Vermiculite

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

Iodide, caesium and strontium adsorption by organophilic vermiculite

Abstract: A B S T R A C T: Distribution coefficients and isotherms for the adsorption of radioiodide, caesium and strontium ions (125I-, 134Cs+ and 85Sr2+) were determined in untreated vermiculite and in vermiculite treated with the chloride salt of hexadecylpyridinium (HDPy+). Experimental data reveal that some of the alkylammonium ions were incorporated as HDPyCI ion pairs into the vermiculite. The fraction of ion pairs adsorbed is reflected by an increase in distribution coefficients with increasing saturation levels. Consequently, a considerable part of the iodide adsorption could be attributed to an anion exchange process. At smaller amounts of Cs § and Sr z+ adsorbed, distribution coefficients of the modified clay mineral are significantly reduced in comparison with the original material. These differences are less pronounced when greater amounts of cations are adsorbed. Generally, larger distribution coefficients were found for the Cs + compared with the Sr z§ ion in the untreated and modified samples. Soils represent an important filter and buffer system for many cations and anions. Generally, their sorption properties are determined by the contents and compositions of clay minerals and humic substances. A great part of the soil organic matter is associated with clay minerals forming organomineral complexes (Greenland, 1965) which are of pronounced importance with respect to element transport and/or retention and to aggregate stability. Clay minerals also interact with organic cations. The replacement of inorganic cations by alkylammonium ions causes considerable modification in the hydration and swelling properties of the clays. Research in this area has significantly increased the

Plaster compositions and products

Abstract: A plaster composition comprises calcined gypsum, 0.03 to 1.0 per cent of glass fibres of 1/4 to 1 inch length, and a comminuted unexfoliated vermiculite mineral of a size and in an amount to give an expansion equivalent to that of 3 1/2 to 7 1/2 per cent. of high grade vermiculite of minus 28 mesh commercial grading. Preferably drawn glass fibres bonded by a water soluble material e.g. starch, or by a thermoplastic resin are used. Retarders, accelerators, and, in making wallboard, core adhesives may be present, and foam for making lightweight products. U.S.A. Specification 2,526,066 is referred to and describes a standard vermiculite material.

Biotite Flakes: Alteration by Chemical and Biological Treatment

Abstract: Biotite alteration under acid conditions proceeds differently from the generally accepted pathway of transformation to vermiculite in which hydrated cations cause interlayer expansion, resulting in a dark-colored peripheral band on mica particles. Acid solutions of synthetic or biologic origin remove octahedral ions, leaving a fragile matrix of amorphous material.

Interpretation of pH and Eh trends in a fluvial‐sand aquifer system

Abstract: Ground waters and aquifer materials from a shallow fluvial-sand aquifer system (1-km-long flow path) were sampled and analyzed to determine the hydrogeochemical processes affecting pH and Eh (measured Pt electrode potential). The aquifer system is a fine-grained sand (K ∼ 10−3 cm/s) composed principally of quartz and plagioclase (70% of all grains) with minor biotite (partially altered to vermicuiite) and trace amounts of calcite. Acid neutralization capacity measurements and X ray diffractograms suggest that acid precipitation recharging the aquifer undergoes a two-step neutralization process; the first step involves reactions with the surfaces of mineral grains, mainly with plagioclase and biotite, and the second step involves an irreversible neutralization involving biotite alteration to vermiculite and carbonate mineral dissolution. During migration through deep confined parts of the aquifer ground waters attain equilibrium with calcite. A thermodynamically based redox model of a closed-oxidant system satisfactorily accounts for the sequential reduction of dissolved oxygen, ferric oxides, and sulfate in the aquifer by the oxidation of dissolved organic carbon and (for oxygen only) ferrous iron. Because of the problems of using Pt electrodes in ground waters it is recommended that Eh measurements be supplemented with dissolved oxygen and sulfide measurements.

Comparison of silicate minerals as sources of potassium for plant nutrition in sandy soil

Abstract: Summary Given the cost of conventional fertilizers and increasing demand as a result of increasing population growth, new sources of potassium (K) for plant nutrition need to be considered. Readily soluble nutrients are rapidly lost from well-drained soils, and so it is appropriate to consider silicate minerals that release K slowly during weathering. In this paper, we compare the availability to plants grown in sandy soils of K from microcline (feldspar), biotite (mica) and nepheline syenite (nepheline + microcline) using leek (Allium ampeloprasum var. porrum L.) as a model plant. Pot experiments were carried out under controlled environmental conditions using natural and artificial soil. The performance of the minerals was compared with treatment with KCl and a negative control (no K added). Plant shoot diameter was measured weekly to assess growth rates. After 10 weeks, plant dry mass and soil and plant contents of soluble K were measured to determine offtake; mineralogical changes in biotite-treated soils were assessed. Results for artificial and natural soil differed, reflecting differences in their mineralogy. With no added K, plant growth ceased after 2 weeks. Growth rates were greatest for KCl, followed by biotite; linear growth continued for 5 weeks in the natural soil and for the entire 10 weeks in the artificial soil. Growth rates with nepheline syenite (natural soil) and microcline (both soils) did not differ significantly from the negative control, but for nepheline syenite, leek shoot K content was significantly greater, demonstrating availability of K from this source. X-ray diffraction analysis showed that biotite reacted to form vermiculite.