CUPRUM – Czasopismo Naukowo-Techniczne Górnictwa Rud nr 2 (75) 2015, s. 5-14 ___________________________________________________________________________ 5 Improved Particle Liberation by High-Velocity Comminution – the new VeRo Liberator ® Gregor Borg 1,2) , Felix Scharfe 1) , Andreas Kamradt 2) 1) PMS, Hamburg, Germany, [email protected]2) Economic Geology and Petrology Research Unit, Martin Luther University Halle-Wittenberg, Germany, [email protected]Abstract The new VeRo Liberator ® has been recently developed by PMS, Hamburg, Germany, and represents a highly efficient impact crushing system for dry comminution of ore, slag, armoured concrete, and aggregate in the 100 t per hour throughput class. The VeRo Liberator® operates with a vertical axle-in-axle system, which is equipped with a total of up to 144 hammer tools, each approximately 90 cm long. The hammer tools rotate on three levels clockwise and anticlockwise against each other at high rotation speeds. The gravitational flow of the material through the machine results in a very low energy consumption. The multiple high-velocity impacts of the tools inflicted on the material achieve unparalleled reduction ratios of up to more than 400 without clogging the system. The VeRo Liberator ® achieves also an unusually high degree of particle liberation. Intergranular breakage is the predominant form of particle separation and is caused by the high velocity impacts, inflicted by the hammer tools, casing, and particles on each other. Apparently, the shock waves travelling through the impacted material stimulate the particles to react individually according to their elasticity “E” and compressibility “K” moduli. The specific “reaction” of the various shock-stimulated particles leads apparently to the pronounced intergranular breakage, separation, and thus particle liberation. Key words: VeRo Liberator ®, comminution, reduction ratio, particle liberation Poprawa uwolnienia ziaren dzięki rozdrabnianiu z wysoką szybkością – nowy VeRo Liberator® Streszczenie PMS, Hamburg, Niemcy opracował ostatnio nową maszynę VeRo Liberator®. Jest to wysoce efektywny, system kruszenia udarowego do rozdrabniania na sucho rud, żużla, zbrojonego betonu i kruszyw, o zdolności przerobowej rzędu 100 Mg/h. VeRo Liberator® posiada pionowy system oś-w-osi, wyposażony w młotki, w ilości do 144 i o długości ok. 90 cm każdy. Młotki, obracające się z wysoką szybkością w kierunku zgodnym i przeciwnym do ruchu wskazówek zegara, zamontowane są na trzech poziomach osi. Kierunek obrotów dwóch sąsiadujących ze sobą poziomów jest przeciwny. Materiał przepływa przez maszynę grawitacyjnie, co skutkuje bardzo niskim zużyciem energii. Wielokrotne, zachodzące z dużą szybkością, uderzenia młotków o materiał zapewniają nieporównywalnie wysoki stopień rozdrobnienia, wynoszący ponad 400, bez zatykania systemu. The VeRo Liberator® zapewnia również nadzwyczaj wysoki stopień uwolnienia ziaren. Dominując formą separacji ziaren jest pęknięcie międzyziarnowe, wywołane wysoką szybkością uderzania przez młotek, obudowę oraz jednych ziaren o drugie. Najwidoczniej fale udarowe, przemieszczające się
Transcript
CUPRUM – Czasopismo Naukowo-Techniczne Górnictwa Rud
nr 2 (75) 2015, s. 5-14 ___________________________________________________________________________
5
Improved Particle Liberation by High-Velocity Comminution – the new VeRo Liberator®
Gregor Borg1,2), Felix Scharfe1), Andreas Kamradt2)
1) PMS, Hamburg, Germany, [email protected] 2) Economic Geology and Petrology Research Unit, Martin Luther University Halle-Wittenberg,
Abstract The new VeRo Liberator® has been recently developed by PMS, Hamburg, Germany, and represents a highly efficient impact crushing system for dry comminution of ore, slag, armoured concrete, and aggregate in the 100 t per hour throughput class. The VeRo Liberator® operates with a vertical axle-in-axle system, which is equipped with a total of up to 144 hammer tools, each approximately 90 cm long. The hammer tools rotate on three levels clockwise and anticlockwise against each other at high rotation speeds. The gravitational flow of the material through the machine results in a very low energy consumption. The multiple high-velocity impacts of the tools inflicted on the material achieve unparalleled reduction ratios of up to more than 400 without clogging the system. The VeRo Liberator® achieves also an unusually high degree of particle liberation. Intergranular breakage is the predominant form of particle separation and is caused by the high velocity impacts, inflicted by the hammer tools, casing, and particles on each other. Apparently, the shock waves travelling through the impacted material stimulate the particles to react individually according to their elasticity “E” and compressibility “K” moduli. The specific “reaction” of the various shock-stimulated particles leads apparently to the pronounced intergranular breakage, separation, and thus particle liberation.
