The kinetics of release of heavy metal ions zinc, lead, nickel, copper and cadmium from the depth of 0 to 10 cm of downstream river sediment located in Hamedan Province, polluted with nitrate salt of these metals, were studied using the leaching column method. The rate of desorption of heavy metals from polluted sediments was initially rapid and, then, gradually declined over time; the behavior of Pb was different and it was released in a gradual and continuous manner. In general, the release of heavy metals from clayey sediments polluted by an inorganic source conformed to a two-site model of first order kinetics; however, the release of Zn, Cd and Pb from sediment (1) and Pb from sediment (2) could also be adequately accounted for by a single-site model. The average coefficients of determination and RMSE for metals in the first order kinetics were 0.905 and 0.054 for a single-site model and for a two-site model were 0.986 and 0.046, respectively. Considering the total heavy metal content of sediments, the cumulative quantity of leached metals was low, indicating a high retention capacity of the sediments for heavy metals. This statement can be elucidated by the low values of the apparent coefficient of desorption in the first order kinetics model.

Mucoadhesive disc is one of the various routes of drug delivery for curing buccal disease.
Everydiscs containing 70 mg stem bark extract of Ziziphus jujuba were formulated by using Carbopol 934, PVP k30 and gelatin as polymers. Discs were made by granulation and direct compression. Discs were standardized based on the total phenol. Properties such as in vitro and in vivo mucoadhesion, drug release, water uptake, and disintegration were carried out.
Discs showed excellent mucoadhesion and released high amount of the active ingredients (47%) immediately and completed after approximately the first hour. They had a good adhesion in buccal cavity.
This study showed that the kinetics of release of the active substance from the mucoadhesive disc obeyed the zero order kinetic and didn’t follow the fick’s law. The water uptake and dissolution (DS), increased with the passing of time.

Organic acids play an important role in improving the bioavailability of soil nutrients. The objectives of this study were to determine the effect of oxalic acid on the release of soluble, exchangeable and non-exchangeable forms of K from micaceous minerals and potassium feldspars, and also to investigate the trend of K release by time. A laboratory study was carried out using a completely randomized design with two replicates. Biotite, phlogopite, muscovite, Zanjan and Yazd K-feldspars (< 50 μm size) were treated with 0, 10 and 100 mM of oxalic acid solutions for a period of 5 hours and 20, 60 and 90 days. The amount of K was determined by flame photometer. The results indicated that most amount of soluble, exchangeable and no-exchangeable K was released by 100 mM of oxalic acid. The maximum soluble K (0.86 gKg-1) was released from phlogopite, and the maximum exchangeable and non-exchangeable K (1.5 and 29.6 gKg-1, respectively) were released from biotite. Muscovite with 0.19, 0.34 and 1.41 gKg-1 of soluble, exchangeable and non-exchangeable K, respectively, had the lowest release of K among the studied minerals. The kinetics K release from minerals consisted of two phases. The first phase was relatively rapid and then it had a slow rate until the end of the experiment. Given that the applied concentration of organic acid was high, potassium release during the experiment period did not reach the steady state. Therefore, a longer period of release experiment is suggested.

Consequences of heavy metals accumulation in soils are of concern. One way of decontaminating heavy metals from soils is the use of chelating agents، particularly EDTA. In this research، three soils contaminated by Zn، Pb and Cd with total amounts (of these metals) of 10. 5، 55. 8 and 80. 6 mmol kg-1 were collected from the surface layer (0-20 cm) of the lands surrounding a zinc-lead smelting plant in Zanjan province. The release of Zn، Pb and Cd by Na2H2EDTA using a one-step batch method for 180 minutes as well as the effects of EDTA concentration، solution/soil ratio، kinetics of release of metals، changes in pH and concentration of Ca and Fe in extracts were investigated. Results showed that increasing concentration of EDTA raised Zn and Pb release much greater than that of Cd. Furthermore، the orders of the release percentages for the three metals were quite different in the three soils. During the release process، pH of the extracts exceeded 7. 2 and then fixed at about 8. 1. Meanwhile، the average concentration of Ca in extracts became more than 1000 times greater than that of Fe. On average، 96 percent of the extracted Cd was released at less than 30 minutes. This figure was 76 percent for Zn and Pb and the release time were sometimes greater than 30 minutes. Compared to other kinetic models، the kinetic data was best described by simplified Elovich، power function and parabolic diffusion equations. According to the results، release of Cd and Pb from the soils was enhanced by low (5:1) and high (50:1) solution/soil ratios، respectively.

