Process for recovering copper from waste liquid of circuit board cleaning

Abstract

This invention discloses a copper recovery process from circuit board cleaning wastewater, belonging to the field of wastewater resource utilization technology. The process includes the following steps: a) neutralization of the circuit board cleaning wastewater and separation of copper-containing sludge; b) oxygen-enriched calcination of the copper-containing sludge; c) pre-selection and impurity removal of the calcination products; d) acid dissolution of the pre-selected products and removal of impurity ions; e) crystallization and removal of calcium sulfate dihydrate; f) evaporation and crystallization to obtain copper sulfate pentahydrate. This process employs neutralization sedimentation, oxygen-enriched calcination, and wet pre-selection to ensure the copper recovery rate from the circuit board cleaning wastewater and improve the production line's capacity to process circuit board cleaning wastewater. Simultaneously, basic copper carbonate is used to precisely control the solution pH value, combined with sand filtration and two-stage sedimentation processes, followed by a two-step evaporation and crystallization process, ultimately obtaining a high-purity and high-value-added copper sulfate pentahydrate product, with a comprehensive copper recovery rate as high as 95.84% and a purity of 99.26%.

Description

Technical Field

[0001] This invention belongs to the field of waste liquid resource utilization technology, specifically relating to a copper recovery process from circuit board cleaning waste liquid. Background Technology

[0002] Circuit board (PCB) cleaning wastewater mainly originates from the cleaning processes during drilling, etching, and electroplating in PCB manufacturing. After chemical flocculation, neutralization, and sedimentation, it forms copper-containing sludge. Although classified as hazardous waste, this sludge has a dry-basis copper content as high as 3%–15%, far exceeding the grade of primary copper ore, thus possessing high resource recovery value. Currently, the main methods for treating this type of PCB cleaning wastewater include wet leaching and biometallurgy. Among these, wet leaching technology is widely used, but its traditional processes suffer from drawbacks such as low reaction efficiency, high reagent consumption, and difficulty in process control. For example, when using the iron displacement method to recover copper, the direct addition of the iron displacement agent can easily lead to violent local reactions, excessively long overall reaction time, excessive consumption of displacement agent, and difficulties in separating reaction products, affecting the economics and operability of copper recovery. Therefore, how to achieve efficient disposal and resource utilization of PCB cleaning wastewater has become a key issue in the fields of non-ferrous metal recovery and hazardous waste management.

[0003] Chinese invention patent CN103803631A discloses a method for producing copper sulfate using copper-containing micro-etching solutions from circuit board etching. This method directly produces copper sulfate pentahydrate through multi-stage countercurrent extraction and freeze crystallization, achieving a copper recovery rate of up to 99.8%. Although the above method has a high copper recovery rate, the recovery and reuse process of the organic phase after extraction is complex and costly. Secondly, the extractant and aviation kerosene used have certain toxicity and volatility, posing a potential environmental pollution hazard. Finally, the method lacks a deep impurity removal step, affecting product purity.

[0004] Chinese invention patent CN102786076A discloses a method for preparing high-purity copper sulfate from copper-containing circuit board waste liquid. Its core lies in combining copper carbonate impurity removal and alcohol crystallization processes, yielding copper sulfate with a purity of 99.9%. Although the copper sulfate product obtained by this method has high purity, the process requires the addition of excessive sulfuric acid, resulting in high reagent consumption. Secondly, acetic acid or soluble acetates need to be added for impurity removal, introducing organic components and increasing the burden on wastewater treatment. Finally, some copper is lost with the filtrate during the copper sludge precipitation step, leaving a small amount of copper ions in the mother liquor, requiring additional sodium carbonate or sodium bicarbonate for recovery, resulting in incomplete copper recovery in the main process. Summary of the Invention

[0005] Based on the above-mentioned technical problems, this invention proposes a process for recovering copper from circuit board cleaning waste liquid.

[0006] The technical solution adopted in this invention is: A process for recovering copper from circuit board cleaning waste liquid includes the following steps: a. Neutralization of circuit board cleaning waste liquid and separation of copper-containing sludge; After the circuit board cleaning waste liquid enters the first mixing tank, NaOH solution is added to carry out a neutralization reaction to obtain a neutralized slurry; The neutralized slurry is discharged from the bottom of the first mixing tank and pumped to the column-type rakeless thickener by the first feed pump for concentration. The overflow obtained from concentration is discarded, and the underflow is copper-containing sludge slurry. The copper-containing sludge slurry is pumped to the filter press by the second feed pump for dewatering. The copper-containing sludge obtained after filtration falls into the copper-containing sludge temporary storage bin, and the filtrate is discarded.

[0007] b. Oxygen-enriched calcination of copper-containing sludge; Copper-containing sludge is discharged from the discharge port at the bottom of the copper-containing sludge temporary storage silo and fed into a rotary kiln via a closed screw conveyor for oxygen-enriched calcination to obtain calcined products.

