Method for grading extraction of metals from waste circuit board

Abstract

The application relates to the technical field of electronic waste resource recycling, and particularly discloses a method for grading extraction of metals from waste circuit boards. The method uses a supercritical water system to efficiently decompose epoxy resin, realizes preliminary separation of metals and non-metals, and extracts glass fibers and enriches metal components through triboelectric separation or flotation. Subsequently, in a supercritical carbon dioxide system, a grading leaching process of sulfuric acid, nitric acid and aqua regia is adopted to realize efficient recovery of metals such as copper, silver, palladium, gold and platinum. Compared with a traditional hydrometallurgical process, the application can significantly reduce the consumption of sulfuric acid and nitric acid while keeping the metal recovery rate greater than or equal to 99%. In addition, a closed exhaust gas circulation system can efficiently recover nitrogen oxides (NO x ), convert them into acidic leaching agents for reuse, and realize waste gas recycling. The application has the advantages of high recovery rate, low energy consumption and environmental protection, and is suitable for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic waste resource recycling, in particular to a method for grading extraction of metals from waste circuit boards, and is especially suitable for green separation and high-value recovery of precious metals such as copper, silver, palladium, gold and platinum. BACKGROUND

[0002] Waste circuit boards are an important component of electronic waste, containing high-value metals such as copper, gold, silver, platinum and palladium, as well as non-metallic materials such as glass fibers and resins. At present, the main methods for metal separation from waste circuit boards include physical sorting, thermal treatment and hydrometallurgy. However, the existing technology has the following problems: physical sorting is difficult to separate fine metal particles, with low recovery rate; thermal treatment has high energy consumption and generates a large amount of secondary pollution; hydrometallurgy technology has high recovery efficiency, but has problems such as large amount of acid used, difficult waste gas treatment, etc. For example, a method for recovering gold, palladium, platinum and silver from waste circuit boards is disclosed in Chinese Patent No. CN102277497B, but it uses a large amount of high-concentration nitric acid (≥60%) and sulfuric acid (100-200g / L), resulting in high toxicity of waste liquid, and the waste gas is not reused (only absorbed by alkali), which is not environmentally friendly, and the comprehensive energy consumption of the process is high, which is difficult to meet the demand of green production. SUMMARY

[0003] The present application provides a method for grading extraction of metals from waste circuit boards, which significantly reduces the amount of acid used, ensures high recovery rate of metals, and realizes green and environmentally friendly production.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present application is:

[0005] A method for grading extraction of metals from waste circuit boards, comprising the following steps:

[0006] S1, crushing and drying the waste circuit boards, then mixing with deionized water and an oxidizing agent, and reacting in a supercritical water system to decompose the epoxy resin, and separating to obtain a filtrate A1 and a residue B1;

[0007] S2, sorting the residue B1 in S1 to obtain glass fibers A2 and a metal residue B2;

[0008] S3, grading leaching of the metal residue B2 in S2 in a supercritical carbon dioxide system, sequentially through sulfuric acid, nitric acid and aqua regia, to obtain leaching solutions in which copper, silver / palladium and gold / platinum are extracted, respectively;

[0009] S4, recovering high-purity metals from the leaching solutions in which copper, silver / palladium and gold / platinum are extracted.

[0010] The application can decompose epoxy resin by supercritical water, strengthen mass transfer by supercritical CO2 acid immersion, ensure high metal recovery rate, and significantly reduce acid consumption.

[0011] According to the embodiments of the application, the application can be further optimized, and the following is the technical scheme formed after optimization:

[0012] In one preferred embodiment, the temperature of the supercritical water system in S1 is 375-400℃, the pressure is 22.05-30 MPa, and the reaction time is 30-120 minutes; preferably, the temperature of the supercritical water system in S1 is 380-390℃, the pressure is 25-30 MPa, and the reaction time is 30-60 minutes.

