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By P. H. Chang, J. E. Gould

"Solidification structures and austenite decomposition in some spot welded O.05%C - O.3%Mn steels have been studied with the aid of a numerical thermal model. The model is a one dimensional finite difference formulation, and accounts for melting, temperature dependent thermal properties, effective heat transfer in the liquid, and contact resistances. The model was used to predict solidification conditions during resolidification of the nugget. These solidification conditions were correlated with the primary dendrite spacing using available primary dendrite spacings modelling. The model was also used to predict cooling rates in the temperature regime for austenite decomposition. These cooling rates were used to interpret the underlying microstructure.INTRODUCTIONThe metallurgical transformations which occur during the spot welding of low carbon steels have traditionally been characterized only in the most general of fashions. This is most probably due to the similarity of spot welded microstructures to other welded microstructures, and that the mechanical integrity of spot welds has not been a concern. In addition, little information about the particular thermal cycles experienced during spot welding has been available. The introduction of HSLA (microalloyed) sheet steels has, however, raised new concerns about the integrity of spot welds. These steels have on occasion shown irregular weldability, as well as brittleness in the weld nugget on destructive testing l - 4 .In response to these concerns, considerable work has been done attempting to characterize thermal cycles in spot welds 5-12. This has largely taken the form of thermal modelling, with the end purpose generally to estimate the size of the nugget formed. This work uses the thermal model developed at Inland Steel 13 ,14 to try and understand, in a more fundamental way, microstructural evolution in spot welds. Two facets of this microstructural evolution are examined in detail:"

Jan 1, 1986

By Sunil S. Gandhi

"The Mountain Lake deposit is a tabular sandstone-type uranium deposit, hosted by the basal unit of Middle Proterozoic Dismal Lakes Group. Uranium occurs mainly as sooty pitchblende disseminated in stratiform lenses within gently dipping quartzose sandstone. It is associated with copper sulphides, pyrite, hematite, and traces of nickel and cobalt arsenides and of silver.Exploration HistoryUranium showings on the PEC claim group were discovered during 1969 by an airborne radiometric survey carried out over the Dismal Lakes-Great Bear Lake area by Aquitaine of Canada Limited (Bizard and Salat, 1969). Some drilling was done in the vicinity of the showings in 1975 by the company under a joint venture with Eldorado Nuclear Limited but the results were not encouraging (Hassard and Woollett, 1975). During 1972, Trigg, Woollett and Associates Limited conducting surveys for Imperial Oil Limited, discovered numerous high-grade radioactive boulders scattered over a distance of several kilometres north and west of the showings, and the area north of the PEC claims was staked as the YUK claims (Ahuja, 1974). A systematic study of the boulder distribution and Pleistocene geology suggested a source additional to the showings. More intensive exploration followed, and in 1976 drilling just north of the PEC claim group boundary intersected the main deposit at a depth of 75 m to 150 m, beneath overburden up to 60 m thick. Part of the deposit extends into the PEC claim group which is under exploration by the Aquitaine-Cominco Joint Venture.The following brief description is based on the presentations in 1978 by F. Hassard of Trigg, Woollett and Associates Limited at the Geoscience Forum in Yellowknife, and by S.S. Gandhi of the Geological Survey of Canada at the Mineralogical Association of Canada Uranium Short Course in Toronto."

Jan 1, 1986

Between February and August of 1986, Dr Alfred Petrick visited New Zealand sponsored under a Fulbright grant administered by the New Zealand-United States Educational Foundation. The grant supported a research project completed by Dr Petrick having as an objective, the preparation of a preliminary economic evaluation of the mining of six Otago lignite deposits as a source of energy for steam power generation or in liquid fuels. The research is limited to consideration of preliminary geological and engineering data on the six deposits and to the time constraints of the Fulbright visit. This paper is a summary of the final Fulbright report. The complete report including the listings of the computer programs is available from the Otago School of Mines.