[0008] c. Pre-selection and impurity removal of calcined products; The calcined product is fed into a trough scrubber under the action of rinsing water for scrubbing to obtain mud and desliming product; the mud is discarded, and the desliming product flows by gravity to a shaking table for fine selection, which is then separated into concentrate, middlings and tailings; the tailings are returned to the trough scrubber for scrubbing and further selection, and the concentrate and middlings are fed into a ceramic filter for dewatering to obtain the pre-selected product after dewatering.

[0009] d. Acid dissolution of preselected products and removal of impurity ions; After the pre-selected product is conveyed to the second mixing tank by a belt conveyor, sulfuric acid solution is added for acid dissolution treatment. The acid-dissolved slurry is filtered through the first filter screen and then flows into the third mixing tank by gravity. Basic copper carbonate is added to the third mixing tank to adjust the pH value and precipitate impurity ions. The slurry treated in the third mixing tank is transported to the sand filter for preliminary filtration by the third feed pump; the filtered slurry enters the inclined plate settling tank for sedimentation to remove solid particles, and the resulting solution is temporarily stored in the pump pool.

[0010] e. Crystallization and removal of calcium sulfate dihydrate; The solution in the temporary storage pump pool is pumped by the fourth feed pump to the first heated conveyor belt device for evaporation and concentration, which is used to crystallize the calcium sulfate dihydrate in the solution. Then, the calcium sulfate dihydrate precipitated in the solution is filtered out through the second filter screen.

[0011] f. Evaporation and crystallization to obtain copper sulfate pentahydrate; The solution filtered through the second filter screen flows by gravity to the second heated conveyor belt device for evaporation and concentration, which is used to crystallize copper sulfate pentahydrate in the solution. Then, at the end of the second heated conveyor belt device, the crystals attached to the belt surface are scraped off by a scraper and fall into the collection tank to obtain the copper sulfate pentahydrate product.

[0012] Preferably, in step a: the neutralization reaction time is 3 to 7 minutes; the concentration of the copper-containing sludge is controlled at 15% to 30%; and the moisture content of the copper-containing sludge is controlled at 20% to 40%.

[0013] Preferably, in step b: the kiln body temperature of the rotary kiln is controlled at 400~800℃, and the oxygen-enriched calcination time is 20~90min; oxygen-enriched calcination is achieved by increasing the air flow rate into the rotary kiln, and the high-temperature waste gas generated during calcination enters the waste heat recovery system to preheat the air entering the rotary kiln.

[0014] Preferably, in step c: the moisture content of the preselected product is controlled at 20%~40%.

[0015] Preferably, in step d: the concentration of the sulfuric acid solution is 1.2~2.0 mol / L, the acid dissolution time is controlled at 3~7 min, and the pH value of the slurry during acid dissolution is controlled at 1.8~2.6; the mesh size of the first filter screen is 100~200 mesh; when basic copper carbonate is added, the pH value of the slurry in the third stirring tank is controlled at 3.8~4.5, and the residence time of the slurry in the third stirring tank is controlled at 1~5 min.

[0016] Preferably, in step d: after the slurry is filtered by a sand filter, it first enters a primary inclined plate settling tank for settling, and the overflow from the primary inclined plate settling tank then enters a secondary inclined plate settling tank for settling.

[0017] Preferably, both the first heated conveyor belt device and the second heated conveyor belt device include a conveyor belt, with water baffles arranged around both sides of the conveyor belt, water guide ribs perpendicular to the conveyor belt running direction arranged on the conveyor belt surface, and a heating plate arranged below the upper layer of the conveyor belt surface.

[0018] Preferably, in the first heated conveyor belt device: the temperature of the heating plate is set to 200~300℃; the belt speed of the conveyor belt is controlled at 0.5~1.5m / min; and the liquid level of the solution on the conveyor belt surface is controlled at 1~3cm.

[0019] Preferably, in the second heated conveyor belt device: the temperature of the heating plate is set to 300~400℃; the belt speed of the conveyor belt is controlled at 0.5~1.5m / min; and the liquid level of the solution on the conveyor belt surface is controlled at 0.5~2cm.

[0020] Preferably, the water vapor generated during the evaporation and concentration process is transported through pipelines to a cooling tower for condensation and reuse.

[0021] The beneficial technical effects of the present invention are as follows: The recycling process provided by this invention breaks through the limitations of traditional wet leaching. Through an integrated design of "neutralization sedimentation - oxygen-enriched calcination - wet pre-selection - precise impurity removal - two-step crystallization," it achieves efficient, stable, low-cost, and high-purity copper recovery, with a comprehensive copper recovery rate as high as 95.84%. This provides a universally applicable technical path for the treatment and high-value utilization of circuit board cleaning wastewater, which also has good economic efficiency and environmental adaptability. Specifically: (1) Continuous and modular design to ensure throughput: The entire process from "neutralization and sedimentation" to "evaporation and crystallization" realizes the continuous flow of materials, avoids the waiting time of batch processing, and greatly improves the processing capacity per unit time.

