RU2845261C2 - Method of producing ferrotitanium from titanium-containing wastes - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly to production of ferrotitanium from titanium production wastes. Method includes preparation of charge materials, stage-by-stage melting of charge materials in electroslag furnace with non-consumable electrode. At the first step, from a mixture consisting of metallized titanium-containing wastes, aluminium in form of chips, ferrosilicon, unalloyed steel wastes, an aluminium-titanium-silicon-iron-containing melt is obtained, containing, wt.%: 20-30 Ti, 25-30 Al, 5-8 Si, iron – balance, and at the second stage, the obtained melt is refined from excess aluminium with an oxidised portion of titanium-containing wastes in an amount based on removal of 70% of aluminium in the melt in the presence of lime. Upon completion of the refining process, the melt is cooled and the ingot is subjected to cutting.

EFFECT: invention enables to obtain ferrotitanium with titanium content of 80-88%, as well as reduce environmental load.

3 cl, 3 tbl, 1 ex

Description

The invention relates to metallurgy, in particular to the production of ferrotitanium grades FTi35S7(8) according to GOST 4761-91 and grades FeTi40Al8(10) according to ISO 5454-80, which are in demand in ferrous metallurgy, where they are used as an alloying component for the production of low-alloy structural and cast steels, as well as stainless and heat-resistant steels.

In the aluminothermic production of ferrotitanium of the specified grades, ilmenite concentrate or its mixture with rutile concentrate is mainly used as titanium-containing raw material, using out-of-furnace or furnace methods [1].

Methods of aluminothermic production of ferrotitanium with increased titanium content are known due to preliminary enrichment of ilmenite concentrates in titanium dioxide by removing iron oxides from them [2]. The disadvantage of such methods is the complication of the technology and the increased cost of titanium in the ferroalloy.

A method is known for introducing waste - crushed slag from ferrotitanium production containing 17-21 wt. % TiO ₂ - into the aluminothermic batch [3]. The disadvantage of this method is the need, from the point of view of the balance of titanium in the batch, to introduce into it ilmenite concentrate with a TiO ₂ content of 59-65 wt. % and crushed electric furnace titanium-containing slag (54-59 wt. % TiO ₂ ) in an amount seven times greater than the volume of crushed slag from ferrotitanium production containing 17-21 wt. % TiO ₂ introduced into the batch.

A method for producing a high-titanium ferroalloy from ilmenite is known [4], according to which, at the first stage of smelting, ilmenite is enriched with titanium oxides by removing most of the iron oxides from it with carbon, and then a mixture of crushed slag rich in titanium oxides and aluminum is formed in a metal shell and such a consumable electrode is melted under a layer of flux in an electroslag furnace. The disadvantage of this technology is the two-stage nature and the complexity of forming the consumable electrode while ensuring uniform density of the filler - a very important characteristic from the point of view of the stability of the electrical parameters of electroslag smelting, and, in addition, the method does not provide for the use of titanium production waste in the charge.

A method is known for processing titanium flame cutting slag (industrial waste from titanium production) to obtain ferrotitanium by reducing titanium oxides from this waste with ferroaluminum in an electroslag furnace [5].

The disadvantage of the method is the use in the charge of only one of the many industrial wastes of titanium production - titanium flame cutting slag and the use of ferroaluminum as a reducing agent, the latter requires a separate processing stage for its manufacture. In addition, the resulting ferrotitanium has a high nitrogen content of 0.82-1.46 wt. % due to the presence in the titanium flame cutting slag of metallized titanium particles (up to 50%) containing 2.5-3.5 wt. % nitrogen, which limits the scope of application of finished ferrotitanium in steelmaking.

The closest in technical essence, the titanium-containing raw materials used, the smelting technology and the achieved result is the method of aluminothermic production of ferrotitanium [6], which allows for the recycling of several types of titanium production waste at once, in particular:

- waste (sludge) from abrasive processing of titanium semi-finished products (BZ);

- titanium scale from hot processing of titanium blanks (HT);

- cyclone dust captured during abrasive processing of titanium semi-finished products (TSP).

