A. R. Mermut

BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: CHEMICAL ANALYSES OF MAJOR ELEMENTS

Chemical analysis is an essential step to establish the nature of minerals (Newman, 1987). The techniques used in rock and mineral analyses are generally valid for the analyses of clays. Additional information from other analytical techniques, which are mentioned here, is needed for accurate interpretation of the chemical analysis results of major elements (Gabis, 1979). In traditional chemical analyses, the aim is to obtain accurate analyses for all elements present in the sample, in such a way that the sum of elements expressed as oxides, including hydration and structural water, approaches the sample weight as closely as possible. The following elements are essential for the calculation of structural formulae of most clay minerals and silicates: Si, Al, Fe3+, Fe2+, Mg, Ti, Mn (in special cases), P, Ca, Na, K and H2O evolved below 105°C (H2O+) and between 105–1000°C (H2O+). For some minerals, additional determinations, such as for F and Li, may be needed for the calculation of the composition of clay minerals. Methods used to determine the chemical composition, for both major and minor elements, are described elsewhere (Jackson, 1979; Lim and Jackson, 1982; Laird et al., 1989; Amonette and Zelazny, 1994). For minor or trace elements of the Source Clays, see Elzea Kogel and Lewis (2001). Despite the progress made in science, and the increased accuracy which can be obtained from very sophisticated instruments, total …

BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: LAYER-CHARGE DETERMINATION AND CHARACTERISTICS OF THOSE MINERALS CONTAINING 2:1 LAYERS

The layer charge is perhaps the single most significant characteristic of 2:1 layer phyllosilicates. Layer charge affects cation-retention capacity and adsorption of water, and various polar organic molecules. The effects of layer charge on the sorptive properties of organo-clays were illustrated by Lee et al. (1990). It is generally agreed that the classification of 2:1 silicate clays, which is a continuing problem, may be resolved by taking into account the magnitude of the layer charge (Bailey et al. , 1971; Malla and Douglas, 1987) Studies on structural chemistry also confirm the importance of the layer charge for the characterization of the 2:1 phyllosilicates (Newman and Brown, 1987). Layer charge involves charge per [O20(OH)4] and the sum of the tetrahedral and octahedral charges. Cation exchange capacity (CEC) results not only from the layer charge, but also pH-dependent edge charges. If the molecular mass ( M ) or formula weight of the phyllosilicates and the layer charge are known, the CEC due to interlayer charge (ξ) can be calculated from the following equation: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[Interlayer\ CEC\ (cmol_{c}kg^{{-}1})\ =\ 10^{5}\ {\times}\ {\xi}/\mathit{M}\] \end{document}(1) The molecular mass (Table 1⇓) is without dimension, because it is a relative property. The mean molecular mass of the 2:1 phyllosilicates varies from 370–390 The total CEC exceeds the interlayer CEC, because of charge at crystal edges. For smectites, the edge charge is between 10 and 30% and on average it is ~20% of the total CEC (Lagaly, 1981). Non-exchangeable cations such as K+ in illite or mica are excluded from the total apparent CEC, but they are included in the layer charge. View this table: Table 1. Approximate layer charge of 2:1 phyllosilicates. Traditionally, the layer charge is calculated from the structural formula of homoionic pure clay mineral specimens (Ross and Hendricks, 1945). From the occupancy of elements in the tetrahedral and octahedral sheets, …

Origin and rate of pedogenic carbonate accumulation in Saskatchewan soils, Canada

