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By Ishwinder Grewal, Michael Fullam

Many factors affect the overall performance of a gravity circuit beyond that of the primary gravity recovery device. It is critical to examine the gravity circuit in its entirety in order to determine the dominant operating variables that affect overall performance. Knelson has developed a mathematical model which has been used to assist in the design of gravity circuits, and in particular, in making accurate predictions of plant scale gravity recovery. More recently, inclusion of recovery by particle size class and additional data from various mine sites and research studies has made the model more robust. The model is now able to predict GRG (gravity-recoverable-gold) recoveries using various devices such as centrifugal concentrators, shaking tables, jigs and flash-flotation within the grinding circuit. The benefits derived by these recent advancements in modeling capability are two-fold; the first is as a tool to assist in circuit design and correct equipment selection and the second is as an analytical tool to help to evaluate and enhance the performance of existing gravity circuits.

Jan 1, 2006

"It is projected that the reactivity of acid generating tailings and waste rock can be minimized by reducing the access of oxygen by placing these materials under water in natural or manmade lakes. A project under the MEND and B.C. AMO Task Forces has been in progress for four years to evaluate active and historic tailing sites in B.C. and Manitoba. The sophisticated geochemistry studies conducted on the interstitial pore water has illustrated encouraging results which are discussed. The additional studies which are needed to complete the scientific database for the study sites, for achieving regulatory and public approval and for the engineering of application of this method of control are outlined.IntroductionWorld wide research effort is in progress to find the solution to the acid mine drainage problem. A great deal is known about acid mine drainage but much work is required to find economic and effective approaches to the problem. Two coordinated programs have been initiated recently in Canada: the National Mine Environment Neutral Drainage (MEND) program and the British Columbia Acid Drainage Task Force.Disposal of tailings materials under a water barrier such as a natural lake, is thought to be one solution to prevent acid generation by preventing oxygen and bacterial action on the sulphide surfaces. The deposition of reactive tailings materials under water in natural lakes has been used historically at various mines in Canada. However, there has never been a thorough review of the long and short term impacts of historic sites which may provide crucial information to understand the physical, chemical and biological processes which are taking place.This paper provides a general overview of a series of studies which examine the general biophysical characteristics and the sediment geochemistry of four lakes where subaqueous disposal has been or is currently being used for acid generating tailings. The subaqueous disposal studies have been conducted from 1989 through 1991 and were initiated and supported by both research task forces. The objectives of this paper are to summarize the history and the background information of the studies conducted, the general results obtained from each lake, an overview of the major collective results and the additional work which is required to achieve the final objective of developing criteria for applying this technology in the industry."

Jan 1, 1992

By P Wood

Loy Yang Power (LYP) owns and operates a 2160 MW brown coal fired, base load power station in the Latrobe Valley, Victoria, Australia (Loy Yang A). It also owns and operates a brown coal mine that supplies fuel to its own power station and a nearby 1000 MW power station owned by International Power (LoyYang B). The mine supplies 32 Mt of coal per annum from an open pit, which is currently about 4 km long by 2 km wide and 180 m deep. LYP has 500 employees and a substantial amount of work is also carried out by contractors and consultants. GHD Pty Ltd(GHD) has been contracted to provide mine planning and earth sciences expertise. GHD is an international professional services company that operates globally in many market sectors including mining, industry and the environment. The company has major offices in Melbourne and also within the Latrobe Valley. This paper sets out the experiences that GHD and LYP have gained in establishing a unique alliance arrangement for GHD to provide a range of mine planning, earth science, dam surveillance and environmental services to LYP. The underlying philosophy of the alliance is to closely align the objectives of the two companies such that GHDÆs recompense for service delivery is proportional to the benefit achieved by LYPÆs business. Quality of service, whole of life costs and risk management are important aspects and are reflected in key performance indicators against which GHDÆs performance is measured. Currently GHD provide 20 000 hours of labour to LYP per annum, which are delivered by up to 120 staff who possess the required diversity of skills. The paper explains how the contract was initially let as a conventional service agreement and explains why the contract was transformed into an alliance. It then illustrates the operation of the alliance with reference to the 2006 work program. The paper concludes with thoughts on how the arrangement can be further developed for the future to the benefit of both parties.

