Current research and trends, part 1

Since 1998, these annual events have been held in the autumn in the auditorium of the Gründer- und Inno­vations­zentrum Freiberg (Start-up and Technology Center, German abbreviation: GIZEF), and have increasingly gained in popularity with each passing year (Fig. 1). The joint organizers are the UVR e.V. and FIA e.   V. Freiberg scientific associations, with the Processing and Recycling Technical Committee of the Society for Mining, Metallurgy, Resource and Environmental Technology (German abbreviation: GDMB) joining them as co-organizer this year. The extremely good response to this two-day conference found expression in its attendance by more than one hundred and sixty specialists from throughout Germany and from other European countries (Fig. 2). The central focuses this year were on current problems in the recycling of building materials, industrial and household waste, and on the preparation of primary raw materials. The speakers with their total of twenty-four papers were well known representatives of commercial companies and scientific institutions. The poster exhibition accompanying the conference additionally presented recent research results, and enabled the participating companies to showcase themselves and their activities. Dr.-Ing. Henning Morgenroth, a director of host organization UVR-FIA GmbH, provided information on its working potentials, and issued an invitation to view the laboratories and experimental facilities, an opportunity which the ­majority of conference participants were pleased to take up (Fig. 3).

The GDMB Processing and Environmental Technology Technical Committee also met in parallel to the event. The term of office of the incumbent committee chairman, Dr.-Ing. Thomas Folgner (TU Bergakademie Freiberg mining and technology academy) was concluded during this meeting, and Prof. Dr.-Ing. Daniel Goldmann (Technical University of Clausthal) elected to replace him.

The participants continued their interesting technical discussions in the stimulating atmosphere of a successful and convivial evening event.

The essential elements of the addresses held during the conference are reported below.

The results achieved in cooperation with industrial partners (Thomas Günther of Dyckerhoff AG Wiesbaden and Guido Kache, of Polysius AG Beckum) were reported in the paper read by Dr. Werner Hintz and Prof. Jürgen Tomas (Otto-von-Guericke University of Magdeburg, Institute for Process Engineering, Department of Mechanical Process Engineer-ing) on the „Development of a hydrometallurgical recycling process for metal-containing steel-plant particulates for recovery of zinc, lead and iron“. Dusts consisting of oxides of various metals, with zinc (20 to 45  %), iron (20 to 35  %) and lead (1 to 2  %) predominating, are suspended in a solution of ammonia and ammonium carbonate (the “AAC” process), with application of a simultaneous integrated mechanically activating grinding and leaching process. Zinc carbonate and metallic lead are then removed in a downstream combined cementation and precipitation process.

Dipl.-Ing. Marco Steinberg and Dr. Wolfgang Rubarth (AKW
Apparate und Verfahren, Hirschau) unveiled in their paper on “Slag processing using gravimetric sorting methods” new solutions for cost-efficient dry preparation of the <  5  mm particle fraction using the AKA-FLOW dry density classifier. This achieves a higher recovery rate for the metals, and better recycling of the tailings for use as building ma-­terials.

In their address on „Development of a separation process
for gypsum-contaminated concrete rubble“, Dipl.-Ing. Thomas Schnellert, Dipl.-Ing. Kati Kehr, Prof. Anette Müller (Bauhaus University of Weimar, Department of Building Materials Processing and Recycling) reported on successful tests for the removal of gypsum from demolition rubble by means of a wet jigging process, including improvement of the product recovered by means of raising of bulk density and the separation of fines elements.

Common chalk is a soft, moist (15 to 28  % H₂O) form of limestone and constitutes the basis for the production of a diverse range of fillers, extenders, pigments, lime and cements. The fundamental concept for the „Development of a semi-mobile elutriator for chalk“, on which Drs. Michael Kapphahn (Holcim AG, Lägerdorf, Germany) and Armin Schlintl (OMYA GmbH, Gummern, Austria) reported, consists of elutriation of the chalk directly downstream the point of mining, instead of via a ramified system of belt conveyors, and then conveying it onward by hydraulic means via a hose pipeline. The benefits of this new technology can be found in the much greater flexibility of excavator operation, the elimination of fixed belt-conveyor routes, the resultant possibility of mining previously inaccessible chalk reserves (an estimated 30 to 40 million tonnes at Lägerdorf alone!), the system‘s higher availability and immunity to operating problems, and the reduced susceptibility of elutriator operation to frost. The 150 t/h pilot plant operated by OMYA since August, 2009, is currently undergoing testing and exploration of its performance limits in continuous operation. Conversion of the entire Holcim mining operation, with a production rate of 800 to 1200 t/h, to this new technology is planned for the mid-term.

