Gold Refining

    The Miller process is one of the most used in the gold refining. In this process the charge is melted in the induction furnace. Chlorine gas is introduced into the molten raw gold through a rotating lance in a very precise and controlled way, so that no break through of chlorine gas occurs. By-metals like silver, copper, nickel etc. as well as amphoteric elements like S, Se, Te, As, Bi are removed into the slag as molten chlorides which float on top of the gold melt.

    Fumes of metal chlorides are removed and filtered (2 stage wet filter or 2 stage dry scrubbing system) that maximizes recovery and cleaning of the exhaust air. The process time is 2 - 4 hours following the input volume and gold content. The gold, containing the platinum group metals, will have a metal content of 99 to 99.5%. The balance is normally only silver and copper.

    The slag is first manually poured off into a de-golding crucible, which is then slowly cooled to allow any trapped gold to sink to the bottom of the crucible to solidify. The molten chloride is then carefully poured off into separation moulds leaving the gold. The remaining gold particles can be removed manually from the crucible and separation mould when they have cooled. After the slag removal the gold melt is poured through a ceramic filter directly into the granulation equipment or anode moulds. The granulation water is treated in a wash water treatment system before discharge. The gold granules are then moved to the Dissolving reactor for wet chemical refining, the anodes go to electrolysis. The slag from the de-golding process is returned to the slimes smelter

    The main advantages are summarized in the next table:

    Short process time - quick refining;

    Variable design capacities 20 kg to 500 kg - or larger;

    Ceramic rotating chlorine lance for optimum diffusion minimizes chlorine consumption, metal losses and scrubber neutralization costs;

    Induction furnaces incorporate high efficiency coil with advanced solid state power supply systems to minimize power consumption - fewer kW required per kilo of metal melted;

    Highly efficient non corrosive extraction hood to minimize emissions - allows obstruction-free access to crucible-contents - easily dismantled for removal of any condensed chloride residues.

    Ceramic crucible with special spout for long service life;

    Computerized control panel to monitor all functions like furnace temperature, flow control of nitrogen/chlorine gas, scrubber functions, exhaust measurement, chlorine leakage detection; including alarm signals;

    A specially designed in-line 2 stage integrated Prior scrubber is placed next to furnace to provide maximum extraction and gas scrubbing efficiency;

    untitledass702Fig. 6.10 Gas chloride reacting with gold