The effect of the thermal properties of alumina and CBN abrasives on workpiece temperatures in grinding was investigated. A review of the literature revealed a lack of knowledge of the thermal properties of CBN limiting the accuracy of theoretical predictions of the heat conduction in CBN grinding. A grain contact analysis was developed to predict the energy partitioning between the workpiece and wheel. The analysis takes into account two dimensional transient heat transfer in the grain and maintains temperature compatibility at the grain wear flatworkpiece interface. The proportion of the total grinding energy entering the workpiece, termed the partition ratio, was estimated by correlating measured temperature distributions with theoretical distributions. The partition ratios when grinding with CBN were substantially lower than grinding with alumina wheels for a range of ferrous materials. The lower partition ratios with CBN grinding were attributed to the higher thermal conductivity of the CBN abrasive. The effective thermal conductivity of alumina and CBN grains were quantified by correlating the theoretical partitioning model with the measured results. The effective thermal conductivity of CBN was found to be considerably lower than the reported theoretical value albeit much higher than the effective thermal conductivity of alumina. A model to predict the background temperature in grinding was proposed based on the experimental findings. The thermal model takes into account a triangular heat flux distribution in the grinding zone, the real length of contact and experimentally validated grain thermal properties. The input parameters to the thermal model were specified. To avoid temper colours on the workpiece surface the maximum background temperature must not exceed 450 to 500deg. C. for commonly used ferrous materials.

M.Sc. / At the very roots of this dissertation lies a commercial process with many as yet unexplored characteristics that will be thoroughly examined, using a rich variety of statistical methods and techniques. Broadly speaking, the main objective of this study involves the development of techniques to control the quality of advanced explosives detonators used in commercial mining operations. To accomplish this task, various statistical characteristics of this detonation process are described and examined in order to obtain a holistic understanding of the underlying process. The parameters of the process are introduced and estimates for unknowns are derived. Real-time quality control techniques based on these results are suggested. 1.2. The role of blasting in mining A major part of South Africa's economy is based on the mining of the rich mineral deposits that are to be found in the country. These mining operations are carried out both above ground (open-pit iron ore mines, for example) and below ground (gold, uranium and others). Open-pit mining, in particular, requires significant amounts of commercial blasting to dislodge the high volumes of material that have to be moved and processed. An average blasting block at Iscor's Sishen mine, for example, contains about 250 000 tons of material, although a world record was established in April 1981 when 7, 2 million tons of rock was broken during a single blast. The chemical quality of the final products is partly controlled by supplying the primary crusher at the mine with a suitable mixture of so-called run-of-mine ore. To determine which material from a specific blasting block may be sent to the plant, and to which waste dump the remaining material should be assigned, factors such as beneficiation properties of the raw material and the content of various by-products are considered. Samples are typically taken from alternate blast holes for every metre drilled. Each drill sample is divided into two parts by means of a riffler for a washed and unwashed sample. The washed samples are examined and the rock types noted. Subsequently, all the samples are grouped and analysed chemically and the densities of the different rock types are determined. The results are processed and those for the washed and unwashed samples correlated. The blasting blocks in the pit are demarcated by means of whitewash lines, according to the divisions on the blasting-block plans, and they are marked with signs to guide shovel operators. Primary drilling is performed by means of electrically-driven rotary drills. At the Sishen mine, 310 mm diameter blast holes are drilled in all rock types. The following table depicts typical drilling 2 patterns for various rock types: Rock type Pattern (m) Drill depth (m) Hard iron ore 2 x 8, 3 3, 0 Medium-hard iron ore 1 x 9, 3 2, 7 Quartzite 8,2 x 9,4 2, 5 Flagstone 8,2 x 9,4 5 Calcrete 8,1 x 9,3 0 Primary blasting is done at Sishen with Heavy Anfo, an explosive that is manufactured by mine personnel at the emulsion plant on site. The ingredients for the explosive blends are transported by pump trucks to the blasting blocks, where it is mixed and pumped down the blast holes. Good fragmentation of the blasted material is a prerequisite for high loading rates by the loading equipment. At Sishen and other similar mines, a blasting efficiency of 3, 2 tons of rock per kilogram of explosives used, is considered to be acceptable.

