Advances in gold recovery from leach solution are again influenced by developments in equipment and reagents. The general principle behind the volume structure is that of flowsheets based on unit operations and applied to a mineralogical classification of gold ore types.
GOLD IN ANCIENT EGYPT
This place and its surroundings were known for the wealth of gold mines and semi-precious stones.
EARLY GOLD-MINING CENTERS
After the discovery of America in the late fifteenth century, the Spaniards transferred significant amounts of gold from the New World to Europe. The strongest impetus for gold production came from the discovery of the gold fields of the Witwatersrand in South Africa in 1885.
GOLD AND ALCHEMY
Gold mining in Ghana (Gold Coast) began to play a modest role in the twentieth century, although the deposits were known in the Middle Ages.
USES OF GOLD
More than one layer of gold leaf is usually required to achieve the desired color. In 1827, Heinrich Ku¨hn discovered a new gilding process at the Meissen factory near Leipzig.
OCCURRENCE OF GOLD
PROCESSING OF GOLD ORES 1. Gold panning
This knowledge was first used in 1851 by Karl Friedrich Plattner of Freiberg to extract gold from his ores using aqueous gas solutions. Extensive research has been carried out in the nascent chemistry of the so-called blue acid and its compounds.
GOLD STANDARDS AND ASSAYING
Gold ores containing carbonaceous material are also known as refractory ores and are difficult to process, not only because some of the gold is bound to organic matter, but also because the dissolved gold adsorbs to the carbon present in the ore, and therefore appears in tailings. In this process, carbon granules are added while the ore is being washed, so that the gold that dissolves is immediately retained by the carbon rather than the carbonaceous matter in the ore.
GOLD IN CURRENCY
The touchstone method of testing is also discussed in Sanskrit texts (third century BC) which describe the manufacture of touch needles (standard alloys) in which the ratio of gold to copper is varied in steps. The Eastern Slovak Museum in Kosˇice has one of the largest collections of gold coins in the world, dating back to the eighteenth century.
BANKS
As a result, the dollar assumed the role of the official monetary price of gold. The interest rate on gold is low compared to most currencies, which probably reflects the lower long-term inflation risk of holding gold compared to.
GOLD MUSEUMS
Low interest rates make it attractive for gold companies to finance in gold rather than currency. Since the mid-1980s, mining companies seeking to raise money to develop new gold mines have typically borrowed gold.
PROJECT DEVELOPMENT
INTRODUCTION
It is still surprising that sampling is often not given the attention it deserves and the task is delegated to personnel who do not fully appreciate the importance and importance of sampling. Cost is usually the driving force behind this phenomenon, and this can result in major flaws in sampling procedures as well as the selection of inappropriate sampling equipment.
SAMPLING BASICS
Once the bias has been addressed, precision can be estimated by determining the overall variance of the final analysisðs2SPAÞby dividing the sampling (and sample processing) variance into its components for each sampling stage, i.e. Once the relative magnitudes of the variance components are known, efforts to reduce the overall variance can be focused on the appropriate area.
COMPONENTS OF SAMPLING ERROR
When sampling a blast hole cone, a full sector of the cutting cone must be selected (accurate boundary determination) and all cuttings in the sector must be collected (correction). When sampling moving streams, all cross-sectional sections of the stream must be deflected by the sample cutter for the same length of time (correction) and the growth must be completely extracted without any material being returned or lost from the cutter (correction ).
PERCUSSION HOLE SAMPLING
Sampling systems that collect only a portion of the drilling from the borehole for subsequent sample splitting should be avoided at all costs. Improperly designed sample divider on the side of a drilling rig that only collects material from one side of the stream of cuttings (see slots on right side of rectangular sample divider).
BLAST-HOLE SAMPLING
In principle, this approach sounds good, but in practice a significant portion of the cuttings are left around the blast hole (usually the coarser particles). Installing an automatic vacuum extraction system on the drill rig to collect the cuttings around the top of the blast hole and pass them through a suitable separator to extract a sample of the correct size.
PLANT SAMPLING
Very large cutter bodies and channels are therefore required to avoid reflux and overflow from the cutter opening. The geometry of the cutter opening must ensure that the cutting time at each point in the flow is equal.
