Nitric-Acid Processing of Phosphorus Production Slag with the Recovery of Rare-Earth Metals

Phosphorus slag which has been currently increasing in consumption is one of the sources for the recovery of rare earth metals (REMs). This article proposes a method for opening the slag with a nitric acid solution to obtain a REM-containing solution and its processing to obtain a collective concentrate of ∑ REMs oxides. We have studied the element-wise behavior of rare-earth elements under leaching in optimal conditions. Among the most demanded rare-earth metals in phosphorus slag, there are yttrium, neodymium, europium, and lutetium, with the degree of extraction of ~98, ~99, ~99, and ~28%, respectively. Further processing of the REM-containing solution includes sequential stages of liquid-phase extraction and stripping andprecipitation of ∑ REMs oxides into the solid phase in the form of a poorly soluble salt. We worked out the process parameters of each stage. Extraction was performed in one stage with a 3.66 mol/dm3solution of tributyl phosphate (TBP) at an organic-to-aqueous (O:A) ratio of 1:20. The concentration of ∑REMs in the extract was 1.03 g/dm3. Reextraction was performed with water, with the maximum concentration of ∑ REM in the reextract (rich aqueous phase) of 6.0 g/dm3. The REM-containing precipitate obtained from the reextract with the use of a 2 mol/dm3oxalic acid solution after ignition at 900 °C for 2 hour in a muffle furnace contained 17.3% of ∑ REMs oxides. The recovery of rare-earth metals from phosphorus production slags at various stages was as follows (%): leaching 95.0; extraction 90.2; stripping ~ 93.2 and obtaining a collective concentrate of ∑ REMs oxides 93.9. Throughout recovery of ∑ REMs oxides was 75%.