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By C. A. Hardie, G. F. Leichtle, J. A. Finch, J. A. Watson

"The recycling of wastepaper has become an important and common process worldwide. Techniques similar to those used in the mineral processing industry are used to produce high quality recycled fibres for use in newsprint. The mineral processing group at McGill University, in conjunction with the Pulp and Paper industry (Mechanical and Chemi-mechanical Wood Pulp Network), has adapted one of these techniques, column flotation, for the purpose of deinking wastepaper. This article describes the typical process of recycling wastepaper from a mineral processing point of view. It also presents results from McGill University’s flotation column test work at a Québec wastepaper recycling facility. IntroductionThe recycling of wastepaper has become an important and common process worldwide, including Canada which is now the world’s largest importer of wastepaper (CPPA, 1996). Much of the current drive to increase the utilization rate of recovered paper is a reaction to the solid-waste disposal problem that faces many Canadian and United States municipalities. The real problem in the disposal of solid waste is not the absolute amount of garbage that must be disposed of each year, but this amount in relation to available disposal capacity.Environmental restrictions on the creation of new landfill sites and incinerators (the two main options for disposal of municipal solid waste) have tightened the demand/supply balance in the solid waste disposal market. This shrinking availability of waste disposal sites in the face of increasing population with greater disposal requirements defines the Developed World’s solid waste crisis. Not only are there fewer disposal sites available, but the costs of using them is skyrocketing. These factors have increased government regulations mandating recycled paper content in newsprint. Conservation and environmental issues make the current drive for wastepaper recycling a real issue and business opportunity."

Jan 1, 1999

By A H. Clemens, P Lindsay

Acid producing potential static tests have been undertaken on sample lithologies from New Zealand coal mines, to rank the lithogies into acid producing waste rock and stable non-acid producing waste rock. Results indicated that the main acid producing waste rock in the Waikato coal region are the marine Whaingaroa siltstone and the Glen Massey formations and the main alkaline producing lithologies were the Tauranga group volcanic-derived sediments (A & D) and the Mesozoic basement. Coal ash analysis of 28 samples from 28 mines have also been analysed for reactive S percentage and their base potential has been quantified by the chemical index of alteration (CIA). The results provide mine management in the Waikato Coal region with a classification of problematic and stable waste rock types. XRF and CIA values determined from wash drill cuttings would provide a method of determining waste rock volumes and magnitude of palaeo-weathering underground.

Jan 1, 1999

By Arndt C. R

The Ispat Mexicana SA de CV (IMEXSA) pelletising plant is located at Lazaro Cardenas on the west coast of Mexico. It is the primary source of feed stock for the adjacent direct reduction (DR) plants and steelmaking facilities. The initial design of the pellet plant began in 1981 for 3 Mtpa of DR grade pellets using local concentrate received by pipeline.' Several construction delays, an ownership change, and a decision to use imported concentrates delivered in 60 000 to 90 000 tonnes ship cargoes required flowsheet modifications and additions. The design concepts are described for the plant which includes concentrate regrind to final pelletising particle size.

Jan 1, 1999

By A. E. Wraith

The tuyère flow rates of Peirce-Smith converters and bath smelting reactors are rendered particularly sensitive to accretion formation, bath depth variations and the general aerodynamic design of the blast delivery system by the limited pressure-flow properties of the conventional single stage centrifugal blower. This sensitivity is examined in terms of tuyère practice, vessel management and fixed engineering parameters for Peirce-Smith converters and the Noranda Reactor by use of the flow resistance factor, R*. New understanding of the effect of accretion growth on the flow behaviour of individual tuyères shows that blowing rates and hence throughputs could be optimised by careful attention to operating detail even within present plant constraints. The concept of the resistance vector is introduced to elucidate comparisons between different practices and to provide reference standards for optimisation. On this basis, the benefits of introducing quite moderate changes in the pressure-flow properties of the blast delivery system are considered. In view of recent developments in the flexible use of converters as hybrid bath smelting vessels for matte production, the foundation is now laid for a searching consideration of relationships between vessel volume and shape, blowing requirements, tuyère performance and production rates, the detail of which will be examined more appropriately in a forthcoming paper.

