A comprehensive treatment method for smelting fume and soot of waste circuit board by fire process

Abstract

The present application relates to solid waste resource processing technical field, specifically to a kind of waste circuit board pyrometallurgy flue dust and ash comprehensive processing method, comprising (1) with hydrochloric acid and ammonium chloride to ash leaching, filtration is obtained filter residue 1 and filtrate 1;(2) filter residue 1 is leached with ammonia water, filtration is obtained filter residue 2 and filtrate 2, filtrate 2 is reduced and silver is deposited, filtration is obtained crude silver powder and filtrate 3, adjust the pH value of filtrate 3 to 11~13, then ammonia is steamed, the ammonia recovered is used in the leaching step of filter residue 1, and the generated miscellaneous salt is used as the raw material for bromine extraction;(3) filtrate 1 is filtered to obtain lead sulfate and filtrate 4, and the filtrate 4 is replaced with zinc powder to obtain copper powder and filtrate 5, and the filtrate 5 is added with ammonium carbonate and filtered to obtain filter residue 6 and filtrate 6, and the filter residue 6 is washed with water, dried and calcined to obtain zinc oxide, and the filtrate 6 is returned to step (1) for ash leaching.The present application realizes the separation and recovery of copper, lead, zinc, silver and tin, and the process flow is compact and the metal recovery rate is high.

Description

Technical Field

[0001] This invention relates to a waste circuit board resource utilization technology, specifically a comprehensive treatment method for waste circuit board smelting fumes and dust. Background Technology

[0002] According to the "China Statistical Yearbook 2021," the number of household appliances owned per 100 households at the end of 2020 was as follows: televisions 120.8, refrigerators 101.8, washing machines 96.7, air conditioners 117.7, computers 54.2, mobile phones 253.8, and range hoods 60.9. With the rapid pace of product updates in the information and electronics industry, electronic products are being phased out and discarded at an increasingly faster rate. To reduce pollution from these discarded electronic products and simultaneously reduce their quantity and increase resource utilization, they are typically dismantled to obtain waste plastics, waste metals, and waste circuit boards, which can be recycled.

[0003] Waste circuit boards are the most valuable and difficult-to-process component of electronic waste. The bare boards after removing electronic components contain a large amount of valuable metals. Pyrometallurgical processes can achieve large-scale and rapid processing and obtain high metal yields. However, pyrometallurgical smelting also produces a large amount of harmful ash, which contains cuprous halides, zinc oxide, lead oxide, tin dioxide, silver halides, etc. Therefore, it is necessary to comprehensively treat the ash from waste circuit board smelting in order to fully recover the valuable metal resources contained therein. Summary of the Invention

[0004] The purpose of this invention is to provide a method for processing pyrometallurgical fumes and soot from waste circuit boards, so as to recover metals such as copper, lead, and zinc, while reducing environmental pollution from pyrometallurgical fumes and soot.

[0005] To address the above problems, this invention provides a comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards, comprising the following steps:

[0006] (1) Acid leaching of smoke and dust

[0007] Under atmospheric conditions, a mixture of hydrochloric acid and ammonium chloride is used to dissolve the cuprous halides, lead oxide, and zinc oxide enriched in the smelting fumes and dust of waste circuit boards. Taking advantage of the insolubility of silver halides and tin dioxide, the copper, lead, and zinc are separated from tin and silver. The leaching reaction of the fumes is as follows, where X represents Cl or Br.

[0008] 4CuX+8HCl+O2=4CuCl2+4HX+2H2O

[0009] ZnO + 2HCl = ZnCl₂ + H₂O

[0010] PbO + 2HCl = PbCl₂ + H₂O

[0011] The filtrate 1 produced by the leaching and filtration of flue gas is a mixed solution of copper chloride, zinc chloride and lead chloride, and the filter residue 1 is a mixture of silver halide and tin dioxide.

