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

In the past few decades, warm mix asphalt (WMA) has been used as advanced technology alternative to hot mix asphalt (HMA) due to the relatively low temperatures required heating the asphalt in the production and application process, reducing environmental damage while providing benefits. Asphalt maintains the hot mix, it is noticeable. However, low manufacturing and processing temperatures may result in asphalt deterioration from moisture. The aim of this study was to evaluate the characteristics of asphalt containing natural zeolite and compare it with synthetic zeolite and WMA organic and chemical additives against deterioration against moisture. Resistance properties of samples against moisture sensitivity using tests.

Hypothesis: 

Among the various pollutants found in natural water, the heavy metal arsenic is more important due to its high toxicity. One of the most efficient methods to remove this pollution from water streams is the surface adsorption method. Zeolite nanocomposites can be considered powerful among arsenic adsorbers. Powder adsorbents are not very effective in industrial systems due to the problems such as clogging of filters, high pressure drop and also the problem of separation from water.

To solve this problem, zeolite nanocomposite powder was transformed into beads using the chitosan gel method in three different types of cross-linking solutions including sodium hydroxide, sodium tripolyphosphate and joint sodium hydroxide/sodium tripolyphosphate. The effect of various parameters such as the type and initial ratio of the materials on the formation of beads was investigated.

The results showed that the beads formed in the sodium hydroxide+sodium tripolyphosphate cross-linking solution and the optimal initial ratio of 1:3 from chitosan to the nanocomposite have a more suitable appearance and strength and better performance in arsenic absorption. In order to confirm and justify the mentioned Findings, SEM, BET and AAS analyses were performed. Operational parameters of initial arsenic concentration and adsorbent dose which are effective on the beads’ adsorption efficiency were investigated and the optimal amount of adsorbent dose was determined as 1 g/L with an efficiency of 92.9%. In order to obtain more information about the method of adsorption and determining the maximum capacity of adsorbents, Langmuir and Freundlich isotherms for granular adsorbents were investigated. The highest adsorption capacity of 7450.7 mg/g was obtained and Freundlich isotherm was in better agreement with the results.

 In recent years, industrial-scale production of propylene based on oxidative dehydrogenation of propane has been of particular importance due to the lack of thermodynamic limitations. In this regard, the use of natural zeolites with high abundance and low price has placed a special position. In this research, perlite natural zeolites were treated with ionic liquid solution and acid, then supported vanadium catalysis were synthesized. Performance of catalysis were investigated in oxidative dehydrogenation of propane to propylene process with a mixed feed of propane and air in a fixed bed quartz reactor under condition of atmospheric pressure and temperature of 500˚C with a flow rate of 40000 h-1 (GHSV).

 In this study, natural perlite support as a source of aluminum oxide (Al2O3) and silica (SiO2) was ion exchanged by one molar solution of ammonium nitrate (NH4NO3 1 M). Continuously, to investigate the effect of delamination, different acid molar concentrations of nitric acid (HNO3) equal to 0.75, 1.5, and 2.25 were used and then compared with the just modified ion exchange sample without acid leaching (V/PERLIT-I). Dry vanadium impregnation, as an active metal, was carried out to synthesize 8% wt. catalysts. X-ray diffraction analyzes (XRD), scanning electron microscopy (FE-SEM), and ammonia Temperature-programmed desorption program (NH3-TPD) were used to characterization and evaluate the properties of the catalyst.
Main

The results showed that the concentration of acid used affects the conversion and selectivity of the catalysis. In comparison, a significant difference was observed between the performance of V/PERLIT-I sample compared to V/PERLIT-IA samples. The maximum selectivity value for V/PERLIT-IA(2.25) was 74%. According to the results, the treated perlite support with suitable selectivity can be considered in the studies of use as an industrial support.

Petroleum based polymer composites could be a factor in the development of fire unlike their numerous applications. The research performed on the fire resistance and flammability of composites is not comparable with those conducted on the mechanical behavior of composites demonstrating the importance of studying multi-functional composites of fire resistance behavior. In this work, two-part polyurethane was reinforced with natural zeolite and graphite nanoplatelets (GNP) to examine fire resistance and optimized mechanical behavior of the composite foams. Moreover, poly urea was added with the optimized ratio of 40% into polyurethane composites based on the study hypothesis. The results showed that zeolite and GNP filled nano/microcomposites led to a 200 and 300% improvement in the tensile modulus of the composites, respectively. It was further sown that both fillers resulted in enhancement in the flexural modulus, too. To enhance the mechanical behavior, fiber glass mat was laminated with the optimized polyurethane/poly urea compound leading to a 600 and 200% improvement in the flexural modulus, respectively, in the case of two-layer reinforcement. The poly urea coating on the optimized composite specimens demonstrated the reduced burning rate of 23 mm/min and a 200 s flame time based on the UL94 standard. The mixed compound of polyurethane/poly urea filled with 2 wt% of zeolite led to the burning rate of 4.9 mm/min being in the allowable range above 80% lower than the maximum possible rate set forth in the standard.

