Trace Elements in Aluminium Smelting Carbon Dust and Their Extraction

Gallium and germanium are practically important trace elements used in various high-tech areas as photovoltaics, electronic equipment, semiconductor gamma-ray detectors, infrared equipment, etc. New secondary raw materials for their extraction are a subject of a thorough search. In this study, new evidence of the presence of germanium and gallium in the wastes from the Hall–Héroult process was demonstrated and comprehensively discussed, and a method of their extraction was proposed. The concentration of gallium in the carbon dust reaches 0.02% and the concentration of germanium is below the detection limit. After the treatment of carbon dust, the concentration of trace elements is drastically increased. The carbon concentrate being a product of carbon dust treatment can be combusted to accumulate gallium in the ash while germanium distributes between the ash and the sublimates from the concentrate combustion due to the volatility of monoxide GeO. The concentration of gallium in the ash reaches 0.5 wt.% and the concentration of germanium highly depends upon the combustion temperature and the partial pressure of oxygen. The results of trace elements extraction in the acidic and basic environment are shown.