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

Municipal waste is a cost-effective and valuable source of organic matter for agricultural soils. In recent years, MSW compost has been widely used in agriculture as a soil conditioner and fertilizer. However, the excessive use of organic and mineral fertilizers in the production of greenhouse crops leads to the accumulation of heavy metals in the soil and health risks for humans. Therefore, this study investigated the effect of the municipal waste and manure application on heavy metals in the soil. Also, the health risks for humans were evaluated through the consumption of cucumber cultivated in these soil. In this study, the concentration of heavy metals Cd, Cu, Ni, Pb and Zn in soil, mobility of metals, bioavailability, fractionation of metals, effects of pollution in the greenhouse soil and uptake of these metals by cucumber plant following 3 cultivation years of application of municipal waste compost and manure were studied in a randomized complete block design with three replicates in a greenhouse located in the south of Theran province. Also, environmental pollution risks were evaluated. The results showed that the application of municipal waste compost and manure increased both the total and available concentration of heavy metals in the soil. However, the concentration of the measured metals was at the permissible limit of the concentrations of heavy metals in Iranian soils. Copper and Zn were detected as the most mobile metals in control and treated soils with municipal waste compost and manure, respectively. The amount of Pb (2.26 mg kg-1) and Cd (0.06 mg kg-1) in cucumber in treated soil with municipal waste exceeded the limit value for edible vegetables. Based on the results obtained from the health risk index, Pb and Cu represented a high potential risk for the health of adults and children by consuming cucumbers in compost-treated soils. The results of this study showed that despite the three-year application of municipal waste compost and manure, the concentration of heavy metals measured was not higher than the allowed guideline level. However, considering the high bioavailability of heavy metals, repeated application of municipal waste compost would carry a risk of gradual accumulation in the soil over time. Therefore, measuring the total and extractable concentration of heavy metals and metal mobility when assessing likely effects on plant yields and metal uptakes and setting soil quality criteria is important.

Municipal waste is a cost-effective and valuable source of organic matter for agricultural soils. In recent years, MSW compost has been widely used in agriculture as a soil conditioner and fertilizer. However, the excessive use of organic and mineral fertilizers in the production of greenhouse crops leads to the accumulation of heavy metals in the soil and health risks for humans. Therefore, this study investigated the effect of the municipal waste and manure application on heavy metals in the soil. Also, the health risks for humans were evaluated through the consumption of cucumber cultivated in these soil. In this study, the concentration of heavy metals Cd, Cu, Ni, Pb and Zn in soil, mobility of metals, bioavailability, fractionation of metals, effects of pollution in the greenhouse soil and uptake of these metals by cucumber plant following 3 cultivation years of application of municipal waste compost and manure were studied in a randomized complete block design with three replicates in a greenhouse located in the south of Theran province. Also, environmental pollution risks were evaluated. The results showed that the application of municipal waste compost and manure increased both the total and available concentration of heavy metals in the soil. However, the concentration of the measured metals was at the permissible limit of the concentrations of heavy metals in Iranian soils. Copper and Zn were detected as the most mobile metals in control and treated soils with municipal waste compost and manure, respectively. The amount of Pb (2.26 mg kg-1) and Cd (0.06 mg kg-1) in cucumber in treated soil with municipal waste exceeded the limit value for edible vegetables. Based on the results obtained from the health risk index, Pb and Cu represented a high potential risk for the health of adults and children by consuming cucumbers in compost-treated soils. The results of this study showed that despite the three-year application of municipal waste compost and manure, the concentration of heavy metals measured was not higher than the allowed guideline level. However, considering the high bioavailability of heavy metals, repeated application of municipal waste compost would carry a risk of gradual accumulation in the soil over time. Therefore, measuring the total and extractable concentration of heavy metals and metal mobility when assessing likely effects on plant yields and metal uptakes and setting soil quality criteria is important.

