Genesis and Effects of Particles Produced during In Situ Chemical Oxidation Using Permanganate

A research effort was undertaken to investigate the genesis of particles produced during in situ chemical oxidation (ISCO) of trichloroethene (TCE) with permanganate (MnO4?) and to explore the effects of those particles on system permeability and metal mobility. The experimental approach included characterization of soil and groundwater samples from an ISCO field site, batch experiments with a replicated 25 factorial design, and flow-through column experiments. Analyses of intact soil cores from an ISCO field site revealed that MnO2 solids were present in the subsurface near an injection well for NaMnO4 but at low levels (2.3–2.5 mg/g dry wt media) calculated to fill <1% v/v of the aquifer porosity. Batch tests revealed that the mass of filterable solids (>0.45 μm) produced during chemical oxidation with MnO4? was increased at higher TCE concentrations (54 versus 7 mg/L) and in the presence of ambient silt/clay-sized particles in the groundwater (750 versus 7.5 mg/L). Under otherwise comparable conditions, increasing the MnO4? dose markedly increases the oxidant consumption and also increases the solids production. The oxidant form (NaMnO4 versus KMnO4) or reaction time (15 versus 300 min) had little effect on oxidant consumption or filterable solids production. During MnO4? oxidation of higher levels of TCE in a groundwater with ambient silt/clay particles present, there can be substantial increases in filterable solids generated, which are <1 μm in size and consist of MnO2, commingled with other mineral matter. Conceivably, low volumetric fillings of these solids could cause permeability loss. Flow-through column experiments revealed that permeability loss was possible during ISCO but only under conditions with very high MnO2 solids production. On the positive side, the MnO2 solids produced can increase the sorption potential for metals such as cadmium and can represent a mode of immobilization. This research demonstrated that ISCO with permanganate has the potential to yield system permeability loss under some conditions as well as to affect metal mobility. The magnitude of these effects is related to the subsurface conditions, target organic chemical mass, and permanganate dose and delivery method. The production of solids during ISCO needs to be carefully considered during process design and operation to avoid solids-related performance problems while exploiting potential benefits.     

Effects of Groundwater Velocity and Permanganate Concentration on DNAPL Mass Depletion Rates during In Situ Oxidation

In situ chemical oxidation (ISCO) using permanganate has been increasingly applied to deplete mass from dense nonaqueous-phase liquid (DNAPL) source zones. However, uncertainty in the performance of ISCO on DNAPL contaminants is partially attributable to a limited understanding of interactions between the oxidant, subsurface hydrology, and DNAPL mass transfer, resulting in failure to optimize ISCO applications. To investigate these interactions, a factorial design experiment was conducted using one-dimensional flow through tube reactors to determine how groundwater velocity, permanganate concentration, and DNAPL type affected DNAPL mass depletion rates. DNAPL mass depletion rates were found to increase with increasing groundwater velocity, or increasing oxidant concentration. An interaction occurred between the two factors, where high oxidant concentrations had little impact on mass depletion rates at high velocities. High oxidant concentration systems experienced gas generation. Mass depletion rates were fastest at high velocities, but required additional oxidant mass and pore volume addition to achieve complete mass depletion. Lower-velocity systems were more efficient with respect to oxidant mass and pore volume requirements, but mass depletion rates were reduced.     

Impact of Inherent Factors on the Radiolytic Degradation of Biorefractory Contaminants

Experiments were carried out to gain insight into the effect of inherent factors on the radiolytic degradation of two biorefractory contaminants, Acid Orange 7 (AO7) and nitrobenzene (NB). The effects of irradiation dose rate (Dr), initial substrate concentration (C0), pH, and temperature of solutions were evaluated in terms of degradation kinetics, degradation efficiency, initial G values of substrate decomposition, and total organic carbon reduction. Higher C0 and lower Dr values were favorable for the efficient utilization of radiation energy, whereas higher Dr and lower C0 levels were beneficial for degradation rate. An increase in pH led to a reduction in degradation rate constant or degradation efficiency. The temperature of solutions had different effects on the radiolytic degradation of AO7 and NB. The degradation of AO7 followed the empirical Arrhenius law, whereas an increase in temperature led to a reduction in the degradation of NB.     

