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By R. D. Doepker

The dissolution of metals from various metal-mine tailings has been studied through a series of submerged tailings batch tests at U.S. Bureau of Mines laboratories. Tailings selected for this study included both reactive (as determined by column leaching studies) and benign tailings. Metal mobilization in aerated (97 pct saturated with oxygen) samples appeared to be consistently greater than metal dissolution from stagnant (79 pct or 70 pct saturated with oxygen) waters. In the early weeks of the study, sulfate concentrations increased with solid-liquid contact time, while calcium dissolution remained nearly constant. Metal concentrations varied in relation to solid-liquid contact time and aeration. Leachate pH appeared to be nearly independent of solid-liquid contact time for basic tailings. Reactive tailings having both a submerged and a surface component demonstrated increased metal mobility.

Jan 1, 1990

By John Keefner, Charles Kocsis, Kyle A. Scalise

Geotechnical modeling of mines is crucial for understanding the many factors that can pose potential hazards or limit production opportunities. The process of back analyses for modeling is often used, but in many instances, the back analyses can be cumbersome and time inefficient.While thesemodels and back analyses may be accurate, these types of back analyses may not be ideal to be used at mines and by engineers because the process is so time-consuming. This paper introduces event-based back analyses that utilize prior events to create more accurate models while eliminating large modeling time because the models are back analyzed from previous events. The completed analyses supply a more detailed insight into the potential hazards at Round Mountain, an open pit operation, as well as provide a better understanding of how improper risk analysis results in missed opportunities. The more we understand about mining activities and processes through modeling, the safer and more productive mines will be.

May 24, 2021

By K. V. Raj

As open pit mines continues to grow deeper, managing air pollution can become challenging. During arctic air inversion, the temperature of the air over the mine increases with altitude, and the cold, heavy, surface air is trapped in the pit. This problem is complex, and any solution will require an extensive understanding of the interactions between the aerodynamic movement of air, air inversion, meteorology, pollutant sources, and transport phenomena in the open pit mines. The availability of computational fluid dynamics (CFD) has elucidated the pollutant flow mechanism in open pit mines. Very few CFD studies have been published, especially the Large Eddy Simulation (LES), on the contaminant transport in deep open pit mines under arctic air inversion. The contaminant transport in an open pit mine under arctic inversion is due to a stable or nocturnal boundary layer in micro-meteorological terms. Understanding the physics of the stable boundary layer (SBL) is relevant to air flow and pollutant transport in deep open pit mines. This paper focuses on a Large Eddy Simulation (WMLES as Sub-Grid Scale Model) modeling of the SBL and pollutant transport in a large open pit mine.

Feb 23, 2014

By A. Yadav, B. Behera, G. S. P. Singh

The size of chain pillars in the Indian geo-mining conditions is primarily decided in accordance with the regulatory provisions. These provisions are of little help for deep longwall workings, exceeding the cover depth of 360 m. Furthermore, these provisions are primarily meant to support pillars in bord and pillar workings. They may not be suitable for the chain pillars owing to a significant difference in layouts and functional requirements. Hence, it is imperative to develop a method to evaluate the stability of the chain pillar considering the complex loading and geo-mining conditions. To this end, a machine learning-based model was developed in this study to assess the stability of the chain pillars under high depth of cover considering the field-representative conditions. The data for this work was generated by conducting a parametric study using a field-validated numerical model. The strength and deformability parameters of the caved, fractured, and continuous deformation zones were established by calibrating the numerical model outcomes against the site-specific field observations. The developed ML model was used to evaluate the influence of pillar width, pillar height, cover depth, abutment angle, face length, coal strength, moduli ratio of the roof and floor strata to the coal seam, and the elastic modulus and unit weight of the overburden on the chain pillar stability. An interesting finding of this study showed that the factor of safety of the chain pillar increased with the increasing abutment angle, which may be indicative of the confining effect of the abutment angle on the pillar. Eventually, the ML model was verified by comparing its outcomes with the calibrated numerical model for a typical longwall working from Indian geo-mining conditions.

