FI118225B - A method for enhancing the dissolution of a sulfide concentrate - Google Patents

Description

't 1 118225

METHOD FOR EFFICIENT SOLUTION OF SULFIDIC CONCENTRATION

FIELD OF THE INVENTION

The invention relates to a process for enhancing the dissolution of a sulphidic 5-valuable metal concentrate in a metal hydrometallurgical process. The purpose is to accelerate the oxidation of sulphidic sulfur during leaching with trivalent iron and thus the dissolution of the precious metal. To accomplish this, at least a portion of the divalent iron solution formed during leaching is oxidized in 10 separate tubular oxidation reactors with static stirrers to form a trivalent iron. The invention is particularly well suited for a hydrometallurgical production process of zinc, wherein the raw material is zinc concentrate and the zinc concentrate is directly dissolved without roasting.

15th

BACKGROUND OF THE INVENTION

On the other hand, the process of the present invention can be similarly used in the hydrometallurgical production of other metals, such as copper, if the raw material is a concentrate containing • · · sulfide-copper compounds.

It is known in the art that precious metals such as zinc, copper or nickel can be leached from sulphide minerals, such as zinc, copper or nickel. 25 soluble forms utilizing the oxidizing power of • · * iron in trivalent form. Below are the principal dissolution reactions which show that, for example, when the zinc sulphide of the concentrate dissolves, ferric iron oxidizes the sulphide into elemental sulfur, and at the same time ferric iron is reduced to ferrous iron. For the solubilization reaction to continue, the ferrous iron must be oxidized back to ferric iron. Oxygen gas, which is as pure as possible, is usually used as the oxidizing agent. In iron oxidation, sulfuric acid is neutralized according to reaction equation (2).

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ZnS + Fe 2 (SO 4) 3 -> Zn SO 4 + 2 FeSO 4 + S ° (1) 2 FeSO 4 + 1/2 O 2 + H 2 SO 4 Fe 2 (SO 4) 3 + H 2 O (2) 5 A precious metal sulphate solution such as zinc sulphate solution after separation for solution purification and further for electrolytic metal recovery. In order to achieve a sufficiently high dissolution rate, sufficient iron must be present in the solution.

Iron in the solution is obtained from the raw material, ie zinc concentrate or on the other hand 10 possibly from the roast, if the process unit also involves the leaching of the roast. Depending on the iron content of the raw material and its soluble iron content, various process engineering solutions, such as internal iron precipitate precipitation and recycling, can be used to maintain sufficient iron content in the leaching process. Sulfur remaining in the solid can be separated, for example, by flotation and the iron is precipitated in the desired form, for example as jarosite, goethite or hematite.

In the concentrate leaching process, the concentrate is first fed to the concentrate lithium reactor, *: * "where 20 aqueous solutions of trivalent iron and free sulfuric acid are also fed. From the lithium reactor, the sludge proceeds to the actual leaching reactors, ♦ ·· some of it occurs in the first and second reactors.

The remainder of the reactors thus act as reactors to increase the duration of the leaching process, in which the remainder of the soluble zinc is leached. Conventionally, the concentrate leaching time 25 in the atmospheric leaching process is of the order of 20-24 hours.

• * * • · ·.

* · «* ·· * * **: * 'It has been observed in the atmospheric direct leaching processes of zinc concentrate that • ·.

"" · Especially at the beginning of the leaching process, the first reactor in the reactor series, * * · the ferric iron content of the solution decreases well due to the bitterness of the leaching reaction. In other words, most of the iron in the solution is in ferrous form. This results from the fact that the oxidation of ferric iron back to ferric iron is generally not fast enough and efficient even when reactors are supplied with excess oxygen 1111525 3: · and since the trivalent oxidized iron reacts immediately with the excess metal sulphide in the concentrate in the slurry. Naturally, this results in the impediment of efficient concentrate leaching and the size of reactors required for leaching and the size of the reactors.

5

Attempts have been made to solve the problems of slow oxidation of iron and slow leaching of the concentrate, for example by the concentrate leaching process described in EP 1 245 686. It is essential that the leaching solution containing free sulfuric acid and ferric iron is already passed to the rich-10 mill. In order to oxidize ferric iron to ferric iron, at least part of the process is carried out in a pressurized state. According to the method, dissolution of the entire concentrate can be done in an autoclave under elevated oxygen pressure. Then iron oxidation and concentrate dissolution are rapid. However, the problems of pressure leaching processes are known problems of autoclave-15 processes, such as high investment and operating costs and complicated and difficult operation due to high pressure. The dispersion of oxygen in the solution is not efficient in the autoclave and therefore relatively high pressures (0.7 to 1.0 MPa) have to be applied to achieve efficient iron oxidation *! ** and rapid concentration of the concentrate.

