RU2115747C1 - Method for reducing metals from mixture of their oxides - Google Patents

Abstract

FIELD: pyrometallurgy, in particular, reduction of metals with solid carbon from mixture of metal oxides dissolved in melt of halides of alkali and/or alkali-earth metals. SUBSTANCE: method includes dissolving of oxides in melt of halides of alkali and/or alkali-earth metals, liquid-phase reduction of oxides with solid carbon at preset temperature, continuous separation of reduced metal from melt-solvent. The latter is repeatedly used for dissolving of initial product. Reduction of less strong oxide is carried out with maintaining its concentration higher than that of stronger oxide. For this purpose. initial product is continuously loaded. When concentration of stronger oxide reaches the concentration of less strong oxide, dissolving of initial product in melt is discontinued and mixture of oxides is reduced by separation of produced alloy from melt-solvent separately from metal reduced from less strong oxide. EFFECT: provision of selective reduction of metals with solid carbon from mixture of their oxides dissolved in melt of halides of alkali and/or alkali-earth metals. 5 tbl

Description

 The invention relates to pyrometallurgy, in particular to the reduction by solid carbon of metals from a mixture of their oxides dissolved in a melt of alkali and / or alkaline earth metal halides.

 In ore dressing and concentrate processing, in many cases semi-products are obtained, which are a mixture of several metal oxides. The separation or purification of ferrous metal resulting from the recovery of such an intermediate is carried out using complex metallurgical processes. An urgent task is the separation of metals at the stage of their reduction from a mixture of oxides.

 A known method of reducing iron from ore-flux melts with carbon, in which a solid carbon reducing agent (semi-coke) interacts in a melt bath with iron oxides and restores them with the release of carbon monoxide [1].

 The disadvantage of this method is that the carbon monoxide released during the reaction due to the increase in melt viscosity due to heat absorption in the reaction zone foams the melt in the furnace bath, interrupting the process.

 A known method for producing iron, including liquid-phase reduction of iron oxides with a solid carbon reducing agent, in which a mixture of ore with lime and coal is introduced from above into a bath of a furnace with a foamed melt of oxides, and natural gas and oxygen are blown from below [2].

 The disadvantages of the method include the complexity of the technical performance, low productivity and technological process instability.

 The known method adopted for the prototype, the production of metals and alloys, including the dissolution of oxides in a melt of halides of alkali and / or alkaline earth metals and liquid-phase reduction of oxides from a solution of them in a melt-solvent, characterized in that the reduction of the oxides is carried out with solid carbon at a temperature corresponding to energy their formation, and after the reduction of the oxides, the melt-solvent is separated from the metal and reused to dissolve the starting product [3].

The disadvantage of the method adopted as a prototype is the impossibility at a given melt temperature of selective separation from a metal melt-solvent of a metal recovered from a less energy-intensive oxide, provided that at this temperature it is thermodynamically possible to recover several oxides at once. For example, when using calcium fluoride CaF ₂ as a melt-solvent contained in fluorspar, at a melt temperature above the melting point of the specified solvent (1418 ^° C), several metals can be reduced and extracted into the alloy at once, for the oxides of which the thermodynamic potential of the reaction is changed ΔG recovery $\genfrac{}{}{0ex}{}{\text{o}}{\text{t}}$ <0..

 The objective of the invention is the selective recovery of solid carbon metals from a mixture of their oxides dissolved in a melt of halides of alkali and / or alkaline earth metals.

The solution to the problem is due to the fact that all the oxides of the elements in terms of their affinity for oxygen or in terms of bond strength with oxygen, or in terms of the heat of formation $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ or by the value of the standard Gibbs energy ΔG $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ can be arranged in a series of gradual increase of the indicated values, if the value of kcal / mol O _{2 is} taken as the unit of measurement of the indicated values. The values of the heats of formation of some oxides taken on the monograph [4] are presented in table. 1.

