Using MgO activated slag and calcium bentonite slurry to produce a novel vertical barrier material: Performances and mechanisms

The pH-responsive polymers, such as polyacrylamide (PAM), show distinct conformational states according to the pH of their environmental groundwater. Therefore, the interactions between clay–polymer and polymer–water molecules, which determine the yield stress of bentonite–polymer composites, can be affected by the pH of groundwater. This study aims to evaluate the effect of pH variation on the yield stress of calcium bentonite treated with PAM. The yield stresses (τy) of untreated and PAM treated clays were measured with varying volume fractions of solid (VF = 10–23%) and under varying pH conditions (pH = 7.6–9.6). In addition, the zeta potential was measured for both untreated and treated clays to figure out the change in the surface charge of the mineral surface due to PAM treatment. The results of this study demonstrate that τy for treated clay is higher than that for untreated clay at a given VF, because van der Walls attraction dominates electrostatic repulsion in the case of treated clay. Due to the change in conformational states of PAM and the consequent change in surface charge that comes with varying pH, the pH-dependent change in τy of treated clay is significantly different from that of untreated clay.

Download Full-text

Sodium hexametaphosphate (SHMP)-amended calcium bentonite for slurry trench cutoff walls: workability and microstructure characteristics

Canadian Geotechnical Journal ◽

10.1139/cgj-2017-0291 ◽

2018 ◽

Vol 55 (4) ◽

pp. 528-537 ◽

Cited By ~ 20

Author(s):

Yu-Ling Yang ◽

Krishna R. Reddy ◽

Yan-Jun Du ◽

Ri-Dong Fan

Keyword(s):

Zeta Potential ◽

Tap Water ◽

Sodium Hexametaphosphate ◽

Microstructural Characteristics ◽

Bentonite Slurry ◽

Cutoff Walls ◽

Calcium Cations ◽

Slurry Trench ◽

Filtrate Loss ◽

Calcium Bentonite

This study aims to investigate workability and microstructural characteristics of sodium hexametaphosphate (SHMP)-treated calcium bentonite (Ca-bentonite) as a potential material for soil–bentonite slurry trench cutoff walls. First, a series of Marsh viscosity, filtrate loss, density, and pH experiments are performed on bentonite – tap water slurries containing Ca-bentonite amended with 0%–8% SHMP dosages. Subsequently, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and zeta potential tests are conducted to explore microstructural characteristics that control the mechanisms of SHMP treatment. The results indicate that the workability of the slurry is significantly improved with SHMP addition. The SEM, XRD, and zeta potential analyses show that SHMP-amended Ca-bentonite possesses a more dispersed structure and higher negative zeta potential relative to the unamended Ca-bentonite. The mechanisms of SHMP amendment are identified to be exchange of bivalent calcium cations in Ca-bentonite by monovalent sodium cations in the SHMP, sorption of the SHMP anions that give the clay system a steric stabilization and increased negative surface charge density, and sequestration of the bivalent calcium cations on the Ca-bentonite. Overall, the SHMP treatment is effective in making the Ca-bentonite slurry amenable for use in the soil–bentonite slurry trench wall construction.

Download Full-text

The Influence of Barrier and Applied Voltage Parameters on the Impulse Surface Discharge Characteristics

Elektrichestvo ◽

10.24160/0013-5380-2020-11-17-27 ◽

2020 ◽

Vol 11 (11) ◽

pp. 17-27

Author(s):

Vadim V. VOEVODIN ◽

◽

Marina V. SOKOLOVA ◽

Viktor R. SOLOV’YEV ◽

Nikolay Yu. LYSOV ◽

...

Keyword(s):

Applied Voltage ◽

Voltage Pulse ◽

Discharge Zone ◽

Surface Discharge ◽

Initial Surface ◽

Barrier Material ◽

Dielectric Barrier ◽

Discharge Ignition ◽

Study Results ◽

Wide Range

The results from an experimental study of impulse surface discharge occurring in an electrode system containing a dielectric plate are presented. On one of its sides, the plate had a corona-producing electrode made of 50 mm thick copper foil grounded through a current shunt for measuring the discharge current. On its other side, the plate had a high-voltage electrode, to which the voltage from a pulse generator was applied. The article presents the results from measurements of the initial voltage and the sizes of the surface discharge area in air when applying single voltage pulses with different pulse front steepness in the range 0,1–3,4 kV/ms and amplitude in the range 7–15 kV. The measurements were carried out for different dielectric barrier materials with the e values from 2 to 35. The dielectric barrier thickness was 0,9–1,8 mm. The study results have shown that the initial surface discharge ignition voltage depends essentially on the voltage pulse parameters, whereas the barrier characteristics have a weaker effect on this voltage. It has been determined that the discharge has different discharge zone length and different structure depending on the dielectric barrier properties and applied voltage parameters. The streamer zone sizes decrease with increasing the barrier material e value at the same voltage pulse steepness and increase with increasing the steepness for each barrier material. The data obtained for a wide range of external conditions can be used in numerical modeling of discharge.

