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By Roberto Galéry, Braz J. C. Filho, Marcelo M. Stopa, Douglas B. Mazzinghy, Priscila M. Esteves

"The purpose of the research is to monitor ball mill filling by means of signals usually measured in its electrical drive. The method is based on the mill torque estimated from rotor speed and induction motor stator voltage and currents. New signal processing is presented in both time and frequency domain for measurements in a dry laboratory ball mill. Statistical analysis is applied to time series resulting in good correlation to mill filling. Fast Fourier Transform (FFT) and power spectral density (PSD) also resulted in an accurate filling indicator. The proposed method does not need any sensor to be installed directly on the mill and requires only sensors usually available for motor control purposes. The experimental results showed that the method have potential to be used to construct an automatic system for monitoring operational variables in ball mills. The aim of this monitoring is to improve energy efficiency, reliability and productivity.INTRODUCTION Recently, a great number of papers have pointed the importance of ball mill filling monitoring and also of grinding control (Lu, et al., 2014) (Ramasamy, et al., 2005) (Tsamatsoulis, 2014) (Zhou, et al., 2009). Additionally, great amount of control techniques have also been presented with several complexity degrees (Tsamatsoulis, 2014). According to Eremenko (2015) the lack of effective and accurate methods for fill level measurement is the main reason that makes mill optimal control so complicated. It happens because nonlinearity, long time delay and time varying features of the ball mill turns difficult to develop a truly efficient method for monitoring filling. At the same time, fill level has a determining role in charge motion and consequently on particle breakage. For low levels of filling many energy is expended in impacts with very low breakage efficiency. Those impacts can also damage mill liner. In contrast, high levels of filling causes damping effects that reduces breakage and can also affect energy consumption. Based on this it is conclusive that fill level measurement of ball mills is an important issue for grinding efficiency. This fill level information can be used for operators to control ball mills and also for engineers to run simulations and improve confidence levels of circuit designs (Shi, 2016)."

Jan 1, 2018

By Rolf Katzenbach

Construction of drilled shaft foundations with the use of hydraulic oscillators and rotators to install temporary casing over the full depth of the shaft is described. The equipment and techniques were developed in the 1960?s in Germany and full-depth casing is now the predominant method of construction in Europe. Its use in North America is increasing. This paper presents an overview of full-depth casing methods and a summary of available load test data evaluated by the authors to compare the load transfer and capacity performance of shafts installed by various construction methods. Results demonstrate that load transfer and capacity of full-depth casing shafts are equal to or exceed that of shafts constructed by dry or slurry methods and that measured capacities are consistent with generally accepted design equations. The principal advantage of full-depth casing methods over other installation techniques is that the risk of defects in the shaft is minimized. Casing is able to penetrate into the ground under any geologic or groundwater condition when this technique is applied. Potential delays and cost overruns can thus be avoided and a safe, economical foundation element is created.

Jan 1, 2007

By Jogeshwar P. Singh, Aser I. Abbas, Mohamed Ashour

The presented methodology predicts the pile head response (i.e. pile head load - displacement curve) and develops the load transfer (t-z) curve of piles in sandy soils under tension forces based on soil/pile properties and soil-pile interaction. The proposed approach improves the prediction of the t-z curve in sandy soils compared to current practice. The method employs a nonlinear soil constitutive model to calculate the mobilized shear stress/strain in soil at the soil-pile interface induced by pile upward displacement. The approach accounts for the influence of the pile slenderness ratio on the predicted t-z curve and is validated through comparisons with measured pile head response and t-z curves from full-scale pile load tests. INTRODUCTION Piles may be subjected to axial uplift forces due to either static loading or cyclic loading. The majority of methods are only concerned with the pile ultimate tensile capacity. However, the mobilized pile stiffness (i.e., pile-head load-displacement relationship) is essential to determine the interaction between the foundation and the superstructure and consequently the performance of the whole structure. Methods that assess the pile ultimate tensile capacity usually assume the failure surface at the soil-pile interface and estimate the local side shear resistance using a lateral earth pressure approach. The Naval Facilities Engineering Command (NAVFAC 1986) and the US Army Corps of Engineers (USACE 1991) employed Eq. 1 to assess the ultimate shear stress (τ) developed at the soil-pile interface.

