Aj. Herbillon

Disaggregation and clay dispersion of oxisols : Na resin, a recommended methodology

Abstract Comparison of five different dispersion techniques on six different low-activity clay-soil pedons showed that Na-resin treatment was the most efficient particle-size distribution method for the very stable Oxisols rich in gibbsite. In these Oxisols, and particularly in their strongly aggregated A horizons, clay dispersion with combined controlled ultrasonic or vigorous mechanical and chemical treatments was lower and was partly pH-dependent. The role of gibbsite, crystalline Fe oxides and oxyhydroxides, organic materials and poorly-ordered Al and Fe hydrous oxides on the aggregate stability of low-activity clay soil and clay dispersion is discussed.

Weathering of chlorite in a soil derived from a chloritoschist under humid tropical conditions

Abstract Eight samples from a soil derived from greenschist were chosen to represent the weathering transformation of chlorite and were subjected to chemical and mineralogical analyses by X-ray, D.T.A., selective and acid dissolution techniques. Regularly interstratified chlorite-vermiculite is the major weathering product in the sand and silt fractions, whereas nontronite predominates in the clay fraction. Kaolinite and a “chlorite-like” mineral progressively appear in the clay fraction as the soil surface is approached. The results show that the genetic link suspected between the clay chloritic component and the kaolinite does not withstand a detailed examination. The clay chloritic mineral is a disordered remnant of the regularly interstratified chlorite-vermiculite and it appears in the clay fraction of the solum concommitantly with the argillitization of the silt fraction. Kaolinite occurs in close association with nontronite and would perhaps form with this mineral a true mixed-layer phase. The unequal distribution of aluminium, iron and magnesium amongst the available sites in the parent chlorite appears to be a factor that strengthens the divergent behaviour of these elements during the weathering.

The Epigenetic Replacement of Kaolinite By Hematite in Laterite - Petrographic Evidence and the Mechanisms Involved

Abstract This paper describes the petrographical and mineralogical transformations accompanying the accumulation of iron oxides within the deep mottled layer of a laterite from Burkina Faso. In this layer, the proportions of purple red hematitic spots or nodules which form at the expense of volumes occupied by a soft microporous kaolinite plasma increase as the surface of the soil is approached. The antagonism between hematite and kaolinite was observed at different levels. In all cases, from the border to the core of the hematitic domains, kaolinite experiences corrosion soon followed by complete destruction. At this later stage, hemalite crystals are organized into thin lamellar structures showing clearly the shapes of former kaolinite platelets. A mechanism explaining coincidence of the accumulation of hematite with the destruction of kaolinite is proposed. We postulate that in the deep layers of laterites fed by Fe 2+ solutions, the protons necessary to dissolve kaolinite are generated by a reaction similar to the oxidation-hydrolysis step of ferrolysis. In the mottled layer of this laterite, therefore, the progressive building up of a high concentration of iron appears to be the result of two closely related processes, i.e., the precipitation of iron oxides from solution and the concommitant dissolution of kaolinite.

