RU2086659C1 - Method of processing iron-silica raw material - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: method includes loading smelting furnace with red sludge from silica production, bauxite ore with silica ratio (Al₂O₃/SiO₂) 2-5, and carbon reducing agent in amount providing reduction of iron oxides, smelting to produce cast iron and alumino-silicate self-spilling slag with its subsequent processing into silica cement or silica. Method is distinguished with that, as carbon reducing agent, blast furnace dust is utilized, and components are loaded into smelting furnace successively: red sludge with added bauxite ore being smelted the first followed by blast furnace dust smelting. According to invention, silica ratio of loaded components is ranged from 0.08 to 0.35, whereas hydraulic index [CaO/(SiO₂+Al₂O₃)] is 0.55-0.80. Required hydraulic index level is maintained by adding calcium oxide or fluoride, or adding calcium or aluminium. EFFECT: enhanced efficiency of process. 5 cl, 1 dwg, 1 tbl

Description

Red sludge is known, which is a waste from the production of alumina from bauxite raw materials. The volume of their production by the Ural aluminum smelter alone exceeds 0.7 million tons per year. Red sludge accumulates in sludge storages and is practically not disposed of, posing a threat to the environment due to leaking caustic alkali into groundwater and leading to the formation of large amounts of dust in dry times. At the same time, waste sludge contains such valuable components as alumina, silica, iron oxide, calcium oxide, etc. with a ratio of them, wt. Al ₂ O ₃ 13-14 SiO ₂ 9-10, Fe ₂ O ₃ 24-40, CaO 12-14.

The most significant component in red mud is iron, and a number of works have been devoted to its extraction. So in (1) the simplest method for processing red mud to iron is described, including its melting together with charcoal at 1500 1600 ^o C. It is noted that in a relatively short time, iron goes into cast iron, which is separated from the slag. The disadvantage of this method is the need to use a special reducing agent: charcoal, which is impossible on an industrial scale. In addition, the composition of the resulting slag is not self-scattering, which complicates its disposal.

 To obtain self-disintegrating slags, their composition is adjusted with slag-forming substances, as a rule, with limestone, in order to obtain dicalcium silicate (2, 3, 6). One of the methods involves solid-phase reduction of iron with magnetic slag separation (4). Due to the low temperatures of solid-phase reduction, energy costs are low here, however, the costs of grinding and magnetic separation are added to the total cost, in addition, the iron yield is not complete. Attempts to combine the advantages of two processes: solid-phase and liquid-phase recovery are made in a technical solution (5). The preliminary enrichment of red mud in iron is provided by patent (7).

 At the same time, the production of pig iron from such iron-poor raw materials as red mud is not justified, if you do not take into account the cost of a by-product - slag, which can be used as raw material for alumina refining or in the cement industry.

 An additional iron ore raw material can be off-balance bauxite deposits, estimated only in the conditions of the Middle and Northern Urals in hundreds of millions of tons. These bauxite can not be used to obtain alumina according to the existing technology at the plants of the Urals (Bogoslovsky and Ural), since they contain a large amount of silicon oxide. In the adopted alumina extraction technologies, silicon oxide is an extremely harmful component, since it binds alkali with the formation of sodium silicate, as well as aluminum oxide.

Off-balance bauxite have the following chemical composition, wt. Al ₂ O ₃ 30 50, SiO ₂ 10 15, Fe ₂ O ₃ 20 25, CaO 3 5. As can be seen from these data, the silicon modulus (ratio Al ₂ O ₃ / SiO ₂ ) for these bauxites lies in the range of 2 5, while for balance sheets, the module is 10 18 (8, p. 135), and therefore they do not find industrial application.

 It is known that slags obtained in the steel industry can be used as binders. Of these, alumina cement has the most valuable characteristics (9), which unlike Portland cement has increased heat resistance and sulfate resistance, provides a quick set of strength (up to several hours). Due to the release of a large amount of heat during hardening, it is used in winter concreting. The valuable properties of this material provided it with various fields of application, including the construction of waterproof structures, drilling of oil and gas wells, etc.

As a prototype, a method for processing red mud from an alumina production (5) was selected, including feeding red sludge from an alumina production, bauxite ore with a silicon module (Al ₂ O ₃ / SiO ₂ ) equal to 2 5 and a carbon reducing agent in an amount that ensures reduction iron oxides, smelting with the production of pig iron and aluminosilicate self-scattering slag, followed by its processing on alumina cement or alumina.

 The disadvantage of the prototype method is the need to use a special reducing agent of coal or coke, which leads to increased costs for the process due to the consumption of expensive energy.

 The aim of the invention is to save energy.

 The goal is achieved in that blast furnace dust is used as the carbon reducing agent, and components are fed to the smelter in sequence, first melting the red mud into which bauxite ore is introduced, and then blast furnace dust.

