Magnetite Sorption Capacity for Strontium as a Function of pH

2008 ◽  
Vol 1107 ◽  
Author(s):  
Joan de Pablo ◽  
Miquel Rovira ◽  
Javier Giménez ◽  
Ignasi Casas ◽  
Frederic Clarens
Keyword(s):  
Spent Nuclear Fuel ◽  
Surface Complexation ◽  
Retardation Factor ◽  
Alkaline Ph ◽  
Layer Model ◽  
Surface Complexation Model ◽  
Ph Values ◽  
End Products ◽  
Diffuse Layer Model ◽  
Ph Range

AbstractThe ubiquity of iron oxide minerals and their ability to retain metals on their surface can represent an important retardation factor to the mobility of radionuclides. In a deep repository for the spent nuclear fuel, the intrusion of the groundwater might produce the anoxic corrosion of the iron, with magnetite as one of the end-products. In this study, as expected considering the strontium speciation in solution, strontium is sorbed onto magnetite at alkaline pH values while at acidic pH the sorption is negligible. Magnetite is able to sorb more than the 50% of the strontium from a 8·10-6 mol·dm-3 solution at the pH range representative of most groundwater (7-9). A surface complexation model has been applied to the experimental data, allowing to explain the results using the Diffuse Layer Model (DLM) and considering the formation of the inner-sphere complex >FeOHSr2+ (with a calculated logK=2.7±0.3). Considering these data, the magnetite capacity to retain strontium and other radionuclides is discussed

Sorption of Molybdenum(VI) on Synthetic Magnetite

2006 ◽  
Vol 932 ◽  
Author(s):  
Miquel Rovira ◽  
Joan de Pablo ◽  
I. Ignasi Casas ◽  
Javier Giménez ◽  
Frederic Clarens ◽  
...  
Keyword(s):  
Experimental Data ◽  
Surface Complexation ◽  
Layer Model ◽  
Liquid Ratio ◽  
Surface Complexation Model ◽  
Synthetic Magnetite ◽  
Diffuse Layer Model ◽  
Monodentate Complex ◽  
Solid Liquid ◽  
Influence Of Ph

ABSTRACTIn this study we experimentally investigated the interaction of Mo(VI) with magnetite, which is a corrosion product of steel. The work was conducted with commercial magnetite, and we studied the influence of pH, pe and solid/liquid ratio on Mo sorption. A Surface Complexation Model (SCM) has been applied tothe experimental data, allowing to explain the results using the Diffuse Layer Model (DLM) and by considering the formation of the monodentate complex: >FeOMo(OH)5. At pH 2, experimental data were satisfactorily fitted to a a Langmuir isotherm.

Ultrafast and highly capture of U(VI) by hierarchical mesoporous carbon

2020 ◽  
Vol 108 (9) ◽  
pp. 717-726 ◽  
Author(s):  
Han Guo ◽  
Ying Li ◽  
Huihui Wang ◽  
Ning Zhang ◽  
Alhadi Ishag ◽  
...  
Keyword(s):  
Mesoporous Carbon ◽  
Surface Complexation ◽  
Batch Adsorption ◽  
Layer Model ◽  
Environmental Cleanup ◽  
Triple Layer ◽  
High Efficient ◽  
Diffuse Layer Model ◽  
Capture Capacity ◽  
Inner Sphere Complexes

AbstractIn this study, the hierarchical mesoporous carbon (HMC) was synthesized by the hydrothermal method. The batch adsorption experiments showed that HMC exhibited the ultrafast equilibrium fate (80 % U(VI) capture efficiency within 5 min), high UO22+ capture capacity (210 mg/g, pH = 4.5) and well recyclability. The investigations of XPS techniques indicated the oxygen-containing functional groups were responsible for high efficient UO22+ adsorption. The pH-dependent adsorption was simulated by three surface complexation modellings, revealing that UO22+ adsorption on HMC was excellently fitted by triple layer model using two inner-sphere complexes (i. e. SOUO2+ and SOUO2(CO3)35− species) compared to constant capacitance model and diffuse layer model. These findings are crucial for expanding actual applications of HMC towards the removal of radionuclides under environmental cleanup.

