Search Documents

By E. Pizarro, A. Videla, G. Compan

One of the main problems related to mining investment decisions is the use of accurate prediction models. Metallurgical recovery is a major source of variability, and in this regard, the Chuquicamata processing plant recovery was modelled as a function of geomining-metallurgical data and ore characteristics obtained from a historical database. In particular, the dataset gathered contains information related to feed grades, ore hardness, particle size, mineralogy, pH, and flotation reagents. A systemic approach was applied to fit a multivariate regression model representing the copper recovery in the plant. The systemic approach consists of an initial projection of the characteristic grinding product size (P80), based upon energy consumption at the particle size reduction step, followed by a flotation recovery model. The model allows for an improvement in the investment decision process by predicting performance and risk. The final geometallurgical model uses eight operational variables and is a significant improvement over conventional prediction models. A validation was performed using a recent data-set, and this showed a high correlation coefficient with a low mean absolute error, which reveals that the geometallurgical model is able to predict, with acceptable accuracy, the actual copper recovery in the plant.

Jan 1, 2015

By P. Falcão Neves

A detailed analysis of the geomechanical behaviour in rock cutting with a diamond saw is provided to obtain a better understanding of the mechanisms involved in the process. The energy of elastic deformation (before failure) and plastic deformation (post failure) was determined in uniaxial compression tests as well as the energy consumed per unit volume in the cutting process. The test samples are White and Ruivina marbles from Borba - Vila Viçosa in Portugal. Correlations between total deformation specific energy and cutting specific energy, normal and tangential forces and diamond indentation are analysed, and some conclusions are presented.

Jan 1, 2012

By M. Wang, Z. Sui, T. Lou

After smelting, the associated mineral ore accompanying Valuable Metal Compounds (VMC),such as titania and borate in BF., most of the VMC were separated from the metal into the molten slag that is an associated slags. Based on several case studies in laboratories and in a practice in a pilot plant on the associated slags , there occur a feasibility to recovery VMC from the slags by anew process- Selective Precipitation Technique (SPT) on which three continuous steps are involved: (1) The selective enriching the dispersed VMC into a designed mineral phase in the molten slag; (2) The selective coarsening the designed mineral phase with large crystal grain size;(3) The selective separating the coarsen phase from tailing by mineral dressing or hydrometallurgical process . Some results on the recovering the VMC from the associated slags by SPT were summarized as examples in present paper. Keywords: selective precipitation technique, associated slag, recovering metals from slag.

Jan 1, 2004

By C. Siyasiya

One of the problems that is occasionally encountered during the continuous casting of DIN 1.4003 stainless steel (hereafter referred to as 1.4003) is the side bulging effect, a problem that is generally prevalent in ferritic stainless steels. This occurs because the unconstrained narrow sides of the solidification shell are not able to withstand the ferrostatic pressure once the strand has emerged from the mould. Coupled with side bulging, there is strand width variation at high temperatures, i.e. when the steel is in the ferrite-austenite dual phase region. Both of these dimensional changes to the slab profile create some processing problems in subsequent hot rolling operations when unacceptable width variations are encountered. The strength of the solidification shell and its ability to withstand the ferrostatic pressure during continuous casting is dependent on its thickness and phase composition when exiting from the mould up to a few metres downstream. From the study of the high temperature metallurgical behaviour of this steel, it was observed that a thicker solidification shell when exiting from the mould and a higher austenite volume fraction in the steel would be favourable for the reduction of the side bulging effect during continuous casting. It was also found that as long as the d-ferrite to austenite phase ratio keeps fluctuating due to variations in chemical composition and process control in the dual phase region from cast to cast, the strand width variation problem would probably persist. The remedy to this effect lies in more strict chemical composition and process control during continuous casting of this steel. The hot ductility experiments revealed that 1.4003 exhibits good hot ductility in the strand straightening temperature range with a minimum of 75 per cent reduction in area and this was attributed to the high volume fraction of ferrite (0.2 to 0.4) in the steel. This would provide a remedy to side bulging by increasing the secondary cooling rate of the strand in order to form a thicker solidification shell without necessarily risking transverse cracking and other surface defects during unbending. Keywords: side wall bulging, resistance bending moment, applied bending moment, ferrostatic pressure.

