Changes in coal waste DOM chemodiversity and Fe/Al oxides during weathering drive the fraction conversion of heavy metals.

The long-term accumulation of coal waste on the surface during natural weathering leads to the inevitable migration of heavy metals contained in the coal waste, which increases the likelihood of environmental contamination and health risks. Dissolved organic matter (DOM) and Fe/Al oxides play crucial roles in the transformation and bioavailability of heavy metals. Thus, we analyzed the Fe/Al oxide content and DOM molecular composition in coal waste with different degrees of weathering and explored the influence of DOM chemical diversity and Fe/Al oxides on the potential mobility of heavy metals.

Neutralization of bauxite residue with high calcium content in abating pH rebound by using ferrous sulfate.

The high alkalinity of bauxite residue and its sustained release impose major limitation on its reuse and ecological disposal. It has been confirmed from sustained rehabilitation that gypsum can effectively reduce the alkalinity of bauxite residue by continuously releasing Ca to react with carbonate and hydroxide. However, the combined bauxite residue with high calcium content exhibits stubborn alkalinity for most alkaline reduction methods employing cations to consume carbonate.