RU2081925C1 - Method and installation for isolation of precious metals from solutions - Google Patents

Abstract

FIELD: recovery of precious metals. SUBSTANCE: invention relates to isolation of precious metals both with their high and low concentrations in solutions and may be applied both by itself and in an integrate process chain with known methods of isolation of precious and other strategically important metals. It may as well be used in system of treatment and neutralization of process wastes(including radioactive ones) and waste water. Method consists in that, in a process including agitation of initial solution in presence of reducing agent followed by selectively separating resultant metal-containing product from solution, agitation of initial solution in presence of reducing agent is conducted at constant temperature under imposed laser emission with frequency corresponding to resonance excitement frequency of metal ions being isolated. Installation is constructed on the basis of centrifugal extractor and provided with variable-emission frequency laser system. Extractor has a window made of material transparent for infra-red, visible, and ultra-violet wavelength regions to pass laser beam into mixing chamber. Method ensures isolation of metals from solutions with metal concentrations below 1 mg/l. Metals are isolated either in neutral state or as solid salts from solutions with acidity four times as high as permissible solution acidity level for conventional chemical procedures, including those conducted with heating. EFFECT: enhanced efficiency of isolation procedure. 16 cl, 3 dwg, 1 tbl

Description

 The invention relates to metallurgy, in particular, to the production of precious metals by the wet method, and can be used both with a high and low content of recoverable metal in solution, in cases where traditional chemical methods for the extraction of precious metals are ineffective. It can find application both independently and in a single technological chain with known methods, including methods of industrial waste treatment, for the separation of precious and other strategically important metals.

 Precipitation methods based on the precipitation of precious metals contained in a solution by adding chemical precipitating agents to it are widely known in the technology for extracting precious metals from solutions. Various reagents are used as precipitants, depending on the type of precious metal recovered. So, in the known method for the separation and purification of platinum group metals, an alkali is added to the solution containing the precious metal as a precipitant, and then it is treated with a reducing agent (ethanol) and boiled [1] The obtained precious metal precipitate is chemically separated from iron and copper salts.

 The specified method, as well as other related thermal methods, are characterized by a low selectivity of metal separation, low productivity due to the duration of the deposition process, the slowness of chemical processes due to the low activity of the platinum group metals, and also high labor intensity due to the variety of operations and the harmfulness of for using biological hazardous reagents in technology. This method is uneconomical for processing solutions with a low content of precious metals. This method is also unacceptable for the extraction of metals from solutions contaminated with radioactive waste, in which, however, the concentration of such metals can reach from 4 to 19 kg / t, that is, hundreds of times higher than the concentration of natural deposits. The reason is that the chemicals necessary for the implementation of this technology (mainly iron sulfate) must be 4-5 times larger than the initial volume of the treated solution, and this does not lead to a decrease, but to an increase in the total volumes of radioactive waste requiring disposal.

 There are also known methods for the extraction of precious metals from liquid solutions, based on the recovery of metal ions contained in the processed solution to the state of a solid neutral metal by adding a chemical reductant to the solution.

 A visual representation of such a technology is provided by the attached flow chart described in [2] of FIG. 3. In the technological solution obtained by dissolving the platinum group metal concentrate in aqua regia, iron sulfate (II) is added as a reducing agent, after which the precipitate obtained is separated from the liquid phase. The contaminated gold recovered as a precipitate is smelted into anodes, which are used for the electrolytic refining of gold. In turn, the filtrate is subjected to further processing to isolate other precious metals contained in the solution (platinum, palladium, etc.). In order to extract all the platinum group metals from the initial solution in the known technology, a number of methods are used that differ significantly in the set of operations, in the reagents used (reducing agents and precipitants), and also in the refining methods of precious metals.

