Werkstoffliche Aufbereitung von Wärmedämmverbundsystemen

Due to increasing energy requirements for buildings, thermal insulation composite systems (TICS) have been used to insulate building facades since the 1970s. In view of the longevity of these composite materials, there has been an increased amount of TICS waste in recent years. Since there is no current recycling concept for these systems, an enormous resource efficiency potential remains unused. Due to the complexity of composite materials this study focuses on the pretreatment and discusses different processing steps in detail.     

Relining efficiency and liner design for improved plant performance

Liners in grinding mills not only protect the mill shell from the aggressive environment inside the mill, but they also play a significant role in the efficiency of grinding. The design of mill liners dictates the charge trajectory and hence the grinding efficiency. The common approach in designing liners is designing for a longer life. However, this approach does not necessarily consider optimum performance over the liner life. It has been observed in many operations that mills under-perform over a significant portion of the liner life (10–25% of the liner life at the beginning and often 5–10% at the end). This paper extends the method proposed by Toor (2013) and Toor et al. (2013) to design liners for performance through investigating the effect of relining efficiency using such an approach in an industrial case.As indicated in the Toor et al. (2013) study, relining efficiency affects the benefits that can be realised by designing liners for efficiency. Russell Mineral Equipment’s Mill Reline Director (MRD) analyses the relining process and provides an accurate estimation of relining time for a given scenario. In this study, five different relining scenarios were simulated and compared against the reference reline (i.e. current liner design) to accurately estimate the time required for relining. This is the first study to demonstrate that incorporating relining constraints in the liner design can be used to inform liner design characteristics of a proper design that meets the requirements of an efficient relining practice.JKSimMet simulation for the industrial case predicts a liner which has same lifter face angle as the current liner design with reduced lifter height from 300 mm to 210 mm, could increase the plant throughput by 8% on average while producing a product with same P80 as the current liner. Considering relining time predictions by MRD for the proposed liner, this study predicts a 3.7% increase on average in throughput per annum. Although the proposed strategy will increase the cost of liners plus relining by 31.5% (i.e. A$ 548,000), the increase in plant throughput is estimated to yield A$ 20.1 M of additional revenue based on data for 12 months to 30 June 2014 from the plant quarterly report.     

Recycling von marinen Sekundärrohstoffen

As a waste product, oyster shells pose a major environmental pollution problem and the reuse of the material is becoming increasingly important. Since the comminution process in the recycling of secondary raw materials defines the properties of the material, oyster shells were grinded using a planetary ball mill and an impact mill and the fractions obtained were analyzed in terms of size and shape and compared with each other. A comminuted material from the impact mill was used for a series of wetting experiments, which helped to demonstrate the surface free energy of the material.     

Research of iron ore grinding in a vertical-roller-mill

The total energy consumption for ore comminution will further increase within the next decades. One contribution to minimise the increase is to use more efficient comminution equipment. Vertical-roller-mills (VRM) are an energy-efficient alternative to conventional grinding technology. One reason is the dry in-bed grinding principle. Results of extensive test works with two types of magnetite iron ores in a Loesche VRM are presented here. Within these test works, mill parameters like grinding pressure, separator speed and dam ring height were varied, following a factorial design of the experiments. The effects of the grinding parameters on the liberation of valuable minerals are characterised using mineral liberation analysis (MLA). It is shown how the different mill parameters influence important performance values like energy consumption, production rate and mineral liberation. Via multiple regression analysis, an optimal parameter range can be modelled for both ore types. The parameter predictions have been successfully verified in practical test works.     

A specific energy-based size reduction model for batch grinding ball mill

A particle size reduction model has been developed as the first component of an upgraded ball mill model. The model is based on a specific energy-size reduction function, which calculates the particle breakage index, t₁₀, according to the size-specific energy, and then calculates the full product size distribution using the t₁₀–t_n relationships and the mass-size balance approach. The model employs an ore-specific and size-dependent breakage function, whose parameters are independently measured with a fine particle breakage characterisation device, the JKFBC. This has effectively overcome the limitation of using a default breakage appearance function for all ores in the perfect mixing ball mill model. Since the ore-specific characteristics and the machine-related specific energy parameters are mechanistically incorporated in the size reduction model, it has the capability to predict size reduction in response to changes in the ball mill feed breakage characteristics and the operation-related specific energy.     

