Coning and Quartering

For a heterogeneous material consisting of large particulates, the original (or gross) sample may be too large to analyze. For example, a Ni-bearing ore with an average particle size of 5 mm may require a sample weighing one ton to obtain a reasonable ssamp. Reducing the sample’s average particle size allows us to collect the same number of particles with a smaller, more manageable mass. In addition, many analytical techniques require that the analyte be in solution and a smaller particle size aids in the dissolution process.

A reduction in particle size is accomplished by a combination of crushing and grinding the gross sample. The resulting particulates are then thoroughly mixed and divided into subsamples of smaller mass. This process seldom occurs in a single step. Instead, subsamples are cycled through the process several times until a final laboratory sample is obtained.

The resulting material is mixed thoroughly to ensure homogeneity and a subsample obtained with a riffle, or by coning and quartering. As shown in this figure, during coning and quartering the gross sample is piled into a cone, flattened, and divided into four quarters. After discarding two diagonally opposed quarters, the remaining material is cycled through the process of coning and quartering until a suitable laboratory sample remains.

Figure7.11

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