RU2402621C1 - Procedure for processing fluorine-containing materials used in electrolytic production of aluminium - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: procedure consists in supply, in mixing fluorine-containing materials with charge components and in heat processing of charge. As fluorine-containing materials there are used secondary fluorine-containing materials with contents of fluorine not less, than 26 %. They are supplied into charge to produce Portland cement clinker as fluorine-containing mineraliser at amount ensuring contents of fluorine in source charge for production of Portland cement clinker 0.07-0.25 wt %. Also as secondary fluorine-containing material there can be used electrolytic carbon foam, return electrolyte, flotation and/or regenerating cryolite, and mixed cryolite. Additionally, calcium fluoride can be introduced into composition of fluorine containing mineraliser at the following ratio of components, wt %: secondary fluorine-containing material used in electrolytic production of aluminium - 30-90; calcium fluorine - the rest. ^ EFFECT: reduced load and power expenditures for separate kinds of equipment for processing primary wastes of electrolytic production of aluminium, expanded raw material base of fluorine containing mineralisers of charge at production of Portland cement clinker, reduced specific consumption of fuel at clinker baking, raised efficiency of baking furnace and increased overhaul life of baking furnace. ^ 6 cl, 18 tbl, 3 ex

Description

The invention relates to the processing of secondary fluorine-containing materials for the electrolytic production of aluminum and can be used in the cement industry in the production of Portland cement clinker.

In the electrolytic production of aluminum per tonne of metal after the primary processing of electrolytic waste and the extraction of valuable components - secondary fluorine-containing materials from them, 40-60 kg of finely dispersed sodium-fluorine-carbon-containing waste are formed in the form of dust from dry gas cleaning electrostatic precipitators, gas cleaning sludges after the wet dust and gas collection stage , tailings of coal foam flotation after flotation enrichment of electrolyte coal foam. The feasibility of extracting valuable components from these types of waste materials, both fuel, in the form of carbon, and fluorine-containing compounds, and their use in various technological processes is not in doubt.

Known technologies for processing secondary finely dispersed sodium-fluorine-carbon-containing aluminum production.

A known method of processing aluminum-containing raw materials, including the preparation of a mixture of aluminum-containing raw materials and limestone, its sintering and leaching of custody, in which aluminum-fluorine-carbon-containing waste from aluminum production is used as a raw material, the mixture is prepared with molar ratios Ca: F ₂ = 0.8- 1,2, Ca: S = 1,0 and sintered at a temperature of 550-800 ° C (RF patent No. 2312815, C01F 7/38, C22B 7/00, 2007 [1]). This solution, when used, allows to increase the efficiency of alumina production and at the same time neutralize waste from aluminum production. But the proposed technological scheme is complex and cumbersome, because includes both pyro- and hydrometallurgical processing. The technology is quite energy intensive and requires additional costs for processing raw materials. The technological possibilities of processing fluorine-containing materials for the electrolytic production of aluminum are limited.

Some primary sodium-fluorine-carbon-containing wastes generated during the electrolytic production of aluminum are processed in order to extract valuable components from them and obtain secondary fluorine-containing material in the form of flotation, regeneration, mixed cryolite and return them to aluminum electrolysis.

So, when processing electrolyte coal foam, flotation cryolite is obtained, purification of fluorine-containing gases from the electrolytic production of aluminum by soda solution followed by regeneration of fluorine from the solution leads to the formation of regeneration cryolite, a mixture of flotation and regeneration cryolites forms mixed cryolite.

A recent change in aluminum electrolysis technology, associated with the transition to acidic electrolytes as a result of a decrease in the cryolite ratio from 2.7-2.8 to 2.2-2.3, has led to a change in the balance of formation and consumption of fluoride salts. Previously, when working on alkaline electrolytes, fresh cryolite and aluminum fluoride were used as primary fluorine salts, in recent years aluminum plants have completely abandoned fresh cryolite. Existing technologies for producing regeneration and flotation cryolite ensure the production of high-modulus products with a cryolite ratio of 2.4-3.5, the large-scale use of which is limited in the electrolytic production of aluminum.

In addition, a decrease in the cryolite ratio of the electrolyte of aluminum electrolysis cells led to the fact that excess electrolyte began to accumulate in the electrolysis cells. The raw materials for its production were mainly aluminum fluoride, used to adjust the composition of the electrolyte, and sodium oxide supplied with alumina. Excess electrolyte is drained from the electrolysers, crystallizes and forms another limitedly needed fluorine-containing material - reverse electrolyte.