Jan 1, 2018

By Mark K. Larson

Calibration of LaModel for deep coal mines begins with adjustment of overburden stiffness for load transfer distance. This calibration determines whether mining induced stresses are concentrated in the immediate abutment of the gob, or spread over a wider area. In the absence of site information, an empirically-based estimate is often used. Where data is available, a recommended calibration procedure can be followed, as is done in this case study at a deep western longwall mine, with minor modifications and extensions. In this case, data sources included borehole pressure cells, flatjacks installed in series with support Cans, and observed changes in ground conditions. Calibration was based on the first detection of mining-induced stress from the advancing longwall. Detection was found to depend on the type and sensitivity of measurement. Borehole pressure cell data with a 20-psi-increase detection threshold were chosen as the standard, in accord with data used in deriving empirical relationships. Application of this standard produced a load transfer distance estimate roughly four times the empirical relationship developed by Peng and Chiang (1984). This is a significant deviation with important implications for panel design at this site. Data from flatjacks, ground condition observations, and borehole pressure cells with higher threshold values, were tightly clustered and show load transfer distances from two to four times empirical guidance. Ratios between various measurements can be used to adjust measurements to the standard (although they may depend on mine geology). Once established, ratios can be used to adjust estimates, say from support flatjacks or ground observations, to the standard, where borehole pressure cell data is not available.`

Jan 1, 2012

By Mark K. Larson, Douglas R. Tesarik, Heather E. Lawson

"Load transfer distance (LTD) is simple in concept and usually evident in underground coal mines. Many people in the mining industry recognize LTD as the distance from the panel to where the mine ribs and pillars show evidence of renewed spalling, floor heave, or other effects of increased weight due to longwall mining or pillaring. Barrier pillars, in particular, are designed to shield mains and other relatively permanent facilities from this loading. LTD is also important in determining the extent and degree to which mining increases the load on pillars and ribs in the gate roads. Generally, a long LTD reduces loads in gate roads, but may require larger barrier pillar widths to protect mains or adjacent panels from excessive loads. Therefore, a long LTD may make it easy or difficult to meet various objectives of mine layout design . LTD reflects overburden geology in two ways: First, overburden that is weak and readily caves will limit both the amount and distance of load transfer. Second, stronger, stiffer, sandier, and more massive overburden increases both the amount and distance of load transfer. As such, LTD is central to coal mine layout design and calibration of numerical models that seek to anticipate these transfers of load during mining. However, the term does not have a consistent definition in the literature, and various instruments and observational techniques with varying sensitivities and thresholds have been used to indicate the onset of mining-induced stress increase and, subsequently, to determine an LTD. Consistency is important for meaningful comparison of ground response between mining sites and for accurate calibration of models.This paper adds to the body of observed and reported LTDs by presenting cases with relatively sandy and massive overburden at two western coal mines. These two cases include observation and measurement of LTD with multiple methods and provide insight into how distances reported relative to different criteria and instrumentation could be adjusted for comparison against a common base. This base is the criteria used by Peng and Chiang (1984) to determine their empirical equation. In one of these two cases, LTD was recently measured at a western U.S. coal mine (Mine A) to be approximately four times that calculated using the Peng and Chiang empirical equation. LTD measurements were examined using various instruments at Mine A and at adjacent Mine B. The measurements at Mine B showed that LTD was significantly greater than that calculated by the Peng and Chiang equation. Difficulties with BPC installation and fittings at Mine B permitted only ranges of LTD to be determined from some BPCs. Even so, the LTDs and ranges of LTDs determined were consistent with the LTDs determined at Mine A."

Jan 1, 2015

By Tarrant GC

Cement and resin encapsulated tendons are widely used in the stabilisation of mine roadways. One of the main factors in controlling the efficiency of the reinforcement is the ability of the tendon to generate load in response to rock deformation. The analysis of field data from instrumented reinforcing tendons complimented with extensive laboratory investigations have more accurately defined the mechanisms by which load generation occurs. The role of reinforcing tendon profiles, hole geometry and encapsulation medium properties in controlling the reinforcement stiffness and capacity are discussed. The results of the investigation have implications in both the design of rock reinforcing systems and the optimisation of encapsulation mediums and tendons.

Jan 1, 1992

By M. W. Fabjanczyk

Cement and resin encapsulated tendons are widely used in the stabilisation of mine roadways. One of the main factors in controlling the efficiency of the reinforcement is the ability of the tendon to generate load in response to rock deformation. The analysis of field data from instrumented reinforcing tendons complimented with extensive laboratory investigations have more accurately defined the mechanisms by which load generation occurs. The role of reinforcing tendon profiles, hole geometry and encapsulation medium properties in controlling the reinforcement stiffness and capacity are discussed. The results of the investigation have implications in both the design of rock reinforcing systems and the optimisation of encapsulation mediums and tendons.

