In the previous article, three sampling techniques were discussed: dry, melt and solution sampling. Each of these incorporates a number of specific methods and equipment, and also offers specific advantages. Determining the most appropriate sampling method depends upon the type of material being processed, as well as its estimated precious metals content. Because of their composition and chemistry, precious metals bearing catalysts are usually sampled with dry sampling processes. Dry sampling is used when materials cannot be dissolved in a solution, or are inappropriate to melt, either because of their structure, or because of the cost associated with melting vs the possible return. As it is difficult to achieve homogeneity, dry sampling is more complex, and potentially less precise, than melt or solution sampling; in fact, this method generally requires better judgment than the others. An ideal dry sampling system is capable of drawing representative samples from free flowing catalyst according to the principles of Pitard2 and Gy3 and the practices of Merks4 at a rate of 2000 - 3000 lb/hr.
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