MXPA06000669A - A process for upgrading an ore or concentrate - Google Patents

Abstract

According to the present invention there is provided a process for upgrading an ore or concentrate that contains metal sulphur minerals and gangue material. The process includes the stages of:a) selectively leaching the ore or concentrate using an ammoniacal solution containing ammonium carbonate that forms soluble metal ammine complexes;b) separating the solid and liquid phases formed in stage a) with the liquid phase forming a solution including soluble metal ammine complexes and the solid phase including at least in part the gangue material;c) removing ammonia and carbon dioxide from the liquid phase formed in step b) under conditions so as to selectively precipitate the valuable metal(s);and d) separating the solid and liquid phases formed in stage c) with the solid phase forming a more-concentrated source of valuable metal.

Description

WO 2005/007900 AI inHBiBninipDniMii Pnblished: - wa 'h imemational seartJi report For two-leler codes and other abbreviations, referred to the "Guidance Noies on Codes and Abbreviations" appearing at the beginning-ning ofeach regular issue oflhe PCI' Gazelie.

PROCESS TO IMPROVE MINERAL OR CONCENTRATE FIELD OF THE INVENTION The present invention relates to a hydrometallurgical process for improving a mineral ore or concentrate to a chiral intermediate or a more concentrated source of metal. In particular, the present invention relates to a process for improving a mineral ore, such as, but not limited to, zinc sulphide minerals. BACKGROUND OF THE INVENTION The present invention was made to further improve the recovery of zinc in the process of a mineral body at Century in Northen Queensland. Most zinc is recovered as a zinc concentrate containing zinc sulphide. Zinc sulfide is usually in the sphalerite mineral form. The dominant process for the production of zinc metal from zinc sulphide concentrates is the Roast-Leach-Electrowinning (RLE) process. This process is conducted in large efficient smelters that are capable of producing high purity zinc metal. The electrolytic extraction stage absorbs too much energy and, consequently, the RLE plants are located in regions that offer low-cost electric power that is generally at a distance from a remote mine site REF.169433. The transportation costs to transfer the concentrates and other materials to the RLE plants, the considerations to carry out the cooking and the need to minimize the amounts of waste generated in the RLE site, generate interest in the use of concentrates from high grade zinc, which are correspondingly low in impurities such as iron and silica. High grade concentrates can be produced in most zinc mines compromising metal recovery, in the extraction and concentration stages. In some cases, despite the rich nature of the deposits, the mineral structure of the minerals is such that suitable concentrate grades can not be produced economically. The responses to this situation have considered the development of processes, such as the Imperial Smelting Process, which are capable of processing medium / low grade concentrates (in the form of mixed lead-zinc concentrates) to metals of moderate purity. Although it has been a relatively high-cost route (which requires a cooking plant, furnace, a lead refinery and a zinc refinery), it has also been a successful alternative and now represents approximately 10% of the world smelting capacity. However, due to low metal prices, a number of these smelters have recently closed.