·: ··: 20 * · EP 1 245 686 also discloses a method of combining atmospheric and pressure leaching. In addition to the acid and ferric iron solution being passed to the milling step, one option of the method involves a pressurized The purpose of the pressurized reactor 25 is to serve as a part of the process of oxidizing ferrous iron to ferric. The pressurized reactor is said to be either direct pressurized * * **; · * tube or more complex autoclave equipment, however, in a pressurized tube alone, oxygen is poorly soluble because it is not efficient to disperse in solution due to insufficient mixing.

·: · 30 * · * ·

From the pressurized reactor, the ferrous iron solution or slurry is returned to the mill and thence to the actual atmospheric leaching reactor. According to Publication 4118225, a plurality of autoclave equipment may be used for efficient oxidation of iron and further lead to ferrous iron-containing slurry or solution for atmospheric leaching. In other words, it is a combination of atmospheric and pressure leaching equipment, which still contains the problems of the autoclave apparatus and process.

One essential feature of the process of EP 1 245 686 is the introduction of an oxidizing solution into the concentrate refining step. Grinding apparently contributes to enhancing the dissolution of the concentrate. However, implementation of a dissolution apparatus containing Ri-10 dewatering on an industrial scale is difficult and costly. On the other hand, especially in the zinc concentrate market, there has been a trend of declining particle size of concentrates for the last 20 years, so the proportion of small particle size concentrates suitable for the direct concentrate leaching process has increased.

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PURPOSE OF THE INVENTION

The object of the process of the present invention is to provide a more efficient method of dissolving metal sulfides, which in particular has improved oxygen *: * ·: dispersion and iron oxidation step. Thus, it is intended to enhance the dissolution of sulfite:: * ·: 20 precious metal concentrate by oxidizing at least a portion of the solution used for leaching and ferro-iron to ferric iron in the dissolution * * · oxidation apparatus, preferably equipped with static mixers for efficient mixing . Thus, according to the method, efficient concentrate dissolution is achieved without feeding the entire concentrate into the autoclave or grinding the concentrate during dissolution.

• · · * · · · · · ·

V. SUMMARY OF THE INVENTION

The invention relates to a process for enhancing the dissolution of a precious metal containing a sulfidic concentrate containing at least one precious metal * · * in the hydrometallurgical process of metal '/ l · 30. The purpose of the process is: "to accelerate the oxidation of the sulfide sulfur during the leaching step and thus the leaching of the precious metal, and to achieve this, at least part of the bivalent iron solution the leaching stage.

5

The oxidation is preferably carried out with as pure oxygen as possible. The concentrate leaching step is carried out at atmospheric pressure and temperature. The temperature of the oxidation step in the oxidation reactor is adjusted to be below the melting point of sulfur. The oxidation reactor operates at either atmospheric pressure or preferably low pressure, up to about 0.5 MPa.

In particular, the invention relates to a hydrometallurgical process for the production of zinc, wherein the raw material is zinc concentrate and the zinc concentrate is directly dissolved without roasting.

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The essential features of the invention will be apparent from the appended claims. LIST OF FIGURES

*: **: Figure 1 is a flow diagram of an embodiment of the invention in which the leaching of zinc concentrate is carried out as a sulphate-based solution, and Figure 2 is a graphical representation of a comparison of a static mixer reactor and a tube reactor-only apparatus for zinc concentrate solutions. • · * plotted against solubility curves.

25 ♦

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, the iron reduced to bivalent ferric iron during leaching of the sulfide concentrate is oxidized back to ferric iron at least * * *.

partially in auxiliary equipment outside the actual dissolution step. Creation · 30 of the oxygen used in the oxidation can also be fed to the leaching reactors of the actual leaching stage. In this case, said auxiliary equipment is used only in addition to the oxygen supply to the reactors, for example.

118225 series first reactor, where dissolution is the fastest and where the oxidizing effect of iron is often insufficient for efficient dissolution. At low ferric iron concentrations, even a small increase in ferric iron content has been found to significantly accelerate concentrate leaching.

