Screening and thermal desorption for remediation of a sediment polluted by the mercury of a chlor-alkaly plant

Thermal desorption tests were performed on samples taken from a mercury polluted sediment (133 mg/kg) in the vicinity of a chlor-alkali plant that has been operating over a long period using mercury cathodes. After characterization of the sediment, by means of TGA/DTA, SEM, XRD and chemical analysis, the material was screened into various size-fractions. Chemical analysis showed that only the finest size-fractions had a mercury content above the regulatory limit (5 mg/kg) establishedfor areas destined for industrial installations. Thermal desorption tests were applied on the finest size-sediment fractions at furnace temperatures between 300degreesC and 400degreesC and solids residence times between 3 minutes and 120 minutes. After 3 minutes at 400degreesC, the treated sediment residue had a mercury content below the regulatory limit. The short solid residence time and the low desorption temperature required to meet the treatment standards would permit the use of a continuous thermal desorption treatment process in a rotatory dryer providing that the values of residence times obtained by the lab-scale plant are suitable for a larger scale plant.