Thesis (M.Eng.). / Written for the Dept. of Mining and Materials Engineering. Title from title page of PDF (viewed 2009/06/17). Includes bibliographical references.

As one of the most abundant elements on earth, iron is nearly always present in metal concentrates. This is specifically true for zinc sulphide concentrates, which can contain up to 18% iron (marmatite). Today more than half of these concentrates are treated in hydrometallurgical- or combined hydrometallurgical¬pyrometallurgical circuits. In hydrometallurgical circuits, iron is solubilised (either in a roast-Ieach-, a direct leach- or bacterial leach circuit) along with zinc and must be removed from the zinc¬rich solution before the electrowinning- or solvent extraction step. Various iron removal processes were developed to address the iron problem in hydrometallurgical circuits. The better known of these include the jarosite-, goethite- and hematite processes also used in the zinc industry. Zincor (Zinc Corporation of South Africa) patented an iron removal process (Zincor Process), which was generally considered to be very similar to the so-called "para-goethite" iron removal process used only in two other zinc smelters notably Porto Vesme (Italy) and Pasminco Hobart (Tasmania). However, since the Zincor Process was patented in 1976, various changes have been made such as a change from a batch parallel to a continuous series process, a change in precipitation pH-profile and the introduction of a pH controlled acid wash in the second tank. The introduction of a weak acid leach step and vacuum belt filters at Zincor's residue treatment plant in the near future and an iron removal process that is not clearly understood, necessitated this further study of the Zincor iron removal process. The study has been conducted in three parts. The first part of the study has focused on the characterisation of the Zincor iron residue and the Zincor process. The second part of the study has been concerned with the definition of an optimum operating window in terms of the filterability of the residue and the third part investigated the use of neutralisation reagents other than zinc calcine to control the pH during iron precipitation. The distribution of iron in the Zincor iron precipitate, which usually contains between 35% and 40% iron, has been found to be as follows: approximately 45% as schwertmannite, 5% as ferrihydrite, 20% as jarosites, 25% as franklinite, trace amounts of pyrite as well as 5% of an unknown phase. This confirmed that goethite is not present in the Zincor iron residue and that iron is mainly removed in the form of amorphous intermediate iron phases such as schwertmannite and ferrihydrite. Of these two phases, schwertmannite was the least expected as most work up until now were done on samples taken from natural environments. The following description of the conditions that promote iron removal, mainly as schwertmannite, is viewed as an expansion of the available literature data, which was gathered at ambient conditions. In terms of the main operating parameters, optimum filterability was achieved under the following conditions: pH of 3.0, temperature as high as possible (70°C) and at least 25 kg/m3 seeding. A retention time of at least 4 hours at a pH of 3.0 and 60°C was required, which decreased by more than 50% at a temperature of 70°C. As these conditions mainly impact on the soluble zinc loss encountered during iron removal, an effort was made to further reduce the insoluble zinc loss, which is the inherent weakness in the Zincor process, and similar processes where zinc calcine is used for pH control, by investigating the use of alternative neutralisation reagents. This study showed that iron can be successfully removed with Ca(OH) 2, a basic zinc sulphate and zinc oxide mixture as well as chemically precipitated CaC03 produced in the paper and pulp industry. Of these alternatives, CaC03 appeared to be the most promising, with filtration rates an order of magnitude higher than the zinc oxide options (calcine and basic zinc sulphate mixture), due to better overall economics than with the use of Ca(OH) 2. Utilisation CaC03 as an alternative neutralisation agent might increase the overall zinc recovery figure at Zincor by up to 1.5%. Based on the findings, it can be concluded that the Zincor process in its current form has a very distinct character compared to what was historically considered to be the very similar patented para-goethite iron removal process, as practiced at the Porto Vesme and the Pasminco Hobart hydrometallurgical zinc plants. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

Zincor's average zinc recovery was 90.29 % (for the period of 1 January 2009 to 30 September 2011), which was well below the industry standard of 96 %. Due to limitations in Zincor's iron removal technology, the maximum achievable recovery was 94 %. The zinc loss through the iron residue was the second biggest contributor to the overall zinc losses, so that there was much room for improvement. The calcine used for neutralisation in the Iron Removal Stage contained a portion of insoluble zinc ferrite. The insoluble zinc loss through the iron residue was associated with the presence of the insoluble zinc ferrite, as well as the phenomenon of coating of unleached neutralising agent by iron precipitate. The soluble zinc loss was a function of the dewatering characteristics of the precipitate. The work included the evaluation of alternative neutralising agents to supplement or replace calcine, as well as the implementation of a seed recycle. A review of literature found that the use of an alternative neutralising agent that contained little or no zinc could potentially reduce the insoluble portion of the zinc loss. Secondly, the presence of seed could potentially reduce both the soluble and insoluble zinc losses by promoting agglomeration growth and providing additional surface area for precipitation to occur (thereby reducing coating of zinc-rich neutralising agents). The laboratory work evaluated a number of alternative neutralising agents, but focused on the use of DRC oxide and limestone for neutralisation. These were evaluated separately and in combination, with and without a seed recycle.

