Method for preparing fine copper powder through suspension reduction roasting of alkaline etching waste liquid

Abstract

The invention discloses a method for preparing fine copper powder by suspension reduction roasting of alkaline etching waste liquid, which comprises the following steps: firstly, adding magnesium chloride into the alkaline etching waste liquid, adjusting the pH value of the solution, forming magnesium hydroxide precipitate and adsorbing impurity metal; then, under a dispersing agent or an ultrasonic system, three-phase separation of copper, ammonia and chlorine of the alkaline etching waste liquid is achieved through an alkalization reaction, and particle size control can be conducted on copper oxide. And then carrying out suspension reduction roasting on the fine copper oxide powder by taking ammonia-containing gas recovered by an alkalization method as carrier gas flow and a reducing agent to finally prepare the fine copper powder. According to the method, an alkalization method and suspension roasting are combined, a new path for clean and efficient recovery of copper in the alkaline etching waste liquid through a pyrogenic process is opened up, and the superfine copper powder with the average particle size smaller than 10 microns is prepared by optimizing alkalization reaction and roasting conditions. Compared with the prior art, the preparation period is short, the resource utilization rate is high, the process is safe and environmentally friendly, and the problem of large-scale production of the fine copper powder is expected to be solved.

Description

Technical Field

[0001] The invention relates to the field of resource utilization of waste etching liquid of printed circuit boards, and in particular to a method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid. Background Art

[0002] Alkaline etching waste liquid is the waste liquid generated in the etching process of printed circuit boards. It contains high concentrations of copper, ammonia, chlorine and other pollutants. It belongs to the national hazardous waste HW22 and needs to be properly handled. On the other hand, alkaline etching waste liquid is an important recycled material of valuable metal copper. Its copper content is 80-180g / L, which has a high recycling value. For the collection of etching waste liquid, enterprises need to pay the corresponding copper fees to suppliers. In addition, the production cost of copper per ton is generally tens of thousands of yuan, which greatly compresses the profit margin of enterprises. In recent years, fine copper powder has become a basic functional powder material with great application potential and high product added value due to its excellent physical and chemical properties. In addition to being affected by the price of copper metal, the selling price of copper powder is also closely related to its particle size. Generally speaking, the smaller the particle size, the higher the selling price. Therefore, if fine copper powder can be prepared using alkaline etching waste liquid as raw material, the economic benefits of the enterprise will be significantly improved.

[0003] The existing methods for preparing copper powder from alkaline etching waste liquid mainly include extraction-electrodeposition method and liquid phase reduction method. The extraction-electrodeposition method is to use an extractant to extract copper from the alkaline etching waste liquid, and then use sulfuric acid to back-extract the extract phase to obtain a copper sulfate electrolyte, which is then electrodeposited on the cathode of the electrolytic cell to produce cathode copper. However, this technology has the following main problems: (1) The extraction produces a large amount of raffinate, and the raffinate contains many types of heavy metals with high content, which increases the cost of wastewater treatment; (2) Electrodeposition uses electric energy to maintain the redox conditions of the system, and high power consumption and frequent replacement of electrode plates lead to increased costs; (3) The cathode copper ingot has a large particle size and needs to be further crushed by ball milling, which easily leads to reduced product purity and uneven particle size distribution.

[0004] Liquid phase reduction is a method for preparing fine copper powder from alkaline etching waste liquid that has emerged in recent years. By adding a reducing agent (such as hydrazine hydrate, borohydride salt, hypophosphite, thiourea dioxide, etc.) to the alkaline etching waste liquid, and in the presence of a dispersant (such as polyvinyl pyrrolidone, polyethylene glycol, hexadecyltrimethylammonium bromide, etc.), the complex copper can be converted into fine copper powder. However, the reagents involved in this technology are expensive, and the reducing agents currently developed generally have safety risks. For example, hydrazine hydrate is highly toxic and unsafe to operate, and sodium hypophosphite reacts violently and is unstable.

[0005] As one of the most commonly used methods in industry, pyrometallurgy has the characteristics of wide adaptability, low energy consumption, high metal recovery rate, and large-scale production. However, since the dry base of alkaline etching waste liquid has a high content of ammonia and chlorine components, the inventors found that if it is directly roasted, not only will the dry base evaporate completely, the copper recovery rate is extremely low, but the chlorine-containing gas and ammonium chloride dust generated will block the pipeline, accelerate the corrosion of equipment, affect the continuity of production, and increase the processing and maintenance costs. Therefore, how to cleanly and efficiently recover copper from alkaline etching waste liquid by pyrometallurgy and prepare fine copper powder is a problem that needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects and shortcomings in the prior art and to provide a method for preparing fine copper powder by suspension reduction roasting of alkaline etching waste liquid.

