Title of Invention:

Procedure for retrieving the precious metal plating and the carrier from electronic components with nickel-containing intermediate layer

The subject of the invention is a procedure for recovering plating containing gold and other precious metals from electronic components that have a nickel-containing layer under the pre cious metal plating, and a copper-containing layer on the carrier under the nickel-containing layer. The component must have a free metal surface, or it must be possible to make the metal surface accessible during preparation. The processible raw materials do not include, among others, printed circuits, complete household appliances, and electronic waste that contains, apart from the metal, other components soluble in sulfuric acid.

With the development of electroplating technologies, utilisation of precious metals became prominent. Gilded or silvered connectors provide better conduction, smaller contact resistance, and longer lasting corrosion prevention, compared to connectors containing solely copper or other carriers susceptible to oxidation. Availability of precious metals is, however, limited throughout the world, therefore retrieving valuable metals, such as gold, from secondary mate rials with high precious metal content is a field of development of high priority. Retrieving the carrier, mostly valuable copper or cooper alloys, from secondary materials is likewise im portant. Further requirements for recycling technologies are to minimise energy consumption and environmental emission. Environmental emission regulations apply to materials released and emitted into the environment both during the production of the materials used and during the application of the technology. The procedure we have developed serves as the basis for a technology that, in contrary to other methods, enables the recovery of the carrier metal and the separated precious metal planting in metallic form. Further technological advantages are the low energy demand, as well as the regenerability and recyclability of the solutions used in the procedure.

The following industrial procedures are used commonly to recover gold and other precious metals (silver, palladium, platinum) from the metallic secondary materials detailed above: Utilisation of strippers, solvents. In the process of acidic dissolution, concentrated acids or their combinations are used (e.g. aqua regia), which first oxidize the precious metals, then dissolve the oxidative products. The disadvantage of this method is that the combination of strong acids produces intense and hard to control reactions during dissolution, and also a large amount of gas is produced due to the exothermic processes, which contains toxic acid anhydrides. Absorp tion and neutralisation of the gas requires a special multi-stage equipment, which increases the costs of the procedure. After the acids dissolve the precious metals, the metal ions have to be reduced in order to recover the precious metal, which increases the time and cost of the process, and impairs recovery. Reduction of precious metals cannot be performed in concentrated solu tions, therefore these have to be diluted. As a result, the volume of the solution significantly increases, as does the wastewater that has to be neutralised. The costs of wastewater treatment are very high, and the reduction is energy- and chemical-consuming. A further disadvantage of the procedure is that the aggressive acids are not selective to precious metals and therefore dissolve the carrier as well. This side reaction consumes excessive quantities of acid and pro duces a large amount of hazardous waste.

Cyanide-containing eluents are also used for the dissolution of precious metals. Their advantage is that they do not dissolve the nickel under the gold plating, therefore they are selective. The great disadvantage of the method is, however, that it involves work with highly toxic cyanides, and the gold too has to be retrieved from a cyanide complex. Due to the toxic effect, the treat ment of waste requires great caution.

