Heavy metal emission reduction and sludge reduction treatment process method for circuit board wastewater

Abstract

The invention discloses a heavy metal emission reduction and sludge reduction treatment process method for circuit board wastewater. The invention provides a layered precipitation strategy of'first acid, second alkali and second sulfur '. The method comprises the following steps: performing acid precipitation on alkaline organic wastewater by using acidic wastewater, and recovering printing ink residues; carrying out air stripping treatment on the copper ammonia wastewater by utilizing an alkaline condition, and precipitating high-purity copper hydroxide; and finally, carrying out deep precipitation on residual complexing heavy metals by utilizing excessive sulfides in the pretreatment stage, and further recovering copper resources in the comprehensive water tank through coprecipitation of copper hydroxide and copper sulfide. Sludge generated in each process is classified and treated; printing ink slag, biochemical residual sludge and copper / nickel sulfide sludge are subjected to synergistic pyrogenic process treatment; copper hydroxide sludge is selectively subjected to acid dissolution to prepare copper sulfate. Lime, ferrous sulfate and polyaluminum are not used in the whole process. According to the method, the medicament is utilized to the maximum extent, the sludge is reduced by 50% or above, and the resource value of valuable metal is increased by 3-5 times.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a process for reducing heavy metal emissions and sludge volume in circuit board wastewater. Background Technology

[0002] The production of printed circuit boards (PCBs) involves wet processes such as developing, etching, copper plating, and electroplating, generating complex wastewater containing pollutants including heavy metals (copper, nickel), ammonia nitrogen, CODcr, and complexing agents. Traditional treatment processes have the following problems:

[0003] 1. Serious waste of reagents: During the acid precipitation of ink, a large amount of sulfuric acid is used to neutralize sodium carbonate instead of actually precipitating ink; during the precipitation of heavy metals, large amounts of inefficient reagents such as lime, ferrous sulfate, and polyaluminum are used, resulting in a large amount of low-value mixed sludge.

[0004] 2. Low value of sludge: Various sludge residues are mixed, and valuable metals are diluted, making it difficult to recycle them as resources and resulting in high disposal costs.

[0005] 3. Fragmented process: Each pretreatment unit operates independently, lacking collaborative optimization, resulting in low reagent utilization efficiency.

[0006] 4. Safety hazards: High salt supersaturation causes scaling and sludge compaction in the system. Frequent and irregular cleaning of the sludge often leads to accidents resulting in personal injury or death, becoming a hidden pain point in the industry. Summary of the Invention

[0007] The present invention aims to provide a process for reducing heavy metal emissions and sludge volume in circuit board wastewater, in order to solve the problems of high reagent consumption, high sludge production, difficulty in recovering valuable metals, and safety hazards caused by scaling of structures in the existing technology.

[0008] This invention proposes a "first acid, then alkali, then sulfur" fractional treatment and stratified precipitation strategy to achieve the ultimate utilization of reagents and the high-value resource utilization of sludge.

[0009] 1. Acidification – Utilizing acidic wastewater to precipitate ink.

[0010] Alkaline organic wastewater from developing and stripping processes is directly added to acidic wastewater, using the waste acid to neutralize the alkalinity and precipitate ink residue. Compared to traditional separate acid precipitation, this method saves over 50% of sulfuric acid while avoiding operational problems caused by large amounts of CO2 escape. This synergistic mechanism realizes the clean production concept of "treating waste with waste."

[0011] 2. Post-alkali treatment – ​​Precipitating high-purity copper hydroxide under alkaline conditions.

[0012] Ammonia gas is removed by adding alkali to copper-ammonia wastewater (such as etching cleaning water) to a pH ≥ 11. The ammonia gas is then absorbed by water to generate ammonia water for reuse. After stripping, copper ions in the wastewater precipitate as copper hydroxide. Due to the purity of the source (no interference from other metal ions), the resulting copper hydroxide sludge has a dry basis copper content of over 95%. It can be directly dried and sold or dissolved in sulfuric acid to prepare electroplating-grade copper sulfate, achieving high-value resource recovery.

