Sabriye Pişkin

Chemical demineralization of a Turkish high ash bituminous coal

Demineralization of coal prior to usage offers some technical and cost-effective advantages since one of the most common limitations on coal processes results from high mineral matter content. In this work aimed at reducing the mineral matter content of high ash, low sulfur Amasra bituminous coal from Turkey, since physical methods were of limited use for reducing the ash content of bituminous coals, demineralization was studied using different acids (HF, HCl, HNO3 and H2SO4) alone and 0.5 N aqueous NaOH in combination with either one or two of the acids. The use of extraction with 0.5 N NaOH followed by leaching with 10% HCl was the optimum approach for the chemical cleaning of the coal under study, the maximum degree of demineralization obtained being 46.78%.

The effect of oxidation on the flotation properties of a Turkish bituminous coal

Abstract It is well known that the behaviour of oxidized coal is different than that of original coal during flotation and that the efficiency of flotation differs according to the degree of oxidation. The degree of oxidation of coal particles can be determined based on their surface properties. For this, the electrokinetic potantial measurement is considered to be an efficient method to determine the surface properties of oxidized coal. In this work, based on the zeta potential and flotation data obtained, it can be concluded that the flotability of Amasra coal deteriorates on oxidation but can be increased by using electrolytes at low concentrations in the flotation media.

Thermal analysis of borogypsum and its effects on the physical properties of Portland cement

Borogypsum, which consists mainly of gypsum crystals, B2O3 and some impurities, is formed during the production of boric acid from colemanite, which is an important borate ore. In this study, the effect of borogypsum and calcined borogypsum on the physical properties of ordinary Portland cement (OPC) has been investigated. The calcination temperature and transformations in the structures of borogypsum and natural gypsum were determined by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. Thermal experiments were carried out between ambient temperature and 500 °C in an air atmosphere at a heating rate of 10 °C min−1. After calculation of enthalpy and determination of conversion temperatures, borogypsum (5% and 7%), hemihydrate borogypsum (5%) and natural gypsum (5%) were added separately to Portland cement clinker and cements were ground in the laboratory. The final products were tested for chemical analysis, compressive strength, setting time, Le Chatelier expansion and fineness properties according to the European Standard (EN 196). The results show that increasing the borogypsum level in Portland cement from 5% to 7% caused an increase in setting time and a decrease in soundness expansion and compressive strength. The cement prepared with borogypsum (5%) was found to have similar strength properties to those obtained with natural gypsum, whereas a mixture containing 5% of hemihydrate borogypsum was found to develop 25% higher compressive strength than the OPC control mixtures at 28 days. For this reason, utilization of calcined borogypsum in cement applications is expected to give better results than untreated borogypsum. It is concluded that hemihydrate borogypsum could be used as a retarder for Portland cement as an industrial side. This would play an important role in reducing environmental pollution.

The effect of premixing on the floatation of oxidized Amasra coal

Abstract In this study factors affecting the floatation efficiency of oxidized Amasra coal containing high quantities of inorganic materials were examined under laboratory conditions. The Amasra coal samples were oxidized by exposing them to atmospheres for a long time with the aim of obtaining coal having a lower ash content. Premixing is applied to condensed pulp containing 60% coal and 40% water to remove the oxidized layer on the coal surface. The oxidized layer is removed as a result of friction between particles during mixing. Premixing periods were 1, 2, 3, 4, 5, 10, 15 and 20 min, and floatation tests were done after each premixing. Some relations were obtained between frothing period, calorific value, combustible matter recovery, and ash content. The relation between premixing and floatation efficiency was another subject of examination. The effect of oxidized coal on floatation was also examined after oxidized coal was exposed to thermal treatment in inert milieu. From the results obtained at the end of an average frothing period of 20–25 min, it was observed that the quantity of product increased and the ash content in the product reached a minimum value. At the same time, the calorific value of the coal and the recovery of combustible matter reached their highest value.

Thermal behavior and dehydroxylation kinetics of naturally occurring sepiolite and bentonite

Sepiolite and bentonite have a wide range of industrial applications based on their physicochemical properties such as surface area, thermal behavior, chemical composition, and mineralogic composition. The thermal behavior and kinetics of naturally occurring sepiolite and bentonite were determined in order to give an idea about the potential use of naturally occurring clay minerals in possible applications. Naturally occurring sepiolite and bentonite samples were heated to the temperature that was achieved at the end of the dehydroxylation process. Mineralogic and thermal characteristics of raw and heat treated samples were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen adsorption/desorption analyses. Changes in the structure following heat treatment were used for the evaluation of the dehydroxylation properties of the samples. The dehydroxylation properties of the minerals are strongly affected by the crystal structure. Kinetic analyses, which were related to the dehydroxylation of naturally occurring sepiolite and bentonite, were conducted using dynamic thermogravimetry/derivative thermogravimetry analysis under nitrogen atmosphere. Flynn–Wall–Ozawa, Kissenger–Akahira–Sunose, and Friedman isoconversional methods were used to determine the activation energies of the dehydroxylation reactions of the samples. The results indicate that the activation energy of naturally occurring sepiolite showed a little variation at a particular conversion rate (0.3–0.7), while the activation energy of naturally occurring bentonite showed a significant variation within the range of variation of the conversion rate. The present study shows that the dehydroxylation reactions of naturally occurring sepiolite and bentonite were single mechanism reaction and complex mechanism reaction, respectively.

