Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H₂SO₄ (concentrations: 0·5 mol dm^?3 and 2·5 mol dm^?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (X_m) and the apparent equilibrium constants (K_a) of the samples; X_m and K_a values range respectively for 4·11 mg g^?1 and 1·90 dm³ g^?1 for the sample acid-treated with 2·5 mol dm^?3 H₂SO₄ [(B)-A(2·5)] up to 16·50 mg g^?1 and 30·67 dm³ g^?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g^?1 and 0·07 dm³ g^?1, also for B-A(2·5), up to 4·54 mg g^?1 and 0·45 dm³ g^?1 [B-N-200], for the adsorption process of zinc. X_m and K_a values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.     

Removal of 1,1′-Dimethyl-4,4′bipyridyl Dichloride from Aqueous Solution by Natural and Activated Bentonite

The sorption of 1,1′-dimethyl-4,4′bipyridilium dichloride (paraquat) on bentonite desiccated at 110°C untreated, and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 M and 1·00 M , from aqueous solution at 30°C has been studied by using batch experiments. In addition, column experiments were carried out with the bentonite sample treated with the 1·00 M H₂SO₄ solution [B-A(1·00)] by using two aqueous solutions of paraquat of different concentrations (C = 29·40 mg dm⁻³ and C = 65·38 mg dm⁻³). The experimental data points have been fitted to the Langmuir equation in order to calculate the sorption capacities (X_m) of the samples; X_m values range from 1·35×10⁵ mg kg⁻¹ for the sample acid-treated with 0·375 M H₂SO₄ [B-A(0·375)] up to 1·96×10⁵ mg kg⁻¹ for the untreated bentonite [B-N]. The removal efficiency (R) has also been calculated; R values ranging from 44·61% for the [B-A(0·375)] sample up to 67·23% for B-N. The batch experiments show that the natural bentonite is more effective than the acid-treated bentonite in relation to sorption of paraquat. The column experiments show that the B-A(1·00) sample might be reasonably used in removing paraquat, the column efficiency increasing from 37·55% for the C = 65·38 mg dm⁻³ aqueous solution of paraquat up to 66·58% for the C = 29·40 mg dm⁻³ one. © 1997 SCI.     

Removal of linuron from water by natural and activated bentonite

The sorption of linuron on bentonite desiccated at 110°C untreated, and acid‐treated with H₂SO₄ solutions over a concentration range between 0.25 M and 1.00 M from aqueous solution at 25°C has been studied by using batch experiments. In addition, column experiments were carried out with the bentonite sample treated with the 1.00 M H ₂SO₄ solution [B‐A(1.00)] by using two aqueous solutions of linuron of different concentrations (C=4.97 mg dm⁻³ and C=7.63 mg dm⁻³ ). The experimental data points have been fitted to the Langmuir equation in order to calculate the sorption capacities (X_m) of the samples; X_m values range from 0.02 g kg⁻¹ for the untreated bentonite [B‐N] up to 0.20 g kg⁻¹ for the sample acid‐treated with the 1.00 M H₂ SO₄ solution. The removal efficiency (R ) has also been calculated; R values ranging from 15.86% for the [B‐N] sample up to 41.54% for [B‐A(1.00)]. The batch experiments show that the acid‐treated bentonite is more effective than the natural bentonite in relation to sorption of linuron. The column experiments show that the B‐A(1.00) sample might be reasonably used in removing linuron, the column efficiency increasing from 61.8% for the C=7.63 mg dm⁻³ aqueous solution of linuron up to 77.6% for the C=4.97 mg dm⁻³ one. © 1999 Society of Chemical Industry     

Removal of 3—(3,4—dichlorophenyl)—1, 1 dimethylurea from aqueous solution by natural and activated bentonite

The adsorption of 3-(3,4-dichlorophenyl)-1,1 dimethylurea (diuron) on bentonite desiccated at 110°C untreated, and acid treated with H₂SO₄ solutions over a concentration range between 0.25 M and 5.00 M, from aqueous solution at 30°C has been studied. In addition, adsorption of diuron on combined acid/heat treated samples (0.50 M and 2.50 M H₂SO₄/200°C and 400°C) has also been studied. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K) of the samples; K values range from 0.92 μg g^?1 for the untreated bentonite up to 974.42 μg g^?1 for the 0.50 M H₂SO₄/400°C acid/heat treated bentonite. The removal efficiency (R) has also been calculated; R values ranging from 2.02% for the untreated bentonite up to 97.17% for the 0.50 M H₂SO₄/400°C acid/heat treated bentonite. The adsorption experiments show that bentonite heat treatment is more effective than bentonite acid treatment in relation to adsorption of diuron.     

