Typical Bentonite Research Articles

Quantitative characterization and comparsion of bentonite microstructure by small angle X-ray scattering and nitrogen adsorption

Quantitative characterization of the pore structure of typical bentonite in China is beneficial to nuclear waste treatment and sludge solidification modeling. A new small angle X-ray scattering (SAXS) method and conventional method low-temperature nitrogen adsorption and desorption (LTNAD) were combined to investigate the pore structure of four Chinese typical bentonites. The pore size and pore size distribution measured by the novel SAXS and conventional LTNAD methods were compared. The results suggested that Gaomiaozi bentonite exhibited Porod positive deviation effect. The GMZ01 had better sortability than GMZ07, and the pore size was concentrated. The average pore size of GMZ01 and GMZ07 calculated by the maximum entropy method were close. LTNAD experiment indicated that the specific surface area (SSA) of bentonite depended on the pore volume of mesopores and micropores and the types of exchangeable cations between layers. The SSA was positively correlated with the adsorption capacity. SAXS revealed that pore size estimated by maximum entropy method was larger than that evaluated by Guinier method. The log-normal distribution method in SAXS model was more suitable for characterizing small pores than maximum entropy method. Compared with maximum entropy method, The LTNAD method was more compatible with the SAXS lognormal distribution method. Compared with LTNAD, the SAXS has a wider detection range. These findings fill a gap in SAXS research on Gaomiaozi bentonite (GMZ01, GMZ07, CaGMZ).

Genetic analysis of bentonite—Permian Wangpo shale in Liangshan, Hanzhong, South Shaanxi Province

Fine pyroclastic materials form bentonites through subsidence, hydrolysis, and argillation in alkaline marine environments, which can further transform to K‐bentonite. Bentonites or K‐bentonites are quite popular with geologists because their formation often reflects geologic events. However, studies mainly focus on K‐bentonite, and research on ordinary bentonites in China is almost nonexistent. Recent research shows that the Wangpo shale consists of ordinary bentonites. Through thorough field investigations, indoor experimentation and analysis, and comparison of petrologic and geochemical characteristics of the Wangpo shale with K‐bentonites, this paper explores the nature and genesis of source rocks and provides a basis for the study of ordinary bentonites. The petrological study shows that the Wangpo shale is a montmorillonite vitric tuff, which is mainly composed of montmorillonite and small amounts of quartz, opal, and heulandite. These indicate that it is a typical bentonite. In addition, the rock contains an abundance of fossils reflecting a coastal–shallow sea depositional environment. We chose the elements with stable chemical characteristics for obtaining source rock characteristics, and the results showed that the Wangpo shale has a genetic relationship with neutral alkaline magma. As a boundary between the Upper Permian and the Middle Permian, the Wangpo shale has an internal connection with eruption of the Emeishan basalt in Southwest China. In combination with previous work, it can be inferred that studying the volcanic activity represented by the Wangpo shale plays an important role in studying Emeishan large igneous provinces and the end‐Guadalupian mass extinction.

Study on Physicochemical Properties and Application Prospect of Several Typical Bentonite

Four kinds of bentonite samples were studied in this paper. Mainly discussing the particle size distribution, mineral composition and physicochemical properties of bentonite, the aim was to provide a useful reference for the efficient development and utilization of bentonite resources. The results indicated that NM-bent., HB-bent. and EZ-bent. were Ca (Mg)-bentonite while XZJ-bent. was Na-bentonite. The physicochemical properties of bentonite mainly depended on interlayer cations. Many properties indexes of Na-bentonite were better than that of Ca (Mg)-bentonite. Some properties indexes showed a poor reproducibility when tested by standard methods. The natural Na-bentonite has excellent properties and extensive application prospects while Ca (Mg)-bentonite needed for further processing to meet the demand of the application field.

10.2478/s11814-009-0162-2

The physico-chemical behavior of Iranian typical bentonite was characterized during the activation process by sulfuric acid. The main variations were studied by evaluating specific surface area, chemical and mineralogical composition, thermal gravimetric curves, Fourier transform infrared spectrometry pattern, and morphology of starting and activated samples. The effects of acid concentration, particle size distribution, activation temperature and time on specific surface area were discussed. It was found that the above parameters have significant role in the activation process. The optimum condition was also obtained for the activation of typical bentonite.

