A Laboratory Manual for X-Ray Powder Diffraction
The presence of organics, which causes a broad hump on X-ray powder diffraction patterns, can obscure the diffraction maxima of mineral species. Unfortunately, just about any treatment to clays involves some risk. With hydrogen peroxide, the danger is oxidizing octahedral iron and changing the layer charge. This is most likely with chlorite and vermiculite. However, one has to do something to resolve clay peaks in some organic-rich samples. The general rule (if there is one) is to go ahead with the peroxide treatment, but if you see some strange diffraction patterns that defy interpretation, suspect that iron oxidation has occurred. This is rarely the case under normal circumstances.
|PROCEDURE FOR TREATMENT WITH HYDROGEN PEROXIDE|
|If the hydrogen peroxide is laboratory grade (30%), prepare a dilute solution of 3% using a graduated cylinder and distilled water. Caution: hydrogen peroxide is a strong oxidizer that can cause severe burns. Wear goggles, plastic gloves, and an apron while working with this chemical.|
|Label the beakers with a pencil or marker.|
|Place a sample in each beaker and add about 50-100 ml of dilute hydrogen peroxide. Stir each beaker with the glass rod to suspend the sample. Rinse the glass rod between each sample and dry with a lab tissue. When bubbling stops or slows, add another 50-100 ml of dilute hydrogen peroxide and restir the suspension.|
|When the addition of hydrogen peroxide to the samples no longer causes bubbling, the organics have been removed. Allow the suspension to settle and carefully siphon or pour off the supernatant liquid, or wash the sample by centrifuging.