RU2619406C2 - Method for complex processing of red and nepheline sludges - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to 100 % processing of red and nepheline (belite) sludges to produce commercial products in the form of iron alloys, cements, as well as amorphous silicon dioxide. At processing of red sludge it is mixed with lime, the produced charge is dried, melted in the arc furnace in presence of a catalyst in the form of cast iron or steel to allow reduction of iron oxides and production of an iron-based alloy, foundry slag removal and granulation and desiliconization of the slag. When processing nepheline sludge desiliconization of the nepheline sludge is performed by washing with soda solution, filtering of the sludge with separation of soda-silicate solution and annealing of produced clinker. Herewith in order to obtain a mixture for cement foundry slag obtained from red sludge is mixed with clinker obtained from nepheline sludge and functional components of cement. Besides, the cement mixture may also contain nanomodifiers in the form of amorphous silicon dioxide and finely dispersed amorphous aluminium hydroxide.

EFFECT: provided higher quality of finished products, simplified process, increased efficiency and reduced power consumption.

6 cl, 1 dwg

Description

The invention relates to ferrous metallurgy, and in particular to the technology of waste-free processing of red and nepheline (belite) sludges to produce marketable products in the form of alloys of iron, cements, and also amorphous silicon dioxide.

The prior art technology for processing red mud using additives from nepheline sludge. According to the method, red and nepheline sludge and limestone are crushed, mixed and the mixture is fired to obtain cement clinker (see USSR copyright certificate 281231, 1970). The disadvantage of this technology is the low quality of the resulting clinker.

The prior art method of processing red mud, including mixing sludge with waste products of lime, drying the resulting mixture and reducing smelting of the mixture in a fuel-oxygen furnace in the presence of a catalyst in the form of cast iron chips, as well as high-carbon material in the form of graphite to ensure the production of cast iron (Patent RU 2479648 04/20/2013). The disadvantage of this technology is the low quality of cast iron, low process productivity and high energy consumption.

The prior art technology for the use of foundry slag obtained after processing red mud to obtain a cement mixture (see, for example, patent RU 2179590, 02.20.2002).

The prior art method of processing nepheline sludge, including leaching of nepheline sludge, filtering it with separation of soda-silicate solution and firing the clinker obtained to obtain a cement mixture (see USSR author's certificate 381628, 1973).

However, in known technologies, the content of SiO ₂ in the foundry slag (or nepheline sludge) significantly exceeds 10% and is not neutralized by the increased content of Al ₂ O ₃ . The mixtures obtained from these components have low astringent properties, that is, are practically neutral, and can only be used as a mineral additive in the amount of 10-30%, while the class of cement obtained from them decreases.

The objective of the claimed invention is to eliminate the disadvantages of analogues and the creation of technology for 100% joint processing of red and nepheline sludge.

The technical result of the invention is to improve the quality of products obtained by co-processing: an alloy based on iron and cement mixture (in particular, to increase the binding properties), simplifying the technology, increasing the productivity of the process and reducing energy costs.

The specified technical result is achieved due to the fact that the method of complex processing of red and nepheline sludge includes the following steps:

(a) processing of red mud, which carry out:

- mixing sludge with lime,

- melting the mixture in an arc furnace in the presence of a catalyst in the form of cast iron or steel, ensuring the reduction of iron oxides and obtaining an alloy based on iron,

- drainage of foundry slag and its granulation,

- desiliconization of slag by washing with soda solution,

- slag filtration with separation of soda-silicate solution;

(b) processing of nepheline sludge, in which carry out:

- desiliconization of nepheline sludge by leaching with soda solution,

- filtering cake with separation of soda-silicate solution,

- firing the obtained one-component mixture;

(C) obtaining a mixture for cement, which carry out the mixing of foundry slag obtained from red mud, and clinker obtained from nepheline sludge, with functional components of cement.

