The process is commonly used to extract metals such as gold, copper, and uranium yellowcake in addition to several other minerals. A number of heap leach operations exhibit poor or lowerthanpredicted metal recovery, loss of solution flow and control within the ore heap, loss of ore heap stability under leach, failure of liner andor solution recovery systems, and overtopping of process water ponds. Heap leaching is a conceptually simple process but has several characteristics that make modelling the flowsheet quite complicated. In 1968 the tonnage of highgrade oxide ores was decreasing and vat leaching was on the decline. To enhance metal recovery, modern leaching processes use. At first glance, heap leaching can appear to be an extremely simple technology.
Heap leaching is one of the oldest and the most traditional mining process used to extract the valuable metals from specific minerals. Several studies have been performed with the goal of improving the leaching process. Heap leaching is generally the chosen process for a low grade ore body that doesnt warrant the opex or capex of milling and intensive processing but also may be chosen to minimise risk or maximise financial return compared to a more capital intensive agitated leach process. The heap leach ore will be sourced from the lower grade stockpiles mined from the mick adamskiora, wadi, kintore, castle hill stage 3 and burgundy open pits. Created using powtoon free sign up at create animated videos and animated presentations for free. Basically the ore is piled to a given height on an inclined impermeable surface, a so called leach pad. Basic efficiency in a heap leaching process is evaluated in terms of percent metal dissolution and the time required for such dissolution. 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. This method of gold recovery is the preferred method for.
The objective is to improve heap leaching kinetics and gold recovery yields. Heap leaching requires the preparation of the ore, primarily size reduction, so as to maximize minerallixiviant interaction and the laying of an impermeable base to prevent lixiviant loss and pollution of water bodies. A dilute sodium cyanide solution is delivered to the heap, usually by sprinkling or drip irrigation. The first process, vat leaching of highgrade copper oxide ore followed by ew of copper from the leach solution, produced low quality copper cathode at relatively high cost. Heap leach pad design and construction practices in the 21 st century by allan j. Basically, this is a hydrometallurgical process in which the solution is applied for the dissolution of minerals from the ore that is used for the extraction of metals.
Heap leach ing is a hydrometallurgical process that, due to its. If wood is used it is covered by a coating of paraffin paint, or by a mixture of asphaltum and coaltar. Heap leaching, shown in exhibit 3, is the least expensive process and therefore, low value ores are most often treated by heap leaching. If ore is mined or if it is gathered from old nine wasterock piles and hauled to specially prepared pads lined with clay, tar, or alon for leaching, the method is heap leach ing figs. In the heap leaching process, inclusions of the valuable minerals copper bearing minerals are to be dissolved from ore particles. The method of recovery of gold from the process slurry is by carbon adsorption. This method is very useful to optimize the heap leaching process design, analysis, control and optimization and also proposes optimal. Metal dissolution is controlled by the degree of liberation of the desired mineral component in the heap, ore particle size, contact between the ore particles, and the lixiviant heap permeability, leach. Pdf a methodology for design and operation of heap leaching. Sustainable issues related to heap leaching operations. Heap leaching is a tried and tested mining technique enabling the processing of different kinds. Examples of a proposed standalone hpgr prepared heap leach. Superiadi had some remarks about the following heap leaching processes superiadi, 2008, pp. Kcaa have been providing engineering and technical services to the process and metallurgical industries for the past twenty five years.
The crushing circuit has been modified as a result of the continuous vat leaching process feed size requirement of 6mm. Introduction heap leaching had become a fairly sophisticated practice at least 500 years ago. Heap leach facility liner system configurations vary depending on the type of leach facility singleuse pad, onoff, or valley leach, site conditions topography, climate, construction materials, and ore type. The objective of heap leaching process is to chemically dissolve the metals out of. 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 reseparate them after their division from other earth materials.
A heap leach project can often be the first stage in the longer term. Basically the ore is piled to a given height on an inclined impermeable surface, a so called leach. Heap leaching as a hydrometallurgical process is one of the cheapest methods and particularly useful in the case of. Heap leaching is well established process used for the treatment of copper, gold and uranium and it is now being used in vary.
The heapleach process briefly stated, gold heap leaching is a hydrometallurgical process designed to treat amenable lowgrade gold ores that contain roughly 0. Heap leaching is a process whereby precious metals such as gold and silver are extracted from rock by placing mineralized material on a lined pad a base in a heap and irrigating with a leaching solvent, such as cyanide or acid. Heap leaching in comparison to the above high complexity processes heap leaching is a simple delinked process that has a straight forward ramp up to steady state production. Heap leaching is bat for suitable ores because it allows the economical processing of ore that would otherwise be uneconomic under con ditions that can technically achieve regulatory acceptable levels of environmental risk mitigation. The mining and material handling process has been unmodified for the 10,000td continuous vat leach case, and modified only as a result of the reduction in processing rate for the 5,000td cvl case. Heap leaching for silver is conducted using the same principles and operating practices as for gold, but heap leach operations produce only a small fraction of world silver production. In heap leaching, the oxygen, essential for the dissolution of gold, is intro duced into the cyanide solution as it is being sprinkled upon the ore heap. The impregnated solution is collected and processed to remove the copper and the cycle is repeated. A typical precious metal heap leaching operation consists of placing crushed ore on an impervious pad.
