Search Documents

By Lawrence P. Goldfarb

The City of Alexandria, Virginia, Public Safety Center (PSC) is a 64,000 square foot facility that houses the Police Department, Office of Sheriff and the Office of Magistrate. In addition, the center includes a detention facility for local and federal inmates, operated by the Sheriff. The PSC is composed of a 3-story building to the west and a 6-story building to the east constructed on a landfill in a wetland area in the flood plains of hunting Creek. The existing ground floor of the 3-story building is a floating slab-on-grade, with the interior and exterior columns, exterior walls and upper floors all supported on belled, drilled shafts. Portions of the floating first floor slab have undergone excessive settlement due to the apparent consolidation of the underlying organic soils. The magnitude of the settlements of the floating first floor slab is sufficient to require replacement of the slab and relocation of a portion of the facility. The rehabilitation was complex and required staged construction, consisting of constructing Auger Pressure Grouted (APG) Piles in low overhead conditions. This paper summarizes the geotechnical conditions that lead to the excessive settlement of the floor slab, the construction of the (APG) Pile foundations in low overhead conditions and the evaluation of potential future settlements.

Jan 1, 2009

By R. M. Santmyers

The chief compounds of boron are borax and boric acid, both of which have important applications in industry. At present the United States furnishes more than half of the world's requirements of borate materials, practically all from California. Nearly the entire production of borax in this country is under the control of four companies: The American Potash and Chemical Corporation, the Pacific Coast Borax Co., the West End Chemical Co., and the Western Borax Co.

Jan 1, 1931

By C. Musingwini

In the past ten to fifteen years, many organizations have applied business process re-engineering (BPR) to significantly improve their business competitiveness or stave off closures. The mining industry in Southern Africa is no exception and documented examples can be drawn from South Africa. Although the concept is superficially simple, its application has been marked by a high failure rate of about 70 per cent because it has been generally misunderstood. Shabanie mine, a chrysotile asbestos fibre producer in Zimbabwe took cognisance of this fact by cautiously embarking on a modular BPR programme in October of 2002. A year was used as a complete cycle or module for re-evaluation of the programme. Shabanie mine adopted BPR as part of management efforts to remain competitive amid serious threats to operational viability. These threats included hyper-inflation driven rising production costs, a declining world asbestos market and a possibility that Russia could take over the shrinking world asbestos market by dumping low-priced asbestos fibre. The only competitive advantage that the mine had was the high quality of its long-fibre chrysotile asbestos. The major BPR thrust was therefore to redesign processes for improved productivity and ultimately achieve a lower cost per ton of final asbestos fibre product. In addition, corporate culture change and cost-saving were also factored into the programme. This paper discusses the implementation experience of the BPR programme at the mine. The main BPR beneficial highlights are improved productivity, sizeable cost-savings, positive corporate culture change and identification of secondary projects. One of the lessons learnt from this programme is that mining companies will have to deal with the HIV/AIDS pandemic if they are to sustain high levels of productivity into the future.

Jan 1, 2005

By E. V. Lilford

Equity investors and project sponsors have divergent views about expected or minimum returns that should be generated by a mineral project. Irrespective of their views, the fundamental estimation of the corporate cost of capital remains singularly determinable, with additive components of risk and uncertainty often incorporated in the final analysis. This paper discusses and details the fundamental, numerical determination of the corporate cost of capital.

Jan 1, 2006

By Sandin E. Phillipson

The Mine Safety and Health Administration?s Roof Control Division responded to a massive ground failure at an underground marble mine in northern Georgia. The ground failure occurred in a benched area that had been abandoned in the early 1990s. It involved the failure of an estimated 19 pillars, in conjunction with a massive roof fall of an undetermined extent that was at least 60 ft high. Pillars in the benched area had been mined nominally 40 x 40 feet to a height of 50 feet ft, with 40-ft mining widths, although it seems likely from measurements and accounts from mining personnel that pillars were even smaller than intended. Average overburden depth was 500 ft, and the rock mass was characterized by three sets of intersecting geological discontinuities that not only defined very blocky conditions that were conducive to pillar spalling and volume loss, but they were also adversely oriented in such a way as to cut diagonally through pillars at a high angle. The recently released S-Pillar software from NIOSH was used to determine pillar safety factors in the failure area and indicated that pillars were undersized for the conditions. S-Pillar was used to assess pillar stability in active areas to evaluate the likelihood of experiencing similar collapses in the future. S-Pillar correctly identified the pillars in the bench area as having been at risk for instability, in light of their ultimate failure. A two-dimensional finite element model was used to evaluate the possible stages of failure and to assess the likelihood of continued failure in the benched area that might affect more distal mine openings. Although stone mines are generally characterized as having more forgiving conditions than those found in softer sedimentary rocks, the failure shares some characteristics with domino-style massive pillar collapses experienced in coal and trona mines. First, the minimum dimension of the benched area approached 350 ft; second, the pillars defined by benching had small width-to-height ratios (0.8), and; third, the pillar failure area was slightly greater than 4 acres. The massive pillar collapse and associated roof fall illustrate the importance of incorporating pillars that have been properly sized for depth and for the final bench height. Furthermore, the designed dimensions must be adhered to during the actual mining process. Finally, the importance of understanding the geological conditions and their effect on the rock mass is critical.

