Characterization of aescin as a biosurfactant for environmental remediation

Surface-tension-lowering capacity and emulsion-forming ability of aescin biosurfactant in pure water, seawater, 3 M urea, and 3 M glucose were investigated. Oils used in the emulsification tests were liquid paraffin, ethylbenzene, kerosene, 1-decene, and heavy oils A and C. Volumetric ratios of oil phase to aqueous (water) phase (O/W) were 0.5∶4.5, 2.5∶2.5, 3.0∶2.0, and 4.5∶0.5. Concentration of aescin was changed from 0.16 to 27.3 mM. The critical micelle concentration of eascin in water and its surface tension effectiveness were shown to be 0.78 mM and 28.5 mN/m, respectively. Surface-tension effectiveness of aescin was found to be highest in sea-water (33.5 mN/m). The emulsifying action of aescin was compared with that of decaglyceryl-monolaurylester (DGML). The performance of aescin was found to be as good as that of DGML and, depending on the O/W ratio and the concentration, aescin could yield emulsification efficiencies as high as 100%. These results indicated that aescin could be classified as a mild surfactant safe for living organisms. Because the surface activity of aqueous aescin solution was not satisfactorily good, attempts were made to improve the situation by addition of alcohols as cosurfactants. Ethanol, isoamyl alcohol, 2-ethylhexanol, n-hexanol, and n-octanol were used. They were added to the solutions at a concentration equimolar to aescin. These cosurfactants improved surface-tension effectiveness of aescin by as much as 53% and its emulsification efficiency by 67%.     

Kinetics, mechanism, isotherm and thermodynamic analysis of adsorption of cadmium ions by surface-modified Strychnos potatorum seeds

The surface-modified Strychnos potatorum seeds (SMSP) were used as an effective low-cost adsorbent for the removal of cadmium ions from aqueous solution. SMSP was characterized by Fourier transform infrared spectroscopy and scanning electron microscopic analyses. The effect of operating variables such as solution pH, adsorbent dose, contact time, initial cadmium ions concentration and temperature on the removal of cadmium ions were studied in a batch mode adsorption operation. The optimum conditions for the adsorption of cadmium ions onto the SMSP were found to be: pH of 5.0, SMSP dose of 2 g/L, contact time of 30min, temperature of 30 °C for an initial cadmium ions concentration of 100 mg/L. Kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic equations, intraparticle diffusion model, Boyd kinetic model and shrinking core model. The characteristic parameters for each model have been estimated. Adsorption of cadmium ions onto the SMSP follows the pseudo-second order kinetic model. The rate-limiting steps in the adsorption process were found to be external and internal diffusion. Equilibrium data were well described by the Langmuir isotherm model than the Freundlich isotherm model, which yields a maximum monolayer adsorption capacity of 200 mg/g. Thermodynamic parameters such as standard free energy change, enthalpy change and entropy change were also estimated. The results show that the removal of cadmium ions by the SMSP was found to be spontaneous and exothermic.     

Dynamics and Thermodynamics Studies on the Lead and Cadmium Removal from Aqueous Solutions by Padina sp. Algae: Studies in Single and Binary Metal Systems

Raw and modified biomasses prepared from Padina sp. algae have been used as sorbent for the removal of lead and cadmium from single and binary aqueous solutions. The effects of chemical pretreatment, exposure time, initial solution pH, initial metal concentration, and temperature on the metal uptake by the algae were investigated. It was observed that initial solution pH considerably influenced Pb and Cd uptake. The maximum removal occurred at initial pH of 5.0 for lead and 6.0 for cadmium. Also, alkali modified biomass has been shown to have a high uptake capacity for both lead and cadmium. The kinetic and equilibrium experimental data fitting tested with various models. The pseudo-first-order kinetic model and Langmuir isotherm provided the best correlation of the kinetic and equilibrium experimental data, respectively. The maximum uptake estimated from the Langmuir isotherm was 264 mg g^?1 for lead and 164 mg g^?1 for cadmium ions. Experimental biosorption data in binary system were well described by the extended Langmuir model. Various thermodynamic parameters, such as ΔG°, ΔH°, and ΔS° were calculated.     

