Characterization of sepiolite as a support of silver catalyst in soot combustion

Turkish sepiolite–zirconium oxide mixtures were applied as a support for the silver catalyst in a soot combustion. Sepiolite–Zr–K–Ag–O catalyst was characterized by XRD, N₂ adsorption, SEM, TPR-H₂ and EGA-MS. The combustion of soot was studied with a thermobalance (TG-DTA). The modification resulted in a partial degradation of the sepiolite structure, however, the morphology was preserved. The adsorption of N₂ of the modified sepiolite is a characteristic for mesoporous materials with a wide distribution of pores. The specific surface area S_BET equals 83 m²/g and the pores volume is 0.23 cm³/g. The basic character of the surface centers of sepiolite is indicated by CO₂ desorption (TPD-MS) at 170 °C and at about 620 °C due to a surface carbonates decomposition. The thermodesorption of oxygen at 650–850 °C indicates the decomposition of AgO_x phases at the surface. The presence of AgO_x phases is also confirmed by TPR-H₂ spectrum (low temperature reduction peak at 130 and 180 °C). The high-temperature reduction at about 570 °C is probably related to Ag–O–M phases on the support.The soot combustion takes place at T₅₀ = 575 °C. Without silver (sepiolite–Zr–K–O) T₅₀ = 560 °C but sepiolite modified with silver (sepiolite–Zr–K–Ag–O) undergoes the same process at T₅₀ = 490 °C.     

Use of zeolite-rich rocks and waste materials for the production of structural lightweight concretes

This paper aims at testing the use of mixtures constituted by natural zeolitized products and SiC-bearing industrial wastes (sludge deriving from polishing of porcelain stoneware tiles, hereafter DPM) for the production of lightweight expanded aggregates as constituents of structural and/or thermo-insulating lightweight concretes. Two commercial products have been used as zeolite natural source: Cab70 (Yellow facies of Campanian Ignimbrite) and IZclino (Turkish clinoptilolite-rich epiclastite). Different amounts of a calcareous material (Pozzano limestones — hereafter CP) from the Sorrento peninsula (Naples — Italy) were also added to a Cab70–DPM mixture. All raw materials were characterized by means of mineralogical (XRPD) and chemical (XRF) analyses. All the products and mixtures were tested from a technological point of view by means of fusibility and firing tests in order to evaluate the expanding properties. It was evidenced that the expansion of the mixture was deeply depending on the occurrence of SiC in the industrial waste. The addition of CP (10 wt.%) to the mixtures accounts for an even increased expansion, though this is accompanied by a worsening of the mechanical features of the material.These results along with literature data allowed to select 3 mixtures (70% Cab70–30% DPM, 70% IZclino–30% DPM, 60% Cab70–30% DPM–10% CP) and each of them was used for the preparation of 5 l of lightweight aggregates afterward employed for the manufacture of lightweight concretes. It was remarked that natural zeolitized materials mixed with DPM (30 wt.%) can provide lightweight aggregates with densities ranging between 0.8 and 1.0 g/cm³ suitable for the preparation of structural lightweight concretes. The addition to the mixture of CP (10 wt.%) produces less dense aggregates (0.6–0.7 g/cm³) potentially useful for the manufacture of thermo insulating lightweight concretes.     

Biodesulfurization of two Colombian coals with native microorganisms

A biodesulfurization process was carried out for two coals from the southwest of Colombia using a consortium of native microorganisms Acidithiobacillus ferrooxidans-like and Acidithiobacillus thiooxidans-like. Characterization techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM/EDX) and chemical analysis were used in order to establish the mineralogy of the process. The sulfur content in coals varies from 2.6% to 5.7%, and pyrite is the main sulphide present in the inorganic phase. Other minerals in the substrates include kaolinite, calcite, dolomite and quartz. An 85–95% reduction of pyritic sulfur and 31–51% of total sulfur in a period of 30 days were achieved, for a particle size of − 74 µm, 10% w/v pulp density and 30 °C.     

Influence of graphite and quartz addition on the thermo–physical properties of bentonite for sealing heat-generating radioactive waste

Bentonite is one of the most favored buffer materials for the deep geological disposal of waste in clay and granite formations all over the world. Buffer material, used to isolate heat emitting waste canisters, has to take up a strong heat load. This paper presents results of investigations on enhancing the heat conduction within the bentonite sealing. Admixtures of quartz and graphite accelerate the heat transfer into the host rock. Test samples consisting of different bentonite–quartz and bentonite–graphite mixtures were prepared. The thermal conductivity was determined as a function of admixture content, temperature, water content, and sample density within 35° to 140 °C at a uniaxial pressure of 2 MPa. The necessary conductivity could not be achieved with quartz, but the addition of graphite led to a suitable thermal conductivity. A set of equations was developed for the calculation of the thermal conductivity and the design of an engineered geotechnical barrier with heat conduction properties similar to those of the particular host rock.     

