Method for recovering gold from waste circuit board

Abstract

The application discloses a method for recovering gold from waste circuit boards, comprising the following steps: washing the waste circuit boards, adding a first acid liquor and a first oxidizing agent, and performing oxidation pretreatment; adding a second acid liquor, a gold dissolving agent and a second oxidizing agent to the waste circuit boards after the oxidation pretreatment, performing leaching, and performing solid-liquid separation to obtain a gold-containing liquid; adding a displacement agent to the gold-containing liquid to completely displace gold in the gold-containing liquid, and performing filtration to obtain filter cake A; dissolving the filter cake A with aqua regia, adjusting the pH of the solution after removing nitrate with sodium hydroxide, and obtaining solution A; adding a reducing agent to the solution A until no more precipitate is generated, and performing filtration to obtain filter cake B; adding dilute nitric acid to the filter cake B, performing heating and boiling, then performing solid-liquid separation, and obtaining filter cake C; washing the filter cake C with deionized water until neutral, and drying to obtain sponge gold.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal recovery and solid waste resource utilization, and particularly relates to a method for recovering gold from waste circuit boards. BACKGROUND

[0002] The rapid development of science and technology and the continuous updating of products have led to the elimination and abandonment of a large number of electronic products. Among them, the circuit board, as an important component of electronic products, contains a large amount of precious metals and non-ferrous metals as well as toxic and harmful substances, and its recycling and harmless treatment is particularly important. Waste circuit boards usually contain 30% of plastics, 30% of refractory oxides and about 40% of metals. Due to different functions, the gold content of waste circuit boards also has a large difference, usually 50-300 grams / ton.

[0003] The existing process for recovering gold from waste circuit boards mainly includes pyrometallurgy and hydrometallurgy. Pyrometallurgy is to directly put the waste circuit board into a furnace for incineration to remove components such as resin, and to recover the metal in the remaining ash by refining, electrolysis and other methods. Since the waste circuit board contains toxic substances such as bromine, benzene, lead and mercury, toxic smoke containing dioxins, furans and polychlorinated biphenyl substances will be generated during combustion, causing serious pollution to the environment, and the recovery rate of valuable metals is low, which is a process that is prohibited by the state. Acid etching method is to treat waste circuit boards with strong oxidizing acid (mainly aqua regia) to oxidize the metal contained therein into ions into the solution, and then recover the metal by using the difference in reducing property of various metal ions through displacement or electrolysis process. Since strong corrosive chemicals are needed, this method is easy to cause secondary pollution. Selective leaching method mainly uses gold and silver and other precious metals to react with some complexing agents (such as cyanide) to generate water-soluble metal complex ions, realizing the separation of precious metals from ordinary metals, but the toxicity of cyanide limits the use of this method, and the leaching solution is difficult to recycle, which is easy to cause secondary pollution. Developing a suitable method and process for recovering gold from circuit boards can not only complete the disposal task of unqualified circuit boards, but also reduce environmental pollution, and at the same time, high-value-added precious metals can also be recovered. SUMMARY

[0004] In view of the problems in the prior art, the application provides a method for recovering gold from waste circuit boards, which can efficiently recover gold from waste circuit boards and obtain high-purity sponge gold. After the circuit board is washed, the method performs oxidation pretreatment, so that the gold on the surface of the circuit board is effectively exposed, and the subsequent gold dissolution efficiency is improved. The oxidation pretreated circuit board is subjected to gold leaching, the amount of acid, gold dissolving agent and oxidizing agent is controlled, so that the gold in the circuit board is selectively dissolved, the gold-containing liquid is obtained, the subsequent impurity removal cost is reduced, and the purity of the recovered gold is improved. Then, the gold in the gold-containing liquid is efficiently extracted by replacement by controlling the replacement conditions. The method does not need to burn or crush the waste circuit board, and has the advantages of low energy consumption, simple process, easy process control and the like.

