Extent Of Leaching Research Articles

Corrosion behavior analyses of metallic membranes in hydrogen iodide environment for iodine-sulfur thermochemical cycle of hydrogen production

HI decomposition in Iodine-Sulfur (IS) thermochemical process for hydrogen production is one of the critical steps, which suffers from low equilibrium conversion as well as highly corrosive environment. Corrosion-resistant metal membrane reactor is proposed to be a process intensification tool, which can enable efficient HI decomposition by enhancing the equilibrium conversion value. Here we report corrosion resistance studies on tantalum, niobium and palladium membranes, along with their comparative evaluation. Thin layer each of tantalum, palladium and niobium was coated on tubular alumina support of length 250 mm and 10 mm OD using DC sputter deposition technique. Small pieces of the coated tubes were subject to immersion coupon tests in HI-water environment (57 wt% HI in water) at a temperature of 125–130 °C under reflux environment, and simulated HI decomposition environment at 450 °C. The unexposed and exposed cut pieces were analyzed using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and secondary ion mass spectrometer (SIMS). The extent of leaching of metal into liquid HI was quantified using inductively coupled plasma-mass spectrometer (ICP-MS). Findings confirmed that tantalum is the most resistant membrane material in HI environment (liquid and gas) followed by niobium and palladium.

Hyperbranched polyglycerol nanoparticles based multifunctional, nonmigrating hindered phenolic macromolecular antioxidants: Synthesis, characterization and its stabilization effect on poly(vinyl chloride)

A facile synthesis of multifunctional hindered phenolic macromolecular antioxidants based on hyperbranched polyglycerol (HbPG) nanoparticles as cores with different molecular weights is reported. The structure of the resulting polymers was verified by 1H NMR and UV–Vis spectroscopies indicating 64–77% antioxidant functionalizations of the hydroxyl groups of the HbPGs. GPC analyses show that polymeric antioxidants with PDI of 1.33–1.66 are formed. DSC and TGA measurements revealed Tg of ∼40 °C and high thermal stability up to ∼300 °C of the multifunctional HbPG-antioxidant conjugates, respectively, confirming that these materials are liquids and stable at usual polymer processing temperatures. The efficiency of the synthesized antioxidants in thermooxidative stabilization of PVC was investigated, keeping in mind that although the importance and wide application of PVC, especially in biomedical fields are incontestable, the utilization of macromolecular antioxidants for the stabilization of PVC has not been examined so far. It was found that the macromolecular antioxidants show similar stabilizing efficiency as the tetrafunctional industrial Irganox1010. Very low extent of leaching of the HbPG-antioxidant from PVC, investigated by extraction tests in both water and hexane, was observed in both extracting agents in contrast to the case of the low molecular weight hindered phenolic antioxidant. Thus, the obtained results confirm the advantages, i.e. high efficiency and highly suppressed leaching, of HbPG-based macromolecular antioxidants in a variety of application fields.

Reducing the leachability of nitrate, phosphorus and heavy metals from soil using waste material

Abstract Contaminants like nitrate (NO3), phosphorus (P) and heavy metals in water are often associated with agricultural activities. Various soil and water remediation techniques have been employed to reduce the risk associated with these contaminants. A study was conducted to examine the extent of leaching of heavy metals (Cd, Ni, Pb and Cr), NO3 and P. For this purpose sandy and silt loam soils were amended with different waste materials, namely wood ash, solid waste ash, vegetable waste, charcoal, and sawdust. The soils were saturated with wastewater. Irrespective of the waste applied, the pH and EC of the amended soils were found to be greater than the control. Charcoal, sawdust and wood ash significantly decreased heavy metals, nitrate and phosphorus concentrations in the leachate. Treatments were more efficient for reducing Ni than other heavy metals concentrations. Waste amendments differed for heavy metals during the process of leaching. Heavy metals in the soil were progressively depleted due to the successive leaching stages. This research suggests that waste material may act as an adsorbent for the above contaminants and can reduce their leachability in soils.

