Neutralization of titania waste acid with iron oxides

The escalating production of titania via the sulfuric acid method has led to increase in the titania waste acid (TWA) production. 6 to 8 tons of waste acid, containing 20 to 25 wt% sulfuric acid, are generated for 1 ton of titania. In China, nearly 30 million tons of TWA were produced in 2021. Currently, various utilization methods are employed for TWA treatment, with limestone neutralization and concentration methods being the most used. These methods have drawbacks such as substantial waste production and high operational costs. This work proposes a new process for directly neutralizing TWA with iron oxides (hematite and magnetite) produced by chemical reduction of ferrous sulfate. The study investigated the rates and limitations of the reactions between TWA and iron oxides under various temperature and liquid-solid ratios. Furthermore, the morphology, chemical composition and reactivity of remaining solid left in the reaction mixture were analyzed, the kinetic and thermodynamic properties of the reactions between iron oxides and TWA were calculated. This work provides a systematical and comprehensive study of the reactions between hematite or magnetite and TWA from the perspectives of thermodynamics and kinetics, providing fundamental data and crucial parameters for the intensification of the TWA treatment processes.