F. Hashemzadeh; S. Parsa
Abstract
Introduction: Increasing freshwater consumption caused to reduce renewable freshwater resources in recent years, and one of the basic strategies would be use of non-conventional water resources. Arsenic is one of the natural elements widely distributed in the Earth’s crust. It is commonly found ...
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Introduction: Increasing freshwater consumption caused to reduce renewable freshwater resources in recent years, and one of the basic strategies would be use of non-conventional water resources. Arsenic is one of the natural elements widely distributed in the Earth’s crust. It is commonly found in compounds with oxygen, chlorine, or sulfur, which generally contain inorganic arsenic compounds. Arsenic organic compounds also contain hydrogen and arsenic carbon. There are several methods that can limit the amount of arsenic in water and wastewater; one of these methods is surface adsorption. In this process, any solid that tends to absorb the fluid environment on its surface is considered as an adsorbent. Absorption capacity, selectivity, reproducibility, kinetics, compatibility, and cost are the most essential characteristics of the adsorbent. Materials and Methods: In this study, activated carbon derived from agricultural waste was used as tertiary treatment. The heated coal powder used in this study was obtained from the almond and walnut peel waste (from Tuyserkan city of Hamedan province). Activated carbon powder was used in laboratory-scale experiments and was performed for arsenic removal from synthetics samples. Physically activated carbon was obtained and then chemically activated by acidification. Characterization tests (i.e., XRD, FT-IR, BETand SEM tests) were carried out on both types of the adsorbent. Arsenic removal was carried out in batch experiments. The effect of laboratory parameters (i.e., contact time, pH, adsorbent dose, and initial concentration) on the removal process was studied. Experiments are carried out step by step, and after optimizing each parameter and keeping the other parameters constant, all the parameters are optimized accordingly. Results and Discussion: The contact time for the adsorption process was considerably decreased in comparison with previous studies. Kinetic and equilibrium studies showed that the adsorption process followed by Langmuir isotherm and second-degree kinetic models. Chemical activation, improved performance, and characteristics of the adsorbent. Acidified charcoal and raw charcoal were compared, and it was found that acidic charcoal had the finest cavities and had a uniform distribution. Although the volume of the cavities has not changed significantly, the structure of the cavities has changed substantially, with the most enormous volume of cavities (0.5 cm3 / g) being less than 5 nm in diameter and the average diameter of the cavities Decreased by 2 nm. According to the results of the Coal Structure Morphological Survey (SEM), in crude coal, the cavities have large openings. Their number is small, but in acidified coal, the number of cavities is increased, and the surface area of the coal is high. The high internal surface area and the presence of microstructural cavities lead to high adsorption of arsenic at the acid-adsorbed sites. With increasing contact time from 0 to 3 minutes, the removal rate of arsenic increases, and after 3 minutes to 10 minutes, it grows with a low gradient and then the removal percentage slightly. In other words, after 10 minutes, there is a balance between the solid and liquid phases. The arsenic removal rate reaches 90% at the third minute and 100% in approximately 13 minutes. As the retention time increases, the contact time of the arsenic with the adsorbent increases, and the adsorption rate increases as the opportunity for contact with the adsorption sites increases. Due to the high specific surface area of the adsorbent and its morphological characteristics, the removal rate reaches 100% with time. Conclusion: The XRD experiment shows that improved coal is closer to the stable structure than the raw coal. According to the FT-IR experiment, the acidified charcoal decreased the oxygen and aliphatic functional groups and increased the hydrophobicity of the charcoal. The BET experiment revealed that the cavity surface size increased, and the cavity diameter decreased. The cavity distribution was such that the largest volume of cavities was in the range of nanomolecular size. The SEM image also shows an increase in the fine cavities. As a result, the adsorbent has a good morphology and reduces the adsorption time. Also, its special surface is high and has uniform cavities distribution, which can be one of the main causes of high removal percentage. The results showed that at concentrations of less than 120 µg / L and 10 min retention time, the removal rate was 100%. At higher concentrations, drinking water standards can be reached by increasing the retention time or adsorbent dose. The rate of uptake depends on both the concentration of arsenic and the amount of the adsorbent
H. Hosseini; M. Fekri; Mohammad Hady Farpoor; M. Mahmoodabadi
Abstract
Introduction: The availability of the applied phosphorus (P) is controlled by sorption-desorption reactions in soil. Since the sorption-desorption reactions are affected by physical and chemical properties of the soil, the presence of organic matter (OM) and carbonates can also effect on the ...
