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By Thomas L. J

A series of tests on rock stress measurement devices used with the overcoring method indicated that improvements could be made in their construction. A prototype inclusion cell was developed with strain gauge rosettes bonded to a 0.05 mm thickness stainless steel sheet which was formed into a cylinder around two end pieces. The finished diameter was slightly larger than previous cells so that the thinner plate and the reduced annulus of Araldite cement in the installation borehole gave a better response in the laboratory than the other cells tested, especially in simulated bedded rock. It was less affected by inhomogeneity and temperature changes. Its high sensitivity should make it suitable for both absolute stress measurement and field monitoring. A table of comparative readings is given for the new cell and for four other devices used in simulated in-situ rock conditions.

Jan 1, 1992

Off-gas cleaning from metallurgical plants requires? in many cases very low dust contents which are difficult to achieve with conventional scrubbers, even with high energy input. Lur.gi has developed a scrubber which improves the separation of the fine dust by electrical charge prior to. the scrubbing zone. An Electrostatic Scrubber has been successfully installed for the off-gas cleaning from slag' granulation after a waelzkiln achieving less than 1 mg/m3 in the clean gas.

Jan 1, 1992

Comminution of solids is surely one of the oldest technologies which even in this day and age of DNAs, chips and space exploration continues to challenge our scientific acumen and engineering ingenuity. In essence, this challenge is two-fold. One, as much as three to four per cent of all electric power generated world-wide is consumed in crushing and grinding primarily because the utilisation of energy is woefully poor. Studies have shown that the efficiency of mechanical size reduction processes is of the order of 1.5 to 12 per cent only (Schoenert 1986). Two, with the grinding technologies available to us, we have, at best, inadequate and, at worst, almost negligible control over the shape of the comminuted particles, size dispersion of the ground mass, and the sharpness of mineral liberation. Low energy efficiency and lack of control in the sense mentioned above have far-reaching implications for resource conservation, performance of down stream unit operations, and damage to the environment. Our problem is in fact central to the mineral-energy resources triangle shown in Figure 1 which depicts the close interrelationships among mineral resources which are becoming poorer in content and more complex in mineralogy each day, energy resources which are depleting rapidly without any viable alternate on the horizon, and environmental concerns which can no longer be ignored. It is evident that any improvement in the efficiency of the comminution process impacts directly on the control of environmental damage, conservation of energy and the economics of the operation. These concerns have special relevance for the processing of non-ferrous ores.

Jan 1, 1992

By Judy Konya Bowles, Calvin J. Konya

Blast vibration and air blast are commonly blamed for damages to residential as well as commercial structures. Mining and construction companies are often required to spend monies in court defending themselves even when vibration and air blast levels have been monitored by seismographs and are extremely low.

Jan 1, 1992

By V. G. Medina

The 15 000 t/d La Coipa mine initiated operation in July of 1991. The complex consists of a conventional, open-pit mining operation and a mill employing cyanide leaching with Merrill-Crowe gold and silver recovery. The process plant includes a primary crushing circuit, a 15,000 t (live) covered stockpile, a semi-autogenous mill/ball mill/crusher or SABC grinding circuit, a leach circuit, a belt filtration/washing circuit, a zinc precipitation circuit and a "dry" tailing disposal system. The process plant is described in detail with major design considerations used in the selection of the processes and equipment. The unique methodology employed in the disposal of the filtered tailings is also described.

Jan 1, 1992

By B. K. Mishra, R. K. Rajamani

A numerical method known as the discrete element method (DEM) is used to track the motion of individual balls in large-diameter ball mills. As a result, the en masse motion of the charge, force distribution, fall-height distribution, and energy distribution emerges from the simulation. Hence, it is possible to investigate the effect of mill diameter, liner profile and ball size distribution on the force regime created within the mill. Simulation results for 14-, 16- and 18-ft diameter mills are shown. The proportion of energy lost in high-intensity impacts and sliding ball motion is discussed. The DEM simulation technique opens the way for a closer examination of liner profiles on ball-charge motion.

