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By B. R. Reddy, Y. V. Swamy, B. V. R. Murthy, H. S. Ray

The Ni oxide was reduced with a CO-CO2-N2 gas mixture and the effects were observed of process variables such as roasting temperature, time and CO partial pressure. Extraction of over 90% of Ni was achieved by ammoniacal leaching of ore that had been reduced for 1 h at 760 degrees C under a gas mixture with a volumetric CO/(CO+CO2) ratio of 0.57. The kinetic data were found to conform to the Ginstling-Brounstein equation. The applicability of this model was confirmed by evaluating the apparent activation energy with the use of independently constructed differential and integral plots, which showed an excellent match

Dec 1, 1995

By R. A. Ixer, R. A. Lord, H. M. Prichard, A. J. Boyce, P. McConville, C. T. Pillinger, I. P. Wright, J. Maynard

Analysis of 62 samples show that the sulphides throughout the igneous stratigraphy have a magmatic signature, with the exception of the uppermost gabbros and the lowermost basal thrust talc-carbonate lithologies. Mean delta-34S values for whole-rock samples from harzburgites, dunite pods in harzburgite, crustal dunites and wehrlites, the main and high-level pyroxenites and gabbros suggest that the primary sulphides derived their sulphur from a magmatic source enriched in 34S. This finding is compatible with the proposed origin of the ophiolite above a subduction zone. Values for pyrite mineralisation in the uppermost part of the gabbros are thought to result from precipitation from a seawater-derived fluid, while isotopically light sulphur in the basal thrust could have been introduced from underlying metasediments. The replacement of pentlandite by heazlewoodite has not led to sulphur fractionation

Jun 19, 1905

By H. R. Thorpe

A floating gold dredge operating in coarse alluvial gravels of the Grey River on the west coast of the South Island, New Zealand, generated high concentrations of clay and colloidal particles in the dredge pond, which entered the groundwater system. Sampling was carried out at depths down to 20 m and it was found that variation of the length of the flow path occurred because of the movement of the dredge towards the piezometers. The alluvial gravels, the suspended sediments, the groundwater system and the water chemistry were all studied. Sediment concentrations were found to be highly variable with depth, but the relative concentrations in the depth profile were generally consistent as the flow distance shortened. The sediments were extremely fine and travelled further through the gravels than predicted. Comparison of field results with the available theory of deep filtration in clean beds of porous media gives some basis for estimating the behaviour of fine sediments in other alluvial systems

Jun 19, 1905

The reduction of zinc from slags by a molten, carbon-saturated bath was examined in a laboratory study under conditions of continuous slag feeding. The results show that it is possible to reduce the bulk of the zinc from the slag before there is a net reduction of iron. However, the recovery of zinc was not as high as in batch tests performed in an earlier study. Lead in the slag was reduced simultaneously with the zinc to very low levels and was volatilised. Copper in the slag was reduced and dissolved in the alloy. An attempt was made to identify potentially commercial ways of treating zinc slags using an iron bath. The approaches that appear to have the greatest potential are reduction in a batch process using electrical heating and reduction in a continuous process with co- or countercurrent flow of the slag and alloy. In the latter the alloy would be prepared in a separate furnace before being contacted with the slag. The purpose of this would be to superheat and carburise the alloy so that no additional heat or reductant would have to be supplied in the slag-alloy reactor

Jul 1, 1991

By S. L. Gay

The conventional mass-balance equations used as constraints can lead to flow estimate values of zero even though the flow estimates should be some positive number. This is because many of the constraint equations are satisfied if the flow rates are zero. The way to overcome the problem is to use a slightly different form of the equations. For example, rather than use the conservation of flow of solids as a constraint it is better to use the constraint that the percentage of solids going into a unit equals the percentage of solids coming out of the unit. Examples are given using mineral processing data sets from Mount Isa, Queensland, and Red Dog, Alaska

Jun 21, 1905

By Y. Ichihara, H. Matsumoto, K. Itakura, H. Eguchi, G. Deguchi, K. Sato

Mechanical data from a rockbolt drilling machine, such as torque, thrust, revolution and stroke, are useful for understanding the geological and geomechanical conditions around roadways and hence selecting the optimum bolt type and density. Laboratory experiments showed that the level of torque or thrust reflects differences in rock type, with separation of strata and cracks appearing as a specific pattern. Algorithms of neural networks based on adaptive resonance theory and back-propagation were used to extract the pattern and estimate the location of discontinuities. For field testing in an underground coal mine, a prototype data acquisition system was attached to a portable drilling machine. Several sets of logging data from one locality were combined to construct a two-dimensional model of the strata, from which the slope angles of discontinuity faces could be estimated

