Temat: activation mechanism

Skocz do pozycji: 1.

Tytuł:: Study of flotation behavior and mechanism of cervantite activation by copper ions
Autorzy:: Wang, J.
Wang, Y.
Fu, K.
Xu, L.
Wang, Z.
Sun, H.
Xiao, J.
Tematy:: flotation
cervantite
copper ions
activation mechanism; Pokaż więcej
Wydawca:: Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Powiązania:: https://bibliotekanauki.pl/articles/110228.pdf Link otwiera się w nowym oknie
Opis:: Copper-ion activation plays a highly important role in cervantite (Sb2O4) flotation. Without metal-ion activation, cervantite cannot be floated by sodium oleate. In this study, flotation tests were conducted to study the effect of Cu2+ on the flotation behaviours of cervantite and quartz (SiO2) as the main gangue mineral. Metal-ion adsorption capacities, zeta potentials, solution chemistry and X-ray photoelectron spectra were analyzed to study the adsorption behavior and mechanism of copper ions and sodium oleate interaction with the minerals surfaces. The results demonstrate that under weakly acidic conditions, cervantite can be flotated and separated from quartz by the addition of copper ions. The reason is that copper ions can be selectively adsorbed on the cervantite surface under weakly acidic conditions, thereby promoting the adsorption of sodium oleate onto the cervantite surface by chemical adsorption. Conversely, copper ions are weakly adsorbed on quartz surfaces below pH 6.1, and sodium oleate cannot be adsorbed on quartz surfaces by chemical adsorption. The hydroxy copper species are integral to the selective activation of cervantite over quartz.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Activating flotation of chalcopyrite using CuSO4 and H2O2 from the cyanide tailings
Autorzy:: Ai, G.
Yan, H.
Qiu, T.
Liu, C.
Tematy:: cyanide tailings
chalcopyrite
CuSO4
H2O2
activation mechanism; Pokaż więcej
Wydawca:: Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Powiązania:: https://bibliotekanauki.pl/articles/109562.pdf Link otwiera się w nowym oknie
Opis:: The effects of CuSO4 and H2O2 on the flotation behavior of cyanide chalcopyrite were investigated by flotation tests, microcalorimetry and X-ray photoelectron spectroscopy (XPS). The underlying activation mechanism was studied in the perspective of micro-thermodynamics and surface properties. The flotation results indicated that cyanide chalcopyrite was strongly inhibited by sodium cyanide, with the maximum flotation recovery of 22.5% only. CuSO4 and H2O2 significantly improved the flotation of cyanide chalcopyrite, and the flotation recovery was increased to 92.28% and 84.35%, respectively. The micro-thermodynamics results indicated that the adsorption heat of butyl xanthate on cyanide chalcopyrite surface increased after the addition of CuSO4 and H2O2, as well as the reaction order. CuSO4 and H2O2 can significantly improve the adsorption of butyl xanthate on the surface of cyanide chalcopyrite by decreasing the apparent activation energy by 80.11% and 66.54%, respectively. XPS analysis indicated that the CuCN was generated on the surface of cyanide chalcopyrite, leading to the loss of sulfur and inhibiting the adsorption of collectors. As a result, the flotation of cyanide chalcopyrite was depressed. It is considered that, CuSO4 and H2O2 can improve the flotation of cyanide chalcopyrite by eleminating CuCN from its surface and increasing the concentration of S by 57.02% and 37.48%, respectively.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Kinetic Studies of Pt(IV) Chloride Complex Ions Reduction Reaction Using Potassium Formate
Autorzy:: Wojnicki, M.
Żabiński, P.
Csapó, Edit
Tematy:: platinum
recovery
recycling
activation energy
reaction mechanism; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/351194.pdf Link otwiera się w nowym oknie
Opis:: In this paper, the kinetics of the platinum(IV) chloride complex ions reduction reaction was studied. It was shown that the mechanism exhibits autocatalytic character. The presence of metallic platinum in the system significantly increases the reaction rate. The influence of the initial concentration of precursor, reductant, ionic strength, initial concentration of the chloride ions as well as the temperature on the process rate was investigated. The activation energy was determined and is equal to 93.57 kJ/mol. Moreover, the obtained metallic phase was analyzed, and it was observed that it has a micrometric size.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Activation of quartz flotation by Cu2+, Ni2+ in the sodium ethylxanthogenate (EX) system
Autorzy:: Liu, Yang
Tong, Xiong
Xie, Rui-Qi
Xie, Xian
Song, Qiang
Fan, Pei-Qiang
Tematy:: quartz
flotation
ions activation
sodium ethylxanthogenate
adsorption mechanism; Pokaż więcej
Wydawca:: Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Powiązania:: https://bibliotekanauki.pl/articles/24085981.pdf Link otwiera się w nowym oknie
