PAC (polyaluminum chloride) serves as a versatile coagulant in industrial water treatment, leveraging its ability to neutralize charges, adsorb contaminants, and facilitate particle aggregation. Below are its key applications across various industries:
Challenges:
Wastewater contains high concentrations of suspended solids (e.g., iron scraps, ore fines), heavy metal ions (zinc, lead), and colloidal matter.
Treatment Approach:
- PAC Dosage: 0.5–1.5‰ (by weight).
- Mechanism: PAC rapidly forms dense flocs through adsorption and bridging, enhancing solid-liquid separation in sedimentation tanks.
- Performance:
- Reduces effluent turbidity by >85%.
- Removes >70% of heavy metal ions, ensuring compliance with discharge regulations.
Challenges:
High chromaticity (residual dyes), elevated COD (chemical oxygen demand), and variable pH levels.
Treatment Approach:
- PAC Dosage: 0.8–1.2‰, paired with pH adjusters.
- Mechanism: PAC generates aluminum hydroxide (Al(OH)₃) colloids that adsorb dye molecules. Combined with air flotation, this process:
- Achieves a 90% color removal efficiency.
- Stabilizes pH and reduces organic load for downstream processing.
Challenges:
Extremely high COD (up to 30,000 mg/L), containing macromolecular organics (e.g., terephthalic acid, ethylene glycol esters).
Treatment Approach:
- PAC Dosage: 0.3–0.5‰ during coagulation.
- Synergy with PAM: PAC neutralizes colloidal charges, while polyacrylamide (PAM) strengthens floc structure.
- Outcome:
- Initial COD reduction of 40%, improving biodegradability.
- Prepares wastewater for advanced treatments like iron-carbon micro-electrolysis and UASB anaerobic digestion.
Challenges:
High surfactant and oil content, plus unstable 水质 (water quality) fluctuations.
Treatment Approach:
- PAC Dosage: 0.2–0.4‰, used with coagulation-sedimentation.
- Key Benefits:
- Removes suspended solids and emulsified oils.
- Reduces COD from 11,000 mg/L to 2,500 mg/L, lightening the load on biological treatment systems.
Challenges:
High alkalinity (pH > 10), glass grinding particles, and non-biodegradable contaminants.
Treatment Approach:
- PAFC Usage: Polymeric aluminum ferric chloride (a PAC variant) neutralizes alkalinity and promotes particle aggregation.
- Performance:
- Removes >90% of suspended solids.
- Lowers effluent turbidity to ≤5 NTU, ensuring smooth operation of subsequent ultrafiltration systems.
Challenges:
Semiconductor and etching wastewater with fluoride concentrations >10 mg/L.
Treatment Approach:
- PAC Mechanism: Aluminum ions (Al³⁺) react with fluoride (F⁻) to form insoluble AlF₃ precipitates.
- Result:
- Reduces fluoride from 14.6 mg/L to 0.4–1.0 mg/L, meeting drinking water quality standards.
Summary:
PAC’s adaptability across industries—from heavy metal removal in steel wastewater to fluoride elimination in semiconductor effluents—makes it a cornerstone of industrial water treatment. Its precise dosing and synergistic use with other chemicals (e.g., PAM, pH adjusters) optimize performance for diverse contaminants and regulatory requirements.
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