Metallurgy of copper. The primary metallurgy of copper from its ores is a multiple- stage pro cess of metal extraction and refining. Companies that use secondary copper metallurgical tech nologies to process precious metal-containing copper-based materials primarily originating from electronic waste only utilise certain steps of copper metallurgy (smelting, refining). The copper (or brass) carrier with the precious metal and other metals (e.g. nickel, tin, etc.) on its surface are added to the converter, smelted, and the processed blister copper is cast into anodes for electrolysis. This smelting is energy-consuming, since a continuously operating smelting furnace, a hot gas system, and a wet gas scrubber are necessary for the process, which require a large investment. The complex technology has to operate continuously, thus the processing of fractional, separate items is difficult to implement. This makes the technology expensive and difficult to manage, also with respect to the protection of the environment. The anodes produced undergo electrolytic refining in order to remove the impurities from them. During the process, the copper content of the anode and the metals with a more negative standard potential dissolve, and pure copper is deposited on the cathode. Impurities in the solution are kept below target levels in order to ensure cathode purity. The metals in the anode with an electrode potential more positive than that of copper, such as precious metals, as well as other insoluble phases, do not dissolve in the anode process, but form a solid sludge. The sludge can be continuously removed from the electrolyte solution circulated in and out of the cells, or the anodes can be placed in bags, preventing the floating particles from depositing on the cathode copper. The two steps described above require costly investments and consume large amounts of energy. The material demand is big, several tons of base material is required for the economic utilisation of the smelting and electrolysis capacity. For these reasons, processing is slow and difficult, and the direct treatment of small amounts of materials with this method is not economic. The anode sludge produced in the process described above contains precious metals, tin, lead (as compound), the hydroxides of so called amphoteric metals, copper oxide and hydroxide pro duced as a result of secondary anode processes, non-metallic inclusions, as well as further im purities of copper insoluble in the sulfuric acidic medium. At the end of the electrolysis, the anode sludge is collected, washed, its acidic pH is neutralised, then the sludge is filtrated, dried, the precious metals are separated with one of the specific precious metal retrieval methods, and the remaining blend of metals is processed with the metallurgical technology most suitable on the basis of its composition, which mostly means that it is returned to the beginning of the copper metallurgical process. The separated precious metals are refined, i.e. highly pure gold, silver, platinum, palladium is produced. In case of precious metals that are on aluminium, zinc- aluminium (zamak), or chrome-nickel steel carriers, these are lost during the copper metallur gical processing, they become part of the converter slag.

The US 2006/037889 A1 and the US 2004/103512 A1 patent documents describe solutions close to the subject of the invention and its technological solution. The documents use dilute hydrochloric acid to recover precious metals, which is then saturated with copper sulphate, and an electrostatic field is established with variable frequency and current intensity. The procedure does not use direct contacting. The base materials of the treatment are crushed printed circuit boards; the copper, nickel, tin, and lead, which compose the metal part of the circuits, are dis solved in a dilute acidic solution. Therefore, the great disadvantage of such methods is the pro duction of wastewater containing non-ferrous metals. Some of the dissolved metals hydrolyse, producing tin- and lead hydroxide, the by-products of which passivate the surfaces, inhibiting further dissolution, therefore blocking the process of recovering the precious metals.

Similarly to the current invention, the one described in announcement No WO2015130965 also implements electrochemical treatment in sulfuric acidic medium. The above announcement uti lises sulfuric acid or phosphorous acid with the addition of a small amount of nitric acid. Alt hough the carrier is recovered to a relatively large percentage in the process, a part of the pre cious metal plating and other alloy materials composing the plating dissolve in the acid mixture. By contrast, the invention in the current submission keeps both the carrier and the precious metal plating intact; these are not the materials that are primarily dissolved during the process.

The invention described in announcement No RU2258768 also implements electrochemical processes for the recovery of precious metals. In the above announcement the precious metals are dissolved by electrochemical processes, and separated from the other components with thi ourea complexing agent. This technological solution is similar to the cyanide process, but clearly distinguishable from the invention of the current submission, because we intend to retain both the carrier and the precious metal plating in solid form. The precious metals are not at all dissolved in our procedure, while the carrier is dissolved only to a negligible extent.

The invention described in announcement No EP1964936 also implements dissolution for the retrieval of precious metals. In the above announcement the waste is ground, metals are selec tively dissolved using various solvents, and then the precious metals are separated from the other components with organic solvents. This solution can be clearly distinguished from the invention in the current submission, because we intend to retain both the carrier and the precious metal plating in solid form, and in our procedure the precious metals are not at all dissolved, while the carrier is dissolved only to a negligible extent.

Unlike the known methods of precious metal recovery described above, our current procedure enables recycling of not only the precious metals, but of the carrier as well, in such a way that these metals do not have to be dissolved and then reduced back to metallic form again during the procedure. Therefore, the main materials may be physically separated in the procedure, which is an advantage with respect to energy consumption. The procedure is environmentally friendly and cost-effective, and there is less wastewater to be cleaned compared to other known solutions. The sulfuric acid used can be cleared of impurities, and therefore can be recycled in the process. As a result, less acid is required for the dissolution of metals, the emission of haz ardous waste is minimised, and the procedure can be performed with relatively small energy consumption, compared to its output.