Jan 1, 2012

By Elli Miettinen, Markku Lahtinen, Ilkka Kojo

"The recent trends of decreasing energy consumption and environmental emissions and utilization of economies of scale are strong drivers favoring continuous copper converting processes. Flash Converting benefits from low off-gas volumes and low investment and operational costs for off-gas treatment. Separate matte and blister furnaces allow the adaptation to concentrate quality changes and flexibility in layout and maintenance.The stationary blister copper bath in Flash Converting furnace is less aggressive to the furnace linings than agitated processes, resulting in low refractory consumption, long campaign life and high on-line availability.Copper Flash Converting has been successfully applied in Kennecott with a campaign life now exceeding five years. A second FCF was started at Xiangguang Copper in China in 2007. The process itself is proven, as its features are similar to those in FSF, Direct-to-Blister and Direct Outotec Nickel Flash Smelting (DON), with one significant difference: it is the easiest of all to operate.The paper presents differences between continuous Flash Converting and conventional converting based on recent experiences and studies."

Jan 1, 2009

By L. R. Plitt, A. A. Turak, B. C. Flintoff

"Since the publication of empirical cyclone models by Lynch and Rao in 1975 and by Plitt in 1976, the technical literature on this subject has consisted primarily of reports of applications, with only a few articles discussing basic modifications or enhancements in model form. In fact, most of the modelling eff ort in this period has been concerned with theoretical models based on the hydrodynamics of multiphase flow. (Preliminary resutls have been encouraging, however, it will be some time before this approach reaches the practical application stage.) This paper presents a review of empirical cyclone modelling technology, with an emphasis on developments since the mid 1970s. The topics addressed include homogeneous and heterogeneous ores, parameter estimation techniques, parameter confidence intervals, and the introduction of a new conceptual model of cyclone operation.IntroductionSince their first reported application in the mineral industry by Driessen (1939), cyclones have become a common unit operation in all of the process industries. The widespread use of the cyclone stems from its relative low cost and its versatility. It can be employed to carry out liquid-liquid, solid-liquid and solid-solid separations. It is the area of solid-solid separation which is of greatest interest to a mineral processing engineer. Historically, this area was divided into two application categories: (I) Separation according to density, the cyclone washer, and, (2) Classification according to particle size, the cyclone ciassifier. (When water is the carrier fluid, the cyclone is more often called the hydrocyclone. For the purposes of this paper the two names are used interchangeably). Classification is the principal application in mineral processing circuit s. Within this category, the cyclone is most commonly employed to provide some positive control over the size distribution of product from a grinding circuit. Other uses include sand-slime separation prior to froth flotation and mill tailings treatment, either for dam construction or in backfill preparation."

Jan 1, 1987

Albert Ladd Colby, New York, N. Y. (communication to the Secretary†):—I observed (Trans., xxxvii., 585) that to obtain tenders from several American mills, the foreign engineer should modify his maximum phosphorus to 0.10 per cent., not as Mr. E. Windsor Richards quotes me, that no American rail-maker can produce rails under 0.10 per cent. of phosphorus. Mr. Richards claims that no English engineer would agree to accept 0.10 per cent. of phosphorus on any terms whatever. Mr. Webster writes that only after an engineer has .been convinced that rails can be made in America equal in every respect to those he is getting abroad, should he be asked to modify ally conditions in his specifications. I know it to be a fact that during recent years in many cases, as, for instance, When delivery could be secured more promptly in the United States than in Europe, the consulting engineers of several British and colonial railroads have frequently agreed to modify their phosphorus requirement to a maximum of 0.10 per cent., and the rails delivered' under these modified specifications have, under like conditions, given just as satisfactory service and proved to be no more brittle than similar sections of 0.07 per cent. phosphorus rails, rolled in England under the same specification except without modification as to phosphorus. Furthermore, it would appear from the analyses of British rails, quoted by E. A. Dancaster,2 in his discussion of Mr.