Oct 18, 2023

By Greg Colzani, Emily Thompson

The 3RPORT Project, includes a 5-mile tunnel excavated by a 19-foot diameter slurry Tunnel Boring Machine below the city of Fort Wayne, IN. The Geotechnical Baseline Report (GBR) indicated vuggy to massive argillaceous dolomite within the tunnel alignment. During excavation of the first reach, the TBM encountered zones of cohesive clay and sandstone presented in full face and mixed face conditions. The occurrence of Sandstone was not a “Baselined Condition” described in the GBR for this reach of the alignment. This paper will discuss the methodology to investigate, mitigate and evaluate the DSC impacts on TBM performance.

Dec 1, 2022

By Scott Rosenthal, Dave Gilkey, Theresa Stack, Daniel Autenrieth, Ciara Kremer

Jackleg drill operators are exposed to harmful levels of hand-arm vibration (HAV). Anti-vibration handles and gloves provide modest reductions in HAV exposures and forearm muscle exertion from the use of anti-vibration handles and gloves by jackleg drill operators. The goal of this pilot study was to investigate changes in HAV with the use of anti-vibration gloves and handles compared to forearm muscle exertion experienced by operators and measured with surface electromyography (EMG). Five subjects operated the drill under four different cases: no anti-vibration controls, anti-vibration gloves only, anti-vibration handle only, and simultaneous anti-vibration handle and glove use. Muscle exertion was expressed as a percent of maximum voluntary contraction (%MVC) and was compared using Welch’s ANOVA with Games-Howell post hoc comparisons. The case with both anti-vibration controls in use simultaneously (largest grip diameter) was associated with a mean %MVC of 36.13% during operation for all forearm muscles combined, which was significantly higher than that of the other cases (p < 0.05). There were no statistically significant differences in mean HAV exposures. The anti-vibration handle with anti-vibration glove case only increased the maximum allowable exposure time by 8 min as compared to the control case without any anti-vibration controls. These results suggest that the modest HAV exposure reductions from the use of anti-vibration handles and gloves may pale in comparison to the increased muscle exertion resulting from their use, and this trade-off among jackleg drill operators is a potential concern that warrants further investigation.

Jul 12, 2021

By Yuemin Zhao, Wenxuan Liu, Maoming Fan, Zhanyuan Long

"Coal is mainly composed of energy-producing elements carbon and hydrogen. In addition to these elements, coal usually contains many other valuable elements, including iron, aluminum, silicon, rare earth elements, lithium, gallium, germanium, vanadium, uranium, titanium, scandium and phosphorus. These coalassociated elements are significantly enriched in coal combustion byproduct fly ash because the majority of the main components, carbon and hydrogen elements, being removed. Table 1 provides the chemical composition range of the main element oxides in 12 Chinese fly ash samples collected from coal power plants located in Northeast China, Northwest China, Southwest China and Southeast China. It can be seen from Table 1 that the major mineral components of different ashes are similar, but the bulk chemistry of different fly ashes may vary due to the changes of ratios of the mineral components in different coals. The major mineral components in various Chinese coal combustion fly ash are silicates, iron oxides and unburned carbon.Chinese coal fly ash usually contains about 5 to 15 percent of unburned carbon, which are generally chars with irregular shapes and wide particle size distribution. In addition to unburned carbon, XRD analysis of four Chinese fly ash samples from Liaoning, Shanxi, Guizhou and Shandong provinces indicates that the fly ash samples are composed of minerals such as quartz (SiO2), mullite (3Al2O3.2SiO2 or 2Al2O3.SiO2), hematite (Fe2O3), maghemite (gamma form of hematite, ?-Fe2O3) and magnetite (Fe3O4). The mullite and quartz particles are usually present as spherical particles because they are formed by melting clays, feldspars, quartz, calcite and other common minerals in coal during coal combustion. The silicate particles have usually entrapped gas to yield hollow spherical particles because their lower melting point facilitates gas entrapment.The iron oxides are usually spherical also. The magnetite (Fe3O4) is derived from pyrite (FeS2), hematite (Fe2O3), siderite (FeCO3) and limonite (2Fe2O3.3H2O) in the coal. Maghemite (?-Fe2O3) is formed by dehydration of the mineral hydrohematite (?-FeO(OH)) and/or oxidation of magnetite (Fe3O4) during coal combustion. Maghemite (?-Fe2O3) and magnetite (Fe3O4) are strongly magnetic, so they are recovered from Chinese coal fly ash and widely used for coal processing in China (Fan et al., 2005, 2000)."

