Amounts Of Carbonate Minerals Research Articles

Carbonation reaction properties and reaction mechanisms of red mud under different carbon dioxide pressures

The carbonation utilization of solid waste such as red mud is an important strategy to deal with greenhouse gas emission control. To explore the carbonation reaction properties of red mud particles under different CO2 curing pressures, experiments were designed. The results show that in the range of 0–14 bar, as the CO2 curing pressure increases, the carbonate content in the carbonation product gradually increases and becomes stable. When the CO2 pressure increases to 18 bar, the amount of carbonate minerals will further increase. The pore change characteristics of red mud particles before and after carbonation are not significant, and no obvious carbon accumulation is observed on the surface of the particles. The carbonation of red mud particles is a liquid phase reaction, and the carbonation products are mainly deposited in the solution. The CaCO3 produced by carbonation is mainly calcite and aragonite types. The relevant results can provide reference for the carbonation utilization of red mud.

Antimony and arsenic contamination in water from antimonite mineralization: a case study from Turhal (Tokat, Northern Turkey)

The sources and fate of antimony (Sb) and arsenic (As) in water resources around antimonite (a.k.a. stibnite) deposits is of great concern due to their adverse effects on the environment and human health. The aim of this study was to determine geochemical compositions of gangue/ore material and water samples collected in and around the antimonite deposits located near Turhal (Tokat, Northern Turkey). Turhal antimonite deposits, recognized as the largest in Turkey, are hosted in pre-Upper Jurassic low-grade metamorphic rocks where the antimonite ore is mainly composed of stibnite and quartz. Quartz is also the dominant gangue mineral, with minor amounts of carbonates. The ore samples contain high concentrations of Sb (27.98 − 60.83 wt.% as Sb2O3) and As (3453 − 5010 ppm). The gangue material contains significant amounts of As (529 ppm), Cr (664 ppm), and Ti (256 ppm). Water samples collected from the study area are characterized by slightly alkaline pH (6.48–8.40) and low Eh (–46 to –5 mV) with electrical conductivity values ranging between 571 and 1607 µS cm−1. There is a significant trace element contamination in the aquifer system, especially in water samples collected from the areas hydrologically downgradient of antimonite deposits, where concentrations (in µg L−1) reach up to 271.6 for Sb, 429.4 for As, and 2203 for B. There is a high risk of toxicity for the livestock, as well as the human population consuming their products, since Sb and As contaminated springs in the region are used for watering farm animals.

Size reduction of oil shale by attrition scrubbing and its effect on kerogen content

ABSTRACT Size reduction of oil shale is an essential process that allows the liberation of organic-rich constituents from inorganic portions to prepare the oil shale for further beneficiation processes. Grinding by conventional methods was impractical and led to technical and economic problems. In this study, the size reduction of the oil shale was conducted by attrition scrubbing process which seems to be an effective process for cleaning the kerogen surface and its disengagement from associated mineral matter. The statistical design was used to study the significance of soaking time, attrition time, and pH on the product in terms of kerogen and LOI contents. The results indicated that the attrition time is the most significant parameter as the wt% of −2.36 mm reaches about 75% after 120 min of attrition. The effect of pH is insignificant unless the ore has an appreciable amount of carbonate minerals. It is worth mentioning that the kerogen content was improved from 10% to 14% by attrition in acidic media. However, the fine fractions had a low-percentage of loss-on-ignition due to the presence of clay.

