Modeling and process optimization for microbial desulfurization of coal by using a two-level full factorial design

The microbial sulfur removal was investigated on high sulfur content (1.9%) coal concentrate from Tabas coal preparation plant. A mixed culture of ferrooxidans microorganisms was isolated from the tailing dam of the plant. Full factorial method was used to design laboratory test and to evaluate the effects of pH, particle size, iron sulfate concentration, pulp density, and bioleaching time on sulfur reduction. Statistical analyses of experimental data were considered and showed increases of pH and particle size had negative effects on sulfur reduction, whereas increases of pulp density and bioleaching time raised microbial desulfurization rate. According to results of designing, and regarding statistical factors, the optimum values for maximum sulfur reduction were obtained; pH (1.5), particle size (?180 μm), iron sulfate concentration (2.7 mmol/L), pulp density (10%) and bioleaching time (14 d), which leaded to 51.5% reduction from the total sulfur of sample.     

Flotation study of oxide zinc ore using cationic-anionic mixed collectors

A representative sample of zinc oxide from Dashteh Sefid mine was obtained and then mineral characterization studies were done. The results of mineralogical analysis showed that the main zinc-bearing minerals are smithsonite, hemimorphite and gangue minerals are quartz and dolomite. In the present paper, the effect of important factors including sodium sulfide, collector type (AC and AC/KAX), collector amount, sodium silicate, CMC dosage and frother type (MIBC and pine oil) were investigated. Design of experiment was carried out by the means of Design Expert 7 using Fractional Factorial 2^6–1. The results indicated that collector type, collector amount, CMC and frother dosage were the most effective factors controlling the zinc flotation recovery. For the zinc grade, it was found that all six parameters play a significant role. The maximum recovery and grade of zinc obtained 97.71% and 10.39% under the following optimum conditions: sodium sulfide, 5935.23 g/t; collector type, AC/KAX; collector amount, 654.09; sodium silicate, 300; CMC dosage, 600; frother type, MIBC. The result of two-stage cleaner flotation showed that zinc grade could be increased up to 16.2% with zinc recovery of 61.39%.     

Predicting river daily flow using wavelet-artificial neural networks based on regression analyses in comparison with artificial neural networks and support vector machine models

This study investigates the ability of wavelet-artificial neural networks (WANN) for the prediction of short-term daily river flow. The WANN model is improved by conjunction of two methods, discrete wavelet transform and artificial neural networks (ANN) based on regression analyses, respectively. The proposed WANN models are applied to the daily flow data of Vanyar station, on the Ajichai River in the northwest region of Iran, and compared with the ANN and support vector machine (SVM) techniques. Mean square error (MSE), mean absolute error (MAE) and correlation coefficient (R) statistics are used for evaluating precision of the WANN, ANN and SVM models. Comparison results demonstrate that the WANN model performs better than the ANN and SVM models in short-term (1-, 2- and 3-day ahead) daily river flow prediction.

     

Novel fabrication of PdCu nanostructures decorated on graphene as excellent electrocatalyst toward ethanol oxidation

In this study, the electrochemical reduction reaction of copper(II) formate on the graphene/glassy carbon electrode (G/GCE) surface in the HCl (5 wt.%) was employed for fabrication of the PdCu nanostructures by galvanic displacement reaction. This method has a number of advantages including being environmentally-friendly, simplicity, inexpensiveness and fast. The PdCu nanostructures decorated on the G/GCE were fabricated in two steps: (1) electrochemical reduction reaction of copper(II) formate to Cu on the G/GCE and (2) the galvanic replacement reaction between Cu and Pd²⁺ ions. The physical and electrochemical properties of as-prepared PdCu/G were investigated via Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Cyclic Voltammetry, Chronoamperometry, and Electrochemical Impedance Spectroscopy. The PdCu/G compositional effect on ethanol oxidation in alkaline media is investigated. The results were shown that the catalytic activity and durability of PdCu/G catalyst are superior to those of Pd/C electrocatalyst for ethanol oxidation. The PdCu/G increased the current density 6.2 times more than Pd/C with a 50 mv negative shift in onset potential for electrooxidation of ethanol. Besides, the novel PdCu/G catalyst exhibits large electrochemically active surface area, lower apparent activation energy, higher levels of stability, poisoning tolerance, and lower charge transfer resistance compared to the Pd/C for the oxidation of ethanol.     