Jan 3, 2018

By Xiaoyan Luo, Congcong Dai, Gaipin Cai, Xin Liu, Lu Zong

To overcome the difficulty of accurately judging the load state of a wet ball mill during the grinding process, a method of mill load identification based on the singular value entropy of the modified ensemble empirical mode decomposition (MEEMD) and a probabilistic neural network (PNN) classifier is proposed. First, the MEEMD algorithm is used to decompose the vibration signals recorded under different load states to obtain the intrinsic mode components, and a correlation coefficient threshold is used to select the sensitive mode components that characterize the state of the original signal. Second, singular value decomposition is used to obtain the singular value entropy. Finally, the load state of the wet ball mill is judged based on the magnitude of the singular value entropy. A characteristic mill load vector is constructed from the singular value entropies of the cylinder vibration signals recorded under different load conditions and is used as the input to a PNN, which then outputs the predicted ball mill load state; in this way, a load state identification model is established. Grinding experiments are presented to verify the effectiveness of the proposed method, showing that the method can accurately identify the load state of a wet ball mill. ()

By Feng Junfa, Du Feng, Li Huamin, Syd S. Peng

"The Ordos coal field is located in the northern midwestern part of China (Fig. 1). Since the mid- 1980s, it has been developed into one of the major coal fields in the world, producing approximately 833 Mt (918 million st) of raw coal in 2013. There were once more than 400 coal mines operating in the region. However, due to the combination of market conditions and implementation of government consolidation policies, the number of coal mines operating in recent years has been reduced considerably, with increasing output.The surface of the Ordos coal field is covered with loess and alluvium layers of varying thicknesses. In many areas, their combined thickness may amount to as much as 100 m (328 ft) underlain by thin bedrock. Many loess and alluvium are aquifers receiving water from rainfalls. There are also gullies of varying depths crossing the coal field. Figure 2 is a typical stratigraphic column highlighting the coal seams and roof and floor rocks of interest.In conjunction with the development of highproductivity coal mines, numerous ground control instrumentation tests have been conducted in the operating longwall panels. Analyses of the results of those tests offer the opportunity to understand the effect of wide-ranging mining and geological factors on the overburden movement. For this reason, trips were made to coal mines of interest to interview mine management and collect their unpublished internal research reports on ground control instrumentation. In addition, literature searches on published thesis/dissertations and papers in the professional journals were performed. Finally, data from a total of 95 fully mechanized longwall panels were collected. The instrumentation involved primarily the monitoring of hydraulic pressures of longwall shields, from which the first roof weighting and first roof caving interval and periodic roof weighting and periodic roof weighting interval were identified and determined. Some panels also included measurements of roofto- floor convergence at the face, roof strata bed separation, longwall face sloughage and the height of caving and fractured zones in the overburden. Those 95 panels were located in 20 coal mines (Fig. 1) congregated along both sides of the Wulunmulun River with the following mining and geological conditions. All together those 20 mines produced more than 224 Mt (246 million st) in 2013, accounting for approximately 27 percent of the total coal production in the Ordos coal field:1. Period of mining: 1991-2013.2. Mining methods: All panels employed the one slice, full-seam natural-caving longwall mining method like those practiced in the United States. All panels were developed with a twoentry system with a single-row of chain pillars measuring 20- x 20-m (65.6- x 98.4-ft) wide.3. Coal seams (Fig. 3): Coal in Ordos coal field is high-quality steam coal, that is very low in sulfur, potassium and ash, but high in Btu. Data were collected in panels mined in a total of 10 seams with 82 panels in four seams and the remaining 13 panels in six seams. The first six seams (1-2, 2-2, 3-1, 3-2, 4-2, 5-2) were mined by the Shenhua Coal Group (the world’s largest coal company) and the #4-2, 5-2, 6R, 62, and 62R seams were mined by both the Shenhua and Yitai Coal groups. In each coal group, the sequence of mining was in descending order. For example, in Shenhua Group, the top seam 1-2 was mined first, followed by the 2-2, 3-1, 3-2, and 4-2 seam in that descending order. In Fig. 3, the top-down sequence of coal seams is listed from left to right in each coal mine group. All seams were near horizontal with dip angles less than 3°."

