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By J. Dubbert, T. H. Jones

"This paper describes a rib-control methodology that uses standing support to provide most of the lateral resistance to the rib. The method is analyzed, and its boundary conditions for rib control are described. In this method, an animal-fencing mesh product covers 80 percent of the rib surface and is sparsely bolted to the rib. Can supports or other similar stiff supports are installed primarily as roof support for the entry. As the rib spalls and dilates, the mesh catches the material and expands, pressing against the standing support. Mining proceeds, and vertical roof loads increase the normal force on the Can supports, causing friction at the top and bottom of the support to go up, thereby improving lateral resistance to rib swelling.At one mine in the western United States, this method has proved excellent at preventing the buildup of rib spall. It substantially reduces the number of bolts used for screen installation, improves installation efficiency, reduces manual labor and provides more rib coverage than many screening methods. Because standing support is typically part of the roof-control plan in longwall tailgates, no additional standing-support costs are incurred. IntroductionRib safety in underground coal mines is an oft-studied topic because ribs are high-hazard areas. An overview of early rib safety research can be found in Jones and Mohammed (2014). There is a significant difference between rib support and rib control. Support improves safety through the installation of strengthening elements, such as bolts and dowels, designed to reduce rib spalling. Although spall reduction is preferred, controlling how the rib fails is enough to ensure safety in some situations. Rib control uses external elements to provide confinement, thereby holding sloughed material in place, or to prevent falling rib material from striking mine personnel. This paper presents a study of a control method used on the pillar side of a longwall coal mine tailgate in the western United States."

Jan 1, 2015

By Stefan Zanon, Ty Faechner, Clayton V. Deutsch

Secondary data are important in geostatistical simulation of continuous variables. Geophysical data and geological trends are used for modeling porosity and permeability. Multiple mineral grades must often be modeled for mining applications. Sequential Gaussian simulation (SGS) is often used because of its relative simplicity and robustness. The two most common approaches to integrate secondary data in Gaussian simulation are with (1) locally varying mean, or (2) collocated cokriging. A significant problem with both of these techniques is variance inflation, that is, the variance of the resulting simulated values is too high because of an inappropriate decision of stationarity or an artifact of choosing a single secondary data in presence of many. We introduce a self-healing procedure for dynamic correction of this problem. The dynamic correction is different for the locally varying mean approach and for collocated cokriging since there are different reasons why each of these methods causes variance inflation. The reasons for variance inflation are discussed and the self-healing is applied to a number of data sets.

Jan 1, 2002

By F. W. Schweitzer

The trend toward development of large low grade ore bodies has accelerated in recent years. It has been estimated within the copper industry that "porphyry" type deposits will provide the bulk of copper production during the next 30 years. It is further estimated that in these deposits the average ore grade by the year 2000 will be 0.25% copper (1). Many of the new porphyry copper discoveries are of such extremely low grade that they are particularly sensitive to small fluctuations in cost variables and copper prices. Because haulage constitutes a major item of surface mining expense, the capability to transport large tonnages of material at increasingly lower unit costs is vital to the profitable operation of many of these mines. High capacity conveyor belts appear to have considerable promise in this area. The heaviest use of high tonnage conveyors has been in the brown coal industry in Germany. In the past 20 years several such installations have proven successful. In addition to the German installations, several other successful systems have been put into operation. Some examples are: The Oroville Dam project in the United States; the tar sand operation in Northwest Canada; the pre-mine stripping and mining of the Twin Buttes Mine in the United States; the Kursk Magnetite 'dine in the U.S.S.R.; and the Nchanga Copper Mine in Zambia. Most of the systems mentioned are handling alluvial material consisting mainly of fines. The noteworthy point regarding these installations is their high continuous capacity. One of the largest lignite mines in the world is at Fortuna, Germany, where over 15,700 tons (15,250mt) per hour of overburden is transported on an 87 inch (221cm) wide belt running, at over 1000 feet (305m) per minute.(2). Another example is a 20,000 ton (18,150mt) per hour system for loading iron ore into barges on the Great Lakes (3).

