Surface-Modified Pyrite with a Schwertmannite Shell: Enhancing the Application Performance of Pyrite-Mediated Advanced Oxidation Processes in a Continuous-Flow System

Most of the current pyrite-based advanced oxidation processes (AOPs) rely on a homogeneous catalytic mechanism mediated by leached Fe 2+ /Fe 3+ from pyrite oxidation. While in continuous-flow water treatment processes, the continual Fe 2+ /Fe 3+ efflux limits pyrite dissolution and the corresponding hydroxyl radical ( • OH) generation for contaminant degradation. To solve this bottleneck problem, a pyrite–schwertmannite (Sch) binary mineral named Sch@py(1:5) was prepared through a simple chemical method where Sch serves as a surface shell coating on the pyrite core. Compared to the pyrite–H 2 O 2 system, the Sch@py(1:5)–H 2 O 2 system exhibits significantly slighter iron leaching and was verified to possess a heterogeneous Fenton process dominant • OH generation pathway, thereby eliminating the reliance of the Sch@py(1:5)–H 2 O 2 system on Fe 2+ /Fe 3+ concentrations in water. Through shielding H 2 O 2 from being directly decomposed by pyrite and the associated Fenton sludge, the Sch–pyrite core–shell structure improves the utilization efficiency of H 2 O 2 5.18 times and 1.15 times than that of the pyrite–H 2 O 2 system in the presence and absence of 0.21 g of Fe·L –1 Fenton sludge, respectively. Furthermore, the Sch shell endows pyrite with the coupling oxidation and adsorption capacity for organoarsenic-bearing contaminants, thus enabling the Sch@py(1:5)-filled fixed bed to purify 2451 BV of highly concentrated (0.1 mg of As·L –1 ) organoarsenic wastewater at a flow rate of 30 BV·h –1 . This study provides a novel strategy to improving the application potential of pyrite, the commonly existing but underutilized mineral resource, in practical water treatment processes.