Jan 1, 2006

By C. Feng, C. Elbaum

Knoop hardness measurements were carried out on large grains of iodide titanium containing different amounts of oxygen. For each oxygen content the hardness is recorded ainingas a function of the crystal orientation and of the angle 4 between the indenter diagonal and the projection of the C (hexad) axis in the surface. The results can be expressed by the following relation; hardness = n-k cos 2ø, where n and k are constants for a given oxygen content and crystal surface orientation. A NISOTROPY of hardness is a well-known phe-nomenon and has been reported for many metals.1-3 At the present time, however, such information is not available in the literature for titanium. Consequently, a systematic study of the simultaneous effects of oxygen content and crystallographic orientation on the hardness of titanium was undertaken in this laboratory. Evaluations of oxygen content in titanium are frequently carried out through hardness tests. Although such procedures may be justified in small grain specimens, the results of the present investigation indicate that the anisotropy of hardness should be taken into account in the case of coarsegrained specimens as well as in the case of pronounced preferred orientation. Materials and Experimental Procedures Iodide titanium, 99.99 pet pure and containing of the order of 0.002 wt pet O, was used throughout this investigation. The metal was arc melted in an argon atmosphere and cold rolled into strips 1/16 in. thick. These strips were subsequently recrystal-lized and strain annealed in vacuum (10" mm Hg or better) at 850°C in order to produce crystals varying in diameter from 10 to 25 mm. Oxygen was introduced into selected large crystals by heating at 700°C in an atmosphere of pure oxygen under an observed pressure of approximately 50 mm Hg. Each sample was subsequently annealed in vacuum at 850°C for 100 hr, in order to homogenize the oxygen content throughout the specimen. It was found that longer annealing was not necessary, for no change of surface hardness in a given direction was detected after prolonged annealing. The oxygen content was determined by the difference in weight of the specimens before and after the oxidation-annealing cycle. The accuracy of oxygen determination is within ±0.1 mg in samples weighing 0.5 to 1 g. A vacuum fusion analysis of oxygen was performed on several samples and gave results in good agreement with the ones obtained by the weight change. It should be emphasized that expected weight losses through evaporation of the metal in vacuum at 850°C' are many orders of magnitude lower than the precision of these measurements. Following the annealing treatment, both oxidized and unoxidized crystals were carefully polished. All detectable traces of surface cold working were removed by repeated polishing and etching. Laue back reflection X-ray patterns were taken for each crystal for the purpose of determining the orientation and ascertaining the absence of substructures detectable by this method. Hardness measurements, using a 1 kg load, were subsequently carried out on a Tukon hardness tester equipped with a Knoop indenter. The Knoop indenter was used throughout this work because indentations obtained by means of a Vickers indenter are considerably distorted due to the anisotropy of the elastic constants in titanium. Such distortions are much less pronounced in the case of Knoop indentations, although for some orientations a cer-

