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Pyrite and arsenopyrite are the most common hosts for invisible gold, but pyrite and arsenic are refractory during conventional sulfide oxidation, which significantly challenges subsequent gold extraction. One option is high-temperature pretreatment of arsenical materials to sequester > 90% of the arsenic as a gas, then convert it to a stable form. This process produces a calcine similar in composition to pyrrhotite (Fe1-xS) but with higher porosity. In this study, the calcine product is oxidized with an efficient, cost-effective atmospheric process using acidic and near-neutral solutions. A sulfur mass balance analysis method based on iron sulfide thermal transformation in nitrogen atmosphere was developed to quantify the oxidation efficiency of pyrrhotite leaching. The optimization confirmed that > 90% of the calcine was oxidized by Fe3+ (5 and 10 g/L) and O2 (0.5 L/min) at pH 1 after 48 h and at 95 °C even without ultrafine grinding. Elemental sulfur was the main oxidation product when the oxidation pH was 1,2. This study provides the foundation for the development of a low-cost and environmentally friendly process option for pretreatment of arsenical sulfide refractory gold materials.

Increasing use and mining of antimony (Sb) has resulted in greater concern involving its fate and transport in the environment. Antimony(V) and (III) are the two most environmentally relevant oxidation states, but little is known about the redox transitions between the two in natural systems. To better understand the behavior of antimony in anoxic environments, the redox transformations of Sb(V) were studied in biotic and abiotic reactors. The biotic reactors contained Sb(V) (2 mM as KSb(OH)6), ferrihydrite (50 mM Fe(III)), sulfate (10 mM), and lactate (10 mM), that were inoculated with sediment from a wetland. In the abiotic reactors, The interaction of Sb(V) with green rust, magnetite, siderite, vivianite or mackinawite was examined under abiotic conditions. Changes in the concentrations of Sb, Fe(II), sulfate, and lactate, as well as the microbial community composition were monitored over time. Lactate was rapidly fermented to acetate and propionate in the bioreactors, with the latter serving as the primary electron donor for dissimilatory sulfate reduction (DSR). The reduction of ferrihydrite was primarily abiotic, being driven by biogenic sulfide. Sb and Fe K-edge X-ray absorption near edge structure (XANES) analysis showed reduction of Sb(V) to Sb(III) within 4 weeks, concurrent with DSR and the formation of FeS. Sb K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy analysis indicated that the reduced phase was a mixture of S- and O-coordinated Sb(III). Reduction of Sb(V) was not observed in the presence of magnetite, siderite, or green rust, and limited reduction occurred with vivianite. However, reduction of Sb(V) to amorphous Sb(III) sulfide occurred with mackinawite. These results are consistent with abiotic reduction of Sb(V) by biogenic sulfide and reveal a substantial influence of Fe oxides on the speciation of Sb(III), which illustrates the tight coupling of Sb speciation with the biogeochemical cycling of S and Fe., Antimony; Biogeochemistry; Dissimilatory sulfate reduction; Microbial reduction; Iron sulfide

Reductive immobilization of 99Tc by a synthetic FeS2 mixture, i.e. marcasite-pyrite 60:40, was studied by a combined approach of batch experiments and powder X-ray diffraction, X-ray photoelectron spectroscopy as well as Raman microscopy. It was found that the FeS2 mixture removes 100% of Tc from the suspension after 7 days in contact at 6.0 < pH ≤ 9.0. The retention outside that pH range was slower and incomplete. Spectroscopic analysis showed that the redox active species at pH 6.0 is Fe2+ as expected from previous works with pyrite. However, at pH 10.0 the surprising oxidation of S2- to SO42- was found responsible for Tc immobilization. This was explained by the high reactivity of marcasite that is easily oxidized to produce H2SO4. Our work provides new molecular insights into the reductive mobilization of Tc(VII) by oxidative formation of sulfate. The assigned molecular reactions may also be relevant for the assessment of other redox reactive contaminants. Technetium re-oxidation essays showed that the fast oxidation of marcasite is associated to the reduction of the remaining Tc(VII) in solution, which gives marcasite the potential of Tc natural remediation since it delays the re-oxidation of Tc(IV).

