MXPA98001250A - Method to recover nickel hydrometallurgically from two different mates of niq - Google Patents

Abstract

The present invention relates to a method for the recovery of nickel in a single process and from two nickel nickels produced pyrometallurgically, one of which contains a remarkable percentage of the iron. The leaching of the nickel matte containing iron is carried out in a step leading to a solution coming from the leaching cycle of a matte with a lower iron content within the leaching of a matte with a higher iron content in a stage where the iron mate with lower iron content is in soluble form. The iron contained in the mattes is advantageously precipitated as jarosite and the solution created in the leaching of the mat with the highest iron content is taken back to the leaching cycle of the matte with lower fiery content.

Description

METHOD TO RECOVER NICKEL HYDROMETALURGICALLY FROM TWO DIFFERENT NICKEL MATES Technical Field The present invention relates to a method for the recovery of nickel in a single process and from two nickel nickels produced pyrometallurgically, one of which contains a remarkable percentage of iron. The leaching of the nickel matte containing iron is carried out in one stage, feeding the solution coming from the leaching cycle of the mat with the lower iron content within the leaching of a matte with a higher iron content in a stage where the iron mate with lower iron content is in soluble form. The iron contained in the mattes is advantageously precipitated as jarosite and the solution created in the leaching of the mate with the highest iron content is taken back to the leaching cycle of the mate with less iron content.

BACKGROUND OF THE INVENTION A large part of the world nickel is produced hydrometallurgically from nickel-sulfur mats, which are produced pyrometallurgically. The mattes produced are mainly nickel-copper with low iron content, because in the hydrometallurgical treatment after the removal of the iron from the process has been difficult.

In order to obtain a lower iron content in the nickel matte, the pyrometallurgical treatment of the nickel concentrate has generally consisted of three stages. In the first stage the concentrate is melted and the product obtained is a nickel mat with a low iron content, which is referred to later in this description as casting mate. The melting furnace used can be, for example, an instant melting furnace. In addition to the matte, from the furnace slag with a high iron content is obtained, said slag is fed in the second stage of the process to an electric furnace. In the electric furnace, the slag is reduced and the products obtained constitute a matte with a high iron content, as well as slag that is discarded. In the third stage, both the casting matte and the matte from the electric furnace are conducted inside a converter where the iron is removed by oxidation, and the matte that advances towards a subsequent hydrometallurgical treatment is now called nickel matte. high grade.

The conversion of the previously described pyrometallurgical process eliminates the iron and sulfur of the fed mate, but as a disadvantage this treatment also causes losses of the recovered, particularly in relation to cobalt, but also in relation to other valuable metals. In relation to this, the metals referred to as valuable metals are, in particular, nickel, copper and cobalt, as well as precious metals. Consequently, the omission of the conversion stage improves the recovery of valuable metals and reduces production costs, but on the other hand, requires a capacity for the treatment of iron in a hydrometalurgical process.

The published patent of the U.S.A. No. 4,323,541 discloses a traditional method for the recovery of nickel from high grade nickel mats and with a remarkably low iron content. The leaching takes place in two stages of atmospheric leaching plus a stage of pressure leaching, where the purpose is to leach the nickel contained in the high grade nickel mat, so that the copper remains unleached. The precipitate containing copper and coming from the pressure leaching stage is returned to a copper smelting cycle.

The published patent of the U.S.A. No. 4,042,474 discloses a method wherein ferronickel, which is a nickel product with a high iron content, is treated in three stages of leaching so that the nickel is dissolved within an anolyte obtained by electrolytic nickel extraction, and the iron is precipitated as jarosita.

The method of the present invention is based on the fact that in pyrometallurgical treatment, the conversion step is omitted, so that two kinds of nickel matte are obtained: cast iron matte and electric furnace matte, the former containing less iron and the last one having a greater iron content. The smelting matte is processed in its own cycle, in at least one stage of leaching at atmospheric pressure and in a stage of pressure leaching. The electric kiln matte (EF matte) is leached in a stage and within a solution that comes from the casting mat leach cycle, coming either from pressure leaching or from the last stage of leaching from pressure leaching atmospheric, and the solution obtained and that comes from the leaching of the EF mate can be fed back into the leaching cycle of the casting mate. The conditions in the solution that come from the leaching cycle of the melting furnace matte to the leaching of the EF matte are adjusted to be such that the iron and other impurities contained in the melting mat are present in dissolved form and can, therefore, be precipitated in relation to the precipitation of the iron in the EF mate.

