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Phosphoric acid by HCl
1. PHOSPHORIC ACID BY HCL
Prepared by- Mr. Vishal B. Thakare
(M.Tech, Chemical SVNIT Surat)
Assistant Professor PARUL UNIVERSITY
Vadodara
vishalbt88@gmail.com
2. PHOSPHORIC ACID
Wet Process by HCL
Raw Material
Phosphate rock of high P2O5 content(>30%),Hydrochloric acid
Organic C4 and C5 alcohol solvent (Butanol or amyl alcohol) to
extract H3PO4 from CaCl2 solution.
Reaction
Ca3(PO4)2 + 6HCl + 6H2O 2H3PO4 + 3CaCl2
Side Reactions
CaF2 + 2HCl 2HF + CaCl2
6HF + SiO2 H2SiF6 + 2 H2O
3.
4. Phosphate rock is ground top pass a 20 mesh screen and fed into a
dissolver where an acid stream of conc. HCl plus make-up wash
water from the counter-current decantation system is added.
Fumes of CO2, HF and HCl are scrubbed for acid recovery.
The mixture is fed to a series of decantation units with overflow
from the first settler moving to the counter-current solvent extraction
operations. The solids underflow goes to 2-3 washing thickeners.
Extraction of H3PO4 plus some free HCl is done in a battery of
mixer-settlers (a) with CaC12 + CaF2 retained in aqueous phase.
The extract is again passed through several more mixer-settlers (b)
for removal of trace impurities of Ca++ which are co-extracted.
5. In extractors (c) water extracts H3PO4 and HCl from solvent phase.
The wash solvent from mixer settler (d) is passed to solvent
recovery column and again recycled for extraction.
The aqueous acid raffinate from (c) is separated and concentrated in
a triple effect evaporator to give three different overhead streams.
a) Weak HCl b) Conc. HCl c) Phosphoric acid.