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Top Curr Chem (2003) 230:153–166 DOI 10.1007/b12113 Aqueous Sulfur Sols Ralf Steudel Institut für Chemie, Sekr. C2, Technische Universität Berlin, 10623 Berlin, Germany E-mail: steudel@schwefel.chem.tu-berlin.de Abstract Sulfur sols are colloidal solutions of elemental sulfur or of sulfur-rich compounds. The particles in these solutions have diameters of 0.1–1.0 mm and consist either of S8 mole- cules (hydrophobic sulfur sols) or of chain-like sulfur compounds with hydrophilic end groups like sulfonate or functionalized organic groups (hydrophilic sulfur sols). Both types of sols are stabilized by the negative charge of the particles which results in mutual repul- sion. Therefore, cations and especially multivalent cations are able to precipitate the sol par- ticles. While hydrophilic sulfur sols can be prepared with sulfur concentrations of up to 600 g l1, hydrophobic sols are much more dilute (<0.1 g l1). Sols of these types occur both in industrial desulfurization plants where sulfide is oxidized to elemental sulfur as well as in cultures of certain oxidizing sulfur bacteria. Keywords Hydrophilic sulfur · Hydrophobic sol · Polythionates · Micelles · Colloidal solution · Stabilization · Precipitation · Coagulation 1 Introduction................................... 153 2 HydrophobicSulfurSols........................... 154 3 HydrophilicSulfurSols............................ 156 3.1 General ...................................... 156 3.2 RaffoSols..................................... 157 3.3 SelmiSols..................................... 161 4 SulfurSolsbyOxidationofHydrogenSulfide . . . . . . . . . . . . . 163 5 SulfurSolsProducedbyBacteria ..................... 163 References........................................ 164 1 Introduction Emulsions of very small droplets of liquid sulfur or of sulfur-rich com- pounds (e.g., polythionates) in water are called “sulfur sols”. Such mixtures can be prepared by a variety of methods. Hydrophobic sulfur sols are ob- tained on dilution of saturated solutions of elemental sulfur in organic sol- vents like ethanol or acetone with a large excess of water. These preparations are usually called Weimarn sols honoring the principal author who first re- Springer-Verlag Berlin Heidelberg 2003PDF Image | Topics in Current Chemistry
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