From Copper Concentrate to Refined Copper
Copper concentrate is processed exclusively through smelting metallurgy (pyrometallurgical). There are multiple reaction steps during the process. The reaction sequence follows as such: smelting into copper matte with a Cu-content of 30 - 80 %, conversion to blister copper (Cu-content 96 - 99 %), and finally, through smoldering refinement, resulting in anode copper with a Cu-content of ≥ 99 %, oxygen content of ≤ 0,2 %.
The majority of those for whom this process is commercialy viable employ flash/levitation smelting (the Outokumpu-Method). One reaction layer serves two purposes simultaneously. The roasting and smelting of the pre-dried concentrate separates the stone from the slag/waste/cinder into a underlying container. The resulting gasses and dusts are isolated downstream from the exhaust stack in the waste heat recovery boiler and filter. The filtered oven gasses are then exposed to sulphuric acid which serves to separate out the remaining SO2. Periodically, the copper matte is scraped from the oven floor and moved over to the converter. The remaining iron sulphide is oxidised by the injection of air and, by doing so, the sulphur (in SO2 form) escapes through the exhaust shaft. As a result, the copper sulphide is disassembled. More recently, extraction can be accomplished through a one-step procedure that combines the reaction steps of roasting, smelting, and fuming.
Finally, the copper is put in melt flow and further refined through electrolysis (fused-salt electrolysis). This process extracts the final 10% of the copper that would otherwise remain after flash smelting.
In fire-refinement, impurities are removed in the air furnace by blowing air through "poles" of the liquid copper matte in the rotary kiln (anode furnace) where the last traces of sulfur are removed. During this process the oxygen content is reduced to between 500 ppm and 2000 ppm. In the past, the "poles" were reduced by the immersion of birch or beech trunks in the liquid metal. Today mostly natural gases, propanes, naphtha, reformate gases, or ammonia are used as reducing agent.