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.
N. Sedaghati; S.J. Hosseinifard; A. Mohammadi Mohammadabadi
Abstract
Unsustainable harvesting of agricultural water resources in the province of Kerman, has caused an annual average of one-meter drop in ground water levels. Surface irrigation methods in pistachio trees have low efficiency because of inherent characteristics and its incorrect application, as well as low ...
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Unsustainable harvesting of agricultural water resources in the province of Kerman, has caused an annual average of one-meter drop in ground water levels. Surface irrigation methods in pistachio trees have low efficiency because of inherent characteristics and its incorrect application, as well as low access to water resource in pistachio regions. Therefore under the current critical condition, basic development of pressurized irrigation systems is an effective step to raise water use efficiency in the pistachio orchards. In this research, two irrigation systems including conventional surface drip irrigation and subsurface drip irrigation (SDI) with two drip line depths (30cm and 50cm) with three levels of water irrigation in each treatment, including 40%, 60% and 80% of irrigation requirement of pistachio in surface irrigation system (2932, 4398 and 5864 m3/ha.year respectively) for four years, was studied. Growth and yield factors, water use efficiency (WUE) and water and salinity distribution in root zone were measured. The results indicated that 30cm installation depth was the best treatment. Between irrigation systems, amounts of 60% and 80% irrigation requirement don't have significant difference, but 40% irrigation requirement treatment, affected negatively on most of evaluated factors significantly. Therefore with regard to all evaluated factors in this research, subsurface drip irrigation with buried drip line at 30cm and 60% of irrigation requirement of pistachio in surface irrigation system, with water use efficiency of 0.290kg/m3 and 25% water saving in comparison with surface drip irrigation system, was the best treatment and recommended.