5

In order to enhance and accelerate oxygen dispersion and iron oxidation, the oxidation reactor preferably utilizes a tubular reactor equipped with static mixers. With static mixers, the size of the oxygen gas bubble can be reduced and thus the mass transfer area 10 increased. In addition, the gas-liquid transfer rate can be improved. As a result, the dissolution of oxygen gas and further oxidation of iron can be accelerated.

Static agitators are generally agitators connected to a tubular reactor which do not contain moving parts, but their mixing efficiency is based on variously shaped elements inside the tubing. The liquid and gas supplied to the tube are forced to change direction continuously, and at the same time divide into several sub-currents, which again converge and then redistribute to random - *: ··· such sub-currents. When the tube is provided with a static mixer, for example, the dispersion of *: ··: 20 gas into the liquid is multiplied by more than the tube alone: ***. In addition, with a static mixer, the mixing is uniform so that the concentration profile * · · '· [[[·] is constant with respect to the cross-section of the pipe and the axial dispersion is small. For this reason, the concentrations and other conditions in the reactor are stable, which facilitates process control. The conditions in the tube reactor 25 influence the flow rate and pressure in the tube to enhance the operation of the tube reactor φ.

* * * • · * * * * * *: * ·: The sulfide concentrate leaching process is described below with reference to flow diagram M »; ... i o 1. The concentrate leaching takes place in the concentrate leaching reactor 1, to which the concentrate 5 is fed. . It is to be noted that the whole leaching step here is described by a · ··· *: *** reactor, although leaching normally comprises several reactors. The rich concentrate and process solution containing ferric iron and free sulfuric acid are mixed in a separate lithium reactor (not shown in detail), whereupon any carbonate compounds present in the concentrate are dissolved and the carbon dioxide formed. During the dissolution of the concentrate, the ferric iron in the solution is reduced to Ferro iron and the oxidizing power of the solution is reduced. Therefore, part of the slurry 5 is pumped by pump 2 through the tubular reactor 3. Before the tubular reactor 3, oxygen is fed to the slurry 4. Oxygen fed to the slurry is dispersed in the tubular reactor with static mixers and possibly a slight elevated pressure (overpressure 1-5 bar = 0.1-0.5 MPa) and the ferrous iron in the solution is effectively oxidized back to ferric iron. The slurry, in which all the iron is ferric iron, is returned to the leaching reactor 1. Furthermore, it should be noted that oxygen can also be fed directly to the first reactor, whereby the tubular reactor is used as an additional process device to enhance oxygen dispersion and iron oxidation. In a continuous operation, the amount of slurry 6 corresponding to the amount fed to the leaching reactor is withdrawn from the reactor.

Ί5

When the tubular reactor is equipped with static stirrers, the dispersion of oxygen in the concentrate leach solution is greatly enhanced. At the same time, the efficiency of oxygen utilization increases and oxygen consumption can be reduced. Maximum *: ··; the benefit of a tubular reactor is obtained when the oxygen supply is as high as possible:::: 20 close to the required amount, that is, when a large excess of oxygen is not used.

In addition, the benefits of a tubular reactor are even more pronounced on an industrial scale as the effects of small-scale equipment on a tubular reactor wall:. · .Ϊ.

In the process of the present invention, no concentration of dissolution rate of the concentrate is required: no host equipment is required other than the off-leaching step, preferably; low-pressure, tubular reactor with static stirrers ** · * “· into which at least part of the oxygen needed for the concentrate leaching reactions is fed. The solution according to the invention is easily connectable to existing process equipment. In this case, the actual process conditions do not need to be changed but the concentration of the concentrate leaching stage, the composition of the solution, the atmospheric conditions and the slurry concentration of the slurry can be maintained.

The invention is further illustrated by the following examples.

5 EXAMPLES:

Example 1

The tests consisted of an apparatus consisting of a 200 liter mixing tank and 10 three meter tube reactors (tube size DN 32). The mixing tank describes the dissolution step of the process. The total amount of solution used in the experiments was 60 liters. Before the start of the experiment, the composition of the solution was as follows: 40 g / l sulfuric acid, 10 g / l ferrosulphate, 1 g / l copper sulfate and 120 g / l zinc concentrate. Copper sulfate is used to adjust the copper content of the solution to approximately 15% of the normal process solution since copper has a catalytic effect on the oxidation of ferric iron. The composition of the concentrate by analysis was as follows: 51.8% zinc, 35.1% sulfur, 3.08% iron, 2.96% lead and 0.052% copper. During the test runs, the sulfuric acid content of the solution was kept approximately ·: **: constant. This was done by adding in several batches:: ·: 20 the amount of sulfuric acid estimated to be consumed in concentrate dissolution and by monitoring the concentration of sulfuric acid in the sample samples.