Jan 1, 1992

By Joshua Calnan, Braden Lusk, Kyle Perry

This paper presents detailed information and data regarding the load transfer characteristics of Blast Resistant Glazing Systems utilizing two different thicknesses of polycarbonate. A series of triaxial load cells, along with surrogates of identical stiffness characteristics, were placed around the glazing perimeter to directly measure the load transferred to the support system from explosions of varying degrees. The blast loads were developed using an explosive driven shock tube administered by the University of Kentucky Explosives Research Team (UKERT) in Georgetown, KY. Results presented include distribution of loading, maximum load transferred to connections, blast pressure-time data, glazing system deflection-time data, and final performance results of each system. The two glazing systems respond differently to the applied blast loading. Differences and similarities in the load transfer characteristics are discussed. The experimental results are then compared to a commonly used blast resistant glazing system analysis software tool utilizing a Single Degree of Freedom (SDOF) method of analysis for each system. Preliminary results show that currently used models do not correspond well with experimental data.

Jan 1, 2014

By Randy R. Williams, Brian W. Wilson, George M. Filz, Marina S. W. Li

"Detailed design of an extensive deep mixing (DM) scheme using the Cutter Soil Mixing (CSM) technique was completed for foundation support of mechanically stabilized earth (MSE) walls for Kitimat Liquefied Natural Gas (LNG) at Bish Cove, British Columbia, Canada. The design was based on the provision of soil-cement structures, constructed in highly variable subsurface conditions that consisted of thick deposits of fine-grained soils overlying granular soils, and required to meet project-specific performance criteria, to support the MSE walls. The design, consisting of rectangular CSM panels constructed to form barrettes connecting to a longitudinal wall of continuous CSM panels, was configured to manage the distribution of stresses and strains that could be developed within the soil-cement structure.The results from 2D finite element analyses were used to determine the necessary arrangement and properties of the CSM panels to accommodate localized areas of relatively high shear, tensile and compressive stresses within the soil-cement structure. The relationships between unconfined compressive strength and elastic modulus for fine-grained and granular soil-cement structures obtained from the Bish Cove data were compared with published references and were found to be significantly different in the higher strength range materials.BACKGROUNDDeep Mixing design was completed for the development of the Kitimat LNG Facility located in Bish Cove, British Columbia, for support of two relatively high MSE walls and associated bulk earthwork operations. Deep mixing was necessary to treat the very weak native deposits in-situ to meet project performance requirements and physical constraints without the need for significant excavation and disposal work. The DM design was undertaken on the basis of adoption of the CSM technique for in-situ ground improvement of the native foundation soils which consisted of very soft to soft fine-grained marine deposits and loose to compact sandy silt to silty sand, overlying dense sand and gravel (Fig. 1). The DM area is located immediately upslope of the Bish Cove beach area, and is “L” shaped in plan, approximately 300 m long by approximately 28.8 m wide (parallel to the beach area) and 165 m long by an average width of 21.0 m (perpendicular to the beach area). The depth of the DM ranged from about 5.0 m to 30.7 m with typically 2.0 m embedment into dense granular soils. Details of the design philosophy, including an overview of the DM design and the project background information are presented by Li et al. (2014a). Details of the construction aspects of the Kitimat LNG deep mixing are presented by Wilson et al. (2014)."

