Water Treatment Chemicals Aluminum Sulfate

Water Treatment Chemicals Aluminum Sulfate

1. Traits

Aluminum sulfate alias is aluminum alum, anhydrous aluminum sulfate is colorless crystal, soluble in water (solubility: 31.3 g/0°C; 89g/100°C), hydrated aluminum sulfate can contain 6, 10, 16, 18 and 27 A crystalline water molecule, the chemical formula is [Al?(SO?)?·xH?O], octadecadecahydrate is relatively stable at room temperature. Industrial aluminum sulfate is white or slightly gray powder or massive crystals. Due to the possible presence of a small amount of ferrous sulfate impurities, the surface of the product may turn yellow, and it is easy to absorb moisture and agglomerate when stored in the air for a long time. Aluminum sulfate is one of the earliest and most widely used coagulants. Among them, the water treatment industry accounts for about 2/3 of the total aluminum sulfate output. After aluminum sulfate is dissolved in water, the basic salt and aluminum hydroxide formed by hydrolysis have the ability to capture impurities in water, thereby condensing colloidal impurities in water.

2. Mechanism of action

When aluminum sulfate is added to water, it can quickly dissolve and separate out SO24-, AP is surrounded by 6 water molecules to [Al(H?O). ] Octahedron exists in water. When its pH value is greater than 3, water molecules are gradually replaced by OH-, that is, Al3+ undergoes a hydrolysis reaction. During hydrolysis, various hydration molecules undergo polymerization reactions. In the process of water treatment, under certain pH conditions, hydrolysis and polymerization reactions occur simultaneously and rapidly, forming various mononuclear and multinuclear coordination compounds. These coordination compounds are all positively charged, and negatively charged suspended particles in water are adsorbed on their surfaces. After the charge is neutralized, the repulsive force between the suspended particles disappears and agglomeration occurs.

3. Purpose

Aluminum sulfate is a particularly widely used flocculant, mainly used for purification of drinking water and industrial water. However, due to its strong acidity, slow hydrolysis speed, and serious harm to the human body caused by aluminum, it is rarely used alone as a flocculant at present.

4. How to use

When performing flocculation treatment, liquid products can be directly added by metering pumps; solid products generally need to be made into liquids before adding, and the mass fraction of the prepared solution is generally 5% to 20%. The dosage of aluminum sulfate is generally 30-100 mg/L. If the dosage is too much, the pH value of the solution will drop, which will affect the coagulation effect and make the water turbid. When aluminum sulfate is hydrolyzed, the solution will become acidic, and lime needs to be added to adjust the pH of the solution. The pH range of aluminum sulfate to water is 5.5-8.0. The water temperature has a great influence on the flocculation effect, and the flocculation effect is better when the water temperature is high; when the water temperature is low, the hydrolysis is difficult, the flocs formed are relatively loose, and the flocculation effect is not as good as that of iron salt. When performing water decolorization, it is best to combine aluminum sulfate and Cl2 to use Cl2 to remove colored substances in oxidized water. Aluminum sulfate neutralizes its surface negative charge, and makes chlorine gas react with the hydrolysis product of aluminum sulfate to be removed.

5. Precautions

Aluminum sulfate decomposes when heated, producing corrosive SO3 vapor. When sulfur trioxide dissolves in water, it forms a strong acid, which has corrosive properties and reacts with strong alkali, and enters the human body through the respiratory and digestive tracts. It is irritating to the eyes and respiratory tract, causing sore throat, coughing, bloodshot eyes, pain when inhaled; abdominal pain when ingested. People should pay attention to protection when using it.