A method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid

Abstract

The application discloses a method for preparing high-purity basic copper carbonate from PCB acidic etching waste liquid, and belongs to the technical field of resource utilization of copper-containing waste liquid. The method comprises the following steps: firstly, solid-liquid separation and acidity adjustment are performed on the PCB acidic etching waste liquid; then, copper is extracted by using an organic phase containing a copper selective extractant; the obtained copper-loaded organic phase is subjected to entrainment removal of a chlorine-containing water phase, low-chlorine washing, acidic pre-back extraction and main back extraction, so as to obtain a low-chlorine copper salt purification liquid; subsequently, basic copper carbonate seeds pre-slurried by polyaspartic acid salt are added into the copper salt purification liquid, and a two-stage carbonation reaction is performed to generate basic copper carbonate slurry; finally, solid-liquid separation, chlorine ion gradient displacement washing and drying are performed to obtain the product. The application can reduce chlorine salt entrainment and fine powder embedding, improve product purity and improve the filtration and washing performance.

Description

Technical Field

[0001] This invention belongs to the field of copper-containing waste liquid resource utilization technology, and more specifically, relates to a method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid. Background Technology

[0002] PCB acid etching wastewater is a type of copper-containing wastewater generated during the production of printed circuit boards. It typically contains high concentrations of copper ions, hydrochloric acid, chloride ions, and sodium salts. Treating this wastewater solely through neutralization and precipitation not only wastes copper resources but also generates copper-containing sludge and high-salt wastewater, increasing the burden of subsequent treatment and disposal. Therefore, converting the copper resources in PCB acid etching wastewater into industrially viable copper salt products is an important direction for the resource utilization of copper-containing etching wastewater.

[0003] Basic copper carbonate is a commonly used copper salt product, serving as a raw material for pigments, catalysts, wood preservatives, feed additives, and other copper salt preparations. Utilizing PCB acid etching wastewater to prepare basic copper carbonate can increase product added value while recovering copper resources. However, PCB acid etching wastewater has high chloride and sodium salt content, and the system has high acidity. During the carbonation and precipitation process, problems such as drastic local pH changes, finer precipitate particles, mother liquor entrainment in the filter cake, and high washing load can easily occur, thus affecting the purity, chloride and sodium salt residues, and filtration and washing performance of the basic copper carbonate product.

[0004] In the prior art, there are already methods for directly preparing basic copper carbonate from acidic etching waste liquid of printed circuit boards. For example, Chinese invention patent application CN105314668A discloses a method for recovering basic copper carbonate from acidic etching waste liquid of printed circuit boards. This method involves diluting the acidic etching waste liquid and then adding it to an alkaline solution to first form internal crystals of basic copper carbonate. Then, the remaining acidic etching waste liquid is added to continue the reaction, and the basic copper carbonate product is obtained through filtration, washing, and drying. This method improves upon the problems of product encapsulation and filtration performance in the direct precipitation process through the internal crystal method, enabling the recovery and utilization of copper from acidic etching waste liquid of printed circuit boards.

[0005] However, the carbonation reaction in the above methods still mainly takes place in a chloride- and salt-containing phase system formed by acidic etching waste liquid. For acidic etching waste liquid with high chloride and sodium salt content, chloride salts may still enter the product system with the interstitial liquid of precipitate particles, fine precipitate particles, or entrained liquid in the filter cake, requiring subsequent filtration and water washing processes to reduce soluble salt residues. When the chloride load in the raw solution is high or the product purity requirements are further increased, there may still be problems such as high washing water consumption, unstable filter cake washing endpoint, and difficulty in controlling chloride ion residues in the product.

[0006] Furthermore, existing technologies also include methods for adjusting the morphology of basic copper carbonate particles using additives. For example, Chinese invention patent application CN115611302A discloses a process for preparing nano-basic copper carbonate, in which a sodium carbonate solution and an additive solution are added dropwise to an acidic etching solution for reaction. The additives may include sodium dodecyl sulfonate, polyvinylpyrrolidone, etc., to improve the dispersion and formation of basic copper carbonate particles. This type of approach mainly uses surfactants or polymeric dispersants to adjust the morphology and agglomeration state of the precipitated particles, which is beneficial for obtaining basic copper carbonate products with specific particle sizes or morphologies.

[0007] However, for high-chlorine, high-salt systems derived from PCB acid etching wastewater, simply relying on conventional dispersants to adjust particle morphology cannot reduce the probability of chloride salts entering the precipitation system with the liquid phase from the overall process perspective. Furthermore, when preparing high-purity basic copper carbonate products, the introduction of additives must consider issues such as complete copper precipitation, residual copper in the mother liquor, filtration performance, and residual organic matter in the product. Improper selection or addition of additives may lead to excessively fine precipitate particles, increased filter cake liquid content, or increased subsequent washing load.

[0008] Therefore, existing technologies for preparing basic copper carbonate from PCB acid etching wastewater still need to address the following issues: how to reduce the adverse effects of high-chlorine-containing systems on the formation of basic copper carbonate precipitation, filter cake entrainment, and washing and desalination processes, while ensuring copper resource recovery; how to reduce mother liquor entrapment caused by fine powder or colloidal precipitates; and how to improve product purity and chloride residue control while simultaneously controlling filtration speed, washing water consumption, and product organic residue. To address these issues, it is necessary to provide a method for preparing high-purity basic copper carbonate from PCB acid etching wastewater. Summary of the Invention

[0009] In the existing process of preparing basic copper carbonate from PCB acid etching waste liquid, chloride salts are easily carried into the product system with the precipitated mother liquor, and fine powder or colloidal precipitates can easily increase the filtration and washing load. This invention provides a method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid, which can reduce chloride salt residue in the product and improve the filtration and washing performance of basic copper carbonate slurry.

[0010] To solve the above problems, the present invention adopts the following technical solution.

[0011] A method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid includes the following steps: S1. Solid-liquid separation is performed on the acidic etching waste liquid of PCB, and its acidity and copper ion concentration are adjusted to obtain the extract to be extracted. S2. Extract the extractant using an organic phase containing a copper selective extractant, so that copper enters the organic phase, and obtain a copper-loaded organic phase and raffinate. S3. The copper-loaded organic phase is subjected to a chlorine-containing aqueous phase removal treatment, and the copper-loaded organic phase after the chlorine-containing aqueous phase removal treatment is washed with a washing solution with controlled chloride ion concentration to obtain a washed copper-loaded organic phase. S4. The washed copper-loaded organic phase is pre-extracted using an acidic pre-extraction solution to obtain a chlorine-containing pre-extraction solution and a pretreated copper-loaded organic phase. The chlorine-containing pre-extraction solution does not enter the subsequent carbonation preparation section. S5. The pretreated copper-loaded organic phase is subjected to main back-extraction using an acidic main back-extraction solution to obtain a copper salt purification solution, and the copper salt purification solution with a chloride ion concentration meeting a preset threshold is introduced into the carbonation preparation section. S6. Add basic copper carbonate seed crystals to a low-chlorinated bicarbonate buffer solution containing polyaspartic acid salt for pre-conditioning to obtain surface-controlled seed crystals; add the surface-controlled seed crystals to the copper salt purification solution entering the carbonation preparation section and carry out the carbonation reaction to obtain basic copper carbonate slurry. S7. The basic copper carbonate slurry is subjected to solid-liquid separation, chloride ion gradient displacement washing and drying to obtain a high-purity basic copper carbonate product.

[0012] Preferably, in step S1, the PCB acid etching waste liquid contains copper ions, hydrochloric acid and chloride salts; after solid-liquid separation, the mass concentration of copper ions in the extract is adjusted to 50 g / L to 180 g / L, and the pH of the extract is adjusted to 0.5 to 2.5.

[0013] Preferably, in step S2, the organic phase includes an aldoxime copper extractant, a water-immiscible hydrocarbon organic diluent, and a phase separation modifier; based on the total volume of the organic phase, the aldoxime copper extractant accounts for 5% to 30%, the hydrocarbon organic diluent accounts for 60% to 94%, and the phase separation modifier accounts for 0.1% to 10%; the volume ratio of the organic phase to the extractant during extraction is 1:3 to 5:1, and the number of extraction stages is 1 to 4.