In their paper on “Alkaline activation of bentonites – Correlation of technical properties and the activation curve”, Dipl.-Ing. Karl-Heinz Ohrdorf (I.B.O. Ingenieurbüro für Bentonit-Techno­logie, of Wiesbaden) and Prof. Dr.-Ing. Helmut Flachberger (Department of Processing and Beneficiation, Leoben University of Mining and Technology, Austria) took up results disclosed during the previous year on the characterization of bentonite suspensions. The technically relevant properties of bentonites correlate directly to the degree of deagglomeration of the montmorillonite crystals, complete deagglomeration being possible only once optimum activation has been achieved.

“The Titania A/S, Norway, ilmenite mine’s preparation plant” was the subject examined by Dipl.-Ing. Anders Qvale and Dr.-Ing. Wolfgang Schubert (Titania A/S, Hauge i Dalane, Norway). The deposit was discovered in 1954 by means of aerial geophysical measurements in the vicinity of Jøssingfjord. With reserves of more than 300 million tonnes of ilmenite ore, it is one of Europe‘s largest deposits of this iron- and titanium-bearing mineral. The preparation process is relatively complex, since the ilmenite sought occurs finely interstratified with feldspar, pyroxene and mica. Comminution to 80  % <  200  µm is accomplished by means of four-stage crushing in a vertical cone crusher, two-stages in a fine cone crusher and ball mills (wet) and after-crushing of the non-digested particles. After removal of the magnetite, the coarser ore fraction of > 100  µm is classified by means of density-based separation on spiral separators into a values fraction (ilmenite and sulfides) and a tailings fraction (feldspar, mica). The finer fraction of the ore (< 100 µm) is firstly deslimed at 10 µm and then conditioned with tall oil and paraffin and flotation-separated, the ilmenite being extracted in the floats. Ilmenite is used primarily for production of titanium dioxide pigments.

Dipl.-Ing. Ferdinand Doppstadt (USG Umweltservice, of Velbert) and Dr. Metodi Zlatev (HAVER & BOECKER OHG Maschinenfabrik/ Engineering Works Münster) reported on the “Treatment of contaminated sediments and sludge in a zone of the Venice lagoon”. The material was dispersed, classified and treated with a flocculent to fix the pollutants. Dewatering and storage of the sludge was effected in oversize Big Bags. The zone requiring treatment covers a surface area of some 100 000 m², to a depth of 80 to 100 cm. Dissolution (liquefaction) of the mixture of sediment and sludge involved the use of a HAVER-Hydro-Clean^® (high-pressure washing unit) supplied by HAVER & BOECKER, using an 8 to 24 mm particle bed which was continuously recirculated in a closed cycle. Closed-cycle reutilization of the process water was achieved by means of appropriate filtration. This system, completed in 2008, permits a daily output of between 1500 and 2800 m³ of finished emulsion.

Dr. Katrin Mackenzie delivered the address, drafted jointly with Steffen Bleyl and Prof. Dr. Frank-Dieter Kopinke (Helmholtz Center for Environmental Research [German abbreviation: UFZ], Department of Environmental Techno-logy, Leipzig), on “Iron-carbon composites for cleaning of groundwater”. Metallic iron can be used in dispersed form for the elimination of chlorinated hydrocarbon and heavy metal contamination in groundwater aquifers. The problem, however, is generating this iron at rational cost, and using it in a stabilized form. The combination of extremely fine activated carbon (0.5 to 2 µm) and metallic iron precipitated on to it (10 to 25  %  m Fe) produces a strong and environmentally friendly reductant. The tight bond between the activated carbon and the iron(0) structures in this “carbo-iron” composite material has benefits for the surface properties of the reductant. The present article reports on the optimization of carbo-iron production and variation of the input materials.

In their paper on “Technical aerosols by means of dry dispersion”, Dipl.-Ing. Sascha Füchsel (Fig. 4), Prof. Dr.-Ing. Urs Peuker und Prof. Dr.-Ing. habil. Klaus Husemann (TU Berg-akademie Freiberg mining and technology acadamy, Institute for Mechanical Process Engineering and Mineral Preparation Technology) examined results obtained in the context of an AiF research project. Dry dispersion of a nano-scale starting material occurring in agglomerated form is accomplished in a fluidized-bed airflow mill with subsequent electrostatic stabilization. The influence of the most important process parameters – dispersion air pressure and separator wheel speed – on the production of a uniform and stable process aerosol was discussed.

