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By C. D. Elifrits, N. B. Aughenbaugh

Introduction Federal and state laws enacted to regulate coal mining and the accompanying public concern about the adverse effects that mining might have on land use have focused much attention on the subsidence of the land surfaces over underground mines. Some questions asked are • Will abandoned mines subside in the future even though they have exhibited no surface adjustment to date? If so, when will subsidence take place? • Can a specific surface area be affected by subsi¬dence more than once? • What surface form will the subsidence feature take? • Is there any way to predict when subsidence will occur and end? An attempt is made here to address these questions insofar as it is possible with available data and experience of evaluation of subcritical extraction conditions. Mining that results in subsidence features can be classified as supercritical, subcritical, and critical with respect to the minimum span lengths of the worked-out rooms (Fig. 1). A complete basin will not develop fully immediately over subcritical conditions because the span lengths of the entries are less than the critical dimension (Wardell, 1983). Passageways, entries, and room-and-pillar panels are all included in the subcritical category. Because of the short span lengths, subcritical mining conditions tend to be stable over the life of the mine unless adverse geologic conditions exist (Gray et al., 1974; Dunrud, 1976). Various roof control and support procedures are employed to maintain entry stability during mining. Little information exists concerning the time factor of subsidence over areas of subcritical extraction. Data that have been collected relate to longwall mines, whereby the cavity sizes are designed large enough to induce caving behind the working faces so that complete subsidence at the surface occurs within a short period of time. The UK's National Coal Board (1975) has reduced the enormous amount of data it has collected to empirical correlations and has published these correlations in its Subsidence Engineers Handbook. The handbook states that "None of the foregoing remarks applies to pillar and stall working," with respect to the section discussing the time factor of subsidence caused by longwall mining (National Coal Board, 1975, p. 40). To understand and evaluate how time relates to subsidence above room-and-pillar mines, one must first recognize how mine cavities deteriorate and fail. The propagation of failure to the surface must then be studied, and, finally, the failures that are manifest at the surface in the form of depressions accompanied by both compressional and tensional movements must be investigated. Failure of mine cavities Any cavity beneath the earth's surface represents a condition of nonequilibrium and tends to close with time. Failure of cavities in a subcritical mine can be classified as failure of the roof, failure of the floor, failure of the supports (pillars, cribs), and elastic rebound of the rock. One mode of failure may dominate, but generally combinations of the four will occur. Also, initial instability of geologic materials and structural features and in situ stress may be unknown factors that can contribute to cavity failure. Roof failure is the most obvious opening stability problem in most operating mines. The bridging capabilities of the roof rock are dependent on the rock's material strength, geologic discontinuities, and reaction to humidity changes in the air of the mine. This type of failure may vary in magnitude from gradual flaking to massive roof falls. Mine floor instability can be manifest in the form of a general heave over a broad area or of individual pillar punching. The weaker and thicker the immediate floor material, the more prone a mine is to experience floor problems. Water seeping into an area can soften the underclay, reduce its bearing capacity, and precipitate failure of support for the overburden.

Jan 1, 1987

By C. R. Everly

"The purpose of this paper is to review the most effective methods of reducing chloride transfer and chloride removal in the solution extraction and electrowinning (SX/EW) process. Elevated chlorides in electrolyte have various negative effects including a reduction in current efficiency, increased handling costs at rod plants and smelters, increased anode corrosion, cobalt losses due to increased electrolyte bleed, degradation of HDPE piping, and increased corrosion in the SX/EW plants. Historical controls that Sierrita has used to control chloride transfer, in order of effectiveness, have been chloride gasification at the EW that is directly correlated to amperage and chloride concentration in electrolyte, wash stage bleed and efficiency, width and velocity of aqueous bands, and electrolyte bleeds. Maintaining high bleed rates and high amperage settings has been a challenge with decreasing pregnant leach solution (PLS) grades, so keeping chlorides out of the electrolyte has become imperative. The effectiveness of reducing aqueous entrainment, optimizing wash stage efficiencies, and improving organic quality to reduce the transfer of chlorides to the electrolyte are illustrated in this study. INTRODUCTION The transfer of impurities from PLS feed streams to electrolyte in the Copper Solution Extraction process is a very common problem and is the reason that the wash stage exists in most SX operations. The main impurities affecting the SX process are iron, chloride, nitrate, and manganese. Elevated chlorides in the electrolyte have various negative effects including reduced current efficiency, increased handling costs at rod plants and smelters, increased anode corrosion, increased cobalt losses due to increased electrolyte bleed, degradation of HDPE piping, and increased corrosion in the SX/EW plants. Freeport-McMoRan Sierrita Hydromet is unique in that a high-chloride byproduct stream from the molybdenum process is pumped into the SX raffinate solution pond. This byproduct steam accounts for the majority of chloride introduced to the circuit, and over the years has built up to a point where 4000ppm chloride is consistently in the PLS feed to the SX. Concentrations of chloride over 70 ppm in electrolyte will result in downgraded cathode, so it is important to limit chloride carryover from SX as much as possible. Historically, Sierrita has been able to manage chloride levels with reactive techniques including increasing electrolyte bleeds and rectifier amps. Decreasing copper in PLS has made high amps harder to maintain, and increasing bleed rates have a direct impact on production goals."

