Grinding Head Contamination Tests

Elizabeth Webber, John G. Pyke and Bill Pappas, Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia

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Abstract

Geoscience Australia's Onshore Energy and Minerals Division Geochemical laboratory performs whole rock analyses on a wide range of geological materials using XRF, ICP-MS and titrimetric and gravimetric methods. Sample preparation plays an important part in the production of accurate and precise representative analyses. The geological material must be reduced to a powder form for all aspects of analysis. This is achieved by splitting and pulverising the material in a series of steps using mechanical and hydraulic equipment. In all these steps, the surface which contacts the geological material introduces contamination, which must be taken into consideration when performing an analysis. The final step involves grinding the sample in a ring mill until the sample is ultra fine. Because the abrasive sample is in contact with the grinding head material for up to three minutes, this step has the potential for introducing the most contamination. Different grinding media must be used when the contaminant contains an element for which an analysis is required.

In this study, a number of grinding head media (Tungsten Carbide, Chrome Steel, Carbon Steel, Partially Stabilised Zirconia and Syalon) were tested to find out the qualitative and quantitative contamination they imparted to samples. High purity quartz granules were ground for 60, 120, and 180 seconds in each head and then analysed to determine the contaminants.

The various grinding head media were found to produce the following contaminants: W (up to 1200 ppm) and Co (up to 160 ppm) from Tungsten Carbide; Fe (up to 0.3%), Cr (up to 550 ppm) and Ni, Cu and Mo (all < 5 ppm) from Chrome Steel; Fe (up to 0.4%) and Cr, Cu and Ni (all < 5 ppm) from Carbon Steel; Zr (up to 500 ppm), Hf (up to 10 ppm), Sr and Ba (both < 5 ppm) from Partially Stabilised Zirconia; and Al (up to 1100 ppm) and Y (< 5 ppm) from Syalon. Generally contamination increased with grinding time.

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Note: This poster presented at the Australian X-ray Analytical Association Conference in Fremantle, 13-18 February 2005.