Abstract Limited information is available about inorganic carbon stocks in the boreal regions. The objective of this study was to determine the amount and accumulation rate of pedogenic carbonate (PC) in soils of the boreal grassland and forest regions of Saskatchewan, Canada. The storage of pedogenic carbonate increases from 134 kg m−2 in semiarid grassland (Brown soils) in the southwest to 165 kg m−2 in the northeast, under forest (Gray soils), within the time decreasing from 17,000 years in the southwest to 11,500 years in the northeast. The rate of pedogenic carbonate accumulation likewise increases from 8.3 to 14.3 g m−2 year−1 in the same direction. The results show that the soils of the prairies and forests have sequestered 1.4 times more C in the form of pedogenic carbonates than as organic matter. Stable carbon isotope values of pedogenic carbonate decreases from southwest to northeast. This is consistent with decreasing representation of C4 plants in the vegetation in the same direction. The rate of pedogenic carbonate accumulation increases with increasing annual precipitation. This suggests that the rate-limiting factor to precipitate with CO2 is Ca in the boreal region of Canada. Silicate weathering is more significant in Luvisols (Alfisols), suggesting that they may be most effective in truly sequestering additional amount of C in the soil.

Some major developments in soil science since the mid-1960s

Although the science of soil was established about 150 years ago with the modern soil science taking off after the Second World War, the new Millennium has brought other challenges and new opportunities. Rapidly increasing population in countries that can least afford it have made them food-insecure. With inadequate inputs in agriculture, developing countries are degrading their lands rapidly and destroying ecosystems. Affluence in the richer countries has precipitated other problems hampering ecosystem functions and quality of land resources. These changing conditions have placed new demands on both the society and the soil science community. The latter has resulted in new areas of soil sub-disciplines such as land and soil quality, land degradation and desertification, cycling of bio-geochemicals, soil pollution assessment and monitoring etc. Advances in information technology have also enabled the science to meet the new demands of the enviro-centric world. In the last decade, noticeable changes are evident in methods and research priorities in the discipline. Soil resource assessment and monitoring is entering a new era, in terms of quality of information produced by new information technologies through the innovative use of Geographic Information Systems and remote sensing and significantly improving the acceptance and use of soil survey information. Electronic technology has dramatically increased the demand for and ability to process more data. Other innovations have resulted in quantitative approaches in soil genetic studies and demonstrated the integral role of soils in ecosystems. For global and regional resource assessment, concepts and procedures were refined. The World Reference Base for soil classification and the Global Soil and Terrain Database are the first steps towards standardisation and a more detailed assessment of global soils. The global assessment of human-induced land degradation and vulnerability to desertification are benchmark products of the databases. Environmental pollution and its effects on human and ecosystem health have become public concerns and soil science has contributed to localising, quantifying, and developing mitigation technologies to address the problems. The challenges of climate change and the charge to maintain ecological integrity have been met with technologies such as conservation tillage, agroforestry, precision agriculture etc. New concepts such as multi-functionality of land, soil quality, sustainability of agriculture and carbon sequestration, have emerged leading to new management strategies and an enhanced quality of life.

Deposition of Harmattan dust and its influence on base saturation of soils in northern Ghana

Ferruginous soils formed from Volta shale deposits in northern Ghana are highly weathered, have high iron and aluminium oxide contents, and a mineralogy dominated by quartz and low activity clays with low effective cec. Despite their advanced weathering state, base saturation values of top soils are generally above 80%, and deficiencies of basic cations are uncommon. We postulated that the annual deposition of dust from the Sahara, carried by the Harmattan weather system may be responsible for the high base saturation. Therefore, we collected dust material for two entire dry seasons at Nyankpala (surrounded by highly weathered Volta shale deposits), and during several events of Harmattan and local dust storms at Bolgatanga (surrounded by a variety of parent materials). Long-distance Harmattan dust had a clearly finer particle size distribution than dust collected during local storms, but angularity and evidence of weathering on dust particles did not distinguish dust from different sources. In Bolgatanga, soils contained unweathered minerals derived from local parent materials, and both local storm and Harmattan dust contained large amounts of bases. Significant amounts of micas and feldspars, and K contents up to 3% in the dust collected at Nyankpala showed Harmattan dust to be the source of K and other bases found on Volta shale soils. Short-distance dust in Nyankpala was mostly quartz and vegetation ashes. Dust deposition during one Harmattan season at Nyankpala amounted to about 15 g m−2, and carried a total of 140, 400, 300 and 60 mg m−2 of Mg, Ca, K and Na, respectively. These amounts could account for the high base saturation of the low cec in Volta shale soils.

