Cesco Solutions, Inc. — Specialists in Pyrophoric Remediation
Cesco provides expert technical services to decontaminate sulfide-laden water, sludge and vessels.
In nature, hydrogen sulfide (H2S) is formed from the anaerobic decomposition of organic matter by sulfate reducing bacteria. Volcanic gases and sea floor vents also contain high levels of H2S.
In the refining industry, naturally occurring sulfur compounds are stripped from petroleum stocks and are converted to stable elemental sulfur to meet environmental (acid rain) concerns. H2S is an extremely toxic gas at very low concentrations. High concentrations of hydrogen sulfide and iron sulfide (FeS) are commonly found in the vessels, columns, storage tanks and wastewater systems of refineries. This presents a cleaning challenge during refinery shutdowns for inspections and maintenance. Iron sulfide is formed when rust and scale (iron oxides) react with H2S. Iron sulfides can spontaneously combust in the presence of air creating a safety hazard.
Oxidizers such as potassium permanganate have long been utilized for control of H2S and iron sulfide in waste streams. Under neutral conditions, the accepted stoichiometry of the redox reaction with H2S is:
4MnO4- + 3 H2S —> 2 SO42- + S (s) + MnO2 (s) + 3 MnO (s) + 3 H2O
The permanganate ion is reduced while the H2S is oxidized to sulfate the sulfur. The above reaction occurs rapidly compared to most competing side reactions so that efficient treatment of the offending H2S is possible. The manganese oxide and dioxide solids are high surface area colloidal materials that can aid in flocculation and potentially reduce the polymer demand of a sludge de-watering operation.
Potassium permanganate in water is a brilliant purple color. The purple color acts as an indicator to determine when sulfides are completely converted. Initially, the permanganate solution turns brown indicating the formation of manganese oxides. As more fresh permanganate solution is added the reaction proceeds to completion and the solution gradually returns to a bright purple color indicating the absence of reactive sulfides and an excess of unreacted permanganate.