Removal of lead ions from wastewater using novel Schiff-base functionalized solid-phase adsorbent

ABSTRACT

This article discusses the synthesis, characterization and lead ions sorption capability of a novel recyclable Schiff-base anchored cross-linked polyacrylamide. The synthesized polymeric adsorbent was characterized by FT-IR technique, XRD and SEM analysis. Sorption parameters, such as solution’s pH, contact time, polymer dose, lead ions initial concentration, etc., were studied and optimized. Experimentally, the optimum sorption pH was around 5.0 and the sorption equilibrium was attained after 30 min. Under the optimal conditions, the maximum sorption capacity was found to be 355 mg/g, which is considered high when compared with different adsorbents. Effect of interfering ions on the sorption capacity was explored. Sorption isotherms, kinetic and thermodynamic studies were considered to identify the sorption behavior of the new polymeric adsorbent. Sorption isotherm studies showed that the maximum sorption capacity was attended as a result of homogeneous monolayer sorption of lead ions on the surface of the synthesized polymeric adsorbent. The mechanism of lead ions sorption by the synthesized polymeric adsorbent was found to be chemisorption complexation mechanism. Moreover, kinetic studies revealed that the sorption process followed a pseudo second order kinetic model. Thermodynamic data depicted that the sorption process is spontaneous, reversible and exothermic in nature. Experiments on elution and reusability of the synthesized polymeric adsorbent were executed and the results showed its validity for reuse for at least four cycles with 11% loss in its original capacity. Finally, the applicability of the synthesized Schiff-base anchored solid phase adsorbent for the removal of lead ions from industrial wastewater was explored and the results indicated its good removal efficiency.     

The removal of copper,cadmium, and lead ions from dilute aqueous solutions using foam fractionation

The removal of copper, lead and cadmium ions from aqueous solution by foam fractionation using sodium dodecylbenzene sulphonate (NaDBS) has been experimentally studied and theoretically predicted for solutions with a pH less than 4. A mathematical model of the system consisting of the equilibrium relations of chemical reactions occurring in the system was solved for the equilibrium concentration of all ions in the solution. Based on this equilibrium concentration and the effective radius of the hydrated ion, a modified theory of the Gouy-Chapman diffuse double layer⁽⁹⁾ was used to predict the distribution factor of the metal ions. The work was extended to systems containing two metal ions for the determination of the separability of the ions with respect to each other. It was found that the distribution factor for solutions containing one metal ion could be predicted theoretically for a bulk solution pH less than four. Deviation of results above this pH was attributed to the limitations of the bulk solution reaction model because it did not include reactions for the formation of poly hydroxyl and poly nuclear hydroxyl complexes. Good agreement was also obtained between experiment and theory in the separability study. The results indicate that the order of removal of the ions from solution is Pb⁺⁺ > Cd⁺⁺ > Cu⁺⁺. This sequence is the reverse order of the effective radii of the hydrated ions. The results support the fact that the mechanism for removal of the ions from solution is that of electrical attraction and that selectivity depends upon the charge and size of the hydrated ion.     

