Peter Carlo Rem

A model for eddy current separation

Abstract We present a model for the motion of particles in an eddy current separation process. The model describes the action of the transient magnetic field of the separator by a first-order linear differential equation for the particle magnetic moment. From the model, qualitative conclusions can be drawn regarding the effects of particle size, shape and conductivity on the particle trajectory. It is also possible to solve the equations of motion for particles of simple shapes by numerical integration. The results of such simulations are compared with experimental data. The aim of the model is to improve the understanding of the behaviour of small particles in eddy current processes in order to optimize separator design and operation.

Upgrading mixed polyolefin waste with magnetic density separation

Polyolefin fractions are often end fractions resulting from the recycling of end-of-life consumer products. Polypropylene (PP) and polyethylene (PE) are present in such fractions as a mixture. For instance, the ratio of PP and PE in car scrap is 70:30 on average. However, the grade of the PP and PE should typically be better than 97% to be reused again as a high quality product. Density separation of the different polyolefins can be a solution. A promising separation technique is the inverse magnetic density separator (IMDS). This paper discusses the potential of shredder residue, one of the possible polyolefins waste stream sources for the IMDS, in detail. Experiments with the separation of polyolefins with an IMDS prototype show both high grade and high recovery. The paper concludes with the economic opportunities of the IMDS in the recycling of polyolefins.

Improved method for prediction of heavy metal recoveries from soil using high intensity magnetic separation (HIMS)

In recent years the soil cleaning industry has developed a number of cleaning strategies mostly based on classification techniques. Sometimes, however, those strategies fail for a number of reasons and as a result cleaning targets are not met. Therefore, some soil cleaning facilities have experimented with HIMS as an alternative process step. This paper describes a prediction method based on magnetic separation techniques for use of HIMS separators in soil cleaning plants. Two types of HIMS separators were used. First a (dry) Frantz isodynamic separator (FIS) and secondly a (wet) Jones high gradient magnetic separator (model P40 KHD and model DP 90 Humboldt Wedag). The FIS was used to separate heavy metals from soil and for observation of heavy metal behaviour in magnetic fields. With the Jones P40, pilot-scale experiments were performed to confirm the FIS results. In total six soil samples uncleanable by soil washing plants and three soil samples prepared by laboratory classification were used in the experiments. Furthermore, three soils were treated on full plant scale. FIS experiments indicated that soils can be distinguished by their different magnetic properties and that each soil shows its own characteristic magnetic susceptibility fingerprint. A similarity, however, was observed between the magnetic properties of soils and the magnetic properties of hematite which is a strong indication for the importance of iron in removing heavy metals from contaminated soil. The Jones P40 experiments showed a similar removal efficiency as the FIS for iron but not for the heavy metals. Soils treated with wet HIMS, however, showed considerably lower heavy metal contents than soils only treated with conventional washing techniques, indicating the usefulness of HIMS in cleaning heavy-metal-contaminated soils. Plant-scale treatment of three polluted soils showed that the Jones separator is a feasible technique for soil washing and treatment of heavy metals.

An innovative recycling process to obtain pure polyethylene and polypropylene from household waste.

An innovative recycling process, based on magnetic density separation (MDS) and hyperspectral imaging (HSI), to obtain high quality polypropylene and polyethylene as secondary raw materials, is presented. More in details, MDS was applied to two different polyolefin mixtures coming from household waste. The quality of the two separated PP and PE streams, in terms of purity, was evaluated by a classification procedure based on HSI working in the near infrared range (1000-1700 nm). The classification model was built using known PE and PP samples as training set. The results obtained by HSI were compared with those obtained by classical density analysis carried in laboratory on the same polymers. The results obtained by MDS and the quality assessment of the plastic products by HSI showed that the combined action of these two technologies is a valid solution that can be implemented at industrial level.

Modelling the throw of metals and nonmetals in eddy current separations

Abstract The trajectories of real scrap particles processed with an eddy current separator are compared to computer simulations to investigate the effects of particle shape and particle–particle interaction, effects that are difficult to catch in a purely theoretical model. The results show that the primary particle parameters are size, conductivity and initial orientation, provided that the size of a particle is defined in relation to the eddy current process. Therefore, the detailed shape of scrap particles is less important. The effects of particle–particle interaction on the grade and recovery can be predicted by considering two different types of collisions between nonferrous and nonmetal particles. This results in a simple theory that can be incorporated into a simulation model.

