Recycling of Iron and Alumina from Red Mud After Co-Sintering with Phosphogypsum

Red mud (RM) and phosphogypsum (PG) are two types of industrial solid waste that not only pollute the environment but also fail to adequately exploit the potential of secondary resources. In this study, a three-step process based on alkali lime sintering, leaching, and magnetic separation was developed to realize the recovery of aluminum and iron by the simultaneous treatment of RM and PG. The effects of the sintering temperature, sintering atmosphere, sintering time, CaO/SiO2 molar ratio (C/S), and Na2O/(Al2O3 + Fe2O3) molar ratio (N/A) on the process were investigated. The aluminum recovery, iron recovery, and iron grade were 69%, 78%, and 83.8%, respectively, for a sintering temperature of 1100 ?, a sintering atmosphere of N-2, a sintering time of 30 min, a C/S ratio of 2.0, and an N/A ratio of 1.3. The main form of S in the slag was CaS, and the final reduction product of hematite was metallic Fe. In comparative experiments using CaO as an alternative Ca source, the use of PG afforded a larger particle size of the obtained metallic Fe, indicating improved agglomeration.