Extraction and purification of quartz using phosphoric acid
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Date
2011-03-24
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Publisher
12th International Conference on Accelerator Mass Spectrometry (AMS-12)
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
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Keywords
Extraction, Purification, Quartz, Phosphonic acids, Beryllium 10, Aluminium 26
Citation
Mifsud C., Fujioka T., Fink D. (2011). Extraction and Purification of Quartz Using Phosphoric Acid. Presentation to the 12th International Conference on Accelerator Mass Spectrometry (AMS 12), 20th - 25th March 2011. Museum of New Zealand: Te Papa Tongarewa, Wellington, New Zealand.