South Africa has large low-grade coal reserves. With the prospect of expanding its coal demands for exports and power generation, it is important that the beneficiation and transport of coal in the country are economical. The current mode of transporting coal has some drawbacks, which include inefficient rail infrastructure, long distances, and several environmental concerns related to air pollution, water pollution, and traffic risks. It is, therefore, important to investigate efficient means of coal transportation, which will also reduce environmental impacts. The transport of highly concentrated coal-water slurries through pipelines has attracted the attention of many researchers as an efficient and economical means of fine coal utilization. The primary objectives of this study are to investigate the importance of surface charge, solids concentration and particle size on the stability and rheological behaviour of Witbank coal. This work was carried out to arrive at a sounder discernment of the function of dispersion addition on coal-water mixtures rheology and stability.

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A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2016 / The feasibility of extracting iron from iron(III) oxide bearing materials with acetylacetone has been under investigation for many years. This is an alternate, environmentally friendly process for the recovery of iron compared to conventional processes that are energy intensive, have numerous costly process steps and produce large quantities of greenhouse gases. Iron(III) oxide bearing waste materials can be used in this process which reduces its environmental impact as it would not require waste storage. This study investigated the feasibility of reducing the reaction time of the liquid phase extraction of iron from iron ore fines by performing the extraction at elevated pressures and temperatures. It was found that that the extraction under pressure was dependent on temperature, pressure, particle size and solid to liquid ratio. It was found that at high temperatures and long extraction times, an unknown secondary reaction occurs that consumes the desired product, iron(III) acetylacetonate, and inhibits the recovery of these crystals. This results in lower extraction yields. It was found that the side reaction was largely dependent on the temperature of the system and the amount of iron(III) acetylacetonate present. The effects of the side reaction could be limited by lower operating temperatures and reducing the total reaction times. An optimum conversion of iron(III) oxide to iron(III) acetylacetonate of 47.2% was achieved for synthetic iron (III) oxide (> 95 wt% Fe2O3) at a total extraction time of 4 h, 160 °C, 0.025 g:1 mL, operating pressure of 1700 kPa, initial N2 feed pressure of 1010 kPa and 375 rpm stirrer speed. The optimum extraction of iron from iron ore fines (> 93 wt% Fe2O3) to iron(III) acetylacetonate was found to be 20.7% at 4 h, 180 °C, 0.025 g:1 mL and operating pressure of 1900 kPa, initial N2 feed pressure of 1010 kPa and 375 rpm stirrer speed. These are the optimum conditions where the side reaction is limited to improve the recovery and desired reaction conversion capabilities of the process. The operation under pressure yielded lower conversions than that of the atmospheric leaching process developed by Tshofu (acetylacetone water system under reflux). It was also found that it was not possible to reduce the extraction time and achieve comparable extractions when operating at higher temperatures and pressures. The formation of an additional unwanted product would also lead to unnecessary treatment costs in an industrial process. Hence, it was found that pressure leaching as an alternative is not currently viable due to the lower yields and associated high costs. Atmospheric leaching seems to be the most economically feasible option until a better alternative is found. / MT2017

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1994 / A quantitative description of galvanic interactions between sulphide minerals based on thermodynamic and kinetic parameters has been developed. The basis for quantitative description involves conducting a voltage balance over the galvanic couple. The contributions to the voltage balance include the galvanic couple cell emf, kinetic descriptions of the anodic and cathodic half reactions, the voltage characteristics 'of mineral-mineral contacts and solution voltage losses. The rates of the anodic and cathodic half' reactions were modelled by the Butler-Volmer equation and ti1ediffusion equation. A potentiostat was used to vary the voltages losses across mineral-mineral contacts. TIle galvanic couples were constructed. as rotating ring disc electrodes and hence electrolyte voltage losses were negligible. Three galvanic couples, copper-platinum, copper-pyrite and galena-pyrite, were electrochemically characterised under different conditions of ferric concentration, electrode rotation rate and temperature. The effect of illumination on the anodic dissolution of galena was investigated. The electrochemical model is in good agreement with experimentally measured galvanic currents. Galvanic interaction is a dynamic function and various models are developed which account for dynamic behaviour in galvanic cells. / MT2017

Thesis advisor: Alfredo Urzua / Thesis advisor: John Ebel / Nine empirical equations that estimate saturated hydraulic conductivity as a func- tion of grain size in well-graded sands with gravels having large uniformity coecients (U > 50) are evaluated by comparing their accuracy when predicting observed conduc- tivities in constant head permeability tests. According to the ndings of this thesis, in decreasing order of accuracy these equations are: USBR (Vukovic and Soro, 1992; USBR, 1978), Hazen (Hazen, 1892), Slichter (Slichter, 1898), Kozeny-Carman (Carrier, 2003), Fair and Hatch (Fair and Hatch, 1933), Terzaghi (Vukovic and Soro, 1992), Beyer (Beyer, 1966), Kruger (Vukovic and Soro, 1992), and Zunker (Zunker, 1932). These re- sults are based on multiple constant head permeability tests on two samples of granular material corresponding to well-graded sands with gravels. Using the USBR equation sat- urated hydraulic conductivities for a statistical population of 874 samples of well-graded sands with gravels forming 29 loads from a heap leaching mine in northern Chile are calculated. Results indicate that, using the USBR equation, on average the hydraulic conductivity of the leaching heaps has a two standard deviation range between 0.18 and 0.15 cm/s. Permeability tests on the actual material used in the heaps provided by the mine shows that the results presented in this thesis are consistent with actual observa- tions and represent saturated conductivities in heaps up to 3 m high under a pressures of up to 62 Kpa. In future work hydraulic conductivities can be combined with water retention curves, discharge rates, irrigation rates, porosities, and consolidation so as to evaluate the relationship between copper yields and the hydraulic conductivities of the heap. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

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