Electrostatic Separation of Fine Particles in Vibrated Fluidized Beds
Very fine particles which cannot be fluidized by means of a flowing gas alone because of entrainment may be effectively individualized and retained in the bed through a combination of gas at low rate flow and mechanical vibrations of selected frequency and amplitude. A mixture of very fine particles may be fluidized and successfully separated and/or concentrated by means of electrostatic fields. Results are presented of a factorial experiment in which the conditions of temperature, humidity, and voltage were investigated for the separation of a (50-50 by weight) synthetic mixture of iron and glass powder of particle size ranging from 15-45¿m. A new and highly efficient particle collection mechanism is introduced, and mathematical models of the process are presented as part of the optimization work.
Slope Stability of Electropacked Beds
The mechanics of packed or fluidized beds of semi- insulating particles are substantially altered by strong applied electric fields. The angle of repose of a loosely packed bed of glass beads increases with the applied electric field; a sufficiently intense field will freeze the bed. An extensive series of angle of repose measurements are reported which suggest three distinct regimes of critical slope equilibria: infinite slope equilibrium for low electric field intensities; finite slope equilibrium for somewhat stronger fields, and the frozen bed limit for strong electric fields. The failure of an infinite slope equilibrium is characterized by individual particle motions confined to a thin layer near the surface. This regime is amenable to analysis, and the electrically induced cohesion can be inferred from the experimental data. The results are compared to Dietz's published expression for the cohesive electrical force acting between two contacting spherical particles. SEM photographs of the particles used experimentally provide evidence that surface asperities and very fine particles may be more important than previously suspected.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.