Fine products in the focus of mineral processing
Symposium on Mineral Processing at Freiberg University of Mining and Technology, Freiberg/Germany (24.-26.02.2011)
Around 100 participants were welcomed by the Chairman of the VDMA Construction Equipment and Building Material Machinery Association, Dr. Christof Kemmann, BHS Sonthofen GmbH, Sonthofen, to this year’s Symposium on Mineral Processing. For the fourth time, representatives of the Friends and Supporters of the Institute of Mineral Processing (IfA) at Freiberg University of Mining and Technology (TU BAF) and other guests from research and industry met from 24. to 26.02.2011 at this event in Freiberg, which was devoted to the topic of “Fine products” (Fig. 1). Focus of the papers was the production, characterization, treatment (drying, separation) and recycling of these products. Dr. Kemmann (Fig. 2) promoted the above-mentioned association, which was set up five years ago and provides machine and plant engineers with an interesting network, finances studentships and campaigns for engineering degrees majoring in mineral processing. Details on the courses to Bachelor of Science and obtaining one of the “Mineral Processing Engineer” certificates awarded by the TU BAF and the VDMA were explained by Dr. Klaus Meltke (Fig. 3), IfA TU BAF. He also outlined the situation with regard to the appointment to the “Professor of Mineral Processing and Mining Machinery”. An appointment to this Chair is to be made by the end of this year.
The following papers covered a range of topics and informed attendees primarily about field-relevant test findings. For example, Dietmar Guldan (Fig. 4), BHS Sonthofen GmbH, Sonthofen, presented the rotor impact crusher or vertical shaft impactor, which are particularly suitable for the production of sands and fine sands. Launched onto the market 35 years ago, since then they have undergone continuous further development with the aim of improving capacity, saving energy and lowering wear costs. Factors influencing the crushing efficiency and applications for the two machine types, rotor centrifugal crusher and rotor impact mill (different rotor designs), were explained. With single-particle comminution with single- or multi-stressing, enormous advantages are gained over conventional comminution techniques. In the company’s own testing centre, crushing tests can be conducted for clients in industrial-scale machines, which include a characterization of the crushed product and a test report.
The use of an impact crusher as a sorting machine was described by Martin Müller (Fig. 5) from the Oberland gravel-asphalt and ready-mix concrete works owned by Strohmaier GmbH, Huglfing, with the example of the production of hard rock high-grade chippings from Alpine glaciofluvial deposits. With selective comminution, which already takes place during primary and secondary crushing if there are large differences in the strength of intergrown minerals, limestone concentrates in the lower particle size ranges, granites and gneiss in the upper particle size ranges. In the tertiary crushing stage, since 2010 polishing-resistant high-grade chippings in the sizes 2/5, 5/8 and 8/11 have been produced from the latter, which are ideally suitable for asphalt road surfacing.
In his paper on combined grinding and drying with hammer mills, Hans-Jürgen Kintrup (Fig. 6), HAZEMAG & EPR GmbH, Dülmen, explained the design criteria for a combined grinding and drying plant, for which technical and material specifications are required. On this basis, a thermal balance is drawn up and from this components for the design are taken. A combined grinding and drying plant with a NOVOROTOR® hammer mill was discussed in detail, which, for example, is used in the cement industry as a machine upstream of ball mills.
A new screening system used in the extraction and processing of raw magnesite was the subject of the talk by Dieter Übler (Fig. 7), JÖST GmbH + Co. KG, Dülmen, and Polycarpos S. Papageorgiou, Grecian Magnesite Mining Industrial Shipping and Commercial Co., Chalkidiki/Greece. It was shown that difficult-to-screen raw material (12-16 % moisture and 50-60 % sticky fines 0-4 mm) extracted from an open pit or taken from recultivated material heaps can be screened very efficiently with a specially developed screening surface on JÖST Grecco screens. The specifics of the screening surfaces are based on a self-cleaning effect as a result of self-movement of the screen rods. Cut-points to 2 mm are possible, the screens work outdoors even in rainy weather. They are also suitable for coals with up to 20 % moisture or in recycling as an alternative to flip-flow screens.
For saving expensive transport capacities and in consideration of the worldwide availability of coal, the further rise in the demand for coal as well as its range (hard coal around 1425 years, soft brown coal around 1264 years), at Loesche GmbH, Düsseldorf, mobile coal grinding plants have been developed, on which Matthias Authenrieth (Fig. 8) reported. In the worldwide growth markets, central plants like those found in Germany cannot be operated cost efficiently and therefore are not usable on account of logistics costs and the lack of infrastructure. Referring to the example of a grinding plant upstream of an asphalt mixing plant, the speaker pointed out the advantages of a mobile plant with 2-4 t/h throughput rate, which can be shipped in containers. It can be used primarily in countries that are less advanced in their industrial development for the optimal preparation and combustion of coal.
Other papers concerned removing filler material at a ballast and chippings plant with variation of the processing equipment (Karsten Schmiedel, Breitenauer Grauwacke GmbH, Oederan), the agglomeration of mineral dusts with the HAVER®Scarabäus pelletizing disk for metals, fertilizer, sewage sludge, filter dusts, etc. (Sandra Weyrauch (Fig. 9), Haver Engineering GmbH, Meissen) and fine grinding of material layers in an arrangement of horizontally mounted rollers, the material layers being prepared outside of the loading zone (Dr.-Ing. Fritz Feige (Fig. 10), Dessau-Rosslau). Finally, Dr. Meltke, IfA TU BAF spoke on the CLP Ordinance 1272/2008 EC and the associated evaluation of the respirable quartz in filler, crushed sand and similar, he pointed out the difficulties caused by the determination of the content of fine silica dust in the products of the minerals industry. One possibility is provided by MLA (Mineral Liberation Analysis), which was presented. An MLA 600 F analyser available at the TU BAF permits reliable detection and characterization of particles to 0.1 µm. The suitability of this method for use in the mineral industry was shown.
The event ended with an honour for Donald A. Longhurst, Polysius Corporation, Atlanta/USA, an eminent scientist who has had a major influence on mineral processing for more than 50 years. The laudation was given by Saxony’s Minister of State for Finances and former Rector of the TU BAF, Prof. Dr.-Ing. Georg Unland. He emphasized the merits of the internationally active mineral processing expert particularly in the area of roll mills, but also in the evaluation and comparability of the Zeisel and Bond grindability indices for the characterization of grinding products (Fig. 11). Donald A. Longhurst then presented some of these findings in his overview lecture “Finish grinding volume and mass flow – a new metric for diagnostics and optimization”.
Besides touring the Institute of Mineral Processing Machinery, the attendees were able to visit the Terra Mineralia in Freiberg and the Staatliche Porzellanmanufaktur in Meissen. The organization of the conference was perfect, the visitors had ample opportunity to exchange ideas and experience.