Influencing factors and fracability of lacustrine shale oil reservoirs

Abstract Shale oil reservoirs need fracturing in order to achieve commercial productivity. A key factor influencing the fracturing process is shale fracability, which is strictly dependent on rock fabric. In this study, we focused on the lacustrine shale oil reservoirs located in Dongying Sag and in the Northern Jiangsu Basin. Through X-ray mineral diffraction, rock mechanics, and P- and S-wave velocity tests, we analyzed the mineral components and mechanics of different shale lithofacies, as well as the influence of these factors on shale fracability. Based on the results of these analyses, we proposed a new method for the evaluation of lake shale oil reservoir fracability. The experimental results showed that the macrostructure, mineral content, lithology, and the presence of microfractures in the shale are the main factors affecting its brittleness. Shales with lamellar and sheet-like structures have relatively high Young's modulous or lower Poisson's ratios; under these conditions, netted fractures are easily formed during fracturing. The fracture toughness of carbonate minerals in shales is strong. An appropriate amount of carbonate minerals seemed to increase the shale brittleness; however, an excessive amount increased its cohesiveness, hindering the initiation and propagation of fractures. Felsic minerals are characterized by high brittleness, a characteristic that favors shale fracability; on the other hand, clay minerals and organic matter are highly plastic, a characteristic that hinders fracturing transformations. Due to their macrostructure and composition, lamellar clayey limestones (dolomite), lamellar clayey siltstones, layered calcareous (dolomitic) siltstones, sheet-like clay-containing siltstones, and flaggy carbonate-containing siltstones are expected to be easily fractured. In addition, the presence of microfractures seemed to reduce the overall fracture toughness of the rock: they penetrated artificial fractures, enhancing rock fracability. Taking into account the fracture toughness of carbonate minerals and the plastic effect of organic matter, we proposed a new formula for the calculation of the brittleness index, based on the mineral component method. The brittleness indices obtained through the proposed formula were linearly correlated with those calculated through the rock mechanics parameters method. Overall, our results indicate that the silty lithological successions occurring in the study area should be the easiest to fracture, followed by the calcareous (dolomitic) and clayey or organic-rich lithological successions. This study is of guiding significance for evaluating the fracability of different lithofacies in lacustrine shale oil reservoirs. Especially, the new proposed brittleness index containing the plastic effect of organic matter can correctly evaluate the actual brittleness of organic-rich shale.

Impacts of diffusive transport on carbonate mineral formation from magnesium silicate-CO2-water reactions.

Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, (13)C NMR spectroscopy tracked the inorganic carbon transport and speciation in situ. The data were compared with the output of reactive transport simulations that accounted for diffusive transport processes, aqueous speciation, and the forsterite dissolution rate. All three approaches found that the onset of magnesium carbonate precipitation was spatially localized about 1 cm from the opening of the forsterite bed. Magnesite was the dominant reaction product. Geochemical gradients that developed in the diffusion-limited zones led to locally supersaturated conditions at specific locations even while the volume-averaged properties of the system remained undersaturated.

Efficient oxidative carbonylation of iPrOH to oxalate catalyzed by Pd(II)–PPh3 complexes using benzoquinone as a stoichiometric oxidant

The catalytic system trans-[PdBr2(PPh3)2]/NEt3/PPh3/LiBr is highly active and selective in the oxidative carbonylation of iPrOH to the corresponding oxalate using benzoquinone (BQ) as a stoichiometric oxidant. The oxalate is formed together with minor amounts of carbonate and acetone. The influence of each component in the catalytic system is discussed together with the influence of the concentration of BQ, reaction time, temperature and CO pressure. NEt3 neutralizes the acid released in the catalytic cycle, thus favouring the formation of a dicarboalkoxy intermediate. Added PPh3 reacts with benzoquinone giving betaine, which is a base that contributes to a further enhancement of the catalytic activity. The Br− anion might coordinate the Pd(0) which is formed in the product forming step thus stabilizing it against decomposition and making its reoxidation easier and reentering into the catalytic cycle. The catalytic activity depends slightly only on the concentration of BQ, suggesting that either uncoordinated BQ is not involved in the slow step of the catalytic cycle or that BQ is strongly coordinated in these species. The catalytic activity toward oxalate increases upon increasing the concentrations of NEt3 and PPh3, whereas the selectivity toward carbonate and the formation of acetone remains practically constant. The increase of the pressure of CO has a similar effect, except that the formation of acetone is suppressed. It is suggested that at relatively high pressure of CO, a pentacoordinated species may be formed so that there is no place for any interaction between palladium and the C–H bond before the β-H elimination. Instead there is a nucleophilic intrasphere attack of the alkoxy ligand onto a CO ligand. After catalysis the precursor trans-[PdBr2(PPh3)2] has been detected, together with trans-[PdBr(COOiPr)(PPh3)2] and [Pd(BQ)(PPh3)2]. PPh3 remains coordinated to the palladium centre during catalysis. A BQ- and halides-assisted catalytic cycle is proposed. In this cycle, the reoxidation occurs through the release of a proton from an ammonium salt or a phosphonium salt, which are formed during the catalysis, with reformation of the catalyst precursor.

