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By John Smyth

Mining through in panel entries and the full face recovery method has been successfully practiced at U.S. Stwl, Mine 50. Suppat of the cut-through entries and recovery room is critical. Traditionally, concrete crib or fly ash cement backfill has been utilized. However, these traditional methods are not feasible at Mine 50 due to the difficulties of the plow face mining through these types of support. Recent development of new cable support systems provides an option for cut-through entry support. Mine 50 and Jennmar Corporation personnel have worked together to design and apply the cable systems in the cut-through entries and full face recovery room to eliminate standing support. To date, a number of full face recovery rooms and cut-through inpanel entries have been successfully mined. The results indicate that the cable systems combined with high capacity shields, have provided sufficient capacity to support the roof. Utilizing the Jennmar Finite Element Analysis (JFEA) computer program (Stankus and Guo, 1996), an analysis of the stress and roof deflection changes as the longwall gradually cut through was conducted. From the finite element analysis data, a supplemental support plan was designed. The history and experiences at Mine 50 are presented. Based on the case experiences and modifications made to the finite element analysis, an improved design criteria for future use has been formulated.

Jan 1, 1998

By Zhang Chuanfu, Tan Pengfu

"A thermodynamic model is developed to simulate nickel flash smelting process. In the nickel flash furnace, oxidation of concentrate occurs at one end, and reduction of slag occurs at the other. The model makes use two zones, namely the reaction shaft/settler zone and the appendage zone and accounts for 6 phases (matte, slag, silica, magnetite, Cu-Ni alloy and gaseous phase), 13 elements (Ni, Co, Cu, Fe, S, 0, N, C, H, Si, Al, Mg and Ca) and 33 chemical components in nickel flash smelting system. The compositions of matte, slag and gaseous phases in equilibrium are calculated by using the data of free energies of formation and activity coefficients of components. Two nickel sulfide species are used to allow for the modeling of sulfur-deficient mattes. The model predictions are compared with the known industrail data from Kalgoorlie Nickel Smelter, and excellent agreement is obtained. The model can be a very useful tool for monitoring and optimizing the actual industrial operations of nickel smelting process. The distribution behaviors of Ni, Co, Cu, Fe, S and 0 in the nickel smelting furnace depend on the process parameters such as smelting temperature, volumes of air, the content of the elements~ charge and oil.1. IntroductionThe nickel flash smelting furnace essentially consists of a reaction shaft where nickel sulfide concentrate is partially oxidized with air, a settle zone where matte and slag are allowed to separate, and a slag cleaning end where coke is added to provide for the reduction of the oxidized nickel from slag, and electrodes are used to provide heat.The theoretical model to consider a mass balance for copper flash furnace is developed by S. Goto and R. Shimpo[1][2J. However, this can not be true for nickel flash furnace as a whole since oxidation of concentrate occurs at one end (in the reaction shaft/settler), and reduction of slag occurs at the other (in the appendage). Despite these limitations, an acceptable pseudo-thermodynamic description of the furnace can be achieved using essentially two zones, namely the reaction shaft/settler zone and the appendage zone. Compositions of gas, slag and matte in two zones are calculated."

Jan 1, 1998

By R. R. Klimpel

The industrial processing of ores containing precious metals such as gold is generally very mining site specific, e. g. McQuiston and Shoemaker (1985), vanZyl et. a1. (1988), Fuerstenau and Hendrix (1990), and Hausen et. a1. (1990). The variety of various mineral processing techniques employed is extensive and includes size reduction, size classification, gravity separation, roasting, cyanidation, chemical and/or bacterial leaching, ion exchange and/or solvent extraction, and froth flotation. Gold occurs in the earth's crust on the average in very low concentration estimated by various sources to be between two and five parts per billion. For a specific ore deposit to be considered as an economic source of gold, generally a concentration of near one part-per million (one gram / Mton) or more is required. From a mineralogical viewpoint, gold often occurs in its native or free form. However, it can also occur as gold compounds of telluride, antimony, and selenium contained within either sulfide minerals such as pyrite, arsenopyrite. and pyrrhotite or, to a less extent, within silicate, oxide, and carbonate minerals. In many locations, alloying of gold with silver is found. The optimal processing method for recovering gold is determined by many factors such as the mineralogy of the gold bearing minerals as well as the associated mineralogy of the gangue minerals, the type of liberation profile of the gold bearing minerals upon' size reduction, and the particle size of the gold itself. Free or native gold particles can vary in size from the extreme of large nuggets to very finely disseminated gold associated in a complex sulfide mineral matrix. Typically free gold particles of several hundred microns or larger are efficiently recovered by one or more of a number of gravity based techniques due to the large specific gravity differential of gold (19.3 to 15) versus typical gangue minerals (5 to 2.7). When gold is associated with a sulfide (usually pyrite) matrix, historically most industrial plants involving size reduction and subsequent liberation have operated in a size range of 50 to 80 percent less than 75 microns. Grinding finer than this has been normally not economical unless the ore has a high gold content in the feed ore.

