No description available.

No description available.

No description available.

No description available.

South Africa is the world’s largest producer of platinum group elements (PGEs). Mining takes place in the Bushveld Complex, and recent statistics, (Mudd, 2010), showed that the UG2 reef is the main source of production, accounting for approximately 60% of world mining production. However, recovery by flotation is complicated by variations in the mineral composition, the need to grind fine and entrainment of chromite, which has an adverse effect on the subsequent smelting of the concentrate. The recovery of PGEs is variable, and it is influenced by PGE feed properties such as degree of liberation, mineral type and grain size. Conventional rougher batch flotation tests on drill core samples do not provide sufficient information for predicting plant performance. The aim of this research was to develop a rigorous method for the testing of UG2 drill core samples. A rougher-cleaner flotation test procedure was developed, and statistical tests were applied to select an appropriate model, which included entrainment of hydrophilic minerals. Fifty UG2 samples from across the Bushveld were milled at a fixed energy input, and the new test procedure was applied to derive model parameters for all samples. There was a significant variability in the PGE recovery, and typical feed characteristics such as PGE feed grade and grind did not show a clear link to the PGE recovery. This was due to the complex mineralogy of the PGE minerals and variations in ore hardness. Hence, a statistical modelling algorithm was used to determine the factors affecting PGE recovery, and an empirical model was developed, which relates the PGE recovery to feed properties. The model can be used to estimate PGE recovery based on feed properties. Samples which had a high base metal content (e.g. high nickel to iron ratio) had a high PGE recovery, and samples which were altered (e.g. high Rb/Sr ratio and loss on ignition) had a low PGE recovery. Depressant addition is used in PGE flotation to control the recovery of gangue, but it also affects the flotation of composite PGE/gangue particles. Seven of the fifty UG2 samples were selected for a more detailed investigation, using a more advanced batch flotation test and a mineralogical liberation analysis. The advanced batch flotation test was a new development, in which flotation model parameters were derived simultaneously for flotation after two stages of grinding and a combined cleaning stage. The effect of a range of depressant additions was also modelled. The floatable PGE fraction, determined from batch modelling, was linked to the mineralogical liberation analysis of the feed. The model is the first of its kind, and it makes it possible to predict the mineralogical characteristics of the feed from flotation data. A spread-sheet simulator was developed, to demonstrate how batch data (from the advanced flotation test) could be used to predict plant performance. Scale-up parameters were derived by using pilot-plant data for one of the ores. The spread-sheet was then used to optimise the plant design and depressant addition for an ore, while constraining, the mass of concentrate and the chromite content. The example showed that there was an optimum depressant addition and rougher-cleaner volume capacity for an ore. The gambit of this study was the linking of feed chemical assay and mineralogical properties to PGE recovery. The application of mineralogical tests and modelling of data from the advanced flotation test has demonstrated that the link is relatively complex. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.

This study explores ways to determine the energy efficiency of a pyrometallurgical ore reduction plant and measures to improve it. The feasibility of building a commercial plant - that is more energy efficient, has a low energy cost, and can operate independently and cost-effectively of external electricity supply - is determined. The need for energy efficiency is expanded to three questions: how should the energy efficiency of the plant be determined, what is the efficiency of the existing plant and to what level it can be improved. Literature and other relevant sources were consulted. Twenty potential energy conservation measures were identified through a literature study. A multi-criteria decision-making approach resulted in the selection of ten measures for conceptual implementation. The measures ranged from high-efficiency motors, solar power, heat recovery with thermal oil and various heat engines, to pressure recovery with turbo-generators. A case study approach was followed with the energy efficiency of an existing prototype plant the subject being studied. The energy usage of the existing plant and feasible measures to improve the performance were empirically observed. The impact of these measures was modelled and the results of the conceptual implementation determined. Two measures that were implemented during the study are also described and the results reported. The study found that the energy efficiency of the plant could be determined by the ratio of product exergy to input energy. By incorporating a number of energy conservation measures conceptually the internal efficiency of the prototype plant was conceptually improved from the current 17% to 22% and as a result externally supplied electricity reduced by 47%. The results were extrapolated to a future commercial plant and energy efficiencies of 26% on-grid and 21% off-grid predicted. This study suggests that a significant improvement in energy efficiency and energy cost can be achieved by integrating appropriate energy conservation measures into the existing and future plants. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

No description available.