[0007] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0008] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid comprises the following steps:

[0009] S1. Impurity removal: adding magnesium chloride to the waste liquid of the circuit board alkaline etching, adjusting the pH value of the waste liquid to 11.2-11.4 with sodium hydroxide solution, so that the magnesium ions are precipitated in the form of magnesium hydroxide and adsorb the impurity metals;

[0010] S2. Preparation of fine copper oxide powder by dispersant system: adding polyvinyl pyrrolidone to the supernatant after impurity removal in step S1 to completely dissolve it; preheating the sodium hydroxide solution and keeping it warm to 60-80°C, then adding the impurity-removed supernatant containing polyvinyl pyrrolidone thereto, stirring continuously at a speed of 500-600 r / min during the addition and reaction process, and recovering and storing the generated ammonia gas for standby use; after the reaction is completed, filtering the solution to recover the copper oxide precipitate, and drying to obtain fine PVP / CuO powder;

[0011] or

[0012] S2. Preparation of fine copper oxide powder by ultrasonic system: preheating the sodium hydroxide solution and keeping it warm to 60-80°C, then adding the supernatant after impurity removal in step S1, and the addition and reaction process are carried out under ultrasonic conditions of more than 40kHz, and the generated ammonia gas is recovered and stored for standby; after the reaction is completed, the solution is filtered to recover the copper oxide precipitate, and dried to obtain fine copper oxide powder;

[0013] S3. Suspended reduction roasting: preheat and keep the fine PVP / CuO powder or fine copper oxide powder obtained in step S2 to 500-600°C, introduce the ammonia-containing gas recovered in step S2 to make the powder in a suspended fluidized state, and carry out reduction roasting at 500-600°C. The roasting time is controlled to be less than 20 minutes to reduce the copper oxide to copper element, and finally obtain fine copper powder.

[0014] The present invention combines the alkalization method with suspension roasting, opening up a new path for cleanly and efficiently recovering copper from alkaline etching waste liquid by pyrolysis. By optimizing the alkalization reaction and roasting conditions, fine copper powder with an average particle size of less than 10 μm is obtained. Specifically, during the alkalization reaction, the impurity metals in the alkaline etching waste liquid of the circuit board will be converted into metal oxides or hydroxide precipitates as the pH value of the alkaline etching waste liquid increases, and the purity of copper oxide will be affected. Therefore, the first step of the present invention is to remove impurities from the alkaline etching waste liquid, and adsorption removal can better maintain the main components of the waste liquid. The alkaline etching waste liquid contains Fe 2+ Mg 2+ 、Al 3+ Plasma, its hydroxide has good adsorption properties, and can adsorb other metals to remove impurities during the sedimentation process. However, if the pH value of the waste liquid is directly increased, the inventors found that due to the low concentration of iron, magnesium and aluminum in the alkaline etching waste liquid, the removal effect of other impurities is not obvious, so additional adsorption agents are needed.

[0015] Magnesium hydroxide is a commonly used water treatment agent. It has a large specific surface area, many surface active sites and strong heavy metal adsorption performance. 2+ It can also form insoluble substances with arsenates, arsenites, etc., and has a good removal effect on metal acid ions. Compared with magnesium hydroxide, the price of magnesium chloride hexahydrate is several times lower, and it has higher economic benefits. But on the other hand, simply adding magnesium chloride is equivalent to introducing a large amount of magnesium impurities into the alkaline etching waste liquid. The inventors found that by adding magnesium chloride to the alkaline etching waste liquid and adjusting the pH value, the Mg in the solution 2+ As the pH increases, it gradually precipitates in the form of magnesium hydroxide and adsorbs other metal impurities during the sedimentation process, which can achieve a better impurity removal effect. When the pH value reaches 11.2, the magnesium ion concentration in the alkaline etching waste liquid is lower than the initial value; when the pH value exceeds 11.4, the copper in the alkaline etching waste liquid will be lost in large quantities. In summary, adsorption impurity removal is beneficial to improving the purity of copper oxide and copper powder, and only by combining the addition of magnesium chloride and the control of the pH value of the alkaline etching waste liquid can higher impurity removal requirements and lower copper loss be met.

[0016] The second step is to use alkalization reaction to separate copper, ammonia and chlorine from the alkaline etching waste liquid. The alkalization reaction refers to adding a strong alkaline solution to the alkaline etching waste liquid, and the following reaction occurs at above 60°C: [Cu(NH3)4] 2+ +2OH - =CuO↓+4NH3↑+H2O. After alkalization treatment, the copper in the alkaline etching waste liquid is precipitated in the form of copper oxide, ammonia escapes in the form of ammonia gas, and chlorine is largely retained in the solution, thus cleverly achieving the three-phase separation of copper, ammonia and chlorine, which is beneficial to the subsequent pyrometallurgical treatment of the alkaline etching waste liquid. In addition, by adding a dispersant or providing an ultrasonic field, it is possible to avoid the agglomeration of copper oxide during the formation process, thereby preparing copper oxide powder with a smaller particle size. Polyvinyl pyrrolidone (PVP) is a non-ionic dispersant, which is less affected by changes in pH value, and the particle size can be regulated by a steric hindrance mechanism. In the present invention, the copper oxide particles are surrounded by the hydrophobic groups of PVP, so that a dense protective layer is formed on the surface thereof, and at the same time, they are separated from each other under the action of the long organic chains of PVP to avoid the occurrence of agglomeration. Ultrasonic waves produce a series of compression and expansion fluctuations through the cavitation effect, which promote the dispersion of copper oxide particles, thereby obtaining fine copper oxide powder.