Characteristics of Thin-layer Infrared Drying of Green Bean

Doymaz I., Kipcak A.S., Piskin S. (2015): Characteristics of thin-layer infrared drying of green bean. Czech J. Food Sci., 33: 83–90. The effect of infrared (IR) power on drying kinetics, rehydration, and colour of green beans was investigated. The drying experiments were carried out at 83, 104, 125, 146, 167, and 188 W. It is observed that drying characteristics, rehydration, and colour of bean slices were greatly influenced by infrared power. The drying data were fitted with five thin-layer drying models available in the literature. Results showed that Midilli et al. and Aghbashlo et al. models are superior to the other models for explaining the drying kinetics of green bean slices. Effective moisture diffusivity was calculated in the range of 6.57 × 10–10 to 4.49 × 10–9 m2/s. Activation energy was estimated by a modified Arrhenius type equation and found to be 11.379 kW/kg.

Utilization of gold tailings as an additive in Portland cement

Mine tailings are formed as an industrial waste during coal and ore mining and processing. In the investigated process, following the extraction of gold from the ore, the remaining tailings are subjected to a two-stage chemical treatment in order to destroy the free cyanide and to stabilize and coagulate heavy metals prior to discharge into the tailings pond. The aim of this study was the investigation of the feasibility of utilization of the tailings as an additive material in Portland cement production. For this purpose, the effects of the tailings on the compressive strength properties of the ordinary Portland cement were investigated. Chemical and physical properties, mineralogical composition, particle size distribution and microstructure of the tailings were determined by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), particle size analyzer (Mastersizer) and scanning electron microscope (SEM). Following the characterization of the tailings, cement mortars were prepared by intergrinding Portland cement with dried tailings. Composition of the cement clinkers were adjusted to contain 5, 15, 25% (wt/wt) dried tailings and also silica fume and fly ash samples (C and F type) were added to clinker in different ratios. The mortars produced with different amounts of tailings, silica fume, fly ashes and also mixtures of them were tested for compressive strength values after 2, 7, 28 and 56 days according to the European Standard (EN 196-1). The results indicated that gold tailings up to 25% in clinker could be beneficially used as an additive in Portland cement production. It is suggested that the gold tailings used in the cement are blended with silica fume and C-type fly ash to obtain higher compressive strength values.

Characterization and Combustion Kinetics of Chars Obtained from Loquat Stones

This paper describes the production of chars from loquat stones in a tube furnace at carbonization temperatures of 600°C, 700°C, and 800°C in a nitrogen flow at a heating rate of 10°C/min. The physical and chemical structures of the stones and chars were investigated by FTIR spectrometer, X-ray diffractometer, and SEM, as well as the combustion reaction and kinetic parameters based on the TG-DTG graphs obtained by thermogravimetric analysis. The combustion reaction was carried out at a heating rate 10°C/min and an oxygen flow rate of 50 ml/min up to 700°C. The kinetic parameters were calculated using the methods by Arrhenius; Coats and Redfern; Horowitz and Metzger; and Ingraham and Marier.

Removal of Mineral Matter from Silopi-Harput Asphaltite by Acid Treatment

The surface properties of fossil fuel show differences according to ranks and mineral matter content. The fossils that have high mineral matter content are treated with some applications before using. This is a kind of enrichment. This process is helpful to both economic and technological points of view. The mineral matter of fossil can be decreased by chemical demineralization. The main purpose of demineralization is to seperate the mineral matter without changing the organic structure. In this study, demineralization was studied using different acids (HCl, H 2 SO 4 and HNO 3 ) at various concentrations. Maximum demineralization degree (approximately 40%) was found of asphaltite sample leaching with 5 and 10% HCl acids. FTIR and XRD were used to determine the functional groups of treated sample and the contents of ash, respectively.

Titanate nanotubes: preparation, characterization and application in adsorption of strontium ion from aqueous solution

Abstract The adsorptive removal potential of Sr2+ ions with titanate nanotubes (TNT) was investigated. Titanate nanotubes were synthesized via hydrothermal treatment of anatase titania powders and concentrated NaOH solution. Morphological and structural properties of titanate nanotubes were determined by XRD, BET and HRTEM. High resolution transmission electron microscopy (HRTEM) showed that uniform nanotubes with inner diameters of ≈ 4 nm and outer diameters of ≈ 12 nm were obtained. The adsorption behaviors of Sr2+ ions on the TNT were also investigated. As a result of the experimental data, it was concluded that TNT are good adsorbents for the removal of Sr2+ ions from aqueous solutions with an adsorption capacity reaching of 66.72 mg/g. The adsorption mechanisms of Sr2+ ions from aqueous solutions onto TNT were examined with aid of model analyses of the adsorption equilibrium and kinetic data of Sr2+ ions. The rate constant has been calculated for 288, 298, 308 and 318 K. Thermodynamic parameters for the sorption system have been determined.