Dissolution kinetics of dehydroxylated nickeliferous goethite from limonitic lateritic nickel ore

The dissolution kinetics in 2 M H₂SO₄ of variously dehydroxylated nickeliferous goethites was investigated for five oxide-type lateritic nickel deposits. Goethite was the main constituent with minor amounts of quartz, talc, kaolinite and Mn oxides. Dissolution of Fe from heated materials followed the Kabai equation. There was a 9–34-fold increase in the Kabai dissolution rate constant (k) for samples heated at 340–400 °C due to both the increased surface area (1.5–2.6 fold) and higher density of structural defects (5–10 fold) in the variously dehydroxylated products. The presence of structural Al and Cr in goethite appears to reduce dissolution rate possibly through the greater M³⁺–OH, O bond strength relative to Fe³⁺, Ni²⁺–OH, O. Nickel showed congruent dissolution with Fe indicating that Ni was uniformly incorporated in the goethite structure. Pre-heating goethite to 600–800 °C for 30 min resulted in incongruent dissolution of Fe and Ni. It is postulated that some Ni is ejected from the neo-formed hematite structure and resides on the crystal surface or in voids. These results may contribute to the development of more efficient procedures for Ni extraction including heap leaching of lateritic nickel ores.     

Investigation of relaxation of nanodiamond surface in real and reciprocal spaces

The structure of a nanodiamond powder with an average grain size of 5 nm was investigated using large-Q neutron diffraction. Both Bragg scattering and PDF analysis were employed. The effect of annealing under vacuum at temperatures up to 1200 °C was studied. The studies lead to a tentative model of nanocrystalline diamond, where the core with a perfect diamond lattice is surrounded by a shell of compressed diamond lattice, and this core–shell structure is enveloped in a non-diamond carbon. The non-diamond envelope of nanograins, a “gas-like” carbon, is stable up to 1000 °C and transforms into a graphite phase (an onion-type structure) at about 1200 °C. The amount of non-crystalline carbon in the powder annealed below 1000 °C is about 10%. In the sample annealed at 1200 °C a graphite-type carbon, with a total of about 15% of sp² bonds is formed.     

Effects of heat treatment on the physical properties of lightweight aggregate from water reservoir sediment

Lightweight aggregates (LWAs) were produced from water reservoir sediment with added calcium oxide by employing four heat treatments, respectively, at temperatures in the range of 1170-1230 °C. The results show that LWAs produced at temperatures above 1200 °C meet European Union regulation EN-13055-1, which states that the unit weight of LWAs should be lower than 2000 kg/m³. The bulk density was easily lowered by extending the soaking time and increasing the heating rate. The ratio of strength to unit weight of the LWA produced at 1230 °C with a short soaking time and a fast heating rate was near that of a commercial product. The level of water adsorption was below 4%, which increased initially and then decreased due to pore connections and pore sealing. The formation of a glassy phase made the LWAs treated at higher temperature rough and sealed small pores (<0.1 mm) connected to the walls of large pores (>0.2 mm). The mineral phases of the LWAs were quartz, anorthite, and hematite.     

Mn-kaolinite synthesis under low-temperature hydrothermal conditions

Mn-kaolinite was hydrothermally synthesized, for the first time, using silicic acid, Mn-carbonate and aluminum nitrate mixed with aqueous solutions of KOH at 100–200 °C for 24–96 h. Without the addition of Mn-carbonate to silicic acid and aluminum nitrate mixture, no crystalline material could be synthesized by hydrothermal treatment up to 200 °C for 6 days. However, by the addition of Mn-carbonate to the above precursors, Mn-kaolinite was synthesized at both 100 and 200 °C for 1 or 2 days, indicating that Mn played an important role in the formation of kaolinite. At a reaction temperature of 100 °C, the Mn-kaolinite peaks became sharper with increasing reaction duration, as expected.     

