Patent Application
20250198031
This specification pertains, as indicated by its title, to an electrorefining installation with interconnectable intercell bars. An electrorefining installation refers to an electro-deposition installation used to purify metals through electrolysis. It comprises at least three cells connected in a series within a circuit between the positive and negative poles of a rectifier. The electrical connection between each cell and the next one is established via a set of at least three bars: a central main bar and two side bars placed between each pair of consecutive cells and positioned parallel to each other a few centimetres apart.
The central bar acts in a conventional way and gives support and electrical connection to one of the ends of all the hangers of the cathodes of the preceding cell in the series of cells, where the first cell is the one connected to the positive pole of the rectifier, this central bar also gives support and electrical connection to one of the ends of all the hangers of the anodes of the next cell. One of the two mentioned side bars, the upper side bar, provides support and connection to all the anodes of the preceding cell, while the other bar, the lower side bar, provides support and connection to all the cathodes of the next cell.
Several high-current electrical switches, installed uniformly along these bars, endow them with the capability of being connectable bars. These switches can create an electrical bridge or connection between the bars, which is done periodically for a short period of time, causing the desired temporary current reversal in the electrodes of a cell. At this point, we say that the cell is in a state of reversal. During a period of tens of times longer, the switches remain open or without establishing the connection. During this period with the switches open, the cell remains in its conventional production state.
The invention relates to the field of metal electro-deposition plants and processes, particularly electrorefining, where production cells containing the electrodes and electrolyte are connected or can be connected to each other via an inter-cell electrical bar.
For more than a hundred years, metal electrorefining processes have been widely used industrially for the purification of metals. When electrorefining is used to create thin coating layers, it is often referred to as “coatings” or “plating”.
The conventional electrical installation or connection for metal electro-deposition, which is the same for both electrowinning and electrorefining of metals, as illustrated in
The metal deposited on the cathode is obtained by circulating a direct current between the anode and the cathode. On an industrial scale, in a production plant, this means tens of thousands of amps applied to thousands of electrodes. The continuous circulation of these amps for hours (amps x hours) causes the deposition of the millions of tons of metal produced annually in these plants.
These electrorefining processes can produce very high-quality metals with very high purity and fineness. However, since their origins a century ago, they have intrinsically presented serious technical challenges with natural limitations that significantly increase the cost and complexity of their operation, while also making these processes more contaminating.
The current density, and consequently the density and manufacturing capacity, have very strict technical limits, above which quality is lost, contamination increases and energy costs skyrocket. In addition, the electrochemistry of the process is very vulnerable to small and inevitable deviations in the composition of the minerals and process variables.
It has been more than a hundred years since the construction of the first industrial plants using conventional intercell bars, called “Walker bars”, with their different versions or profiles. During this time, extensive research and efforts have been undertaken to mitigate and overcome the identified difficulties and technical problems.
Accidental short circuits may occur due to positioning error, due to the non-alignment of the electrodes in parallel, or due to their physical deformations. It is evident that an improvement in the work discipline of their placement and in the quality of the plates involved can resolve and has resolved this accidental difficulty.
But, in addition to this, during the metal deposition process, protrusions appear, naturally and unpredictably, in the flat layer of metal generated, on the cathode plate, which usually has a surface of approximately one square meter. These irregularities quickly grow in the form of dendrites and can easily come into contact with the anode, which is located just five centimetres from the cathode. These contacts cause short circuits with high, destructive currents, which reduce production, destroy the physical integrity of the electrodes, contaminating the electrolyte and thus the metal produced, and ultimately impact the environment.
A solution adopted from the beginning to this important problem is to detect the overcurrent as soon as possible and manually eliminate the short-circuit contact. Given the thousands of electrodes involved, and in a very hostile and dangerous environment, it has the disadvantage that it is a high-cost and low-efficiency task.
Another palliative procedure consists of the application of additives that refine the granulation of the deposited metal crystal and reduce the likelihood of dendrite formation. However, these additives are somewhat contaminant, expensive and only relatively effective.