Jan 1, 2005

By P. Falcão Neves

A detailed analysis of the geomechanical behaviour in rock cutting with a diamond saw is provided to obtain a better understanding of the mechanisms involved in the process. The energy of elastic deformation (before failure) and plastic deformation (post failure) was determined in uniaxial compression tests as well as the energy consumed per unit volume in the cutting process. The test samples are White and Ruivina marbles from Borba - Vila Viçosa in Portugal. Correlations between total deformation specific energy and cutting specific energy, normal and tangential forces and diamond indentation are analysed, and some conclusions are presented.

Jan 1, 2012

By G. Hangone

Paper written on project work carried out in partial fulfilment of MSc thesis This paper investigates the effects of thiol collectors: xanthates, dithiophosphates, dithiocarbamates and mixtures of these on the froth flotation performance obtained with a bornite-rich copper sulphide ore from Okiep Copper Mine with a feed grade of 1.8%copper. Batch flotation tests were used to assess the performance in terms of mass-water recovery, sulphur grade-recovery and copper grade-recovery relationships and the Klimpel rate constant for copper recovery. The results showed that the di-ethyl-dithiocar-bamate (di C2-DTC) was the weakest collector of copper sulphide minerals. Highest copper recoveries were obtained with the di-ethyl-dithiophosphate (di C2-DTP), which were accompanied with more watery froths and lower copper grades demonstrating frothing properties in addition to collector action. Superior copper recoveries were obtained with the 90% ethyl xanthate (C2-X):10% di-ethyl-dithiophosphate (di C2-DTP) and 90% ethyl xanthate (C2-X):10%di-ethyl-dithiocarbamate (di C2-DTC) collector mixtures compared to that obtained with ethyl xanthate at an equivalent collector dosage of 0.139 mol/ton ore (a dosage equivalent to 20 g sodium ethyl xanthate per ton ore). A superior copper grade was obtained with the 90% ethyl xanthate: 10% di-ethyl-dithiocarbamate collector mixture at a dosage of 0.0695 mol/ton ore compared to that obtained with ethyl xanthate at the same equivalent dosage. Keywords: flotation, collector mixtures, copper sulphide ore

Jan 1, 2005

By B. Andresen, S. T. Johansen, H. Tveit, S. Grådahl, B. Ravary

The Norwegian ferroalloy industry has high ambitions regarding environmental standards. Basic research work has been performed to improve the fundamental understanding of ferroalloy processes and the environ-mental aspects. This paper will present work dealing with the understanding of formation and control of NOx, PAH and dioxins. During this work various techniques and methods have been applied, such as comprehensive industrial measurements, laboratory experiments, model development and application of Computational Fluid Dynamics (CFD). The main goal has been to reduce the environmental impact of ferroalloy plants, by means of improving the combustion processes done by introducing new charging routines and optimized furnace operations, instead of installing expensive gas treatment systems. The Norwegian obligations in accordance with the Gothenburg protocol are to reduce the NOx emissions by 30%, compared with the 1990 level within 2010. Measures developed in this work have resulted in 40-60%reduction in NOx emission, and major reductions in PAH and dioxins for ferrosilicon and silicon metal plants. This has been achieved by introducing semi continuous charging and improved furnace operations. Semi continuous charging and optimized furnace operations are shown to reduce the blowing activity (i.e. emission of large quantity of SiO over the charge by direct channelling from the crater zone). It also reduces variation in off-gas temperature and dust production. To understand the processes and to achieve our results we have used online equipment, with fast sample rates and response times, to measure the off-gas compositions and temperatures. Most of the measuring techniques used are based upon optical principles making use of the absorption- and emission spectrum of the gases. In addition a new prototype instrument is developed for continuous measurement of off-gas characteristics, total dust amount and off-gas temperature. The presented work is a result of a long term co-operation research and development teamwork, between the industry and the research community, and has improved both the process and reduced the emissions. The work has introduced new process design and operation standards, and has resulted in ferroalloy production with better environmental standards.

