WO2015056121A1

WO2015056121A1 - Metal-electrowinning or -electrorefining process comprising the application of an electrical power signal formed of an alternating current superimposed on a direct current

Info

Publication number: WO2015056121A1
Application number: PCT/IB2014/064876
Authority: WO
Inventors: Christian Hermann Domingo Hecker Cartes
Original assignee: Hecker Electrónica De Potencia Y Proceso S.A.
Priority date: 2013-09-26
Filing date: 2014-09-26
Publication date: 2015-04-23
Also published as: CL2013002772A1

Abstract

The invention relates to a process of electrowinning or electrorefining of metals, in particular noble metals, such as copper, that is carried out in an aqueous and strongly acidic medium and comprises the application of an electrical feed signal formed of an alternating current superimposed on a direct current, where the alternating current (AC) is in a range between 400 and 600 A/m² and is superimposed on a direct current (DC) in the range between 240 and 600 A/m², and where the frequency (f) is greater than or equal to 5,000 Hz and less than or equal to 10,000 Hz. The electrowinning process operates in a temperature range between 15 and 52°C, in a Cu²⁺ concentration range of between 33 and 43 gpl, having a dosage of flocculation additives and a grain refiner of less than 200g/ton of copper produced (Cu°), and having a concentration of CoSo4 less than 170 ppm of Cu²⁺in the electrolyte bath. The electrorefining process operates in a temperature range between 40 and 60°C, in a range of concentration of Cu²⁺ between 40 and 56 gpl, and having a dosage of flocculation additives with a grain refiner of less than 100g/ton of Cu°.

Description

ELECTRO-OBTAINING OR ELECTRO-REFINING METALS PROCESS, WHICH INCLUDES APPLYING AN ELECTRIC POWER SIGNAL FORMED BY AN ALTERNATE CURRENT SUPERPOSED TO THE LEVEL OF A CONTINUOUS CURRENT

DESCRIPTIVE MEMORY

Field of the Invention

The invention relates to the electro-obtaining (EW) and electro-refining (ER) process.

The invention comprises the joint application of alternating current (AC) and direct current (DC) in the electro-obtaining and electro-refining processes. Background of the Invention

Copper electrolytic refining or electro-refining (ER), from impure anodes from the fusion and conversion of copper concentrates, is a conventional electrolysis process that has been industrially applied for more than a century. On the other hand, the recovery of copper from Cu ²⁺ solutions in the combined LX-SX-EW process (solvent leaching-electro-obtaining) has been carried out industrially and commercially for more than thirty years.

The chemical quality of the cathodes obtained by ER and EW reaches a degree of copper purity of "five nines" (99.999%), with extremely low levels of impurities such as lead, oxygen, sulfur, hydrogen, carbon, arsenic, antimony and bismuth. In general, more than 90% of the production of cathodes in most of the ER and EW plants is "high grade", that is, with a quality superior to the Grade A classification defined by the London Metal Exchange LME. Currently, the production capacity of electrolytic copper in Chile exceeds 5.0 million metric tons per year.

The ER and EW plants of Cu aim to maximize the production of metal cathodes with high chemical and physical purity, and with the lowest consumption specific energy In these processes, external electrical energy is applied, setting the production based on the level of DC current imposed. This process is carried out in aqueous and strongly acidic medium (> 180 gpl H ₂ S0 ₄ ), with permanent stainless steel cathodes or starting Cu sheets, and impure copper anodes (ER), or rolled anodes of an alloy Pb-Ca-Sn in the case of EW. The main electrochemical reactions are presented in Table 1

Table 1 Main reactions in ER and Cu EW

In order to reconcile production, specific energy consumption and chemical quality of the cathodes, the EW and ER copper plants operate with DC design current density levels of the order of 300 A / m ² , with 92-97% of current efficiency, and with specific energy consumption around 250-350 kWh / ton in the case of an ER of Cu and 91 -93% of current efficiency and 1 .800 - 2,300 kWh / ton in Cu EW. The operating variables that are externally manipulable such as the concentration of the cupric ion in solution, the temperature of the electrolyte and the flow of electrolyte to cell, must be set according to the imposed DC current. The range in which each of these variables moves is as follows: Table 2

Where g / ton corresponds to grams of the additive per ton of copper produced.