Catalytic degradation of chlorinated organic pollutants over CexFe1−xO2 (x: 0, 0.25, 0.5, 0.75, 1) nanocomposites at mild conditions

Oxidation of chlorinated organic pollutants (COPs) like 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4-dichlorophenoxy acetic acid (2,4-D) using aqueous hydrogen peroxide (30% v/v) over CexFe1−xO2 (x: 0, 0.25, 0.5, 0.75, 1) nanocatalysts was studied. The catalysts were characterised by temperature programmed reduction (H2-TPR) and desorption (NH3-TPD and CO2-TPD) techniques. The reducing power of ceria increased on iron doping as revealed by TPR analysis. CexFe1−xO2 were effective catalysts for Wet Peroxide Oxidation of 4-CP, 2,4-DCP and 2,4-D pollutants. 4-CP (500mg/L) was completely degraded with 37.38% TOC and 58.75% COD removal after 90min at 70°C using Ce0.25Fe0.75O2 catalyst. Complete 2,4-DCP (250mg/L) conversion with 21.60% TOC and 42.44% COD removal was observed at 45min over Ce0.5Fe0.5O2 catalyst at 50°C. 100% catalytic oxidative conversion of 2,4-D (250mg/L) with 23.64% TOC and 45.78% COD removal was achieved at 70°C at 60min. Atomic Absorption Spectrometry (AAS) indicated the extent of leaching of iron from the catalytic structure to be negligible. The mixed oxides were reusable and stable on consecutive uses as indicated by X-ray diffraction (XRD) and surface area measurements. The catalytic efficiency was retained after five successive runs.

Cobalt Encapsulated in N-Doped Graphene Layers: An Efficient and Stable Catalyst for Hydrogenation of Quinoline Compounds

Porous nitrogen-doped graphene layers encapsulating cobalt nanoparticles (NPs) were prepared by the direct pyrolysis process. The resulting hybrids catalyze the hydrogenation of diverse quinoline compounds to access the corresponding tetrahydro derivatives (THQs), important molecules present in fine and bulk chemicals. Near-quantitative yields of the corresponding THQs were obtained under optimized conditions. Notably, various useful substituted quinolines and other biologically important N-heteroarenes are also viable. The enhanced stability of the catalyst is ascribed to the encapsulation structure, which can enormously reduce the extent of leaching of base metals and protect metal NPs from growing larger. The achieved success in the encapsulation of metal NPs within graphene layers opens an avenue for the design of highly active and reusable heterogeneous catalysts for more challenging molecules.

Hierarchical Pore Structures as Highways for Enzymes and Substrates

The use of enzymes in chemical reactions needs packaging inside a porous matrix. In this issue of Chem , Farha et al. show that a hierarchical metal-organic framework with large and small pores allows orthogonal access of enzymes and their substrates.

Differences in Leaching Characteristics of Mg and Ca from Various Biomass Components of Mallee Tree in Hot-Compressed Water

In hot-compressed water (HCW), water-insoluble Mg and Ca become leachable from mallee wood, leaf, or bark. The extent of leaching of Mg and Ca varies from component to component in order of leaf > wood > bark for Mg and wood > leaf > bark for Ca. Such differences are due to two reasons: differences in the occurrence forms of Mg and Ca and differences in hemicellulose decomposition for different biomass components. For example, most water-insoluble Mg in wood and bark is ion-exchangeable, but only part of water-insoluble Mg in leaf is ion-exchangeable, with the rest being acid-soluble but not ion-exchangeable. Most water-insoluble Ca in wood is ion-exchangeable, but those in leaf and bark are acid-soluble but not ion-exchangeable. The results show that water-insoluble Mg or Ca in the ion-exchangeable form can be rapidly leached in HCW, but the leaching of water-insoluble Mg or Ca in the acid-soluble but not ion-exchangeable form is considerably slower as a result of the poor solubility of these species in ...

