SOLVENT-EXTRACTION FOR CLEANING PHOSPHORIC-ACID IN FERTILIZER PRODUCTION

Phosphorites of sedimentary origin utilized in manufacturing of fertil izer contain uranium, thorium and products of their radioactive decay, as well as health-endangering compounds of cadmium, arsenic and fluor ides. Some of them may transit into the phosphoric acid, when breaking down the phosphorites with sulphuric acid, and then into the fertiliz er. The purpose of the phosphoric acid cleaning is its decontamination from uranium and thorium as well as the removal of toxic cadmium. The above task can be achieved by solvent extraction. The paper presents the results of the extraction of uranium and cadmium from phosphoric a cid using polyalkyl phosphasene and trioctyl amine, respectively. The extraction kinetics, equilibrium distribution of uranium and cadmium w ithin the phases, the effect of extractant concentrations and temperat ure of the process is also discussed. The technological schemes for cl eaning phosphoric acid from uranium and cadmium are given.