Jan 1, 2014

By Connor Langford, Murray Gant, Ken Massé

For public organizations, preparing accurate project cost estimates is a critical component in capital project planning. Project delivery methods provide a structured approach to moving projects through the design and construction lifecycle, and typically use cost estimates as key inputs at each stage to determine if the project will advance. As design stages can occur years or even decades before construction contracts are awarded, estimates need to make reasonable assumptions about how the work may be executed (means and methods) as well as potential future market trends so that appropriate values for material pricing, labour costs, escalation, and owner’s costs can be included. This process is challenging enough during stable markets, as historic trends can often be misleading and require a suitable understanding of economic factors to use appropriately. When you mix in the market volatility that has been observed since 2020, developing accurate project cost estimates becomes even more challenging. In cases such as this, having a structured approach to cost estimating that includes an adequate risk-based reserves cannot be overstated as it provides the basis for ongoing project decisions. This paper explores some of the historic and more recent market trends that have impacted key aspects of project cost estimates for capital project planning. It also provides recommendations on how to develop cost estimates for infrastructure projects, with examples from Metro Vancouver, which plans for and delivers regional-scale services to 2.6 million residents. A brief commentary on the use of escalation clauses in contracts is also presented.

Jun 13, 2023

By C. D. Harrison, J. W. Parkinson

This paper compares the ash slagging potential of Illinois No. 6 seam coal as raw coal, as commercially cleaned coal processed in a baum-jig plant, and as coal cleaned to a reduced ash specification at the Electric Power Research Institute&apos;s (EPRI) Coal Cleaning Test Facility. The comparison is based on ASTM ash fusibility data, a slagging index, gravity fractionation analyses of critical mineral matter compounds, and comparative pilot combustion tests. The first three grounds of comparison are laboratory data. The final comparison involves burning about 13.6 t (15 st) of each coal at Conoco&apos;s 4.40-kW/h (1.5 million-Btu per hr) test combustor. The evidence of these four comparisons indicates that lowering the ash specification of coal before combustion can significantly improve the ash slagging characteristics of Illinois No. 6 seam coal.

Jan 1, 1987

By Ihsan Berk Tulu, Haochen Zhao, Deniz Tuncay

This paper proposes a new method to estimate the percentage of load carried by the gob in underground coal mines using a new parameter that introduces the site-specific overburden geology. The new parameter was defined as the total strong layer thickness (tstr) that represents the strength and stiffness of the overburden with a single value. Twelve field measurement case studies from 11 different U.S. longwall mines with different overburden geologies were used to develop the new methodology. 2D numerical models of these case studies (and additional parametric runs with different panel widths) were verified against field measurements such as surface subsidence and stress. Statistical analyses using the model results were conducted for a loading model with the new tstr parameter as one of the variables. The new methodology was found to have a coefficient of determination (R2) of 85% when compared to the field measurements and the parametric models. The method was then tested for practical implementation for pillar design. The percentages of load carried by the gob as estimated by the new method were implemented into the LaModel program, that is commonly used in the coal industry. The results obtained from LaModel were compared to the available field stress measurements, and the new method implemented into LaModel was found to give successful results.