Diffusive Transport of Permanganate during In Situ Oxidation

The transport of permanganate in low permeability media (LPM) and its ability to degrade trichloroethylene (TCE) in situ were studied through diffusive transport experiments with intact soil cores. A transport cell was developed to measure the effective diffusion coefficient (Deff) of a Br? tracer through intact cores of silty clay LPM obtained from a field site and enable calculation of the apparent tortuosity (τa) of the medium. Then, 5000 mg?L?1 of KMnO4 was added to the cell and diffusive transport and soil matrix interactions were observed. After three months, the soil cores were dissected for morphologic examination and characterization of matrix ions, total organic carbon, MnO4?, and manganese oxides (MnO2). The experiment was then repeated after 2 μL of pure phase TCE were delivered into the center of each of two intact cores. Permanganate transport was observed for one month and then an extraction of the entire soil core was made to determine the extent of TCE degradation. This research demonstrated that permanganate can migrate by diffusion and yield reactive zones that can be predicted based on the properties of the LPM and the oxidant source. Under the experimental conditions examined, permanganate had little effect on the LPM’s pore structure or continuity, and appreciable soil organic matter remained even after 40–60 days of exposure to the oxidant. MnO2 solids, an oxidation by-product, were observed in the LPM, but not at levels sufficient to cause pore filling or alter the apparent matrix tortuosity, even when TCE was present. During diffusive transport of permanganate, TCE in the silty clay LPM was degraded by 97%.     

Degradation of MTBE Intermediates using Fenton’s Reagent

In a previous study, the chemical oxidation of methyl tert-butyl ether (MTBE) at low concentrations in water using Fenton’s reagent (FR) was investigated. At certain reaction conditions the process achieved 99.99% degradation of MTBE but it did not result in complete MTBE mineralization. In the present study, the major intermediate by-products generated during the reaction, such as tert-butyl formate (TBF), tert-butyl alcohol (TBA), methyl acetate, and acetone were separately used as parent contaminants and treated under the same reaction conditions initially used for MTBE (i.e., pH of the water, molar ratio of pollutant to FR) in order to compare their degradability by hydroxyl radicals generated from Fenton’s reaction. The results were compatible with the second order reaction rate constants for the reaction of hydroxyl radicals with each contaminant commonly available in the literature. The comparison of the degradation kinetics for each intermediate by-product provided information that aims at unveiling the limiting step(s) of the entire MTBE degradation pathway. In this context, it was found that (1) TBA was generated by reactions subsequent to those that produced TBF, (2) acetone was originated by at least three independent pathways involving direct hydroxyl radical attack on MTBE, TBF, and TBA, and (3) methyl acetate was formed exclusively from MTBE.     

Oxidation of Methyl Tert-Butyl Ether in Aqueous Solution by an Ozone/UV Process

In this paper, the oxidation of methyl tert-butyl ether (MTBE) in aqueous solution by an ozone/ultraviolet (UV) process was described. The oxidation process was investigated experimentally in a semibatch reactor under various operational conditions, i.e., ozone gas dosage, UV light intensity, and water quality in terms of varying bicarbonate concentration. The ozone/UV process was very successful in oxidizing MTBE. The rate of removal of MTBE increased when the incident UV light intensity increased for the same concentration of influent ozone gas. Similarly, an increase in influent ozone gas concentration resulted in faster removal of MTBE for the same incident UV light intensity. However, bicarbonate in the range of 2–8?mM showed no significant effect on MTBE removal for MTBE concentration ( ～ 1.0?mM) used in this study. Moreover, it was observed that the reaction intermediates could react well in the ozone/UV process, and complete mineralization could be achieved by the ozone/UV process, if desired.     

Characteristics of Potassium Permanganate Encapsulated in Polymer

Potassium permanganate was encapsulated in various polymers to create microcapsules with slow-release properties. Batch tests were conducted to evaluate the rates at which the microcapsules release permanganate. The release histories of 18 different polymer formulations varied strongly, but average initial release rate was 2.70?g KMnO4 released g KMnO4 initial?1?d?1, and the release rate typically decreased with time. The total duration of release ranged from 3?to?80?days, with an average of 27?days. In other batch tests trichloroethene (TCE) was degraded to below detectable amounts by the microcapsules. The degradation rate for TCE was three to four times faster during the initial reaction period than predicted based on permanganate release rates. There appear to be several promising environmental applications for this method of creating a slow-release oxidant.     