Note: Influence of pH on the Extraction Yield and Functional Properties of Macadamia (Macadamia Integrofolia) Protein Isolates

2004 ◽  
Vol 10 (4) ◽  
pp. 263-267 ◽  
Author(s):  
P. S. Bora ◽  
D. Ribeiro
Keyword(s):  
Functional Properties ◽  
Extraction Yield ◽  
Emulsifying Properties ◽  
Alkaline Ph ◽  
Protein Isolates ◽  
Ph Values ◽  
Macadamia Nut ◽  
Isoelectric Ph ◽  
Ph Range ◽  
Influence Of Ph

Three protein isolates from de-fatted macadamia nut kernel flour were prepared by extraction at acidic (pH2.0), neutral (pH7.2 with 0.2M phosphate buffer containing 0.5MNaCl) and alkaline (pH12.0) conditions. Extraction at pH2.0 solubilised nearly 52.0% of the proteins present in defatted macadamia flour, while extraction with buffer (pH7.2) and alkaline pH (12.0) solubilised about 83.0% of proteins. The yield of isoelectrically precipitated protein from acidic extract (pH2.0, isolate A) was about 65.2% and from neutral (isolate B) and alkaline extracts (isolate C) was slightly over 83.0% which accounted for 33.7, 69.1 and 69.4% of the proteins present in defatted flour. The protein content of the isolates was 80.1, 92.1 and 92.0% in A, B and C isolates respectively. The functional properties of these isolates were significantly different. Isolate A presented better solubility at pH below isoelectric pH, isolate C at pH above isoelectric pH and isolate B intermediate solubility at the pH range studied. Isolate B showed best water and oil absorption capacities followed by isolate C and least by isolate A. For each isolate, the emulsifying properties were also significantly different at different pH values.

Electrokinetics of Carbonate/Brine Interface in Low-Salinity Waterflooding: Effect of Brine Salinity, Composition, Rock Type, and pH on ?-Potential and a Surface-Complexation Model

SPE Journal ◽  
2016 ◽  
Vol 22 (01) ◽  
pp. 53-68 ◽  
Author(s):  
Hassan Mahani ◽  
Arsene Levy Keya ◽  
Steffen Berg ◽  
Ramez Nasralla
Keyword(s):  
Surface Charge ◽  
Carbonate Rock ◽  
Rock Type ◽  
Surface Complexation ◽  
Surface Complexation Model ◽  
Ζ Potential ◽  
Low Salinity ◽  
Ph Values ◽  
Different Types ◽  
Brine Salinity

Summary Laboratory studies have shown that wettability of carbonate rock can be altered to a less-oil-wetting state by manipulation of brine composition and reduction of salinity. Our recent study (Mahani et al. 2015b) suggests that surface-charge alteration is likely to be the driving mechanism of the low-salinity effect in carbonates. Various studies have already established the sensitivity of carbonate-surface charge to brine salinity, pH value, and potential-determining ions in brines. However, in the majority of the studies, single-salt brines or model-carbonate rocks have been used and it is fairly unclear how natural rock reacts to reservoir-relevant brine as well as successive brine dilution; whether different types of carbonate-reservoir rocks exhibit different electrokinetic properties; and how the surface-charge behavior obtained at different brine salinities and pH values can be explained. This paper presents a comparative study aimed at gaining more insight into the electrokinetics of different types of carbonate rock. This is achieved by ζ-potential measurements on Iceland spar calcite and three reservoir-related rocks—Middle Eastern limestone, Stevns Klint chalk, and Silurian dolomite outcrop—over a wide range of salinity, brine composition, and pH values. With a view to arriving at a more-tractable approach, a surface-complexation model (SCM) implemented in PHREEQC software (Parkhurst and Appelo 2013) is developed to relate our understanding of the surface reactions to measured ζ-potentials. It was found that regardless of the rock type, the trends of ζ-potentials with salinity and pH are quite similar. For all cases, the surface charge was found to be positive in high-salinity formation water (FW), which should favor oil-wetting. The ζ-potential successively decreased toward negative values when the brine salinity was lowered to seawater (SW) level and diluted SW. At all salinities, the ζ-potential showed a strong dependence on pH, with positive slope that remained so even with excessive dilution. The sensitivity of the ζ-potential to pH change was often higher at lower salinities. The existing SCMs cannot predict the observed increase of ζ-potential with pH; therefore, a new model is proposed to capture this feature. According to modeling results, formation of surface species, particularly >CaSO4− and to a lower extent >CO3Ca+ and >CO3Mg+, strongly influence the total surface charge. Increasing the pH turns the negatively charged moiety >CaSO4− into both negatively charged >CaCO3− and neutral > CaOH entities. (Note that throughout this paper, the symbol > indicates surface complexes.) This substitution reduces the negative charge of the surface. The surface concentration of >CO3Ca+ and >CO3Mg+ moieties changes little with change of pH. Nevertheless, besides similarities in ζ-potential trends, there exist notable differences in terms of magnitude and the isoelectric point (IEP), even between carbonates that are mainly composed of calcite. Among all the samples, chalk particles exhibited the most negative surface charges, followed by limestone. In contrast to this, dolomite particles showed the most positive ζ-potential, followed by calcite crystal. Overall, chalk particles exhibited the highest surface reactivity to pH and salinity change, whereas dolomite particles showed the lowest.

