Adsorption of diquat, paraquat and methyl green on sepiolite: experimental results and model calculations

Adsorption of the divalent organic cations paraquat (PQ), diquat (DQ) and methyl green (MG) on sepiolite was determined experimentally and investigated with an adsorption model. The largest amounts of DQ, PQ and MG adsorbed were between 100% and 140% of the cation exchange capacity (CEC) of sepiolite. In previous experiments with monovalent organic cations (dyes), the largest amounts of dyes adsorbed were about 400% of the CEC of sepiolite. Consequently, it was proposed that most of this adsorption was to neutral sites of the clay. The large differences between the adsorption of these divalent organic cations and the monovalent dyes may indicate that there is almost no interaction between DQ, PQ and MG and the neutral sites of sepiolite. This assumption was confirmed by infrared (IR) spectroscopy measurements, that did not show changes in the peaks arising from the vibrations of external Si---OH groups of the clay when the divalent organic cations were added. Adsorption results were compared with calculations of an adsorption model that combines the Gouy–Chapman solution and specific binding in a closed system. The model considers cation adsorption on neutral sites of the clay, in addition to adsorption to mono- or divalent negatively charged sites, forming neutral or charged complexes. The model could adequately simulate the adsorption of the divalent organic cations DQ and PQ when added alone, and could yield good fit for the competitive adsorption experiment between the monovalent dye methylene blue and DQ. In competitive adsorption experiments, when total cationic charges exceeded the CEC, monovalent organic cations were preferentially adsorbed on the clay at the expense of the divalent cations.     

Adsorption of difenzoquat on montmorillonite: model calculations and increase in hydrophobicity

The adsorption of difenzoquat (DZ) on montmorillonite was studied at a wide range of concentrations and ionic strengths. Up to difenzoquat loadings of 0.4 mmol/g clay, all the added cation were adsorbed. Maximal adsorbed amounts exceeded slightly the cation exchange capacity (CEC) of the clay (0.8 mol_c/kg). The adsorbed amounts did not change upon increasing the concentration of NaCl in the medium to 500 mM. An adsorption model that combines electrostatic equations with specific binding in a closed system could adequately predict the adsorbed amounts of DZ, even at high ionic strength. Simultaneous adsorption of the divalent cationic herbicide diquat (DQ) and DZ was also determined and the predictions of the model were adequate for total loadings up to the CEC of the clay. At higher loads the model adequately predicts the DZ adsorbed, but underestimates the amounts of DQ adsorbed. The influence of adsorbed DZ on the hydrophobicity of montmorillonite was tested by using the hydrophobic herbicide pendimethalin (PM). The adsorption isotherm of PM on crude montmorillonite is of the S type, indicating very low adsorption at low added amounts, and increasing affinity after part of the surface is covered with the hydrophobic molecules. Adsorption of PM on montmorillonite saturated with DZ up to 80% of the CEC showed a C behavior, indicating a partition mechanism between the solvent and the adsorbent even at low added amounts. The enhanced hydrophobicity of DZ–montmorillonite was also demonstrated in qualitative experiments in a mixed chloroform–water environment: whereas the crude clay mineral stayed in the water phase, DZ–montmorillonite concentrated in the chloroform phase.     

Organo-clay formulations of pesticides: reduced leaching and photodegradation

Adsorption of organic cations on several clay minerals is reviewed with an emphasis on the effect of ionic strength and modeling. The clay exchanged with suitable organic cations forms a basis for ecologically acceptable formulations of herbicides with reduced leaching, ground water contamination and enhanced weed control efficacy. Incomplete neutralization of the clay surface charge by an organic cation may be advantageous in achieving maximal adsorption of hydrophobic herbicides. One conclusion from these studies is that optimization of clay-based herbicide formulations requires a selection of structurally compatible organic cations preadsorbed on the clay at optimal coverage. New experimental results are presented for alachlor formulations, which significantly reduce herbicide leaching under conditions of heavy irrigation. We were able to demonstrate that organo-clay formulations of alachlor and metolachlor can increase crop yields in a 1-year field experiment. The photostabilization of pesticides is reviewed and improved organo-clay formulations of the herbicides trifluralin and norflurazon are described. A pillared clay, nanocomposite micro- and/or meso porous material, was effective in reducing leaching and in conferring photostabilization, without added organic cations.     

