جستجوی مقالات مرتبط با کلیدواژه « electrokinetics » در نشریات گروه « عمران »

Every year, millions of tons of toxic and hazardous waste, including heavy metals, are generated. Numerous studies have been conducted to develop more effective and environmentally safe methods for removing contaminants from soil. Electrokinetics remediation is an emerging technology that has received significant interest among environmental scientists. The primary mechanisms driving contaminant movement in electrokinetics include ion migration, electro-osmosis, electrolysis, and electrophoresis. This research primarily aims to ascertain the influence of kaolinite's different phases on the retention of heavy metal contaminants. The secondary goal is to evaluate the efficacy of EDTA in extracting heavy metals from various phases of kaolinite. The results of this study is applicable to optimize the choice of enhancement materials for contaminant removal via electrokinetics, leading to reduced material requirements, consistent contaminant removal throughout the sample, and heightened soil decontamination efficiency. To meet these objectives, a range of tests were conducted, including batch equilibrium, zeta potential measurement, and selective sequential extraction on kaolinite, contaminated kaolinite, and EDTA-treated contaminated kaolinite samples. The soil sample analyzed contained primarily kaolinite, calcite, and quartz, as revealed by XRD diffraction. Lead nitrate served as the heavy metal contaminant, and the GBC 932 AA Plus apparatus was employed for its quantification. For zeta potential analysis, 0.05 g of soil was mixed with 50 ml of distilled water, agitated on a mechanical shaker, and measured using the Zeta Sizer Nano Zs after pH adjustment. The SSE tests further investigated the role of soil phases in contaminant retention, providing insight for the optimal selection of enhancement materials in electrokinetics remediation. The findings of this study indicate that by monitoring the variations in soil surface potential and understanding contaminant retention in soil phases, it is possible to propose an optimal enhancement strategy to improve the efficiency of heavy metal removal. The study also reveals that using either 0.01 or 0.1 molar concentrations of EDTA results in a similar level of contaminant extraction. Moreover, applying 4 cmol/kg of EDTA and washing the soil five times can remove approximately 87% of heavy metals. Given that electrokinetics remediation primarily employs electric current for contaminant extraction, using a lower concentration of EDTA combined with multiple soil washes is a more practical and cost-effective approach.

One of the most critical discussions about environmental pollution is soil pollution. Contaminated soil can endanger the life of organisms. For this reason, removing all types of soil contamination and even reducing the types of soil contamination is a fundamental and critical issue. One of the ways to clean and improve contaminated soils is the electrokinetic method; The principle of this method is to transfer the contaminated ions in the soil by an electric field and to eliminate and neutralize the contaminated ion or remove them from the soil. This practical method can remove various contaminants such as petroleum products and heavy metals. In some cases, this method can be seen along with other methods of soil improvement or even combining this method with some other methods to see a much better result. The present study will present the research on soil contamination by the electrokinetic method and its limitations.

In the present era, environmental pollution is a global crisis, increasing population growth and urban development, industrial expansion and unlimited use of natural resources, are among the increasingly important factors of pollutants (Reilley, 1996). Vocciante (2021) found in the study of stability in electrokinetic modification processes that the electrokinetic method is suitable for cleaning inorganic pollutants from clay. Zhou (2021) found that using the electrokinetic method is effective in removing heavy metals zinc, cadmium, and manganese from the soil and leads to the removal of about 72% of the pollutant from the soil sample. Vaishnavi (2021) in the study of bio-electrokinetic modification of diesel-contaminated environment with biosurfactant found that this method is an effective method for cleaning and cleaning soils contaminated with diesel hydrocarbons. Hanaei et al. (2021) found that the direct shear test showed that the adhesion of the soil sample increased and the friction angle decreased after oil contamination, and the permeability test showed that the contamination of the soil sample decreased the permeability of sandy soil and this change It is a function of the amount of oil and the viscosity of oils.

