RU2843353C1 - Method of processing leucoxene flotation concentrate - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy of rare and scattered metals, namely to methods for processing of leucoxene flotation concentrate from ores of Yaregskoe deposit so that pigment titanium dioxide is obtained. Method involves annealing leucoxene concentrate with a carbonaceous reducing agent, pre-pressed into briquettes with size of not more than 20 mm, containing ground to a size of less than 0.063 mm leucoxene concentrate and carbonaceous reducing agent in an amount necessary to reduce rutile to anosovite, and iron to a metal phase, at temperature 1330-1350 °C for 20-25 minutes. Obtained reduced briquettes are cooled to 220-270 °C in an inert atmosphere and subjected to screening with separation of residual carbonaceous reducing agent, which is reused for blending with initial concentrate or filling briquettes from anosovite concentrate. Then anosovite concentrate is crushed, mixed with concentrated sulphuric acid and leached.

EFFECT: reduced duration of the process, exclusion of sintering of the concentrate during annealing and its secondary oxidation during cooling, reduced thermal power consumption.

3 cl, 2 dwg, 3 tbl

Description

The invention relates to the metallurgy of rare and dispersed metals, namely to methods for processing leucoxene flotation concentrate from the ores of the Yaregskoye deposit to obtain pigment titanium dioxide.

This deposit is unique in its kind: it contains the richest reserves of titanium in Russia (up to 40%) and heavy viscous oil. The quality of the titanium ore of the Yaregskoye deposit allows us to expect the production of high-quality pigment titanium dioxide, which is widely used in the production of paints and varnishes, plastics, paper, rubber and artificial fibers. The problems of enrichment and processing of this raw material are related to the fact that the titanium-containing component of the ore, leucoxene, is a polymineral product of alteration of ilmenite with a rutile lattice of the sagenite type, the pores of which are filled with quartz, which complicates the process of separation of titanium and silicon.

A method is known for separating titanium and silicon oxides, which make up leucoxene concentrate, using the hydrodynamic method. The essence of the method is that at the beginning of the process, leucoxene microaggregates are disintegrated by grinding them in rotor-type impact disintegrators to a size of less than 74 μm. The subsequent operation of separating the TiO ₂ and SiO ₂ phases, based on the difference in their densities (2.65 g/cm ³ for quartz and 4.2 g/cm ³ for rutile), is carried out in a water flow on screw sluices (B.A. Ostashchenko, I.N. Burtsev, N.N. Uskov. Method for processing leucoxene concentrates, Russian Federation Patent No. 2032756, cl. 6 C22B 34/12, B03B 5/00, application 06.16.1992).

The disadvantages of the method are the low degree of separation of oxides, the use of complex low-productivity and energy-intensive equipment for grinding the concentrate, high water consumption, and a high residual content of silicon oxide. The resulting material is a semi-finished product and requires further processing to obtain the pigment. When producing pigment by the chlorination method, the use of such material requires additional costs for chlorination of silicon oxide into silicon chloride and its separation from titanium chloride.

A method for processing leucoxene concentrate is known, including its oxidative roasting at temperatures of 900-1000°C, autoclave alkaline leaching to obtain titanium-rich products (71-80% TiO ₂ and 12-20% SiO ₂ ), treatment with hydrochloric acid and subsequent finishing on a concentration table, which makes it possible to obtain a concentrate containing up to 80-85% TiO ₂ (Fedorova M.N. Chemical finishing of titanium concentrate by autoclave leaching of silicic acid. In the book Titanium and its alloys, v. 9. Moscow: Publishing house of the USSR Academy of Sciences, 1963, pp. 36-41).

The main disadvantages of this method are: high consumption of alkaline reagent, the need for an additional operation - acid leaching - to increase the TiO ₂ content in the final product, the difficulty of utilizing a large volume of spent alkaline solutions due to the high SiO ₂ content: when using CaO to precipitate SiO ₂ , the pulp turns into a thick mass, is difficult to mix and is not filtered. As in the previous method, the resulting material is a semi-finished product and requires further processing to obtain pigment.

A method for processing leucoxene concentrate is known, including its roasting with an iron-containing additive, which is a waste product of alumina production in the form of red mud at a ratio of quartz-leucoxene concentrate to the mass of red mud of 1:1.1-1.2, followed by cooling and leaching with sulfuric acid at a temperature of 160-170 ° C. Roasting is carried out at a temperature of 1350-1550 ° C, and sulfuric acid is taken with a concentration of 55-80% in a ratio of 1:1-20 (Patent of the Russian Federation No. 2759100, IPC C22B 34/12, published on 10.04.1995). The main disadvantage of the method is the high costs of preparing the raw materials and transporting them to the processing site.