Fluridone adsorption–desorption on organo-clays

The adsorption–desorption of the herbicide fluridone on Na-montmorillonite and several organo-montmorillonite complexes was studied at a variety of loadings of the organic cation and pH levels. The aim was to find the organo-clay complex, which would be an optimal adsorbent for the hydrophobic fluridone. The organic cations studied were hexadecyltrimethylammonium (HDTMA), benzyltriethylammonium (BTEA), benzyltrimethylammonium (BTMA) and methylene blue (MB) at loadings equal to 25%, 50% and 100% of the cation exchange capacity (CEC) of the clay-mineral. The adsorbed amount of fluridone increased several-fold when montmorillonite was preadsorbed by the organic cation HDTMA up to its CEC and with BTMA at a loading of 5/8 of the CEC. BTEA and MB did not improve the adsorption capacity of the clay for fluridone. The results suggest that interactions between the phenyl rings of the herbicide and that of a small organic cation are geometrically easier to establish than with a larger organic cation. A reduced interaction between the phenyl rings of MB and those of fluridone may account for the low affinity of fluridone adsorption on montmorillonite-MB. In all cases, fluridone adsorption increased with decreasing pH and reached 100% for pH 2.7. Protonation of fluridone molecules with decreasing pH would result in increased adsorption through cation exchange. Thus, by regulating the pH, complete fluridone adsorption can be achieved. Desorption isotherms demonstrate high degree of irreversibility of the adsorption–desorption process and suggest that strong binding mechanisms dominate the fluridone-clay and organo-clay interactions. The results for fluridone adsorption–desorption demonstrate that, for similar molecules, a clay-based slow release formulation can be designed by first lowering the pH.     

Applying a Gouy–Chapman–Stern model for adsorption of organic cations to soils

An effective adsorption model was developed by S. Nir in 1978 for predicting adsorption to synthetic membranes and was also adapted by him afterwards to clay minerals. The main principles of the model are the solution of the electrostatic Gouy–Chapman equations while calculating the adsorbed amounts of the cations as the sum of those residing in the double-layer region and the cations that are chemically bound in a closed system. Thus, the equilibrium concentration in solution is influenced by the adsorption as the function of the amounts bound. The model was later developed and adapted for the adsorption of organic cations, and, in most cases, the fit of calculated results to measured adsorbed amounts of cations was very good, after calibrating the model for the chemical tested, with only two adjustable parameters for each chemical. In the current work, we tested the applicability of this model for the adsorption of a monovalent and a divalent organic cation by several soils, by considering the cation exchange capacities (CEC) and the specific surface areas (SSA) of the soils. For three out of four soils, a very good fit was obtained by using the required parameters for the calculations from previous studies of cation adsorption on clay minerals. The main advantage of the presented model over Langmuir and Freundlich adsorption isotherms is that no additional changes in the parameters were needed when the background concentration of salts in the suspensions was increased from 10 to 50 or 500 mM.     