Jan 1, 1908

By M. M. Oosterveld

"In South West Africa diamonds are mined from ancient beach deposits by the Consolidated Diamond Mines of South West Africa, Limited.To improve the control of mining production, a computer is used for the calculation of statistically more accurate and homogeneous ore blocks. Geological and sampling information has been digitized and stored on magnetic files.The figures derived for each block entail the calculation of the diamond size frequency distribution, the diamond density distribution and the ore reserve by using the density distribution.The diamond size frequency distribution is used for estimating the revenue in an ore block.A description is given of how a linear programming system can be used for production planning."

Jan 1, 2014

By J. Koster

In the western United States occurs deposits of low-grade chromite which, when concentrated, may be reduced to ferrochromiun in electric furnaces that derive energy from dams and hydro plants now in course of construction. Montana ore was chosen for the experiments. A 1-ton sample contained 26 percent Cr203, 17 percent Fed, and 17 percent SiO2, plus other constituents, and the concentrates therefrom assayed 44 -percent Cr203, 23 percent FeO, and 0,79 per cent SiO2, Gravity concentration was found to be the best method. Ferrochromiums are of two grades - high-carbon with 66 to 70 percent chromium and 4-112 to 6 percent carbon and low-carbor with 67 to 72 percent chromium and 0.6 to 2 percent carbon. Both are made in electric furnaces that use anthracite as a reducer and suit-able fluxes. The concentrates mentioned mere smelted under different conditions, and it was concluded that domestic ore could be reduced with anthracite to produce a ferrochromium of S to 10 percent carbon content at yields of 90 percent without re-treating the slag. This carbon may be lowered to required proportion with calcium and silicon, but the former requires a great excess and the latter leaves an alloy high in silicon. INTRODUCTION Chromite occurs in several regions of the United States, but the known deposits of this mineral have not been large enough or high grade enough to permit them to compete under normal conditions with imported ores. There are numerous deposits of chrome ore along the West coast. These are generally conceded to be relatively small, although some were worked during the World War. There are some indications of a revival of interest in California chromites. Montana contains large chromite deposits in Stillwater and Sweetgrass Counties. The utilization of chromite for ferrochromium and. the manufacture of stainless steels is distinctly an electrometallurgical problem; consequently, a study of methods for treatment of chromite might pave the way for the establishment of new electrometallurgical industries in the Western States. This thought is supported by the cheap power that is soon to become available from the western dams, Farther, submarginal domestic chrome deposits might thus be turned into profitable producers.

Jan 1, 1936

By J. Koster

In the western United States occurs deposits of low-grade chromite which, when concentrated, may be reduced to ferrochromiun in electric furnaces that derive energy from dams and hydro plants now in course of construction. Montana ore was chosen for the experiments. A 1-ton sample contained 26 percent Cr203, 17 percent Fed, and 17 percent SiO2, plus other constituents, and the concentrates therefrom assayed 44 -percent Cr203, 23 percent FeO, and 0.79 per cent SiO2, Gravity concentration was found to be the best method. Ferrochromiums are of two grades - high-carbon with 66 to 70 percent chromium and 4-112 to 6 percent carbon and low-carbor with 67 to 72 percent chromium and 0.6 to 2 percent carbon. Both are made in electric furnaces that use anthracite as a reducer and suit-able fluxes. The concentrates mentioned mere smelted under different conditions, and it was concluded that domestic ore could be reduced with anthracite to produce a ferrochromium of S to 10 percent carbon content at yields of 90 percent without retreating the slag. This carbon may be lowered to required proportion with calcium and silicon, but the former requires a great excess and the latter leaves an alloy high in silicon. INTRODUCTION Chromite occurs in several regions of the United States, but the known deposits of this mineral have not been large enough or high grade enough to permit them to compete under normal conditions with imported ores. There are numerous deposits of chrome ore along the West coast. These are generally conceded to be relatively small, although some -were worked during the World War. There are some indications of a revival of interest in California chromites. Montana contains large chromite deposits in Stillwater and Sweetgrass Counties. The utilization of chromite for ferrochromium and. the manufacture of stainless steels is distinctly an electrometallurgical problem; consequently, a study of methods for treatment of chromite might pave the way for the establishment of new electrometallurgical industries in the Western States. This thought is supported by the cheap power that is soon to become available from the western dams. Farther, submarginal domestic chrome deposits might thus be turned into profitable producers.

Jan 1, 1936

By Wenshan Zhang

Three important methods of removing Fe in hydrometallurgy of zinc, manganese, copper, nickel, cobalt and etc are described, including neutralized hydrolysis method, jarosite method and goethite method. The reactions, technical requirements and thermodynamic analysis during Fe removal process are also discussed in this paper.

