UNIVERSITY OF SOUTH AUSTRALIASchool of Advanced Manufacturing and Mechanical Engineering

Bachelor of EngineeringIn

Mechanical and Manufacturing EngineeringPlus

Bachelor of Technology and Double Degrees

Final Year ProjectThesis Guide

PeterCourse coordinator

2014

Table of Contents

Background And Significance:.........................................................................................2Introduction:..................................................................................................................................................................... 3Aim:....................................................................................................................................................................................... 4Significance:...................................................................................................................................................................... 4Scope:................................................................................................................................................................................... 4

HEAP CONSTRUCTION :.............................................................................................................................................. 9Carlin-Type Sedimentary Ores............................................................................................................................... 12Low Sulfide Acid Volcanics Or Intrusives..........................................................................................................13Oxidized Massive Sulfides......................................................................................................................................... 13Saprolites / Laterites................................................................................................................................................. 13Clay-Rich Deposits....................................................................................................................................................... 14Silver-Rich Deposits.................................................................................................................................................... 14Gold and Silver Ores:.................................................................................................................................................. 14

LIXIVIANTS:....................................................................................................................................................................15Application of Lixiviant (Recent study)............................................................................................................. 15

Methodology:...............................................................................................................17

References:...................................................................................................................17

Background And Significance:

Introduction:

The objective of mining is to provide valuable minerals needed by the society. For doing so, mining companies extract resources from mineral deposits around the globe and use different techniques to recover the valuable mineral resources from the ore.

The choice of a suitable technique, which is both environmentally sound and economically viable, to process mineral resources very much depends on the type of ore which is mined as well as of the physical conditions linked to the location of the mine site.

Heap leaching is a tried and tested mining technique enabling the processing of different kinds of ores, which could not otherwise be exploited under viable economic conditions. Heap leaching had become a fairly sophisticated practice at least 500 years ago. Georgiou’s Agricola, in his book De Re Metallica (1556 1912)illustrates a heap leach with a 40-day leach cycle (Figure 1), which could pass in many ways for a modern heap leach. The Agricola heap leaches recovered aluminium (actually alum) for use in the cloth dying industry. Copper heap and dump leaches in southern Spain were common by about 1700. Gold and silver heap leaching began with the first Cortez heap leach in 1969.

Modern day heap leaching, which has a relatively low level of energy consumption, is successfully used for the beneficiation of certain types of gold ores.

(W.Kappes)

Figure 1 "The rocks are Piled in Heaps fifty feet long, eight feet wide and four feet high, which are sprinkled for forty days with water. The rocks begin to fall to pieces like slaked lime, and there originates a new material". Drawing and text from

As the qualities of ores in the world are continuously decreasing the necessity for better leaching techniques are becoming need of the moment. But this process is very poorly understood which requires a lot of ground level improvement in the industry.

One of the most important things in leaching is the transport of the lixiviant through (the porous media) the ore. The lixiviant leaches the ore and dissolves the valuables. This Report will analyze in detail about the impact of lixiviants in heap leaching.

Aim:

To characterize the synthetic and real ores particularly to determine important microstructural changes during heap leaching process. The role of cracks and pores in improving the efficiency of leaching will also be studied in detail. In this study to understand the flow of lixiviants through the cracks, model crack (microfluidic device) narrow channels will be designed. The experiments will be performed and results will be analysed for deeper understanding.

Significance:

As mentioned earlier the qualities of ores are decreasing around the world continuously. For better recovery higher quality pretreatment is becoming necessary which is very expensive. In order to avoid this various other methods are being improved and researches are being carried on. Among them all the understanding and improvement of flow of lixiviant through the ores is very significant. So thus the data and results from this study will further aid the mainstream researchers.

Scope:

In this project synthetic ores will be prepared at in-situ conditions in the laboratory their microstructural properties will be studied under microscopes. Further the real ores collected from the field also will be studied for its properties. The results of both the studies will be compared.

LITERATURE REVIEW:

The primary objective of mining is to supply raw materials to downstream users, extracted from ore deposits in the earth’s crust, using applicable excavation and ore enrichment processes with economically feasible and environmentally sound engineering operations.

In a typical metal ore mining operation, ores are selectively excavated from an open pit or underground workings, crushed and milled for further treatment in ore beneficiation units for enrichment and/or production of metals and metal compounds.

