Vermiculite

About: Vermiculite is a research topic. Over the lifetime, 2320 publications have been published within this topic receiving 37142 citations.

Direct Measurement of the Electric Double-Layer Structure in Hydrated Lithium Vermiculite Clays by Neutron Diffraction

Abstract: Neutron diffraction, in conjunction with isotopic substitution of Li-6 for Li-7 and H-2 for H-1, has been used to determine the structure of the electric double-layer region close to hydrated lithium vermiculite clay platelets. We have measured the intensities of the first 27 (OOl) Bragg reflections for samples in which the clay platelet spacing is 14.67 Angstrom. Difference analysis has then allowed us to establish the interlayer counterion and water distributions. We find that the lithium counterions are located midway between the clay platelets and form octahedral hydration complexes with six water molecules. The behavior of lithium is therefore rather different from that of the larger alkali-metal ions; sodium, potassium, and cesium. These ions prefer to bind directly to vermiculite clay surfaces, rather than fully solvate. Since only lithium-substituted vermiculites will swell macroscopically when soaked in water, we conclude that interlayer cations must detach themselves from the clay surfaces if the particles are to expand colloidally.

The specific sorption of cobalt and zinc by layer silicates

Abstract: The sorption of Co and Zn by layer silicates was studied in dilute mineral suspensions containing, in most cases, about 10 –6 M Co or Zn Electrostatic adsorption was eliminated by the presence of 01 N CaCl 2 Co and Zn were determined by a radioisotopic technique Detailed studies on montmorillonite and to a lesser extent vermiculite, muscovite and biotite revealed the presence of at least two forms of specifically sorbed Co, one of which was exchangeable by certain ions such as Cu, Ni, Zn, Fe, Mn or more Co and the other, occurring in much smaller amounts, was not exchangeable by these cations The latter form is considered to result from lattice penetration; the former is associated with surface groups These forms may be separated quantitatively by several desorption procedures including successive extractions with dilute acetic acid The total amount and relative proportion of these forms of sorbed Co and Zn depend on the pH of the system, time of reaction, mineral species used, and amount of Co or Zn added Equilibrium is not readily attained but tends to approach a slow steady state after several days Isotherms indicate a variation in bonding energy with surface coverage The sorption of Co and Zn from dilute solutions by any mineral is related to its stability These studies, considered in conjunction with published data, suggest that a common mechanism may be involved in the specific sorption of many heavy metal cations by many minerals

Weathering sequences of clay minerals in soils along a serpentinitic toposequence

Abstract: There has been limited research on clay mineral transformation in serpentinitic soils under humid tropical conditions. In this study, four soil pedons were selected along a toposequence from the summit (Entisol), shoulder (Vertisol), backslope (Alfisol) to footslope (Ultisol) positions to explore the contributions and the significance of landscape and weathering status of serpentinitic rock with regard to clay mineral transformations in eastern Taiwan. Experimental results indicated that the large amount of dithionite-citrate-bicarbonate-extractable Fe (Fed) and clay in the subsurface horizon were mainly caused by the strong leaching potential from intensive rainfall and weathering of the fine-grained parent rocks. The clay mineralogy reflected the clear weathering trend of the soils along the toposequence: (1) the soils on the summit and shoulder contained smectite and serpentine, which are predominant in the young soils derived from serpentinitic rocks; and (2) vermiculite gradually increased in the relatively old soils on backslope and footslope. The mineralogical transformations observed along the toposequence indicated that chlorite and serpentine, initially present in the Entisol on the summit, weather into smectite and interstratified chlorite-vermiculite in the intermediate soil on the shoulder under strong leaching and oxidizing conditions. Furthermore, vermiculite formed as the major weathering product of chlorite and smectite in the soil developed on the backslope. In addition to vermiculite, kaolinite and quartz formed in the soils on the footslope with the greatest concentration of Fed along the toposequence.

Fire resistant vermiculite composition board and method of manufacture

Abstract: A fire resistant vermiculite composition board comprises, in percent by weight, from 40 to 90% heat expanded vermiculite particles; from 5 to 20% ceramic clay particles; from 10 to 30% hydrated cellulosic gel having a TAPPI drainage time of at least 900 seconds; from 1 to 20% defiberized wood; and from 1 to 20% starch. The vermiculite is in an incompletely expanded condition of a degree predetermined to permit its further expansion upon subsequent exposure to heat. This results in a corresponding expansion of the composition board of which it is a component when the board is exposed to fire, preventing the formation of cracks and insuring continued fire protecting coverage of the area across which the board is applied.