Jan 1, 1992

By Jeffrey M. Listak, Gregory J. Chekan

The U. S. Bureau of Mines is investigating longwall panel layouts to maximize coal recovery and minimize interactive problems in multiple-seam operations. When coalbeds are longwall mined in descending order, the transfer of stress from overlying gate roads is a major design constraint affecting pillar stability in the lower mine. The lower mine gate road pillars must be properly designed to withstand the additional load transfer if gate roads are superpositioned in successive seams. The Bureau's MULSIM/NL model, a boundary element computer program, was used to analyze load transfer mechanics for superpositioned gate road pillars. Analysis of Longwall Pillar Stability (ALPS), an empirically based design method for longwall gate road pillars, was used to calibrate model input parameters. ALPS provided a basis to verify model trends and to recommend limits for safe pillar design when superpositioning longwall gate roads. The attributes of the MULSIM/NL model and ALPS were combined to develop a modified method for estimating pillar stress for multiple-seam cases. The modified method uses a multiple-seam factor (MS) to estimate the stress on superpositioned lower mine gate road pillars. Numerical analysis shows that MS depends on the interburden thickness and pillar width.

Jan 1, 1992

By M. J. Zdunczyk

Located approximately 50 miles northeast of Knoxville, Tennessee, Short Mountain Silica mines the Clinch Formation, an orthoquarzite, for silica sand. In 1980, a Knoxville resident and area contractor visualized mining Short Mountain for silica sand. Because APG Industries, the main market for the glass sand product, was only 48 kilometers from the site, many silica sand companies became interested in the property. In 1986, J.D. Nicewonder began to develop the site, and in May of 1988, APG Industries received the first sand shipment.

Jan 1, 1992

By G. Raspa

This article describes a procedure for calculating the recoverable reserves of stratified orebodies characterised by a thin and irregular layers. An application on the phosphate deposits in the N'Zeto region of the Popular Republic of Angola is also described. The procedure consists in building a block model of the deposit through the conditioned multivarial geostatistical simulation of small areal units. The recoverable reserves are then calculated and defined by applying to the model a selection processes based on measured geological/economic parameters taken from the drillholes: thickness of overburden and mineralised layers, economic grain-size fraction, grade. The procedure also takes account both of the geometrical constraints of the mining method and dilution. For reasons of confidentiality, a multiplier has been applied to the values adopted for the sampling data.

Jan 1, 1992

By S. Tandon

Equilibria studies of selenium distribution for sodium-borate slags were initiated at 1473k under reducing condition as a function of slag composition and alloy composition. The Se distribution coefficient (% Se in slag/% Se in metal) increased from 0.4 to 2.9 with increase in basicity (0.53 to 0.86) for Cu-0.446% Se alloy. However, the results are not very useful from industrial application viewpoint. Therefore, in order to improve the distribution of Se, CaO (10% to 50%) was added to the sodium-borate slag of basicity 0.864. On addition of 502 CaO, the distribution coefficient increased roughly by 100% for slag composition - 44.5% Borax, 22.2% Na2C03, 33.3% CaO and Cu-0.44677 Se alloy. Further, the value of this distribution coefficient has been found to increase by an additional 80% on addition of 20% CaF2 to the above slag for all Cu-Se alloy compositions. Also with increase in initial concentration of Se, the distribution coefficient has been noted to increase.

Jan 1, 1992

By R. G. Haire

Studies of the f-elements under pressure provide important insights into their solid state chemistry and physics. From such studies, of the elements and their alloys, it has been established that the normally localized f- electrons of several of these elements can become, involved in bonding under pressure. The electronic behavior of f-element compounds under pressure tend to be more difficult to interpret, due to the variety and the nature of electronic orbitals that are present. The 4f-elements and some 60% of the 5f-elements have been studied under The systematic comparisons that have been established for these materials are discussed.

Jan 1, 1992

By S. P. Fleming

An acid mine drainage sludge containing 0.26% nickel, 0.21 % cobalt and 4.5% manganese was leached in a one-liter reactor with sulfuric acid in the absence and presence of sodium sulfite. The effects of temperature (25°C and 52°C) and sodium sulfite concentration (up to 0.03 molar) on the leaching rate were particularly investigated. The leaching rates of nickel and cobalt with sulfuric acid have been determined to be controlled by diffusion through product layer. It has been found that effective leaching conditions to give more than 90% extraction of nickel, cobalt and manganese while keeping the iron extraction below 10% come with an elevated temperature and a low sodium sulfite concentration at pH 3; for example, 52°C and 0.01 molar sodium sulfite.

