“Processing and Recycling 2016” Conference in Freiberg

On 9 and 10 November 2016, 130 professionals met in the “Alte Mensa” auditorium at Freiberg University of Mining and Technology for the annual conference (Fig. 1). Joint organizers were the registered society UVR-FIA, the Helmholtz Institute Freiberg for Resource Technology and Freiberg University of Mining and Technology with the Institute of Mechanical Process Engineering and Mineral Processing. In 25 oral papers and ten posters and company presentations, new findings in the field were reported. Focuses of the conference 2016 in 2016 were ore beneficiation and mineral processing, extracting recoverables from recycling products, new research findings and developments concerning equipment and processes.

The conference was opened by Dr Andre Kamptner, Managing Director of UVR-FIA GmbH, who took the opportunity to give the conference participants an insight into the company’s activities (Fig. 2). He explained that in numerous laboratories and a large testing facility an extensive array of machines and equipment was available for processing to the pilot scale of 1 t/h for demonstration purposes, for the development of new processes and process optimization as well as for the production of relatively large product samples. For process control and product characterization, suitable analysis and measurement systems were also in use. The company, he continued, maintained close cooperation with the Helmholtz Institute Freiberg for Resource Technology, which has now taken up its activities at the same location as the UVR-FIA GmbH on Chemnitzer Strasse, and with Freiberg University of Mining and Technology.

1 Accolade for Prof. Heinrich Schubert

At the beginning of 2016, Prof. Heinrich Schubert celebrated his 90th birthday. In his honour, a special issue of the renowned “International Journal of Mineral Processing” (Issue no. 156, 2016 ISSN 0301-7516) was compiled including 15 papers (176 pages, 50 authors from12 countries) hailing from all over the world, with particular reference to Prof. Schubert’s work (Fig. 3). A special focus were recent papers on the turbulent hydrodynamic study of the flotation process, a development in research inspired by Prof. Schubert that is now attracting more and more attention. In the paper presented by Dr Martin Rudolph (Helmholtz Institute Freiberg for Resource Technology) and Prof. Urs A. Peuker (Freiberg University of Mining and Technology, MVT-AT), key aspects of the published papers were presented and an overview of the long-lasting impact of the innovative ideas and approaches developed by the “Freiberg School” around Prof. Schubert. Special merits in this field were also earned by Prof. Schubert with the organization of the “XVIIth International Mineral Processing Congress” in Dresden in 1991.

2 Ore beneficiation and mineral processing

The possibilities for mineral processing and mineralogical analysis methods have improved considerably in recent decades so that it is worth reassessing the extraction of valuable components from ores with complex composition. Related problems were addressed in the paper “The Hämmerlein-Tellerhäuser exploration project – challenges and potential solutions for the mineral processing of complex skarn ores” by Dr Marco Roscher (Fig. 4), Lars Starke, Tony Truelove (Saxore Bergbau GmbH Freiberg). Thanks to the work of SDAG Wismut, a uranium mining company in the former GDR, the ore deposit has been very well explored. Building on this, the reserves were reassessed in compliance with the international (JORC) standard. This confirmed that, judged on a world scale, the Hämmerlein and Tellerhäuser deposits together boast outstanding content and tonnage. With a content of 0.46 % Sn, around 1000 t Sn metal, with 1.12 % Zn around 200 000 t Zn metal and with 127 ppm In around 2000 t In metal can be extracted. The biggest problem in this project are the small-scale intergrowth, lateral and horizontal variations of the content as well as constantly changing mineralogical and lithologic alternation in the ore, all of which makes processing very complicated. Saxore Bergbau GmbH is currently working together with several research projects in the scope of the R4 invitation for research projects in the FONA Research for Sustainable Development funded by Germany’s Federal Ministry of Education and Research (BMBF) as well as the European FAME project to research new methods for the beneficiation of these ores. New approaches for preliminary sorting (sensor-assisted sorting) for tailings, various possible combinations of classical processes of magnet and density separation in wide-ranging particle size fractions have been tested.