Jul 18, 2022

By S. A. McGhee

Introduction ASARCO&apos;s Ray Operations include an open-pit copper mine in the Mineral Creek Mining District of Pinel County. The district is located in east central Arizona, 132 km (82 miles) southeast of Phoenix, AZ, and 126 km (78 miles) north of Tucson, AZ. The mine lies 8 km (5 miles) north of the Gila River in Mineral Creek Valley, between the Tortilla Mountains to the west and the Dripping Springs Range to the east. The rich copper deposits of the Mineral Creek mining district were first noted by a US Army Officer in 1847. The Ray Copper Company was the first major operation in the area. The company was named after the Ray mining claim, which was one of the earliest recorded claims. After decades of sporadic and unsuccessful mining ventures, the Ray Consolidated Mining Company was formed in 1910. The company introduced one of the first successful block caving operations in the world. In 1933, the Kennecott Copper Corporation acquired the Ray Consolidated Mining Company and continued operation of the mine under the same name until 1943, when the property was renamed the Ray Mines Division of Kennecott. Underground mining continued until 1955, when the mine was converted to an open pit operation. In November 1986, ASARCO Inc. purchased the Ray Mines Division and related facilities from Kennecott. The purchase also included the Hayden concentrator and the Ray Smelter, located approximately 32 km (20 miles) from the Ray Mine. This paper summarizes the 54,400 tpd (60,000 stpd) in-pit crusher and overland-conveying system and the 24,200 tpd (30.000 stpd) copper SAG concentrator and tailings disposal system constructed at ASARCO&apos;s Ray Complex - Ray Operations. General description of facilities The Ray concentrator includes a sulfide SAG concentrator, a "relocatable" in-pit primary-crushing plant and overland-conveyor system, a concentrator tailings-disposal system and plant ancillary facilities, The major elements of the project include: • A relocatable Fuller-Traylor in-pit 1524-mm (60-in) x 2261-mm (89-in) primary gyratory crusher at the 442 m (1450 ft) mine elevation. The crushing plant has a nominal capacity of 54,400 tpd (60,000 stpd) of sulfide ore. • A 1524-mm (60-in) wide x 1253-m (4110-ft) long overland belt conveyor, which runs from the in-pit crushing facility to a transfer station serving both the Ray Concentrator and the existing Hayden concentrator railroad load-out facility. • A 1524-mm (60-in) wide x 152-m (500-ft) long stackerbelt conveyor, which delivers a nominal 27,200 tpd (30,000 stpd) of ore from the transfer station to a 23,600 t (26,000 st) live-capacity coarse-ore stockpile serving the Ray Concentrator. • A nominal 27,200-tpd (30,000-stpd) concentrator, including semiautogenous grinding, flotation, copper concentrate filtration and associated plant ancillary facilities. • A tailings disposal system. Flotation tailings are pumped from the Ray Concentrator to a 122-m (400-ft) diam. thickener, located 4.8 km (3 miles) southeast of the Ray Concentrator site. The thickener overflow is pumped to two 76.2-m (250-ft.) diam. concrete process-water reservoirs. The thickener underflow, at 45% solids, is pumped to a new tailings disposal site located at Elder Gulch. • An HDPE-lined temporary-containment area to collect material from Ray Concentrator plant upsets and local storm-water run-off from a 100-year, 24-hour rain event. •A reclaim-water system from the Elder Gulch tailing pond area to the Ray Concentrator. • A 610-mm (24-in.) diam. x 31.9-km (19.2 mile) long fresh-water pipeline from the Hayden fresh-water-well field system to the Ray Concentrator. The overall process design criteria for the new Ray Concentrator is based on a nominal throughput of 27,200 tpd (30,000 stpd) of ore at 90% plant availability. However, based on the maximum performance capacity of the installed grinding equipment, it may be possible to achieve a sustained operating level in excess of 36,300 tpd (40,000 stpd) when processing soft ores. The balance of this paper will cover the major process systems including:

Jan 1, 1995

By J. A. Organiscak

Longwall mining technological improvements have provided significant increases in productivity over the last 15 years. Longwall productivity is anticipated to continue to escalate with expanded application of automated equipment. Automation technology that will likely be adopted over the next 5 years is memory cut with shearer initiation of shield movement supervised by a couple of face workers. Operations using this technology will most likely relocate many production workers from the face to the outby gate entries and position several face workers outby the shearer, exposing workers to different health and safety risks. These changing risks are primarily related to worker relocation and expected increased production levels. Workers outby the face will most likely have less dust and noise exposure, but will be exposed to other safety hazards associated with outby equipment movement, materials handling, and gate entry ground movements. The face workers will most likely be exposed to higher respirable dust and noise levels generated by the equipment at elevated production rates. Methane gas emission is also expected to increase with faster mining rates. These operational changes and the control technologies needed to reduce redefined longwall worker hazards at semiautonomous longwall operations require examination to maintain the health and safety of mine workers.

Jan 1, 1996

By K Martin, C. J. Nelsen, J. L. Schutz, S. R. Maynard

Investigations in the Ortiz Mountains have revealed the relationship of igneous activity and gold mineralization to the Tijeras-Canoncito Fault System (TCFS). The northeast-trending TCFS passes through the southeastern part of the Ortiz Mountains where its principal structure is the asymmetric Ortiz Graben. Several fault blocks, containing up to 305 m (1000 ft ) of Eocene Galisteo Formation, comprise the graben that has up to 1220 and 610 m (4000 and 2000 ft) of stratigraphic separation on its southeast and northwest sides, respectively. Intrusions in the Ortiz Mountains can be subdivided into two petrochemical types: an older calcalkaline suite and a younger alkaline suite. The calc-alkaline rocks are characterized by extensive sill, dike, and laccolithic bodies of latite-andesite intrusives and at least one younger (?) granodiorite stock at Candelaria Mountain. The alkaline rocks consist of a large nepheline-bearing augite-monzonite stock, a latite-porphyry hypabyssal plug, the Ortiz diatreme (vent breccia), and trachytic-latite dikes radial to the diatreme. K-Ar age determinations suggest the older suite to be 34 +/-2.2 million years while the younger alkaline rocks range from about 30 to 26 million years. Gold mineralization in the Ortiz Mountains occurs in five distinct environments: brecciapipes, skarns, veins, porphyry-like stockworks, and placers. Lode mineralization is associated with the alkaline suite of intrusive rocks postdating the Ortiz diatreme and predating most of the trachytic-latite radial dikes.

