Ultra clean coal production by microwave irradiation pretreatment and sequential leaching with HF followed by HNO3

The goal of this project was to develop and test an innovative coal cleaning process to reduce the ash content of coal and produce ultra clean coal (UCC). Coal samples that were prepared from concentrates of Iran's Zirab and Tabas coal preparation plants were found to have initial ash contents of 8.31 and 10.36%, respectively. These coals were demineralized with the combination of microwave irradiation pretreatment and dual acid leaching processes with HF followed by HNO₃ in a batch reactor. For samples that were microwaved and leached with HF, the reduction in ash ranged from 22 to 76% and from 22 to 82% for Zirab and Tabas coal samples, respectively, depending on leaching conditions. Microwave irradiation pretreatment had a positive effect on demineralization with HF, especially for the coarse size fractions. For the fine size fractions, reduced leaching times were found to enhance the effect of microwave irradiation. The microwave-irradiated, HF-leached product was leached further using a 1.4 M HNO₃ solution at a leaching temperature of 65 °C to remove fluoride sediments and pyritic sulfur. The ash content of the Zirab coal was reduced from 2.57 to 0.69% by leaching with the HNO₃ solution for 1 h. The ash content of the Tabas coal was reduced from 2.44 to 0.39% by leaching with the HNO₃ solution for 3 h. The results show that microwave irradiation can be considered as a pretreatment process in the chemical leaching of coal to produce UCC.     

Demineralization of a UK bituminous coal using HF and ferric ions

A UK bituminous coal has been used to study demineralization by two-stage chemical leaching. The first-stage uses hydrofluoric acid (HF) at 65 °C and reduces the ash content from 5.30 wt% to 1.37 wt% by mainly removing Al and Si containing minerals. Subsequent leaching by ferric ions decreases the ash content further to 990 ppm by removing most of the pyrite and fluorides formed during the HF leaching. Calorific value of the coal shows no change following leaching, which suggests no oxidation is occurring to the coal carbonaceous matrix. The mercury and sulfur contents after the two-stage leaching sequence decrease by 40% and 26%, respectively.     

Phosphorus-containing activated carbon as acid support in a bifunctional Pt–Pd catalyst for tire oil hydrocracking

A bifunctional Pt–Pd catalyst supported on phosphorus-containing activated carbon has been prepared, characterized and tested in the hydrocracking of a hydrotreated tire pyrolysis oil. The product has a very interesting composition: 48–78 wt% naphtha and 19–42 wt% diesel fractions, with moderate amounts of aromatics (< 40 wt%) and sulfur (< 250 ppm). The challenge was to prepare a stable, porous, selective and acid carbonaceous catalyst from a waste (olive stone), which has been confirmed from the catalytic properties and product distribution point of view. In fact, phosphate groups in the activated carbon are stable hydrocracking sites, with comparable performance to that of the acid sites present in amorphous SiO₂–Al₂O₃.     

Effect of pressure on corrosion of Inconel 625 in supercritical water up to 100 MPa with acids or oxygen

The corrosion behavior of Inconel 625 in supercritical water was investigated under high pressure (30–100 MPa at 400 °C) with the addition of acids (5 mmol/kg CH₃COOH or 0.5 mmol/kg HNO₃) or O₂ (2.5–250 mmol/kg). Ni and Cr ions were the main dissolved metal ions in the effluent. The Ni ion concentration showed no clear dependence on the O₂ concentration or pressure in the experiment with O₂; the concentration was lower than 0.05 ppm. The concentration increased with pressure up to 0.09 ppm and 3 ppm (at 100 MPa) in the experiment with CH₃COOH and HNO₃, respectively. The Cr ion concentration increased with the O₂ concentration and pressure; the maximum value of the concentration was about 0.5 ppm. The Cr ion concentration was lower than 0.01 ppm in the experiment with CH₃COOH, while the concentration was considerably higher in the experiment with HNO₃: the concentration increased with pressure up to 0.87 ppm at 100 MPa. The effect of pressure on the corrosion behavior of Inconel 625 was discussed using potential-pH diagrams, metal oxide solubilities, pH, and equilibrium of ionic reactions. Pressure dependence of the metal ion concentrations was analyzed using a model with water density as a parameter; the log–log plots revealed a linear relationship.     

