How to Obtain Deuterium from Heavy Water

Deuterium, also known as heavy hydrogen, is crucial in various scientific and industrial applications. One primary method of obtaining deuterium from heavy water is through electrolysis, which involves splitting water into its constituent elements: hydrogen and oxygen. Heavy water, or deuterium oxide (D2O), requires slightly more voltage to electrolyze, making it possible to enrich the resulting liquid water with deuterium.

Natural Occurrence and Enrichment

Ordinary water, as sourced from most natural sources, contains approximately one deuterium atom for every 6,760 hydrogen atoms. Consequently, the residual water is enriched in deuterium content. To achieve nearly pure deuterium oxide (D2O), the process involves repeated electrolysis of large volumes of water until only a few millilitres remain. This method is straightforward but time-consuming, as it can take a long time to produce the desired result.

The Girdler-Sulfide Process: An Industrial Dominant Method

The Girdler-Sulfide (G-S) process is widely used in the industrial sector due to its efficiency. This method comprises two main steps: liquid/gas reaction and fractional distillation.

Liquid/Gas Reaction

The first step involves a liquid/gas reaction between heavy water (D2O) and hydrogen sulfide (H2S). The reaction can be represented as:

H2O HDSg HDO H2S

The equilibrium constant for this reaction varies with temperature:

2.35 at 30 deg C 1.91 at 130 deg C

This temperature difference is exploited using a series of hot and cold countercurrent gas/liquid contacting columns to concentrate the HDO to about 10-20%. The design and operation of these columns are detailed in various references, which can be accessed through the following links:

[Link 1] [Link 2] [Link 3]

Fractional Distillation

The second step in the G-S process involves conventional fractional distillation to concentrate the enriched water to almost pure heavy water (HDO). The normal boiling point of HDO is 101 deg C, which is 1 deg C higher than that of regular water. This small difference allows for straightforward chemical engineering design.

Several plants were established in Canada and the USA, but most of them have since been decommissioned due to the high energy costs and the use of toxic and corrosive hydrogen sulfide (H2S).

Alternative Technologies

Distillation remains the most preferred method, although the need for massive amounts of water makes it less viable for certain applications. Other common methods include chemically catalyzed distillation using liquefied hydrogen and amines, which require fewer resources and less energy.

Conclusion

The extraction of deuterium from heavy water is essential for various scientific and industrial applications. While the traditional G-S process remains dominant, alternative technologies offer promising solutions, particularly in terms of energy efficiency and resource requirements.