Within the framework of the BMBF project “Resource efficiency for Germany-France: EcoMetals collaborative project – innovative environmentally friendly processes for the extraction of strategic and rare metals from primary and secondary resources”, UVR-FIA GmbH is studying the comminution and flotation of copper slate. Juliane Schaefer (UVR-FIA GmbH) and Andreas Kamradt (Martin Luther University of Halle) presented the results of the “Flotation of copper ore at the Rudna deposit” (Fig. 5). The material in question is a copper ore with the three lithotypes carbonate, sandstone and slate with a starting content of 3.5 % copper. The problem, however, consists in the very complex intergrowth of the valuable minerals and the simultaneous presence of organic carbon components averaging around 7 %. In laboratory flotation tests conducted so far, it has been shown that with single-stage flotation in a mechanical flotation machine, a concentrate with 10 % copper content at a yield of more than 70 % can be achieved and with modification of the flotation conditions, a carbon content conforming to the required < 5 % can be achieved.

The “Study of fine particle flotation of high-carbonate apatite ores from Vietnam” was addressed in the paper by H. H. Duong (Fig. 6) (Department of Mineral Processing, Faculty of Mining, Hanoi University of Mining and Geology), M. Rudolph (Helmholtz-Institute Freiberg for Ressource Technology) and H. Schubert (TU Bergakademie Freiberg, MVT-AT). The selectivity and yield in the flotation of phosphate ores are severely impaired by the complex and fine intergrowth of the minerals. With a dedicated reagent regime and the optimization of hydrodynamics of the three-phase system, possibilities for efficient separation of the fine-particle mineral phases are seen and have been empirically underpinned with tests in a 1.2 l flotation cell.

With the “Application of hybrid flotation of iron ore – pneumatic flotation for the removal of sulphur”, on which Lukas Petzold and Jan Martens (Primetals Technologies Austria GmbH) reported (Fig. 7), it is possible to take a Fe concentrate from Iran with 67 % iron and 1.3 % sulphur, and, with a yield of more than 95 %, to produce a concentrate with less than 0.4 % sulphur. With the hybrid flotation technology from Primetals, a pneumatic spray principle is combined with a column method, as a result of which the contact frequency between the very fine solid particles and the very small gas bubbles is increased. The system works without an impeller system consisting of rotor and stator, which brings certain advantages in terms of energy consumption and wear.

Complex, strongly intergrown ores require very fine liberation, which effects increasingly fine-grained feed materials in the downstream separation processes. With the paper “Comparative study of ultrafine flotation approaches” by Markus Buchmann (Fig. 8), Alexander Knöppel, Urs Peuker (Freiberg University of Mining and Technology, MVT-AT),Tom Leister, Martin Rudolph (Helmholtz Institute Freiberg for Resource Technology), a process variant was presented for improving the efficiency of the separation of product and gangue material by means of the additional use of microbubbles in conventional froth flotation. Furthermore, oil-based liquid-liquid flotation or agglomerate flotation offers possibilities for improving selectivity in the separation of ultrafine particle mixes. On the basis of the example of a synthetic material mix of magnetite and quartz with a particle size distribution under 20 µm, the above-mentioned methods were compared in the flotation column. Furthermore, the different arrangements in respect of microbubbles or the addition of oil droplets and combinations of the various ultrafine flotation approaches were tested in respect of their influence on the sorting efficiency.

The paper “Benefits of regular grindability review: BGM case study” by Alphonce Wikedzi, Thomas Mütze, Urs A. Peuker (Freiberg University of Mining and Technology, MVT-AT) informed attendees about possibilities for optimizing the grinding process in the Buzwagi gold mine in Tanzania (Fig. 9). Comminution and grinding processes are designed on the basis of material-specific parameters such as hardness, mineralogy and work indices. The parameters were determined in tests conducted during the concluding feasibility study of the mining project. Later the material-specific parameters were verified and modified during putting into operation. The change in the ore hardness, for example, affects the specific energy consumption for the grinding process, while on the other hand changes in the mineralogy can bring challenges for downstream processes such as leaching and flotation. For the optimization of the grinding processes, with three ore mixes, the standard Bond ball mill test was conducted for determination of the grindability and the work index. Furthermore, batch grinding tests were performed to determine the fracture rate and the separation function and the standard ball mill tests were conducted for determination of mineral liberation with use of an automated process (scanning electron microscope).

