Cesium Formate And Coal Classification

In addition to its wide use in the gas and oil industry, caesium formate has one very specific laboratory application: coal grading and classification.

Solutions with varying densities are prepared, and coal is tested to determine its quality under specific conditions.

How Is The Test Carried Out?

To carry out this test, a 1 kg sample of coal is sequentially immersed in caesium formate solutions with increasing densities. For the first step, the entire sample is placed in the lowest density solution, and allowed to either sink of float. The floating fraction is simply removed, while the sinking fraction is transferred to a higher density solution. This step is repeated until the entire sample floats. Depending on the proportion of coal that sinks and floats in each dilution, the final quality is awarded.

To recover the coal after the test, the floating fraction is drained, washed and oven dried to remove any residue of the caesium formate solution. In addition, all the solutions used are recyclable, and even the water used for washing coal can be re-concentrated via evaporation and used again in the test.

Exposure During The Test

This procedure may represent an exposure risk, as samples are usually placed in the caesium formate solutions by hand. Although non-corrosive, laboratory staff must wear goggles and protective gloves while carrying out the test, as this chemical is still considered a slight eye and skin irritant. Accidental inhalation is unlikely, as caesium formate is highly hygroscopic and does not produce dry dust.

Envronmental Release

Although the process of washing the coal following the test is quite exhaustive, it is expected that a minute fraction remains absorbed in the coal pores. Tested coal is traditionally returned to the market to be sold. As this coal is burnt, the formate component is destroyed and converted into CO2 and water; while the caesium becomes associated with various elements in the ash, such as oxides or carbonates.

In theory, when this ash reaches the landfill, any remnants of caesium may be susceptible to leaching and potentially contaminating the aquatic environment. In reality, this refers to such low levels that can be considered negligible. However, even is accidental releases, caesium formate is biodegradable and it’s expected that most would be used by bacteria within a few days. Similarly to what happens during combustion, only the formate fraction is metabolised, while the caesium cannot be used by micro-organisms.

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