The specified extraction method, considered as a prototype, essentially has the same disadvantages as the previously described analogue:
low productivity due to the low activity of platinum metals and the duration of chemical processes (for example, to extract rhodium — to obtain a “rhodium mirror” a solution of rhodium trichloride in hydrochloric acid in the presence of formic acid is boiled for 24 hours);
high complexity and material consumption in terms of the volume of equipment used (for the implementation of the method and technology for the entire platinum group of metals, a large set of electrolytic baths, calcining and melting furnaces, chemical reactors, mixers and water treatment equipment, as well as ventilation exhaust equipment, ensuring safety when working with cyanides, are used in the extraction of gold);
limited use for solutions with a low content of precious metals;
low efficiency, which pays off only by the high price of the recoverable product;
environmental hazard of environmental pollution due to the use of cyanides;
unacceptability for the extraction of precious and other strategically important metals from solutions contaminated with radioactive waste;
complexity for remote control of the metal extraction process when working with liquid radioactive waste;
low selectivity for the isolation of a single metal from a complex solution containing a mixture of various metals, including base metals, such as ions of iron, copper, nickel and other metals used as a reducing agent.

 None of the methods considered makes it possible to extract all the platinum group metals contained in it with a set of operations of the same type and techniques, as a result of which technologies are used in practice, which are a combination of many different methods that make up a multi-stage process with a huge number of different operations and techniques. The main reason for such an abundance of operations, as can be seen from the technological scheme [2], is that at the stage of reduction of metal ions to a neutral state, the selectivity of the release of each metal is not ensured, and only a contaminated product (conglomerate) is obtained, which contains in its composition like the others precious metals, and foreign impurities, which requires further processing of the product (mainly, refining by various methods).

 From equipment that is used to extract precious and other metals, there is a known installation for separating a metal-containing product from solutions, which includes a centrifugal extractor and means for dispensing the treated solution [3] Such installations are used in extraction technology of nuclear energy, as they are easy to maintain and reliable. The combination of intensive mixing of liquid and solid components with effective phase separation under the action of centrifugal forces provides high performance with a relatively small size of these devices. However, they are not suitable for laser extraction processes.

 The method is based on the task of such an interaction of a solution of precious metal ions and a reducing agent, as a result of which selective metal evolution would be ensured already at the stage of metal reduction.

 The solution of the problem in the method of extracting precious metals from liquid solutions, including the recovery of the precious metal with the subsequent separation of the metal-containing product from the solution, is achieved by the fact that the reducing agent is superimposed by laser radiation with a frequency corresponding to the resonant excitation frequency of the ions of the extracted metal with selective separation of the metal-containing product.

 Selective metal precipitation at the reduction stage is ensured by the fact that under the action of laser radiation (the radiation frequency of which is chosen so that it corresponds to the frequency of natural vibrations of the metal ions to be extracted), ions of this metal are excited and enter a more active state and enter the interaction with the reducing agent is faster than the ions of other metals present in the solution that have not received such a “charge of activity”. In this process, the low activity of the platinum group metals promotes the selective release of the desired metal from the complex solution.

 The solution to this problem is also provided by the fact that the processing of the solution by laser radiation is carried out in the process of mixing; the separation of the metal-containing product and its withdrawal from the irradiation zone occurs continuously as it forms; formic acid, or acetic acid, or oxalic acid, or malonic acid, or formate salts, or acetate salts, or oxalate salts, or salts of malonic acid, or hydrazium, or methanol, or methanol, or ethanol, or salts, are used as reducing agent uranium.

 Selective metal precipitation at the stage of metal reduction is ensured by the indicated operations and conditions due to the fact that when combining the mixing and irradiation of the solution with laser radiation, not only the chemical interaction of the treated solution with the reducing agent is accelerated, but also the time required for contacting the interacting components and the selection of the desired metal, without simultaneously involving in this process other metals and impurities contained in the solution.

