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By A. Kalmes, B. Dehler, D. Kopp

Nutrien has six potash mines in Saskatchewan and has been proactive in maintaining the integrity of their tailings facilities through ongoing assessment, design, operation, inspection, and monitoring. Nutrien commissioned a system inventory and semi-quantitative risk analysis (SQRA) of all dikes to further environmental stewardship at their potash facilities. The inventory assessed nearly 100 dikes; each dike was rated according to a probability and consequence factor and assigned a risk score. The risk scores were used to develop a risk matrix for each of the six sites and risk-response actions for each dike and segment. The inventories and SQRAs will help each site assess priorities for investigation and risk mitigation, if necessary. The study results will also help Nutrien refine corporate wide tailings governance standards and demonstrate compliance with various governance regulatory obligations.

Mar 2, 2022

By J. Zhai, Z. Yin

"The electrokinetic and flotation behaviors of ilmenite using lead ions as the activator and sodium oleate as the collector were studied. The results of microflotation show that the flotability of ilmenite can be improved by lead ions obviously. The isoelectric point of ilmenite increases from 5.32 to 7.7 after the addition of lead ions because of the adsorption of Pb2+ and Pb(OH)+. The results of zeta potential measurements and the collector adsorption density calculation show that the adsorption of sodium oleate on the ilmenite surface via chemisorptions in addition to electrostatic interactions. Besides, the adsorption density calculation results show that as the addition of lead ions as the activator, the adsorption amounts of collector are greater than those without activation which is in aggrement with the flotation behaviors. INTRODUCTION Ilmenite, as an oxide mineral of formula FeTiO3, is usually used as the main resource of the extraction of titanium (Bulatovic and Wyslouzil, 1999). There are many researches showing that the conventional methods, such as gravity separation, magnetic separation and flotation, do not work efficiently as expected (Mehdilo et al., 2015; Zhu et al., 2011). Nowadays, to produce ilmenite concentration feasibly and efficiently, these separation methods above are combined for a reason that the raw ilmenite ores are characteristic of poor, fine and complicated. Moreover, surface modification, such as surface dissolution method, microwave irradiation and oxidation roasting, is applied to improve the flotability of ilmenite currently (Welham and Llewellyn, 1998; Zhang and Ostrovski, 2002). Generally, fatty acid salts are used as the collector for the flotation of oxide minerals and sodium oleate is usually used as the collector for the flotation of imenite ores (Fuerstenau and Pradip, 2005). The mechanism, such as individual ion electrostatic adsorption, chemical adsorption, ion–molecule dimeric complex adsorption, and the coadsorption of ion and molecule, have not been discussed systematically using sodium oleate as the collector in the flotation of ilmenite (Somasundaran, 1983). Under the activation circumstance using the lead ion as the activator and sodium oleate as the collector, the interaction mechanism seems to be still unclear. In the present study, the interaction mechanism between ilmenite and sodium oleate using lead ion as the activator are studied by microflotation, zeta potential measurements and adsorption density calculation. EXPERIMENTAL Materials and reagents Pure ilmenite minerals were obtained from Panzhihua, Sichuan province, China. The minerals were ground in a porcelain mill with an agate ball. Following that, the prosucts were sieved, and the samples of -0.074+0.038 mm size fraction were used for the microflotation experiments. The results of XRF show that the content of titanium element is 30.58%, showing that the purity of ilmenite is above 90%. On the basis of the results of XRF, it is determined that the purity of ilmenite is very high and meets the needs of microflotation"