Jan 1, 1998

The removal of tritium from tritiated water (-0.5 µCiIL) was studied by metallothermic reduction using aluminum. The influence of the three variables namely the aluminum powder amount, the NaOH concentration and the reaction time has been studied on the tritium activity reduction. The experimental results and statistical analysis showed that more than 85% of tritium can be removed from the tritiated water. Further work on the tritium recovery as well as efforts to totally decontaminate water by incorporating a cryogenic concept is currently pursued.

Jan 1, 1998

By D. E. Woolley

The rate of reduction of iron oxide from calcia-silica-alumina slag by carbon in liquid iron has been measured over the temperature range 1400-1600°C by monitoring the rate of carbon monoxide (CO) evolution. Slags containing ferric iron have been used in order to study the reduction of both ferric and ferrous cations. Results show that ferric iron is reduced before ferrous iron, so that the ferrous iron concentration increases initially. It is also shown that the rate constant, k, decreases at low reaction rates, or, equivalently, at low concentrations. The authors conclude that the reaction occurs in two periods. During the first period, ferric iron is reduced to ferrous iron. During the second period, ferrous iron is reduced to metallic iron, and the rate-limiting step during the second period is the mass transfer of ferrous cations in the slag phase to the slag-metal interface.

Jan 1, 1998

By Jinsheng Chen

The major functions of longwall headgate entries are to provide access ways to the outby submains or mains for coal transportation and to the longwall face for fresh air and for transporting men and material during longwall operations. Any roof control problems such as cutter roofs or roof falls in the outby headgate entries could result in significant production delays to the longwall face and may be a threat to miners' safety Under a thinly laminated immediate roof and a high horizontal stress field, even a longwall headgate entry that has an angle of less than 45 degree to the maximum horizontal stress may experience roof deterioration in the outby headgate if the longwall panel mining sequence and retreat direction are not properly considered. This paper attempts to analyze the causes of the roof control problems experienced in the longwall gate entries at our Cumberland and Emerald mines in Pennsylvania and to determine the optimal longwall panel mining sequence and retreat direction for the future mining area at Cumberland

Jan 1, 1998

By W. H. (Bill) Jay

The destruction of cyanide creates a significant impost on the financial returns of gold mines. These losses increase substantially when ores containing cyanide-soluble copper are treated. Failure to remove or destroy free or WAD cyanide before it is discharged into tailings dams has, on a number of occasions, led to significant fish, bird and animal deaths. Thus, the retention of cyanide within the leach circuit and the recovery or removal of stable metal cyanide complexes needs to become standard practice for all gold mining operations. Furthermore, reducing cyanide purchases will minimise the quantity of cyanide transported to the mine site thereby reducing the opportunity for spillage of this chemical. Many different physical and chemical methods have been investigated for the removal of cyanide from process solutions. All cyanide destruction methods create a financial impost on the economic viability of the gold mine. To reduce these costs, the recycle of cyanide and the economic recovery of the metals solubilised by cyanide is of prime importance. The alternative methods currently in use, or under consideration for the treatment of copper cyanide, entail high reagent costs, produce the recovered metal in a contaminated form and require the safe handling of hydrogen cyanide. These processes will be briefly discussed within this report Environmental and financial benefits are enhanced by recent laboratory and pilot plant studies conducted by Oretek Limited. The Oretek CPC process for the recovery of copper and the recycle of cyanide from copper cyanide-containing solutions does not require pH adjustment to the alkaline cyanide leach conditions. Copper ions are coordinated to a water-soluble and/or an organic soluble polychelating agent under alkaline conditions and the cyanide ions are displaced Membrane separation, or phase separation of the polychelated copper from the cyanide ions enables the cyanide ions to be recycled and the copper to be directly electrowon from the polychelating polymer. The polychelating polymer is then recycled. Ion exchange resins and solvent extraction systems which may be incorporated into the above process will also be discussed in detail.

