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Home > Black dross,what is black dross?

Black Dross, what is black dross? black dross definition

 

Many aluminum scrap melters use reverberatory furnaces with external side bays for charging. It is a common practice to charge the scrap to the furnace metal pool through this side bay. The bay often contains a salt flux layer to help protect the molten aluminum pool from oxidation and to improve the metal recovery of the scrap. This type of furnace is especially common when processing light gauge or high surface area scraps such as turnings or UBC.

 

The flux usually consists of sodium chloride (NaCl) and potassium chloride (KCl) with the possible addition of a fluoride salt compound. A mixture of chloride salts is used to lower the melting point of flux. The flux-containing dross resulting from this melting operation is called “black dross” because of its characteristic dark color.

 

The black dross consists of a mixture of salt, oxides and metal. At temperatures above the melting point of the salt flux mixture, the black dross consists of two immiscible liquid phases: aluminum metal and liquid salt containing oxide particles and films. As the oxide content increases in the salt flux, the mixture becomes less fluid and more viscous in nature. The flux is very efficient in trapping and holding the oxide compounds.

 

The metal content of the black dross will vary depending on the scrap type being charged and the processing conditions, but varies from 7 to 35% and in special circumstances as high as 50%. The oxide content of the black dross will be approximately equal to the salt flux content.

 

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black dross, what is black dross, black dross definition