Coal Preparation

Options For Sink / Float Analysis - Economic & Technical Review

Coal Preparation » Gravity Separation

Published: January 10Project Number: C18010

Get ReportAuthor: Michael Campbell and Robert England | ALS Coal Technology

Float and sink testing is the standard laboratory method for determining, with respect to relative density, the washability characteristics of a wide range of coal samples, from bore core to mine production and coal preparation plant products.

The medium used to separate particles into their various density fractions is generally a mixture of organic liquids, specifically Tetrabromoethane (TBE), Bromoform, Perchloroethelyene, and White Spirit.  These organic liquids are toxic, environmentally hazardous and may also interfere with the properties of interest for a coal producer or end user.

Research over the last few decades have identified a number of alternative approaches to organic liquids for float and sink testing.  Some of these have had a very short-lived and limited acceptance into coal testing laboratories (eg hematite), the vast majority however have not been trialed on a large scale but may still remain a potential solution to what is a world-wide problem.

Safety concerns for operators using organic liquids as a media have led to improvements in laboratory design, fume extraction and greater policing of personal protective equipment.  However, the elimination of organic chemicals from coal laboratories remains a high priority.

Taking into account various economic and technical considerations, the most likely replacements at this point in time, to float sink testing with organics would appear to be:

  • Caesium Formate (in conjunction with Potassium Formate); and
  • Zirconium Dioxide.

Further research is still required to remove what are presently barriers to their use, especially in the case of zirconium dioxide.

Perchloroethylene could be eliminated from the current suite of organic liquids.  This may even be required to satisfy some future regulatory condition, however it needs to be confirmed if this translates into a real improvement in health and safety.  

If the matters surrounding the acceptance of the various alternatives cannot be resolved, or other more desirable approaches cannot be found, the option remains to isolate the people from the organic chemicals through a complete re-engineering of the process.


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