Thus, there is an excess of secondary fluorine-containing materials, and with it the need for processing or disposal of these types of materials, including in related industries.

A known method for producing agglomerated material, including mixing, molding and heat treatment of a mixture containing agglomerated material, a carbon-containing component, flux and finely dispersed fluorocarbon-containing waste from aluminum production in the form of flotation tailings of coal foam in an amount of 0.3-2.5 wt.% (RF patent No. 2291208, C22B 1/245, 2007 [2]).

By technical nature, the presence of similar features, this solution is selected as the closest analogue.

Using the well-known solution in the agglomeration of iron-containing materials for blast furnace production will allow expanding the raw material base, partially replacing fuel (coke breeze) and flux (limestone) with aluminum waste.

The main disadvantage of this solution is the ability to efficiently use only one type of secondary finely dispersed sodium-fluorine-carbon-containing waste from aluminum electrolytic production — carbon foam flotation tailings, which reduces the technological capabilities of processing other fluorine-containing materials.

The objective of the proposed technical solution is a large-scale, complex processing of secondary fluorine-containing materials in the form of coal foam, circulating electrolyte, flotation, regeneration, mixed cryolite, increasing the technical and economic indicators of the process of obtaining Portland cement clinker.

Technical results are:

- disposal of excess secondary fluorine-containing materials in the form of coal foam, recycled electrolyte, flotation, regeneration, mixed cryolite;

- reducing the load and energy costs for certain types of equipment for the processing of primary waste from the electrolytic production of aluminum, in particular electrolyte coal foam, gas cleaning solutions;

- expansion of the raw material base of fluorine-containing mineralizers of the mixture to obtain Portland cement clinker;

- reduction of specific fuel consumption for clinker firing;

- increasing the productivity of the kiln;

- increase in the overhaul period of the kiln.

Technical results are achieved by the fact that in the method of processing fluorine-containing materials used in the electrolytic production of aluminum, including feeding, mixing fluorine-containing materials with charge components and heat treatment of the charge, secondary fluorine-containing materials with a fluorine content of at least 26 wt.% Are used as fluorine-containing materials, which served in the mixture to obtain Portland cement clinker as a fluorine-containing mineralizer, in an amount providing the fluorine content in the original ichte to obtain Portland cement clinker 0.07-0.25 wt.%.

Moreover, as a secondary fluorine-containing material, electrolyte carbon foam, reverse electrolyte, flotation and / or regenerative cryolite, mixed cryolite can be used.

In addition, calcium fluoride can be added to the composition of the fluorine-containing mineralizer in the following ratio of components, wt.%:

- secondary fluorine-containing material used in the electrolytic production of aluminum, - 30-90;

- calcium fluoride - the rest.

A comparative analysis of the solution for the closest analogue and the proposed solution shows the following.

The known solution and the proposed are characterized by similar features:

- the use of a mixture of fluorine-containing materials for the electrolytic production of aluminum;

- mixing fluorine-containing materials with the components of the mixture;

- heat treatment of the charge.

The proposed solution differs from the closest analogue in the following features:

- as fluorine-containing materials use secondary fluorine-containing materials with a fluorine content of at least 26 wt.%;

- secondary fluorine-containing materials are fed into the mixture to obtain Portland cement clinker as a fluorine-containing mineralizer;

- fluorine-containing mineralizer is fed in an amount that provides the fluorine content in the original mixture to obtain Portland cement clinker 0.07-0.25 wt.%.

Moreover, electrolyte carbon foam, reverse electrolyte, flotation and / or regenerative cryolite, mixed cryolite can be used as secondary fluorine-containing material.

In addition, calcium fluoride can be added to the composition of the fluorine-containing mineralizer in the following ratio of components, wt.%:

- secondary fluorine-containing material used in the electrolytic production of aluminum, - 30-90;

- calcium fluoride - the rest.

The presence in the proposed technical solution of signs that are different from those of the closest analogue allows us to conclude that the proposed condition for patentability of the invention is “novelty”.

The technical essence of the proposed solution is as follows.

The main redistribution of the production of Portland cement clinker is firing before sintering of the components of the initial cement raw material mixture, containing mainly calcium, aluminosilicate and ferrous components. Depending on the requirements for Portland cement, and the composition of the main feedstock, various corrective active additives, including mineralizers, are introduced into the charge.

