Search Documents

By J. A. Finch, D. Lin

The robustness of the large-sections correction procedure, Hill's fast approximation, Barbery's correction and the PARGEN correction was examined by comparing their ability to reconstruct the true liberation distribution using sectioning data from computer-generated spheres. The results indicate that the flexibility of a correction procedure is related to the assumptions it makes about the continuity of the liberation distribution, locked-particle characteristics and ore texture. Overall, the large-sections procedure appeared to be the most generally applicable. The Hill fast approximation performed well, but this was probably because it partially incorporates the sphere model; the performance of the PARGEN and Barbery corrections varied from case to case.

Dec 1, 1995

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 J. D. T. Capocchi, M. B. Mourao

The rate of reaction between iron oxides and carbonaceous materials, agglomerated as pellets, was studied experimentally by measuring the weight loss as a function of time. The effects of temperature, carbon type, inert gas flow rate, pellet size and additions (sodium. carbonate and Portland cement) were determined. It was shown that the value of the apparent activation energy can display large deviations under different experimental conditions; in the present work it was found to be 226.6 kJ/mol. The reaction with coke is slower than with charcoal, and the rate increases as the flow of inert gas in the reaction vessel decreases. Comparison of the rates for pellets of different sizes has shown that for small pellets the initial rate is faster but that it slows down at high conversions owing to the penetration of inert gas into the pellet. Additions of sodium carbonate and Portland cement increase the rate; sodium. carbonate promotes the catalysis of the Boudouard reaction, which is the slowest of the partial reactions. The increase in the rate with Portland cement is attributed to the release of water vapour

Jun 18, 1905

By B. Gazea, A. Kontopoulos, A. Kourtis, K. Adam

Static tests give a measure of the balance between acid-producing and acid-neutralising mineral components in a material, while kinetic tests determine acid generation and neutralisation over a long period. Drill-core samples from the amphibolite and gneiss host rocks of the Stratoni lead-zinc sulphide deposit in Greece and mine/mill waste samples from Stratoni and Olympias were examined by the standard acid base accounting, BCR and net acid production tests. Mineralogical data on the materials and resulting residues were used to illustrate the differences between the methods and establish their ranges of applicability. BCR seems to simulate most closely the conditions prevailing during generation of acid mine drainage but is time-consuming and requires elaborate equipment. Acid base accounting is suggested for standard screening; net acid production might be used in the field or for solids with less than 10% S

Jun 19, 1905

By G. E. Christidis, P. W. Scott

The deposits were formed from low-temperature alteration of pyroclastic rocks. Properties investigated include their cation exchange capacity, swelling capacity, pH, rheological properties, the green and dry compressive strengths, shatter index, wet tensile strength, compactability and permeability. It was found that deposits with abundant opal-CT have poor physical properties. The rheological and swelling properties were found to be influenced by the bentonite grade (smectite content) and the degree of disaggregation of the smectite quasi-crystals. The only deposits of high grade which had good foundry properties were those with no opal-CT. Hydrothermal alteration was detrimental to the physical and chemical properties of bentonites in that it decreased the smectite content and the pH and changed the smectite layer charge and the lattice dimensions

Jun 18, 1905

By R. R. Tatiya

Data obtained from a copper mine were used in a comparative study of the reserve estimates generated by applying geostatistical methods to surface borehole data, underground core drilling results and assay values from chip sampling. Global estimation of the deposit performed by kriging of the low-density sampling data from the surface boreholes did not provide reliable results, but could identify the potentially mineralised zones. The reserve generated from core drilling results correlated well with that estimated from chip sample data and with that estimated by the conventional methods used at the mine. A satisfactory reserve evaluation could, therefore, be obtained by kriging of the data from the underground core drilling alone, provided that a systematic sampling procedure was adopted. Estimates based on chip sampling information could be used as a check, which could avoid the current practice of chip sampling of most of the mine workings. The aim should be to develop a semi-variogram for the deposit, which could be used to estimate the reserves by kriging