[0012] (2) Silver-tin recycling

[0013] The main components of filter residue 1 are silver halide and tin dioxide. Both silver chloride and silver bromide are soluble in concentrated ammonia and sodium thiosulfate solution. Since sodium thiosulfate solution is unstable and difficult to recover, the present invention preferably uses concentrated ammonia to leach the silver in filter residue 1, and the following reaction occurs, where X represents Cl or Br. After filtration, filtrate 2 is obtained, thereby achieving the separation of silver and tin.

[0014] AgX+2NH3·H2O=[Ag(NH3)2]X+2H2O

[0015] This invention uses hydrazine hydrate, formaldehyde and other reducing agents to reduce silver in filtrate 2, which can effectively avoid the influence of reducing agents such as zinc and copper on the quality of silver powder, and can obtain silver powder with a purity of 99% and a silver recovery rate of not less than 98%. The main reactions that occur are as follows, where X represents Cl or Br.

[0016] 4[Ag(NH3)2]X+N2H4+4H2O=4Ag↓+N2↑+4NH4X+4NH3·H2O

[0017] 2[Ag(NH3)2]X+HCHO=2Ag↓+2NH4X+2NH3↑+CO↑

[0018] The main components of the filtrate after silver reduction (3) are ammonium chloride / bromide and ammonia. First, the pH is adjusted to strong alkalinity with NaOH to promote the decomposition of ammonium salts into free ammonia. Then, the ammonia is evaporated. The mixed salts produced by the ammonia evaporation are a mixture of sodium chloride and sodium bromide, which can be used as raw materials for bromine extraction.

[0019] Considering the compositional differences between filtrate 3 (after silver reduction) and filtrate 6 (after zinc precipitation), this invention does not combine the two for processing.

[0020] (3) Copper, lead and zinc recycling

[0021] Filtrate 1 is first treated with ammonium sulfate to remove lead, and the filtered solution yields lead sulfate. Filtrate 4 consists of zinc chloride, copper chloride, and ammonium chloride, which facilitates subsequent processing. This is why ammonium sulfate is preferred for lead precipitation in this invention.

[0022] (NH4)2SO4+PbCl2=PbSO4↓+2NH4Cl

[0023] The filtrate after lead precipitation (4) is then used to replace copper with zinc powder.

[0024] Zn + CuCl₂ = ZnCl₂ + Cu

[0025] The main components of the filtrate 5 after copper replacement are zinc chloride and ammonium chloride. Zinc carbonate (filter residue 6) and filtrate 6 are obtained by chemical precipitation of zinc.

[0026] ZnCl2+(NH4)2CO3=ZnCO3↓+2NH4Cl

[0027] The present invention preferably uses ammonium carbonate to precipitate zinc, which does not introduce other impurity ions. The main component of filtrate 6 is only ammonium chloride, which is more conducive to reuse or treatment.

[0028] In this application, smoke and / or soot refers to dust such as flue dust generated during the pyrometallurgical smelting of waste circuit boards, dust accumulated on the heating surfaces of waste heat boilers, and dust collected from dust collectors.

[0029] The present invention provides a comprehensive resource-based treatment method for the ash and dust generated from the pyrometallurgical smelting of waste circuit boards, achieving the separation and resource utilization of copper, lead, zinc, silver and tin. The process is compact and the metal recovery rate is high. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention.

[0031] Figure 1 This is a process flow diagram of a comprehensive treatment method for waste circuit board smelting fumes and dust in this embodiment. Detailed Implementation

[0032] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the field, or in accordance with the product manual.

[0033] In the description of this invention, unless otherwise stated, the terms "upper" and "lower" indicate the orientation or state relationship based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0034] In the following embodiments, all instruments and equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise stated, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0035] Example 1

[0036] like Figure 1As shown, this embodiment provides a comprehensive treatment method for waste circuit board smelting fumes and dust, including the following steps:

[0037] (1) Acid leaching of soot

[0038] The ash from the smelting of waste circuit boards was first leached with a mixture of hydrochloric acid and ammonium chloride. The hydrochloric acid concentration was 8 mol / L, the ammonium chloride concentration was 4 mol / L, the leaching temperature was 40℃, the liquid-to-solid ratio was 8:1 L / kg, and the leaching time was 90 min. After leaching, the mixture was filtered to obtain filter residue 1 and filtrate 1.

