Abstract:
Rare-earth elements (REEs) are especially relevant to produce luminescent materials, magnetic alloys, and even catalysts. Monazite is a REEs phosphate that has 21.93 Mt with 2.35% to 3.02% of rare earth oxides contained, located in Araxá-MG, Brazil. This work proposes an alkaline conversion under high pressure with NaOH solution, followed by hydrochloric leaching of REEs’ hydroxides route. The authors designed a Plackett-Burman design of 8 tests, 5 factors and 2 levels (high and low) for the alkaline conversion. The leaching had no parameter variation. The analysis of the effect of the variables on the extraction of Fe and La was performed using Pareto diagrams. In them, it was identified that concentration and temperature are positively significant for both elements and that the solid-liquid ratio is negatively significant for lanthanum. Agitation and reactional time were not significant in any of the elements. A desirability function was also made to maximize %La and minimize %Fe. From these analyses, the authors concluded that, in order to improve the process, it is necessary to carry out a new experiment with lower solid-liquid ratios and temperatures, and higher concentrations of NaOH