How does polyaluminium chloride treat wastewater generated by the electronic semiconductor industry? The following is a detailed introduction by the Xinhuan polyaluminium chloride manufacturer. The wastewater produced by polysilicon and monocrystalline silicon belongs to the wastewater produced by the electronic semiconductor industry. The amount of wastewater generated during the production and grinding of polysilicon is very large. The toxic metal ions and fluorine discharged by traditional methods are not stable, which causes serious pollution to the water resources environment. In this case, we often use polyaluminium chloride to treat this wastewater.
1. Characteristics of electronic semiconductor wastewater
Pollut types: heavy metals (Cu, Ni, Pb, etc.), fluoride (F⁻), organic pollutants (photoresist, solvents), suspended solids, acids and alkalis, etc.
Difficulties in treatment: high toxicity, high concentration, complex composition, and strict emission standards must be met (such as fluoride <10 mg/L, heavy metals <0.5 mg/L).
2. Mechanism of action of polyaluminium chloride (PAC)
Electroneutralization:
PAC hydrolyzes to generate positively charged multinuclear complexes, neutralizing the negative charge of suspended particles and colloids, causing them to destabilize and aggregate.
Adsorption bridging:
Polymer chains adsorb multiple particles to form large flocs, accelerating sedimentation.
Co-precipitation:
Co-precipitate with heavy metal ions (such as Cu²⁺, Ni²⁺), or adsorb fluoride to form Al-F complexes.
3. Specific treatment process flow
1. Pretreatment
pH adjustment:
Wastewater is usually strongly acidic or alkaline, and needs to be adjusted to neutral (pH 6.5-7.5) by adding acid (H₂SO₄) or alkali (NaOH/Ca(OH)₂) to optimize the PAC coagulation efficiency.
Fluoride removal (if present):
Add lime (CaO) to generate CaF₂ precipitation to initially reduce the fluoride concentration.
2. Coagulation reaction
PAC addition:
The dosage is usually 50-200 mg/L (adjusted according to water quality), and the agent is fully mixed by rapid stirring (200-300 rpm, 1-3 minutes).
pH control:
The optimal pH range is 6-8. Too high or too low will affect the hydrolysis form of Al and the coagulation effect.
3. Flocculation
Coagulant combination:
Add polyacrylamide (PAM, 0.5-2 mg/L) and stir slowly (30-50 rpm, 10-15 minutes) to promote floc growth.
4. Solid-liquid separation
Sedimentation/flotation:
The flocs are separated in the sedimentation tank (residence time 1-2 hours) or flotation tank, and the supernatant enters the subsequent treatment.
Filtration:
Sand filtration or activated carbon filtration further removes tiny particles and residual pollutants.
5. Deep treatment
Heavy metal removal:
If the residual heavy metal exceeds the standard, sodium sulfide (Na₂S) or chelating agent (such as DTCR) can be added for chemical precipitation.
Organic matter treatment:
Activated carbon adsorption or oxidation (such as ozone, Fenton) degrades insoluble organic matter.
Ion exchange:
For trace ion pollutants (such as As, Cr), resin exchange is used to ensure that the standard is met.
6. Sludge treatment
After dehydration (plate and frame filter press/centrifugation), the precipitated sludge is disposed according to hazardous waste standards (including heavy metals).
IV. Advantages of PAC application
Broad spectrum: effective for suspended solids, colloids, some heavy metals and fluorides.
Strong adaptability: wide pH range (5-9), large and dense flocs, fast sedimentation.
Economical: small dosage, lower cost than traditional aluminum salts (such as aluminum sulfate).
The main products of flocculant manufacturer Xinhuan Water Treatment are:
White polyaluminium chloride (food grade), drinking grade polyaluminium chloride, industrial grade polyaluminium chloride, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, petroleum recycling polyacrylamide, oil recovery polyacrylamide, polyacrylamide, polymer flocculant polymer flocculation coagulant, polymeric ferrous sulphate, polyferric aluminium chloride and other water treatment chemicals. Welcome customers to write to us to negotiate business! Tel/WhatsApp：+8619003830067 Email：joanna@xhwtm.com Contact:Joanna
