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By Angus Campbell, Michael J. Gobla

Numerous techniques for treating, controlling, and preventing acid rock drainage have been applied at the Summitville Mine Superfund Site. Challenging aspects of the remote mine site include the wide-spread occurrence of acid-generating soils and rocks, extensive surface and underground mine workings, and a cold and wet climate. Water treatment was an immediate necessity when the Government took control of the abandoned site in December of 1992. Subsequent reclamation activities have emphasized prevention and control of ARD to minimize future water treatment requirements. A combination of conventional, innovative, and experimental methods are being applied to successfully mitigate ARD at Summitville.

Jan 1, 2000

By Kathleen S. Smith, Katherine Walton-Day, James F. Ranville

Four different scales of observation were used to evaluate the potential effects of a fluvial tailings deposit on water quality along the flood plain of the upper Arkansas River south of Leadville, Colorado. First, we collected surficial material and subjected it to batch water-leaching test. Second, we excavated and leached an intact eight-inch diameter core. Third, we examined the water quality of the shallow ground water beneath the fluvial tailings deposit, and fourth, we monitored water quality along a 5-km reach of the adjacent Arkansas River. Leaching of surficial samples indicates that there is a reservoir of readily water-soluble material yielding elevated metal concentrations and high acidity. However, there are minimal measurable water quality effects of the fluvial tailings deposit on the adjacent reach of the Arkansas River.

Jan 1, 2000

By R. L. Guerguerian

Nowadays, most grinding mills driven by a wrap-around ring motor are operating successfully. Some of the earlier problems could be attributed to the lateral stiffness and stability of their bearings. As a result, modifications to the bearings included the rearrangement of the shoes, or the addition of more shoes, closer to the horizontal centerline. This technical paper reports a study of the effects of bearings on the lateral stiffness of grinding mills driven by a wrap-around ring motor. The discussions cover the design of the four shoe trunnion bearings and examine the effects of the angular location of the shoes.

Jan 1, 2000

By E. J. Beckman, R. M. Enick, C. Shi

A novel liquid-liquid separation for the recovery of free or liberated gold from mixtures of fine particles was evaluated. Two inexpensive and environmentally benign fluids were selected for the study, water and carbon dioxide. The separation, which is conducted at 295 K and at the vapor pressure of carbon dioxide (6.0 MPa), is based on differences in wettability between the precious metals and other minerals. Contact-angle results indicated that, in the presence of water and liquid CO2, gold is slightly hydrophobic. The addition of CO2-soluble fluoroalkyl thiols or f uoroetherthiols increased the hydrophobicity of gold exposed to water and CO2 to a greater extent than alkylthiols. Minerals, including quartz, pyrite and magnetite, were hydrophilic. During the separation, an aqueous slurry of fine mineral and gold particles was mixed with liquid carbon dioxide. Pure gold particles (-325 mesh) were found to agglomerate at the H2O-CO2 interface. The minerals tended to remain in the aqueous phase. Despite these promising preliminary results, very poor gold recoveries were obtained when applying the procedure to an Australian gravity concentrate. This was attributed to the native gold particles in the concentrate being either too large, agglomerated in slimes or coated with minerals. Although this particular application was unsuccessful, this water-CO2 biphase technique may be applicable for other separations that require the removal of very fine, hydrophobic particles from an aqueous slurry.

Jan 1, 2000

By T. L. Owen

Since 1993 Cyprus Amax has brought $2.5 billion dollars of greenfield and expansion projects into production, taking it from a mid-sized domestic minerals company into a major international minerals organization. The near simultaneous development of these multiple mineral projects in different locations around the world provided the opportunity for Cyprus Amax to develop a formal project management approach based, in large part, on an outsourcing philosophy. This formal project management system along with its outsourcing philosophy has served the growth agenda of Cyprus Amax extremely well. These preceding factors, coupled with the in-house retention of a core project group that fully understands the breadth of skills and abilities needed to undertake development of multiple large projects successfully, have been the cornerstone of Cyprus Amax’s project development success.

