Reduction In Cation Exchange Capacity Research Articles

Physico-Chemical Properties of Wetland Soils Affected by Crude Oil Spillage in Niger Delta Area, Nigeria

Loss of soil fertility through loss of soil organic matter, leaching of nutrients, loss of the nutrient-laden topsoil, changes in soil-pH, reduction in cation exchange capacity, salinization, water logging and other forms of soil degradation are major problems associated with agricultural productivity in the oil producing areas of Nigeria. This analysis investigated some selected physico-chemical properties of wetland soils affected by crude oil spillage in Bodo city in the Niger Delta region of Nigeria. Field reconnaissance survey using a handheld Geographic Positioning system (GPS) and survey technique involving random sampling, was used in siting soil profile pits. The unpolluted samples were collected 50 meters away from the polluted site but in the same geographic region and was used as control site. Soil samples were collected based on degree of horizon differentiation and analyzed using routine and special analytical techniques. Soil data were subjected to analysis of variance using Genstat program. Result shows that soil physical properties of the polluted site: moisture content, soil bulk density, and soil texture were highly significant (p=0.01 and 0.05) when compared to the unpolluted site while some chemical soil properties analysed especially soil pH, organic matter, carbon-nitrogen ratio, available phosphorus were affected by crude oil spillage. Results from this study affirm that crude oil can have detrimental effect on soil physico-chemical properties, which implies low soil fertility and thereby affect crop production and increase food insecurity within the study site. Further studies involving more edaphic properties, biotoxic metals and their bioaccessibility in crops growing on waterside affected by crude oil spill will surely enhance knowledge and management of the these highly industrially influenced soils. Also, international and national oil and gas companies should carry out their activities with international best practice.

Toxicological Indices of Crude Oil-Polluted Soil Ecosystem

Assessment of the level of contaminations from possible impact of crude oil on soil ecosystem is imperative for the determination of environmental acceptability. This study investigated this impact ex-situ using a culture-dependent approach to evaluate the total microbial counts; physicochemical tools to determine the cation exchange capacity (CEC), metal leachates, exchangeable bases (Mg, Ca, Na and K), pH, total petroleum hydrocarbon (TPH) and the overall effects on plants as indices of toxicity. The experiment demonstrated that at 1.5 – 3.5% contamination across days-zero to -28, there was a significant (p<0.05) increase in total petroleum hydrocarbon (TPH) from 0.03 ± 0.00 to 0.07 ± 0.00 with increase in acidity from pH 5.2 ± 0.00 to 4.0 ± 0.00 and a reduction in cation exchange capacity (CEC) from 0.82 ± 0.05 to 0.70 ± 0.11mEq and exchangeable bases with an augmented increase in phytotoxic elements and metal leachates. A reduction in microbial biomass from control, 1.30 x 109, to 3.6 x 108 cfu on week one as contamination increased and induction of hydrocarbonclastic organisms thereafter across weeks two and four, 3.88 x 108 and 4.40 x 108 cfu respectively was an indication of a reduction in microbial diversity. Ecosystem dynamics and mineralization were impaired and disrupted and the entire soil biochemistry altered with adverse effects on plant health.

A meta-analysis of soil microbial and physicochemical properties following native forest conversion

The conversion of natural forest to artificial vegetation may deplete nutrients and thus affect the soil quality. However, little is known about synergetic changes of microbial and physicochemical dynamics in soils after natural forest conversion and their implications. In the current study, we synthesized the responses of soil microbial and physicochemical properties in the uppermost soil layer (<20 cm) following natural forest conversion, as reported in 51 published studies (127 sites). Our results showed that the response ratios of soil moisture, soil microbial carbon and nitrogen, bacteria, fungi, enzymatic activities, soil organic carbon, total carbon, total nitrogen, NO3–, total phosphorus, available phosphorus, cations (K+, Mg2+ and Ca2+), and cation exchange capacity (CEC) overall declined following natural forest replacement. In contrast, natural forest conversion caused significant increases in soil bulk density, soil pH and NH4+. Reductions of microbial carbon, organic carbon and total nitrogen in soil were independent of revegetation type, but variations in soil pH, available phosphorus and fungi were correlated to land use. Soil CEC reduction increased soil pH, allowing soils to retain NH4+, which promoted fungal growth. Moreover, natural forest replacement led to the loss of soil cations in regions of higher precipitation. Revegetation practices led to greater consumption of soil microbial and chemical nutrients and produced “harder” soils (increased soil compaction and decreased moisture content) in warmer regions. Stand age influenced ratios of soil carbon to nitrogen and ratios of bacteria to fungi following natural forest conversion. Altogether, our study suggests that natural forest conversion results in decreased soil microbial and chemical fertility, and desirable soil properties are more likely to be lost in warmer regions and over time as global climate warming exacerbates, which in turn may potentially damage ecosystem sustainability.

