Samih Bayrakçeken

Evaluation of response of brown coal to selective oil agglomeration by zeta potential measurements of the agglomerates

Abstract The effects of suspension pH, concentration of surfactant (cetyltrimethylammonium bromide, CTAB) and concentrations of electrolytes (FeCl3, CaCl2 and NaCl) on the recovery of agglomerate and on the reductions in ash and pyritic sulfur in selective oil agglomeration were investigated. The correlation between recovery and reductions in ash and pyritic sulfur and the zeta potential of the agglomerates was also studied. It was found that there was a close correspondence between them and that zeta potential measurements on the agglomerates would give a measure of the effectiveness of oil agglomeration.

The conceptual change approach to teaching chemical equilibrium

This study investigates the effect of a conceptual change approach over traditional instruction on students’ understanding of chemical equilibrium concepts (e.g. dynamic nature of equilibrium, definition of equilibrium constant, heterogeneous equilibrium, qualitative interpreting of equilibrium constant, changing the reaction conditions). This study consisted of 85 undergraduate students from two classes enrolled on an introductory chemistry course. One of the classes was assigned randomly to the control group, and the other class was assigned randomly to the experimental group. During teaching of the topic of chemical equilibrium concepts in the chemistry curriculum, the conceptual change approach was applied in the experimental group whereas ‘traditional instruction’ was followed in the control group. The data were analyzed using analysis of covariance. The results showed that the students in the experimental group performed better compared to the control group. The average percent of correct responses of the experimental group was 70%, and that of the control group was 51%, after treatment. In addition, it was found that students’ science process skills made a statistically significant contribution to the variation in students’ understanding of chemical equilibrium concepts.

The effect of a ‘Science, Technology and Society’ course on prospective teachers’ conceptions of the nature of science

The aim of this study is to assess prospective teachers’ views of some aspects of the nature of science (NOS) and the effects of a “Science, Technology and Society” (STS) course embedded with scientific investigation (SI) on these views. A questionnaire consisting of 13 items was given to 212 prospective teachers enrolled in a STS course before and after teaching. During the semester, participants were engaged in a specially designed pilot SI combined with explicit NOS instruction. Majority of the participants held traditional views of the target NOS aspects at beginning of the study. After the course there were significant changes in the conceptions of prospective teachers in majority target aspects of NOS as the results of a Sign test indicate. We suggest that the more suitable SI, performed in an active learning environment, related to target aspects of NOS must be selected to develop the more constructivist views about the NOS.

Thermal decomposition of pyrite in the nitrogen atmosphere

Abstract The effects of gas flow rate, reaction temperature, particle size, and time on thermal decomposition of pyrite have been investigated between 673 and 1073 K in a nitrogen gas environment in which the gas–solid contact is effective. The decomposition reaction is well represented by the “shrinking core” model and can be divided into two regions with different rate controlling step. The rate-controlling step was found to be the heat transfer through the gas film for low conversion, but the mass transfer through product ash layer for high conversion. The activation energies for the heat transfer through the gas film and mass transfer through product ash layer-controlled cases were calculated as 113 and 96 kJ mol −1 , respectively.

Adsorption of CTAB at lignite-aqueous solution interface

The adsorption of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) from aqueous solution onto the lignite was investigated. The samples used for the adsorption experiments were: fresh; demineralized; demineralized then oxidized. The oxidation process was conducted by dry method (in air at 150 and 200°C). The UV spectrophotometric techniques were used for the analysis of CTAB in solution. The adsorption isotherms were measured experimentally at 21 and 45°C, and it was found that the adsorption capacities of all samples increased with rising temperature, and the adsorption of CTAB decreased by demineralization and oxidation. The changes in the thermodynamic quantities, enthalpy and entropy, related adsorption process that occured in some steps were calculated. Isosteric heats of adsorption and the corresponding changes in entropy have found to be negative for all of the samples. From the abrupt difference between ΔH and ΔS for the demineralized sample and those of fresh sample, it was concluded that the orientation of CTAB molecules on the surface of the demineralized sample differs than that of fresh sample, and also that the adsorption of CTAB on the demineralized sample takes place with the hydrophobic interactions in addition to the electrostatic interactions, while in the case of fresh sample, the predominant mechanism of adsorption is through electrostatic interactions. Also, the lower values of ΔH for both demineralized and oxidized samples in comparison with the demineralized sample indicates that the oxidation process diminishes the contribution of the hydrophobic interactions to the adsorption of CTAB.