Interactions of pendimethalin with organo-montmorillonite complexes

Pendimethalin (PM) is a dinitroaniline herbicide, highly hydrophobic and with a very low solubility in water. It is used for pre-emergence weed control, is usually applied before sowing, and mechanically incorporated into the soil. We tested sorption of PM on montmorillonite and on two different organo-montmorillonites in a mixed water–chloroform environment, to determine the feasibility of developing an environmentally oriented formulation of the herbicide. FTIR measurements show that the interactions of PM with montmorillonite on which difenzoquat (DZ) or mepiquat (MQ) were previously adsorbed are via the nitro and methyl groups of the herbicide. The pre-adsorbed organocations cause a dehydration of the interlayer space, leading to hydrophobicity of the organoclay. Changes in the electrokinetic surface charge of the organoclay, measured using a particle charge detector, confirm these results. The high affinity to PM and the hydrophobic behavior of the used organoclays were also demonstrated in experiments using a mixed chloroform–water environment. The crude clay mineral stayed in the water phase, whereas DZ- and MQ-montmorillonites concentrated in the PM-chloroform phase. Amounts of PM adsorbed to the organoclays using this method were very high (up to 0.65 mol PM kg⁻¹ compound), which suggests a very efficient technology of preparation of herbicide-clay formulations, compared with techniques used in the past for similar herbicide-organoclay compounds. Plant experiments using the organoclay-herbicide formulation with higher amount of active ingredient (based on DZ-clay) demonstrate efficient herbicidal activity with 30% less active ingredient.     

Reduction of photodegradation and volatilization of herbicides in organo-clay formulations

The use of commercially available emulsifiable concentrate (EC) formulations of alachlor and metolachlor may be an environmental hazard because of their volatilization to the atmosphere and photodecomposition, which requires increased applied amounts. The objectives of this study were to develop organo-clay based formulations which would be less volatile and better protected from photodegradation. Bioassays have shown that the use of organo-clay formulations improves photoprotection, reduces volatilization and maintains herbicidal activity in the soil under laboratory and field conditions. Largest adsorption of herbicides by organo-clays correlates with an optimal reduction of photodecomposition and volatilization. It appears that the role of the organic cation, e.g., benzyltrimethylammonium (BTMA) is to enhance the adsorption of the non-polar herbicides to the organo-clay complex, whereas the actual photoprotection is mainly provided by the clay.     

SPAD值在内吸传导型除草剂药效评价中的应用

[目的]绿色植物叶片SPAD值与植物的生长状态密切相关,研究除草剂作用后杂草叶片SPAD值的变化规律以及叶片SPAD值与除草剂对杂草防除效果的关系,对于除草剂药效评价具有重要的意义。[方法]采用室内生测法,选用3个内吸传导型除草剂设置5个试验剂量,分析不同处理下稗草和金色狗尾草叶片SPAD值与目测防效和杂草地上部鲜质量的相关性,研究杂草叶片SPAD值与除草剂对其防除效果的相互关系。[结果]同一种内吸传导型除草剂不同剂量处理供试杂草,经过吸收反应,使用剂量越高杂草叶片SPAD值越低;相同剂量的不同内吸传导型除草剂处理供试杂草,经过吸收反应,其对杂草的相对防除效果越好杂草叶片SPAD值越低。[结论]除草剂作用后,杂草叶片SPAD值与防除效果负相关,SPAD值可用于内吸传导型除草剂药效评价。     

世界除草剂的发展及趋向——兼介我国有发展前途的新除草剂

除草剂是当今最大的农药市场，也是衡量一个国家农药水平的尺子。在目前的农药市场中，传统除草剂仍是除草剂市场的主体。近年来，非选择性除草剂出现了迅速的发展。然而，新的除草剂仍在不断诞生，这是由于对除草剂作用机理的成功研究促进了新除草剂的开发。     

Formulation of muds for pelotherapy: effects of “maturation” by different mineral waters