Geotechnical Properties and Microstructure of a Diesel Contaminated Lateritic Soil Treated with Lime

ABSTRACT Studies involving oil-contaminated lateritic fine-grained soils are still scarce in literature, especially regarding treatments for improving soils mechanical properties. In this study, geotechnical properties and microstructure of a diesel-contaminated lateritic soil treated with lime are investigated and compared to tests conducted on lime-treated soil (2% to 8% lime) and diesel-contaminated soil (2 to16% diesel). The presence of diesel had no significant effect on soil plasticity but decreased soil strength. Lime stabilization applied to diesel-contaminated soils significantly improved soil properties after 6% of lime stabilizer. The diesel presence led to an inhibition of lime reaction due to reduction of cation exchange capacity and flocculation, which reflected in loss of its effectiveness in improving strength as compared to natural soil response. The water retention behavior and unsaturated hydraulic conductivity of soil were affected by diesel contamination, leading to curve shapes similar to clay materials. Adding 2% of lime to the contaminated soil, increase in the soil pores and changes in the shapes of water retention curve and k-functions were observed with similar behavior of a course-grained material. Overall, this study highlights how the presence of diesel and lime affects lateritic soil properties and microstructure.

Sorption of Cu2+ Ions by Bentonite Modified with Al Keggin Cations and Humic Acid in Solutions with pH 4.5

The sorption of Cu2+ onto bentonite modified with Al Keggin cations and humic acid from CuCl2 solutions at pH 4.5 was studied. Modification of Na-bentonite with Al Keggin cations was found to result in an increase in the basal spacing of montmorillonite from 1.29 nm for N-form to 1.85 and 1.78 nm for HAl13 and Al13 forms respectively, in a reduction of CEC (cation exchange capacity) and in the formation of additional sites with a variable charge with pHPZC 4.2. Al13-bentonite is not affected by heat. Under the conditions of the experiments at pH of 4.5 Na-bentonite adsorbs more Cu2+ from CuCl2 solutions then Al13 forms of bentonites. The main mechanism of copper sorption on Na-bentonite is the cation exchange Cu2+–Na+. The reduction of CEC of Na-bentonite after modification with Al Keggin cations leads to a decrease in the Cu2+ sorption. pH-dependent sorption sites on Al13-bentonites have a pHPZC of 4.2 and, therefore, under conditions of the experiment have positive charge which prevents Cu2+ sorption. Na-bentonite adsorbs more humic acid solution (HA) then Al13-bentonite and the proportion of adsorbed HA remains constant over the entire concentration range. Treatment of the Al13-bentonite with HA leads to the formation of the additional sorption sites. The amount of sorbed Cu2+ and the percentage of their extraction from solutions by HAAl13-bentonite is similar to those values for Na-bentonite.

