WO2021116742A1

WO2021116742A1 - Method for obtaining an alkaline earth metal compound

Info

Publication number: WO2021116742A1
Application number: PCT/IB2019/060780
Authority: WO
Inventors: Patricia Alejandra ARANCIBIA MARTÍNEZ
Original assignee: Scarab Chile Spa
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2021-06-17

Abstract

The invention relates to a method for obtaining an alkaline earth metal compound from mined materials, which comprises: (i) leaching a quantity of a mined material, using a leaching solution comprising at least one first acid; (ii) filtering the mixture resulting from step (i) to obtain a solid phase and a liquid phase, the solid phase being discarded; and (iii) adding a second acid to the liquid phase obtained in step (ii), the second acid allowing a low-solubility alkaline earth metal salt to be obtain by recovering the leaching solution.

Description

A PROCESS FOR OBTAINING AN ALKALINE EARTH METAL COMPOUND

FROM MINING MATERIALS

FIELD OF THE INVENTION

The present invention relates to non-metallic mining, specifically to the mining industry related to obtaining alkaline earth metal compounds. In particular, the present invention is related to the industry for the treatment of materials and waste with considerable concentrations of alkaline earth metals in the form of basic salts, such as mineral tailings with a high content of carbonates, slags and other solid waste, which even having Considerable concentrations are not of interest to traditional extraction and treatment mining. These materials have alkaline earth metals in low concentrations that do not allow a conventional treatment, but high to treat exhausted materials.

STATE OF THE ART

Currently, mining comprises one of the activities of extraction of organic and inorganic resources that, after a special treatment, are transformed into products that due to their physical and / or chemical properties can be applied to different industrial, agricultural or pharmacological uses, among others. areas.

One of the major areas of mining is non-metallic mining, and among the products obtained through this non-metallic mining are compounds of alkaline earth metals, such as sulfates and their oxides.

Currently, one of the most widely used sulfates and oxides as an industrial resource are gypsum or calcium sulfate hemihydrate (CaSC> ₄ · 1 / 2H ₂ 0) and lime or calcium oxide, which correspond to products from resources with good geological prospects and abundant in certain geographic areas.

Although at first glance these materials have a low unit value and high production volumes, recent market analysis shows their positioning as critical inputs, especially in mining, and specifically in metal mining.

An example of this is copper mining, which, among other production processes, has calcium oxide, commonly called lime, as a critical input. This input is used in the form of "quicklime" (calcium oxide), "slaked lime" (calcium hydroxide) or "milk of lime" (aqueous suspension) depending on the nature of the requirement.

In the coming years, a significant demand for lime is expected for the treatment of sulphides by flotation. However, over time the limestone mines, which corresponds to The raw material for the manufacture of lime has been depleted in the world, causing the supply of lime, both for mining purposes and for other purposes, to decrease. Faced with this eventuality, Chile and other countries have compensated for the calcium oxide deficit with the import of lime, which translates into higher metal mining costs. Lime or calcium oxide is obtained from the calcination of calcareous minerals or carbonates, mostly limestone extracted from a mine in concentrations higher than 85%. There is also the calcium carbonate flotation process for minerals with a grade of close to 65%, where it is brought to the concentrations required to continue in the cement production line. There are different types of calcination furnaces used, where the process is basically the same, the temperature of the rock is raised to a range between 900 ° and 1200 ° C, with different residence times, as required. Under these conditions, the decomposition of calcium carbonate into calcium oxide and carbon dioxide occurs.

However, the mining sectors with low grades are left as environmental liabilities since, when they are extracted for advance, they end up constituting dumps. On the other hand, if a medium-grade mineral is used to float and concentrate, it generates a tailings with a high content of calcium carbonate, which constitutes another type of environmental liability. According to current environmental legislation, these wastes must be disposed of through a third party, which implies a unit cost with respect to the mass involved or a deposit limit that restricts the useful life of the project, as is the case of tailings.

As can be seen, there is currently no process applied to obtain or recover alkaline earth metals from low grade minerals (less than 45%) or from waste material to, for example, obtain alkaline earth metal oxides or sulfates from them, so they are left waiting for the closure of the mine or its disposal in a sanitary bed.

Both the environmental liability and the low-grade minerals disposed of in a sanitary bed correspond to an inheritance derived from the mining activity, which without proper management become a threat to the environment and especially to the communities near them. It is observed that these mining materials can range from particulate matter to large rocks that generate a significant environmental impact on their communities, which translates into social and economic problems that are often irreparable.

