South African Ore Research Articles

The role of manganese ore reduction morphology development in setting reduction mechanisms

Manganese ores differ extensively in their mineralogical and bulk chemical composition. Consequently these ores follow different mineralogical morphology development paths as the reduction reaction proceeds in the production furnace. Mineralogical factors such as composition and distribution of initial liquid silicate formed at specific temperatures, as well as iron and manganese metallisation patterns, are significant determining factors in the relative importance of different parallel reduction reaction mechanisms in each ore type. Applied mineralogy techniques were used to identify and analyse matrix liquid silicate phase formation in manganese ore reacted at 1300 °C with Carbon Black reductant. The study includes three South African ores from the Kalahari Manganese Field, the ores represent both the Wessels-type and Mamatwan-type mineralogy. FactSage computational thermodynamic calculations were made to explain liquid silicate phase formation and its evolution with increased reaction time. Matrix silicate phase liquidus temperatures and pseudo-ternary phase diagrams in the MnO-FeO-SiO2-CaO-MgO-Al2O3 composition system were calculated. Matrix liquid silicate formed at the relatively low reaction temperature of 1300 °C within all three ores, although different quantities of liquid silicate formed along differing composition paths set by ore mineralogy.

Phase Relations in Ferromanganese Production During Prereduction: South African Ores

In the steel industry, ferromanganese is an important additive. During the production of ferromanganese the ore goes through prereduction and reduction. The prereduction step is very important, as the degree of reduction during ferromanganese is important. Although many investigations have been conducted on different manganese ores, the current study investigated different phases that formed during prereduction when South African ore was used. The ore was mixed with carbon in excess as the reducing agent, and no fluxes were added while CO gas was blown in the furnace. The temperature was varied from 1000°C to 1200°C with 100°C interval. For each temperature, the time varied from 30 min to 90 min with 30 min interval. The ore to carbon ratio was 4:1. After the experiments, the resulting products were subjected to chemical and phase analysis using XRD, XRF and SEM.

Enhanced performance of manganese ore as oxygen carrier for chemical-looping with oxygen uncoupling (CLOU) by combination with Ca(OH)2 through spray-drying

Chemical-looping with oxygen uncoupling (CLOU) is an innovative combustion technology with inherent capture of the CO2 and potential to drastically reduce the cost of capture. The process requires two interconnected reactors, between which the oxygen carrier particles are circulated while carrying oxygen from the combustion air to the fuel. In this work, the reactivity and mechanical stability of five materials were studied; three natural ores and two materials which were combinations of an ore and Ca(OH)2. The overall aim was to investigate the feasibility of making a reactive and mechanically stable material using cheap raw materials and an industrially relevant particle manufacturing process.The two combined materials behaved differently from their natural counterparts. The Brazilian ore+Ca(OH)2 showed a decrease in reactivity towards methane, but higher reactivity towards syngas in comparison to the pure ore. The South African ore+Ca(OH)2 showed a major improvement in reactivity towards both syngas and methane, which could be attributed to formation of a perovskite-structure material with significant CLOU properties. A comparison between the pure ores and the combined materials show that the addition of Ca(OH)2 had generally a beneficial impact on the mechanical stability of the oxygen carriers. As a significant change in the particle size distribution was seen for all oxygen carrier materials after repeated redox cycles with long reduction periods, the particle disintegration was likely caused by the chemical phase transformations occurring inside the particles, rather than by mechanical forces.

Investigation of Manganese–Iron Oxide Materials based on Manganese Ores as Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU)

AbstractOxygen carrier materials were synthesized using five different types of manganese ores with addition of iron oxide (Fe2O3), and they were investigated for their reactivity and properties in chemical looping with oxygen uncoupling (CLOU). Two different Mn/Fe molar ratios (1:2 and 2:1) were examined. The samples were manufactured by using a lab‐scale extrusion method followed by sintering at 950 °C for 4 h. To measure their reactivity, the materials were exposed to gaseous CH4 and syngas (50:50 CO/H2) as well as solid fuel (petroleum coke), in a batch fluidized‐bed reactor. With CH4, the materials based on ores from Brazil and Gabon with a Mn/Fe molar ratio 2:1 showed the best reactivity. For reduction using syngas, samples based on Eastern European and South African ores provided higher amounts of oxygen equivalent, up to 3–5 % of their mass. To investigate the ability of the samples to release gas‐phase oxygen, solid fuel experiments using 0.1 g of petroleum coke in a bed of 10 g oxygen carrier were performed at 950 °C with Brazilian, Gabon, and Eastern European ores. In these solid fuel tests samples with a Mn/Fe molar ratio of 1:2 showed higher uncoupling rates. Based on X‐ray diffraction analysis, the primary phase detected in all fresh particles was the oxidized form of MnyFe1−yOx, that is, bixbyite [(Mn,Fe)2O3]. All of the particles showed sufficiently high crushing strength (>2 N) and a reasonable attrition resistance (attrition index <6 wt % h−1). This suggests that the materials could be suitable for practical applications. It is concluded that the oxygen carriers made by manganese ores have the potential to be used as oxygen carriers for chemical‐looping combustion and chemical looping with oxygen uncoupling.

