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By A. E. Tercan, D. Mamurekli

Ordinary kriging on the assumption of a gaussian error distribution and indicator kriging were used to derive the probability that a given calorific value would or would not be exceeded by coal from an area of a deposit. The two techniques led to similar probability maps despite local differences; the lack of an absolute reference makes it impossible to judge which method is better for this particular application

Jun 19, 1905

By L Besra, A. R. Prasad, B. P. Singh

The role of surface-chemical phenomena and the physical processes that participate in the dewatering of a suspension of alumina trihydrate were subjected to a systematic investigation, which has increased understanding of the influence of surface tension, contact angle and adsorption in the process. The residual moisture content of the cake can be reduced significantly through the use of surface-active agents in slurry pretreatment or as wash-water additives. The effectiveness of a particular surfactant is hard to predict from any single parameter, but is dependent on its ability to reduce surface tension and possibly to modify the solid-liquid contact angle. If scaled up to industrial operation of the dewatering step of the Bayer process in India, the use of these chemical additives could substantially improve its process economics, reducing the fuel costs for thermal drying by a much as Rs 50/t

Jun 21, 1905

By Bakker J. de, P. A. Leest, W. L. Dalmijn, H. J. Glass

The test facility at the Delft University of Technology, in the Netherlands, was characterised. Advantages include the possibility of separating particles with high but different densities up to 9 g/cm3, the ease of adjustment to any required separation density and the absence of moving parts. Simultaneous separation of more than two types of particles is possible and the magnetic fluid is safe and convenient to use compared with other heavy liquids. Disadvantages include loss of magnetic fluid with outgoing particles (cost approx US $10/l) and degeneration of fluid due to bacterial activity, reaction with particles and with surroundings. Only non-magnetic materials can be separated, there is limited potential for scaling up and high investment is required on account of the cost of magnets. Future improvements in the design of the apparatus and the properties of the magnetic fluids can only enhance its attractiveness for commercial applications

Jun 18, 1905

By J. M. Jimenez, G. D. Schena, A. J. Cazorla

A full-scale Deister column was operated in parallel with the conventional cleaning bank of cells and a pilot Jameson cell in parallel with the conventional rougher cells. Flotation column performance was appreciably enhanced by use of an improved washing system and an internal launder. The performance of the rougher bank of cells, Jameson cells, cleaner cell bank and column were described by simple linear functions. These allowed calculation of overall circuit recoveries and evaluation of alternative circuits. An evaluation procedure based on a financial criterion is demonstrated with a simplified example, illustrating how revenues and operating margins are often of more concern than concentrate grade and recovery

Jun 18, 1905

By R. A. Halatchev

A risk model for assessment of the uncertainty in the forecasts of the planned profit is developed. It is based on the selling price of the metal recovered from the ore and the production per shift of the excavators. These two critical variables characterise the economic and technical aspects of the mining venture. Time-series methodology is used to describe the behaviour of the economic variable, which improves the adequacy of the modelling. A hypothetical open-pit gold mine is used to illustrate the application of the model. Results obtained show that the model is a good alternative to sensitivity analysis in taking account of the stochastic character of the price of the metal recovered from the excavated ore and the production per shift of the excavators used. The model can be extended by the inclusion of new variables that have a probabilistic nature

Dec 1, 1996

By R. J. Pine, J. S. Coggan

Distinct-element modelling has been used to study the mechanisms associated with observed deformation of the western face of the quarry. A complex failure mechanism involving distinct planar surfaces that was proposed for a slope failure in 1967 has been modelled and shown to be plausible. In addition, deep-seated flexural toppling may contribute to the slope instability. Modelling has confirmed the detrimental influence of a raised water-table on the stability of the slope and also indicates that the observed cyclic opening and closing of tension cracks may be attributed to seasonal rise and fall of the groundwater level

Apr 1, 1996

By M. J. Beus, B. Stewart, S. Iverson

Ore-pass hazards are a significant safety problem in US underground metal mines. From 1975 to 1995, nearly 75% of injuries during pulling or freeing of ore-pass chutes were related to falls of broken rock or the use of hand tools. Risk assessment methods are being used to identify the most probable causes of ore-pass failures and analyse the factors that result in malfunctioning or safety reduction. Static and dynamic loads are being measured in the laboratory and by field testing, with data from test ore passes compared with mine data to characterise true system behaviour. Computer modelling using closed-form solutions, finite element analysis and a newly developed particle flow code are being use to predict loads from ore and waste flow and impact. Preliminary results indicate that dynamic impacts may be much less than expected, as a result of damping factors, normal and shear stiffness and mass frictional characteristics

Jun 19, 1905

By G. D. Schena, C Chiaruttini

The feasibility is demonstrated of reconstructing the volumetric distribution of liberated particles and middlings by use of a damped, weighted least-square regularisation method. This allows a precise mass balance to be obtained around a separation/concentration unit, permitting evaluation of the partition curve (Tromp curve) of the separator. Areal grade measurements are made on polished sections of feed, concentrate and tailings and a kernel-based inversion technique is then used to obtain the volumetric grade distribution of the three assemblages. A plain kernel (number of occurrences) and a weighted kernel (each occurrence counted with its area) are used for the solution. Testing of the method on computer-generated synthetic areal grade measurements indicates that it offers a valid alternative to the tedious conventional procedure of conducting experiments with heavy liquids