Publisher Summary This chapter illustrates the mandatory bacterial controls required to combat the damage to reservoirs. Microbiologically influenced corrosion (MIC) represents the most serious form of degradation that results in severe corrosion; iron sulfide formation; higher operating costs; and reduced revenue of oil production facilities, chemical processing plants, paper mills, ships, and water distribution networks. Thus, an effective control of bacteria responsible for these undesired effects is mandatory. Several biocides and nonbiocidal techniques to control bacterial corrosion are available. Procedures and techniques to detect bacteria have also been developed. A mathematical model for reservoir souring caused by the growth of sulfate reducing bacteria is also present. The model is a one-dimensional numerical transport model based on conservation equations and includes bacterial growth rates and the effect of nutrients, water mixing, transport, and adsorption of H2S in the reservoir formation. Chemical treatments for bacteria control represent significant cost and environmental liability. Because the regulatory pressure on the use of toxic biocides is increasing, more environmentally acceptable control measures are being developed.

Iron-based heterogeneous Fenton systems have been widely proposed for recalcitrant contaminants degradation. However, low efficiency of H2O2 decomposition and Fe(II)/Fe(III) recycling quite limited their applications. In this work, Co-doped iron sulfide (FeS) was successfully prepared through a modified hydrothermal method, and characterized by XRD, FESEM, HRTEM, XPS and BET. With Co(II) substitution, FeS structure transformed from pyrrhotite to mackinawite. The 10% Co-FeS was highly effective in H2O2 activation toward Rhodamine B (RhB) degradation. The pseudo first-order kinetic constant of 10% Co-FeS was 0.323 min−1, which was 31.4 and 85 times higher than that of CoS2 and FeS, respectively. Quenching experiments and EPR analysis illustrated that •OH was the dominant radicals for RhB degradation and the role of Co(II) in H2O2 direct decomposition was negligible. Batch experiment suggested that the excellent catalytic performance of 10% Co-FeS were ascribed to: (i) Co incorporation into FeS structure facilitated electron transfer between S species and Fe3+, thus accelerating Fe(II)/Fe(III) conversion on the surface, and (ii) more active sites were exposed. The Co-doped FeS exhibited high stability with low Fe/Co leaching and great recyclability. This novel strategy brought potential insights to develop highly efficient catalyst like metal sulfides for wastewater treatment.

Iron pyrite (FeS2) exhibits dynamic thermal stability and represents an ideal model system to probe complex phase transformations in materials. At elevated temperatures, the sublimation of S atoms from the FeS2 lattice results in a phase transformation to one of the many polymorphic forms of pyrrhotite, i.e., from Fe1-XS (where 0 ≤ X

Bioelectrochemical removal of Cr(VI) and consequent renewable energy generation from wastewater is a promising technology. However, slow reaction kinetics, expensive catalysts, and hydrophobic binders remain a significant challenge for the commercialization of this emerging technology. In the present study, for the first time, graphite felt modified with iron sulfide wrapped with reduced graphene oxide (FeS@rGO) nanocomposites were used as a cathode in a dual-chamber microbial fuel cell (MFC) for concurrent Cr(VI) reduction and power generation. The MFC with FeS@rGO nanocomposites (MFC-FeS@rGO) exhibited 100% Cr(VI) removal efficiency for the concentration of 15 mg/L and also acquired a high reduction rate of 1.43 mg/L/h, which was approximately 4.6 times higher than MFC-blank. MFC-FeS@rGO delivered the maximum power density of 154 mW/m2, and it was 328% high as that of MFC-blank (36 mW/m2). High cathodic coulombic efficiency for MFC-FeS@rGO (61 ± 0.8%) indicated that the substantial amount of charge produced by exoelectrogens was mainly consumed for Cr(VI) reduction. Overall improved electrochemical performance of MFC-FeS@rGO was attributed to the high conductivity, low internal resistance, and better reaction kinetics of FeS@rGO nanocomposites. This study has demonstrated the highest reduction rate and high power production compared with previous studies, which have used very high concentrations of Cr(VI). Hence, it is expected that current findings will help to scale up the simultaneous Cr(VI) reduction and power generation from real wastewater.