The essentially novel features of the invention will become clearer from the appended claims.

The method of the present invention is based on the surprise discovery that the rate of dissolution of a mat containing iron is not very dependent on the acid content of the solution, but on the other hand, the precipitation rate of the iron is markedly increased , when the acid content is reduced. Therefore, it is important that the pH or acid content of the solution be maintained within a region where the iron can be precipitated as advantageously as possible. It has been proven that by choosing an appropriate acid content and delaying time, the nickel contained in the EF mate can be virtually completely leached in a single stage, and at the same time the iron is precipitated while the solution can be returned to any Leaching stage of the casting matte.

When the iron is precipitated in the leaching and precipitation stage of the EF mate, some elements that are harmful to the hydrometalurgical process, such as arsenic and antimony, are also precipitated. These elements are obtained mainly and jointly with the casting mate and under certain conditions they are contained in the solution. Under similar conditions it is also possible to obtain the iron in the solution in ferrous form. When the impurities (Fe, As, Sb) contained in the mat of the melting furnace are obtained in the solution and this solution is subsequently conducted to the treatment of the EF mate, the impurities of the melting mat can be precipitated simultaneously with the precipitation of the iron. It is advantageous to precipitate the iron as jarosite, but when desired, the iron can also be precipitated as goethite.

Brief Description of the Figures Figure 1 is a flowchart of the process of the present invention. Figure 2 is a schematic diagram illustrating the leaching of the iron with different partial pressures of oxygen.

Detailed Description of the Preferred Modalities. In accordance with the flow chart of Figure 1, finely ground cast matte, that is, nickel-copper matte obtained from a melting furnace, such as an instant melting furnace, is taken to the first stage of atmospheric leaching 1 . In substitution of nickel-copper matte, high-grade nickel matte can naturally be used. The nickel content of the nickel-copper matte occurs in several different forms, for example as elemental nickel Ni0 or Ni3S2 nickel sulphide, which at this stage could be called primary sulfide, because it is obtained from matte foundry. The finely ground mate is leached with nickel sulfate solution containing copper sulfate and obtained from the following atmospheric leaching 2, and in addition to this, air or oxygen is fed into the leaching stage. Due to the effect of copper sulphate and oxygen, elemental nickel and nickel sulfide are oxidized to nickel sulfate. In the process, alkaline copper sulphate or copper oxidule is also created, which precipitates at this stage. The leaching is carried out under atmospheric conditions and at a temperature of 80-100 ° C.

After leaching, separation of liquid and precipitates is carried out in step 3 according to a normal separation procedure. The solution of nickel sulphate created in the leaching is carried, after the purification of the solution (cobalt removal) 4 towards the electrolytic extraction of the nickel 5.

The precipitate formed in the first stage of atmospheric leaching 1 is conducted to the second stage of leaching 2 at atmospheric pressure, to which is now added the nickel sulphate solution that was obtained from a later stage of the process, that is, from the leaching of the matte from the electric furnace, as well as the anolyte coming from the electrolytic extraction, of the nickel 5. Due to the effect of the free sulfuric acid (approximately 50 g / l) contained in the anolyte, the primary nickel sulphide contained in the matte Nickel-copper is dissolved and one mole of nickel sulfate and two moles of NiS secondary nickel sulfide are formed by one mole of Ni3S2. In the second stage of leaching also the primary copper sulphide, chalcocite Cu2S, dissolves when reacted with sulfuric acid and forms copper sulphide secondary CuS and copper sulfate. The previously formed alkaline copper sulfate also dissolves under these conditions and creates more copper sulfate in the solution. Oxygen (air) is also required for leaching reactions at this stage.

The solution created in the second stage of leaching 2 at atmospheric pressure is conducted, after the separation stage 6, to the first atmospheric leaching 1, and the copper sulfate contained in this solution leaches the elemental nickel and the primary nickel sulfate. contained in the mate. After the second stage of atmospheric leaching it can be argued that all of the elemental nickel and primary nickel sulfide contained in the mate is virtually leached, and as regards nickel compounds, the precipitate formed mainly contains only secondary nickel sulphide . Moreover, the precipitate contains copper compounds without leaching, precious metals, different forms of iron previously contained in the casting mat, as well as arsenic and antimony compounds.

