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By F. Forbes

For many years, the Machinery Division of Dravo Corporation has been designing and constructing bins and hunkers as part of overall plant facilities. We have designed bins to handle a variety of materials including coal, coke, iron ores and concentrates, sintered and pelletized ores, calcined and raw limestone, bentonite, alloys for BOF shops, and even cast iron chips from machining operations. We, along with everyone else in this business, have had our bin problems. The bins either plug, rathole, segregate, wear out, flood the discharge device, or overload it. Surprisingly, sometimes they have worked. As engineers, it has long concerned us that something as important as bin design should be so imprecise and that it has been so conspicuously avoided in research and in literature. In past years, rule-of-thumb design criteria had been to keep the sides of the bins as steep as possible and the outlets of the bin as large as possible. This criteria led to the design of bins with 600 to 700 side slopes and table feeders which were very large. Unfortunately, this meant trying to fit tall, skinny bins into a layout where minimum building height was required for obvious economic reasons. Like everyone else in the industry, we found that this design procedure was expensive and ineffective.

Jan 1, 1968

By V. Roze, M. E. A. Robertson, C. J. Sharland

Current Techniques - Fire Assay Fire assay of gold has been used for several thousand years and is a well known technique to the traditional assayer. Very few assayers wish to use the method but to date there has been no viable alternative. Fire assay is expensive in labour, time, capital and running costs. Workers can be exposed to hazards and uncomfortable working conditions such as lead fumes, heat stress, dust and eye strain. The high capital cost of putting up the building and equipping it, together with running costs which increase annually at a prohibitive rate makes the technique less attractive each year. The main requirement in most assay laboratories is to maximise throughput economically. This is difficult with fire assay as it is impossible to automate. Each sample for analysis is handled by at least 12 people and each person represents a potential source of error. Record keeping and report generation has to be done manually which is both slow and prone to errors. Replacement of staff requires a considerable training period and with a large turnover of personnel this presents yet another problem. The presence of silver and dross in the gold sample affects the accuracy at low gold values. X-ray fluorescent analysis Two methods of XRF instrumentation have been used with limited success. The first type is a laboratory instrument employing L X-rays. Small samples of a few grams, which are not representative,

Jan 1, 1988

By David M. Mchaina, Michel Grenier, Stephen G. Hardcastle

An airborne dust survey was conducted at the Arthur W. White mine of Dickenson Mines Limited by CANMET/MRL and Dickenson Mines Limited Staff in April 1990 for the purpose of evaluating environmental conditions underground and in the surface mining plants. The survey was designed to measure respirable silica, total arsenic and lead concentrations at several workplaces. In addition, settled dust and rock samples were collected from workplaces and analysed for total arsenic content. More importantly, arsenic exposure data were needed to evaluate the impact of Ontario Regulation 176/86 as amended by Ontario Regulation 23/87. A total of 165 area and personal air filter samples were collected during the study. Of these, 85, 67 and 13 samples were for arsenic, silica and lead respectively. Sampling aid analyses were performed according to the Ontario Ministry of Labour Regulations. More than 90% of the workplaces sampled for respirable silica, total arsenic and lead were below the Ontario Ministry of Labour Regulations; and 10% of the workplaces sampled for arsenic shaved concentrations above the Threshold Limit value (TLV) proposed in the Ontario Regulation 176/86 as amended by Ontario Regulation 23/87. These results were used to identify occupations and/or workplaces where more sampling and control measures were required respirable silica, total arsenic and lead. This paper describes the results of the dust sampling program conducted at Dickenson Mines Limited.

Jan 1, 1991

By P-M. Dupond, S. Lowrie, C. Tauziéde, Z. Pokryszka, A. D. Jones

A physical model has been developed to simulate the flows and mixing of gases in the waste of a longwall retreat coalface. The model is used in conjunction with computational modelling, and the distributions of permeability and gas emission in the model waste follow those in computer simulations (Pokryszka et al 1996). The physical model represents at 1170th scale a 200 m long, 3 m high coalface with a waste extending up to 280 m to the face start line. The model is tilted to the same seam slopes as the real face, e.g. 22° ascensional ventilation along the face and 7" slope to the dip. The purpose is to investigate the flow of three components: ventilation seepage flow through the waste; methane; and nitrogen injected to quell spontaneous combustion. A heavier-than-air surrogate gas (SF,) is used in place of methane, and therefore the model is inverted so that gas layers form along the 'roof". The main forces driving the flows in the waste (pressure gradients due to ventilation and the density difference of gas layers) are kept in proportion by appropriate scaling of the permeability. Calibration and validation used data from a coalface at a mine in the Lorraine coalfield. The model is now in operational use.

