RU2187580C1 - Technology of extraction of gold from golden coat on substrate of copper or its alloy - Google Patents

Abstract

FIELD: electrolytic extraction of gold from scrap of electron and electrical articles with substrates of copper or its alloy. SUBSTANCE: golden coat is subjected to electrolytic solution in single-component electrolyte containing sulfuric acid with concentration of 93.5-95.5 per cent by mass with starting voltage 3.0-4.0 V at room temperature. Precipitate of hydroxide of trivalent gold formed in process of electrolysis is separated from electrolyte by centrifugation and is calcined at temperature of 200-300 C with winning of metal gold. Given technology produces result consisting in winning of metal gold with purity not less than 99.8 per cent by mass and in extraction of 99.1-99.2 % of gold. EFFECT: improved efficiency of proposed technology. 3 cl

Description

 The present invention relates to the field of noble metals, mainly gold, and can be used in the electrolytic extraction of gold from scrap electronic and electrical products.

 When disposing of electronic and electrical products with the release of scrap containing gold coatings based on copper or its alloys, the problem arises of the selective extraction of gold without destroying the base and the intermediate layer, usually accompanying a copper substrate, for example, nickel, to obtain high-purity metallic gold as the final product.

A known method of extracting gold from a gold coating on a substrate of copper or its alloy (see US patent 3788958, N. CL. 204-146, 1974), including carrying out electrolysis in an electrolyte containing, about. %: 75.0-93.5 H ₂ SO ₄ , 20.0-6.0 alcohol and 5.0-0.5 aromatic nitrocarbon compounds, with the transfer of gold from the coating into solution at a temperature of 20-60 ^o C and voltage 4-12 V.

 The disadvantage of this method is that in the used multicomponent electrolyte, the gold is in a dissolved state and it can be removed from the electrolyte only by additional chemical treatment. At the same time, some metals, usually accompanying a copper substrate, for example nickel, pass into the electrolyte, which negatively affects the purity of the extracted gold. In addition, one of the components of the electrolyte (aromatic nitrocarbon compound) is a potent toxic substance.

There is also known a method of extracting gold from a gold coating on a substrate of copper or its alloy (see US patent 4539087, N. CL. 204-146, 205-717; 1985), including carrying out electrolysis in an electrolyte containing, about. %: 40-60 H ₂ SO ₄ , 30-60 H ₃ PO ₄ and 20-30 organic acids, at a current value determined during the electrolysis, and electrolysis is stopped when the current value becomes less than a predetermined threshold, which is significant (in 100 times) lower than the current value at the beginning of electrolysis.

 The disadvantage of this method is that the gold is in the used multicomponent electrolyte in a dissolved state and it can be removed from the electrolyte only by additional chemical treatment. At the same time, some metals, usually accompanying a copper substrate in the form of an intermediate layer, for example, nickel, pass into a multicomponent electrolyte, which negatively affects the purity of the extracted gold.

 The present invention is directed to solving the problem of selective electrolytic extraction of gold from a gold coating on a substrate of copper or its alloy with the technical result of obtaining high-purity metallic gold without additional chemical treatment of the electrolyte.

 The technical result is achieved by the fact that in the method for extracting gold from a gold coating on a substrate of copper or its alloy, comprising dissolving the gold coating by electrolysis in an electrolyte containing sulfuric acid and recovering gold from an electrolyte, according to the invention, the electrolysis is carried out using an electrolyte from sulfuric acid concentration 93.5-95.5 wt.% At an initial voltage of 3-4 V with the formation of a precipitate of trivalent gold hydroxide, which is separated from the electrolyte and calcined to obtain metallic gold.

 The technical result is also achieved by the fact that the electrolysis is carried out at room temperature.

 To achieve a technical result, it is directed that the precipitate of trivalent gold hydroxide is separated from the electrolyte by centrifugation.

The achievement of the technical result also aims that the calcination of the precipitate of hydroxide of trivalent gold is carried out at 200-300 ^o C.