The precipitate from the second atmospheric leaching is taken into a third stage of leaching, pressure leaching 7, where the precipitate is leached using the anolyte from the electrolytic extraction of the nickel. The process may also include another stage of pressure leaching (not illustrated in the flow chart of Figure 1), in which case the leaching of the first pressure leaching is carried out by means of the copper sulphate solution created in the second stage of pressure leaching. In the third stage of leaching 7 the temperature is at least 110 ° C. In an autoclave it is advantageous to maintain a mild oxidation temperature by feeding air. The NiS secondary nickel sulphide created in the second leaching at atmospheric pressure is dissolved in the reactions that take place between said NiS nickel sulphide, copper sulphate and water, so that after this leaching stage, it can be said that the whole of nickel has been dissolved. In the leaching process, copper is precipitated as Cu18S digenite, and CuS secondary copper sulfide also partially reacts with copper sulfate, thus creating more digenite and sulfuric acid. Under these conditions the iron contained in the leach cycle is dissolved from way that bivalent soluble ferrosulfate is created From the leaching step, the solution created is taken, after the step of separating the precipitate 8, to the leaching step 9 of the electric kiln matte Generally a mat with a high iron content is an electric oven mat (EF matte), but also suitable ferronickel matte can be leached at the stage of the process according to the present invention Matte also contains a small amount of copper and cobalt The amount of sulfur is very small and therefore the iron and nickel can be considered to be present in the mate primarily in elemental form. Within the leaching stage 9 also some oxygen containing gas is carried, such as oxygen or air, because the oxidation of iron to the trivalent state depends, among other factors, on the partial pressure of oxygen. If air is used in oxidation, it is clear that the reactions progress more slowly than with oxygen. The temperature of the leaching-precipitation stage is at least 80 ° C, advantageously at least 90 ° C, in order to obtain a precipitate that can be filtered under practical conditions. Sodium sulphate is also used in the leaching stage. created in the preceding stages of the process, for example in the purification of solution 4, in order to precipitate the trivalent iron created as jarosite. If the amount of sodium sulphate coming from the stages of the process is not enough, it is fed by Separate to the process a suitable compound of Na On the other hand, if there is an excess of sodium sulphate, it is crystallized. When the leaching stage starts-prec ipitation, kernels of jarosite are fed to the stage in order to initiate precipitation, but in a continuous process the last addition of nuclei is not necessary, because in the precipitation stage there always remains a sufficient quantity of crystal nuclei. following reactions take place in the leach stage of the EF mate: Ni0 + H2S04 + 02 > NiS04 + H20 (1) 6Fe ° + Na2S04 + 3H2SO4 + 41/202 + 6H20 > 2NaFe3 (S04) 2 (OH) 6 (2) The bivalent ferrous iron obtained from the leaching of the casting mat is precipitated as follows: 3Fe ° + 3FeS04 + Na2S04 + 302 + 6H20 > 2NaFe3 (S04) 2 (OH) 6 (3) Arsenic and antimony are also precipitated within the jarosite precipitate. The solution containing nickel sulfate which was obtained in the separation step 10 and which also contains other valuable minerals in dissolved form is carried back into the second leaching at atmospheric pressure 2. The precipitate of created jarosite is processed in a form appropriate it can be retroaligned within the pyrometallurgical or discarded process.

As previously stated, we have now discovered that the rate of dissolution of the iron-containing matte is not very dependent on the oxygen content in the solution, but on the other hand, the rate of iron precipitation is markedly increased when the acid content is reduced. It is therefore advantageous to adjust the leaching conditions of the EF mate in the region of a pH of 1-1.5, advantageously 1.2-2.2, wherein the amount of free acid contained in the solution is only a few grams per liter. Consequently, the solution obtained from the first autoclave leaching is extremely suitable for the leaching of the EF mate. In order to correctly adjust the degree of oxidation, oxide-reduction measurements can be applied, and in iron precipitation the redox potential with respect to the hydrogen electrode must be at least +700 mV.