[0014] Preferably, in step S3, the removal of the entrained chlorine-containing aqueous phase is a coalescence separation process, which removes the chlorine-containing aqueous phase entrained in the copper-loaded organic phase, such that the mass content of entrained water in the copper-loaded organic phase after coalescence separation is not higher than 0.3%; the washing solution contains sulfuric acid and copper sulfate, wherein the mass concentration of sulfuric acid in the washing solution is 5 g / L to 50 g / L, the mass concentration of copper ions is 5 g / L to 40 g / L, and the mass concentration of chloride ions is not higher than 0.5 g / L.

[0015] Preferably, in step S4, the acidic pre-extraction solution is a sulfuric acid solution with a sulfuric acid mass concentration of 20 g / L to 100 g / L; the volume ratio of the acidic pre-extraction solution to the acidic main extraction solution in step S5 is 0.05:1 to 0.25:1; the resulting chlorine-containing pre-extraction solution is returned to the PCB acidic etching waste pretreatment section, the raffinate treatment section, or the high-chlorine salt treatment section.

[0016] Preferably, in step S5, the acidic main back-extraction solution is a sulfuric acid solution with a sulfuric acid mass concentration of 100 g / L to 220 g / L; the chloride ion mass concentration in the copper salt purification solution entering the carbonation preparation section is not higher than 0.2 g / L, or the mass ratio of chloride ions to copper ions is not higher than 0.002:1; copper salt purification solutions with chloride ion concentrations that do not meet the preset threshold are returned to step S3 or step S4 for processing.

[0017] Preferably, in step S6, the polyaspartic salt is polyaspartic ammonium, and the average molecular weight of the polyaspartic ammonium is 1000 to 6000; based on the theoretical mass of basic copper carbonate produced, the amount of polyaspartic ammonium added is 0.005% to 0.10%; the pH of the low-chlorine bicarbonate buffer solution is 6.0 to 7.2, and the chloride ion mass concentration is not higher than 0.05 g / L; based on the theoretical mass of basic copper carbonate produced, the amount of basic copper carbonate seed crystals added is 1% to 10%.

[0018] Preferably, in step S6, the carbonation reaction includes a first-stage carbonation and a second-stage carbonation; the first-stage carbonation controls the pH of the system to be 5.2 to 5.8, and adds 20% to 45% of the theoretical total carbonate dosage; the second-stage carbonation controls the pH of the system to be 6.0 to 6.8, and adds the remaining portion of the theoretical total carbonate dosage; the carbonation reaction temperature is 45°C to 75°C, and the second-stage carbonation is followed by aging for 30 min to 180 min.

[0019] Preferably, in step S7, the chloride ion gradient replacement washing includes at least three stages of washing, with the washing liquid obtained from the later stage being at least partially reused from the previous stage; the high-chlorine washing liquid obtained from the first stage is returned to the raffinate treatment section or the high-chlorine salt treatment section; the washing endpoint is that the chloride ion mass concentration in the final washing filtrate is not higher than 50 mg / L.

[0020] Preferably, the purity of the obtained high-purity basic copper carbonate product is not less than 99.2%, the chloride ion content is not more than 80 mg / kg, the sodium content is not more than 100 mg / kg, the total organic carbon content is not more than 0.05%, and the total copper recovery rate in the PCB acid etching waste liquid is not less than 98%.

[0021] Compared to existing technologies, this invention selectively extracts and transfers copper from PCB acid etching waste liquid to the organic phase, followed by sequential removal of entrained chlorine-containing aqueous phase, low-chlorine washing, acidic pre-extraction to remove chlorine, and chloride ion threshold access in the main back-extraction solution. This ensures that the copper salt purification solution entering the carbonation preparation stage is in a low-chlorine state, reducing the probability of chloride ions and sodium salts entering the basic copper carbonate product system with the precipitate mother liquor. Simultaneously, this invention uses polyaspartic acid salt to pre-mix the basic copper carbonate seed crystals, allowing the polyaspartic acid salt to preferentially act on the seed crystal surface in trace amounts. Combined with a two-stage carbonation reaction, this guides copper ions to nucleate and mature on the seed crystal surface, reducing the formation of fine powdery or colloidal precipitates, thereby reducing the filter cake entrainment rate and improving filtration performance. Furthermore, through chloride ion gradient replacement washing, residual soluble chloride and sodium salts in the filter cake are effectively replaced, reducing the consumption of fresh washing water. Therefore, this invention can simultaneously improve the purity of basic copper carbonate products, reduce chloride ion and sodium salt residues, improve slurry filtration and filter cake washing performance, and reduce washing water consumption and subsequent wastewater treatment load during the preparation process, while ensuring copper recovery rate. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0023] The specific embodiments of the present invention are described below. The following content is intended to help understand the technical solution of the present invention and does not constitute a limitation on the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can appropriately adjust the specific process parameters according to the copper content, acidity, chloride ion content of the PCB acid etching waste liquid, and equipment conditions.

[0024] This invention provides a method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid. The method uses PCB acid etching waste liquid as raw material. First, copper is selectively extracted to transfer copper from a high-chlorine, high-salt, and high-acid aqueous system. Then, the chlorine-containing aqueous phase entrained in the copper-loaded organic phase is removed and cut off to maintain a low chloride ion load in the copper salt purification solution entering the carbonation preparation stage. Subsequently, basic copper carbonate seed crystals are pre-mixed using polyaspartic acid salt, and carbonation is carried out in the presence of these surface-controlled seed crystals, allowing basic copper carbonate to be directionally generated in the low-chlorine copper salt purification solution. Finally, chloride ion gradient displacement washing further reduces the residual chloride and sodium salts in the filter cake, thereby obtaining a high-purity basic copper carbonate product.

[0025] PCB acid etching wastewater typically originates from the acid etching process in printed circuit boards. This liquid contains copper ions, hydrochloric acid, chloride ions, sodium salts, and small amounts of suspended solids, insoluble particles, or organic impurities. If alkali and carbonates are directly added to this wastewater for precipitation, copper ions readily form fine powdery or colloidal precipitates in areas where the local pH rapidly increases. These precipitates have a large specific surface area and fine filter cake pores, easily entraining chloride-containing mother liquor, making subsequent washing difficult to stably reduce chloride residue in the product. This invention reduces the chance of chloride entering the basic copper carbonate product system and improves slurry filtration and filter cake washing performance through a combination of front-end phase transfer purification, mid-stage seed crystal surface control, and back-end gradient displacement washing.

[0026] S1. Solid-liquid separation of PCB acid etching waste liquid and conditioning of the extract. First, the PCB acid etching waste liquid undergoes solid-liquid separation to remove suspended solids, insoluble particles, and impurities that could easily cause emulsification during extraction. Solid-liquid separation is achieved using one or more methods, including filtration, sedimentation, centrifugation, and microfiltration. After solid-liquid separation, the acidity and copper ion concentration of the waste liquid are adjusted to obtain the extractant.

[0027] The extractant refers to the aqueous phase material that has undergone solid-liquid separation and been adjusted to a state suitable for selective copper extraction. In one embodiment, the copper ion concentration in the extractant is adjusted to 50 g / L to 180 g / L, and the pH is adjusted to 0.5 to 2.5. When the copper ion concentration is below 50 g / L, the copper concentration in the subsequent back-extraction solution is too low, resulting in decreased carbonation preparation efficiency; when the copper ion concentration is above 180 g / L, the organic phase loading pressure increases, easily leading to incomplete extraction or phase instability. When the pH is below 0.5, the extraction capacity of aldoxime copper extractants for copper decreases; when the pH is above 2.5, there is a risk of premature hydrolysis of copper ions or the formation of basic salt precipitates, which is detrimental to the stable progress of subsequent extraction.

[0028] The S1 treatment ensures that the waste liquid entering the extraction section is within a relatively stable range of acidity and copper concentration, and reduces the interference of solid impurities on the extraction interface. This step provides stable feed conditions for the subsequent selective transfer of copper from the high-chlorine aqueous phase to the organic phase.