Description of what is known in the field.

Industrial processes of electro-refining (ER), and electro-obtaining (EW) of copper, are characterized by operating with continuous levels of electric current and involving electrochemical reactions of cathodic reduction and anodic oxidation, which occur at the inferred level. electrode-solution on the cathodes and on the anodes respectively.

Technical problems that affect energy consumption and the cathodic quality of Cu, due to the use of current signals currently in use. The most important variables that affect production and cathodic quality are the following:

• Current imposed

• Electrolyte temperature

• Ion concentration in the electrolyte

• Electrolyte flow to cell

• Electrochemical behavior of electrodes (cathodes and anodes)

In industrial Cu electrolysis processes, the key to maintaining or increasing production at the same installed capacity is to increase the DC current density. However, with current cell designs and current technology, any indiscriminate increase in current density to increase production results in a deterioration of the physical-chemical quality of the product. Increase energy consumption (cell voltage and electrolyte temperature), resulting in a further increase in the concentration of Cu ²⁺ ; the electrolyte flow and the dosage of additives in order not to deteriorate the physical-chemical quality of the cathodes. As a consequence of the above, the cost of production of cathodes and energy consumption increases at the expense of an increase in production. In the EW process of Cu, the emission of acid mist into the environment is also increased and in ER of Cu the risks of anodic passivation.

Recent technological developments.

The most important technological developments that have allowed to improve the process of electro-obtaining copper from the point of view of production and cathodic quality, are the following:

Permanent cathode technology.

This technology has been applied for 20 years in copper EW and ER plants worldwide, and has allowed significant benefits such as operating with higher current density, reaching levels of up to 400 A / m ² in some plants, and with Higher productivity rates.

Equipotential intercell bars. New designs of intercell bars, such as that of Asturiana de Cinc used in plants of EW of Cu (Mining Company Doña Inés de Collahuasi and CODELCO Norte Planta RT, in Chile), which have allowed reducing the voltage up to 10 mV / cell, with respect to a triangular base design or bone bar. Considering that the distribution of the current in the electrodes of the cells is of the parallel type, new designs of bars that are in process of industrial patent, (Outokumpu, Optibar), consider a better control of the quality of the distribution of the current in electrolysis cells, improving process control indicators in this way.

Insoluble Ti / MeO anodes in Cu EW.

Several types of anodes have been developed that consider the incorporation of noble metal oxides on a Ti substrate (Ru, Ir oxides, etc.), in order to catalyze the oxidation reaction of water, reducing energy consumption. by reduction of cell potential, over 250 mV. These anodes are currently under test in some industrial plants in the world. Ti base anode technology, initially referred to as "DSA" anodes (translated from English "Dimensionally Stable Anodes") was developed in the 1970-1980 for Chloro-Soda production electrolysis plants. There they have given excellent results in graphite anode replacement. However, the application in copper electrolysis processes has not been completely successful because in strongly acidic media such as Cu EW, the metal oxide oxides films deteriorate more rapidly, thus losing their catalytic properties for the oxidation reaction of the Water in time.

New Electrolysis Processes.

An interesting technological innovation is the so-called EMEW process which considers the design of more compact and closed cells for electro-obtaining copper. In this technology, copper electro-deposition is performed in closed cylindrical cells, with stainless steel tubular cathodes and DSA anodes (titanium anodes coated by titanium and ruthenium oxides). The cells have operated at current densities greater than 600 A / m ^2. The operational key of this technology lies in the high mass flow with which it works. This cell has been used industrially to treat diluted solutions of Cu ²⁺ , obtaining High quality chemical cathodes without environmental contamination due to acid mist. However, its massive application is still unfeasible, since it requires a total change of the technology currently in use, which implies a high cost and also for technical problems not yet fully resolved.

Acid mist control in Cu EW plants.

