Sulfur dioxide, sulfided iron oxide regeneration

Iron Sponge Also called Dry box. An obsolete process for removing hydrogen sulfide from gas streams by reaction with iron oxide monohydrate. The ferric sulfide that is formed is periodically re-oxidized to regenerate ferric oxide and elemental sulfur. When this process becomes inefficient because of pore-blockage, the sulfur is either oxidized to sulfur dioxide for conversion to sulfuric acid, or is extracted with carbon disulfide. 

Ammonium sulfate and elemental sulfur are produced during solution regeneration. To regenerate the solution, a portion of the solution is withdrawn from all four towers and divided into three parts. One part is regenerated by aeration during which iron sulfide and ammonium hydrosulfide oxidize to form elemental sulfur. The second part is treated with sulfur dioxide, and the sulfur formed is recovered by filtration. The third part is also treated with sulfur dioxide, having first been decanted from the solids. The resulting liquid is then combined with the filtrate from the second part of the solution and heated under pressure at 350°F. In this step the thiocyanate and the other thio-compounds are converted to ammonium sulfate and elemental sulfur. 

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