Jan 1, 1997

By S. P. Mehrotra, P. C. Kapur

A phase-species classification is suggested for the mathematical models of flotation kinetics. Important models are discussed and the structure of their rate constants and parameters is analyzed. Split or enhancement factors are formulated for different kinetic models. The steady state dynamics of the flotation circuits can always be described in terms of these factors. For simulation of circuits, feed is characterized in a formal manner starting from a multivariate distribution of particles in flotation rate, size and mineral content. Synthesis of optimum circuits which simultaneously searches for the best process variables and structural parameters from a generalized master network is described. Trends in the areas of search algorithms, role of middlings and feed identification etc. are indicated.

Jan 1, 1989

By G. D. Hood, B. E. Davis

A problem that has continued to plague the Florida phosphate industry is loss of coarse phosphate in the flotation circuit. Attempts to remedy this problem such as floating the coarse material (plus 425 µm) in a separate circuit have resulted in limited success, but recovery is still not optimum. A fundamental examination of the mechanisms involved in the conditioning of the coarse phosphate has led to results that seem to supersede common paradigms. The Bureau of Mines investigated conditioning parameters such as fatty acid/fuel oil dosage, residual clay content in the feed, conditioning time, mixing intensity, and conditioner solids content. The study revealed that the effect of all these parameters was important. However, it was discovered that contrary to common beliefs, the conditioning time affected the grade of the rougher concentrate much more than the recovery. Specifically, the longer the conditioning time, the less quartz that was floated. It was also discovered that high mixing intensity conditioners could lower the conditioning time required for good grade. Many phosphate operators use low intensity drum type conditioners. Optimizing the conditioning time, mixing intensity, and other conditioning parameters resulted in a rougher concentrate grading 30 pct P.2O5, with an attendant recovery of 95 pct.

Jan 1, 1993

By T. B. Whitmoyer, J. E. Sneckenberger, M. A. Jerabek, C. F. Stanley

The measurement of acoustic impedance at frequencies up to 6,400 Hz has been proposed as a diagnostic tool to yield more detailed information about lung condition. A three generation branching system of plastic Y-tubes has been constructed. The impedance of the branched system is measured by an impedance tube using the two-microphone technique. The impedance spectrum is used to calculate the reflection coefficient spectrum, which is converted to an impulse response by an inverse FFT. The area function is extracted from the impulse response by the Ware-Aki algorithm. Measurements of acoustic impedance of the branched system were made for several different end conditions of the eight terminal outlets. The outlets were either blocked with modeling clay, plastic packing material, or aluminum blocks or were unblocked. Six measurements were made of each configuration. In general, the more outlets blocked, the larger the shift to the right of the impedance magnitude peaks for frequencies above 3000 Hz. The impedance magnitude peaks for the plastic packing material were shifted in frequency to the right relative to the peaks of the other system terminations. The impedance magnitude peaks for the clay and aluminum system terminations were significantly different in magnitude but not shifted in frequency. The area functions at the end of the branched system were significantly different (a > 99%) for most of the end conditions. Area functions for the modeled branched lung systems between the end of the impedance tube and the termination outlets of the branched system were similar but distinctively different for the various end conditions. These results indicate that the two-microphone technique can sense small changes in the terminating end conditions of a rigid system of branched tubes and thus may sense impedance changes due to lung disease in the conducting airways. Keywords: acoustic impedance, lung model, area function.

Jan 1, 1991

By A. De Daio, D. W. Fuerstenau, P. C. Kapur

Because of its pronounced tendency to undergo visco-plastic flow, coal ground in the energy- efficient high-pressure roll mill invariably comes out as a briquetted product which must be disintegrated in a conventional type of grinding device such as the ball mill. The aggregates comprise comminuted coal particles that are apparently extensively cracked and weakened during passage of the coal through the high-pressure rolls. Their deaggregation in a ball mill in the second stage is accompanied by further grinding of the coal with a relatively small expenditure of energy. Thus in spite of energy dissipation in briquetting in the roll mill and in disintegrating the briquettes in the ball mill, significant energy savings are possible in the fine grinding of coal in a two-stage serial grinding mode, as compared to ball mill grinding alone. It has been determined that for the best results the energy invested in the two grinding stages must be apportioned in an optimal manner, the energy consumption in the ball milling step is comparable to, even in excess of, the energy spent in the high- pressure roll mill; and 20 to 50 percent energy savings might be possible in grinding coal to minus 200-mesh size by this two-step process, as compared to conventional milling.