A simple and effective process for fabrication of Gd0.1Ce0.9O1.95 solid electrolyte ceramics

Ce_0.9Gd_0.1O_1.95 ceramics were prepared using a simple and effective process in this study. Without any prior calcination, the mixture of raw materials was pressed and sintered directly. The reaction of the raw materials occurred during the heating up period by passing the calcination stage in the conventional solid-state reaction method. More than 99.5% of theoretical density was obtained for Ce_0.9Gd_0.1O_1.95 sintering at 1500–1600 °C. Fine grains (<1 μm) formed in pellets sintered at 1450 °C. The homogeneity of grains increased with the sintering temperature. The grains grew to >4.5 μm in pellets sintered at 1600 °C. The reactive-sintering process is proved to be a simple and effective method in preparing Ce_0.9Gd_0.1O_1.95 ceramics for solid electrolyte application.     

Preparation of Co–Al layered double hydroxides by the hydrothermal urea method for controlled particle size

In order to control particle size and the distribution, Co–Al layered double hydroxides were prepared from aqueous glycerol solutions of cobalt chloride and aluminum chloride by urea hydrolysis under hydrothermal conditions. Effects of the synthetic conditions including heating temperature and time, and glycerol/water ratio on the particle size and its distributions of Co–Al layered double hydroxide were discussed. Particle diameter was controlled from 1.0 (glycerol/water ratio = 10 g/40 mL) to 38.3 μm (glycerol/water ratio = 0 g/40 mL, heating at 50 °C for 150 days). Narrow particle diameter distribution as low as 20% coefficient of variation was achieved under optimized synthetic conditions (glycerol/water ratio = 10 g/40 mL, heating temperature < 80 °C).     

Spectroscopic and porosimetry studies to estimate the firing temperature of some archaeological pottery shreds from India

The present study aims to estimate the firing temperature of archaeological pottery shreds collected from the three archaeological sites namely Maligaimedu, Thiruverkadu and Palur in Tamilnadu state, India. The spectroscopic method Fourier Transform Infrared Spectroscopy (FT-IR) has been employed to find the lower limit of firing temperature of the archaeological pottery shreds by refiring the samples to four different temperatures from 200 °C to 800 °C. From the observation of the hydroxyl band and appearance/disappearance of octahedral sheet structure the firing temperature of the shreds has been estimated. The samples from Maligaimedu site named as MM1, MM3 and MM5, Thiruverkadu and Palur samples were fired to a temperature above 800 °C and the samples of Maligaimedu MM2, MM4 and MM6 were fired below 800 °C. Additionally, porosimetry measurements such as water absorption and mercury intrusion (MIP) were also carried out. The samples MM1, MM3, TK2–TK6, PL3 and PL5 were fired to a temperature less than 900 °C and the other samples to less than 1000 °C.     

Removal of the persistent pollutant chlorobenzene by adsorption onto activated montmorillonite

The potential of activated bentonite was assessed for adsorption of chlorobenzene from aqueous solution. The bentonite used was treated by chemical and thermal activation over 100–500 °C. The thermal activation increased the adsorption capacity more strongly than chemical activation which consists to acid and hydrogen peroxide treatment. The removal is dominated by adsorption at low initial concentrations and low temperatures and favourable in acidic media. The dependence of the adsorption on pH appears to be related to the solubility of chlorobenzene. Thermodynamic parameters such as ΔH°, ΔS°, ΔG° and Ea have been calculated. The adsorption process is spontaneous and exothermic in nature. The Freundlich isotherm described the adsorption data over the concentration range (20–270 °C).     

Pakistani bentonite in mortars and concrete as low cost construction material

A Pakistani bentonite, in “as is” (21 °C) and “heated” (150 °C, 250 °C, 500 °C, 750 °C and 950 °C) conditions, was incorporated in mortar cubes, concrete cylinders and concrete beams as a partial substitute for Ordinary Portland cement (OPC) and studied in detail. Results showed that OPC mortars and concrete containing 20% “as is” and 25% “heated to 150 °C” bentonite could be used as low-cost construction materials. They will also reduce energy consumption, preserve natural resources and solve environmental problems related to cement production as well as augment the durability and life cycle of the concrete structures.The X-ray diffraction patterns showed that bentonite possessed both crystalline and amorphous phases. The strength activity indices (SAI) after 7 and 28 days were higher than 75% for “as is” and “heated” bentonite, except for the 950 °C samples, which was below the ASTM C618 specified limit of 75%. The maximum SAI was shown by “150 °C heated” bentonite. The compressive strength data also showed similar results for OPC mortar cubes and concrete cylinders containing “150 °C heated” bentonite. When compared with the control mixture, the compressive strength values were the same as for mortar containing 25% bentonite as replacement of OPC. However, these values decreased in concrete initially and started to gain strength remarkably after 28 days. Resistance to sulphate attack and water absorption tests on mortar cubes soaked in 2% magnesium sulphate and 5% sodium sulphate solutions demonstrated consistent improvement as the bentonite content in them was increased. The modulus of rupture of all concrete beams decreased as the OPC substitution level by bentonite increased from 20% to 40%. Bond strength of OPC mortar containing 20% “as is” and 25% “heated to 150 °C” bentonite in brick prisms was almost the same as that of control mixture.     