[0029] S2, copper selective extraction and formation of copper-supported organic phase. The extract obtained in S1 is brought into contact with an organic phase containing a copper selective extractant, so that the copper in the extract enters the organic phase, resulting in a copper-loaded organic phase and a raffinate.

[0030] The organic phase here is an oil-phase system that is immiscible with the aqueous phase and is used for the selective extraction of copper. This organic phase includes an aldoxime-based copper extractant, a water-immiscible hydrocarbon organic diluent, and a phase separation modifier. The aldoxime-based copper extractant forms copper complexes soluble in the organic phase with copper ions in the aqueous phase; the hydrocarbon organic diluent carries the aldoxime-based copper extractant and adjusts the viscosity and flowability of the organic phase; the phase separation modifier improves the separation properties of the organic and aqueous phases after extraction, reducing emulsification and entrainment in the aqueous phase.

[0031] In one embodiment, based on the total volume of the organic phase, the aldoxime copper extractant accounts for 5% to 30%, the hydrocarbon organic diluent accounts for 60% to 94%, and the phase separation modifier accounts for 0.1% to 10%. The hydrocarbon organic diluent is selected from one or more of sulfonated kerosene, No. 260 solvent oil, aliphatic hydrocarbon solvent oil, and isoparaffinic hydrocarbon solvent oil. The phase separation modifier is selected from one or more of higher alcohol modifiers, ester modifiers, and phosphate ester modifiers. During extraction, the volume ratio of the organic phase to the extractant is controlled at 1:3 to 5:1, and the number of extraction stages is 1 to 4.

[0032] After extraction, copper transitions from the high-chlorine, high-salt, acidic aqueous phase into the organic phase, forming a copper-loaded organic phase. This copper-loaded organic phase contains the copper extraction complex. The remaining aqueous phase after extraction is the raffinate, which retains most of the chloride ions, sodium salts, and free acids.

[0033] This step achieves the initial separation of copper from the original high-chlorine saline solution. Compared with directly precipitating basic copper carbonate in the acidic etching waste liquid of PCBs, allowing copper to enter the organic phase first reduces the degree to which subsequent product preparation stages are directly exposed to the high-chlorine mother liquor, laying the foundation for obtaining a low-chlorine copper salt purified solution.

[0034] S3. Removal of chlorine-containing aqueous phase entrained in the copper-loaded organic phase and low-chlorine washing. Although the copper-loaded organic phase obtained in S2 has achieved copper phase transfer, a small amount of aqueous droplets from the extract solution will be entrained in the copper-loaded organic phase during the actual extraction process. These aqueous droplets contain chloride ions, sodium ions, and free acid. Although the amount entrained is small, the chloride ion concentration is high. If it enters the back-extraction section with the copper-loaded organic phase, it is easy to mix with the subsequent copper salt purification solution and be carried into the basic copper carbonate product with the precipitate mother liquor during the carbonation reaction.

[0035] Therefore, the copper-loaded organic phase undergoes a process to remove entrained chlorine-containing aqueous phase. The entrained chlorine-containing aqueous phase refers to the tiny chlorine-containing water droplets that accompany the copper-loaded organic phase into subsequent processes. The removal of entrained chlorine-containing aqueous phase employs one or more of the following methods: coalescence separation, static stratification, inclined plate coalescence, fiber coalescence, packing coalescence, or membrane coalescence. In a preferred embodiment, the removal of entrained chlorine-containing aqueous phase employs coalescence separation, causing the tiny chlorine-containing water droplets dispersed in the copper-loaded organic phase to aggregate into larger droplets and then be discharged in stratification. After coalescence separation, the mass content of entrained water in the copper-loaded organic phase is no higher than 0.3%, more preferably no higher than 0.1%.

[0036] After removing the entrained chlorine-containing aqueous phase, the copper-loaded organic phase is washed with a washing solution of controlled chloride ion concentration. This washing solution contains sulfuric acid and copper sulfate, with the sulfuric acid concentration controlled at 5 g / L to 50 g / L, the copper ion concentration controlled at 5 g / L to 40 g / L, and the chloride ion concentration not exceeding 0.5 g / L, more preferably not exceeding 0.2 g / L.

[0037] This washing solution differs from ordinary water. Ordinary water easily disrupts the acidity and copper concentration balance between the copper-loaded organic phase and the aqueous phase, causing some copper to migrate from the organic phase into the washing water, and may also increase the risk of emulsification. The low-chlorine washing solution containing sulfuric acid and copper sulfate can replace the residual high-chlorine entrainment in the copper-loaded organic phase under a lower chloride ion environment, while reducing copper loss through the control of acidity and copper ion concentration.

[0038] After coalescence separation and low-chlorine washing, chloride ions migrating with tiny water droplets in the copper-loaded organic phase are pre-reduced. Thus, some chloride ions are removed before entering the back-extraction solution, reducing the chloride ion load in the subsequent copper salt purification solution obtained from the main back-extraction.

[0039] S4, Acidic pre-extraction cuts out chlorine-containing pre-extraction solution The copper-loaded organic phase after S3 treatment enters the pre-extraction step. Pre-extraction is a small-volume acidic contact operation set before the main extraction. Its purpose is to concentrate and remove the residual interfacial water, microemulsion aqueous phase, and chlorine-containing components that easily enter the aqueous phase in the early stage of extraction from the copper-loaded organic phase, rather than completing the main copper extraction.

[0040] In one embodiment, the acidic pre-extraction solution is a sulfuric acid solution with a sulfuric acid concentration controlled at 20 g / L to 100 g / L. The volume ratio of the acidic pre-extraction solution to the subsequent acidic main extraction solution is controlled at 0.05:1 to 0.25:1. The aqueous phase obtained from the pre-extraction is called the chlorine-containing pre-extraction solution, and the organic phase after pre-extraction is called the pretreated copper-loaded organic phase. The chlorine-containing pre-extraction solution does not enter the subsequent carbonation preparation section, but is returned to the PCB acid etching waste pretreatment section, the raffinate treatment section, or the high-chloride salt treatment section.

[0041] After entrained aqueous phase removal and low-chlorine washing, most of the separable chlorine-containing aqueous phase in the copper-loaded organic phase has been removed. However, a small amount of chloride ions may still remain in the interface layer or microemulsion aqueous phase. This residual chlorine-containing component tends to preferentially enter the aqueous phase during the initial stage of acidic back-extraction. If the main back-extraction is performed directly, the chloride ion concentration in the main back-extraction solution will be increased, affecting the low-chlorine environment of the subsequent carbonation preparation stage. By performing small-volume acidic pre-back-extraction, the chlorine-containing components released during the initial stage of back-extraction can be concentrated and transferred into a chlorine-containing pre-back-extraction solution, which can then be excluded from the carbonation preparation stage.

[0042] The pre-extraction step prevents high chlorine fluctuations at the beginning of the back-extraction process from being directly transmitted to the product preparation stage. When the organic phase after pre-extraction is reintroduced into the main back-extraction process, the resulting copper salt purified solution is more likely to meet the requirements of subsequent low-chlorine carbonation.

[0043] S5. Main back-extraction to obtain copper salt purified solution and chloride ion threshold access. The pretreated copper-loaded organic phase, after S4 pre-extraction, is then subjected to primary back-extraction. The acidic primary back-extraction solution is a sulfuric acid solution, with a sulfuric acid concentration controlled between 100 g / L and 220 g / L. During the primary back-extraction process, the copper loaded in the organic phase is transferred to the acidic aqueous phase, forming a copper salt purification solution.

[0044] Copper salt purification solution refers to the copper-containing acidic aqueous solution obtained from the main back-extraction process, primarily used for subsequent carbonation to prepare basic copper carbonate. Compared to the original PCB acidic etching waste solution, the chloride and sodium salt loads in the copper salt purification solution are significantly reduced. Before entering the carbonation preparation stage, the chloride ion concentration in the copper salt purification solution is monitored. The chloride ion mass concentration in the copper salt purification solution entering the carbonation preparation stage should not exceed 0.2 g / L, or the chloride-to-copper ion mass ratio should not exceed 0.002:1. Copper salt purification solution with a chloride ion concentration that does not meet the preset threshold is returned to S3 or S4 for further processing.