SAMPLING FROM STATIONARY SITUATIONS 1. Sampling from stockpiles
If this ratio is significantly less than 1, the cause should be identified and corrective action should be taken to correct the problem, e.g. reflux of ore from the cutter opening or hanging in the cutter chute due to performance problems or blockages in the cutter chute. Full-depth sampling, in which several full vertical columns are drawn from the container (usually impossible).
SAMPLE PROCESSING
CONCLUSIONS
Sampling and measurement – the basis for accurate metallurgical accounting, In: Proceedings of the Value Tracking Symposium, 7-8. October 2002, Brisbane, Australia, Australasian Institute of Mining and Metallurgy, Melbourne, pp. Dr. Holmes is a fellow of the Australasian Institute of Mining and Metallurgy and the Australian Institute of Physics.
GOLD MINERALOGY Gold minerals and alloys
Pyrite is the most common of the sulphide minerals and can also include significant amounts of gold in its crystal structure, to the point where solid-solution gold becomes the main form of gold in the ore, and pyrite its main carrier (Thomas, 1997). Other minerals that may contain significant concentrations of gold in solid solution include loellingite (Pirila, Finland; Lupin, NWT, Canada), enargite (Chuquicamata and Pascua, Chile; Yanacocha, Peru´), and tennantite (El Indio, Chile). Table 2 summarizes the measured gold zones in various sulphide and arsenide minerals.
PROCESS MINERALOGY OF GOLD 1. Gravity concentration
At the other end of the gold grain size spectrum, the coarsest gold in the last tails (for example, see Plate 1) is invariably. Free gold losses within the navigable size classes (7-150 mm) typically represent less than 10% of the gold in the tailings.
METHODOLOGY FOR STUDYING GOLD MINERALS
Speciation of surface gold on carbonaceous matter provides valuable information on the mechanism of gold dissolution and the source of the unwanted gold ligand. Given the low waste rate, large samples (1-100 kg, depending on the gold assay) are used, paying special attention to the characterization of gold in the tailings fraction.
INSTRUMENTAL ANALYSIS FOR GOLD
XPS was also used to confirm the identity of gold species adsorbed on activated carbon (Dimovet al., 2003). Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is most suitable for surface organic microanalysis, after careful selection of operating conditions to preserve molecular ions (see Chryssouliset al., 1995).
CONCLUDING REMARKS
Mineralogical location and distribution of gold in quartz veins and sulphide ores of the Ashanti mine and other deposits in the Ashanti belt of Ghana: genetic implications. The presence of preg-rob carbon will require flow sheet inclusions to achieve acceptable recovery without gross losses of gold to CIL tailings.
COMMINUTION PROCESS OPTIONS 1. Overview
Low capacity may allow the use of lower capital cost crushing and grinding equipment such as MMD cellers, single-stage primary mills and SAG mills. At higher throughputs, such circuits may consider the use of HPGRs in place of SAG milling.
FREE-MILLING ORE PROCESS OPTIONS 1. Overview
The relative merits of SAG and AG milling may need to be evaluated in such situations. In high rainfall areas it may be necessary to discharge water to the environment and this will involve some form of cyanide destruction system (see Chapters 28 and 29).
COMPLEX ORE PROCESS OPTIONS 1. Overview
The advantages of the resin over activated carbon are much higher equilibrium gold loadings which can be achieved together with greater resistance to fouling in the presence of kerosene. From the point of view of achieving the completion of the gold dissolution reaction, it is important to maintain a high level of dissolved oxygen in the liquor pulp.
REFRACTORY ORE PROCESS OPTIONS
REFRACTORY PROCESS SELECTION
It is emphasized that the choice of the final process route should not be made too early in the assessment process and especially without an appropriate Table 7. Furthermore, the level of detail in the final study highlighted a greater difference in costs than previously . has been established.
FACTORS FOR CONSIDERATION IN REFRACTORY PROCESS SELECTION
Variations in the relative proportions of the various sulfide minerals must be considered, in particular the presence of the reactive but acid-consuming mineral pyrrhotite (Fe(1 x)S). For most oxidation processes, there are limitations on the capacity of particular unit operations.
DISCUSSION
These then need to be considered in the context of process location constraints. Dave Luntis is recognized by the mineral processing industry worldwide as one of the industry's most experienced technical professionals.