Removal of Cadmium and Chromium Ions Using Modified α, β, and γ-Cyclodextrin Polymers

The adsorption of cadmium and chromium from aqueous solutions with epichlorohydrin cross-linked α, β, and γ-cyclodextrin polymers (CDPs) was investigated under a wide range of experimental conditions including pH, metal concentration, and CDP amounts. Recent studies have shown that α, β, and γ-CDPs follow the Freundlich, Langmuir, and Brunauer–Emmett–Teller models and are capable of reducing heavy metal ion concentrations in water to desirable levels with enhanced sorption capabilities. The removal of cadmium and chromium achieved equilibrium in 4 h. The pH of effective cadmium removal was 6.5 to 7.5, and phosphate buffer favored the removal of cadmium in the presence of potassium ion. Chromium removal was optimal at pH 3.6 to 6.5. Current technologies can remove 99% cadmium ions from solution, yet this process is not very efficient for chromium ions. Furthermore, a small amount of CDPs can remove large quantities of heavy metal ions and can then be regenerated with acid for reuse. The present results are promising for using inexpensive CDPs as a low-cost material that is effective in remediating waters contaminated with heavy metal species. The sorption kinetics of CDPs along with the conditions to adsorb cadmium and chromium are reported here for the first time.     

Electrocoagulation studies on removal of cadmium using magnesium electrode

The removal of cadmium from aqueous solution was carried out by electrocoagulation using magnesium as anode and stainless steel as cathode. Various operating parameters on the removal efficiency of cadmium were investigated, such as initial cadmium ion concentration, initial pH, current density and temperature. The optimum removal efficiency of 98.6% was achieved at a current density of 0.2 A dm⁻² at a pH of 7.0. The experimental data were tested against different adsorption isotherm models for describing the electrocoagulation process. The adsorption of cadmium preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. First and second-order rate equations were applied to study adsorption kinetics. The adsorption process follows second order kinetics model with good correlation. Temperature studies showed that adsorption was endothermic and spontaneous in nature.     

Removal of Cadmium from Aqueous Solution using Wheat Stem,Corncob, and Rice Husk

Three kinds of agricultural by-products, wheat stem, corncob, and rice husk, were tested as biosorbents for cadmium removal from aqueous solution. The study was focused on the evaluation and comparison of the potential of the agriculture by-products as biosorbents of cadmium with the sorption isotherms determination. The impact of solution pH and kinetic study was also discussed. The result indicated that cadmium removal was strongly dependent on solution pH and the optimum pH range is 4.5 ～ 6.0. The sorption process was fast, and the sorption equilibrium can be attained within 60 min. The kinetic process fit well with the pseudo-second-order kinetic model. For the three kinds of biosorbents, the initial sorption rate as well as the maximum sorption capacity q _max calculated from the Langmuir isotherm equation showed the following tendency: rice husk > wheat stem > corncob. The maximum sorption capacity of the three kinds of biosorbents enhanced after being base treated, especially for wheat stem and corncob. This study indicated that wheat stem, corncob, and rice husk displayed the potential to be used as biosorbents for cadmium removal from aqueous solution.     

Separation of neutral lipid,free fatty acid and phospholipid classes by normal phase HPLC

Normal phase high performance liquid chromatography methods are described for the separation of neutral lipid, fatty acid and five phospholipid classes using spectrophotometric detection at 206 nm. Separations were accomplished in less than 10 min for each lipid class. A mobile phase consisting of hexane/methyltertiarybutylether/acetic acid (100∶5∶0.02) proved effective in separating cholesteryl ester and triglyceride with recoveries of 100% for radiolabeled cholesteryl oleate and 98% for radiolabeled triolein. Free fatty acid and cholesterol were separated by two different mobile phases. The first, hexane/methyltertiarybutylether/acetic acid (70∶30∶0.02) effectively separated free fatty acids and cholesterol, but did not separate cholesterol from 1,2-diglyceride. A mobile phase consisting of hexane/isopropanol/acetic acid (100∶2∶0.02) effectively separated free fatty acid, cholesterol, 1,2-diglyceride and 1,3-diglyceride. Recoveries of oleic acid and cholesterol were 100% and 97%, respectively. Five phospholipid classes were separated using methylteriarybutylether/methanol/aqueous ammonium acetate (pH 8.6) (5∶8∶2) as the mobile phase. The recoveries of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were each greater than 96%.     