[0045] The carbonation preparation section here refers to the reaction process of converting copper in copper salt purification solution into basic copper carbonate slurry, including operations such as seed crystal addition, carbonation agent addition, pH control, crystal growth and maturation.

[0046] After the copper salt purification solution obtained from the main back-extraction undergoes chloride ion concentration detection and diversion, the copper salt purification solution with the required chloride ion concentration proceeds to the subsequent carbonation reaction, while the copper salt solution with a high chloride ion concentration is returned to the front-end treatment. This method avoids copper salt solutions with abnormally high chloride ion concentrations directly entering the precipitation system, maintaining the formation environment of basic copper carbonate in a relatively low-chlorine state. Compared to direct precipitation in PCB acidic etching waste liquid, this method reduces the possibility of chloride salts being entrained or buried by particles during the precipitation formation stage.

[0047] S6, polyaspartate-assisted seed crystal pre-mixing slurry and carbonation reaction After the low-chlorinated copper salt purification solution obtained from S5 enters the carbonation preparation section, it undergoes seed crystal pre-conditioning. Basic copper carbonate seed crystals are added to a low-chlorinated bicarbonate buffer solution containing polyaspartic acid salt for pre-conditioning to obtain surface-controlled seed crystals.

[0048] The preferred polyaspartic salt is ammonium polyaspartic acid. The average molecular weight of ammonium polyaspartic acid is controlled between 1000 and 6000. The ammonium polyaspartic acid molecular chain contains multiple carboxylate groups, exhibiting a certain weak coordination ability with copper ions and crystal face adsorption capacity. This property is not necessarily advantageous in the preparation of conventional precipitated copper salts, because if a large amount of ammonium polyaspartic acid is present in the mother liquor, it may inhibit copper ion precipitation and increase organic residues in the product. This invention controls its addition at a low amount and allows it to first act on the surface of basic copper carbonate seed crystals, primarily forming a surface conditioning effect.

[0049] The low-chlorine bicarbonate buffer solution is selected from sodium bicarbonate buffer solution and ammonium bicarbonate buffer solution, prepared by low-chlorine water and the corresponding bicarbonate, with the pH controlled at 6.0 to 7.2 and the chloride ion mass concentration not exceeding 0.05 g / L. Based on the theoretically generated mass of basic copper carbonate, the amount of polyaspartic acid ammonium added is controlled at 0.005% to 0.10%, preferably 0.02% to 0.06%; the amount of basic copper carbonate seed crystals added is controlled at 1% to 10%.

[0050] During the pre-mixing process, ammonium polyaspartate forms a trace, reversible adsorption layer on the seed crystal surface. Simultaneously, a low-chlorine bicarbonate buffer solution displaces the residual mother liquor and soluble salts on the seed crystal surface, resulting in surface-controlled seed crystals. After entering the low-chlorine copper salt purification solution, these surface-controlled seed crystals provide a nucleation carrier for the carbonation deposition of copper ions and reduce the tendency for massive transient homogeneous nucleation in the bulk solution.

[0051] Subsequently, surface-controlled seed crystals are added to the copper salt purification solution entering the carbonation preparation section, and a carbonating agent is added to carry out the carbonation reaction. The carbonating agent is selected from one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate, or carbon dioxide and alkaline solution are used to provide carbonate or bicarbonate ions.

[0052] In a preferred embodiment, the carbonation reaction is controlled in two stages. In the first stage, the pH of the carbonation system is controlled at 5.2 to 5.8, and 20% to 45% of the theoretical total carbonate dosage is added. This stage is used to form the initial deposition layer. Under relatively mild pH conditions, copper ions will not rapidly form large amounts of colloidal copper hydroxide or extremely fine basic copper carbonate due to localized strong alkaline impacts. Surface-controlled seed crystals provide nucleation sites, and the weak coordination and crystal face adsorption of ammonium polyaspartate reduce the instantaneous supersaturation of localized free copper ions, making copper more prone to carbonation deposition near the seed crystal surface.

[0053] The second-stage carbonation system was maintained at a pH of 6.0 to 6.8, with the remaining portion of the theoretical total carbonate dosage added. This stage was used for crystal ripening and growth. The initial deposit formed in the first stage continued to absorb copper ions, carbonate ions, and hydroxyl groups, gradually growing into more compact basic copper carbonate particles. The carbonation reaction temperature was controlled at 45°C to 75°C, and the second-stage carbonation was followed by ripening for 30 to 180 minutes.

[0054] Introducing basic copper carbonate seed crystals pre-treated with polyaspartic acid salt into a low-chlorine copper salt purification solution alters the nucleation mechanism of the carbonation reaction. While polyaspartic acid ammonium naturally exhibits a certain tendency for copper complexation and scale inhibition, direct addition in large quantities to the mother liquor may result in incomplete copper precipitation or increased organic residues. This invention pre-treats it in trace amounts onto the seed crystal surface, primarily regulating nucleation and growth behavior on the seed crystal surface, rather than causing large-scale copper complexation in the mother liquor. This allows copper ions in the initial stages of carbonation to deposit and grow on the seed crystal surface, reducing the formation of large amounts of fine powder or colloidal precipitates in the solution.

[0055] This effect requires the use of the aforementioned low-chlorine copper salt purification solution to function stably. If the chloride ion concentration in the copper salt purification solution is too high, chloride ions easily participate in copper coordination and interfere with the surface environment of the newly formed crystals, making polyaspartic acid salt more likely to act as a common complexing agent or dispersant. After the copper salt purification solution is kept in a low-chlorine state through S3 to S5, the trace adsorption of polyaspartic acid ammonium on the seed crystal surface is more conducive to regulating the nucleation site and crystal growth mode. The subsequent two-stage carbonation ensures that this regulation mainly occurs in the early stage of nucleation, gradually transitioning to crystal growth during the ripening and growth stage, thus taking into account both the improvement of particle morphology and the completeness of copper precipitation.

[0056] It should be noted that the reduction of chloride residue in the product in this invention does not rely on the direct removal of chloride ions by ammonium polyaspartate. The pretreatment first reduces the total amount of chloride ions entering the carbonation preparation stage; seed crystal pre-conditioning and two-stage carbonation reduce fine powder and colloidal precipitates, thus reducing the amount of mother liquor entrained in the filter cake; subsequent washing then replaces the residual soluble chloride and sodium salts. Therefore, the reduction of chloride residue in the product is the result of the combined effects of low-chlorine feed, directional crystal growth, and easy filter cake washing.

[0057] S7, solid-liquid separation, chloride ion gradient displacement washing and drying After the S6 carbonation reaction is completed, a basic copper carbonate slurry is obtained. This slurry is then subjected to solid-liquid separation to obtain a basic copper carbonate filter cake. The solid-liquid separation is performed using one of the following methods: pressure filtration, centrifugation, vacuum filtration, or plate and frame filtration.

[0058] Because surface-controlled seeding and two-stage carbonation in S6 reduce fine powder and colloidal phases, the resulting filter cake has a more favorable particle structure for liquid passage, resulting in a lower liquid content and easier replacement of residual mother liquor in the filter cake by the washing liquid. Therefore, a chloride ion gradient displacement washing method is subsequently used.

[0059] Chloride gradient replacement washing refers to multi-stage washing based on a decreasing chloride ion concentration in the washing solution, with at least a portion of the low-chlorine washing solution obtained from each subsequent stage being reused in the preceding stage. In one embodiment, chloride gradient replacement washing includes at least three stages. The first stage primarily replaces the high-salt mother liquor in the filter cake, using the reused washing solution from the subsequent stage; the second stage further reduces the soluble chloride salts in the filter cake; the third stage uses fresh low-conductivity water or low-chlorine water for fine washing. The high-chlorine washing solution obtained from the first stage is returned to the raffinate treatment section or the high-chlorine salt treatment section. The washing endpoint is controlled so that the chloride ion concentration in the final washing filtrate does not exceed 50 mg / L.