It is known that the galvanic layer is almost never applied directly onto the carrier in electronic components. Normally, the carrier is pure copper or its alloy, but other metals and metal alloys are often used as well. If the carrier is not copper or its alloy, it is over-layerd with copper or copper alloy before nickel plating. The process is uniform after this step: a nickel plating is placed on the copper or copper alloy (or copper or copper alloy plating) before the precious metal layer. This can be explained by the molecular structure of copper, nickel, and precious metals and the proportions between their relative atomic radiuses. In the absence of the inter mediate nickel layer, the diffusion of gold and copper atoms at the phase boundary is, due to the same metal grid structure and the closeness of their relative atomic radiuses, almost unim peded; the copper diffuses through the extremely thin precious metal layer to the surface of the gold layer, where it oxidizes within a relatively short period of time, cancelling the desired effects that the precious metal plating is supposed to provide: protection against corrosion and good conductivity. However, the diffusion of copper through the nickel-containing intermediate layer is inhibited due to the larger atomic radius of nickel, therefore the nickel-containing layer prevents the diffusion of copper, the mixing of copper and the precious metal, and the diffusion of copper to the surface of the precious metal layer.

It is known that in a sulfuric acid medium the metal connected as anode dissolves during elec trolysis, therefore copper and nickel can dissolve as well. The ion concentration of the electro lyte essentially determines the electrochemical processes of the anode. Dissolution of the anode metal is significantly affected by the concentration of the sulfuric acid, the temperature, and the concentration of copper ions in the electrolyte. Equation (1) shows the dissolution of copper in hot, concentrated sulfuric acid. Different reactions will take place depending on the concentra tion of the sulfuric acid and the temperature (2), a balance characteristic to the given parameters will develop, and a layer containing Cu _x O and CuS will be formed, which passivates the sur face, significantly hindering further dissolution. Cu + 2 cc. H2SO4 = CuS0 ₄ + 2 H2O + S0 ₂ † (1)

4 Cu + 4 H2SO4 = 3 CuS0 ₄ + CuS + 4 H ₂ 0

5 Cu + 4 H2SO4 = 3 CuS0 ₄ + Cu ₂ S + 4 H ₂ 0

Cu + 2 H2SO4 = CuS0 ₄ + S0 ₂ + 2 H2O

(2)

Cu + H2SO4 = CuO + S0 ₂ + H2O

2 Cu + 2 H2SO4 = Cu ₂ S0 ₄ + S0 ₂ + 2 H2O

2 Cu + H ₂ SO ₄ = Cu ₂ 0 + S0 ₂ + 2 H ₂ O

The layer formed by copper oxide and copper sulphide can be mechanically removed, but if not removed, the oxide and sulphide layer can protect the copper carrier from further dissolution. Nickel-containing galvanic layers dissolve well when connected as anodes in concentrated sul furic acidic medium (3). Similarly to copper, secondary reactions occur here as well, but the intermediate products (sulphides and oxides) have a greater tendency to dissolve as nickel sul phates in a sulfuric acidic medium.

Ni + H2SO4 = N1SO4 + H ₂ † (3)

From our perspective, the electrochemical processes on the anode are most beneficial, if the reaction of the copper surface proceeds only until passivation, and the intermediate layer be tween the precious metal and the carrier can be fully removed from the surface. The sludge produced on the anode and settled at the bottom of the electrolyte contains all the precious metals, as well as any other compound that might be produced in the reaction.

The base materials of the procedure are primarily electronic devices that are partly layered with precious metals. The main mass of the base material to be processed can be copper-based (cop per or brass), iron-based (corrosion resistant steel), or light metal alloy (aluminium or zinc al loy); important is that there is a nickel-containing layer under the precious metal-containing plating, and if the main mass is not copper or copper alloy, then there is a copper or copper alloy layer under the nickel-containing layer as well. Apart from recovering gold efficiently, the procedure can be applied for the recycle of other precious metals or precious metal alloys (e.g. silver, gold-palladium, gold-nickel, gold-cobalt, etc.). The essence of the procedure is the electrochemical removal of the diffusion-inhibiting nickel- containing intermediate layer from between the copper or copper-containing carrier or plating and the precious metal-containing plating.

The electrolyte solution used in our invention is a water-based electrolyte that contains 695- 1,760 g/1 sulfuric acid. In one suitable form of implementation, a sulphate salt mix can be used as additive to improve the conductivity of the electrolyte; in the other suitable form of imple mentation, the procedure can be performed without additive, using only water and sulfuric acid. The optimal temperature range of the electrolyte is 25-60 °C. The applied concentration ranges enable the processing of the above-described base materials in the cell.