With the population growth, technological advancement, and the increase in heavy metal pollutants, besides the location of a quarter of the earth's surface in cold regions, it is necessary to study the effect of freeze-thaw cycles on clay and predict its behavior over time. The effect of freeze-thaw cycles on the behavior of clay contaminated with heavy metals has been less studied. In addition, low plasticity clay and shale sedimentary rock are frequent in Iran. As an innovation in this article, the effect of the freeze-thaw cycles on the compressibility behavior of shale-clay soil in the presence of lead and zinc heavy metal pollutants is investigated. The combination of low plasticity clay with 40 and 60% crushed shale was investigated. For this purpose, 60 one-dimensional and Atterberg limit tests were conducted on the samples in the presence of 0, 5 and 25 cmol/kgsoil of lead nitrate and zinc nitrate pollutants. According to the obtained results, the most changes in liquid limit are related to the samples contaminated with 25 cmol of lead nitrate after 12 cycles of freeze-thaw cycles with a 43% reduction. And the lowest changes in liquid limit are related to the combination of 40% kaolinite with 25 cmol of zinc nitrate pollutant. Also, the results obtained from the consolidation test indicate that the compressibility of the samples was affected by the concentration of lead and zinc heavy metal pollutants and the freeze-thaw cycles. The increase of heavy metal pollutants led to a decrease in the initial void ratio and compressibility index of the samples compared to freeze-thaw cycle, which led to an increase in these ratios. The maximum changes were made in the first four cycles of the freeze-thaw cycle, and the changes were insignificant until the 12th cycle.

The presence of heavy metal ions in polluted wastewater represents a serious threat to human health, making proper disposal extremely important. The utilization of nanofiltration (NF) membranes has emerged as one of the most effective methods of heavy metal ion removal from wastewater due to their efficient operation, adaptable design, and affordability. NF membranes created from advanced materials are becoming increasingly popular due to their ability to depollute wastewater in a variety of circumstances. Tailoring the NF membrane’s properties to efficiently remove heavy metal ions from wastewater, interfacial polymerization, and grafting techniques, along with the addition of nano-fillers, have proven to be the most effective modification methods. This paper presents a review of the modification processes and NF membrane performances for the removal of heavy metals from wastewater, as well as the application of these membranes for heavy metal ion wastewater treatment. Very high treatment efficiencies, such as 99.90%, have been achieved using membranes composed of polyvinyl amine (PVAM) and glutaraldehyde (GA) for Cr3+ removal from wastewater. However, nanofiltration membranes have certain drawbacks, such as fouling of the NF However, nanofiltration membranes have certain drawbacks, such as fouling of the NF membrane. Repeated cleaning of the membrane influences its lifetime. membrane. Repeated cleaning of the membrane influences its lifetime.

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.

Due to strong oxidizing properties, titanium dioxide or titania nanoparticles are widely used in the water and wastewater treatment industry to remove or reduce various contaminants. The extraordinary properties of titania have led to the neglect of its side effects on the environment, especially on the aquatic ecosystems. In this study, different concentrations of titania nanoparticles were used over a period of 96 hours in lab scale to evaluate their impact on the heavy metals distribution in an aqueous media. The sediment samples of Anzali wetland contaminated with heavy metals were applied in all experiments. The results revealed that arsenic (As) was strongly affected by titania nanoparticles and its exchangeable bonds were desorbed from the sediment. Subsequently, 50 ppb titania led to concentration of As in the water column, which increased from 0 to 9 ppb. In addition to As, nickel (Ni) was desorbed from sediment through the separation of its organic bonds. On the other hand, 50 ppb titania reduced the concentrations of manganese (Mn), copper (Cu) and zinc (Zn) in the water column from 42, 32 and 29 ppb to 17.7, 2.87 and 20.9 ppb, respectively. According to the chemical extraction analysis, heavy metals adsorption in the sediment was mainly in the form of exchangeable and sulfide bonds. However, lead (Pb) and cobalt (Co) were not affected by titania and exhibited a conservative behavior.

