Digestion of Coal and Graphite Samples for Element Analysis with ICP

Carbon-based samples such as coal, coke and graphite are a challenge regarding closed vessel acid digestion. The temperature required for a complete digestion increases with the grade of mineralization from charcoal to graphite. In addition to high temperatures, a suitable mixture of acids with sufficiently high oxidation potential and durable high-performance vessels are required for a successful digestion. Due to a large amount of reaction gases generated during the digestion which again leads to high pressure a fast and reliable pressure control is important to manage highly exothermic reactions.

Rotor 20SVT50 in Multiwave 5001 provides the already well-established SmartVent technology at an advanced temperature and pressure level. Overpressure release is a safe and convenient way to overcome named challenges, as high target temperatures of up to 250 °C can be reached and maintained while reaction gases such as CO₂ and NO_x are released safely.

Additionally, the SmartTemp sensor ensures quick, accurate and contactless internal temperature measurement for reliable control of the digestion process.

As a result, excellent digestion quality even for those hard to digest and reactive samples can be achieved. The goal for this report was to offer a generic method for a wide range of carbon-based samples of different properties and reactivities. It provides

• the safety for the reactive types like carbon black or active carbon,
• the acid mixture to also dissolve impurities of silica, which is found in natural coal and graphite samples as well as
• the high oxidation power required to destroy synthetic and natural graphite species.

If only a specific type has to be digested and analyzed on a routine basis this generic approach can be optimized accordingly.