Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl₂, Na₂SO₄, and MgSO₄) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.     

Iron-modified light expanded clay aggregates for the removal of arsenic(V) from groundwater

Iron modified materials have been proposed as a filter medium to remove arsenic compounds from groundwater. This research investigated the removal of arsenate, As(V) from aqueous solutions by iron-coated light expanded clay aggregates (Fe-LECA). Arsenic is effectively adsorbed by Fe-LECA in the optimum pH range 6-7 by using a 10 mg mL^− 1 adsorbent dose. Kinetics experiments were performed to investigate the adsorption mechanisms. Electrostatic attraction and surface complexation were proposed to be the major arsenic removal mechanisms. The experimental data fitted the pseudo-first-order equation of Lagergren. For an arsenic concentration of 1 mg L^− 1, the rate constant (k₁) of pseudo-first-order was 0.098 min^− 1, representing a rapid adsorption in order to reach equilibrium early. Equilibrium sorption isotherms were constructed from batch sorption experiments and the data was best described by the Langmuir isotherm model. Large scale column experiments were conducted under different bed depths, flow rates, coating duration and initial iron salts concentration to determine the optimal arsenic removal efficiency by Fe-LECA column. Volumetric design as well as higher hydraulic detention time was proposed to optimize the efficiency of the column to remove arsenic. In addition, concentrated iron salts and longer coating duration were also found to be crucial parameters for arsenic removal. The maximum arsenic accumulation was 3.31 mg of As g^− 1 of Fe-LECA when the column was operated at a flow rate of 10 mL min^− 1 and the LECA was coated with 0.1 M FeCl₃ suspension for a 24 h coating duration.     

Use of peat-based sorbents for removal of arsenic compounds

It is important to apply sorbent materials for purification of water from arsenic contamination due to serious arsenic pollution worldwide. We have developed new sorbents based on natural materials that provide a cheap and environmentally friendly alternative. For the first time, peat modified with iron compounds and iron humates were tested for sorption of arsenic compounds. The highest sorption capacity was found in peat modified with iron compounds. We have found that sorption of different arsenic speciation forms was strongly dependent on solution pH, reaction time and temperature. Calculations of the sorption process using thermodynamic parameters indicate the spontaneity of sorption process and its endothermic nature. Sorption kinetics showed that most arsenates are removed within 2 hours, and the kinetics of arsenate sorption on modified peat can be described by the pseudo-second order mechanism.      

Arsenic sorption and redox transformation on iron‐impregnated ordered mesoporous carbon

Ordered mesoporous carbon has been actively investigated for its potential applications as catalyst supports, electrochemical materials and gas separation media. In this study, we tested an iron‐modified ordered mesoporous carbon (FeOMC) for its ability to adsorb arsenic from the aqueous phase. The FeOMC synthesis involved the preparation of an ordered silica template SBA‐15, in situ polymerization of acrylic acid in the template, carbonization and template removal to obtain the ordered mesoporous carbon, and iron impregnation. Batch experiments showed that the pH level of the solution had a major impact on arsenic sorption. Further, we found that the presence of anions (i.e. PO₄^3? and SiO₃^2?) could significantly decrease the sorption of both arsenate and arsenite. Arsenite oxidation to arsenate was observed in alkaline solutions, with or without anions being present. The oxidation of arsenite was attributed to both direct and catalytic reactions with the surface functional groups on the ordered mesoporous carbon. Adsorption of arsenic on FeOMC could be well explained by the surface complexation model. Copyright © 2007 John Wiley & Sons, Ltd.     

Study of the effect of oxidative-bisulfite modification of the cotton cellulose on its ion exchange properties

The effect of chemical modification on the sorption properties of cotton cellulose toward Cu(II) and Ni(II) ions was studied. The modification was carried out in two stages: oxidation of cellulose with the formation of dialdehydocellulose, followed by its sulfonation. The optimal conditions for modifying the cellulose to produce a sorbent capable to remove effectively the heavy metal ions from aqueous solutions of corresponding salts were elucidated. The modified sorbent exceeds the native cellulose in the sorption capacity (in terms of sorption maximum) about 3 times, therewith the time of extraction of heavy metal ions is reduced from 45 to 8 min. The high sorption properties are defined by the formation of new sorption sites -SO₃Na along with initially formed -COOH groups on the sorbent surface.     

