MXPA06004151A - Process for the electrolytic recovery of cooper, nickel, cadmium, zinc, gold, silver and further metals dissolved in an aqueous medium and equipment for applying said process. - Google Patents

Abstract

The present invention is related to the electroplating and metal recovery industries using a device and method for recovering metals through aqueous dissolutions containing the same by electrochemical methods. The advantages of the present equipments and methods with regard to those of the state-of the art equipments and methods are that those of the invention effectively carry out an electro-recovery of copper, nickel, cadmium, zinc, gold, silver and further metals in powder without any vibration, thus avoiding the formation of metallic hydroxides and hydrides, these latter elements causing the cathodic recovery f said metallic ions to be ineffective. The present invention structurally consists in an electrochemical reactor of the type formed by a shaft including a rotary electrode, which is characterised in that said electrode comprises a groove across the wall.

Description

PROCEDURE FOR THE ELECTROLYTIC RECOVERY OF COPPER, NICKEL, CADMIUM, ZINC, GOLD, SILVER AND OTHER METALS DISSOLVED IN AQUEOUS MEDIUM AND APPLIED EQUIPMENT THIS PROCESS.

FIELD OF THE INVENTION The present invention relates to the electroplating industry and the metal recovery industry with a device and method for recovering metals from aqueous solutions containing them by electrochemical methods.

BACKGROUND OF THE INVENTION The electroplating industry involves different stages of the process, among which are the deposits of different metals such as copper, nickel, cadmium, palladium and zinc, either by means of electrolysis or by deposits without current. It is important to mention that in each of the aforementioned stages, the modified pieces are rinsed before entering the next stage, using 10-100 m3 water day-1. These waters generated in the rinses contain dissolved metal ions in the order of 1000-10000 ppm in acidic conditions (pH ~ 2), with conductive vices of the order of 1-20 mS.

The traditional physicochemical treatment that this type of industry gives to its effluents consists, in precipitation, raising the pH of the solutions with sodium hydroxide and the generated sludge requires confinement. The global cost of treating these effluents ranges around $ 200-300 m-3, in local currency. Despite this costly treatment, the quality of the water, in some cases does not comply with the environmental requirements, to be discharged to the municipal drainage.

The concept of recovering metals by electrolysis is not new; However, water treatment of rinses, which contain metals such as copper, nickel, cadmium, palladium and zinc, generated by the electroplating industry, is uncommon.

US Patent 4,028,199 (1977) claims the application of an electrochemical reactor with a rotating cylinder electrode for the cathodic recovery of copper and zinc from diluted solutions, principally; In addition, this patent claims the way how to make dendritic deposits, that is, in the form of dust. However, in some cases, such as when nickel and zinc cations are dissolved, this type of electrode is usually not very efficient, so this type of electrodes does not allow both to be recovered.

The patent US 4,406,753 (1983) which consists of the development of an electrochemical reactor with rotating cylinder electrode claims the application of this cell for the recovery of silver, mainly. While the patent US 5,587,064 claims the removal of metal deposits through the use of a mechanical device. In the same way this type of reactor has limitations regarding the electrorecuperación of nickel and zinc.

The patent US 5,628,884 (1997) claims the protection of a rotating cylinder cathode reactor, to be used in the cathodic recovery of metals contained in conductive solutions, in order that the water treated by this technology be reused. The device presented in this patent is not very efficient, given that the current efficiencies obtained by these inventors are in some cases 7% for silver, 13.9% for Au and 64% for Cu. The fact that these inventors obtain low efficiencies is due to a poor design of the anodes and cathodes, which are inefficient in their performance.

Recently, the international patent WO 2005/026412 claims an electrochemical reactor with a rotating cylinder electrode, for the removal of metals and organic matter contained in effluents. These inventors claim the versatility of the rotating electrode for: i) cathodically recovering metals and // ') oxidizing electrochemically organic matter, with the manipulation of the current applied In addition, in this same document the use of an ultrasonic generator that helps the removal of the material deposited in the rotating electrode is protected; in addition to a filtering system that is included in the same device, and that allows to remove the generated dust during electrolysis. Despite what this patent protects, the recovery of metals is not very efficient because the design of the rotating cylinder electrode is not adequate.