More sophisticated solutions are known, such as the application of segmented titanium anodes such as those described in patent WO2015/079072 “Anode structure for metal electrowinning cells”, but have the drawback that they have a high cost as they require a coating composed of scarce materials given their high demand, such as ruthenium, iridium or rhodium. These anodes automatically disconnect the partial section where the short-circuit contact occurs, thus avoiding high currents. However, as a result of the disconnection of the anode segment, a small collateral issue inevitably appears: the disconnected anode segment becomes coated with a layer of copper. This copper coating dissolves naturally once the dendrite is removed. Although this is a lesser issue, this solution should be operational. However, its real implementation and industrial validation face unexpected difficulties.
Electrode plates work efficiently at very low current densities, around 300 Amps per m2 (or 30 mA per cm2), in contrast to a copper conductor of a few millimetres, which can carry tens of thousands of mA. As a consequence, this requires working in very large plants with a high construction and operating cost. Exceeding current density limits in the interest of greater productivity or productive concentration means paying the price of poorer metal quality, a drastic increase in dendrite short circuits as described above, a loss of performance and greater contamination.
It is surprising and very interesting to know that for decades there have been clear and conclusive studies that show and propose a recognized technical solution to all the natural difficulties of these electrochemical processes, eliminating the root of the intrinsic background limitation suffered by these electro-deposition processes, as for example described in U.S. Pat. No. 4,140,596 “Process for the electrolytic refining of copper”. This solution consists of the periodic reversal of the electric current in electrodes, as proposed in the patent, for 0.355 seconds, followed by 7.1 seconds of direct productive operation. This would apparently mean cyclically reversing or undoing 5 percent of what was previously manufactured. However, reality proves, and theories justify, that on the contrary, this short current reversal clears the barriers of electrochemical potentials that cake and are the source of all the natural difficulties pointed out above for these processes.
There are established and accepted studies by the scientific community that explain this phenomenon through the study of the ionic layers that originate on or near the surface of the electrodes. These studies also demonstrate the effectiveness of periodic current reversal, or, in other words, the application of periodically repeated current pulses and/or reverse pulses. Thus appears the concept of the existence of a capacitive ionic layer, the Helmholtz layer, whose creation would be the root of the severe limitations of these processes described above.
The theoretical procedure of applying a current in the opposite direction to that of the production current periodically seems to be the solution, but the real technical problem is the serious difficulty of how to make it a reality or how to implement it practically and operationally on a large scale in a real industrial production plant. In a laboratory with cathode plates of a few square centimetres operating under a few amps, it is easy to implement an electrical installation that allows us to experiment, find and apply a highly satisfactory solution. However, in an industrial plant the few square centimetres are converted into thousands and thousands of square meters of electrode surface, and a few amps into tens of thousands of amps.
The sudden and periodic change of direction of these high currents, which reach tens of thousands of amps, has been tried to obtain by superimposing or adding an alternating current to the conventional direct current. This standard alternating current, with a sinusoidal temporal profile that reaches our homes and is also used in the industry, which in its negative peak exceeds the amplitude of the always positive direct current, resulting in the sum of both having a long period of positive values against a reverse current moment, as described in patents WO2015056121 “Metal-electrowinning or -electrorefining process comprising the application of an electrical power signal formed of an alternating current superimposed on a direct current” and WO2015075634 “Method of superimposing alternating current on direct current for methods for the electrowinning o electrorefining of copper or others products, wherein the alternating current source is connected between two consecutive cells of the electrolytic cell group using an inductor for injecting alternating current and a capacitor for closing the electric circuit”. The problem with these solutions is the extreme magnitude of the electrical devices necessary to couple both alternating and direct currents, with large capacitors and enormous coils operating at thousands of hertz. The technical challenges that they entail make their practical industrial implementation currently infeasible. These solutions, in addition, require an external supplementary energy supply in alternating current.
Another solution is also known, as described in U.S. Pat. No. 1,930,869 P2 “Electro-deposition installation with active intercell bars”, corresponding to a SAIB or BIAI type installation that also uses periodic current reversal, and which, like our current invention, makes use of the internal energy stored in the production process. This is done by dividing or distributing the magnitude of the problem into millions of switching microdevices inserted into the intercell bars of the plant, in each of them we work with amplitudes affordable for today's modern transistors. This is a viable solution although it has the disadvantage of constructive complexity, given the very high number of production switch devices that have to be integrated into the copper of the intercell connection bars, which forces a complex manufacture of these bars, and complicates their maintenance and/or repair.