Chemistry of cement hydration in polymer-modified pastes containing lead compounds

The role of polymeric additives on the hydration process of cement pastes admixed with a lead compound (Pb₃O₄) was investigated. Three series of pastes were prepared: the reference series, mixing water with Ordinary Portland Cement (OPC), and two series in which whether a styrene–butadiene rubber latex or a superplasticiser based on acrylic-modified polymer was added to the pastes. For each series, 5 and 10 wt% of Pb were mixed with the pastes. Phase analysis and microstructural characterisation were carried out by means of X-ray powder diffraction and SEM–EDX. Thermogravimetric analysis was performed to monitor the hydration degree of the three pastes; indeed, quantitative determination of portlandite and calcite was performed.Dynamic leach tests were performed on solidified monoliths to evaluate the effective immobilisation of Pb₃O₄. After 384 h leaching, excellent results were obtained by pastes mixed with superplasticiser that showed a cumulative release of Pb equal to 0.62 mg/l for samples containing 5 wt% of Pb, and equal to 0.84 mg/l for samples bearing 10 wt% of Pb.     

Gas phase oxidation as a tool to introduce oxygen containing groups on metal-loaded carbon nanofibers

Oxygen containing groups were introduced, onto carbon nanofibers (CNFs) that were previously loaded with palladium, using HNO₃ vapor. Using traditional liquid-phase oxidations this is not possible due to severe metal leaching. For the samples oxidized using HNO₃ vapor temperature programmed desorption and X-ray photoelectron spectroscopy revealed the presence of two major classes of oxygen containing groups, i.e. carboxylic acid groups which are thermally stable up to 300 °C and less acidic (e.g. phenol) and basic groups which were stable up to 700 °C. The amount of acidic oxygen containing groups introduced by this gas-phase treatment ranged from 0.1 to 0.3 mmol/g, as determined by titration. The latter amount is comparable to that introduced by traditional liquid-phase treatment in 65% HNO₃ on bare CNFs. Transmission electron microscopy and H₂-chemisorption measurements show a gradual increase of the average metal particle size from 2.1 nm for the starting Pd/CNF to 4.5 nm for Pd/CNF treated for 75 h in HNO₃ vapor indicating that the extent of sintering with gas-phase treatment is limited. Elemental analysis showed that no leaching occurred upon gas-phase oxidation, whereas 90% of the metal was lost with a liquid-phase reflux HNO₃ treatment.     

Coal liquefaction with in situ impregnated Fe2(MoS4)3 bimetallic catalyst

Daliuta subbituminous coal (DL), loaded with Fe₂(MoS₄)₃ bimetallic catalyst, was liquefied in a 50 ml micro-autoclave with tetralin as solvent at 440 °C, initial hydrogen of 6.0 MPa, soaking time of 30 min in attempt to produce one to four ring aromatic chemicals. The catalytic effects of in situ impregnated Fe₂(MoS₄)₃ in water solution with and without surfactant were investigated in terms of coal conversion, oil+gas yield and the yields of aromatic, aliphatic and polar compound fractions in the oil. The conversion, oil+gas, aromatics and polar compound yields of DL coal, loaded with 1 wt% daf FeMo of Fe₂(MoS₄)₃ bimetallic catalyst, were 78.2, 70.5, 20.8 and 16.7 wt% daf, respectively, which were higher than those with 1.0 wt% Fe (based on daf coal) of Fe₂S₃ (62.6, 54.2, 13.4, 13.2 wt% daf, respectively) or 1.0 wt% Mo of ammonium tetrathiomolybdate (70.8, 63.2, 16.7, 14.1 wt% daf, respectively) alone under the same conditions. When the catalyst was impregnated on coal in surfactant solution, the coal conversion and product yields were further increased.     

Low temperature catalytic steam gasification of HyperCoal to produce H2 and synthesis gas

HyperCoal is an ultra clean coal with ash content <0.05 wt%. Catalytic steam gasification of HyperCoal was carried out with K₂CO₃ at 775–650 °C for production of H₂ rich gas and synthesis gas. The catalytic gasification of HyperCoal showed nearly four times higher gasification rate than raw coal. The major gases evolved were H₂: 63 vol%, CO: 6 vol% and CO₂: 30 vol%. Catalyst was recycled for four times without any significant rate loss. The partial pressure of steam was varied from 0.5 atm to 0.05 atm in order to investigate the effect of steam pressure on H₂/CO ratio. The H₂/CO ratio decreased from 9.5 at 0.5 atm to 1.9 at 0.05 atm. No significant decrease in gasification rate was observed due to change in partial pressure of steam. Gasification rate decreased with decreasing temperature and become very slow at 650 °C. The preliminary results showed that HyperCoal, an ash less coal, could be a potential hydrocarbon resource for H₂ and synthesis gas production at low temperature by catalytic steam gasification process.     

