Lixiviation of argillaceous rocks: Impact of oxidation degree states on organic compound mobilization

This work aims to study the influence of oxidation degree state which reached by organic matter included in argillaceous rocks on lixiviation and mobilization of compounds. Experimental lixiviation was carried out on two argillaceous rocks sampled in the surface deposit of the Andra laboratory (Bure, France). Molecular and spectroscopic characterizations of the organic matter extracts reveal two different oxidation levels reached by these samples: (i) a well preserved and (ii) an oxidized samples. Dissolved organic matter content and molecular investigation of sediment bitumen show that hydrophobic molecules (hydrocarbons) remain stable during lixiviation whereas specific polar compounds (alkanoic acids) are progressively removed by water. Moreover, occurrence of secondary alkanols with a molecular distribution similar to initial n-alkanes suggests that even in the well preserved sample, oxidation already occurs and that secondary alkanols can be used as specific markers for low intensity oxidation.