Maohong Fan

SYNTHESIS, PROPERTIES, AND ENVIRONMENTAL APPLICATIONS OF NANOSCALE IRON-BASED MATERIALS: A REVIEW

Due to their special properties, people have been increasingly interested in studying applications of nanoscale metal materials in environmental engineering. Literature about the current research on the synthesis, properties, and environmental applications of nanoscale iron-based materials is reviewed and summarized in this article. Different physical and chemical methods used for synthesizing nano-iron-based particles with desired size, structure, and surface properties are described. We also emphasize important properties of nano-iron-based particles, including the density and intrinsic reactivity of surface sites. These properties directly influence the chemical behavior of such particles and, consequently, affect their applications in water and wastewater treatment and in air pollution control. Environmental applications of nano-iron particles are discussed in detail, including removal of chlorinated organics, heavy metals, and inorganics.

Effect of competing solutes on arsenic(V) adsorption using iron and aluminum oxides.

The study focused on the effect of several typical competing solutes on removal of arsenic with Fe2O3 and Al2O3. The test results indicate that chloride, nitrate and sulfate did not have detectable effects, and that selenium(IV) (Se(IV)) and vanadium(V) (V(V)) showed slight effects on the adsorption of As(V) with Fe2O3. The results also showed that adsorption of As(V) on Al2O3 was not affected by chloride and nitrate anions, but slightly by Se(IV) and V(V) ions. Unlike the adsorption of As(V) with Fe2O3, that with Fe2O3 was affected by the presence of sulfate in water solutions. Both phosphate and silica have significant adverse effects on the adsorption of As(V) adsorption with Fe2O3 and Al2O3. Compared to the other tested anions, phosphate anion was found to be the most prominent solute affecting the As(V) adsorption with Fe2O3 and Al2O3. In general, Fe2O3 has a better performance than Al2O3 in removal of As(V) within a water environment where multi competing solutes are present.

Oxidation of As(III) by potassium permanganate

The oxidation of As(III) with potassium permanganate was studied under conditions including pH, initial As(III) concentration and dosage of Mn(VII). The results have shown that potassium permanganate was an effective agent for oxidation of As(III) in a wide pH range. The pH value of tested water was not a significant factor affecting the oxidation of As(III) by Mn(VII). Although theoretical redox analyses suggest that Mn(VII) should have better performance in oxidization of As(III) within lower pH ranges, the experimental results show that the oxidation efficiencies of As(III) under basic and acidic conditions were similar, which may be due to the adsorption of As(III) on the Mn(OH)2 and MnO2 resulting from the oxidation of As(III).

Precision and accuracy of photoacoustic measurements of unburned carbon in fly ash

This research investigates factors influencing precision and accuracy of photoacoustic measurements of unburned carbon in fly ash. This information is useful for the development of instruments to monitor the performance of coal-fired boilers. Important factors identified by this research include the protocols for sampling and preparing fly ash for measurements, the ambient conditions at which photoacoustic measurements are performed, and the wavelength of the excitation source. Since the quantity of fly ash interrogated by the photoacoustic technique is usually small, representative sampling is critically important. Most fly ash is extremely heterogeneous and grinding is an important precursor to sampling material for testing in the photoacoustic apparatus. Bulk properties of the fly ash also affected the photoacoustic signal. The effects of both ambient temperature and humidity on precision were evaluated through statistical testing. Temperature control of the photoacoustic cell to within a few tenths of a degree Centigrade proved to be important. The wavelength of the excitation source has two major effects on accuracy of measurements. Although mineral matter in fly ash is a relatively weak absorber of radiation compared to carbon, its concentration is typically so high that a pronounced background signal can arise from the mineral components. Careful selection of excitation wavelength can mitigate this effect on accuracy. Another factor influencing accuracy was signal saturation, which occurred at relatively low carbon concentrations when using 940 nm infrared radiation as an excitation source; this effect was avoided by diluting fly ash samples with optically non-absorbing powders.

The kinetics of producing sulfate-based complex coagulant from fly ash

This paper studies the kinetics of reactions between iron and aluminum oxides in fly ash and sulfuric acid for the production of a complex sulfate-based coagulant. The important part of this research was to monitor the change in the concentration of product during the reaction. The ratio of concentration of ferric sulfate to aluminum sulfate during reaction, and the linearity of plots of a derived concentration of function versus time at different temperatures show that reactions of both iron and aluminum oxides in fly ash with sulfuric acid are second-order with respect to sulfuric acid concentration. Furthermore, the ratio of the concentration of the ferric sulfate to that of aluminum sulfate and the slopes of the derived concentration function versus time were used to obtain the rate constants of reactions. Finally, based on the rate constants obtained at different temperatures, the empirical Arrhenius expressions of iron and aluminum extracting reactions were derived.