[0013] The reaction conditions of 375-400℃ and 22.05-30 MPa of the supercritical water system in S1 are based on the following technical effects:

[0014] If the temperature is lower than 375℃, the supercritical water cannot be fully activated, the decomposition rate of epoxy resin is significantly reduced (<95%), the separation of metal and non-metal is not complete, and the subsequent sorting efficiency is reduced. If the temperature is higher than 400℃, the energy consumption of the reaction system increases sharply, and high temperature accelerates equipment corrosion and shortens equipment life.

[0015] If the pressure is lower than 24 MPa, the supercritical state of water cannot be maintained, and the reaction activity is insufficient. If the pressure is higher than 40 MPa, the sealing property and safety of the equipment are too high, and the industrialization cost increases significantly.

[0016] In one preferred embodiment, the temperature of the supercritical carbon dioxide system in S3 is 50-75℃, the pressure is 20-25 MPa, and the reaction time is 230-290 minutes; preferably, the temperature of the supercritical carbon dioxide system in S3 is 50-60℃, the pressure is 22-25 MPa, and the reaction time is 240-280 minutes.

[0017] The reaction conditions of 50-75℃ and 20-25 MPa of the supercritical CO2 system in S3 are based on the following technical effects:

[0018] If the temperature is lower than 50℃, it is difficult for CO2 to maintain a supercritical state, the mass transfer efficiency is reduced, and the acid immersion rate is reduced. If the temperature is higher than 75℃, the acidic leaching solution is partially decomposed (such as nitric acid is decomposed into NO2 gas at high temperature), the oxidation ability is reduced, harmful by-products are produced, and the metal leaching rate is reduced (the copper recovery rate is reduced to <98%).

[0019] If the pressure is lower than 20 MPa, the supercritical CO2 cannot effectively strengthen the penetration of acid solution. If the pressure is higher than 25 MPa, the equipment cost increases significantly, and the economy decreases.

[0020] In one preferred embodiment, the metal grading extraction method of the waste circuit board further comprises recycling nitrogen oxides produced in the S3 leaching process and converting them into acidic leaching agent for reuse.

[0021] The application adopts closed waste gas recycling technology, significantly reduces the amount of acid, and realizes green and environmentally friendly production.

[0022] In one preferred embodiment, the oxidizing agent in S1 is one or more of hydrogen peroxide, oxygen, sodium peroxide, calcium peroxide, potassium peroxide, lithium peroxide, and ozone.

[0023] In one preferred embodiment, the concentration of sulfuric acid in S3 is 0.2-0.3 mol / L.

[0024] In one preferred embodiment, the concentration of nitric acid is 0.25-0.4 mol / L.

[0025] In one preferred embodiment, the liquid-solid ratio of aqua regia is 0.5 mL / g-1.0 mL / g.

[0026] After conversion, the mass concentration of sulfuric acid in this application is 19.6-29.4 g / L, and the concentration of nitric acid is 0.25-0.4 mol / L, which is much lower than the mass concentration of sulfuric acid (100-200 g / L) and the concentration of nitric acid (≥60%) in the Chinese patent with publication number CN102277497B.

[0027] In one preferred embodiment, the particle size of the crushed waste circuit board in S1 is 1-5 cm, preferably 1-3 cm.

[0028] In one preferred embodiment, in S4, a copper precipitant is added to the leaching solution from which copper, silver / palladium, and gold / platinum have been extracted, forming Cu(OH)2 precipitate, which is dried and calcined to obtain copper oxide and filtrate A4; silver powder is electrolytically separated from the filtrate A4; the remaining filtrate is adjusted to pH, a palladium precipitant is added, sponge palladium is precipitated, and the remaining filtrate A5 is obtained; gold powder is precipitated by adding a gold reducing agent to the filtrate A5, and platinum powder is obtained by adding a platinum precipitant to the remaining filtrate A6 to form a platinum precipitate, which is calcined.

[0029] Preferably, the liquid-solid ratio of deionized water to waste circuit board in S1 is 1-3:1.

[0030] Preferably, the mass percentage of oxidizing agent in S1 is 1-5%.

[0031] Preferably, the sorting in S2 is triboelectric sorting or flotation.

