FeSO4+ drives the H2O-losing transformation of iron(III)-phosphate-bearing secondary minerals with significant effect on immobilization of arsenic in AMD environments

• Published in: The Science of the total environment Vol. 959; p. 178205
• Main Authors: Xia, Xu, Zhou, Yu-hang, Wang, Ben-Fei, Nie, Zhen-yuan, Xia, Jin-lan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.01.2025
• Subjects: Acid mine drainage; adsorption; AIMD simulation; arsenic; environment; FeSO4; H2O-lossing transformation; heavy metals; iron; Iron(III)-bearing secondary minerals; molecular dynamics; phosphates; QCM-D; quartz crystal microbalance; FeSO4; H2O-lossing transformation; AIMD simulation; Acid mine drainage; Iron(III)-bearing secondary minerals; QCM-D
• ISSN: 0048-9697
• DOI: 10.1016/j.scitotenv.2024.178205

Due to its broad distribution and high affinity for Fe3+, phosphate is always involved in iron(III)-bearing secondary minerals (ISMs) formation, but its effect on the ISMs formation in acid mine drainage (AMD) and the resulting effect on heavy metal immobilization are still largely unknown. In this study, we integrated Quartz Crystal Microbalance with Dissipation (QCM-D), Ab Initio Molecular Dynamics (AIMD) and multiple-microanalytical techniques to investigate the ISMs formation and transformation in simulated AMD (AMDsim) with Fe:P molar ratios increased and the resulting effect on As(III/V) immobilization. We found that the ISMs composite, amorphous FePO4·2H2O bearing FeSO4+, spontaneously formed when phosphate exists, and the bound FeSO4+ can drive losing of the bound H2O, triggering disaggregating of ISMs clusters, which can reduce the size and mass of ISMs composite when bound is in high amounts, thus causing an increase in mobility of the ISMs composite. Those can cause a parabolic change in As(III/V) immobilization, which is determined by Fe:P molar ratios and the parabolic vertex occurred near 6 of Fe:P molar ratio, and when Fe:P molar ratio > 6, an obvious decrease in ISMs size and mass can lead to lower immobilization of arsenic. These findings emphasize the key roles of the binding H2O and binding FeSO4+ on the formation and transformation of ISMs as phosphate exists and provide a new mechanistic insight of ISMs transformation and the resulting effect on As adsorption and immobilization, deepening the understanding of the relationship between AMD components and ISMs transformation and providing an alternative strategy for AMD management. [Display omitted] •The H2O-losing transformation of ISMs driven by FeSO4+ was studied by QCM-D and AIMD.•FeSO4+ bound is critical to ISMs transformation with drastic decreases in size and mass.•ISMs transformation has significant effect on arsenic adsorption and immobilization.•A parabolic change in As(III/V) immobilization was determined by Fe: P molar ratio.