Ag ₂ O - 14.6
CuO - 74.2
Bi ₂ O ₃ - 90.0
PbO - 104.9
Sb ₂ O ₃ - 112.8
CoO - 114.2
NiO - 115.0
MoO ₃ - 118.7
FeO - 126.4
SnO ₂ - 138.8
P ₂ O ₅ - 146.3
V ₂ O ₅ - 148.0
Cr ₂ O ₃ - 180.0
MnO - 184.0
ZnO - 187.6
SiO ₂ - 217.6
TiO ₂ - 225.8
Al ₂ O ₃ - 253.2
ZrO ₂ - 263.1
BaO - 264.6
MgO - 286.7
CaO - 303.2
Each subsequent metal in the series presented is a reducing agent for all oxides of previous metals (such reactions occur in almost all processes where the metal and oxide phases exist). Therefore, not a single subsequent metal oxide in the present energy series can be completely reduced until all previous metal oxides have been reduced. The degree of reduction by solid carbon from a solution of a mixture of oxides of each subsequent metal oxide in the presented energy series depends on the degree of reduction of all previous oxides and on the numerical difference in the strength characteristics of the reduced oxides.

When recovering metals from a solution of a mixture of their oxides, the metal whose oxide has the lowest ΔH $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ . . The content in it of a metal whose oxide has a higher ΔH $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ will be the smaller, the greater the difference in ΔH $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ reducible oxides and the higher the concentration in the solution of a less durable oxide.

 The specified technical result is achieved in that in a method for the selective reduction of metals from a mixture of their oxides, including the dissolution of oxides in a melt of halides of alkali and / or alkaline earth metals, liquid-phase reduction of oxides with solid carbon at a given temperature, continuous separation of the reduced metal from the melt-solvent, which is repeatedly used to dissolve the starting product, according to the invention, the reduction of a less durable oxide is carried out, maintaining in the melt-solvent its concentration is barely higher than the concentration of the stronger oxide, by continuously loading the initial product, and when the concentration of the stronger oxide reaches the concentration level of the less durable oxide, the initial product dissolves in the solvent melt and the oxide mixture is restored, separating the resulting alloy from the solvent melt in isolation from the metal reduced from a less durable oxide.

 The effect of selective reduction of metals from a mixture of their oxides is achieved by the fact that when the oxides in the melt-solvent are maintained in an excess concentration of a less durable metal oxide, a more durable metal oxide is not restored until its oxide concentration reaches a concentration level of a less durable oxide, after which the loading of the starting product into the melt-solvent is stopped and all dissolved oxides are reduced together, and the resulting alloy is removed from the solution separately from the metal, anovlennogo from less durable oxide.

 The method is as follows.

In the bath of an electric arc furnace, lined with carbon mass, or equipped with water cooling to form a skull, a fluorspar is loaded, melted in an arc mode and brought to a liquid-mobile state in the ore-thermal mode. Then, a mixture consisting of a mixture of metal oxides and a carbon reducing agent (coke) is continuously charged into the furnace bath. In this case, metal oxide with a smaller value of ΔH $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ reduced and continuously separated from the melt-solvent, and metal oxides with a larger value of ΔH $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ ,, accumulate in the solvent melt. When an equal concentration level is reached (according to chemical analysis and theoretical calculations), the starting product is stopped loading, the metal oxides remaining in the solvent melt are reduced together, and the resulting alloy is separated from the solvent melt.

 Examples of the method.

 Example 1 (prototype). In the experiment, an electric arc furnace with a capacity of 100 kVA was used, which allows loading up to 100 kg of charge materials. 50 kg feldspar was loaded into the furnace bath with carbon lining, which was melted in an arc mode and brought in a liquid-ore mode to a liquid-mobile state within 25-30 minutes. Then, in the furnace bath, redistributed low-phosphorous manganese slag (MFS) in the amount of 40 kg and metallurgical coke in the amount of 8 kg were loaded. The duration of the experiment since loading the charge was 45 minutes

 Chemical analysis of the initial low-phosphorous slag and the resulting products are given in table. 2.

 From the above chemical analysis data it follows that the oxides of iron and phosphorus, as the least durable, were the first to recover completely from their solution in the melt. Manganese oxide was reduced solely until its concentration in the solution was equal to the concentration of silicon oxide, after which silicon was actively restored, the content of which in the alloy reached 10%.

 Example 2 (prototype). A 40-kVA electric arc furnace, which allows loading up to 100 kg of charge materials equipped with a carbon lining, was loaded with 15 kg fluorspar, which was melted and brought to a liquid-mobile state within 25-30 minutes. Then, nickel cinder in the amount of 31.5 kg and metallurgical coke in the amount of 8 kg, containing C - 69.7%, ash - 23.4% were loaded into the furnace bath. The duration of the reduction smelting was 0.5 h; its end was recorded by the absence of a flame of burning carbon monoxide above the furnace bath. As a result of melting, a metal ingot weighing 24.2 kg and slag in the amount of 13.6 kg were obtained.