[0032] Preferably, the time for leaching by sulfuric acid in S3 is 70-90 minutes, the time for leaching by nitric acid is 70-90 minutes, and the time for leaching by aqua regia is 90-110 minutes.

[0033] Preferably, the conditions for drying and calcining of Cu(OH)2precipitate are 350-380℃ for 1-2 hours. The conditions for electrolysis of filtrate A4 are a current density of 180 A / m 2 . The remaining filtrate is adjusted to a pH of 0.8-1, and the precipitant in S4 includes formic acid as a precipitant for palladium, with a molar ratio of formic acid to palladium of 1:4-6. The molar ratio of the gold reducing agent to gold is 1:3-5. The molar ratio of the platinum precipitant to platinum is 2-4:1. The calcination conditions are 700-800℃ for 2-3 hours.

[0034] Preferably, the precipitation in S4 includes a copper precipitant and a platinum precipitant, the copper precipitant being one or more of sodium hydroxide, ammonium hydroxide, and calcium hydroxide, and the platinum precipitant being ammonium chloride.

[0035] Preferably, reduction in S4 is performed using a gold reducing agent, the gold reducing agent being sodium sulfite.

[0036] The order of the steps of the present application is designed based on the following technical synergistic effects:

[0037] S1 decomposes the epoxy resin. The supercritical water system completely decomposes the epoxy resin (decomposition rate ≥ 99.6%), completely separates the metal from the non-metal (glass fiber, etc.), and provides high-purity raw materials for subsequent sorting and leaching. If the resin is not first decomposed and is directly crushed and sorted, the resin-coated metal particles will cause the efficiency of triboelectric separation or flotation to decrease (metal recovery rate decreases by 5%-10%), and additional acid is required to dissolve the resin residue in subsequent leaching.

[0038] S2 separates the metal from the non-metal. S2 achieves metal enrichment, with the metal content in the metal slag B2 increasing to ≥ 95%, reducing the interference of impurities in the subsequent leaching process. If the sorting step is skipped and direct leaching is performed, non-metals such as glass fibers will be mixed into the leaching system, resulting in an increase of 20%-30% in acid consumption, and a decrease in the purity of the noble metal leaching solution (gold purity < 99%).

[0039] S3 is a staged leaching sequence (sulfuric acid → nitric acid → aqua regia). Sulfuric acid preferentially leaches copper (lower potential metal), avoiding the early dissolution of noble metals by strong acid; nitric acid selectively leaches silver / palladium, and aqua regia finally dissolves gold / platinum (which requires a strong oxidizing environment), ensuring that the metals are extracted step by step without interfering with each other. If the leaching sequence is reversed (e.g., aqua regia first and then sulfuric acid), copper and other base metals will consume the strong oxidizing agent (such as HClO3) in aqua regia, resulting in a decrease in the leaching rate of gold / platinum to < 95%, and an increase of more than 50% in acid consumption.

[0040] Synchronous recovery of waste gas. The present application is a closed system synchronous recovery, real-time conversion of NO x ≥40% for reuse of acidic leaching agent, reducing the amount of nitric acid supplement. If the waste gas treatment is lagging (such as concentrated treatment after leaching is completed), NO x The escape rate is ≥30%, and additional alkali absorption device is needed, which increases the environmental protection cost and cannot realize the internal circulation of leaching agent.

[0041] Compared with the prior art, the present application has at least the following beneficial effects:

[0042] 1. Supercritical CO2 (50-75℃, 20-25MPa) significantly improves the diffusion efficiency of acid, compared with the traditional hydrometallurgy process, the method significantly reduces the use concentration and dosage of acidic reagent, compared with the dosage of patent CN102277497B, the dosage of sulfuric acid and nitric acid is reduced by 41% and 94.7% respectively.

[0043] 2. Based on the supercritical water decomposition of epoxy resin (decomposition rate ≥99.6%) and the staged leaching process, the recovery rates of copper, silver, palladium, gold and platinum are 99.7%, 99.6%, 99.3%, 99.7% and 99.7% respectively. The purity of the metals is ≥99.5%.