A method is known for the complex processing of leucoxene concentrate, including roasting with a carbonaceous reducing agent, grinding the resulting cake and leaching it with a mineral acid, characterized in that the leucoxene concentrate is mixed with a carbonaceous reducing agent in an amount ensuring the production of metal carbides and heated at 1600-2000°C, and the ground carbide cake is treated with an aqueous solution of nitric acid with a density of at least 1.05 g/ ^cm3 at a temperature of 35-75°C with the separation of silicon carbide, then metal hydroxides are sequentially precipitated from the solution (RU Patent No. 2090509, IPC C01G 23/047 (1995.01), C01B 31/30 (1995.01), published 09.20.1997).

The method has the following disadvantages. Processing of the sinter with nitric acid of density close to 1.05 g/ ^cm3 at temperature of about 35-40°C is accompanied by low rate of dissolution of titanium carbide (holding time more than 20 hours). Use of concentrated nitric acid of density 1.31 g/ ^cm3 reduces the processing time at 65-75°C to 4 hours. However, when mixing the sinter with acid, uncontrolled heating of the mixture to temperatures above 85°C is possible due to exothermic dissolution reaction, which reduces titanium extraction into solution due to transition of formed titanium hydrate into solid sediment. Additional equipment is required to carry out the process at temperature of 65-75°C. When titanium carbide interacts with nitric acid, a large amount of ultrafine soot carbon is formed, which worsens the filtration process.

The closest in technical essence to the invention is a method for processing leucoxene concentrate, including roasting in the presence of a carbonaceous reducing agent to obtain an anosovite concentrate, grinding it, mixing it with concentrated sulfuric acid, decomposition and leaching.

The restorative roasting is carried out at temperatures of 1200-1350°C for 20-150 minutes, the roasted concentrate is ground to a size of 75 microns and mixed with concentrated sulfuric acid, the mixture is heated to 180-200°C and held for 1.5-2.0 hours, followed by cooling and leaching with water.

During the decomposition process, more than 85% of rutile contained in the leucoxene concentrate passes into anosovite. The degree of titanium oxide extraction into the solution can reach 98% (RU Patent No. 2001138, IPC C22B 34/12, published 03.07.1991).

The method has the following disadvantages. The size of the batch requires the use of rotary kilns for its reduction, which are characterized by a long firing time. Additional time is required to heat the batch to the firing temperature. The process is accompanied by material losses (up to 20%) due to dust removal. Other units (shaft kilns, rotary hearth kilns, etc.) are not suitable for firing without preliminary agglomeration and strengthening of the batch. The carbonaceous reducing agent that has not reacted with the rutile of the leucoxene concentrate during the reduction firing remains in the fired anosovite concentrate, which negatively affects its further processing. The exhaust gases from the firing kiln used for cooling have an excess (more than 300-400°C) temperature and contain CO ₂ and H ₂ O vapors, which can lead to secondary oxidation of anosovite into rutile. During the roasting process, part of the _SiO2 binds with impurity components of the concentrate (oxides of iron, aluminum, calcium, magnesium, manganese, sodium) into silicates of complex composition, which form a solid solution in the form of glass with cristobalite and are distributed along the boundaries between the grains of rutile and free cristobalite. This leads to the formation of a sinter, which can complicate the unloading of the roasted product. The resulting anosovite concentrate, after cooling and grinding in water, must be dried before mixing with concentrated sulfuric acid to prevent its dilution, which increases energy costs.

The technical result of the claimed invention can be implemented using a cost-effective technology for processing oil-titanium ores from the Yaregskoye deposit, which is based on thermal activation of titanium-containing concentrate, which makes it possible to reduce the duration of the process, eliminate sintering of the concentrate during roasting and its secondary oxidation during cooling, and reduce heat and energy costs for the process while maintaining high recovery rates.

The specified technical result is achieved by the fact that in the known method for processing leucoxene flotation concentrate, including roasting leucoxene concentrate in the presence of a carbonaceous reducing agent to obtain an anosovite concentrate, grinding it, mixing with concentrated sulfuric acid and leaching, according to the invention, leucoxene concentrate with a carbonaceous reducing agent, pre-pressed into briquettes no larger than 20 mm in size, containing leucoxene concentrate and a carbonaceous reducing agent ground to a size of less than 0.063 mm in an amount necessary for reducing rutile to anosovite and iron to a metallic phase, is subjected to roasting at a temperature of 1330-1350 ° C for 20-25 minutes, the resulting reduced briquettes are cooled to 220-270 ° C in an inert atmosphere and subjected to screening with separation of residual carbonaceous reducing agent, which is reused for blending with the original concentrate or filling briquettes from anosovite concentrate.