[0022] (2) Good process stability and easy reaction control: Pre-selection and impurity removal are carried out in advance to remove mud impurities and soluble salts, reducing interference from subsequent processes; in the acid dissolution step, precise acid dissolution and basic copper carbonate are used to regulate pH instead of iron replacement in traditional wet leaching to avoid local violent reactions; through heating conveyor belt, copper sulfate pentahydrate is gradually concentrated, allowing it to crystallize in an orderly manner, making the reaction process easier to control and reducing the consumption of reagents (such as sulfuric acid and basic copper carbonate).

[0023] (3) Multi-stage impurity removal system to ensure high product purity: In the oxygen-enriched calcination step, Fe is oxidized to the highest valence state so that it can be completely removed in the subsequent wet process, while removing organic matter and improving the purity of copper products; by combining a tank scrubbing machine and a shaking table gravity separation, siliceous impurities such as silica are removed and copper-containing materials are enriched; by combining sand filtration and two-stage inclined plate sedimentation, solid particles are deeply removed; finally, calcium sulfate dihydrate is removed first by a primary heating conveyor belt, and then copper sulfate pentahydrate is crystallized by a secondary heating conveyor belt to finally obtain high-purity copper sulfate pentahydrate products.

[0024] (4) Environmental friendliness and realization of waste resource utilization: oxygen-enriched calcination removes organic matter and harmful components, and heavy metals are transformed into precipitates and stable products through precipitation and crystallization, realizing the harmless treatment of copper-containing sludge; after treatment, copper is recovered as a high-value-added product (copper sulfate pentahydrate), while the waste residue (sludge, tailings, etc.) is reduced, eliminating the need for excessive post-treatment steps, reducing costs, and conforming to the concept of circular economy.

[0025] (5) The present invention uses a combination of “water guide ribs + heating plate + water blocking plate”, with the conveyor belt as the carrier, the upper belt surface carrying the solution, and the heating plate suspended in the lower layer to heat the solution, thereby achieving conduction evaporation; the water guide ribs are distributed at intervals and perpendicular to the running direction, guiding the solution to be evenly distributed on the belt surface, avoiding local over-thickness or under-thickness, and promoting uniform evaporation and crystallization; the above structure achieves uniform solution spreading, stable heat transfer, low-loss evaporation, and good consistency of crystal particles.

[0026] (6) Better economic efficiency and reduced operating costs: calcination exhaust gas enters the waste heat recovery system to preheat the air entering the rotary kiln, reducing energy consumption; water vapor generated by the heating conveyor belt is condensed and reused by the cooling tower, saving water; conventional equipment such as trough scrubbing machine, shaking table, and ceramic filter are used to avoid high investment in special equipment; basic copper carbonate is used to replace elemental iron, and pH is precisely controlled to reduce reagent consumption. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the copper recovery process from the circuit board cleaning waste liquid of the present invention. Figure 2 The X-ray diffraction patterns of copper-containing sludge and calcination products obtained in the embodiments of the present invention are shown below. Figure 3 The X-ray diffraction pattern of calcium sulfate dihydrate removed by the first heated conveyor belt device according to an embodiment of the present invention; Figure 4 This is a front view of the first heated conveyor belt device of the present invention; Figure 5 This is a top view of the first heated conveyor belt device of the present invention.

[0028] In the diagram: 1-Ion concentration meter; 2-Flow meter; 3-First mixing tank; 4-First feed pump; 5-Flocculant dosing device; 6-Column-type rakeless thickener; 7-Second feed pump; 8-Filter press; 9-Copper-containing sludge temporary storage bin; 10-Enclosed screw conveyor; 11-Rotary kiln; 12-Waste heat recovery system; 13-Trough scrubbing machine; 14-Shaking table; 15-Ceramic filter; 16-Belt conveyor; 17-Second mixing tank; 18-First filter screen; 19-Third mixing tank; 20-Third feed pump; 21-Sand filter; 22-First-stage inclined plate sedimentation tank; 23-Second-stage inclined plate sedimentation tank; 24-Pump tank; 25-Fourth feed pump; 26-First heated conveyor belt device; 27-Second filter screen; 28-Second heated conveyor belt device; 29-Scraper; 30-Collection tank; 31-Fan; 32-Cooling tower.

