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The adsorption of imidacloprid [1-(6-chloro-3-pyridinylmethyl)-N-nitroimidazolidin-2-ylideneamine] on heat-treated kerolite samples at 110 Celsius (K-110), 200 Celsius (K-200), 400 Celsius (K-400) and 600 Celsius (K-600) from pure water solution at 25 Celsius has been studied. The evolution of the surface properties of the kerolite samples, such as specific surface area and porosity, after heat treatment were analysed. The clays were characterised by using FTIR spectroscopy, X-ray diffraction, thermogravimetric and differential thermogravimetric analysis, surface analysis and Hg porosimetry. The experimental adsorption data points were fitted to the Freundlich equation in order to calculate the adsorption capacities (K[sub f]) of the samples; K[sub f] values ranged from 242 mg kg[sup-1] for the K-110 sample to 1005 mg kg[sup-1] for the K-600 sample. The values obtained for the removal efficiency (R) ranged from 62.8% for K-110 to 87.2% for K-600. The adsorption experiments showed that the stronger the heat treatment, the more effective was the adsorption of imidacloprid from pure water. This work shows the potential use of heat-activated kerolite for the removal of imidacloprid from environmental waters and drinking water resources. [ABSTRACT FROM AUTHOR]

Studies water release kinetics and soil mobility in controlled release of isoproturon from an alginate-bentonite formulation. Preparation and evaluation of controlled-release formulations; Sorption capacity.

Studies the adsorption of paraquat and atrazine from aqueous solution onto two mont-morillonite phosphate cross-linked compounds at different temperatures. Classification of the adsorption isotherms obtained for paraquat on both adsorbents; Affinity of the compounds for the herbicide.

The herbicides diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and atrazine [6-chloro-N2 -ethyl-N4-isopropyl-1,3,5-triazine-2,4- diamine] were incorporated in alginate-based grannies to obtain controlled release (CR) properties. The basic formulation [sodium alginate (14.0 g kg-1)-herbicide(6.0 g kg-1)-water] was modified by addition of sorbents. The effect on diuron and atrazine release rate, caused by incorporation of natural bentonite and humic acid in the alginate formulation, was studied by immersion of the granules in water under static conditions. The release ofthe active ingredient from alginate-based CR granules in water was affected by the addition of natural bentonite, and to a greater extent, by the addition of the humic acid. The water uptake, permeability, and the time taken for 50% of active ingredient to be released into water, T50, were calculated for the comparison of the preparations. Addition of both bentonite and humic acid samples to the basic alginate-based formulation produced the higher T50 values (43.11 and 50.49 d for diuron and atrazine formulations, respectively), indicating a slower release of herbicide. Based on parameters of an empirical equation used to fit the herbicide release data, it appears that the release of diuron and atrazine from the various formulations into water is controlled by a diffusion mechanism. Sorption capacity of the sorbent and the permeability of the formulations (ranging from 3.77 to 20.83 mg d-1 mm-1) were the most influential factors affecting herbicide release. [ABSTRACT FROM AUTHOR]

The mobility of imidacloprid [1-(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazo lidinimine] from alginate-based controlled-release (CR) formulations was investigated in two different soil profiles. In one, a layered bed system simulating the typical arrangement under a plastic greenhouse, which is composed of sand, peat, amended soil and native soil, was used. In the other, the layer containing amended soil was used in order to determine the mobility of the insecticide in a soil system with a low content of organic matter and a high content of clay. Two CR formulations based on sodium alginate (1.87% wt/wt), imidacloprid (1.21%), natural or acid-treated bentonite (3.28%), and water (93.64%) were compared to technical grade imidacloprid. The use of alginate CR formulations produced less vertical mobility of the active ingredient as compared to the technical product. With the technicalgrade product treatment, the total amount of imidacloprid leached from columns packed with amended soil was 82.3% of that applied, whereas for the alginate-based CR formulations containing natural or acid-treated bentonite, the leached percentages were 44.7% and 37.1%, respectively. In the column experiments simulating the layered bed system,no insecticide was found in the leachate when the alginate-based CR formulations containing natural bentonite were used. However, 3% of the applied imidacloprid appeared when the treatment was carried out with technical grade material. Sorption-desorption capacities of the various soil layers for imidacloprid molecules were also calculated using batch experiments. [ABSTRACT FROM AUTHOR]

In order to prepare a formulation to be used for controlled release,imidacloprid was incorporated into alginate granules by using calcium chloride as gellant. The formulation prepared (alginate-imidacloprid-water) was modified by the addition of different sorbents. The effects on release rate of the addition of natural bentonite desiccated at 105 deg.C, untreated, acid-treated with sulfuric acid solutions over a concentration range between 0.5 mol dm-3 and 2.5 mol dm-3 , and a commercial humic acid, were studied by immersion of the granules in water under static conditions. The time taken for 50% of the active ingredient to be released into water, (T50), was calculated from the data obtained. On the other hand, thesorption-desorption processes of imidacloprid from a 0.01 M aqueous calcium chloride solution at 25 deg.C, by natural, acid-treated bentonite samples, and humic acid, have been studied by using batch experiments in order to evaluate the potential of these materials for theirapplication in controlled-release formulations of pesticides. The experimental data have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf). Kfvalues ranged from 1.76 mg kg-1 for the untreated bentonite up to 126.9 mg kg-1 for the humic acid. A correlation study was performed with T50, the surface area (S) and the Freundlich parameter (Kf) of the bentonite samples in order to know the factors that affect release rate of imidacloprid from bentonite granules. A linear correlation of the T50 values and both S and Kf parameters was observed. (C) 1999 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