Cambrian rocks and faunas of the Wachi La, Black Mountains, Bhutan

AbstractThe Pele La Group in the Wachi La section in the Black Mountains of central Bhutan represents the easternmost exposure of Cambrian strata known in the Himalaya. The group contains a succession of siliciclastic rocks with minor amounts of carbonate, the uppermost unit of which, the Quartzite Formation, bears age-diagnostic trilobite body fossils that are approximately 493 Ma old. Trilobite species includeKaolishania granulosa, Taipaikia glabraand the new speciesLingyuanaspis sangae.A billingsellid brachiopod,Billingsellacf.tonkiniana, is co-occurrent. This fauna is precisely correlated with that of a specific stratigraphic horizon within the upper part of theKaolishaniaZone, Stage 9 of the Cambrian System, Furongian Epoch of the North China block, and thus represents the youngest Cambrian sedimentary rocks yet known from the Himalaya. The faunal similarity suggests proximity between North China and the Himalayan margin at this time. This unit was deposited in a predominantly storm-influenced shelf and shoreface environment. U–Pb geochronological data from detrital zircon grains from the fossil-bearing beds of the Quartzite Formation and strata of the underlying Deshichiling Formation show grain age spectra consistent with those from Cambrian rocks of the Lesser and Tethyan Himalaya in Tibet, India and Pakistan. These data support continuity of the northern Gondwanan margin across the Himalaya. Prominent peaks of approximately 500 Ma zircons in both the Quartzite and Deshichiling formations are consistent with the Furongian (late Cambrian) age assignment for these strata. The presence of these relatively young zircon populations implies rapid post-cooling erosion of igneous bodies and subsequent deposition which may reflect the influence of a widespread Cambro-Ordovician orogenic event evident in the western Himalaya.

Characteristics of soure region and tectonic implications of Early Indosinian Weiya gabbroic rock, eastern Tianshan mountains

Based on the detailed petrographic study, the characteristics of source region of the Weiya gabbro and tectonic implications were studied. The results show that the gabbroic rock consists mainly of gabbro, with less amount of ultra-mafic rocks. The ultra-mafic rocks show cumulate texture and are gradually transitional contact with gabbro, indicating that they are cumulate products of parental magma. The ultra-mafic rocks consist mainly of spinel periodite and spinel clinopyroxenite. The former is mainly composed of olivine (65%–70%), spinel (10%–15%), hornblende (5%–10%) and phlogopite (5%–10%); the latter consists mainly of clinopyroxene (70%–80%), spinel (15%–20%) and phlogopite (0–10%), with minor amounts of carbonate (0–2%). No olivine or orthopyroxene is found. The gabbro is composed mainly of clinopyroxene (35%–40%), plagioclase (An 55–65, 40%–45%), hornblende (5%–15%), with variable amounts of carbonate (0–5%). Petrographic observations show that the source region of the Weiya gabbroic rock is water-rich due to intensive intra-continental A-type subduction occurring in this region during late Permian to early Triassic.

