Precipitate Flotation of Complexed Cyanide

Abstract

Precipitated cyanide, complexed with Fe(II) at a molar Fe/CN ratio of 0.550, can be floated readily from aqueous suspension with a cationic surfactant, ethylhexadecyldimethylammonium bromide. The effects of three distinct mixing times of significance in preparing the precipitate and contacting it with surfactant, of pH, of initial cyanide concentration, of initial surfactant concentration, and of ionic strength have been established experimentally. Mixing times and the initial cyanide concentration have little influence on the flotation, while increases in pH and ionic strength have a most pronounced influence, part of which can be overcome with increased surfactant concentrations. At pH 6.0, 95% of the complexed cyanide can be foam separated from distilled water suspensions 1.5 to 3.1 mM in total cyanide. About 0.04 mole surfactant/mole complexed cyanide is required; about 0.08 mole/mole is required to increase the flotation to 99% or to overcome ionic strength effects.     

Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques

Nuclear magnetic resonance (NMR) is explored as a technique for noninvasively monitoring emulsion droplet formation and destabilization. The method makes use of the fact that the diffusion of oil molecules within oil-in-water emulsion droplets results in attenuation of a coherent magnetic signal that emanates from those molecules. If oil diffusion is limited by the size of the droplet, the shape of a plot of attenuation over time is directly affected by the droplet radius. We use this approach to determine noninvasively the effect of surfactant type, surfactant concentration, pH, and ionic strength on droplet sizes within a 40 wt% octane and water emulsion, stabilized by Tween 20 or β-lactoglobulin (β-Lg). We find that addition of the low-molecular-weight Tween 20 forms finer emulsion droplets than does addition of the protein, and that the Tween 20 emulsion is sensitive to surfactant concentration below a threshold “saturation” concentration. The droplet sizes in β-Lg-containing emulsions increase as pH increases above the isoelectric point and as ionic strength increases. The fact that the NMR technique does not mistake clusters of droplets for single large droplets makes the analysis of these effects unambiguous. We further extend the use of NMR diffusion techniques to monitor the effect of surfactant type, surfactant concentration, and convection on the rate of droplet coalescence. The ability of NMR methods to distinguish between large single droplets and droplet clusters makes it well-suited to monitor coalescence processes independently from flocculation.     

Amino acid solubilization in cationic reversed micelles: factors affecting amino acid and water transfer

The aim of this work is to investigate the driving forces involved in amino acid solubilization in cationic reversed micelles, and to determine in which way different parameters affect the reversed micellar structure and amino acid solubilization, in order to select the best conditions to optimize amino acid extraction. To this end, extraction equilibrium experiments were performed using different experimental conditions and three amino acids with different structures: aspartic acid – a hydrophilic amino acid, phenylalanine – a slightly hydrophobic amino acid, and tryptophan – a hydrophobic amino acid. The study of the effect of amino acid related parameters, such as pH and the initial amino acid concentration in the aqueous phase, and the effect of parameters that influence the reversed micellar structure, such as surfactant concentration, ionic strength and co‐surfactant concentration, provides useful information about the driving forces involved, solute–micelle interfacial interactions and solute location in the cationic system trioctylmethylammonium chloride (TOMAC)/hexanol/n‐heptane. These parameters can be adjusted to optimize amino acid extraction. It is shown that amino acids with the same isoelectric point can be selectively separated by exploring the different interactions they establish with the reversed micellar interface. © 1999 Society of Chemical Industry     

Nano-sized graphene oxide as sole surfactant in miniemulsion polymerization for nanocomposite synthesis: Effect of pH and ionic strength

Miniemulsion polymerization of styrene using AIBN as initiator at 70 °C has been performed with nano-dimensional graphene oxide (GO) sheets as surfactant (no conventional surfactants employed) with a view to exploring the effects of pH and ionic strength (NaCl concentration). The pH value of the emulsion exerted a relatively minor influence on the polymerization, with a somewhat narrower particle size distribution being obtained at pH = 3.2 relative to pH = 2.4 and 5.2. The ionic strength had a more significant effect – the presence of a suitable concentration of NaCl resulted in increased colloidal stability and narrower particle size distribution. The results are explained in terms of the effects of pH on degree of ionization of COOH groups of GO and the influence of ionic strength on the electric double layer, and have implications with regards to synthesis of polymer/graphene nanocomposite materials for a variety of applications.     