A Colombian metallurgical coke was modified in its surface chemistry and was used as support of iron sulfide catalysts for direct coal liquefaction. The modification was made by treatments with diluted oxygen and HNO3 at different conditions. Changes in surface chemistry were studied by determining the point of zero charge (PZC), the isoelectric point (IEP), thermogravimetric analysis (TGA), temperature programmed decomposition-mass spectrometry (TPD-MS), Diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) and nitrogen adsorption at 77 K. The results show that the materials obtained have a wide range of functional groups incorporated in a different proportion and quantity. The textural parameters indicate that treatment with diluted oxygen increases the surface area and incorporates micropores while the samples treated with HNO3 maintain the textural properties of the original material. The catalysts were also characterized by Raman spectroscopy. It was found that impregnation with the iron sulfide precursor does not significantly affect the Raman characteristics of the support. Additionally, XRD analysis shows smaller pyrite crystallites in the coke enriched with oxygenated groups of phenol and lactone indicating better dispersion of the active phase. The amount of oxygen chemisorbed per gram of catalyst shows that both, oxygen and nitric acid treatments, improve the relative dispersion of the active phase. It was found that the presence of the catalysts increases the conversion and yields towards oils and gases with respect to those of the tests without catalysts. Cokes modified by dilute oxygen gaseous treatment contain surface phenol and lactone groups and present the highest yield to oils. Ministerio de Economía y Competitividad ENE2017-82451-C3-3-R

Sour corrosion has been a major problem for the oil and gas industry for more than half a century. Despite comprehensive research efforts, prediction and mitigation of localized corrosion in pipelines and process facilities remain challenges that require further research. The current understanding and knowledge gaps of sour corrosion mechanisms are discussed in this chapter, including the effects of iron sulfide layers, elemental sulfur, steel microstructure, and other critical parameters.

Corrosion in solutions of acidic gases, notably carbon dioxide and hydrogen sulfide, is very important in oil and gas production and can be expected to become important in processes for the sequestration of carbon dioxide. Carbon dioxide exhibits an equilibrium between dissolved CO 2 and carbonic acid, and this effectively buffers the hydrogen ion concentration, such that the rate of hydrogen evolution is much higher than for a solution of a strong acid with the same pH. Corrosion in CO 2 solution can be modeled using conventional electrochemical kinetic theory, and the results are in good agreement with experimental observations. Corrosion in H 2 S solution is less well understood, but models can be developed based on the premise that corrosion occurs through surface films of iron sulfide.

Inorganically driven fouling of metal heat-transfer surfaces employed in crude oil refining operations is not well understood. The object of this study is twofold: First, we systematically elucidate the time-dependent mechanism of the interrelated carbonaceous and sulfidic build up that occurs at high temperatures on a metal surface (540 °C metal temperature, 250 °C oil bath temperature). Second, we demonstrate that additions of 0.5, 1.3 and 5.7 vol% thiophene (C 4 H 4 S) cause a 2×, 10×, and 20× reduction in the fouling factor after a 1400 min exposure. Analytical techniques including TEM, SEM–EDX, FIB, Auger electron spectroscopy and XRD were employed to detail the fouling phenomenology for a heated stainless steel wire immersed in atmospheric bottoms fraction crude oil, exposed for 1–1400 min. A key microstructural observation is the transformation of the wire’s as-received near-surface textured austenitic grain structure into a micron scale (e.g. ∼10 μm at 1400 min) highly porous inner-sulfide/chromium oxide bilayer composite. Additionally, we observe significant localized sulfidic attack into the bulk of the metal. During testing, an iron sulfide (pyrrhotite Fe (1 − x ) S) corrosion product forms almost instantaneously at the metal surface, followed by coke formation around its periphery at longer times. This temporal sequence, combined with the observation that the thicker regions of the foulant are clearly associated with detached plumes of the sulfide, leads us to argue that the sulfide is essential for promoting organic fouling. This is brought about by the sulfide’s action as a potent dehydrogenation catalyst that drives the transformation of pitch to coke. We hypothesize that the tremendous fouling inhibition effect of the thiophene originates from its adsorption onto the sulfide surfaces, thereby blocking the dehydrogenation reactions.