The solution to the problem of ensuring the possibility of conducting laser recovery in the installation for the extraction of precious metals from liquid solutions containing a centrifugal extractor and chemical dosing means is achieved by the fact that it is equipped with a laser system, while the extractor is made with a window of transparent material in visible UV and IR wavelength range for the passage of laser radiation. Due to the selectivity of metal extraction, it is already at the stage of its recovery, thus providing a significant reduction in the volume of necessary equipment, reducing the complexity of the process, increasing productivity, efficiency and safety. Reducing the amount of equipment, the uniformity of operations for all recoverable metals makes this process easily automated, which is especially important to ensure safety when working with radioactive solutions (waste). The method is attractive for its environmental friendliness both because of the lack of the need to use cyanides, and because after intensive photochemical reactions of metal reduction and their evolution, additional harmful waste is not formed, all added reagents decompose during water chemistry, water, nitrogen, methane, СО ₂ and, when processing radioactive waste, a high degree of extraction is ensured while maintaining the initial volumes of the processed radioactive raw materials.

 In FIG. 1 is a flow chart of a method for extracting precious metals from solutions; in FIG. 2 Christmas tree setup for the extraction of precious and other strategically important materials from solutions.

To implement the proposed method, the metal ion solution received for processing is mixed with a reducing agent, exposed to laser radiation at a frequency corresponding to the resonant frequency of the ions of the metals extracted in turn, and the formed metal-containing product is separated (Fig. 1). In this case, several options for the sequence of these operations are possible:
mixing, processing by laser radiation and separation of the metal-containing product is carried out in separate technological apparatuses interconnected by transfer channels, that is, alternately, with the separation of operations in time;
mixing the solution and processing with laser radiation is carried out simultaneously in time, and the separation of the metal-containing product separately;
mixing the solution, processing by laser radiation and separation of the metal-containing product are combined and carried out in one technological apparatus having the functions of three apparatuses of a mixer, a laser reactor and a separator.

 The best sequence of operations of the proposed method is the combined execution of the three indicated operations in time, since this helps to increase the productivity of the precious metal extraction process and makes an additional contribution to the selectivity of the separation of metals present in the solution: quick removal of the first recovered metal from the solution into the solid phase, restores disturbed by the presence of metal particles the properties of the solution and creates the necessary prerequisites for isolation Nia second, third, etc. metals.

 The installation diagram shown in FIG. 2, illustrates precisely this variant of the process. The installation is as follows.

 Mixed components with specified speeds from pressure vessels 1 (for the solution being treated) and 2 (for reducing agent) using a proportional batcher 3, which allows you to strictly maintain the flow ratio, through pipelines 4 enter the centrifugal extractor 5 into its mixing chamber 6 and mix with a mixer 7 The mixing chamber 6 of the extractor 5 is equipped with a window 8 made of a transparent material in the IR, visible and UV wavelength range, through which from the laser system 9 into the mixing chamber 6 of the extractor 5 passes tunable nichromatic radiation in the IR, visible and UV wavelength range. To extract each specific metal, the resonance frequency of the ions of the metal being recovered is previously known. It is determined on standard mono-solutions of a specific precious metal spectrophotometrically, according to the corresponding absorption peak of radiation tunable in frequency. To increase the area processed in the mixing chamber 6, the irradiating laser has an expanded beam. The product formed after mixing and processing with laser radiation in the form of a solid fine suspension of a metal-containing product or in the form of an emulsion during the extraction of a metal ion with an organic solvent is fed by a transporting device 10 into the rotor 11, where they are separated into phases by the action of centrifugal forces. Pure phases from the rotor enter the annular collectors 12 and 13, respectively, for the heavy and light phases and are removed from the extractor. A centrifugal extractor is driven by a direct current electric motor 14. The total consumption of the starting components varied from 1 to 30 l / h, which corresponds to a change in the duration of laser treatment of the solution from 20 to 0.7 s.

 As the laser system 9 in the proposed installation can be applied to any known system that provides the generation of tunable laser radiation in the range of resonant frequencies of excitation of ions of the extracted metals. During the experiments, a laser system was used, consisting of a dye laser 15 pumped by an excimer laser 16.

