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By M. Pakala, Z. Fan, Ray Y. Lin

Deposition of hard chromium coatings using electrodeposition is accompanied by emission of hexavalent chromium mists which is a carcinogenic. Hence alternative chromium deposition technologies are being investigated. Sputter deposition is a strong candidate to economically deposit hard chromium coatings in an environmentally friendly way. Chromium coatings of 2-3 µ m thickness were deposited on plain carbon steel coupons using RF magnetron sputter deposition. Depositions were carried out with 0 to 22 vol% nitrogen in the plasma. Structure of the coatings was studied using x-ray diffraction analysis With increasing nitrogen contents, formation of the two nitride phases was observed. The pure chromium phase was detected in coatings with up to 7% nitrogen in the sputtering gas. The solid solution of nitrogen in the pure Cr phase coating was identified by shifts of Cr x-ray diffraction peaks to higher d-spacing. The microhardness of the coatings deposited at a substrate temperature of 200°C showed an increase in hardness with increasing nitrogen content from 600 kgf/mm2 (5.9 GPa) at 0% nitrogen to I250 kgf/mm2 (I2.25 GPa) at 9.5 % nitrogen and a subsequent decrease in hardness to I 100 kgf/mm2 (11 GPa) beyond 9.5 % nitrogen in the sputtering gas. This corresponds to the formation of the hard Cr2N phase, at 9.5 % nitrogen, and CrN phase, at I5.7 % nitrogen. The reported bulk hardness values of Cr2N and CrN are I600 kgf/mm2 (I5.7 GPa) and I 100 kgf/mm2 (11 GPa) respectively. For pure Cr phase coatings, there is a slight increase in hardness for coatings deposited at 7. I % nitrogen from that without nitrogen in the sputtering gas. This could possibly result from the solid solution strengthening of the Cr lattice by nitrogen. For films deposited at 200°C, phases of the deposited films seem to be the overwhelming factor in controlling the microhardness.

Jan 1, 1998

By S. M. Bradshaw

The principles of microwave heating are discussed with reference to dielectric properties, heating phenomena and microwave equipment. Microwave regeneration of granular activated carbon for the carbon-in-pulp process is examined on a laboratory scale, with special attention being given to highlight the problem areas and specific considerations related to microwave heating. Results indicate that microwave regeneration of carbon with 40% moisture on a wet basis by heating to 650°C with steam addition regenerates the carbon to virgin carbon activity levels but with a higher abrasion resistance. A preliminary economic assessment showed that the capital cost for 120 kg/h microwave unit would be R540 000 with an annual operating cost of R 320/t carbon. These figures yield a return on investment of 12%. The aim of this paper is to provide an introduction to microwave heating and to illustrate its application to the microwave regeneration of granular activated carbon for the carbon-in-pulp (CIP) process.

