Sodium bentonite

Clays used in foundries include hydrous alumina silicates, known as bentonites. Their properties provide cohesion and plasticity in the green state and also high strength when dried. There are three clays that are commonly used in foundries western bentonite [sodium bentonite, burnout point 1290°C (2350°F)], southern bentonite [calcium bentonite, burnout point 1065°C (1950°F)], and fire clay [kaolinite, burnout point 1425°C (2600°F)]. 

Due to a lack of naturally occurring soils at a site, it is sometimes necessary to blend imported clay minerals with on-site soils to achieve a suitable blended material. The most common blend is a combination of on-site sandy materials and imported sodium bentonite. 

Figure 26.8 shows the influence of sodium bentonite on the hydraulic conductivity of the silt/sand soil. The addition of only 4% or 5% sodium bentonite to this particular soil drops the hydraulic conductivity from 10 4 to 10 7 cm/s, a rather dramatic reduction. 

Calcium bentonite, as though more permeable than sodium bentonite, has also been used for soil blends. Approximately twice as much calcium bentonite typically is needed however, to achieve a hydraulic conductivity comparable with that of sodium bentonite. One problem with using sodium bentonite, however, is its vulnerability to attack by chemicals and waste leachates, a problem that will be discussed later. 

FIGURE 26.8 Influence of sodium bentonite on hydraulic conductivity. (Adapted from U.S. EPA, Requirements for Hazardous Waste Landfill Design, Construction, and Closure, EPA/625/4-89/022, U.S. Environmental Protection Agency, Cincinnati, OH, August 1989.)... 

Since calcium bentonite, typically, is 100-1000 times more permeable than sodium bentonite, the introduction of this permeating liquid could change hydraulic conductivity substantially. 

Sodium azide, 13 597 Sodium azidodithiocarbonate, 4 827 Sodium bentonite, 6 696 Sodium bentonites, 6 664—665 Sodium benzoate... 

Sodium bentonite with a cation exchange capacity (CEC) of 75 meq/100 g of clay, supplied by Commercial Minerals Ltd., Australia, was used as starting clay material, to prepare samples for SCD and surfactant treatments. Besides, sodium montmorillonite (Kunipia G), from Kunimine Industrial Company, Japan, was used as the starting clay for samples of pore opening modification. CEC of this clay is 100 meq/100 g of clay. 

Smiles, D.E., Kirby, J.M., and Little, I.P. (1996) Hydrodynamic dispersion and chemical reaction in sodium bentonite during filtration in the presence of calcium sulphate. Chem. Engng Sci. 51, 3647-3655... 

FIG. 13 The amount of NaCl needed to flocculate a clay (i.e., sodium bentonite suspension) as a function of the polyelectrolyte concentration (i.e., sodium car-boxymethylcellulose). The inserted figure is an enlargement of the initial addition of the polyelectrolyte. The lines are redrawn from An Introduction to Clay Colloid Chemistry by van Olphen [51]. 

The microenvironment of iron can well be studied by Mossbauer spectroscopy (Kuzmann et al. 1998). The Mossbauer spectra (taken at room temperature) of sodium-bentonite, treated with pure acetone and acetoneous FeCl3 solution, are shown in Figure 2.21 (upper figure). 

The Mossbauer spectrum of the original sodium-bentonite shows the isomer shift and quadrupole splitting values as usual for montmorillonite (Stevens et al. 1983). The values 6 and d, exhibit Fe3+, while the values of S2 andd2reveal Fe2+ microenvironments. These values are typical for Fe3+ and Fe2+ ions that are in the central positions of octahedrons of aluminosilicates (Kuzmann et al. 1998 Stevens and Stevens 1978). The relative areas (A s) show that the Fe3+ species is dominant as usual for Na-bentonites (Stevens et al. 1983). The spectra at the temperature of liquid nitrogen show no magnetically split components. 

The treatment of sodium-bentonite with acetone causes no significant changes in the Mossbauer spectrum. The Fe2+ Fe3+ ratio practically remains approximately the same. It is in agreement with the results of x-ray diffraction studies showing no change in the lattice parameters. 

FIGURE 2.21 57Fe Mossbauer spectra of sodium-bentonite (a), after treatment with acetone (b), and acetoneous solution of FeCl3 (c), taken at room temperature (upper). Mossbauer spectra of bentonite before (a) and after (b) treatment with FeCl3 in acetone, recorded at 74 K (lower). (Reprinted from Komlosi et al. 2007, with permission from the Clay Mineral Society.)... 

The influence of addition of sodium bentonite (a commonly used antisettling system) on the rheological behaviour of a pesticide suspension concentrate (250 g dm ) has been investigated. Steady state shear stress-shear rate curves were carried out to obtain the yield value and viscosity as a function of shear rate. The shear modulus was also measured using a pulse shearometer, and the residual viscosity was obtained in afew cases from creep measurements. The rheological parameters Tg (Bingham yield value),... 

French town (Montmorillon) where it was first discovered. In the USA, bentonite is principally mined in Wyoming - hence the term Wyoming clay . The type of bentonite, the source, and its purity influence its properties (Marchal et al. 1995). Bentonite is a complex hydrated aluminum silicate with exchangeable cationic components (Al, Fe, Mg) Si40io (0H)2 (Na+, Ca++). The most commonly used bentonite form in enology is the sodium bentonite. Sodium bentonite has enhanced protein binding capabilities over calcium bentonite. 

Wyoming Granular Bentonite, Bentonite 200, 325 (sodium bentonite)... 

Benna, M. et al.. Effect of pH on rheological properties of purified sodium bentonite suspensions, 7. Colloid Interf. Sci., 218, 442, 1999. 

Polarite. [Ant Colloid] Sodium bentonite suspending agent, geUant for household and industrial specialties. 

Voklay. [Am. ColloitQ Sodium bentonite suspending agent gellant binder for hous ld, cosinetics, pharrnaceuti-cal use, automotive prods., aerosols, paints, enamels. 

---