Removal and recovery of vanadium(V) by adsorption onto ZnCl2 activated carbon: Kinetics and isotherms

Adsorption of vanadium(V) from aqueous solution onto ZnCl₂ activated carbon developed from coconut coir pith was investigated to assess the possible use of this adsorbent. The influence of various parameters such as agitation time, vanadium concentration, adsorbent dose, pH and temperature has been studied. First, second order, Elovich and Bangham’s models were used to study the adsorption kinetics. The adsorption system follows second order and Bangham’s kinetic models. Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherms have been employed to analyze the adsorption equilibrium data. Equilibrium adsorption data followed all the four isotherms—Langmuir, Freundlich, D-R and Temkin. The Langmuir adsorption capacity (Q ₀) was found to be 24.9 mg g^{− 1} of the adsorbent. The per cent adsorption was maximum in the pH range 4.0–9.0. The pH effect and desorption studies showed that ion exchange mechanism might be involved in the adsorption process. Thermodynamic parameters such as ΔG ⁰, ΔH ⁰ and ΔS ⁰ for the adsorption were evaluated. Effect of competitive anions in the aqueous solution such as PO₄ ^{3 −}, SO₄ ²⁻, ClO₄ ⁻, MoO₄ ²⁻, SeO₃ ²⁻, NO₃ ⁻ and Cl⁻ was examined. SEM and FTIR were used to study the surface of vanadium(V) loaded ZnCl₂ activated carbon. Removal of vanadium(V) from synthetic ground water was also tested. Results show that ZnCl₂ activated coir pith carbon is effective for the removal of vanadium(V) from water.     

Highly sensitive spectrofluorimetric determination of cysteine by Cu2+-morin complex

p-Toluenesulfonylamide was immobilized on silica gel and on nm-sized silicium dioxide (SiO₂). Their adsorption efficiency toward metal ions was investigated by the batch equilibrium technique. Although silica gel and nm-SiO₂ have the same composition (silicon and oxygen), the difference in their sizes and surface structures results in distinct chemical activity and selectivity. At pH 4, the adsorption capacity of modified silica gel adsorbent was found to be 4.9, 5.0, 33.2, and 12.6 mg g⁻¹ for Cr(III), Cu(II), Pb(II) and Zn(II), respectively. However, the adsorption capacity of nm-SiO₂ adsorbent toward Cr(III) was 26.7 mg g⁻¹ under ultrasonic dispersing. The potential application of p-toluenesulfonylamide-modified silica gel for simultaneous preconcentration of trace chromium, copper, lead and zinc from two standard reference materials and two food samples was performed with satisfactory results. Correspondence: Xijun Chang, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Characteristics of sorption of uncomplexed and complexed Pb(II) from aqueous solutions onto peat

Batch experiments aimed at the sorption of Pb(II) onto peat were performed from an aqueous solution in both the absence and presence of common complexing agents (acetate or citrate). The influence of the initial pH of the solution, metal ion concentration and contact time on the sorption efficiency of Pb(II) was examined at ambient temperature (18 ± 0.5) °C for each experiment. The results showed that the presence of acetate improved the efficiency of the sorption process, while the presence of citrate in the aqueous solution decreased the efficiency of the Pb(II) sorption onto peat. The equilibrium data fitted well with the Langmuir isotherm model and confirmed the monolayer sorption of uncomplexed and complexed Pb(II) species onto peat. The values of maximum sorption capacities (q _max) were 135.13 mg g⁻¹ for Pb(II) complexed with acetate, q > 79.36 mg g⁻¹ for uncomplexed Pb, q > 38.46 mg g⁻¹ for Pb(II) complexed with citrate. The kinetics of Pb(II) sorption onto peat, in both the absence and presence of complexing agents, indicated a pseudosecond order mechanism. Analysis of IR spectra showed that carboxylic and hydroxyl groups had an important role in the binding process of Pb(II) species onto peat.     

