Iron(III) removal and rare earth element recovery from a synthetic wet phosphoric acid solution using solvent extraction

Phosphoric acid produced from phosphate rock is an intermediate product in mineral fertilizer production. Purification stages are commonly used to extract unwanted elements such as iron associated with the phosphate rock after the initial wet acid treatment. The current work presents a process that extracts iron(III) and recovers high-value rare earth elements (REEs) during phosphoric acid purification. A cross-flow solvent extraction process with four stages is used and a final raffinate with 684 mg/L P without losses during the process is obtained. Iron(III) removal (98.1 ± 0.7%) was achieved after the first two stages using Cyanex 572 as extractant. The metal loaded was fully stripped using 2 mol/L HCl with a single-stage reaching a solution purity >99.8%. 96.6 ± 1.2% REEs were subsequently recovered by Cyanex 923 in the next two solvent extraction stages. Water as a strip solution was used to re-extract these valuable metals from the organic phase. The purity of the aqueous solution was >99.6%. The study presents a promising approach in which a single technique was utilized for phosphoric acid purification and valuable byproduct recovery that next needs to be tested under industrial conditions.