Sorption of radiactive strontium on binary systems of some alkaline earth sulfates

Equilibrium and metastable solid solutions of binary mixtures of BaSO₄−CaSO₄ and SrSO₄−CaSO₄, and sorbents based on mixtures of compounds in the systems BaSO₄−MgSO₄ and SrSO₄−MgSO₄ were prepared by special heat treatments. The sorption properties of such systems were studied in relation to their structural characteristics. A positive effect of the dynamic reconstruction of the lattice on the sorption of strontium ions was found in all cases. Good sorption properties were found for the systems BaSO₄−CaSO₄ and BaSO₄−MgSO₄ An effort was made to explain the mechanism of sorption on such systems, using several independent methods.     

Sorption of iron(III) in ionic and colloidal states on iron(III) oxide deposited on a silica gel sufrace

The sorption of iron(III) in ionic and colloidal states on iron(III) oxide deposited on a silica gel surface has been studied as a function of pH of aqueous solution by batch equilibrations. The behaviour of Fe³⁺ and colloidal Fe(III) on the sorbent column has also been investigated. Conditions for sorption of iron from aqueous solutions are given. The colloidal iron(III) can be quantitatively separated from Fe³⁺ on the sorbent column under given experimental conditions.     

Interaction of U(VI) with Na-attapulgite in the presence and absence of humic acid as a function of pH, ionic strength and temperature

The interaction of U(VI) with Na-attapulgite was studied by using batch technique at different experimental conditions. The effect of contact time, solid content, pH, ionic strength and temperature on the sorption of U(VI) onto Na-attapulgite in the presence and absence of humic acid was also investigated. The results showed that the sorption of U(VI) on Na-attapulgite achieved sorption equilibrium quickly. Sorption of U(VI) on Na-attapulgite increased quickly with increasing pH at pH < 6.5, and then decreased with pH increasing at pH > 6.5. The sorption curves were shifted to left in low NaClO₄ solutions as compared those in high NaClO₄ solutions. The sorption was strongly dependent on pH and ionic strength. The sorption was dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere surface complexation or surface precipitation at high pH values. The thermodynamic parameters (i.e., ΔH ⁰, ΔS ⁰, and ΔG ⁰) for the sorption of U(VI) were calculated from the temperature dependent sorption isotherms, and the results suggested that the sorption reaction was an endothermic and spontaneous process. The Na-attapulgite is a suitable material in the removal and preconcentration of U(VI) from large volumes of aqueous solutions in nuclear waste management.     

Sorption of plutonium from low level liquid waste using nano MnO2

Nano-crystalline MnO₂ has been synthesized by the method of alcoholic hydrolysis of KMnO₄ and its potential as a sorbent for plutonium present in the low level liquid waste (LLW) solutions was investigated. The kinetic studies on the sorption of Pu by MnO₂ reveal the attainment of equilibrium sorption in 15 h, however 90 % of sorption could be achieved within an hour. In the studies on optimization of the solution conditions for sorption, it was observed that the sorption increases with the pH of the aqueous solution, attains the maximum value of 100 % at pH = 3 and remains constant thereafter. The sorption was found to be nearly independent of the ionic strength (0.01–1.0 M) of the aqueous solutions maintained using NaClO₄, indicating the inner sphere complexation between the Pu⁴⁺ ions and the surface sites on MnO₂. Interference studies with different fission products, viz., Cs⁺, Sr²⁺ and Nd³⁺, revealed decrease in the percentage sorption with increasing pH of the suspension indicating the competition between the metal ions. However, at the metal ion concentrations prevalent in the low level liquid waste solutions, the decrease in the Pu sorption was only marginally decreased to 90 % at pH = 3, the decrease being more in the case of Nd³⁺ than that in the case of Cs⁺. This study, therefore, shows nano-crystalline MnO₂ can be used as a sorbent for separation of Pu from LLW solutions.     

The Oxidation of Luminol an Experiment to Maximize the Efficiency of Chemiluminescence from Luminol

In this work, seven inorganic salts, KCl, Na₂SO₄, MgSO₄-7H₂O, ZnCl₂, Na₂CrO₄, CuSO₄-5H₂O, and K₃[Fe(CN)₆], were used as catalysts to induce chemiluminescent luminol oxidation in alkaline aqueous media. It was observed that simple salts containing either Mg²⁺, Zn²⁺, Na⁺ and K⁺ cations or SO₄^2– and Cl^– anions, are not active as catalysts. On the other hand, the relative order of activity detected for the active chemiluminescent salts containing Fe(III), Cu(II) and Cr(VI) cations is K₃[Fe(CN)₆] < CuSO₄-5H₂O < Na₂CrO₄. The intensity of the emitted light agrees with the standard reduction potentials of the corresponding redox couple and with the presence of paramagnetic species in the aqueous solutions. The inhibition effect of mannitol was also studied.     

