The Origins of Copper

The Chuquicamata Copper Mine in Chile

Raw ore contains considerably less copper than pure copper minerals. Today's processed ore often contains roughly only 1 % Cu, and in some cases even less than 0,5 % Cu.  In the latter case, copper is only extracted using the most cost-efficient strip-mining procedures and by using the most current extraction technologies. The terraced copper strip-mines are among the largest metals mines of the world.  Although these mines often produce far less copper than iron, the amount of earth moved is comparable to the total of the world's iron mines. 

The major providers of ore and copper-concentrate are found in Chile, where more than a third of the world's copper is extracted.

From Ore to Copper Concentrate

Before smelting, the sulfuric ore with copper content in it is separated from that without.  The ore is broken down by an ore crusher and then further reduced to powder by a powder mill.  The resulting grains are often smaller than 100 μm.

Flotation

The ore enrichment of copper concentrate is accomplished through a technique called flotation.  With flotation, the different surface properties of the minerals cause them to separate.  Copper concentrate normally contains between 20 to 30% copper, and in very favorable conditions up to 50%.

In cases where there are significantly lower quantities to extract, particularily in oxidic ores, copper is extracted using hydrometallurgical or other specialised procedures. 

Smelting Metallurgy Extraction

 

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.

Anode Casting Wheel

Some of the fire-refined tough pitch copper is worked on continuous casters into forms such as round bars and billets, however the majority are cast as anodes to go through electrolytic refining.

The anodes are then poured into the 20 -30 open spaces of the casting wheel. The resulting plates weigh between 300 and 500 kg and have a copper concentration of approximately 99.5%.

Electrolysis Refinement

Electrolytic refinement is necessary because even very small amounts of impurities can significantly reduce the thermal and electrical conductivity of copper. For this reason, electrolysis baths (made with relatively impure copper anode plates and electrolytic copper) are filled with copper sulphate solution and hung in modern, high-quality, steel electrolysis units. Electric current separates the copper from the anode and attaches it to the cathode as pure copper, while the impurities remain in solution or sink into the anode sludge. The cathode plates that are generated are then resmelted and formed into semi-finished product.

(concentration approximately 99,99% Cu)