Predation by jellyfish on large and emergent zooplankton: Implications for benthic–pelagic coupling

Stable carbon isotopes were used to determine the contribution of emergent demersal zooplankton to the diet of the scyphozoan jellyfish Catostylus mosaicus at Smiths Lake, New South Wales, Australia. A preliminary study in 2004 indicated that there was no difference in the δ 13C of ectodermal tissue and mesoglea of the medusae. In 2005, medusae and zooplankton present during the day and night were sampled and isotopic signatures were modelled using IsoSource. Modelling indicated that: (1) mollusc veligers and copepods sampled during the day contributed <13% of the carbon to the jellyfish; (2) copepods sampled at night contributed up to 25%; and (3) the large, emergent decapod Lucifer sp. contributed 88–94%. We hypothesised, therefore, that medusae derive most of their carbon from emergent species of zooplankton. In 2006, sampling done in 2005 was repeated three times over a period of 4 weeks to measure short-term temporal variation in isotopic signatures of medusae and zooplankton, and emergent demersal zooplankton was specifically sampled using emergence traps. Short-term temporal variation in isotopic signatures was observed for some taxa, however, actual variations were small (<1.5‰) and the values of medusae and zooplankton remained consistent relative to each other. IsoSource modelling revealed that mysid shrimp and emergent copepods together contributed 79–100% of the carbon to the jellyfish, and that the maximum possible contribution of daytime copepods and molluscs was only 22%. Jellyfish apparently derive most of their carbon from emergent zooplankton and by capturing small numbers of relatively large taxa, such as Lucifer sp. or mysid shrimp. Small but abundantly captured zooplankton (such as mollusc veligers) contribute only minor amounts of carbon. Jellyfish have a major role in the transfer of carbon between benthic and pelagic food webs in coastal systems.

Geochemical signatures of the Namibian diatom belt: Perennial upwelling and intermittent anoxia

A gravity core from the Nambian diatom belt (83 m water depth) was analyzed for major (Al, Ca, Fe, K, Mg, P, Si, Ti) and minor elements (Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Mn, Mo, Ni, Rb, Re, Se, Sr, Tl, U, V, Zn, Zr), as well as C and S. The major element geochemistry is dominated by the contribution of biogenic phases (opal and minor amounts of carbonate and phosphate), whereas terrigenous components of eolian and fluvial origin form only a minor admixture of &lt;15%. Examination of the Fe/S/C‐relationship reveals a completion of pyritization close to the sediment‐seawater interface. Higher than average shale Fe/Al ratios reflect the presence of highly reactive iron oxides in terrigenous source material from the Namibian desert and suggest little loss of Fe within the OMZ. The low total Fe content likely represents an important factor responsible for sporadic H2S eruptions. The upwelling system off Namibia may be regarded as an intermediate system, combining high productivity typical for upwelling areas with the sporadic presence of H2S in the water column. By examining the source‐sink relationship of individual trace metals, two different trends are discernible: Mo, Re, and U accumulate following seawater availability, whereas Ag, Cd, Cu, Ni, Tl, and Zn require a biological preconcentration step. Trace metals like As, Ba, Cr, Se, and V show an intermediate behavior. Metal enrichment is favored by high interstitial water sulfide concentrations close to the sediment‐seawater interface, leading to slightly elevated Co contents as opposed to extremely low Mn/Al ratios, reflecting the overall reducing character of the Namibian system. Maximum contents of Cu, Ni, and Zn are significantly lower than those reported previously. This may in part be related to the absence of fecal material and a stronger dilution by biosiliceous material at this location compared to the seaward flank of the diatom belt.

Characterization and dewatering of fine coal tailings by dual-flocculant systems

Characterization of fine coal tailings using a variety of techniques reveal that it is composed of 30% clay minerals (kaolinite and illite), 23% muscovite, 26% quartz and 20% coal with little amount of carbonate minerals. Various flocculant combinations and their order of additions are utilized to understand the ability of dual flocculant systems on dewatering of these fine coal tailings. Settling rate and turbidity are used as criteria for screening and measuring the performance of anionic, cationic and nonionic flocculants. Dual flocculation of tailings has been tested with the aim of identifying if the synergy reported for mono-disperse systems is also valid for multicomponent systems. While the nonionic–cationic combination leads to the highest settling rates, the lowest turbidity values were obtained when using the anionic–nonionic combinations. The mechanism of interaction of dual polymers with particle surfaces and their synergy are discussed with the help of settling and turbidity data. The turbidity values obtained in mono-flocculation tests using nonionic and cationic flocculants and those made with dual flocculation combinations reveal that this kind of flocculant combinations play an unfavorable role in the flocculation of coal preparation plant tailings though there are contrary systems reported in the literature.