Jan 1, 2015

By W. C. Patrick

Introduction The availability of a thorough, simple-to-use roof fall classification system is desirable for several reasons. First, such a system would expedite the reporting of falls for the purposes of estimating material removal costs, analyzing damage levels, and complying with federal regulations to report falls in certain areas of the mine. Second, the classification system would allow the mining engineer to record falls routinely with little time and effort expended. This would encourage him to make observations concerning what type of roof support would work best in a given situation. Third, and probably most important, an adequate roof fall classification system is the first step toward developing a means of predicting the occurrence and extent of future falls. It was with these three reasons in mind that the following classification system was developed. The type of classification chosen reflects the background of the developer and the intended purposes of the system. Hylbert has proposed a geologic-based classification which groups falls as to structural and compositional origin. The need for similar systems is noted by Cox and by Ferm and Melton. Each of these researchers is confronted with a situation requiring a relationship between local geology and roof fall occurrence. Such a relationship would allow the prediction of the relative frequency of falls from a knowledge of local geologic features. The current research is aimed at fulfilling somewhat different requirements, as noted above. Fall geometry has been chosen as the basis of the classification system so fall type can be reported independent of local geological, environmental, and tectonic conditions. This approach parallels that used in the common slope failure classification with groups failures relatively independent of

Jan 1, 1977

By David Lunt, Paul Messenger, Peter Allen

The Rawas Gold Project in Indonesia has a high silver ore with a ratio of approximately 25:1 Ag/Au. Four process flow­sheets were considered during the development phase, ie. full Merrill Crowe, CIP, CIP with zinc cementation of eluate and a hybrid Merrill Crowe - CIP circuit. The process plant was constructed using a CIP circuit with zinc cementation of eluate. Unusual aspects of the design include an elution circuit designed to strip three batches of car­bon per day and an elution column designed to operate with either upward or downward solution flow. Significant improvements implemented since starting up the plant include the use of local materials and labour for relining the mill, a change from lime to caustic soda for pH modification and the elimination of caustic soda dosing to the elution pre-soak step.

Jan 1, 1998

By Paul A. Lahti

Independence Mining Company, Inc. (IMC) has for the past several years processed refractory gold ores at its Jerritt Canyon operation near Elko, Nevada. The ore is typical of those of the Carlin Trend and is refractory due to physical encapsulation of gold in carbon, pyrite, and arsenopyrite. It is also "preg robbing" due to the contained organic carbon that acts as a gold adsorber. Refractory ores require some form of pretreatment before cyanidation to enable economical recovery of gold. The metallurgical facility at Jerritt Canyon is unique in that it consists of two distinct pretreatment methods for the recovery of gold: a chemical process utilizing chlorine and a pyro-metal­lurgical process employing oxidative roasting. This paper pro­vides a comparison of the two methods highlighting flow sheets, pretreatment operation detail, performance comparisons, and pertinent environmental data.

Jan 1, 1996

The solution mining review did not arrive in time for publication in the May issue. The term solution mining is commonly used to refer to heap leaching, dump leaching, in situ mining and bore hole slurry mining technologies. The US Bureau of Mines is continuing with research in these areas. Commercial application of these technologies is progressing. There is an ongoing cooperative research project between the Bureau of Mines and the Santa Cruz Joint Venture to evaluate in situ copper mining at a field site near Casa Grande, AZ. The project is currently in the environmental permitting stage. The Bureau is preparing an environmental assessment for the project as part of the National Environmental Policy Act. The Bureau is also continuing with laboratory experiments to study the leaching characteristics of atacamite ore from the field test site, as

Jan 1, 1993

By J. Ugarte-Núñez

Biodiversity assessments that are developed in different stages of a mining project, have different objectives that define the methodology to be used in each of these stages. In this way, we define two stages of a project: 1) the time at which assesses the state of biodiversity or biological components, before any intervention in the project area, previously defining the area of direct influence and indirect influence of the project for each biological group to be evaluated and 2) the time when certain groups or biological, are monitored during the developmental stages of the project with you to obtain information about the level impact they may have, for project activities. It discusses the methodological differences that must be used in both biodiversity assessments: to develop biological baselines and in those assessments aimed at monitoring different components of biodiversity.