Jan 1, 2007

The acoustic signals emitted from a laboratory-scale ball mill were used for the estimation of the comminution of two complex sulphide ores, viz. Merensky and UG2 ores from the Bushveld Igneous Complex in South Africa. The digital acoustic signals were transformed to power spectral densities that could be related to particle size distributions (-75 µm to 4000 µm) in the mill by use of continuum regression. This approach is more general than principal component regression methods or Kalman filtering used previously and resulted in significantly more accurate calibration in the case of the Merensky ore, where approximately 93.4% of the variance in the particle size distributions could be explained. With fewer data available, the variance in the particle size distributions in the UG2ore could be explained less accurately (82.4%), but still satisfactorily. In addition, smaller particle sizes (less than 300 µm) could be modelled more accurately in the case of the UG2 ore.

Jan 1, 2000

By O. Naiker, T. Riley

Keywords: Pyrometallurgy, furnace, Xstrata, ferrochromium, Premus Technology The presentation will give a basic overview of Xstrata Alloys. Included will be a brief history of the Alloys division as well as of each plant within the division. The Xstrata chrome plants utilise a wide variety of production processes, including Xstrata's Premus process, the Outokumpu process, and the conventional process. Xstrata?s Lion Project is underway, with commissioning expected in the third quarter of 2006. The new smelter will utilize Xstrata?s patented Premus process, and the competitiveness of the Premus process is discussed.

Jan 1, 2006

By E. V. Lilford

The South African Minerals Development Act (?the Act?) has been promulgated and will come into full force and effect once it is gazetted. Thereafter, all Old Order mineral rights will have to be converted into New Order mineral rights within a 5-year period, probably by the end of 2008. The conversion of rights will be achieved only with the demonstrated inclusion of empowerment groups in the conversion applications. In addition to the Act, the first draft of the proposed Royalty Bill (?the Bill?) was released during the week beginning 17 March 2003. Comments on the Bill?s contents had to be submitted before 30 April 2003. The contents were to be considered in terms of applicability and acceptability to the South African minerals industry, where after proposed comments and suggested amendments were to be submitted to the relevant State Treasury office. Specifically referring to the Bill, the general response from the industry is one of concern. Since any royalty is tantamount to a tax, the general feeling is that the current mining taxation rates are already internationally competitive and to increase these effective rates, notably at differing rates depending on commodity type, will have an adverse impact on the South African mining industry. A number of these impacts can be mitigated to some degree, depending on the flexibility of the State to address the major concerns.

Jan 1, 2003

By M. F. Handley

Sequential grid mining has been employed as the primary mining strategy at the AngloGold West Wits Elandsrand Mine since the inception of stoping operations from the sub-vertical shaft system in 1988. Little has been published on sequential grid mining as a mining strategy since, and the purpose of this paper is to describe sequential grid mining, its history, its implementation at Elandsrand, and the outcome to date. The results obtained using sequential grid mining have been evaluated from seismic data, productivity statistics, and rock related accident statistics. Comparisons with neighbouring mines namely Western Deep Levels and Deelkraal, have been made to substantiate the improved conditions observed at Elandsrand, and to compare sequential grid mining directly with longwall mining in similar conditions and at similar depths. Sequential grid mMining is shown to be cost-effective, more flexible, and safer than long wall mining in similar conditions, at least on the Ventersdorp Contact Reef in the western part of the Carletonville Goldfield. More work is necessary to establish it as the favoured mining strategy at depths exceeding 3000 metres, and for reefs other than the Ventersdorp Contact Reef.

Jan 1, 2000

Novel flotation reagents were developed to improve the flotation of coarse particles. Laboratory tests conducted on an anthracite coal sample from Kyung-Dong Coal Company, Korea, showed that the reagents can successfully clean 2?3 mm top-size materials. Pilot-scale tests conducted on a 1.41 mm x0 coal gave substantially better results than those obtained using kerosene as collector. The pilot-scale test results were used to develop a flowsheet, in which the 1.41 mm x0 fraction is cleaned by flotation and the 4 x1.41 mm coal is cleaned by single-stage spirals. The performance of this circuit was compared with another flowsheet, in which the 0.5 mm x0coal is floated using the conventional flotation reagent, with the 4 x0.5 mm material being cleaned using two separate spiral circuits. The performance of the two flowsheets was compared by computer simulation. The results showed that the flowsheet consisting of the coarse particle flotation circuit can give substantially higher yield sat a given product grade. Keywords: coal flotation, coarse particle flotation, collector, spirals, computer simulation.

