Ball-milled natural pyrite coupled with sulfite for enhanced arsenic adsorption and oxidation: Performance and mechanisms

Abstract

The combination of natural minerals and ball-milling technology has garnered significant attention for decontamination. However, comprehensive investigation on how ball-milling alters the surface properties of minerals, especially iron sulfides, is currently lacking. In this study, ball-milled natural pyrite (Pyrite^bm) was employed to evaluate its adsorption performance for As(III)/As(V) and catalytical ability for sulfite (S(IV)) to detoxify As(III). Results showed that ball-milling improved the arsenic adsorption capacity of natural pyrite and its catalytical ability for S(IV) by 4.2–7.4 times and 82 times, respectively. Multiple spectroscopic characterizations and electrochemical analysis revealed that ball-milling not only reduced the particle size, but also significantly activated structural Fe(II) through severely destroying crystal structures of pyrite and surface iron oxides. This led to the formation of a positively charged surface, abundant labile Fe(II), numerous vacancy defects, and high electron transfer efficiency. Under oxic conditions, the activated structural Fe(II) of Pyrite^bm underwent rapid oxidative dissolution and recrystallization, generating substantial ferrihydrite and Fe(III) for arsenic adsorption and FeAsO₄ formation. Additionally, the newly formed Fe(III) was also served as effective activator of S(IV), triggering the generation of SO₄⁻, OH and O₂⁻, which facilitated fast oxidation of As(III). This study provided new insights into the modification of iron sulfides through ball-milling, and proposed two strategies for unlocking the potential of natural pyrite in arsenic attenuation.