In general, as the uniaxial compressive strength of rock samples is tested, the uniaxial strength of the rock decreases with increasing sample size until a strength is reached beyond which no further decrease in strength is observed for further increases in size. The size at which this occurs was termed the critical size by Bieniawski (1968) and the corresponding strength the critical strength. Once these values are obtained no significant changes in strength may be expected as a result of further volume changes. For the purposes of pillar design, this strength should be adjusted to account for other factors that affect pillar strength, the main factors being the width to height ratio (w/h) effect, jointing and contact conditions. Further test work on Merensky Reef was required to clarify the: 1. Values of it’s critical size and strength 2. Effect of the w/h on it’s strength 3. Effect of the frictional contacts between the reef and the surrounding rock on the reefs uniaxial strength. These results could then be integrated into a holistic pillar design methodology to improve current pillar designing practices. These effects were examined through the laboratory testing of samples originating from Amandelbult Platinum mine. A critical strength of approximately 110 MPa was obtained for samples with diameters, 130 - 250 mm (w/h =1). Increasing the frictional contacts between sample and loading platens was found to increase the sample's strength. A marked difference was found between the insitu and laboratory contact friction angles for Merensky Reef. The insitu contact friction angle was found to be approximately 2.5 times larger then the laboratory contact friction angle. The uniaxial strength increased linearly with increasing w/h ratios up to a w/h ratio of 6. For w/h ratios greater then 6 the strength continued to increased with increasing w/h ratios, but no curve could be acceptably fitted to the data to describe this trend. The results of this study can be applied to mine pillar design in the Bushveld Igneous complex. / Dissertation (MEng (Mining Engineering))--University of Pretoria, 2007. / Mining Engineering / unrestricted

The testing undertaken for this dissertation is intended to help quantify the various time-dependant deformation processes around typical deep level hard rock tabular excavations. Three mechanisms were investigated and two different hard rock types, Ventersdorp Lava and Elsburg Quartzite were used. Uniaxial compression creep studies were done as the first part of the study followed by shear creep studies on discontinuities where crushed lava and crushed quartzite as well as a natural gouge were used as infilling. An important conclusion made is that the relationship between grain size and infilling thickness is more important than previously might have been assumed. The last part of the study consisted of triaxial post-failure relaxation tests. As far as could be determined, this is the first time triaxial post-failure tests were attempted, particularly on typical South African hard rocks. An important finding of this study is that during compression creep as well as during triaxial post-failure relaxation the amount of energy dissipated for the lava is significantly less than for quartzite. For mines operating at great depth (more than 2000m) the implication is that the rock material might relax much more slowly than might have been assumed and this means that after failure the rock mass continues to store large amounts of strain energy. This study provides the first data available for energy change calculations in fractured rock masses. Three mechanisms of time-dependant deformation were quantified providing valuable data for numerical investigations. / Dissertation (MSc (Mine Strata Control))--University of Pretoria, 2006. / Mining Engineering / unrestricted