Jan 1, 1976

By Gary Krix

The Amdel Thickener Interface Gauge (TIG) provides continuous on-line measurement of the level of the liquid/solid interface in thickeners and Counter Current Decantation (CCD) washers. Unlike other interface level measurement systems, the TIG also determines the span of the transition zone. The transition zone is the region between the clear liquid overflow zone and the compressed solids zone. The Thickener Interface Gauge determines the level of the interface by measuring the natural radioactivity of the solids in the thickener tank using an array of up to twelve detectors mounted vertically in a stainless steel probe. All solids contain low levels of natural radioactivity while the liquid phase generally does not. The concentration of natural radioactivity at each level in the thickener therefore depends on the concentration of solids. The radiation emitted by the solids is converted to electrical pulses by the detectors in the probe and the pulse-rate provides an accurate measurement of the density. A typical count-rate profile is presented in Figure 1. The vertical axis indicates the depth in the tank referenced to the surface of the liquid. The horizontal axis indicates the count-rate measured by the TIG probe, this count-rate is proportional to the density and can be used to determine the settling rate. The count-rate at the top of the graph is relatively low, this region corresponds to the clear overflow zone which contains virtually no solids. Moving down the vertical axis the count-rate increases dramatically at the level of the transition zone where the solids content increases with the depth in the tank. In this region the settling conditions of the solid particles change from free settling to compression. Moving further down the vertical axis the count-rate reaches a plateau where the count-rate remains relatively constant although there are often small fluctuations, this region corresponds to the solids compression zone. The liquid/solid interface as measured by the TIG corresponds to the depth at which the count-rate crosses the target count-rate which is generally selected to be midway between the liquid count-rate and the compressed solids count-rate. The length of the TIG probe is selected to cover the typical operating range of the liquid/solid interface in the thickener or washer. If, for example, the minimum bed level is 3.0 metres below the surface of the liquid then the probe length is selected to extend 30 metres below the surface. The TIG probe can include up to twelve detectors and the se are spaced over the measurement range. For small measurement ranges of around one metre 4 to 6 detectors would normally be used while for larger measurement ranges of three metres or more twelve detectors would be supplied.

Jan 1, 1993

By Walter Hoecker

The dissolution of gold in cyanide_ leaching has been we11 published with the genera1 acceptance that gold is oxidised by oxygen and stabilized by complexation with cyanide [1]. The dissolution of gold is essentially an electrochemical process. The rate of the anodic gold dissolution is controlled by the cyanide concentration. - (2) While the cathode reduction of oxygen is controlled by dissolved oxygen concentration - (3) There are a number of factors influencing the concentration of oxygen, and if 1owered substanth.lly will effect the efficiency of the leaching plant. These include: "' salinity "' temperature "'partial pressure "'oxygen consumption rate The use of pure oxygen for· cyanidation is only beneficial if oxygen is rate limiting, Conversely a slurry saturated with air (typically 5 - 8 ppm) may not be enough for maximum leach rate. The diagram below shows the maximum dissolved oxygen levels obtainable with pure oxygen and air. DISSOLVED OXYGEN (MAXIMUM) IN WATER At steady state, the rate of the cathodic reaction must equal the rate of the anodic reaction. Thus the rate of gold dissolution is dependent on both the· cyanide and oxygen concentrations. - (4) Using an average of Do/Den =· 1.5 [2] (where Do and Den are the oxygen and cyanide diffusion coefficients) the table below illustrates the maximum effective oxygen concentrations for given cyanide levels in clean water [3].

Jan 1, 1992

By Joseph Matoney, B. K. Parekh

INTRODUCTION The term "dewatering" refers to removal of water from coal. Water associated with coal can be categorized as "free or surface" and "inherent or chemically bound" moisture.' The free moisture is found on the surface of coal, in capillaries and small spaces between two or more particles. The inherent or chemically bound water is found in the interior of the coal and as part of coal structure. A significant amount of free moisture can be removed by mechanical dewatering techniques. However, inherent moisture can only be removed by applying energy intensive techniques, e.g., direct or indirect heating. Moisture in the coal offsets some of the benefits of coal cleaning. Extra water in clean coal adds to extra cost in transportation, heat lost during vaporization, and plugging of chutes. From a utility perspective, a 1 % increase in moisture can offset a 4.5% decrease in ash.2 Mechanical dewatering can be classified into two major process categories according to the principles involved, namely, 1. Sedimentation-liquid is constrained and particles move freely. 2. Filtration-particles are constrained by a medium and the liquid flows through. Each of the process categories is composed of various separation techniques shown in Fig. Equipment currently being used by the mechanical dewatering of coal of varying size ranges and final moisture content is illustrated in Fig. 8-2. This figure indicates that sizes larger than 13/, in. (37.5 mm) present no particular dewatering problem. Shaker screens of the very crudest types and designs are capable of producing these sizes at low surface moistures. High-speed vibrators are used for the intermediate sizes and can be used for smaller sizes down to 0.02 in. (0.5 mm) if high moistures (15% surface moisture or greater) can be tolerated in the product. Usually, however, the vibrator is not used below 3/, to 3/, in. (9.5 to 6.3 mm) because of the moisture associated with these fine sizes. At this level, centrifugal force is usually employed to aid dewatering. Centrifuges of various types and designs are used practically