Spa centres in northern Italy use clayey admixtures for the formulation of muds to be used in pelotherapy. The basic ingredient (“virgin” clay) is a dressed bentonitic geomaterial with mineralogical composition: smectite 60–70%, illite 5–10%, kaolinite 10–15%, quartz 5–10%, calcite 5–10% and feldspars 2–3%.The peloid muds are obtained by “maturation” of the virgin clay with mineral waters gushing out in situ which have different geochemistry: sulphureous, Ca-sulphate, Ca–Mg-sulphate and Br–I-salty (after the Italian regulation DPR 105/92). The maturation treatment is varying with respect to the mixing procedure and lasting time.Peculiar parameters have been tested to verify the effects of various maturation treatments, i.e., changes with respect to virgin clay.Formation of organic matter is due to the presence of microorganisms and algae in the maturation habitat. The <2 μm fraction is generally decreased due to clay particles agglomeration. Mineralogical changes are mainly concerning the degradation of clay minerals, as smectite and illite, and subordinately to the dissolution of calcite. Cation exchange capacity (CEC), soluble salts, water retention, swelling index, activity, consistency parameters (WL, WP and PI), thermal behaviour and cooling kinetics are influenced by the geochemistry of mineral waters used for the maturation treatments but with some opposite trends for Br–I-salty water, and for sulphureous and Ca-sulphate waters, respectively.Noteworthy was the influence of high-pH value of the virgin clay on the pH of peloid muds (in fact, the pH of the used mineral waters is ranging around the natural value). Furthermore, the temperature reached by the peloid muds after 20 min of application (calculated after an innovative mathematical model) is influenced by water retention. An increase in plasticity index and a slower cooling are considered to improve the quality of the obtained peloid muds for pelotherapy.The observed different cation exchange behaviour and soluble salt content could be discriminant for either dermatological masks or thermal body cataplasms.A need of regulation (standard procedures) is suggested to certificate the clay geomaterials suitable for pelotherapy and also for drugs formulation.     

以微生物代谢物进行除草剂开发的研究进展

概述了以微生物代谢产物进行除草剂研究的主要方向,即以下5个方面:筛选微生物从中分离具有除草活性的新化合物;对高除草活性的微生物菌株的市场化研究;对微生物源高活性化合物的全合成或结构改造;对微生物源除草活性系列化合物的构效关系研究;对天然除草活性化合物的作用机制研究。这些研究表明,以微生物代谢物进行除草剂的研究仍将是除草剂开发的一个重要热点。     

Entrapping pesticides by coagulating smectites

Highly delaminated montmorillonite (from Wyoming) with a high specific surface area when dispersed in water was used as an adsorbent of the hydrophobic herbicide metolachlor. The montmorillonite was coagulated with Na⁺, Ca²⁺, Al³⁺ and benzyl trimethylammonium ions. Ca²⁺ and Al³⁺ screened the surface charges and the adsorption of metolachlor was strongly enhanced by the interaction of metolachlor with the hydrophobic siloxane oxygen atoms and the water molecules of the hydration shell of the interlayer cations. With increasing salt concentration the mechanism changed from a cooperative adsorption process on a heterogeneous surface (S-type isotherm) to adsorption on a homogeneous surface (L-type). Coagulation with Ca²⁺ and Al³⁺ increased the amounts of metolachlor adsorbed from 14–41% (Na⁺) to 57–86% (Ca²⁺) and 67–91% (Al³⁺). The light microscopic images revealed that increasing amounts of metolachlor changed the band-type network into spherical “potato-like” aggregates. The enhanced herbicide adsorption hydrophobized the particles that crowded together to form spherical aggregates. Entrapping the herbicide molecules in clay mineral aggregates—either band-type networks or spherical aggregates—offers a useful tool in creating leaching-resistant herbicide formulations.     

Cation exchange capacity methodology II: A modified silver–thiourea method

The silver–thiourea method for the determination of the cation exchange capacity (CEC) has been critically examined. The chemical instability of the exchange solution used causes silver sulphide precipitation on the walls of tubes resulting in a loss of the index cation. This produces misinterpretation and yields usually in an overestimation of the CEC. Furthermore, when expandable clay minerals are investigated excess adsorption occurs leading to unreliable CEC results dependent on solution/solid ratio and ionic strength of the exchange solution. A modified silver–thiourea method is proposed, which uses a chemically more stable exchange solution, eliminating silver sulphide precipitation and substantially lowering excess adsorption, which is abolished by additional washings. The results are comparable to the ammonium acetate method.     