In this case, before firing, the briquettes are pre-dried at a temperature of 250°C for 10-12 minutes. In addition, a monolayer of briquettes is fired, which are covered with a 10-15 mm layer of carbonaceous reducing agent before firing.

The predominant mass of leucoxene grains is covered on the outside with shirts or rims of fine-grained chlorite-quartz aggregate. Grinding the concentrate to a size of less than 0.063 mm allows them to be "revealed", and grinding simultaneously with the concentrate of the carbonaceous reducing agent and subsequent briquetting of the batch increases the contact between rutile and the carbonaceous reducing agent, improves the efficiency of the solid-phase reaction of interaction of TiO ₂ and C and, as a result, increases the speed of the reduction process.

Briquettes larger than 20 mm significantly increase the drying time, which can be reduced by raising the temperature above 250°C, but this will lead to cracking of the briquettes and a sharp decrease in their strength.

When firing briquettes in natural gas combustion products with an air flow rate of 0.9-1.0, which provides the maximum thermal effect, a backfill layer of solid reducing agent less than 10 mm high leaves the possibility of secondary oxidation of the concentrate, and with a layer height of more than 15 mm, the duration of the process increases.

Firing at a temperature below 1330°C requires a longer process duration, and increasing it above 1350°C requires an increase in heat costs.

Unloading briquettes cooled to a temperature below 220°C after screening and grinding to a size of less than 75 µm reduces the temperature of the roasted anosovite concentrate and requires additional heating of the anosovite concentrate mixture with sulfuric acid. At temperatures above 270°C, secondary oxidation of anosovite and titanium losses with the solid residue after acid leaching are possible.

The method was implemented in laboratory conditions.

A mixture of leucoxene concentrate (the chemical composition is presented in Table 1) (100 g) and coke (3.5 g) with a particle size of less than 0.063 mm, bentonite (0.5%) and water (10%) was prepared in advance. (The amount of coke was determined as follows. 100 g of concentrate contains 54.26 g of rutile (TiO ₂ ). To convert it to anosovite (Ti ₃ O ₅ ), 54.26/20 = 2.7 g of carbon is required. To reduce 2.31 g of FeO to Fe, 0.4 g of carbon is consumed. Coke contains 88% C. Coke consumption is (2.7 + 0.4) / 0.88 = 3.5 g per 100 g of concentrate). The mixture was pressed into briquettes in the form of equilateral cylinders (d equals h) measuring 10–30 mm with a force of 300 kg/ ^cm2 .

Table 1. Chemical composition of the leucoxene concentrate sample

Content, mass % _{TiO2 SiO2} FeO _{Al2O3 ​} CaO MgO _ZrO2 54.26 38.18 2.31 3.97 0.27 0.17 0.84

The drying process of briquettes was studied using the thermogravimetric method.

Crushed refractory of 5-10 mm size was loaded into a quartz reactor installed in a resistance furnace in a 20 cm layer. A basket with briquettes coupled with scales was placed in the upper part of the reactor. The furnace was heated to a specified temperature in the range of 150-300°C with a step of 50°C. Air was supplied through the refractory layer at a filtration rate of 0.1 m/s. The temperature of the heated air near the basket and the loss in weight of the briquettes were recorded (Fig. 1).

Analysis of the obtained data showed that in the studied temperature range the drying process proceeds according to a three-stage mechanism: first the wet body slowly warms up with the transition of moisture into steam, then a period of constant drying rate begins with the movement of moisture to the surface of the material and finally the drying rate slows down - steam from the surface is removed into the environment.

When drying 20 mm briquettes with an increase in temperature from 150 to 300°C, the drying time is reduced from 23 to 6 minutes. In briquettes dried at a temperature of 300°C, cracks appear, reducing their strength.

With an increase in the size of briquettes from 10 to 30 mm, dried at a temperature of 250°C, the drying time increases from 6 to 30 min. The optimal size of briquettes is less than 20 mm, the optimal drying temperature is 250°C, the drying time is 10-12 min.

The briquettes dried at 250°C (particle size of the batch less than 0.063 mm, briquette size 20 mm) were loaded into a basket, suspended from scales, installed in a quartz reactor and placed in a resistance furnace heated to a given temperature. The weight loss and duration of the process were recorded. Firing was carried out in a neutral atmosphere.

During the reduction process, the weight loss of the briquettes was about 7.9%, which corresponds to the almost complete transition of rutile leucoxene to anosovite with an insignificant formation of a mixture of Ti _n O _2n-1 oxides - Magneli phases. When the isothermal holding temperature is increased from 1250°C to 1350°C, the weight loss of 7.9% occurs 5 times faster - the firing time is reduced from 100 to 20 min (Fig. 2, Table 2).

