Impact of environmental factors on the removal of chloramphenicol by zero-valent iron and pyrite mixture

Chloramphenicol (CAP) is an effective bacteriostatic pharmaceutical that has been widely applied in clinical prescriptions, animal husbandry and aquaculture, but the residues excreted by human and animals have resulted in environmental pollution. Here, we investigated the mechanism of enhanced removal of CAP by zero-valent iron (ZVI) and pyrite mixture, the effect of environmental factors (i.e., initial pH, and co-solutes (anions, cations and organic matter)) as well as the potential applications and environmental safety of ZVI/pyrite mixture. Results show that the mixing of pyrite with ZVI enhanced the removal efficiency of CAP from 14.2% to 80–100% with a range of pyrite/ZVI mass ratios from 1.0 to 4.0. The environmental factors can change the surface reactivity and composition of pyrite/ZVI mixture, consequently altering the removal of CAP. Mechanism study revealed that pyrite could suppress the pH increase, mitigate the passivation of ZVI surface, and accelerate the production of reactive Fe(II). The X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization results of the solids after reacting at different pH conditions indicated formation of highly reactive secondary minerals (such as green rust and iron sulfide (FeS)). In addition, in different co-solutes systems, the secondary minerals are differed, leading to the change of ZVI surface reactivity. This study extends the knowledge of the effect of environmental condition on ZVI technology in practical engineering systems.