Anode Slime

Our process solutions recover precious metals from anode slime produced in electrorefining plants. We offer two types of processes for this industry; both of which produce the same end products including selenium, silver, gold and platinum group metals also known as PGM.


  • Furnace

    The furnace is a compact and energy-efficient reactor with high capacity. Energy is introduced with an oxygen/fuel burner lance. Converting and refining is done with a special lance using air at supersonic speed, giving high oxidizing efficiency.

  • Selenium Roast

    In the selenium roasting furnace, copper-free anode slime is dried and selenium evaporates as selenium dioxide gas using oxygen an SO2 gas as reagents. The selenium is recovered from the off-gases into an aqueous solution. The purity of the product selenium is over 99.5% and even higher purity can be reached by treating the selenium in a distillation furnace.

  • KILN

    The KILN converter takes care of the smelting, reduction and refining steps in the same furnace, which is energy efficient. The compact KILN unit consists of a feeding unit, smooth tilting and a rotating converter. Doré anodes are casted with a special fully automated casting machine. Off-gases are led in a controlled way from the KILN

  • Silver Refining

    In order to separate silver from gold and platinum group metals, Doré anodes are electrolytically processed in new, improved Moebius cells at current densities as high as 1,000A/m2. Silver dissolves in the nitric electrolyte and precipitates as crystals, which are scraped off the stainless steel cathodes. Silver anode slime is collected in bags that surround the anodes. This mud contains gold, platinum metals and silver.

  • Gold Refining

    The silver electrolysis anode slime or any other similar gold-containing material can be refined in Outotec’s Wet Chemical Chlorination Process. Materials like gold alloy bars can be pre-treated by melting and atomizing into fine powder, before being leached and refined. Silver Doré anodes with extremely high gold content can also be atomized and taken to gold refining before going to silver electrolysis refining. In this way, gold can be extracted as early as possible.