Jan 1, 2011

By F. P. de Kock, P. West-Sells, B. Wassink, D .. B. Dreisingerl

During the cyanide leaching of gold ores containing copper minerals, aurocyanide (Au(CN)f) is produced and typically recovered using activated carbon. However, free cyanide, as well as cyanide associated with cuprous cyanide complexes, are generally not recovered from the barren liquor. This results in a significant economic penalty in high cyanide consumption due to the dissolution of copper. 1\vo different configurations of a novel method for the treatment of barren liquor streams for cop­per recovery and cyanide recycle are described. Recovery of copper and cyanide is affected using solvent extraction (XI 7950). Loaded organic is stripped with a high copper, high caus­tic solution which is electrowon to produce copper metal. Depleted electrolyte is treated with sulfuric acid to recover cyanide which is returned to the leaching circuit. Results of benchscale and mini-pilot plant experiments are presented.

Jan 1, 1996

By Wayne A. Ericson, Kirk S. Davis, Cornelis Winkler

BCI has developed a chemical process known as Ecophos® for the multi-industrial Pine Level Project in DeSoto County, Florida. Approximately 85 percent of the phosphogypsum at Pine Level will be converted to a very clean gypsum. The remaining 15 percent, including impurities plus some quartz tailings sand, constitutes what is termed redigestion solids. BCI has developed an alternative to the practice of disposing phosphogypsum in large above-ground impoundments. The proposed disposal method consists of mixing the redigestion solids with clays and reacting the mixture (leached tailings) with lime prior to disposal into the mine excavations as a reclamation soil material. Leachate water quality testing using lysimeter equipment indicates that the pore water associated with neutralized leached tailings meets maximum contaminant levels set for the drinking water standards of radium and selected primary metals.

Jan 1, 1992

By R. A. Wharton, Z. Yang, R. W. Smith

The electrokinetic and flotation behavior of the green alga Chlorella vulgaris was studied in the absence and presence of Pb(II), Al(III) and flotation collectors. It was found that the presence of Al(III) is necessary for good flotation of the organism, whether or not Pb(II) is present, when dodecylammonium chloride or sodium dodecylsulfate is used as collector. Best flotation using dodecylamine is at about pH 8, and best flotation when using sodium dodecylsulfate is at about pH 4. It appears because of the small size of the organisms that the Al(III) is necessary for flocculation to enhance bubble-cell contact and C. vulgaris removal from water. When N-dodecyl-2-aminopropionic acid is used as collector, good flotation occurs at about pH 4 without the addition of Al(III).

Jan 1, 1992

By Y. J. Wang

In the, mathematical analysis of electrical networks, the electrical devices are often modeled using idealized network elements such as current sources, voltage sources and resistors. An analogous approach is outlined for the modeling of mine ventilation networks, which can be considered nonlinear resistive networks. The proposed modeling technique uses the following five basic (nonreducible) elements: H, Q, D, R and N. These elements are characterized by their pressure gain or loss, their air quantity and their pressure-vs. -quantity relationships, each of which may be known or unknown. In addition to the definition of the basic elements, the necessary conditions for which there exists a unique solution are discussed This is performed using theoretical developments derived from electrical circuit theory and illustrated in example networks. The proposed procedures are useful in the solution and characterization of mine-ventilation networks.

Jan 1, 1997

By Jan M. Mutmansky, Y. J. Wang

In the mathematical analysis of electrical networks, the electrical devices are often modeled using idealized network elements such as current sources, voltage sources and resistors. An analogous approach is outlined for the modeling of mine ventilation networks, which can be considered nonlinear resistive networks. The proposed modeling technique uses the following five basic (nonreducible) elements: H, Q, D, R and N. These elements are characterized by their pressure gain or loss, their air quantity and their pressure-vs.-quantity relationships, each of which may be known or unknown. In addition to the definition of the basic elements, the necessary conditions for which there exists a unique solution are discussed. This is performed using theoretical developments derived from electrical circuit theory and illustrated in example networks. The proposed procedures are useful in the solution and characterization of mine-ventilation networks.