Jan 1, 1999

By S. Seetharaman

The present paper presents. the concept of micro-models and illustrates the application of the same in the simulations metallurgical processes. Development of micromodels requires access to accurate thermodynamic, thermophysicaland kinetic information for the relevant systems with suitable models to extrapolate the data as functions of temperature and composition. Experimental measurements and modelling of the thermodynamic properties, sulphide capacities and viscosities of oxide melts carried out in the department are presented. The incorporation of these models in process models, with special reference to ladle refining of steel is illustrated. Typical example of micro-modelling of solid-gas reactions is also presented.

Jan 1, 1999

By S. Viswanathan, Q. Han, A. S. Sabau

"In spite of recent advances in the mathematical modeling of fluid dynamics for materials processing applications, no significant advances have been made in the numerical discretization of these equations. In this work, the application of two-step projection methods for the numerical simulation of interdendritic flows is discussed. Unlike previous methods, the methods presented here are constructed for the exact equations which are characterized by variable density and volumetric fraction of the liquid. The drag terms, which describe the momentum loss due to the flow around and through the dendrite structures, are treated implicitly. Numerical examples for shrinkage-induced flow during solidification of an Al-4.5% Cu alloy bar is used to illustrate the effectiveness of the proposed algorithm.IntroductionLiquid contraction during solidification plays an important role in the formation of casting defects such as shrinkage voids, microporosity, and macrosegregation. Owing to their importance, the study of transport processes during solidification have received considerable attention during the past years [1, 2]. By the use of volume-averaging techniques, the mass and momentum equations for flow through a stationary dendritic structure were derived [3]. By using the volume-averaging techniques for multi-phase systems, two-phase transport equations for solidification problems were derived [4]."

Jan 1, 1999

By E. Almendras de Siegel

Pyrometallurgical processes have the thermodynamic capability of treating complex and dirty ores and concentrates to produce high purity metals and inert slags. Modem pyrometallurgical processes are environmentally sound and competitive with other processes. However, there is still a need for sensors and other practical tools that permit a rapid evaluation of the performance of these processes. In order to contribute to satisfying this fundamental requirement, the authors developed the IDENT.LA software that permits the automatic mineralogical analyses of inorganic materials, including the final and intermediate products of pyrometallurgical processes. The technique allows determining the grain size distribution of mineralized inclusions, the surface relations between metallic phases, and conducting modal analyses of the essential phases that are present in the samples. Three basic automatic operations are performed: creating a representative image of the sample; identifying the metallic and non-metallic phases; and measuring the features of the resulting image. The results are used to evaluate the performance of pyrometallurgical and other processes. In this paper, the authors discuss the application of the technique to a sample of slag from a slag cleaning process that uses a carbonaceous reductant. In this case, process performance impacts not only on the efficient reduction of the slag magnetite and on copper recovery but also on the quality of the process off-gas. The mineralogical analysis of the slag is a valuable tool in assessing process performance and in recommending changes of operating conditions.

Jan 1, 1999

By J Aydin Bilgin, Sedat Esen

This paper describes the ideality of some commercial explosives with the help of the detonation theory and detonation velocity measurement. Ideality of an explosive can be determined by comparing experimentally measured and ideal detonation velocities. A measured detonation velocity at a certain charge diameter markedly lower than the ideal value indicates incomplete reaction and thus non-ideal detonation. Since it is shown that commercial explosives exhibit non-ideal behavior, two-dimensional detonation theory should be used to evaluate the performance of explosives. This theory enables to compute the detonation properties of explosives (detonation velocity, detonation pressure, etc.) as a function of charge diameter and confinement. The use of the one-dimensional detonation theory to compute the detonation properties for commercial explosives has an error associated with it as these calculated properties are independent of charge diameter and confinement. It assumes that shock front is planar. Hence, it is incapable of assessing the ideality of the explosives due to its assumptions. Shock front in real situation is curved in shape but not planar as in one-dimensional detonation theory. In this paper, the non-ideal behavior of some commercial explosives is modeled using EXRINT code based on the steady-state two-dimensional detonation theory firstly. Then the degree of ideality of each explosive found from the code is checked using detonation velocity test results conducted at a quarry. It has been shown that idealities of the tested explosives determined by the code agree well with the field detonation velocity test results.