The process of the dissolution of copper in concentrated sulfuric acid is well described by sci ence. For example, in the case of a copper carrier (4):

Cu + H2SO4 CuO + H2O + S0 ₂ (4)

CuO + H2SO4 C11SO4 + H2O

Performing the electrolysis in the electrolyte solution with the composition developed in the experiments ensures that the carrier or the copper or copper alloy protecting the carrier, which will get into contact with the electrolyte, is only involved in the electrochemical process until passivation and that the nickel-containing intermediate layer can be removed from the surface of the base material functioning as the anode, while the precious metal-containing layer does not react with the solution and gets into the anode sludge during dissolution of the nickel-con taining layer and the passivation of the copper-containing surface.

Products of the electrochemical process are the fine anode sludge that develops through the separation of the precious metal layer and contains nickel and copper compounds not dissolved in the electrolyte, the remaining carrier, and the sulfuric acid medium containing nickel and copper compounds.

The precious metal-containing particles can be separated from the electrolyte solution by peri odic or continuous filtration technology. Our invention prevents the production of large amounts of wastewater by impeding the dissolution of the carrier, and, at the end of the process, the valuable carrier can be reused after the removal of the plating layers. The precious metal content of the sludge can be separated from the other components using current technology (e.g. dissolution with aqua regia, followed by the selective reduction of gold). In one suitable form of implementation, the base material to be processed is connected as anode using a copper-based, i.e. electrically conductive basket, which practically does not participate in the electrochemical reaction for the reasons described above.

For the process to be successful, it is important to maintain a continuous electric connection between the base material and the electrode basket. Due to the varying geometric characteris tics, different current densities may develop in different parts of the base material, resulting in the disproportionate dissolution of the parts. Current density, and thus dissolution, can be equal ised (in case this is required due to the shapes of components) through the intermittent or con tinuous movement of the anode basket or through an external vibration system. In one suitable form of implementation, this can be achieved through the oscillating movement of the anode basket or the ultrasound treatment of the electrolyte: smaller base materials will move and their active surface will rearrange faster, therefore the speed at which the gold layer is removed from the surface will increase.

The precious metal layers dissociating into the electrolyte solution can physically remain con nected to the carrier by simply sticking to the surface. In one beneficial form of implementation, the efficiency of the removal can be improved by circulating the electrolyte solution and filter ing out small solid particles. The intense movement of the solution also facilitates the detach ment of particles sticking to the surface. In one suitable form of implementation, the particles sticking to the surface, which therefore reduce the surface that can participate in the reaction, can be lifted out together with the anode basket and removed by washing with water. As the rinsed particles may also contain precious metals, the washing water has to be filtered. After washing, the anode basket, together with the raw material, is placed back into the electrolysis cell.

In order to control the voltage or the applied current intensity, a power supply providing direct current can be used during electrolysis. In case of adjustment to current, the cell voltage may continuously change, which also indicates the changes with time in the processes taking place on the electrodes. Apart from the parts with fixed resistance (conductivity of electrolyte, metal connection points), the cell voltage depends on the potentials developing on the anode and the cathode. For a given current density, the current density on the surface of the base material in the cell is basically determined by the specific surface area of the material actively participating in the process. In order to monitor and control the operation of the system, a data collection device may be installed that, apart from the basic data concerning cell voltage, current density, and temperature, is also suitable for measuring the potential on the electrodes, which could provide information about the ongoing processes in the cell. We know from the data collected, that at the end of the process, ever increasing anode potential values and current intensity values decreasing to zero will be required to reach the desired current density, which clearly indicates the complete removal of the soluble nickel-containing layer and the passivation of the carrier. Below the sulfuric acid concentration of 695 g/L, the electrolysis will continue after the disso lution of the nickel layer with the dissolution of the non-passivated copper-containing surface and subsequently the bulk phase (i.e. the carrier), therefore the end of the dissolution of the nickel-containing layer cannot be detected on the basis of the decrease in current intensity to zero and the steep increase in voltage. Above the sulfuric acid concentration of 1,760 g/L, a passivated protective layer cannot form either, as the concentrated sulfuric acid dissolves the components of that layer as well, therefore the end of the electrolysis of the nickel -containing layer cannot be detected, and retention of the carrier cannot be ensured.

