Antimony (V) Adsorption at the Hematite–Water Interface: A Macroscopic and In Situ ATR-FTIR Study

The environmental mobility of antimony (Sb) is largely unexplored in geochemical environments. Iron oxide minerals are considered major sinks for Sb. Among the different oxidation states of Sb, (+) V is found more commonly in a wide redox range. Despite many adsorption studies of Sb (V) with various iron oxide minerals, detailed research on the adsorption mechanism of Sb (V) on hematite using macroscopic, spectroscopic, and surface complexation modeling is rare. Thus, the main objective of our study is to evaluate the surface complexation mechanism of Sb (V) on hematite under a range of solution properties using macroscopic, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic, and surface complexation modeling. The results indicate that the Sb (V) adsorption on hematite was highest at pH 4–6. After pH 6, the adsorption decreased sharply and became negligible above pH 9. The effect of ionic strength was negligible from pH 4 to 6. The spectroscopic results confirmed the presence of inner- and outer-sphere surface complexes at lower pH values, and only outer-sphere-type surface complex at pH 8. Surface complexation models successfully predicted the Sb (V) adsorption envelope. Our research will improve the understanding of Sb (V) mobility in iron-oxide-rich environments

Probing the Influence of Veterinary Antibiotics on Boron Retention/ Release Mechanism at the Mineral / Water Interface

Boron (B) is an essential micronutrient required by plants and has a narrow range between its toxicity and deficiency. The fate and mobility of B in the environment is largely controlled by adsorption reactions with various soil constituents and clay minerals forming surface complexes. Biogeochemical cycling of B in the environment is affected by different soil factors like pH, soil texture, organic matter, and presence of competing ions. There is intensive use of antibiotics as veterinary medicines and growth promoters. They may appear in the environment from land applications of manure, sewage, and wastewater effluents. Raising concern on the effect of their residual concentrations as they have been frequently detected in the environment and they may pose a serious threat to the ecosystem. Antibiotic retention in soil may affect the availability of micronutrients such as B, therefore an evaluation of B sorption mechanisms in single ion and in competitive sorption situation is important for predicating its availability in the environment. This study evaluates B competitive sorption with oxytetracycline (OTC) one of the widely used antibiotic in livestock production on clay mineral (kaolinite) and an Al oxide (gibbsite) as a function of pH, and concentrations using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and macroscopic study to understand their mechanisms of interaction. Interactions of B on both kaolinite and gibbsite was through inner and outer sphere complexation with stronger adsorption with the trigonal B(OH)3. From the IR spectra there was negligible competition between OTC and B for the adsorption sites. B was seen to have specific adsorption sites on the mineral surfaces. OTC showed stronger competitive effect on both gibbsite and kaolinite surfaces than B. Sorption of OTC on the mineral surfaces showed that OTC forms strong complexes through the -CONH2, phenol group OH, and -N(CH3)2 functional groups. The macroscopic study showed that OTC had little effect on the adsorption of B on gibbsite. With increased organic farming that involves animal manure applications the results from this study are useful in providing fundamental knowledge on the management of micronutrients in the environment in the presence of antibiotics