[0013] 3. Resulfurization – utilizing excess sulfides for deep precipitation

[0014] Excess sodium sulfide added during the pretreatment of nickel-containing and EDTA wastewater continues to play a role in the combined treatment tank, deeply precipitating residual complexed heavy metals in the form of copper / nickel sulfide. Simultaneously, the mixed wastewater still contains a certain concentration of copper ions, which, under pH 7–8 conditions, react with the excess sulfides from the pretreatment stage to form copper sulfide precipitate, which then co-precipitates with copper hydroxide in the wastewater, further recovering copper resources. This "reactionary relay" mechanism requires no additional chemical addition, achieving optimal utilization of sulfide reagents.

[0015] 4. Targeted resource utilization of sludge and residue

[0016] • Ink residue and biochemical waste sludge: Both are organic and combustible. They can be co-processed with copper sulfide / nickel sludge using pyrometallurgical methods, allowing smelters to simultaneously recover copper and utilize the calorific value of the organic matter.

[0017] • Copper hydroxide sludge (from copper ammonia wastewater): High purity, selectively acid-dissolved to prepare copper sulfate, with the small amount of residue filtered out returned to pyrometallurgical treatment.

[0018] • Copper hydroxide / copper sulfide mixed sludge (from integrated water tank): sold to copper smelters, priced according to copper content.

[0019] • Nickel sulfide filter residue and copper sulfide filter residue: sold to nickel / copper smelters.

[0020] 5. Full-process drug control

[0021] This invention follows these principles: caustic soda is used as the primary ingredient, while the amounts of sodium sulfide, sulfuric acid, and bleach are controlled; lime, ferrous sulfate, and polyaluminum sulfate are not used. This eliminates scaling and packing caking problems in structures caused by calcium salt supersaturation at the source, thoroughly removing potential safety hazards.

[0022] The "layered sedimentation" described in this invention refers to the use of different solid-liquid separation methods at different processing stages to separate sludge of different forms. As a preferred embodiment, this invention uses multi-stage filtration to replace traditional gravity sedimentation: after each stage of chemical reaction, solid-liquid separation is immediately performed through a bag filter or plate and frame filter press, avoiding the mixing of different sludge types, while shortening processing time and reducing equipment footprint.

[0023] Beneficial effects

[0024] •Optimal utilization of reagents: Acids, alkalis, and sulfur each perform their functions and work in tandem, reducing reagent consumption by 30% to 50%, saving more than 50% of sulfuric acid, and completely eliminating the use of inefficient reagents such as lime, ferrous sulfate, and polyaluminum sulfate.

[0025] • Reduced sludge volume and improved quality: The total amount of sludge is reduced by 50% to 60%, the copper content of copper hydroxide sludge is >95%, and the copper content of mixed sludge in the integrated water tank can reach 15% to 25%, increasing the resource value by 3 to 5 times.

[0026] • Efficient and collaborative processes: Each processing unit is organically combined to form a complete resource utilization closed loop.

[0027] •Safe and environmentally friendly: No lime is used, eliminating the risk of scaling on structures; wastewater containing cyanide and ammonia is treated in a closed system, and waste gas is recovered, preventing secondary pollution.

[0028] • Stable compliance: Effluent COD < 80 mg / L, ammonia nitrogen < 10 mg / L, total copper < 0.3 mg / L, meeting the most stringent discharge standards. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention, showing the diversion routes of each wastewater stream, the pretreatment unit, the integrated sedimentation tank, the biological system, and the sludge classification and disposal path. Specifically, it includes:

[0030] Wastewater collection area: Copper ammonia wastewater, cyanide-containing wastewater, nickel-containing wastewater, EDTA wastewater, developing wastewater, film stripping wastewater, acidic wastewater, and mixed wastewater are collected separately.

[0031] Preprocessing area:

[0032] • The copper ammonia wastewater is stripped by an alkali-adding ammonia stripping tower (pH≥11), and the ammonia gas is absorbed to obtain ammonia water / ammonium salt, which is then filtered to obtain copper hydroxide sludge;

[0033] • Cyanide-containing wastewater is stripped by an acidification cyanide stripping tower (pH≤3), absorbed by HCN alkaline solution, and the filtrate is sent to a comprehensive water tank;

[0034] • Nickel-containing wastewater is reacted in a sulfidation reaction tank and filtered to obtain nickel sulfide filter residue;

[0035] • EDTA wastewater is reacted in a sulfidation reaction tank (pH 7-9) and filtered to obtain copper sulfide filter residue;

[0036] • The developing wastewater, stripping wastewater and acidic wastewater are mixed in an acidic wastewater tank (pH≤5), and filtered to obtain ink residue;

[0037] • Combined wastewater enters the combined water tank directly.

