A method for preparing fine copper powder by suspension reduction roasting of alkaline etching waste liquid

Abstract

This invention discloses a method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid. The method involves first adding magnesium chloride to the alkaline etching waste liquid to adjust the pH value, forming magnesium hydroxide precipitate and adsorbing impurity metals. Subsequently, under the influence of a dispersant or an ultrasonic system, the alkalinization reaction not only achieves the separation of copper, ammonia, and chlorine phases in the alkaline etching waste liquid but also allows for particle size control of copper oxide. Then, ammonia-containing gas recovered from the alkalinization method is used as a carrier gas and reducing agent to perform suspension reduction calcination on the fine copper oxide powder, ultimately yielding fine copper powder. This invention combines alkalinization with suspension calcination, opening up a new path for the clean and efficient recovery of copper from alkaline etching waste liquid using pyrometallurgical methods. By optimizing the alkalinization reaction and calcination conditions, fine copper powder with an average particle size of less than 10 μm is obtained. Compared with existing technologies, this invention has a shorter preparation cycle, higher resource utilization, safer process, and is more environmentally friendly, and is expected to solve the problem of large-scale production of fine copper powder.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of etching waste liquid from printed circuit boards, specifically to a method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid. Background Technology

[0002] Alkaline etching waste liquid is generated during the etching process of printed circuit boards. It contains high concentrations of pollutants such as copper, ammonia, and chlorine, and is classified as HW22 hazardous waste in China, requiring proper disposal. On the other hand, alkaline etching waste liquid is also an important recycled material for valuable copper, with a copper content of 80-180 g / L, possessing high recycling value. Collecting etching waste liquid requires companies to pay suppliers for the corresponding copper, and coupled with the generally high production cost of tens of thousands of yuan per ton of copper, this significantly compresses profit margins. In recent years, fine copper powder, with its excellent physicochemical properties, has become a basic functional powder material with great application potential and high added value. The price of copper powder is influenced not only by the price of copper metal but also by its particle size; generally, the smaller the particle size, the higher the price. Therefore, if fine copper powder can be prepared using alkaline etching waste liquid as a raw material, the economic benefits for enterprises will be significantly improved.

[0003] Existing technologies for preparing copper powder from alkaline etching waste liquid mainly include the extraction-electrodeionization method and the liquid-phase reduction method. The extraction-electrodeionization method involves using an extractant to extract copper from the alkaline etching waste liquid, and then using sulfuric acid to back-extract the extract phase to obtain copper sulfate electrolyte, which is then electrodeposited onto 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 a variety of heavy metals with high content, which increases the cost of wastewater treatment; (2) Electrodeposition requires electrical energy to maintain the redox conditions of the system, resulting in high power consumption and frequent replacement of electrode plates, which increases costs; (3) The cathode copper ingot has a large particle size and needs to be further crushed by ball milling, which can easily lead to a decrease in 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, hypophosphite, thiourea dioxide, etc.) to the alkaline etching waste liquid, and in the presence of a dispersant (such as polyvinylpyrrolidone, polyethylene glycol, hexadecyltrimethylammonium bromide, etc.), complexed copper can be converted into fine copper powder. However, the reagents involved in this technology are expensive, and currently developed reducing agents generally pose safety risks. For example, hydrazine hydrate is highly toxic and its operation is unsafe, while sodium hypophosphite reacts violently and is unstable.

[0005] Pyrometallurgy, as one of the most commonly used industrial methods, is characterized by its wide adaptability, low energy consumption, high metal recovery rate, and large-scale production capability. However, due to the high content of ammonia and chlorine components in the dry basis of alkaline etching waste liquid, the inventors discovered that direct calcination not only results in the complete volatilization of the dry basis and extremely low copper recovery rate, but also generates chlorine-containing gases and ammonium chloride dust, which clog pipelines, accelerate equipment corrosion, affect production continuity, and increase treatment and maintenance costs. Therefore, how to cleanly and efficiently recover copper from alkaline etching waste liquid using pyrometallurgy and prepare fine copper powder is an urgent problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects and deficiencies 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 suspension reduction calcination of alkaline etching waste liquid includes the following steps:

[0009] S1. Impurity Removal: Add magnesium chloride to the alkaline etching waste liquid of the circuit board, and adjust the pH of the waste liquid to 11.2-11.4 with sodium hydroxide solution, so that magnesium ions precipitate in the form of magnesium hydroxide and adsorb impurity metals.

