MINERÍA la mejor puerta de acceso al sector minero MINERÍA / SEPTIEMBRE 2022 / EDICIÓN 540 48 influencia en el arrastre mecánico, siendo uno de ellos el tamaño de partícula. Esto es usualmente evaluado usando una curva de recuperación a diferentes tamaños, y comparando los resultados con el tamaño promedio de partícula evaluado. En el análisis, las partículas reportadas por arrastre mecánico muestran un mayor desplazamiento cuando se reduce el tamaño[16]. Es decir, la flotación a un tamaño grueso puede reducir parcialmente la presencia de ganga en el concentrado, pero también pueden reportarse en las espumas partículas de muy poca liberación, con lo cual se puede complicar el diseño y/o operación del circuito de remolienda y limpieza. Celdas de flotación La flotación de gruesos ha sido practicada desde el siglo pasado y no es un tema nuevo, ya que los primeros estudios se realizaron en los años 30[17]. Hay dos celdas que han mostrado su efectividad en el proceso, una es la Celda de Flotación Unitaria y la otra es la Celda Flash (SkimAir®). En base a la eficiencia de estas, otros fabricantes han intentado desarrollar otras celdas, pero sin llegar a la eficiencia de los modelos mencionados anteriormente. Para la gran mayoría de los minerales, la recuperación es buena para tamaños de partícula entre 50 y 150 µm, particles on which flotation can occur, set primarily by the physical limitations of the bubble in lifting coarse particles. The upper limit of para floatation rarely exceeds 500 μm and is usually below 300 μm. Optimal flotation size is typically in the range of 10 to 100 μm. Second, the flotation of coarse particles become more significant if gold flake is present during cleaner flotation stage, where the cells are designed for small particle processing [12]. Figure 8 shows the gold flakes found in the tailings of a cleaning flotation circuit. Mineralogy The mineralogy is one of the main factors to be evaluated to determine if it is advisable and feasible to perform the flotation at a coarse size, for which the degree of liberation must be determined. The liberation of valuable minerals from gangue is achieved by size reduction, which consists of crushing and grinding to such a size that the product is a mixture of relatively clean particles of valuable minerals and gangue [13]. One objective of comminution is the liberation at the coarsest possible particle size. If that objective is achieved, then not only energy is saved, it is possible to reduce the production of fines. In this way, the flotation process becomes easier and cheaper to operate. If high grade products are required, then good liberation is essential. To perform the mineralogical study, a study by QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) or MLA (Mineral Liberation Analyzer) is recommended. The potential liberation of valuable minerals can be determined by characterizing grain sizes of the minerals present in the ore. This can be achieved by reducing the drill core samples to a relatively coarse size (typically around 600 μm) to preserve the texture of the samples, including grain size, association, and shape [13, 14]. Figure 9 shows images from an MLA study. The presence of liberated chalcopyrite and pyrite particles is shown in a coarse size fraction, -4000+1000 µm. The presence of free sulphides in a coarse size fraction suggests that when milling the ore, a coarse flotation could be obtained, but with some competition due to collector adsorption. A QEMSCAN study allows minerals to be classified into different groups according to the percentage that a mineral of interest occupies within an area of the studied section. Thus, there are totally free particles when they occupy ≥ 95% of the area, liberated when it is ≥ 80%, and not liberated when it is < 80% of the area. Non-liberated grains can be classified into groups according to their mineralogical association as binary or complex [13,15]. It may also indicate the need for fine Figura 11. Celda unitaria instalada en el circuito de molienda[19].
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