Separation of Calcium and Cadmium by Electrodialysis in the Presence of Ethylenediaminetetraacetic Acid

ABSTRACT

The separation of calcium and cadmium ions in a system containing ethylenedi-aminetetraacetic (EDTA) as the complexing agent has been studied using a laboratory-scale batch electrodialyzer. The theoretical distribution diagram constructed for the Ca—Cd—EDTA system suggested that cadmium preferably formed negatively charged complexes while calcium remained in the positively charged uncomplexed form. The experimental results confirmed that under the influence of an electric field, calcium was exclusively transported to the cathode while more than 90% of cadmium totally removed from the middle compartment of the batch electrodialyzer migrated toward the anode. The separation effect resulting from EDTA complexation was studied within the 1·l5–4·0 pH range.     

Removal of cadmium(II) from aqueous solution by agricultural waste cashew nut shell

Cashew nut shell (CNS) is a low cost adsorbent that has been used for the removal of cadmium(II) from an aqueous solution. The effects of various parameters such as solution pH, CNS concentration, contact time, initial cadmium(II) concentration and temperature were examined. The CNS was effective for the quantitative removal of cadmium(II) ions in acidic conditions and equilibrium was achieved in 30 min. The experimental data were analyzed by two-parameter (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich) and three-parameter models (Redlich- Peterson, Koble-Corrigan, Toth and Sips) by nonlinear regression analysis. The characteristic parameters for each isotherms and related correlation coefficients have been determined by using MATLAB 7.1. Thermodynamic parameters such as ??G ^o , ??H ^o and ??S ^o have also been evaluated, and it was found that the sorption process was feasible, spontaneous and exothermic. Pseudo-first-order, pseudo-second-order, Elovich kinetic and intraparticle diffusion models were selected to follow the adsorption process. The results of the kinetic study show that the adsorption of cadmium(II) could be described by the pseudo-second order equation, suggesting that the adsorption process is presumably chemisorption. A single-stage batch adsorber was designed for different adsorbent dose-to-effluent volume ratios using the Freundlich equation. The results indicate that the cashew nut shell could be used to effectively adsorb cadmium(II) from an aqueous solution.     

Adsorption studies on copper,cadmium, and zinc ion removal from aqueous solution using magnetite/carbon nanocomposites

Magnetite/carbon nanocomposites were tested as adsorbents for removal of metal ions from aqueous solutions. The effect of adsorption parameters such as solutions pH (ranging between 2 and 9), the nature and the quantity of the sorbent (10, 20, 40, and 60 mg), initial concentration of metal ions (10, 30, 50, 100, and 150 mg/L), and temperature (25, 45, and 65°C) was evaluated. The removal efficiency of metal ions depends on solution pH and increases with increasing carbon content, the dose of magnetite/carbon nanocomposites, and the temperature and decrease with initial concentration of the metal ions. The adsorption kinetics was described by pseudo-second-order model, and the equilibrium experimental data were well fitted to the Sips isotherm, yielding a maximum adsorption capacity of 41.11, 76.67, and 48.45 mg/g for copper, cadmium, and zinc, respectively. The thermodynamic parameter Gibbs free energy was determined to be negative, which indicated that the adsorption process is spontaneous. The optimum conditions (1 g/L adsorbent, 25°C, and pH 6) were selected for removal of metal ions from real wastewaters, with good results indicating that investigated nanocomposites could be used for the application in real systems.     

