In the opening speech by one of the managing directors at UVR-FIA, Dr.-Ing. Henning Morgenroth, presented the company‘s current work focuses. Then one of the directors of the HIF, Prof. Dr Reuter, took the opportunity to inform the attendees about the work areas and perspectives of this institute. On the afternoon of 9 November, the conference attendees were given the opportunity to tour the laboratories and testing facilities of UVR-FIA, the HIF as well as those at the MVT-AT Institute. The evening event for the conference attendees, which they used for lively discussions, was held on the first day of the conference in the Schankhaus 1863 in Freiberg‘s Ratskeller restaurant.
Processing of primary resources
Mineral processing is confronted increasingly with ores that have a complex mineralogy associated with fine-grained, strongly intergrown value minerals. “Fine grinding of complex, fine-grained ores” was the focus of the paper by Markus Buchmann1, Karsten Grossmann1, Thomas Leissner1, Marius Kern2, Edgar Schach2, Martin Rudolph2, Irina Bremerstein3 and Urs Peuker1 (1MVT-AT, 2HIF, 3UVR-FIA). For a useful assessment of comminution efficiency, besides the particle size distribution and degree of liberation of the individual minerals, the effects of selective comminution and the mineral grain size distributions for the comminution products were determined. Automatic mineral liberation analysis (MLA) was applied in this study. With reference to the example of the comminution of a cassiterite ore in an agitated ball mill and the associated characterization of the comminuted products with MLA, the problems of the resolution limit of measurement methods and the increasing agglomeration in the fines range were outlined and discussed.
“Studies on flotation and density separation on ore samples from the Hämmerlein-Tellerhäuser deposit (Western Ore Mountains)” were presented by Irina Bremerstein (UVR-FIA). This deposit containing tin, indium and magnetite is the subject of an r4 project funded by Germany‘s Federal Ministry of Education and Research (New Strategies for the Processing of Complex Ores from Domestic Deposits). The comminution behaviour, magnetic separation, density separation and flotation of bulk samples extracted by SAXORE Bergbau GmbH from five different extraction sites in the deposit were studied. In this paper, specifically the results of the sulphide and cassiterite flotation as well as of systematic analyses on a “Falcon” sorting centrifuge were presented. The flotation of sulphides upstream of cassiterite flotation and a change of water for the removal of iron ions were determined as an expedient variant with regard to the process engineering.
“Flotation characteristics of tin-containing skarn from the Hämmerlein polymetallic complex deposit in the Ore Mountains” were reported by Edgar Schach1, Markus Buchmann2, Jennifer Astoveza1,2, Irina Bremerstein3, Marius Kern1, Urs A. Peuker2, Martin Rudolph1 (1HIF, 2MVT-AT, 3UVR-FIA). As pre-treatment, density separation, magnetic separation, sulphide flotation, and desliming as well as the influence of another comminution step to improve the degree of liberation of the relatively coarse-grained (x80.3 < 250 µm) feed material were studied. Besides the styrene phosphonic acid used by UVR-FIA for the flotation tests, the anion-active sulphosuccinamate (Aerosol22®) was used as a collector, MIBC as a foamer and sodium hexafluorosilicate as a depressant. Flotation was performed at pH 3 in a flotation cell from Outotec® (GTK LabCell™). For characterization of the behaviour of the individual minerals during the different processing steps, X-ray fluorescence analysis and mineral liberation analysis (MLA) were applied. To determine the influence of interfering metal ions on flotation, in some tests the water was changed after preconditioning with sodium hexafluorosilicate. Furthermore, water samples were taken from the tests and analysed with regard to the ion content by means of ICP-OES. Result of the analyses was a flowchart for the beneficiation of comparable ores.
In the paper “Comparing existing froth flotation models in a case study with a scheelite ore” by Nathalie Kupka, Martin Rudolph (HIF), three models for foam flotation described in the literature were presented. These include the models of Pyke, Yoon as well as of Schwarz and Koh. With a scheelite ore as test material, with ten repeats of the specific flotation tests and analysis of the products with ICP-MS, XRF, MLA, ICP-OES, characterization of the foam structures as well as water analysis (pH, Eh, oxygen content, conductivity), detailed results were determined, and corresponding model calculations performed to describe the course of flotation. Studied specifically were the efficiencies for collision, adhesion and stability in the individual models, each model exhibiting different advantages, and accordingly no universal model could be proven.