Mineralizers are substances that are actively involved in the formation of clinker minerals during firing and are partly part of them themselves. As mineralizers in the cement industry, CaF ₂ fluorspar in the form of fluorite ore or fluorite concentrate is used predominantly. It is also known that phosphogypsum, sodium silicofluoride Na ₂ SiF ₆ , apatite Ca ₅ (PO ₄ ) ₃ F, gypsum, etc. are used as mineralizers.

Of the fluorine-containing mineralizers, fluorspar CaF ₂ (fluorite), a mineral containing 48.8% F and 51.2% Ca, has found the greatest industrial application. In cement production, fluorspar is used with impurities; while the content of the basic substance (CaF ₂ ) in the mineralizer can vary from 20 wt.% to 95 wt.%.

It is known that due to the introduction of small additives of fluorine salts, an increase in the varying degree of reactivity of the raw materials at all stages of firing is observed. Fluoride salts during heating to 1100 ° C interact with calcium carbonate and give intermediate compounds such as double salts having relatively low melting points. Therefore, in the firing process, already in the preparation zones in the presence of fluoride compounds, the interaction of materials with the participation of the liquid phase occurs, which intensifies the interaction of lime with silica, aluminum oxides and iron.

A number of researchers have shown that the presence of fluoride compounds in conventional raw material mixtures leads to a change in the mineralogical composition of clinkers - complex aluminoferrites C ₈ A ₂ F and low-basic calcium aluminates C ₁₂ A ₇ appear instead of tetra-calcium aluminoferrite C ₄ AF and tricalcium aluminate C ₃ A. Data generation of the compounds suggests that the liberated free calcium oxide reacts with dicalcium silicate C ₂ S with the formation of an additional amount of tricalcium silicate C ₃ S. the content of C ₃ S increases by 10-12%, the sintering ability of the granules and the strength of the resulting cement are improved.

According to the results of numerous scientific studies confirmed by industrial tests, it was found that under the influence of fluorine compounds during firing of a clinker charge, the temperature of formation of the liquid phase decreases and the formation of the main clinker minerals is significantly accelerated.

Thus, the positive effect of the fluorine ion on the firing process is realized under the condition of the optimal content of the fluorine-containing mineralizer. However, many natural mineralizers are scarce material, their use in factories is limited. Therefore, a large reserve of fluoride mineralizers is more accessible technogenic products, for example, secondary fluorine-containing materials for aluminum production. The component composition of these materials allows you to use them as a mineralizer in the production of Portland cement clinker. Table 1-4 shows the chemical composition of secondary fluorine-containing materials.

Table 1 The chemical composition of fresh and stale electrolyte foam No. Items The average content of elements in the foam, wt.% fresh stale one Sodium 18.43 17.15 2 Aluminum 14.84 14.31 3 Fluorine 29.71 28.85 four Calcium 1,0 0.9 5 Magnesium 0.23 0.25 6 Iron 1.27 1.47 7 Silicon 0.14 0.26 8 Sulfur 0.50 0.45 9 Potassium 0.27 0.27 table 2 The average composition of regeneration cryolite, wt.% No. Item name Item Content Connection Name Compound Content one Na 30.00 Cryolite Na ₃ AlF ₆ 75.24 2 Al 11.21 Sodium hydroalumocarbonate NaAl (CO ₂ ) (OH) ₂ 8.36 3 F 43.20 four K 1.10 Elpazolite K ₂ NaAlF ₆ 3.41 5 Ca 0.62 Calcium Fluoride CaF ₂ 1,208 6 Mg 0.10 Magnesium Fluoride MgF ₂ 0.256 7 Fe 0.43 Iron oxide Fe ₂ O ₃ 0.615 8 Si 0.11 Silicon Dioxide SiO ₂ 0.235 9 S 2.21 Sodium Sulfate Na ₂ SO ₄ 9.79 10 C 0.89 Carbon C 0.89 Table 3 The average composition of flotation cryolite, wt.% No. Item name Item Content Connection Name Compound Content one Na 23.30 Na ₃ AlF ₆ 54.61 2 Al 19.13 Al ₂ O ₃ 13.90 3 F 43.87 Na ₅ Al ₃ F ₁₄ 18.52 four Ca 0.86 CaF ₂ 1.68 5 Mg 0.51 MgF ₂ 1.31 6 K 1.33 K ₂ NaAlF ₆ 4.12 7 S 0.25 Na ₂ SO ₄ 1,11 8 C 1.09 C 1.09 9 Fe 0.15 Fe ₂ O ₃ 0.21 10 Si 0.17 SiO ₂ 0.36 Al metallic. 1.05 Resinous 1,50 Other 0.54 Note. Calcium and magnesium fluorides can be present in the form of complex compounds, for example: CaAlF ₅ , NaF · 1,5CaF ₂ · AlF ₃ , NaMgF ₃ , Na ₂ MgAlF ₇ . Table 4 The average composition of the circulating electrolyte, wt.% No. Item name Item Content Connection Name Compound Content one Na 25.10 Na ₃ AlF ₆ 47.78 2 Al 14.91 Al ₂ O ₃ 3.87 3 F 52.36 Na ₅ Al ₃ F ₁₄ 38.16 four Ca 4.11 CaF ₂ 8.1 5 Mg 0.38 MgF ₂ 0.98 6 C 0.10 C 0.10 7 Fe 0.08 Fe ₂ O ₃ 0.11 8 Si 0.06 SiO ₂ 0.13 9 Other 2.90 Other 0.83

