The Girdler Sulfide process is an industrial production method for making heavy water (dideuterium oxide), an important component of many nuclear reactors because it acts as a neutron moderator. The method is a isotopic exchange process between H2S and H2O ("light" water), that produces heavy water over several steps. It is a highly energy intensive process. Normal water contains less than 200 parts per million of deuterium. "The production of a single pound of heavy water requires 340,000 pounds of feed water." [1]
The process
Each of a number of steps consists of two sieve tray columns. One column is maintained at 30°C and is called the cold tower and the other at 130°C and is called the hot tower. Deuterium extraction is done based on the difference in separation between 30°C and 130°C.
Hydrogen sulfide gas is circulated in a closed loop between the cold tower and the hot tower. Demineralised and deaerated water is fed to the cold tower where deuterium migration preferentially takes place from the hydrogen sulfide gas to the liquid water. This "enriched" water from the cold tower is fed to the hot tower where deuterium transfer takes place from the liquid water to the hydrogen sulfide gas. An appropriate "cascade" setup accomplishes enrichment.
Normally in this process, water is enriched to 15% to 20% deuterium. Further enrichment to "reactor-grade" heavy water (>99% deuterium) is done in a vacuum distillation unit.
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