Waste products of phosphates acid processing. Removal of fluorine compounds презентация

Plan:
Conditions of sewage formation
Clearing of such waters
Recycling of sludge

Conditions of sewage formation
The extractive way of phosphoric acid production consists in decomposition of natural phosphates by sulfuric acid and separation of formed firm phase – calcium sulfate – from phosphoric acid solution:

The phosphoric acid produced by this way has low concentration (25-32 % of Р2О5), therefore it is evaporated up to higher concentration. Depending on the process temperature and concentration of the phosphoric acid obtained the calcium sulfate formed can be separated as dihydrate CaSO4•2H2O (gypsum), half-hydrate CaSO4•0,5H2O and anhydrite CaSO4 (anhydrous salt).
Depending on it three ways of wet-process phosphoric acid production are distinguished: dihydrate (CaSO4•2H2O), half-hydrate (CaSO4•0,5H2O), anhydrite (CaSO4) methods. The dihydrate way is the most widespread; it provides obtaining the phosphoric acid at 65-800С contained 25-32% of Р2О5.

The process of wet process phosphoric acid production by dehydrative method includes the following stages:
Absorption of fluorine – containing gases with preparation of hydrofluosilicic acid

Treatment of such the waters is carried out by means of neutralization by limy milk with the subsequent coagulation of the deposit formed with help of polyacrylamide. As a result of the waste water treatment the sludge is formed, which contains fluorine and phosphorus compounds. Besides, circulating water flows are not completely consumed; therefore unbalanced flows arise, which demand additional purification before discharge in reservoirs.
Fig. 4.6 – A schematic diagram of a neutralization installation of fluorine-containing waste water by chalk: 1, 6 – bunkers; 2 – a conveyer; 3 – a storage of chalk; 4 – a clamshell crane; 5 – a collector-balancing tank; 7 – a reactor; 8 – a fan

Recycling the sludge
The sludge contains (mass %): 10-15 % of Р2О5, 8-10 of F in terms of a dry substance and 60 % of Н2О. Recycling the sludges is expedient
from the point of view using valuable components containing in them;
2) with the purpose of environmental protection from toxic fluorine and phosphorus compounds.