Influence of the Disk Diameter and Baffle Position on the Performance of Generated Colloidal Gas Aphrons

Aphrons are surfactant‐stabilized microbubbles with thick soapy shells. Colloidal gas aphrons (CGA) with an average diameter of 50 μm have some unique properties: a high interfacial area due to their small size, a thick soapy shell and, above all, high stability compared to conventional foams. Various factors that can influence the performance of CGA dispersion, such as the type and concentration of surfactant, mixing time and processing parameters, have already been extensively studied. However, although CGA applications in various fields continue to advance, the influence of the disk diameter and baffle position of the aphron generator on the performance of CGAs has not been well studied. In this experimental work, the influences of the spinning disk diameter and baffle position inside the aphron generator have been investigated. Analyzing the drainage curve of various experimental runs revealed that the disk diameter and baffle position might have a positive impact on the stability of CGA dispersion particularly when the generation time or surfactant concentration is low. The experimental findings have been supported by other techniques such as half‐life time and a new stability index, T_0.1, the time elapsed when the drained liquid from CGA dispersion reaches ten percent of its final height.     

Parametric study of surfactant effect on mechanical and dissolution properties of detergent tablets

The aim of this study is to investigate the functional characteristics (mechanical strength and disintegration time) of effervescent detergent tablets containing chlorine provider in the presence of surfactant. A preliminary study high-lighted that the presence of 2% of sodium dodecyl sulfate (SDS) was not favorable to the tablet mechanical properties, inducing a lower “bonding ability,” whereas the disintegration time increased, compared with the reference tablets without surfactant. The linear relationship between the disintegration time and the end-dissolution time led us to consider just the disintegration time to express the behavior of the tablets in water. A parametric study has been completed to assess the influence of the mixing method, the nature, the hydrophilic-lipophilic balance, the granulometry, and the concentration of the surfactant on the tablet properties. In all cases, surfactant presented adverse effects on the mechanical properties and had a retarding effect on disintegration time, but neither solubility, hydrophilic-lipophilic balance, interfacial properties, nor ionic character could be clearly involved to explain surfactant contribution. Furthermore, tablet dissolution could not be correlated to surfactant available surface, as evidenced by granulometry comparison on one side and concentration impact on the other side (a similar effect was observed from 1 to 15%). On the contrary, mechanical properties were damaged as much as the area developed by surfactant particles increased. On the basis of this work, it has been concluded that SDS interacts with the other compounds of the formula by creating weak interparticle bonds and limiting water uptake responsible for disintegration.     

聚丙烯酸/聚丙烯酰胺/凹凸棒复合材料对亚甲基蓝的吸附性能

将聚(丙烯酸-co-丙烯酰胺)/凹凸棒复合吸附剂用于亚甲蓝的吸附,研究了时间、浓度、酸度、表面活性剂和离子强度等因素对吸附性能的影响。复合吸附剂对亚甲蓝的吸附是吸热过程,60℃时吸附量达到1 273.3 mg.g-1,吸附过程符合Langmuir单分子层吸附等温模式,并计算了热力学常数ΔG、ΔH和ΔS。在实验考察范围内吸附过程均符合准二级动力学特征。该复合吸附剂具有高吸附容量和较快的吸附速率,是良好的亚甲蓝吸附剂。     

Swelling–deswelling behavior of poly(acrylamide‐co‐maleic acid) hydrogels

In this study the poly(acrylamide‐co‐maleic acid) hydrogels containing small amounts of maleic acid have been synthesized, and the effect of pH, ionic strength, and nature of counterions on the equilibrium water uptake has been investigated. The incorporation of small amount of maleic acid results in the transition of swelling mechanism from Fickian to non‐Fickian. The equilibrium mass swelling has been found to increase with pH of the swelling medium while increase in ionic strength causes a decrease in the swelling. The amount of maleic acid present in the hydrogel affects the swelling behavior in rather an unusual way. With lower acid contents, the equilibrium mass swelling increases while higher concentrations of maleic acid cause a decrease in the degree of swelling. The hydrogels have been found to undergo a number of swelling–deswelling cycles when pH of the swelling medium changes from 8.0 to 2.0. Hydrogels require more time to deswell compared to the time required for swelling, which has been explained on the basis of the fact that gels follow different mechanisms for the two processes. Various swelling parameters such as equilibrium mass swelling, diffusion coefficient, intrinsic diffusion coefficient, swelling exponent, etc., have been evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2782–2789, 2001     

