The Kinetics of Pb Removal from Brass Scrap Using Compound Separation

Abstract

2 wt% Ca was added to molten brass containing 3.2 wt% Pb. The composition and grain size of the formed Ca-Pb compound were examined in detail using SEM-EDS and XRD. This revealed that the composition of the Ca-Pb compound depends on the grain size of the liquid phase Pb and the diffusion phenomenon of the Ca in the Ca-Pb compound formed on the surface of the Pb. When the Pb has a fine grain, a compound composed only of Ca-Pb compounds is formed. When the grain size of the Pb is several μm, Ca-Pb compounds containing unreacted Pb in the center are formed. These compounds aggregate into a larger compound grain. From the evaluation of the floating force (the resultant force of the weight and buoyancy of the Ca-Pb compounds formed) and the rising terminal velocity of the Ca-Pb compound within the molten brass, it was found that the floating force and rising terminal velocity depend on the composition and grain size of the Ca-Pb compound. It was found that since Ca-Pb compounds with a floating force greater than 10-6 g ·cm/s2 have a very large rising terminal velocity, they reach the surface of the molten brass in a short time after compound formation and then continue to float on the surface of the molten brass. Thus they can be removed by skimming. The effects of the grain size of the Ca-Pb compound on the floating force and the rising terminal velocity were greater than those of the composition of the Ca-Pb compound.