Jan 1, 1959

By Paul S. Fisk, Arne Fareth, Julie Frietas, Francis Lo, Fidel L. Mallonga

INTRODUCTION This report describes the inspection of parts of the New Croton Aqueduct (NCA)undertaken for the New York City Department of Environmental Protection (NYCDEP)by Parsons Brinckerhoff Quade & Douglas, Inc., (PB) in association with Montgomery Watson Engineers of New York, P.C. (MWH). Support for the inspection was provided by AFC Enterprises, Inc., under Construction Contract CRO-333, “WM-11 New Croton Aqueduct Rehabilitation and Inspection Program.” The scope of the inspection work under CRO-333 included assessing the condition of the 10.3 km (6.4 mile) long, pressurized section of NCA and inspection of shafts, head houses and blow-off structures in both the pressurized and gravity sections. The CRO-333 inspection continued investigation work begun under ContractCRO-196, which ran from 1993 to 1997. The CRO-333 inspections were conducted from November 2004 to September 2005. Background The New Croton Aqueduct was put into service in 1891 to deliver water from the Croton River Watershed in Westchester County to consumers in New York City. Figure 1 shows the location plan of Croton Water Supply System. The design flow into Jerome Park Reservoir was 12.7 m3/s (290 mgd) and into the135th Street Gate House, further south, was 10.9 m3/s (250 mgd). The NCA has been operated as a gravity conduit from Croton Lake to Gate House No. 1, just north of Jerome Park Reservoir, since its original construction. The length from Gate House No. 1to 135th Street, which includes a major siphon under the Harlem River, has been operated under pressure. Croton Lake gate house, the north end of the alignment lies at Station 4+75; Shaft 33, the south end of the alignment lies at Station 1628+05. The diameter of the tunnel is 3.2 m (10.5 ft) in the siphon and 3.7 m (12.3 ft) in the Bronx and Manhattan sections. The pressurized sections, constructed in rock, consist of a brick lining surrounded by a mortared and grouted rubble backing. Figure 2depicts a typical tunnel cross section. The objective of the shaft and tunnel inspections was to locate and document defects, such as leaks, deterioration of lining material, cracks, spalls, delaminations,

Jan 1, 2007

By Peter Faust

The foundations for the new South Viaduct Bridge in San Francisco were extremely challenging due to the requirement for very large and deep piles installed adjacent to historic structures. Drilled shafts up to 12? foot in diameter were constructed to a maximum depth of 200? feet in alluvial soils and Franciscan Bedrock using an oscillator system for the installation of the permanent steel casing. This paper provides an overview of the construction techniques, the equipment, and the challenges associated with constructing 12? foot diameter shafts on this very complex project in one of the nation?s nicest landscape setting.

Jan 1, 2011

By R. S. Montgomery

Laboratory experiments simulating rock drilling were conducted on a number of commercial grades of tungsten carbide in order to determine their wear rates when they are used as inserts in percussive rock drill bits. The test rock was Barre granite and tests were made at conditions similar to those of the carbide buttons near the periphery of a large, down-hole, button bit. In addition, some wear rate measurements were made at a low blow energy. Wear rates of these carbide buttons were an extremely sensitive function of their cobalt contents and hardnesses and were proportional to e-°.57Hup to a hardness of about 91 RA. The point of minimum wear rate, which occurs at about 92 RA, corresponds to the point of maximum compressive strength. Modern percussive rock drill bits have inserts of cemented tungsten carbide on their wear faces. These inserts have drastically reduced bit wear in comparison to that of earlier all steel bits. The most common cemented carbide grade used in percussive rock drill bits contains about ten weight percent cobalt, although grades containing more or less cobalt are also used. Contrary to the case with carbide in metal-cutting tools, alloying materials are rarely used in mining grades. There are a number of designs of rock bits in current use. The most common form is an X bit which has four chisel-form radial wings. The button bit is another important design and one which has been recently developed. This design uses a flat steel face studded with relatively small hemispherically tipped carbide buttons. These types are illustrated in Fig. 1. Studies have been made of the sliding wear of cemented tungsten carbide on rock 1-4 and multiple-impact fracture', 5-6, b~t there has been comparatively little published on the percussive wear of this material although the wear of the impact face is the most important. There is some available data on the rate of dulling of rock bit inserts in actual drilling 7 but no laboratory studies. Sliding wear studies are useful for understanding the wear of coal and mineral cutting tools and gauge wear of percussive drill bits. but the

Jan 1, 1970

By R. V. Ramani

One area of study in the Coal Mine Injury Analysis project was to illustrate and enhance the ability of mine safety management personnel to apply analytical techniques to injury experience data and to justify requests for funds for safety enhancement actions on a cost/benefit and other quantitative basis. Four volumes of this final project report detail (1) the objective and scope of the mine safety management research, (2) the results of literature review, and case studies, and (3) models developed for mine safety management. The four volumes are titled as Volume III: Mine Safety Management, Volume IV: Analytical Techniques for Mine Safety Management; Volume V: Mine Safety Management Case Studies and Volume IX: Training Cost Model. In this volume, the following material is presented: (i) review of related literature, (ii) mathematical models to perform quantitative analyses of accident/ injury experience data using the tools and techniques of risk analysis, time series analysis, and the Markov process, and (iii) descriptions of the HDBSEL and ACIM programs which are used to perform accident/injury experience analyses and cost analyses, respectively.

