Despite the growing interest in reducing the direct environmental impact of steel and aluminum production, little effort has been made in the recovery of these two elements from the wastes deriving from their working processes, namely mill scale and aluminum dross. Since they are mainly oxidic materials, the recovery of metals from such matrixes requires the use of a reductant, usually fossil derived carbon. Therefore, one promising possibility is to exploit carbon sources of biogenic origin, which would on the one hand be capable to adequately carbo-thermal reduces the oxidic wastes and on the other hand creates a process that can be environmentally sustainable and characterized by neutral carbon dioxide footprint. For these reasons, the BioMet project aims to create a supply chain of biocarbon for metallurgical use from both industrial and furniture wood processing wastes. In fact, the wood industry offers a wide range of waste derived from wood processing (wood chips and wood sawdust) or from end-of-life products (pallets). This waste could be suitably treated by pyrolysis (a process in which the biomass, the wood waste, is heated to 350÷750 °C in an inert atmosphere) to obtain a high-value carbonaceous mass (biochar) capable of being used as a reducer in substitution of the fossil carbon. The possibility of exploiting agglomeration techniques would allow the creation of easily handling products (e.g., briquettes, pellets, etc.) that could be easily reduced by appropriate process. Specifically, mill scale would be reduced by a traditional carbothermal reaction using cupola or resistance ovens. However, exploiting new possible heating source to fulfil the reduction and smelting of iron-bearing waste material can open to new competitive processes capable to be extended also for the reduction of aluminum foundry wastes. This is the reason why innovative microwave-assisted carbothermal reaction will be tested on both iron mill scale and aluminum dross in order to compare the two possible reduction routes. This should auspicial open to a new primary aluminum production in competition to the energy-intensive Hall-Heroult process. All these activities still rely on low TRL (2-4). The BioMet project would thus ensure a more efficient utilization of wood waste, as opposed to its actual and low-efficient use as a fuel and, most importantly, the creation of a stable market for biochar, which can be further linked to the agricultural sector. The Project also aims to enhance the economic, environmental and social aspects through the reduction of dependence on the raw materials market and the possibility of creating a “zero km” supply chain, the reduction of waste disposal in landfills and the creation of new carbon neutral metallurgical pathways, further to the creation of a domestic market independent of external sources, through interoperability between industrial sectors and the attraction of new specialized figures.
The BioMet project aims to investigate possible new pathways for the valorization of three different waste materials, namely mill scale, aluminum dross, and wood wastes (wood chips, wood sawdust in form of pellet and industrial pallet).
The initial study of the wood waste pyrolysis process will provide insight into the best process parameters (heating rate, pyrolysis temperature, and holding time) for obtaining high-value biochar, i.e., with high rate of fixed carbon, low volatiles content and minimization of ashes (6 month).
The volatile products (e.g., pyrolysis gas and liquid usually more than 50% mass yield) obtained as pyrolysis byproducts would be characterized and biologically processed to obtain renewable bioplastic (e.g., PHA) (12 month) and/or by their reutilization in metallurgical application, i.e., methane replacement in steelmaking or aluminum foundries.
The use of traditional and new carbothermal processes for metal oxide reduction, on the other hand, would provide new proofs of concept of metal recovery pathways. In particular, the use of a traditional carbothermal process for mill scale reduction would confirm the possibility of using a biogenic carbon-derived feedstock for the recovery of iron, which would create a carbon neutral way to produce iron and steel (12 month).
Electroheat technologies and in particular microwave (MW) will be employed as an alternative heating source for the carbothermal reduction of iron oxides and for the production of biocoal, as an alternative to common pyrometallurgical processes (cupola or resistance furnaces) and pyrolysis, respectively. A specific prototype of a MW system will be designed and built in order to perform an energy-based comparison on a laboratory scale to assess the sustainability of microwave-assisted processes toward traditional ones (12 month)
The use of the microwave or other high-energy electrothermal sources (infrared, plasma, radiofrequency) for carbothermal aluminum dross reduction would allow for the investigation of an additional possibility to the current aluminum recovery routes. This will open to a competitive and carbon neutral process than Hall-Heroult for primary aluminum production. An energy-based comparison will be made to assess the sustainability of such alternatives processes to the traditional one (18 month).