[0017] Reaction temperature is one of the most important factors affecting the alkalization reaction. When the temperature is lower than 60°C, the produced copper hydroxide cannot be effectively dehydrated and converted into copper oxide; when the temperature is higher than 80°C, ammonia escapes quickly, the solution boils violently, and it is difficult to control. When the temperature is too high, the copper oxide particles undergo violent Brownian motion, and collide with each other, causing the particle size to increase. In addition, the stirring rate also has a certain degree of influence on the formation and particle size change of copper oxide. The present invention adopts a faster stirring rate, which can, on the one hand, enable the reactants to fully contact, promote the synthesis of copper oxide and the escape of ammonia; on the other hand, the shear force generated by strong stirring can also disperse the copper oxide. However, too high a stirring rate will cause the copper hydroxide to be continuously thrown out of the solution, resulting in incomplete conversion.

[0018] The third step is to use the fine copper oxide powder obtained in the second step and the recovered ammonia-containing gas for suspension reduction roasting, and use the ammonia-containing gas as the carrier gas flow and reducing agent in the suspension reduction roasting stage of fine copper oxide, and the following reaction mainly occurs: 3CuO+2NH3=3Cu+N2+3H2O. Sintering is a phenomenon that may occur during the reduction roasting process and is not conducive to the realization of the technical objectives of the present invention. It refers to the transformation of powdered materials into a dense body through partial or complete fusion between particles at high temperature. Sintering will cause a significant increase in the particle size of copper powder, and the present invention uses a suspended fluidized roasting method to cause strong turbulence and mixing of fine copper oxide powder in an ammonia-containing gas flow, thereby strengthening the heat and mass exchange between the gas and solid phases, increasing the reaction rate, and reducing the roasting temperature for efficient reduction, thereby effectively reducing the degree of sintering. At the same time, the ammonia-containing gas flow can also perform pressure-assisted dispersion of copper powder, which is beneficial to the preparation of fine copper powder to a certain extent.

[0019] The roasting temperature and reaction time are the main factors affecting the sintering degree of fine copper powder. The inventors found that when the roasting temperature is lower than 500°C, the reduction rate of copper oxide is slow, which easily causes waste of ammonia; when the temperature is higher than 600°C, the copper powder obtained by roasting begins to sinter more seriously. As for the reaction time, when the reaction time is short, there is not enough ammonia to react with copper oxide, and the conversion of copper oxide is not complete; when the reaction time is long, on the one hand, ammonia is wasted, and on the other hand, the copper powder obtained by reduction has a longer residence time at high temperature, resulting in an increase in particle size.

[0020] In summary, fine copper powder with an average particle size of less than 10 μm can be prepared by controlling the conditions of alkalization reaction and reduction roasting.

[0021] Preferably, the concentration of impure metal zinc in the alkaline etching waste liquid described in step S1 is less than 70 mg / L, and the concentration of nickel is less than 10 mg / L. As mentioned above, most of the metal impurities in the alkaline etching waste liquid can be efficiently removed by adsorption and precipitation caused by "adding magnesium chloride + controlling the pH value of the etching waste liquid". However, for zinc and nickel, due to their chemical properties similar to those of copper, they are stably present in the form of ammine complexes in the alkaline etching waste liquid. Their strong complexing ability makes it difficult to effectively remove them by conventional methods such as precipitation, adsorption, and ion exchange, or they will inevitably be accompanied by a large loss of copper during the removal process. Therefore, in order to obtain copper oxide with higher purity, alkaline etching waste liquid with lower initial concentrations of zinc and nickel can be used.

[0022] Furthermore, the magnesium chloride in step S1 is magnesium chloride hexahydrate, and its addition amount is 10-40 g / L.

[0023] Furthermore, the mass fraction of the sodium hydroxide solution in step S1 is 35-45%, preferably 40%.

[0024] Furthermore, the suspension obtained by adding magnesium chloride and adjusting the pH value in step S1 is allowed to settle for more than 4 hours. The inventors found that the effect of adding stirring means on the adsorption of impurity metals by magnesium hydroxide is not obvious in the suspension obtained by adding magnesium chloride and adjusting the pH value. At the same time, when the settling time is more than 4 hours, the components of the solution tend to be stable, and obvious solid-liquid stratification occurs.

[0025] Furthermore, the amount of polyvinyl pyrrolidone added in step S2 is 10 to 40 g / L. As described above, PVP can control the particle size of copper oxide through a steric hindrance mechanism, and its addition amount is one of the key factors affecting the particle size. When the amount of PVP added is small, there are not enough hydrophobic groups to coat the particles, and the exposed parts collide due to thermal motion or Brownian motion, and the particles agglomerate to increase the particle size; when the amount of PVP added is large, the excess PVP will dissociate the hydrophobic groups coated on the surface of the particles, and the particles will also be in a state of not being completely coated. Therefore, it is necessary to control the amount of PVP added within an appropriate range in order to obtain small-particle copper oxide.