Effects of Reagent Concentrations on Advanced Oxidation of Amoxicillin by Photo-Fenton Treatment

The degradation and mineralization of amoxicillin in an aqueous solution was accomplished by using a photo-Fenton treatment. An ultraviolet light source with a 254-nm wavelength was used with hydrogen peroxide (H2O2) and iron(II). The effects of reagent concentrations on amoxicillin degradation and mineralization were investigated systematically by using the Box-Behnken statistical experiment design. Amoxicillin (10–200??mgL-1), H2O2 (10–500??mgL-1), and iron(II) (0–50??mgL-1) concentrations were considered independent variables; the percent amoxicillin degradation and the total organic carbon (TOC) removal (mineralization) were the objective functions to be maximized. Both H2O2 and iron(II) concentrations affected the extent of the amoxicillin degradation and mineralization. The amoxicillin degradation was completed within 2.5?min, and 53% mineralization took place within 60?min. The optimum H2O2∶Fe∶amoxicillin ratio that resulted in complete amoxicillin degradation and 53% mineralization was 100∶40∶105??mgL-1.     

Treatment of TCE-Contaminated Groundwater Using Fenton-Like Oxidation Activated with Basic Oxygen Furnace Slag

The industrial solvent trichloroethylene (TCE) is among the ubiquitous chlorinated organic compounds found in groundwater contamination. The objective of this study was to evaluate the potential of applying basic oxygen furnace (BOF) slag as the catalyst to enhance the Fenton-like oxidation to remediate TCE-contaminated groundwater. Results indicate that TCE oxidation via the Fenton-like process can be enhanced with the addition of BOF slag. Results from the X-ray powder diffraction analysis reveal that the major iron type of BOF slag/quartz sand media was iron oxyhydroxide (α-Fe2O3). Approximately 81% of TCE removal was observed (with initial TCE concentration of approximately 5?mg?L?1), with the addition of 1,000?mg?L?1 of H2O2 and 10?g?L?1 of BOF slag. Results also show that TCE concentrations dropped from 5 to 1.1?mg?L?1, and chloride concentrations increased from 0 to 2.7?mg?L?1 after 60 min of reaction with the presence of H2O2 and BOF slag. This indicates that the depletion of TCE corresponded with the oxidation reactions and release of chloride ions very well in this study. Results demonstrate that the BOF slag can be used to supply catalysts continuously, and it can be installed in a permeable barrier system to enhance the Fenton-like process in situ.     

Evaluation of UV LEDs Performance in Photochemical Oxidation of Phenol in the Presence of H2O2

A novel application of ultraviolet (UV) light emitting diodes (LEDs) as a light source for the degradation of organic contaminant has been investigated. Photocleaving of hydrogen peroxide (H2O2) via UV LEDs photolysis resulted in the generation of hydroxyl radicals. It was found that phenol removal was insignificant in the absence of hydrogen peroxide, therefore oxidation of phenol was attributed to the formed radicals. Two criteria were selected to provide detailed information on the performance of UV LEDs in phenol oxidation: (1) the reaction quantum efficiency and (2) the energy consumption. Statistical tools such as the response surface methodology and the ANOVA were applied to estimate the influence of various process parameters such as the wavelength (255, 269, and 276 nm) and H2O2 to phenol molar ratio (5, 50, and 100) on phenol degradation reaction quantum efficiency. The decay of phenol (initial concentration of 1.06 mM) was the most pronounced at 255 nm and H2O2 to phenol molar ratio of 50. Finally, the “figure-of-merit” was used to estimate the specific energy consumption of the UV LED-based process.     

Effect of Oxide Scale Formation on the Behaviour of Cu in Steel during High Temperature Oxidation in O2‐N2 and H2O‐N2 atmospheres

Cu enrichment at the steel‐scale interface and its migration from there was investigated during the heating of steel cast at 1200°C under various oxidizing conditions. The behaviour of Cu enrichment was found to be largely dependent on the morphology of oxide scale formed during oxidation. At the early stage of oxidation, Cu‐rich phase formed and accumulated at the steel‐scale interface in both O₂‐N₂ and H₂O‐N₂ atmosphere. However, as the oxidation proceeded, the enrichment was vastly different for each oxidizing atmosphere. In the case of O₂‐N₂ oxidation, an oxide layer was formed initially at the steel surface, but a gap was developed soon after at the steel‐scale interface and grew in size, which practically separated the scale from the steel substrate. The scale layer formed under this condition was porous. The Cu‐rich phase initially formed at the interface seemed to migrate to the scale layer, leaving no Cu‐rich phase at the interface. In the case of H₂O‐N₂ oxidation, however, the scale layer formed was dense and tightly attached to the steel surface, and the Cu rich‐phase continued to accumulate at the interface. Regarding the behaviour of the Cu‐rich phase formed at the interface, it is proposed with experimental evidences that, when a gap forms at the steel‐scale interface, it is the vaporization of Cu in the Cu‐rich phase through the gap that brings Cu to the scale.     

