جستجوی مقالات مرتبط با کلیدواژه « bentonite » در نشریات گروه « فنی و مهندسی »

Today, the large production of cement in the world, especially in Iran, has become critical. Because the production of cement has caused the production of carbon dioxide gas and increased air pollution in cities. Therefore, in this research, the combination of bentonite and zeolite was used to increase the quality of concrete and reduce the consumption of stone and cement powder. The laboratory program of this research includes five mixed designs with the simultaneous combination of bentonite and zeolite in different ratios of 0%, 2.5%, 5%, 7.5% and 10% by weight of cement in SCC concrete. The results of this research showed that the simultaneous use of zeolite and bentonite up to 5% by weight of cement can have acceptable results. It increases the compressive strength by 8% and the tensile strength by 11%. But these pozzolans increase the hardness of SCC concrete due to their high water absorption and the possibility of the concrete being blocked behind the rebar density increases.

The behavior of the cohesive soil depends on many factors. Atterberg limits play an important role in the evaluation and classification of clays. In this paper, the relationship between the Liquid limit of the cone penetrometer methods and Casagrande cup of sand and clay mixed soils has been evaluated. The main purpose of this study is to compare the Liquid limit values obtained from the hard-base Casagrande device with the cone penetration method and to present the relationship between the Liquid limit values obtained from the two methods in terms of the percentage of sand in the mixed soil.

One of the suggested techniques to inhibit the spread of contaminants in the soil is cement-based stabilization/solidification. The production of hydration products and the attainment of an alkaline pH are the two primary processes in this method. In natural conditions, contaminants enter the soil simultaneously and in combination with each other. The simultaneous presence of organic and heavy metal contaminants alters how the soil-cement system interacts with each contaminant. The objective of this study is to compare the leaching and retention amount of cadmium and phenol separately and simultaneously in cement-based stabilization/solidification. In this context, the TCLP test has been used to assess the leaching amount of phenol and cadmium, as well as their retention capacity in single and combined systems. An X-ray diffraction test was also carried out to examine the microstructure of the stabilization/solidification process. The results indicate that the retention percentage of phenol in the presence of cadmium did not differ much compared to the single system, while the amount of cadmium retention decreased in the presence of phenol. In a combined system, the simultaneous presence of phenol and cadmium causes a reduction in the intensity of the C-S-H peak compared to single systems. However, the presence of cadmium had a greater effect on reducing the intensity of the C-S-H peak than phenol. Furthermore, in the presence of cadmium, the amount of phenol extracted during the TCLP test has increased compared to the single system.

The presence of heavy metal contaminants in clays causes changes in soil properties, which increases the risk of contaminant transport into the clay layer. Various techniques have been developed recently to remediate contaminated soil. These methods include electrokinetics, biological treatment, and immobilization. Among them, cement-based stabilization/solidification technique is very common. Generally, cement-based systems are frequently used because of their affordability and great durability. This method uses the two mechanisms of chemical stabilization and physical solidification to retain heavy metals and decrease the mobility of contaminants. Even though several researches have been performed to address the different aspects of cement-based solidification/stabilization, there has been a lack of research on the stabilization/solidification of heavy metals in the presence of two different heavy metal ions. Therefore, the objective of this study is to determine to what extent the pH variations affect lead and cadmium retention and release in single and double-component cement-based stabilization/solidification systems. To accomplish the aforementioned objective, first, the retention capacity of lead and cadmium, in cement-based S/S of contaminated bentonite in single and double-component heavy metal systems is investigated. The effect of pH on the stabilization/solidification process was determined by conducting a series of XRD tests in order to investigate and differentiate the stabilization and solidification mechanisms. In the next step, the amount of released cadmium and lead ions during the TCLP test was determined in single and double-component systems in order to investigate the effect of pH and the simultaneous presence of lead and cadmium in the release of these heavy metals. According to the achieved results, the maximum retention capacities of lead and cadmium occur in the pH ranges of 8.5 to 11 and 10 to 12, respectively. Furthermore, retention in the double-component system is always lower than that of the single-component system, assuming a similar initial concentration. In addition, XRD results illustrate that the intensity of the peaks of cadmium and lead chemical compounds has increased for the samples their pHs take place in the safe zones. This indicates an increase in the contribution of the stabilization mechanism. According to the results of this paper, at a similar contaminant concentration, the intensity of the C-S-H peak increases with an increase in cement percentages. This indicates progress in the contribution of the solidification mechanism in the retention of heavy metals. Still, the release of these heavy metals is always lower than the maximum allowable value reported by the US EPA in the above-mentioned pH ranges. Moreover, the results of this research show that the amount of released cadmium and lead in the double-component system is more than that of the single-component system, assuming similar initial concentrations. Based on the definition of the safe zone, in the defined pH range, the contaminant is retained during the TCLP test mainly by chemical stabilization (precipitation). In fact, in the above range, an increase in the amount of cement has not shown a significant effect on the amount of heavy metal desorption. This finding is supported by the results of retention tests.

