Özgür Arar

ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART II: CHROMIUM TRANSPORT THROUGH INORGANIC ION-EXCHANGER AND COMPOSITE CERAMIC MEMBRANE

Cr (VI) transport through a composite ceramic membrane containing an ion-exchange component, namely xerogel of hydrated zirconium dioxide, was investigated. The diffusion coefficient of Cr (VI) species through the membrane, which has been determined under open circuit conditions, is 1.80 × 10−10 m2 s−1. The transport number of Cr (VI) species through the ceramic membrane was found to rise with increasing voltage and reached 0.17 under “over-limiting current” conditions. On the other hand, the transport of chromate ions through hydrogel of hydrated zirconium dioxide becomes more intensive with a decrease in potential drop through the system involving ion-exchanger bed and ceramic membrane due to decrease in the membrane resistance. The diffusion coefficient of Cr (VI) ions in hydrogel of the inorganic ion exchanger was estimated as 4.36 × 10−12 m2 s−1. A possibility of Cr (VI) removal from a weakly acidic diluted solution using an electro-deionization method was shown: the degree of solution purification was found to reach 50%. The transport of species is realized through both the solution and the ion exchanger.

Removal of Nitrate from Ground Water by a Hybrid Process Combining Electrodialysis and Ion Exchange Processes

Abstract In regions where agricultural activities are highly intensive, nitrate concentrations in ground water are usually above the permissible level for nitrate in drinking water. There are several physicochemical and biological treatment processes typically used to remove nitrate contamination from ground water. In this study, an electrodialysis‐ion exchange hybrid process was used for the removal of nitrate from ground water obtained from an agricultural area in the Western Anatolia religion in Turkey. Nitrate was effectively removed from the ground water. The effect of other ionic species such as chloride and sulfates on nitrate removal by electrodialysis has also been studied using deionized water that was dosed with selected anionic and cationic species.

Removal of Fluoride from Geothermal Water by Electrodialysis (ED)

Abstract Removal of fluoride from geothermal water by electrodialysis (ED) was studied. ED operation was performed according to two methods. In the first method, before the ED operation, the pH of geothermal waters was adjusted to 7−7.5 by the addition of the HCl solution to prevent the precipitation of divalent salts in the concentrate compartment. In the second method, geothermal water was pretreated to precipitate the calcium ions. It was obtained that fluoride was effectively removed from geothermal water by electrodialysis using both of these pretreatment methods. However, it is preferable to use the first method because of its technically simple procedure and lower cost of chemicals used.

Separation of Low Concentration of Fluoride from Water by Electrodialysis (ED) in the Presence of Chloride and Sulfate Ions

Abstract Removal of low concentration of fluoride (2 mg F−/L) in the presence of chloride and sulfate ions from aqueous solution by electrodialysis was studied. The equivalent ratios of sulfate and/or chloride were investigated as co-existing ions on fluoride removal from aqueous solution. The separation performance was evaluated in terms of mass transfer and energy consumption. It was obtained that the separation performance increased when the equivalent ratios of chloride to fluoride and sulfate to fluoride were increased. After 13 min of operation time, 63% of fluoride was removed from the solution when a binary mixture of F− : Cl− (1 : 25) was employed. In the case of a binary mixture of F− : (1 : 25), removal of fluoride was 93% in 16 min. For a ternary mixture of F− : Cl− : (1 : 25 : 25), fluoride was separated from the mixture with a 96% of removal in 20 min.

ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART I: CHROMIUM TRANSPORT THROUGH GRANULATED INORGANIC ION-EXCHANGER

Kinetics of Cr (VI) → OH− exchange on both hydrogel and xerogel of hydrated zirconium dioxide was investigated. Self-diffusion coefficient of Cr (VI) species has been determined by analysis of kinetic curves. Transport of Cr (VI) anions through the inorganic ion exchangers under the influence of applied voltage was also researched. In the case of hydrogel, the ions are transported mainly through the solid phase. Diffusion coefficient of chromate anions through this material was estimated as 9.00 × 10−12 m2 s−1. This is in agreement with self-diffusion coefficient of Cr (VI) obtained from kinetic measurements (1.60 × 10−12–9.92 × 10−12 m2 s−1). Owing to the rather high mobility of Cr (VI) through hydrogel of hydrated zirconium dioxide, this material was recommended for electro-deionization processes. On the other hand, the use of polymer anion-exchange membrane must be excluded to prevent poisoning of the inorganic ion exchanger with Cr (III) cations to be formed during chemical interaction of Cr (VI) with organic materials.

Removal of lead(II) from water by di (2-ethylhexyl) phosphate containing ion exchange resin

AbstractIn the present study, commercially available chelating resin with the di (2-ethylhexyl) phosphate functional group (Lewatit VP OC 1026) has been evaluated for its suitability for the removal of Pb2+ from water. Studies for the removal of Pb2+ in different resin doses, pH of the solution, adsorption mechanism, and kinetic performance of resin were carried out. The obtained results showed that the removal performance of resin strongly depends on solution pH. More than 99% removal of Pb2+ was achieved at pH ⩾ 3. The experimental equilibrium data were tested for the Langmuir and Freundlich isotherms. Correlation coefficients indicate that the Langmuir isotherm fits better than the Freundlich isotherm. Pseudo-first- and -second-order kinetic models were used to describe kinetic data. It was determined that the removal of Pb2+ well-fitted by second-order reaction kinetics.

