The traditional annual “Processing and Recycling” conference held in Freiberg on 13 and 14 November 2013 this year achieved a record attendance, with more than 180 participants. The “Alte Mensa” (“Old Refectory”) of the Freiberg University of Mining and Technology in the centre of Freiberg, selected this year for the first time as the event venue, provided excellent conditions for the efficient delivery of twenty-five papers plus thirty posters and company presentations. As in the previous year, the organisers were “UVR-FIA Freiberg” and the “Helmholtz Institute Freiberg for Resource Technology”, with UVR-FIA GmbH Freiberg employees bearing responsibility for preparation of the conference. The central focuses of the event were on current problems in the processing of mineral resources, the recovery of useful materials from recycling processes, and the process-engineering necessary for this.
1 Processing of primary mineral resources
In his opening address, Dr.-Ing. Henning Morgenroth, General Manager of UVR-FIA GmbH, firstly provided an overview of his company’s Research & Development work, complete with up-to-the-minute information on the commissioning of the Niederschlag (in the Erzgebirge mountains) fluorspar-barytes mine and on the preparation plant recently installed at Aue, at which a flotation process is used to recover fluorspar and barytes. The central topic of the technical paper was then the “Preparation of fine-particled lepidolite from Zinnwald”, where investigations have been performed at UVR-FIA GmbH into high-gradient magnetic separation and flotation of lithium concentrates from the deposits in the Erzgebirge in the context of the “Growth nucleus potential – Joint project: Hybrid lithium recovery” funded by the Federal Ministry of Education and Research (BMBF; Project Funding Code: 03WKP18B). A two-stage magnetic-separation process has made it possible to achieve lepidolite yields of a maximum of 65 %, maximum lepidolite contents being 75 %. The flotation experiments were performed both on a laboratory (1 to 5 l agitation cell) and a semi-commercial (100 l agitation cell) scale. Two-stage flotation incorporating roughing and cleaning flotation made it possible to achieve a lepidolite yield of around 90 %, with a maximum lepidolite content of 85 %.
Dr.-Ing. Espig (of the “Technologieberatung Freiberg” consultancy) and co-authors Dr. Morgenroth, Dipl.-Ing. Plate (UVR-FIA GmbH Freiberg), and Dipl.-Ing. Ebert (EFS GmbH, Oberwiesenthal) reported on “Supporting model calculations of the grinding and flotation of a fluorspar-barytes ore” from the Niederschlag mine. Tests for batch-wise grinding, wet-screening and determination of the flotation kinetics were conducted using a sample of ore from these deposits. The data obtained were used for the design of the wet-grinding circuit and of the downstream flotation system. The model calculations for the grinding circuit indicated, for example, that the percentage of poorly floatable particles >150 µm can be reduced to around 5 % if 125 µm screen decks are used instead of the original 150 µm decks. Model calculations for two flotation circuits for the separation of barytes and fluorspar were used for quantitative estimation of mass flows and contents with the highest possible values yield. The results obtained made it possible to provide the flotation-system supplier with detailed design input data.
In their paper “Fundamental investigations into selective separation of extremely fine particle systems using liquid-liquid flotation in the magnetite/quartz system”, Dipl.-Ing. Leistner and co-authors Rudolph (Helmholtz Institute Freiberg for Resource Technology, Department of Minerals Processing), Müller and Prof. Peuker (Freiberg University of Mining and Technology, MVT-AT Institute) perceived new potentials for expanding the range of efficient use of sorting processes in the field of ultra-fine particle systems (0.1 to 10 µm). In this heterocoagulation process (which is similar to flotation), fine droplets of a water-non-miscible non-polar liquid are used instead of air bubbles for the selective extraction of solids particles. The non-polar liquid is isooctane. Selective accumulation of the solids particles on the isooctane/water phase boundary, and transfer to the isooctane phase, were studied and quantified as a function of selected process parameters, such as the pH of the aqueous suspension and the addition of surfactant substances.
Not only optimisation of the mechanical properties of green and dried pellets, but in many cases also the behaviour of the agglomerates during a subsequent thermal hardening process, are of interest in the development of formulations for the pelletisation of ores, industrial minerals and secondary resources. Dipl.-Ing. Michael Lanthaler and Dr. Böhm (University of Leoben, Austria) reported on the “Development of a test facility for drying and firing of iron-ore pellets”. The type and quantity of binder, the influence of the energy source (coke) in the pellet, and questions concerning phase transitions as a function of the plot of temperature against time, play an important role here. Since drying cabinets and muffle furnaces are not suitable, an apparatus containing a bed of pellets, through which hot gas flows, was developed for sample masses of up to around 3 kg per test. In addition to industrial heating-up rates with simultaneously high waste-gas volumetric flows and defined waste-gas compositions, the targets included good test-condition and test-result repeatability.
“Selective comminution for preconcentration in ore preparation” is being investigated by Dipl.-Ing. Hesse and Prof. Lieberwirth (Freiberg University of Mining and Technology – Institute of Mineral Process Machines) as a method of removing from the previously prepared ore the fraction for which further processing would not be economically justifiable. The differing comminution behaviour of the various constituents of an ore are to be exploited in this context to raise the content of them in various particle fractions of the comminution product. Electrodynamic disintegration is considered a promising process for selective comminution along the particle boundaries. The difference between the product to be defibered and the cubically fracturing reject minerals is exploited particularly efficiently in impact loading in dry mineral-fibres preparation.