После достижения возле анода определенной концентрации сульфата одновалентного золота начинает протекать окислительно-восстановительная реакция между концентрированной серной кислотой и сульфатом одновалентного золота. При этом золото окисляется до трехвалентного состояния, а сера, содержащаяся в серной кислоте, восстанавливается с шестивалентного до четырехвалентного состояния и образующаяся газообразная двуокись серы начинает выделяться из электролита. Этот процесс можно представить в виде химической реакции

Далее при достижении определенной концентрации сульфат трехвалентного золота начинает взаимодействовать с водой, содержащейся в концентрированной серной кислоте, с образованием нерастворимого гидроксида трехвалентного золота. При этом электролит начинает темнеть. Этот процесс можно представить в виде химической реакции

Суммируя реакции (2-4), получаем итоговую реакцию

Из этой реакции следует, что для окисления 1 г металлического золота с образованием гидроксида трехвалентного золота необходимо 0,091 г воды. Так как в 1 см³ серной кислоты концентрацией, например, 95 мас.%, содержится 0,092 г Н₂O, то использование в качестве электролита серной кислоты концентрацией 93,5-95,5 мас.% вполне обеспечивает протекание электрохимического снятия золотого покрытия.The invention consists in the following. When voltage is applied to the anode, the electrochemical dissolution of the gold coating begins. In this case, gold is oxidized to a monovalent state, and monovalent gold sulfate is formed in the electrolyte near the anode. At the same time, the restoration of the equivalent amount of hydrogen cations present in the electrolyte due to the partial dissociation of sulfuric acid begins at the cathode. The resulting gaseous hydrogen is released from the electrolyte. This process can be represented as an electrochemical reaction.
2Au-2e = 2H ⁺ 2e, (1)
which is equivalent to the reaction

After reaching a certain concentration of monovalent gold sulfate near the anode, a redox reaction begins between concentrated sulfuric acid and monovalent gold sulfate. In this case, the gold is oxidized to the trivalent state, and the sulfur contained in sulfuric acid is reduced from the hexavalent to the tetravalent state and the resulting gaseous sulfur dioxide begins to be released from the electrolyte. This process can be represented as a chemical reaction

Further, when a certain concentration is reached, trivalent gold sulfate begins to interact with water contained in concentrated sulfuric acid, with the formation of insoluble hydroxide of trivalent gold. In this case, the electrolyte begins to darken. This process can be represented as a chemical reaction

Summing up the reactions (2-4), we obtain the final reaction

From this reaction it follows that for the oxidation of 1 g of metallic gold with the formation of trivalent gold hydroxide, 0.091 g of water is required. Since 1 cm ^{3 of} sulfuric acid with a concentration of, for example, 95 wt.% Contains 0.092 g of H ₂ O, the use of sulfuric acid as a electrolyte with a concentration of 93.5-95.5 wt.% Fully ensures the course of electrochemical removal of the gold coating.

 The use of a one-component electrolyte from sulfuric acid with a concentration of 93.5-95.5 wt.% Provides selective anodic dissolution of the gold coating and the formation of a fine precipitate of trivalent gold hydroxide. When the concentration of sulfuric acid is less than 93.5 wt.% There is a side electrolysis of water, resulting in a decrease in the yield of the target product in current.

 The implementation of electrolysis at a voltage of 3-4 V provides selective and intense anodic dissolution of gold. At voltages greater than 4 V, partial anodic dissolution of the metal base and solder occurs. At a voltage of less than 3 V, the current decreases sharply, which leads to an increase in the duration of removal of the gold coating.

 The implementation of electrolysis at room temperature provides more favorable conditions for the process, and also reduces the likelihood of anodic dissolution of the metal base and solder.

 The use of centrifugation provides almost complete separation of the precipitate of gold hydroxide from the electrolyte. The first washing of the precipitate with water is also carried out by centrifugation.

Calcination of the washed gold hydroxide at a temperature of 200-300 ^o With provides metal gold. At a temperature of less than 200 ^o With the resulting gold may contain an admixture of monovalent gold oxide. Temperature above 300 ^o With is not advisable due to excessive energy intensity of the process.

 The implementation of electrolysis followed by calcination of gold hydroxide in accordance with the above process conditions allows you to selectively extract gold from gold coatings on substrates of copper or copper alloys to obtain metallic gold of high purity.

 The above features and advantages of the claimed invention can be more clearly explained by the following examples.