One of the future problems of humans is environmental pollution. Negligence and lack of management of greenhouse gas production threatens human life on the planet. Considering the emission of CO2 gas due to the production of cement, it is important to find a way to reduce the consumption of cement in concrete as the most consumed building material. The use of pozzolans to make strong and durable concretes has become very important in the past years. In this research, two widely used pozzolans, namely zeolite and bentonite, were tried to improve the behavior and durability of SCC concrete. Therefore, the combination of zeolite and bentonite in weight ratios of 2.5%, 5%, 7.5% and 10% was used instead of cement. The tests performed include slump flow, concrete viscosity, compressive strength, and durability of concrete against melting and freezing cycles at different ages. The results of this research showed that the use of these pozzolans will reduce the strength in the early ages of concrete, but this problem will be solved with the increase in the age of concrete. So that using a combination of 5% zeolite and 5% bentonite can increase the final compressive strength (90 days) of concrete up to 8.6%.

Cement-based solidification/stabilization is one of the common methods for increasing the stability of heavy metals in contaminated soils. However, the presence of some of the heavy metals such as lead ions causes a delay and prevention in cement hydration which makes this method as an inapplicable. Enhancement of contaminated clayey soils by NaOH can remove the problems associated with cement hydration delay in presence of heavy metal ions. The main objective of this paper is to determine the impact of enhancement on solidification/stabilization of contaminated soils in extreme acidic and alkaline environment. To achieve the above mentioned objective, samples of contaminated bentonite by 50 and 100 cmol/kg-soil of lead nitrate at two different conditions of enhancement by NaOH and without enhancement were solidified/stabilized by 10 and 50 percentages of cement. The extreme acidic and alkaline conditions simulated by performing of equilibrium soil washing, endorsed TCLP test in solidified/stabilized cured samples. In addition, series of XRD experiments were performed to address the rate and quantity of CSH formation. The achieved results indicate that at extreme alkaline conditions the enhancement of contaminated bentonite has decreased the leach-ability of lead ions around 96%. With a decrease in pH of samples to the quantities less than 5, the use of enhanced samples has reduced the quantity of leachate in enhanced samples in comparison to unenhanced samples around 90%. This is attributed to the contaminant retention by clay fraction of bentonite and contaminant solidification by CSH gels.