Rhizosphere is a small zone with different biological and chemical properties from bulk soil. In this research، kinetics of zinc (Zn) release was compared in wheat (Rowshan Back Cross) rhizosphere and bulk soil in 10 calcareous soils by using rhizobox at greenhouse conditions. The rhizosphere and bulk soil samples were extracted with DTPA-TEA for 1 to 504 h at 25±1 0C. In addition، available Zn was evaluated by chemical extractions (DTPA-TEA، AB-DTPA and Mehlich 3). Results showed that the amount of available Zn، cumulative released Zn and rate of Zn release in the rhizosphere soils were significantly (p<0. 05) higher than the bulk soils. Power equation was the best descriptive of Zn release in rhizosphere and bulk soils. In addition، parabolic diffusion، first order and simple Elovich equations could be used to describe kinetics of Zn release. The obtained correlation coefficients between wheat responses and characteristics of Zn release showed that higher significant correlations in the rhizosphere soils were found as compared to the bulk soils.

Manganese release kinetics was studied in six composite soil samples by using DTPA as the extracting solution in %35 of saturation moisture and in time range of 0.25- 960 hrs. In all the samples, the release of Mn was initially, relatively fast (with 25 – 55 % of total Mn released during the first 10 hrs), then the rate diminished gradually, approaching zero after a lapse of 720 hrs. Six mathematical equations (zero-order, first-order, second-order, power function, simplified Elovich and parabolic diffusion) were employed to describe and evaluate the kinetics of manganese release. A comparison of the equations, by means of comparing the coefficient of determination (r2) and the standard error of the estimate (SEE) of the equations, indicated that the power function equation best described the kinetics of Mn release, as evidenced by the highest correlation coefficient (r2) along with the lowest value of the standard error of the estimate(SEE).The first-order, second-order, and parabolic diffusion equations, because of their relatively high correlation coefficients and small standard errors, could also be used to describe Mn release kinetics. However, the zero-order and the simplified Elovich equations did not so properly describe manganese release.

Use of organic fertilizers such as vermicompost in agricultural soils with low organic matter content is almost considered as a one way for adding nutrients in these soils. However, application of these fertilizers may affect micronutrient release characteristics. Micronutrient release Kinetics in soils especially in amended soils give information about potential of amended soils to release these elements into solution. Although it is important to study kinetics of micronutrient release from soils to identify soil micronutrients buffering capacity, little attention has been paid to micronutrients desorption rate studies especially in amended soils. The rate of release micronutrients from soil solid phase by considering micronutrients as adsorbed ions or in mineral forms is an important parameter in nutrition of plants by microelements and a dynamic factor that regulates its continuous supply to growing plants; nonetheless, little attention has been paid to micronutrients kinetics inrelease studies.
Material and In this study, kinetics of zinc (Zn) and copper (Cu) were compared in one calcareous soil amended with 0, 0.5, and 1% (w/w) of manure and vermicompost in a completely randomized design and then amended and un-amended soils were incubated at field capacity, for 30 days. After incubation period, amended and un-amended soils were air-dried and were prepared to kinetics study. Kinetics of Zn and Cu release were studied by successive extraction with DTPA-TEA solution. Two grams of the amended and un-amended soils, in triplicate, suspended in 20 ml DTPA-TEA solution were equilibrated at 25±10C for 1, 8, 24, 48, 72, 96, 120, 144, 168, 336 and 504 h by shaking for 15 min. before incubation and 15 min. before the suspensions were centrifuged. Seven drops of toluene were added to each 1000 ml of extractant to inhibit microbial activity. Zinc and copper desorption with time was fitted by using different equations (Zero-order, First-order, Parabolic diffusion, Simplified Elovich, and Power function).
Results showed that released Zn in soils amended with manure and vermicompost compared to control soil significantly increased (p0.05) and released Cu in soil amended with vermicompost decreased significantly (p Our results revealed that the rate of released Zn and Cu in soils amended with vermicompost was lower than the soils amended with manure. In the other words the difference between rates of release constants indicated that Zn and Cu supplying power of the amended soils with manure was higher than amended soils with vermicompost.

