Recognition of starches by Raman spectroscopy

This paper describes the use of Raman spectroscopy to identify modi®ed starches with regard to their origin and type of modi®cation. Using Principal Component Analysis, natural groupings of similarly modi®ed samples can be obtained on a two dimensional plane. Such mapping provides the expert with the possibility of analyzing the distribution of samples by using their relative position with respect to the existing clusters. On the basis of the available information in the Raman spectra, a Partial Least Squares calibration was built with the intensities of the derivative Raman spectra as input and the starch modi®cations as output, allows the user to identify the modi®ed starches present in a sample.

Structural analysis of xCsCl(1−x)Ga₂S₃ glasses by means of DFT calculations and Raman spectroscopy

The alkali metal halide doping of gallium-sulfide glasses yields improvements in the optical, thermal and glass forming properties. To understand these improvements, the short-range order of xCsCl(1 − x)Ga2S3 glasses was probed by Raman spectroscopy. Raman spectra have been interpreted using density functional theory (DFT) harmonic frequency calculations on specific clusters of GaS4H4 and/or GaS3H3Cl tetrahedral subunits. The assignment of the observed vibrational bands confirms the main structural conclusions obtained with X-ray and neutron diffraction experiments and gives some new insights into the gallium-network present in the xCsCl(1 − x)Ga2S3 glasses. At the lowest concentration, the observed spectrum may be interpreted with small clusters such as dimers and trimers connected by corner-sharing (CS) GaS4H4 tetrahedral subunits. The vibrational fingerprints of tri-clusters with three-fold coordinated sulfur atoms have also been identified; however, no Raman signature of chlorine-doped subunits has been found to be caused by their insufficient intensity. For higher CsCl concentrations, distinct spectral features corresponding to chlorine-doped clusters appear and are increasing in intensity with x. In other words, undoped and Cl-doped tetrahedra coexist in the xCsCl(1 − x)Ga2S3 glasses. The added chlorine atoms induce a fragmentation of the glass network and replace the sulfur atoms in the CS tetrahedral environment. The comparison of the observed spectra with theoretical predictions and diffraction data favoured one-fold coordinated chlorine atoms in the glass network

Chemistry of metal sulfides in anoxic sediments

Using sequential extraction of solid sulfides, the determination of acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS) in anoxic sediments from the Authie Bay (in northern France) has been undertaken because of the importance of the sediments as sinks for iron, sulfur and trace metals and as possible sources of pollution when reduced sediments are mixed with oxic waters (as a result of a sediment remobilization induced by physical disturbances such as tidal currents and dredgings), and subsequently oxidized. Chemical analysis of solutions recovered after sequential leaching of sediments with 1 M HCl, 1 M HF and concentrated HNO3 has enabled us to obtain profiles, s. sediment depth, of trace metals associated with pyrite. Porewater concentration profiles s. depth have been determined for several cations (Ca2+, Cd2+, Cu2+, Fe2+, Mg2+, Mn2+, Na+, Pb2+, Sr2+ and Zn2+) and anions (CO32–, PO43–, SO42– and S2–). Using the chemical equilibrium modeling program MINEQL+ with these analytical data, thermodynamic calculations have given information about the possibility of precipitation of discrete metal sulfide phases (FeS as greigite and amorphous FeS; ZnS, PbS, CuS and CdS), and coprecipitation with adsorption on solid FeS to produce solid solutions with iron sulfides. The degree of trace metal pyritization, DTMP, has been determined for these metals and compared to the degree of pyritization, DOP. The findings suggest that in Authie-bay sediments Mn is well pyritized; whereas Zn, Cu, Ni and above all Cd are weakly pyritized (MnZnCu>NiCd). These observations seem to be intimately related to the existence of the discrete/separate solid phases CuS, CdS and ZnS, as predicted by thermodynamic calculations. Finally, analysis of crude sediments, heavy minerals and pyrite extracted by a heavy liquid density separation method, has been performed with a Raman microprobe to gain information about the geochemical and mineralogical characteristics of these sediments. The efficiency of sequential leachings of sediments (which were used for sedimentary pyrite recovery/attack and analysis of pyritic Fe and trace metal) has also been evaluated by these techniques

Analytical and thermodynamic approach to the mineralogical and compositional studies on anoxic sediments