Influence of the physical-chemistry properties of an acid-activated bentonite in the bleaching of olive oil

The bleaching process at 90°C of an olive oil from Jaen (Spain) using natural bentonite and bentonite acid treated with H₂SO₄ (over a concentration range between 0.50 M and 5.00 M) has been studied. The bleaching capacities of the bentonite samples were calculated by applying the Freundlich equation to the experimental data points corresponding to the bleaching process. The bleaching capacities (K_F parameter) range from 2.5 × 10^?7 for non-treated bentonite up to 0.85 for 2.50 M H₂SO₄ treated bentonite. The bleaching capacity of the 5.00 M H₂SO₄ treated bentonite (K_F = 0.81) is less than that of the 2.50 M H₂SO₄ treated bentonite.     

Removal of trivalent chromium(III) from solution by biosorption in cork powder

The removal of trivalent chromium from solutions using biosorption in cork powder is described. The adsorption isotherm was determined, along with the effect of different variables, such as biomass particle size, solid–liquid ratio, reaction time, metal concentration and pH, on the efficiency of chromium removal. It was concluded that the adsorption is slow and favoured by an increase in pH. Therefore, using a solid–liquid ratio of 4 g dm^?3 it is possible to reduce the chromium concentration in the solution from 10 mg dm^?3 to less than 1.5 mg dm^?3 in 2 h at 22 °C. The kinetic studies verified that the sorption of chromium by cork was described by a second‐order model. The elution results showed that 50% of the chromium bound to the cork was eluted using 0.5 mol dm^?3 H₂SO₄ and that cork maintains its binding capacity over four cycles of biosorption/elution. © 2002 Society of Chemical Industry     

Utilization of response surface methodology to optimize the culture media for the production of rhamnolipids by Pseudomonas aeruginosa AT10

Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 2⁴ full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO₃), the phosphate content (K₂ HPO₄/KH₂PO₄ 2:1) and the iron content (FeSO₄·7H₂O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm^?3 DCW, when the medium contained 50 g dm^?3 carbon source, 9 g dm^?3 NaNO₃, 7 g dm^?3 phosphate and 13.7 mg dm^?3 FeSO₄·7H₂O. The maximum concentration of rhamnolipid, 18.7 g dm^?3, was attained in medium that contained 50 g dm^?3 carbon source, 4.6 g dm^?3 NaNO₃, 1 g dm^?3 phosphate and 7.4 mg dm^?3 FeSO₄·7H₂O. © 2002 Society of Chemical Industry     

Effect of vibration on the rate of mass transfer

The rate of mass transfer at vibrating electrodes was measured using an electrochemical technique. The system chosen was stress-free polycrystalline electrolytic copper in CuSO₄/H₂SO₄ solution. The concentration of the electrolyte was 0·05 mol dm^?3 CuSO₄ and 1·5 mol dm^?3 H₂SO₄. Electrodes (160mm ×25 mm ×3 mm) were subjected to vertical vibrations and the limiting current density was determined at a section not subjected to end effects. The electrodes were especially designed so that the results would be unaffected by the turbulence generated at the leading vibrating edge. This enabled the investigation of the effect of parallel fluid vibrations without interference from the other factors. The vibration frequency was varied up to 48 Hz while amplitudes of up to 8 mm were used. The rate of mass transfer was found to increase upon the application of vibration and enhancements of up to six fold were obtained. It was observed that when large amplitudes were used, a pronounced peak in the limiting current occurred. This is attributed to the amplification of fluid vibrations around the natural frequency of the boundary layer.     