International audience; Influence of sulfidogenic bacteria, from a North Sea seawater injection system, on the corrosion of S235JR carbon steel was studied in a flow bioreactor; operating anaerobically for 100 days with either inoculated or filtrated seawater. Deposits formed on steel placed in reactors contained magnesium and calcium minerals plus iron sulfide. The dominant biofilm-forming organism was an anaerobic bacterium, genus Caminicella, known to produce hydrogen sulfide and carbon dioxide. Open Circuit Potentials (OCP) of steel in the reactors was, for nearly the entire test duration, in the range − 800 < E(OCP)/mV (vs. SCE) < − 700. Generally, the overall corrosion rate, expressed as 1/(Rp/Ω), was lower in the inoculated seawater though they varied significantly on both reactors. Initial and final corrosion rates were virtually identical, namely initial 1/(Rp/Ω) = 2 × 10− 6 ± 5 × 10− 7 and final 1/(Rp/Ω) = 1.1 × 10− 5 ± 2.5 × 10− 6. Measured data, including electrochemical noise transients and statistical parameters (0.05 < Localized Index < 1; − 5 < Skewness < − 5; Kurtosis > 45), suggested pitting on steel samples within the inoculated environment. However, the actual degree of corrosion could neither be directly correlated with the electrochemical data and nor with the steel corrosion in the filtrated seawater environment. Further laboratory tests are thought to clarify the noticed apparent discrepancies.

It has been proposed that blending of Navan Conglomerate Group Ore (CGO) with Pale Beds Ore (PBO), the latter which floats well in isolation, results in sub-optimal Pb recovery with increased abundance of pyrite reporting to the concentrate and increased abundance of galena reporting to the tails. QEMSCAN data indicate that poor liberation of galena particles is not the primary cause of sub-optimal recovery of galena. Rather, principal component analysis (PCA) of time of flight secondary ion mass spectrometry (ToF-SIMS) reveals that chemically altered surface species interfere with the selectivity and recovery of froth flotation indicating that there is some poisoning of galena mineral surfaces particularly with Fe-containing species possibly leading to loss of recovery. Analysis of the Pb-circuit cleaner tails indicates Pb-species association with sphalerite surfaces, as was observed for the flotation feed and rougher tails but with insufficient induced hydrophobicity by Pb–collector interaction for flotation. A small population of relatively clean galena surfaces is also observed which may result from low bubble–particle collision efficiency or insufficient liberation. Fine-grained framboidal pyrite is the main diluting phase in the cleaner concentrate and is likely present due to entrainment. The presence of framboidal pyrite in CGO is of particular significance as its large surface area increases the rate of galvanic interaction with other metal sulfide minerals. We propose that increased abundance of refractory framboidal pyrite in CGO is the critical factor affecting the performance of the Navan Pb flotation circuit rather than purely high pyrite abundance. Irish Research Council Boliden Tara Mines Ltd Enterprise Partnership Scheme PhD scholarship

Corrosion in solutions of acidic gases, notably carbon dioxide and hydrogen sulfide, is very important in oil and gas production and can be expected to become important in processes for the sequestration of carbon dioxide. Carbon dioxide exhibits an equilibrium between dissolved CO2 and carbonic acid, and this effectively buffers the hydrogen ion concentration, such that the rate of hydrogen evolution is much higher than for a solution of a strong acid with the same pH. Corrosion in CO2 solution can be modeled using conventional electrochemical kinetic theory, and the results are in good agreement with experimental observations. Corrosion in H2S solution is less well understood, but models can be developed based on the premise that corrosion occurs through surface films of iron sulfide.

Iron is the most abundant metal in the universe. Chemically pure iron is obtained by the reduction of pure iron oxide using hydrogen. This article briefly describes the physical and chemical properties of iron. In the field of applied electrochemistry of iron, corrosion, electrochemical machining, electrodeposition, and power sources are of utmost economic importance. Electrochemistry of iron with special emphasis on power sources, namely, nickel–iron, silver–iron, iron–air, lithium–iron sulfide, lithium-ion and super-iron batteries, capacitors, and fuel cells, is also briefly discussed.

