RU2393255C1 - Procedure for exracting uranium from crude ore - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in crushing and wet crumbling of source raw material producing pulp. Also ore containing brannerite is used as source raw material. Upon wet crumbling pulp is concentrated, leached with sulphuric acid and separated. Upon separation upper discharge is directed to counter flow sorption of uranium, while lower discharge containing brannerite fraction is acidated with sulphuric acid to 40-80 g/l producing acidic pulp with S:L<1:4. Produced acidic pulp is radiated with a flow of accelerated electrons at energy of absorbed radiation dose 1.5-1.6 kgr/s during 4-8 min. Further uranium is leached at mixing and at temperature 60-70°C during 2-3 hours and produced pulp is condensed. Upon condensation there is formed upper discharge which is supplied to source raw material leaching, while lower discharge goes to waste.

EFFECT: extraction of uranium from hard opened brannerite crude ore.

3 cl, 7 tbl, 1 dwg, 2 ex

Description

The invention relates to the field of hydrometallurgical processing of uranium ore raw materials and can be used for sulfuric acid leaching of uranium from hard-to-open (brannerite) ores.

It is known that for leaching uranium with sulfuric acid with an acceptable recovery, i.e. 90-95%, from the refractory ore of the Elliot Lake deposit, containing 0.14% of uranium in the form of uraninite and mainly brannerite, the presence of an oxidizing agent (sodium chlorate, hydrogen peroxide) is required with heating to a temperature of 75 ° C, residual acidity ~ 50 g / l and with a high duration of the process of 96 hours (Haque KE, Ritcey GM "Comparison of oxidants for the leaching of uranium ores in sulphuric acid". CI M Bull. 1982, 75, No. 84, 127).

The main disadvantages of the method are the necessity of using oxidizing agents and the high duration of leaching of uranium, i.e. significant operational, mainly energy costs.

A known method of roasting hard-to-open uranium ore for the destruction of brannerite / G.K. Krivokoneva. New data on the behavior of metamict brannerite during heat treatment. WMO Notes, issue 5, pp. 254-266 /.

It has been established that when firing brannerite in air at temperatures of 600-900 ° C, the mineral decomposes with the formation of oxides U ₃ O ₈ and TiO ₂ . Uranium oxide is dissolved in sulfuric acid environments under approximately the same conditions as the natural oxides uraninite and nasturan. Therefore, when leaching cinder, harsh leaching conditions are not required for the processing of brannerite ores. In addition, during the process of ore roasting in the above temperature range, the sulfides contained in it are oxidized with the formation of sulfur dioxide, which is partially absorbed by the carbonates and chlorites contained in the ore, reducing the subsequent leaching of acid.

The main disadvantage of this method is its inapplicability to radioactive ore raw materials. Oxidative roasting of crushed (or crushed) ore containing radioactive elements (uranium, thorium) is accompanied by the inevitable formation of highly toxic fine particles of radioactive material, aerosols and gaseous decomposition products (rhodon, etc.). The creation and operation of an appropriate dust and gas collection system that meets modern environmental standards is associated with high capital and energy costs, which make it unprofitable to process radioactive ore by this method.

In the world uranium mining industry, "dry" grinding, ore burning has not been used for a quarter of a century, with the exception of two Nigerian factories owned by French companies and located 250 km from the nearest settlement almost in the center of the Sahara.

The closest adopted for the prototype is a method of hydrometallurgical processing of ores, including crushing, wet grinding, thickening the pulp, dividing it into two streams, leaching of iron in one of them, mixing with the second, oxidizing the extracted iron with atmospheric oxygen and acid transfer of uranium to solution sulfuric acid. The proportion of ore in the first stream directed to leaching iron is 35-70%. The opening of iron is carried out in the range of pH 2.0-4.2, the acid transfer of uranium to the solution is carried out by introducing an additional oxidizing agent, for example, a compound of manganese (IV) and / or ferric iron, maintaining the pH of the leached pulp in the range of pH 1.5-2.5 (RF patent No. 2154121 C22B 60/02, published October 8, 2000).