[0026] Further, the molar amount of sodium hydroxide in the sodium hydroxide solution of step S2 is 2.0 to 2.5 times the molar amount of copper in the supernatant after impurity removal in step S1. As mentioned above, according to the alkalization reaction equation, theoretically 1 mol of copper needs to react with 2 mol of hydroxide ions, but ammonia nitrogen and other metal impurities are also present in the alkaline etching waste liquid, which will also consume part of the hydroxide ions. Therefore, in order to ensure the efficient recovery of copper, it is necessary to use an excess of sodium hydroxide. However, when the amount of sodium hydroxide added is too large, copper oxide will be converted into a hydroxy complex and redissolved in the solution, thereby affecting the recovery rate of copper.

[0027] Preferably, the reaction volume ratio of the sodium hydroxide solution in step S2 to the supernatant after impurity removal in step S1 is 1:1. The concentration of the solution will have a significant effect on the particle size of the dispersed phase. When the solution concentration is high, the interaction force between the particles will be enhanced, resulting in a larger particle size of the synthesized copper oxide. However, excessive dilution will affect the escape efficiency of ammonia, and the present invention adopts a reaction volume ratio of 1:1 to achieve a balance between the two aspects.

[0028] Furthermore, the feeding in step S2 is multi-channel feeding, and the feeding rate of each channel is 5-10 mL / min. Avoid feeding too fast to cause the local concentration of the reaction solution to be too high, and the copper oxide particles grow quickly, resulting in an increase in particle size.

[0029] Furthermore, the material addition method described in step S2 is to drip the alkaline etching waste liquid into the preheated sodium hydroxide solution drop by drop, and react for 5 to 20 minutes after the addition is completed. The inventors found that the material addition method of dripping the alkaline etching waste liquid into the preheated sodium hydroxide solution shortens the preparation time of copper oxide by 90% compared with other currently disclosed feeding methods, and only takes 20 minutes at most to achieve complete conversion of copper hydroxide, which greatly improves the production rate. This is because copper hydroxide often exhibits stronger dehydration performance under higher alkalinity conditions. At the same time, shortening the reaction time can also reduce the probability of collision of copper oxide particles under higher reaction temperature conditions, which is conducive to the preparation of fine copper oxide.

[0030] Preferably, after the copper oxide precipitate is prepared by the ultrasonic system in step S2, ultrasonic enhanced water washing is also included, the ultrasonic frequency is 24 to 40kHz, the water temperature is room temperature to 80°C, the solid-liquid ratio of the water washing is less than 1:10, the single water washing time is more than 10 minutes, the number of water washings is more than 2 times, and the chlorine content of the copper oxide powder after water washing and drying is controlled to be less than 0.015%. The copper oxide obtained by the alkalization reaction will have a small amount of free and adsorbed sodium chloride on its surface. For the fine copper oxide prepared by the ultrasonic system, the sodium chloride impurity can be removed more efficiently by conventional water washing or ultrasonic enhanced water washing, and the dried copper oxide can also be sold directly as a product.

[0031] Further, in the preheating and heat preservation stage described in step S3, nitrogen is introduced into the reaction vessel to exclude air, the heating rate is above 10°C / min, and the corresponding reaction temperature is reached and the temperature is kept for 5 to 20 minutes. The purpose of preheating and heat preservation is, on the one hand, to provide the activation energy required for the reduction reaction of copper oxide, so that the reaction can proceed quickly after the ammonia-containing gas is introduced; on the other hand, it is to pyrolyze and remove the PVP coated on the surface of the fine PVP / CuO powder, otherwise it will affect the contact between ammonia and copper oxide and hinder the reduction reaction. At the same time, the inventors found that the pyrolysis products of PVP include low molecular weight unsaturated alkanes, volatile gases such as CO and NH3, and a very small amount of residual carbon, all of which have certain reducing properties, and can reduce all copper oxide to cuprous oxide, and further reduce part of the cuprous oxide to elemental copper. Therefore, by preheating and heat preservation, the reducing substances produced by the pyrolysis of PVP can be fully utilized, and the amount of ammonia-containing gas introduced in the subsequent suspension reduction roasting can be reduced. Excess ammonia can be used to produce ammonium chloride products to improve the economic benefits of the enterprise.

[0032] Furthermore, the powder is placed in a suspended fluidized state in step S3 by uniformly introducing the ammonia-containing gas recovered in step S2 from bottom to top, and the gas flow rate is greater than the critical fluidization velocity of the copper oxide particles, that is, the copper oxide powder is observed to be in a fluidized state.

[0033] Preferably, the sintering degree of copper powder can be reduced by reducing the amount of copper oxide reaction or increasing the flow rate of ammonia-containing gas, thereby shortening the time of copper oxide reduction roasting. However, the flow rate of ammonia-containing gas should be controlled below the maximum fluidization velocity of copper oxide particles, that is, it is observed that the copper oxide powder is just not carried out of the reactor by the fluid.