There is also no great difference with the extractive processes of this non-metallic mining, since they correspond mostly to coarse mining processes that involve the extraction of the rock after blasting, transportation within the mine to the crusher that grinds the material according to the needs of the final treatment and transport to the final place. As can be seen, the impact of this process is strong and its consequences range from destruction of agricultural quality land, changes in the ethnic structure of the area, noise and suspended dust, to changes in local tradition and demographic changes in the vicinity. Another similar case is observed in the materials used as a resource in the agriculture and chemical industry such as magnesium sulfate and magnesium oxide, which both come from the treatment of magnesium carbonate or magnesite mineral. Both require a mineralogical matrix for their preparation and elaboration. This form of production clearly develops residues that are again disposable and piled up in specific sites as environmental liabilities since, although they still contain good percentages of salvageable magnesium, they cannot be extracted from known obtaining and extraction techniques because they are not effective. at those concentration levels, or else, they are not very profitable.

As observed in the mining of magnesium and in the mining of calcium, alkaline earth metal mining has not developed techniques that allow the extraction and obtaining of compounds from the residues of said mining or from low-grade minerals, and that also comply with being efficient and commercially effective with respect to the ancestral technique.

Patent application US20140127096 describes hydrometallurgical systems, methods and compositions in which organic amine-based lixiviants are used in the selective recovery of alkaline earth elements. The leachate can be reclaimed and recycled for use in subsequent iterations of the process. Multiple alkaline earth elements can be recovered from a sample in parallel or in serial applications of the described methods. Likewise, it is described that a particle size is necessary, specifying that it must be between 0.05 mm and 1 mm, with greater effectiveness between 0.05 mm and 0.25 mm, indicating that its ideal configuration corresponds to the interval of 0 .05mm to 0.125mm. This condition does not allow working with materials of various configurations in the reactor, which necessarily implies the use of crushing and / or pulverizing in the process, increasing its costs. In the same way, the process of US20140127096 requires that there is a control of the alkaline earth metal content in the solution, specifically in its examples applied with calcium, in order to improve the efficiency of the reaction. In particular, the mass ratio of calcium expressed as CaO to water is between 0.02 and 0.25 in some cases, preferably using between 0.1 and about 0.15. Finally, the process of patent US20170127096 presents reaction mechanisms that necessarily involve the interaction of metal hydroxide-forming species with a counterion with which they form a more soluble salt, which clearly hinders the recovery of alkaline earth metals from their oxosalts present in minerals, tailings, slags and other residues solid.

For its part, the invention described here proposes a very different line of work to obtain sulfates and oxides after the recovery of alkaline earth metal elements, in order to generate a commercial product and at the same time reduce the mass of the original residue; without the need to decrease the particle size to such small values during the process that they only make it more expensive, and without requiring to control the content of alkaline earth metals in the solution to improve the efficiency of the method.

This process will be carried out on mining materials, specifically for discarded or low-grade mining materials, which currently generate environmental impacts, providing a solution to an economic and social problem such as mining environmental liabilities.

SUMMARY DESCRIPTION OF THE INVENTION

The present invention relates to a process for obtaining an alkaline earth metal compound from mineral materials and the compounds obtained from said process.

Currently, alkaline earth metals in low concentrations are a set of elements that are not of commercial interest and, therefore, become an important part of the mining waste that is collected, and even prevent the commercialization of minerals of interest because they are considered contaminated by these, beyond what the main process can absorb. Finally, these minerals become environmental liabilities.

For this reason, it is proposed to extract from these materials or mining waste, the still important percentage of alkaline earth metals that ranges from 10% to 80%, with a simple, efficient and commercially effective technique.

The present invention is related to a process for obtaining an alkaline earth metal compound from mining materials that comprises:

(i) leaching a quantity of a mineral material with a leaching solution comprising at least one first acid;

(ii) filtering the resulting mixture in step (i) to obtain a solid phase and a liquid phase, where the solid phase is discarded; Y (iii) adding a second acid to the liquid phase obtained from step (ii), wherein said second acid makes it possible to obtain a salt of an alkaline earth metal with low solubility, recovering the leaching solution.

Where, the second acid used corresponds to one selected from among those that generate water-insoluble alkaline earth metal salts to reduce the recirculation of said salts, where the water solubility of said salts must be less than 5 g / l at 25 ° C. When precipitating the alkaline earth metal salts, the reaction time of step (iii) should not exceed between 5 and 60 minutes.

Alternatively, it is possible to calcine the high purity salt obtained in step (iii) and thus produce alkaline earth metal oxides.

DESCRIPTION OF THE FIGURES

Figure 1 shows a diagram of the process of obtaining an alkaline earth metal compound from waste or exhausted minerals.