Heavy metals are a major environmental problem and have become a global problem due to their high toxicity and their ability to accumulate in the body of living organisms. The aim of this study was to investigate the concentrations of heavy metals such as arsenic (As), cadmium (Cd), chromium (Gago-Ferrero et al.), copper (Cu), silver (Hg), manganese (Mn), nickel (Ni) and zinc (Zn) in samples of water and fish from the Malayer Dam in Hamadan Province, Iran. Samples of water and fish were collected in five steps (in May, June, September, October, February) from 19 locations in Kalan dam route of Malayer, in Hamedan, Iran. Water and fish species including Vimba vimba and Cyprinus carpio species were transferred to the laboratory. Fish samples were digested by 4 ml HNO3 and 1 ml HClO4. The amounts of heavy metals in water and fish were determined using ICP-AES and Duncan's test (0.05) was used for data analysis with SAS software. Results showed that the mean concentrations of the studied heavy metals were lower than the WHO, FAO, and USEPA guidelines for drinking water. The mean concentrations of Zn and Cr were significantly higher than other heavy metals in water samples. The results also showed that the highest concentrations of heavy metals (except Zn) were observed in spring than other seasons. The mean concentration of the heavy metals for Cyprinus carpio followed the sequence Cr≥ Zn>Ni>Cu>Cd>Hg>As>Mn in first sampling. There were significant correlations between all heavy metals’ accumulation in the Cyprinus carpio fish with heavy metals concentration in water samples. The results showed that the concentration of heavy metals in fish samples was correlated with the concentration of heavy metals in water samples and the accumulation of heavy metals in fish increased with increasing concentrations of heavy metals in water samples. The concentrations of heavy metals studied in fish are lower than those limits in the WHO and FAO guidelines and will not cause any harm in human consumption.

A novel bio-composite produced from coal fly ash accompanied by rhamnolipid biosurfactants was produced and used as an efficient adsorbent for the removal of cadmium from aqueous solution. Effects of initial solution pH (3-11) and absorbent to cadmium ratio (40-200) on cadmium removal, as process response, were studied and optimized using a central composite type response surface methodology. Results showed that both factors significantly affect the removal efficiency. Optimum adsorption conditions, resulting in over 99% cadmium removal, were achieved at pH 10 and absorbent to cadmium ratio of 40. Time-wise studies revealed that a maximum removal can be achieved following a classic first order model with a rate of 548.57 min-1. The cadmium adsorption on activated fly ash was also found to follow the Langmuir isotherm model with monolayer adsorption mechanism. Moreover, the bio-composite yielded a maximum adsorptive capacity of 67.11 mg/g. The selectivity study in bimetal aqueous systems using copper, lead and zinc metals also confirmed the high adsorption capacity of bio-composite. This study demonstrated that rhamnolipid-fly ash bio-composite could be considered as a promising efficient, low-cost resource material for the treatment of heavy metal polluted wastewaters.

Stabilization/Solidification (S/S) is an attractive technology which helps to reduce the toxicity and facilitate the disposal of sediments containing heavy metals, industrial wastes, and contaminated soils. The efficiency of the S/S technology can be enhanced by the use of clay nanoparticles. The S/S process incorporating Montmorillonite nanoparticles can be employed to prevent the dissemination of heavy metals effectively. Although many studies have addressed the stabilization of contaminant by the use of cement, few have discussed the microstructural interactions between montmorillonite nanoparticles, heavy-metal contaminants, and cement in different time intervals. In addition, there are not enough researches on the impact of montmorillonite nanoparticles in the efficiency of solidification process. Therefore, this study aims to investigate the interactions between montmorillonite nanoparticles, heavy metals, and cement in different time intervals from microstructural point of view and to determine the impact of clay nanoparticles on toxicity leaching from solidified/stabilized contaminants. To achieve the above mentioned objectives, different concentrations of heavy metal (zinc) and different percentages of Portland cement were added to nano-montmorillonite. The contaminant retention mechanism was then experimentally analyzed through monitoring the changes in pH, evaluating microstructural changes (using X-Ray Diffraction), and Toxicity Characteristic Leaching Procedure (TCLP) measurement. The results indicate the role of clay nanoparticles in retaining the heavy-metal contaminant and the lack of linear relation between the quantity of cement content of the specimen and the contaminant retention efficiency.

