科研之友
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摘要
The composition of processed wood fuels, such as pellets, is important, since large quantities of pellets are used to heat buildings and generate electricity. Prior work identified heavy metal contaminants in pellets as a result of waste wood being part of the input materials. Preparation methods for the analysis of the elemental composition of wood fuels with ICP-MS were evaluated using standard reference materials (SRM) and real wood pellet samples. The effect of different degrees of grinding (10-20 mu m and 60-100 mu m) on the homogeneity of the resulting samples was investigated. The finer-ground samples (particle size 10-20 mu m) demonstrated good homogeneity. The amount of mass required for digestion was evaluated based on the relative mean error (%) for the elemental analyses for both direct HNO3-H2O2 and Ash-HNO3-H2O2 digestion methods. Well ground, larger pellet samples (10-20 mu m and similar to 1.0 g) demonstrated good agreement between two digestion methods. The precision of the analysis with ICP-MS was evaluated by repeatability standard deviation (S-r) measurements. The ratio of S-r(Dir)/S-r(Ash)) was between 0.29 and 2.78, implying very good agreement between the two digestion methods. The elemental" compositions of 30-pellet samples were analyzed, and the relative standard deviation (RSD) was within 10% forboth methods. Since the direct digestion method requires fewer steps, it was chosen as the preferred method. Thus, this work suggests the need for a reevaluation of the current standard method such that the sample size would increase and better grinding to finer particle sizes would be employed to ensure reliable measurements of the wood pellets' elemental contents.
- 出版日期2017-5
