ENERGY EFFICIENT SALT-FREE RECOVERY OF METAL FROM DROSS

摘要

A process and an apparatus are disclosed for improved recovery of metal from hot and cold dross, wherein a dross-treating furnace is provided with a filling material with good capacity to store heat. This filling material is preheated to a desired temperature by injection of an oxidizing gas to burn non-recoverable metal remaining in the filling material after tapping of the recoverable metal contained in the dross and discharging of the treatment residue. When dross is treated in such furnace, the heat emanating by conduction from the filling material is sufficient to melt and separate the recoverable metal contained in the dross, without addition of an external heat source, such as fuel or gas burners, plasma torches or electric arcs and without use of any salt fluxes. Furthermore, the recovered metal being in the molten state can be fed to the molten metal holding furnace without cooling the melt; in addition, the non-use of fluxing salt for the treatment means that the non-contaminated residue can be used as a cover for the electrolytic cells in the case of aluminum. In the case of zinc dross, the residue is a valuable zinc oxide by-product very low in contaminants.

主权项

1. A process for treating dross containing a recoverable metal, in order to recover said metal, comprising:
(a) charging a batch of dross, resulting from skimming of said dross in a metallurgical plant, into a furnace containing a filling material preheated to a high enough temperature to insure that said dross is thereby heated above the melting point of the metal to be recovered by transfer of energy stored in the filling material; (b) providing an inert atmosphere in the furnace by filling the furnace with inert gas, to prevent oxidation of the dross during the process; (c) rotating or oscillating the dross within the furnace to ensure proper transfer of heat between the hot filling material and the dross and heating of the dross to a temperature above the melting point of the recoverable metal, a separation thereof from a dross residue and from the filling material and its agglomeration at the bottom of the furnace; (d) removing from the furnace the recoverable free metal through a taphole or through the door and the dross residue through the door while leaving inside the furnace the filling material and a fraction of non-recoverable metal which stays with said filling material as it cannot be separated from it; (e) thereafter, injecting a controlled amount of an oxidizing gas into the furnace while rotating or oscillating the furnace, so as to oxidize sufficient non-recoverable metal within the filling material to evenly heat and store in the filling material sufficient energy for treating a new batch of dross resulting from a further skimming of the dross in the metallurgical plant; (f) thereafter, stopping the oxidation reaction by providing an inert atmosphere in the furnace by filling the furnace with inert gas; and (g) charging into the furnace the new batch of dross and repeating the process.