Jun 19, 1905

By S Colak, M Tunc, C Celik, M. M. Kocakerim

The most important parameters affecting the solubility of ulexite (sodium calcium borate) in H2SO4 were found to be reaction temperature and solid:liquid ratio, in that order. Dissolution increased with increase in temperature and stirring speed and with decrease in solid:liquid ratio, particle size and acid concentration, the last effect as a result of decreased precipitation of CaSO4 on unreacted particles. Optimum conditions, in which around 99.5% of the ulexite could be dissolved, were a reaction temperature of 60 degrees C, a solid:liquid ratio of 1:8 g/ml, an acid concentration of 8 mol/l, particle size smaller than 425 micrometres, a stirring speed of 52.33/s, a reaction time of 1 800 s, a calcining time of 3 600 s and a calcining temperature of 170 degrees C. These conditions, determined by the Taguchi method, are reproducible in a commercial production environment

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 S. G. Beattie, N. Mojtabai

A study was carried out which aimed to: determine the effects of blasting on excavation perimeters and nearby slopes; establish a low-cost blast monitoring and field observation programme to determine peak particle velocities and blast damage; and to develop criteria for observable blast damage that are based on the peak particle velocity. Full-scale production blasts in a large open pit copper mine were monitored and studied to develop damage criteria for various rock types. Better blast designs can be achieved by correlating the results of blast monitoring with field observations of damage at the pit walls and on benches. Back-break and damage are related to blast-induced ground vibration. Peak particle velocity is accepted as a reliable measure for the prediction of ground vibration levels. Empirical models for the estimation of rock damage can be developed and used for blast design. The models are used to determine the zones of damage within the rock face. Rock damage models can also be used to design trim shots to achieve further reduction of back-break in more critical areas

Apr 1, 1996

By P. H. Morris

Nineteen field trials of the co-disposal of fine coal tailings and coarse coal wastes were conducted at the dual Goonyella-Riverside mine in Queensland and at the Hunter Valley No. 1 and Warkworth mines in New South Wales, Australia. The profiles of and the sorting that occurred on the co-disposal deltas are described and an existing theory of subaerial deposition, originally developed for mine tailings alone, is shown to apply to the co-disposed wastes. This enables the dimensionless profiles of large deltas, which may take years to deposit, to be predicted from data obtained from a small delta formed in a few days or even hours

Jun 19, 1905

By A. M. Tunstall, N. Djordjevic, H. A. Villalobos

The damage zone behind a typical smooth-wall blast in the open pit was assessed by visually examining diamond drill core to identify blast-induced cracking, mapping core rock quality designations to identify changes in fracture frequency and conducting uphole seismic testing to determine changes in rock mass characteristics. The results from the three techniques show reasonable correlation. They suggest that major damage, in the form of fracturing of intact rock, occurs at least 7 m behind the smooth-wall blast and significant damage, in the form of opening and extension of calcite-filled fractures, at least 12 m from the blast. At greater distances the dominant damage mechanism is the loosening of existent joints within the rock mass. In the trachytes at El Soldado these damage mechanisms correspond to peak particle velocities of 2 000, 900 and 500 mm/s respectively

Jun 19, 1905

By T. C. Alex, S Srikanth, Premchand

It has been suggested that reduction of the iron and manganese phases as far as FeO and MnO is preferred for the complete liberation and selective reduction of the copper, nickel and cobalt oxides in manganese nodules. The oxygen partial pressure/temperature regime suitable for this purpose has been delineated. Free-energy minimisation and thermogravimetric results indicate that the requisite conditions can be achieved if more than 10% of neutral oil is used at temperatures greater than 923 degrees C. Neutral oil content, temperature and roasting time have been optimised to maximise leaching recoveries of Cu, Ni and Co: up to 96% of Cu and Ni and up to 85% of Co can be recovered if 15% of neutral oil is used as a reductant at 973 K for 90 min

Jun 21, 1905

By F. J. Tavera, J. A. Finch

A probe suitable for on-line measurements of gas hold-up in industrial flotation systems has been developed. It is based on an open cell for measurement of slurry-gas conductivity and a novel syphon cell for measurement of slurry-only conductivity. The desired behaviour of the two cells was demonstrated and estimates of gas hold-up were shown to be in good agreement with independent measurements. The gas hold-up probe was used as a diagnostic tool to assess the operation of flotation columns. Differences in gas hold-up between baffled sections in two industrial columns were detected