3 Recovery of resources from secondary sources

Phosphate recovery from secondary resources is essential for Germany and funding programmes have been initiated by the German government for the recovery of phosphor. Presented by Peter Fröhlich, Jürgen Eschment, Reinhard Lohmeier, Gunther Martin (Freiberg University of Mining and Technology, ITC) was the “PARFORCE technology – development of an innovative, industrial process for the recovery of phosphate from secondary sources”, which enables recovery of phosphor from high-phosphor sewage sludge ashes and other industrial and animal phosphate sources (Fig. 10). As a product, phosphoric acid in different qualities is formed. Compared to other P-recycling processes, the PARFORCE technology uses mainly electric energy and can be switched on and off completely within a few minutes, so that excess energy from the power grid can be used. Currently, in the scope of a spin-off project, the technology is being scaled up to an educt throughput to one tonne per day in order to demonstrate the industrial feasibility and economic efficiency of the process.

With the current state of the art, suitable processing methods can be applied to recover large quantities of NF metals from coarse-grained fractions from waste incineration plant grate ashes. In their paper “Recovery of copper and other NF metals from WIP grate ashes < 2 mm”, Boris Breitenstein, Daniel Goldmann (Clausthal University of Technology, Institute of Mineral and Waste Processing, Waste Disposal and Geomechanics) showed that copper, aluminium and zinc can be recovered even from the fine-grained fractions. With the RENE process or its further development, the RENE-Adapt process, it is possible in three stages (dry-mechanical, wet-mechanical, hydrometallurgical) to recover the contained NF metals even when the particle sizes are < 100 µm. With selective comminution of the copper-iron mineral phases as well as copper mineral phases, liberation takes places, enabling sorting of the valuable metal components and a yield of more than the 65 % of the copper load with a copper concentration > 20 %. From the residue of the mechanical processing, with a hydrometallurgical process the copper yield can be increased to over 85 %. One use for the mineral residue is as partly deacidified calcium carrier in the binder industry as the Ca-Al-Si ratio is favourable and an immense contribution to climate protection can be made. Research on this is currently underway.

Norbert Berg, Stefan Eisert (ImpulsTec GmbH Dresden; Mineral Projekt Chemnitz) and Gunther Pieplow (Mineral Projekt Chemnitz) reported on the “Efficient processing of metallurgical slags with the use of shockwave technology” (Fig. 11). With selective high-voltage discharge under water, intensive, mechanical shockwaves are generated, which take effect selectively at the transitions of mineralogical phases of the slags. This enables the realization of selective liberation of metallurgical slags so that the slag components can be recovered separately in downstream sorting. For example, with the application of weak-field magnetic separation, it is possible to separate copper, recover a Fe concentrate and a pozzolanic phase, enabling economic utilization.

A paper interesting particularly for environmental protection reasons entitled “Iron from the Spree???” was given by Simona Schwarz (Leibniz-Institute of Polymer Research Dresden e.V.). As a consequence of mining, both heavy metal ions and various anions are contaminating ground and surface waters (Fig. 12). With the closure of many open pits and their flooding, the groundwater is rising again and flushing iron salts and iron hydroxide from dump areas and naturally occurring pyrite strata. This leads to a substantial contamination of the surface water by iron hydroxide in the form of reddish brown ochre sludge and increasing acidification caused by a steadily rising sulphate load. With precipitation of iron oxide/hydroxide with lime, iron can be separated, but a high content of sulphate remains in the waters. With chitosan, a naturally occurring, ecological biopolymer with the properties of a super adsorber, both iron ions and sulphate ions can be removed at the same time. These grow as iron sulphate and iron hydroxide aggregates on the surface of the chitosan up to an iron content of around 40 %, so that smelting of the material could be worthwhile.