In geotechnical and geo-environmental projects such as thermal stabilization, thermal remediation of contaminated soils and nuclear waste disposal, clays are always exposed to heat and heavy metal contamination. The study of the effect of heavy metal contaminants and thermal treatment on the geo-environmental engineering properties of clayey soils has long been considered by many researchers. Calcium carbonate as a major component of clay soils and as a non-plastic material reduces the plasticity properties of the soil. Calcium carbonate affects the process of heavy metal adsorption by clay particles. Accordingly, the presence or absence of calcium carbonate in the soil can have a secondary effect on the plasticity properties of clay. Generally, clayey soils retain the heavy metal contaminants by four phases. These phases include retention by cation exchange, precipitation by hydroxide carbonates (oxide and hydroxide), organic fraction and residual retention. A review of the literature studies has shown that little attention has been paid to the effect of retention phases of heavy metal contaminant on the plasticity properties of bentonite in thermal improvement from a micro-structural point of view. For this reason, this study is aimed to investigate the influence of retention phases of heavy metal contaminant on the behaviour of bentonite in thermal process. A natural bentonite soil is used in this study. The soil has been decarbonated by the use of hydrochloric acid.  To achieve the above mentioned objective, carbonated and decarbonated bentonite was prepared in a non-contaminated state and laboratory contaminated with heavy metal zinc (Zn) at concentrations of 5, 10, 20, 70 and 120 cmol/kg-soil. Contaminated and non-contaminated samples are first ground and then subjected to a temperature of 20, 110, 300, 400 and 500 °C for two hours. Then, by the use of Atterberg limit, XRD, pH and SSE experiments, micro-structural and macro-structural analysis of changes in carbonated and decarbonated bentonite plasticity properties has been investigated. According to the achieved results, in low concentrations of zinc heavy metals, calcium carbonate phase of heavy metal retention is the dominant phase in soil contaminant interaction process which prevents the change of bentonite structure. Therefore, the reason for the reduction of the Liquid limit is the reduction of the electrical charge of the clay particles, which is the result of lowering the pH. By an increase in contaminant content, all of the soil retention phases contribute to soil contaminant interaction process. Therefore, the role of calcium carbonate reduces in soil plasticity behaviour changes. As the temperature rises, Zinc metal as an accelerating agent has further reduced the Liquid limit in carbonated bentonite and decarbonated bentonite. In decarbonated bentonite, due to the absence of calcium carbonate, the clay particles adsorb more zinc. As a result, the effect of lowering the Liquid limit during increasing temperature by the heavy metal zinc in decarbonated bentonite is greater than in carbonated bentonite. Bentonite with its predominant sodium and zinc exchange cations loses its plasticity properties at temperatures of 400 and 500 °C, respectively, and the plastic limit for them is not measurable.

In recent years the use of nano materials in engineering projects has significantly increased. In fact, the impact of nano materials as a component in composite materials is one of the new horizons in engineering science. On the other hand, existence of heavy metal contaminated soils is one of the common problems in geo-environmental projects all around the world. In the process of retention of heavy metals by clayey soils, the pH of soil solution plays a significant role. In fact, an increase in pH of soil pore fluid causes a noticeable increase in contaminant retention. On the other hand, the use of additives in soil can increase the contaminant retention as well. In comparison with other additives such as cement, polymers do not require a long curing conditions. In addition, they have a positive impact on permeability of compacted soil, in which their presence decrease the soil permeability. In spite of several researches on the interaction process of clay minerals and polymer, there are very limited researches on the interaction process of polymer-clay minerals-heavy metal contaminant. Therefore, the main objective of this paper is to investigate the role of polyacrylamide polymer in retention of heavy metals in bentonite. To achieve the above mentioned objective, at the first step, the buffering capacity of polymer treated bentonite samples were measured. In this series of experiments, different concentrations of nitric acid from 0.002 to 0.02 molar were prepared. Then, 4 grams of bentonite and bentonite treated with different concentrations of polymer were poured in centrifuged tubes. Then, 40 cc of nitric acid were added to each centrifuge tube. After equilibrium period, the pH of soil suspension was measured and reported. In the second step of this research, two different series of experiments were performed. In the first series of experiments of this research, bentonite treated by polymer were exposed to different concentrations of heavy metal contaminants. In the second series of experiments, contaminated bentonite samples were treated by different percentages of polymer. The contaminant retention of these samples was investigated by performance of sets of batch equilibrium experiments. The achieved results indicate that the polymer treated bentonite sample (with 3% polymer), after exposure to 200 cmol/kg-soil has shown 19% increase in contaminant retention in comparison to bentonite sample. However, the addition of 3% polymer to contaminated bentonite with 200 cmol/kg-soil lead nitrate has shown 72% increase in contaminant retention in comparison to contaminant retention of bentonite sample. Based on the achieved experimental results it is concluded that there are three phases in heavy metal contaminants in interaction process of bentonite-polymer-heavy metal. These phases include retention by double-layer of clay, the contaminant retention in micro pores of clay minerals which are solidified by polymer, and the contaminate retention capability of polymer. According to the achieved results, the solidification effect of polymer has more contribution to the contaminant retention than the polymer buffering capacity. This proves that post-solidification of contaminated bentonite is a practical method for efficient prevention of contaminant transport in clayey soils.