Immersion enthalpy and the constants of Langmuir model in the 3-chloro phenol adsorption on activated carbon

The adsorption process of 3-chloro phenol from aqueous solution on a activated carbon prepared from African palm stone and which presents a specific surface area of 685 m² g⁻¹, a greater quantity of total acid groups and a pH_PZC of 6.8 is studied. The adsorption isotherms are determined at pH values of 3, 5, 7, 9 and 11. The adsorption isotherms are fitted to the Langmuir model and the values of the maximum quantity adsorbed that are between 96.2 and 46.4 mg g⁻¹ are obtained along with the constant K_L with values between 0.422 and 0.965 L mg⁻¹. The maximum quantity adsorbed diminishes with the pH and the maximum value for this is a pH of 5. The immersion enthalpies of the activated carbon in a 3-chloro phenol solution of constant concentration, of 100 mg L⁻¹, are determined for the different pH levels, with results between 37.6 and 21.2 J g⁻¹. Immersion enthalpies of the activated carbon in function of 3-chloro phenol solution concentration are determined to pH 5, of maximum adsorption, with values between 28.3 and 38.4 J g⁻¹, and by means of linearization, the maximum immersion enthalpy is calculated, with a value of 41.67 J g⁻¹. With the results of the immersion enthalpy, maximum quantity adsorbed and the constant K_L, establish relations that describe the adsorption process of 3-chloro phenol from aqueous solution on activated carbon.     

Adsorption of reactive brilliant red K-2BP on activated carbon developed from sewage sludge

Activated carbon was prepared from the sewage sludge of municipal wastewater treatment plant by chemical activation (activation reagent is ZnCl₂) and was used for the adsorption of dye (reactive brilliant red K-2BP). The impact of adsorbent amount, adsorption time and pH value on adsorption effect, the adsorption kinetics, and the adsorption thermodynamics were discussed according to batch adsorption tests. The results indicated that the activated carbon developed from sewage sludge (ACSS), which was mesoporous, possessed opened porous structures. The iodine number of the ACSS was 326 mg·g⁻¹. The rate of achievement was 51.31%. The BET surface area was 298 m²·g⁻¹ and the contents of heavy metals in the leachate didn’t exceed the contents limit. The adsorption kinetics of reactive brilliant red K-2BP on the ACSS was accorded with the two-step kinetics rate equation and pseudo-second-order kinetics equation. Compared to the Freundlich isotherm equation, the Langmuir isotherm equation showed better applicability for the adsorption. The adsorption which was favorable was an endothermic (enthalpy ΔH > 0) and spontaneous (free energy ΔG < 0) process and was accompanied by an increase in entropy (ΔS > 0). __________ Translated from Journal of Shandong University (Natural Science), 2007, 42(3): 64–70 [译自: 山东大学学报(理学版)]     

Removal of Mn(II) and Cd(II) from wastewaters by natural and modified clays

The adsorption capacities of commercial and Brazilian natural clays were evaluated to test their applications in wastewater control. We investigated the process of sorption of manganese(II) and cadmium(II) present in synthetic aqueous effluents, by calculating the adsorption isotherms at 298 K using batch experiments. The influence of temperature and pH on the adsorption process was also studied. Adsorption of metals was best described by a Langmuir isotherm, with values of Q ₀ parameter, which is related to the sorption capacity, corresponding to 6.3 mg g^{− 1} for K-10/Cd(II), 4.8 mg g^{− 1} for K-10/Mn(II), 11.2 mg g^{− 1} for NT-25/Cd(II) and 6.0 mg g^{− 1} for NT-25/Mn(II). We observed two distinct adsorption mechanisms that may influence adsorption. At the first 5 min of interaction, a cation exchange mechanism that takes place at exchange sites located on (001) basal planes is predominant. This process is inhibited by low pH values. After this first and fast step, a second sorption mechanism can be related to formation of inner-sphere surface complexes, which is formed at edges of the clay. The rate constants and the initial sorption rates correlate positively with temperature in all studied systems, denoting the predominance of a physisorption process. The addition of complexing agents that are incorporated within the K10 structure, enhance metal uptake by the adsorbent. The results have shown that both Cd(II) and Mn(II) were totally retained from a 50 mg L^{− 1} solution when K10 grafted with ammonium pyrrolidinedithiocarbamate (APDC) was used as adsorbent.     

Adsorption heats of phenol on activated carbon using adapted method of immersion calorimetry

Simple adaptation of the technique of immersion calorimetry enables determining both integral and differential adsorption heats as well as the course of the adsorption isotherm of phenol on activated carbon. The innovative aspect of the applied procedure consists in bringing the phenol aqueous solution to contact with the suspension of carbon with water. Thus, the “interfering” heat effect of carbon interaction with water is eliminated, and only the net adsorption heat of phenol is monitored. The value of −52.5 kJ mol⁻¹ was ascertained as the molar differential adsorption heat at the low surface coverage (cca 0.2 mmol g⁻¹) of the sample of microporous carbon. As the adsorption process continues, for adsorption uptakes exceeding the value of about 1 mmol g⁻¹, molar differential adsorption heats appear to be established at a level of about −20 + 5 kJ mol⁻¹.     