Assessing and modifying China bentonites for aflatoxin adsorption

Bentonites have been used to reduce or to diminish the toxicity of aflatoxins to animals and humans. Due to bentonites' large variations in mineral composition, and the dominant mineral smectite can differ in interlayer cation composition, charge density, charge origin, bentonites demonstrated more than ten fold of differences in aflatoxin adsorption capacity. To maximize the efficiency of local bentonites for aflatoxin detoxification, modifications of bentonites are often needed. The objectives of this study are to asses and to modify selected bentonites from China for aflatoxin detoxification. Thirteen Chinese bentonites were collected and evaluated for montmorillonite contents. A 6-fold difference in aflatoxin B1 (AfB1) adsorption capacity among these 13 natural bentonites were observed. Six bentonites, representing the low-, medium-, and high- adsorption for AfB1, were selected for detailed assessment and modification. The clay fractions of the bentonites (Na-saturated) were harvested and exposed to the following three treatments: (1) Ca saturation (Ca_), (2) Mg saturation and heating (Mg_Heat), (3) Mg saturation and heating then Ca saturation (Mg_Heat_Ca), respectively. These three treatments enhanced the AfB1 adsorption capacity of the six bentonites and the relative efficiency of the treatments follows the order of Mg_Heat_Ca>Mg_Heat>Ca_ in most of the six bentonites. Calcium saturation or heating can improve the clays' adsorption affinity and capacity for AfB1 mainly because of the reduction of cation exchange capacity (CEC). This assumption was confirmed by the change of CEC and single-point AfB1 adsorption capacity of bulk bentonites before and after heating. Our adsorption data suggest that some Chinese bentonites are generally suitable for AfB1 adsorption, and high selectivity can be achieved by optimizing their charge density. Similar approach should be applicable to other local bentonites worldwide.

Effects of cover crops on soil quality: Part II. Soil exchangeable bases (potassium, magnesium, sodium, and calcium), cation exchange capacity, and soil micronutrients (zinc, manganese, iron, copper, and boron)

Maintaining and conserving essential soil nutrients using soil management practices, such as incorporating cover crops and no-tillage into crop rotation, has the potential to improve soil quality and fertility as well soil productivity. The effects of cover crops in a no-tillage seed maize (Zea mays L.) production system on soil exchangeable bases and soil micronutrients were investigated in Beaver Crossing (Seward County), Nebraska. The main objective of the research was to investigate the effects of growing cover crops under conservation tillage on soil exchangeable bases (potassium [K], magnesium [Mg], calcium [Ca], and sodium [Na]), cation exchange capacity (CEC), and soil micronutrients (zinc [Zn], copper [Cu], boron [B], iron [Fe], and manganese [Mn]). Extensive field research was conducted in four cover crop growing seasons (2012 to 2013, 2013 to 2014, 2014 to 2015, and 2015 to 2016) on three center pivot-irrigated seed maize or soybean (Glycine max L.) and cover crop rotation large-scale production fields. While extensive soil samples were taken to quantify and analyze the changes in soil exchangeable bases and soil micronutrients from the beginning of 2012 to the end of 2015, all large-scale production fields had cover crops in either seed maize or soybean rotation since 2002. Thus, it is anticipated that the changes in soil exchangeable bases, CEC, and micronutrients are a result of long-term (from early 2002 to late 2015) cover crop impacts on soil in all three research fields. The treatment effects exhibited variation not only between the treatments, but also between the soil layers for the same treatment. Cover crops in seed maize or soybean treatment (SCCC) had a significant effect on soil exchangeable K in the topsoil (0 to 5 cm soil layer). Cover crops did not affect exchangeable K concentration below the 5 cm soil layer. Exchangeable Ca concentrations were unaffected by any land cover treatment imposed in this research. Incorporating cover crops into a no-tillage seed maize or soybean cropping system (SCCC) might help in maintaining the exchangeable Mg concentration more effectively than no cover crop treatment (SC), especially in the 20 to 40 cm soil layer. Cover cropping has significant effects on CEC in the 5 to 40 cm soil depth. At the 5 to 20 cm soil depth, the SCCC treatment resulted in increased CEC by 8.4%, whereas bare soil, cover crop only without seed maize or soybean residue (CC), and SC treatments resulted in 10%, 4.1%, and 21% reduction in CEC, respectively. The SCCC treatment reduced the concentration of micronutrients in the topsoil (0 to 5 cm soil layer). Overall, cover crops (SCCC) have the potential in maintaining the optimum levels of Zn, B, Fe, and Mn in the topsoil (0 to 5 cm soil layer) as compared to the SC treatment. The results of this research suggest that cover cropping has the potential to alter several very important soil chemical properties (and significantly in some cases); however, the impacts primarily occur in the topsoil.