Jun 18, 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

By A. D. Fowler, M. T. Anderson

A phenomenological model is presented that relates Pb-Zn mineralisation to proximal geopressure zones. Typically, geopressure zones (GPZ) consist of masses of undercompacted sediment encapsulated within impermeable shales and are characterised by high formation fluid pressures. Heat flow is perturbed in some GPZ on account of their insulating properties. Geothermal gradients as high as 150 degrees C/km have been observed over short distances in the sediments of the US coast of the Gulf of Mexico. Some modern geopressure zones are known to reach temperatures of 120-150 degrees C at depths of 2.5-3.5 km. It is demonstrated that the zones may act as proximal sources of hydrothermal fluids, thus explaining the high temperatures of mineralisation observed in the deposits, which are hosted in basins characterised by thick, rapidly deposited, shale-rich clastic sequences

Jan 1, 1991

By K. C. Dunham, M. Solomon, T. A. Rafter

Sulphur isotope ratios have been determined for 81 sulphides and S and O isotope ratios for 26 barites from the Alston Block in the northern Pennine ore field. In addition, both isotope ratios have been determined for 29 evaporitic anhydrites of various ages from European and Australian localities. The consistency of the sulphate isotope ratios over a wide area of the northern Pennines, and their similarity to values for Lower Carboniferous evaporites, suggests that the sulphate originated from Lower Carboniferous connate waters. It is suggested that these mingled with warm brines rising through granitic plutons beneath Tynehead and Upper Weardale, the aqueous sulphide ion in these brines having a delta34S value of approximately +10 per mille. The delta34S values for the sulphides range from +15.0 to -5.9 per mille and show an outward zoning with higher values in the central fluorite zones and mainly negative values in the outer barite zones. The wide range of delta34S values for the sulphide S is not characteristic of magmatic S and there is no adequate local source in the Carboniferous sediments. It is suggested that formation waters, probably mainly of connate origin, sank down sufficiently deep to become heated above 200°C before rising through Caledonian granite plutons into the Carboniferous sediments, where they spread laterally to mingle with cooler sulphatic connate water. The rising fluids were hypersaline brines carrying F, Ba, Pb, Zn, Cu and S. Temperatures of deposition calculated from galena-sphalerite isotope fractionation are similar to temperatures previously determined from fluid inclusion studies.

Dec 1, 1971

By L. J. Cabri, J. M. D. Wilson, R Lastra

An image analysis program can search for gold minerals in polished sections by scanning about 100 x 100 back-scattered electron images at a magnification of x400, allowing gold grains as small as 1 micrometre in diameter to be detected. Typically, a c.15 h overnight search of a product smaller than 45 micrometres will scan c.1 500 000 particles, providing data that are not easily obtained through manual operation of an optical microscope. The program locates grains of the correct brightness, acquires gold X-rays from them by wavelength-dispersive spectrometry, filters the data to remove artefacts and record the images and stage locations for subsequent retrieval. At the end of the run, the program allows the operator to verify and identify the grains found. Industrial studies at Canmet have included determining the nature of gold in cyanidation tailings, checking the mineralogy and size of gold grains in samples from an Indonesian Cu-Au concentrator and locating and measuring gold liberation and grain sizes in an ore

Jun 21, 1905

By Marshall Charles Riddell, John Carlon

local news

Jan 12, 1997

By A. S. W. Kurny, M. Z. Huq

Bangladesh ilmenite is partially altered, containing pseudorutile, rutile and haematite as well as the predominant ilmenite phase. A typical analysis is 39.45% TiO2, 24.19% FeO and 33.0% Fe2O3. Reduction of the ilmenite by charcoal was found to involve two major reactions: conversion of pseudorutile into ilmenite and rutile, and change of ilmenite into metallic iron and rutile. The first, which was much the faster reaction, was responsible for an initial increase in ilmenite content with reduction time at lower temperatures. Apart from these two major reactions, rutile was reduced to lower oxides at 1 100 degrees C with a consequent decrease in its XRD peak height

Jun 19, 1905

By C. L. Schneider, C. O. Gomes, R. P. King, J. A. Finch, D. Lin

Discussion is presented by Prof. King and Dr. Schneider of the paper by Lin, Gomez and Finch published in Trans.IMM C, vol.104, 1995, p.C155-C161. They conclude that the correction procedures used for simulated observations of simulated capped spheres are not reliable when applied to mineralogical data and that their relative ranking should not be extrapolated to other situations. Properly regularised solutions obtained with the use of appropriate kernels can be safely used for routine mineral liberation work and can be calibrated accurately against real mineralogical samples in the laboratory

Jun 19, 1905