Nonexchangeable potassium has a critical role in crops nutrition, therefore the study of nonexchangeable release rate in cultivated lands is necessary. Information about release kinetics of nonexchangeable potassium in Kerman province soils is limited. In this research 15 soil samples were collected from Rafsanjan lands under pistachio trees and mineralogical properties and release kinetics of nonexchangeable potassium using successive extraction with 0.01 M CaCl2 were determined. In order to determine correlation coefficient between the constant rate of kinetics equation and potassium concentration in pistachio leaf, leaf samples were collected from studied sites. Results indicated that montmorilonite, illite and chlorite clays are present in studied region and between kinetics equations including zero order, first order, second order, parabolic diffusion, power function(two constant rate) and elovich, according to R2 and SE values, power function model is able to describe nonexchangeable release rate satisfactorily. Constant rate values for this model varied between 57.83- 107.86. Constant rate of studied equations have not significant correlation with the potassium concentration of pistachio trees. It is recommended that release rate of nonexchangeable potassium be studied with other methods and extractants.

The release rate of non-exchangeable K (NEK) plays a significant role in supplying necessary K for plants, particularly in soils containing K bearing minerals. Information about NEK release rate in Golestan soils is limited. Kinetics of non-exchangeable potassium release, therefore is necessary in management and optimum use of soil resources. Laboratory experiment was conducted on NEK release of saturated soil sample by calcium from 2 to 1844 (h) duration in 12 dominant soil series of Golestan province. Different soils indicated various responses in successive extractions. The rate of K released was lower in CaCl2 than organic acid. The mean of the potassium release by oxalic acid was 2.33 times higher than potassium release by CaCl2. K release was faster in earlier periods in all soils followed with a lower release rate. The Elovich and Parabolic diffusion equations described well the NEK release kinetics by organic acid and power, first order and Elovich equations were suitable to describe the NEK release kinetics for CaCl2, based on their highest coefficient of determination, and their lowest value of the standard error of the estimate. Therefore, NEK release kinetics of soils were found to be influenced by diffusion, indicating that NEK release rate was controlled by K diffusion out of the mineral interlayer.

In this paper, chemically-crosslinked gelatin/chitosan hydrogels containg zinc oxide nanoparticles (ZNPs), were loaded with curcumin (CUR), and their microstructural features, physical properties, curcumin entrapment efficiency, and drug release kinetics were evaluated using scanning electron microscopy (SEM), the liquid displacement method, and UV–Vis spectroscopy. The in vitro kinetics of drug release was also studied using First-order, Korsmeyer-Peppas, Hixon-Crowell, and Higuchi kinetic models. The SEM micrographs confirmed the formation of highly porous structures possessing well-defined, interconnected pore geometries. A significant reduction in the average pore sizes of the drug-loaded hydrogels was observed with the addition of ZNPs and CUR to the bare hydrogels. High value of drug loading efficiency (~ 72 %) and maximum drug release of about 50 % were obtained for the drug-loaded scaffolds. It was found that curcumin was transported via the non-Fickian diffusion mechanism. It was also shown that the kinetics of curcumin release was best described in order by Hixon-Crowell, Higuchi, and Korsmeyer-Peppas models, demonstrating that drug release was controlled by diffusion, degradation, and swelling of the drug carrier. However, lower degree of fitting was observed with First-order kinetic model.