In order to solve the currently existing problem caused by the intrinsic background limitation of these industrial processes, dendrite short circuits and performance losses in metal electro-deposition installations, the interconnectable intercell bar electrorefining installation object of the present invention has been devised, which comprises
We refer generically to at least three cells, the first cell, any intermediate cell and the last cell, to represent in the simplest way a conventional industrial plant composed of hundreds of cells and explain the invention applied to it. This requirement is not exclusive for the operation of our invention, as a single cell, or two cells, could also be directly benefited by our invention, although it does not represent an actual industrial installation.
The electric switches may be either solid-state electronic switches, power electromechanical switches or relays, or any combination of both. They can be associated with a printed circuit board featuring a microcontroller capable of communication via digital communication protocols with the control system, and optionally include current sensors as well.
High-current electrical switches allow electrical connections to be selectively established between the bars associated with a cell. These connections are periodically activated and deactivated by establishing for a short period of time an electrical contact between some of the bars adjacent to a cell, which causes a temporary reversal of current in the electrodes of said cell with natural discharge of the Helmholtz ionic layer without the need for external energy supply, and, for a period tens of times longer, the contacts of the electrical switches remain open. For example, one second of contact or connection and twenty seconds open without connection.
The activation of the reversal switches must be applied periodically to each cell of the cell series circuit. Closing the switches of all the cells at the same time would cause a short circuit collapse in the general rectifier. If we let it be the chance of non-synchronized clocks, or let the various controllers of the different cells randomly trigger the instant of connection or reversal, we will obtain a statistical distribution in the form of the known binomial distribution that would result in a naturally homogeneous performance for large numbers. But we would face infrequent but safe coincidences of simultaneous reversals that could produce some small instability in the general rectifier.
As a result of the above lines, an orderly and simple deterministic action is proposed for the current reversal procedure in the circuit cells.
We act in an orderly manner using an index “i” which is the cell number to which we apply the short inversion period, that is, with switches activated, so that when cell one finishes its reversal state, cell two starts it, and so on (i=i+1), one by one. Once the reversal has reached the last cell, it would start again.
If the number of cells is large, which is the most common case in an industrial facility, it is clear that we may need to reverse cell one again before reaching the last cell. We must establish some parameters to analyse the problem and its solution:
The sweep time for the reversal wave across the NC cells of the circuit, by sequentially connecting the electrical switches of the cells, is NC×T1 following the explained sequence.
The time it takes for cell one to request its second or next reversal is T0+T1.
As mentioned, the problem arises when the number of cells is large and NC×T1>T0+T1. In this case, it becomes necessary to reach the E1 state in more than one cell at a time.
When NC×T1=T0+T1, just at the end of E1 in cell NC (last cell), cell one will enter E1. If NC is cleared, and now using NCP as the number of cells per package, we have the formula NCP=(T0+T1)/T1, always adjusting decimals of T0 and T1 to be an integer.
The number of cell packages on which the cycle should be performed will be NP=NC/NCP
If p is referred to as the cell package number, each package p will be composed of cells (p−1)×NCP+i, where i ranges from i=1 to i=NCP. If NP is not an integer, it is rounded up: NP=truncate (NP)+1.
Thus, in general, the sweep of cells in reversal E1 will be:
where i ranges from i=1 to i=NCP, and p ranges from p=1 to p=NP. In this way, at all times there are NP cells with switches closed, in a stable way, avoiding fluctuations in the supply of the rectifier.
Applying the formulation to the example proposed above with the times of T0=7.1 sec. and T1=0.355 sec. yields NCP=(7.1+0.355)/0.355=21.
In a case of a circuit of, for example, 63 cells, then NP=63/21=3. 3 packages of 21 cells each are considered. Each package will be applied the same sequence procedure:
Following this sequence, there would be 3 cells at a time with the switches closed making the reversal, but never consecutive, with which the process would be carried out in a stable manner, avoiding fluctuations.
To explain the interconnection between the bars that causes the reversal of currents in the electrodes of a cell, we will first name the bars for reference.
In an electrorefining installation, the current-reversing electrical switches for the cell electrodes are placed between the two preceding side bars and between the two following side bars. These switches will be activated and deactivated simultaneously in each cell, causing a current reversal in the electrodes of the cell.