Sulfur variability and element geochemistry of the No. 11 coal seam from the Antaibao mining district,China

The roof, bottom and 24 coal ply samples were collected by finely partitioning No. 11 coal seam from Antaibao mining district, Shanxi, China in terms of lithotypes. Proximate and sulfur analyses, ICP-AES, ICP-MS, AFS, XRD, SEM–EDX techniques were used on these samples, in order to investigate the vertical variability and origin of sulfur and also the geochemistry of major and trace elements in the seam. The weighted mean content of total sulfur of the 24 coal plies is 2.4 wt%, belonging to the medium-sulfur coal, but there are great differences in the contents of total sulfur and forms of sulfur between the 24 plies: total sulfur content >3.0 wt% for 5 plies, organic sulfur content >1.0 wt% for 13 plies and pyritic sulfur content >2.0 wt% for 4 plies. It is found that the differences were mainly caused by the degree of marine influences and the contents of clay minerals as well as the organic matter. The ply 21 has an abnormal high content of inorganic sulfur (pyritic sulfur 9.45 wt% and sulfate sulfur 5.97 wt%). This was caused by the presence of bauxite minerals-bearing kaolinite in the underlying ply 22 blocking the further infiltration of sulfate from the overlying plies during the deposition. The seam is dominated in kaolinite and, to a lesser extent, in pyrite, and there also exist minor amounts of szomolnokite, diaspore, boehmite, calcite, siderite, dolomite, magnesite, feldspar, gypsum. Szomolnokite and gypsum possibly resulted from the oxidation of pyrite. The seam is greatly characterized by finely-grained pyrite concentrating in cutinite. Hazardous trace elements Hg, Pb and As are mainly concentrated in pyrite, so that they can be partially removed by physical coal cleaning with an aim of removal of sulfur, while thalassophile elements Br, Ca, Cl, Mg and Sr, are clearly associated with the organic sulfur, reflecting that their contents can be decreased by coal blending means due to a partial organic affinity.     

Mullite whiskers derived from kaolin

Short mullite whiskers prepared by firing compacts of kaolin and NH₄Al(SO₄)₂·12H₂O powders, with a small addition (0.8, 1.5 wt%) of NaH₂PO₄·2H₂O, in air 1300 and 1400 °C for 15 h have been characterized in terms of whisker morphology, composition and structure. Relatively uniform whisker shaped crystals grew within the silicate glass matrix. After chemically leaching the glass matrix with HF solution using a microwave heating source, the resulting whiskers were exposed as isolated crystals and exhibited an aspect ratio of >17 (～0.5 μm in diameter). The mullite whiskers had a composition of 51.06 mol% Al₂O₃ and 48.94 mol% SiO₂, with an orthorhombic crystallographic structure.     

Influence of TiO2 additive on sintering temperature and microwave dielectric properties of Mg0.90Ni0.1SiO3 ceramics

(1-x)Mg_0.90Ni_0.1SiO₃-xTiO₂ (x = 0, 0.01, 0.03, 0.05) ceramics were successfully formed by the conventional solid-state methods and characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), and their microstructure and microwave dielectric properties systematically investigated. It was observed that when TiO₂ content increased from 0 to 5 wt%, the Q_uf_o of the sample decreased from 118,702 GHz to 101,307 GHz and increases the τ_f value from −10 ppm/°C to +3.14 ppm/°C accompanied by a notable lowering in the sintering temperature (125 °C). A good combination of microwave dielectric properties (ε_r ∼ 8.29, Q_uf_o ∼ 101,307 GHz and τ_f ∼ −2.98 ppm/°C) were achieved for Mg_0.90Ni_0.1SiO₃ containing 3 wt% of TiO₂ sintered at 1300 °C for 9 h which make this material of possible interest for millimeter wave applications.     

