Product Application
Water Treatment
Flocculant
Municipal Drinking Water Treatment: Neutralizes surface charges of colloidal particles to form flocs (alum effect), rapidly removing suspended solids, colloids, and color.
Wastewater Treatment: Used in industrial wastewater (e.g., textile, papermaking) for decolorization and COD (Chemical Oxygen Demand) reduction.
Sludge Dewatering: Combined with polyacrylamide (PAM) to enhance sludge settling.
pH Regulator
Neutralizes alkaline wastewater, adjusting pH to neutral to prevent pipeline corrosion or interference with subsequent biological processes.
Paper Industry
Sizing Agent
Reacts with rosin to form aluminum rosinate, improving water resistance and printability (e.g., book paper, packaging paper).
Enhances fiber bonding in recycled paper production.
Filler Retention Agent
Promotes uniform distribution of fine fibers and fillers (e.g., calcium carbonate) in paper, reducing material loss.
Textile and Dyeing
Mordant
Fixes natural dyes (e.g., indigo, alizarin) in traditional dyeing processes to improve color fastness.
Regulates dye-fiber binding for uniform coloration.
Wastewater Decolorization
Removes residual dye molecules (especially reactive dyes) via flocculation in textile effluent treatment.
Firefighting and Flame Retardancy
Foam Fire Extinguisher
Reacts with sodium bicarbonate to generate CO₂ foam for extinguishing oil fires (e.g., petroleum storage tanks).
Wood Flame Retardation
Impregnates wood to form an alumina insulating layer after dehydration, delaying combustion.
Agriculture and Horticulture
Soil Amendment
Acidifies alkaline soil (releases H⁺ via hydrolysis) for acid-loving plants (e.g., blueberries, azaleas).
Supplies aluminum ions to enhance phosphorus uptake in certain plants.
Water Purifier
Removes suspended organic matter in aquaculture ponds to prevent fish diseases.
Chemical and Material Production
Aluminum Salt Precursor
Produces derivatives like aluminum hydroxide [Al(OH)₃] and polyaluminum chloride (PAC).
Prepares catalyst supports (e.g., petroleum cracking catalysts).
Titanium Dioxide Production
Neutralizes waste acid and recovers aluminum in the sulfate process for TiO₂ manufacturing.
Other Specialized Applications
Food Additive (E520)
Firming agent in jellyfish preservation and fruit/vegetable processing (strict residue limits apply).
Education and Research
Demonstrates hydrolysis and flocculation in school chemistry experiments.
Precautions
High Acidity: Overuse may corrode equipment (requires corrosion inhibitors).
Aluminum Residue: Control Al³⁺ concentration in drinking water (<0.2 mg/L per WHO guidelines) to mitigate health risks.
Sludge Disposal: Manage aluminum-rich sludge from water treatment responsibly.
Alternatives and Trends
High-Efficiency Replacements: Gradually replaced by composite flocculants like polyaluminum chloride (PAC) and polysilicate aluminum iron (PSAF) due to lower dosage, larger flocs, and broader pH adaptability.
Green Chemistry: Development of bio-based aluminum salts or aluminum-organic composite flocculants to minimize secondary pollution.
Aluminum sulfate's broad utility stems from its low cost, strong flocculation, and chemical stability. However, application-specific dosage optimization and environmental impact monitoring remain critical.