The proposed solution uses secondary fluorine-containing materials with a fluorine content of at least 26 wt.%, Which is fed into the mixture to obtain Portland cement clinker as a fluorine-containing mineralizer in an amount that provides a fluorine content of 0.07-0.25 wt.% In the initial charge.

The minimum fluorine content (26 wt.%) Of all secondary fluorine-containing materials is electrolyte carbon foam. In other fluorine-containing materials, the fluorine content is higher. In particular, the minimum fluorine content in regeneration cryolite is ~ 39 wt.%, In flotation cryolite ~ 40 wt.%, In the circulating electrolyte ~ 48 wt.%.

With optimal dosing of secondary fluorine-containing materials for the electrolytic production of aluminum into the raw clinker board, they can be considered a full-fledged alternative to natural fluorine-containing mineralizers.

When using these materials for the electrolytic production of aluminum as a fluorine-containing mineralizer, it is necessary to take into account the fact that a certain amount of alkali metals, mainly sodium, in the form of sodium fluoroaluminates is introduced with the fluorine-containing material. Sodium fluoroaluminates (cryolite and chiolite), which form the basis of the proposed fluorine-containing mineralizer, interact with calcium oxide during sintering of the raw material charge, resulting in the formation of fluorspar. Moreover, the first formation of fluorspar occurs as a result of the interaction of calcium oxide with aluminum fluoride - the product of thermal dissociation of cryolite and chiolite. In this case, fluoride compounds during sintering mainly go into clinker.

The alkaline phases of clinker are not useful, therefore, when calculating the clinker charge, the amount and composition of the proposed secondary fluorine-containing materials (mineralizers) must be selected taking into account the alkaline load introduced by the main components of the raw material charge (limestone, clay, cinder ...).

As a result of laboratory studies, confirmed by industrial tests, it was found that the addition of the proposed secondary fluorine-containing materials should be kept in the range of 0.07 ÷ 0.25 wt.% In terms of fluorine. Moreover, the additive can be either a single type of material of a secondary fluorine-containing material, or a mixture of several types of materials.

The choice as an additive of one or another type of material or their combination is also the value of the mineralizer additive is determined based on the quality indicators of the main components of the initial raw material charge. In the case of easily sintering the main components of the charge (for example, chalk and clay), the amount of mineralizer introduced into the charge corresponds to the region near the lower declared limit (0.07-0.12 wt.% In terms of fluorine). Upon receipt of clinker from difficultly sintered raw materials (marble, fuel ash ...), the addition of a mineralizer from secondary fluorine-containing materials will vary in the region of the upper claimed limit (0.20-0.25 wt.% In terms of fluorine). It is also necessary to control the total alkali content in the clinker charge.

With a high content of alkali metals in the initial charge, it is advisable to reduce the volume of the additive, and the proportion of the additive is determined individually for each specific production, taking into account the raw materials and technology used. The lower limit of 0.07 wt.% In terms of fluorine, as claimed in the claims, is determined, firstly, from the point of view of economic feasibility of using the proposed method. Secondly, practical confirmation has been obtained that even when using basic cement raw materials with a high initial content of alkaline and alkaline earth elements, regenerative cryolite is added as the most saturated waste in the alkali metal part (25-30 wt.% Na, 0.8-1.2 wt.% K) in an amount of 0.07 wt.% (in terms of fluorine), it is possible to obtain cement of satisfactory quality with a moderate degree of salt formation. The upper limit of the content of fluorine-containing materials (0.25 wt.%) Was also determined during laboratory tests for the similar raw materials mentioned above, but electrolyte carbon foam with the content of Na - 16-18 wt.% And K - 0.1 was used as an additive -0.3 wt.%. In the case when it is necessary to introduce an increased amount of mineralizer, and the total alkali content exceeds acceptable limits, it is proposed to use a combined mineralizer, including secondary fluorine-containing materials and fluorspar.