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Introduction: The availability of the applied phosphorus (P) is controlled by sorption-desorption reactions in soil. Since the sorption-desorption reactions are affected by physical and chemical properties of the soil, the presence of organic matter (OM) and carbonates can also effect on the P sorption capacity in soil. The purpose of this study was to investigate the effects of OM and carbonates on phosphorus sorption isotherms in some calcareous soils of Kerman province.
Materials and Methods: Six surface soil composite samples (0-30) were collected from Kerman Province located in southeast of Iran. The soils with a wide range of OM and calcium carbonate were selected for sampling. Samples were air dried and passed through a sieve of 2 mm. Physicochemical properties of the soil samples were determined according to the Soil Survey Laboratory Manual. Thereafter, the soil samples were divided into three parts. One portion was used for treatment with sodium hypochlorite to remove organic matter. The second part was treated with sodium acetate buffer (pH = 5) to remove carbonates. The third was used as a control without any treatment. Batch experiments were carried out to determinthe P-sorption isotherms in soil. The sorption behavior of P was studied by Langmuir and Freundlich isotherm models. All experiments were conducted in three replications.
Results and Discussion: The results showed that organic matter and equivalent calcium carbonate, removed from the studied soils with an average efficiency of 86.7% and 84.9%, respectively. Although the isotherms data showed that both Langmuir and Freundlich equations fits to data,Langmuir equation with higher mean of correlation coefficient (R2=0.982) and lower standard error (0.022) showed the best fit to P-sorption data for all soil samples (with and without treatment). Removal of organic matter by sodium hypochlorite increased the phosphorus adsorption capacity in the studied soils. After removal of soil organic matter, an increase in phosphorus adsorption capacity in the studied soils. With respect to control, removing the organic matter increased the adsorption capacity parameters (qmax and kf) about 37 to 104 mg.kg-1 and 11 to 23 L.kg-1, respectively. These results indicate that Fe- and Al-oxides and other available adsorption sites on the mineral surfaces are coated by organic matter and are activated after removal of OM. Removal of carbonates from the soil significantly reduced the P-sorption capacity. qmax and kf were decreased by 17% and 32%, respectively, compared to untreated soils. It is, therefore suggested that available P adsorbing surfaces decreases by removing carbonates from the soil.Constants related with bonding energy increased by 17.03% and decreased by 28.78% by removal of OM and calcium carbonate, respectively. The P maximum buffering capacity is an important indicator for assessing phosphorus stabilization capacity in soil. The greater P buffering capacity, the fewer ability of phosphorus replacement to soil solution. After removal of carbonates, this parameter decreased by an average of 42.5%. The results suggested that carbonates is an important factor in availability of phosphorus in soil. The required phosphorus standard increased by 14.43% by removing OM in the studied soils. However, the removal of carbonates reduced the need of soil for phosphorus by 40.5%.
Conclusion: In this study was investigated the effect of removing organic matter and carbonates on phosphorus sorption isotherms in some calcareous soils of Kerman province. The results of this study showed that P sorption capacity is affected by the amount of carbonates and organic matter. Removal of organic matter from the soil increased the sorption capacity of phosphorus due to Fe- and Al-oxides. Other available adsorption sites on the mineral surface which are coated by the organic matter are active. Carbonates is known as an active site for maintaining phosphorus in the soil and its removal from soils reduces the phosphorus adsorption capacity. Applying/Preserving organic matters to/in soil can increases the efficiency of phosphate fertilizer application and improves plant nutrition. The removal of carbonates from the studied soils reduced their need for phosphorus. Therefore, as well as the addition of organic matter to soil, the removal or reduction of carbonates from agricultural soils is important for improving phosphorus utilization efficiency and plant nutrition management.
Malihe Talebi Atouei; Rasoul Rahnemaie; Esmaiel Goli Kalanpa; Mohammad Hossein davoodi
Abstract
Introduction: Natural environments, including soils and sediments, are open and complex systems in which physico-chemical reactions are in semi equilibrium state. In these systems, bioavailability of plant nutrients, like phosphate, is influenced by environmental conditions and concentrations of other ...