[0039] (2) Silver-tin recycling

[0040] Silver was leached from filter residue 1 with 11 mol / L ammonia solution at 50°C, a liquid-to-solid ratio of 5:1 L / kg, and a leaching time of 3 hours. After leaching, the residue was filtered to obtain filter residue 2 and filtrate 2. The main component of filter residue 2 was SnO2. Filtrate 2 was used to reduce the silver precipitate with hydrazine hydrate (NH2-NH2·H2O) at 40°C for 40 minutes. Filtrate 2 was then filtered to obtain crude silver powder and filtrate 3. The pH of filtrate 3 was adjusted to 11 with NaOH, and then ammonia was evaporated.

[0041] (3) Copper, lead and zinc recycling

[0042] The filtrate 1 from the acid leaching of flue gas is first treated with ammonium sulfate to precipitate lead and then filtered to obtain PbSO4 and filtrate 4. Copper in filtrate 4 is recovered by zinc powder displacement, and zinc in filtrate 5 is precipitated with ammonium carbonate and then filtered. The filter residue is washed with water, dried, and then calcined at 500℃ for 120 min to obtain zinc oxide. Filtrate 6 is reused in the flue gas leaching step.

[0043] Example 2

[0044] The method in this embodiment is basically the same as that in Embodiment 1, with the main difference being the selection of parameters.

[0045] (1) Acid leaching of soot

[0046] The ash from the smelting of waste circuit boards was first leached with hydrochloric acid at a concentration of 3 mol / L and an ammonium chloride concentration of 10 mol / L. The leaching temperature was 60℃, the liquid-to-solid ratio was 3:1 L / kg, the leaching time was 60 min, and the pH during the leaching process was 3. After leaching, the mixture was filtered to obtain filter residue 1 and filtrate 1.

[0047] (2) Silver-tin recycling

[0048] Silver was leached from filter residue 1 with 13 mol / L ammonia solution at 80℃, a liquid-to-solid ratio of 2:1 L / kg, and a time of 1 h. After leaching, the residue was filtered to obtain filter residue 2 and filtrate 2. Filtrate 2 was used to reduce the silver precipitation with hydrazine hydrate (NH2-NH2·H2O) at 70℃ for 20 min, and then filtered to obtain crude silver powder and filtrate 3. The pH of filtrate 3 was adjusted to 13 with NaOH, and then ammonia was evaporated.

[0049] (3) Copper, lead and zinc recycling

[0050] The filtrate 1 from the acid leaching of flue ash was treated with ammonium sulfate to precipitate lead and then filtered to obtain lead sulfate and filtrate 4. After copper was recovered by replacing filtrate 4 with zinc powder, the resulting filtrate 5 was treated with ammonium carbonate to precipitate zinc and then filtered. The filter residue 6 was washed with water, dried, and then calcined at 600℃ for 60 min to obtain zinc oxide. Ammonium chloride was recovered by evaporating and crystallizing filtrate 6.

[0051] Example 3

[0052] The method in this embodiment is basically the same as that in Embodiment 1, with the main difference being the selection of parameters.

[0053] (1) Acid leaching of soot

[0054] The ash from the smelting of waste circuit boards was first leached with nitric acid. The specific method had the following characteristics: hydrochloric acid concentration of 5 mol / L, ammonium chloride concentration of 6 mol / L, leaching temperature of 50℃, liquid-to-solid ratio of 5:1 L / kg, and leaching time of 70 min. After leaching, the residue was filtered to obtain filter residue 1 and filtrate 1.

