INVESTIGATING SELECTIVE REMOVAL OF Cr(VI) AND Zinc IONS FROM AQUEOUS MEDIA BY MECHANICAL-CHEMICAL ACTIVATED RED MUD

In this study, the adsorption of hexavalent chromium and zinc ions from the solution is investigated by raw red mud and mechanical-chemical activated red mud along with the possibility of selective reclamation of these ions from the solution. The mechanical-chemical activation of red mud was done by employing high-energy milling and subsequent acid treatment with HNO3. Raw red mud (RRM) and mechanical-chemical activated red mud (MCARM) adsorbents were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) methods. In order to determine the suitable adsorption conditions, effects of pH of the solution, amount of adsorption, temperature, and time of adsorption were investigated. It was found that the optimum pH for the adsorption of hexavalent chromium and zinc ions by MCARM adsorbent was 2 and 6, respectively. According to these pH values, MCARM had the ability to separately adsorb more than 95 and 79% of hexavalent chromium and zinc ions from the solution, respectively. Experimental results were in good agreement with Langmuir and Freundlich isotherms. By considering the kinetic models of adsorption, the kinetics of the adsorption of both ions followed the pseudo-second-order reaction model. It was also determined that almost 25.8 and 61.8% of the hexavalent chromium and zinc ions adsorbed in MCARM could be recovere

MECHANO-THERMAL REDUCTION OF HEMATITE AND ANATASE MIXTURE BY TWO DIFFERENT FORMS OF CARBON AS REDUCTANT FOR IN-SITU PRODUCTION OF Fe-T iC - NANO CRYSTALLINE COMPOSITE

In this research, two different carbonaceous materials (Graphite:G and Petrocoke:P) were separately compared in terms of the carbothermic reduction of hematite and anatase in order to synthesize Fe-TiC nanocrystalline composite by mechanically activated sintering method. Powders were activated in a planetary high-energy ball mill under argon atmosphere for 0, 2, 5, 10,and 20 h. Then, the activated powders were analyzed by XRD and SEM to investigate phase constituents and microstructure of the mixtures. Results proved that Fe 2 O 3 and TiO 2 were not reduced by carbonaceous materials even after 20h of milling. SEM investigations showed that G-mixture was more homogenous than P-mixture after 20h of milling, meaning that graphite-anatase-hematite was mixed satisfactorily. Thermogravimetry analysis was done on 0 and 20h milled powders. TG and DTG curves showed that mechanical activation led to almost 300°C decrease in the reduction temperature of hematite and anatase in both mixtures. In the next step, the powders were sintered in a tube furnace under argon atmosphere. In the G-mixture, anatase was reduced to titanium carbide at 1100°C but, in the P-mixture, temperature of 1200°C was essential for completely reducing anatase to titanium carbide.Results of phase identification of the sintered powders showed that anano-crystalline ironbased composite with titanium carbide, as the reinforcement was successfully synthesized after 20 h high-energy milling of the initial powders and subsequent sintering occurred at 1200˚C for 1

KINETIC STUDIES FOR GOLD LEACHING OF A REFRACTORY SULFIDE CONCENTRATE BY CHLORIDE–HYPOCHLORITE SOLUTION

In this paper, gold leaching of a refractory sulfide concentrate by chloride–hypochlorite solution was investigated and effects of stirring speed, temperature and particle size on the leaching rate were reported. Experimental data for leaching rate of gold were analyzed with the shrinking–core model. Results were consistent with chemical reaction control mechanism in the first 1 h of leaching and diffusion control mechanism in the second 1 h. Apparent activation energy also was found to be 22.68 kJ/mol in the first step and 3.93 kJ/mol in the second step of leaching

An Evaluation of Tissue Destruction Time in Phrenic Nerve after Death and Counting the Number of Nerve Fibers in C3, C4 and C5 Branches

BACKGROUND AND OBJECTIVE: Most studies related to phrenic nerve are conducted based on an anatomical perspective and there is no histological study associated with this nerve. Since detecting the approximate time of death based on tissue destruction and determining the main branch of phrenic nerve based on the number of nerve fibers is extremely important, the histological examination of phrenic nerve was evaluated in the present study. METHODS: In this experimental study, the left and right phrenic nerves, obtained from 10 male corpses, were described using Grant's method of dissection after cutting the chest. In order to count the number of nerve fibers in the constituent branches (C3, C4 and C5), Hematoxylin and Eosin staining and Bielschowsky staining were used. In addition, to determine tissue destruction time, phrenic nerve of 8 rabbits were examined one to eight days after their death. FINDINGS: The results regarding tissue destruction time demonstrated that phrenic nerve starts to degenerate on the sixth day after death and is completely degenerated on the seventh and eighth days. Moreover, mean nerve fibers in C3, C4 and C5 were 41.2% (2224), 44.9% (2428) and 13.9% (749), respectively. The differences between the number of nerve fibers in these branches was statistically significant (p<0.05). CONCLUSION: The results of this study demonstrated that a significant part of phrenic nerve fibers are originated from C4 branch. In addition, tissue destruction of this nerve starts on the sixth day after death

EFFECTS OF MO ADDITION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF CAST MICROALLOYED STEEL

In industry, the cost of production is an important factor and it is preferred to use conventional and low cost procedures for producing the parts. Heat treatment cycles and alloying additions are the key factors affecting the microstructure and mechanical properties of the cast steels. In this study an attempt was made to evaluate the influence of minor Mo addition on the microstructure and mechanical properties of conventionally heat treated cast micro-alloyed steels. The results of Jominy and dilatometry tests and also microstructural examinations revealed that Mo could effectively increase the hardenability of the investigated steel and change the microstructure features of the air-cooled samples. Acicular microstructure was the consequence of increasing the hardenability in Mo-added steel. Besides, it was found that Mo could greatly affect the isothermal bainitic transformation and higher fraction of martensite after cooling (from isothermal temperature) was due to the Mo addition. The results of impact test indicated that the microstructure obtained in air-cooled Mo-added steel led to better impact toughness (28J) in comparison with the base steel (23J). Moreover, Mo-added steel possessed higher hardness (291HV), yield (524MPa) and tensile (1108MPa) strengths compared to the base one

Evolution of Pearlite Microstructure in Low-Carbon Cast Microalloyed Steel Due to the Addition of La and Ce

The effects of rare earth elements (RE) addition on the pearlite microstructure in low-carbon microalloyed steels have been investigated under two heat treatment conditions: (1) a normalizing treatment (as a conventional heat treatment used industrially to obtain the final mechanical properties of such steels), and (2) an isothermal treatment at 650 °C. This research reports the following effects due to the addition of RE: (i) refinement of the nodule and colony size of pearlite along with the ferrite grain size in the normalized condition, without a significant change in the volume fraction of pearlite. This microstructural refinement observed at room temperature is a consequence of the refinement of cast and austenitic microstructures formed during cooling in the presence of RE; (ii) the interlamellar spacing of pearlite isothermally transformed at 650 °C, as observed by SEM and TEM, is effectively reduced in the RE-added steel. This is likely due to two different effects combined: (i) direct influence of RE on atom carbon diffusion; and (ii) pearlite growth being boundary diffusion controlled by RE partitioning.The authors from the University of Tehran gratefully acknowledge the financial support provided by the Office of International Affairs and the Office of Research Affairs, College of Engineering, for the project number 8107009.6.34. The authors from CENIM-CSIC would like to acknowledge the financial support from Comunidad de Madrid through DIMMAT-CM_S2013/MIT-2775 Project.Peer Reviewe