Soil loss by splash and wash during rainfall from two loess soils

Abstract Physical processes occurring during surface seal formation through a rainstorm are well understood, but limited information is available regarding the quantity and particle size distribution of splash and runoff at certain time intervals. In this study, we evaluated the quantity and particle size distribution of suspensions of both splash and interrill runoff in two loess soils with different mineralogy and aggregate stability, and somewhat different particle size distribution, but similar organic matter content. The soils were subjected to simulated rainstorms of ∼ 40 turn h − 1 and 100 mm h −1 intensities. The amount of splash was about four times higher for the Saskatchewan soil (Typic Haploboroll) with high smectite than for the Grenada soil (Typic Fragiudalf) which is rich in Fe-oxyhydroxides. The amount of splashed material and sediment load increased with increased rainfall intensity for both soils. Splash was decreased after wetting of the soil surface. The decrease in splash rate was more rapid with high rainfall intensity. The amount of clay size particles of the splash was similar to the original soil material. Micromorphological observations confirmed the fluctuations in clay content with time, at the very surface. Soil materials splashed were much higher (10 to 20 times) than the interrill runoff losses. The latter was controlled by the rainfall intensity. The soil material from Saskatchewan, produced more than 11 Mg ha − 1 of interrill runoff with low rainfall intensity. High rainfall intensity produced 10 times more soil loss than low rainfall intensity. High amount of soil loss clearly shows that the Saskatchewan soil would benefit from erosion control measures. Both rainfall intensities removed preferentially more clay from the Saskatchewan B horizon material. This has important agronomic and environmental implications for this soil. Interrill soil losses from the Granada A horizon material were much less, with no clear evidence of preferential removal of clay size particles.

Sorption of selected cationic and neutral organic molecules on palygorskite and sepiolite

Palygorskite and sepiolite show a high sorption capacity for organic molecules. Adsorption of 2 organic cations, methylene blue (MB) and crystal violet (CV), by palygorskite and sepiolite were examined. The maximum sorption of MB and CV far exceeded the cation exchange capacity (CEC) of these minerals. This shows that, besides the contribution of free negative sorption sites (P-), the sites satisfied with sorption of single cations (PXi0) and neutral sorption sites (N) on clay surfaces may contribute to the sorption of organic cations. The number of neutral sites was determined by examining the sorption of 2 neutral organic molecules, triton-X 100 (TX100) and 15 crown ether 5 (15C5), and by application of the Langmuir isotherm.To determine the contribution of different sites, an adsorption model that applies the Gouy-Chapman equation and takes into account the formation of different clay-organic complexes in a closed system was employed. Application of this model to sorption data provided the calculation of binding coefficients for neutral sites, as well as the surface potential of the minerals at different sorbate concentrations.At sorption maxima, for both palygorskite and sepiolite, the contribution of neutral sites for sorption of organic cations was the highest, followed by the PXi0 sites in case of CV sorption, while in sorption of MB the contribution of P- sites was the second highest. The Fourier transform infrared (FTIR) patterns of clay-organic cation complexes compared with pure clays confirm that the sorption of organic cations is by silanol groups located at the edge of fibrous crystals, which account for neutral sorption sites.

Retention of dissolved organic carbon from vinasse by a tropical soil, kaolinite, and Fe-oxides