With his paper headed “B.O.M.® – Biological, Organic, Mineral fertilizers made from manure, silage and/or paper sludges as well as mineral additives”, Dirk A. Osing (DOS-CONSULTING Meerbusch) gave an insight into possibilities for expedient utilization of waste products (Fig. 13). In a compulsory mixer, the organic components are mixed intensively/homogenized with mineral additives such as fine-grained fly ash, lime or slags from iron metallurgy and a granulated product is produced. The B.O.M.® product is then screened to a certain size and can be stored and sold as bulk solids or in sacks. B.O.M.® offers outstanding properties for establishing bacteria strains in the soil as a basis for good humus formation. A primary advantage of the process is that from regions with high levels of livestock and therefore the danger of overfertilization with manure or dung, a saleable product can be supplied for regions with deficient organic soil improvement.

The share of construction and demolition waste totalling around 200 mill. t makes up more than 50 % of the annually produced waste in Germany. In the paper by Christian Stier, Ansilla Bayha, Jens Forberger (Fraunhofer-Institute for Chemical Technology ICT), Neyir Sevilmis (Fraunhofer-Institut for Computer Graphics Research IGD), Rebekka Volk (Karlsruher Institute of Technology KIT, Institute for Industrial Production) entitled “ResourceApp: Innovative approach for identifying and development of resources in building construction as well as requirements for future action and research in the recycling of construction waste”, a demonstrator was presented, which for the first time enables the mobile, three-dimensional and semantic acquisition of buildings and building elements in real time. For this purpose, by means of a Kinect Sensor, depth information and image data are transferred to a laptop and evaluated in respect of 3D data and image recognition. With this, the resources inventory of the recorded building can be determined in different degrees of detail depending on the component and material and the subsequent activities for separation, dismantling and sorting selected.

Starting from a progress report on “Recycling of fresh concrete in concrete production”, Johannes Haufe, C. Nobis, A. Vollpracht (Institute of Building Materials Research and Chair of Building Materials, Faculty of Civil Engineering, RWTH University of Aachen) reported on the common recycling processes for the utilization of concrete residue (Fig. 14). Here in comparison to the recycling of construction waste or broken-up road surfaces, a much more homogeneous RC aggregate can be obtained as the starting material is available in an unmixed state. In Germany, fresh concrete residue is usually separated into aggregate particles and residual water – an aqueous suspension of cement and very fine materials to a particle size of 0.25 mm. For ecological and economic reasons, the residual water is used again in the production of concrete. In another process, with the addition of a “recycling aid” the hydration process can be delayed, the washing water remains in the ready-mix concrete truck and must be taken into account when the water is metered for refilling. The direct reuse of residual concrete in the ready-mix concrete truck within a maximum of three days can also be realized with a recycling aid, although freshly produced concrete in at least four times the amount of residual concrete must be mixed in. With an alternative method, the residual concrete is processed directly in the truck mixer to granulates of aggregates and hardened cement paste. Here, first a superabsorbent polymer is added that removes the free water from the fresh concrete and then a second, accelerating component is added. The concrete granulated in this way is mixed again and then unloaded. The properties of the concrete produced with concrete granulate are only insignificantly poorer than standard concrete, so that this granulation in the truck mixer represents a good alternative to the other methods.

With regard to the recycling of waste electronics in Europe, in the years to come, besides the recoverable metals, around 2 mill. tpa plastics can be expected. Rainer Köhnlechner (WERSAG GmbH & Co. KG, Grossschirma) reported on the “Recovery of valuable plastic fractions from waste electronics” (Fig. 15). Whereas proven solutions are available for the recovery of the metal fractions, the recycling of a wide range of plastics to clean, reusable products presents a big problem. In the process developed by WERSAG GmbH in collaboration with the affiliated company Hamos GmbH Penzberg, a combination of wet and dry processing methods is applied to produce unmixed products made of PS, ABS or PP. Sink-float separation is performed in water and salt solution (density 1.08 g/cm³) as well as electrostatic separation with triboelectric charging, which is the only one of the technologies available on the market able to separate mixed black plastics into unmixed fractions.