[0005] To achieve the above object, the application adopts the following technical scheme:

[0006] The application provides a method for recovering gold from waste circuit boards, comprising the following steps:

[0007] Step (1): after the waste circuit board is washed, a first acid and a first oxidizing agent are added for oxidation pretreatment;

[0008] Step (2): the oxidation pretreated waste circuit board is added with a second acid, a gold dissolving agent and a second oxidizing agent for leaching, and a gold-containing liquid is obtained after solid-liquid separation;

[0009] Step (3): a replacement agent is added to the gold-containing liquid to completely replace the gold in the gold-containing liquid, and filter cake A is obtained after filtration;

[0010] Step (4): the filter cake A is dissolved with aqua regia, and after the nitrate is removed, the pH of the solution is adjusted with sodium hydroxide to obtain solution A;

[0011] Step (5): a reducing agent is added to the solution A until no more precipitate is generated, and filter cake B is obtained after filtration;

[0012] Step (6): dilute nitric acid is added to the filter cake B, and then heating and boiling are performed, and then solid-liquid separation is performed to obtain filter cake C;

[0013] Step (7): the filter cake C is washed with deionized water until neutral, and sponge gold is obtained after drying;

[0014] The rare and precious metal in the waste circuit board used in the application is mainly gold. The gold layer is formed by gold deposition or electroplating. First, the surface gold is effectively exposed by washing and oxidation pretreatment, and the subsequent gold dissolution efficiency is improved. Then, gold is dissolved by leaching. By controlling the amount of acid, gold dissolving agent and oxidizing agent, gold in the circuit board is selectively dissolved to obtain a gold-containing liquid, reduce the cost of subsequent impurity removal, and improve the purity of the recovered gold. Gold is efficiently extracted from the gold-containing liquid by displacement under controlled conditions. By using the above method, gold in the waste circuit board can be efficiently recovered to obtain high-purity sponge gold, realizing the resource utilization of waste circuit board.

[0015] Preferably, in step (1), the first acid solution is a sulfuric acid solution. The pH value of the sulfuric acid solution is 0-3, such as 0, 0.5, 0.8, 1.4, 1.5, 2.5, etc., but not limited to the listed values. Other values not listed in this range are also applicable, and more preferably 0.5-2.

[0016] Preferably, in step (1), the oxidation pretreatment reaction temperature is 20-80°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, etc., but not limited to the listed values. Other values not listed in this range are also applicable, and preferably 20-40°C.

[0017] Preferably, in step (1), the oxidation pretreatment time is 30-180 min, such as 30 min, 40 min, 60 min, 80 min, 100 min, 130 min or 150 min, etc., but not limited to the listed values. Other values not listed in this range are also applicable, and preferably 30-90 min.

[0018] Preferably, in step (1), the first acid solution is added in an amount of 1-10:1 mL / g, preferably 2-8 mL / g, such as 3 mL / g, 4 mL / g, 5 mL / g, 6 mL / g, 7 mL / g, 8 mL / g, 9 mL / g or 10 mL / g, etc., but not limited to the listed values. Other values not listed in this range are also applicable, and more preferably 3-6 mL / g.

[0019] Preferably, in step (1), the first oxidizing agent includes at least one of ferric chloride or ferric sulfate.

[0020] Preferably, in step (1), the first oxidizing agent is added in an amount such that the content of ferric iron after the addition of the acid solution is 1-10 g / L, preferably 2-8 g / L, such as 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, etc., but not only limited to the listed values, other values not listed in the range of values are also applicable, more preferably 3-6 g / L.

[0021] The present application preferably exposes the gold on the surface of the waste circuit board after the oxidation pretreatment, thereby improving the dissolution efficiency of the subsequent gold.

[0022] Preferably, in step (2), the second acid solution is a sulfuric acid solution. The pH value of the sulfuric acid solution is 0-3, such as 0, 0.5, 0.8, 1.4, 1.5, 2.5, etc., but not only limited to the listed values, other values not listed in the range of values are also applicable, more preferably 0.5-2.

[0023] Preferably, in step (2), the leaching temperature is 20-80°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, etc., but not only limited to the listed values, other values not listed in the range of values are also applicable, preferably 20-40°C.