Jan 1, 1995

By A. C. Lyons

Foreword Sir William Halcrow and Partners are responsible for the design of the Ahmed Hamdi Tunnel as Sub-contractor to the Contractor, Osmac, a joint venture formed by the Arab Contractors, Osman Ahmed Osman and Company of Cairo, and Tarmac International of London. Throughout the paper the term "Client" refers to the Employer, the Ministry of Housing and Reconstruction, which latterly became the Ministry of Development and New Communities of the Arab Republic of Egypt. At the time of writing of this paper only a few hundred metres of the tunnel have been driven, but the design is substantially complete. Introduction The Ahmed Hamdi Tunnel, which is at present under construction, will be a two-lane tunnel crossing beneath the Suez Canal approximately 15 km north of the town of Suez at El Shallufa. It will become the first permanent connection across the Canal since 1967 and is visualised by the Egyptian Government as an early step in the development of the Sinai Desert along the eastern bank. The tunnel will carry pipelines for treated water and electric power cables to assist in this development. The tunnel, which will be 1640 m in length, is being driven through hard clay and mudstone using a tunnel shield fitted with hydraulic excavators. The primary lining is being constructed with precast, bolted reinforced concrete segments with an internal diameter of 10.4 m. The road deck structure and the walls of the air supply ducts beneath it are formed with precast, reinforced concrete units erected immediately behind the shield.

Jan 1, 1979

By Zhongxue Li, Shuang Gao, Zhixin Zhen, Yiqing Zhao, Xuan Qin

If not well-managed, a mine-tailings facility may become a major source of risks, endangering the community and environment, and damaging the reputation of the minerals industry regarding sustainability. Identifying, characterizing, and mitigating the hazards and risks associated with tailings facilities have been critical to the maintenance of community-safe and environmentally sound mine-tailings facilities. Herein, a complex network model for characterizing the hazards and risks associated with the lifecycle of tailings facilities is presented. In this approach, the hazards are modeled as vertices of the complex network, and the interactions among the hazards are modeled as edges of the complex network. The complex network for modeling the hazard and risk spreading of mine-tailings impoundments is analyzed and characterized by using network metrics such as the network density, geometrical characteristics, characteristic path length, network efficiency, and clustering coefficient. The degree distribution of the network obeys a power-law distribution, indicating that the network for characterizing the risk spreading associated with a tailings facility is scale-free. According to the results of calculations and existing research results, the network is ultrasmall-world. By analyzing the change of the global network efficiency under four kinds of different methods to remove network nodes and edges, network nodes with higher between centrality (BC) are identified as critical. The removal of those critical nodes helps mitigate risks associated with a tailings facility and reveals the vulnerabilities to BC attacks.

Jan 1, 2017

By E. W. Hawk

he power generation industry may be required to reduce carbon dioxide (C02) emissions if regulations related to global climate change are enacted. Coal-fired generation emits more than 80% of the power sector CO2 and would be a likely target for CO2 reductions. Compliance with the Kyoto Protocol will require a 33% reduction from the projected year 2012 emission level, even with moderate load growth. This article describes an analysis of power industry CO2 reduction options and their costs. It assesses how a generator would make compliance decisions under a mandatory CO2 emissions reduction program. Carbon sequestration, fuel switching and new plant construction are considered. The Global Climate Change Treaty signed at the Rio de Janiero Earth Summit in June 1992 set the long-term goal of stabilizing CO2 concentration in the atmosphere. The December 1997 Kyoto Protocol established short-term mandatory targets for the United States and 37 other developed countries. The United States' target is a 7% decrease by 2012 from the 1990 "greenhouse gas" level. Developing countries are exempted from reductions, according to the Kyoto Protocol, despite projections that indicate a significant increase in their emission levels. The Kyoto Protocol must be ratified by the US Senate. US power industry carbon emissions were 490 Mt (540 million st) in 1990 and are projected to be 680 Mt (749 million st) in 2012, according to the US Energy Information Administration. Coal-fired generation emits more than 80% of the power sector CO2. Assuming that the power industry is only required to reduce emissions by a proportional share, a 33% emission reduction, or 225 Mt (248 million st) of carbon, would be required to comply with