[0010] S2. Preparation of fine copper oxide powder using a dispersant system: Polyvinylpyrrolidone (PVP) is added to the supernatant after impurity removal in step S1 and completely dissolved. The sodium hydroxide solution is preheated and kept at 60–80°C, and then the supernatant containing PPVP is added. The addition and reaction process are continuously stirred at a speed of 500–600 r / min. The generated ammonia gas is recovered and stored for later use. After the reaction is completed, the solution is filtered to recover the copper oxide precipitate and dried to obtain fine PVP / CuO powder.

[0011] or

[0012] S2. Preparation of fine copper oxide powder using an ultrasonic system: The sodium hydroxide solution is preheated and kept at 60-80°C. Then, the supernatant after impurity removal in step S1 is added to it. The addition and reaction process are carried out under ultrasonic conditions above 40kHz. The generated ammonia gas is recovered and stored for later use. 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. Suspension reduction calcination: The fine PVP / CuO powder or fine copper oxide powder obtained in step S2 is preheated and kept at 500-600℃. The ammonia-containing gas recovered in step S2 is introduced to make the powder in a suspended fluidized state. Reduction calcination is carried out at 500-600℃ for a calcination time of less than 20 minutes to reduce copper oxide to elemental copper and finally obtain fine copper powder.

[0014] This invention combines alkalization with suspension roasting, opening up a new path for the clean and efficient recovery of copper from alkaline etching waste liquid using pyrometallurgical methods. 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, impurity metals in the alkaline etching waste liquid of circuit boards will be converted into metal oxides or hydroxide precipitates as the pH value of the alkaline etching waste liquid increases, affecting the purity of copper oxide. Therefore, the first step of this invention requires impurity removal treatment of the alkaline etching waste liquid, and adsorption removal can better retain the main components of the waste liquid. The alkaline etching waste liquid contains Fe. 2+ Mg 2+ Al 3+ Plasma, whose hydroxides have good adsorption properties, can adsorb other metals to remove impurities during sedimentation. However, if the pH value of the waste liquid is directly increased, the inventors found that the removal effect on other impurities is not significant due to the low concentration of iron, magnesium, and aluminum in the alkaline etching waste liquid, thus requiring additional adsorption agents.

[0015] Magnesium hydroxide is a commonly used water treatment agent due to its large specific surface area and numerous surface active sites, resulting in strong heavy metal adsorption capabilities. Furthermore, Mg... 2+ It can also form insoluble compounds with arsenates and arsenites, and has a good removal effect on metal anions. Compared with magnesium hydroxide, magnesium chloride hexahydrate is several times cheaper, making it more economical. However, simply adding magnesium chloride is equivalent to introducing a large amount of magnesium impurities into alkaline etching waste liquid. The inventors discovered that by adding magnesium chloride to alkaline etching waste liquid in conjunction with pH adjustment, the amount of Mg in the solution... 2+ As the pH increases, magnesium ions gradually precipitate as magnesium hydroxide, adsorbing other metallic impurities during the settling process, thus achieving a good impurity removal effect. When the pH reaches 11.2, the magnesium ion concentration in the alkaline etching waste liquid is lower than the initial value; when the pH exceeds 11.4, a large amount of copper in the alkaline etching waste liquid is lost. In summary, adsorption impurity removal is beneficial for improving the purity of copper oxide and copper powder, but only by combining the addition of magnesium chloride and controlling the pH of the alkaline etching waste liquid can high impurity removal requirements and low copper loss be met.

[0016] The second step involves using an alkalization reaction to separate the copper, ammonia, and chlorine phases in the alkaline etching waste liquid. This alkalization reaction involves adding a strongly alkaline solution to the alkaline etching waste liquid, where the following reaction occurs at a temperature above 60°C: [Cu(NH3)4] 2+ +2OH - =CuO↓ + 4NH3↑ + H2O. After alkalization, copper in the alkaline etching waste liquid precipitates as copper oxide, ammonia escapes as ammonia gas, and chlorine is largely retained in the solution. This cleverly achieves the separation of copper, ammonia, and chlorine into three phases, facilitating subsequent pyrometallurgical treatment of the alkaline etching waste liquid. Furthermore, by adding dispersants or providing an ultrasonic field, agglomeration of copper oxide during formation can be avoided, resulting in finer copper oxide powder. Polyvinylpyrrolidone (PVP) is a non-ionic dispersant, less affected by pH changes, and its particle size can be controlled through steric hindrance. In this invention, copper oxide particles are surrounded by hydrophobic groups of PVP, forming a dense protective layer on their surface. Simultaneously, the long organic chains of PVP separate them from each other, preventing agglomeration. Ultrasonic waves generate a series of compression and expansion waves through cavitation, promoting the dispersion of copper oxide particles and thus obtaining fine copper oxide powder.

