Effect of sulfide on morphology and particle size of biologically produced elemental sulfur from industrial desulfurization reactors.

We investigated the effect of polysulfide formation on properties of biologically produced elemental sulfur (S) crystals, which are produced during biological desulfurization (BD) of gas. The recent addition of an anoxic-sulfidic reactor (AnSuR) to the BD process resulted in agglomerated particles with better settleability for S separation. In the AnSuR, polysulfides are formed by the reaction of bisulfide (HS) with S and are subsequently oxidized to S in a gas-lift reactor. Therefore, sulfur particles from the BD are shaped (i.e. morphology and particle size) both by formation and dissolution. We assessed the reaction of HS with S particles in anoxic, abiotic experiments in a batch reactor using two S samples from industrial BD reactors. Under these conditions, the sulfur particle surface became coarser and more porous, and in addition the smallest particles disappeared. Agglomerates initially fell apart but were reformed at a later stage. Moreover, we found different observed polysulfide formation rates for each S sample, which was related to the initial morphology and size. Our findings show that particle properties can be controlled abiotically and that settleability of S is increased by increasing both the HS-S ratio and retention time.