Estimation of the Maximum Consumption of Permanganate by Aquifer Solids Using a Modified Chemical Oxygen Demand Test

Knowledge of the consumption of permanganate by naturally occurring reduced species associated with aquifer materials is required for site screening and design purposes to support permanganate in situ chemical oxidation (ISCO) applications. It has been established that this consumption is not a singled-valued quantity, but rather is kinetically controlled. Current methods to determine this permanganate natural oxidant demand (NOD) involve the use of well-mixed batch tests, which are time consuming and subject to test variables (e.g., concentration, mass of oxidant to solid ratio, reaction duration, and mixing conditions) that significantly affect the results. In this paper, we propose a modified chemical oxygen demand (COD) test using permanganate, which can be used to determine the maximum permanganate NOD of an aquifer material. As an initial point of comparison, we tested aquifer materials collected from eight potential ISCO sites using this modified or permanganate COD method, the traditional dichromate COD method, and a method based on well-mixed batch reactors. The results from this comparison indicated that there was no statistically significant difference (α = 5%) between the results of the permanganate COD test and the maximum NOD from the well-mixed batch reactors, while on average the dichromate COD test overestimated the maximum NOD by 100%. The permanganate COD test results were highly correlated to the batch-test maximum NOD data (r = 0.996), and to the total organic carbon and amorphous Fe content of the aquifer materials (r = 0.91). A limited sensitivity investigation of this proposed permanganate COD test revealed that the suspected formation of manganese oxides, a reaction byproduct, may lead to increased experimental variability. However, in spite of this concern we recommend that this proposed permanganate COD method is a quick and economical approach for estimating the maximum permanganate NOD for aquifer materials to support permanganate ISCO site screening and initial design purposes.     

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.     

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%.     

Rates of Trace Mineral-Catalyzed Decomposition of Hydrogen Peroxide

Rapid hydrogen peroxide (H2O2) decomposition is a significant limitation of catalyzed H2O2 propagations (i.e., modified Fenton’s reagent) for the remediation of contaminated soil and groundwater by in situ chemical oxidation. Rates of H2O2 decomposition mediated by seven trace minerals and four iron and manganese oxides were evaluated in batch reactors containing slurries of H2O2 and each of 11 minerals. At pH 3, the dominant catalysts in the decomposition of H2O2 on a per surface area basis were the manganese and iron oxides pyrolusite, goethite, and hematite, while decomposition rates in the presence of the manganese oxyhydroxide manganite and the trace mineral siderite were one to two orders of magnitude lower. At pH 7, the dominant catalysts were hematite and pyrolusite, and decomposition rates were one to two orders of magnitude lower in the presence of goethite, manganite, and siderite. The trace minerals anatase, bauxite, cuprite, ilmenite, magnesite, and willemite provided the least activity for decomposing H2O2 at both pH regimes. The results of this study document that the trace minerals anatase, bauxite, cuprite, ilmenite, magnesite, siderite, and willemite do not provide a significant pathway for H2O2 decomposition in the subsurface, and efforts to stabilize H2O2 for ISCO should focus on reactions occurring on the surfaces of iron and manganese oxides.     

Factors Affecting Effectiveness and Efficiency of DNAPL Destruction Using Potassium Permanganate and Catalyzed Hydrogen Peroxide

This paper describes laboratory studies conducted to evaluate the impact of varying environmental conditions (dense nonaqueous phase liquid (DNAPL) type and mass, and properties of the subsurface porous media) and design features (oxidant type and load) on the effectiveness and efficiency of in situ chemical oxidation (ISCO) for destruction of DNAPL contaminants. Porous media in 160?mL zero-headspace reactors were employed to examine the destruction of trichloroethylene and perchloroethylene by the oxidants potassium permanganate and catalyzed hydrogen peroxide. Measures of oxidation effectiveness and efficiency include (1) media demand (mg-oxidant/kg-porous media), (2) oxidant demand (mol-oxidant/mol-DNAPL), (3) reaction rate constants for oxidant and DNAPL depletion (min?1), (4) the percent (%) DNAPL destroyed, and (5) the relative treatment efficiency, i.e., the rate of oxidant depletion versus rate of DNAPL destruction. While an obvious goal of ISCO for DNAPL treatment is high effectiveness (i.e., extensive contaminant destruction), it is also important to focus on oxidation efficiency, or to what extent the oxidant is utilized for contaminant destruction instead of competing side reactions, for improved cost effectiveness and/or treatment times. Results indicate that DNAPL contaminants can be treated both effectively and efficiently under many environmental and design conditions. In some cases, DNAPL treatment was more effective and efficient than dissolved/sorbed phase treatment. In these experiments, permanganate was a more effective oxidant, however catalyzed hydrogen peroxide treated contaminants more efficiently (e.g., less oxidant required per mass contaminant treated). Results also indicate that oxidation treatment goals can be dictated by environmental conditions, and that specific treatment goals can dictate remediation design parameters (e.g., faster contaminant destruction was realized in catalyzed hydrogen peroxide systems, whereas greater contaminant destruction occurred in permanganate systems).     