Publisher Summary This chapter presents a study in which permeable reactive barriers, composed of zero valent iron (ZVI), were installed and operated at U.S. Department of Energy sites located at the Y-12 Plant in Oak Ridge, Tennessee, and at the uranium mill tails repository near Durango, Colorado. The ZVI medium was intended to remove select toxic solutes, especially uranium (U), from contaminated groundwater. Core samples from these barrier installations were sampled after prolonged exposure to contaminated groundwater. Core samples were protected from exposure to the ambient atmosphere by packaging them in argon-purged containers for shipment to an off-site laboratory. The aim was to protect media from exposure to oxygen, which could alter the valence state of the treatment medium itself and of the metal deposits therein. Samples were then subjected to a battery of analytical techniques, including X-ray photoelectron spectroscopy (XPS), a surface-sensitive technique that can be used to determine the average valence state of elements. One of the major findings of this study was that ZVI media had extensive surface deposition of various mineral phases including amorphous iron sulfide and iron oxyhydroxide, and crystalline calcite and gypsum. U was present within the media at somewhat modest levels and the U on the ZVI surface was at least partially oxidized.

The surface oxidation of metal sulfides in air and aqueous solution is of central importance in mineral separation and environmental control of acid mine drainage. Mechanisms of oxidation, dissolution and surface restructuring have been extensively studied using XPS. High binding energy components in S 2p XPS spectra have been attributed to metal-deficiency, formation of polysulfide S n 2− , elemental sulfur and electronic defect structures (ie Cu(I)/ZnS). The assignment of these components in S 2p XPS spectra has, however, left significant uncertainties particularly in the formation of SS bonding in polysulfide species requiring confirmation from other surface analytical techniques. The use of static ToF-SIMS has provided a new avenue for identification of these species and their development in oxidation of the sulfide surfaces. For the iron sulfides, there is a systematic change in the FeS 2 /FeS fragment ratio from troilite (FeS) through pyrrhotite (Fe 1−x S) to pyrite (FeS 2 ) with ratios varying from 0.59, 1.2 to 32 respectively. Similarly, high ratios for FeS n /FeS are found for pyrite compared with pyrrhotite and troilite mirrored in the S n /S fragment ratios. Changes in surface oxidation, represented in atomic concentrations and S 2p XPS spectra, are seen in the ToF-SIMS signals for S n /SO n ratios in the same iron sulfide sequence. These mass markers, reflecting increased SS bonding, increase in surfaces after oxidation giving further confidence in XPS assignment to polysulfide species. Freshly cleaved galena PbS surfaces reacted in pH8 aqueous solution for increasing periods of time have also shown a systematic increase in S n /S ratios with increasing at.% of oxidised S n 2− species from XPS spectra. Statistical analysis of oxidised galena has shown that the ratios 206 PbO + / 206 Pb + and 208 PbOH + / 208 Pb + directly reflect the degree of oxidation of the surface lead species whilst the O − /S − , S − /total — ion yield and SO 3 − /S − are the best measures for following the oxidation of sulfur species. Results from these ratios suggest that initial air oxidation takes place predominantly on the S sites rather than Pb sites but, in solution at pH9, both sites are oxidised. The ToF-SIMS results appear to directly reflect the surface chemistry of the metal and sulfur species and are not consistent with recombination or fragmentation of secondary neutral or ionic species. The results strongly suggest increasing polymerisation of SS species with increasing oxidation in accord with the XPS assignment to polysulfide of increasing chain length.

Publisher Summary Corrosion of metals in aqueous solutions and soils is essentially oxygen corrosion with a cathodic partial reaction. Estimation of corrosion results from the consideration of characteristics of the soils and of the installed object. A relatively high degree of corrosion arises from microbial reduction of sulfates in anaerobic soils. Here, an anodic partial reaction is stimulated and the formation of electrically conductive iron sulfide deposits also favors the cathodic partial reaction. In addition, corrosion susceptibility in aqueous media is assessed on the basis of the rating numbers that are different from those of soils. An increased occurrence of corrosion is generally found only in the splash zone. In particular, severe local corrosion can occur in tidal regions due to the intensive cathodic action of rust components. Because cathodic protection cannot be effective in such areas, the only possibility for corrosion protection measures in the splash zone is increased thickness of protective coatings. Anodic enhancement gives rise to high corrosion susceptibility. The danger due to the contact with foreign cathodic structures must be treated just as seriously as the danger from emerging stray currents.

