A Laboratory Manual for X-Ray Powder Diffraction
It may be necessary to dissolve the carbonates in some limestones and sediments before the clay minerals can be identified. However, treatment with strong acids to remove carbonate can attack the structure of clay minerals (e.g. trioctahedral minerals are often destroyed by such treatment), and even dilute acid can attack the silicate layers via interlayer regions and exposed edges. Generally, dilute acetic acid is preferred over hydrochloric acid because it less likely to affect clay crystallinity.
|PROCEDURE FOR ACETIC ACID TREATMENT|
|Add 1 part acid to 4 parts distilled water in the graduated cylinder and mix throughly with the glass rod. Caution: acetic acid can cause burns. Wear safety goggles, plastic gloves, and an apron while working with this chemical.|
|Label 300-ml beakers and add sample.|
|Add 50-75 ml of the acetic acid solution slowly to avoid foaming and overflow of beaker. A glass pipette may be used to transfer the acid solution. When effervescence subsides, add another 50-75 ml of acid. Stir and allow to stand overnight. Repeat until suspension no longer effervesces.|
|Allow the suspension to settle and carefully siphon or pour off the supernatant liquid or wash sample by centrifuging. Dispose of acid waste properly. We place it in a 20-liter container of ground-up mollusc shells until neutralized.|