When necessary, the iron can also be precipitated as a geotite, and in that case the pH of the solution is advantageously adjusted within the region of 2-3. The temperature can be lower than that of the precipitation of the jarosite, this is, 60 - 100 ° C. The iron can also be precipitated as hematite. In both cases, corresponding crystal cores must be brought within the precipitation stage when the process starts. When precipitation occurs as goethite or hematite, sodium sulphate is not required in the precipitation stage.

It is also clear that the leaching of a matte with a high iron content can be carried out with a solution obtained from some other stage of leaching the melting mat, but generally the solution obtained from the first stage of atmospheric leaching is advantageous for the mass precipitation of the iron and for the leaching of the nickel. The leaching can also be carried out for example with a solution obtained from the second atmospheric leaching. In that case, in the second atmospheric leaching the pH of the solution is adjusted to be 3 and the maximum redox potential with respect to the hydrogen electrode is +700 mV, advantageously approximately + 500mV, so that the faith is maintained in a bivalent way in the solution. In this alternative, the solution created in the leaching of the matte EF is fed back into the cycle of leaching of the melting mat, into the first atmospheric leaching. Separated from the process described above, the leaching of iron-rich matte can also be carried out by conducting a solution both from the autoclave leaching stage and from the second stage of atmospheric leaching, so that the solution created in the leaching of matte rich in iron is conducted to the mat leach cycle with low iron content, towards the first atmospheric leaching.

In the mat leach cycle with low iron content, the precipitate obtained from pressure leaching 7 and separated in separation step 8 is a precipitate containing mainly copper and precious metals. It is a particular advantage of the method that the precious metals are separated into a precipitate with a low iron content. The precipitate containing precious metals can be processed according to the needs of the particular situation; if a pyrometallurgical copper process is available, the precipitate can be brought there, but in other cases the precipitate can be further processed, for example, in the second stage of pressure leaching; from the resulting precipitate precious metals can be separated, from the solution copper sulphate can be crystallized and cathodic copper or copper powder with oxygen reduction be produced, according to known methods.

The above description relates to a nickel recovery method based on the principle that the nickel sulphate solution created in the nickel mat leaching is carried out within electrolytic nickel extraction and the anolyte from the electrolytic nickel extraction is used in the leaching of mate. However, the reduction of nickel sulfate to metallic nickel can also be carried out in other forms within the scope of the invention, for example, as hydrogen reduction, in which case the leaching is carried out within some other solution containing acid. sulfuric instead of anolyte. Similarly, part of the solution may be fed into the electrolytic nickel extraction and part may be reduced in some other way.

The invention is further described with reference to the following examples.

Example 1 25 g of electric oven matte was leached into an acid solution at the temperature of 95 ° C by oxidation with gaseous oxygen. The progress of the experiment is described in the following table.

The experiment shows that nickel dissolves at the same time the iron precipitates. The precipitate created is goethite and is poorly filtered. The iron content in the solution was higher than in the initial condition. The percentage of precipitation was approximately 70%.

Example 2 An experiment similar to that of Example 1 was carried out, but 25 g of jarosite nuclei were added in order to improve the precipitation. The first row of the table provides the analysis of the initial jarosite, as well as the analysis of the mixture of mate and jarosite.

The experiment shows that the nickel contained in the mate dissolves almost completely (99.4%) when the resulting jarosite (last row of the table) is purer than the one that was fed. Thus, it can be argued that the production is extremely good, and more iron is precipitated than that which was fed together with the mate: the iron content in the initial solution was 3.8 g / l, the final Fe value was 2.4 g / l. The filtration capacity was good.

The solution used in this experiment was made by leaching matte with low iron content according to the process flow diagram. The solution was obtained from step 7. The experiment shows that the iron leached at this stage can be at least partially precipitated.

Example 3 As examples 1 and 2 show, the oxidation of the iron is the slowest step in the process. This is obvious because the partial pressure of oxygen at the temperature of 95 ° C is about 0.15 bar. In a large-scale operation, a useful aid is the frequently remarkable static pressure - or so when at least an excessive pressure in the region of 0.3-5 bar is easily fixed.

In order to intensify the effect of the pressure a series of experiments was carried out, where experiment 2 was repeated in a pressure tank with several partial pressures of oxygen. The iron content of the solution was observed and is described in the attached diagram. In a situation corresponding to example 2, the partial pressure of the oxygen is 0.15 bar, and the points located on the respective curve are marked with an "x". The curve of 0.5 bar in the diagram corresponds to conditions where the reactor is 3 m high, and the points located on the respective curve are marked with 0. The conditions of the curve of 1 bar are easily reached in a process to production scale. In the diagram this curve is represented below, and the points are marked with the symbol 0.