scholarly journals The action of trialkyltin compounds on mitochondrial respiration. The effect of pH

1974 ◽  
Vol 138 (3) ◽  
pp. 349-357 ◽  
Author(s):  
Alan P. Dawson ◽  
Michael J. Selwyn
Keyword(s):  
Maximum Rate ◽  
Ph Dependence ◽  
Acid Value ◽  
Alkaline Ph ◽  
Free Medium ◽  
Succinate Oxidation ◽  
Ph Values ◽  
Acid Ph ◽  
Internal Ph ◽  
Ph Range

1. Inhibition of 2,4-dinitrophenol-stimulated respiration by trialkyltins is dependent on the presence of Cl− in the assay medium and is only apparent at acid pH values. It appears to be a result of the Cl−–OH− exchange mediated by trialkyltins. 2. In a KCl medium at alkaline pH values, the maximum rate of respiration produced by uncouplers is further increased by the presence of trialkyltins. 3. The inhibition of uncoupled succinate oxidation at acid pH values is not reversed by increasing the external substrate concentration, suggesting that depletion of intramitochondrial succinate is not an important factor in the inhibition. 4. It is suggested that the probable explanation for these observations is that in the presence of Cl− trialkyltins alter the internal pH to a more acid value and this directly affects the activity of one or more steps in succinate oxidation. 5. The oligomycin-like action of trialkyltins in a Cl−-free medium shows considerable pH-dependence over the pH range 6.6–7.6 in the presence of 10mm-phosphate, but very much less pH-dependence in the presence of 1mm-phosphate. 6. The binding of triethyltin to mitochondria shows a pK at pH6.3 and does not change greatly over the pH range 6.6–7.6. 7. It is suggested that the pH-dependence of the oligomycin-like action described by Coleman & Palmer (1971) is the result of the pH-dependence of the formation of a hydrophilic complex between trialkyltins and Pi.

Actinide Sorption onto Silica in the Presence of Humic Substances: Proposal of Retentionmechanisms

1991 ◽  
Vol 257 ◽  
Author(s):  
N. Labonne ◽  
V. Moulin ◽  
D. Stammose
Keyword(s):  
Ionic Strength ◽  
Humic Substances ◽  
Humic Acids ◽  
Surface Complexation ◽  
Complexing Agents ◽  
Complexation Constants ◽  
Surface Complexation Model ◽  
Physico Chemical ◽  
Ph Range ◽  
Geological Formations

ABSTRACTThe experimental investigation and modelling of radionuclides sorption processes is an essential part of safety analyses of an underground repository of radioactive wastes in geological formations. Physico—chemical phenomena at oxide/solution interfaces have been studied in the case of the system constituted by amorphous silica and americium (III) in the presence of humic substances as organic complexing agents. The retention behaviour of Am(III) onto silica appears dependent on pH, ionic strength and in particular humic concentration. At a ionic strength of 0.1 M, the presence of low concentration of humic acids (1 mg/l) enhances the Am(III) retention in the pH range 3-5.5, whereas at higher pH, its uptake is largely decreased. At lower ionic strength (0.001 M), Am(III) retention on silica is highly lowered, in the pH range 3-7 in the presence of humic acids. Reversibility experiments show the desorption of americium in the absence of humic substances, and also the desorption of the humics on the silica with respect of the pH. The surface complexation model has been applied to our results in the different systems and apparent surface complexation constants have been determined.

The Malachite Green Biodegradation in Bioreactors on Various pH Domains

2019 ◽  
Vol 70 (8) ◽  
pp. 2996-2999
Author(s):  
Viorel Gheorghe ◽  
Catalina Gabriela Gheorghe ◽  
Andreea Bondarev ◽  
Vasile Matei ◽  
Mihaela Bombos
Keyword(s):  
Malachite Green ◽  
Contact Time ◽  
Dominant Species ◽  
Wastewater Treatment Plants ◽  
Organic Substances ◽  
Biological Degradation ◽  
Growth Promoters ◽  
Ph Values ◽  
Biological Sludge ◽  
Ph Range

In the experimental study was studied the malachite green colorant biodegradation in biological sludge with biological activity. The biodegradability tests were carried out in laboratory bioreactors, on aqueous solutions of green malachite contacted with microorganisms in which the dominant species is Paramecium caudatum, in a pH range between 8 and 12, temperatures in the ranges 25-350C, using pH neutralizing substances and biomass growth promoters. The colorant initial concentrations and those obtained after biological degradation depending on the contact time, at certain pH values, were established through UV-Vis spectrometry. The studies have shown the measure of possible biological degradation of some organic substances with extended uses, with largely aromatic structure, resistance to biodegradation of microorganisms, commonly used in wastewater treatment plants.

