Cation exchange capacity- An alternative method to investigate the geological barrier for landfills?

Clays and clay minerals are ideal raw materials for geological barriers and landfill liners because of their low-hydraulic permeabilities, their swelling properties and adsorption capacities. The geological barrier is a supplementary barrier beneath the body of the landfill, intended to protect the environment from uncontrolled leachate from the waste material. An Austrian standard defines the process for site exploration and the required laboratory tests and parameters for the analysis of the geological barrier. The most important laboratory tests besides grain size analysis are the Atterberg limits and the determination of the clay mineralogy using X-ray diffraction. However, the analysis of the cation exchange capacity (CEC) is not included in the list of laboratory tests. CEC is a numerical value that describes the physical properties of clays, such as the diffusion of charged and uncharged molecules and the cation retention. Hence, the objective of this study is to clarify whether the determination of the CEC using the Cu-trien method represents a possible alternative to currently used laboratory tests. For this purpose, three samples (loess, sand and clay) from two landfill sites owned and operated by Zöchling GmbH as well as six mixtures of these samples with varying compositions were examined for their mineralogical, chemical and geotechnical properties. The samples consisted of varying amounts of quartz, feldspar, calcite, dolomite and the clay minerals smectite, illite, kaolinite, vermiculite and chlorite. The results showed that the bulk clay mineralogy correlates well with the Atterberg liquid limit (R² = 0.73) and the CEC (R² = 0.88) and furthermore, the results of the two methods – Atterberg liquid limit and CEC- even correlated better (R² = 0.95). This demonstrates that the CEC can be an alternative to the Atterberg liquid limit and/or the analysis of the mineralogical composition of the material. Advantages of the CEC are rapidness, its good reproducibility and cost-efficiency of the analyses compared to the other two methods. Based on the results of this study, a partial substitution of the currently used laboratory tests is considered feasible and CEC could at least be used for fast and efficient screening.