In addition, the specified technical result is achieved in private variants of the method due to the fact that:

- at stage a) after granulation of the slag, the kings of the iron alloy are captured from the granulator and sent to the charge melting operation;

- a solution of soda ash and silicic acid obtained after desalination of casting slag in step (a) and desilination of nepheline sludge in step (b) is subjected to carbonization to produce amorphous silicon dioxide, while the resulting desilted solution of calcined soda is used as reverse;

- gypsum is used as a functional component of cement;

- powder nanomodifier in the form of amorphous silica obtained after carbonization is additionally introduced into the mixture;

- the powder nanomodifier is additionally introduced into the mixture in the form of highly dispersed amorphous aluminum hydroxide.

In contrast to the known analogues in the claimed invention is the joint use of foundry slag from the processing of red mud and clinker from nepheline sludge to produce high quality cements.

The methods used for processing red mud with the aim of producing an alloy based on iron (slurry preparation, smelting reduction operations) can significantly improve the quality of the resulting alloy. The casting slag processing operations used (granulation, desiliconization), as well as nepheline sludge (desiliconization, filtration) make it possible to obtain a cement mixture with a high astringency. In addition, powder modifiers (nano-additives) can be added to the mixture to produce building and special cements with low water conductivity.

The method is as follows.

1. Treatment of red mud

Caked chunks of the original red mud are crushed (if necessary).

Then lime is added to the sludge in an amount of 7-10% by weight of the sludge. This is necessary in order to neutralize Na ₂ O by binding NaOH.

The resulting mixture is heated with flue gases to a temperature of 600-800 ° C in order to remove surface and hydrated moisture (drying) and partial saturation with carbon.

After that, the resulting mixture is subjected to reduction smelting in an arc furnace. For stable and high-quality work, it is recommended to use a furnace with a melting bath having a cross lining, for example, PPD-93 grade with a mass fraction of magnesium oxide of at least 93%. This will completely eliminate the harmful effects on the lining of Na ₂ O.

To carry out melting, a catalyst is first laid in the furnace bath, for example, high-carbon pig-iron shavings. The mass of the loaded catalyst is approximately 30% of the content of Fe ₂ O ₃ in the mixture. Depending on the C content in the chips (catalyst) and the amount of Fe ₂ O in the sludge, it is possible to add to the catalyst a high-carbon material in the form of chips from waste graphite electrodes with the calculation of the total C and Si content of 3.0-4.0%. As a catalyst, you can also use steel chips and scale, while it is necessary to increase the carbon addition in the form of graphite chips to achieve the specified content of C and Si in the charge. The mixture should be low silicon based on the content in the alloy C and Si of 3.0-4.0%;

After loading the catalyst into the furnace bath, the charge is loaded in parts.

First, 30-35% of the charge material is fed in the form of a mixture of red mud and lime, and the charge is melted under the slag-forming flux material in an amount of 0.1-0.5% by weight of the charge at a temperature of 1500-1580 ° C for 3-8 minutes .

Then a second portion of the charge is supplied in a volume of 30-35%, flux is introduced and melting occurs for 3-8 minutes at the same temperature. In conclusion, the last third of the charge is fed and the operation is repeated until an iron-based alloy with a content of C and Si of 3.0-4.0 wt. % The molten metal is poured into the casting ladle and fed to the spill site, in particular to a centrifugal injection machine.

Foundry slag (1) is downloaded and sent to a granulator, where it cools and granulates. Then, by means of magnets, the bulk of the metal is separated from the slag, which is returned to the foundry. After that, the slag is crushed in a cone vibratory crusher, where it is crushed to a size of 3 mm (initial size of approximately 50 mm) and fed to screens, where flat metal particles are separated and returned to the casting shop, and the mineral part enters the electrostatic separator, where it is finally there is a separation of the metal powder and the mineral part.

The mineral part is subjected to desiliconization by leaching (2), which is carried out using a 15% solution of soda ash (3), after which the product is filtered (4) and dried. As a result, the mineral part (one-component mixture (5)) acquires initial astringent properties.

Remaining after filtering a solution of soda ash and silica (soda-silicate solution (6)) enters the carbonation, wherein by carbonizing CO ₂ (7) (exhaust gases calcium furnaces and smelters) is released amorphous silica (fine silica (11) ), which is separated from the solution by filtration (8) and washing (10), and the desilted solution of soda ash is neutralized (9) and used as reverse (see drawing).

The resulting foundry slag enters the cement bin.

