RU2103401C1 - Method of aluminothermic production of metal chromium - Google Patents

Abstract

FIELD: nonferrous metallurgy. SUBSTANCE: method includes stepped loading and melting charge containing chromium oxide, oxidant, lime, and aluminum, after which molten products are discharged. In the first step, charge to be melted contains (in % based on total weight of components in the overall process): chromium oxide, 53-64; oxidant, 60-80; lime, 30-40, and aluminum in quantity constituting 0.8-0.94 stoichiometrically required amount to reduce chromium oxide, charge loading rate being 180-280 kg/sq.m. In the second step, corresponding values are as follows: 36-47, 20-40, 60-70, 1.02-1.2, and 170-275. When chromium metal with low nitrogen content (at most 0.05%) is produced, charge in the both steps contains, as oxidant, chromic anhydride and potassium bichromate or sodium with added calcium hydroxide, sodium chloride, and fluorite concentrate in proportion to the weight of used chromium oxide: (0.1-0.2):(0.02-0.04):(0.03-0.08):(0.001-0.02):(0.001-0.02):1. EFFECT: enhanced efficiency of process. 2 cl, 1 tbl

Description

 The invention relates to the field of metallurgy, in particular, to a method for aluminothermic production of metallic chromium.

 There is a method of aluminothermic production of metallic chromium, which consists in loading and melting a mono-mixture consisting of chromium oxide, an oxidizing agent / sodium nitrate /, lime and aluminum, followed by the discharge of smelting products.

 To obtain chromium with a low nitrogen content / ≤0.05% / in the composition of the charge, chromic anhydride and potassium dichromate with the addition of calcium hydroxide, sodium chloride and fluorite concentrate are used as an oxidizing agent [1].

 The disadvantage of this method is the low extraction of chromium (90-91%), which is associated with the melting of the charge and the occurrence of reduction reactions of chromium oxides on the surface of the melt (top) and a decrease in the efficiency of use of aluminum.

 A known method of aluminothermic production of refractory metals, in particular, metallic chromium, including stage loading, smelting the charge and the release of smelting products.

 At the first stage of melting, the entire mass of the oxidizing agent — chromic anhydride, lime and aluminum in the amount of 0.2–0.75 of the stoichiometrically necessary for the reduction of chromium oxides from oxide and chromic anhydride — the amount of which is 10–50% of the total mass for melting, is loaded.

 At the second stage, the remaining part of chromium oxide and aluminum is loaded and melted in the amount of 1.1-1.65 of the stoichiometrically necessary for the reduction of chromium oxides [2].

 The disadvantage of this method is the freezing of metal and the formation of deposits in the smelter and a decrease in yield, which is associated with deposition at the first stage of melting of metal in small quantities (up to 20% of the total mass) and increased heat loss at the beginning of melting.

The closest technical solution to the invention is a method of aluminothermic production of chromium (prototype), which includes stage loading and melting of the charge and the release of smelting products. At the first stage, the charge components are melted, containing 55-75% of chromium oxide from the total mass for melting, the entire mass of the oxidizing agent - sodium nitrate, lime and aluminum in the amount of 0.77-0.92 of the stoichiometrically necessary for the reduction of chromium oxide with a loading speed charge 180-260 kg / m ² min.

At the second stage of melting, the remaining chromium and aluminum oxide are loaded and melted in an amount of 1.1-1.65 of the stoichiometrically necessary for the reduction of chromium oxide with a charge loading speed of 130 kg / m ² min. [3].

 The technical result of this invention is to increase the extraction of chromium in the metal and improving the quality of the alloy.

The technical result is achieved due to the fact that the proposed method of aluminothermic production of metallic chromium involves the stepwise loading and melting of a mixture containing chromium oxide, oxidizing agent / sodium nitrate or chromic anhydride /, lime, aluminum and the release of smelting products. At the first stage, the charge is melted, consisting of components from the total mass for melting; chromium oxide 53-65%, oxidizing agent 60-80%, lime 30-40 and aluminum in an amount of 0.8-0.94 of the stoichiometrically necessary for the reduction of chromium oxide with a charge loading rate of 180-280 kg / m ² • min.