[0024] Preferably, in step (2), the leaching time is 30-180 min, such as 30 min, 40 min, 60 min, 80 min, 100 min, 130 min or 150 min, etc., but not only limited to the listed values, other values not listed in the range of values are also applicable, preferably 30-90 min.

[0025] Preferably, in step (2), the liquid-solid ratio of the second acid solution to the waste circuit board is 1-10:1 mL / g, preferably 2-8 mL / g, such as 3 mL / g, 4 mL / g, 5 mL / g, 6 mL / g, 7 mL / g, 8 mL / g, 9 mL / g or 10 mL / g, etc., but not only limited to the listed values, other values not listed in the range of values are also applicable, more preferably 3-6 mL / g.

[0026] Preferably, in step (2), the gold dissolving agent is selected from at least one of thiourea, ammonium thiocyanate and potassium thiocyanate, when the gold dissolving agent is thiourea, the addition amount of the thiourea is 5-30 g / L, such as 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, etc., but not only limited to the listed values, other values not listed in the range of values are also applicable, more preferably 10-20 g / L.

[0027] Preferably, in step (2), the second oxidizing agent is selected from at least one of ferric chloride, ferric sulfate.

[0028] Preferably, in step (2), the second oxidizing agent is added in an amount that, calculated as trivalent iron, the trivalent iron content after adding the acid solution is 1-10 g / L, preferably 2-8 g / L, such as 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, etc., but not only limited to the listed values, other values not listed in this range are also applicable, more preferably 3-6 g / L.

[0029] Preferably, in step (3), the displacement agent is selected from any one of zinc powder, aluminum powder.

[0030] Preferably, in step (3), the volume of the gold-containing solution and the amount of displacement agent is 1-10 L / g, preferably 1-8 L / g, such as 3 L / g, 4 L / g, 5 L / g, 6 L / g, 7 L / g, 8 L / g, 9 L / g or 10 mL / g, etc., but not only limited to the listed values, other values not listed in this range are also applicable, more preferably 1-5 L / g.

[0031] Preferably, in step (3), the reaction temperature of the displacement is 20-80℃, such as 40℃, 50℃, 60℃, 70℃, 80℃, etc., but not only limited to the listed values, other values not listed in this range are also applicable, preferably 20-40℃.

[0032] Preferably, in step (3), the displacement time is 30-240 min, such as 30 min, 40 min, 60 min, 80 min, 100 min, 130 min or 150 min, etc., but not only limited to the listed values, other values not listed in this range are also applicable, preferably 120-180 min.

[0033] Preferably, in step (4), the pH of the solution A is 0-3. Such as 0, 0.5, 0.8, 1.4, 1.5, 2.5, etc., but not only limited to the listed values, other values not listed in this range are also applicable, more preferably 0.5-2.

[0034] Preferably, in step (5), the reducing agent is selected from at least one of sodium sulfite, sodium bisulfite.

[0035] The technical scheme of the present application has the following beneficial effects:

[0036] The rare and precious metal in the waste circuit board used in the application is mainly gold, and the gold layer is formed by gold deposition or electroplating. First, the surface gold is effectively exposed by washing and pre-oxidation treatment, and the subsequent gold dissolution efficiency is improved, then gold is dissolved by leaching, the gold in the circuit board is selectively dissolved by controlling the amount of acid, gold dissolving agent and oxidizing agent, the gold-containing liquid is obtained, the subsequent impurity removal cost is reduced, the purity of the recovered gold is improved, and the gold in the gold-containing liquid is efficiently extracted by replacement by controlling the replacement conditions. By using the above method, the gold in the waste circuit board can be efficiently recovered, and high-purity sponge gold is obtained, realizing the resource utilization of waste circuit board.

[0037] The method of the application can recover high-purity sponge gold from waste circuit boards without incineration or crushing, and has the advantages of environmental friendliness, low energy consumption, low equipment requirement, simple process, easy process control, etc.