[0060] The effectiveness of gradient displacement washing is closely related to the preceding steps. If the chlorine load entering the carbonation stage is not reduced at the front end, the initial chlorine content of the filter cake will be high, requiring more washing water. If a large amount of fine powder or colloidal precipitate is generated during the carbonation stage, the washing liquid will have difficulty effectively penetrating the filter cake, and the displacement efficiency will also decrease. This invention first reduces the chlorine load, then improves the particle structure, and finally performs gradient displacement washing, thus achieving a better desalination effect with lower washing water consumption.

[0061] The washed filter cake is dried to obtain high-purity basic copper carbonate. Drying is achieved using one of the following methods: hot air drying, vacuum drying, or low-temperature circulating drying, with the drying temperature controlled between 60℃ and 110℃. Excessive drying temperature may cause decomposition of the basic copper carbonate or adverse changes in its crystal form and color; excessively low drying temperature reduces drying efficiency.

[0062] The high-purity basic copper carbonate product obtained by the above method has a purity of not less than 99.2%, a chloride ion content of not more than 80 mg / kg, a sodium content of not more than 100 mg / kg, a total organic carbon content of not more than 0.05%, and a total copper recovery rate of not less than 98% in PCB acid etching waste liquid.

[0063] In summary, this invention, following the sequence of S1 to S7, first transfers copper from the high-chlorine aqueous phase to the organic phase in the PCB acid etching waste liquid. Then, through entrainment aqueous phase removal, low-chlorine washing, pre-extraction, and chloride ion threshold access in the main stripping solution, a low-chlorine copper salt purification solution suitable for product preparation is formed. Subsequently, polyaspartic acid salt-assisted seed crystal pre-conditioning and two-stage carbonation are used to preferentially form and mature basic copper carbonate on the seed crystal surface, reducing fine powder, colloidal precipitates, and mother liquor embedding. Finally, chloride ion gradient displacement washing further reduces chloride salt residue. The steps are sequentially connected, enabling the copper in the high-chlorine PCB acid etching waste liquid to be converted into a low-chlorine, high-purity basic copper carbonate product with good filtration and washing performance.

[0064] The effects of the present invention will be further illustrated below through specific embodiments and comparative data.

[0065] The following examples and comparative examples all use PCB acid etching waste liquid as raw material. Unless otherwise specified, the PCB acid etching waste liquid is first filtered by filter bags and microfiltration to remove suspended solids and insoluble impurities. The purity of the obtained product is expressed as basic copper carbonate; the chloride ion content, sodium content, and total organic carbon content are all expressed as dried product mass; the copper recovery rate is expressed as the total amount of copper in the original PCB acid etching waste liquid; and the washing water consumption is expressed as per ton of dried basic copper carbonate product. Specifically, the chloride ion content is determined by ion chromatography or argentometric titration, the sodium content is determined by ICP-OES or atomic absorption spectrometry, and the total organic carbon content is determined by a total organic carbon analyzer.

[0066] Example 1: Take 100L of PCB acid etching waste liquid, and after solid-liquid separation, adjust the copper ion mass concentration in the extract to 120g / L and the pH to 1.5.

[0067] Extraction was performed using an organic phase, which consisted of 18% copper aldoxime extractant, 78% sulfonated kerosene, and 4% isooctanol by total volume. The volume ratio of the organic phase to the extract was 1:1, and the extraction process consisted of two stages, yielding a copper-loaded organic phase and raffinate.

[0068] The copper-loaded organic phase was coalesced and separated using a fiber coalescer to reduce the entrained water content in the copper-loaded organic phase to 0.12%. It was then washed with a washing solution containing sulfuric acid and copper sulfate, with sulfuric acid concentration of 20 g / L, copper ion concentration of 20 g / L, and chloride ion concentration of 0.18 g / L.

[0069] The washed copper-loaded organic phase enters the pre-extraction step. The acidic pre-extraction solution is a sulfuric acid solution with a mass concentration of 60 g / L, and the volume ratio of the acidic pre-extraction solution to the subsequent acidic main extraction solution is 0.12:1. The chlorine-containing pre-extraction solution obtained from the pre-extraction does not enter the subsequent carbonation preparation section but is returned to the raffinate treatment section.

[0070] The organic phase after pre-extraction was subjected to primary back-extraction with an acidic primary back-extraction solution containing 160 g / L sulfuric acid to obtain a copper salt purified solution. The chloride ion concentration in the copper salt purified solution was measured to be 0.11 g / L, and the solution then proceeded to the carbonation preparation stage.

[0071] The previous batch of wet basic copper carbonate was used as seed crystals and pre-mixed in a sodium bicarbonate buffer solution with low chloride content. The pH of the sodium bicarbonate buffer solution was 6.6, and the chloride ion concentration was 0.028 g / L. The average molecular weight of polyaspartic acid ammonium was 3000. Based on the theoretical mass of basic copper carbonate produced, the amount of polyaspartic acid ammonium added was 0.04%, and the amount of seed crystals added was 5%.

[0072] Surface-controlled seed crystals were added to the copper salt purification solution for a two-stage carbonation reaction. In the first stage, the pH was controlled at 5.5, and 35% of the theoretical total carbonate dosage was added. In the second stage, the pH was controlled at 6.4, and 65% of the theoretical total carbonate dosage was added. The carbonation temperature was 60℃, and after the second stage, the mixture was allowed to mature for 90 minutes to obtain a basic copper carbonate slurry.

[0073] The slurry was filtered through a plate and frame filter press to obtain a filter cake. The filter cake was washed using a three-stage chloride ion gradient displacement wash. The washing liquid from the later stage was reused for the previous stage, while the first stage high-chlorine washing liquid was returned to the raffinate treatment section. Washing was stopped when the chloride ion concentration in the final washing filtrate decreased to 42 mg / L. The filter cake was then vacuum dried at 85°C to obtain high-purity basic copper carbonate product.

[0074] Example 2: The main difference between this example and Example 1 is that the mass concentration of copper ions in the extract is lower, the proportion of aldoxime copper extractant in the organic phase is reduced accordingly, the amount of polyaspartic acid ammonium and seed crystals added is also reduced accordingly, and the carbonation reaction is carried out under milder pH conditions.

[0075] Take 100L of PCB acid etching waste liquid, and after solid-liquid separation, adjust the copper ion concentration in the extract to 60g / L and the pH to 0.8.

[0076] Based on the total volume of the organic phase, it consists of 8% aldoxime copper extractant, 90% isoparaffin solvent oil, and 2% isodecanol. The volume ratio of the organic phase to the extract is 1:2, and the extraction process is three stages. After extraction, a copper-loaded organic phase and raffinate are obtained.

[0077] After the copper-loaded organic phase was separated by inclined plate agglomeration, the entrained water content was reduced to 0.25%. It was then washed with a low-chlorine washing solution containing sulfuric acid and copper sulfate, with sulfuric acid concentration of 8 g / L, copper ion concentration of 8 g / L, and chloride ion concentration of 0.32 g / L.

[0078] The washed copper-loaded organic phase was pre-extracted using an acidic pre-extraction solution. The acidic pre-extraction solution was a sulfuric acid solution with a mass concentration of 30 g / L, and the volume ratio of the acidic pre-extraction solution to the acidic main extraction solution was 0.06:1. The chloride-containing pre-extraction solution obtained was not introduced into the subsequent carbonation preparation stage. The organic phase after pre-extraction was then subjected to main extraction using an acidic main extraction solution with a mass concentration of 120 g / L sulfuric acid. The resulting purified copper salt solution had a chloride ion mass concentration of 0.16 g / L and was then introduced into the carbonation preparation stage.

[0079] Basic copper carbonate seed crystals were added to a low-chlorinated ammonium bicarbonate buffer solution for slurry preconditioning. The low-chlorinated ammonium bicarbonate buffer solution had a pH of 6.2 and a chloride ion concentration of 0.041 g / L. The polyaspartic acid ammonium had an average molecular weight of 1500. Based on the theoretical mass of basic copper carbonate produced, the amount of polyaspartic acid ammonium added was 0.01%, and the amount of seed crystals added was 2%.