Table 2. Effect of temperature on the duration of briquettes firing

Temperature, °C 1250 1275 1300 1325 1350 Firing time, min 100 68 40 28 20

To determine the influence of the particle size of the charge (leucoxene concentrate and carbonaceous reducing agent) Samples of the initial concentrate with a size of (-0.5 mm), (-0.3 mm) and (-0.1 mm) were prepared for the duration of briquettes firing. Sample weights (100 g) were mixed with coke of the same size (3.5 g), bentonite (0.5%) and water (10%). Briquettes of 20 mm in size were prepared from the mixture and, after drying, fired at a temperature of 1350°C. It was found that with a decrease in the particle size of the batch from 0.5 mm to 0.063 mm, the firing time was reduced from 35 to 20 min (Table 3).

Table 3. Effect of batch particle size on the duration of briquettes firing

Particle size of the batch, mm Duration of briquettes firing, min 0.5 35 0.3 30 0,1 22 0.063 20

The optimal particle size of the batch is less than 0.063 mm, the firing temperature is 1330-1350°C, the firing duration is 20-25 min.

The effect of filling a layer of carbonaceous reducing agent on the process of titanium oxide reduction during firing was assessed as follows.

Dried 20 mm briquettes from a batch smaller than 0.063 mm in size were placed in a crucible. Coke smaller than 3 mm in size was poured on top. The crucible with briquettes was loaded into a resistance furnace heated to 1350°C and fired for 20 min in an atmosphere of 65 _N2 +35 _CO2 (vol.%) simulating the composition of natural gas combustion products. At a coke layer height of 7 mm, a coating of Magneli and wustite phases, products of secondary oxidation of anosovite and iron, respectively, was observed on the surface of the briquettes. At a filling height of 10-15 mm, titanium was completely represented by anosovite, and iron by metal. At a layer height of 20 mm, a small amount of Magneli phases was present in the center of the briquette, indicating that the anosovite formation reaction was not complete.

The technology was tested in laboratory conditions.

The leucoxene concentrate, the composition of which is presented in Table 1 (100 g), was mixed with coke (3.5 g). The mixture was ground to a particle size of less than 0.063 mm. Bentonite (0.5%) and water (10%) of the batch weight were added. The mixture was pressed into 20 mm briquettes with a force of 300 kg/cm ² . The resulting briquettes were dried at a temperature of 250 ° C for 12 min in a graphite crucible. The dried briquettes were covered with coke of a size of less than 3 mm in a layer 12 mm high. The crucible with briquettes was loaded into a resistance furnace heated to a temperature of 1350 ° C and fired for 20 min. The crucible was cooled in a neutral atmosphere to 250 ° C. The briquettes were separated from the coke by screening, crushed to a particle size of the roasted concentrate of less than 0.075 mm in a ball mill. The anosovite concentrate, cooled to a temperature of 210 °C, was mixed with concentrated sulfuric acid heated to 200 °C and held at this temperature for 1.5-2.0 hours, then cooled and leached with water. The degree of decomposition of the anosovite concentrate was 88.2-94.8%, which is comparable with the results obtained in the prototype.

The technology for obtaining pigment titanium dioxide from leucoxene flotation concentrate, based on the claimed invention, is relevant and quite feasible, as it allows expanding the raw material base for the production of in-demand titanium products, which today is limited to the processing of iron-titanium (ilmenite) concentrates, complicated by iron removal operations and waste disposal.

Claims (3)

1. A method for processing leucoxene flotation concentrate, comprising roasting leucoxene concentrate in the presence of a carbonaceous reducing agent to obtain an anosovite concentrate, grinding it, mixing it with concentrated sulfuric acid and leaching, characterized in that the leucoxene concentrate with a carbonaceous reducing agent, pre-pressed into briquettes no larger than 20 mm in size, containing leucoxene concentrate and a carbonaceous reducing agent ground to a size of less than 0.063 mm in an amount necessary to reduce rutile to anosovite and iron to a metallic phase, is roasted at a temperature of 1330-1350°C for 20-25 minutes, the resulting reduced briquettes are cooled to 220-270°C in an inert atmosphere and screened with the separation of the residual carbonaceous reducing agent, which is reused for batching with the initial concentrate or filling of briquettes from anosovite concentrate. 2. The method according to item 1, characterized in that the briquettes are pre-dried at a temperature of 250°C for 10-12 minutes before firing. 3. The method according to item 1, characterized in that a monolayer of briquettes is subjected to firing, which, before firing, is covered from above with a layer of carbonaceous reducing agent 10-15 mm high.