Cement production is one of the major pollution contributors owing to its large rates of energy consumption and gas emission. Moreover, high temperatures could detrimentally impact the concrete infrastructure and thus, it would be essential to study performance of such structures under exposure to the elevated temperatures. In this paper, post-heat performance of the concrete whose cement has been replaced by zeolite and bentonite at ratios of 6 and 10% (by cement weight) under exposure to temperatures of 28, 150, 300 and 700°C, was studied. For this purpose, cubic specimens with sizes of 100×100×100, 150×150×150 and 200×200×200mm and cylindrical specimens with sizes of 200×100 and 300×150mm, were produced. Based on the results, replacing cement by zeolite and bentonite at the age of 90 days under ambient temperature, increases the compressive strength compared to the control specimen. Moreover, it was observed that heating the cubic and cylindrical specimens containing 10% bentonite at 150°C, increase the compressive strength by 40%.Conversely, the results indicate that when exposed to temperatures of 300 and 700°C, a decreasing trend is seen in the tensile strength of both cubic and cylindrical specimens containing the pozzolans. Besides, to study micro-structure of the specimens, the X-ray diffraction tests were carried out on the specimens at the age of 28 days. The difference between conversion ratio of the cubic and cylindrical specimens in this study, to the values provided by the codes, is less than 10%.

In recent years, the use of nano-materials in different engineering and science projects has increased. The study of the impact of nano-materials in combination with other civil engineering constituents in different geotechnical and geo-environmental engineering projects is very common. This study is aimed to investigate the mechanism of cadmium retention in the process of cement based solidification/stabilization of cadmium contaminated bentonite in the presence of nano-silica. The mechanism of contaminant retention is investigated with the evaluation of cadmium and nano-silica behaviour with change in pH of the environment, adsorption, TCLP results, and evaluation of XRD experimental achievements. The bentonite sample for this research is taken from Iran-Barit Company. To establish the availability of silica ions for interaction with cement and bentonite at different pH, a series of solubility experiments of nano-silica at different pH levels were performed. The results of solubility experiments show that as the pH increases to the alkaline range, the solubility of nano-silica noticeably increases. This fact proves that at the high range of pH due to the use of cement, the required pH conditions for solubility of nano-silica will be provided. Therefore, there will be more possibility for the formation of CSH component. Cadmium nitrate was used to contaminate the bentonite sample for the experimental part. For this purpose, bentonite samples were mixed with 10, 30, and 50 cmol/kg-soil of cadmium nitrate in the electrolyte soil ratio of 20:1. Then, these samples were shaken for two hours in every 24 hours. This process was repeated for 96 hours. After this equilibrium step, the soil suspension was centrifuged. After drying these laboratory contaminated samples, they were solidified/stabilized with different percentages of cement and nano-silica. The results of this paper indicate that the contaminant adsorption and retention of cadmium by bentonite is less than that of adsorption for zinc and lead. The achieved results of TCLP experiments for solidified/stabilized samples with different percentages of cement indicate that the EPA criteria for TCLP experiment which emphasizes for test performance after 28 days, is not suitable for solidification and stabilization of cadmium. In fact, a longer period is necessary to achieve equilibrium and stable results. Furthermore, the results show that due to the low adsorption of cadmium by bentonite and due to the noticeable reduction of pH at the presence of cadmium ions, the required percentages of cement for solidification/stabilization of cadmium contaminated bentonite is much more than the required quantity of cement for other heavy metal contaminated bentonite samples. In addition, the results of XRD experiments show that the pozzolanic interaction process is more efficient in the presence of nano-silica. Furthermore, based on the results of TCLP experiments, the formation of CSH in the presence of nano-silica contributes to the contaminant retention by solidification/stabilization of cement based cadmium contaminated bentonite. Finally, according to the results of this study, in solidified/stabilized samples by mixtures of cement and nano-silica, it is shown that due to the contribution of silica ions in pozzolanic interactions, the solidification is the governing phenomenon for the prevention of heavy metal leachate from solidified/stabilized samples.

