The role of different minerals from red mud assemblage in Co(II) sorption mechanism

A range of industrial by-products are currently under the consideration as cost-effective alternatives to conventional sorbent materials for environmental clean-up and remediation applications. Bauxite residue (red mud) has demonstrated exceptionally high potential for the immobilization of cationic pollutants. Due to heterogeneity of such material, determination of the role of individual mineral phases in the overall sorption mechanism is a challenging task. To enlighten the mechanism of Co(II) sorption by mineral assemblage of the red mud, sequential extraction analysis of Co-loaded sample was combined with the microscopic and spectroscopic studies performed by Scanning Field Emission Electron Microscope (FE-SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). Sorbed Co(II) ions were found associated with operationally defined Fe,Mn-oxide and carbonate/acid soluble fractions. Binding of Co(II) by the red mud was achieved primarily by means of chemisorption/surface precipitation on Fe- and Ti-oxides. In coexistence with these highly selective surfaces, gibbsite and silica appeared to be low affinity sites for Co(II). Incongruent dissolution of sodalite phase was detected, indicating that its function was not to ensure sorption centers, but to increase the solution pH creating favorable environment for Co(II) binding by Fe- and Ti-oxides. The results demonstrate high stability of sorbed Co(II) and synergistic action of mineral constituents as essentially important property for red mud implementation as a purifying and remediation agent

Surface modifications on as-grown boron doped CVD diamond films induced by the B2O3-ethanol-Ar system

The surface termination of as-grown microcrystalline (MCD) and nanocrystalline (NCD) boron-doped diamond films was assessed by X-ray photoelectron spectroscopy (XPS) and water contact angle techniques. The diamond coatings were grown on mirror-polished silicon nitride ceramic substrates using the hot-filament chemical vapor deposition (HFCVD) technique. The boron doping source, boron oxide (B2O3) diluted in ethanol, was dragged by a constant Ar flow at different CH4/H-2 gas ratios and system pressures. The electrical resistivity of these semiconducting diamond films was obtained and their surfaces were further characterized by scanning electron microscopy (SEM) and Raman spectroscopy. The results have shown that the increasing total pressure particularly affects the crystal size of the boron doped MCD samples by enhancing diamond renucleation due to the higher residence time of Ar. Also, both as-grown MCD and NCD surface types were found to be inherently hydrophobic, with contact angles similar to 90 degrees C, but retain significant amounts of oxygen bonded to carbon atoms mainly as C-O-C and C = O terminations. Such partial diamond surface oxidation is the result of a very unique stable gas mixture containing hydrogen, carbon and oxygen, when boron oxide and ethanol are added to methane during the CVD process. (C) 2016 Elsevier B.V. All rights reserved