Identification of clay minerals in coal and wastes from main coal washery, Zonguldak, Turkey

Identification of clay minerals present in coal and washery wastes is important in cleaning fine coal by froth flotation and in flocculation and dewatering. Therefore samples of wastes from jigs and the flotation cell at the Zonguldak main coal washery were collected and analyzed petrographically for their mineral matter content and by X-ray diffraction for their clay content. The “loss on ignition” method was carried out to determine their organic carbon and carbonates. The waste samples contain 48–68% clay minerals in addition to silicates, carbonates, sulfides and coal. Three clay minerals were identified, namely illite, kaolinite and chlorite. Illite seemed to be the dominant clay mineral in washery wastes. Loss on ignition indicated high percentages of organic matter in the fine jig tailings (21%) and flotation tailings (33%). 3%–6.5% of carbonates have also been found.     

Strategies for the successful preparation of homoionic smectites

Many chemical, mechanical and thermal properties of smectites depend on the interlayer cations. Therefore, homoionic exchanged smectites are prepared in order to investigate the reaction exchange mechanisms and to improve their behavior as function of the interlayer cation. Presently no general protocol exists and many of the suggested procedures lack proof of achieved exchange. Thus, the aim of the present study was to depict strategies and to determine factors for successful preparation of homoionic smectites. Three natural bentonites and one purified bentonite were saturated by different compensator cations using different (Na⁺, Li⁺, K⁺, Ca^2 +, Mg^2 +, Cu^2 +, or Zn^2 +) chloride solutions. Concentration of the cations in solution varied between 1 and 20 times of CEC. The exchange was repeated one to three times. Extent of smectite interlayer saturation was studied by measurements of cation exchange capacity (CEC) and subsequent determination of the exchanged interlayer cations.Chemical properties of used solution salts influence pH and the surface properties of the smectites. As a result CEC of the smectites was altered by changing contribution from edge charges. It is established that divalent cation exchange was more successful than monovalent cation exchange (Bergaya et al., 2006). Moreover, fractions of high charged 2:1 layers could also hinder homoionic exchange. Finally, successful cation exchange reaction was strongly influenced by soluble accessory minerals and experimental setup.It was found that there is no simple recipe which is equally applicable for all smectites and bentonites, but there is a general protocol considering the following parameters: mineral composition of the sample, smectite CEC and/or layer charge, chemical and mechanical pretreatment, initial interlayer cations, type and concentration of saturating salt, solid–liquid ratio, reaction time, number of repetitions and washing procedure. Finally, proof of interlayer occupation is mandatory.     

Cation exchange capacity methodology I: An efficient model for the detection of incorrect cation exchange capacity and exchangeable cation results

In this study a model is proposed enabling the detection of incorrect cation exchange capacity (CEC) and exchangeable cation values. Numerous CEC and exchangeable cation analyses of clayey sediments, soils and bentonites were performed using triethanolamine-buffered barium chloride, ammonium acetate, silver thiourea and other exchange techniques. As long as these naturally clayey materials only contain adsorbents like clay minerals, organic substances and a group of mainly detrital minerals like quartz, feldspar and mica, results obtained with most procedures are correct. Problems arise when materials contain secondary phases like soluble Ca-carbonates and -sulphates. During the CEC-experiments, these phases interact with the exchange solution. According to expectations, results of exchangeable calcium values are incorrect but CEC is also affected [Deller, B., 1981. Determination of exchangeable acidity, carbonate ions and change of buffer in triethanolamine-buffered solutions percolated through soil samples containing carbonates. Commun. Soil Sci. Plant Analysis 12, 161–177.]. Using the proposed Carbonate and Sulphate Field Model (CSF model) an evaluation of the accuracy of results is possible.     