Jan 1, 1999

By Paula N. Wilson, W. T. Parry

Carbonaceous and metalliferous black shales occur in close proximity to Mercur-type gold deposits in the southern Oquirrh Mountains, Utah. These shale units, the Manning Canyon shale and the Long Trail shale, have undergone regional hydrothermal alteration. Hydrothermal solutions oxidized organic matter and pyrite, replaced shale by hydrothermal phyllosilicates and silica, and replaced fossils by phyllosilicates. The shales are depleted in organic carbon, calcium carbonate, alkali and alkaline earth metals, and enriched in aluminum and hydrogen. Hydrothermal veins containing illite, chlorite, pyrophyllite, kaolinite, Fe-oxides, and sulfides are present throughout the study area.The illite in veins is an ammonium illite that contains up to 2 % NH4 and is correspondingly depleted in K. Correlations among Au, As, Hg, TI, Sc, and rare earth elements indicate that hydrothermal fluids responsible for formation of ammonium illite were gold bearing. K/Ar ages of illite veins and illite-rich, clay-size separates of altered shales indicate hydrothermal activity occurred in the time range 193 to 122 Ma. Several ages from clay-size separates within the Mercur district cluster near 160 Ma. These ages are coeval with thrust faulting recognized to the north and west.

Jan 1, 1990

By H. Wilcox, M. Prichard, Y. P. Chugh

Environmental considerations related to the disposal of coal combustion byproducts (CCBs) and the impacts of deforestation associated with the harvesting of timber for utilization as roof supports in mines should become more severe in the future, as landfill space and suitable timber reserves become more scarce. To help address these concerns, lightweight artificial supports, such as post and crib elements, that use large percentages of coal combustion byproducts as aggregate have been developed for use in underground mines. These structural products show equal or better engineering characteristics than timber, and they have the potential to replace timber support in underground mines. CCB-based ultralight structural material (ULSM) has also been developed and commercialized for use in the construction of ventilation stoppings in underground mines. The bulk densities of these blocks range from 0.40 to 0.64 g/cm3 (25 to 40 lb per cu ft) with more than 75% CCBs. Efforts are also given to develop and demonstrate large volume CCB-based subgrade improvement technique for road construction. Soil treated with SIUC fluidized-bed combustion (FBC) fly ash developed an immediate bearing value exceeding 25% with a swelling strain of less than I %, which is greater than untreated soils, and met Illinois Department of Transportation (IDOT) standard specifications. In this paper, development procedures, engineering characteristics and beneficial uses of CCB-based structural products are given.

Jan 1, 2002

By Michael C. Stanley

The set of discoveries for a mining district or camp is a reflection of the exploration history. In the western Abitibi greenstone belt of Ontario, future exploration can be guided by a study of statistical trends of known gold deposits. In this area simple trends indicate a strong decrease in the contained quantity of gold discovered through time. Much of this decrease is attributed not to falling mining grades but to smaller tonnages of ore. A plot of the largest discovery in each ten year time period suggests that deposit discoverability is following a size-biased sampling model. Cumulative ounces of discovered gold indicate that an asymptotic value has been reached where exploration is not expected to add significantly to known reserves. This is substantiated by a downward trend in the exploration success ratio of the number of new deposits discovered versus the number of new mineral prospects. The set of discovered deposits reflects a non-random sampling process where size- biased modeling suggests that the largest deposits will be discovered early in the exploration effort. It is the exceptionally large deposit contributing to the observed size-biased distribution. Although this pattern is observed for the western Abitibi the model is complicated by recent, large reserve additions that are attributed to the original discovery. There is present in this area a subtle learning process in exploration leading up to the largest discovery. For comparison a learning model was estimated using cumulative size of discovery per unit of time. This model yielded results consistent with the statistical trends and is thought to be a superior forecast of future discoveries in this region.

