The amount of sample required in an analysis experiment is generally a few tenths of a gram to a few grams, while the amount of the original solid sample is generally large (kilograms to tens of kilograms), and its composition is complex, and the distribution of chemical components is often uneven. Therefore, they need to be processed so that they are substantially reduced in number but still represent the original specimen. It is usually processed into a final sample of about 100~300g for analysis, that is, a laboratory sample. Since the liquid and gas samples are relatively uniform, a small amount can be taken for analysis after mixing. Therefore, the preparation of samples is mainly for inhomogeneous solid samples. Here, the ore sample is taken as an example to briefly introduce the preparation method of the solid sample.
The solid original sample is processed into an analysis sample, which needs to go through the following process.
1.Crushing and Screening
The sample is gradually broken by mechanical or manual methods, generally divided into coarse crushing, medium crushing and fine crushing stages. For coarse crushing, use jaw crusher to crush the sample to pass No. 4~6 sieve. The sample after coarse crushing shall be ground to pass the No. 20 sieve by using a disc type crushing prototype for medium crushing. The fine crushing shall be further ground with a disc type crushing prototype, and if necessary, it shall be ground with a mortar until it can pass the required sieve. The particle size required for the analysis sample is related to the difficulty of sample decomposition and other factors. It is generally required to pass the No. 100~200 sieve.
The chemical composition of coarse particles in ore is often different from that of fine particles. Therefore, during any screening, the coarse particles that do not pass through the sieve hole should be further broken until all of them pass the sieve, and the coarse particles should not be discarded, otherwise the representativeness of the analysis sample will be affected.
Sieve number of standard sieve
2.Mixing and Splitting
After each crushing, use mechanical or manual methods to take out some representative samples and continue to crush them, so that the sample size can be gradually reduced. This process is called shrinkage. The commonly used manual division method is quartering. This method is to fully mix the crushed sample and pile it into a cone, then press it into a round cake, and then divide it into four equal parts according to the cross shape through the center of the round cake. Discard the two pieces at any angle, and collect the remaining half of the sample together for mixing. In this way, the sample is reduced by half, which is called one shrinkage. After multiple reduction, the remaining sample can be reduced to the required amount. However, the number of divisions is not random, but determined according to the amount of samples retained. The amount of sample to be retained after each reduction is related to the particle size of the sample. To reduce the sample size, the particle size should be reduced accordingly, otherwise, it should be further broken and then reduced.