Rare earth elements (REEs) are a group of 15 elements in the lanthanide series along with scandium and yttrium. They are often grouped together because of their similar chemical properties. As a result of their increased application in advanced technologies and electronics including electric vehicles, the demand of REEs and other critical elements has increased in recent decades and is expected to significantly grow over the next decade. As the majority of REEs are produced and utilized within the manufacturing industry in China, concerns over future supplies to support national defense technologies and associated manufacturing industries has generated interest in the recovery of REEs from alternate sources such as coal and recycling. A solvent extraction (SX) process and circuit was developed to concentrate REEs from dilute pregnant leach solutions containing low concentrations of REEs and high concentrations of contaminant ions. The separation processes used for concentrating REEs from leachates generated by conventional sources are not directly applicable to the PLS generated from coal-based sources due to their substantially different composition. Parametric effects associated with the SX process were evaluated and optimized using a model test solution produced based on the composition of typical pregnant leach solution (PLS) generated from the leaching of pre-combustion, bituminous coal-based sources. Di-2(ethylhexyl) phosphoric acid (DEHPA) was used as the extractant to selectively transfer the REEs in the PLS from the aqueous phase to the organic phase. The tests performed on the model PLS found that reduction of Fe3+ to Fe2+ prior to introduction to the SX process provided a four-fold improvement in the rejection of iron during the first loading stage in the SX circuit. The performances on the model system confirmed that the SX process was capable of recovering and concentrating the REEs from a dilute PLS source. Subsequently, the process and optimized parametric values were tested on a continuous basis in a pilot-scale facility using PLS generated from coal coarse refuse. The continuous SX system was comprised of a train of 10 conventional mixer settlers having a volume of 10 liters each. A rare earth oxide (REO) concentrate containing 94.5% by weight REO was generated using a two- stage (rougher and cleaner) solvent extraction process followed by oxalic acid precipitation. The laboratory evaluations using the model PLS revealed issues associated with a third phase formation. Tributyl Phosphate (TBP) is commonly used as a phase modifier in the organic phase to improve the phase separation characteristics and prevent the formation of a third phase. The current study found that the addition of TBP affected the equilibrium extraction behavior of REE as well as the contaminant elements., The effect on each metal was found to be different which resulted in a significant impact on the separation efficiency achieved between individual REEs as well as for REEs and the contaminant elements. The effect of TBP was studied using concentrations of 1% and 2% by volume in the organic phase. A Fourier Transform Infrared (FTIR) analysis on the mixture of TBP and DEHPA and experimental data quantifying the change in the extraction equilibrium for each element provided insight into their interaction and an explanation for the change in the extraction behavior of each metal. The characteristic peak of P-O-C from 1033 cm-1 in pure DEHPA to 1049 cm-1 in the 5%DEHPA-1%TBP mixture which indicated that the bond P-O got shorter suggesting that the addition of TBP resulted in the breaking of the dimeric structure of the DEHPA and formation of a TBP-DEHPA associated molecule with hydrogen bonding. The experimental work leading to a novel SX circuit to treat dilute PLS sources was primarily focused on the separation of REEs from contaminant elements to produce a high purity rare earth oxide mix product. The next step in the process was the production of individual REE concentrates. To identify the conditions needed to achieve this objective, a thermodynamic model was developed for the prediction of distribution coefficients associated with each lanthanide using a cation exchange extractant. The model utilized the initial conditions of the system to estimate the lanthanide complexation and the non-idealities in both aqueous and organic phases to calculate the distribution coefficients. The non-ideality associated with the ions in the aqueous phase was estimated using the Bromley activity coefficient model, whereas the non-ideality in the organic phase was computed as the ratio of the activity coefficient of the extractant molecule and the metal extractant molecule in the organic phase which was calculated as a function of the dimeric concentration of the free extractant in the organic phase. To validate the model, distribution coefficients were predicted and experimentally determined for a lanthanum chloride solution using DEHPA as the extractant. The correlation coefficient defining the agreement of the model predictions with the experimental data was 0.996, which is validated the accuracy of the model. As such, the developed model can be used to design solvent extraction processes for the separation of individual metals without having to generate a large amount of experimental data for distribution coefficients under different conditions.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Mining and Metallurgy, September 1967. / Archives copy is a reproduction from microfiche; issued in pages. / "August, 1967." Vita. / Includes bibliographical references (leaves 122-124). / by Henry Ralph Piehler. / Sc.D.

M.Sc. (Eng.),Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2012 / Mining is a sensitive business that yields high returns and at the same time is associated with high risk of injuries/fatalities and potential losses of revenue. There is increasing intolerance for injuries and fatalities by governments and the other stakeholders involved in the mining business often resulting in mine closures and revenue loss. Chief among the mining risks is the occurrence of rockfalls where people work and access. The rockfalls are bound mainly by joints that intersect the rockmass thereby forming rock blocks that may fall once an excavation has been created. There are many methods that have been used over time to predict the occurrence of rockfalls. More recently probabilistic methods have gained more ground over deterministic methods. The properties of the joints that are identifiable on exposed excavations are the main inputs used in simulating rockfalls. To date there has been little work that has been done to compare predicted rockfalls to actual rockfalls. This dissertation presents a practical method for collecting rockfall and joint data in the stope hangiwall at two mines in the Bushveld Complex. The joint data has been used in simulating rockfalls using JBlock (a probabilistic keyblock stability programme). A comparison between simulated rockfalls and mapped rockfalls has been presented. Based on this comparison, a number of iterations were done to calibrate the JBlock results until near realistic rockfalls were achieved. Three case studies have been conducted to investigate the effectiveness of different stope support systems in reducing rockfall. The potential losses and injury risk associated with the different support systems have been quantified for all the individual rockfalls. In general the rockfall frequency is directly proportional to the risks associated with the rockfalls. Through this research it has been demonstrated that it is possible to use joint data found on excavation surfaces to statistically predict the occurrence of potential rockfalls in similar ground conditions. The optimum support system that has minimum injury and cost risk can also be selected from a comparison of a number of support systems. Armed with this information, rock engineers can now make strategic decisions versus the existing common tactical approach.

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Thesis: M.S., Massachusetts Institute of Technology, Dept. of Mining Engineering and Metallurgy, 19098 / MIT Institute Archives copy has the following paper bound with thesis: Design of plant for smelting and converting a sulphide copper ore, by C.Y. Wen. 1909. (29 leaves, [1] leaf of plates : ill.; 27 cm.). / Includes bibliographical references. / by Ching Yu Wen. / M.S. / M.S. Massachusetts Institute of Technology, Dept. of Mining Engineering and Metallurgy

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