Jan 1, 2017

By Meng Wang

"In this study, multiple methods that include geological surveying, laboratory studies, and numerical modeling have been used to study the deformation characteristics of a “deep inclined rock roadway with weak planes” (DIRRWP). Failure of the DIRRWP was found to be triggered initially by the shearing of the rock near the weak plane. The movement of the failed rock resulted in reduced confinement of the deeper rocks, and causing the failure of the supporting units and the severe deformation of the surrounding rocks. Hence, it is concluded that DIRRWP stability is affected predominantly by rocks near the weak plane. Corresponding control strategies for DIRRWP deformation were proposed: (1) greater support intensity is necessary to maintain the stability of the whole DIRRWP; (2) additional support is needed for rocks near the weak plane to reduce the potential of failure; (3) to increase the bearing capacity of the floor strata, as the floor needs to be supported; and (4) a supplementary support technique should be considered for cases of large deformation. The case study presented here indicates that the proposed control strategies can significantly reduce the potential of failure in rocks near the weak plane, thus preventing severe deformation of the DIRRWP.INTRODUCTIONAs shallow seams are mined out, the cover depths in most Chinese coalmines have become increasingly greater. Deep cover in a coalmine is considered to occur when the cover depth exceeds 800 m (Sun, Chen, and Miao, 2018). The loading and failure behavior of rocks in a deep cover setting are quite different from those in a shallow cover setting owing to the increase in in-situ stress, temperature, and hyperosmosis (Lobanova, 2008; Zhang et al., 2013). For instance, experience shows that bulking and dilating deformation in deep roadways is much greater than that which occurs in shallow roadways (Hou and Yang, 2018; Zhang et al., 2016). In addition, anisotropic behavior and thickness deviation of coal measure rocks, combined with the appearance of weak planes (e.g., faults, joints, and coal cleats) in coal and/or rocks, can significantly affect the stability of an underground roadway (Ghazvinian et al., 2013; Sun, Chen, and Miao, 2018). The presence of weak planes can significantly complicate displacement and stress transmission in nearby rocks. Additionally, tensile, compressive, and/or shearing failure in rocks near weak planes can be easily caused by high in-situ stresses in deep roadways; such failures may lead to further severe deformation of the surrounding rocks, resulting in roof falls and rib spalling (Kamata and Mashimo 2001; Wu, Ohnishi, and Nishiyama, 2004). A typical failure of the so-called “deep inclined rock roadway with weak planes” (DIRRWP) is shown in Figure 1. Severe deformation can be found near the weak plane. In this study, a plane or thin layer of rock/coal parting that can significantly reduce the strength of the surrounding rocks—and thus affect roadway stability—is defined as the weak plane."

Jan 1, 2019

By R. J. Morlock

Prior to 1912, coal research for Republic Steel, Corporation was limited to a periodic box test conducted in a commercial coke oven. Then in 1912, a Koppers movable-wall test oven was -built to research wall pressures for selected blends and to conduct other varied research work. In the 1950's economic pressures caused a reassessment of position resulting in the establishment of a Coal and Coal Chemical research group in 1956. In 1958 this group, along with other groups of research endeavor were incorporated into the new Republic Steel Corporation Research Center at Independence¬ Ohio. Currently this section is divided into four groups. 1) Coal Preparation, 2) Coal-Chemicals, 3) Coal Characterization, and 4) Coal Carbonization. The objective of each group is described, and a brief listing of the work done under the first three groups is indicated. A more detailed description of the studies by the Coal Carbonization group of the coking characteristics of Republic Steel Corporation's coals as blended among themselves or in conjunction with selected purchased coals follows. The wall pressure, contraction, and stability index criteria are specified, and the method of assessing these criteria as a function of blend composition is indicated.

Jan 1, 1963

By J. Hilgers

Metal prices are often predicted by relying on time trend projections of various economic indicators or even the trend in price itself Thus, time is the underlying explanatory variable acting through at best, a limited selection of economic variables. The price prediction method described in this paper differs from this by analyzing hundreds of economic variables to develop a few principle components that automatically capture the fundamental changes in the economy and delete duplicate or irrelevant information. This leaves a few principle variables to describe a state-space representation of the economy which can then be used for prediction. Forecasts of the price of a metal are then made based on these principle variables.

Jan 1, 1995

By Richard C. Corson

The objective of blending materials in a bedding pile is to reduce the variation in successive samples taken from the materials to be blended. In designing a bedding and reclaiming operation, several mechanisms are available to effect the reduction of variability, or increase in homogeneity, of the materials. These mechanisms can act before stacking, in the stacking process, in reclaiming and after reclaiming. In evaluating alternative methods of stacking and reclaiming, the potential user must judge each method on the basis of certain criteria; the capital cost of the equipment, the allowable absolute variability of the reclaimed product and the effectiveness of blending. Several stacking and reclaiming methods have been tested using a computer simulation. Based on the results of this program, factors were developed to describe the effectiveness of blending for chevron stacking of discrete materials and preblended materials, bucket wheel reclaiming and drum reclaiming. From these factors, the total effectiveness of a combined stacking and reclaiming system can be determined.

Jan 1, 1985

By W. Todd

The Robbins Company has developed a boring machine, with a rubber packer serving as the gripper system, for blind boring of raises without using drill pipe. This machine is the BorPak and has many applications for use in the mining industry which will improve productivity. In addition to the cost savings, the boring method will lead to increased safety in constructing blind raises. The advantages of using the BorPak in a mining environment will be discussed together with possible applications.