Infrared Studies of Ni-bearing Clay-minerals of the Kerolite-pimelite Series

Two kerolite and one garnierite samples were subjected to progressive heat treatments prior to their examination by infrared spectroscopy (IR) in the 1200-600-cm−1 and 3800-3000-cm−1 regions. The heat treatment of the garnierite (a mixture of nepouite and pimelite) selectively dehydroxylated the nepouite thus allowing an examination to be made of the OH-vibration bands due to the pimelite. Both the relative intensities of the 710-670-cm−1 doublet and of the different OH-stretching bands indicated the Ni content of this pimelite to be about 70%. The heat treatments did not modify the 1200-600-cm−1 region of the spectra of kerolites but caused a noticeable sharpening in the OH-stretching region. The relative intensities of the structural OH-stretching bands of dehydrated kerolites showed that they differ from Ni-talcs of similar composition in the distribution of Ni and Mg in the octahedral sites. These cations are randomly distributed in Ni-talc but are mainly segregated into Mg and Ni domains in kerolite. Changes in sharpness, intensity, and position of the structural OH-stretching bands of the kerolites as temperature increases and dehydration progresses are similar to those undergone by Mg- or Li-saturated trioctahedral smectites. Also thermal analysis curves of these minerals show similarities with those of Mg- and Ni-saturated smectites, and suggest that in kerolites too, the hydration water is associated with interlayer (though non-exchangeable) Ni and/or Mg cations.РезюмеДва образцы керолита и один образец гарниерита были подвержены постепенной термической обработке перед исследованием путем инфракрасной спектроскопии (ИС) в спектральных областях от 1200 до 600 см−1 и от 3800 до 3000 см−1. Термическая обработка гарниерита (смесь непуита и пимелита) селективно дегидроксилировала непуит, таким образом допуская возможность исследования колебательных полос ОН вследствие присутствия пимелита. Как относительные интенсивности двойной полосы 710–670 см−1, так и различные валентные полосы ОН указывали на то, что содержание Ni в этом пимелите было около 70%. Термические обработки не изменяли область 1200–600 см−1 спектра керолитов, но вызывали заметные сужения полос в области валентных колебаний ОН. Относительные интенсивности структурных валентных полос ОН обезвоженных керолитов показали, что они отличаются по распределению катионов Ni и Мg в октаэдрических местах от Ni-nn mrjd gjlj4yjuj сjсnfdf. Эти катионы беспорядочно распределены в Ni-тальке, но, в основном, находятся в отдельных областях Ni и Мg в керолите. С увеличением температуры и прогрессом дегидратации изменения формы (остроты), интенсивности и положения структурных валентных полос ОН керолитов похожи на изменения, которые происходили с Мg- или Ni-насыщенными трехоктаэдрическими смектитами. Кривые этих минералов по термическому анализу также являются подобными кривым для Мg- или Ni-насыщенных смектитов, и наводят на мысль, что также в керолитах гидратационная вода связана с межслойными (хотя необменными) катионами Ni и/или Мg. [Е.С.]ResümeeZwei Kerolit- und eine Garnierit-Probe wurden auf ansteigende Temperaturen erhitzt bevor sie mittels Infrarotspektroskopie (IR) im Bereich von 1200 bis 600 cm−1 und 3800 bis 3000 cm−1 untersucht wurden. Das Erhitzen von Garnierit (ein Gemenge aus Nepouit und Pimelit) führte zu einer selektiven Dehydroxylierung von Nepouit, wodurch eine Untersuchung der OH-Schwingungsbanden von Pimelit möglich wurde. Die relativen Intensitäten des 710 bis 670 cm−1 Dubletts und der verschiedenen OH-Streckschwingungsbanden deuten darauf hin, daß der Ni-Gehalt des untersuchten Pimelit bei etwa 70% liegt. Die Erhitzungsversuche veränderten den Bereich von 1200 bis 600 cm−1 der Kerolitspektren nicht. Sie bewirkten jedoch eine beachtliche Verschärfung im Bereich der OH-Streckschwingung. Die relativen Intensitäten der strukturellen OH-Streckschwingungsbanden der dehydratisierten Kerolite zeigten, daß sie anders sind als die von Ni-Talk-Proben, die eine ähnliche Zusammensetzung im Hinblick auf die Verteilung von Ni und Mg auf den Oktaederplätzen haben. Diese Kationen sind im Ni-Talk statistisch verteilt, während sie in Kerolit in Mg- und Ni-Domänen auftreten. Die Veränderungen in der Schärfe, der Intensität und in der Lage der strukturellen OH-Streckschwingungsbanden der Kerolite mit zunehmender Temperatur und zunehmenden Dehydratationsprozessen sind ähnlich denen, die bei Mg- oder Li-gesättigten trioktaedrischen Smektiten auftreten. Auch die Kurven der Differentialthermoanalyse dieser Minerale zeigen Ähnlichkeiten mit denen von Mg- und Ni-gesättigten Smektiten. Dies deutet darauf hin, daß das Hydratationswasser auch in den Keroliten an die Zwischenschichtkationen Ni und/oder Mg gebunden ist (die jedoch nicht austauschbar sind). [U.W.]RésuméDeux kérolites et une garniérite ont été soumises à des traitements thermiques progressifs avant d’être examinées par spectroscopie infrarouge dans les régions spectrales 1200–600-cm−1 et 3800–3000-cm−1. Le chauffage de la garniérite (qui était un mélange de népouite et de pimélite) provoque la déshydroxylation sélective de la népouite et permet d’examiner les bandes de vibration des hydroxyles structuraux de la pimélite. Tant les intensités relatives des bandes formant un doublet à 710 et 670 cm−1 que celles des vibrations de valence des hydroxyles structuraux permettent d’estimer que le contenu en nickel de cette pimélite est proche de 70%. Les traitements thermiques n’affectent guère la région spectrale 1200–600-cm−1 des kérolites mais ils provoquent un affinement notable de la région où sont localisées les vibrations de valence des hydroxyles structuraux, L’intensité relative des différentes vibrations dues à ces hydroxyles permettent d’établir que la répartition des cations octaédriques Ni et Mg dans les kérolites déshydratées est très différente de celle des talcs nickelifères de même composition. Les cations octaédriques sont répartis au hasard dans les talcs et répartis en domaines magnésiens et nickelifères dans les kérolites. Les modifications de position, d’intensité et de largeur qui affectent les bandes de vibration des hydroxyles structuraux des kérolites au fur et à mesure que progresse leur déshydratation, sont semblables à celles de smectites trioctaédriques saturées par Mg ou Li. De même, les kérolites montrent des courbes thermogravimétriques et des diagrammes ATD qui ressemblent à ceux de smectites saturées par Mg2+ et/ou par Ni2+. Ces analogies suggèrent que, dans les kérolites aussi, l’eau d’hydratation est liée à des cations interfoliaires. Cependant, duns les kérolites, ces cations ne sont pas échangeables.