The solution was fed into the mixing tank and heated to a temperature slightly below 100 ° C at the beginning of the experiment. Thereafter, concentrate and copper sulfate were added to the vessel. 25 The moment of concentrate feeding was considered as the beginning of the experiment. The tests were carried out at 105 ° C and 3 bar (abs) pressure, i.e. 0.2 MPa overpressure.

* * · * · • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 37.5 l / min pumped solution into centrifugal pump · · · tubular reactor. ·· «: ***: Enhances material and heat transfer in the reaction mixture.

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From the tubular reactor, the solution was returned to the mixing tank, where insoluble gas was separated from the solution phase and discharged from the tank. The exhaust gases were cooled to separate the water bound to the gas. The water was not returned to the reactor, but its mass was taken into account when calculating the mass balances.

Sludge samples were taken from the reactor while the experiment was running. The sample was filtered to separate the solution phase and the solid phase. A sample of the solution was analyzed for dissolved zinc to determine the zinc yield and the sulfuric acid content of the solution was determined. The solid samples were washed and some of the solid samples analyzed for remaining zinc. This was done to ensure the accuracy of the solution samples. The zinc yields calculated from the analyzes at different time points in the experiments are shown in Table 1.

Table 1 Zinc leaching yields in Example 1.

Time Zinc Yield Zinc Yield Based on Precipitation Solution Analysis ·: * ·: Based on · *. · *: [Rnini [%] [%] »» * ---:. * 0 0, 15 15 ': .i .: 3Ö 26 * * *! '* ···: 6Ö 49 ~~ 9Ö 66 • »t 120 76 ~ * * **: ** iso 83' *; * / 24Ö 91 '• * V * 360 94 97 • · * - - _, | I__ ··· «* · ·» · * · ··· 10 118225

Example 2

The tests consisted of an equipment consisting of a 200 liter mixing tank and a three meter tube reactor (tube size DN 32). The mixing tank describes the dissolution step of the process. The total volume of solution used in the experiments was 5 to 60 liters. Before the start of the experiment, the composition of the solution was as follows: 40 g / l H2SO4 (10 g / l ferrosulphate, 1 g / l copper sulphate and 120 g / l zinc concentrate. Copper sulphate adjusts the copper content of the solution to approximately normal compared to the process solution The concentration of the concentrate as determined by analysis was 10 as follows: 51.8% zinc, 35.1% sulfur, 3.08% iron, 2.96% lead and 0.052% copper. During the test runs, the sulfuric acid content of the solution was kept approximately constant. batch the amount of sulfuric acid estimated to be consumed in concentrate dissolution and by monitoring the concentration of sulfuric acid in the slurry samples.

15

At the beginning of the experiment, the solution was fed to a mixing tank and heated to a temperature slightly below 100 ° C. Thereafter, concentrate and copper sulfate were added to the vessel. The moment of concentrate feed was considered as the start of the experiment. The tests were carried out at a temperature of 105 ° C and a pressure of 3 bar (abs) or 0.2 MPa.

...: 20

The solution was pumped from the mixing tank at 37.5 l / min by centrifugal pump into a tubular reactor. At the beginning of the tube reactor, pure oxygen was introduced into the solution. A tubular reactor equipped with Sulzer SMX-type static mixers was used to enhance the material and heat transfer in the reaction mixture. 25

From the tubular reactor, the solution was returned to the mixing tank where the insoluble * * * · ... * gas was separated from the solution phase and discharged from the tank. Exhaust gases *: * ·: cooled to remove water bound to gas. The water was not returned to the reactor, but its mass was taken into account when calculating the mass balances * 30.

···· · • · • · • · • · · "118225

Sludge samples were taken from the reactor while the experiment was running. The sample was filtered to separate the solution phase and the solid phase. The solution sample was analyzed for dissolved zinc to determine the zinc yield and the sulfuric acid content of the solution was determined. The solid samples were washed and some of the 5 solid samples analyzed for the amount of zinc remaining. This was the intention. to ensure the accuracy of the solution samples. The zinc yields calculated from the analyzes at different time points in the experiments are shown in Table 2.

