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	Heap leaching - Wikipedia, the free encyclopedia
		Heap leaching is an industrial mining process to extract precious metals and copper compounds from ore.
		A particular byproduct is iron(II) sulfate, jarosite, which is produced as a byproduct of leaching pyrite, and sometimes even the same sulphuric acid that is needed for the process.
		Although the heap leaching is a low cost process, it normally has recovery rates of 60-70%, although there are exceptions.
	en.wikipedia.org /wiki/Heap_leaching (389 words)

	De-sliming Versus Agglomeration in Heap Leach Projects
		Heap or dump leaching is typically suited to small, low grade deposits of fully oxidised gold/silver or oxidised and sulphide (other than chalcopyrite) copper deposits due to the low CAPEX required to treat such ore bodies.
		Heap leaching is generally the chosen process for an ore body that doesn't warrant the OPEX or CAPEX of milling and intensive processing.
		Heap leaching paid for the stripping costs of the higher grade mill feed as the heap leach revenue "paid" for the mining of what would otherwise be low grade waste.
	www.biomet.com.au /Leach/Deslime.htm (1626 words)

	American Metal Market: Heap leaching: high marks for low grades - gold mines and mining
		Heap leach cyanidation techniques hold considerable potential for application where fine grinding is not necessary for good extraction.
		For heap leaching to be successful, these resources must have good permeability, after being crushed and heaped, to achieve uniform distribution of the cyanide leach solution throughout the heaps.
		Heap leaching problem ores with fines can be aggravated during stacking and preparation of the heaps by a natural sorting of coarse and fine material.
	www.findarticles.com /p/articles/mi_m3MKT/is_v94/ai_4544385 (928 words)

	[No title] (Site not responding. Last check: 2007-10-14)
		Bio-assisted heap leaching, as opposed to milling and flotation of copper sulphides to produce a copper concentrate, is the only economic process available, known to the applicant, for treating low-grade sulphide ores.
		Thus the temperature in the heap is primarily determined by the sulphide content of the ore in the heap.
		The chalcopyrite concentrate is leached in an agitated tank bioleaching reactor and the waste heat may, according to the method of the invention, be applied to a tower-grade portion of the same orebody, suitably crushed, in a heap leach.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=02/29124.020411&ELEMENT_SET=DECL (3892 words)

	European Nickel PLC - Acid Heap Leaching (Site not responding. Last check: 2007-10-14)
		Heap leaching of metallic ores is a well-proven process, especially in the copper industry, where many millions of tonnes of cathode copper have been produced using solvent-extraction and electro-winning for many years.
		The heap leaching of low grade nickel sulphide ores has been tested on a large scale in Australia by Titan Resources NL and its subsidiary Pacific Ore Technology ("POT").
		The heaps are covered with a network of plastic pipes that drip sulphuric acid onto the crushed ore. The acid dissolves the nickel, cobalt and some other minerals and the solutions flow on to the HDPE to the collection ponds.
	www.enickel.co.uk /acidheap_leaching.htm (452 words)

	Technical Articles
		Heap leaching was introduced in the 1970’s as a means to drastically reduce gold recovery costs.
		Heap leaching generally requires 60 to 90 days for processing ore that could be leached in 24 hours in a conventional agitated leach process.
		Heap leach solutions are frequently high in solids due to fine particle washing from heaps.
	www.denvermineral.com /basicp~1.html (2872 words)

	H
		heap - (3) a large, engineered pile of ore over which chemical agents such as cyanide are sprinkled in in the process of extracting metals by heap leaching.
		Leaching solutions, generally weak acids or alkaline cyanide, are percolated through heaps of ore. Leachate is collected and metals contained in the leachate are extracted chemically or electrochemically.
		Typically, the particle size of the ore to be leached is reduced to increase surface exposure of metal-containing minerals.
	ecorestoration.montana.edu /resources/glossary/h.htm (691 words)

	United States Patent: 5,449,397 (Site not responding. Last check: 2007-10-14)
		State-of-the-art precious metal heap leach practice varies with the nature of the ore. Bio-oxidation process steps may include ore crushing, acid pretreatment, inoculation with appropriate sulfide-oxidizing bacteria, addition of nutrients, recirculating the biolixiviant and cooling the heap (for 3 to 8 days), and allowing the heap to "rest" (for 3 to 8 days).
		In heap 200, conventional bio-oxidation of crushed ore particles 200 is accomplished to free precious metals dispersed or occluded within the ore. Air 206 may be introduced to heap 200 via plenum 208.
		Heap 202 is leached by recirculating portion 292 of neutral bisulfide lixiviant 282 saturated with H.sub.2 S through it by means of plenum 284, pump 286, and distributor 290.
	www.webpatent.com /patents/p5449397.htm (6021 words)

	Processing (Site not responding. Last check: 2007-10-14)
		Heap leaching is employed to process the clayey saprolite ore, plus the laterite ore that has a higher grade, or high-fines, making it less permeable and thereby unsuitable for dump leaching.
		For Heap leaching, without screening the ore passes through a mechanical preparation plant consisting of two stage crushing followed by cement addition and agglomeration in a rotating drum where cyanide rich water is added.
		For Dump leaching there is little preparation of the ore. The mining contractor has to control the ore to a top size of 600 mm.
	www.kenor.no /operations/processing.html (560 words)

