Outotec's gold recovery process is purely hydrometallurgical. Its main advantage for the producer is that it offers a high direct recovery rate as well as a very low inventory of metals bound in the process.
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.
The raw material is leached in 1) hydrochloric acid and hydrogen peroxide or 2) in hydrochloric acid and chlorine gas. The complete process achieves an exceptionally fast and total leaching of gold and the platinum group metals.
Gold is precipitated out of the solution and recovered with a high degree of purity. The leaching residue, mainly silver chloride, can be recycled in the Doré smelting process. Platinum metals are precipitated as a concentrate, which can be further refined or sold on the market.
The total process time is only a couple of days and gold inventory in the process is very low.