[0044] 3. The closed oxidation system converts waste gas into acidic leaching liquid for reuse, and the recovery rate of nitrogen oxide (NO x ) is ≥95%. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a flowchart of a metal staged extraction method provided by the present application in waste circuit boards. DETAILED DESCRIPTION

[0046] The technical solutions of the present application will be further specifically described below through specific embodiments. It should be understood that the implementation of the present application is not limited to the following examples, and any form of variation or change of the present application will fall within the scope of protection of the present application.

[0047] Example 1

[0048] The waste circuit board was crushed to an average particle size of 3 cm, dried, and mixed with deionized water (liquid-solid ratio 2:1) and 2% hydrogen peroxide, and placed in a supercritical water reactor (temperature 380°C, pressure 25 MPa) for 50 minutes. The filtrate A1 (containing decomposed organic matter) and the residue B1 (metal content 98.6%) were separated. The residue B1 was treated by a triboelectric separator (voltage 12 kV) to separate glass fibers A2 (non-metal content 99.0%) and metal residue B2 (metal enrichment degree 99.2%). The metal residue B2 was reacted with 0.2 mol / L sulfuric acid (prepared from 98% concentrated sulfuric acid 10.87 mL / L) at a liquid-solid ratio of 1.5 mL / g in a supercritical CO2 system (temperature 55°C, pressure 22 MPa) for 80 minutes. The copper ion concentration in the filtrate A3 was 12.5 g / L. The residue B3 was reacted with 0.3 mol / L nitric acid (prepared from 65% concentrated nitric acid 20.77 mL / L) at a liquid-solid ratio of 1.5 mL / g in a supercritical CO2 system (temperature 58°C, pressure 22 MPa) for 80 minutes. The silver ion concentration in the filtrate A4 was 5.0 g / L, and the palladium ion concentration was 1.7 g / L. The residue B4 was reacted with aqua regia at a liquid-solid ratio of 0.8 mL / g in a supercritical CO2 system (temperature 60°C, pressure 22 MPa) for 100 minutes. The gold ion concentration in the filtrate A5 was 3.2 g / L, and the platinum ion concentration was 1.0 g / L. NaOH was added to the filtrate A3 to pH = 4.0 to form Cu(OH)2 precipitate, which was dried and calcined (380°C, 1.5 hours) to obtain copper oxide (purity 99.8%, recovery rate 99.5%). The filtrate A4 was electrolyzed (current density 180 A / m 2 ), and silver powder (purity 99.9%, recovery rate 99.5%) was precipitated. The remaining filtrate was adjusted to pH = 0.8, and formic acid was added (palladium molar ratio 1:5) to precipitate sponge palladium (purity 99.6%, recovery rate 99.2%). Sodium sulfite was added to the filtrate A5 (gold molar ratio 1:4) to precipitate gold powder (purity 99.96%, recovery rate 99.4%). Ammonium chloride was added to the remaining filtrate (platinum molar ratio 3:1) to form (NH4)2PtCl6, which was calcined (750°C, 2.5 hours) to obtain platinum powder (purity 99.6%, recovery rate 99.4%). The NO x gas recovered in the nitric acid leaching stage (recovery rate 97%) was converted into nitric acid for reuse.

[0049] Example 2

[0050] The difference between this comparative example and Example 1 is that: 1. the supercritical water oxidation temperature is increased to 390°C; 2. the sulfuric acid concentration is 0.30 mol / L, and the nitric acid concentration is 0.40 mol / L; 3. the supercritical CO2 extraction reaction time is 120 minutes.

[0051] Results: Copper recovery rate: 99.7%; silver recovery rate: 99.6%; palladium recovery rate: 99.3%; gold recovery rate: 99.7%; platinum recovery rate: 99.7%;

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 1 is that the supercritical water temperature is 360°C.