Jan 1, 1986

By Slechta J. J

An evaluation of a pilot scale Delkor horizontal belt filter at Bellambi's South Bulli Colliery showed high productivities and low moisture contents for a range of feed slurries. When treating flotation concentrate, a productivity in excess of 1000 kg/m2/hr (dry) at a moisture content of less than 22 per cent was obtained. The results indicated the belt filter had a capacity twice that of conventional drum or disc filters, and was capable of dewatering a very fine, thickened, classifying cyclone overflow slurry to an acceptable moisture content. The superior performance of this filter is discussed in terms of the factors influencing cake formation and the stratification of solids in the filter bowl of a conventional rotary vacuum drum filter.

Jan 1, 1986

By Valois R. Shea-Albin

Increasing pressure from State and Federal agencies to mitigate mining-induced subsidence damage to overlying structures has presented a unique problem to the coal industry in the western United States. Because sandstone escarpments are an environmental issue, millions of tons of coal reserves that underlie these escarpments risk being classified as unminable by regulatory agencies. At this time, the effect of subsidence on escarpments has not been well documented or characterized. The Bureau of Mines is using numerical modeling techniques to analyze escarpment response to longwall mining. Two- and three-dimensional finite element models have been constructed for a study area near Price, Utah, where longwall panels were mined near an escarpment. This status report includes preliminary results showing that the pattern of subsidence surrounding the escarpment can be simulated through numerical modeling. Models that include such structural details as joint and fracture patterns will better simulate subsidence patterns .and magnitude. By locating longwall panels strategically in relation to the escarpment, stability may be preserved throughout the mining process. Numerical modeling provides a method to analyze relatively quickly the effects of longwall panel location and resulting subsidence on escarpment stability. The goal is to provide a relatively accurate predictive tool for mine planning to determine if escarpment stability can be maintained while maximizing extraction of the coal reserves.

Jan 1, 1986

By J. Dean Warner

In 1984, as part of a project to evaluate Alaskan occurrences of certain critical and strategic minerals, the Bureau of Mines investigated a columbium-bearing regolith on upper Idaho Gulch, near Tofty, AK. The regolith is derived from weathering of a dolomitic marble and consists mostly of iron oxide minerals with accessory apatite, zircon, xenotime, rutile, monazite, and the columbium minerals aeschynite, columbite, and ilmenorutile. Two regolith lenses contain 340,000 lb of columbium resources at an average grade of 0.07 pct. Calculated composite concentrates from two regolith samples (approximately 200 lb each) contained 53 and 57 pct of the columbium at grades of 0.97 and 0.86 pct, respectively. In each case the grade could be improved to 1.1 pct Cb with a sacrifice of 9-pct recovery. The regolith's mineralogy, trace-element geochemistry, and similarity to descriptions of other columbium-enriched regoliths suggest that the underlying marble may be a carbonatite. The lack of associated alkalic igneous rocks and the stratiform nature of the regolith, however, may be interpreted as evidence for sedimentary origin of the marble. The marble and regolith are a lode source for some of the minerals in the Idaho Gulch placer deposit.

Jan 1, 1986

By J. Lancaster

World demand of sulphur-in-all-forms (SAF), which in 1985 is estimated to total 57.5 million tonnes S equivalent, is expected to increase to 77.6 million tonnes S by the year 2000. Key factors are the evolution of sulphur demand in the USSR, China, and the developing countries notably India, Brazil, and the countries in North Africa and the Near East with vertically integrated phosphate industries. Brimstone will remain the dominant sulphurous raw material notwithstanding the progressive increase in the supply and use of sulphur in other forms resulting mainly from the enhanced recovery df pollution sulphur and the increased use of sulphur in pyrites in those countries with this sulphur resource. Sulphur demand for phosphate fertilizer manufacture is expected to have the main impact on world sulphur demand, but in contrast to the industrially advanced countries where non- fertilizer sulphur use is not expected to increase measurably, this demand sector is expected to be of some importance in those developing countries with dynamic economies and in the centrally planned economies of East Europe and the Far East.