The processes to directly leach minerals or metal sulfur concentrates have been studied extensively. A ferric leaching of the oxidative acid, for example, conveniently produces a solution of zinc sulfate, from which (after purification of the solution) the zinc can be removed via electrolysis. Acid leaching of concentrates, in pressure vessels, is practiced in two plants in Canada and acid leaching at ambient pressure has been introduced in another plant in Finland. There are few hydrometallurgical plants in the mine site, indicating the common difficulty in obtaining low cost energy in remote locations and the understandable refusal to invest capital for a smelter unless a long life of the mine is secured. An alternative process is to use a hydrometallurgical process in the place where the mine is located to produce a zinc chemical intermediate, with only the electrolytic extraction stage being conducted in the second location. From a solution of zinc sulfate, for example, a precipitate of zinc sulfate (ZnS04) or basic zinc sulfate (3Zn (OH) 2.ZnS04) can be easily produced. The transfer of the sulfate to the electrolytic plant can, however, create a problem of sulphate disposal in the melter. It is an object of the present invention to provide an alternative process for separating valuable metal and sulfur components from a mineral or concentrate to provide the most concentrated source of valuable metal substantially in a sulfate-free form. BRIEF DESCRIPTION OF THE INVENTION The present invention is based on the embodiment that the sulfur compounds of the metal can be dissolved apart from their mineral ore or host concentrate using an ammonium solution containing ammonium carbonate (AAC solution) and then selectively precipitated for make a more concentrated source of metal that is, relatively, sulfur-free. In a situation in which the mineral ore or concentrate contains a valuable metal such as zinc in the form of sphalerite, the present invention allows the zinc and sulfur components to be separated so that the zinc component can form a product that is attractive to electrolytic plants. According to the present invention, a process for improving a mineral or concentrate containing the metallic sulfur minerals and the gangue material is provided. The process includes the steps of: a) selectively leaching the ore or concentrate using an ammonium solution containing ammonium carbonate that forms soluble metal amine complexes; b) separating the solid and liquid phases formed in step a) with the liquid phase which forms a solution including the soluble metal amine complexes and the solid phase which includes at least in part the gangue material; c) removing the carbon dioxide and ammonia from the liquid phase formed in step b) under conditions that are selected to facilitate the precipitation of the valuable metal (s) and minimize the sulfur content in the valuable metal (s) precipitated; and d) separating the solid and liquid phases formed in step c) with the solid phase forming a more concentrated source of valuable metal. It will be appreciated by one skilled in the art of the present invention that steps a) to d), or any of the other steps described above, can be performed consecutively or. disjunctively and can be, for example, carried out in various sites of the plant. Depending on the operating conditions under which steps a) and c) are carried out, the solids formed can. preferably comprise oxides, hydroxides and metal carbonates. An advantage provided by the present invention is that the valuable metals precipitated in step c), such as zinc, silver and copper can form a metal salt with an anion with the exception of a sulfur-containing anion such as a sulfate. It has been observed that the conditions under which valuable metals are precipitated impact on whether the valuable metals can be precipitated as a salt with an anion except for the anion that. contains sulfur. This has greater ramifications because the minimization of sulfur in the precipitate provides significant benefits in downstream processes. Another advantage is that very few of the major components of the gangue material (notably iron and silica) are soluble in an AAC solution and, therefore, will form a significant portion of the solid phase formed in step b). It is preferred that the AAC solution used in step a) have a pH ranging from 7 to 10.5. It is preferred that step a) is carried out at a temperature ranging from 60 to 99 ° C at atmospheric pressure. It is possible that step a) can be carried out at higher temperatures and pressures. It is preferred that the method includes the addition to step a) of a metal oxidant that undergoes a reduction reaction to facilitate the dissolution of the metal sulfur compounds. It is preferred that the metal oxidant be in the form of a cupric cation (ie Cu2 +). This copper can be a source of the mineral by itself during the leaching reaction, or it can be supplemented by being added in the form of a copper chemical.

In a situation in which the valuable metal is zinc and the material to be improved, for example in the form of sphalerite (ZnS), the sphalerite solution can be represented by the following reaction: ZnS + '8Cu (NH3) 4C03 + 4H20? Zn (NH3) 4C03 + 4Cu2 (NH3) 4C03 + (NH4) 2S04 + 3 (NH4) 2C03 + 4NH3 Reaction A One advantage when using a bivalent copper cation as the metal oxidant is that it can be regenerated using oxygen by the following reaction of oxidation: 2Cu2 (NH3) 4C03 + 02 + 4NH3 + 2 (NH4) 2C03? 4Cu (NH3) 4C03 + 2H20 Reaction B Although it is possible for reaction B to occur in a separate step, it is preferred that an oxygen-containing gas be provided to step a) such that Reactions A and B can occur simultaneously. In fact, a difficulty that can be encountered if the oxygen is not supplied to stage a) is that the copper in the solution can be precipitated as copper sulfide. Although air can be used as the oxygen-containing gas, it is preferred that a source of purified oxygen be used while providing a faster reaction rate and reducing heat losses for the associated nitrogen gas. In addition, to facilitate continuous operation, an amount of copper constituted will need to be added to stage a). When oxygen is supplied simultaneously, the total reaction that occurs in step a) can be represented by the following reaction: ZnS + 202 + 4NH3 + (NH4) 2C03? Zn (NH3) 4C03 + (NH4) 2S04 Reaction C It is preferred that the concentration of the copper cations in the ammonium solution used in step a) is at least 0.15 g / 1 so that the concentration of copper does not limit the speed of the reaction. It is preferred that the ammonia solution in step a) contains ammonia in a concentration that is sufficient to keep the metal ions, which form amine complexes, stable in the solution. To do this, it is considered that an excess of ammonia will be required over the stoichiometric minimum. As a guide, the minimum total level of ammonia (for the case of zinc with copper) can be calculated by the following formula: [NH3] > ([Zn] + [Cu]) x 8) + ([S04] x 2) formula A where, the concentrations are in mol / L. As an example, in a situation where the concentration of zinc in step a) is 30 g / 1, the concentration of ammonia (total) in the solution in step a) should be approximately not less than 80 g / 1.

