Showing papers on "Vermiculite published in 1974"

Experimental Transformation of a Chlorite Into a Vermiculite

Abstract: An orthochlorite (sheridanite) was heated to 610~ to dehydroxylate the hydroxide sheet and to oxidize ferrous iron. The heated sample was shaken for 20 min in a mixed solution of 0"2 N HCI and 0'2 N NaC1 to dissolve the dehydroxylated hydroxide sheet. X-ray diffraction, thermal, infrared absorption and chemical analyses showed that the resulting product was similar to Kenya vermiculite. The procedure shows promise for the individual determination of the composition of the hydroxide sheet and of the mica layer in the chlorite structure. The experiments indicate that the hydroxide sheet in orthochlorites must be structurally disturbed before it can be selectively removed. In nature, structural disorganization of the hydroxide sheet of chlorite by dehydroxylation and oxidation of ferrous iron might occur during meta- morphic processes, and chlorite to vermiculite transformation could take place during subsequent acid weathering. In pedogenic weathering conditions it is likely that oxidation of ferrous iron plays a major role in initiation of the structural disorder required for the selective removal of the hydroxide sheet in the weathering of chlorite to vermiculite.

Mineralogical changes associated with deep weathering of gabbro in Aberdeenshire

Abstract: The distribution, profile morphology and mineralogy of deeply weathered gabbroic rocks in the basic igneous masses of Insch and Bogancloch, Aberdeenshire, have been studied. The saprolite is characterized by granular disintegration and spheroidal weathering with a relatively low degree of secondary mineral development. The upper part of the profile often shows evidence of mass movement and incorporation into overlying drift but below this zone the degree of alteration is generally uniform with depth. Feldspar and hornblende are largely unaffected, except by disintegration, but pyroxenes show varying degrees of weathering from the incipient development of amorphous iron oxides to replacement by reticulate networks or complete pseudomorphs of trioctahedral vermiculite. Biotite weathers to hydrobiotite and vermiculite, giving rise also, under certain conditions, to kaolinite-gibbsite vermiforms. The correspondence between occurrences of deep weathering and coarser textured biotite-bearing rocks can be related to the instability of this mineral. Consideration of the mineralogical changes found and the morphology of the profile of weathering suggest their formation under a warm, humid climatic regime, probably during the mid Tertiary times.

`Vermiculite' Determination on Whole Soils by Cation Exchange Capacity Methods*

Abstract: The proposed method is a modification of one by Alexiades and Jackson (1965). Calcium exchange capacity (CaEC) and potassium exchange capacity (KEC) are determined, after removal of organic matter and free iron oxides, by saturating the exchange complex with centrifuge washings of pH 7 acetate solutions of Ca or K, respectively. Excess salt in solutions remaining in contact with the soil after saturation is determined by measuring the weight and concentration of the excess solution. The exchangeable cations and excess salt are then replaced by centrifuge washings with 1 N acetate solutions of Mg (for CaEC) or NH4 (for KEC), after overnight 110°C oven-drying to enhance K fixation for KEC. The replaced cations are determined and CaEC and KEC values are calculated. Per cent ‘vermiculite’ is based on the difference between CaEC and KEC (expressed in m-equiv/100 g) and an assumed ‘vermiculite’ in-terlayer exchange capacity of 154 m-equiv/100 g; percentage Vr = (CaEC-KEC/154) × 100. The ‘vermiculite’ interlayer fraction (VIF) of the CaEC may also be calculated; VIF= CaEC-KEC/CaEC. The measured ‘vermiculite’ is shown in quotation marks since the method is open to criticism regarding exactly what is being measured, the assumptions made, etc. and to emphasize that the determination procedure is an operational one for the characterization of cation exchange complexes.

Layer Charge Decrease by Tetrahedral Cation Removal and Silicon Incorporation during Natural Weathering of Phlogopite to Saponite1

Abstract: A substantial layer charge decrease, from 210 to 140 meq/100 g, occurred during the natural weathering of phlogopite through vermiculite to saponite in Kansas. A comparison of the Fe²⁺ content and layer charge of the coarse fraction (72% phlogopite) and the fine fraction (71% saponite) indicated that iron oxidation cannot account for the layer charge decrease during the transformation. Control studies on iron oxidation during vermiculitization of biotites and lepidomelane did not correlate with layer charge decrease. Elemental analysis of the coarse and fine fractions revealed gains and losses of cations during the weathering of the mica flakes to fine particles. The Si⁴⁺ and Mg²⁺ increased by 2.66 and 0.84%, respectively, while Al³⁺ and total Fe³⁺ plus Fe²⁺ decreased by 0.34 and 1.21%, respectively, in the two fine fractions compared to the macroflakes. The elemental analyses also revealed the unique nature of this phlogopite which contained fewer moles of Al³⁺ than K⁺; the presence of some isomorphously substituted tetrahedral Fe³⁺ contributed 17% of the total negative layer charge. Loss of layer charge was found to be a result of the loss of isomorphically substituted tetrahedral Al³⁺ and Fe³⁺ by authigenic recrystallization with an increase in tetrahedral Si⁴⁺. In control studies, removal of isomorphously substituted tetrahedral Al³⁺ from Ontario phlogopitic vermiculite and Transvaal micaceous vermiculite by citrate chelation also resulted in an equivalent layer charge decrease.