[0038] Integrated sedimentation zone: The filtrates from each stream are collected in the integrated water tank, and the pH is adjusted to 7-8. Excess sulfides from the pretreatment stage are used for deep sedimentation. Residual copper ions in the integrated wastewater simultaneously generate copper hydroxide and copper sulfide precipitates. The filtered water yields a mixed sludge of copper hydroxide and copper sulfide.

[0039] Biological treatment zone: The filtrate sequentially enters the anaerobic tank (sulfate-reducing bacteria, denitrifying bacteria), the aerobic tank (nitrifying bacteria), and the secondary sedimentation tank. The nitrified liquid from the aerobic tank is returned to the anaerobic tank (100% to 300%). The effluent from the secondary sedimentation tank meets the discharge standards. The remaining sludge is filtered by a filter press to obtain copper-containing sludge.

[0040] Sludge treatment by grade:

[0041] • Copper hydroxide sludge → selective acid dissolution → electroplating grade copper sulfate

[0042] • Nickel sulfide filter residue, copper sulfide filter residue, mixed copper hydroxide / copper sulfide sludge → sold to copper / nickel smelters

[0043] • Ink residue and copper-containing sludge → co-processed pyrometallurgical treatment (copper recovery + calorific value utilization)

[0044] Process control labeling: No lime, ferrous sulfate, or polyaluminum are used throughout the entire process; use of sulfuric acid and bleach is controlled. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific embodiments, but it should not be construed as a limitation of the present invention.

[0046] Example 1: Application in a small-scale circuit board factory

[0047] A small circuit board factory generates approximately 80 tons of wastewater daily, including 2 tons of nickel-containing wastewater, 5 tons of cyanide-containing wastewater, 10 tons of copper-ammonia wastewater, 8 tons of EDTA wastewater, 15 tons of developing wastewater, 10 tons of film stripping wastewater, 15 tons of acidic wastewater, and 15 tons of mixed wastewater. The original process consumed 3 tons of ferrous sulfate, 2 tons of lime, 1.2 tons of caustic soda, 1.5 tons of sodium sulfide, and 2.5 tons of bleaching water monthly, producing 6 tons of copper-containing sludge and 3 tons of ink residue, making it difficult to meet CODcr standards.

[0048] Modification using the process of this invention:

[0049] S1 diversion: Each stream of wastewater is collected separately.

[0050] S2 fractional pretreatment:

[0051] ①Developing wastewater (pH 13, COD about 20000 mg / L) and stripping wastewater (pH 13, COD about 8000 mg / L) are gradually added to the acidic wastewater tank (pH 2). After mixing, the pH is controlled to be < 5. Organic ink residue is obtained by bag filtration, and the filtrate is sent to the comprehensive water tank.

[0052] ② Add caustic soda to copper ammonia wastewater (NH3-N about 2000 mg / L, Cu²⁺ about 500 mg / L) to pH 12, remove ammonia under vacuum, absorb the ammonia gas with water to obtain ammonia water for reuse; filter the wastewater through a bag filter to obtain copper hydroxide filter residue (copper content >95% on a dry basis), and send the filtrate into a comprehensive water tank;

[0053] ③ Cyanide-containing wastewater (CN⁻ approximately 100 mg / L) is treated with sulfuric acid in a closed tank until the pH reaches 3. The stripped gas is then absorbed by a two-stage alkali system, and the wastewater is discharged into a comprehensive water tank.

[0054] ④ Add sodium sulfide to the nickel-containing wastewater (Ni²⁺ approximately 50 mg / L) to a molar ratio of 1.5, filter by plate and frame filter press to obtain nickel sulfide filter residue (containing approximately 22% nickel), and send the filtrate into the integrated water tank;

[0055] ⑤ Adjust the pH of the EDTA wastewater (approximately 800 mg / L of Cu²⁺) to 8, add sodium sulfide to a molar ratio of 2, react for 30 minutes, filter by bag to obtain copper sulfide filter residue (containing approximately 32% copper), and send the filtrate into the integrated water tank.