Key words: VeRo Liberator ®, comminution, reduction ratio, particle liberation
Poprawa uwolnienia ziaren dzięki rozdrabnianiu z wysoką szybkością – nowy VeRo Liberator®
Streszczenie PMS, Hamburg, Niemcy opracował ostatnio nową maszynę VeRo Liberator®. Jest to wysoce efektywny, system kruszenia udarowego do rozdrabniania na sucho rud, żużla, zbrojonego betonu i kruszyw, o zdolności przerobowej rzędu 100 Mg/h. VeRo Liberator® posiada pionowy system oś-w-osi, wyposażony w młotki, w ilości do 144 i o długości ok. 90 cm każdy. Młotki, obracające się z wysoką szybkością w kierunku zgodnym i przeciwnym do ruchu wskazówek zegara, zamontowane są na trzech poziomach osi. Kierunek obrotów dwóch sąsiadujących ze sobą poziomów jest przeciwny. Materiał przepływa przez maszynę grawitacyjnie, co skutkuje bardzo niskim zużyciem energii. Wielokrotne, zachodzące z dużą szybkością, uderzenia młotków o materiał zapewniają nieporównywalnie wysoki stopień rozdrobnienia, wynoszący ponad 400, bez zatykania systemu. The VeRo Liberator® zapewnia również nadzwyczaj wysoki stopień uwolnienia ziaren. Dominując formą separacji ziaren jest pęknięcie międzyziarnowe, wywołane wysoką szybkością uderzania przez młotek, obudowę oraz jednych ziaren o drugie. Najwidoczniej fale udarowe, przemieszczające się
6 G. Borg, F. Scharfe, A. Kamradt, Improved Particle Liberation…
przez rozdrabniany materiał, stymulują indywidualną reakcję, zgodnie z jego modułem sprężystości „E” i ściśliwości „K”. Specyficzna reakcja różnych ziaren stymulowanych udarem prowadzi najwidoczniej do pogłębionego międzyziarnowego pękania, separacji i – w rezultacie – do uwolnienia ziarna.
Słowa kluczowe: VeRo Liberator ®, rozdrabnianie, stopień rozdrobnienia, uwolnienie ziarna
Introduction Comminution in the form of crushing and grinding is well known to be the biggest or at least among the biggest single cost factors in mining and mineral processing. Recently, Napier-Munn [2] has phrased his surprise that – over the last few decades – relatively little attention has been paid to substantial innovation and optimization of the techniques involved. This involves both comminution efficiency as well as energy consumption and thus highly substantial reductions cost in costs and environmental impact.
An innovative engineering start-up company, PMS GmbH, based in Hamburg, Germany, has developed the VeRo Liberator®, a comminution machine with a high potential to solve several efficiency issues at the same time. The VeRo Liberator® (patents pending) is a dry-crushing system with very low energy consumption and achieves impressive reduction ratios between 200 to > 480 in a single pass. Thus the VeRo Liberator® is capable, in some mineral processing circuits, to replace several comminution stages. The VeRo Liberator® is suitable for primary ores of sulphides, silicates, carbonates and oxides, slags from metallurgical smelters, power plants, and waste incinerators as well as armoured concrete and other heterogeneous solid materials.
Fig. 1. The VeRo Liberator® with feeding funnel and conveyor belt fitted in the foreground
Besides featuring impressive reduction ratios, the VeRo Liberator® achieves also a particularly high degree of particle liberation. This is caused by high velocity impacts of the hammer tools inflicted onto the ore particles. Apparently this leads preferentially to inter-particle breakage rather than cross-particle fractures, the latter causing both incomplete particle liberation and high percentages of middlings [4, 3].