OBJECTIVES OF THE INVENTION One of the objectives of the present invention is to achieve an electrochemical reactor that allows electro-recovery efficiently of copper, nickel, cadmium, zinc, gold, silver and other metals, in powder form.

Another objective is to achieve this electro-recovery by preventing the formation of hydroxides and metal hydrides, which are responsible for the low efficiencies in the cathodic recovery of these metal ions.

Other objects and advantages of the present invention may be apparent from the study of the following description and the accompanying drawings for illustrative purposes only and not imitative BRIEF DESCRIPTION OF THE INVENTION In a few words, the present invention, in one of its facets, takes shape in an electrochemical rotary cylinder electrode reactor. The reactors comprising the teachings of the present invention are hollow cylindrical electrode reactors with a series of slots passing through the cylinder wall. The configuration, dimensions and number of slots is variable, and will depend on the composition and quantity of the solution to be treated, but any size, configuration and number of slots will achieve a better performance of these reactors. This grooving allows the formation of metal deposits in powder form, without adhering to the electrode, allowing the removal of the dust at the bottom of the reactor. The presence of grooves achieves a retromixing of interfacial fluid that also prevents the formation of hydrides and metal hydroxides.

In another of its facets, our invention consists of applying a current determined by the peripheral speed (u) and the concentration of the metallic ion (C). The equation that allows to determine the optimal current (I) to apply in our invention is described by means of the following equation: I = ° -042faFAPCRe "« Sc "* (1) d Where z is the number of electrons consumed by the deposit reaction, F is the Faraday constant, D the diffusion coefficient, C the concentration of the metal ion in the solution, d the cylinder diameter, Re the Reynolds number (Re = úlv) and Se the Schmidt number (Sc =? / D); v being the kinematic viscosity. It is important to mention that equation (1) was obtained with the experimental data shown in this work.

In order to better understand the characteristics of the invention, the present description, as an integral part thereof, is accompanied by the drawings, which are illustrative but not limitative, which are described below.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows a diagram of the electrochemical reactor of the present invention.

Figure 2 illustrates the detail of the electrode (No. 1) of Figure 1.

For a better understanding of the invention, a detailed description of some of the modalities of the invention will be made, This is illustrated in the drawings that are annexed to the present description for illustrative but not limitative purposes.

DETAILED DESCRIPTION OF THE INVENTION The present invention consists in the design of an electrochemical reactor for the cathodic recovery of copper, nickel, cadmium, zinc, gold, silver and other metals that can be recovered, from the aqueous solutions containing them, and which may come from the industry of electroplating, hydrometallurgical, mechanical-mechanical, or from some other source.

The electrochemical reactor used is one with a rotating cylinder electrode, which allows recovering the different metals in powder form, with a high degree of purity, which are easily removed, allowing the continuous operation mode of this device. Unlike the aforementioned patents, this reactor has a novel rotating cylindrical electrode which has been drilled, allowing the removal of copper, nickel, cadmium, zinc, gold and silver efficiently. This electrode prevents the formation of hydroxides and metal hydrides, which are responsible for obtaining low efficiencies of electro-recovery of metals.

With this new rotary-cylindrical rotary electrode design, it is not necessary to use a pallet or an ultrasonic generator to remove the deposited metal, because the shape of the deposits are controlled with hydrodynamic conditions (a through the peripheral speed, caused by the rotation of the electrode), as well as the current density applied to the rotating electrode, allowing them to detach continuously during electrolysis. This presents an additional advantage over the aforementioned patents, since it facilitates the operation of the reactor, making its control easier. The solutions that are treated by this invention can contain dissolved metal concentrations of 100000 to 10 ppm, since outside these concentrations, the electrode is no longer efficient.