Clinoptilolite is a natural zeolite which is prone to use in the removal of contaminants due to its abundance, cheapness, suitable specific surface area and surface functional groups. In this research, the removal of iron and phosphate ions in aqueous solution has been investigated using natural clinoptilolite zeolite. The amount of removal of these contaminants has been investigated by the adsorbent in conditions such as the type of corrective method, the concentration of adsorbent to the contaminant, contact time and different pH. Modification of the adsorbent with acidic solutions results in the removal of 87% of iron at pH = 6.2 and D/C = 40, and 91% of phosphate at pH = 5.4 and D/C = 40. The ratio of adsorbent concentration to pollutant and pH have also been investigated as important factors in this study. Examination of different adsorption isotherm models showed that Langmuir model is suitable for phosphate with the maximum adsorption capacity of 62.25 mg/g and Freundlich model is suitable for iron with the maximum adsorption capacity of 48.35 mg/g. The present study showed that clinoptilolite can be used as an effective and inexpensive adsorbent to remove iron and phosphate from aqueous solutions.

The present investigation is studied the effect of the replacement of different percentages of natural zeolite (Ze) pozzolan powder on the mechanical properties of recycled concrete made from coarse masonry recycled aggregates. In made concretes, natural aggregates were replaced with recycled coarse masonry aggregates at 25%, 50% and 100% levels. For improve the mechanical properties, natural zeolite was replaced by cement at 10%, 20% and 30% levels. In total, 195 standard cubic and cylindrical concrete samples in the 16 mixing designs were made and compressive strength tests at 7, 28 and 91 days, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity at 28 days of age were evaluated. the results showed that, at replacement levels of 20% natural zeolite with cement was had the greatest improvement in the mechanical properties of natural concrete but in combination with recycled aggregates, the replacement of 10% natural zeolite by cement was improved the mechanical properties of recycled concrete. also the results showed that, 10% of natural zeolite, using up to 50% of coarse masonry recycled aggregates, Improvement some mechanical properties of recycled concrete was showed relative to conventional concrete without pozzolan, but replace 100% coarse natural aggregates with recycled masonry, mechanical properties of recycled concrete have significantly decreased compared to natural concrete without pozzolan.

The main objective of this study was to assess engineering properties of self-compacting concrete (SCC) incorporating magnetic water and various percentages of natural zeolite. The fresh properties of SCC were investigated by means of slump flow, T50, V-funnel, L-box and visual stability index (VSI). At hardened state, mechanical properties and durability characteristics of concrete were evaluated by means of compressive and tensile strength tests, modulus of elasticity test and water absorption test at different ages under both wet and dry curing conditions. The results of fresh concrete indicated that magnetic water and natural zeolite in SCC can improve the rheological properties and stability of SCC where the magnetic water is able to increase the slump flow up to 3% and decrease plastic viscosity of concrete mixture up to 6% without aggregates segregation. In addition, the presence of magnetic water and natural zeolite improves mechanical properties and durability of SCC. According to this, compressive and tensile strengths and modulus of elasticity of SCC containing magnetic water and 20% natural zeolite were increased up to 42, 12 and 33 %, respectively, at the age of 90 days. In the same concrete mixture, the value of water absorption was decreased up to 48%.

Today, restrictions on access to natural aggregate resources in concrete production have become one of the problems in many countries. Concrete, as one of the most widely used human products, is a factor in consuming a large amount of aggregate. To meet this need, today many developed countries use different types of recycled aggregates as a suitable alternative to natural aggregates. The present study investigates the effect of complete replacement of recycled concrete coils instead of coarse natural aggregates in concrete. In order to improve the quality of recycled concrete, the pozzolans like as micro-silica, natural zeolite and fly ash were used in different percentages. In order to determine and compare the mechanical properties of concrete, 11 mixing designs were made and compressive strength tests at 7, 28 and 91 days, indirect tensile strength (SPT), modulus of elasticity and ultrasound velocity tests at 28 days of age were performed. The results showed that micro-silica, especially at the 10% replacement level, has a dramatic effect on the improvement of the compressive strength of fully recycled concrete compared to other pozzolans. The results of the application of natural zeolite in fully recycled concrete showed that this pozzolan, especially in the 10% substitution, act as a cementitious reducing agent and play a lesser role in improving the mechanical properties of recycled concrete compared to recycled concrete without pozzolan. On the other hand, pozzolanic materials, in a way that improves the compressive strength of recycled concrete, are not able to improve the tensile strength and the modulus of elasticity of the recycled concrete compared to conventional concrete.

