Abstract
The Mechanism of Pb removal from brass scrap by compound separation using Ca and NaF addition was investigated. Because large Ca-Pb compound particles formed by Ca addition rise to the surface of the molten brass, they can be skimmed off from the molten brass. However, fine Ca-Pb compound particles remain in the molten brass because of low buoyancy. By subsequent NaF addition, the reaction between Ca-Pb compound and NaF takes place at their contact regions, resulting in the formation of solid CaF2, liquid Pb and Na gas. Pb is mainly present at the Ca-Pb compound-CaF2 interface. CaF2 acts as a binder for aggregation of fine Ca-Pb compound particles, resulting in the formation of light and large composite compounds, which rise to the surface of the molten brass. A high Pb removal rate is achieved by skimming off.
Highlights
The machinability of brass alloys containing Pb is better than those of other metallic materials
The results show that Ca2Pb is formed in the molten brass after Ca addition and Ca2PbO4 is formed by atmospheric oxidation of Ca2Pb during air cooling after skimming off
The large Ca2Pb particles that rise to the surface of the molten brass can be skimmed off, but fine Ca2Pb particles remain in the molten brass
Summary
The machinability of brass alloys containing Pb is better than those of other metallic materials. Pb is a harmful substance that has neurotoxic effects and affects fertility. In Japan, the permitted level leached Pb in drinking water supplies was revised to 0.01 mg/L in April 2003 [1]. In European-based REACH program, the limit Pb content in brass alloys has been decreased 0.5 wt % from June 2016 [2]. In the USA, the Pb content in water-bearing materials has been limited to 0.25 wt % since 2014 [3].
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