[0017] Reaction temperature is one of the most significant factors affecting the alkalization reaction. Below 60°C, the produced copper hydroxide cannot be effectively dehydrated and converted into copper oxide; above 80°C, ammonia gas escapes rapidly, the solution boils violently and becomes difficult to control, and at excessively high temperatures, copper oxide particles undergo violent Brownian motion, colliding with each other and increasing in particle size. Furthermore, the stirring rate also has a certain influence on the formation and particle size change of copper oxide. This invention employs a relatively fast stirring rate, which on the one hand allows for sufficient contact of the reactants, promoting the synthesis of copper oxide and the escape of ammonia gas; on the other hand, the shear force generated by strong stirring can also disperse the copper oxide. However, excessively high stirring rates can cause copper hydroxide to be continuously thrown out of the solution, leading to incomplete conversion.

[0018] The third step involves using the fine copper oxide powder obtained in the second step to perform suspension reduction roasting with the recovered ammonia-containing gas. The ammonia-containing gas serves as both the carrier gas and the reducing agent in this suspension reduction roasting stage, and the main reaction is: 3CuO + 2NH3 = 3Cu + N2 + 3H2O. Sintering is a phenomenon that can occur during reduction roasting and is detrimental to achieving the technical objectives of this invention. It refers to the transformation of powdered materials into a dense body through partial or complete interparticle fusion at high temperatures. Sintering leads to a significant increase in copper powder particle size. This invention, through suspension fluidized bed roasting, causes intense turbulence and mixing of the fine copper oxide powder in the ammonia-containing gas stream, enhancing the heat and mass exchange between the gas and solid phases, increasing the reaction rate, and lowering the roasting temperature for efficient reduction, thereby effectively mitigating the degree of sintering. Simultaneously, the ammonia-containing gas stream can also provide pressure-assisted dispersion of the copper powder, which is beneficial to the preparation of fine copper powder to some extent.

[0019] Calcination temperature and reaction time are the main factors affecting the sintering degree of fine copper powder. The inventors found that when the calcination temperature is below 500℃, the reduction rate of copper oxide is slow, which easily leads to the waste of ammonia gas; when the temperature is above 600℃, the copper powder obtained from calcination begins to show more serious sintering. As for the reaction time, when the reaction time is short, there is not enough ammonia gas to react with copper oxide, and the conversion of copper oxide is incomplete; when the reaction time is long, on the one hand, it causes the waste of ammonia gas, and on the other hand, the copper powder obtained from reduction has a longer residence time at high temperature, resulting in an increase in particle size.

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

[0021] Preferably, the concentration of zinc impurities in the alkaline etching waste liquid 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 metallic impurities in the alkaline etching waste liquid can be efficiently removed through adsorption and precipitation caused by adding magnesium chloride and controlling the pH value of the etching waste liquid. However, for zinc and nickel, due to their similar chemical properties to copper, they exist stably in the alkaline etching waste liquid as ammonia complexes. Their strong complexing ability makes them difficult to remove effectively by conventional methods such as precipitation, adsorption, and ion exchange, or the removal process will inevitably involve a large loss of copper. Therefore, in order to obtain copper oxide with higher purity, an alkaline etching waste liquid with lower initial concentrations of zinc and nickel can be used.

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

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

[0024] Furthermore, the suspension obtained in step S1 by adding magnesium chloride and adjusting the pH value is allowed to settle for more than 4 hours. The inventors found that increasing stirring in the suspension obtained by adding magnesium chloride and adjusting the pH value has little effect on the adsorption of impurity metals by magnesium hydroxide. Simultaneously, when the settling time is more than 4 hours, the components of the solution tend to stabilize, and obvious solid-liquid stratification occurs.

[0025] Further, the amount of polyvinylpyrrolidone added in step S2 is 10–40 g / L. As mentioned above, PVP can control the particle size of copper oxide through steric hindrance, and its addition amount is one of the key factors affecting 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, causing particle agglomeration and increasing particle size. When the amount of PVP added is large, the excess PVP will dissociate the hydrophobic groups coated on the particle surface, which will also leave the particles in an incompletely coated state. Therefore, it is necessary to control the amount of PVP added within a suitable range in order to obtain copper oxide with a small particle size.

