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Leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within the ore, into soluble salts while the impurity remains insoluble. These can then be washed out and processed to give the pure metal; the materials left over are commonly known as tailings .
In-situ leach for uranium has expanded rapidly since the 1990s, and is now the predominant method for mining uranium, accounting for 45 percent of the uranium mined worldwide in 2012. [2] Unlike open-pit and underground mining, in-situ leaching does not rely on burial depth as a criterion but is based on the properties of the uranium deposit.
Ball-and-stick model of the aurocyanide or dicyanoaurate(I) complex anion, [Au(CN) 2] − [12] Cyanide leaching "heap" at a gold mining operation near Elko, Nevada. The chemical reaction for the dissolution of gold, the "Elsner equation", follows: 4 Au + 8 NaCN + O 2 + 2 H 2 O → 4 Na[Au(CN) 2] + 4 NaOH
Often opposed by environmentalists because it uses cyanide, heap leaching is pitched by the mining industry as a fully matured, safe method. But as the saying goes, it only takes one bad apple to ...
Any more than a few percent carbonate minerals means that alkali leach must be used in preference to the more efficient acid leach. The Australian government has published a best practice guide for in situ leach mining of uranium, which is being revised to take account of international differences. [33]
Biological substances can experience leaching themselves, [2] as well as be used for leaching as part of the solvent substance to recover heavy metals. [6] Many plants experience leaching of phenolics, carbohydrates, and amino acids, and can experience as much as 30% mass loss from leaching, [5] just from sources of water such as rain, dew, mist, and fog. [2]
Pellets of soda lye (sodium hydroxide) Pellets of potash lye (potassium hydroxide)Lye is a hydroxide, either sodium hydroxide or potassium hydroxide.The word lye most accurately refers to sodium hydroxide (NaOH), [citation needed] but historically has been conflated to include other alkali materials, most notably potassium hydroxide (KOH).
In a mining setting it is leading practice to carry out a geochemical assessment of mine materials during the early stages of a project to determine the potential for AMD. The geochemical assessment aims to map the distribution and variability of key geochemical parameters, acid generating and element leaching characteristics. [17]