It is also desirable that an excess be supplied over the stoichiometry of the dissolved carbon dioxide (or carbonate / bicarbonate) -. It is preferred that step c) be carried out under conditions to minimize the precipitation of sulfur and sulfur-containing compounds. More particularly, it is preferred that step c) is carried out at a temperature ranging from 90 ° C to the boiling point to reduce the equilibrium levels of the carbon dioxide and ammonia dissolved in such a way as to destabilize the metal amine compounds. It is preferred that the steam be sprayed through the liquid phase of step c) since it not only provides an efficient source of heat but also provides a carrier gas for further removal of ammonia. While the ammonia is removed, the metals begin to precipitate as a mixture of hydroxide-carbonate compounds substantially free of sulfur and in particular sulfate compounds. This is surprising, since the level of sulfur in the solution is approximately 50% higher than for zinc - in terms of mass per liter. While the reaction proceeds and the concentrations of carbon dioxide and dissolved ammonia decrease (a trend readily followed by monitoring the pH), the metals tend more and more to precipitate as the basic metal sulfate. This is undesirable since the grades effectively lower the attraction of the precipitate to the melter. It is preferred that step c) be carried out at a final pH of 6.8 or more to avoid the formation of excessive amounts of metal sulfate. Those skilled in the art will appreciate that other operating parameters such as temperature and residence time also influence the properties of the precipitate. In a situation in which the valuable metal is zinc, the precipitation of zinc and the evaporation of the ammonia that occurs in stage c), can be represented by a reaction such as: HZn (NH3) 4C03 + 48H20? 8Zn (OH) 2.3ZnC03.4H20 i + 8 (NH4) 2C03 + 28NH4OH Reaction D Although Reaction D shows a precipitate of zinc hydroxide carbonate, zinc can also be precipitated in other forms including basic carbonate and sulfate. basic zinc. Ammonium carbonate and ammonium hydroxide are also unstable under conditions under which step c) is preferably carried out and can be analyzed according to the following reactions. (NH4) 2C03. ? H20 + C02 t + 2NH3 t Reaction E NH4OH - >; H20 + NH3 t Reaction F For further increasing the proportion of valuable metal in the solid phase formed in step c), it is preferred that the process includes a step of calcining the solid phase recovered in step d). The calcination step involves at least part of the metal carbonates and possibly the hydroxides are converted to a metal oxide. It is preferred that the calcination step be performed by heating the solid phase formed in step c) to a temperature of 100 ° C or more to remove the water and 300 ° C or more to decompose the carbonate. The liquid phase of stage d contains significant amounts of ammonium sulfate that can be crystallized using standard equipment to form a by-product that can be used by agricultural fertilizer manufacturers. It is preferred that the liquid phase of step d) be treated to precipitate the sulfur and the sulfur-containing compounds from the liquid phase as a salt. An advantage provided by this preferred aspect of the invention is that the additional ammonia can be recovered for reuse. It is preferred that the liquid phase of step d) be treated by adding a neutralizing agent to the liquid phase. An example of a convenient neutralizing agent is lime (CaO) and the salt with sulfur produced is calcium sulfate (ie, gypsum). It is preferred that the neutralizing agent maintain the pH above 7 during the precipitation step of the sulfate para. reduce minimize the remaining ammonia level such as ammonium hydroxide. It is preferred that the ammonia be removed from the liquid phase in step d) by heating the liquid phase and spraying with steam. This can occur simultaneously with, or subsequently, the treatment with lime. The sulphate precipitation stage can be represented by the following reaction: (NH4) 2S04 + Ca (OH) 2? 2NH3 t + CaS04 i (gypsum) + 2H20 Reaction G It is preferred that the volatized / vaporized ammonia from step c) and / or the step to precipitate the sulfate ions, be recovered and reused in step a). The standard equipment and the known process of - how - to involve packed towers for the recovery of carbon dioxide and ammonia from the vapors and distillation columns for the production of a concentrated ammonia / liquid ammonium carbonate for recycling - are available, for this . The present invention also comprises a solid phase made substantially of a metal oxide and of any other solid and liquid phase including the gypsum formed in the sulphate precipitation step made according to the process of the present invention. The present invention also comprises a plant that includes at least two reactor vessels for performing steps a) and c) and at least two solid / liquid separation devices for performing steps b) and d) of the process. DETAILED DESCRIPTION OF THE INVENTION A detailed description of a preferred embodiment of the present invention will now be described with reference to Figure 1. The description is in the context of a zinc refining plant. However, the present invention is not confined to treating this valuable metal and is equally applicable to other valuable metals, such as copper. In terms of process flow, the preferred embodiment includes an ammonia-leaching step 11 which is supplied with a zinc-containing feed material such as a mineral or concentrate, an AAC solution and oxygen. The AAC solution and the feed material form a mixture in the leaching step 11. Once reacted in the