BACKGROUND
All of the above has led to significant changes in the testing methodology and philosophies now widely adopted in the major gold mining countries. This includes more proactive cyanide management plans, which inevitably involves a comprehensive understanding of cyanide use throughout the plant.
ORE PREPARATION AND ASSESSMENT
By utilizing gravity prior to the leach train, early recovery of gold in the process can also have economic benefits and avoid potential losses. This is the basis of the vast majority of gold operations around the world (Hedley and Tabachnick, 1968).
BENEFITS OF SIMULATION
However, a careful simulation study can shed light on the question by simulating the operation of the plant in its current configuration and as it would function with the proposed changes. This task has been made much easier in recent years by the development of excellent software packages that automatically provide many of the features needed to build a simulation model.
ALTERNATIVES TO COMPUTER SIMULATION
CLASSIFICATION OF SIMULATION MODELS
The decision to use a discrete or a continuous model for a particular operation depends on the specific objectives of the study. Alternatively, if the movement of the trucks could be averaged over time, the flow of ore could be described by differential equations in a continuous model.
STEADY-STATE CONTINUOUS SIMULATION
Once the required information is obtained, the simulation of the miniaturization circuit can be performed. A simulation model requires all the processes in the plant to be defined and configured.
DYNAMIC CONTINUOUS SIMULATION
It can therefore be used to produce a mass and energy balance, which can be extended to the dynamical world, if necessary. A dynamic model can be used as a tool to help design, test and tune a control system.
DYNAMIC DISCRETE SIMULATION
COMPUTATIONAL FLUID DYNAMICS
CFD modeling is used to determine the distribution of the gold and carbon particles over the leach vessels. The CFD software is used to convert this data into a complex model of an individual vessel, showing the amount of mixing achieved and also any areas of little or no mixing.
THE FUTURE OF PROCESS SIMULATION
Only enough design is completed to back up the capital and operating cost estimates with the appropriate level of accuracy to determine design feasibility. This chapter provides an overview of some of the key drivers for process plant design on an area basis.
GENERAL SITE ISSUES
The design should address the key issues that drive capital and operating costs. The local topography should be used as efficiently as possible to ensure that the ratio of excavation and filling is kept to a minimum.
CRUSHING AND ORE STORAGE
In addition, in the event of a breakdown, a smaller plant can be kept in operation with a small loader and emergency hopper. The product size is often a compromise between what is required of the milling cycle and what can be achieved in the crushing cycle.
GRINDING
The main effect of feed size is on the diameter of the feed spout to the primary mill. In this configuration, the gravity circuit is usually fed by means of a start from the bottom of the cyclone's underflow sink.
GRAVITY CONCENTRATION
Due to the coarse and dense nature of the feed, a scour screen is usually located above the gravity device. Consequently, the gravity device should normally be located above the mill discharge tray (usually in the cyclone tower).
LEACHING AND ADSORPTION
The main disadvantage of the thickener with leaching is the cost, especially for ores with poorer sedimentation. This allows the height of the cyclone tower to be reduced in some cases.
CYANIDE DETOXIFICATION AND TAILINGS DISPOSAL
In this circumstance, the regeneration furnace is located at a lower level and the regenerated carbon is transported hydraulically to a screen above the adsorption tanks. A system for positive flushing of the tail line with process water after plant shutdown should always be included.
ELUTION AND GOLD ROOM
For the Zadar circuit, this can also be affected by the location of the gold room in the milling circuit, which can push the stripping circuit further down the stack of tanks. In some more remote overseas operations, security is a primary concern and the gold room is placed within sight of the offices/security complex in a separate complex.
FLOTATION
One of the contributors to flexibility is the ability to send concentrate streams to a number of different destinations. This can be accomplished by elevating equipment high enough to allow laundry detergents to flow to either destination.
REFRACTORY ORE PROCESSING
This is usually determined by modeling the test portion of the batch with due consideration of the number of compartments in the autoclave and possible short-circuiting. For arsenic-bearing ores, the handling of arsenic trioxide in the gas stream can be difficult.
SERVICES AND UTILITIES 1. Reagents
Oxidation greater than 95% sulfur is usually targeted and depends on cyanidation performance and gold recovery behavior. Depending on the oxygen demand, a pressure swing adsorption (PSA) or cryogenic oxygen supply is required.