Degradation and Mineralization of Simazine in Aqueous Solution by Ozone/Hydrogen Peroxide Advanced Oxidation

Advanced oxidation of simazine in aqueous solution by the peroxone (hydrogen peroxide/ozone) treatment was investigated using Box-Behnken statistical experiment design and response surface methodology. Effects of pH, simazine and H2O2 concentrations on percent simazine and total organic carbon (TOC) removals were investigated. Ozone concentration was kept constant at 45?mg?L?1. The optimum conditions yielding the highest simazine and TOC removals were also determined. Both simazine and peroxide doses affected simazine removal while pH and pesticide dose had more pronounced effect on mineralization (TOC removal) of simazine. Nearly 95% removal of simazine was achieved within 5 min for simazine and peroxide concentrations of 2.0 and 75?mg?L?1, respectively at pH = 7. However, mineralization of simazine was not completed even after 60 min at simazine doses above 2?mg?L?1 indicating formation of some intermediate compounds. The optimum H2O2/pH/Simazine ratio resulting in maximum pesticide (94%) and TOC removal (82%) was found to be 75/11/0.5(mg?L?1).     

Investigation of Ultraviolet Light-Enhanced H2O2 Oxidation of NOx Emissions

Injecting aqueous solutions of hydrogen peroxide (H2O2) into hot flue gases can convert nitric oxide (NO) to higher oxidation states (NO2, HNO2, and HNO3), which can then be removed in a wet scrubber. The optimum temperature for such conversion is 500°C (930°F), at which H2O2 is thermally “activated” (split into free radicals). At lower temperatures ultraviolet (UV) light can be used to activate the peroxide molecules. In this pilot plant study at Kennedy Space Center, experiments were done with none, one, or two UV lamps on, with and without SO2 present in the flue gases, at various temperatures, and with various injection rates of peroxide. Temperatures ranged from 117 to 350°C (243 to 660°F), and the molar ratios (peroxide to NOx) ranged from 0.68 to 5.02. Conversions of NO varied from below 10 to above 70%, with the highest conversions occurring with higher temperatures, higher dosages of hydrogen peroxide, and with both UV lamps turned on. Conversions of NOx ?(NO+NO2) varied from below 5 to above 40%. The presence of SO2 did not inhibit NO or NOx conversion.     

高锰酸钾氧化预处理某难浸金矿的研究

在酸性条件下以高锰酸钾为氧化剂,打开难浸金矿中金的硫化物、砷化物包裹,提高金浸出率。结果表明,最佳的氧化预处理条件为:高锰酸钾用量40g/L、液固比12∶1、H2SO4初始浓度1.0mol/L、氧化温度80℃、氧化时间5h。预处理后金浸出率可达87.75%。     

Modeling the Transformation of Chromophoric Natural Organic Matter during UV/H2O2 Advanced Oxidation

This research developed a differential kinetic model to predict the partial degradation of natural organic matter (NOM) during ultraviolet plus hydrogen peroxide (UV/H2O2) advanced oxidation treatment. The absorbance of 254?nm UV, representing chromophoric NOM (CNOM) was used as a surrogate to track the degradation of NOM. To obtain reaction rate constants not available in the literature, i.e., reactions between the hydroxyl radical (?OH) and NOM, experiments were conducted with “synthetic” water, using isolated Suwannee River NOM, and parameter estimation was applied to obtain the unknown model parameters. The reaction rate constant for the reaction between ?OH and total organic carbon (TOC), k?OH,TOC, was estimated at 1.14(±0.10)×104??L?mg-1?s-1, and the reaction rate constant between ?OH and CNOM, k?OH,CNOM, was estimated at 3.04(±0.33)×104??L?mol-1?s-1. The model was evaluated on two natural waters to predict the degradation of CNOM and H2O2 during UV/H2O2 treatment. Model predictions of CNOM degradation agreed well with the experimental results for UV/H2O2 treatment of the natural waters, with errors up to 6%. For the natural water with additional alkalinity, the model also predicted well the slower degradation of CNOM during UV/H2O2 treatment, owing to scavenging of ?OH by carbonate species. The model, however, underpredicted the degradation of H2O2, suggesting that, when NOM is present, mechanisms besides the photolysis of H2O2 contribute appreciably to H2O2 degradation.     

