Oxidation of copper-sulphur matte by submerged gas injection, mass transfer rates and physical phenomena

grantor: University of TorontoPeirce-Smith converters have been used for converting a variety of base metal sulphide mattes for most of this century. Although they are environmentally undesirable, their use in the industry is sustained by high levels of flexibility and productivity. The mass transfer rates inside a Peirce-Smith converter are very high. Air is typically injected at 0.2 $\rm m\sp3/s$ through each of 40 tuyeres at an immersion depth of less than 0.5 m while exceeding 90% oxygen utilization. Injection is carried out under constant flowrate conditions in the bubbling regime. Oxygen utilization and bubble frequency were measured on a laboratory scale while injecting air/oxygen mixtures into molten copper-sulphur melts through a submerged orifice. Purging of the liquid surface and varying lance immersion were used to separate the extent of reaction into the following stages of gas-liquid contact; bubble growth, bubble rise and bubble rupture. Bubble rupture is defined as a combination of the spout zone on the liquid surface and the dispersion zone in the overlying gas. Gas injection was carried out under constant flowrate conditions in the constant frequency bubbling regime. Bubble volumes correlated well with semi-empirical relationships specifically for liquid metals. Changes in the gas and liquid phase composition confirmed gas phase mass transfer control. The bubble rupture stage was found to be very important in achieving high levels of oxygen efficiency. The extent of reaction in this stage depends on gas flowrate, orifice orientation and orifice diameter. For gas injection through a downward facing nozzle, a critical gas flowrate has been identified as the point at which the mass transfer coefficient increases substantially. This critical value was found to decrease with decreasing nozzle diameter, and x-ray imaging of the liquid surface indicates the formation of an expanded spout zone. This is analogous to the transition from a packed bed to a fluidized bed in a gas-solid system. The expanded spout may also be thought of as a foam, resulting from the gas injection rate exceeding the bubble rupture rate in the absence of an expanded spout. The influence of temperature above $\rm 1300\sp\circ C$ suggests a possible transition in the mass transfer mechanism. This requires further investigation.Ph.D