Pollution of soils containing petroleum products is one of the most important environmental challenges. Therefore, it is necessary to take measures for the purification of petroleum products, including diesel, to clean these compounds from the soil, various solutions are used, including the use of electrokinetic process. The result of the electrokinetic process in the soil is the movement of water, ions and charged particles due to the difference in electrical potential. In this study, the purification of diesel-contaminated clay by electrokinetic method in the presence of ABTS and saponin surfactants is investigated and the effect of pH control on catolite and anolite on the electrokinetic modification process of clay is evaluated, The results show that in the absence of the surfactant, the electrokinetic method has a very low removal efficiency of 3% to 7%, but in the presence of the surfactant, the efficiency is significantly increased by 20% to 54%, with pH control in Velit. and anolyte and the amount of active substance increase the level of efficiency of diesel removal from soil. With the use of Saponin, the lowest amount of removal at a concentration of 0.05% equal to 20% has been obtained, while ABTS has been able to remove about 54% of diesel at the highest concentration of surfactant (0.15%), in the continuation of the research A uniaxial test has been conducted to determine the unconfined compressive strength of the soil sample, which shows that the cleaning process increases the compressive strength of the soil by 15%.

Electrokinetics is known as a common method for improvement of soil engineering properties and contaminant removal from soils. In carbonated soils due to the soil buffering capacity, the acid front does not form through the soil sample. Therefore, the soil improvement usually caused by hydrogen ion effect will not occur. Consequently, a reduction in electrokinetics efficiency happens. One of the methods to overcome this problem is the application of enhancement methods. In this paper the influence of enhancement by the use of calcium chloride solution on two mechanisms of electrolysis and electro osmosis in electrokinetics remediation of carbonated clay is experimentally investigated. For this purpose, an un enhancement and enhance electrokinetics process with 0.2, and 0.5 molar concentrations of calcium chloride has been applied on  carbonated natural clay  samples. The calcium chloride solutions were added to anode reservoir. The achieved results of this paper indicate that due to the noticeable percentages of carbonate calcium in soil sample, not only the pH of soil in electrokinetics process has not decrease, but also because of alkaline condition of soil sample due to the presence of calcium carbonate and calcium chloride solution, the pH of soil has increased. Furthermore, in enhancement electrokinetics with calcium chloride, the presence of calcium ions and an increase in electro migration process have caused an increase in efficiency of electro osmosis. For this reason, the volumetric flow rate of enhanced electrokinetics experiments with 0.5 molar calcium chloride has been almost 250% more than that of for un-enhanced experiments.

Every year with the expansion and development of industrial and mining activities, millions of tonnes of toxic waste are produced throughout the world. Soil contamination by organic material as a result of various incidents and the leakage of organic compounds into the soil solid porous media will have an adverse effect on the environment. There are several methods for soil remediation contaminated with hydrocarbon compounds. Electrokinetic is one of the effective remediation which includes three main mechanisms for remediation, electroosmotic flow, ionic migration and electrophoresis. Electrokinetic is suitable in terms of cost and time for solid and porous fine-grained environment media that have high adsorption capacity of moisture and also organic pollutants. Kerosene is considered as one of the hydrophobic organic compounds with harmful physical and chemical properties to ecosystems and high adsorption onto the water and soil media. It has different hydrocarbons in its composition, each molecule having an average of 10 to 16 carbon atoms. It is so durable in the ecosystem, including the soil environment. The soil used in this study was fine-grained kaolinite due to the nature and effectiveness of the electrokinetic method for porous media. In this study, five series of experiments were carried out using electrokinetic method and its combination with improved techniques. The parameters including cumulative electroosmotic flow, electrical current intensity, reservoir and soil pH variation and residual kerosene concentrations in soil were studied. The highest electrical current devoted to increased voltage and pH control tests with 48 and 94 mA respectively for a time interval of 80 to 90 hours after the start of the tests were observed. The higher electric current intensity causes faster migration of ionic species to the opposite-electrode, resulting in greater electroosmotic flow transportation. In the present study, the removal percentage of kerosene from kaolinite soil through the different electrokinetic techniques including changing the electrolyte solution (nitrate potassium and tap water), increasing the-voltage (2 volts per cm of soil), and pH control over 5 and 7 days were investigated. Results revealed, using potassium nitrate as electrolyte solution, the the removal efficiency of kerosene was 47.24% and 50%, respectively, according to the remediation time of 5 and 7 days. With an increase of 2.9 times in the electroosmotic flow over a period of 48 hours from 5 to 7 days, the removal efficiency of the kerosene increased by 2.76%. Using distilled water as electrolyte solution despite the volume of 555 milliliters of electroosmotic flow, kerosene removal efficiency decreased to 33.02% in 7 days. The percentage of kerosene removal by pH control and increased voltage up to 2 v/cm, respectively with electroosmotic flow of 372 and 452 was 47.69 and 61.43%. Hence, a higher volume of electroosmotic flow represents a greater removal of kerosene in the soil. According to the obtained results, the best removal efficiency of kerosene (inspite of higher electroosmotic flow in tests with no enhancement technique) was due to the use of electrokinetic method by combining the higher voltage enhancement technique and the use of potassium nitrate electrolyte as solution over a period of 7 days.