[0029] 2601-Water barrier plate; 2602-Heating plate; 2603-Conveyor belt; 2604-Water guide bar. Detailed Implementation

[0030] like Figure 1 As shown, a process for recovering copper from circuit board cleaning waste liquid includes the following steps: a. Neutralization of circuit board cleaning waste liquid and separation of copper-containing sludge; The circuit board cleaning wastewater first enters a first stirring tank 3 equipped with an ion concentration meter 1 and a flow meter 2. The first stirring tank 3 has a NaOH solution inlet at the top. The NaOH solution is used to neutralize the circuit board cleaning wastewater and precipitate copper ions; its concentration is prepared at 2~10 mol / L, preferably 4~6 mol / L. The amount of NaOH solution used is automatically matched according to the ion type and concentration in the circuit board cleaning wastewater, specifically as follows: before the circuit board cleaning wastewater flows into the first stirring tank 3 by gravity, it flows through a pipe equipped with an ion concentration meter 1 and a flow meter 2 to obtain the flow rate and H₂O of the circuit board cleaning wastewater. + Cu 2+ The concentration of the plasma is calculated using the following formula to determine the amount of NaOH solution required.

[0031] In the formula, V NaOH This refers to the volume of NaOH solution used, in units of m. 3 / h; V0 is the volumetric flow rate of the circuit board cleaning waste liquid, which is directly measured by flow meter 2, and the unit is m³ / h. 3 / h; The concentration of divalent ions in the circuit board cleaning waste liquid is expressed in mol / L. The concentration of trivalent ions in the circuit board cleaning waste liquid, in mol / L; C(H) + H in circuit board cleaning waste liquid + The concentration is expressed in mol / L; C NaOH The concentration of the NaOH solution is expressed in mol / L. To comprehensively consider factors such as reaction efficiency and measurement error, an adjustment coefficient α is introduced, with a value ranging from 1 to 1.2, preferably from 1.05 to 1.1.

[0032] To ensure that Cu in the circuit board cleaning waste liquid is within safe limits 2+ For effective precipitation and neutralization of plasma, the reaction time is 3-7 min, preferably 4-6 min.

[0033] After the neutralization reaction is completed, the neutralized slurry is discharged from the bottom of the first mixing tank 3 and pumped to the column-type rakeless thickener 6 for concentration using the first feed pump 4. To improve the settling velocity of solid particles in the neutralized slurry, flocculant is added to the column-type rakeless thickener 6 using the flocculant dosing device 5. The amount of flocculant is determined based on the dry basis mass of solid particles in the neutralized slurry, and is 60~150 g / t, preferably 80~120 g / t. The overflow of the column-type rakeless thickener 6 is discarded, and the underflow is copper-containing sludge slurry with a concentration controlled at 15%~30%, preferably 20%~30%. The copper-containing sludge slurry is pumped to the filter press 8 for dewatering using the second feed pump 7. The filter cake (i.e., copper-containing sludge) after filtration falls into the copper-containing sludge temporary storage bin 9, with a moisture content controlled at 20%~40%. The filtrate is discarded.

[0034] b. Oxygen-enriched calcination of copper-containing sludge; Copper-containing sludge is discharged from the discharge port at the bottom of the copper-containing sludge temporary storage bin 9 and fed into the rotary kiln 11 via a closed screw conveyor 10 for oxygen-enriched calcination to obtain the calcined product. Oxygen-enriched calcination is achieved by increasing the airflow into the rotary kiln 11. Its purpose is to convert hydroxides in the copper-containing sludge into oxides and, under oxygen-enriched conditions, oxidize Cu and Fe to their highest oxidation states, while simultaneously removing organic matter from the copper-containing sludge. Specifically, the ability to fully oxidize iron to ferric iron (Fe3+) is crucial. 3+ This directly affects the separation efficiency of iron impurities in subsequent processes. Insufficient oxidation leads to iron being converted to ferrous iron (Fe²⁺). 2+ The copper sludge remains in the form of iron (Fe2+) and iron (Fe3+). Because the pH conditions required for the precipitation of ferrous and ferric iron differ significantly, it is difficult to completely remove them by adjusting the pH during subsequent wet processing, thus affecting the purity of the copper product. The kiln temperature of rotary kiln 11 is controlled at 400~800℃, preferably 500~600℃, and the calcination time of the copper-containing sludge is 20~90min, preferably 30~50min. The high-temperature exhaust gas generated during calcination enters the waste heat recovery system 12 to preheat the air entering rotary kiln 11.

[0035] c. Pre-selection and impurity removal of calcined products; To improve the processing capacity of the production line, wet pre-selection is performed on the calcined products after oxygen-enriched calcination. The calcined products are introduced into a trough scrubber 13 for scrubbing under the action of rinsing water, simultaneously dissolving soluble salts such as Na2SO4 in the calcined products. After scrubbing, the calcined products form slurry and deslimed products. The slurry is discarded, and the deslimed products flow by gravity to a shaking table 14 for further selection. After selection by the shaking table 14, the deslimed products are separated into concentrate, middlings, and tailings. The tailings are returned to the trough scrubber 13 for further scrubbing and selection, while the concentrate and middlings enter a ceramic filter 15 for dewatering. After dewatering by the ceramic filter 15, the moisture content of the pre-selected products is controlled at 20%~40%, and they are conveyed by a belt conveyor 16 to the second mixing tank 17 for subsequent processing.