[0038] The application mainly solves the problem of efficient and selective recovery of gold from waste circuit boards, and obtains high-purity sponge gold. After oxidation pretreatment, a non-cyanide leaching agent is used to replace the traditional cyanide leaching agent to selectively dissolve gold, and then the gold is separated by filtration to reduce the subsequent impurity removal cost, realize resource recycling, not only greatly shorten the process flow of precious metal recovery, but also have good economic benefits due to easy process control, and is conducive to industrialization. At the same time, the recovery process avoids the pollution of a large amount of smoke gas caused by incineration. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The figure is a schematic diagram of the method of the application. DETAILED DESCRIPTION

[0040] The application is further described below in combination with the drawings and specific examples.

[0041] The raw materials, reagents or devices used in the following examples are commercially available or can be obtained by known methods unless otherwise specified.

[0042] The content of gold in the waste circuit board used in the following examples and comparative examples is 98g / t, and the specification is: length x width x height = 234mm x 144mm x 1.2mm, and the weight of a single block is: 110.84g.

[0043] Example 1

[0044] Reference Figure 1 The application provides a method for recovering gold from waste circuit boards, comprising the following steps:

[0045] Step (1): after washing the waste circuit board, add first acid and first oxidizing agent, the first acid is a sulfuric acid solution with pH value of 1.5, the first acid adding amount and the liquid-solid ratio of waste circuit board is 5:1 mL / g, the first oxidizing agent is ferric chloride, the first oxidizing agent adding amount is calculated by the content of ferric ion, the content of ferric ion after adding the first acid is 3g / L, oxidation pretreatment is carried out, the oxidation pretreatment reaction temperature is 30℃, the oxidation pretreatment time is 60 min;

[0046] Step (2): add second acid, gold dissolving agent and second oxidizing agent to the waste circuit board after oxidation pretreatment, the second acid is a sulfuric acid solution with pH value of 1.5, the second acid adding amount and the liquid-solid ratio of waste circuit board is 5:1 mL / g, the gold dissolving agent is thiourea, the adding amount of thiourea is 10g / L, the second oxidizing agent is ferric chloride, the second oxidizing agent adding amount is calculated by the content of ferric ion, the content of ferric ion after adding the second acid is 3g / L, leaching is carried out, the leaching reaction temperature is 30℃, the leaching time is 90 min, after leaching, the solid-liquid separation is carried out to obtain a gold-containing solution.

[0047] Step (3): add a displacement agent to the gold-containing solution, the displacement agent is aluminum powder, the use amount of gold-containing solution and displacement agent is 10 L / g, the displacement reaction temperature is 30℃, the displacement time is 120 min, after complete displacement, filtration is carried out to obtain filter cake A;

[0048] Step (4): dissolve the filter cake A with aqua regia, adjust the solution pH to 2.0 with sodium hydroxide after removing nitrate to obtain solution A;

[0049] Step (5): add a reducing agent sodium sulfite to the solution A until no more precipitate is generated, then filter to obtain filter cake B;

[0050] Step (6): add dilute nitric acid to the filter cake B, heat and boil, then carry out solid-liquid separation to obtain filter cake C;

[0051] Step (7): wash the filter cake C with deionized water until neutral, dry to obtain sponge gold.

[0052] Example 2

[0053] A method for recovering gold from waste circuit board, comprising the following steps:

[0054] Step (1): after washing the waste circuit board, add first acid and first oxidizing agent, the first acid is a sulfuric acid solution with pH value of 1.5, the first acid adding amount and the liquid-solid ratio of waste circuit board is 5:1 mL / g, the first oxidizing agent is ferric sulfate, the first oxidizing agent adding amount is calculated by the content of ferric ion, the content of ferric ion after adding the first acid is 6g / L, oxidation pretreatment is carried out, the oxidation pretreatment reaction temperature is 30℃, the oxidation pretreatment time is 60 min;

[0055] Step (2): the oxidized pretreated waste circuit board is added into a second acid liquor, a gold dissolving agent and a second oxidizing agent, the second acid liquor is a sulfuric acid solution with a pH value of 1.5, the second acid liquor is added in an amount of 5:1 mL / g of liquid to solid ratio of the waste circuit board, the gold dissolving agent is ammonium thiocyanate, the ammonium thiocyanate is added in an amount of 30 g / L, the second oxidizing agent is iron sulfate, the second oxidizing agent is added in an amount of 6 g / L of ferric ion content after the addition of the second acid liquor, leaching is performed at a reaction temperature of 30℃ for 90 min, and a gold-containing liquid is obtained after solid-liquid separation.