A novel multienzyme electrode for the determination of citrate

A novel amperometric biosensor for the determination of citric acid in food samples and fermentation broths has been developed. The sensor is composed of citrate lyase (CL, EC 4.1.3.6), oxaloacetate decarboxylase (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3), co-immobilized in gelatin, and an amperometric transducer. A Clark-type O₂-electrode and a modified Clark-type H₂O₂-electrode were alternatively used as a transducer. The biosensor covers a linear detection range from 1 μmol dm^?3 to 1 mmol dm^?3 citrate, with a response time of 2·5 min for the steady state response. The lower detection limit for citrate is 0·5 μmol dm^?3. The response of the sensor remained constant for 8 days and decreased to 25% after 18 days at 20–23°C. The results obtained from citrate determinations in food samples and fermentation broths agree well with those determined by enzymatic sample anlaysis. The relative standard deviation for citrate determinations with the new biosensor was 2·2% (n = 7).     

Electrodeposition of catalytically active nickel powders from sulphate baths. I. Effect of bath constituents

A detailed study was made of the influence of the sulphate bath constituents: 0.3 - 0.0125 NiSO₄·7H₂O (I), 0.05 – 0.23 (NH₄)₂SO₄ (II), 0.1 – 0.4 H₃BO₃ (III) and 0.07 – 0.35 mol l^?1 Na₂SO₄·10H₂O (IV) on the electrodeposition of nickel powder. The cathodic polarization, current efficiency, growth morphology, crystallite size and catalytic activity of the electrodeposited nickel powders were affected to different extents by the bath constituents. A highly pure nickel powder characterized by a small crystallite size (776 Å) and moderate catalytic activity was obtained from a bath containing: 0.0125 (I), 0.23 (II), 0.1 (III) and 0.07 mol l^?1 (IV) at a current density of 10 A dm^?2 and electrolysis time 60 min. at 25 °C. Structural studies with a scanning electron microscope are given and a reaction mechanism for the electrolytic powder deposition is discussed.     

Fourier-transform infrared assay of bile salt-stimulated lipase activity in reversed micelles

A Fourier-transform infrared (FT-IR) spectroscopic method has been developed for assaying the bile salt-stimulated human milk lipase (BSSL, EC3.1) catalyzed hydrolysis of triolein in AOT reversed micelles in iso-octane. At 37°C in 50 mmol dm^?3 AOT the molar absorbtivities for the carbonyl stretching frequencies for triolein (at 1751 cm^?1) and oleic acid (at 1714 cm^?1) were 1646 dm³ mol^?1 cm^?1 and 743 dm^?3 mol^?1 cm^?1, respectively. The rate was linearly dependent upon the concentration of enzyme in the water pool up to 10 mg cm^?3 and maximum activity was observed at a ratio (w₀) of [H₂O]:[AOT] = 16·7. Using these conditions, and in the presence of 10 mmol dm^?3 sodium taurocholate (TC), the derived Michaelis–Menten parameters V_max and K_m were 57·5 μmol min^?1 mg^?1 and 5·53 mmol dm^?3, respectively. These results are compared with those obtained in an oil-in-water microemulsion system and are discussed in terms of the relative partitioning of the enzyme and the substrate in the aqueous and oil phases and the interfacial concentration of the substrate in the two systems.     

Electrodeposition of cobalt-nickel alloys from ammoniacal single-complex baths

The electrodeposition of cobalt-nickel alloys has been studied from ammoniacal single-complex baths containing 5–50 CoSo₄·7H₂O, 5–50 NiCl₂·46H₂O, 20–50 g dm^?3 (NH₄)₂SO₄ and 250–350 cm³ dm^?3 NH₄OH (20.5% solution). The effects of the plating current density and the concentrations of the bath constituents on the cathodic polarisation, current efficiency and composition of the alloy were investigated. A wide range of alloy compositions with a current efficiency of 60–80% could be obtained from the main baths examined. The alloy plating system interchanged between the normal and the anomalous types depending upon the plating current density and the concentration of NH⁺₄ ion in the bath. Electron microscopic and X-ray diffraction studies proved that the structure of the electrodeposited alloy was controlled by the alloy composition.     