Jan 1, 1999

By Walter Valery, Peter Radziszewski

"The NewCrest Cadia operation boasts the largest SAG mill commissioned last June 1998. A request was made to shed some more light on possible SAG mill charge behaviour. Three different software were used to simulate SAG mill charge behaviour:Mishra/Rajamanis MillSoft DEM charge motion program, Radziszewskis agglomerated DEM charge motion program and Powell/Nuricks MillTraj outer trajectories program. The contexts simulated are: 20/30 % charge volume, 65/75/85 % critical speed using the Hi-Lo lifter configuration specified for the mill as well as a Hi-Lo 60 degre lifter face configuration. Further, lifter interval was also studied to determine the effect on power draft. Power predictions are compared with those obtained during the commissioning period.INTRODUCTIONThe NewCrest Cadia operation is located outside of Orange, New South Wales, Australia. With proven reserves of 190 million tonnes at a grade of 0.75 g/t Au, the mill was designed to process 17 Mtpa (2065 tph) of ore with an 86% copper and 73% gold recovery. The grinding circuit (Fig. 1, Table I) boasts the largest SAG mill (Fig. 2) and was commissioned last June 1998."

Jan 1, 1999

Asian countries are now facing very crucial aspects of urban living under the recession of the economy. The current situation is such that those hard aspects may make the living standards worse and worse in the next century, unless proper measures are taken on the infrastructure for urban lives. More than half of the population in Asian countries are now living in cities. Nowadays, the socio-economic development of the Asian countries has been closely linked to the development of world economy because of the border-less economy system. The population inflow to big cities is inevitable as the Asian countries step into an industrialised economy. Such a tendency will be further accelerated when Asia becomes a centre of financial business in the 21st century. The government of any country has realised the situation very well. The United Nations has established a specific agency to solve the problems caused by the rapid urbanisation. This global agency for urbanisation is named United Nations Center for Human Settlement and it is so called Habitat. There are three Habitat offices in the world, Nairobi in Kenya, Santiago in Chile and Fukuoka in Japan. The activities of Habitat offices cover a wide field of issues such as housing, urban development, infrastructure and environment, etc. Habitat Fukuoka Office is serving Asia and Pacific in co-operation with the government offices concerned.

Jan 1, 1999

By Dennis W. Boehm

The building boom of the late 1970's and early 1980's has all but used up most of the better sites across the more populated metropolitan areas of the United States. This means that current buildings and other types of structures are being founded on more marginal sites. The use of marginal sites has placed ever-increasing quality control on the installation of the deep foundation systems utilized for these sites. Several remedial techniques are available for the repair of the deep foundation systems. These include minipiles, compaction grouting and jet grouting. Eight case histories are cited where these methods have been utilized to repair deep foundations.

Jan 1, 1999

By Timothy Ross

The Pittsburg & Midway Coal Mining Co.'s Kemmerer Mine is one of the deepest surface coal operations in the world, with the highwall extending to approximately 1,000 ft above the pit floor. To increase recovery, auger mining is being evaluated beneath the highwalls of several seams representing the current economic limit of pit development. The primary augered seam is over 50 ft thick, can approach 100 ft thick, and dips into the highwall at an average of 17 degrees. The seam thickness and dip present many geotechnical design and operational challenges for multiple Sup to five) lift augering. This paper presents the design criteria and methodology applied to determine appropriate web and septum thicknesses for the various cover depths anticipated, as well as operational measures that can be taken to increase overall coal recovery. The primary tool used in the design was the finite difference code FLAG. Models incorporating typical strata sequences associated with the coal seam were run at several different cover depths corresponding to the maximum anticipated auger penetration. Web and septum thicknesses were varied until the minimum thickness satisfying a given safety factor criterion was determined. Using this procedure, design curves were developed for web and septum thickness versus cover depth. Operationally, several recommendations were developed to ensure that overall coal recovery is maximized. By angering across the scam dip, auger penetration per hole can he increased dramatically, and by carefully planning maximum planned auger penetration versus hole spacing, increased coal recovery can be safely attained.

