Long-term behaviour of the Wyoming bentonite MX-80 in high saline solutions

The mineralogical and chemical changes of bentonites were studied under the boundary conditions of a repository in salt formations by means of a literature review, a natural analogue study, and laboratory experiments. In the natural analogue study the expandability of clays from deep boreholes in the East Slovakian Basin was found to be dependent not only on depth and temperature but also on the salinity of the pore waters. In laboratory experiments the fraction <2 μm of the MX-80 bentonite was reacted with two high saline solutions, a NaCl- and a MgCl₂-rich brine at 25, 90 and 150 °C, at three different pH levels, 1, 6.5, and 13. In all experiments, montmorillonite remained at all temperatures and all pH the predominant mineral phase over 580 days, with full ethylene–glycol expandability to 17 Å. However, significant changes could be detected by looking at parameters like morphology, crystallinity, particle height, particle surface, interlayer charge, and chemistry of octahedral layers. The experimental results of this study suggest that under repository conditions a certain percentage the MX-80 montmorillonites will be transformed in kaolinites and pyrophyllites rather than in illites. The investigated reactions not only caused mineralogical changes but also considerable changes of the water uptake capacity. The MX-80 montmorillonites in salt solutions lost about half of their water uptake capacity compared with pure water. The reduction was found to be dependent on the reaction time and temperature. Smectites in salt solutions with cement lost their water uptake capacity almost completely.     

Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H₂SO₄ (concentrations: 0·5 mol dm^?3 and 2·5 mol dm^?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (X_m) and the apparent equilibrium constants (K_a) of the samples; X_m and K_a values range respectively for 4·11 mg g^?1 and 1·90 dm³ g^?1 for the sample acid-treated with 2·5 mol dm^?3 H₂SO₄ [(B)-A(2·5)] up to 16·50 mg g^?1 and 30·67 dm³ g^?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g^?1 and 0·07 dm³ g^?1, also for B-A(2·5), up to 4·54 mg g^?1 and 0·45 dm³ g^?1 [B-N-200], for the adsorption process of zinc. X_m and K_a values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.     

Influence of interlayer cations on the water sorption and swelling–shrinkage of MX80 bentonite

The potential of water sorption and swelling–shrinkage in the expansive clays is practically defined by the nature of interlayer cations. The purpose of this paper is to estimate the effects of the cation saturation (Mg⁺, Ca⁺, Li⁺, Na⁺, and K⁺) on the swelling–shrinkage behaviour of the MX80 bentonite.The MX80 bentonite (a “commercial clay”) was treated with concentrated solutions (1 N) of sodium, calcium, magnesium, potassium, and lithium chlorides. This treatment was made three times with constant agitation for 1 h. Then, the clay was washed three times with distilled water. The scanning transmission electron microscopy (STEM) and inductively coupled plasma atomic emission microscopy (ICP-AES) analyses were used to verify the efficiency of the cation saturation.Finally, two techniques were employed to estimate the effect of the cation saturation on the swelling–shrinkage behaviour of the bentonite: the first one uses an isothermal system of water adsorption, where the water activity is controlled by a supersaturated salt solution. In the second, environmental scanning electron microscopy (ESEM), coupled with a digital image analysis (DIA) program, was used to estimate the swelling–shrinkage potential at different water activities. The swelling–shrinkage isotherms were always estimated on isolated aggregates.The isotherms of water adsorption and swelling–shrinkage of the bentonite MX80 show that the amount of adsorbed water and the swelling–shrinkage potential depend directly on the interlayer cation. For example, the sodium bentonite presents an excellent capacity to swell while the lithium bentonite does not swell significantly at the aggregate scale. In addition, other textural properties may be modified by the cation saturation, such as the specific surface, the particle size, porosity, etc.     

Adsorption of Pb(II) from aqueous solution to MX-80 bentonite: Effect of pH, ionic strength, foreign ions and temperature

The adsorption of Pb(II) from aqueous solution to MX-80 bentonite was studied using batch technique under ambient conditions. Removal percent (%) and distribution coefficient (K_d) were determined as a function of shaking time, pH, ionic strength and temperature. The results showed that the adsorption behavior of Pb(II) on bentonite was strongly dependent on pH and ionic strength. The presence of complementary cations depressed the adsorption of Pb(II) on bentonite in the order of Li⁺ ≈ Na⁺ > K⁺ at pH 2–5. The adsorption isotherms were simulated by the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) models very well. The thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) for the adsorption of Pb(II) were determined at three different temperatures of 291 K, 308 K and 328 K. The adsorption reaction was exothermic and the process of adsorption was favored at low temperature. The results suggest that bentonite is suitable as a sorbent material for the recovery and adsorption of Pb(II) from aqueous solution.     

Evaluation of geotechnical properties of bentonite from Lieskovec deposit, Slovakia

Chemical and mineralogical composition and geotechnical properties of Ca²⁺-bentonite samples from Lieskovec deposit, Slovakia, are reported. The main mineral is Fe-montmorillonite. Its content as obtained by the methylene blue adsorption method is relatively low, 28 to 49%; however, it is the dominant variable affecting geotechnical parameters of this bentonite. Rather low liquid limit values of 64–80% and water adsorption (Enslin test) data in a broad range of 123–606% were obtained. Permeability coefficients of the order of 10^− 11 m s^− 1 suggest the possible suitability of this bentonite for geosynthetic clay liners and other civil engineering applications.     

