In times of climate change and energy transition, innovation in the typically energy-intense mining and minerals processing industry are of crucial importance for mankind in general and for Europe in particular.
The scientific discipline of “mineral processing” must contribute to resource-saving, energy-optimised process technology, too. A possible approach to do so is to promote processing technology with a water-free mode of operation. This approach preserves the resource "water" and eliminates energy-intense process water treatment or the dewatering and drying of concentrates and products.
The utilization of the dry-operated electrostatic separation technology for the processing of mineral commodities - apart from the processing of salt minerals – is of limited importance. Nevertheless, electrostatic separation has the certain potential to contribute to an environmentally friendly and sustainable approach to the necessary supply of mineral commodities.
The aim of this thesis is to demonstrate this potential by applying the technology on a representative from the group of industrial minerals. The thesis deals with the processing of rich in talc run-of-mine by applying electrostatic separation including triboelectric charging.
The extensive test work investigated the research-relevant question whether electrostatic separation processes can produce a high-quality talc concentrate from a rich in talc run-of-mine and, if so, in what way. A special focus is on the efficient separation of fractions smaller than 63 µm. Not only free-fall separators but also triboelectric belt separators were successfully used for the separation test work.
Tests were carried out in batches on the triboelectric belt separator. The test work was based on the principles of the Design of Experiments. Fractional factorial test designs were used to investigate the influence of machine-related, feed-related, and environmental factors.
The test work on the free-fall separator was carried out in batches and in continuous operating methods. Based on the experience and the results from batch tests, sophisticated concepts for closed-loop tests were developed to simulate a continuous mode of operation on a single machine in the laboratory. By utilization of the closed-loop mode of operation, separation results from an industrial operation were concluded. Circulation effects were observed and described.
As a result, proposals for flow sheets for processing plants were developed. The flow sheets included the setup of the separators in the counter-current cascade as well as statements on the preparation of the feed.
The samples used for the tests within the scope of the thesis differed greatly in some cases in their storage history. After carrying out tests in batch-wise mode, serious differences in the charging behaviour and in the recovery of talc were witnessed. Fractions from samples that had been exposed to the weathering conditions for years performed significantly worse in terms of recovery than fractions from samples, which were stored under sealed conditions and were milled and classified shortly before the separation tests. With regard to these results, it must be stated that the sample history has a great influence on the separation result. Close attention must be put on to the precise selection and definition of samples for basic investigations as well as for plant designs.
The investigations within this thesis prove the applicability of the separation in the electrostatic field with triboelectric charging for the production of the desired concentrates. Talc concentrates with a loss on ignition of less than 6.5 % could be produced, which corresponds to a talc grade of about 95 %. The significance of influencing factors such as the relative humidity, the feed temperature, the structure of the aggregates and the flow scheme of the tests were investigated and discussed.
The recovery of talc could keep up with established technologies such as flotation. However, this thesis also shows the limitations of the technology and highlights problems that remain unsolved to date.