Effects of water–cement solutions on the composition of organic compounds leached from oxidized Callovo–Oxfordian argillaceous sediment

Abstract

Both oxygen penetration, due to excavation, and the use of hydraulic cement as engineering barrier has led to the investigation of effects of high pH solutions on the oxidized host rock formation. A Callovo–Oxfordian sediment has been oxidized in a ventilated drying oven at 130 °C between 2 and 1024 h. The geochemical characterization of oxidized samples shows that oxidation induces transformations in extractable organic matter similar to those observed during thermal maturation. Rock-Eval analyses of extracted solid residues reveal a loss of hydrogen while oxygen is incorporated into the kerogen structure during oxidation experiments. The oxidized samples have been leached with deionized water and cement solution. Comparisons between basic and near-neutral leaching treatments showed that the amounts and nature of leached organic species are pH-dependent. The dissolved organic compound amounts are higher at basic pH than at pH close to neutrality. Gas chromatography–mass spectrometry (GC-MS) analyses show that aromatic carboxylic acids are preferentially leached by deionized water, while n-carboxylic acids predominate in cementitious solution. The data reveal that kerogen oxygen content may constrain the dissolved concentration of organic species. The DOC concentration and the CO functionality of leachable organic molecules increase with increasing duration of oxidation.