At current densities greater than 200 A / m ² , the generation of acid mist is very important in the electro-obtaining copper cells, so that appropriate measures are taken for its control. The use of ventilated hoods or covers located above the cell (SAME and OUTOTEC), and the forced air in the ship (DESOM process), have given good operational results, as well as the use of anti-foaming surfactants, such as FC 1 100 of 3M and the quillay extract recently patented by a Chilean company. These additives are added in small quantities to the electrolyte, (<5 ppm), to mitigate the emission of acid mist into the environment.

Increase in operating current in Cu EW plants.

The techniques used to increase the operating current density in copper electro-obtaining plants have been mainly two:

• ultrasonic vibration;

• Stirring the solution by air injection.

Of the proposed alternatives, only the agitation of the electrolyte by means of air injection has had possibilities of application in the electro-obtaining of copper.

So far the alternatives for solving the technical problem that implies an increase in production due to an increase in direct current are based on addressing the problem from the hydrodynamic point of view, that is, by applying "agitation" of the electrolyte around the electrodes: cathodes and anodes. This is observed extremely in the EMEW process in which the circulating flow is extremely high, but the physical structure of the cells is designed to operate with a high specific flow and completely different from large-scale industrial installations for copper EW. . It should be noted that this technology has not been tested in ER of Cu because of the design problems of impure Cu anodes and the high probability of anodic passivation. Another technology to improve Cu EW processes refers to the injection of air with diffusers installed in the cell walls. While it is true that significant improvements have been made in the physicochemical quality of electro-obtained copper, there is no impact on energy consumption or the emission of acid mist into the environment. This operational improvement is impracticable in Cu ER because it affects the movement of solids that come from the anodic dissolution of impure copper (anodic mud), with a negative impact on the physical-chemical quality of the product.

As we have seen, there is still a need to have electro-obtaining and electro-refining processes that allow hydrodynamics to be improved in the cells; reduce energy costs and have better quality cathodes.

The objective of the present invention is to have an electro-refining process that allows obtaining cathodes of greater purity and quality.

Another objective that the present invention intends to implement is to have an electro-obtaining process that allows obtaining cathodes of greater purity and quality.

Furthermore, another objective of the present invention is to have an electro-refining process that allows obtaining cathodes of greater purity and quality while reducing production costs.

At the same time, another objective of the present invention is to have an electro-obtaining process that allows obtaining cathodes of greater purity and quality while reducing production costs.

Summary of the Invention

The present invention corresponds to a process of electro-obtaining and electro-refining of noble minerals, such as copper, which comprises applying an alternating current superimposed on the level of a direct current.

Brief Description of the Drawings

The invention will be described below with reference to the accompanying drawings, in which:

Figure 1 shows an electrical power signal of a conventional electro-obtaining process (DC signal). Figure 2 shows the electrical power signal of the process of the present invention (AC signal superimposed on a DC signal).

Figures 3 to 26 show images of the cathode plates obtained experimentally, in conventional processes and in processes according to the present invention, visualized by microscope analysis.

Figures 27 to 30 show images of the cathode plates obtained experimentally, in conventional processes and in processes according to the present invention, visualized by analysis of the plate metallography.

Figure 31 shows the process diagram of the pilot test plant.

Figures 32 to 36 show images of cathodes obtained in the pilot tests.

Detailed description of the invention

The present invention corresponds to a process of electro-obtaining (EW) and electro-refining (ER) of metals, in particular noble metals, such as copper, which comprises applying an electrical power signal formed by an alternating current superimposed on the level of A direct current. The alternating signal is of defined frequency and variable amplitude from 25 to 600 A / m ²

The electro-obtaining and electro-refining process of the present invention is based on a conventional electro-obtaining and electro-refining process, respectively, which does not require changes in cell technology or in trans-rectifiers, only It has been modified in the application of an alternating current superimposed on a direct current and in the working ranges of some operating conditions, which have allowed to obtain products of similar physical-chemical quality and of better physical-chemical quality, and where it was possible to reduce operating costs, through the following ways:

• Reduction of electrical energy consumption due to a decrease in the cell's electrical potential.

• Reduction of energy consumption in heating large volumes of solutions.

• Reduction of the concentration of copper in the circulating electrolyte, reducing inventories in both ER and Cu EW. • Reduction in operating costs of solvent extraction processes in Cu EW.