leach step 11, the suspension is fed to a solid / liquid separator 12 in. wherein the liquid phase is separated from the solid phase which is constituted largely by the insoluble gangue material. The liquid phase is then supplied to a zinc precipitation step 13 in which a solid phase containing zinc is precipitated and whereby a suspension is formed. The suspension is then fed to another solid / liquid separator 14 r in which the liquid phase is separated from the solid phase. The phase containing solid zinc is then fed to an optional calcination step 15 to produce a product that is substantially zinc oxide. The liquid phase formed in the separator 14 is further treated in an optional step of precipitation of sulfate 16 to recover more ammonia and precipitate gypsum - which is a valuable by-product in some circumstances. The carbon dioxide and ammonia are evaporated in the precipitation stages of zinc- and sulfate 13 and 16, and are recycled back to the stage that leaches the ammonia 11. The operational characteristics of each stage will now be described in more detail. The ore or concentrate fed in the ammonia leaching step 11 comprises the sphalerite (ZnS) and the gangue material includes iron and silicate minerals. An ammonium / ammonium stream is fed to the ammonia leaching stage. If the amount of soluble copper in the ore is insufficient, a source of copper ions is also added to the reactor. This may conveniently be in the form of a solution of copper sulfate in water. Copper (Cu1 + and Cu2 +) will form copper amine ions in the AAC. • According to Reaction A, the cupric cations function as an oxidation agent such that the zinc constituent of the feedstock also forms a soluble amine complex. There are several advantages to using copper as an oxidizing agent. First, soluble amine complexes are formed in a pH range of 7.0 to 10.5 and at a temperature ranging from 60 to 95 ° C, whereas the gangue in the feedstock is substantially insoluble under these conditions. Secondly, the copper oxidation agent can be conveniently regenerated using oxygen according to Reaction B indicated above. The complete oxidation / reduction that dissolves the sphalerite in the leaching stage 11 is represented by Reaction C, indicated above. In some cases, sphalerite can be oxidized directly by oxygen according to the following reaction: ZnS + '4NH3 + 202? Zn (NH3) 4S04 Reaction H However, it will be appreciated that the "products" formed by Reactions C and H will exist in the solution as dissociated ions and ammonia carbonate will exist in the solution as a mixture of bicarbonate, carbonate and free ammonia. . In the case when the raw material includes zinc carbonate, it can be dissolved according to the following reaction: ZnC03 + 4NH3? Zn (NH3) 4C03 reaction I Ammonia is distributed in the solution between copper and zinc amine complexes, ammonium bicarbonate, ammonium sulfate and as hydrolyzed ammonia. The amount of ammonia in the solution will affect the amount of zinc and copper ions that can be kept in the solution. As a guideline, the minimum ammonia level required can be estimated by the following formula in which the concentrations of zinc, copper and sulfate are the concentrations (mol / L) present in stage 11. [NH3] min = ([Zn] + [Cu]) x 8) + ([S04] x 2) When the concentration of zinc present in step a) is 30g / l, the minimum recommended concentration of NH3 in the AAC solution is 80 g / l. The rate at which zinc is leached at the stage 11 is temperature dependent. A temperature between 60 and 95 ° C has been adequate for tests conducted to date. It may be beneficial to drive the leach stage 11 at high temperatures and pressures to achieve a higher reaction rate. The leaching step 11 is also dependent on sufficient oxygen that is available to regenerate the Cu 2+ ions. In principle, air could be used, but purified oxygen is preferred since it provides faster reaction rates and heat losses will be lower. If the dissolved oxygen level is not maintained during the course of the leaching reaction, the copper is probably precipitated, removing it from an active paper according to the following reaction: 2Cu2 (NH3) 4C03 + ZnS? Zn (NH3) 4C03 + Cu2S? Reaction J Any gas formed, or introduced with oxygen, will need to be discharged from the stage of leaching ammonia 11. While ammonia and carbon dioxide are totally volatile, there will be a loss of ammonia with these gases, requiring discharge treatment • gaseous using condensers or water purifiers (not illustrated in the figure 1) - Once the zinc has dissolved, and the unreacted material removed in the solid / liquid separator 12, the objective is to recover the zinc. The zinc amine complex can be broken by heating the (near) solution boiling and spraying with steam. This removes the ammonia and carbon dioxide and precipitates the zinc as the hydroxide carbonate according to Reaction D indicated above. Zinc carbonates may also be present in the solid phase. As can be seen in Figure 1, the ammonia and carbon dioxide are recyclable again in the leaching step 11. The composite AAC solution can also be fed to the leaching stage 11, if necessary. While the ammonia is removed, the zinc will precipitate, ideally as a hydroxide carbonate according to Reaction D. Zinc can also be precipitated as a basic zinc carbonate according to the following reaction: 5Zn (NH3) 4C03 + 3H20? 3 (Zn0.H20) .2ZnC03 | + 20NH3t + 3C02t Reaction K While reaction K does not contaminate the zinc product, with sulfate ions, it reduces the total degree of the precipitate because the zinc content of the solids in the hydroxide form is about 66%, while the Basic zinc carbonate only contains approximately 60% zinc.