Jan 1, 1999

The viscosity of high magnesium content FeO-Fe3O4-SiO2-CaO-MgO slags at nickel flash smelting conditions was investigated using a commercial rotational viscometer. The studied parameters were compositions of slag and temperature. The viscosity of these slags was measured as a function of CaO, MgO, SiO2, FeO. Fe3O4 and Fe/SiO2 in temperature range from 1473K to 1723K. These slags contained 5.81 to 10.59 pct MgO, 0 to 10.37 pct CaO, 28.21 to 36.21 pct SiO2, 39.40 to 55.42 pct Fe and 1.1 to 1.5 Fe/SiO2.

Jan 1, 1999

By J. A. Organiscak

Two types of airflow splitting methods for improving longwall dust control were investigated by NIOSH's Pittsburgh Research Laboratory. These methods included a translucent mesh barrier and a staged spray barrier system to confine the shearer-generated dust to the coal extraction side of the long wall face while maintaining a cleaner split of airflow on the opposing worker walkway side of the longwall face. The translucent mesh barrier was shown to provide notable dust control effectiveness up to 60 m downstream of the shearer in both the laboratory experiments and a long wall field evaluation, provided the mesh barrier remains relatively parallel to the airflow. The staged spray barrier system showed marginal dust control effectiveness in the laboratory and subsequently was not field tested.

Jan 1, 1999

By M. T. Ityokumbul

Flotation is a surfaced-based separation process that exploits the differences in the hydrophobicities of the components. In the present paper, a review of both established and emerging nonmineral applications of flotation (oil removal, paper de-inking and separation of plastics) is presented and discussed. For each application, the theory of the process is compared and contrasted with mineral flotation. It is shown that the mass-transfer approach to flotation offers a good starting point for the analysis of these separation processes.

Jan 1, 1999

By G. Michael Lloyd

The term phosphate beneficiation often conjures up visions of processing technologies that physically separate the phosphate rock from some impurity and do not result in a change in the chemical nature of the phosphate rock. However, when we consider hydrometallurgical processing as a phos¬phate beneficiation technique we have to include all chemical treatments that convert phosphate rock into a more useful product. With most of the phosphate rock mined being used for fertilizer pro¬duction, the best known and most widely employed hydrometallurgical process is wet process phospho¬ric acid manufacture. In general, all phosphate rocks are so insoluble that there is no physical treat¬ment that will allow the phosphate content to be used by vegetation in a timely manner. However, after chemical treatment, 100% of the phosphate is readily available for vegetation nutrition. If there is a chemical beneficiation process that could be considered the standard method of treat¬ing phosphate rock it would have to be the wet pro¬cess for phosphoric acid production. In this process finely ground phosphate is reacted with sulfuric acid to give phosphoric acid and phosphogypsum. The phosphogypsum crystals are removed from the phosphoric acid solution and discarded; the phos¬phoric acid is further processed to give the finished fertilizer product. The primary reason that this pro¬cess was adopted so widely is because the phosphogypsum solid that is formed can be easily separated from the phosphoric acid, thereby removing the calcium portion of the phosphate rock and the sul¬fate portion of the sulfuric acid. Other acids have been used to treat phosphate rock but nitric acid is the only other acid used commercially. Nitric acid gives a mixture of phos¬phoric acid and nitrates that can be further pro¬cessed into N-P fertilizers, but the range of N/P grades that can be produced is limited. Hydrochlo¬ric acid has been used to react with phosphate rock, and it can be used to generate a pure phos¬phoric acid but only after solvent extraction to separate the calcium chloride from the phosphoric acid. And then there is the problem of what to do with the calcium chloride. The acid that has received the most attention as a substitute for sulfuric acid is phosphoric acid. In this process, the phosphoric acid reacts with the phosphate rock to give a mono-calcium phosphate solution. This process does not dissolve all the impurities in the phosphate rock, and these solids can be removed from the solution before sulfuric acid is added to convert the soluble calcium to insoluble phosphogypsum. Despite all the claimed advantages, this process has not found favor. A suc¬cessful application of this process to treat some of the lower grade phosphate rocks being used today would seem to have some distinct advantages. Other beneficiation schemes have been pro¬posed or practiced on specific phosphate rocks on a limited scale. These include calcination followed by water leaching to remove lime, weak acid