Jun 19, 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 R. D. Stewart

Paper presented at the conference: Risk assessment in the extractive industries, held in Exeter, UK, 23-24 March 1994, and first published London: IMM, 1994, preprint volume, 18pp., 5 refs. A seismic risk assessment method has been developed for application to rockburst prone deep-level mining sites which have sufficient seismic coverage. The technique utilises several seismic hazard parameters simultaneously and assesses the seismic risk on a daily basis according to the individual levels of these parameters. Critical levels are determined from investigation of the long-term behaviour of the parameters in relation to recorded potentially damaging seismic events. The method has been applied to a data set comprising 15 months' worth of seismic data, with encouraging results

Aug 1, 1995

By I. W. Farmer

High horizontal stresses and high horizontal to vertical in-situ principal stress ratios in the plane of underground drifts and entries can damage weakly laminated roof rocks quite severely. Such stresses are difficult to measure accurately, as illustrated by case histories of in-situ stress measurement at Wistow and Lea Hall mines, in the UK. Their direction and relative magnitude can, however, be estimated from the absolute velocity vectors of continental plates. With the preliminary results from the World Stress Map project now available it is possible to indicate mining areas where regional horizontal stresses are low, such as Europe, and high, such as Australia and Asia

Jun 19, 1905

By S. P. Singh

The purpose of the cut is to provide a free face to which the remainder of a development or breasting round can break. The results of field testing in drifts and at a quarry face were used as a basis for a description of the rock breakage and flushing mechanism in the cut. It was concluded that the important features of a cut design are proper hole spacing, sufficient relief volume, drilling accuracy and relief holes slightly longer than the planned length of the round. The void space provided by the relief holes should be about 15% of the cut volume, with more required in weak, highly fissured rocks. The importance of drilling accuracy increases with round length, an error being magnified by the small blasthole spacing. The first hole pulls only about 20% of the round length, 4-6 holes having to be fired before the cut is pulled close to its design depth. The first four blastholes should be fired with a minimum inter-hole delay of 100 ms to provide progressive relief of burden and avoid the superimposition of ground vibrations. The earliest-firing charge should be closest to the relief area and act laterally, while the first of the vertically-fired charges to be detonated should be the uppermost. Problems during cut-pulling include sympathetic detonation, dynamic pressure desensitisation, charge disruption and freezing of the cut

Dec 1, 1995

By P Stone, J. M. Cook, P. R. Simpson, C Mcdermott

Paper presented at the conference Economic geology in Europe and beyond II, models for mineral deposits in sedimentary basins, held in Keyworth, UK, 13-14 April 1994. The SW part of the Southern Uplands is a back-arc section of an accretionary thrust system, divided into structural blocks by major NE-SW shear zones and NW-SE faults forming the margins of Permian half-grabens. The highest arsenic levels in stream sediments (over 65 ppm) are associated with those blocks carrying brittle-ductile transition fabrics. Three factors combine to recomend the area as having potential for gold mineralisation: As-rich greywackes as country rock, felsic intrusions and a major shear zone. Selected stream sediments were analysed for gold using lead fire assay with ultra-pure flux and ICP-MS finish. Several localities showed over 15 ppb Au, the three most significant being within the hanging wall of the Orlock Bridge Fault and each having distinct characteristics

Aug 1, 1995

By D. M. Evans, D. L. Buchanan

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks, held in Orleans, France, 1-3 September 1993. The Zinca area was chosen as a suitable location for an investigation of the weathering and secondary dispersion of platinum group metals from the Zone. It was concluded that platinum is immobile while within weathered rock, its mineral phases tending to alter from primary sulphides and tellurides to secondary Pt-Fe alloys. Palladium is variably mobile in weathered rock. In stream sediments Pt occurs mainly as small, dense, discrete particles, giving rise to a nugget effect, whereas Pd probably occurs as much finer particles or chemically adsorbed on to a suitable substrate. Pt shows a rapid decrease in sediments downstream from mineralisation, whereas Pd has a much slower downstream decay