Jan 1, 2000

By Monica Pavlik, Thomas Wildeman

Water from the Forest Queen mine adit near Silverton, Colorado drains into a natural wetland. Because the pH of the water averages 5 and the iron concentration averages 18 mg/L, it was thought that the wetland might naturally treat the water. Of most concern with respect to the aquatic environment is zinc whose concentration averages 0.60 mg/L. Starting in October 1997, the surface waters, ground waters in the peat substrate, and the sediments in the wetland were sampled and analyzed four times over the course of four months. The adit water primarily remains as surface water where Fe, minor amounts of Al, and no Zn are removed. After the adit water enters the peat, then it is found that the pH rises to 5.8-6.5 and sulfate is reduced. The removal of Zn and A1 is caused by these two changes. However, Fe in its reduced state is quite soluble and may be remobilized in the reduced environment of the peat.

Jan 1, 2000

By W. Douglas Gould, Mei-Lin K. Stichbury, Jeffrey G. Bain, Blowes David W.

The mechanisms of release of arsenic in gold mine tailings were investigated. The highest concentration of dissolved As (75 mg/L) was observed near the base of the tailings impoundment, in close association with a peat layer. Elevated concentrations of reduced iron and hydrogen sulfide were also measured at the base of the impoundment. High numbers of iron-reducing and sulfate-reducing bacteria were detected at depths within the impoundment which correlated with dissolved As, Fe and H2S. The data presented in this paper suggest that arsenic is released from the tailings by bacterially-mediated reductive dissolution of As-bearing iron minerals.

Jan 1, 2000

By Harry H. Posey, John Woodling, Miriam L. Renkin

Natural acid drainage is generated from pyritic rock underlying 17 percent of the upper Alamosa River basin. About one-third of these acid producing rocks have nil carbonate buffering capacity; there the streams carry significant acid plus dissolved Al, Cu, Fe, and Zn. In part of the basin, aquatic life is limited by the natural acid drainage. In the four miles where the Alamosa flows through pyritic rock the river grows toxic to trout. Inhospitable conditions continue downstream for at least another four miles. The waters become refreshed, naturally, through metal dilution, metal oxide and hydroxide precipitation, and acid neutralization. Water quality fluctuates in seasonal cycles. Dissolved metals and acid, which are generated year-round by weathering, are stored over winter in the unsaturated zone in the retained water and in soluble metal- sulfate minerals that form by evaporation of acid-metal waters. Seasonal discharge variations cause metal concentrations and pH to shift in the trunk stream; the acid drainage source streams, however, shift only slightly by season. In early spring, metal concentrations and metal loads increase as metals and acid are flushed from the unsaturated zones by melting snow. Peak metal loads occur at this time, and precede peak flow by up to two months. Other metal load peaks occur during peak flow and monsoon flow, even though metal concentrations are diluted at that time by precipitation. In late spring and thereafter, discharge of neutral pH water wanes, so trunk stream pH falls and metal concentrations return to previous high levels. Metal concentrations appear to be low from November through January when dilution from precipitation is lowest, but rise in February to near peak yearly concentrations. In years with high monsoonal flows, metal-laden waters apparently flush from the unsaturated zone and metal concentrations remain low from about October through January. In years with low monsoonal flows, however, metal concentrations in October and November at least are higher.

Jan 1, 2000

By G. J. Olson, K. S. Noah

A combined physical/biochemical process for the precombustion removal of 13 inorganic hazardous air pollutant (HAP) precursors, i.e., Sb, As, Be, Cd, Cr, Cl, Co, F, Pb, Hg, Mn, Ni and Se, from coal was tested. Biochemical processes for removal of HAP precursors from coal potentially offer advantages of deeper cleaning, more specificity and less coal loss. The slurry column is a second-generation process for the beneficiation o f fine (60-mesh x µm coal by a combination of physical separation of mineral matter and biooxidation of pyrite. Sixty-seven percent removal of pyrite from a 60-mesh Pittsburgh #8 coal was achieved at a 35% (w/w) slurry concentration and a five-day reactor residence time. Ninety percent of the heating value of the feed coal was recovered. Among the HAP precursors of most concern, over half of the Se, As and Hg were removed from the feed coal. From 40% to 70% of most HAP precursors were removed from the feed coal. Hg in the feed coal was reduced from 0.12 to 0.054 ,µg/g in the product coal, while waste coal contained 0.24 µg/g.