 In the process of mixing and irradiating the solution with a laser at a frequency corresponding to the resonant frequency (natural vibration frequency) of the ions of the metal being recovered, the latter, as a result of this interaction, become excited and, therefore, acquire high chemical activity, which significantly accelerates their reaction with the reducing agent). The effectiveness of such excitation of metal ions can be judged, for example, by the fact that irradiation of a solution of rhodium trichloride in hydrochloric acid in the presence of formic acid as a reducing agent leads to the appearance of metallic rhodium after 30 minutes, while traditional boiling of a hydrochloric acid solution, ceteris paribus the conditions require 24 hours. Moreover, the selective isolation of rhodium by the proposed method occurs at the stage of metal reduction, and not after refining from a conglomerate of metals, as it is There is a place in the known technologies with heating the solution.

 In the process of separating the metal-containing product combined with stirring, the reduced metal is intensively removed from the solution, which allows us to proceed to the next cycle to recover the next metal. The next cycle can be a cycle of repeated processing of the solution by laser radiation with the same or with a different reducing agent or with a reducing agent, which is a mixture of several types of reducing agents.

 In addition to formic acid as a reducing agent in the proposed method can be used: acetic acid, oxalic acid, malonic acid, acetates, formates, oxalates, malonates, hydrazine, methanol, ethanol and other reagents that under the action of laser radiation exhibit the properties of reducing agents, as well as a mixture of these reagents.

 It is not possible to preliminarily indicate the specific type of reducing agent needed to isolate a specific metal, since the choice of reducing agent depends on a large number of factors characterizing the solution being treated. When choosing a reducing agent for the isolation of a specific metal, the component composition of the solution, the valence state of the metal ions, the acidity of the solution, etc. are important. So, if at least two metals are present in a particular solution that are extracted with the same reducing agent (for example, oxalic acid) at the same time since the start of irradiation, it may be appropriate to use another reducing agent to ensure extraction selectivity, which would allow the extraction of these metals in a single laser cycle spread exposure over time. The need for such a choice becomes apparent if the resonant excitation frequencies of these ions are very close. The possibility of such a separation of metal evolution in time is available. For example, the process of laser generation of metallic palladium in the presence of oxalic acid begins almost instantly from the moment the solution is irradiated with a laser at a resonant frequency. In the presence of formic acid, palladium recovery begins after 20-25 minutes of irradiation at this frequency, and in the presence of formic acid with the addition of alcohol after 12-15 minutes.

 Depending on the characteristics of the solution, even the resonant frequency of the excitation of ions of the same metal can be slightly different, since the ligand environment of the ion can be different in different media.

 The method is illustrated by the following examples of the extraction of platinum group metals from liquid solutions, combined in a table. The experiments included in the group of examples were carried out in the facility of FIG. 2. The radiation sources in the experiments were an excimer laser λ = 308 nm with a pulse energy of 70-80 mJ and a pulse frequency of 10 Hz, a tunable dye laser or an argon laser λ = 458 nm with a power of 260 mW. The resonance frequency was corrected for the corresponding absorption peak.

 The metal phase, which was obtained in some cases after separation, was a finely divided metal powder, suitable for use already in this form (for example, as a catalyst) or for melting. In one case, during the reduction of iridium (IV) to iridium (III), the resulting product was separated by liquid extraction in the same installation using a number of extractants (for example, tributyl phosphate in kerosene).

Example 1 illustrates the capabilities of the described method when working with radioactive solutions. In the experiment, we used a complex solution containing palladium ions d ⁺² and uranyl ions UO $\genfrac{}{}{0ex}{}{\text{+2}}{\text{2}}$ This solution is a model of a technological solution resulting from the processing of waste from nuclear power plants. Under the influence of light, uranyl ions UO $\genfrac{}{}{0ex}{}{\text{+2}}{\text{2}}$ in acidic solutions, as a result of redox reactions, they transfer to the U state, which is characterized by a strong reducing ability. Under the action of this reducing agent, Pd ^{+ 2} ions become neutral, which becomes the nucleus of the solid (metal) phase. As a result of such interactions of the treated solution with laser radiation at the excitation frequency of palladium ions, a phase transition of palladium from the solution to the metallic state was observed, the appearance of palladium black.