The main disadvantage of this method is an inefficient, costly method of producing an oxidizing agent - ferric iron: the oxidation of ferrous iron leached from ore with atmospheric oxygen in a slightly acidic environment requires continuous heating and mixing (aeration) of the pulp and acid consumption to dissolve the formed iron hydroxide. In addition, at the stage of acid transfer of uranium to solution, an additional consumption of an oxidizing agent is required, for example, manganese (IV) and / or ferric compounds. It should be noted that the scope of this method is limited only by easily-discovered ores, the extraction of uranium from which is possible by the so-called “pH” leaching.

The main reserves of natural uranium in Russia are concentrated in ores of deposits of the Elkonsky region, which are mainly classified as hard-to-recover, brannerite type (“Uranium of Russia. Collection of reports of scientific and technical meetings. November 20-21, 2007” Moscow, FSUE TsNIIATOMInform, 2008. )

The technical result of the invention is the extraction of uranium from hard, hard-to-open (brannerite) ore raw materials without the use of an oxidizing agent.

The technical result of the invention is achieved by the fact that in the method of extracting uranium from ore raw materials, including crushing, wet grinding of the feedstock to produce pulp, ore containing brannerite is used as the feedstock. After wet grinding, the pulp is thickened, and after sulfuric acid leaching, the pulp is separated. After separation, the upper discharge is directed to countercurrent sorption of uranium, and the lower discharge containing the brannerite fraction is acidified with sulfuric acid to 40-80 g / l to produce acid pulp and irradiated with an accelerated electron beam with an absorbed dose rate of 1.5-1.6 kGy / s for 4-8 minutes, followed by leaching of uranium at a temperature of 60-70 ° C for 2-3 hours and thickening the resulting pulp with the formation of the upper discharge, which serves to leach the feedstock, and the lower discharge, which is sent to dump.

High extraction of uranium into the solution from the refractory brannerite fraction occurs as a result of the radiation-chemical oxidation of uranium and iron under the influence of short-term irradiation of acidified pulp with an electron stream generated by a linear accelerator.

The following are examples of the extraction of uranium from refractory (brannerite) ore raw materials by the proposed method. As a starting material, a sample (see Tables 1, 2) of ore from the Yuzhnoye deposit in the Elkonsky district was used. Uranium in the sample is represented by easily opened nasturan, coffinite and hardly opened brannerite.

table 2 The mineral composition of the sample for the main components Component Content% Kalishpat 43.5 Carbonates 15,5 Quartz 10.0 Plagioclase 9.0 Sericite 6.0 Pyrite, Marcasite 5,0 Biotite, chlorite 3,5 Fluorite 1.7 Magnetite 1,0

The ore sample was ground in a ball mill to a particle size of 0.16 mm 100%. The pulp was thickened to T: W = 1: 1-1.5. The ore was leached with sulfuric acid under the conditions of a traditional sulfuric acid process in the presence of an oxidizing agent - manganese dioxide. At a consumption of MnO ₂ 1%, a temperature of 60-70 ° C, pH≥1 (residual acidity 10-15 g / l) for 3 hours, the degree of extraction of uranium in the solution was 70%.

The degree of uranium extraction into the solution was calculated according to the uranium content in the dry washed cake, taking into account the yield of the latter, acid intensity - taking into account the moisture content of the cake after the 1st filtering of the pulp. According to the data obtained, the presence of uranium in the ore sample in the form of easily revealing nasturan, coffinite (65-70%) and hard-to-discover brannerite (~ 30%) was established. With an initial acidity of 42 g / l, even for 4 hours of leaching, 0.26% of the cake remains. The main technological indicators characterize the ore as resistant and acid-intensive. Direct leaching of uranium from such raw materials is unprofitable.

To evaluate the effectiveness of the radiation-chemical effect of the electron beam on the intensification of the process of sulfuric acid leaching of uranium from the refractory component, it was necessary to first remove the easily opened mineral components of the ore, including nasturan and coffinite, and concentrate the brannerite fraction. For this purpose, the sample was treated with a solution of sulfuric acid at an initial acidity of 30-40 g / l, a temperature of 70 ° C and a duration of 1 hour. The uranium content in the thus obtained Brannerite fraction No. 1 was 0.34%, i.e. 90% of the uranium was in the form of brannerite.

Example 1. Brannerite fraction No. 1.