[0036] d. Acid dissolution of preselected products and removal of impurity ions; The pre-selected product is fed into the second mixing tank 17 via a feed chute for acid dissolution treatment to convert copper in the copper-containing material into Cu. 2+ The acid dissolution treatment uses a sulfuric acid solution with a concentration of 1.2~2.0 mol / L, preferably 1.2~1.6 mol / L; the acid dissolution time is controlled at 3~7 min, preferably 4~6 min; the pH value of the slurry during acid dissolution is controlled between 1.8~2.6, preferably 2.0~2.2. The acid-dissolved slurry flows by gravity through a first filter screen 18 into a third mixing tank 19. The first filter screen 18 has a mesh size of 100~200 mesh, the purpose of which is to remove acid-insoluble matter. After removing acid-insoluble matter, the solution in the third mixing tank 19 is subjected to basic copper carbonate to adjust the pH value, in order to precipitate the Fe contained therein. 3+ Impurity ions, etc.

[0037] To reduce Cu 2+ To minimize losses, the pH of the slurry in the third mixing tank 19 is controlled at 3.8~4.5, preferably 3.9~4.2, when basic copper carbonate is added. At this pH, Fe... 3+ A large amount of Fe(OH)3 is precipitated, while ensuring that Cu... 2+ No precipitation occurs, thus minimizing copper loss while achieving deep iron removal. The residence time of the slurry in the third mixing tank 19 is controlled at 1~5 min, preferably 2~4 min. The main reactions occurring in this process are as follows: The slurry treated in the third mixing tank 19 is transported by the third feed pump 20 to the sand filter 21 for preliminary solid-liquid separation. After being filtered by the sand filter 21, the slurry enters the primary inclined plate settling tank 22. The overflow of the primary inclined plate settling tank 22 enters the secondary inclined plate settling tank 23 for further settling to remove solid particles. The resulting solution is temporarily stored in the pump tank 24.

[0038] e. Crystallization and removal of calcium sulfate dihydrate; like Figure 4 , Figure 5As shown, the first heated conveyor belt device 26 includes a conveyor belt 2603, water baffles 2601 are arranged around the two sides of the conveyor belt 2603, water guide ribs 2604 perpendicular to the running direction of the conveyor belt are arranged on the surface of the conveyor belt, and a heating plate 2602 is arranged below the upper surface of the conveyor belt. The heating plate 2602 is fixed and does not move with the conveyor belt. Multiple water-guiding ribs 2604 are provided and distributed at intervals on the surface of the conveyor belt 2603. The length of the water-guiding ribs 2604 is equal to the width of the conveyor belt surface, and the cross-section of the water-guiding ribs 2604 is a raised arc shape. This size and raised structure design is mainly to form multiple liquid storage tanks for storing solutions on the surface of the conveyor belt and the water-blocking plate 2601. Since the conveyor belt 2603 is made of stainless steel, the solution on the conveyor belt 2603 can easily move backward when the conveyor belt 2603 moves forward. The water-guiding ribs 2604 can provide a forward thrust for the solution, guiding the solution to be evenly distributed on the belt surface and avoiding local areas that are too thick or too thin. The bottom edge of the water barrier 2601 is bonded and fixed to the two side edges of the conveyor belt 2603 with a high-temperature resistant adhesive. The water barrier 2601 is mainly used to prevent the solution from flowing out from the edge of the conveyor belt. In addition, when the water barrier 2601 moves with the conveyor belt 2603 to the curved position at the end, it needs to be able to deform to adapt to the curved structure of the conveyor wheel, and then quickly spring back to its original shape when it reaches the horizontal position. Therefore, the material of the water barrier 2601 should be a high-temperature resistant flexible material, specifically polyimide (PI) elastomer or fluorosilicone rubber (FVMQ).

[0039] The solution in the temporary storage tank 24 is pumped by the fourth feed pump 25 to the first heated conveyor belt device 26 for crystallization and removal of calcium sulfate dihydrate. The temperature of the heating plate 2602 is 200~300℃, preferably 220~260℃, and the belt speed of the conveyor belt 2603 is controlled at 0.5~1.5m / min, preferably 0.8~1.2m / min. The liquid level is controlled at 1~3cm. The purpose is to rapidly heat and evaporate and concentrate the solution during the conveying process to remove calcium sulfate impurities contained in the solution. A second filter screen 27 is provided at the discharge port of the conveyor belt 2603. The filter screen 27 has a mesh size of 100~400 mesh to filter out the calcium sulfate dihydrate precipitated in the solution. A steam collection hood is located above the first heated conveyor belt device 26. The water vapor generated during the heating process is transported to the cooling tower 32 for condensation and reuse through the pipe in the middle of the steam collection hood and the fan 31.