Electrokinetics is a common and practical method for contaminant removal from fine grain soils. In spite of several researches performed on the factors affecting the application of electrokinetics method for contaminant removal from soils، there are still extensive attentions of researches on the influence of soil components on the efficiency of this method upon contaminant removal. The main objective of this research is to investigate on the impact of carbonate elimination and contaminant concentration on the Pb removal from carbonated kaolinite in electrokinetics process. To achieve this objective a natural kaolinite sample which had 4% natural carbonate and a carbonate eliminated kaolinite were laboratory contaminated with 5 and 20 cmol/kg-soil of lead nitrate. After achieving equilibrium، the laboratory contaminated samples were dried in oven at 40 centigrade temperature for 96 hours. Then، 27% water was added to samples as initial water content. To achieve homogeneous distribution of water content، the sample was kept in a plastic bag for 24 hours. Then sample was passed through #10 sieve to have a more homogeneous sample. Finally، the soil sample was compacted in five layers at dry density of 1. 7 g/cm3 in the electrokinetics cell. Then، the electrokinetics method was performed on these samples for contaminant removal. Electrokinetics experiments performed for a 240 hours period. After the end of experiment، the soil sample was taken from cell and sectioned in 5 slides. Each slice was analyzed for water content، soluble and adsorbed contaminant. In addition to electrokinetics experiment، buffering capacity test was performed by titration of soil sample with nitric acid. For this purpose، the diluted nitric acid in 1:10 soil: acid solution was added to sample. The soil solution sample kept on the shaker for 96 hours. After equilibrium the pH of soil solution was measured. This experiment was performed for different concentration of nitric acid. The final type of experiment include batch equilibrium experiment in which different concentrations of 5، 10، 20، and 30 cmol/kg-soil of lead nitrate was prepared. Then 20 milligram of each solution was added to 2 grams of kaolinite sample. After the shaking period and centrifuging the sample، the pore fluid was analyzed to measure the soluble and retained heavy metal. The results of experimental study indicate that the reduction of carbonate in carbonate rich kaolinite and an increase in contaminant concentration causes a reduction in soil buffering capacity. This means that as the concentration of carbonate in soil sample decreases، one faces with a reduction in contaminant retention capacity of soil. In addition، in such a case a reduction in pH happens which consequently enhances the contaminant removal from soil. Furthermore، carbonate elimination causes an increase in contribution of electro-osmosis on soil improvement which is followed by water content variation and consolidation of soil.

In this study, a non-plastic silt is grouted by sodium silicate in an electrokinetic cell. The silicate solutions are injected through the reservoir next to the anode electrode. The injection of Na- silicate solution increases the strength adjacent to the anode electrode between 5 to 8 times compared with the base soil. Increasing silicate concentration generates lower increase in strength across the specimen. This means that decreasing the silicate concentration increases the penetration length of the grout. Neglecting the results for anode side of the specimens, the maximum increase in strength has been observed for injection of 5% silicate solution through the anode with acid in the cathode chamber. The obtained strength is 3.3 to 4.0 times greater than the strength of the base soil with the highest penetration length. The application of this technology for increasing the strength of the soil underneath an existing foundation or generation of pile through the soil is proven.