The raw material containing brannerite was wet milled, then pulp thickening and sulfuric acid leaching were carried out. After leaching, pulp was separated. The upper discharge after separation was directed to countercurrent sorption of uranium, and the lower discharge containing the brannerite fraction was acidified with sulfuric acid to 40 g / l and sent for irradiation.

For subsequent comparison, blank experiments (without irradiation) were performed on brannerite fraction No. 1 (0.34% of uranium) on leaching of uranium at an initial acid concentration of 75 g / l, mechanical stirring of the pulp, lasting 3 hours and temperatures of 85 and 25 ° FROM. The leached pulp was filtered, the cake was washed and dried in air at 105 ° C to constant weight. The degree of uranium extraction into the solution was calculated from the content in the dried washed cake. The data obtained (see table 3) showed that:

- at 85 ° C for 3 hours (with an acidity of 72-73 g / l), the degree of uranium extraction increases to 91.2%.

- at a low temperature (25 ° С) and acidity also at the level of 70-73 g / l (as at 85 ° С), the degree of uranium extraction into the solution turned out to be much lower: ~ 46%, respectively.

For pulp irradiation, a linear electron accelerator of the LUE-8 type was used. Irradiation of brannerite fraction No. 1 (0.34% of uranium) in the form of an acidic pulp with T: W = 1: 4 was carried out at a kinetic energy of an electron beam of 6.4 MeV and a constant absorbed dose rate calculated by the formula / A. Pikaev. “Modern radiation chemistry. The main provisions. Experimental technique and methods. ” M., "Science." 1985, p.297 /:

D _m = ηIE / m = 0.95 · 25 · 10 ^-6 · 6.4 · 10 ⁶ / 0.1 = 1.52 kGy / s,

where η is the coefficient equal to the ratio of the energy of the beam absorbed in the sample to the energy stored in the beam, for the pulp it is accepted η = 0.95, I = 25 μA, E = 6.4 MeV, m is the pulp mass of 0.1 kg. Irradiation was carried out at an initial acid concentration in the liquid phase of the pulp of 40 and 80 g / l for 8 and 3.5 minutes, i.e. at an absorbed dose of 730 and 320 kGy. During irradiation, the pulp temperature increased from 37 to 88 (8 min) and to 76 ° C (4 min).

Acid pulp after irradiation was treated for 1-3 hours with mechanical stirring and a temperature of 70 ° C. The leached pulp was separated, the upper discharge was a reverse solution, and the feed was leached. The lower discharge was directed to the dump. A sample of leached pulp was filtered, the cake was washed and dried in air to constant weight (see table 4).

The data in Table 4 show that, with a residual acid concentration of 37-40 g / l, the degree of uranium extraction in the solution increases to 91%. At an acidity of 74 g / l, the leaching process is almost complete: only 0.015% of uranium remains in the cake, which corresponds to the degree of uranium extraction into the solution at the level of 96%. The acid intensity in this case is not more than 6%. Reducing the duration of irradiation to 3.5 min leads only to a slight decrease in the degree of uranium extraction to ~ 95%.

Table 4 Conditions and results of experiments on leaching of irradiated pulp of Brannerite fraction No. 1. τ is the duration of irradiation, E is the through degree of uranium extraction into the solution (over cake), K is the acid intensity №№ op.p.p. Conditions The liquid phase of the pulp S.O. cake,% E% K,% τ min Ref. H ₂ SO _4, g / l U, g / l H ₂ SO _4, g / l O-VP, mV Exit U 7 8 40 0.12 40,0 420 85.3 0,035 91.3 3.0 8 8 0.18 37.5 86.7 0,032 91.3 4.0 9 8 80 0.10 73.8 84.8 0.015 96.4 6.0 10 four 0.10 76.0 440 86.8 0,020 94.9 6.0

During even short-term irradiation of the initial pulp, the main mass of uranium passes from 60 to 80% (depending on acidity) (see Table 5).

