Preparation method of polyferric sulfate (PFS)

[Preparation method] There are many production routes for polymeric ferric sulfate , including air oxidation catalytic method, pyrite slag pressurized acid solution method, potassium chlorate oxidation method, and ferric oxide ore acid solution oxidation method

(1) Production of PFS from the by-product of titanium dioxide In the process of producing titanium dioxide by the sulfuric acid method, ferrous sulfate is produced as a by-product

2NO+O ₂ →2NO ₂

4FeSO ₄ +(2-n)H ₂ SO ₄ +NO ₂ →Fe ₂ (OH) _m (SO ₄ ) _3-n/2 +2(1-n)H ₂ O

(2) Using industrial sulfuric acid waste liquid as the raw material, sodium nitrite as the catalyst, the raw material ratio of waste sulfuric acid and ferrous sulfate is (0.

(3) Add ferrous sulfate (FeSO ₄ ·7H ₂ O) and sulfuric acid to the reaction kettle one by one, add water and mix to form an 18%-20% aqueous solution under stirring

The reaction equation is:

4FeSO ₄ +(2-n)H ₂ SO ₄ +O ₂ →2Fe ₂ (OH) _n (SO ₄ ) _3-n/2 +2(1-n)H ₂ O+mFe ₂ (OH) _n (SO ₄ ) _3-n/2 →[Fe ₂ (OH) _m (SO ₄ ) _3-n/2 ] _m

In the formula, 0<n<2, m=f(n)

(4) Preparation of polymeric ferric sulfate by reaction tower method

At present, the reactor method is mostly used to produce polyferric sulfate in China, which has defects such as long reaction cycle, serious equipment corrosion, and heavy daily maintenance tasks

At present, the reactor method is mostly used to produce polyferric sulfate in China.

According to the characteristics of the oxidation reaction of ferrous sulfate by oxygen, a reaction tower made of corrosion-resistant materials is used, and the huge specific surface area formed when the mixed liquid flows in the tower is used to enhance gas absorption, thereby speeding up the reaction

4FeSO ₄ +(2-n)H ₂ SO ₄ +O ₂ →2Fe ₂ (OH) _n (SO ₄ ) _3-n/2 +2(1-n)H ₂ O+mFe ₂ (OH) _n (SO4 ) _3-n/2 →Fe ₂ (OH) _m (SO ₄ ) _3-n/2

Where: 0<n<2, m=f(n)

The production process of polymeric ferric sulfate is as follows: add ferrous sulfate, sulfuric acid and water in proportion to the dissolution tank, heat up to the dissolution of ferrous sulfate, pour the solution into the storage tank, use a corrosion-resistant pump to pump the solution into the reaction tower to adjust the liquid flow At the same time, oxygen and catalyst are added into the tower, and the mixed liquid will undergo catalytic oxidation polymerization reaction

(5) Potassium chlorate oxidation method

Potassium chlorate is an oxidant, and its oxidizing ability is stronger in acidic medium.

6FeSO ₄ + KCIO ₃ +3H ₂ SO ₄ →3Fe(SO ₄ ) ₃ +KCl+3H ₂ O

The preparation process of this method is simple, the reaction is relatively mild, the amount of oxidant is small, and no harmful gas is generated, but the potassium chlorate is expensive, the production cost is high, and the inclusion of potassium salt impurities also affects the product quality

Preparation method 2 Catalytic oxidation of nitric acid

A certain amount of ferrous sulfate, sulfuric acid, nitric acid and water are added to the reaction kettle and stirred, and the reaction temperature is controlled at 60-90°C, while air is introduced for oxidation

The reaction principle is as follows:

For example: take iron filings, iron ore powder or iron ore slag powder as raw materials, react with sulfuric acid to produce ferrous sulfate, and then pass O2 and nitric acid (as a catalyst) for polymerization to produce liquid PFS

Figure 2-15 Process flow of polyferric sulfate

PFS solid products: generally prepared by spray drying liquid polyiron, but also prepared by telomerization, solidification, aging, pulverization and other processes after oxidative polymerization