[0026] Furthermore, the molar amount of sodium hydroxide in the sodium hydroxide solution described in 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. However, the alkaline etching waste liquid also contains ammonia nitrogen and other metallic impurities, which will also consume some hydroxide ions. Therefore, in order to ensure efficient copper recovery, an excess of sodium hydroxide is required. However, when the amount of sodium hydroxide added is too large, copper oxide will be converted into hydroxyl complexes and redissolve in the solution, thereby affecting the copper recovery rate.

[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 has a significant impact on the particle size of the dispersed phase. When the solution concentration is high, the interaction force between particles will be enhanced, resulting in a larger particle size of the synthesized copper oxide. However, excessive dilution will affect the ammonia escape efficiency. The 1:1 reaction volume ratio used in this invention can achieve a balance between the two aspects.

[0028] Furthermore, the feeding in step S2 is a multi-channel feeding method, with a feeding rate of 5-10 mL / min for each channel. This avoids excessively rapid feeding, which could lead to excessively high local concentrations of the reaction solution, causing rapid growth of copper oxide particles and resulting in increased particle size.

[0029] Furthermore, in step S2, the material addition method involves dropwise addition of alkaline etching waste liquid into a preheated sodium hydroxide solution, followed by a reaction time of 5–20 minutes after addition. The inventors discovered that this method of adding alkaline etching waste liquid dropwise into a preheated sodium hydroxide solution reduces the copper oxide preparation time by 90% compared to other currently disclosed feeding methods. Complete conversion of copper hydroxide can be achieved in a maximum of only 20 minutes, significantly increasing production speed. This is because copper hydroxide often exhibits stronger dehydration properties under higher alkalinity conditions. Simultaneously, shortening the reaction time also reduces the probability of collisions between copper oxide particles at higher reaction temperatures, which is beneficial for the preparation of fine copper oxide.

[0030] Preferably, step S2, after obtaining copper oxide precipitate using an ultrasonic system, further includes ultrasonic-enhanced water washing. The ultrasonic frequency is 24–40 kHz, the water temperature is room temperature–80°C, the solid-liquid ratio during washing is below 1:10, the single washing time is above 10 minutes, the number of washing cycles is above 2, and the chloride content of the washed and dried copper oxide powder is controlled below 0.015%. The copper oxide obtained from the alkalization reaction will have a small amount of free and adsorbed sodium chloride remaining on its surface. For the micro-fine copper oxide prepared by the ultrasonic system, conventional water washing or ultrasonic-enhanced water washing can efficiently remove sodium chloride impurities, and the dried copper oxide can be sold directly as a product.

[0031] Further, in the preheating and holding stage described in step S3, nitrogen gas is introduced into the reaction vessel to purge air, and the heating rate is above 10℃ / min. After reaching the corresponding reaction temperature, the temperature is held for 5–20 min. The purpose of preheating and holding is twofold: firstly, to provide the activation energy required for the reduction reaction of copper oxide, allowing the reaction to proceed rapidly after the introduction of ammonia gas; secondly, to pyrolyze and remove PVP coated on the surface of the fine PVP / CuO powder, otherwise it would affect the contact between ammonia gas and copper oxide, hindering the reduction reaction. Simultaneously, the inventors discovered that the pyrolysis products of PVP, including low-molecular-weight unsaturated alkanes, volatile gases such as CO and NH3, and a very small amount of residual carbon, all possess certain reducing properties, capable of completely reducing copper oxide to cuprous oxide and further reducing some cuprous oxide to elemental copper. Therefore, preheating and holding can fully utilize the reducing substances produced by PVP pyrolysis, reducing the amount of ammonia gas introduced in the subsequent suspension reduction roasting. Excess ammonia gas can be used to produce ammonium chloride products, improving the economic efficiency of the enterprise.

[0032] Furthermore, step S3, which involves placing the powder in a suspended fluidized state, is achieved by uniformly introducing the ammonia-containing gas recovered in step S2 from bottom to top, with the gas flow rate being greater than the critical fluidization velocity of the copper oxide particles, thus observing that the copper oxide powder is in a fluidized state.

[0033] Preferably, the sintering degree of copper powder can be reduced by shortening the copper oxide reduction calcination time through reducing the amount of copper oxide reacted or increasing the flow rate of ammonia-containing gas. However, the flow rate of ammonia-containing gas should be controlled below the maximum fluidization rate of copper oxide particles, i.e., the copper oxide powder should be observed to be just not carried out of the reactor by the fluid.

