published_or_final_version / Applied Geosciences / Master / Master of Science

No description available.

No description available.

No description available.

The basic objective of this study was to evaluate the environmental performance of two abrasives Copper Slag and Barshot in terms of productivity (in terms of area cleaned- ft2/hr), consumption and or used-abrasive generation rate (of the abrasive- ton/2000ft2; lb/ft2) and particulate emissions (mg/ft2; mg/lb; lb/lb; lb/kg; lb/ton). This would help in evaluating the clean technologies for dry abrasive blasting and would help shipyards to optimize the productivity and minimize the emissions by choosing the best combinations reported in this study to their conditions appropriately. This project is a joint effort between the Gulf Coast Region Maritime technology Center (GCRMTC) and USEPA. It was undertaken to simulate actual blasting operations conducted at shipyards under enclosed, un-controlled conditions on plates similar to steel plates commonly blasted at shipyards.

Student Number : 0210528 - PhD thesis - School of Mining Engineering - Faculty of Engineering and the Built Environmnet / This thesis describes the development of a directional primer charge for use in blasting in mining operations. The directional primer charge is an explosive gun which takes the place of a standard primer charge in a blasthole. It is a shaped charge which directs the explosive energy forwards into the blasthole. Its effectiveness is enhanced by a metal liner which is located at a specified stand-off distance from the toe of the hole. The explosive energy of the column charge is converted into the kinetic energy of the metal liner which transforms into an ultrasonic slug. This in turn converts into the impact energy of the slug impacting on the rock. This rock is axially compressed to such a degree that a radial fracture is developed. This radial fracture is termed an umbrella crack. Prior to the development of the directional primer charge, the phenomenon of the umbrella crack had only been observed in experimental Perspex blasting models and its formation mechanism had never been satisfactorily explained. If the directional primer charge could cause an umbrella crack in hard rock mining at the end of blastholes, then more rock would be broken out per blast than is currently achieved in practice. This thesis records the historical development of the explosive shaped charge with particular reference to the development of the explosively-forged projectile. It describes the classical theories and models which apply in determining the theoretical prediction of the physical properties of the designed directional primer charge. It describes the experimental procedures and measurements using flash X-ray radiography and electronic shorting screens to freeze the flight of a metal slug traveling at speeds of over 2000 metres per second. Underground tests were undertaken under full mining production conditions to compare the rock breaking effects of various designs. The theoretical calculation of the extent of the movement of the rock at the toe of the blasthole indicates that umbrella cracks should be formed. The underground tests confirm their formation. It is concluded that the use of the directional primer charge in stoping operations can improve the blasting efficiency in South African hard rock mines by up to 15 %.

No description available.

Abstract DEM (Distinct Element Method) models have found numerous applications in a number of engineering disciplines, such as material handling and transport, chemical, industrial, civil, mining and mineral processing. The thesis describes developments using PFC3D (Particle Flow Code in 3D) for simulating rock fragmentation by commercial explosives. Emphasis is on the realistic simulation of explosive detonation in the blasthole as well as the flow of explosive gas from the blasthole, through the fracture network and venting to the atmosphere. Detonation can be initialized at any point along discretized blastholes and proceed up or down the hole according to the Velocity of Detonation of the explosive. Each of the explosive properties (pressure, density, extent of reaction, energy and their time derivatives) is computed according to the conservation equations and the explosive equation of state at any point along the hole. At initiation, the product calculation begins at the sonic locus with input of the detonation product provided by the non-ideal detonation code Vixen-n. The Taylor wave is then computed as a function of the blasthole expansion, which depends on the rock mass response to loading. The explosive gas is treated as a non-steady, compressible fluid and can flow through an arbitrary and evolving fracture network developed in the rock mass as a function of explosive loading. The fracture network (and flow paths) is defined by the coalescence of discrete macro-cracks. The gas has the effect of draining the blasthole and loading the fracture surface by its pressure and drag forces. Fracture intersection with free-surfaces is monitored and venting to the atmosphere is allowed. Validation of the fluid flow scheme is performed by comparing numeric results to analytic solutions for flow in shock tubes. The complete model is demonstrated by simulating stress only models, gas flow models and complete models of field-scale blasts.