The compositional options for adding a mineralizer when using secondary fluorine-containing materials in the form of electrolyte coal foam, reverse electrolyte, flotation and / or regenerative cryolite, mixed cryolite, as well as combinations of various types of the main components of the initial cement raw material mixture are endless. Therefore, the specific composition of the additive of secondary fluorine-containing materials for aluminum electrolytic production is determined for each specific production, each specific type of raw material.

A comparative analysis of the proposed technical solutions with other known solutions in this field revealed the following.

1. Known "A method of manufacturing Portland cement and a method of manufacturing concrete and reinforced concrete products based on manufactured Portland cement" (RF patent No. 2060979 C04B 7/02, 09/29/1995, [3]), in which as the mineralizer used: calcium fluoride, sulfate calcium, silica gel, phosphogypsum.

In the proposed solution, secondary fluorine-containing materials for the production of aluminum with a fluorine content of at least 26 wt.% Are used as a mineralizer. They are fed into the charge to obtain Portland cement clinker in an amount providing a fluorine content of 0.07-0.25 wt.% In the initial charge.

2. The known "Method for producing pellets of fluorspar" (ed. St. USSR No. 979512, C22B 1/243, 1982 [4]), in which aluminum binder dust is used as a binder in an amount of 2-2.5 weight. %

The proposed solution uses secondary fluorine-containing materials for the production of aluminum with a fluorine content of at least 26 wt.% And feed them into the mixture to obtain Portland cement clinker as a fluorine-containing mineralizer in an amount providing a fluorine content of 0.07-0.25 weight in the initial charge. %

3. The well-known "Method of manufacturing quick-hardening Portland cement and a method of manufacturing concrete based on it" (RF patent No. 2304562, C04B 7/42, 04/12/2005 [5]). In the method, the raw mixture contains calcium, aluminosilicate and glandular components, includes sodium and potassium oxides, as well as calcium sulfates and calcium fluoride. The content of calcium fluoride in the feed mixture in terms of fluorine is 0.15-0.4 wt.%. The sulphates of the feed mixture are alkali and / or alkaline earth metal sulfates.

The use of calcium fluoride in the form of ore or concentrate is associated with additional costs for its extraction, concentration, and in the case of using poor ore with CaF ₂ content of 20-30%, the cost of transporting waste rock. This increases the cost of commodity Portland cement compared with the cost of replacing CaF ₂ (in whole or in part) with secondary fluorine-containing materials for the electrolytic production of aluminum with a fluorine content of at least 26 wt.%, As in the proposed solution, which is fed to the mixture to produce Portland cement clinker as fluorine-containing mineralizer in an amount providing a fluorine content in the initial charge of 0.07-0.25 wt.%.

As a result of the comparative analysis, no technical solutions have been identified that are characterized by a combination of features similar to the combination of features that characterize the proposed technical solution, which allows us to conclude that the proposed solution meets the patentability condition of "inventive step".

The proposed technology is as follows.

Example 1

Obtaining Portland cement clinker from easily sintered materials

Prepared 4 charges for the production of Portland cement clinker using the following raw materials.

Charge 1: chalk - 79.5%, clay - 15.8%, cinder - 3.5%, high aluminate clay - 1.2%. Without the addition of a mineralizer.

Charge 2: The basic composition is identical to charge 1, to which carbon electrolyte foam was added as a mineralizer based on the fluorine content of the initial charge 0.05 wt.%.

Charge 3: The basic composition is identical to charge 1, to which carbon electrolyte foam was added as a mineralizer based on the fluorine content of the initial charge 0.07 wt.%.

Charge 4: The basic composition is identical to charge 1, to which carbon electrolyte foam was added as a mineralizer based on the calculation of fluorine content in the initial charge of 0.10 wt.%.

The chemical composition of the raw materials is given in table 5-9. The use of chalk as the main calcium-containing component of the mixture to obtain Portland cement clinker provides “soft” conditions for sintering of the main clinker components. In this regard, the addition of a fluorine-containing mineralizer is selected in the region of the lower recommended limit (0.07 wt.%).

Sintering of a clinker charge No. 1-4 with and without a different mineralizer addition in the form of carbon electrolyte coal foam was carried out in a tubular rotary kiln with a diameter of 5.5 m and a length of 135 m. The average water content in the raw material charge was 40.1 wt.%. With the introduction of a fluorine-containing mineralizer in the composition of the raw material charge, according to operational technological indicators, the operation of the furnace was adjusted in terms of changing the productivity of the charge and the consumption of natural gas for the sintering process.