Jan 1, 2006

By B. Meddings, O. J. I. Evans

"This paper is mainly concerned with the present and probable future role of hydrometallurgy in the production of base metals.The economic and technological bases of the hydro-metallurgical plants built and operative in the mid-fifties are compared to those in production in the mid-sixties. The trends observed are extrapolated and some estimates made concerning the probable size and type of hydrometallurgical plants which will be operative in the mid-seventies.The impact of emerging socio-economic factors such as pollution control and the market demand for specialized metal products which favour hydrometallurgical recovery processes are also discussed."

Jan 1, 1971

By H. H. Li

Reverse flotation is usually used for hematite/silica or bauxite/clay flotation separation in which the silica or clay is floated and rejected. Some properties of these silicate minerals such as particle size and surface characteristics have significant effect on their flotation behaviours. Firstly, the silicate mineral particles (especially clay minerals) generally have fine particle size (< 5 microns) in their natural states or due to overgrinding and they display poor flotation kinetics, consequently having low flotation recovery. Secondly, the wettability difference on different particle basal planes influences the affinity for adsorptions of different types of chemicals such as collectors or macro-molecule. Common polyacrylamide (PAM) flocculants can be used to minimize the exposure of the most hydrophilic planes of clay particles via hydrogen bonding but they can not efficiently enhance the overall particle surface floatability due to the hydrophilic properties of this type of macromolecules. A novel method to improve both flotation kinetics and surface wettability of silicate minerals has been developed and studied. That is to use a temperature-sensitive polymer, poly (N-isopropyl acrylamide) (PNIPAM), as a process aid in the flotation of silicate minerals. Unlike PAM polymers, PNIPAM can induce a hydrophilic/hydrophobic transition on the particle surface when the temperature is changed to be lower or higher than its critical solution temperature (CST). At a lower temperature, the PNIPAM adsorbs on the particle surface via hydrogen bond similar to PAM. It induces strong hydrophobic aggregation when the temperature is increased above the CST. Thus, both floc size and mineral floatability are greatly increased. The flotation results show very good flotation performance and the addition of conventional flotation collector was no more required because the increased particle surface hydrophobicity induced by PNIPAM. Contact angle measurements explained the role of PNIPAM in manipulating particle surface hydrophilic/hydrophobic transition.

Jan 1, 2014

By C. Mosoane

ERPM was formed in 1893 and as a result of its age, a large volume of data exists in a paper-based format and it was decided to electronically capture data in one of two critical mining areas?namely at Far East Vertical (FEV) Shaft Area (Lower Areas) and Hercules Shaft Area (Upper Areas). The life of mine is dependent on tonnage and grade from these areas. Geostatistical evaluation of the gold reserves has been applied on an ad hoc basis in the Hercules Shaft Area and on a continuous basis in the FEV area. This is the first evaluation using geostatistics that was performed on the Upper Areas. This paper is based on the premise that regardless of cut-off grades, geostatistical estimation (kriging) estimates and locates reserves better than ?traditional? methods e.g. polygonal method, inverse squared distance method and it endeavours to estimate and locate the high grade reserves in the Main Reef Leader of Upper Areas.

Jan 1, 2003

By M. L. Liu

This work reports the results about the determination of mean activity coefficients and relative partial molar free energies for copper sulfide mineral bioleaching solutions by potentiometric method at 25ºC. The experimental potentiometric data were obtained by combining a solid state membrane-cupric ion selective electrode (Cu2+ ISE), containing a KNO3 filling solution, and an Ag/AgCl electrode. The measurements were performed in different series of copper sulfide mineral bioleaching solutions. The non-ideal behavior of the system was described on the base of the Pitzer ion-interaction model for mixed salts. Meanwhile, the relative partial molar free energies of bioleaching solution were investigated. The determination of the thermodynamic properties offers a basic data for the study of copper sulfide mineral bioleaching solutions.