In this case, in an electroslag furnace with a non-consumable electrode, ferrotitanium is obtained containing 35-50 wt.% titanium, and its quality is improved by reducing the nitrogen content in the resulting alloy to a level of less than 0.5 wt.%.

The disadvantage of the method is the need for portioned feeding of the main and settling parts of the charge into the furnace through different chutes with a regulated interval of 1-3 minutes between these parts. Such regulation complicates the work of smelters in the conditions of systematic use of such technology. In addition, to reduce the nitrogen content in the finished ferrotitanium, metallized parts of the sludge from the abrasive treatment of titanium semi-finished products, which contain 2-3 wt. % nitrogen, are excluded from the charge.

The objective of the present invention is to simplify the technology of smelting ferrotitanium using the above-mentioned titanium production waste in the charge, using metallized parts of the waste and obtaining ferrotitanium containing more than 35 wt.% titanium and ensuring the nitrogen content in the resulting alloy at a level of less than 0.6 wt.%, as in traditional 35% ferrotitanium.

When solving the problem, we proceeded from the following assumptions:

- from the ternary diagram of the elements aluminum-titanium-iron [7] it follows that in a wide range of ratios of these elements, the component composition has low melting points - no more than 1340°C, therefore it is easily alloyed and can be considered as a base alloy for its subsequent conversion into ferrotitanium;

- our own research has shown that when metallized nitrogen-containing parts of titanium-containing waste (in which nitrogen is present in the form of titanium nitrides) are melted together with metallic aluminum, nitrogen is redistributed toward the formation of aluminum nitrides, which are insoluble in the alloy, are lighter, and float to the slag. This is how denitrification of the metal system occurs.

Taking into account the above, the stated task is achieved by the fact that in the claimed method for producing ferrotitanium, including the preparation of charge materials, the step-by-step melting of charge materials in an electroslag furnace with a non-consumable electrode, at the first stage, from a charge consisting of metallized titanium-containing waste, scrap or shavings of secondary aluminum, ferrosilicon, unalloyed waste of low- or medium-carbon steels, an aluminum-titanium-silicon-iron-containing melt is obtained with the composition (wt.%): 25-30 Al, 20-30 Ti, 6-8 Si, iron is the rest.

At the second stage of melting, the obtained melt is refined from aluminum with oxidized titanium-containing waste, mainly titanium scale in an amount calculated to remove about 70% of the aluminum in the melt in the presence of lump (20-40 mm) non-hydrated lime. The use of lime pieces of a fraction of 20-40 mm ensures bubbling of the melt, which contributes to more efficient refining reactions. After refining, the obtained ferrotitanium melt is poured into ingots (or left in the furnace), cooled and crushed to the desired fraction.

Metallized parts of waste (sludge) from abrasive processing of titanium semi-finished products and (or) slag from flame cutting of titanium are used as metallized titanium-containing waste.

In addition to titanium scale, oxidized titanium-containing wastes are used that contain titanium oxides: the oxidized portion of sludge from abrasive processing of titanium semi-finished products and (or) the oxidized portion of slag from flame cutting of titanium and (or) dust from titanium gas cleaning.

To evaluate the specific parameters of the two-stage technology, mathematical modeling of such technology was performed, then on this basis laboratory melts were carried out in a Tamman furnace, taking into account the production of an aluminum-titanium-silicon-iron alloy (base melt) at the first stage of melting, and its refining from aluminum at the second stage.

As a result, we obtained the optimal ratio of elements in the base melt and the consumption of oxidizing and fluxing materials. The ratio of elements in the base melt is, wt. %: aluminum 25-30; titanium 20-30; silicon 6-8, the rest is iron.

When the aluminum content in the base melt is below 25%, the volume of titanium-containing refining waste involved in the process decreases, due to which the titanium content in the final ferrotitanium does not reach the declared minimum value of 35%. When the aluminum content in the base melt is more than 30%, an increased volume of titanium-containing refining materials and fluxing agents is required, which leads to an increase in the slag multiplicity during this period and deterioration of the refining processes from aluminum.

When the titanium content in the base melt is below 20%, the volume of metallized parts of titanium-containing waste involved in the melting is reduced - the most problematic titanium-containing waste. In addition, to achieve a titanium content of more than 35% in the finished alloy after refining, it will be necessary to have an aluminum content of more than 30% in the base melt, which leads, as indicated above, to increased consumption of refining materials and a decrease in the efficiency of refining.