Jan 1, 1992

In west-central England, 183 m (600 ft) below the Cheshire Plain, lie the evaporate remains of an ancient sea. Stratified into nine beds of salt separated by marl bands, the deposit stretches roughly 21 x 12 km (13 x 7.5 miles) and contains reserves of rock salt estimated as high as 400 Gt (440 billion st). The Winsford Salt Works, one of England's largest underground mines, extracts the Cheshire salt and sells it for use as animal feed, for application in de-icing programs, and as a key ingredient in sodium fertilizer production and a variety of other industrial processes. Because road de-icing is an important market, demand for Winsford's salt varies with the severity of British winters. Design capacity is 2.25 Mt/a (2.5 million/year). However, production peaked at 2 Mt (2.2 million st) in 1987. Over the past five years, annual production has averaged 1.6 Mt (1.7 million st). Run-of-mine salt averages 92.5% NaCl, mixed with about 5% marl. The marl was formed by deposition of a reddish dust blown into the Cheshire basin from deserts in what is now central Europe. Association with the marl adds color to the salt, producing tea-colored crystals that resemble unrefined sugar. Adaptation of coal mining systems Rock salt mining in the Winsford district began at least as early as 1682. Mining at the current site dates from 1844 but was shut down from 1892 to 1928. In the early 1900s, a series of catastrophic collapses and floods plagued and ultimately shut down then-active Cheshire brine-salt producers. Subsequently, Winsford reopened and began adapting mechanized underground coal mining systems to rock salt extraction.

Jan 1, 1992

By Robert P. Edwards, Brian C. Flintoff

Crushing plants (multiple stage) are an integral part of most conventional comminution circuits (ball mill, rod mill - ball mill). Although conventional circuitry is now the design exception, there are still many older, and some newer plants that include crushing in the process flowsheet. In most of these installations the operating objective is to maximize throughput at some minimum product size, in an effort to balance the comminution load between crushing and grinding. To achieve this goal, while avoiding production losses due to overloads, generally requires the use of automatic control strategies. This paper reviews the crushing plant control problem and describes several approaches that have been successfully implemented in different plants.

Jan 1, 1992

By N. I. Aziz

The importance of using disc cutters for rock excavation is reflected by their wide application in hard rock cutting machines such as tunnel boring machines and raise borers. The forces involved in the cutting process are those due mainly to thrust and rolling forces and are greater than that required by cutting picks. An interesting feature of cutting with discs is the formation of surface crushing, surface and sub-surface chipping and primary crack formation. Experimental, as well as analytical, work has been carried out to determine the optimum spacing between the disc cutters to control primary crack orientation. Wedge bit indenters were used to simulate disc cutters. The paper concludes by proposing a new approach to rock excavation by hybrid cutting based on controlling the primary crack orientation.

Jan 1, 1992

By D. S. Cronan

Pitcairn Island, the last remaining British Colony in the Pacific Ocean, falls in the S.E. Pacific. Its location, on top of a hotspot volcano, suggests the presence of submarine hydrothermal deposits in its EEZ. Such environments are known to contain hydrothermal mineral deposits, as in the case of Loihi submarine volcano near Hawaii, and Macdonald and Teahitia-Mehitia seamounts in the South Pacific. The hydrothermal deposits in these areas are formed as a result of the interaction of seawater with hot volcanic rock, producing a hydrothermal fractionation sequence comprising sulphides of Fe, Cu and Zn, oxides and silicates of Fe and oxides of Mn. In 1988, a GLORIA survey from the RRS Charles Darwin confirmed the existence of recent volcanism within the Pitcairn Island EEZ. A later bathymetric and sampling survey by the FS Sonne of the region round Pitcaim Island revealed submarine volcanoes approximately 80 km ESE of the island. Hydrothermal mineral deposits were recovered from them, and comprise finely laminated crusts of Fe oxides containing up to 50% Fe, and laminated hydrothermal Mn crusts up to 5 cm thick. Both morphologically and chemically the latter are similar to those from mid-ocean ridge and island arc settings, containing up to 50% Mn, associated with sulphides, and represent first discovery of such deposits associated with mid-plate "hotspot" volcanoes. Massive sulphide deposits are thought to occur within the volcanic pile.