Dr. Sergej Aman and Prof. Dr. Jürgen Tomas (Department of Mechanical Process Engineering, Otto-von-Guericke University of Magdeburg) reported in their paper on fundamental investigations into “The probability of fracture in the compression of individual, irregularly shaped particles” consisting of glass, sodium chloride, sugar, basalt and marble. Around one hundred selected particles from five particle fractions in each case were exposed to pressure until fracture occurred, the fracture loading determined, and the ratio of the fifty fracture force distributions obtained and the corresponding fifty fracture energy distributions analyzed. The distributions were, in addition, converted to a dimensionless form. All the experimental distributions obtained can be approximated by means of a logarithmic normal distribution function. The parameters for these dimensionless approximation functions of the force distributions, characterized by the anticipated values and standard deviations, can be calculated using the system of two linear equations of the corresponding parameters of energy distributions. The coefficients of these equation systems remain constant for all particle sizes and all materials. The fracture energy distribution can therefore be found from a known fracture force distribution, and vice versa.

Drum mills with steel cylinder armouring systems are the main equipment used for grinding of bulk products to finenesses of 100 µm (several hundred million tonnes annually in Germany alone). These armouring systems take the form, in mills of corresponding length (tubular mills) either of pure sliding armouring or also of classifying armour systems. In the latter case, axial crushing element motion is generated by means of a special shell geometry. This achieves adjustment of crushing element size to the increasing product fineness along the mill‘s grinding bed. The address on „Fine grinding in drum mills with ceramic classifying armour systems“ by Dipl.-Ing. (FH) Katrin Schmidt (Fig. 5), Dr.-Ing. Andre Kamptner, Dipl.-Ing. Mathias Polster (UVR-FIA GmbH Freiberg) and Dipl.-Ing. Bernd Ebertz (CeramTec-ETEC GmbH, Lohmar) reported the results of tests using an innovative ceramic classifying armouring. Contamination with discoloring abraded metal from the mill armouring system and the grinding elements must be excluded in processing of sensitive special products, such as fillers and extenders, glazes, glass and ceramic feed materials, and pigments. A classifying armouring system consisting of aluminium oxide has been developed and tested in a semi-commercial-scale drum mill (diameter 0.71 x length 2.0 m). The extremely good classification achieved by the newly developed armouring system has been demonstrated in grinding tests using ceramic balls for grinding of quartz sand and limestone. Throughput could be increased by up to 9  % or as much as 15  % energy saved, compared to conventional, non-classifying armouring systems.

The question of “The ram compactor as a scale-up basis for modern material-bed roll mills?” was posed as a discussion topic by Dipl.-Ing. Felix Heinicke (Polysius AG). Thanks to fundamental re­search activities into ram compactors for material bed comminution, the action of the principal parameters, such as compaction pressure, moisture, loading geometry, etc., can be considered proven. The basic tendencies of material behaviour can be also be anticipated upon application to material-bed roll mills. It remains questionable whether direct scale-up to semi-commercial-scale systems and application to large modern material-bed roll mills with diameters of up to 2.4 m will be possible. This basic reservation was also voiced in the discussion on Prof. Heinrich Schubert’s (Fig. 6) address.

Dr.-Ing. Jürgen Stein (Hosokawa Alpine AG, Augsburg) discussed the “Alpine Picoline” series of machines in his paper on “Preparation technology for ultra-small product quantities in research and in the laboratory”. This is a range of extremely small machines for quantities of material extending from less than one up to several grams. Jet mills, impact mills, agitator mills, classifiers and mixers can be set up on a standard modular platform for all machines. All components can be dismantled quickly and easily, and the range’s good cleaning facilities permit use in a clean environment. All supply systems are integrated into the basic platform, as is modern touch-panel operation. All these machines have been derived from the familiar series of production facilities. The “Alpine Picoline” was also highlighted in the poster exhibition.

The report on the lectures of the second day of the event, which will deal with waste recycling and sorting, as well as on the poster exhibition and the company presentations will be continued in the April issue of AT INTERNATIONAL.

Prof. Dr. habil. Hanspeter Heegn