Y. Aşçı

Investigation of sorption/desorption equilibria of heavy metal ions on/from quartz using rhamnolipid biosurfactant

In the present study, the sorption characteristics of Cd(II) and Zn(II) ions on quartz, a representative soil-component, and the desorption of these metal ions from quartz using rhamnolipid biosurfactant were investigated. In the first part of the studies, the effects of initial metal ion concentration and pH on sorption of Cd(II) and Zn(II) ions by a fixed amount of quartz (1.5g) were studied in laboratory batch mode. The equilibrium sorption capacity for Cd(II) and Zn(II) ions was measured and the best correlation between experimental and model predicted equilibrium uptake was obtained using the Freundlich model. Although investigations on the desorption of heavy metal ions from the main soil-components are crucial to better understand the mobility and bioavailability of metals in the environment, studies on the description of desorption equilibrium were performed rarely. In the second part, the desorption of Cd(II) and Zn(II) from quartz using rhamnolipid biosurfactant was investigated as a function of pH, rhamnolipid concentration, and the amounts of sorbed Cd(II) and Zn(II) ions by quartz. The Freundlich model was also well fitted to the obtained desorption isotherms. Several indexes were calculated based on the differences of the quantity of Cd-Zn sorbed and desorbed. A desorption hysteresis (irreversibility) index based on the Freundlich exponent, concentration-dependent metal distribution coefficients, and the irreversibility index based on the metal distribution coefficient were used to quantify hysteretic behavior observed in the systems.

Removal of cobalt ions from water by ion-exchange method

AbstractIn the present work, the removal of Co(II) ions from aqueous solutions using an ion-exchange resin (Lewatit MonoPlus SP 112) was investigated. For this purpose, batch adsorption studies were carried out with various parameters such as pH and contact time. The Langmuir and Freundlich isotherm models were applied to analyze the experimental data. The best interpretation for the experimental data was given by the Langmuir isotherm and the maximum adsorption capacity was found to be 21.93 mg/g. The kinetic data were tested using pseudo-first-order, pseudo-second-order, liquid film diffusion, and intraparticle diffusion kinetic models. In addition, diffusion models were applied to explore the rate-determining step in cobalt diffusion behavior. The numerical values of the different rate constants, correlation coefficients, and effective diffusion coefficients as well as activation energy were determined. Data clarified that the adsorption process followed pseudo-second order reaction-base kinetic model....

Equilibrium, hysteresis and kinetics of cadmium desorption from sodium-feldspar using rhamnolipid biosurfactant.

In this study, the sorption/desorption equilibruim and the desorption kinetics of Cd by rhamnolipid biosurfactant from Na-feldspar as a soil component were investigated. The linear, Langmuir and Freundlich isotherms adequately fitted the equilibrium sorption data with regression coefficients ranging from 0.9836–0.9879. However, both the sorption/desorption equilibria were well characterized by the Freundlich model. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the quantity of Cd(II) sorbed, the Freundlich exponent, concentration-dependent metal distribution coefficients, and the irreversibility index based on the metal distribution coefficient. The kinetics of desorption of Cd from Na-feldspar was investigated using 77 mM rhamnolipid and at pH 6.8. The first-order, an empirical first-order desorption model (two-coefficient), Lagergren-pseudo-first-order, pseudo-second-order, Elovich and modified Freundlich models were used to describe the kinetic data to estimate the rate constants. To determine the rate-controlling step, the intra-particle diffusion model was also applied to the desorption process. The desorption kinetics of Cd(II) on Na-feldspar was represented better by the pseudo-second-order, Elovich and modified Freundlich equations with correlation coefficients ranging from 0.9941–0.9982 than by first-order equations. The rate-controlling stage was suggested to be mainly the surface reaction mechanism.

Decolorization of Direct Orange 26 by heterogeneous Fenton oxidation

AbstractIn this work, the decolorization of Direct Orange 26 (DO26) was conducted using Fe(III)-sepiolite catalyst in the presence of hydrogen peroxide (H2O2) in a batch process. The catalyst was prepared by ion exchange. All experiments were performed on a laboratory-scale setup. The effects of different parameters such as solution pH, catalyst concentration, initial concentration of H2O2 and DO26, stirring speed on the decolorization efficiency of the process were studied. The best reaction conditions were found to be an initial pH of 2.0 when the concentration of catalyst was 1.5 g/L with [H2O2]o of 35 mM, [DO26]o of 40 mg/L, and a stirring speed of 250 rpm at a temperature of 25°C. Under optimal conditions, a 98% decolorization efficiency of DO26 was achieved within 60 min of the reaction. The kinetics of decolorization of DO26 followed second-order reaction kinetics. Stability and reuse of the catalyst were also tested. This catalyst successfully overcomes the two problems faced by the heterogeneous ...

Adsorption of Zn(II) onto Turkish soil: equilibrium, kinetic and thermodynamic studies

Abstract Study on the adsorption of Zn(II) onto soil is important since it relates to the bioavailability, potential toxicity of this metal and improving remediation strategies. In the present study, sorption of Zn onto soil was investigated in batch reactors with a maximum contact time of 180 min. Adsorption tests of Zn(II) were carried out using a solution concentration of 1.22 mM at initial pH = 5 and soil dosage of 1:20. The Langmuir and Freundlich models were applied to describe equilibrium isotherms. Sorption isotherms were well described by the Freundlich equation and Dubinin–Radushkevich (D–R) isotherm model was also applied to the equilibrium data. The mean free energy of adsorption (10.33 kJ mol−1) indicated that the adsorption of Zn(II) onto soil may have been carried out via chemical ion-exchange mechanism. Kinetics of sorption was characterized using Lagergren-first-order, pseudo-second-order and intraparticle diffusion models. The sorption kinetics was well described by pseudo-second-order m...

Sorption of cobalt(II) from an aqueous medium using Amberlite 200C and Dowex 88 resins: Equilibrium and kinetic studies

AbstractCobalt is a toxic heavy metal found in various industrial wastewaters. In this study, the sorption mechanisms of Co(II) onto Amberlite 200C and Dowex 88 resins were investigated using batch reactors. The removal of Co(II) was examined by varying experimental conditions, such as the solution pH, sorbent dose, and temperature. The most effective pH range for cobalt removal was pH 4–8 for both resins. Langmuir, Freundlich, Redlich–Peterson, and Temkin models were applied to describe equilibrium isotherms. The sorption of Co(II) on the resins followed pseudo-second-order kinetics, and thermodynamic data indicated an endothermic and spontaneous process. ΔG° decreased with increasing temperature, indicating that the sorption process of Co(II) on both resins was more favorable at high temperatures. Desorption studies were conducted using various reagents. For both resins, the maximum percent of metal ion desorption was reached when 2 M H2SO4 was used as the reagent.