Minable phosphate is found in a number of places throughout the world, and in many of these deposits small quantities of uranium are found complexed with the phosphate values. The large phosphate deposit in central Florida, for example, contains from 0.01 to 0.02 weight percent uranium. This uranium is taken into solution when the phosphate is acidulated with mineral acid to produce wet-process phosphoric acid.
The early work on the recovery of uranium from wet-process acid is described in a publication referred to as DOW-81 and entitled "Recovery of Uranium from Industrial Phosphoric Acid by Solvent Extraction" . Alkyl pyrophosphoric acid was found to be very efficient in selectively extracting uranium from phosphoric acid and several flow sheets utilizing this type of extractant are shown in U.S. Pat. No. 2,866,680. Prior processes for recovering uranium using a pyrophosphoric acid extractant include processes in which uranium is stripped from the extractant into an acidic stripping solution. It is also known to strip uranium from the extractant into an alkaline stripping solution as disclosed in French Pat. No. 2,423,545. In this process, part of the pyrophosphoric acid esters is stripped into the alkaline stripping solution and is subsequently redissolved in the diluent of the organic extractant solution. A modifier such as a long chain alcohol is added to the extractant for the purpose of retarding hydrolysis of the pyrophosphoric acid esters.
It is an object of the present invention to provide an improved process for recovering uranium from wet-process phosphoric acid using an alkyl pyrophosphoric acid extractant and an alkaline stripping solution.
A further object of the present invention is to provide an improved process for recovering uranium from wet-process acid in which uranium is precipitated from an alkyl pyrophosphoric acid extractant into an alkaline stripping solution.
Still a further object of the present invention is to provide a process for recovering uranium from wet-process phosphoric acid using an alkyl pyrophosphoric acid extractant and alkaline stripping solution in which the pyrophosphoric acid esters remain dissolved in the extractant solution during stripping.
Yet a further object of the present invention is to provide a process for recovering uranium from wet-process acid including means for handling any ferric iron which may also be precipitated in the alkaline stripping solution and for removing pyrophosphoric acid ester decomposition products from the extractant.
A still further object of the present invention is to provide a process for recovering uranium from wet-process acid which is economical and minimizes consumption of costly reagents.