Experimental Study of Montmorillonite Structure and Transformation of Its Properties under Treatment with Inorganic Acid Solutions

This paper discusses the mechanism of montmorillonite structural alteration and modification of bentonites’ properties (based on samples from clay deposits Taganskoye, Kazakhstan and Mukhortala, Buriatia) under thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). Treatment conditions were chosen according to those accepted in chemical industry for obtaining acid modified clays as catalysts or sorbents. Also, more intense treatment was carried out to simulate possible influence at the liquid radioactive site repositories. A series of methods was used: XRD, FTIR, ICP-AES, TEM, nitrogen adsorption, and particle size analysis. It allowed revealing certain processes: transformation of montmorillonite structure which appears in the leaching of interlayer and octahedral cations and protonation of the interlayer and –OH groups at octahedral sheets. In turn, changes in the structure of the 2:1 layer of montmorillonite and its interlayer result in significant alterations in the properties: reduction of cation exchange capacity and an increase of specific surface area. Acid treatment also leads to a redistribution of particle sizes and changes the pore system. The results of the work showed that bentonite clays retain a significant portion of their adsorption properties even after a prolonged and intense thermochemical treatment (1 M HNO3, 60 °C, 108 h).

The geotechnical and microstructural properties of desilicated fly ash lime stabilised expansive soil

This study presents the use of marginal material as a stabiliser for expansive soil and therefore provides opportunity for high volume use of waste material for low cost, low volume road construction. Desilicated fly ash (DFA) was stabilised with lime up to 40 %. The effect of composite moisture content, lime content and curing temperature was studied. A 70:30 DFA:lime composite cured at 80 °C for 96 h had the highest unconfined compressive strength (UCS) of 8.57 MPa, a 19.5 % water absorption after a 24 h soak with a corresponding 23.5 % reduction in UCS. The green composite (70:30) was then used to stabilise expansive soil. Expansive soil stabilised with 30 % 70:30 DFA: lime composite was found to have a UCS of 4.1 MPa and resulted in a 50.1 % reduction in the liquid limit and a 15.1 meq/100 g reduction in cation exchange capacity of the soil. The formation of calcium silicate hydrate and tricalcium aluminate in the expansive soil was responsible for the strength gain in the stabilised soil. The stabilised soil met the minimum requirements for the American Concrete institute’s requirements for rigid pavement layers.

Experimental aluminization of vermiculite interlayers: An X-ray diffraction perspective on crystal chemistry and structural mechanisms

Natural aluminization of swelling clay minerals is ubiquitous in acidic soils leading to the formation of hydroxy-interlayered (HI) minerals. This process has drawn special attention over the last 4–5 decades owing to the negative impact on soil fertility of the induced reduction of cation exchange capacity. Combination of chemical analyses and of X-ray diffraction profile modeling on a series of experimentally self-aluminized samples aimed at an improved description of HI minerals and more especially of their interlayer crystal chemistry. Both exchangeable alkali cations and hydroxy (Al, Fe) cations coexist within HI vermiculite interlayers. The latter form discontinuous gibbsite-like interlayer sheets with ~15% completeness, despite layer-to-layer distances similar to that of chlorite. From charge compensation considerations, the isolated hydroxy (Al, Fe) cation clusters bear ~1.5 positive charges per cation. Analysis of X-ray diffraction data indicates that aluminization of initially swelling interlayers is a layer-by-layer process leading to mixed layers composed of randomly interstratified swelling and aluminized layers, all aluminized layers likely hosting a similar number of hydroxy (Al, Fe) cations along the aluminization process. This model contradicts the widely accepted description of HI minerals as a solid solution between expandable 2:1 clay and aluminous chlorite end-members. As a consequence, the proportion of HI layers in the mixed layer is a robust estimate of aluminization progress and both the amount of extractible (Al, Fe) and the extent of CEC decrease are positively correlated to this essential parameter.

