Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8910815 | Geochimica et Cosmochimica Acta | 2018 | 16 Pages |
Abstract
The proposed reaction path for the formation of sepiolite is based on the temporal evolution of the chemical compositions of the experimental solution and solids: (i) Nucleation and growth of Al-sepiolite occurred during the first 8â¯days of the experimental runs via condensation and polymerization of SiOH tetrahedra onto Mg-Al-O-OH template sheets at a precipitation rate of â¼2.19â¯Â±â¯0.01â¯Ãâ¯10â10â¯molâ¯sâ1. (ii) At decreasing pH and in the absence of [Al]aq this intermediate phase transformed into aluminous sepiolite at a slower crystal growth rate of â¼1.08â¯Â±â¯0.02â¯Ãâ¯10â12â¯molâ¯sâ1. This finding explains the high abundances of sepiolite in highly alkaline, evaporitic, lacustrine and soil environments, where the growth rates of sepiolite are considered faster (10â11 to 10â10â¯molâ¯sâ1, Brady, 1992). We propose that (i) low rates of Mg2+ ion dehydration and silica condensation and polymerization at the surface of the initial precipitate, (ii) the formation of MgS040 aquo-complexes and (iii) the reduced sorption rates of [Si]aq and [Mg]aq at the active growth sites on sepiolite surfaces at pHâ¯â¤â¯8.3 retard the precipitation of sepiolite in marine-diagenetic environments.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Andre Baldermann, Vasileios Mavromatis, Paula M. Frick, Martin Dietzel,