[0034] Preferably, step S3, after obtaining the fine copper powder using the dispersant system, further includes ultrasonic-enhanced water washing. The ultrasonic frequency is 24–40 kHz, the water temperature is room temperature, the solid-liquid ratio during water washing is below 1:10, and the single water washing time is 5–10 min. The washed fine copper powder can be freeze-dried under vacuum or dried in a vacuum drying oven at 45°C. Due to the coating effect of PVP, the water washing removal efficiency of sodium chloride residue on the copper oxide surface of the fine PVP / CuO powder is relatively low. However, because sodium chloride has strong ionic bonds, and Na… + and Cl - Sodium chloride has a low ionic energy level and weak redox properties, making it difficult to gain or lose electrons. Therefore, sodium chloride exhibits high stability at high temperatures. Within the calcination temperature range of this invention, it will not melt, sublimate, or pyrolyze, nor will it react chemically with copper compounds or ammonia. After removing PVP from the surface of the fine PVP / CuO powder through pyrolysis, 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] This invention discloses a method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid. The method involves first adding magnesium chloride to the alkaline etching waste liquid to adjust the pH value, forming magnesium hydroxide precipitate, which adsorbs impurities to remove impurities. Subsequently, under a dispersant or ultrasonic system, an alkalization reaction is used to achieve not only the separation of copper, ammonia, and chlorine phases in the alkaline etching waste liquid but also to control the particle size of copper oxide. Then, ammonia-containing gas recovered by the alkalization method is used as a carrier gas flow and reducing agent to perform suspension reduction calcination on the fine copper oxide powder, ultimately obtaining fine copper powder. This invention combines alkalization with suspension calcination, opening up a new path for the clean and efficient recovery of copper from alkaline etching waste liquid using pyrometallurgical methods. By optimizing the alkalization reaction and calcination conditions, fine copper powder with an average particle size of less than 10 μm is obtained.

[0037] Compared with existing technologies, this invention utilizes ammonia in alkaline etching waste liquid, saving the high cost of reducing agents in liquid-phase reduction methods or the energy consumption and electrode wear costs of electrodeposition methods. This results in high resource utilization and a significant reduction in production costs. Furthermore, this invention effectively shortens the preparation time of fine copper oxide and fine copper powder by adjusting the material addition method and employing suspension reduction calcination.

[0038] The dispersant polyvinylpyrrolidone involved in this invention is non-toxic, non-irritating, and readily biodegradable, belonging to the next generation of "green products." Furthermore, the tail liquid after the alkalization reaction, because its compound composition is essentially the same as that of the alkaline etching solution and the copper concentration is effectively reduced, can be regenerated and formulated into an alkaline etching solution for reuse in the circuit board etching process. Therefore, the process of this invention is relatively safe and environmentally friendly.

[0039] The equipment that may be involved in the industrial production process of this invention includes evaporation towers, stirred tanks, fluidized beds, etc., all of which are currently technologically mature devices and widely used in engineering practice. Enterprises with the necessary equipment can meet the production requirements of this invention with simple modifications. Attached Figure Description

[0040] Figure 1 This is a process flow diagram of the present invention.

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

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

[0043] Figure 4 The image shows the XRD pattern of fine copper powder.

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

[0045] Figure 6 This is a SEM image of fine copper powder obtained by suspension reduction calcination of fine copper oxide powder. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

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

[0048] The alkaline etching waste liquid used in the examples was a production sample from Guangdong Pengrui Environmental Resources Co., Ltd.

[0049] The process route diagram of this invention is as follows: Figure 1 As shown, it includes the following steps:

[0050] (1) Add magnesium chloride to the alkaline etching waste liquid, adjust the pH value of the solution with sodium hydroxide solution so that magnesium ions precipitate in the form of magnesium hydroxide, and adsorb other metals during the sedimentation process to remove impurities.

[0051] (2) Under the influence of a dispersant or ultrasonic system, the supernatant after impurity removal is added dropwise to a preheated sodium hydroxide solution for alkalization. The generated ammonia gas is recovered and stored for later use. The reaction solution is filtered and copper oxide precipitate is recovered. The copper oxide precipitate is washed and dried to obtain fine copper oxide powder. Since the compound types of the alkalization tail liquid are basically consistent with those of the alkaline etching solution and the copper concentration is effectively reduced, it can be regenerated and prepared into an alkaline etching solution for reuse in the circuit board etching process.