Carbon dioxide adsorption on the microporous ACC carbon adsorbent

Adsorption isotherms of carbon dioxide on the microporous ACC carbon adsorbent and the adsorption deformation of the adsorbent were measured. The heats of adsorption at temperatures raising from 243 to 393 K and pressures from 1 to 5⋅10⁶ Pa were measured. In the low-temperature region (243 K), an increase in the amount adsorbed is accompanied by adsorbent contraction, and at high micropore fillings (a > 10 mmol g⁻¹) the ACC carbon adsorbent expands. At high temperatures, adsorbent expansion is observed in the whole region of micropore filling. At 243 K in the low filling region (a < 1 mmol g⁻¹), the heat of adsorption decreases smoothly from 27 to 24 kJ mol⁻¹. The heat of adsorption remains virtually unchanged in the interval 2 mmol g⁻¹ < a < 11 mmol g⁻¹ and then decreases to 8 kJ mol⁻¹ at a = 12 mmol g⁻¹. Taking into account the nonideal character of the gas phase and adsorbent deformation the heats of adsorption are strongly temperature-dependent in a region of high pressures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1331–1335, June, 2005.     

Sorption behavior of Sn(II) onto Haro river sand from aqueous acidic solutions

The sorption behavior of Sn(II) onto Haro river sand has been examined with respect to nature of electrolyte, agitation time, dosage of sorbent and concentration of sorbate. Maximum sorption (95.5%) has been achieved from 0.034M hydrochloric acid solution after equilibrating sorbate (2·10⁻⁵M) and sorbent (50 mg) for 120 minutes at aV/W ratio of 90 cm³·g⁻¹. The kinetic data have been subjected to Morris-Weber and Lagergren equations. The kinetics of sorption proceeds a two stage process consisting of a relatively slow initial uptake followed by a much rapid increase in the sorption. The rate constant of intraparticle transport, K_d, comes out to be 8.75·10⁻⁸ mol·g⁻¹·min^−1/2 and the first order rate constant for sorption is 0.0416 min⁻¹. The sorption data of Sn(II) onto Haro river sand followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) type isotherms. The Langmuir constant,Q, related to sorption capacity and,b, related to sorption energy are computed to be 10.6±1.1 μmol·g⁻¹ and 1123±137 dm³·mol⁻¹, respectively. The D-R isotherm yields the values ofC _m=348±151 μmol·g⁻¹ and β=−0.01044±0.0008 mol²·kJ⁻² and ofE=6.9±0.3 kJ·mol⁻¹. In all three isotherms correlation factor (γ) is ≥0.99. The influence of common anions and cations on the sorption has been investigated. Zn(II), Mg(II), oxalate, Pb(II), Mn(II) and tartrate reduce the sorption significantly whereas Fe(II) causes substantial increase in the sorption. It is essential that all ions causing a decrease in the sorption of Sn(II) must be absent from the sorptive solution otherwise low sorption yields would result.     

A quantum chemical study of lead(II) thiocomplexes with mono- and bidentate ligands

Model Pb(II) thiocomplexes with mono- and bidentate ligands of the composition [Pb(L^1,2) _n ]²⁻ⁿ (L¹ is (SC₆H₅)⁻ (thiophenolate ion), L² is (S₂CN(CH₃)₂)⁻ (dithiocarbamate ion), n is the number of ligands of 2–6), which simulate fragments of the crystal structures of Pb(II) complex compounds with organic ligands, are studied within density functional theory. Geometric and energy parameters of model complexes with different coordination geometries of the Pb atom are determined and the stereochemical activity of the lone electron pair (LEP, E) of the Pb²⁺ ion is estimated in them. In the studied complexes, the highest Pb-S binding energy is found for the Pb atom surrounded by 2–4 ligands. The geometry of the Pb atom coordinated by S donor atoms can be described in terms of the valence shell electron pair repulsion (VSEPR) model with stereochemically active LEP. The coordination number (cn) of the Pb atom in the most energetically favorable complexes [Pb(SC₆H₅) _n ]²⁻ⁿ is (3+E) − (4+E), and in [Pb(S₂CN(CH₃)₂) _n ]²⁻ⁿ complexes, it is (4+E) and (6+E). Configurations with the mentioned cns are most often observed in the crystal structures of Pb(II) thiocomplex compounds.     

Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

Adsorption syntax of Au(III) on unloaded polyurethane foam

The nature of adsorption behavior of Au(III) on polyurethane (PUR) foam was studied in 0.2M HCl aqueous solution. The effect of shaking time and amount of adsorbent were optimized for 3.16·10⁻⁵M solution of Au(III) in 0.2M HCl. The classical Freundlich and Langmuir adsorption isotherms have been employed successfully. The Freundlich parameters 1/n and adsorption capacityK are 0.488±0.016 and (1.40±0.22)·10⁻² mol·g⁻¹, respectively. The Langmuir constants of saturation capacityM and binding energyb are (1.66±0.08)·10⁻⁴mol·g⁻¹ and 40294±2947 l·g⁻¹, respectively, indicating the monolayer chemical sorption. The mean free energy (E) of adsorption of Au(III) on PUR foam has been evaluated using D-R isotherm and found to be 11.5±0.16 kJ·mol⁻¹ reflecting the ion exchange type of chemical adsorption. The effect of temperature on the adsorption has also been studied. the isosteric heat of adsorption was found to be 44.03±1.66 kJ·mol⁻¹. The thermodynamic parameters of ΔG, ΔH, ΔS and equilibrium constantK _c have been calculated. The negative values of ΔG, ΔH and ΔS support that the adsorption of Au(III) on PUR foam is spontaneous, exothermic and of ion exchange chemisorption. The nature of the Au(III) species sorbed on PUR foam have been discussed.     

Production of Butyric Acid from Glucose and Xylose with Immobilized Cells of <Emphasis Type="Italic">Clostridium tyrobutyricum</Emphasis> in a Fibrous-bed Bioreactor

Butyric acid has many applications in chemical, food, and pharmaceutical industries. In the present study, Clostridium tyrobutyricum ATCC 25755 was immobilized in a fibrous-bed bioreactor to evaluate the performance of butyrate production from glucose and xylose. The results showed that the final concentration and yield of butyric acid were 13.70 and 0.46 g g⁻¹, respectively, in batch fermentation when 30 g L⁻¹ glucose was introduced into the bioreactor. Furthermore, high concentration 10.10 g L⁻¹ and yield 0.40 g g⁻¹ of butyric acid were obtained with 25 g L⁻¹ xylose as the carbon source. The immobilized cells of C. tyrobutyricum ensured similar productivity and yield from repeated batch fermentation. In the fed-batch fermentation, the final concentration of butyric acid was further improved to 24.88 g L⁻¹ with one suitable glucose feeding in the fibrous-bed bioreactor. C. tyrobutyricum immobilized in the fibrous-bed bioreactor would provide an economically viable fermentation process to convert the reducing sugars derived from plant biomass into the final bulk chemical (butyric acid).     

Scale up and Application of Biosurfactant from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> in Enhanced Oil Recovery

There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass (Y _p/x), biosurfactant on sucrose (Y _p/s), and the volumetric production rate (Y) for shake flask were obtained about 0.45 g g⁻¹, 0.18 g g⁻¹, and 0.03 g l⁻¹ h⁻¹, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y _x/s, Y _p/x, Y _p/s, and Y of 0.42 g g⁻¹, 0.595 g g⁻¹, 0.25 g g⁻¹, and 0.057 g l⁻¹ h⁻¹, respectively. The biosurfactant maximum production, 2.5 g l⁻¹, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient (K _L a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s⁻¹, respectively. Comparison of K _L a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with K _L a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water flooding in the sand pack.     

Enthalpic characterization of activated carbons obtained from <Emphasis Type="Italic">Mucuna Mutisiana</Emphasis> with different burn-offs

Immersion enthalpies of activated carbon samples obtained by activation with steam at temperatures between 600 and 900 °C and activation times between 1 and 10 h were determined. The calorimetric liquids of immersion are CCl₄, water, NaOH, and HCl 2 M solutions, and the values of the immersion enthalpies are related to other properties of the activated carbons such as the surface area B.E.T., the micropore volume, the content of acid, and basic surface groups. The highest values for the immersion enthalpies take place for the polar solvent CCl₄ and for HCl solution, with values between 4.0 and 75.2 J g⁻¹ and 9.15 and 48.3 J g⁻¹, respectively.     