While the pH decreases with the removal of ammonia and carbon dioxide, there is a greater tendency for zinc to precipitate as a basic sulphate according to the following reaction: 4Zn (NH3) 4C03 + (NH4) 2S04 + 2H20? 3Zn (OH) 2. ZnSO + 4C02 t + 18NH3 Reaction L The endpoint selected for the precipitation reaction in step 13 is a tradeoff between maximizing zinc precipitation and minimizing sulfate contamination of the precipitate.

Alternatively, zinc can be further promoted to be precipitated in the hydroxide form by the addition of an alkali (eg, caustic soda) which maintains the pH at a convenient, higher value. The suspension formed in the zinc precipitation step 13 is then fed to a solid / liquid separator. 14 and the solid phase containing the zinc constituents is fed to the calcination step 15.

The calcination step 15 essentially converts the zinc hydroxide carbonates to zinc oxide. This will reduce the mass that will be transported to the extraction refinery by electrolytic route and will minimize the contamination of the product with ammonia. The calcination step 15 is carried out by heating the precipitate above 300 ° C. The liquid phase of step 14 contains significant amounts of ammonium sulfate that can be crystallized using standard equipment to form a by-product that can be used by agricultural fertilizer manufacturers. Alternatively, ammonia can be recovered.

This is accomplished by reacting the liquid phase in step 16 with a reagent such as lime or limestone to form the gypsum, which precipitates. By boiling and / or spraying with steam, the liquid is used simultaneously with, or subsequently, lime treatment to volatilize the dissolved ammonia. If not evaluated as a by-product, the gypsum suspension resulting in step 16 can be fed conveniently and directly to a barrage dam at a mine site. The ammonia and carbon dioxide evaporated in steps 13 and 16 can be recovered and reused in step 11.

With the known standard equipment and process, the packaging towers for the recovery of ammonia and carbon dioxide from the steams and distillation columns for the production of a concentrated ammonia / ammonium carbonate liquid for recycling can be involved - they are available, for this. A description of an assay performed according to the preferred embodiment of the present invention is specified below. Example 1: Leachate of ammonia A stage of leaching from AAC was conducted in a 3 1 reactor at 85 ° C for 5 hours, with the oxygen spray at 600 ml / min. The starting material was 200 g of a lower quality concentrate containing 15% Zn, in the form of sphalerite, suspended with water at a pulp density of 200 g of the solid solution / dry liter. After heating to 85 ° C, 400 g of ammonium hydrogen carbonate was then added together with 250 ml of 25% by weight of the ammonia solution. The cupric ions were added in the form of copper sulfate (3 g in 30 ml of water) and the reaction started. The pH was controlled during the test at 8.7 by automatic additions of the ammonia solution. At the conclusion of the test the suspension was filtered, washed and analyzed. The filtrate is fed by the zinc precipitation step and the solid is the waste gangue material. The results of the filtrate analysis provided an assay as indicated below.

