Jean-Claude Touray

Experimental seawater-basaltic glass interaction at 50°C: Study of early developed phases by electron microscopy and X-ray photoelectron spectrometry

Experiments on seawater-basaltic glass interaction were made using a particulary high seawater-basaltic glass ratio (14.5 g/cm2; weight ratio: 50). A layered alteration skin is observed at the glass surface, while the variations in the composition of the seawater are imperceptible. Three zones of different composition and structure are distinguished: 1. 1) An external zone, the composition of which evolved to saponite. 2. 2) A median zone of hydrotalcite-like hydroxycarbonate (Mg6Al2CO3(OH)164H2O). 3. 3) An internal zone, between glass and hydroxycarbonates, richer in Fe and in Mg and in which a 10 A interval is observed (by dark field examination) compatible with a TOT type clay mineral. The composition of this zone indicates a mixing of poorly crystalline products. The principal chemical exchanges between glass and solution are the release of Ca in solution and the contribution of Mg and CO2 from seawater to form hydroxycarbonates, which are considered precursors of phyllosilicates. Comparison with natural phenomena (palagonitization) is made.

Mineralogical control on inorganic contaminant mobility in leachate from lead-zinc metallurgical slag: experimental approach and long-term assessment

Abstract Lead, zinc and arsenic mobilization/attenuation processes during interactions between smelter slag and water show differences depending on the origin of the slag. The studied samples, waste from ore and car-battery processing, were submitted to long-term (365 days) batch leaching at two different initial pH values. The leachate analyses were input to the EQ3NR speciation-solubility code to speciate the solutions and determine the degree of saturation with respect to different phases, and a mineralogical investigation was made of the newly formed phases. An ‘oxidizing’ scenario can be proposed for slag waste disposal, considering that cerussite (PbCO3) at pH >6 becomes a major solubility-controlling phase for Pb, and newly formed hydrous ferric oxides (HFO - common secondary phases under oxidizing conditions) efficiently adsorb As. No efficient scavenging mechanism was found for Zn, which was progressively leached from the slag and in particular from the ore-processing slag. Quenched glass-rich slag from old car-battery processing was found to release significant amounts of Pb, especially in acidic environments. Neither slag would therefore be suitable for recycling for civil engineering purposes. Conversely, extremely low releases of Pb, Zn and As were observed for recent car-battery processing slag, which could therefore be considered for road construction.

An XPS study of the dissolution kinetics of chrysotile in 0.1 N oxalic acid at different temperatures

The dissolution of chrysotile is studied in regard to the surfaces analysis by photoelectron spectrometry. After leaching of chrysotile (Provenance: Thetford; about 200 mg of fibers of 1 cm length) in nonstirred 0.1 N oxalic conditions, the composition of the mineral surfaces is determined by XPS; kinetic curves of dissolution are given in the range 22–80°C.Two conditions for the rate-limiting step are involved for the explanation of the dissolution: diffusion of Mg2+ through the fibrous gel or dissociation of chrysotile. By the former, some values of the diffusion coefficient are proposed: D varies from 5·10−19 cm2s−1 to 5·10−16 cm2s−1, in the range 22–80°C. By the second model, the leaching rate is estimated from 3 Å (22°C) per h to 250 Å (80°C) per h. For the 2 models, the activation heat energy is in the range 15–20 Kcal.

Leaching of polished sections : an integrated approach for studying the liberation of heavy metals from lead-zinc metallurgical slags