• Reduction of energy consumption to pump large volumes of solutions.

• Availability to increase copper production to the same installed capacity.

• Reduction of investment costs for new plants.

The electro-obtaining and electro-refining processes are carried out in aqueous and strongly acidic medium, between approximately 180 and 200 gpl (grams per liter) of H ₂ S0 ₄ .

Figure 1 represents the direct current signal applied in a conventional electro-obtaining and electro-refining process, in contrast Figure 2 represents the alternating current signal that is superimposed on the direct current signal, according to the process of The present invention.

The electro-obtaining process of the present invention comprises applying an alternating current (AC) in a range of 400 to 600 A / m ² superimposed on a direct current (DC) in the range of 240 to 600 A / m ² , preferably in the range of 240 to 450 A / m ² , more preferably in the range of 250 to 500 A / m ² and where the frequency (f) of the overlapping alternating current is greater than or equal to 5,000 Hz and less than or equal to than 10,000 Hz; and includes establishing the following operating conditions in commercial cells:

- temperature range from 15 to 52 ° C,

- concentration of Cu ²⁺ in a range from 33 to 43 gpl,

- dosage of flocculant additives and grain tuner less than 200g / ton of copper produced (Cu °), and

- concentration of (cobalt sulfate) CoS0 ₄ less than 170 ppm of Cu ²⁺ in the electrolyte bath.

The EW process according to the present invention can work under the same operating conditions of the conventional process, however preferably, the temperature value is at least 5 ° C less and the concentration value is at least 3 gpl less that the temperature and concentration values, respectively, of the conventional process. Where, in conventional processes, the flocculant used is guar gum and the grain tuner is dextrin (DXG). For its part, cobalt sulfate has the function of inhibiting anodic corrosion. Additionally, a surfactant or antifoam is added, such as FC-1 .100.

In Table 3, it is possible to observe a comparative table of the operating conditions of a conventional electro-obtaining process versus the electro-obtaining process of the present invention.

Table 3: Comparison of the operating variables of a conventional electro-obtaining process versus the electro-obtaining process of the present invention.

Conventional Process Cu Process EW of the

Cu EW present invention

Direct current density less than 450 A / m ²

Specific Consumption Range of Specific Energy Consumption Range (CEE) [1 .800-2,000] (kWh / t Energy (CEE) <1 .700 (kWh / t Cu)

Cu)

Operational Conditions

Electrolyte Temperature Range Electrolyte Temperature Range in Commercial Cells in Commercial Cells

(T [48 - 52] ° C T) [40-46] ° C

Incoming Copper Concentration to Incoming Copper Concentration to Commercial Cells Commercial Cells 38 <Cu ^{2 +} <43 gpl 35 <Cu ^{2 +} <42 gpl

Dosage of Flocculant Additives and Dosage of Flocculant Additives and

Grain Tuner Grain Tuner (Guar + DXG) 200 - 300 g / ton of Cu ° (Guar + DXG) <200 g / ton of Cu °

Concentration cos 0 _4: concentration cos 0 _4:

Co ²⁺ <200 ppm in the electrolyte Co ²⁺ <100 ppm in the electrolyte As can be seen in Table 3, the electro-obtaining process of the present invention reduces the density of direct current to be applied, the temperature ranges, the concentration of incoming copper to the cells and the amounts to be added of additives. The new operational values of the electro-obtaining process of the present invention make it possible to reduce the specific energy consumption and positively affect the following variables:

- The emission of acid mist decreases when operating the electrolyte of cells with lower temperature, with respect to the Environmental Standard in the CAMP Ship (concentration of acid mist emitted by the cells to the environment in a Cu EW ship) <0.50 ( mg / m ³ ) of air, measured at an atmospheric pressure CAMP <0.45 mg / m ³ at 3,000 meters above sea level.

- Increases the estimated useful life of the anodes of Pb-Ca-Sn over 5 years, compared to conventional processes in which the useful life of the anodes is around 4 to 5 years.

- Increases the production of cathodes grade "A", is expected to be greater than or equal to 90%, compared to the conventional process that is about 80%.