Analysis of bentonite specific surface area by kinetic model during activation process in presence of sodium carbonate

In this paper activation of a typical bentonite in the presence of sodium carbonate was studied by a modified kinetic model. Activation process was carried out at different concentrations of sodium carbonate, ranging 3.0–4.5 wt.%. The effects of sodium carbonate concentration, particle size distribution of natural bentonite, activation time and temperature on specific surface area were investigated. It was found that the activation rate significantly depends on sodium carbonate concentration and it was maximized in presence of 4.5 wt.% of alkali solution. Also, the specific surface of bentonite was greatly affected by particle size distribution of starting raw material. The kinetic calculation results indicated that the concentration of alkali solution and particle size of starting bentonite negligibly change the activation energy. The mathematical calculations showed that there is an optimum activation time to achieve the maximum specific surface area in each condition. The validity of proposed model to estimate the optimum activation time was substantiated by comparing computational results with experimental data.

Physico-chemical variation in bentonite by sulfuric acid activation

The physico-chemical behavior of Iranian typical bentonite was characterized during the activation process by sulfuric acid. The main variations were studied by evaluating specific surface area, chemical and mineralogical composition, thermal gravimetric curves, Fourier transform infrared spectrometry pattern, and morphology of starting and activated samples. The effects of acid concentration, particle size distribution, activation temperature and time on specific surface area were discussed. It was found that the above parameters have significant role in the activation process. The optimum condition was also obtained for the activation of typical bentonite.

Kinetic model for the isothermal activation of bentonite by sulfuric acid

The activation mechanism of typical bentonite powder with sulfuric acid was studied from variations in their surface area during the reaction. The surface area of activated samples at different activation temperatures and times were measured by methylene blue adsorption to quantify the effect of acid. The influence of activation time was investigated by isothermal experiments, performed at different temperatures. The specific surface area–time data were analyzed by using a modified kinetic model and the values of kinetic parameters were calculated. Also, the influence of acid concentrations on kinetic parameters was evaluated. The validity of proposed model to describe the bentonite activation kinetic was substantiated by computation of reaction time to achieve maximum value of specific surface area in other temperatures.

Modelling the FEBEX THM experiment using a state surface approach

Abstract Buffer materials being considered as engineered barriers in nuclear fuel waste (NFW) disposal systems possess a pronounced nonlinear behaviour in the unsaturated state. In order to simulate such non-linear responses,the authors adopted an incrementally nonlinear poro-elastic approach where the coefficients of the governing equations are assumed to be functions of suction and the void ratio. These functions are in turn developed from a state-surface equation obtained from suction-controlled oedometric tests. In this paper we show the derivation of the governing equations of the poro-elastic model. A finite element computer code, FRACON, was developed by the authors to numerically solve the above equations. We first use the code to simulate laboratory tests to characterize the swelling properties of a typical bentonite. That same bentonite was used in the FEBEX in-situ heater experiment, conducted at the Grimsel site, Switzerland. The FRACON code was also used to perform blind predictions of the FEBEX heater experiment. It is shown that the model correctly predicts drying of the bentonite near the heaters and re-saturation near the rock interface. The evolution of temperature and the heater thermal output were also reasonably well predicted by the model. The trends in the total stresses developed in the bentonite were correctly predicted; the absolute values however were underestimated probably due to the omission of pore pressure build-up in the rock mass.

Squeeze-film rheometry of non-uniform mudcakes

The standard lubrication analysis for a squeeze flow of a Bingham fluid is reviewed, and then extended to the case of a fluid in which the yield stress varies as a function of depth. These analyses are used to obtain the yield stress τ 0 from squeeze-film measurements made on uniform mudcakes formed by filtration of a typical bentonite mud. Over the solids volume fraction range 0.09 < φ < 0.6 we find τ 0 (bar) = 3.9φ 1.9 for this mud. If the cake remains under an applied differential pressure p ∞ for a sufficiently long time, the volume fraction φ eventually reaches a limiting equilibrium value, and the yield stress may then be expressed in terms of p ∞ as ln (φ 0 (Pa)) = 0.72 ln ( p ∞ (bar)) + 9.3. Non-uniform mudcakes are also investigated, both directly, by the squeeze-film technique, and also indirectly, by combining measured filtercake concentration profiles with results for τ 0(φ) obtained from uniform cakes. There is some agreement between the two sets of results, though further work would have to be done to make the direct measurement technique useful. Once deformation ceases, the relaxation of the stress within the cake is monitored; the relaxation time increases as the bentonite concentration within the cake increases.