Optimal Factor Evaluation for the Extraction of Alumina from Clays by Sulfuric Acid Leaching Process Using Box–Behnken Design Methodology

Calcination experiments were carried out using calcined clay and optimum calcination conditions were determined as 750°C and 60 min. The Box–Behnken design (BBD) was used to model, predict, and optimize the experimental parameters. The effective parameters and their interactions were explained with a mathematical model. The correlation coefficient (R²) of the proposed model for the relationship between the yield of alumina extraction and experimental parameters was calculated as 0.9573 and it was determined that the predicted and actual values were in good agreement. The modeling results showed that the significance order of the parameters was leaching temperature > acid concentration > leaching time > acid/clay ratio. Finally, an extra optimization study was carried out to maximize the yield of alumina extraction and the yield was found to be 88.15% under the optimum conditions determined by the model (2.56 M acid concentration, 154.46 min leaching time, 89.77°C leaching temperature, and 53.21% acid/clay ratio).