Jan 1, 1998

By D. Eugene Rannels, Yu-Chen Lee

"Lee, Yu-Chen, and D. Eugene Rannels. Alveolar macrophages modulate the epithelial cell response to coal dust in vitro. Am. J. Physicl. 270 (Lung Cell. Mol. Physiol. 14): L123-L132, 1996.-The response of the alveolar epithelium to coal dust exposure is poorly understood. Coal or other dusts may act on the epithelium directly or indirectly through nearby alveolar macrophages (AM) that produce cytokines and other soluble products. AM and type II pneumocytes (T2P) were thus exposed to dust in coculture to evaluate their possible interactions. Anthracite coal dust PSOC 867 increased synthesis of extracellular matrix (ECM) components by T2P. AM alone did not produce ECM. Similarly, coculture ofT2P with AM (3.75:1) had little effect on epithelial ECM synthesis. In contrast, coculture ofT2P with AM significantly increased PSOC 867 effects on T2P rates of ECM synthesis, ECM fibronectin content, and T2P levels of fibronectin mRNA. AM-conditioned medium did not change the PSOC 867 effect on T2P. Neither control nor PSOC 867-treated AM on Falcon culture inserts (0.45-µm pore size) over T2P stimulated ECM synthesis by either untreated or dust-exposed epithelium. Thus AM-mediated changes in ECM synthesis by PSOC 867-treated T2P require close cell-cell interactions, suggesting a role for cell-cell contact or for short-lived soluble mediators of the AM effects. DEVELOPMENT OF PNEUMOCONIOSIS, a chronic disease of coal workers that results in pulmonary fibrosis and low lung compliance, is associated with inhalation of mineral or coal dust in the work place (14). Although the pathology of pneumoconiosis has been studied extensively, cellular mechanisms that cause changes in lung structure and function are not fully understood. Particulate matter that enters the respiratory system distributes according to size, with larger particles being removed in proximal airways. Dust components of small size may enter distal alveolar region, which is populated by two types of epithelial cells, type I and - type II cells, and by alveolar macrophages (16). Each of these cell types may interact with inhaled particles, but only the effects of coal dust on alveolar macrophages have been studied extensively. Less is known regarding the response of the alveolar epithelium, or of effects on epithelial cell-alveolar macrophage interactions, in the dust-exposed lung.Function of the alveolar epithelium is well known to be influenced by the underlying basement membrane, or extracellular matrix (28). Alveolar epithelial cell extracellular matrix interactions, which may involve modulation of cell migration, attachment, or differentiation (17), are reflected in type II cell morphology, metabolism, secretory activity, hormone responsiveness, lamellar body content, and gene expression (21). The extent to which basement membrane modulates differentiation of the overlying epithelium is determined by both molecular composition and three-dimensional structure of the matrix. Type II epithelial cells in vitro synthesize, secrete, assemble, and degrade a variety of basement membrane components, including laminin, fibronectin, type IV collagen, and thrombospondin (22, 27). How expression of these components is regulated, directly or indirectly, upon exposure of the alveolar epithelium to injury by coal dust or by other particulates remains to be resolved."

Jan 1, 1998

By Randall M. Wheeler

"Fourier analysis is a very powerful frequency analysis tool. However, it is frequently misunderstood and sometimes used inappropriately. Part of this workshop will involve the basics of Fourier series, the Fourier integral and finally the Fourier transform. Included will be a brief discussion of analysiswindows, including the box and Hamring windows."

Jan 1, 1998

By H. Sevim

Placement of coal combustion byproducts into abandoned sections of underground coal mines for the purpose of subsidence mitigation has been investigated in Illinois. Several handling and transportation systems have been examined. Prototype pneumatic and hydraulic placement systems have been developed and demonstrated. The demonstration site, Peabody No. 10 mine in Pawnee Illinois, is selected as a case study. It is found that, for a project of 5 years, transporting 150,000 tons of byproduct annually from a power plant located 32 km (20 miles) to the mine would cost $1.80 per ton and placement into underground would cost $3.07 per ton.