The objectives of the invention can be achieved by the procedure described in Claim 1, and its suitable methods of implementation are described in the subclaims.

The invention is described in detail with reference to the enclosed drawings, in which

- image 1 shows the procedure in a flow chart,

- image 2 shows the treatment reactor used for electrolysis.

Stages and steps of the procedure of our invention:

Step 1: Our procedure is an electrochemical treatment that is implemented in a sulfuric acidic medium. The electrolyte solution contains 695-1,760 g/L sulfuric acid and optionally 20-100 g/L sulphate salt mixture that is typically based on sodium sulphate.

Step 2: The raw materials are pre-sorted in order to introduce materials to the procedure with characteristics described in the beginning of the submission. Other materials (e.g. thermoplastic materials, organic impurities) might react with the sulfuric acid medium, which could result in unwanted by-products and a disadvantageous alteration of the concentration of the sulfuric acid. The metal layer has to be accessible, in order to enable sufficient contact between the basket assisting the process and the raw material. The electrolysis tanks utilised in the procedure are made of plastic that is resistant to concentrated sulfuric acid, e.g. polypropylene. The structure of the tank is shown in image 1. The tank (2) is rectangular with a double wall that enables the control of the solution’s temperature by the use of the cooling water entering through taps (5) and exiting through tap (6). The solution has to be tempered due to the exothermic effect taking place in electrochemical processes and in an electrolyte permeated by electricity, as well as due to the environmental temperature. Higher temperatures negatively affect the operation of the cell, because they increase the possibility of the carrier dissolving and the electrolyte foaming with the gases produced on the electrodes, which are disadvantageous and even dangerous from technological point of view.

Step 3: For the electrolysis, the base material is connected as the anode, while an electrically conductive material, that is inert under the applied circumstances, is connected as the cathode. The selected metal-containing waste is placed in the anode basket (7). During the procedure, the anode basket (7) contains the raw material, and the material and structure of the anode basket (7) ensures electronic contact, but is insoluble in the electrolyte. An external power source is connected to the electrodes. The anode basket (7) containing the electronic waste is sunk into the sulfuric acid medium. The electrodes (4) on the long side serve as the cathodes in the electrochemical procedure. The cathode is made of a copper layer that sinks into the elec trolyte solution; it can be replaced with a titanium-based electrode that is chemically more re sistant than copper. The anode is the anode basket (7) containing the raw material to be pro cessed; the anode basket (7) sinks into the tank (2), it is positioned with its rim at the short side of the tank, and is supported by the electrical connection (3). The proportion between the tank (2) and the anode basket (7) was determined through experiments, taking into consideration the optimal output, the aspects of manageability, and the geometric characteristics of the base ma terial to be processed. Other than the example shown, the geometric configuration of the anode basket can also be cylindrical, enabling the rotation of the basket, which can be an advantage if the base material is to be moved.

An external power source is connected to the electrodes. The initial current density of the pro cedure is set between 50-200 A, depending on the quantity, geometric properties, and specific surface area of the base material. The voltage ensured by the direct current provides, apart from the voltage drop on fixed parts (electricity feed, resistance of wires and the electrolyte), the overvoltage necessary for the reactions taking place on the two electrodes. The voltage con nected to the electrodes is determined by the rectifier equipment, but it is min. 0.23 V, which is the difference between the electrode potential of the H ₂ /H ₃ 0 ⁺ and the Ni/Ni ²⁺ systems. The surface of the cathode is constant, thus so is the current density on its surface. In case of the anode, current density and current directions depend on the active surface of the base materials momentarily participating in the electrochemical process. In case of smaller raw materials, the movement of raw materials is important to ensure that the electrochemical reaction of the in termediate nickel-containing layer is continuous, in order to maintain a relatively stable voltage and current density. After the removal of the precious metal-containing layer and the dissolution of the nickel-containing layer, the still active copper-containing surfaces (under the above-de scribed layers) are passivated through the electrochemical treatment performed in the sulfuric acid medium of specific concentration, and a non-conductive layer develops on the surfaces. A continuous increase can be experienced in the cell voltage, and the power consumption becomes more and more impeded. By lifting out the basket, a rinsing cycle with water can be included, which removes all particles and materials physically attached to the surface.

