|
Heap leaching is an industrial mining process to extract precious metals, copper, uranium, and other compounds from ore via a series of chemical reactions that absorb specific minerals and then re-separates 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. 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 sulfate〔Industrial England in the Middle of the Eighteenth Century, (''Nature'' ), Vol, 83, No. 2113, Thursday, April 28, 1910; page 267.〕 ==Process== The mined ore is usually crushed into small chunks and heaped on an impermeable plastic and/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 then 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 easiest to leach ores (some oxide gold ores). In recent years, the addition of an agglomeration drum has improved on the heap leaching process by allowing for a more efficient leach. The rotary drum agglomerator, such as the tyre driven Sepro Agglomeration Drum works by taking the crushed ore fines and agglomerating them into more uniform particles. This makes it much easier for the leaching solution to percolate through the pile, making its way through the channels between particles. The addition of an agglomeration drum also has the added benefit of being able to pre-mix the leaching solution with the ore fines, to achieve a more concentrated, homogeneous mixture, and allowing the leach to begin prior to the heap.〔(【引用サイトリンク】url=http://feeco.com/2012/04/23/agglomeration-drums-in-the-heap-leaching-process/ )〕 Although heap leach design has made significant progress over the last few years through the use of new materials and improved analytical tools, industrial experience shows that there are significant benefits from extending the design process beyond the liner and into the rock pile itself. Consulting firm (HydroGeoSense, Inc. ) pioneered the characterization of the physical and hydraulic (hydrodynamic) properties of ore-for-leach an approach which has been adopted by several industry leaders such as FMI, Rio Tinto and Mintek and has been applied to the design and troubleshooting of many modern heap leach facilities worldwide. Hydrodynamic characterization focuses on the direct measurement of the key properties of the ore, namely: * 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heap leaching」の詳細全文を読む スポンサード リンク
|