Slow Adsorption Stage Research Articles

Carbon Dioxide (CO₂) Adsorption Behaviour and Its Relationship with Nano-Structure in an Organic-Rich Shale: A Case Study of the Longmaxi Shale in Southeast Chongqing.

Carbon capture and storage (CCS) technologies in shale reservoirs have attracted increasing interest in recent years. To study the CO₂ adsorption behaviour in the Longmaxi shale, isothermal adsorption experiments, scanning electron microscopy (SEM) and other techniques were employed in this study. The results show that when the pressure is less than 7.37 MPa, the Langmuir model fits well with the experimental CO₂ adsorption data in the shale. In contrast, when the pressure is greater than 7.37 MPa, the D+R-K model fits better with the experimental data. From low pressure to high pressure (>20 MPa), the CO₂ adsorption isothermal curves can be divided into four stages: rapid adsorption stage, slow adsorption stage, linear decreasing stage and slightly decreasing stage. With increases in temperature, the CO₂ adsorption capacity decreases as expected. In addition, the effects of the Longmaxi shale nano-structure on the CO₂ adsorption behaviour were also investigated. It was found that organic matter has a greater influence than clay and quartz on the CO₂ adsorption behaviour. Based on the SEM observations, large numbers of nanoscale organic pores were found in the shale samples, and these nanoscale organic pores may control the CO₂ adsorption behaviour in organic-rich Longmaxi shale. With increasing total organic carbon (TOC) content, the CO₂ adsorption capacity increases linearly. In this study, the characteristics of the CO₂ adsorption in shale and its relationship with the shale nano-structure were studied, which may be helpful for understanding CCS technologies and their application in enhanced shale gas recovery.

Removal Behavior of Methylene Blue from Aqueous Solution by Tea Waste: Kinetics, Isotherms and Mechanism.

Tea waste (biosorbent) was characterized by BET, SEM, FTIR, XPS, solid state 13C-NMR and applied to remove methylene blue (MB) from aqueous solution. The effect of different factors on MB removal, kinetics, isotherms and potential mechanism was investigated. The results showed that tea waste contains multiple organic functional groups. The optimum solid-to-liquid ratio for MB adsorption was 4.0 g·L−1 and the initial pH of the MB solution did not need to be adjusted to a certain value. The pseudo-second-order model could well fit the adsorption kinetic process. The adsorption process could be divided into two stages: a fast adsorption stage and a slow adsorption stage. The adsorption isotherm could be well described by Langmuir and Temkin isotherm models. The maximum adsorption amount could reach 113.1461 mg·g−1 based on Langmuir isotherm fitting. Desorption and reusability experiments showed that MB adsorption onto tea waste could be stable and could not cause secondary pollution. The interaction mechanism between tea waste and MB involved electrostatic attraction, hydrogen bond, ion exchange, π-π binding. The organic functional groups of tea waste played an important role during the MB removal process. Therefore, tea waste has the potential to act as an adsorbent to remove MB from aqueous solution.

Adsorption behavior of condensed phosphate on aluminum hydroxide

Sodium pyrophosphate (pyro-P, Na 4P 2O 7), sodium tripolyphosphate (tripoly-P, Na 5P 3O 10), and sodium hexametaphosphate (meta- P, (NaPO 3) 6) were selected as the model compounds of condensed phosphate to investigate the adsorption behavior of condensed phosphate on aluminum hydroxide. The adsorption was found to be endothermic and divisible into two stages: (1) fast adsorption within 1 h; and (2) slow adsorption between 1 and 24 h. The modified Freundlich model simulated the fast adsorption stage well; the slow adsorption stage was described well by the first-order kinetics. The activation energies of pyro-P, tripoly-P, and meta-P adsorption on aluminum hydroxide were determined to be 20.2, 22.8 and 10.9 kJ/mol P adsorbed, respectively, in the fast adsorption stage and to be 66.3, 53.5 and 72.5 kJ/mol P adsorbed, respectively, in the slow adsorption stage. The adsorption increased the negative charge of the aluminum hydroxide surface. Transmission electron microscopy and energy dispersive X-ray analysis analyses provided evidence that the adsorption was not uniform on the surface and that the small crystals contributed more to the fast adsorption than the normal sites did. The results from X-ray fluorescence spectrometry and X-ray photoelectron spectroscopy tests also revealed the uneven adsorption of condensed phosphate as a function of the penetration depth. More condensed phosphates were adsorbed on the outer surface of aluminum hydroxide than in its inner parts.

Impedance study of adsorption of iodide ions at Bi(001) electrode from the aqueous solutions with constant ionic strength

Abstract The adsorption of iodide ions from the aqueous solution with constant ionic strength on the Bi(0 0 1) single crystal plane electrode has been studied by impedance spectroscopy. The complex impedance plane and Bode plots have been fitted and analyzed, using the non-linear regression analysis method. The probable limiting kinetic steps of the process were obtained and discussed. At moderate ac frequency (from 1 Hz to 10 Hz) the adsorption process of the I − ions is limited mainly by a slow adsorption stage. In the region of intensive increase of the differential capacitance in the capacitance vs. electrode potential curves ( E

Slow Adsorption Reaction between Arsenic Species and Goethite (α-FeOOH): Diffusion or Heterogeneous Surface Reaction Control

The slow stage of phosphate or arsenate adsorption on hydrous metal oxides frequently follows an Elovich equation. The equation can be derived by assuming kinetic control by either a diffusion process (either interparticle or intraparticle) or a heterogeneous surface reaction. The aim of this study is to determine whether the slow stage of arsenic adsorption on goethite is more consistent with diffusion or heterogeneous surface reaction control. Adsorption kinetics of arsenate and dimethylarsinate (DMA) on goethite (alpha-FeOOH) were investigated at different pH values and inert electrolyte concentrations. Their adsorption kinetics was described and compared using Elovich (Gamma vs ln time) plots. Desorption of arsenate and DMA was studied by increasing the pH of the suspension from pH 4.0 to pH 10.0 or 12.0. The effective particle sizes and zeta-potential of goethite were also determined. Effective particle size increased rapidly as the pH approached pH(IEP), both in the absence and presence of arsenic. Inert electrolyte concentrations and pH had no effect on the slow stage of arsenate adsorption on goethite, while the kinetics of DMA adsorption on goethite was influenced by both parameters. The slow stage of arsenate adsorption on goethite follows an Elovich equation. Since effective particle size changes with both pH and inert electrolyte concentrations, and effective particle size influences interparticle diffusion, the arsenate adsorption kinetics indicate that the slow adsorption step is not due to interparticle diffusion. DMA also has complex adsorption kinetics with a slow adsorption stage. DMA desorbed completely and rapidly when the pH was raised, in contrast to the slow adsorption kinetics, indicating that the slow adsorption step is not due to intraparticle diffusion. The slow adsorption is not the result of diffusion, but rather is due either to the heterogeneity of the surface site bonding energy or to other reactions controlling arsenic removal from solution.

Sorption Isotherms and Kinetics of Sediment Phosphorus in a Tropical Reservoir

The sorption of phosphorus, in the form of dissolved phosphate, on aquatic sediments collected from the tropical Kranji reservoir in Singapore was investigated under oxic and anoxic conditions. Kinetic experiments on sediment samples, collected from three monitoring stations, show that the sorption process consists of fast and slow adsorption stages followed by an equilibrium stage in which further adsorption or desorption may take place. The periods for each stage are in the scale of minutes, hours, and days, respectively. About 67.3–96.6% of the sorption is completed in the first stage under oxic and anoxic conditions. First-order kinetic constants are estimated to be from 4.60 to 12.26 h−1 for the fast adsorption stage, from 0.15 to 0.71 h−1 for the slow adsorption stage, and from 0.005 to 0.028 h−1 for the equilibrium stage. There were no significant differences observed between the sorption kinetic rates under oxic and anoxic conditions. The sorption isotherms of dissolved phosphate are found to be a...

The interaction of CO with Cu(100)-Fe surfaces

The interaction of CO with Cu(100)Fe surfaces containing 0–1.7 ML of Fe was studied with ellipsometry and Auger electron spectroscopy. Only reversible molecular adsorption was observed. Dissociation was not observed at temperatures up to 620 K and pressures up to 0.1 Pa. Apparently, fcc Fe(lOO) surfaces do not dissociate CO under these conditions. Depending on the iron coverage and the pretreatment of the surface, rapid and slow adsorption stages are observed. The rapid adsorption only occurs on surfaces that contain iron clusters or are completely covered with iron, whereas slow adsorption occurs only on surfaces containing bare copper. During the slow adsorption stage iron carbonyl-like species are formed, iron clusters are broken up into single iron atoms, or both processes occur together. Since the Cu(100)Fe surfaces are not thermo-stable, it was not possible to determine the heat of adsorption.

Water adsorption kinetics on Si(111) [sbnd]7 × 7: defect generation mechanism

Hydrogen accumulation on the Si(111) 7 × 7 surface due to water adsorption at room temperature was investigated by the flash desorption technique. The water pressure varied from 10 −11 to 10 −7 Torr. The sticking coefficient S turns out to decrease from S = 0.08 at a water pressure of 10 −9 Torr to 0.009 at 10 −7 Torr, i.e. S does depend not only on exposure but on the exposure time itself. We suppose that the chemisorbed water might form a 2D phase of the Si, OH, H and O species. Probably, the phase starts at steps (fast adsorption stage). The number of Si atoms in the new phase layer should not necessarily be equal to the effective Si surface density in the clean (111) 7 × 7 layer. Surface diffusion of Si atoms to or from the growing chemisorbed phase (slow adsorption stage) determines the dependence of the sticking coefficient not only on exposure but also on time itself.