Determination of mercury thermospecies in coal

- A technique for mercury thermospeciation study is proposed.
- Coals can be divided into three groups by prevailing of low-, mid-, and high-temperature Hg species.
- The technique can identify mercury bond by sorption and to sulfides lattice.
- Points of mercury accumulation in coal matrix and inclusions were revealed.

The mercury concentration in coal varies in a wide range with the world average (the Clarke value) of 100 ppb. Mercury in coal can be represented by various forms having different matrix binding energy that govern different properties and behavior both in geochemical cycling and in technological processing. The technique of gradual heating (thermoscannig) of samples based on standard available equipment was developed to reveal and study the dynamic behavior of mercury release from coals. Analyses of coals of different types from deposits in Russia, Ukraine, and South Africa revealed the presence of various mercury thermospecies, part of which can be attributed to absorbed elemental mercury and mercury bound to pyrites. Microprobe analysis exhibited points of mercury accumulation up to tenths of percent by weight within coal organic matrix and mineral inclusions. The thermoscanning technique gives additional information about mercury speciation in coal for better understanding of mercury geochemistry in fossil fuels and also for enhancement of the coal pre-treatment technology before combustion or gasification to reduce mercury emission to environment.