Electrostatic Splitting of the Emulsion Used in Liquid Surfactant Membranes Process for Metals Separation

Abstract

A study has been carried out to investigate the effect of different parameters on the splitting process of the emulsion used in the liquid surfactant membranes process for metals separation. The influence of electric field strength, frequency of the applied ac voltage, and membrane recycling on emulsion stability have been studied. The investigations have revealed that there exists a unique optimal frequency range in which the best separation of the emulsion phases is obtained. The effect of the membrane composition and the variation of tri-n-butyl phosphate (TBP) concentration has been shown to vary linearly with the splitting efficiency. This finding correlates quite well with Sadek and Hendrick's equation on the force causing coalescence in an electric field.     

Kinetics of glycine oxidation by N-bromophthalimide in the presence of sodium dodecyl sulfate

The kinetics of oxidation of glycine by N-bromophthalimide (NBP) were studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP] and fractional-order dependence on [glycine] and [H⁺]. The addition of reduced product of the oxidant had no significant effect on the rate of reaction. Increasing [Hg(OAc)₂] and [Br⁻] increased the rate of reaction, whereas a change in ionic strength (μ) of the medium had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. HCN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable mechanism consistent with the experimental findings has been proposed. The index of cooperativity and the micelle binding constant have been calculated.     

Water Uptake Kinetics and Control Release of Agrochemical Fertilizers from Nanoclay-Assisted Semi-interpenetrating Sodium Acrylate-Based Hydrogel

Semi-interpenetrating composite hydrogels composed of poly(acrylic acid-co-sodium acrylate)/polyethylene glycol for the controlled release of fertilizers were synthesized by using nano-phyllosilicate. Hydrogel was characterized by infrared spectral analysis (Fourier transform infrared), X-ray diffraction, and scanning electron microscopy. The cross-link density (ρ_c), average molecular weight between cross-links (M_c), and the mesh size of the network (?) were also determined. The degree of neutralization of acrylic acid component has a positive impact in the swelling behavior of hydrogel, which was investigated through its swelling study and pH-oscillatory behavior. The dependency of synthesis parameters, pH and ionic strength on swelling characteristics were investigated. The type of the diffusion phenomena was investigated by calculating various kinetic parameters such as the diffusion coefficient, diffusion rate constant, swelling exponents, etc. The swelling ratio with varying synthetic parameters was recorded to investigate fourth-order factorial model. The model gives the idea of the effect of the independent parameters on the swelling ratio.     

On the Applicability of Gardon's Equations for the Calculation of Particle Size in Emulsion Polymerisation

Gardon's revision of the Smith-Ewart theory of emulsion polymerisation makes it possible to calculate the average particle size of the latex produced from the conditions used for the polymerisation at least for monomers with a low monomer transfer constant. Good agreement has been found between the calculated particle sizes and the turbidity averages measured by light scattering for polystyrene latices prepared with various emulsifiers. However the theory neglects the effect of the ionic strength of the aqueous phase although Gardon's own results show this to be a significant parameter: increase of ionic strength increases the average size of the latex particles by reducing electrostatic stabilisation. The difference between the total and the micellar surfactant concentration is significant for surfactants with relatively high critical micelle concentrations and a considerable improvement in agreement between measured and calculated particle sizes is found when the concentration of micellar surfactant is used in the calculation. The theory requires the reaction rate to depend on the 3/5ths power of the concentration of micellar surfactant and although this would appear to have been satisfactorily verified experimentally, replotting of the extensive series of precise results published by Bartholome, Gerrens, Herbeck and Weitz shows that the double logarithmic plot is not actually linear. This is probably the result of a slow change of micelle size as the surfactant concentration is increased.     

Investigation of the adsorption of tropocollagen type I on titanium and Ti6Al4V

The adsorption of tropocollagen type I on titanium and Ti6Al4V has been investigated using physicochemical (zeta potential measurements), biochemical (ELISA), and imaging methods (SEM, AFM). Zeta potential measurements on both materials showed isolectric points in the pH_iep range 4.3-4.8 if the metal surfaces were covered with amorphous oxide layers. Adsorption of both collagen molecules and fibrillar collagen led to a shift of about 0.5 pH units towards the alkaline region. From ELISA-based results it can be concluded that in the investigated concentration range of 0.01-0.5 mg/ml, the adsorption of collagen molecules leads to the formation of a rather uniform covering. The influence of pH and ionic strength on the adsorption behavior has been investigated. A model of the competitive adsorption of both tropocollagen molecules and in vitro reconstituted fibrils is presented. Based on this model, two methods are proposed for the improved adsorption of collagen fibrils: (i) adsorption from solutions that are essentially free from tropocollagen and oligomeric species; and (ii) use of already adsorbed tropocollagen as nucleation sites for further fibrillar growth.     