[0056] S3 Comprehensive Sedimentation: The comprehensive water tank collects approximately 70 tons / day of filtrate from various streams, adjusts the pH to 8, and utilizes the excess sodium sulfide in S2④ and S2⑤ for deep precipitation. The residual copper ions in the comprehensive wastewater simultaneously generate copper hydroxide and copper sulfide precipitates. After stirring for 20 minutes, the mixture is filtered to obtain a copper hydroxide / copper sulfide mixed sludge (copper content approximately 18%).

[0057] S4 biological treatment: The S3 filtrate enters an anaerobic tank (100m³, HRT 24h, containing sulfate-reducing bacteria and denitrifying bacteria) and an aerobic tank (200m³, HRT 48h, containing nitrifying bacteria) for treatment. The nitrified liquid from the aerobic tank is recycled back to the anaerobic tank (recycle ratio 200%). The effluent from the secondary sedimentation tank has COD < 70mg / L, ammonia nitrogen < 8mg / L, and total copper < 0.2mg / L, meeting discharge standards. The remaining sludge is filtered by a filter press to obtain copper-containing sludge (copper content approximately 5%).

[0058] S5 sludge classification and disposal:

[0059] ① Dissolve copper hydroxide sludge in sulfuric acid, filter out insoluble matter, and crystallize to obtain electroplating grade copper sulfate (98%).

[0060] ② Nickel sulfide filter residue, copper sulfide filter residue, and mixed copper hydroxide / copper sulfide sludge are sold to copper / nickel smelters;

[0061] ③ The ink residue and copper-containing sludge are sent to a smelter for pyrometallurgical treatment.

[0062] After the renovation, the monthly chemical usage is reduced to 1.2 tons of sodium sulfide, 0.5 tons of caustic soda flakes, and 0.8 tons of sulfuric acid. Ferrous sulfate, lime, polyaluminum hydroxide, and bleaching water are no longer used. The total amount of sludge is reduced to 3.5 tons (a 56% reduction), including approximately 0.8 tons of copper hydroxide sludge (copper content > 95%) and approximately 1.5 tons of mixed copper hydroxide / copper sulfide sludge (copper content approximately 18%). The annual savings in chemical and sludge disposal costs are approximately 300,000 yuan, and the renovation investment is recovered within the same year.

[0063] Example 2: Application in a medium-sized PCB factory

[0064] A medium-sized circuit board factory treats 400 tons of wastewater daily using the process of this invention. To address the large volume of wastewater, the copper-ammonia wastewater in S2 is continuously treated using a stripping tower, the comprehensive sedimentation in S3 uses a high-efficiency sedimentation tank, and the biological treatment in S4 uses A... 2 O process. Data after one year of operation: reagent costs decreased by 38%, sludge production decreased by 55%, and effluent consistently met the standards in Table 3 of the "Electroplating Pollutant Discharge Standard". Sulfate-reducing bacteria activity in the anaerobic tank remained stable, with S²⁻ concentration maintained at 5–15 mg / L, ensuring deep removal of residual copper and nickel. No scaling occurred in the structures after two years of operation, reducing cleaning frequency from once per quarter to no cleaning required.

[0065] Example 3: Validation of treatment for wastewater containing high concentrations of sulfate

[0066] A circuit board factory's acidic wastewater contained up to 5000 mg / L of sulfuric acid. Traditional processes required large amounts of lime for neutralization, generating substantial amounts of gypsum sludge. This invention utilizes sulfate-reducing bacteria in an S4 anaerobic tank to convert sulfate into sulfides, simultaneously achieving sulfate reduction and heavy metal precipitation. Operational results show that the influent SO4... 2- The concentration of sulfur dioxide in the treated effluent decreased from 5000 mg / L to 800 mg / L, achieving a removal rate of 84%. Simultaneously, residual copper decreased from 2 mg / L to below 0.1 mg / L. The sulfide content in the biological sludge remained stable, with no risk of H2S emission.