Jan 1, 2014

By G. Demi

The biggest chromium mineral processing plant in Albania is Bulqiza plant. It has been in operation for more than 20 years, treating low-grade chromium ores grade 20 ? 26 % Cr2O3 and producing chromium concentrates grade 48 ? 50 % Cr2O3. About 2 million tons of tailings with 13 % Cr2O3 content are stocked in a dam close to the plant. Mineral processing of low-grade chromium ores with less than 16% Cr2O3 content is unprofitable because the mining expenses are high comparing with the current market prices of chromium concentrate. Recycle and enrichment of existing tailings is profitable, because there are no underground mining expenses in this case and because that this kind of raw material does not need expenses operation of crushing and grinding. The existing plant is in operation for more than 8 years treating existing tailings as raw material. Grade of concentrate in the value 40 % Cr2O3 and Cr2O3 recovery in the value 30-35% in the plant are considered low. The main reason of low concentrate grade and recovery is high content of particles under 100 microns, the slimes, in raw material. In the paper is described the study carried out to improve enrichment of the tailings, as well as analyses of existing process, raw material and products. It is concluded that majority of lost is present in the slimes which are not separated in existing spiral separators and shaking tables. Basing in the study is composed the new flow sheet of recycling and concentration of the tailings to produce chromium concentrate grade 41 ? 42 % Cr2O3 and recovery 60 %, decreasing in this way the concentrate production cost two times. In the paper are presented the tests and results of concentration of particle size fraction under 100 microns, using gravimetric, magnetic and flotation methods, as well as equipment and machines suitable for slimes treatment and concentration.

Sep 1, 2012

Understanding multiphase particulate systems is essential for the further advancement of mineral processing technology. Characterisation, analysis, and simulation of these complex systems provide a fundamental basis for the development of improved mineral processing technology. One of the more recent tools that can be used to help provide a foundation for improved mineral processing technology is high resolution cone beam X-ray micro computed tomography (CT). During the past ten years point-projection X-ray micro CT systems have been used for 3D visualisation and quantitative analysis of multiphase particulate systems. Analysis of packed particle beds containing as many as 30 000 particles can be accomplished in less than three hours with special software to establish the 3D characteristics of each particle in the population and the spatial organisation of the packed particle bed. Now, due to advances in X-ray optics, the resolution afforded with point-projection micro CT systems has been improved by at least an order of magnitude using a lens-based X-ray micro CT system. The development of software tools for the 3D characterisation, analysis, and simulation of packed particle beds using high resolution X-ray micro tomography (HRXMT) is discussed including examples of application in the areas of comminution (particle damage and preferential grain boundary fracture), exposure/liberation analysis (liberation-limited separation efficiency, including coal washability), and filtration/heap leaching (pore network structure of packed particle beds and simulated flow using the LB method of computational fluid dynamics).

Sep 13, 2010

By G. A. Harrison

The introduction of extra low profile (XLP) mechanized equipment within Anglo Platinum is aligned with the overall New Mining Technologies strategy to focus on continuing modernization of our mining operations` incorporating injury-free production and cost-effective mining technologies. The method allows for the introduction of a suite of ultra-low profile equipment in narrow reef (1.2 m) stoping operations. For the first time it is now possible to achieve total trackless mechanization at these widths and indications are that XLP mining has the potential to add more value when benchmarked with conventional mining and low profile (1.8 m) room and pillar methods. Various mine layouts were tested at different sites within Anglo Platinum and the XLP breast mining layout proved to be the most effective. This paper describes the results of the trials at Waterval Shaft and concludes with recommendations on our future strategy on implementation of XLP technology within Anglo Platinum.

Jan 1, 2006

By Carnevale Francesco, Bracci Laudiero Alberto, Pampanin Piero

"SummaryIn the Port of Naples a slurry wall has been realized through a sandy layer up to a deep tuff layer using the Cutting Soil Mixing technique.The executed panels have dimensions of 2.8 m x0.65 m in plan and a total length of 25 m. Primary and secondary panels have been executed using the wet to wet technique. During the panels execution the following parameters had been measured: injection pressure, injected volume, verticality. At the end of the works an exploratory campaign has been carried out through boreholes collecting samples for laboratory tests in order to verify the diaphragm thickness and its physical and mechanical properties (i.e. unit weight, unconfined compressive strength).The interpretation of the collected data allowed to verify the efficiency of the method, the volume of slurry loss due to permeation during the panels execution, the quantity of the obtained spoil compared to the volume balance equation, both for the sand and the tuff layer.Eventually, the measured physical and mechanical characteristics of the panels have been correlated to the execution method performed.IntroductionIn the Naples Port area there is a polluted site which has to be hydraulically isolated in order to prevent the pollution of the groundwater that flows from land to the sea through the Port area. A hydraulic cut-off wall has to be realized and particularly a slurry-wall realized using the CSM method had been executed.To date, two stretches have been executed, 140 an 110 m in length respectively, as shown in Figure 1 and Figure 2.After execution, the slurry-walls have been investigated with boreholes. In-situ and laboratory tests on the recovered samples of grout have been carried out; furthermore, the geotechnical parameters of the mix composing the wall have been measured."

Jan 1, 2014