The present study studies the effect of the replacement of different levels of recycled concrete aggregates on the mechanical behavior of recycled concrete. In made concretes, natural aggregates have been replaced at three levels of 25%, 50% and 100% with recycled concrete coarse aggregates. In order to enhance the mechanical performance of these concrete, each of the pozzolans including micro-silica, fly ash and natural zeolite has been replaced with cement at three different levels. A total of 360 cube and cylindrical concrete specimens were made in the form of 40 mixing designs, and tests of compressive strength, tensile strength, static modulus of elasticity and ultrasonic pulse velocity at 28 days of age were performed. The results showed that, without the use of pozzolanic materials, up to 25% replacement of recycled coarse aggregate, there was no significant change in the mechanical performance of this concrete, while the higher replacement rates resulted in a significant drop in the mechanical performance of this concrete. The use of micro-silica, especially at the replacement level of 10%, has led to a very good performance of recycled concrete even in the case of full replacement of recycled coarse aggregates. Other pozzolanic materials used were also relatively less and in lesser intervals of recyclable materials to improve their mechanical properties.

The present study was conducted to compare the effect of natural zeolite (Z) and silica fume (SF) pozzolans on the mechanical properties of recycled aggregates concrete (RAC’s). The RCA’s made with using different levels of recycled coarse aggregates instead of natural coarse aggregates. To improve quality of RCA’s, the introduced pozzolans were replaced with different levels of ordinary Portland cement (OPC). To determine and compare the mechanical properties of concretes, 24 mix designs were made and different tests done as compressive strength at the ages 7, 28 and 91 days, and the tests as splite cylinder tests (SPT), modulus of elasticity and ultra-pulse velocity (UPV) at the age of 28- day. The obtained results generally showed that in duration of 28 days, the usage of silica fume could results in about 40 MPa compressive strength for RCA’s with 100% of recycled coarse aggregates; meanwhile using natural zeolite was not able to give target strength of design. Using 10% of silica fume instead of OPC in RCA’s specially RCA’s having 25% of recycled aggregates caused in the mechanical properties of RCA’s be rarely like those natural aggregate concretes. Although, using 10% of zeolite in concrete could improve some mechanical properties, but the concretes containing silica fume gave superior mechanical properties than those of zeolite.

Recently, the electrochemical impedance spectrometry (EIS) has been found as a key method in the field of materials science and electrochemistry for determination of electrical behavior of concrete and especially the interfacial zone of steel-concrete layer. In this paper, EIS of reinforced concretes made with binary and ternary combination of zeolite and copper slag as supplementary cementitious material were examined in an experimental research. Moreover, equivalent electrical circuits fitted for evaluation of steel/concrete interface of such concretes. The results showed that zeolite and copper slag enhanced the durability properties of concrete including the water and chloride permeability indexes. Also, with aid of electrical models and determining the polarization resistance with stern- geary equation, it was found that these martials increased the polarization resistance leading to the decrease of corrosion rate up to 65%.

Recently the low-cost adsorbent for heavy metals removal such as Lead in recent years has been noticed by researchers. In this study, lead removal by clinoptilolite has been investigated. Non-continuous lead absorption from aqueous solution was carried out by using clinoptilolite. The zeolite characteristics were analyzed with SEM and XRD. The effect of pH variables (1, 3, 5, 7, 10), contact time (15, 30, 45, 60, 90 min), clinoptilolite adsorbent dosage (1, 3, 5, 7, 10 g) and lead concentrations (10, 20, 40, 50, 60, 70, 80 & 100 mg/L) were studied on lead removal efficiency and adsorption isotherms and kinetics in constant temperature and stirrer speed of 250 rpm. According to the results, optimum conditions of lead removal by natural zeolite were pH of 8, adsorbent dosage of 5 g/L and contact time of 45 min., the highest removal efficiency of 89.6 achieved. By increasing metal concentration, the amount of removed lead was decreased while absorption capacity increased. Of the two studied models, the Langmuir isotherm had better conformity for lead adsorption (R2=0.99) than other isotherms. Also the pseudo second order kinetics model had better conformity with achieved data than other models. Results of this study indicated that natural clinoptilolite zeolite can be considered as an efficient and cost effective adsorbent for lead removal from aqueous solutions.

One of the drinking water resources has been selected for research based on chemical analysis with nitrate concentration of 53/7 mg/l in northern part of Gorgan city. In this research, natural zeolite has been used for reducing nitrate under laboratory conditions. The results indicated that natural zeolite reduced nitrate at about 13 mg/lit and also reduced hardness by passing 1 lit water through zeolitic bed (at about 1 kg) during a 30-minute time lag. In the chemical analysis, the pH of the water was 7/5 which chaned to 7/3 after passing through zeolitic bed. In this research, the hardness of raw water was 670 mg/l and the hardness was reduced 85 mg/lit in 40 grms zeolite with a time lag of 10 minutes whereas if zeolite weight was 160 grams, during a 30-minute timelag, the hardness would reduce to 175 mg/lit. Therefore, it can be concluded that natural zeolite could be used for reduction of nitrate in contaminated water wells all over the country.