پديد آورندگان :
گودرزي، اميررضا نويسنده گروه عمران,دانشگاه آزاد اسلامي واحد همدان,ايران Goodarzi, Amir reza , ميرمومن، متين نويسنده دانشگاه آزاد اسلامي واحد همدان,ايران Mirmomen, Matin
كليدواژه :
مشخصات مايع منفذي , فلزات سنگين , ريزساختار , زمان , الكتروكينتيك
چكيده فارسي :
در پژوهش حاضر تأثير مشخصات مايع منفذي و اثر زمان بر بازده روش الكتروكينتيك، ارزيابي شد. به اين منظور، ابتدا رس كائولينيت با محلولهاي حاوي نيترات روي و سرب بطور مجزا آلوده و با گراديان ولتاژ V/cm 2 در زمانهاي 3 الي 48 روز، در مقياس آزمايشگاهي مورد آزمايش الكتروكينتيك قرار گرفت. از اسيد نيتريك نيز به عنوان محلول كاتوليت، با هدف امكان شدتبخشي فرآيند پالايش خاك استفاده شد. نتايج بدست آمده نشان ميدهد پاسخ خاك به اصلاح الكتروكينتيك تابعي از مشخصات ماده آلاينده، pH سيستم خاكالكتروليت و زمان انجام آزمايش است. بر اين اساس در شرايط يكسان بخصوص در زمانهاي كم، بازده استخراج آلودگي از نمونه حاوي سرب به دليل تمايل بيشتر اين فلز به جذب سطحي و همچنين تشكيل رسوب، تقريباً 70 درصد نمونه آلوده به روي اندازه گيري شد. با توجه به طيفهاي اشعه ايكس و تصاوير SEM، تقويت جبهه اسيدي محيط پيرامون كاتد با افزايش غلظت يون H+ درون توده خاك، سبب تغيير ساختار، افزايش تحركپذيري فلز سنگين و در نهايت تشديد قابليت رفع آلودگي از خاك ميشود. مشخص شد ميزان اصلاح خاك به ويژه در قطعات نزديك به آند ابتدا با گذشت زمان، به شدت بهبود يافته اگرچه افزايش بيشتر زمان خصوصاً در نمونه هاي با غلظت زياد فلز روي، تاثير محدودي بر نتايج دارد. اين يافته بيانگر وجود يك زمان بهينه متناسب با نوع و غلظت آلاينده در فرآيند پاكسازي فلزات سنگين از خاك به روش الكتروكينتيك بوده بنحويكه كاهش pH محيط تاثير بسزايي در كاهش اين زمان و افزايش راندمان استخراج دارد.
چكيده لاتين :
The electrokinetic (EK) approach is one of the popular choices for the extraction of inorganic contaminants (e.g. heavy metals) from a soil matrix. On the other hand, many factors can affect the performance of EK contaminant remediation. Therefore, in the present study a series of macro and micro level tests including electrokinetic experiments, pH and electrical conductivity (EC), adsorption and desorption, Xray diffraction (XRD) and scanning electron microscope (SEM) analyses were performed to investigate the effects of time and pore fluid characteristics on the efficiency of EK remediation. For this purpose, the kaolinite clay was separately infected with different solutions containing zinc nitrate and lead nitrate in concentrations of 20 and 40 cmol/kg and then electrokinetic experiments on a laboratory scale were conducted at 2 V/cm voltage gradient in time periods of 3, 6, 12, 24 and 48 days. Nitric acid was also used as a catholyte solution to enhance the soil remediation process. The results obtained show that the soil response to the EK remediation is a function of the contaminant characteristics, the pH of soilelectrolyte system and the time of testing. In EK contaminant remediation from a soil matrix, it is significant to pay particular attention to the effect of the concentration and type of contaminant on the applicability and efficiency of this method. The results reveal that under the same conditions, especially in the low times, extraction efficiency from sles containing lead was measured approximately 70 percent of the sles containing zinc. This is because the lead tends to more adsorbe on the clay surface and has a greater tendency to form precipitate. In addition to the type of contaminants, it was found that the increase in concentration of contaminants in the soil through a series of physicalchemical reactions accelerates clean up capabilities, particularly in the initial time period of the EK experiments. Catholyte conditioning with acidic solution enhanced the removal of heavy metals, which is mainly due to microstructural changes and an increase in the mobility of pollutants. In fact, based on the Xray diffraction and scanning electron microscope analyses, the microstructural characteristics and the arrangement of the clay particles have an important role in the process of electrokinetic soil remediation. The formation of flocculated structure decreases the retention capacity of the clay particles and also increases the flow path, which enhance the efficiency of pollutant extraction. It was found that the soil remediation, especially in the parts close to the anode, greatly enhanced with increase the time of EK test however, the further increase in time had a limited impact on results, especially in the sles containing high concentrations of zinc. This indicates that there is an optimum time in the process of cleaning up heavy metals from the soil by EK method, which depends on the type and concentration of contaminant. Moreover, it was seen that the extent of contaminant removal from anode side towards the cathode side is considerable when catholyte conditioning with acidic solution is used. In other words, reducing the pH of soilelectrolyte system has a significant impact in increasing the efficiency of pollutant extraction.
