Soil Chemistry and Pollution
Zahra Albozahar; Neda Moradi; ُSaeid Hojati
Abstract
Introduction: Today, water consumption has increased dramatically as a result of technological advancement, extraordinary industrial development and urbanization, which has caused the production of large amounts of toxic waste. Zinc (Zn) is an essential element for plants and humans, however, excessive ...
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Introduction: Today, water consumption has increased dramatically as a result of technological advancement, extraordinary industrial development and urbanization, which has caused the production of large amounts of toxic waste. Zinc (Zn) is an essential element for plants and humans, however, excessive concentrations of zinc can cause problems for humans such as abdominal pain, nausea and vomiting. Zinc is the most toxic pollutant that enters the aquatic system through industrial wastewater. World health organization (WHO) has recommended limit concentration of zinc in drinking water of 5.0 mg L-1. Adsorption is one of the most efficient ways to remove heavy metals from the environment. Clay minerals are one of the good adsorbents for the adsorption of heavy metals due to their large surface areas, high ion exchange capacity and layered structure. Some factors such as temperature, pH, size of adsorbent, type of adsorbent and amount of adsorbent are considered as important factors in controlling the behavior of heavy metals in aqueous solution. The temperature of the solution can increase or decrease the adsorption of elements, which indicates the exothermic or exothermic nature of the surface adsorption reaction. Therefore, this research was carried out with the aim of investigating the effect of temperature on the kinetics and thermodynamics of Zn removal using sepiolite and kaolinite minerals.Materials and Methods: In this research, two clay minerals (kaolinite and sepiolite) in a size of 25-53 µm were used as zinc metal adsorbents. Sepiolite mineral was collected from mines in Fariman region of Razavi Khorasan province and kaolinite was collected from Lalejin in Hamadan province. The kinetics and thermodynamics of Zn absorption from aqueous solutions by sepiolite and kaolinite were investigated. For kinetic studies, 0.1 g of sepiolite and kaolinite adsorbent was poured into a centrifuge tube and 20 ml of Zn solution with a concentration of 50 mg L-1 of zinc nitrate background solution was added to it and at different times (5, 10, 15, 20, 30, 60, 120, 240, 480, 720, 1440 and 2880 minutes) was stirred. The experiment of adsorption kinetics was performed at pH 5 and at a temperature of 25 ± 1 °C. The thermodynamics of zinc adsorption was investigated at temperatures of 25, 35 and 45 ℃. The adsorption behavior of zinc metal by sepiolite and kaolinite minerals was evaluated at different times with pseudo-first-order, pseudo-second-order, Ilovich and intraparticle diffusion kinetic models through non-linear regression and using Solver software. Then, the thermodynamic parameters of adsorption process including: the activation energy (Ea), gibbs free energy (ΔG), entropy (ΔS) and enthalpy (ΔH) were determined.Results and Discussion: The results of this research showed that by increasing the contact time and decreasing the temperature of the solution from 45 to 25 ℃, the amount of Zn adsorption by both minerals increased. Also, the equilibrium time was determined to be 720 minutes. The results showed that the adsorption efficiency decreases with increasing temperature and the highest removal percentage was observed at 25 ℃. Based on the results obtained from the fitting of kinetic models with experimental data, the pseudo-second order model with the highest explanatory coefficient (R2=0.99) was selected as the best model. Adsorption capacity (qe) of Zn estimated from the pseudo-second order model for sepiolite and kaolinite at 25℃ compared to 45℃ decreased by 44.30 and 38.19%, respectively. Also, the amount of Zn adsorption capacity for sepiolite mineral was higher than kaolinite. The activation energy (-9.79 to -23.81 kJ mol-1) revealed the physical adsorption of Zn by sepiolite and kaolinite. The activation energy of Zn adsorption onto the sepiolite (-23.81 kJ mol-1) and Kaolinite (-9.79 kJ mol-1) indicated that Zn was more strongly sorbed by sepiolite than kaolinite. Conclusion: the results obtained showed that sepiolite and kaolinite can be used an adsorbed to remove Zn from aqueous solution with good efficiency and low cost, while sepiolite had higher Zn adsorption capacity compared to kaolinite. Adsorption of Zn decreased with increasing temperature. The optimal temperature in this study for maximum adsorption of Zn by sepiolite and kaolinite was 40℃. Thermodynamic parameters including changes in Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) showed that zinc adsorption process by the studied minerals is an exothermic and spontaneous reaction. As a conclusion, sepiolite has a high potential for remove of Zn from wastewater.
Plant Nutrition, Soil Fertility and Fertilizers
Faranak Ghasemi; ُSaeid Hojati; Ahmad Landi; Roya Zalaghi
Abstract
Introduction Clay minerals are considered as the main source of ion exchange and storage of nutrients in the soil. Knowledge of change and transformation of minerals, in relation to plant nutrition, fixation and release of elements is important. Sepiolite and palygorskite are fibrous clay minerals widely ...