There are several mainframe ore preparation/beneficiation methods available in mining practice based on physical, chemical and smelting processes.

Concentration: o Gravity concentration (Heavy/dense media, Shaking tables, Spiral separators,

jigs) o Electrostatic separation o Magnetic separation o Flotation

Hydrometallurgy

o Leaching o Electrolysis o Precipitation (cementation)

Pyro metallurgy o Calcining, Roasting o Smelting o Refining

All of these processes require crushing and/or, grinding/milling of run-of-mine ores for liberation of mineral particles of interest for efficient application of appropriate processes of beneficiation.

1. Selection of a beneficiation technology is based on economic viability which is directly dependent on the:

o Ore type (namely, oxide or sulphide), o Mineral composition, matrix features of ore o Reserves and average grade (based on the “cut-off grade”) of the ore.

It should be borne in mind that lowering the cut-off grade of ores:

o Increases asymptotically the quantity ore to be excavated and treated (Figure 2), o Increases energy and chemical usage in pressure/tank leaching technologies,

generating larger Volumes of tailings to be managed; o Decreases profitability, making beneficiation processes uneconomical below

certain grades.

Figure 2 Relationship Between Excavation Quantity and Average Grade of Mined Ore as a function of “cut-off grade”

(B 2006)

In response to global increases in metal commodity prices, the low-grade base metal and precious metal ores (<1% copper, <1g/ton gold, < 0.5% nickel) previously considered uneconomical, became feasible with introduction of heap leaching technologies (J.O 2009).

In consideration of ore types, a generalized diagram showing the applicable ore beneficiation technologies for oxide and sulphide ores versus ore grade is given in Figure 3.

Figure 3 Applicable Ore Beneficiation Technologies as a Function of Ore Grade

(Robertson 2005)

A chart showing identified applicable process categories for gold ore recovery is given Figure 4 ((B 2006)). This chart is based on a preliminary analysis of 2,832-bulk leach extractable Gold (BLEG) results for shear-hosted Achaean metasediment ores in Western Australia.

Figure 4 Process categories based on leach recovery vs ore gold grade

(B 2006)

Leaching:

Leaching is a physico-chemical process where minerals in rock masses go through dissolution under percolating water and anion/cation exchange reactions to generate metal salts in solute/colloid phase that migrate and accumulate under hydrological forces. Depending on the presence of pyrite (FeS) or pyrrhotite (F and acidic/alkaline conditions, biological process of iron and sulphur oxidation by certain natural bacteria may also catalyse the leaching process. Lateritic ore deposits, the major resources of aluminium, nickel, platinum, cobalt and some gold, are clear evidence of ongoing natural leaching process through geological times. Leaching is the second fundamental step following physical alteration (fractioning under extreme temperature changes and erosional forces) in the rock-to-soil weathering cycle taking place in nature under atmospheric pressure conditions.

Similarly, leaching is also a major natural process that occurs at depths in the evolution of hydrothermal-origin ore deposits. Hydrothermal ore deposits are the products of complex chemical interaction processes involving hydrothermal fluids and gases with the host rocks; namely, a “natural high temperature and pressure leaching” followed by a cooling process on a geologic time scale.

Heap Leaching:

Heap leaching is the process to extract precious metals like gold, silver, copper and uranium from their ore by placing them on a pad (a base) in a heap and sprinkling a leaching solvent, such as cyanide or acids, over the heap. This process dissolves the metals and they collect at the bottom of the pad. The metal is then further processed. This methodology is mostly used for low-grade ores, and the basic processing steps involve crushing and sometime grinding.

The stages for heap leaching can be described as:

1.Ground Preparation and pad construction: Here the soil on a slightly sloping ground is compacted and covered by an impermeable pad (can be made of plastic).

2.Ore stacking: Then the crushed ore is stacked in the form of big heaps. Amount of fines is decreases as low as possible to improve permeability.

3.Then the leaching agent such as cyanide or acid is sprayed over the heap.4.As, the reagent passes through the heap; the valuable metals get dissolved in it.5.The solution containing metal is drained from the heap and collected in a pond and

the solution is sent for subsequent process for metal recovery.