 The process of reducing palladium can proceed with laser resonant excitation of its ions in the presence of other reducing agents: methanol, ethanol, oxalic acid, formic acid, etc., as well as from solutions of different in nature acids (nitric, hydrochloric, sulfuric).

The reducing agent may initially be present in industrial process solutions (e.g., uranyl, ethanol). Example 2 illustrates this option. Typically, the reduction of palladium in the presence of ethanol is carried out by heating the solutions to 60-70 ^o C. Ethanol is a two-electron reducing agent and oxidizes to aldehydes during the process.

 Under the action of laser radiation, the process of palladium (II) reduction proceeds at room temperature at a rate much higher than that observed for thermal processes. When studying the processes of the formation of metallic palladium in the presence of ethanol under the action of laser radiation, it was shown that the reaction rate depends on the concentration of ethanol in the solution.

 It was also shown that the palladium recovery rate is affected by the acidity of the solution. The upper limit of acidity, at which the formation of a black precipitate of freshly precipitated palladium is not observed, is 4 M / L with the traditional chemical method of reducing palladium, which uses solution heating, palladium black does not form even at acid concentrations above 0.07 M / L. Thus, the method of laser exposure allows you to work with solutions of high acidity.

Examples 3-5 show the possibility of extracting palladium from solutions containing other organic and inorganic reducing agents: oxalic acid H ₂ C ₂ O ₄ , hydrazine hydrochloric acid N ₂ H ₄ • Hcl, formic acid HCOOH when irradiated with an excimer laser at a wavelength of 308 nm.

It turned out that the process of laser generation of palladium in the presence of oxalic acid H ₂ C ₂ O ₄ begins almost instantly from the beginning of irradiation. However, the acidity threshold of the solution lay in the region of 0-1.5 M / L acid (Example 5). If the solution is irradiated at a wavelength of 430 nm (which is more correlated with the absorption band of the palladium solution in the presence of oxalic acid), then the acidity threshold of the solution at which the formation of metallic palladium is observed increases significantly to 4-5 M / L (example 6).

Hydrazine hydrochloric acid N ₂ H ₄ • Hcl also has a significant effect on the recovery of palladium (example 3). The formation of a black precipitate of metallic palladium is observed within a few minutes (≈5-8 min) after the start of irradiation.

 In the presence of formic acid HCOOH (example 4), the reaction proceeds much more slowly, the formation of a black precipitate begins after 20-25 minutes of irradiation.

 At the same time, the addition of alcohol initiates the formation of palladium metal after 12-15 minutes.

This series of activity of reducing agents H ₂ C ₂ O ₄ <N ₂ H ₄ • Hcl <C ₂ H ₅ OH <HCOOH) during the laser reduction of palladium ions coincides with a number of short-wavelength shifts in the absorption band of palladium in the presence of these ligands in electronic spectra.

The activated palladium ion has an intense absorption band at 380 nm. The presence of other ligands such as chloride ion, oxalate and hydrocassalate ions, ethyl alcohol, formic acid, hydrazine hydrochloride shifts the palladium absorption band. So, in a hydrochloric acid solution, the peak of absorption of Pd ⁺² is observed at 465 nm, and the addition of alcohol shifts the absorption band of palladium to the short-wavelength region to 435 nm. In the presence of oxalic acid, the palladium absorption peak is already observed at 404 nm, and the addition of hydrazine shifts the bands even further to 394 nm in the short-wavelength region.

 Examples 7.8 show the results of a study on the laser excitation of platinum.

 In a solution, platinum compounds can exist in solutions in two valence states of PT (IV) and PT (II).

Unlike palladium, pure aquated platinum ion does not exist in any valence state; therefore, one can consider the electronic spectra of only complex platinum ions. For example, in the spectrum of PtCl $\genfrac{}{}{0ex}{}{\text{-2}}{\text{4}}$ two distinct regions are distinguishable: two intense absorption bands at 330 and 390 nm, which are attributed to charge-shift transitions from the ligand to metal (L _ → M) and weak bands at 220 nm. However, for complexes containing stronger ligands, the bands of the ligand field are shifted to a shorter wavelength region. The electronic spectra of Pt (IV) consist of ligand field bands and charge transfer bands, which partially overlap and are located at 450 nm.

