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UCL Home  /  Geography  /  Resources  /  Laboratory  /  Laboratory Methods  /  Lake Sediment Analysis  /  Fly Ash Particles

Fly Ash Particles

There are two types of fly-ash particle - carbonaceous particles and inorganic ash spheres. Carbonaceous particles are made, surprisingly enough, principally of elemental carbon and so strong acids can be used to remove the unwanted sediment fractions (see Safety below). Inorganic ash spheres on the other hand are composed of the same sorts of compounds as many sediment minerals i.e. oxides of silicon, aluminium and iron. Consequently, the technique for extracting these particles is less ruthless but also leaves more material at the end of the preparation.

It is important to remember that these are supposed to be a quantitative techniques and so care should be taken to ensure that particles have settled out properly before pipetting off supernatant liquid and when transferring sample residues from one container to another. Also it should be remembered that fly-ash particles are in the air all the time especially in large cities like London and so all containers must be kept covered unless they are in the fume cupboard with the extractor on. This is especially important when doing preparations from lakes in 'clean' areas.

Safety

The preparation procedure for carbonaceous particles described below uses some pretty nasty acids and so the utmost care must be taken when handling these chemicals.

In particular hydrofluoric acid (HF) can give very bad burns and the information on how to treat these (in the lab user manual) should be read before HF is used. A protective PVC apron is available for use, and safety glasses, gloves, and lab coat should also be worn at all times. The other acids (hydrochloric and nitric) are perhaps not as nasty but should also be treated with the same care.

If a small amount of HCl or HNO3 comes into contact with skin this should be washed under running water for a few minutes. For larger quantities - follow the same procedure, but seek medical advice as soon as possible and report this to the Laboratory Supervisor and the Departmental Safety Officer (Mark Maslin). For contact with eyes - use the eye-wash bottles to irrigate the eye and then follow the same procedure as above.

Making up dilute acids

When making up dilute acids from concentrated ones remember to always add acid to water NOT the other way round. For example, when making up 1 litre of 6M HCl from conc. HCl, put about 450ml of distilled water into a 1 litre volumetric flask, then CAREFULLY add 500ml of conc. HCl and then finally top up the flask with distilled water from a wash bottle until the bottom of the meniscus is level with the line on the neck of the flask.