No abstract

We determined the concentrations, geochemical fractions, and potential environmental implications of arsenic (As) via pH-static extraction experiments, X-ray photoelectron spectroscopy (XPS), and sequential extraction. Compared with the corresponding soils, the enrichment factors followed the order As (4.27) > Fe (2.14) > P (1.71) > Mn (1.41) > Al (0.95) > Ti (0.44) > Si (0.39) > Mg (0.28) > K (0.13). As showed a higher enrichment factor than all other elements. Arsenic showed a high linear correlation with iron in the FMNs, which can be expressed as As = 18.68Fe − 175.89 (r2 = 0.97, p < 0.01), indicating that Fe plays an important role in the geochemical behavior of As. Most of the As occurred as As (V) (83.79%) in the Fe–Mn nodules (FMNs), and As (III) (16.21%) only occupied a small portion. The distribution of As in the geochemical fractions of the FMNs followed the order F5 (99.54%) > F3 (0.25%) > F4 (0.10%) > F2 (0.09%) > F1 (0.02%), indicating that the residual fraction (F5) of As is the most dominant component. The total release of As from the nodules was extremely low (<0.01%) under neutral pH conditions (pH 6.0–8.0), and As was adsorbed and stabilized by the FMNs under neutral pH conditions (pH 6.0–8.0). However, overacidification or alkalization of the soil environment will promote As release, with subsequent ecological hazards.

The promotion of pollutant oxidation degradation efficiency by adding organic catalysts has obtained widespread attention in recent years. Studies have shown that organic substances promote the process of traditional oxidation reactions by accelerating the redox cycle of transition metals, chelating transition metals, activating oxidants directly to generate reactive oxygen species such as hydroxyl and sulfate radical, or changing the electron distribution of the target pollutant. Based on the promotion of typical organic functional groups on the chemical oxidative process, a metal-organic framework has been developed and applied in the field of chemical catalytic oxidation. This manuscript reviewed the types, relative merits, and action mechanisms of common organics which promoted oxidation reactions so as to deepen the understanding of chemical oxidation mechanisms and enhance the practical application of oxidation technology.