Jan 1, 1986

By A. G. Journel

The indicator random function formalism allows a common coding of hard numerical data, constraint intervals, and soft qualitative information as prior probability distributions. The soft kriging algorithm allows interpolating these priors into posterior probability distributions of the unknown. The curse of ?negative kriged grades? is solved. The consideration of additional soft information, whenever deemed necessary, becomes possible within the framework of well-proven kriging techniques.

Jan 1, 1986

By Robert R. Thompson

Retreat pillar mining is highly productive but dangerous. The primary danger during pillar removal is premature caving of the roof. Because the safety of the miners is dependent on successfully controlling the roof, the roof must cave in a predictable and dependable manner. Temporary support during retreat is usually obtained by setting posts. They are set manually by a miner working in a dangerous area. A solution to this problem would be a system which could set and retrieve roof supports remotely and safely. The Bureau of nines has developed a remotely operated Mobile Roof Support (PIPS) machine which will place and retrieve temporary roof support. Two PIPS machines were fabricated under a cost-sharing agreement with Southern Utah Fuel Company and mining equipment manufacturer. Each machine carries four 50-ton jacks and is remotely- Controlled by radio. The machines are presently being used by Southern Utah Fuel Company under a long-team cooperative agreement. Not only have there been material and manpower cost savings in not having to set posts, but also the time saved bas resulted in increased productivity. The projected costs of mass-produced machines with tethered remote control rather than radio remote control are estimated at $150,000 each. The radio remote control is more expensive and is considered an optional extra.

Jan 1, 1986

By Scales PJ, Ralston J

Fine coal particles have been examined with respect to dustiness and its connection with various physical and chemical properties. It appears that a given coal will tend to be dusty ifthe moisture content is low and if the inert maceral content and overall rank are high. The hydrophobicity ofa coking coal (Young-Wallsend) and a steaming coal (Blair Athol) was examined in detail by a dynamic contact angle technique. The YoungWallsend coal had a higher contact angle, on average, than the Blair Athol sample. This result has important implications for dust suppression and associated processes.

Jan 1, 1986

By M. R. Wormald

A real time data acquisition system has been developed for implementing standard radiometric analytical techniques, applied to the monitoring and control of mineral processing plants. The system uses standard ECB-bus microprocessors and peripherals, in conjunction with a specially designed nucleonic pulse ADC. It is being applied to the accurate on-line analysis of naturally-,occurring radioelements in processing plants, for example by simultaneously measuring the intensity of 1.46 MeV gamma-rays from the naturally-occurring radioisotope K-40, and the stream density by gamma-ray transmission of 662 keV gamma-rays. Gain stabilisation of the NaI(T1) scintillation detectors is maintained by the microprocessor in slave units, each of which may control up to four sample presentation systems. Data analysis - including corrections for bulk density, radioactive decay of the Cs-137 gamma-ray source, pulse pile-up, dead time and external background - is carried out in a master computer which is connected to the slave unit, and can be interfaced to the plant control computer via data links.

Jan 1, 1986

By B. Pesic

This is an extension of the work on recovery of silver and manganese from Ag-Mn ores, and recovery of silver and gallium from flue dust from phosphate industry. Carbon adsorption was considered as the most adequate method for recovery of silver from thiourea leach solutions. For this reason it was decided to examine the characteristics of adsorption of silver on activated carbon. Coconut hard shell activated carbon was used for this study. Ag(TU)2C1 complex was dissolved into thiourea solution to give 2 gpl stock solution. Thy studied parameters were: loading isotherms at 25°C, 35°C, and 45°C, initial kinetics as a function of thiourea concentration, temperature, pH, N2, and O2. It was found that the loading capacity of carbon for silver and thiourea was 137-150 mg/g and 514 mg/g, respectively, at 25 °C.

