Chemical Process Industries

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

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.