Influence of surfactant properties on thermal behavior and sol–gel transitions in surfactant‐HPMC mixtures

Four surfactants, namely, sodium n‐decyl sulfate (SDeS), sodium n‐hexadecyl sulfate (SHS), sodium n‐dodecyl sulfate (SDS), and Triton X‐100, were used as additives to study thermal behavior and sol–gel transformations in dilute aqueous hydroxypropyl methyl cellulose (HPMC)/surfactant mixtures using micro‐differential scanning calorimetry. The influence of anionic surfactant, SDS on the gelation varied with SDS concentration where the sol–gel transition started at a higher temperature. Shape of the thermograms changed from single mode to dual mode at the SDS concentration of 6 mM and higher. SDeS and SHS, however, resulted in “salt‐in” effect of a different magnitude during gelation. Triton X‐100, being a non‐ionic surfactant, showed a minor “salt‐out” effect on the thermo‐gelation process. On the basis of different thermal behavior of anionic and non‐ionic surfactant/HPMC systems, a mechanism is proposed explaining how the chemical structure and electro‐charge of the surfactants affect the polymer/surfactant binding and polymer/polymer aggregation because of hydrophobic interaction during the sol–gel transition. © 2009 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2009     

Influence of ultrasound on diffusion through skin/leather matrix

Leather is a unique porous material, which is composed of a three-dimensional weave of tanned collagen fibre bundles. Collagen is a fibrous protein well organized in the formation of skin as building block. This paper studies the use of ultrasound in improving the diffusion process through porous skin/leather matrix. A diffusion model for leather processing has been proposed taking into account of pore characteristics in leather. Dye diffusion experiments have been carried out with leather and powdered leather to show the influence of ultrasound under two different diffusion conditions. Apparent diffusion coefficient (D) of dye through leather matrix has been calculated from the experimental dye uptake data. The results indicate that the use of ultrasound could achieve, 16.2 and 8.56 times improvement in D value for leather at 50 °C and 30 °C, respectively as compared to 2.99 and 1.55 times for powdered leather. Scanning electron microscopy (SEM) analysis of leather has also been performed which shows that fibre structure and morphology are not affected by the use of ultrasound. This study throws some light on enhanced transport through porous materials of complex nature such as skin/leather using ultrasound.     

Preparation of poly(acrylic acid‐co‐acrylamide)/kaolin and release kinetics of urea from it

A series of poly(acrylic acid‐co‐acrylamide)/kaolin [poly(AA‐co‐Am)/kaolin] composites were prepared by aqueous solution copolymerization of partially neutralized acrylic acid and acrylamide in the presence of kaolin nanopowder, which was synthesized to act as a release carrier of urea fertilizer. The superabsorbent composite was swollen in aqueous solution of urea to load urea, and the effect of urea concentration on the swelling was investigated. Furthermore, the effects of the contents of crosslinker, kaolin, and acrylamide, the neutralization degree of acrylic acid, and temperature, pH, and ionic strength of release medium on water absorbency and diffusion coefficient of urea release from poly(AA‐co‐Am)/kaolin were studied systematically. It was found that urea loading percentage could be adjusted by urea concentration of swelling medium, and urea diffusion coefficient could be regulated through the contents of crosslinker, kaolin, and acrylamide, and the neutralization degree of acrylic acid. Additionally, temperature and ionic strength of release medium may also affect the urea release process. The conclusions obtained could provide theoretical basis for urea diffusion behavior in superabsorbent used in agriculture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Sorption of boron by invasive marine seaweed: Caulerpa racemosa var. cylindracea