In his paper “Recovery of strategic metals with biotechnological processes”, Benedikt Hoffmann (Research Engineer & Project Manager) first presented the work focuses of the biotechnology company BRAIN AG based in Zwingenberg, which cooperates with numerous leading industrial enterprises, develops and markets its own production candidates for the bioeconomy. As a typical application from metal extraction from diverse sources, tests on bioadhesion and biosorption in combination with flotation techniques and bioleaching processes were cited. For these applications termed Urban & Green Mining, microorganisms from the pool of several tens of thousands of the BRAIN BioArchive were selected and optimized. So, for example, around 90 % of the gold content could be recovered from slags. For the technical upscaling of the laboratory results, the transportable BRAIN BioXtractor pilot plant was developed. With this plant, the biotechnological metal extraction on the basis of microorganisms from secondary and waste streams as well as primary resources can be tested on customers‘ sites and adapted to specific requirements.
Machines, equipment and sensors
In the paper headed “Limited availability of water? Experience with the AKA-FLOW dry-operating gravimetric sorting device”, Robert Claussnitzer (AKW-Apparate + Verfahren GmbH, Hirschau) showed how waste water could be reduced or avoided completely in mineral processing. The AKA-FLOW is used for pre-separation or concentration of materials with different density as a possible preliminary stage for wet-mechanical separation. This principle of operation is based on a combination of air-induced fluidized bed and a specially developed discharge system. A prediction of the suitability of the dry sorting process is possible with tests on small samples in an AKA-FLOW laboratory-scale device. Models with maximum throughput rates of 4 t/h and 15 t/h are available. Especially for recycled material (e.g. removal of timber remnants from construction waste), good separation efficiency has been achieved.
In the processing of mineral resources, requirements are constantly increasing with regard to the fineness of the products and efficiency of the processes. The paper “Higher throughput rate and finer products thanks to wear protection of classifier wheels with ATP/NG technology” presented by Dominik Knauer, Steffen Sander, Horst Skirde (Hosokawa Alpine AG, Augsburg) was devoted to this topic. The development of Turboplex ATP/NG classifiers and models derived from these (TTC, TTD) effects a considerable reduction of the pressure loss at the classifier wheel based on suppression of the potential vortex. In the processing of abrasives, polishing and hard materials and other wear-intensive materials, increasingly fine products free of any contamination are demanded. With the new development of a wear-protected classifier wheel of the type ATP/NG, the process engineering advantages associated with NG geometry can also be used in the processing of abrasive materials. In the grinding of a rare earth oxide with a Mohs hardness of 5 – 6 with a fluidized bed opposed jet mill of the type 400 AFG (integrated classifier: 200 ATP/steel), it was possible to achieve around 15 % finer particle sizes of the finished product (d90 = 1.0 µm) and, with the new wear protection, at the same time the total contamination with Fe-compounds in the finished product could be reduced from 50 – 100 ppm earlier to 5 – 6 ppm now. In a fluidized bed opposed jet mill 630 AFG (integrated classifier: 315 ATP/ceramic) in hot gas operation, with the use of the wear-protected classifier wheel, the speed could be halved while constant fineness of the finished product maintained, which has a positive effect on the energy consumption and wear and opens up the possibility of producing much finer products without additional measures.
Hagen Müller1 and Uwe Schridde2 (1Haver Engineering, Freiberg, 2Rump & Salzmann, Osterrode) reported on “Operational experience in the processing of stockpiled raw gypsum material with the HAVER Friction-Clean”. Starting from positive tests in a pilot plant at Dorste Quarry, in a washing plant operated by Rump & Salzmann in a gypsum quarry, a first prototype of the HAVER Friction-Clean was installed on industrial scale. Set-up and principle of operation of the Friction Clean were explained and first operational experience from the industrial field described. It was shown that even for heavily contaminated material from mining debris heaps, significant quality improvements with regard to whiteness and gypsum content could be achieved, and accordingly a high-grade starting material could be produced for the gypsum-processing industry.
