Mineralogical introduction

Metal-Aid focuses on the development, synthesis and application of mineral components as reactants to remediate soil and groundwater, which are contaminated by heavy metals and/or organic solvents. The studied minerals belong to the group of the layered double hydroxides (LDHs). Like clay minerals, LDHs have a layered structure, which is basically derived from the structure of the mineral brucite Mg(OH)2 [1]. The metal hydroxide layers of the LDHs obtain a net positive charge due to the substitution of bivalent (Me2+) by trivalent (Me3+) metal cations (e.g. Mg2+ ↔ Al3+) [1]. This charge is compensated by the intercalation of negative charged anions (A-) between the positive charged layers (e.g. Cl, CO32-, SO42-). In addition, neutral molecules (e.g. H2O, MgSO4) can be intercalated into the interlayer space, too. The general formula for LDHs can be written as:

[Me2+1-xMe3+x(OH)2]x+[Ar-x/r•nH2O]x-

Not only inorganic anions can be intercalated between the layers but also long organic substituents such as sulfonates or carboxylates are reported [2]. This could be a possibility to intercalate organic contaminates into stable LDHs. By that, they could become immobilised and nonreactive to the environment.

Another focus of this project lies on redox active minerals. This is especially well known for the LDH subgroup, which is colloquially called as “green rust”. The green rust subgroup is represented by the natural minerals fougérite and trébeurdenite, which both contain Fe2+ and Fe3+ as metal cations [3]. For these minerals, it is reported, that they are able to reduce e.g. Cr(VI) [4,5], NO3 [6] or CCl4 [7]. This implies a possible application as a reactant for the decontamination of other organic solvents.

By,

Tobias Linke

University of Iceland

References:

[1] Bookin and Drits (1993) Clays Clay Min., 41(5), 551-557

[2] de Roy et al. (2001) Layered double hydroxides: Synthesis and post-synthesis modification, 1-39; in: Rives (ed.) Layered double hydroxides: Present and future, Nova science pub., NY

[3] Mills et al. (2012) Min.Mag.,76(5),1289-1336

[4] Lawniczak et al. (2000) Environ. Sci. Technol., 34(3), 438-443

[5] Génin et al. (2001) Appl. Geochem., 16(5), 559-570

[6] Hansen et al. (1996) Environ. Sci. Technol., 30 (6), 2053-2056

[7] Maithreepala and Doong (2005) Environ. Sci. Technol., 39 (11), 4082-4090

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