- •4. Purification, neutralization and recycling industrial waste products in technology of inorganic substances
- •4.1. Environmental problems of soda ash production
- •Control questions on the topic “Environmental problems of soda ash production”
- •4.2. Ways of processing the waste water and industrial waste formed at ammoniac saltpeter manufacture
- •Treatment and use of the waste water
- •Treatment of the vapour condensate by ion exchange method
- •Treatment of the vapours in gas washers
- •Control questions on the topic “Ways of processing of sewage and industrial wastes by ammoniac saltpeter manufacture”
- •4.3. Waste products formed at caustic soda manufacture and methods of their processing
- •Control questions on the topic “Waste products formed at caustic soda manufacture and methods of their processing”
- •4.4. Waste products of acid processing phosphate raw material. Removal of fluorine compounds. Waste water treatment. Processing solid waste products (phosphogypsum, limy sludge).
- •Possible ways of phosphogypsum processing
- •1. Manufacture of sulfuric acid and lime
- •2. Obtaining ammonium sulfate
- •Control questions on the topic “Waste products of phosphates acid processing”
- •4.5. Waste products of sulphuric acid manufacture. Methods of purification, processing and neutralization of solid waste products, sulphurous anhydride and waste water
- •Recycling of selenium sludge
- •Cleaning of departing gases from so2 and a fog of sulphuric acid
- •Sewage treatment
- •4.6. Waste products of phosphorus production. The characteristic of departing gases, dust, sludge and slag. Circuits of their clearing, neutralization and recycling.
- •Control questions on the topic Waste products of phosphorus production. The characteristic of departing gases, dust, sludge and slag. Circuits of their clearing, neutralization and recycling.
- •Literature
Possible ways of phosphogypsum processing
1. Manufacture of sulfuric acid and lime
A possibility of phosphogypsum processing into elemental sulfur and lime attracts interest. For this purpose calcium sulfate is reduced by coke or the products of natural gas conversion:
CaSO4 + 2C = CaS + 2CO2 (10)
CaSO4 + 4CO = CaS + 4CO2 (11)
CaSO4 + 4H2 = CaS + 4H2O (12)
Then calcium sulfide is processed by water, and the suspension formed – by carbon dioxide:
CaS + H2O + CO2 = H2S + CaCO3 (13)
The hydrogen sulphide obtained can be completely oxidized, and the formed kiln gas is processed by sulfuric acid in accordance with a wet catalysis method.
2. Obtaining ammonium sulfate
This process consists in the interaction of a preliminary prepared ammonium carbonate solution with a phosphogypsum suspension:
CaSO4 + (NH4)2CO3 = (NH4)2SO4 + CaCO3 (14)
The process can be carried out at atmospheric and increased pressure. The reaction equilibrium is displaced to the right as the CaCO3 formed is a less soluble salt, than CaSO4. The CaCO3 precipitated is separated from a 35-40 % ammonium sulfate solution. Ammonia excess in this solution is neutralized by sulfuric acid. The solution obtained is evaporated; the precipitated (NH4)2SO4 crystals are separated on a centrifuge and dried. 1340 kg of gypsum, 340 kg of СО2, 60 kg of Н2SO4 and 260 kg of ammonia are consumed for production of 1 t of (NH4)2SO4. On 1 t of (NH4)2SO4 about 0,76 t of CaCO3 is formed, which can be used for lime pretreatment of soil or for manufacture of building materials.
Also it is possible to use phosphogypsum in agriculture for reduction of soil salinity. At applying phosphogypsum in soil there is formation of sodium sulfate, which is easily washed away by irrigation water, and the soil cover is demineralizated.
Control questions on the topic “Waste products of phosphates acid processing”
1. Ways of wet process phosphoric acid production.
2. Call basic stages of the dehydrate method of wet process phosphoric acid production.
3. What substances are contained in the waste water of wet process phosphoric acid production?
4. What methods are used for purification of the waste water formed at wet process phosphoric acid production?
5. Problems of the waste water purification.
6. What ways of phosphorus-containing sludge utilization you know?
7. What end-products can be produced with use of the sludge formed at the wet process phosphoric acid manufacture?
8. Which harmful substances are contained in phosphogypsum?
9. What possible ways of the phosphogypsum processing you know?
10. Explain the method of sulphuric acid and lime production from phosphogypsum.
11. Explain the method of ammonium sulphate production from phosphogypsum.