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10^− 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10^− 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10²⁰ cm^− 3. Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.     

Non-invasive monitoring of water content and textural changes in clay-rocks using spectral induced polarization: A laboratory investigation

Seven well-characterized clay-rocks have been taken from three test sites to perform spectral induced polarization (SIP) measurements during desiccation of these samples. These test sites include (1) the Tournemire site (IRSN) located in south of France, (2) The Bure test site (ANDRA) located in west of France, and (3) the Super-Sauze earthflow located in south western of France. We dried the samples at ambient temperature followed by heating between 65 °C and 105 °C. The quadrature conductivity, at very low-frequency, was able to discriminate between the loss of free water from the macropores and the loss of water in the micropores associated with textural changes. The calcite and quartz grain size distributions had a significant effect on the low-frequency spectrum. The inversion of our SIP data demonstrated that the generalized Cole–Cole model is an appropriate empirical and practical model for monitoring changes in water content of clay-rocks.     

Pore structure development of in-situ pyrolyzed coals for pollution prevention in iron foundries

A protocol was devised for preparing pyrolyzed coals that could be made in-situ at foundries to capture volatile organic compound (VOC) emission. This pyrolysis created extensive micropore volume in lignite over a broad range of temperature and time; and could use waste heat from cupola exhaust gases by a heat-exchange tube. For foundry application, moderate porous carbon with relatively uniform pores over wide ranges of temperature and time would be more practical than highly porous activated carbon (AC) that requires narrowly-controlled operations. This pyrolysis protocol was developed in a thermogravimetric analyzer (TGA) and in a small tube furnace, while using lignite, bituminous coal, and anthracite. The lignite yielded the most pore volume; and this was relatively uniform (0.1–0.13 mL/g of pores) while temperatures were 600–900 °C, and times were 0–60 min. Smaller grain sizes yielded improved porosity; and this corresponded to more release of phenols and naphthalenes from smaller grains, as discerned by TGA–mass spectroscopy (MS). TGA–MS also revealed that improved pore development between 600–800 °C corresponded to the release of CO₂ and H₂O; and concurrently higher slurry pH linked to less oxygenated functionality. Adsorption of benzene was compared between the in-situ porous carbon and a commercial AC.     

Technological characterization and ceramic application of gravel pit by-products from middle-course Jarama river deposits (central Spain)

This work, unlike previous others, deals with ceramic products obtained exclusively from gravel pit by-products. The residues are originated from the sand and gravel washing process of middle-course Jarama river Quaternary sediments, located in Madrid region, central Spain. These natural aggregates allow an intense exploitation, because of quality (well-rounded quartzite) and reserves (up to 700×10⁶ m³), generating considerable waste volumes.Thirty silty–clay by-products, collected from seven gravel pits, have been tested at a laboratory scale. The mineralogical composition of these materials is mainly represented by phyllosilicates (muscovite-illite, smectite, kaolinite and chlorite), quartz and feldspars.For the technological characterization, six representative mixtures (M1 to M6) were designed combining suitable mineralogy and grain-size distribution of the 30 raw samples. A wide range of values was measured on mixture powders, determining specific surface (13–76 m² g⁻¹, BET method), methylene blue index (5–20) and Atterberg limits (W_l: 43–90; W_p: 25–38).Ceramic characterization was performed on extruded bodies, testing drying sensitivity (Bigot curves and Ratzemberger test). Smectitic content influences directly the parameters measured on dried bodies. This influence can be controlled by increasing the silty component, and the ceramic properties measured on these mixtures (M3, M4 and M5) get better: hygroscopicity (less than 2%), drying shrinkage (4–7 cm m⁻¹), keeping the bending strength above 5 MPa.Three maximum firing temperatures were studied: 850, 950 and 1050 °C. On mixtures fired at 950 °C, firing shrinkage is less than 4 cm m⁻¹, bending strength may reach 69 MPa and water absorption range from 23% to 0.5%. Efflorescence susceptibility is faint, and colour is red for all the samples, getting darker for increasing temperature.The positive results obtained in this set of preliminary tests drive to envisage new research programs, focused on testing these by-products on a semi-industrial scale, assessing the effective possibilities of using them as ceramic raw materials.     