Publisher Summary Coal liquefaction refers to the formation of lower molecular weight products from coal. In so-called first-stage direct coal liquefaction (DCL), there may be relatively low yields of products in the oil range, suitable for liquid fuels; upgrading to high-quality liquid fuels is typically conducted in various steps. The aerosol technique can be used to prepare DCL catalysts. These are mixtures of pyrite and pyrrhotite in intimate contact, present in the form of small, hollow particles and the corresponding fragments. The relative amount of pyrite and pyrrhotite depends on the preparation conditions; the type of nonstoichiometric pyrrhotite also depends on these parameters. The catalysts prepared to date have been characterized by a variety of techniques. X-ray diffraction (XRD) yields gross results of the species present. Auger electron spectroscopy (AES) and X-ray analysis (EDX); yield atomic ratios on the surface and the bulk, respectively. He pycnometry yields information on the density of the particles, and therefore on the extent of the shell-like behavior of the particles. Average sizes are obtained by laser light-scattering and by TEM. The two measurements do not agree, due to clumping effects expected in the presence of the solvent used for the light-scattering measurements.

The oxidation of pyrrhotite and pyrite initiates a series of weathering reactions in aggregates extracted from the Mont Palau quarry (Barcelona, Spain). The lithotypes enclosing the sulfides, however, play an important role in controlling the progress of weathering: whilst expansive hydrated Fe-sulfates characteristic of acidic environments formed in the black shales, the neutralizing capacity of calcite dissolution prevents the formation of these harmful mineral phases in the limestones. This study received financial support from the Spanish Government CICYT PAT91-0992 project.

Publisher Summary This chapter discusses the catalysis of iron sulfide catalyst, which is affected by the sulfursulfursulfur to iron (S/Fe) ratio, the activity increased with pyrrhotite formation and accelerated by the presence of excess sulfur. Activity of pyrite for phenanthrene hydrogenation and activity of natural ground pyrites for coal liquefaction decreased with storage under air. The NEDOL process of a coal liquefaction pilot plant of 150 t/d uses pyrites as one of the catalysts for the first stage, because iron sulphide (FeS 2 ) has high activity and is low in price. The relationship between the oxidation of pyrite and the activity and selectivity for the hydrogenation of 1-methylnaphthalene is discussed in the chapter. Effects of the oxidation of pyrite catalyst under air for the hydrogenation of 1-methylnaphthalene are investigated under coal hydro-liquefaction conditions. Pyrite is oxidized to ferrous sulfates at room temperature under atmospheric oxygen, and the catalytic activities of FeS 2 oxidized decreased by increasing the storage time. The deactivation of pyrites is enhanced by raising the atmospheric temperature. It is proved that pyrites deactivated by air oxidation are reactivated by the addition of sufficient sulfur to the reaction system.

Publisher Summary This chapter explores the liquefaction of Wandoan coal by lt/d Process Supporting Unit. In a study described in the chapter, Wandoan coal from Australia was used as the raw coal, synthetic iron sulfide was the catalyst, and a 50–50 mixture of creosote oil and anthracene oil was the initial solvent. The liquefied oil yield increased until the temperature rose to 450°C and decreased at a temperature higher than this. The gas yield increased with the increasing reaction temperature and sharply increased over 450°C. The residue yield decreased with the increasing reaction temperature. These results suggest that the liquefied oil yield reached its maximum at 450°C because, although the decomposition of coal progressed with the rising temperature, the gasification reaction became more accelerated over 450°C. Although the increase in reaction pressure suppressed the generation of gas and increased the liquefied oil yield, the effect of the reaction pressure on the product yield was small when the partial pressure of hydrogen exceeded a certain value.