Jan 1, 1994

By G. E. McClelland

Agglomeration techniques have been successfully applied to commerical heap leach cyanidation operations for the recovery of precious metals from low-grade ores, mine wastes, and tailings. The major parameters important for successful agglomeration pretreatment of these feed materials are discussed. Several commercial agglomeration-heap leaching operations are described. Two of the operations converted from conventional heap leaching to agglomeration-heap leaching after coventional heap leaching proved unsuccessful. Heap performance before and after agglomeration is discussed. A fairly recent operation that began production using agglomeration-heap leaching technology is also described. Two operations that processed milled tailings by agglomeration are discussed. The tailings feeds could not have been economically processed by means other than agglomeration-heap leaching.

Jan 1, 1986

By J. E. Oberholtzer, M. G. Fernald

INTRODUCTION Approximately six years ago the U.S. Bureau of Mines (USBM) developed a data acquisition system (DAS) specifically designed for measuring radon levels and other environmental parameters during studies of means to control radiation hazards in underground uranium mines. The DAS system records data in machine readable form using a paper tape punch, which represented the state-of-the-art at that time for a moderate cost output device. However, the use of paper tape as a recording medium for field studies is somewhat unwieldy. Reducing the raw data required either that the tape be shipped to a computer center equipped with a high-speed paper tape reader or that the tape be transmitted at low speed over the telephone lines to a remote computer. Transmitting, at ten characters per second, the data from a 10-channel DAS taking Four readings per hour would require about 30 minutes For each 24-hour day's data. Telephone lines from remote mine sites are often of marginal quality and data errors can be introduced during transmission. Paper tape punches are also prone to occasional punching errors. Both problems make it necessary to carefully check for and correct data errors, a process which is possible because each DAS produces an independent printed data record, but the error checking and correction process can be quite laborious. Aware of recent advances in microcomputer technology which have brought the price of a personal computer down to about the cost of a paper tape punch 5-10 years ago, the Bureau decided to explore the feasibility of using a low-cost personal computer in the field to process DAS data in real time. On behalf of the Bureau, Arthur D. Little, Inc., developed a simple interface circuit which permits an Apple II computer to accept data from one or two DAS units as it is being transmitted to the paper tape punches. Computer software converts each measurement to appropriate engineering units, e.g., radon concentration, Working Levels, air velocity, temperature, or barometric pressure. The computer also calculates 1-hour and 8-hour running averages of all converted data and prints those results as soon as they are obtained on a line printer located at the test site for immediate inspection. After development, the system was used continuously and successfully for a 5-month period at a Utah uranium mine. DAS DESIGN AND MODIFICATION Each of the two USBM data acquisition systems used in this work consists of two separate modules. A multiplexer module located below ground near the measurement transducers acquires signals from each of nine tranducers. Six input channels were devoted to measurements of radon or Working Level. The outputs of those transducers, photomultiplier tubes or G-M tubes, respectively, are digital pulse trains which are accepted directly by the mutliplexer. Three channels were used for environmental parameters--air velocity, temperature, and/or barometric pressure. Each of the environmental tranducers is fitted with dedicated linearizing and voltage-to-frequency conversion circuitry so that the outputs to the multiplexer are also pulse trains having frequencies of one tenth of the value of the measured parameter expressed in the appropriate engineering units. A 100-Hz reference signal was input into the tenth channel for use in monitoring system integrity and performance. All ten pulse trains are then timeseries multiplexed into a signal line for transmission to the above-ground data acquisition module. Above ground, the composite signal is de-multiplexed into ten separate lines, each of which is connected to a digital counter which converts the pulse train to a numerical value. The acquisition of each set of readings is initiated by an adjustable "scan cycle comparator" timer. The acquisition process proceeds in three phases. First, radon and Working Level channels are counted for an extended period of time, typically 5-10 minutes depending on activity, because of the low pulse rates involved. Then the other four channels are counted for ten seconds, and finally, all ten readings, along with the Julian day and time of day are output serially onto paper tape and printed on a strip printer. When the scan cycle comparator reaches its preset time (15-minute cycle times were used in this work), it resets itself, initiates another readout cycle, and begins timing again. The only modification made to the data acquisition systems used in this work was to disconnect the scan cycle comparator in one unit, which became the "slave" and bring in the scan cycle comparator signal from the other unit, the "master", to initiate data acquisition cycles in the slave. Synchronizing the two data acquisitions in this fashion and using two slightly different radon counting times insured that the two systems never attempted to output data to the Apple II at the same time. THE APPLE II COMPUTER The Apple II computer used in this work was equipped with 48 KBytes of semiconductor random access memory (RAM), two floppy diskette drives, a Centronics Model 730 impact matrix printer and a modulator for driving an ordinary color television as a video display device. A single California Computer Systems Model 7720A dual 8-bit bidirectional parallel input/output (I/O) card was installed in the Apple to accept the digital data from both data acquisition systems. This card is

