Studies on uranium extraction from phosphoric acid using di-nonyl phenyl phosphoric acid-based synergistic mixtures

During acidulation of phosphate rock with sulphuric acid to produce phospho ric acid for fertilizer application, the uranium values contained in the ro ck also become solubilised. The phosphoric acid produced by the 'di-hydrate ' process, containing 26-30% P2O5, called the 'weak phosphoric acid' (WPA), is concentrated to > 50% P2O5 grade, known as 'merchant grade acid' (MGA). The 'hemi-hydrate' process directly yields acid of high P2O5 content. The uranium concentration varies with acid concentration, provided oxidising co nditions are maintained so that selective precipitation of uranium does not take place. Depending on the rock used, the acid produced can contain 0.00 50-0.05 g U3O8/L. Separation of uranium by solvent extraction employing a n ovel synergistic combination of organo-phosphorus reagents is reported in t his paper. In particular, the solvent mixture of di-nonyl phenyl phosphoric acid (DNPPA) with di-butyl butyl phosphonate (DBBP) in an aliphatic diluen t has been found to be a stronger extractant than the commonly used combina tion of di-(2-ethyl-hexyl) phosphoric acid (DEHPA) with tri-n-octyl phosphi ne oxide (TOPO). The DNPPA-TOPO mixture is an even stronger extractant. Res ults on extraction from both WPA and MGA are reported. Stripping of uranium from the organic phase was achieved with concentrated phosphoric acid in t he presence of Fe+2 reducing agent at elevated temperature. Stripped uraniu m was subjected to a second cycle of extraction-stripping and recovered as a peroxide precipitate of high purity. Brief results on allied areas of aci d pre-treatment and post-treatment are included. (C) 2001 Elsevier Science B.V. All rights reserved.