 In all examples, electrolysis is carried out in an electrolytic cell, the casing of which is a glass beaker with a capacity of 0.7 L. As a cathode, a strip of sheet molybdenum 0.3 mm thick and 50 mm wide in the form of an open ring, which is inserted into the cup body, is used. Due to its considerable elasticity, the molybdenum ring fits snugly against its walls. By means of a copper current supply, the molybdenum ring is connected to the negative pole of the direct current source. A perforated fluoroplastic cup with a diameter of 4.5 cm and a height of 5.0 cm was used as an anode basket into which gold-coated products are loaded. To make electrical contact, the fluoroplastic cup contains a central copper electrode and thin strips of metal lead fixed to the inner wall a cup. The copper electrode is connected to the positive pole of the current source. Before electrolysis, 0.5 l of sulfuric acid of a given concentration is poured into the casing and the anode basket is immersed in it. An initial voltage of 3-4 V is set with an open circuit. When the circuit is closed, the voltage at the terminals drops sharply, and the current reaches its maximum value. As the gold coating dissolves, the current decreases and the voltage increases. With the complete removal of the gold coating, the voltage value exceeds the initial one by 0.3-0.6 V, and the current value decreases by 10-15 times.

 After electrolysis, the anode basket is removed from the electrolyte and repeatedly immersed in a vessel with water, it and its products are deposited from fine particles of gold hydroxide deposited on them. Then these particles are filtered off and dried to give product 1. To extract the gold hydroxide precipitate, the electrolyte is centrifuged at a speed of 3000 rpm for 15 minutes. After decantation of the electrolyte, the gold hydroxide precipitate is washed with water and dried to obtain product 2. Products 1 and 2 are combined and calcined to obtain metallic gold.

 Example 1

Gold is extracted from the gold coating on the brass parts of the connectors of the electronic boards. In these details, gold is deposited on an intermediate nickel layer. The total weight of the parts 16.6 g with a gold content of 1.2 wt.%. Sulfuric acid with a concentration of 95.5 wt.% Is used as an electrolyte. The electrolysis is carried out at room temperature and an initial voltage of 3 V. After the circuit is closed, the current value is 0.7 A, and the voltage drops sharply to 2.4 V. At the cathode, hydrogen begins to be released immediately. At the anode, gas evolution is initially absent, then 1 minute after the start of electrolysis, intense release of SO ₂ begins and the electrolyte stains in the dark color near the anode. The electrolysis process is completed when gas evolution ceases at the anode. In this case, the current decreases to 0.05 A, and the voltage rises to 3.4 V. The electrolyte turns black. The duration of electrolysis was 45 minutes The separated gold hydroxide is calcined at a temperature of 250 ^o C. The weight of the obtained metallic gold is 0.198 g, purity - 99.8% with an impurity content of wt.%: Cu - 0.1; Ni is 0.03; Pb - 0.01; Sn is 0.03. Gold recovery - 99.2%. On the surface of washed and dried parts, there are no signs of gold plating and corrosion.

 Example 2

Gold is extracted in accordance with the conditions of Example 1. The difference is that the initial voltage is 4 V and the total weight of the brass parts is 18.2 g. After the circuit is closed, the current is 1 A and the voltage is 3.5 V. The duration of the electrolysis until the SO ₂ evolution ceased was 29 min, while the current reached 0.07 A and the voltage was 4.5 V. The separated gold hydroxide was calcined at a temperature of 300 ^o C. The weight of the obtained metallic gold was 0.217 g, purity 99 , 8% when the content of impurities, wt.%: Cu - 0.1; Ni is 0.06; Pb - 0.01; Sn is 0.03. Gold recovery - 99.2%. On the surface of washed and dried parts, there are no signs of gold plating and corrosion.

 Example 3

Gold is extracted in accordance with the conditions of Example 1. The difference is that the regeneration is carried out from the gold coating on copper coaxial connectors with a total weight of 17.4 g and a gold content of 1 wt. % As the electrolyte, sulfuric acid of a concentration of 93.5 wt. % After the circuit is closed, the current value is 0.75 A and the voltage is 2.3 V. The duration of electrolysis until the SO ₂ emission ceases is 30 minutes, while the current reaches 0.05 A and the voltage is 3.4 V. The allocated hydroxide gold is calcined at a temperature of 200 ^o C. the Weight of the obtained metallic gold is 0.173 g, purity - 99.9% when the content of impurities, wt. %: Cu - 0.006; Pb - 0.01; Sn is 0.01. Gold recovery is 99.3%. On the surface of washed and dried parts, there are no signs of gold plating and corrosion.