Jan 1, 1981

By Jr. Watts

The American Mining Congress and the U.S. Bureau of Mines have formed a collaborative research team to develop, implement, and evaluate a comprehensive control strategy to reduce diesel particulate matter concentrations without degrading other air quality parameters at an underground noncoal mine. Other participating organizations include Caterpillar, Inc., the Mine Safety and Health Administration, and the University of Minnesota. After extensive baseline information and air quality data are collected, available control strategies to reduce diesel particulate matter exposures will be implemented, individually or in combination, and evaluated. This paper discusses the objectives and protocol of the collaborative effort to evaluate diesel particulate control technology.

Jan 1, 1995

By Yeonuk Choi, Gus Van Weert

cyanide control in effluents is becoming a critical environmental issue for the gold extraction industry. Silver impregnated carbon removes free cyanide effectively to the ppb level from solution in high throughput columns. By re-calcining the cyanide saturated carbon, the impregnated silver is restored to activity and the cyanide destroyed outside the effluent stream. Many gold mills already have an activation kiln on site, which could make retrofit relatively easy.

Jan 1, 1993

By H. H. Murray

In the past thirty years, there have been a large number of ownership changes in the industrial minerals arena and many medium to large companies have made industrial mineral acquisitions. Industrial minerals are exceedingly important to the achievement and maintenance of a high standard of living in the United States and in other developed countries. In the developed countries of the world the value of industrial minerals exceeds the values of the metallic minerals. In the U.S., the value of our industrial minerals is some 2 112 times that of the value of our metallic minerals. Almost every single thing we use or touch in our daily lives can be related to an industrial mineral. Examples are the construction industry, agriculture, ceramics, paper, paint, plastics, electronics, glass, petroleum, and many more in which an industrial mineral or minerals playa functional role. Industrial minerals are exceedingly diverse in their values, properties, and applications. Sand and gravel is an example of an essential industrial mineral commodity which has a low price but moves in very high volumes. Geographic location of this commodity is critical because of transportation costs. High calcium limestone or marble has a moderately high price particularly if it is white enough for use as a pigment or extender. This moves in moderately high tonnages and location is not as critical be-cause it can be shipped for considerable distances and still be competitive. Some specialty industrial minerals such as a white tale or white bentonite sells at a high price at low volumes and geographic location is not a major factor in marketing. Prices of industrial minerals do not tend to be cyclic and generally keep up with inflationary increases. Because of the diversity of industrial minerals very careful analyses of acquisitions or divestitures must be undertaken by buyers and/or sellers in order to prevent serious mistakes.

Jan 1, 1994

By G. Xu, A. R. Kumar, N. A. Amoah

Prolonged exposure to high concentrations of respirable coal mine dust causes coal workers’ pneumoconiosis and silicosis. Underground coal mine roof bolter operators are more prone to elevated exposure to coal and silica dust. The canopy air curtain (CAC) was developed by NIOSH to protect roof bolter operators from the exposure. The CAC supplies filtered air over the breathing zone of the operator. This dilutes the high coal dust concentrations and provides for an impenetrable air curtain. Many studies have been carried out to improve CAC efficiency. However, field test has shown variable dust control efficiencies indicating rooms to further improve due to the nonuniform airflow distribution across the plenum and ineffective perimeter flow. This study therefore redesigns the CAC with optimized flow distribution that effectively protects roof bolters from coal dust exposures. Computational fluid dynamics (CFD) simulations are used to optimize the uniformity of airflow distribution across the plenum to achieve the best possible uniformity. A lab experiment validates the CFD model and confirms the ability of this design to reduce floor dust pickup, prevent external wind infiltration, and offer an improved protection efficiency

Mar 2, 2022

By Daniel J. Turk, William R. Banning, John Paterson, Thomas J. Weitz, Michael L. Clark