[0052] (3) Under air-isolated conditions, the fine copper oxide powder is preheated and kept at a constant temperature to provide the activation energy required for the reduction reaction and to promote the pyrolysis of the PVP coating on the surface of the fine PVP / CuO powder. Subsequently, the ammonia-containing gas recovered from the alkali treatment is used as the carrier gas and reducing agent to perform suspension reduction roasting on the fine copper oxide powder. The roasting tail gas can be used to produce ammonium chloride after absorption. The fine copper powder is subjected to ultrasonic-enhanced water washing to promote its further dispersion and improve its purity.

[0053] Example 1

[0054] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid specifically includes the following steps:

[0055] Step 1: The copper concentration of the alkaline etching waste solution used is 87.9680 g / L. Add 4 g of magnesium chloride hexahydrate to 200 mL of the alkaline etching waste solution, and adjust the pH value of the etching waste solution to 11.3 using a 40% sodium hydroxide solution. Let it stand for 6 hours to settle. Then, centrifuge at 4000 r / min for 4 minutes. The supernatant is the purified alkaline etching waste solution.

[0056] Step two, the preparation of fine PVP / CuO powder was carried out in a constant-temperature magnetically stirred water bath. 50 mL of the purified supernatant was taken, and 1 g of polyvinylpyrrolidone (PVP K30) was added, stirring until the dispersant was completely dissolved. 6.2313 g of sodium hydroxide was taken and completely dissolved in 50 mL of distilled water to obtain a sodium hydroxide solution. The sodium hydroxide solution was preheated to 80°C, and then the purified supernatant containing the dispersant was added dropwise to the sodium hydroxide solution at a rate of 5 mL / min using a peristaltic pump. Stirring was continuous during the feeding and reaction process at a stirring rate of 600 r / min. Ammonia-containing gas escaping during the reaction was collected in a gas collection bag for later use. After reacting for 20 min, solid-liquid separation was performed, and the precipitate was dried in a 65°C forced-air drying oven for 48 h. The SEM image of the dried fine PVP / CuO powder is shown below. Figure 2 As shown, the PVP / CuO powder exhibits good dispersibility, with particle sizes generally reaching the submicron level, and a smooth, irregular quadrilateral structure.

[0057] Step 3: The reduction calcination process of the fine PVP / CuO powder was carried out in a vertical tube furnace. 2g of fine PVP / CuO powder was placed in the furnace and heated to 500℃ at a rate of 10℃ / min, held for 20min. During the heating and holding process, nitrogen gas was introduced at a flow rate of 20mL / min to purge air from the furnace. Subsequently, a high-precision peristaltic pump was used to introduce ammonia-containing gas recovered from the gas collection bag into the furnace at a flow rate of 90mL / min to provide suspension calcination conditions. Reduction calcination was carried out at 500℃ for 15min. After the reaction, the fine copper powder was dispersed in distilled water at a solid-liquid ratio of 1:10 and washed and dispersed for 10min under ultrasonic conditions at 40kHz. The particle size results are shown in Table 1, and the SEM images are shown below. Figure 3 As shown in the figure, the copper powder particles are mostly submicron in size and exhibit a spherical structure with an uneven surface. This indicates that after the pyrolysis treatment of PVP / CuO, the PVP coating on the surface completely decomposes, exposing the copper oxide hidden inside. The copper oxide is then converted into copper powder through reduction calcination. The ultrasonically enhanced water-washed fine copper powder is dried in a vacuum drying oven at 45℃. The XRD pattern of the dried fine copper powder is shown in the figure. Figure 4 As shown, the diffraction peaks of the product are consistent with the standard XRD pattern of elemental copper, and there are no obvious diffraction peaks of copper oxide, indicating that the final product is elemental copper powder. Furthermore, the sharp diffraction peaks observed in the XRD pattern indicate that the copper powder has a small particle size and good crystallinity.

[0058] Example 2

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

[0060] Example 3

[0061] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 1 is that the calcination temperature in step three is 550℃, 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 suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 3 is that the sample amount of fine PVP / CuO powder in step 3 is 3g, the calcination time is 20min, and the particle size results of fine copper powder are shown in Table 1.

[0064] Example 5

[0065] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 1 is that the calcination temperature in step three is 600℃, and 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 suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 5 is that the sample amount of fine PVP / CuO powder in step three is 3g, the calcination time is 20min, and the particle size results of fine copper powder are shown in Table 1.