	Innovations in Copper: Mining & Extraction: Producing copper nature's way: Bioleaching (Site not responding. Last check: 2007-10-14)
		Heap leaching — newly mined run-of-the-mine (ROM) material (intermediate grade, oxides and secondary sulfides) is deposited in a heap on an impervious natural surface or a pad and leached.
		The first is that the overall leaching process occurs by the microbial oxidation of ferrous to ferric ions followed by the chemical oxidation of the sulfide mineral by the ferric ion.
		The heap is inoculated with thermophilic bacteria and a process leach solution consisting of sulfuric acid, ferric iron and nutrients is applied to the heap.
	www.copper.org /innovations/2004/May/producing_copper_natures_way_bioleaching.html (4345 words)

	Biological Leaching (Site not responding. Last check: 2007-10-14)
		Heap leaching is also used in recovering metals from their ores.
		The theory and practice of leaching are well-developed because for many years leaching has been used to separate metals from their ores and to extract sugar from sugar beets.
		In industrial leaching, solvent and solid are mixed, allowed to approach equilibrium, and the two phases are separated.
	www.digistar.mb.ca /minsci/future/leach.htm (424 words)

	Temperature and Bacterial Heap Leaching (Site not responding. Last check: 2007-10-14)
		The feed leach liquor was allowed to drip onto the bed of crushed quartz at the top of the column which acted to distribute the feed liquor.
		Copper transition type ore leaching may be considered as a shrinking core type process in which the rates of diffusion become significant in the latter stages of leaching.
		For a significant number of bacteria to build up quickly on the solids in the leach, the rate at which they multiply must be considerably greater than the rate at which they are washed from the leach (heap or column).
	www.users.bigpond.com /biomet/leach/Vtemp.htm (1517 words)

	Heap Leaching (Site not responding. Last check: 2007-10-14)
		The successful application of heap leaching to the extraction of gold from low-grade deposits has been one of the main factors in higher output since the 1970s, especially in the United States.
		Heap leaching of gold was pioneered in the United States in 1973 at Placer Development's Cortez open pit in Nevada and proved on a larger scale at Pegasus Gold's Zortman Landusky mine in Montana.
		In the United States, where heap leaching is used most extensively, half of all production is won by this method.
	www.pamp.com /gold_c/Info_site/in_glos/in_glos_heapleaching.html (239 words)

	Remediation of Chromium-Containing Soils by Heap Leaching: Column Study (Site not responding. Last check: 2007-10-14)
		Heap leaching, a technique used extensively in the mining industry, has been investigated as a method for remediation of hazardous metal contamination of the vadose zone.
		The metals are removed by passing a special leaching solution through the ore. In this study, the removal of Chromium (VI) from four New Mexico soils (sand, sandy loam, and clay) using heap leaching was evaluated at a column scale.
		The heap leaching study demonstrated greater than 99% removal of Cr(VI), using tap water as the leaching agent.
	www.pubs.asce.org /WWWdisplay.cgi?9305411 (190 words)

	Electrochemistry Encyclopedia --- Extracting metals from sulfide ores
		The Sherritt-Gordon pressure leach procedure for the treatment of zinc sulfide concentrates was introduced in 1981; zinc sulfide is oxidized by oxygen in sulfate solutions to form zinc sulfate and sulfur.
		The zinc is recovered by electrolysis as it is in the roast leach process already described.
		The rate of the leaching of sulfides in sulfuric acid media is significantly less than that of oxides, but the intervention of bacteria accelerates the process.
	yces.case.edu /ed/encycl/art-m02-metals.htm (5694 words)

	MIT Western Hemisphere Project: Cyanide & Gold
		The leaching technique was used in small measure by miners in the early 1900s to draw gold and copper out of ore so low in mineral content that large-scale operators would have tossed it out as waste.
		In the old days, leaching was done by misting cyanide over a barrel or large vat filled with crushed ore. The cyanide dissolved microscopic specks of gold from the rock, much as water dissolves sugar.
		Crushed ore is piled in huge heaps and sprayed with a dilute alkaline-cyanide solution, which percolates through the pile to extract the gold, which is separated from the effluent in a processing plant.
	web.mit.edu /hemisphere/events/porvenir.shtml (1071 words)

	MTU Tech Alive Explore Research Project
		Currently, heap-leaching operations are plagued by poor permeability of the heap, which leads to uneven distribution of the leaching solution, unleached zones in the heap, and low metal recovery.
		Because of problems with effectiveness or cost, all binders that have been evaluated to date for use in acidic heap leaching have either performed poorly, or proved to be too expensive for commercial use.
		The project will improve energy efficiency by increasing metal recovery during heap leaching, reducing the quantity of ore that must be handled and prepared to produce a given amount of metal.
	techalive.mtu.edu /explore/020529.htm (592 words)