[0040] f. Evaporation and crystallization to obtain copper sulfate pentahydrate; The solution passing through the second filter sieve 27 flows by gravity to the second heated conveyor belt device 28, where high-purity copper sulfate pentahydrate is obtained through evaporation and crystallization. The second heated conveyor belt device 28 has the same structure and materials for its components as the first heated conveyor belt device 26, both designed to store and heat the solution for concentration. In the second heated conveyor belt device 28, the heating plate temperature is 300~400℃, preferably 340~380℃, the conveyor belt speed is controlled at 0.5~1.5m / min, preferably 0.8~1.2m / min, and the liquid level is controlled at 0.5~2cm to ensure rapid crystallization of copper sulfate pentahydrate in the solution. At the end of the second heated conveyor belt device 28, a scraper 29 scrapes off the crystals adhering to the belt surface, which fall into the collection tank 30, yielding the high-purity copper sulfate pentahydrate product. The water vapor generated during the heating process is also transported to the cooling tower 32 for condensation and reuse via a pipe in the middle of the steam collection hood and a fan 31.

[0041] This invention provides a copper recovery process from circuit board cleaning wastewater, mainly comprising six steps: neutralization of the circuit board cleaning wastewater and separation of copper-containing sludge, oxygen-enriched calcination of the copper-containing sludge, pre-selection and impurity removal of the calcination products, acid dissolution of the pre-selected products and removal of impurity ions, crystallization and removal of calcium sulfate dihydrate, and evaporation crystallization to obtain copper sulfate pentahydrate. This process aims to achieve efficient copper recovery from circuit board cleaning wastewater, providing a universally applicable and economically and environmentally friendly technical pathway for the treatment and high-value utilization of circuit board cleaning wastewater.

[0042] The invention will be further explained below with reference to specific application examples.

[0043] Example of copper recovery process from circuit board cleaning waste liquid (1) Neutralization of circuit board cleaning waste liquid and separation of copper-containing materials Before being pumped into the first mixing tank 3, the waste liquid from circuit board cleaning flows through flow meter 2 and ion concentration meter 1, and its volumetric flow rate is measured to be 1905.15 m³ / s. 3 / h, H + The concentration was 6.31 × 10⁻⁶. -4 mol / L, Cu 2+ The concentration is 1.50 × 10⁻⁶. -3 mol / L, Fe 2+ The concentration of divalent impurity ions is 8.89 × 10⁻⁶. -4 mol / L, Fe 3+ The concentration of trivalent impurity ions is 6.25 × 10⁻⁶. -4The circuit board cleaning waste liquid was neutralized using a 5 mol / L NaOH solution with an adjustment factor of 1.10. Based on the calculation formula for NaOH solution dosage, the required NaOH solution addition was 3052.94 L / h. The neutralization reaction time was 6 min, and the pH of the slurry after the reaction was 10.9.

[0044] The neutralized slurry is discharged from the bottom of the first mixing tank 3 and pumped to the column-type rakeless thickener 6 for concentration. The flocculant dosing device 5 adds a 0.5‰ concentration of anionic polyacrylamide flocculant solution to the thickener at a dosage of 90 g / t (dry basis). After concentration by the column-type rakeless thickener 6, the concentration of copper-containing sludge reaches 29.83%. Subsequently, the concentrated copper-containing sludge is pumped to the filter press 8 for dewatering using the second feed pump 7. The moisture content of the filter cake after filtration is 27.52%, and the output is 997.76 kg / h. The filter cake falls into the copper-containing sludge temporary storage bin 9.

[0045] (2) Oxygen-enriched calcination of copper-containing sludge Copper-containing sludge is discharged from the bottom discharge port of the copper-containing sludge temporary storage silo 9 at a rate of 997.76 kg / h, and then fed into the rotary kiln 11 for oxygen-enriched calcination via a closed screw conveyor 10. The air intake of the rotary kiln 11 is controlled at 240 m³ / h. 3 The kiln temperature is controlled at 520 ℃, and the calcination time is 40 min. During the calcination process, water and organic matter are removed from the copper-containing sludge, and metal hydroxides are dehydrated and converted into oxides. The yield of the calcined product is 535.31 kg / h, with a water content of 4.78% and a copper grade of 35.63%. The calcination exhaust gas enters the waste heat recovery system 12 to preheat the air entering the rotary kiln 11.

[0046] X-ray diffraction experiments were conducted on the copper-containing sludge and calcination products obtained in steps (1) and (2) above. The experimental results are as follows: Figure 2 As shown in the figure, the calcined product exhibits multiple distinct CuO diffraction peaks, demonstrating that the copper-containing sludge generated a large amount of CuO products after oxygen-enriched calcination.

