Ahmet Gürses

Electrocoagulation of some reactive dyes: a statistical investigation of some electrochemical variables.

In this study, the decolorization of strong colored solutions containing the reactive textile dyes by electrocoagulation was investigated. The experiments were statistically designed and carried out according to a 2(4) full factorial design with two replicate and four center points. This design was extended with eight additional axial points. Then, the non-linear regression was applied on the data by using MINITAB software. The variables chosen for this work are mixing rate, cell voltage, electrolysis time and current density. Results showed that the effective variables on decolorization process are cell voltage, electrolysis time and current density. In addition, to determine the effect of dye and electrode type on decolorization, the additional experiments were carried out. It was determined the dye and electrode type are important on the decolorization process.

An investigation into the effectiveness of problem‐based learning in a physical chemistry laboratory course

The aim of this study was to investigate the effectiveness of a problem‐based learning (PBL) approach in a physical chemistry laboratory course. The parameters investigated were students’ attitudes towards a chemistry laboratory course, scientific process skills of students and their academic achievement. The design of the study was one group pre‐test–post‐test. Four experiments, covering the topics adsorption, viscosity, surface tension and conductivity were performed using a PBL approach in the fall semester of the 2003/04 academic year at Kazim Karabekir Education Faculty of Atatürk University. Each experiment was done over a three week period. A total of 40 students, 18 male and 22 female, participated in the study. Students took the Physical Chemistry Laboratory Concept Test (PCLCT), Attitudes towards Chemistry Laboratory (ATCL) questionnaire and Science Process Skills Test (SPST) as pre and post‐tests. In addition, the effectiveness of the PBL approach was also determined through four different scales; Scales Specific to Students’ Views of PBL. A statistically significant difference between the students’ academic achievement and scientific process skills at p < 0.05 level was found. No statistically significant difference was found at the students’ attitude towards the physical chemistry laboratory. The results suggests that the PBL approach promoted critical thinking and problem‐solving skills; active participation in the learning process including self‐direction, identification of own learning needs, teamwork, creative discussion and learning from peers; and the integration and synthesis of a variety of knowledge.

The investigation of adsorption thermodynamics and mechanism of a cationic surfactant, CTAB, onto powdered active carbon

In this study, the adsorption mechanism of cethyltrimethylammonium bromide (CTAB), a cationic surfactant, onto powdered active carbon (PAC) from aqueous solution was investigated and also some thermodynamic quantities such as isosteric adsorption enthalpy and entropy for this system were determined. In addition, the mechanistic and thermodynamic results of the experiments were supported with the surface zeta potential measurements. It was found that 5 min is sufficient in order to reach adsorption equilibrium. The adsorption of CTAB onto active carbon/water interface mainly takes place through ion exchange, the ion pairing and hydrophobic bonding. The predominant mechanisms in the lower CTAB concentrations are probably ion exchange and ion pairing. The hydrophobic bonding mechanism predominates with the increasing CTAB concentration. It was determined that the signs of isosteric adsorption enthalpy (ΔHζ) and isosteric adsorption entropy (ΔSζ) for adsorption of CTAB onto PAC are negative and positive, respectively. As temperature increases, the amount of CTAB adsorbed is decreased indicating the exothermic nature of adsorption process. This decreasing verifies the negative sign expected of (ΔHads)ζ. As a result of the adsorption, since the number of the water molecules surrounding the hydrocarbon tails of CTAB molecules decreases and thus the degree of freedom of the water molecules increases, the positive sign of (ΔSads)ζ points out the hydrophobic bonding mechanisms.

REMOVAL OF PHOSPHATE FROM WASTEWATERS

Abstract Gas concrete waste was used to remove phosphate from aqueous solutions in this study. The influence of suspension pH, temperature, mixing rate, and gas concrete dosage on phosphate removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy, measurements of zeta potential of particles, both values of BET–N 2 specific surface area, and images of scanning electron microscopy (SEM) of the particles before and after adsorption. In this study, phosphate removal in excess of 99% was obtained and it was concluded that wastes of gas concrete are an efficient adsorbent for the removal of phosphate. The removal of phosphate predominantly takes place by precipitation mechanism and the weak physical interactions between the surface of adsorbent and the metallic salts of phosphate.

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.

Thermodynamics and kinetic studies of biosorption of a basic dye from aqueous solution using green algae Ulothrix sp.