G. Borg, F. Scharfe, A. Kamradt, Improved Particle Liberation…
1. Equipment Parameters The new VeRo Liberator® is a machine in the 100 t per hour throughput class. The machine has been built in a modular fashion and is thus easy to transport, assemble, or modify according to customer’s demands. The main feature is a vertical axle-in-axle system, which carries a total of up to 144 hammer tools of approximately 90 cm radius. These hammer tools are mounted individually on three separate levels, which rotate clockwise and anticlockwise against each other at high speeds; causing high-velocity impacts. The material falls gravitationally through the cylindrical armoured comminution chamber, where it is impacted by the hammer tools and impacts onto the armoured housing and other particles. The maximum size of the feed for the VeRo Liberator® is 120 mm in diameter. Depending on the input material and the process in mining, mineral processing, or recycling, this could be material from a primary crusher or could replace the primary crusher itself. Reduction ratios in classical dry crushing are generally small and typically range between three and six in a single crushing stage [3]. More innovative single level impact crushers and hammer mills reach reduction ratios as high as 40 to 60 (pers. comm. Prof. Dr. Holger Lieberwirth, Managing Director Institute of Mineral Processing Machines, TUBA Freiberg, Germany). The reduction ratio of the VeRo Liberator is fundamentally larger and can exceed even the value of 450. This has, for example, been achieved on bulk ore samples of massive sulphide ore from Rio Tinto, Spain, where an ore feed of 120 mm diameter has been reduced in a single pass to 94% diameter of less than 250 µm, thus representing an impressive reduction ratio of 480.
Technically, the equipment is easy to maintain since the housing can be lifted hydraulically and the entire drive shaft/tool unit can be lifted from the main frame easily. This allows the quick exchange with another drive shaft/tool unit or alternatively the replacement of individual tools. The precise determination of the energy consumption (Bond work index) of the VeRo Liberator® is currently being prepared, but from the maximum material throughput of 100 t/h and the maximum energy consumption of all four electrical motors; the calculated maximum consumption is in the range of 230 kWh and thus highly energy efficient. It goes without saying that various feed solutions, e.g. conveyor belts etc. and output solutions, e.g. sorting and filter systems can be added easily due to the modular construction concept.
2. Case Studies of Test Material and Comminution Results The VeRo Liberator® has been tested on a wide variety of bulk samples of ores and slag in order to test and document the performance and efficiency and to optimize the process and equipment in a continuous technical improvement. To date, test materials from 9 industrial suppliers have been treated (Table 1). Additional materials that are currently tested are bulk samples from the famous Kupferschiefer, i.e. black shale-hosted copper-lead-zinc ore from the Mansfeld-Sangerhausen Mining District, Germany. These bulk samples are from historical low grade ore dumps and from an abandoned underground mine, the Röhrig Shaft at Wettelrode, Central Germany. These samples will be treated within the German-French-Polish research project Ecometals, which aims to develop innovative bioleaching processes, but will also try to identify alternative and more efficient comminution techniques such as the VeRo Liberator®. The samples are typically in the order of
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one big bag or four to six 200 l drums. It is important to note that each material has been disintegrated by a single pass through the VeRo Liberator®. All materials have been characterized mineralogically, geochemically, and granulometrically both prior and subsequent to comminution by the VeRo Liberator®. The granulometric grain size distribution has been determined by standardized sieve analysis according to the German Industrial Standard DIN 66165. The feed materials have been studied mineralogically, both macroscopically as well as by light and scanning electron microscopy (SEM) on standardized polished thin sections. The comminution products, i.e. the different sieve fractions, have been additionally analysed by hand-held XRF analysis (Niton XL3t 900 He). These analyses revealed how the commodity metals are distributed within the separate grain size fractions.
Brief summaries of the results of the scientific investigation of all feed and output materials are available on the VeRo Liberator® website www.veroliberator.de. More detailed and comprehensive factsheets for each treated material can be made available upon request from [email protected].