Heavy metals are among the environmental pollutants that human exposure to some of them through water and food can cause chronic and dangerous poisoning. The problem of poisoning drinking water to arsenic is a pervasive problem and has been seen in almost all countries, whether developed or developing, which endangered the lives of many people. In the present study, the removal of arsenic from water using iron / N-isopropyl acrylamide / chitosan nano-adsorbent was studied and evaluated. In this research, a magnetic nanoparticle was used to absorb arsenic, which is an innovative method. In order to increase the absorption capacity, we use polymer grafting operations on the surface of the nanoparticles, which will greatly increase the specific surface of the adsorbent. In fact, by placing polymers on the adsorbent, the combined desire increases. The results show that synthesized nano-adsorbants have the ability to absorb arsenic at different concentrations. But its concentration varies in different concentrations. Langmuir, Freundlich, Tamkin and Dobbin Radhushev isotherms were fitted with arsenic adsorption at 45 °C, pH = 7.5 at different concentrations. And the results show that a high (R = 0.995) R2 value for Langmuir model confirms that this model is suitable for fitting experimental data. The percentage of arsenic removal in optimal conditions at pH= 7.5, the amount of adsorbent 10 mg, contact time 60 min, temperature 45 °C and concentration of 10 μg/ml was 82.2%.

Lead is one of the most dangerous and toxic elements that is considered a serious threat to human and the environment. One of the effective technologies for removing this metal from wastewater is use the adsorption with natural adsorbents. The main objective of this study was to investigate the chitin Nano-fiber as natural absorption for removal of lead metal from aqueous solutions in a discontinuous system. X-ray diffraction (XRD), infrared spectrometer (FT-IR) and transient electron microscopy (TEM) were used to identify the physical, chemical and structural characteristics of chitin Nano-fiber. In the discontinuous system, pH (4-9), absorption dose (0.1-1 g), contact time (15-120 min), lead initial concentration (10-50 mg/L) and temperature (15-40 °C) were studied. The results were analyzed by one-way ANOVA and Duncan's tests for significant evaluation of changes in parameters. The highest percentage of removal of lead (98.95%.) was obtained at 25 °C, pH 5, 60 min contact time, absorbent dose of 0.3 g and lead concentration of 10 mg/L. The results of this study showed that chitin Nano-fiber is considered as an optimal absorber for removal of lead from aqueous solutions by removing more than 98% of lead from aqueous solutions.

Stabilization/solidification (S/S) has emerged as a cost-effective method for treating a variety of wastes, particularly heavy metal (HM) contaminated soils. Among the many available fixing agents, Portland cement (PC) has been used extensively for the remediation of contaminated sites. However, there are significant environmental and technical impacts associated with PC application. Thus, the present research was conducted to address the efficacy of cement and nano-clay mixture in enhancing the S/S process. In so doing, artificially contaminated soils were first prepared by mixing kaolinite with zinc (Zn) at levels of 0 to 2%. Afterward, tow type of nano-clay (Na-Montmorillonite and Na-Cloisite), cement and cement/nano-clay (CNC) were separately added to the sample, and then, a set of macro and micro level experiments including batch equilibrium, pH, toxicity characteristic leaching procedure (TCLP), unconfined compression strength (UCS), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analyses were carried out at various curing periods (1, 7 and 28 days) to assess the effectiveness of the additives. The results obtained show that the addition of nano-clay can increase the HM retention capability of soil; however, this may be partly lost when the treated soil are subjected to acidic TCLP solution. In addition, with increasing the HM content, due to the decrease in buffering capacity of system and the restructuring of the clay particles, the soil remediation potential at presence of nano-clay is decreased considerably. It was found that the application of sole cement may significantly enhance the HM retention capacity of soil. But in this case, the physicochemical reactions of Zn ions with cement could hinder and/or reduce the generation of hydration products phases such as calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), resulting in the degradation of cementation structure-bonding of S/S matrix, as clearly confirmed by the formation of calcium zincate and the diminution in the cementitios compounds peak intensity in the XRD patterns of cement-treated soils. Therefore, the leaching characteristics and the mechanical properties of the S/S material with sole cement are adversely affected by increasing the amount of HM ions. As a result, a large quantity of cement (20 wt% per one percent of HM) and a long time of curing (≈ 28 days) should be employed to meet the full needs of HM immobilization in contaminated soil and give the EPA-acceptable UCS value (≥ 0.35 MPa). The TCLP and XRD test results indicate that the cement/nano-clay combination can expedite the S/S process and alleviate the deleterious influences of metal ions and acidic attack on the stabilized sample. The EDX analyses also support the increase in the development of hydration reactions and the formation of cementing materials in the presence of CNC, providing the enhancement of binding capacity that will lead to the greater strength (up to 50%) in comparison to cement application. Hence, the CNC binary system is more efficient in modifying the contaminated soil with a lower amount of binder (to about 40%) and shorter curing ages (by nearly 4 times) than that of the sole cement. Overall, it is concluded that the cement/nano-clay mixture can be utilized as an effective S/S amendment and CNC content of 15 wt% per 1% of HM can successfully remediate the contaminated soil after 7 days of curing.

