Aluminous Chlorite Origin of pH-Dependent Cation Exchange Capacity Variations

Abstract-Deferration by reduction of free Fe203 with Na,zS20~ in the presence of Na citrate and NaHCO~ caused a change in valence state of I 0 to 35 per cent of the total structural iron in micaceous vermiculites, soils, nontronite, and muscovite. An increase in FC + on deferration was accompanied by an equivalent decrease in Fe 3.. Subsequent treatment with H202 reoxidized the structural Fe z+ previously formed.Sesquioxide coatings on micaceous vermiculites were examined electron microscopically, These coatings were composed predominantly of Fe203 with approximately 10 per cent by weight of AI2Oa and small amounts of SiO2, as determined by chemical analysis of the deferration extracts.The cation exchange capacity (CEC) increased 10-60 per cent as a result of deferration of micaceous vermiculites and soils. Treatment of the deferrated sample with H202 restored the Fe 3+ content to approximately the original value but the CEC was not affected. Consequently, the increase in CEC on deferration was attributed to the removal of the positively charged sesquioxide coating. The reversible change in valence of structural iron without an equivalent change in CEC was attributed to deprotonation-protonation of the structure (OH-~ 02 ) simultaneous with the oxidation-reduction of iron (FC + ~ Pe a+) in the phyllosilicate layer.

Section: Introductionmentioning

confidence: 99%

Deferration Effect on Structural Ferrous-Ferric Iron Ratio and CEC of Vermiculites and Soils

Roth

1969

“…Different metals (hydrous oxides) have been used for this purpose and in recent years data has accumulated on the preparation and characterization of hydroxy aluminum-montmorillonite complexes (Barnishel and Rich, 1963;Brydon and Kodama, 1966;de Villiers and Jackson, 1967;Gupta and Malik, 1969;Hsu, 1968;Hsu and Bates, 1964;Kawaski and Aomine, 1965;Rich, 1968;and Turner and Brydon, 1967). Caillere and Henin (1949) were the first to study the Mg(OH)~-montmorillonite complex.…”

Section: Introductionmentioning

confidence: 99%

Chloritization of Montmorillonite by Its Coprecipitation with Magnesium Hydroxide

Gupta

1969

Abstract-A magnesium hydroxide-montmorillonite complex prepared at an OH/Mg molar ratio of 2 (16 meq Mg/g clay) and immediately cleaned of any free Mg(OH)2 behaves like magnesium-chlorite and shows no change during 3 months ageing. Magnesium hydroxide completely precipitates within the interlayer space of montmorillonite. X-ray diffraction analysis, thermal (DTA and TGA) studies, i.r. absorption analysis, polarographic reduction behaviour, and cation exchange capacity measurements confirm the transformation of montmorillonite to a chloriteqike structure. Further ageing of the complex results in the release of brucite from the interlayer space and expansion of the compJex on glycerol treatment. X-ray analysis of the 6 months aged sample shows the presence of free brucite but not montmorillonite. A small but significant increase in CEC of the complex is observed on ageing. When the Mg(OH)2-montmorillonite complex is allowed to age in the presence of free Mg(OH)2 (external to montmorillonite unit layers) in a dry state, a "seeding" effect takes place and the "fixed" Mg(OH)z starts coming out from the interlayer space after 10 days.

“…Cation exchange capacity for the clay of sample 17-5 was determined at pH 7, after Jackson (1956), and for the clay of sample 3-2 at pH 4 and 8 following the procedure of de Villiers and Jackson (1967).…”

Section: Methodsmentioning

confidence: 99%

Hydrothermal Origin of the Clays from the Upper Slopes of Mauna Kea, Hawaii

Ugolini

1974

Abstract--The soils of the summit region of Mauna Kea are similar to the soils of the high mountain deserts and to the soils of cold deserts. Dramatic differences, however, exist between the soils of the summit and other neighboring cones and the soils of the glaciated terrain. The soils of some of the cones of the summit area are clay rich and contain phyllosilicate minerals; the soils of the glaciated terrain are sandy and contain X-ray amorphous clay. Montmorillonite and a Mg-rich trioctahedral mineral identified as saponite are the clay minerals of the summit. Because the summit area of Mauna Kea supported an ice cap at the time of the formation of the cones, the origin of the smectite minerals could have resulted from the alteration of the tephra by steam and water released in the melting of the ice. Hypogene fluids are, however, more likely to be responsible for the genesis of the phyllosilicate minerals.