The impact of nonpolar coagulation bath‐immiscible liquid additives on the polyethersulfone membranes structure and performance

In this study, the impact of several normal alkanes as additives on the structural parameters and the morphologies of flat sheet PES membranes were investigated. The asymmetric membranes were fabricated by phase inversion method. Also n‐hexane, n‐decane, and n‐tetradecane were used as additives. The effects of different concentrations of these additives were investigated by producing the ternary phase diagrams. Further the membranes were characterized by means of solute transport test, contact angle, pure water flux, porosity measurement, and scanning electronic microscopy. It was expected that two distinct phase inversions to be occurred since both the polymer and the additives were insoluble in the coagulation bath. Observations revealed that n‐hexane and n‐decane were less effective compared with n‐tetradecane in terms of binodal shifting toward PES/NMP axis. In conclusion, it was revealed that the coagulation bath immiscible‐liquid additives had a major impact on the membranes structure in order to achieve the enhanced properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44509.     

The density current head velocity in expansion reaches

The velocity of the density current head in the expansion reach in which a river enters a dam reservoir, lake or sea is a key parameter for evaluating the extent to which suspended material travels, and for determining the type and distribution of sediment in the water body. This study experimentally evaluated the effects of the reach degree of expansion on the density current head velocity. Experiments were conducted in a 6.0‐m‐long, 0.72‐m‐wide flume. The head velocity was measured at three expansion degrees (8; 12; 26) and two slopes (0.009; 0.016) for various discharges. For the same slope and discharge, the results illustrated that the head velocity increases in the reaches expanded up to 20 degrees, compared to that for a uniform cross‐section reach. As anticipated, the velocity head increased directly with the bed slope.     

Detecting the Source of Contaminant Zones Down-Gradient of the Alborz Sharghi Coal Washing Plant Using Geo-electrical Methods,Northeastern Iran

Environmental contamination from the Alborz Sharghi coal washing plant in northeast Iran was evaluated with geo-electrical techniques. The internal structure of a coal waste pile was first studied using one dimensional geo-electrical techniques, including a Schlumberger array. The oxidised zone had low resistivity while the unoxidised shallower and middle to deeper levels had higher resistivity. Next, the geo-electrical surveys were repeated after 6 months to investigate possible changes in the oxidation zone associated with seasonal variations. Precipitation affected the shallower levels of the pile. Two dimensional geo-electrical surveys, including a dipole–dipole array, were then conducted between the pile and tailings impoundments. Low resistivity values in the area appeared to indicate contaminated zones at depth. Again, two surveys were conducted at a 6 month interval. Results indicate the transportation of contaminants to deeper layers due to atmospheric precipitation. Considering the expansion of the contamination zones, the results of prior chemical analysis of the tailings impoundment water, and the increasing trend of the resistivity values in the deeper layers of the pile, seepage from the tailings impoundment is the most likely source of pollution in the area.     

A Beneficiation Study on a Low Grade Iron Ore by Gravity and Magnetic Separation

In this paper, a sample from Tange-zagh iron mine was characterized by gravity and magnetic separation methods. The mineralogical studies showed that hematite and goethite are the main iron-bearing minerals with insignificant amounts of FeO. The results indicated that spiral separation yields higher separation efficiency than others. The combination of spiral and multi gravity methods showed that the grade and recovery could be obtained 58.7 and 55.6%, respectively. Scrubbing and de-sliming stages increased the recovery in the wet high intensity magnetic process. With a four-stage process of separation, the WHIMS by scrubbing and de-sliming was applied to achieve a final concentrate with grade of 62.6% Fe and recovery of 57.1% Fe.     

Response of low-grade gold ore to cyanidation and thiourea leaching

In this study, leaching tests were conducted on representative samples provided from Hamze-Qarnein gold deposit with grade of 0.8?ppm using cyanidation and thiourea leaching. Effective parameters including particle size, reagent concentration, oxidant concentration, pH, and dissolution time were examined in both cyanidation and acidic extraction with thiourea. Gold recovery and reagent consumptions (lime, cyanide, thiourea, ferric sulfate, and sulfuric acid) were measured under different leaching conditions. The results showed that cyanidation method was efficient with 95.21% gold recovery with following conditions: d₈₀?=?63?µm, pH 10.5, cyanide consumption of 1.23?kg/t, and 12?h cyanidation time. The acidic leaching using thiourea, required more chemical reagents and maximum gold recovery of 90.48% was achieved with thiourea consumption, leaching time, and pH equal to 13.32?kg/t, 5?h, and 1.7, respectively. According to the results, there was an interaction between ferric sulfate and thiourea concentrations and modeling of this process utilizing historical data design confirmed that the most effective parameter was the molar ratio of ferric sulfate to thiourea. Maximum recovery of gold obtained at molar ratio of 1/1. In addition, based on the experimental results, kinetics parameters of first-order reaction for gold dissolution were determined for cyanidation and thiourea leaching separately; therefore, for cyanidation, R_∞ and K were 95.59% and 0.59?h^?1 respectively, while R_∞ and K were in order of 78% and 0.87?h^?1 for acidic leaching using thiourea.