FINEST Disperse Metals

Introduction

Sub-project 3 develops and demonstrates mixed mineral/plastic waste recycling value chains by combining pyrolysis of mechanically pretreated demolition ETICS with minerals calcination to maximize both, utilization of organic and inorganic as secondary industrial feedstock. Main achievement is a ready-to-transfer demonstration of the generic value chain at TRL 5 level, making use of the pyrolysis pilot plant and the new “R-Zement” calcination pilot plant at KIT. We will evaluate toxicological risk of waste feedstocks, intermediate and recycled materials and develop a networked concept for waste ETICS.

The research objectives of the overall project are summarized as follows: how fine-grained residues from various sources can be processed through cleaning, separation, and blending in order to recov-er more valuables with a special focus on their refinement, and to generate inert residues in an eco-nomically viable and ecologically benign way.
Fine and very fine-grained residues are produced in significant quantities in almost all industrial cycles and are characterized by an enormous variety of chemical and physical properties. For all material flows that cannot be returned to the technological cycles, these properties are only known to the ex-tent that they represent relevant information for safe disposal. However, this is only one of the signif-icant hurdles in solving the problem.
Two classes of materials will serve as representative targets that both represent the overall aim of the project and, if the research and transfer parts are successfully implemented, will have a clearly meas-urable economic and environmental impact towards the United Nation’s Sustainable Development Goals [84] as well as the almost identical EU sustainability goals in different industrial sectors.
Material class 1 covers shredder fines from end-of-live vehicles (EoLVs) [72] and material class 2 includes fine-grained and ultra-fine-grained non-recyclable residual materials from non-ferrous metallurgy [16] that are often summarized under the term flue dust.
Despite increasing reuse/recovery/recycling rates [23, 52, 72] of the end-of-life products or the dusty phases used as intermediate products, which in some cases exceed 90 %, these are very substantial material flows, some of which have a very high valuable material content, which are currently not re-turned to the industrial cycle. Their landfilling has to be carried out mainly in compliance with strict conditions with high technological and financial expenditure due to minimizing environmental risks.
All these materials are characterized by their fineness combined with high metal contents. Due to the anthropogenic character, the metals are present either directly in the metallic state as alloys or in non-silicate and non-sulfide compounds. As a result of the technological processes, very small particles with high surface areas are present. The resulting reactivity on the one hand complicates the handling of the materials, but on the other hand it is also an advantage in principle for the material (re)use, which should not be underestimated.
Shredder Fines
The shredding of recycled material essentially serves to reduce the volume and, to a lesser extent, to improve the degree of liberation of the individual components. Applied processes and techniques [72] always produce a fine-grained fraction (by definition 0-20 mm) [31], which is essentially removed by screening and filtering techniques [72] and then deposited. Globally, the annual generation from end-of-life vehicle shredding alone is estimated at about four million tons, largely split between the regions of Europe and the U.S., with a relatively small proportion coming from Asia [30]. The compo-sition of these materials essentially mirrors the composition of the class of materials referred to as shredder residues (SR). SR normally contains plastics, textiles, metals and glass. It is considered a hazardous waste [1] due to its contents of toxic substances such as heavy metals, polychlorinated biphenyls (PCBs) and brominated flame retardants (BFRs) [29, 53, 54, 68, 90].

Even as advanced treatment processes are targeted to enable further recovery of metals, plastics and rubber from the coarser fractions of shredder residues, fine and ultra-fine-grained shredder waste continues to be disposed of around the world. It has been proven by numerous studies [52, 53] that the particles from this fraction are very often material composites. The selective dismantling of end-of-life vehicles by robot-assisted processes, which is expected to increase significantly in the future, will lead to better pre-separation of the components and thus to a reduction in material composites. However, this development will be counteracted by the increasing use of adhesive bonding technolo-gy in the automotive industry [see Figure 13].
This heterogeneity combined with the small grain size represent the main factors that make valorisa-tion (defined as upgrading and recovery) technically challenging and economically unattractive [24]. Political regulation, especially in Europe, has gradually increased the pressure for shredder fines re-covery. Under the safe assumption that shredder fines account for about 70 % of shredder residues [14], recovery will be the decisive factor in the fulfilment of the EoLVs directive targets of 95 % re-covery and 85 % recycling [4].
Overall, it can be concluded that the current scientific knowledge regarding the material characteristics is anecdotal and not representative. It is estimated that in the last decades several hundred kilograms of shredder fines have been analyzed exclusively from European sources compared to the annual production of about 1 million tons. The research in process development is mainly focused on labora-tory scale tests. Very few studies were conducted at pilot scale and one process was studied at in-dustrial scale [47].
Flue dusts
Residues of Non-Ferrous Metals industries
A significant proportion of these fine-grained and ultra-fine-grained materials is recycled using the metallurgical production process. This requires a relatively high homogeneity of the chemical and phase composition. In particular, materials produced during various processing stages of the feed-stock as well as during gas cleaning do not meet these requirements and are therefore essentially landfilled or subject to downcycling processes. A summary of Best Available Techniques for this industry, including a basic definition of the waste streams generated, can be found in [16]. The chem-ical and phase composition is extremely varied and depends on the starting materials and the respec-tive technology. In general, however, it is dominated by high-temperature phases, which exhibit signif-icantly increased reactivity. In some cases, cleaning and initial inerting is done with water, leaving the materials as slurries. This reduces chemical reactivity and requires new handling procedures. In some special cases, particularly in residues from electrometallurgical processes with carbon anodes (nickel, aluminum), organic pollutants also occur in the fine-grained dusts. These are polycyclic aromatic hy-drocarbons (PAH), total volatile organic carbon (TVOC) and polychlorinated dibenzodioxins and fu-rans (PCDD/F). In many cases, the materials must be classified as hazardous in some cases as ex-tremely hazardous. This requires appropriate measures for storage and disposal [16].
A systemic scientific approach is chosen for the material flows described above. This is based on a close linkage of the three steps material characterization, technology development and assessment. A major obstacle in the valorization of fine- and ultra-fine-grained material flows is the often chosen isolated approach to both material characterization and technology development. Thus, significant aspects and interactions are overlooked. The focus has thus always been on isolated material streams as well as specific and thus greatly reduced opportunities for resource recovery or environ-mental risk reduction.
The novel approach chosen by us throughout the project to escape the limitations described above is to achieve a targeted merging of locally occurring material streams that are extremely different in terms of chemical and phase composition. The aim is to synergistically utilize specific chemical or physical properties of one material stream when recycling a material stream from another source in such a way that it becomes possible to provide both material streams with comprehensive recycling, both economically and ecologically. Remaining residual material streams are also safely returned to the natural cycles. This principle of blending is intended to encompass all material streams processed in the project.
We are aware that the basic regulations of the Kreislaufwirtschaftsgesetz (Recycling Management Act) in principal forbid the mixing and processing (hazardous) waste from different material streams. Howev-er, it is an essential knowledge transfer objective to formulate clear proposals for amendments to these regulations. An amendment of the Recycling Management Act will provide a legal basis for both, a valor-isation of the residues, and an inertisation of the remaining residues with the aim of returning valuable materials to the industrial cycle and defining the inert residues as benign final residues.

The principle is illustrated using the example of one property from each of the two material flows we selected in the sub-project. The high contents of specific metals in the residues of the non-ferrous metal industry and the high proportion of plastic-metal composite particles in the shredder fines are taken into account.