CexV1−xO2 (x: 0, 0.25–1) nanocomposites as efficient catalysts for degradation of 2,4 dichlorophenol

Composite oxides of CexV1−xO2 (x: 0, 0.25–1) were synthesized, characterized and applied for removal of 2,4-dichlorophenol. The catalysts were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), N2 adsorption at −196°C, Fourier transform Infra Red (FT-IR) and Fourier Transform Raman (FT-Raman) techniques. The X-ray diffractograms of Ce –V oxide powders with different Ce/V molar ratios revealed the coexistence of CeO2 with a tetragonal CeVO4 and orthorhombic V2O5 phase. The Brunauer–Emmet–Teller (BET) surface areas and pore volumes of synthesised composites were in the range of 26.21–1.26m2/g and 0.01–0.0007cm3/g respectively. FT-Infra Red and FT-Raman measurements confirmed the formation of different mixed oxides. Effects of Ce-V ratio, H2O2 dose, reaction temperature, and 2,4-dichlorophenol (2,4-DCP) concentration on CWPO of 2,4-DCP were investigated in detail. CexV1−xO2 were effective catalysts for wet peroxide oxidation of 2,4-DCP and the highest catalytic activity was obtained using the Ce0.5V0.5O2 catalyst with complete 2,4-DCP degradation at 60min, and at 180min COD and TOC removal percentage was 84% and 41.03% respectively. Atomic Absorption Spectrometry (AAS) indicated the extent of leaching of vanadium to be negligible. The mixed oxides were reusable and stable on consecutive use as indicated by XRD and surface area measurements.

Leaching Behavior of Heavy Metals from Cement Pastes Using a Modified Toxicity Characteristic Leaching Procedure (TCLP).

As the standard toxicity characteristic leaching procedure (TCLP) can not exhaust the acid neutralizing capacity of the cement rotary kiln co-processing solid wastes products which is particularly important for the assessment of the leaching concentrations of heavy metals. A modified TCLP was proposed. The extent of leaching of heavy metals is low using the TCLP and the leaching performance of the different metals can not be differentiated. Using the modified TCLP, however, Zn leaching was negligible during the first 180h and then sharply increased (2.86±0.18 to 3.54±0.26mg/L) as the acidity increased (pH<6.0). Thus, Zn leaching is enhanced using the modified TCLP. While Pb leached readily during the first 126h and then leachate concentrations decreased to below the analytical detection limit. To conclude, this modified TCLP is a more suitable method for these cement rotary kiln co-processing products.

RADIONUCLIDES DISTRIBUTION NEAR FORMER URANIUM MINING

The paper shows, that radionuclides from the stony rocks of uranium mines can be leached by atmospheric precipitations. In acid conditions, a degree of leaching is greater. Goal. The aim of this investigation was to study the distribution of radionuclides in uranium minings and their impact on the environmental contamination. Materials and methods. The study was carried out in two stages. In the first stage, a blade of rock was mixed with distilled water in proportions of 0,3 kg of gravel and 1 liter of water. After thirty days of soaking, water was sent to the gamma-spectrometric analysis to Canberra’s spectrometer (USA) with a high-purity germanium detector. In the second stage, we carried out the similar experiment with water, wich was acidified to pH = 3. Contamination levels of areas near the in-situ leaching mine were determined. Intervention levels were used to estimate risk and possible water consumption by the population. Estimations were carried out taking into account the combined presence of several radionuclides in the water. Results. The results of these studies have shown that the distribution of radionuclides from the source of the contamination is about 360 meters during the 30 y period. The stream, along which samples of soil were collected and studied, was formed by the miner waters that flow along small ruts towards a village, thereby increasing the likelihood of water use by the public. Conclusions. The uranium mines are the source of radioactive contamination. Radionuclides are distributed due to the erosion of rocks and leached out of the stony rock by precipitations. The extent of leaching is significantly increased in an acidic environment, which takes place near the in-situ leaching mines.

Dealloyed Pt-Ni Polymer Electrolyte Fuel Cell Cathodes: Effects of Catalyst-Ionomer Ink Composition on Structure and Performance