Table 9 The chemical composition of chalk (for SSPTs 500-D0) p.p.p. Si Al Fe Ca Mg S K Na F W Average value 26,50 0.21 16,20 1.37 1.10 0.22 0.49 0.24 18.50 29.20 3.60

Some technological indicators of the furnace are given in table 10. The chemical and modular composition of the resulting clinkers is presented in table 11.

Table 10 Raw material charge Medium produces. Clinical furnace, t / h Average specific gas consumption, m ³ / t clinker Average weight 1 dm ³ clinker, g Charge 1 51 174 1410 Charge 2 52 172 1470 Charge 3 54 166 1520 Charge 4 55 163 1580

The results of physical and mechanical tests of cements obtained from clinkers are given in table 12.

Table 12 Physico-mechanical characteristics of cements PC-500-D0 Cement SO ₃ Beats dressings-st, cm ² / g Grind, sieve 0.08 (ost.) Setting time, hour: min. Ultimate Strength hardening, MPa Bend Compression Start The end. 3 days 3 days 28 days Cliner 1 2.60 3220 3.8 2:35 4:35 5.1 33.1 50,0 Cliner 2 2.68 3210 3.6 2:30 4:40 5.3 33.8 50.3 Cliner 3 2.62 3250 3,7 2:35 4:40 5.2 33.7 50,5 Cliner 4 2.65 3110 5.1 2:45 4:55 4.4 32,5 49.2

Based on the obtained data from industrial tests, the following conclusions are made:

1. The introduction of a fluorine-containing mineralizer in the form of electrolyte coal foam in the composition of the charge practically does not affect the phase and modular composition of the clinker, while ensuring the simultaneous:

- increase the specific productivity of the sintering furnace;

- decrease in specific consumption of natural gas;

- an increase in the weight of a liter of clinker.

2. The optimal addition of fluorine-containing mineralizer is ~ 0.07 wt.% For fluorine. This provides:

- increase the specific productivity of the sintering furnace by 5.5-6%;

- decrease in specific consumption of natural gas by 4.5%;

- an increase in the weight of a liter of clinker by 7.8%.

3. An increase in the addition of a fluorine-containing mineralizer of more than 0.07% is impractical despite a further increase in furnace productivity and a decrease in gas consumption, because leads to burnout of clinker due to the formation of an excess amount of the liquid phase in the furnace. As a result

the clinker grinding ability is deteriorating during the production of cement from it, the setting time of the resulting cement is increased, and its activity is also reduced. In addition, the consumption of the mineralizer itself increases.

Example 2

Obtaining Portland cement clinker from difficultly sintered materials

We prepared 3 charges for the production of Portland cement clinker of the same composition using the following raw materials: marble + fuel ash from a thermal power plant. The marble used contains a significant amount of undesirable impurities - magnesium oxide and inclusions of low reactivity silica. Fuel ash, unlike clay used in most plants, prevents the normal formation of granules in rotary kilns, which leads to increased dust removal from the furnaces, and unregulated dust return creates an instability of the clinker firing mode. In addition, significant fluctuations in the chemical composition of ash and the presence of inactive forms of silica in it are also an obstacle to obtaining high-quality clinker.

As a fluorine-containing mineralizer, a circulating electrolyte from electrolysis cells was added to the mixture to produce aluminum of the following composition, wt.%: F = 51.9; Na = 25.2; Al = 15.3; Ca = 3.95; Mg = 0.31; Si = 0.09; Fe = 0.11. The amount of mineralizer was selected taking into account the fact that the raw material used is difficult to sinter and amounts to fluorine, respectively, wt.%: 0.20; 0.25; 0.30. The chemical composition of raw sludge with the addition of fluorine-containing circulating electrolyte is given in table.13.

Sintering of a clinker charge No. 1-3 with various addition of a mineralizer in the form of a reverse electrolyte was carried out in a tubular rotary kiln with a diameter of 3.6 m and a length of 150 m.

The chemical and mineralogical composition of clinkers with the addition of a fluorine-containing reverse electrolyte is presented in Table 14.

The clinkers obtained are quite similar in composition; while their modular characteristics were:

KH = 0.92-0.93; n = 2.10-2.13; p = 1.29-1.33.

The estimated content of the main clinker minerals was common for Portland cement for general construction purposes and varied within the following limits:

C ₃ S = 59-60%; C ₂ S = 13-14%; C ₃ A = 7.3-7.6%; C ₄ AF = 13%.