Jan 1, 1998

By J. K. Wolski

This paper addresses the effects of using jet fans as booster fans in mine ventilation networks. A method was developed to determine the pressure generated by jet fans using the momentum theory. The influence of a reduction cone and other ventilation parameters on the jet fan pressure was analyzed. Verification experiments conducted in the Waldo Mine are described. Examples are given to demonstrate the conditions for the effective use of jet fans.

Jan 1, 1998

By Shane Andrews, Gustavo Vasquez, S. K. Varma

"The effect of solutionizing time on the corrosive wear behavior of 2014 aluminum alloy has been studied using the impact and continuous mode of scratching techniques. The transient currents (TC) evolved during the scratching of the alloy shows a linear dependence between the TC and the solutionizing time. Higher TC values at longer solutionizing time may be associated with the changes in the concentration of quenched-in vacancies, grain sizes and dislocations generated during scratching. These factors can either create (a) anodic sites or (b) pitting corrosion resulting in the generation of transient currents. The results have been compared with the similar study carried out for 6061 aluminum alloys. This 6061 aluminum alloy shows similar behavior but the rate of TC generation per unit solutionizing time is much lower than 2014 aluminum alloy. The morphological changes in the impact scratches and the TEM investigation in the scratch have been presented in this paper.IntroductionThe technique of studying corrosive wear of composites of 6061 aluminum in the monolithic and reinforced forms has been reported in the literature [1]. Two modes of scratching, consisting of impact and continuous, in a corrosive environment indicate that the composites, containing 0.10 and 0.20 volume fractions of alumina particles (VFAP), have higher corrosive wear rates than the monolith. A graph between the transient current (TC) generated during the impact scratching as a function of solutionizing time at 540°C indicates linear relationship between them. A similar slopes for the composites were observed and the TC values were less for the composite containing lesser VFAP."

Jan 1, 1998

By M. F. Almeida

"Due to the randomness of all factors influencing the sintering operation, a two-stepped procedure is proposed to find the best way of using stocked fines at a plant producing Fe-Mn alloys for the steelmaking industry. The approach is based on the following: (1) predict the result of the sintering operation by establishing the best multilinear regression model using some of the characteristics of the loaded material; and (2) find the best solution under a minimizing cost criteria by solving a linear optimization problem using the regression equation plus constraints on the feed and product. IntroductionSome tests carried out using 20% to 30% of sinter in the material loaded into a 60 000 KVA Tysland-Hole electric furnace producing Fe-Mn alloys for the steelmaking industry indicated: (1) a meaningful decrease in the off-gas temperature and, consequently, a better energy use due to the material higher porosity; (2) more uniform heat distribution as a consequence of the electrode reaction zone enlargement; (3) an improved furnace control resulting in a smoother operation; and (4) a decrease in gas production facilitating the off-gas treatment. For some years, this plant used only the coarse fraction of the Mn ores, thus stocking all the received and own-generated fine particles. In view of the mentioned results, a strategy for increasing the use of stocked fines was formulated, including a step where it was necessary to decide which components and respective quantities should be used in the blends to be sintered (Almeida, 1984).It is well known that several factors affect productivity and energy consumption in sinter production, also influencing the product quality. Raw materials characteristics, namely chemical and size composition, affect permeability to gases and may or may not allow a deeper bed. In general, finer ores decrease permeability, increasing electricity consumption by fans, but due to their higher specific surface area, react more completely with other components in the mixture. For coke granulometry, a compromise must be obtained in order not to burn it too quickly nor to widen the flame front, therefore decreasing productivity. Decreasing coke in the blend also acts in sinter bonding, decreasing its consistency and increasing crushing and return fines. Moisture addition also influences components mixing, pre-agglomeration, bed permeability and, consequently, sintering productivity. Therefore, optimum conditions must be established for both a given sintering plant and the components in the feed (Dawson, 1993)."