Jan 1, 1992

By A. C. Lyons, A. J. Reed

INTRODUCTION A trend which is obvious in the United Kingdom and is thought to be evident in other parts of the Western world is the disproportionate rise in the cost of tunnel mining labour compared with other tunnel cost increases. This disproportionate increase in labour costs has been accompanied by, and may be the result of, a shortage of skilled working labour. To combat this problem there has been a steady increase in the use of machines for excavation and for the erection of tunnel linings to keep the amount of skilled labour working below ground to a minimum. The typical tunnelling cycle, where the ground needs continuous support can be excavation, temporary support, temporary lining, grouting and permanent lining. It is obviously an advantage to combine as many of these operations as possible and carry out as much as possible by machine. Machines have been developed which will, either alone or used in combination with a shield, excavate and, when necessary, temporarily support the excavation. If a segmental lining is used, it can be so designed that it will form the permanent lining and reduce the cycle time and skilled labour requirement to a minimum. In cases in which the ground can be cut accurately to a smooth profile and will stand without support for a sufficient time, the lining can be expanded against the ground and the necessity of grouting eliminated. In cases in which ground will not stand without support, the usual method is to use a bolted lining and to grout behind it preferably as the shield is shoved forward. Whichever technique is used (this is largely determined by the ground) it is an advantage to make the segments as large

Jan 1, 1974

By Y. J. Wang

Optimal sizing of a ventilation shaft is a classical subject in mine ventilation economics.. The shaft size is optimized by minimizing the sum of shaft-construction and ventilation-power costs, or owning and operating costs. The length and air quantity of the shaft are held constant, and the location of the shaft, affecting its depth, and construction and ventilation power costs, is not considered (Hartman, 1961; Lambrechts, 1974; Wang et al., 1978). This paper proposes an approach by which the location and size for a new pair of shafts (intake and return shafts) are optimized for a coal-mine ventilation network. Specifically, the problem is to determine the location and size for a new pair of shafts, and the distribution of air between the new and old shafts so that the combined cost of shaft construction and ventilation power is minimized. The shaft length or depth corresponds to the height of overburden at any shaft location. To simplify the problem, the shaft locations will be limited to the line along the main or submain entries, and the connection entries at the shaft bottom neglected. In order to calculate the ventilation-power cost, the air power of the system should be determined. This in turn requires the calculations of the air quantity and pressure of each fan in the network, satisfying Kirchhoff's laws and Atkinson equation. After obtaining the air power, the cost calculation is straightforward. In the following, we shall assume that the resistances of all airways, and the quantity for each mining section, which is controlled by adjusting the air regulator, are all known. The resistances for the shafts are determined from the estimated friction factors, and shaft dimensions and lengths. Furthermore, it will be assumed that the fans can be selected to meet the duties called for by any network solutions.

Jan 1, 1982

By Lawrence W. Teufel

Knowledge of in situ stress and natural fracture distribution at depth improves our ability to stimulate and produce low permeability reservoirs. The focus of this study is three closely spaced, 2.5 km deep vertical wells in the Piceance Basin of Colorado. The wells were completed through the tight lenticular and blanket gas sands of the Mesaverde Group. In situ stress directions and magnitudes were determined from hydraulic fracture tests and anelastic strain recovery measurements of oriented core. The distribution, orientation, and characteristics of natural fractures in the subsurface were determined from detailed observations of over 1300 m of core, of which 400 m was oriented. Stress measurements clearly show that horizontal stresses are strongly influenced by lithology. In a sandstone/shale sequence at a depth of about 2.0 km in situ stresses in sandstone formations are anisotropic, with the average ratios of the minimum and maximum horizontal stresses to the overburden stress being 0.82 and 0.96, respectively. In sharp contrast bounding shale formations are lithostatic. This stress contrast between sandstones and bounding shale formations could act as a barrier to hydraulic fracture propagation during stimulation and impede vertical fracture growth. Natural calcite-filled fractures are present in over 7 percent of the core, with several horizons having a much higher frequency of fractures. Fractures are found primarily in sandstone. The fractures have a strong preferred orientation of N 1060E[+]110, which is aligned with the maximum horizontal stress and direction of hydraulic fracture propagation. The interaction between a well developed fracture fabric and anisotropic stresses in sandstone formations produces a permeability anisotropy, with the maximum permeability aligned with the fracture fabric and maximum horizontal stress.

Jan 1, 1986

By Malcolm J. McPherson

Observations of environmental parameters in mines have traditionally been made by means of hand-held instruments, these being employed as a basis to ensure that atmospheric conditions in the mine remain within limits commensurate with safety, to safeguard the health of personnel, and to ensure that statutory requirements are met. Thus, starting from the first flame safety lamps of the early nineteenth century, numerous portable instruments have been devised over the years to indicate levels of dust, temperature, humidity, and concentrations of gases including oxygen, methane, and carbon monoxide. Similarly, portable instruments have been used to measure air velocity and pressure. For routine monitoring purposes, hand-held equipment suffers from many disadvantages. Readings are intermittent, often with long delays between successive observations, making short-term trend analysis impossible. Portable instruments are more liable to damage; they are labor intensive and provide a very limited amount of information either for control or planning purposes. The 1960's and 1970's have seen an accelerated development of mine environmental monitoring equipment. Alarm methanometers to give localized audiovisual signals became more common. These were followed by a variety of instruments which gave local, then local/remote continuous records, particularly of methane concentration and airflow. More sophisticated transducers and transmission systems were developed allowing further parameters to be monitored. This led to a proliferation of paper strip and chart recorders which had to be maintained and inspected regularly for trends and abnormalities.

