Study on the Solvent Extraction of Phosphoric Acid from phosphate Ore-HCI Digestion Liquor and Pre-treatment with Amines—Part II

Abstract

The purpose of this work to study the effect of iron content on the

solubility of the phosphoric acid produced by dissoluion of Abu-Tartor

phosphate ore in HCl at the optimum conditions of dissolution. Also, this

work extends to study the pre-treatment of the produced liquor with amines

to trap out the iron before extracting and stripping the phosphoric acid.

Phase diagrams of organic solvent- H₃PO₄-H₂O systems show that as the

iron content increases the solubility of phosphoric acid in the organic

solvent decreases. Trioctyl amine (TOA) and tridodecyl amine (TDA) were

used to extract iron from the medium of the dissolution. The obtained

results indicate that the efficiency of amines to extract iron depends on the

molarity of amine, the nature of the diluent, and the concentration of HCl

and the length of the hydrocarbon chain of the amine. The mechanism of

removing iron by amines in HCl medium was suggested. The analysis of

the obtained data show that both trioctyl amine and tridodecyl amine are

good extractant to remove about 95% of iron content and TDA is preferable

to TOA because it has low concentration (O.I.M./diluent). This may be

attributed to the long chain of the hydrocarbon which leads to relatively

high amounts of the donor groups. The aromatic diluent is more suitable

than the aliphatic one to avoid emulsion formation. It is found that the

order of efficiency of the different solvents to extract H₃PO₄ is:

Tret-amyl alcohol > TBP > Bu-OH > DIPA

and the order of efficiency of the different reagents to remove iron is:

TDA > TOA > DIPA > MIBK > Diethyl ether > (DIPA, 20%).