Eddy Current Separation of Fine Non-Ferrous Particles from Bulk Streams

Recovery of fine non-ferrous metals from waste streams is a notoriously difficult problem in eddy current separation technology. Existing processes either have a low capacity or an incomplete recovery for particle sizes below 5 mm. In a new process, the particles are fed slightly wet to make them stick to the surface of the conveyor belt. The action of the magnet rotor makes the non-ferrous particles tumble, so that they break loose from the belt and end up in front of the rotor. The new process combines a relatively high capacity with an almost complete recovery, even for heavy and poorly conducting non-ferrous metals.

Upgrading of PVC rich wastes by magnetic density separation and hyperspectral imaging quality control

Polyvinylchloride (PVC) is one of the most produced polymers in Europe, with a share of 11% in terms of mass (8 milliontons) of total polymer consumption, but in 2010 only 5% of the total PVC production came from recycled materials, where other polymer recycling achieves a level of 15% on average. In order to find an innovative process to extract PVC from window frames waste, a combination of two innovative technologies was tested: magnetic density separation (MDS) and hyperspectral imaging (HSI). By its nature, MDS is a flexible high precision density separation technology that is applicable to any mixture of polymers and contaminants with non-overlapping densities. As PVC has a very distinctive high density, this technology was tested to obtain high-grade PVC pre-concentrates from window frame waste. HSI was used to perform a quality control of the products obtained by MDS showing that PVC was clearly discriminated from unwanted rubber particles of different colors. The results showed that the combined application of MDS and HSI techniques allowed to separate and to check the purity of PVC from window frame waste.

Simulation of eddy-current separators

A model is presented for the simulation of rotary drum eddy-current separators. The most important part of the model is an improved first-order differential equation for the magnetic moment of nonferrous particles in the field of the separator magnets. The model also includes the mechanical interaction between the particles and the transportation belt, as well as aerodynamic forces. The resulting particle trajectories are compared to experimental data, both on the basis of full trajectories and statistically, in terms of the calculated and measured throw.

The W2Plastics Project: Exploring the Limits of Polymer Separation

The efficient large-scale recycling of plastic waste is of increasing interest from an ecological and economic point of view but it represents a goal that has yet to be achieved by the recycling industry. The W2Plastics project aims at a fundamental change of the present status of plastics recycling by creating a breakthrough technology for the recycling of polyolefins from complex wastes, i.e., wastes such as Waste from Electric and Electronic Equipment (WEEE), Construction and Demolition Waste (CDW), household waste and Automotive Shredder Residue (ASR). Polyolefins are a very important family of polymers, constituting more than a third of the total plastics consumption in Europe (EU) and complex wastes provide the vastest, presently unused potential resource of secondary polyolefins. In spite of that, Polyolefins (PP, LDPE, HDPE) are the least recycled plastics materials. Only one million ton out of 14 million tons yearly sold in EU is being recycled. Nowadays, Polyolefin recyclers focus mainly on the relatively pure post-industrial or single-product wastes, since these wastes can be made into high-purity product materials by existing and cost-effective process technology. Post-industrial wastes are increasingly exported outside the EU, however, and so the Polyolefin recycling industry and their end-users are forced to look for alternative resources. In principle, post-consumer wastes, such as WEEE, CDW, household waste and ASR provide such a resource. They are a five to ten times larger reservoir of polyolefins than do post-industrial wastes, but these wastes are also much more complex mixtures of materials and hence much more difficult to recycle. Technologies that are to address these resources need to be extremely powerful, since they must be relatively simple to be cost-effective, but also accurate enough to create high-purity products and able to valorise a substantial fraction of the materials that are present in the waste into useful products of consistent quality in order to be economical. The European FP7 Project: W2Plastics is developing a number of novel concepts, in particular Magnetic Density Separation (MDS) and Ultrasound process and quality control by HyperSpectral Imaging (HSI), into a new technology to recover high-purity polyolefins from complex wastes at low cost. The unique promise of this new concept derives from its ability to accurately separate many different materials in a single process step, resulting in an environmentally friendly and cheap process.

Aluminium alloys in municipal solid waste incineration bottom ash

With the increasing growth of incineration of household waste, more and more aluminium is retained in municipal solid waste incinerator bottom ash. Therefore recycling of aluminium from bottom ash becomes increasingly important. Previous research suggests that aluminium from different sources is found in different size fractions resulting in different recycling rates. The purpose of this study was to develop analytical and sampling techniques to measure the particle size distribution of individual alloys in bottom ash. In particular, cast aluminium alloys were investigated. Based on the particle size distribution it was computed how well these alloys were recovered in a typical state-of-the-art treatment plant. Assessment of the cast alloy distribution was carried out by wet physical separation processes, as well as chemical methods, X-ray fluorescence analysis and electron microprobe analysis. The results from laboratory analyses showed that cast alloys tend to concentrate in the coarser fractions and therefore are better recovered in bottom ash treatment plants.