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Concept
Riffle splitter
Résumé
The riffle splitter is a static and fractional sub-sampling device that can be used for dividing a lot of dry particulate material into two half-lots. The device is usually constructed with steel sheet and should be designed to have an even number of opposing inclined chutes (the riffles), with each chute having the same width. The recommended chute width should be at least 2.5× the size of the maximum particle diameter that can be found in the lot to be split. Riffle splitters are typically used in assay and analytical laboratories to reduce the size of samples provided from other sources (crushed rock, soils, powders and so on) to a lot size that is appropriate for the next stage of analytical sample preparation.
There are many different versions of the riffle splitter. However, not all can be considered correct sub-sampling devices, in that the two sub-sample halves are deemed to be representative of the original lot. The issue of correctness of a riffles split sub-sample are function of both the design and the use of the splitter.
The design key items are:
The splitter should have an even number of riffles so the two sub sample have the same mass
The chute widths should be 2.5× the maximum particle size so as to preclude blocking of the chutes by groups larger fragments in the lot. Typically this maximum particle size is in the order of 15 mm for most commercially available riffle splitters
The chutes should have relatively sharp edges so a fragment falling onto a chute edge is directed into an adjacent chute and does not bounce away into a non-edge-adjacent chute
The feeder to the chute (either a pan or dump-box) should have the same width as the set of riffles
The design of tiered riffle splitters (splitters stacked in tiers above one another) is often incorrect as the outflow from an upper tier does not usually fall vertically in the centre of the next tier (see correct use below)
Incorrect use of a riffle splitter will lead to sample biases, with the subs lot potentially having unacceptably higher or lower concentrations of the lot analytes or attributes being measured.
Source officielle
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