Jan 1, 1993

By Mark Coleman

Pnuematic Conveying and Process Injection Technologies have been implimented in the metals markets for the last 40 years and have consideribly improved the productivity and the performance of many processes. There have been many steps forward in handling technology and this paper seeks to consider those now offered by Clyde Materials Handling who as an established customer-driven solutions provider, which has turned its attention to supporting the Metals Market. Clyde seek to utilises its knowledge, expertise and technologies to transform the production processes of its customers, who operate in the ferrous and non-ferrous metals industries. With over 30 years experience in the process improvement industry, Clyde Materials Handling has helped their global customer base transform the way in which they operate their processes, which has enabled them to generate sustainable economic benefit and maintain their positions as leaders in their respective markets. Operators within the metals market have developed and deployed pneumatic conveying and pneumatic injection technologies. These environmentally supportive and sustain-able solutions have been used to transport raw materials within operating facilities, from storage to silo, as well as injecting these materials directly into the heart of production processes. Operators, such as Codelco in Chile, Corus Steel in the UK, and many others across the World have seen pneumatic injection solutions transform their process and costs. To inject a consistent, pulseless and accurate flow of material to a copper concentrate bath smelter, or injecting granular or pulverized coal as a coke substitute in to a blast furnace via the Tuyeres helps to increase the operational capacity, availability and productivity and reduce the cost of the operation. This paper will discuss and highlight the ways in which pneumatic conveying and injection technologies, created by Clyde Materials Handling, and applied in partnership with the customer, have helped to improve the operational performance of the production processes of operators across the non-ferrous metals markets with specific reference to applications in the Lead and Zinc Industries. With examples from Zinc Fuming in Australia, Zinc Calcine and Powder Handling in Korea, Precision coal injection to QSL and TSL Furnaces, and metered distribution of Zinc Calcine to Reactors.