Drawing Out the Structural Information About the First Hydration Layer of the Isolated Cl− Anion Through the FTIR-ATR Difference Spectra

The Fourier transform infrared-attenuated total reflectance (FTIR-ATR) difference spectra of aqueous MgSO₄, Na₂SO₄, NaCl and MgCl₂ solutions against pure water were obtained at various concentrations. The difference spectra of the solutions showed distinct positive bands and negative bands in the O–H stretching region, indicating the influences of salts on structures of hydrogen-bonds between water molecules. Furthermore the difference spectra of MgCl₂ solutions against NaCl solutions and those of MgSO₄ solutions against Na₂SO₄ solutions with the same concentrations of anions (Cl^? or SO ₄ ^2? , respectively) allowed extracting the structural difference of the first hydration layer between Mg²⁺ and Na⁺. Using SO ₄ ^2? as a reference ion, structural information of the first hydration layer of the Cl^? anion was obtained according to the difference spectra of MgCl₂ solutions against MgSO₄ solutions and those of NaCl solutions against Na₂SO₄ solutions containing the same concentrations of cations (Mg²⁺ or Na⁺, respectively). The positive peak at ~3,407 cm^?1 and negative peak at ~3,168 cm^?1 in these spectra indicated that adding Cl^? decreased the strongest hydrogen-bond component and increased the relatively weaker one.     

Properties and Application of a Chelating Sorbent Prepared by Modification of LiChroprep-NH<Subscript>2</Subscript> with Calcon

A new chelating sorbent for metal ions was prepared by modification of chemically modified silica – LiChroprep-NH₂ with Calcon. The molecular mechanism of binding this reagent to the surface of the applied carrier is presented. The properties of this sorbent were compared to analogous sorbents with a plain silica carrier and chemically modified silicas – LiChroprep-RP containing Calcon. The advantages of the new sorbent compared to the silica and LiChroprep-RP chelating sorbents are demonstrated. The sorbent obtained was applied as stationary phase in solid-phase extraction (SPE) for separations of some chosen mixtures of metal ions and for additional purification of aqueous solutions of salts of alkali metals from trace amounts of heavy metals. The multiple use of the sorbent based on LiChroprep-NH₂ in sorption-desorption processes of metal ions without deterioration of its sorption capacity is demonstrated.     

Preparation of Sorbents Containing Straetlingite Phase from Zeolitic By-Product and Their Performance for Ammonium Ion Removal

In this study, straetlingite-based sorbents were used for NH₄⁺ ion removal from a synthetic aqueous solution and from the wastewater of an open recirculation African catfish farming system. This study was performed using column experiments with four different filtration rates (2, 5, 10, and 15 mL/min). It was determined that breakthrough points and sorption capacity could be affected by several parameters such as flow rate and mineral composition of sorption materials. In the synthetic aqueous solution, NH₄⁺ removal reached the highest sorption capacity, i.e., 0.341 mg/g with the S30 sorbent at a filtration rate of 10 mL/min and an initial concentration of 10 mg/L of NH₄⁺ ions. It is important to emphasize that, in this case, the Ce/C0 ratio of 0.9 was not reached after 420 min of sorption. It was also determined that the NH₄⁺ sorption capacity was influenced by phosphorus. In the wastewater, the NH₄⁺ sorption capacity was almost seven times lower than that in the synthetic aqueous solution. However, it should be highlighted that the P sorption capacity reached 0.512 mg/g. According to these results, it can be concluded that straetlingite-based sorbents can be used for NH₄⁺ ion removal from a synthetic aqueous solution, as well as for both NH₄⁺ and P removal from industrial wastewater. In the wastewater, a significantly higher sorption capacity of the investigated sorbents was detected for P than for NH₄⁺.     

Performance of immobilized moss in the removal of 137Cs and 90Sr from actual low-level radioactive waste solutions

The efficiency of immobilized moss as a bio-sorbent for the removal of ¹³⁷Cs and ⁹⁰Sr radionuclides from actual low-level radioactive waste (LLW) solutions was investigated. Preliminary batch experiments with the moss (Funaria hygrometrica) for the sorption of Cs and Sr have shown a pH dependent binding trend from pH 1–13, with maximum binding between pH 5–10. Time dependence of the batch studies showed that a contact time of 30 minutes was sufficient to reach equilibrium. Column experiments for the sorption of Cs and Sr by moss after immobilizing in polymer silica matrix demonstrated that the sorbent is capable of removing considerable amounts of Cs and Sr from actual LLW solutions under constant flow conditions. The adsorption capacity was estimated to be 8.5 mg/g for Cs and 15 mg/g for Sr. These sorbed metal ions from the column could be leached out using 0.20M nitric acid. The regenerated sorbent exhibited relatively the same initial binding capacity of both Cs and Sr even after 3 cycles of reuse. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis, characterization and application of a novel sorbent, glucamine-modified MCM-41, for the removal/preconcentration of boron from waters