[0055] (2) Silver-tin recycling

[0056] Silver was leached from filter residue 1 with 12 mol / L ammonia solution at 60℃, a liquid-to-solid ratio of 4:1 L / kg, and a time of 2 h. After leaching, the residue was filtered to obtain filter residue 2 and filtrate 2. Filtrate 2 was used to reduce the silver precipitation with hydrazine hydrate (NH2-NH2·H2O) at 50℃ for 30 min, and then filtered to obtain crude silver powder and filtrate 3. The pH of filtrate 3 was adjusted to 12 with NaOH, and then ammonia was evaporated.

[0057] (3) Copper, lead and zinc recycling

[0058] The filtrate 1, obtained from the hydrochloric acid leaching of flue gas, was treated with ammonium sulfate to precipitate lead and then filtered to obtain PbSO4 and filtrate 4. After copper was recovered by replacing zinc powder with zinc powder, filtrate 5 was treated with ammonium carbonate to precipitate zinc and then filtered. The filter residue was washed with water, dried, and then calcined at 550℃ for 90 min to obtain zinc oxide.

[0059] The above process separates crude silver, tin dioxide, lead sulfate, copper, and zinc oxide. Those skilled in the art can obtain the corresponding metals by conventional processing using existing techniques. The selection of other reagents with similar properties and similar reaction parameters can be determined by those skilled in the art based on common knowledge. In addition, percentages not explicitly stated in this application are usually mass percentages and will not be elaborated further.

[0060] The above descriptions are merely embodiments of the present invention. Commonly known structures, properties, and reactant ratios are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. For example, simply adjusting the parameter selection within or near a specified parameter range should also be considered within the scope of protection of the present invention, and these will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards, characterized in that... The steps include the following: (1) Soot leaching The flue dust was leached with a mixture of hydrochloric acid and ammonium chloride at a liquid-to-solid ratio of 3:1 to 8:1 L / kg, a leaching time of 60 to 90 min, and a leaching temperature of 40 to 60 °C. After leaching, the residue was filtered to obtain filter residue 1 and filtrate 1. (2) Silver-tin recycling Filter residue 1 is leached with ammonia water at a temperature of 50-80℃, a liquid-to-solid ratio of 2:1-5:1 L / kg, and a time of 1-3 hours. After leaching, filter residue 2 and filtrate 2 are obtained. Filtrate 2 is then subjected to reduction silver precipitation at a temperature of 40-70℃ for 20-40 minutes. After filtration, crude silver powder and filtrate 3 are obtained. The pH of filtrate 3 is adjusted to 11-13, and then ammonia is evaporated. The recovered ammonia is used in the leaching step of filter residue 1. The main component of filter residue 2 is SnO2. (3) Copper, lead and zinc recycling Filtrate 1 is filtered to obtain lead sulfate and filtrate 4. Filtrate 4 is replaced with zinc powder or iron powder to obtain copper powder and filtrate 5. Filtrate 5 is reacted with ammonia or soluble carbonate and filtered to obtain filter residue 6 and filtrate 6. Filter residue 6 is washed with water, dried and calcined to obtain zinc oxide.

2. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: The concentration of hydrochloric acid in the mixture of step (1) is 3~8 mol / L, and the concentration of ammonium chloride is 4~10 mol / L.

3. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: The concentration of ammonia in step (2) is 10~13 mol / L.

4. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: The reagents used to reduce the silver in step (2) include at least one of formaldehyde, formic acid, hydrazine hydrate, zinc powder, and copper powder.

5. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: In step (2), NaOH is used to adjust the pH value of filtrate 3.

6. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: The reagents used for lead precipitation in step (3) include at least one of sulfuric acid, ammonium sulfate, zinc sulfate, sodium sulfate, and potassium sulfate.

7. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: In step (3), the calcination temperature of filter residue 6 is 500~600℃ and the calcination time is 60~120min.

8. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: In step (3), the filtrate 5 reacts with ammonium carbonate, and the filtrate 6 is returned to step (1) to leach out the soot.

9. The comprehensive treatment method for pyrometallurgical dust and ash from waste circuit boards according to claim 1, characterized in that: In step (3), the filtrate 6 is first crystallized to recover ammonium chloride.

Images