2. Treatment of nepheline sludge

The processing of nepheline sludge (1) is carried out similarly to the processing of the mineral part of foundry slag from red mud and is based on soda leaching (2) of sludge dumps and subsequent filtration (4) with separation of soda-silicate solution (6) from the obtained single-component charge (5) (cm) .Drawing).

The average chemical composition of dump nepheline sludge is represented by oxides CaO = 56-58%; SiO ₂ = 29-31%; Al ₂ O ₃ = 2.8-3.0%; Fe ₂ O ₃ = 3.0-3.2%; R ₂ O = 1.0-1.2%; pp = 2.5-4.0%. As the main phase in the sludge there is dicalcium silicate (Ca ₂ SiO ₂ ) in an amount of 85-90%.

Before leaching, nepheline sludge, if necessary, is crushed. Leaching (2) is carried out with a 15% soda solution (3), which results in the chemical extraction of silicon dioxide from dicalcium silicate (desiliconization of nepheline sludge). The term "desiliconization" in this case should be understood to be the extraction of silicon dioxide from the solid phase - dicalcium silicate, which is part of nepheline sludge, during its hydrochemical processing by leaching by reaction:

Ca ₂ SiO ₄ + 2Na ₂ CO ₃ + H ₂ O↔2CaCO ₃ + Na ₂ SiO ₃ + 2NaOH

Moreover, it is necessary to decompose only such an amount of 2CaO⋅SiO ₂ and the accumulation of such an amount of CaCO ₃ , which would ensure an increase in the basicity of the mixture required for the synthesis of tricalcium silicate. The calcium carbonate formed by the reaction is insoluble and, together with the initial anhydrous dicalcium silicate, as well as partially formed calcium hydrosilicate, forms a solid phase, which is separated from the liquid phase after the completion of the reaction. Thus, the solid phase after desiliconization is a mixture of:

a) the initial unreacted nepheline (belite) sludge;

b) calcium carbonate formed during "desiliconization" and leaching;

c) calcium hydrosilicates - partially initial, partially newly formed.

For a given degree of completion of the reaction (obtaining the necessary KN value), the solid phase is a ready-made one-component mixture for the production of Portland cement clinker.

Such a raw material mixture is one-component and does not require limestone mixing to obtain specified values of the saturation coefficient (KH). The specific features of such a mixture are: the silicate module value reduced in comparison with a traditional charge and the presence of finely dispersed calcium carbonate, which determine the high reactivity of such a mixture upon receipt of Portland cement clinker from it.

The composition of clinkers synthesized from a single-component batch is characterized from pure belite clinkers to high alite clinkers (68.5% at KN = 0.93).

The liquid phase (filtrate) in this case is a soda-alkaline silicate solution containing Na ₂ CO ₃ , NaOH and Na ₂ SiO ₃ .

Next, the soda solution is regenerated with the associated production of technical products based on active silicon dioxide SiO ₂ by carbonization according to the scheme:

followed by separation of silicic acid by filtration and the return of soda solution to leach nepheline sludge. As a source of CO ₂ , flue gases are used. In this case, SiO ₂ precipitates in the form of nanodispersed amorphous flakes. The resulting filtered “white soot” (silicon dioxide or finely divided silica (11)) is dried and used as a commercial product or as a nanoadditive in the production of special cements.

The chemical composition leached with soda solution of nepheline sludge is in the range of SiO ₂ - 17.5-20.0%; CaO - 50-51%; Al ₂ O ₃ - 2.60-2.65%; Fe ₂ O ₃ - 2.45-2.70%. The phase characteristics of nepheline sludge after leaching are presented: Ca ₂ SiO ₄ - 45-50%; CaCO ₃ - 30-35%; CSH phase - calcium hydrosilicates (10-15%).

The product of carbonization of soda-silicate solutions is highly dispersed silica, characterized by a specific surface area of up to 300 m ² / g, as well as a soda solution returned to the process for the hydrochemical processing of nepheline sludge.

The obtained siliceous nepheline sludge (single-component charge) is fired.

That is, as a result of processing nepheline sludge, a single-component batch is formed, suitable for producing a standard Portland cement clinker and not requiring limestone dressing, as is done by traditional technology.