[0080] The pre-treated slurry was added to a copper salt purification solution for a two-stage carbonation reaction. In the first stage, the pH was controlled at 5.2, and 25% of the theoretical total carbonate dosage was added. In the second stage, the pH was controlled at 6.1, and 75% of the theoretical total carbonate dosage was added. The reaction temperature was 50℃, and the mixture was allowed to mature for 45 minutes after the second stage. The resulting slurry was then subjected to pressure filtration, three-stage chloride ion gradient replacement washing, and hot air drying at 80℃ to obtain a high-purity basic copper carbonate product.

[0081] Example 3: The main difference between this example and Example 1 is that the copper ion mass concentration in the extract is higher, the proportion of aldoxime copper extractant in the organic phase is increased, the entrained water content after agglomeration and separation is further reduced, and a higher amount of polyaspartic acid ammonium, seed crystal, and maturation time are used.

[0082] Take 100L of PCB acid etching waste liquid, and after solid-liquid separation, adjust the copper ion concentration in the extract to 170g / L and the pH to 2.2.

[0083] Based on the total volume of the organic phase, it consists of 28% copper aldoxime extractant, 63% No. 260 solvent oil, and 9% tributyl phosphate. The volume ratio of the organic phase to the extract is 3:1, and the extraction process is two stages. After extraction, a copper-loaded organic phase and raffinate are obtained.

[0084] After the copper-loaded organic phase was separated by coalescence in the packing material, the entrained water content was reduced to 0.08%. It was then washed with a low-chlorine washing solution containing sulfuric acid and copper sulfate. The washing solution had a sulfuric acid concentration of 45 g / L, a copper ion concentration of 35 g / L, and a chloride ion concentration of 0.12 g / L.

[0085] The washed copper-loaded organic phase was pre-extracted using an acidic pre-extraction solution. The acidic pre-extraction solution was a sulfuric acid solution with a concentration of 90 g / L, and the volume ratio of the acidic pre-extraction solution to the acidic main extraction solution was 0.22:1. The chloride-containing pre-extraction solution obtained was not introduced into the subsequent carbonation preparation stage. The organic phase after pre-extraction was then subjected to main extraction using an acidic main extraction solution with a sulfuric acid concentration of 210 g / L. The resulting purified copper salt solution had a chloride ion concentration of 0.07 g / L and was then introduced into the carbonation preparation stage.

[0086] Basic copper carbonate seed crystals were added to a low-chlorine sodium bicarbonate buffer solution for slurry preconditioning. The pH of the low-chlorine sodium bicarbonate buffer solution was 7.0, and the chloride ion concentration was 0.018 g / L. The average molecular weight of polyaspartic acid ammonium was 5500. Based on the theoretical mass of basic copper carbonate produced, the amount of polyaspartic acid ammonium added was 0.08%, and the amount of seed crystals added was 8%.

[0087] The pre-treated slurry was added to a copper salt purification solution for a two-stage carbonation reaction. In the first stage, the pH was controlled at 5.8, and 42% of the theoretical total carbonate dosage was added. In the second stage, the pH was controlled at 6.7, and 58% of the theoretical total carbonate dosage was added. The reaction temperature was 70℃, and the mixture was allowed to mature for 150 minutes after the second stage. The resulting slurry was centrifuged, filtered, washed using a three-stage chloride ion gradient, and vacuum dried at 90℃ to obtain a high-purity basic copper carbonate product.

[0088] Example 4: The main difference between this example and Example 1 is that: a medium-to-high copper concentration extractant is used, and through multi-stage extraction, more thorough removal of entrained aqueous phase, and control of the low chloride ion main back-extraction solution, the copper salt purification solution entering the carbonation preparation section has a low chloride ion load.

[0089] Take 100L of PCB acid etching waste liquid, and after solid-liquid separation, adjust the copper ion concentration in the extract to 145g / L and the pH to 1.2.

[0090] Based on the total volume of the organic phase, it consists of 22% aldoxime copper extractant, 74% aliphatic hydrocarbon solvent oil, and 4% dodecanol. The volume ratio of the organic phase to the extract is 2:1, and the extraction process is four stages. After extraction, a copper-loaded organic phase and raffinate are obtained.

[0091] After membrane coalescence separation, the entrained water content of the copper-loaded organic phase was reduced to 0.06%. It was then washed with a low-chlorine washing solution containing sulfuric acid and copper sulfate, with a sulfuric acid concentration of 30 g / L, a copper ion concentration of 25 g / L, and a chloride ion concentration of 0.09 g / L.

[0092] The washed copper-loaded organic phase was pre-extracted using an acidic pre-extraction solution. The acidic pre-extraction solution was a sulfuric acid solution with a mass concentration of 70 g / L, and the volume ratio of the acidic pre-extraction solution to the acidic main extraction solution was 0.18:1. The chloride-containing pre-extraction solution obtained was not introduced into the subsequent carbonation preparation stage. The organic phase after pre-extraction was then subjected to main extraction using an acidic main extraction solution with a mass concentration of 180 g / L sulfuric acid. The resulting purified copper salt solution had a chloride ion mass concentration of 0.05 g / L and was then introduced into the carbonation preparation stage.

[0093] Basic copper carbonate seed crystals were added to a low-chlorinated ammonium bicarbonate buffer solution for slurry preconditioning. The low-chlorinated ammonium bicarbonate buffer solution had a pH of 6.8 and a chloride ion concentration of 0.015 g / L. The polyaspartic acid ammonium had an average molecular weight of 4200. Based on the theoretically generated basic copper carbonate mass, the amount of polyaspartic acid ammonium added was 0.05%, and the amount of seed crystals added was 6%.

[0094] The pre-treated slurry with surface-controlled seed crystals was added to a copper salt purification solution for a two-stage carbonation reaction. In the first stage, the pH was controlled at 5.6, and 38% of the theoretical total carbonate dosage was added. In the second stage, the pH was controlled at 6.5, and 62% of the theoretical total carbonate dosage was added. The reaction temperature was 65℃, and the mixture was allowed to mature for 120 minutes after the second stage. The resulting slurry was then subjected to vacuum filtration, three-stage chloride ion gradient replacement washing, and low-temperature cyclic drying at 85℃ to obtain a high-purity basic copper carbonate product.

[0095] Example 5: The main difference between this example and Example 1 is that the extract solution with a copper ion mass concentration close to the upper limit is used for treatment, and basic copper carbonate is prepared under conditions of higher organic phase content, higher polyaspartic acid ammonium content, higher seed crystal content, and longer aging time.

[0096] Take 100L of PCB acid etching waste liquid, and after solid-liquid separation, adjust the copper ion concentration in the extract to 180g / L and the pH to 2.5.

[0097] Based on the total volume of the organic phase, it consists of 30% aldoxime copper extractant, 60% isoparaffin solvent oil, and 10% ester phase separation and conditioning agent. The volume ratio of the organic phase to the extract is 5:1, and the extraction stage is 1 stage. After extraction, a copper-loaded organic phase and raffinate are obtained.

[0098] After fiber agglomeration and static stratification, the entrained water content of the copper-loaded organic phase was reduced to 0.10%. It was then washed with a low-chlorine washing solution containing sulfuric acid and copper sulfate, with a sulfuric acid concentration of 50 g / L, a copper ion concentration of 40 g / L, and a chloride ion concentration of 0.20 g / L.

[0099] The washed copper-loaded organic phase was pre-extracted using an acidic pre-extraction solution. The acidic pre-extraction solution was a sulfuric acid solution with a mass concentration of 100 g / L, and the volume ratio of the acidic pre-extraction solution to the acidic main extraction solution was 0.25:1. The chloride-containing pre-extraction solution obtained was not introduced into the subsequent carbonation preparation stage. The organic phase after pre-extraction was then subjected to main extraction using an acidic main extraction solution with a mass concentration of 220 g / L sulfuric acid. The resulting purified copper salt solution had a chloride ion mass concentration of 0.10 g / L and was then introduced into the carbonation preparation stage.

