Octyl pyrophosphoric acid

The extractant is octyl pyrophosphoric acid (OPPA process). The stripping is by concentrated hydrofluoric acid. Yields UF4. Extracts uranium in tetravalent state. It is, therefore, necessary to use metallic iron as a reducing agent. 

Tributyl and trioctyl phosphine oxides are also available commercially as extractants. The extraction of uranium from wet process phosphoric acid, as U , can be effected with the latter (TOPO) in kerosine. Other processes devised for this purpose are based on commercial octyl pyrophosphoric acid, or the synergistic mixture 2-ethylhexyl phosphoric acid/trioctyl phosphine oxide in kerosine. For extraction of U +, monooctylphenyl/dioctylphenyl phosphoric acids in kerosine can be employed. TOPO can be used for the extraction of Cr, Zr, Ee, Mo and Sn [18] and for making quantum... 

---