[0067] Industrial Application Effect Comparison

[0068] index Original process (lime + ferrous sulfate + polyaluminum) The process of this invention change Chemical cost (RMB / ton of water) 26.5 10.5 ↓60% Sludge production (kg / ton of water) 12.5 5.5 ↓56% Copper content in copper-containing sludge 3～5% 15～95% ↑3~15 times Sludge disposal fee (RMB / ton of water) 8.5 3.5 ↓59% Copper recycling revenue (RMB / ton of water) 0 8.0 New Overall operating cost (RMB / ton of water) 26.5 6.0 ↓77%

[0069] The above embodiments demonstrate that the present invention can effectively reduce heavy metal emissions, reduce sludge volume, and lower costs in PCB factories of different sizes and with different water quality characteristics, and has wide applicability and significant economic and environmental benefits.

Claims

1. A process for reducing heavy metal emissions and sludge volume in circuit board wastewater, characterized in that, The treatment and sedimentation are carried out according to the order of acid, alkali, and sulfur addition, including: • First, acidic wastewater is used to precipitate alkaline organic wastewater to remove and recover ink residue; • The copper-ammonia wastewater is then stripped under alkaline conditions to precipitate and recover copper hydroxide; • Finally, the excess sulfides from the pretreatment stage are used to deeply precipitate the residual complexed heavy metals, while copper resources are further recovered by co-precipitation of copper hydroxide and copper sulfide in the integrated water tank.

2. The process method according to claim 1, characterized in that, Includes the following steps: S1: Divert and collect cyanide-containing wastewater, copper-ammonia wastewater, nickel-containing wastewater, EDTA wastewater, developing wastewater, film stripping wastewater, acidic wastewater, and mixed wastewater; S2: Separate pretreatment: ① The developing wastewater and stripping wastewater are added to the acidic wastewater until the pH is <5, filtered to obtain ink residue, and the filtrate is sent to the comprehensive water tank; ② Add alkali to copper ammonia wastewater until pH≥11 and strip it off. Absorb ammonia gas and filter to obtain copper hydroxide sludge. Send the filtrate to the comprehensive water tank. ③ The cyanide-containing wastewater is acidified and stripped to pH ≤ 3, the waste gas is absorbed by alkaline solution, and the filtrate is sent to the comprehensive water tank; ④ After reacting with sodium sulfide, the nickel-containing wastewater is filtered. The amount of sodium sulfide added is 1.1 to 2.0 times the molar concentration of nickel ions, resulting in nickel sulfide filter residue. The filtrate is sent to the comprehensive water tank. ⑤ Adjust the pH of the EDTA wastewater to 7-9, add sodium sulfide and filter after reaction. The amount of sodium sulfide added is 1.5-2.5 times the molar concentration of copper ions to obtain copper sulfide filter residue. The filtrate is sent to the comprehensive water tank. S3: Comprehensive sedimentation: Collect the filtrates from S2 into the comprehensive water tank, adjust the pH to 7-8, and use the excess sulfides in S2④ and S2⑤ for deep sedimentation. The residual copper ions in the comprehensive wastewater simultaneously generate copper hydroxide and copper sulfide precipitates. Filter to obtain a mixed sludge of copper hydroxide / copper sulfide. S4: Biochemical treatment: The S3 filtrate is sequentially fed into the anaerobic tank and the aerobic tank for treatment. The nitrified liquid from the aerobic tank is returned to the anaerobic tank at a return ratio of 100% to 300%. After sedimentation, the effluent meets the discharge standards.

3. The process method according to claim 2, characterized in that, In step S2, ammonia gas is absorbed by water to generate ammonia water.

4. The process method according to claim 2, characterized in that, In step ④ of S2, the reaction pH is controlled between 6 and 8.

5. The process method according to claim 2, characterized in that, In step S2, before adding sodium sulfide to the EDTA wastewater, the pH should be adjusted to 7-9 with acid or alkali.

6. The process method according to claim 2, characterized in that, In S3, the excess sulfides from S2④ and S2⑤ are used for deep precipitation, eliminating the need for additional sulfides.

7. The process method according to claim 2, characterized in that, In the S4 anaerobic tank, sulfate-reducing bacteria are used to reduce sulfate to produce S. 2- It reacts with residual heavy metals to form sulfide precipitates.

8. The process method according to claim 2, characterized in that, No lime, ferrous sulfate, or polyaluminum are used in the entire process.

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