Apr 1, 1994

By J. E. Misiewicz, A Rozendaal

Paper presented at Geofluids '93, held in Torquay, UK, 4-7 May 1993. The tin field consists of a fragment of Lower Proterozoic volcanosedimentary rocks surrounded by granitoids. Almost all the significant deposits are hosted by arkoses and are classified as replacement and space-filling types, with particular styles of mineralisation dominating at different mines. Petrological and geochemical investigation of borehole cores from four centres indicated the presence of a stratified zone 500-600 m thick and continuous over at least 20 km along strike, consisting of pervasively altered clastic arenitic sediments. The alteration is zoned into a grey-green sodic albitised footwall, an 80 m thick sericitised-tourmalinised sulphidic tin zone and a red haematitic potassic hanging-wall. The zoning and the localisation of three cassiterite phases are consistent with the tectonic history and with multiple pulses of stanniferous hydrothermal fluids derived from late differentiates of the granites over a prolonged period. Areas of high fracture density acted as conduits for the fluids, whose initially rapid ascent was retarded by decreasing pressure contrast, limited development of fracturing and/or impermeable shaly arkose to cause lateral spreading and pervasive alteration over a broad, stratified front. Lateral overlapping of local fronts at the various centres suggests a continuous zone, while the many petrological and geochemical similarities point to a shared fluid composition

Aug 1, 1995

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. Lahtinen, M. Tiainen, R. Salminen

The application of similarity analysis derived from regional geochemical mapping data to the location of Ni-bearing intrusions was tested in southwest Finland, where a well-known nickel belt is situated. Samples of till from the vicinity of the Vammala and Kylmakoski Ni-Cu deposits, which were collected independently of the Geological Survey of Finland's regional geochemical mapping programme, were used to provide geochemical modelling data. The data consist of the aqua regia-leachable concentrations of 20 elements from the less than 0.06-mm fraction of glacial till. The variables used in the similarity analysis were selected on the basis of a factor analysis in which the method of oblique rotation was used. A hierarchical clustering of the modelling samples produced two main groups. The first group was described as the "nickel deposit environment model" and the second as the "nickel deposit location model". The data for the standardised variables were compared sample by sample with the model data by similarity analysis using the Simana program with a cos theta measure of pattern similarity. The nickel deposit environment model delineated the known Ni belt and indicated an extension to the east. The nickel deposit location model identified target areas of reasonable size with the greatest potential for Ni ores within the nickel belt

Dec 1, 1991

By B. J. Breen, C. S. Mogg

Considerable borehole investigation work has been completed at a proposed site at Sellafield in Cumbria, supplemented by seismic surveys, other geophysical sensing and geological mapping. The focussing of investigation on the rock mass itself will be achieved by means of the planned underground rock characterisation facility, giving access to depths of about 800 m in the strong, low-permeability basement rocks of the Borrowdale Volcanic Group. Characterisation work undertaken during the sinking phase and interaction with continuing surface-based exploration and monitoring should permit a firmer assessment of the long-term safety of a repository. Key considerations in the choice of a design for the repository include the waste handling method, underground inlet cell, underground vaults, vault environment and environmental effects

Aug 1, 1994

By D. K. Bose, R. H. Rakhasia, V. D. Shah, J. C. Sehra

A series of experiments was conducted to determine the effects of roasting temperature, soaking period and quantity of soda ash added. At a laboratory scale, under optimum conditions of roasting at 873 K for 2 700 s with soda ash 10 wt% in excess of stoichiometric, molybdenum recovery was 99%. The investigations indicate the technical feasibility of producing high-purity MoO3 by combining the roasting process with carbon adsorption/desorption. The process uses low-cost chemicals, can be scaled up readily and is free of the SO2 pollution generated by conventional roasting, as the sulphur content of the concentrate is converted to sodium sulphate

Jun 18, 1905

By S. P. Mishra, G. R. Chaudhury

The adsorption of Cu2+ ions by Penicillium sp. displayed a dual rate, with an initial faster phase followed by a slower one. The adsorption rate increased with increasing pH due to chemical and biochemical reactions. The Cu-loading capacity of the biomass increased at higher initial Cu2+ concentrations. Above 40 degrees C the adsorption rate decreased which may be due to partial hydrolysis of biopolymers which are essential constituents of the cell wall. Adsorption kinetics followed the Freundlich isotherm and the equilibrium concentration that was calculated on the basis of the isotherm matched the observed value well. A series of theoretical adsorption curves were produced using mathematical correlations between the mass transfer coefficient, the Cu2+ ion concentration at equilibrium and at time t. The correlation between the theoretical and observed adsorption rates for different experimental conditions was good. It was concluded that the results from the study were best explained using a mass-transfer adsorption model

Aug 1, 1995

By V. A. Melezhik, A. H. Green, L. N. Grinenko

Finally, a theoretical model is constructed that takes

Aug 1, 1994

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