The electro-refining process comprises applying an alternating current (AC) in a range of 400 to 600 A / m ² superimposed on a direct current (DC) in the range of 240 to 600 A / m ² , preferably in the range of 240 to 450 A / m ² , more preferably in the range of 250 to 500 A / m ² and where the frequency (f) of the overlapping alternating current is greater than or equal to 5,000 Hz and less than or equal to 10,000 Hz; and includes establishing the following operating conditions in commercial cells:

- temperature range from 40 to 60 ° C,

- concentration of Cu ²⁺ in a range from 40 to 56 gpl, and

- dosage of flocculant additives and grain tuner less than 100g / ton of

Cu °

The ER process according to the present invention can work under the same operating conditions of the conventional process, however preferably the temperature value is at least 5 ° C less and the concentration value is at least 3 gpl less than the temperature and concentration values, respectively, of the conventional process. Where, generally, in conventional processes the flocculant is avitone and the grain tuner is cola and thiourea and the percentages to be added of each, with respect to the aggregate total are 30% avitone, 30% tail and 40% tail.

In Table 4, it is possible to observe a comparative table of the operating conditions of a conventional electro-refining process versus the electro-refining process of the present invention.

Table 4: Comparison of the operating variables of a conventional electro-refining process versus the electro-refining process of the present invention.

As can be seen in Table 4, the electro-refining process of the present invention reduces the density of direct current to be applied, the temperature ranges, the concentration of incoming copper to the cells and the amounts to be added of additives. The new operational values of the process of electro-refining of the present invention, allow to reduce the specific energy consumption and positively affect the following variables:

- Increases the production of cathodes grade "A", is expected to be greater than or equal to 90%, compared to the conventional process that is about 80%. EXPERIMENTAL RESULTS

Examples of application of different direct current signals are listed in Tables 5 and 6, according to the conventional process and different alternating current signals superimposed on a direct current and different frequency values applied in processes according to the present invention, in application times of 5 and 10 hours of permanence in the electrolytic reaction.

Table 5: Operational conditions in experimental tests in a conventional process versus the process of the present invention, the values of direct current, alternating current and frequency in 5 and 10 hours of application are evaluated.

The cathode samples obtained at 5 hours of reaction were analyzed by means of a scanning electron microscope (SEM) (Scanning Electron Microscope). From each test performed, one of the cathodes obtained with the SEM microscope was analyzed and the cathodes were observed in two different magnification values, at 300 and 1,200. Figures 3 and 4 represent the analysis performed at a cathode obtained with the conditions of test 1, measured at 300 and 1,200, respectively. All things being equal, figures 5 and 6 represent test 2, figures 7 and 8 represent test 3, figures 9 and 10 represent test 4, figures 1 1 and 12 represent test 5, and Figures 13 and 14 represent test 6.

Figures 3, 4 and 9, 10 correspond to tests 1 and 4, respectively, which represent the use of DC signals, according to the conventional procedure. In these figures it is observed that the crystalline growth structure makes it possible to clearly appreciate the separation of the grains that highlight the interstitial spaces between them. These interstitial spaces impact the entrapment of impurities in cathodic deposits. Instead in figures 5, 6; 7, 8; 1 1, 12 and 13, 14 corresponding to tests 2, 3, 5 and 6, respectively, it is observed that said interstitial spaces decrease as the frequency of the AC signal superimposed on the DC level increases, that is to say when applying a AC signal superimposed on a DC signal is less likely to trap impurities in cathodic deposits, as interstitial spaces decrease.

The above is clearly seen in Figures 7 and 8 where it can be seen that the interstitial spaces are smaller with respect to those of Figures 5 and 6, and in turn the interstitial spaces of Figures 5 and 6 are smaller with respect to those of the Figures 3 and 4. Figures 7 and 8 correspond to a frequency of 10,000 Hz, Figures 5 and 6 correspond to a frequency of 5,000 Hz and Figures 3 and 4 without AC signal.

In the same way, in Figures 13 and 14 it can be seen that the interstitial spaces are smaller with respect to those of Figures 1 1 and 12, and in turn the interstitial spaces of Figures 1 1 and 12 are smaller with respect to those of Figures 9 and 10. Figures 13 and 14 correspond to a frequency of 10,000 Hz, Figures 1 1 and 12 correspond to a frequency of 5,000 Hz and Figures 9 and 10 without AC signal.