Opis:: During the flotation of metal sulfide minerals, due to the interference of unavoidable ions, the quartz also partially floats in some cases. The studies on the mechanism of quartz being activated and floating up are still insufficient. In this study, the influence of the Cu2+ and Ni2+ unavoidable ions on the floatation of quartz was studied by micro-flotation experiments, adsorption detection, zeta potential measurement, solution composition calculation, infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses, and atomic force microscopy (AFM) observation. This provides a theoretical reference for further understanding the mechanism of sodium ethylxanthogenate and quartz surface, as well as the development of a new quartz depressant. The results of flotation showed that after activation by Cu2+ (1×10-4 mol/dm3) and Ni2+ (5×10-5 mol/dm3), the quartz was captured by sodium ethylxanthogenate (EX: 1.4×10-4 mol/dm3) under alkaline conditions (pH=10), while the best recoveries were obtained as 80% and 43%, respectively. The results of adsorption and zeta potential measurements showed that the precipitation rate of Cu2+ was greater than that of Ni2+ under alkaline conditions. Additionally, both Cu2+ and Ni2+ electrostatically adsorbed on the quartz surface and changed the zeta potential of quartz. The solution composition calculation further showed that Cu(OH)+, Cu(OH)2(s), and Ni(OH)+, Ni(OH)2(s) were the main components in the solution under alkaline conditions. The FT-IR and XPS analyses and AFM observations demonstrated that Cu and Ni species adsorbed on O atoms on the quartz surface, providing active sites for EX adsorption, and EX combines with Cu and Ni species on the quartz surface to generate -O-Cu-EX and -O-Ni-EX complexes. Finally, the quartz floated up due to the formation of hydrophobic products and firm adsorption.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Thermal behavior and kinetic decomposition of sweet potato starch by non-isothermal procedures
Autorzy:: Liu, Ying
Yang, Liutao
Zhang, Yingzhe
Tematy:: starch
kinetic analysis
thermal degradation
activation energy
mechanism; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/240460.pdf Link otwiera się w nowym oknie
Opis:: In this study, X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry (DSC) method were used to analyze the main characteristics of sweet potato starch, and to analyze the thermal degradation process of sweet potato starch. Specifically, X-ray diffraction to study its structure, thermogravimetric analysis to study the thermal degradation kinetics, and differential scanning calorimetry to study the thermogram of sweet potato starch. The thermal decomposition kinetics of sweet potato starch was examined within different heating rates in nitrogen atmosphere. Different models of kinetic analysis were used to calculate the activation energies using thermogravimetric data of the thermal degradation process. Activation energies obtained from Kissinger, Flynn-WallOzawa, and Šatava-Šesták models were 173.85, 174.87 and 174.34 kJ/mol, respectively. The values of activation energy indicated that the thermal degradation of the sweet potato starch was a single reaction mechanism or the combination of multi-reaction mechanisms. The differential scanning calorimetry analysis show that two decomposition stages were presented: the first at a low temperature involves the decomposition of long chain; and the second at a high temperature represents the scission of glucose ring. This information was helpful to design the processing process of many natural polymers. Thermogravimetric Fourier transform-infrared (TG–FTIR) analysis showed that the main pyrolysis products included water, methane, carbon dioxide, ammonia, and others.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Autorzy:: Macyk, Wojciech
Franke, Alicja
Stochel, Grażyna
Opis:: The activation of small molecules has a significant impact in biology, medicine, industrial catalysis and environmental protection. Two molecules, especially, oxygen and nitric oxide have attracted considerable interest for many years. Reactive oxygen species (ROS) and reactive nitric oxide species (RNOS) may be generated thermally or photochemically in systems consisting of metal compounds. In homogeneous systems metal species serve as a coordination and/or electron (eventually energy) transfer centre. In heterogeneous systems small molecules can undergo adsorption followed by electron or energy transfer processes with semiconductor participation. This review presents recent trends in studies on the metal assisted processes in which activated forms of NO or O_{2} are formed and play a key biological and medical role.
Dostawca treści:: Repozytorium Uniwersytetu Jagiellońskiego

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Skocz do pozycji: 7.

