Performance introduction of common chemicals for water treatment

I. coagulants commonly used in water supply treatment include inorganic salts, polymers of inorganic salts and organic compounds

1. Inorganic salts

(1) aluminum salt.

The commonly used aluminum salts are al (SO4) 3.18h, 0 and alum AI (so.) 3.kso.24h0d, which are white crystals. They contain different crystal water. The most common one is al (so.) 30.18h. 00 aluminum sulfate is very soluble in water. Its solubility can reach about 50% at room temperature. The aqueous solution is acid, and the pH value is below 2.5.

Aluminum sulfate industrial products can be divided into rough products and refined products according to the impurity content. The content of Al, 03 in refined products is not less than 15%, and the content of insoluble impurities is not more than 0.3%. The price is relatively expensive. However, the content of A1203 in crude products is not less than 14%, and the content of insoluble impurities is less than 2.4%. The price is relatively low, but the quality is unstable, containing free acid, so the acidity is high, the corrosiveness is strong, the waste residue discharged is more, and the dispensing operation is troublesome. Zhimengzhang of hezhai is hard to be cowardly. It is convenient to use and has no adverse effect on the treated water quality. However, when the water temperature is low, it is difficult to hydrolyze and form a loose flocculate center, which is not as effective as iron salt. In addition, the pH value of the water is suitable for a narrow range, generally 5.5 ~ 8. The dosage is generally dozens of mg / L to 100ng / L. if the dosage is too much, the pH value of the water will be reduced, but the coagulation effect will be affected, and the water will be muddy.

@Alum is a white massive crystal. The coagulation component is aluminum sulfate, so its coagulation characteristics are the same as shuopal.

(2) iron salt.

The commonly used iron salts are ferric chloride hydrate FeCl, · 6h, 0 and ferrous sulfate hydrate FeSO. · 7h, 0.

D ferric chloride hydrate is a kind of dark brown crystal, which is very soluble in water. The solubility increases with the increase of temperature. The alum density is large and it is easy to settle. The effect of treating low temperature and low turbidity water is better than aluminum salt. Its suitable pH value range is also wide, between 5.0 and 11. However, ferric chloride is a kind of crystal which is easy to absorb moisture. Its aqueous solution is very corrosive, so we must pay attention to anticorrosion. In addition, the chroma of treated water is higher than that of aluminum salt.

Adding ferric chloride into water can react with the alkalinity of water to form iron hydroxide colloid. The reaction is: 2fecl, + 3CA (HCO,) 2Fe (OH) + 3cac + 60 when the alkalinity of water is low or the dosage is large, proper amount of lime should be added to water first to improve the alkalinity.

2 ferrous sulfate hydrate is a translucent green crystal, commonly known as "green alum", soluble in water. Fe * dissociated from ferrous sulfate can only form mononuclear complex, and its coagulation effect is not as good as that of trivalent iron salt. Therefore, Fe,, should be oxidized to fe'o before use.

When the pH of water is more than 8, Fe * is easily oxidized to Fe * by the dissolved oxygen in water. Therefore, when the pH is less than 8, some lime can be added appropriately to improve the alkalinity and pH value. If the dissolved oxygen in the water is insufficient, the chlorine gas or hypochlorite can be properly added to oxidize Fe * to Fe *, and the reaction is as follows:

The coagulation of r6feso4 + 3ch2fe (so.) + 2fecl is similar to that of aluminum salt.

2. Inorganic salt polymers

Polyaluminium chloride, also known as basic aluminum chloride, has the molecular formula of [al (OH), Cl -, J, where n is any integer between 1 and 5, and M is the integer of 10, which represents the polymer of M Al (OH), cl. -, and (hydroxyaluminum chloride) monomers. Therefore, polyaluminium chloride is actually an inorganic polymer. In the molecular formula, the ratio of Oh to a * has a great influence on the coagulation effect. Generally, it is expressed by the basicity (Alkalinity) B, that is, B = oh1. For example, when n = 4 days, B = 43x2x100% = 66.7%

Generally, it is required that the content of Al0 in liquid polyaluminium chloride is more than 10%, alkalinity B is 50% ~ 85%, and insoluble matter is less than 0.5%. Polyaluminium chloride has good coagulation effect on water with high turbidity, low turbidity, high chroma and low temperature. It forms flocs

(also known as alum flower) fast and large and heavy particles, easy to precipitate, the dosage is lower than aluminum sulfate, the applicable pH range is wide, between 5-92. Moreover, the most suitable polyaluminium chloride can be prepared according to the different water quality, but aluminum sulfate can not.