Jan 1, 1998

By James M. Kramer

This paper introduces an analytical approach for the determination of the vertical stress in the chain pillar system between two adjacent longwall panels. The development of this approach is based on the principles of fracture mechanics and superposition. Some empirical formulae have also been incorpomted into the development of the mathematical model. The mine entries and longwall gobs are treated as Mode I cracks in an infinite plate while the resistance of gob material and the characteristics of the pillar yield zone are considered as the distributed forces on the surface of the cracks. An user- friendly computer program has been developed to facilitate the calculation involved in this task. This approach is as accurate as the numerical analysis methods but requires much less expertise and computer hardware and software to apply

Jan 1, 1998

By A. Perry

Latin America is in the path of economic growth characterized by increased privatization, joint-venture projects, and reduced trade barriers. Privatization is changing the industrial operating mode from Government-owned/Government-operated to a privately-owned/government-regulated regime. The establishment of joint ventures, such as in construction and management of infrastructure, energy and mining projects, and deregulated industries (electricity/gas/ telecommunications), is now a common practice in the region. These changes, coupled with the growing awareness of environmental protection issues, have led to a sincere effort on the part of the countries of Latin America to establish reasonable environmental regulations and controls (RERCs) for all industries, including mining and energy, for the benefit of present and future generations. However, RERCs require further consideration of many factors with respect to environmental, geologic, economic, and social impacts in the region. The process must find a balance between the need to sustain profitable operations and the need to adequately protect the environment. While striving to find a balance between continued industrial profitability and environmental protection, the RERCs must be scientifically sound, pragmatic, flexible, and enforceable. There has been worldwide attention focused on the environment, and international symposia have been held on such issues as global warming, water pollution, air pollution, and hazardous wastes. Organizations such as the United Nations (UN) and the Organization of American States have performed rather extensive studies on the environment for various industries and activities, and have developed some broad general plans to address environmental concerns. This technical information is available for the asking, and should be considered a starting point for countries embarking on the passage and enforcement of their own RERCs.

Jan 1, 1998

By A C. Robertson

Studies by Tennent, Isokangas Pty Ltd (TIP) have indicated that underground quarrying of backfill may be a cost competitive option for providing backfill for specialised situations in underground mining. Situations where suitable bulk fill material may not be available on the surface, and where the total cost of setting up a fill distribution system are prohibitive, could favour the mining of fill material underground adjacent to the stopes being mined. Considerations include environmental impact, scheduling, surface constraints and total costs. The examples quoted in this paper, and the case studies are based on the authorsÆ personal observations and experience.

Jan 1, 1998

By N. Shi, T. C. Lowe, S. J. Zhou, M. L. Lovato, Y. T. Zhu, J. A. Valdez, W. R. Blumenthal, M. G. Stout

"A major problem of short-fiber composites is that the interfaces between the fiber and matrix become a limiting factor in improving mechanical properties such as strength. For a short fiber, a strong interface is desired to effectively transfer load from matrix to fiber, thus reducing the ineffective fiber length. However, a strong interface will make it difficult to relieve fiber stress concentration in front of an approaching crack. Stress concentrations result in fiber breakage. We report in this paper an innovative approach to overcome this problem: reinforcement morphology design. Short-fibers with enlarged ends are processed and used to reinforce a polyester matrix. The initial results show that the bone-shaped short-fibers produce a composite with significantly higher strength than can be attained with conventional short, straight fibers.IntroductionThese interfaces between the fiber and the matrix in short-fiber composites play a critical role and, in many cases, become a limiting factor in improving such mechanical properties as strength and toughness of the composites (1-4). For a short fiber, a strong interface is desired to effectively transfer load from matrix to fiber. A stronger interface can reduce the ineffective length at both ends of the fiber and, therefore, can increase the effective length that carries load (5-9). However, with a strong interface it is difficult to relieve fiber stress concentration -in front of an approaching crack; and such stress concentration can result in fiber breakage (10, 11). This effect is particularly severe for ceramic matrix composites, because of their low matrix toughness and lack of plasticity. Even for a composite with a highly ductile matrix, such as plastics, too strong an interface may still cause successive adjacent fiber breakage and subsequently reduce composite toughness (1, 11). On the other hand, a weak interface significantly decreases the fiber load-carrying length due to ineffective load transfer and complete fiber interfacial debonding and pullout during loading. A compromise in the interfacial bond strength will also compromise the load-carrying potential of short fibers."