Figure 2 shows a graph of water of hydration in calcium sulfate.

DETAILED DESCRIPTION OF THE INVENTION

Currently, mining comprises one of the extraction activities of organic and inorganic resources in territories for this. The products obtained from this mining have physical and / or chemical properties that can be applied to different industrial, agricultural or pharmacological uses, in other areas.

One of the large mining companies is non-metallic mining, and among the products obtained through this non-metallic mining are alkaline earth metal compounds, especially their sulfate and oxide compounds.

In particular, the present invention relates to a process for obtaining an alkaline earth metal compound from mining materials that comprises:

(ii) filtering the resulting mixture in step (i) to obtain a solid phase and a liquid phase, where the solid phase is discarded; Y

(iii) adding a second acid to the liquid phase obtained from step (ii), wherein said second acid makes it possible to obtain a salt of an alkaline earth metal with low solubility, recovering the leaching solution.

The first acid used in stage (i) of the process for obtaining the present invention is selected from a pKa value that dissolves the metal compound alkaline earth of interest; wherein the pKa of the first acid used in step (i) is between 4.5 and 5.

The concentration of the first acid in the leaching solution is calculated so that, at the end of the leaching reaction, the water in the solution is equivalent to at least 20 times the content of the alkaline earth metal in the mixture.

Specifically, the leaching of stage (i) of the process for obtaining the present invention is carried out in a solid-liquid contact reactor selected from a fluidized bed reactor, settling columns, leaching pile or pan.

The leaching stage (i) of the process for obtaining the present invention is carried out by controlling the temperature and pressure, where the temperature is controlled between 20 ° C and 105 ° C, and where the pressure is controlled in a range of between 1 to 5 bar.

The solid phase that is discarded in step (i) of leaching is washed with an unsaturated solution of the alkaline earth metal oxide that is to be obtained until a pH value equal to or greater than 7 is achieved in the solid phase; wherein once the washing stage is finished, the mixture is separated, by means of filtration, decantation, or another form of separation; and wherein the liquid resulting from the separation of this washing step will join the liquid phase resulting from the leaching.

Prior to precipitation stage (iii), the excess water is separated from the liquid phase, where said separation is carried out through a stage separation system such as a kettle or still.

The second acid, used in the precipitation stage (iii) of the production process, has the function of being the precipitation agent and corresponds to an acid whose pKa is less than the pKa of the first acid of stage (i); wherein the conjugated anion of the second acid forms at least one salt insoluble in water (solubility less than 5 g / l at 25 ° C) with the alkaline earth metal to be recovered; and where the second acid is concentrated and free of heavy metals. In particular, the solubility in water of the salt formed between the anion of the second acid and the alkaline earth metal to be recovered must be less than 5 g / l at 25 ° C.

Specifically, the second acid is added as a limiting reagent of the reaction, in a maximum ratio of between 80% and 98%, specifically between 85% and 95% of that required.

Likewise, stage (iii) of precipitation is carried out by controlling the temperature and pressure, where the temperature is controlled between 0 ° C and 120 ° C, and where the pressure is controlled in a range between 1 to 20 bar . The precipitation stage (iii) is carried out in a precipitation time that should not exceed between 5 and 60 minutes, specifically between 10 and 30 minutes, preferably 10 minutes to avoid hydration of the salt obtained.

The leaching liquid phase left over from the precipitation stage (iii) is recirculated to the leaching stage (i).

Once the precipitation time indicated above has elapsed, in precipitation step (iii), the precipitate of the resulting alkaline earth metal salt is entered into a separation phase that can be carried out by means of filtration, decantation, or other.

From the present invention, it is possible to work with different particle sizes of the starting material, that is, for particle sizes less than 0.038 mm up to 1 mm, in other specific configurations less than 0.038 mm and finally in others up to greater than 20 mm, which allows materials to be processed in various reactor configurations, saving preparation costs by grinding and pulverizing.

In a preferred embodiment of the present invention, the precipitate of the alkaline earth metal salt, once separated, is entered into one-stage calcination.

The decomposition gases resulting from the calcination stage are cooled and taken to an acid plant for the recovery of the second acid.

In general, the mining material leached in stage (i) is selected from metal mining waste, non-metallic mining waste, alkali metal ores, alkaline earth ores, transition metal ores, rare earth ores, actinide ores and low grade non-metallic mining ores.

Furthermore, the present invention relates to an alkaline earth metal compound obtained from the described process consisting of an alkaline earth metal oxide.