Arsenite oxidation by ferrate in aqueous solution

Abstract Arsenite [As(III)] is much more toxic and difficult in removal than arsenate [As(V)]. Therefore, a method for removing As(III) is more urgently needed than for As(V). The precondition for better As(III) removal is to oxidize it to As(V). This study investigates the oxidation ability of ferrate, Fe(VI), under different pH conditions, different initial concentrations of As(III) and different dosages of Fe(VI). The results show that Fe(VI) is an effective oxidizer for As(III) under basic condition. The pH value of tested water is a significant factor affecting the oxidation efficiency of As(III) by Fe(VI). Although theoretical redox analyses suggest that Fe(VI) is a better oxidizer under acidic condition, the experimental results show that basic condition is more efficient than acidic condition for As(III) oxidation by Fe(VI) due to the acid-catalyzed redox reaction between Fe(VI) and H 2 O. Initial As(III) concentration does not play an important role in affecting the oxidation efficiency. The results in this study also reveal that the final product of Fe(VI) is Fe(III) and the needed mole ratio of Fe(VI):As(III) for complete As(III) oxidation under basic condition is 2:3.

Photoacoustic measurement of iron in composite coagulant

Abstract Iron concentrations of composite coagulant powders were measured by means of the photoacoustic effect. The onset of photoacoustic signal saturation for iron in the powders was 5 wt.%. This problem was solved by adding one of the components of the composite coagulant as a diluent to the samples. Based on the findings of this research, photoacoustic response of composite coagulant is closely correlated to iron concentration in the coagulant powders. Photoacoustic signal was found to be a function of excitation power of photoacoustic set-up. Sample grinding helps improve the accuracy of photoacoustic measurement of iron in composite coagulant.

Relationships among loss-on-ignition and unburned carbons, and the FTIR photoacoustic spectra of fly ashes

Loss-on-ignition (LOI) and unburned carbon (UC) concentrations of fly ash are two very important indices for evaluating combustion efficiencies of boilers. They are also very important factors affecting the utilisation of fly ashes. The LOI and UC of five fly ash samples collected from different power plants were analysed. The Fourier-transform infrared (FTIR) photoacoustic spectra (PAS) of these fly ash samples were observed. The LOI and UC of fly ashes were found to correlate with the heights of the baselines of their FTIR PAS. The strength of the photoacoustic signal of fly ash has a stronger relationship with its UC than its LOI. Moreover, the LOI of fly ash is always higher than its UC.

Hydrogen Storage on Carbon Adsorbents

Publisher Summary Global energy demand and global warming due to greenhouse gas emissions have spurred intensive research for alternative fuel. Hydrogen (H 2 ), an ideal energy carrier, is obviously a promising candidate. Its use efficiency is high; for instance, it is 2.75 times greater than gasoline for the same weight. The onboard storage of H 2 is obviously one of the most, if not the most, critical issues in developing an H 2 -based energy system. H 2 can be produced indirectly from coal gasification and reforming processes for which advanced technologies are available; these processes, combined with carbon dioxide (CO 2 ) separation and sequestration, have the potential to manufacture substantial quantities of H 2 with minimum greenhouse gas emissions. Synthesized H 2 can be deployed to generate electricity from fuel cells; alternatively, it can be combusted for providing energy for space heating, replacing natural gas in industry, and fueling aircraft. The most promising method for H 2 storage appears to be through materials-based storage technologies, which are inherently safe and should be more energy efficient than pressurization or liquefaction.Publisher Summary nGlobal energy demand and global warming due to greenhouse gas emissions have spurred intensive research for alternative fuel. Hydrogen (H2), an ideal energy carrier, is obviously a promising candidate. Its use efficiency is high; for instance, it is 2.75 times greater than gasoline for the same weight. The onboard storage of H2 is obviously one of the most, if not the most, critical issues in developing an H2-based energy system. H2 can be produced indirectly from coal gasification and reforming processes for which advanced technologies are available; these processes, combined with carbon dioxide (CO2) separation and sequestration, have the potential to manufacture substantial quantities of H2 with minimum greenhouse gas emissions. Synthesized H2 can be deployed to generate electricity from fuel cells; alternatively, it can be combusted for providing energy for space heating, replacing natural gas in industry, and fueling aircraft. The most promising method for H2 storage appears to be through materials-based storage technologies, which are inherently safe and should be more energy efficient than pressurization or liquefaction.

SYNTHESIS OF SULFUR-BASED WATER TREATMENT AGENT FROM SULFUR DIOXIDE WASTE STREAMS

Absorption of sulfur dioxide from a simulated flue gas was investigated for the production of polymeric ferric sulfate (PFS), a highly effective coagulant useful in treatment of drinking water and wastewater. The reaction for PFS synthesis took place near atmospheric pressure and at temperatures of 30-80 C. SO{sub 2} removal efficiencies greater than 90% were achieved, with ferrous iron concentrations in the product less than 0.1%. A factorial analysis of the effect of temperature, oxidant dosage, SO{sub 2} concentration, and gas flow rate on SO{sub 2} removal efficiency was carried out, and statistical analyses are conducted. The solid PFS was also characterized with different methods. Characterization results have shown that PFS possesses both crystalline and non-crystalline structure. The kinetics of reactions among FeSO{sub 4} {center_dot} 7H{sub 2}O, NaHSO{sub 3} and NaClO{sub 3} was investigated. The PFS product was used in pilot-scale tests at a municipal water treatment facility and gave good results in removal of turbidity and superior results in removal of disinfection byproduct precursors (TOC, DOC, UV-254) when compared with equal doses of ferric chloride.