Jan 1, 2008

By Hayel M. El-Naggar, Sherif A. Akl

Although grouted piles have been used for several decades since the idea was proposed in the 1970s, their design is mostly based on experience and unpublished proprietary methods. There is little research on grouting drilled shaft tips and even less on grouting shaft sides. This paper presents the analysis of 4 instrumented pile loads tests on base and shaft grouted piles from different sites in Egypt; with emphasis on one of the tests, to demonstrate the analysis process. The data from the tests are analyzed to model the development of unit side friction (USF) with relative displacement. A numerical model using the finite element software PLAXIS is used to investigate the effect of grouting on the surrounding soil stress state. The paper combines the observations from full scale pile load tests and results from the numerical model to suggest an idealized behavior of side friction development with relative displacement of the grouted part of the shaft. The suggested model considers an envelope of Unit Side Friction (USF) with relative displacement, initially dominated by the grout resistance then at higher relative displacements, the friction with radially pressured soil takes over. The grout provides very high USF values up to a relative displacement of 2mm. Then, the USF drops to a typical pile soil side friction behavior; however, this friction is affected by the contact stress between pile and soil, which significantly increases due to compaction grouting. INTRODUCTION Base and shaft pile grouting has been significantly developing in recent years to accommodate the unfavorable conditions in major projects such as the high loads in high rise building and founding on problematic soil formations. Grouting aims to decrease settlements and increase the capacity of the pile under axial load. The technique is first introduced by Kraft (1974) but gained popularity in the 1980s. Typically there are two types of grouting; compaction, and permeation. Compaction grouting is more common in pile foundations practice, and many researchers have provided case histories of pile load tests on base grouted piles and base and shaft grouted piles (Gouvenot and Gabaix,1975; Stocker, 1983; Ghazali et al., 1988; Fleming, 1993; Kusakabe et al., 1994; Robson and Wahby,1994; Joer and Randolph, 1998; Hamza and Leoni, 1998; Mullins et al. 2000; Littlechild et al., 2000; Suckling and Eager, 2001; Dapp and Mullins, 2002; Ho, 2003; Fu and Zhou, 2003; Brettmann and NeSmith, 2005; Ruiz, 2005; Mullins, 2006; Dapp and Brown, 2010; Beadman et al., 2012; Nguyen et al., 2013; Miller et al., 2013; Sinnreich and Simpson, 2015; Hui and Lin, 2015). Compaction grouting is meant to densify the soil around the pile and below the base rather than permeate this soil and increase its cohesion. Research showed that grouting increases the capacity of the piles by a factor of 2~5. The variation in capacity increase depends on pile type, grouting process, and especially grouting pressure. Although there are many case histories of pile load tests on grouted piles but there is no well-defined agreed-upon method to predict grouted pile capacity as typically done in ungrouted piles. Few lab experiments discussed the shaft grouting effects on the soil especially the compaction grouting. The experiments concluded that the compaction grouting forms a homogeneous layer between the pile and the soil, and a residual effective stress is achieved simultaneously with a significant densification of the soil around the pile with noticeable decreasing in void ratio. (Fattahpour et al., 2015; Wang et al., 2015). Recently, studies used numerical analysis to investigate the behavior of the grouted piles and the changes in the surrounding soil (Chiang et al., 2013). That study presents a simulation of the base pressure grouting with a simple FE model and predicts the reduction of the pile settlement by 10 to 20%. Another numerical study using a complex model conducted by Zhou et al. (2017), pr

Jan 1, 2018

By J. A. Finch, A. R. Laplante, R. Espinosa-Gomez

"The Niobec concentrator rejects up to /5% of the Nb as slimes (-10u.m). The recovery of Nb from these slimes by column flotation is being studied. An essential condition for selective flotation is slimes dispersion. A particle size analyzer, the Sedigraph 5000D, was used to monitor dispersion in plant waters with combinations of organic and inorganic dispersants and flotation reagents. Flotation reagents were particularly detrimental to dispersion with sodium silicate. The best dispersion conditions were selected for column flotation tests. These tests revealed that reagent combination had a pronounced effect on froth stability. Careful frother selection achieved good froth stability under conditions of good dispersion. Plant water increased the required dispersant concentration causing mineral depression.IntroductionSlimes (-10 u.m) rejected at Niobec contain up to 15070 of the over-all Nb content . Recovery of Nb from these slimes would significantly increase over-all recovery. A suggested recovery route involves two phases: (1) carbonate flotation (to remove most of the carbonates) depressing silicates and pyrochlore (as currently done at Niobec); and (2) selective (direct) pyrochlore flotation from the silicates. Phase 2 has been addressed and several routes to achieve selective flotation are available. Phase I was attempted with the selective reagent scheme used at Niobec but a considerable amount of pyrochlore floated with the carbonates due to poor slimes dispersion."

Jan 1, 1987

A systematic study of groundwater conditions at eight underground mine sites exhibiting a wide range of groundwater qualities throughout Australia has been completed at the WA School of Mines. This has resulted in a new corrosivity classification for groundwater driven corrosion processes for cement grouted cable strand used in the Australian underground mining industry. The new corrosivity classification is simple to use and corrosion rates may be predicted from readily obtained in situ measurements of groundwater dissolved oxygen.