When the titanium content in the base melt is more than 30%, the effect of its denitrification is reduced during the joint smelting of metallized titanium-containing waste with the presence of nitrogen with the identified optimal aluminum content.

The total consumption of oxidized titanium-containing materials (mainly titanium scale and additionally oxidized parts of sludge from abrasive processing of titanium semi-finished products, from slag from flame cutting of titanium, dust from gas cleaning of titanium) for refining the base alloy from excess aluminum in the second period of melting is calculated based on the stoichiometric ratio of the reaction components: 3TiO ₂ +4Al = 3Ti + 2Al ₂ O ₃ taking into account the content of titanium oxides in these materials, removal of about 70% of aluminum from the base melt, with an excess of 10-15% to ensure the passage of refining reactions, as is used in ferroalloy processes.

Under these conditions, the calculated consumption of titanium scale, if only it is used for refining, will be 480 kg per ton of base melt with a content of 25% aluminum in the base melt and 580 kg with a content of 30% aluminum.

The consumption of lime at the second stage of smelting is taken based on the ratio of aluminum participating in the reactions and lime of approximately 1:1, as we practice when smelting ferrotitanium in an electroslag furnace from ilmenite concentrates using standard technology.

At the end of the refining stage of smelting, upon visual assessment of the presence of thick slag, thinners can be introduced in an amount of up to 5% (weight) of the slag volume in the form of quartzite and (or) cryolite, which improves the separation of the metal and slag phases and reduces metal losses with the refining slag during cutting of ferrotitanium.

Ferrosilicon is introduced at the first stage of melting based on the calculation of obtaining 5-8% silicon in the melt. The specified amount of silicon has virtually no effect on the melting temperature of the aluminum-titanium-iron alloy. Silicon is introduced into the charge when smelting ferrotitanium from ilmenite concentrate, since silicon helps to increase the extraction of titanium from the raw material due to the formation of strong titanium silicides [1, pp. 272, 275]. The silicon content in the first stage melt of 5-8% is selected taking into account that grade ferrotitanium according to GOST 4761-91 and ISO 5454-80 grades FTi35S7(8), FeTi40Al8(10) contains up to 5-8% silicon.

Examples of specific implementation

Ferrotitanium melting using titanium-containing industrial waste was carried out in an electroslag furnace with a non-consumable carbon electrode. Furnace type USh 148, transformer power - 760 kW, electrode diameter 150-200 mm, refractory brick shaft. Metal capacity up to 250 kg.

To calculate the weight amount of components in the composition of the first stage of melting batch, the following was adopted (based on preliminary melting of the alloying components): aluminum burnout - 20%, titanium transfer to the melt from its amount contained in titanium-containing metallized waste - 85%. Silicon and iron burnout were not taken into account due to their insignificance.

The calculated volume of the melt, based on the furnace capacity, was taken as 220 kg. The amount of titanium scale and other oxidized titanium-containing materials in the refining stage of the melt was calculated based on the stoichiometric ratios of the oxidation reaction of aluminum with titanium dioxide, taking into account:

- the calculated volume of the melt for which the first stage of melting was prepared - 220 kg;

- data from express analysis of the aluminum content in the melt;

- known content of titanium dioxide in the oxidized titanium-containing materials used;

- increasing the amount of refining materials containing titanium dioxide by 10-15% to intensify refining processes.

Table 1 shows the options for using metallized titanium-containing waste at the first stage - melting of components and oxidized titanium-containing waste at the second stage - refining of the base melt, where titanium-containing waste is designated:

B3 - sludge from abrasive processing of titanium semi-finished products;

SHOR - titanium fire cutting slag;

CP - titanium gas cleaning dust (cyclone dust).

Good alloyability of charge materials containing titanium, aluminum, iron in the presence of silicon and stability of obtaining the declared quantitative composition of the specified chemical elements in the base melt at the first stage of melting were confirmed (Table 2, express analysis).

Table 3 shows the compositions of the finished ferrotitanium after completion of the second stage - refining from aluminum.