One of the important steps in the process of removing water turbidity is the use of coagulants. Amongst the most applied materials is poly aluminum chloride (PAC) which is used to precipitate colloidal particles. The use of this compound, which contains Aluminum, in the coagulation causes some residual aluminum in the water. Natural and synthetic coagulants aid can be used to reduce the effects of overuse of poly aluminum chloride. In this study, the effect of bentonite and polyelectrolyte coagulant aid in the turbidity removal process of Babasheikhali water treatment plant is investigated. The results showed that optimum pH for turbidity removal was 8 and the optimal concentration of poly aluminum chloride at the optimum pH was 10 mg/L. In the presence of bentonite, the optimal PAC concentration decreased to 4mg/L and the turbidity removal efficiency increased to 92%. The results also showed that the combination of PAC and polyelectrolyte together can be used to reduce the concentration of heavy metals in the incoming water. Therefore, bentonite and polyelectrolyte coagulants aid can be used as a suitable option along with poly aluminum chloride to remove turbidity from the water treatment plant.

In this research, the possibility of decorating SnO2 nanoparticles on bentonite as a support in supercritical water environment has been investigated. Synthesis process of bentonite-SnO2 nanocomposite was performed in a reactor made of L316 stainless steel with a volume of 20 ml. The synthesis temperature and the duration was 480 °C and two hours, respectively. The manufactured nanocomposite was evaluated by various analyzes such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to confirm the immobilization of SnO2 nanoparticles on the support. The specific surface area, size and volume of nanocomposite cavities were determined using BET analysis. The appearance of SnO2 peaks in the XRD spectrum of the nanocomposite confirmed the successful synthesis of nanoparticles on bentonite. The immobilization of SnO2 nanoparticles with a size of less than 15 nm on bentonite plates was confirmed according to SEM and TEM images. The produced nanocomposite possessed a specific surface area of 50.36 m2/g and a pore volume of 0.13 cm/g due to the presence of bentonite in its structure, which makes it suitable for use as a catalyst in various reactions.

Global water demand is constantly increasing, while freshwater resources are limited due to increased demand and the effects of climate change, especially in arid and semi-arid regions such as Iran. The cost of water production is one of the most important factors in choosing a desalination method. In the adsorption method using natural materials, the cost of desalination can be reduced. In this study, Iranian zeolite and bentonite were used to reduce salinity by batch test. The adsorbents were identified by EDx, XRD, and BET. Clays were also modified with 1 M hydrochloric acid. The results showed that Iranian zeolite and bentonite used in this study as mineral adsorbents do not have the efficiency to reduce salinity and increase the electrical conductivity and sodium content of water. The highest increase in sodium concentration in samples was related to natural bentonite (102.5 mg/g) at the highest salinity concentration (64000 mg/L) and the lowest increase in sodium concentration was related to natural zeolite at 0.066 mg/g in the lowest salinity concentration (640 mg/L). Also, the highest increase in electrical conductivity was related to natural bentonite with an increase of 4.3 dS/m. It is noteworthy that after acid correction, the amount of electrical conductivity increased significantly in both clays. Therefore, due to the differences between the clays, it is better to first examine them in terms of construction and then use them in the field of desalination.

Cement is one of the most widely used materials in the construction industry, which emits large amounts of carbon dioxide into the environment during production. Environmental challenges and the reduction of energy consumption and the use of natural raw materials have led to increased study and research to find a suitable alternative to cement. Zeolite and bentonite have cement properties. These materials are environmentally friendly and can be easily extracted and also have lower production costs than cement. Since concrete has a low tensile strength, straw fibers, which are natural fibers, have also been used. In this research, 9 different mixing ratios with the amount of 250 kg / m3 cement were made in which different percentages of bentonite and zeolite replaced part of the original cement and the percentage of fibers varied by 1% and 3%. After fabrication, the compressive strength and tensile strength of the samples compared to the reference sample at 7 and 28 days have been compared. Then, two concrete mixtures with 6% zeolite, 1% straw fiber and 6% and 16% bentonites were selected and three-point bending strength test was performed on beams with dimensions of 10 * 10 * 50 cm. The flexural strength of the reference sample in this section, which contains 350 kg / m3 of cement, is 5.37 MPa. The best composition contains 6% zeolite, 6% bentonite and 1% straw fiber, which was able to achieve 98% flexural strength compared to the reference sample.

