Biomedical subjects

Chuanyong Jing

Publications and source records attributed to Chuanyong Jing.

8 recordsLinked to original sources

PubMed2006

Adsorption mechanism of arsenic on nanocrystalline titanium dioxide.

Arsenate [As(V)] and arsenite [As(III)] interactions at the solid-water interface of nanocrystalline TiO2 were investigated using electrophoretic mobility (EM) measurements, Fourier transform infrared (FTIR) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. The adsorption of As(V) and As(III) decreased the point of zero charge of TiO2 from 5.8 to 5.2, suggesting the formation of negatively charged inner-sphere surface complexes for both arsenic species. The EXAFS analyses indicate that both As(V) and As(III) form bidentate binuclear surface complexes as evidenced by an average Ti-As(V) bond distance of 3.30 A and Ti-As(III) bond distance of 3.35 A. The FTIR bands caused by vibrations of the adsorbed arsenic species remained at the same energy levels at different pH values. Consequently, the surface complexes on TiO2 maintained the same nonprotonated speciation at pH values from 5 to 10, and the dominant surface species were (TiO)2AsO2- and (TiO)2AsO- for As(V) and As(III), respectively. The surface configurations constrained with the spectroscopic results were formulated in the diffuse layer model to describe the adsorption behavior of As in the pH range between 4 and 12. The study suggests that TiO2 is an effective adsorbent for As removal due to its high surface area and the presence of high affinity surface hydroxyl groups.

Adsorption↗

PubMed2006

Leaching behavior of Cr(III) in stabilized/solidified soil.

The leaching behavior of chromium was studied using batch leaching tests, surface complexation modeling and X-ray absorption near edge structure (XANES) spectroscopy. A contaminated soil sample containing 1330 mg-Cr kg(-1) and 25600 mg-Fe kg(-1) of dry soil was stabilized/solidified (S/S) with 10% cement, 25% cement, 10% lime and a mixture of 20% flyash and 5% lime. The XANES analysis showed that Cr(III) was the only Cr species in untreated soil and S/S-treated samples. The leachate Cr concentration determined using the toxicity characteristic leaching procedure (TCLP) was reduced from 5.18 mg l(-1) for untreated soil to 0.84 mg l(-1) for the sample treated with 25% cement. The Cr leachability in untreated and treated soil samples decreased dramatically as the pH increased from 3 to 5, remained at similar levels in the pH range between 5 and 10.5, and further decreased at pH>10.5. Modeling results indicated that the release of Cr(III) was controlled by adsorption on iron oxides at pH<10.5, and by precipitation of Ca(2)Cr(2)O(5).6H(2)O at pH>10.5.

Adsorption↗

PubMed2005

Surface complexation of organic arsenic on nanocrystalline titanium oxide.

The adsorption mechanisms of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) on nanocrystalline titanium oxide (TiO2) were investigated with X-ray absorption spectroscopy (XAS), surface charge and zeta potential measurements, adsorption edge, and surface complexation modeling. XAS data demonstrated that MMA and DMA formed bidentate and monodentate inner sphere complexes with the TiO2 surface, respectively. The charge and zeta potential behaviors of TiO2 as a function of ionic strength suggested that the point of zero charge (PZC) and isoelectric point (IEP) of TiO2 were identical at pH 5.8. Adsorption of MMA and DMA on TiO2 shifted the IEP to pH 4.1 and 4.8, respectively, indicating the formation of negatively charged surface complexes. A satisfactory interpretation of the experimental data was provided by the charge distribution (CD) multi-site complexation (MUSIC) model with the triple plane option under the constraint of the XAS evidence.

Adsorption↗

PubMed2005

Arsenic leachability in water treatment adsorbents.

Arsenic leachability in water treatment adsorbents was studied using batch leaching tests, surface complexation modeling and extended X-ray absorption fine structure (EXAFS) spectroscopy. Spent adsorbents were collected from five pilot-scale filters that were tested for removal of arsenic from groundwater in Southern New Jersey. The spent media included granular ferric hydroxide (GFH), granular ferric oxide, titanium dioxide, activated alumina, and modified activated alumina. The As leachability determined with the Toxicity Characteristic Leaching Procedure (TCLP, 0.1 M acetate solution) was below 180 microg L(-1) for all spent media. The leachate As concentration in the California Waste Extraction Test (0.2 M citrate solution) was more than 10 times higher than that in the TCLP and reached as high as 6650 microg L(-1) in the spent GFH sample. The EXAFS results indicate that As forms inner-sphere bidentate binuclear surface complexes on all five adsorbent surfaces. The As adsorption/desorption behaviors in each media were described with the charge distribution multisite complexation model. This study improved the understanding of As bonding structures on adsorptive media surfaces and As leaching behavior for different adsorbents.

