Thermo-electrochemical reduction of sulfate to sulfide using a graphite cathode

A thermoelectrochemical process which allows reduction of sulfate to sulfide with current efficiency of 80% using graphitic carbon as an electrode is presented. The mechanism which requires undissociated sulfide (6.5 M H2SO4) and works at temperatures close to 120 degrees C, proceeds at low overpotential and in the absence of hydrogen evolution. A molecular model describing the interaction of H2SO4 With the carbon lattice of graphite leading to the liberation of H2S is discussed on the basis of electrochemical and photoelectron spectroscopic data. Applications of this process in energy and environmental technology (sulfide as energy source for CO2 reducing chemoautotrophic bacteria) and for elimination of sulfuric acid waste are discussed.