Polymer assisted ultrafiltration for copper–citric acid chelate removal from wash solutions of contaminated soil

The removal of heavy metals from aqueous systems such as wash-solutions of contaminated soil by using Polymer-Assisted Ultrafiltration (PAUF) has been studied. For the extraction of metal ions from contaminated soil citric acid is used as a chelating agent. Cu²⁺ as metal ion and the polymer polyethylenimine (PEI) as ligand were used in the various experiments. Optimal chemical conditions for copper complexation by citric acid were determined by means of complexation tests. The results showed that citric acid is able to chelate copper ions at pH 5.5, while decomplexation occurs at pH 2. Maximum bonding capacity (saturation condition) was 0.625 mg Cu²⁺ per mg citric acid, meaning 2 mol Cu²⁺ per mol citric acid. Complexation tests in the system polyethylenimine–citric acid–copper showed that the polymer is able to complex the copper–citric acid chelate at pH = 6 while release occurs at pH < 3. The saturation condition was 0.333 mg Cu²⁺ per mg PEI. The ultrafiltration tests, carried out at three trans-membrane pressures (2, 3 and 4 bar), showed the possibility of using the PAUF technique for copper ion removal from aqueous solutions.     

Removal of Lead and Nickel Ions Using Zeolite Tuff

The capacity of Jordanian zeolite tuff for the removal of lead and nickel ions from aqueous solutions has been investigated under different conditions, namely zeolite particle size, initial solution pH, initial metal ion concentration, slurry concentration and solution temperature. Equilibrium data obtained have been found to fit both the Langmuir and Freundlich adsorption isotherms. It has been found that this zeolite (phillipsite) tuff is an efficient ion exchanger for removing both lead and nickel ions. Its removal capability is considerably higher for lead ions than for nickel ions under all conditions tested; however, the actual exchange capacities are far below the theoretical values. The finer the zeolite particles used, the higher the metal exchange capacity. An initial solution pH of 4·0 is favourable for obtaining high metal removal. © 1997 SCI.     

Removal of Cu2+ and Pb2+ ions from aqueous solutions by starch-graft-acrylic acid/montmorillonite superabsorbent nanocomposite hydrogels

In this study, the removal of copper(II) and lead(II) ions from aqueous solutions by Starch-graft-acrylic acid/montmorillonite (S-g-AA/MMT) nanocomposite hydrogels was investigated. For this purpose, various factors affecting the removal of heavy metal ions, such as treatment time with the solution, initial pH of the solution, initial metal ion concentration, and MMT content were investigated. The metal ion removal capacities of copolymers increased with increasing pH, and pH 4 was found to be the optimal pH value for maximum metal removal capacity. Adsorption data of the nanocomposite hydrogels were modeled by the pseudo-second-order kinetic equation in order to investigate heavy metal ions adsorption mechanism. The observed affinity order in competitive removal of heavy metals was found Cu²⁺ > Pb²⁺. The Freundlich equations were used to fit the equilibrium isotherms. The Freundlich adsorption law was applicable to be adsorption of metal ions onto nanocomposite hydrogel.     

Removal of lead,cadmium and zinc from aqueous solutions by precipitation with sodium Di‐(n‐octyl) phosphinate

Sodium di‐(n‐octyl) phosphinate (NaL) was used as a precipitating agent to remove heavy metals from aqueous nitrate solutions. Cadmium, zinc and mixtures of lead, cadmium and zinc were precipitated in the form of PbL_2(s), CdL_2(s), and ZnL_2(s). Lowering the pH of the feed solution reduced the removal of the metals as some of the phosphinate precipitated in the acid form as HL_(S). The removal of lead, cadmium, and zinc, from a solution containing the three metals gave a selectivity in the order Zn > Pb > Cd. Predictions of an equilibrium‐constant model, using measured solubility products of the precipitates and literature values of stability constants, gave metal removals, loss of precipitating agent, and equilibrium pH in good agreement with measured values.     

