| Abstract (english) | Mineral particles play a major role in biogeochemical processes in nature, particularly in binding,
transport and deposition of different organic and inorganic compounds. Among them, the colloidal mineral
phases, particles in the submicron- and the nanosized range represent the most reactive mineral surfaces in the
environment (HOCHELLA et al., 2008; TANG et al., 2009; PLATHE et al., 2013). Through complex
physico-chemical processes associated with their surfaces, these solids affect bioavailability, toxicity and the
fate of the associated inorganic and organic compounds. Their unique surface reactivity is a consequence of
their size-related structural and surface physico-chemical properties.
In marine sediments, the colloidal mineral fraction mostly consists of clay minerals, metal oxides and
oxyhydroxides, sulphides, and, sporadically, carbonates (PERRET et al., 1994). Carbonate minerals are rarely
found in the nanosized range and mostly occur as lithogenic and biogenic fragments in coarser fractions
(BUFFLE et al., 1998). The results obtained in this study show the mineral composition, occurrence,
distribution and the surface physico-chemical properties; specific surface area (SSA) and cation exchange
capacity (CEC) of different size fractions collected in various sedimentological environments in the Adriatic
Sea. The influence of organic and inorganic surface coatings on the reactivity of mineral surfaces was
investigated. A detailed mineralogical investigation revealed significant changes in the composition of mineral
particles in the clay fraction. The obtained results revealed presence of nanosized particles mainly in the form
of microaggregates in strong associations with organic matter, difficult to disrupt even despite of chemical
treatments. The authigenic precipitation seems to be the main mechanism leading to a more significant share
of carbonates in the colloidal size range. In sediments where weathering of carbonates is the main source of
their origin, their occurrence was limited to coarser size fractions and clay minerals were the dominant
mineral phase in the colloidal size range. These changes in the mineralogical composition were reflected in
the surface physico-chemical parameters. As a result, size fractions with predominance of submicron-sized
clay minerals showed a significant increase in SSA and CEC with particle size lowering. |