For plastic waste mixes from cable, waste electronic, domestic appliances and automotive recycling, to this day no closed systems for unmixed systems and high-quality recycling are available. With the “Development of process and equipment for thermosensitive sorting” on which Miriam Labbert, Toni Baloun, Jürgen Schoenherr (Zittau/Görlitz University of Applied Sciences, Institute of Process Development and Research into Peat and Natural Materials) and Christian Winkler, Michael Zocher (Zittau/Görlitz University, Faculty of Electrical Engineering and Computer Sciences) reported, one possibility was shown for solution of the problem. Here a sorting process has been investigated in which the microwave heating ability of plastics is used as a separation criterion. In the continuous belt process, the plastics are first selectively heated in a microwave applicator. Then the temperatures reached by the individual particles are determined in a non-contact process by means of infrared detection. On the basis of these temperatures, the particles are classified in the separation criterion classes and sorted by means of air nozzles into the different fractions.

The “Problems of recycling wind turbines“ were examined by Hans-Georg Jäckel, L. Wuschke (Freiberg University of Mining and Technology, IMB/RM) in their paper. In recent years, the efforts to replace conventional energy generation plants with renewable systems have led to a boom especially in wind power plants (Fig. 16). As they have a lifetime of around 20 years, currently a large number of relatively small and old wind turbines are being replaced with much bigger plants. With regard to the aspect of sustainability, in the assessment of economic efficiency, the problem of dismantling the plants and the cost and effort of recycling should also be taken into account. Besides the actual dismantling costs, this includes especially the recycling and disposal costs for the foundations and rotor vane materials. By way of example, the costs for a WKA E126 (around 6-7 MW) with a height of 200 m, a rotor diameter of 130 m, a concrete foundation of about 6900 t (reinforcing steel 180 t), concrete tower elements 2800 t, turbine building and generator 650 t as well as the rotor (hub and three rotor vanes) 364 t were listed. The recycling of the concrete components is relatively easy with the state of the art, but presents a logistics problem owing to the locations of the wind power plants. Equally, the recycling of the rotor vanes with a mass of 65 t of a multicomposite (steel plate, GFP, CFP, Al tip) is a problem that should not be underestimated. Finally, on the basis of known energy consumptions, for a medium-sized wind power plant, the energy requirement expected for the production of recyclable products was estimated and compared with the gross energy output relative to the lifetime. The result allows a rough assessment of the economic efficiency of wind power plants with consideration of the cost of recycling. According to this, 2/3 of the revenue for the generated power has to be estimated to recover the investment and finance recycling.

4 Process and machine developments

An increasing problem in industrial countries is the problem of the introduction of medicine residues via waste water into the environment. A promising possibility for eliminating these pollutants is oxidation to water and carbon dioxide by means of radiation of the preclarified waste water with UV light in the presence of photocatalysts, e.g. TiO2. Necessary for this, however, is the “Immobilization of TiO2 powders for the photocatalytic after-cleaning of the waste water”, about which Caroline Goedecke, Regine Sojref (Germany’s Federal Institute for Materials Research and Testing in Berlin) informed the attendees (Fig. 17). For the comparative testing of the photocatalytic activity of TiO2 submicron and nanopowders on laboratory scale, methylene blue was chosen as a model substance and the degradation of methylene blue over time under radiation with UV light registered. With regard to the technical utilization of the photocatalytic waste water cleaning, for environmental protection and economic reasons, the immobilization of the powders used with the possibility of recovery is necessary. By means of agglomeration by agitation, granulates on the basis of submicron SiO2 were produced with the addition of an inorganic binder in an intensive mixer. The photocatalytically active TiO2 was added in proportions of 10–25 mass% either to the starting powder or applied at the end of the granulation process as a granulate coating. By means of tempering at 300–500° C, sufficient stability of the granules for use in methylene blue solution in batch processing was achieved. Tests on the use of the SiO2-TiO2 granulates as photocatalysts for the degradation of methylene blue solutions under UV irradiation were successful. It could be shown that the granules following degradation of the dye can be recovered from the solutions, the recycled granulate exhibiting similar photocatalytic behaviour to that of the freshly produced granulate.