[0056] Step (3): a displacement agent is added into the gold-containing liquid, the displacement agent is aluminum powder, the gold-containing liquid and the displacement agent are used in an amount of 10 L / g, displacement is performed at a reaction temperature of 30℃ for 120 min, and filter cake A is obtained after complete displacement and filtration.

[0057] Step (4): the filter cake A is dissolved with aqua regia, nitrate is removed, and the solution pH is adjusted to 2.0 with sodium hydroxide to obtain solution A.

[0058] Step (5): a reducing agent sodium sulfite is added into the solution A until no more precipitate is generated, and filter cake B is obtained after filtration.

[0059] Step (6): dilute nitric acid is added into the filter cake B, heating and boiling are performed, then solid-liquid separation is performed, and filter cake C is obtained.

[0060] Step (7): the filter cake C is washed with deionized water until neutral, and sponge gold is obtained after drying.

[0061] Example 3

[0062] A method for recovering gold from waste circuit boards, comprising the following steps:

[0063] Step (1): after the waste circuit board is washed, a first acid liquor and a first oxidizing agent are added, the first acid liquor is a sulfuric acid solution with a pH value of 1.5, the first acid liquor is added in an amount of 3:1 mL / g of liquid to solid ratio of the waste circuit board, the first oxidizing agent is ferric chloride, the first oxidizing agent is added in an amount of 9 g / L of ferric ion content after the addition of the first acid liquor, and oxidation pretreatment is performed at a reaction temperature of 30℃ for 90 min.

[0064] Step (2): the oxidized pretreated waste circuit board is added into a second acid solution, a gold dissolving agent and a second oxidizing agent, the second acid solution is a sulfuric acid solution with a pH value of 1.5, the second acid solution is added in an amount of 5:1 mL / g of the liquid-solid ratio of the waste circuit board, the gold dissolving agent is potassium thiocyanate, the potassium thiocyanate is added in an amount of 20 g / L, the second oxidizing agent is iron sulfate, the second oxidizing agent is added in an amount of 5 g / L of ferric iron content after the addition of the second acid solution, leaching is performed at a reaction temperature of 30°C for 90 min, and a gold-containing liquid is obtained after solid-liquid separation.

[0065] Step (3): a displacement agent is added to the gold-containing liquid, the displacement agent is zinc powder, the amount of the gold-containing liquid and the displacement agent is 8 L / g, the displacement reaction is carried out at a reaction temperature of 30°C for 120 min, and filter cake A is obtained after the displacement is completed and filtration;

[0066] Step (4): filter cake A is dissolved with aqua regia, nitrate is removed, and the pH of the solution is adjusted to 2.0 with sodium hydroxide to obtain solution A;

[0067] Step (5): sodium bisulfite is added to solution A until no more precipitate is produced, and filter cake B is obtained after filtration;

[0068] Step (6): dilute nitric acid is added to filter cake B, heated and boiled, then solid-liquid separation is performed, and filter cake C is obtained;

[0069] Step (7): filter cake C is washed with deionized water until neutral, and sponge gold is obtained after drying.

[0070] Comparative Example 1

[0071] A method for recovering gold from waste circuit boards, comprising the following steps:

[0072] Step (1) of the comparative example 1 is not oxidized pretreated, and the other processes are exactly the same as those of example 1.

[0073] Effect test

[0074] The gold leaching rate is calculated as follows: gold leaching rate (%) = total mass of gold in the leaching liquid / total mass of gold in the waste circuit board * 100%.

[0075] The gold-containing liquid obtained by the example and the comparative example is tested for gold content by inductively coupled plasma (ICP) spectroscopy, and the gold leaching rate is calculated, and the results are shown in Table 1.