A novel sorbent was prepared by the functionalization of an inorganic support material, MCM-41, with N-methylglucamine for the uptake of boron from aqueous solutions prior to its determination by inductively coupled plasma optical emission spectrometry (ICP-OES). Characterization of the newly synthesized material was performed using BET, XRD, TEM, SEM and DRIFTS techniques, in addition to its C and N elemental content. Sorption behavior of the novel sorbent for boron was also investigated and found to obey Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The maximum amount of B (as H₃BO₃) that can be sorbed by the sorbent was calculated from the D-R isotherm and was found to be 0.8 mmol B g⁻¹ of sorbent. The applicability of the new sorbent for the removal/preconcentration of boron from aqueous samples was examined by batch method. It was found that the sorbent can take up 85% of boron in 5 min whereas quantitative sorption is obtained in 30 min. Any pH greater than 6 can be used for sorption. Desorption from the sorbent was carried out using 1.0 M HNO₃. The sorption efficiency of the new sorbent was also compared to that of Amberlite IRA 743, a commercial resin with N-methylglucamine functional groups. Within the experimental conditions employed, the new sorbent was found to have higher sorption efficiency than the commercial resin. For method validation, spike recovery tests were performed at various concentration levels in different water types and were found to be between 83-95 and 75-92% for ultra pure water and geothermal water, respectively.     

Sorption of chromium(III) and chromium(VI) on lead sulfide

The sorption of chromium(III) and chromium(VI) on lead sulfide has been investigated in dependence on pH, time of sorption and the concentrations of sorbate and sorbent. The mechanisms of the sorption of Cr³⁺ and CrO ₄ ^2– traces on lead sulfide are discussed; a difference between CrO ₄ ^2– sorption on PbS and -Fe₂O₃ has been found. Sulfates and molybdates affect the removal of chromates from aqueous solutions. Lead sulfide carrier prepared in this work was also used for the preconcentration of chromium(III) and chromium(VI) from tap water.     

Sorption of phosphorus(V) by polymeric sorbents based on aminopolystyrene and 4-amino-<Emphasis Type="Italic">N</Emphasis>-azobenzenesulfamide

Phosphorus(V) sorption on sorbents based on aminopolystyrene and 4-amino-N-azobenzenesfulamide from aqueous solutions is studied. The following sorption parameters are determined: the optimum acidity, pH_opt; 50% sorption pH, pH₅₀; optimal time τ, min; quantitative-sorption temperature; and phosphorus(V) sorption capacity of the sorbent (SCS). Sorption isotherms are plotted.     

Correlation between thermodynamic properties and coordination states of aqueous bivalent transition metal sulfates

The osmotic coefficients for CoSO₄, NiSO₄, CuSO₄, MnSO₄, and ZnSO₄ have been found to be approximately the same up to very highest concentrations, while they are significantly higher for MgSO₄. Negligible changes in the visible spectra of CoSO₄ and NiSO₄ induced by increasing concentration indicate little, if any, coordination of the sulfate anion, while the UV spectral effects indicate outer-sphere association. More distinct spectral effects are observed for CuSO₄. However, the free sulfate anion concentration is found to be the same in equimolal solutions of CoSO₄, NiSO₄, and ZnSO₄, and probably also in CuSO₄, while it is higher in the solutions of MgSO₄. The conclusion is drawn that the four isopiestic transition metal sulfates at any given molality are in corresponding coordination states. The general problem of correlation between thermodynamic properties of solutions and the coordination states of the dissolved salts is discussed.     

Kinetics of Antibiotic Sorption by Monocarboxyl Cellulose

Kinetics of the sorption of lincomycin and gentamicin from aqueous solutions of their salts and bases, as well as a cephalosporin group antibiotic cephalexin having the zwitterionic nature, by monocarboxyl cellulose is studied. It is disclosed that the sorption of the studied antibiotics is characterized by a combined diffusion type of kinetics. Effective diffusion coefficients (D _eff) are determined, and it is shown that they correspond to the times (t _1/2) of half-equilibrium establishment and increase with passing from lincomycin to gentamicin and, further, to cephalexin. The D _eff and t _1/2 values are found to depend on solution pH and the degree of cellulose sorbent swelling.