Adsorption of Dyes from Aqueous Textile By-Products on Activated Carbon from Scenedesmus obliquus

The adsorption of activated carbon prepared from Scenedesmus obliquus (algae) was evaluated through adsorption of Astrazon red. The adsorption efficiency of activated carbon was determined based on the specific surface area and pore size distribution. These results were compared with the results obtained with untreated algae. Approximately a 3-fold increase in the percentage of dye removal was observed for activated carbon compared to the untreated material. The primary reason for this observation may be the increase in specific surface area and total pore volume by chemical activation from 0.0136 to 423.7001?m²?g^?1 and from 0.0012 to 0.1643?cm³?g^?1, respectively. A pseudo-second-order model was fit with the kinetic data and the results indicate chemical adsorption. The maximum adsorption capacity of activated carbon was 181.82?mg?g^?1 at 25°C according to Langmuir isotherm model.     

Preparation and electrochemical performance of activated carbon thin films with polyethylene oxide-salt addition for electrochemical capacitor applications

The effect of polymer–salt addition in the activated carbon electrode for electric double-layer capacitor (EDLC) has been investigated. A series of composite thin film electrode consisting of activated carbon, carbon black, polytetrafluoroethylene and polymer–salt complex (polyethyleneoxide–LiClO₄) with an appropriate weight ratio were prepared and examined their performance for EDLCs using 1 mol L⁻¹ LiClO₄ in ethylene carbonate:diethylcarbonate electrolyte solution. The electrochemical capacitance performances of these electrodes with different compositions were characterized by cyclic voltammetry, galvanostatic charge–discharge cycling, and AC impedance measurements. By comparison, the best results were obtained with a composite electrode rich in polymer–salt additive (132 F g⁻¹ at 100 mA g⁻¹ of galvanostatic experiment). In general, the polymer–salt-containing electrode had shown improved performance over activated carbon electrodes without polymer–salt at high current density.     

Design of silica microparticles with oligopeptide brushes and their interaction with proteins

Synthesis of small oligopeptide brushes (oligo(S-benzyl-l-cysteine)) onto polyelectrolyte functionalized silica microparticles was developed. Poly(vinyl amine) (PVAm) adsorbed from salt-free and KCl 10⁻¹ mol L⁻¹ aqueous solution onto silica microparticles was chemically and naturally cross-linked by epichlorohydrin and CO₂, respectively. After the adsorption of PVAm onto microporous silica particles and stabilization by cross-linking, five repeated coupling reactions of Boc-S-benzyl-l-cysteine were performed. To test the protein interactions with the newly designed surface, human serum albumin (HSA) has been selected as a model protein. X-ray photoelectron spectroscopy, total organic carbon, potentiometric and polyelectrolyte titrations, and electrokinetic analysis were employed to obtain information about the polyelectrolyte adsorption and the amount of the amino acid S-benzyl-l-cysteine that was covalently bound to the solid surface and for determination of the protein amount adsorbed onto functionalized surface. The amount of HSA adsorbed onto modified silica microparticles decreased in order: silica/PVAm-cross-linked (silica/PVAm-C) (8.00 mg g⁻¹) > silica/PVAm-C/S-benzyl-l-cysteine (6.34 mg g⁻¹) > silica (4.86 mg g⁻¹) > silica/PVAm-C/(S-benzyl-l-cysteine)₅ (1.86 mg g⁻¹).     

CO<Subscript>2</Subscript> adsorption on binderless activated carbon monoliths

A series of activated carbon monoliths have been prepared by chemical activation of two lignocellulosic precursors, coconut shell (CACM) and African palm stones (PACM). The incorporation of a conforming step between the impregnation with H₃PO₄ and the activation step allows the successful development of disc-shape monoliths without the use of a binder. Textural characterization results using N₂ adsorption at 77 K show that the effect of the activating agent highly depends on the nature of the carbon precursor used. While chemical activation with phosphoric acid has mainly no effect when using coconut shell, a large development of both micro- and mesoporosity is observed for African palm stones. Large concentrations of the activating agent produce the partial shrinkage of the narrow microporous structure independently of the precursor used. Concerning the adsorption of CO₂ at atmospheric pressure and 273 K, both series of activated carbon monoliths exhibit an improved adsorption behaviour with the activation degree up to an optimum value around ∼164 mg CO₂/g, for sample CACM-32, and ∼162 mg CO₂/g, for sample PACM-28, the amount adsorbed decreasing thereafter. Apparently, the total amount of CO₂ adsorbed under these experimental conditions is defined by the volume of narrow micropores (V _n ).