Introduction Pegasus Gold's Montana Tunnels mine is a large surface gold, silver, lead, and zinc mine located 37 km (23 miles) south of Helena in southwestern Montana. Milling operations commenced in late March 1987. The concentrator achieved full production in May that year after undergo¬ing several modifications and improvements. Production for 1988 is projected to be 2.48 t ,80,000 oz) of gold, 34.2 t (1.1 million oz) of silver, along with 8.5 kt (9400 st) of lead, and 22.6 kt (25,000 st) of zinc from lead and zinc concentrates. Mill throughput currently averages 11.7 kt/d (12,900 stpd), compared to the origi¬nally designed capacity of 11.3 kt/d (12,500 stpd). Cash production costs, net of bypro¬duct revenues for the third quarter 1988, were below $3.20/g ($100 per oz). The introduction of ore to the concen¬trator marked the culmination of 12 years ex¬ploration, evaluation, and development. Initial milling operations encountered diffi¬culties with the circuit as designed. As a result, several modifications and improve¬ments were made to the plant. This article is intended to assist other companies developing projects of this type and complexity. It discusses the mine's de¬velopment from feasibility and construction through start-up. The operation, as it exists today, is reviewed including the modifica¬tions and improvements made since start-up. History The mine is situated in Jefferson County, MT within the historic Corbin-Wickes min¬ing district. Underground mining began in 1864 and flourished until the early 1900s. Between 1864 and 1900 the vein deposits in the district produced about $41 million dol¬lars worth of lead and silver ores containing subordinate amounts of zinc, copper, and gold. At various times, three smelters were operated in the area.

Jan 1, 1989

By Ryan Marsters, Adam Pring, Robin Dornfest

Raw water supply in the central Rocky Mountains often relies on trans-basin conveyance. Many of these older diversions incorporate high-elevation, miles-long tunnels driven over a century ago in hard rock. Tunnels were excavated using conventional drill-and-blast mining and weak ground was supported by timber sets and other various means. Over time, timbers rot and fail, rock quality deteriorates, and the timbers are gradually replaced by more timber, steel patches and braces, formed concrete, rock bolts, split sets, shotcrete, and other means which are commonly applied over existing support, thereby reducing tunnel cross sections, obscuring previous support systems, and rarely addressing the failing rock itself, leading to further deterioration of both the rock and the existing support. Traditional investigation techniques to assess compromised areas are often unfeasible due to access, depth, rubble and voids behind weight-bearing existing supports, confined space, poor invert conditions, poor ventilation, and flowing water. This presentation will discuss design procedures for assessing obscured ground conditions, assigning support classes which accommodate for unknowns, and implementing contractual means to address inevitable surprises or quantity overruns. Case studies include raw water supply tunnels in the Rocky Mountain region constructed between early to mid-20th century.