Jan 1, 2002

By Y. Mao, D. Xie

The viscosity of TiO2-containing blast furnace slags may increase rapidly (commonly referred to as thickening) under strong reducing conditions in the blast furnace. To elucidate the mechanisms for slag thickening, measurements have been made of changes in the composition and rheological properties of TiO2-CaO-SiO2-Al2O3-MgO slags during the reduction process. The slag composition covered the range of 17–33 wt% TiO2, 9–19% Al2O3, 8–16% MgO and theCaO/SiO2from 0.8 to 1.4. The viscosities were measured using the rotating cylinder method at temperatures up to 1550ºC and the fusibility temperatures were determined from ‘breaks’ in the viscosity-temperature curves. The reduction of the slag was carried out in graphite crucibles at1500ºC for 2–6 hours The rheological properties of the slags during reduction were predominantly influenced by the slag basicity (CaO/SiO2), and the effect of other components depended largely on basic or acidic behaviour of the oxide. The reduction of TiO2in the slag by carbon was initially fast to formTi2O3, followed by further reduction to TiO and TiC. Correspondingly, the viscosity showed initially a slight decrease, followed by a gradual and then rapid increase. The thickening was found to be accelerated by an increase in TiO2content and a decrease in the CaO/SiO2in the slag. In addition to the existence of 1~3 wt% TiC, the thickened slags also had a significant amount of TiO (3~7 wt%), suggesting that TiO may play an important role in the ‘thickening phenomena’ ,possibly by forming solid solutions with TiC to significantly increase the number of solid particles in the heterogeneous slag. Keywords: TiO2slags, viscosity

Jan 1, 2004

By Q. G. Reynolds

DC arc furnaces are widely used for steel scrap melting, and are increasingly being used for smelting applications as well. The electrical resistivity of slags varies widely, from highly conductive slags in ilmenite smelting, to highly resistive slags in applications such as cobalt recovery from non-ferrous slags, and nickel laterite smelting. Models have been developed to predict the electrical behaviour of the DC open plasma arc and the molten slag bath. These models allow the voltage and current ranges of furnace power supplies to be specified.

Jan 1, 2004

By H. Pei

PZH (Pan Zhi Hua) Iron and Steel (Group) Corporation, the biggest steel company in southwest China, has been using titanium-vanadium-magnetite as the main raw materials for blast furnace iron making processing for over 30 years. One of the problems that has a negative affect on the blast furnace operation is slag foaming. Based on the chemical components of the blast furnace slag-bearing higher TiO2, the foaming properties were studied. The TiO2content, which is calculated according to the total titanium content in all the forms of titanium compound in the slag, in this research is 30% weight per cent. Different forms of titanium compounds have different actions on the slag foaming behaviour that depends on the reduction condition in the blast furnace. The relationships among slag foaming performance and the binary alkalinity of the slag, the content of CaF2, MnO in slag, and the amount of gas injected in slag are investigated. The results show CaF2 and MnO have a stronger anti-foaming affect on the slag, even in the lower percentage. The way to measure high TiO2slag foaming performance and how to eliminate foamy slag are also discussed. Keywords: blast furnace slag bearing TiO2, foamy slag, foaming performance

Jan 1, 2004

By Conné Spangenberg

Contents ?Introduction ?Metal accounting environment ?Problem statement ?Investigations & Achievements ?Metal Accounting ?Principles ?Standards ?Audits ?Questions