Change of water redox potential, pH and rH in contact with magnesium enriched kaolinite–bentonite ceramics

It was established that the addition of Mg to the mixtures of kaolinite and bentonite can provide clay compositions which, after sintering at high temperatures, produce very porous ceramics with microcrystalline and amorphous regions of stoichiometric and nonstoichiometric oxides and highly developed metallized surfaces (in this case mainly with magnesium surplus). The ceramics surface exhibited high electrochemical and chemical activity when placed in contact with water. This leads to pH, E_ROX and rH changes of the treated waters, which can be controlled (magnesium aluminium silicate ceramics reduces or oxidises waters). In fact, with careful planning and appropriate selection of active components of the aluminium silicate ceramics it is possible to build in tailor made electric capacity, electrochemical activity and consequently program their effects on the structure and the content of the waters it interacts with.     

Polymer-water interactions. Origin of perturbed infrared intensities of water in polymeric systems

We explore the possible reasons for the huge infrared intensity perturbations of water molecules sorbed onto a variety of polymer surfaces. We demonstrate that strong polymer-water interactions, not always obvious from qualitative approaches to examination of the water vibrational spectra, are probably responsible for such effects. The deviations from Beer’s law for water adsorption is semi-quantitatively correlated with the level of water uptake (i.e. water activity in the polymer). This clearly demonstrates the dependence on water-polymer proximity and intermolecular interaction strength, to the extent that donor-acceptor charge transfer interactions may well control this interesting, and potentially useful, phenomenon.     

Comparisons of clear coating degradation in NaCl solution and pure water

Organic coating's degradation behavior is essential to its corrosion protective function and has been widely studied. A main function of anti-corrosive organic coatings is acting as barriers to water uptake and ion diffusion. It is of great fundamental importance to study the influence of different working fluids on the degradation of organic coatings. In this study, a 3.5 wt% NaCl solution and the pure water are adopted as the working fluids based on their distinct properties. The commercially available polyurethane and epoxy based clear coatings are chosen for evaluation. The coating degradation is monitored by electrochemical impedance spectroscopy (EIS) measurement. Equivalent circuit models are employed to interpret the EIS spectra. The time evolution of coating resistance, capacitance, and water volume fraction of the coating is analyzed. Besides the fact that the coating's barrier property is deteriorated by the percolating of both NaCl solution and pure water, we also discover that pure water leads to faster coating degradation, demonstrated by a more substantial decrease in coating resistance, a more prominent increase in coating capacitance, and a greater saturated water volume fraction.     

300MW空冷机组除盐水补水率偏高的分析及治理

本文了介绍300MW空冷机组除盐水补水率超过设计值的分析方法,通过分析采取相应的措施,达到了预期的效果,供同类机组参考。     

Later-stage spinodal decomposition in polymer solution under high pressure—analyses of qm and Im

Later-stage spinodal decomposition (SD) of polymer solutions (polypropylene/trichlorofluoromethane) induced by pressure-jump was examined in situ as a function of pressure P by using time-resolved light scattering method with the cell designed for high pressure and high temperature. The time-evolution of the magnitude of scattering vector q_m(t,P) at maximum scattered intensity and the maximum scattered intensity I_m(t,P) were analyzed in order to characterize the coarsening processes of the later-stage SD, where t refers to time after the onset of pressure-jump. The changes in q_m(t,P) and I_m(t,P) with t at different P's were found to fall onto the respective master curves on the reduced plots, indicating that the scaling postulate is valid not only for the coarsening behaviors at different temperatures but for those at different P's.     

FTIR and electrochemical observation of water content reduction in a thin Nafion film induced by an impregnation of metal complex cations

A thin Nafion^® ion exchange membrane was coated on a graphite electrode, and then impregnated by a metal complex couple of Os(bpy)₃^2+/3+, which served as a typical system to investigate the water content change induced by ion exchange. Cyclic voltammetry and FTIR reflection-adsorption spectroscopic methods were employed to characterize the complex loading, electrochemical behavior of the impregnates inside the film and the water content change. A direct observation of the water content reduction induced by the cation impregnation in the Nafion^® film was achieved. A monotonic relationship between the water reduction percentage and the Os(bpy)₃^2+/3+ loading was also obtained, that is, the heavier the complex loading, the more the water content will be reduced. The FTIR spectroscopic results suggested that the structure of the Nafion^® film could also be changed with water content reduction.     

Determination of water uptake and diffusion of Cl ion in epoxy primer on aluminum alloys in NaCl solution by electrochemical impedance spectroscopy

The electrochemical impedance spectroscopy (EIS) of epoxy-coated aluminum alloy LY12 has been investigated during exposure to 3.5% NaCl solution. Using the continuous simulation of EIS by expanded general electrical model, the time-dependent impedance model of the alloy/coating/solution system was deduced. The results shown that the composite electrode displayed a barrier behavior before water and oxygen penetrated to alloy base. After water and oxygen reached the base, the impedance associated with corrosion of alloy base changed with the immersion time as following: (i) active corrosion period at the beginning (double-layer capacitance, C_dl, in parallel to the charge transfer resistance of electrochemical corrosion R_ct), (ii) impeding of the diffusion of corrosion production at the intermediate period as a result of the presence of coated film (a constant phase element Z_diff was additionally in series with R_ct), and (iii) appearance of the characteristic impedance related to Cl⁻ ion-participating reaction with alloy base at the later stage. From the linear part of ln C_c–t^0.5 curve in the early immersion stage, the apparent diffusion coefficient of water was obtained. The diffusion coefficient of water and Cl⁻ ion through the coating was also calculated by the required time for diffusion of permeation species through the coating to the metal interface obtained from the simulation of EIS data by which the occurrence of characteristic impedance element(s) corresponding to special species arrival can be determined.