The chemistry of mineral surfaces is of great importance in many different areas including natural processes occurring in oceans, rivers, lakes and soils. Manganese (hydr)oxides are one important group to these natural processes, and the thermodynamically most stable trivalent manganese (hydr)oxide, manganit (γ-MnOOH), is studied in this thesis. This thesis summarises six papers in which the surface chemistry of synthetic manganite has been investigated with respect to surface acid-base properties, dissolution, and adsorption of Cd(II) and the herbicide N-(phosphonomethyl)glycine (glyphosate, PMG). In these papers, a wide range of analysis techniques were used, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), potentiometry, electrophoretic mobility measurements and wet chemical techniques, in order to obtain a more complete understanding of the different processes occurring at the manganite-water interface.From the combined use of these techniques, a 1-pKa acid-base model was established that is valid at pH>6. The model includes a Na+ interaction with the surface:=MnOH2+½ –> =MnOH-½ + H+ log β0 (intr.) = -8.20 = -pHiep=MnOH2+½ + Na+ –> =MnOHNa+½ + H+ log β0 (intr.) = -9.64At pH<6 the manganite crystals dissolve and disproportionate into pyrolusite (β-MnO2) and Mn(II)-ions in solution according to:2 γ-MnOOH + 2H+ –> β-MnO2 + Mn2+ + 2H2O log K0 = 7.61 ± 0.10 The adsorption and co-adsorption of Cd(II) and glyphosate at the manganite surface was studied at pH>6. Cd(II)…
Contents
Introduction
Aim of the Thesis
Manganese – General Chemistry
Manganese – Geochemistry
Manganese – Geochemical Cycle
Manganese Oxides – Structures
Manganite (γ-MnOOH)
Surface Structure
Mineral Synthesis
Methods
Spectroscopy and Diffraction
X-ray Photoelectron Spectroscopy (XPS)
X-ray Absorption Spectroscopy
Infrared Spectroscopy
X-ray Diffraction
Microscopy
Equilibrium Analysis
Potentiometric Titrations
Batch Adsorption Experiments
Electrophoretic Mobility Measurements
Modelling
Manganite Surface Processes
Surface Charge and Acid-base Properties
Dissolution at Low pH
Surface Complexes with Glyphosate and Cd(II)
Manganite-Glyphosate
Manganite-Glyphosate-Cadmium(II)
Summary
Future Research
References
Acknowledgements
Author: Ramstedt, Madeleine
Source: Umea University
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