[0100] Basic copper carbonate seed crystals were added to a low-chlorine sodium bicarbonate buffer solution for slurry preconditioning. The pH of the low-chlorine sodium bicarbonate buffer solution was 7.2, and the chloride ion concentration was 0.020 g / L. The average molecular weight of polyaspartic acid ammonium was 6000. Based on the theoretical mass of basic copper carbonate produced, the amount of polyaspartic acid ammonium added was 0.10%, and the amount of seed crystals added was 10%.

[0101] The pre-treated surface-controlled seed crystals were added to the copper salt purification solution for a two-stage carbonation reaction. In the first stage, the pH was controlled at 5.8, and 45% of the theoretical total carbonate dosage was added. In the second stage, the pH was controlled at 6.8, and 55% of the theoretical total carbonate dosage was added. The reaction temperature was 75℃, and the mixture was allowed to mature for 180 minutes after the second stage. The resulting slurry was filtered through a plate and frame filter, washed with a three-stage chloride ion gradient, and vacuum dried at 95℃ to obtain a high-purity basic copper carbonate product.

[0102] Comparative Example 1: This comparative example uses direct internal crystal precipitation to treat PCB acid etching waste liquid from the same source as in Example 1.

[0103] Take 100L of PCB acid etching waste liquid, and after solid-liquid separation and dilution, pour the acid etching waste liquid into an alkaline solution containing sodium carbonate and sodium bicarbonate. First, basic copper carbonate internal crystals are formed, and then the remaining acid etching waste liquid is added to continue the reaction. After the reaction is completed, the resulting slurry is filtered, washed with ordinary water, and dried to obtain the basic copper carbonate product.

[0104] This comparative example did not undergo copper selective extraction, removal of entrained chlorine-containing aqueous phase, low-chlorine washing, pre-extraction, chloride ion threshold access of the main back-extraction solution, pre-conditioning of polyaspartic acid ammonium seed slurry, or chloride ion gradient displacement washing.

[0105] Comparative Example 2: The difference between this comparative example and Example 1 is that the washed copper-loaded organic phase is not subjected to acidic pre-extraction, but is directly subjected to primary extraction using acidic primary extraction solution. The copper salt solution obtained from the primary extraction enters the carbonation preparation section, and the remaining process conditions are consistent with those of Example 1.

[0106] Comparative Example 3: The difference between this comparative example and Example 1 is that the washed copper-loaded organic phase is still pre-extracted using an acidic pre-extraction solution, but the chlorine-containing pre-extraction solution obtained from the pre-extraction is not discharged separately, but is combined with the copper salt solution obtained from the main back-extraction and then enters the carbonation preparation section. The remaining process conditions are consistent with those of Example 1.

[0107] Comparative Example 4: The difference between this comparative example and Example 1 is that no polyaspartic acid ammonium is added during the seed crystal pre-mixing process; only sodium bicarbonate buffer solution with low chloride content is used to pre-mix the basic copper carbonate seed crystals. All other process conditions remain the same as in Example 1.

[0108] Comparative Example 5: The difference between this comparative example and Example 1 is that, instead of using a low-chlorinated bicarbonate buffer solution containing ammonium polyaspartate to pre-mix the basic copper carbonate seed crystals, the same mass of ammonium polyaspartate as in Example 1 was directly added to the copper salt purification solution before the carbonation reaction. All other process conditions remained the same as in Example 1.

[0109] Comparative Example 6: The difference between this comparative example and Example 1 is that polyvinylpyrrolidone of the same mass as in Example 1 was used to replace polyaspartic acid ammonium in the pre-slurry preparation of basic copper carbonate seed crystals. All other process conditions remained the same as in Example 1.

[0110] Comparative Example 7: The difference between this comparative example and Example 1 is that the basic copper carbonate filter cake after the carbonation reaction is washed with ordinary single-use water, without the subsequent washing liquid being reused for chloride ion gradient replacement washing of the previous stage. All other process conditions remain the same as in Example 1.

[0111]

[0112] As shown in Table 1, Examples 1 to 5 were carried out under different copper ion concentrations, different pH values ​​of the extractant, different organic phase ratios, different amounts of pre-extraction solution, different amounts of polyaspartic acid ammonium, different amounts of seed crystals, and different carbonation conditions. Each example covers low, medium, and high copper loading conditions within the scope of the claims, as well as low, medium, and high amounts of polyaspartic acid ammonium. This demonstrates that the method of the present invention is not limited to a single optimal operating condition, but can operate stably over a wide range of processes.

[0113] As shown in Table 2, the purity of the basic copper carbonate products obtained in Examples 1 to 5 is not less than 99.23%, the chloride ion content is 39 mg / kg to 74 mg / kg, the sodium content is 68 mg / kg to 95 mg / kg, the copper recovery rate is 98.1% to 98.9%, the filtration time is 24 min to 34 min, and the washing water consumption is 2.8 m³ / t to 3.5 m³ / t. These results indicate that under the different process conditions listed in Table 1, the present invention can simultaneously achieve high product purity, low chloride residue, high copper recovery rate, and low washing water consumption.

[0114] Compared to Example 1, Comparative Example 1, which used direct internal crystal precipitation to treat PCB acidic etching wastewater, resulted in a decrease in product purity to 98.31%, an increase in chloride ion content to 168 mg / kg, an increase in sodium content to 236 mg / kg, an extension of filtration time to 63 min, and an increase in washing water consumption to 6.2 m³ / t. These results indicate that when basic copper carbonate is directly formed in high-chlorine, high-salt acidic etching wastewater, even with an internal crystal precipitation method, chloride salts are easily carried over with the mother liquor, and the filter cake washing load is relatively high. Example 1, by first obtaining a low-chlorine copper salt purified solution and then performing carbonation, significantly reduced chloride ion and sodium salt residues in the product, while also improving filtration and washing performance.

[0115] Comparative Example 2, which did not include an acidic pre-extraction step, saw its product chloride ion content rise to 132 mg / kg, with a filtration time of 42 min and a washing water consumption of 4.8 m³ / t. Comparative Example 3, although it included pre-extraction, combined the chlorine-containing pre-extraction solution with the main extraction solution before entering the carbonation preparation stage, yet the product chloride ion content still reached 126 mg / kg. These two sets of data demonstrate that the value of the pre-extraction step lies not in ordinary acid washing, but in separating the chlorine-containing components released during the initial extraction phase and preventing this chlorine-containing liquid from entering the product preparation stage. If pre-extraction is omitted, or if the pre-extraction solution is re-incorporated into the main extraction solution, both the residual chloride salts in the product and the subsequent washing load significantly increase.

[0116] Comparative Example 4, without the addition of ammonium polyaspartate, produced a product with a chloride ion content of 96 mg / kg, a D50 reduced to 22.6 μm, an extended filtration time of 48 min, and a filter cake moisture content increased to 41.2%. Compared to Example 1, although this comparative example retained the front-end extraction, washing, and pre-back-extraction steps, the particle size of the carbonation-derived particles was significantly reduced, and the filter cake liquid content and filtration difficulty increased. These results indicate that simply reducing the chloride ion load entering the carbonation stage is insufficient to obtain the optimal product state; further improvements in carbonation nucleation and particle growth behavior are needed through seed surface regulation.

[0117] In Comparative Example 5, polyaspartic acid ammonium was directly added to the copper salt purification solution without pre-conditioning the slurry with seed crystals. The product purity decreased to 98.62%, the copper recovery rate decreased to 96.9%, and the total organic carbon content increased to 0.083%. These results indicate that the method of adding polyaspartic acid ammonium significantly affects the technical effect. Directly adding it to the mother liquor can easily lead to adverse effects on copper precipitation due to its weak copper coordination and scale inhibition, and increase organic residues in the product. In contrast, Example 1 first applied it to the surface of basic copper carbonate seed crystals before initiating a two-stage carbonation process, which improved the particle state while maintaining the copper recovery rate.

