Copper mining and smelting has not undergone major technological revolutions except in terms of scale and mechanisation. This is largely because extracting the copper metal from the rock remains a complex business both in the preparation of the ore and the repeated stages of roasting, melting and remelting that takes places in furnaces.
This historic footage of mining and smelting in Utah, USA was published in 1949 [thank you James for pointing out my error which arose from my misreading of the video’s description on YouTube!] and demonstrates the processes of extracting copper that had been taking place since the turn of the twentieth century. The Utah mine was at the time one of the largest in the world. An open pit mine, dynamite was used to blast the rock face to reveal the copper ore lodes.
A significant change in preparing the ore for smelting is demonstrated with the ball rolling mills which grinds up the copper ore to a fine powder enabling it to be easily dissolved so the copper-bearing copper sulphide more readily floats to the top and the waste slurry can be tapped off and not interfere with smelting. The roasting and melting takes place in a blast furnace using a technique similar to that developed by Bessemer in the 1850s.
This process was developed originally for intensifying the production of steel from pig iron but was adopted by copper smelters, especially in the USA, in the 1880s. Prior to this the ‘Welsh Process’ of smelting copper relied on a series of roasting or calcining, melting and refining in reverberatory furnaces.
The principle of the reverberatory furnace was to separate the ore and flux from the smelting fuel (coal). The Bessemer or blast furnace method, crudely speaking, introduces hot (pressurised) air into the furnace through Tuyeres (pipes). After the roasted ore and flux (e.g. coke, sand, lime) are added to the furnace and reaches a temperature exceeding 1000 degrees Celsius the hot air pumped in stimulates the separation of ferrous sulphide or slag from the smelted copper matte. The slag is lighter and floats to the top and is tapped off and then the heavier copper matte which settles underneath can be tapped off separately and further refined into blister copper. The sulphurous gases are released through a chimney at the top of the furnace.