Mineralogical-petrological supporting research of a impact crusher for primary and secondary raw materials
Comminution products of the impact crusher VeRo Liberator were investigated in cooperation with the PMS GmbH from Hamburg. The project was running from December 2012 to December 2013 and include investigations of highly diverse ore types of the deposits listed in table 1.
Table 1: Overview of ore deposits and ore types of which crude ores and comminution products were investigated within the project.
The deposits were sampled partly personally or otherwise the samples were provided as pre-crushed crude ore by the operators for the mineralogical characterization. Several tons of crude ore of the listed deposits were shipped to the location of the impact crusher for comminution tests.
Hand specimen of the crude ore were investigated at the Institute of Geoscience and Geography in Halle/Saale with microscopical methods (optical microscopy, SEM-EDX) in order to determine the mineralogical composition and intergrowth textures. By the determination of the mineral paragenesis in the crude ore it concludes which mineral phases can be expected in the corresponding comminution products.
During the process of comminution the impact crusher cracks 15 cm sized crude ore pieces, which have been pre-crushed in the primary crusher stage at the mine operations. The comminution products are achieved by a number of striking tools that are arranged on several contrary rotating stroke planes. All investigated comminution products were crushed within few seconds in a single throughput to particles of less than 1mm (d90) diameter.
Fig. 1: Selected samples of the pre-crushed crude ore from the Wolfram Camp Mine with a grain size < 15 cm comprising pieces with dark aggregates of wolframite and metallic shining molybdenite ore associated with massive quartz as well as greisen representing the wallrock.
Fig. 2: SEM-Images of coarse grained wolframite (Wof) surrounded in the left image by a matrix of intergrown quartz (Qz) and potassic feldspar (Ksp). Pyrite (Py) und phlogopite (Phl) are interlocked with wolframite, scheelite (Sch) occurs isolated within the matrix. Right side shows a detail of intergrowth of wolframite (Wof) with pyrite (Py) and xenotime (Xtm) that occupy cavities partially.
Fig. 3: Left: Association of completely liberated valuable minerals in the grain size fraction 63 – 125 µm. Fully exposed particles of molybdenite (Mol), pyrite (Py), scheelite (Sch) und wolframite (Wof) besides predominant gangue minerals(Qz=quartz, Ms=muscovite)
Right: Detail of the comminuted ore in grain size range < 63 µm shows the extremely fine grained intergrowth of xenotime (Xtm) and quartz (Qz) as well as completely exposed wolframite particles (Wof) within the comminution product.
The comminuted crude ores were granulometrically examined and the grain size classes were analyzed in regards to the content of valuable resources at the Institute of Geoscience and Geography in Halle (Saale). Grain size fraction commonly used in the mineral processing of the specific ores were investigated by Scanning Electron Microscopy in order to determine the degree of liberation of valuable phases, gangue type and their intergrowth textures, respectively.
Fig. 4: Grain size distribution curve of the Wolfram Camp-ore after the comminution with the impact crusher. The crushed bulk sample contains nearly 90 % (d90) particles < 1 mm that reflect a suitable size to be extracted in the subsequent mineral processing stages, e. g. by gravity separation.
The investigations have shown that the impact crusher “VeRo Liberator” of the PMS GmbH crushes different crude ore types successfully, whereby large portions of grain size fraction have been achieved that are utilizable in the further steps of the mineral processing. It is particularly remarkable that the degree of liberation of valuable minerals is generally high to very high which supports high recovery rates in the subsequent processing steps. Furthermore, gangue minerals were also separated clearly to each other. Both, elastically flexible, e.g. graphite-laths, and brittle minerals can be liberated by the impact comminution. Further it can be pointed out that both, the degree of liberation and the concentration of valuable elements increase in the lower grain size classes.
The impact comminution with the “VeRo Liberator” of the firm PMS GmbH is a fast and effective method to crush primary ores and mineral-metal recycling materials as concretes or slags effectively and by relatively limited expenditure on energy. Valuable minerals are preferentially separated along grain boundaries from the waste rock and interlocks of minerals, respectively, and are recoverable liberated. In particular the issue of “incomplete particle liberation“, which affects negatively the effective flotation process, can be prevented largely by comminution with the “VeRo Liberator”. The impact crusher consumes significantly lower energy expenditure in comparison to the established communition methods, e.g. ball mills, which can be attributed to its vertical rotation axis and equally to the gravitationally falling throughput of the process material being crushed. Rock mechanically should the separation of different ore- and rock fragments attributed to differential elasticity- and compression moduli of the interlocked particles. High velocity impacts of the striking tools targeting the material being crushed shocks apparently the rock in such a way that it leads preferentially to either extensive or sheared separation of along particle boundaries on different particles. Recently petrological as well as rock-mechanical / engineering-geological investigations are ongoing.