There have been numerous studies on the effects of catalyst-ionomer ink composition and electrode fabrication on the performance of Pt/C-containing polymer electrolyte fuel cell cathodes.1-9 There have been relatively few studies, however, on relating the ink composition to its agglomerate structure10 and in relating the structure to the resulting electrode performance, in particular for the more recently-developed Pt alloy and dealloyed Pt alloy catalysts.11 There have also been few studies on the effects of ink composition and electrode preparation on the composition of the alloy nanoparticles. In this presentation we report on studies using anomalous small angle X-ray scattering (ASAXS), ultra-small angle X-ray scattering (USAXS),10 X-ray near-edge absorption spectroscopy (XANES), and X-ray fluorescence spectroscopy (XRF) to characterize catalyst-ionomer inks and the resulting electrodes as a function of ionomer to carbon ratio, solvent concentration and type, and catalyst type (Pt or PtNi alloy). It was found that Ni leaches from the PtNi alloy and the extent of leaching is dependent on both the ionomer to carbon ratio and solvent in the ink. We also correlate the properties determined using the X-ray techniques to the electrode performance in a polymer electrolyte fuel cell. For example, Ni has been found to negatively impact the transport properties of the cathode catalyst layer.12 Acknowledgements This work is part of a collaborative project with Johnson Matthey Fuel Cells, United Technologies Research Center, the University of Texas-Austin, and Indiana University-Purdue University Indianapolis which is supported by the U.S. Department of Energy’s Fuel Cell Technologies Office. This research used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The USAXS work was performed at APS Sector 15, ChemMatCARS, which is supported by the National Science Foundation/Department of Energy under grant number NSF/CHE-1346572. The XANES and ASAXS work were performed at APS Sector 12, BESSRC. References J. Xie, F. Xu, D.L. Wood, III, K.L. More, T.A. Zawodzinski, and W.H. Smith, Electrochim. Acta, 55, 7404 (2010).C.-M. Lai, J.-C. Lin, F.-P. Ting, S.-D. Chyou, and K.-L. Hsueh, Int. J. Hydrog. Energy, 33, 4132 (2008).D. Lee and S. Hwang, Int. J. Hydrog. Energy, 33, 2790 (2008).K. Bolwin, E. Gülzow, D. Bevers, and W. Schnurnberger, Solid State Ionics, 77, 324 (1995).P. Gode, F. Jaouen, G. Lindbergh, A. Lundblad, and G. Sundholm, Electrochim. Acta, 48, 4175 (2003).S.J. Lee, S. Mukerjee, Y.W. Rho, Y.T Kho, T.H. Lee, Electrochim. Acta, 43, 3693 (1998).E. Antolini, L. Giorgi, A. Pozio, and E. Passalacqua, J. Power Sources, 77(2), 136 (1999).G. Sasikumar, J.W. Ihm, H. Ryu, Electrochim. Acta, 50(2-3) 601 (2004).Y. Liu, M.W. Murphy, D.R. Baker, W. Gu, C. Ji, and J. Jorne, J. Electrochem. Soc., 156(8), B970 (2009).F. Xu, H.Y. Zhang, J. Ilavsky, L. Stanciu, D. Ho, M.J. Justice, H. I. Petrache, and J.A. Xie, Langmuir, 26(24), 19199 (2010).B. Han, C.E. Carlton, A. Kongkanand, R.S. Kukreja, B.R. Theobald, L. Gan, R. O'Malley, P. Strasser, F.T. Wagner, and Y. Shao-Horn, Energy Environ. Sci., DOI: 10.1039/c4ee02144d.J.V. Yang and M.Perry, “BOL Performance of Advanced Pt-Ni Alloy Catalyst in PEM Fuel Cells”, 226th Electrochemical Society Meeting, Cancun, Mexico, Oct. 29-Nov. 3, 2014.

Effects of thin-film accelerated carbonation on steel slag leaching

This paper discusses the effects of accelerated carbonation on the leaching behaviour of two types of stainless steel slags (electric arc furnace and argon oxygen decarburisation slag). The release of major elements and toxic metals both at the natural pH and at varying pH conditions was addressed. Geochemical modelling of the eluates was used to theoretically describe leaching and derive information about mineralogical changes induced by carbonation. Among the investigated elements, Ca and Si were most appreciably affected by carbonation. A very clear effect of carbonation on leaching was observed for silicate phases; geochemical modelling indicated that the Ca/Si ratio of Ca-controlling minerals shifted from ∼1 for the untreated slag to 0.5–0.67 for the carbonated samples, thus showing that the carbonation process left some residual Ca-depleted silicate phases while the extracted Ca precipitated in the form of carbonate minerals. For toxic metals the changes in leaching induced by carbonation appeared to be mainly related to the resulting pH changes, which were as high as ∼2 orders of magnitude upon carbonation. Depending on the specific shape of the respective solubility curves, the extent of leaching of toxic metals from the slag was differently affected by carbonation.