Jan 1, 2008

By S. Y. Chen

A new process comprising metallizing reduction, magnetic separation, and electroheat melting separation is proposed with the aim of achieving high recoveries of iron, vanadium, and titanium from vanadium titanomagnetite. The effects of magnetic intensity, reduction temperature, reduction time, carbon ratio, and coal particle size on the efficiency of reductionmagnetic separation were investigated, the reaction mechanisms elucidated by SEM and EDS analysis, and the optimal process parameters established. Recoveries of up to 80.08% for titanium, 95.07% for iron, and 71.60% for vanadium were achieved. The reduction sequence is shown to be: Fe2O3 ? Fe3O4 ? FeO ? Fe; Fe2TiO5 ? Fe2TiO4 + TiO2 ? Fe + FeTiO3 ? Fe + FeTi2O5 ? Fe + TiO2.

Jan 1, 2014

By M. W. Hildyard

A blast was engineered close to a tunnel in a deep-level mine with the purpose of studying the wave interaction with the tunnel. Numerical modelling of seismic wave propagation was used in both the forward planning and the back-analysis of this experiment. This paper presents the forward analysis. A likely model for a propagating blast was investigated and developed. This model predicts the influence of the velocity of detonation of the blast and the rise-time of the blast on the radiation pattern, and hence on the expected positions of maximum velocity at the tunnel surface. An attempt was made to quantify the parameters of the blast model, using waveform data from two other blast experiments. The blast model caused particle velocities which were an order of magnitude lower than these measured velocities. Large values for blast pressure were required to match the amplitudes of the recorded velocities. An alternative ?effective? source with a similar mechanism but increased diameter was proposed to account for the higher velocities. It was established that distant velocities scale with the square of the borehole diameter. A calibration blast at the experimental site was also modelled. Agreement in the waveforms was not sufficient for conclusive statements to be made about the validity of the source model. However, the modelled waveforms show an encouraging correspondence with some measured waveforms. This gave confidence that the model could be used to examine wave propagation around the tunnel, and allowed a scaled source to be developed for forward analysis of the main experiment.

Jan 1, 2001

By D. Dodgen, L. Larrimore

Electric utilities depend heavily on coal as a major fuel source for power generation, annually producing more than 85 million tom of ash, boiler slag and FGD (flue gas desulfurization - "scrubber") materials as by-products. Utilities and others who bum coal have traditionally disposed of these by-products in ponds or landfills. However, in the last 10-15 years there has been a greatly increased emphasis on beneficial utilization of these materials by the producers themselves as well as by customers who purchase the by-products. Regulatory, cost and technical performance issues currently impact the use of coal ash and other coal combustion by-products (CCB).

Feb 24, 1997

By Sterling J. Anderson

Through the use of nondestructive testing techniques, the Bureau of Mines is pursuing a goal of improving the efficiency of the rock excava-tion process. Toward this end, 44 laboratory tests were conducted to identify a practical method of monitoring fracture development in rock, as caused by an excavation tool. An acoustic emission CAE) transducer was used to monitor the test samples as they were loaded. The signal from this instrument was recorded in real time along with the radial and axial loads generated by the fracturing device. Through the review of these signals on a common-time base, it was possible to see the relationship between the developing fracture and the loading conditions. As a part of the posttesting investigations, samples that were pletely fractured were sawn and ground to expose the fractures. examination of these samples allowed approximations to be made incom-Visual of the total surface created. Surface area approximations were also made for the completely fractured samples. Quantitative analyses· of the AE signals were conducted for comparisons with the calculated surface areas.

Jan 1, 1987

At Great Boulder Gold Mines Ltd. a number of attempts were made to remove water soluble copper and iron salts from calcined pyritic concentrates but variou~ problems arose and the methods were abandoned.A method of rapid washing has been developed and although some problems still exist a workable process was established which resulted in substantial savings of reagents used for the cyanidation of calcine.INTRODUCTIONIn the Great Boulder flowsheet crude ore is ground in cyanide solution, then thickened, agitated and subjected to two stage filtering. Secondary filter discharge is pulped with flotation circuit water, gassed with sulphur dioxide to precipitate soluble gold and activate pyrite, and after the addition of copper sulphate and xanthate, the pyrite and tellurides are recovered by flotation. Flotation tailings are thickened and pumped to the disposal area and concentrates are calcined in Edwards roasters. Calcine is washed to remove water soluble copper and iron salts and the washings pumped to the flotation section where the copper is used as an activator. The washed calcine is cyanided and returned to the crude ore circuit via the thickeners. Solution for precipitation in the Merrill Crowe is drawn from the crude ore thickeners.Prior to the introduction of calcine washing the calcine contained 7 lb/ton copper of which approximately 60 per cent was water soluble. It also contained approximately 90 lb/tol'l of water soluble iron salts. Both the copper and...