The content of free calcium oxide and iron oxide is negligible, which indicates a satisfactory burning of clinkers. The vibration limits of these oxides were:

CaO _st = 0.18-0.31%; FeO = 0.06-0.25%.

Table 13 The chemical composition of raw sludge with the addition of fluorine-containing circulating electrolyte source series The content of oxides,% ppp SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ Cao MgO SO ₃ Na ₂ O K ₂ O TiO ₂ P ₂ P ₅ CrO ₃ Σ F one 2 3 four 5 6 7 8 9 10 eleven 12 13 fourteen fifteen Charge1 34.00 12.86 3.21 2.75 42.90 2.40 0.26 0.38 0.40 0.20 0.12 no 99.48 0.20 Charge 2 34.00 12.86 3.21 2.75 42.90 2.40 0.26 0.38 0.40 0.20 0.12 no 99.48 0.25 Charge 3 34.00 12.86 3.21 2.75 42.90 2.40 0.26 0.38 0.40 0.20 0.12 no 99.48 0.30

Результаты физико-механических испытаний цементов лабораторного помола, полученных на основе клинкеров с добавкой фторсодержащего оборотного электролита, приведены в табл.15.

The results of physical and mechanical tests of laboratory grinding cements obtained on the basis of clinkers with the addition of a fluorine-containing circulating electrolyte are given in Table 15.

Table 15 Physico-mechanical characteristics of laboratory grinding cements Cement SO ₃ Beats dressings-st, cm ² / g Grind, sieve 0.08 (ost.) Setting time, hour: min. Ultimate Strength hardening, MPa Bend Compression Start The end. 3 days 3 days 28 days 1 day Cliner 1 2,50 3060 6.8 4:40 7:20 a.m. 6.0 33.5 47.4 27.1 Cliner 2 2,55 3050 6.6 4:40 7:10 a.m. 5.8 35.0 47.8 27.5 Cliner 3 2,52 3010 7.3 5:45 a.m. 8 a.m. 5,4 31.9 46.2 24.4

Tests have shown that an increase in the CaF ₂ content in clinker above 0.25% leads to a decrease in grade cement strength by ~ 1.5 MPa and strength after steaming by ~ 2.5-3 MPa.

It was noted that with an increase in the F content in cements of more than 0.25%, the setting time, already quite considerable, increases, which is undesirable and has a retarding effect on hardening processes, especially in the first hours of hardening. This leads to a decrease in the early strength and tendency of cements to salt formation.

The degree of salt formation (K v _{/ v} ) of cements was determined by the known Hyprocement technique. According to this technique, the K _{/ V} value is the total content of calcium, sodium, and potassium oxides (mg / l) in aqueous extracts from hardening cement slurry samples taken over 4 days. For the final result, which determines the tendency of cements to salt formation, the average value of the 3 values of K _{in / about is} taken.

The results of determining the degree of efflorescence of laboratory grinding cements are given in table.16.

Table 16 The results of determining the degree of efflorescence Content F% SQ / o, mg / l Clinker 1 0.20 825-867 Clinker 2 0.25 917-967 Clinker 3 0.30 1025-1065

An analysis of the results showed that cements with the addition of a circulating electrolyte of 0.20-0.25% are characterized by a moderate degree of salt formation. With an increase in the input of the addition of a fluorine-containing mineralizer of more than 0.25% _{, the w / v} increases to 1025-1065 mg / l, as a result of which the construction and technical properties of cement deteriorate.

Example 3

Obtaining Portland cement clinker from charge materials with a high alkali content

In the case when the initial raw material mixture for the production of Portland cement clinker contains an increased amount of alkali, it is proposed to use a combined fluorine-containing mineralizer consisting of secondary fluorine-containing materials and fluorspar.

Table 17 shows the calculation of the composition of the raw material charge and the resulting clinker when using mixed cryolite with a fluorine content of 43 wt.% In an amount of 0.20% of the weight of dry starting components as a mineralizer.

