Novel Agglomeration Strategy for Elemental Sulfur Produced during Biological Gas Desulfurization

[Image: see text] This article presents a novel crystal agglomeration strategy for elemental sulfur (S) produced during biological desulfurization (BD). A key element is the nucleophilic dissolution of S by sulfide (HS(–)) to polysulfides (S(x)(2–)), which was enhanced by a sulfide-rich, anoxic reactor. This study demonstrates that with enhanced S(x)(2–) formation, crystal agglomerates are formed with a uniform size (14.7 ± 3.1 μm). In contrast, with minimal S(x)(2–) formation, particle size fluctuates markedly (5.6 ± 5.9 μm) due to the presence of agglomerates and single crystals. Microscopic analysis showed that the uniformly sized agglomerates had an irregular structure, whereas the loose particles and agglomerates were more defined and bipyramidal. The irregular agglomerates are explained by dissolution of S by (poly)sulfides, which likely changed the crystal surface structure and disrupted crystal growth. Furthermore, S from S(x)(2–) appeared to form at least 5× faster than from HS(–) based on the average S(x)(2–) chain length of x ≈ 5, thereby stimulating particle agglomeration. In addition, microscopy suggested that S crystal growth proceeded via amorphous S globules. Our findings imply that the crystallization product is controlled by the balance between dissolution and formation of S. This new insight has a strong potential to prevent poor S settleability in BD.