Jan 1, 1964

By X. Gu

Mining operations, especially surface coal mines, have great impacts on the local ecosystem and the environment. However, it has been a common practice in mine design that the economic evaluation considers only the operating and capital costs, while the costs incurred due to ecological damage are left out. Such practice underestimates the total cost of mining and ignores the difference in ecological impacts between different mine design alternatives. With growing interest in sustainable development, the mining industry is under increasing pressure to operate not only based on economic and engineering principles but also on principles of sustainability. Therefore, estimating ecological costs of mining and considering such costs in the mine design process is an important step towards reducing ecological impacts at the design stage. The objective of this paper is to quantify the ecological costs of open pit coal mining and to demonstrate the influence of such costs on the ultimate pit design. The ecological costs of mining are estimated based on the areas and types of land damaged by mining activities and the carbon emission from energy consumption. Four major components of ecological cost are identified, namely, lost value of direct eco-services, lost value of indirect eco-services, prevention and restoration costs, and the cost of carbon emission from energy consumption. Necessary equations are given for estimating these costs. An algorithm is described for ultimate pit optimization in coal deposits with near-horizontal coal seams. A case study is presented in which the ultimate pits with and without ecological costs are optimized and compared to show the influence of ecological costs on the pit design outcome.

Aug 1, 2013

By T. Tamura

It is known that the CaO-FetO-P2O5slag system has a wide liquid miscibility gap at steelmaking temperatures and this two-liquid slag phase has many advantages such as high activities of both FetO and CaO and high amount of P2O5. The phosphorus distribution ratio between the two-liquid slag and molten steel was confirmed to be higher than that between CaOsat.-FetO-P2O5slag and molten steel. The two-liquid slag may be useful for dephosphorization of molten steel and reduction of slag volume. Furthermore, the phase equilibrium of two-liquid CaO-FetO-P2O5slagsaturated with MgO was measured to determine the applicability of the two-liquid slag to dephosphorization in steelmaking process. Keywords: slag, refractories, solid solution, two-liquid phase, dephosphorization, steelmaking, phase equilibrium.

Jan 1, 2004

By R. T. Jones

Slags have been produced as by-products from pyrometallurgical processes for thousands of years, and have generally been regarded as waste. Many of these slags are no longer seen as residues merely to be discarded, but as potential economic sources of metals, or as useful by-products in their own right. Slag cleaning can enhance the recovery of valuable metals in existing pyrometallurgical processes, or can produce economic value from recycling old slag dumps. For example, a process has been developed and implemented industrially for recovering cobalt from copper smelting slag in a DC arc furnace. The relatively non-leachable behaviour of glassy slags allows them to be used as a very safe means of disposal of metallurgical waste streams, including many that are classified as hazardous. The high temperatures, reducing conditions, and good mixing that can be achieved in a DC arc furnace enable the effective functioning of this environmentally beneficial means of disposal. Lead blast furnace slag can be rendered safe for disposal by treating it using the Enviroplas process, which strips most of the hazardous lead from the slag (and traps the rest in an insoluble glassy slag) and recovers economic quantities of zinc by absorbing (in a lead splash condenser)the zinc vapour that is fumed off in the furnace. Another example can be seen in the recovery of a chromium- and nickel-containing alloy from stainless steel plant dust, while producing a disposable residual slag. The examples presented here illustrate that it is possible to develop processes that are both economic and environmentally beneficial. Keywords: DC arc furnace, plasma, slag cleaning, cobalt recovery, zinc fuming, Enviroplas, jigging, re-melting fines, environmental, economic

Jan 1, 2004