Irradiation of PtBr Platinum Solutions $\genfrac{}{}{0ex}{}{\text{-2}}{\text{6}}$ in the presence of alcohol C ₂ H ₅ OH, oxalic acid H ₂ C ₂ O ₄ , formic acid, HCOOH only leads to the reduction of PT (IV) to PT (II), which is observed by changing the color of the solution from orange to pale yellow and by absorption spectra. No further changes in solutions were observed (Example 7).

 However, if you first restore PT (IV) to PT (II) under the action of laser radiation in the presence of formic acid, and then add ethanol to the solution and irradiate the solution again, then a black suspension of metallic platinum is formed (Example 8).

 Examples 9, 10 show experiments on the separation of a mixture of palladium and platinum. Depending on the wavelength used, the reducing agent and the acidity of the medium, it is possible to simultaneously co-precipitate palladium and platinum, as well as selectively separate them.

Similar experiments were carried out with rhodium solutions. Rhodium, as well as palladium, is a simpler system to study, since it is present in solution only in the Rh (III) state. The electronic absorption spectrum of RhCl ₃ • H ₂ O in a hydrochloric acid solution exhibits a single strong absorption band at 460 nm. The addition of oxalic acid or its salts shifts the absorption band to 566 nm, and in the presence of formic acid, the absorption peak of rhodium (III) is at 425 nm.

 Example 11 shows that irradiation of rhodium solutions in the presence of alcohol for 1 h did not lead to a change in the solutions. No changes in the absorption spectra before and after irradiation were observed.

 Irradiation of rhodium solutions for 30 min in the presence of formic acid (Example 12) changes the color of the solution from purplish red to yellow and, accordingly, the absorption spectrum of rhodium changes. After 10 minutes of aging, a gray precipitate of metallic rhodium begins to precipitate from the irradiated solution. The process is significantly accelerated by the addition of oxalic acid (Example 13) instead of formic acid. However, the resulting rhodium oxalates are photochemically active only at 560 nm. That is why laser activation is used here at a band of 560 nm with the formation of a gray powder of metallic rhodium.

Apparently, upon irradiation of RhCl ₃ • nН ₂ О solutions in the presence of reducing agents, monovalent rhodium complexes Rh (I) are formed
RhCl ₃ • nH ₂ O + HCOOH (H ₂ C ₂ O ₄ ) _ → Rh (I),
which, when exposed to air, decompose to rhodium (O).

 Example 14 illustrates the possibility of selective separation of palladium and rhodium. Separating rhodium selectively from palladium and platinum is not difficult because of their fundamental differences in chemical properties.

Iridium compounds, like platinum compounds, exist in solution in two valence states Ir (IV) and Ir (III). However, only Ir (IV) compounds are photochemically active. The electronic spectra of IrCl $\genfrac{}{}{0ex}{}{\text{-2}}{\text{6}}$ a large number of peaks are observed at 320, 410, 425, 490 nm. Therefore, irradiation of iridium (IV) solutions can be carried out at different wavelengths. Irradiation of IrCl solutions $\genfrac{}{}{0ex}{}{\text{-2}}{\text{6}}$ in the presence of reducing agents (oxalic acid H ₂ C ₂ O ₄ , alcohol C ₂ H ₅ OH, formic acid HCOOH) showed that in most cases Ir (IV) is reduced to Ir (III). However, the speed of the process depended strongly on the nature of the reducing agent: Ir (IV) was reduced almost instantly in the presence of oxalic acid (Example 15), but no changes were observed in the presence of ethanol when irradiated for 30 minutes (Example 16). The radiation wavelength also influenced the rate of the process of reduction of Ir (IV) to Ir (III): when the solution was irradiated at 308 nm, the recovery took 2–3 min, but at 458 nm this process proceeded more slowly in 30–40 min.

