An Improved Method for Removing Light Metals from Molten Aluminum in a Reduction Plant

摘要

Both modern magnetically compensated and modernized cells using low ratio bath with quiet metal pads can produce aluminum with sodium content higher than preferred. Older potlines using LiF-modified bath as a means to enhance profitability, produce virgin Al with 10-20 PPM Li in addition to some Na. To improve both quality and efficiency in processing Al to obtain premium grades or meet specifications for certain products, the light metals should be removed before the tapping crucibles are loaded into the casthouse furnaces. Technologies ranging from a bed of (charcoal + AlF_3) to treatment-in-crucible (TAC) with powdered AlF_3 added to a vortex for dispersion are being used to lower the concentration of light metals. Here, an improved TAC method is described based upon the efficient dispersion of powdered NaAlF_4 introduced on a carrier gas stream down a hollow impeller, which further disperses the fluoride, which, because of its higher vapor pressure, vaporizes and improves the contact with molten Al. The system includes other advantageous features. This process has the expectation for removing light metals more efficiently and will reduce concentrations of Na and Li to 1 PPM within 10-12 minutes.