Vol.9 No.2 2016
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Research paper : Development and utilization of geochemical reference materials (T. OKAI)−67−Synthesiology - English edition Vol.9 No.2 (2016) 4.2.1 Examination of grinding methods without contaminationThe most important issue in grinding samples is contamination that may come from grinding equipment. Details of the examination process for grinding were summarized by Ando (1984),[6] so only an outline is provided here. During the development stage at GSJ, the biggest issue was contamination from the steel crushers. If the whole process was conducted with steel equipment, trace components such as manganese and nickel (contained in iron materials) in addition to iron would be likely contaminants, and in a grinding experiment at GSJ using silica stone, the contamination of iron could not be avoided. However, considering that samples are ground in units of 100s of kg, the use of a steel crusher is extremely efficient. When the USGS prepared G-1, a steel jaw crusher was used and the contamination of some iron was unavoidable. The South African metallurgical laboratory (National Institute for Metallurgy, NIM), which began development at the same time as Japan, has removed iron contamination from the steel jaw crusher using a magnet (magnetic separator) to prevent contamination. The disadvantage of this method is that it also removes magnetic minerals included in the original samples, such as magnetite, along with the iron contamination. As mentioned earlier, considering that the USGS method and the NIM method use the chemical analysis of elements as the standard, this problem is actually not a big issue. However, focusing on the basic concept of development at GSJ, because a method that contains contamination and removes specific substances can potentially change the original characteristics of samples and because it was deemed desirable to prepare reference materials retaining as much of the original characteristics as possible, a method that was not impacted by contamination was searched. The results led to “tomozuri,” in which samples are ground in a crusher made of the same material as the sample. An outline of this grinding process is shown in Fig. 6. For JG-1 and JB-1, a mortar and pestle was prepared using granite and basalt, respectively. Samples were first ground roughly in these mortars and pestles and then ground and mixed in a ceramic pot mill. Because samples are ground by hand using mortar and pestle, despite the lack of contamination, a large amount of effort and time is required. However, at the time, no other reference materials in the world were prepared with the care and attention given to this grinding process. Because of the extreme care used in the preparation of these samples, high praise was received, as mentioned earlier, and it contributed strongly to subsequent development of reference materials.4.2.2 Efficient grinding methodIn the 1980s, the preparation of reference materials received project status, and reference materials were prepared each year. At this point, it became difficult to expend the effort that was put into the first reference materials, and it became necessary to examine the efficiency of grinding. For the third reference material, JA-1 (andesite, Mount Hakone), coarse grinding was conducted using a mortar and pestle made of the same rock as JB-1 and pulverization was done using a ball mill with an alumina lining.[6] This method allowed the processing of much larger amounts of samples compared to using a pot mill, and as the alumina used as the lining is contained in rock samples at high concentration, it did not affect the samples easily by contamination. In addition, another effort was made: the ball used for Fig. 6 Schematics of sample grinding processGuideline to place 100 g and prepare 1,000 samplesSource rock ball after grindingAbout 120 kg of powdered sampleextractionJG-1 and JB-1 were ground with a pot mill. Subsequently, an alumina-lined ball mill was used (figure above). Pulverization with a ball mill produces about 130 kg of coarsely ground sample, whereas balls made of the same source rock or alumina balls produce about 150 kg of sample.JG-1, JB-1, and JA-1 were ground by a mortar and pestle, as shown below, made of the same rock. Subsequently, samples were pulverized with a steel jaw crusher, shown to the right.coarsegrindingSource rocks broken down to fist-size, about 140 kgpulverization

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