Effect of mechanical activation on the rheology and casting performance of kaolin/talc/alumina suspensions for manufacturing dense cordierite bodies

Previous work studied the rheological behaviour of 40 vol.% slips of kaolin/talc/alumina mixtures with relative weight ratios of 40/43.8/16.2 for manufacturing cordierite foams. However, the manufacture of the corresponding dense bodies makes it necessary to reduce the starting particle sizes through intensive ball milling. The rheological behaviour and the slip casting performance of both milled and unmilled slips have been studied. Milling did not significantly change the rheological behaviour but served to improve the casting performance. Sintering tests and XRD analysis demonstrated that at 1250 °C some reflections of sapphirine, spinel, mullite and cristobalite can still be detected, as well as coarse quartz particles, but at 1280 °C and above the cordierite phase is practically the only phase detected whereas in the unmilled powder the coarse silica was detected even at 1350 °C. In contrast with unmilled slips, where a large porosity is always observed, milled slips lead to highly dense structures without remaining pores, as a consequence of the activation of the raw materials.     

Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants

The thermal stability of seven organically modified montmorillonites (‘organoclays’) has been investigated using differential thermal analysis, differential scanning calorimetry, and thermogravimetry in conjunction with X-ray diffractometry. Six organoclays were synthesised by replacing the interlayer inorganic cations, initially present, with quaternary phosphonium and ammonium surfactant cations. The samples modified with tetrabutylphosphonium (TBP), and butyltriphenylphosphonium (BTPP) ions have an appreciably higher thermal stability than the octadecyltrimethylammonium (ODTMA)-modified clays. Thus, in the case of TBP- and BTPP-modified montmorillonites, the onset temperature of decomposition is close to 300 °C. Samples modified with hexadecyltributylphosphonium (HDTBP) ions have a lower onset temperature of decomposition of 225 °C. In comparison, the onset temperature for ODTMA-montmorillonites (obtained at different concentrations of ODTMA-bromide) ranges from 158 to 222 °C, being highest where the concentration of intercalated surfactant is lowest. The onset temperature for a commercial alkylsilane-treated quaternary ammonium-modified organoclay (S-BEN N-400FP) is 207 °C. The basal spacing of the TBP- and BTPP-modified clays is 1.7–1.8 nm, indicating a monolayer arrangement of quaternary phosphonium ions in the interlayer space, while the value of 2.5 nm for HDTBP-montmorillonite indicates a more open structure. The ODTMA-modified samples have basal spacings ranging from 1.9 to 2.1 nm, indicative of a bilayer to pseudo-trilayer arrangement. The exceptionally high basal spacing of 3.4 nm for the S-BEN N-400FP organoclay might be due to interlayer penetration of organosilane hydrolysis products during synthesis. The thermal properties of organoclays are apparently related to the nature of the surfactants and their arrangement in the interlayer space of montmorillonite.     

Production of desiccants from Turkish bentonites

Representative samples of three Turkish bentonites were investigated with the aim of producing moisture adsorbents, so-called desiccants, of commercial grade: 1) Ca-bentonite from Lalapaşa–Edirne region (LLP), 2) Na/Ca-bentonite from Çankırı region (CNK), and 3) Na-bentonite from Reşadiye–Tokat region (RSD). The samples were composed of smectite and small amounts of quartz, feldspar, calcite and opal-CT and minor amounts of zeolite and dolomite. The clay mineral contents of the raw samples were estimated at 75–80% for LLP, 50–55% for CNK and 75–80% for RSD.The bentonites were upgraded by mineral processing techniques and modified by addition of calcium chloride. The effect of particle size, heat treatment conditions such as drying temperature and drying time were examined. A maximum moisture adsorption capacity of 17.1% was obtained after heating at 150–200 °C for LLP Ca-bentonite. The mixed bentonite (CNK) achieved a maximum moisture adsorption capacity of 8.3% at 105 °C and the Na-type bentonite (RSD) exhibited the lowest adsorption capacity of 6.4% at 105 °C. In addition to the standard tests and parameters, chemical additives such as calcium chloride which is known as a hygroscopic material were mixed with the bentonites. Moisture adsorption capacities of the bentonites were raised to a level about 20% above required as standards. The results obtained in this study together with the standard specifications were compatible with the commercial counterparts.