The zinc extraction was 91.4% after 5 hours. Zinc in the form of zinc silicate was not extracted from the solid phase. There was an extraction of other elements (ie lead, - manganese) but they are not stable in the solution and precipitated (probably as carbonates) and are located in the gangue. Cadmium and copper (in the feed material) are extracted and stable in the solution. Table 1: Test for leaching ammonia The solid residue containing the gangue material was tested washed. The concentration of ammonia before washing was approximately 0.1% and < 0.1% after three washes. This shows that the ammonia can be effectively recovered by washing the residue. Example 2: Precipitation of zinc The solution of the ammonia leachate stage was heated to about 95 ° C and sprayed with oxygen (as an experiment, a convenient carrier gas) at 400 ml / min for 3.5 hours. About this time, a precipitate formed and the pH dropped from 8.8 to 6.8. In a series of 'experiments, the reaction was interrupted at various levels of the final pH and the resulting precipitates were filtered and analyzed. The analysis provided the following tests. -Table 2: Zinc precipitation tests The purity of the zinc product can be improved by stopping the reaction at a higher pH at the expense of zinc recovery as shown below. There will be an economic compensation between these two factors.

In the case when the zinc precipitation stage was stopped at a pH of 6.8, the solid test comprised approximately 85% zinc hydroxide carbonate (8Zn (0H) 2.3ZnC03), 7% basic zinc sulfate and 2.3% of basic copper carbonate. Therefore, a total of 96.8% of the zinc in the liquid phase fed to the zinc precipitation (stage 2) was precipitated. In the case when the zinc precipitation step was stopped at a pH of 7.5, the solid test comprised approximately 87% zinc hydroxide carbonate (8Zn (OH) 2.3ZnC03), 6% basic zinc sulfate and 0.7% basic copper carbonate. Therefore, in this case a total of approximately 88.1% of the zinc in the feed for stage 2 was precipitated. Copper precipitation starts after zinc, at about pH 7.5. Lead and silica seem to precipitate relative and rapidly and therefore their solid tests subsequently decline over the course of the experiment. Example 3: Precipitation of the sulfate The solution of Example 2 was again heated to about 95 ° C and sprayed with oxygen for 2 hours. The lime was added as a suspension of 500 g / 1 to maintain the pH at approximately 7.0. During this time, a formed precipitate and analysis of the collected samples collected (table 3) indicates that the precipitate contained a mixture of calcium carbonate and calcium sulfate. The final liquor contained very low levels of zinc, copper and ammonia. Table 3: Plaster precipitation tests The majority of the precipitate contains calcium compounds, 60% calcium carbonate and 26% gypsum (calcium sulfate). Approximately 85% of the sulfate was precipitated, and 92% of the ammonia was volatilized from the solution. Example 4: Calcination Using a muffle furnace, samples of 10 grams of the precipitated zinc product were heated between 200 ° C and 500 ° C, at 100 ° C intervals, for a minimum of two hours. The results are presented below in table 4. Table 4: Calcination Results At 300 ° C, the zinc content of the product had increased by 10% to 63-65% zinc. The concentration of ammonia had decreased from 2.0% to 0.5% at 300 ° C, and to less than 0.1% at 400 ° C. This is equivalent to 82% (sample 1) and 71% 'of zinc hydroxide (sample 2), with minimal amounts of the present zinc carbonate. There being approximately 18-24% of the basic zinc sulphates in the product. Calcination of the product at 300 ° C increased the concentration of zinc by removing carbonate to less than 1%. After calcining the product at 400 ° C, the ammonia in the product was decreased below its limit of detection. This minimizes the release of ammonia during the dissolution of the zinc product. Calcination of the product at approximately 400 ° C resulted in increasing zinc concentration and complete ammonia removal. Therefore, treating the precipitated product results in the reduction of the amount of final product to be transported and the problems of the Occupational Health and Safety associated with the release of ammonia by dissolving the product in a hydrometallurgical circuit. It will be appreciated by those skilled in the art of the present invention that modifications can be made to the preferred embodiment of the invention without departing from the spirit and scope of the invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the clear result of the present description of the invention.

