Claus tail gas treating is a process used to further purify the waste gases emited by the Claus sulfur recovery units in refineries and natural gas processing plants. The Claus process is used to recover sulfur from hydrogen sulfide (H2S) gas produced during the refining and processing of crude oil and natural gas. However, the tail gas (waste stream) after the Claus process still contains residual H2S, sulfur dioxide (SO2), and other impurities. In order to prevent these harmful gases being released into the atmosphere a second gas purfication step is necessary. The Claus tail gas treating involves the removal of H2S and SO2 from the tail gas in two stages: the first stage involves the conversion of SO2 to H2S through a process known as reduction, while the second stage involves the absorption of H2S using a suitable absorbent. After the Claus tail gas treatment over 99.5% of the initital sulfur content can be recovered.