Effect of pre-oxidation on the porosity development in a heavy oil fly ash by CO2 activation

The effect of pre-oxidation on the porosity evolution in heavy-oil fly ash subjected to activation with CO₂ has been investigated. After preliminary acid leaching, used to reduce the mineral matter content, the leached fly ash has been oxidised in air at 250 °C for 36 h. Pyrolysis was conducted on the unoxidised and oxidised leached fly ash at 900 °C for 2 h and the resultant chars were activated with CO₂ at 900 °C for different times. The activated samples have been characterised as regards the surface area and the pore volume.The pre-oxidation enhances the porosity development mainly in terms of mesoporosity leading to obtain activated products with higher surface area (about 270 m²/g at a 40% burn-off).     

Microwave dielectric properties of low-fired Li2MnO3 ceramics co-doped with LiF–TiO2

Li₂MnO₃ ceramics co-doped with 2 wt% LiF and x wt% TiO₂ (x=0, 3, 5, 7, 10) were prepared by solid-state reaction for low-temperature co-fired ceramics (LTCC) applications. The sintering temperatures of Li₂MnO₃ ceramics were successfully lowered to 925°C due to the formation of a LiF liquid phase. Their temperature stability was improved by doping with TiO₂. A typical Li₂MnO₃-2 wt% LiF-5 wt% TiO₂ sample with well-densified microstructures displayed optimum dielectric properties (ε_r=13.8, Q×f= 23,270 GHz, τ_f=1.2 ppm/°C). Such sample was compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications in wireless communication systems.     

Effect of pre-oxidation on the porosity development in a heavy oil fly ash by CO2 activation

The effect of pre-oxidation on the porosity evolution in heavy oil fly ash subjected to activation with CO₂ has been investigated. After preliminary acid leaching, used to reduce the mineral matter content, the leached fly ash has been oxidised in air at 250 °C for 36 h. Pyrolysis was conducted on the unoxidised and oxidised leached fly ash at 900 °C for 2 h and the resultant chars were activated with CO₂ at 900 °C for different times. The activated samples have been characterised as regards the surface area and the pore volume.The pre-oxidation enhances the porosity development mainly in terms of mesoporosity leading to obtain activated products with higher surface area (about 270 m²/g at a 40% burn-off).     

Properties and vibrational spectra of magnesium phosphate glasses for nuclear waste immobilization

The leaching behavior and structure of magnesium phosphate glasses containing 45–55 mol% MgO incorporated with simulated high level nuclear wastes (HLW) were studied. The leach rate of the waste glasses decrease with increasing of the simulated HLW content. The gross leach rate of the glass waste form containing 50 mol% MgO and 45 mass% simulated HLW is of the order of 10⁻⁶ g/cm² day at 90 °C, which is small enough as compared with the corresponding release from a currently used borosilicate glass waste form. The isolated ions such as dimeric (P₂O₇)⁴⁻ and monomeric (PO₄)³⁻ ions increase upon as increasing the incorporating amount of the simulated HLW. The changes in properties can be attributed to the structure changes owing to the incorporation of the simulated HLW.     

Preparation of separated and open end TiO2 nanotubes

Separated and open end TiO₂ nanotubes with large surface area and through-hole structure exhibit exciting functionalities in energy and environmental applications. In this study, TiO₂ nanotube membranes are created using high purity titanium sheets as raw materials by anodic oxidation at 100 V for 12 h in ethylene glycol+0.25 wt% NH₄F+5 vol% H₂O. The pore size of the nanotubes is 215 nm with uniform diameters. Close-packed TiO₂ nanotube arrays are separated by immersion in a 0.15 wt% HF water solution. With further dissolution by 40% HF water solution for 10 min, the barrier layer at the back of the TiO₂ nanotubes completely disappears and the nanotubes become open at both ends. This study offers a facile approach of making separated and open-end nanotubes for electrocatalytic purposes.     