Pdf a conceptual flowsheet for heap leaching of platinum. However in the rush to reduce costs we have seen many failures. Heap leaching is usually carried out in the open and on slightly sloping ground covered with a watertight plastic sheet or clay layer onto which a heap of crushed ore is placed. Heap leaching experiencebased approach to successful. Interest on heap leaching of uranium ores motivated by expected increased participation of low grade ore. Alkaline heap leaching of cementagglomerated ore is a proven lowcost method that is commonly used for extraction of gold and silver. Heap leach basics simple process short construction period low capital expenditures low operating costs radiation exposures less than at conventional mill sites major exposures dusting of ore piles dusting for ore heap moisture addition consider geotextiles on heap 24. The cheapest but slowest technique is heap leaching. For mill, agitatedtank leaching operations, gold is extracted directly from the leached. Adsorption is a term used to describe the attraction of a mineral compound to the surface of another material. Heap leaching experiencebased approach to successful heap. The leaching period is 2 4 days and gold recovery lies in the order of 70 80%.
Heap leaching belongs to the group of percolation leaching processes and operates over ground. Heap leaching is one of the oldest and the most traditional mining process used to extract the valuable metals from speci. In general, liner systems configurations can be described as. There is a substantial time lag between stacking ore and producing the final product. Cyanide heap leaching is a process for recovering gold and silver by trickling cyanide solutions through lowgrade ore that has been stacked. Particular emphasis is placed on avoiding or coping with common technical problems of interest to all existing and potential local heap leach operators.
The heap leaching with computation process is a newly developed heap leaching methodology that combines analytical modeling and the bernoulli type model to achieve a heap leaching scale up process. In typical operations, heap leaching processes operate in approximate times of three months for sulfide ores in chloride media, and also with. For heap leach operation, gold cyanide is extracted from pregnant leach liquors onto carbon in a series of columns, by upflowing leach solution through columns that are packed with carbon. Cyanide heap leaching introduction cyanide heap leaching is a process for recovering gold and silver by trickling cyanide solutions through lowgrade ore that has been stacked on openair pads fig. Heap leaching is considered an alternative to the toll treatment and joint venture options the company is currently considering. The reagents used and the chemistry of leaching are metal specific, but the basic principles are similar to all ore types. Design components of a heap leach unit gravelpebblesize crushed ore stacked on an impermeable lined pad by applying lixiviant solutions onto the heaped ore. Preg solution flowrates from the base of the heaps average 2,000 2,400 m. Heap leaching of gold and silver ores is conducted at approximately 120 mines worldwide. Nov 26, 2004 a very broad range of processes are used for the recovery of valuable metals.
The authors are currently developing and have patented a new twostage heap leach process wo 2012114165 a1, 30 august 2012 that may serve as an alternative to the conventional process route. A very broad range of processes are used for the recovery of valuable metals. Pdf a brief note on the heap leaching technologies for the. The chemistry involved in the dissolution of gold in the heap leach cya nidation treatment is the same as that for the agitationcyanidation process. Feb 01, 2014 heap leaching is a hydrometallurgical process that is widely used in the mining industry, in which lowgrade metals, such as copper, gold, silver and uranium, are extracted. It is a process usually applied to low grade gold ore.
Processing gold ores using heap leachcarbon adsorption methods. Optimal design and planning of heap leaching process. Heap leaches and tailings, office of solid waste special waste branch, 1994, pp. Gavin mudd about the proposed heap leaching expansion of ranger uranium mine in kakadu national park. Prefeasibility study ni43101 technical report cerro del. Two common types of pads used in gold heap leaching include permanent heap construction on a pad from which the leached ore is not removed and onoff pads, which allow the spent ore to be removed following the leach cycle and fresh ore to be placed on the pad. For copper and other metal sulfide minerals, the heap leach process has evolved to incorporate bacteria and nutrients into the barren solution promoting the biooxidation of sulfides. Cerro del gallo heap leach project ni 43101 technical report january 31, 2020 page iv. This process is followed by heap reclamation, a water wash step and restacking of the heap onto a new pad for a high temperature cyanide leach, achieved via solar heating of solution, to extract precious metals pt, pd and au eksteen et al. Therefore this author believes the current design and construction practices. Particle size distribution for copper heap leaching. The present invention relates to a new process of heap leaching and comprises the following steps.