The sulfidation of carbon-supported iron oxide catalysts was studied by means of in-situ Mössbauer spectroscopy at temperatures down to 4.2 K. The catalysts were dried in two different ways and then sulfided in a flow of 10% H2S in H2 at temperatures between 293 and 773 K. Thiophene hydrodesulfurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The iron content varied from 1.1 to 9.0 wt.-% Fe. In the oxidic catalyst precursors, dried in air at 293 K, nitrate anions were still present. These anions could be removed by means of an additional H2 treatment up to 393 K. This treatment also led to an increase in the interaction strength between the iron (III) oxide particles and the carbon support. It is shown that the transition from iron (III) oxide to iron sulfide proceeded through two intermediate phases, viz. an oxidic high-spin Fe2+-phase and FeS2. A correlation between the HDS activity per mole of iron and the mean iron sulfide particle size was observed, with the mean particle size being dependent on the preparational treatments of the oxidic catalyst precursors.

A sample of bauxite, containing 28% Fe 2 O 3 , was activated by hydrothermal treating and molybdenum impregnation, and tested as a catalyst in the hydro-treating of a heavy petroleum residue in a bench-scale trickle-bed reactor. The thermally treated bauxite exhibited a significant demetalation activity, attributable to iron sulfide. After addition of a small amount of molybdenum (4.7% MoO 3 ) to the activated bauxite, hydrodesulfurization was strongly promoted. At highest conversion, hydrogen consumption was less than 100 Nm 3 /m 3 of oil. NMR analysis of the products showed a limited saturation of aromatic rings. Hydrocracking, significant in the presence of activated bauxite, was somewhat reduced by molybdenum addition.

Catalysis of coal hydroliquefaction (HL) was studied over highly dispersed and non porous iron sulfide catalysts (non stoichiometric pyrrhotites). The active interface between the bulk catalyst and the reactional mixture was built during liquefaction and a coke layer was deposited on the Fe1-xS surface. During HL the first role of this coke was to prevent the sintering of the catalyst particles. Two kinds of coke were identified according to the mode of sulfidation and introduction of the catalyst into the autoclave. The catalytic roles of the interface were discussed in terms of solvent rehydrogenation, pool of active hydrogen (spillover effect) and stabilization of radicals.

Massive sulfide deposits and sulfide-bearing veins in Saudi Arabia show a wide range in δ 34 S values from very negative to strongly positive and cover almost the entire range observed for ore deposits in nature. Massive iron sulfide deposits that have very negative values (Wadi Wassat and Wadi Qatan) formed as syngenetic sedimentary deposits in stagnant, euxinic basins. Deposits that have large positive values (Khnaiguiyah and Al-Amar) were formed by seawater hydrothermal systems.

Δημοσίευση σε επιστημονικό περιοδικό Summarization: This paper aims to present the aspects of oxidation of pyrite and arsenopyrite in the sulphidic spoils in Lavrion and to assess the environmental impact of this process. Sulphidic spoils, under the combined action of atmospheric oxygen, water and bacteria are oxidised and toxic elements are released and migrate to surrounding areas contributing to widespread soil contamination and severe deterioration in the quality of surface and underground waters. The critical factors which control the generation of acidic waters are availability of oxygen and water, temperature, bacterial activity and rate of oxygen diffusion through the pores in the upper zones of spoils. Special emphasis will be given in the oxidation of sulphidic spoils at Lavrion, Greece, where the generation of acidic waters causes widespread contamination. This study is focused in the first part on the preferential oxidation of arsenopyrite. Flotation products containing pyrite and arsenopyrite were subjected to bacterial leaching tests at 3% w/v pulp density and the degrees of oxidation were calculated and compared to with previous experimental studies. These results provided the basis to assess the behaviour of the above minerals in waste stockpiles. Moreover, and in order to assess the oxidation and precipitation mechanisms, several samples were collected up to a depth of 20 cm from the surface from the same spoils profile, where successive layers of oxidation products were present and characterised chemically and mineralogically. The above information is critically evaluated for the determination of the environmental impact of the oxidation of sulphide phases in spoils. Presented on: Minerals Engineering