Here is an illustration of the process:

(Biomine)

Figure 5 Heap Leaching Process

Heap leaching was first practiced by piling up heaps of copper ore and irrigating them with leach solution ((Kappes 1978)). Heap leaching can be defined as the practice of piling a large tonnage of mineral- bearing material over a liquor collection system and feeding a leaching solution onto the surface of the heaped pile ((Mashbir 1964)). Modern heap leaching is a controlled process whereby a complex or low-grade ore is stacked in short lifts (under 10 m in most cases), usually crushed and often agglomerated, on a carefully prepared containment system (the leach pad) and irrigated in a controlled manner with a solution to extract the optimum amount of metal from the ore (usually copper, gold, silver, uranium and nickel). The first commercial modern-day style of heap leaching was probably introduced to the uranium industry in the 1950’s ((Scheffel 2002)). The application of heap leaching technology revolutionized gold production in the United States, Peru and other countries in the 1970’s and 1980’s ((Brunk 1997)). The rapid expansion of the heap leach-solvent extraction-electrowin (L-SX-EW) copper production occurred in Chile during 1990’s ((Taylor 2007)). In the past decade, heap leaching of nickel laterites ((Taylor 2007)) and mixed metal sulphide ores ((Taylor 2007)) have been demonstrated and appear to be moving into commercial practice.

Heap leaching has been demonstrated as a viable and low cost approach to open-pit mining operations with low-grade and complex run of mine (ROM) ores, agglomerated flotation tailings and also for the treatment of coarse rejects from semi-autogenously grinding (SAG) circuits ((Hiskey 1983)). Rising costs of milling and concentration forces more low to medium grade ores to be available for heap leaching ((Hiskey 1983)).

While heap leaching is a well-established technology, which continues to grow in use, there are certain criteria that justify its selection over other treatment options. Ore grade and mineral leachability are two of these criteria. Gold and silver can be recovered from

their ores by a variety of methods, including gravity concentration, flotation, and agitated tank leaching. Methods similar to heap leaching can be employed: dump leaching and vat leaching (vat leaching is the treatment of sand or crushed ore in bedded vats with rapid solution percolation).

Typically, heap leaching is chosen for basic financial reasons - for a given situation, it represents the best return on investment. For small operations or operations in politically unstable areas, it may be chosen because it represents a more manageable level of capital investment.

HEAP CONSTRUCTION :

The construction of heap fills involves the placement of precious or base metal ore materials in controlled individual loose and relatively dry fill lifts stacked at the natural angle-of-repose. The heap ore lifts are typically stacked at 15 to 30 feet (5 to 10 meters) in thickness and leached to typical maximum heights in the range of 100 to 200 feet (30 to 60 meters). The highest heap stacks to date exceed 500 feet (150 meters) above the geomembrane lined pad foundation. A geomembrane lined leach pad with a stacked and leached ore heap in the background is shown on Figure 6.

Figure 6 GEOMEMBRANE LINED GOLD HEAP LEACH OPERATION IN MONTANA

These Crushed ore placement in the heap leach operations can be done either by trucks and/or by conveyor systems. Truck dumping generally causes segregation of the ore where the fines remain near the top surface, and the coarse material rolls to the base of the lift creating a highly permeable zone at the base. To control the degree of

this segregation the ore may be partially agglomerated (wetted to cause the fines to stick to the coarse material) prior to placing in the trucks. Short lifts also result in less segregation. Truck dumping can also result in compaction of ore under the roadways on top of the heap. To mitigate this problem, most operations rip the ore surface after stacking (prior to leaching). However this requires substantial bulldozer traffic on the heap surface, which can also lead to compaction and loss of permeability for some ores ((D.W 2002)).

Conveyors stacking systems where wheels, discharge angle, and stinger position are all motorized and are moved continuously by the operator as the heap is built, commonly include the following equipment ((D.W 2002)):

One or more long (overland) conveyors that transport the ore from the crushing (and agglomeration) plant to the heap. These may consist of conveyors up to several kilometres in length.

A series of "grasshopper" conveyors to transport the ore across the active heap area. Grasshoppers are inclined conveyors some 30 meters long, with a tailskid and a set of wheels located near the balance point.

A transverse conveyor to feed the stacker-follower conveyor A stacker-follower conveyor, typically a horizontal mobile conveyor that retracts

behind the stacker A radial stacker 25 to 50 meters long, with a retractable 5 - 10 meter conveyor

“stinger” at its tip.

