Byungryul An

Immobilization of As(III) in soil and groundwater using a new class of polysaccharide stabilized Fe–Mn oxide nanoparticles

A new class of stabilized Fe-Mn binary oxide nanoparticles was prepared with a water-soluble starch or carboxymethyl cellulose (CMC) as a stabilizer. The nanoparticles were characterized and tested with respect to sorption of As(III) and As(V) from water and for immobilization of As(III) in soil. While arsenic sorption capacities were comparable for bare, or stabilized Fe-Mn nanoparticles, particle stabilization enabled the nanoparticles to be delivered into soil for in situ immobilization of arsenite. High As(III) sorption capacity was observed over a broad pH range of 5-9. Column breakthrough tests demonstrated soil mobility of CMC-stabilized nanoparticles. Once delivered, the nanoparticles remain virtually immobile in soil under typical groundwater conditions, serving as a fixed sink for arsenic. When an As(III)-laden soil was treated with CMC-stabilized Fe-Mn at an Fe-to-As molar ratio of 6.5-39, the water leachable arsenic was reduced by 91-96%, and the TCLP leachability was reduced by 94-98%. Column elution tests of an As(III)-laden soil indicated that application of CMC-stabilized Fe-Mn transferred nearly all water-soluble As(III) to the nanoparticle phase. Consequently, As(III) is immobilized as the nanoparticles are immobilized in the soil. The nanoparticle amendment was able to reduce the TCLP leachability of As(III) remaining in the soil bed by 78%.

Characterization of natural organic matter treated by iron oxide nanoparticle incorporated ceramic membrane-ozonation process.

In this study, changes in the physical and structural properties of natural organic matter (NOM) were observed during hybrid ceramic membrane processes that combined ozonation with ultrafiltration ceramic membrane (CM) or with a reactive ceramic membrane (RM), namely, an iron oxide nanoparticles (IONs) incorporated-CM. NOM from feed water and NOM from permeate treated with hybrid ceramic membrane processes were analyzed by employing several NOM characterization techniques. Specific ultraviolet absorbance (SUVA), high-performance size exclusion chromatography (HPSEC) and fractionation analyses showed that the hybrid ceramic membrane process effectively removed and transformed relatively high contents of aromatic, high molecular weight and hydrophobic NOM fractions. Fourier transform infrared spectroscopy (FTIR) and 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy revealed that this process caused a significant decrease of the aromaticity of humic-like structures and an increase in electron withdrawing groups. The highest removal efficiency (46%) of hydroxyl radical probe compound (i.e., para-Chlorobenzoic acid (pCBA)) in RM-ozonation process compared with that in CM without ozonation process (8%) revealed the hydroxyl radical formation by the surface-catalyzed reaction between ozone and IONs on the surface of RM. In addition, experimental results on flux decline showed that fouling of RM-ozonation process (15%) was reduced compared with that of CM without ozonation process (30%). These results indicated that the RM-ozonation process enhanced the destruction of NOM and reduced the fouling by generating hydroxyl radicals from the catalytic ozonation in the RM-ozonation process.

Determining the selectivity of divalent metal cations for the carboxyl group of alginate hydrogel beads during competitive sorption.

To investigate the competitive sorption of divalent metal ions such as Ca(2+), Cu(2+), Ni(2+), and Pb(2+) on alginate hydrogel beads, batch and column tests were conducted. The concentration of carboxyl group was found to be limited in the preparation of spherical hydrogel beads. From kinetic test results, 80% of sorption was observed within 4h, and equilibrium was attained in 48 h. According to the comparison of the total uptake and release, divalent metal ions were found to stoichiometrically interact with the carboxyl group in the alginate polymer chain. From the Langmuir equation, the maximum capacities of Pb(2+), Cu(2+), and Ni(2+) were calculated to be 1.1, 0.48, and 0.13 mmol/g, respectively. The separation factor (α) values for αPb/Cu, αPb/Ni, and αCu/Ni were 14.0, 98.9, and 7.1, respectively. The sorption capacity of Pb(2+) was not affected by the solution pH; however, the sorption capacities of Cu(2+) and Ni(2+) decreased with increasing solution pH, caused by competition with hydrogen. According to the result from the fixed column test, Pb(2+) exhibited the highest affinity, followed by Cu(2+) and Ni(2+), which is in exact agreement with those of kinetic and isotherm tests. The sorbent could be regenerated using 4% HCl, and the regenerated sorbent exhibited 90% capacity upto 9 cycles.

Modified composites based on mesostructured iron oxyhydroxide and synthetic minerals: a potential material for the treatment of various toxic heavy metals and its toxicity.

The composites of mesostructured iron oxyhydroxide and/or commercial synthetic zeolite were investigated for use in the removal of toxic heavy metals, such as cadmium, copper, lead and arsenic, from aqueous solution. Four types of adsorbents, dried alginate beads (DABs), synthetic-zeolite impregnated beads (SZIBs), meso-iron-oxyhydroxide impregnated beads (MIOIBs) and synthetic-zeolite/meso-iron-oxyhydroxide composite beads (SZMIOIBs), were prepared for heavy metal adsorption tests. Laboratory experiments were conducted to investigate the removal efficiencies of cations and anions of heavy metals and the possibility of regenerating the adsorbents. Among these adsorbents, the MIOIBs can simultaneously remove cations and anions of heavy metals; they have high adsorption capacities for lead (60.1mgg(-1)) and arsenic (71.9mgg(-1)) compared with other adsorbents, such as DABs (158.1 and 0.0mgg(-1)), SZIB (42.9 and 0.0mgg(-1)) and SZMIOIB (54.0 and 5.9mgg(-1)) for lead and arsenic, respectively. Additionally, the removal efficiency was consistent at approximately 90%, notwithstanding repetitive regeneration. The characteristics of meso-iron-oxyhydroxide powder were confirmed by X-ray diffraction, Brunauer-Emmett-Teller and transmission electron microscopy. We also performed a comparative toxicity study that indicated that much lower concentrations of the powdered form of mesostructured iron oxyhydroxide had stronger cytotoxicity than the granular form. These results suggest that the granular form of meso iron oxyhydroxide is a more useful and safer adsorbent for heavy metal treatment than the powdered form. This research provides promising results for the application of MIOIBs as an adsorbent for various heavy metals from wastewater and sewage.