The continuous growth of the population will guarantee a massive demand for cement in the near future. Using pozzolanic materials in concrete manufacturing is intended as an optimal solution to lower the rate of greenhouse gas emission, and diminish energy resources and cement consumption. This research is aimed at evaluating Semnan Bentonite as partial replacement of cement. Seven bentonite mixes and control mix (CM) were examined. The main variable is the proportion of bentonite (5%, 10%, 15%, 20%, 25%, 30% and 35% by weight of cement) in replacement mode while the amount of cementitious material, water to cementitious material ratio, fine aggregate content were kept constant. To study properties of hardened concrete, compressive strength, splitting tensile strength tests and prediction of the modulus of rupture were performed. According to the results of compressive strength test, using 5% bentonite as partial replacement of cement, results in 8% increase in compressive strength 28 days as compared with the control mix. By replacing 35% of bentonite with the weight of cement, the compressive strength 28 days is reduced by 21%. According to the results in mixtures containing bentonite, if the amount of bentonite is more than 20% by weight of cement, the tensile strength 28 days is reduced by 45% compared to CM. According to the results, replacing 5% and 10% (by weight) of cement with bentonite, the predicted rupture modulus will increase by 3.7% and 3.1% compared to the CM, respectively

Cadmium is a heavy metal with many environmental degradation effects that is available in various industries. Considering the use of concrete as the most expensive construction materials, this study investigates the removal of heavy cadmium metal by concrete modified with bentonite, Bentonite, as a clay absorber from the clay family, has a Monte Morillonite. Bentonite has good absorption properties as well as good mixing with concrete materials. In recent years, the use of various wastes, including glass and bricks in concrete has been greatly appreciated. In this study, the construction and testing of green mixing concrete (concrete in accordance with the plan for the use of recycled materials and reducing environmental damage) using recyclable glass and brick materials. This concrete has non-structural standard concrete properties with bentonite. Green mixing concrete has the property of removing cadmium, one of the most hazardous materials and heavy metals. It is a concrete for use with various constructional concrete, and especially industrial sewage ponds.

Bentonite is an industrial soil with thousands of applications. Most of the Iranian bentonite mines, especially the mines of South Khorasan province, which is the center of the Iranian bentonite, are operating in a semi-closed or limited operation due to lack of reserves and dispersion. The construction of mobile processing plants will boost these mines, create added value, create jobs in deprived areas and make proper use of the country's reserves. In addition, flexibility, reducing the cost of transporting raw materials, the need for low investment, quick and easy installation and improving the knowledge of equipment manufacturing and mining are also the most important advantages of these processing plants. A mobile processing plant to produce bentonite concentrate requires primary crushing (jaw crusher), secondary crushing (impact crusher), heavy intermediate separator (cyclone or Dyna whirlpool), drying (rotary dryer), grinding (roller mill), packaging, power supply and control and monitoring units, that each of them can be mounted on a trailer. Technical and economic studies show that such a mobile processing plant with a capacity of 200 tons per day requires about 530 billion rials of fixed capital and about 30.5 billion rials of working capital. Also, the annual operating costs of this project are estimated at about 180 billion rials. With these specifications, the plan will have a payback period of 1.8 years, a positive net present value and an internal rate of return of 48%, which is appropriate and cost-effective in terms of investment. Also, the most important risks of this plan in terms of investment include operating processes, exchange rate fluctuations and prices. Other parameters of this plan are medium and low risk>

In past few decades, the expansion of industrial areas and increasing the effluents has led to increase the contamination of heavy metal in soil and groundwater resources. Adsorption is one of the most important processes that affecting in the leakage of contamination. Prevention the leakage of heavy metal contamination and economic considerations are always one of the basic principles in designs. Thus the use of natural and inexpensive adsorbents ,like clay and zeolite, is feasible procedure for the improvement of contaminated soil. In this study, with triaxial tests, the behavior of mixed sandy clay (base composition) with 10% of different low plasticity (kaolinite and zeolite) and high plasticity (bentonite) adsorbents is studied in both contaminated and uncontaminated states. The results show, as the concentration of lead heavy metal increase in soils with low plasticity adsorbent, the shear strength and internal friction angle decrease by about 20% and 14% respectively. As the type of adsorbent mineral changed, the resistance parameters of contaminated soil show different trend. Increasing the concentration of lead in the soil with bentonite adsorbent, has led to form the flocculation structure and it cause shear strength and internal friction angle increase a bout 18% than uncontaminated state. Also, cohesion in compositions with low and high adsorbent increases and decreases by about 30% and 19%, respectively.