Atomic Layer Deposition of Photocatalytic TiO2 Thin Films from Titanium Tetramethoxide and Water

AbstractTitanium dioxide thin films were grown by atomic layer deposition (ALD) at 200–400 °C from a new titanium precursor, titanium tetramethoxide, and water. As compared with other titanium alkoxides studied earlier, titanium methoxide shows the highest stability with respect to thermal decomposition, and can thus be used over the widest range of temperatures. The films deposited at 250 °C and above were polycrystalline with the anatase structure, whereas those deposited at 200 °C were amorphous. Except for the film deposited at 200 °C, the films contained only minor amounts of carbon and hydrogen residues. The crystalline films were shown to have photocatalytic activity in decomposing both methylene blue in aqueous solution, and solid stearic acid coated on the film surface.

Thermal decomposition of the natural hydrotalcites carrboydite and hydrohonessite

A combination of high-resolution thermogravimetric analysis (HRTGA) coupled to a gas evolution mass spectrometer combined with infrared emission spectroscopy has been used to study the thermal decomposition of two Australian hydrotalcites carrboydite (Ni 6Al 2(SO 4,CO 3)(OH) 16·4H 2O) and hydrohonessite (Ni 6Fe 2(SO 4,CO 3)(OH) 16·7H 2O). High-resolution thermal analysis shows the decomposition takes place in five steps. Each step is related to the loss of water, hydroxyl units, carbonate and sulphate. Infrared emission spectroscopy clearly identifies the presence of these molecular species and the temperature at which they are lost. Minor amounts of carbonate are observed in the minerals. Water is in two states in the structure, namely weakly hydrogen bonded and strongly hydrogen bonded. The symmetry of the sulphate anion is reduced through this hydrogen bonding.

Spinel fibers from carboxylate precursor

A spinel precursor was synthesized from a 1:2 stoichiometric mixture of Al(O 2CH) 3·3H 2O and Mg(O 2CCH 3) 2·4H 2O dissolved in H 2O with stabilizing additives. The precursor, as well as individual compounds were characterized using TGA, DTA, DRIFTS and XRD techniques to establish decomposition profiles. During pyrolysis, Mg(O 2CCH 3) 2·4H 2O decomposes first to an amorphous oxide contaminated with minor amounts of carbonate. At 300°C, rock salt (MgO) crystallizes. The spinel precursor behaves like a separate compound and decomposes directly to crystalline spinel at ≈600°C without any evidence of phase separation. The spinel precursor is easily extruded or hand drawn to form well-defined green fibers. Extruded green fibers (20 μm dia.) were pyrolyzed at 300°C/2 h/air to remove carboxylate ligands, and then heated at 15°C/min to 1500°C/2 h/air to sinter. The mechanical strength of these fibers was evaluated using a bending test method. The final fibers are ≈10 μm in dia., with 1·2±0·4 μm grain size and offer an average bend strength of 1·0±0·4 GPa. ©

Evolution of a Permian carbonate platform to siliciclastic basin: Indochina Plate, Thailand

