In this paper, we discuss the difficulties in recovering mercury from the radioactive sludge slurry to serve as a purge point for mercury. Some of these difficulties include the poor design for the mercury decanter, the poor agglomeration of nanometer sized mercury droplets, the mixing caused by the addition of 10 gallons per minute of condensate to the mercury decanter, the mixing provided by the bubbler level probes, the dissolution of mercury by the acidic condensate and equipment problems that have prevented the removal of mercury from the facility.
We will also discuss the results of testing that has been completed to improve the agglomeration of the mercury and to minimize the dissolution and oxidation of the mercury during idle time. The fast agglomeration of mercury is achieved under high ionic strength conditions or at a neutral condensate pH. The generated condensate has a pH of 2, which leads to very slow coalescence and high dissolution rates by the acidic condensate (nitric acid).
To improve the recovery of mercury, the collection of mercury in the mercury decanter needs to be abandoned and the focus should be on collecting the mercury in the condensate storage tank. In addition, the collected mercury needs to be frequently pumped out of the condensate storage tank to prevent dissolution and oxidation of the elemental mercury. Based on the testing performed, optimum storage tank conditions are proposed to maximize the rate of agglomeration of the fine mercury particles and minimize the rate for dissolution or oxidation of the mercury. The establishment of a purge for mercury will shorten future batch processing time, allowing the facility to be shut down earlier.