As a by-product in this process, highly dispersed silica (white soot) is formed, which is in demand in many industries. The soda solution used for leaching is recycled and returned to the process head. The process is complex and the waste sludge is 100% utilized (non-waste).

3. Obtaining a cement mixture.

Silicon-free foundry slag obtained from red mud and clinker obtained from nepheline mud are mixed with the functional components of cement to obtain a cement mixture, for example, gypsum (gypsum stone), in an amount of 2-5%, which controls the setting speed. At the same time, the content of foundry slag and clinker in the mixture can vary within wide limits, depending on the type of cement to be obtained. The resulting mixture is subjected to grinding, while during grinding or after grinding, nanomodifiers in an amount of 1-5 wt. % to give the cement mixture certain properties. As nanomodifiers can be used:

- amorphous silicon dioxide obtained after desiliconization and carbonization during processing of foundry slag from red mud and nepheline sludge to increase strength,

- finely dispersed amorphous aluminum hydroxide (AmGA), increasing heat resistance, etc.

The result is a mixture for cement (special cement) with low water demand (CNV).

An example implementation of the method

The average chemical composition of dump nepheline sludge is represented by oxides CaO = 56-58%; SiO ₂ = 29-31%; Al ₂ O ₃ = 2.8-3.0%; Fe ₂ O ₃ = 3.0-3.2%; R ₂ O = 1.0-1.2%; pp = 2.5-4.0%. As the main phase in the sludge, dicalcium silicate (Ca ₂ SiO ₂ ) is present in an amount of 85-90%.

Red and nepheline sludge was prepared according to the technology described above.

The chemical composition leached with soda solution of nepheline sludge is in the range of SiO ₂ = 17.5-20.0%; CaO = 50-51%; Al ₂ O ₃ = 2.60-2.65%; Fe ₂ O ₃ = 2.45-2.70%. The phase characteristics of nepheline sludge after leaching are presented: Ca ₂ SiO ₄ - 45-50%; CaCO ₃ - 30-35%; CSH phase - calcium hydrosilicates (10-15%).

The nepheline sludge after hydrochemical processing (leaching) in terms of chemical composition is a raw material mixture to produce Portland cement clinker. Such a raw material mixture is one-component and does not require limestone mixing to obtain specified values of the saturation coefficient (KH).

The chemical composition of the cast slag before leaching: Al ₂ O ₃ = 23-30%; Fe ₂ O ₃ = 7-15%; SiO ₂ = 23-25%; CaO = 35%; Na ₂ O = 1.5-2.5%; SO ₃ = 0.1-0.2%; TiO ₂ = 3-3.5%.

The chemical composition of the slag after leaching: Al ₂ O ₃ = 21.4-27.0%; Fe ₂ O ₃ = 5.7-12.3%; SiO ₂ = 13.8%; CaO = 31.8%. The phase characteristics of the slag after leaching are presented: Ca ₂ SiO ₄ = 35.0-45.0%; CaCo = 25.0-30.0%.

A certain excess of silicon oxide of 13.8% (norm <10%) is neutralized by an excess of Al ₂ O ₃ = 20-25%, by 1% SiO _{2 it} neutralizes 1.7% Al ₂ O ₃ .

The composition of the foundry slag (wt.%):

Before desiliconization:

Al ₂ O ₃ 23-30

Fe ₂ O ₃ 7-15

SiO ₂ 23-25

CaO ~ 35

TiO ₂ 3-3.5

Na ₂ O 1.5-2.5

SO ₃ 0.1-0.2

After desalination, with a solution of soda ash:

Al ₂ O ₃ 22.4-27.0

Fe ₂ O ₃ 5.7-12.3

SiO ₂ ~ 13.8

CaO ~ 31.8

TiO ₂ 3-3.5

Na ₂ O 0.5-1.01

SO ₃ 0,05

Next, several versions of cement mixtures were prepared.

1. Clinker and slag were mixed in a ratio by weight of 90:10, 2-3% of gypsum was added to the mixture and subjected to grinding. The result was cement grade 800.

