SAMPLING FOR ON-STREAM ANALYSIS AND COMPOSITE SAMPLES

It is not practical to feed a full mineral processing plant process flow through an analyzer system in most cases. A representative sample is much easier to handle and analyze accurately. Typical mineral processing plant slurries can be considered to behave almost like a liquid, but because the slurry contains particles and trash, sampling system design must also take these into account. A primary sample is taken from process stream in one or more steps. The flow rate of the primary sample has to be high enough to allow reliable transfer to an analyzer or composite sampler by pumped or gravity flows. Often the primary sample has to be re-sampled as the sample presentation system to the analyzer uses a lower secondary sample flow rate than the primary sample. Primary samplers can be classified into two groups: samplers for process flows under pressure and samplers for gravity flows. The present trend to use high capacity big flotation cells has increased the process flows. Thus frequently two stage or even three stage primary sampling is needed to get suitable primary sample flow. Some of the most common sampler types are presented. The sample flow must have a minimum speed to keep the solids in suspension. There is frequently trash in the process stream to be sampled. The engineering and installation of sample lines requires more attention than is generally realized. The paper gives simple rules, which can be used in addition to common sense to implement dependable sampling systems for on-stream analysis and composite sampling.