Morphology, Texture, and Microstructure of Halloysitic Soil Clays As Related To Weathering and Exchangeable Cation

This paper aims at characterizing the morphology, texture, and microstructure of three hydrated kaolin rich clays (f > 0.2 μm) from volcanic soils. These clays represent a weathering sequence in which CEC, halloysite content with respect to kaolinite, as well as smectite content in the halloysite-smectite mixed-layer clays decrease with increased weathering. The clay samples were made homoionic (K+ or Mg2+) and hydrated under a low suction pressure (3.2 kPa). After replacing water by a resin, ultrathin sections were cut and examined by TEM. Particle shape varies with increased weathering, as follows: spheroids → tubes → platelets. Higher aggregation and dispersion are observed by TEM after Mg2+ and K+ saturation, respectively, at two levels of the clay-water system organization: intraparticle and interparticle. The microstructure variations induced by the nature of the exchangeable cation become less pronounced with decreasing layer charge of the 2:1 layers. They are thus related here to the presence of smectite layers localized in the halloysite habitus, mostly at the particle periphery. These results show that small amounts of smectite largely affect the organization of clays rich in kaolins at a high water content, and that K+ behaves here as a dispersing ion.

Occurrence and genesis of secondary magnesium-bearing calcites in soils☆

The presence of magnesium-bearing calcites is indicated in soil carbonate accumulation layers and concretions. A differential solubility method permitted estimation of the mol percent magnesium-carbonate content of calcites in the presence of dolomite. The relationship between diffraction spacings and mol percent MgCO3, of selected samples is in good agreement with that depicted by other workers for biogenic magnesium-bearing calcites. Magnesium-containing calcites are concentrated in clay (< 2 μ) and fine silt (2–10 μ) sizes of Cca horizons. Their presence in the clay fraction of Ck horizons is an indication that carbonate mineralogy may change at profile depths often considered to be unaffected by pedogenic processes. The dissolution of existing carbonates within solum horizons, the translocation of ions in solution and the reprecipitation of calcite in Cca and underlying horizons are the main processes applicable to a variety of different natural situations. The Mg level of the secondary calcites is likely regulated by the partitioning effect during their precipitation. Periodic moisture movement to greater depths and lateral movement of soil solutions serve as a regulating factor in maintaining soluble Mg at levels favorable to the precipitation of low-magnesium calcites in upland chernozemic soils of central Saskatchewan; higher magnesium contents occur in calcites occurring in subsoils underlying solonetzic and depressional chernozemic soils of the same area. Formation of magnesium-bearing calcites within concretions in soils of the Rusizi basin in Africa were likely influenced by Mg-rich ground waters; associated dolomite may also have been of a secondary nature.