This study addresses removal of a basic dye, methylene blue, from aqueous solutions by using dried Ulothrix sp. biomass as biosorbent. The effects of the initial dye concentration, contact time, temperature, solution equilibrium pH, biosorbent dosage, and mixing rate on biosorption of the dye have been investigated. It was found that 30min is sufficient in order to reach adsorption equilibrium. The amount of methylene blue adsorbed onto Ulothrix sp. increased with increasing equilibrium pH and mixing rate, in contrary, it decreased with increasing temperature and sorbent dosage. The process followed the pseudo-second-order kinetic model. The isosteric enthalpy and entropy values were calculated as -11.8kJ/mol and 37.5J/(molK), respectively. In addition, the results suggest that the physical interactions between sorbent particles and sorbate ions play an important role for the adsorption of methylene blue onto the biosorbent.

Removal of Phosphate from Waste Waters by Adsorption

In this study, the adsorption of phosphate on gas concrete from aqueous solutions has been studied as functions of temperature, mixing rates and suspension pH. Over 99% of phosphate removal was found. The chemical composition of the gas concrete has been defined by X-ray analysis. Experimental data was fitted to the Langmuir equation in order to Langmuir coefficients. After calculating Langmuir coefficients, adsorption free energy (Δ G0ads.) has been determined. In order to gather information about adsorption mechanism, electrophoretic mobilites of particles were measured at various pHs by using Zeta meter 3.0+. It has been found that the adsorption is driven by the interactions between the ionizations of CaO and Al2O3 and the formation of AlPO4. According to the BET (N2) measurements, the specific surface area of gas concrete was found as 22 m2g-1. The surface area after adsorption has been found as 17 m2g-1. The surface area covered by adsorbate has been found as 5.23 m2g-1 by usingas = nsm. am. NA. These two areas determined by BET and Langmuir model were close to each other (BET: 22 m2g-1–17 m2g-1).

Removal of Remazol Red Rb by using Al (III) as Coagulant-Flocculant: Effect of Some Variables on Settling Velocity

This study addresses the research of the removal of a textile dye from aqueous solutions by using aluminum ions as coagulant-flocculant. A simulated textile wastewater was prepared from Remazol Red RB textile dye. The purpose of this study was to investigate the effects of temperature, pH, and concentrations of the cationic surfactant and electrolyte concentration on the settling velocity ofthe simulated textile wastewater. While investigating these factors, levels of variables were determined by considering the characteristicsof traditional textile wastewater like pH, temperature, and dye concentration. Although traditional coagulation-flocculation processesmake use of different aluminium salts as coagulant-flocculent, in this study, Al ions dissolved in pH and temperature of traditional textilewastewater were used. Furthermore, sludge volume index values (SVI) were determined and conductivity measurements carried out. The resultsshowed that, in the working range of these variables, the spectroscopic color measurement revealed 100% decolorization yieldof wastewater. In conclusion, researchers found that the optimum settling velocity conditions were as follows: low temperature (273K),surfactant concentration of 0.10 g L-1, electrolyte concentration of 0.10 g L-1, dye concentration of 0.025 g L-1 and a pH of 10.05. Finally, by conducting experiments twice under the obtained optimum values, mean settling velocity was 0.014 m min-1 and the mean sludge volume index 140 mL g-1.

Modeling of adsorption isotherms and kinetics of Remazol Red RB adsorption from aqueous solution by modified clay

Abstract The adsorption of an anionic dye Remazol Red RB, from aqueous solution on modified clay was investigated at 298, 313, and 333 K. Different parameters that influence the adsorption process such as contact time, initial dye concentration, solution pH, and temperature were systematically studied. Adsorption capacity increased with increasing of temperature, initial dye concentration, and pH. The value of zeta potential decreased with increasing of pH. Experimental adsorption data were modeled by different equilibrium isotherms such as Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (D–R), Brunauer-Emmett-Teller (BET), Halsey, Harkins–Jura, Smith, and Henderson isotherms. The adsorption process followed the Langmuir isotherm model with high coefficients of correlation (R 2 > 0.99) at different temperatures. The pseudo-second-order kinetic model fitted well in correlation to the experimental results. Activation energy of the adsorption process (Ea ) was found to be 34.49 kJ mol−1 and 40.27 kJ mol−1...

Investigation of agglomeration rates of two Turkish lignites

Abstract Oil agglomeration is an effective technique for recovering and reducing the ash of coal fines. In this study, the effects of some parameters that markedly influence the effectiveness of selective oil agglomeration, such as solids concentration, amount of agglomeration oil and agglomeration time, on the recovery of agglomerate and the ash and the pyritic sulphur content of the agglomerates were investigated. In order to delineate the relation between the formation rate of coal–oil agglomerates and the removal of ash and pyritic sulphur, the rates of agglomeration for Balkaya and Askale lignites were also calculated by using experimental data. It was found that the success of the process in terms of both recovery and selectivity for lignites was highly dependent on the parameters and control of the agglomeration rate.