnesium and in the presence of a deviation of the magnesium content from a given one, it is possible to introduce an additional calculated amount of magnesium slag based on the analysis data. Before introducing an additional amount of magnesium slag, the melt, as a rule, will need to be heated.

 If there are two or more melting furnaces at the production site, magnesium slag and silicon or / and copper melt can be combined by pouring the melt into magnesium slag, in which magnesium metal is in the molten state (mainly between particles of chloride salts and magnesium oxide). When pouring a melt of silicon and / or copper onto magnesium slag with liquid magnesium, magnesium dissolves in silicon and / or copper, and chloride salts and magnesium oxide float to the surface of the ligature melt due to a significant difference in the density of the melt and the flux-oxide mixture. As an advantage of this method of combining a melt and magnesium slag, it is possible to note the possibility of using a silicon melt and / or copper with a lower temperature; as a disadvantage, the need to have two melting furnaces.

 Below are examples of the proposed method and the results obtained.

Example 1. A graphite crucible was installed in the stuffed crucible of the IST-0.16 furnace and 5 kilograms of copper were melted, then 0.5 kilograms of silicon were introduced into the melt. The introduction of silicon was carried out to reduce the melting point (solidification) of the melt. After the dissolution of silicon at a melt temperature of 1000 ^o C over the crucible of the furnace installed cap with a bell rod threaded through the opening of the cap. The bell contained 0.4 kilograms of magnesium slag containing about 45% magnesium. From the cylinder, nitrogen was fed through a flexible hose under the cap and the bell was introduced into the melt. After the end of the twitching of the bell, which indicates the end of the dissolution of magnesium, the nitrogen supply was turned off and the bell was removed from the melt, the cap was removed. Then the slag was removed from the melt surface, the melt was heated to 1100 ^° C; the cap with the bell was again installed, nitrogen was supplied, 0.4 kilograms of magnesium slag was introduced into the melt, the nitrogen supply was turned off, the bell and cap were removed. Again, the slag was removed from the surface of the melt, a bell with a bell was installed, nitrogen was fed and at a temperature of 940 ^° C 0.3 kilograms of slag were introduced, the bell and bell were removed. In the latter case, about a quarter of the introduced magnesium slag turned out to be unreacted - the low temperature of the melt did not allow the chloride salts to melt and this slowed down the dissolution of magnesium from magnesium slag. The melt was heated to 950 ^o C, the slag was removed from the surface of the melt and the ligature melt was poured into the mold.

The resulting composition ligature,%:
Cu - 80
Mg - 7.5
Si - 9.2
Al - 0.9
Zn - 0.4
Fe - Else
tested to modify cast iron.

The chemical composition of cast iron after modification,%:
C - 3.4
Si - 2.95
Mn - 0.28
P - 0.12
Cr - 0.03
Cu - 1.32
Al - 0.05
S - 0.05
Zn - <0.005
In the table. 3 shows the properties of cast iron modified by the resulting alloy.

 In the table. 4 shows a comparison of the properties of cast iron obtained by modification with a master alloy made by the proposed method, and cast iron according to GOST 7293-85 (corresponding grades VCh 50, VCh 70, VCh 80). The properties of the obtained cast iron significantly exceed the properties of cast iron of the corresponding grades given in GOST 7293-85.

 An analysis of the results indicates that the proposed method for processing slag in a copper melt to obtain a magnesium-containing ligature is practically feasible, and the ligature can be used to produce castings from cast iron with spherical graphite. Photos of the microstructures of the obtained cast irons are shown in the drawing.

Example 2. In an IST-0.16 furnace, 50 kilograms of an alloy of 60% silicon and 40% iron were melted. The main function of iron is to lower the melting point of the melt (from 1423 ^o C to 1200-1220 ^o C). A cap with a bell rod threaded through the opening of the cap was installed over the crucible of the furnace. The bell contained 8 kilograms of magnesium slag containing about 50% magnesium. From the cylinder, nitrogen was fed through a flexible hose under the cap. 10 seconds after the start of the supply of nitrogen into the melt at a temperature of 1380 ^o C introduced a bell with magnesium slag. After the dissolution of magnesium from the slag, as evidenced by the termination of the vibration of the bell, the flow of nitrogen was stopped. The bell was removed from the melt. Removed the bell cap from the crucible of the furnace. They removed the slag from the surface of the melt. Conducted rapid analysis of the melt for magnesium content. Its content was equal to 7.5%. The required magnesium content is 9 ± 0.5%. Calculated the additional amount of magnesium slag (Q _W ) in kg, which must be entered in order to reach the required magnesium content in the ligature. The calculation was made according to the formula
Q _W = P _W · (C _t - C _a ) (1 + C _a : 100): C _a ,
where P _W - the amount of magnesium slag introduced into the melt, kg;
C _t - the required magnesium content in the ligature,%;
C _a - magnesium content in the melt according to the express analysis,%.

Placed in the bell the estimated amount of magnesium slag:
8 · (9.25-7.5) (1 + 0.075); 7.5 = 2 kg.

The melt was heated to a temperature of 1350 ^o C. A bell rod was pierced through the hole in the bell, a bell and bell were installed over the crucible of the furnace, nitrogen was fed into the space above the melt and the bell was introduced into the melt. After the dissolution was completed, the nitrogen supply was shut off from the magnesium slag, the bell was removed from the melt, the bell and cap were removed, the slag was removed from the melt surface, the resulting ligature melt was released into a casting ladle and poured into molds.

Analysis of the ligature showed the following composition:
Mg = 9.1%; Si = 55%; Al = 0.5%; Zn = 0.1%; Fe is the rest.

 The proposed method allows the processing of magnesium slag with a significant economic effect by combining the process of extracting magnesium from magnesium slag and preparing a master alloy for the production of castings from cast iron with spherical graphite.

 Industrial use of the proposed method will allow us to solve not only a purely economic problem as a result of the production of ligatures based on magnesium extracted from slag, but will also contribute to solving the environmental problem by removing magnesium from the slag and reducing the slag volume by 30-40% compared to the original volume.

LITERATURE
1. The table of physical quantities. Directory. Ed. Acad. I.K. Kikonin. M., Atomizdat, 1976, 1008 pp.

 2. Brief chemical encyclopedia in five volumes. Moscow, 1961. Publishing house "Soviet Encyclopedia". Volume 1, p. 378.

Claims (4)

1. A method of processing magnesium slag containing magnesium metal, chloride salts and magnesium oxide, including the preparation of a molten metal and a compound of a molten metal and magnesium slag, characterized in that silicon and / or copper are used as the base of the melt, the temperature of the melt when it is connected to slag is maintained within the range above the maximum melting point of chloride salts, equal to 960 ^o C, and below the minimum boiling point, equal to 1413 ^o C.  2. The method according to claim 1, characterized in that a protective gas is supplied into the space in which the melt and magnesium slag are connected.  3. The method according to claim 1, characterized in that nitrogen is used as the protective gas. 4. The method according to claim 1, characterized in that the melt temperature for copper-based alloys is maintained above the melting point of chloride salts, equal to 960 ^o C, and below the boiling point of magnesium, equal to 1120 ^o C.

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