Resumen de Strategic minerals milling modelling of high pressure grinding rolls and process parameters dependency
Hernán Francisco Anticoi Sudzuki
Comminution is the most energy consuming process in mining industry, where nearly 60 % of the electricity expenditure is due to grinding purposes. In the nature most of the ore minerals are found, finely disseminated and intimately associated with the gangue, thus, liberation is the main target to recover these minerals. In order to optimize the size reduction process, the correct prediction of the charactrisstic of the product in a milling reactor turns into a crucial task, and is the main motivation to develop this thesis. The materials used in this study belong to the so-called strategic raw materials, according to the European Commission, to increase competitiveness on the local production to those materials that are key to the industry and their supply is in a risky situation. Tantalum and tungsten ores were selected from the critical raw materials list, and the model developed was based on these two types of ores.
The material was characterised in minerals and mechanical terms. The mineral composition was determined before being tested under a new methodology, the piston-die test, to find the breakage distribution function. After the test, the samples were also analysed to find breakage mechanism patterns. The experimental session were done using a reformed roll crusher, which was modified in order to have a high pressure environment during compression. The validation stage was performed at the Technische Universität Bergakademie Freiberg facilities, Germany, where the company Köppern Aufbereitungstechnik GmbH & Co.KG has a High Pressure Grinding Roll pilot plant.
The product prediction is presented using an approach of the Population Balance Model (PBM). Such model treats comminution as a single plug flow reactor where selection and breakage functions are involved. In the process of determining parameters of one of these function, more in concrete, the breakage distribution function, by means of the new methodology, novel discoveries on the breakage phenomena were included into this new approach. It has been found that the breakage distribution function is non-normalizable when comminution is done in two compressive conditions: bed particle compression and single particle compression. Some differences on the breakage function parameters where found when varying the specific pressing force for a certain particle size range. These function parameters are closely linked with the mineral composition of the tested material. The content of competent minerals or the presence of altered phases, resulted on variation on these parameters values.
The prediction model obtained using the lab-scale experiments data show consistency, but when the specific pressing force is included into the breakage function determination and into the model itself, it turns in a remarkable good fitting. In this case, the simulated product is compared with an industrial scale device test data. The used feed size distribution was several mono-size particles ranges but an heterogeneous particle size distribution was also tested, being the most similar material that is processed in mining industry. The working gap was studied to determine its dependency on operative conditions or material characteristics as composition, size or moisture. The energy consumption was also studied and it has been found how the roll speed is the most energy demanding concept in this type of machinery, and is the responsible of the plant throughput. The specific pressing force, which has an influenced on the product characteristic, has an important influence on the energy demand as well, but is not that relevant as in the case of the increment on the roll speed.