Jan 1, 1991

By Hans W. Brodbeck

The Advisory Conference on Tunnelling of the OECD, held in Washington, D.C. in June 1970, has established the following definition: "Tunnelling refers to the construction by any method of a covered cavity of predesigned geometry whose final location and use are under the surface, whose cross-sectional area is greater than 2 square metres". (1) The definition makes clear that the term includes all types of underground construction, be it in hard rock, soft ground, under mixed conditions, underwater, etc. Small-sized tunnels in rock therefore constitute but one part of the tunnelling scene. With an ever-growing urbanisation taking place in industrialized as well as developing countries, the demand for small-sized tunnels is, however, rapidly increasing and requires a far-reaching mechanization of excavation and support functions. This trend is accentuated by the fact that small-sized tunnels are far more labor-intensive than large ones, and, with wages raising at a much faster rate than costs for plant and equipment, this will accelerate the introduction of new tunnelling systems. SMALL-SIZED ROCK TUNNELS The main field of application for a tunnelling system for small sized hardrock bores is thus defined. It is in fact the numerous relatively short tunnels required under cities and other populated

Jan 1, 1974

By K. C. Kane, D. L. Meredith, B. E. Davis, D. A. Stanley, O&apos

Computer control of the minerals beneficiation process is limited by a lack of adequate sensors to provide information on the current state of the process. Recent reduction in the cost of image acquisition and powerful inexpensive computers make use of computer vision as sensory input in process control a possibility. In the phosphate industry, the amount of apatite in phosphate tailings is estimated by inspection. For machine vision, a simple 256 x 512 color image of the tailings was captured via an inexpensive color video camera on an IBM PC. Initially, the image is converted to gray scale and displayed on an EGA color monitor. A program was written which identifies the different constituents of the sample by analyzing the gray scale levels for the digitized picture. In other instances the minerals are identified by their relative color intensities. The amount of each constituent is determined with good accuracy from the area it occupies on the image.

Jan 1, 1990

By Enrique Hermana, Raymond F. Dalton, Raymond Price, Barry Hoffman

Introduction Chloride leaching of sulfidic ores has been known about for 100 years. It is recognized as a highly efficient process to produce concentrated leach solutions. Despite this, chloride leaching found little practical application until recently because of the highly corrosive nature of concentrated chloride solutions. This situation changed with the advent of modern construction materials such as GRP, polypropylene, butyl rubber, etc. And in the past 20 years, research has burgeoned in the area of chloride hydrometallurgy. The research impetus stemmed from the belief that chloride leaching can provide an alternative to smelters for treating conventional copper concentrates. In addition, chloride leaching was thought to be suitable for on-site refining of copper at small tonnage operations located in remote areas. And chloride leaching was seen as a logical choice for treating unusual or complex concentrates that smelters could not handle. Underpinning these beliefs is the attraction of chloride-based hydrometallurgical processes for sulfidic ores. Sulfur is liberated in the environmentally acceptable elemental form rather than as sulfur dioxide. Consequently, sulfidic copper ores have received much attention. A review of Edmiston in 1984 describes 12 chloride-based processes. All managed to progress past the "laboratory beaker" stage of evaluation. In nine of these processes, copper is recovered electrolytically. Key features of these processes are summarized in Table 1. Table 1 shows that the processes must include a copper solvent-extraction step. Only these processes produce a clean copper electrolyte capable, with no further refining, of directly producing high quality cathode copper. The ICI/Elkem process is the exception here. The rest of these processes use o-hydroxyaryloxime reagents for the solvent extraction of copper and are constrained by the performance of these reagents. This is governed by hydrogen ion concentration (Equation 1). The practical result is that only relatively dilute copper solutions can be treated (Canmet, Phelps Dodge), or careful pH control or adjustment is necessary (Minimet Recherche, B.H.A.S.). This negates one of the attractive features of chloride leaching - its ability to produce very concentrated copper solutions, up to 40-45 gl-1. [ ] In all four processes using o¬hydroxyaryloxime extractants, solvent extraction transfers the copper from the chloride to the sulfate medium. To minimize cross-contamination of the two anions, the loaded organic solvent has to be scrubbed to remove the chloride ion. This represents an additional complication in the solvent extraction circuit. And it