M2和M2Al高速钢的氧化和脱碳

研究了高速钢Ｍ２和Ｍ２Ａｌ在空气介质中加热时的氧化和脱碳特性。分析了铝对高速钢的氧化和脱碳的影响。结果得出铝对Ｍ２钢的氧化有保护作用，但增加钢的脱碳倾向。     

Effects of Seepage Velocity and Temperature on the Dechlorination of Chlorinated Aliphatic Hydrocarbons

The influence of seepage velocity and groundwater temperature on the dechlorination rates of trichloroethylene (TCE) and tetrachloroethylene (PCE) by zero-valent iron (Fe0) were investigated by running laboratory column tests at seepage velocities ranging from 31 to 1,884?m/year at temperatures of 10 and 23°C. By increasing the seepage velocity from 31 to 1,884?m/year at 10°C, there were approximately seven- and nine-fold increases in the normalized dechlorination rate constants (SA) of TCE and PCE, respectively. Similarly, a four-fold increase in the SA of TCE and PCE was also observed at 23°C when increasing the seepage velocity from 103 to 1,183?m/year. Raising the groundwater temperature from 10 to 23°C at a given seepage velocity resulted in 2.7 and 1.1 times increases in the TCE SA and PCE SA, respectively. With the application of the Arrhenius equation, activation energies of 70.3?kJ/mol for TCE and 38.6?kJ/mol for PCE dechlorination were determined, indicating domination of the electron transfer process over the mass transfer as a major rate-limiting step of the dechlorination reactions by Fe0.     

Injection Nozzle for Ultraviolet Light-Enhanced H2O2 Oxidation of Air Pollutants in Flue Gas

Injecting aqueous solutions of hydrogen peroxide (H2O2) into hot flue gases can split the peroxide into OH and HO2 radicals. These reactive radicals readily oxidize air pollutants such as CO, VOCs, NO, mercury, and others. H2O2 is thermally “activated” (split into free radicals) rapidly at temperatures of 500°C and above. At lower temperatures, such as found in boiler exhaust flue gases, ultraviolet (UV) light can be used to activate the peroxide molecules. However, placing the UV lamps directly in the flue gases can lead to operating and maintenance problems, and “dilutes” the UV energy due to absorption by other gases. A “UV nozzle” has been developed that produces H2O2 radicals and delivers them into a flowing stream of boiler flue gases. Using a previously constructed pilot scale system at NASA's Kennedy Space Center, experiments were run to prove the concept of the nozzle, measuring the oxidation of NO as an indicator of radical formation and delivery. Data were taken at three temperatures, with none, one, or two UV lamps on, and with various injection rates of peroxide. Flue gas temperatures ranged from 85 to 304°C (186 to 580°F), and the molar ratios (inlet peroxide to inlet NOx) ranged from about 1.5 to over 15. Conversions of NO varied from 0% (at the lowest temperature tested) to above 50% (at highest temperature). Although increasing temperature had a marked effect on conversion, the activation of hydrogen peroxide by UV light was demonstrated in the temperature range of final flue gas exhaust gases (290–350°F). These results indicate that radicals can be created from hydrogen peroxide at reasonable temperatures using UV light, and that the radicals can be delivered into a flue gas stream where they can oxidize pollutants.     

H2O2氧化水热晶化法制备超细钨粉

通过H2O2氧化工业级钨粉颗粒制备出纳米级WO3粉体,采用两段还原法对所得的产物进行氢还原后得到超细钨粉。用XRD、SEM、BET等对所得产物进行了一系列的表征。结果表明:工业级钨粉经氧化水热晶化处理后所得产物为单斜相WO3,平均粒径约为60 nm;将制得的WO3在氢气氛下还原,800℃下保温45 min后得到颗粒分布较窄、平均粒径约150 nm的立方相钨粉。当还原温度升高至900℃时,所得的钨粉颗粒明显长大,部分粒径长大至2~3μm,但颗粒的球形度更好。     

Destruction of Trichloroethylene and Perchloroethylene DNAPLs by Catalyzed H2O2 Propagations

The destruction of trichloroethylene (TCE) and perchloroethylene (PCE) dense nonaqueous phase liquids (DNAPLs) using catalyzed H2O2 propagations (CHP), an in situ chemical oxidation process based on Fenton’s reagent, was investigated in batch, bench scale reactors. TCE and PCE masses were quantified over time in DNAPLs, aqueous phases, and off gasses, and the rate of DNAPL destruction was compared to the corresponding rate of gas purge dissolution. TCE and PCE DNAPLs were rapidly destroyed by CHP at 1.7 and 4.4 times the rate of gas purge dissolution, respectively. Use of reactions in which a single reactive oxygen species was generated demonstrated that both hydroxyl radical and superoxide were involved in TCE and PCE DNAPL destruction, with superoxide having the major role in the destruction of the DNAPLs. These results show that DNAPLs composed of contaminants highly reactive with hydroxyl radical, such as TCE and PCE, are destroyed primarily through reaction with superoxide.