[0118] Comparative Example 6 used polyvinylpyrrolidone instead of ammonium polyaspartate. The product had a chloride ion content of 112 mg / kg, a total organic carbon content of 0.071%, and a filtration time of 44 min, all significantly worse than Example 1. This result indicates that the ammonium polyaspartate in this invention is not an equivalent replacement for ordinary polymeric dispersants. Although polyvinylpyrrolidone has a certain dispersing effect, it cannot achieve the comprehensive improvement effect of ammonium polyaspartate on nucleation site, particle growth, and filter cake washability under low-chlorine copper salt purification solution and seed slurry pre-conditioning.

[0119] Comparative Example 7 did not employ a chloride ion gradient displacement washing method. The product purity was 99.10%, with chloride ion content increasing to 118 mg / kg and sodium content to 142 mg / kg. The D50 and filtration time of this comparative example were close to those of Example 1, indicating that front-end low-chlorine control and seed crystal regulation had improved particle state. However, due to the subsequent use of only ordinary single-pass water washing, residual soluble chloride and sodium salts in the filter cake were not fully replaced, resulting in a significant increase in residual salt content in the final product. Therefore, gradient displacement washing is necessary to further reduce residual chloride salts in the product while maintaining lower washing water consumption.

[0120] As can be seen from Tables 1 and 2, Examples 1 to 5 all exhibited stable low-chlorine, high-purity, and easily filterable characteristics under different process conditions. The comparative examples, however, showed adverse results due to the absence of key steps or changes in the key addition methods. In particular, Comparative Examples 2 and 3 demonstrate that the chlorine-containing pre-extraction solution must be excluded from the product preparation stage. Comparative Examples 4 to 6 show that ammonium polyaspartate needs to be used in a seed crystal pre-mixing process and cannot be simply omitted, directly added, or replaced with a common dispersant. Comparative Example 7 demonstrates that front-end low-chlorine and mid-stage particle control still need to be combined with back-end gradient displacement washing to stably obtain a low-chlorine product.

[0121] Therefore, the technical effect of this invention is not generated independently by a single dechlorination, a single additive, or a single washing step, but is formed by the combined effects of pre-extraction dechlorination, low-chlorine access of the main extraction solution, pre-conditioning of the slurry with ammonium polyaspartate seed crystals, two-stage carbonation, and chloride ion gradient displacement washing. This combination simultaneously improves product purity, chloride ion residue, sodium salt residue, filtration time, filter cake moisture content, washing water consumption, and copper recovery rate, demonstrating a superior overall technical effect compared to direct precipitation and conventional dispersant control methods.

Claims

1. A method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid, characterized in that, Includes the following steps: S1. Solid-liquid separation is performed on the acidic etching waste liquid of PCB, and its acidity and copper ion concentration are adjusted to obtain the extract to be extracted. S2. Extract the extractant using an organic phase containing a copper selective extractant, so that copper enters the organic phase, and obtain a copper-loaded organic phase and raffinate. S3. The copper-loaded organic phase is subjected to a chlorine-containing aqueous phase removal treatment, and the copper-loaded organic phase after the chlorine-containing aqueous phase removal treatment is washed with a washing solution with controlled chloride ion concentration to obtain a washed copper-loaded organic phase. S4. The washed copper-loaded organic phase is pre-extracted using an acidic pre-extraction solution to obtain a chlorine-containing pre-extraction solution and a pretreated copper-loaded organic phase. The chlorine-containing pre-extraction solution does not enter the subsequent carbonation preparation section. S5. The pretreated copper-loaded organic phase is subjected to main back-extraction using an acidic main back-extraction solution to obtain a copper salt purification solution, and the copper salt purification solution with a chloride ion concentration meeting a preset threshold is introduced into the carbonation preparation section. S6. Add basic copper carbonate seed crystals to a low-chlorinated bicarbonate buffer solution containing polyaspartic acid salt for pre-conditioning to obtain surface-controlled seed crystals; add the surface-controlled seed crystals to the copper salt purification solution entering the carbonation preparation section and carry out the carbonation reaction to obtain basic copper carbonate slurry. S7. The basic copper carbonate slurry is subjected to solid-liquid separation, chloride ion gradient displacement washing and drying to obtain a high-purity basic copper carbonate product.

2. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S1, the PCB acid etching waste liquid contains copper ions, hydrochloric acid and chloride salts; after solid-liquid separation, the mass concentration of copper ions in the extract is adjusted to 50 g / L to 180 g / L, and the pH of the extract is adjusted to 0.5 to 2.

5.

3. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S2, the organic phase includes an aldoxime copper extractant, a water-immiscible hydrocarbon organic diluent, and a phase separation modifier; based on the total volume of the organic phase, the aldoxime copper extractant accounts for 5% to 30%, the hydrocarbon organic diluent accounts for 60% to 94%, and the phase separation modifier accounts for 0.1% to 10%; the volume ratio of the organic phase to the extractant during extraction is 1:3 to 5:1, and the number of extraction stages is 1 to 4.

4. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S3, the removal of the entrained chlorine-containing aqueous phase is a coalescence separation process. The coalescence separation process removes the chlorine-containing aqueous phase entrained in the copper-loaded organic phase, ensuring that the mass content of entrained water in the coalescence-separated copper-loaded organic phase is not higher than 0.3%. The washing solution contains sulfuric acid and copper sulfate. The mass concentration of sulfuric acid in the washing solution is 5 g / L to 50 g / L, the mass concentration of copper ions is 5 g / L to 40 g / L, and the mass concentration of chloride ions is not higher than 0.5 g / L.

5. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S4, the acidic pre-extraction solution is a sulfuric acid solution with a sulfuric acid mass concentration of 20 g / L to 100 g / L; the volume ratio of the acidic pre-extraction solution to the acidic main extraction solution in step S5 is 0.05:1 to 0.25:1; the resulting chlorine-containing pre-extraction solution is returned to the PCB acidic etching waste pretreatment section, the raffinate treatment section, or the high-chlorine salt treatment section.

6. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S5, the acidic main back-extraction solution is a sulfuric acid solution with a sulfuric acid mass concentration of 100 g / L to 220 g / L; the chloride ion mass concentration in the copper salt purification solution entering the carbonation preparation section is not higher than 0.2 g / L, or the mass ratio of chloride ions to copper ions is not higher than 0.002:1; copper salt purification solutions with chloride ion concentrations that do not meet the preset threshold are returned to step S3 or step S4 for processing.

7. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S6, the polyaspartic salt is polyaspartic ammonium, and the average molecular weight of the polyaspartic ammonium is 1000 to 6000; based on the theoretical mass of basic copper carbonate produced, the amount of polyaspartic ammonium added is 0.005% to 0.10%; the pH of the low-chlorine bicarbonate buffer solution is 6.0 to 7.2, and the chloride ion mass concentration is not higher than 0.05 g / L; based on the theoretical mass of basic copper carbonate produced, the amount of basic copper carbonate seed crystals added is 1% to 10%.

8. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S6, the carbonation reaction includes a first-stage carbonation and a second-stage carbonation; the first-stage carbonation controls the pH of the system to be 5.2 to 5.8, and adds 20% to 45% of the theoretical total carbonate dosage; the second-stage carbonation controls the pH of the system to be 6.0 to 6.8, and adds the remaining portion of the theoretical total carbonate dosage; the carbonation reaction temperature is 45°C to 75°C, and the second-stage carbonation is followed by aging for 30 min to 180 min.

9. The method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to claim 1, characterized in that, In step S7, the chloride ion gradient replacement washing includes at least three stages of washing, with at least a portion of the washing liquid obtained from the later stage being reused in the previous stage; the high-chlorine washing liquid obtained from the first stage is returned to the raffinate treatment section or the high-chlorine salt treatment section; the washing endpoint is that the chloride ion mass concentration in the final washing filtrate is not higher than 50 mg / L.

10. A method for preparing high-purity basic copper carbonate from PCB acid etching waste liquid according to any one of claims 1 to 9, characterized in that, The purity of the obtained high-purity basic copper carbonate product shall not be less than 99.2%, the chloride ion content shall not be higher than 80 mg / kg, the sodium content shall not be higher than 100 mg / kg, the total organic carbon content shall not be higher than 0.05%, and the total copper recovery rate in the PCB acid etching waste liquid shall not be less than 98%.

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