With reference to Figure 1, the rotating cylinder (No. 1) is the cathode. In FIG. 2 this novel electrode is described in detail. This cylinder (No. 1) has a diameter of 3.8 cm with a height of 11.1 cm. This electrode is a hollow cylinder that has eighteen perforations in rectangular shape, 0.5x4.7 cm, each perforation is separated equidistantly to 0.5 cm, as shown in (No. 1). This cylinder has an arm of 8.2 cm with a diameter of 1.1 cm. The perforations in the hollow cylinder (No. 1) allow the cathodic recovery of metals efficiently, overcoming the deficiencies exemplified in the patents cited in this document. This innovative electrode design The formation of hydroxides and metal hydrides during the electro-recovery of metals, which are responsible for the low removal efficiencies of the metallic ones.

The cylinder current feeder (No. 4) is a copper chip attached to a spring that allows contact when the electrode is rotating.

The cylindrical electrode is rotated by means of an electric motor with resistor arrangement (No. 3) that allows to control the revolutions per minute.

The counter-electrodes are four anodes (No. 2), which are rectangular bars, 13.3x2x1 cm. These four counter-electrodes are attached to the walls of the reactor body (No. 6) and are distributed equidistantly between them. The distance between the cathode and the anodes is 1.6 cm. The anode feeders are four cables, connected to each electrode by means of a screw with nut in each case, these four electrodes are connected in series.

The (No. 6) is the body of the reactor, which has a diameter of 9 cm and a height of 11 cm, with a volume of 0.7 L. This has a cavity in the upper part (No. 7) and an olive (No. 8) that allows the entry and exit of the solution, respectively.

The selection of the electrode materials depends on the metal to be recovered and on the chemical composition of the solutions to be treated, and these can be very diverse. On the other hand, the magnitude of the cell will depend on the amount of electrolytic solution to be treated. This particular invention is not intended to be limited to a certain use of electrode materials, nor to a certain cell size.

Examples Example 1. Treatment of a rinse water generated by an electroplating industry. The copper water for rinsing.

Table I shows the characterization of the rinse water of the copper process provided by an industry dedicated to the coating of polymers. As it can be seen, this rinse contains high concentrations of copper in solution (866 p.m.) in an acid medium, and also low amounts of nickel, chromium and iron in solution.

The electrolysis was carried out in the electrochemical reactor with rotary cylinder electrode in laboratory size using 0.35 L of solution to be treated. The cylindrical electrode used (No. 1) was made of 316 stainless steel with exposed area in contact with the 97 cm2 solution, and as four counter electrodes, four graphite bars with an exposed area of 96 cm2 were selected.

The electrolysis consisted of applying a potential to the 1.3 V cylindrical electrode versus a reference electrode of mercury sulfate (0.615 mV vs. normal hydrogen electrode); in addition, the electrode was rotated to give angular velocities of 21488 cm s-1. The electrolysis was carried out without pH control. After 25 minutes of electrolysis, 99% electrorecovery was achieved for copper. However, nickel, chromium and iron remained in the solution with their initial compositions, see Table I. It is important to mention that during the electrolysis the copper electro-deposits are released in powder form and precipitate in the bottom of the reactor; this facilitates the continuous operation of the reactor and also avoids the incorporation of a mechanical device, as is the case of the patents cited in this document. On the other hand, it was noticed that the pH slightly decreased (from 1.88 to 1.81) and the conductivity consequently rose from 10.04 to 15.65 mS (Table I). This water has the characteristics to be reused as rinse water in the copper process.

Table 11 shows the analysis of the electrolysis performance of the copper rinsing water. It is striking that the process was developed with current efficiencies of 99%, which also generated an energy consumption of 3.91 KWh m-3, allowing to determine the treatment cost per cubic meter of $ 5.60 nr3, in national currency. Despite the low cost of treatment, less than half of what it costs to deal with them effluents by the traditional physical-chemical route, through the copper resale value ($ 44 Kg-1), the cost of this electrochemical treatment is paid by itself; In addition, this generates a high additional added value.

'Analysis performed by atomic absorption, a. t .: Before the treatment; d. t .: After treatment Table II. Analysis of the performance of the electrochemical treatment given to the rinsing water of the copper process.

Example 2. Treatment of a rinse water generated by an electroplating industry. The nickel-plating rinse water.

