Chemical dissolution techniques in the study of soil clays: Part I

Abstract

The mineralogy of the clay fractions of two soil profiles representin~ the end-members of a catena developed on a glacial till derived from basic lavas has been determined. Particular attention has been given to the assessment of the nature of the amorphous inorganic material in the clay fraction of these soils. Chemical dissolution techniques were used and their effects on the clay fraction were followed by X-ray diffraction, differential thermal, infrared absorption, electron-optical and surface area measurements. The principal conclusion is that the soil clays are a continuum from completely disordered, through poorly ordered to well crystallized material.

Readily-extractable hydroxyaluminium interlayers in clay- and silt-sized vermiculite

“…Extraction characteristics of AI, Fe, Si and C (in %) and hydroxyl released by fluoride (mEq/100 g) from the air dry < 2 mm soil and its component size fractions. Subscript c refers to cold 5~ Na2CO3 for 16 h (Follett et al, 1965).…”

Characterization of X-ray amorphous material in a Scottish soil by selective chemical techniques

“…The methods used in this investigation involved dissolution by alkali (Follett et aL, 1965), dithionite (Mitchell et aL, 1971), acid oxalate (Smith, 1984) and pyrophosphate (McKeague, 1967), trimethylsilylation (Smith et al, 1982) and fluoride exchange (Perrott et al, 1976).…”

“…In this particular study the mildest treatment (cold 5% Na2CO3) was adopted to assess the amount of readily soluble aluminium and silicon in total soil samples. This procedure does not affect crystalline material, unlike hot 5% NazCO 3 which dissolves gibbsite (Jorgensen et al, 1970) and hot 0-5 M NaOH which, in some cases, may attack crystalline aluminosilicates (Follett et al, 1965). The highest content of readily soluble aluminium and silicon is in the A horizon (Table 1) and is roughly twice that in the illuvial horizons, with insignificant amounts in the basal horizon.…”

“…The techniques currently used are (i) hot 0.5 N NaOH, (Hashirnoto & Jackson, 1960) and (ii) hot 5% NazCO 3 and cold 5% Na2CO 3 Follett et al, 1965). The degree of dissolution is in the order: hot 0.5 M NaOH >> hot 5% Na2CO 3 >> cold 5% NazCO 3, which is in accord with the relative chemical reactivities of the reagents.…”

“…Many of the early mineralogical studies of Scottish soils were largely concerned with crystalline inorganic components since it was generally thought that poorly-ordered material was mainly restricted to soils in regions of recent volcanic activity (Fieldes, 1955). Although in soils the amount of inorganic gel material is seldom high, it would appear to be frequently associated with the surface of primary soil particles (Follett et al, 1965;Jones & Uehara, 1973;Farmer et al, 1983) and therefore has an influence on soil properties incommensurate with the actual amount present (Kirkman et al, 1966).…”