Jan 1, 1998

By Kuniaki Murase, Tetsuji Hirato, Yasuhiro Awakura

"Electrodeposition of CdTe was studied using aqueous ammonia-alkaline electrolytic baths in which Cd11-and Te1V-ions are dissolving as Cd11(NH3)/+ and Te1vol-ions, respectively. Ca-thodic polarization curves of the baths suggest the presence of strong interaction between the Cd11-and Te1V-ions; electrodeposition of tellurium is inhibited by the presence of Cd(NH3)/+ ions. The interaction makes it possible to electrodeposit CdTe films with stoichiometric composition. Polycrystalline CdTe thin film of about 1 µm thickness was electrodeposited at 343 K from ammonia-alkaline solutions (pH= 10.7) containing TeO32-(<20 mmol dm-3) and Cd(NH3)/+ ( < 60 mmol dm-3) ions. Increasing Cd(NH3)/42+/TeO32- mole ratio or decreasing total concentration of ammonia/ammonium-ion gave flat and smooth crystalline CdTe deposits at constant cathode potential-0.70 to -0.30 V vs SHE at 343 K.IntroductionCadmium telluride (CdTe) is well-known as a compound semiconductor whose band gap, i.e. 1.44 eV, is suitable for solar energy conversion with a photovoltaic cell. Various methods, such as CVD (chemical vapor deposition) and electrodeposition, of preparing CdTe thin films for solar cells have been investigated.Acidic sulfate solutions with a pH of 1-2 are usually employed for CdTe processing by electrodeposition.1-3) The electrodeposition of compound semiconductors is usually achieved (i) at a higher cathode potential than the redox potential of less-noble species, can in this case, and (ii) under the condition of diffusion-limiting current of a more noble species, Te1Y.4) There-fore, a suitable CdII/TeIV concentration ratio in the acidic electrolytic baths, resulting in the deposition of stoichiometric CdTe, is determined by the diffusion-limiting current density of TeIV- reduction, i.e. the concentration of HTeIVO2+ · Since the solubility ofTe1v species HTeIVO2+ in the acidic solutions is quite low, the rate at which CdTe is deposited from the acidic solutions is extremely slow."

Jan 1, 1998

By I P. Hodkinson

SMC Resources Limited is implementing a selective mining approach at the Hadleigh Castle mine, formerly operated by Aurora Gold Limited. The main ore zone has a length of 250 metres and dips at 40 - 45¦ to the south. Gold mineralisation occurs in a variety of quartz-sulphide lodes in sericitised granodiorite. Shallow dips, alteration intensity and mineralisation style combine to make mining relatively difficult. Previously unworked, high-grade, shallow dipping (30 - 45¦), narrow quartz-sulphide lodes within the hanging-wall of the deposit are also being selectively exploited. Annual production of 35 000 oz Au is forecast from 185 000 tpa ore grading 6.5 g/t Au over a currently envisaged mine life of six years. Operations completed to-date include deepening the decline and access development of the first two levels beneath the previous workings. Longhole stoping operations have commenced in the main ore zone with air leg stoping also underway in the hanging wall lodes.

Jan 1, 1998

By Xun An

Slag from an electric slag cleaning furnace was injected with methane and air mixtures to facilitate the recovery of copper and cobalt. The effects of methane-to-air ratio, gas flow rate and temperature on the reduction and metal separation were investigated. The results showed that over 90 percent copper and up to 60 percent cobalt could be recovered from the slag with a gas utilisation of around 70 percent, as calculated by thermodynamic simulation. Methane-to- air ratio was a major factor affecting the rate of reduction under the present experimental conditions. Further, injection of gaseous reductants greatly enhanced the coalescence and settling of entrained metal droplets. A reduction mechanism is proposed and the factors influencing the coalescence of copper droplets are discussed.

Jan 1, 1998

By Takahiro Miki

In order to use metallurgical grade silicon (MG-Si) as a starting material for solar cell, phosphorus has to be removed from silicon because phosphorus is a n-type dopant. On the other hand, silicon, ferrosilicon, and silicomanganese are widely used as deoxidizers in steel refining processes. Since most of the phosphorus introduced during the deoxidation process is brought into final products, it is important -to lower the phosphorus content of these alloys. Hence, thermodynamics of phosphorus in such metals is important for the evaluation of dephosphorization processes. In the present study, thermodynamic properties of phosphorus in molten Si-P alloys at 1723- 1848K and those of Si-Fe-P and Si-Mn-P alloys at 1723K have been determined by equilibrating respective metals in a controlled phosphorus partial pressure. The results are expressed as follows.