Pedogenetic investigation of soil degradation on a deforested loess hillslope of Golestan Province, Northern Iran

Genesis, mineralogy, and micromorphology of soils formed on a forest and adjacent cultivated loess hillslope were investigated to assess the effects of deforestation and hillslope position on soil properties and the intensity of soil degradation. The study revealed that deforestation caused a loss of soil organic carbon, a reduction of cation exchange capacity, and an increase in carbonates in the surface soil. The soils of the different slope positions of the forest land were Alfisols and Mollisols with well-developed argillic horizons. Speckled b-fabric of the argillic horizons and the crystallitic b-fabric of the underlying calcic horizon are evidence for a more stable landscape under forest ecosystem. Downward leaching caused decalcification of the upper horizons and clay movement in the profile. Formation of the mollic epipedon in the forest land confirms the accumulation of organic carbon and lower erosion in the surface soil. Soils of the adjacent cultivated area however, are less-developed, and classified as Inceptisols and Mollisols. Absence of the mollic epipedon in the shoulder, backslope and footslope positions, presence of the near surface calcic horizon and absence of argillic horizon in all slope positions are due to severe erosion. Absence of speckled b-fabric in all the slope positions of the deforested land is evidence that downward and surface movements of water have resulted in soil erosion and flooding. Higher smectite concentrations and occurrence of vermiculite in the forest area indicate favorable moisture availability. Pedology is an effective way of documenting the adverse effects of land use change especially in the hilly regions.

FTIR study and cation exchange capacity of Fe 3+- and Mg 2+-substituted calcium silicate hydrates

Single phases calcium silicate hydrates (1.1 nm tobermorite; Ca 5Si 6O 16(OH) 2·4H 2O), with Fe 3+ and Mg 2+ substitutions, were synthesized under hydrothermal conditions at 175 °C. The structure of different tobermorite samples was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The results indicated that Fe and Mg ions played a key role in crystallization, morphology and structure of tobermorite. Mg 2+ increases crystallinity of tobermorite and changes its morphology from platy-shape at 4 h curing time to lamellar-shape at longer curing time. Fe 3+ increases imperfection of tobermerite at short curing time, however it increases crystallinity at longer curing time and the morphology of tobermorite changes magnificently from reticulated-shape to fiber-shape. FTIR proved that Fe + and Mg + increase silicate chains polymerization and increase the chain cross-linkage, which is consistent with tobermorite lamellar and fibers morphology that grow parallel to the b-axis (along the silicate chains). The cations exchange capacity (CEC) of Fe- and Mg-substituted tobermorites is lower than that of the unsubstituted tobermorite. Cross-linkage in the silicate chains was found to cause a reduction in cation exchange capacity.

Morphology and properties of nanocomposites from organoclays with reduced cation exchange capacity

AbstractOrganoclays with different levels of reduction in the original cation exchange capacity (CEC) were prepared to characterize the morphology and Young's modulus of their melt‐processed nanocomposites made from nylon 6 (PA‐6) and polypropylene/polypropylene grafted with maleic anhydride (PP/PP‐g‐MA). Wide‐angle X‐ray scattering (WAXS), transmission electron microscopy (TEM), and Young's modulus data are reported. Three different levels of CEC reduction were obtained; WAXS analysis and percentage loss on ignition (LOI) calculations for these organoclays showed a reduction in both the intergallery spacing and in the amount of organic modifier contained in the clay with CEC reduction. The morphology and modulus results show that these reduced‐CEC organoclays led to lower exfoliation and modulus enhancement for both PA‐6 and PP/PP‐g‐MA nanocomposites. The results may be influenced by differences in layer charge and charge distribution that could have been produced during the charge reduction process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Alterações físicas e químicas de um Argissolo amarelo sob diferentes sistemas de uso e manejo