 Chemical analysis of the initial cinder, as well as the resulting metal and slag are given in table. 3.

 From a chemical analysis of the products obtained, it is seen that all the metal oxides contained in the cinder have recovered almost completely.

 Example 3 (by the proposed method).

In the experiment, a three-phase electric arc furnace with a capacity of 4000 kVA was used. 1100 kg of fluorspar were loaded into the skull bath of the furnace, which was melted in an arc mode and brought to a liquid-fluid state in ore-thermal mode. For three hours, iron ore was continuously loaded into the melt in the amount of 1800 kg, class - 30 mm, of the following composition,%: Fe - 56.28; FeO - 2.78; CaO - 0.54; MgO - 0.17; SiO ₂ - 12.85; S 0.155; P is 0.01; p.p.p. - 4.08; and metallurgical coke in the amount of 400 kg, class - 10 mm, chemical composition,%: ash content - 36.31; S _total - 0.545; P _ash - 0.056.

 Immediately after loading, the melt was frozen.

 As a result of reduction melting, 635 kg of metal was obtained.

 Chemical analysis of the obtained metal and slag are given in table. 4.

 From the chemical analysis it is seen that, while maintaining a concentration of iron oxides in the melt-solvent exceeding the concentration of silicon oxide by 2.5 times, silicon practically does not recover and does not transfer to metal. This makes it possible to obtain high-purity iron directly from iron ores and concentrates.

 Example 4 (by the proposed method).

 A 40-kVA electric arc furnace, which allows loading up to 100 kg of charge materials equipped with a carbon lining, was loaded with 10 kg fluorspar, which was melted and brought to a liquid-mobile state within 25-30 minutes. Then, a nickel cinder in an amount of 20 kg and metallurgical coke in an amount of 2 kg containing C - 67.3%, ash - 25.0% were continuously loaded into the furnace bath for 15 minutes. Immediately after loading, the melt was frozen. As a result of melting, an ingot of metal weighing 8.5 kg and slag in an amount of 17.5 kg were obtained.

 Chemical analysis of the initial cinder, as well as the resulting metal and slag are given in table. 5.

 From the chemical analysis data presented, it can be seen that while maintaining a concentration of nickel oxide in the melt-solvent exceeding the concentration of iron oxide by 15 times, some of the iron in the initial cinder (33%) nevertheless passes into the metal phase. At the same time, a significant portion of iron (67%) remains in the slag. This makes it possible to partially refine nickel from iron in the process of agar reduction and to obtain a nickel alloy with a reduced iron content.

 It should be noted that the higher the difference between the heats of formation of metal oxides, the better these metals are separated in the recovery process by the proposed method.

With a difference in the heats of formation of iron and silicon oxides equal to 91.2 kcal / mol O ₂ , you can leave almost all of the silicon oxide in the melt-solvent, getting almost pure silicon silicon (example 3). When the difference in the heats of formation of nickel and iron oxides is equal to 11.4 kcal / mol O ₂ , that is, significantly less than that of iron and silicon oxides, iron is partially reduced together with nickel and passes into the alloy (example 4). In this case, we can only speak of a decrease in the iron content in the nickel alloy.

 Thus, according to the proposed method, it is possible to carry out selective reduction by solid carbon of metals from a mixture of their oxides dissolved in a melt of alkali and / or alkaline earth metal halides.

Claims (1)

 The method of reducing metals from a mixture of their oxides, including the dissolution of oxides in a melt of halides of alkali and / or alkaline earth metals, liquid-phase reduction of oxides with solid carbon at a given temperature, the separation of the reduced metal from the melt-solvent, which is reused to dissolve the starting product, characterized in that the reduction of the less stable oxide is carried out by constantly maintaining its concentration in the melt-solvent above the concentration of the more durable oxide by continuous implicit load starting material, wherein at achieving concentration of more durable oxide concentration level less durable oxide dissolving the starting material in the melt-solvent is stopped and the reduced mixture of oxides, separating the resulting alloy from the dissolver melt separately from the metal recovered from the less durable oxide.

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