Ore Stacking typically proceeds in an upslope direction. It may proceed in the downslope direction provided that the advancing face is stable (Figure 4).

In lateritic ore leaching operations, where the permeability of the clay-rich heap materials may significantly decrease at the end of each leaching cycle (cycles may take over a year), use of an intermediate geomembrane layer after each lift (inter-lift liners) may be considered to minimize leach cycles and consumption of lixiviant specifically by iron containing minerals and for effective collection of leach solutions.

Each ore lift surface is wetted uniformly during leaching by using irrigation drip emitters or sprinkler sprays. Leaching is generally conducted in 30 to 120 day or longer leach cycles with barren or recirculated alkaline (gold and silver) or acidic (copper) process solutions.

The maximum rock size of the granular ore materials ranges from large run of mine cobble and boulder rock fragments to fine crushed sand and gravel particles. The crusher operations may include agglomeration as needed to provide a more efficient distribution of fines (minus No. 200 sieve size material) for improved permeability and recovery of the target metals. The individual ore lifts are offset with benches along the exterior slope, as required for establishing the overall stable design slopes for operations.

Figure 7 Ore Stacking directions

There are three main things to be considered with regards to stacking

a) Static Stability: Evaluation of the static stability of the ore heap should include all possible mechanisms of failure modes (circular, block and random failure surfaces). Generally, the stability failure mechanism for lined leach pad facilities is of block type failure along the liner interface that typically has the lowest shear strength parameters. Circular failure mechanisms may be critical when deep saprolitic type foundation materials underlie the heap facility, particularly when associated with high water tables and potential generation of pore water pressures due to rapid loading of the heap or seismic events. Static factors of safety values of 1.3 and greater are considered acceptable good engineering practice.

b) Seismic Stability: Many mining operations are located in seismically active areas. A detailed seismic evaluation of the particular mining location should be conducted to assess design factors and ground accelerations to be considered in both structural (buildings) and geotechnical design of water and tailings impoundments, and heap leach facilities. Typically, seismic stability analyses for heap leach ore facilities are evaluated using conventional limit equilibrium analysis with a pseudo-static coefficient.

Pseudo-static analysis is a very conservative procedure used as the first step in most seismic stability analyses. It is not a dynamic analysis procedure and does not directly account for dynamic/vibratory loading (i.e., the periodicity or cyclic character of the loads and the short duration of loading). Rather, the procedure models seismic impacts by applying a uniform horizontal static force to slices in a conventional limit equilibrium analysis. For a maximum credible earthquake of up to a magnitude of 8.5, a pseudo-static acceleration coefficient of 0.15g could be used ((Seed 1979)). Seismic factors of safety of greater than 1.0, as determined by pseudo-static analyses, are acceptable for heap leach facilities as a good engineering practice. In rare cases where seismic stability concerns cannot be satisfied using a simple pseudo-static analysis, more detailed analyses of expected seismic displacement may be required to asses seismic stability of the structures.

Liquefaction Potential: Liquefaction potential of heaps should also be taken into consideration, especially in earthquake-prone regions ((Thiel 2003)). Liquefaction (flow slides) typically occurs when saturated or near-saturated (greater than 85%), loose granular material contracts or collapses under some triggering event causing a sudden surge of excess pore water pressure build-up and a reduction in shear strength. A classic triggering event is seismic shaking. Seismically induced liquefaction is typically limited to approximately 20 m in depth, as the confining pressures at greater depths reduce susceptibility to this type of failure. Generally, heap materials are maintained at saturation levels much less than 85%; therefore, liquefaction risk is minimal.

Type of ores:

Heap leach recovery is very dependent on the type of ore being processed. Some typical examples are discussed below.

Carlin-Type Sedimentary Ores

These ores consist of shales and "dirty" limestones, containing very fine (submicroscopic) gold. Oxidized ores leach very well, with low reagent consumption and production recovery of 80% or better. Ores are typically coarse-crushed (75mm) but may show recovery of 70% or better at run- of-mine sizes. The largest of the northern Nevada heap leaches (Carlin, Goldstrike, Twin Creeks) treat this type of ore. Unoxidized ore contains gold locked in sulfides, and also contains organic (carbonaceous) components, which absorb the gold from solution. This ore shows heap leach recovery of only 10 to 15% and is not suitable for heap leaching. Because of the different ore types, the northern Nevada operations (for instance, Barrick's Goldstrike Mine) may employ roasters, autoclaves, agitated leach plants and heap leaches at the same minesite. Crushing is usually done in conventional systems (jaw and cone crushers) and ores are truck stacked.

