Sara Molaali abasiyan; Farahnaz Dashbolaghi; Gholamreza Mahdavinia
Abstract
Introduction: Due to the negative effects on human being health, the decrease of cadmium bioavailability in waters and soils is necessary. The main origins of cadmium ions in environment consist of batteries, phosphate fertilizers, mining, pigments, stabilizers, and alloys. Many methods such as ion exchange, ...
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Introduction: Due to the negative effects on human being health, the decrease of cadmium bioavailability in waters and soils is necessary. The main origins of cadmium ions in environment consist of batteries, phosphate fertilizers, mining, pigments, stabilizers, and alloys. Many methods such as ion exchange, chemical precipitation, flotation, ultrafiltration, nanofiltration membranes, reverse osmosis, and electrocoagulation have been used for the removal of cadmium. Notably, adsorption is proven the most practical technique for heavy metal ions removal of pollutants from wastewater and contaminated soils. Among the various adsorbents, chitosan has introduced to be an efficient one, due to its unique characteristics such as antimicrobial activity, biocompatibility, non-toxicity, and being low-cost bio-adsorbent. Chitosan is a derivative of N-deacetylated of chitin, a naturally occurring polysaccharide taken from crustaceans i.e. shrimps and crabs, and fungal biomass. The presence of amine and hydroxyl groups in the backbone of chitosan gives the polymer its high binding capacity in adsorption processes. Chitosan can decrease the metal ion concentration to near zero. This work evaluates the modified chitosan’s potential as a bio-adsorbent in the water system and also its potential as a soil amendment in the soil system in terms of the adsorption and desorption of Cd2+. It is also worth noting that there is no report on the removal of cadmium ions by ionically crosslinked chitosan/κ-carrageenan materials, especially in soil systems.
Materials and Methods: The chitosan-based magnetic bio-adsorbent was prepared through in situ co-precipitation of iron ions in the presence of chitosan with high molecular weight. The surface (0-30cm) soil samples were collected from a field in University of Maragheh in the North East of Iran. Some physio- chemical properties of the soil used in this study were determined. Adsorption of cadmium on the bio-adsorbent was investigated using batch experiments. After adsorption, the adsorbent loaded with cadmium ions was washed with distilled water before treating it with 90 ml of 0.1M ethylenediaminetetraacetic acid (EDTA) for the determination of the metal desorption. The experimental data of Cd2+ adsorption and desorption isotherm were fitted by Freundlich and Longmuir models.
Results and Discussion: The crystalline nature and phase analysis for pure chitosan and magnetic chitosan bio-adsorbent was confirmed by XRD analysis. The diffractogram of chitosan consisted of two typical crystalline peaks at 2θ= 10.8A° and 20.42A°, corresponding to the partial crystalline structure of chitosan and the hydrated crystals of the remained α-chitin chains in pure chitosan, respectively. The characteristic peaks of chitosan in the XRD pattern of the magnetic bio-adsorbent disappeared, indicating of the amorphous structure of chitosan. It suggests that the addition of magnetite nanoparticles obviously affects the crystallinity of chitosan. On analyzing the values of r2 and RMSE obtained using Freundlich and Langmuir models, it was observed that Freundlich model provided the best fit for the experimental adsorption and desorption data at the ranged of the Cd2+ concentration studied in the soil and water systems. To evaluate the efficiency of the modified chitosan as an efficient bio-adsorbent in water and soil system, the difference between adsorption and desorption amounts, Δq, was calculated. The less amounts of Δq, the more efficient adsorbent in a water system. This means that the adsorbent can be reused several times. In contrast, in a soil system, a positive relationship was found between the amounts of Δq and the efficiency of the adsorbent. This means that the adsorbent can immobilize the adsorbatesand therefore, may be used as a metal immobilizing amendment in soil. As the initial concentrations raised, the amounts of Δq increased in the water system; therefore, it seems that the bio-adsorbent may not efficient at high initial concentrations. In the soil system, the more amounts of Δq decreases, the more efficiency of the adsorbent as a cadmium immobilization increases. Therefore, the bio-adsorbent used can be relatively efficient as a soil modifier.
Conclusions: The results revealed the magnetic bio-adsorbent based on chitosan can be sorb Cd2+ from water and soil systems. The maximum adsorption capacity (b) of cadmium onto the adsorbent appeared to increase from the water system to the soil system, from 750.2 to 992.7 µmol/g, respectively. On analyzing the values of r2 and RMSE obtained using Freundlich and Langmuir models, it found that Freundlich model provided the best fit for the experimental adsorption and desorption data at the ranged of the Cd2+ concentration studied in both water and soil systems. By comparing the amounts of Δq, the difference between adsorption and desorption amounts, the bio-adsorbent is not economically feasible at high initial concentrations in the water system. But, the more decrease amounts of Δq in the soil system, the more increase efficiency of the adsorbent as a cadmium immobilization. So that, the bio-adsorbent used can be relatively economic as a soil modifier.
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.
