What is aluminium sulfate used for?

In the field of chemical raw materials, aluminum sulfate stands as a widely used and crucial basic chemical product. With its excellent flocculation properties, water purification effects, and diverse applications across industries such as papermaking, tanning, and building materials, it has long held a significant position. The market value and application scenarios of aluminum sulfate are now encountering new development opportunities. This article will introduce the basic properties, production processes, characteristics, application fields, and current industry status of aluminum sulfate, helping readers gain a deeper understanding of this chemical product.

1. Fundamental Properties of Aluminum Sulfate

Aluminum sulfate exhibits good stability but may decompose into aluminum oxide and sulfur trioxide at elevated temperatures. Due to its reactive chemical nature, storage must avoid humid environments to prevent caking or dissolution. It possesses moderate corrosiveness toward metals, necessitating corrosion-resistant packaging materials during transportation and handling.

Aluminum sulfate is a common inorganic salt with the chemical formula Al₂(SO₄)₃. It typically appears as a white or grayish-white crystalline powder, though transparent lumps may also occur. Its primary characteristics include:

(1) High Solubility: Aluminum sulfate dissolves readily in water, forming an acidic solution with a pH generally between 3 and 4.

(2) Outstanding flocculation capacity: Aluminum sulfate releases large quantities of aluminum ions (Al³⁺), which undergo electrostatic neutralization with impurities in water to form aluminum hydroxide colloids. These colloids adsorb suspended particles, achieving purification.

(3) Good stability: It remains stable at room temperature but decomposes at high temperatures to form aluminum oxide (Al₂O₃) and sulfur trioxide (SO₃).

(4) Diverse crystalline forms: Depending on hydration levels, it exists as anhydrous aluminum sulfate or aluminum sulfate octadecahydrate (Al₂(SO₄)₃·18H₂O), with the latter being more prevalent in industrial applications.

Note: Aluminum sulfate exhibits corrosive properties toward metals. Therefore, corrosion-resistant packaging materials (e.g., plastic bags, composite woven bags) must be used during storage and transportation to prevent moisture absorption and caking.

2. Production Processes of Aluminum Sulfate

Two primary methods exist for producing aluminum sulfate: the bauxite process and the aluminum hydroxide process.

(1) Bauxite Process

Bauxite serves as a key raw material for aluminum sulfate production. First, bauxite is crushed and reacted with sulfuric acid under specific conditions to form an aluminum sulfate solution. This solution undergoes filtration, concentration, and crystallization to yield the final product. This method offers lower costs but imposes certain requirements on ore quality.

(2) Aluminum Hydroxide Process

Aluminum hydroxide reacts directly with sulfuric acid to form aluminum sulfate solution. The solution is then processed through evaporation and crystallization to produce the final product. This method features a simpler process and yields higher product purity, but involves relatively higher raw material costs.

3. Properties of Aluminum Sulfate

(1) Excellent Water Treatment Performance: Industrial aluminum sulfate effectively removes suspended solids, impurities, and metal ions from water, enhancing water purity and clarity. Simultaneously, it effectively controls water pH levels, maintaining them within suitable ranges.

(2) Excellent Stability in High-Concentration Solutions: Containing two cations (Al³⁺) per molecule, aluminum sulfate forms stable solutions even at high concentrations, resisting precipitation or flocculation. This property is crucial for large-scale water purification and treatment processes.

(3) Wide application scope: Industrial aluminum sulfate is suitable for environments involving water and acid-base reactions across various sectors, such as textile printing and dyeing, papermaking, and petroleum extraction. It effectively improves water quality in these settings, thereby enhancing operational efficiency and quality standards.

(4) Non-toxic, environmentally safe: Compared to chlorine-containing compounds, aluminum sulfate does not leave harmful residues in water, posing minimal risks to the environment and human health. This makes it highly favored in domestic and international markets, where it enjoys widespread application and promising market prospects.