Main reactions taking place on the electrodes (5 and 6): cathode (5)

anode (6)

The SO2 gas that is being produced is neutralised after extraction in an alkaline aqueous washer. If the nickel-containing intermediate layer is dissolved and the precious metal-containing par ticles detach from the surface into the electrolyte, they will form a sediment. No precious metal layer can remain on the surface of the base material remaining in the basket. In case of smaller base materials, which have a significant surface area, the particles physically attached to the surface can be efficiently removed by washing with water at the end of the cycle.

Step 4: With the complete dissolution of the nickel-containing layer, the next electrochemical process would be the dissolution of the copper-containing layer or carrier, which is impeded by the passivation layers developing under the given circumstances. The cell voltage steeply in creases and the current intensity temporarily decreases to zero, which indicate the end of the electrochemical process and the processing of the base material, as well as the need to replace the base material in the anode basket (7). Step 5: The next step of the procedure is to remove the solid components from the electrolyte, for which the state of the art methods include decantation and fractional or continuous filtration. This way, the electrolyte solution can be cleaned from solid particles and reused.

The chemical composition of the electrolyte solution can be monitored periodically by deter mining the concentration of the acid and the amount of dissolved ions (Cu, Ni). The hydrogen ions exiting in the cathode process can be replaced with concentrated sulfuric acid. The speci fied concentrations have to be maintained for the successful operation of the process.

Step 6: The product of the electrochemical procedure and the subsequent filtration is the sludge that contains the precious metals, from which the precious metals can be separated using com mon technical methods (e.g. dissolution with aqua regia and subsequent reduction with sodium sulphate), and then recovered in the required purity.

The procedure is suitable for the recovery of precious metals with at least 95% purity, and it retains more than 95-98% of the mass of the carrier, depending on its mass/surface ratio. The procedure is suitable for processing bulk and pre-sorted electronic components that fit the char acteristics described in the beginning of the submission.

The advantage of this procedure compared to other technologies used for the retrieval of pre cious metals is its lower demand for solvent and energy, the absence of the need for shredding the base material, and the preservation of the solid metallic state of the plating containing the precious metal and the carrier throughout the procedure. The carrier cleaned from the nickel- containing layer and the precious metal-containing plating is another product of the technology, which can be marketed in its pure form.

Several methods are available for creating different gold and gold alloy layers on different car riers, therefore the in-process or amortisation raw materials that could be the base materials for our technology can appear in different shapes and forms. The advantage of the procedure we developed is its flexibility regarding the base material, therefore it can be used to process a great variety of existing and continuously evolving electronic components.

Example 1: Processing of electronic metal waste from the telecommunications industry (assem bly line waste of cell phone chip production). The raw material is a copper alloy carrier with a nickel and then a gold layer on its surface. With the selective dissolution of the nickel layer from the copper surface, the gold layer can be separated and extracted from the anode sludge. Steps of the technology:

1. Sulfuric acid with the concentration of 1,300 g/L is added into the reactor tank.

2. The waste pieces, which are typically 50x150 mm in size, are strung onto the copper anode console that has been designed for this purpose, and the anode is placed into the reactor tank and is completely covered with the electrolyte. Contact is ensured by the proper design of the electrode. The cathodes, also made of copper, are placed into the opposite side of the tank.

3. The current intensity is set to 110 A on the rectifier. After starting the device, the elec trochemical process begins, and the voltage continuously increases until the 10 V limit. After reaching the maximal voltage, the current intensity slowly decreases, as the sur face participating in the process is passivated. During the process, the temperature of the reactor is kept at about room temperature (20 °C) by the cooling agent (preferably water) circulated in the cooling jacket. Dissolution is not yet complete at this point due to superficial impurities, therefore the anode basket is placed into a rinsing tank, where the surface of the material is cleaned with water spray. The anode basket is subsequently placed back into the electrolyte solution, and the electrolysis is continued.

4. Complete dissolution can be ascertained, if upon placing the rinsed material back into the electrolyte the voltage immediately jumps to 10 V, but there is no current consumed and no further reaction takes place.

