THE RELATIONSHIP BETWEEN MINERALOGY, METAL CONCENTRATION, AND CATION EXCHANGE IN THE MARCELLUS SHALE

This research investigates the relationship between mineralogy, trace metal composition, and cation exchange capacity in the Marcellus Shale. Thirty samples of shale, including both cores and outcrops, have been analyzed. Bulk and clay mineralogy were identified and quantified using X-ray Diffraction Spectroscopy. Major, minor, and trace elemental compositions of the shale were determined without sample digestion by Instrumental Neutron Activation Analysis and also following digestion by Inductively Coupled Plasma Mass Spectrometry. Cation exchange values were collected for bulk samples and also for clay separates that were isolated from the bulk mineralogy by centrifugation. Cation exchange was determined by measuring exchange with a copper-ethylenediamine complex via UV-VIS spectroscopy.

Shale mineralogy is typical and dominated by quartz and calcite while the clay content is predominantly illite. Cation exchange capacities are low but typical for samples with little to no montmorillonite. Organic carbon content (TOC), which ranges from <0.1 to >13 wt%, does not correlate to cation exchange or trend strongly with mineralogy. Although some metal concentrations do correlate strongly to TOC, there is no evidence that metals are adsorbed onto or physically bound to the organic material. A summary of statistically significant correlations between cation exchange and both mineralogy and elemental compositions will be presented.