In this work, natural sediment was used as an alternative and green inorganic source to synthesize valuable structured Al-MCM-41 material by a hydrothermal process. This intertidal sediment contains a mixture of clay minerals (montmorillonite and ilite) and minerals (quartz and feldspar) providing large SiO2 (∼64%) and Al2O3 (∼15%) content which were efficiently extracted by alkaline fusion. The synthesized mesoporous material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance infrared Fourier transform spectroscopy (FT-IR), N2 physisorption, and 27Al solid-state magic angle spinning nuclear magnetic resonance spectroscopy (27Al MAS NMR). The results achieved reveal that pure and highly ordered hexagonal mesoporous aluminosilicate MCM-41 containing structural aluminum has been successfully synthesized. Moreover, it was evidenced that the obtained solid presents uniform pore size distribution (3.6 Å) as well as high pore volume (0.59 cm3g–1) and elevated specific surface area (807 m2g–1).

The burrowing and semiterrestrial crab Neohelice granulata actively and constantly builds its burrows in the intertidal zone of the Bahía Blanca Estuary during low tide. Differences in structural morphology of N. granulata burrows and burrowing activities in contrasting microhabitats (saltmarsh and mudflat) were analyzed and related to several conditions, such as tide level, substrate type, sediment properties, and population density. In the mudflat the higher density of total burrows in autumn (172 burrows•m-2) was associated with molt timing, and the higher density of active burrows in summer (144 burrows•m-2) was associated with reproductive migration. Sediments from biogenic mounds (removed by crabs) showed higher water content and penetrability than surface sediments (control), suggesting that bioturbation increases the values of these parameters. Grain size distribution profiles and mineralogical composition did not vary between microhabitats or between seasons. Burrows were all tunnel-shaped and only those from the saltmarsh had chambers inside the tunnels, possibly used for reproductive purposes. Burrows from the saltmarsh had narrow entrances and deep tunnels, and burrows from the mudflat presented very narrow entrances and surface tunnels. Differences in burrow features and burrow activity of N. granulata between microhabitats were confirmed and associated with biotic and abiotic factors, indicating that this species has an adaptive burrowing behavior.

The suspended sediment contribution arising from the bioturbation activity of Neohelice granulata at intertidal sites of the Bahía Blanca estuary was analysed using several approaches, ranging from field experiments to numerical modelling. Crabs from the mudflat remove, trap and erode more sediment from their burrows per unit area than those from saltmarshes, as a consequence of the high population density and the mobility of cohesive sediments. The results obtained through the MOHID simulations showed that the sediments that were bioavailable in the intertidal of Puerto Cuatreros were maintained in the water column much longer than sediments in Villa del Mar. This longer residence time in the area could be because of the geomorphological and hydrodynamic characteristics of the internal area of the estuary, where numerous tidal channels coexist and phenomena of “retention” occur before entry into the main channel. By contrast, in Villa del Mar, located in the middle of the estuary, the sediments are affected by a greater water depth and higher tidal current speeds. In addition, the waves caused by the winds can be a determining factor in the spatio-temporal evolution of the bioavailable sediment in the water column of the study areas.

This paper aims to characterize a natural sediment from Bahía Blanca estuary (Argentina) as a new clay source and determine the catalytic capacity after its structural modification by an acid activation process. The acid treatment was performed by employing H 2 SO 4 at different concentrations at 353 K and 60 min. The raw material and acid-activated samples were characterized by XRD, XRF, FTIR, N 2 physisorption, TGA, SEM, EDX, potentiometric titration and pyridine adsorption monitored by FTIR. Moreover, the catalytic activity on lauric acid esterification with methanol was evaluated as a test reaction. From the structural characterization, it was determined that the material studied contains mainly Ca-montmorillonite, illite, albite and quartz. Likewise, the results obtained showed that the acid-treatment impacts the material characteristics, predominantly surface acidity and textural properties. Particularly, it was evidenced that the samples treated under medium acid activation conditions lead to an increase in acid site number and strength and specific surface area and consequently improve the catalytic activity. The results obtained evidenced that this low cost and widely available raw material presents an interesting mineralogical composition with a high clay mineral content. Additionally, the catalytic performance showed a good conversion in the test reaction regarding other heterogeneous catalysts. Hence, considering these results, this natural sediment merits further research on its purification and application.