Highly concentrated ammonium nitrate emulsions are extensively used as an explosive in the mining industry. The emulsion is made from a supercooled aqueous salt solution with various stabilisers and an organic hydrocarbon phase under vigorous stirring to room temperature. The resulting emulsion is thermodynamically unstable and tends to crystallise over time. This is not suitable for the transportation or pumping of the emulsion in its application. This study showed that the crystallisation process of highly concentrated ammonium nitrate emulsions can be influenced by varying the emulsion droplet size as well as the types and ratios of surfactants used during the preparation stage. The results showed that there were significant differences in the rheological properties of the freshly-prepared emulsion, based on both the emulsion droplet size, and the type of surfactant and ratio of surfactants used. A decrease of the emulsion droplet size resulted in the increase of the elastic character, which can be explained by more compact network organisation of droplets. In terms of the different surfactants, it was shown that the Pibsa-Imide stabilised emulsions resulted in an emulsion with the highest storage modulus over the entire strain amplitude regions as well as the highest shear stresses over the whole shear rate region. The study showed that the relatively slow emulsion crystallisation process can be studied by using powder X-ray diffraction (PXRD). The amount of amorphous and crystalline phases present in the sample can be effectively quantified by using the Partial Or No Known Crystal Structural (PONKCS) method which can model accurately the contributions of the amorphous halo. An external standard calibration method, which used a different amorphous material with the crystalline material to obtain a suitable calibration constant, was employed. The results showed that the method would quantify the amount of the fully crystallised emulsion to be between 80 and 90 percent, which was in agreement with the solid content added during sample preparation and confirmed by Thermal Gravimetric Analysis (TGA). The simultaneous TGA / DSC results were able to show the number of solid/solid peak transitions as well as the total moisture content to be around 20 percent by mass in various emulsion samples studied. The study was able to model the crystallisation by using the Avrami and Tobin kinetic relationships which are commonly used for the crystallisation processes of polymers. The Avrami relationship proved to be useful in describing the type of crystallisation that occurred. This was based on literature where the exponent parameter (n) which was between 1 and 4 would relate to different types of crystallisation models. The results of this study showed that the crystallisation process would change for the samples that had shown a longer crystallisation process. The results indicated that the samples prepared with the lower Pibsa-Urea ratio showed a more sporadic crystallisation process, whereas the samples with the higher ratio of Pibsa-Urea showed a more controlled crystallisation process. The study also considered the rheological properties of the fresh emulsion, which showed that droplet size also had an influence on the stress strain relationship of the emulsion droplets.

During the past two decades many efforts have been made to increase the control of blast furnace conditions to ensure a homogeneous product. The dissections on blast furnaces by various iron and steel companies in Japan in the early 70s provided valuable information on the high temperature properties of charging material. Standard tests (ISO) to determine ore, sinter and pellet qualities only provide information of up to 1100°C . By using the REAS apparatus - a high temperature reduction vessel that simulates the blast furnace process from stockline to melting - the high temperature properties of burden materials have been investigated. The REAS process not only provides an insight into the reactions occurring during the softening and melting process but a range of indices with which to judge the blast furnace performance. Since 1993 new developments started and a test method for Iscor blast furnaces was specifically developed. Although certain indices have been established, uncertainties around the melting mechanisms still existed. These uncertainties include: • Why does the maximum pressure over the sample bed vary extensively between different samples? • Why does a temperature decrease occur only in certain samples and what determines the extent of the temperature decrease? • Which low melting phase forms that causes the initial rise in pressure drop over the sample bed? Four tests were performed on a mixture of Sishen and Thabazimbi ore to determine the phase changes in the test sample. During the reduction of the iron ore, five distinct phases are present. Above 1200°C two liquid phases, an alkali rich phase and a liquid phase with a fayalite composition is present. The rest of the iron reports at different stages in various forms of metallic iron and wustite. Small amounts of a high melting oxide phase, hercynite, also occurs. Softening of the sample is said to occur when the ΔP over the sample bed increases by more than 200 mm H2O. For the specific tests evaluated, this occurred at 1200°C. At this temperature, the liquid with a fayalite composition as well as the alkali rich liquid are present. The formation of the low melting fayalite phase with a high viscosity appears to cause the sudden rise in ΔP. A temperature arrest occurs at the same time supporting the suggestion that liquid formation is responsible for the pressure increase. The results indicate that the mechanisms responsible for the observed pressure drop (decreased gas permeability) and dripping may well be different from those given in the literature. The literature mechanisms emphasise the importance of the amount of FeO available to act as flux for the silica which is present as gangue; hence a greater degree of (indirect) reduction below the melting point of fayalite gives poorer fluxing of silica since less FeO is available. However, the charge materials considered in this study appear to be of substantially higher grade than those used in the previous work. For this reason, there does not appear to be any shortage of FeO to act as flux. This abundance of FeO, and the observation that the peak in pressure drop is not associated with any great change in the amount of liquid, together imply that the literature mechanism regarding changes in the amount and composition of the liquid (i.e. becoming more Si02-rich and viscous as the FeO is reduced) cannot explain the pressure fluctuations observed here. Rather, the increase in pressure appears to be a joint effect of liquid being present (giving the first increase in pressure) and compaction of the sample. Loss of voidage in the sample by this substantial amount of compaction appears the likely cause of the pressure increase. The subsequent decrease in the pressure drop is probably associated with lower viscosity as the sample temperature increases. The importance of compaction means that the amount of indirect reduction does playa role in the development of the pressure drop, but not for the reasons cited in the literature. Pure iron is more malleable than the oxides, and reduction gives a porous iron structure which is more easily compacted. F or both these reasons, the metallic product of indirect reduction favours compaction (and hence the pressure increase). The sharp increase in reduction rate close to the peak pressure presumably results from better contact between the remaining iron oxide (in the fayalite-based liquid, and wustite) with the coke reductant, so favouring direct reduction; this increased reduction (endothermic because of the Boudouard reaction) results in one of the noticeable temperature arrests on the sample temperature curve. The correspondence between the temperature arrests and the changes within the sample do imply that these arrests can be used to gain some information on the reduction mechanisms. However, the reliability of the temperature arrests as indicators of the state of the sample and the reaction conditions within the sample must be tested by further work. / Dissertation (MSc (Metallurgy))--University of Pretoria, 1998. / Materials Science and Metallurgical Engineering / unrestricted