Mineralogy and uranium leaching response of low grade South African ores

The efficiency of uranium leaching determines the economic viability of treating low grade uranium deposits, and is quite sensitive to ore characteristics. The interrelationship between mineralogy, mineral liberation and the leaching behaviour of uranium is not well defined. Uraninite’s leaching kinetics are well studied, but relatively little leaching research has been conducted for other uranium minerals. Dissolutions higher than 90% are very difficult to achieve under the normal operating conditions employed for acid leaching of South African ores. In this paper, a mineralogy-leachability explanation is presented to rationalise the difficulty in exceeding 90% dissolution from low grade uranium ores in the Vaal River region (averaging 0.3 kg U 3O 8/t). Based on the findings, further discussed in the paper, it appears that brannerite’s intrinsic inertness is responsible for not obtaining optimum recoveries. It is also shown that for low grade uranium ores in the Witwatersrand context, the real value of uranium leaching could lie in the unlocking of extra gold (0.4–0.6 g/t) by the uranium leaching process that typically precedes cyanide leaching of gold.

Determination of gold, platinum and uranium in South African ores by high‐energy XRF spectrometry

AbstractAn automated energy‐dispersive x‐ray fluorescence spectrometer, called the AZTEC, was developed for the non‐destructive determination of gold, platinum and uranium in Witwatersrand ores, by utilizing the high‐energy spectral regions of the K x‐ray lines of these elements. It provides a viable alternative to fire assay, and measures gold concentrations down to <1 ppm. About 100 g of pulverized sample are presented for analysis in a 20 mm diameter tube, and the fluorescent x‐rays are detected by an array of up to 12 high‐purity germanium detectors. Count‐rates of up to 106 counts per second per detector can be processed by the signal processing electronics. The AZTEC technique is a variant of the scattered radiation technique. Concentration is related to peak intensities corrected for background, matrix variations, density and line overlaps. Provided that the samples are finely pulverised, the AZTEC analyses compare well with those obtained by fire assay. Production instruments are being used mainly in the gold mining industry, where they have analysed over 107 samples to date. Copyright © 2004 John Wiley & Sons, Ltd.

Heavy metal contamination of soils in a mining area in South Africa and its impact on some biotic systems

In soils, animals and plants from selected sites in the Rustenburg mining area, a part of the South African ore belt, the heavy metal burden was examined. These sites belong to different soil types and are characterized by different land-use (agriculture, grassland). The heavy metal contamination of the soil samples is relatively high and is dominated by chromium and nickel, metals, which are extracted in the mine near the sampling sites. These high heavy metal concentrations had no clear inhibitory influence on micro-organisms or the enzyme activity of soils. It appears that the high clay content of the soils may counteract the influence of heavy metals. On the other hand, tolerant microbial populations may have been established. In addition, the investigated culture plants there was no correlation between the heavy metal content of the soils and the concentrations in roots and shoots. The dangerous, potential contamination of organs in humans seems to be modest, with the exception of tobacco leaves. The heavy metal content of tissues in the examined animals reflect the environmental habitat in situ with no obvious influence on the health of the animals.

Energy consumption and liberation of minerals in explosive electrical breakdown of ores

The disintegration of brittle composite dielectrics—in particular, ores and smelting slags—by explosive electrical breakdown is discussed. Electrical pulses are used to produce intergranular fragmentation and can liberate the constituents of composite solids with higher efficiency than conventional mechanical comminution. The energy consumption of the process can be reduced by the choice of the electrode configuration and by adjustment of the waveform of the pulses according to the spark constant of the disintegrating dielectric. As an example, the liberation of platinum-group metals from a South African ore is analysed from metallurgical and energy consumption perspectives.

Fiber contamination of vermiculites: A potential occupational and environmental health hazard

Vermiculite ores from Montana, Virginia, and South Africa have been analyzed for the presence of amphibole contamination. Fibrous actinolite was found in unexpanded Montana vermiculite ore at a maximum concentration of 2.0%. The fibers persisted in the expanded ore at a maximum concentration of 0.6%. Actinolite was also found in the Virginia vermiculite ore but at a lower concentration and mostly as cleavage fragments with low length-to-width ratios. South African ore contained rare anthophyllite fibers also with low length-to-width ratios. Vermiculite ores have the potential for amphibole contamination and can represent potential health hazards without proper occupational and environmental control measures.

Asthma Caused by the Complex Salts of Platinum

Platinum is a rare metal of the group which in cludes ruthenium, rhodium, palladium, osmium and iridium. Up to 1915 almost the whole of the world's platinum production came from alluvial deposits in Russia and Colombia. In these deposits the platinum occurs as native metal alloyed with small amounts of the other metals of the group and with iron. In more recent years other sources of the platinum metals have become available. The most important new source is the nickel-copper-iron sulphide ores of the Sudbury district of Ontario, Canada, which are worked primarily for their nickel and copper contents, but which yield in addition very important amounts of the platinum metals. A second new source is the sulphide-bearing norite of the Potgietersrust and Rustenburg districts of the Transvaal. In the Sudbury ores the platinum is present chiefly in combination with arsenic, and in the South African ores it is combined with sulphur. New alluvial deposits have also been developed in Alaska, Abyssinia and elsewhere.