Abstract Vinasse is a sugarcane distillery waste water commonly applied to soil in Brazil. The content of dissolved organic matter (DOM) in vinasse is high, varying from 10,973 to 14,801 mg l −1 of dissolved organic carbon (DOC). This study examines the capacity of an Ultisol (from a sugarcane-growing region), kaolinite and synthetic Fe-oxides to retain DOM extracted from vinasse. Adsorption isotherms of the A, BA, Bt1, Bt3 and Bt4 horizons of the Ultisol, as well as of those of the kaolinite and Fe-oxides, were obtained through batch equilibrium experiments using DOC concentrations, simulating vinasse additions of 0, 43, 86, 344, 688 and 1376 m 3 ha −1 . Adsorption isotherms of DOM extracted from vinasse on different horizons of the Ultisol indicated that DOM adsorption increased with depth. Distinct adsorption capacity of these horizons was related to differences in dithionite-citrate-bicarbonate (DCB) extracted Fe, native organic matter and clay content. At an initial DOC concentration of 160 mg l −1 (equivalent to the application of 688 m 3 vinasse ha −1 ), the A horizon retained 7.1% and the Bt4 horizon retained 27.4% of the total DOC in solution, suggesting that this soil has a relatively low adsorption capacity for DOM from vinasse. Adsorption isotherms of DOC on pure kaolinite, synthetic goethite and hematite showed that the maximum adsorption capacity of the Fe oxides was as much as about five times the maximum adsorption capacity of kaolinite. Desorption studies indicated that while all DOC adsorbed by kaolinite were completely desorbed, only 28 to 35% of the adsorbed DOC were desorbed by Fe-oxides. These findings highlight the importance of the goethite and hematite on the adsorption of DOM in tropical soils.

Phosphorus sorption and properties of ferruginous nodules from semiarid soils from Ghana and Brazil

Abstract The morphology of ferruginous nodules from Ghana and Brazil was examined, and their P soprtion potentials and P sorption related to chemical and morphological properties of soil fines and nodules were measured. Despite already elevated P contents of nodules, sorption capacities of ferruginous nodules were higher than those of soil fines. In a residual fertilizer trial, nodules acted as an effective sink for P, removing P from plant-available pools in the soil and fixing about 180 kg P ha−1 over 3 years. Micromorphological observation showed significant porosity in nodules, and X-ray microprobe scans revealed high Fe and Al concentrations in pores and on nodule surfaces. These properties allow the penetration of nutrient solutions into inert-appearing lateritic nodules, and cause very efficient and rapid fixation of phosphate.

Micromorphological and mineralogical components of surface sealing in loess soils from different geographic regions

Mineralogy of clay sized particles and rainstorm characteristics are among the major factors that determine the nature of soil sealing. This research was designed to further our knowledge about the role of clay mineralogy and rainstorm characteristics on crust formation. Four loess soils from different geographic locations (Canada, USA, China, and Belgium) were used in this study. Preliminary studies were carried out on Grenada Bt (USA), Lishi (China), and Bierbeek Bt (Belgium) horizons. Detailed infiltration and microscopic studies were performed only on the Bm1 horizon of the Saskatchewan soil, Canada and the Ap horizon of the Grenada soil, Mississippi, USA. Two levels of rainstorm were applied (∼ 40 and 80 mm h−1). While smectite was the major component in the Saskatchewan Bm 1 horizon, vermiculite and illite were found to be the dominant clay minerals in the Bt horizon of the Grenada soil. Formation of the washed layer together with thin lamellar crust coincided with the preferential movement of clay sized particles through runoff in both the Saskatchewan Bm1 and Grenada Ap horizons. The higher initial infiltration rate with higher rainfall intensity in both soils were likely due to higher matric suction, but rapid reduction in infiltration in this treatment was due to rapid aggregate destruction and a dense packing of the fundamental soil particles. No washed-in zone could be observed in the Bm1 horizon of the Saskatchewan soil in both rainstorm intensities. However, drastic reduction in infiltration, especially with high rainstorm intensity (after 7–8 min), was attributed mainly to the swelling of smectite in this soil material. Washed-in materials were visible in the Ap horizon of Grenada under high rainstorm intensity. Due to the presence of iron oxides and clay coatings, aggregates were stable and no sealing could be observed in the Grenada Bt and Bierbeek Bt materials. The degree of seal development in the Lishi soils was low. This was due to low clay and high carbonate contents. This study shows clearly that higher and continuous rainstorm intensity causes rapid seal development and as a result more erosion would occur, especially in the soils with high smectite content.