Formation and Stability of Hydroxy-Mg Interlayers in Phyllosilicates

Abstract

Abstract-A study was conducted to (1) determine the conditions of hydroxy-Mg interlayer formation with respect to type of clay mineral, acidity, and time; (2) evaluate the stability of this interlayer to dissolution treatments; and (3) ascertain the effects of such treatments upon the determination of clay minerals in soils and sediments. Hydroxy-Mg interlayers were formed in montmorillonite and vermiculite by adding MgCI~ and NaOH in amounts to give a wide range of pH. The resulting chloritic intergrades were examined after 10 days, 6 months, and 1 yr.Alkaline conditions favored the formation of hydroxy magnesium interlayers in phyllosilicates. Hydroxy-Mg interlayered montmoriUonite which resulted from 10 days equilibration at pH 10.4 did not expand upon solvation with ethylene glycol and exhibited practically no collapse after K-saturation and heating at 550~ A small amount of interlayer was formed between pH 6.8 and 9.8 (10 days). In contrast, vermiculite exhibited no evidence of interlayer formation at pH values up to 9-7 (10 days). Chloritic intergrades formed at pH 10-7 did not collapse after K-saturation and heating at 300~ but did so at 550~ Hydroxy-Mg interlayers were not formed in either mineral by using a drying method. This method apparently failed to provide the required alkaline conditions for interlayer formation.The amount of magnesium interlayers present in the phyllosilicate systems decreased with time. The interlayers formed in vermiculite decreased more sharply than those in montmorillonite.Sequential dissolution treatments included boiling 2 per cent Na~CO3, buffered sodium citratedithionite, a second citrate-dithionite treatment, and boiling NaOH. Hydroxy-Mg interlayers in montmorillonite exhibited a higher stability to sequential treatments than the interlayers formed in vermiculite. A stable 14 ,~ line was observed in interlayered montmorillonite after the dithionitecitrate and NaOH treatments.The interlayers in montmorillonite showed a relatively high stability to HCI dissolution treatments. In contrast, most of the magnesium interlayer in vermiculite was removed by two HC1 washings.The reagents used in this study are sometimes used to remove coatings and cementing agents from soil surfaces prior to particle size and clay analysis. The present data show that these treatments also remove some hydroxy-Mg interlayers and produce changes in properties of clays, A proper interpretation of data for clay mineral identification and characterization must recognize these changes due to treatment.

Formation, Compositions, and Properties of Hydroxy-Al- and Hydroxy-Mg-Montmorillonite

“…In 100% RH, expansion gave rise to mixed-layering; a fully developed 18.8-A spacing was not observed. Carstea et al (1970b) remarked that [Mg(OH)] + is "an intermediate step towards hydroxide formation," which is confirmed by the present results. Yamanaka and Brindley (1978), discussing the mechanism of formation of hydroxy-Ni interlayers, suggested an internal mechanism related to dissociation of interlayer H20 molecules, as follows:…”

“…Caill~re and H6nin (1949) and Slaughter andMilne (1960) included Fe 3+ andCr 3+ ions, Carstea (1968) and Carstea et al (1970a, 1970b) considered Fe 3+ ions, and Brindley and Yamanaka (1979 studied Cr 3+ ions. In this last study it was found that without addition of NaOH to the system, the interlayer composition corresponded very closely to cations of the form [Cr(OH)(H20)~] 2+, and with a very small addition of NaOH, to cations of the form [Cr(OH)2(H20)4] +.…”

“…Rich (1968) gave a detailed review of naturally occurring and laboratory-prepared smectites and vermiculites containing hydroxy interlayers. Extensive references to the literature are given by Hsu (1968), Gupta and Malik (1969a, 1969b, 1969c, Carstea et al (1970aCarstea et al ( , 1970b, Brydon and Turner (1972), and Lahav et al (1978). Earlier work was reviewed by Marshall (1964, especially Ch.…”

Regularly Interstratified Chlorite/Vermiculite in Contact Metamorphosed Red Beds, Newark Group, Connecticut Valley

“…The aggrading model, as synthesized from information in Weaver and Pollard (1975), Carstea et al (1970), Basset (1959, Wyatt and Sabatier (1966), Dunoyer de Segonzac (1970), andShover (1964), assumes that the initial clay material is a 2:1 layer silicate, such as smectite or vermiculite. When exposed to a diagenetic or metasomatic environment rich in magnesium, the mineral may aggrade by random fxation of Mg-hydroxy (brucitic) sheets in the interlayer space.…”

Trioctahedral Smectite and Interstratified Chlorite/Smectite in Jurassic Strata of the Connecticut Valley

“…Hay (1966) reported the precipitation of analcime directly from strongly alkaline (pH = 9.70), sodium carbonate brines in Lake Natron, Tanzania. Continued removal of Na § and Ca 2 § with further evaporation of the lake waters would have ultimately produced conditions favorable for the formation of Mghydroxy (brucitic) layers (Carstea et al, 1970). The lack of typical evaporite mineral assemblages in the gray mudstone, however, indicates that such conditions were probably not attained.…”