[0034] Preferably, after the fine copper powder is prepared by the dispersant system in step S3, ultrasonic enhanced water washing is also included, the ultrasonic frequency is 24-40kHz, the water temperature is room temperature, the solid-liquid ratio of water washing is less than 1:10, and the single water washing time is 5-10min. The fine copper powder after water washing can be vacuum freeze-dried or dried in a vacuum drying oven at 45°C. Due to the coating effect of PVP, the water washing removal efficiency of the sodium chloride remaining on the surface of copper oxide is low. However, since sodium chloride has a strong ionic bond and Na + and Cl - The ion energy level is low, the redox property is weak, and it is not easy to gain or lose electrons. Therefore, sodium chloride can show high stability at high temperature. Within the roasting temperature range of the present invention, it will neither melt, sublimate, nor pyrolyze, nor react chemically with copper compounds and ammonia. After the PVP on the surface of the fine PVP / CuO powder is removed by pyrolysis, the sodium chloride impurities can be efficiently removed by ultrasonic enhanced water washing.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The invention discloses a method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which comprises the following steps: firstly, magnesium chloride is added to the alkaline etching waste liquid, the pH value of the solution is adjusted, a magnesium hydroxide precipitate is formed, and impurity metals are adsorbed to remove impurities. Subsequently, under a dispersant or an ultrasonic system, an alkalization reaction is used to not only realize the three-phase separation of copper, ammonia, and chlorine of the alkaline etching waste liquid, but also the particle size of copper oxide can be controlled. Then, the ammonia-containing gas recovered by the alkalization method is used as a carrier gas flow and a reducing agent to suspend and reduce roast the fine copper oxide powder, and finally obtain fine copper powder. The invention combines the alkalization method with the suspended roasting, opens up a new path for cleanly and efficiently recovering copper in alkaline etching waste liquid by pyrolysis, and obtains fine copper powder with an average particle size of less than 10 μm by optimizing the alkalization reaction and roasting conditions.

[0037] Compared with the prior art, the present invention utilizes ammonia in the alkaline etching waste liquid, saving the high cost of reducing agents in the liquid phase reduction method or the power consumption and electrode loss cost in the electrodeposition method, with high resource utilization and the production cost is expected to be greatly reduced. In addition, the present invention effectively shortens the preparation time of fine copper oxide and fine copper powder by adjusting the material addition method and adopting suspension reduction roasting and other means.

[0038] The dispersant polyvinyl pyrrolidone of the present invention is non-toxic, non-irritating, and has good biodegradability, and belongs to a new generation of "green products". In addition, the tail liquid after the alkalization reaction has basically the same compound type as the alkaline etching solution, and the copper concentration is effectively reduced, and can be regenerated and formulated into an alkaline etching solution for reuse in the circuit board etching process. Therefore, the process of the present invention is relatively safe and environmentally friendly.

[0039] The equipment that may be involved in the industrial production process of the present invention includes evaporation towers, stirring tanks, fluidized beds, etc., which are all devices with mature technology and widely used in engineering practice. Enterprises with such equipment conditions can meet the production requirements of the present invention after simple transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the process route diagram of the present invention.

[0041] Figure 2 This is the SEM image of fine PVP / CuO powder.

[0042] Figure 3 This is the SEM image of fine copper powder obtained by suspension reduction calcination of fine PVP / CuO powder.

[0043] Figure 4 This is the XRD pattern of fine copper powder.

[0044] Figure 5 This is the SEM image of fine copper oxide powder.

[0045] Figure 6 This is the SEM image of fine copper powder obtained by suspension reduction calcination of fine copper oxide powder. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0047] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0048] The alkaline etching waste liquid used in the embodiment is a product produced by Guangdong Pengrui Environmental Resources Co., Ltd.

[0049] The process route diagram of the present invention is as follows: Figure 1 As shown, the following steps are included:

[0050] (1) adding magnesium chloride to the alkaline etching waste liquid, adjusting the pH value of the solution with sodium hydroxide solution to precipitate the magnesium ions in the form of magnesium hydroxide, and adsorbing other metals during the sedimentation process to remove impurities;

[0051] (2) In the presence of a dispersant or ultrasonic system, the impurity-removed supernatant is dripped dropwise into a preheated sodium hydroxide solution for alkalization reaction, the generated ammonia gas is recovered and stored for standby use, the reaction solution is filtered and the copper oxide precipitate is recovered, and the copper oxide precipitate is washed and dried to obtain fine copper oxide powder. The alkalized tail liquid has basically the same compound type as the alkaline etching solution, and the copper concentration is effectively reduced, so it can be regenerated and formulated into an alkaline etching solution for reuse in the circuit board etching process;

[0052] (3) Preheating and keeping the fine copper oxide powder warm under air-tight conditions to provide the activation energy required for the reduction reaction and promote the thermal decomposition of the PVP coated on the surface of the fine PVP / CuO powder. Then, the ammonia-containing gas recovered from the alkalization treatment is used as a carrier gas flow and a reducing agent to suspend and reduce the fine copper oxide powder. The roasting tail gas can be used to produce ammonium chloride after absorption, and the fine copper powder is ultrasonically enhanced and washed to promote its further dispersion and improve its purity.