Dec 1, 2022

By Don Suttie, Frank Roybal, John Wright

The Roybal Raise incorporates the simplicity and low cost of a short bald-headed raise while overcoming the usual impediments to driving a high baldheaded raise. The concept provides for speedy excavation and maximizing the use of the excavated opening, using the rock for structural support. The design is simple: two baldheaded raises are driven parallel to one another, interconnected by dogholes about 8 m (25 ft) apart. In this fashion, the raise can be driven safely and efficiently to 60 m (200 ft) or more. When the raise is complete, the excavation requires no timber for support or partitioning. Rather, the rock itself supports the construction. As a test, a two-compartment Roybal Raise was attempted at the Independence mine in the Willow Creek District of Alaska. One side was driven 2 x 2 m (6 x 6 ft), intended for a manway and equipment skip. The other was driven 1.5 x 1.5 m (5 x 5 ft) for a muck compartment. Both sides were driven at a 65° angle from horizontal and 1 x 1 m (4 x 4 ft) dogholes spanned the 4.6-m (15-ft) pillar between the two compartments. After topping out at 50 m (160 ft), the raise was found to meet all expectations of efficiency, low cost, and practical simplicity. Technique Preparing the Roybal Raise for driving involves no elaborate or costly site prep except assembling materials and providing for muck removal. Normally, the raise muck falls directly onto the sill or track and is picked up either by an overshot mucker or a front-end loader. Raise mining proceeds initially by taking up both compartments simultaneously to the first doghole. It progresses by alternating one side as a clear manway for access with the other side, the active side, as a muck compartment (Fig. 1A). This stage proceeds quickly for no mucking or staging is required to cycle the first three rounds. On the fifth round, in addition to the normal raise round, rib holes are winged out toward the adjacent raise, thus starting the dogholes. Finally, as the sixth raise rounds are drilled and shot, the first doghole is also completed from both sides. The second stage commences by establishing one side as a clear manway for access while the other side, used as a muck compartment, is prepared for active mining. Figure 1B illustrates this step in the succession of raising with the active side advancing to the second doghole level. During this stage, services are maintained through the manway side and equipment is stowed in the doghole during blasting. As the active side advances, muck may be allowed to fill the bottom portion of that side since it is unnecessary to clear it for access. The next stage of raising involves cleaning out the former muck compartment and preparing it for use as a manway. At the same time, the former manway is prepared for advance and use as a muck compartment (Fig. 1C). As in the previous step, the same doghole is used for access and equipment storage. The active side advances until the second doghole is completed, at which point equipment and access are moved to the new doghole. From there, the active side is driven past the second doghole 8 m (25 ft) more to the third doghole level. Again, half of the doghole and the next raise round are mined. The fourth stage involves switch ing back the manway side for the muck side (Fig. ID). The new muck side is driven to the third doghole where equipment storage and access are reestablished. From there, the active side is advanced to the fourth doghole. In the same fashion, the raise is advanced to the top, alternating the manway side with the active side, maintaining access through the inactive manway, and storing equipment in the uppermost doghole. The cycle time for driving each compartment, regardless of the raise height, is greatly improved over that for normal bald-headed raises of comparable height. By storing equipment in the upper-

Jan 1, 1984

Geostatistics is well known as a tool for ore reserves calculations at the exploration stage. The goal of this paper is to show geoscatistics can also contribute to productivity gains, allow better selection of the mining methods and better control of the grades during production. The first two examples show how geostatistics can provide sophisticated models, using conditional simulations and the use of them for simulations or optimizations of mining processes. A third example will show how to use geostatistics for short term planning in a large polymetallic vein type mine.

Jan 1, 1983

By H. J. Brown

Pluess-Staufer (California) Inc. Lucerne Valley California operation is one of the largest producers of high brightness high purity fme grind limestone products in western North America. The San Bernardino Mountains area of southern California contains the largest high brightness, high purity limestone mining operations and undeveloped reserves in western North America (Fig. 1, Brown 1987). Combined annual production of high brightness limestone products from several operations is approximately 1.5 million tons, with an estimated gross value of $75 million dollars per year (Fig. 2). An additional 5.0 million tons of cement grade limestone is mined by several large cement producers in the nearby Mojave area (Brown, in press). The purpose of this paper is to summarize the geologic setting, genesis and mining of white, high purity crystalline limestone by Pluess-Staufer (California) Inc.

Jan 1, 1994

Selective Flocculation process development generally involves single mineral flocculation tests to identify the appropriate polymer and experimental conditions for achieving the desired selectivity. Invariably the selectivity predicted on the basis of such tests is not realized when mixed mineral tests are conducted. A systematic experimental investigation revealed that adsorption of the polymer on various substrates is critical to selecting the suitable flocculent. Simultaneously, a mathematical model was developed to predict the overall process efficiency with a given polymer. In this paper, results of these efforts to scientifically design a suitable selective flocculation process are presented.

Jan 1, 1991

By L. H. E. Weyher

Minerals beneficiation commonly requires initial crushing and grinding so that the mineral phase we seek to concentrate is adequately liberated to obtain a product of specified grade at optimum recovery. To some degree this also is true for coal preparation. In the comminution process we liberate not only the product but also the tailings phase. The true objective is, therefor, to eliminate from the comminution circuit whatever particulate matter has reached specified liberation, regardless of whether the particle is product or tailings material. Overgrinding either of the two phases ties up mill capacity and usually also burdens the downstream processing steps by increasing costs or decreasing recovery, or both. In view of this situation, one would expect concentration steps to be commonly incorporated into the cominution circuit. The reasons this is not done may vary, but probably include the desire to utilize large scale unit operations, e.g., large mills, in conjunction with very simple processes. Hydrocyclones have satisfied this desire but may not always be employed for the right reasons. Hydrocyclones are indeed simple. They also are rugged and forgiving. Unfortunately, these virtues are frequently misused. The direct results are inefficient classification and overgrinding. The indirect results are added costs through recovery losses, unnecessary recirculation, and so on,

Jan 1, 1985