	Heap Leaching (Quarterly Bulletin Article) Introduction (Site not responding. Last check: 2007-10-14)
		Heap leaching for gold and silver recovery is a fairly simple process that eliminates many complicated steps needed in conventional milling.
		A "typical" precious metal heap leaching operation consists of placing crushed ore on an impervious pad.
		The pregnant (gold bearing) solution drains from the heap and is collected in a large plastic-lined pond.
	geoheat.oit.edu /public/bulletin/bi009.htm (242 words)

	What is BioHeap? (Site not responding. Last check: 2007-10-14)
		These strains of bacteria are capable of leaching metals from sulphide minerals, minerals that would otherwise require an autoclave or smelter to process.
		Heap leaching is utilised in recovering copper from the more easily oxidised secondary copper minerals such as covellite and chalcocite.
		Importantly, the leach does not require extreme temperatures, nor does it require fine grinding, as is usually the case with conventional indirect leaching.
	www.pacificore.com.au /index.php?id=5&type=1 (855 words)

	[No title] (Site not responding. Last check: 2007-10-14)
		Thermophilic heap leaching may be a feasible alternative, provided that the necessary high temperature environment can be maintained within the heap without external heating.
		A comprehensive heap heat conservation model (Dixon, 2000) is used to determine whether thermophilic temperatures can be achieved and maintained in a full-scale heap with the calculated heat generation rates.
		The effect of heap height on the temperature profiles is only marginal, although shorter heaps tend to retain less heat, achieving slightly lower average temperatures under given conditions.
	www.min-eng.com /protected/bio02ex/petersen.doc (1351 words)

	Geobiotics - Innovators in Biooxidation Technology
		Both heap leaching and stirred tank biooxidation are accepted in the minerals industry and are in commercial operation worldwide.
		The heap is bioleached to produce a solution from which copper is recovered by solvent extraction and electrowinning.
		Since the heap is typically not reclaimed after biooxidation, rinsing may need to be more thorough than for a refractory gold heap to ensure maximum recovery of valuable metals.
	www.geobiotics.com /pages/tech_all.cfm (5663 words)

	Caitlin Allen (Site not responding. Last check: 2007-10-14)
		Heap leaching is a method used most commonly for the mining of gold.
		The leach pads help prevent toxic solutions from running off into the surrounding areas and therefore they decrease the risk of harming any living organisms living in the area the mining is occurring in.
		While, the environmental considerations concerning heap leaching are important, it is not necessary to stop this form of mining because of regulations placed on heap leaching methods such as the ones mentioned.
	www.personal.psu.edu /users/c/r/cra135/TopicalEssay3.htm (610 words)

	Going for the Gold
		The leaching process varies depending upon the character of the deposit being mined.
		In heap leaching, crushed ore is placed on a specially designed impervious pad and sprayed with a dilute solution of sodium cyanide, which percolates downward, dissolving the gold.
		Build a classroom heap leach operation with a pan and a mixture of sand, gravel, and sugar cubes.
	www.blm.gov /education/going_4_the_gold/modern_tech.html (400 words)

	Nat' Academies Press, Evolutionary and Revolutionary Technologies for Mining (2002)
		Bioleaching for heaps and dumps was developed by the copper mining industry and adapted to treat refractory gold.
		To speed up leaching rates and improve recovery rates, successful heap-leaching and dump-leaching operations require a combination of geology, mineralogy, hydrometallurgy, hydrology, and modeling, and sometimes biology (when bioleaching is used).
		An important advance in heap leaching and dump leaching would be the development of new lixiviants that could effectively extract metals directly in an environmentally friendly manner, especially metals from refractory sulfide minerals (Sparrow and Woodcock, 1995).
	www.nap.edu /openbook/0309073405/html/42.html (844 words)

	Leach, Inc.'s Home Page (Site not responding. Last check: 2007-10-14)
		Leach, Inc. offers design and supervision of laboratory and field test programs to evaluate the heap leaching of copper and gold ores.
		Leach, Inc. is the only company offering scale-up of laboratory test results based on the shrinking core model of particle leaching.
		In addition, Leach, Inc. designs heap leaching irrigation systems and develops operating schedules to insure constant preg grade and metal production rate from the heap leach operation and performs economic evaluations designed to optimize the heap leaching operation.
	members.aol.com /leachinc (126 words)

	Laterite heap leaching produces first nickel (Site not responding. Last check: 2007-10-14)
		The first heap consists of 4200t of 1.15% nickel ore crushed, agglomerated and stacked on a multi-layered plastic liner.
		The second heap of 9000t is operational and the third heap is under construction.
		It is designing the full scale heaps and metallurgical plant and is determining the capital and operating costs for the commercial scale operation.
	www.ferret.com.au /articles/b4/0c02fcb4.asp (503 words)

	Gold
		Heap Leaching: extraction of gold using heap leaching and carbon recovery
		Cyanide ions have a natural affinity for gold, which reacts with the gold solid particles to make gold cyanide complexes which are soluble in water.
		The gold is now in the metal element state with zero charge and appears as fine specks of gold to be precipitated out and the precipitate is then refined.
	www.elmhurst.edu /~chm/vchembook/327gold.html (492 words)

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