The “Design of FAM special hammer mills for comminution and drying of bulk solids” was presented in the paper by Jens Hanisch (FAM, Magdeburg) and Rüdiger Schramm. Moist bulk solids can be comminuted and dried or calcined in one step with this mill. The required size of the special hammer mill is determined based on a compromise depending on the evaluation of comminution and drying. For medium-hard feed material with moisture content up to around 10 %, the design of the special hammer mill is oriented to the requirements of the comminution. For higher material moisture content to around 30 %, the design of the special hammer mill is influenced by the drying process, data for moisture content, specific heat, air flow, temperatures, etc. being input in the presented calculation program.
In the paper “Ultrafine grinding of pyrolysis coke – challenges for plant design”, Stefan Jäckel and Raphael Sperberg (Gebrüder Jehmlich GmbH, Nossen) gave an insight into the approach to plant design. In the recycling of scrap tyres based on pyrolysis, ultrafine comminution of the carbon black is necessary, which can be realized with fine impact mills from the Jehmlich REKORD series. The achievable particle size distribution can be selectively influenced with variation of loading rate and load. During ultrafine grinding, foreign bodies with silicate components and other abrasive fillers from scrap tyres lead to notable wear of grinding elements (rotor and stator), which can be reduced with the use of hard steel and pin material made of tungsten carbide. Referencing the example of a recently delivered, inertized, explosion-protected grinding mill, the speakers described the operating parameters for a specified particle size distribution and the incurred wear costs on the basis of tests in the Jehmlich test facility.
In the paper “Influences of selective comminution (SC) with impact stress”, Max Hesse (IAM) explained that SC can be used for the separation of ore and secondary rock, for the separation of ore varieties and for the separation of ore and tailings. Here, either the predominant crack propagation in a constituent or the predominant crack propagation along grain boundary between different constituents in the feed material is utilized. SC as an element of a sorting process depends on three system components: the feed material, the comminution machine and the machine for separation. With tests on impact loading of lead-zinc ore (Pomorzany near Krakow/Poland), copper-molybdenum ore (Los Pelambres/Chile) and fluorite-baryte ore (Marienberg, Ore Mountains/Germany), the influences of the material potential and the comminution machine on the separability of the constituents were studied. As material variables, the differences in the density and strength between the respective constituents as well as the feed particle size were investigated. To determine the machine influences, the impact rate based on single particle comminution in a shot apparatus (MVT-AT) was varied. For various feed particle sizes (6.33 – 1.5 mm) and impact velocities (17.5 - 70 m/s), an always considerable dominance of the difference in strength compared with the difference in density was shown. The feed particle size (material influencing variable) and the impact velocity (machine influencing variable) must be adapted for a given ore. In the analysed parameter range, the influence of the impact velocity is higher or the equal to the influence of the feed particle size.
Luca Benvenuti (CADFEM GmbH, Grafing near Munich) explained in the paper “Discrete element method – simulation and validation for a high-pressure roller mill” that this method can be used to evaluate the effectiveness of a comminution process. Focus is on maximization of the throughput rate, the homogeneity of the produced ground product also being taken into account at the same time. In addition, the required drive power can be determined and optimized with balancing of the process parameters and grinding results. Equally, wear on mills can be investigated and minimized. The comparison of test results with conducted simulations showed a good agreement with regard to power consumption, the roller forces and particle size distribution.
A new technological standard for the sorting process and a contribution to the resource-saving management was presented in the paper “ProRec – a compact analysis module for fast and spatially resolved material identification with X-ray fluorescence for use in recycling and raw material processing” presented by Reiner Wedell and Marius Scheiner, Institute for Applied Photonics (registered association). The system is designed to achieve high spatial resolution for processing small particles on belt conveyors. This requires, besides smaller track widths, a high speed of the signal processing so that the required material throughput rate is achieved. With compact analysis modules (160 mm x 150 mm x 360 mm) consisting of collimator, detector line and full signal processing electronics for synchronous scanning of all channels with a measurement time of 10 ms, this is achieved. Compared to conventional XRF-systems, the spatial resolution is improved from around 25 mm to much smaller 5 mm track width. A high flexibility of the new XRF module allows the fast adaption to different measurement applications and in combination with other analysis methods (IR spectroscopy, LIBS), material identification beyond the elements with atomic numbers > 22 accessible with XRF.