Tytuł:: Uptake of copper ion using protonated dry alginate beads from dilute aqueous solutions
Autorzy:: Aracena, Alvaro
Álvarez, César
Jerez, Oscar
Guajardo, Nadia
Tematy:: removal mechanism
copper ions
alginate beads
pseudo-first order kinetics model
activation energy; Pokaż więcej
Wydawca:: Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Powiązania:: https://bibliotekanauki.pl/articles/109473.pdf Link otwiera się w nowym oknie
Opis:: This research aimed to identify the copper ion removal mechanism when using protonated dry alginate beads. This mechanism was explained through ion exchange between Cu ions and the protons from the functional groups of the alginate beads. Copper removal increased with stirring velocity, reaching values of 97.5 mg g-1 (97.5×10-3 kg/kg of PDAB) of dry alginate at 200 rev min-1, at a solution pH of 6.0 and a run time of 360 min. For the lowest level of copper concentrations, at 10 mg dm-3 (10×10-6 kg dm-3), full removal was attained. The removal kinetics was represented by a pseudo- first order model. A value of 0.0131 min-1 was found for the velocity constant. Under equilibrium conditions, the experiment data was fit to the Langmuir adsorption model, and the highest removal values were 270.3, 222.2 (222.2×10-3 kg/kg of PDAB) and 49 mg g-1 (49×10-3 kg/kg of PDAB) for pH values of 5.0, 3.5 and 2.5, respectively. These are higher than most sorbents used in the literature for copper removal. Increased temperature leads to higher Cu removal. The activation energy was calculated at 9.3 kJ mol-1 for the temperature range of 283 to 343K. Observations using SEM and composition measurements of the alginate cross-section taken by EDS showed a uniform distribution of the copper concentration through the structure of the alginate beads, independent of the solution pH, contact time and temperature.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Temperature- and pressure-dependent stopped-flow kinetic studies of jack bean urease : implications for the catalytic mechanism
Autorzy:: van Eldik, Rudi
Krajewska, Barbara
Brindell, Małgorzata
Opis:: Urease, a Ni-containing metalloenzyme, fea- tures an activity that has profound medical and agricultural implications. The mechanism of this activity, however, has not been as yet thoroughly established. Accordingly, to improve its understanding, in this study we analyzed the steady-state kinetic parameters of the enzyme (jack bean), K M and k cat , measured at different temperatures and pres- sures. Such an analysis is useful as it provides information on the molecular nature of the intermediate and transition states of the catalytic reaction. We measured the parame- ters in a noninteracting buffer using a stopped-flow tech- nique in the temperature range 15–35 ° C and in the pressure range 5–132 MPa, the pressure-dependent mea- surements being the first of their kind performed for urease. While temperature enhanced the activity of urease, pres- sure inhibited the enzyme; the inhibition was biphasic. Analyzing K M provided the characteristics of the formation of the ES complex, and analyzing k cat , the characteristics of the activation of ES. From the temperature-dependent measurements, the energetic parameters were derived, i.e. thermodynamic D H o and D S o for ES formation, and kinetic D H = and D S = for ES activation, while from the pressure- dependent measurements, the binding D V b and activation D V 6 ¼ cat volumes were determined. The thermodynamic and activation parameters obtained are discussed in terms of the current proposals for the mechanism of the urease reaction, and they are found to support the mechanism proposed by Benini et al. ( Structure 7:205–216; 1999), in which the Ni–Ni bridging hydroxide—not the terminal hydroxide—is the nucleophile in the catalytic reaction.
Dostawca treści:: Repozytorium Uniwersytetu Jagiellońskiego

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Skocz do pozycji: 9.

Tytuł:: Struktura i reaktywność klasterów tlenkowych wybranych metali przejściowych osadzonych na nośnikach w reakcji katalitycznego usuwania antropogenicznego metanu z powietrza
Structure and reactivity of supported transition metal oxoclusters in catalytic lean methane combustion process
Autorzy:: Zapała, Piotr
Współwytwórcy:: Sojka, Zbigniew
Dostawca treści:: Repozytorium Uniwersytetu Jagiellońskiego

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