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Introduction: Natural environments, including soils and sediments, are open and complex systems in which physico-chemical reactions are in semi equilibrium state. In these systems, bioavailability of plant nutrients, like phosphate, is influenced by environmental conditions and concentrations of other ions such as calcium and magnesium. Magnesium is a dominant cation in irrigation water and in the soil solution of calcareous soils. Recent evidences show relative increase in the concentration of magnesium in irrigation water. Because of the importance of chemical kinetics in controlling concentrations of these ions in the soil solution and for understanding their effects of adsorption kinetics of magnesium and phosphate ions, in this research, adsorption kinetics of these two ions on goethite is investigated as function of time and pH in single ion and binary ion systems. The experimental data are described by using the adsorption kinetics equations. These data are of the great importance in better understanding adsorption interactions and ion adsorption mechanism.With respect to the importance of these interactions from both economical and environmental point of view, in this research, the kinetics and thermodynamics of phosphate and Mg2adsorption interactions were investigated as function of pH on soil model mineral goethite in both single and binary ion systems.
Materials and Methods: Kinetics experiments were performed in the presence of 0.2 mM magnesium and 0.4 mM phosphate in 0.1 M NaCl background solution and 3 g L-1 goethite concentration as function of pH and time (1, 5, 14, 24, 48. 72 and 168 h) in single ion and binary ion systems. After reaction time, the suspensions were centrifuged and a sample of supernatant was taken for measuring ions equilibrium concentrations.Phosphate concentration was measured calorimetrically with the ammonium molybdate blue method by spectrophotometer (Jenway-6505 UV/Vis). Magnesium concentration was determined by atomic absorption spectrophotometer (AA-670Shimadzu AA/FE). The amounts of adsorbed ions were calculated from the difference of the initial and the equilibrium concentrations. The experimental data were described by using the several widely-used kinetic models. Models performance was evaluated based on their ability to describe experimental data and obtained values for coefficient of determination (R2) and standard error of the estimate (SE).
Results and Discussion: The results demonstrate that phosphate and magnesium adsorption on goethite reached equilibrium within the 24 h equilibration time. The equilibration time is, however, pH-dependent. No systematic differences are observed among time-dependent adsorption isotherms for phosphate at pHpHPZC. It seems that the effect of pH on kinetics of phosphate and magnesium adsorption is related to the mineral surface charge, which influences electrostatic interactions between the ions and the surface charges.thus electrostatic attractive and repulsive forces dominantly control the reaction. The equilibration time for phosphate and magnesium adsorption on goethite was calculated to be ≤1 h when electrostatic forces are attractive and approximately 24 h when electrostatic forces are repulsive. In binary ion systems, phosphate and magnesium enhanced the amount and accelerated the adsorption rate of each other. Adsorption of phosphate could reverse electrostatic forces from repulsive to attractive for the adsorption of magnesium and vice versa. Also, because of the smaller ionic radius of magnesium (0.065 nm) in comparison with phosphate (0.22 nm), reduction in equilibration time of magnesium adsorption in the presence of phosphate could be partly diffusion-controlled. Fitting different kinetic models on experimental data showed that pseudo-second order model can successfully describe phosphate and magnesium adsorption data in both single and binary ion systems with highest determination coefficient (R2~0.99) and lowest standard error of the estimate (SE
Atefeh Amouzadeh; Ahmad Landi; Saeid Hojati
Abstract
Introduction: Adsorption plays a determinant role in the mobility and bioavailability of potassium in soils. Adsorption decreases the solution phase concentration, resulting in very low diffusive fluxes and small transfer by mass flow of soil solution. The K fixation in soils which occurs bytransformation ...
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Introduction: Adsorption plays a determinant role in the mobility and bioavailability of potassium in soils. Adsorption decreases the solution phase concentration, resulting in very low diffusive fluxes and small transfer by mass flow of soil solution. The K fixation in soils which occurs bytransformation of available forms into unavailable ones, influences the effectiveness of fertilization in soil-plant system. Thus, understanding the mechanism that involves adsorption of K in soil is important because soils may contain widely variable pools of K which are potentially mobilized by chemical weathering of soil minerals. The clay minerals types, pH, soil organic matter (SOM), hydroxide aluminum, soil moisture status, cation exchange capacity (CEC), fertilization and tillage system are the major factors affecting the equilibrium. Adsorption sites for K by organic matter are similar to planar surfaces like kaolinite clays. Soil pH has also significant effect on K adsorption as CEC increases with increase in pH. Knowledge about the variation in behavior of K adsorption among different soils is necessary to predict the fate of applied K fertilizers in soils and to make precise K fertilizer recommendations. The objective of this study was to evaluate the effect of soil organic matter and pH on the adsorption of K by three calcareous soils of Khuzestan Province, at southwest of Iran, having different mineralogical properties.