Jan 1, 1988

By Richard L. Ash

Less than optimum production in mining always results when poorly blasted material is provided at loading points. More often than not the cause is due to blasting founds that fail to fully control and utilize explosive energy. In many cases the problem exists because too few blasters understand how blastholes actually break rock and recognize that blasting is a three-dimensional process in designing their blasts. To better understand how blasts can be more effectively designed the two major rock breakage processes are described. In addition, the respective contributions of the borehole and detonation pressures are defined as are the specific roles of the several important blasting design variables. The concept of stiffness as an engineering principle and its significance in blasting design is introduced for explaining the breakup of rock. Basic guidelines for affecting control over fragmentation and side effects like over-break are offered.

Jan 1, 1975

By Christopher J. Bise

INTRODUCTION Perhaps no other area reflects the art as well as the science of mining-engineering design quite as obviously as strata control. This is due to the fact that the design of mining structures is difficult because rock rarely behaves as a homogeneous medium. Further, the original state of stress and the mechanical proper- ties of the in situ rock are somewhat difficult to deter- mine. However, those aspects that are hard to treat mathematically can and have been successfully approached by model studies and in situ measurements. This chapter will review the fundamentals of strata- control design and will provide examples of applications to typical problems. STRESSES AROUND MINE OPENINGS A close examination of Fig. 1 reveals that, prior to mining, stresses exerted in the overburden can be in both the horizontal and vertical directions. In the example problems of Chapter 1, it was shown that the maximum compressive stress (uv) at any depth (D) below the surface can be approximated as follows: [ ] Further, the lateral stress (oh) is related to the maxi- mum compressive stress by utilizing Poisson's ratio (µ): [ ] As soon as a heading is driven, such as the one in the coal seam shown in Fig. 2, the stresses shift to the sides, or abutments, of the opening. Clearly, these compressive stresses around the opening exceed the pre-mining conditions. The problem of designing an underground opening, therefore, is to determine the maximum stresses and to note if they exceed the ultimate strength of the rock. Table 1 lists several rocks with their corresponding strengths. Figs. 3 to 5 depict the boundary stress concentrations around circular, ovaloidal, and rectangular openings. M is the ratio of the horizontal stress to the vertical stress, or as defined above, p/(l-p). This text will concentrate on the state of stress represented by M = 0.33, which corresponds to the condition of no lateral deformation in a rock having a Poisson's ratio of 0.25. For an ovaloid with an opening width-to-height ratio of 2.0 (Fig. 4), the boundary stress concentrations are at their maximum values at the comers of the opening, with values in excess of 3.0. If the depth of overburden is 500 ft, then the maximum boundary tangential stress ([ ] ) of the ovaloid is: [ ]

Jan 1, 1986

By J. C. Hower

The Hardgrove grindability index (HGI) is a widely used coal-quality parameter with applications in coal mining, beneficiation, and utilization. An understanding of the petrology of the coal is fundamental to understanding the validity of the HGI in the given application. The HGI varies with coal rank, increasing (greater ease of grinding) with increasing rank through the high-volatile bituminous rank range; and the HGI varies with changes in the maceral and microlithotype composition, decreasing with an increase in liptinite and liptinite-rich microlithotypes. In this review, the .fundamental relationship between HGI and coal petrology, and consequently its relationship to coal utilization, is examined.

Jan 1, 1999

By Hassan El-Shall, G. L. Zucker, T. S. Jordan

INTRODUCTION This chapter will discuss, both from fundamental and practical points of view, the flotation of non-sulfide min- eral s. The flotation characteristics of silicates, salt-type minerals, oxides and coal will be reviewed. Dup- lication of the thorough and excellent presentations by many authors is not intended and a comprehensive list of references is included. GENERAL PRINCIPLES Collectors for Non-Sulfide Minerals : All minerals, with only a few exceptions are readily wetted by water, that is, they are said to be hydrophilic. The purpose of a collector is to coat the mineral surface and render it hydrophobic, preferring an environment of air over an environment of water. Relative to sulphide minerals, the non- sulfides are more naturally hydrophilic and therefore, require a collector with a greater chain length. This is accomplished by using a collector which has a proportionally longer hydrocarbon chain. Both anionic and cationic flotation collectors are used in non- sulfide flotation. Anionic Collectors. These are collectors which ionize in solution to give a negatively charged radical. They have the general structure R-A, where R is a hydrocarbon having 8 or more carbon atoms and A is a hydrogen or an alkali metal. The most common collectors in this group are fatty acids which could have saturated or unsaturated hydrocarbon chains. Such chains may be straight or branched. The configuration of the chains affects their solubility in water and their adsorption characteristics. In general, as the chain length increases the adsorption and the collecting power increases. However, it should be noted that the solubility decreases. The solubility of unsaturated chains is greater than that of saturated fatty acids because double or triple bonds are polar and thus attract water molecules. Solubility data for collector metal salts, even though important for a proper understanding of flotation are not available for all collector systems. Solubilities and structures of different fatty acids are reported by Fuerstenau (1982). Values for the solubility products of fatty acid salts selected from a paper by Du Rietz (1958) are given in Table 1.

