Pre-concentration at crushing sizes for low-grade ores processing - ore macro texture characterization and liberation assessment

摘要

Mineral processing of low-grade ores requires high processing flow rates. Pre-concentration is a clever technological solution for this mining industry challenge because, simultaneously, it increases the head grade and reduces the input flow rate of the concentration plant, by rejecting barren rock in the early stages of the processing flowsheet.As pre-concentration at crushing sizes is dependent of the ore texture, and consequently, it relies on the achieved mineral liberation degree, a straightforward methodology to assess quantitative mineralogical data of the ore macro-texture, based on image analysis, was developed. For the purpose, photos of hand samples collected at the mine site were converted using image analysis algorithms to generate a digital texture representative of the ore macro-texture. Then, a random comminution algorithm was applied to simulate the coarse crushing stage, generating particles in size range 19.3/6.7 mm. The grade of each particle was calculated by pixel counting and subsequent conversion to mass, allowing for the computation of the grade histograms (wt%) and then for the construction of ultimate upgrading descriptors, which has been proved to be a useful tool to assess the pre-concentration feasibility and the separation efficiency.This methodology was applied to assess the pre-concentration feasibility of a lepidolite ore from Alvarroes deposit (Portugal) by simulating several separation scenarios based on the obtained ultimate upgrading descriptors. It was shown that pre-concentration would only be feasible if the rejected material can be valorized as a commercial product for ceramics. The separation efficiency of an optical sorting device was also assessed, pointing out for a high technical inefficiency of the process. Furthermore, it was possible to predict the influence of mineral liberation at different size ranges on the global separation efficiency.This study shows the importance of quantitative mineralogical data in the study of the pre-concentration process. It is evident that data acquisition must be improved, taking advantage of the more accurate and faster systems, such as the modern ore sorting technologies.