In Thailand, during the Permian, an extensive carbonate platform developed on the margin of the Indochina Plate and near to a coeval and deeper siliciclastic-dominated marine basin. This basin separated the Indochina Plate, to the east, from the Shan Thai Plate to the west. Sedimentation in the area of both platform (Pha Nok Khao Platform) and basin (Nam Duk Basin) was ended by a late Permian/early Triassic orogenic event that caused closure of the Palaeo-Tethys ocean. Tectonism has controlled the pattern of platform sedimentation and supplies of carbonate and clastic sediments into the basin area. The Pha Nok Khao Platform developed on an extensive distally steepened ramp-like margin along which carbonates and siliciclastics accumulated. Adjacent to this platform, to the west, the Nam Duk Basin received coeval hemipelagic siliciclastics and minor amounts of carbonates. Biostratigraphic evidence, based on foraminiferal assemblages, suggests an early to middle Permian age equivalence between platform and basin lithofacies. The platform strata are exposed along the Loei fold and thrust belt in northeast Thailand and basin strata are exposed within the Phetchabun fold and thrust belt in central Thailand, respectively. The two belts extend in a north–south direction and their rocks exhibit extensive karstification. On the basis of seismic data, platform lithologies extend further east in the subsurface, beneath the continental sediments of the Khorat Group into Kampuchea and Laos. Facies groups of the platform environments include restricted platform, platform interior, and outer platform. The facies groups of the basin environments include basin margin and basin plain. Minor layers of volcaniclastics and green coloured tuffites are interbedded with both the platform carbonate layers and basinal pelagic layers, suggesting active volcanism during sedimentation. The carbonate lithofacies of the shallow platform to the east (in the Loei Fold Belt) grade westward into turbidites (in the Phetchabun fold belt), and include shales and sandstones with minor carbonates. Farther to the west they pass into hemipelagic lithofacies of shale and carbonate. Lithologies and fauna of the limestones suggest tropical to subtropical climate during deposition.

Carbonates in fractures of Martian meteorite Allan Hills 84001: petrologic evidence for impact origin.

Carbonates in Martian meteorite Allan Hills 84001 occur as grains on pyroxene grain boundaries, in crushed zones, and as disks, veins, and irregularly shaped grains in healed pyroxene fractures. Some carbonate disks have tapered Mg-rich edges and are accompanied by smaller, thinner and relatively homogeneous, magnesite microdisks. Except for the microdisks, all types of carbonate grains show the same unique chemical zoning pattern on MgCO3-FeCO3-CaCO3 plots. This chemical characteristic and the close spatial association of diverse carbonate types show that all carbonates formed by a similar process. The heterogeneous distribution of carbonates in fractures, tapered shapes of some disks, and the localized occurrence of Mg-rich microdisks appear to be incompatible with growth from an externally derived CO2-rich fluid that changed in composition over time. These features suggest instead that the fractures were closed as carbonates grew from an internally derived fluid and that the microdisks formed from a residual Mg-rich fluid that was squeezed along fractures. Carbonate in pyroxene fractures is most abundant near grains of plagioclase glass that are located on pyroxene grain boundaries and commonly contain major or minor amounts of carbonate. We infer that carbonates in fractures formed from grain boundary carbonates associated with plagiociase that were melted by impact and dispersed into the surrounding fractured pyroxene. Carbonates in fractures, which include those studied by McKay et al. (1996), could not have formed at low temperatures and preserved mineralogical evidence for Martian organisms.

Influence of gas phase chemistry on the properties of hydrogenated amorphous silicon and silicon–carbon alloys grown by HACVD

We report on the properties of a-/ μc-Si:H and a-SiC:H grown by hydrogen assisted chemical vapour deposition (HACVD) of different gas mixtures depending on various deposition parameters. Silicon films were grown by using gas mixtures of H 2/SiH 4 and H 2/Si 2H 6, whereas silicon–carbon films were deposited using H 2/CH 4/SiH 4, H 2/C 2H 4/SiH 4, H 2/C 2H 4/Si 2H 6 and H 2/SiH 3CH 3. The composition and bulk properties of the deposited films are investigated by FT–IR and Raman, XPS, RBS, SEM, conductivity measurements and UV/VIS. As proved by Raman and conductivity measurements, μc-Si:H films are obtained using total pressures P tot smaller than 5.5 Torr. Above a certain total pressure P tot (6.5 Torr) a-Si:H films are obtained. As shown by SEM, the amorphous films exhibit a rather smooth surface morphology, whereas the μc films show a grain structure. In the pressure range from 5.5 to 6.5 Torr, a phase transition occurs. Carbon-rich a-SiC:H-films (up to X C=0.7) are obtained using C 2H 4 as carbon source, whereas the use of CH 4 leads to films with minor amounts of carbon. Films based on CH 3SiH 3 exhibit a nearly stoichiometric composition and a high degree of chemical order. The composition is influenced by several gas phase parameters, e.g., total pressure P tot, substrate temperature T s and the mole fraction of the reaction gases. A gas phase kinetic simulation has been carried out and the validation of the model is tested by comparison with experimental results of silicon film deposition. As a result, the pressure P calc, at which the concentration of disilene is a hundred fold higher than that of atomic hydrogen, and the characteristic pressure P * of the μc-/a-Si:H phase transition plotted as a function of Φ(SiH 4)/ Φ tot behave very similar. These results were used to extend the model to the deposition of silicon–carbon films in order to correlate and to discuss the material properties of the silicon–carbon system.