Download Full-text

Competitive adsorption of organic solvents using modified and unmodified calcium bentonite clay mineral

10.31221/osf.io/w9dj6 ◽

2019 ◽

Author(s):

Chem Int

Keyword(s):

Adsorption Isotherm ◽

Adsorption Capacity ◽

Organic Solvents ◽

Competitive Adsorption ◽

Correlation Factor ◽

Isotherm Model ◽

Isotherm Models ◽

High Concentration ◽

Dual Purpose ◽

Calcium Bentonite

Dodecyltrimethylammonium bromide (DTAB)–modified and unmodified calcium bentonite were both used for the competitive adsorption of aromatics (xylene, ethylbenzene and toluene) and petroleum products (gasoline, dual purpose kerosene and diesel) from their aqueous solution. Infrared spectroscopy (IR) and expansion tests (adsorption capacity and Foster swelling) measurement were performed in order to evaluate the performance of the adsorbents. The Foster swelling index and adsorption capacity of the DTAB modified calcium bentonite in the organic solvents follow the trend: xylene > ethylbenzene > toluene > gasoline > dual purpose kerosene (DPK) > diesel > water. However, the adsorption capacity of the adsorbent in diesel outweighed the adsorption capacity in DPK at high concentration of DTAB indicating that diesel has higher affinity for high DTAB concentration than DPK. The percentage removal of the solvent is directly proportional to the concentration of DTAB used in modifying the bentonite as well as the contact time between the adsorbent and the solvent, hence modified calcium bentonite adsorbed a higher percentage of organic solvents than the unmodified calcium bentonite. The adsorption characteristics of both adsorbents improved remarkably after proper agitation of the organic solvents, the unmodified calcium bentonite however adsorbed more water than the modified bentonite. Data obtained from adsorption isotherm models confirms that Freundlich adsorption isotherm model was favored more than Langmuir adsorption isotherm model with the correlation factor (R2) of the former tending more towards unity. The adsorption of ethylbenzene using DTAB modified and unmodified calcium bentonites follow a pseudo second order kinetics mechanism, suggesting that the rate determining step of adsorption involves both the adsorbent and the organic solvent.

Download Full-text

The Effects of Nano Structure on the Properties Cementitious Materials as a Barrier Material

Concrete Journal ◽

10.3151/coj.56.5_403 ◽

2018 ◽

Vol 56 (5) ◽

pp. 403-408

Author(s):

D. Minato

Keyword(s):

Cementitious Materials ◽

Barrier Material ◽

Nano Structure

Download Full-text

Approximate analysis of the containment of contaminated sites prior to remediation

Water Science & Technology ◽

10.2166/wst.2000.0332 ◽

2000 ◽

Vol 42 (1-2) ◽

pp. 319-324 ◽

Cited By ~ 1

Author(s):

H. Rubin ◽

A. Rabideau

Keyword(s):

Steady State ◽

Peclet Number ◽

Dimensionless Parameter ◽

Contaminated Sites ◽

Unsteady State ◽

Péclet Number ◽

Vertical Barrier ◽

Time Period ◽

Barrier Performance ◽

Vertical Barriers

This study presents an approximate analytical model, which can be useful for the prediction and requirement of vertical barrier efficiencies. A previous study by the authors has indicated that a single dimensionless parameter determines the performance of a vertical barrier. This parameter is termed the barrier Peclet number. The evaluation of barrier performance concerns operation under steady state conditions, as well as estimates of unsteady state conditions and calculation of the time period requires arriving at steady state conditions. This study refers to high values of the barrier Peclet number. The modeling approach refers to the development of several types of boundary layers. Comparisons were made between simulation results of the present study and some analytical and numerical results. These comparisons indicate that the models developed in this study could be useful in the design and prediction of the performance of vertical barriers operating under conditions of high values of the barrier Peclet number.

Download Full-text