Table 6: Operational conditions in experimental tests in a conventional process versus the process of the present invention, the values of direct current, alternating current and frequency in 10 hours of application are evaluated.

As in the case of tests 1 to 6, the cathode samples obtained at 10 hours of reaction were analyzed by a scanning electron microscope. From each test performed, one of the cathodes obtained with the SEM microscope was analyzed and the cathodes were observed in three different magnification values, at 20, at 300 and at 1,200. Figures 15, 16 and 17 represent the analysis performed at a cathode obtained with the conditions of test 7, measured at 20, at 300 and at 1,200, respectively. All things being equal, figures 18, 19 and 20 represent test 8; Figures 21, 22 and 23 represent test 9; and Figures 24, 25 and 26 represent test 10.

Figures 15, 16 and 17 correspond to test 7, which represents the use of DC signals, according to the conventional procedure. In these figures a deposit with abundant nodules is observed (figure 15), unlike the results obtained by superimposing AC signals on the DC level (figures 18 to 26). It is observed that the nodulation disappears and the texture becomes more even as the frequency and signal amplitude increases.

The above is clearly seen in Figures 24, 25 and 26 where you can see the small nodulation and the more even texture with respect to Figures 21, 22 and 23; and in turn, figures 21, 22 and 23 have less nodulation and more even texture with respect to figures 18, 19, 20, which also have less nodulation and more even texture with respect to figures 15, 16 and 17. Figures 24 , 25 and 26 correspond to a frequency of 10,000 Hz, Figures 18, 19, 20, 21, 22, 23 correspond to a frequency of 5,000 Hz and Figures 15, 16 and 17 are without AC signal. In greater abundance, in Figure 15, which corresponds to applying only direct current, according to the conventional process, the nodulation can be seen in the center and at the edges, showing a marked preferential growth at the edges. In contrast, in Figure 18, where an alternating current superimposed on a direct current has been applied, according to the process of the present invention, it can be seen that the copper deposit is very even and practically without nodulation, and there is no preferential growth on the edges

Additionally, the cathode plates were analyzed by metallography, in order to observe the variations of their crystalline structure. Figures 27, 28, 29 and 30, represent tests 7, 8, 9 and 10, respectively. As can be seen, figures 28, 29 and 30 show a clear improvement of the crystalline structure as the amplitude and frequency of the AC signal superimposed on the DC level increase, with respect to Figure 27 which is without AC signal.

From the tests carried out, it can be concluded that the surface of the copper deposits of the cathodes obtained with direct current signals have an abundant presence of nodules and preferential growth at the edges, instead the cathodes obtained with alternating current signals superimposed on a Direct current shows a clear difference in the type of deposit, since its copper deposit surface is more even and without preferential growth at the edges.

In turn, the metallographic analysis, performed on the samples obtained, indicates that the internal structure of the deposits is remarkably different in terms of grain morphology and type of crystal growth, depending on whether DC or DC current signals are used. + AC.

At high current densities with conventional process (i> 400 A / m ² ), the deposits obtained with DC signals are characterized by having a fine, spongy and messy grain structure without preferential orientation, approaching a crystalline structure type UD (Fl ) (small grains, without consistent structure) in the Fisher classification. The deposits obtained with DC + AC signals, on the other hand, are characterized by a continuous crystalline growth with a clear field orientation, approaching a TC structure (FT) (crystalline structure of grain oriented in the body) in the Fisher classification which make boast a better chemical quality for cathodes, however operate with current densities that exceed 400 A / m ² . Figures 15 and 18 show the images of a cathode sample obtained by the conventional process, with respect to a cathode sample obtained by the process of the present invention, respectively. Furthermore, in Figures 18, 21 and 24 it can be clearly seen, as the crystalline structure has a more continuous growth as the amplitude and frequency of the AC signal superimposed on the DC level increase.