Table 2 Zinc leaching yields in Example 2.

10

Time Zinc intake Zinc intake based on analysis of precipitate solution analysis irnini i% i i% j Ö - ^ 9 3Ö 37 - - * • · · «· ^ - _ '. . .. _ *; 90 77 - 85 • ·

Yeah 90

• I

'"F 24Ö 94» · · • · * _________ __ 360 96 97 • · * · · L ......... _ _. - - <• · · •'

The differences in the zinc leaching yield are illustrated in Figure 1, which shows the experimental results * · · in Examples 1 and 2. Solubility yield curves show that • *, * ···. Using 15 static mixers allows faster dissolution of zinc concentrate. The same figure shows the percentage difference between the leaching yields of these two experiments. This curve unequivocally shows that, particularly in the early stages of the leaching process, when the leaching is the fastest and the Ferri iron is deficient in the leaching reactor. The use of a 12: 118225 reactor containing mixer achieves maximum increase in dissolution rate, and for this purpose a combination of a separate oxygen dispersion and iron oxidation apparatus containing a static mixer, in addition to the actual leaching reactor, provides a significant improvement over existing concentrate leaching equipment.

5

Figure 2 shows that, for example, a static mixer requires only about 120 minutes to achieve a solubilization yield of 85%, whereas it takes about 200 minutes without a static mixer to achieve the same solubility.

10

As described in the prior art, for example, the dissolution time of a conventional zinc concentrate is 20 to 24 hours. According to the example described above, more than 95% recovery is achieved in 4 to 6 hours, which is completely sufficient considering the other steps of the process. When, according to the invention, at least a portion of the slurry from the leaching step is conducted to an oxidation step in the tubular reactor in which oxygen is dispersed in the slurry, the length of the leaching step is reduced to at least a fourth. It is advantageous for the process that the oxidation is carried out at low overpressure, whereby the requirements for the reactor are considerably lower than for reactors requiring a higher pressure. On the other hand, the use of higher pressure in a 20-tube reactor is less expensive than, for example, autoclave equipment. Efficient oxidation is achieved at low overpressure or even under atmospheric conditions by equipping the reactor with ** i .: static mixing means.

# 1 · • · • 1 ♦ · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·IRurgres: -: 1 • 1 ··. ’> • · · · 1 · • ·« • · 2 • · • · ·

Claims (8)

A process by which leaching of a sulphidic zinc concentrate is effected in a hydrometallurgical manufacturing process, wherein the concentrate is leached by means of an aqueous solution containing trivalent iron and free sulfuric acid, characterized in that transverse iron formed in connection with the oxidation of the concentrate and the dissolution of the host metal is oxidized to trivalent iron in an at least partially separate tubular oxidation reactor equipped with static agitators and the oxidized ferric iron-containing solution is returned to the leaching phase of the concentrate in the leaching reactor. 2. A process according to claim 1, characterized in that the oxidation reactor operates under atmospheric pressure. • · · • · • · • · 1 3. Process according to claim 1, characterized in that the oxidation reactor operates under a low overpressure. «· · •« • · • · «25 4. A process according to claim 1 or 3, characterized in that the overpressure of the ··: · ·· oxidation reactor is maximum in the class of 0.5 MPa. t 1 1 • · • • · * · · · * Process according to any of claims 1-4, characterized in that the leaching phase of the concentrate is carried out at atmospheric pressure and temperature. . 30 • · · ··· · • · · • ♦ ♦ • · 118225 6. A process according to any one of claims 1 to 5, characterized in that the temperature of the oxidation phase that takes place in the oxidation reactor is adjusted to be below the melting temperature of the sulfur. 5 Process according to any one of claims 1-6, characterized in that part of the oxygen used in the oxidation of cross-iron is supplied in the leaching phase. Process according to any of claims 1-7, characterized in that the leaching step of the concentrate comprises several reactors, the solution oxidized in the oxidation reactor being returned to the first reactor of the step. «M ··· Φ · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Φ ·· • Φ φ ΦΦ • • il Φ · φ Φ φ # Φ · ΦΦ · Φ · · Φ · Φ · φ Φ · Φ · Φ 1 ♦ ·· • φ Φ · φ φ Φ φ φ φ φ · Φ φ Φ · • Φ