Jun 21, 1905

By A. R. Naderian

Laboratory strength and deformation testing of freshly blasted sandstone and claystone overburden from Jeebropilly colliery in Queensland and in-situ plate-bearing tests on four backfills of different ages showed that the bearing capacity of backfill is a function mainly of compaction, not of age. The modulus or stiffness of the backfill is significantly increased by previous loading, in some cases up to threefold. Backfill material experiences some compaction through the passage of mining vehicles, likely to provide a bearing capacity that will support normal construction activities; the limited testing performed suggested that completed backfills are capable of supporting loads of up to 200 kN/m2 while sustaining displacements acceptable for a wide range of residential and industrial uses, but may be susceptible to collapse settlements due to saturation in the long term

Jun 19, 1905

During a programme to determine the suitability of the UK site for deep disposal of radioactive wastes, geostatistical methods were used to characterise rock heterogeneity on the basis of seismic and wireline acoustic-impedance data. The data were analysed to yield semi-variogram models that quantified the three-dimensional spatial heterogeneity of acoustic impedance. These models were reconciled with geological interpretations of the area and used to generate simulations of acoustic impedance, with wireline acoustic impedance as conditioning data. The three-dimensional simulated images were compared with actual seismic acoustic impedance. The variography confirmed a vertical zoning effect in the Borrowdale Volcanics, showing that it is caused by preferential clusters of high acoustic impedance values corresponding to regions of relatively low porosity. The method provided realistic three-dimensional models from sparse, one-dimensional wireline data

Jun 19, 1905

By P. H. Morris

The profile of a delta formed by fine-grained mineral processing wastes, disposed of as aqueous slurries by subaerial deposition from a pipeline, has a significant bearing on the volume that is available for waste and water storage in a given containment structure. Earlier field data and laboratory experiments suggested that mine waste delta profiles could be predicted with high levels of accuracy using data from small-scale laboratory deposition tests. The relationships between the profiles of full-size and laboratory-model deltas were analysed using the principles of kinematic similarity and a recent theory of delta formation based on engineering hydraulics. Measured profiles of full-size and model coal-mine tailings deltas are compared and the prediction of full-size profiles discussed. It is shown that the data-derived laboratory-model deltas are insufficient to allow accurate prediction of full-size delta profiles. Initial slope data or other, equivalent data for the full-size delta are also required

Apr 1, 1996

By D. M. Milne, P. J. Lunder, R. C. Pakalnis

During the mining of an open stope, deformation of the hanging-wall and the potential for dilution generally increase with the size of the exposed hanging-wall. Excluding discrete structures that may delineate unstable blocks, the mechanisms that drive hanging-wall deformation and possible dilution comprise several factors which can include elastic, plastic and discontinuum deformation. These stages of deformation are not mutually exclusive and at any point during mining all three of these mechanisms may be acting on the hanging-wall rock mass. Computer modelling techniques are available to analyse the three stages of deformation, but the difficulty lies in trying to obtain realistic rock mass properties for input and in determining when each stage of deformation is acting. Instrumentation data can be used to predict the effect of continued mining. However, it is often difficult to calibrate numerical models against field data owing to the large number of input parameters required. An empirical approach is recommended that uses two new parameters, the radius factor and the effective radius factor. A method is proposed for predicting the effect of continued mining from existing deformation and dilution data for a given hanging-wall

Apr 1, 1996

By P. E. J. Pitfield, S. D. G. Campbell

The regional shear zone runs along or near the southern margin of the Chinhoyi greenstone belt. It hosts four of the seven mines in the southern part of the belt with recorded production above 100 kg Au, including the top two current producers. Displacement occurred in the late Archaean, producing a shear zone with a trend ranging from northeast at Golden Kopje to east at Muriel. The orebodies at the two mines formed synchronously with the shearing and show strong but contrasting structural controls on mineralisation. The Golden Kopje orebodies plunge to the southwest, parallel to the intersection of curved foliation with discrete shear planes and sub-perpendicular to local stretching lineations. The Muriel orebodies plunge steeply west but parallel to local stretching lineations. The greatest fluid flow during mineralisation of the shear zone was along either the intersection of fabrics (Golden Kopje) or the extension direction (Muriel). There is no unique relation between the orebodies and the extension or shear direction. Where earlier mining has not established the directions of the oreshoots it is essential to understand the possible structurally controlled geometries of orebodies before planning a drilling programme to evaluate their potential

Apr 1, 1996

By G. D. Schena, M Zanin

A numerical approach is presented for predicting the liberation of phases during comminution, with direct calculation of a liberation spectrum giving the fraction of the particulate system in each narrow size-composition class. The numerical model uses a Poisson flat process for stochastic generation of the non-convex three-dimensional Poisson polyhedral textures and the system of fractures that give rise to convex fragments. With this numerical approach, there is no need to assume random uniform isotopic fracture (lack of selective liberation); only computational geometry primitives are exploited for the derivation. The agreement with relationships obtained previously under the random uniform isotopic fracture hypothesis demonstrates that the approach is capable of deriving full liberation spectra directly. Both volumetric and superficial composition can be calculated