Selective oil agglomeration of brown coal: a systematic investigation of the design and process variables in the conditioning step

Oil agglomeration is an effective technique for recovering and deashing coal fines. Conditioning is the most important unit operation prior to agglomeration or size enlargement. In this study, the effects of the design and process parameters in the conditioning step, which markedly influences the effectiveness of selective oil agglomeration, on the recovery of agglomerate and the ash and pyritic sulfur content of the agglomerates were investigated. It was found that the success of the process in terms of both recovery and selectivity for a brown coal was highly dependent on the conditioning parameters. In addition, an empirical equation which relates the recovery with all the conditioning parameters was developed. The values calculated by this equation closely matched the experimental values.

Dissolution mechanism of ulexite in H2SO4 solution

Abstract This work comprises an investigation of the dissolution mechanism of ulexite in H 2 SO 4 solution and the effect of SO 4 2− ions and acid concentration on the dissolution process, using H 2 SO 4 , HCL+H 2 SO 4 and H 2 SO 4 +Na 2 SO 4 solutions. From the experimental observations, it can be suggested that the overall dissolution reaction can be written as Na 2 O·2CaO·5B 2 O 3 ·16H 2 O (s) +3H 2 SO 4(aq) →2Na + (aq) +2CaSO 4 ++10H 3 BO 3(aq) +SO 2− 4(aq) +4H 2 O (l) (6) or Na 2 O·2CaO·5B 2 O 3 ·16H 2 O (s) +3H 2 SO 4(aq) →2Na + (aq) +2CaSO 4 ·2H 2 O (s) +10H 3 BO 3(aq) +SO 2− 4(aq) depending upon the experimental conditions. It was observed that, increasing H 3 O + acid concentration increased the dissolution rate, but increasing SO 4 2− concentration reduced dissolution rate due to the precipitation of a solid film of CaSO 4 and/or CaSO 4 ·2H 2 O, determined by X-ray and SEM measurement.

Adsorption of o-cresol from aqueous solution on coal

Abstract The adsorption of o -cresol, which is commonly used in coal flotation as frother, on two lignites and a bituminous coal has been studied. Coal samples used for the adsorption experiments were: fresh; oxidized, demineralized; demineralized then oxidized. The oxidation processes were conducted by dry (in air at 100, 150 and 200°C) and wet (with 15% H 2 O 2 ) methods. The extent of the coal oxidation was quantified by determining the amounts of the two principal oxygen-containing functional groups, carboxylic and phenolic, in the coal samples. The UV spectrophotometric technique was used for the analysis of o -cresol in solution. The adsorption for the lignites was found to increase by oxidation, but to decrease by demineralization, implying that o -cresol is adsorbed by hydrophilic interactions at the coal surface. In contrast, for the bituminous coal, the adsorption was increased by demineralization while it was decreased by slight oxidation, indicating that the adsorption occurs predominantly through hydrophobic interactions between the frother molecule and the coal surface. However, further oxidation of the bituminous coal resulted in an increase in the extent of adsorption in comparison with the fresh coal sample. Among the coal samples used, the adsorption on the bituminous coal samples conformed to the Langmuir equation, and adsorption free energies for these samples were found to be in the range −22.6 to −29.3 kJ mol −1 .

Kinetics of the chlorination of pyrite in aqueous suspension

Abstract The kinetics of chlorination of pyrite in aqueous suspension have been investigated. The effects of pyrite particle size (106–125, 125–150, 150–180, 180–250, 250–425 μm), reaction time (0–14400 s), temperature (13–60°C), and speed of stirring (5–20 s −1 ) were studied. The experimental data were analyzed on the basis of the unreacted shrinking core model. The rate-controlling step was found to be the chemical reaction between chlorine and pyrite for the temperature range 13–35°C, but the diffusion of chlorine through the fluid film for the temperature range 40–60°C. The activation energies for the chemical- and diffusion-controlled cases were calculated as 36.7 and 3.7 kJ mol −1 respectively.

Changes in physical structure and chemical composition of phosphate rock during calcination in fluidized and fixed beds

Abstract The present study deals with the effects of important variables on the calcination of phosphate rock in fluidized and fixed beds. Further, the calcined samples were characterized for variation in physical structure and chemical composition as compared to the raw ore by X-ray diffractometry (XRD), scanning electron microscopy (SEM), mercury porosimetry as well as BET surface area techniques. Calcination extent was found to increase slightly with gas flow rate. In studying the effect of particle size on calcination in the fluidized bed, the calcination extent increased with decreasing particle size. Calcination in the fluidized bed was found to be faster than that in the fixed bed. The XRD patterns showed that the chief mineral constituents of calcined samples were calcium oxide and fluorapatite, while those in the raw ore were calcite, fluorapatite and carbonate-fluorapatite. The carbonate-fluorapatite changed to fluorapatite during calcination. SEM micrographs of the calcined samples showed that macro pores occur in the carbonate during calcination. In addition, shrinkage and cracks in the surrounding parts of the phosphate due to sintering were observed. The pore size distribution indicated an increase in macro pores and a decrease in micro pores upon calcinations.