The sorption of boron from aqueous solution onto Caulerpa racemosa var. cylindracea (CRC), collected from Seferihisar/Izmir region in Turkey, was investigated as a function of pH, temperature, initial boron concentration, adsorbent dosage, contact time and ionic strength. Optimum conditions for the sorption of boron were obtained at pH 7.5, 318 K, 8 mg L⁻¹ initial boron concentration, 0.2 g of CRC, 2.5 h contact time and greater ionic strength (10⁻¹ M NaCl). As the temperature was increased the boron removal took place with higher percentages. In experiments conducted at optimum conditions, maximum boron sorption was determined to be about 63%. The experimental data were analyzed by Freundlich, Langmuir and Dubinin–Radusckevich (DR) equations. Freundlich and DR models provide best conformity with the experimental data. In order to describe kinetics of boron sorption onto CRC, first-order Lagergren equation, pseudo-second-order kinetic model and intraparticle diffusion model were used. It was seen that the first order Lagergren equation was better described than the pseudo-second-order kinetic model. Thermodynamic parameters of sorption process were also calculated. It was obtained that sorption process was not spontaneous. The characterization of CRC was carried out by Fourier transform infrared spectroscopy (FTIR) analysis.     

Rheological behavior of mixed system of ionic liquid [C8mim]Br and sodium oleate in water

We report on the rheological behavior of wormlike micelles constructed by ionic liquid surfactant [C₈mim]Br (1-octyl-3-methylimidazolium bromide) and anionic surfactant sodium oleate (NaOA) in aqueous solution. The effects of surfactant composition, total surfactant concentration, added salts, and temperature were investigated. The prevailing surfactant effect at lower concentration and the leading cosolvent effect at higher concentration of [C₈mim]Br may be the main reasons for appearance of well-established maximum in key rheological parameters with variation of surfactant composition and total surfactant concentration. The Cole-Cole plots demonstrate that the systems (total surfactant concentration falls within 0.17–0.35 mol·L^-1 and molar ratio 0.33≤R≤0.50) fit the Maxwell’s mechanical model as linear viscoelastic fluid. The addition of NaBr or sodium salicylate decreases significantly the viscosity and the relaxation time of the wormlike micelle solution but cannot change the value of plateau modulus G₀. The present system has low rheological tolerance to temperature. The increase of temperature decreases the average contour length and viscosity of wormlike micelles and thus strengthens the relaxation progress of diffusion and weakens the relaxation progress of reptation. Increasing the temperature also decreases the value of plateau modulus G₀ and shifts the minimum value of the loss modulus G^″_min to higher frequencies.     

Removal of Direct Yellow 27 Dye by Ionic Flocculation: The Use of an Environmentally Friendly Surfactant

The presence of dyes is one of the main contributors to the organic load in textile effluents. In this study a mixture of surfactants, produced from animal/vegetable fats, was used to remove the Direct Yellow 27 dye from a synthetic wastewater through an ionic flocculation process. It was evaluated the effect of contact time, temperature, and surfactant concentration on dye removal efficiency. It was also evaluated the kinetics, equilibrium, and diffusion mechanism of the process. The kinetics of the process was well described by both Pseudo-second order and Elovich models. The transport of dye molecules to the surfactant flocs is controlled by the external layer. Equilibrium data showed a good fit to the Langmuir model. A removal rate of 93% was achieved in a single stage, after 5 h of contact time.     

Sorption of tannic acid on zirconium pillared clay

Zirconium pillared clay (PILC) was prepared using montmorillonite as the base clay. Adsorption of tannic acid (tannin) was studied by a batch equilibrium technique, as a function of adsorbate concentration, temperature, pH, agitation speed, particle size of the adsorbent and ionic strength. The process of uptake is governed by diffusion controlled first‐order reversible rate kinetics. The higher uptake for the pH range 4.0–6.0 was attributed to external hydrogen bonding between phenolic‐OH groups of tannin molecules and the hydrogen bonding sites on the clay. The removal of tannin by adsorption was found to be >99.0% depending on the initial concentration in the pH range of 4.0–6.0. The process involves both film and pore diffusion to different extents. The effects of solute concentration, temperature, agitation speed and particle size on the diffusion rate were investigated. Tannin uptake was found to increase with ionic strength due to the compression of diffuse double layers. The applicability of Langmuir and Freundlich isotherm models has been tested. The maximum adsorption capacity of PILC was found to be 45.8 µmol g^?1 of clay and the affinity constant is 2.9 × 10^?2 dm³ µmol^?1 at 30 °C. Thermodynamic parameters such as ΔG °,ΔH ° and ΔS ° were calculated to predict the nature of adsorption. The isosteric enthalpies of adsorption were also determined and found to decrease with increasing surface coverage. Regeneration with hot water (60 °C) has been investigated for several cycles with a view to recovering the adsorbed tannin and also restoring the sorbent to its original state. Copyright © 2001 Society of Chemical Industry