Jan 1, 2000

By S. K. Kawatra, T. C. Rao, J. P. Barnwal, Durga D. Patil

Coal macerals differ widely in their surface properties and in their hydrophobicities. Therefore, it is necessary to study the flotation time dependence of coal macerals using varying concentrations of various frothers and collectors. In the present study, froth flotation is used to explore the possibility of segregating coal macerals based on their relative rates of flotation. Petrographic analysis of the various macerals in the concentrate were carried out, and the results are expressed in terms of the recoveries of various maceral groups and mineral matter. Results show that it is possible to recover a good volume of the reactive macerals without mach loss of calorific value.

Jan 1, 2000

Most statistical and geostatistical methods of re-source and reserve estimation work extremely well for Normal (Gaussian) well-behaved information. However, most interesting mineral deposits exhibit far from this idealistic distribution of values. It seems that the more valuable the mineral, the less likely the data are to have a Normal distribution. Values tend to be "positively skewed" with a long tail into the high values. Using averaging techniques, such as inverse distance or ordinary kriging may result in consider-able overestimation of grades and tonnages unless such values are cut or otherwise modified. This paper presents some real case studies where distributions are (a) highly skewed and (b) the product of multiple phases of mineralisation. Practical methods are presented for solving such problems including combinations of indicator and log normal kriging methods. The emphasis of the presentation is on developing operational methods which can be used on project evaluation or grade control in producing mines.

Jan 1, 2000

By Yannis Faitakis, Brenda M. Wright, Gail Powley, Mark Hamblin, Randy B. Paine

A major problem in the ore extraction process is the high degree of variation in the mix of materials that make up the mined ore. The mix of materials makes it extremely difficult to characterize and predict the behavior of the ore when it is processed. The Quality Production Database (QPD) tool was successfully used in order to predict and transfer information regarding the quality characteristics of the ore being delivered to the extraction and hydrotransport unit operators. This paper describes the use of QPD in the prediction of various ore characteristics at the Syncrude Canada Ltd. processing facility.

Jan 1, 2000

By J. F. T. Agapito

OCI Wyoming mines two flat-lying trona seams that are 3- to 3.5-m- (10- to 11.5-ft-) thick, about10 m (33 ft) apart and 250-m- (820-ft-) deep at its Big Island Mine in Wyoming. Continuous miners and a yielding-pillar system have contributed to improvements in resource recovery and productivity. The use of yield pillars minimizes the stresses transmitted from the upper to the lower seam. However, yielding must not impact the good, long-term stability needed to prevent subsidence for a large portion of the mine beneath the Green River channel.

Jan 1, 2000

By J. L. González-Chávez, A. Ballester, M. L. Blázquez, F. González

In recent years, the bioleaching of sulfidic raw materials has been of great interest. However, the application of this biotechnology is now very limited for many different complex reasons. The mechanism of the chemical and electrochemical reactions taking part in the process is not well understood. The application of electrochemical techniques is useful in its elucidation. Among the common sulfides, galena has been studied very little with respect to its behavior during bioleaching. Therefore, the electrochemical evolution of massive electrodes of lead sulfide in the presence and absence of' a mixed culture of mesophilic microorganisms was investi¬gated by the application of potentiometry, anodic and ca¬thodic polarization and cyclic voltammetry. The agitation rate, the use of pH control and the composition of the nutrient mediums did not have any significant affects on the oxidation of galena. However, the temperature (25 'to 45 °C), the scan rate (4 to 100 mV/s) and the acid used to adjust the pH were significant variables that influenced sulfide oxidation. There¬fore, the peak (600 to 1,000 mV) corresponding to the oxida¬tion of sulfide ions from the mineral was only detected in the presence of a complexing anion of lead. In the presence of bacteria, the peaks corresponding to galena oxidation de¬creased and, at the same time, new peaks appeared both during the oxidation at -300 mV and during the reduction of the mineral surface at 150 and -300 mV. These signals were more important when the attack time increased. The rest potential of bioleached mineral increased with an increase in leaching time, which was related to the electrochemical transformation of the galena surface.