Table 5 Characterization of the liquid phase of the pulp immediately after irradiation for 8 minutes Uranium Extraction Rate: E1 - into the liquid phase of the pulp after irradiation, E2 - into the liquid phase of the pulp after leaching at 70 ° C for 3 hours №№ op.p.p. Ref. H ₂ SO ₄ , g / l The liquid phase of the pulp E1,% E2,% K,% U, g / l H ₂ SO ₄ , g / l O-VP, mV 7 40 0.42 38.5 470 60.9 30,4 2.1 9 80 0.54 71.6 480 78.3 18.1 3.8

Thus, short-term irradiation of acid pulp (3.5-8 min) with an absorbed dose rate of 1.5 kGy / s ensured a high degree of uranium extraction into the solution - by 95-96%, with subsequent leaching of the persistent brannerite ore fraction. Compared with unirradiated pulp of persistent brannerite fraction No. 1 (see Table 3), ceteris paribus, the degree of uranium extraction into solution after pulp irradiation increased by ~ 5%.

Example 2. Brannerite fraction No. 2.

A more resistant brannerite fraction No. 2, with a large initial content of brannerite and 0.23% uranium, was prepared similarly (see above). The “blank” experiments necessary for a comparative assessment of the irradiation effect were also carried out at initial T: W = 1: 4, acid concentration 40 g / l, mechanical stirring, temperature 70-75 ° С and (see Table 6) leaching duration 0, 5-3 hours without and in the presence of an oxidizing agent - manganese peroxide (72% MnO ₂ ). The oxidizer consumption is 1% in terms of MnO ₂ .

From the data in Table 6 it follows that without an oxidizing agent, the leaching process of uranium proceeds at a low speed. In 3 hours, only ~ 60% of uranium passes into the solution. The residual acidity is ~ 36 g / l, the value of 0-VP 410 mv. As expected, the value of O-VP increases (up to 480-500 mV) in the presence of an oxidizing agent and, without a noticeable decrease in acidity, the leaching process proceeds more intensively and the degree of uranium extraction increases by 15-20%, reaching ~ 74% in 3 hours. In this case, no Fe ^{2+ ions} were found in solution. All iron (0.05 g / l), regardless of the leaching duration, is in the trivalent state. Irradiation of Brannerite fraction No. 2 in the form of an acidic pulp with T: W = 1: 4 (25 g sample) was carried out at a kinetic energy of an electron beam of 6.4 MeV, a constant absorbed dose rate of 1.5 kGy / s and an initial acid concentration of 40 g / l The effect of the duration of irradiation processes (3.5 and 8 min) at a sulfuric acid concentration of 40 g / l and leaching of irradiated pulp on the degree of uranium extraction into the solution are shown in Table 6. The pulp temperature during irradiation increased from 40 to 88 ° C.

Table 6 Leaching of uranium from unirradiated brannerite fraction No. 2 with sulfuric acid at a concentration of 40 g / l, temperature 70-75 ° C, depending on the duration and presence of an oxidizing agent - manganese dioxide No. Op.
p.p. Conditions The liquid phase of the pulp S.O. cake,% E% K,% No. MnO ₂ ,% τ min U, g / l H ₂ SO ₄ , g / l O-VP, mV Exit U 9 - thirty 0.24 38.7 420 91.0 0.160 36.8 0.9 8 10 60 0.24 34.5 420 91.2 0.140 43.5 1,0 9 eleven 180 0.34 35.8 410 91.8 0,100 59.6 1,2 10 9 1,0 thirty 0.36 40.8 540 91.3 0,100 59.6 1.8 7p 10 60 0.37 32,0 500 91.2 0,079 68,2 2,4 8p eleven 180 0.39 31.9 480 91.6 0,066 74.3 2.6 9p

Uranium from the irradiated pulp was leached with mechanical stirring and a temperature of 70-75 ° C for 0.5-3 hours (see drawing).

With an increase in the leaching time, the degree of uranium extraction into the solution increased from 74 to 86%. The bulk of uranium passed into solution already during irradiation. The residual acid concentration remained almost constant (~ 38 g / l). A reduction in the duration of irradiation from 8 to 3.5 min only slightly affected the decrease in the degree of uranium extraction (<2%) with constant acidity (~ 38 g / l). The value of 0-VP was even slightly lower than in the “blank” experiments with an oxidizing agent (Table 4). At the same time, iron (uranium oxidizer), regardless of the duration of irradiation and leaching, completely went into solution in the form, oxidized to a 3-valence state. The acid intensity of the solid irradiated pulp after leaching (Table 7) was only ~ 2% higher than that obtained without irradiation (Table 6). A high degree of uranium extraction into the solution - at a level of 90%, was achieved with a pulp acidity of about 40 g / l. For almost complete extraction of uranium into the solution, the acidity should be increased to 60-70 g / l (see table 4).

