DISPROPORTIONATION OF AQUEOUS SULFUR AND SULFIDE - KINETICS OF POLYSULFIDE DECOMPOSITION

Thermodynamically, aqueous polysulfide solutions are unstable, and sul fur, dissolved as polysulfide species, S-x(2-), x = 2-5, will decompos e to thiosulfate, S2O32- in accord with the net consumption of dissolv ed sulfur: S-dissolved + OH- --> 1/4S(2)O(3)(2-) + 1/2HS(-) + 1/4H(2)O . The distribution of species, and measured and modeled rate of polysu lfide decomposition, are investigated for a wide range of polysulfide solution compositions from 25 to 85 degrees C. The observed decomposit ion of sulfur concentration, C-s, is consistent with an activation ene rgy for sulfur decomposition of 104(+/-5) kJ mol(-1) in accord with th e following rate of sulfur loss: -dC(s)/dt = -k(f)[S-5(2-)] [OH-]/[HS- ]; k(f) = 10-((10.7-5430/T(K))), where C-s is the concentration of dis solved zerovalent sulfur distributed among all polysulfide species. At temperatures up to 85 degrees C, polysulfide solutions are extremely stable under conditions of high polysulfide concentration (>5 m K2S4) and low KOH concentrations. Under these conditions, zerovalent sulfur dissolved in these solutions should be stable on the order of years.