Artificial alteration of biotite into a 14 a, layer silicate with hydroxy- aluminium interlayers

Abstract: Biotite was altered by boiling in 0.2 M A1C13 solution, and the products were examined by X-ray powder and single-crystal diffraction, chemical analysis and thermogravimetry. The altered material is a 14 A clay mineral with hydroxy-Al interlayers. It has a stacking sequence characteristic of vermiculite and its silicate layers are similar in chemical composition to trioctahedral vermiculite. The results of extracting the interlayer material with sodium citrate solution, X-ray examinations after heating and thermogravimetry show that the interlayer material is composed of Al associated with OH and H2O. The chemistry and kinetics of the alteration reaction and the orientational between the altered and original biotites are also discussed.

Vermiculite products produced by exfoliation pulverization and calcination

Abstract: A process for the preparation of vermiculite particles having enhanced properties which comprises exfoliating crude vermiculite without substantially changing its structural strength, pulverizing the exfoliated particles and subjecting them to a heat treatment so as to cause at least partial calcination.

Effect of Hydrolysis of Aluminum on Competitive Adsorption of Potassium and Aluminum by Expansible Phyllosilicates

Abstract: The competitive adsorption of K and Al on montmorillonite and vermiculite as influenced by the degree of hydrolysis and polymerization of solution Al was examined. The Na-saturated minerals (0.2–2μ) were suspended in the hydroxy-Al solutions of basicites (OH/Al molar ratios) of 0, 0.5, 1.0, 1.5, 2.0, and 2.5 in the presence of a fixed concentration of K, and the suspensions were then equilibrated at 25 ± 0.2°C. Compared to Al, K became more competitive for the exchange sites in vermiculite with the increase in initial basicity of solution Al, and the reverse trend was true for montmorillonite. The more unrestricted Z-axis expansibility of montmorillonite favors the diffusion of a given size polymer in the interlayer space; thus the hydroxy-Al ions with higher charge are more competitive than K. In the case of vermiculite, the limited expansibility, the presence of wedge zones, the charge and size of the hydroxy-Al ions, and the presence of strongly competing K ions greatly hinder the adsorption of Al over K as the degree of hydrolysis of Al increases. The products of adsorption were found to vary significantly with the mineral and initial basicity. With the increase in the initial basicity, an increasingly ordered micalike mineral was formed from vermiculite. It is evident that the degree of hydrolysis and polymerization of solution Al greatly affects the adsorption of K and Al by 2:1 expansible phyllosilicates, and would thus affect the competitive formation of micalike minerals and Al interlayers of expansible phyllosilicates in soils and sediments.

Selective dissolution and formula derivation of clay vermiculite from some tuscan soils

Abstract: The chemical composition and structural characteristics of clays from samples of eight Tuscan soils were investigated. Using simple selective dissolution method (successive boiling in 1 N HCl and 0"5 N NaOH) it was possible to distinguish two types of low charge dioctahedral vermiculite; one easily HC1 soluble the other practically insoluble. Structural formulae for the soluble type were calculated from the chemical analysis of the dissolved material; for the insoluble type it was possible to calculate only an 'average' structural formula which included the micaceous material. Since the HCl soluble vermiculites sb_ow a high content of Fe and Mg, they can be considered either as alteration products of glauconites or biotites, or as a result of a synthesis, at least in soils derived from basic rocks which do not contain mica. The aluminous insoluble type, present also in parent material, may be the result of an incomplete 'illitization' in a marine environment.

Mineralogy and Cation Exchange Properties of Libby Vermiculite Separates as Affected by Particle-Size Reduction*

Abstract: A vermiculite (Libby, Montana) sample obtained from the Zonolite company contained mostly coarse-grained separates with only 8.7 per cent clay. The 2-50 #m fraction was used for particle-size reduction studies by wet and dry grinding, and size-fractionated into hyd- robiotite > biotite.