金属锰粉氮化过程动力学研究

为研究金属锰粉的渗氮机理,采用热重分析法分别研究了等温和非等温条件下的氮气中,不同粒度的金属锰粉的氮化反应动力学。研究表明:金属锰粉发生氮化反应的起始温度和氮化锰的分解温度分别为470℃和1 016℃。同一粒度下,随着温度升高,表观速率常数增大,但饱和氮含量反而下降,出现吐氮现象;同一温度下,锰粉粒度越小,氮化速率越快,达到平衡的时间越短。金属锰粉粒度从40目降到100目,氮化反应的表观活化能从189.2 kJ/mol降低到115.2 kJ/mol。不同温度下和不同粒度金属锰粉的氮化过程中界面化学反应是整个过程的控制步骤。     

多金属结核金属化还原多元合金磁性能

用自动矿物分析仪、金相显微镜和扫描电镜,从多元合金颗粒尺寸、锰含量、金相组织结构等进行研究,以饱和磁感应强度Ms和剩磁Mr来衡量合金磁性能变化规律,研究多金属结核金属化还原工艺中多元合金磁性能。结果表明,多金属结核金属化还原多元合金磁性能主要受合金颗粒尺寸和锰含量影响,多元合金晶粒尺寸越大,锰含量越低,合金颗粒磁性能越强。因此,工艺过程中应该尽可能增大多元合金晶粒尺寸,抑制锰的还原。     

用球形化学二氧化锰制备锰酸锂的研究

采用液相氧化还原的方法,制备了适合于锰酸锂合成的高密度、高纯度球形化学二氧化锰。实验结果表明反应温度、反应物浓度、pH值、加料速度是影响生成物物理化学性质的主要因素。通过优化反应条件,在溶液的pH=2,温度T=50qC,反应物硫酸锰浓度C=0．3mol／L,加料速度10mL／min的条件下,可以制备出高密度球形化学二氧化锰;通过H^＋离子交换法降低二氧化锰中钾离子含量,从而得到高纯度化学二氧化锰。     

Influence of oxalic acid on the dissolution kinetics of manganese oxide

The kinetics and electrochemical processes of the dissolution of manganese oxides with various oxidation states in sulfuric acid solutions containing oxalate ion additives is studied under variable conditions (concentration, pH, temperature). The parameters favoring a higher degree of the dissolution of manganese oxides in acidic media are determined. The optimal conditions are found for the dissolution of manganese oxides in acidic media in the presence of oxalate ions. The mechanism proposed for the dissolution of manganese oxides in sulfuric acid solutions containing oxalic acid is based on the results of kinetic and electrochemical studies. The steps of the dissolution mechanism are discussed.     

Experimental investigation and three-dimensional computational fluid-dynamics modeling of the flash-converting furnace shaft: Part I. Experimental observation of copper converting reactions in terms of converting rate, converting quality, changes in particle size, morphology, and mineralogy

An experimental investigation was conducted to elucidate the main features of the processes taking place in the shaft of a continuous flash-converting furnace for solid copper mattes. The experiments were conducted in a large laboratory furnace. The test variables included the matte grade, oxygen content in the process gas, particle size of the feed material, and oxygen-to-matte ratio. The observed variables included the fractional completion of the oxidation reactions, fraction of sulfur remaining in the particles, copper-to-iron atomic ratio, particle-size distribution, morphology, and mineralogy of the reacted particles. The experiments showed substantial differences in the oxidation behavior of high-grade (72 pct Cu) and low-grade (58 pct Cu) matte particles. Low-grade matte particles reacted evenly throughout the furnace, increased in size, and experienced no substantial fragmentation during oxidation. High-grade matte particles tended to be oxidized unevenly and experienced severe fragmentation leading to generation of dust. The order of the effects of the test variables on the observed variables was found to be (1) the oxygen-to-matte ratio, (2) the particle size of the feed material, and (3) the oxygen content in the process gas. Microscopic examination revealed that the oxides of copper and iron were the main oxidation products, with little elemental copper present in the reacted particles. Potential implications of the experimental findings on the operation of an industrial flash-converting furnace are discussed.     