In this case, the components are supplied in an amount providing a silicate module (SiO ₂ / Al ₂ O ₃ ) equal to 0.08 0.35.

The components are supplied in an amount providing a hydraulic module (Ca / (SiO ₂ + Al ₂ O ₃ )) equal to 0.50 0.80.

 The maintenance of the hydraulic module at the desired level is carried out by the addition of calcium oxide or fluoride.

 The maintenance of the hydraulic module at the desired level is also carried out by the addition of calcium or aluminum.

The addition of blast furnace dust to the red mud, firstly, solves the issue of its disposal. Blast furnace dust is the same production waste in the steel industry as red mud in non-ferrous. Due to the high dispersion in the steel industry, like red mud in non-ferrous. Due to its high dispersion, it cannot be used in blast furnace production, since it is immediately blown out of the blast furnace by a stream of exhaust gases. The reserves of blast furnace dust at metallurgical plants are huge, it poses the same threat to the environment as red mud. So, the reserves of the Serov Metallurgical Plant are estimated at 350 thousand tons and replenished annually by 14 thousand tons. Secondly, blast furnace dust contains such valuable components, wt. Coke up to 30, Fe ₂ O ₃ 40-50, Al ₂ O ₃ 3 7, SiO ₂ 8 12, CaO 8 12. From this we can conclude that the dust itself can be a reducing agent, and on the other hand contains an iron ore component and slag-forming substances. From the point of view of obtaining a slag of minimum viscosity, which facilitates the separation of iron during melting, it is more advantageous to have a slag with a weight ratio of CaO / SiO _{2 of} about 1, and CaO / Al ₂ O _{3 of} 0.3 to 1.0.

 The amount of reducing agent in blast furnace dust is much higher than that required for the reduction of iron oxides of the dust itself. This is due to the fact that in the blast furnace process the carbon-containing material is introduced in such an amount as to serve as a reducing agent and fuel. When melting with an external supply of heat, carbon is spent only on recovery and it is enough to process a large amount of additional raw materials. Slag-forming dust components make it possible to obtain slag with a good combination of necessary properties. A specific ratio between the amount of blast furnace dust and the remaining components of the charge should be established in a specific melting, since the fluctuations in the chemical composition of the starting materials can be quite large.

The value of cement increases with increasing aluminum oxide content. For alumina redistribution, it is more profitable to obtain raw materials with the highest possible content of aluminum oxide. In the red mud, the CaO / Al ₂ O ₃ ratio is approximately equal to unity, but in blast furnace dust it is quite large: CaO / Al ₂ O ₃ 2, i.e. alumina could be larger and the viscosity of the slag would not have changed much. From this we can conclude that it is possible to add additional iron ore raw materials with a high content of aluminum oxide to the mixture.

The main characteristics of cements in general and alumina, in particular, are the hydraulic module (9, p. 10)
H _M CaO / (SiO ₂ + Al ₂ O ₃ + Fe ₂ O ₃ ) (1)
and silicate module
S _M SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) (2)
It should be noted that if iron ore materials are melted to completely reduce iron, then in formulas (1) and (2) the content of Fe ₂ O ₃ in the slag will be absent, then
H _M CaO / (SiO ₂ + Al ₂ O ₃ ) and S _M SiO ₂ / Al ₂ O ₃ (3)
To obtain alumina cement, condition (9) must be fulfilled.

H _M 0.55 0.80 and S _M 0.08 0.35. (4)
If the desired silicate module can be implemented by the addition of bauxite ore, then the desired hydraulic module can be achieved only by either adding calcium oxide or removing excess silicon oxide. In turn, calcium oxide in the slag can be obtained by adding oxide to the mixture in the form of limestone or chalk or by adding calcium fluoride to the mixture, which leads to the formation of volatile silicon tetrafluoride and removes excess silicon oxide.

 Excess silicon oxide can also be removed by the addition of a silicon reducing agent, for example calcium or aluminum, as a result of which the hydraulic module can be increased.

 It is proposed to first melt the red mud, then add bauxite, and then blast furnace dust. Violation of this order leads to the formation of refractory iron compounds or to a sharp increase in the temperatures necessary for the melting to occur, which affects the performance of the process.

 The drawing shows a graph of the dependence of the hydraulic module on the composition of the charge.

 Example 1. Spent the melting of the starting components, the composition of which is indicated in the table.

 As can be seen from the table, none of the starting materials satisfies the requirements for producing alumina cement. Red sludge has a small hydraulic module and silicate, a large amount of off-balance bauxite has a small hydraulic module, and, for blast furnace dust, the latter is too large. At the same time, such a selection of a combination of starting materials and methods for their processing is possible that would provide the properties necessary for the binder.