Jan 1, 1998

By J. Litsenberger, T. E. Marshall, P. R. Coyle, L. J. Prosser, A. T. Iannacchione

For the first time in an underground stone mine, the relationship between roof movement and microseismic emissions was examined in conjunction with two distinct roof fall areas. As roof monitoring increases in acceptance and monitoring technology advances, the goal of providing reliable roof fall detection systems to enhance the safety of underground mine workers moves closer to reality. Instrumental to reaching that goal is the ability to interpret accurately and completely roof movement and microseismic emissions, which can serve as precursors to roof falls. This paper examines the capabilities of convergence and microseismic monitoring systems to better understand roof rock failure mechanics and to anticipate roof falls. An understanding of how these techniques are used and how they interact with each other is critical in developing the most effective ground control strategy for our nation’s mines.

Jan 1, 2004

By Qing Wang

A longterm overburden removal plan can be realistic and optimum only when the cost and capacity profiles off the equipment assigned to the operation are taken into consideration. Therefore, the planning should involve the proper assignment of equipment capacity by insuring a timely investment and a timely replacement policy throughout the mine life. A dynamic solution algorithm has been developed, by which all possible truck fleet alternatives are evaluated for each year off the operation. Cumulative cost off the operation is carried throughout the analysis. The optimum solution is obtained by selecting the minimum cumulative cost at the last year and tracing backward the best fleet alternative for each year. The solution provides: 1. the optimum amount of overburden to be removed each year; 2. the best fleet to be assigned to the job; and 3. the best equipment replacement policy.

Jan 1, 1989

By O. J. R. Baena, D. E. Chaverra, C. D. L. Ramirez

Cyanide is one of the most used reagents in the precious metal extraction process; as well as the most efficient from the point of view of the dissolution process; but it is also a toxic product that requires a lot of care in handling. Likewise, the residual solutions of the process must be followed because they can be a risk of contamination of water, animals and human health. In the artisanal processes of obtaining gold and silver, neutralization of the residual solutions is used to passivate the present cyanide. During this process ammonium cyanate is formed which decomposes rapidly in the presence of air and sunlight in carbon dioxide and ammonia gas, contributing to the greenhouse effect. In this work the use of the ammonium cyanate obtained in the process of neutralization of the cyanide solutions as a reagent to obtain urea is proposed. Urea was obtained indirectly through the use of the reagent kit UREA/BUN-COLOR. The process is effective at pH ≤ 4.5 with a rapid increase in solution temperature, and addition of hydrogen peroxide. The urea crystals begin to form at 50°C. The cyanide / urea ratio obtained was 1 / 7.5 INTRODUCTION In the processes of extractive gold metallurgy, the use of cyanide leaching is perhaps the most widely used method worldwide; by the ease of operation, its low cost and high levels of precious metal recovery. However, neutralization, in most processing plants, is not done properly, and leftovers of solution with free cyanide are dumped in concentrations harmful to the environment, in particular animals and humans. Cyanide can enter surface water through releases from industries using cyanides. Due to its high toxicity, the presence of cyanide in water is a matter of great concern (Jawale et al., 2017). The pollution generated by the effluents from the leaching of gold ores is one of the main obstacles of social opposition presented by mining activity due to the impact of both surface and groundwater. During the cyanide decomposition process, a compound known as ammonium cyanate OCN(NH4), which is a raw material for the manufacture of urea, CO(NH2)2 is generated. In the case of good neutralization, cyanide is no longer a toxic compound through oxidizing reagents, but as a result, there is the generation and emission of ammonia and carbon dioxide into the atmosphere, generating both a greenhouse effect (Gómez, 2012). This is evidenced by the strong effervescence of the reaction, and a penetrating smell of ammonia, which can irritate respiratory mucous membranes and eyes; however because they are greenhouse gases they are considered pollutants.

Jan 1, 2019

By J. C. Watts

Ball mill grinding circuit control has received increasing emphasis in the past few years due to such factors as declining ore grades, increasing production costs, and advances in analytical devices and minicomputer technology. Since ball mill circuits have been a traditional bottleneck in mineral processing plant throughput, control systems often improve through- put without requiring additional processing equipment. In addition, much of the variability of the grinding product size and consistency is often removed, allowing better process operation downstream. Among the problems which arise in designing and implementing a process control strategy for ball mill circuits are circuit constraints imposed by processing equipment and local management, proper instrument selection, installation and maintenance, and use of calculated or inferred variables for process measurements. This paper discusses these problems and attempts to identify valid approaches to their solution.