[0053] Example 1

[0054] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid specifically comprises the following steps:

[0055] Step 1: The copper concentration of the alkaline etching waste liquid used is 87.9680 g / L. 4 g of magnesium chloride hexahydrate is added to 200 mL of alkaline etching waste liquid, and the pH value of the etching waste liquid is adjusted to 11.3 using a 40% mass fraction sodium hydroxide solution, and the solution is allowed to settle for 6 hours. The solution is then centrifuged at a speed of 4000 r / min for 4 minutes, and the upper clear liquid is the alkaline etching waste liquid after impurities are removed.

[0056] Step 2, the preparation process of fine PVP / CuO powder is carried out in a constant temperature magnetic stirring water bath. Take 50mL of the impurity-removed supernatant, add 1g of polyvinyl pyrrolidone (PVP K30) thereto, and stir until the dispersant is completely dissolved. Take 6.2313g of sodium hydroxide and completely dissolve it in 50mL of distilled water to obtain a sodium hydroxide solution. Preheat the sodium hydroxide solution to 80°C, and then use a peristaltic pump to dropwise add the impurity-removed supernatant containing the dispersant into the sodium hydroxide solution at a rate of 5mL / min. The feeding and reaction process are continuously stirred at a stirring rate of 600r / min. The ammonia-containing gas escaping during the reaction is passed into a gas collection bag for storage and standby. After 20 minutes of reaction, the solid and liquid are separated, and the precipitate is dried in a 65°C blast drying oven for 48 hours. The SEM image of the dried fine PVP / CuO powder is as follows Figure 2 As shown in the figure, the PVP / CuO powder has good dispersibility, the particle size is basically submicron, and the morphology presents an irregular trapezoidal structure with a smooth surface.

[0057] Step three, the reduction roasting process of the fine PVP / CuO powder is carried out in a vertical tube furnace. Take 2g of fine PVP / CuO powder and place it in a vertical furnace. Heat it to 500℃ at a rate of 10℃ / min and keep it warm for 20min. During the heating and insulation process, nitrogen is introduced at a flow rate of 20mL / min to exclude the air inside the tube furnace. Subsequently, a high-precision flow rate peristaltic pump is used to pass the ammonia-containing gas recovered in the gas collecting bag into the vertical furnace at a flow rate of 90mL / min to provide suspension roasting conditions. Reduction roasting is carried out at 500℃ and the reaction is carried out for 15min. After the reaction is completed, the fine copper powder is dispersed in distilled water at a solid-liquid ratio of 1:10, and washed and dispersed at an ultrasonic frequency of 40kHz for 10min. The particle size results are shown in Table 1, and the SEM picture is as follows Figure 3 The copper powder particle size is basically submicron, and the morphology shows a spherical structure with an uneven surface, indicating that after the PVP / CuO is pyrolyzed, the PVP wrapped on the surface is completely decomposed, exposing the copper oxide hidden inside, and then the copper oxide is reduced and roasted to convert into copper powder. The fine copper powder after ultrasonic enhanced water washing is dried in a vacuum drying oven at 45°C. The XRD pattern of the fine copper powder after drying is shown in Figure 4 As shown. The diffraction peak of the product is consistent with the standard XRD spectrum of pure copper, and there is no obvious diffraction peak of copper oxide, which can be judged that the final product is pure copper powder. At the same time, the diffraction peak observed from the XRD spectrum is relatively sharp, indicating that the copper powder has a small particle size and good crystallinity.

[0058] Example 2

[0059] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 1 in that the sampling amount of fine PVP / CuO powder in step three is 3g, the roasting time is 20min, and the particle size results of the fine copper powder are shown in Table 1.

[0060] Example 3

[0061] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 1 in that the roasting temperature in step three is 550° C. and the particle size results of the fine copper powder are shown in Table 1.

[0062] Example 4

[0063] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 3 in that the sampling amount of fine PVP / CuO powder in step three is 3g, the roasting time is 20min, and the particle size results of the fine copper powder are shown in Table 1.

[0064] Example 5

[0065] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 1 in that the roasting temperature in step three is 600° C. The particle size results of the fine copper powder are shown in Table 1.

[0066] Example 6

[0067] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 5 in that the sampling amount of fine PVP / CuO powder in step three is 3g, the roasting time is 20min, and the particle size results of the fine copper powder are shown in Table 1.

[0068] Example 7

[0069] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid specifically comprises the following steps:

[0070] Step 1: The copper concentration of the alkaline etching waste liquid used is 111.4050 g / L. 4 g of magnesium chloride hexahydrate is added to 200 mL of alkaline etching waste liquid, and the pH value of the etching waste liquid is adjusted to 11.3 using a 40% mass fraction sodium hydroxide solution, and the solution is allowed to settle for 6 hours. The solution is then centrifuged at a speed of 4000 r / min for 4 minutes, and the upper clear liquid is the alkaline etching waste liquid after impurities are removed.