5. The reactor tank is subsequently drained off through the appropriate tap, the electrolyte is filtered, and the anode sludge is retained on a filter cloth.

6. The precious metal is recovered from the gold-containing anode sludge using common technological methods, then it is smelted and cast into a product of high purity.

Example 2: Dissolution of the precious metal-containing galvanic layer of electronic waste from the automotive industry (gilded connector), recovery of the precious metal content

Gold and nickel galvanic layer can be found on the workpiece. With the selective dissolution of the latter from the copper surface, the gold layer can be separated and extracted from the anode sludge. Steps of the technology:

1. Sulfuric acid with the concentration of 1,200 g/L is added into the eluent tank. 2. The workpieces are placed into the anode basket, which is then placed into the eluent tank and completely covered by the electrolyte. Contact is ensured by the proper design of the anode basket and its movement. The cathodes, made of copper, are placed into the opposite side of the tank.

3. The current intensity is set to 110 A on the rectifier. After starting the device, the elec trochemical process begins, and the voltage continuously increases until the 10 V limit. After reaching the maximal voltage, the current intensity slowly decreases, as the sur face participating in the process is passivated. During the process, the temperature of the reactor is kept at around room temperature (20 °C) by the cooling agent (preferably water) circulated in the cooling jacket. Dissolution is not yet complete at this point due to surface impurities, therefore the anode basket is placed into a rinsing tank, where the surface of the material is rinsed with water. The anode basket is subsequently placed back into the electrolyte solution, and the electrolysis is continued.

4. Complete dissolution can be ascertained, if upon placing the rinsed material back into the electrolyte the voltage immediately jumps to 10 V, but there is no current and no further reaction takes place.

5. The eluent tank is subsequently drained off through the appropriate tap, the electrolyte is filtered, and the anode sludge is retained on a filter cloth.

6. The precious metal is recovered from the gold-containing anode sludge using common technological methods, then it is smelted and cast into a product of high purity.

Example 3: Dissolution of the precious metal-containing galvanic layer from coaxial tube con nector components electronic waste (gilded yellow copper or gilded bronze) to retrieve the pre cious metal content

Gold and nickel galvanic layer can be found on the workpiece. With the selective dissolution of the latter from the brass or bronze surface, the gold layer can be separated and extracted from the anode sludge. Steps of the technology:

1. Sulfuric acid with the concentration of 1,600 g/L is added into the eluent tank.

2. The workpieces are strung onto the copper anode console that has been designed for this purpose, and the anode is placed into the eluent tank and is completely covered with the electrolyte. Contact is ensured by the proper design of the electrode. The cathodes, also made of copper, are placed into the opposite side of the tank. The current intensity is set to 110 A on the rectifier. After starting the device, the elec trochemical process begins, and the voltage continuously increases until the 10 V limit. After reaching the maximal voltage, the current intensity slowly decreases, as the sur face participating in the process is passivated. During the process, the temperature of the reactor is kept at about room temperature (20 °C) by the cooling agent (preferably water) circulated in the cooling jacket. Dissolution is not yet complete at this point due to superficial impurities, therefore the anode basket is placed into a rinsing tank, where the surface of the material is rinsed with water. The anode basket is subsequently placed back into the electrolyte solution, and the electrolysis is continued.

Complete dissolution can be ascertained, if upon placing the rinsed material back into the electrolyte the voltage immediately jumps to 10 V, but there is no current consumed and no further reaction takes place.

The eluent tank is subsequently drained off through the appropriate tap, the electrolyte is filtered, and the anode sludge is retained on a filter cloth.

The precious metal is retrieved from the gold-containing anode sludge using common technological methods, then it is smelted and cast into a product of high purity.

Reference marks

1 - electrolysis equipment

2 - tank

3 - electrical connection

4 - katod (elektrod)

5 - entering through tap

6 - exiting through tap

7 - anode basket

Step 1: filling of the the electrolysis tank with a sulfuric acid medium

Step 2: carrier is cleaned and placed into the electrolysis tank

Step 3: an external power source is connected to the anode and cathode electrodes

Step 5: the precious metal is separated from the other components of the produced sludge using a physical or a chemical procedure

Step 6: the precious metal is separated from the other components of the sludge using a physical or a chemical procedure