GLOSSARY OF TERMS USED IN THE DRAWINGS Figure 1 1.- Atmospheric Pressure Leach (I) 2.- Atmospheric Pressure Leach (II) 3.- Liquid-Solid Separation 4.- Solution Purification 5.- Electrolytic Nickel Extraction 6.- Liquid-Solid Separation 7 .- Pressure Leaching (I) 8.- Liquid-Solid Separation 9.- Leaching of the Foundry Matte 10.- Liquid-Solid Separation 100.- Foundry Matte 200.- Anolite 300.- Nickel Cathode 400.- Matte of Casting 500.- Cu Precipitate Containing Precious Metals 600. - Precipitate Jarosita.

Claims (13)

1. Novelty of the Invention 1. A method to recover nickel and other valuable metals and to precipitate iron from two nickel mattes produced pyrometallurgically and containing different amounts of iron, characterized in that the iron mat containing less iron is leached at least an atmospheric leaching and at least one pressure leaching by applying the countercurrent principle and a solution containing nickel sulfate and sulfuric acid, in which case the nickel from the casting mat dissolves as nickel sulfate and is carried from the first stage of leaching within a process step wherein the nickel sulfate is reduced in metallic nickel; the iron of the casting mat is converted to a soluble form in some subsequent leaching step and this solution is brought to the leaching of the mat with the highest iron content, where the pH is adjusted to at least 1, in which case the nickel of the mate with greater content of iron dissolves and the iron contained in both mates is precipitated in a stage in the presence of precipitation nuclei; The solution obtained from the leaching of the mat with the highest iron content is fed back into the mat leaching cycle with lower iron content, towards a previous leaching stage.
2. 2. A method according to claim 1, characterized in that the iron contained in the casting mat and the mat with the highest iron content is precipitated as jarosite, while the pH is in the region of 1-2.5.
3. 3. A method according to claims 1 and 2, characterized in that sodium sulphate and some oxygen-containing gas are fed into the iron precipitation step.
4. 4 A method according to claims 1 and 2, characterized in that the temperature of the iron precipitation stage is at least 80 ° C
5. A method according to claim 1, characterized in that the iron contained in the casting mat and the mat with the highest iron content is precipitated as goethite, while the pH is in the region of 2-3.
6. 6 A method according to claims 1 and 5, characterized in that the temperature of the iron precipitation stage is at least 60-100 ° C
7. A method according to claim 1, characterized in that the redox potential in the step of iron precipitation with respect to the hydrogen electrode is at least +700 mV
8. 8. A method according to claim 1, characterized in that the arsenic and the antimony of the casting mate are precipitated inside the precipitate of iron.
9. A method according to claim 1, characterized in that the solution within the mat with the highest iron content is fed from the first stage of pressure leaching of the casting mat leach cycle
10. A method according to claim 9, characterized in that the solution obtained from the leaching of the matte with higher iron content and iron precipitation is carried within the leaching cycle of the melting mat, within the second atmospheric leaching.
11. 11. A method according to claim 1, characterized in that the solution within the leaching of the mat with the highest iron content is conducted from the second stage of atmospheric leaching of the leaching cycle of the casting mat.
12. 12. A method according to claim 11, characterized in that the solution obtained from the leaching of the mat with the highest iron content is carried within the first stage of atmospheric leaching in the leaching cycle of the casting mat.
13. 13. A method according to claim 1, characterized in that the precipitate obtained from the pressure leaching of the leaching cycle of the casting mat contains precious metals and has a low iron content. Extract of the Description The invention relates to a method for the recovery of nickel in a single process and from two nickel nickels produced pyrometallurgically, one of which contains a remarkable percentage of iron. The leaching of the nickel matte containing iron is carried out in a step leading to a solution coming from the leaching cycle of a mat with a lower iron content within the leaching of a matte with a higher iron content in a stage where the iron mate with lower iron content is in soluble form. The iron contained in the mattes is advantageously precipitated as jarosite and the solution created in the leaching of the mate with the highest iron content is taken back to the leaching cycle of the mate with less iron content.