Effect of nitrogen doping on titanium carbonitride-derived adsorbents used for arsenic removal.

Arsenic in water and wastewater is considered to be a critical contaminant as it poses harmful health risks. In this regard, to meet the stringent regulation of arsenic in aqueous solutions, nitrogen doped carbon-based materials (CN) were prepared as adsorbents and tested for the removal of arsenic ion from aqueous solutions. Nitrogen-doped carbon (CNs) synthesized by chlorination exhibited well-developed micro- and small meso-pores with uniform pore structures. The structure and characteristics of the adsorbents thus developed were confirmed by field-emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Among the CNs developed, CN700 exhibited high adsorption capacity for arsenic (31.08 mg/g). The adsorption efficiency for arsenic ion was confirmed to be affected by pyrrolic nitrogen and micro-pores. These results suggest that CNs are useful adsorbents for the treatment of arsenic, and in particular, CN700 demonstrates potential for application as an adsorbent for the removal of anionic heavy metals from wastewater and sewage.

Preparation and characterization of an organic/inorganic hybrid sorbent (PLE) to enhance selectivity for As(V).

For the selective removal of arsenate (As(V)) a hybrid sorbent was prepared using a non-toxic natural organic material, chitosan, by loading a transition metal, nickel. The immobilization of nickel was achieved by coordination with a deprotonated amino group (NH2) in the chitosan polymer chain. The amount of nickel was directly correlated to the presence of the amino group and was calculated to be 62 mg/g. FTIR spectra showed a peak shift from 1656 to 1637 cm(-1) after Ni(2+) loading, indicating the complexation between the amino group and nickel, and a peak of As(V) was observed at 834 cm(-1). An increase of sulfate concentration from 100 mg/L to 200 mg/L did not significantly affect As(V) sorption, and an increase in the concentration of bicarbonate reduced the As(V) uptake by 33%. The optimal pH of the solution was determined at pH 10, which is in accordance with the fraction of HAsO4(2-) and AsO4(-3). According to a fixed column test, a break through behavior of As(V) revealed that selectivity for As(V) was over sulfate. Regeneration using 5% NaCl extended the use of sorbent to up to uses without big loss of sorption capacity.

Enhanced phosphate selectivity from wastewater using copper-loaded chelating resin functionalized with polyethylenimine.

In water and wastewater, phosphate is considered a critical contaminant due to cause algae blooms and eutrophication. To meet the stringent regulation of phosphate in water, a new commercial chelating resin functionalized with polyethylenimine was tested for phosphate removal by loading Cu(2+) and Fe(2+)/Fe(3+) to enhance selectivity for phosphate. Batch and column experiments showed that CR20-Cu exhibited high selectivity for phosphate over other strong anions such as sulfate. The average binary phosphate/nitrate and phosphate/sulfate factors for CR20-Cu were calculated to be 7.3 and 4.8, respectively, which were more than 0.97 and 0.22 for a commercial anion exchanger (AMP16). The optimal pH for the phosphate removal efficiency was determined to be 7. According to the fixed-bed column test, the breakthrough sequence for multiple ions was HPO4(2-)>SO4(2-)>NO3(-)>Cl(-). Saturated CR20-Cu can be regenerated using 4% NaCl at pH 7. More than 95% of the phosphate from CR20-Cu was recovered, and the phosphate uptake capacity for CR20-Cu was not reduced after 7 regeneration cycles.

Removal and Immobilization of Arsenic in Water and Soil Using Polysaccharide-Modified Magnetite Nanoparticles

Magnetite nanoparticles were synthesized in the presence of polysaccharides and tested for enhanced arsenate removal. The nanoparticles were characterized and tested with respect to sorption of As(III) and As(V) from water and for immobilization in soil. Polysaccharide-modified magnetite nanoparticles offer a much higher As sorption capacity compared with that offered by their nonstabilized counterparts. The polysaccharide-to-iron ratio can be altered to yield nanoparticles of various properties. One of the potential uses of the starch-bridged magnetite nanoparticles is to remove As from spent ion exchange brine and provide easy separation from water by gravity. Stabilized magnetite nanoparticles are readily deliverable to soils, and the spent particles would be retained under normal groundwater conditions. The nanoparticle amendment provides an environmentally friendly and cost-effective way to comply with the newly enforced maximum contaminant level of 10 μg/L.

Effective surface immobilization of nanoparticles using bubbles generated by sonication

A nanoscale material represents a promising adsorbent material for water treatment due to its large surface area and its ability to incorporate compounds with specific functions. In this research, the effective immobilization of nanoparticles using an ultrasonic technique and the change of the surface morphology of the substrate by sonication was investigated. The effective surface immobilization of the nano-magnetite powder and an increase in the reactive area with aqueous contaminant were caused by bubbles generated by the sonication method. The effect of the frequency of the ultrasonic wave on the immobilization of the nano-powder was also investigated.