At the second stage, the charge components are melted from the total mass for melting: chromium oxide 36-47%, oxidizing agent 20-40%, lime 60-70% and aluminum in the amount of 1.02-1.02 from the stoichiometrically necessary for the reduction of chromium oxide with the loading speed of the batch is 170-275 ^o kg / m ² • min, and upon receipt of metallic chromium with a low nitrogen content / 0.05% / in the composition of the charge at both stages in the amount of oxidizing agent, chromic anhydride and potassium or sodium dichromate are added with additions the mixture of calcium hydroxide, sodium chloride and fluorite concentrate in the ratio to the weight of the sample of chromium oxide / 0.1-0.2 /: / 0.02-0.04 /: / 0.03-0.08 /: / 0.001-0.02 /: / 0.001-0.02 /:
The following are examples characterizing the proposed method.

 Example 1 (prototype).

Smelting of metallic chromium by an aluminothermic out-of-furnace method was carried out in laboratory conditions. The mixture was divided into 2 parts, smelting 32.5 kg of chromium oxide, 3 kg of sodium nitrate, 3 kg of lime and 11.4 kg of aluminum / total / for the restoration of sodium nitrate 1.6 kg, the rest 0.85 stoichiometrically necessary to reduce chromium oxide / with a charge loading speed of 180 kg / m ² min., in the second stage of melting melted 17.5 kg of chromium oxide and aluminum 8.1 kg with a charge loading speed of 130 kg / m ² min. The extraction of chromium in the heat of 94.2% / table 1 /.

 Example 2

 Smelting of metallic chromium with obtaining a low nitrogen content was carried out in an industrial environment by melting a mono-mixture consisting of 4620 kg of chromium oxide, 600 kg of chromic anhydride, 120 kg of potassium dichromate, 300 kg of lime, 160 kg of calcium hydroxide, 60 kg of sodium chloride and aluminum 1950 kg.

 After melting the mono-charge, 40 kg of fluorite concentrate were given to the melt and the melting products were drained. Received chrome brand X99H-4. The extraction of chromium in the metal was 90.38%.

 The proposed method for producing metallic chromium is tested in an industrial environment according to the described technology.

 The results of the heats of the known method (examples 1, 2) and the proposed (examples 3-11) are shown in the table.

 Example 3

 In the melting furnace, a stage loading and melting of the charge was carried out with the subsequent release of smelting products.

At the first stage of melting, a mixture of composition was loaded and melted: chromium oxide - 2600 kg, sodium nitrate - 240 kg, lime on top - 130 kg and aluminum 995 kg with a charge loading speed of 220 kg / m ² • min.

In the second stage, the charge was loaded and melted: chromium oxide 2300 kg, sodium nitrate - 130 kg, lime - on the top - 190 kg and aluminum 905 kg, with a charge loading speed of 210 kg / m ² • min.

 Further reduction of aluminum deficiency in the first stage and excess in the second stage of the smelting process reduces the efficiency of aluminum in smelting by reducing the deep reduction of chromium oxides in the second stage, which increases the aluminum content in the alloy and reduces chromium extraction.

 Example 4

 A charge was gradually loaded and melted into the smelting furnace with the subsequent release of smelting products.

At the first stage, a mixture of composition was loaded and melted: chromium oxide - 3140 kg, sodium nitrate - 290 kg, lime was set on top - 95 kg. and aluminum 1120 kg with a charge loading rate of 200 kg / m ² • min. In the second stage, the charge was loaded and melted: chromium oxide 1760 kg, sodium nitrate - 70 kg, lime on the top - 225 kg, and aluminum 780 kg with a charge loading speed of 170 kg / m ² min.

 A further increase in the excess of aluminum in the second stage and a decrease in the termite additive (sodium nitrate) in the second stage of smelting leads to a violation of the charge penetration - the charge is melted unevenly and the smelting proceeds violently with melt emissions, which reduces the degree of aluminum utilization and chromium extraction.

Example 5-9 / table 1 /
In the correct hearth, stage loading was carried out, the charge was melted, followed by the release of smelting products.