[0068] Example 7

[0069] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid specifically includes the following steps:

[0070] Step 1: The copper concentration of the alkaline etching waste solution used is 111.4050 g / L. Add 4 g of magnesium chloride hexahydrate to 200 mL of the alkaline etching waste solution, and adjust the pH value of the etching waste solution to 11.3 using a 40% sodium hydroxide solution. Let it stand for 6 hours to settle. Then, centrifuge at 4000 r / min for 4 minutes. The supernatant is the purified alkaline etching waste solution.

[0071] Step two: The preparation of fine copper oxide powder was carried out in a 40kHz ultrasonic bath. 7.8915g of sodium hydroxide was completely dissolved in 50mL of distilled water to obtain a sodium hydroxide solution. The sodium hydroxide solution was preheated to 70℃, and then 50mL of purified supernatant was added dropwise to the sodium hydroxide solution at a rate of 5mL / min using a peristaltic pump. A 40kHz ultrasonic condition was continuously provided during the feeding and reaction process. Ammonia-containing gas escaping during the reaction was collected in a gas collection bag for later use. After reacting for 10 minutes, solid-liquid separation was performed. Copper oxide was then dispersed in distilled water at 80℃ at a solid-liquid ratio of 1:10 and stirred at 180r / min for 10 minutes. After the first water wash, solid-liquid separation was performed again, and copper oxide was dispersed in distilled water at 80℃ at a solid-liquid ratio of 1:10 and washed in a 40kHz ultrasonic field for 10 minutes. The precipitate after the second water wash was dried in a 65℃ forced-air drying oven for 48 hours. The dried fine copper oxide powder has a chlorine content of 0.0079%, meeting 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 shown below. Figure 5 As shown, the copper oxide powder has good dispersibility, with a particle size that is basically at the single micrometer level. Its morphology exhibits a spherical structure formed by the accumulation of needle-like flakes with various shapes and sharp edges.

[0072] Step 3: The reduction roasting process of fine copper oxide was carried out in a vertical tube furnace. 2g of fine copper oxide powder was placed in the furnace, and the temperature was increased to 500℃ at a rate of 10℃ / min, held for 5min, and nitrogen gas was introduced at a flow rate of 20mL / min during the heating and holding process to purge air from the furnace. Subsequently, a high-precision peristaltic pump was used to introduce ammonia-containing gas from the gas collection bag into the furnace at a flow rate of 90mL / min to provide suspension roasting conditions. Reduction roasting was carried out at 500℃ for 15min. After the reaction, fine copper powder was obtained, and its particle size is shown in Table 1. SEM images are shown below. Figure 6 As shown, the copper powder particles are mostly in the single-micrometer range, exhibiting a rice-grain-like structure with varying shapes and uneven surfaces. This is due to the adhesion between adjacent spherical copper oxide particles. While some agglomeration still exists, it is significantly improved compared to conventional reduction roasting.

[0073] Example 8

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

[0075] Example 9

[0076] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 7 is that the calcination temperature in step three is 550℃, 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 suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 9 is that the sample amount of fine copper oxide powder in step three is 3g, the calcination time is 20min, and the particle size results of fine copper powder are shown in Table 1.

[0079] Example 11

[0080] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid, wherein the difference from Example 7 is that the calcination temperature in step three is 600℃, 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 examples.

[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 Example 11 9.8050 Example 6 1.3990

[0083] Comparative Example 1

[0084] A method for preparing fine copper powder by suspension reduction roasting of alkaline etching waste liquid is disclosed, the difference from Example 7 being that the alkaline etching waste liquid used in step two for preparing fine copper oxide powder was not subjected to impurity removal treatment. The main metal element contents of the two types of copper oxide are shown in Table 2. The results show that the content of metal impurities in the fine copper oxide powder prepared by the alkaline etching waste liquid after impurity removal is reduced by several times compared with that without impurity removal, and the copper oxide content is significantly increased, indicating that impurity 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 after impurity removal and before impurity removal.

[0086]

[0087] Comparative Example 2

[0088] A method for preparing fine copper powder by suspension reduction roasting of alkaline etching waste liquid, which differs from Example 7 in that: in step two, the material addition method for preparing fine copper oxide powder is to add sodium hydroxide solution dropwise into the preheated impurity-removed supernatant. Results show that after 60 minutes of reaction, a considerable portion of copper hydroxide in the container remains unconverted into copper oxide.