Jan 1, 1986

By Don McColman

"Tires, although not always the largest single cost item in open-pit mining operations, will place in the top three, along with explosives and fuel. How this high-cost supply is controlled is dependent upon on an efficient tire program. The success of this program is, in turn, dependent upon the people who are directly associated with tires and their use, namely: the mine's tire personnel, the tire sales representatives and a technician for the rubber company. The technician will relay his observations and information received from the mine personnel back to the manufacturer with recommendations to overcome current problems .Haulage truck tire life and costs in a hard rock open-pit mine are governed and controlled by four important factors:I) Field control.2) Operating within manufacturer's guidelines.3) Different tire purchasing methods.4) Scrap piles.Field ControlPerhaps the most influential people involved in this program are those who live with the tire through every hour of its lifespan: the truck driver, the shovel operator, the dozer operator, the grader operator and the shift boss. Of these, the truck driver has the most control, in that he can drive over or around rock s as these situations arise. The loading area, the edge of the haul road and the dump account for most of the tire injuries.This is why shovel, dozer and grader operators must appreciate their influence on haulage tire life. Spillage cleanup must be ongoing and is not being done adequately if any of these operators are idle. The shift boss that drives by a rock on the road without removing it or calling for a cleanup has little recourse with the truck driver who runs over it-he has sanctioned the driver's actions by his own neglect."

Jan 1, 1986

By Preston JC, Richards DJ

A multicommodity exploration programme was mounted in the 1970s by CRA Exploration Pty. Limited over a major part of the southern Murray Basin in Victoria. Commodities sought were brown and black coal, gold, uranium, diamonds, titanium and zirconium rich heavy minerals, and base metals. An area of 40 000 km2 was held under exploration licences by the Company. Exploration techniques used were literature research, airborne magnetics and gamma ray spectrometry, drilling, and geophysical well logging. Targets were defined in both the Tertiary basin sediments and the underlying Palaeozoic sedimentary and igneous rocks. Although exploration is continuing, large resources of brown coal and low grade titanium rich heavy minerals have already been discovered. Exploration for uranium was abandoned in accordance with statutory requirements. The search for significant resources of the other commodities has not been successful.

Jan 1, 1986

Blast performance is related to rock structure and strength, as well as to factors such as site geometry, drill patterns, explosives loading, firing sequences and delays.

Jan 1, 1986

By Gregory E. Tieman

Hydrologic impacts of longwall mining were studied in 1986 after mining had occurred at mine "Z" in northern West Virginia. This mine is 700 to 1,300 ft deep, with a surface topographic relief of 300 to 500 ft. Five springs and one dug well were reportedly dewatered by mining. All such supplies are above nearby streams in elevation, and at least 800 ft above the subsided mine. Three of these six supplies showed partial recovery within one year. Only supplies within 50 ft in elevation of a nearby stream showed apparent partial recovery. Measured perennial streams showed notable depletion in streamflow over mined longwall panels that were less than two years old. Normal stream discharge was measured over panels more than two years old. Most apparent hydrologic dewatering impacts appear to be temporary, and the most vulnerable areas for these impacts are hill sides.

Jan 1, 1986

By S. Eugene Sankey, Geoffrey L. Payne

Modern metallurgical processing often depends heavily on the use of flocculants to achieve the high levels of efficiency required. Selection of the optimum polymer can be complicated by the effects of process streams on the chemical and physical stability of the chosen polymer. Similarly, the presence of the polymer can have positive or negative side effects on process streams, such as phase disengagement in solvent extraction, foaming at filters and thickeners, crystal growth modification or flotation performance. Guidelines are given to highlight areas where problems may occur and suggestions made as to how these can be overcome. Practical advice on the preparation and application of polymers in process liquors is provided.

Jan 1, 1986

By L. G. Austin

A program has been written to combine the Klimpel-Austin approximate model for liberation in a binary system with a mill model applicable to ball milling. The model applies for a system where the volume fraction of valuable B in host matrix A is small. The mill model is treated as an equivalent series of fully-mixed reactors. Twenty-three classes of material are considered: pure A; pure B; unchanged AB; 0-10.2 B in AB either as surfac- exposed B or as wholly-contained grains of B; 10-20% B in AB, surface-exposed or wholly- contained;etc.. to 90-100% /b ub /ABm syrface-exposed or wholly-contained. Illustrative cases are given making reasonable assumptions concerning relative rates of breakage and primary breakage distribution functions for each class of material.