In Figure 1, you can see the diagram of the production process that describes the present invention. The diagram describes that the mineral material (MC) enters a leaching stage in the pond (1), where it comes into contact with the leaching solution contained in the pond (8) to extract the element of interest.

There is a stage of separation of the liquid and solid phases (2), which may correspond to filtering, decantation, or other; The resulting solid is considered the treated waste and is disposed as such in a treated waste tank (5), which can be a tailings, fill or other, as deemed convenient. The charged solution or liquid fraction enters a precipitation reactor (3) where it comes into contact with the second acid generating the precipitation of alkaline earth metal salts. The resulting suspension is separated in the separation system (4), which can be of the same type or different from the leaching separation system (2), resulting in a solid fraction that in a preferred embodiment is carried to drying (6) and subsequent storage (10), which can occur in silos, dome, or another type. The liquid fraction goes directly to the pond (8) from where it is added again as a leaching solution in the extraction of the metal of interest. There is an inlet for the first acid for replenishment (9), which can be from a storage pond, plastic containers or another, which goes to the pond (8). The second acid used for precipitation is added from the pond (7).

From the drying stage (6) decomposition gases and steam are generated.

EXAMPLES OF APPLICATION Example 1.

250 g of discard mineral from a limestone mining site, also called calcareous mineral, with a particle size less than 1000 pm were taken and allowed to react for 30 min at 25 ° C and atmospheric pressure, in a magnetically stirred balloon at 800 rpm, with 270mL of an aqueous solution of propionic acid (pKa = 4.874) at 33% w / w. The pulp was separated by vacuum filtration, washing with distilled water to obtain a sample at pH 7.

The only difference between the resulting rubble and the original mineral that was leached is the effect of removing the calcium present in the sample.

CaC0 ₃ + 2 C ₃ H ₆ 0 ₂ ® Ca (C ₃ H ₃ 0 ₂ ) ₂ + C0 ₂ + H ₂ 0

A portion of 100mL of the resulting leaching solution was precipitated with 17.1 g of hydrofluoric acid solution at 45% w / w, for 5 minutes, which was filtered by means of a vacuum system.

The resulting liquid presents the regenerated leaching agent, which is confirmed by verifying the pH of the solution, indicative of the binding of the protons to the propionate anion.

The resulting precipitate was brought to a constant mass by drying in an air oven, confirming the obtaining of 13.7g of product, for a yield of 89%.

Ca (C ₃ H ₅ 0 ₂ ) 2 + 2HF CaF ₂ + 2C ₃ H ₆ 0 ₂

Calcium fluoride is commonly used as a glass-making material as it is transparent in the infrared and ultraviolet wave regions and shows a extremely low refractive index. It is also used as a flux in the smelting and liquid processing of iron, steel and their compounds.

With this process of obtaining, the ability to generate valuable products from a material initially classified as waste is shown.

Example 2.

250 g of calcareous mineral similar to that of the previous example were taken, and they were put in contact with 283 ml_ of an aqueous solution of butyric acid C4H8O2 (pKa = 4.819) at 32% w / w. It was allowed to react for 30 min at 25 ° C and atmospheric pressure, in a magnetically stirred balloon at 800 rpm. The pulp was separated by vacuum filtration, bringing it to pH 7 with distilled water to obtain a sample.

C3CO3 + 2 C4 Hbq2 - * Ca (C4 H 702) 2 + CO2 + H2O

A portion of 100mL of the resulting leaching solution was precipitated with 31 g of precipitating solution of sulfuric acid at 50% w / w, for 5 minutes, which was filtered by means of a vacuum system.

The resulting liquid presents the regenerated leaching agent, which is confirmed by verifying the pH of the solution, indicative of the binding of the protons to the butyrate anion.

The resulting precipitate was brought to 110 ° C, a necessary condition to reach calcium sulfate hemihydrate. After obtaining constant mass, the obtaining of 9.7 g of product was confirmed, for a yield of this stage of 90.6%.

Ca (C4 H 702) 2 + H2SO4 - * C3SO4 + 2 C4 Hbq2

The calcium sulfate obtained is of great industrial application, in areas as diverse as pharmacology, food, construction and industry.

One of the variables that determines its application and quality is the level of hydration of calcium sulfate, which is naturally found as a dihydrate and has to be dehydrated to bring it to its anhydrous form, with the subsequent energy cost.

The initial calculations showed that the calcium sulfate obtainable by this technology could, under the appropriate conditions, consist mainly of the hemihydrate, which was confirmed by example 3.

