Dipolar recoupling sequences in 13C and 31P nuclear magnetic resonance studies of mineral surfaces

Abstract: Solid state magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) experiments, both cross polarization (CP) and dipole-dipole recoupling, were used as tools in the investigation of the reaction products at the surface of synthetic galena (PbS) mineral and O,O'-dialkyldithiophosphate potassium salts. Various dipole-dipole recoupling sequences have been tested on powder glycine-13C2 NMR and a polycrystalline powder sample of O,O'-diethyldithiophosphate2-Ni(II) to find one or several sequences suitable for the surface experiments. The purpose of the analysis is to better understand the chemical surface reactions taking place in froth flotation of sulfide minerals. The purpose of the experiments is to also investigate the possibilities of using NMR techniques in surface analysis. Two dipole-dipole recoupling sequences, XY8-DRAMA and IRS-DRAMA were found suitable for the 31P NMR experiments both on polycrystalline powders and on the synthetic galena mineral. R14 and IRS-DRAMA was the best performing dipole-dipole recoupling sequences for the 13C NMR experiments on glycine-13C2.