Table 1. Suppliers and characteristics of ores and slag as test materials for comminution by VeRo Liberator®
Operational Unit, Owner, Country Type of Material
Pyhäsalmi Mine Oy (Finland) INMET Mining Corp. (Canada) – now First Quantum Mining (Canada) Pyhäjarvi (Oulu, Finland)
Polymetallic massive sulphide ore (pyrite, sphalerite, and chalcopyrite) in silicate gangue matrix
Minas de Aguas Teñidas SAU MATSA Trafigura Mining Group Almonaster la Real (Huelva), Spain
VHMS/SHMS massive sulphides. Complex and extremely finely intergrown pyrite, sphalerite, and chalcopyrite in metavolcanic and metasedimentary gangue
Rio Tinto Mine, Huelva, Spain EMED Tartessus Mining (Huelva, Spain)
VHMS/SHMS massive sulphides (pyrite, chalcopyrite, and silicate gangue)
AURUBIS AG Base Metal Smelter Lünen (Germany)
Anode smelter slags
Clara Mine, Black Forest (Germany) Sachtleben Bergbau AG (Germany)
Spatial constraints of this paper do not allow full descriptions of all tested materials and the outcome of the comminution process by VeRo Liberator®. The comminution results of Cu-rich base metal massive sulphide ore from the famous Rio Tinto Mine in Spain (Fig. 2) thus serve as an exemplary case study. Pyrite represents the main ore mineral in the massive sulphide ore and builds up xenomorphic masses of pyrite, fractured intensively, with polymorphic texture. The fractures have been caused, assumedly, by brittle deformation and were subsequently filled by anhedral intergrown aggregates of chalcopyrite and sphalerite that, in turn, enclose euhedral to subhedral secondary cubic pyrite crystals up to 0.5 mm in diameter. Where in direct spatial association with vein fillings, the primary pyrite shows partially embayed crystal surfaces caused by resorption by the ore mineral parageneses precipitated from hydrothermal Cu- and Zn-rich fluids. Thus, chalcopyrite and sphalerite are typically found as fillings of cracks and interstices. Rare galena is also found amongst the sulphide ore minerals and the gangue minerals comprise phlogopite and quartz. Some portions of the cracks have been replaced, in turn, by iron oxihydroxides, caused by partial oxidation and weathering of the ore.
Fig. 2. Chalcopyrite-rich massive sulphide copper ore from Rio Tinto Mine, Spain, as feed for comminution by a single pass through the VeRo Liberator®
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Fig. 3. Scanning electron microscope (SEM-BSE) image of the 63-125 micron fraction of Rio Tinto massive sulphide ore after comminution by VeRo Liberator®. Chalcopyrite, and
pyrite ore particles (white) have been perfectly liberated from silicate gangue minerals (grey) along their mineral boundaries
After the single pass comminution through the VeRo Liberator®, the massive
sulphide ore particles display a very high degree of particle liberation (Fig. 3). The ore and gangue particles have disintegrated and have particularly separated along grain boundaries by inter-granular fracturing. Particles of still intergrown and thus incompletely liberated ore and gangue minerals do not occur. Various silicate gangue minerals (e.g. quartz and phlogopite), however, are still complexly intergrown with each other but not with sulphide minerals (Fig. 3).
This implies that the mineral-specific physical parameters, that characterize the various silicate gangue minerals, are relatively similar and thus do not lead to physical liberation and separation from each other. The significantly different physical mineral properties between gangue (silicate minerals) and ore minerals (pyrite, chalcopyrite, sphalerite, and minor galena) have apparently caused the high degree of ore particle liberation by inter-granular breakage.
Some of the liberated sulphide ore minerals in this ore, but also in other ores treated, display mineral surfaces with a marked micro-roughness. This micro-roughness might be an additionally favourable feature in subsequent mineral processing stages such as froth flotation and solvent extraction due to a significantly increased reactive mineral surface. Further test work on the possibly improved hydrometallurgical processability of VeRo Liberator®-treated materials is needed for a more thorough understanding of these phenomena.
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Fig. 4. Grain size distribution curve of copper-rich massive sulphide ore from Rio Tinto Mine, Spain, after comminution by a single pass through the VeRo Liberator®. Note that the mill-
feed had a diameter of 100-120 mm.
The granulometric sieve curve of the processed massive sulphide ore (Fig. 4) documents an impressive reduction ratio. After a single pass, the particle size of the processed ore is 98% smaller than 0.5 mm and 94% smaller than 250 µm. Taking into account that the feed material had particle sizes between 100 mm and 120 mm, this result accounts for reduction ratios between 200 and 480. These results define a completely new class of comminution efficiency.
3. Working Principle and Conclusions The new VeRo Liberator® offers a number of innovative and highly efficient features, which are due its technical layout and unusual working principle. Energy consumption is very low, mainly due to the fact that the comminution material falls gravitationally through the VeRo Liberator® and that the number of impacts is tripled due to the anticyclical rotation of the three tool levels. The system can operate in a dry state, i.e. without added process water and, as a consequence, water consumption is not an issue and can thus save valuable resources. Another special feature of the VeRo Liberator ® is the extremely low operational noise level, although detailed decibel measurements still need to be carried out.
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Probably the most important innovative features of the VeRo Liberator® are the extreme reduction ratios (up to > 480) and the high degree of particle liberation. As shown by the various test materials, the fracture separation of different particles occurs predominantly along particle boundaries. This avoids that fractures cross-cut particle boundaries of various materials at high angles, which is a major cause for incomplete particle liberation [4] in classical comminution systems such as ball mills (Fig. 5 A and B). Incomplete particle liberation, in turn, is a major cause for subsequent inefficient separation and extraction by processes such as froth flotation and solvent extraction.