Jan 1, 1979

By E. Peuraniemi, S. Strömberg, S. Jyrkönen, A. Jokilaakso

Several sulfidic raw materials have been flash oxidized in a laboratory furnace in oxidizing atmospheres at temperatures of 500-1100°C. Chemical analysis was used to determine the oxidation degree, and optical and scanning electron microscopy combined with energy dispersive analysis were used for characterization of the reacted particles. The studied materials included both Cu and Ni concentrates and mattes. In fixed conditions, the temperature dependence of sulphur removal rate was found to be equal for all the copper concentrates studied. Nickel concentrates and Cu- and Ni-mattes were, however, found to be less reactive. Most of the particles were found to spheroidize and to fragment to small droplets under intensively oxidizing conditions. The product particles were frequently found to be iron oxide cenospheres or dense spheres with a composition of mixed Cu-(Ni-)Fe oxides.

Jan 1, 1998

By John E. Dreier

The Pachuca-Real Del Monte district, Hidalgo, Mexico (Figure 1) has produced roughly 1,500,000,000 oz Ag., 6,000,000 oz Au. and minor Pb., Zn, and Cu from about 100,000,000 tons of ore since discovery early in the 16th century. Production has come from epithermal vein deposits that have been up to 8 km in length, 650 m in vertical extent and 45 m in width but which averaged 200-400 m in length and vertical extent and 2-4 m in width. Ore deposits occur through-out an area about 12 km E-W by 10 km N-S (Figure 2) and between the elevations of 2000 and 2800 m above sea level. The deposits occur as shoots in the veins and terminate laterally where the veins narrow, upward where the veins pinch out and downward where the veins decrease in silver con-tent to below the cut-off grade; the veins are known to extend 500 m below the bottoms of the ore bodies and probably extend to much greater depths. The district lies wholly within a mid-to-late Tertiary volcanic rock sequence that is made up principally of andesite and dacite lava flows and flow-breccias. Although the bottom of the sequence is not exposed in the district, stratigraphic constructions indicate the volcanic rocks to have an aggregate thickness of 2000 to 2500 m. Structurally, the area is characterized by gentil warping and normal faulting of the volcanic rocks. Pre-ore modifications to the volcanic rock sequence consisted mainly of faulting along west-trending, south-dipping normal faults and north-trending high-angle faults.

Jan 1, 1978

The CERAMEC pressure filter is used for the filtration of fine materials whose cake moisture cannot be achieved with vacuum. Development work has been carried out to achieve a well-controlled cake forming and cleaning of the filter media as well as an efficient solids discharge system. Operating costs are low due to low energy input and negligible consumption of pressurized air.

Jan 1, 1999

By W. Everett Smith

Factors that have influenced mineralization in the Valley and Ridge and Piedmont provinces in Alabama are not clearly understood. Lithology and structure are recognizable factors in the Valley and Ridge province, where barite, lead, and zinc sulfides occur in structurally complex areas of Cambrian and Ordiovician carbonate rocks. Metal mineralization in the Piedmont province indicates a complex relationship with factors such as favorable host rock, proximity to intrusive or high-grade metamorphic rocks, several metamorphic events and separate or related structural events. Lineaments, as used herein, refer to naturally occurring linear features consisting of topographic, vegetative or soil tonal alignments that are at least partially continuous for distances greater than a mile (Lattman, 1958). Lineaments in Alabama were first recognized by J. G. Newton in 1970, using Apollo 9 series photographs. Subsequent studies delineated the features (Powell and others, 1970) and suggested relationships to structural and hydrologic factors. More recent work has explored relationships to mineralization, environmental geology and the tectonic framework of the Appalachians (Drahovzal and Copeland, 1970; Drahovzal and Neathery, in press). The lineaments recognizable on Apollo 9 photography probably represent fractures, some of which may reflect geofractures that bound major basement blocks. The lineaments defined in Alabama range from about 4 miles to nearly 200 miles in length. Most of the lineaments are straight, but some are arcuate; some appear to terminate at the intersections with other lineaments but most cross each other with no offset. Some lineaments pass through areas of structural disruption such as terminations, offsets and changes in structural style, but others show no such relationships. Most of the lineaments appear to cross topographic features with little or no obvious disruption. Orientation analyses of the lineaments divide them into three directional groupings

Jan 1, 1972