Effect of port configuration on discharge from a HICOM® mill

The discharge behaviour of different port configurations in a HICOM mill is investigated using DEM simulation. The charge in the mill is strongly sheared and circulates rapidly but has a free surface shape that is constant and which rotates with the mill rotation. The horizontal cross-sectional area of the charge decreases with increasing height. Particles within the mill discharge when the rotating charge flows over and is pushed towards the discharge ports. DEM enables the prediction of transient and steady state mass flow rates from each of the individual discharge ports. Twelve discharge ports at different locations in the mill are used here to explore the optimality of the various size and location options and to explore if there is any interaction in the discharge between adjacent ports. This provides information relevant to the operation of this type of mill, guidance for port selection and provides a general demonstration of how DEM can be used to predict transport and discharge behaviour of mills.     

Reducing the greenhouse gas footprint of primary metal production: Where should the focus be?

The mineral processing and metal production sector is endeavouring to identify opportunities to improve the sustainability of its operations and reduce its greenhouse gas footprint, with improved energy efficiency receiving increased attention. However, if truly sustainable outcomes are to be obtained it is essential that a life cycle approach be adopted in evaluating these opportunities. In this paper, life cycle assessment methodology is used to indicate where in the metal production life cycle this focus on energy efficiency should be and to evaluate a number of potential opportunities for reducing the greenhouse gas footprint of primary metal production.Results from life cycle assessments of the main primary metal production processes, together with current and predicted global metal production rates, ore grades and grind or liberation size, have been used in a broad analysis to indicate that endeavours to improve the energy efficiency of primary metal production should focus mainly on the metal extraction stage, particularly for steel and aluminium. Declining ore grades and more complex ore bodies anticipated in the future can be expected to significantly increase the energy required for comminution of the main metal ores and will present opportunities for improving the energy efficiency of primary metal production. However, these opportunities will still be appreciably less than potential energy efficiency improvements in the extraction stage for these metals.     

The effect of using different comminution procedures on the flotation of Platinum-Group Minerals

The use of High Pressure Grinding Rollers (HPGR) has been widely reported to have major benefits in the treatment of minerals such as iron ore and diamonds. To date there have been few investigations into its use in the treatment of ores containing Platinum-Group Minerals (PGMs). HPGRs are known to reduce energy consumption and wear costs and improve the throughput in the circuit. In the present investigation the effect of the comparative use of HPGR and conventional crushing in combination with either dry or wet rod milling on the flotation of PGMs was studied using batch flotation. Previous studies of a base metal sulphide had shown that either HPGR or conventional crushing followed by dry milling produced the highest grades and recoveries (Palm et al., 2010). However in the present study it was observed that a similar treatment of Platinum-Group Minerals produced the poorest results and the highest grades and recoveries were obtained for the case of conventional crushing in combination with wet milling. The HPGR showed no advantages in terms of flotation performance and dry milling produced particularly poor flotation results.The results were investigated further using various surface characterization techniques in order to determine the reason for the decrease in grades and recoveries of platinum when using dry milling and HPGR as opposed to the case for base metal sulphides. The feed and product samples were analysed using ToF-SIMS, XPS and MLA. The paper will propose reasons to explain the different flotation behaviour of the two ore types following the various comminution processes focusing on the surface characteristics of the ores, the particle size distribution and the pulp chemistry.     

Batch Grinding in Laboratory Ball Mills: Selection Function

The selection functions and the breakage distribution functions are based on the experimentally‐determined particle size distribution on the basis of comminution of one size fraction particles. Therefore, to obtain a clear picture of the product properties during comminution of the “real” polydisperse sample, a number of experiments are needed. This work introduces the tested methodology for the selection function determination based on the starting and maximal values of the selection function. The principle was tested on the planetary ball mill and the horizontal laboratory ball mill, and according to the results obtained, it can be concluded that the proposed methodology can be useful for the evaluation of the selection function during batch comminution in different mills.     

An energy benchmarking model for mineral comminution

A method for determining the minimum practical energy for comminution was developed and is presented in this paper. An objective of the method was to determine experimentally the energy-breakage relationship for a wide size range in order to evaluate the energy performance of both crushing and grinding processes using one energy benchmarking value.Single-particle compression breakage, referred to in the field of comminution as one of the more efficient forms of mechanical comminution, was the basis for a test regimen to characterize the energy-breakage properties of ores. Existing models for impact breakage were found to be valid for single-particle compression breakage when used in a modified form. A key parameter of the adopted model, the threshold energy, was also investigated for three ore types and a range of particle sizes.The energy performance of comminution processes at a Canadian mining operation was determined by comparing the determined minimum practical energy, using the new method, with actual site specific energy requirements. In order to evaluate the energy performance of different crushing and grinding technologies, the proposed energy benchmarking method was used to compare the energy performance of alternative comminution flowsheets.