Oualid Hamdaoui

Removal of mercury(II) from aqueous media using eucalyptus bark: Kinetic and equilibrium studies

In this study, eucalyptus camaldulensis bark, a forest solid waste, is proposed as a novel material for the removal of mercury(II) from aqueous phase. The operating variables studied were sorbent dosage, ionic strength, stirring speed, temperature, solution pH, contact time, and initial metal concentration. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly pH-dependent. Kinetic measurements showed that the process was uniform and rapid. In order to investigate the mechanism of sorption, kinetic data were modeled using the pseudo-first-order and pseudo-second-order kinetic equations, and intraparticle diffusion model. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the sorption process. Equilibrium isotherm data were analyzed using the Langmuir and the Freundlich isotherms. The Langmuir model yields a much better fit than the Freundlich model. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The maximum sorption capacity was 33.11mgg(-1) at 20 degrees C and the negative value of free energy change indicated the spontaneous nature of sorption. These results demonstrate that eucalyptus bark is very effective in the removal of Hg(II) from aqueous solutions.

Effects of ultrasound on adsorption–desorption of p-chlorophenol on granular activated carbon

The aim of this work is the evaluation of the effects of ultrasound on p-chlorophenol adsorption-desorption on granular activated carbon. Adsorption equilibrium experiments and batch kinetics studies were carried out in the presence and the absence of ultrasound at 21 kHz. Results indicate that the adsorption of p-chlorophenol determined in the presence of ultrasound is lower than the adsorption observed in the absence of ultrasound. Desorption of p-chlorophenol from activated carbon with and without the application of ultrasound was studied. The desorption rates were favoured by increased ultrasound intensity. This rise is more noticeable as temperature increases. The addition of ethanol or NaOH to the system causes an enhancement of the amount of p-chlorophenol desorbed, especially in the presence of ultrasound. A synergetic enhancement of the desorption rate was observed when ultrasonic irradiation was coupled with ethanol chemical regeneration.

Influence of bicarbonate and carbonate ions on sonochemical degradation of Rhodamine B in aqueous phase

The influence of bicarbonate and carbonate ions on sonolytic degradation of cationic dye, Rhodamine B (RhB), in water was investigated. As a consequence of ultrasonic cavitation that generates .OH radicals, carbonate radicals were secondary products of water sonochemistry when it contains dissolved bicarbonate or carbonate ions. The results clearly demonstrated the significant intensification of sonolytic destruction of RhB in the presence of bicarbonate and carbonate, especially at lower dye concentrations. Degradation intensification occurs because carbonate radicals sonochemically formed undergo radical-radical recombination at a lesser extent than hydroxyl radicals. The generated carbonate radicals are likely able to migrate far from the cavitation bubbles towards the solution bulk and are suitable for degradation of an organic dye such as RhB. Therefore, at low dye concentrations, carbonate radical presents a more selective reactivity towards RhB molecules than hydroxyl radical. In the presence of bicarbonate, degradation rate reached a maximum at 3 g L(-1) bicarbonate, but subsequent addition retards the destruction process. In RhB solutions containing carbonate, the oxidation rate gradually increased with increasing carbonate concentration up to 10 g L(-1) and slightly decreased afterward. Carbonate radicals sonochemically generated are suitable for total removal of COD of sonicated RhB solutions.

Sonochemical and photosonochemical degradation of 4-chlorophenol in aqueous media

The degradation of 4-chlorophenol (4-CP) in aqueous media by 516 kHz ultrasonic irradiation was investigated in order to clarify the degradation mechanism. The degradation of concentrated 4-CP solution by means of ultrasound, UV irradiation and their combined application was also studied. The obtained results indicate that *OH radical are the primary reactive species responsible for 4-CP ultrasonic degradation. Very little 4-CP degradation occurs if the sonolysis is carried out in the presence of the *OH radical scavenger tert-butyl alcohol, also indicating that little or no pyrolysis of the compound occurs. The dominant degradation mechanism is the reaction of substrate with *OH radicals at the gas bubble-liquid interface rather than high temperature direct pyrolysis in ultrasonic cavities. This mechanism can explain the lower degradation rate of the ionic form of 4-CP that is partly due to the rapid dissociation of *OH radicals in alkaline solutions. The sonochemical destruction of concentrated 4-CP aqueous solution is obtained with low rate. Coupling photolysis with ultrasound irradiation results in increased efficiency compared to the individual processes operating at common conditions. Interestingly, the photosonochemical decomposition rate constant is greater than the additive rate constants of the two processes. This may be the result of three different oxidative processes direct photochemical action, high frequency sonochemistry and reaction with ozone produced by UV irradiation of air, dissolved in liquid phase because of the geyser effect of ultrasound streaming. Additionally, the photodecomposition, at 254 nm, of hydrogen peroxide produced by ultrasound generating *OH radical can partly explain the destruction enhancement.