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Introduction Clay minerals are considered as the main source of ion exchange and storage of nutrients in the soil. Knowledge of change and transformation of minerals, in relation to plant nutrition, fixation and release of elements is important. Sepiolite and palygorskite are fibrous clay minerals widely distributed in arid and semi-arid soils. Both minerals are rich in Mg and therefore, their weathering can significantly affect the chemistry of Mg in soil. Biological weathering which is carried out by living organisms (i.e. plant roots, soil fungi and bacteria) plays an important role in providing nutrients to plants. Hence, the use of microorganisms such as mycorrhizal fungi in the rhizosphere of agricultural crops has become more widespread. In recent years several studies have been conducted in relation to the weathering of minerals in the rhizosphere soil. However, few studies in terms of mycorhizal symbiosis with plant roots were carried out on release of Mg from sepiolite and palygorskite. Therefore, a pot experiment with a factorial arrangement through a completely randomized design was conducted to identify how symbiosis of sorghum roots with Glomus mosae mycorhizae affects release of Mg from sepiolite and palygorskite. Materials and Methods Pots containing sterile quartz sand and sepiolite or palygorskite (25-53 µm) were prepared and fungal treatments including presence or absence of fungus Glomus mosae were applied to the pots and then sorghum seeds were sown. Johnson nutrient solutions containing magnesium and without magnesium were used to feed plants during 70 days of experiment. After harvesting, the chlorophyll content, plants height and stem diameter were measured by SPAD, tape measure and caliper, respectively. Afterwards, the roots and shoots were separated and plants biomass and the percentage of roots colonization determined. Then, plants were oven-dried, ground, and the magnesium contents of them after extraction with 1M hydrochloric acid were determined using Agilent 7000 ICP analyzer. The chemical composition of palygorskite, sepiolite, and quartz sand was determined using X-ray fluorescence (XRF) and their mineralogical composition was determined using X-ray diffraction (XRD) approach. Results and Discussion Analysis of variance for the main effect of treatments on plant height, stem diameter, shoot dry weight and root dry weight showed that the effect of different sources of magnesium on plant height, stem diameter and shoot dry weight was significant (P < 0.01). The highest and lowest height, stem diameter, root and shoot dry matter were found in treatments fed with complete Johnson solutions and the palygorskite, respectively. The results also illustrated that application of Glomus mosae symbiotic mycorhizae significantly increased plant height, stem diameter, and root and shoot dry matter compared with non-mycorhizal treatments. This could be attributed to the fact that Mycorrhizal fungi (Glomus mosae) absorb more water and nutrients through increased photosynthesis and plant growth, consequently leading to improved plant characteristics when compared with non-mycorhizal crops. The results also showed the highest percentage of root colonization in palygorskite treatments and the lowest one in control. In general, a symbiotic relationship is created to improve low nutrition of elements that the amount of them in the soilwith a little mobility. Therefore, anything that exacerbates this deficiency, leads to an increase in symbiosis between plants and fungi. On the other hand, When plant is faced with more nutrient deficiencies, the demand for a symbiothic fungusGlomus mosae increases. Besides, the greatest magnesium concentration and chlorophyll contents were found in control, sepiolite and palygorskite treatments, respectively. In all treatments, magnesium intake was sufficient to grow sorghum, but as the results show, the amount of magnesium in the control and that of sepiolite was much more than palygorskite. These results clearly show that sepiolite mineral is able to release more Mg than palygorskite. The results also showed that the presence of the fungus Glomus mosae has significantly affected the release of Mg from both minerals. Conclusion In both sepiolite and palygorskite treatments, magnesium and chlorophyll content increased in symbiosis with fungi. This shows the positive effect of Glomus mosae fungus on release of Mg from these two minerals, especially sepiolite. Although, both sepiolite and palygorskite were able to provide enough amounts of Mg for sorghum plants, however, it seems that in long-term Mg released from sepiolite can more easily meet the need of plants when compared with palygorskite.
Saeid Hojati; Ahmad Landi; Heyam Alekasiri
Volume 36, Issue 1 , September 2013, , Pages 13-22
Abstract
Wastewaters from different industries contain great amounts of heavy metals which can contaminate the ground water after entering the soil. Few studies have been conducted on the application of clay minerals such as sepiolite in preventing the leaching of these elements. This study was conducted to evaluate ...
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Wastewaters from different industries contain great amounts of heavy metals which can contaminate the ground water after entering the soil. Few studies have been conducted on the application of clay minerals such as sepiolite in preventing the leaching of these elements. This study was conducted to evaluate sepiolite as a strong and inexpensive adsorbent in preventing the leaching of lead and zinc from sandy soil columns under laboratory conditions. Therefore, 400 ml of solutions containing lead and zinc with a concentration of 75 mg/l, were passed through pre-saturated soil columns with different amounts of sepiolite (2, 4, 6 and 8 weight percent) in two sizes, < 2 and 20- 50 microns, under a flow rate of 1.2 liter h-1. The concentration of lead and zinc in the successive 20 ml leachate was then measured using atomic absorption spectrophotometer. Results showed that application of sepiolite in soil columns decreased leached amount of Pb and Zn as compared to control treatments. Also, with increasing sepiolite application rate, and decreasing its particle size, leaching of zinc and lead from the soils was reduced. However, the amount of lead leached was less than that of zinc. It seems that sepiolite mineral could be utilized as suitable materials to reduce the leaching of lead and zinc from soil to ground waters.