In situ scanning tunneling microscopy study of selective dissolution of Au3Cu and Cu3Au (0 0 1)

We present an electrochemical study of Au₃Cu (0 0 1) single crystal surfaces in 0.1 mol dm⁻³ H₂SO₄ and 0.1 mol dm⁻³ H₂SO₄ + 0.1 mmol dm⁻³ HCl, and of Cu₃Au (0 0 1) in 0.1 mol dm⁻³ H₂SO₄. The focus is on in situ scanning tunneling microscopy experiments. The changes of the surface morphology, which are time- and potential-dependent, have been observed, clearly resolving single atomic steps and mono-atomic islands and pits. Chloride additives enhance the surface diffusion and respective morphologies are observed earlier. All surfaces have shown considerable roughening already in the passive region far below the critical potential.     

Dilute solution properties of cationic poly(dimethyl sulfate quaternized dimethylaminoethyl methacrylate)

The dilute solution properties of a cationic polyelectrolyte, poly(dimethyl sulfate quaternized dimethylaminoethyl methacrylate) [poly(DMAEM · C₂H₆SO₄)], are studied by measurements of intrinsic viscosity, degree of binding, and flocculation application. The intrinsic viscosity of this polyelectrolyte is related to the type and concentration of added salt. The intrinsic viscosity behavior for cationic polyelectrolyte resulting from the electrostatic repulsive force of the polymer chain is contrasted with polyampholyte. The polyelectrolyte in the presence of KCl has a lower degree of binding, indicating that the proton ion (H⁺) is relatively difficult to bind to the CH₃SO₄^? at the polymer end. The polymerization of DMAEM · C₂H₆SO₄ in 0.5M KCl aqueous solution proceeded more easily than that of DMAEM · C₂H₆SO₄ in pure water. The polymerization rate of DMAEM · C₂H₆SO₄ is found to pass through an extreme value as a function of pH. Optimum flocculation, corresponding to the complete removal of turbidity in the supernatant, is achieved. Beyond the optimum flocculation, high polymer dosages redisperse the bentonite suspensions.     

Adsorption of Microamounts of Silver on Manganese Dioxide from Acid Solutions

Abstract

Adsorption of microamounts of silver on manganese dioxide from nitric and perchloric acid solutions has been studied and optimized with respect to shaking time, concentrations of electrolyte, adsorbent, and adsorbate. Maximum adsorp- tion (>99.5%) has been achieved from 0.01 mol/dm³ acid solution using 50 mg oxide at 10^?5 mol/dm³ silver concentration after 30 min shaking. The adsorption decreases with increasing concentration of acid and adsorbate from both the acids. The presence of a 10⁴-fold greater concentration of cyanide, thiocyanate, thiosulfate, and Pb(II) than silver reduces the adsorption drastically. The adsorption of silver follows the Freundlich adsorption isotherm over the entire concentration range investigated from 9.27 × 10^?6 to 2.92 × 10^?3 mol/dm³ with a value of A = 49 mmol/g and 1/n = 0.93. Moreover, the Langmuir adsorption isotherm is also valid except at the lowest and highest concentrations. The values of the limiting adsorption concentrtion (C_m ) have been found to be 1 mmol/g and of the equilibrium constant for adsorption 87 dm³/mol at 23 ± 2°C.     

Kinetics of aspartame precursor synthesis catalysed by Pseudomonas aeruginosa elastase

Elastase isolated from Pseudomonas aeruginosa IFO 3455 was found to be an efficient protease to catalyse the synthesis of N-benzyloxycarbonyl-aspartyl-phenylalanine methyl ester, the precursor of the dipeptide sweetener, aspartame. The influence of methanol as a cosolvent in this synthetic reaction was investigated. It was found that the synthesis of the dipeptide precursor was most efficient in 25% (v/v) methanol, pH 7·0 at about 25°C for a reaction time of about 3 h. However, the activity of the enzyme was greatly reduced in 90% methanol. The values of K and k₂ for N-benzyloxycarbonyl-aspartic acid were 0·17 mol dm^?3 and 11·9 mol dm^?3 s^?1 respectively.     