Materials and Methods: Three soil samples (Izeh, Shavour, Ahvaz) were collected from different areas of Khuzestan Province and their physicochemical and mineralogical properties were determined. Potassium adsorption experiments were performed by pouring 2g of each air-dried and Ca+2-saturated soils, with (control) and without (H2O2) organic matter into polyethylene tubes and adding 20 ml of the stock solution of KCl with initial concentrations of 10, 20, 50, 100 and 200 mg l-1 at pH=6 and pH=7.5. The tubes were shaken at 150 rpm for 24h, as the equilibrium time, at 25 ˚C. The pH of the soils was adjusted by application of 0.1 N HCl and NaOH solutions every 4 hours during the shaking period. The soil samples dissolved in potassium solutions (1:10w/v) were centrifuged at 3000 rpm for 15min. Then, the supernatant was filtered through filter paper (Wathman filters No.42) and the potassium concentrations in the supernatants were determined by flame photometer method. The amount of sorbed potassium in soils was calculated with the equation:
(1)
where q (mg kg−1) is the amount of adsorbed K onto soil particles, Co and Ce (mg l−1) are the initial and equilibrium concentration of the potassium in solution, respectively; V is the solution volume (ml), and M is the weight of air-dried soil (kg). The data were then fitted by linear Freundlich and Langmuir models.
Results and discussion: Among the important geochemical properties of soils for the adsorption of cations are the contents of organic matter, pH, clay contents, and cation exchange capacity (CEC). Accordingly, organic matter, pH, clay and cation exchange capacity contents were 3.09%, 7.62, 20.5% and 16.7 cmol (+) /kg for Izeh, 0.79%, 7.52, 50.5% and 11.31cmol (+) / kg for Shavoor soil and 0.95%, 7.15, 20% and 7.39 cmol (+) / kg for Ahvaz soils. The mineralogical experiments showed that the order of dominant clay minerals in the soils are Vermiculite > Illite > Chlorite > in Izeh, Illite >Vermiculite > Chlorite in Shavoor and Vermiculite > Chlorite >Illite in Ahvaz soils. The results indicated that potassium sorption isotherms in the soils are L-type and both Freundlich and Langmuir equations are able (r2>0.9) to explain the results of the potassium adsorption in the soils studied. Potassium sorption capacity of Freundlich equation (kf) and maximum sorption capacity of potassium (a) in Langmuir equation were obtained between 12.47 to 32.59 (l g-1) and 7.50 to 22.13 mg kg-1, respectively at control and 22.34 to 41.16 (l g-1) and 17.81 to 28.59 mg kg-1, respectively at H2O2 treatments. The distribution coefficient is used to characterize the mobility of cations in soil; low Kd values imply that most of the cation remains in solution, and high Kd values indicate that the cation has great affinity for the surface of adsorbents. Mean content of potassium distribution coefficient at Shavoor soil was significantly higher than other soils which can be attributed to the high content of clay minerals such as illite. Moreover, the results indicated that by increasing the pH values of the soils from 6 to 7.5 the adsorption efficiency of potassium in Izeh, Shavoor and Ahvaz soils increased to 38.3, 8.3, and 26.1%, respectively.
Conclusion: Potassium adsorption in soil is affected by content and type of clay minerals. so that the soils with high illite content have more capacity for sorption and fixation of potassium in soil. On the other hand, organic matter removal from soils increased the potassium sorption by mineral components (especially clay minerals) of the soil studied. Moreover, with an increase in soil pH the potassium sorption increased significantly.
F. Zareapour Rafsanjani; M. Hamidpour; Hossein Shirani; M. Heshmati; seyed javad hosseinifard
Abstract
Introduction: Boron is one of the eight essential micronutrients required for plant growth and development. The optimal concentration range (between deficiency and phytotoxicity) for boron is narrower than for other plant essential nutrients. Generally, irrigating water containing concentrations of B ...