To evaluate the potential use of two montmorillonite-(Ce or Zr) phosphate crosslinked compounds in removing organic pollutants such as aniline, p-toluidine, and p-acetylaniline from water, adsorption experiments were performed under conditions of varied temperature (288 and 308 K). Adsorption on the montmorflionite-Ce-phosphate compound was best described by a hyperbolic (H-type) isotherm, whereas for the montmorillonite-Zr-phosphate compound, S-type isotherms were obtained forp-toluidine and aniline and L-type for p-acetylaniline. Amines adsorption increases with increasing temperature on the cerium crosslinkedmaterial, while for the zirconium- crosslinked compound, adsorption decreases as temperature increases from 288 to 308 K, possibly due toa mainly physical process. Fourier- transform infrared (FTIR) spectroscopy indicated that at the pH generated by the adsorbents, the protonated species of these amines plays an important role in the adsorption process. X-ray diffraction analysis showed that the aromatic amines are intercalated into the adsorbents. for any given amine, the cerium-montmorillonite adsorbent shows a higher capacity of adsorption compared with zirconium-montmorillonite adsorbent, so it might be reasonably used in removing aromatic amines from water. [ABSTRACT FROM AUTHOR]

To evaluate the potential use of bentonite in removing atrazine [2-chloro-4-ethylamino-6-isopropilamino-1,3,5-tria zineI from water, the adsorption of atrazine on bentonite desiccated at 383 K untreated, and acid-treated with H2SO4 solutions over a concentration range between 0.25 x 103 cmol L-1 and1.00 x 103 cmol L-1, from aqueous solution at 303 K has been studied by using batch experiments. In addition, column experiments were carried out with the bentonite samples treated with the 1.00 x 103 cmol L-1 H2S04 [B-A (1.00)] using two aqueous atrazine solutions at C = 5.91 mg L-1 and C = 9.78 mg L-1 concentrations. The experimental data points have been rifted to the Langmuir equation tocalculate the adsorption capacities (Xm). Values for Xm ranged from 0.07 g kg-1 for the untreated bentonite up to 13.4 g kg-1 for the [B-A (1.00)] samples. The removal efficiency (R) ranged from 2.71% for the B-N up to 83.5% for B-A (1.00). The batch experiments show that the acid-treated bentonite is more effective than the natural bentonite in relation to the adsorption of atrazine. The column experiments show that the B-A (1.00) sample might be reasonably used in removing atrazine, the column efficiency increasing from 47.5% for the C = 9.78 mg L -1aqueous solution of atrazine up to 63.4% for the C = 5.91 mg L-1 one. [ABSTRACT FROM AUTHOR]

Different alginate-based systems of isoproturon, imidacloprid, and cyromazine have been investigated in order to obtain controlled release (CR) properties. The basic formulation [sodium alginate (1.50%), pesticide (0.30%), and water] was modified using different amounts of bentonite and activated carbon. The higher values of encapsulation efficiency corresponded to those formulations prepared with higher percentages of activated carbon, showing higher encapsulation efficiency values for isoproturon and imidacloprid than for cyromazine, which has a higher water solubility. The kinetic experiments of imidacloprid/isoproturon release in water have shown us that the release rate is higher in imidacloprid systems than in those prepared with isoproturon. Moreover, it can be deduced that the use of bentonite and/or activated carbon sorbents reduces the release rate of the isoproturon and imidacloprid in comparison with the technical product and with alginate formulation without modifying agents. The highest decrease in release rate corresponds to the formulations prepared with the highest percentage of activated carbon. The water uptake, permeability, and time taken for 50% of the active ingredient to be released into water, T50, were calculated to compare the formulations. On the basis of a parameter of an empirical equation used to fit the pesticide release data, the release of isoproturon and imidacloprid from the various formulations into water is controlled by a diffusion mechanism. The sorption capacity of the sorbents and the permeability of the formulations were the most important factors modulating pesticide release. Finally, a linear correlation of the T50 values and the content of activated carbon in formulations were obtained.

The knowledge of the adsorption processes of nonelectrolytes from liquid solution on solid materials involves the study of their kinetic and equilibrium aspects as well as the understanding of their thermodynamic functions. However, in most published papers adsorption isotherms are analyzed by using the Giles classification and other proposed equations which are either empirical or based on kinetic or thermodynamic criteria. Our opinion is that both the kinetic and the equilibrium studies must be complementary and that, in general, equations describing the adsorption isotherms come from the kinetic laws governing the different partial processes which determine the global process. These kinetic laws may be derived from single models. In this paper a single model is proposed, which makes it possible to establish a kinetic law satisfactorily fitting a great number of C (concentration) vs t (time) isotherms. This model has been applied to study the adsorption process of prednisolone by six carbonaceous materials from ethanol solution, the specific adsorption rate, and the activation thermodynamic functions being calculated. The results obtained have also been used to analyze the influence of the intraparticle diffusion on the kinetics of the process.