Table 7 The conditions and results of irradiation of acidic pulp (T: W = 1: 4) after leaching of uranium at an initial concentration of sulfuric acid of 40 g / l and a temperature of 70 ° C, E - the degree of extraction of uranium in solution, K - acid intensity №№ op.p.p. Time min The liquid phase of the pulp S.O. cake,% E% K,% exposure Leaching U, g / l H ₂ SO ₄ , g / l O-VP, mV Exit U eleven 8 thirty 0.145 39.2 460 77.8 0,075 74.1 2.0 12 8 60 0.170 39.0 450 81.9 0,064 77.6 3.0 13 8 180 0.170 37.8 450 82,2 0,041 86.2 3.0 fourteen four 180 0.175 38.3 440 82,2 0,046 84.5 4,5

The positive effect of short-term (≤8 min) irradiation of the pulp with an electron stream at a temperature of 37-88 ° С and a relatively low (40 g / l) acid concentration was manifested (see Tables 6, 7) in the increase in the degree of uranium extraction into solution after 3- x hourly (70 ° C) leaching to:

- 11.9 in the presence of an oxidizing agent (1% manganese dioxide),

- 26.6% without oxidizing agent.

This effect becomes even more significant with a shorter leaching time.

The drawing shows the dependence of the degree of extraction of uranium into the solution (E,%) on the leaching duration at a concentration of sulfuric acid and a temperature of 70 ° C for irradiated for 8 min (row 1) and unirradiated pulp with an oxidizing agent (row 2) and without an oxidizing agent (row 3) (according to the data of Tables 6 and 7). With a leaching time of 15 minutes (see the drawing), 70% of uranium passes from the previously irradiated pulp into a solution, while from unirradiated with an oxidizing agent only 30%, and without an oxidizing agent - only 18%. In this case, the increase in uranium extraction due to irradiation reaches 40 and 52%, respectively. Calculated graphically from the initial sections of the curves (see drawing) for the same time 8 min, the speed of the uranium leaching process is:

- irradiated pulp (extraction 60%) - 4 mg U / min,

- pulp in the presence of an oxidizing agent (extraction 15%) - 1 mg U / min,

- pulp without oxidizing agent (9% recovery) - 0.6 mg U / min.

The rate of leaching of uranium from the irradiated pulp of the brannerite fraction, ceteris paribus, is 6-7 times higher than from unirradiated. The addition of an oxidizing agent - manganese dioxide - to the pulp somewhat accelerates the leaching process, but even in this case, the extraction of uranium from the irradiated pulp occurs 4 times faster.

Thus, short-term irradiation of acidic pulp of persistent brannerite fraction No. 2 provides an intensification of the process of subsequent leaching without the use of oxidizing agents (air oxygen, manganese dioxide, etc.) with an increase in the degree of uranium extraction into the solution by 10-15% compared with unirradiated pulp.

Claims (3)

1. A method of extracting uranium from ore raw materials, including crushing, wet grinding of the feedstock to produce pulp, sulfuric acid leaching to produce pulp, characterized in that the ore containing brannerite is used as feedstock, the pulp is thickened after wet grinding, and after sulfuric acid leaching carry out the separation of the pulp, the upper discharge after separation is directed to countercurrent sorption of uranium, and the lower discharge containing the brannerite fraction is acidified with sulfuric acid to 40-80 g / l by teaching acidic pulp and irradiating it with a stream of accelerated electrons with an absorbed dose rate of 1.5-1.6 kGy / s for 4-8 minutes, followed by leaching of uranium and thickening of the resulting pulp with the formation of an overflow that serves to leach the feedstock, and bottom discharge, which is sent to the dump. 2. The method according to claim 1, characterized in that the brannerite fraction in the form of an acidic pulp with T: W <1: 4 is irradiated. 3. The method according to claim 1, characterized in that the irradiated pulp is leached with stirring at a temperature of 60-70 ° C for 2-3 hours