Jan 1, 1998

By E. Oshilna

The Mitsubishi process has many advantages pertaining to economical and environmental matters. These advantages have led to the installations of the Mitsubishi process in constructing new smelters: The Mitsubishi process utilizes highly oxygen enriched blast air and uses a special lime slag in the C?furnace. These characteristics change the . distribution of Impurities from other processes which use P.S. converters, Recently an Increased amount of secondary materials which contain impurities Is being treated at Naoshima Smelter. In order to cope with an Increment of the Impurities load and maintain the cathode quality, many Improvements have been Implemented. This paper discusses the impurities behavior In the Mitsubishi process and describes the measures taken to treat an Increased ?amount of secondary materials:

Jan 1, 1998

By S. M. Smouse

Total world energy consumption is projected to continue its strong growth of recent years. Because coal is the most abundant fossil fuel, it will likely remain an important energy source, particularly for power generation, into at least the early years of the next millennium. Clean coal technologies are available today that can economically reduce air pollution, primarily SO2 NOx and particulates, and for the higher efficiency technologies, CO2, from power generation. U.S. Department of Energy analyses show that the adoption of clean coal technologies could decrease carbon emissions worldwide while creating a strong export market with attendant creation of jobs in the U.S.

Jan 1, 1998

By K. Lapakko

Kinetic tests results are influenced by methodological variables, including test duration and mine waste particle size. Some samples tested produced neutral drainage in kinetic tests for more than two years prior to drainage acidification. The potential for long "lag times" can be assessed based on the mine waste mineralogy. The lag time duration can be estimated using this mineralogy in conjunction with dissolution rates observed in the kinetic tests. The influence of particle size on the drainage quality is dependent on the variation of the availability of acid-producing and acid-neutralizing minerals with particle size.

Jan 1, 1998

By Jason M. Ryan

"Along with recent advances in computer technology have come cost-effective systems desiiedto evaluate fragmentation distributions through digital images of particles. In mining operations andmineral processing plants, important data from these systems is obtained through monitoring sizedistributions at key stages of the comminution process. Blast engineers apply this technology as atool for the validation of empirical fragmentation models so that predicted results are more meaningful."

Jan 1, 1998

A comprehensive understanding of the effects of autoclave configuration (batch, semi-batch, continuous) on the residence time necessary to achieve a target conversion is a prerequisite for design of commercial scale autoclaves. Particle size distribution, mineral and reagent concentrations, temperature and mixing also influence the conversion. This paper outlines the bases of using test data to predict performance of commercial scale autoclaves. Recommendations for coordinating test program design with selection of scale-up method are provided. Examples are given to illustrate the different levels of engineering effort needed to meet corresponding levels of design optimization and accuracy.

Jan 1, 1998

By P O. Andersson

Mining of sill pillars is more difficult than the ordinary mining. The sill pillar mining is performed under more difficult conditions and the mining of the sill pillar itself produces more problems; failure of the rock due to high stresses, difficulties in controlling the fill above, overall stability of the stope and special requirements on the technique for backfilling. Altogether this makes sill pillar mining technically difficult and often not profitable. A project was therefore initiated with the aim to increase the mineable ore reserve by making sill pillars mineable, both technically and economically. The project aimed at developing technique for already existing sill pillars as well as planned sill pillars. For the existing sill pillars a technique would have to be developed for mining beneath unstabilised fill. For sill pillars that would be created in the future, the most suitable mining method and methods of supporting or stabilising the fill in the stope above was to be chosen within the project.

Jan 1, 1998