Jan 1, 1999

The history of civilisation continues to register a steady tide towards the urban life as the basis of its social organisation. The manifestation of this movement is a continuous growth and increasing density of population in our towns and cities, as the favourite space for the development of humanity. Naturally, this trend raises a certain number of problems which grow proportionally with the size of the city. The use of the underground space has an important role to play in solving such urban problems. But various issues must be taken into account when developing urban underground space.

Jan 1, 1999

By J E. Lynch

The Weda Bay nickel and cobalt laterite deposits on Halmahera Island, Republic of Indonesia were first drilled in May 1996 by Strand Minerals Pte Ltd (Strand). Subsequent exploration has delineated four large laterite provinces, parts of which have been diamond drilled to outline an indicated nickel resource of 59.9 Mt of 1.51 per cent Ni and 0.09 per cent Co within a total indicated and inferred resource of 117 Mt of 1.36 per cent Ni and 0.12 per cent Co. The project is held as a Seventh Generation Contract of Work (COW) by PT Weda Bay Nickel, which is jointly owned by Strand (90 per cent) and PT Aneka Tambang (ten per cent). Strand is a wholly owned subsidiary of Weda Bay Minerals Inc, a company listed on the Toronto and Alberta Stock Exchanges in Canada. Halmahera is located in the north-eastern part of the Indonesian archipelago at the convergent junction of three major plates and is a region of considerable tectonic and geological complexity. The western arms of Halmahera form a classic volcanic island arc while the central region and eastern arms contain ophiolite complexes and interlayered sediments. The extensive areas of laterite discovered at Weda Bay have developed over serpentinised harzburgites and dunites of pre-Cretaceous age. Weathering of these rocks has produced laterite profiles that are enriched in nickel and cobalt. There are three economically mineralised laterite types, namely limonites, ferruginous saprolites and saprolites and all are amenable to rapid pressure acid leaching with recoveries of 98 per cent nickel and 94 per cent cobalt in less than 20 minutes.

Jan 1, 1999

Blasting is an essential component of most mining operations, and is used to reduce the rock mass to a workable size distribution, as well as to create stable openings and pit walls. Frequently, there is little difference between the designs of blasts to achieve these two functions, though more advanced operations have developed different designs for these very different functions. To assist in the appreciation of how blasting practices can impact on the stability of rock openings and pit excavations, this paper reviews the role of high pressure explosion gases on final block stability. It is assumed that the stability of all surface and underground excavations are, to a greater or lesser extent, controlled by the interaction between discrete rock blocks. Typically, these blocks will be defined by either natural, or excavation induced, jointing.

Jan 1, 1999

By Richard Burt

"In seeking to supply the ever increasing needs for raw materials, the mining industry has been required to develop lower grade resources in increasingly remote regions of the world. This has resulted in the extension of many frontiers, both technologically and geographically.The accent of mineral processing research over the last few decades has been to “do existing things better”. There have been many breakthroughs in equipment and processes; however in general the accent has been to increase capacity of existing unit processes, often by orders of magnitude, or to refine the process itself by basic research and development. This has lead to added sophistication, enabling the process engineer to maintain optimum performance of his equipment while reducing the cost, and the amount of labour needed to operate the plant.While much of the increased requirement for resources is handled by the development of ever larger, lower grade orebodies, a significant portion still comes from the small miner - even the artisanal miner - operating in remote and often politically sensitive parts of the world. For them, innovation and simplicity are the keys, not sophistication.The tension between sophistication and simplicity - or research and reality - is specially evident in the area of gravity concentration of rare metals, such as tin and tantalum. This paper looks at this tension, primarily from the eyes of an operator and seeks to put into perspective the two paradigms."

Jan 1, 1999