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|Title: ||Extraction and Purification of Quartz Using Phosphoric Acid|
|Authors: ||Mifsud, C|
|Issue Date: ||24-Mar-2011|
|Publisher: ||12th International Conference on Accelerator Mass Spectrometry (AMS-12)|
|Citation: ||Mifsud C., Fujioka T., Fink D. (2011). Extraction and Purification of Quartz Using Phosphoric Acid. 12th International Conference on Accelerator Mass Spectrometry (AMS 12), 20th - 25th March 2011. Museum of New Zealand: Te Papa Tongarewa, Wellington, New Zealand.|
|Abstract: ||Quartz extraction and purification from rocks, sediment, soil and dust samples is essential for the
successful measurement of 10Be and 26Al by Accelerator Mass Spectrometry (AMS). The common
procedure used involves initial water washing to remove fines then Aqua Regia treatment followed
by density separation using lithium silicon tungstate then magnetic separation and finally selective
etching of powder samples by ultrasonic heating and agitation in a dilute aqueous (~2% w/w)
hydrofluoric acid solution (HF). This technique has proven adequate for quartz rich rock types ( ie
granite, quartzite). The etching method alone typically involves 4-5 cycles of HF 2% etchings and
the result is ~10-30% mass loss. However for fine grained and or low quartz (non-felsic) bearing
samples such as flint, silcrete, andesite, diorite) density and magnetic separation are inefficient.
Furthermore, HF etching will readily dissolve fine quartz grains and thus severely affects yields. We
have developed an alternative method using hot phosphoric acid (~250°C), which preferentially
dissolves silicates and many other minerals but not quartz. Differentiation of quartz from other
minerals (e.g., feldspars, plagioclase) is excellent, density and magnetic separation is not required
and usually fewer cycles are required than with conventional HF etching. Hence the hot phosphoric
acid method is particularly effective on rocks containing fine grain quartz, e.g., greywacke, silcrete
and chert, to enhance quartz recovery. As a bonus this method will bulk extract zircons if required.
The technique is far more cost effective by using cheap commercial grade reagents and reduced
risk compared to handling highly hazardous HF solutions. We present semi-quantitative data that
compares the efficiency and the benefits of the two methods. Copyright (c) 2011 AMS12|
|Appears in Collections:||Conference Publications|
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