98/00058 Effect of magnetite size on the coal purification process in a fluidized bed

Characterization of fine coal tailings using a variety of techniques reveal that it is composed of 30% clay minerals (kaolinite and illite), 23% muscovite, 26% quartz and 20% coal with little amount of carbonate minerals. Various flocculant combinations and their order of additions are utilized to understand the ability of dual flocculant systems on dewatering of these fine coal tailings. Settling rate and turbidity are used as criteria for screening and measuring the performance of anionic, cationic and nonionic flocculants. Dual flocculation of tailings has been tested with the aim of identifying if the synergy reported for mono-disperse systems is also valid for multicomponent systems. While the nonionic–cationic combination leads to the highest settling rates, the lowest turbidity values were obtained when using the anionic–nonionic combinations. The mechanism of interaction of dual polymers with particle surfaces and their synergy are discussed with the help of settling and turbidity data. The turbidity values obtained in mono-flocculation tests using nonionic and cationic flocculants and those made with dual flocculation combinations reveal that this kind of flocculant combinations play an unfavorable role in the flocculation of coal preparation plant tailings though there are contrary systems reported in the literature.

Influence of surface treatments developed for oral implants on the physical and biological properties of titanium. (I) Surface characterization.

We present an investigation of the physico-chemical surface properties of commercially pure titanium coverslips which were submitted to various treatments designed to optimize their topography in view of application in oral implantology. The surface microroughness, chemical composition and water wettability were analyzed on titanium coverslips prepared by mechanical polishing, acid attack in HCl/H2SO4, after mechanical polishing or sandblasting, and titanium plasma-spray. The chemical composition has been measured by Auger electron spectroscopy. The treatments have no major influence on the surface chemical composition and all the samples display a composition approaching that of TiO2 with minor amounts of carbon, sulfur, silicon and calcium as impurities. The roughness has been measured by scanning force microscopy on an area of 20 microns x 20 microns on each sample. Polished titanium is smooth (peak-to-valley roughness 81 nm), whereas the acid-attacked surfaces exhibit a micro-roughness in the microns range (2100 nm for polished and acid attacked; 3600 nm for sandblasted and acid attacked) which is quite reproducible over large areas of the sample. The acid attacked samples present a subsurface layer which contains hydrogen below the native passivating oxide layer. Water wettability measurement shows that all surfaces are hydrophobic with a slightly higher contact angle for the acid attacked surfaces. The different treatments analyzed in this study essentially influence the surface roughness by preserving the chemical composition and the wettability properties of titanium native oxide surface layer.

Mineralogical Composition of the Highvale Mine Coals and Its Impact on Plant Performance

Abstract Mineralogical analysis of the Highvale Mine coals using X-ray diffraction (XRD) shows quartz, kaolinite, illite, and feldspars to dominate. Minor amounts of carbonate and unknown hydrate minerals are also present, and most minerals reported by XRD have been verified by scanning electron microscopy-energy-dispersive X-ray spectrometry (SEM-EDX) on selected samples using back-scattered electron imaging on coal pellets, The coal ash indices show the Highvale Mine coals to have low to medium propensity to form slagging or fouling deposits in the boilers. The relationship between ash content of mill samples and opacity in the electrostatic precipitators (ESPs) is not clear. However, there appears to be a correspondence between ash resistivity and ESP performance. As resistivity is a function of ash chemical composition, the differences in ash composition, notably in its Fe2O3 content, may have contributed to the increase in opacity recorded for seam 1. The production of submicron particles, via fragme...