s. mohammadnejad

The adsorption of gold and copper cyanide complexes on the activated carbon is investigated using the Density Functional Theory (DFT). In order to represent the activated carbon, two fullerene-like model (presenting structural defect sites) and a simple graphene layer containing different functional groups (presenting chemical active sites) are employed. The structural defect sites show a much lower adsorption tendency toward all the cyano complexes comparing to the chemical active sites. The interaction energy for all of the complexes with structural defect sites (concave) is very low. However, the graphene layer with unsaturated active sites displays the highest level of interaction almost for all the complexes except Cu(CN)4-3. The effect of oxygen functional groups on the graphite edges shows a crucial role in the selectivity of gold adsorption over copper complexes. It has increased adsorption energy for Cu(CN)2- in the presence of OH and COOH, and has decreased adsorption energy for Au(CN)2- by OH and increased by COOH. The study results elucidate the lower selectivity for adsorption of gold over copper cyanides by high oxygen content activated carbon. The energy levels of the HOMO and LUMO orbitals show adsorption of unpaired cyanide anions on the activated carbon surface occurs by electron transfer from the complex to the adsorbent and adsorption onto the activated carbon edges by transferring electrons from the absorbent to the complex. The result has clearly demonstrated that the functional groups increase the adsorption tendency for both the gold (only COOH) and copper complexes (OH and COOH) but deteriorate the selectivity of gold over copper cyanides.

In the wastewater of many industrial plants and mining industries, there are halogen compounds such as chlorine, fluorine, bromine and iodine, which can redce the quality of recycled water. One way to remove halogenated anions from wastewaters is to use layered double hydroxides, which have several advantages such as simplicity and low price. In this study, the adsorption properties of layered double magnesium / aluminum hydroxide is investigated by laboratory studies and molecular modeling for fluoride to iodine halogens. Laboratory studies have been performed to compare the ability to absorb different types of halogens by synthetic magnesium aluminum LDH (original and calcinated at 400 ˚C) and molecular modeling studies to understand effective mechanisms for different halogenated anions. The results of laboratory studies showed that both original and calcinated layered magnesium / aluminum hydrochloride have the highest absorption potential for fluoride ions and the lowest absorption for iodide ions. Calcination significantly increases absorption for all types of halogens. The predominant mechanism for the uptake of halogenated anions by non calcinated layered double hydroxides is ion-exchange and in calcinated products, surface and physical absorption. The electronegativity seems to be the determining parameter. The results of the energy calculation of the interaction obtained from the molecular modeling show that the preferred position for all halogens is the hollow hexagonal structure of the double-layer hydroxide. Also, the absorption rate in the hollow hexagonal position is the highest for the fluorine and the lowest for iodine. In addition to confirming the results of laboratory studies, these modelling results confirm the possibility of using molecular modeling methods as a powerful tool in examining the behavior and understanding the process mechanisms.

In this work, the mechanism of zinc hydroxide and ammine complexation in caustic and ammonia leaching is investigated by molecular modelling using the density functional theory method. The speciation of zinc complexes is defined based on the thermodynamic data and Pourbiax diagrams. The mechanism of Zn+2 complexation by hydroxide and ammine ligands is simulated by molecular modeling. The structure of reactants in the form of individual clusters is modelled using the density function theory. In order to compare the hydroxide and ammine species structures, the geometry studies are carried out as well. The ammoniacal salt effectiveness to improve the dissolution and stability of the ammine species is studied. The ligand single molecule interaction with a smithsonite molecule is done for a better understanding. Molecular modeling show that the zinc hydroxide species are more stable based on the higher reaction free energies. The reaction free energies decrease by adding the OH- and NH3 ions to the complexes from -30.12 kcal/mol to -16.943 kcal/mol, and -22.590 kcal/mol to 66.516 kcal/mol, respectively. The Zn-OH bonds are shorter than Zn-NH3, and the ammine species show more regular structures in comparison with the hydroxide structures. The change of free energies in the presence of ammoniacal salts indicate that the sulfate ions can significantly improve the dissolution of zinc oxide in ammonia. The smithsonite interaction with ammonia and hydroxide reveal that hydroxide ions lead to a higher interaction energy than ammonia (-36.396 vs. -28.238), which is consistent with the higher stability of hydroxide species. The results obtained well-explain the experimental results obtained before, and can be effectively used to optimize the alkaline leaching of zinc oxide ore.

A comprehensive utilization of concentrated seawater is crucial in order to promote the development of the desalination industry as a key solution to global freshwater. Debromination of the desalination plant effluent as well as the bromine product extraction are two parallel goals, which have been the subject of many research studies as well as industrial operations. In this investigation, bromine extraction is investigated experimentally form the effluent of the Konarak desalination plant located in Chabahar bay, Iran. For this purpose, an air blow-out method is used, and the effects of the operating parameters including the temperature, pH, and chlorine gas flow rate are examined in a continuous reactor. The parameters are optimized, and the trend is discussed in details. The bromine concentration of the sample collected from the Pozm Tiyab area, close to the plant discharge point, has been determined to be 1.172 g/L using ion chromatography. A pre-concentration procedure is conducted in order to reach a concentration of 3.100 g/L by evaporation. A reactor with the dimensions of 60 mm × 800 mm is designed and assembled for the experimental studies. In order to investigate the operating parameters, a central composition design (CCD) method is used. Among the factors studied, only the chlorine gas flow rate has a substantial effect on the bromine recovery, and the effects of the other two factors are negligible in the pH range of 2-3 and the temperature range of 50-70 °C. At the three chlorine concentrations of 1, 1.5, and 2 L/min, the bromine production increases almost linearly with the increasing chlorination injection rate. The Br2 gas is recovered with a maximum rate of 93.8% and a bromine loss of 185 mg/L in the mother liquid. The optimum operating parameters to achieve this recovery are a pH of 2.5, a temperature of 60 ˚C, and a chlorine gas flow rate of 1.5 L/min.

Reports indicates a higher mortality rate of Covid-19 in the elderly. A limited number of studies have been performed on elderly patients in Iran. In the present study, we investigated the clinical features and survival of elderly patients with Covid-19 in Baharloo Hospital, Tehran, Iran. 

This retrospective cohort study was conducted on the data of elderly patients with Covid-19 admitted to Baharloo Hospital, Tehran, Iran. The data of the hospitalized patients were followed until discharge or death. Finally, survival-related factors were analyzed using Cox regression. 

A total of 522 patients were enrolled in the study, of whom 53.8% were male and 101 died. The mean age of the deceased was 76.3 years, with a standard deviation of 8.6 years. The most common clinical symptoms at the time of admission were respiratory distress (69.5%), cough (61.1%), and fever (51.1%). Cox regression results showed that the risk of death increased by 5% for each one-year increase in age. In addition, calcium supplementation reduced the risk of death by 35%.

The results of the present study showed that calcium supplementation could be associated with increased survival of the elderly and reduced mortality. Due to calcium insufficiency in the Iranian population and the protective role of calcium in Covid-19, this issue is essential in the elderly patients warranting further investigation in the future.

Since 1970s the use of laser based range-finders has become a necessary part of many military and domestic systems. According to the needs and the circumstances, many different types of such systems have been developed and their technologies are adapted to the local needs. Distance or displacement measurement in the medium range is mainly divided to three groups; time of flight, frequency modulation continuous wave, and phase-shift laser range finder. In this paper we present the design, implementation and/or simulation of three such systems and compare their characteristics.