So, the added bauxite to the red mud reduces the silicate module to the required level, as shown in the graph shown in the drawing, which shows the dependence of the silicate module S _M on the bauxite content in the charge (wt.), The number of curves with blast furnace content (wt.) , shading marks the region of acceptable values for alumina cement. As can be seen from this figure, the content of bauxite in the charge from 55 to 100% is acceptable. However, for conducting smelting, at least 20% of blast furnace dust is necessary, since the iron reduction reaction requires at least 16% carbon (by weight) of the amount iron oxide. Then, with the mixture composition of 20% red mud + 60% bauxite + 20% blast furnace dust, we obtain S _M = 0.34, which satisfies condition (4). In this case, the carbon content in the charge will be 0.3 • 20 = 6% and the total content of iron oxides 0.20 • 36.3 + 0.6 • 22 + 0.2 • 42 = 29%, the restoration of which requires 4.8% carbon
200 g of red mud was melted in a graphite crucible placed in a Tamman electric furnace, 600 g of bauxite and 200 g of blast furnace dust were added. After separation of iron weighing 172 g (yield 95%), a slag of the composition was obtained, wt. CaO 14.7, Al ₂ O ₃ 62.3, SiO ₂ 21.5 with a silicate module of 0.35, which corresponds to condition (4). Such slag can be used to obtain alumina cement by sintering, provided that the necessary amount of calcium oxide is added in order to achieve the necessary hydraulic module.

Example 2. The required module can be achieved in the smelting process, which eliminates the need for subsequent sintering and increases the efficiency of the process as a whole. To do this, adjust the ratio between calcium oxide and silicon oxide based on the receipt of a hydraulic module of 0.55 0.80 already in the process of melting. For this purpose, melting was performed under the conditions of the above example with the addition of 159 g of calcium oxide (15.9 wt. To the composition of the charge) and the content of calcium oxide in the scale of 33% silica 15.1% and aluminum oxide 44.9% hydraulic module H _M 33 / (15 + 45) = 0.55, which meets the requirements of (4).

Example 3. In the conditions of the previous example, melting was performed with the addition of 266 g of calcium oxide (26.6 wt.% To the composition of the charge) and the content of calcium oxide in the slag was 42.1% of silicon oxide 13.0% and aluminum oxide 38.9% hydraulic module H _M = 42.1 / (13 + 38.9) = 0.77, which corresponds to the requirements of (4).

 Example 4. Performed melting in the conditions of the prototype. 100 g of red mud was mixed with 30 g of graphite and 20 g of calcium oxide. Smelted 18 g of cast iron, the metal yield was 72%, which is significantly lower than by the proposed method. On a scale of 21.1% alumina and 17.0% silica, the silicate modulus is 0.81, which does not satisfy condition (4) to obtain alumina cement. It should be noted that slag formation in this case was accompanied by the formation of calcium carbide, which extremely negatively affects the quality of the binder (9, p. 83). These negative results were the result of the irrational composition of the mixture, as well as the wrong order of its spraying.

Example 5. Under the conditions of example 2, calcium fluoride in the same amount was added instead of calcium oxide. Got slag with a content of calcium oxide of 37.0% and silicon oxide of 11.1% of aluminum oxide of 47.1% and a hydraulic module of 0.64. The increase in module compared to example 2 is due to the formation of a volatile compound SiF ₄ .

 Example 6. Under the conditions of Example 1, 100 g of calcium metal was added and, as a result of melting, the metal and slag of the composition were obtained: calcium oxide 40.2% silica 5.1% alumina 49.7, hydraulic module 0.75 and silicate module 0.11, which satisfies condition (4).

 The invention allows to solve such a technical problem as energy saving, since no special carbon-containing materials — coke or coal — were required to restore iron. At the same time, waste from ferrous and non-ferrous metallurgy is being disposed of, which is still harmful to the environmental situation.

Claims (5)

1. A method of processing iron-alumina raw materials, including feeding red sludge from an alumina production, bauxite ore with a silicon module (Al ₂ O ₃ / SiO ₂ ) 2 5, and a carbon reducing agent, in an amount providing reduction of iron oxides, smelting to produce pig iron and aluminosilicate self-scattering slag with its subsequent processing into alumina cement or alumina, characterized in that blast furnace dust is used as a carbon reducing agent, and the components are fed into a smelting furnace suschestvlyayut sequentially first melting the red mud, which is introduced into the bauxite ore, and then the flue dust. 2. The method according to claim 1, characterized in that the components are supplied in an amount that provides a silicate module (SiO ₂ / Al ₂ O ₃ ) of 0.08 0.35. 3. The method according to claims 1 and 2, characterized in that the components are fed in an amount that ensures the receipt of a hydraulic module (CaO / SiO ₂ + Al ₂ O ₃ ) 0.55 0.80.  4. The method according to claim 3, characterized in that the hydraulic module is maintained at the desired level by the addition of calcium oxide or fluoride.  5. The method according to p. 3, characterized in that the maintenance of the hydraulic level at the desired level is carried out by the addition of calcium or aluminum.

Images