Field tests (pilot tests) according to an electro-obtaining process according to the present invention

Long-term tests were performed at 350 A / m ² with conventional process and process according to the present invention, but maintaining the operating conditions according to the conventional process.

Short duration tests were carried out, with conventional process and with process according to the present invention, but modifying the operating conditions of the conventional process (temperature ° C, concentration of Cu ²⁺ (g / l), and incoming flow to cells (l / min / m ² )).

Metallurgical tests included:

Plate Sowing Process

Controls during planting

Cathode harvest

Cathode takeoff

Sample preparation and shipment

In figure 31 you can see the scheme of the pilot plant with visualization of the two cells that comprise it and the electrical circuit.

The electrical circuit, visualized through the segmented line, is composed of a transfo-rectifier (1) for the generation of the DC signal and an electrical equipment (2) to generate the AC signal from the DC signal that feeds EW cells. The electric current that leaves the trans-rectifier (1) feeds the anodes of cell 1 (3), then passes to the electrolyte and then to the cathode of said cell 1, then said current leaves the cathode towards the equipotential rod. Then from said equipotential rod, the current feeds the anodes of cell 2 (4), then going to the electrolyte and cathode of said cell 2, then it goes back to the transfounder (1) thus closing the electrical circuit of the system.

In parallel, the hydraulic circuit is represented with the continuous lines and operates with the following sequence:

- The rich electrolyte from the solvent extraction process (8) passes through filters and is transported in 1 m3 so-containers to the rich electrolyte receiving ponds of the pilot plant (9 and 10);

- Then, the rich electrolyte passes to the gray pond (1 1), which is responsible for having the rich electrolyte (7) inside the pilot plant, the transfer of rich electrolyte is done every 3 to 4 hours, depending on consumption of electrolyte inside the pilot plant;

- Next, the rich electrolyte is fed from the gray pond (1 1) to the rich side recirculation pond (12), there it is mixed with the poor electrolyte (6) from the poor side recirculation pond (13) to form the mixture of incoming electrolyte (5) to the cells, with a defined copper concentration (usually 43 g / l);

- The incoming electrolyte (5) feeds in parallel to the two electrolysis cells (3 and 4), the outgoing electrolyte of the cells corresponds to the poor electrolyte (6) and this is divided into two flows, one that returns to the recirculation pond poor side (13) and another that will discard (14);

- The discards are accumulated in a pool (sink) (15) of the pilot plant and subsequently said discards are transported in containers to the stack (16).

Table 7 shows the operational values or experimental conditions of the long-term tests for the conventional process and the process according to the present invention.

Table 8 shows the operational values or experimental conditions of the short duration tests, for the conventional process and the process according to the present invention.

Table 7: Long comparative tests, for the conventional process and the process according to the present invention.

Long-term tests, as indicated, are performed with the same operational conditions that work in the plant. Two tests were performed for each type of process and given that the pilot plant consists of two cells, it means that in each test two cathodes are obtained, therefore finally 4 cathodes were obtained for each type of process.

Table 8: Comparative short tests, for the conventional process and the process according to the present invention.

( ^* ) Means initial condition to final condition in the test performed. The short duration tests, as indicated, are carried out with modification of the operating conditions in the plant. In tests 5-6 the temperature of the electrolyte in the cell is varied and in tests 7-8A the concentration of incoming Cu, the temperature of the electrolyte, the electrolyte flow and the specific flow are varied.

The cathodes obtained in the long tests were subjected to chemical analyzes, in order to evaluate the sulfur content present in each cathode, the results obtained from the long-term tests can be seen in Table 9. Said Table 9 shows the results of the chemical analyzes performed on the cathode samples, in relation to evaluating the ppm of sulfur present in the cathodes obtained.

Table 9: Sulfur concentration in the cathodes obtained in the long tests.

As can be seen in Table 9, the sulfur concentration is lower in the cathodes obtained with the tests performed according to the process of the present invention, which is beneficial, since it decreases the formation of nodules on the surface of the sheet .

The cathodes obtained in the short tests were also subjected to chemical analysis, in order to evaluate the sulfur content present in each cathode, the results obtained from the short duration tests can be seen in Table 10. Said Table 10 shows the results of chemical analyzes made to the cathode samples, in relation to evaluating the ppm of sulfur present in the cathodes obtained, additionally for comparative purposes, Table 10 also includes the average values obtained in the long-term tests.