SiC particle cracking in powder metallurgy processed aluminum matrix composite materials

Particle cracking is one of the key elements in the fracture process of particulate-reinforced metal-matrix composite (MMC) materials. The present study quantitatively examined the amount of new surface area created by particle cracking and the number fraction of cracked particles in a series of SiC-reinforced aluminum-matrix composite materials. These composite materials were fabricated by liquid-phase sintering and contained 9 vol pct of 23, 63, or 142 μm SiC. The matrix properties were varied by heat treating to either an underaged or peak-aged condition. In general, the new surface area created by particle cracking (S _v ) and the number fraction of cracked particles (F_no) were linearly dependent on the local strain along the tensile specimen. Multiple cracks were frequently observed in the composites containing large particles. It was found that the new surface area created by particle cracking per unit strain was higher for the case of high-strength matrices and was not systematically affected by particle size within the range studied. The number fraction of cracked particles was affected by both particle size and matrix strength. A higher number fraction of particles cracked in the composites reinforced with large particles and with high matrix yield strengths. These results are interpreted in terms of the size of the particle defects, which is a function of particle size, and the critical flaw size necessary to crack a given particle, which is a function of the stress on the particle. The new surface area created by cracking and the fraction of cracked particles were related and are in good agreement for the large and medium sized particles.     

Dissolved Component Recovery Following Resin Exchange Based DOM Fractionation

Organic and inorganic components in natural waters are intimately interrelated and constitute a dissolved material matrix (DMM). The objective of this study was to systematically investigate the distribution and recovery of both organic and inorganic components in chemically fractionated natural waters. Untreated and previously coagulated natural waters were fractionated into hydrophobic and hydrophilic acid, base, and neutral DMM fractions using a resin exchange based protocol. Mass balances on nonpurgable dissolved organic carbon, aluminum, iron, and manganese were used to evaluate DMM component recovery. Quantitative recovery of dissolved organic matter was achieved, whereas, aluminum, iron, and manganese recoveries were largely incomplete (30–92%). Coagulation increased the recovery of all metals examined. Incomplete metals recovery was attributed to imperfect elution from MSC-1 cation exchange resin and appeared related to the distribution coefficient Kd of each metal with this resin. DMM component distribution among chemical fractions was altered by coagulation, with dissolved organic matter preferentially removed in the hydrophobic acid fraction. Unrecovered metals appeared to consist primarily of colloidal mineral (hydr)oxides solubilized by acidic pH conditions imposed during fractionation.     

Magneto-acoustic Interfacial Reaction-Based Nanoparticle Synthesis: A Direct Path to Manufacturing Metal Matrix Nanocomposites

This work investigates a novel nanoparticle fabrication methodology: combined reaction and acoustic cavitation abrasion of a solid in contact with a liquid. Magneto-Acoustic Mixing Technology is used to produce nanometer- to micron-sized particles by chemical and acoustic mechanisms between diamond particles and a stainless steel surface in the presence of a metallic liquid (Mg), where it is found that particle–surface interactions and cavitation generate particles more efficiently together than independently, producing unique chemistries. The individual and combined influence of sonic power and chemical reaction on particle size, volume fraction, chemistry, magnetic properties, and applicability to metal matrix nanocomposite fabrication are studied.     

