Details of each material such as weight and analysis of platinum group metals is the initial step of any refinery so that suitable blends can be prepared for processing through the smelting process. The smelting department is the hearth of the operation feeding downstream processes with suitable and timely feed for the ultimate recovery of pure precious metals. Material for smelting will have an analysis available for control purposes. In this way, for powders, Inductively Coupled Plasma (ICP) analysis or for metals, X-Ray Fluorescence (XRF) analysis must be performed. In the case of Powders, various batches will be mixed together to obtain an optimum blend to minimize precious metals loss to slag, slag volume, cost of processing, formation of other phases and flux addition. Also, analysis will help to maximize precious metals yield to bullion stream, payload capacity for material, speed of processing, control of processes and slag forming tendency.
Refineries are used to perform a computer survey of the available material to produce blends which are appropriate for processing. The material available for process must be considered in terms of weight and analysis of the precious metals and the portion to be removed. This is to help to produce the most effective material flow through the smelter. The powdered material is charged into a ribbon blade mixer and mixed with suitable flux/binding agent (calcium hydroxide or sodium carbonate). It is then discharged into a rotating pan to form homogeneous 20-30 mm pellets. Basically, there are two circuits operated in the smelter, one circuit is for the processing of gold, silver, platinum and palladium; and the other circuit is for the processing of platinum, palladium, iridium, rhodium and ruthenium.
Gold, silver, platinum, and palladium are collected in copper. Some refineries employ lead. If copper is employed, the process can be performed at high temperatures due to the presence of refractory oxides in much of the intake. Copper is easier to remove than lead to keep the circuit in balance. Too much copper in the circuit would cause an increase in stocks and tight control is essential if precious metals lockup is to be avoided. A sulphuric acid leach is needed to remove copper, but lead is more difficult to remove. Copper is more environmentally accepted than lead. The furnaces are charged with pelletized feed and appropriate fluxes are added to produce inert stable silicates slags and copper oxides is added to produce copper bullion containing the precious metals.
TBRC, Top Blown Rotary Converter
Smelting Flowsheet