Origins Heap leaching dates back to the second century BC in China, where iron was combined with
copper sulfate. By the time of the
Northern Song dynasty, a copper
alloy was able to be recovered by leaching. Early examples of leaching performed by alchemists resembled mixing iron with copper sulfate, yielding a layer of metallic copper. From 1767 to 1867, the production of
potash in
Quebec became an important industry to supply France's glass and soap manufacturers. Von Patera's process, though successful, did not generate much use due partly to the price of hyposulphite. Additionally, with Patera's process, if the sodium hyposulphite failed to dissolve perfectly, silver would often be caught in the extra solution and not properly extracted. Prior leaching processes often could not concentrate ores with too much base metal, something thing the Russel Process was able to solve thus making it more lucrative. In 1887, when the cyanidation process was patented in England, it began to phase out the existing Russell Process. Cyanidation was much more efficient and had a recovery rate of up to 90%. Leading up to World War I, many new ideas for leaching processes were experimented. This included using ammonia solutions for copper sulfides, and nitric acid for leaching sulfide ores. Most of these ideas were phased out into obscurity due to the high cost of the leaching agents required.
Modern leaching In the 1940s, as a result of the
Manhattan Project, the United States government needed ready access to
uranium. Many different techniques in leaching were quickly employed at a large scale. Both synthetic resins and organic solvents were used early on to
extract uranium. Ultimately, the use of organic solvents was less tedious compared to ion exchange through synthetic resins, and further production of uranium and other rare earth metals moved towards solvent extraction. In the 1950s, pressure hydrometallurgy was developed for the leaching of multiple different metals, such as sulfide concentrates and laterites. Particularly at the Mines Branch in Ottawa (now known as
CANMET), it was demonstrated that
pyrrhotite-
penthandite concentrate could be treated in
autoclaves, with the resulting
nickel in a solution while iron oxide and sulfur remain in the residue. This process was later used in other nickel recovery operations across the globe. In the 1960s, heap and in situ leaching became widely practiced, particularly for copper. In situ leaching was later used for the extraction of uranium as well. Pressure leaching was further refined in the 1970s and 80s. ==See also==