Jun 21, 1905

By E Oktay, I Yusufoglu, C Kahruman

Powder and spherical pellets of MoO2 were oxidised under controlled conditions in the temperature range 674-791 K at oxygen partial pressures of 8.1-30.4 kPa. Weight increase during the reaction was determined by thermogravimetric analysis. It was concluded that the reaction is 0.6th order with respect to oxygen concentation and that the activation energy is 148 kJ/mole. In experiments conducted with powder, fast transfer of reaction heat to the gas phase created isothermal conditions, but the temperature of pellets rose by a maximum of 54 K at 674 K and 105 K at 791 K. The rise in temperature caused structural changes such as sintering and crack formation, which had a considerable effect on the reaction rate. The findings should be taken into account in the design of equipment and choice of operating conditions for roasting MoS2

Jun 21, 1905

By J. A. Finch, Zhenghe Xu, Z. A. Zhou

Whether the microscopic bubbles generated by the high energy dissipation and high feed-slurry velocities in new flotation cells are stable in solution and what roles they play in particle collection are of great interest for the flotation of fines. Experimental work has shown that, with fast flow of liquid through an orifice, stable microscopic bubbles can form in flotation systems by hydrodynamic cavitation in the absence of gas supersaturation. The minimum flow rate at which bubble formation is initiated varies from 8 to 15 m/s, depending on the design of the cavitation tube, which is within the range of feed slurry velocities of some newly developed cells. Feed aeration enhances the formation of micro-bubbles by hydrodynamic cavitation. The study suggests that the fast flotation kinetics of some new cells may be attributed in some degree to the formation of microscopic bubbles

Jun 21, 1905

By M. C. Ruiz, M. E. Godoy, J. B. Rivarola, M. W. Ojeda

The amount of Pd recovered from an exhausted olefin hydrogenation catalyst was found to depend on mixing technique, particle size, carbon percentage, chlorine flow, reaction time and temperature. Pd extraction was total when a sample in the 125-175 micrometre particle size range was chlorinated for 60 min at 723 K with 20 cm3 Cl2/min, for 60 min at 748 K with 30 cm3 Cl2/min and for 30 min at 773 K with 30 cm3 Cl2/min. No C addition was needed; the initial C content of the catalyst was sufficient for total recovery. Pd extraction was also affected by heat treatment in different atmospheres before chlorination. Treatment with O2, N2 and N2 with traces of O2 led to different degrees of oxidation of C and permitted the formation of oxidised Pd species. Thermal pretreatment in N2 with traces of O2 was most conducive to Pd extraction

Jun 21, 1905

By A Cox

It has been demonstrated that all the cadmium from spent batteries, typically 4 g per battery, can be recovered by burning polyvinyl chloride waste to yield hydrogen chloride; this reacts to produce volatile calcium chloride, which can then be condensed and collected in a separate reactor. Alternatively, chlorine may be used to chlorinate the cadmium with equal efficiency. There is also a prospect of using very low concentrations of these gases, less than 1%, to effect the separation. The Cd was recovered more quickly when exposed to sustained, controlled flow rates of chlorinating gases, whereas when PVC was burnt most of the gas was produced in a very short time, not allowing complete reaction. This problem can be overcome by recirculation of the gas into the reactor. The technology is efficient and clean and the equipment used is simple, enhancing the prospects for a pilot-scale version of the process

Jun 21, 1905

By A. L. Grabovski

The potential of eccentric cone crushers for fine crushing has been improved by increasing the swing frequency of the moving cone, balancing the crusher, ensuring uniform feed via a rotating funnel with sideways discharge, introducing hyperbolic motion and employing the inertia crushing method, but further improvements to the specifications of existing cone crusher designs are limited by the rigidity of their kinematic coupling. A new design has been developed which combines two crushing modes, stone on liner and stone on stone, each with its own advantages. The main aims are to produce finer materials and to reduce liner weight. The benefits include an increase of more than 10% in the output of fine particles, improved protection of the liner against wear, as a result of filling of the cavities by material being crushed, and the use of almost 20% less material in casting of the liner. The chamber can be used in place of the usual liners of fine cone crushers

Jun 21, 1905

By P. Golledge, A. D. S. Gillies

An investigation has been carried on samples of three Queensland coal dusts to determine the potential explosibility of dust-gas mixtures. The explosion potential of the samples was classified by the lean and rich limits of explosibility and the limiting oxygen concentrations for each sample. Plotting of these points showed 2-dimensional flammability limit surfaces for coal dust/oxygen, methane/oxygen and coal dust/methane mixtures. From these plots the 3-dimensional flammability envelopes defining the explosibility of the mixtures were defined. The explosion limits of the coal dust/methane/oxygen system were seen to be influenced most by the explosibility characteristics of coal dust. Methane exerted a stronger influence over the explosion limits when the coal had a low volatile content

Jun 19, 1905