At the first stage, the mixture was melted: chromium oxide - 2940 kg, sodium nitrate - 240-2 50 kg, lime on the top 120 kg and aluminum in the amount of 1045-1055 kg with a charge loading speed of 185-230 kg / m ² • min, the second stage melted the mixture composition: chromium oxide - 1960 kg, sodium nitrate - 120-130 kg, lime on the top 180-200 kg and aluminum 845-855 kg with a charge loading speed of 240-275 kg / m ² • min. Swimming trunks flowed quietly. When the charge was melted at the second stage, “instrumentation” was observed on the melt surface as a result of the deep reduction of chromium oxides. The degree of use of aluminum was 99.6-99.8% (the ratio of aluminum spent on the reduction of oxides to the total amount). Received metal chromium grade X-99, the extraction of chromium in swimming trunks was 94.3-94.9%.

 Example 10-11

 Smelting of metallic chromium was carried out in order to obtain a low nitrogen content in the alloy. Chromic anhydride and potassium dichromate with the addition of calcium hydroxide, sodium chloride and fluorite concentrate were specified as an oxidizing agent in the charge. The mixture was divided into two parts in the indicated ratios of the components (table), loaded and smelted in stages in the smelter, followed by the release of smelting products.

 Received standard metallic chromium with a low nitrogen content / ≤ 0.04% / brand X99N-4. The extraction of chromium into metal amounted to 92.6-93.2%, which is 2.2-2.8% higher than the extraction of chromium obtained by melting the components of the charge with a mono-charge (table).

The technological difference of the proposed method from the known one is that at the first stage of melting, the minimum amount of lime (30-40% of the total mass) is melted, which is necessary for binding alumina (Al ₂ O ₃ ) in the slag and reducing the viscosity of high-alumina slag.

A further increase in calcium oxide in the slag reduces the extraction of chromium, which is associated with the formation of calcium chromates and a decrease in the activity of Cr ₂ O ₃ .

 In the second stage of smelting, up to 20-40% of the oxidizing agent and the rest of the lime are melted in the mixture, which ensures uniform heat generation and, from the occurrence of exothermic reactions, the optimum temperature of the smelting process and the fluidity of high-alumina slag are maintained.

 Moreover, the introduction of lime charge improves the thermal conditions of smelting, reduces the contact of lime with the resulting drops of metal, reducing clogging of the alloy with carbon.

According to the proposed method, the rational distribution of the charge components in the indicated ratios over the melting stages and their melting ensures the optimal heat of the process (19-20 Kcal / gr.at) and high charge loading speed (170-280 kg / m ² • min), which is crucial to maintain the optimum temperature of the aluminothermic process of chromium smelting and increase the conditions for the efficiency of using aluminum for the reduction of chromium oxides: at the first stage of melting - due to the excess concentration of chromium oxides relative to the reducing agent s, in the second stage with excess aluminum - due to the surface and deep reduction of chromium oxides from chromium oxide and slag melt with a Cr ₂ O ₃ content _of 13-18%, from the melting of the charge in the first melting stage.

 The extraction of chromium in the metal amounted to 94.3-94.9%, which is 0.7% higher than the extraction according to the known method.

 Reducing aluminum in the metal by increasing the efficiency of its use and silicon - due to its underreduction with a lack of a reducing agent at the 1st stage of smelting and increasing the extraction of chromium into metal, provides the production of X-99 grade metal chromium.

Claims (2)

1. A method for aluminothermally producing metallic chromium, comprising the stepwise loading and melting of a mixture containing chromium oxide, an oxidizing agent, lime, aluminum, and the release of smelting products, characterized in that in the first stage, the mixture is melted, consisting of components from their total mass for melting : chromium oxides 53 64% oxidizing agent 60 80% lime 30 40% and aluminum in the amount of 0.8 0.94 of the stoichiometrically necessary for the reduction of chromium oxide with a charge loading rate of 180 280 kg / m ² • min, at the second stage components are melted charge of the total weight for melting: chromium oxide 35 47% oxidizing agent 20 40% lime 60 70% and aluminum in the amount of 1.02 1.2 of the stoichiometrically necessary for the reduction of chromium oxide with a charge loading rate of 170 275 kg / m ² • min.  2. The method according to p. 1, characterized in that when producing chromium metal with a low nitrogen content <0.05% in the mixture in both stages, chromic anhydride and potassium or sodium dichromate are added as an oxidizing agent with the addition of calcium hydroxide, cooked to the mixture salt and fluorite concentrate in the ratio to the mass of chromium oxide (0.1 0.2) (0.02 0.04) (0.03 0.08) (0.001 0.02) (0.001 0.02) 1.0.

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