Pb-Zn metallurgical slags are defined by European Community regulations either as waste (hazardous materials) or as secondary commercial substances. The knowledge of their stability is essential in order to assess strategies for their management. A scientific understanding of metal release requires (i) knowledge of the phases hosting the different hazardous metals (e.g., Pb) and (ii) knowledge of the relative solubility of these phases. This paper is devoted to a mineralogical characterisation of slags resulting from different processing technologies and to long-term static leaching experiments run under different pH-conditions. The main mineral phases of slags are spinel-family oxides, Ca-Fe aluminosilicates (clinopyroxene, olivine-type phases, melilite, garnet), silicate glass, sulphide (galena, wurtzite) and intermetallic droplets. Leaching experiments were conducted on polished sections, which were introduced into batch reactors and leached by the following solutions: (i) citric acid-sodium citrate buffer at pH ~ 3 (organic soil-simulating solution), (ii) deionised water without any pH control and (iii) calcium hydroxide saturated solution buffered at pH ~ 12.5 (concrete-simulating solution). Sulphide/metallic phases display an extremely low stability whatever the solution. Under organic-acid conditions, Ca-rich (melilite) and Fe-rich (fayalite) phases are preferentially dissolved. Spinel-family oxides are always extremely stable. SEM observations evidence the important role of citrate, which favours the extraction through chelation of metallic elements on the slag surface. The silicate glass and sulphide/metallic droplets are the most unstable phases under intermediate conditions (deionised water). However, under such conditions, the mobility of Pb, Zn and As is drastically limited by precipitation/adsorption processes, as shown by geochemical modelling (PHREEQC, EQ3NR). A preferential dissolution of glass, clinopyroxene and garnet occurs in alkaline environments. Additionally, lead is significantly released by the dissolution of galena and remains dissolved. On the contrary, zinc content is likely controlled by precipitation of secondary zincite (ZnO) or zinc hydroxide, as predicted by the EQ3NR calculations. The results of static leaching experiments under various conditions confirm that the disposal of slag in organic-rich environments (e.g., peat soil) or the use of slag in concrete technology should be avoided due to the high mobilisation of Pb and other toxic elements.

Study of the early hydration of Ca3SiO5 by X-ray photoelectron spectrometry

C3S pastes (W/S = 0.5), have been studied from 5 seconds to 4 hours by X-ray Photoelectron Spectrometry. XPS reveals surface transformations of C3S grains from very early ages of hydration. The modifications have been evidenced by a change in the environment of Si atoms and a variation of the Ca/Si ratio. A Primary Hydrate (C/S << 3), a Secondary Hydrate (C/S ⋍2) and a Tertiary Hydrate (CSH type I) have been identified. XPS is a sensitive and reproducible method for the study of the surface C3S hydration.

Experimental hydration of two synthetic glassy blast furnace slags in water and alkaline solutions (NaOH and KOH 0.1 N) at 40° C: structure, composition and origin of the hydrated layer

The hydration of blast furnace slags has been modelled using two synthetic (CaO, SiO2, Al2O3, MgO) glasses with different Al2O3/MgO values. Experiments (duration: 16 h to 150 d) were performed at 40° C in deionized water (pH 6.5) and in NaOH and KOH (0.1 N) solutions (pH=12.9). The hydrated layer was characterized from a combination of several techniques at different scales: surface analysis by XPS and SEM; TEM of ultrathin diamond-cut sections including electron microdiffraction and EDS analysis; X-ray diffraction of scratched powders. In water, the hydrated zone is only about 0.5μm thick after 150 d with a leached layer covered by a thin siliceous film on which are scattered rare amorphous lamellae. In alkali media, the hydrated zone is composed of three parts: an inner layer made of modified residual glass, calcium-depleted and richer in magnesium and aluminium than the initial glass; an intermediate lamellar of constant thickness (O.3μm) after 15 d with magnesium and aluminium as major components (“hydrotalcite type” composition) and labelling the initial solid-solution interface, an outer layer with initially abundant C-S-H more or less carbonated after reaction with atmospheric CO2. The “hydrotalcite-type” layer separates the inner domain dominated by the formation and evolution of a leached glass layer from an outer one, where the precipitation of C-S-H and other amorphous or crystalline compounds, followed by carbonation, are the major processes.

Native-sulphur-bearing fluid inclusions in the CO2H2SH2OS system — Microthermometry and Raman microprobe (MOLE) analysis — Thermochemical interpretations☆

