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Determination of Calcium in Wolframite Concentrates by Fluorescent X-Ray Spectrography

  • William J. Campbell (a1) and John W. Thatcher (a1)

Abstract

The purpose of this investigation was to develop a rapid, accurate method of analysis for small amounts of calcium in wolframite concentrates. This analysis is necessary to determine if wolframite concentrates meet the U. S. National Stockpile Specification P-57R2, which limits the calcium content to 0.2 per cent.

Because of the small depth of sample analyzed in fluorescent x-ray spectrography the calcium Kα line intensity was found to be a function of the chemical composition of the calcium-bearing particle as well as the matrix composition. This particle-conn position effect was particularly important in this analysis because the calcium may be present as a carbonate, tungstate, phosphate, etc. Three methods of sample preparation were found to eliminate the variation of calcium Kα intensity with mineralogical occurrences: (1) Reduction in particle size by extensive grinding, (2) chemical fusion wtli sodium carbonate, and (3) solution of the calcium by an add.

Determinations by all three procedures are believed to be accurate to within ± 5 per cent for more than 0.30 per cent calcium and ± 10 per cent at the 0.1-per cent level. The lower limit of detectability is in the order of 0.005-0.01 per cent.

The operating characteristics of a gas-flow proportional counter used in conjunction with a pulse-height analyzer were studied in detail. This detector was found to have a high counting efficiency for calcium Ka radiation, to have a low counting efficiency for overlapping higher order radiation and to have counting stability equivalent to Geiger tubes.

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References

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1 Kohler, T. R. and Parrish, W., “Conversion of Quantum Counting Rate to Roentgens,” Rev. Sci. Inst. r., Vol. 27, 1956, p. 705706.
2 Hendee, C. F., Fine, S., and Brown, W. B., “Gas-Flow Proportional Counter Cor Soft X-Ray Detection,” Rev. Sci. Instr., Vol. 27, 1956, p. 531535.
3 Parrish, W., Hokler, T. R., “Use of Counter Tubes in X-ray Analysis,” Rev. Sci Instr., Vol. 27, 1956, p. 795808.
4 Claisse, F., “Accurate X-Ray Fluorescence Analysis Without Internal Standard,” Norelco Reporter, Vol. 3, 1957, p. 3.
5 Claisse, T., “Letters to the Editor,” Norelco Reporter, Vol. 4, 1957, p. 9596.

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