[0047] (3) Pre-selection and impurity removal of calcined products The calcined product is fed into a trough-type scrubbing machine 13 for scrubbing under the action of rinsing water. The rinsing water consumption of the trough-type scrubbing machine 13 is 1.48m³. 3The process involves scrubbing at a rate of 415.71 kg / h to produce desliming products and slurry. The desliming products have a concentration of 36.48%, a yield of 75.31%, and a copper grade of 53.40%. The slurry has a concentration of 22.32%, a yield of 41.96%, and a copper grade of 1.51%, and is either discarded or subjected to other recycling treatments. The desliming products are then further refined by shaking table 14 to obtain concentrate, middlings, and tailings. The combined yield of concentrate and middlings is 58.04%, with a copper grade of 60.29%. The tailings yield is 17.27%, with a copper grade of 30.23%, and is returned to the trough scrubber 13 for further scrubbing and re-selection. The concentrate and middlings are then dewatered by ceramic filter 15 to obtain pre-selected products. The pre-selected products have a flow rate of 415.71 kg / h and a moisture content of 28.83%, and are conveyed by belt conveyor 16 to the second mixing tank 17 for further processing.

[0048] (4) Acid dissolution of preselected products and removal of impurity ions The pre-selected product was fed into the second mixing tank 17 via a feed chute, and a 1.2 mol / L sulfuric acid solution was added for acid dissolution. The amount of sulfuric acid added was 2.76 m³. 3 The acid dissolution time was 6 minutes, and the pH of the slurry was controlled at 2.0. After acid dissolution, the slurry was filtered through a first sieve 18 (100 mesh) to remove acid-insoluble matter before entering a third mixing tank 19. The amount of acid-insoluble matter was 33.61 kg / h. 175.02 kg / h of basic copper carbonate was added to the filtrate to adjust the pH to 4.0, and the Fe content in the precipitate solution was reduced. 3+ After removing impurity ions and adjusting the pH value, the resulting slurry is held for 4 minutes in the third mixing tank 19. The reacted slurry undergoes preliminary solid-liquid separation in a sand filter 21, and then settles in a primary inclined plate settling tank 22 and a secondary inclined plate settling tank 23 to obtain a copper-containing solution after impurity removal, which is temporarily stored in a pump tank 24.

[0049] (5) Crystallization and separation of calcium sulfate dihydrate The copper-containing solution in the temporary storage tank 24 is pumped by the fourth feed pump 25 to the first heated conveyor belt device 26 for heating and crystallization. The conveyor belt 2603 is 10m long (referring to the length of the upper belt surface), 3.5m wide, and has a speed of 1m / min. The heating plate 2602 is at a temperature of 240℃, and the liquid level is controlled at approximately 2cm. As the solution temperature rises, some water evaporates, and calcium sulfate precipitates after reaching supersaturation. Subsequently, the solution flows by gravity to the second filter screen 27 (200 mesh) at the end of the first heated conveyor belt device 26 to remove calcium sulfate dihydrate impurities from the solution. The solution passing through the second filter screen 27 flows by gravity to the second heated conveyor belt device 28. Water vapor from the heating process is transported through pipes to the cooling tower 32 for condensation and reuse. The X-ray diffraction pattern of the calcium sulfate dihydrate removed by the first heated conveyor belt device 26 is shown below. Figure 3 As shown.

[0050] (6) Evaporation and crystallization to obtain copper sulfate pentahydrate The solution passing through the second filter sieve 27 flows by gravity onto the conveyor belt of the second heated conveyor belt device 28, where high-purity copper sulfate pentahydrate is obtained through evaporation and crystallization. The conveyor belt is 12m long (referring to the length of the upper belt surface), 5m wide, with a belt speed controlled at 1m / min, a liquid level controlled at approximately 1cm, and a heating temperature set at 360℃. During the heating process, the water in the solution evaporates rapidly, and copper sulfate pentahydrate crystals precipitate. At the end of the second heated conveyor belt device 28, a scraper 29 scrapes off the crystals adhering to the belt surface, which fall into the collection tank 30, yielding the high-purity copper sulfate pentahydrate product. The water vapor generated during the heating process is transported through pipelines to a cooling tower 32 for condensation and reuse.

[0051] Finally, after the above-mentioned process, the concentration can be reduced from 1905.15m. 3 1021.16 kg of copper sulfate pentahydrate was obtained from the waste liquid of circuit board cleaning. The comprehensive copper recovery rate was 95.84%, and the purity of copper sulfate pentahydrate reached 99.26%, which meets the technical requirements specified in GB 437-2009 Copper Sulfate (Agricultural Use) and HG / T 5215-2017 Industrial Copper Sulfate.

[0052] For any parts not mentioned in the above embodiments, existing technologies can be adopted or referenced.