Jan 1, 1986

By Stephen C. Tadolini

The Bureau of Mines conducted field investigations in two underground mines to determine the actual loads to which bearing plates were subjected when installed in conjunction with full-column resin-grouted bolts and the roof movements generated by the applied loads. Measured loads indicate that the bearing plate is an integral part of the support system. Vertical displacement gauges installed to monitor roof displacements in the test sites show that the highest degrees of loading occur in conjunction with the largest amounts of movement.

Jan 1, 1986

By Basil S. Fee

INTRODUCTION Probably the most important family of chemicals used in mineral processing today is a category of basic commodity chemicals loosely denoted as pH regulators. Typical chemicals which are referred to as pH regulators include lime, magnesium hydroxide, soda ash, caustic soda, ammonia, sulfuric acid, and hydrochloric acid. These chemicals are often used in very significant amounts in almost all of the major mineral processing operations such as flotation, hydrometallurgy, etc. (in dosages up to ten pounds per ton of feed ore treated). While cheaper in cost per unit weight of chemical than more specific chemicals such as collectors, frothers, extractents, etc., the overall cost to the mill operator is generally higher with pH regulators per ton of ore processed than with any other given processing chemical. For example, a rough rule of thumb in sulfide mineral flotation is that the cost of lime is double that of the collector(s) used. The symbol pH is used to designate hydrogen ion concentration. When acids, salts, and bases are dissolved in water, individual molecules are dissociated into their constituent radicals or ions. The strength of an acid or a base increases with the extent of such dissociation or ionization. An alkaline solution is one in which the number of Qydroxyl ions (OH ) exceeds the hydrogen ions (H ). In an acid solution, the hydrogen ions predominate. In either case, both ions are always present as water itself ionizes to a limited extent, that is: [ ] The pH scale is logarithmic and the pH value is the negative of the logarithm (base 10) of the molar concentration of hydrogen ions per liter of solution. For example, a pH of 5 means that the molar concentration of hydrogen ions per liter is 0.00001 (1 x 10-5). Likewise, a pH of 9 means that the molar concentration of hydrogen ions per liter is 1 x 10-9. Normally, the relationship between hydrogen ion and hydroxyl ion concentration is based on the relationship: Concentration of H ion x concentration of OH- ion = constant. Eq. (1) In dilute and/or moderately concentrated solutions that are normally used in mineral procygsing processes, the constant at 25°C is 10-14. On the pH scale, the value of pH equal to 7 represents the hydrogen ion concentration of a neutral solution. pH values lower than pH 7 indicate increasing acidity and higher values than 7 indicate alkalinity. Table 1 shows the nature of the pH scale at 25°C. Temperature affects the extent of ionization of dissolved acids, salts, bases, and water so that the hydrogen ion concentration (hence pH) of a solution is also affected by temperature. As a means of demonstrating this dependency, Table 2 shows the change of the exponent of the constant (base 10) in Eq. 1 and the pH value corresponding to neutrality as a function of temperature. It is also important, for example, that alkalinity or acidity expressed by pH not be confused with total alkalinity or total acidity. For example, total alkalinity is commonly determined by titration with a standard acid solution (usually HC1). pH is a measure of the hydroxyl ion concentration of an alkaline solution, whereas titration is a measure of an alkaline solution's acid neutralizing capacity. Thus, if one takes a series of various alkaline solutions prepared using different chemicals but all of exactly the same pH (and temperature) and then subsequently carries out a titration on each solution with a standard acid, it would be observed that the various alkaline solutions would neutralize entirely different amounts of acid. As an example, 0.08 grams of caustic (NaOH) , 6.32 grams of soda ash (Na2CO3), and 8.17 grams of ammonium hydroxide (NH4OH) all have a pH of 11.3 at 25°C. One liter of each of the above solutions neutralizes 0.073, 4.348 and 8.496 grams of HC1, respectively. Therefore, depending on the specific use of any given pH regulator, special tests need to be run by the mill operator to determine factors such as: the specific technical goals to be accomplished by

Jan 1, 1986