 In examples 4-7, the extraction of gold from the gold coating is carried out at exorbitant values of the process parameters.

 Example 4

Gold is extracted in accordance with the conditions of Example 1. The difference is that the initial voltage is 2.5 V. The total weight of the brass parts is 17.5 g. After the circuit is closed, the current is 0.35 A and the voltage is 2, 4 V. The duration of the electrolysis until the termination of the release of SO ₂ was 68 min, while the current reached 0.05 A and the voltage was 2.9 V. The recovered gold hydroxide was calcined at a temperature of 300 ^o C. The weight of the metallic gold obtained was 0.208 g. purity - 99.9% when the content of impurities, wt.%: Cu - 0.03; Ni is 0.01; Pb - 0.006; Sn is 0.03. Gold recovery is 98.9%. On the surface of washed and dried parts, micro-traces of gold plating are observed.

 Example 5

Gold is extracted in accordance with the conditions of Example 1. The difference is that the initial voltage is 4.5 V. The total weight of the brass parts is 17.1 g. After the circuit is closed, the current is 1.5 A and the voltage is 3, 9 V. The duration of electrolysis until the termination of SO ₂ evolution was 18 minutes, while the current reached 0.1 A and the voltage was 5.1 V. The weight of the metal gold obtained was 0.204 g, purity - 99.1% with an impurity content, wt.%: Cu - 0.4; Ni is 0.1; Pb - 0.1; Sn is 0.3. Gold recovery is 99.1%. There are no traces of gold plating on the surface of the washed and dried parts, but micro-traces of corrosion are observed.

 Example 6

 Gold is extracted in accordance with the conditions of Example 3. The difference is that sulfuric acid with a concentration of 90 wt.% Is used as an electrolyte. The weight of the copper coaxial connectors is 17.0 g. After the circuit is closed, the current is 0.85 A and the voltage is 2.7 V. At the same time, strong gas evolution starts at the cathode and anode, which is explained by the electrolysis of water. Upon reaching a current value of 0.1 A (voltage 3.5 V), electrolysis was stopped. The duration of electrolysis was 50 minutes The weight of the obtained gold is 0.167 g, purity - 97.4% when the content of impurities, wt.%: Cu - 1.25; Pb - 0.3; Sn is 1.0. Gold recovery is 95.7%. On the surface of washed and dried parts, traces of gold plating and corrosion are observed.

 Example 7

Gold is extracted in accordance with the conditions of Example 1. The difference is that the temperature of the electrolyte is 45 ^o C. The total weight of the brass parts is 17.6 g. After the circuit is closed, the current is 1.1 A and the voltage is 2.2 B. The duration of the electrolysis until the termination of the release of SO ₂ was 15 minutes, while the current reached 0.05 A and the voltage was 3.3 V. The weight of the metal gold obtained was 0.210 g, purity 99.1% with an impurity content, wt. .%: Cu - 0.3; Ni is 0.1; Pb - 0.1; Sn is 0.3. Gold recovery is 99.1%. Traces of corrosion are observed on the surface of washed and dried parts.

 From the above examples it is seen that the claimed method allows for the selective electrochemical extraction of gold from scrap of electronic and electrical products without destroying the base from copper or its alloys to produce gold hydroxide in the electrolyte without further chemical treatment, after calcination of which metal gold with a purity of at least 99 , 8 wt.% When it is extracted 99.1-99.2%.

Claims (4)

 1. The method of extracting gold from a gold coating on a substrate of copper or its alloy, comprising dissolving the gold coating by electrolysis in an electrolyte containing sulfuric acid, and separating gold from the electrolyte, characterized in that the electrolysis is carried out using an electrolyte from sulfuric acid at a concentration of 93.5 -95.5 wt.% At an initial voltage of 3-4 V with the formation of a precipitate of trivalent gold hydroxide, which is separated from the electrolyte and calcined to obtain metallic gold.  2. The method according to claim 1, characterized in that the electrolysis is carried out at room temperature.  3. The method according to claims 1 or 2, characterized in that the precipitate of trivalent gold hydroxide is separated from the electrolyte by centrifugation. 4. The method according to any one of claims 1 to 3, characterized in that the precipitate is calcined at a temperature of 200-300 ^o C.