Element Desorption from and Crystal Dissolution of a Smectite by Interaction with the Bacteria Escherichia coli and/or Varied Amino Acids
Résumé
Three-week experiments were completed to evaluate the interaction of the bacteria Escherichia coli and amino acids (glutamic acid, alanine, arginine, serine and leucine) on the dissolution and/or desorption rates of a smectite-type clay mineral. A systematic dominant leaching of Na confirms that the initial smectite was Na-enriched. The bacteria Escherichia coli induced leaching of a Si/Al ratio far from that released by either the amino acids or by a combination of the bacteria and amino acids. Conversely, this ratio is close to the value of the smectite itself. Therefore, the bacteria has a probable dissolution impact rather than a desorption action. This preferential action is indirectly corroborated by a low removal of Na by the bacteria. Removal impact of the bacteria on the smectite decreased when mixed with any of the amino acid. The highest releases of Si, Al, Mn and Fe characterize batches without amino acids, while most released Ca and K occurred with the amino acids. Potassium, P, Mg, Na and Ca are more released into solutions containing several amino acids, while Fe is preferentially leached by solutions with only one amino acid. This study highlights also the potential roles of amino acids in soils and other surficial geological systems. The distribution patterns of the leached rare-earth elements (REEs) confirm a clear distinction between the impact of the bacteria that produces a progressively decreasing contents of the light REEs and a flat distribution for the heavy REEs and those, more variable, of the amino acids. The impact of the amino acids influences the REE distributions, probably along complexation processes due to strong metal sorption on oxides by organic complexes.
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