Leaching kinetics of lanthanum in sulfuric acid from rare earth element (REE) slag

REE slag was obtained from reduction smelting of magnetite ore containing monazite. Using the REE slag, the leaching kinetics of lanthanum from the slag was studied under the conditions of slurry density of 1.5g slag per L of 0.3M H2SO4, agitation of 750rpm and temperature ranging from 30 to 80°C. After five hours of leaching, the lanthanum was completely leached from the slag. Leaching kinetics can be described by the shrinking core model for spherical particles of unchanging size and leaching was found to occur in two stages. The initial leaching rate was controlled by chemical reaction. Using the Arrhenius equation, the apparent activation energy of the chemical reaction rate controlling step was determined to be 10.0kJmol−1. As leaching of the lanthanum increased, the reaction rate was controlled by diffusion through an ash layer. The apparent activation energy of the second stage was determined to be 24.8kJmol−1. The leaching rate and extent of leaching of lanthanum from the slag increased with an increase in leaching temperature.

Leaching of mercury from soils at extremely contaminated historical roasting sites (Idrija area, Slovenia)

Mercury (Hg) solubility and reactivity in soils at two extremely contaminated ancient small scale cinnabar roasting sites in the surroundings of the Hg mining area of Idrija (Slovenia) were determined in order to assess the mobility of Hg in the aqueous phase and to evaluate the extent of leaching of Hg into Idrijca River and further downstream. Water leaching experiments were performed on soil and SOM (soil organic matter) samples from historical roasting sites Pšenk and Frbejžene trate. The determined concentrations of leachable Hg in soil samples from the studied areas range from 16 to exceptionally high concentration of 18,000μg/kg, representing 0.0002 to 1.1% of total Hg in these samples, while in SOM samples leachable Hg concentrations range between 13.3 and 6000μg/kg, which corresponds to 0.0017–0.074% of total Hg determined in SOM. The soluble Hg concentrations in investigated soil profiles range from 183 to 18,000μg/kg (0.038–1.7% of total Hg). On the average, more than 90% of soluble Hg occurs in a non-reactive complex bound form, suggesting the preferential binding of Hg to humic matter. Soluble Hg in studied soil profiles generally increases with depth. The obtained results show that Hg is effectively transported to deeper soil layers, mainly as soluble organic complexes. It is estimated that there is still about 10kg of soluble Hg stored in soils of the investigated roasting sites, which is continuously leached to surface waters and deeper into the soil.

Leaching of vanadium(V) from the mixture after potassium metavanadate synthesis based on KCl and spent vanadium catalyst

Abstract The results of the leaching of vanadium(V) from the mixture after potassium metavanadate synthesis from KCl and spent vanadium catalyst in the presence of steam were presented. Spent vanadium catalyst was obtained from the waste storage of a chemical plant producing sulfuric acid(VI) by the contact method. The reaction mixture was leached using different solutions: 1 M Na2CO3, 20% CO(NH2)2, 15% NaOH, 15% KOH, 2 M H2SO4. The effect of time and temperature was studied. The results showed that for reaction mixture leached for 4 h at 303 K in the presence of 15% sodium hydroxide solution at a liquid:solid ratio of 10:1, the extent of leaching of vanadium(V) was 95.43%.

