Intensified removal of copper from waste water using activated watermelon based biosorbent in the presence of ultrasound

Copper is one of the most toxic heavy metals having significant effects on the living organisms and hence effective removal of copper from waste water is crucial. The current work investigates the application of activated watermelon shell based biosorbent for the removal of copper from aqueous solution. The effect of activation using calcium hydroxide and citric acid as well as the effect of operating parameters like contact time, adsorbent dosage, temperature, pH, initial concentration and ultrasonic power on the extent of removal has been investigated. Experiments performed in the presence of ultrasound to investigate the degree of intensification as compared to the conventional agitation based treatment revealed that the adsorption rate significantly increases in the presence of ultrasound and also the time required for reaching the equilibrium reduces from 60 min in conventional approach to only 20 min in the presence of ultrasound. The extent of adsorption of Cu(II) on adsorbents was found to increase with an increase in the operating pH till an optimum value of 5. The extent of adsorption also increased with a decrease in the initial concentration and particle size as well as with an increase in ultrasonic power till an optimum. Kinetics and isotherm study revealed that all the experimental data was found to best fit the pseudo second order kinetics and Langmuir adsorption isotherm model respectively. Maximum adsorption capacity was found to be 31.25 mg/g for watermelon treated with calcium hydroxide and 27.027 mg/g for watermelon treated with citric acid. Overall present study established that activated watermelon is an environmentally friendly, low cost and highly efficient biosorbent that can be successfully applied for the removal of copper from aqueous solution with intensification benefits based on the ultrasound assisted approach.     

Studies on the removal of As(III) and As(V) through their adsorption onto granular activated carbon/MnFe2O4 composite: isotherm studies and error analysis

The granular activated carbon/MnFe₂O₄ composite with a mass ratio of 2:1 was synthesized using a simple chemical coprecipitation procedure and used for the removal of As(III) and As(V) from synthetically prepared wastewater. Physicochemical analysis of the composite was carried out through Brunauer, Emmett and Teller surface area and total pore volume, Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Micrograph and Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). The impact of various adsorption parameters such as the initial pH, adsorbent dose, contact time, temperature and initial arsenic concentration were systematically investigated to evaluate the optimum operating conditions. Nonlinear regression analysis was employed to identify the best-fit isotherm on the basis of three correlation coefficients and three error functions and also to predict the parameters involved in one one-parameter, six two-parameter, nineteen three-parameter, three four-parameter and one five-parameter isotherms. The maximum adsorption capacities estimated using the Langmuir model were 1253 mg/g for As(III) and 1314 mg/g for As(V) at 30 °C temperature and 70 min contact time. The results showed that As(III) and As(V) removal was strongly pH-dependent with an optimum pH value of 7.0 and 4.0, respectively. The mean adsorption energy (E) calculated from the D–R model indicated the nature of adsorption being ion exchange type.     

Investigation on the isotherm of silica gel+water systems

This article presents results of the experimental investigation on the adsorption of the water vapor on silica gel. Two independent experimental methods has been used, viz. the constant-volume-variable-pressure (CVVP) system and variable pressure thermogravimetry (TG). Results from these two methods are compared with each other. Also the isosteric heat of adsorption of this system has been determined from the equilibrium data. The silica gels investigated here are Fuji Davison type 'A' and type 'RD'. Adsorption isotherm of water vapor have been measured under a variety of conditions all referring to chiller operation cycles, i.e. temperatures from 303 to 358 K and pressures from 500 to 7000 Pa. The data collected from the two independent experiments compare very favorably with each other and their trends are consistent with those of the adsorption chiller manufacturer. This lends significant weight to our experimental data on silica gel+water systems as being valuable to the adsorption chiller manufacturers and the scientific community. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

Islanding and critical phenomena in multi-component adsorption layer with lateral interactions

The conditions for the occurrence of critical phenomena in multi-component adsorption layers are discussed for the case of lateral interactions and clustering of adsorbed molecules. It is demonstrated, that the critical temperature.i.e. the temperature below which surface phase transformation can occur, is independent of the size of clusters.     

Application of the chromatographic step profile method for determination of water film pressure and surface free energy of quartz

Summary Investigation of water adsorption by the step profile method (Glueckauf method) was carried out with the help of a modified gas chromatography equipped with thermal-conductivity detector. On the basis of the adsorption isotherm obtained, the water film pressure and the polar component of the surface free energy of quartz were calculated. The calculated value of the polar component of the surface free energy of quartz agrees with analogous values obtained by other methods.     

Adsorption behavior of Vulkan-7H graphitized carbon black

The adsorption behavior of Vulkan-7H carbon black graphitized at 3073 K was studied. Benzene adsorption isotherms at 293 K were measured by the static method and by gas chromatography. It was shown that Vulkan-7H carbon black may be considered as a supermicroporous adsorbent with a pore size of 1.05 nm.The sample was provided by N. N. Lezhnev.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1544–1546, September, 1993.     

The role of Pb ions doping in the mechanism of chromate adsorption by goethite

Pure and 0.384% Pb²⁺ ions doped goethite samples were prepared in the laboratory by the coprecipitation method. The laboratory-prepared goethite samples were characterized for pH of point of zero charge (pH_pzc), surface area, XRD, TG-DTA, TEM, SEM and FTIR analysis, which suggest that the Pb²⁺ ions are incorporated into the crystals of goethite and are also present on the surface in the hydroxylated form. Chromate adsorption studies were carried out in the concentration range 0.25-2.01 mmol L⁻¹ at pH 3, 5 and 7, which show that maximum chromate is adsorbed at the lowest pH of 3 by both the samples of goethite. Effect of temperature on the adsorption of chromate, in the range 303-323 K, shows that the process of adsorption is endothermic in case of pure goethite and exothermic in case of Pb-doped goethite. The values of isosteric heat of adsorption were positive for pure goethite and negative for Pb-doped goethite, which are consistent with the effect of temperature on the process of adsorption. Langmuir isotherm was found applicable to the experimental data. FTIR analysis and equilibrium pH changes reveal that at pH 3 outersphere while at pH 5 and 7 innersphere complexation is the dominant mechanism for chromate adsorption by both the samples of goethite.     

Enantioseparation of flurbiprofen on amylose-derived chiral stationary phase by supercritical fluid chromatography

The separation of the enantiomers of flurbiprofen on an amylose-derived chiral stationary phase, Chiralpak AD-H, by supercritical fluid chromatography (SFC) under both linear and non-linear conditions is studied. Pulse injections were implemented using supercritical CO₂modified with methanol as a mobile phase at a temperature of 30 °$°$C. At linear conditions, the isotherm is determined directly from the chromatogram. Under overload conditions, the elution profiles were described by competitive Langmuir and bi-Langmuir isotherm. Isotherm parameters were estimated using the inverse method and the effects of operation variables such as pressure and modifier composition were studied. The value of selectivity is from 1.9 to 2.1 while the value of resolution is from 5.3 to 11.8. The number of theoretical plates is always greater than 5000 indicating high efficiency of SFC.