[0071] Step 2, the preparation process of fine copper oxide powder is carried out in a 40kHz ultrasonic tank. Take 7.8915g of sodium hydroxide and completely dissolve it in 50mL of distilled water to obtain a sodium hydroxide solution. Preheat the sodium hydroxide solution to 70°C, then use a peristaltic pump to drop 50mL of impurity-removing supernatant into the sodium hydroxide solution at a rate of 5mL / min, and continuously provide 40kHz ultrasonic conditions during the feeding and reaction process. The ammonia-containing gas escaping during the reaction is passed into the gas collection bag for storage and standby. After 10 minutes of reaction, the solid-liquid separation is carried out, and then the copper oxide is dispersed in 80°C distilled water at a solid-liquid ratio of 1:10, and stirred at a speed of 180r / min for 10 minutes. After the first water washing, the solid-liquid separation is completed, and the copper oxide is dispersed in 80°C distilled water at a solid-liquid ratio of 1:10, and washed in a 40kHz ultrasonic field for 10 minutes. The precipitate after secondary water washing is dried in a blast drying oven at 65°C for 48 hours. The chlorine content of the dried fine copper oxide powder is 0.0079%, which meets the relevant requirements of the National Standard of the People's Republic of China - Copper Oxide Powder (GB / T 26046-2010). The SEM image is as follows Figure 5 The copper oxide powder has good dispersibility, the particle size is basically at the single micron level, and the morphology presents a spherical structure formed by the accumulation of needle-shaped flakes with various shapes and sharp edges.

[0072] Step three, the reduction roasting process of fine copper oxide is carried out in a vertical tubular furnace. Take 2g of fine copper oxide powder and place it in a vertical furnace. Heat it to 500℃ at a rate of 10℃ / min and keep it warm for 5min. During the heating and insulation process, nitrogen is introduced at a flow rate of 20mL / min to exclude the air inside the tubular furnace. Subsequently, a high-precision flow rate peristaltic pump is used to pass the ammonia-containing gas in the gas collecting bag into the vertical furnace at a flow rate of 90mL / min to provide suspension roasting conditions. Reduction roasting is carried out at 500℃ and the reaction is carried out for 15min. After the reaction is completed, fine copper powder is obtained. The particle size results are shown in Table 1 and the SEM picture is shown in Table 1. Figure 6 As shown in the figure. The copper powder particle size is basically at the single micron level, and the morphology presents a rice-like structure with various shapes and uneven surfaces, which is formed by the adhesion between adjacent spherical copper oxides. At the same time, there is still a small amount of agglomeration in the copper powder, but compared with conventional reduction roasting, the situation has been greatly improved.

[0073] Example 8

[0074] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 7 in that the sampling amount of the fine copper oxide powder in step three is 3g, the roasting time is 20min, and the particle size results of the fine copper powder are shown in Table 1.

[0075] Example 9

[0076] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 7 in that the roasting temperature in step three is 550° C. and the particle size results of the fine copper powder are shown in Table 1.

[0077] Example 10

[0078] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 9 in that the sampling amount of the fine copper oxide powder in step three is 3g, the roasting time is 20min, and the particle size results of the fine copper powder are shown in Table 1.

[0079] Embodiment 11

[0080] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 7 in that the roasting temperature in step three is 600° C. and the particle size results of the fine copper powder are shown in Table 1.

[0081] Table 1 Particle size of fine copper powder in the embodiment

[0082] Dispersant system Average particle size / μm Ultrasonic system Average particle size / μm Example 1 0.4317 Example 7 7.5950 Example 2 0.5722 Example 8 8.0500 Example 3 0.6087 Example 9 7.9190 Example 4 0.3999 Example 10 8.9220 Example 5 0.7280 Embodiment 11 9.8050 Example 6 1.3990

[0083] Comparative Example 1

[0084] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, wherein the difference from Example 7 is that the alkaline etching waste liquid used in step 2 to prepare fine copper oxide powder has not been treated with impurities. The contents of the main metal elements of the two copper oxides are shown in Table 2. The results show that the fine copper oxide powder prepared from the alkaline etching waste liquid after impurities removal has a multiple decrease in the content of metal impurities compared with the unimpurities removal, and the copper oxide content is significantly increased, indicating that impurities removal is beneficial to improving the purity of copper oxide and copper powder.

[0085] Table 2 Metal content of copper oxide prepared from alkaline etching waste liquid with and without impurities removed

[0086]

[0087] Comparative Example 2

[0088] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, wherein the difference from Example 7 is that the material addition method for preparing fine copper oxide powder in step 2 is to dropwise add sodium hydroxide solution into the preheated impurity-removed supernatant. The results show that after 60 minutes of reaction, a considerable portion of copper hydroxide in the container is still not converted into copper oxide.

