Influence of milling on representative sample preparation for the analysis of trace elements in waste wood

Abstract

In Germany, waste wood can be used in various ways. The main ones are recycling in particleboards and energy production if the quality is insufficient for material utilisation. For the decision of usage, it is necessary to determine the wood quality by measuring the concentrations of certain pollutants. If given legal limits are exceeded, energetic utilisation in heat and power plants is recommended.Waste wood is a heterogeneous material. Therefore, special attention has to be given to the sample preparation in order to achieve representative analytical results. This article investigates whether the sample preparation according to ISO 14780 is also useable for a highly heterogeneous material such as waste wood or if a method with better homogenisation is needed. Furthermore, the effect of outliers on the interpretation of measurement results is considered.For this purpose, two milling methods are compared concerning their homogenisation capability. The samples were milled to 4 mm and homogenised. From this total amount, one half was milled directly to 0.25 mm (full milled), while the other half was separated in a sample divider until 100 g of the sample remained (according to ISO 14780), which was milled to 0.25 mm (partial milled).The results show that both milling procedures do not achieve a satisfactory homogenisation of the sample. However, with a sufficient number of measurements, limit value monitoring can still be carried out, as individual outliers are not decisive in whether a limit value is exceeded or not.