As a specialist for industrial comminution systems, Gebrüder Jehmlich GmbH is a company that offers solutions for a wide range of comminution applications. The “Optimization of the design of impact mills for ultrafine grinding of sugar” was the focus of the paper by Raphael Sperberg (Fig. 18), Sebastian Kleinschmidt, Thomas Kleinschmid (Anhalt University of Applied Sciences, Department of Applied Biosciences and Process Engineering, Köthen) and Stefan Jäckel (Gebrüder Jehmlich GmbH, Nossen). For the REKORD 224 mill, the influence of throughput rate and loading rate on the particle size and the specific comminution energy were examined. The fine impact mill used can be fitted with various grinding tools. The particle size distributions were determined by means of laser diffraction (HELOS, Sympatec). On the basis of characteristic diagrams, the results can be summarized, the grinding tools used can be assessed with regard to comminution efficiency, and input values for upscaling the plant engineering as well as optimum operating parameters can be determined. With increasing speed and decreasing mass flow, the particle sizes d50 and d90 tend to decrease for all rotors. The specific comminution energy reaches a maximum at the highest speed and the largest throughput rate. Optimum with regard to energy aspects are lightweight rotors that exhibit a lower comminution energy for the finest possible particle size.

In his paper, Roland Scholl (UVR-FIA GmbH Freiberg) reported on the “Operation of an eccentric vibrating mill in inert conditions for the production of powder products” (Fig. 19). Used in the study were the eccentric vibrating mills (ESM324; ESM654) supplied by the company Siebtechnik in batch operation and in inert gas. This is required for a narrow stress-loading spectrum, long residence times as well as specifications for the application and processing. Physical and chemical reactions can be easily determined with in-situ gas pressure and temperature measurements so that the progress of mechano-chemical reactions can be monitored based on the measured heat tone and any gas reactions. Based on the example of “Direct granulation of powders” and the “Fine comminution of ductile alloy powders”, the special quality of the produced products was explained. At present, at UVR-FIA GmbH a pilot plant is operated, with which product quantities of 50 to 100 kg can be supplied for test purposes. By the end of the year, a fully automatic plant will go into trial operation, which will reach a capacity of 50 to above 100 t per year.

The improvement of the energy utilization in the fine grinding of hard and brittle materials is the preferred objective of development work. With the paper “The new bed roller mill – review and development status”, Fritz Feige (journal CEMENT INTERNATIONAL, Dessau-Rosslau) presented his findings (Fig. 20). In the cement industry, the specific energy requirement for grinding clinker and foundry sand is still relatively high at 30 to 80 kWh/t finished material depending on the type of cement and grinding process applied. According to the author’s findings, the relatively widely used high-compression roller mill operating according to the compaction principle demonstrates very unfavourable operating behaviour. With this mill, the parameters that determine the comminution efficiency, that is the material bed thickness and the grinding force as well as the throughput rate, cannot be adjusted independently of each other. The circumferential speeds of the rollers are limited to around 1.0 m/s and the grinding forces to guarantee a certain load gap with all negative impact on wear and energy consumption must be set much higher than actually necessary. All these disadvantages are avoided with the new horizontal bed roller mill, which consists of two horizontally supported rollers, of which the bigger roller is displaced downwards at a certain angle by means of pneumatic adjustment, fed with a determined material bed and dragged by the power-driven smaller roller in a frictional connection. With a feed proportional to speed, a comminution device configured in this way can be operated at circumferential speeds up to 4.0 m/s and more; it works vibration-free in the entire speed range and, thanks to the existing scraping effect, produces after only one pass a comminuted product with a considerable content of finished material. Since mid-2011, the first horizontal bed roller mill has been used successfully in the double function as an industrial mill for fine grinding of broken glass and test mill for process and machine further development as well as material testing. The mill with roller diameters of 0.75/1,00 m and a loading width of 100 mm, is operated in a circuit with a high-capacity classifier. For a grinding fineness corresponding to a R63 residue of < 25 %, the mill operates at a throughput rate of 4.0 t/h with a specific energy requirement < 10 kWh/t. With grinding forces of 4000 kN/m², the broken glass is comminuted with almost no noise and dust. In the meantime, other mills are being successfully operated for the fine grinding of cement clinker, foundry sand and burnt lime.