Jan 1, 1991

By T. J. Close

The Silver Peak Range North Wilderness Study Area was deleted from the list of US Bureau of Land Management lands in Nevada to be considered for wilderness designation. This decision was based in part on the US Bureau of Mines mineral investigation of the wilderness study area which found indications of precious- and base-metal-resources. The study area lies between the Silver Peak and Dyer mining districts of west-central Nevada. The Bureau examined 13 mineralized sites, most of which were previously unknown and unclaimed. These sites are along two zones that cross the study area from the Silver Peak mining district to the Dyer mining district. The two zones transect a volcanic center of fractured and altered rocks that contain epithermal veins of quartz and calcite with gold, silver, and base-metals. At the surface, these veins are poorly defined. Exposures of the more than forty veins examined were as thick as 17 ft and as long as 1000 ft. Samples from these veins contained significant amounts of precious- and base-metals-as much as 0.02 oz per ton gold, 2.1 oz per ton silver, 1.0% copper, 2.6% lead and 0.4 % zinc. No vein large enough or of high enough grade to be classified a mineral resource was disclosed by the sample data. However, most do have indications of precious- and base-metal-resources at depth. Subsurface exploration of some of the veins is recommended.

Jan 1, 1995

By Ting Ren, Jon Roberts, Zhongbei Li, Ming Qiao, Jianming Wu

Spontaneous heating of coal continues to present a health and safety hazard in underground coal mines. The influence of seam gas composition on gas flow dynamics and distribution characteristics in the active longwall goaf has not been studied in-depth, and corresponding effective proactive goaf inertization strategies for preventing potential spontaneous heating from occurring have limited investigation. To advance this knowledge, an 80-m-height goaf model was constructed and developed based on specific conditions of an Australian underground coal mine, and onsite gas monitoring data was collated to verify base model results, which allowed for various scenarios of seam gas composition to be simulated and investigated with confidence. This study involved modeling five different gas composition scenarios for the goaf atmosphere, namely, 100% CO2 (case 1), 80% CO2 and 20% CH4 (case 2), 50% CO2 and 50% CH4 (case 3), 20% CO2 and 80% CH4 (case 4), and 100% CH4 (case 5). Simulation results show that O2 is primarily distributed at the middle and upper part of the CO2- dominant goaf model, while it is mainly layered at the floor level of the CH4- dominant goaf model. N2 is superior to CO2 in the goaf inertization for the CO2- dominant goaf model, whereas CO2 performs better than N2 for the CH4- dominant goaf model. The optimal inert gas flowrates for case 1 to case 5 are 1.5, 1.75, 0.75, 0.5, and 1.0 m3/ s, and the oxidation zone area is reduced by 55.76%, 67.21%, 58.04%, 78.17%, and 81.82%, respectively. The simulation results allow for increased insight and understanding of the gas distribution patterns in the active goaf with different seam gas composition and the development of corresponding proactive goaf inertization practices, thus minimizing potential spontaneous-heating-related hazards and improving mining safety.