2. Clinker and slag were mixed in a ratio by weight of 50:50, 2-3% of gypsum was added to the mixture and subjected to grinding. The result was cement grade 700.

3. Clinker and slag were mixed in a ratio by weight of 40:60, 2-3% gypsum was added to the mixture and subjected to grinding. The result was cement grade 650.

4. Clinker and slag were mixed in a ratio by weight of 20:80 and 2-3% gypsum was added to the mixture to obtain cement of grade 400. After that, the mixture was milled and 3 wt. % nanomodifier in the form of amorphous silicon dioxide. As a result, 900 grade cement was obtained.

Thus, the proposed method has several advantages compared with known technologies.

The method allows to obtain nanocement based on foundry siliceous slags with latent hydraulic properties of strength classes 42.5-82.5 (grades 500-900).

The resulting cement does not contain harmful components - phosphates, thiosulfates, sulfites, slowing down its interaction with water and hardening, hindering the manufacture of nanocement of low-clinker compositions.

Cement is sulfate-resistant regardless of the mineralogical composition of the nepheline Portland cement clinker with which it is made, including the content of aluminates in it. Therefore, aluminates in casting slag, which are more passive than clinker, cannot cast a lowering effect on the sulfate resistance of nanocement made with their use and impede its effective use in hydraulic engineering, including seaports, platforms, etc., defense and underground structures .

The resulting cements are characterized by general construction and special purposes, in terms of their technical properties, at least not inferior to Portland cement of the same classes (grades) when used in general construction areas, but significantly superior to Portland cement in special areas requiring increased resistance to corrosive environmental agents .

The proposed technology is one of the few currently possible ways of using foundry slag in the industrial complex as a component of highly effective cement for general construction and special purposes and a reliable technological basis for the investment project under consideration.

In this case, it is possible to add up to 80% of the finely ground foundry slag of red sludge to the obtained finely ground clinker of nepheline sludge and produce cements with a grade of at least M400.

An even greater effect can be obtained if activating additives are added when grinding clinker and slags together, which are most cost-effective to use highly dispersed silica (“white soot”) and highly dispersed amorphous aluminum hydroxide (AmGA). This produces the so-called "nanocements", or cements of low water demand (CNV). Such cements may contain from 20 to 60% of foundry slag with grades from M600 to M800 with the addition of activating additives about 1% by weight of cement (some up to 3-5%). Some of the main additives are used in the production of special cement of central nervous system from nepheline clinker and foundry slag of red mud.

Claims (18)

1. The method of complex processing of red and nepheline sludge, comprising the following steps: (a) processing of red mud, which carry out: - mixing sludge with lime, - melting the resulting mixture in an arc furnace in the presence of a catalyst in the form of cast iron or steel, ensuring the reduction of iron oxides and obtaining an alloy based on iron and cast slag, - drainage of foundry slag and its granulation, - desiliconization of slag by washing with soda solution, - slag filtration with separation of soda-silicate solution, and - slag firing; (b) processing of nepheline sludge, in which carry out: - desiliconization of nepheline sludge by washing with soda solution, - sludge filtration with separation of soda-silicate solution, and - sludge firing to produce clinker; (C) obtaining a mixture for cement, which carry out the mixing of the calcined foundry slag obtained from red mud, clinker obtained from nepheline sludge, and at least one functional component of cement. 2. The method according to p. 1, in which at the stage of processing the red mud after granulation of the slag, the kings of the iron alloy are captured from the granulator and sent to the charge melting operation. 3. The method according to p. 1, in which the soda-silicate solution obtained after desalination of casting slag at the stage of processing red mud and desilination of nepheline sludge at the stage of processing nepheline sludge, is subjected to carbonization to obtain amorphous silicon dioxide, while the resulting desilted solution of soda ash use as negotiable. 4. The method according to p. 1, in which gypsum is used as a functional component of cement. 5. The method according to p. 3, in which at the stage of obtaining the mixture for cement, powder nanomodifier in the form of amorphous silicon dioxide obtained after carbonization is additionally introduced into it. 6. The method according to p. 1, in which at the stage of obtaining a mixture for cement, powder nanomodifier is additionally introduced into it in the form of highly dispersed amorphous aluminum hydroxide.

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