5 Process principles

The deflector wheel classifier is of great importance in industrial applications for the separation of fine-grained particle fractions. With the “Visualization of particle movements in a deflector wheel classifier”, on which Christian Spötter, Kurt Legenhausen, Alfred P. Weber (Clausthal University of Technology, Institute of Mechanical Engineering) reported (Fig. 21), new findings on the optimization of the classifier operating principle are expected. A deflector wheel classifier was redesigned to enable optical access to a classifier wheel and recording of the classifying process with a high-speed camera. For demonstration of the gas flow, limestone feed with an x50 of 2.15 µm was used and for elucidation of the particle movement between the blades a feed material with a x50 of around 60 µm was used. It was possible to determine that, depending on the speed, a classifying air flow vortex is formed, which increasingly influences the path of particle movement. The particle flow between the blades is increasingly constricted by the classifier air vortex, which leads to an increased number of particles in the constricted flow and therefore to increased particle-particle and particle-wall interactions. First observations of the periphery of the deflector wheel showed that strands form from the deflected particles and the subsequent feed particles. These strands have an additional screening/filtering effect on the feed material particle fraction flowing into the wheel, which has a further influence on the separation efficiency.

In the paper on “Segregation phenomena in air classification” by Gunnar Kretschmar (Knauf Gips KG), Thomas Mütze, Thomas Leissner (Freiberg University of Mining and Technology, MVT-AT) and Frank van der Meer (WEIR Minerals), information was provided about the classification of heterogeneous material mixes in which the recoverable minerals and tailings exhibit considerable differences in density (Fig. 22). Iron ore samples with different moisture content with the particle size < 315 µm were used as test material. These were characterized extensively not only regarding mineralogy and granulometry with in respect of the binding of the moisture in the material and its effect on the strength of the particles and agglomerates to be classified. As the classifier in the tests, a laboratory deflector wheel classifier 100 MZR (Alpine) was used, which was set to a cut-point of 45 µm. Starting from dried material samples, the feed material was selectively remoistened to 6 mass%. Besides the moisture content of the products as well as the yield of fines as product fraction, the efficiency of the classification was assessed based on the misplaced percentage, cut-point and separation sharpness. An automated mineral liberation analysis (MLA) provided information on the concentration and segregation of the individual mineral phases of the ore in the classified products. Basically, wet feed materials can also be sharply classified in deflector wheel classifiers. Up to a classifier-specific critical value, with increasing moisture of the feed materials, the misplaced percentage, i.e. the percentage of agglomerates discharged unclassified in the coarse material, increases and accordingly the mass yield of fines and the recovery of fine-grained particles decrease. The comparison of results of laser diffraction and the automated mineralogical analysis of the classified products showed the selective comminution of the mineral phases and particularly the overgrinding of the product mineral grains. With this, for the first time, evaluation of the separation of individual mineral phases and a comparison with the classical evaluation based on particle size analysis become possible.