Chromium has been widely used in many industrial applications. As a result of chromite ore processing, large amounts of chromite ore processing waste (COPW) material that can be classified as hazardous have been produced and released into the environment. Therefore, knowledge of migration behavior and leaching rates of chromium through waste materials and soils are of primary concern for environmentally sound management of land-disposal hazardous wastes. Hask&ouml / k (1998) experimentally studied leaching rates of total Cr and Cr(VI) using laboratory columns packed with chromium COPW material produced by a sodium chromite plant. Based on the experimental results of Hask&ouml / k (1998), present study aim, through mathematical modeling, to understand the dissolution kinetics of chromium during leaching of COPW material and to investigate the effectiveness of intermittent leaching involving a sequence of batch (dissolution) and leaching (mass flushing) operational modes. Obtained results show that a coupled system of two first order differential equations was able to capture the essential characteristics of leaching behavior of COPW material. In addition, the kinetics of chromium dissolution from COPW appeared to be controlled by the difference between aqueous phase concentration and a saturation concentration, by the mass fraction of dissolvable chromium remaining in the solid phase, and finally by the contribution of a constant dissolution rate manifested as a steady-state tailing behavior. As a result of performed simulations it was seen that intermittent leaching could be 65%and 35% more effective than continuous leaching for total Cr and Cr(VI), respectively.

Thesis (MAppSc(ChemTech))--University of South Australia, 2000

Ore floatability is defined as the propensity of particles to float within a flotation environment and any effective mathematical model of the flotation process must incorporate its effect. The objective of this thesis was to review the ore floatability models in the literature and for those considered appropriate: • investigate their basic assumptions, • evaluate the type of experimental data required to derive model parameters, • and test their predictive capability. A review of the literature identified three different methods of representing ore floatability in flotation circuit models. Two approaches were studied within this thesis, namely the empirically derived floatability component model and the property based floatability component model. The third shaped distribution modelling approach was considered too inflexible a methodology to represent all types of ore floatability distributions. Ore floatability cannot be directly measured but must be inferred from a flotation response. In this thesis, it was investigated using batch laboratory flotation tests which, for a particular system, were all performed using the same set of operating conditions. Any difference in response between tests performed in this way was attributed to a change in ore floatability. Within this thesis, hundreds of batch laboratory flotation tests were performed using samples collected from the streams of seven different industrial flotation circuits. These tests, in combination with circuit survey data, were used to investigate various assumptions underpinning the ore floatability models. The tests also provide the experimental information required to derive the flotation properties of the two chosen ore floatability models. Both the two models investigated in this thesis assume the floatability of a particle in a flotation circuit to remain the same before and after processes in the circuit. A nodal analysis technique was developed by the author to compare the floatability in the feed and product of a flotation circuit process using batch laboratory flotation test information. This technique was used to show that ore floatability is a conserved property across most flotation, mixing and cycloning processes. In the cases where floatability was not conserved, it is suspected that the surfaces of the particles have changed due to oxidation, adsorption of hydrophilic species or decomposition of reagent surface species. Ore floatability was usually not conserved across processes which are designed to change particle properties (e.g. reagent addition and regrinding). An additional requirement of the ore floatability models is that all particles assigned to a particular component must float with a similar flotation rate. Sizing and liberation analysis of batch laboratory flotation test data showed that property based floatability component models based on size and liberation alone do not satisfy this criteria. It was concluded that a property based model would need to include information about the chemical state of the particle surfaces. As this type of measurement was considered beyond the scope of this thesis, no further analysis of this type of model was possible. Techniques for determining the empirically derived floatability component model parameters were studied using statistical techniques. This analysis showed that unique, stable parameters could be obtained by fitting the models to match multiple batch flotation test data collected at the same time as a circuit survey. It was found that a minimum of four batch laboratory flotation tests were required to derive statistically stable parameters. The use of one laboratory batch flotation test (the traditional method of parameter derivation) results in parameters which are highly sensitive to the error in the batch laboratory flotation test data. A methodology to simulate and predict ore grade and recovery in a flotation circuit based on different ore floatability particle groupings was developed by the author. A theoretical analysis was performed using this algorithm which showed that a two floating component and one non-floating component model produced similar predictions to a multi-component model developed using size and liberation information in a circuit subject to changes in cell operation, residence time and circuit configuration. It was therefore concluded that a discrete floatability component model has the ability to represent, what is in reality, a more complex particle floatability distribution. The analysis performed in this thesis shows that the empirically derived ore floatability component model is a valid method of representing ore floatability within a flotation circuit model which does not contain grinding or reagent addition processes. Parameters of the model can be derived with statistical confidence using multiple batch flotation test data. To effectively model ore floatability in circuits containing regrinding or staged reagent addition, ore floatability models need to be developed which incorporate parameters related to the physical properties of the ore. It is therefore recommended that research be performed to determine the effect of size, liberation and chemical conditioning on the ore floatability of a particle and how these effects are best incorporated into an ore floatability model.