The effect of particle size on back-scattered X-ray correction methods in on-stream X-ray fluorescence analysis

Abstract

THE measurement of back-scattered fluorescent X-rays from a block containing a suitable element, placed on the side of the slurry flow remote from the X-ray source has been described.' It was used as a means of correcting for variations in the fluorescent X-ray intensity from the slurry, caused by changes in the composition and content of the solid component of the slurry. If this method is used for on-stream analysis without considering the effect of changes in particle size, further errors could occur. It can be predicted quite easily from basic X-ray absorption theory2 that this back-scattered fluorescent X-ray intensity should increase as the particle size in a slurry of constant Composition increases. However, it has also been shown3 that the fluorescent X-ray intensity from particles in an aqueous slurry will decrease as the particle size in a slurry of constant composition increases.Percentage of solids in slurry Fig. 1. Effect of change in particle size on back-scattered cadmium I<, intensity : curve A, particles from 100 to 150 mesh; curve B, particles less than 300 mesh Percentage of iron in slurry Fig. 2. Effect of change in particle size on iron I<, intensity from the slurry: curve A, particles from 100 to 150 mesh; curve B, particles less than 300 mesh I t was decided to test these predictions experimentally, with a Phillips PW 1540 X-ray spectrograph adapted to take an inverted slurry presenter. It was found that the fluorescent intensity from the reference block-in this case made of cadmium-increased with increasing particle size in the haematite -water slurry (see Fig. l ) , while the fluorescent iron Ka intensity from the particles in the slurry decreased (see Fig. 2). Similar effects would be expected with all elements capable of being determined on-stream by X-ray fluorescence analysis.

X-ray absorption and emission

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