Jan 1, 2005

By L. Bbosa

Paper written on project work carried out in partial fulfilment of BSc (Hons) (Eng) (Mechanical) degree Discrete element methods (DEM) are being used to provide detailed impact histories of the particles in comminution devices, such as mills. To match this immense detail of information, far more informative breakage tests than those that are generally conducted are now required. The split Hopkinson pressure bar apparatus is used in this study, as it allows the calculation of breakage forces and absorbed energies. The geometry of rock particles has been identified as significant, so this project undertook to identify the influence of shape on the breakage pattern of blue stone. Comparisons are then made between the breakage pattern of angular rocks and rounded, milled rocks for single impact fracture and consecutive impact loading at low energy. Results of this experiment indicate that although breakage for both geometries occurs over a similar energy range, rounded particles have the greater probability of fracture because they absorb more of the impact energy for a given loading. Size distributions of progeny show that five pebbles or more are sufficient to predict the distribution of most particles in small energy regimes. Cumulative impact testing shows that considerably more energy is required to break a rock through cumulative damage than through a single impact?this is of considerable importance in the light of the indications from DEM simulations that most breakage in a mill will be from cumulative damage rather than single impact breakage.

Jan 1, 2006

The excavation of ramps and tunnels often requires high-speed development with (or without) the use of high-energy mining equipment such as loaders, dump trucks, TBMs and roadheaders. This high-speed development creates a challenge in terms of providing a safe and productive working environment. For example, heat from continuously exposed surrounding rock, heat from broken rock, heat generated by mining equipment, potential in flows of hot ground water, pollution from associated diesel equipment and the distance of the advancing face from fresh through-ventilation all have to be taken into account when designing ventilation systems for high-speed ramp and tunnel developments. This paper discusses methods of achieving acceptable environments at the face and along the length of the tunnel. The methodology has been successfully implemented in the development of long (up to 20 km) TBM drives in the Lesotho Highlands Project and in mining projects in hot rock using drill and blast methods as well as mechanized methods using continuous miners and roadheaders. The determination of heat loads includes calculation of the heat flow within the surrounding rock, evaluation of the operating cycle of the equipment and the contribution to the overall heat load of the broken rock as it travels out of the tunnel. The determination of heat loads from surrounding rock in new tunnels required a modification of the algorithms generally used for established excavations. The paper also examines the use of, for example, mobile duct and fan systems to ensure that fresh air is delivered to the specific areas where workers are located.

Jan 1, 2000

By D. W. Nel

Nanofiltration (NF) has attracted much attention over the past few years due to the reduced energy consumption compared to reverse osmosis (RO) and better separation performance compared to ultrafiltration (UF). Although research has been done in the area of NF of nickel ions, sodium ions, and acid separation, not much attention has been given to the separation of high nickel concen¬trations from sulphuric acid streams. The use of NF for the separation of nickel and acid from a spent nickel electrolyte is an innovative process alternative for future industrial application within a base metal refinery. In this study, the separation performance of a composite polyamide NF membrane on a spent nickel electrolyte was investigated by varying the sodium sulphate concentration in the feed (50-150 g/l), the trans-membrane pressure (35-55 bar), and cross-flow velocity (1.5-3.5 m/s), and measuring quantities such as total permeate flux, acid rejection, nickel rejection, and sodium rejection. The nickel and acid concentration in the feed were kept constant with variations between 40-60 g/l and 25-40 g/l respectively, while the temperature of the experiments was kept constant at 50°C. The membrane was found to be very selective for nickel ions, with the rejection of nickel ions varying between 54.4% and 98.2%. The rejection of acid ions varied between -5.9% and 21.8%. The rejection of sodium ions varied between 16.6% and 72.4% at a cross-flow velocity of 2.5 m/s and sodium sulphate concentration of 50 g/l in the feed solution. An increase in trans-membrane pressure increased the rejection of nickel, sodium, and acid ions, while an increase in sodium sulphate concentration decreased the rejection of nickel and acid ions. The total permeate flux was found to increase with an increase in trans-membrane pressure and decrease with an increase in sodium sulphate concentration. The cross-flow velocity had an insignificant effect on the total permeate flux and the rejection of nickel, sodium and acid ions.

Jan 1, 2013

Existing processes for the recovery of platinum group metals (PGM) from UG-2 ores place stringent requirements with regard to chromite content upon feed material to the plant. An alternative hydrometallurgical process for which this is not an issue is proposed that involves reductive roasting of the ore followed by leaching with HCl/chlorine, ion exchange, and recovery of PGM from the ion exchange eluate by reduction. Problems associated with leaching of PGM are discussed and results of laboratory testwork for each of the process steps are given.

Jan 1, 2004