Arsenates and inorganic pollutants

Surface of a typical gypsum grain after < 1 day of reaction with a As(V)-bearing solution. (Left) Overall grain aspect. The original surface is covered by crystalline aggregates formed by individuals with laminar shapes. (Right) Precipitate aspect at a higher magnification.

Surface of a typical gypsum grain after < 1 day of reaction with a As(V)-bearing solution. (Left) Overall grain aspect. The original surface is covered by crystalline aggregates of guerinite (Ca arsenate) formed by individuals with laminar shapes. (Right) Precipitate aspect at a higher magnification.

Is it possible to use common minerals like gypsum or calcite to trap inorganic pollutants like As5+, Cd2+ or Pb2+?

During my PhD I worked on the evaluation of the capacity of gypsum to remove pollutants like arsenate or lead from natural waters, the understanding of the mechanisms involved in these processes and the characterisation of newly formed solid phases derived from these interactions. This arsenate-gypsum interaction included the structural determination of new AsO43--bearing minerals, growth morphologies, crystallographic analyses of oriented overgrowths on mineral surfaces, as well as calculation of thermodynamic solubility products.

The same experimental methodology was used to study the effectiveness of gypsum to sequester Pb2+ from water, discovering a rapid removal (< 1 hour) via surface precipitation of anglesite (PbSO4).

KEY PAPERS

Rodríguez-Blanco, J.D., Jiménez, A., and Prieto. M. (2007) Oriented Overgrowth of Pharmacolite (CaHAsO4·2H2O) on Gypsum (CaSO4·2H2O). Crystal Growth & Design, 12, 2756-2763. doi: 10.1021/cg070222+   [PDF]

Köhler, S., Cubillas, P., Rodríguez-Blanco, J.D., Prieto, M. (2007) Removal of cadmium from wastewaters by aragonite shells and the influence of other divalent cations. Environmental Science and Technology, 41, 112-118. doi: 10.1021/es060756j   [PDF]

Rodríguez, J.D., Jiménez, A., Prieto, M., Torre, L., and García-Granda, S. (2008) Interaction of gypsum with As(V)-bearing aqueous solutions: Surface precipitation of guerinite, sainfeldite, and Ca2NaH(AsO4)2·6H2O, a synthetic arsenate. American Mineralogist, 93, 928-939. doi: 10.2138/am.2008.2750.   [PDF]

Astilleros, J.M., Godelitsas, A., Rodriguez-Blanco, J.D., Fernandez-Diaz, L., Prieto, M., Lagoyannis, A., Harissopulos, S. (2010) Interaction of gypsum with lead in aqueous solutions. Applied Geochemistry, 25, 1008-1016. doi: 10.1016/j.apgeochem.2010.04.007.   [PDF]