نشریه علوم و مهندسی جداسازی
سال پنجم شماره 1 (پیاپی 9، بهار و تابستان 1392)

The process of mass transfer in packed beds by increasing the gravitational field is intensified, these beds called the rotating packed bed. In rotating packed beds, mass transfer affected by the hydrodynamics of gas and liquid phases, rotational speed and geometric parameters of packing. In this study, the mass transfer coefficient data for the absorption of volatile organic compounds in rotating packed beds were modeled. To correction of mass transfer coefficient in rotating packed bed, used dimensionless effective rotating acceleration factor ("), instead of centrifugal acceleration. For the systems studied, good agreement between experimental data and predicted mass transfer coefficient is observed for the relationships presented. In this study, the maximum prediction error is about 20 percent that has higher accuracy than previous works.

A non-isothermal, isobaric and one-dimensional mathematical model has been developed for the production of hydrogen by steam reforming of methane. Mass and energy balances for reacting and scrubbing phases provide a system of algebraic and differential equations solution of which gives concentration and temperature distributions along the reactor. After validation of the model against available experimental data, the effect of heating method of the reactor and different operating parameters including temperature and pressure of feed, ratio of steam and scrubbing gas to methane on hydrogen recovery and methane conversion has been investigated. The results of this study show that hydrogen recovery and methane conversion may be increased by increasing the feed temperature and incremental heating of the membrane reactor.

In the present work, the nanostructured titania ultrafiltration membrane with photocatalytic and physical separation capabilities was synthesized for methyl orange removal of aqueous solution. Thus, a polymeric titania sol was deposited and calcined on the colloidal titania-coated alumina substrates. The properties of samples were investigated by dynamic light scattering (DLS), thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), field emission electron microscopy (FESEM), and atomic force microscopy (AFM) techniques. Photocatalytic activity of titania membrane was investigated by photodegradation of methyl orange in the presence of UVradiation. Also, physical separation of methyl orange was obtained by determination of the solution concentration changes after passing of titania membrane. Based on photocatalytic degradation, the removal efficiency of methyl orange was determined to be 61% that by coupling separation technique, it was improved to 83%.

A controlled potential flotation separation of chalcocite from pyrite using potassium ethyl xanthate (PEX) as a collector was investigated at different pH values. It was found that the oxidation-reduction state of the pulp can have a pronounced influence on the flotation separation of these minerals. Potential range between -100 mV to 0 mV (SHE) at pH 11 was found as optimum condition for separation of chalcocite from pyrite. Cyclic voltammetry method was used to identify the flotation behavior of these minerals. According to flotation results and cyclic voltammetry curves, appropriate separation of chalcocite from pyrite at above mentioned condition attributed to the formation and stability of copper-xanthate species which is responsible for the flotation of chalcocite and the instability or lack of dixanthogen that is responsible for the flotation of pyrite.

Ammonia and Ammonium salts have been focused by the researchers of leaching process for several years due to low toxicity and cost, easy recovery and high selective recovery of metal, although the extent of researches were less than the chemical agents used in acid leaching. In this research, tank and column leaching methods of Meskani mine copper oxide ore using ammonium hydroxide and ammonium carbonate reagents have been studied. For the tank leaching experiments, response surface methodology (RSM) with input parameters as the ammonium hydroxide concentration, liquid to solid ratio and time was used. The high correlation coefficient obtained (0.96) indicates a good conformity of the proposed quadratic model with experimental data. Copper recovery under optimal conditions (88 g/L ammonium hydroxide concentration, liquid to solid ratio of 7 and leaching time of 120 minutes) was found to be 96.22 percent.For the column leaching experiments, selected parameters were ammonium hydroxide concentration, flow rate, size and leaching time, designed and analyzed in three levels using L9 array of Taguchi method. According to the results, the optimum value of abovementioned parameters were estimated at 40 gr/L, 15.6 L/m2h, 1-4.75 mm and 10 days, respectively. Also the most important parameters influencing leaching process were identified as ammonium hydroxide concentration, size and leaching time, respectively. Recovery of 80.6 percent was obtained at the proposed optimum conditions confirming the model obtained from the regression. Finally, kinetics of copper column leaching was studied briefly and it was found that the diffusion mechanism shows a good conformity with experimental data.

In this study, simulation of residence time distribution of materials in a mixer-settler system was investigated in order to achieve the optimum extraction time and flow rate in the pilot plant. The liquid and organic phases were water and kerosene, respectively; and salt was used as a tracer reagent in the liquid phase. The salt tracer changes were recorded continuously by using a conductivity meter. The results were analyzed applying Matlab software and Weller and N-Mixer models in RTDWEN software. It was found for the mixing period of 5 min, the mean residence time was obtained 6.44 and 6.62 min by RTDWEN, respectively for Weller and N-Mixer models. Also, it was found to increase the number of perfect mixer vessels, set the mean residence time close to extraction time in the batch scale. Under these conditions, the fluid flow pattern in the mixer was similar to the plug flow.

In the previous works, the floatability of pyrolusite has been studied using different collectors but the capability of its separation from gangue minerals has not been considered significantly. In this research the flotation behavior of pyrolusite and calcite and their separation from each other using oleic acid as an anionic collector were investigated. The results showed that the pyrolusite flotation recovery contains two peaks at pHs 5 and 9 occurred due to oleate ions physisorption and chemisorptions mechanisms, respectively. Using 10-4 M oleic acid, the maximum flotation recovery of pyrolusite was obtained 30.8% at pH=9. At this condition, flotation recovery of calcite was 68%. It was found that copper sulfate (CuSO4.5H2O) acts as pyrolusite activator and calcite depressant agent in a dosage range of 250 to 1250 g/t. It depresses both minerals at high dosages. The best results were obtained using 1000 g/t copper sulfate in the presence of 10-4 M oleic acid at pH=8. At these condition the flotation recovery of pyrolusite and calcite are 83.6% and 38%, respectively. Copper sulfate increases the pyrolusite surface zeta potential and decreases the electrostatic repulsion forces; and results in the increase in oleate adsorption and flotation recovery. In the ore sample flotation tests, using copper sulfate the MnO grade of the concentrate was increased from 19.1 to 22.7% while the recovery was improved from 40.5 to 66.8%.