Jan 1, 2015

By Robert M. Stevens, Arnoldo Acuña

INTRODUCTION In the early 1950s, underground miners and tunnel¬ing contractors were experimenting with ways to supple¬ment or eliminate track-bound loading and hauling equipment. Diesel-powered crawler and rubber-tire mounted front-end loaders and trucks designed for use on the surface were being modified and tried with limited but encouraging success. Miners began working with interested manufacturers to explore the develop¬ment of vehicles specifically designed to meet the de¬mands and constraints of underground material han¬dling. By the mid 1960s, load-haul-dump (LHD) vehicles were firmly established as a fundamental part of what has become known as the "trackless" mining concept, used in many mines and many countries around the world. The flexibility, mobility, and versatility of these units have given the industry a useful tool and have added new dimensions to mine development and produc¬tion. Many old mines have been redesigned to accom¬modate these trackless vehicles, and few new mining plans have failed to find some use for the concept during some phase of development and production. By 1977, several manufacturers in several different countries were producing a variety of LHD vehicles to meet the growing worldwide demand. GENERAL DESCRIPTION LHD vehicles combine certain characteristics of conventional front-end loaders and dump trucks, spe¬cifically designed for materials handling in underground mining and tunneling. The design intent is to provide one vehicle with one man, with the vehicle loading itself, hauling the load over level or inclined haulageways, and dumping the load. A typical production cycle of the most popular units has the operator driving the vehicle forward, forcing the bucket into the muck at or near floor level, and using the tractive effort of the vehicle and the prying action of the bucket to roll out and tilt back the load as shown in Fig. 1. With the bucket rolled back into the carrying position on the boom and the boom resting on the main frame of the vehicle, the load is hauled (trammed) to the dump point as shown in Fig. 2. At the dump point, the boom is raised, the bucket is rolled forward, and the load slides out as shown in Fig. 3. After dumping, the bucket is rolled back to the carrying position, the boom is returned to rest on the main frame, and the unit is driven back to the loading point for another load. There are two other types of LHD units that are slightly different in the cycles that they perform. One uses a hopper arrangement carried on the front of the machine, with a small bucket mounted ahead of the hopper. Several passes with the small bucket load the hopper, which is dumped by opening its floor. Al¬though this concept is several years old, it has gained less than 0.5% of the total market. The most recent LHD concept differs in that it has one bucket nesting inside another. The smaller inner bucket is loaded first, and it is then tilted back and above the larger bucket. When the larger bucket has been loaded, it is rolled back, and the total load is trammed to the dumping point. The dumping operation tilts the buckets in the reverse order from that of the loading operation. The impact of this new concept on the mining industry has not been measured yet. This chapter concentrates on the LHD vehicles employing the cycle described by Figs. 1 through 3, since these LHD units constitute an estimated 99% of the units in current use. MAIN VEHICLE FEATURES In general, the LHD vehicles available from most manufacturers share the same basic features.

Jan 1, 1982

By Thomas Fraser, David R. Mitchell

THE primary purpose of the loading plant is to transfer the finished product from the preparation machines to the railroad car, truck, or barge in which it is to go to market. Secondary purposes of the loading plant are: to prevent excessive degradation of sizes during loading, to reduce segregation as much as possible, and to prevent excessive quantities of very good or off-grade coal from entering any one car. Nonuniformity of consignments is one of the chief sources of com- plaints by consumers and coal merchants. A properly designed loading plant will do much to reduce complaints and ensure uniformity, not only from shipment to shipment but also in each individual consignment along the length of the car and in cross section. DEGRADATION IN STORAGE, LOADING AND SHIPMENT The object in loading is not only to handle the coal without breakage and segregation, but also to produce a well-trimmed load that will ride to its destination without spillage or breakage en route. The small sizes present in a car of prepared coal as received by the purchaser consist-of: missed small sizes not screened out in the preparation plant, breakage during loading, and breakage caused by handling en route. For domestic sizes of anthracite shipped from the Pennsylvania anthracite field to Atlantic coast cities, the dealers' lass because of breakage in loading and shipment amounts to from 2 to 5 per cent and for anthracite shipped to Middle West cities, the loss is 8 to 9 per cent. This difference is in part because dealers in the Middle West rescreen their coal more thoroughly than is usual in the East. One dealer handling Illinois No. 6 coal shipped from southern Illinois mines to Chicago reports an average size loss of 10 per cent when lump coal is unloaded with a fork. This runs as low as 5 per cent for carefully loaded coal and as high as 15 per cent for carelessly loaded coal.

Jan 1, 1943

By Thomas Fraser, David R. Mitchell

THE primary purpose of the loading plant is to transfer the finished product from the preparation machines to the railroad car, truck, or barge in which it is to go to market. Secondary purposes of the loading plant are: to prevent excessive degradation of sizes during loading, to reduce segregation as much as possible, and to prevent excessive quantities of very good or off-grade coal from entering any one car. Nonuniformity of consignments is one of the chief sources of com- plaints by consumers and coal merchants. A properly designed loading plant will do much to reduce complaints and ensure uniformity, not only from shipment to shipment but also in each individual consignment along the length of the car and in cross section. DEGRADATION IN STORAGE, LOADING AND SHIPMENT The object in loading is not only to handle the coal without breakage and segregation, but also to produce a well-trimmed load that will ride to its destination without spillage or breakage en route. The small sizes present in a car of prepared coal as received by the purchaser consist of: missed small sizes not screened out in the preparation plant, breakage during loading, and breakage caused by handling en route. For domestic sizes of anthracite shipped from the Pennsylvania anthracite field to Atlantic coast cities, the dealers' loss because of break- age in loading and shipment amounts to from 2 to 5 per cent and for anthracite shipped to Middle West cities, the loss is 8 to 9 per cent. This difference is in part because dealers in the Middle West rescreen their coal more thoroughly than is usual in the East. One dealer handling Illinois No. 6 coal shipped from southern Illinois mines to Chicago reports an average size loss of 10 per cent when lump coal is unloaded with a fork. This runs as low as 5 per cent for carefully loaded coal and as high as 15 per cent for carelessly loaded coal.