Example 17 illustrates the possibility of extracting gold from a solution. The electronic spectrum of the HAuCl ₄ solution has a single pronounced and very intense absorption peak at 310 nm. Since the excimer laser possesses radiation precisely in the region of 308 nm, the reduction of gold in the laser radiation field proceeds almost instantly at acid concentrations up to 5 M / L.

 The same picture is observed for silver. The absorption peak of silver (I) is at 300 nm. Therefore, its recovery proceeds as easily as gold (example 18).

 The possibility of separation of silver and gold is provided by the rate of flow of the solution and, accordingly, the duration of the processing of the solution by laser radiation (example 19). When extracting gold from a solution containing both gold and silver ions, they maintain a high flow rate, which is also determined by the initial content of gold in the solution, then after separation of the gold, the solution containing already exclusively silver is laser-treated again to extract metallic silver.

 Since real solutions of radioactive and industrial wastes contain mixtures of various metals, Example 20 illustrates the possibility of sequential extraction of precious metals from solutions containing both noble metal ions: platinum, rhodium, iridium, gold, silver, and metal ions of copper6 nickel, iron, etc. As a result of laser irradiation of these complex solutions, selective precipitation of gold, then silver, metallic palladium, platinum and rhodium was recorded. Iridium is recovered as iridium (III) using suitable extractants.

 With high efficiency, the invention can also be used in the treatment of industrial radioactive waste with the parallel extraction of precious and strategically important metals.

Claims (16)

 1. The method of extracting precious metals from solutions, including the recovery of precious metals, followed by separation of the obtained metal-containing product from the solution, characterized in that the reduction is carried out with stirring of the initial solution in the presence of a reducing agent when applying laser radiation with a frequency corresponding to the resonant frequency of excitation of the ions of the extracted metal, with selective separation of the metal-containing product.  2. The method according to p. 1, characterized in that the selective separation of the obtained metal-containing product in the presence of a reducing agent is carried out by adjusting the frequency of laser excitation of the ions of the extracted metal according to the absorption peak.  3. The method according to PP. 1 and 2, characterized in that formic acid is used as a reducing agent.  4. The method according to PP. 1 and 2, characterized in that as the reducing agent use acetic acid.  5. The method according to PP. 1 and 2, characterized in that as a reducing agent use oxalic acid.  6. The method according to PP. 1 and 2, characterized in that as the reducing agent use sodium formate, or ammonium, or potassium.  7. The method according to PP. 1 and 2, characterized in that as the reducing agent use sodium acetate, or ammonium, or potassium.  8. The method according to PP. 1 and 2, characterized in that as the reducing agent use sodium oxalate, or ammonium, or potassium.  9. The method according to PP. 1 and 2, characterized in that as a reducing agent use hydrazine.  10. The method according to PP. 1 and 2, characterized in that methanol is used as a reducing agent.  11. The method according to PP. 1 and 2, characterized in that ethanol is used as a reducing agent.  12. The method according to PP. 1 and 2, characterized in that as a reducing agent use a mixture of several different reducing agents.  13. The method according to p. 12, characterized in that the introduction of reducing agents into the solution is carried out sequentially: after mixing the solution in the presence of one reducing agent when applying laser irradiation, another reducing agent is introduced into the solution and the solution is re-treated with laser irradiation while mixing it with the reducing agent, followed by separation metal-containing product.  14. The method according to p. 13, characterized in that when the second reducing agent is introduced, the radiation frequency is adjusted according to the absorption peak of the extracted metal.  15. Installation for the extraction of precious metals from solutions, containing a centrifugal extractor and a means of dispensing reagents, characterized in that it is additionally equipped with a laser system, and the centrifugal extractor is made with a window of a transparent material in the ultraviolet, visible and infrared wavelength range for transmitting laser radiation into the mixing chamber.  16. Installation according to p. 15, characterized in that the laser system is made adjustable in frequency of radiation.

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