Studies on removal of lead ions from aqueous solutions using iron ore slimes as adsorbent

Iron ore slimes, a waste material generated during iron ore mining have been employed for the removal of lead ions from aqueous solutions by a batch adsorption technique. The slime sample contains 45.8% Fe, 13.6% SiO₂, and 13.9% Al₂O₃. It is characterized by X-ray diffraction (XRD) and optical microscopy to determine the presence of different phases such as hematite, goethite, limonite, quartz and kaolinite. It is assumed that the adsorption of lead ions is mainly due to the presence of pores and cavities in goethite mineral. The FTIR studies showed the presence of Si-OH and Fe-OH sites responsible for adsorption. Furthermore, the point of zero charge (pzc) of iron ore slime is shifted from 6.2 to 5.8 due to the adsorption of lead ions. Batch adsorption experiments have been conducted to study the sorption behavior of lead ions on iron ore slime. The effects of agitation time, concentration of lead ions, adsorbent doses, solution pH, other metal ions and temperature on the amount of lead ions adsorbed have been investigated. Lead ion adsorption is fast, and equilibrium could be achieved within 15 minutes of time. The adsorption increased with increase in temperature suggesting an endothermic adsorption. Under the conditions, it is possible to remove 95% lead from an aqueous solution bearing ∼20 mg/l at pH∼5.1. The equilibrium adsorption isotherm data fitted very well to both Langmuir and Freundlich adsorption models.     

Preparation and properties of chelating ion exchangers with quinaldic acids as complexing groups. Influence of the structure of the coordinating ligands on the complexing properties

Quinoline-2-carboxylic acids with different substituents in the 4- and 8-positions of the quinoline ring have been grafted onto styrene-divinylbenzene polymers and tested for their ability to extract metal ions from aqueous sulfate solutions at low pH values. The position and nature of the substituents were found to play a major role in the metal ion selectivities, whereas the nature of the polymeric support mainly influenced the metal ion capacities and rates of equilibration. A remarkably high preference for cadmium ions was shown by a reagent containing a quinaldic acid with a phenacyloxy group in the 8-position of the quinoline ring. This reagent proved useful for the removal of cadmium from 30% phosphoric acid.     

Enhanced adsorption properties of interpenetrating polymer network hydrogels for heavy metal ion removal

In this study, sequential interpenetrating polymer network (IPN) hydrogels based on poly(polyethylene glycol diacrylate) poly(PEGDA) and poly(methacrylic acid) (PMAA) were prepared with enhanced adsorption properties for heavy metal ion removal. The swelling behavior and mechanical property of the IPN hydrogels were characterized. It was found that swelling ratio increased, and mechanical strength decreased with the PMAA content in the IPN. The IPN hydrogels were used to remove heavy metal ions from aqueous solution under the non-competitive condition. The effects of pH values of the feed solution at the range of 3–5 and PMAA content in the IPN on the adsorption capacity were investigated. The results indicated that the adsorption capacity of the IPN hydrogels increased with the pH values and PMAA content in the IPN. Furthermore, the synergistic complexation of metal ions with two polymer networks in the IPN was found in the adsorption studies. Regeneration studies suggested that metal rebinding capacity of the IPN hydrogels did not change significantly through repeated applications compared with the first run. It was concluded that the poly(PEGDA)/PMAA hydrogels could be used as fast-responsive, high capacity, and renewable sorbent materials in heavy metal removing processes.     

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated soil

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated sand and clayey soils has been investigated under laboratory‐scale conditions. Soil extracts of heavy metals (by 1 M HCl solution) were analysed by optical emission spectrometry. The efficiency of electrochemical remediation was partially dependent on the pH of the soil media. With pH increase, the migration of heavy metal ions toward the cathode was limited. When acetic acid was added to the sandy soil, almost complete remediation was achieved. A clay layer inserted in the cathode area did enhance the remediation rate. The most effective clean‐up was achieved for zinc and cadmium, with less effective clean‐up being achieved for lead. The effectiveness of the electrokinetic remediation of heavy metal‐contaminated clayey soil was low. The appropriate acidity was not achieved using acetic acid because of the high buffering capacity of clay, and metal ion migration was impeded by its sorption onto some clay components. The conclusion was made that clays could be used as immobilizing media for heavy metal ions by electrokinetic remediation of various soils. © 2001 Society of Chemical Industry