Copper recovery in the dark ages
We have already seen that both prehistoric man and Romans were aware of how to efficiently recover the lower melting point copper oxide and carbonate ores.
Mining continued in a small way during the medieval period, mostly by means of bell pits. These were shallow shafts with short chambers off at the bottom. Lacking the necessary technology, miners found it easier to sink another adjacent shaft rather than extend the workings. Such old workings can be identified by lines of in filled shafts and spoil heaps
The large mines at Rio Tinto in Spain help maintain the Roman empire’s demand for copper. However, the technology of the time had exhausted all the workable ore by the fall of the Roman empire.
Barbarian invasions of Europe in the fifth century AD pushed it into the dark ages. Europe became a chaotic place with no substantial mining taking place until the 10th century.
By the middle ages the Moors were living in Spain. They had started to reuse copper in cooking utensils and for ornaments. They were unable to recover copper from the remaining copper sulphide ores in the Rio Tinto area as the high iron, lead and zinc content meant that simple smelting did not work. A new process had to be developed which oxidised the ore to remove impurities before the copper could be gained.
The Moores learnt to collect the ore and break it into small pieces. These were then piled into heaps and water was allowed to seep down through them. The water was then collected and contained a solution of copper sulphate.
This copper sulphate solution contains far more copper than the mine water collected by the Romans.
The Moors also discovered that if Iron was placed into the water a reaction occurred in which the iron dissolved in the water and the copper precipitated.
CuSO4 + Fe = Cu + FeSO4
The process however was very slow and it could take years to get the copper sulphate and to precipitate it with iron.
The abundance of used iron tools meant that the Moors were able to sustain the demand for copper using this process which although slow was more efficient that the Roman method of collecting copper sulphate as chalcanthite.
This discovery of the Moors was the basis of some recovery of Copper from Parys mountain from recommencement of mine in the 18th century up to the early part of the 20th century.
The Moors continued to operate at Rio Tinto until around 1472 when they were driven out by the Spanish King Ferdinand. The Spanish leased the mine to a succession of Europeans. In 1873 they were brought by the London firm of Mathesons.
The Rio Tinto miners in the late 19th century also made the next big discovery in ore processing which was the effect of roasting ores. It was discovered that if ores were roasted before leaching took place as much copper could be recovered in 6 months as had previously taken 3 years with un-roasted ore.
The process had one major drawback. roasting the sulphide ores released sulphur dioxide gas. Clouds of this gas choked the Rio Tinto miners, and smelter workers and killed vegetation for 15 miles around the great mine.
The roasting of the crude ore was also done at Parys mountain with similar, though less dramatic affects. More on this process can be found of the section on processing copper ores.