For several years now, grinding in high-compression roller mills has been regarded as an excellent method for grinding clinker in cement plants to the required product fineness. Other possible applications include, for example, the comminution of copper and iron ore, although agglomerates in the form of flakes can be formed. The “Effects of deagglomeration in the particle size analysis of products from high-compression roller mills” were addressed in the paper by Tony Lyon (Freiberg University of Mining and Technology, Institute of Mechanical Engineering, Process and Energy Engineering), Andre Kamptner (UVR-FIA GmbH Freiberg) und Marcel Pfeifer, Felix Heinicke (Köppern Aufbereitungstechnik GmbH & Co. KG). If agglomerates consisting of very fine particles are only insufficiently deagglomerated, the primary particles are classified in the coarser particle sizes in particle size analysis. In the paper, the effect of deagglomeration in fine grinding of iron ore concentrates in a laboratory ball mill on measurement with dry and wet laser diffractometry was studied. The results of air jet and wet sieve analyses were also evaluated. In the paper, Blaine surface area measurement was evaluated, as was the impact of the analysis error on industrial practice in the grinding of iron ore concentrates in high-compression roller mills.

For the dimensioning of silos within the scope of process engineering, besides the characterization of the bulk solids properties, the friction between bulk solids and silo wall are determined. With the paper “Contribution to the characterization of the wall friction angle” by Karl Krüger, T. Mütze, U. Peuker (Freiberg University of Mining and Technology, MVT-AT), new insights were presented on the impact of production-related processes for the silo wall material, e.g. grinding, rolling and surface treatment, on the friction conditions (Fig. 23). The tests were performed with differently modified wheat starch products with a mean particle size of x50 = 35 µm in a Jenike shear cell with variation of the wall material type and roughness. Supported by current research, it could be shown that it is not possible to make any generalized conclusion regarding the dependence between roughness and friction conditions.

6 Poster exhibition and company presentations

At the poster exhibition, some of the subjects addressed in the papers presented at the conference were covered in greater depth in ten posters (Fig. 24). Besides posters from Freiberg University of Mining and Technology and the Helmholtz Institute Freiberg for Resource Technology, posters from Clausthal University of Technology (Institute of Mechanical Engineering), Braunschweig University of Technology (Institute of Particle Engineering), the Leibniz Institute of Polymer Research in Dresden with Loser Chemie, Zittau/Görlitz University of Applied Sciences together with EUROIMMUN Medizinische Labordiagnostika AG as well as the Fraunhofer Institute ICT Karlsruhe were on show. Company presentations were provided by the industry representative of the company Eirich in Jena and Eurofins Umwelt Ost GmbH Freiberg.

7 Summary and outlook

As in the last few years, in 2016 the organizers “Gesellschaft für Verfahrenstechnik UVR-FIA e.V. Freiberg” in cooperation with the “Helmholtz Institute Freiberg for Resource Technology” and “Freiberg University of Mining and Technology” and the staff of UVR-FIA GmbH Freiberg succeeded again in arranging an excellent conference both in terms of content and organization.

The conference leaders for the different subject blocks Dr Kamptner and Dr Morgenroth (UVR-FIA Freiberg), Dr Hermann (Omya GmbH), Prof. Peuker and Dr Mütze (Freiberg University of Mining and Technology, IMV-AT), Dr Rudolph (Helmholtz-Institute, Freiberg) and Prof. Schönherr (Zittau/Görlitz University of Applied Sciences) moderated interesting discussions on the papers. At the poster exhibition and during the breaks, technical discussions could be continued in greater depth (Fig. 25). The convivial get-together of the conference attendees on the first evening at the restaurant Ratskeller in Freiberg also went down well.

The next conference on “Mineral Processing and Recycling” is scheduled for 8 and 9 November 2017 in Freiberg. Organizers are again the “Gesellschaft für Verfahrenstechnik UVR-FIA e.V. Freiberg” in cooperation with the “Helmholtz Institute Freiberg for Resource Technology” and “Freiberg University of Mining and Technology”. Up to the end of July 2017, the organizers are inviting the submission of abstracts for papers, posters and company presentations to the conference organization UVR-FIA GmbH at the internet address www.uvr-fia.de. E-Mail info@uvr-fia.de:info@uvr-fia.de%3C/a%3E">. Via the above-­mentioned internet address, abstracts of the conference papers can also be accessed.

Autor/Author:

Prof. Dr. rer. nat. habil. Hanspeter Heegn

Gesellschaft für Verfahrenstechnik UVR-FIA e.V. Freiberg

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