With the paper by Christopher Robben and Jens-Michael Bergmann (TOMRA Sorting GmbH, Wedel) “Processing with the light sabre – TOMRA‘s trail-blazing laser sorting technology enables the production of high-purity quartz products and preliminary separation of tailings for quartz-associated gold ores”, a new process was presented that is based on the principle of the refraction of various lasers on the surface of individual particles. In this process, large and pure crystals can be clearly differentiated from other rocks or minerals with a smaller crystal structure, independent of the colour or the chemical composition. With examples involving the sorting of quartz for the extraction of silicon for solar applications as well as of quartz with gold content, the effectiveness of the new process was described. It was possible in gold processing to recover 97.5 % of the gold in 40 % of the mass.
Processing secondary resources/recycling
In smelting plants for the production of iron and steel, during cleaning of the flue gases, large quantities of dust of predominantly iron or iron oxides are produced. In the paper “Air classification as a potential process step during recycling of smelting plant dusts”, Christof Lanzerstorfer1 and Robert Neuhold2 (1University of Applied Sciences Upper Austria – Process and Environmental Engineering, Campus Wels, 2University of Applied Sciences Upper Austria) discussed possibilities for improving efficiency. On account of the high process temperatures, in the various process stages (sintering plant, blast furnace, steel plant) contaminants can evaporate (especially Zn and Pb as well as KCl and NaCl). During cooling of the flue gases, these materials tend to deposit on the surface of the present dust particles and concentrate in the fine dust fractions. With air classification into a fine fraction with higher concentration and a coarse fraction with lower concentration of contaminants, it is possible to discharge these in the fine fraction. From the fine fraction, Zn can be recovered. The coarse fraction is recycled after briquetting. In the paper, various possibilities for the use of air classification for treatment of dusts from flue gas cleaning in integrated smelting plants were discussed. Both possible effects on the material streams in the smelting plant as well as the requirements for the necessary air classifier were detailed.
Ivan Züst (DHZ AG Lufingen/Switzerland) reported on an “Innovative process for dry-mechanical recovery of NF metals from WIP fine slag > 0.5 mm and sorting into an unmixed light and heavy metal fraction”. From the moist fine slag < 5 mm from waste incineration plants, with the novel ballistic separation method of “Supersort”, a coarse fraction > 0.5 mm with a third each of heavy, light metals and foreign substances was recovered. This concentrated coarse fraction can be further processed efficiently with NF separators. With diverse additional dry-mechanical processes, separation into a light and a heavy non-ferrous metal fraction with a high degree of purity is possible. This can be further processed directly in a metallurgical process.
With the paper “Selective leaching of copper slag tailings from Chile”, Carolina López and Gerhard Heide (Institute of Mineralogy, Freiberg University of Mining and Technology) presented findings gained in cooperation with Frank Haubrich (G.E.O.S. Ingenieur GmbH Freiberg) as well as Ursula Kelm (GEA Universidad de Concepcion, Chile) on leaching with different systems (e.g. sulphuric acid, oxalic acid, soda lye).
With a new process, about which René Dechange (JÖST GmbH + Co. KG, Dülmen) reported in his paper “Extended fine process in the processing of ASR (Automobile Shredder Residue)”, all metal can be efficiently separated from glass and mineral components with purities > 98 %. Classification is performed at 4 mm and 12 mm into three fractions with the multideck flip-flow screen (TOPCILLA) with flexible screen panels as well as adapted air separators. TOPCILLA combines the advantages of two different screening principles in one machine: the proven JÖST 3D cascade screen TopSpin on the upper deck and the OSCILLA flip flow screen on the lower deck.
To enable more effective recycling of mobile telephones, it is essential to determine in as much detail as possible their components, the presence of the elements in them as well as their comminution behaviour. With the “Characterization of a comminuted mobile telephone by means of mineral liberation analysis (MLA)”, a contribution to this was provided by Dirk Sandmann (HIF, ERZLABOR spin-off project). A key problem in the recycling of mobile telephones is their complex composition including many individual components. It is made more difficult by the fact that many elements are only present in trace amounts and/or are found in highly complex material composites. Mobile telephones can contain up to 60 different elements, for most elements the recycling rates being well under 50 % and for rare earths, indium, tantalum or gallium, even under 1 %. The existing studies were conducted with three screen fractions of Nokia mobile telephone model 5228, type RM-625 comminuted at the Department of Recycling Machines at Freiberg University of Mining and Technology with a UG300 universal granulator with the help of mineral liberation analysis (MLA) with the MLA 650F apparatus. In the analysis, approx. 130 different phases were detected. More than 100 of these are present with contents of < 1 weight percent. A comparison of the modal content of the three screen fractions showed a concentration of certain components in specific fractions.
In a bilateral research project with the BMW Group in Munich, a high-performance and energy-efficient recycling process for Li ion batteries was developed that is based mainly on classical mechanical basic processes like comminution, classification and sorting. “Compaction of electrode films from lithium ion batteries” is intended to improve the product quality of the metal concentrates. Findings on this were presented in the paper given by Denis Werner, Lutz Wuschke, Hans-Georg Jäckel and Urs A. Peuker (MVT-AT). The mix of electrode films was first comminuted in a hammer mill and then separated by means of airstream sorting in the zigzag separator. Separation characteristic is the different quasi-stationary settling rate of the copper and aluminium particles, which depend on the particle shape, size and particle density. As at constant particle size, specifically lighter and spherical particles have the same quasi-stationary settling rates as specifically heavy and platy particles, only relatively low separation efficiency is achieved for airstream sorting. With selective compaction/balling, the shape of the aluminium and copper particles can be influenced so that during subsequent airstream sorting, higher separation sharpness and therefore better concentrate grades can be obtained. In the paper, current test findings on the characterization of the degree of compaction and the effects on separation sharpness for air stream sorting were presented. An outlook on the further approach and proposals for modern technological applications for the processing method were given.
Fabian Knappich1, Martin Schlummer1, Dominik Knauer2, Robert Patalewski2 (1Fraunhofer IVV, Freising, 2Hosokawa Alpine AG, Augsburg) reported under the heading “Plastics with a new shine – material recycling for electroplating waste” on a process with which it is possible to recycle the plastic-metal composites produced as waste (approx. 2000 t/a in Germany). These composites consist of polymers such as acrylonitrile-butadiene-styrene (ABS) coated with a system consisting of chromium, nickel and copper. In the innovative recycling concept, the pre-comminuted material is fed to a multistage mechanical liberation unit, and, with the help of a separator, a metal fraction with a purity exceeding 95 % is recovered. The plastic fraction with just 5 – 7 % residual metal can, following melt filtration, be used as metal-free regranulate. The metal concentrate from the melt filtration with 15 – 25 % residual polymer is recovered after treatment with solvent systems (CreaSolv® process). The two cleaned metal fractions have such a high quality that much higher revenue can be obtained for them. In the paper, Fabian Knappich described the overall concept for recycling electroplating waste. The process step for combined liberation and comminution was described by Dominik Knauer.
“Process-optimized influencing of the material feed stream in recycling plants” was addressed by Alexander Feil1, Marcel Bosling1, Sebastian Kaufeld1, Erdogan Coskun1, Thomas Pretz1 and Claudius Schnörr2 (1Department of Processing and Recycling, RWTH University of Aachen, 2CORSNAV Research Group – Munich University of Applied Sciences). In recycling plants, the technological challenge is to process material streams with widely varying material composition as well as changing mass flows. Especially overfilling in the first separation stage leads to worsening of the separation efficiency of the commonly used trommel screens and consequently the downstream sorting stages producing the recyclables. Studies in mechanical-biological treatment plants for household waste showed that already with the adaption of the volumetric feed to the intended area of the trommel screen, the technical-economic processing efficiency can be improved. A further increase in the efficiency of the process can be expected if the separation behaviour in the trommel screen is considered as a function of the volume flow and material composition of the input stream. Based on the example of a sorting plant for lightweight packaging, the requirements and possible technological solutions for a sensor-based control concept were presented.