A
B
Fig. 5. A) Compressive fracture formation in classical comminution systems. B) Fracture orientation across particle boundaries, leading to incomplete liberation.
It goes without saying that it is far easier to describe the improved communition results achieved be the VeRo Liberator® than to explain the working principle in detail. Rock mechanical uniaxial stress tests are currently carried out to test our present working hypothesis on how the VeRo Liberator® achieves these impressive results. According to our model, the high velocity impact that is inflicted by the rotating hammers tools onto the inhomogeneous solid material (ore or slag) sends a high velocity shock wave through the material (Fig. 5A).
The various components (particles or minerals) that are stimulated by the seismic shock wave react differently to this stimulation according to their individual petrophysical properties (Fig. 5B). These are primarily the compressibility modulus (“K”) and the elasticity modulus (“E” or “Young’s modulus”) of heterogeneous solid materials. The different particles thus react in their individual “manner” and orientation within the heterogeneous material. This differential behaviour results in inter-granular stress, particularly along the particle boundaries [1], which eventually leads to breakage and formation of fractures, preferentially along these particle or mineral boundaries. The breakage, separation, and liberation preferentially along particle boundaries are due to either dilatation (extension) (Fig. 5C) or inter-granular shearing. Thus, the material separates virtually in all three spatial directions (Fig. 5D), which is rather different from the typical mechanisms of predominantly compressive deformation, e.g. in classical ball mills, that leads to extensional fracture development parallel to the direction of sigma 1.
G. Borg, F. Scharfe, A. Kamradt, Improved Particle Liberation…
Fig. 5. Schematic illustration of the proposed working principle of high-velocity
comminution by the VeRo Liberator®. A) High-velocity impacts inflicted on inhomogeneous material (e.g. ore, slag, armoured
concrete) by rotating hammer tools send shock waves through the material. B) The various particles react differently according to their specific compressibility and
elasticity moduli. C) This results in tensional and/or shear stress between different particles and eventually leads to inter-particle breakage along particle boundaries from
either extensional separation or shearing. D) The result is a predominance of inter-granular, rather than intra- or cross-granular fracturing, which leads to the observed high
degree of particle liberation
Ongoing rock mechanical uniaxial compression test work indicates that dynamic loading appears to simulate best the internal shock wave stimulation of heterogeneous materials. Initial results show that this dynamic loading results in breakage at significantly lower stress levels compared to breakage under static loading conditions. However, further research in the field of rock mechanics is necessary to gain a better understanding of the highly efficient working mechanism of the VeRo Liberator®.
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The staff of EMED Mining’s Rio Tinto Mine, Spain is gratefully acknowledged for generously supplying ore for test work with the VeRo Liberator®. We thank Christof Lempp, Rock Mechanics Group, Institute for Geosciences and Geography at Martin Luther University Halle-Wittenberg for valuable comments and discussions on the working principle of the VeRo Liberator®. Nick Wilshaw, Grinding Solutions, Truro, UK, and Christian Cymorek, H.C. Starck, Goslar, Germany are acknowledged for valuable discussions. The test work on samples of Kupferschiefer ore is carried out as part of the German-French-Polish Ecometals project, funded by the German BMBF and the French ANR with generous logistical support by KGHM Polska Miedz, Poland.
References
[1] Lempp Ch., Natau A., Friz-Töpfer A., Althaus E., 1992, Die Zusammensetzung von Gesteinsfluiden und ihr Einfluß auf das Festigkeitsverhalten von Gesteinen bei erhöhten Drücken und Temperaturen. (The composition of rock fluids and their influence on the strength behaviour of rocks under increased pressures and temperatures.) Sonderforschungsbereich 108 Spannung und Spannungsum-wandlung in der Lithosphäre, Berichtsband 1990-1992 Teil B, Projekt D5, p. 823-898, Universität Karlsruhe.
[2] Napier-Munn T., 2014, Is progress in energy-efficient comminution doomed? Minerals Engineering, 73, pp. 1-6.
[3] Wills B.A., K. Atkinson, 1993, Some observations on the fracture and mineral assemblies. Minerals Engineering, 6 (7), pp. 697-706.
[4] Wills B.A., T.J. Napier-Munn, 2007, Will’s Mineral Processing Technology. Butterworth-Heimann/Elsevier, 7th Edition, 444 p.