Adsorption↗

PubMed2005

Arsenic leachability and speciation in cement immobilized water treatment sludge.

Arsenic leachability and speciation in cement immobilized water treatment sludge were investigated with leaching tests and X-ray absorption near edge structure (XANES) spectroscopy. The As leachability in the sludge determined with the toxicity characteristic leaching procedure (TCLP) and the waste extraction test (WET) was 283 and 7490 microgl(-1), respectively. Extractions with a lower liquid to solid ratio, under anaerobic conditions, and using citric acid buffer solution dramatically increased the leachate As concentration. XANES results showed that the As(III) composition was reduced from 51.1% of the total As content in the sludge to 16.3% in the cement treated sample with 28 days of cure. When the cement treated sample was cured for two years, the As(III) composition was decreased to 7.4%. The cement treatment reduced the As leachability. The leachate As(III) and total As concentrations were of the same order of magnitude in the samples cured for 28 days as for 2yr. However, consistently lower concentrations were detected in samples with longer cure time. The results of this study improve our understanding of arsenic speciation and leachability in the cement matrix after long cure times.

Arsenic↗

PubMed2004

Lead leachability in stabilized/solidified soil samples evaluated with different leaching tests.

Leaching tests and model calculations were performed to investigate the immobilization mechanisms of Pb and compare different leaching protocols. Stabilization/solidification (S/S) treatments reduced Pb concentrations in the toxicity characteristic leaching procedure (TCLP) leachate from 5.9 mg/L for untreated soil to less than 0.7 mg/L. The results of eight different leaching protocols show that: (1) the main factor controlling the Pb concentration in the leachate is the final pH; (2) the final pH is a function of the leachant acidity; and (3) for a given final pH, the type of leachant has a relatively minor effect on leachability. The diffuse layer adsorption model, aqueous and precipitation reactions were employed in the MINTEQA2 program to describe the Pb leaching behavior. Both leaching tests and model simulations indicate that the Pb leaching behavior can be divided into three stages based on the leachate pH: a high alkalinity leaching stage at pH > 12, where Pb formed soluble hydroxide anion complexes and leached out; a neutral to alkaline immobilization stage in the pH range of 6-12, which was characterized by low Pb leachability caused by adsorption and precipitation; and an acid leaching stage with pH < 6, where the acid neutralizing capacity (ANC) of the S/S materials was totally consumed and therefore free Pb-ion leached out.

Adsorption↗

PubMed2004

Performance of a household-level arsenic removal system during 4-month deployments in Bangladesh.

A simple arsenic removal system was used in Bangladesh by six households for 4 months to treat well water containing 190-750 microg/L As as well as 0.4-20 mg/L Fe and 0.2-1.9 mg/L P. The system removes As from a 16-L batch of water in a bucket by filtration through a sand bed following the addition of about 1.5 g of ferric sulfate and 0.5 g of calcium hypochlorite. Arsenic concentrations in all but 1 of 72 samples of treated water were below the Bangladesh drinking water standard of 50 microg/L for As. Approximately half of the samples also met the World Health Organization (WHO) guideline of 10 microg/L. At the two wells that did not meet the WHO guideline, observations were confirmed by additional experiments in one case ([P] = 1.9 mg/L) but not in the other, suggesting that the latter household was probably not following the instructions. Observed residual As levels are consistent with predictions from a surface complexation model only if the site density is increased to 2 mol/mol of Fe. With the exception of Mn, the average concentrations of other inorganic constituents of health concern (Cr, Ni, Cu, Se, Mo, Cd, Sb, Ba, Hg, Pb, and U) in treated water were below their respective WHO guideline for drinking water.

Arsenic↗

PubMed2003

Immobilization mechanisms of arsenate in iron hydroxide sludge stabilized with cement.

Leaching tests, Fourier transform infrared spectroscopy (FTIR), extended X-ray absorption fine structure (EXAFS) spectroscopy, and thermodynamic modeling were performed to investigate arsenate [As(V)] immobilization mechanisms in iron hydroxide sludge stabilized with cement. The sludge from a groundwater remediation site in Tacoma, WA was mixed and immobilized with premixed cement to reach cement-to-sludge ratios of 2.5, 3.3, 5, 10, and 20 (wt premixed cement/wt dry sludge). The EXAFS analysis determined that As(V) formed bidentate mononuclear complexes on the iron hydroxide surface in the sludge. The adsorbed As(V) had a characteristic FTIR band at 830 cm(-1). Cement treatment converted the adsorbed As(V) to calcium arsenate precipitate with a FTIR peak at 860 cm(-1). The chemical forms of the As(V) were incorporated in an adsorption triple layer model (TLM) to describe the leaching behavior of As(V) in a pH range between 3 and 12. Cement treatment significantly reduced arsenic mobility because of the formation of the sparingly soluble calcium arsenate.

Arsenates↗