Extraction of Mercury: Process and Environmental Implications

Mercury, despite its liquid state at room temperature, is extracted from mineral sources known as cinnabar. While mercury is a pure metal at room temperature, its primary ore, cinnabar (HgS), is a solid sulfide compound. This article explores the extraction process of mercury from cinnabar and discusses the environmental implications of its extraction and analysis.

Extraction Process

Mining mercury primarily involves the extraction of cinnabar, a mercury sulfide, which is found in rocks. The cinnabar is first heated in a controlled environment to mercury's vaporization point, which is 356 degrees Celsius. At this temperature, the sulfur bonds break, and the mercury vaporizes. The resulting vapor is then condensed into liquid mercury, which can be collected and further processed.

This process is based on the principles of thermodynamics, specifically the fact that mercury has a lower boiling point than the other elements in cinnabar, allowing for the separation of the metals. Additionally, this method ensures that only the purest form of liquid mercury is obtained without the contamination of impurities.

Environmental Aspects and Analysis

Given the potential environmental impact of mercury, its presence in water and soil must be analyzed accurately. The following methods are commonly used:

Chemical Digestion for Mercury Analysis

The standard chemical digestion method involves digesting the sample in nitric and sulfuric acid, with the addition of excess permanganate and persulfate. After heating, the solution turns purple and is then treated with sodium chloride (NaCl) and hydroxylamine, resulting in a clear solution with all available mercury in the mercuric form.

The clear solution is then reduced using tin chloride (SnCl2) to release mercury as a gas at room temperature, which can be easily quantified using atomic absorption spectroscopy with a mercury lamp. This method, as detailed by the U.S. Environmental Protection Agency (EPA), is described in methods SW7470 and SW7471.

While this approach is effective, it may not capture all forms of mercury present in the sample. The U.S. EPA's methods SW7472 and SW7473 provide more comprehensive analysis to address these limitations.

Conclusion

The extraction of mercury from its primary ore, cinnabar, involves a carefully controlled process that ensures purity and efficiency. The environmental implications of mercury extraction and analysis are significant and require thorough methods to ensure accurate and reliable results. By understanding the extraction process and the analytical techniques, we can better manage the use and disposal of mercury to mitigate environmental harm.