Jan 1, 1943

By Roland Hunt

This paper deals with the practical problems as sociated with blasting a heated pillar remnant. This pillar remnant was the final stage in the blasting of a multi-stag e pillar blast. Production from the previous stages had produced burning sulphide ore, resulting in high rock temperatures in the final unblasted stage. This is an account of how, under difficult conditions, the pillar remnant was blasted.

Jan 1, 1977

By Saskia Duyvesteyn

For many applications in hydrometallurgy and water treatment it would be advantageous to use ion-exchange resins in stirred reactors. However, attrition of the resin may lead to significant losses of both resin and metal values and prevent water quality goals from being reached. We have studied the recovery of fine resin particles by froth flotation, using the model copper - Dow XFS4195 chelating resin system. As the functional group on the resin is a bis-picolylamine, the resin should be amenable to flotation by anionic collectors, such as sodium dodecylsulfate and sodium dodecylsulfonate. The kinetics of copper loading from dilute aqueous solutions in an agitated vessel were studied as a function of copper concentration, pH and resin bead size. The flotation of unloaded resin was investigated for different types of collector, collector concentration, conditioning time, and resin bead size. Potential applications are discussed.

Jan 1, 1995

By James J. Wise

INTRODUCTION One basic design feature utilized in all caving and sublevel stoping techniques is the drawpoint. These draw- points may be located on sublevels when using sublevel caving methods, or may be located at the floor pillar when using block caving, sublevel stoping, or vertical crater retreat methods. How the drawpoint is designed and developed, how the ore is withdrawn from it, and how the ore is hauled to the shaft or portal encompasses the loading and hauling function. Historically, predominate loading and hauling equipment for caving and sublevel stoping has been scraper slushes, air powered overshot loaders, and rail mounted train haulage. All of this equipment has two common constraints. 1. The equipment locked into specific work sites and is not easily shifted to another work site. This constraint can often lead to low utilization and low productivity of the equipment. 2. The equipment is designed to work in the horizontal plane, which requires that the various horizontally-oriented working levels be connected by vertical raises. Vertical development by means of raises is not only increasingly expensive, but also is not well adapted to movement of large equipment into the s topes. In the last 20 years, two revolutionary labor saving concepts have become common in caving and sublevel stoping. 1. Long-hole drilling, which has mechanized the development of the drawpoint extraction structures as well as the actual stoping and undercutting. 2. Vertical access by means of trackless ramps between levels, and the consequent use of rubber-tired vehicles not only for loading and hauling ore, but also for the rapid movement of men, material, and equipment into the stopes. The introduction of trackless mining systems for loading and hauling has not been easy. Mine planners have had to re-orient their thinking to the larger operating space required by trackless equipment. Larger access drifts have necessitated reconsideration of mine layouts to insure proper ground support. Spiral ramp developments were often laid out on slopes steeper than the equipment could negotiate economically. Mine operators had to accept the added responsibility of roadway maintenance, water removal, increased ventilation, and more technical mechanical maintenance. As the mine operators enthusiastically embraced the superior productivity of trackless mining systems, they some- times disregarded opportunities to combine the older types of equipment with trackless vehicles to maximize productivity at lowest cost. In order to gain a proper perspective on this problem, it is necessary to review the various techniques of loading and hauling and to become more aware of the advantages or disadvantages that each system or combination contributes. LOADING Loading consists of two functions, (1) primary loading from a drawpoint and (2) secondary loading into long- haul system, a truck, train, or possibly a belt conveyor. Mine planners have four basic loading systems available to fit various operating conditions. These are, (1) gravity, (2) scrapers, (3) rail-mounted loaders, and (4) trackless loaders. Each system can produce optimum results under specific conditions. Gravity Loading Gravity loading is probably the oldest system in general use today.

