doubt

[Saurabh Ailawar 11CHE1015]

Sir, in the wet process including phosphate rock leaching, the hydrofluoric and hydrofluorosilicic acids formed are poisonous as well as corrosive. given the temperature, these corrosive acids should be vapours. Releasing them in the atmosphere doesn't make any sense at all. What is done to resolve this issue?  

[Sahil Bhujbal 11CHE1035]

Major emissions from wet process acid production includes gaseous fluorides, mostly silicon

tetrafluoride (SiF4) and hydrogen fluoride (HF). Phosphate rock contains 3.5 to 4.0 percent fluorine.

In general, part of the fluorine from the rock is precipitated out with the gypsum, another part is

leached out with the phosphoric acid product, and the remaining portion is vaporized in the reactor or

evaporator. The relative quantities of fluorides in the filter acid and gypsum depend on the type of

rock and the operating conditions. Final disposition of the volatilized fluorine depends on the design

and operation of the plant.Scrubbers may be used to control fluorine emissions. Scrubbing systems used in phosphoric

acid plants include venturi, wet cyclonic, and semi-cross-flow scrubbers. The leachate portion of the

fluorine may be deposited in settling ponds. If the pond water becomes saturated with fluorides,

fluorine gas may be emitted to the atmosphere.