Poster exhibition and company presentations
Before the lunch break on the first day of the conference, every poster exhibitor had the opportunity to present his contribution in a short talk. A total of six posters came from the MVT-AT. The poster by Thomas Mütze et al. focussed on the “Production of high-grade permeable dolomite grades for the firing process”. Here the influences of the particle size distribution, particle shape and packing density and the extension of the currently used grain size range from 25 – 70 mm to include smaller particle sizes were investigated to achieve better resource efficiency. Karsten Grossmann and Urs. A. Peuker informed on the “Scale-up of a vertical agitated ball mill for the liberation of high-grade ores”, within the scope of which the wear behaviour, energy efficiency and product properties in the beneficiation of a gold ore were analysed. In the poster “Breakage characterization based on ore components” by Alphonce Wikadzi et al., with a heterogeneous copper-gold ore, the influence of the mineral components of different hardness on the grindability and degree of liberation of the individual ore components was evaluated with granulometry and X-ray diffractometry. Lieven Schützenmeister et al. studied in cooperation with Dr Kache from thyssenkrupp Industrial Solutions AG the “Modelling of the compaction behaviour of cement clinker” in the roller gap of a high-pressure roller mill as a function of the fracture behaviour of the feed material, the particle size distribution and the loading rate.
With the “Analysis of the structure and pore volume filter cake with the use of X-ray microscopy” in the poster by Erik Löwer and Urs A. Peuker, experimental data was linked with characteristic network parameter to obtain reliable information on microprocesses during filtration and the subsequent dewatering of filter cake for a more precise design of industrial filtration processes. Using model systems, Paul Knüpfer et al. in the poster “Metal melt filtration – study of the microprocesses for separation and agglomeration (SFB 920)” studied the possible production of higher metal qualities. As the high process temperatures of metal melts make the testing of real systems difficult, experiments were conducted with aqueous model melts, alumina particles and ceramic filters. Besides the analysis of adhesive forces by means of an atomic force microscope to analyse the wetting properties, in a semi-industrial testing plant, filtration experiments were conducted on larger scale.
From the Institute of Technical Ceramics at Freiberg University of Mining and Technology, the poster “Selective extraction of rare earths with liquid-liquid extraction with preorganized calixarenes” was presented by Norbert Schreiter et al. The new class of extraction media with a basic structure of fourring tetracyclically connected phenol units modified with phosphor- and nitrogen-based complex ligands feature high coordination strength against rare earths. The components were analysed in respect of solubility in various solvents as well as parameters for extraction and re-extraction to enable separation of accessory elements and individual separation of rare earths.
The HIF was represented with two posters for the application of biotechnology in processing. Guillermo Luque Consuegra et al. informed on “Screening the potential of halophilic bacteria for pyrite bio depression” in combination with flotation of copper-molybdenum ores and Sylvi Schrader et al. on “Bioflotation – combination of biotechnology with the classical process of flotation”. Objective here is to replace the environmentally damaging traditional flotation reagents and but also to improve the efficiency of the processes. In another poster from HIF on “System-integrated metal production – the Fairphone example” by Markus Reuter, based on the example of a modern smart phone it was proven that the raw materials used, the production, the use and the recycling of the device is oriented to sustainability. With the modular design with only five elements connected by means of robust spring contacts and the battery, the user can make simple repairs himself. This lengthens the lifetime and improves the ecobalance.
Company presentations were given by the industry representatives of the companies Eirich (Ingenieurbüro Dill, Misch- und Verfahrenstechnik Jena), Neumann & Esser GmbH & Co. KG- Mahl- und Sichtsysteme Übach-Palenberg as well as the CEM TOP Network for plants for the construction industry in Magdeburg.
Closing words and announcement of the annual conference 2018
The next “Processing and Recycling” conference is set to take place on 14t and 15 November 2018 at the same venue in Freiberg in the auditorium at the site of HIF/HZDR (former FIA building). Organizers are again the Gesellschaft für Verfahrenstechnik UVR-FIA e.V. Freiberg in cooperation with the Helmholtz-Institute Freiberg for Resource Technology and the Freiberg University of Mining and Technology. It is requested that abstracts for papers, posters and company presentations be sent to the conference organization at UVR-FIA GmbH at the internet address ww