Jan 1, 1979

By G. Piegols, J. A. Lombardi

Substantial volumes of cyanide are consumed in precious metals mining due to the purposeful destruction of base metal cyanide complexes and free cyanide to meet surface discharge regulations. This destruction of cyanide resource runs counter to the prevailing social ethic of resource conservation wherein cyanide recovery-and-reuse is considered a more socially responsible cyanide use pattern than systematic cyanide destruction. HW Process Technologies, Inc. (HWPT) has developed membrane based methods for the recovery of cyanide from barren solution as a means to reduce cyanide waste. The HWPT Engineered Membrane Separation (EMS™) system uses state-of-the-art spiral wound membrane elements that are engineered specifically for the treatment of high pH cyanide process solutions. The membranes fully reject WAD CN, SAD CN and most minor metals, and partially reject SCN, Free CN and precious metal cyanide from a high clarity barren solution feed to a small volume EMS™ “concentrate” stream. The EMS™ “concentrate” stream is returned to the process. The large percentage of the EMS™ process feed exits the system as cyanide lean EMS™ “permeate.” The EMS™ permeate, after residual cyanide destruction, polishing, and pH adjustment, is, thereafter, typically suitable for discharge. Separately, the HWPT EMS™-PLS method of cyanide recycling is an internal plant cyanide recovery step that removes base metal cyanides from a pregnant leach solution to a small volume EMSTM concentrate stream. The concentrate stream is then typically processed further for the recovery of metals and recovery-recycling of cyanide. The method makes it economically practical to recover gold from Merrill-Crowe or car-bon plant “fouling” solutions, e.g., those with greater than 400 ppm Cu, as might result from the use of the EMS™ method wherein EMS™ concentrate is constantly thrown back into the mine leach solution pool as part of the free cyanide recycle process, or as might result from the single-pass leach treatment of high copper content ores or concentrates. The EMS™ cyanide recovery method for barren solution treatment is shown to be “economic” for the treatment of clear solutions at the approximately 200 ppm total cyanide level (CNT), and for slurries at the approximately 400 ppm total cyanide level, where economic is defined as a 2 year EMS™ plant payback. The EMS™ plant payback calculation includes the beneficial monetary impacts of gold and free cyanide recycling and the avoided operating cost of cyanide destruction.• The cyanide recovery plant payback period is reduced further when the avoided capital costs for cyanide destruction (EMS™ permeate “clear solution CN destruction polish” only required) and/or metals precipitation are considered.

Jan 1, 2004

By Phoebe L. Hauff, Jeffrey P. Kurtz, Paul D. Chamberlin

Clay minerals can be a source of problems in heap leaching operations. The ore for many heap leach operations is commonly acid-sulfate alteration zone rocks which may be found in hot springs deposits as well as the supergene zone of other near- surface gold deposits. Clays can be important constituents of these ores. Swelling clays, such as smectite, can come loose from the agglomerated ore, migrate within the heap, concentrate in pore spaces and often plug up flow channels in the heap Cement is often added to the ore as a binder during the agglomeration process. Lime is added for pH control. Their presence, combined with the sodium cyanide commonly used to leach, can raise the pH of the leach solution to 10 or even 12. This very alkaline solution can cause dissolution of some mineral Some clays, such as kaolinite, are not very stable in high pH solutions. They can be dissolved and reprecipitated as other clay species if sufficient silica and the appropriate cations are available in solution. Silica gels and amorphous materials can also be created from the dissolved kaolinite and other minerals and act as retardants to the flow of leach solutions in the heap. Therefore, before a heap leach operation is built, the operator should evaluate the clays in the ore and test the agglomeration procedure. It is important to know not only the mineralogy and the chemistry of the leach environment but how the minerals and solutions interact and what the products of this interaction are. A hypothesis is presented in this paper that expanding smectite- bearing clays can be generated within the heap. How and why this happens will be explained.

Jan 1, 1987