Kinetics of the Selective Extraction of Iron-oxides in Geochemical Samples - Association Between Fe and Cu in Acid Brown Soils

Warnant, P., Martin, H. and Herbillon, A.J., 1981. Kinetics of the selective extraction of iron oxides in geochemical samples. Association between Fe and Cu in acid brown soils. In: A.W. Rose and H. Gundlach (Editors), Geochemical Exploration 1980. J. Geochem. Explor., 15: 635–644. The use of Tamms reagent at 60° C and at different reaction times enables the progressive dissolution of iron oxides from the different horizons of acid brown soils. This technique is used to evaluate the association between Cu and Fe in soils from a zone mineralized in Cu. This association is quantified by the coefficient α (moles Cu/moles Fe) which represents the degree of doping of the iron oxides by Cu. For the B horizon of these soils, α values range from 5 to 10 × 10−3 mole Cu/mole Fe. Calculation of the coefficient a (range = 0.4 to 2.0 × 10−3) for 150 soil samples of the same type enabled the differentiation of two geochemical populations. Treatment of the total Cu values of these samples did not permit such differentiation.

Distribution et localisation du Zn et du Pb dans un sol complexe situe a l'aplomb d'un gossan en milieu carbonate (Famenne belge)

Abstract Within the study area, a sulphide mineralization consisting of marcasite, sphalerite and accessory galena, as well as its subsurface oxidation product, a gossan in which the dominant mineral is goethite, are intricately intermixed with a gangue of calcite. The open profile at the mineralized site shows the succession of two soils: a leached brown soil (Hapludalf) developed in the loessic cover is underlain by a paleosol of the terra fusca type. The presence within the terra fusca of limonitic gravels indicates its genetic relationship with the underlying gossan. This is further confirmed by the distribution of Fe, Pb, Zn and Mn within the different horizons of the profile. The high values of Pb, and Zn, which are found both in the limonitic gravels and in the major B horizon of the terra fusca contrast strongly with the low values for the soil developed in loess. The different particle-size fractions from the major B horizons of both the leached brown soil and the terra fusca have been submitted to a selective dissolution method using five reagents sequentially (ammonium acetate, hydroxylamine, ammonium oxalate in darkness, ammonium oxalate under ultra violet (U.V.) radiation, strong acids). The crystalline iron oxides (which are dissolved by ammonium oxalate under U.V.) are concentrated in the sand fractions of the terra fusca and their extraction is accompanied by that of Zn. In the same particle-size fraction, hydroxylamine dissolves selectively Mn oxides and also extracts the major part of the Pb. A similar behaviour is observed when the same extraction sequence is applied to a limonitic gravel. The best evidence for the underlying mineralization is therefore found in the coarse and very coarse fractions of the terra fusca where the disintegration products of the gossan are concentrated. These products are absent in the loess covering the terra fusca.

Interaction of Stable and Metastable Monomeric Iron (III) Species with a Kaolinitic Soil Clay

The polymeric hydrolysis products of Fe(III) solutions recently have received special attention as chemical agents able to promote the flocculation which is necessary for the formation of stable clay microaggregates. (Rengasamy and Oades, 1977a, 1977b; Kavanagh and Quirk, 1978; Oades, 1984). It was shown that polymeric Fe(III) cations of controlled nominal size or molecular weight, when added in appropriate amounts to a clay suspension, were effective for modifying the electrophoretic mobility, and for promoting the coagulation of different types of clay silicates. Other experiments also (Shanmuganathan and Oades, 1982) have revealed the beneficial effects of similar polymers for the promotion of improved structure in clays and soils.