(5) Excellent Flocculation Properties: When mixed with alkaline agents, aluminum sulfate rapidly forms aluminum hydroxide colloids. These colloids adsorb and precipitate particulate pollutants in wastewater, delivering superior water purification effects.

4. Primary Applications of Aluminum Sulfate

(1) Water Treatment Sector

Application: Aluminum sulfate is one of the most commonly used flocculants in water treatment, employed to remove suspended solids, colloidal substances, and certain dissolved impurities from water. It is widely applied in drinking water, industrial wastewater, and sewage treatment.

Principle: Aluminum ions dissociated from aluminum sulfate react with water to form aluminum hydroxide colloids. These colloids possess a large specific surface area, enabling them to adsorb suspended particles in water and form larger flocs that can be easily removed by sedimentation or filtration.

(2) Paper Industry

Application: Aluminum sulfate is used as a sizing agent for paper, enhancing its water resistance and printability.

Principle: Aluminum sulfate reacts with substances like rosin to form water-insoluble aluminum soaps that deposit on fiber surfaces, reducing paper's moisture absorption.

(3) Textile Industry

Application: Used as a mordant to enhance dye adhesion to fibers and improve dyeing results.

Principle: Aluminum sulfate forms complexes with dyes, strengthening fiber-dye bonding and increasing colorfastness.

(4) Pharmaceuticals and Personal Care

Application: Serves as an astringent and antidiarrheal agent for treating certain gastrointestinal disorders.

Principle: Forms a protective film in the intestines to reduce irritation and alleviate inflammation.

(5) Firefighting

Application: Mixed with other compounds to create foam extinguishing agents for oil fires.

Principle: Reacts with sodium bicarbonate to produce carbon dioxide and aluminum hydroxide foam, which covers the oil surface to block oxygen access.

(6) Building Materials

Application: Used as an early strength agent in concrete to accelerate cement hardening and enhance initial strength.

Principle: Reacts with calcium hydroxide in cement to form hydration products like calcium aluminate, promoting early strength development of the cement paste.

(7) Cosmetics and Personal Care

Application: Used as an adsorbent in certain talcum powders, antiperspirants, and similar products to absorb sweat and oils.

Principle: Aluminum sulfate exhibits hygroscopic properties, reducing moisture on the skin's surface.

5. Safety Precautions

When using and handling aluminum sulfate, observe the following safety measures:

(1) Protective Measures: Personnel handling aluminum sulfate should wear appropriate protective gear, such as gloves, masks, and goggles, to prevent skin contact and inhalation.

(2) Storage Conditions: Store aluminum sulfate in a cool, dry place, away from direct sunlight and moisture, to prevent performance degradation.

(3) Disposal: Dispose of waste aluminum sulfate in compliance with local environmental regulations to prevent pollution. Waste must be properly managed and must not be dumped indiscriminately.

6. Market Trends and Future Development of Aluminum Sulfate

(1) Demand Drivers: The rapid growth of the water treatment industry has made it the largest consumption sector for aluminum sulfate.

(2) Technological Advancements: Some enterprises are developing high-purity aluminum sulfate for expansion into fields like electronic materials and new energy batteries.

(3) Environmental Pressure: Tightening national environmental policies require manufacturers to upgrade processes and reduce wastewater and sulfur dioxide emissions.

(4) International Market: Developing regions like Southeast Asia and Africa show increasing demand for water treatment chemicals, presenting significant export potential.

(5) Future Direction: Green production, energy conservation, and high-value-added products will become core drivers of industry development.

As a traditional yet ever-evolving chemical product, aluminum sulfate has become deeply embedded in modern industrial systems and daily life due to its stable properties, excellent flocculation performance, and broad applications. It plays a critical role in drinking water purification, papermaking and printing, textile dyeing and finishing, as well as concrete and building materials. With heightened environmental requirements and the development of emerging industries, the aluminum sulfate sector faces new challenges and opportunities.

Production efficiency, energy conservation, and reduced consumption, along with high-value-added products, will become the core drivers of industry development.