Role of initial effective stress on the thermal volume change of normally consolidated clay

This paper focuses on the results from thermal triaxial tests on normally consolidated Georgia Kaolinite. The hypothesis evaluated in this study is whether the initial mean effective stress has an impact on the thermal volume change encountered during drained heating. To that effect, specimens at three different initial mean effective stresses were considered in this study. The clay specimens were first isotropically consolidated to a normally consolidated state, then subjected to a drained heating cooling cycle followed by further mechanical loading to higher effective stresses. The results indicate contractive volumetric strain during drained heating where the volumetric strain was found to increase with increasing initial mean effective stress. A rebound in volume was observed during subsequent cooling where the net change in volume transitioned from zero volume change of the specimen to net contraction of the specimen after a heating cooling cycle as the initial mean effective stress increased. The results indicate the need for considering the effect of initial mean effective stress when assessing in-situ heating as a method of soil improvement.

Dissolution behaviour of soil kaolinites in acidic solutions

Highly weathered soils of the tropics and subtropics commonly have kaolinitedominated clay fractions. Under acidic conditions prevailing in these soils kaolinite dissolution occurs, contributing to the high levels of soluble Al in these soils. This study evaluates the dissolution behaviour of kaolinites from subsurface horizons of highly weathered soils from Thailand, along with a soil kaolinite from Western Australia (WA kaolinite) and Georgia kaolinite (KGa-2). Kaolinite-dominated clay fractions were isolated from soils by sedimentation and chemically treated to remove iron oxides. The dissolution rate of kaolinites was measured in 0.01 M NaCl as a function of pH (1–4; HCl) at 25±1°C using non-stirred flow-through reactors. Kaolinite dissolution rates were calculated from the release of Al and Si at the steady state. In most of the experiments and at all pH values, the release of both Si and Al underwent a distinct transition from an initial period of rapid release to significantly slower release at the steady state. Aluminium and Si concentrations at the steady state were higher for soil kaolinites than the reference sample (KGa-2). At the steady state the dissolution of all kaolinites was stoichiometric except for the soil kaolinites from Thailand at pH 4, where the Al/Si ratio was well below the stoichiometric ratio. Log dissolution rate (RSi) of soil kaolinites ranged from –13.75 to –12.51, with the dissolution rate increasing significantly with decreasing solution pH. However, the dissolution rate was similar or pH independent between pH 2 and 3, which is the pH range of the point of zero net charge (PZNC) for both soil and reference kaolinites. The dissolution rate of soil kaolinite was significantly higher than the KGa-2 sample at pH < 3. The results obtained on kaolinite samples from highly weathered soils show that in highly acidic systems kaolinite is a source of soluble Al. Soil kaolinites with poorly ordered small crystals dissolve faster than better crystalline reference kaolinite (KGa-2) with larger crystals.

Comparative adsorption of norwalk virus, poliovirus 1 and F+ RNA coliphage MS2 to soils suspended in treated wastewater

Enteric viruses such as Norwalk virus (NV) are important agents of waterborne disease from faecally contaminated groundwater. Viruses are more resistant to inactivation than most enteric bacteria and they may not be removed efficiently during land application. Adsorption is one of the major factors in viral removal and persistence in soils. The adsorption of NV by soils suspended in wastewater has not been determined. Therefore, we determined the adsorption of NV to six soils (Cecil clay-loam, Corolla sand, Georgia Kaolinite (clay), Wyoming Bentonite (clay), Ponzer organic muck and Flushing Meadows sand-loam) suspended in treated wastewater and compared it to that of poliovirus 1 (PV1) (strongly adsorbed) and MS2 (weakly adsorbed). NV is shown to be less sorptive than PV1 and more sorptive than MS2. Furthermore, relative virus adsorption among soils was similar for all three enteric viruses with viruses most adsorbed by clays and least adsorbed by sand and organic soils.

Reactivity of a long-spacing ammonium-propionate-kaolinite intercalate toward diol, diamines and quaternary ammonium salts

This paper describes reactions occurring between the 25.5 Å ammonium propionate (AP) intercalate of a well-crystallized Georgia kaolinite with ethylene glycol, 1-6-diaminohexane and a quaternary amine (QA), namelyAn ethylene glycol kaolinite complex is obtained with a strong d001 reflection at 10.9 Å. Seven 00l orders are observed easily. The IR spectrum shows bands at 3697, 3654 (weak shoulder) 3644 and 3622 cm−1, assigned to OH stretching of kaolinite and a strong OH band of E.G. at 3300 cm−1. No absorption band of AP is observed.The 1.6-diaminohexane product is characterized by two broad reflections at 16.6 and 7.4 Å. Distinct Amide I and Amide II IR bands imply that the carboxyl group of the propionic acid has reacted with the amino group. By treating the AP complex with QA a very stable kaolinite-QA complex suspension in benzene was obtained. On drying an X-ray amorphous solid with no reflection at spacing & 20 Å was obtained. The hydroxyl stretching bands of the original kaolinite are drastically modified, a very strong band at 3560 cm−1, a strong doublet at 3620 and 3605 cm−1 were observed. A weak singlet is obtained at 3695 cm−1. The two OH bending bands are replaced by a single band at 912 cm−1. A complicated set of interactions results in the loss of stacking order about the C-axis, accompanied by some curling of layer packets. A prolonged treatment with water restores the X-ray and IR spectra of the original kaolinite.

Hydrothermal and dry-heat fixation of K by soil clays and the effects on C.E.C., surface area and mineralogy

Fixation of K by soil clays and selected reference clay minerals was induced by dry heat and hydrothermal procedures, at 100°C, 200°C and 380°C. Appreciable amounts were fixed at all temperatures. In the cases of the samples treated hydrothermally the amounts fixed increased with pressure.Fixation by dry heating at 380°C was significantly greater than at 100°C and 200°C respectively. Fixation under hydrothermal conditions increased in order 380°C > 200°C > 100°C.Reductions in cation exchange capacities (and surface areas) were associated with fixation, indicating that some fixation was due to ion exchange. Changes in mineralogy in some of the samples also support the conclusion that ion exchange was partly responsible for fixation. Some of the fixation under hydrothermal conditions was due to the formation of insoluble K-compounds - as for example the synthesis of a new mineral when one sample was treated.The lattice-iron content of the clays may have influenced their hydrothermal behaviour. Thus the Princes Town Clay ( > 7-5 % lattice-iron) and three nontronites (≫ 7-5 % lattice-iron) showed appreciable lattice collapse after hydrothermal treatment, while Wyoming bentonite and hectorite (<3-5%) lattice-iron) showed no collapse at all.The degree of crystallinity of the mineral may also have influenced its hydrothermal reaction. For example, the highly disordered soil kaolinite (St John's) was much more reactive than the more ordered Georgia kaolinite. Also, the more-ordered reference clays fixed relatively less K at 380°C than the less-ordered soil clays.