Jan 1, 1998

By R. Q. Honaker

Recent research has shown that enhanced gravity separators provide the opportunity to effectively clean I mm x 37 micron coal. At Southern Illinois University, a detailed experimental program was performed on a continuous Falcon Concentrator, which was found to achieve separations at mass throughput capacity values in excess of 100 tonnes/hour. The apparent particle separation density for I mm x 73 micron coal was about 1.60 with relatively high efficiency (Ep = 0.12). Typical ash and sulfur rejection values of 85% and 70%, respectively, were achieved while recovering 85% of the combustible material. Metallurgical and efficiency data from the evaluation are presented in this publication.

Jan 1, 1998

Newmont Gold&apos;s methods for deposit modeling vary, depending on geology, mining and processing methods, economic feasibility and availability of historical information. It is argued that successful modeling requires understanding these factors, knowing the strengths and weaknesses of the various modeling techniques and being flexible in selecting the appropriate methods. Newmont is one of the world&apos;s largest gold mining companies, with operations in the United States, Peru, Mexico, Indonesia and Uzbekistan. And it is active in exploration worldwide. At the end of 1996, Newmont declared a total reserve of 1.15 equity kt (37.1 million equity oz) of gold and 2.17 equity Mt (2.39 million st) of copper. The gold deposits managed by Newmont totaled 752 Mt (829 million st) of ore containing 1.28 kt (41.3 million oz) of gold averaging 1.71 g/t (0.05 oz/st). In addition, Newmont is developing a porphyry copper-gold deposit that totals 9.1 Gt (1 billion st) of ore containing 380 t (12.1 million oz) of gold and 4.82 Mt (5.32 million st) of copper. (In May 1997, Newmont Gold Co. merged with Santa Fe Pacific Gold Corp., thus increasing Newmont&apos;s reserves to 1.72 kt or 55.2 million oz of gold and 2.17 Mt or 2.39 million st of copper.)

Jan 1, 1998

By P Geddes, K Grohs, C K. McKenzie, M Morrish

Low grade surface gold mining at the Acacia Resources, Union Reefs Gold Mine in Australia's Northern Territory, involves the excavation of benches in three slices after blasting. Blast patterns span zones of high and low grade ore, as well as zones of waste, and selective excavation is required in order to maintain economical head grades for the carbon-in-leach processing plant.

Jan 1, 1998

By Isrun Bohlinger

Resources recovery of brasses for semifinished products often results in the formation of hard spots impairing the quality of following abrasive and/or surface finishing processes. A short survey is given on the recycling processes, followed by the actual knowlegde of genesis, composition, and possibilities of avoidance of hard spots. Informations on genesis and composition of hard spots are completed by data from recent experiments.

Jan 1, 1998

By A. Anttila

The grinding mill is probably the most common unit operation used in mineral processing. There is, however, much which can still be done in the way of optimization. This paper discusses the results of a well controlled pilot scale test in which the performance of a tumbling mill with a conventional rubber lining equipped with lifter bars is compared to that with a smooth rubber lining of the magnetic type. The results indicate that the smooth lining is about 14 percent more effective with respect to energy consumption. By optimizing the size of the grinding media, the mill capacity can be increased in many grinding operations. In this specific case the -20 mm ball charge required 26 percent less grinding energy than one with a -30 mm ball charge. The energy savings can. in most cases, be converted to increased capacity. The wear of the grinding media is difficult to assess over a short period test but the results suggest it is somewhat less when a smooth lining is used. The wear of the linings has not been included in this study but it is generally accepted that the use of the magnetic lining reduces the lining costs dramatically. Computer simulation using the Millsoft code, developed by Mishra e.a. confirms and explains the increased effectiveness of comminution when smooth lining and smaller grinding balls are used.

Jan 1, 1998

Within CRLÆs lifetime there have been a number of products that have proceeded through their life cycles. In each case market forces and technological advances have forced the cessation of the product. The company has then had to develop alternative outlets for its copper. Sometimes it has produced a similar product to fill the same market. In other cases the extra copper is sold as cathode. Today, CRL produces no semi-fabricated copper products and all cathode is sold. More recently, CRL has ventured into the sale of technology and manufacture of cathode motherplates. This area, whilst it is not what had been a traditional area of core business, has been found to be profitable.

