تاثیر نانو آهن صفرظرفیتی پایدار شده با اسید آسکوربیک بر توزیع شکل‌های مختلف کادمیوم در سه نوع خاک

آلودگی خاک ها با فلزات سنگین یکی از مشکلات زیست محیطی عمده در جوامع بشری است. در این راستا استفاده از نانو ذرات آهن صفرظرفیتی به عنوان اصلاح کننده آلودگی های محیط زیست مورد توجه محققان می باشد. بدین منظور سنتز و تعیین مشخصات نانو آهن صفرظرفیتی پایدار شده با اسیدآسکوربیک (aas – zvin) در شرایط هوازی و ارزیابی تاثیر آن بر قابلیت جذب کادمیوم در خاک و توزیع شکلهای شیمیایی آن در سه خاک شنی، اسیدی و آهکی مورد بررسی قرار گرفت. بدین منظور، آزمایش فاکتوریل در قالب طرح کاملاً تصادفی با تیمارهایی شامل کادمیوم در سطوح 15 و 45 میلی گرم بر کیلوگرم و aas – zvin در سطوح 0، 5/0، 1 و 2 درصد وزنی در سه خاک شنی، اسیدی و آهکی در دو دوره زمانی یک و چهار هفته با سه تکرار انجام شد. توزیع شکل های شیمیایی کادمیوم با استفاده از عصاره گیری دنباله ای تعیین گردید. نتایج تصاویر sem، xrd نشان داد که نانو آهن سنتز شده با اسیدآسکوربیک به ترتیب دارای اندازه کمتر از 50 نانومتر، حداکثر پیک در2θ برابر 8/44 درجه دارد. نتایج نشان داد که در هر سه خاک شنی، اسیدی و آهکی، کاربرد 5/0، 1 و 2 درصد وزنی از aas zvin در هر دو سطح آلودگی 15 و 45 میلی گرم بر کیلوگرم مقدار کادمیوم قابل جذب کاهش یافت. با گذشت زمان از یک به چهار هفته با کاربرد aas – zvin تغییرات کادمیوم قابل جذب، روند کاهشی داشت. هم چنین نتایج حاصل از عصاره گیری دنباله ای نشان داد که در هر سه خاک شنی، اسیدی و آهکی با افزایش غلظت aas – zvin از صفر به 2 درصد وزنی، شکل های محلول و تبادلی و کربناتی کاهش و شکل های متصل به ماده آلی و اکسید آهن و منگنز و باقیمانده کادمیوم افزایش یافت. بنابراین می‌توان بیان داشت کارایی نانو آهن صفرظرفیتی در کاهش کادمیوم از خاک بالا بوده و می‌تواند به عنوان یک روش کارآمد در رفع آلودگی این قبیل خاک ها معرفی شود.

The effect of ascorbic acidstabilized zero valent iron nanoparticles on the distribution of different forms of cadmium in three spiked soils

Introduction: Increases in pollution of water resources due to the contaminants have made researchers to develop the various methods in the remediation and the reuses of polluted resources contamination of soils with heavy metals is one of great environmental concerns for the human beings. Cadmium (Cd) as a toxic heavy metal is of significant environmental and occupational concern. Contamination of soils with heavy metals is one of great environmental concerns for the human beings. The numbers of sorbents that have been used for Cd (II) reductive removal are biopolymers, fly ash, activated carbon, metal oxides, clays, zeolites, dried plant parts, microorganisms, and sewage sludge. However, most of the mentioned sorbents had limitations of cost and durability that call a needed approach by cost effective remediation technique with high efficiency. Application of zero valent iron nanoparticles (ZVINs) as a promising technique for remediation of heavy metals are being increasingly considered by researchers. This study was conducted to synthesis and characterize the ZVINs stabilized with ascorbic acid (AAS ZVIN) in aerobic conditions and to assess their ability for removal efficiency of cadmium (Cd) from the soils and changes in different fraction of Cd in three spiked soils including sandy, acidity and calcareous soils were also studied. Materials and Methods: The stabilized ZVINs were prepared in cold distilled water by reducing Fe (III) to Fe0 using sodium borohydride in the presence of ascorbic acid as stabilizer and reducing agent. The freshly synthesized AASZVIN washed three times and then used for the subsequent analysis. Characterization of the synthesized AASZVIN was carried out by scanning electron microscope (SEM). Xray diffraction (XRD) was performed using a Philips D500 diffract meter with Nifiltered Cu ka radiation. To determine the availability of Cd, the DTPAextractable amounts of Cd in the spiked soils so sandy, acid and calcareous soils with three replications was studied were studied in an experiment of randomized completely design with a factorial arrangement of treatments consisting of AASZVIN dosage (0, 0.5, 1 and 2 w/w %), Cd contamination levels (15 and 45 mg kg1) in two time periods of 1 and 4 weeks in the three spiked soils. Moreover, the distribution of the chemical forms of Cd was determined using the sequential extraction method. Results Discussion: The results of this study show that zero valent iron nanoparticles can be sustained in the future by ascorbic acid under aerobic conditions in a laboratory that is to reduce the cadmium as a useful method, simple, fast and high performance in the decontamination of soils contaminated with lead that require further research to investigate other heavy elements. The results from the obtained SEM and XRD analyses indicated that AASZVINs had the mean size of less than 50 nm, the maximum 2θ peak at 44.8°. Therefore, the particle size of ZVINs produced in this study, measured by SEM images, are less than 100 nm. Chain structure formations have been attributed to the magnetic interactions between the adjacent metal particles. Furthermore, there was an apparent separation between these ZVIN with a little aggregation. Results also showed that the DTPAextractable Cd in three sandy, acid and calcareous spiked soils decreased with increasing of AASZVIN dosages at both level of contaminations. The availability of Cd in sandy, acid and calcareous spiked soils at 15 and 45 mg kg1 of contamination were 71 and 49.5 % and 47.52 and 49.47; and 36.05 and 61.3 percentages, respectively. Availability of Cd after four weeks application at two contamination level was also decreased significantly. The results of sequential extraction of sandy, acid and calcareous soils showed that with increasing the level of AASZVIN application from 0 to 2 %, the soluble, exchangeable and carbonatebound of Cd decreased but organic matterbound, Fe/Mn oxides bound and residual Cd were increased. Over four weeks after application of AASZVIN in three spiked soils the soluble, exchangeable and carbonatebound were decreased but organic matterbound, Fe/Mn oxides bound and residual Cd increased. Conclusions: The results of this study show zero valent iron nanoparticles can be sustained in the future by ascorbic acid under aerobic conditions in a laboratory that is, To reduce the cadmium as a useful method, simple, fast and high performance in the decontamination of soils contaminated with lead that require further research to investigate other heavy elements. Moreover, the high resolution transmission electronmicroscopy, energy dispersive Xray analysis, xray diffraction spectrophotometer measurements are potentially needed to reveal the accurate morphology, composition, crystal structure, functionality and stability of the prepared stabilizedZVINs. Moreover, these synthesized ZVINs can also possibly applicable for remediation of soils and wastewater.