Salt Free Treatment of Aluminium Dross

Abstract

Aluminium dross is composed of metallic aluminium and non-metallic compounds such as oxides, nitrides and carbides. The dross created during primary and secondary aluminium production can amount up to 1% of the total tonnage and may contain up to 90% aluminium metal. The conventional procedure for dross treatment is to use salt for separating the metallic aluminium and the non-metallic compounds. The resulting salt cake has to be processed further. This paper describes a process using a plasma rotary furnace with a non-oxidizing atmosphere and heated by a graphite plasma torch to separate the aluminium from the non-metallic compounds. A pilot scale furnace (charge 500kg) has been designed and tested. In the experiment presented here a mixture of aluminium and aluminium dross were charged into the furnace. Good atmosphere control was maintained during the experiment. No wear on the refractory and only minor wear on the graphite electrodes was observed after the experiment. The result shows that 98.9% of the aluminium in the charged raw materials was recovered in tapped metal without using any salt anywhere in the process. The aluminium metal tapped from the process had only minor increase in the trace elements compared to the metal originally produced. The inclusion content in the metal was also not increased significantly. The residual non-metallic compounds should be possible to recycle in the electrolysis or used in the cement industry.