1.Two production processes of sodium pyrosulfite: dry process and wet process:

1. Dry process :  stir the soda ash and water evenly according to a certain molar ratio, and put them into the reactor when the Na2CO3. nH2O generated is in the form of blocks, keep a certain gap between the blocks, and then add SO2 until the reaction is finished, take out the blocks, and crush them to get the finished product.

2. Wet process :  add a certain amount of soda ash into the sodium bisulfite solution to make it form a suspension of sodium bisulfite, and then add SO2 to form sodium pyrosulfite crystals, which are centrifuged and dried to obtain the finished product.

2.Traditional wet process of sodium pyrosulfite with sulfur as raw material

First, crush the sulfur into powder, and send compressed air into the combustion furnace at 600~800 ℃ for combustion. The amount of air added is about twice the theoretical amount, and the concentration of SO2 in the gas is 10~13. After cooling, dust removal and filtration, sublimated sulfur and other impurities are removed, and the gas temperature is reduced to 0 ℃, left to right, and then sent to the series reactor

Slowly add mother liquor and soda ash solution to the third reactor for neutralization reaction. The reaction formula is as follows:

2NaHSO4+ Na2CO3→ 2 Na2SO4+ CO2+ H2O

The generated sodium sulfite suspension is passed through the second and first stage reactors in turn, and then absorbed and reacted with SO2 to generate sodium pyrosulfite crystal

3.Introduction to Sodium Metabisulfite in application of metal mineral processing

Sodium Metabisulfite is widely used for mining industry. Methods of mineral processing are as follows:

Gravity | Magnetic separation | Electric selection |  Flotation | chemical selction |  Photoelectric election |  Friction selection  | Hand picking

Flotation: Flotation is the technique of separating useful minerals from the ore, based on the physical and chemical properties of mineral particles. Almost all of the ore can be used in flotation separation.

Flotation reagents commonly used in flotation: collector, foaming agent, modifier. Among them, the modifier also includes the inhibitor, activator, pH adjusting agent, dispersing agent, flocculant, etc..

Catching agent: Catching agent is flotation reagents that changes hydrophobicity of mineral surface, makes planktonic mineral particle adhere to bubble. Xanthate, black powder is anionic collector.

Flotation of lead and zinc ores

Galena (i.e. PBS) is a relatively common mineral, it is a kind of sulfide. Xanthate and black powder are commonly used as catching agent (potassium dichromate is an effective inhibitor).

Sphalerite (ZnS)   chemical composition is sulfide minerals such as ZnS, Crystals. 

The catching capacity of short chain alkyl xanthate on sphalerite is weak or not available. ZnS or Marmatite without activation can be selected only by long chain type xanthate.

In the next period of time, the applications of xanthate catching agents will continue to occupy the dominant position. In order to adapt to the demand of increasingly complex Sphalerite flotation, the combination of pharmacy is imperative, it is also an effective way to fully tap the potential of traditional medicine.

 The main flotation inhibitor are as follows:

1.  Lime (CaO) has strong water absorption, acted with water to produce hydrated lime Ca(OH)2. Lime is used to improve pH of the pulp, inhibit of iron sulfide minerals. In the sulfide copper, lead, zinc ore, often associated with sulfided iron ore.  

2. Cyanide (KCN, NaCN) is an effective inhibitor for the separation of lead and zinc. In alkaline pulp, CN concentration increases, which is in favor of inhibition. 

3. The sterling of Zinc Sulfate is white crystal, soluble in water, is the inhibitor of sphalerite, usually in the alkaline pulp it has effect of inhibition.

4. The key that plays inhibition roles in sulfite, sulfite, SO2 is mainly HSO3－.  Sulfur dioxide and sub sulfuric acid (salt) are mainly used in inhibition of Pyrite and sphalerite. Weak acid mine pulp made of lime from Sulfur dioxide (pH=5～7), or use Sulfur dioxide, zinc sulfate, ferrous sulfate and ferric sulfate together as inhibitor. Thus galena, pyrite, sphalerite are inhibited. The inhibited sphalerite can be activated by small amount of copper sulfate. Also can use Sodium thiosulfate, sodium metabisulfite to replace sulfite, to inhibit sphalerite and iron pyrites (commonly known as FeS2).