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The dust produced by the electric arc method in the ferrochrome factory contains high amounts of hexavalent chromium, which has a high solubility in water and causes high environmental pollution. The present research has proposed a new method for neutralization of hexavalent chromium present in ferrochrome dust in solution environment by using chemical precipitation method. After checking conventional and non-conventional additives for neutralization by co-precipitation method, Iron sulfate is added to the aforementioned wastewater before release into the environment as a reducing agent of hexavalent chromium to trivalent chromium. Next, calcium sulfate was used as a stable complex forming factor in the system to remove chromium. XRD and XRF analyzes were used to characterize the dust and UV-Visible to determine the amount of chromium removed from the wastewater. The results showed that for 100 g/l of dust dissolved in water, adding 30 g of iron sulfate in the first stage and 20 g of calcium sulfate in the second stage reduces the content of hexavalent chromium from high values to below 10 ppm. Easy, high speed, cheapness and availability of additives are the merits of this method.


 

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Interference fitting widely used in the industry for connecting shafts and bushes. These type of joints are widely used as support of bearing machine parts. Rrepeated disassembling of shaft and bush interference fit, performed to repair and maintenance of machine parts, may cause serious damage to surface of joint parts depending on the roughness and surface quality of contact surface of joint parts. Bushes are usually expendable parts, but the shaft parts are long integrated and complex parts which supports other components of machine. So providing a way to repair the shaft surface can be considered crucial and leads to restoration of damaged shaft and reduced costs. In this study, we have investigated the effect of interference surface roughness on strength, friction coefficient of the contact surface and surface damage of interference fit joints during the disassembling procedure. Finite element and experimental analysis were performed to estimate friction coefficient in contact surface of joint parts. Also, magnified pictures of contact surfaces were applied, to evaluate the extent of damage in contact surface after disassembling of joints parts. Hard chromium plating was proposed to repair the shaft surface and the effect of hard chromium plating on strength of shaft and bush joints were measured experimentally. The results confirm successful use of hard chrome plating in repairing the shaft surface so that the strength of restored shaft joints were equal and in some instances even more than the initial joints.

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The toxic effects of chromium in plants, animals and human beings in the environment have been widely studied. In the present study, pot experiment was conducted to determine the effects of chromium on photosynthetic pigments, Nitrate Reductase (NR) activity and total amino acid, proline, total protein and leghaemoglobin content of Sesbania grandiflora (L.) Pers. The seedlings were treated with Chromium Cr (VI), concentrations ranging from 0.38-1.92 mM Kg^-1 of soil with 0.35 mM Ethylene Diamine Tetra Acetic acid (EDTA) and without EDTA. The efficacy of EDTA in its presence and absence was compared for periods of 30, 60 and 90 days. Our results in comparison with our control indicate the inhibitory effect of chromium to S.grandiflora. From the results it has been observed that, increasing concentrations of chromium in the presence of EDTA showed a significant increase in proline and total amino acid contents, while the total chlorophyll, leghaemoglobin content and total protein content decreased and the NR activity of the plant was also affected greatly.

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The present study aimed to remove hexavalent chromium from aqueous solution by manganese ferrite nanoparticle. In this study, MnFe₂O₄ was prepared based on co-precipitation method. The adsorbent properties were determined using scanning electron microscopy (SEM), X-ray diffraction (XRD). In this research, the effects of pH (2, 5, 7, 9 and 11), contact time of 2 to 360 minutes and concentrations of 1 to 200 mg/l and temperature (283 to 328 K) for the removal of hexavalent chromium were investigated. The agitation parameter was kept constant for all experiments at 170 rpm. The results of nanoparticle synthesis showed that the nanoscale dimensions were less than 200 nm, and the shape of the spherical particles followed the cubic spinel structure. Moreover, the pH of zero point of the nanoparticle was 6.8. Kinetic studies showed that the removal of chromium followed the second-order kinetic model. Intrinsic particle diffusion model showed that single-particle intrusiveness was not present and absorption consists of two steps: first, pushing the absorbent layer onto the adsorbent surface and then penetrating the molecule inside the pores. It was found that the removal of chromium is followed the Langmuir model, and the maximum absorption capacity of the hexavallent-chrome is 34.84 mg/g. The resulting value of n=2.92 (Freundlich isotherm) indicates the chemical absorption of chromium on the adsorbent of hexavalent chromium. The highest adsorption rate occurred at 328 ° K. The amount of ΔG was negative and ΔH reacted positively. This is because that chromium-reacted manganese ferrite is chemically thermostable and spontaneous.
 

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Nowadays, heavy metals are one of the greatest environmental problems. This problem intensifies by development of great industries and increasing of pollutant and contaminant resources daily. Increasing of population and reduction of water resources detect importance of waste treatment and reuse of water resources. Studies on treatment of effluents containing heavy metals have showed that adsorption to be a highly effective technique for removing heavy metals from aqueous solutions. The aim of this research was to use of absorbent materials (kaolin clay) to remove chromium (VI) from the wastewater in discontinuous system According to the results, optimum conditions of chromium removal were, pH=5, primary concentration of pollutant: 1000(mg/l), fine grained weight of consumed kaolin in constructing concrete: 30%, equilibrium time: 360 minutes, absorbing capacity: 3.06 mg/g absorbent. Covering the concrete surface with kaolin absorbent can be an innovative and useful solution for increasing the rate of elimination of pollutant and contaminants, cost reduction and accelerating the absorption process. Absorbing capacity of chromium is 29.5 mg/g absorbent in this condition respectively. Real waste sample are used for confirming the application of concrete in ordinary conditions of wastewater basin in accordance of optimum conditions of kinetics wastewater. Elimination rates of heavy metal of chromium were 90.3% in optimum condition with real samples that has been got from industrial factory. Therefore, it could be concluded that modified concert presents a good potential for treatment of Cr in wastewater. However, further research should be applied for continuous removal of heavy metal in large-scale. According to the result , mixing Kaolin in the concrete could be used to increase the Durability and adsorption efficiency of Chromium .