Insight into the degradation of ammonium dibutyl dithiophosphate by natural pyrrhotite-activated peroxydisulfate: Activation mechanisms, DFT studies

Ammonium dibutyl dithiophosphate (ADD) is one of the most important flotation reagents in sulfide mineral processing, causing severe environmental pollution. In this study, natural pyrrhotite (NP)-activated peroxydisulfate (PDS) was applied to treat ADD, which can alleviate mine tailing problems and reduce the cost of treating mine wastewater. PDS can be efficiently activated by NP for ADD degradation, achieving complete ADD removal with 0.35 g/L NP and 1.0 mM PDS. The PDS activation not only occurred in solution but on the NP surface. Dissolved Fe2+, dissolved Fe3+, surface-bound Fe2+, and surface-bound Fe3+ had been undergoing interconversion as the degradation reaction proceed. The generated sulfate radicals and hydroxyl radicals synergistically remove ADD in the NP/PDS system over a wide pH range. The excess O-2 might cause the transformation of SO4 center dot- to SO3 center dot- in the NP/PDS/ADD system. Based on the density functional theory (DFT) calculation and the identification of intermediates, a pathway of ADD degradation in the NP/PDS system is proposed.