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Introduction: Boron is one of the eight essential micronutrients required for plant growth and development. The optimal concentration range (between deficiency and phytotoxicity) for boron is narrower than for other plant essential nutrients. Generally, irrigating water containing concentrations of B greater than 1 mg L-1 would be detrimental for most plants. Although, there are a large number of different studies on the removal of B ions from aqueous solutions using different adsorbents, every special adsorbent material requires individual research. Information about the chemical behavior of muscovite for boron is very limited. Therefore, the objective of this study was to investigate boron adsorption on muscovite as a function of solution pH, ionic strength of the background electrolyte, kinds of cation, and initial boron concentration.
Materials and Methods: The muscovite sample was obtained from a mine near Hamadan city in western Iran. It was powdered in a mortar and sieved before sorption experiment. Boron adsorption experiments were performed in batch systems using 15 mL polyethylene (PE) bottles in 0.01 M Ca(NO3)2 electrolyte solution at a adsorbent concentrations of 10 g L-1, and at room temperature (23±2 ◦C). All samples were prepared in duplicate. Blank samples (without adsorbent) were prepared for all experiments. For pH dependent B adsorption, aliquots of B stock solution (1000 mg L−1) were added to obtain initial B concentrations of 5 and 15 mg L-1. The pH of the solutions were adjusted to values of 6.8, 7.7 and 8.8 by adding negligible predetermined volumes of 0.03M NaOH or 0.03M HNO3 solution. To study the effects of kinds of cation on boron adsorption, samples of adsorbent (0.1 g) were mixed with 10 mL background electrolyte solutions (0.01M Ca(NO3)2, Mg(NO3)2 and NaNO3) in 15 mL centrifuge tubes. Then, predetermined amount of B were added to the centrifuge tubes to obtain final concentrations of 5 mg L-1 B. For determination of boron adsorption isotherm, after 10 ml 0.01 M of Ca(NO3)2 was transferred into 15 ml centrifuge tubes, 0.1 g sample of muscovite was added to obtain adsorbent concentration of 10 g L-1. Then a predetermined amount of boron from the stock solution was added to give final concentration range between 1 and 15 mg B per liter. Initial pH of the solution was adjusted to 8.2 ± 0.1 by predetermined amount of 0.03 M NaOH solution. Suspensions were then shaken for 24h. At the end of equilibrium time, final pH was measured in the suspensions and the tubes were then centrifuged for 10 min at 5000 g. Half of the supernatant volume (5 mL) was pipetted out from each tube and then B in the supernatants were measured using the colorimetric Azomethin-H method. The amount of B adsorbed on the adsorbent was calculated as the difference between the B concentration in the blanks and the concentration in the solution after equilibration. Chemical species in the solutions were also predicted using Visual MINTEQ, a chemical speciation program developed to simulate equilibrium processes in aqueous systems.
Results and Discussion: The effect of pH on the amount of B retained depended on the initial B concentration. The amount of boron adsorption increased with increasing equilibrium pH. Boron adsorption on muscovite increased with increasing ionic strength. Greater adsorption was observed in the presence of Mg2+ as compared with Ca2+ at the same ionic strength. Calculations using Vminteq showed that the concentration of Mg-borate ion pairs (MgH2BO3+) were higher than the concentration of Ca and Na-borate ion pairs (CaH2BO3+ and NaH2BO3°). It thus seems that the much greater loss of B from solution observed in the Mg system was caused by Mg-borate ion pair adsorption. Sorption isotherm of B were well described by the Freundlich, Langmuir and Sips models but the Sips sorption model describes the interaction between B and the mineral better than the Langmuir model. On the basis of n value of Freundlich model, adsorption isotherm of boron on muscovite was classified as L-type (n≤ 1). This kind of adsorption behavior could be explained by the high affinity of the adsorbent for the adsorptive at low concentrations, which then decreases as concentration increases. Maximum sorption capacity (qmax) was obtained to be 13.98 mmol kg-1 for muscovite.
Conclusion: The experimental data showed that less than 5% of initial boron concentration was adsorbed by muscovite, thus this mineral has not a reasonable adsorption capacity for B.
Keywords: Boron, Adsorption, Muscovite, Speciation.