Jan 1, 1992

By K. Najim, D. Hodouin

"The raw ores which are processed in mineral processing plants exhibit very strong variations of their physical and chemical properties. As a consequence, the performances of the comminution and separation processes vary greatly from time to time. Model-based control strategies improve the performance of the plant; however, they require some form of adaptation to cope with the variations of the are properties.This paper deals with the use of adaptive techniques for the control of mineral processes. It begins with a survey on adaptive control algorithms including parameters estimation aspects. Then several examples dealing with crushing, rod, ball, autogenous and semi-autogenous grinding, flotation , drying and calcination processes are reviewed.IntroductionThe operation of the various processes of mineral processing plants (crushing, grinding, flotation, dewatering, etc.) is generally controlled using empirically tuned regulators of constant structure, such as PID controllers. To improve the operation performance, mineral processors try to implement specifically designed controllers, i.e. controllers based on plant dynamic models. Most of the time, these techniques improve the control of the mineral processing installations. However, modelling is a complex procedure because of the problems of measurement and data management, specific to this industry, and because of the variations of the model parameters. In this context model-based control strategies do not always bring the expected improvements or are sometimes discarded and replaced by more conventional techniques .The sources of variation of the dynamic behaviour of mineral processing systems can be classified into three categories: (I) the inherent changes of the raw ore properties (composition, grindability, mineralogical texture, etc.); (2) the process tuning modifications (grinding media loads, number of hydrocyclones, slurry level in flotation cells, agitation speeds, etc.); (3) the feedrate variation of the ore, water, chemical reagents, etc. All these factors change the fundamental properties of the process dynamics such as the grinding or flotation rates and the residence time in the equipment. The simplified linear models which are used to describe the process dynamics are not able to track the complex behaviour of the mineral processing systems when the amplitude of the sources of variation are too large. The mismatch between the model and the plant behaviour is then frequently a cause of model-based controller failures."

Jan 1, 1992

The Resource Management Act has been in force now for approximately ten months. This Act, and the Crown Minerals Act which accompanied it, have substantially changed the manner by which mining operations and other resource uses obtain access to resources and are subject to controls of their environmental effects. This paper briefly summarises the key elements of the regulatory provisions of the Resource Management Act. It identifies the types of resource consents required, and discusses these and procedural matters in relation to mining in Otago. It addresses the transitional provisions and highlights inconsistencies and difficulties in the implementation of these provisions. This paper identifies potential future developments in the planning and regulatory environment relating to mining in Otago.

Jan 1, 1992

By E. Fregeau-Wu

To recycle steelmaking slags for their iron, manganese, and lime contents, removal of the phosphorus-bearing dicalcium silicate and calcium phosphate is essential. Slow-cooling of slags was necessary to promote the sufficient grain growth to achieve liberation. In-situ grain size distribution determination showed that a high soaking temperature, a long soaking time, a very slow cooling rate, and the addition of fluorspar were shown to promote grain growth. High gradient magnetic separation on slow-cooled slags removed much of the dicalcium silicate. Liberation modelling was used to discuss the breakage and beneficiation characteristics of the slow-cooled slags.

Jan 1, 1992

By Jun Li

Rate processes of silver cyanidation were studied with the objective of understanding the reaction mechanism. The research was divided into three sections: anodic dissolution of silver in cyanide solutions, cathodic reduction of oxygen on silver surfaces and the direct leaching of silver in oxygenated cyanide solutions. The charge transfer steps plus the diffusion of reactants from bulk solutions to the silver surface were identified as rate-limiting and the rates of both anodic and cathodic reactions can be calculated using the Butler-Volmer equation and Fick's first law. Based on mixed potential theory and the results of electrochemical studies, a comparison of the rate obtained from direct leaching with that predicted from the calculation is made. Calculated results agree well with the experimental data.

Jan 1, 1992