The use of hydrous iron (III) oxides for the removal of hydrogen sulphide in aqueous systems

The potential for iron (hydr)oxides to remove dissolved hydrogen sulphide from seawater has been examined under flow-through conditions. Ferrihydrite (a hydrous iron (III) oxide) was stabilised by precipitation onto zeolite pellets, and rates of sulphide removal were determined under laboratory conditions at pH 8.5. Sulphide removal kinetics were dependent on the initial sulphide concentration, substrate mass and flow rate. The experimental data suggest that these parameters can be optimised to result in the rapid and effective removal of hydrogen sulphide. The results from laboratory experiments compared favourably with sulphide removal kinetics determined in a series of experiments performed online in a recirculating mariculture production system. However, the presence in solution of ligands such as phosphate may also significantly affect reaction rates; a 50% reduction in sulphide removal rate for substrate removed from an online system was partly attributed to phosphate adsorption. The formation of a more crystalline, less reactive iron (hydr)oxide in recharged substrate was the likely result of FeS oxidation, which may also have contributed to the observed reduction in sulphide removal rates. Ferrihydrite-coated zeolite would appear to provide an efficient, low-cost method for sulphide removal, which is particularly suited to relatively small-scale aqueous flow-through systems. The reaction of iron (hydr)oxides with dissolved sulphide is also accompanied by a distinct colour change due to the formation of black FeS_(s) which, under appropriate conditions, may be used as a rapid indicator of sulphidic conditions.