Example 3

A sample of calcium sulfate obtained in this process through a precipitation time of 5 minutes, was brought to 110 ° C, a necessary condition to reach the hemihydrate of calcium sulfate, decreasing in weight only 10.7%, with which it is concluded that the sulfate formed was mainly hemihydrated at the time of filtering the solution.

The resulting product was sent to the XRD laboratory, which confirmed that 99% of the solid corresponded to calcium sulfate hemihydrate. The test was repeated allowing the reaction to run for 1.30 minutes. The results in the remaining water in the sulfate obtained are shown in Figure 2, where it is seen that the hydration of the sulfate is proportional to the time in which it is allowed to react in solution. However, after repeating with 30 minutes of stirring, the dihydrate still does not form completely. It was possible to observe a balance between the initial mass of the sample, the analysis of sulfates with an Elemental Sulfur Analyzer and chemical analysis.

As studied, thanks to the process of the present invention, there is the potential to industrially obtain calcium sulfate, mainly constituted by its hemihydrated species, which will represent an important energy saving when being treated to obtain commercial products.

Claims

1. A process for obtaining an alkaline earth metal compound from mining materials, CHARACTERIZED because it comprises:

(Ni) adding a second acid to the liquid phase obtained from step (ii), wherein said second acid makes it possible to obtain a salt of an alkaline earth metal with low solubility, recovering the leaching solution.

2. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the first acid used in step (i) is selected from a pKa value that dissolves the compound of the alkaline earth metal of interest.

3. The process for obtaining an alkaline earth metal compound from mining materials according to claim 2, CHARACTERIZED in that the pKa of the first acid used in stage (i) is between 4.5 and 5.

4. The process for obtaining an alkaline earth metal compound from mining materials according to claim 3, CHARACTERIZED in that the concentration of the first acid in the leaching solution is calculated so that, at the end of the leaching reaction, the water in the solution is equivalent to at least 20 times the content of the alkaline earth metal in the mixture.

5. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the leaching of stage (i) is carried out in a solid-liquid contact reactor selected from a bed reactor fluidized, settling columns, leach pad, stirred pond or pan.

6. The process of obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the leaching stage (i) is carried out by controlling the temperature and pressure, where the temperature it is controlled between 20 ° C and 105 ° C, and where the pressure is controlled in a range between 1 to 5 bar.

7. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the solid phase that is discarded in step (i) is washed with an unsaturated solution of the alkaline earth metal oxide that it is desired to obtain until achieving a pH value equal to or greater than 7 in the solid phase; wherein once the washing stage is finished, the mixture is filtered; and wherein the liquid resulting from the filtering of this washing stage will join the liquid phase resulting from the leaching stage.

8. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that prior to stage (iii) the excess water is separated from the liquid phase, wherein said separation is carried out at through a stage separation system such as a kettle or still.

9. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED because the second acid used in stage (iii) as a precipitation agent corresponds to an acid whose pKa is less than the pKa of the first acid of step (i); wherein the conjugated anion of the second acid forms at least one water insoluble salt with the alkaline earth metal to be recovered; and where the second acid is concentrated and free of heavy metals.

10. The process for obtaining an alkaline earth metal compound from mining materials according to claim 9, CHARACTERIZED in that the solubility in water of the salt formed between the anion of the second acid and the alkaline earth metal to be recovered is less than 5 g / l at 25 ° C.

11. The process of obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the precipitation stage (iii) is carried out by controlling the temperature and pressure, where the temperature is controlled between 0 ° C and 120 ° C, and where the pressure is controlled in a range between 1 to 20 bar.

12. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the phase The leaching liquid left over from the precipitation stage (iii) is recirculated to the leaching stage (i).

13. The process for obtaining an alkaline earth metal compound from mining materials according to claim 11, CHARACTERIZED in that in step (iii) of precipitation, once the precipitation has elapsed, the precipitate of the resulting alkaline earth metal salt is it enters a filtering phase.

14. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the precipitate of the alkaline earth metal salt once filtered is entered into one-stage calcination.

15. The process for obtaining an alkaline earth metal compound from mining materials according to claim 14, CHARACTERIZED in that the decomposition gases resulting from the calcination stage are cooled and taken to an acid plant for the recovery of the second acid.

16. The process for obtaining an alkaline earth metal compound from mining materials according to claim 1, CHARACTERIZED in that the mining material leached in stage (i) is selected from metal mining waste, mining waste not metallic, alkali metal ores, alkaline earth ores, transition metal ores, rare earth ores, actinide ores, and low grade non-metallic mining ores.

17. An alkaline earth metal compound obtained from the process described in claim 14, CHARACTERIZED in that it comprises an alkaline earth metal oxide.