aluminium-origins In the aluminium refining process, scrap is melted in rotary or reverbatory furnaces under a bath of molten salt which floats on the metal surface. The salt is typically a eutectic or near-eutectic mixture of sodium and potassium chlorides containing low levels of fluorides (cryolite).

Molten metallic aluminium and its salt cover are successively tapped from the rotary drum surface. The last salt mix tapped from the furnace contains residual aluminium metal (around 5%) and various metal oxides, mainly aluminium oxide. This mixture solidifies in pans to become what is termed “salt slag.”The molten salt layer performs two functions:

  1. Salt coats the metallic aluminium in the melt phase, minimizing oxidation losses.
  2. Fluoride in the salt facilitates break-down of prior oxide layers on the surface of the scrap and thence promotes improved separation between the aluminium and non-metallic contaminant.
At the end of the melt cycle the salt layer is tapped off and, on cooling, solidifies into a salt slag. This salt slag is a hazardous waste which must be disposed of under controlled conditions. Historically, in Europe, aluminium salt slag was landfilled. More recently, a combination of tighter environmental regulation and high landfill costs has terminated this practice. Instead, aluminium salt slag is recycled in dedicated plants such as RVA.
Reprocessing is recognized across the EU as the best practicable environmental option for salt slags. RVA’s reprocessing technology converts salt slag from a waste stream to a source of essential raw materials.