Formation and transformation of schwertmannite in the classic Fenton process.

The massive amount of sludge generated by the classic Fenton process, which has often been hypothesized to consist of ferric hydroxide, remains a major obstacle to its large-scale application. Therefore, reutilization of Fenton sludge has recently gained more attention. Understanding the formation, transformation, and properties of Fenton sludge combined with the stages of the Fenton reaction is pivotal, but not well illustrated yet.