Study On The Elimination Of Iron Impurity In The Molten Aluminum

Iron is considered to be the most harmful impurity element to the aluminum and itsalloys and not easy to be removed during the purification process, which block the recyclingof Al alloy and become a big problem for the aluminum industry around the world. Nowadays,the flux with the aim of removing Fe in the aluminum and its alloy has not been reported.Based on Na₂B₄O₇as an effective component, addition amount, reaction temperature andsettling time on the iron-removal efficiency and the related mechanism are studied by meansof direct-reading spectrometer, OM, SEM, EDS, XRD, DSC and Brinell hardness, effect offlux components. The conclusions can be summarized as follow:1,Melting point of flux with NaCl-KCl-Na₂B₄O₇system is about711℃. Layering is dueto its lower mobility when the flux is melted, which lowers the efficiency of iron removal.2,Melting point of flux with NaCl(5g)-KCl(5g)-Na₂B₄O₇(50g)-AlF₃(50g) system isabout596℃. The mobility of this quanternary flux is better than the ternary one. Whenappropriate parameters of additional amount, processing temperature and holding time ischosen, the average iron-removing efficiency(η) would research26.75%, which is70%higherthan that of the ternary flux.3,NaCl(3.5g)-KCl(3.5g)-Na₂B₄O₇(35g)-AlF₃(35g)-Na₂SO₄(7.6g) system flux isformedwith the addition of Na₂SO₄. The melting point of this quintuple flux is about576℃. Theaverage iron-removing efficiency(η) would research9%with the reaction temperature of785℃and the holding time of90minutes.4,Reaction between Na₂B₄O₇of the above flux and Fe in the molten Al produces Fe₂Bphase with high melting point and density that would be removed during the gravitysettlement.5,When RE-contained flux with NdF₃and Na₂B₄O₇is used for iron elimination in themolten Al, Fe is removed by the form of Nd₄Fe₆with higher density besides Fe₂B.