As alterações nas condições químicas do solo em virtude de diferentes sistemas de manejo com cana-de-açúcar podem causar modificações na dispersão de argila e no estado de agregação do solo. Estudaram-se os efeitos de diferentes sistemas de manejo com cana-de-açúcar nas propriedades físicas e químicas de um Argissolo Amarelo Coeso, selecionando-se quatro sistemas de uso e manejo, constituídos de uma área não irrigada, uma área irrigada, uma com aplicação de vinhaça e uma sob floresta nativa como condição original. Foram retiradas amostras de cada área a 0-0,2, 0,2-0,4 e 0,4-0,8 m de profundidade, para determinação das alterações nas propriedades físicas e químicas do solo. Os sistemas de manejo com cana-de-açúcar afetaram as propriedades químicas do solo, ocorrendo redução da capacidade de troca de cátions e aumento da condutividade elétrica, pH em água e concentração crítica de floculação. Essas alterações químicas resultaram numa dispersão maior de argila nos solos cultivados com cana-de-açúcar, reduzindo a estabilidade dos agregados em água.

Reversible collapse and Mg 2+ release of de- and rehydroxylated homoionic cis-vacant montmorillonites

Homoionic Na +, Ca 2+, Sr 2+, Li +, Cu 2+ and Zn 2+ samples of the <2 μm fraction of a cis-vacant montmorillonite from Linden (Bavaria) were steam treated at 200°C (≈1.5 MPa), 240°C (≈3.3 MPa) and 300°C (≈8.0 MPa) after dehydroxylation at temperatures up to 630°C. Cation exchange capacity (CEC) measurements, determination of exchangeable cations and X-ray diffraction (XRD), supplemented by thermoanalytical investigations of the evolved water in a thermobalance linked to a mass spectrometer, infrared (IR) and electron spin resonance (ESR) spectroscopy were employed to obtain information about the state of expandability and structural changes of swellable montmorillonite and the sites of interlayer and octahedral cations after heating and rehydroxylation. The XRD pattern of the initial samples showed a well-defined (001) reflection according to the interlayer cation and its hydration state under laboratory atmosphere. After dehydroxylation the pattern exhibited (001) reflections between 9.6 and 9.8 Å, corresponding to a collapsed structure for all samples. The Na +-, Ca 2+- and Sr 2+-rich montmorillonites regained partial expandability after rehydroxylation at 200°C and full expandability after rehydroxylation at 300°C if the dehydroxylation temperature was less than 630°C. Rehydroxylation at 300°C of the Cu 2+- and Zn 2+-rich montmorillonites did not cause reexpansion, whereas the Li +-rich samples recovered a partial swellability after rehydroxylation at 240°C and nearly the full swellability after rehydroxylation at 300°C. The Li +-, Cu 2+- and Zn 2+-rich samples underwent a strong CEC reduction due to migration of the interlayer cations into the 2:1 layer before dehydroxylation started. After rehydroxylation under water steam Cu 2+- and Zn 2+-rich samples released 16–30 meq/100 g of Mg 2+ from the structure, increasing with the steam temperature. Mg 2+ release was not observed for the Li +-rich montmorillonite.

Agricultural sustainability under small-holder farming in Kano, northern Nigeria

The agricultural sustainability of small-holder agriculture in semi-arid northern Nigeria was assessed. Topsoil (0–30 cm) samples from cultivated and uncultivated soils were analysed for texture, pH, exchangeable cations, cation exchange capacity, organic carbon, total nitrogen, and total and available potassium and phosphorus. Comparison of data from cultivated and uncultivated soils revealed that cultivation led to losses of fine soil particles, organic carbon and total nitrogen as well as a reduction in cation exchange capacity and available water-holding capacity. The level of soil clay was shown to have the greatest influence on agricultural sustainability. It is recommended that soil conservation, especially the reduction of soil loss by erosion, should be emphasized in order to enhance agricultural sustainability.