BACKGROUND, AIM AND SCOPE. The identification of certain minerals directly in the raw sediment has proved to be difficult, if not impossible, because of their instability and/or low contents. This explains why the characterization/composition/crystalline nature of multiple (co)precipitates and solid solutions often necessitate the combined use of density separation methods and macro and microanalytical techniques, and in some cases the possible existence of certain mineral solids is only sustained from thermodynamic considerations. In this context, the comparison of porewater concentration profiles with thermodynamic calculations recently proved to be a convenient way of obtaining clues relative to the potential occurrence of natural minerals. METHODS. Porewaters and sedimentary-solid phases were extracted from sliced sediment samples collected in the Seine estuary (northern France), and studied as a function of sediment depth. Porewater concentration profiles were determined for Ca, Fe, Mg, Mn, Na, P and Sr using inductively coupled plasma atomic emission spectroscopy, and for dissolved sulfur using square wave, cathodic stripping voltammetry. To obtain information about sediment mineralogy, sedimentary solid phases were analysed directly and after density separation with a heavy liquid (CHBr3) by means of several techniques: X-ray diffraction; electron spin resonance and micro-Raman spectroscopies. Furthermore, using sequential extraction procedures, the chemical speciation versus depth of several elements (Al, Ca, Fe, Mg, Mn, P, Pb, Sr, Ti, and Zn) and particularly sulfur [i.e. acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS)] were undertaken. RESULTS AND DISCUSSION. From these analytical data, some thermodynamic calculations [using ion activity products (IAP)] were attempted for the anoxic porewaters where most of the ionic complexing species were measured to support the involvement of relevant geochemical equilibria between these ions and some metals and the existence of any discrete solid phases (calcite, dolomite, greigite and probably vivianite, apatite and siderite), as well as coprecipitates and solid solutions in calcium carbonate. CONCLUSIONS. Thermodynamic equilibria in sedimentary media are rarely achieved because many chemical processes in these systems are established in long periods. Nevertheless, these calculations remain useful to increase our insight into the considered system. They help to support our view about the possible existence of certain minerals (iron sulfides, calcite, dolomite...). They also help account for the real power of ESR for indicating the presence of hypothesised solid solutions, MnxCa1-xCO3. The critical investigations of the authors, however, reveal some weaknesses of XRD and Raman microscopy for identifying minor minerals/precipitates, which result from combinations between the inorganic anions PO43–, CO32– and S2– and the metallic cations Fe2+, Mn2+, Mg2+, and Sr2+

Behavior of Zn-bearing phases in base metal slag from France and Poland: A mineralogical approach for environmental purposes

International audienceSlag samples from three pyrometallurgical sites (two in France, one in Poland) were studied for their Zn-phase content, evolution and potential release of metals over time. Mineral assemblages were observed and analyzed using various complementary tools and approaches: chemical extractions, optical microscopy, cathodoluminescence, X-ray diffraction, Scanning Electron Microscopy, Electron ProbeMicro-Analysis, and micro-Raman spectrometry. The primary assemblages are composed of analogs to willemite, hardystonite, zincite, wurtzite, petedunnite and franklinite. Some of these phases are sensitive to alteration (e.g., deuteric processes during cooling and by weathering) and, as a result, goslarite, smithsonite and hemimorphite have been identified as secondary products. In comparing these results to the geochemical conditions at each site in relation to mineralogical investigations, different steps of Zn-rich mineral destabilization could be identified. This procedure allows assessing potential environmental impacts due to a release of metals that may contain slag. The destabilization of zincite leads to the precipitation of both goslarite and smithsonite, whereas only smithsonite is formed once hardystonite has beenweathered. The Ca released by hardystonite dissolution will indeed limit goslarite formation and moreover favor gypsum precipitation. The relative degree of hydration necessary to form goslarite is supplied by water released during primary phase dissolution and/or smithsonite precipitation. A hydrated form of willemite was observed here, despite being rarely reported in previous studies, corresponding to an intermediate alteration product. The hydrated willemite ultimately evolved towards hemimorphite, which has been identified at the very outer part of the weathered willemite by means of EPMA and confocal Raman spectroscopy. On the basis of these results, we are able to propose a sequence from the least to most stable phase with: hardystonite and zincite > hemimorphite > willemite. Our results are critical for decisions like whether Zn-rich slagmay be reused as a material for geotechnical purposes and thus contribute to the sustainable management of similar industrial wastes