Elemental assessment and extraction of the waste rock tailings from a Free State goldmine
Mining activities normally produce large quantities of different waste products after the separation and isolation of the economically valuable elements present in the mineral ores. The mine waste dumps do not only tarnish the natural environment, but also have the capacity to liberate potentially harmful elements which contaminate local natural resources such as water and air. However, the same waste may also be a source of economically valuable elements which have been mined simultaneously with other valuable elements (then target elements), but were not of any economic importance during the previous mining activities. The aim of this study was to determine the elemental composition of gold mine waste material in the Free State. The possible separation and isolation of some of the more valuable elements in waste material also formed a part of the study. Samples were collected from various dump sites near Welkom in the Free State. Flux-fusion decomposition was extensively employed in the dissolution of the solid samples and the elemental contents of these samples were determined, using the inductively coupled plasma optical emission spectrometer (ICP-OES) for elemental content. The water samples were also analysed with the same instrument. The ICP-OES was used throughout the study in order to monitor and evaluate the success of numerous separation techniques which were carried out to recover some of the valuable elements. Waste dumps in the Welkom/Virginia are in the Northern Free State were selected for this study. Waste rock sampling was carried out at six dump sites, where five samples were randomly collected at various points in order to include waste with different particle-sizes and surfaces colours. The sub-samples were milled and equal masses of those taken from one site were combined and homogenised manually. Tailings were collected at three dumps from different layers. Mine water samples were also collected at two sites in ditches surrounding the tailings. Decomposition by flux-fusion was carried out with different fluxes, some of which did not dissolve the waste rock completely. Lithium tetraborate (Li2B4O7) was used for the waste rock samples and the resulting melts were dissolved with H3PO4. The tailings were also decomposed with Li2B4O7 and the melts were dissolved with HNO3. Water samples were acidified immediately after collection and those that were collected with sediments were filtered. All the samples were analysed by means of ICP-OES. The waste rock generally contained, Cr, Mn, Zr, Pt, Th, with significantly high concentrations of Al, S, Ti and Fe. The tailings generally comprised Ti, Cr, Mn and high concentrations of Fe and S. The EDS spectrum indicated the presence of a very high concentration of Al. Many more elements with various degrees of economic importance were found in the water samples collected in the vicinity of the tailings dams. Elements identified in these water samples with stream bed sediments included P, S, Ti, Cr, Mn, Fe, Co, Cu, As, Cd, Pt, Hg, Pb, Th and U. Electro-winning was carried out to recover copper selectively from mine wastewater, using electrolysis apparatus with platinum gauze electrodes, resulting in a copper recovery of 81.13% and a Ti recovery of 106.27%. In another part of the study, oxine, in the presence of NH4OH, was used in the selective precipitation of copper in an acetic acid matrix. The analysis of the dissolved precipitate in HNO3 revealed the presence of Fe, Co and S in the precipitate. The recoveries of 56.89% Cu, 5.51% S, 89.27% Fe and 54.66% Co were obtained. Manganese was recovered selectively by ion exchange chromatography using the Dowex 66 free base anion exchange resin and 0.5 M orthophosphoric acid for elution. This resulted in the Mn recovery of 77(7)%. Adsorption of Pt onto activated carbon was attempted, at an elevated temperature. This procedure was not regarded as effective as since only 17% Pt was adsorbed, while many other elements were also adsorbed, leading to lack of selectivity. The use of banana peel as sorbent for Th was also attempted. The sorbent was prepared by rinsing, drying and crushing banana peels, for use as possible sorbent. Analysis of the filtrate revealed adsorption of various elements, the adsorption percentage of Th being 61.37%. These results indicated lack of selectivity within the method. Desorption of the elements from the loaded banana peel sorbent with H2SO4 resulted in 28.08% Th recovery, while larger recoveries were obtained for Cd, Hg and Mn. From this study, it is clear that mine waste dump sites may be a valuable source of economically valuable elements. Moreover, very modest hydrometallurgical methods may be used in the isolation and recovery of these elements, thus making mine waste sites valuable alternative elemental sources with economic value.