Effect of heating temperature on Li-fixation, layer charge and properties of fine fractions of bentonites

The fine fractions (<2 µm) of four bentonites, in which the dominant minerals were Al-rich montmorillonites of various chemical compositions, have been Li-saturated. The admixtures identified in the fine fractions include pyrophyllite in Otay (USA), amorphous SiO2 in Ivancice (Czech Republic) and opal CT in Sarigus (Armenia) samples, while the Kriva Palanka sample (Macedonia) was a pure montmorillonite. The sample portions were heated at different temperatures (110 to 300°C) for 24 h to promote Li-fixation in the layers in order to reduce the negative charge on the layers in a systematic manner. Hence a series of materials with gradually decreasing charge, cation exchange capacity (CEC) and swelling ability were prepared. The CEC of the prepared samples was affected by the admixtures present and by the extent of Li+ for Ca2+ exchange in the starting material. The largest reduction in CEC (by 81%) was obtained for Otay montmorillonite, the mineral with the lowest tetrahedral and the highest octahedral charge, heated at 300°C. The extent of Li-fixation was very sensitive to the treatment temperature in the range 110–200°C. The development of uncharged layers with non-swelling interlayers occurred in all materials heated above 150°C. The shift of the OH-stretching band to higher wavenumber and a new band due to an AlMgLiOH stretching vibration in the infrared spectra confirmed the penetration of Li into the previously vacant octahedral sites.

Dehydroxylation Behavior of Heat-Treated and Steam-Treated Homoionic cis-Vacant Montmorillonites

AbstractLi+, Na+, Ca2+, Sr2+, Cu2+, or Zn2+-saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200–700°C. Half of each heated sample was subsequently autoelaved under steam at 200°C (∼1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer.Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li+, Cu2+, and Zn2+ ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu2+ and Zn2+-rich samples release 16–23 meq/100 g of Mg2+ from the structure. No Mg2+ release is observed for the Li+-rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu2+, Zn2+, and Li+-rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu2+ and Zn2+-rich smectites show a peak doublet between 480–700°C. For the Li+, Na+, Ca2+, and Sr2+-rich montmorillonites, the second peak disappeared and a third peak at ∼760°C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.

The cation exchange properties and microbial carbon, nitrogen and phosphorus in savanna Alfisol under continuous cultivation

The study reports on the impact of inorganic fertilisers with or without farmyard manure on the cation exchange capacity (CEC), cationic balance and microbial biomass carbon (C), nitrogen (N) and phosphorus (P) in a savanna Alfisol after 45 years of cultivation. Soils for the study were fertilised with N or N + P + K, cow dung (D), D + N and D + N + P + K for 45 years. Inorganic fertiliser significantly reduced CEC, exchangeable cations and upset the cationic balance. The reduction in CEC and exchangeable cations seemed to operate via organic matter depletion and pH reduction. Similarly inorganic fertiliser stressed microbial activity evidenced by the low amounts of microbial biomass C, N and P compared to the soil under native vegetation and the soils fertilised with D + N and D + N + P + K. From the perspective of the flows of C, N and P through soil microbial biomass, and cation exchange properties and prevention of nutritional imbalances involving basic cations, a rational fertilisation program for savanna Alfisols is one that combines inorganic fertilisers with farmyard manures.

The cation exchange properties and microbial carbon, nitrogen and phosphorus in savanna Alfisol under continuous cultivation

The study reports on the impact of inorganic fertilisers with or without farmyard manure on the cation exchange capacity (CEC), cationic balance and microbial biomass carbon (C), nitrogen (N) and phosphorus (P) in a savanna Alfisol after 45 years of cultivation. Soils for the study were fertilised with N or N+P+K, cow dung (D), D+N and D+N+P+K for 45 years. Inorganic fertiliser significantly reduced CEC, exchangeable cations and upset the cationic balance. The reduction in CEC and exchangeable cations seemed to operate via organic matter depletion and pH reduction. Similarly inorganic fertiliser stressed microbial activity evidenced by the low amounts of microbial biomass C, N and P compared to the soil under native vegetation and the soils fertilised with D+N and D+N+P+K. From the perspective of the flows of C, N and P through soil microbial biomass, and cation exchange properties and prevention of nutritional imbalances involving basic cations, a rational fertilisation program for savanna Alfisols is one that combines inorganic fertilisers with farmyard manures. ©1997 SCI