Removal of aqueous hydrogen sulfide by granular ferric hydroxide-kinetics, capacity and reuse

Aqueous hydrogen sulfide causes a number of sulfide-related problems in sediment/aqueous environments. This paper investigates the use, regeneration and reuse of granular ferric hydroxide (GFH) for removal of aqueous hydrogen sulfide in batch experiments simulating water environments. The sulfide removal by GFH can be described by pseudo-first-order reaction kinetics with respect to dissolved sulfide concentrations and the removal rate was proportional to the GFH dosage. The sulfide removal rate almost tripled as pH decreased from 9.0 to 7.2. An increasing ionic strength (in NaCl solution) and the presence of SO4(2-) in simulated seawater decreased the removal rate while Ca(2+) and Mg(2+) in seawater hardly had any influence. The aqueous sulfide was mainly oxidized to elemental sulfur with the concurrent reduction of solid Fe(III) to Fe(II). The accumulation of the products (elemental sulfur, iron sulfide and surface-associated Fe(II)) on the surface of GFH eventually led to the latter's exhaustion. By mixing with water containing dissolved oxygen, the exhausted GFH was able to recover with the simultaneous oxidation of Fe(II) to ferric (hydr)oxides and of solid sulfide to elemental sulfur and sulfur of higher valence states. The recovery in removal capacity could be attributed to the formation of amorphous or less ordered ferric (hydr)oxides on the GFH surface and the reduction in GFH granule size. This study suggests that GFH is a promising renewable material for removal of aqueous hydrogen sulfide in sediment/aqueous systems.