Comparative Two-Dimensional Gel Electrophoresis of Trypanosoma cruzi Mammalian-Stage Forms in an Alkaline pH Range

2015 ◽  
Vol 22 (12) ◽  
pp. 1066-1075 ◽  
Author(s):  
Adriana Magalhães ◽  
Rayner Queiroz ◽  
Izabela Bastos ◽  
Jaime Santana ◽  
Marcelo Sousa ◽  
...  
Keyword(s):  
Trypanosoma Cruzi ◽  
Gel Electrophoresis ◽  
Two Dimensional ◽  
Alkaline Ph ◽  
Two Dimensional Gel Electrophoresis ◽  
Ph Range

Comparison of a Non Electrostatic Surface Complexation Model and Surface Phase Theories for Prediction of Future Sorption Properties.

2004 ◽  
Vol 824 ◽  
Author(s):  
Allan T. Emrén ◽  
Anna-Maria Jacobsson
Keyword(s):  
Aqueous Solution ◽  
Chemical Potential ◽  
Surface Complexation ◽  
Sorption Properties ◽  
Phase Method ◽  
Detailed Knowledge ◽  
Surface Phase ◽  
Surface Complexation Model ◽  
Advantages And Disadvantages ◽  
The One

AbstractIn performance assessments, sorption of radionuclides dissolved in groundwater is mostly handled by the use of fixed Kd values. It has been well known that this approach is unsatisfying. Only during the last few years, however, tools have become available that make it possible to predict the actual Kd value in an aqueous solution that differs from the one in which the sorption properties were measured.One such approach is surface complexation (SC) that gives a detailed knowledge of the sorption properties. In SC, one tries to find what kinds of sorbed species are available on the surface and the thermodynamics for their formation from species in the bulk aqueous solution. Recently, a different approach, surface phase method (SP), has been developed. In SP, a thin layer including the surface is treated as a separate phase. In the bulk aqueous solution, the surface phase is treated as a virtual component, and from the chemical potential of this component, the sorption properties can be found.In the paper, we compare advantages and disadvantages of the two kinds of models. We also investigate the differences in predicted sorption properties of a number of radionuclides (Co, Np, Th and U). Furthermore, we discuss under which circumstances, one approach or the other is preferable.

scholarly journals Effect of alkaline pH on photosynthetic water oxidation and the association of extrinsic proteins with Photosystem Two

1989 ◽  
Vol 258 (2) ◽  
pp. 357-362 ◽  
Author(s):  
D J Chapman ◽  
J De Felice ◽  
K Davis ◽  
J Barber
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Binding Sites ◽  
Partial Recovery ◽  
Alkaline Ph ◽  
Ph Values ◽  
Extrinsic Proteins ◽  
Reversible Phase ◽  
Photosynthetic Water Oxidation ◽  
Optimal Ph

Incubation of a membrane preparation enriched in Photosystem Two (PSII) at alkaline pH inhibited the water-splitting reactions in two distinct steps. Up to pH 8.5 the inhibition was reversible, whereas at higher alkalinities it was irreversible. It was shown that the reversible phase correlated with loss and rebinding of the 23 kDa extrinsic polypeptide. However, after mild alkaline treatments a partial recovery was possible without the binding of the 23 kDa polypeptide when the assay was at the optimal pH of 6.5 and in a medium containing excess Cl-. The irreversible phase was found to be closely linked with the removal of the 33 kDa extrinsic protein of PSII. Treatments with pH values above 8.5 not only caused the 33 kDa protein to be displaced from the PSII-enriched membranes, but also resulted in an irreversible modification of the binding sites such that the extrinsic 33 kDa protein could not reassociate with PSII when the pH was lowered to 6.5. The results obtained with these more extreme alkaline pH treatments support the notion that the 23 kDa protein cannot bind to PSII unless the 33 kDa protein is already bound. The differential effect of pH on the removal of the 23 kDa and 33 kDa proteins contrasted with the data of Kuwabara & Murata [(1983) Plant Cell Physiol. 24, 741-747], but this discrepancy was accounted for by the use of glycerol in the incubation media.

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