Jan 1, 1981

By M. M. D. S. Vemba

Paper written on project work carried out in partial fulfilment of B.Sc. Eng (Mining Engineering) degree Engineering refers to the application of mathematics and other sciences to logically develop solutions to problems. However, in opencast mining, due to the randomness of operations, the use of mathematics is often neglected. Instead, practices that have proven successful elsewhere tend to apply. At the other end of the scale, mathematical models have been developed to identify and quantify all the operational parameters involved in the loading and haulage of ore. These are then used to optimize the operation. Optimization in this context, refers to the reduction of cost through effective utilization of the available time and resources. Considering these mathematical models, the loading and transport system at SMC (Catoca Mining Society) will be assessed with a view to its optimization. The discussion will be introduced by considering the mine background and other general information, which will highlight the main operational variables.

Jan 1, 2004

By Emil Szaks

[A great number of papers have been presented at various Engineering Society meetings on the Unit Train subject. Moat are descriptions of facilities that have been constructed or are abort to be built. Many describe the facility as being the World's fastest, newest, largest, incorporating the latest technology and so forth, Many are duplications of installations that have been recently constructed, sort of carbon copies but perhaps arranged differently. The trend has been to incorporate loop tracks, rotary dumpers, indexers and, of course, the snivel coupler equipped unit train. How that the energy crisis has increased the use of coal, there has been a tremendous Increase in applications for permits to construct rail to river coal loading facilities. This paper is different. It does not describe any single existing facility, but is given to alert prospective terminal owners and engineers that there are items that require considerable study and evaluation beside merely selecting an indexer, car dumper, stacker, ship or berg loader and so on. An important item is the selection of the railway car which in turn can affect the selection of the method of loading and unloading. Let us list a few of the items that should be considered and discuss the areas that require examination:]

Jan 1, 1979

By R. K. Mensah-Biney, M. T. Hepworth, K. J. Reid

The loading characteristics of gold-bromide species onto activated carbon were evaluated using a batch system. The overall loading of gold onto activated carbon was rapid for the first few hours, but it continued without cessation as a result of the reduction of gold. Therefore, conventional equilibrium considerations were not applicable. Although loading continued slowly after several days, an abnormally high, loading capacity value of 10-12 meq/g carbon (650-800 kg Au/t) could be attained in 72 hours. The loading of gold-bromo species by activated carbon was by the mass transfer of (AuBr4)- species to the external surface to be reduced to metallic gold by carbon. Elution of gold from loaded carbon was feasible provided the carbon had not been loaded to high capacity values. If loading is carried to high levels, complete elution becomes impractical, and the gold may be recovered by ashing the carbon. For the high loading capacities observed, this option would appear to be cost effective. The effect of several variables on the loading capacity of the activated carbon for gold-bromo species is discussed.

Jan 1, 1994

By R. Mensah-Biney

The loading characteristics of gold-tetrabromide species onto activated carbon have been evaluated using a completely mixed batch reactor system. The overall loading of gold onto carbon was rapid for the first hour but continued slowly without cessation as a result of reduction of gold. Conventional equilibrium considerations were therefore not applicable. Although loading continued slowly after several days, abnormally high loading capacity values of 10-12 meq/g carbon (650-800 kgAu/tonne) could be attained within 72 hours. The loading of gold-bromo species by activated carbon was by the mass transfer of [AuBr4l-onto the carbon surface where reduction to metallic gold took place. Elution of gold from the loaded carbon was feasible provided the carbon had not been loaded to too high capacity values. If loading is carried to high levels, complete elution becomes impractical and the gold may be recovered by ashing the carbon. For the high loading capacities observed, this option would appear to be cost effective. The effect of several variables on the loading capacity of the activated carbon is discussed.

Jan 1, 1992

By Robert Mensah-Biney

The loading characteristics of gold-tetrabromide species onto a weak-base resin, PAZ-4, were evaluated using a completely mixed batch reaction system. The time. to attain equilibrium loading was substantial, on the order of several days. However, abnormally high loading capacity values of 15 to 20 meq Au/g dry resin (1000 to 1300 kgAu/tonne) were attainable in 24 hours. The loading of gold-bromo species by P AZ-4 was visualized as consisting of two processes: (i) the rapid adsorption of [AuBr4r species by simple ion exchange mechanisms and (ii) reduction of [AuBr4r to metallic gold by an electron exchange mechanism. Elution of gold from loaded resin was feasible provided the resin had not been loaded to high capacity values. If loading is carried to high levels, complete elution becomes impractical and the gold may be recovered by ashing the loaded resin. For the high loading capacities observed this option would appear to be cost effective.

Jan 1, 1991