Sintering kinetics and alumina yield in lime-soda sinter process for alumina from coal wastes

An investigation of the application of the lime-soda sinter process to alumina extraction from coal wastes has been carried out. In the sintering stage, the optimal operating conditions have been obtained for the highest yield of alumina. The kinetics of sodium aluminate formation have also been studied in the sintering stage. The sinter mixes have been fired isothermally in air in the temperature range 1100 to 1350 °C. Alumina recovery of about 80 pct has been obtained by sintering coal-waste mixes having molar ratios of Na₂O/Al₂O₃ = 1.3 and CaO/SiO₂ = 1.8 at 1200 to 1250 °C for 20 to 30 minutes. Insoluble alumina compounds are responsible for the incomplete recovery. The major sinter components are identified as sodium aluminate and β-dicalcium silicate. The nucleation and growth kinetics equation is used to correlate the experimental data of sodium aluminate formation obtained under atmospheric pressure in the temperature range 1000 to 1200 °C. An activation energy of 286 kJ/mol has been calculated for fine coal-waste powder mixtures. Formerly Graduate Student in Metallurgy.     

Desulfurization kinetics of molten copper by gas bubbling

Molten copper with 0.74 wt pct sulfur content was desulfurized at 1523 K by bubbling Ar-O₂ gas through a submerged nozzle. The reaction rate was significantly influenced not only by the oxygen partial pressure but also by the gas flow rate. Little evolution of SO₂ gas was observed in the initial 10 seconds of the oxidation; however, this was followed by a period of high evolution rate of SO₂ gas. The partial pressure of SO₂ gas decreased with further progress of the desulfurization. The effect of the immersion depth of the submerged nozzle was negligible. The overall reaction is decomposed to two elementary reactions: the desulfurization and the dissolution rate of oxygen. The assumptions were made that these reactions are at equilibrium and that the reaction rates are controlled by mass transfer rates within and around the gas bubble. The time variations of sulfur and oxygen contents in the melt and the SO₂ partial pressure in the off-gas under various bubbling conditions were well explained by the mathematical model combined with the reported thermodynamic data of these reactions. Based on the present model, it was anticipated that the oxidation rate around a single gas bubble was mainly determined by the rate of gas-phase mass transfer, but all oxygen gas blown into the melt was virtually consumed to the desulfurization and dissolution reactions before it escaped from the melt surface.     

The ignition and combustion of chalcopyrite concentrate particles under suspension-smelting conditions

The ignition and combustion of chalcopyrite particles under suspension-smelting conditions, in which the particle-particle interaction is neglected, has been analyzed by considering the in-trinsic kinetics of oxidation and heat and mass transfer between the particle and its surroundings. Reasonable agreement has been obtained between the calculated results and experimental results from a laminar-flow furnace reported in the literature. This computational procedure has also been applied to flash-smelting conditions. Under suspension-smelting conditions (Sh = Nu = 2), chalcopyrite particles ignite at approximately 960 K. The effects of various parameters, such as oxygen concentration, particle size, and gas temperature, have also been evaluated. Comparison between calculated results in this work and experimental observations indicates that SO is the important gaseous product that forms at the particle surface. P.C. CHAUBAL, formerly Assistant Professor, Department of Metallurgical Engineering, University of Utah.     

Synthesis and characterization of new alkali-soluble polyimides and preparation of alternating multilayer nano-films therefrom

New alkali-soluble aromatic polyimides were prepared by a direct one-step polycondensation of 3,6-di(4-carboxyphenyl)pyromellitic dianhydride with common aromatic diamines in the presence of isoquinoline at 170 °C. The obtained polymers with inherent viscosities of the 0.62-1.01 g/dl range were all amorphous and highly soluble in dilute aqueous NaOH and tetramethylammonium hydroxide. Upon heating in TGA, the carboxylic acid groups degraded away at lower temperatures and the chain backbone did at higher temperatures. In DSC, no glass transition could be detected before decomposition. The alternating multilayer nano-films from the polyimides and poly(ethyleneimine) were prepared by the molecular self-assembly method and characterized by ellipsometry and X-ray reflectivity.     

Mathematical modeling of sulfide flash smelting process: Part III. Volatilization of minor elements

The mathematical model described in Part I^[14] was extended to include the minor element behavior inside a flash-furnace shaft during flash smelting of copper concentrate. The volatilization of As, Sb, Bi, and Pb was computed, and experiments were carried out for Sb and Pb in a laboratory flash furnace. Satisfactory agreement between the predicted and measured results was obtained for antimony and lead. From the computational results, the behavior of each minor element was predicted for various target matte grades. The model predictions show that the elimination of As and Bi to the gas phase increases sharply at about 0.3 m from the burner; however, that of the Sb increases gradually along the flash-furnace shaft, and that of lead occurs suddenly at about 0.6 m from the burner. The predicted results also show that the elimination increases for Bi and Pb as the target matte grade increases; however, it is relatively independent of the target matte grade between 50 and 60 pet Cu for As and Sb. At higher target matte grades above 60 pet Cu, the elimination of As and Sb decreases as matte grade increases. formerly Graduate Student, Department of Chemical Engineering, University of Utah,     

On the oxidation of cyanides in the stack region of the blast furnace

Computed results are reported on the oxidation of KCN particles carried by blast furnace gas through the stack region of the furnace. The calculations were performed on the assumption that the oxidation process is mass transfer controlled, but proper allowance was made for the variable CO/CO₂ ratios and temperatures to which the particles are exposed during their passage through the stack. The results of these calculations show that for cyanide particles in the range 0.02 to 0.1 cm in diameter the system may be extremely sensitive both to the temperature profiles and to the CO/CO₂ ratios within the stack; thus the control of these parameters could provide a means of controlling cyanide emissions.     

"Determinism, choice, responsibility and the psychologist's role as an expert witness": Reply.

Takes exception to H. Silverman's (see record 1969-08897-001) position that the deterministic nature of the theory of behavior subscribed to by most psychologists is of no relevance to the role of the expert witness or to the issue of criminal responsibility. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrochemical properties of Si–Zn–C composite as an anode material for lithium-ion batteries

A Si–Zn–C composite material is prepared by mechanical ball-milling and investigated as an anode material for lithium-ion batteries. Electrochemical tests show that the first charge and discharge capacities are approximately 852 and 607 mAh g⁻¹, respectively, and that 91% of the initial discharge capacity of 607 mAh g⁻¹ can be maintained for up to 40 cycles. This improved cycling performance is attributed to the use of the third element Zn. Li₂ZnSi is partially formed at the interface between Si and Zn and graphite to provide superior cycling performance compared with that of the binary system.     

Formation and Evaluation of Protective Layer Over Magnesium Melt Under SF6/Air Atmospheres

Molten magnesium oxidizes rapidly when exposed to air causing melt loss and handling difficulties. The use of certain additive gases such as SF₆, SO₂, and CO₂ to form a protective MgO layer over a magnesium melt has been proposed. The oxidation behavior of molten magnesium in air containing various concentrations of SF₆ was investigated. Measurements of the kinetics of the oxide layer growth at various SF₆ concentrations in air and temperatures were made. Experiments were performed using a thermogravimetric analysis unit in the temperature range of 943 K to 1043 K (670 °C to 770 °C). Results showed that a thin, coherent, and protective MgF₂ layer was formed under SF₆/Air mixtures, with a thickness ranging from 300 nm to 3 μm depending on SF₆ concentration, temperature, and exposure time. Rate parameters were calculated and a model for the process was developed. The morphology and composition of the surface films were studied using scanning electron microscope and energy-dispersive spectroscope.