Vermiculite

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

The influence of magnesium in saline and sodic soils: a specific effect or a problem of cation exchange?

Abstract: Summary Na-Mg and Na-Ca exchange isotherms were determined at electrolyte concentrations of 500, 50, 5 and 1 meq per litre for illite, vermiculite and montmorillonite and for three soils containing illite and montmorillonite. This enabled comparisons to be made of clay swelling, dispersion and soil hydraulic conductivity changes between the Na-Mg and Na-Ca systems at known SAR, ESP and electrolyte concentration. Na-Mg montmoriUonite and a montmorillonitic soil behaved identically to the Na-Ca systems at the same ESP and electrolyte concentration: there was no specific effect. At the same SAR, the higher ESP in the Na-Mg system caused greater changes than in the Na-Ca systems. The Na-Mg vermiculite, illite, illitic soil and mixed illite-montmorillonitic soil showed greater changes than the Na-Ca systems at the same ESP, and there was a specific effect. At the same SAR, the higher ESP in all the Na-Mg systems apart from vermiculite increased the differences, but for vermiculite with a lower ESP, the differences were reduced. The lack of a specific effect for montmorillonite is probably related to the demixing of cations with the divalent ions concentrated on the non-swelling (internal) surfaces of the crystals.

Fixation of radiocaesium traces in a weathering sequence mica vermiculite hydroxy interlayered vermiculite

Abstract: Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs+ fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite --> trioctahedral vermiculite --> oxidized vermiculite --> hydroxy interlayered vermiculite (HIV) and quantified the Cs' fixation of each mineral both in a fixed K+-Ca2+ background and in acid conditions. The transformation process was achieved through K depletion by Na-tetraphenylboron, oxidation with Br-2 and Al-intercalation using NaOH and AlCl3. In a constant K+-Ca2+ background, vermiculite fixed 92-95% of the initial Cs-137(+) contamination while biotite and HIV fixed only 18-33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy-Al groups (HIV) strongly limited Cs+ fixation to 1-4% of the initial Cs-137(+) contamination. Cs+ fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs+ amounts in a constant K+-Ca2+ background (92-95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78-84% against 54-59%), because of its dioctahedral character.

Biochar as a Substitute for Vermiculite in Potting Mix for Hybrid Poplar

Abstract: The purpose of this study was to evaluate biochar as a substitute for vermiculite in potting mixes for unrooted vegetative cuttings of hybrid poplar as represented by the clone ‘NM6’ (Populus nigra L. × Populus suaveolens Fischer subsp. maximowiczii A. Henry). We compared three treatments (peat moss (control), peat moss mixed with vermiculite, and peat moss mixed with biochar) at three times (pre-experiment, pre-fertilizer, and post-fertilizer). The biochar and vermiculite mixes had significantly higher cation exchange capacity (CEC) and pre-experiment exchangeable K than the control. Trees grown in the biochar and vermiculite mixes had significantly higher shoot K than the control at pre-fertilizer and post-fertilizer and significantly higher shoot and total biomass at post-fertilizer. The biochar mix was also associated with lower root biomass and higher shoot/root biomass ratio than the vermiculite mix at post-fertilizer. Vector analysis indicated that all treatments were deficient in N at pre-fertilizer, and the control was also deficient in K at pre-fertilizer and post-fertilizer. Linear regression confirmed that shoot biomass was strongly correlated (R2 = 0.97) with N and K uptake (in addition to initial cutting diameter), also, root biomass was strongly correlated (R2 = 0.96) with potting mix CEC (in addition to shoot biomass). Luxury consumption of K at pre-fertilizer indicates that the increases in shoot and total biomass observed with the biochar and vermiculite treatments arise from this nutrient being “pre-loaded” in both mixes. We conclude that biochar provides benefits equivalent to vermiculite in terms of key nutrient availability and total biomass productivity.

The intercalation of a vermiculite by cationic surfactants and its subsequent swelling with organic solvents.

Abstract: We have measured the dimensions of the interlamellar space following intercalation of a vermiculite by a range of cationic surfactants and followed the subsequent swelling of the organoclay compounds with several organic solvents. A single vermiculite (Eucatex) was used with three series of surfactants, N-alkyltrimethylammonium bromides, N,N′-dialkyldimethylammonium bromides, and the gemini cationic surfactants, α,ω-bis (N-alkyldimethylammonium) alkanes. In all cases well-defined stoichiometric compounds are obtained and the amount of surfactant intercalating the layer indicates that there are two factors controlling this amount, charge neutralization of the clay and hydrophobic packing. Packing arguments are used to deduce the fraction of non-charge-neutralizing material in the interlamellar space. It is clear that by altering the surfactant charge and structure it is possible to control the degree to which adsorption beyond charge neutralization occurs in these complexes, which is important when the capacity of such complexes to sorb other materials is considered. The general pattern of swelling of the surfactant/vermiculite complex by toluene suggests that the maximum expansion of the intralamellar space is limited by the longest chain in the surfactant. In contrast to earlier results we found that these vermiculites could be swollen by alkanes as well as aromatic solvents. This is attributed to the greater hydrophobicity of the interior of an organoclay formed from a clay of higher charge density.