Effects of some plating variables on the electrodeposition of catalytically active nickel-thallium alloy powders

The electrodeposition of nickel-thallium alloy powders was investigated from a selected bath of the composition 0.0125 NiSO₄·6H₂O, 0.01 TICI, 0.10 (NH₄)₂SO₄, 0.10 H₃BO₃ and 0.07 Na₂SO₄·10 H₂O (mol dm^?3). The effects of the pH of the bath, deposition current density and deposition time on the cathodic polarisation, current efficiency and composition of the electrodeposited alloy were determined. The properties of the electrodeposits examined, as a function of the above-mentioned variables, were surface morphology and catalytic activity towards the decomposition of 0.4% H₂O₂ solution. It was found from this investigation that the operating variables influence to a great extent the current efficiency, composition and surface morphology of the electrodeposited alloys; and the catalytic activity is primarily controlled by the surface morphology.     

Removal of chloridazon from water by kerolite/stevensite and bentonite: a comparative study

The adsorption of chloridazon (5‐amino‐4‐chloro‐2‐phenylpyridazin‐3(2H)‐one) on a new type of material formed by kerolite/stevensite bearing lithofacies and on a bentonite, desiccated at 110 °C from aqueous solution at 25 °C has been studied by using batch experiments. In addition, column experiments were carried out with these samples using aqueous solutions of chloridazon at a concentration (C) of 45 × 10⁻⁴ cmol dm⁻³. The experimental data points have been fitted to the Langmuir equation to calculate the adsorption capacities (X_m). Values for X_m ranged from 0.072 cmol kg⁻¹ for bentonite up to 1.30 cmol kg⁻¹ for kerolite. The removal efficiency, R, ranged from 17.1% for bentonite up to 85.1% for kerolite. The batch experiments show that the kerolite is more effective than bentonite in adsorbing chloridazon. The column experiments show that kerolite might be reasonably used in removing chloridazon, the data indicating that a readily available and inexpensive Spanish kerolite can be employed as a filter for contaminated waters with chloridazon, so controlling its release to the environment. © 2000 Society of Chemical Industry     

Mathematical modelling of the alcoholic fermentation of glucose by Zymomonas mobilis mobilis

The kinetics of alcoholic fermentation of a strain of Zymomonas mobilis, isolated from sugarcane juice, has been studied with the objective of determining the constansts of a non-structured mathematical model that represents the fermentation process. Assays in batch and in continuous culture have been carried out with different initial concentrations of glucose. The final concentrations of glucose, ethanol and biomass were determined. The following kinetic parameters were obtained: μ_max, 0·5 h^?1; K_s, 4·64 g dm^?3; P_max, 106 g dm^?3; Y_x/s, 0·0265 g g^?1; m, 1·4 g g^?1 h^?1; α, 17·38 g g^?1; β, 0·69 g g^?1 h^?1.     

Isomer Directed Synthesis of Two 3D Cadmium(II) Compounds: Structure Variation and Energetic Performance

Two inorganic mixtures of copper and sodium compounds have been synthesized and characterized with different measurement techniques. The thermal property of these mixtures has been studied to low temperature up to 223 from 573 K with DSC. The specific heat capacity of this mixture has been measured in atmospheric O₂ at a rate of 10 K min^?1 from 573 to 223 K and vice versa in two thermal cycles. The net specific heat capacity of these mixtures is found endothermic in first and second thermal cycles. The net specific heat capacity of 0.5Cu₂(PO₄)(OH); 3.5CuH(PO₄)₂·H₂O; 2NaHSO₄·H₂O (CuPHS) during first thermal cycle is ?71203.05 J kg^?1 K^?1 and in second thermal cycle is ?73881.67 J kg^?1 K^?1 between temperature range of 303–223 K. The net specific heat capacity of mixture 0.5Cu₂(PO₄)(OH); 3.5CuH(PO₄)₂; 2Na₂SO₄(CuPS) in first thermal cycle is ?21158.37 J kg^?1 K^?1 and in second thermal cycle is?45739.92 J kg^?1 K^?1 between temperature range of 298–573 K. As both mixtures are endothermic in nature in all cycles, it can be used as heat storage material.The average crystallite size of mixture 0.5Cu₂(PO₄)(OH); 3.5CuH(PO₄)₂·H₂O; 2NaHSO₄·H₂O and 0.5Cu₂(PO₄)(OH); 3.5CuH(PO₄)₂; 2Na₂SO₄ is ~47 and ~17.3 nm, respectively.