Dipl.-Ing. Reichert also reported on the work of the Institute of Mineral Process Machines at the Freiberg University of Mining and Technology, and specifically on “Experience in comminution of ore using a Loesche mill”. This paper examines the results of comminution tests using a roller mill specifically designed for the grinding of ores. The investigations are part of a co-operative project with Loesche GmbH. Roller mills permit the achievement of high throughput rates, and also possess operational advantages. Optimisation of the mill for important target variables, such as specific energy requirement and degree of liberation for a number of different ores, were examined.
The use of sensor-assisted sorting systems in the field of minerals and ore sorting has increased greatly in recent years. A range of extremely diverse technologies, such as near-infrared spectroscopy, greatly differing camera systems, X-ray transmission and X-ray fluorescence, for example, can be used for identification of the various minerals and ores. Ing. Berghofer (BT-Wolfgang Binder GmbH, Gleisdorf/Austria) spoke on the relatively new technology of “Sorting of minerals using REDWAVE-XRF (X-ray fluorescence analysis)”, in which both qualitative and semi-quantitative analysis of the material to be sorted are also performed. This technique can, for example, be used for the sorting of iron ore, the removal of undesirable extraneous compounds in ores, for the sorting of manganese ore, and also with great versatility in an extremely wide range of industries and for the most diverse materials (glass, metals, plastics, ores, etc.).
The results of a multi-year co-operative research project into the “Sensor-assisted sorting of industrial minerals in the UV/VIS/NIR wavelength range” were examined by Dipl.-Ing. Huber (Binder+Co AG, Gleisdorf/Austria) and Weingrill (Chair of Mineral Processing, University of Leoben, Austria). Mineral-specific absorption properties in the NIR range and UV-induced fluorescence obviously open up a wider spectrum of applications for this sorting technology. Sorting of talcum and magnesite, for which a significant increase in process efficiency has been attained, was cited as a specific example.
Dr. Kutschke, Dr. Raff and Dr. Pollmann (Helmholtz Institute Freiberg for Resource Technology) provided an overview of “Microbiological processes in hydrometallurgy”. Attention was drawn, in particular, to the bioleaching of sulphidic ores by means of Acidithiobacillus sp., which is operated on an industrial scale in Chile. Biological components, such as phages, for instance, which react specifically with metal ions, or can be modified in hydrophobised form to meet the requirements of flotation by means of variations of the phage surface, can also be used for sinks/floats separation and precipitation processes.
2 Trends in mechanical process-engineering
Dr.-Ing. Coppers and Ing. Spiegelberg (Siebtechnik, Mülheim), after short theoretical observations concerning the jigging process, provided examples of the use of jigs, and information on the mineral-processing machines manufactured by Siebtechnik, in their address entitled “Pulsator jigs – important components in wet-preparation systems for mineral resources and excavated/recycled materials”.
In a paper entitled “New developments in hydrocyclone technology: 3-way functional principle versus 4-way”, Dipl.-Ing. Bräumer (mbb, Bendorf) discussed original solutions in the field of hydrocyclone systems. Feed into the hydrocyclone takes place tangentially and under pressure. Particles coarser than the cut-off are thrust by the high centrifugal forces thus generated into the primary eddy and then migrate downwards along the inner wall to the underflow nozzle. In a three-way hydrocyclone, this is located centrally, whereas it consists in a four-way hydrocyclone of a tangential outlet, with a counterflow inlet located on the central axis. This configuration makes it possible to improve the separation selectivity of the hydrocyclone and, in particular, to reduce the undersize content in the coarse fraction extracted in the underflow. A further benefit of the four-way hydrocyclone can be found in the fact that a pump stage can be omitted in multi-circuit systems.
“Specimen uses of mechanical screens for grading in the bulk materials and recycling industries” were examined by Dipl.-Ing. Landsmann (Rhewum GmbH, Remscheid). This address reported on successful solutions and specimen applications for a range of screening tasks from various sectors of the bulk-materials and recycling industries, such as the screening of wood flour for the production of floor coverings, anode coke, abrasives, high-purity KCl for the foodstuffs industry, and cat litter.
“New developments in the field of screen decks for fine wet and dry screening”, with a focus on Derrick’s polyurethane screen decks, were examined by Dipl.-Ing. Bruder (Hirschau). Totally new perspectives can be opened up in the preparation of ores and minerals using screen decks for wet screening up to 45 µm and dry screening up to 104 µm.
Results of basic research into “The elastoplastic deformation behaviour of product beds” were the subject of the address by Dr.-Ing. Mütze (Freiberg University of Mining and Technology, MVT-AT Institute). Examples of the compaction behaviour of polydisperse and tightly graded limestone, silicon carbide, glass-bead and quartz fractions, and also of bimodal mixed fractions, were cited to investigate in more detail elastic resilience, in particular, and the factors influencing it. An exemplary description of the purely plastic deformation of product beds was then derived from this. The size-range encompasses fine-particled product beds of between 1 μm and 1000 μm, the breadth of size-distributions (x90/x10) a range of 1 to 1000, the loading rate 0.05 to 30 cm/s. It became apparent that up to 15 % (and up to 35 % in extreme cases) of the energy imparted are stored in the elastic stress field of a product bed.
Prof. Fürll and Dr. Hoffmann (Institute of Agricultural Engineering Potsdam-Bornim) spoke on the “Evaluation of the rheological properties of bulk materials citing the example of comminuted cereal product”. Jenike’s criteria, tried and proven for mineral products, were validated for their applicability to comminuted cereals; the influence of product density and the correlation between flowability and the geometry of the extraction aperture were studied, in particular. The results permit the conclusion that Jenike’s recommendation of the use of the minimum necessary aperture geometry as a measure of flowability is relevant for scientific and practical observations.
Author: Prof. Dr. habil. Hanspeter Heegn, Freiberg