[0054] Results: The epoxy resin decomposition rate is reduced to 94.2%, resulting in incomplete separation of metals and non-metals, and the metal enrichment degree after triboelectric sorting is reduced to 96.5%, and the final copper recovery rate is reduced to 97.8%.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that the supercritical CO2 pressure is 18 MPa.

[0057] Results: The acid mass transfer efficiency is reduced, resulting in a decrease in copper, silver, and palladium leaching rates to 97.5%, 97.0%, and 96.8%, respectively.

[0058] Comparative Example 3

[0059] The difference between this comparative example and Example 1 is that nitrohydrochloric acid is used directly for one-time leaching, and the sequence of sulfuric acid→nitric acid→nitrohydrochloric acid is not followed.

[0060] Results: Copper and other base metals preferentially consume the oxidizing agent in nitrohydrochloric acid, resulting in a decrease in gold and platinum leaching rates to 95.2% and 95.1%, respectively, and an increase in acid consumption of 53%.

[0061] Table 1 Comparison of experimental data of Example and patent with publication number CN102277497B (amount of metal residue used per kilogram)

[0062]

[0063]

[0064] Note: The acid amount in this table is the volume of 98% sulfuric acid and 65% nitric acid.

Claims

1. A method for the fractional extraction of metals from waste printed circuit boards, characterized in that, The method comprises the following steps: S1, crushing and drying the waste circuit board, mixing with deionized water and oxidizing agent, and reacting in a supercritical water system to decompose the epoxy resin, and separating to obtain filtrate A1 and residue B1; S2, sorting the residue B1 in S1 to obtain glass fiber A2 and metal residue B2; S3, the metal residue B2 in S2 is sequentially subjected to graded leaching by sulfuric acid, nitric acid and aqua regia in a supercritical carbon dioxide system to obtain leaching liquor in which copper, silver / palladium and gold / platinum are extracted, respectively; The temperature of the supercritical carbon dioxide system in S3 is 50-75℃, and the pressure is 20-25 MPa; S4, recovering high-purity metals from the leaching liquor in which copper, silver / palladium and gold / platinum are extracted.

2. The method according to claim 1, wherein the waste circuit board is a waste printed circuit board. The temperature of the supercritical water system in S1 is 375-400℃, the pressure is 22.05-30 MPa, and the reaction time is 30-120 minutes.

3. The method according to claim 1, wherein the waste circuit board is a waste printed circuit board. The temperature of the supercritical water system in S1 is 380-390℃, the pressure is 25-30 MPa, and the reaction time is 30-60 minutes.

4. The method according to claim 1, wherein the method is characterized by, The reaction time of the supercritical carbon dioxide system in S3 is 230-290 minutes.

5. The method according to claim 1, wherein the method is characterized by, The temperature of the supercritical carbon dioxide system in S3 is 50-60℃, the pressure is 22-25 MPa, and the reaction time is 240-280 minutes.

6. The method according to claim 1, wherein the metal is classified and extracted from the waste circuit board. It also includes recovering nitrogen oxides produced in the leaching process in S3 and converting them into acidic leaching agents for reuse.

7. The method according to claim 1, wherein the metal is classified and extracted from the waste circuit board. The oxidizing agent in S1 is one or more of hydrogen peroxide, oxygen, sodium peroxide, calcium peroxide, potassium peroxide, lithium peroxide and ozone.

8. The method according to claim 1, wherein the metal is classified and extracted from the waste circuit board. The concentration of sulfuric acid in S3 is 0.2-0.3 mol / L.

9. The method according to claim 1, wherein the metal is classified and extracted from the waste circuit board. The concentration of nitric acid is 0.25-0.4 mol / L.

10. The method according to claim 1, wherein the method is characterized by, The liquid-solid ratio of aqua regia is 0.5-1.0 mL / g.

11. The method according to claim 1, wherein the method is characterized by, The particle size of the crushed waste circuit board in S1 is 1-5 cm.

12. The method according to claim 1, wherein the metal is classified and extracted from the waste circuit board. The particle size of the crushed waste circuit board in S1 is 1-3 cm.

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