The typical operation procedure is as follows, which is carried out simultaneously in each cell package, in the event that there are several cell packages:
Thus, when i=1 we set the first cell in all packages to E1, when i=2 we set the second cell in all packages to E1, . . . when i=NCP we set the last cell to all packages to E1.
Obviously, in case the number of cells is not high, only one cell package would be considered to exist.
In this electrorefining installation, the first cell in the circuit will not have the upper lateral preceding bar to which the switches are connected, where the cathodes of the preceding cell are supported. Similarly, the last cell in the circuit will not have the lower side following bar where the switches are connected. The following possible solutions are proposed:
The great value of this invention consists in the substantial improvements in quality and productivity that its application causes in the annual production of millions of tons of metals, such as copper, nickel, zinc . . . , together with the simplicity and robustness of the mechanism that supports it, which make it immediately industrially applicable.
This intercell bar installation with current reversal applies the periodic reversal of currents through an arrangement of high-current electronic switches that provides multiple advantages over the systems currently available, the most important being that it improves the current state of the art, especially the electrorefining installations with active intercell bars that require millions of switching microdevices inserted into the intercell bars of the plant, one for each segment.
Unlike solutions known in the state of the art that require an external supplementary power supply in alternating current, the present invention has the great advantage that it makes use of its own switching strategy wherein the power is extracted for the current reversal of the structure itself or voltage scaling in the series cascade of the cells.
Among these improvements, we must highlight the increased operational robustness and safety, since the main transistors or switches that require, in an enormous amount, the electrorefining installations with known active intercell bars, intercept the passage of the total production current, so their potential breakage or breakdown affects production until their repair or replacement, operations that are very complicated and delicate since these switches are embedded within the intercell bar. This is solved in the present invention since the electrical switches act in parallel with the main current, and do so only for the short period of time that the investment lasts, so in case of breakage, it does not affect the production current.
Another advantage is that, when operating the electrical switches in parallel, the neighbouring switch devices, which are suitably oversized, provide sufficient reverse current for effective operational continuity. Thus, the system is fault-tolerant, in terms of its subsequent replacement by not being embedded in the intercell bar, but simply coupled and installed on it. This makes this operation much more feasible and straightforward.
It is also important to note that electrical switches, as they do not have to withstand the load of the plant through them, and only contribute or superimpose the reversal current for a short period, are significantly reduced in number and also in their ease of installation, reducing both the economic cost of the installation, which is reduced by almost half, and the probability of failures and breakdowns.
Another notable advantage is that the control system is much simpler and more general, as it does not necessarily require wireless and low-power activity for control. Given its simplicity and the reduced number of switches required, wiring through the bar itself is possible using the plastic channel that supports the secondary intercell bars. This avoids the consumption of thousands and thousands of batteries and the difficult management of such a complex synchronized control through a radio network, which is required in the known electrorefining installations with active intercell bars.
Finally, we must highlight the ease of initial installation and commissioning, unlike the known electro-deposition installations with active intercell bars. This allows for even subsequent maintenance to be handled by the clients themselves or by a company with low-control specialization, as required in facilities in the mining environment.
In order to better understand the object of the present invention, the attached drawing shows a conventional installation and two practical embodiments of an electrorefining installation with interconnectable intercell bars. In the relevant figures, the symbol of an open-headed arrow (>) has been used to represent the production currents, and a closed-headed arrow () to represent the reverse currents that can be obtained with this invention.
The constitution and characteristics of the invention may be better understood with the following description made with reference to the attached figures.
To understand the invention, it is advisable to take into account the configuration of representative elements of a conventional electrorefining installation for metals, as illustrated in
As can be seen in
To facilitate the understanding of the operation, we will take the convention that:
In this electrorefining installation, as illustrated in
The side bars (4) and (5) will preferably have a section ranging from 50 mm2 to 200 mm2, while the central bar (1) will be the one typically used in the plant, usually ranging from 575 mm2 to 975 mm2, depending on whether more complex profiles are employed. In this installation, the amplitude of reverse currents (12) obtained through the bridges is of short duration and not very intense, approximately 0.3 times the production current. For this purpose, preferably 16 or 32 electrical switches (7) will be installed per cell, with these switches being oversized for robustness (7). They should preferably have a contact resistance ranging from 20 to 30 micro-ohms.