Low Sulfide Acid Volcanics Or Intrusives

Typical operations treating this type of ore are Round Mountain, Nevada, and Wharf Mine, South Dakota. Original sulfide content is typically 2 to 3% pyrite, and the gold is often enclosed in the pyrite. Oxidized ores yield 65 to 85% recovery but may have to be crushed to below 12 mm (1/2 inch). Usually the tradeoff between crush size and percent recovery is a significant factor in process design. Unoxidized ores yield 45 to 55% gold recovery and nearly always need crushing. At Round Mountain, Nevada, approximately 150,000 tons per day of low grade oxide ore is treated in truck-stacked run-of-mine heaps, 30,000 tons per day of high grade oxide ore is treated in crushed (12mm), conveyor-stacked heaps, and 12,000 tons per day of unoxidized ore is treated in a processing plant (gravity separation followed by leaching in stirred tanks). Crushing is done using jaw and cone crushers; fine crushed ore contains enough fines that conveyor stacking is preferred over truck stacking.

Oxidized Massive Sulfides

The oxide zone of massive sulfide ore deposits may contain gold and silver in iron oxides. Typically these are very soft and permeable, so crushing below 75mm often does not increase heap leach recovery. The Filon Sur orebody at Tharsis, Spain (Lion

Mining Company) and the Hassai Mine, Sudan (Ariab Mining Company) are successful examples of heap leaches on this type of ore. Because the ore is fine and soft, the ore is agglomerated using cement (Hassai uses 8 kg cement/tonne), and stacking of the heaps is done using conveyor transport systems.

Saprolites / Laterites

Volcanic- and intrusive-hosted orebodies in tropical climates typically have undergone intense weathering. The surface "cap" is usually a thin layer of laterite (hard iron oxide nodules). For several meters below the laterite, the ore is converted to saprolite, a very soft water-saturated clay sometimes containing gold in quartz veinlets. Silver is usually absent. These ores show the highest and most predictable recovery of all ore types, typically 92 to 95% gold recovery in lab tests, 85% or greater in field production heaps. Ores are processed at run-of-mine size (which is often 50% minus 10 mesh) or with light crushing. Ores must be agglomerated, and may require up to 40 kg of cement per tonne to make stable permeable agglomerates. Many of the West African and Central

5

Central American heap leaches process this type of ore. Good examples are Ity in the Ivory Coast, and Cerro Mojon (La Libertad) in Nicaragua. When crushing is required, one or two stages of toothed roll crushers (Stammler-type feeder-breaker or MMD Mineral Sizer) are usually employed. Conveyor systems are almost always justified; ore can be stacked with trucks if operations are controlled very carefully.

Clay-Rich Deposits

In some Carlin-type deposits, as well as in some volcanic-hosted deposits, clay deposition or clay alteration occurred along with gold deposition. The Buckhorn Mine, Nevada (Cominco, now closed) and the Barney's Canyon Mine, Utah (Kennecott) are good examples. These ores are processed using the same techniques as for saprolites, except that crushing is often necessary. Because of the mixture of soft wet clay and hard rock, a typical crushing circuit design for this type of ore is a single-stage impact crusher. Truck stacking almost always results in some loss of recovery. Agglomeration with cement may not be necessary, but conveyor stacking is usually employed.

Barney's Canyon employs belt agglomeration (mixing and consolidation of fines as it drops from conveyor belts) followed by conveyor stacking. The new La Quinua operation at Yanacocha employs belt agglomeration followed by truck stacking.

Silver-Rich Deposits

Nevada deposits contain varying amounts of silver, and the resulting bullion may assay anywhere from 95% gold, 5% silver to 99% silver, 1% gold. Silver leaches and behaves chemically the same as gold, although usually the percent silver recovery is significantly less than that of gold. Examples of nearly pure silver heap leaches are Coeur Rochester and Candelaria in Nevada, and Comco in Bolivia.

