The phenomenology and the mathematical modeling of the silicone-supported chemical oxidation of aqueous sulfide to elemental sulfur by ferric sulphate

Abstract

When pumping a sulfide solution through a silicone cylinder immersed in a solution of ferric sulfate, a cloud of elemental sulfur is formed in the ferric sulfate if the pH of the sulfide solution is below about 8.5. The elemental sulfur subsequently sediments as orthorhombic α-sulfur particles. H 2 S(aq) diffuses through the pores of the hydrophobic silicone membrane and simultaneously reacts to become sulfur. This was confirmed by a mass balance between the amount of sulfide removed from the sulfide solution and the amount of solid product formed in the ferric solution. During the experiment, the pH of the non-buffered sulfide solution rises up to a maximum of 8.5; this is explained by the continuous protonation of HS caused by the removal of H 2 S(aq). The pH of the strongly acidic (pH 1.5) ferric sulfate solution hardly decreased. A mathematical model has been developed to quantify the phenomena related to the removal of H 2 S(aq). The model has been succesfully validated with the data of batch experiments. An Arrhenius-like relationship was found between the process temperature and the overall mass transfer coefficient K. A sulfide oxidation rate of 2.5 g S/dm 3 .day was predicted for a plug flow reactor. The integration of the novel process with biological sulfate reduction was studied.