The means of communication between the control equipment (13) and the electrical switches (7) are preferably selected from the group consisting of wired or wireless options.
The electric switches (7) may be either solid-state electronic switches, power electromechanical switches or relays, or any combination of both. It is envisaged that, in an alternative embodiment, the electrical switches (7) will be associated with a printed circuit board equipped with a microcontroller capable of communication via digital communication protocols with the control equipment (13). Optionally, the printed circuit boards associated with the electrical switches (7) will also have current sensors.
The high-current electrical switches (7) allow to establish electrical connections selectively between the bars (1, 4, 5). These connections are periodically activated and deactivated by establishing an electrical contact between said bars for a short period of time, which causes a temporary reversal of current with natural discharge of the Helmholtz ionic layer, without the need for external energy supply. During a period of tens of times longer, the contacts of the electrical switches (7) remain open.
This installation involves a characteristic current reversal procedure, aimed at ensuring the stability of the general power supply to the series circuit of cells, wherein,
the following sequence is carried out simultaneously in each of the cell packages:
Thus, when i=1 we set the first cell in all packages to E1, when i=2 we set the second cell in all packages to E1, . . . when i=NCP we set the last cell to all packages to E1.
Obviously, in case the number of cells is not high, only one cell package would be considered to exist.
In this electrorefining installation, the first cell in the circuit will not have the upper lateral preceding bar to which the switches are connected, where the cathodes of the preceding cell are supported. Similarly, the last cell in the circuit will not have the lower side following bar where the switches are connected. To address this, the following possible solutions are proposed:
The objective we aim to achieve and have accomplished is the periodic reversal of the current in each and every electrode of a cell, through the appropriate design of the aforementioned bars and the proposed switches that make up the invention. This has been experimentally confirmed in our laboratory by discovering the surprising phenomenon that simply establishing an electrical bridge between an anode (3) and a cathode (2) produces a significant desired reverse current (12) of more than 600 A/m2. We include the discovery of this fact, obtained experimentally, to explain that the current is generated by the energy stored in the plates and behaves like the voltage generated by a battery.
The small-scale experimental replication of the invention in the laboratory and the performance of dozens of tests confirm the most optimistic reports about the immediate benefits of periodic current reversal when executed with the described switching design, as shown in
In an electrorefining installation, as shown in
In the electrorefining process, an anode (3) cathode (2) bridge is only a bypass of the current that stops circulating between both electrodes through the electrolyte. As the energy is not available in the electrodes themselves, we must look for the reverse current (12) using the set of established bars, in the electrical power supply structure of the series circuit of cells. As defined by our invention, the action of the switches (7) involves at least three cells connected in series. In this situation, the first main bar (1) will be the most positive, and it will decrease stepwise through the circuit of cells until it reaches the final one with the most negative potential. Now, what the electrical switches (7) do is to take and transfer through the side bars (4) and (5) incorporated in the invention and the hangers themselves, a more negative potential from downstream (reverse) to the anode and a more positive potential from upstream (reverse) to the cathode. As a consequence, the reverse current (12) appears, which is our objective.
The small-scale replication of the invention in our laboratory and the performance of dozens of tests confirm the most optimistic estimates regarding the immediate benefits of periodic current reversal when operating with the switching design described above. The resistance of the micro cell operating at low load, at about 200 A/m2, is in the order of 0.96 mOHM per m2. If the current density is increased to 900 A/m2, which is 4.5 times higher, but applying the described periodic current reversal procedure, also known as pulsing, with the invention, the passivation or polarization of the anode (3) does not occur. Instead, the resistance of our micro cell decreases to 0.77 mOHM per m2. The copper plate produced at this high current density for about 14 hours with pulsing has a perfectly acceptable grain. The application of 900 A/m2 to the same cell under the same conditions without pulsing results in an anode (3) to cathode (2) resistance of about 1.85 mOHM per m2 within a few hours, an increase that shows the inevitable passivation of the anode (3).
Persons skilled in the art will easily understand that the characteristics of different embodiments can be combined with characteristics of other possible embodiments whenever such a combination is technically possible.
All the information referring to examples or modes of embodiment, form part of the description of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| P202230234 | Mar 2022 | ES | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/ES2023/070169 | 3/17/2023 | WO |
