Performance of FeCl_3 Precipitation Method in Removing Pharmaceutical Antibiotics from Aqueous Solutions

Pharmaceutical antibiotic (PA) residues are pervasive in soil and water environments; current biological or photochemical degradation methods are difficult to effectively remove PA residues due to constraints on removal efficiency and possible carcinogenic by-products. Up to now, it is not clear about the adsorption/complexation mechanism of metal ions with PA. In this work, two commonly used PAs-levofloxacin hydrochloride (LH) and tamsulosin hydrochloride (TH) were removed from aqueous solution using FeCl_3; it was found that Fe~(3+) in the form of Fe-PA precipitate (Fe-PAp) separated PA from aqueous solution at pH=7.5-8.5. About 90.3% and 87.5% of LH and TH were removed in the form of Fe-PAp after five successive precipitations from the corresponding aqueous solutions with FeCl_3, respectively. The IR characteristics of original LH and TH and Fe-PAp were also studied comparatively, and it was found that: 1) the main IR peaks of LH and TH exhibited: 3 433 and 3 329 cm~(-1)(carboxylic acids OH and NH_2), 1 676 cm~(-1)(-COO-), 1 467 cm~(-1)(aliphatic C-H) and 1 022 cm~(-1)(-S=O), 2) the intensity of the aforementioned IR peaks in Fe-PAp decreased or disappeared completely. The chemical bonding analysis shows that during the formation of Fe-PAp, electrons are transferred from various PA functional groups to the unpaired d orbitals of Fe~(3+), forming a pi-d electron bonding system. FeCl_3 has a wide range of practical applications: 1) as an efficient and promising inorganic adsorbent for the removal of PA from water, which in turn may open new fields in the large-scale separation of organic pollutants from domestic and industrial wastewater; 2) Fe-PAp formation indicates that metal-organic complexes can be stabilized in alkaline soils and water for a long time, explaining the long-term stabilization/sequestration mechanism of Fe-DOM complexes in the environment.