Modelling the acid-base surface properties of aquatic sediments

BORGNINO L; GARCIA M.G; HIDALGO M. DEL V.; AVENA M.; DE PAULI C.P.; BLESA M.A; DEPETRIS P.J

AQUATIC GEOCHEMISTRY

SPRINGER

Año: 2010 vol. 16 p. 279 - 291

1380-6165

We propose a model that explains the acid–base surface properties of clasticsediments from two Argentinean reservoir lakes. The model uses potentiometric titrationdata sets and fixed parameters such as the apparent stability constants and reaction stoichiometriesof acid–base equilibriums involving known mineral phases. The model considersthat sediments act as a set of independent sorption surfaces, such as organic matter,clay silicate, and iron (hydr)oxides, thus the acid–base equilibrium and the correspondentprotolytic constants are represented by a humic acid, a Na-illite, and a poor crystalline Fehydr(oxide). In agreement with experimental data, the model predicts that all sedimentsamples show a similar charging behavior, increasing the negative charge as the pHincreases. The net charge of sediments is controlled by the presence of negatively chargedminerals and/or organic matter coatings. This reveals the great influence of clays and organic matter functional groups on the acid–base surface properties of sediments, andconsequently on the surface reactivity toward contaminant transport.