[0076] Table 1

[0077] Leaching rate of gold (%) Example 1 96.74 Example 2 97.35 Example 3 96.53 Comparative Example 1 80.65

[0078] From the results of Table 1, it can be seen that the present application needs to perform oxidation pretreatment on the waste circuit board, control the oxidation pretreatment conditions, and waste circuit board leaching conditions, and the acid solution, gold dissolving agent and oxidizing agent in the oxidation pretreatment and leaching process need to be matched within a certain range to achieve the high-efficiency leaching effect of gold. After the oxidation pretreatment is adopted in the present application, the gold on the surface of the waste circuit board is effectively exposed, and the subsequent gold dissolution efficiency is improved. The selective leaching of gold is adopted, the amount of acid solution, gold dissolving agent and oxidizing agent is controlled, the gold in the waste circuit board is selectively dissolved, the gold leaching rate is significantly improved, and the subsequent impurity removal cost is reduced. According to the method described in the present application, high-purity sponge gold can be recovered without burning or crushing the waste circuit board. The method of the present application is environmentally friendly, low in energy consumption, low in equipment requirement, simple in process, easy to control, and has significant economic benefits.

[0079] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structural transformation, direct / indirect application in other related technical fields, or direct / indirect application in other related technical fields within the inventive concept of the present application, using the content of the present application specification and drawings, are included in the patent protection scope of the present application.

Claims

1. A method for recovering gold from waste circuit boards, characterized in that, Includes the following steps: Step (1): After cleaning the waste circuit board, add the first acid solution and the first oxidant for oxidation pretreatment; Step (2): Add the waste circuit board after oxidation pretreatment to the second acid solution, gold solvent and second oxidant, leach, and obtain gold-containing solution after solid-liquid separation; Step (3): Add a displacement agent to the gold-containing solution to completely displace the gold in the solution, and filter to obtain filter cake A; Step (4): Dissolve the filter cake A in aqua regia, remove the nitrate, and adjust the pH of the solution with sodium hydroxide to obtain solution A; Step (5): Add a reducing agent to the solution A until no more precipitate is produced, and filter to obtain filter cake B; Step (6): Add dilute nitric acid to the filter cake B, heat and boil, then separate the solid and liquid to obtain filter cake C; Step (7): Wash filter cake C with deionized water until neutral, and dry to obtain sponge gold; The first acid solution is a sulfuric acid solution, and the pH of the first acid solution is 0~3; the liquid-to-solid ratio of the first acid solution added to the waste circuit board is 1~10:1 mL / g; In step (1), the first oxidant is selected from at least one of ferric chloride and ferric sulfate; the oxidation pretreatment reaction temperature is 20~80℃, and the oxidation pretreatment time is 30~180 min; the amount of the first oxidant added is calculated based on ferric iron, and the ferric iron content after adding the first acid solution is 1~10 g / L; In step (2), the second acid solution is a sulfuric acid solution, and the pH of the second acid solution is 0~3; the amount of the second acid solution added is 1~10:1 mL / g of the liquid-solid ratio of the waste circuit board. In step (2), the gold solvent is selected from at least one of thiourea, ammonium thiocyanate, and potassium thiocyanate; the amount of gold solvent added is 5~30g / L.

2. The method for recovering gold from waste circuit boards according to claim 1, characterized in that, In step (2), the second oxidant is selected from at least one of ferric chloride and ferric sulfate; the amount of the second oxidant added is calculated as ferric iron, and the ferric iron content after adding the second acid solution is 1~10g / L.

3. The method for recovering gold from waste circuit boards according to claim 2, characterized in that, In step (2), the leaching reaction temperature is 20~80℃ and the leaching time is 30~180 min.

4. The method for recovering gold from waste circuit boards according to claim 1, characterized in that, In step (3), the displacement agent is selected from either zinc powder or aluminum powder; The volume of the gold-containing liquid and the amount of the displacement agent are 1~10 L / g, the displacement reaction temperature is 20~80℃, and the displacement time is 30~240 min.

5. The method for recovering gold from waste circuit boards according to claim 1, characterized in that, In step (4), the pH of solution A is 0 to 3.

6. The method for recovering gold from waste circuit boards according to claim 1, characterized in that, In step (5), the reducing agent is selected from at least one of sodium sulfite and sodium bisulfite.

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