Jan 1, 1998

By A. Rawat

The removal of oxyanions of arsenic present in mine process water and drinking water to a regulatory level is a challenging problem. Recently a patented adsorbent lanthanum oxide has been developed which has shown strong specificity for the anions of arsenic. In this paper the kinetic and thermodynamic aspects of arsenic adsorption on to lanthanum oxide are discussed. Adsorption tests were performed at different temperatures using synthetic solutions of arsenic of varying concentrations. From the kinetic data and adsorption isotherms thermodynamic properties such as Gibb&apos;s free energy, standard enthalpy of adsorption, standard entropy, isosteric heat of adsorption and activation energy were determined. The results showed that temperature had a positive effect on the rate and degree of adsorption:The activation energy decreased with increase in the initial concentration thus indicating solute-solute interactions in the system. Also, the isosteric heat was found to decrease with increase in the adsorption density implying a heterogeneous adsorbent surface.

Jan 1, 1998

By R Lethlean

The mining industry in its drive to optimise equipment use and minimise cost simply to remain profitable in an uncertain commodity market needs to develop a greater understanding of equipment capabilities and cost. The factors influencing mobile equipment fleet cost and performance commence at the time of mine planning and continue to exert an influence over the life of the mine. These factors must be understood at the early stages of any operationÆs planning process as they continue to impact both positively and negatively on fleet performance and operating cost throughout the life of the mine. The key factors examined in this paper include: grades; rolling resistance; fragmentation and truck loading.

Jan 1, 1998

Rehabilitation, reclamation and restoration are all terms used to describe the repair of land after mining. Here, restoration is used to mean restoring the land&apos;s original use, capability or productivity. Effective restoration is dependent on good planning before mining commences and must include a clear definition of post-mining objectives. The physical condition of the land within the mining licence was that of an imperfectly drained soil in permanent pasture, supporting a seasonal supply dairying unit. During the mining process, the soil layers were separated, with the topsoil stockpiled separately. As part of the restoration process, the land was recontoured to encourage surface drainage, with topsoil spread evenly over the recontoured tailings. Low grond pressure machinery was used to minimise soil compaction, with light discing and harrowing used to increase water infiltration. A permanent pasture was sown, with weed species controlled by spraying, both before and after pasture establishment. &nbsp;Soil testing has been used extensively to ensure there were no nutrient deficiencies that good compromise pasture establishment and performance. Controlled grazing practices were used to ensure that the sown pastures became well established.

Jan 1, 1998

By J. C. Ashby

Electric utility response to certain amendments of the Clean Air Act has resulted in a production of several types of alkaline coal combustion byproducts. Alkaline combustion byproducts are gaining increasing usage for acid mine drainage mitigation as research leads to a better understanding of their beneficial applications. Since January of 1997, Mettiki Coal Corporation has been injecting alkaline flue gas desulfurization material from Virginia Power&apos;s Mt. Storm Unit #3 wet limestone scrubber into abandoned portions of the active Mettiki mine. This paper provides an overview of the key design, transportation, regulatory, and environmental issues faced in the project.

Jan 1, 1998

By Alfred W. Eustes III

The first of a series on the evaluation of rock cutting tools, this paper discusses the results of full-scale laboratory drilling tests that compare the performances of several polycrystalline diamond cutter (PDC) coring bits. The tests were performed in welded tuff as part of a site characterization program. Number of cutters, size of cutters, air course design, and other parameters were evaluated as they affect penetration rate, but this paper focuses mainly on the relationships of torque vs. thrust (weight-on-bit), specific energy vs. penetration rate, and thrust vs. penetration rate. These relationships change in diagnostic ways according to bit type, bit condition, and type of welded tuff.

Jan 1, 1998