[0053] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the above embodiments. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A process for recovering copper from circuit board cleaning waste liquid, characterized in that, Includes the following steps: a. Neutralization of circuit board cleaning waste liquid and separation of copper-containing sludge; After the circuit board cleaning waste liquid enters the first mixing tank, NaOH solution is added to carry out a neutralization reaction to obtain a neutralized slurry; The neutralized slurry is discharged from the bottom of the first mixing tank and pumped to the column-type rakeless thickener for concentration by the first feed pump. The overflow obtained from concentration is discarded, and the underflow is copper-containing sludge slurry. The copper-containing sludge slurry is pumped to the filter press for dewatering by the second feed pump. The copper-containing sludge obtained after filtration falls into the copper-containing sludge temporary storage bin, and the filtrate is discarded. b. Oxygen-enriched calcination of copper-containing sludge; Copper-containing sludge is discharged from the discharge port at the bottom of the copper-containing sludge temporary storage silo and fed into the rotary kiln via a closed screw conveyor for oxygen-enriched calcination to obtain calcined products. c. Pre-selection and impurity removal of calcined products; The calcined product is fed into a trough scrubber under the action of rinsing water for scrubbing to obtain mud and desliming product; the mud is discarded, and the desliming product flows by gravity to a shaking table for fine selection, and after fine selection, it is divided into concentrate, middlings and tailings; the tailings are returned to the trough scrubber for scrubbing and further selection, and the concentrate and middlings enter a ceramic filter for dewatering to obtain the dewatered pre-selected product. d. Acid dissolution of preselected products and removal of impurity ions; After the pre-selected product is conveyed to the second mixing tank by a belt conveyor, sulfuric acid solution is added for acid dissolution treatment. The acid-dissolved slurry is filtered through the first filter screen and then flows into the third mixing tank by gravity. Basic copper carbonate is added to the third mixing tank to adjust the pH value and precipitate impurity ions. The slurry treated in the third mixing tank is transported to the sand filter for preliminary filtration by the third feed pump; the filtered slurry enters the inclined plate settling tank for settling to remove solid particles, and the resulting solution is temporarily stored in the pump tank. e. Crystallization and removal of calcium sulfate dihydrate; The solution in the temporary storage pump pool is pumped by the fourth feed pump to the first heated conveyor belt device for evaporation and concentration, which is used to crystallize the calcium sulfate dihydrate in the solution. Then, the calcium sulfate dihydrate precipitated in the solution is filtered out through the second filter screen. f. Evaporation and crystallization to obtain copper sulfate pentahydrate; The solution filtered through the second filter screen flows by gravity to the second heated conveyor belt device for evaporation and concentration, which is used to crystallize copper sulfate pentahydrate in the solution. Then, at the end of the second heated conveyor belt device, the crystals attached to the belt surface are scraped off by a scraper and fall into the collection tank to obtain the copper sulfate pentahydrate product.

2. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, In step a: the neutralization reaction takes 3-7 minutes; The concentration of the copper-containing sludge is controlled at 15% to 30%, and the moisture content of the copper-containing sludge is controlled at 20% to 40%.

3. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, In step b: the temperature of the rotary kiln is controlled at 400~800℃, and the oxygen-enriched calcination time is 20~90min; Oxygen-enriched calcination is achieved by increasing the airflow into the rotary kiln. The high-temperature waste gas generated during calcination enters the waste heat recovery system to preheat the air entering the rotary kiln.

4. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, In step c: the moisture content of the preselected product is controlled at 20%~40%.

5. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, In step d: the concentration of the sulfuric acid solution is 1.2~2.0 mol / L, the acid dissolution time is controlled at 3~7 min, and the pH value of the slurry during acid dissolution is controlled at 1.8~2.6; the mesh size of the first filter screen is 100~200 mesh. When adding basic copper carbonate, the pH value of the slurry in the third mixing tank is controlled at 3.8~4.5, and the residence time of the slurry in the third mixing tank is controlled at 1~5 minutes.

6. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, In step d: After being filtered by a sand filter, the slurry first enters the primary inclined plate settling tank for settling, and the overflow from the primary inclined plate settling tank then enters the secondary inclined plate settling tank for settling.

7. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, Both the first and second heated conveyor belt devices include a conveyor belt, with water baffles arranged around the edges of both sides of the conveyor belt, water guide ribs perpendicular to the direction of conveyor belt operation arranged on the surface of the conveyor belt, and a heating plate arranged below the upper layer of the conveyor belt.

8. The copper recovery process from circuit board cleaning waste liquid according to claim 7, characterized in that, In the first heated conveyor belt device: the temperature of the heating plate is set to 200~300℃; the belt speed of the conveyor belt is controlled at 0.5~1.5m / min; and the liquid level of the solution on the conveyor belt surface is controlled at 1~3cm.

9. The copper recovery process from circuit board cleaning waste liquid according to claim 7, characterized in that, In the second heated conveyor belt device: the temperature of the heating plate is set to 300~400℃; the belt speed of the conveyor belt is controlled at 0.5~1.5m / min; and the liquid level of the solution on the conveyor belt surface is controlled at 0.5~2cm.

10. The copper recovery process from circuit board cleaning waste liquid according to claim 1, characterized in that, The water vapor generated during the evaporation and concentration process is transported through pipelines to a cooling tower for condensation and reuse.

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