Sep 26, 2023

By MAURICE SUNKPAL, Taghi Sherizadeh, Kutay E. Karadeniz, Dogukan Guner, Samuel Nowak

Despite numerous empirical, numerical, and hybrid studies conducted on the subject of coal rib failure, mine fatalities related to rib failures continue to occur at around 1.5 per year between 2009 and 2021. To date, a standard methodology for the design of coal rib supports that can accommodate the wide range of unique conditions found in coal mines in the USA has not been developed, forcing mine operators to rely on the trial-and-error process or industrial legacy practices for the design of coal rib support patterns. In this study, to better understand the support systems’ effectiveness, various rib bolting scenarios were investigated. A coal mass constitutive model is implemented to a distinct element method (DEM) code, and rib factor-of-safety (RibFOS) analyses were performed by applying strength-reduction for the coal matrix and explicitly modeled face cleats. Ribs with various overburden depths and mining heights composed of solid Banded-Bright coal (BBC) were considered in this study. Different scenarios such as rib bolt length and the number of bolts were studied to quantify the effect of primary rib support density on rib stability. As a result of the unsupported coal rib analyses, a decaying exponential relationship is proposed between the mining height-overburden depth and the RibFOS. The developed coal rib models clearly show the coal-rib bolt interaction and illustrate how the addition of rib bolts restricts the movement of the coal rib. The results reveal that the strength reduction method in DEM code with the coal-mass model can aid in the development of practical primary support charts, which can help in the rib support design process. In addition, an unsupported RibFOS cutoff is proposed, beyond which the addition of primary support cannot stabilize the failed rib structure.

Aug 5, 2023

By Éder Domingos Oliveira, Carlos Antonio Morais, Ruberlan Gomes Silva

The objective of this study is to assess the impact of different reagents, such as limestone, lime, magnesium oxide, and sodium hydroxide, in experiments carried out in the single purification step and in two consecutive purification steps by raising the pH of a rare earth sulfuric liquor with the aim to remove or reduce the impurity concentrations in the rare earth sulfuric liquor. The choice for the best purification condition was made based on the minimum loss of rare earth elements (REEs), reagent consumption, and residue generation. The exploratory experiments show that it takes place in the two consecutive purification steps, the first one consists in dosing the limestone pulp until it reaches a pH of 3.5 followed by an addition of a lime pulp reaching a pH of 5.0. Under this condition, the results were a total removal of Fe3+, PO4 3− , and Th4+ ions and a reduction of 99%, 87%, and 37% w/w in the Al3+, UO2 2+, and SO4 2− concentrations, respectively, in the purified rare earth liquor. Furthermore, the lowest REE losses (8.3% w/w) and reagent consumption (4.3 kg/m3 ) and also a low residue generation (7.5 kg/m3 ) were observed in this condition. Despite reaching similar results regarding impurity removal, the experiments done with the addition of limestone, lime, magnesium oxide pulps, and sodium hydroxide solution in the single purification step, where the pH was raised to 5.0, presented higher REE losses (64.9%, 42.5%, 44.8%, and 60.9% w/w, respectively) and a higher residue generation (43.2, 25.1, 11.1, and 13.6 kg/m3 , respectively). This occurred due to the co-precipitation of salts containing rare earth elements in their composition. The experiments conducted with limestone, lime, and MgO resulted in a higher consumption of reagents, while the same result was observed when NaOH was used (4.3 kg/m3 ). In the experiments carried out with the addition of magnesium oxide and sodium hydroxide, the respective purified rare earth liquors presented a high concentration of magnesium, sulfate, or sodium, which could impact the quality of the marketable rare earth salts, whereas the salts obtained under the best condition observed in this study seem to be amenable for use as raw material in an attempt to obtain rare earth products with an acceptable chemical quality.

By Charles H. Dowding

INTRODUCTION "On many projects, the tendency is to drop interest and support of the geological service as soon as it seems safe. That . . . is a short-sighted policy . . . It would be of further service perhaps to learn whether predictions were reasonably true to life." --C.P. Berkey, 1938 (3) This paper quantitatively compares predicted and encountered shear zone size and location and rock type for tunnels in the Colorado Mineral Belt. The Colarado Mineral Belt is composed of igneous formations with associated metamorphic rocks and faulting. As such, it represents the most complex of provinces for at-grade predictions (27). Shear zone and rock type data are assumed to be statistically homogeneous because of the common geology of the seven tunnels. It is often felt by geologists and engineers that the amount of information from which a geological model is created is so low that any statistical inferences are unstable. In other words, the addition of new data may drastically alter the means and variances suggested by the model. Therefore, predictions are rarely couched in quantitative statistical terms but modified with "probably," "most likely" or "possibly." Comparison of predicted and encountered data from past geological models will permit the "probably&apos;s" to be quantified and distilled from the art of geological prediction. To date, two other studies of the validity of predictions have been made (26 and 16). Together, these two studies indicate that

Jan 1, 1976