Jan 1, 1986

One of the major objectives of cost analysis is to enable the manager to predict the financial outcomes of decisions. To accomplish this, the future costs and benefits of alternative courses of action must be determined. If care- fully used, information about past financial performance can be helpful in this analysis despite the fact that, by definition, financial reporting information is historical. In many cases, both revenues and costs need to be estimated for decision- making. For the production manager, additional revenue is a result of increased throughput or recovery of valuable material from the stream of mined material. A reduction in operating cost, although similar to a revenue increase in its financial impact, is estimated using slightly different techniques. Generally, the estimation of cost is more difficult than the estimation of revenue. Most cost estimates have two components: an estimate of fixed costs and an estimate of variable costs. As discussed in chapter 5, the total cost of an activity during a specified period can be expressed as: Total cost = (Variable cost per unit of activity) x (Units of activity) + Fixed cost or TC = VX+F

Jan 1, 1999

By R. Edward Williams

The Spa1lation Process Because of the low thermal conductivity of many hard rocks, rapid heating of these rocks produces a thin surface layer in which the temperatures attain high values. Thermal expansion of this surface layer is constrained by the reminder of the still cool rock, and when stresses within the surface rock become high enough, the surface rock breaks away from the cooler rock behind it and flies or falls off as a thin flake called a spall. Then the next, newly exposed surface is heated, and the process continues. This process is the basis of spallation drilling. The hot gases from a jet burner provide the heat for spallation to occur, and their high velocity provides a scouring action that transfers heat to the rock and removes the spalls as rapidly as they form. Spallation is a process which works in very hard rock. It is dependent upon the thermal expansion coefficient and the thermal diffusivity of the rock but is also affected by any discontinuities in the rock. To date the efforts which have been made to evaluate the various rock according to their spallability has been minimal. As the success of this process is dependent upon the characteristics of rock it is expected that the study of rock mechanics will prove to be of greater value to this program than to the other mechanism for drilling and excavating rock. Commercial Uses of SPALLATION In the 19408s, the Linde Air Products Division of Union Carbide (UC 1 began developing spallation for use in mining taconite ore, which is presently the chief source of iron in the United States. In this work UC developed a jet-piercing tool that burned fuel oil with oxygen to produce spallation and contained mechanical cutters to remove rock that was not amenable to spallation. The UC jet-piercing machines have since produced about 40 million feet of shallow blast holes used for emplacing explosives in the taconite mines. During this work it was found that hole diameters could be increased by merely reducing the advance rate of the burners and that existing holes could be enlarged by making another pass through the hole with the same burner. The Browning Engineering Go. of Hanover, N.H., has developed a hand-held spallation burner to cut slots in granite. It has been used for a quarter of a century and is now standard equipment for quarrying granite throughout the world. This burner, which resembles a small jet engine oriented with its exhaust pointed downward, is the forerunner of a flame jet burner used to spall experimental holes in granite at maximum rates in excess of 100 ft/hr when operating in hard, competent granite. It uses No. 2 fuel oil, which is burned with compressed air. The system uses water to cool the burner and the exhaust gases. These gases, along with the steam produced from the cooling water, blow the spalls from the hole. Experimental Work Theoretical and experimental work has been accomplished by the Massachusetts Institute of Technology and the Los Alamos National Laboratory. This work is reported in Refs. (3) and (4). To verify the experimental results of this work laboratory scaled down field tests were conducted using two we1 1 characterized granites from quarries in Barre, VT and Westerby, RI, under defined heating conditions. In the laboratory tests a propane - oxygen heating torch was used to direct a flame at the granite surface and the spal 1 ing process was examined at various heating rates with a high-speed video taping system operated at 200 frame per second. This produced a time-lapse sequence where the onset of the spallation process was easily distinguished. Also the heat flux from the torch to a flat surface at various stand off distances and flows was measured. A similar set of tests was conducted using the more easily quantified and uniform heat source of a 1.5 kw GO2 laser. This allowed accurate