Claims (44)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Process for improving a mineral or concentrate containing metallic sulfur minerals and the gangue material, characterized in that it includes the steps of: a) selectively leaching the mineral or concentrate using an ammonium solution containing ammonium carbonate which forms soluble metal amine complexes; b) separating the solid and liquid phases formed in step a) with the liquid phase which forms a solution including the soluble metal amine complexes and the solid phase which includes at least in part the gangue material; c) removing the carbon dioxide and ammonia from the liquid phase formed in step b) under conditions that are selected for. facilitate the precipitation of the valuable metal (s) and minimize the sulfur content in the valuable metal (s) precipitated; and d) separating the solid and liquid phases formed in step c) with the solid phase forming a more concentrated source of valuable metal.
2. 2. Process according to claim 1, characterized in that step a) is carried out at a pH ranging from 7 to 10.5.
3. 3. Process according to claim 1 or 2, characterized in that step a) is carried out at a temperature ranging from 60 to a temperature just below the boiling point.
4. 4. Process according to any of claims 1 to 3, characterized in that it includes the addition to step a) of a metal oxidant that undergoes a reduction reaction to facilitate the dissolution of the metal sulfur compounds.
5. 5. Process according to claim 4, characterized in that the metal oxidant can be regenerated by oxidation.
6. 6. Process according to claim 4 or 5, characterized in that the metal oxidant is in the form of a cupric cation.
7. Process according to claim 6, characterized in that the concentration of copper cations supplied to stage a) in the ammonium solution is at least 0.15 g / 1.
8. Process according to claim 6 or 7, characterized in that when the metal is zinc and the mineral contains sphalerite (ZnS), the leaching of the sphalerite can be represented by the following reaction: ZnS + 8Cu (NH3) 4C03 + 4H20 ? Zn (NH3) 4C03 + 4Cu2 (NH3) 4C03 + (NH4) 2S04 + 3 (NH4) 2C03 + H3.
9. 9. Process according to claim 8, characterized in that it includes maintaining the concentration of ammonia in step a) at a level 'according to the following formula: [NH3] ([Zn] + [Cu]) x 8) + ([S04] x 2)
10. 10. Process according to any of claims 6 to 9, characterized in that the copper copper is regenerated by oxidation with oxygen according to the following reaction: 2Cu2 (NH3) 4C03 + 02 + 4NH3 + 2 (NH4) 2C03? 4Cu (NH3) 4C03 + 2H20
11. 11. Process according to any of claims 1 to 10, characterized in that an oxygen-containing gas is supplied to step a).
12. 12. Process according to any of claims 1 to 11, characterized in that a gas rich in oxygen is supplied to stage a).
13. 13. Process according to any of claims 1 to 12, characterized in that step c) is carried out at a temperature ranging from 90 ° C to the boiling point to evaporate the ammonia and thereby facilitating the precipitation of the compounds metallic
14. 14. Process according to claim 13, characterized in that step c) includes spraying the liquid phase with steam to regulate the temperature and provide a carrier gas for the removal of the additional ammonia.
15. 15. Process according to any of claims 1 to 14, characterized in that step c) is carried out at a final pH of 6.8 or more to minimize the precipitation of metal sulphate minerals.
16. 16. Process according to any of claims 13 to 15, characterized in that when the metal is zinc, the precipitation of zinc and the evaporation of ammonia occurring in step c), can be represented by the following reaction: HZn (NH3) 4C03 + 48H20? 8Zn (OH) 2.3ZnC03.4H20 + 8 (NH4) 2C03 + 28NH4OH
17. 17. Process according to any of claims 1 to 16, characterized in that it also includes a step of calcining the solid phase recovered in step d).
18. 18. Process according to claim 17, characterized in that the calcination step is carried out by heating the solid phase formed in step c) at a temperature ranging from 100 ° C to 500 ° C.
19. 19. Process according to any of claims 1 to 18, characterized in that the liquid phase recovered from step d) is treated to precipitate the sulfur and sulfur-containing compounds from the liquid phase as a salt.
20. Process according to claim 19, characterized in that a neutralizing agent is added to the liquid phase of step d).
21. 21. Process according to claim 20, characterized in that the neutralizing agent maintains the pH above 7 during the sulphate precipitation step to minimize the remaining ammonia level such as ammonium hydroxide.
22. 22. Process according to any of claims 19 to 21, characterized in that the ammonia is removed from the liquid phase recovered from step d) by heating the liquid phase.
