A facile method of resource recovery from bauxite residue by phosphoric acid treatment

Bauxite residue (BR) is an industrial waste from alumina refineries. Despite being comprised of valuable secondary materials, utilization of BR is limited owing to its high alkalinity and presence of some toxic constituents. Acid neutralization is widely used as a pre-treatment step to mitigate the problems caused by the alkalinity of BR. In this work, BR was treated with various concentrations of phosphoric acid (1 M, 3 M, 5 M, 8 M) followed by thermal treatment to recover the valuables (metals) in terms of metal phosphates. Phosphates of Al and Si were the main constituents of the residue while the supernatant contained mainly Fe and Al. The supernatant solution was acidic (pH between 1.5 and 1.9) and hence can be used to treat BR in place of phosphoric acid to obtain the metal phosphates as before. The 1 M sample residue showed presence of P2O5 like superphosphate fertilizer. The water leaching test showed insignificant levels of metal dissolution in the 8 M sample, thus exhibiting its ability toward immobilizing the constituents of BR. Additionally, the phosphates can be melted at 1000-1100 degrees C indicating their suitability for glass forming. Thus, phosphoric acid treatment of BR can result in phosphates that can be used in a range of applications.

Automated summary

This study investigated the treatment of bauxite residue (BR) with phosphoric acid to recover valuable metal phosphates. The results showed that the treated residue contained aluminum and silicon phosphates, while the supernatant contained iron and aluminum. The water leaching test demonstrated that the high concentration phosphoric acid treatment effectively immobilized the constituents of BR. Additionally, the metal phosphates obtained from the treatment could be melted at a high temperature, making them suitable for various applications such as glass forming.