Effect of process parameters on separation performance of nitrate by electrodialysis

Abstract The electrodialytic separation of nitrate from water was investigated as a function of feed characteristics such as applied voltage, feed flow rate, and nitrate concentration in the solution. The separation performance was evaluated in terms of percent removal of nitrate, process time, and energy consumptions. TS‐1‐10 electrodialysis equipment (Tokuyama) was used in experimental studies. During the unsteady state run of the ED system, both inlet and outlet concentrations of nitrate and conductivities of streams were measured at certain time intervals until the current drops to 0.01 A. It was obtained that the percent removal of nitrate from the solution increased when the concentration of nitrate in the feed solution increased. The operation time became shorter when a high potential was applied.

Removal of tartaric acid by gel and macroporous ion-exchange resins

AbstractThe objective of this study is to investigate the removal efficiency of tartaric acid from aqueous solution and wine waste by gel and macroporous ion-exchange resins. The resin amount and pH have an important effect on the removal rate. The maximum removal of tartaric acid was achieved at pH ≥ 4. Tartaric acid adsorption isotherms were analyzed using Langmuir and Freundlich models. The results obtained have shown that Langmuir model fits well for both resins. Sorption kinetics for these resins fit to Ho pseudo-second-order kinetics model. The hybrid precipitation-cation exchange resin system was used for recovery of tartaric acid from liquid wine wastes. The obtained results showed that hybrid system can be used as an alternative method for the recovery of tartaric acid. The 90% of tartaric acid was recovered by hybrid system.

Release of Nanoparticles from Ion Exchange Resins and Their Detection

Nanoparticles released from commercial ion exchange resins were analyzed by laser-induced breakdown detection (LIBD). It was shown that virgin resins release a considerable amount of nanoparticles which may harm sensitive production lines, if the resins are used without proper pretreatment. Particle release is reduced to below 1 ppb after regeneration and rinsing of the resins. However, the nanoparticle concentration can still be detected quantitatively by LIBD.

Boron Removal in Seawater Desalination by Reverse Osmosis Membranes – the Impacts of Operating Conditions

Production of drinking water through seawater desalination using reverse osmosis (RO) membranes is becoming increasingly attractive especially in coastal areas with limited freshwater sources. However, one challenge in such conventional desalination RO plants is the difficulty of meeting boron standards in product waters. Therefore, most of the current desalination plants employ additional treatment steps including pH adjustment of feedwater, dilution of RO permeate with other sources, ion exchange post-treatment of RO permeate, and/or double-pass staging for permeate. All these further treatment options increase the cost of desalination. Although membrane manufacturers have been developing modified RO membranes with enhanced boron removal capacities such membranes still should be improved from operational flux and pressure perspectives. The main objective of this work was to determine the impacts of operational conditions (membrane pressure, cross-flow velocity and flux) and water chemistry on boron rejections using two commercial RO membranes specified for enhanced boron removal (TorayTM UTC-80-AB and FilmtecTM SW30HR). A lab-scale cross-flow flat-sheet configuration test unit (SEPA CF II, Osmonics) was used for all RO experiments. Seawater samples were collected from the Mediterranean Sea, Alanya-Kizilot shores, south Turkey. For all experiments, mass balance closures were between 91 and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Boron rejections were relatively constant (a maximum change of ±3%) during the 14 h of operation period for all experiments, suggesting that steady state dynamic membrane conditions were immediately achieved within couple hours. Boron rejections obtained with Toray and FilmTec membranes at pH of original seawater (8.2) and at other various operating conditions ranged between 85 and 92%, resulting in permeate boron concentrations of about 0.2–0.9 mg/L. On the other hand, for both membranes, much higher boron removals were achieved at a pH of 10.5 (>98%), resulting in permeate boron concentrations less than 0.1 mg/L. The charged boron species are expected to be dominant at pH values >9.24 (pKa of boric acid) compared to the neutral boric acid. Therefore, as expected, both membranes exhibited higher boron rejections at a pH of 10.5. Salt rejections (as measured by conductivity) were generally 97–99% at both pH values. Boron rejections were independent of feed water boron concentrations up to 6.6 mg/L. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5. The ranges of permeate fluxes measured in all experimental conditions were 11–15, 13–17 and 19–21 L/m2-h for 600, 700 and 800 psi (41, 48 and 55 bar) pressures, respectively, after an operation period of 14 h. For all experimental conditions, permeate fluxes gradually decreased during the 14 h operation although a leveling off was observed after 12 h. At constant membrane pressure of 800 psi and pH of 8.2, feed flowrate thus the cross-flow velocity (0.9 and 0.5 m/s) did not exert any significant impact on boron rejection.