Preparation and Characterization of Acid and Alkaline Treated Kaolin Clay

Kaolin was refluxed with HNO3, HCl, H3PO4, CH3COOH, and NaOH of 3M concentration at 110 °C for 4 hours followed by calcination at 550 °C for 2 hours. The physico-chemical characteristics of resulted leached kaolinite clay were studied by XRF, XRD, FTIR, TGA, DTA, SEM and N2 adsorption techniques. XRF and FTIR study indicate that acid treatment under reflux conditions lead to the removal of the octahedral Al3+ cations along with other impurities. XRD of acid treated clay shows that, the peak intensity was found to decrease. Extent of leaching of Al3+ ions is different for different acid/base treatment. The acid treatment increased the Si/Al ratio, surface area and pore volume of the clay. Thus, the treated kaolin clay can be used as promising adsorbent and catalyst supports. © 2013 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Recovery of vanadium, potassium and iron from a spent vanadium catalyst by oxalic acid solution leaching, precipitation and ion exchange processes

A spent vanadium catalyst was leached in an oxalic acid solution to recover vanadium, potassium and iron. The effects of time, temperature, acid concentration, phase ratio and catalyst particle size were studied. The results showed that for a 180–250μm catalyst leached for 4h at 323K in the presence of 2% oxalic acid solution at a liquid:solid ratio of 25:1, the extent of leaching of V, K and Fe was about 91%, 92% and 63%, respectively. Studies on the separation of vanadium from iron were conducted. The effect of pH on the concentration of the investigated compounds in post-leaching solution was presented. Additionally, separation of vanadium from such a solution was investigated by the ion exchange method. Three types of polymer strongly acidic ion exchangers were used. The ion exchange tests indicate that only potassium and iron were loaded from the post-leaching solution. On this basis a flowsheet for the proposed process of a complex utilization of spent vanadium catalyst is presented.

Aluminum Leaching from Calcined Coal Waste Using Hydrochloric Acid Solution

Coal waste is the largest industrial solid waste generated from coal preparation plants during the processing and cleaning of coal for electric power generation. Aluminum oxide (Al2O3, 16–36%), silicon dioxide (SiO2, 45–58%), and carbon (4–25%) account for more than 90% of the coal waste. In this paper the results of aluminum leaching from calcined coal waste are reported. Techniques including XRD, SEM, and FTIR were used to characterize the coal waste before and after calcination. Three additives were evaluated during the calcination process to improve the extraction of Al2O3 by hydrochloric acid dissolution. The results from the leaching experiments show that coal waste is activated after calcination at a temperature between 650°C and 750°C. With addition of sodium fluoride effective aluminum dissolution of 90% was achieved under certain conditions. The extent of leaching was found to be 20% higher than that achieved without sodium fluoride addition.

A preliminary study on leachability of chromium from a contaminated site

In the present article, chromite ore processing residue (COPR) and soil samples were collected from a chromium contaminated site in Tamil Nadu State, India. Around 155.02 and 28.01 mg g−1 of Cr(VI) was present in COPR and soil samples, respectively. Leachability studies were carried out to assess the leachability of Cr(VI) and Cr(III) from COPR and soil samples following the toxicity characteristic leaching procedure (TCLP) test protocol using (i) acetic acid and (ii) water as leaching medium. Cr(VI) had leached out in both the mediums, whereas Cr(III) leached only in acetic acid as leaching medium since Cr(III) is insoluble at pH &gt; 6. TCLP test results are requisite to assess the extent of leaching of chromium from the contaminated soil or COPR and are a helpful tool for implementation of remediation measures to avoid further contamination. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 1096–1100, 2013

A kinetic study on hydrochloric acid leaching of nickel from Ni–Al2O3 spent catalyst

Hydrochloric acid leaching of nickel from spent Ni–Al2O3 catalyst (12.7% Ni, 39.2% Al and 0.68% Fe) has been investigated at a range of conditions by varying particle size (50–180μm), acid concentration (0.025–2M), pulp density (0.2–0.4%, w/v) and temperature (293–353K). Nickel was selectively leached from the catalyst, irrespective of the different conditions. Under the most suitable conditions (1M HCl, 323K, stirring at 500rpm, 50–71μm particle size), the extent of leaching of Ni and Al after 2h was 99.9% and 1%, respectively. The XRD pattern of the spent catalyst corresponded to crystalline α-Al2O3 along with elemental Ni. The peak due to elemental Ni was absent in the residue sample produced at the optimum leaching conditions, confirming the complete dissolution of Ni from the spent catalyst. The leaching results were well fitted with the shrinking core model with apparent activation energy of 17kJ/mol in the temperature range of 293–353K indicating a diffusion controlled reaction.