[0089] Comparative Example 3

[0090] A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid is disclosed, differing from Examples 1 and 7 in that no dispersant is added or an ultrasonic field is provided during the preparation of fine copper oxide powder. Results show that the average particle size of copper oxide without particle size control is 22.9 μm. Suspension reduction calcination with this copper oxide cannot produce fine copper powder with an average particle size less than 10 μm. This is because the copper content of the alkaline etching waste liquid is 80–180 g / L, which is a high-copper-concentration solution. At higher concentrations, the interaction forces between particles increase, leading to rapid particle growth and easy agglomeration. Therefore, only through external interference can the copper oxide particle size be controlled within the target range.

[0091] Comparative Example 4

[0092] A method for preparing fine copper powder by suspension reduction roasting of alkaline etching waste liquid is disclosed, the difference from Example 7 being that the flow rate of ammonia-containing gas is reduced, making it impossible to provide the conditions for suspension roasting of copper oxide. Results show that under conventional reduction roasting conditions, the reduction effect of fine copper oxide powder is poor at roasting temperatures below 700℃. If reduction is performed at 700℃, the resulting copper powder exhibits severe sintering, with an average particle size of 24.0 μm.

Claims

1. A method for preparing fine copper powder by suspension reduction calcination of alkaline etching waste liquid, characterized in that, Includes the following steps: S1. Impurity Removal: Add magnesium chloride to the alkaline etching waste liquid of the circuit board, and adjust the pH of the waste liquid to 11.2-11.4 with sodium hydroxide solution, so that magnesium ions precipitate in the form of magnesium hydroxide and adsorb impurity metals. S2. Preparation of fine copper oxide powder using a dispersant system: Polyvinylpyrrolidone (PVP) is added to the supernatant after impurity removal in step S1 and completely dissolved. The sodium hydroxide solution is preheated and kept at 60–80 °C, and then the supernatant containing PPVP is added. The addition and reaction process are continuously stirred at a speed of 500–600 r / min. The generated ammonia gas is recovered and stored for later use. After the reaction is completed, the solution is filtered to recover the copper oxide precipitate and dried to obtain fine PVP / CuO powder. or S2. Preparation of fine copper oxide powder using an ultrasonic system: The sodium hydroxide solution was preheated and kept at 60-80 °C. Then, the supernatant after impurity removal in step S1 was added to it. The addition and reaction were carried out under ultrasonic conditions above 40 kHz. The generated ammonia gas was recovered and stored for later use. After the reaction was completed, the solution was filtered to recover the copper oxide precipitate and dried to obtain fine copper oxide powder. S3. Suspension reduction calcination: The fine PVP / CuO powder or fine copper oxide powder obtained in step S2 is preheated and kept at 500-600 ℃. The ammonia-containing gas recovered in step S2 is introduced to make the powder in a suspended fluidized state. Reduction calcination is carried out at 500-600 ℃ for a calcination time of less than 20 min to reduce copper oxide to elemental copper and finally obtain fine copper powder.

2. The method according to claim 1, characterized in that, The magnesium chloride mentioned 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 stand for sedimentation for more than 4 hours.

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

5. The method according to claim 1, characterized in that, The molar amount of sodium hydroxide in the sodium hydroxide solution in 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 in step S1 is 1:

1.

6. The method according to claim 1, characterized in that, The feeding in step S2 is a multi-channel feeding method, with a feeding rate of 5 to 10 mL / min for each channel.

7. The method according to claim 1, characterized in that, In step S2, the material is added dropwise by adding the supernatant containing polyvinylpyrrolidone or the supernatant after purification in step S1 into the preheated sodium hydroxide solution. After the addition is completed, the reaction is carried out for 5 to 20 minutes.

8. The method according to claim 1, characterized in that, Step S2, after obtaining copper oxide precipitate using an ultrasonic system, also includes ultrasonic-enhanced water washing. The ultrasonic frequency is 24–40 kHz, the water temperature is room temperature–80 ℃, the solid-liquid ratio of the water wash is less than 1:10, the single water wash time is more than 10 min, the number of water washes is more than 2, and the chlorine content of the copper oxide powder after 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 described in step S3, nitrogen gas is introduced into the reaction vessel to remove air, the heating rate is above 10 ℃ / min, and the temperature is maintained for 5 to 20 min after reaching the corresponding reaction temperature.

10. The method according to claim 1, characterized in that, Step S3, after obtaining fine copper powder with a dispersant system, also includes ultrasonic-enhanced water washing. The ultrasonic frequency is 24-40 kHz, the water temperature is room temperature, the solid-liquid ratio of the water is below 1:10, the single water washing time is 5-10 min, and the fine copper powder after water washing is dried.

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