Table 10: Concentration of sulfur "S" in the cathodes obtained in the long and short tests, for conventional process (DC) and process according to the present invention (AC + DC).

In Table 10 it can be seen that the chemical quality of the cathodes obtained in the DC tests is lower, since the sulfur content is on average 2 to 4 times higher than the sulfur content in the AC + DC tests.

On the other hand, the physical quality confirms the above, since the samples obtained from the DC tests show greater formation of nodules on the surface of the copper sheets and that greater amount of nodules and imperfections is associated with the higher sulfur content in The body of the cathodes. In Figure 32 a comparative image of a cathode can be seen, showing the imperfections described above, where the upper sample corresponds to the cathode C2 with the AC + DC process and the lower sample to the cathode C2 with the DC process.

In figures 33 to 36 you can see the morphology of the copper deposit in the cathodes. Figures 33 and 34 correspond to the AC + DC process, for a long duration test. Figure 33 represents cathode C1 and figure 34 to cathode C3. The crystalline structure obtained is of the TC type, that is, crystals oriented in the field, without crystalline imperfections.

For their part, Figures 35 and 36 correspond to the DC process, for a long-term test. Figure 35 represents cathode C1 and Figure 36 represents cathode C3. The crystalline structure obtained is of the BR type, that is to say crystals of irregular size and of disorderly growth from the base. It is also observed a significant number of imperfections and porosities throughout the region of the analyzed samples.

Finally, all tests showed that there is a decrease in cell potential when operating with DC (350 A) + AC (60 A amplitude and 9,999 Hz frequency) signals. The potential decrease (voltage) ranged between 22 and 44 mV per cell. It was possible to demonstrate that it is possible to improve these values if one considers in the design of the electrical system, a greater amplitude of the alternating signal.

Claims

one . Electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, which is carried out in aqueous and strongly acidic medium, CHARACTERIZED because it comprises applying an electrical power signal formed by an alternating current superimposed on the level of a direct current, where the alternating current (AC) is in a range of 400 to 600 A / m ² and is superimposed on a direct current (DC) in the range of 240 to 600 A / m ² and where the frequency (f) is greater than or equal to 5,000 Hz and less than or equal to 10,000 Hz.

2. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, according to claim 1, CHARACTERIZED because in the electro-obtaining processes the operating conditions in commercial cells are:

- temperature range from 15 to 52 ° C,

- concentration of Cu ²⁺ in a range from 33 to 43 gpl,

- CoSo4 concentration of less than 170 ppm of Cu ²⁺ in the electrolyte bath.

3. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, according to claim 2, CHARACTERIZED because preferably the temperature value is at least 5 ° C less and the value of the concentration is at least 3 gpl less than the temperature and concentration values, respectively, of a conventional electro-obtaining process.

4. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, in accordance with any of the claims 2 to 3, CHARACTERIZED because in the electro-obtaining process the specific energy consumption is less than 1 .700 (kWh / t Cu) if working with a direct current signal less than 450 A / m ²

5. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, according to claim 1, CHARACTERIZED because in the electro-refining processes the operating conditions in the commercial cells are:

- temperature range from 40 to 60 ° C,

- concentration of Cu ²⁺ in a range from 40 to 56 gpl, and

- dosage of flocculant additives and grain tuner less than 100g / Ton of

Cu °

6. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, according to claim 5, CHARACTERIZED because preferably the temperature value is at least 5 ° C less and the value of the concentration is at least 3 gpl less than the temperature and concentration values, respectively, of a conventional electro-refining process.

7. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, according to any of claims 5 to 6, CHARACTERIZED because in the electro-refining process the specific energy consumption is less than 250 (kWh / t Cu) if working with a direct current signal less than 350 A / m ² .

8. The electro-obtaining or electro-refining process of metals, in particular noble metals, such as copper, according to any of claims 1 to 7, CHARACTERIZED because the alternating current signal has a variable amplitude in the range from 25 to 600 A / m ² .