A study similar to that shown in the previous example was developed, Table III shows the characterization of the rinse water of the nickel plating process before and after the electrochemical treatment. The electrolysis was carried out at a density of current of 58 A pr2, with a peripheral speed applied to the rotating electrode of 21488 cm s-1, and with pH control during electrolysis in a value ~ 7, allowing to remove 99% of nickel, in an electrolysis time of 120 minutes (see Table III). According to what is presented in this document, the electrochemical nickel removal process was satisfactory. The current efficiencies obtained were 90%, the energy consumption of 31.42 KWh m-3 and the treatment cost of $ 38.42 nr3 (Table IV). It is important to distinguish that the cost of treating effluents containing nickel is more expensive than copper, this fact is associated to the fact that the nickel reduction overpotential is 1.1 V more negative than the corresponding one for copper. Notwithstanding the aforementioned treatment cost, through the resale value of nickel ($ 155 Kg-1), the cost of this electrochemical treatment is paid for itself. In addition, this water also has the characteristics to be reused as rinse water in the nickel plating process.

Table III. Characterization of the rinsing water of the nickel plating process before and after * Analysis performed by atomic absorption, a. t .: before treatment, d. t .: after the treatment Table IV. Analysis of the performance of the electrochemical treatment given to the rinsing water of the Nickel plating process. E. consumed (KWh nv Effluent Current efficiency (%) 3) $ (m3) Copper rinsing 90 31.42 38.42 From the analysis of the two examples shown above it was possible to recover both metals with satisfactory current efficiencies. This makes our invention different, given that the technologies proposed by other inventors have proven to be inefficient, because in those electrodes, the formation of hydrides and metal hydroxides are responsible for poor performance 10 of those reactors. In the present invention the fact of having a rotating cylindrical electrode, with the perforations described in Figure 2, allows to remove the protons and hydroxides from the interface (avoiding the formation of hydrides and metal hydroxides), besides, that with the densities of current and with the angular velocities applied to the rotating electrode, it is possible to obtain dendritic deposits that are continually detached during electrolysis. The latter avoids the use of a mechanical device to remove the metals deposited on the cylinder, as is the case of the use of conventional cylinders that have been protected by other inventors.

On the other hand, at the end of electrolysis, water is practically free of dissolved metals, so this treated water can be re-used in the rinsing process, avoiding discharges to the municipal drainage, bringing as a benefit the saving of potable water.

The invention has been sufficiently described so that a person with average skill in the art can reproduce and obtain the results that we mentioned in the present invention. However, any person skilled in the art who is competent in the present invention may be able to make modifications not described in the present application, however, if for the application of these modifications in a certain structure or in the manufacturing process thereof, the subject matter claimed in the following claims is required, said structures shall be included within the scope of the invention.

Claims (3)

R E I V I N D I C A C I O N S Having described our invention in detail, we consider as novelty and claim as our exclusive property, what is contained in the following vindicatory clauses:

1. Electrochemical reactor of the type that is formed by a tank with a rotating electrode, characterized in that said electrode comprises a groove running through the wall.

2. Electrochemical reactor, as claimed in the previous claim, characterized in that the grooving comprises several rectangular grooves.

3. Process for the electrochemical recovery of metals, characterized in that the process is carried out with the reactor claimed in the two previous claim clauses, and the intensity of current is determined by means of the following equation: - = 0.0426zFADCRco.844gc0.356 d Where z is the number of electrons consumed by the deposit reaction, F is the Faraday constant, D the diffusion coefficient, C the concentration of the metallic ion in the solution, meter of the cylinder, Re the number of Reynolds (Re = ud / v) and Be the number of Schmidt (Sc = D); v being the kinematic viscosity. R E S U E N The present invention relates to the electroplating industry and the metal recovery industry with a device and method for recovering metals from aqueous solutions containing them by electrochemical methods. The advantages of the equipment and processes that apply the present invention with respect to the equipment and processes of the state of the art are that the ones of our invention achieve the efficient electro-recovery of copper, nickel, cadmium, zinc, gold, silver and other metals, in the form of powder without the need of any vibration and avoid the formation of hydroxides and metal hydrides, which are responsible for the low efficiencies in the cathodic recovery of these metallic ones. Structurally, our invention consists of an electrochemical reactor of the type that is formed by a tank with a rotating electrode, characterized in that said electrode comprises a groove running through the wall.