23. 23. Plant for improving a mineral or concentrate containing metallic sulfur minerals and the gangue material, characterized in that it includes: a first stage in which an ammonium solution containing ammonium carbonate can selectively leach the metal (s) ) and metallic compounds of the mineral or concentrate to form soluble metal amine complexes; a separator for separating the solid and liquid phases formed, in which the liquid phase includes soluble metal amine complexes and the solid phase includes at least part of the gangue material; a second stage that is supplied with the liquid phase formed in the separator and from which the carbon dioxide and ammonia are removed under conditions that are selected to facilitate the precipitation of valuable metals and to minimize the sulfur content in the metal (it is ) valuable (s) precipitated (s); and another separator for separating the solid and liquid phases formed in the second stage whereby the solid phase forms a more concentrated source of valuable metal (s).
24. 24. Plant according to claim 23, characterized in that the pH in the first container is in a range of 7 to 10.5.
25. 25. Plant according to claims 23 to 25, characterized in that the temperature in the first stage goes from 60 to a temperature just below the boiling temperature.
26. 26. Plant according to any of claims 23 to 25, characterized in that a metal oxidant is supplied to the first stage undergoing a reduction reaction to facilitate the dissolution of the metal sulfur compounds.
27. 27. Plant according to claim 26, characterized in that the metal oxidant can be regenerated by oxidation.
28. 28. Plant according to claim 27, characterized in that the metal oxidant is in the form of a cupric cation.
29. 29. Plant according to claim 28, characterized in that the concentration of the copper cations supplied to the first stage in the ammonia solution is at least 0.15 g / 1.
30. Plant according to claim 27 or 28, characterized in that the metal is zinc and the mineral contains sphalerite (ZnS), the leaching of the sphalerite can be represented by the following reaction: ZnS + 8Cu (NH3) 4C03 + 4H20? Zn (NH3) 4C03 + 4Cu2 (H3) 4C03 + (NH4) 2S04 + 3 (NH4) 2C03 + 4NH3.
31. 31. Plant according to claim 30, characterized in that the ammonia concentration in the first stage is maintained at a level according to the following formula: [H3] > ([Zn] + [Cu]) x 8) + ([S04] x 2)
32. 32. Plant according to any of claims 28 to 31, characterized in that the metallic oxidant is cupric copper, the reduced copper is regenerated by oxidation with oxygen according to the following reaction: 2Cu2 (NH3) 4C03 + 02 + 4NH3 + 2 (NH4) 2Ca3 - »4Cu (NH3) 4C03 + 2H20
33. 33. Plant according to any of claims 29 to 32, characterized in that a Gas containing oxygen is supplied. to the first stage to regenerate the metal oxidant.
34. 34. Plant according to claim 33, characterized in that the oxygen-containing gas is purified oxygen.
35. 35. Plant according to any of claims 23 to 34, characterized in that the second stage is carried out at a temperature ranging from 90 ° to the boiling point to evaporate the ammonia and thereby facilitate the precipitation of the metal compounds.
36. 36. Plant according to claim 35, characterized in that steam is sprayed through the liquid phase of the second stage to provide heat and a carrier gas for further removal of ammonia.
37. 37. Plant according to any of claims 23 to 36, characterized in that the second step is carried out at a final pH of 6.8 or more to avoid excessive amounts of metal sulfate formation.
38. 38. Plant according to any of claims 25 to 37, characterized in that when the metal is zinc, the precipitation of the zinc and the evaporation of the ammonia that occurs in step c), can be represented by a reaction of the form: llZn ( NH3) 4C03 + 48H20? 8Zn (0H) 2.3ZnC03.4H20 ^ + 8 (NH4) 2C03 + 28NH4OH
39. 39. Plant according to any of claims 23 to 38, characterized in that it additionally includes a step of calcining the solid phase recovered in the additional separator.
40. 40. Plant according to claim 39, characterized in that the calcination step is carried out by heating the solid phase formed in step c) to a temperature of at least 100 ° C and preferably, above 300 ° C.
41. 41. Plant according to any of claims 23 to 40, characterized in that the liquid phase of the separator stage d) is treated to precipitate the sulfur and sulfur-containing compounds of the liquid phase as a salt.
42. 42. Plant according to claim 41, characterized in that the liquid phase of step d) is treated by adding a neutralizing agent for the liquid phase.
43. 43. Plant according to claim 42, characterized in that the neutralizing agent maintains the pH higher than 7 during the sulphate precipitation step to minimize the remaining ammonia level such as ammonium hydroxide.
44. 44. Plant according to any of claims 41 to 43, characterized in that the ammonia is removed from the liquid phase in step d) by heating the liquid phase and spraying with steam. Figure 1 Composition Recycling NH3 and C02 Mineral or concentrate containing zinc Product Zinc oxide