Temperature stability and high-Qf of low temperature firing Mg2SiO4–Li2TiO3 microwave dielectric ceramics

In this work, a series of low-temperature-firing (1−x)Mg₂SiO₄–xLi₂TiO₃–8 wt% LiF (x = 35–85 wt%) microwave dielectric ceramics was prepared through conventional solid state reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that the Li₂TiO₃ phase was transformed into cubic phase LiTiO₂ phase and secondary phase Li₂TiSiO₅. Partial substitution of Mg²⁺ ions for Ti³⁺ ions or Li⁺Ti³⁺ ions increased the cell volume of the LiTiO₂ phase. The dense microstructures were obtained in low Li₂TiO₃ content (x ≤ 65 wt%) samples sintered at 900 °C, whereas the small quantity of pores presented in high Li₂TiO₃ content (x ≥ 75 wt%) samples sintered at 900 °C and low Li₂TiO₃ content (x = 45 wt%) sintered at 850 and 950 °C. Samples at x = 45 wt% under sintering at 900 °C for 4 h showed excellent microwave dielectric properties of ε_r = 10.7, high Q × f = 237,400 GHz and near-zero τ_f = − 3.0 ppm/°C. The ceramic also exhibited excellent chemical compatibility with Ag. Thus, the fabricated material could be a possible candidate for low temperature co-fired ceramic (LTCC) applications.     

Silver cofirable (Ca0.9, Mg0.1)SiO3 microwave dielectric ceramics with Li2CO3–Bi2O3 additive

The effects of Li₂CO₃–Bi₂O₃ (LB) additive on the microstructure, phase formation, microwave dielectric properties and applicability for low-temperature co-fired ceramics (LTCC) technology of (Ca_0.9Mg_0.1)SiO₃ (CMS) ceramics were investigated. The sintering temperature of the CMS ceramics was reduced from 1290 °C to 890 °C by the addition of LB. Secondary phases SiO₂ and Bi₄(SiO₄)₃ were detected when LB content was less than 9 wt%. Low melting point liquid phases were formed when LB content was 11–14 wt%. The Q_f value initially increased with the addition of LB and attained the maximum value for the 9 wt% LB-doped CMS ceramic. When the LB content exceeded 9 wt%, the Q_f value decreased because of the presence of liquid phase and abnormal growth of grains. ?_r of 6.92, Q_f of 27,600 GHz and τ_f of ?43.6 ppm/°C were obtained for 9 wt% LB-doped CMS ceramics sintered at 890 °C for 2 h. Also the ceramics can be well co-fired with Ag electrode.     

Microstructure and mechanical properties of Ti (C,N) based cermets reinforced with different ceramic particles processed by spark plasma sintering

The addition effect of different ceramic particles such as TiB₂, TiN and nano-Si₃N₄ on the microstructure and mechanical properties of TiCN-WC-Co-Cr₃C₂ based cermets, which are prepared by spark plasma sintering, was studied. Microstructural characterization of the cermets was done by scanning electron microscope. X-ray diffraction was performed to study the crystal structures. Mechanical properties such as hardness and fracture toughness were measured for the different developed cermets. The hardness and fracture toughness of the TiCN-WC-Co-Cr₃C₂ cermets without TiN, TiB₂, and nano-Si₃N₄ were 8.4 GPa and 3.4 MPa m^1/2, respectively. It was found that 5 wt% TiB₂ addition alone improved the corresponding hardness and fracture toughness to 19.2 GPa and 6.9 MPa m^1/2, respectively. The addition of 5 wt% TiN, improved the hardness and fracture toughness to 16.7 GPa and 6.9 MPa m^1/2, respectively. With the combination of 5 wt% TiN and 5 wt% TiB₂, the hardness and fracture toughness were improved to 15.5 GPa and 6.6 MPa m^1/2, respectively. But, the addition of 5 wt% Si₃N₄ showed a balanced improvement in both hardness (17.6 GPa) and toughness (6.9 MPa m^1/2). Fracture toughness did not change much for all the above cermets with different ceramic inclusions.     

Direct mineralogical composition of a MgO-C refractory material obtained by Rietveld methodology

Magnesia-graphite refractory materials are used in large quantities in the steelmaking process. The chemical characterization of this type of refractories is an arduous task that requires a rigorous set of laboratory tests and analyses. In the present paper, proper characterization of magnesia-graphite refractories has been approached by X-ray powder diffraction combined with Rietveld methodology. The quantitative phase analysis of a MgO-graphite refractory has been 68.3 wt% of MgO, 8.1 wt% of graphite, 13.5 wt% of Al₂O₃, 4.4 wt% of SiC, 0.6 wt% of Si, 1.2 wt% of Al, 1.5 wt% of AlPO₄ and 2.4 wt% of silicone. These results have been checked and validated with those obtained by other analysis procedures used to determine the crystalline and non-crystalline phases present in these materials.