Extraction of anionic dye from aqueous solutions by emulsion liquid membrane

In this work, the extraction of Congo red (CR), an anionic disazo direct dye, from aqueous solutions by emulsion liquid membrane (ELM) was investigated. The important operational parameters governing emulsion stability and extraction behavior of dye were studied. The extraction of CR was influenced by a number of variables such as surfactant concentration, stirring speed, acid concentration in the feed solution and volume ratios of internal phase to organic phase and of emulsion to feed solution. Under most favorable conditions, practically all the CR molecules present in the feed phase were extracted even in the presence of salt (NaCl). At the optimum experimental conditions, total removal of antharaquinonic dye Acid Blue 25 was attained after only 10 min. Influence of sodium carbonate concentration as internal receiving phase on the stripping efficiency of CR was examined. The best sodium carbonate concentration in the internal phase that conducted to excellent stripping efficiency (>99%) and emulsion stability was 0.1N. The membrane recovery was total and the permeation of CR was not decreased up to seven runs. ELM process is a promising alternative to conventional methods and should increase awareness of the potential for recovery of anionic dyes.

Removal of copper(II) from aqueous phase by Purolite C100-MB cation exchange resin in fixed bed columns: modeling.

The dynamic removal of copper by Purolite C100-MB cation exchange resin was studied in packed bed columns. The values of column parameters are predicted as a function of flow rate and bed height. Batch experiments were performed using the Na-form resin to determine equilibrium and kinetics of copper removal. The uptake of Cu(II) by this resin follows first-order kinetics. The effect of stirring speed and temperature on the removal kinetics was studied. The activation energy for the exchange reaction is 13.58kJmol(-1). The equilibrium data obtained in this study have been found to fit both the Langmuir and Freundlich isotherm equations. A series of column tests were performed to determine the breakthrough curves with varying bed heights and flow rates. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Bohart-Adams, Bed Depth Service Time (BDST), Clark and Wolborska models are applied to experimental data. All models are found suitable for describing the whole or a definite part of the dynamic behavior of the column with respect to flow rate and bed height. The simulation of the whole breakthrough curve is effective with the Bohart-Adams and the Clark models, but the Bohart-Adams model is better. The breakthrough is best predicted by the Wolborska model. The breakthrough data gave a good fit to the BDST model, resulting in a bed exchange capacity very close to the value determined in the batch process.

Influence of experimental parameters on sonochemistry dosimetries: KI oxidation, Fricke reaction and H2O2 production

Central events of the ultrasonic action are the cavitation bubbles that can be considered as microreactors. Adiabatic collapse of cavitation bubbles leads to the formation of reactive species such as hydroxyl radicals (*OH), hydrogen peroxide (H(2)O(2)) and hydroperoxyl radicals (HOO*). Several chemical methods were used to detect the production of these reactive moieties in sonochemistry. In this work, the influence of several operational parameters on the sonochemistry dosimetries namely KI oxidation, Fricke reaction and H(2)O(2) production using 300 kHz ultrasound was investigated. The main experimental parameters showing significant effect in KI oxidation dosimetry were initial KI concentration, acoustic power and pH. The solution temperature showed restricted influence on KI oxidation. The acoustic power and liquid temperature highly affected Fricke reaction dosimetry. Operational conditions having important influence on H(2)O(2) formation were acoustic power, solution temperature and pH. For the three tested dosimetries, the sonochemical efficiency was independent of liquid volume.

Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound

This work describes the results of investigations carried out to examine the adsorption kinetics of 4-chlorophenol (4-CP) from aqueous solution containing tert-butyl alcohol (10%, v/v) onto granular activated carbon (GAC) in the presence of ultrasound of different high frequencies (516, 800 and 1660 kHz) and acoustic powers (15.2, 21.5, 31.1 and 38.3 W). The main objective of this study is to describe the mechanism of ultrasound-assisted adsorption rather than the enhancement of adsorption capacity. Sonochemical degradation of 4-CP was studied in the absence and presence of tert-butyl alcohol. The sonolysis of 4-CP is effectively inhibited by the addition of tert-butyl alcohol (10%, v/v) and very little 4-CP degradation occurs, indicating that little or no pyrolysis of the compound occurs. Without addition of tert-butyl alcohol, after 300 min and at 1660 kHz, the removal of 4-CP in the presence of ultrasound for an acoustic power of 38.3 W was nearly total (99%), but in the conventional method only 60% was eliminated. In this case, the removal of 4-CP by GAC in the ultrasound-assisted technique is due to both adsorption and ultrasonic degradation, but the removal by simple stirring is only due to adsorption, which makes a direct comparison unacceptable. In order to distinguish sonochemical degradation and adsorption of 4-CP onto GAC and to make an exact and practical comparison of the adsorption in the absence and presence of ultrasound, kinetic adsorption experiments were conducted using aqueous solution containing 10% (v/v) tert-butyl alcohol. The obtained results show that both adsorption rate and adsorbed amount were significantly enhanced and improved in the presence of ultrasound for all the studied frequencies and powers. The enhancement of adsorption is favored by increasing ultrasonic power. Adsorption kinetic data were modeled using the liquid-film mass transfer equation and intraparticle diffusion model. The values of the intraparticle diffusion coefficient obtained in the presence of ultrasound are greater than that obtained in the absence of ultrasound. In the initial period of adsorption, where external mass transfer is assumed to predominate, liquid-film mass transfer coefficients significantly increased by the assistance of ultrasound. These results indicate that ultrasound enhances the mass transport in the pores as well as across the boundary layer. This effect increased with increasing ultrasonic power for the three studied frequencies. The average order for the studied ultrasonic waves according to the initial adsorption rate, the intraparticle diffusion coefficient and the liquid-film mass transfer coefficient is 516 kHz>800 kHz>1660 kHz.

Degradation of Acid Blue 25 in aqueous media using 1700 kHz ultrasonic irradiation: ultrasound/Fe(II) and ultrasound/H2O2 combinations

In this work, the sonolytic degradation of an anthraquinonic dye, C.I. Acid Blue 25 (AB25), in aqueous phase using high frequency ultrasound waves (1700kHz) for an acoustic power of 14W was investigated. The sonochemical efficiency of the reactor was evaluated by potassium iodide dosimeter, Fricke reaction and hydrogen peroxide production yield. The three investigated methods clearly show the production of oxidizing species during sonication and well reflect the sonochemical effects of high frequency ultrasonic irradiation. The effect of operational conditions such as the initial AB25 concentration, solution temperature and pH on the degradation of AB25 was studied. Additionally, the influence of addition of salts on the degradation of dye was examined. The rate of AB25 degradation was dependent on initial dye concentration, pH and temperature. Addition of salts increased the degradation of dye. Experiments conducted using distilled and natural waters demonstrated that the degradation was more efficient in the natural water compared to distilled water. To increase the efficiency of AB25 degradation, experiments combining ultrasound with Fe(II) or H(2)O(2) were conducted. Fe(II) induced the dissociation of ultrasonically produced hydrogen peroxide, leading to additional OH radicals which enhance the degradation of dye. The combination of ultrasound with hydrogen peroxide looks to be a promising option to increase the generation of free radicals. The concentration of hydrogen peroxide plays a crucial role in deciding the extent of enhancement obtained for the combined process. The results of the present work indicate that ultrasound/H(2)O(2) and ultrasound/Fe(II) processes are efficient for the degradation of AB25 in aqueous solutions by high frequency ultrasonic irradiation.

Ultrasound-assisted removal of malachite green from aqueous solution by dead pine needles

The dead needles of Aleppo pine (Pinus halepensis) were tested as a possible sorbent for the removal of malachite green from aqueous solutions in the absence and presence of ultrasound. Batch process was employed for sorption kinetic and equilibrium studies. Sorption experiments indicated that the sorption capacity was dependent of operating variables. Both the rate and the amount of malachite green sorption are markedly increased in the presence of the ultrasonic field. The dye removal with the assistance of ultrasound was enhanced with the increase of sorbate initial concentration and temperature, and with the decrease of sorbent dosage and ionic strength. The combination of stirring and ultrasound leads to an improvement of the removal of dye. The sorption kinetics was controlled by the intraparticle diffusion. The intraparticle diffusion coefficient increased 1.7 times in the presence of ultrasound and up to 3.6 times in the combined process. The sorption capacity, estimated according to the Freundlich model, indicates that ultrasound enhanced the sorption properties of the sorbent. The effect of ultrasound on the improvement of dye sorption is due to a variety of physical and mechanical effects as well as to thermal properties. The combination of ultrasound and stirring for the sorption process was shown to be of interest for the treatment of wastewaters contaminated with malachite green.