Investigative study into the hydrodynamics of heap. A heap leach project can often be the first stage in the longer term development of a project and can allow a small company to establish an operation which can pay for further resource development and funding of the. Adsorption is a term used to describe the attraction of a mineral. Heap leach is an important metallurgical process, that has shown huge potential for reducing costs or liberating metals for challenging deposits. Chemical reactions of gold leaching and cementation. Okay to apply low cost option, but do not reduce to point of failure final word uram conference, vienna 2014 uranium. During this reaction time, the used acid reacts with the minerals. Precious metal heap leach design and practice oremax. Pdf heap leaching as a key technology for recovery of. A brief note on the heap leaching technologies for the.
During the last ten years, attention has shifted towards the leaching solution and the ore particles, as the installation of lowpressure blowers has fast become standard practice in sulfide heap leaching, thus eliminating the oxygen limitation. In this work, this theoretical process was simulated at a laboratory. It is proposed that these two proven processes could be combined into a single lowcost and effective method for vanadium extraction. The processing of low grade ores by the heap leaching method suffers from an. All of the materials used in heap leaching process and industry specifications of materials are. The process also boasts many features which can contribute to sustainable development in the pgm industry. Cyanide solution is pumped onto the heap through polypropylene pipes with drip emitters and makeup cyanide sodium cyanide is added to recycled barren and low grade preg solutions. In 1998, approximately 70% of gold recovered from cyanide use was from vat leaching operations, about 30% from heap leaching operations. It consists of the of solidliquid mass transfer than can occur in ambient conditions. Pdf stochastic analysis of heap leaching process via. Processing gold ores using heap leachcarbon adsorption.
The heap leaching process is an operation a third modelling approach is also possible. Mineral beneficiation by heap leaching technique in mining core. Feb 17, 2021 heap leaching is an industrial process for extracting precious metals and minerals by dissolving them from ore with liquids known as leaching solutions. Estimated water requirements for gold heapleach operations. Heap bio leaching has also been demonstrated for the preoxidation of refractory gold ores prior to cyanide leaching logan et al. Heap leach solutions, 2015 reno, nevada, usa 266 design and construction silo effect this term refers to a culture that induces a lack of communication and crossdepartmental sharing of information amongst people involved in the same project. Geomembrane lined copper heap leach pads started in mexico and arizona as early as 1983, however the copper heap leach dump operations have gradually changed to geomembrane lined foundations and interlift liners within the last 5 to 10 years. Kinross gold corporations maricunga mine in chile presents an ideal opportunity to apply the sart process to.
At the particle level, heap leaching is governed by the migration of reactive species into and dissolved species out of pores and cracks, which is based on molecular diffusion, invariably a very slow process. Cyanide heap leach methods are viewed by industry as offering a lowcost means of producing precious metals. The leach pad itself is a key element of the heap or dump leach process. Uram conference, vienna 2014 uranium heap leaching. The now barren cyanide solution is pumped to a holding basin, where lime and cyanide are added to repeat the leaching process.
Currently, heap leaching finds important applications in the recovery of copper from its ores because of its low cost, short construction time, operational simplicity, good performance, and environmental advantages. A novel sequential heap leach process for treating crushed. Vanadium extraction and recovery by alkaline heap leaching. Heap leaching is one of several alternative process methods for. Improvements in copper heap leaching by use of wetting agents. Examples of a proposed standalone hpgr prepared heap leach flowsheet and a hpgr. The geomembrane lined heap leach pads for the 21 st century have estimated operating time periods of 10 years or more compared to the more typical past gold and silver heap leach operational time periods of 3 to 5 years. Gold and silver leaching practices in the united states.
In this paper, some ideas from the models developed by roman et al. An enriched solution containing the targeted metal is collected at the bottom. Heap leaching technology moving the frontier for treatment. In 1993, heap leaching account ed for 39 percent of gold production. A hlf includes heap leach pads, process solution ponds, solution transport pipes, solution application devices, leach pad process plants, and process solution channels. In the mining sector, heap leaching is a distinguished method for the recovery of valuablebeneficial metals from lowquality ore.
After the leaching process is complete, the soluble gold must be concentrated and separated from the process slurry. Since the 1970s and early 1980s, heap leaching has developed into an efficient way to beneficiate a variety of lowgrade, oxidized gold ores. Briefly stated, gold heap leaching is a hydrometallurgical process. Heap leaching is a very slow process, where the acid is spread dropwise on a heap, slowly pouring to the bottom. Pdf leaching is a hydrometallurgical activity widely used in mineral. The invention discloses a method of controlling a heap leach process through controlling an irrigation rate of a heap as a function of at least one of an aeration rate of the heap, a determination of advection at least at one predetermined point in the heap, and a determination of temperature at least at one predetermined point in the heap. The oxide copper ore is piled up on leach pads, which have a slight slope of approx. Compared to tank leaching, heap leaching has several advantages, including simplicity of design, lower capital and operating costs, and shorter startup times.
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