[0089] Comparative Example 3

[0090] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, which is different from Example 1 and Example 7 in that: in the process of preparing fine copper oxide powder, no dispersant is added and no ultrasonic field is provided. The results show that the average particle size of copper oxide without particle size control is 22.9μm, and fine copper powder with an average particle size of less than 10μm cannot be obtained by suspended reduction roasting of this copper oxide. This is because the copper content of the alkaline etching waste liquid is 80-180g / L, which is a high copper concentration solution. When the solution concentration is high, the interaction force between the particles will be enhanced, the particles will grow fast, and they will be easy to agglomerate. Therefore, the copper oxide particle size can only be controlled within the target range by external interference.

[0091] Comparative Example 4

[0092] A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, wherein the difference from Example 7 is that the flow rate of the ammonia-containing gas is reduced so that it cannot provide conditions for suspended roasting of copper oxide. The results show that under conventional reduction roasting conditions, the reduction effect of fine copper oxide powder is poor when the roasting temperature is lower than 700°C. If the reduction is carried out at 700°C, the copper powder obtained by roasting can be observed to be more severely sintered, and the average particle size is 24.0μm.

Claims

1. A method for preparing fine copper powder by suspended reduction roasting of alkaline etching waste liquid, characterized in that: The steps include: S1. Impurity removal: adding magnesium chloride to the waste liquid of the circuit board alkaline etching, adjusting the pH value of the waste liquid to 11.2-11.4 with sodium hydroxide solution, so that the magnesium ions are precipitated in the form of magnesium hydroxide and adsorb the impurity metals; S2. Preparation of fine copper oxide powder by dispersant system: adding polyvinyl pyrrolidone to the supernatant after impurity removal in step S1 to completely dissolve it; preheating the sodium hydroxide solution and keeping it warm to 60-80°C, then adding the impurity-removed supernatant containing polyvinyl pyrrolidone thereto, stirring continuously at a speed of 500-600 r / min during the addition and reaction process, and recovering and storing the generated ammonia gas for standby use; after the reaction is completed, filtering the solution to recover the copper oxide precipitate, and drying to obtain fine PVP / CuO powder; or S2. Preparation of fine copper oxide powder by ultrasonic system: preheating the sodium hydroxide solution and keeping it warm to 60-80°C, then adding the supernatant after impurity removal in step S1, and the addition and reaction process are carried out under ultrasonic conditions of more than 40kHz, and the generated ammonia gas is recovered and stored for standby; after the reaction is completed, the solution is filtered to recover the copper oxide precipitate, and dried to obtain fine copper oxide powder; S3. Suspended reduction roasting: preheat and keep the fine PVP / CuO powder or fine copper oxide powder obtained in step S2 to 500-600°C, introduce the ammonia-containing gas recovered in step S2 to make the powder in a suspended fluidized state, and carry out reduction roasting at 500-600°C. The roasting time is controlled to be less than 20 minutes to reduce the copper oxide to copper element, and finally obtain fine copper powder.

2. The method according to claim 1, characterized in that: The magnesium chloride in step S1 is magnesium chloride hexahydrate, and its addition amount is 20-40 g / L.

3. The method according to claim 1, characterized in that: The suspension obtained by adding magnesium chloride and adjusting the pH value in step S1 is allowed to settle for more than 4 hours.

4. The method according to claim 1, characterized in that: The amount of polyvinyl pyrrolidone added in step S2 is 10 to 40 g / L.

5. The method according to claim 1, characterized in that: The molar amount of sodium hydroxide in the sodium hydroxide solution of step S2 is 2.0 to 2.5 times the molar amount of copper in the supernatant after impurity removal in step S1, and the reaction volume ratio of the sodium hydroxide solution to the supernatant after impurity removal is 1:

1.

6. The method according to claim 1, characterized in that: The material addition in step S2 is multi-channel sample addition, and the material addition rate of each channel is 5-10 mL / min.

7. The method according to claim 1, characterized in that: The material adding method in step S2 is to drip the alkaline etching waste liquid drop by drop into the preheated sodium hydroxide solution, and react for 5 to 20 minutes after the addition is completed.

8. The method according to claim 1, characterized in that: After the copper oxide precipitate is prepared by the ultrasonic system in step S2, ultrasonic enhanced water washing is also included, the ultrasonic frequency is 24 to 40 kHz, the water temperature is room temperature to 80° C., the solid-liquid ratio of the water washing is less than 1:10, the single water washing time is more than 10 minutes, the number of water washings is more than 2 times, and the chlorine content of the copper oxide powder after water washing and drying is controlled to be less than 0.015%.

9. The method according to claim 1, characterized in that: In the preheating and heat preservation stage of step S3, nitrogen is introduced into the reaction container to exclude air, the heating rate is above 10°C / min, and the temperature is kept for 5 to 20 minutes after reaching the corresponding reaction temperature.

10. The method according to claim 1, characterized in that: After the fine copper powder is obtained by the dispersant system in step S3, ultrasonic enhanced water washing is also performed, the ultrasonic frequency is 24 to 40 kHz, the water temperature is room temperature, the solid-liquid ratio of the water washing is less than 1:10, the single water washing time is 5 to 10 minutes, and the fine copper powder after water washing is dried.

Images