During melting No. 1, when cutting the melt products, a noticeable amount of small ferrotitanium droplets entangled in the slag were found. During subsequent meltings, quartzite or cryolite was added at the end of the process to liquefy the slag in an amount of 6-7 kg, which improved the settling of ferrotitanium droplets from the slag.

As a result of melting according to the selected parameters, ferrotitanium was obtained with the following content, wt. %: titanium 38.9-52.6; aluminum 6.4-8.1; silicon 4.8-6.6 with the impurity content within the limits of the standards for ferrotitanium grades FTi35S7(8) according to GOST 4761-91 and grades FeTi40Al8(10) according to ISO 5454-80.

In this case, the idea of joint melting of aluminum and metallized titanium waste containing nitrogen at the first stage was justified, when conditions are created for the redistribution of nitrogen between titanium and aluminum and the floating of aluminum nitrides into the slag, i.e. the amount of nitrogen in the melt of the base alloy is reduced. As a result, the nitrogen content in the final ferrotitanium alloy was 0.48-0.56%, which corresponds to its content in traditional 35% ferrotitanium [1, p. 280].

The extraction of titanium from titanium-containing waste into ferrotitanium was 80-88%, which is higher than with the traditional aluminothermic technology of its production from ilmenite concentrate (77-79%).

Thus, the smelting of ferrotitanium from titanium-containing waste according to the parameters of the proposed invention is realized with the production of quality grade ferrotitanium and allows to involve in production simultaneously a wide range of solid waste of titanium production, both in the form of their metallized part and oxidized parts. This simplifies the disposal of waste in order to reduce the environmental load on the territory. At the same time, the cost price of the obtained ferrotitanium is reduced due to the cheapness of titanium-containing waste in comparison with traditional raw materials - ilmenite or rutile concentrate.

At present, the proposed method for obtaining ferrotitanium from titanium-containing industrial waste is being implemented according to the selected technological parameters in a pilot industrial version with the release of batches of ferrotitanium purchased by consumers.

Sources of information

1. M.A. Ryss, Ferroalloy production, Moscow, Metallurgy, 1985, p. 269-281.

2. Russian Federation Patent No. 2398907, Method for producing high-percentage ferrotitanium, published 10.09.2010.

3. Russian Federation Patent No. 2608936, Charge and method for aluminothermic production of ferrotitanium using it, published 26.01.2017.

4. Russian Federation Patent No. 2329322, Method for producing high-titanium ferroalloy from ilmenite, published 20.07.2008.

5. Russian Federation Patent No. 2196843, Method of Furnace Melting of Ferrotitanium from Titanium Oxides, published 20.01.2003.

6. Russian Federation Patent No. 2755187, Method for aluminothermic production of ferrotitanium, published 09.14.2021.

7. O.A. Bannykh, P.B. Budberg, S.P. Alisova, et al. Phase diagrams of binary and multicomponent iron-based systems: /reference publication/, M; Metallurgy, 1986.

Claims (3)

1. A method for producing ferrotitanium from titanium-containing waste, including the preparation of charge materials, the step-by-step melting of the charge materials in an electroslag furnace with a non-consumable electrode, characterized in that, at the first stage, from a charge consisting of metallized titanium-containing waste, aluminum in the form of chips, ferrosilicon, unalloyed steel waste, an aluminum-titanium-silicon-iron-containing melt is obtained, containing, by weight %: 20-30 Ti, 25-30 Al, 5-8 Si, iron is the rest, and at the second stage, the obtained melt is refined from excess aluminum by the oxidized portion of the titanium-containing waste in an amount calculated to remove 70% of the aluminum contained in the melt in the presence of lime, and after the refining process is completed, the melt is cooled and the ingot is cut. 2. The method according to paragraph 1, characterized in that metallized nitrogen-containing parts of titanium-containing waste from abrasive processing of titanium semi-finished products and/or slag from flame cutting of titanium are used as metallized titanium-containing waste. 3. The method according to paragraph 1, characterized in that titanium scale and an oxidized portion of waste from abrasive processing of titanium semi-finished products containing titanium oxides, and/or an oxidized portion of slag from flame cutting of titanium, and/or dust from gas cleaning of titanium are used as the oxidized portion of titanium-containing waste.