Abstract Fluorite and quartz samples from Oseja (Oviedo, Spain) and Sierra de Lujar (Granada, Spain) contain multiphase fluid inclusions with two immiscible liquids, a gas and a solid phase at room temperature. Studies by Raman scattering microspectrometry permitted: 1. (a) An unambiguous identification of native sulphur daughter solid. 2. (b) Determination of CO 2 H 2 S molar ratios in the gas phase and in the two liquids (aqueous solution and a mixture of liquefied CO2 and H2S). 3. (c) In H2S-rich inclusions, identification of a H2S hydrate (probably the clathrate H2S · 5.75 H2O), observed at low temperature. A check of internal consistency is given by the comparison of the theoretical ( CO 2 H 2 S ) gas ( CO 2 H 2 S ) water ratio (value = 3) and the observed ratio (mean value = 3.3). Homogenization of the gas and (CO2 + H2S) liquid occurs generally in the liquid phase. In the Lujar samples it occurs between +24° and 38°C and there is a fair correlation with H2S content. In the Oseja samples it occurs between +27° and +48°C, and the trend with composition is not clear. H2S hydrate was observed during some freezing runs in fluorite from Oseja and CO2 hydrate in samples from Sierra de Lujar. Because of decrepitation, total homogenization was observed only in small inclusions of the quartz from Lujar at above 300°C. The temperature of total homogenization corresponds to the vanishing of the sulphur droplet, which determines the paleofugacity of S2 in the fluid (10−3.6 bar). The main equilibria describing the composition of the fluid inclusions before total homogenization are the following: 1. (a) 2S /af S2 (buffering fS2) 2. (b) H 2 S + 1 2 O 2 /af H 2 O + 1 2 S 2 (buffering fO2). An example of calculation is given at +250°C. One may see that inclusions are just outside the graphite field and that CH 4 CO 2 is very low which explains that methane was not detected by Raman scattering microspectrometry. The origin of the sulphur-rich fluid at Sierra de Lujar is presently poorly understood. It could result from diagenetic processes, similar to those responsible for deposition of sulphur ores in the neighbouring Sierra de Gador.

The Ribeira fluorite district, southern Brazil

The origin and evolution of different ore deposits grouped in the same district are often complex and may involve inheritance from crustal or mantle geochemical anomalies, remobilization of former ore deposits and a polyphase hydrothermal history. Localized in a Proterozoic basement in the Parana state, the Ribeira fluorite district is such an example composed of three deposit types with distinct geological and geochemical characters. Emplaced at different periods from the late Proterozoic to the Cretaceous, they are roughly aligned along a belt nearly 10 km in width and 50 km in length, the southern boundary of which is a transcurrent fault. Two main ore facies are present: (1) microcrystalline ore (< 0.1 mm grains) and (2) macrocrystalline ore (with a grain size of several millimetres). The former results from the replacement of metalimestones or internal karstic sediments and the latter from microcrystalline ore dissolution and pore precipitation or recrystallization. At least two different groups of source rocks can be proposed for the trapped REE in CaF2: (1) fluorite samples associated with the Mato Preto carbonatitic rocks display a slightly negative ɛNd compatible with a mantle source and a REE pattern with the higher ΣREE and La/Yb ratio in the district; (2) other fluorites have a strongly negative ɛNd (− 14 to − 20) which indicates a crustal source. That fluorine and REE have the same source is possible in strata-bound and fracture-filling deposits, but is doubtful at Mato Preto, the only economic fluorite deposit associated with carbonatite rocks in Brazil. This occurrence within a Precambrian fluorite belt suggests that remobilization of a former strata-bound deposit was a more significant metallogenic process than magmatic differentiation.

X-ray photoelectron spectroscopy and chemical study of the adsorption of biological molecules on chrysotile asbestos surface☆

Abstract The sorptive properties of chrysotile and Mg-depleted chrysotile fibers were determined. Chemical analysis and X-ray photoelectron spectroscopy (XPS) were used in order to study the adsorption of albumin and of dipalmitoyl phosphatidyl choline liposomes on the fibers. The macromolecules are adsorbed on the surface of chrysotile fibers, the albumin being in the “end-on” position. The adsorption on Mg-depleted chrysotile fibers is different, there is a bulk incorporation of the macro-molecules in the fibers. However, the chemical analysis shows that similar amounts of macromolecules were adsorbed on the undepleted or Mg-depleted fibers. These observations suggest that some biological effects of chrysotile fibers may be related to their physicochemical properties.

Blast-furnace slag hydration. Surface analysis

Abstract X-ray photoelectron spectrometry (XPS) was used to determine the variation of the characteristic ratios Ca/Si, Al/Si and Mg/Si of two different slags (one in granulated, the other in pelletized form) during hydration. The results show that the slag surface is modified as soon as it becomes in contact with water or alkaline solution. The hydrated superficial layer is depleted of calcium but contains alkali ions if instead of water, NaOH or KOH solutions are used in mixing.