Recrystallization and stability of Zn and Pb minerals on their migration to groundwater in soils affected by Acid Mine Drainage under CO2 rich atmospheric waters.

The extent of vertical contamination is intimately related to the soil solution and surface chemistry of the soil matrix with reference to the metal and waste matrix in question. The present research demonstrated the impact that the dissolved CO2 of the meteoric waters, which acidify the environment with pH values below 4, has in the increase of the metal mobility. Although under the given conditions the Zn remains mainly dissolved, the initial PbS and ZnS have evolved into newly formed secondary carbonates and sulphates (i.e., hydrozincite, gunningite, hydrocerussite) that can be found in the efflorescences. The chemical simulation done on the weathering of the original sulphide ores for the formation of these secondary minerals has proved the transient storage mainly of Pb. Nonetheless, many of the minerals formed inside the galleries will be easily dissolved in the next rains and release in an ionic form to the groundwater. The analytical procedure exposed has been proved to be useful not only for the characterization of AMD but also for the prediction of the mobility of metals.

Non-destructive crystal size determination in geological samples of archaeological use by means of infrared spectroscopy.

The determination of crystal size of chert samples can provide suitable information about the raw material used for the manufacture of archeological items. X-ray diffraction (XRD) has been widely used for this purpose in several scientific areas. However, the historical value of archeological pieces makes this procedure sometimes unfeasible and thus, non-invasive new analytical approaches are required. In this sense, a new method was developed relating the crystal size obtained by means of XRD and infrared spectroscopy (IR) using partial least squares regression. The IR spectra collected from a large amount of different geological chert samples of archeological use were pre-processed following different treatments (i.e., derivatization or sample-wise normalization) to obtain the best regression model. The full cross-validation was satisfactorily validated using real samples and the experimental root mean standard error of precision value was 165 Å whereas the average precision of the estimated size value was 3%. The features of infrared bands were also evaluated in order to know the background of the prediction ability. In the studied case, the variance in the model was associated to the differences in the characteristic stretching and bending infrared bands of SiO(2). Based on this fact, it would be feasible to estimate the crystal size if it is built beforehand a chemometric model relating the size measured by standard methods and the IR spectra.

Beachrock formation in temperate coastlines: examples in sand-gravel beaches adjacent to the Nerbioi-Ibaizabal Estuary (Bilbao, Bay of Biscay, North of Spain).

Beachrocks are coastal sedimentary formations resulting from a relative rapid cementation of beach sediments by the precipitation of carbonate cements. These lithified structures are not usually observed at temperate settings. The present work is focused on the occurrence of a significant intertidal cementation in sand-gravel beaches formed among 43°N latitude coastline, close to the Nerbioi-Ibaizabal estuary (Bilbao, Bay of Biscay, North of Spain). Raman micro-spectroscopy combined with SEM-EDX analyses and petrographic descriptions have been applied for the determination of the cement generations and the cemented materials compositions of the beachrock outcrops. In general terms, the cements described were: Cement Generation 1 (CG 1, aragonite, high-magnesium calcite and silicate mixtures), Cement Generation 2 (CG 2, aragonite) and Cement Generation 3 (CG 3, mixtures of CaCO(3) polymorphs and iron oxides). The rest of the interstitial porosity of the rocks appeared either empty or filled with heterogeneous cemented mixtures of previously reworked compounds. The mineralogy, the regular distribution and the isopachous character of the carbonate cements together with the accurate cementation at advanced seaward bands propose a possible marine-phreatic context for the beachrock formation. However, the impure cements and the materials covering the interstitial porosity seem to be the result of both, the weathering actions consequences and the surface alterations of specific grains. Moreover, the presence of modern cemented materials (e.g. slag, bricks and pebbles) suggest a recent formation of the phenomenon.

Comprehensive two-dimensional gas chromatography to characterize hydrocarbon mixtures in lithic materials.

The analysis of organic biomarkers in chert samples offers key information about the environmental conditions in which these samples were formed, and this information can be used to track the lithic materials of many archaeological artifacts. Since the content of the organic fraction is very low and the complexity of the organic extracts is quite high, we have optimized the GC×GC separation of these mixtures. Making use of mixture of C(16)H(34)-C(44)H(90)n-alkane standards, a central composite design was carried out taking into account the carrier flow in the first and second columns, the modulation period and the discharge time. Regarding the measured responses, though the initially considered one was the peak volume, we have also evaluated the effects on the number of modulated peaks per analyte, the symmetry of the modulated peaks and the number of detected compounds. The final optimum conditions were defined as follows: a hydrogen flow of 1.2 mL/min in the first column and 18 mL/min in the second one, a modulation period of 1.4 s and a discharge time of 0.1 s and under these conditions all the response variables showed optimum values. Based on this optimized method several chert samples obtained from different stratigraphic levels in an ancient quarry were studied and we were able to distinguish them on the basis of the different constituents of organic biomarkers, such as mono-methylated alkanes, cyclic n-alkanes, branched alkanes, steranes and hopanes.