Gold and Silver Ores:

The chemistry of leaching gold and silver from their ores is essentially the same for both metals. A dilute alkaline solution of sodium cyanide dissolves these metals without dissolving many other ore components (copper, zinc, mercury and iron are the most common soluble impurities). Solution

Solution is maintained at an alkaline pH of 9.5 to 11. Below a pH of 9.5, cyanide consumption is high. Above a pH of 11, metal recovery decreases.

Many heap leachable ores contain both gold and silver. Of the 28 mines that reported bullion assays, five produce a dore (impure gold-silver bullion ) bar that is greater than 70% silver. Another five produce a bullion greater than 30% silver. Only five produce a bullion with less than 5% silver. Deposits in western Africa and Australia tend to be very low in silver, while those in Nevada are highly variable, ranging from pure gold to pure silver.

Silver is usually not as reactive with cyanide as gold. This is because gold almost always occurs as the metal, whereas silver may be present in the ore in many different chemical forms some of which are not cyanide-soluble. Reported heap leach recoveries (32 operations) averaged 71% gold, and ranged from 49% to 90%. Reporting run-of-mine heap leaches averaged 63%. Typical recovery for silver is 45-60%, although when silver is a minor constituent, its recovery may be only 15-25%.

The level of cyanide in the heap on flow solution ranges from 100 to 600 ppm NaCN, and averages 240 ppm for the 28 operations reporting. Forty-five percent of the operations reported cyanide strength below 200 ppm, 25% were above 300 ppm. Heap discharge solution (pregnant solution) averages 110 ppm.

Cyanide consumption, via complexation, volatilization, natural oxidation or oxidation by ore components, typically ranges from 0.1 to 1.0 kg per tonne of ore. Price of sodium cyanide is currently at a historical low of $1.00 per kg. Cement and/or lime consumption ranges from 0.5 to 40 kg per tonne of ore. Several operations use cement for alkalinity control (instead of lime) as well as for agglomeration. The price of cement or lime is $60 to $100 per tonne, $160 delivered to remote African locations.

Other leaching agents - thiosulfate, thiourea, hypochlorite, and bromine - have been experimented with as an alternative to cyanide, but cyanide is by far the most effective and the most environmentally friendly leaching agent.

LIXIVIANTS:

The primary objectives of leaching processes applied in mining are the selective dissolution of metals of interest in ores, segregate the loaded (pregnant) solution from solids and recover available metals either in metal compounds or in metallic forms through further hydrometallurgical treatment.

Lixiviant are chemical solutions used in leach mining to enhance dissolution of metals in ores. Sulphuric acid and cyanide salts are the most common demonstrated lixiviants used in heap or vat (tank) leaching processes applied under atmospheric conditions.

Thiourea and thiosulphate are also known lixiviants for copper and gold ores; however, they are not used in world mining practice for their more complicated chemical management issues and environmental concerns. Currently, there are no successfully demonstrated applications of these lixiviant on an industrial scale that can be considered within the context of Best Available Techniques (BATs).

Application of Lixiviant (Recent study)The materials in a heap leach pad constitute a heterogeneous, anisotropic mass. Material hydraulic conductivities vary greatly from point to point. This random variation from point to point of hydraulic conductivity is the result of the inherent in-situ variability in the ore being mined, variations in the combination of the ore as a result of blasting, loading, and dumping, and segregation and blinding that occur during placement.While it is tempting to think of seepage of leach solution and lixiviants as a uniform vertically downward flow regime, this is not the case. The paths that the solution will take as it flows down through the mass of heap leach material will depend on these, and probably many other factors:

The heterogeneity of the mass, and hence the presence and pattern of channels or paths of greater permeability.

The moisture content of the ore which depend on the moisture content as mines, as placed, and as resulting from ambient conditions including antecedent rainfall percolation

The rate and pattern of application of the solution and lixiviant.

O’Kane Consultants have carried out much research into the area and they note:

Figure 8 Movement of lixiviants in fine and coarse ores

Layers of coarse and fine textured ore inevitably develop within heap and dump leach piles as natural processes segregate coarse and fine material during material placement. Segregation of heap leach material will occur regardless of whether the material is agglomerated or non-agglomerated. Under such conditions leaching solution flows preferentially in the more conductive layer, potentially leaving areas within the heap unleached. The preferred flow path is not dependent entirely on the physical properties of each layer, but also on the stress state and resulting degree of saturation, and therefore the solution application rate. For this reason either the coarse or the finer material can be the preferred flow path.

