Application of Plackett-Burman Design in the Screening of Factors Acting on the Sulfuric Leaching Process of Rare Earths from Moroccan Phosphogypsum

Abstract

As the main waste of the phosphates industry (200–300 million tons per annum produced globally), phosphogypsum (PG) is a major environmental concern (85% of PG is disposed of on land or at sea). The valorization of PG as a secondary source of rare earth elements (REE) is one of the most recent valorization options under investigation. This study investigated the sulfuric acid leaching process of REE from a Moroccan PG. Plackett -Burman design was used to statistically screen significant factors affecting the leaching efficiency of REE named the studied response (Y). Seven factors considered potentially influential were studied as the model variables : Sulfuric acid concentration (X1); Solid to liquid ratio (X2); Drying temperature (X3); Leaching time (X4); Stirring speed (X5); Temperature (X6), Particle size (X7). According to the results, the predicted values of the fitted model were in good agreement with the experimental values by a coefficient of determination (R2) equal to (99 %). drying temperature has a statistically insignificant effect with p=0.336 > 0.05. All the other six variables have significant effects (p < 0.05), but 97,91 % of Y was affected only by the following four factors: X1 (63.71%), X4 (17.94%), X2 (9.98%) , X5 (6.24% ).