Table 17 The composition of the starting materials and raw material charge, wt.% Components p.p.p. SiO ₂ Al ₂ os Fe ₂ O ₃ Cao MgO F R ₂ O Ocher 0.17 1.12 0.49 0.22 0,07 0.06 - 0,07 Limestone 32.61 1,64 0.59 0.36 42.25 0.56 - 0.09 Clay 1.45 10.71 2,37 1.17 1,11 0.50 - 0.52 Fe sod. additive 0.06 0.46 0.11 0.76 0,07 0.01 - 0.02 Secondary mixed cr 0.01 - * 0.23 - * 0.01 - * 0.20 0.16 Raw material charge 34.30 13.93 3.79 2,51 43.51 113 0.20 0.86 Clinker 21.45 5.84 3.87 67.01 1.74 0.31 1.32 Note. * - the content of the compound is less than 0.01%

Due to the fact that the initial charge materials (especially clay and ocher) contain an increased amount of alkali, the introduction of a mixed cryolite with a high alkali content into the charge leads to the fact that the resulting raw material charge and Portland cement clinker do not meet established standards for alkali oxide content (not more than 1.20% R ₂ O in clinker).

Table 18 shows the calculation of the composition of the raw material charge and the resulting clinker using a combined cryolite mineralizer with a fluorine content of 43 wt.% In the amount of 0.10% and CaF ₂ fluorspar concentrate in the amount of 0.10% with the content of the main substance 92% .

Table 18 The composition of the starting materials and raw material charge, wt.% Components p.p.p. SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ Cao MgO F R ₂ O Ocher 0.17 1.12 0.49 0.22 0,07 0.06 - 0,07 Limestone 32.61 1,64 0.59 0.36 42.25 0.56 - 0.09 Clay 1.45 10.71 2,37 1.17 1,11 0.50 - 0.52 Fe sod. additive 0.06 0.46 0.11 0.76 0,07 0.01 - 0.02 Secondary mixed cryol. - * - * 0.12 - * - * - * 0.10 0.08 CaF ₂ Concentrate - * - * - * - * 0.11 - * 0.10 - Raw material charge 34.29 13.93 3.68 2,51 43.61 1.13 0.20 0.78 Clinker 21.45 5.67 3.87 67.16 1.74 0.31 1.20 Note. * - the content of the compound is less than 0.01%

The initial raw material charge prepared in accordance with the calculation in Table 18 corresponds to the established standards (not more than 1.20% R ₂ O in clinker) and has the following modular characteristics: KN = 0.937; n = 2.31; p = 1.41. When sintering the mixture, the following mineralogical composition of clinker was obtained: C ₃ S = 65.6%; C ₂ S = 11.5%; C ₃ A = 7.8%; C ₄ AF = 11.6%.

Due to the use of secondary fluorine-containing materials for the electrolytic production of aluminum with a fluorine content of at least 26 wt.%, The following are ensured:

- disposal of excess secondary fluorine-containing materials from aluminum electrolytic production;

- reduction of the technological load on certain types of equipment and energy costs at aluminum plants;

- expansion of the raw material base of fluorine-containing mineralizers of the mixture to obtain Portland cement clinker with the replacement of scarce traditionally used mineralizers;

- reduction of specific fuel consumption for clinker firing;

- increasing the productivity of the kiln;

- increase in the overhaul period of the kiln;

- a moderate degree of salification of the resulting cement;

- sufficient strength indicators of cement in the early stages of hardening;

- reduction in the cost of cement.

Literature

1. RF patent No. 2312815, C01F 7/38, C22B 7/00, 2007

2. RF patent No. 2291208, C22B 1/245, 2007

3. RF patent No. 2060979 C04B 7/02, 09/29/1995

4. A.S. USSR No. 979512, C22B 1/243, 1982

5. RF patent No. 2304562 C04B 7/42, 04/12/2005

Claims (6)

1. A method of processing fluorine-containing materials used in the electrolytic production of aluminum, including feeding, mixing fluorine-containing materials with charge components and heat treatment of the charge, characterized in that secondary fluorine-containing materials with a fluorine content of at least 26 wt.% Are fed, which are supplied as a fluorine-containing mineralizer in an amount that provides the fluorine content in the original mixture to obtain Portland cement clinker 0.07-0.25 wt.%. 2. The method according to claim 1, characterized in that the electrolyte carbon foam is used as the secondary fluorine-containing material. 3. The method according to claim 1, characterized in that a recycled electrolyte is used as the secondary fluorine-containing material. 4. The method according to claim 1, characterized in that flotation and / or regenerative cryolite is used as a secondary fluorine-containing material. 5. The method according to claim 1, characterized in that mixed cryolite is used as the secondary fluorine-containing material. 6. The method according to claim 1, characterized in that the composition of the fluorine-containing mineralizer is additionally introduced calcium fluoride in the following ratio of components, wt.%:
secondary fluorine-containing material used in electrolytic aluminum production 30-90 calcium fluoride rest