Heap leaching

Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other earth materials. Similar to in situ mining, heap leach mining differs in that it places ore on a liner, then adds the chemicals via drip systems to the ore, whereas in situ mining lacks these liners and pulls pregnant solution up to obtain the minerals. Most mining companies favor the economic feasibility of heap leaching, considering that heap leaching is a better alternative to conventional processing methods such as such as flotation, agitation, and vat leaching. Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other earth materials. Similar to in situ mining, heap leach mining differs in that it places ore on a liner, then adds the chemicals via drip systems to the ore, whereas in situ mining lacks these liners and pulls pregnant solution up to obtain the minerals. Most mining companies favor the economic feasibility of heap leaching, considering that heap leaching is a better alternative to conventional processing methods such as such as flotation, agitation, and vat leaching. Additionally, dump leaching is an essential part of most copper mining operations and determines the quality grade of the produced material along with other factors. Due to the profitability that the dump leaching has on the mining process, i.e. it can contribute substantially to the economic viability of the mining process, it is advantageous to include the results of the leaching operation in the economic overall project evaluation. This, in effect, requires that the key controllable variables, which have an effect on the recovery of the metal and the quality of solution coming from a dump leaching process. The process has ancient origins; one of the classical methods for the manufacture of copperas (iron sulfate) was to heap up iron pyrite and collect the leachate from the heap, which was then boiled with iron to produce iron(II) sulfate. The mined ore is usually crushed into small chunks and heaped on an impermeable plastic or clay lined leach pad where it can be irrigated with a leach solution to dissolve the valuable metals. While sprinklers are occasionally used for irrigation, more often operations use drip irrigation to minimize evaporation, provide more uniform distribution of the leach solution, and avoid damaging the exposed mineral. The solution then percolates through the heap and leaches both the target and other minerals. This process, called the 'leach cycle,' generally takes from one or two months for simple oxide ores (e.g. most gold ores) to two years for nickel laterite ores. The leach solution containing the dissolved minerals is then collected, treated in a process plant to recover the target mineral and in some cases precipitate other minerals, and recycled to the heap after reagent levels are adjusted. Ultimate recovery of the target mineral can range from 30% of contained run-of-mine dump leaching sulfide copper ores to over 90% for the ores that are easiest to leach, some oxide gold ores. The essential questions to address during the process of the heap leaching are as following: