Applicability of the SER method for quality control of clays from the German 'Westerwald'

摘要

The SER method was developed in 1998 for the in situ quality control of Bavarian bentonites. By considering water content and temperature, the cation exchange capacity (CEC) could be calculated from specific electrical resistivity (SER) data, gathered directly in the open pit. The CEC in turn is used for the estimation of the smectite content of bentonites which to a great extent determines the raw material quality. In this study the SER method was applied to clays from the Westerwald (Germany) that are mainly used for the industrial production of ceramics. The aim of this study was to a) assess the applicability of the SER method for fast quality estimation of industrial clays other than bentonites and b) increase the knowledge about electrical conductivity mechanisms of clays. A set of 25 samples from four different pits was gathered and the specific resistivity measured simultaneously. The obtained data were set in connection with laboratory results for cation exchange capacity (CEC) measurements, quantitative chemical and mineralogical composition (XRD, Rietveld analysis) and particle size. The specific electrical resistivity of the 'Westerwald' clays is mainly determined by the CEC and the water content at a given temperature. For these clays a similar correlation function as for Bavarian bentonites was obtained. Therefore, the specific electrical resistivity of 'Westerwald' clays is strongly influenced by the presence of smectitic layers (smectite and smectitic layers in illite/ smectite mixed layer minerals) since smectitic layers significantly determine the CEC even in the presence of other clay minerals like kaolinite or illite. In conclusion, smectitic layer and the water content determine the electrical properties of the investigated clays containing only 10-20% w/w smectitic layers. The SER method is applicable for the in situ estimation of the CEC of Westerwald clays being relevant for their industrial application.