Thus it is not quite as simple as multiplying the area of the pad by the saturated hydraulic conductivity if you want to establish the maximum possible application rate.

If you do succeed in applying enough solution to the top of the pad to create fully saturated flow through the heap leach materials, you will certainly be getting lots of solution through the materials, but you may not be getting the metal recovery you seek or could achieve by less aggressive solution application. To get the metal out of the finer materials and into the solution, you need to get the solution to seep through these finer materials. And that happens best when the material is partially saturated, and the seepage retreats, as it were, into the finer channels.

This leads to the counterintuitive conclusion: to increase recovery, it may be better to reduce solution application rates, rather than increase them.

Keep in mind also if you increase application rates too much you may create a saturated zone near the base of the pad, and that could induce slope failure.

Methodology:

After a detailed literature review and understanding of Heap leaching, model ores, ore boundaries and crack I further moved to the experimental part of the project.

In this initially I will prepare model ores (synthetic ores) in laboratory similar to the real ores. Before starting my work at the laboratory I completed safety inductions and got trained under expert supervision in handling the equipments. The model ores are prepared at 3 different sizes (.5,1.5 and 8µ) under sintering temperatures varying from 1000 to 1200 C.

After the Ore preparation model cracks will be created in this ores with the help of microfluidic device and the flow of lixiviant through this channel will be characterised and corresponding AU thickness will be noted. The Mechanical strength and density of the model ore also will be measured.

In parallel to this the real ores will be collected from the field and they will be prepared for characterisation.

Advanced equipments like SEM, BET, QEMSCAN, XRF and XRD will be used for characterisation the ores.

For model ores SEM will be used to study the microstructure, compression test will lead us towards the mechanical strength and the Pycnometer will give us the density.

In case of real ores Mechanical strength will be measured in a similar way as earlier. Porosity will be noted form BET; Assay/XRF should give us the elemental composition, XRD and QEMSCAN for further analysis.

References:

1556, A. G. (1912). "De Re Metallica."

B, M. (2006). Exploring HPGR Technology For Heap Leaching of Fresh Rock Gold Ores. IIR Crushing & Grinding Conference, , Townsville, Australia,.

Biomine. from http://wiki.biomine.skelleftea.se/wiki/.

Brunk, K. A. (1997). “Process technology: Its role as a component of a strategic business plan”, . – Global exploitation of heap leachable gold deposits, Orlando, Florida.

D.W, K. (2002). "Precious Metal Heap Leach Design and Practice, in Proc. Mineral Processing Plant design, Practice and Control, ." SME Vol.2, .

Hiskey, J. B. (1983). “Heap leaching practice at Alligator Ridge,” Chapter 1, Current status of U.S. Gold and Silver Heap Leaching Operations, Heap and Dump Leaching practice,. SME fall meeting.

J.O, M. (2009). , Lessons Learned from the Copper Industry Applied to Gold Extraction, Keynote Presentation World Gold 2009 Conference. Johanessberg, South Africa.

Kappes, W. (1978). “Precious Metals Heap Leaching: Simple - Why not Successful?”, Presentation to the Northwest Mining Assn., .

Mashbir, D. S. (1964). “Heap leaching of low-grade uranium ore. Mining Congress

Robertson, S., Vercuil, A., van Staden, PJ, Craven, P., (2005). A Bacterial Heap Leaching Approach for the Treatment of Low Grade Primary Copper Sulphide Ore. 3rd S. African Conf. on Base Metals,SAIMM Symp.

Scheffel, R. (2002). "“Copper Heap Leach Design and Practice”, ." Mineral processing plant design, practice, and control 2.

Seed, H. B. (1979). Considerations in the Earthquake Design of Earth and Rockfill Dams. Geotechnique. 29: 215 -263.

Taylor, A. (2007). Innovations & Trends in Uranium Ore Treatment”, . ”, ALTA 2009-Nickel/Cobalt, Copper and Uranium conference,. perth, australia.

Thiel, R. S., Smith, M.E. (2003). "State Of The Practice Review of Heap Leach Pad Design " vol. 22(, Proc. GRI-18,): 555- 568.

W.Kappes, D. "Precious metal heap leach desing and practice."