Jan 1, 1986

By C. D. Anderson

A variety of processing technologies exist for recovery from both primary and secondary sources of rhenium. Currently, there are no known primary rhenium deposits; thus, the method in which primary rhenium is produced is dependent on the commodity of which it is a byproduct, e.g., copper, molybdenum, uranium, etc. In addition, focus on the recovery of rhenium from secondary sources, such as alloy scraps and catalysts, is continually growing. This paper presents a review of both primary and secondary processing technologies for the recovery of rhenium.

By Yi Luo

Bolting the mine roof is one of the noisiest underground mining operations. The main contribution to the high noise is the drilling of the roof bolt holes, especially in hard rock. A previous research shows that the specific energy consumed in drilling the bolt holes is inversely proportional to the bite depth (i.e., penetration per drill revolution). Less specific energy at a reasonably high bite depth means less energy is wasted in the drilling process to produce heat, bit wear and noise. Therefore, control of drilling operation to achieve a higher bite depth can provide an opportunity to reduce drilling noise from its sources as a proactive noise control approach. In order to explore the feasibility and to develop the proactive technology for reducing drilling noise, drilling tests have been conducted in laboratory settings. The preliminary results show significant reduction in noise dose can be achieved by drilling in medium hard rock at a reasonably high bite depth. This paper presents the findings from the laboratory experimental studies conducted so far.

Jan 1, 2013

By G. Abramov

The 20th Century saw the modern mining industry enriched by one outstanding method of extracting of mineral resources called Borehole Mining (BHM). Mean while, despite its successful track record in wide ranging locales, few specialists are yet aware of this technology. The intent of this article is to introduce borehole mining to a wider spectrum of drilling and mining professionals. The BHM method is based on in-situ water jet cutting of rock mass. On Fig. 1 the schematic of the method is presented. The borehole mining tool 1 is lowered into the borehole 2 and high pressure water 3 is pumped down. At the bottom part of the tool, one portion of that water comes out through the hydromonitor nozzle 4 in a shape of water jet 5 and cuts the material 6 creating slurry 7. The other portion of high pressure water then comes to the hydroelevator 8 (jet pump, eductor) which produces a vacuum. When the slurry reaches this vacuum zone, the eductor sucks the slurry and pumps it up to the surface, where rock parts are separated from water in a tank 9 or a pond and clarified water is pumped down again closing the re-circulating BHM water supply system. The borehole mining tool is suspended on a drill rig tower 10 which allows the tool to rotate and move vertically along the borehole axis. While extracting rock mass, underground caverns (stopes) 11 are created. If necessary, compressed air 12 can be injected to the raising slurry flow to create an airlift effect. Also, a secondary agent 13 (such as oil, foam, etc.) can be added to the stope through the gap between the tool and the casing. As seen from the illustration, BHM is the remote mining method of extracting of mineral resources through boreholes by high pressure water jets.

Jan 1, 2001

By M. C. Williams, T. P. Meloy

For over thirty years the Population Balance Model, PBM, has been the mainstream modeling method for comminution unit operations and comminution circuits. For commercial comminution circuits the method is based on erroneous physics and dubious numerical mathematical methods leading to non unique solutions that have little extrapolative value and faulty control strategies. In short the PBM is wrong. Given is a detailed analysis showing a number of non trivial flaws in the linear PBM. Moreover, a simpler model is presented that leads to a solution of the comminution circuit predicting the size distribution output over a variety of conditions. Because the linear PBM is firmly entrenched, an award is offered, $10,000, to any researcher that can use the linear PBM and its present numerical methods to predict the typical straight line, self similar, output of wet mills over a variety of grinding times.

Jan 1, 1992

By Ruiren Jin

In alkaline pulp, galena is depressed by sodium carboxymethyl cellulose (NaCMC), while Cu(II)-activated sphalerite exhibits a high flotability so that satisfied separation can be achieved. In addition to hydrogen bonding, chemical bonding of NaCMC with galena is confirmed by IR; only hydrogen bonding is involved between NaCMC and Cu(II)-activated sphalerite. It is also found that the greater the degree of substitute and polymerization of NaCMC, the stronger the depressive effect of NaCMC and that lower stirring speed favors the depression.

Jan 1, 1987