Wilton F. Espenscheid

Removal of thiosulfate/sulfate from spent Stretford solution

Thiosulfate accumulation presents a serious disposal problem (because of its high COD) in the Stretford process for removing hydrogen sulfide from contaminated gas streams. In a method for treating spent Stretford solution, to dispose of thiosulfate and recover the vanadium and anthraquinonedisulfonic acids (ADA) that it contains: the solution is acidified with sulfuric acid to decompose the thiosulfate to sulfur and sulfur dioxide; steam stripped to remove the sulfur dioxide and sulfur; and limed to remove added sulfate and restore the solution pH. The clear solution is recycled to the Stretford process. A laboratory test of this method with used Stretford solution showed 99% removal of the thiosulfate, 93.5 and 97.6% removal of the sulfate and calcium, respectively, and 91% recovery of ADA. Although the vanadium recovery was not determined, based on solubility data, it was estimated that 60% recovery is possible.