蒈烷-3, 4-二醇的除草活性

采用平皿培养法考察蒈烷-3, 4-二醇在水溶液中对一年生黑麦草和油菜根、茎伸长的抑制作用, 探讨其作为水基除草剂的应用潜力。结果表明: 蒈烷-3, 4-二醇微溶于水, 可在少量亲水性有机溶剂和表面活性剂作用下配制成浓度大于20mmol/L水乳液, 能够抑制黑麦草和油菜根、茎的伸长, 表现与浓度相关的除草活性, 对黑麦草的根、茎伸长的半数抑制浓度(IC₅₀)分别达到1.12和1.73mmol/L, 而对油菜根、茎伸长的IC₅₀分别达到1.23和2.12mmol/L。其除草活性明显高于天然单萜二醇对孟烷-3, 8-二醇, 而稍低于商业除草剂草甘膦, 有望进一步研究开发作为水基植物源除草剂。     

Abrasivity by bentonite dispersions

Bentonites are used for various industrial applications. Their physicochemical properties depend on the mineralogical and chemical composition, the type of smectite, the grain size distribution, the cation exchange capacity (CEC), the dominant interlayer cation (Na⁺, Ca²⁺, Mg²⁺), and the layer charge density. All these parameters can be measured with acceptable precision. Nevertheless, the performance of a bentonite in a given application is often unpredictable. An additional relevant parameter is the “microfabric” describing the arrangement of minerals and/or the intergrowth of the minerals with glass. The microfabric is supposed to affect different bentonite properties such as swelling capacity and rheology. The present study focuses on the influence of different microfabrics on the abrasivity by bentonite dispersions.The abrasivity of bentonite dispersions mainly depended on two factors: 1) on the amount of hard and sharp accessory minerals and volcanic glass and 2) the grain size distribution, which was produced by different grinding techniques. The abrasivity increased with decreasing grain size, which was caused by breaking the hard components (minerals and glass) leading to an increased number of sharp edges.In addition, there was evidence for a subordinate influence of the type of exchangeable cations. This influence is explained by the different relative arrangements of smectite particles towards the surfaces of hard and sharp minerals. Na⁺ exchanged glass rich samples showed higher abrasion values than the Ca²⁺ exchanged samples.     

Adsorption of berberine on commercial minerals

There is interest in studying interactions between organic modifiers and raw commercial clays aiming the production of low-cost “organoclays”. In this study we report the interaction between berberine — a monovalent organic cation — and three commercial bentonites and a Turkish zeolite. The Turkish zeolite exhibited adsorption at values of 5–10% of the cation exchange capacity (CEC) with no neutralization of the particles. Adsorption of the organo-cation on Egyptian bentonite, Volclay KWK and Pure-Flo B80, was above the CEC of the bentonites, yielding neutral and even slightly positively charged particles. Electron microscopy and X-ray diffraction results showed expansion of the basal spacing of the smectite. Such low-cost organo-bentonites might be suitable for environmental applications as removal of pollutants, drug and pesticides delivery, or water treatment. Application in turbidity reduction of industrial effluents is demonstrated.     

The Effect of Lithium on the Cation Exchange Behaviour of Crystalline and Amorphous Clays

The amount of cations displaced by LiCl—LiOAc from standard clay minerals and soil clays was dependent on the concentration and pH of the replacing solution. Lithium was more effective in replacing monovalent ions than ammonium. Appreciable quantities of Li were adsorbed by replacement on the broken bonds of the clay surfaces, especially in the amorphous clays. Certain montmorillonite clays fixed some of the sorbed Li. In general, the cation exchange behaviour was highly dependent on the structure of the clay mineral and the nature of its surface. The sum of displaced cations can be taken as representing the exchange capacity of the clay at the experimental conditions, while the amount of retained Li provides supplemental information on the nature of the bonds.