Soils contaminated with heavy metals are among the common environmental geotectonic problems all around the globe. Clay is considered as one of the best protective layers for environment to absorb polluters. Considerable SSA, very low permeability and the clays cationic capacity have been good factors to use these materials in geo-environmental projects vastly. It can react with the materials existing in the polluters because of the layered structure and special vast surface so the clay can absorb all or some of the dangerous polluter materials passing through the soil. Each part of the mineral materials constituting the clay, carbonate, organic materials, oxides, amorphous materials or remained phases can play a role in the process retention heavy metals. Carbonates play a special role in the process of the clay and metallic polluters’ interaction. The effect of the soil structure in retention heavy metal has been studied in many researches. In geotechnical environment view the clay mineral montmorillonite is one of the clays used in geo-environmental projects. Among the clay minerals montmorillonite has the highest property absorbing polluters. In the absence of clayey soils, compacted bentonite-enhanced sand mixtures are attracting greater attention as suitable material for contaminant barrier systems. The efficiency of these insulated barriers depends largely on their hydraulic and mechanical behavior. In landfills, as the main function of the liner is to minimize the movement of water out of the waste disposal facility, Landfill should satisfy three performance criteria if it is to perform satisfactorily as a barrier material. It should have low hydraulic conductivity (typically less than 1×10-9 m/s), should have sufficient strength in order to be stable during construction and operation, and it should not be susceptible to excessive shrinkage cracking due to water content changes that usually occur during the lifetime of the landfill. On the other hand, provision of the proper platform for landfills has been a concern of geotectonic and environmental geotectonic researchers in the past three decades. One of the objectives of this research was to introduce a material with suitable environmental geotectonic properties, minimum permeability, and maximum contaminant absorption potential. The process of producing nanoclay particles from bentonite clay with a top-down approach involves omission of some materials in the form of tailings. In related studies, the bentonite clay sample was divided into the following two main parts through physical and chemical processes: nano-montmorillonite (SLB) and process tailings (BLB). In this research, through a series of geotectonic and environmental geotectonic experiments the interaction of nano-montmorillonite interaction (SLB), process tailings (BLB), and bentonite clay samples with heavy metal contaminants was studied and analyzed experimentally. It shall be mentioned that the process of separating bentonite clay sample components was analyzed through microstructural X-ray diffraction (XRD) and specific surface area (SSA) experiments as well as scanning electron microscope (SEM) imaging. The tests conducted in the study were mostly on the basis of ASTM standard and the geo-environmental tests directions issued by McGill University of Canada. The soil carbonate percentage was defined by titration method. The specific surface area (SSA) was determined using the ethylene glycol-monoethyl ether (EGME) method. CEC was determined by the BaCl2 replacement method. The carbonate content of the soil was determined by titration, and the soil pH was measured in 1:10 soil solution.Also the soil pollution retention capacity was measured by titration test and HNO3 in different concentrations was added to the samples. Results of the present research suggest that process tailings (BLB) contain approximately 80% of copper as a heavy metal contaminant at a concentration of 100 cmol/kg-soil. In addition, permeability of the BLB sample and its inflation are approximately 5.2 10-10 m/sec and 70%, respectively.