3种还原剂对锰氧化物结构和形貌的影响

锰氧化物的性能很大程度上受其形貌结构的影响。以高锰酸为氧化剂,乙酸锰、双氧水和硫酸锰为还原剂制备锰氧化物,对产物的结构、形貌和热稳定性分别用XRD、SEM、TEM和TG分析,讨论了不同还原剂对产物、结构、形貌和热稳定性的影响。     

An analytical model for the interaction between an insoluble particle and an advancing solid/liquid interface

In this article, the behavior of particles in front of an advancing solidJliquid interface was analyzed. In the analytical model presented, the critical velocity for the transition from particle pushing to engulfment by the interface was calculated as a function of relevant material parameters and processing variables. In particular, the effect of the difference in the thermal properties of the particle and the matrix on the particle/interface interaction was examined. It was demonstrated that the presence of particles could destabilize the interface which, in turn, affected the behavior of particles at the interface. Based on the analysis, a particle behavior map was constructed to illustrate the complex particle behaviors in different material systems under various growth conditions. Theoretical predictions were compared against experimental results obtained in transparent organic materials as well as in metallic systems. The relevance of these observations to the melt processing of particulate-reinforced metal matrix composites (MMCs) was discussed. Formerly Assistant Research Engineer, The University of Alabama, is now Manufacturing Engineer     

Effect of Heat Input on Fume Generation and Joint Properties of Gas Metal Arc Welded Austenitic Stainless Steel

 The effect of heat input on fume and their compositions during gas metal arc welding (GMAW) of AISI 316 stainless steel plates are investigated. Fume generation rate (FGR) and fume percentage were determined by ANSI/AWS F12 methods. Particle characterization was performed with SEM-XEDS and XRF analysis to reveal the particle morphology and chemical composition of the fume particles. The SEM analysis reveals the morphology of particles having three distinct shapes namely spherical, irregular, and agglomerated. Spherical particles were the most abundant type of individual particle. All the fume particle size falls in the range of less than 100 nm. Mechanical properties (strength, hardness and toughness) and microstructural analysis of the weld deposits were evaluated. It is found that heat input of 115 kJ/mm is beneficial to weld stainless steel by GMAW process due to lower level of welding fume emissions and superior mechanical properties of the joints.     

In situ stress-strain response of small metal particles embedded in a ceramic matrix

The in situ stress-strain response of metal particles embedded in a ceramic matrix was obtained by combining the measurement and the modeling of the crack opening displacement field of a crack in a brittle material bridged by metal particles. The experiments were done on a composite made from platinum particles with a volume fraction of 10% in a magnesium aluminate spinel matrix. The size of the platinum particles was varied from 1 to 12 μm to study the influence of scale on the deformation behavior. Large strain to failure (85%) and ultimate tensile strength of 550 MPa were obtained for the 1 μm particles. But the larger particles failed at a strain of less than 25%; the ultimate tensile strength was also lower. This difference in ductility is explained in terms of debonding at the metal ceramic interface. It is argued that the debonding depends on the length of the dislocation pile up at the interface, and, therefore, on the particle size. The results and the metallographic observations are consistent with a model presented here; in this model the failure condition is given by a combination of the intrinsic yield stress of platinum, and the hydrostatic constraining stress in the metal particle.     

稀土氧化物粒子对钼合金粉末冶金过程及力学性能的影响

试验研究了掺杂La2O3、Y2O3、CeO2稀土氧化物颗粒对钼合金的粉末物性、烧结进程、制品的烧结致密度及压力加工丝材的室温力学性能的影响规律。试验结果表明,掺杂稀土氧化物粒子细化了钼粉的粒度,降低了松装密度和粒度分布范围,同时导致粉末团聚现象增多;稀土氧化物粒子延迟了钼合金的烧结进程,降低了烧结制品的致密度,同时细化了烧结体晶粒尺寸。稀土氧化物粒子以弥散强化和细晶强化的形式,提高了钼合金丝的室温强度。CeO2显著提高了钼合金丝的室温韧性,La2O3、Y2O3则降低了钼合金丝的室温韧性。     

Lidocaine-loaded biodegradable nanospheres. I. Optimization Of the drug incorporation into the polymer matrix

Spherical nanoparticulate drug carriers made of poly(d,l-lactic acid) with controlled size were designed. A local anesthetic, lidocaine, a small hydrophobic molecule, was incorporated in the core with loadings varying from about 7 to 32% (w/w) and increasing with the particle size. Particles with sizes from about 250 to 820 nm and low polydispersity were prepared with good reproducibility; the polymer concentration (at constant surfactant concentration) governed the particle size. The large particles with a high loading ( approximately 30%) showed under in vitro conditions a slow release over 24-30 h, the medium sized carriers (loading of approximately 13%) released the drug over about 15 h, whereas the small particles with small loading ( approximately 7%) exhibited a rapid release over a couple of hours. It seems that the drug release rate is related to the state (crystallized or dispersed) of the drug incorporated in the polymer matrix.