Jan 1, 2000

By Daniel Hodouin, Antoine Berton

Mineral processing plants are monitored and controlled using measurements that are usually processed by on-line material balance calculation techniques. However, gross errors, due to sensor biases or failures, may corrupt all the process variable estimates. On-line gross error detection methods are required to ensure efficient mass balance evaluation. In the proposed approach, material imbalances and raw measurement corrections are tested by statistical techniques designed to detect and isolate sensor problems.

Jan 1, 2000

By Jerry Demchuk, Allan Flemming, Stephan Day

Luscar Ltd. is currently developing open pit mining plans for the Telkwa Coal Project. Most waste rock is predicted to be non-acid generating but a proportion (less than 20%) is potentially acid generating. The waste management plan includes in-pit and ex-pit disposal of blended and till-capped waste rock, segregation and in-pit encapsulation of strongly potentially acid generating materials, and in-pit underwater disposal of coarse and fine tailings. The paper will present the steps used to design the waste management plan including the development of geochemical design criteria using various tests and theoretical and practical knowledge of waste behaviour.

Jan 1, 2000

By V. B. Achanti, A. W. Khair

This paper deals with the effects of various bit geometric parameters on the failure characteristics of rock material. Improving the rock-cutting efficiency of continuous mining machines has proven to be an interesting research topic during the last few decades. In the current study, an automated rotary rock-cutting simulator, duplicating a continuous miner, was used to study these parameters in the laboratory. The improvement of bit performance in terms of its life, cutting efficiency, dust production and energy consumption has drawn widespread attention. Research has demonstrated that optimizing bit parameters can result in efficient fragmentation of rock. Indiana limestone rock material was used in this study. The bit tip angle, bit tip size, bit spacing, depth of cut and cutting velocity of the rotary drum were varied to investigate the failure characteristics. The cutting pressure, penetrating pressure and the depth of cut were monitored on the simulator during the cutting process. Airborne dust and settled dust were measured for each experiment. Then, the specific airborne dust and specific energy were determined for each type of bit. Triaxial tests were carried out to correlate the failure angle of the rock in the static case to the dynamic cutting process failure. The physical and mechanical properties of the rock were also determined to assess their influence on the wear characteristics of each bit.

Jan 1, 2000

Environmental conflict management approaches and procedures have been used to successfully address and resolve a variety of issues, problems, and conflicts related to the extraction of natural resources. Companies in the mining industry have been involved in a range of controversies over planning, siting, permitting, environmental, and enforcement issues. Through the use of conflict resolution case studies, this paper will present approaches and procedures that can help companies and other involved parties to successfully manage and resolve differences in a mutually acceptable manner.

Jan 1, 2000

By Osvaldo Bascur, Laurent Garrigues, Nouna Kettaneh, Svante Wold

The chemical, oil, semiconductor, mining, and paper and pulp industries, as well as most other modern industries, are rapidly expanding the range of measurements used to characterize raw materials, process steps, intermediates, and final products. In addition, process variables such as temperature, pressure, and flow become more and more numerous, providing extra information on the state of the process. However, no matter how many sensors are added, the underlying sources of variations that drive the process behavior remain constant. On the other hand, the measuring frequency of these data has increased from once a day or once an hour to once, ten, or even hundred times a minute. This gives masses of data that are swelling in both directions (more variables and more observations). These data need to be properly stored, managed, and analyzed to provide diagnostics about the state of the process as well as an understanding of the relationships between different parts of the process and the product properties. Projection methods such as PCA (principal components analysis) and PLS (projection to latent structures) compress process data to informative summaries of the original variables. These can be shown on line, providing an efficient, graphically oriented suite of diagnostics regarding the "health" and performance of the process. The power of these methods is illustrated by two examples of industrial data in the mining industry.

Jan 1, 2000

By N. Parra, M. N. Herrera, T. Vargas, B. Escobar, C. Gonzalez

originally published May 1998, Vol. 15, No. 2, pp. 15-1 9 Discussion by G. Rossi, University of Cagliari Reply by T. Vargas, University of Chili

Jan 1, 2000